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Kajani S, Laker RC, Ratkova E, Will S, Rhodes CJ. Hepatic glucagon action: beyond glucose mobilization. Physiol Rev 2024; 104:1021-1060. [PMID: 38300523 DOI: 10.1152/physrev.00028.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Revised: 01/10/2024] [Accepted: 01/11/2024] [Indexed: 02/02/2024] Open
Abstract
Glucagon's ability to promote hepatic glucose production has been known for over a century, with initial observations touting this hormone as a diabetogenic agent. However, glucagon receptor agonism [when balanced with an incretin, including glucagon-like peptide 1 (GLP-1) to dampen glucose excursions] is now being developed as a promising therapeutic target in the treatment of metabolic diseases, like metabolic dysfunction-associated steatotic disease/metabolic dysfunction-associated steatohepatitis (MASLD/MASH), and may also have benefit for obesity and chronic kidney disease. Conventionally regarded as the opposing tag-team partner of the anabolic mediator insulin, glucagon is gradually emerging as more than just a "catabolic hormone." Glucagon action on glucose homeostasis within the liver has been well characterized. However, growing evidence, in part thanks to new and sensitive "omics" technologies, has implicated glucagon as more than just a "glucose liberator." Elucidation of glucagon's capacity to increase fatty acid oxidation while attenuating endogenous lipid synthesis speaks to the dichotomous nature of the hormone. Furthermore, glucagon action is not limited to just glucose homeostasis and lipid metabolism, as traditionally reported. Glucagon plays key regulatory roles in hepatic amino acid and ketone body metabolism, as well as mitochondrial turnover and function, indicating broader glucagon signaling consequences for metabolic homeostasis mediated by the liver. Here we examine the broadening role of glucagon signaling within the hepatocyte and question the current dogma, to appreciate glucagon as more than just that "catabolic hormone."
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Affiliation(s)
- Sarina Kajani
- Early Cardiovascular, Renal and Metabolism, Biopharmaceuticals R&D, AstraZeneca, Gaithersburg, Maryland, United States
| | - Rhianna C Laker
- Early Cardiovascular, Renal and Metabolism, Biopharmaceuticals R&D, AstraZeneca, Gaithersburg, Maryland, United States
| | - Ekaterina Ratkova
- Early Cardiovascular, Renal and Metabolism, Biopharmaceuticals R&D, AstraZeneca, Mölndal, Sweden
| | - Sarah Will
- Early Cardiovascular, Renal and Metabolism, Biopharmaceuticals R&D, AstraZeneca, Gaithersburg, Maryland, United States
| | - Christopher J Rhodes
- Early Cardiovascular, Renal and Metabolism, Biopharmaceuticals R&D, AstraZeneca, Gaithersburg, Maryland, United States
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2
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Acreman S, Ma J, Denwood G, Gao R, Tarasov A, Rorsman P, Zhang Q. The endoplasmic reticulum plays a key role in α-cell intracellular Ca 2+ dynamics and glucose-regulated glucagon secretion in mouse islets. iScience 2024; 27:109665. [PMID: 38646167 PMCID: PMC11033163 DOI: 10.1016/j.isci.2024.109665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 02/13/2024] [Accepted: 04/02/2024] [Indexed: 04/23/2024] Open
Abstract
Glucagon is secreted by pancreatic α-cells to counteract hypoglycaemia. How glucose regulates glucagon secretion remains unclear. Here, using mouse islets, we studied the role of transmembrane and endoplasmic reticulum (ER) Ca2+ on intrinsic α-cell glucagon secretion. Blocking isradipine-sensitive L-type voltage-gated Ca2+ (Cav) channels abolished α-cell electrical activity but had little impact on its cytosolic Ca2+ oscillations or low-glucose-stimulated glucagon secretion. In contrast, depleting ER Ca2+ with cyclopiazonic acid or blocking ER Ca2+-releasing ryanodine receptors abolished α-cell glucose sensitivity and low-glucose-stimulated glucagon secretion. ER Ca2+ mobilization in α-cells is regulated by intracellular ATP and likely to be coupled to Ca2+ influx through P/Q-type Cav channels. ω-Agatoxin IVA blocked α-cell ER Ca2+ release and cell exocytosis, but had no additive effect on glucagon secretion when combined with ryanodine. We conclude that glucose regulates glucagon secretion through the control of ER Ca2+ mobilization, a mechanism that can be independent of α-cell electrical activity.
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Affiliation(s)
- Samuel Acreman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK
- Institute of Neuroscience and Physiology, Department of Physiology, Metabolic Research Unit, Sahlgrenska Academy, University of Gothenburg, Box 430, S-405 30 Gothenburg, Sweden
| | - Jinfang Ma
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK
- Department of Endocrinology and Metabolism, West China Hospital, Sichuan University, Chengdu, China
| | - Geoffrey Denwood
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK
| | - Rui Gao
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK
| | - Andrei Tarasov
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK
- Biomedical Sciences Research Institute, School of Biomedical Sciences, Ulster University, Coleraine, Northern Ireland, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK
- Institute of Neuroscience and Physiology, Department of Physiology, Metabolic Research Unit, Sahlgrenska Academy, University of Gothenburg, Box 430, S-405 30 Gothenburg, Sweden
- Biomedical Sciences Research Institute, School of Biomedical Sciences, Ulster University, Coleraine, Northern Ireland, UK
| | - Quan Zhang
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK
- CNC - Center for Neuroscience and Cell Biology, CIBB - Centre for Innovative Biomedicine and Biotechnology, University of Coimbra, Coimbra, Portugal
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3
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Armour SL, Frueh A, Chibalina MV, Dou H, Argemi-Muntadas L, Hamilton A, Katzilieris-Petras G, Carmeliet P, Davies B, Moritz T, Eliasson L, Rorsman P, Knudsen JG. Glucose Controls Glucagon Secretion by Regulating Fatty Acid Oxidation in Pancreatic α-Cells. Diabetes 2023; 72:1446-1459. [PMID: 37494670 PMCID: PMC10545563 DOI: 10.2337/db23-0056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Accepted: 07/16/2023] [Indexed: 07/28/2023]
Abstract
Whole-body glucose homeostasis is coordinated through secretion of glucagon and insulin from pancreatic islets. When glucose is low, glucagon is released from α-cells to stimulate hepatic glucose production. However, the mechanisms that regulate glucagon secretion from pancreatic α-cells remain unclear. Here we show that in α-cells, the interaction between fatty acid oxidation and glucose metabolism controls glucagon secretion. The glucose-dependent inhibition of glucagon secretion relies on pyruvate dehydrogenase and carnitine palmitoyl transferase 1a activity and lowering of mitochondrial fatty acid oxidation by increases in glucose. This results in reduced intracellular ATP and leads to membrane repolarization and inhibition of glucagon secretion. These findings provide a new framework for the metabolic regulation of the α-cell, where regulation of fatty acid oxidation by glucose accounts for the stimulation and inhibition of glucagon secretion. ARTICLE HIGHLIGHTS It has become clear that dysregulation of glucagon secretion and α-cell function plays an important role in the development of diabetes, but we do not know how glucagon secretion is regulated. Here we asked whether glucose inhibits fatty acid oxidation in α-cells to regulate glucagon secretion. We found that fatty acid oxidation is required for the inhibitory effects of glucose on glucagon secretion through reductions in ATP. These findings provide a new framework for the regulation of glucagon secretion by glucose.
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Affiliation(s)
- Sarah L. Armour
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Alexander Frueh
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Margarita V. Chibalina
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, U.K
| | - Haiqiang Dou
- Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Lidia Argemi-Muntadas
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Alexander Hamilton
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
- Department of Clinical Sciences in Malmö, Islet Cell Exocytosis, Lund University Diabetes Centre, Lund University, Malmö, Sweden
| | - Georgios Katzilieris-Petras
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Peter Carmeliet
- Laboratory of Angiogenesis and Vascular Metabolism, Centre for Cancer Biology, Vlaams Instituut voor Biotechnologie (VIB), Department of Oncology, Leuven Cancer Institute, Katholieke Universiteit Leuven, Leuven, Belgium
- Laboratory of Angiogenesis and Vascular Heterogeneity, Department of Biomedicine, Aarhus University, Aarhus, Denmark
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangdong, People’s Republic of China
| | - Benjamin Davies
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, U.K
| | - Thomas Moritz
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lena Eliasson
- Department of Clinical Sciences in Malmö, Islet Cell Exocytosis, Lund University Diabetes Centre, Lund University, Malmö, Sweden
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, U.K
- Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Jakob G. Knudsen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
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4
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Armour SL, Stanley JE, Cantley J, Dean ED, Knudsen JG. Metabolic regulation of glucagon secretion. J Endocrinol 2023; 259:e230081. [PMID: 37523232 PMCID: PMC10681275 DOI: 10.1530/joe-23-0081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2023] [Accepted: 07/31/2023] [Indexed: 08/01/2023]
Abstract
Since the discovery of glucagon 100 years ago, the hormone and the pancreatic islet alpha cells that produce it have remained enigmatic relative to insulin-producing beta cells. Canonically, alpha cells have been described in the context of glucagon's role in glucose metabolism in liver, with glucose as the primary nutrient signal regulating alpha cell function. However, current data reveal a more holistic model of metabolic signalling, involving glucagon-regulated metabolism of multiple nutrients by the liver and other tissues, including amino acids and lipids, providing reciprocal feedback to regulate glucagon secretion and even alpha cell mass. Here we describe how various nutrients are sensed, transported and metabolised in alpha cells, providing an integrative model for the metabolic regulation of glucagon secretion and action. Importantly, we discuss where these nutrient-sensing pathways intersect to regulate alpha cell function and highlight key areas for future research.
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Affiliation(s)
- Sarah L Armour
- Section for cell biology and physiology, Department of Biology, University of Copenhagen, DK
| | - Jade E. Stanley
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, USA
| | - James Cantley
- Division of Cellular and systems medicine, School of Medicine, University of Dundee, UK
| | - E. Danielle Dean
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, USA
- Division of Diabetes, Endocrinology, & Metabolism, Vanderbilt University Medical Center school of medicine, USA
| | - Jakob G Knudsen
- Section for cell biology and physiology, Department of Biology, University of Copenhagen, DK
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5
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Brown A, Tzanakakis ES. Mathematical modeling clarifies the paracrine roles of insulin and glucagon on the glucose-stimulated hormonal secretion of pancreatic alpha- and beta-cells. Front Endocrinol (Lausanne) 2023; 14:1212749. [PMID: 37645413 PMCID: PMC10461634 DOI: 10.3389/fendo.2023.1212749] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Accepted: 07/21/2023] [Indexed: 08/31/2023] Open
Abstract
Introduction Blood sugar homeostasis relies largely on the action of pancreatic islet hormones, particularly insulin and glucagon. In a prototypical fashion, glucagon is released upon hypoglycemia to elevate glucose by acting on the liver while elevated glucose induces the secretion of insulin which leads to sugar uptake by peripheral tissues. This simplified view of glucagon and insulin does not consider the paracrine roles of the two hormones modulating the response to glucose of α- and β-cells. In particular, glucose-stimulated glucagon secretion by isolated α-cells exhibits a Hill-function pattern, while experiments with intact pancreatic islets suggest a 'U'-shaped response. Methods To this end, a framework was developed based on first principles and coupled to experimental studies capturing the glucose-induced response of pancreatic α- and β-cells influenced by the two hormones. The model predicts both the transient and steady-state profiles of secreted insulin and glucagon, including the typical biphasic response of normal β-cells to hyperglycemia. Results and discussion The results underscore insulin activity as a differentiating factor of the glucagon secretion from whole islets vs. isolated α-cells, and highlight the importance of experimental conditions in interpreting the behavior of islet cells in vitro. The model also reproduces the hyperglucagonemia, which is experienced by diabetes patients, and it is linked to a failure of insulin to inhibit α-cell activity. The framework described here is amenable to the inclusion of additional islet cell types and extrapancreatic tissue cells simulating multi-organ systems. The study expands our understanding of the interplay of insulin and glucagon for pancreas function in normal and pathological conditions.
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Affiliation(s)
- Aedan Brown
- Department of Chemical and Biological Engineering, Tufts University, Medford, MA, United States
| | - Emmanuel S. Tzanakakis
- Department of Chemical and Biological Engineering, Tufts University, Medford, MA, United States
- Genetics, Molecular and Cellular Biology, Tufts University, Boston, MA, United States
- Pharmacology and Drug Development, Tufts University, Boston, MA, United States
- Clinical and Translational Science Institute, Tufts University, Boston, MA, United States
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6
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Eriksson JW, Emad RA, Lundqvist MH, Abrahamsson N, Kjellsson MC. Altered glucose-dependent secretion of glucagon and ACTH is associated with insulin resistance, assessed by population analysis. Endocr Connect 2023; 12:e220506. [PMID: 36752854 PMCID: PMC10083665 DOI: 10.1530/ec-22-0506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Accepted: 02/08/2023] [Indexed: 02/09/2023]
Abstract
This study aimed to characterize how the dysregulation of counter-regulatory hormones can contribute to insulin resistance and potentially to diabetes. Therefore, we investigated the association between insulin sensitivity and the glucose- and insulin-dependent secretion of glucagon, adrenocorticotropic hormone (ACTH), and cortisol in non-diabetic individuals using a population model analysis. Data, from hyperinsulinemic-hypoglycemic clamps, were pooled for analysis, including 52 individuals with a wide range of insulin resistance (reflected by glucose infusion rate 20-60 min; GIR20-60min). Glucagon secretion was suppressed by glucose and, to a lesser extent, insulin. The GIR20-60min and BMI were identified as predictors of the insulin effect on glucagon. At normoglycemia (5 mmol/L), a 90% suppression of glucagon was achieved at insulin concentrations of 16.3 and 43.4 µU/mL in individuals belonging to the highest and lowest quantiles of insulin sensitivity, respectively. Insulin resistance of glucagon secretion explained the elevated fasting glucagon for individuals with a low GIR20-60min. ACTH secretion was suppressed by glucose and not affected by insulin. The GIR20-60min was superior to other measures as a predictor of glucose-dependent ACTH secretion, with 90% suppression of ACTH secretion by glucose at 3.1 and 3.5 mmol/L for insulin-sensitive and insulin-resistant individuals, respectively. This difference may appear small but shifts the suppression range into normoglycemia for individuals with insulin resistance, thus, leading to earlier and greater ACTH/cortisol response when the glucose falls. Based on modeling of pooled glucose-clamp data, insulin resistance was associated with generally elevated glucagon and a potentiated cortisol-axis response to hypoglycemia, and over time both hormonal pathways may therefore contribute to dysglycemia and possibly type 2 diabetes.
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Affiliation(s)
- Jan W Eriksson
- Department of Medical Sciences, Uppsala University, Uppsala, Sweden
| | - Reem A Emad
- Department of Pharmacy, Uppsala University, Uppsala, Sweden
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7
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Hædersdal S, Andersen A, Knop FK, Vilsbøll T. Revisiting the role of glucagon in health, diabetes mellitus and other metabolic diseases. Nat Rev Endocrinol 2023; 19:321-335. [PMID: 36932176 DOI: 10.1038/s41574-023-00817-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 33.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 02/17/2023] [Indexed: 03/19/2023]
Abstract
Insulin and glucagon exert opposing effects on glucose metabolism and, consequently, pancreatic islet β-cells and α-cells are considered functional antagonists. The intra-islet hypothesis has previously dominated the understanding of glucagon secretion, stating that insulin acts to inhibit the release of glucagon. By contrast, glucagon is a potent stimulator of insulin secretion and has been used to test β-cell function. Over the past decade, α-cells have received increasing attention due to their ability to stimulate insulin secretion from neighbouring β-cells, and α-cell-β-cell crosstalk has proven central for glucose homeostasis in vivo. Glucagon is not only the counter-regulatory hormone to insulin in glucose metabolism but also glucagon secretion is more susceptible to changes in the plasma concentration of certain amino acids than to changes in plasma concentrations of glucose. Thus, the actions of glucagon also include a central role in amino acid turnover and hepatic fat oxidation. This Review provides insights into glucagon secretion, with a focus on the local paracrine actions on glucagon and the importance of α-cell-β-cell crosstalk. We focus on dysregulated glucagon secretion in obesity, non-alcoholic fatty liver disease and type 2 diabetes mellitus. Lastly, the future potential of targeting hyperglucagonaemia and applying dual and triple receptor agonists with glucagon receptor-activating properties in combination with incretin hormone receptor agonism is discussed.
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Affiliation(s)
- Sofie Hædersdal
- Clinical Research, Copenhagen University Hospital - Steno Diabetes Center Copenhagen, Herlev, Denmark.
- Center for Clinical Metabolic Research, Copenhagen University Hospital - Herlev and Gentofte, Hellerup, Denmark.
| | - Andreas Andersen
- Clinical Research, Copenhagen University Hospital - Steno Diabetes Center Copenhagen, Herlev, Denmark
- Center for Clinical Metabolic Research, Copenhagen University Hospital - Herlev and Gentofte, Hellerup, Denmark
| | - Filip K Knop
- Clinical Research, Copenhagen University Hospital - Steno Diabetes Center Copenhagen, Herlev, Denmark
- Center for Clinical Metabolic Research, Copenhagen University Hospital - Herlev and Gentofte, Hellerup, Denmark
- Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - Tina Vilsbøll
- Clinical Research, Copenhagen University Hospital - Steno Diabetes Center Copenhagen, Herlev, Denmark.
- Center for Clinical Metabolic Research, Copenhagen University Hospital - Herlev and Gentofte, Hellerup, Denmark.
- Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark.
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Abstract
Plasma glucose is tightly regulated via the secretion of the two glucose-regulating hormones insulin and glucagon. Situated next to the insulin-secreting β-cells, the α-cells produce and secrete glucagon-one of the body's few blood glucose-increasing hormones. Diabetes is a bihormonal disorder, resulting from both inadequate insulin secretion and dysregulation of glucagon. The year 2023 marks the 100th anniversary of the discovery of glucagon, making it particularly timely to highlight the roles of this systemic metabolic messenger in health and disease.
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Affiliation(s)
- Patrick E MacDonald
- Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford, UK.
- Metabolic Physiology, Institute of Neuroscience and Physiology, University of Göteborg, Gothenburg, Sweden.
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9
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Dobosz AM, Janikiewicz J, Krogulec E, Dziewulska A, Ajduk A, Szpila M, Nieznańska H, Szczepankiewicz AA, Wypych D, Dobrzyn A. Inhibition of stearoyl-CoA desaturase 1 in the mouse impairs pancreatic islet morphogenesis and promotes loss of β-cell identity and α-cell expansion in the mature pancreas. Mol Metab 2022; 67:101659. [PMID: 36529318 PMCID: PMC9801219 DOI: 10.1016/j.molmet.2022.101659] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Revised: 12/02/2022] [Accepted: 12/10/2022] [Indexed: 12/23/2022] Open
Abstract
Abnormalities that characterize the pathophysiology of type 2 diabetes (T2D) include deficiencies of β-cells and the expansion of α-cells in pancreatic islets, manifested by lower insulin release and glucagon oversecretion. The molecular mechanisms that determine intra-islet interactions between pancreatic α- and β-cells are still not fully understood. The present study showed that stearoyl-coenzyme A (CoA) desaturase 1 (SCD1), an enzyme that is implicated in fatty acid metabolism, serves as a checkpoint in the control of endocrine cell equilibrium in pancreatic islets. Our data showed that SCD1 activity is essential for proper α-cell and β-cell lineage determination during morphogenesis of the pancreas and the maintenance of mature β-cell identity. The inhibition of SCD1 expression/activity led to both a decrease in the expression of β-cell signature genes (e.g., Pdx1, Nkx6.1, MafA, and Neurod1, among others) and induction of the expression of the dedifferentiation marker Sox9 in mature pancreatic islets. The transcriptional repression of Pdx1 and MafA in SCD1-deficient β-cells was related to the excessive methylation of promoter regions of these transcription factors. In contrast, SCD1 ablation favored the formation of α-cells over β-cells throughout pancreas organogenesis and did not compromise α-cell identity in adult pancreatic islets. Such molecular changes that were caused by SCD1 downregulation resulted in the mislocalization of α-cells within the core of islets and increased the ratio of pancreatic α- to β-cell mass. This was followed by islet dysfunction, including impairments in glucose-stimulated insulin release, simultaneously with elevations of basal glucagon secretion. Altogether, these findings provide additional mechanistic insights into the role of SCD1 in the pathogenesis of T2D.
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Affiliation(s)
- Aneta M. Dobosz
- Laboratory of Cell Signaling and Metabolic Disorders, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland,Corresponding author.
| | - Justyna Janikiewicz
- Laboratory of Cell Signaling and Metabolic Disorders, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.
| | - Ewelina Krogulec
- Laboratory of Cell Signaling and Metabolic Disorders, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.
| | - Anna Dziewulska
- Laboratory of Cell Signaling and Metabolic Disorders, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.
| | - Anna Ajduk
- Department of Embryology, Institute of Developmental Biology and Biomedical Sciences, Faculty of Biology, University of Warsaw, Warsaw, Poland.
| | - Marcin Szpila
- Department of Embryology, Institute of Developmental Biology and Biomedical Sciences, Faculty of Biology, University of Warsaw, Warsaw, Poland.
| | - Hanna Nieznańska
- Laboratory of Electron Microscopy, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.
| | - Andrzej A. Szczepankiewicz
- Laboratory of Electron Microscopy, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
| | - Dorota Wypych
- Laboratory of Cell Signaling and Metabolic Disorders, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.
| | - Agnieszka Dobrzyn
- Laboratory of Cell Signaling and Metabolic Disorders, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.
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10
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Brüning D, Morsi M, Früh E, Scherneck S, Rustenbeck I. Metabolic Regulation of Hormone Secretion in Beta-Cells and Alpha-Cells of Female Mice: Fundamental Differences. Endocrinology 2022; 163:6656576. [PMID: 35931024 DOI: 10.1210/endocr/bqac125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Indexed: 11/19/2022]
Abstract
It is unclear whether the secretion of glucagon is regulated by an alpha-cell-intrinsic mechanism and whether signal recognition by the mitochondrial metabolism plays a role in it. To measure changes of the cytosolic ATP/ADP ratio, single alpha-cells and beta-cells from NMRI mice were adenovirally transduced with the fluorescent indicator PercevalHR. The cytosolic Ca2+ concentration ([Ca2+]i) was measured by use of Fura2 and the mitochondrial membrane potential by use of TMRE. Perifused islets were used to measure the secretion of glucagon and insulin. At 5 mM glucose, the PercevalHR ratio in beta-cells was significantly lower than in alpha-cells. Lowering glucose to 1 mM decreased the ratio to 69% within 10 minutes in beta-cells, but only to 94% in alpha-cells. In this situation, 30 mM glucose, 10 mM alpha-ketoisocaproic acid, and 10 mM glutamine plus 10 mM BCH (a nonmetabolizable leucine analogue) markedly increased the PercevalHR ratio in beta-cells. In alpha-cells, only glucose was slightly effective. However, none of the nutrients increased the mitochondrial membrane potential in alpha-cells, whereas all did so in beta-cells. The kinetics of the PercevalHR increase were reflected by the kinetics of [Ca2+]i. increase in the beta-cells and insulin secretion. Glucagon secretion was markedly increased by washing out the nutrients with 1 mM glucose, but not by reducing glucose from 5 mM to 1 mM. This pattern was still recognizable when the insulin secretion was strongly inhibited by clonidine. It is concluded that mitochondrial energy metabolism is a signal generator in pancreatic beta-cells, but not in alpha-cells.
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Affiliation(s)
- Dennis Brüning
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D 38106 Braunschweig, Germany
| | - Mai Morsi
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D 38106 Braunschweig, Germany
- Department of Pharmacology, Faculty of Pharmacy, Assiut University, Assiut 71526, Egypt
| | - Eike Früh
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D 38106 Braunschweig, Germany
| | - Stephan Scherneck
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D 38106 Braunschweig, Germany
| | - Ingo Rustenbeck
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D 38106 Braunschweig, Germany
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11
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Zaborska KE, Jordan KL, Thorson AS, Dadi PK, Schaub CM, Nakhe AY, Dickerson MT, Lynch JC, Weiss AJ, Dobson JR, Jacobson DA. Liraglutide increases islet Ca 2+ oscillation frequency and insulin secretion by activating hyperpolarization-activated cyclic nucleotide-gated channels. Diabetes Obes Metab 2022; 24:1741-1752. [PMID: 35546791 PMCID: PMC9843726 DOI: 10.1111/dom.14747] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 04/28/2022] [Accepted: 04/29/2022] [Indexed: 01/19/2023]
Abstract
AIM To determine whether hyperpolarization-activated cyclic nucleotide-gated (HCN) channels impact glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) modulation of islet Ca2+ handling and insulin secretion. METHODS The impact of liraglutide (GLP-1 analogue) on islet Ca2+ handling, HCN currents and insulin secretion was monitored with fluorescence microscopy, electrophysiology and enzyme immunoassays, respectively. Furthermore, liraglutide-mediated β-to-δ-cell cross-communication was assessed following selective ablation of either mouse islet δ or β cells. RESULTS Liraglutide increased β-cell Ca2+ oscillation frequency in mouse and human islets under stimulatory glucose conditions. This was dependent in part on liraglutide activation of HCN channels, which also enhanced insulin secretion. Similarly, liraglutide activation of HCN channels also increased β-cell Ca2+ oscillation frequency in islets from rodents exposed to a diabetogenic diet. Interestingly, liraglutide accelerated Ca2+ oscillations in a majority of islet δ cells, which showed synchronized Ca2+ oscillations equivalent to β cells; therefore, we assessed if either cell type was driving this liraglutide-mediated islet Ca2+ response. Although δ-cell loss did not impact liraglutide-mediated increase in β-cell Ca2+ oscillation frequency, β-cell ablation attenuated liraglutide-facilitated acceleration of δ-cell Ca2+ oscillations. CONCLUSION The data presented here show that liraglutide-induced stimulation of islet HCN channels augments Ca2+ oscillation frequency. As insulin secretion oscillates with β-cell Ca2+ , these findings have important implications for pulsatile insulin secretion that is probably enhanced by liraglutide activation of HCN channels and therapeutics that target GLP-1Rs for treating diabetes. Furthermore, these studies suggest that liraglutide as well as GLP-1-based therapies enhance δ-cell Ca2+ oscillation frequency and somatostatin secretion kinetics in a β-cell-dependent manner.
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Affiliation(s)
- Karolina E Zaborska
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Kelli L Jordan
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Ariel S Thorson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Charles M Schaub
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Arya Y Nakhe
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Matthew T Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Joshua C Lynch
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Adam J Weiss
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Jordyn R Dobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
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12
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Singh B, Khattab F, Gilon P. Glucose inhibits glucagon secretion by decreasing [Ca2+]c and by reducing the efficacy of Ca2+ on exocytosis via somatostatin-dependent and independent mechanisms. Mol Metab 2022; 61:101495. [PMID: 35421610 PMCID: PMC9065434 DOI: 10.1016/j.molmet.2022.101495] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Revised: 03/15/2022] [Accepted: 04/04/2022] [Indexed: 11/15/2022] Open
Abstract
Objective Methods Results Conclusions Glucose modulates [Ca2+]c in α-cells within islets but not in dispersed α-cells. In α-cells within islets, it decreases [Ca2+]c independently of their KATP channels. It decreases α-cell [Ca2+]c partly via somatostatin. All glucose-induced [Ca2+]c changes trigger parallel changes in glucagon release. Glucose also decreases the efficacy of Ca2+ on exocytosis (attenuating pathway).
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Affiliation(s)
- Bilal Singh
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium
| | - Firas Khattab
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium
| | - Patrick Gilon
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium.
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13
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Armour SL, Frueh A, Knudsen JG. Sodium, Glucose and Dysregulated Glucagon Secretion: The Potential of Sodium Glucose Transporters. Front Pharmacol 2022; 13:837664. [PMID: 35237171 PMCID: PMC8882857 DOI: 10.3389/fphar.2022.837664] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Accepted: 01/26/2022] [Indexed: 01/01/2023] Open
Abstract
Diabetes is defined by hyperglycaemia due to progressive insulin resistance and compromised insulin release. In parallel, alpha cells develop dysregulation of glucagon secretion. Diabetic patients have insufficient glucagon secretion during hypoglycaemia and a lack of inhibition of glucagon secretion at higher blood glucose levels resulting in postprandial hyperglucagonaemia, which contributes to the development of hyperglycaemia. Sodium-glucose co-transporter 2 (SGLT2) inhibitors are an efficient pharmacologic approach for the treatment of hyperglycaemia in type 2 diabetes. While SGLT2 inhibitors aim at increasing glycosuria to decrease blood glucose levels, these inhibitors also increase circulating glucagon concentrations. Here, we review recent advances in our understanding of how SGLTs are involved in the regulation of glucagon secretion. Sodium plays an important role for alpha cell function, and a tight regulation of intracellular sodium levels is important for maintaining plasma membrane potential and intracellular pH. This involves the sodium-potassium pump, sodium-proton exchangers and SGLTs. While the expression of SGLT2 in alpha cells remains controversial, SGLT1 seems to play a central role for alpha cell function. Under hyperglycaemic conditions, SGLT1 mediated accumulation of sodium results in alpha cell dysregulation due to altered cellular acidification and ATP production. Taken together, this suggests that SGLT1 could be a promising, yet highly underappreciated drug target to restore alpha cell function and improve treatment of both type 1 and 2 diabetes.
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Affiliation(s)
| | | | - Jakob G. Knudsen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
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14
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Dai XQ, Camunas-Soler J, Briant LJB, Dos Santos T, Spigelman AF, Walker EM, Arrojo E Drigo R, Bautista A, Jones RC, Avrahami D, Lyon J, Nie A, Smith N, Zhang Y, Johnson J, Manning Fox JE, Michelakis ED, Light PE, Kaestner KH, Kim SK, Rorsman P, Stein RW, Quake SR, MacDonald PE. Heterogenous impairment of α cell function in type 2 diabetes is linked to cell maturation state. Cell Metab 2022; 34:256-268.e5. [PMID: 35108513 PMCID: PMC8852281 DOI: 10.1016/j.cmet.2021.12.021] [Citation(s) in RCA: 34] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Revised: 10/08/2021] [Accepted: 12/22/2021] [Indexed: 02/03/2023]
Abstract
In diabetes, glucagon secretion from pancreatic α cells is dysregulated. The underlying mechanisms, and whether dysfunction occurs uniformly among cells, remain unclear. We examined α cells from human donors and mice using electrophysiological, transcriptomic, and computational approaches. Rising glucose suppresses α cell exocytosis by reducing P/Q-type Ca2+ channel activity, and this is disrupted in type 2 diabetes (T2D). Upon high-fat feeding of mice, α cells shift toward a "β cell-like" electrophysiological profile in concert with indications of impaired identity. In human α cells we identified links between cell membrane properties and cell surface signaling receptors, mitochondrial respiratory chain complex assembly, and cell maturation. Cell-type classification using machine learning of electrophysiology data demonstrated a heterogenous loss of "electrophysiologic identity" in α cells from donors with type 2 diabetes. Indeed, a subset of α cells with impaired exocytosis is defined by an enrichment in progenitor and lineage markers and upregulation of an immature transcriptomic phenotype, suggesting important links between α cell maturation state and dysfunction.
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Affiliation(s)
- Xiao-Qing Dai
- Department of Pharmacology, University of Alberta, Edmonton, AB T6G2R3, Canada; Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Joan Camunas-Soler
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; Chan Zuckerberg Biohub, San Francisco, CA 94518, USA
| | - Linford J B Briant
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, Churchill Hospital, Oxford OX3 7LE, UK
| | - Theodore Dos Santos
- Department of Pharmacology, University of Alberta, Edmonton, AB T6G2R3, Canada; Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Aliya F Spigelman
- Department of Pharmacology, University of Alberta, Edmonton, AB T6G2R3, Canada; Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Emily M Walker
- Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48105, USA
| | - Rafael Arrojo E Drigo
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Austin Bautista
- Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Robert C Jones
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA
| | - Dana Avrahami
- Endocrinology and Metabolism Department, Hadassah-Hebrew University Medical Centre, Jerusalem, Israel
| | - James Lyon
- Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Aifang Nie
- Department of Pharmacology, University of Alberta, Edmonton, AB T6G2R3, Canada; Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Nancy Smith
- Department of Pharmacology, University of Alberta, Edmonton, AB T6G2R3, Canada; Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Yongneng Zhang
- Department of Medicine, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Janyne Johnson
- Department of Pharmacology, University of Alberta, Edmonton, AB T6G2R3, Canada; Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Jocelyn E Manning Fox
- Department of Pharmacology, University of Alberta, Edmonton, AB T6G2R3, Canada; Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | | | - Peter E Light
- Department of Pharmacology, University of Alberta, Edmonton, AB T6G2R3, Canada; Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada
| | - Klaus H Kaestner
- Department of Genetics and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Seung K Kim
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA; Stanford Diabetes Research Center, Stanford University, Stanford, CA 94305, USA
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, Churchill Hospital, Oxford OX3 7LE, UK
| | - Roland W Stein
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Stephen R Quake
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; Chan Zuckerberg Biohub, San Francisco, CA 94518, USA; Department of Applied Physics, Stanford University, Stanford, CA 94305, USA
| | - Patrick E MacDonald
- Department of Pharmacology, University of Alberta, Edmonton, AB T6G2R3, Canada; Alberta Diabetes Institute, University of Alberta, Edmonton, AB T6G2R3, Canada.
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15
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Miranda C, Begum M, Vergari E, Briant LJB. Gap junction coupling and islet delta-cell function in health and disease. Peptides 2022; 147:170704. [PMID: 34826505 DOI: 10.1016/j.peptides.2021.170704] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 11/12/2021] [Accepted: 11/19/2021] [Indexed: 12/12/2022]
Abstract
The pancreatic islets contain beta-cells and alpha-cells, which are responsible for secreting two principal gluco-regulatory hormones; insulin and glucagon, respectively. However, they also contain delta-cells, a relatively sparse cell type that secretes somatostatin (SST). These cells have a complex morphology allowing them to establish an extensive communication network throughout the islet, despite their scarcity. Delta-cells are electrically excitable cells, and SST secretion is released in a glucose- and KATP-dependent manner. SST hyperpolarises the alpha-cell membrane and suppresses exocytosis. In this way, islet SST potently inhibits glucagon release. Recent studies investigating the activity of delta-cells have revealed they are electrically coupled to beta-cells via gap junctions, suggesting the delta-cell is more than just a paracrine inhibitor. In this Review, we summarize delta-cell morphology, function, and the role of SST signalling for regulating islet hormonal output. A distinguishing feature of this Review is that we attempt to use the discovery of this gap junction pathway, together with what is already known about delta-cells, to reframe the role of these cells in both health and disease. In particular, we argue that the discovery of gap junction communication between delta-cells and beta-cells provides new insights into the contribution of delta-cells to the islet hormonal defects observed in both type 1 and type 2 diabetes. This reappraisal of the delta-cell is important as it may offer novel insights into how the physiology of this cell can be utilised to restore islet function in diabetes.
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Affiliation(s)
- Caroline Miranda
- Institute of Neuroscience and Physiology, Metabolic Research Unit, University of Göteborg, 405 30, Göteborg, Sweden
| | - Manisha Begum
- Institute of Neuroscience and Physiology, Metabolic Research Unit, University of Göteborg, 405 30, Göteborg, Sweden; University of Skӧvde, Department of Infection Biology, Högskolevägen 1, 541 28, Skövde, Sweden
| | - Elisa Vergari
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, OX4 7LE, Oxford, UK
| | - Linford J B Briant
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, OX4 7LE, Oxford, UK; Department of Computer Science, University of Oxford, OX1 3QD, Oxford, UK.
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16
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Asadi F, Dhanvantari S. Pathways of Glucagon Secretion and Trafficking in the Pancreatic Alpha Cell: Novel Pathways, Proteins, and Targets for Hyperglucagonemia. Front Endocrinol (Lausanne) 2021; 12:726368. [PMID: 34659118 PMCID: PMC8511682 DOI: 10.3389/fendo.2021.726368] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Accepted: 09/13/2021] [Indexed: 12/15/2022] Open
Abstract
Patients with diabetes mellitus exhibit hyperglucagonemia, or excess glucagon secretion, which may be the underlying cause of the hyperglycemia of diabetes. Defective alpha cell secretory responses to glucose and paracrine effectors in both Type 1 and Type 2 diabetes may drive the development of hyperglucagonemia. Therefore, uncovering the mechanisms that regulate glucagon secretion from the pancreatic alpha cell is critical for developing improved treatments for diabetes. In this review, we focus on aspects of alpha cell biology for possible mechanisms for alpha cell dysfunction in diabetes: proglucagon processing, intrinsic and paracrine control of glucagon secretion, secretory granule dynamics, and alterations in intracellular trafficking. We explore possible clues gleaned from these studies in how inhibition of glucagon secretion can be targeted as a treatment for diabetes mellitus.
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Affiliation(s)
- Farzad Asadi
- Department of Pathology and Laboratory Medicine, Western University, London, ON, Canada
- Program in Metabolism and Diabetes, Lawson Health Research Institute, London, ON, Canada
| | - Savita Dhanvantari
- Department of Pathology and Laboratory Medicine, Western University, London, ON, Canada
- Program in Metabolism and Diabetes, Lawson Health Research Institute, London, ON, Canada
- Imaging Research Program, Lawson Health Research Institute, London, ON, Canada
- Department of Medical Biophysics, Western University, London, ON, Canada
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17
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Abstract
This review focuses on the human pancreatic islet-including its structure, cell composition, development, function, and dysfunction. After providing a historical timeline of key discoveries about human islets over the past century, we describe new research approaches and technologies that are being used to study human islets and how these are providing insight into human islet physiology and pathophysiology. We also describe changes or adaptations in human islets in response to physiologic challenges such as pregnancy, aging, and insulin resistance and discuss islet changes in human diabetes of many forms. We outline current and future interventions being developed to protect, restore, or replace human islets. The review also highlights unresolved questions about human islets and proposes areas where additional research on human islets is needed.
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Affiliation(s)
- John T Walker
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Diane C Saunders
- Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Marcela Brissova
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Alvin C Powers
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
- Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- VA Tennessee Valley Healthcare System, Nashville, Tennessee, USA
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18
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Martínez MS, Manzano A, Olivar LC, Nava M, Salazar J, D’Marco L, Ortiz R, Chacín M, Guerrero-Wyss M, Cabrera de Bravo M, Cano C, Bermúdez V, Angarita L. The Role of the α Cell in the Pathogenesis of Diabetes: A World beyond the Mirror. Int J Mol Sci 2021; 22:9504. [PMID: 34502413 PMCID: PMC8431704 DOI: 10.3390/ijms22179504] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2021] [Revised: 08/26/2021] [Accepted: 08/26/2021] [Indexed: 12/11/2022] Open
Abstract
Type 2 Diabetes Mellitus (T2DM) is one of the most prevalent chronic metabolic disorders, and insulin has been placed at the epicentre of its pathophysiological basis. However, the involvement of impaired alpha (α) cell function has been recognized as playing an essential role in several diseases, since hyperglucagonemia has been evidenced in both Type 1 and T2DM. This phenomenon has been attributed to intra-islet defects, like modifications in pancreatic α cell mass or dysfunction in glucagon's secretion. Emerging evidence has shown that chronic hyperglycaemia provokes changes in the Langerhans' islets cytoarchitecture, including α cell hyperplasia, pancreatic beta (β) cell dedifferentiation into glucagon-positive producing cells, and loss of paracrine and endocrine regulation due to β cell mass loss. Other abnormalities like α cell insulin resistance, sensor machinery dysfunction, or paradoxical ATP-sensitive potassium channels (KATP) opening have also been linked to glucagon hypersecretion. Recent clinical trials in phases 1 or 2 have shown new molecules with glucagon-antagonist properties with considerable effectiveness and acceptable safety profiles. Glucagon-like peptide-1 (GLP-1) agonists and Dipeptidyl Peptidase-4 inhibitors (DPP-4 inhibitors) have been shown to decrease glucagon secretion in T2DM, and their possible therapeutic role in T1DM means they are attractive as an insulin-adjuvant therapy.
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Affiliation(s)
- María Sofía Martínez
- MedStar Health Internal Medicine, Georgetown University Affiliated, Baltimore, MD 21218-2829, USA;
| | - Alexander Manzano
- Endocrine and Metabolic Diseases Research Center, School of Medicine, Universidad del Zulia, Maracaibo 4002, Venezuela; (A.M.); (L.C.O.); (M.N.); (J.S.); (C.C.)
| | - Luis Carlos Olivar
- Endocrine and Metabolic Diseases Research Center, School of Medicine, Universidad del Zulia, Maracaibo 4002, Venezuela; (A.M.); (L.C.O.); (M.N.); (J.S.); (C.C.)
| | - Manuel Nava
- Endocrine and Metabolic Diseases Research Center, School of Medicine, Universidad del Zulia, Maracaibo 4002, Venezuela; (A.M.); (L.C.O.); (M.N.); (J.S.); (C.C.)
| | - Juan Salazar
- Endocrine and Metabolic Diseases Research Center, School of Medicine, Universidad del Zulia, Maracaibo 4002, Venezuela; (A.M.); (L.C.O.); (M.N.); (J.S.); (C.C.)
| | - Luis D’Marco
- Department of Nephrology, Hospital Clinico Universitario de Valencia, INCLIVA, University of Valencia, 46010 Valencia, Spain;
| | - Rina Ortiz
- Facultad de Medicina, Universidad Católica de Cuenca, Ciudad de Cuenca, Azuay 010105, Ecuador;
| | - Maricarmen Chacín
- Facultad de Ciencias de la Salud, Universidad Simón Bolívar, Barranquilla 080022, Colombia; (M.C.); (V.B.)
| | - Marion Guerrero-Wyss
- Escuela de Nutrición y Dietética, Facultad de Ciencias Para el Cuidado de la Salud, Universidad San Sebastián, Valdivia 5090000, Chile;
| | | | - Clímaco Cano
- Endocrine and Metabolic Diseases Research Center, School of Medicine, Universidad del Zulia, Maracaibo 4002, Venezuela; (A.M.); (L.C.O.); (M.N.); (J.S.); (C.C.)
| | - Valmore Bermúdez
- Facultad de Ciencias de la Salud, Universidad Simón Bolívar, Barranquilla 080022, Colombia; (M.C.); (V.B.)
| | - Lisse Angarita
- Escuela de Nutrición y Dietética, Facultad de Medicina, Universidad Andres Bello, Sede Concepción 4260000, Chile
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19
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Ng XW, Chung YH, Piston DW. Intercellular Communication in the Islet of Langerhans in Health and Disease. Compr Physiol 2021; 11:2191-2225. [PMID: 34190340 PMCID: PMC8985231 DOI: 10.1002/cphy.c200026] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Blood glucose homeostasis requires proper function of pancreatic islets, which secrete insulin, glucagon, and somatostatin from the β-, α-, and δ-cells, respectively. Each islet cell type is equipped with intrinsic mechanisms for glucose sensing and secretory actions, but these intrinsic mechanisms alone cannot explain the observed secretory profiles from intact islets. Regulation of secretion involves interconnected mechanisms among and between islet cell types. Islet cells lose their normal functional signatures and secretory behaviors upon dispersal as compared to intact islets and in vivo. In dispersed islet cells, the glucose response of insulin secretion is attenuated from that seen from whole islets, coordinated oscillations in membrane potential and intracellular Ca2+ activity, as well as the two-phase insulin secretion profile, are missing, and glucagon secretion displays higher basal secretion profile and a reverse glucose-dependent response from that of intact islets. These observations highlight the critical roles of intercellular communication within the pancreatic islet, and how these communication pathways are crucial for proper hormonal and nonhormonal secretion and glucose homeostasis. Further, misregulated secretions of islet secretory products that arise from defective intercellular islet communication are implicated in diabetes. Intercellular communication within the islet environment comprises multiple mechanisms, including electrical synapses from gap junctional coupling, paracrine interactions among neighboring cells, and direct cell-to-cell contacts in the form of juxtacrine signaling. In this article, we describe the various mechanisms that contribute to proper islet function for each islet cell type and how intercellular islet communications are coordinated among the same and different islet cell types. © 2021 American Physiological Society. Compr Physiol 11:2191-2225, 2021.
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Affiliation(s)
- Xue W Ng
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri, USA
| | - Yong H Chung
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri, USA
| | - David W Piston
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri, USA
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20
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Keller JP, Marvin JS, Lacin H, Lemon WC, Shea J, Kim S, Lee RT, Koyama M, Keller PJ, Looger LL. In vivo glucose imaging in multiple model organisms with an engineered single-wavelength sensor. Cell Rep 2021; 35:109284. [PMID: 34161775 DOI: 10.1016/j.celrep.2021.109284] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Revised: 03/06/2020] [Accepted: 06/01/2021] [Indexed: 12/23/2022] Open
Abstract
Glucose is arguably the most important molecule in metabolism, and its dysregulation underlies diabetes. We describe a family of single-wavelength genetically encoded glucose sensors with a high signal-to-noise ratio, fast kinetics, and affinities varying over four orders of magnitude (1 μM to 10 mM). The sensors allow mechanistic characterization of glucose transporters expressed in cultured cells with high spatial and temporal resolution. Imaging of neuron/glia co-cultures revealed ∼3-fold faster glucose changes in astrocytes. In larval Drosophila central nervous system explants, intracellular neuronal glucose fluxes suggested a rostro-caudal transport pathway in the ventral nerve cord neuropil. In zebrafish, expected glucose-related physiological sequelae of insulin and epinephrine treatments were directly visualized. Additionally, spontaneous muscle twitches induced glucose uptake in muscle, and sensory and pharmacological perturbations produced large changes in the brain. These sensors will enable rapid, high-resolution imaging of glucose influx, efflux, and metabolism in behaving animals.
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Affiliation(s)
- Jacob P Keller
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA.
| | - Jonathan S Marvin
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Haluk Lacin
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - William C Lemon
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Jamien Shea
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Soomin Kim
- Harvard Department of Stem Cell and Regenerative Biology, Harvard Stem Cell Institute, Harvard Medical School, Brigham and Women's Hospital, Cambridge, MA, USA
| | - Richard T Lee
- Harvard Department of Stem Cell and Regenerative Biology, Harvard Stem Cell Institute, Harvard Medical School, Brigham and Women's Hospital, Cambridge, MA, USA; The Cardiovascular Division, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Cambridge, MA, USA
| | - Minoru Koyama
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Philipp J Keller
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Loren L Looger
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA.
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21
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Singh B, Khattab F, Chae H, Desmet L, Herrera PL, Gilon P. K ATP channel blockers control glucagon secretion by distinct mechanisms: A direct stimulation of α-cells involving a [Ca 2+] c rise and an indirect inhibition mediated by somatostatin. Mol Metab 2021; 53:101268. [PMID: 34118477 PMCID: PMC8274344 DOI: 10.1016/j.molmet.2021.101268] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 05/10/2021] [Accepted: 06/03/2021] [Indexed: 02/06/2023] Open
Abstract
Objective Glucagon is secreted by pancreatic α-cells in response to hypoglycemia and its hyperglycemic effect helps to restore normal blood glucose. Insulin and somatostatin (SST) secretions from β- and δ-cells, respectively, are stimulated by glucose by mechanisms involving an inhibition of their ATP-sensitive K+ (KATP) channels, leading to an increase in [Ca2+]c that triggers exocytosis. Drugs that close KATP channels, such as sulfonylureas, are used to stimulate insulin release in type 2 diabetic patients. α-cells also express KATP channels. However, the mechanisms by which sulfonylureas control glucagon secretion are still largely debated and were addressed in the present study. In particular, we studied the effects of KATP channel blockers on α-cell [Ca2+]c and glucagon secretion in the presence of a low (1 mM) or a high (15 mM) glucose concentration and evaluated the role of SST in these effects. Methods Using a transgenic mouse model expressing the Ca2+-sensitive fluorescent protein, GCaMP6f, specifically in α-cells, we measured [Ca2+]c in α-cells either dispersed or within whole islets (by confocal microscopy). By measuring [Ca2+]c in α-cells within islets and glucagon secretion using the same perifusion protocols, we tested whether glucagon secretion correlated with changes in [Ca2+]c in response to sulfonylureas. We studied the role of SST in the effects of sulfonylureas using multiple approaches including genetic ablation of SST, or application of SST-14 and SST receptor antagonists. Results Application of the sulfonylureas, tolbutamide, or gliclazide, to a medium containing 1 mM or 15 mM glucose increased [Ca2+]c in α-cells by a direct effect as in β-cells. At low glucose, sulfonylureas inhibited glucagon secretion of islets despite the rise in α-cell [Ca2+]c that they triggered. This glucagonostatic effect was indirect and attributed to SST because, in the islets of SST-knockout mice, sulfonylureas induced a stimulation of glucagon secretion which correlated with an increase in α-cell [Ca2+]c. Experiments with exogenous SST-14 and SST receptor antagonists indicated that the glucagonostatic effect of sulfonylureas mainly resulted from an inhibition of the efficacy of cytosolic Ca2+ on exocytosis. Although SST-14 was also able to inhibit glucagon secretion by decreasing α-cell [Ca2+]c, no decrease in [Ca2+]c occurred during sulfonylurea application because it was largely counterbalanced by the direct stimulatory effect of these drugs on α-cell [Ca2+]c. At high glucose, i.e., in conditions where glucagon release was already low, sulfonylureas stimulated glucagon secretion because their direct stimulatory effect on α-cells exceeded the indirect effect by SST. Our results also indicated that, unexpectedly, SST-14 poorly decreased the efficacy of Ca2+ on exocytosis in β-cells. Conclusions Sulfonylureas exert two opposite actions on α-cells: a direct stimulation as in β-cells and an indirect inhibition by SST. This suggests that any alteration of SST paracrine influence, as described in diabetes, will modify the effect of sulfonylureas on glucagon release. In addition, we suggest that δ-cells inhibit α-cells more efficiently than β-cells. KATP channel blockers control glucagon secretion by two mechanisms. The first one is the direct stimulation of α-cell by a [Ca2+]c rise, as in β-cells. The second one is an indirect inhibition mediated by δ-cells releasing somatostatin. Somatostatin mainly reduces the efficacy of Ca2+ on exocytosis in α-cells. Somatostatin more potently inhibits glucagon than insulin secretion.
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Affiliation(s)
- Bilal Singh
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium
| | - Firas Khattab
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium
| | - Heeyoung Chae
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium
| | - Lieven Desmet
- Université Catholique de Louvain, SMCS, Louvain Institute of Data Analysis and Modeling in economics and statistics, Louvain-la-Neuve, Belgium
| | - Pedro L Herrera
- Department of Genetic Medicine and Development, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Patrick Gilon
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium.
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Chatterjee N, Perrimon N. What fuels the fly: Energy metabolism in Drosophila and its application to the study of obesity and diabetes. SCIENCE ADVANCES 2021; 7:7/24/eabg4336. [PMID: 34108216 PMCID: PMC8189582 DOI: 10.1126/sciadv.abg4336] [Citation(s) in RCA: 72] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 04/23/2021] [Indexed: 05/16/2023]
Abstract
The organs and metabolic pathways involved in energy metabolism, and the process of ATP production from nutrients, are comparable between humans and Drosophila melanogaster This level of conservation, together with the power of Drosophila genetics, makes the fly a very useful model system to study energy homeostasis. Here, we discuss the major organs involved in energy metabolism in Drosophila and how they metabolize different dietary nutrients to generate adenosine triphosphate. Energy metabolism in these organs is controlled by cell-intrinsic, paracrine, and endocrine signals that are similar between Drosophila and mammals. We describe how these signaling pathways are regulated by several physiological and environmental cues to accommodate tissue-, age-, and environment-specific differences in energy demand. Last, we discuss several genetic and diet-induced fly models of obesity and diabetes that can be leveraged to better understand the molecular basis of these metabolic diseases and thereby promote the development of novel therapies.
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Affiliation(s)
| | - Norbert Perrimon
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA.
- Howard Hughes Medical Institute, Boston, MA 02115, USA
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23
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Role of cAMP in Double Switch of Glucagon Secretion. Cells 2021; 10:cells10040896. [PMID: 33919776 PMCID: PMC8070687 DOI: 10.3390/cells10040896] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 04/12/2021] [Accepted: 04/12/2021] [Indexed: 01/03/2023] Open
Abstract
Glucose metabolism plays a crucial role in modulating glucagon secretion in pancreatic alpha cells. However, the downstream effects of glucose metabolism and the activated signaling pathways influencing glucagon granule exocytosis are still obscure. We developed a computational alpha cell model, implementing metabolic pathways of glucose and free fatty acids (FFA) catabolism and an intrinsically activated cAMP signaling pathway. According to the model predictions, increased catabolic activity is able to suppress the cAMP signaling pathway, reducing exocytosis in a Ca2+-dependent and Ca2+ independent manner. The effect is synergistic to the pathway involving ATP-dependent closure of KATP channels and consequent reduction of Ca2+. We analyze the contribution of each pathway to glucagon secretion and show that both play decisive roles, providing a kind of "secure double switch". The cAMP-driven signaling switch plays a dominant role, while the ATP-driven metabolic switch is less favored. The ratio is approximately 60:40, according to the most recent experimental evidence.
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Sokolowska P, Zukowski K, Janikiewicz J, Jastrzebska E, Dobrzyn A, Brzozka Z. Islet-on-a-chip: Biomimetic micropillar-based microfluidic system for three-dimensional pancreatic islet cell culture. Biosens Bioelectron 2021; 183:113215. [PMID: 33845292 DOI: 10.1016/j.bios.2021.113215] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 03/15/2021] [Accepted: 03/28/2021] [Indexed: 12/14/2022]
Abstract
Type 2 diabetes is currently one of the most common metabolic diseases, affecting all ages worldwide. As the incidence of type 2 diabetes increases, a growing number of studies focus on islets of Langerhans. A three-dimensional research model that maps islet morphology and maintains hormonal balance in vivo is still needed. In this work, we present an Islet-on-a-chip system, specifically a micropillar-based microfluidic platform for three-dimensional pancreatic islet cell culture and analysis. The microfluidic system consisted of two culture chambers that were equipped with 15 circular microtraps each, which were built with seven round micropillars each. Micropillars in the structure of microtraps supported cell aggregation by limiting the growth surface and minimizing wall shear stress, thereby ensuring proper medium diffusion and optimal culture conditions for cell aggregates. Our system is compatible with microwell plate readers and confocal laser scanning microscopes. Because of optimization of the immunostaining method, the appropriate cell distribution and high viability and proliferation up to 72 h of culture were confirmed. Enzyme-linked immunosorbent assays were performed to measure insulin and glucagon secretion after stimulation with different glucose concentrations. To our knowledge, this is the first Lab-on-a-chip system which enables the formation and three-dimensional culture of cell aggregates composed of commercially available α and β pancreatic islet cells. The specific composition and arrangement of cells in the obtained model corresponds to the arrangement of the cells in rodent pancreatic islets in vivo. This Islet-on-a-chip system may be utilized to test pathogenic effectors and future therapeutic agents.
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Affiliation(s)
- Patrycja Sokolowska
- Medical Biotechnology, Faculty of Chemistry, Warsaw University of Technology, Poland; Laboratory of Cell Signaling and Metabolic Disorders, Nencki Institute of Experimental Biology of Polish Academy of Sciences, Warsaw, Poland
| | - Kamil Zukowski
- Centre for Advanced Materials and Technologies CEZAMAT, Warsaw University of Technology, Poland
| | - Justyna Janikiewicz
- Laboratory of Cell Signaling and Metabolic Disorders, Nencki Institute of Experimental Biology of Polish Academy of Sciences, Warsaw, Poland
| | - Elzbieta Jastrzebska
- Medical Biotechnology, Faculty of Chemistry, Warsaw University of Technology, Poland
| | - Agnieszka Dobrzyn
- Laboratory of Cell Signaling and Metabolic Disorders, Nencki Institute of Experimental Biology of Polish Academy of Sciences, Warsaw, Poland
| | - Zbigniew Brzozka
- Medical Biotechnology, Faculty of Chemistry, Warsaw University of Technology, Poland.
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25
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Lundqvist MH, Almby K, Wiklund U, Abrahamsson N, Kamble PG, Pereira MJ, Eriksson JW. Altered hormonal and autonomic nerve responses to hypo- and hyperglycaemia are found in overweight and insulin-resistant individuals and may contribute to the development of type 2 diabetes. Diabetologia 2021; 64:641-655. [PMID: 33241460 PMCID: PMC7864814 DOI: 10.1007/s00125-020-05332-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 10/01/2020] [Indexed: 12/27/2022]
Abstract
AIMS/HYPOTHESIS Results from animal models and some clinical work suggest a role for the central nervous system (CNS) in glucose regulation and type 2 diabetes pathogenesis by modulation of glucoregulatory hormones and the autonomic nervous system (ANS). The aim of this study was to characterise the neuroendocrine response to various glucose concentrations in overweight and insulin-resistant individuals compared with lean individuals. METHODS Overweight/obese (HI, n = 15, BMI ≥27.0 kg/m2) and lean (LO, n = 15, BMI <27.0 kg/m2) individuals without diabetes underwent hyperinsulinaemic euglycaemic-hypoglycaemic clamps and hyperglycaemic clamps on two separate occasions with measurements of hormones, Edinburgh Hypoglycaemic Symptom Scale (ESS) score and heart rate variability (HRV). Statistical methods included groupwise comparisons with Mann-Whitney U tests, multilinear regressions and linear mixed models between neuroendocrine responses and continuous metabolic variables. RESULTS During hypoglycaemic clamps, there was an elevated cortisol response in HI vs LO (median ΔAUC 12,383 vs 4793 nmol/l × min; p = 0.050) and a significantly elevated adrenocorticotropic hormone (ACTH) response in HI vs LO (median ΔAUC 437.3 vs 162.0 nmol/l × min; p = 0.021). When adjusting for clamp glucose levels, obesity (p = 0.033) and insulin resistance (p = 0.009) were associated with elevated glucagon levels. By contrast, parasympathetic activity was less suppressed in overweight individuals at the last stage of hypoglycaemia compared with euglycaemia (high-frequency power of HRV, p = 0.024). M value was the strongest predictor for the ACTH and PHF responses, independent of BMI and other variables. There was a BMI-independent association between the cortisol response and ESS score response (p = 0.024). During hyperglycaemic clamps, overweight individuals displayed less suppression of glucagon levels (median ΔAUC -63.4% vs -73.0%; p = 0.010) and more suppression of sympathetic relative to parasympathetic activity (low-frequency/high-frequency power, p = 0.011). CONCLUSIONS/INTERPRETATION This study supports the hypothesis that altered responses of insulin-antagonistic hormones and the ANS to glucose fluctuations occur in overweight and insulin-resistant individuals, and that these responses are probably partly mediated by the CNS. Their potential role in development of type 2 diabetes needs to be addressed in future research. Graphical abstract.
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Affiliation(s)
| | - Kristina Almby
- Department of Medical Sciences, Uppsala University, Uppsala, Sweden
| | - Urban Wiklund
- Department of Radiation Sciences, Biomedical Engineering, Umeå University, Umeå, Sweden
| | | | - Prasad G Kamble
- Department of Medical Sciences, Uppsala University, Uppsala, Sweden
| | - Maria J Pereira
- Department of Medical Sciences, Uppsala University, Uppsala, Sweden
| | - Jan W Eriksson
- Department of Medical Sciences, Uppsala University, Uppsala, Sweden.
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26
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Bahl V, Lee May C, Perez A, Glaser B, Kaestner KH. Genetic activation of α-cell glucokinase in mice causes enhanced glucose-suppression of glucagon secretion during normal and diabetic states. Mol Metab 2021; 49:101193. [PMID: 33610858 PMCID: PMC7973249 DOI: 10.1016/j.molmet.2021.101193] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 02/03/2021] [Accepted: 02/11/2021] [Indexed: 12/31/2022] Open
Abstract
Objective While the molecular events controlling insulin secretion from β-cells have been documented in detail, the exact mechanisms governing glucagon release by α-cells are understood only partially. This is a critical knowledge gap, as the normal suppression of glucagon secretion by elevated glucose levels fails in type 2 diabetes (T2D) patients, contributing to hyperglycemia through stimulation of hepatic glucose production. A critical role of glycolytic flux in regulating glucagon secretion was supported by recent studies in which manipulation of the activity and expression of the glycolytic enzyme glucokinase altered the setpoint for glucose-suppression of glucagon secretion (GSGS). Given this precedent, we hypothesized that genetic activation of glucokinase specifically in α-cells would enhance GSGS and mitigate T2D hyperglucagonemia. Methods We derived an inducible, α-cell-specific glucokinase activating mutant mouse model (GckLoxPGck∗/LoxPGck∗; Gcg-CreERT2; henceforth referred to as “α-mutGCK”) in which the wild-type glucokinase gene (GCK) is conditionally replaced with a glucokinase mutant allele containing the ins454A activating mutation (Gck∗), a mutation that increases the affinity of glucokinase for glucose by almost 7-fold. The effects of α-cell GCK activation on glucose homeostasis, hormone secretion, islet morphology, and islet numbers were assessed using both in vivo and ex vivo assays. Additionally, the effect of α-cell GCK activation on GSGS was investigated under diabetogenic conditions of high-fat diet (HFD) feeding that dysregulate glucagon secretion. Results Our study shows that α-mutGCK mice have enhanced GSGS in vivo and ex vivo, independent of alterations in insulin levels and secretion, islet hormone content, islet morphology, or islet number. α-mutGCK mice maintained on HFD displayed improvements in glucagonemia compared to controls, which developed the expected obesity, glucose intolerance, elevated fasting blood glucose, hyperinsulinemia, and hyperglucagonemia. Conclusions Using our novel α-cell specific activation of GCK mouse model, we have provided additional support to demonstrate that the glycolytic enzyme glucokinase is a key determinant in glucose sensing within α-cells to regulate glucagon secretion. Our results contribute to our fundamental understanding of α-cell biology by providing greater insight into the regulation of glucagon secretion through α-cell intrinsic mechanisms via glucokinase. Furthermore, our HFD results underscore the potential of glucokinase as a druggable target which, given the ongoing development of allosteric glucokinase activators (GKAs) for T2D treatment, could help mitigate hyperglucagonemia and potentially improve blood glucose homeostasis. Inducible and cell type-specific point mutation in glucokinase enables analysis of glucose suppression of glucagon secretion. Glycolytic flux through glucokinase determines the set-point for glucagon secretion in pancreatic α-cells. Pancreatic α-cells are a physiologically relevant target of glucokinase activator drugs.
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Affiliation(s)
- Varun Bahl
- Institute of Diabetes, Obesity, and Metabolism, Perelman School of Medicine, The University of Pennsylvania, 3400 Civic Center Boulevard, Philadelphia, PA 19104, USA; Department of Genetics, Perelman School of Medicine, The University of Pennsylvania, 3400 Civic Center Boulevard, Philadelphia, PA 19104, USA.
| | - Catherine Lee May
- Institute of Diabetes, Obesity, and Metabolism, Perelman School of Medicine, The University of Pennsylvania, 3400 Civic Center Boulevard, Philadelphia, PA 19104, USA; Department of Genetics, Perelman School of Medicine, The University of Pennsylvania, 3400 Civic Center Boulevard, Philadelphia, PA 19104, USA.
| | - Alanis Perez
- Institute of Diabetes, Obesity, and Metabolism, Perelman School of Medicine, The University of Pennsylvania, 3400 Civic Center Boulevard, Philadelphia, PA 19104, USA; Department of Genetics, Perelman School of Medicine, The University of Pennsylvania, 3400 Civic Center Boulevard, Philadelphia, PA 19104, USA.
| | - Benjamin Glaser
- Endocrinology and Metabolism Department, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel.
| | - Klaus H Kaestner
- Institute of Diabetes, Obesity, and Metabolism, Perelman School of Medicine, The University of Pennsylvania, 3400 Civic Center Boulevard, Philadelphia, PA 19104, USA; Department of Genetics, Perelman School of Medicine, The University of Pennsylvania, 3400 Civic Center Boulevard, Philadelphia, PA 19104, USA.
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27
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Aslanoglou D, Bertera S, Sánchez-Soto M, Benjamin Free R, Lee J, Zong W, Xue X, Shrestha S, Brissova M, Logan RW, Wollheim CB, Trucco M, Yechoor VK, Sibley DR, Bottino R, Freyberg Z. Dopamine regulates pancreatic glucagon and insulin secretion via adrenergic and dopaminergic receptors. Transl Psychiatry 2021; 11:59. [PMID: 33589583 PMCID: PMC7884786 DOI: 10.1038/s41398-020-01171-z] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 10/13/2020] [Accepted: 10/26/2020] [Indexed: 01/14/2023] Open
Abstract
Dopamine (DA) and norepinephrine (NE) are catecholamines primarily studied in the central nervous system that also act in the pancreas as peripheral regulators of metabolism. Pancreatic catecholamine signaling has also been increasingly implicated as a mechanism responsible for the metabolic disturbances produced by antipsychotic drugs (APDs). Critically, however, the mechanisms by which catecholamines modulate pancreatic hormone release are not completely understood. We show that human and mouse pancreatic α- and β-cells express the catecholamine biosynthetic and signaling machinery, and that α-cells synthesize DA de novo. This locally-produced pancreatic DA signals via both α- and β-cell adrenergic and dopaminergic receptors with different affinities to regulate glucagon and insulin release. Significantly, we show DA functions as a biased agonist at α2A-adrenergic receptors, preferentially signaling via the canonical G protein-mediated pathway. Our findings highlight the interplay between DA and NE signaling as a novel form of regulation to modulate pancreatic hormone release. Lastly, pharmacological blockade of DA D2-like receptors in human islets with APDs significantly raises insulin and glucagon release. This offers a new mechanism where APDs act directly on islet α- and β-cell targets to produce metabolic disturbances.
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Affiliation(s)
- Despoina Aslanoglou
- grid.21925.3d0000 0004 1936 9000Translational Neuroscience Program, Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA USA
| | - Suzanne Bertera
- grid.417046.00000 0004 0454 5075Institute of Cellular Therapeutics, Allegheny Health Network Research Institute, Allegheny Health Network, Pittsburgh, PA USA
| | - Marta Sánchez-Soto
- grid.94365.3d0000 0001 2297 5165Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD USA
| | - R. Benjamin Free
- grid.94365.3d0000 0001 2297 5165Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD USA
| | - Jeongkyung Lee
- grid.21925.3d0000 0004 1936 9000Division of Endocrinology, Diabetes & Metabolism, Department of Medicine, Diabetes and Beta Cell Biology Center, University of Pittsburgh, Pittsburgh, PA USA
| | - Wei Zong
- grid.21925.3d0000 0004 1936 9000Department of Biostatistics, University of Pittsburgh, Pittsburgh, PA USA
| | - Xiangning Xue
- grid.21925.3d0000 0004 1936 9000Department of Biostatistics, University of Pittsburgh, Pittsburgh, PA USA
| | - Shristi Shrestha
- grid.412807.80000 0004 1936 9916Division of Diabetes, Endocrinology, and Metabolism, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN USA
| | - Marcela Brissova
- grid.412807.80000 0004 1936 9916Division of Diabetes, Endocrinology, and Metabolism, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN USA
| | - Ryan W. Logan
- grid.21925.3d0000 0004 1936 9000Translational Neuroscience Program, Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA USA ,grid.249880.f0000 0004 0374 0039Center for Systems Neurogenetics of Addiction, The Jackson Laboratory, Bar Harbor, ME USA
| | - Claes B. Wollheim
- grid.8591.50000 0001 2322 4988Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - Massimo Trucco
- grid.417046.00000 0004 0454 5075Institute of Cellular Therapeutics, Allegheny Health Network Research Institute, Allegheny Health Network, Pittsburgh, PA USA ,grid.147455.60000 0001 2097 0344Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA USA ,grid.166341.70000 0001 2181 3113College of Medicine, Drexel University, Philadelphia, PA USA
| | - Vijay K. Yechoor
- grid.21925.3d0000 0004 1936 9000Division of Endocrinology, Diabetes & Metabolism, Department of Medicine, Diabetes and Beta Cell Biology Center, University of Pittsburgh, Pittsburgh, PA USA
| | - David R. Sibley
- grid.94365.3d0000 0001 2297 5165Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD USA
| | - Rita Bottino
- grid.417046.00000 0004 0454 5075Institute of Cellular Therapeutics, Allegheny Health Network Research Institute, Allegheny Health Network, Pittsburgh, PA USA ,grid.147455.60000 0001 2097 0344Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA USA ,grid.166341.70000 0001 2181 3113College of Medicine, Drexel University, Philadelphia, PA USA
| | - Zachary Freyberg
- Translational Neuroscience Program, Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, USA. .,Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA, USA.
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28
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Früh E, Elgert C, Eggert F, Scherneck S, Rustenbeck I. Glucagonotropic and Glucagonostatic Effects of KATP Channel Closure and Potassium Depolarization. Endocrinology 2021; 162:5892293. [PMID: 32790843 DOI: 10.1210/endocr/bqaa136] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Accepted: 08/05/2020] [Indexed: 02/08/2023]
Abstract
The role of depolarization in the inverse glucose-dependence of glucagon secretion was investigated by comparing the effects of KATP channel block and of high potassium. The secretion of glucagon and insulin by perifused mouse islets was simultaneously measured. Lowering glucose raised glucagon secretion before it decreased insulin secretion, suggesting an alpha cell-intrinsic signal recognition. Raising glucose affected glucagon and insulin secretion at the same time. However, depolarization by tolbutamide, gliclazide, or 15 mM KCl increased insulin secretion before the glucagon secretion receded. In contrast to the robust depolarizing effect of arginine and KCl (15 and 40 mM) on single alpha cells, tolbutamide was of variable efficacy. Only when applied before other depolarizing agents had tolbutamide a consistent depolarizing effect and regularly increased the cytosolic Ca2+ concentration. When tested on inside-out patches tolbutamide was as effective on alpha cells as on beta cells. In the presence of 1 µM clonidine, to separate insulinotropic from glucagonotropic effects, both 500 µM tolbutamide and 30 µM gliclazide increased glucagon secretion significantly, but transiently. The additional presence of 15 or 40 mM KCl in contrast led to a marked and lasting increase of the glucagon secretion. The glucagon secretion by SUR1 knockout islets was not increased by tolbutamide, whereas 40 mM KCl was of unchanged efficiency. In conclusion a strong and sustained depolarization is compatible with a marked and lasting glucagon secretion. KATP channel closure in alpha cells is less readily achieved than in beta cells, which may explain the moderate and transient glucagonotropic effect.
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Affiliation(s)
- Eike Früh
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Braunschweig, Germany
| | - Christin Elgert
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Braunschweig, Germany
| | - Frank Eggert
- Institute of Psychology, Technische Universität Braunschweig, Braunschweig, Germany
| | - Stephan Scherneck
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Braunschweig, Germany
| | - Ingo Rustenbeck
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Braunschweig, Germany
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Hædersdal S, Lund A, Nielsen-Hannerup E, Maagensen H, van Hall G, Holst JJ, Knop FK, Vilsbøll T. The Role of Glucagon in the Acute Therapeutic Effects of SGLT2 Inhibition. Diabetes 2020; 69:2619-2629. [PMID: 33004472 PMCID: PMC7679772 DOI: 10.2337/db20-0369] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Accepted: 09/24/2020] [Indexed: 12/15/2022]
Abstract
Sodium-glucose cotransporter 2 inhibitors (SGLT2i) effectively lower plasma glucose (PG) concentration in patients with type 2 diabetes, but studies have suggested that circulating glucagon concentrations and endogenous glucose production (EGP) are increased by SGLT2i, possibly compromising their glucose-lowering ability. To tease out whether and how glucagon may influence the glucose-lowering effect of SGLT2 inhibition, we subjected 12 patients with type 2 diabetes to a randomized, placebo-controlled, double-blinded, crossover, double-dummy study comprising, on 4 separate days, a liquid mixed-meal test preceded by single-dose administration of either 1) placebo, 2) the SGLT2i empagliflozin (25 mg), 3) the glucagon receptor antagonist LY2409021 (300 mg), or 4) the combination empagliflozin + LY2409021. Empagliflozin and LY2409021 individually lowered fasting PG compared with placebo, and the combination further decreased fasting PG. Previous findings of increased glucagon concentrations and EGP during acute administration of SGLT2i were not replicated in this study. Empagliflozin reduced postprandial PG through increased urinary glucose excretion. LY2409021 reduced EGP significantly but gave rise to a paradoxical increase in postprandial PG excursion, which was annulled by empagliflozin during their combination (empagliflozin + LY2409021). In conclusion, our findings do not support that an SGLT2i-induced glucagonotropic effect is of importance for the glucose-lowering property of SGLT2 inhibition.
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Affiliation(s)
- Sofie Hædersdal
- Steno Diabetes Center Copenhagen, Gentofte, Denmark
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
- Danish Diabetes Academy, Odense University Hospital, Odense, Denmark
| | - Asger Lund
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
| | | | - Henrik Maagensen
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
| | - Gerrit van Hall
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Clinical Metabolomics Core Facility, Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Jens J Holst
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Filip K Knop
- Steno Diabetes Center Copenhagen, Gentofte, Denmark
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Tina Vilsbøll
- Steno Diabetes Center Copenhagen, Gentofte, Denmark
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
- Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Moede T, Leibiger B, Vaca Sanchez P, Daré E, Köhler M, Muhandiramlage TP, Leibiger IB, Berggren PO. Glucokinase intrinsically regulates glucose sensing and glucagon secretion in pancreatic alpha cells. Sci Rep 2020; 10:20145. [PMID: 33214580 PMCID: PMC7678872 DOI: 10.1038/s41598-020-76863-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Accepted: 11/02/2020] [Indexed: 01/08/2023] Open
Abstract
The secretion of glucagon by pancreatic alpha cells is regulated by a number of external and intrinsic factors. While the electrophysiological processes linking a lowering of glucose concentrations to an increased glucagon release are well characterized, the evidence for the identity and function of the glucose sensor is still incomplete. In the present study we aimed to address two unsolved problems: (1) do individual alpha cells have the intrinsic capability to regulate glucagon secretion by glucose, and (2) is glucokinase the alpha cell glucose sensor in this scenario. Single cell RT-PCR was used to confirm that glucokinase is the main glucose-phosphorylating enzyme expressed in rat pancreatic alpha cells. Modulation of glucokinase activity by pharmacological activators and inhibitors led to a lowering or an increase of the glucose threshold of glucagon release from single alpha cells, measured by TIRF microscopy, respectively. Knockdown of glucokinase expression resulted in a loss of glucose control of glucagon secretion. Taken together this study provides evidence for a crucial role of glucokinase in intrinsic glucose regulation of glucagon release in rat alpha cells.
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Affiliation(s)
- Tilo Moede
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska Sjukhuset L1:03, 17176, Stockholm, Sweden.
| | - Barbara Leibiger
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska Sjukhuset L1:03, 17176, Stockholm, Sweden
| | - Pilar Vaca Sanchez
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska Sjukhuset L1:03, 17176, Stockholm, Sweden
| | - Elisabetta Daré
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska Sjukhuset L1:03, 17176, Stockholm, Sweden
| | - Martin Köhler
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska Sjukhuset L1:03, 17176, Stockholm, Sweden
| | - Thusitha P Muhandiramlage
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska Sjukhuset L1:03, 17176, Stockholm, Sweden
| | - Ingo B Leibiger
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska Sjukhuset L1:03, 17176, Stockholm, Sweden
| | - Per-Olof Berggren
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska Sjukhuset L1:03, 17176, Stockholm, Sweden
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Koyama T, Texada MJ, Halberg KA, Rewitz K. Metabolism and growth adaptation to environmental conditions in Drosophila. Cell Mol Life Sci 2020; 77:4523-4551. [PMID: 32448994 PMCID: PMC7599194 DOI: 10.1007/s00018-020-03547-2] [Citation(s) in RCA: 64] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Revised: 04/19/2020] [Accepted: 05/11/2020] [Indexed: 02/07/2023]
Abstract
Organisms adapt to changing environments by adjusting their development, metabolism, and behavior to improve their chances of survival and reproduction. To achieve such flexibility, organisms must be able to sense and respond to changes in external environmental conditions and their internal state. Metabolic adaptation in response to altered nutrient availability is key to maintaining energy homeostasis and sustaining developmental growth. Furthermore, environmental variables exert major influences on growth and final adult body size in animals. This developmental plasticity depends on adaptive responses to internal state and external cues that are essential for developmental processes. Genetic studies have shown that the fruit fly Drosophila, similarly to mammals, regulates its metabolism, growth, and behavior in response to the environment through several key hormones including insulin, peptides with glucagon-like function, and steroid hormones. Here we review emerging evidence showing that various environmental cues and internal conditions are sensed in different organs that, via inter-organ communication, relay information to neuroendocrine centers that control insulin and steroid signaling. This review focuses on endocrine regulation of development, metabolism, and behavior in Drosophila, highlighting recent advances in the role of the neuroendocrine system as a signaling hub that integrates environmental inputs and drives adaptive responses.
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Affiliation(s)
- Takashi Koyama
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Michael J Texada
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Kenneth A Halberg
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Kim Rewitz
- Department of Biology, University of Copenhagen, Copenhagen, Denmark.
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Ng JCM, Schooling CM. Effect of Glucagon on Ischemic Heart Disease and Its Risk Factors: A Mendelian Randomization Study. J Clin Endocrinol Metab 2020; 105:5837127. [PMID: 32407514 DOI: 10.1210/clinem/dgaa259] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Accepted: 05/08/2020] [Indexed: 01/10/2023]
Abstract
CONTEXT Glucagon acts reciprocally with insulin to regular blood glucose. However, the effect of glucagon on cardiovascular disease has not been widely studied. It has been suggested that insulin may increase the risk of ischemic heart disease. OBJECTIVE To investigate whether glucagon, the main counteracting hormone of insulin, plays a role in development of ischemic heart disease. DESIGN, SETTING, AND PARTICIPANTS In this 2-sample Mendelian randomization study, we estimated the causal effect of glucagon on ischemic heart disease and its risk factors using the inverse-variance weighted method with multiplicative random effects and multiple sensitivity analyses. Genetic associations with glucagon and ischemic heart disease and its risk factors, including type 2 diabetes and fasting insulin, were obtained from publicly available genome-wide association studies. MAIN OUTCOME MEASURE Odds ratio for ischemic heart disease and its risk factors per 1 standard deviation change in genetically predicted glucagon. RESULTS Twenty-four single-nucleotide polymorphisms strongly (P < 5 × 10-6) and independently (r2 < 0.05) predicting glucagon were obtained. Genetically predicted higher glucagon was associated with an increased risk of ischemic heart disease (inverse-variance weighted odds ratio, 1.03; 95% confidence interval, 1.0003-1.05) but not with type 2 diabetes (inverse-variance weighted odds ratio, 0.998, 95% confidence interval, 0.97-1.03), log-transformed fasting insulin (inverse-variance weighted beta, 0.002, 95% confidence interval, -0.01 to 0.01), other glycemic traits, blood pressure, reticulocyte, or lipids. CONCLUSION Glucagon might have an adverse impact on ischemic heart disease. Relevance of the underlying pathway to existing and potential interventions should be investigated.
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Affiliation(s)
- Jack C M Ng
- School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China
| | - C Mary Schooling
- School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China
- Graduate School of Public Health and Health Policy, The City University of New York, New York, USA
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Mechanisms of the Regulation and Dysregulation of Glucagon Secretion. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2020; 2020:3089139. [PMID: 32774668 PMCID: PMC7396046 DOI: 10.1155/2020/3089139] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 07/11/2020] [Indexed: 02/06/2023]
Abstract
Glucagon, a hormone secreted by pancreatic alpha cells, contributes to the maintenance of normal blood glucose concentration by inducing hepatic glucose production in response to declining blood glucose. However, glucagon hypersecretion contributes to the pathogenesis of type 2 diabetes. Moreover, diabetes is associated with relative glucagon undersecretion at low blood glucose and oversecretion at normal and high blood glucose. The mechanisms of such alpha cell dysfunctions are not well understood. This article reviews the genesis of alpha cell dysfunctions during the pathogenesis of type 2 diabetes and after the onset of type 1 and type 2 diabetes. It unravels a signaling pathway that contributes to glucose- or hydrogen peroxide-induced glucagon secretion, whose overstimulation contributes to glucagon dysregulation, partly through oxidative stress and reduced ATP synthesis. The signaling pathway involves phosphatidylinositol-3-kinase, protein kinase B, protein kinase C delta, non-receptor tyrosine kinase Src, and phospholipase C gamma-1. This knowledge will be useful in the design of new antidiabetic agents or regimens.
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Xu SFS, Andersen DB, Izarzugaza JMG, Kuhre RE, Holst JJ. In the rat pancreas, somatostatin tonically inhibits glucagon secretion and is required for glucose-induced inhibition of glucagon secretion. Acta Physiol (Oxf) 2020; 229:e13464. [PMID: 32145704 DOI: 10.1111/apha.13464] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Revised: 02/28/2020] [Accepted: 03/04/2020] [Indexed: 12/20/2022]
Abstract
AIM It is debated whether the inhibition of glucagon secretion by glucose results from direct effects of glucose on the α-cell (intrinsic regulation) or by paracrine effects exerted by beta- or delta-cell products. METHODS To study this in a more physiological model than isolated islets, we perfused isolated rat pancreases and measured glucagon, insulin and somatostatin secretion in response to graded increases in perfusate glucose concentration (from 3.5 to 4, 5, 6, 7, 8, 10, 12 mmol/L) as well as glucagon responses to blockage/activation of insulin/GABA/somatostatin signalling with or without addition of glucose. RESULTS Glucagon secretion was reduced by about 50% (compared to baseline secretion at 3.5 mmol/L) within minutes after increasing glucose from 4 to 5 mmol/L (P < .01, n = 13). Insulin secretion was increased minimally, but significantly, compared to baseline (3.5 mmol/L) at 4 mmol/L, whereas somatostatin secretion was not significantly increased from baseline until 7 mmol/L. Hereafter secretion of both increased gradually up to 12 mmol/L glucose. Neither recombinant insulin (1 µmol/L), GABA (300 µmol/L) or the insulin-receptor antagonist S961 (at 1 µmol/L) affected basal (3.5 mmol/L) or glucose-induced (5.0 mmol/L) attenuation of glucagon secretion (n = 7-8). Somatostatin-14 attenuated glucagon secretion by ~ 95%, and blockage of somatostatin-receptor (SSTR)-2 or combined blockage of SSTR-2, -3 and -5 by specific antagonists increased glucagon output (at 3.5 mmol/L glucose) and prevented glucose-induced (from 3.5 to 5.0 mmol/L) suppression of secretion. CONCLUSION Somatostatin is a powerful and tonic inhibitor of glucagon secretion from the rat pancreas and is required for glucose to inhibit glucagon secretion.
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Affiliation(s)
- Stella F. S. Xu
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
| | - Daniel B. Andersen
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
| | | | - Rune E. Kuhre
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
| | - Jens J. Holst
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
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Reduced somatostatin signalling leads to hypersecretion of glucagon in mice fed a high-fat diet. Mol Metab 2020; 40:101021. [PMID: 32446876 PMCID: PMC7322681 DOI: 10.1016/j.molmet.2020.101021] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Revised: 05/11/2020] [Accepted: 05/14/2020] [Indexed: 11/29/2022] Open
Abstract
Objectives Elevated plasma glucagon is an early symptom of diabetes, occurring in subjects with impaired glucose regulation. Here, we explored alpha-cell function in female mice fed a high-fat diet (HFD). Methods Female mice expressing the Ca2+ indicator GCaMP3 specifically in alpha-cells were fed a high-fat or control (CTL) diet. We then conducted in vivo phenotyping of these mice, as well as experiments on isolated (ex vivo) islets and in the in situ perfused pancreas. Results In HFD-fed mice, fed plasma glucagon levels were increased and glucagon secretion from isolated islets and in the perfused mouse pancreas was also elevated. In mice fed a CTL diet, increasing glucose reduced intracellular Ca2+ ([Ca2+]i) oscillation frequency and amplitude. This effect was also observed in HFD mice; however, both the frequency and amplitude of the [Ca2+]i oscillations were higher than those in CTL alpha-cells. Given that alpha-cells are under strong paracrine control from neighbouring somatostatin-secreting delta-cells, we hypothesised that this elevation of alpha-cell output was due to a lack of somatostatin (SST) secretion. Indeed, SST secretion in isolated islets from HFD-fed mice was reduced but exogenous SST also failed to suppress glucagon secretion and [Ca2+]i activity from HFD alpha-cells, in contrast to observations in CTL mice. Conclusions These findings suggest that reduced delta-cell function, combined with intrinsic changes in alpha-cells including sensitivity to somatostatin, accounts for the hyperglucagonaemia in mice fed a HFD. HFD feeding causes hyperglucagonaemia in vivo. Glucagon is inadequately suppressed by glucose in HFD-fed mice. Alpha-cell [Ca2+]i oscillations and glucagon output are elevated ex vivo in response to HFD feeding. SST secretion from HFD islets is reduced. Alpha-cells from HFD-fed mice become ‘resistant’ to SST.
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Omar-Hmeadi M, Lund PE, Gandasi NR, Tengholm A, Barg S. Paracrine control of α-cell glucagon exocytosis is compromised in human type-2 diabetes. Nat Commun 2020; 11:1896. [PMID: 32312960 PMCID: PMC7171169 DOI: 10.1038/s41467-020-15717-8] [Citation(s) in RCA: 55] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Accepted: 03/23/2020] [Indexed: 01/05/2023] Open
Abstract
Glucagon is released from pancreatic α-cells to activate pathways that raise blood glucose. Its secretion is regulated by α-cell-intrinsic glucose sensing and paracrine control through insulin and somatostatin. To understand the inadequately high glucagon levels that contribute to hyperglycemia in type-2 diabetes (T2D), we analyzed granule behavior, exocytosis and membrane excitability in α-cells of 68 non-diabetic and 21 T2D human donors. We report that exocytosis is moderately reduced in α-cells of T2D donors, without changes in voltage-dependent ion currents or granule trafficking. Dispersed α-cells have a non-physiological V-shaped dose response to glucose, with maximal exocytosis at hyperglycemia. Within intact islets, hyperglycemia instead inhibits α-cell exocytosis, but not in T2D or when paracrine inhibition by insulin or somatostatin is blocked. Surface expression of somatostatin-receptor-2 is reduced in T2D, suggesting a mechanism for the observed somatostatin resistance. Thus, elevated glucagon in human T2D may reflect α-cell insensitivity to paracrine inhibition at hyperglycemia. Glucagon is elevated Type-2 diabetes, which contributes to poor glucose control in patients with the disease. Here the authors report that secretion of the hormone is controlled by paracrine inhibition, and that resistance of α-cells to somatostatin can explain hyperglucagonemia in type-2 diabetes.
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Affiliation(s)
- Muhmmad Omar-Hmeadi
- Medical Cell Biology, Uppsala University, Box 571, BMC, 751 23, Uppsala, Sweden
| | - Per-Eric Lund
- Medical Cell Biology, Uppsala University, Box 571, BMC, 751 23, Uppsala, Sweden
| | - Nikhil R Gandasi
- Medical Cell Biology, Uppsala University, Box 571, BMC, 751 23, Uppsala, Sweden
| | - Anders Tengholm
- Medical Cell Biology, Uppsala University, Box 571, BMC, 751 23, Uppsala, Sweden
| | - Sebastian Barg
- Medical Cell Biology, Uppsala University, Box 571, BMC, 751 23, Uppsala, Sweden.
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Grubelnik V, Zmazek J, Markovič R, Gosak M, Marhl M. Modelling of energy-driven switch for glucagon and insulin secretion. J Theor Biol 2020; 493:110213. [PMID: 32109481 DOI: 10.1016/j.jtbi.2020.110213] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 02/19/2020] [Accepted: 02/24/2020] [Indexed: 12/14/2022]
Abstract
We present a mathematical model of the energy-driven metabolic switch for glucagon and insulin secretion from pancreatic alpha and beta cells, respectively. The energy status related to hormone secretion is studied for various glucose concentrations. Additionally, the physiological response is studied with regards to the presence of other metabolites, particularly the free-fatty acids. At low glucose, the ATP production in alpha cells is high due to free-fatty acids oxidation in mitochondria, which enables glucagon secretion. When the glucose concentration is elevated above the threshold value, the glucagon secretion is switched off due to the contribution of glycolytic ATP production, representing an "anaerobic switch". On the other hand, during hypoglycemia, the ATP production in beta cells is low, reflecting a "waiting state" for glucose as the main metabolite. When glucose is elevated above the threshold value, the oxidative fate of glucose in mitochondria is the main source of energy required for effective insulin secretion, i.e. the "aerobic switch". Our results show the importance of well-regulated and fine-tuned energetic processes in pancreatic alpha and beta cells required for efficient hormone secretion and hence effective blood glucose regulation. These energetic processes have to be appropriately switched on and off based on the sensing of different metabolites by alpha and beta cells. Our computational results indicate that disturbances in cell energetics (e.g. mitochondrial dysfunction), and dysfunctional metabolite sensing and distribution throughout the cell might be related to pathologies such as metabolic syndrome and diabetes.
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Affiliation(s)
- Vladimir Grubelnik
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor SI-2000, Slovenia
| | - Jan Zmazek
- Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor SI-2000, Slovenia
| | - Rene Markovič
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor SI-2000, Slovenia; Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor SI-2000, Slovenia
| | - Marko Gosak
- Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor SI-2000, Slovenia; Faculty of Medicine, University of Maribor, Maribor SI-2000, Slovenia
| | - Marko Marhl
- Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor SI-2000, Slovenia; Faculty of Medicine, University of Maribor, Maribor SI-2000, Slovenia; Faculty of Education, University of Maribor, Maribor SI-2000, Slovenia.
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Cherkas A, Holota S, Mdzinarashvili T, Gabbianelli R, Zarkovic N. Glucose as a Major Antioxidant: When, What for and Why It Fails? Antioxidants (Basel) 2020; 9:antiox9020140. [PMID: 32033390 PMCID: PMC7070274 DOI: 10.3390/antiox9020140] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 02/01/2020] [Accepted: 02/03/2020] [Indexed: 02/07/2023] Open
Abstract
A human organism depends on stable glucose blood levels in order to maintain its metabolic needs. Glucose is considered to be the most important energy source, and glycolysis is postulated as a backbone pathway. However, when the glucose supply is limited, ketone bodies and amino acids can be used to produce enough ATP. In contrast, for the functioning of the pentose phosphate pathway (PPP) glucose is essential and cannot be substituted by other metabolites. The PPP generates and maintains the levels of nicotinamide adenine dinucleotide phosphate (NADPH) needed for the reduction in oxidized glutathione and protein thiols, the synthesis of lipids and DNA as well as for xenobiotic detoxification, regulatory redox signaling and counteracting infections. The flux of glucose into a PPP—particularly under extreme oxidative and toxic challenges—is critical for survival, whereas the glycolytic pathway is primarily activated when glucose is abundant, and there is lack of NADP+ that is required for the activation of glucose-6 phosphate dehydrogenase. An important role of glycogen stores in resistance to oxidative challenges is discussed. Current evidences explain the disruptive metabolic effects and detrimental health consequences of chronic nutritional carbohydrate overload, and provide new insights into the positive metabolic effects of intermittent fasting, caloric restriction, exercise, and ketogenic diet through modulation of redox homeostasis.
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Affiliation(s)
- Andriy Cherkas
- Department of Internal Medicine # 1, Lviv National Medical University, 79010 Lviv, Ukraine
- Correspondence:
| | - Serhii Holota
- Department of Pharmaceutical, Organic and Bioorganic Chemistry, Lviv National Medical University, 79010 Lviv, Ukraine;
- Department of Organic Chemistry and Pharmacy, Lesya Ukrainka Eastern European National University, 43025 Lutsk, Ukraine
| | - Tamaz Mdzinarashvili
- Institute of Medical and Applied Biophysics, I. Javakhishvili Tbilisi State University, 0128 Tbilisi, Georgia;
| | - Rosita Gabbianelli
- Unit of Molecular Biology, School of Pharmacy, University of Camerino, 62032 Camerino, Italy;
| | - Neven Zarkovic
- Laboratory for Oxidative Stress (LabOS), Institute “Rudjer Boskovic”, HR-10000 Zagreb, Croatia;
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Gilon P. The Role of α-Cells in Islet Function and Glucose Homeostasis in Health and Type 2 Diabetes. J Mol Biol 2020; 432:1367-1394. [PMID: 31954131 DOI: 10.1016/j.jmb.2020.01.004] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 12/23/2019] [Accepted: 01/06/2020] [Indexed: 01/09/2023]
Abstract
Pancreatic α-cells are the major source of glucagon, a hormone that counteracts the hypoglycemic action of insulin and strongly contributes to the correction of acute hypoglycemia. The mechanisms by which glucose controls glucagon secretion are hotly debated, and it is still unclear to what extent this control results from a direct action of glucose on α-cells or is indirectly mediated by β- and/or δ-cells. Besides its hyperglycemic action, glucagon has many other effects, in particular on lipid and amino acid metabolism. Counterintuitively, glucagon seems also required for an optimal insulin secretion in response to glucose by acting on its cognate receptor and, even more importantly, on GLP-1 receptors. Patients with diabetes mellitus display two main alterations of glucagon secretion: a relative hyperglucagonemia that aggravates hyperglycemia, and an impaired glucagon response to hypoglycemia. Under metabolic stress states, such as diabetes, pancreatic α-cells also secrete GLP-1, a glucose-lowering hormone, whereas the gut can produce glucagon. The contribution of extrapancreatic glucagon to the abnormal glucose homeostasis is unclear. Here, I review the possible mechanisms of control of glucagon secretion and the role of α-cells on islet function in healthy state. I discuss the possible causes of the abnormal glucagonemia in diabetes, with particular emphasis on type 2 diabetes, and I briefly comment the current antidiabetic therapies affecting α-cells.
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Affiliation(s)
- Patrick Gilon
- Université Catholique de Louvain, Institute of Experimental and Clinical Research, Pole of Endocrinology, Diabetes and Nutrition, Avenue Hippocrate 55 (B1.55.06), Brussels, B-1200, Belgium.
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Grubelnik V, Markovič R, Lipovšek S, Leitinger G, Gosak M, Dolenšek J, Valladolid-Acebes I, Berggren PO, Stožer A, Perc M, Marhl M. Modelling of dysregulated glucagon secretion in type 2 diabetes by considering mitochondrial alterations in pancreatic α-cells. ROYAL SOCIETY OPEN SCIENCE 2020; 7:191171. [PMID: 32218947 PMCID: PMC7029933 DOI: 10.1098/rsos.191171] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Accepted: 12/16/2019] [Indexed: 05/15/2023]
Abstract
Type 2 diabetes mellitus (T2DM) has been associated with insulin resistance and the failure of β-cells to produce and secrete enough insulin as the disease progresses. However, clinical treatments based solely on insulin secretion and action have had limited success. The focus is therefore shifting towards α-cells, in particular to the dysregulated secretion of glucagon. Our qualitative electron-microscopy-based observations gave an indication that mitochondria in α-cells are altered in Western-diet-induced T2DM. In particular, α-cells extracted from mouse pancreatic tissue showed a lower density of mitochondria, a less expressed matrix and a lower number of cristae. These deformities in mitochondrial ultrastructure imply a decreased efficiency in mitochondrial ATP production, which prompted us to theoretically explore and clarify one of the most challenging problems associated with T2DM, namely the lack of glucagon secretion in hypoglycaemia and its oversecretion at high blood glucose concentrations. To this purpose, we constructed a novel computational model that links α-cell metabolism with their electrical activity and glucagon secretion. Our results show that defective mitochondrial metabolism in α-cells can account for dysregulated glucagon secretion in T2DM, thus improving our understanding of T2DM pathophysiology and indicating possibilities for new clinical treatments.
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Affiliation(s)
- Vladimir Grubelnik
- Faculty of Electrical Engineering and Computer Science, University of Maribor, 2000 Maribor, Slovenia
| | - Rene Markovič
- Faculty of Electrical Engineering and Computer Science, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
| | - Saška Lipovšek
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Chemistry and Chemical Engineering, University of Maribor, 2000 Maribor, Slovenia
- Division of Cell Biology, Histology and Embryology, Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical University of Graz, Neue Stiftingtalstrasse 6, 8010 Graz, Austria
| | - Gerd Leitinger
- Division of Cell Biology, Histology and Embryology, Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical University of Graz, Neue Stiftingtalstrasse 6, 8010 Graz, Austria
| | - Marko Gosak
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
| | - Jurij Dolenšek
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
| | - Ismael Valladolid-Acebes
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital L1, 171 76 Stockholm, Sweden
| | - Per-Olof Berggren
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital L1, 171 76 Stockholm, Sweden
| | - Andraž Stožer
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
| | - Matjaž Perc
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Department of Medical Research, China Medical University Hospital, China Medical University, Taichung, Taiwan
- Complexity Science Hub Vienna, 1080 Vienna, Austria
- Authors for correspondence: Matjač Perc e-mail:
| | - Marko Marhl
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Education, University of Maribor, 2000 Maribor, Slovenia
- Authors for correspondence: Marko Marhl e-mail:
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Grubelnik V, Markovič R, Lipovšek S, Leitinger G, Gosak M, Dolenšek J, Valladolid-Acebes I, Berggren PO, Stožer A, Perc M, Marhl M. Modelling of dysregulated glucagon secretion in type 2 diabetes by considering mitochondrial alterations in pancreatic α-cells. ROYAL SOCIETY OPEN SCIENCE 2020. [PMID: 32218947 DOI: 10.5061/dryad.9n2k1vk] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Type 2 diabetes mellitus (T2DM) has been associated with insulin resistance and the failure of β-cells to produce and secrete enough insulin as the disease progresses. However, clinical treatments based solely on insulin secretion and action have had limited success. The focus is therefore shifting towards α-cells, in particular to the dysregulated secretion of glucagon. Our qualitative electron-microscopy-based observations gave an indication that mitochondria in α-cells are altered in Western-diet-induced T2DM. In particular, α-cells extracted from mouse pancreatic tissue showed a lower density of mitochondria, a less expressed matrix and a lower number of cristae. These deformities in mitochondrial ultrastructure imply a decreased efficiency in mitochondrial ATP production, which prompted us to theoretically explore and clarify one of the most challenging problems associated with T2DM, namely the lack of glucagon secretion in hypoglycaemia and its oversecretion at high blood glucose concentrations. To this purpose, we constructed a novel computational model that links α-cell metabolism with their electrical activity and glucagon secretion. Our results show that defective mitochondrial metabolism in α-cells can account for dysregulated glucagon secretion in T2DM, thus improving our understanding of T2DM pathophysiology and indicating possibilities for new clinical treatments.
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Affiliation(s)
- Vladimir Grubelnik
- Faculty of Electrical Engineering and Computer Science, University of Maribor, 2000 Maribor, Slovenia
| | - Rene Markovič
- Faculty of Electrical Engineering and Computer Science, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
| | - Saška Lipovšek
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Chemistry and Chemical Engineering, University of Maribor, 2000 Maribor, Slovenia
- Division of Cell Biology, Histology and Embryology, Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical University of Graz, Neue Stiftingtalstrasse 6, 8010 Graz, Austria
| | - Gerd Leitinger
- Division of Cell Biology, Histology and Embryology, Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical University of Graz, Neue Stiftingtalstrasse 6, 8010 Graz, Austria
| | - Marko Gosak
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
| | - Jurij Dolenšek
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
| | - Ismael Valladolid-Acebes
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital L1, 171 76 Stockholm, Sweden
| | - Per-Olof Berggren
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital L1, 171 76 Stockholm, Sweden
| | - Andraž Stožer
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
| | - Matjaž Perc
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Department of Medical Research, China Medical University Hospital, China Medical University, Taichung, Taiwan
- Complexity Science Hub Vienna, 1080 Vienna, Austria
| | - Marko Marhl
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Medicine, University of Maribor, 2000 Maribor, Slovenia
- Faculty of Education, University of Maribor, 2000 Maribor, Slovenia
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42
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Asadi F, Dhanvantari S. Stathmin-2 Mediates Glucagon Secretion From Pancreatic α-Cells. Front Endocrinol (Lausanne) 2020; 11:29. [PMID: 32117057 PMCID: PMC7011091 DOI: 10.3389/fendo.2020.00029] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Accepted: 01/14/2020] [Indexed: 01/26/2023] Open
Abstract
Inhibition of glucagon hypersecretion from pancreatic α-cells is an appealing strategy for the treatment of diabetes. Our hypothesis is that proteins that associate with glucagon within alpha cell secretory granules will regulate glucagon secretion, and may provide druggable targets for controlling abnormal glucagon secretion in diabetes. Recently, we identified a dynamic glucagon interactome within the secretory granules of the α cell line, αTC1-6, and showed that select proteins within the interactome could modulate glucagon secretion. In the present study, we show that one of these interactome proteins, the neuronal protein stathmin-2, is expressed in αTC1-6 cells and in mouse pancreatic alpha cells, and is a novel regulator of glucagon secretion. The secretion of both glucagon and Stmn2 was significantly enhanced in response to 55 mM K+, and immunofluorescence confocal microscopy showed co-localization of stathmin-2 with glucagon and the secretory granule markers chromogranin A and VAMP-2 in αTC1-6 cells. In mouse pancreatic islets, Stathmin-2 co-localized with glucagon, but not with insulin, and co-localized with secretory pathway markers. To show a function for stathmin-2 in regulating glucagon secretion, we showed that siRNA-mediated depletion of stathmin-2 in αTC1-6 cells caused glucagon secretion to become constitutive without any effect on proglucagon mRNA levels, while overexpression of stathmin-2 completely abolished both basal and K+-stimulated glucagon secretion. Overexpression of stathmin-2 increased the localization of glucagon into the endosomal-lysosomal compartment, while depletion of stathmin-2 reduced the endosomal localization of glucagon. Therefore, we describe stathmin-2 as having a novel role as an alpha cell secretory granule protein that modulates glucagon secretion via trafficking through the endosomal-lysosomal system. These findings describe a potential new pathway for the regulation of glucagon secretion, and may have implications for controlling glucagon hypersecretion in diabetes.
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Affiliation(s)
- Farzad Asadi
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada
| | - Savita Dhanvantari
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada
- Department of Medical Biophysics, Western University, London, ON, Canada
- Lawson Health Research Institute, London, ON, Canada
- *Correspondence: Savita Dhanvantari
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43
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Briant LJB, Dodd MS, Chibalina MV, Rorsman NJG, Johnson PRV, Carmeliet P, Rorsman P, Knudsen JG. CPT1a-Dependent Long-Chain Fatty Acid Oxidation Contributes to Maintaining Glucagon Secretion from Pancreatic Islets. Cell Rep 2019; 23:3300-3311. [PMID: 29898400 PMCID: PMC6581793 DOI: 10.1016/j.celrep.2018.05.035] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 03/19/2018] [Accepted: 05/11/2018] [Indexed: 12/30/2022] Open
Abstract
Glucagon, the principal hyperglycemic hormone, is secreted from pancreatic islet α cells as part of the counter-regulatory response to hypoglycemia. Hence, secretory output from α cells is under high demand in conditions of low glucose supply. Many tissues oxidize fat as an alternate energy substrate. Here, we show that glucagon secretion in low glucose conditions is maintained by fatty acid metabolism in both mouse and human islets, and that inhibiting this metabolic pathway profoundly decreases glucagon output by depolarizing α cell membrane potential and decreasing action potential amplitude. We demonstrate, by using experimental and computational approaches, that this is not mediated by the KATP channel, but instead due to reduced operation of the Na+-K+ pump. These data suggest that counter-regulatory secretion of glucagon is driven by fatty acid metabolism, and that the Na+-K+ pump is an important ATP-dependent regulator of α cell function. Glucagon secretion in low glucose is maintained by CPT1a-dependent FAO Loss of CPT1a-dependent FAO in mouse and human islets decreases glucagon secretion CPT1a-dependent FAO maintains glucagon secretion by supplying ATP to the Na+-K+-ATPase CPT1a-dependent FAO contributes to the counter-regulatory secretion of glucagon
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Affiliation(s)
- Linford J B Briant
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK; Department of Computer Science, University of Oxford, Oxford OX1 3QD, UK
| | - Michael S Dodd
- Department of Physiology, Anatomy & Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK; Faculty of Health and Life Sciences, Coventry University, Coventry CV1 5FB, UK
| | - Margarita V Chibalina
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK
| | - Nils J G Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK
| | - Paul R V Johnson
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK; Oxford National Institute for Health Research, Biomedical Research Centre, Churchill Hospital, Oxford OX3 7LJ, UK
| | - Peter Carmeliet
- Laboratory of Angiogenesis and Vascular Metabolism, VIB-KU Leuven Center for Cancer Biology, Leuven, Belgium
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK; Metabolic Research, Department of Neuroscience and Physiology, Sahlgrenska Academy, University of Göteborg, Box 433, 405 30 Göteborg, Sweden
| | - Jakob G Knudsen
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK.
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44
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Wewer Albrechtsen NJ, Pedersen J, Galsgaard KD, Winther-Sørensen M, Suppli MP, Janah L, Gromada J, Vilstrup H, Knop FK, Holst JJ. The Liver-α-Cell Axis and Type 2 Diabetes. Endocr Rev 2019; 40:1353-1366. [PMID: 30920583 DOI: 10.1210/er.2018-00251] [Citation(s) in RCA: 106] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Accepted: 03/19/2019] [Indexed: 02/08/2023]
Abstract
Both type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD) strongly associate with increasing body mass index, and together these metabolic diseases affect millions of individuals. In patients with T2D, increased secretion of glucagon (hyperglucagonemia) contributes to diabetic hyperglycemia as proven by the significant lowering of fasting plasma glucose levels following glucagon receptor antagonist administration. Emerging data now indicate that the elevated plasma concentrations of glucagon may also be associated with hepatic steatosis and not necessarily with the presence or absence of T2D. Thus, fatty liver disease, most often secondary to overeating, may result in impaired amino acid turnover, leading to increased plasma concentrations of certain glucagonotropic amino acids (e.g., alanine). This, in turn, causes increased glucagon secretion that may help to restore amino acid turnover and ureagenesis, but it may eventually also lead to increased hepatic glucose production, a hallmark of T2D. Early experimental findings support the hypothesis that hepatic steatosis impairs glucagon's actions on amino acid turnover and ureagenesis. Hepatic steatosis also impairs hepatic insulin sensitivity and clearance that, together with hyperglycemia and hyperaminoacidemia, lead to peripheral hyperinsulinemia; systemic hyperinsulinemia may itself contribute to worsen peripheral insulin resistance. Additionally, obesity is accompanied by an impaired incretin effect, causing meal-related glucose intolerance. Lipid-induced impairment of hepatic sensitivity, not only to insulin but potentially also to glucagon, resulting in both hyperinsulinemia and hyperglucagonemia, may therefore contribute to the development of T2D at least in a subset of individuals with NAFLD.
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Affiliation(s)
- Nicolai J Wewer Albrechtsen
- Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.,Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens Pedersen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Department of Cardiology, Nephrology and Endocrinology, Nordsjællands Hospital Hillerød, University of Copenhagen, Hillerød, Denmark
| | - Katrine D Galsgaard
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Marie Winther-Sørensen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Malte P Suppli
- Steno Diabetes Center Copenhagen, Gentofte Hospital, Hellerup, Denmark
| | - Lina Janah
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | | | - Hendrik Vilstrup
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Filip K Knop
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Steno Diabetes Center Copenhagen, Gentofte Hospital, Hellerup, Denmark.,Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens J Holst
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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45
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Abstract
Controlling the excess and shortage of energy is a fundamental task for living organisms. Diabetes is a representative metabolic disease caused by the malfunction of energy homeostasis. The islets of Langerhans in the pancreas release long-range messengers, hormones, into the blood to regulate the homeostasis of the primary energy fuel, glucose. The hormone and glucose levels in the blood show rhythmic oscillations with a characteristic period of 5-10 min, and the functional roles of the oscillations are not clear. Each islet has [Formula: see text] and [Formula: see text] cells that secrete glucagon and insulin, respectively. These two counter-regulatory hormones appear sufficient to increase and decrease glucose levels. However, pancreatic islets have a third cell type, [Formula: see text] cells, which secrete somatostatin. The three cell populations have a unique spatial organization in islets, and they interact to perturb their hormone secretions. The mini-organs of islets are scattered throughout the exocrine pancreas. Considering that the human pancreas contains approximately a million islets, the coordination of hormone secretion from the multiple sources of islets and cells within the islets should have a significant effect on human physiology. In this review, we introduce the hierarchical organization of tripartite cell networks, and recent biophysical modeling to systematically understand the oscillations and interactions of [Formula: see text], [Formula: see text], and [Formula: see text] cells. Furthermore, we discuss the functional roles and clinical implications of hormonal oscillations and their phase coordination for the diagnosis of type II diabetes.
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Affiliation(s)
- Taegeun Song
- Department of Physics, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea
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46
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Yu Q, Shuai H, Ahooghalandari P, Gylfe E, Tengholm A. Glucose controls glucagon secretion by directly modulating cAMP in alpha cells. Diabetologia 2019; 62:1212-1224. [PMID: 30953108 PMCID: PMC6560012 DOI: 10.1007/s00125-019-4857-6] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Accepted: 02/22/2019] [Indexed: 01/18/2023]
Abstract
AIMS/HYPOTHESIS Glucagon is critical for normal glucose homeostasis and aberrant secretion of the hormone aggravates dysregulated glucose control in diabetes. However, the mechanisms by which glucose controls glucagon secretion from pancreatic alpha cells remain elusive. The aim of this study was to investigate the role of the intracellular messenger cAMP in alpha-cell-intrinsic glucose regulation of glucagon release. METHODS Subplasmalemmal cAMP and Ca2+ concentrations were recorded in isolated and islet-located alpha cells using fluorescent reporters and total internal reflection microscopy. Glucagon secretion from mouse islets was measured using ELISA. RESULTS Glucose induced Ca2+-independent alterations of the subplasmalemmal cAMP concentration in alpha cells that correlated with changes in glucagon release. Glucose-lowering-induced stimulation of glucagon secretion thus corresponded to an elevation in cAMP that was independent of paracrine signalling from insulin or somatostatin. Imposed cAMP elevations stimulated glucagon secretion and abolished inhibition by glucose elevation, while protein kinase A inhibition mimicked glucose suppression of glucagon release. CONCLUSIONS/INTERPRETATION Glucose concentrations in the hypoglycaemic range control glucagon secretion by directly modulating the cAMP concentration in alpha cells independently of paracrine influences. These findings define a novel mechanism for glucose regulation of glucagon release that underlies recovery from hypoglycaemia and may be disturbed in diabetes.
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Affiliation(s)
- Qian Yu
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, SE-751 23, Uppsala, Sweden
| | - Hongyan Shuai
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, SE-751 23, Uppsala, Sweden
| | - Parvin Ahooghalandari
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, SE-751 23, Uppsala, Sweden
| | - Erik Gylfe
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, SE-751 23, Uppsala, Sweden
| | - Anders Tengholm
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, SE-751 23, Uppsala, Sweden.
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47
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Schwartsburd P. Cancer-Induced Reprogramming of Host Glucose Metabolism: "Vicious Cycle" Supporting Cancer Progression. Front Oncol 2019; 9:218. [PMID: 31019893 PMCID: PMC6458235 DOI: 10.3389/fonc.2019.00218] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2019] [Accepted: 03/12/2019] [Indexed: 12/21/2022] Open
Abstract
Unrestricted cancer growth requires permanent supply of glucose that can be obtained from cancer-mediated reprogramming of glucose metabolism in the cancer-bearing host. The pathological mechanisms by which cancer cells exert their negative influence on host glucose metabolism are largely unknown. This paper proposes a mechanism of metabolic and hormonal changes that may favor glucose delivery to tumor (not host) cells by creating a cancer-host "vicious cycle" whose prolonged action drives cancer progression and promotes host cachexia. To verify this hypothesis, a feedback model of host-cancer interactions that create the "vicious cycle" via cancer-induced reprogramming of host glucose metabolism is proposed. This model is capable of answering some crucial questions as to how anabolic cancer cells can reprogram the systemic glucose metabolism and why these pathways were not observed in pregnancy. The current paper helps to better understanding a pathogenesis of cancer progression and identify hormonal/metabolic targets for anti-cancer treatment.
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Affiliation(s)
- Polina Schwartsburd
- Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Russia
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48
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Dickerson MT, Dadi PK, Altman MK, Verlage KR, Thorson AS, Jordan KL, Vierra NC, Amarnath G, Jacobson DA. Glucose-mediated inhibition of calcium-activated potassium channels limits α-cell calcium influx and glucagon secretion. Am J Physiol Endocrinol Metab 2019; 316:E646-E659. [PMID: 30694690 PMCID: PMC6482666 DOI: 10.1152/ajpendo.00342.2018] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Pancreatic α-cells exhibit oscillations in cytosolic Ca2+ (Ca2+c), which control pulsatile glucagon (GCG) secretion. However, the mechanisms that modulate α-cell Ca2+c oscillations have not been elucidated. As β-cell Ca2+c oscillations are regulated in part by Ca2+-activated K+ (Kslow) currents, this work investigated the role of Kslow in α-cell Ca2+ handling and GCG secretion. α-Cells displayed Kslow currents that were dependent on Ca2+ influx through L- and P/Q-type voltage-dependent Ca2+ channels (VDCCs) as well as Ca2+ released from endoplasmic reticulum stores. α-Cell Kslow was decreased by small-conductance Ca2+-activated K+ (SK) channel inhibitors apamin and UCL 1684, large-conductance Ca2+-activated K+ (BK) channel inhibitor iberiotoxin (IbTx), and intermediate-conductance Ca2+-activated K+ (IK) channel inhibitor TRAM 34. Moreover, partial inhibition of α-cell Kslow with apamin depolarized membrane potential ( Vm) (3.8 ± 0.7 mV) and reduced action potential (AP) amplitude (10.4 ± 1.9 mV). Although apamin transiently increased Ca2+ influx into α-cells at low glucose (42.9 ± 10.6%), sustained SK (38.5 ± 10.4%) or BK channel inhibition (31.0 ± 11.7%) decreased α-cell Ca2+ influx. Total α-cell Ca2+c was similarly reduced (28.3 ± 11.1%) following prolonged treatment with high glucose, but it was not decreased further by SK or BK channel inhibition. Consistent with reduced α-cell Ca2+c following prolonged Kslow inhibition, apamin decreased GCG secretion from mouse (20.4 ± 4.2%) and human (27.7 ± 13.1%) islets at low glucose. These data demonstrate that Kslow activation provides a hyperpolarizing influence on α-cell Vm that sustains Ca2+ entry during hypoglycemic conditions, presumably by preventing voltage-dependent inactivation of P/Q-type VDCCs. Thus, when α-cell Ca2+c is elevated during secretagogue stimulation, Kslow activation helps to preserve GCG secretion.
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Affiliation(s)
- Matthew T Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Molly K Altman
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Kenneth R Verlage
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
- School of Medicine, Texas Tech University Health Sciences Center , Lubbock, Texas
- Department of Urology, Oregon Health and Science University , Portland, Oregon
| | - Ariel S Thorson
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Kelli L Jordan
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Nicholas C Vierra
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
- Department of Neurobiology, Physiology and Behavior University of California , Davis, California
| | - Gautami Amarnath
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
- Experimental and Clinical Neurosciences, University of Regensburg , Regensburg , Germany
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
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49
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Jansson L, Carlsson PO. Pancreatic Blood Flow with Special Emphasis on Blood Perfusion of the Islets of Langerhans. Compr Physiol 2019; 9:799-837. [PMID: 30892693 DOI: 10.1002/cphy.c160050] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The pancreatic islets are more richly vascularized than the exocrine pancreas, and possess a 5- to 10-fold higher basal and stimulated blood flow, which is separately regulated. This is reflected in the vascular anatomy of the pancreas where islets have separate arterioles. There is also an insulo-acinar portal system, where numerous venules connect each islet to the acinar capillaries. Both islets and acini possess strong metabolic regulation of their blood perfusion. Of particular importance, especially in the islets, is adenosine and ATP/ADP. Basal and stimulated blood flow is modified by local endothelial mediators, the nervous system as well as gastrointestinal hormones. Normally the responses to the nervous system, especially the parasympathetic and sympathetic nerves, are fairly similar in endocrine and exocrine parts. The islets seem to be more sensitive to the effects of endothelial mediators, especially nitric oxide, which is a permissive factor to maintain the high basal islet blood flow. The gastrointestinal hormones with pancreatic effects mainly influence the exocrine pancreatic blood flow, whereas islets are less affected. A notable exception is incretin hormones and adipokines, which preferentially affect islet vasculature. Islet hormones can influence both exocrine and endocrine blood vessels, and these complex effects are discussed. Secondary changes in pancreatic and islet blood flow occur during several conditions. To what extent changes in blood perfusion may affect the pathogenesis of pancreatic diseases is discussed. Both type 2 diabetes mellitus and acute pancreatitis are conditions where we think there is evidence that blood flow may contribute to disease manifestations. © 2019 American Physiological Society. Compr Physiol 9:799-837, 2019.
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Affiliation(s)
- Leif Jansson
- Uppsala University, Department of Medical Cell Biology, Uppsala, Sweden
| | - Per-Ola Carlsson
- Uppsala University, Department of Medical Cell Biology, Uppsala, Sweden.,Uppsala University, Department of Medical Sciences, Uppsala, Sweden
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50
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Matschinsky FM, Wilson DF. The Central Role of Glucokinase in Glucose Homeostasis: A Perspective 50 Years After Demonstrating the Presence of the Enzyme in Islets of Langerhans. Front Physiol 2019; 10:148. [PMID: 30949058 PMCID: PMC6435959 DOI: 10.3389/fphys.2019.00148] [Citation(s) in RCA: 159] [Impact Index Per Article: 31.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Accepted: 02/07/2019] [Indexed: 01/05/2023] Open
Abstract
It is hypothesized that glucokinase (GCK) is the glucose sensor not only for regulation of insulin release by pancreatic β-cells, but also for the rest of the cells that contribute to glucose homeostasis in mammals. This includes other cells in endocrine pancreas (α- and δ-cells), adrenal gland, glucose sensitive neurons, entero-endocrine cells, and cells in the anterior pituitary. Glucose transport is by facilitated diffusion and is not rate limiting. Once inside, glucose is phosphorylated to glucose-6-phosphate by GCK in a reaction that is dependent on glucose throughout the physiological range of concentrations, is irreversible, and not product inhibited. High glycerol phosphate shuttle, pyruvate dehydrogenase, and pyruvate carboxylase activities, combined with low pentose-P shunt, lactate dehydrogenase, plasma membrane monocarboxylate transport, and glycogen synthase activities constrain glucose-6-phosphate to being metabolized through glycolysis. Under these conditions, glycolysis produces mostly pyruvate and little lactate. Pyruvate either enters the citric acid cycle through pyruvate dehydrogenase or is carboxylated by pyruvate carboxylase. Reducing equivalents from glycolysis enter oxidative phosphorylation through both the glycerol phosphate shuttle and citric acid cycle. Raising glucose concentration increases intramitochondrial [NADH]/[NAD+] and thereby the energy state ([ATP]/[ADP][Pi]), decreasing [Mg2+ADP] and [AMP]. [Mg2+ADP] acts through control of KATP channel conductance, whereas [AMP] acts through regulation of AMP-dependent protein kinase. Specific roles of different cell types are determined by the diverse molecular mechanisms used to couple energy state to cell specific responses. Having a common glucose sensor couples complementary regulatory mechanisms into a tightly regulated and stable glucose homeostatic network.
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Affiliation(s)
- Franz M Matschinsky
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States
| | - David F Wilson
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States
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