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Song J, Wang L, Wang L, Guo X, He Q, Cui C, Hu H, Zang N, Yang M, Yan F, Liang K, Wang C, Liu F, Sun Y, Sun Z, Lai H, Hou X, Chen L. Mesenchymal stromal cells ameliorate mitochondrial dysfunction in α cells and hyperglucagonemia in type 2 diabetes via SIRT1/FoxO3a signaling. Stem Cells Transl Med 2024; 13:776-790. [PMID: 38864709 PMCID: PMC11328933 DOI: 10.1093/stcltm/szae038] [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: 11/21/2023] [Accepted: 04/24/2024] [Indexed: 06/13/2024] Open
Abstract
Dysregulation of α cells results in hyperglycemia and hyperglucagonemia in type 2 diabetes mellitus (T2DM). Mesenchymal stromal cell (MSC)-based therapy increases oxygen consumption of islets and enhances insulin secretion. However, the underlying mechanism for the protective role of MSCs in α-cell mitochondrial dysfunction remains unclear. Here, human umbilical cord MSCs (hucMSCs) were used to treat 2 kinds of T2DM mice and αTC1-6 cells to explore the role of hucMSCs in improving α-cell mitochondrial dysfunction and hyperglucagonemia. Plasma and supernatant glucagon were detected by enzyme-linked immunosorbent assay (ELISA). Mitochondrial function of α cells was assessed by the Seahorse Analyzer. To investigate the underlying mechanisms, Sirtuin 1 (SIRT1), Forkhead box O3a (FoxO3a), glucose transporter type1 (GLUT1), and glucokinase (GCK) were assessed by Western blotting analysis. In vivo, hucMSC infusion improved glucose and insulin tolerance, as well as hyperglycemia and hyperglucagonemia in T2DM mice. Meanwhile, hucMSC intervention rescued the islet structure and decreased α- to β-cell ratio. Glucagon secretion from αTC1-6 cells was consistently inhibited by hucMSCs in vitro. Meanwhile, hucMSC treatment activated intracellular SIRT1/FoxO3a signaling, promoted glucose uptake and activation, alleviated mitochondrial dysfunction, and enhanced ATP production. However, transfection of SIRT1 small interfering RNA (siRNA) or the application of SIRT1 inhibitor EX-527 weakened the therapeutic effects of hucMSCs on mitochondrial function and glucagon secretion. Our observations indicate that hucMSCs mitigate mitochondrial dysfunction and glucagon hypersecretion of α cells in T2DM via SIRT1/FoxO3a signaling, which provides novel evidence demonstrating the potential for hucMSCs in treating T2DM.
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Affiliation(s)
- Jia Song
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Lingshu Wang
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Liming Wang
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Xinghong Guo
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Qin He
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Chen Cui
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Huiqing Hu
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Nan Zang
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Mengmeng Yang
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Fei Yan
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Kai Liang
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Chuan Wang
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Fuqiang Liu
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Yujing Sun
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Zheng Sun
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
| | - Hong Lai
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
- Institute of Endocrine and Metabolic Diseases of Shandong University, Jinan 250012, Shandong, People's Republic of China
- Key Laboratory of Endocrine and Metabolic Diseases, Shandong Province Medicine and Health, Jinan 250012, Shandong, People's Republic of China
- Jinan Clinical Research Center for Endocrine and Metabolic Disease, Jinan 250012, Shandong, People's Republic of China
| | - Xinguo Hou
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
- Institute of Endocrine and Metabolic Diseases of Shandong University, Jinan 250012, Shandong, People's Republic of China
- Key Laboratory of Endocrine and Metabolic Diseases, Shandong Province Medicine and Health, Jinan 250012, Shandong, People's Republic of China
- Jinan Clinical Research Center for Endocrine and Metabolic Disease, Jinan 250012, Shandong, People's Republic of China
| | - Li Chen
- Department of Endocrinology and Metabolism, Qilu Hospital of Shandong University, Jinan 250012, Shandong, People's Republic of China
- Institute of Endocrine and Metabolic Diseases of Shandong University, Jinan 250012, Shandong, People's Republic of China
- Key Laboratory of Endocrine and Metabolic Diseases, Shandong Province Medicine and Health, Jinan 250012, Shandong, People's Republic of China
- Jinan Clinical Research Center for Endocrine and Metabolic Disease, Jinan 250012, Shandong, People's Republic of China
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Deguchi-Horiuchi H, Suzuki S, Lee EY, Miki T, Yamanaka N, Manabe I, Tanaka T, Yokote K. Pancreatic β-cell glutaminase 2 maintains glucose homeostasis under the condition of hyperglycaemia. Sci Rep 2023; 13:7291. [PMID: 37147373 PMCID: PMC10162969 DOI: 10.1038/s41598-023-34336-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Accepted: 04/27/2023] [Indexed: 05/07/2023] Open
Abstract
Glutaminase 2 (GLS2), a master regulator of glutaminolysis that is induced by p53 and converts glutamine to glutamate, is abundant in the liver but also exists in pancreatic β-cells. However, the roles of GLS2 in islets associated with glucose metabolism are unknown, presenting a critical issue. To investigate the roles of GLS2 in pancreatic β-cells in vivo, we generated β-cell-specific Gls2 conditional knockout mice (Gls2 CKO), examined their glucose homeostasis, and validated the findings using a human islet single-cell analysis database. GLS2 expression markedly increased along with p53 in β-cells from control (RIP-Cre) mice fed a high-fat diet. Furthermore, Gls2 CKO exhibited significant diabetes mellitus with gluconeogenesis and insulin resistance when fed a high-fat diet. Despite marked hyperglycaemia, impaired insulin secretion and paradoxical glucagon elevation were observed in high-fat diet-fed Gls2 CKO mice. GLS2 silencing in the pancreatic β-cell line MIN6 revealed downregulation of insulin secretion and intracellular ATP levels, which were closely related to glucose-stimulated insulin secretion. Additionally, analysis of single-cell RNA-sequencing data from human pancreatic islet cells also revealed that GLS2 expression was elevated in β-cells from diabetic donors compared to nondiabetic donors. Consistent with the results of Gls2 CKO, downregulated GLS2 expression in human pancreatic β-cells from diabetic donors was associated with significantly lower insulin gene expression as well as lower expression of members of the insulin secretion pathway, including ATPase and several molecules that signal to insulin secretory granules, in β-cells but higher glucagon gene expression in α-cells. Although the exact mechanism by which β-cell-specific GLS2 regulates insulin and glucagon requires further study, our data indicate that GLS2 in pancreatic β-cells maintains glucose homeostasis under the condition of hyperglycaemia.
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Affiliation(s)
- Hanna Deguchi-Horiuchi
- Department of Endocrinology, Hematology and Gerontology, Graduate School of Medicine, Chiba University, Chiba, Japan
- Department of Diabetes, Metabolism and Endocrinology, Chiba University hospital, Chiba, Japan
| | - Sawako Suzuki
- Department of Endocrinology, Hematology and Gerontology, Graduate School of Medicine, Chiba University, Chiba, Japan.
- Department of Diabetes, Metabolism and Endocrinology, Chiba University hospital, Chiba, Japan.
| | - Eun Young Lee
- Department of Medical Physiology, Graduate School of Medicine, Chiba University, Chiba, Japan
| | - Takashi Miki
- Department of Medical Physiology, Graduate School of Medicine, Chiba University, Chiba, Japan
| | - Noriko Yamanaka
- Department of Disease Biology and Molecular Medicine, Graduate School of Medicine, Chiba University, Chiba, Japan
| | - Ichiro Manabe
- Department of Disease Biology and Molecular Medicine, Graduate School of Medicine, Chiba University, Chiba, Japan
| | - Tomoaki Tanaka
- Department of Molecular Diagnosis, Graduate School of Medicine, Chiba University, Chiba, Japan
| | - Koutaro Yokote
- Department of Endocrinology, Hematology and Gerontology, Graduate School of Medicine, Chiba University, Chiba, Japan
- Department of Diabetes, Metabolism and Endocrinology, Chiba University hospital, Chiba, Japan
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Importance of multiple endocrine cell types in islet organoids for type 1 diabetes treatment. Transl Res 2022; 250:68-83. [PMID: 35772687 DOI: 10.1016/j.trsl.2022.06.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2022] [Revised: 06/08/2022] [Accepted: 06/21/2022] [Indexed: 11/21/2022]
Abstract
Almost 50 years ago, scientists developed the bi-hormonal abnormality hypothesis, stating that diabetes is not caused merely by the impaired insulin signaling. Instead, the presence of inappropriate level of glucagon is a prerequisite for the development of type 1 diabetes (T1D). It is widely understood that the hormones insulin and glucagon, secreted by healthy β and α cells respectively, operate in a negative feedback loop to maintain the body's blood sugar levels. Despite this fact, traditional T1D treatments rely solely on exogenous insulin injections. Furthermore, research on cell-based therapies and stem-cell derived tissues tends to focus on the replacement of β cells alone. In vivo, the pancreas is made up of 4 major endocrine cell types, that is, insulin-producing β cells, glucagon-producing α cells, somatostatin-producing δ cells, and pancreatic polypeptide-producing γ cells. These distinct cell types are involved synergistically in regulating islet functions. Therefore, it is necessary to produce a pancreatic islet organoid in vitro consisting of all these cell types that adequately replaces the function of the native islets. In this review, we describe the unique function of each pancreatic endocrine cell type and their interactions contributing to the maintenance of normoglycemia. Furthermore, we detail current sources of whole islets and techniques for their long-term expansion and culture. In addition, we highlight a vast potential of the pancreatic islet organoids for transplantation and diabetes research along with updated new approaches for successful transplantation using stem cell-derived islet organoids.
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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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Song J, He Q, Guo X, Wang L, Wang J, Cui C, Hu H, Yang M, Cui Y, Zang N, Yan F, Liu F, Sun Y, Liang K, Qin J, Zhao R, Wang C, Sun Z, Hou X, Li W, Chen L. Mesenchymal stem cell-conditioned medium alleviates high fat-induced hyperglucagonemia via miR-181a-5p and its target PTEN/AKT signaling. Mol Cell Endocrinol 2021; 537:111445. [PMID: 34464683 DOI: 10.1016/j.mce.2021.111445] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Revised: 08/08/2021] [Accepted: 08/25/2021] [Indexed: 12/24/2022]
Abstract
BACKGROUND α-cell dysregulation gives rise to fasting and postprandial hyperglycemia in type 2 diabetes mellitus(T2DM). Administration of Mesenchymal stem cells (MSCs) or their conditioned medium can improve islet function and enhance insulin secretion. However, studies showing the direct effect of MSCs on islet α-cell dysfunction are limited. METHODS In this study, we used high-fat diet (HFD)-induced mice and α-cell line exposure to palmitate (PA) to determine the effects of bone marrow-derived MSC-conditioned medium (bmMSC-CM) on glucagon secretion. Plasma and supernatant glucagon were detected by enzyme-linked immunosorbent assay(ELISA). To investigate the potential signaling pathways, phosphatase and tensin homolog deleted on chromosome 10 (PTEN), AKT and phosphorylated AKT(p-AKT) were assessed by Western blotting. RESULTS In vivo, bmMSC-CM infusion improved the glucose and insulin tolerance and protected against HFD-induced hyperglycemia and hyperglucagonemia. Meanwhile, bmMSC-CM infusion ameliorated HFD-induced islet hypertrophy and decreased α- and β-cell area. Consistently, in vitro, glucagon secretion from α-cells or primary islets was inhibited by bmMSC-CM, accompanied by reduction of intracellular PTEN expression and restoration of AKT signaling. Previous studies and the TargetScan database indicate that miR-181a and its target PTEN play vital roles in ameliorating α-cell dysfunction. We observed that miR-181a-5p was highly expressed in BM-MSCs but prominently lower in αTC1-6 cells. Overexpression or downregulation of miR-181a-5p respectively alleviated or aggravated glucagon secretion in αTC1-6 cells via the PTEN/AKT signaling pathway. CONCLUSIONS Our observations suggest that MSC-derived miR-181a-5p mitigates glucagon secretion of α-cells by regulating PTEN/AKT signaling, which provides novel evidence demonstrating the potential for MSCs in treating T2DM.
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Affiliation(s)
- Jia Song
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Qin He
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Xinghong Guo
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Lingshu Wang
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Jinbang Wang
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Chen Cui
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Huiqing Hu
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Mengmeng Yang
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Yixin Cui
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Nan Zang
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Fei Yan
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Fuqiang Liu
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Yujing Sun
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Kai Liang
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Jun Qin
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Ruxing Zhao
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Chuan Wang
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Zheng Sun
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China
| | - Xinguo Hou
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China; Institute of Endocrine and Metabolic Diseases of Shandong University, Jinan, 250012, Shandong, China; Key Laboratory of Endocrine and Metabolic Diseases, Shandong Province Medicine & Health, Jinan, 250012, Shandong, China; Jinan Clinical Research Center for Endocrine and Metabolic Disease, Jinan, 250012, Shandong, China
| | - Wenjuan Li
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China; Institute of Endocrine and Metabolic Diseases of Shandong University, Jinan, 250012, Shandong, China; Key Laboratory of Endocrine and Metabolic Diseases, Shandong Province Medicine & Health, Jinan, 250012, Shandong, China; Jinan Clinical Research Center for Endocrine and Metabolic Disease, Jinan, 250012, Shandong, China.
| | - Li Chen
- Department of Endocrinology, Qilu Hospital of Shandong University, Jinan, 250012, Shandong, China; Institute of Endocrine and Metabolic Diseases of Shandong University, Jinan, 250012, Shandong, China; Key Laboratory of Endocrine and Metabolic Diseases, Shandong Province Medicine & Health, Jinan, 250012, Shandong, China; Jinan Clinical Research Center for Endocrine and Metabolic Disease, Jinan, 250012, Shandong, China.
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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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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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8
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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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9
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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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10
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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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11
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Insulin Secretion Depends on Intra-islet Glucagon Signaling. Cell Rep 2019; 25:1127-1134.e2. [PMID: 30380405 DOI: 10.1016/j.celrep.2018.10.018] [Citation(s) in RCA: 215] [Impact Index Per Article: 43.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Revised: 06/11/2018] [Accepted: 10/02/2018] [Indexed: 12/20/2022] Open
Abstract
The intra-islet theory states that glucagon secretion is suppressed when insulin secretion is stimulated, but glucagon's role in intra-islet paracrine regulation is controversial. This study investigated intra-islet functions of glucagon in mice. We examined glucagon-induced insulin secretion using isolated perfused pancreata from wild-type, GLP-1 receptor (GLP-1R) knockout, diphtheria toxin-induced proglucagon knockdown, β cell-specific glucagon receptor (Gcgr) knockout, and global Gcgr knockout (Gcgr-/-) mice. We found that glucagon stimulates insulin secretion through both Gcgr and GLP-1R. Moreover, loss of either Gcgr or GLP-1R does not change insulin responses, whereas combined blockage of both receptors significantly reduces insulin secretion. Active GLP-1 is identified in pancreatic perfusate from Gcgr-/- but not wild-type mice, suggesting that β cell GLP-1R activation results predominantly from glucagon action. Our results suggest that combined activity of glucagon and GLP-1 receptors is essential for β cell secretory responses, emphasizing a role for paracrine intra-islet glucagon actions to maintain appropriate insulin secretion.
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12
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Lee M, Kim M, Park JS, Lee S, You J, Ahn CW, Kim KR, Kang S. Higher glucagon-to-insulin ratio is associated with elevated glycated hemoglobin levels in type 2 diabetes patients. Korean J Intern Med 2019; 34:1068-1077. [PMID: 28882024 PMCID: PMC6718759 DOI: 10.3904/kjim.2016.233] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2016] [Accepted: 06/26/2017] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND/AIMS The importance of α-cell dysfunction in the pathogenesis of type 2 diabetes has re-emerged recently. However, data on whether relative glucagon excess is present in clinical settings are scarce. We aimed to investigate associations between glucagon-to-insulin ratio and various metabolic parameters. METHODS A total of 451 patients with type 2 diabetes naïve to insulin treatment were recruited. Using glucagon-to-insulin ratio, we divided subjects into quartiles according to both fasting and postprandial glucagon-to-insulin ratios. RESULTS The mean age of the subjects was 58 years, with a mean body mass index of 25 kg/m2 . The patients in the highest quartile of glucagon-to-insulin ratio had higher glycated hemoglobin (HbA1c) levels. HbA1c levels were positively correlated with both fasting and postprandial glucagon-to-insulin ratios. Subjects in the highest quartile of postprandial glucagon-to-insulin ratio were more likely to exhibit uncontrolled hyperglycemia, even after adjusting for confounding factors (odds ratio, 2.730; 95% confidence interval, 1.236 to 6.028; p for trend < 0.01). CONCLUSION Hyperglucagonemia relative to insulin could contribute to uncontrolled hyperglycemia in type 2 diabetes patients.
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Affiliation(s)
- Minyoung Lee
- Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
| | - Minkyung Kim
- Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
| | - Jong Suk Park
- Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
- Severance Institute for Vascular and Metabolic Research, Yonsei University College of Medicine, Seoul, Korea
| | - Sangbae Lee
- Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
| | - Jihong You
- Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
| | - Chul Woo Ahn
- Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
- Severance Institute for Vascular and Metabolic Research, Yonsei University College of Medicine, Seoul, Korea
| | - Kyung Rae Kim
- Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
| | - Shinae Kang
- Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
- Severance Institute for Vascular and Metabolic Research, Yonsei University College of Medicine, Seoul, Korea
- Correspondence to Shinae Kang, M.D. Division of Endocrinology, Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, 211 Eonju-ro, Gangnam-gu, Seoul 06273, Korea Tel: +82-2-2019-3335 Fax: +82-2-3463-3882 E-mail:
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13
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Cell Autonomous Dysfunction and Insulin Resistance in Pancreatic α Cells. Int J Mol Sci 2019; 20:ijms20153699. [PMID: 31357734 PMCID: PMC6695724 DOI: 10.3390/ijms20153699] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2019] [Revised: 07/23/2019] [Accepted: 07/26/2019] [Indexed: 12/23/2022] Open
Abstract
To date, type 2 diabetes is considered to be a "bi-hormonal disorder" rather than an "insulin-centric disorder," suggesting that glucagon is as important as insulin. Although glucagon increases hepatic glucose production and blood glucose levels, paradoxical glucagon hypersecretion is observed in diabetes. Recently, insulin resistance in pancreatic α cells has been proposed to be associated with glucagon dysregulation. Moreover, cell autonomous dysfunction of α cells is involved in the etiology of diabetes. In this review, we summarize the current knowledge about the physiological and pathological roles of glucagon.
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14
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Araujo TR, da Silva JA, Vettorazzi JF, Freitas IN, Lubaczeuski C, Magalhães EA, Silva JN, Ribeiro ES, Boschero AC, Carneiro EM, Bonfleur ML, Ribeiro RA. Glucose intolerance in monosodium glutamate obesity is linked to hyperglucagonemia and insulin resistance in α cells. J Cell Physiol 2018; 234:7019-7031. [DOI: 10.1002/jcp.27455] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 08/29/2018] [Indexed: 12/25/2022]
Affiliation(s)
- Thiago R. Araujo
- Campus UFRJ‐Macaé, Universidade Federal do R io de Janeiro Macaé Brazil
| | - Joel A. da Silva
- Campus UFRJ‐Macaé, Universidade Federal do R io de Janeiro Macaé Brazil
| | - Jean F. Vettorazzi
- Departamento de Biologia Estrutural e Funcional Instituto de Biologia, Universidade Estadual de Campinas Campinas Brazil
| | | | - Camila Lubaczeuski
- Departamento de Biologia Estrutural e Funcional Instituto de Biologia, Universidade Estadual de Campinas Campinas Brazil
| | | | - Juliana N. Silva
- Campus UFRJ‐Macaé, Universidade Federal do R io de Janeiro Macaé Brazil
| | - Elane S. Ribeiro
- Campus UFRJ‐Macaé, Universidade Federal do R io de Janeiro Macaé Brazil
| | - Antonio C. Boschero
- Departamento de Biologia Estrutural e Funcional Instituto de Biologia, Universidade Estadual de Campinas Campinas Brazil
| | - Everardo M. Carneiro
- Departamento de Biologia Estrutural e Funcional Instituto de Biologia, Universidade Estadual de Campinas Campinas Brazil
| | - Maria L. Bonfleur
- Centro de Ciências Biológicas e da Saúde Universidade Estadual do Oeste do Paraná (UNIOESTE) Cascavel Brazil
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15
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Hughes JW, Ustione A, Lavagnino Z, Piston DW. Regulation of islet glucagon secretion: Beyond calcium. Diabetes Obes Metab 2018; 20 Suppl 2:127-136. [PMID: 30230183 PMCID: PMC6148361 DOI: 10.1111/dom.13381] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Revised: 05/03/2018] [Accepted: 05/23/2018] [Indexed: 12/19/2022]
Abstract
The islet of Langerhans plays a key role in glucose homeostasis through regulated secretion of the hormones insulin and glucagon. Islet research has focused on the insulin-secreting β-cells, even though aberrant glucagon secretion from α-cells also contributes to the aetiology of diabetes. Despite its importance, the mechanisms controlling glucagon secretion remain controversial. Proper α-cell function requires the islet milieu, where β- and δ-cells drive and constrain α-cell dynamics. The response of glucagon to glucose is similar between isolated islets and that measured in vivo, so it appears that the glucose dependence requires only islet-intrinsic factors and not input from blood flow or the nervous system. Elevated intracellular free Ca2+ is needed for α-cell exocytosis, but interpreting Ca2+ data is tricky since it is heterogeneous among α-cells at all physiological glucose levels. Total Ca2+ activity in α-cells increases slightly with glucose, so Ca2+ may serve a permissive, rather than regulatory, role in glucagon secretion. On the other hand, cAMP is a more promising candidate for controlling glucagon secretion and is itself driven by paracrine signalling from β- and δ-cells. Another pathway, juxtacrine signalling through the α-cell EphA receptors, stimulated by β-cell ephrin ligands, leads to a tonic inhibition of glucagon secretion. We discuss potential combinations of Ca2+ , cAMP, paracrine and juxtacrine factors in the regulation of glucagon secretion, focusing on recent data in the literature that might unify the field towards a quantitative understanding of α-cell function.
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Affiliation(s)
- Jing W. Hughes
- Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Alessandro Ustione
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - Zeno Lavagnino
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - David W. Piston
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
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16
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Abstract
Type 1 diabetes is characterized by selective loss of beta cells and insulin secretion, which significantly impact glucose homeostasis. However, this progressive disease is also associated with dysfunction of the alpha cell component of the islet, which can exacerbate hyperglycemia due to paradoxical hyperglucagonemia or lead to severe hypoglycemia as a result of failed counterregulation. In this review, the physiology of alpha cell secretion and the potential mechanisms underlying alpha cell dysfunction in type 1 diabetes will be explored. Because type 1 diabetes is a progressive disease, a synthesized timeline of aberrant alpha cell function will be presented as an attempt to delineate the natural history of type 1 diabetes with respect to the alpha cell.
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Affiliation(s)
- Gina L C Yosten
- Department of Pharmacology and Physiology, Saint Louis University School of Medicine, 1402 S. Grand Blvd, Saint Louis, MO 63104, United States.
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17
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Kawamori D. Exploring the molecular mechanisms underlying α- and β-cell dysfunction in diabetes. Diabetol Int 2017; 8:248-256. [PMID: 30603330 PMCID: PMC6224887 DOI: 10.1007/s13340-017-0327-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 06/20/2017] [Indexed: 01/09/2023]
Abstract
Pancreatic islet dysfunction, including impaired insulin secretion in β cells and dysregulated glucagon secretion in α cells, is the chief pathology of diabetes. In β cells, oxidative stress, evoked by chronic hyperglycemia, was found to induce dysfunction of a critical transcription factor, PDX1, caused by its nucleocytoplasmic translocation via interactions with the insulin and JNK signaling pathways and another transcription factor, FOXO1. The significance of α-cell insulin signaling in the physiological and pathological regulation of α-cell biology was demonstrated in α-cell-specific insulin receptor knockout mice, which exhibited dysregulated glucagon secretion. Moreover, a high-glucose load directly induced excessive glucagon secretion in a glucagon-secreting cell line and isolated islets, together with impairment of insulin signaling. These findings indicate that disordered insulin signaling is central to the pathophysiology of islet dysfunction in both α and β cells. On the other hand, certain beneficial effects of GLP-1 on dysfunctional α and β cells indicate that it has therapeutic potential for diabetes patients who exhibit insulin resistance in islets. These studies, involving basic medical research approaches, have-at least in part-clarified the molecular mechanisms underlying α- and β-cell dysfunction in diabetes, and offer important clues that should aid the development of future therapeutic approaches to the disease.
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Affiliation(s)
- Dan Kawamori
- Department of Metabolic Medicine, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871 Japan
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18
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Müller TD, Finan B, Clemmensen C, DiMarchi RD, Tschöp MH. The New Biology and Pharmacology of Glucagon. Physiol Rev 2017; 97:721-766. [PMID: 28275047 DOI: 10.1152/physrev.00025.2016] [Citation(s) in RCA: 206] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
In the last two decades we have witnessed sizable progress in defining the role of gastrointestinal signals in the control of glucose and energy homeostasis. Specifically, the molecular basis of the huge metabolic benefits in bariatric surgery is emerging while novel incretin-based medicines based on endogenous hormones such as glucagon-like peptide 1 and pancreas-derived amylin are improving diabetes management. These and related developments have fostered the discovery of novel insights into endocrine control of systemic metabolism, and in particular a deeper understanding of the importance of communication across vital organs, and specifically the gut-brain-pancreas-liver network. Paradoxically, the pancreatic peptide glucagon has reemerged in this period among a plethora of newly identified metabolic macromolecules, and new data complement and challenge its historical position as a gut hormone involved in metabolic control. The synthesis of glucagon analogs that are biophysically stable and soluble in aqueous solutions has promoted biological study that has enriched our understanding of glucagon biology and ironically recruited glucagon agonism as a central element to lower body weight in the treatment of metabolic disease. This review summarizes the extensive historical record and the more recent provocative direction that integrates the prominent role of glucagon in glucose elevation with its under-acknowledged effects on lipids, body weight, and vascular health that have implications for the pathophysiology of metabolic diseases, and the emergence of precision medicines to treat metabolic diseases.
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Affiliation(s)
- T D Müller
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
| | - B Finan
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
| | - C Clemmensen
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
| | - R D DiMarchi
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
| | - M H Tschöp
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
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19
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Glucotoxicity induces abnormal glucagon secretion through impaired insulin signaling in InR1G cells. PLoS One 2017; 12:e0176271. [PMID: 28426798 PMCID: PMC5398759 DOI: 10.1371/journal.pone.0176271] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Accepted: 04/07/2017] [Indexed: 11/19/2022] Open
Abstract
The significance of glucagon in the pathophysiology of diabetes mellitus is widely recognized, but the mechanisms underlying dysregulated glucagon secretion are still unclear. Here, we explored the molecular mechanisms of glucagon dysregulation, using an in vitro model. Hamster-derived glucagon-secreting InR1G cells were exposed to high glucose (25 mM) levels for 12 h before analyzing glucagon secretion and the activity of components involved in insulin signaling. High-glucose treatment induced increased glucagon secretion in InR1G cells, which represents a hallmark of diabetes mellitus. This treatment reduced the phosphorylation of Akt, indicating the deterioration of insulin signaling. Simultaneously, oxidative stress and JNK activity were shown to be increased. The inhibition of JNK signaling resulted in the amelioration of high-glucose level-induced glucagon secretion. Abnormally elevated glucagon secretion in diabetes can be reproduced by high-glucose treatment of InR1G cells, and the involvement of high glucose-oxidative stress-JNK-insulin signaling pathway axis has been demonstrated. These data elucidate, at least partly, the previously unclear mechanism of abnormal glucagon secretion, providing insights into a potential novel approach to diabetes treatment, targeting glucagon.
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20
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Briant LJB, Zhang Q, Vergari E, Kellard JA, Rodriguez B, Ashcroft FM, Rorsman P. Functional identification of islet cell types by electrophysiological fingerprinting. J R Soc Interface 2017; 14:20160999. [PMID: 28275121 PMCID: PMC5378133 DOI: 10.1098/rsif.2016.0999] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Accepted: 02/15/2017] [Indexed: 01/18/2023] Open
Abstract
The α-, β- and δ-cells of the pancreatic islet exhibit different electrophysiological features. We used a large dataset of whole-cell patch-clamp recordings from cells in intact mouse islets (N = 288 recordings) to investigate whether it is possible to reliably identify cell type (α, β or δ) based on their electrophysiological characteristics. We quantified 15 electrophysiological variables in each recorded cell. Individually, none of the variables could reliably distinguish the cell types. We therefore constructed a logistic regression model that included all quantified variables, to determine whether they could together identify cell type. The model identified cell type with 94% accuracy. This model was applied to a dataset of cells recorded from hyperglycaemic βV59M mice; it correctly identified cell type in all cells and was able to distinguish cells that co-expressed insulin and glucagon. Based on this revised functional identification, we were able to improve conductance-based models of the electrical activity in α-cells and generate a model of δ-cell electrical activity. These new models could faithfully emulate α- and δ-cell electrical activity recorded experimentally.
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Affiliation(s)
- Linford J B Briant
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
- Department of Computer Science, University of Oxford, Oxford OX1 3QD, UK
| | - Quan Zhang
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
| | - Elisa Vergari
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
| | - Joely A Kellard
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
| | - Blanca Rodriguez
- Department of Computer Science, University of Oxford, Oxford OX1 3QD, UK
| | - Frances M Ashcroft
- Department of Physiology, Anatomy, and Genetics, University of Oxford, South Parks Road, Oxford OX1 3PT, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
- Metabolic Research, Department of Physiology, Institute of Neuroscience and Physiology, University of Göteborg, SE-405 30 Göteborg, Sweden
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21
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Dapagliflozin stimulates glucagon secretion at high glucose: experiments and mathematical simulations of human A-cells. Sci Rep 2016; 6:31214. [PMID: 27535321 PMCID: PMC4989223 DOI: 10.1038/srep31214] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Accepted: 06/07/2016] [Indexed: 01/10/2023] Open
Abstract
Glucagon is one of the main regulators of blood glucose levels and dysfunctional stimulus secretion coupling in pancreatic A-cells is believed to be an important factor during development of diabetes. However, regulation of glucagon secretion is poorly understood. Recently it has been shown that Na+/glucose co-transporter (SGLT) inhibitors used for the treatment of diabetes increase glucagon levels in man. Here, we show experimentally that the SGLT2 inhibitor dapagliflozin increases glucagon secretion at high glucose levels both in human and mouse islets, but has little effect at low glucose concentrations. Because glucagon secretion is regulated by electrical activity we developed a mathematical model of A-cell electrical activity based on published data from human A-cells. With operating SGLT2, simulated glucose application leads to cell depolarization and inactivation of the voltage-gated ion channels carrying the action potential, and hence to reduce action potential height. According to our model, inhibition of SGLT2 reduces glucose-induced depolarization via electrical mechanisms. We suggest that blocking SGLTs partly relieves glucose suppression of glucagon secretion by allowing full-scale action potentials to develop. Based on our simulations we propose that SGLT2 is a glucose sensor and actively contributes to regulation of glucagon levels in humans which has clinical implications.
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22
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Watts M, Ha J, Kimchi O, Sherman A. Paracrine regulation of glucagon secretion: the β/α/δ model. Am J Physiol Endocrinol Metab 2016; 310:E597-E611. [PMID: 26837808 PMCID: PMC4835945 DOI: 10.1152/ajpendo.00415.2015] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 01/19/2016] [Indexed: 01/17/2023]
Abstract
The regulation of glucagon secretion in the pancreatic α-cell is not well understood. It has been proposed that glucose suppresses glucagon secretion either directly through an intrinsic mechanism within the α-cell or indirectly through an extrinsic mechanism. Previously, we described a mathematical model for isolated pancreatic α-cells and used it to investigate possible intrinsic mechanisms of regulating glucagon secretion. We demonstrated that glucose can suppress glucagon secretion through both ATP-dependent potassium channels (KATP) and a store-operated current (SOC). We have now developed an islet model that combines previously published mathematical models of α- and β-cells with a new model of δ-cells and use it to explore the effects of insulin and somatostatin on glucagon secretion. We show that the model can reproduce experimental observations that the inhibitory effect of glucose remains even when paracrine modulators are no longer acting on the α-cell. We demonstrate how paracrine interactions can either synchronize α- and δ-cells to produce pulsatile oscillations in glucagon and somatostatin secretion or fail to do so. The model can also account for the paradoxical observation that glucagon can be out of phase with insulin, whereas α-cell calcium is in phase with insulin. We conclude that both paracrine interactions and the α-cell's intrinsic mechanisms are needed to explain the response of glucagon secretion to glucose.
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Affiliation(s)
- Margaret Watts
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Maryland; and
| | - Joon Ha
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Maryland; and
| | - Ofer Kimchi
- Department of Physics, Princeton University, Princeton, New Jersey
| | - Arthur Sherman
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Maryland; and
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23
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Solomou A, Meur G, Bellomo E, Hodson DJ, Tomas A, Li SM, Philippe E, Herrera PL, Magnan C, Rutter GA. The Zinc Transporter Slc30a8/ZnT8 Is Required in a Subpopulation of Pancreatic α-Cells for Hypoglycemia-induced Glucagon Secretion. J Biol Chem 2015; 290:21432-42. [PMID: 26178371 PMCID: PMC4571871 DOI: 10.1074/jbc.m115.645291] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Indexed: 12/02/2022] Open
Abstract
SLC30A8 encodes a zinc transporter ZnT8 largely restricted to pancreatic islet β- and α-cells, and responsible for zinc accumulation into secretory granules. Although common SLC30A8 variants, believed to reduce ZnT8 activity, increase type 2 diabetes risk in humans, rare inactivating mutations are protective. To investigate the role of Slc30a8 in the control of glucagon secretion, Slc30a8 was inactivated selectively in α-cells by crossing mice with alleles floxed at exon 1 to animals expressing Cre recombinase under the pre-proglucagon promoter. Further crossing to Rosa26:tdRFP mice, and sorting of RFP+: glucagon+ cells from KO mice, revealed recombination in ∼30% of α-cells, of which ∼50% were ZnT8-negative (14 ± 1.8% of all α-cells). Although glucose and insulin tolerance were normal, female αZnT8KO mice required lower glucose infusion rates during hypoglycemic clamps and displayed enhanced glucagon release (p < 0.001) versus WT mice. Correspondingly, islets isolated from αZnT8KO mice secreted more glucagon at 1 mm glucose, but not 17 mm glucose, than WT controls (n = 5; p = 0.008). Although the expression of other ZnT family members was unchanged, cytoplasmic (n = 4 mice per genotype; p < 0.0001) and granular (n = 3, p < 0.01) free Zn2+ levels were significantly lower in KO α-cells versus control cells. In response to low glucose, the amplitude and frequency of intracellular Ca2+ increases were unchanged in α-cells of αZnT8KO KO mice. ZnT8 is thus important in a subset of α-cells for normal responses to hypoglycemia and acts via Ca2+-independent mechanisms.
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Affiliation(s)
- Antonia Solomou
- From the Section of Cell Biology and Functional Genomics, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London W12 0NN, United Kingdom
| | - Gargi Meur
- From the Section of Cell Biology and Functional Genomics, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London W12 0NN, United Kingdom
| | - Elisa Bellomo
- From the Section of Cell Biology and Functional Genomics, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London W12 0NN, United Kingdom
| | - David J Hodson
- From the Section of Cell Biology and Functional Genomics, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London W12 0NN, United Kingdom
| | - Alejandra Tomas
- From the Section of Cell Biology and Functional Genomics, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London W12 0NN, United Kingdom, the Department of Cell Biology, Institute of Ophthalmology, University College London, Greater London EC1V 9EL, United Kingdom
| | - Stéphanie Migrenne Li
- the University Paris Diderot-Paris 7, Unit of Functional and Adaptive Biology (BFA) EAC 7059 CNRS, 75013 Paris, France, and
| | - Erwann Philippe
- the University Paris Diderot-Paris 7, Unit of Functional and Adaptive Biology (BFA) EAC 7059 CNRS, 75013 Paris, France, and
| | - Pedro L Herrera
- the Department of Genetic Medicine and Development, Faculty of Medicine, University of Geneva, 1 rue Michel-Servet, 1211 Geneva-4, Switzerland
| | - Christophe Magnan
- the University Paris Diderot-Paris 7, Unit of Functional and Adaptive Biology (BFA) EAC 7059 CNRS, 75013 Paris, France, and
| | - Guy A Rutter
- From the Section of Cell Biology and Functional Genomics, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London W12 0NN, United Kingdom,
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24
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Pulsatile insulin secretion, impaired glucose tolerance and type 2 diabetes. Mol Aspects Med 2015; 42:61-77. [PMID: 25637831 DOI: 10.1016/j.mam.2015.01.003] [Citation(s) in RCA: 151] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Revised: 01/09/2015] [Accepted: 01/10/2015] [Indexed: 12/28/2022]
Abstract
Type 2 diabetes (T2DM) results when increases in beta cell function and/or mass cannot compensate for rising insulin resistance. Numerous studies have documented the longitudinal changes in metabolism that occur during the development of glucose intolerance and lead to T2DM. However, the role of changes in insulin secretion, both amount and temporal pattern, has been understudied. Most of the insulin secreted from pancreatic beta cells of the pancreas is released in a pulsatile pattern, which is disrupted in T2DM. Here we review the evidence that changes in beta cell pulsatility occur during the progression from glucose intolerance to T2DM in humans, and contribute significantly to the etiology of the disease. We review the evidence that insulin pulsatility improves the efficacy of secreted insulin on its targets, particularly hepatic glucose production, but also examine evidence that pulsatility alters or is altered by changes in peripheral glucose uptake. Finally, we summarize our current understanding of the biophysical mechanisms responsible for oscillatory insulin secretion. Understanding how insulin pulsatility contributes to normal glucose homeostasis and is altered in metabolic disease states may help improve the treatment of T2DM.
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Bessho M, Murase-Mishiba Y, Imagawa A, Terasaki J, Hanafusa T. Possible contribution of taurine to distorted glucagon secretion in intra-islet insulin deficiency: a metabolome analysis using a novel α-cell model of insulin-deficient diabetes. PLoS One 2014; 9:e113254. [PMID: 25393115 PMCID: PMC4231115 DOI: 10.1371/journal.pone.0113254] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Accepted: 10/24/2014] [Indexed: 01/30/2023] Open
Abstract
Glycemic instability is a serious problem in patients with insulin-deficient diabetes, and it may be due in part to abnormal endogenous glucagon secretion. However, the intracellular metabolic mechanism(s) involved in the aberrant glucagon response under the condition of insulin deficiency has not yet been elucidated. To investigate the metabolic traits that underlie the distortion of glucagon secretion under insulin deficient conditions, we generated an αTC1-6 cell line with stable knockdown of the insulin receptor (IRKD), i.e., an in vitro α-cell model for insulin-deficient diabetes, which exhibits an abnormal glucagon response to glucose. A comprehensive metabolomic analysis of the IRKD αTC1-6 cells (IRKD cells) revealed some candidate metabolites whose levels differed markedly compared to those in control αTC1-6 cells, but also which could affect the glucagon release in IRKD cells. Of these candidates, taurine was remarkably increased in the IRKD cells and was identified as a stimulator of glucagon in αTC1-6 cells. Taurine also paradoxically exaggerated the glucagon secretion at a high glucose concentration in IRKD cells and islets with IRKD. These results indicate that the metabolic alterations induced by IRKD in α-cells, especially the increase of taurine, may lead to the distorted glucagon response in IRKD cells, suggesting the importance of taurine in the paradoxical glucagon response and the resultant glucose instability in insulin-deficient diabetes.
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Affiliation(s)
- Megumi Bessho
- Department of Internal Medicine (I), Osaka Medical College, Osaka, Japan
| | | | - Akihisa Imagawa
- Department of Internal Medicine (I), Osaka Medical College, Osaka, Japan; Department of Metabolic Medicine, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Jungo Terasaki
- Department of Internal Medicine (I), Osaka Medical College, Osaka, Japan
| | - Toshiaki Hanafusa
- Department of Internal Medicine (I), Osaka Medical College, Osaka, Japan
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26
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High-fat diet consumption during pregnancy and the early post-natal period leads to decreased α cell plasticity in the nonhuman primate. Mol Metab 2012; 2:10-22. [PMID: 24024126 DOI: 10.1016/j.molmet.2012.11.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Revised: 11/05/2012] [Accepted: 11/07/2012] [Indexed: 12/26/2022] Open
Abstract
We investigated the impact of poor maternal nutrition and metabolic health on the development of islets of the nonhuman primate (NHP). Interestingly, fetal offspring of high fat diet (HFD) fed animals had normal total islet and β cell mass; however, there was a significant reduction in α cell mass, and decreased expression of transcription factors involved in α cell differentiation. In juvenile animals all offspring maintained on a HFD during the postweaning period demonstrated increases in total islet mass, however, the control offspring displaying increased islet number, and HFD offspring displayed increased islet size. Finally, while control offspring had increases in α and β cells, the HFD offspring had increases only in β cell number. These studies indicate that consumption of a HFD diet during pregnancy in the NHP, independent of maternal metabolic health, causes long-term abnormalities in α cell plasticity that may contribute to chronic disease susceptibility.
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27
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Le Marchand SJ, Piston DW. Glucose decouples intracellular Ca2+ activity from glucagon secretion in mouse pancreatic islet alpha-cells. PLoS One 2012; 7:e47084. [PMID: 23077547 PMCID: PMC3471958 DOI: 10.1371/journal.pone.0047084] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 09/12/2012] [Indexed: 11/18/2022] Open
Abstract
The mechanisms of glucagon secretion and its suppression by glucose are presently unknown. This study investigates the relationship between intracellular calcium levels ([Ca2+]i) and hormone secretion under low and high glucose conditions. We examined the effects of modulating ion channel activities on [Ca2+]i and hormone secretion from ex vivo mouse pancreatic islets. Glucagon-secreting α-cells were unambiguously identified by cell specific expression of fluorescent proteins. We found that activation of L-type voltage-gated calcium channels is critical for α-cell calcium oscillations and glucagon secretion at low glucose levels. Calcium channel activation depends on KATP channel activity but not on tetrodotoxin-sensitive Na+ channels. The use of glucagon secretagogues reveals a positive correlation between α-cell [Ca2+]i and secretion at low glucose levels. Glucose elevation suppresses glucagon secretion even after treatment with secretagogues. Importantly, this inhibition is not mediated by KATP channel activity or reduction in α-cell [Ca2+]i. Our results demonstrate that glucose uncouples the positive relationship between [Ca2+]i and secretory activity. We conclude that glucose suppression of glucagon secretion is not mediated by inactivation of calcium channels, but instead, it requires a calcium-independent inhibitory pathway.
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Affiliation(s)
- Sylvain J. Le Marchand
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States of America
| | - David W. Piston
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States of America
- * E-mail:
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28
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Gaisano HY, Macdonald PE, Vranic M. Glucagon secretion and signaling in the development of diabetes. Front Physiol 2012; 3:349. [PMID: 22969729 PMCID: PMC3432929 DOI: 10.3389/fphys.2012.00349] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Accepted: 08/10/2012] [Indexed: 12/19/2022] Open
Abstract
Normal release of glucagon from pancreatic islet α-cells promotes glucose mobilization, which counteracts the hypoglycemic actions of insulin, thereby ensuring glucose homeostasis. In treatment of diabetes aimed at rigorously reducing hyperglycemia to avoid chronic complications, the resulting hypoglycemia triggering glucagon release from α-cells is frequently impaired, with ensuing hypoglycemic complications. This review integrates the physiology of glucagon secretion regulating glucose homeostasis in vivo to single α-cell signaling, and how both become perturbed in diabetes. α-cells within the social milieu of the islet micro-organ are regulated not only by intrinsic signaling events but also by paracrine regulation, particularly by adjacent insulin-secreting β-cells and somatostatin-secreting δ-cells. We discuss the intrinsic α-cell signaling events, including glucose sensing and ion channel regulation leading to glucagon secretion. We then discuss the complex crosstalk between the islet cells and the breakdown of this crosstalk in diabetes contributing to the dysregulated glucagon secretion. Whereas, there are many secretory products released by β- and δ-cells that become deficient or excess in diabetes, we discuss the major ones, including the better known insulin and lesser known somatostatin, which act as putative paracrine on/off switches that very finely regulate α-cell secretory responses in health and diabetes. Of note in several type 1 diabetes (T1D) rodent models, blockade of excess somatostatin actions on α-cell could normalize glucagon secretion sufficient to attain normoglycemia in response to hypoglycemic assaults. There has been slow progress in fully elucidating the pathophysiology of the α-cell in diabetes because of the small number of α-cells within an islet and the islet mass becomes severely reduced and inflamed in diabetes. These limitations are just now being surmounted by new approaches.
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Affiliation(s)
- Herbert Y Gaisano
- Departments of Medicine and Physiology, University of Toronto Toronto, ON, Canada
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29
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Abstract
Glucagon, a peptide hormone secreted from the α-cells of the pancreatic islets, is critical for blood glucose homeostasis. We reviewed the literature and employed a computational systems analysis of intracellular metabolic and electrical regulation of glucagon secretion to better understand these processes. The mathematical model of α-cell metabolic parameters is based on our previous model for pancreatic β-cells. We also formulated an ionic model for action potentials that incorporates Ca ( 2+) , K (+) , Na (+) and Cl (-) currents. Metabolic and ionic models are coupled to the equations describing Ca ( 2+) homeostasis and glucagon secretion that depends on activation of specific voltage-gated Ca ( 2+) channels. Paracrine and endocrine regulations were analyzed with an emphasis on their effects on a hyperpolarization of membrane potential. This general model simulates and gives insight into the mechanisms of regulation of glucagon secretion under a wide range of experimental conditions. We also reviewed and analyzed dysfunctional mechanisms in α-cells to determine key pharmacological targets for modulating glucagon secretion in type 1 and 2 diabetes.
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Affiliation(s)
- Leonid E Fridlyand
- The Kovler Diabetes Center, Departments of Medicine and Pediatrics, The University of Chicago, Chicago, IL, USA.
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30
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Koh DS, Cho JH, Chen L. Paracrine interactions within islets of Langerhans. J Mol Neurosci 2012; 48:429-40. [PMID: 22528452 DOI: 10.1007/s12031-012-9752-2] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Accepted: 03/12/2012] [Indexed: 01/05/2023]
Abstract
Glucose supply fluctuates between meal and fasting periods and its consumption by the body varies greatly depending on bodily metabolism. Pancreatic islets of Langerhans secrete various endocrine hormones including insulin and glucagon to keep blood glucose level relatively constant. Additionally, islet hormones regulate activity of neighboring cells as local autocrine or paracrine modulators. Moreover, islet cells release neurotransmitters such as glutamate and γ-aminobutyric acid (GABA) to gain more precise regulation of hormones release kinetics. Excitatory glutamate is co-released with glucagon from α-cells and activates glutamate receptors in the neighboring cells. GABA released from β-cells was shown to inhibit α-cells but to activate β-cells by acting GABA(A) receptors. This review summarizes the recent progress in understanding the paracrine/autocrine interactions in islets.
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Affiliation(s)
- Duk-Su Koh
- University of Washington, Seattle, WA, USA.
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31
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Isosteviol has beneficial effects on palmitate-induced α-cell dysfunction and gene expression. PLoS One 2012; 7:e34361. [PMID: 22479612 PMCID: PMC3313988 DOI: 10.1371/journal.pone.0034361] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Accepted: 03/01/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Long-term exposure to high levels of fatty acids impairs insulin secretion and exaggerates glucagon secretion. The aim of this study was to explore if the antihyperglycemic agent, Isosteviol (ISV), is able to counteract palmitate-induced α-cell dysfunction and to influence α-cell gene expression. METHODOLOGY/PRINCIPAL FINDINGS Long-term incubation studies with clonal α-TC1-6 cells were performed in the presence of 0.5 mM palmitate with or without ISV. We investigated effects on glucagon secretion, glucagon content, cellular triglyceride (TG) content, cell proliferation, and expression of genes involved in controlling glucagon synthesis, fatty acid metabolism, and insulin signal transduction. Furthermore, we studied effects of ISV on palmitate-induced glucagon secretion from isolated mouse islets. Culturing α-cells for 72-h with 0.5 mM palmitate in the presence of 18 mM glucose resulted in a 56% (p<0.01) increase in glucagon secretion. Concomitantly, the TG content of α-cells increased by 78% (p<0.01) and cell proliferation decreased by 19% (p<0.05). At 18 mM glucose, ISV (10(-8) and 10(-6) M) reduced palmitate-stimulated glucagon release by 27% (p<0.05) and 27% (p<0.05), respectively. ISV (10(-6) M) also counteracted the palmitate-induced hypersecretion of glucagon in mouse islets. ISV (10(-6) M) reduced α-TC1-6 cell proliferation rate by 25% (p<0.05), but ISV (10(-8) and 10(-6) M) had no effect on TG content in the presence of palmitate. Palmitate (0.5 mM) increased Pcsk2 (p<0.001), Irs2 (p<0.001), Fasn (p<0.001), Srebf2 (p<0.001), Acaca (p<0.01), Pax6 (p<0.05) and Gcg mRNA expression (p<0.05). ISV significantly (p<0.05) up-regulated Insr, Irs1, Irs2, Pik3r1 and Akt1 gene expression in the presence of palmitate. CONCLUSIONS/SIGNIFICANCE ISV counteracts α-cell hypersecretion and apparently contributes to changes in expression of key genes resulting from long-term exposure to palmitate. ISV apparently acts as a glucagonostatic drug with potential as a new anti-diabetic drug for the treatment of type 2 diabetes.
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32
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Tsui S, Gao J, Wang C, Lu L. CTCF mediates effect of insulin on glucagon expression. Exp Cell Res 2012; 318:887-95. [PMID: 22426149 DOI: 10.1016/j.yexcr.2012.03.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Revised: 02/29/2012] [Accepted: 03/01/2012] [Indexed: 11/15/2022]
Abstract
Pancreatic islet α-cell development and glucagon production are mainly regulated by Pax6 in the homeobox gene families. However, the molecular mechanism fine-tuning the regulation of these events in α-cell still remains unclear. In ocular cells, Pax6 transcription is regulated by CTCF through its binding to specific sites in Pax6 promoter. In this study, CTCF-mediated regulations of islet α-cell development and glucagon production were investigated in both CTCF transgenic mice and α-TC-1-6 cells. Over-expression of CTCF in transgenic mice affected development of pancreatic islets by significantly suppressing α-cell population in both embryonic and adult pancreases. The effect of CTCF on Pax6 gene expression and subsequently, on pro-glucagon production was however, examined in pancreatic islet α-cells. Over-expression and knock-down of CTCF directly affected Pax6 expression. More importantly, the CTCF binding sites upstream from Pax6 p0 promoter were required for regulating p0 promoter activity in islet α-cells. Stimulation of α-cells with insulin resulted in a significant increase in CTCF expression and a decrease in Pax6 expression, and consequently suppressed pro-glucagon expression. In contrast, these insulin-induced effects were blocked by knockdown of CTCF mRNA with specific siRNA in α-cells. Altogether, our results demonstrated for the first time that CTCF functions as a switch-like molecule between the insulin signaling and the regulations of Pax6 and glucagon expression in pancreatic islet α-cells.
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Affiliation(s)
- Shanli Tsui
- Department of Medicine, David Geffen School of Medicine University of California Los Angeles, Torrance, CA 90502, USA
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33
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Kawamori D, Akiyama M, Hu J, Hambro B, Kulkarni RN. Growth factor signalling in the regulation of α-cell fate. Diabetes Obes Metab 2011; 13 Suppl 1:21-30. [PMID: 21824253 DOI: 10.1111/j.1463-1326.2011.01442.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Glucagon plays critical roles in regulating glucose homeostasis, mainly by counteracting the effects of insulin. Consequently, the dysregulated glucagon secretion that is evident in type 2 diabetes has significant implications in the pathophysiology of the disease. Glucagon secretion from pancreatic α-cells has been suggested to be modulated by blood glucose, signals from the nervous system and endocrine components. In addition to these regulators, intraislet factors acting in a paracrine manner from neighbouring β-cells are emerging as central modulator(s) of α-cell biology. One of the most important of these paracrine factors, insulin, modulates glucagon secretion. Indeed, the α-cell-specific insulin receptor knockout (αIRKO) mouse manifests hypersecretion of glucagon in the postprandial stage and exhibits defective secretion in fasting-induced hypoglycaemia, together mimicking the α-cell defects observed in type 2 diabetes. Interestingly, αIRKO mice display a progressive increase in β-cell mass and a concomitant decrease in α-cells. Lineage trace analyses reveal that the new β-cells originate, in part, from the insulin receptor-deficient α-cells indicating a critical role for α-cell insulin signalling in determining β-cell origin. Our studies also reveal that glucagon-like peptide-1 (GLP-1) treatment of αIRKO mice suppresses glucagon secretion despite absence of functional insulin receptors precluding a role for insulin in GLP-1 action on α-cells in this model. These findings highlight the significance of insulin signalling in the regulation of α-cell biology.
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Affiliation(s)
- D Kawamori
- Section of Islet Cell Biology and Regenerative Medicine, Joslin Diabetes Center and Harvard Medical School, Boston, MA 02215, USA.
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34
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Hardy AB, Serino AS, Wijesekara N, Chimienti F, Wheeler MB. Regulation of glucagon secretion by zinc: lessons from the β cell-specific Znt8 knockout mouse model. Diabetes Obes Metab 2011; 13 Suppl 1:112-7. [PMID: 21824264 DOI: 10.1111/j.1463-1326.2011.01451.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In type-2 diabetes, hyperglucagonaemia aggravates elevated blood glucose levels. Relative to our knowledge of the β-cell and insulin secretion, there remains a limited understanding of glucagon secretion in α-cells. Regulation of glucagon may be dependent on a combination of factors, which include direct glucose sensing by the α-cell, innervations from the autonomic nervous system and potential 'paracrine' actions by hormones and factors that are released by adjacent endocrine cells within the islets. The list of potential 'paracrine' regulators within the islet includes insulin, somatostatin, γ-aminobutyric acid, glutamate and zinc. Zinc crystallises with insulin in β-cells and is co-secreted with insulin. In the scientific literature, the effect of exogeneous zinc on glucagon secretion has been debated. Here, we confirm that an increase in exogeneous zinc does inhibit glucagon secretion. To determine if there are physiological effects of zinc on glucagon secretion we used a β-cell-specific ZnT8 knockout (Znt8BKO) mouse model. Znt8BKO mice, despite showing lower granular zinc content in β-cells, showed no changes in fasted plasma glucagon levels and glucose regulated glucagon secretion. These findings suggest that zinc secreted from β-cell does not regulate glucagon secretion.
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Affiliation(s)
- A B Hardy
- Department of Physiology, University of Toronto, 1 King's College Circle, Toronto, ON, Canada
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35
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Leung YM, Huang CF, Chao CC, Lu DY, Kuo CS, Cheng TH, Chang LY, Chou CH. Voltage-gated K+ channels play a role in cAMP-stimulated neuritogenesis in mouse neuroblastoma N2A cells. J Cell Physiol 2011; 226:1090-8. [PMID: 20857407 DOI: 10.1002/jcp.22430] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Neuritogenesis is essential in establishing the neuronal circuitry. An important intracellular signal causing neuritogenesis is cAMP. In this report, we showed that an increase in intracellular cAMP stimulated neuritogenesis in neuroblastoma N2A cells via a PKA-dependent pathway. Two voltage-gated K(+) (Kv) channel blockers, 4-aminopyridine (4-AP) and tetraethylammonium (TEA), inhibited cAMP-stimulated neuritogenesis in N2A cells in a concentration-dependent manner that remarkably matched their ability to inhibit Kv currents in these cells. Consistently, siRNA knock down of Kv1.1, Kv1.4, and Kv2.1 expression reduced Kv currents and inhibited cAMP-stimulated neuritogenesis. Kv1.1, Kv1.4, and Kv2.1 channels were expressed in the cell bodies and neurites as shown by immunohistochemistry. Microfluorimetric imaging of intracellular [K(+)] demonstrated that [K(+)] in neurites was lower than that in the cell body. We also showed that cAMP-stimulated neuritogenesis may not involve voltage-gated Ca(2+) or Na(+) channels. Taken together, the results suggest a role of Kv channels and enhanced K(+) efflux in cAMP/PKA-stimulated neuritogenesis in N2A cells.
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Affiliation(s)
- Yuk-Man Leung
- Graduate Institute of Neural and Cognitive Sciences, China Medical University, Taichung, Taiwan.
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36
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Abstract
OBJECTIVE The physiologic significance of the nitric oxide (NO)/cGMP signaling pathway in islets is unclear. We hypothesized that cGMP-dependent protein kinase type I (cGKI) is directly involved in the secretion of islet hormones and glucose homeostasis. RESEARCH DESIGN AND METHODS Gene-targeted mice that lack cGKI in islets (conventional cGKI mutants and cGKIα and Iβ rescue mice [α/βRM] that express cGKI only in smooth muscle) were studied in comparison to control (CTR) mice. cGKI expression was mapped in the endocrine pancreas by Western blot, immuno-histochemistry, and islet-specific recombination analysis. Insulin, glucagon secretion, and cytosolic Ca²(+) ([Ca²(+)](i)) were assayed by radioimmunoassay and FURA-2 measurements, respectively. Serum levels of islet hormones were analyzed at fasting and upon glucose challenge (2 g/kg) in vivo. RESULTS Immunohistochemistry showed that cGKI is present in α- but not in β-cells in islets of Langerhans. Mice that lack α-cell cGKI had significantly elevated fasting glucose and glucagon levels, whereas serum insulin levels were unchanged. High glucose concentrations strongly suppressed the glucagon release in CTR mice, but had only a moderate effect on islets that lacked cGKI. 8-Br-cGMP reduced stimulated [Ca²(+)](i) levels and glucagon release rates of CTR islets at 0.5 mmol/l glucose, but was without effect on [Ca²(+)](i) or hormone release in cGKI-deficient islets. CONCLUSIONS We propose that cGKI modulates glucagon release by suppression of [Ca²(+)](i) in α-cells.
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Affiliation(s)
- Veronika Leiss
- FOR 923, Technische Universität München, München, Germany, and Center for Integrated Protein Science, Ludwig-Maximilians-Universität München, München, Germany
- Institut für Pharmakologie und Toxikologie, Abteilung Pharmakologie und Experimentelle Therapie, Universitätsklinikum Tübingen, Tübingen, Germany
| | - Andreas Friebe
- Lehrstuhl für Physiologie I, Julius-Maximilians Universität Würzburg, Würzburg, Germany
| | - Andrea Welling
- FOR 923, Technische Universität München, München, Germany, and Center for Integrated Protein Science, Ludwig-Maximilians-Universität München, München, Germany
- Institut für Pharmakologie und Toxikologie, Technische Universität München, München, Germany
| | - Franz Hofmann
- FOR 923, Technische Universität München, München, Germany, and Center for Integrated Protein Science, Ludwig-Maximilians-Universität München, München, Germany
| | - Robert Lukowski
- FOR 923, Technische Universität München, München, Germany, and Center for Integrated Protein Science, Ludwig-Maximilians-Universität München, München, Germany
- Institut für Pharmazie, Abteilung Pharmakologie, Toxikologie und Klinische Pharmazie, Universität Tübingen, Tübingen, Germany
- Corresponding author: Robert Lukowski,
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Huang YC, Rupnik M, Gaisano HY. Unperturbed islet α-cell function examined in mouse pancreas tissue slices. J Physiol 2010; 589:395-408. [PMID: 21078586 DOI: 10.1113/jphysiol.2010.200345] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Critical investigation into α-cell biology in health and diabetes has been sparse and at times inconsistent because of the technical difficulties with employing conventional strategies of isolated islets and dispersed single cells. An acute pancreas slice preparation was developed to overcome the enzymatic and mechanical perturbations inherent in conventional islet cell isolation procedures. This preparation preserves intra-islet cellular communication and islet architecture in their in situ native state. α-Cells within tissue slices were directly assessed by patch pipette and electrophysiologically characterized. The identity of the patched cells was confirmed by biocytin dye labelling and immunocytochemistry. α-Cells in mouse pancreas slices exhibited well-described features of I(Na) (excitable at physiological membrane potential), I(KATP), small cell size, low resting membrane conductance, and inducible low and high voltage-activated I(Ca), the latter correlating with exocytosis determined by capacitance measurements. In contrast to previous reports, our large unbiased sampling of α-cells revealed a wide range distribution of all of these parameters, including the amount of K(ATP) conductance, Na+ and Ca2+ current amplitudes, and capacitance changes induced by a train of depolarization pulses. The proposed pancreas slice preparation in combination with standard patch-clamping technique allowed large sampling and rapid assessment of α-cells, which revealed a wide distribution in α-cell ion channel properties. This specific feature explains the apparent inconsistency of previous reports on these α-cell ion channel properties. Our innovative approach will enable future studies into elucidating islet α-cell dysregulation occurring during diabetes.
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Affiliation(s)
- Ya-Chi Huang
- Institute of Medical Science, University of Toronto, Toronto, ON, Canada
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Piro S, Maniscalchi ET, Monello A, Pandini G, Mascali LG, Rabuazzo AM, Purrello F. Palmitate affects insulin receptor phosphorylation and intracellular insulin signal in a pancreatic alpha-cell line. Endocrinology 2010; 151:4197-206. [PMID: 20573722 DOI: 10.1210/en.2009-1472] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
This study investigated in a pancreatic alpha-cell line the effects of chronic exposure to palmitate on the insulin and IGF-I receptor (IGF-IR) and intracellular insulin pathways. alpha-TC1-6 cells were cultured in the presence or absence of palmitate (0.5 mmol/liter) up to 48 h. Glucagon secretion, insulin and IGF-IR autophosphorylation, and insulin receptor substrate (IRS)-1, IRS-2, phosphatidylinositol kinase (PI3K) (p85 alpha), and serine-threonine protein kinase (Akt) phosphorylated (active) forms were measured. Erk 44/42 and p38 phosphorylation (P) (MAPK pathway markers) were also measured. Because MAPK can regulate Pax6, a transcription factor that controls glucagon expression, paired box gene 6 (Pax6) and glucagon gene and protein expression were also measured. Basal glucagon secretion was increased and the inhibitory effect of acute insulin exposure reduced in alpha-TC1 cells cultured with palmitate. Insulin-stimulated insulin receptor phosphorylation was greatly reduced by exposure to palmitate. Similar results were observed with IRS-1-P, PI3K (p85 alpha), and Akt-P. In contrast, with IGF-IR and IRS-2-P, the basal levels (i.e. in the absence of insulin stimulation) were higher in cells cultured with palmitate. Similar data were obtained with Erk 44/42-P and p-38-P. Pax6 and glucagon gene and protein expression were higher in cells cultured with palmitate. In these cells cultured, specifics MAPKs inhibitors were able to reduce both Pax6 and glucagon gene and protein expression. These results indicate that alpha-cells exposed to palmitate show insulin resistance of the IRS-1/PI3K/Akt pathway that likely controls glucagon secretion. In contrast, the IRS-2/MAPKs pathway is stimulated, through an activation of the IGF-IR, leading to increased Pax6 and glucagon expression. Our data support the hypothesis that the chronic elevation of fatty acids contribute to alpha-cell dysregulation frequently observed in type 2 diabetes.
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Affiliation(s)
- Salvatore Piro
- Department of Internal Medicine, University of Catania, Catania 95122, Italy
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Drews G, Krippeit-Drews P, Düfer M. Electrophysiology of islet cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:115-63. [PMID: 20217497 DOI: 10.1007/978-90-481-3271-3_7] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Stimulus-Secretion Coupling (SSC) of pancreatic islet cells comprises electrical activity. Changes of the membrane potential (V(m)) are regulated by metabolism-dependent alterations in ion channel activity. This coupling is best explored in beta-cells. The effect of glucose is directly linked to mitochondrial metabolism as the ATP/ADP ratio determines the open probability of ATP-sensitive K(+) channels (K(ATP) channels). Nucleotide sensitivity and concentration in the direct vicinity of the channels are controlled by several factors including phospholipids, fatty acids, and kinases, e.g., creatine and adenylate kinase. Closure of K(ATP) channels leads to depolarization of beta-cells via a yet unknown depolarizing current. Ca(2+) influx during action potentials (APs) results in an increase of the cytosolic Ca(2+) concentration ([Ca(2+)](c)) that triggers exocytosis. APs are elicited by the opening of voltage-dependent Na(+) and/or Ca(2+) channels and repolarized by voltage- and/or Ca(2+)-dependent K(+) channels. At a constant stimulatory glucose concentration APs are clustered in bursts that are interrupted by hyperpolarized interburst phases. Bursting electrical activity induces parallel fluctuations in [Ca(2+)](c) and insulin secretion. Bursts are terminated by I(Kslow) consisting of currents through Ca(2+)-dependent K(+) channels and K(ATP) channels. This review focuses on structure, characteristics, physiological function, and regulation of ion channels in beta-cells. Information about pharmacological drugs acting on K(ATP) channels, K(ATP) channelopathies, and influence of oxidative stress on K(ATP) channel function is provided. One focus is the outstanding significance of L-type Ca(2+) channels for insulin secretion. The role of less well characterized beta-cell channels including voltage-dependent Na(+) channels, volume sensitive anion channels (VSACs), transient receptor potential (TRP)-related channels, and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels is discussed. A model of beta-cell oscillations provides insight in the interplay of the different channels to induce and maintain electrical activity. Regulation of beta-cell electrical activity by hormones and the autonomous nervous system is discussed. alpha- and delta-cells are also equipped with K(ATP) channels, voltage-dependent Na(+), K(+), and Ca(2+) channels. Yet the SSC of these cells is less clear and is not necessarily dependent on K(ATP) channel closure. Different ion channels of alpha- and delta-cells are introduced and SSC in alpha-cells is described in special respect of paracrine effects of insulin and GABA secreted from beta-cells.
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Affiliation(s)
- Gisela Drews
- Institute of Pharmacy, Department of Pharmacology and Clinical Pharmacy, University of Tübingen, 72076 Tübingen, Germany.
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Kawamori D, Welters HJ, Kulkarni RN. Molecular Pathways Underlying the Pathogenesis of Pancreatic α-Cell Dysfunction. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:421-45. [DOI: 10.1007/978-90-481-3271-3_18] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Abstract
Cell-cell communication within any given tissue is an important aspect of correct organ function. The islets of Langerhans forming the endocrine pancreas are composed of alpha-, beta-, delta-, epsilon- and PP-cells, and interactions between these cells are required for fine-tuning glucose homeostasis of the body. The endocrine cells communicate through homotypic or heterotypic cell-cell adhesion, or in a paracrine fashion, and this communication is involved in the regulated secretion of islet hormones. This review discusses how islet hormones, secreted molecules and ions influence the endocrine cells and how cell adhesion molecules such as neural cell adhesion molecule, cadherins, connexin-36, Eph receptors and ephrin ligands, as well as extracellular matrix proteins, modulate pancreatic islet function.
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Affiliation(s)
- R Jain
- Institute of Metabolic Physiology, Heinrich-Heine-University, Düsseldorf, Germany
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42
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Insulin signaling in alpha cells modulates glucagon secretion in vivo. Cell Metab 2009; 9:350-61. [PMID: 19356716 PMCID: PMC2694613 DOI: 10.1016/j.cmet.2009.02.007] [Citation(s) in RCA: 241] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/19/2008] [Revised: 01/29/2009] [Accepted: 02/12/2009] [Indexed: 12/21/2022]
Abstract
Glucagon plays an important role in glucose homeostasis by regulating hepatic glucose output in both normo- and hypoglycemic conditions. In this study, we created and characterized alpha cell-specific insulin receptor knockout (alphaIRKO) mice to directly explore the role of insulin signaling in the regulation of glucagon secretion in vivo. Adult male alphaIRKO mice exhibited mild glucose intolerance, hyperglycemia, and hyperglucagonemia in the fed state and enhanced glucagon secretion in response to L-arginine stimulation. Hyperinsulinemic-hypoglycemic clamp studies revealed an enhanced glucagon secretory response and an abnormal norepinephrine response to hypoglycemia in alphaIRKO mice. The mutants also exhibited an age-dependent increase in beta cell mass. Furthermore, siRNA-mediated knockdown of insulin receptor in glucagon-secreting InR1G cells promoted enhanced glucagon secretion and complemented our in vivo findings. Together, these data indicate a significant role for intraislet insulin signaling in the regulation of alpha cell function in both normo- and hypoglycemic conditions.
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Hauge-Evans AC, King AJ, Carmignac D, Richardson CC, Robinson ICAF, Low MJ, Christie MR, Persaud SJ, Jones PM. Somatostatin secreted by islet delta-cells fulfills multiple roles as a paracrine regulator of islet function. Diabetes 2009; 58:403-11. [PMID: 18984743 PMCID: PMC2628614 DOI: 10.2337/db08-0792] [Citation(s) in RCA: 219] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
OBJECTIVE Somatostatin (SST) is secreted by islet delta-cells and by extraislet neuroendocrine cells. SST receptors have been identified on alpha- and beta-cells, and exogenous SST inhibits insulin and glucagon secretion, consistent with a role for SST in regulating alpha- and beta-cell function. However, the specific intraislet function of delta-cell SST remains uncertain. We have used Sst(-/-) mice to investigate the role of delta-cell SST in the regulation of insulin and glucagon secretion in vitro and in vivo. RESEARCH DESIGN AND METHODS Islet morphology was assessed by histological analysis. Hormone levels were measured by radioimmunoassay in control and Sst(-/-) mice in vivo and from isolated islets in vitro. RESULTS Islet size and organization did not differ between Sst(-/-) and control islets, nor did islet glucagon or insulin content. Sst(-/-) mice showed enhanced insulin and glucagon secretory responses in vivo. In vitro stimulus-induced insulin and glucagon secretion was enhanced from perifused Sst(-/-) islets compared with control islets and was inhibited by exogenous SST in Sst(-/-) but not control islets. No difference in the switch-off rate of glucose-stimulated insulin secretion was observed between genotypes, but the cholinergic agonist carbamylcholine enhanced glucose-induced insulin secretion to a lesser extent in Sst(-/-) islets compared with controls. Glucose suppressed glucagon secretion from control but not Sst(-/-) islets. CONCLUSIONS We suggest that delta-cell SST exerts a tonic inhibitory influence on insulin and glucagon secretion, which may facilitate the islet response to cholinergic activation. In addition, delta-cell SST is implicated in the nutrient-induced suppression of glucagon secretion.
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Affiliation(s)
- Astrid C Hauge-Evans
- Beta Cell Development and Function Group, Division of Reproduction and Endocrinology, King's College London, London, UK.
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Quoix N, Cheng-Xue R, Mattart L, Zeinoun Z, Guiot Y, Beauvois MC, Henquin JC, Gilon P. Glucose and pharmacological modulators of ATP-sensitive K+ channels control [Ca2+]c by different mechanisms in isolated mouse alpha-cells. Diabetes 2009; 58:412-21. [PMID: 19008345 PMCID: PMC2628615 DOI: 10.2337/db07-1298] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
OBJECTIVE We studied how glucose and ATP-sensitive K(+) (K(ATP)) channel modulators affect alpha-cell [Ca(2+)](c). RESEARCH DESIGN AND METHODS GYY mice (expressing enhanced yellow fluorescent protein in alpha-cells) and NMRI mice were used. [Ca(2+)](c), the K(ATP) current (I(KATP), perforated mode) and cell metabolism [NAD(P)H fluorescence] were monitored in single alpha-cells and, for comparison, in single beta-cells. RESULTS In 0.5 mmol/l glucose, [Ca(2+)](c) oscillated in some alpha-cells and was basal in the others. Increasing glucose to 15 mmol/l decreased [Ca(2+)](c) by approximately 30% in oscillating cells and was ineffective in the others. alpha-Cell I(KATP) was inhibited by tolbutamide and activated by diazoxide or the mitochondrial poison azide, as in beta-cells. Tolbutamide increased alpha-cell [Ca(2+)](c), whereas diazoxide and azide abolished [Ca(2+)](c) oscillations. Increasing glucose from 0.5 to 15 mmol/l did not change I(KATP) and NAD(P)H fluorescence in alpha-cells in contrast to beta-cells. The use of nimodipine showed that L-type Ca(2+) channels are the main conduits for Ca(2+) influx in alpha-cells. gamma-Aminobutyric acid and zinc did not decrease alpha-cell [Ca(2+)](c), and insulin, although lowering [Ca(2+)](c) very modestly, did not affect glucagon secretion. CONCLUSIONS alpha-Cells display similarities with beta-cells: K(ATP) channels control Ca(2+) influx mainly through L-type Ca(2+) channels. However, alpha-cells have distinct features from beta-cells: Most K(ATP) channels are already closed at low glucose, glucose does not affect cell metabolism and I(KATP), and it slightly decreases [Ca(2+)](c). Hence, glucose and K(ATP) channel modulators exert distinct effects on alpha-cell [Ca(2+)](c). The direct small glucose-induced drop in alpha-cell [Ca(2+)](c) contributes likely only partly to the strong glucose-induced inhibition of glucagon secretion in islets.
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Affiliation(s)
- Nicolas Quoix
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
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Affiliation(s)
- David A Jacobson
- Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, The University of Chicago, Chicago, Illinois, USA
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46
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Zhang Y, Zhang N, Gyulkhandanyan AV, Xu E, Gaisano HY, Wheeler MB, Wang Q. Presence of functional hyperpolarisation-activated cyclic nucleotide-gated channels in clonal alpha cell lines and rat islet alpha cells. Diabetologia 2008; 51:2290-8. [PMID: 18850083 DOI: 10.1007/s00125-008-1166-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2008] [Accepted: 08/22/2008] [Indexed: 11/28/2022]
Abstract
AIMS/HYPOTHESIS The hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels, discovered initially in cardiac and neuronal cells, mediate the inward pacemaker current (I (f) or I (h)). Recently, we have demonstrated the presence of HCN channels in pancreatic beta cells. Here, we aim to examine the presence and function of HCN channels in glucagon-secreting alpha cells. METHODS RT-PCR and immunocytochemistry were used to examine the presence of HCN channels in alpha cells. Whole-cell patch-clamp, calcium imaging and glucagon secretion experiments were performed to explore the function of HCN channels in alpha cells. RESULTS HCN transcripts and proteins were detected in alpha-TC6 cells and dispersed rat alpha cells. Patch-clamp recording showed hyperpolarisation-activated currents in alpha-TC6 cells, which could be blocked by HCN channel inhibitor ZD7288. Glucagon secretion RIA studies demonstrated that at both low and high glucose concentrations (2 and 20 mmol/l), ZD7288 significantly enhanced glucagon secretion in alpha-TC6 and IN-R1-G9 cell lines. Conversely, activation of HCN channels by lamotrigine significantly suppressed glucagon secretion at the low glucose concentration. Calcium imaging studies showed that blockade of HCN channels by ZD7288 significantly increased intracellular calcium in alpha-TC6 cells, while lamotrigine or the Na(+) channel blocker tetrodotoxin suppressed the effect of ZD7288 on intracellular calcium. Furthermore, we found the HCN channel inhibitors ZD7288 and cilobradine both significantly increased glucagon secretion from rat islets. CONCLUSIONS/INTERPRETATION These results suggest a potential role for HCN channels in regulation of glucagon secretion via modulating Ca(2+) and Na(+) channel activities.
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Affiliation(s)
- Y Zhang
- Department of Physiology, University of Toronto, Toronto, ON, Canada
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Abstract
Glucose homeostasis is regulated primarily by the opposing actions of insulin and glucagon, hormones that are secreted by pancreatic islets from beta-cells and alpha-cells, respectively. Insulin secretion is increased in response to elevated blood glucose to maintain normoglycemia by stimulating glucose transport in muscle and adipocytes and reducing glucose production by inhibiting gluconeogenesis in the liver. Whereas glucagon secretion is suppressed by hyperglycemia, it is stimulated during hypoglycemia, promoting hepatic glucose production and ultimately raising blood glucose levels. Diabetic hyperglycemia occurs as the result of insufficient insulin secretion from the beta-cells and/or lack of insulin action due to peripheral insulin resistance. Remarkably, excessive secretion of glucagon from the alpha-cells is also a major contributor to the development of diabetic hyperglycemia. Insulin is a physiological suppressor of glucagon secretion; however, at the cellular and molecular levels, how intraislet insulin exerts its suppressive effect on the alpha-cells is not very clear. Although the inhibitory effect of insulin on glucagon gene expression is an important means to regulate glucagon secretion, recent studies suggest that the underlying mechanisms of the intraislet insulin on suppression of glucagon secretion involve the modulation of K(ATP) channel activity and the activation of the GABA-GABA(A) receptor system. Nevertheless, regulation of glucagon secretion is multifactorial and yet to be fully understood.
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Affiliation(s)
- Pritpal Bansal
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
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48
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Abstract
Glucagon release by pancreatic alpha cells is stimulated by low glucose through unclear mechanisms. In this issue of Cell Metabolism, Cabrera et al. (2008) show that glutamate released from alpha cells acts on glutamate receptors in a positive autocrine fashion that drives glucagon secretion during small physiological fluctuations of blood glucose.
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Gyulkhandanyan AV, Lu H, Lee SC, Bhattacharjee A, Wijesekara N, Fox JEM, MacDonald PE, Chimienti F, Dai FF, Wheeler MB. Investigation of transport mechanisms and regulation of intracellular Zn2+ in pancreatic alpha-cells. J Biol Chem 2008; 283:10184-97. [PMID: 18250168 DOI: 10.1074/jbc.m707005200] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During insulin secretion, pancreatic alpha-cells are exposed to Zn(2+) released from insulin-containing secretory granules. Although maintenance of Zn(2+) homeostasis is critical for cell survival and glucagon secretion, very little is known about Zn(2+)-transporting pathways and the regulation of Zn(2+) in alpha-cells. To examine the effect of Zn(2+) on glucagon secretion and possible mechanisms controlling the intracellular Zn(2+) level ([Zn(2+)](i)), we employed a glucagon-producing cell line (alpha-TC6) and mouse islets where non-beta-cells were identified using islets expressing green fluorescent protein exclusively in beta-cells. In this study, we first confirmed that Zn(2+) treatment resulted in the inhibition of glucagon secretion in alpha-TC6 cells and mouse islets in vitro. The inhibition of secretion was not likely via activation of K(ATP) channels by Zn(2+). We then determined that Zn(2+) was transported into alpha-cells and was able to accumulate under both low and high glucose conditions, as well as upon depolarization of cells with KCl. The nonselective Ca(2+) channel blocker Gd(3+) partially inhibited Zn(2+) influx in alpha-TC cells, whereas the L-type voltage-gated Ca(2+) channel inhibitor nitrendipine failed to block Zn(2+) accumulation. To investigate Zn(2+) transport further, we profiled alpha-cells for Zn(2+) transporter transcripts from the two families that work in opposite directions, SLC39 (ZIP, Zrt/Irt-like protein) and SLC30 (ZnT, Zn(2+) transporter). We observed that Zip1, Zip10, and Zip14 were the most abundantly expressed Zips and ZnT4, ZnT5, and ZnT8 the dominant ZnTs. Because the redox state of cells is also a major regulator of [Zn(2+)](i), we examined the effects of oxidizing agents on Zn(2+) mobilization within alpha-cells. 2,2'-Dithiodipyridine (-SH group oxidant), menadione (superoxide generator), and SIN-1 (3-morpholinosydnonimine) (peroxynitrite generator) all increased [Zn(2+)](i) in alpha-cells. Together these results demonstrate that Zn(2+) inhibits glucagon secretion, and it is transported into alpha-cells in part through Ca(2+) channels. Zn(2+) transporters and the redox state also modulate [Zn(2+)](i).
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50
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MacDonald PE, De Marinis YZ, Ramracheya R, Salehi A, Ma X, Johnson PRV, Cox R, Eliasson L, Rorsman P. A K ATP channel-dependent pathway within alpha cells regulates glucagon release from both rodent and human islets of Langerhans. PLoS Biol 2007; 5:e143. [PMID: 17503968 PMCID: PMC1868042 DOI: 10.1371/journal.pbio.0050143] [Citation(s) in RCA: 179] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Accepted: 03/20/2007] [Indexed: 12/18/2022] Open
Abstract
Glucagon, secreted from pancreatic islet α cells, stimulates gluconeogenesis and liver glycogen breakdown. The mechanism regulating glucagon release is debated, and variously attributed to neuronal control, paracrine control by neighbouring β cells, or to an intrinsic glucose sensing by the α cells themselves. We examined hormone secretion and Ca2+ responses of α and β cells within intact rodent and human islets. Glucose-dependent suppression of glucagon release persisted when paracrine GABA or Zn2+ signalling was blocked, but was reversed by low concentrations (1–20 μM) of the ATP-sensitive K+ (KATP) channel opener diazoxide, which had no effect on insulin release or β cell responses. This effect was prevented by the KATP channel blocker tolbutamide (100 μM). Higher diazoxide concentrations (≥30 μM) decreased glucagon and insulin secretion, and α- and β-cell Ca2+ responses, in parallel. In the absence of glucose, tolbutamide at low concentrations (<1 μM) stimulated glucagon secretion, whereas high concentrations (>10 μM) were inhibitory. In the presence of a maximally inhibitory concentration of tolbutamide (0.5 mM), glucose had no additional suppressive effect. Downstream of the KATP channel, inhibition of voltage-gated Na+ (TTX) and N-type Ca2+ channels (ω-conotoxin), but not L-type Ca2+ channels (nifedipine), prevented glucagon secretion. Both the N-type Ca2+ channels and α-cell exocytosis were inactivated at depolarised membrane potentials. Rodent and human glucagon secretion is regulated by an α-cell KATP channel-dependent mechanism. We propose that elevated glucose reduces electrical activity and exocytosis via depolarisation-induced inactivation of ion channels involved in action potential firing and secretion. Glucagon is a critical regulator of glucose homeostasis. Its major action is to mobilize glucose from the liver. Glucagon secretion from α cells of the pancreatic islets of Langerhans is suppressed by elevated blood sugar, a response that is often perturbed in diabetes. Much work has focused on the regulation of α-cell glucagon secretion by neuronal factors and by paracrine factors from neighbouring cells, including the important islet hormone insulin. In contrast, we provide evidence in support of a direct effect of glucose on α cells within intact rodent and human islets. Notably, our work implicates an α-cell glucose-sensing pathway similar to that found in insulin-secreting β cells, involving closure of ATP-dependent K+ channels in the presence of glucose. Furthermore, we find that membrane depolarisation results in inhibition of Na+ and Ca2+ channel activity and α-cell exocytosis. Thus, we propose that elevated blood glucose reduces α-cell electrical activity and glucagon secretion by inactivating the ion channels involved in action potential firing and secretion. Elevated glucose levels reduce electrical activity and the release of glucagon via inactivation of ion channels in pancreatic islet cells.
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Affiliation(s)
- Patrick E MacDonald
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford, United Kingdom.
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