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Singh A, Abhilasha KV, Acharya KR, Liu H, Nirala NK, Parthibane V, Kunduri G, Abimannan T, Tantalla J, Zhu LJ, Acharya JK, Acharya UR. A nutrient responsive lipase mediates gut-brain communication to regulate insulin secretion in Drosophila. Nat Commun 2024; 15:4410. [PMID: 38782979 PMCID: PMC11116528 DOI: 10.1038/s41467-024-48851-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Accepted: 05/15/2024] [Indexed: 05/25/2024] Open
Abstract
Pancreatic β cells secrete insulin in response to glucose elevation to maintain glucose homeostasis. A complex network of inter-organ communication operates to modulate insulin secretion and regulate glucose levels after a meal. Lipids obtained from diet or generated intracellularly are known to amplify glucose-stimulated insulin secretion, however, the underlying mechanisms are not completely understood. Here, we show that a Drosophila secretory lipase, Vaha (CG8093), is synthesized in the midgut and moves to the brain where it concentrates in the insulin-producing cells in a process requiring Lipid Transfer Particle, a lipoprotein originating in the fat body. In response to dietary fat, Vaha stimulates insulin-like peptide release (ILP), and Vaha deficiency results in reduced circulatory ILP and diabetic features including hyperglycemia and hyperlipidemia. Our findings suggest Vaha functions as a diacylglycerol lipase physiologically, by being a molecular link between dietary fat and lipid amplified insulin secretion in a gut-brain axis.
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Affiliation(s)
- Alka Singh
- Department of Molecular, Cell and Cancer Biology, UMass Chan Medical School, Worcester, MA, 01605, USA
| | | | - Kathya R Acharya
- Department of Molecular, Cell and Cancer Biology, UMass Chan Medical School, Worcester, MA, 01605, USA
- Cancer and Developmental Biology Laboratory, National Cancer Institute, Frederick, MD, 21702, USA
- University of Cincinnati College of Medicine, 3230 Eden Ave, Cincinnati, OH, 45267, USA
| | - Haibo Liu
- Department of Molecular, Cell and Cancer Biology, UMass Chan Medical School, Worcester, MA, 01605, USA
| | - Niraj K Nirala
- Program in Molecular Medicine, UMass Chan Medical School, Worcester, MA, 01605, USA
| | - Velayoudame Parthibane
- Cancer and Developmental Biology Laboratory, National Cancer Institute, Frederick, MD, 21702, USA
| | - Govind Kunduri
- Cancer and Developmental Biology Laboratory, National Cancer Institute, Frederick, MD, 21702, USA
| | - Thiruvaimozhi Abimannan
- Cancer and Developmental Biology Laboratory, National Cancer Institute, Frederick, MD, 21702, USA
| | - Jacob Tantalla
- Cancer and Developmental Biology Laboratory, National Cancer Institute, Frederick, MD, 21702, USA
| | - Lihua Julie Zhu
- Department of Molecular, Cell and Cancer Biology, UMass Chan Medical School, Worcester, MA, 01605, USA
| | - Jairaj K Acharya
- Cancer and Developmental Biology Laboratory, National Cancer Institute, Frederick, MD, 21702, USA.
| | - Usha R Acharya
- Cancer and Developmental Biology Laboratory, National Cancer Institute, Frederick, MD, 21702, USA.
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Ježek P, Holendová B, Jabůrek M, Dlasková A, Plecitá-Hlavatá L. Contribution of Mitochondria to Insulin Secretion by Various Secretagogues. Antioxid Redox Signal 2022; 36:920-952. [PMID: 34180254 PMCID: PMC9125579 DOI: 10.1089/ars.2021.0113] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Significance: Mitochondria determine glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells by elevating ATP synthesis. As the metabolic and redox hub, mitochondria provide numerous links to the plasma membrane channels, insulin granule vesicles (IGVs), cell redox, NADH, NADPH, and Ca2+ homeostasis, all affecting insulin secretion. Recent Advances: Mitochondrial redox signaling was implicated in several modes of insulin secretion (branched-chain ketoacid [BCKA]-, fatty acid [FA]-stimulated). Mitochondrial Ca2+ influx was found to enhance GSIS, reflecting cytosolic Ca2+ oscillations induced by action potential spikes (intermittent opening of voltage-dependent Ca2+ and K+ channels) or the superimposed Ca2+ release from the endoplasmic reticulum (ER). The ATPase inhibitory factor 1 (IF1) was reported to tune the glucose sensitivity range for GSIS. Mitochondrial protein kinase A was implicated in preventing the IF1-mediated inhibition of the ATP synthase. Critical Issues: It is unknown how the redox signal spreads up to the plasma membrane and what its targets are, what the differences in metabolic, redox, NADH/NADPH, and Ca2+ signaling, and homeostasis are between the first and second GSIS phase, and whether mitochondria can replace ER in the amplification of IGV exocytosis. Future Directions: Metabolomics studies performed to distinguish between the mitochondrial matrix and cytosolic metabolites will elucidate further details. Identifying the targets of cell signaling into mitochondria and of mitochondrial retrograde metabolic and redox signals to the cell will uncover further molecular mechanisms for insulin secretion stimulated by glucose, BCKAs, and FAs, and the amplification of secretion by glucagon-like peptide (GLP-1) and metabotropic receptors. They will identify the distinction between the hub β-cells and their followers in intact and diabetic states. Antioxid. Redox Signal. 36, 920-952.
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Affiliation(s)
- Petr Ježek
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Blanka Holendová
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Martin Jabůrek
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Andrea Dlasková
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Lydie Plecitá-Hlavatá
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
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Oberhauser L, Jiménez-Sánchez C, Madsen JGS, Duhamel D, Mandrup S, Brun T, Maechler P. Glucolipotoxicity promotes the capacity of the glycerolipid/NEFA cycle supporting the secretory response of pancreatic beta cells. Diabetologia 2022; 65:705-720. [PMID: 35018486 DOI: 10.1007/s00125-021-05633-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2021] [Accepted: 10/12/2021] [Indexed: 11/03/2022]
Abstract
AIMS/HYPOTHESIS Chronic exposure of pancreatic beta cells to high glucose and fatty acids has been proposed to induce glucolipotoxicity. However, contradictory results suggest adaptations of the beta cells, which might be instrumental for partial preservation of the secretory response. In this context, we delineated the expression pattern of genes related to lipid pathways along with fat storage/mobilisation during glucose-stimulated insulin secretion. METHODS Insulin-secreting cells were cultured for 3 days at different glucose concentrations (5.5, 11.1, 25 mmol/l) without or with BSA-complexed 0.4 mmol/l palmitate and oleate. Then, transcriptomic analyses of lipid pathways were performed in human islets by RNA-Seq and in INS-1E cells and rat islets by quantitative RT-PCR. Storage of fat was assessed in INS-1E cells by electron microscopy and Bodipy staining, which was also used for measuring lipid mobilisation rate. The secretory response was monitored during acute 15 mmol/l glucose stimulation using online luminescence assay for INS-1E cells and by radioimmunoassay for rat islets. RESULTS In human islets, chronic exposure to palmitate and oleate modified expression of a panel of genes involved in lipid handling. Culture at 25 mmol/l glucose upregulated genes encoding for enzymes of the glycerolipid/NEFA cycle and downregulated receptors implicated in fatty acid signalling. Similar results were obtained in INS-1E cells, indicating enhanced capacity of the glycerolipid/NEFA cycle under glucotoxic conditions. Exposure to unsaturated C18:1 fatty acid favoured intracellular lipid accumulation in a glucose-dependent way, an effect also observed with saturated C16:0 fatty acid when combined with the panlipase inhibitor Orlistat. After the glucolipotoxic culture, intracellular fat mobilisation was required for acute glucose-stimulated secretion, particularly in oleate-treated cells under glucotoxic culture conditions. The lipid mobilisation rate was governed chiefly by the levels of stored fat as a direct consequence of the culture conditions rather than energetic demands, except in palmitate-loaded cells. CONCLUSIONS/INTERPRETATION Glucolipotoxic conditions promote the capacity of the glycerolipid/NEFA cycle thereby preserving part of the secretory response. The cycle of fat storage/mobilisation emerges as a mechanism helping the beta cell to cope with glucotoxic conditions.
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Affiliation(s)
- Lucie Oberhauser
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland
| | - Cecilia Jiménez-Sánchez
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland
| | - Jesper Grud Skat Madsen
- Functional Genomics and Metabolism Research Unit, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Dominique Duhamel
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland
| | - Susanne Mandrup
- Functional Genomics and Metabolism Research Unit, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Thierry Brun
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland
| | - Pierre Maechler
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland.
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland.
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Wagner R, Eckstein SS, Yamazaki H, Gerst F, Machann J, Jaghutriz BA, Schürmann A, Solimena M, Singer S, Königsrainer A, Birkenfeld AL, Häring HU, Fritsche A, Ullrich S, Heni M. Metabolic implications of pancreatic fat accumulation. Nat Rev Endocrinol 2022; 18:43-54. [PMID: 34671102 DOI: 10.1038/s41574-021-00573-3] [Citation(s) in RCA: 55] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 09/13/2021] [Indexed: 12/15/2022]
Abstract
Fat accumulation outside subcutaneous adipose tissue often has unfavourable effects on systemic metabolism. In addition to non-alcoholic fatty liver disease, which has received considerable attention, pancreatic fat has become an important area of research throughout the past 10 years. While a number of diagnostic approaches are available to quantify pancreatic fat, multi-echo Dixon MRI is currently the most developed method. Initial studies have shown associations between pancreatic fat and the metabolic syndrome, impaired glucose metabolism and type 2 diabetes mellitus. Pancreatic fat is linked to reduced insulin secretion, at least under specific circumstances such as prediabetes, low BMI and increased genetic risk of type 2 diabetes mellitus. This Review summarizes the possible causes and metabolic consequences of pancreatic fat accumulation. In addition, potential therapeutic approaches for addressing pancreatic fat accumulation are discussed.
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Affiliation(s)
- Robert Wagner
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Sabine S Eckstein
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
| | - Hajime Yamazaki
- Section of Clinical Epidemiology, Department of Community Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Felicia Gerst
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Jürgen Machann
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Section of Experimental Radiology, Department of Diagnostic and Interventional Radiology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Benjamin Assad Jaghutriz
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Annette Schürmann
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Experimental Diabetology, German Institute of Human Nutrition (DIfE), Potsdam-Rehbrücke, Germany
- Institute of Nutritional Science, University of Potsdam, Potsdam, Germany
| | - Michele Solimena
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Molecular Diabetology, University Hospital and Faculty of Medicine Carl Gustav Carus, TU Dresden, Dresden, Germany
- Paul Langerhans Institute Dresden (PLID), Helmholtz Center Munich, University Hospital and Faculty of Medicine Carl Gustav Carus, TU Dresden, Dresden, Germany
| | - Stephan Singer
- Institute of Pathology, University of Tübingen, Tübingen, Germany
| | - Alfred Königsrainer
- Department of General, Visceral, and Transplant Surgery, University Hospital Tübingen, Tübingen, Germany
| | - Andreas L Birkenfeld
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Hans-Ulrich Häring
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Andreas Fritsche
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Susanne Ullrich
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Martin Heni
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany.
- German Center for Diabetes Research (DZD), Tübingen, Germany.
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany.
- Institute for Clinical Chemistry and Pathobiochemistry, Department for Diagnostic Laboratory Medicine, University Hospital Tübingen, Tübingen, Germany.
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Oberhauser L, Maechler P. Lipid-Induced Adaptations of the Pancreatic Beta-Cell to Glucotoxic Conditions Sustain Insulin Secretion. Int J Mol Sci 2021; 23:324. [PMID: 35008750 PMCID: PMC8745448 DOI: 10.3390/ijms23010324] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 12/22/2021] [Accepted: 12/27/2021] [Indexed: 12/16/2022] Open
Abstract
Over the last decades, lipotoxicity and glucotoxicity emerged as established mechanisms participating in the pathophysiology of obesity-related type 2 diabetes in general, and in the loss of β-cell function in particular. However, these terms hold various potential biological processes, and it is not clear what precisely they refer to and to what extent they might be clinically relevant. In this review, we discuss the basis and the last advances of research regarding the role of free fatty acids, their metabolic intracellular pathways, and receptor-mediated signaling related to glucose-stimulated insulin secretion, as well as lipid-induced β-cell dysfunction. We also describe the role of chronically elevated glucose, namely, glucotoxicity, which promotes failure and dedifferentiation of the β cell. Glucolipotoxicity combines deleterious effects of exposures to both high glucose and free fatty acids, supposedly provoking synergistic defects on the β cell. Nevertheless, recent studies have highlighted the glycerolipid/free fatty acid cycle as a protective pathway mediating active storage and recruitment of lipids. Finally, we discuss the putative correspondence of the loss of functional β cells in type 2 diabetes with a natural, although accelerated, aging process.
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Affiliation(s)
| | - Pierre Maechler
- Department of Cell Physiology and Metabolism, Faculty Diabetes Center, University of Geneva Medical Center, 1206 Geneva, Switzerland;
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Ibáñez CF. Regulation of metabolic homeostasis by the TGF-β superfamily receptor ALK7. FEBS J 2021; 289:5776-5797. [PMID: 34173336 DOI: 10.1111/febs.16090] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Revised: 05/28/2021] [Accepted: 06/11/2021] [Indexed: 12/13/2022]
Abstract
ALK7 (Activin receptor-like kinase 7) is a member of the TGF-β receptor superfamily predominantly expressed by cells and tissues involved in endocrine functions, such as neurons of the hypothalamus and pituitary, pancreatic β-cells and adipocytes. Recent studies have begun to delineate the processes regulated by ALK7 in these tissues and how these become integrated with the homeostatic regulation of mammalian metabolism. The picture emerging indicates that ALK7's primary function in metabolic regulation is to limit catabolic activities and preserve energy. Aside of the hypothalamic arcuate nucleus, the function of ALK7 elsewhere in the brain, particularly in the cerebellum, where it is abundantly expressed, remains to be elucidated. Although our understanding of the basic molecular events underlying ALK7 signaling has benefited from the vast knowledge available on TGF-β receptor mechanisms, how these connect to the physiological functions regulated by ALK7 in different cell types is still incompletely understood. Findings of missense and nonsense variants in the Acvr1c gene, encoding ALK7, of some mouse strains and human subjects indicate a tolerance to ALK7 loss of function. Recent discoveries suggest that specific inhibitors of ALK7 may have therapeutic applications in obesity and metabolic syndrome without overt adverse effects.
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Affiliation(s)
- Carlos F Ibáñez
- Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.,Peking-Tsinghua Center for Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University School of Life Sciences and Chinese Institute for Brain Research, Beijing, China.,Department of Physiology and Life Sciences Institute, National University of Singapore, Singapore
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Calamita G, Delporte C. Involvement of aquaglyceroporins in energy metabolism in health and disease. Biochimie 2021; 188:20-34. [PMID: 33689852 DOI: 10.1016/j.biochi.2021.03.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 02/23/2021] [Accepted: 03/01/2021] [Indexed: 11/27/2022]
Abstract
Aquaglyceroporins are a group of the aquaporin (AQP) family of transmembrane water channels. While AQPs facilitate the passage of water, small solutes, and gases across biological membranes, aquaglyceroporins allow passage of water, glycerol, urea and some other solutes. Thanks to their glycerol permeability, aquaglyceroporins are involved in energy homeostasis. This review provides an overview of what is currently known concerning the functional implication and control of aquaglyceroporins in tissues involved in energy metabolism, i.e. liver, adipose tissue and endocrine pancreas. The expression, role and (dys)regulation of aquaglyceroporins in disorders affecting energy metabolism, and the potential relevance of aquaglyceroporins as drug targets to treat the alterations of the energy balance is also addressed.
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Affiliation(s)
- Giuseppe Calamita
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", Bari, Italy
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium.
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Ježek P, Holendová B, Jabůrek M, Tauber J, Dlasková A, Plecitá-Hlavatá L. The Pancreatic β-Cell: The Perfect Redox System. Antioxidants (Basel) 2021; 10:antiox10020197. [PMID: 33572903 PMCID: PMC7912581 DOI: 10.3390/antiox10020197] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 01/20/2021] [Accepted: 01/25/2021] [Indexed: 12/12/2022] Open
Abstract
Pancreatic β-cell insulin secretion, which responds to various secretagogues and hormonal regulations, is reviewed here, emphasizing the fundamental redox signaling by NADPH oxidase 4- (NOX4-) mediated H2O2 production for glucose-stimulated insulin secretion (GSIS). There is a logical summation that integrates both metabolic plus redox homeostasis because the ATP-sensitive K+ channel (KATP) can only be closed when both ATP and H2O2 are elevated. Otherwise ATP would block KATP, while H2O2 would activate any of the redox-sensitive nonspecific calcium channels (NSCCs), such as TRPM2. Notably, a 100%-closed KATP ensemble is insufficient to reach the -50 mV threshold plasma membrane depolarization required for the activation of voltage-dependent Ca2+ channels. Open synergic NSCCs or Cl- channels have to act simultaneously to reach this threshold. The resulting intermittent cytosolic Ca2+-increases lead to the pulsatile exocytosis of insulin granule vesicles (IGVs). The incretin (e.g., GLP-1) amplification of GSIS stems from receptor signaling leading to activating the phosphorylation of TRPM channels and effects on other channels to intensify integral Ca2+-influx (fortified by endoplasmic reticulum Ca2+). ATP plus H2O2 are also required for branched-chain ketoacids (BCKAs); and partly for fatty acids (FAs) to secrete insulin, while BCKA or FA β-oxidation provide redox signaling from mitochondria, which proceeds by H2O2 diffusion or hypothetical SH relay via peroxiredoxin "redox kiss" to target proteins.
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Calamita G, Perret J, Delporte C. Aquaglyceroporins: Drug Targets for Metabolic Diseases? Front Physiol 2018; 9:851. [PMID: 30042691 PMCID: PMC6048697 DOI: 10.3389/fphys.2018.00851] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Accepted: 06/15/2018] [Indexed: 12/29/2022] Open
Abstract
Aquaporins (AQPs) are a family of transmembrane channel proteins facilitating the transport of water, small solutes, and gasses across biological membranes. AQPs are expressed in all tissues and ensure multiple roles under normal and pathophysiological conditions. Aquaglyceroporins are a subfamily of AQPs permeable to glycerol in addition to water and participate thereby to energy metabolism. This review focalizes on the present knowledge of the expression, regulation and physiological roles of AQPs in adipose tissue, liver and endocrine pancreas, that are involved in energy metabolism. In addition, the review aims at summarizing the involvement of AQPs in metabolic disorders, such as obesity, diabetes and liver diseases. Finally, challenges and recent advances related to pharmacological modulation of AQPs expression and function to control and treat metabolic diseases are discussed.
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Affiliation(s)
- Giuseppe Calamita
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari Aldo Moro, Bari, Italy
| | - Jason Perret
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
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Fatty Acid-Stimulated Insulin Secretion vs. Lipotoxicity. Molecules 2018; 23:molecules23061483. [PMID: 29921789 PMCID: PMC6100479 DOI: 10.3390/molecules23061483] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Revised: 06/13/2018] [Accepted: 06/15/2018] [Indexed: 12/29/2022] Open
Abstract
Fatty acid (FA)-stimulated insulin secretion (FASIS) is reviewed here in contrast to type 2 diabetes etiology, resulting from FA overload, oxidative stress, intermediate hyperinsulinemia, and inflammation, all converging into insulin resistance. Focusing on pancreatic islet β-cells, we compare the physiological FA roles with the pathological ones. Considering FAs not as mere amplifiers of glucose-stimulated insulin secretion (GSIS), but as parallel insulin granule exocytosis inductors, partly independent of the KATP channel closure, we describe the FA initiating roles in the prediabetic state that is induced by retardations in the glycerol-3-phosphate (glucose)-promoted glycerol/FA cycle and by the impaired GPR40/FFA1 (free FA1) receptor pathway, specifically in its amplification by the redox-activated mitochondrial phospholipase, iPLA2γ. Also, excessive dietary FAs stimulate intestine enterocyte incretin secretion, further elevating GSIS, even at low glucose levels, thus contributing to diabetic hyperinsulinemia. With overnutrition and obesity, the FA overload causes impaired GSIS by metabolic dysbalance, paralleled by oxidative and metabolic stress, endoplasmic reticulum stress and numerous pro-apoptotic signaling, all leading to decreased β-cell survival. Lipotoxicity is exerted by saturated FAs, whereas ω-3 polyunsaturated FAs frequently exert antilipotoxic effects. FA-facilitated inflammation upon the recruitment of excess M1 macrophages into islets (over resolving M2 type), amplified by cytokine and chemokine secretion by β-cells, leads to an inevitable failure of pancreatic β-cells.
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11
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Abstract
The pancreatic β-cell secretes insulin in response to elevated plasma glucose. This review applies an external bioenergetic critique to the central processes of glucose-stimulated insulin secretion, including glycolytic and mitochondrial metabolism, the cytosolic adenine nucleotide pool, and its interaction with plasma membrane ion channels. The control mechanisms responsible for the unique responsiveness of the cell to glucose availability are discussed from bioenergetic and metabolic control standpoints. The concept of coupling factor facilitation of secretion is critiqued, and an attempt is made to unravel the bioenergetic basis of the oscillatory mechanisms controlling secretion. The need to consider the physiological constraints operating in the intact cell is emphasized throughout. The aim is to provide a coherent pathway through an extensive, complex, and sometimes bewildering literature, particularly for those unfamiliar with the field.
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Affiliation(s)
- David G Nicholls
- Buck Institute for Research on Aging, Novato, California; and Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, Malmo, Sweden
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12
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Inhibition of Monoacylglycerol Lipase Activity Decreases Glucose-Stimulated Insulin Secretion in INS-1 (832/13) Cells and Rat Islets. PLoS One 2016; 11:e0149008. [PMID: 26867016 PMCID: PMC4750965 DOI: 10.1371/journal.pone.0149008] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Accepted: 01/26/2016] [Indexed: 01/06/2023] Open
Abstract
Lipid signals derived from lipolysis and membrane phospholipids play an important role in glucose-stimulated insulin secretion (GSIS), though the exact secondary signals remain unclear. Previous reports have documented a stimulatory role of exogenously added mono-acyl-glycerol (MAG) on insulin secretion from cultured β-cells and islets. In this report we have determined effects of increasing intracellular MAG in the β-cell by inhibiting mono-acyl-glycerol lipase (MGL) activity, which catalyzes the final step in triacylglycerol breakdown, namely the hydrolysis of MAG to glycerol and free fatty acid (FA). To determine the role of MGL in GSIS, we used three different pharmacological agents (JZL184, MJN110 and URB602). All three inhibited GSIS and depolarization-induced insulin secretion in INS-1 (832/13). JZL184 significantly inhibited both GSIS and depolarization-induced insulin secretion in rat islets. JZL184 significantly decreased lipolysis and increased both mono- and diacyglycerol species in INS-1 cells. Analysis of the kinetics of GSIS showed that inhibition was greater during the sustained phase of secretion. A similar pattern was observed in the response of Ca2+ to glucose and depolarization but to a lesser degree suggesting that altered Ca2+ handling alone could not explain the reduction in insulin secretion. In addition, a significant reduction in long chain-CoA (LC-CoA) was observed in INS-1 cells at both basal and stimulatory glucose following inhibition of MGL. Our data implicate an important role for MGL in insulin secretion.
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Cantley J, Burchfield JG, Pearson GL, Schmitz-Peiffer C, Leitges M, Biden TJ. Deletion of PKCepsilon selectively enhances the amplifying pathways of glucose-stimulated insulin secretion via increased lipolysis in mouse beta-cells. Diabetes 2009; 58:1826-34. [PMID: 19401415 PMCID: PMC2712791 DOI: 10.2337/db09-0132] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
OBJECTIVE Insufficient insulin secretion is a hallmark of type 2 diabetes, and exposure of beta-cells to elevated lipid levels (lipotoxicity) contributes to secretory dysfunction. Functional ablation of protein kinase C epsilon (PKCepsilon) has been shown to improve glucose homeostasis in models of type 2 diabetes and, in particular, to enhance glucose-stimulated insulin secretion (GSIS) after lipid exposure. Therefore, we investigated the lipid-dependent mechanisms responsible for the enhanced GSIS after inactivation of PKCepsilon. RESEARCH DESIGN AND METHODS We cultured islets isolated from PKCepsilon knockout (PKCepsilonKO) mice in palmitate prior to measuring GSIS, Ca(2+) responses, palmitate esterification products, lipolysis, lipase activity, and gene expression. RESULTS The enhanced GSIS could not be explained by increased expression of another PKC isoform or by alterations in glucose-stimulated Ca(2+) influx. Instead, an upregulation of the amplifying pathways of GSIS in lipid-cultured PKCepsilonKO beta-cells was revealed under conditions in which functional ATP-sensitive K(+) channels were bypassed. Furthermore, we showed increased esterification of palmitate into triglyceride pools and an enhanced rate of lipolysis and triglyceride lipase activity in PKCepsilonKO islets. Acute treatment with the lipase inhibitor orlistat blocked the enhancement of GSIS in lipid-cultured PKCepsilonKO islets, suggesting that a lipolytic product mediates the enhancement of glucose-amplified insulin secretion after PKCepsilon deletion. CONCLUSIONS Our findings demonstrate a mechanistic link between lipolysis and the amplifying pathways of GSIS in murine beta-cells, and they suggest an interaction between PKCepsilon and lipolysis. These results further highlight the therapeutic potential of PKCepsilon inhibition to enhance GSIS from the beta-cell under conditions of lipid excess.
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Affiliation(s)
- James Cantley
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia
| | - James G. Burchfield
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Darlinghurst, New South Wales, Australia
| | - Gemma L. Pearson
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia
| | - Carsten Schmitz-Peiffer
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Darlinghurst, New South Wales, Australia
| | - Michael Leitges
- Biotechnology Centre of Oslo, University of Oslo, Oslo, Norway
| | - Trevor J. Biden
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Darlinghurst, New South Wales, Australia
- Corresponding author: Trevor Biden,
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Lamontagne J, Pepin E, Peyot ML, Joly E, Ruderman NB, Poitout V, Madiraju SRM, Nolan CJ, Prentki M. Pioglitazone acutely reduces insulin secretion and causes metabolic deceleration of the pancreatic beta-cell at submaximal glucose concentrations. Endocrinology 2009; 150:3465-74. [PMID: 19406947 PMCID: PMC2717855 DOI: 10.1210/en.2008-1557] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Thiazolidinediones (TZDs) have beneficial effects on glucose homeostasis via enhancement of insulin sensitivity and preservation of beta-cell function. How TZDs preserve beta-cells is uncertain, but it might involve direct effects via both peroxisome proliferator-activated receptor-gamma-dependent and -independent pathways. To gain insight into the independent pathway(s), we assessed the effects of short-term (<or=90 min) exposure to pioglitazone (Pio) (10 to 50 microM) on glucose-induced insulin secretion (GIIS), AMP-activated protein kinase (AMPK) activation, and beta-cell metabolism in INS 832/13 beta-cells and rat islets. Pio caused a right shift in the dose-dependence of GIIS, such that insulin release was reduced at intermediate glucose but unaffected at either basal or maximal glucose concentrations. This was associated in INS 832/13 cells with alterations in energy metabolism, characterized by reduced glucose oxidation, mitochondrial membrane polarization, and ATP levels. Pio caused AMPK phosphorylation and its action on GIIS was reversed by the AMPK inhibitor compound C. Pio also reduced palmitate esterification into complex lipids and inhibited lipolysis. As for insulin secretion, the alterations in beta-cell metabolic processes were mostly alleviated at elevated glucose. Similarly, the antidiabetic agents and AMPK activators metformin and berberine caused a right shift in the dose dependence of GIIS. In conclusion, Pio acutely reduces glucose oxidation, energy metabolism, and glycerolipid/fatty acid cycling of the beta-cell at intermediate glucose concentrations. We suggest that AMPK activation and the metabolic deceleration of the beta-cell caused by Pio contribute to its known effects to reduce hyperinsulinemia and preserve beta-cell function and act as an antidiabetic agent.
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Affiliation(s)
- Julien Lamontagne
- Department of Nutrition and Biochemistry, Molecular Nutrition Unit and Montreal Diabetes Research Center, Université de Montréal, Montréal, Québec, Canada
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15
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Peyot ML, Guay C, Latour MG, Lamontagne J, Lussier R, Pineda M, Ruderman NB, Haemmerle G, Zechner R, Joly É, Madiraju SRM, Poitout V, Prentki M. Adipose triglyceride lipase is implicated in fuel- and non-fuel-stimulated insulin secretion. J Biol Chem 2009; 284:16848-16859. [PMID: 19389712 DOI: 10.1074/jbc.m109.006650] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Reduced lipolysis in hormone-sensitive lipase-deficient mice is associated with impaired glucose-stimulated insulin secretion (GSIS), suggesting that endogenous beta-cell lipid stores provide signaling molecules for insulin release. Measurements of lipolysis and triglyceride (TG) lipase activity in islets from HSL(-/-) mice indicated the presence of other TG lipase(s) in the beta-cell. Using real time-quantitative PCR, adipose triglyceride lipase (ATGL) was found to be the most abundant TG lipase in rat islets and INS832/13 cells. To assess its role in insulin secretion, ATGL expression was decreased in INS832/13 cells (ATGL-knockdown (KD)) by small hairpin RNA. ATGL-KD increased the esterification of free fatty acid (FFA) into TG. ATGL-KD cells showed decreased glucose- or Gln + Leu-induced insulin release, as well as reduced response to KCl or palmitate at high, but not low, glucose. The K(ATP)-independent/amplification pathway of GSIS was considerably reduced in ATGL-KD cells. ATGL(-/-) mice were hypoinsulinemic and hypoglycemic and showed decreased plasma TG and FFAs. A hyperglycemic clamp revealed increased insulin sensitivity and decreased GSIS and arginine-induced insulin secretion in ATGL(-/-) mice. Accordingly, isolated islets from ATGL(-/-) mice showed reduced insulin secretion in response to glucose, glucose + palmitate, and KCl. Islet TG content and FFA esterification into TG were increased by 2-fold in ATGL(-/-) islets, but glucose usage and oxidation were unaltered. The results demonstrate the importance of ATGL and intracellular lipid signaling for fuel- and non-fuel-induced insulin secretion.
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Affiliation(s)
- Marie-Line Peyot
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada
| | - Claudiane Guay
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada
| | - Martin G Latour
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada
| | - Julien Lamontagne
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada
| | - Roxane Lussier
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada
| | - Marco Pineda
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada
| | - Neil B Ruderman
- Departments of Medicine and Physiology and Biophysics, Boston University School of Medicine and Diabetes Unit, Section of Endocrinology, Boston University School of Medicine and Boston Medical Center, Boston, Massachusetts 02118
| | - Guenter Haemmerle
- Institute of Molecular Biosciences, Karl-Franzens-University, Graz 8010, Austria
| | - Rudolf Zechner
- Institute of Molecular Biosciences, Karl-Franzens-University, Graz 8010, Austria
| | - Érik Joly
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada
| | - S R Murthy Madiraju
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada
| | - Vincent Poitout
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada; Departments of Nutrition, Montreal, Quebec H1W 4A4, Canada; Medicine, University of Montreal, Montreal, Quebec H1W 4A4, Canada
| | - Marc Prentki
- From the Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec H1W 4A4, Canada; Departments of Nutrition, Montreal, Quebec H1W 4A4, Canada.
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Abstract
Lipids have been implicated in beta-cell stimulus-secretion coupling. In such a role, lipases in beta-cells would be required to generate lipid coupling factors. We have shown previously that glucose stimulates lipolysis in rodent islets. In addition, lipolysis and diacylglycerol lipase activity in islets are abolished by orlistat, an irreversible lipase inhibitor with a broad specificity for substrates. Moreover, orlistat dose-dependently inhibits glucose- and forskolin-stimulated insulin secretion, while leaving glucose oxidation and the rise in the ATP/ADP ratio intact. In an effort to identify beta-cell lipase(s), we found that HSL (hormone-sensitive lipase), the rate-limiting enzyme for acylglycerol hydrolysis in adipocytes, is expressed in rodent beta-cells. To resolve the role of this lipase, we have created global and beta-cell-specific knockout mice. Although our line of global HSL-knockout mice is moderately glucose-intolerant owing to reduced peripheral insulin sensitivity and exhibits normal islet metabolism and insulin secretion, other HSL-knockout lines have displayed impaired insulin secretion under certain conditions. In contrast, beta-cell-specific HSL-knockout mice, which are less prone to genetic redundancy, are hyperglycaemic, presumably caused by a perturbation of first-phase insulin secretion. Thus studies by us and others demonstrate that lipases, such as HSL, play a regulatory role in beta-cell stimulus-secretion coupling.
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Frangioudakis G, Gyte AC, Loxham SJG, Poucher SM. The intravenous glucose tolerance test in cannulated Wistar rats: a robust method for the in vivo assessment of glucose-stimulated insulin secretion. J Pharmacol Toxicol Methods 2008; 57:106-13. [PMID: 18280184 DOI: 10.1016/j.vascn.2007.12.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2007] [Accepted: 12/21/2007] [Indexed: 11/19/2022]
Abstract
INTRODUCTION Glucose-stimulated insulin secretion (GSIS) is critical in mammalian fuel homeostasis and is diminished early in the evolution of beta-cell dysfunction, ultimately contributing to the development of Type 2 diabetes. We sought to standardise and validate the intravenous glucose tolerance test (IVGTT), a commonly used technique to assess GSIS, in anaesthetised and conscious cannulated male Han Wistar rats. METHODS Male Han Wistar rats were cannulated via the right jugular vein and left carotid artery. Anaesthetised and chronically cannulated conscious models underwent IVGTT using increasing doses of glucose (0.2, 0.5 and 1.0 g glucose/kg LBM) or following pre-treatment with Exendin-4 (EX-4) before receiving a 0.5 g glucose/kg LBM bolus dose. Blood glucose, plasma insulin and plasma C-peptide were measured at time-points throughout the experiments. RESULTS Dose-dependent increases in blood glucose, insulin and C-peptide (where measured) were observed following administration of increasing doses of an intravenous glucose bolus in both the anaesthetised and conscious cannulated rats. The 0.5 g glucose/kg LBM bolus resulted in an intermediate response and was used in the second part of the study. EX-4 pre-treatment in combination with glucose resulted in GSIS potentiation, as assessed by plasma insulin measurement alone (anaesthetised model) or insulin and C-peptide measurements (conscious model). DISCUSSION The IVGTT was standardised in anaesthetised and conscious cannulated male Han Wistar rats by performing a glucose dose response study and validated by examining GSIS potentiation using EX-4. Based on these results, the 0.5 g glucose/kg LBM bolus dose is recommended as the dose to use to assess GSIS in any standardised screening phase of new compounds with the potential to enhance glucose-sensitive pancreatic function. The experimental conditions described in these studies could be transferred to disease models for more detailed assessment of novel compound efficacy.
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Affiliation(s)
- Georgia Frangioudakis
- Cardiovascular and Gastrointestinal Discovery Department, AstraZeneca Pharmaceuticals, Alderley Park, Macclesfield, Cheshire, United Kingdom
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18
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Nunes E, Peixoto F, Louro T, Sena CM, Santos MS, Matafome P, Moreira PI, Seiça R. Soybean oil treatment impairs glucose-stimulated insulin secretion and changes fatty acid composition of normal and diabetic islets. Acta Diabetol 2007; 44:121-30. [PMID: 17721750 DOI: 10.1007/s00592-007-0252-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/12/2006] [Accepted: 03/19/2007] [Indexed: 10/22/2022]
Abstract
We investigated the effect of sub-chronic soybean oil (SO) treatment on the insulin secretion and fatty acid composition of islets of Langerhans obtained from Goto-Kakizaki (GK), a model of type 2 diabetes, and normal Wistar rats. We observed that soybean-treated Wistar rats present insulin resistance and defective islet insulin secretion when compared with untreated Wistar rats. The decrease in insulin secretion occurred at all concentrations of glucose and arginine tested. Furthermore we observed that soybean-treated normal islets present a significant decrease in two saturated fatty acids, myristic and heneicosanoic acids, and one monounsaturated eicosenoic acid, and the appearance of the monounsaturated erucic acid. Concerning diabetic animals, we observed that soybean-treated diabetic rats, when compared with untreated GK rats, present an increase in plasma non-fasting free fatty acids, an exacerbation of islet insulin secretion impairment in all conditions tested and a significant decrease in the monounsaturated palmitoleic acid. Altogether our results show that SO treatment results in a decrease of insulin secretion and alterations on fatty acid composition in normal and diabetic islets. Furthermore, the impairment of insulin secretion, islet erucic acid and fasting plasma insulin levels are similar in treated normal and untreated diabetic rats, suggesting that SO could have a deleterious effect on beta-cell function and insulin sensitivity.
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Affiliation(s)
- E Nunes
- Faculty of Medicine, Institute of Physiology, Rua Larga, PT-3004-504, Coimbra, Portugal
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19
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Hurley RL, Barré LK, Wood SD, Anderson KA, Kemp BE, Means AR, Witters LA. Regulation of AMP-activated protein kinase by multisite phosphorylation in response to agents that elevate cellular cAMP. J Biol Chem 2006; 281:36662-72. [PMID: 17023420 DOI: 10.1074/jbc.m606676200] [Citation(s) in RCA: 217] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The AMP-activated protein kinase (AMPK) and cAMP signaling systems are both key regulators of cellular metabolism. In this study, we show that AMPK activity is attenuated in response to cAMP-elevating agents through modulation of at least two of its alpha subunit phosphorylation sites, viz. alpha-Thr(172) and alpha1-Ser(485)/alpha2-Ser(491), in the clonal beta-cell line INS-1 as well as in mouse embryonic fibroblasts and COS cells. Forskolin, isobutylmethylxanthine, and the glucose-dependent insulinotropic peptide inhibited AMPK activity and reduced phosphorylation of the activation loop alpha-Thr(172) via inhibition of calcium/calmodulin-dependent protein kinase kinase-alpha and -beta, but not LKB1. These agents also enhanced phosphorylation of alpha-Ser(485/491) by the cAMP-dependent protein kinase. AMPK alpha-Ser(485/491) phosphorylation was necessary but not sufficient for inhibition of AMPK activity in response to forskolin/isobutylmethylxanthine. We show that AMPK alpha-Ser(485/491) can be a site for autophosphorylation, which may play a role in limiting AMPK activation in response to energy depletion or other regulators. Thus, our findings not only demonstrate cross-talk between the cAMP/cAMP-dependent protein kinase and AMPK signaling modules, but also describe a novel mechanism by which multisite phosphorylation of AMPK contributes to regulation of its enzyme activity.
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Affiliation(s)
- Rebecca L Hurley
- Department of Medicine and Biochemistry, Dartmouth Medical School, Remsen 322, N. College St., Hanover, NH 03755, USA
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Sakaki N, Iida Y, Okazaki Y, Kawamura S, Takemoto T. Magnifying endoscopic observation of the gastric mucosa, particularly in patients with atrophic gastritis. Endoscopy 1978; 43:10-3. [PMID: 738222 DOI: 10.1016/j.biocel.2010.10.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2010] [Revised: 10/21/2010] [Accepted: 10/30/2010] [Indexed: 01/25/2023]
Abstract
The gastric mucosal surface was observed using the magnifying fibergastroscope (FGS-ML), and the fine gastric mucosal patterns, which were even smaller than one unit of gastric area, were examined at a magnification of about 30. For simplicification, we classified these patterns by magnifying endoscopy in the following ways; FP, FIP, FSP, SP and MP, modifying Yoshii's classification under the dissecting microscope. The FIP, which was found to have round and long elliptical gastric pits, is a new addition to our endoscopic classification. The relationship between the FIP and the intermediate zone was evaluated by superficial and histological studies of surgical and biopsy specimens. The width of the band of FIP seems to be related to the severity of atrophic gastritis. Also, the transformation of FP to FIP was assessed by comparing specimens taken from the resected and residual parts of the stomach, respectively. Moreover, it appears that severe gastritis occurs in the gastric mucosa which shows a FIP. Therefore, we consider that the FIP indicates the position of the atrophic border.
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