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Deepa Maheshvare M, Raha S, König M, Pal D. A pathway model of glucose-stimulated insulin secretion in the pancreatic β-cell. Front Endocrinol (Lausanne) 2023; 14:1185656. [PMID: 37600713 PMCID: PMC10433753 DOI: 10.3389/fendo.2023.1185656] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 06/08/2023] [Indexed: 08/22/2023] Open
Abstract
The pancreas plays a critical role in maintaining glucose homeostasis through the secretion of hormones from the islets of Langerhans. Glucose-stimulated insulin secretion (GSIS) by the pancreatic β-cell is the main mechanism for reducing elevated plasma glucose. Here we present a systematic modeling workflow for the development of kinetic pathway models using the Systems Biology Markup Language (SBML). Steps include retrieval of information from databases, curation of experimental and clinical data for model calibration and validation, integration of heterogeneous data including absolute and relative measurements, unit normalization, data normalization, and model annotation. An important factor was the reproducibility and exchangeability of the model, which allowed the use of various existing tools. The workflow was applied to construct a novel data-driven kinetic model of GSIS in the pancreatic β-cell based on experimental and clinical data from 39 studies spanning 50 years of pancreatic, islet, and β-cell research in humans, rats, mice, and cell lines. The model consists of detailed glycolysis and phenomenological equations for insulin secretion coupled to cellular energy state, ATP dynamics and (ATP/ADP ratio). Key findings of our work are that in GSIS there is a glucose-dependent increase in almost all intermediates of glycolysis. This increase in glycolytic metabolites is accompanied by an increase in energy metabolites, especially ATP and NADH. One of the few decreasing metabolites is ADP, which, in combination with the increase in ATP, results in a large increase in ATP/ADP ratios in the β-cell with increasing glucose. Insulin secretion is dependent on ATP/ADP, resulting in glucose-stimulated insulin secretion. The observed glucose-dependent increase in glycolytic intermediates and the resulting change in ATP/ADP ratios and insulin secretion is a robust phenomenon observed across data sets, experimental systems and species. Model predictions of the glucose-dependent response of glycolytic intermediates and biphasic insulin secretion are in good agreement with experimental measurements. Our model predicts that factors affecting ATP consumption, ATP formation, hexokinase, phosphofructokinase, and ATP/ADP-dependent insulin secretion have a major effect on GSIS. In conclusion, we have developed and applied a systematic modeling workflow for pathway models that allowed us to gain insight into key mechanisms in GSIS in the pancreatic β-cell.
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Affiliation(s)
- M. Deepa Maheshvare
- Department of Computational and Data Sciences, Indian Institute of Science, Bangalore, India
| | - Soumyendu Raha
- Department of Computational and Data Sciences, Indian Institute of Science, Bangalore, India
| | - Matthias König
- Institute for Biology, Institute for Theoretical Biology, Humboldt-University Berlin, Berlin, Germany
| | - Debnath Pal
- Department of Computational and Data Sciences, Indian Institute of Science, Bangalore, India
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2
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Deepa Maheshvare M, Raha S, König M, Pal D. A Consensus Model of Glucose-Stimulated Insulin Secretion in the Pancreatic β -Cell. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.10.532028. [PMID: 36945414 PMCID: PMC10028967 DOI: 10.1101/2023.03.10.532028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/13/2023]
Abstract
The pancreas plays a critical role in maintaining glucose homeostasis through the secretion of hormones from the islets of Langerhans. Glucose-stimulated insulin secretion (GSIS) by the pancreatic β -cell is the main mechanism for reducing elevated plasma glucose. Here we present a systematic modeling workflow for the development of kinetic pathway models using the Systems Biology Markup Language (SBML). Steps include retrieval of information from databases, curation of experimental and clinical data for model calibration and validation, integration of heterogeneous data including absolute and relative measurements, unit normalization, data normalization, and model annotation. An important factor was the reproducibility and exchangeability of the model, which allowed the use of various existing tools. The workflow was applied to construct the first consensus model of GSIS in the pancreatic β -cell based on experimental and clinical data from 39 studies spanning 50 years of pancreatic, islet, and β -cell research in humans, rats, mice, and cell lines. The model consists of detailed glycolysis and equations for insulin secretion coupled to cellular energy state (ATP/ADP ratio). Key findings of our work are that in GSIS there is a glucose-dependent increase in almost all intermediates of glycolysis. This increase in glycolytic metabolites is accompanied by an increase in energy metabolites, especially ATP and NADH. One of the few decreasing metabolites is ADP, which, in combination with the increase in ATP, results in a large increase in ATP/ADP ratios in the β -cell with increasing glucose. Insulin secretion is dependent on ATP/ADP, resulting in glucose-stimulated insulin secretion. The observed glucose-dependent increase in glycolytic intermediates and the resulting change in ATP/ADP ratios and insulin secretion is a robust phenomenon observed across data sets, experimental systems and species. Model predictions of the glucose-dependent response of glycolytic intermediates and insulin secretion are in good agreement with experimental measurements. Our model predicts that factors affecting ATP consumption, ATP formation, hexokinase, phosphofructokinase, and ATP/ADP-dependent insulin secretion have a major effect on GSIS. In conclusion, we have developed and applied a systematic modeling workflow for pathway models that allowed us to gain insight into key mechanisms in GSIS in the pancreatic β -cell.
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3
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Zara V, Assalve G, Ferramosca A. Multiple roles played by the mitochondrial citrate carrier in cellular metabolism and physiology. Cell Mol Life Sci 2022; 79:428. [PMID: 35842872 PMCID: PMC9288958 DOI: 10.1007/s00018-022-04466-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Revised: 06/17/2022] [Accepted: 07/03/2022] [Indexed: 11/18/2022]
Abstract
The citrate carrier (CIC) is an integral protein of the inner mitochondrial membrane which catalyzes the efflux of mitochondrial citrate (or other tricarboxylates) in exchange with a cytosolic anion represented by a tricarboxylate or a dicarboxylate or phosphoenolpyruvate. In this way, the CIC provides the cytosol with citrate which is involved in many metabolic reactions. Several studies have been carried out over the years on the structure, function and regulation of this metabolite carrier protein both in mammals and in many other organisms. A lot of data on the characteristics of this protein have therefore accumulated over time thereby leading to a complex framework of metabolic and physiological implications connected to the CIC function. In this review, we critically analyze these data starting from the multiple roles played by the mitochondrial CIC in many cellular processes and then examining the regulation of its activity in different nutritional and hormonal states. Finally, the metabolic significance of the citrate flux, mediated by the CIC, across distinct subcellular compartments is also discussed.
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Affiliation(s)
- Vincenzo Zara
- Department of Biological and Environmental Sciences and Technologies, University of Salento, 73100, Lecce, Italy
| | - Graziana Assalve
- Department of Biological and Environmental Sciences and Technologies, University of Salento, 73100, Lecce, Italy
| | - Alessandra Ferramosca
- Department of Biological and Environmental Sciences and Technologies, University of Salento, 73100, Lecce, Italy.
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Diane A, Al-Shukri NA, Bin Abdul Mu-u-min R, Al-Siddiqi HH. β-cell mitochondria in diabetes mellitus: a missing puzzle piece in the generation of hPSC-derived pancreatic β-cells? J Transl Med 2022; 20:163. [PMID: 35397560 PMCID: PMC8994301 DOI: 10.1186/s12967-022-03327-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 03/01/2022] [Indexed: 11/28/2022] Open
Abstract
Diabetes mellitus (DM), currently affecting 463 million people worldwide is a chronic disease characterized by impaired glucose metabolism resulting from the loss or dysfunction of pancreatic β-cells with the former preponderating in type 1 diabetes (T1DM) and the latter in type 2 diabetes (T2DM). Because impaired insulin secretion due to dysfunction or loss of pancreatic β-cells underlies different types of diabetes, research has focused its effort towards the generation of pancreatic β-cells from human pluripotent stem cell (hPSC) as a potential source of cells to compensate for insulin deficiency. However, many protocols developed to differentiate hPSCs into insulin-expressing β-cells in vitro have generated hPSC-derived β-cells with either immature phenotype such as impaired glucose-stimulated insulin secretion (GSIS) or a weaker response to GSIS than cadaveric islets. In pancreatic β-cells, mitochondria play a central role in coupling glucose metabolism to insulin exocytosis, thereby ensuring refined control of GSIS. Defects in β-cell mitochondrial metabolism and function impair this metabolic coupling. In the present review, we highlight the role of mitochondria in metabolism secretion coupling in the β-cells and summarize the evidence accumulated for the implication of mitochondria in β-cell dysfunction in DM and consequently, how targeting mitochondria function might be a new and interesting strategy to further perfect the differentiation protocol for generation of mature and functional hPSC-derived β-cells with GSIS profile similar to human cadaveric islets for drug screening or potentially for cell therapy.
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5
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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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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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7
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Corkey BE, Deeney JT, Merrins MJ. What Regulates Basal Insulin Secretion and Causes Hyperinsulinemia? Diabetes 2021; 70:2174-2182. [PMID: 34593535 PMCID: PMC8576498 DOI: 10.2337/dbi21-0009] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 07/28/2021] [Indexed: 12/12/2022]
Abstract
We hypothesize that basal hyperinsulinemia is synergistically mediated by an interplay between increased oxidative stress and excess lipid in the form of reactive oxygen species (ROS) and long-chain acyl-CoA esters (LC-CoA). In addition, ROS production may increase in response to inflammatory cytokines and certain exogenous environmental toxins that mislead β-cells into perceiving nutrient excess when none exists. Thus, basal hyperinsulinemia is envisioned as an adaptation to sustained real or perceived nutrient excess that only manifests as a disease when the excess demand can no longer be met by an overworked β-cell. In this article we will present a testable hypothetical mechanism to explain the role of lipids and ROS in basal hyperinsulinemia and how they differ from glucose-stimulated insulin secretion (GSIS). The model centers on redox regulation, via ROS, and S-acylation-mediated trafficking via LC-CoA. These pathways are well established in neural systems but not β-cells. During GSIS, these signals rise and fall in an oscillatory pattern, together with the other well-established signals derived from glucose metabolism; however, their precise roles have not been defined. We propose that failure to either increase or decrease ROS or LC-CoA appropriately will disturb β-cell function.
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Affiliation(s)
- Barbara E Corkey
- Department of Medicine, Boston University School of Medicine, Boston, MA
| | - Jude T Deeney
- Department of Medicine, Boston University School of Medicine, Boston, MA
| | - Matthew J Merrins
- Department of Biomolecular Chemistry and Section of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI
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8
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Benito-Vicente A, Jebari-Benslaiman S, Galicia-Garcia U, Larrea-Sebal A, Uribe KB, Martin C. Molecular mechanisms of lipotoxicity-induced pancreatic β-cell dysfunction. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2021; 359:357-402. [PMID: 33832653 DOI: 10.1016/bs.ircmb.2021.02.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Type 2 diabetes (T2D), a heterogeneous disorder derived from metabolic dysfunctions, leads to a glucose overflow in the circulation due to both defective insulin secretion and peripheral insulin resistance. One of the critical risk factor for T2D is obesity, which represents a global epidemic that has nearly tripled since 1975. Obesity is characterized by chronically elevated free fatty acid (FFA) levels, which cause deleterious effects on glucose homeostasis referred to as lipotoxicity. Here, we review the physiological FFA roles onto glucose-stimulated insulin secretion (GSIS) and the pathological ones affecting many steps of the mechanisms and modulation of GSIS. We also describe in vitro and in vivo experimental evidences addressing lipotoxicity in β-cells and the role of saturation and chain length of FFA on the potency of GSIS stimulation. The molecular mechanisms underpinning lipotoxic-β-cell dysfunction are also reviewed. Among them, endoplasmic reticulum stress, oxidative stress and mitochondrial dysfunction, inflammation, impaired autophagy and β-cell dedifferentiation. Finally therapeutic strategies for the β-cells dysfunctions such as the use of metformin, glucagon-like peptide 1, thiazolidinediones, anti-inflammatory drugs, chemical chaperones and weight are discussed.
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Affiliation(s)
- Asier Benito-Vicente
- Department of Molecular Biophysics, Biofisika Institute (University of Basque Country and Consejo Superior de Investigaciones Científicas (UPV/EHU, CSIC)), Leioa, Spain; Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), Leioa, Spain
| | - Shifa Jebari-Benslaiman
- Department of Molecular Biophysics, Biofisika Institute (University of Basque Country and Consejo Superior de Investigaciones Científicas (UPV/EHU, CSIC)), Leioa, Spain; Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), Leioa, Spain
| | - Unai Galicia-Garcia
- Department of Molecular Biophysics, Biofisika Institute (University of Basque Country and Consejo Superior de Investigaciones Científicas (UPV/EHU, CSIC)), Leioa, Spain; Department of Molecular Biophysics, Fundación Biofísica Bizkaia, Leioa, Spain
| | - Asier Larrea-Sebal
- Department of Molecular Biophysics, Biofisika Institute (University of Basque Country and Consejo Superior de Investigaciones Científicas (UPV/EHU, CSIC)), Leioa, Spain; Department of Molecular Biophysics, Fundación Biofísica Bizkaia, Leioa, Spain
| | - Kepa B Uribe
- Center for Cooperative Research in Biomaterials (CIC biomaGUNE), Basque Research and Technology Alliance (BRTA), Donostia San Sebastián, Spain
| | - Cesar Martin
- Department of Molecular Biophysics, Biofisika Institute (University of Basque Country and Consejo Superior de Investigaciones Científicas (UPV/EHU, CSIC)), Leioa, Spain; Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), Leioa, Spain.
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9
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Campbell JE, Newgard CB. Mechanisms controlling pancreatic islet cell function in insulin secretion. Nat Rev Mol Cell Biol 2021; 22:142-158. [PMID: 33398164 DOI: 10.1038/s41580-020-00317-7] [Citation(s) in RCA: 255] [Impact Index Per Article: 85.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/19/2020] [Indexed: 02/07/2023]
Abstract
Metabolic homeostasis in mammals is tightly regulated by the complementary actions of insulin and glucagon. The secretion of these hormones from pancreatic β-cells and α-cells, respectively, is controlled by metabolic, endocrine, and paracrine regulatory mechanisms and is essential for the control of blood levels of glucose. The deregulation of these mechanisms leads to various pathologies, most notably type 2 diabetes, which is driven by the combined lesions of impaired insulin action and a loss of the normal insulin secretion response to glucose. Glucose stimulates insulin secretion from β-cells in a bi-modal fashion, and new insights about the underlying mechanisms, particularly relating to the second or amplifying phase of this secretory response, have been recently gained. Other recent work highlights the importance of α-cell-produced proglucagon-derived peptides, incretin hormones from the gastrointestinal tract and other dietary components, including certain amino acids and fatty acids, in priming and potentiation of the β-cell glucose response. These advances provide a new perspective for the understanding of the β-cell failure that triggers type 2 diabetes.
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Affiliation(s)
- Jonathan E Campbell
- Sarah W. Stedman Nutrition and Metabolism Center and Duke Molecular Physiology Institute, Duke University Medical Center, Durham, NC, USA.,Department of Medicine, Endocrinology and Metabolism Division, Duke University Medical Center, Durham, NC, USA.,Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC, USA
| | - Christopher B Newgard
- Sarah W. Stedman Nutrition and Metabolism Center and Duke Molecular Physiology Institute, Duke University Medical Center, Durham, NC, USA. .,Department of Medicine, Endocrinology and Metabolism Division, Duke University Medical Center, Durham, NC, USA. .,Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC, USA.
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10
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Vanderkruk B, Hoffman BG. Metabolism as a central regulator of β-cell chromatin state. FEBS J 2020; 288:3683-3693. [PMID: 32926557 DOI: 10.1111/febs.15562] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 08/06/2020] [Accepted: 09/07/2020] [Indexed: 02/06/2023]
Abstract
Pancreatic β-cells are critical mediators of glucose homeostasis in the body, and proper cellular nutrient metabolism is critical to β-cell function. Several interacting signaling networks that uniquely control β-cell metabolism produce essential substrates and co-factors for catalytic reactions, including reactions that modify chromatin. Chromatin modifications, in turn, regulate gene expression. The reactions that modify chromatin are therefore well-positioned to adjust gene expression programs according to nutrient availability. It follows that dysregulation of nutrient metabolism in β-cells may impact chromatin state and gene expression through altering the availability of these substrates and co-factors. Metabolic disorders such as type 2 diabetes (T2D) can significantly alter metabolite levels in cells. This suggests that a driver of β-cell dysfunction during T2D may be the altered availability of substrates or co-factors necessary to maintain β-cell chromatin state. Induced changes in the β-cell chromatin modifications may then lead to dysregulation of gene expression, in turn contributing to the downward cascade of events that leads to the loss of functional β-cell mass, and loss of glucose homeostasis, that occurs in T2D.
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Affiliation(s)
- Ben Vanderkruk
- Diabetes Research Group, British Columbia Children's Hospital Research Institute, Vancouver, BC, Canada.,Department of Surgery, University of British Columbia, Vancouver, BC, Canada.,Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Brad G Hoffman
- Diabetes Research Group, British Columbia Children's Hospital Research Institute, Vancouver, BC, Canada.,Department of Surgery, University of British Columbia, Vancouver, BC, Canada.,Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
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11
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Abstract
Anaplerosis and the associated mitochondrial metabolite transporters generate unique cytosolic metabolic signaling molecules that can regulate insulin release from pancreatic β-cells. It has been shown that mitochondrial metabolites, transported by the citrate carrier (CIC), dicarboxylate carrier (DIC), oxoglutarate carrier (OGC), and mitochondrial pyruvate carrier (MPC) play a vital role in the regulation of glucose-stimulated insulin secretion (GSIS). Metabolomic studies on static and biphasic insulin secretion, suggests that several anaplerotic derived metabolites, including α-ketoglutarate (αKG), are strongly associated with nutrient regulated insulin secretion. Support for a role of αKG in the regulation of insulin secretion comes from studies looking at αKG dependent enzymes, including hypoxia-inducible factor-prolyl hydroxylases (PHDs) in clonal β-cells, and rodent and human islets. This review will focus on the possible link between defective anaplerotic-derived αKG, PHDs, and the development of type 2 diabetes (T2D).
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Affiliation(s)
- M. Hoang
- School of Pharmacy, University of Waterloo, Kitchener, Ontario, Canada
| | - J. W. Joseph
- School of Pharmacy, University of Waterloo, Kitchener, Ontario, Canada
- CONTACT J. W. Joseph School of Pharmacy, University of Waterloo, Kitchener, ONN2G1C5, Canada
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12
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Metabolomics Analysis of Nutrient Metabolism in β-Cells. J Mol Biol 2020; 432:1429-1445. [DOI: 10.1016/j.jmb.2019.07.020] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 07/03/2019] [Accepted: 07/11/2019] [Indexed: 01/05/2023]
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13
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Prentki M, Corkey BE, Madiraju SRM. Lipid-associated metabolic signalling networks in pancreatic beta cell function. Diabetologia 2020; 63:10-20. [PMID: 31423551 DOI: 10.1007/s00125-019-04976-w] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Accepted: 05/29/2019] [Indexed: 01/01/2023]
Abstract
Significant advances have been made in deciphering the mechanisms underlying fuel-stimulated insulin secretion by pancreatic beta cells. The contribution of the triggering/ATP-sensitive potassium (KATP)-dependent Ca2+ signalling and KATP-independent amplification pathways, that include anaplerosis and lipid signalling of glucose-stimulated insulin secretion (GSIS), are well established. A proposed model included a key role for a metabolic partitioning 'switch', the acetyl-CoA carboxylase (ACC)/malonyl-CoA/carnitine palmitoyltransferase-1 (CPT-1) axis, in beta cell glucose and fatty acid signalling for insulin secretion. This model has gained overwhelming support from a number of studies in recent years and is now refined through its link to the glycerolipid/NEFA cycle that provides lipid signals through its lipolysis arm. Furthermore, acetyl-CoA carboxylase may also control beta cell growth. Here we review the evidence supporting a role for the ACC/malonyl-CoA/CPT-1 axis in the control of GSIS and its particular importance under conditions of elevated fatty acids (e.g. fasting, excess nutrients, hyperlipidaemia and diabetes). We also document how it is linked to a more global lipid signalling system that includes the glycerolipid/NEFA cycle.
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Affiliation(s)
- Marc Prentki
- Department of Nutrition, University of Montreal, Montréal, QC, Canada.
- Department of Biochemistry and Molecular Medicine, University of Montreal, Montréal, QC, Canada.
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Viger Tour, 900 rue Saint Denis, Room R08-412, Montréal, QC, H2X 0A9, Canada.
| | - Barbara E Corkey
- Evans Department of Medicine, Obesity Research Center, Boston University School of Medicine, Boston, MA, USA
| | - S R Murthy Madiraju
- Department of Nutrition, University of Montreal, Montréal, QC, Canada
- Department of Biochemistry and Molecular Medicine, University of Montreal, Montréal, QC, Canada
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Viger Tour, 900 rue Saint Denis, Room R08-412, Montréal, QC, H2X 0A9, Canada
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14
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Kuok IT, Rountree AM, Jung SR, Sweet IR. Palmitate is not an effective fuel for pancreatic islets and amplifies insulin secretion independent of calcium release from endoplasmic reticulum. Islets 2019; 11:51-64. [PMID: 31084524 PMCID: PMC6548485 DOI: 10.1080/19382014.2019.1601490] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The aim of the study was to determine the acute contribution of fuel oxidation in mediating the increase in insulin secretion rate (ISR) in response to fatty acids. Measures of mitochondrial metabolism, as reflected by oxygen consumption rate (OCR) and cytochrome c reduction, calcium signaling, and ISR by rat islets were used to evaluate processes stimulated by acute exposure to palmitic acid (PA). The contribution of mitochondrial oxidation of PA was determined in the presence and absence of a blocker of mitochondrial transport of fatty acids (etomoxir) at different glucose concentrations. Subsequent to increasing glucose from 3 to 20 mM, PA caused small increases in OCR and cytosolic calcium (about 20% of the effect of glucose). In contrast, the effect of PA on ISR was almost 3 times that by glucose, suggesting that the metabolism of PA is not the dominant mechanism mediating PA's effect on ISR. This was further supported by lack of inhibition of PA-stimulated OCR and ISR when blocking entry of PA into mitochondria (with etomoxir), and PA's lack of stimulation of reduced cytochrome c in the presence of high glucose. Consistent with the lack of metabolic stimulation by PA, an inhibitor of calcium release from the endoplasmic reticulum, but not a blocker of L-type calcium channels, abolished the PA-induced elevation of cytosolic calcium. Notably, ISR was unaffected by thapsigargin showing the dissociation of endoplasmic reticulum calcium release and second phase insulin secretion. In conclusion, stimulation of ISR by PA was mediated by mechanisms largely independent of the oxidation of the fuel.
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Affiliation(s)
- Iok Teng Kuok
- University of Washington Diabetes Research Institute, University of Washington, Seattle, WA, USA
| | - Austin M. Rountree
- University of Washington Diabetes Research Institute, University of Washington, Seattle, WA, USA
| | - Seung-Ryoung Jung
- University of Washington Diabetes Research Institute, University of Washington, Seattle, WA, USA
| | - Ian R. Sweet
- University of Washington Diabetes Research Institute, University of Washington, Seattle, WA, USA
- CONTACT Ian R. Sweet UW Diabetes Institute, University of Washington, Box 358062, 750 Republican Street, Seattle, WA 98195-8062
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15
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Chronic palmitic acid-induced lipotoxicity correlates with defective trafficking of ATP sensitive potassium channels in pancreatic β cells. J Nutr Biochem 2018; 59:37-48. [DOI: 10.1016/j.jnutbio.2018.05.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 04/13/2018] [Accepted: 05/10/2018] [Indexed: 01/09/2023]
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16
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Elmorsy E, Al-Ghafari A, Helaly ANM, Hisab AS, Oehrle B, Smith PA. Editor's Highlight: Therapeutic Concentrations of Antidepressants Inhibit Pancreatic Beta-Cell Function via Mitochondrial Complex Inhibition. Toxicol Sci 2018; 158:286-301. [PMID: 28482088 DOI: 10.1093/toxsci/kfx090] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Diabetes mellitus risk is increased by prolonged usage of antidepressants (ADs). Although various mechanisms are suggested for their diabetogenic potential, whether a direct effect of ADs on pancreatic β-cells is involved is unclear. We examined this idea for 3 ADs: paroxetine, clomipramine and, with particular emphasis, fluoxetine, on insulin secretion, mitochondrial function, cellular bioenergetics, KATP channel activity, and caspase activity in murine and human cell-line models of pancreatic β-cells. Metabolic assays showed that these ADs decreased the redox, oxidative respiration, and energetic potential of β-cells in a time and concentration dependent manner, even at a concentration of 100 nM, well within the therapeutic window. These effects were related to inhibition of mitochondrial complex I and III. Consistent with impaired mitochondrial function, lactate output was increased and insulin secretion decreased. Neither fluoxetine, antimycin nor rotenone could reactivate KATP channel activity blocked by glucose unlike the mitochondrial uncoupler, FCCP. Chronic, but not acute, AD increased oxidative stress and activated caspases, 3, 8, and 9. A close agreement was found for the rates of oxidative respiration, lactate output and modulation of KATP channel activity in MIN6 cells with those of primary murine cells; data that supports MIN6 as a valid model to study beta-cell bioenergetics. To conclude, paroxetine, clomipramine and fluoxetine were all cytotoxic at therapeutic concentrations on pancreatic beta-cells; an action suggested to arise by inhibition of mitochondrial bioenergetics, oxidative stress and induction of apoptosis. These actions help explain the diabetogenic potential of these ADs in humans.
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Affiliation(s)
- Ekramy Elmorsy
- Department of Forensic Medicine and Clinical Toxicology, Faculty of Medicine, Mansoura University, Mansoura, Egypt
| | - Ayat Al-Ghafari
- Biochemistry Department, Faculty of Science, King Abdulaziz University (KAU), Jeddah, Kingdom of Saudi Arabia
| | - Ahmed N M Helaly
- Department of Forensic Medicine and Clinical Toxicology, Faculty of Medicine, Mansoura University, Mansoura, Egypt
| | - Ahmed S Hisab
- University of Nottingham Medical School, University of Nottingham, Nottinghamshire, UK
| | - Bettina Oehrle
- University of Nottingham Medical School, University of Nottingham, Nottinghamshire, UK
| | - Paul A Smith
- University of Nottingham Medical School, University of Nottingham, Nottinghamshire, UK
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17
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Lu M, Li C. Nutrient sensing in pancreatic islets: lessons from congenital hyperinsulinism and monogenic diabetes. Ann N Y Acad Sci 2017; 1411:65-82. [PMID: 29044608 DOI: 10.1111/nyas.13448] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Revised: 07/05/2017] [Accepted: 07/14/2017] [Indexed: 12/14/2022]
Abstract
Pancreatic beta cells sense changes in nutrients during the cycles of fasting and feeding and release insulin accordingly to maintain glucose homeostasis. Abnormal beta cell nutrient sensing resulting from gene mutations leads to hypoglycemia or diabetes. Glucokinase (GCK) plays a key role in beta cell glucose sensing. As one form of congenital hyperinsulinism (CHI), activating mutations of GCK result in a decreased threshold for glucose-stimulated insulin secretion and hypoglycemia. In contrast, inactivating mutations of GCK result in diabetes, including a mild form (MODY2) and a severe form (permanent neonatal diabetes mellitus (PNDM)). Mutations of beta cell ion channels involved in insulin secretion regulation also alter glucose sensing. Activating or inactivating mutations of ATP-dependent potassium (KATP ) channel genes result in severe but completely opposite clinical phenotypes, including PNDM and CHI. Mutations of the other ion channels, including voltage-gated potassium channels (Kv 7.1) and voltage-gated calcium channels, also lead to abnormal glucose sensing and CHI. Furthermore, amino acids can stimulate insulin secretion in a glucose-independent manner in some forms of CHI, including activating mutations of the glutamate dehydrogenase gene, HDAH deficiency, and inactivating mutations of KATP channel genes. These genetic defects have provided insight into a better understanding of the complicated nature of beta cell fuel-sensing mechanisms.
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Affiliation(s)
- Ming Lu
- Division of Endocrinology and Diabetes, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania.,Department of Pediatrics & Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.,Department of Endocrinology, Shandong Provincial Hospital affiliated to Shandong University, Jinan, Shandong, China
| | - Changhong Li
- Division of Endocrinology and Diabetes, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania.,Department of Pediatrics & Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
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18
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Lamontagne J, Al-Mass A, Nolan CJ, Corkey BE, Madiraju SRM, Joly E, Prentki M. Identification of the signals for glucose-induced insulin secretion in INS1 (832/13) β-cells using metformin-induced metabolic deceleration as a model. J Biol Chem 2017; 292:19458-19468. [PMID: 28972173 DOI: 10.1074/jbc.m117.808105] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Revised: 09/13/2017] [Indexed: 12/23/2022] Open
Abstract
Metabolic deceleration in pancreatic β-cells is associated with inhibition of glucose-induced insulin secretion (GIIS), but only in the presence of intermediate/submaximal glucose concentrations. Here, we used acute metformin treatment as a tool to induce metabolic deceleration in INS1 (832/13) β-cells, with the goal of identifying key pathways and metabolites involved in GIIS. Metabolites and pathways previously implicated as signals for GIIS were measured in the cells at 2-25 mm glucose, with or without 5 mm metformin. We defined three criteria to identify candidate signals: 1) glucose-responsiveness, 2) sensitivity to metformin-induced inhibition of the glucose effect at intermediate glucose concentrations, and 3) alleviation of metformin inhibition by elevated glucose concentrations. Despite the lack of recovery from metformin-induced impairment of mitochondrial energy metabolism (glucose oxidation, O2 consumption, and ATP production), insulin secretion was almost completely restored at elevated glucose concentrations. Meeting the criteria for candidates involved in promoting GIIS were the following metabolic indicators and metabolites: cytosolic NAD+/NADH ratio (inferred from the dihydroxyacetone phosphate:glycerol-3-phosphate ratio), mitochondrial membrane potential, ADP, Ca2+, 1-monoacylglycerol, diacylglycerol, malonyl-CoA, and HMG-CoA. On the contrary, most of the purine and nicotinamide nucleotides, acetoacetyl-CoA, H2O2, reduced glutathione, and 2-monoacylglycerol were not glucose-responsive. Overall these results underscore the significance of mitochondrial energy metabolism-independent signals in GIIS regulation; in particular, the candidate lipid signaling molecules 1-monoacylglycerol, diacylglycerol, and malonyl-CoA; the predominance of KATP/Ca2+ signaling control by low ADP·Mg2+ rather than by high ATP levels; and a role for a more oxidized state (NAD+/NADH) in the cytosol during GIIS that favors high glycolysis rates.
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Affiliation(s)
- Julien Lamontagne
- From the Molecular Nutrition Unit and Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Montréal, Québec H2X 0A9, Canada
| | - Anfal Al-Mass
- From the Molecular Nutrition Unit and Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Montréal, Québec H2X 0A9, Canada.,the Department of Medicine, McGill University, Montréal, Québec H4A 3J1, Canada
| | - Christopher J Nolan
- the Department of Endocrinology, Canberra Hospital and the Medical School, Australian National University, Canberra ACT 2605, Australia, and
| | - Barbara E Corkey
- the Department of Medicine, Obesity Research Center, Boston University School of Medicine, Boston, Massachusetts 02118
| | - S R Murthy Madiraju
- From the Molecular Nutrition Unit and Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Montréal, Québec H2X 0A9, Canada
| | - Erik Joly
- From the Molecular Nutrition Unit and Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Montréal, Québec H2X 0A9, Canada
| | - Marc Prentki
- From the Molecular Nutrition Unit and Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Montréal, Québec H2X 0A9, Canada, .,the Departments of Nutrition and Biochemistry, Université de Montréal, Montréal, Québec H3T 1J4, Canada
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19
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Bill N, Tomasch J, Riemer A, Müller K, Kleist S, Schmidt-Hohagen K, Wagner-Döbler I, Schomburg D. Fixation of CO 2 using the ethylmalonyl-CoA pathway in the photoheterotrophic marine bacterium Dinoroseobacter shibae. Environ Microbiol 2017; 19:2645-2660. [PMID: 28371065 DOI: 10.1111/1462-2920.13746] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Revised: 03/25/2017] [Accepted: 03/25/2017] [Indexed: 01/26/2023]
Abstract
The ability of aerobic anoxygenic photoheterotrophs (AAPs) to gain additional energy from sunlight represents a competitive advantage, especially in conditions where light has easy access or under environmental conditions may change quickly, such as those in the world´s oceans. However, the knowledge about the metabolic consequences of aerobic anoxygenic photosynthesis is very limited. Combining transcriptome and metabolome analyses, isotopic labelling techniques, measurements of growth, oxygen uptake rates, flow cytometry, and a number of other biochemical analytical techniques we obtained a comprehensive overview on the complex adaption of the marine bacterium Dinoroseobacter shibae DFL12T during transition from heterotrophy to photoheterotrophy (growth on succinate). Growth in light was characterized by reduced respiration, a decreased metabolic flux through the tricarboxylic acid (TCA) cycle and the assimilation of CO2 via an enhanced flux through the ethylmalonyl-CoA (EMC) pathway, which was shown to be connected to the serine metabolism. Adaptation to photoheterotrophy is mainly characterized by metabolic reactions caused by a surplus of reducing potential and might depend on genes located in one operon, encoding branching point enzymes of the EMC pathway, serine metabolism and the TCA cycle.
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Affiliation(s)
- Nelli Bill
- Institute for Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, Rebenring 56, Braunschweig, D-38106, Germany
| | - Jürgen Tomasch
- Department of Microbial Communication, Helmholtz-Centre for Infection Research (HZI), Inhoffenstrasse 7, Braunschweig, D-38124, Germany
| | - Alexander Riemer
- Institute for Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, Rebenring 56, Braunschweig, D-38106, Germany
| | - Katrin Müller
- Institute for Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, Rebenring 56, Braunschweig, D-38106, Germany
| | - Sarah Kleist
- Institute for Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, Rebenring 56, Braunschweig, D-38106, Germany
| | - Kerstin Schmidt-Hohagen
- Institute for Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, Rebenring 56, Braunschweig, D-38106, Germany
| | - Irene Wagner-Döbler
- Department of Microbial Communication, Helmholtz-Centre for Infection Research (HZI), Inhoffenstrasse 7, Braunschweig, D-38124, Germany
| | - Dietmar Schomburg
- Institute for Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, Rebenring 56, Braunschweig, D-38106, Germany
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20
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Mulder H. Transcribing β-cell mitochondria in health and disease. Mol Metab 2017; 6:1040-1051. [PMID: 28951827 PMCID: PMC5605719 DOI: 10.1016/j.molmet.2017.05.014] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Revised: 05/13/2017] [Accepted: 05/22/2017] [Indexed: 12/17/2022] Open
Abstract
Background The recent genome-wide association studies (GWAS) of Type 2 Diabetes (T2D) have identified the pancreatic β-cell as the culprit in the pathogenesis of the disease. Mitochondrial metabolism plays a crucial role in the processes controlling release of insulin and β-cell mass. This notion implies that mechanisms controlling mitochondrial function have the potential to play a decisive pathogenetic role in T2D. Scope of the review This article reviews studies demonstrating that there is indeed mitochondrial dysfunction in islets in T2D, and that GWAS have identified a variant in the gene encoding transcription factor B1 mitochondrial (TFB1M), predisposing to T2D due to mitochondrial dysfunction and impaired insulin secretion. Mechanistic studies of the nature of this pathogenetic link, as well as of other mitochondrial transcription factors, are described. Major conclusions Based on this, it is argued that transcription and translation in mitochondria are critical processes determining mitochondrial function in β-cells in health and disease.
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Key Words
- AMPK, AMP-dependent protein kinase
- ATGL, adipocyte triglyceride lipase
- COX, Cytochrome c oxidase
- CYTB, Cytochrome b
- ERR-α, Estrogen-related receptor-α
- Expression quantitative trait locus (eQTL)
- GDH, Glutamate dehydrogenase
- GSIS, Glucose-stimulated insulin secretion
- GWAS, Genome-wide association study
- Genome-wide association study (GWAS)
- HSL, Hormone-sensitive lipase
- ICDc, Cytosolic isocitrate dehydrogenase
- Insulin secretion
- Islets
- KATP, ATP-dependent K+-channel
- MTERF, Mitochondrial transcription termination factor
- Mitochondria
- ND, NADH dehydrogenase
- NRF, Nuclear respiratory factor
- NSUN4, NOP2/Sun RNA methyltransferase family member 4
- OXPHOS, Oxidative phosphorylation
- PC, Pyruvate carboxylase
- PDH, pyruvate dehydrogenase
- PGC, Peroxisome proliferator-activated receptor-γ co-activator
- POLRMT, Mitochondrial RNA polymerase
- POLγ, DNA polymerase-γ
- PPARγ, Peroxisome proliferator-activated receptor-γ
- PRC, PGC1-related coactivator
- SENP1, Sentrin/SUMO-specific protease-1
- SNP, Single Nucleotide Polymorphism
- SUR1, Sulphonylurea receptor-1
- T2D, Type 2 Diabetes
- TCA, Tricarboxylic acid
- TEFM, Mitochondrial transcription elongation factor
- TFAM, Transcription factor A mitochondrial
- TFB1M, Transcription factor B1 mitochondrial
- TFB2M, Transcription factor B2 mitochondrial
- eQTL, Expression quantitative trait locus
- β-Cell
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Affiliation(s)
- Hindrik Mulder
- Unit of Molecular Metabolism, Lund University Diabetes Centre, Malmö, Sweden
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21
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Mugabo Y, Zhao S, Lamontagne J, Al-Mass A, Peyot ML, Corkey BE, Joly E, Madiraju SRM, Prentki M. Metabolic fate of glucose and candidate signaling and excess-fuel detoxification pathways in pancreatic β-cells. J Biol Chem 2017; 292:7407-7422. [PMID: 28280244 DOI: 10.1074/jbc.m116.763060] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Revised: 03/06/2017] [Indexed: 12/28/2022] Open
Abstract
Glucose metabolism promotes insulin secretion in β-cells via metabolic coupling factors that are incompletely defined. Moreover, chronically elevated glucose causes β-cell dysfunction, but little is known about how cells handle excess fuels to avoid toxicity. Here we sought to determine which among the candidate pathways and coupling factors best correlates with glucose-stimulated insulin secretion (GSIS), define the fate of glucose in the β-cell, and identify pathways possibly involved in excess-fuel detoxification. We exposed isolated rat islets for 1 h to increasing glucose concentrations and measured various pathways and metabolites. Glucose oxidation, oxygen consumption, and ATP production correlated well with GSIS and saturated at 16 mm glucose. However, glucose utilization, glycerol release, triglyceride and glycogen contents, free fatty acid (FFA) content and release, and cholesterol and cholesterol esters increased linearly up to 25 mm glucose. Besides being oxidized, glucose was mainly metabolized via glycerol production and release and lipid synthesis (particularly FFA, triglycerides, and cholesterol), whereas glycogen production was comparatively low. Using targeted metabolomics in INS-1(832/13) cells, we found that several metabolites correlated well with GSIS, in particular some Krebs cycle intermediates, malonyl-CoA, and lower ADP levels. Glucose dose-dependently increased the dihydroxyacetone phosphate/glycerol 3-phosphate ratio in INS-1(832/13) cells, indicating a more oxidized state of NAD in the cytosol upon glucose stimulation. Overall, the data support a role for accelerated oxidative mitochondrial metabolism, anaplerosis, and malonyl-CoA/lipid signaling in β-cell metabolic signaling and suggest that a decrease in ADP levels is important in GSIS. The results also suggest that excess-fuel detoxification pathways in β-cells possibly comprise glycerol and FFA formation and release extracellularly and the diversion of glucose carbons to triglycerides and cholesterol esters.
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Affiliation(s)
- Yves Mugabo
- From the Montreal Diabetes Research Center and Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Québec H2X 0A9, Canada.,Departments of Nutrition, Biochemistry and Molecular Medicine, Faculty of Medicine, University of Montréal, Montreal, Québec H3C 3J7, Canada, and
| | - Shangang Zhao
- From the Montreal Diabetes Research Center and Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Québec H2X 0A9, Canada.,Departments of Medicine and Human Genetics, McGill University, Montreal, Québec H3A 1B1, Canada
| | - Julien Lamontagne
- From the Montreal Diabetes Research Center and Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Québec H2X 0A9, Canada
| | - Anfal Al-Mass
- From the Montreal Diabetes Research Center and Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Québec H2X 0A9, Canada.,Departments of Medicine and Human Genetics, McGill University, Montreal, Québec H3A 1B1, Canada
| | - Marie-Line Peyot
- From the Montreal Diabetes Research Center and Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Québec H2X 0A9, Canada
| | - Barbara E Corkey
- Department of Medicine, Obesity Research Center, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Erik Joly
- From the Montreal Diabetes Research Center and Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Québec H2X 0A9, Canada
| | - S R Murthy Madiraju
- From the Montreal Diabetes Research Center and Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Québec H2X 0A9, Canada
| | - Marc Prentki
- From the Montreal Diabetes Research Center and Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Québec H2X 0A9, Canada, .,Departments of Nutrition, Biochemistry and Molecular Medicine, Faculty of Medicine, University of Montréal, Montreal, Québec H3C 3J7, Canada, and
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22
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Mulder H. Metabolic coupling in pancreatic beta cells: lipolysis revisited. Diabetologia 2016; 59:2510-2513. [PMID: 27660005 DOI: 10.1007/s00125-016-4111-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 09/07/2016] [Indexed: 11/28/2022]
Affiliation(s)
- Hindrik Mulder
- Unit of Molecular Metabolism, Lund University Diabetes Centre, Malmö, Sweden.
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23
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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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24
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Hozumi Y, Nakano T, Tanaka T, Goto K. Localization of diacylglycerol kinase ζ in rat pancreatic islet cells under normal and streptozotocin-induced stress conditions . ACTA ACUST UNITED AC 2016. [DOI: 10.1679/aohc.76.23] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Yasukazu Hozumi
- Department of Anatomy and Cell Biology, Yamagata University School of Medicine,
| | - Tomoyuki Nakano
- Department of Anatomy and Cell Biology, Yamagata University School of Medicine,
| | - Toshiaki Tanaka
- Department of Anatomy and Cell Biology, Yamagata University School of Medicine,
| | - Kaoru Goto
- Department of Anatomy and Cell Biology, Yamagata University School of Medicine,
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25
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26
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Methods for measuring CoA and CoA derivatives in biological samples. Biochem Soc Trans 2015; 42:1107-11. [PMID: 25110010 DOI: 10.1042/bst20140123] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
CoA (coenzyme A) is a ubiquitous and essential cofactor that acts as an acyl group carrier in biochemical reactions. Apart from participating in numerous metabolic pathways as substrates and intermediates, CoA and a number of its thioester derivatives, such as acetyl-CoA, can also directly regulate the activity of proteins by allosteric mechanisms and by affecting protein acetylation reactions. Cellular levels of CoA and CoA thioesters change under various physiological and pathological conditions. Defective CoA biosynthesis is implicated in NBIA (neurodegeneration with brain iron accumulation). However, the exact role of CoA in the pathogenesis of NBIA is not well understood. Accurate and reliable assays for measuring CoA species in biological samples are essential for studying the roles of CoA and CoA derivatives in health and disease. The present mini-review discusses methods that are commonly used to measure CoA species in biological samples.
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27
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Pancreatic β-cell identity, glucose sensing and the control of insulin secretion. Biochem J 2015; 466:203-18. [PMID: 25697093 DOI: 10.1042/bj20141384] [Citation(s) in RCA: 251] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Insulin release from pancreatic β-cells is required to maintain normal glucose homoeostasis in man and many other animals. Defective insulin secretion underlies all forms of diabetes mellitus, a disease currently reaching epidemic proportions worldwide. Although the destruction of β-cells is responsible for Type 1 diabetes (T1D), both lowered β-cell mass and loss of secretory function are implicated in Type 2 diabetes (T2D). Emerging results suggest that a functional deficiency, involving de-differentiation of the mature β-cell towards a more progenitor-like state, may be an important driver for impaired secretion in T2D. Conversely, at least in rodents, reprogramming of islet non-β to β-cells appears to occur spontaneously in models of T1D, and may occur in man. In the present paper, we summarize the biochemical properties which define the 'identity' of the mature β-cell as a glucose sensor par excellence. In particular, we discuss the importance of suppressing a group of 11 'disallowed' housekeeping genes, including Ldha and the monocarboxylate transporter Mct1 (Slc16a1), for normal nutrient sensing. We then survey the changes in the expression and/or activity of β-cell-enriched transcription factors, including FOXO1, PDX1, NKX6.1, MAFA and RFX6, as well as non-coding RNAs, which may contribute to β-cell de-differentiation and functional impairment in T2D. The relevance of these observations for the development of new approaches to treat T1D and T2D is considered.
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28
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Nocito L, Kleckner AS, Yoo EJ, Jones IV AR, Liesa M, Corkey BE. The extracellular redox state modulates mitochondrial function, gluconeogenesis, and glycogen synthesis in murine hepatocytes. PLoS One 2015; 10:e0122818. [PMID: 25816337 PMCID: PMC4376787 DOI: 10.1371/journal.pone.0122818] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Accepted: 02/24/2015] [Indexed: 01/13/2023] Open
Abstract
Circulating redox state changes, determined by the ratio of reduced/oxidized pairs of different metabolites, have been associated with metabolic diseases. However, the pathogenic contribution of these changes and whether they modulate normal tissue function is unclear. As alterations in hepatic gluconeogenesis and glycogen metabolism are hallmarks that characterize insulin resistance and type 2 diabetes, we tested whether imposed changes in the extracellular redox state could modulate these processes. Thus, primary hepatocytes were treated with different ratios of the following physiological extracellular redox couples: β-hydroxybutyrate (βOHB)/acetoacetate (Acoc), reduced glutathione (GSH)/oxidized glutathione (GSSG), and cysteine/cystine. Exposure to a more oxidized ratio via extracellular βOHB/Acoc, GSH/GSSG, and cysteine/cystine in hepatocytes from fed mice increased intracellular hydrogen peroxide without causing oxidative damage. On the other hand, addition of more reduced ratios of extracellular βOHB/Acoc led to increased NAD(P)H and maximal mitochondrial respiratory capacity in hepatocytes. Greater βOHB/Acoc ratios were also associated with decreased β-oxidation, as expected with enhanced lipogenesis. In hepatocytes from fasted mice, a more extracellular reduced state of βOHB/Acoc led to increased alanine-stimulated gluconeogenesis and enhanced glycogen synthesis capacity from added glucose. Thus, we demonstrated for the first time that the extracellular redox state regulates the major metabolic functions of the liver and involves changes in intracellular NADH, hydrogen peroxide, and mitochondrial respiration. Because redox state in the blood can be communicated to all metabolically sensitive tissues, this work confirms the hypothesis that circulating redox state may be an important regulator of whole body metabolism and contribute to alterations associated with metabolic diseases.
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Affiliation(s)
- Laura Nocito
- Department of Medicine, Boston University, Boston, Massachusetts, United States of America
| | - Amber S. Kleckner
- Department of Medicine, Boston University, Boston, Massachusetts, United States of America
| | - Elsia J. Yoo
- Department of Medicine, Boston University, Boston, Massachusetts, United States of America
| | - Albert R. Jones IV
- Department of Medicine, Boston University, Boston, Massachusetts, United States of America
| | - Marc Liesa
- Department of Medicine, Boston University, Boston, Massachusetts, United States of America
| | - Barbara E. Corkey
- Department of Medicine, Boston University, Boston, Massachusetts, United States of America
- * E-mail:
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29
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Roles of Sphingolipid Metabolism in Pancreatic β Cell Dysfunction Induced by Lipotoxicity. J Clin Med 2014; 3:646-62. [PMID: 26237395 PMCID: PMC4449690 DOI: 10.3390/jcm3020646] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Revised: 04/10/2014] [Accepted: 04/11/2014] [Indexed: 12/31/2022] Open
Abstract
Pancreatic β cells secrete insulin in order to maintain glucose homeostasis. However, various environmental stresses such as obesity have been shown to induce loss of secretory responsiveness in pancreatic β cells and pancreatic β cell apoptosis which can favor the development of type 2 diabetes (T2D). Indeed, elevated levels of free fatty acids (FFAs) have been shown to induce β cell apoptosis. Importantly, the chronic adverse effects of FFAs on β cell function and viability are potentiated in the presence of hyperglycaemia, a phenomenon that has been termed gluco-lipotoxicity. The molecular mechanisms underlying the pathogenesis of gluco-lipotoxicity in pancreatic β cells are not completely understood. Recent studies have shown that sphingolipid metabolism plays a key role in gluco-lipotoxicity induced apoptosis and loss of function of pancreatic β cells. The present review focuses on how the two main sphingolipid mediators, ceramides and sphingoid base-1-phosphates, regulate the deleterious effects of gluco-lipotoxicity on pancreatic β cells. The review highlights the role of a sphingolipid biostat on the dysregulation of β cell fate and function induced by gluco-lipotoxicity, offering the possibility of new therapeutic targets to prevent the onset of T2D.
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30
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Huang M, Joseph JW. Assessment of the metabolic pathways associated with glucose-stimulated biphasic insulin secretion. Endocrinology 2014; 155:1653-66. [PMID: 24564396 DOI: 10.1210/en.2013-1805] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Biphasic glucose-stimulated insulin secretion involves a rapid first phase followed by a prolonged second phase of insulin secretion. The biochemical pathways that control these 2 phases of insulin secretion are poorly defined. In this study, we used a gas chromatography mass spectroscopy-based metabolomics approach to perform a global analysis of cellular metabolism during biphasic insulin secretion. A time course metabolomic analysis of the clonal β-cell line 832/13 cells showed that glycolytic, tricarboxylic acid, pentose phosphate pathway, and several amino acids were strongly correlated to biphasic insulin secretion. Interestingly, first-phase insulin secretion was negatively associated with L-valine, trans-4-hydroxy-L-proline, trans-3-hydroxy-L-proline, DL-3-aminoisobutyric acid, L-glutamine, sarcosine, L-lysine, and thymine and positively with L-glutamic acid, flavin adenine dinucleotide, caprylic acid, uridine 5'-monophosphate, phosphoglycerate, myristic acid, capric acid, oleic acid, linoleic acid, and palmitoleic acid. Tricarboxylic acid cycle intermediates pyruvate, α-ketoglutarate, and succinate were positively associated with second-phase insulin secretion. Other metabolites such as myo-inositol, cholesterol, DL-3-aminobutyric acid, and L-norleucine were negatively associated metabolites with the second-phase of insulin secretion. These studies provide a detailed analysis of key metabolites that are either negatively or positively associated with biphasic insulin secretion. The insights provided by these data set create a framework for planning future studies in the assessment of the metabolic regulation of biphasic insulin secretion.
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Affiliation(s)
- Mei Huang
- School of Pharmacy, University of Waterloo, Waterloo, Ontario, N2G 1C5, Canada
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31
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Patterson JN, Cousteils K, Lou JW, Manning Fox JE, MacDonald PE, Joseph JW. Mitochondrial metabolism of pyruvate is essential for regulating glucose-stimulated insulin secretion. J Biol Chem 2014; 289:13335-46. [PMID: 24675076 DOI: 10.1074/jbc.m113.521666] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
It is well known that mitochondrial metabolism of pyruvate is critical for insulin secretion; however, we know little about how pyruvate is transported into mitochondria in β-cells. Part of the reason for this lack of knowledge is that the carrier gene was only discovered in 2012. In the current study, we assess the role of the recently identified carrier in the regulation of insulin secretion. Our studies show that β-cells express both mitochondrial pyruvate carriers (Mpc1 and Mpc2). Using both pharmacological inhibitors and siRNA-mediated knockdown of the MPCs we show that this carrier plays a key role in regulating insulin secretion in clonal 832/13 β-cells as well as rat and human islets. We also show that the MPC is an essential regulator of both the ATP-regulated potassium (KATP) channel-dependent and -independent pathways of insulin secretion. Inhibition of the MPC blocks the glucose-stimulated increase in two key signaling molecules involved in regulating insulin secretion, the ATP/ADP ratio and NADPH/NADP(+) ratio. The MPC also plays a role in in vivo glucose homeostasis as inhibition of MPC by the pharmacological inhibitor α-cyano-β-(1-phenylindol-3-yl)-acrylate (UK5099) resulted in impaired glucose tolerance. These studies clearly show that the newly identified mitochondrial pyruvate carrier sits at an important branching point in nutrient metabolism and that it is an essential regulator of insulin secretion.
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Affiliation(s)
- Jessica N Patterson
- From the School of Pharmacy, University of Waterloo, Waterloo, 10A Victoria Street South, Ontario N2G 1C5, Canada and
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32
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Cho S, Lee S, Jeong SH, Kim Y, Kim SC, Hwang W, Park J. Anodic aluminium oxide membranes for immunoisolation with sufficient oxygen supply for pancreatic islets. Integr Biol (Camb) 2013; 5:828-34. [PMID: 23546334 DOI: 10.1039/c3ib20226g] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Immunoisolation membranes have been developed for various cell encapsulations for therapeutic purposes. However effective encapsulation systems have been hindered by low oxygen (O2) permeability or imperfect immunoisolation caused by either low porosity or non-uniform pore geometry. Here, we report an encapsulation method that uses an anodic aluminum oxide membrane formed by polyethylene oxide self-assembly to obtain nanochannels with both high selectivity in excluding immune molecules and high permeability of nutrients such as glucose, insulin, and O2. The extracorporeal encapsulation system composed of these membranes allows O2 flux to meet the O2 demand of pancreatic islets of Langerhans and provides excellent in vitro viability and functionality of islets.
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Affiliation(s)
- Siwoo Cho
- Dept. Mechanical Engineering POSTECH, San 31, Hyoja-dong, Nam-gu, Pohang, Gyoengbuk, Republic of Korea
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Kurohane Kaneko Y, Kobayashi Y, Motoki K, Nakata K, Miyagawa S, Yamamoto M, Hayashi D, Shirai Y, Sakane F, Ishikawa T. Depression of type I diacylglycerol kinases in pancreatic β-cells from male mice results in impaired insulin secretion. Endocrinology 2013; 154:4089-98. [PMID: 24035999 DOI: 10.1210/en.2013-1356] [Citation(s) in RCA: 26] [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
Diacylglycerol kinase (DGK) catalyzes the conversion of diacylglycerol (DAG) to phosphatidic acid. This study investigated the expression and function of DGK in pancreatic β-cells. mRNA expression of type I DGK isoforms (α, β, γ) was detected in mouse pancreatic islets and the β-cell line MIN6. Protein expression of DGKα and DGKγ was also detected in mouse β-cells and MIN6 cells. The type I DGK inhibitor R59949 inhibited high K(+)- and glucose-induced insulin secretion in MIN6 cells. Moreover, single knockdown of DGKα or DGKγ by small interfering RNA slightly but significantly decreased glucose- and high K(+)-induced insulin secretions, and the double knockdown further decreased them to the levels comparable with those induced by R59949. R59949 and DiC8, a membrane permeable DAG analog, decreased intracellular Ca(2+) concentration elevated by glucose and high K(+) in MIN6 cells. Real-time imaging in MIN6 cells expressing green fluorescent protein-tagged DGKα or DGKγ showed that the DGK activator phorbol 12-myristate 13-acetate rapidly induced translocation of DGKγ to the plasma membrane, whereas high K(+) slowly translocated DGKα and DGKγ to the plasma membrane. R59949 increased the DAG content in MIN6 cells when stimulated with high KCl, whereas it did not increase the DAG content but decreased the phosphatidic acid content when stimulated with high glucose. Finally, R59949 was confirmed to inhibit high K(+)-induced insulin secretion from mouse islets and glucose-induced insulin secretion from rat islets. These results suggest that DGKα and DGKγ are present in β-cells and that the depression of these DGKs causes a decrease in intracellular Ca(2+) concentration, thereby reducing insulin secretion.
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34
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Guay C, Joly É, Pepin É, Barbeau A, Hentsch L, Pineda M, Madiraju SRM, Brunengraber H, Prentki M. A role for cytosolic isocitrate dehydrogenase as a negative regulator of glucose signaling for insulin secretion in pancreatic ß-cells. PLoS One 2013; 8:e77097. [PMID: 24130841 PMCID: PMC3795013 DOI: 10.1371/journal.pone.0077097] [Citation(s) in RCA: 36] [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: 05/28/2013] [Accepted: 08/30/2013] [Indexed: 01/24/2023] Open
Abstract
Cytosolic NADPH may act as one of the signals that couple glucose metabolism to insulin secretion in the pancreatic ß-cell. NADPH levels in the cytoplasm are largely controlled by the cytosolic isoforms of malic enzyme and isocitrate dehydrogenase (IDHc). Some studies have provided evidence for a role of malic enzyme in glucose-induced insulin secretion (GIIS) via pyruvate cycling, but the role of IDHc in ß-cell signaling is unsettled. IDHc is an established component of the isocitrate/α-ketoglutarate shuttle that transfers reducing equivalents (NADPH) from the mitochondrion to the cytosol. This shuttle is energy consuming since it is coupled to nicotinamide nucleotide transhydrogenase that uses the mitochondrial proton gradient to produce mitochondrial NADPH and NAD(+) from NADP(+) and NADH. To determine whether flux through IDHc is positively or negatively linked to GIIS, we performed RNAi knockdown experiments in ß-cells. Reduced IDHc expression in INS 832/13 cells and isolated rat islet ß-cells resulted in enhanced GIIS. This effect was mediated at least in part via the KATP-independent amplification arm of GIIS. IDHc knockdown in INS 832/13 cells did not alter glucose oxidation but it reduced fatty acid oxidation and increased lipogenesis from glucose. Metabolome profiling in INS 832/13 cells showed that IDHc knockdown increased isocitrate and NADP(+) levels. It also increased the cellular contents of several metabolites linked to GIIS, in particular some Krebs cycle intermediates, acetyl-CoA, glutamate, cAMP and ATP. The results identify IDHc as a component of the emerging pathways that negatively regulate GIIS.
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Affiliation(s)
- Claudiane Guay
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Érik Joly
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Émilie Pepin
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Annie Barbeau
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Lisa Hentsch
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Marco Pineda
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - S. R. Murthy Madiraju
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Henri Brunengraber
- Department of Nutrition, School of Medicine, Case Western Reserve University, Cleveland, Ohio, United State of America
| | - Marc Prentki
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
- Departments of Nutrition and Biochemistry, University of Montreal, Montreal, Quebec, Canada
- * E-mail:
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35
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Panten U, Willenborg M, Schumacher K, Hamada A, Ghaly H, Rustenbeck I. Acute metabolic amplification of insulin secretion in mouse islets is mediated by mitochondrial export of metabolites, but not by mitochondrial energy generation. Metabolism 2013; 62:1375-86. [PMID: 23790612 DOI: 10.1016/j.metabol.2013.05.006] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/04/2012] [Revised: 04/22/2013] [Accepted: 05/08/2013] [Indexed: 12/26/2022]
Abstract
OBJECTIVE The β-cell metabolism of glucose and of some other fuels (e.g. α-ketoisocaproate) generates signals triggering and acutely amplifying insulin secretion. As the pathway coupling metabolism with amplification is largely unknown, we aimed to narrow down the putative amplifying signals. MATERIALS/METHODS An experimental design was used which previously prevented glucose-induced, but not α-ketoisocaproate-induced insulin secretion. Isolated mouse islets were pretreated for one hour with medium devoid of fuels and containing the sulfonylurea glipizide in high concentration which closed all ATP-sensitive K(+) channels. This concentration was also applied during the subsequent examination of fuel-induced effects. In perifused or incubated islets, insulin secretion and metabolic parameters were measured. RESULTS The pretreatment decreased the islet ATP/ADP ratio. Whereas glucose and α-ketoisovalerate were ineffective or weakly effective, respectively, when tested separately, their combination strongly enhanced the insulin secretion. Compared with glucose, the strong amplifier α-ketoisocaproate caused less increase in NAD(P)H-fluorescence and less mitochondrial hyperpolarization. Compared with α-ketoisovalerate, α-ketoisocaproate caused greater increase in NAD(P)H-fluorescence and greater mitochondrial hyperpolarization. Neither α-ketoacid anion enhanced the islet ATP/ADP ratio during onset of the insulin secretion. α-Ketoisocaproate induced a higher pyruvate content than glucose, slowly elevated the citrate content which was not changed by glucose and generated a much higher acetoacetate content than other fuels. α-Ketoisovalerate alone or in combination with glucose did not increase the citrate content. CONCLUSIONS In β-cells, mitochondrial energy generation does not mediate acute metabolic amplification, but mitochondrial production of acetyl-CoA and supplemental acetoacetate supplies cytosolic metabolites which induce the generation of specific amplifying signals.
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Affiliation(s)
- Uwe Panten
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technical University of Braunschweig, Mendelssohnstrasse 1, D-38106 Braunschweig, Germany.
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36
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Chowdhury A, Satagopam VP, Manukyan L, Artemenko KA, Fung YME, Schneider R, Bergquist J, Bergsten P. Signaling in Insulin-Secreting MIN6 Pseudoislets and Monolayer Cells. J Proteome Res 2013; 12:5954-62. [DOI: 10.1021/pr400864w] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Azazul Chowdhury
- Department
of Medical Cell Biology, Uppsala University, Box 571, SE-75123 Uppsala, Sweden
| | - Venkata P. Satagopam
- Department
of Structural and Computational Biology, EMBL, Meyerhofstrasse
1, D-69126 Heidelberg, Germany
- Luxembourg
Centre For Systems Biomedicine (LCSB), University of Luxembourg, Campus Belval, House of Biomedicine, 7 Avenue des Hauts-Fourneaux, L-4362 Esch-sur-Alzette, Luxembourg
| | - Levon Manukyan
- Department
of Medical Cell Biology, Uppsala University, Box 571, SE-75123 Uppsala, Sweden
| | - Konstantin A. Artemenko
- Analytical
Chemistry, Department of Chemistry−Biomedical Center and SciLifeLab, Uppsala University, Box
599, SE-75124 Uppsala, Sweden
| | - Yi Man Eva Fung
- Department
of Chemistry, State Key Laboratory of Synthetic
Chemistry, and Open Laboratory of Chemical
Biology of the Institute of Molecular Technology for Drug Discovery
and Synthesis, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Reinhard Schneider
- Department
of Structural and Computational Biology, EMBL, Meyerhofstrasse
1, D-69126 Heidelberg, Germany
- Luxembourg
Centre For Systems Biomedicine (LCSB), University of Luxembourg, Campus Belval, House of Biomedicine, 7 Avenue des Hauts-Fourneaux, L-4362 Esch-sur-Alzette, Luxembourg
| | - Jonas Bergquist
- Analytical
Chemistry, Department of Chemistry−Biomedical Center and SciLifeLab, Uppsala University, Box
599, SE-75124 Uppsala, Sweden
| | - Peter Bergsten
- Department
of Medical Cell Biology, Uppsala University, Box 571, SE-75123 Uppsala, Sweden
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37
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Klett EL, Chen S, Edin ML, Li LO, Ilkayeva O, Zeldin DC, Newgard CB, Coleman RA. Diminished acyl-CoA synthetase isoform 4 activity in INS 832/13 cells reduces cellular epoxyeicosatrienoic acid levels and results in impaired glucose-stimulated insulin secretion. J Biol Chem 2013; 288:21618-29. [PMID: 23766516 DOI: 10.1074/jbc.m113.481077] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) in pancreatic beta-cells is potentiated by fatty acids (FA). The initial step in the metabolism of intracellular FA is the conversion to acyl-CoA by long chain acyl-CoA synthetases (Acsls). Because the predominantly expressed Acsl isoforms in INS 832/13 cells are Acsl4 and -5, we characterized the role of these Acsls in beta-cell function by using siRNA to knock down Acsl4 or Acsl5. Compared with control cells, an 80% suppression of Acsl4 decreased GSIS and FA-potentiated GSIS by 32 and 54%, respectively. Knockdown of Acsl5 did not alter GSIS. Acsl4 knockdown did not alter FA oxidation or long chain acyl-CoA levels. With Acsl4 knockdown, incubation with 17 mm glucose increased media epoxyeicosatrienoic acids (EETs) and reduced cell membrane levels of EETs. Further, exogenous EETs reduced GSIS in INS 832/13 cells, and in Acsl4 knockdown cells, an EET receptor antagonist partially rescued GSIS. These results strongly suggest that Acsl4 activates EETs to form EET-CoAs that are incorporated into glycerophospholipids, thereby sequestering EETs. Exposing INS 832/13 cells to arachidonate or linoleate reduced Acsl4 mRNA and protein expression and reduced GSIS. These data indicate that Acsl4 modulates GSIS by regulating the levels of unesterified EETs and that arachidonate controls the expression of its activator Acsl4.
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Affiliation(s)
- Eric L Klett
- Department of Medicine, Division of Endocrinology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7172, USA.
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Lorenz MA, El Azzouny MA, Kennedy RT, Burant CF. Metabolome response to glucose in the β-cell line INS-1 832/13. J Biol Chem 2013; 288:10923-35. [PMID: 23426361 PMCID: PMC3624472 DOI: 10.1074/jbc.m112.414961] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells is triggered by metabolism of the sugar to increase ATP/ADP ratio that blocks the KATP channel leading to membrane depolarization and insulin exocytosis. Other metabolic pathways believed to augment insulin secretion have yet to be fully elucidated. To study metabolic changes during GSIS, liquid chromatography with mass spectrometry was used to determine levels of 87 metabolites temporally following a change in glucose from 3 to 10 mM glucose and in response to increasing concentrations of glucose in the INS-1 832/13 β-cell line. U-[(13)C]Glucose was used to probe flux in specific metabolic pathways. Results include a rapid increase in ATP/ADP, anaplerotic tricarboxylic acid cycle flux, and increases in the malonyl CoA pathway, support prevailing theories of GSIS. Novel findings include that aspartate used for anaplerosis does not derive from the glucose fuel added to stimulate insulin secretion, glucose flux into glycerol-3-phosphate, and esterification of long chain CoAs resulting in rapid consumption of long chain CoAs and de novo generation of phosphatidic acid and diacylglycerol. Further, novel metabolites with potential roles in GSIS such as 5-aminoimidazole-4-carboxamide ribotide (ZMP), GDP-mannose, and farnesyl pyrophosphate were found to be rapidly altered following glucose exposure.
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Affiliation(s)
- Matthew A Lorenz
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48105, USA
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Gudkova D, Panasyuk G, Nemazanyy I, Zhyvoloup A, Monteil P, Filonenko V, Gout I. EDC4 interacts with and regulates the dephospho-CoA kinase activity of CoA synthase. FEBS Lett 2012; 586:3590-5. [PMID: 22982864 DOI: 10.1016/j.febslet.2012.08.033] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 08/22/2012] [Accepted: 08/30/2012] [Indexed: 12/19/2022]
Abstract
Coenzyme A synthase (CoAsy) is a bifunctional enzyme which facilitates the last two steps of Coenzyme A biogenesis in higher eukaryotes. Here we describe that CoAsy forms a complex with enhancer of mRNA-decapping protein 4 (EDC4), a central scaffold component of processing bodies. CoAsy/EDC4 complex formation is regulated by growth factors and is affected by cellular stresses. EDC4 strongly inhibits the dephospho-CoA kinase activity of CoAsy in vitro. Transient overexpression of EDC4 decreases cell proliferation, and further co-expression of CoAsy diminishes this effect. Here we report that EDC4 might contribute to regulation of CoA biosynthesis in addition to its scaffold function in processing bodies.
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Affiliation(s)
- Daria Gudkova
- State Key Laboratory of Molecular and Cellular Biology, Institute of Molecular Biology and Genetics, Kyiv 03680, Ukraine.
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40
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Cheng K, Delghingaro-Augusto V, Nolan CJ, Turner N, Hallahan N, Andrikopoulos S, Gunton JE. High passage MIN6 cells have impaired insulin secretion with impaired glucose and lipid oxidation. PLoS One 2012; 7:e40868. [PMID: 22808281 PMCID: PMC3396628 DOI: 10.1371/journal.pone.0040868] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Accepted: 06/18/2012] [Indexed: 12/20/2022] Open
Abstract
Type 2 diabetes is a metabolic disorder characterized by the inability of beta-cells to secrete enough insulin to maintain glucose homeostasis. MIN6 cells secrete insulin in response to glucose and other secretagogues, but high passage (HP) MIN6 cells lose their ability to secrete insulin in response to glucose. We hypothesized that metabolism of glucose and lipids were defective in HP MIN6 cells causing impaired glucose stimulated insulin secretion (GSIS). HP MIN6 cells had no first phase and impaired second phase GSIS indicative of global functional impairment. This was coupled with a markedly reduced ATP content at basal and glucose stimulated states. Glucose uptake and oxidation were higher at basal glucose but ATP content failed to increase with glucose. HP MIN6 cells had decreased basal lipid oxidation. This was accompanied by reduced expressions of Glut1, Gck, Pfk, Srebp1c, Ucp2, Sirt3, Nampt. MIN6 cells represent an important model of beta cells which, as passage numbers increased lost first phase but retained partial second phase GSIS, similar to patients early in type 2 diabetes onset. We believe a number of gene expression changes occurred to produce this defect, with emphasis on Sirt3 and Nampt, two genes that have been implicated in maintenance of glucose homeostasis.
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Affiliation(s)
- Kim Cheng
- Diabetes and Transcription Factors Group, Garvan Institute of Medical Research (GIMR), Sydney, NSW, Australia
| | | | | | - Nigel Turner
- Diabetes and Obesity Program, Garvan Institute of Medical Research (GIMR), Sydney, NSW, Australia
| | - Nicole Hallahan
- Diabetes and Obesity Program, Garvan Institute of Medical Research (GIMR), Sydney, NSW, Australia
| | | | - Jenny E. Gunton
- Diabetes and Transcription Factors Group, Garvan Institute of Medical Research (GIMR), Sydney, NSW, Australia
- Faculty of Medicine, University of Sydney, Sydney, NSW, Australia
- St. Vincent’s Clinical School, University of New South Wales, Sydney, NSW, Australia
- Department of Diabetes and Endocrinology, Westmead Hospital, Sydney, NSW, Australia
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Abstract
Defining the key metabolic pathways that are important for fuel-regulated insulin secretion is critical to providing a complete picture of how nutrients regulate insulin secretion. We have performed a detailed metabolomics study of the clonal β-cell line 832/13 using a gas chromatography-mass spectrometer (GC-MS) to investigate potential coupling factors that link metabolic pathways to insulin secretion. Mid-polar and polar metabolites, extracted from the 832/13 β-cells, were derivatized and then run on a GC/MS to identify and quantify metabolite concentrations. Three hundred fifty-five out of 527 chromatographic peaks could be identified as metabolites by our metabolomic platform. These identified metabolites allowed us to perform a systematic analysis of key pathways involved in glucose-stimulated insulin secretion (GSIS). Of these metabolites, 41 were consistently identified as biomarker for GSIS by orthogonal partial least-squares (OPLS). Most of the identified metabolites are from common metabolic pathways including glycolytic, sorbitol-aldose reductase pathway, pentose phosphate pathway, and the TCA cycle suggesting these pathways play an important role in GSIS. Lipids and related products were also shown to contribute to the clustering of high glucose sample groups. Amino acids lysine, tyrosine, alanine and serine were upregulated by glucose whereas aspartic acid was downregulated by glucose suggesting these amino acids might play a key role in GSIS. In summary, a coordinated signaling cascade elicited by glucose metabolism in pancreatic β-cells is revealed by our metabolomics platform providing a new conceptual framework for future research and/or drug discovery.
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42
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Affiliation(s)
- Owen Chan
- Department of Internal Medicine, Section of Endocrinology, Yale School of Medicine, New Haven, Connecticut, USA
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Abstract
The Banting Medal for Scientific Achievement Award is the American Diabetes Association's highest scientific award and honors an individual who has made significant, long-term contributions to the understanding of diabetes, its treatment, and/or prevention. The award is named after Nobel Prize winner Sir Frederick Banting, who codiscovered insulin treatment for diabetes. Dr. Barbara E. Corkey received the American Diabetes Association's Banting Medal for Scientific Achievement at the Association's 71st Scientific Sessions, 24-28 June 2011, San Diego, California. She presented the Banting Lecture, "Hyperinsulinemia: Cause or Consequence?" on Sunday, 26 June 2011.
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Affiliation(s)
- Barbara E Corkey
- Obesity Research Center, Evans Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, USA.
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Huypens PR, Huang M, Joseph JW. Overcoming the spatial barriers of the stimulus secretion cascade in pancreatic β-cells. Islets 2012; 4:1-116. [PMID: 22143007 DOI: 10.4161/isl.18338] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The ability of the pancreatic β-cells to adapt the rate of insulin release in accordance to changes in circulating glucose levels is essential for glucose homeostasis. Two spatial barriers imposed by the plasma membrane and inner mitochondrial membrane need to be overcome in order to achieve stringent coupling between the different steps in the stimulus-secretion cascade. The first spatial barrier is overcome by the presence of a glucose transporter (GLUT) in the plasma membrane, whereas a low affinity hexokinase IV (glucokinase, GK) in the cytosol conveys glucose availability into a metabolic flux that triggers and accelerates insulin release. The mitochondrial inner membrane comprises a second spatial barrier that compartmentalizes glucose metabolism into glycolysis (cytosol) and tricarboxylate (TCA) cycle (mitochondrial matrix). The exchange of metabolites between cytosol and mitochondrial matrix is mediated via a set of mitochondrial carriers, including the aspartate-glutamate carrier (aralar1), α- ketoglutarate carrier (OGC), ATP/ADP carrier (AAC), glutamate carrier (GC1), dicarboxylate carrier (DIC) and citrate/isocitrate carrier (CIC). The scope of this review is to provide an overview of the role these carriers play in stimulus-secretion coupling and discuss the importance of these findings in the context of the exquisite glucose responsive state of the pancreatic β-cell.
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Affiliation(s)
- Peter R Huypens
- School of Pharmacy; Health Science Campus; University of Waterloo; Kitchener, CN Canada
| | - Mei Huang
- School of Pharmacy; Health Science Campus; University of Waterloo; Kitchener, CN Canada
| | - Jamie W Joseph
- School of Pharmacy; Health Science Campus; University of Waterloo; Kitchener, CN Canada
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Fahien LA, Macdonald MJ. The complex mechanism of glutamate dehydrogenase in insulin secretion. Diabetes 2011; 60:2450-4. [PMID: 21948999 PMCID: PMC3178282 DOI: 10.2337/db10-1150] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2010] [Accepted: 07/01/2011] [Indexed: 11/29/2022]
Affiliation(s)
- Leonard A Fahien
- The Children’s Diabetes Center, University of Wisconsin School of Medicineand Public Health, Madison, Wisconsin, USA.
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46
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Huypens P, Pillai R, Sheinin T, Schaefer S, Huang M, Odegaard ML, Ronnebaum SM, Wettig SD, Joseph JW. The dicarboxylate carrier plays a role in mitochondrial malate transport and in the regulation of glucose-stimulated insulin secretion from rat pancreatic beta cells. Diabetologia 2011; 54:135-45. [PMID: 20949348 DOI: 10.1007/s00125-010-1923-5] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Accepted: 08/27/2010] [Indexed: 01/02/2023]
Abstract
AIMS/HYPOTHESIS We have previously described a strong correlation between pyruvate cycling and insulin secretion. We have also demonstrated a particularly important role for a pyruvate-isocitrate cycling pathway involving the mitochondrial citrate/isocitrate carrier (CIC) and cytosolic NADP-dependent isocitrate dehydrogenase. CIC requires cytosolic malate as a counter-substrate during citrate and isocitrate export. Thus, considering that the mitochondrial dicarboxylate carrier (DIC) provides an important source of cytosolic malate, we investigated the potential role of DIC in control of glucose-stimulated insulin secretion (GSIS). METHODS We used pharmacological and small interfering RNA (siRNA) tools to assess the role of DIC in insulin release in clonal insulin-secreting 832/13 cells and isolated rat islets. RESULTS Butylmalonate, an inhibitor of malate transport, reduced cytosolic malate and citrate levels, and inhibited GSIS in a dose-dependent manner in 832/13 cells. Suppression of DIC expression resulted in inhibition of GSIS by 5% to 69%, the extent of inhibition of insulin secretion being proportional to the level of Dic (also known as Slc25a10) gene knockdown. The most effective siRNA duplex against Dic did not affect glucose utilisation, glucose oxidation or ATP/ADP ratio, but did suppress glucose-induced increments of the NADPH/NADP(+) ratio. Confirmation of our results in primary cultures of isolated rat islets showed that butylmalonate and an adenovirus expressing an siRNA against Dic-inhibited GSIS. CONCLUSIONS/INTERPRETATION Malate transport by DIC may play an important role in GSIS, possibly by providing cytosolic malate as a counter-substrate for citrate and/or isocitrate export by CIC. These studies also suggest that malate transport by DIC is (1) a critical component of NADPH production mediated by pyruvate-cycling and (2) regulates GSIS.
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Affiliation(s)
- P Huypens
- University of Waterloo, Kitchener, ON, Canada
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Pillai R, Huypens P, Huang M, Schaefer S, Sheinin T, Wettig SD, Joseph JW. Aryl hydrocarbon receptor nuclear translocator/hypoxia-inducible factor-1{beta} plays a critical role in maintaining glucose-stimulated anaplerosis and insulin release from pancreatic {beta}-cells. J Biol Chem 2010; 286:1014-24. [PMID: 21059654 DOI: 10.1074/jbc.m110.149062] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The metabolic pathways that are involved in regulating insulin secretion from pancreatic β-cells are still incompletely understood. One potential regulator of the metabolic phenotype of β-cells is the transcription factor aryl hydrocarbon receptor nuclear translocator (ARNT)/hypoxia-inducible factor (HIF)-1β. ARNT/HIF-1β levels are profoundly reduced in islets obtained from type 2 diabetic patients. However, no study to date has investigated key pathways involved in regulating insulin release in β-cells that lack ARNT/HIF-1β. In this study, we confirm that siRNA-mediated knockdown of ARNT/HIF-1β inhibits glucose-stimulated insulin secretion. We next investigated the metabolic consequence of the loss of ARNT/HIF-1β knockdown. We demonstrate that β-cells with reduced ARNT/HIF-1β expression levels exhibit a 31% reduction in glycolytic flux without significant changes in glucose oxidation or the ATP:ADP ratio. Metabolic profiling of β-cells treated with siRNAs against the ARNT/HIF-1β gene revealed that glycolysis, anaplerosis, and glucose-induced fatty acid production were down-regulated, and all are key events involved in glucose-stimulated insulin secretion. In addition, both first and second phase insulin secretion in islets were significantly reduced after ARNT/HIF-1β knockdown. Together, our data suggest an important role for ARNT/HIF-1β in anaplerosis, and it may play a critical role in maintaining normal secretion competence of β-cells.
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Affiliation(s)
- Renjitha Pillai
- School of Pharmacy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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Abdel-Ghany M, Sharp GWG, Straub SG. Glucose stimulation of protein acylation in the pancreatic β-cell. Life Sci 2010; 87:667-71. [PMID: 20883703 DOI: 10.1016/j.lfs.2010.09.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Revised: 08/03/2010] [Accepted: 09/22/2010] [Indexed: 11/26/2022]
Abstract
AIMS To determine whether protein acylation plays a role in the effects of glucose on the insulin secreting β-cell. MAIN METHODS The measurement of (3)H-palmitate incorporation into protein in the INS 832/13 cell that has a robust and well-characterized biphasic insulin secretory response to stimulation with glucose. KEY FINDINGS Stimulating the cells with glucose increased the incorporation of (3)H-palmitic acid into protein by up to 90%. Similarly, 2-aminobicyclo [2.2.1] heptane-2-carboxylic acid (BCH) the non-metabolizable analog of leucine that mimics the stimulatory effect of glucose on insulin secretion also increased the incorporation of (3)H-palmitic acid into protein. Treatment of cell lysates with hydroxylamine substantially reduced the incorporation indicating that most of the incorporation was due to enzymatic palmitoylation of proteins. Cerulenin, a classical inhibitor of protein acylation also substantially reduced the incorporation. Using PAGE and autoradiography a glucose-induced increase in protein palmitoylation and specific glucose-induced increases in the palmitoylation of proteins of 30, 44, 48 and 76kD were identified. SIGNIFICANCE The data suggest that protein acylation plays multiple roles in β-cell function.
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Affiliation(s)
- Mossaad Abdel-Ghany
- The Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
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Pepin E, Guay C, Delghingaro-Augusto V, Joly E, Madiraju SRM, Prentki M. Short-chain 3-hydroxyacyl-CoA dehydrogenase is a negative regulator of insulin secretion in response to fuel and non-fuel stimuli in INS832/13 β-cells. J Diabetes 2010; 2:157-67. [PMID: 20923481 DOI: 10.1111/j.1753-0407.2010.00076.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
BACKGROUND Hyperinsulinemia associated with non-ketotic hypoglycemia is observed in patients with mutated β-oxidation enzyme short-chain 3-hydroxyacyl-CoA dehydrogenase (HADHSC). In the present study, we investigated the mechanism underlying HADHSC-mediated regulation of insulin secretion. METHODS Knockdown of HADHSC expression by RNA interference in INS832/13 β-cells was achieved using short hairpin RNA and short interference RNA. RESULTS Knockdown of HADHSC increased both fuel- (glucose or leucine plus glutamine) and non-fuel (high KCl)-induced insulin secretion. Enhanced glucose-stimulated insulin secretion (GSIS) induced by HADHSC knockdown was independent of changes in cytosolic Ca(2+) and also occurred in the presence of fatty acids. L-Carnitine, used in the formation of acyl-carnitine compounds, increased GSIS in control cells, but was unable to further increase the augmented GSIS in HADHSC-knockdown cells. The pan transaminase inhibitor amino-oxyacetate reversed HADHSC knockdown-mediated increases in GSIS. Oxidation of [1-(14) C]-palmitate and -octanoate was not reduced in HADHSC-knockdown cells. L-3-Hydroxybutyryl-carnitine (tested using its precursor L-3-hydroxybutyrate) and L-3-hydroxyglutarate, which accumulate in blood and urine, respectively, of HADHSC-deficient patients, did not change insulin secretion. CONCLUSIONS Insulin secretion promoted by both fuel and non-fuel stimuli is negatively regulated by HADHSC. Enhanced secretion after HADHSC knockdown is not due to inhibition of fatty acid oxidation causing an accumulation of long-chain fatty acids or their CoA derivatives. L-3-Hydroxybutyrate and L-3-hydroxyglutarate do not mediate enhanced secretion caused by reduced HADHSC activity. Transamination reaction(s) and the formation of short-chain acylcarnitines and CoAs may be implicated in the mechanism whereby HADHSC deficiency results in enhanced insulin secretion and hyperinsulinemia.
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Affiliation(s)
- Emilie Pepin
- Montreal Diabetes Research Center, CRCHUM, Montréal, Québec, Canada
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Arumugam R, Horowitz E, Noland RC, Lu D, Fleenor D, Freemark M. Regulation of islet beta-cell pyruvate metabolism: interactions of prolactin, glucose, and dexamethasone. Endocrinology 2010; 151:3074-83. [PMID: 20484462 PMCID: PMC2903933 DOI: 10.1210/en.2010-0049] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Prolactin (PRL) induces beta-cell proliferation and glucose-stimulated insulin secretion (GSIS) and counteracts the effects of glucocorticoids on insulin production. The mechanisms by which PRL up-regulates GSIS are unknown. We used rat islets and insulinoma (INS-1) cells to explore the interactions of PRL, glucose, and dexamethasone (DEX) in the regulation of beta-cell pyruvate carboxylase (PC), pyruvate dehydrogenase (PDH), and the pyruvate dehydrogenase kinases (PDKs), which catalyze the phosphorylation and inactivation of PDH. PRL increased GSIS by 37% (P < 0.001) in rat islets. Glucose at supraphysiological concentrations (11 mm) increased PC mRNA in islets; in contrast, PRL suppressed PC mRNA levels in islets and INS-1 cells, whereas DEX was without effect. Neither PRL nor DEX altered PC protein or activity levels. In INS-1 cells, PRL increased PDH activity 1.4- to 2-fold (P < 0.05-0.001) at glucose concentrations ranging from 2.5-11 mm. DEX reduced PDH activity; this effect was reversed by PRL. PDK1, -2, -3, and -4 mRNAs were detected in both islets and insulinoma cells, but the latter expressed trivial amounts of PDK4. PRL reduced PDK2 mRNA and protein levels in rat islets and INS-1 cells and PDK4 mRNA in islets; DEX increased PDK2 mRNA in islets and INS-1 cells; this effect was reversed by PRL. Our findings suggest that PRL induction of GSIS is mediated by increases in beta-cell PDH activity; this is facilitated by suppression of PDKs. PRL counteracts the effects of DEX on PDH and PDK expression, suggesting novel roles for the lactogens in the defense against diabetes.
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Affiliation(s)
- Ramamani Arumugam
- Pediatric Endocrinology, Duke University Medical Center, Box 102820, Duke University Medical Center, Durham, NC 27710, USA.
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