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Perrier J, Nawrot M, Madec AM, Chikh K, Chauvin MA, Damblon C, Sabatier J, Thivolet CH, Rieusset J, Rautureau GJP, Panthu B. Human Pancreatic Islets React to Glucolipotoxicity by Secreting Pyruvate and Citrate. Nutrients 2023; 15:4791. [PMID: 38004183 PMCID: PMC10674605 DOI: 10.3390/nu15224791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Revised: 11/07/2023] [Accepted: 11/10/2023] [Indexed: 11/26/2023] Open
Abstract
Progressive decline in pancreatic beta-cell function is central to the pathogenesis of type 2 diabetes (T2D). Here, we explore the relationship between the beta cell and its nutritional environment, asking how an excess of energy substrate leads to altered energy production and subsequent insulin secretion. Alterations in intracellular metabolic homeostasis are key markers of islets with T2D, but changes in cellular metabolite exchanges with their environment remain unknown. We answered this question using nuclear magnetic resonance-based quantitative metabolomics and evaluated the consumption or secretion of 31 extracellular metabolites from healthy and T2D human islets. Islets were also cultured under high levels of glucose and/or palmitate to induce gluco-, lipo-, and glucolipotoxicity. Biochemical analyses revealed drastic alterations in the pyruvate and citrate pathways, which appear to be associated with mitochondrial oxoglutarate dehydrogenase (OGDH) downregulation. We repeated these manipulations on the rat insulinoma-derived beta-pancreatic cell line (INS-1E). Our results highlight an OGDH downregulation with a clear effect on the pyruvate and citrate pathways. However, citrate is directed to lipogenesis in the INS-1E cells instead of being secreted as in human islets. Our results demonstrate the ability of metabolomic approaches performed on culture media to easily discriminate T2D from healthy and functional islets.
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Affiliation(s)
- Johan Perrier
- Laboratoire CarMeN, UMR INSERM U1060/INRAE U1397, University of Lyon, Université Claude Bernard Lyon 1, 69310 Pierre-Bénite, France
| | - Margaux Nawrot
- Laboratoire CarMeN, UMR INSERM U1060/INRAE U1397, University of Lyon, Université Claude Bernard Lyon 1, 69310 Pierre-Bénite, France
| | - Anne-Marie Madec
- Laboratoire CarMeN, UMR INSERM U1060/INRAE U1397, University of Lyon, Université Claude Bernard Lyon 1, 69310 Pierre-Bénite, France
| | - Karim Chikh
- Laboratoire CarMeN, UMR INSERM U1060/INRAE U1397, University of Lyon, Université Claude Bernard Lyon 1, 69310 Pierre-Bénite, France
- Department of Endocrinology and Diabetes, Hospices Civils de Lyon, Hopital Lyon Sud, 69310 Pierre-Bénite, France
| | - Marie-Agnès Chauvin
- Laboratoire CarMeN, UMR INSERM U1060/INRAE U1397, University of Lyon, Université Claude Bernard Lyon 1, 69310 Pierre-Bénite, France
| | - Christian Damblon
- Unité de Recherche MolSys, Faculté des Sciences, Université de Liège, 99131 Liège, Belgium
| | - Julia Sabatier
- Laboratory of Cell Therapy for Diabetes (LTCD), PRIMS Facility, Institute for Regenerative Medicine and Biotherapy (IRMB), University Hospital of Montpellier, 34295 Montpellier, France
| | - Charles H. Thivolet
- Laboratoire CarMeN, UMR INSERM U1060/INRAE U1397, University of Lyon, Université Claude Bernard Lyon 1, 69310 Pierre-Bénite, France
- Department of Endocrinology and Diabetes, Hospices Civils de Lyon, Hopital Lyon Sud, 69310 Pierre-Bénite, France
| | - Jennifer Rieusset
- Laboratoire CarMeN, UMR INSERM U1060/INRAE U1397, University of Lyon, Université Claude Bernard Lyon 1, 69310 Pierre-Bénite, France
| | - Gilles J. P. Rautureau
- Centre de Résonance Magnétique Nucléaire à Très Hauts Champs, UMR 5082 CNRS, ENS Lyon, UCBL, Université de Lyon, 69100 Villeurbanne, France
| | - Baptiste Panthu
- Laboratoire CarMeN, UMR INSERM U1060/INRAE U1397, University of Lyon, Université Claude Bernard Lyon 1, 69310 Pierre-Bénite, France
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Morrish F, Gingras H, Noonan J, Huang L, Sweet IR, Kuok IT, Knoblaugh SE, Hockenbery DM. Mitochondrial diabetes in mice expressing a dominant-negative allele of nuclear respiratory factor-1 ( Nrf1 ) in pancreatic β-cells. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.22.524153. [PMID: 38014068 PMCID: PMC10680558 DOI: 10.1101/2023.01.22.524153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
Genetic polymorphisms in nuclear respiratory factor-1 ( NRF1 ), a key transcriptional regulator of nuclear-encoded mitochondrial proteins, have been linked to diabetes. Homozygous deletion of Nrf1 is embryonic lethal in mice. Our goal was to generate mice with β-cell-specific reduction in NRF1 function to investigate the relationship between NRF1 and diabetes. We report the generation of mice expressing a dominant-negative allele of Nrf1 (DNNRF1) in pancreatic β-cells. Heterozygous transgenic mice had high fed blood glucose levels detected at 3 wks of age, which persisted through adulthood. Plasma insulin levels in DNNRF1 transgenic mice were reduced, while insulin sensitivity remained intact in young animals. Islet size was reduced with increased numbers of apoptotic cells, and insulin content in islets by immunohistochemistry was low. Glucose-stimulated insulin secretion in isolated islets was reduced in DNNRF1-mice, but partially rescued by KCl, suggesting that decreased mitochondrial function contributed to the insulin secretory defect. Electron micrographs demonstrated abnormal mitochondrial morphology in β- cells. Expression of NRF1 target genes Tfam , T@1m and T@2m , and islet cytochrome c oxidase and succinate dehydrogenase activities were reduced in DNNRF1-mice. Rescue of mitochondrial function with low level activation of transgenic c-Myc in β-cells was sufficient to restore β-cell mass and prevent diabetes. This study demonstrates that reduced NRF1 function can lead to loss of β-cell function and establishes a model to study the interplay between regulators of bi- genomic gene transcription in diabetes.
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Santo-Domingo J, Lassueur S, Galindo AN, Alvarez-Illera P, Romero-Sanz S, Caldero-Escudero E, de la Fuente S, Dayon L, Wiederkehr A. SLC25A46 promotes mitochondrial fission and mediates resistance to lipotoxic stress in INS-1E insulin-secreting cells. J Cell Sci 2023; 136:jcs260049. [PMID: 36942724 DOI: 10.1242/jcs.260049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Accepted: 03/01/2023] [Indexed: 03/23/2023] Open
Abstract
Glucose sensing in pancreatic β-cells depends on oxidative phosphorylation and mitochondria-derived signals that promote insulin secretion. Using mass spectrometry-based phosphoproteomics to search for downstream effectors of glucose-dependent signal transduction in INS-1E insulinoma cells, we identified the outer mitochondrial membrane protein SLC25A46. Under resting glucose concentrations, SLC25A46 was phosphorylated on a pair of threonine residues (T44/T45) and was dephosphorylated in response to glucose-induced Ca2+ signals. Overexpression of SLC25A46 in INS-1E cells caused complete mitochondrial fragmentation, resulting in a mild mitochondrial defect associated with lowered glucose-induced insulin secretion. In contrast, inactivation of the Slc25a46 gene resulted in dramatic mitochondrial hyperfusion, without affecting respiratory activity or insulin secretion. Consequently, SLC25A46 is not essential for metabolism-secretion coupling under normal nutrient conditions. Importantly, insulin-secreting cells lacking SLC25A46 had an exacerbated sensitivity to lipotoxic conditions, undergoing massive apoptosis when exposed to palmitate. Therefore, in addition to its role in mitochondrial dynamics, SLC25A46 plays a role in preventing mitochondria-induced apoptosis in INS-E cells exposed to nutrient stress. By protecting mitochondria, SLC25A46 might help to maintain β-cell mass essential for blood glucose control.
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Affiliation(s)
- Jaime Santo-Domingo
- Department of Cell Biology, Nestlé Institute of Health Sciences, Nestlé Research, CH-1015 Lausanne, Switzerland
- Department of Biochemistry and Molecular Biology, Unidad de Excelencia Instituto de Biología y Genética Molecular (IBGM), Faculty of Medicine, 47003 Valladolid, Spain
| | - Steve Lassueur
- Department of Cell Biology, Nestlé Institute of Health Sciences, Nestlé Research, CH-1015 Lausanne, Switzerland
| | - Antonio Núñez Galindo
- Proteomics, Nestlé Institute of Food Safety & Analytical Sciences, Nestlé Research, CH-1015 Lausanne, Switzerland
| | - Pilar Alvarez-Illera
- Department of Biochemistry and Molecular Biology, Unidad de Excelencia Instituto de Biología y Genética Molecular (IBGM), Faculty of Medicine, 47003 Valladolid, Spain
| | - Silvia Romero-Sanz
- Department of Biochemistry and Molecular Biology, Unidad de Excelencia Instituto de Biología y Genética Molecular (IBGM), Faculty of Medicine, 47003 Valladolid, Spain
| | - Elena Caldero-Escudero
- Department of Biochemistry and Molecular Biology, Unidad de Excelencia Instituto de Biología y Genética Molecular (IBGM), Faculty of Medicine, 47003 Valladolid, Spain
| | - Sergio de la Fuente
- Center for Translational Medicine, Department of Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA
| | - Loïc Dayon
- Proteomics, Nestlé Institute of Food Safety & Analytical Sciences, Nestlé Research, CH-1015 Lausanne, Switzerland
- Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - Andreas Wiederkehr
- Department of Cell Biology, Nestlé Institute of Health Sciences, Nestlé Research, CH-1015 Lausanne, Switzerland
- Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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4
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Haythorne E, Lloyd M, Walsby-Tickle J, Tarasov AI, Sandbrink J, Portillo I, Exposito RT, Sachse G, Cyranka M, Rohm M, Rorsman P, McCullagh J, Ashcroft FM. Altered glycolysis triggers impaired mitochondrial metabolism and mTORC1 activation in diabetic β-cells. Nat Commun 2022; 13:6754. [PMID: 36376280 PMCID: PMC9663558 DOI: 10.1038/s41467-022-34095-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 10/13/2022] [Indexed: 11/16/2022] Open
Abstract
Chronic hyperglycaemia causes a dramatic decrease in mitochondrial metabolism and insulin content in pancreatic β-cells. This underlies the progressive decline in β-cell function in diabetes. However, the molecular mechanisms by which hyperglycaemia produces these effects remain unresolved. Using isolated islets and INS-1 cells, we show here that one or more glycolytic metabolites downstream of phosphofructokinase and upstream of GAPDH mediates the effects of chronic hyperglycemia. This metabolite stimulates marked upregulation of mTORC1 and concomitant downregulation of AMPK. Increased mTORC1 activity causes inhibition of pyruvate dehydrogenase which reduces pyruvate entry into the tricarboxylic acid cycle and partially accounts for the hyperglycaemia-induced reduction in oxidative phosphorylation and insulin secretion. In addition, hyperglycaemia (or diabetes) dramatically inhibits GAPDH activity, thereby impairing glucose metabolism. Our data also reveal that restricting glucose metabolism during hyperglycaemia prevents these changes and thus may be of therapeutic benefit. In summary, we have identified a pathway by which chronic hyperglycaemia reduces β-cell function.
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Affiliation(s)
- Elizabeth Haythorne
- Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.
| | - Matthew Lloyd
- Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - John Walsby-Tickle
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK
| | - Andrei I Tarasov
- School of Biomedical Sciences, Ulster University, Coleraine, BT52 1SA, Northern Ireland, UK
| | - Jonas Sandbrink
- Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Idoia Portillo
- Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Raul Terron Exposito
- Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.,Institute for Diabetes and Cancer (IDC), Helmholtz Center, Munich, Neuherberg, 85764, Germany
| | - Gregor Sachse
- Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.,Brandenburg Medical School (Theodor Fontane), ZTM-BB, Brandenburg a. d. H, 14770, Germany
| | - Malgorzata Cyranka
- Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Maria Rohm
- Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.,Institute for Diabetes and Cancer (IDC), Helmholtz Center, Munich, Neuherberg, 85764, Germany
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - James McCullagh
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.
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5
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Tremmel DM, Sackett SD, Feeney AK, Mitchell SA, Schaid MD, Polyak E, Chlebeck PJ, Gupta S, Kimple ME, Fernandez LA, Odorico JS. A human pancreatic ECM hydrogel optimized for 3-D modeling of the islet microenvironment. Sci Rep 2022; 12:7188. [PMID: 35504932 PMCID: PMC9065104 DOI: 10.1038/s41598-022-11085-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 04/04/2022] [Indexed: 02/07/2023] Open
Abstract
Extracellular matrix (ECM) plays a multitude of roles, including supporting cells through structural and biochemical interactions. ECM is damaged in the process of isolating human islets for clinical transplantation and basic research. A platform in which islets can be cultured in contact with natural pancreatic ECM is desirable to better understand and support islet health, and to recapitulate the native islet environment. Our study demonstrates the derivation of a practical and durable hydrogel from decellularized human pancreas that supports human islet survival and function. Islets embedded in this hydrogel show increased glucose- and KCl-stimulated insulin secretion, and improved mitochondrial function compared to islets cultured without pancreatic matrix. In extended culture, hydrogel co-culture significantly reduced levels of apoptosis compared to suspension culture and preserved controlled glucose-responsive function. Isolated islets displayed altered endocrine and non-endocrine cell arrangement compared to in situ islets; hydrogel preserved an islet architecture more similar to that observed in situ. RNA sequencing confirmed that gene expression differences between islets cultured in suspension and hydrogel largely fell within gene ontology terms related to extracellular signaling and adhesion. Natural pancreatic ECM improves the survival and physiology of isolated human islets.
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Affiliation(s)
- Daniel M Tremmel
- Division of Transplantation, Department of Surgery, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA.
| | - Sara Dutton Sackett
- Division of Transplantation, Department of Surgery, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA.
| | - Austin K Feeney
- Division of Transplantation, Department of Surgery, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA
| | - Samantha A Mitchell
- Division of Transplantation, Department of Surgery, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA
| | - Michael D Schaid
- Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA.,William S. Middleton Memorial Veterans Hospital, Madison, WI, USA
| | - Erzsebet Polyak
- Division of Transplantation, Department of Surgery, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA
| | - Peter J Chlebeck
- Division of Transplantation, Department of Surgery, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA
| | - Sakar Gupta
- Division of Transplantation, Department of Surgery, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA
| | - Michelle E Kimple
- Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA.,William S. Middleton Memorial Veterans Hospital, Madison, WI, USA
| | | | - Jon S Odorico
- Division of Transplantation, Department of Surgery, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA
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6
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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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7
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Chareyron I, Wall C, Thevenet J, Santo-Domingo J, Wiederkehr A. Cellular stress is a prerequisite for glucose-induced mitochondrial matrix alkalinization in pancreatic β-cells. Mol Cell Endocrinol 2019; 481:71-83. [PMID: 30476561 DOI: 10.1016/j.mce.2018.11.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Revised: 11/20/2018] [Accepted: 11/22/2018] [Indexed: 11/24/2022]
Abstract
Changes in mitochondrial and cytosolic pH alter the chemical gradient across the inner mitochondrial membrane. The proton chemical gradient contributes to mitochondrial ATP synthesis as well as the uptake and release of metabolites and ions from the organelle. Here mitochondrial pH and ΔpH were studied for the first time in human pancreatic β-cells. Adenoviruses were used for rat insulin promoter dependent expression of the pH sensor SypHer targeted to either the mitochondrial matrix or the cytosol. The matrix pH in resting human β-cells is low (pH = 7.50 ± SD 0.17) compared to published values in other cell types. Consequently, the ΔpH of β-cells mitochondria is small. Glucose stimulation consistently resulted in acidification of the matrix pH in INS-1E insulinoma cells and β-cells in intact human islets or islet monolayer cultures. We registered acidification with similar kinetics but of slightly smaller amplitude in the cytosol of β-cells, thus glucose stimulation further reduced the ΔpH. Infection of human islets with high levels of adenoviruses caused the mitochondrial pH to increase. The apoptosis inducer and broad-spectrum kinase inhibitor staurosporine had similar effects on pH homeostasis. Although staurosporine alone does not affect the mitochondrial pH, glucose slightly increases the matrix pH of staurosporine treated cells. These two cellular stressors alter the normal mitochondrial pH response to glucose in pancreatic β-cells.
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Affiliation(s)
- Isabelle Chareyron
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland
| | - Christopher Wall
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland
| | - Jonathan Thevenet
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland
| | - Jaime Santo-Domingo
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland
| | - Andreas Wiederkehr
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland.
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8
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Taddeo EP, Stiles L, Sereda S, Ritou E, Wolf DM, Abdullah M, Swanson Z, Wilhelm J, Bellin M, McDonald P, Caradonna K, Neilson A, Liesa M, Shirihai OS. Individual islet respirometry reveals functional diversity within the islet population of mice and human donors. Mol Metab 2018; 16:150-159. [PMID: 30098928 PMCID: PMC6157638 DOI: 10.1016/j.molmet.2018.07.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Revised: 06/25/2018] [Accepted: 07/01/2018] [Indexed: 11/25/2022] Open
Abstract
OBJECTIVE Islets from the same pancreas show remarkable variability in glucose sensitivity. While mitochondrial respiration is essential for glucose-stimulated insulin secretion, little is known regarding heterogeneity in mitochondrial function at the individual islet level. This is due in part to a lack of high-throughput and non-invasive methods for detecting single islet function. METHODS We have developed a novel non-invasive, high-throughput methodology capable of assessing mitochondrial respiration in large-sized individual islets using the XF96 analyzer (Agilent Technologies). RESULTS By increasing measurement sensitivity, we have reduced the minimal size of mouse and human islets needed to assess mitochondrial respiration to single large islets of >35,000 μm2 area (∼210 μm diameter). In addition, we have measured heterogeneous glucose-stimulated mitochondrial respiration among individual human and mouse islets from the same pancreas, allowing population analyses of islet mitochondrial function for the first time. CONCLUSIONS We have developed a novel methodology capable of analyzing mitochondrial function in large-sized individual islets. By highlighting islet functional heterogeneity, we hope this methodology can significantly advance islet research.
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Affiliation(s)
- Evan P Taddeo
- Department of Medicine, Division of Endocrinology, Diabetes and Hypertension, and Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Center for Health Sciences, 650 Charles E. Young St., Los Angeles, CA 90095, USA
| | - Linsey Stiles
- Department of Medicine, Division of Endocrinology, Diabetes and Hypertension, and Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Center for Health Sciences, 650 Charles E. Young St., Los Angeles, CA 90095, USA
| | - Samuel Sereda
- Department of Medicine, Endocrinology, Diabetes, Nutrition and Weight Management Section, Boston University School of Medicine, 650 Albany St., Room 840, Boston, MA 02118, USA
| | - Eleni Ritou
- Department of Medicine, Division of Endocrinology, Diabetes and Hypertension, and Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Center for Health Sciences, 650 Charles E. Young St., Los Angeles, CA 90095, USA
| | - Dane M Wolf
- Department of Medicine, Division of Endocrinology, Diabetes and Hypertension, and Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Center for Health Sciences, 650 Charles E. Young St., Los Angeles, CA 90095, USA
| | - Muhamad Abdullah
- Department of Surgery and Schulze Diabetes Institute, University of Minnesota School of Medicine, Minneapolis, MN 55455, USA
| | - Zachary Swanson
- Department of Surgery and Schulze Diabetes Institute, University of Minnesota School of Medicine, Minneapolis, MN 55455, USA
| | - Josh Wilhelm
- Department of Surgery and Schulze Diabetes Institute, University of Minnesota School of Medicine, Minneapolis, MN 55455, USA
| | - Melena Bellin
- Department of Pediatrics, Division of Pediatric Endocrinology, University of Minnesota School of Medicine, Minneapolis, MN 55455, USA
| | - Patrick McDonald
- Center for Health Research Innovation, University of Alberta, Edmonton, AB T6G 2E1, Canada
| | | | | | - Marc Liesa
- Department of Medicine, Division of Endocrinology, Diabetes and Hypertension, and Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Center for Health Sciences, 650 Charles E. Young St., Los Angeles, CA 90095, USA.
| | - Orian S Shirihai
- Department of Medicine, Division of Endocrinology, Diabetes and Hypertension, and Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Center for Health Sciences, 650 Charles E. Young St., Los Angeles, CA 90095, USA; Department of Medicine, Endocrinology, Diabetes, Nutrition and Weight Management Section, Boston University School of Medicine, 650 Albany St., Room 840, Boston, MA 02118, USA.
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9
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Liu W, Aerbajinai W, Li H, Liu Y, Gavrilova O, Jain S, Rodgers GP. Olfactomedin 4 Deletion Improves Male Mouse Glucose Intolerance and Insulin Resistance Induced by a High-Fat Diet. Endocrinology 2018; 159:3235-3244. [PMID: 30052841 PMCID: PMC6098226 DOI: 10.1210/en.2018-00451] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Accepted: 07/13/2018] [Indexed: 01/09/2023]
Abstract
Glucose-stimulated insulin secretion (GSIS) is essential for blood glucose homeostasis and is impaired in type 2 diabetes mellitus. Understanding the regulatory components of GSIS has clinical implications for diabetes treatment. In this study, we found that olfactomedin 4 (OLFM4) is endogenously expressed in pancreatic islet β cells and further investigated its potential roles in glucose homeostasis and the pathogenesis of type 2 diabetes using mouse models. Olfm4-deficient mice showed significantly improved glucose tolerance and significantly increased insulin levels after glucose challenge compared with wild-type (WT) mice. GSIS, mitochondrial ATP production, and mitochondrial respiration were all significantly increased in islets isolated from Olfm4-deficient mice compared with those isolated from WT mice. In a high-fat diet (HFD)-induced diabetic mouse model, the increase in insulin levels after glucose challenge was significantly higher in Olfm4-deficient mice compared with WT mice. The impaired glucose tolerance and insulin resistance in HFD-fed mice were improved by loss of Olfm4. Olfm4 was found to be mainly localized in the mitochondria and interacts with GRIM-19 (a gene associated with retinoid-interferon mortality) in Min6 pancreatic β cells. Collectively, these studies suggest that Olfm4 negatively regulates GSIS. OLFM4 may represent a potential therapeutic target for impaired glucose tolerance and patients with type 2 diabetes.
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Affiliation(s)
- Wenli Liu
- Molecular and Clinical Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
- Correspondence: Wenli Liu, MD, Molecular and Clinical Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Building 10, Room 9N113, 9000 Rockville Pike, Bethesda, Maryland 20892. E-mail:
| | - Wulin Aerbajinai
- Molecular and Clinical Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Hongzhen Li
- Molecular and Clinical Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Yueqin Liu
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland
| | - Oksana Gavrilova
- Mouse Metabolism Core, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
| | - Shalini Jain
- Mouse Metabolism Core, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
| | - Griffin P Rodgers
- Molecular and Clinical Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
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10
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Gerencser AA. Metabolic activation-driven mitochondrial hyperpolarization predicts insulin secretion in human pancreatic beta-cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2018; 1859:817-828. [PMID: 29886047 DOI: 10.1016/j.bbabio.2018.06.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Revised: 05/18/2018] [Accepted: 06/05/2018] [Indexed: 12/31/2022]
Abstract
Mitochondrial metabolism plays a central role in insulin secretion in pancreatic beta-cells. Generation of protonmotive force and ATP synthesis from glucose-originated pyruvate are critical steps in the canonical pathway of glucose-stimulated insulin secretion. Mitochondrial metabolism is intertwined with pathways that are thought to amplify insulin secretion with mechanisms distinct from the canonical pathway, and the relative importance of these two pathways is controversial. Here I show that glucose-induced mitochondrial membrane potential (MMP) hyperpolarization is necessary for, and predicts, the rate of insulin secretion in primary cultured human beta-cells. When glucose concentration is elevated, increased metabolism results in a substantial MMP hyperpolarization, as well as in increased rates of ATP synthesis and turnover marked by faster cell respiration. Using modular kinetic analysis I explored what properties of cellular energy metabolism enable a large glucose-induced change in MMP in human beta-cells. I found that an ATP-dependent pathway activates glucose or substrate oxidation, acting as a positive feedback in energy metabolism. This activation mechanism is essential for concomitant fast respiration and high MMP, and for a high magnitude glucose-induced MMP hyperpolarization and therefore for insulin secretion.
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Affiliation(s)
- Akos A Gerencser
- Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, United States; Image Analyst Software, 43 Nova Lane, Novato, CA 94945, United States.
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11
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Mitok KA, Freiberger EC, Schueler KL, Rabaglia ME, Stapleton DS, Kwiecien NW, Malec PA, Hebert AS, Broman AT, Kennedy RT, Keller MP, Coon JJ, Attie AD. Islet proteomics reveals genetic variation in dopamine production resulting in altered insulin secretion. J Biol Chem 2018; 293:5860-5877. [PMID: 29496998 DOI: 10.1074/jbc.ra117.001102] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Revised: 01/29/2018] [Indexed: 12/11/2022] Open
Abstract
The mouse is a critical model in diabetes research, but most research in mice has been limited to a small number of mouse strains and limited genetic variation. Using the eight founder strains and both sexes of the Collaborative Cross (C57BL/6J (B6), A/J, 129S1/SvImJ (129), NOD/ShiLtJ (NOD), NZO/HILtJ (NZO), PWK/PhJ (PWK), WSB/EiJ (WSB), and CAST/EiJ (CAST)), we investigated the genetic dependence of diabetes-related metabolic phenotypes and insulin secretion. We found that strain background is associated with an extraordinary range in body weight, plasma glucose, insulin, triglycerides, and insulin secretion. Our whole-islet proteomic analysis of the eight mouse strains demonstrates that genetic background exerts a strong influence on the islet proteome that can be linked to the differences in diabetes-related metabolic phenotypes and insulin secretion. We computed protein modules consisting of highly correlated proteins that enrich for biological pathways and provide a searchable database of the islet protein expression profiles. To validate the data resource, we identified tyrosine hydroxylase (Th), a key enzyme in catecholamine synthesis, as a protein that is highly expressed in β-cells of PWK and CAST islets. We show that CAST islets synthesize elevated levels of dopamine, which suppresses insulin secretion. Prior studies, using only the B6 strain, concluded that adult mouse islets do not synthesize l-3,4-dihydroxyphenylalanine (l-DOPA), the product of Th and precursor of dopamine. Thus, the choice of the CAST strain, guided by our islet proteomic survey, was crucial for these discoveries. In summary, we provide a valuable data resource to the research community, and show that proteomic analysis identified a strain-specific pathway by which dopamine synthesized in β-cells inhibits insulin secretion.
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Affiliation(s)
| | | | | | | | | | | | - Paige A Malec
- the Department of Chemistry, University of Michigan-Ann Arbor, Ann Arbor, Michigan 48109
| | - Alexander S Hebert
- the Genome Center of Wisconsin, University of Wisconsin-Madison, Madison, Wisconsin 53706 and
| | | | - Robert T Kennedy
- the Department of Chemistry, University of Michigan-Ann Arbor, Ann Arbor, Michigan 48109
| | | | - Joshua J Coon
- Chemistry, and .,the Genome Center of Wisconsin, University of Wisconsin-Madison, Madison, Wisconsin 53706 and
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12
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Bansal A, Rashid C, Xin F, Li C, Polyak E, Duemler A, van der Meer T, Stefaniak M, Wajid S, Doliba N, Bartolomei MS, Simmons RA. Sex- and Dose-Specific Effects of Maternal Bisphenol A Exposure on Pancreatic Islets of First- and Second-Generation Adult Mice Offspring. ENVIRONMENTAL HEALTH PERSPECTIVES 2017; 125:097022. [PMID: 29161229 PMCID: PMC5915189 DOI: 10.1289/ehp1674] [Citation(s) in RCA: 80] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Revised: 07/26/2017] [Accepted: 07/26/2017] [Indexed: 05/17/2023]
Abstract
BACKGROUND Exposure to the environmental endocrine disruptor bisphenol A (BPA) is ubiquitous and associated with the increased risk of diabetes and obesity. However, the underlying mechanisms remain unknown. We recently demonstrated that perinatal BPA exposure is associated with higher body fat, impaired glucose tolerance, and reduced insulin secretion in first- (F1) and second-generation (F2) C57BL/6J male mice offspring. OBJECTIVE We sought to determine the multigenerational effects of maternal bisphenol A exposure on mouse pancreatic islets. METHODS Cellular and molecular mechanisms underlying these persistent changes were determined in F1 and F2 adult offspring of F0 mothers exposed to two relevant human exposure levels of BPA (10μg/kg/d-LowerB and 10mg/kg/d-UpperB). RESULTS Both doses of BPA significantly impaired insulin secretion in male but not female F1 and F2 offspring. Surprisingly, LowerB and UpperB induced islet inflammation in male F1 offspring that persisted into the next generation. We also observed dose-specific effects of BPA on islets in males. UpperB exposure impaired mitochondrial function, whereas LowerB exposure significantly reduced β-cell mass and increased β-cell death that persisted in the F2 generation. Transcriptome analyses supported these physiologic findings and there were significant dose-specific changes in the expression of genes regulating inflammation and mitochondrial function. Previously we observed increased expression of the critically important β-cell gene, Igf2 in whole F1 embryos. Surprisingly, increased Igf2 expression persisted in the islets of male F1 and F2 offspring and was associated with altered DNA methylation. CONCLUSION These findings demonstrate that maternal BPA exposure has dose- and sex-specific effects on pancreatic islets of adult F1 and F2 mice offspring. The transmission of these changes across multiple generations may involve either mitochondrial dysfunction and/or epigenetic modifications. https://doi.org/10.1289/EHP1674.
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Affiliation(s)
- Amita Bansal
- Center for Research on Reproduction and Women's Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Center of Excellence in Environmental Toxicology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Division of Neonatology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Cetewayo Rashid
- Center for Research on Reproduction and Women's Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Center of Excellence in Environmental Toxicology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Division of Neonatology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Frances Xin
- Center of Excellence in Environmental Toxicology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Epigenetics Institute, Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Changhong Li
- Division of Endocrinology and Diabetes, Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Erzsebet Polyak
- Division of Human Genetics, Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Anna Duemler
- Center for Research on Reproduction and Women's Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Eberly College of Science, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Tom van der Meer
- Center for Research on Reproduction and Women's Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Department of Pediatrics, University of Groningen, Groningen, Netherlands
| | - Martha Stefaniak
- Epigenetics Institute, Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Sana Wajid
- Exposure Biology Informatics Core, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Nicolai Doliba
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Marisa S Bartolomei
- Center for Research on Reproduction and Women's Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Center of Excellence in Environmental Toxicology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Epigenetics Institute, Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Rebecca A Simmons
- Center for Research on Reproduction and Women's Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Center of Excellence in Environmental Toxicology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Division of Neonatology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
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Abstract
The pancreatic β-cell secretes insulin in response to elevated plasma glucose. This review applies an external bioenergetic critique to the central processes of glucose-stimulated insulin secretion, including glycolytic and mitochondrial metabolism, the cytosolic adenine nucleotide pool, and its interaction with plasma membrane ion channels. The control mechanisms responsible for the unique responsiveness of the cell to glucose availability are discussed from bioenergetic and metabolic control standpoints. The concept of coupling factor facilitation of secretion is critiqued, and an attempt is made to unravel the bioenergetic basis of the oscillatory mechanisms controlling secretion. The need to consider the physiological constraints operating in the intact cell is emphasized throughout. The aim is to provide a coherent pathway through an extensive, complex, and sometimes bewildering literature, particularly for those unfamiliar with the field.
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Affiliation(s)
- David G Nicholls
- Buck Institute for Research on Aging, Novato, California; and Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, Malmo, Sweden
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14
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De Marchi U, Hermant A, Thevenet J, Ratinaud Y, Santo-Domingo J, Barron D, Wiederkehr A. A novel ATP-synthase-independent mechanism coupling mitochondrial activation to exocytosis in insulin-secreting cells. J Cell Sci 2017; 130:1929-1939. [PMID: 28404787 DOI: 10.1242/jcs.200741] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 04/11/2017] [Indexed: 12/16/2022] Open
Abstract
Pancreatic β-cells sense glucose, promoting insulin secretion. Glucose sensing requires the sequential stimulation of glycolysis, mitochondrial metabolism and Ca2+ entry. To elucidate how mitochondrial activation in β-cells contributes to insulin secretion, we compared the effects of glucose and the mitochondrial substrate methylsuccinate in the INS-1E insulin-secreting cell line at the respective concentrations at which they maximally activate mitochondrial respiration. Both substrates induced insulin secretion with distinct respiratory profiles, mitochondrial hyperpolarization, NADH production and ATP-to-ADP ratios. In contrast to glucose, methylsuccinate failed to induce large [Ca2+] rises and exocytosis proceeded largely independently of mitochondrial ATP synthesis. Both glucose- and methylsuccinate-induced secretion was blocked by diazoxide, indicating that Ca2+ is required for exocytosis. Dynamic assessment of the redox state of mitochondrial thiols revealed a less marked reduction in response to methylsuccinate than with glucose. Our results demonstrate that insulin exocytosis can be promoted by two distinct mechanisms one of which is dependent on mitochondrial ATP synthesis and large Ca2+ transients, and one of which is independent of mitochondrial ATP synthesis and relies on small Ca2+ signals. We propose that the combined effects of Ca2+ and redox reactions can trigger insulin secretion by these two mechanisms.
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Affiliation(s)
- Umberto De Marchi
- Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland
| | - Aurelie Hermant
- Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland
| | - Jonathan Thevenet
- Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland
| | - Yann Ratinaud
- Natural Bioactives and screening, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building H, Lausanne CH-1015, Switzerland
| | - Jaime Santo-Domingo
- Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland
| | - Denis Barron
- Natural Bioactives and screening, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building H, Lausanne CH-1015, Switzerland
| | - Andreas Wiederkehr
- Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland
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15
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Gerencser AA, Mookerjee SA, Jastroch M, Brand MD. Positive Feedback Amplifies the Response of Mitochondrial Membrane Potential to Glucose Concentration in Clonal Pancreatic Beta Cells. Biochim Biophys Acta Mol Basis Dis 2016; 1863:1054-1065. [PMID: 27771512 DOI: 10.1016/j.bbadis.2016.10.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2016] [Revised: 10/16/2016] [Accepted: 10/18/2016] [Indexed: 02/07/2023]
Abstract
Analysis of the cellular mechanisms of metabolic disorders, including type 2 diabetes mellitus, is complicated by the large number of reactions and interactions in metabolic networks. Metabolic control analysis with appropriate modularization is a powerful method for simplifying and analyzing these networks. To analyze control of cellular energy metabolism in adherent cell cultures of the INS-1 832/13 pancreatic β-cell model we adapted our microscopy assay of absolute mitochondrial membrane potential (ΔψM) to a fluorescence microplate reader format, and applied it in conjunction with cell respirometry. In these cells the sensitive response of ΔψM to extracellular glucose concentration drives glucose-stimulated insulin secretion. Using metabolic control analysis we identified the control properties that generate this sensitive response. Force-flux relationships between ΔψM and respiration were used to calculate kinetic responses to ΔψM of processes both upstream (glucose oxidation) and downstream (proton leak and ATP turnover) of ΔψM. The analysis revealed that glucose-evoked ΔψM hyperpolarization is amplified by increased glucose oxidation activity caused by factors downstream of ΔψM. At high glucose, the hyperpolarized ΔψM is stabilized almost completely by the action of glucose oxidation, whereas proton leak also contributes to the homeostatic control of ΔψM at low glucose. These findings suggest a strong positive feedback loop in the regulation of β-cell energetics, and a possible regulatory role of proton leak in the fasting state. Analysis of islet bioenergetics from published cases of type 2 diabetes suggests that disruption of this feedback can explain the damaged bioenergetic response of β-cells to glucose. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.
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Affiliation(s)
- Akos A Gerencser
- Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, United States; Image Analyst Software, 43 Nova Lane, Novato, CA 94945, United States.
| | - Shona A Mookerjee
- Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, United States; Touro University California College of Pharmacy, 1310 Club Drive, Vallejo, CA 94592, United States
| | - Martin Jastroch
- Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, United States
| | - Martin D Brand
- Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, United States
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16
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Gerencser AA, Mookerjee SA, Jastroch M, Brand MD. Measurement of the Absolute Magnitude and Time Courses of Mitochondrial Membrane Potential in Primary and Clonal Pancreatic Beta-Cells. PLoS One 2016; 11:e0159199. [PMID: 27404273 PMCID: PMC4942067 DOI: 10.1371/journal.pone.0159199] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 06/28/2016] [Indexed: 12/22/2022] Open
Abstract
The aim of this study was to simplify, improve and validate quantitative measurement of the mitochondrial membrane potential (ΔψM) in pancreatic β-cells. This built on our previously introduced calculation of the absolute magnitude of ΔψM in intact cells, using time-lapse imaging of the non-quench mode fluorescence of tetramethylrhodamine methyl ester and a bis-oxonol plasma membrane potential (ΔψP) indicator. ΔψM is a central mediator of glucose-stimulated insulin secretion in pancreatic β-cells. ΔψM is at the crossroads of cellular energy production and demand, therefore precise assay of its magnitude is a valuable tool to study how these processes interplay in insulin secretion. Dispersed islet cell cultures allowed cell type-specific, single-cell observations of cell-to-cell heterogeneity of ΔψM and ΔψP. Glucose addition caused hyperpolarization of ΔψM and depolarization of ΔψP. The hyperpolarization was a monophasic step increase, even in cells where the ΔψP depolarization was biphasic. The biphasic response of ΔψP was associated with a larger hyperpolarization of ΔψM than the monophasic response. Analysis of the relationships between ΔψP and ΔψM revealed that primary dispersed β-cells responded to glucose heterogeneously, driven by variable activation of energy metabolism. Sensitivity analysis of the calibration was consistent with β-cells having substantial cell-to-cell variations in amounts of mitochondria, and this was predicted not to impair the accuracy of determinations of relative changes in ΔψM and ΔψP. Finally, we demonstrate a significant problem with using an alternative ΔψM probe, rhodamine 123. In glucose-stimulated and oligomycin-inhibited β-cells the principles of the rhodamine 123 assay were breached, resulting in misleading conclusions.
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Affiliation(s)
- Akos A. Gerencser
- Buck Institute for Research on Aging, Novato, California, United States of America
- Image Analyst Software, Novato, California, United States of America
| | - Shona A. Mookerjee
- Buck Institute for Research on Aging, Novato, California, United States of America
- Touro University California College of Pharmacy, Vallejo, California, United States of America
| | - Martin Jastroch
- Buck Institute for Research on Aging, Novato, California, United States of America
| | - Martin D. Brand
- Buck Institute for Research on Aging, Novato, California, United States of America
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17
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Tomita T. Apoptosis in pancreatic β-islet cells in Type 2 diabetes. Bosn J Basic Med Sci 2016; 16:162-79. [PMID: 27209071 DOI: 10.17305/bjbms.2016.919] [Citation(s) in RCA: 109] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 01/16/2016] [Accepted: 01/20/2016] [Indexed: 12/25/2022] Open
Abstract
Apoptosis plays important roles in the pathophysiology of Type 2 diabetes mellitus (T2DM). The etiology of T2DM is multifactorial, including obesity-associated insulin resistance, defective insulin secretion, and loss of β-cell mass through β-cell apoptosis. β-cell apoptosis is mediated through a milliard of caspase family cascade machinery in T2DM. The glucose-induced insulin secretion is the principle pathophysiology of diabetes and insufficient insulin secretion results in chronic hyperglycemia, diabetes. Recently, hyperglycemia-induced β-cell apoptosis has been extensively studied on the balance of pro-apoptotic Bcl-2 proteins (Bad, Bid, Bik, and Bax) and anti-apoptotic Bcl family (Bcl-2 and Bcl-xL) toward apoptosis in vitro isolated islets and insulinoma cell culture. Apoptosis can only occur when the concentration of pro-apoptotic Bcl-2 exceeds that of anti-apoptotic proteins at the mitochondrial membrane of the intrinsic pathway. A bulk of recent research on hyperglycemia-induced apoptosis on β-cells unveiled complex details on glucose toxicity on β-cells in molecular levels coupled with cell membrane potential by adenosine triphosphate generation through K+ channel closure, opening Ca2+ channel and plasma membrane depolarization. Furthermore, animal models using knockout mice will shed light on the basic understanding of the pathophysiology of diabetes as a glucose metabolic disease complex, on the balance of anti-apoptotic Bcl family and pro-apoptotic genes. The cumulative knowledge will provide a better understanding of glucose metabolism at a molecular level and will lead to eventual prevention and therapeutic application for T2DM with improving medications.
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18
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Gwóźdź K, Szkudelski T, Szkudelska K. Characteristics of metabolic changes in adipocytes of growing rats. Biochimie 2016; 125:195-203. [PMID: 27060433 DOI: 10.1016/j.biochi.2016.04.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 04/01/2016] [Indexed: 12/11/2022]
Abstract
Adipocytes, cells of white fat tissue, store energy in the form of lipids and have also endocrine functions. Disturbances in adipocyte metabolism lead to decreased or excessive fat tissue accumulation and are associated with numerous diseases. Pathologic alterations in adipose tissue are known to develop with age, however, changes in young, growing subjects are poorly elucidated. In the present study, glucose transport and metabolism, hyperpolarization of the inner mitochondrial membrane and the lipolytic activity were compared in the epididymal adipocytes of 8-week-old and 16-week-old rats. It was demonstrated that glucose conversion to lipids, glucose transport and oxidation was decreased in the adipocytes of the older animals. These effects were accompanied by increase in lactate release and by decrease in hyperpolarization of the mitochondrial membrane. Lipolytic response to epinephrine was increased (at lower concentrations of the hormone) or reduced (at higher concentration) in the adipocytes of the older rats. However, induction of lipolysis by the direct activation of protein kinase A induced similar response. It was also demonstrated that inhibition of phosphodiesterase 3B or adenosine A1 receptor blocking caused lower lipolysis in the cells of the older rats. Moreover, antilipolytic action of insulin was impaired in the adipocytes of these rats, probably due to changes in the initial steps of the insulin signaling pathway. However, the use of the pharmacologic inhibitor of protein kinase A instead of insulin resulted in similar antilipolysis in both groups of cells. These results show that, in spite of relatively small age difference, substantial changes in adipose tissue metabolism develop in these animals. Decreased response to insulin action seems to be particularly relevant finding.
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Affiliation(s)
- Kinga Gwóźdź
- Department of Animal Physiology and Biochemistry, Poznan University of Life Sciences, Wolynska 35, 60-637 Poznan, Poland
| | - Tomasz Szkudelski
- Department of Animal Physiology and Biochemistry, Poznan University of Life Sciences, Wolynska 35, 60-637 Poznan, Poland
| | - Katarzyna Szkudelska
- Department of Animal Physiology and Biochemistry, Poznan University of Life Sciences, Wolynska 35, 60-637 Poznan, Poland.
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Gerencser AA. Bioenergetic Analysis of Single Pancreatic β-Cells Indicates an Impaired Metabolic Signature in Type 2 Diabetic Subjects. Endocrinology 2015. [PMID: 26204464 DOI: 10.1210/en.2015-1552] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Impaired activation of mitochondrial energy metabolism by glucose has been demonstrated in type 2 diabetic β-cells. The cause of this dysfunction is unknown. The aim of this study was to identify segments of energy metabolism with normal or with altered function in human type 2 diabetes mellitus. The mitochondrial membrane potential (ΔψM), and its response to glucose, is the main driver of mitochondrial ATP synthesis and is hence a central mediator of glucose-induced insulin secretion, but its quantitative determination in β-cells from human donors has not been attempted, due to limitations in assay technology. Here, novel fluorescence microscopic assays are exploited to quantify ΔψM and its response to glucose and other secretagogues in β-cells of dispersed pancreatic islet cells from 4 normal and 3 type 2 diabetic organ donors. Mitochondrial volume densities and the magnitude of ΔψM in low glucose were not consistently altered in diabetic β-cells. However, ΔψM was consistently less responsive to elevation of glucose concentration, whereas the decreased response was not observed with metabolizable secretagogue mixtures that feed directly into the tricarboxylic acid cycle. Single-cell analysis of the heterogeneous responses to metabolizable secretagogues indicated no dysfunction in relaying ΔψM hyperpolarization to plasma membrane potential depolarization in diabetic β-cells. ΔψM of diabetic β-cells was distinctly responsive to acute inhibition of ATP synthesis during glucose stimulation. It is concluded that the mechanistic deficit in glucose-induced insulin secretion and mitochondrial hyperpolarization of diabetic human β-cells is located upstream of the tricarboxylic acid cycle and manifests in dampening the control of ΔψM by glucose metabolism.
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Affiliation(s)
- Akos A Gerencser
- Buck Institute for Research on Aging and Image Analyst Software, Novato, California 94945; and College of Pharmacy, Touro University California, Vallejo, California 94592
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20
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Andersson LE, Valtat B, Bagge A, Sharoyko VV, Nicholls DG, Ravassard P, Scharfmann R, Spégel P, Mulder H. Characterization of stimulus-secretion coupling in the human pancreatic EndoC-βH1 beta cell line. PLoS One 2015; 10:e0120879. [PMID: 25803449 PMCID: PMC4372368 DOI: 10.1371/journal.pone.0120879] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Accepted: 02/09/2015] [Indexed: 02/07/2023] Open
Abstract
Aims/Hypothesis Studies on beta cell metabolism are often conducted in rodent beta cell lines due to the lack of stable human beta cell lines. Recently, a human cell line, EndoC-βH1, was generated. Here we investigate stimulus-secretion coupling in this cell line, and compare it with that in the rat beta cell line, INS-1 832/13, and human islets. Methods Cells were exposed to glucose and pyruvate. Insulin secretion and content (radioimmunoassay), gene expression (Gene Chip array), metabolite levels (GC/MS), respiration (Seahorse XF24 Extracellular Flux Analyzer), glucose utilization (radiometric), lactate release (enzymatic colorimetric), ATP levels (enzymatic bioluminescence) and plasma membrane potential and cytoplasmic Ca2+ responses (microfluorometry) were measured. Metabolite levels, respiration and insulin secretion were examined in human islets. Results Glucose increased insulin release, glucose utilization, raised ATP production and respiratory rates in both lines, and pyruvate increased insulin secretion and respiration. EndoC-βH1 cells exhibited higher insulin secretion, while plasma membrane depolarization was attenuated, and neither glucose nor pyruvate induced oscillations in intracellular calcium concentration or plasma membrane potential. Metabolite profiling revealed that glycolytic and TCA-cycle intermediate levels increased in response to glucose in both cell lines, but responses were weaker in EndoC-βH1 cells, similar to those observed in human islets. Respiration in EndoC-βH1 cells was more similar to that in human islets than in INS-1 832/13 cells. Conclusions/Interpretation Functions associated with early stimulus-secretion coupling, with the exception of plasma membrane potential and Ca2+ oscillations, were similar in the two cell lines; insulin secretion, respiration and metabolite responses were similar in EndoC-βH1 cells and human islets. While both cell lines are suitable in vitro models, with the caveat of replicating key findings in isolated islets, EndoC-βH1 cells have the advantage of carrying the human genome, allowing studies of human genetic variants, epigenetics and regulatory RNA molecules.
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Affiliation(s)
- Lotta E. Andersson
- Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, CRC, Malmö, Sweden
- * E-mail:
| | - Bérengère Valtat
- Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, CRC, Malmö, Sweden
| | - Annika Bagge
- Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, CRC, Malmö, Sweden
| | - Vladimir V. Sharoyko
- Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, CRC, Malmö, Sweden
| | - David G. Nicholls
- Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, CRC, Malmö, Sweden
- Buck Institute for Research on Aging, Novato, California, United States of America
| | - Philippe Ravassard
- Université Pierre et Marie Curie-Paris 6, Biotechnology and Biotherapy Team, Centre de Recherche de I’Institut du Cerveau et de la Moelle épiniére (CRICM), UMRS 975, Paris, France
| | - Raphael Scharfmann
- INSERM U1016, Cochin Institute, Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine, Faculty Cochin, Paris, France
| | - Peter Spégel
- Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, CRC, Malmö, Sweden
| | - Hindrik Mulder
- Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, CRC, Malmö, Sweden
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Luo X, Li R, Yan LJ. Roles of Pyruvate, NADH, and Mitochondrial Complex I in Redox Balance and Imbalance in β Cell Function and Dysfunction. J Diabetes Res 2015; 2015:512618. [PMID: 26568959 PMCID: PMC4629043 DOI: 10.1155/2015/512618] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Revised: 11/26/2014] [Accepted: 11/27/2014] [Indexed: 12/25/2022] Open
Abstract
Pancreatic β cells not only use glucose as an energy source, but also sense blood glucose levels for insulin secretion. While pyruvate and NADH metabolic pathways are known to be involved in regulating insulin secretion in response to glucose stimulation, the roles of many other components along the metabolic pathways remain poorly understood. Such is the case for mitochondrial complex I (NADH/ubiquinone oxidoreductase). It is known that normal complex I function is absolutely required for episodic insulin secretion after a meal, but the role of complex I in β cells in the diabetic pancreas remains to be investigated. In this paper, we review the roles of pyruvate, NADH, and complex I in insulin secretion and hypothesize that complex I plays a crucial role in the pathogenesis of β cell dysfunction in the diabetic pancreas. This hypothesis is based on the establishment that chronic hyperglycemia overloads complex I with NADH leading to enhanced complex I production of reactive oxygen species. As nearly all metabolic pathways are impaired in diabetes, understanding how complex I in the β cells copes with elevated levels of NADH in the diabetic pancreas may provide potential therapeutic strategies for diabetes.
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Affiliation(s)
- Xiaoting Luo
- Department of Pharmaceutical Sciences, UNT System College of Pharmacy, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
- Department of Biochemistry and Molecular Biology, Gannan Medical University, Ganzhou, Jiangxi 341000, China
| | - Rongrong Li
- Department of Pharmaceutical Sciences, UNT System College of Pharmacy, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
| | - Liang-Jun Yan
- Department of Pharmaceutical Sciences, UNT System College of Pharmacy, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
- *Liang-Jun Yan:
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Ogata M, Iwasaki N, Ide R, Takizawa M, Uchigata Y. GLP-1-related proteins attenuate the effects of mitochondrial membrane damage in pancreatic β cells. Biochem Biophys Res Commun 2014; 447:133-8. [DOI: 10.1016/j.bbrc.2014.03.143] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 03/25/2014] [Indexed: 12/25/2022]
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Kim C, Patel P, Gouvin LM, Brown ML, Khalil A, Henchey EM, Heuck AP, Yadava N. Comparative Analysis of the Mitochondrial Physiology of Pancreatic β Cells. ACTA ACUST UNITED AC 2014; 3:110. [PMID: 25309834 DOI: 10.4172/2167-7662.1000110] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The mitochondrial metabolism of β cells is thought to be highly specialized. Its direct comparison with other cells using isolated mitochondria is limited by the availability of islets/β cells in sufficient quantity. In this study, we have compared mitochondrial metabolism of INS1E/β cells with other cells in intact and permeabilized states. To selectively permeabilize the plasma membrane, we have evaluated the use of perfringolysin-O (PFO) in conjunction with microplate-based respirometry. PFO is a protein that binds membranes based on a threshold level of active cholesterol. Therefore, unless active cholesterol reaches a threshold level in mitochondria, they are expected to remain untouched by PFO. Cytochrome c sensitivity tests showed that in PFO-permeabilized cells, the mitochondrial integrity was completely preserved. Our data show that a time-dependent decline of the oligomycin-insensitive respiration observed in INS1E cells was due to a limitation in substrate supply to the respiratory chain. We predict that it is linked with the β cell-specific metabolism involving metabolites shuttling between the cytoplasm and mitochondria. In permeabilized β cells, the Complex l-dependent respiration was either transient or absent because of the inefficient TCA cycle. The TCA cycle insufficiency was confirmed by analysis of the CO2 evolution. This may be linked with lower levels of NAD+, which is required as a co-factor for CO2 producing reactions of the TCA cycle. β cells showed comparable OxPhos and respiratory capacities that were not affected by the inorganic phosphate (Pi) levels in the respiration medium. They showed lower ADP-stimulation of the respiration on different substrates. We believe that this study will significantly enhance our understanding of the β cell mitochondrial metabolism.
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Affiliation(s)
- Chul Kim
- Pioneer Valley Life Sciences Institute, Springfield, MA, USA
| | - Pinal Patel
- Pioneer Valley Life Sciences Institute, Springfield, MA, USA
| | - Lindsey M Gouvin
- Departments of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA, USA
| | - Melissa L Brown
- Pioneer Valley Life Sciences Institute, Springfield, MA, USA
| | - Ahmed Khalil
- Department of Biology, University of Massachusetts, Amherst, MA, USA
| | | | - Alejandro P Heuck
- Departments of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA, USA
| | - Nagendra Yadava
- Pioneer Valley Life Sciences Institute, Springfield, MA, USA ; Department of Biology, University of Massachusetts, Amherst, MA, USA ; Division of Endocrinology, Diabetes & Metabolism at Baystate Medical Center of Tufts University School of Medicine, Springfield, MA, USA
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Zippin JH, Chen Y, Straub SG, Hess KC, Diaz A, Lee D, Tso P, Holz GG, Sharp GWG, Levin LR, Buck J. CO2/HCO3(-)- and calcium-regulated soluble adenylyl cyclase as a physiological ATP sensor. J Biol Chem 2013; 288:33283-91. [PMID: 24100033 DOI: 10.1074/jbc.m113.510073] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The second messenger molecule cAMP is integral for many physiological processes. In mammalian cells, cAMP can be generated from hormone- and G protein-regulated transmembrane adenylyl cyclases or via the widely expressed and structurally and biochemically distinct enzyme soluble adenylyl cyclase (sAC). sAC activity is uniquely stimulated by bicarbonate ions, and in cells, sAC functions as a physiological carbon dioxide, bicarbonate, and pH sensor. sAC activity is also stimulated by calcium, and its affinity for its substrate ATP suggests that it may be sensitive to physiologically relevant fluctuations in intracellular ATP. We demonstrate here that sAC can function as a cellular ATP sensor. In cells, sAC-generated cAMP reflects alterations in intracellular ATP that do not affect transmembrane AC-generated cAMP. In β cells of the pancreas, glucose metabolism generates ATP, which corresponds to an increase in cAMP, and we show here that sAC is responsible for an ATP-dependent cAMP increase. Glucose metabolism also elicits insulin secretion, and we further show that sAC is necessary for normal glucose-stimulated insulin secretion in vitro and in vivo.
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25
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Sinha K, Das J, Pal PB, Sil PC. Oxidative stress: the mitochondria-dependent and mitochondria-independent pathways of apoptosis. Arch Toxicol 2013; 87:1157-80. [PMID: 23543009 DOI: 10.1007/s00204-013-1034-4] [Citation(s) in RCA: 1109] [Impact Index Per Article: 100.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Accepted: 02/28/2013] [Indexed: 12/15/2022]
Abstract
Oxidative stress basically defines a condition in which prooxidant-antioxidant balance in the cell is disturbed; cellular biomolecules undergo severe oxidative damage, ultimately compromising cells viability. In recent years, a number of studies have shown that oxidative stress could cause cellular apoptosis via both the mitochondria-dependent and mitochondria-independent pathways. Since these pathways are directly related to the survival or death of various cell types in normal as well as pathophysiological situations, a clear picture of these pathways for various active molecules in their biological functions would help designing novel therapeutic strategy. This review highlights the basic mechanisms of ROS production and their sites of formation; detail mechanism of both mitochondria-dependent and mitochondria-independent pathways of apoptosis as well as their regulation by ROS. Emphasis has been given on the redox-sensitive ASK1 signalosome and its downstream JNK pathway. This review also describes the involvement of oxidative stress under various environmental toxin- and drug-induced organ pathophysiology and diabetes-mediated apoptosis. We believe that this review would provide useful information about the most recent progress in understanding the mechanism of oxidative stress-mediated regulation of apoptotic pathways. It will also help to figure out the complex cross-talks between these pathways and their modulations by oxidative stress. The literature will also shed a light on the blind alleys of this field to be explored. Finally, readers would know about the ROS-regulated and apoptosis-mediated organ pathophysiology which might help to find their probable remedies in future.
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Affiliation(s)
- Krishnendu Sinha
- Division of Molecular Medicine, Bose Institute, P-1/12, CIT Scheme VII M, Calcutta 700054, West Bengal, India
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26
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Abstract
In the endocrine fraction of the pancreas, the task of the beta-cell is to continuously and perfectly adjust insulin secretion to fluctuating blood glucose levels, thereby maintaining glycemia and nutrient homeostasis. This glucose sensing coupled to insulin exocytosis depends on transduction of metabolic signals into intracellular messengers recognized by the exocytotic machinery. Central to this metabolism-secretion coupling, mitochondrial signal transduction refers to both integration and generation of metabolic signals, connecting glucose sensing to insulin exocytosis. In response to a glucose rise, nucleotides and metabolites are generated by mitochondria and participate, together with cytosolic calcium, in the stimulation of insulin release. This review describes the role of mitochondria in metabolic signal transduction regulating insulin secretion.
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Affiliation(s)
- Pierre Maechler
- Department of Cell Physiology and Metabolism, University of Geneva Medical Centre, rue Michel-Servet 1, CH-1211 Geneva 4, Switzerland.
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27
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Abstract
The 'thrifty phenotype' hypothesis proposes that the fetus adapts to an adverse intrauterine milieu by optimizing the use of a reduced nutrient supply to ensure survival, but by favoring the development of certain organs over that of others, this leads to persistent alterations in the growth and function of developing tissues. This concept has been somewhat controversial, however recent epidemiological, clinical, and animal studies provide support for the developmental origins of disease hypothesis. Underlying mechanisms include reprogramming of the hypothalamic-pituitary-adrenal axis, islet development, and insulin signaling pathways. Emerging data suggests that oxidative stress and mitochondrial dysfunction may also play a critical role in the pathogenesis of type 2 diabetes in individuals who were growth retarded at birth.
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Affiliation(s)
- Rebecca A Simmons
- Department of Pediatrics, Children's Hospital Philadelphia and University of Pennsylvania, Philadelphia, Philadelphia, PA 19104, USA.
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Supale S, Li N, Brun T, Maechler P. Mitochondrial dysfunction in pancreatic β cells. Trends Endocrinol Metab 2012; 23:477-87. [PMID: 22766318 DOI: 10.1016/j.tem.2012.06.002] [Citation(s) in RCA: 182] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Revised: 06/02/2012] [Accepted: 06/02/2012] [Indexed: 12/17/2022]
Abstract
In pancreatic β cells, mitochondria play a central role in coupling glucose metabolism to insulin exocytosis, thereby ensuring strict control of glucose-stimulated insulin secretion. Defects in mitochondrial function impair this metabolic coupling, and ultimately promote apoptosis and β cell death. Various factors have been identified that may contribute to mitochondrial dysfunction. In this review we address the emerging concept of complex links between these factors. We also discuss the role of the mitochondrial genome and mutations associated with diabetes, the effect of oxidative stress and reactive oxygen species, the sensitivity of mitochondria to lipotoxicity, and the adaptive dynamics of mitochondrial morphology. Better comprehension of the molecular mechanisms contributing to mitochondrial dysfunction will help drive the development of effective therapeutic approaches.
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Affiliation(s)
- Sachin Supale
- Department of Cell Physiology and Metabolism, University of Geneva Medical Centre, 1211 Geneva 4, Switzerland
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Akhmedov D, De Marchi U, Wollheim CB, Wiederkehr A. Pyruvate dehydrogenase E1α phosphorylation is induced by glucose but does not control metabolism-secretion coupling in INS-1E clonal β-cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1823:1815-24. [PMID: 22809973 DOI: 10.1016/j.bbamcr.2012.07.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2012] [Revised: 06/25/2012] [Accepted: 07/09/2012] [Indexed: 12/24/2022]
Abstract
Glucose-induced insulin secretion from pancreatic β-cells depends on mitochondrial activation. In the organelle, glucose-derived pyruvate is metabolised along the oxidative and anaplerotic pathway to generate downstream signals leading to insulin granule exocytosis. Entry into the oxidative pathway is catalysed by pyruvate dehydrogenase (PDH) and controlled in part by phosphorylation of the PDH E1α subunit blocking enzyme activity. We find that glucose but not other nutrient secretagogues induce PDH E1α phosphorylation in INS-1E cells and rat islets. INS-1E cells and primary β-cells express pyruvate dehydrogenase kinase (PDK) 1, 2 and 3, which mediate the observed phosphorylation. In INS-1E cells, suppression of the two main isoforms, PDK1 and PDK3, almost completely prevented PDH E1α phosphorylation. Under basal glucose conditions, phosphorylation was barely detectable and therefore the enzyme almost fully active (90% of maximal). During glucose stimulation, PDH is only partially inhibited (to 78% of maximal). Preventing PDH phosphorylation in situ after suppression of PDK1, 2 and 3 neither enhanced pyruvate oxidation nor insulin secretion. In conclusion, although glucose stimulates E1α phosphorylation and therefore inhibits PDH activity, this control mechanism by itself does not alter metabolism-secretion coupling in INS-1E clonal β-cells.
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Affiliation(s)
- Dmitry Akhmedov
- Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
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30
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Goehring I, Gerencser AA, Schmidt S, Brand MD, Mulder H, Nicholls DG. Plasma membrane potential oscillations in insulin secreting Ins-1 832/13 cells do not require glycolysis and are not initiated by fluctuations in mitochondrial bioenergetics. J Biol Chem 2012; 287:15706-17. [PMID: 22418435 DOI: 10.1074/jbc.m111.314567] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Oscillations in plasma membrane potential play a central role in glucose-induced insulin secretion from pancreatic β-cells and related insulinoma cell lines. We have employed a novel fluorescent plasma membrane potential (Δψ(p)) indicator in combination with indicators of cytoplasmic free Ca(2+) ([Ca(2+)](c)), mitochondrial membrane potential (Δψ(m)), matrix ATP concentration, and NAD(P)H fluorescence to investigate the role of mitochondria in the generation of plasma membrane potential oscillations in clonal INS-1 832/13 β-cells. Elevated glucose caused oscillations in plasma membrane potential and cytoplasmic free Ca(2+) concentration over the same concentration range required for insulin release, although considerable cell-to-cell heterogeneity was observed. Exogenous pyruvate was as effective as glucose in inducing oscillations, both in the presence and absence of 2.8 mM glucose. Increased glucose and pyruvate each produced a concentration-dependent mitochondrial hyperpolarization. The causal relationships between pairs of parameters (Δψ(p) and [Ca(2+)](c), Δψ(p) and NAD(P)H, matrix ATP and [Ca(2+)](c), and Δψ(m) and [Ca(2+)](c)) were investigated at single cell level. It is concluded that, in these β-cells, depolarizing oscillations in Δψ(p) are not initiated by mitochondrial bioenergetic changes. Instead, regardless of substrate, it appears that the mitochondria may simply be required to exceed a critical bioenergetic threshold to allow release of insulin. Once this threshold is exceeded, an autonomous Δψ(p) oscillatory mechanism is initiated.
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Cline GW. Fuel-Stimulated Insulin Secretion Depends upon Mitochondria Activation and the Integration of Mitochondrial and Cytosolic Substrate Cycles. Diabetes Metab J 2011; 35:458-65. [PMID: 22111036 PMCID: PMC3221020 DOI: 10.4093/dmj.2011.35.5.458] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The pancreatic islet β-cell is uniquely specialized to couple its metabolism and rates of insulin secretion with the levels of circulating nutrient fuels, with the mitochondrial playing a central regulatory role in this process. In the β-cell, mitochondrial activation generates an integrated signal reflecting rates of oxidativephosphorylation, Kreb's cycle flux, and anaplerosis that ultimately determines the rate of insulin exocytosis. Mitochondrial activation can be regulated by proton leak and mediated by UCP2, and by alkalinization to utilize the pH gradient to drive substrate and ion transport. Converging lines of evidence support the hypothesis that substrate cycles driven by rates of Kreb's cycle flux and by anaplerosis play an integral role in coupling responsive changes in mitochondrial metabolism with insulin secretion. The components and mechanisms that account for the integrated signal of ATP production, substrate cycling, the regulation of cellular redox state, and the production of other secondary signaling intermediates are operative in both rodent and human islet β-cells.
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Affiliation(s)
- Gary W. Cline
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
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32
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Karaca M, Frigerio F, Maechler P. From pancreatic islets to central nervous system, the importance of glutamate dehydrogenase for the control of energy homeostasis. Neurochem Int 2011; 59:510-7. [DOI: 10.1016/j.neuint.2011.03.024] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 03/21/2011] [Accepted: 03/23/2011] [Indexed: 11/25/2022]
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Szkudelski T, Szkudelska K. Short-term effects of palmitate and 2-bromopalmitate on the lipolytic activity of rat adipocytes. Life Sci 2011; 89:450-5. [PMID: 21819998 DOI: 10.1016/j.lfs.2011.07.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2011] [Revised: 06/01/2011] [Accepted: 07/07/2011] [Indexed: 12/18/2022]
Abstract
AIMS Fatty acids are involved in the regulation of lipolysis in adipocytes; however, this regulatory action is unclear. The present study aimed to determine the short-term influence of palmitate and its non-metabolisable analogue, 2-bromopalmitate, on the lipolytic activity of adipocytes. MAIN METHODS Freshly isolated rat adipocytes were exposed to lipolytic modulators with or without palmitate or 2-bromopalmitate. Glycerol released from cells was determined as an indicator of lipolysis. Moreover, cAMP, ATP and changes in mitochondrial membrane potential were measured in cells treated with 2-bromopalmitate. KEY FINDINGS It was demonstrated that glycerol release from adipocytes incubated with epinephrine alone or epinephrine with insulin was unchanged by palmitate. However, 2-bromopalmitate was found to significantly decrease lipolysis stimulated by epinephrine or dibutyryl-cAMP. The inhibitory effect of 2-bromopalmitate on lipolysis was accompanied by reduced cAMP in adipocytes. Moreover, 2-bromopalmitate diminished hyperpolarisation of the inner mitochondrial membrane. Adipocyte exposure to 2-bromopalmitate also resulted in a substantial ATP depletion. The effects of 2-bromopalmitate on lipolysis and on ATP content were prevented neither by high glucose nor by alanine in the incubation medium. SIGNIFICANCE These findings demonstrate that short-term adipocyte exposure to palmitate disturbs neither the lipolytic action of epinephrine nor the antilipolytic action of insulin. However, 2-bromopalmitate significantly decreases lipolysis probably due to impaired metabolic activity of mitochondria.
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Affiliation(s)
- Tomasz Szkudelski
- Department of Animal Physiology and Biochemistry, Poznan University of Life Sciences, Wolynska 35, 60-637 Poznan, Poland.
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Jermendy A, Toschi E, Aye T, Koh A, Aguayo-Mazzucato C, Sharma A, Weir GC, Sgroi D, Bonner-Weir S. Rat neonatal beta cells lack the specialised metabolic phenotype of mature beta cells. Diabetologia 2011; 54:594-604. [PMID: 21240476 PMCID: PMC3045081 DOI: 10.1007/s00125-010-2036-x] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Accepted: 11/25/2010] [Indexed: 01/01/2023]
Abstract
AIMS/HYPOTHESIS Fetal and neonatal beta cells have poor glucose-induced insulin secretion and only gain robust glucose responsiveness several weeks after birth. We hypothesise that this unresponsiveness is due to a generalised immaturity of the metabolic pathways normally found in beta cells rather than to a specific defect. METHODS Using laser-capture microdissection we excised beta cell-enriched cores of pancreatic islets from day 1 (P1) neonatal and young adult Sprague-Dawley rats in order to compare their gene-expression profiles using Affymetrix U34A microarrays (neonatal, n = 4; adult, n = 3). RESULTS Using dChip software for analysis, 217 probe sets for genes/38 expressed sequence tags (ESTs) were significantly higher and 345 probe sets for genes/33 ESTs significantly lower in beta cell-enriched cores of neonatal islets compared with those of adult islets. Among the genes lower in the neonatal beta cells were key metabolic genes including mitochondrial shuttles (malate dehydrogenase, glycerol-3-phosphate dehydrogenase and glutamate oxalacetate transaminase), pyruvate carboxylase and carnitine palmitoyl transferase 2. Differential expression of these enzyme genes was confirmed by quantitative PCR on RNA from isolated neonatal (P2 until P28) and adult islets and with immunostaining of pancreas. Even by 28 days of age some of these genes were still expressed at lower levels than in adults. CONCLUSIONS/INTERPRETATION The lack of glucose responsiveness in neonatal islets is likely to be due to a generalised immaturity of the metabolic specialisation of pancreatic beta cells.
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Affiliation(s)
- A. Jermendy
- Section on Islet Cell and Regenerative Biology, Research Division, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA; 1st Department of Pediatrics, Semmelweis University, Budapest, Hungary
| | - E. Toschi
- Section on Islet Cell and Regenerative Biology, Research Division, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA
| | - T. Aye
- Section on Islet Cell and Regenerative Biology, Research Division, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA
| | - A. Koh
- Section on Islet Cell and Regenerative Biology, Research Division, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA
| | - C. Aguayo-Mazzucato
- Section on Islet Cell and Regenerative Biology, Research Division, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA
| | - A. Sharma
- Section on Islet Cell and Regenerative Biology, Research Division, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA
| | - G. C. Weir
- Section on Islet Cell and Regenerative Biology, Research Division, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA
| | - D. Sgroi
- Molecular Pathology Unit, Massachusetts General Hospital, Department of Pathology, Harvard Medical School, Boston, MA, USA
| | - S. Bonner-Weir
- Section on Islet Cell and Regenerative Biology, Research Division, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA
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Yang J, Chi Y, Burkhardt BR, Guan Y, Wolf BA. Leucine metabolism in regulation of insulin secretion from pancreatic beta cells. Nutr Rev 2010; 68:270-9. [PMID: 20500788 DOI: 10.1111/j.1753-4887.2010.00282.x] [Citation(s) in RCA: 138] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Leucine, a branched-chain amino acid that must be supplied in the daily diet, plays an important role in controlling protein synthesis and regulating cell metabolism in various cell types. In pancreatic beta cells, leucine acutely stimulates insulin secretion by serving as both metabolic fuel and allosteric activator of glutamate dehydrogenase to enhance glutaminolysis. Leucine has also been shown to regulate gene transcription and protein synthesis in pancreatic islet beta cells via both mTOR-dependent and -independent pathways at physiological concentrations. Long-term treatment with leucine has been shown to improve insulin secretory dysfunction of human diabetic islets via upregulation of certain key metabolic genes. In vivo, leucine administration improves glycemic control in humans and rodents with type 2 diabetes. This review summarizes and discusses the recent findings regarding the effects of leucine metabolism on pancreatic beta-cell function.
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Affiliation(s)
- Jichun Yang
- Department of Physiology and Pathophysiology, Peking University Diabetes Center, Peking University Health Science Center, Beijing, China.
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36
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Fridlyand LE, Philipson LH. Glucose sensing in the pancreatic beta cell: a computational systems analysis. Theor Biol Med Model 2010; 7:15. [PMID: 20497556 PMCID: PMC2896931 DOI: 10.1186/1742-4682-7-15] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2009] [Accepted: 05/24/2010] [Indexed: 12/29/2022] Open
Abstract
Background Pancreatic beta-cells respond to rising blood glucose by increasing oxidative metabolism, leading to an increased ATP/ADP ratio in the cytoplasm. This leads to a closure of KATP channels, depolarization of the plasma membrane, influx of calcium and the eventual secretion of insulin. Such mechanism suggests that beta-cell metabolism should have a functional regulation specific to secretion, as opposed to coupling to contraction. The goal of this work is to uncover contributions of the cytoplasmic and mitochondrial processes in this secretory coupling mechanism using mathematical modeling in a systems biology approach. Methods We describe a mathematical model of beta-cell sensitivity to glucose. The cytoplasmic part of the model includes equations describing glucokinase, glycolysis, pyruvate reduction, NADH and ATP production and consumption. The mitochondrial part begins with production of NADH, which is regulated by pyruvate dehydrogenase. NADH is used in the electron transport chain to establish a proton motive force, driving the F1F0 ATPase. Redox shuttles and mitochondrial Ca2+ handling were also modeled. Results The model correctly predicts changes in the ATP/ADP ratio, Ca2+ and other metabolic parameters in response to changes in substrate delivery at steady-state and during cytoplasmic Ca2+ oscillations. Our analysis of the model simulations suggests that the mitochondrial membrane potential should be relatively lower in beta cells compared with other cell types to permit precise mitochondrial regulation of the cytoplasmic ATP/ADP ratio. This key difference may follow from a relative reduction in respiratory activity. The model demonstrates how activity of lactate dehydrogenase, uncoupling proteins and the redox shuttles can regulate beta-cell function in concert; that independent oscillations of cytoplasmic Ca2+ can lead to slow coupled metabolic oscillations; and that the relatively low production rate of reactive oxygen species in beta-cells under physiological conditions is a consequence of the relatively decreased mitochondrial membrane potential. Conclusion This comprehensive model predicts a special role for mitochondrial control mechanisms in insulin secretion and ROS generation in the beta cell. The model can be used for testing and generating control hypotheses and will help to provide a more complete understanding of beta-cell glucose-sensing central to the physiology and pathology of pancreatic β-cells.
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Affiliation(s)
- Leonid E Fridlyand
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA.
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37
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Mastrandrea LD, Sessanna SM, Del Toro A, Laychock SG. ATP-independent glucose stimulation of sphingosine kinase in rat pancreatic islets. J Lipid Res 2010; 51:2171-80. [PMID: 20371493 DOI: 10.1194/jlr.m000802] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sphingosine kinase (SPHK) catalyzes sphingosine 1-phosphate production, promoting cell survival and reducing apoptosis in isolated rat pancreatic islets. Glucose, the primary islet beta-cell growth factor and insulin secretagogue, increased islet SPHK activity by 3- to 5-fold following acute (1 h) or prolonged (7 days) stimulation. Prolonged stimulation of islets with glucose induced SPHK1a and SPHK2 mRNA levels; there were no changes in SPHK protein expression. To isolate the metabolic effects of glucose on SPHK activation, islets were stimulated with glucose analogs or metabolites. 2-deoxy-D-glucose (2-DG), an analog phosphorylated by glucokinase but not an effective energy source, activated SPHK similarly to glucose. In contrast, 3-o-methylglucose (3-oMeG), which is transported but neither phosphorylated nor metabolized, did not increase islet SPHK activity. Glyceraldehyde and alpha-ketoisocaproic acid (KIC), metabolites that stimulate glycolysis and the citric acid cycle, respectively, did not activate islet SPHK. Moreover, inorganic phosphate blocked glucose-induced SPHK activation. A role for SPHK activity in beta-cell growth was confirmed when small interfering (si)SPHK2 RNA transfection reduced rat insulinoma INS-1e cell SPHK levels and activity and cell growth. Glucose induced an early and sustained increase in islet SPHK activity that was dependent on glucose phosphorylation, but independent of ATP generation or new protein biosynthesis. Glucose-supported beta-cell growth appears to be in part mediated by SPHK activity.
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Affiliation(s)
- L D Mastrandrea
- Department of Pediatrics, University at Buffalo, Buffalo, NY, USA.
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Role of mitochondria in beta-cell function and dysfunction. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:193-216. [PMID: 20217499 DOI: 10.1007/978-90-481-3271-3_9] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Pancreatic beta-cells are poised to sense glucose and other nutrient secretagogues to regulate insulin exocytosis, thereby maintaining glucose homeostasis. This process requires translation of metabolic substrates into intracellular messengers recognized by the exocytotic machinery. Central to this metabolism-secretion coupling, mitochondria integrate and generate metabolic signals, thereby connecting glucose recognition to insulin exocytosis. In response to a glucose rise, nucleotides and metabolites are generated by mitochondria and participate, together with cytosolic calcium, to the stimulation of insulin release. This review describes the mitochondrion-dependent pathways of regulated insulin secretion. Mitochondrial defects, such as mutations and reactive oxygen species production, are discussed in the context of beta-cell failure that may participate to the etiology of diabetes.
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Peyot ML, Gray JP, Lamontagne J, Smith PJS, Holz GG, Madiraju SRM, Prentki M, Heart E. Glucagon-like peptide-1 induced signaling and insulin secretion do not drive fuel and energy metabolism in primary rodent pancreatic beta-cells. PLoS One 2009; 4:e6221. [PMID: 19593440 PMCID: PMC2704866 DOI: 10.1371/journal.pone.0006221] [Citation(s) in RCA: 50] [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: 04/14/2009] [Accepted: 06/15/2009] [Indexed: 11/24/2022] Open
Abstract
Background Glucagon like peptide-1 (GLP-1) and its analogue exendin-4 (Ex-4) enhance glucose stimulated insulin secretion (GSIS) and activate various signaling pathways in pancreatic β-cells, in particular cAMP, Ca2+ and protein kinase-B (PKB/Akt). In many cells these signals activate intermediary metabolism. However, it is not clear whether the acute amplification of GSIS by GLP-1 involves in part metabolic alterations and the production of metabolic coupling factors. Methodology/Prinicipal Findings GLP-1 or Ex-4 at high glucose caused release (∼20%) of the total rat islet insulin content over 1 h. While both GLP-1 and Ex-4 markedly potentiated GSIS in isolated rat and mouse islets, neither had an effect on β-cell fuel and energy metabolism over a 5 min to 3 h time period. GLP-1 activated PKB without changing glucose usage and oxidation, fatty acid oxidation, lipolysis or esterification into various lipids in rat islets. Ex-4 caused a rise in [Ca2+]i and cAMP but did not enhance energy utilization, as neither oxygen consumption nor mitochondrial ATP levels were altered. Conclusions/Significance The results indicate that GLP-1 barely affects β-cell intermediary metabolism and that metabolic signaling does not significantly contribute to GLP-1 potentiation of GSIS. The data also indicate that insulin secretion is a minor energy consuming process in the β-cell, and that the β-cell is different from most cell types in that its metabolic activation appears to be primarily governed by a “push” (fuel substrate driven) process, rather than a “pull” mechanism secondary to enhanced insulin release as well as to Ca2+, cAMP and PKB signaling.
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Affiliation(s)
- Marie-Line Peyot
- Molecular Nutrition Unit and Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal and Departments of Nutrition and Biochemistry, Université de Montréal, Montréal, Quebec, Canada
| | - Joshua P. Gray
- Department of Chemistry, United States Coast Guard Academy, New London, Connecticut, United States of America
| | - Julien Lamontagne
- Molecular Nutrition Unit and Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal and Departments of Nutrition and Biochemistry, Université de Montréal, Montréal, Quebec, Canada
| | - Peter J. S. Smith
- BioCurrents Research Center (NIH:NCRR), Marine Biological Laboratory, Woods Hole, Massachusetts, United States of America
| | - George G. Holz
- State University of New York, Upstate Medical University, Syracuse, New York, United States of America
| | - S. R. Murthy Madiraju
- Molecular Nutrition Unit and Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal and Departments of Nutrition and Biochemistry, Université de Montréal, Montréal, Quebec, Canada
| | - Marc Prentki
- Molecular Nutrition Unit and Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal and Departments of Nutrition and Biochemistry, Université de Montréal, Montréal, Quebec, Canada
- * E-mail:
| | - Emma Heart
- BioCurrents Research Center (NIH:NCRR), Marine Biological Laboratory, Woods Hole, Massachusetts, United States of America
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Casimir M, Lasorsa FM, Rubi B, Caille D, Palmieri F, Meda P, Maechler P. Mitochondrial glutamate carrier GC1 as a newly identified player in the control of glucose-stimulated insulin secretion. J Biol Chem 2009; 284:25004-14. [PMID: 19584051 DOI: 10.1074/jbc.m109.015495] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The SLC25 carrier family mediates solute transport across the inner mitochondrial membrane, a process that is still poorly characterized regarding both the mechanisms and proteins implicated. This study investigated mitochondrial glutamate carrier GC1 in insulin-secreting beta-cells. GC1 was cloned from insulin-secreting cells, and sequence analysis revealed hydropathy profile of a six-transmembrane protein, characteristic of mitochondrial solute carriers. GC1 was found to be expressed at the mRNA and protein levels in INS-1E beta-cells and pancreatic rat islets. Immunohistochemistry showed that GC1 was present in mitochondria, and ultrastructural analysis by electron microscopy revealed inner mitochondrial membrane localization of the transporter. Silencing of GC1 in INS-1E beta-cells, mediated by adenoviral delivery of short hairpin RNA, reduced mitochondrial glutamate transport by 48% (p < 0.001). Insulin secretion at basal 2.5 mM glucose and stimulated either by intermediate 7.5 mM glucose or non-nutrient 30 mM KCl was not modified by GC1 silencing. Conversely, insulin secretion stimulated with optimal 15 mM glucose was reduced by 23% (p < 0.005) in GC1 knocked down cells compared with controls. Adjunct of cell-permeant glutamate (5 mM dimethyl glutamate) fully restored the secretory response at 15 mM glucose (p < 0.005). Kinetics of insulin secretion were investigated in perifused isolated rat islets. GC1 silencing in islets inhibited the secretory response induced by 16.7 mM glucose, both during first (-25%, p < 0.05) and second (-33%, p < 0.05) phases. This study demonstrates that insulin-secreting cells depend on GC1 for maximal glucose response, thereby assigning a physiological function to this newly identified mitochondrial glutamate carrier.
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Affiliation(s)
- Marina Casimir
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1211 Geneva 4, Switzerland
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41
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Martens GA, Pipeleers D. Glucose, regulator of survival and phenotype of pancreatic beta cells. VITAMINS AND HORMONES 2009; 80:507-39. [PMID: 19251048 DOI: 10.1016/s0083-6729(08)00617-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The key role of glucose in regulating insulin release by the pancreatic beta cell population is not only dependent on acute stimulus-secretion coupling mechanisms but also on more long-term influences on beta cell survival and phenotype. Glucose serves as a major survival factor for beta cells via at least three actions: it prevents an oxidative redox state, it suppresses a mitochondrial apoptotic program that is triggered at reduced mitochondrial metabolic activity and it induces genes needed for the cellular responsiveness to glucose and to growth factors. Glucose-regulated pathways may link protein synthetic and proliferative activities, making glucose a permissive factor for beta cell proliferation, in check with metabolic needs. Conditions of inadequate glucose metabolism in beta cells are not only leading to deregulation of acute secretory responses but should also be considered as causes for increased apoptosis and reduced formation of beta cells, and loss of their normal differentiated state.
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Abstract
Intrauterine growth retardation (IUGR) has been linked to development of type 2 diabetes in adulthood. Using a rat model, we tested the hypothesis that uteroplacental insufficiency disrupts the function of the electron transport chain in the fetal beta-cell and leads to a debilitating cascade of events. The net result is progressive loss of beta-cell function and eventual development of type 2 diabetes in the adult. Studies in the IUGR rat demonstrate that an abnormal intrauterine environment induces epigenetic modifications of key genes regulating beta-cell development; experiments directly link chromatin remodeling with suppression of transcription. Future research will be directed at elucidating the mechanisms underlying epigenetic modifications in offspring.
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Affiliation(s)
- Rebecca A Simmons
- Department of Pediatrics, Children's Hospital, Philadelphia, PA, USA.
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43
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Mármol P, Pardo B, Wiederkehr A, Del Arco A, Wollheim CB, Satrústegui J. Requirement for aralar and its Ca2+-binding sites in Ca2+ signal transduction in mitochondria from INS-1 clonal beta-cells. J Biol Chem 2008; 284:515-524. [PMID: 18996845 DOI: 10.1074/jbc.m806729200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Aralar, the mitochondrial aspartate-glutamate carrier present in beta-cells, is a component of the malate-aspartate NADH shuttle (MAS). MAS is activated by Ca2+ in mitochondria from tissues with aralar as the only AGC isoform with an S0.5 of approximately 300 nm. We have studied the role of aralar and its Ca2+-binding EF-hand motifs in glucose-induced mitochondrial NAD(P)H generation by two-photon microscopy imaging in INS-1 beta-cells lacking aralar or expressing aralar mutants blocked for Ca2+ binding. Aralar knock-down in INS-1 beta-cell lines resulted in undetectable levels of aralar protein and complete loss of MAS activity in isolated mitochondria and in a 25% decrease in glucose-stimulated insulin secretion. MAS activity in mitochondria from INS-1 cells was activated 2-3-fold by extramitochondrial Ca2+, whereas aralar mutants were Ca2+ insensitive. In Ca2+-free medium, glucose-induced increases in mitochondrial NAD(P)H were small (1.3-fold) and unchanged regardless of the lack of aralar. In the presence of 1.5 mm Ca2+, glucose induced robust increases in mitochondrial NAD(P)H (approximately 2-fold) in cell lines with wild-type or mutant aralar. There was a approximately 20% reduction in NAD(P)H response in cells lacking aralar, illustrating the importance of MAS in glucose action. When small Ca2+ signals that resulted in extremely small mitochondrial Ca2+ transients were induced in the presence of glucose, the rise in mitochondrial NAD(P)H was maintained in cells with wild-type aralar but was reduced by approximately 50% in cells lacking or expressing mutant aralar. These results indicate that 1) glucose-induced activation of MAS requires Ca2+ potentiation; 2) Ca2+ activation of MAS represents a larger fraction of glucose-induced mitochondrial NAD(P)H production under conditions where suboptimal Ca2+ signals are associated with a glucose challenge (50 versus 20%, respectively); 3) inactivation of EF-hand motifs in aralar prevents activation of MAS by small Ca2+ signals. The results suggest a possible role for aralar and MAS in priming the beta-cell by Ca2+-mobilizing neurotransmitter or hormones.
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Affiliation(s)
- Patricia Mármol
- Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa CSIC-UAM, CIBER de Enfermedades Raras (CIBERER), Universidad Autónoma, 28049 Madrid, Spain, the Area de Bioquímica, Centro Regional de Investigaciones Biomádicas (CRIB), Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, 48071 Toledo, Spain, and the Department of Cell Physiology and Metabolism, University Medical Center, CH-1211 Geneva, Switzerland
| | - Beatriz Pardo
- Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa CSIC-UAM, CIBER de Enfermedades Raras (CIBERER), Universidad Autónoma, 28049 Madrid, Spain, the Area de Bioquímica, Centro Regional de Investigaciones Biomádicas (CRIB), Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, 48071 Toledo, Spain, and the Department of Cell Physiology and Metabolism, University Medical Center, CH-1211 Geneva, Switzerland
| | - Andreas Wiederkehr
- Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa CSIC-UAM, CIBER de Enfermedades Raras (CIBERER), Universidad Autónoma, 28049 Madrid, Spain, the Area de Bioquímica, Centro Regional de Investigaciones Biomádicas (CRIB), Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, 48071 Toledo, Spain, and the Department of Cell Physiology and Metabolism, University Medical Center, CH-1211 Geneva, Switzerland
| | - Araceli Del Arco
- Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa CSIC-UAM, CIBER de Enfermedades Raras (CIBERER), Universidad Autónoma, 28049 Madrid, Spain, the Area de Bioquímica, Centro Regional de Investigaciones Biomádicas (CRIB), Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, 48071 Toledo, Spain, and the Department of Cell Physiology and Metabolism, University Medical Center, CH-1211 Geneva, Switzerland; Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa CSIC-UAM, CIBER de Enfermedades Raras (CIBERER), Universidad Autónoma, 28049 Madrid, Spain, the Area de Bioquímica, Centro Regional de Investigaciones Biomádicas (CRIB), Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, 48071 Toledo, Spain, and the Department of Cell Physiology and Metabolism, University Medical Center, CH-1211 Geneva, Switzerland
| | - Claes B Wollheim
- Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa CSIC-UAM, CIBER de Enfermedades Raras (CIBERER), Universidad Autónoma, 28049 Madrid, Spain, the Area de Bioquímica, Centro Regional de Investigaciones Biomádicas (CRIB), Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, 48071 Toledo, Spain, and the Department of Cell Physiology and Metabolism, University Medical Center, CH-1211 Geneva, Switzerland
| | - Jorgina Satrústegui
- Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa CSIC-UAM, CIBER de Enfermedades Raras (CIBERER), Universidad Autónoma, 28049 Madrid, Spain, the Area de Bioquímica, Centro Regional de Investigaciones Biomádicas (CRIB), Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, 48071 Toledo, Spain, and the Department of Cell Physiology and Metabolism, University Medical Center, CH-1211 Geneva, Switzerland.
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Hasan NM, Longacre MJ, Stoker SW, Boonsaen T, Jitrapakdee S, Kendrick MA, Wallace JC, MacDonald MJ. Impaired anaplerosis and insulin secretion in insulinoma cells caused by small interfering RNA-mediated suppression of pyruvate carboxylase. J Biol Chem 2008; 283:28048-59. [PMID: 18697738 DOI: 10.1074/jbc.m804170200] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Anaplerosis, the synthesis of citric acid cycle intermediates, by pancreatic beta cell mitochondria has been proposed to be as important for insulin secretion as mitochondrial energy production. However, studies designed to lower the rate of anaplerosis in the beta cell have been inconclusive. To test the hypothesis that anaplerosis is important for insulin secretion, we lowered the activity of pyruvate carboxylase (PC), the major enzyme of anaplerosis in the beta cell. Stable transfection of short hairpin RNA was used to generate a number of INS-1 832/13-derived cell lines with various levels of PC enzyme activity that retained normal levels of control enzymes, insulin content, and glucose oxidation. Glucose-induced insulin release was decreased in proportion to the decrease in PC activity. Insulin release in response to pyruvate alone, 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) plus glutamine, or methyl succinate plus beta-hydroxybutyrate was also decreased in the PC knockdown cells. Consistent with a block at PC, the most PC-deficient cells showed a metabolic crossover point at PC with increased basal and/or glucose-stimulated pyruvate plus lactate and decreased malate and citrate. In addition, in BCH plus glutamine-stimulated PC knockdown cells, pyruvate plus lactate was increased, whereas citrate was severely decreased, and malate and aspartate were slightly decreased. The incorporation of 14C into lipid from [U-14C]glucose was decreased in the PC knockdown cells. The results confirm the central importance of PC and anaplerosis to generate metabolites from glucose that support insulin secretion and even suggest PC is important for insulin secretion stimulated by noncarbohydrate insulin secretagogues.
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Affiliation(s)
- Noaman M Hasan
- Childrens Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706, USA
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45
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Tissue specificity of mitochondrial glutamate pathways and the control of metabolic homeostasis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:965-72. [PMID: 18486589 DOI: 10.1016/j.bbabio.2008.04.031] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Revised: 04/11/2008] [Accepted: 04/22/2008] [Indexed: 11/24/2022]
Abstract
Glutamate is implicated in numerous metabolic and signalling functions that vary according to specific tissues. Glutamate metabolism is tightly controlled by activities of mitochondrial enzymes and transmembrane carriers, in particular glutamate dehydrogenase and mitochondrial glutamate carriers that have been identified in recent years. It is remarkable that, although glutamate-specific enzymes and transporters share similar properties in most tissues, their regulation varies greatly according to particular organs in order to achieve tissue specific functions. This is illustrated in this review when comparing glutamate handling in liver, brain, and pancreatic beta-cells. We describe the main cellular glutamate pathways and their specific functions in different tissues, ultimately contributing to the control of metabolic homeostasis at the organism level.
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46
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Affourtit C, Brand MD. On the role of uncoupling protein-2 in pancreatic beta cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:973-9. [PMID: 18433713 DOI: 10.1016/j.bbabio.2008.03.022] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2008] [Revised: 02/26/2008] [Accepted: 03/19/2008] [Indexed: 10/22/2022]
Abstract
Pancreatic beta cells secrete insulin when blood glucose levels are high. Dysfunction of this glucose-stimulated insulin secretion (GSIS) is partly responsible for the manifestation of type 2 diabetes, a metabolic disorder that is rapidly becoming a global pandemic. Mitochondria play a central role in GSIS by coupling glucose oxidation to production of ATP, a signal that triggers a series of events that ultimately leads to insulin release. Beta cells express a mitochondrial uncoupling protein, UCP2, which is rather surprising as activity of such a protein is anticipated to lower the efficiency of oxidative phosphorylation, and hence to impair GSIS. The mounting evidence demonstrating that insulin secretion is indeed blunted by UCP2 agrees with this prediction, and has provoked the idea that UCP2 activity contributes to beta cell pathogenesis and development of type 2 diabetes. Although this notion may be correct, the evolved function of UCP2 remains unclear. With this paper we aim to provide a brief account of the present state of affairs in this field, suggest a physiological role for UCP2, and highlight some of our own recent results.
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MacDonald MJ, Longacre MJ, Stoker SW, Brown LJ, Hasan NM, Kendrick MA. Acetoacetate and β-hydroxybutyrate in combination with other metabolites release insulin from INS-1 cells and provide clues about pathways in insulin secretion. Am J Physiol Cell Physiol 2008; 294:C442-50. [DOI: 10.1152/ajpcell.00368.2007] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mitochondrial anaplerosis is important for insulin secretion, but only some of the products of anaplerosis are known. We discovered novel effects of mitochondrial metabolites on insulin release in INS-1 832/13 cells that suggested pathways to some of these products. Acetoacetate, β-hydroxybutyrate, α-ketoisocaproate (KIC), and monomethyl succinate (MMS) alone did not stimulate insulin release. Lactate released very little insulin. When acetoacetate, β-hydroxybutyrate, or KIC were combined with MMS, or either ketone body was combined with lactate, insulin release was stimulated 10-fold to 20-fold the controls (almost as much as with glucose). Pyruvate was a potent stimulus of insulin release. In rat pancreatic islets, β-hydroxybutyrate potentiated MMS- and glucose-induced insulin release. The pathways of their metabolism suggest that, in addition to producing ATP, the ketone bodies and KIC supply the acetate component and MMS supplies the oxaloacetate component of citrate. In line with this, citrate was increased by β-hydroxybutyrate plus MMS in INS-1 cells and by β-hydroxybutyrate plus succinate in mitochondria. The two ketone bodies and KIC can also be metabolized to acetoacetyl-CoA and acetyl-CoA, which are precursors of other short-chain acyl-CoAs (SC-CoAs). Measurements of SC-CoAs by LC-MS/MS in INS-1 cells confirmed that KIC, β-hydroxybutyrate, glucose, and pyruvate increased the levels of acetyl-CoA, acetoacetyl-CoA, succinyl-CoA, hydroxymethylglutaryl-CoA, and malonyl-CoA. MMS increased incorporation of14C from β-hydroxybutyrate into citrate, acid-precipitable material, and lipids, suggesting that the two molecules complement one another to increase anaplerosis. The results suggest that, besides citrate, some of the products of anaplerosis are SC-CoAs, which may be precursors of molecules involved in insulin secretion.
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48
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Dual role of proapoptotic BAD in insulin secretion and beta cell survival. Nat Med 2008; 14:144-53. [PMID: 18223655 DOI: 10.1038/nm1717] [Citation(s) in RCA: 246] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Accepted: 12/20/2007] [Indexed: 12/25/2022]
Abstract
The proapoptotic BCL-2 family member BAD resides in a glucokinase-containing complex that regulates glucose-driven mitochondrial respiration. Here, we present genetic evidence of a physiologic role for BAD in glucose-stimulated insulin secretion by beta cells. This novel function of BAD is specifically dependent upon the phosphorylation of its BH3 sequence, previously defined as an essential death domain. We highlight the pharmacologic relevance of phosphorylated BAD BH3 by using cell-permeable, hydrocarbon-stapled BAD BH3 helices that target glucokinase, restore glucose-driven mitochondrial respiration and correct the insulin secretory response in Bad-deficient islets. Our studies uncover an alternative target and function for the BAD BH3 domain and emphasize the therapeutic potential of phosphorylated BAD BH3 mimetics in selectively restoring beta cell function. Furthermore, we show that BAD regulates the physiologic adaptation of beta cell mass during high-fat feeding. Our findings provide genetic proof of the bifunctional activities of BAD in both beta cell survival and insulin secretion.
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Satrústegui J, Contreras L, Ramos M, Marmol P, del Arco A, Saheki T, Pardo B. Role of aralar, the mitochondrial transporter of aspartate-glutamate, in brain N-acetylaspartate formation and Ca(2+) signaling in neuronal mitochondria. J Neurosci Res 2008; 85:3359-66. [PMID: 17497669 DOI: 10.1002/jnr.21299] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Aralar, the Ca(2+)-dependent mitochondrial aspartate-glutamate carrier expressed in brain and skeletal muscle, is a member of the malate-aspartate NADH shuttle. Disrupting the gene for aralar, SLC25a12, in mice has enabled the discovery of two new roles of this carrier. On the one hand, it is required for synthesis of brain aspartate and N-acetylaspartate, a neuron-born metabolite that supplies acetate for myelin lipid synthesis; and on the other, it is essential for the transmission of small Ca(2+) signals to mitochondria via an increase in mitochondrial NADH.
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Affiliation(s)
- Jorgina Satrústegui
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma, 28049, Cantoblanco, Madrid, Spain
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50
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MacDonald MJ, Dobrzyn A, Ntambi J, Stoker SW. The role of rapid lipogenesis in insulin secretion: Insulin secretagogues acutely alter lipid composition of INS-1 832/13 cells. Arch Biochem Biophys 2007; 470:153-62. [PMID: 18082128 DOI: 10.1016/j.abb.2007.11.017] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2007] [Revised: 11/20/2007] [Accepted: 11/22/2007] [Indexed: 11/28/2022]
Abstract
Pancreatic beta cell mitochondria convert insulin secretagogues into products that support insulin exocytosis. We explored the idea that lipids are some of these products formed from acyl group transfer out of mitochondria to the cytosol, the site of lipid synthesis. There are two isoforms of acetyl-CoA carboxylase, the enzyme that forms malonyl-CoA from which C(2) units for lipid synthesis are formed. We found that ACC1, the isoform seen in lipogenic tissues, is the only isoform present in human and rat pancreatic islets and INS-1 832/13 cells. Inhibitors of ACC and fatty acid synthase inhibited insulin release in islets and INS-1 cells. Carbon from glucose and pyruvate were rapidly incorporated into many lipid classes in INS-1 cells. Glucose and other insulin secretagogues acutely increased many lipids with C14-C24 chains including individual cholesterol esters, phospholipids and fatty acids. Many phosphatidylcholines and phosphatidylserines were increased and many phosphatidylinositols and several phosphatidylethanolamines were decreased. The results suggest that lipid remodeling and rapid lipogenesis from secretagogue carbon support insulin secretion.
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Affiliation(s)
- Michael J MacDonald
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Room 3459 Medical Science Center, 1300 University Avenue, Madison, WI 53706, USA.
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