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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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Rustenbeck I, Schulze T, Morsi M, Alshafei M, Panten U. What Is the Metabolic Amplification of Insulin Secretion and Is It (Still) Relevant? Metabolites 2021; 11:metabo11060355. [PMID: 34199454 PMCID: PMC8229681 DOI: 10.3390/metabo11060355] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 05/27/2021] [Accepted: 05/31/2021] [Indexed: 12/24/2022] Open
Abstract
The pancreatic beta-cell transduces the availability of nutrients into the secretion of insulin. While this process is extensively modified by hormones and neurotransmitters, it is the availability of nutrients, above all glucose, which sets the process of insulin synthesis and secretion in motion. The central role of the mitochondria in this process was identified decades ago, but how changes in mitochondrial activity are coupled to the exocytosis of insulin granules is still incompletely understood. The identification of ATP-sensitive K+-channels provided the link between the level of adenine nucleotides and the electrical activity of the beta cell, but the depolarization-induced Ca2+-influx into the beta cells, although necessary for stimulated secretion, is not sufficient to generate the secretion pattern as produced by glucose and other nutrient secretagogues. The metabolic amplification of insulin secretion is thus the sequence of events that enables the secretory response to a nutrient secretagogue to exceed the secretory response to a purely depolarizing stimulus and is thus of prime importance. Since the cataplerotic export of mitochondrial metabolites is involved in this signaling, an orienting overview on the topic of nutrient secretagogues beyond glucose is included. Their judicious use may help to define better the nature of the signals and their mechanism of action.
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Affiliation(s)
- Ingo Rustenbeck
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
- Correspondence: ; Tel.: +49-(0)53-139-156-70
| | - Torben Schulze
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
| | - Mai Morsi
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
- Department of Pharmacology, Faculty of Pharmacy, Assiut University, Assiut 71526, Egypt
| | - Mohammed Alshafei
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
| | - Uwe Panten
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
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Ramakrishna MP, Pavithran PV, Bhavani N, Kumar H, Nair V, Menon AS, Menon UV, Abraham N. Mitochondrial Diabetes: More Than Just Hyperglycemia. Clin Diabetes 2019; 37:298-301. [PMID: 31371866 PMCID: PMC6640889 DOI: 10.2337/cd18-0090] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Affiliation(s)
- Manjunath P Ramakrishna
- Department of Endocrinology, Amrita Institute of Medical Sciences and Research Centre, Kochi, Kerala, India
| | - Praveen V Pavithran
- Department of Endocrinology, Amrita Institute of Medical Sciences and Research Centre, Kochi, Kerala, India
| | - Nisha Bhavani
- Department of Endocrinology, Amrita Institute of Medical Sciences and Research Centre, Kochi, Kerala, India
| | - Harish Kumar
- Department of Endocrinology, Amrita Institute of Medical Sciences and Research Centre, Kochi, Kerala, India
| | - Vasantha Nair
- Department of Endocrinology, Amrita Institute of Medical Sciences and Research Centre, Kochi, Kerala, India
| | - Arun S Menon
- Department of Endocrinology, Amrita Institute of Medical Sciences and Research Centre, Kochi, Kerala, India
| | - Usha V Menon
- Department of Endocrinology, Amrita Institute of Medical Sciences and Research Centre, Kochi, Kerala, India
| | - Nithya Abraham
- Department of Endocrinology, Amrita Institute of Medical Sciences and Research Centre, Kochi, Kerala, India
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Yaribeygi H, Atkin SL, Sahebkar A. Mitochondrial dysfunction in diabetes and the regulatory roles of antidiabetic agents on the mitochondrial function. J Cell Physiol 2019; 234:8402-8410. [DOI: 10.1002/jcp.27754] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Accepted: 10/22/2018] [Indexed: 08/30/2023]
Abstract
AbstractThe prevalence of type 2 diabetes mellitus (T2DM) is increasing rapidly with its associated morbidity and mortality. Many pathophysiological pathways such as oxidative stress, inflammatory responses, adipokines, obesity‐induced insulin resistance, improper insulin signaling, and beta cell apoptosis are associated with the development of T2DM. There is increasing evidence of the role of mitochondrial dysfunction in the onset of T2DM, particularly in relation to the development of diabetic complications. Here, the role of mitochondrial dysfunction in T2DM is reviewed together with its modulation by antidiabetic therapeutic agents, an effect that may be independent of their hypoglycemic effect.
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Affiliation(s)
- Habib Yaribeygi
- Chronic Kidney Disease Research Center, Shahid Beheshti University of Medical Sciences Tehran Iran
| | | | - Amirhossein Sahebkar
- Neurogenic Inflammation Research Center, Mashhad University of Medical Sciences Mashhad Iran
- Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences Mashhad Iran
- School of Pharmacy, Mashhad University of Medical Sciences Mashhad Iran
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Wollam J, Mahata S, Riopel M, Hernandez-Carretero A, Biswas A, Bandyopadhyay GK, Chi NW, Eiden LE, Mahapatra NR, Corti A, Webster NJG, Mahata SK. Chromogranin A regulates vesicle storage and mitochondrial dynamics to influence insulin secretion. Cell Tissue Res 2017; 368:487-501. [PMID: 28220294 PMCID: PMC10843982 DOI: 10.1007/s00441-017-2580-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Accepted: 01/16/2017] [Indexed: 01/01/2023]
Abstract
Chromogranin A (CgA) is a prohormone and a granulogenic factor that regulates secretory pathways in neuroendocrine tissues. In β-cells of the endocrine pancreas, CgA is a major cargo in insulin secretory vesicles. The impact of CgA deficiency on the formation and exocytosis of insulin vesicles is yet to be investigated. In addition, no literature exists on the impact of CgA on mitochondrial function in β-cells. Using three different antibodies, we demonstrate that CgA is processed to vasostatin- and catestatin-containing fragments in pancreatic islet cells. CgA deficiency in Chga-KO islets leads to compensatory overexpression of chromogranin B, secretogranin II, SNARE proteins and insulin genes, as well as increased insulin protein content. Ultrastructural studies of pancreatic islets revealed that Chga-KO β-cells contain fewer immature secretory granules than wild-type (WT) control but increased numbers of mature secretory granules and plasma membrane-docked vesicles. Compared to WT control, CgA-deficient β-cells exhibited increases in mitochondrial volume, numerical densities and fusion, as well as increased expression of nuclear encoded genes (Ndufa9, Ndufs8, Cyc1 and Atp5o). These changes in secretory vesicles and the mitochondria likely contribute to the increased glucose-stimulated insulin secretion observed in Chga-KO mice. We conclude that CgA is an important regulator for coordination of mitochondrial dynamics, secretory vesicular quanta and GSIS for optimal secretory functioning of β-cells, suggesting a strong, CgA-dependent positive link between mitochondrial fusion and GSIS.
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Affiliation(s)
- Joshua Wollam
- Department of Medicine, University of California, San Diego, La Jolla, CA, USA
| | - Sumana Mahata
- Division of Biology & Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Matthew Riopel
- Department of Medicine, University of California, San Diego, La Jolla, CA, USA
| | | | - Angshuman Biswas
- Department of Medicine, University of California, San Diego, La Jolla, CA, USA
| | | | - Nai-Wen Chi
- Department of Medicine, University of California, San Diego, La Jolla, CA, USA
- VA San Diego Healthcare System, San Diego, CA, USA
| | - Lee E Eiden
- Section on Molecular Neuroscience, NIMH-IRP, Bethesda, MD, USA
| | - Nitish R Mahapatra
- Department of Biotechnology, Indian Institute of Technology Madras, Chennai, 600036, India
| | - Angelo Corti
- IRCCS San Raffaele Scientific Institute, San Raffaele Vita-Salute University, Milan, Italy
| | - Nicholas J G Webster
- Department of Medicine, University of California, San Diego, La Jolla, CA, USA
- VA San Diego Healthcare System, San Diego, CA, USA
| | - Sushil K Mahata
- Department of Medicine, University of California, San Diego, La Jolla, CA, USA.
- VA San Diego Healthcare System, San Diego, CA, USA.
- Metabolic Physiology & Ultrastructural Biology Laboratory, Department of Medicine, University of California, San Diego (0732), 9500 Gilman Drive, La Jolla, CA, 92093-0732, USA.
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Cataldo LR, Mizgier ML, Bravo Sagua R, Jaña F, Cárdenas C, Llanos P, Busso D, Olmos P, Galgani JE, Santos JL, Cortés VA. Prolonged Activation of the Htr2b Serotonin Receptor Impairs Glucose Stimulated Insulin Secretion and Mitochondrial Function in MIN6 Cells. PLoS One 2017; 12:e0170213. [PMID: 28129327 PMCID: PMC5271329 DOI: 10.1371/journal.pone.0170213] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Accepted: 01/02/2017] [Indexed: 11/23/2022] Open
Abstract
Aims Pancreatic β-cells synthesize and release serotonin (5 hydroxytryptamine, 5HT); however, the role of 5HT receptors on glucose stimulated insulin secretion (GSIS) and the mechanisms mediating this function is not fully understood. The aims of this study were to determine the expression profile of 5HT receptors in murine MIN6 β-cells and to examine the effects of pharmacological activation of 5HT receptor Htr2b on GSIS and mitochondrial function. Materials and Methods mRNA levels of 5HT receptors in MIN6 cells were quantified by RT qPCR. GSIS was assessed in MIN6 cells in response to global serotonergic activation with 5HT and pharmacological Htr2b activation or inhibition with BW723C86 or SB204741, respectively. In response to Htr2b activation also was evaluated the mRNA and protein levels of PGC1α and PPARy by RT-qPCR and western blotting and mitochondrial function by oxygen consumption rate (OCR) and ATP cellular content. Results We found that mRNA levels of most 5HT receptors were either very low or undetectable in MIN6 cells. By contrast, Htr2b mRNA was present at moderate levels in these cells. Preincubation (6 h) of MIN6 cells with 5HT or BW723C86 reduced GSIS and the effect of 5HT was prevented by SB204741. Preincubation with BW723C86 increased PGC1α and PPARy mRNA and protein levels and decreased mitochondrial respiration and ATP content in MIN6 cells. Conclusions Our results indicate that prolonged Htr2b activation in murine β-cells decreases glucose-stimulated insulin secretion and mitochondrial activity by mechanisms likely dependent on enhanced PGC1α/PPARy expression.
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Affiliation(s)
- Luis Rodrigo Cataldo
- Department of Nutrition, Diabetes and Metabolism, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - María L. Mizgier
- Department of Nutrition, Diabetes and Metabolism, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Roberto Bravo Sagua
- Institute of Nutrition and Food Technology (INTA), University of Chile, Santiago, Chile
| | - Fabián Jaña
- Anatomy and Developmental Biology Program, Institute of Biomedical Sciences, University of Chile, Santiago, Chile
| | - César Cárdenas
- Anatomy and Developmental Biology Program, Institute of Biomedical Sciences, University of Chile, Santiago, Chile
- Geroscience Center for Brain Health and Metabolism, Santiago, Chile
- Buck Institute for Research on Aging, Novato, CA, United States of America
| | - Paola Llanos
- Institute for Research in Dental Sciences, School of Odontology, University of Chile, Santiago, Chile
| | - Dolores Busso
- Department of Nutrition, Diabetes and Metabolism, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Pablo Olmos
- Department of Nutrition, Diabetes and Metabolism, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - José E. Galgani
- Department of Nutrition, Diabetes and Metabolism, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
- UDA-Health Sciences, Nutrition and Dietetic Program, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - José L. Santos
- Department of Nutrition, Diabetes and Metabolism, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Víctor A. Cortés
- Department of Nutrition, Diabetes and Metabolism, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
- * E-mail:
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Moore WT, Bowser SM, Fausnacht DW, Staley LL, Suh KS, Liu D. Beta Cell Function and the Nutritional State: Dietary Factors that Influence Insulin Secretion. Curr Diab Rep 2015; 15:76. [PMID: 26294335 DOI: 10.1007/s11892-015-0650-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Approximately 366 million people worldwide have been diagnosed with type-2 diabetes (T2D). Chronic insulin resistance, decreased functional β-cell mass, and elevated blood glucose are defining characteristics of T2D. Great advances have been made in understanding the pathogenesis of T2D with respect to the effects of dietary macronutrient composition and energy intake on β-cell physiology and glucose homeostasis. It has been further established that obesity is a leading pathogenic factor for developing insulin resistance. However, insulin resistance may not progress to T2D unless β-cells are unable to secret an adequate amount of insulin to compensate for decreased insulin sensitivity. Therefore, pancreatic β-cell dysfunction plays an important role in the development of overt diabetes. This paper reviews recent research findings on the effects of several micronutrients (zinc, vitamin D, iron, vitamin A), leucine, and the phytochemical, genistein on pancreatic β-cell physiology with emphasis on their effects on insulin secretion, specifically in the context of T2D.
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Affiliation(s)
- William T Moore
- Department of Human Nutrition, Foods and Exercises, College of Agricultural and Life Sciences, Virginia Tech Corporate Research Center, 1981 Kraft Drive, Blacksburg, VA, 24061, USA
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Nile DL, Brown AE, Kumaheri MA, Blair HR, Heggie A, Miwa S, Cree LM, Payne B, Chinnery PF, Brown L, Gunn DA, Walker M. Age-related mitochondrial DNA depletion and the impact on pancreatic Beta cell function. PLoS One 2014; 9:e115433. [PMID: 25532126 PMCID: PMC4274008 DOI: 10.1371/journal.pone.0115433] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Accepted: 11/24/2014] [Indexed: 01/21/2023] Open
Abstract
Type 2 diabetes is characterised by an age-related decline in insulin secretion. We previously identified a 50% age-related decline in mitochondrial DNA (mtDNA) copy number in isolated human islets. The purpose of this study was to mimic this degree of mtDNA depletion in MIN6 cells to determine whether there is a direct impact on insulin secretion. Transcriptional silencing of mitochondrial transcription factor A, TFAM, decreased mtDNA levels by 40% in MIN6 cells. This level of mtDNA depletion significantly decreased mtDNA gene transcription and translation, resulting in reduced mitochondrial respiratory capacity and ATP production. Glucose-stimulated insulin secretion was impaired following partial mtDNA depletion, but was normalised following treatment with glibenclamide. This confirms that the deficit in the insulin secretory pathway precedes K+ channel closure, indicating that the impact of mtDNA depletion is at the level of mitochondrial respiration. In conclusion, partial mtDNA depletion to a degree comparable to that seen in aged human islets impaired mitochondrial function and directly decreased insulin secretion. Using our model of partial mtDNA depletion following targeted gene silencing of TFAM, we have managed to mimic the degree of mtDNA depletion observed in aged human islets, and have shown how this correlates with impaired insulin secretion. We therefore predict that the age-related mtDNA depletion in human islets is not simply a biomarker of the aging process, but will contribute to the age-related risk of type 2 diabetes.
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Affiliation(s)
- Donna L. Nile
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
| | - Audrey E. Brown
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
| | - Meutia A. Kumaheri
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
| | - Helen R. Blair
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
| | - Alison Heggie
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
| | - Satomi Miwa
- Newcastle University Institute for Ageing, Newcastle University, Newcastle upon Tyne, NE4 5PL, United Kingdom
| | - Lynsey M. Cree
- Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, University of Auckland, Auckland 1142, New Zealand
| | - Brendan Payne
- Wellcome Centre for Mitochondrial Research, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, United Kingdom
| | - Patrick F. Chinnery
- Wellcome Centre for Mitochondrial Research, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, United Kingdom
| | - Louise Brown
- Unilever R&D, Colworth Science Park, Sharnbrook, Bedford, MK44 1LQ, United Kingdom
| | - David A. Gunn
- Unilever R&D, Colworth Science Park, Sharnbrook, Bedford, MK44 1LQ, United Kingdom
| | - Mark Walker
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
- * E-mail:
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Groschner LN, Alam MR, Graier WF. Metabolism-secretion coupling and mitochondrial calcium activities in clonal pancreatic β-cells. VITAMINS AND HORMONES 2014; 95:63-86. [PMID: 24559914 DOI: 10.1016/b978-0-12-800174-5.00003-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Pancreatic β-cells are the only cells capable of lowering blood glucose by secreting insulin. The β-cell continuously adjusts its secretory activity to substrate availability in order to keep blood glucose levels within the physiological range--a process called metabolism-secretion coupling. Glucose is readily taken up by the β-cell and broken down into intermediates that fuel oxidative metabolism inside the mitochondria to generate ATP. The resulting increase in the ATP/ADP ratio causes closure of plasma membrane KATP channels, thereby depolarizing the cell and triggering the opening of voltage-gated Ca²⁺ channels. Consequential oscillations of cytosolic Ca²⁺ not only mediate the exocytosis of insulin granules but are also relayed to other subcellular compartments including the mitochondria, where Ca²⁺ is required to accelerate mitochondrial metabolism in response to nutrient stimulation. The mitochondrial Ca²⁺ uptake machinery plays a fundamental role in this feed-forward mechanism that guarantees sustained insulin secretion and, thus, represents a promising therapeutic target for type 2 diabetes.
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Affiliation(s)
- Lukas N Groschner
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Graz, Austria
| | - Muhammad Rizwan Alam
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Graz, Austria
| | - Wolfgang F Graier
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Graz, Austria.
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Qiao X, Zhang H, Wu S, Yue H, Zuo J, Feng D, Qi G. Effect of β-hydroxy-β-methylbutyrate calcium on growth, blood parameters, and carcass qualities of broiler chickens. Poult Sci 2013; 92:753-9. [DOI: 10.3382/ps.2012-02341] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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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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12
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Reactive oxygen species in health and disease. J Biomed Biotechnol 2012; 2012:936486. [PMID: 22927725 PMCID: PMC3424049 DOI: 10.1155/2012/936486] [Citation(s) in RCA: 431] [Impact Index Per Article: 35.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2012] [Revised: 07/17/2012] [Accepted: 07/18/2012] [Indexed: 02/06/2023] Open
Abstract
During the past decades, it became obvious that reactive oxygen species (ROS) exert a multitude of biological effects covering a wide spectrum that ranges from physiological regulatory functions to damaging alterations participating in the pathogenesis of increasing number of diseases. This review summarizes the key roles played by the ROS in both health and disease. ROS are metabolic products arising from various cells; two cellular organelles are intimately involved in their production and metabolism, namely, the endoplasmic reticulum and the mitochondria. Updates on research that tremendously aided in confirming the fundamental roles of both organelles in redox regulation will be discussed as well. Although not comprehensive, this review will provide brief perspective on some of the current research conducted in this area for better understanding of the ROS actions in various conditions of health and disease.
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13
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Ramadan JW, Steiner SR, O'Neill CM, Nunemaker CS. The central role of calcium in the effects of cytokines on beta-cell function: implications for type 1 and type 2 diabetes. Cell Calcium 2011; 50:481-90. [PMID: 21944825 DOI: 10.1016/j.ceca.2011.08.005] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Revised: 07/20/2011] [Accepted: 08/16/2011] [Indexed: 12/29/2022]
Abstract
The appropriate regulation of intracellular calcium is a requirement for proper cell function and survival. This review focuses on the effects of proinflammatory cytokines on calcium regulation in the insulin-producing pancreatic beta-cell and how normal stimulus-secretion coupling, organelle function, and overall beta-cell viability are impacted. Proinflammatory cytokines are increasingly thought to contribute to beta-cell dysfunction not only in type 1 diabetes (T1D), but also in the progression of type 2 diabetes (T2D). Cytokine-induced disruptions in calcium handling result in reduced insulin release in response to glucose stimulation. Cytokines can alter intracellular calcium levels by depleting calcium from the endoplasmic reticulum (ER) and by increasing calcium influx from the extracellular space. Depleting ER calcium leads to protein misfolding and activation of the ER stress response. Disrupting intracellular calcium may also affect organelles, including the mitochondria and the nucleus. As a chronic condition, cytokine-induced calcium disruptions may lead to beta-cell death in T1D and T2D, although possible protective effects are also discussed. Calcium is thus central to both normal and pathological cell processes. Because the tight regulation of intracellular calcium is crucial to homeostasis, measuring the dynamics of calcium may serve as a good indicator of overall beta-cell function.
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Affiliation(s)
- James W Ramadan
- Department of Medicine, University of Virginia, Charlottesville, United States
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Role of mitochondrial phosphate carrier in metabolism-secretion coupling in rat insulinoma cell line INS-1. Biochem J 2011; 435:421-30. [PMID: 21265734 DOI: 10.1042/bj20101708] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In pancreatic β-cells, glucose-induced mitochondrial ATP production plays an important role in insulin secretion. The mitochondrial phosphate carrier PiC is a member of the SLC25 (solute carrier family 25) family and transports Pi from the cytosol into the mitochondrial matrix. Since intramitochondrial Pi is an essential substrate for mitochondrial ATP production by complex V (ATP synthase) and affects the activity of the respiratory chain, Pi transport via PiC may be a rate-limiting step for ATP production. We evaluated the role of PiC in metabolism-secretion coupling in pancreatic β-cells using INS-1 cells manipulated to reduce PiC expression by siRNA (small interfering RNA). Consequent reduction of the PiC protein level decreased glucose (10 mM)-stimulated insulin secretion, the ATP:ADP ratio in the presence of 10 mM glucose and elevation of intracellular calcium concentration in response to 10 mM glucose without affecting the mitochondrial membrane potential (Δψm) in INS-1 cells. In experiments using the mitochondrial fraction of INS-1 cells in the presence of 1 mM succinate, PiC down-regulation decreased ATP production at various Pi concentrations ranging from 0.001 to 10 mM, but did not affect Δψm at 3 mM Pi. In conclusion, the Pi supply to mitochondria via PiC plays a critical role in ATP production and metabolism-secretion coupling in INS-1 cells.
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15
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The awakening of an advanced malignant cancer: an insult to the mitochondrial genome. Biochim Biophys Acta Gen Subj 2011; 1820:652-62. [PMID: 21920409 DOI: 10.1016/j.bbagen.2011.08.017] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Revised: 08/26/2011] [Accepted: 08/29/2011] [Indexed: 02/08/2023]
Abstract
BACKGROUND In only months-to-years a primary cancer can progress to an advanced phenotype that is metastatic and resistant to clinical treatments. As early as the 1900s, it was discovered that the progression of a cancer to the advanced phenotype is often associated with a shift in the metabolic profile of the disease from a state of respiration to anaerobic fermentation - a phenomenon denoted as the Warburg Effect. SCOPE OF REVIEW Reports in the literature strongly suggest that the Warburg Effect is generated as a response to a loss in the integrity of the sequence and/or copy number of the mitochondrial genome content within a cancer. MAJOR CONCLUSIONS Multiple studies regarding the progression of cancer indicate that mutation, and/or, a flux in the copy number, of the mitochondrial genome content can support the early development of a cancer, until; the mutational load and/or the reduction-to-depletion of the copy number of the mitochondrial genome content induces the progression of the disease to an advanced phenotype. GENERAL SIGNIFICANCE Collectively, evidence has revealed that the human cell has incorporated the mitochondrial genome content into a cellular mechanism that, when pathologically actuated, can de(un)differentiate a cancer from the parental tissue of origin into an autonomous disease that disrupts the hierarchical structure-and-function of the human body. This article is part of a Special Issue entitled: Biochemistry of Mitochondria.
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Fujimoto S, Mukai E, Inagaki N. Role of endogenous ROS production in impaired metabolism-secretion coupling of diabetic pancreatic β cells. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:304-10. [PMID: 21839765 DOI: 10.1016/j.pbiomolbio.2011.07.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 07/30/2011] [Accepted: 07/31/2011] [Indexed: 12/25/2022]
Abstract
One of the characteristics of type 2 diabetes is that the insulin secretory response of β cells is selectively impaired to glucose. In the Goto-Kakizaki (GK) rat, a genetic model of type 2 diabetes mellitus, glucose-induced insulin secretion is selectively impaired due to deficient ATP production derived from impaired glucose metabolism. In addition, islets in GK rat and human type 2 diabetes are oxidatively stressed. In this issue, role of endogenous reactive oxygen species (ROS) production in impaired metabolism-secretion coupling of diabetic pancreatic β cells is reviewed. In β cells, ROS is endogenously produced by activation of Src, a non-receptor tyrosine kinase. Src inhibitors restore the impaired insulin release and impaired ATP elevation by reduction in ROS production in diabetic islets. Src is endogenously activated in diabetic islets, since the level of Src pY416 in GK islets is higher than that in control islets. In addition, exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist, decreases Src pY416 and glucose-induced ROS production and ameliorates impaired ATP production dependently on Epac in GK islets. These results indicate that GLP-1 signaling regulates endogenous ROS production due to Src activation and that incretin has unique therapeutic effects on impaired glucose metabolism in diabetic β cells.
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Affiliation(s)
- Shimpei Fujimoto
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.
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Lee JW, Kim WH, Yeo J, Jung MH. ER stress is implicated in mitochondrial dysfunction-induced apoptosis of pancreatic beta cells. Mol Cells 2010; 30:545-9. [PMID: 21340672 DOI: 10.1007/s10059-010-0161-5] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Revised: 08/25/2010] [Accepted: 10/22/2010] [Indexed: 12/11/2022] Open
Abstract
Mitochondrial dysfunction induces apoptosis of pancreatic β-cells and leads to type 2 diabetes, but the mechanism involved in this process remains unclear. Chronic endoplasmic reticulum (ER) stress plays a role in the apoptosis of pancreatic β-cells; therefore, in current study, we investigated the implication of ER stress in mitochondrial dysfunction-induced β-cells apoptosis. Metabolic stress induced by antimycin or oligomycin was used to impair mitochondrial function in MIN6N8 cells, which are mouse pancreatic β-cells. Impaired mitochondria dysfunction increased ER stress proteins such as p-eIF2α, GRP78 and GRP 94, as well as ER stress-associated apoptotic factor, CHOP, and activated JNK. AMP-activated protein kinase (AMPK) was also activated under mitochondria dysfunction by metabolic stress. However, the inhibition of AMPK by treatment with compound C, inhibitor of AMPK, and overexpression of mutant dominant negative AMPK (AMPKK45R) blocked the induction of ER stress, which was consist-ent with the decreased β-cell apoptosis and increase of insulin content. Furthermore, mitochondrial dysfunction increased the expression of the inducible nitric oxide synthase (iNOS) gene and the production of nitric oxide (NO), but NO production was prevented by compound C and mutant dominant negative AMPK (AMPK-K45R). Moreover, treatment with 1400W, which is an inhibitor of iNOS, prevented ER stress and apoptosis induced by mitochondrial dysfunction. Treatment of MIN6N8 cells with lipid mixture, physiological conditions of impaired mitochondria function, activated AMPK, increased NO production and induced ER stress. Collectively, these data demonstrate that mitochondrial dysfunction activates AMPK, which induces ER stress via NO production, resulting in pancreatic β-cells apoptosis.
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Affiliation(s)
- June Woo Lee
- School of Korean Medicine, Pusan National University, Yangsan 609-735, Korea
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Jitrapakdee S, Wutthisathapornchai A, Wallace JC, MacDonald MJ. Regulation of insulin secretion: role of mitochondrial signalling. Diabetologia 2010; 53:1019-32. [PMID: 20225132 PMCID: PMC2885902 DOI: 10.1007/s00125-010-1685-0] [Citation(s) in RCA: 220] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/24/2009] [Accepted: 01/06/2010] [Indexed: 12/23/2022]
Abstract
Pancreatic beta cells are specialised endocrine cells that continuously sense the levels of blood sugar and other fuels and, in response, secrete insulin to maintain normal fuel homeostasis. During postprandial periods an elevated level of plasma glucose rapidly stimulates insulin secretion to decrease hepatic glucose output and promote glucose uptake into other tissues, principally muscle and adipose tissues. Beta cell mitochondria play a key role in this process, not only by providing energy in the form of ATP to support insulin secretion, but also by synthesising metabolites (anaplerosis) that can act, both intra- and extramitochondrially, as factors that couple glucose sensing to insulin granule exocytosis. ATP on its own, and possibly modulated by these coupling factors, triggers closure of the ATP-sensitive potassium channel, resulting in membrane depolarisation that increases intracellular calcium to cause insulin secretion. The metabolic imbalance caused by chronic hyperglycaemia and hyperlipidaemia severely affects mitochondrial metabolism, leading to the development of impaired glucose-induced insulin secretion in type 2 diabetes. It appears that the anaplerotic enzyme pyruvate carboxylase participates directly or indirectly in several metabolic pathways which are important for glucose-induced insulin secretion, including: the pyruvate/malate cycle, the pyruvate/citrate cycle, the pyruvate/isocitrate cycle and glutamate-dehydrogenase-catalysed alpha-ketoglutarate production. These four pathways enable 'shuttling' or 'recycling' of these intermediate(s) into and out of mitochondrion, allowing continuous production of intracellular messenger(s). The purpose of this review is to present an account of recent progress in this area of central importance in the realm of diabetes and obesity research.
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Affiliation(s)
- S Jitrapakdee
- Molecular Metabolism Research Group, Department of Biochemistry, Faculty of Science, Mahidol University, Rama 6 Road, Phya-Thai, Bangkok 10400, Thailand.
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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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Zehetner J, Danzer C, Collins S, Eckhardt K, Gerber PA, Ballschmieter P, Galvanovskis J, Shimomura K, Ashcroft FM, Thorens B, Rorsman P, Krek W. PVHL is a regulator of glucose metabolism and insulin secretion in pancreatic beta cells. Genes Dev 2009; 22:3135-46. [PMID: 19056893 PMCID: PMC2593613 DOI: 10.1101/gad.496908] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Insulin secretion from pancreatic beta cells is stimulated by glucose metabolism. However, the relative importance of metabolizing glucose via mitochondrial oxidative phosphorylation versus glycolysis for insulin secretion remains unclear. von Hippel-Lindau (VHL) tumor suppressor protein, pVHL, negatively regulates hypoxia-inducible factor HIF1alpha, a transcription factor implicated in promoting a glycolytic form of metabolism. Here we report a central role for the pVHL-HIF1alpha pathway in the control of beta-cell glucose utilization, insulin secretion, and glucose homeostasis. Conditional inactivation of Vhlh in beta cells promoted a diversion of glucose away from mitochondria into lactate production, causing cells to produce high levels of glycolytically derived ATP and to secrete elevated levels of insulin at low glucose concentrations. Vhlh-deficient mice exhibited diminished glucose-stimulated changes in cytoplasmic Ca(2+) concentration, electrical activity, and insulin secretion, which culminate in impaired systemic glucose tolerance. Importantly, combined deletion of Vhlh and Hif1alpha rescued these phenotypes, implying that they are the result of HIF1alpha activation. Together, these results identify pVHL and HIF1alpha as key regulators of insulin secretion from pancreatic beta cells. They further suggest that changes in the metabolic strategy of glucose metabolism in beta cells have profound effects on whole-body glucose homeostasis.
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Affiliation(s)
- Jens Zehetner
- Institute of Cell Biology and Competence Center for Systems Physiology and Metabolic Diseases, ETH Zurich, 8093 Zurich, Switzerland
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Sproule DM, Kaufmann P. Mitochondrial encephalopathy, lactic acidosis, and strokelike episodes: basic concepts, clinical phenotype, and therapeutic management of MELAS syndrome. Ann N Y Acad Sci 2008; 1142:133-58. [PMID: 18990125 DOI: 10.1196/annals.1444.011] [Citation(s) in RCA: 216] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Since the initial description almost 25 years ago, the syndrome of mitochondrial encephalopathy, lactic acidosis, and strokelike episodes (MELAS) has been a useful model to study the complex interplay of factors that define mitochondrial disease. This syndrome, most commonly caused by an A-to-G transition mutation at position 3243 of the mitochondrial genome, is typified by characteristic neurological manifestations including seizures, encephalopathy, and strokelike episodes, as well as other frequent secondary manifestations including short stature, cognitive impairment, migraines, depression, cardiomyopathy, cardiac conduction defects, and diabetes mellitus. In this review, we discuss the history, pathogenesis, clinical features, and diagnostic and management strategies of mitochondrial disease in general and of MELAS in particular. We explore features of mitochondrial genetics, including the concepts of heteroplasmy, mitotic segregation, and threshold effect, as a basis for understanding the variability and complicated inheritance patterns seen with this group of diseases. We also describe systemic manifestations of MELAS-associated mutations, including cardiac, renal, endocrine, gastrointestinal, and endothelial abnormalities and pathology, as well as the hypothetical role of derangements to COX enzymatic function in driving the unique pathology and clinical manifestations of MELAS. Although therapeutic options for MELAS and other mitochondrial diseases remain limited, and recent trials have been disappointing, we also consider current and potential therapeutic modalities.
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Affiliation(s)
- Douglas M Sproule
- Columbia University, Pediatric Neurology, 180 Fort Washington Ave., Harkness Pavilion, 5th floor, New York, NY 10032, USA.
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9-cis retinoic acid induces retinoid X receptor localized to the mitochondria for mediation of mitochondrial transcription. Biochem Biophys Res Commun 2008; 377:351-354. [DOI: 10.1016/j.bbrc.2008.09.122] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Accepted: 09/26/2008] [Indexed: 11/19/2022]
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Kominato R, Fujimoto S, Mukai E, Nakamura Y, Nabe K, Shimodahira M, Nishi Y, Funakoshi S, Seino Y, Inagaki N. Src activation generates reactive oxygen species and impairs metabolism-secretion coupling in diabetic Goto-Kakizaki and ouabain-treated rat pancreatic islets. Diabetologia 2008; 51:1226-35. [PMID: 18449527 DOI: 10.1007/s00125-008-1008-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2008] [Accepted: 03/16/2008] [Indexed: 11/29/2022]
Abstract
AIMS/HYPOTHESIS Na(+)/K(+)-ATPase inhibition by ouabain suppresses ATP production by generating reactive oxygen species (ROS) and impairs glucose-induced insulin secretion from pancreatic islets. To clarify the signal-transducing function of Na(+)/K(+)-ATPase in decreasing ATP production by the generation of ROS in pancreatic islets, the involvement of Src was examined. In addition, the significance of Src activation in diabetic islets was examined. METHODS Isolated islets from Wistar rats and diabetic Goto-Kakizaki (GK) rats (a model for diabetes) were used. ROS was measured by 5-(and 6)-chloromethyl-2',7'-dichlorofluorescein fluorescence using dispersed islet cells. After lysates were immunoprecipitated by anti-Src antibody, immunoblotting was performed. RESULTS Ouabain caused a rapid Tyr(418) phosphorylation, indicating activation of Src in the presence of high glucose. The specific Src inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) restored the ouabain-induced decrease in ATP content and the increase in ROS production. Both PP2 and ROS scavenger restored the impaired insulin release and impaired ATP elevation in GK islets, but had no such effect in control islets. PP2 reduced the high glucose-induced increase in ROS generation in GK islet cells but had no effect on that in control islet cells. Moreover, ouabain had no effect on ATP content and ROS production in the presence of high glucose in GK islets. CONCLUSIONS/INTERPRETATION These results indicate that Src plays a role in the signal-transducing function of Na(+)/K(+)-ATPase, in which ROS generation decreases ATP production in control islets. Moreover, ROS generated by Src activation plays an important role in impaired glucose-induced insulin secretion in GK islets, in which Src is endogenously activated independently of ouabain.
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Affiliation(s)
- R Kominato
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto, 606-8507, Japan
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Jeng JY, Yeh TS, Lee JW, Lin SH, Fong TH, Hsieh RH. Maintenance of mitochondrial DNA copy number and expression are essential for preservation of mitochondrial function and cell growth. J Cell Biochem 2008; 103:347-57. [PMID: 18072287 DOI: 10.1002/jcb.21625] [Citation(s) in RCA: 132] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
To examine whether a reduction in the mtDNA level will compromise mitochondrial biogenesis and mitochondrial function, we created a cell model with depleted mtDNA. Stable transfection of small interfering (si)RNA of mitochondrial transcription factor A (Tfam) was used to interfere with Tfam gene expression. Selected stable clones showed 60-95% reduction in Tfam gene expression and 50-90% reduction in cytochrome b (Cyt b) gene expression. Tfam gene knockdown clones also showed decreased mtDNA-encoded cytochrome c oxidase subunit I (COX I) protein expression. However, no significant differences in protein expression were observed in nuclear DNA (nDNA)-encoded mitochondrial respiratory enzyme subunits. The cell morphology changed from a rhombus-like to a spindle-like form as determined in clones with decreased expressions of Tfam, mtRNA, and mitochondrial proteins. The mitochondrial respiratory enzyme activities and ATP production in such clones were significantly lower. The proportions of mtDNA mutations including 8-hydroxy-2'-deoxyguanosine (8-OHdG), a 4,977-bp deletion, and a 3,243-point mutation were also examined in these clones. No obvious increase in mtDNA mutations was observed in mitochondrial dysfunctional cell clones. The mitochondrial respiratory activity and ATP production ability recovered in cells with increased mtDNA levels after removal of the specific siRNA treatment. These experimental results provide direct evidence to substantiate that downregulation of mtDNA copy number and expression may compromise mitochondrial function and subsequent cell growth and morphology.
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Affiliation(s)
- Jaan-Yeh Jeng
- Department of General Surgery, Cathay General Hospital, Taipei, Taiwan, Republic of China
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Fujimoto S, Nabe K, Takehiro M, Shimodahira M, Kajikawa M, Takeda T, Mukai E, Inagaki N, Seino Y. Impaired metabolism-secretion coupling in pancreatic beta-cells: role of determinants of mitochondrial ATP production. Diabetes Res Clin Pract 2007; 77 Suppl 1:S2-10. [PMID: 17449130 DOI: 10.1016/j.diabres.2007.01.026] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 01/29/2007] [Indexed: 12/21/2022]
Abstract
Glucose-induced insulin secretion from beta-cells is often impaired in diabetic condition and by exposure to diabetogenic pharmacological agents. In pancreatic beta-cells, intracellular glucose metabolism regulates exocytosis of insulin granules, according to metabolism-secretion coupling in which glucose-induced mitochondrial ATP production plays an essential role. Impaired glucose-induced insulin secretion often results from impaired glucose-induced ATP elevation in beta-cells. Mitochondrial ATP production is driven by the proton-motive force including mitochondrial membrane potential (DeltaPsi(m)) generated by the electron transport chain. These electrons are derived from reducing equivalents, generated in the Krebs cycle and transferred from cytosol by the shuttles. Here, roles of the determinants of mitochondrial ATP production in impaired glucose-induced insulin secretion are discussed. Cytosolic alkalization, H(+) leak in the inner membrane by uncoupler (e.g. free fatty acid exposure), decrease in the supply of electron donors including NADH and FADH(2) to the respiratory chain, and endogenous mitochondrial ROS (e.g. Na(+)/K(+)-ATPase inhibition) all reduce hyperpolarlization of DeltaPsi(m) and ATP production, causing decresed glucose-induced insulin release. The decrease in the supply of NADH and FADH(2) to the respiratory chain derives from impairments in glucose metabolism including glycolysis (e.g. MODY2 and exposure to NO) and the shuttles (e.g. diabetic state and exposure to ketone body).
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Affiliation(s)
- Shimpei Fujimoto
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
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Araki E, Miyazaki JI. Metabolic disorders in diabetes mellitus: impact of mitochondrial function and oxidative stress on diabetes and its complications. Antioxid Redox Signal 2007; 9:289-91. [PMID: 17184179 DOI: 10.1089/ars.2006.1486] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Nishikawa T, Araki E. Impact of mitochondrial ROS production in the pathogenesis of diabetes mellitus and its complications. Antioxid Redox Signal 2007; 9:343-53. [PMID: 17184177 DOI: 10.1089/ars.2006.1458] [Citation(s) in RCA: 298] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In this review, the impacts of mitochondrial reactive oxygen species (ROS) on diabetes and its complications are described. In endothelial cells, high-glucose treatment increases mitochondrial ROS and normalization of the ROS production by inhibitors of mitochondrial metabolism, or by overexpression of UCP-1 or MnSOD, prevents glucose-induced activation of PKC, formation of AGE, and accumulation of sorbitol, all of which are believed to be the main molecular mechanisms of diabetic complications. Glomerular hyperfiltration, one of the characteristics of early diabetic nephropathy, may be caused by mitochondrial ROS through activation of COX-2 gene transcription, followed by PGE2 overproduction. In pancreatic beta cells, hyperglycemia also increases mitochondrial ROS, which suppresses the first phase of glucose-induced insulin secretion, at least in part, through the suppression of GAPDH activity. In liver cells, similar to that in hyperglycemia, TNF-alpha increases mitochondrial ROS, which in turn activates apoptosis signal-regulating kinase 1 (ASK1) and c-jun NH2-terminal kinases (JNK), increases serine phosphorylation of IRS-1, and decreases insulin-stimulated tyrosine phosphorylation of IRS-1, leading to insulin resistance. These results suggest the importance of mitochondrial ROS in the pathogenesis of diabetes mellitus and its complications through modification of various cellular events in many tissues, including vessels, kidney, pancreatic beta cells, and liver.
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Affiliation(s)
- Takeshi Nishikawa
- Department of Metabolic Medicine, Faculty of Medical and Pharmaceutical Sciences, Kumamoto University, Kumamoto, Japan.
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Maechler P, de Andrade PBM. Mitochondrial damages and the regulation of insulin secretion. Biochem Soc Trans 2007; 34:824-7. [PMID: 17052207 DOI: 10.1042/bst0340824] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Pancreatic beta-cells are able to respond to nutrients, principally glucose, as the primary stimulus for insulin exocytosis. This unique feature requires translation of metabolic substrates into intracellular messengers recognized by the exocytotic machinery. Central to this signal transduction mechanism, mitochondria integrate and generate metabolic signals, thereby coupling glucose recognition with insulin secretion. In response to a glucose rise, nucleotides and metabolites are generated by mitochondria and participate, together with cytosolic Ca2+, in the stimulation of insulin exocytosis. Mitochondrial defects, such as mutations and ROS (reactive oxygen species) production, might be associated with beta-cell failure in the course of diabetes. mtDNA (mitochondrial DNA) mutation A3243G is associated with MIDD (mitochondrial inherited diabetes and deafness). A common hypothesis to explain the link between the genotype and the phenotype is that the mutation might impair mitochondrial metabolism expressly required for beta-cell functions, although this assumption lacks direct demonstration. mtDNA-deficient cellular models are glucose-unresponsive and are defective in mitochondrial function. Recently, we used clonal cytosolic hybrid cells (namely cybrids) harbouring mitochondria derived from MIDD patients. Compared with control mtDNA from the same patient, the A3243G mutation markedly modified metabolic pathways. Moreover, cybrid cells carrying patient-derived mutant mtDNA exhibited deranged cell Ca2+ handling and elevated ROS under metabolic stress. In animal models, transgenic mice lacking expression of the mitochondrial genome specifically in beta-cells are diabetic and their islets are incable of releasing insulin in response to glucose. These various models demonstrate the fragility of nutrient-stimulated insulin secretion, caused primarily by defective mitochondrial function.
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Affiliation(s)
- P Maechler
- Department of Cell Physiology and Metabolism, University Medical Centre, rue Michel-Servet 1, CH-1211 Geneva 4, Switzerland.
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de Andrade PBM, Rubi B, Frigerio F, van den Ouweland JMW, Maassen JA, Maechler P. Diabetes-associated mitochondrial DNA mutation A3243G impairs cellular metabolic pathways necessary for beta cell function. Diabetologia 2006; 49:1816-26. [PMID: 16736129 DOI: 10.1007/s00125-006-0301-9] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/24/2005] [Accepted: 04/06/2006] [Indexed: 10/24/2022]
Abstract
AIMS/HYPOTHESIS Mitochondrial DNA (mtDNA) mutations cause several diseases, including mitochondrial inherited diabetes and deafness (MIDD), typically associated with the mtDNA A3243G point mutation on tRNALeu gene. The common hypothesis to explain the link between the genotype and the phenotype is that the mutation might impair mitochondrial metabolism expressly required for beta cell functions. However, this assumption has not yet been tested. METHODS We used clonal osteosarcoma cytosolic hybrid cells (namely cybrids) harbouring mitochondria derived from MIDD patients and containing either exclusively wild-type or mutated (A3243G) mtDNA. According to the importance of mitochondrial metabolism in beta cells, we studied the impact of the mutation on key parameters by comparing stimulation of these cybrids by the main insulin secretagogue glucose and the mitochondrial substrate pyruvate. RESULTS Compared with control mtDNA from the same patient, the A3243G mutation markedly modified metabolic pathways leading to a high glycolytic rate (2.8-fold increase), increased lactate production (2.5-fold), and reduced glucose oxidation (-83%). We also observed impaired NADH responses (-56%), negligible mitochondrial membrane potential, and reduced, only transient ATP generation. Moreover, cybrid cells carrying patient-derived mutant mtDNA exhibited deranged cell calcium handling with increased cytosolic loads (1.4-fold higher), and elevated reactive oxygen species (2.6-fold increase) under glucose deprivation. CONCLUSIONS/INTERPRETATION The present study demonstrates that the mtDNA A3243G mutation impairs crucial metabolic events required for proper cell functions, such as coupling of glucose recognition to insulin secretion.
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Affiliation(s)
- P B M de Andrade
- Department of Cell Physiology and Metabolism, University Medical Center, 1 rue Michel-Servet, CH-1211 Geneva 4, Switzerland
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Foye OT, Uni Z, Ferket PR. Effect of in ovo feeding egg white protein, β-hydroxy-β-methylbutyrate, and carbohydrates on glycogen status and neonatal growth of turkeys. Poult Sci 2006; 85:1185-92. [PMID: 16830858 DOI: 10.1093/ps/85.7.1185] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In ovo feeding (IOF), injecting dietary components into the amnion about 1 d prior to internal pipping, may enhance growth by altering glycogen status. This hypothesis was evaluated with 5 IOF solutions containing protein, beta-hydroxy-beta-methylbutyrate (HMB), and carbohydrate. Four IOF treatments were arranged as a factorial of 2 levels of egg white protein (EWP; 0 and 18%) and 2 levels of HMB (0 and 0.1%). An IOF solution of carbohydrates (S; 20% dextrin and 3% maltose) was evaluated for contrast purposes. At 23 d of incubation, 1.5 mL of IOF solution was injected into the amnion of 100 eggs per treatment. At hatch, feed and water were provided ad libitum. At hatch and 3 and 7 d of age, BW were determined, and 10 poults per treatment were sampled to determine liver (LG) and pectoralis muscle (PC) glycogen content. Poults on IOF treatments A (18% EWP), B (18% EWP + HMB), and D (HMB) weighed 6.0, 2.7, and 3.3% more than the controls at hatch, respectively (P < 0.05) with an EWP x HMB interaction (P < 0.05) sustained to 3 and 7 d only in treatment D (P < 0.005). At hatch, A and D poults had greater percentages of PC (P < 0.05) than controls, and the percentage of PC in treatment D was sustained until 7 d. Total LG was enhanced by A and B at 7 d (P < 0.05) over the controls, whereas total PC glycogen was enhanced at 7 d by IOF treatment D (P < 0.05). The IOF A and S poults had greater BW than the controls at hatch only (P < 0.05). The IOF treatment A had greater LG at hatch (P < 0.05), but by 7 d, A and S had greater LG than controls (P < 0.05). Poults fed S in ovo had enhanced total PC glycogen over controls, whereas poults on treatment A had less total PC glycogen than controls (P < 0.05). The results of this experiment demonstrate that IOF of A or S poults may enhance hatch BW and glycogen status of poults during the neonatal period by inclusion of HMB.
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Affiliation(s)
- O T Foye
- Department of Poultry Science, North Carolina State University, Raleigh 27695-7608, USA
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31
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Affourtit C, Brand MD. Stronger control of ATP/ADP by proton leak in pancreatic beta-cells than skeletal muscle mitochondria. Biochem J 2006; 393:151-9. [PMID: 16137248 PMCID: PMC1383673 DOI: 10.1042/bj20051280] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Pancreatic beta cells respond to rising blood glucose concentrations by increasing their oxidative metabolism, which leads to an increased ATP/ADP ratio, closure of K(ATP) channels, depolarization of the plasma membrane potential, influx of calcium and the eventual secretion of insulin. Such a signalling mechanism implies that the ATP/ADP ratio is flexible in beta cells (beta-cells), which is in contrast with other cell types (e.g. muscle and liver) that maintain a stable ATP/ADP poise while respiring at widely varying rates. To determine whether this difference in flexibility is accounted for by mitochondrial peculiarities, we performed a top-down metabolic control analysis to quantitatively assess how ATP/ADP is controlled in mitochondria isolated from rat skeletal muscle and cultured beta cells. We show that the ATP/ADP ratio is more strongly controlled (approx. 7.5-fold) by proton leak in beta cells than in muscle. The comparatively high importance of proton leak in beta cell mitochondria (relative to phosphorylation) is evidenced furthermore by its relatively high level of control over membrane potential and overall respiratory activity. Modular-kinetic analysis of oxidative phosphorylation reveals that these control differences can be fully explained by a higher relative leak activity in beta cell mitochondria, which results in a comparatively high contribution of proton leak to the overall respiratory activity in this system.
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Maechler P, Carobbio S, Rubi B. In beta-cells, mitochondria integrate and generate metabolic signals controlling insulin secretion. Int J Biochem Cell Biol 2006; 38:696-709. [PMID: 16443386 DOI: 10.1016/j.biocel.2005.12.006] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2005] [Revised: 12/08/2005] [Accepted: 12/12/2005] [Indexed: 12/14/2022]
Abstract
Pancreatic beta-cells are unique neuroendocrine cells displaying the peculiar feature of responding to nutrients, principally glucose, as primary stimulus. This requires translation of a metabolic substrate into intracellular messengers recognized by the exocytotic machinery. Central to this signal transduction mechanism, mitochondria integrate and generate metabolic signals, thereby coupling glucose recognition to insulin secretion. In response to a glucose rise, nucleotides and metabolites are generated by mitochondria and participate, together with cytosolic calcium, to the stimulation of insulin exocytosis. This review describes the mitochondrion-dependent pathways of regulated insulin secretion. In particular, importance of cataplerotic and anaplerotic processes is discussed, with special attention to the mitochondrial enzyme glutamate dehydrogenase. Mitochondrial defects, such as mutations and reactive oxygen species production, are presented in the context of beta-cell failure in the course of type 2 diabetes.
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Affiliation(s)
- Pierre Maechler
- Department of Cell Physiology and Metabolism, University Medical Centre, Geneva, Switzerland.
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Lee YY, Park KS, Pak YK, Lee HK. The role of mitochondrial DNA in the development of type 2 diabetes caused by fetal malnutrition. J Nutr Biochem 2005; 16:195-204. [PMID: 15808323 DOI: 10.1016/j.jnutbio.2004.11.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2004] [Revised: 10/12/2004] [Accepted: 11/05/2004] [Indexed: 01/06/2023]
Abstract
Epidemiological studies have revealed strong and reproducible links between indices of poor fetal growth and susceptibility to the development of glucose intolerance and insulin resistance syndrome in adult life. To explain these associations, the thrifty phenotype hypothesis has been proposed. Mitochondrial DNA abnormalities have been known to cause insulin deficiency, insulin resistance and diabetes mellitus. In this review, we propose that mitochondrial dysfunction is a link between malnutrition during early life and disease in adult life. The potential mechanism for mitochondrial dysfunction will be focused on availability of the taurine and nucleotides, and imprinting on the genes.
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Affiliation(s)
- Yun Yong Lee
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul 110-744, South Korea
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Grishko V, Rachek L, Musiyenko S, Ledoux SP, Wilson GL. Involvement of mtDNA damage in free fatty acid-induced apoptosis. Free Radic Biol Med 2005; 38:755-62. [PMID: 15721986 DOI: 10.1016/j.freeradbiomed.2004.11.023] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2004] [Revised: 11/12/2004] [Accepted: 11/12/2004] [Indexed: 10/26/2022]
Abstract
A growing body of evidence indicates that free fatty acids (FFA) can have deleterious effects on beta-cells. It has been suggested that the beta-cell dysfunction and death observed in diabetes may involve exaggerated activation of the inducible form of nitric oxide synthase (iNOS) by FFA, with the resultant generation of excess nitric oxide (NO). However, the cellular targets with which NO interact have not been fully identified. We hypothesized that one of these targets might be mitochondrial DNA (mtDNA). Therefore, experiments were initiated to evaluate damage to mtDNA caused by exposure of INS-1 cells to FFA (2/1 oleate/palmetate). The results showed that FFA caused a dose-dependent increase in mtDNA damage. Additionally, using ligation-mediated PCR, we were able to show that the DNA damage pattern at the nucleotide level was identical to the one induced by pure NO and different from damage caused by peroxynitrite or superoxide. Following exposure to FFA, apoptosis was detected by DAPI staining and cytochrome c release. Treatment of INS-1 cells with the iNOS inhibitor aminoguanidine protected these cells from mtDNA damage and diminished the appearance of apoptosis. These studies suggest that mtDNA may be a sensitive target for NO-induced toxicity which may provoke apoptosis in beta-cells following exposure to FFA.
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Affiliation(s)
- Valentina Grishko
- Department of Cell Biology and Neuroscience, University of South Alabama College of Medicine, Mobile, AL 36688, USA
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35
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Li N, Wang Q, Li J, Wang X, Hellmich MR, Rajaraman S, Greeley GH, Townsend CM, Evers BM. Inhibition of mitochondrial gene transcription suppresses neurotensin secretion in the human carcinoid cell line BON. Am J Physiol Gastrointest Liver Physiol 2005; 288:G213-20. [PMID: 15358593 DOI: 10.1152/ajpgi.00043.2004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Mitochondria, organelles essential for ATP production, play a central role in a number of cellular functions, including the regulation of insulin secretion. Neurotensin (NT), an important regulatory intestinal hormone, has been implicated in fatty acid translocation, gut motility and secretion, and intestinal cell growth; however, mechanisms regulating NT secretion have not been entirely defined. The purpose of this study was to determine the effect of inhibition of mitochondrial gene transcription on NT secretion. BON cells, a novel human carcinoid cell line that produces and secretes NT peptide and expresses the gene encoding NT (designated NT/N), were treated with ethidium bromide (EB; 0.05, 0.1, and 0.4 microg/ml), an inhibitor of DNA and RNA synthesis, or vehicle over a time course (1-4 days). Cells were then stimulated with either ACh (100 microM) or phorbol 12 myristate,13-acetate (PMA, 10 nM) for 30 min. Media and cells were extracted, and NT peptide measured by RIA. Treatment with EB had no effect on BON cell viability or cell cycle distribution over the 4-day course. In contrast, EB treatment produced a dose-dependent reduction of mitochondrial gene expression; however, NT/N gene expression was not altered. Mitochondrial inhibition by EB treatment suppressed NT secretion induced by ACh and PMA, both in a dose-dependent manner. EB-mediated inhibition of NT secretion and mitochondrial gene expression was reversed with removal of EB. Our results demonstrate that inhibition of mitochondrial gene transcription suppresses both ACh- and PMA-stimulated NT release. These findings are the first to demonstrate that mitochondrial function is important for agonist-mediated NT secretion.
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Affiliation(s)
- Nan Li
- Department of Surgery, The University of Texas Medical Branch, Galveston, Texas 77555-0536, USA
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36
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Maassen JA, 'T Hart LM, Van Essen E, Heine RJ, Nijpels G, Jahangir Tafrechi RS, Raap AK, Janssen GMC, Lemkes HHPJ. Mitochondrial diabetes: molecular mechanisms and clinical presentation. Diabetes 2004; 53 Suppl 1:S103-9. [PMID: 14749274 DOI: 10.2337/diabetes.53.2007.s103] [Citation(s) in RCA: 289] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Mutations in mitochondrial DNA (mtDNA) associate with various disease states. A few mtDNA mutations strongly associate with diabetes, with the most common mutation being the A3243G mutation in the mitochondrial DNA-encoded tRNA(Leu,UUR) gene. This article describes clinical characteristics of mitochondrial diabetes and its molecular diagnosis. Furthermore, it outlines recent developments in the pathophysiological and molecular mechanisms leading to a diabetic state. A gradual development of pancreatic beta-cell dysfunction upon aging, rather than insulin resistance, is the main mechanism in developing glucose intolerance. Carriers of the A3243G mutation show during a hyperglycemic clamp at 10 mmol/l glucose a marked reduction in first- and second-phase insulin secretion compared with noncarriers. The molecular mechanism by which the A3243G mutation affects insulin secretion may involve an attenuation of cytosolic ADP/ATP levels leading to a resetting of the glucose sensor in the pancreatic beta-cell, such as in maturity-onset diabetes of the young (MODY)-2 patients with mutations in glucokinase. Unlike in MODY2, which is a nonprogressive form of diabetes, mitochondrial diabetes does show a pronounced age-dependent deterioration of pancreatic function indicating involvement of additional processes. Furthermore, one would expect that all mtDNA mutations that affect ATP synthesis lead to diabetes. This is in contrast to clinical observations. The origin of the age-dependent deterioration of pancreatic function in carriers of the A3243G mutation and the contribution of ATP and other mitochondrion-derived factors such as reactive oxygen species to the development of diabetes is discussed.
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Affiliation(s)
- J Antonie Maassen
- Department of Molecular Cell Biology, Leiden University Medical Centre, Leiden, the Netherlands.
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37
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Lee B, Miles PD, Vargas L, Luan P, Glasco S, Kushnareva Y, Kornbrust ES, Grako KA, Wollheim CB, Maechler P, Olefsky JM, Anderson CM. Inhibition of mitochondrial Na+-Ca2+ exchanger increases mitochondrial metabolism and potentiates glucose-stimulated insulin secretion in rat pancreatic islets. Diabetes 2003; 52:965-73. [PMID: 12663468 DOI: 10.2337/diabetes.52.4.965] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The mitochondrial Na(+)-Ca(2+) exchanger (mNCE) mediates efflux of Ca(2+) from mitochondria in exchange for influx of Na(+). We show that inhibition of the mNCE enhances mitochondrial oxidative metabolism and increases glucose-stimulated insulin secretion in rat islets and INS-1 cells. The benzothiazepine CGP37157 inhibited mNCE activity in INS-1 cells (50% inhibition at IC(50) = 1.5 micro mol/l) and increased the glucose-induced rise in mitochondrial Ca(2+) ([Ca(2+)](m)) 2.1 times. Cellular ATP content was increased by 13% in INS-1 cells and by 49% in rat islets by CGP37157 (1 micro mol/l). Krebs cycle flux was also stimulated by CGP37157 when glucose was present. Insulin secretion was increased in a glucose-dependent manner by CGP37157 in both INS-1 cells and islets. In islets, CGP37157 increased insulin secretion dose dependently (half-maximal efficacy at EC(50) = 0.06 micro mol/l) at 8 mmol/l glucose and shifted the glucose dose response curve to the left. In perifused islets, mNCE inhibition had no effect on insulin secretion at 2.8 mmol/l glucose but increased insulin secretion by 46% at 11 mmol/l glucose. The effects of CGP37157 could not be attributed to interactions with the plasma membrane sodium calcium exchanger, L-type calcium channels, ATP-sensitive K(+) channels, or [Ca(2+)](m) uniporter. In hyperglycemic clamp studies of Wistar rats, CGP37157 increased plasma insulin and C-peptide levels only during the hyperglycemic phase of the study. These results illustrate the potential utility of agents that affect mitochondrial metabolism as novel insulin secretagogues.
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Affiliation(s)
- Bumsup Lee
- Division of Metabolic Diseases, MitoKor, San Diego, California 92121, USA
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38
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Jazayeri M, Andreyev A, Will Y, Ward M, Anderson CM, Clevenger W. Inducible expression of a dominant negative DNA polymerase-gamma depletes mitochondrial DNA and produces a rho0 phenotype. J Biol Chem 2003; 278:9823-30. [PMID: 12645575 DOI: 10.1074/jbc.m211730200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We report the inducible, stable expression of a dominant negative form of mitochondria-specific DNA polymerase-gamma to eliminate mitochondrial DNA (mtDNA) from human cells in culture. HEK293 cells were transfected with a plasmid encoding inactive DNA polymerase-gamma harboring a D1135A substitution (POLGdn). The cells rapidly lost mtDNA (t1/2 = 2-3 days) when expression of the transgene was induced. Concurrent reduction of mitochondrial encoded mRNA and protein, decreased cellular growth rate, and compromised respiration and mitochondrial membrane potential were observed. mtDNA depletion was reversible, as demonstrated by restoration of mtDNA copy number to normal within 10 days when the expression of POLGdn was suppressed following a 3-day induction period. Long term (20 days) expression of POLGdn completely eliminated mtDNA from the cells, resulting in rho0 cells that were respiration-deficient, lacked electron transport complex activities, and were auxotrophic for pyruvate and uridine. Fusion of the rho0 cells with human platelets yielded clonal cybrid cell lines that were populated exclusively with donor-derived mtDNA. Respiratory function, mitochondrial membrane potential, and electron transport activities were restored to normal in the cybrid cells. Inducible expression of a dominant negative DNA polymerase-gamma can yield mtDNA-deficient cell lines, which can be used to study the impact of specific mtDNA mutations on cellular physiology, and to investigate mitochondrial genome function and regulation.
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39
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Noda M, Yamashita S, Takahashi N, Eto K, Shen LM, Izumi K, Daniel S, Tsubamoto Y, Nemoto T, Iino M, Kasai H, Sharp GWG, Kadowaki T. Switch to anaerobic glucose metabolism with NADH accumulation in the beta-cell model of mitochondrial diabetes. Characteristics of betaHC9 cells deficient in mitochondrial DNA transcription. J Biol Chem 2002; 277:41817-26. [PMID: 12169697 DOI: 10.1074/jbc.m207690200] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To elucidate the mechanism underlying diabetes caused by mitochondrial gene mutations, we created a model by applying 0.4 microg/ml ethidium bromide (EtBr) to the murine pancreatic beta cell line betaHC9; in this model, transcription of mitochondrial DNA, but not that of nuclear DNA, was suppressed in association with impairment of glucose-stimulated insulin release (Hayakawa, T., Noda, M., Yasuda, K., Yorifuji, H., Taniguchi, S., Miwa, I., Sakura, H., Terauchi, Y., Hayashi, J.-I., Sharp, G. W. G., Kanazawa, Y., Akanuma, Y., Yazaki, Y., and Kadowaki, T. (1998) J. Biol. Chem. 273, 20300-20307). To elucidate fully the metabolism-secretion coupling in these cells, we measured glucose oxidation, utilization, and lactate production. We also evaluated NADH autofluorescence in betaHC9 cells using two-photon excitation laser microscopy. In addition, we recorded the membrane potential and determined the ATP and ADP contents of the cells. The results indicated 22.2 mm glucose oxidation to be severely decreased by EtBr treatment compared with control cells (by 63% on day 4 and by 78% on day 6; both p < 0.01). By contrast, glucose utilization was only marginally decreased. Lactate production under 22.2 mm glucose was increased by 2.9- and 3.5-fold by EtBr treatment on days 4 and 6, respectively (both p < 0.01). Cellular NADH at 2.8 mm glucose was increased by 35 and 43% by EtBr on days 4 and 6 (both p < 0.01). These data suggest that reduced expression of the mitochondrial electron transport system causes NADH accumulation in beta cells, thereby halting the tricarboxylic acid cycle on one hand, and on the other hand facilitating anaerobic glucose metabolism. Glucose-induced insulin secretion was lost rapidly along with the EtBr treatment with concomitant losses of membrane potential depolarization and the [Ca(2+)](i) increase, whereas glibenclamide-induced changes persisted. This is the first report to demonstrate the connection between metabolic alteration of electron transport system and that of tricarboxylic acid cycle and its impact on insulin secretion.
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Affiliation(s)
- Mitsuhiko Noda
- Department of Metabolic Diseases, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Japan
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40
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Nakazaki M, Kakei M, Ishihara H, Koriyama N, Hashiguchi H, Aso K, Fukudome M, Oka Y, Yada T, Tei C. Association of upregulated activity of K(ATP) channels with impaired insulin secretion in UCP1-expressing insulinoma cells. J Physiol 2002; 540:781-9. [PMID: 11986368 PMCID: PMC2290263 DOI: 10.1113/jphysiol.2001.013048] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Insulin-secreting MIN6 cells overexpressing uncoupling protein-1 (UCP1) were studied regarding insulin secretion in response to various secretagogues. Overexpression of UCP1 prevented an increase of cytosolic ATP levels induced by glucose. In contrast, glucose utilization was not affected, nor was glycerol phosphate flux. The UCP1-expressing cells showed an inability to increase cytosolic Ca(2+) concentration ([Ca(2+)](i)) in response to glucose or alpha ketoisocaproate and this resulted in less insulin secretion, whereas initial reduction in [Ca(2+)](i) occurring upon either nutrient addition was not affected. Moreover, the effectiveness of tolbutamide on [Ca(2+)](i) increase was reduced and the dose-response relations for insulin secretion induced by the agent was shifted toward the right in the UCP1-expressing cells. The resting membrane potential of the UCP1-expressing cells was significantly hyperpolarized by 6.2 mV compared with control cells. In the perforated and conventional whole-cell patch-clamp configurations, the conductance density of ATP-sensitive K(+) (K(ATP)) channels of the UCP1-expressing cells was 6-fold and 1.7-fold greater than that of the control cells, respectively. The sensitivity of K(ATP) channels for tolbutamide was not different between two groups, indicating that in intact cells more than 6-fold higher concentrations of tolbutamide were required to reduce the K(ATP) channel currents of UCP1-expressing cells to the same levels as of the control cells. The current density of the voltage-dependent Ca(2+) channels was not influenced. In conclusion, UCP1-expressing cells showed a refractoriness to respond to tolbutamide as well as nutrients. An upregulated activity of K(ATP) channels was associated with unresponsiveness to the agent in the cells with impaired mitochondrial function.
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Affiliation(s)
- Mitsuhiro Nakazaki
- First Department of Internal Medicine, Faculty of Medicine, Kagoshima University, Kagoshima 890-8520, Japan.
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41
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Abstract
The aetiology of type 2, or non-insulin-dependent, diabetes mellitus has been characterized in only a limited number of cases. Among these, mitochondrial diabetes, a rare subform of the disease, is the consequence of pancreatic beta-cell dysfunction caused by mutations in mitochondrial DNA, which is distinct from the nuclear genome. The impact of such mutations on beta-cell function reflects the importance of mitochondria in the control of insulin secretion. The beta-cell mitochondria serve as fuel sensors, generating factors that couple nutrient metabolism to the exocytosis of insulin-containing vesicles. The latter process requires an increase in cytosolic Ca2+, which depends on ATP synthesized by the mitochondria. This organelle also generates other factors, of which glutamate has been proposed as a potential intracellular messenger.
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Affiliation(s)
- P Maechler
- Division of Clinical Biochemistry, Department of Internal Medicine, University Medical Centre, 1211 Geneva 4, Switzerland.
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42
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Amuthan G, Biswas G, Zhang SY, Klein-Szanto A, Vijayasarathy C, Avadhani NG. Mitochondria-to-nucleus stress signaling induces phenotypic changes, tumor progression and cell invasion. EMBO J 2001. [PMID: 11296224 DOI: 10.1093/emboj/20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Recently we showed that partial depletion of mitochondrial DNA (genetic stress) or treatment with mitochondrial-specific inhibitors (metabolic stress) induced a stress signaling that was associated with increased cytoplasmic-free Ca(2+) [Ca(2+)](c). In the present study we show that the mitochondria-to-nucleus stress signaling induces invasive phenotypes in otherwise non-invasive C2C12 myoblasts and human pulmonary carcinoma A549 cells. Tumor-specific markers cathepsin L and transforming growth factor beta (TGFbeta) are overexpressed in cells subjected to mitochondrial genetic as well as metabolic stress. C2C12 myoblasts subjected to stress showed 4- to 6-fold higher invasion through reconstituted Matrigel membrane as well as rat tracheal xenotransplants in Scid mice. Activation of Ca(2+)-dependent protein kinase C (PKC) under both genetic and metabolic stress conditions was associated with increased cathepsin L gene expression, which contributes to increased invasive property of cells. Reverted cells with approximately 70% of control cell mtDNA exhibited marker mRNA contents, cell morphology and invasive property closer to control cells. These results provide insights into a new pathway by which mitochondrial DNA and membrane damage can contribute to tumor progression and metastasis.
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Affiliation(s)
- G Amuthan
- Department of Animal Biology and Mari Lowe Center for Comparative Oncology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
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43
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Amuthan G, Biswas G, Zhang SY, Klein-Szanto A, Vijayasarathy C, Avadhani NG. Mitochondria-to-nucleus stress signaling induces phenotypic changes, tumor progression and cell invasion. EMBO J 2001; 20:1910-20. [PMID: 11296224 PMCID: PMC125420 DOI: 10.1093/emboj/20.8.1910] [Citation(s) in RCA: 237] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Recently we showed that partial depletion of mitochondrial DNA (genetic stress) or treatment with mitochondrial-specific inhibitors (metabolic stress) induced a stress signaling that was associated with increased cytoplasmic-free Ca(2+) [Ca(2+)](c). In the present study we show that the mitochondria-to-nucleus stress signaling induces invasive phenotypes in otherwise non-invasive C2C12 myoblasts and human pulmonary carcinoma A549 cells. Tumor-specific markers cathepsin L and transforming growth factor beta (TGFbeta) are overexpressed in cells subjected to mitochondrial genetic as well as metabolic stress. C2C12 myoblasts subjected to stress showed 4- to 6-fold higher invasion through reconstituted Matrigel membrane as well as rat tracheal xenotransplants in Scid mice. Activation of Ca(2+)-dependent protein kinase C (PKC) under both genetic and metabolic stress conditions was associated with increased cathepsin L gene expression, which contributes to increased invasive property of cells. Reverted cells with approximately 70% of control cell mtDNA exhibited marker mRNA contents, cell morphology and invasive property closer to control cells. These results provide insights into a new pathway by which mitochondrial DNA and membrane damage can contribute to tumor progression and metastasis.
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Affiliation(s)
| | | | - Shi-Yu Zhang
- Department of Animal Biology and Mari Lowe Center for Comparative Oncology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104 and
Department of Pathology, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, PA 19111, USA Corresponding author e-mail:
| | - Andres Klein-Szanto
- Department of Animal Biology and Mari Lowe Center for Comparative Oncology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104 and
Department of Pathology, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, PA 19111, USA Corresponding author e-mail:
| | | | - Narayan G. Avadhani
- Department of Animal Biology and Mari Lowe Center for Comparative Oncology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104 and
Department of Pathology, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, PA 19111, USA Corresponding author e-mail:
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44
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Xu G, Kwon G, Cruz WS, Marshall CA, McDaniel ML. Metabolic regulation by leucine of translation initiation through the mTOR-signaling pathway by pancreatic beta-cells. Diabetes 2001; 50:353-60. [PMID: 11272147 DOI: 10.2337/diabetes.50.2.353] [Citation(s) in RCA: 179] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Recent findings have demonstrated that the branched-chain amino acid leucine can activate the translational regulators, phosphorylated heat- and acid-stable protein regulated by insulin (PHAS-I) and p70 S6 kinase (p70S6k), in an insulin-independent and rapamycin-sensitive manner through mammalian target of rapamycin (mTOR), although the mechanism for this activation is undefined. It has been previously established that leucine-induced insulin secretion by beta-cells involves increased mitochondrial metabolism by oxidative decarboxylation and allosteric activation of glutamate dehydrogenase (GDH). We now show that these same intramitochondrial events that generate signals for leucine-induced insulin exocytosis are required to activate the mTOR mitogenic signaling pathway by beta-cells. Thus, a minimal model consisting of leucine and glutamine as substrates for oxidative decarboxylation and an activator of GDH, respectively, confirmed the requirement for these two metabolic components and mimicked closely the synergistic interactions achieved by a complete complement of amino acids to activate p70s6k in a rapamycin-sensitive manner. Studies using various leucine analogs also confirmed the close association of mitochondrial metabolism and the ability of leucine analogs to activate p70s6k. Furthermore, selective inhibitors of mitochondrial function blocked this activation in a reversible manner, which was not associated with a global reduction in ATP levels. These findings indicate that leucine at physiological concentrations stimulates p70s6k phosphorylation via the mTOR pathway, in part, by serving both as a mitochondrial fuel and an allosteric activator of GDH. Leucine-mediated activation of protein translation through mTOR may contribute to enhanced beta-cell function by stimulating growth-related protein synthesis and proliferation associated with the maintenance of beta-cell mass.
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Affiliation(s)
- G Xu
- Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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45
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Maechler P, Wollheim CB. Mitochondrial signals in glucose-stimulated insulin secretion in the beta cell. J Physiol 2000; 529 Pt 1:49-56. [PMID: 11080250 PMCID: PMC2270172 DOI: 10.1111/j.1469-7793.2000.00049.x] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Glucose-induced insulin secretion is determined by signals generated in the mitochondria. The elevation of ATP is necessary for the membrane-dependent increase in cytosolic Ca2+, the main trigger of insulin exocytosis. Beta cells depleted of mitochondrial DNA fail to respond to glucose while still secreting insulin in response to membrane depolarisation. This cell model resembles the situation of defective insulin secretion in patients with mitochondrial diabetes. On the other hand, infants with activating mutations in the mitochondrial enzyme glutamate dehydrogenase are characterised by hyperinsulinism and hypoglycaemia. We have recently proposed that glutamate, generated by this enzyme, participates in insulin secretion as a glucose-derived metabolic messenger. In this model, glutamate acts downstream of the mitochondria by sensitising the exocytotic process to Ca2+. The evidence in favour of such a role for glutamate is discussed in the present review.
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Affiliation(s)
- P Maechler
- Division of Clinical Biochemistry, Department of Internal Medicine, University Medical Center, 1211 Geneva 4, Switzerland
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46
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Minami K, Yano H, Miki T, Nagashima K, Wang CZ, Tanaka H, Miyazaki JI, Seino S. Insulin secretion and differential gene expression in glucose-responsive and -unresponsive MIN6 sublines. Am J Physiol Endocrinol Metab 2000; 279:E773-81. [PMID: 11001758 DOI: 10.1152/ajpendo.2000.279.4.e773] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have established two sublines derived from the insulin-secreting mouse pancreatic beta-cell line MIN6, designated m9 and m14. m9 Cells exhibit glucose-induced insulin secretion in a concentration-dependent manner, whereas m14 cells respond poorly to glucose. In m14 cells, glucose consumption and lactate production are enhanced, and ATP production is largely through nonoxidative pathways. Moreover, lactate dehydrogenase activity is increased, and hexokinase replaces glucokinase as a glucose-phosphorylating enzyme. The ATP-sensitive K(+) channel activity and voltage-dependent calcium channel activity in m14 cells are reduced, and the resting membrane potential is significantly higher than in m9 cells. Thus, in contrast to m9, a model for beta-cells with normal insulin response, m14 is a model for beta-cells with impaired glucose-induced insulin secretion. By mRNA differential display of these sublines, we found 10 genes to be expressed at markedly different levels. These newly established MIN6 cell sublines should be useful tools in the analysis of the genetic and molecular basis of impaired glucose-induced insulin secretion.
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Affiliation(s)
- K Minami
- Department of Molecular Medicine, Chiba University Graduate School of Medicine, Chiba 260 - 8670, Japan
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Zhou YP, Pena JC, Roe MW, Mittal A, Levisetti M, Baldwin AC, Pugh W, Ostrega D, Ahmed N, Bindokas VP, Philipson LH, Hanahan D, Thompson CB, Polonsky KS. Overexpression of Bcl-x(L) in beta-cells prevents cell death but impairs mitochondrial signal for insulin secretion. Am J Physiol Endocrinol Metab 2000; 278:E340-51. [PMID: 10662719 DOI: 10.1152/ajpendo.2000.278.2.e340] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To study effects of Bcl-x(L) in the pancreatic beta-cell, two transgenic lines were produced using different forms of the rat insulin promoter. Bcl-x(L) expression in beta-cells was increased 2- to 3-fold in founder (Fd) 1 and over 10-fold in Fd 2 compared with littermate controls. After exposure to thapsigargin (10 microM for 48 h), losses of cell viability in islets of Fd 1 and Fd 2 Bcl-x(L) transgenic mice were significantly lower than in islets of wild-type mice. Unexpectedly, severe glucose intolerance was observed in Fd 2 but not Fd 1 Bcl-x(L) mice. Pancreatic insulin content and islet morphology were not different from control in either transgenic line. However, Fd 2 Bcl-x(L) islets had impaired insulin secretory and intracellular free Ca(2+) ([Ca(2+)](i)) responses to glucose and KCl. Furthermore, insulin and [Ca(2+)](i) responses to pyruvate methyl ester (PME) were similarly reduced as glucose in Fd 2 Bcl-x(L) islets. Consistent with a mitochondrial defect, glucose oxidation, but not glycolysis, was significantly lower in Fd 2 Bcl-x(L) islets than in wild-type islets. Glucose-, PME-, and alpha-ketoisocaproate-induced hyperpolarization of mitochondrial membrane potential, NAD(P)H, and ATP production were also significantly reduced in Fd 2 Bcl-x(L) islets. Thus, although Bcl-x(L) promotes beta-cell survival, high levels of expression of Bcl-x(L) result in reduced glucose-induced insulin secretion and hyperglycemia due to a defect in mitochondrial nutrient metabolism and signaling for insulin secretion.
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Affiliation(s)
- Y P Zhou
- Department of Medicine, Section of Endocrinology, University of Chicago, Chicago, Illinois 60637, USA
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Eto K, Suga S, Wakui M, Tsubamoto Y, Terauchi Y, Taka J, Aizawa S, Noda M, Kimura S, Kasai H, Kadowaki T. NADH shuttle system regulates K(ATP) channel-dependent pathway and steps distal to cytosolic Ca(2+) concentration elevation in glucose-induced insulin secretion. J Biol Chem 1999; 274:25386-92. [PMID: 10464266 DOI: 10.1074/jbc.274.36.25386] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The NADH shuttle system is composed of the glycerol phosphate and malate-aspartate shuttles. We generated mice that lack mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH), a rate-limiting enzyme of the glycerol phosphate shuttle. Application of aminooxyacetate, an inhibitor of the malate-aspartate shuttle, to mGPDH-deficient islets demonstrated that the NADH shuttle system was essential for coupling glycolysis with activation of mitochondrial ATP generation to trigger glucose-induced insulin secretion. The present study revealed that blocking the NADH shuttle system severely suppressed closure of the ATP-sensitive potassium (K(ATP)) channel and depolarization of the plasma membrane in response to glucose in beta cells, although properties of the K(ATP) channel on the excised beta cell membrane were unaffected. In mGPDH-deficient islets treated with aminooxyacetate, Ca(2+) influx through the plasma membrane induced by a depolarizing concentration of KCl in the presence of the K(ATP) channel opener diazoxide restored insulin secretion. However, the level of the secretion was only approximately 40% of wild-type controls. Thus, glucose metabolism through the NADH shuttle system leading to efficient ATP generation is pivotal to activation of both the K(ATP) channel-dependent pathway and steps distal to an elevation of cytosolic Ca(2+) concentration in glucose-induced insulin secretion.
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Affiliation(s)
- K Eto
- Department of Metabolic Diseases, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
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49
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50
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Xu G, Kwon G, Marshall CA, Lin TA, Lawrence JC, McDaniel ML. Branched-chain amino acids are essential in the regulation of PHAS-I and p70 S6 kinase by pancreatic beta-cells. A possible role in protein translation and mitogenic signaling. J Biol Chem 1998; 273:28178-84. [PMID: 9774438 DOI: 10.1074/jbc.273.43.28178] [Citation(s) in RCA: 200] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Amino acids have been identified as important signaling molecules involved in pancreatic beta-cell proliferation, although the cellular mechanism responsible for this effect is not well defined. We previously reported that amino acids are required for glucose or exogenous insulin to stimulate phosphorylation of PHAS-I (phosphorylated heat- and acid-stable protein regulated by insulin), a recently discovered regulator of translation initiation during cell mitogenesis. Here we demonstrate that essential amino acids, in particular branched-chain amino acids (leucine, valine, and isoleucine), are largely responsible for mediating this effect. The transamination product of leucine, alpha-ketoisocaproic acid, also stimulates PHAS-I phosphorylation although the transamination products of isoleucine and valine are ineffective. Since amino acids are secretagogues for insulin secretion by beta-cells, we investigated whether endogenous insulin secreted by beta-cells is involved. Interestingly, branched-chain amino acids stimulate phosphorylation of PHAS-I independent of endogenous insulin secretion since genistein (10 microM) and herbimycin A (1 microM), two tyrosine kinase inhibitors in the insulin signaling pathway, exert no effect on amino acid-induced phosphorylation of PHAS-I. Furthermore, branched-chain amino acids retain their ability to induce phosphorylation of PHAS-I under conditions that block insulin secretion from beta-cells. In exploring the signaling pathway responsible for these effects, we find that rapamycin (25 nM) inhibits the ability of branched-chain amino acids to stimulate the phosphorylation of PHAS-I and p70(s6) kinase, suggesting that the mammalian target of rapamycin signaling pathway is involved. The branched-chain amino acid, leucine, also exerts similar effects on PHAS-I phosphorylation in isolated pancreatic islets. In addition, we find that amino acids are necessary for insulin-like growth factor (IGF-I) to stimulate the phosphorylation of PHAS-I indicating that a requirement for amino acids may be essential for other beta-cell growth factors in addition to insulin and IGF-I to activate this signaling pathway. We propose that amino acids, in particular branched-chain amino acids, may promote beta-cell proliferation either by stimulating phosphorylation of PHAS-I and p70(s6k) via the mammalian target of rapamycin pathway and/or by facilitating the proliferative effect mediated by growth factors such as insulin and IGF-I.
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Affiliation(s)
- G Xu
- Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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