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Merrins MJ, Kibbey RG. Glucose Regulation of β-Cell KATP Channels: It Is Time for a New Model! Diabetes 2024; 73:856-863. [PMID: 38768366 PMCID: PMC11109790 DOI: 10.2337/dbi23-0032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Accepted: 01/04/2024] [Indexed: 05/22/2024]
Abstract
An agreed-upon consensus model of glucose-stimulated insulin secretion from healthy β-cells is essential for understanding diabetes pathophysiology. Since the discovery of the KATP channel in 1984, an oxidative phosphorylation (OxPhos)-driven rise in ATP has been assumed to close KATP channels to initiate insulin secretion. This model lacks any evidence, genetic or otherwise, that mitochondria possess the bioenergetics to raise the ATP/ADP ratio to the triggering threshold, and conflicts with genetic evidence demonstrating that OxPhos is dispensable for insulin secretion. It also conflates the stoichiometric yield of OxPhos with thermodynamics, and overestimates OxPhos by failing to account for established features of β-cell metabolism, such as leak, anaplerosis, cataplerosis, and NADPH production that subtract from the efficiency of mitochondrial ATP production. We have proposed an alternative model, based on the spatial and bioenergetic specializations of β-cell metabolism, in which glycolysis initiates insulin secretion. The evidence for this model includes that 1) glycolysis has high control strength over insulin secretion; 2) glycolysis is active at the correct time to explain KATP channel closure; 3) plasma membrane-associated glycolytic enzymes control KATP channels; 4) pyruvate kinase has favorable bioenergetics, relative to OxPhos, for raising ATP/ADP; and 5) OxPhos stalls before membrane depolarization and increases after. Although several key experiments remain to evaluate this model, the 1984 model is based purely on circumstantial evidence and must be rescued by causal, mechanistic experiments if it is to endure.
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Affiliation(s)
- Matthew J. Merrins
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Wisconsin—Madison
- William S. Middleton Memorial Veterans Hospital, Madison, WI
| | - Richard G. Kibbey
- Departments of Internal Medicine (Endocrinology) and Cellular & Molecular Physiology, Yale University, New Haven, CT
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2
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Rutter GA, Sweet IR. Glucose Regulation of β-Cell KATP Channels: Is a New Model Needed? Diabetes 2024; 73:849-855. [PMID: 38768365 PMCID: PMC11109788 DOI: 10.2337/dbi23-0031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Accepted: 12/18/2023] [Indexed: 05/22/2024]
Abstract
The canonical model of glucose-induced increase in insulin secretion involves the metabolism of glucose via glycolysis and the citrate cycle, resulting in increased ATP synthesis by the respiratory chain and the closure of ATP-sensitive K+ (KATP) channels. The resulting plasma membrane depolarization, followed by Ca2+ influx through L-type Ca2+ channels, then induces insulin granule fusion. Merrins and colleagues have recently proposed an alternative model whereby KATP channels are controlled by pyruvate kinase, using glycolytic and mitochondrial phosphoenolpyruvate (PEP) to generate microdomains of high ATP/ADP immediately adjacent to KATP channels. This model presents several challenges. First, how mitochondrially generated PEP, but not ATP produced abundantly by the mitochondrial F1F0-ATP synthase, can gain access to the proposed microdomains is unclear. Second, ATP/ADP fluctuations imaged immediately beneath the plasma membrane closely resemble those in the bulk cytosol. Third, ADP privation of the respiratory chain at high glucose, suggested to drive alternating, phased-locked generation by mitochondria of ATP or PEP, has yet to be directly demonstrated. Finally, the approaches used to explore these questions may be complicated by off-target effects. We suggest instead that Ca2+ changes, well known to affect both ATP generation and consumption, likely drive cytosolic ATP/ADP oscillations that in turn regulate KATP channels and membrane potential. Thus, it remains to be demonstrated that a new model is required to replace the existing, mitochondrial bioenergetics-based model.
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Affiliation(s)
- Guy A. Rutter
- Centre de Recherche du CHUM, Faculté de Médicine, Université de Montréal, Montréal, Québéc, Canada
- Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith Hospital Campus, London, U.K
- Lee Kong Chian Imperial Medical School, Nanyang Technological University, Singapore
| | - Ian R. Sweet
- University of Washington Medicine Diabetes Institute, University of Washington, Seattle, WA
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3
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van Niekerk DD, van Wyk M, Kouril T, Snoep JL. Kinetic modelling of glycolytic oscillations. Essays Biochem 2024; 68:15-25. [PMID: 38206647 DOI: 10.1042/ebc20230037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Revised: 12/18/2023] [Accepted: 12/19/2023] [Indexed: 01/12/2024]
Abstract
Glycolytic oscillations have been studied for well over 60 years, but aspects of their function, and mechanisms of regulation and synchronisation remain unclear. Glycolysis is amenable to mechanistic mathematical modelling, as its components have been well characterised, and the system can be studied at many organisational levels: in vitro reconstituted enzymes, cell free extracts, individual cells, and cell populations. In recent years, the emergence of individual cell analysis has opened new ways of studying this intriguing system.
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Affiliation(s)
- David D van Niekerk
- Department of Biochemistry, Stellenbosch University, Matieland, South Africa
| | - Morne van Wyk
- Department of Biochemistry, Stellenbosch University, Matieland, South Africa
| | - Theresa Kouril
- Department of Biochemistry, Stellenbosch University, Matieland, South Africa
| | - Jacky L Snoep
- Department of Biochemistry, Stellenbosch University, Matieland, South Africa
- Molecular Cell Biology, Vrije Universiteit, Amsterdam, The Netherlands
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4
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Metabolic cycles and signals for insulin secretion. Cell Metab 2022; 34:947-968. [PMID: 35728586 PMCID: PMC9262871 DOI: 10.1016/j.cmet.2022.06.003] [Citation(s) in RCA: 44] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2022] [Revised: 06/01/2022] [Accepted: 06/04/2022] [Indexed: 02/03/2023]
Abstract
In this review, we focus on recent developments in our understanding of nutrient-induced insulin secretion that challenge a key aspect of the "canonical" model, in which an oxidative phosphorylation-driven rise in ATP production closes KATP channels. We discuss the importance of intrinsic β cell metabolic oscillations; the phasic alignment of relevant metabolic cycles, shuttles, and shunts; and how their temporal and compartmental relationships align with the triggering phase or the secretory phase of pulsatile insulin secretion. Metabolic signaling components are assigned regulatory, effectory, and/or homeostatic roles vis-à-vis their contribution to glucose sensing, signal transmission, and resetting the system. Taken together, these functions provide a framework for understanding how allostery, anaplerosis, and oxidative metabolism are integrated into the oscillatory behavior of the secretory pathway. By incorporating these temporal as well as newly discovered spatial aspects of β cell metabolism, we propose a much-refined MitoCat-MitoOx model of the signaling process for the field to evaluate.
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5
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Fletcher PA, Marinelli I, Bertram R, Satin LS, Sherman AS. Pulsatile Basal Insulin Secretion Is Driven by Glycolytic Oscillations. Physiology (Bethesda) 2022; 37:0. [PMID: 35378996 PMCID: PMC9191171 DOI: 10.1152/physiol.00044.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
In fasted and fed states, blood insulin levels are oscillatory. While this phenomenon is well studied at high glucose levels, comparatively little is known about its origin under basal conditions. We propose a possible mechanism for basal insulin oscillations based on oscillations in glycolysis, demonstrated using an established mathematical model. At high glucose, this is superseded by a calcium-dependent mechanism.
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Affiliation(s)
- P. A. Fletcher
- 1Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Maryland
| | - I. Marinelli
- 2Centre for Systems Modelling and Quantitative Biomedicine, University of Birmingham, United Kingdom
| | - R. Bertram
- 3Department of Mathematics and Programs in Neuroscience and Molecular Biophysics, Florida State University, Tallahassee, Florida
| | - L. S. Satin
- 4Department of Pharmacology and Brehm Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, Michigan
| | - A. S. Sherman
- 1Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Maryland
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6
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Marinelli I, Fletcher PA, Sherman AS, Satin LS, Bertram R. Symbiosis of Electrical and Metabolic Oscillations in Pancreatic β-Cells. Front Physiol 2021; 12:781581. [PMID: 34925070 PMCID: PMC8682964 DOI: 10.3389/fphys.2021.781581] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Accepted: 11/08/2021] [Indexed: 11/13/2022] Open
Abstract
Insulin is secreted in a pulsatile pattern, with important physiological ramifications. In pancreatic β-cells, which are the cells that synthesize insulin, insulin exocytosis is elicited by pulses of elevated intracellular Ca2+ initiated by bursts of electrical activity. In parallel with these electrical and Ca2+ oscillations are oscillations in metabolism, and the periods of all of these oscillatory processes are similar. A key question that remains unresolved is whether the electrical oscillations are responsible for the metabolic oscillations via the effects of Ca2+, or whether the metabolic oscillations are responsible for the electrical oscillations due to the effects of ATP on ATP-sensitive ion channels? Mathematical modeling is a useful tool for addressing this and related questions as modeling can aid in the design of well-focused experiments that can test the predictions of particular models and subsequently be used to improve the models in an iterative fashion. In this article, we discuss a recent mathematical model, the Integrated Oscillator Model (IOM), that was the product of many years of development. We use the model to demonstrate that the relationship between calcium and metabolism in beta cells is symbiotic: in some contexts, the electrical oscillations drive the metabolic oscillations, while in other contexts it is the opposite. We provide new insights regarding these results and illustrate that what might at first appear to be contradictory data are actually compatible when viewed holistically with the IOM.
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Affiliation(s)
- Isabella Marinelli
- Centre for Systems Modelling and Quantitative Biomedicine (SMQB), University of Birmingham, Birmingham, United Kingdom
| | - Patrick A Fletcher
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, MD, United States
| | - Arthur S Sherman
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, MD, United States
| | - Leslie S Satin
- Department of Pharmacology, Brehm Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Richard Bertram
- Programs in Neuroscience and Molecular Biophysics, Department of Mathematics, Florida State University, Tallahassee, FL, United States
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7
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Ng XW, Chung YH, Piston DW. Intercellular Communication in the Islet of Langerhans in Health and Disease. Compr Physiol 2021; 11:2191-2225. [PMID: 34190340 DOI: 10.1002/cphy.c200026] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Blood glucose homeostasis requires proper function of pancreatic islets, which secrete insulin, glucagon, and somatostatin from the β-, α-, and δ-cells, respectively. Each islet cell type is equipped with intrinsic mechanisms for glucose sensing and secretory actions, but these intrinsic mechanisms alone cannot explain the observed secretory profiles from intact islets. Regulation of secretion involves interconnected mechanisms among and between islet cell types. Islet cells lose their normal functional signatures and secretory behaviors upon dispersal as compared to intact islets and in vivo. In dispersed islet cells, the glucose response of insulin secretion is attenuated from that seen from whole islets, coordinated oscillations in membrane potential and intracellular Ca2+ activity, as well as the two-phase insulin secretion profile, are missing, and glucagon secretion displays higher basal secretion profile and a reverse glucose-dependent response from that of intact islets. These observations highlight the critical roles of intercellular communication within the pancreatic islet, and how these communication pathways are crucial for proper hormonal and nonhormonal secretion and glucose homeostasis. Further, misregulated secretions of islet secretory products that arise from defective intercellular islet communication are implicated in diabetes. Intercellular communication within the islet environment comprises multiple mechanisms, including electrical synapses from gap junctional coupling, paracrine interactions among neighboring cells, and direct cell-to-cell contacts in the form of juxtacrine signaling. In this article, we describe the various mechanisms that contribute to proper islet function for each islet cell type and how intercellular islet communications are coordinated among the same and different islet cell types. © 2021 American Physiological Society. Compr Physiol 11:2191-2225, 2021.
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Affiliation(s)
- Xue W Ng
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri, USA
| | - Yong H Chung
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri, USA
| | - David W Piston
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri, USA
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8
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Systems modeling predicts that mitochondria ER contact sites regulate the postsynaptic energy landscape. NPJ Syst Biol Appl 2021; 7:26. [PMID: 34078916 PMCID: PMC8172538 DOI: 10.1038/s41540-021-00185-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Accepted: 04/25/2021] [Indexed: 12/14/2022] Open
Abstract
Spatiotemporal compartmentation of calcium dynamics is critical for neuronal function, particularly in postsynaptic spines. This exquisite level of Ca2+ compartmentalization is achieved through the storage and release of Ca2+ from various intracellular organelles particularly the endoplasmic reticulum (ER) and the mitochondria. Mitochondria and ER are established storage organelles controlling Ca2+ dynamics in neurons. Mitochondria also generate a majority of energy used within postsynaptic spines to support the downstream events associated with neuronal stimulus. Recently, high resolution microscopy has unveiled direct contact sites between the ER and the mitochondria (MERCs), which directly channel Ca2+ release from the ER into the mitochondrial membrane. In this study, we develop a computational 3D reaction-diffusion model to investigate the role of MERCs in regulating Ca2+ and ATP dynamics. This spatiotemporal model accounts for Ca2+ oscillations initiated by glutamate stimulus of metabotropic and ionotropic glutamate receptors and Ca2+ changes in four different compartments: cytosol, ER, mitochondria, and the MERC microdomain. Our simulations predict that the organization of these organelles and inter-organellar contact sites play a key role in modulating Ca2+ and ATP dynamics. We further show that the crosstalk between geometry (mitochondria and MERC) and metabolic parameters (cytosolic ATP hydrolysis, ATP generation) influences the neuronal energy state. Our findings shed light on the importance of organelle interactions in predicting Ca2+ dynamics in synaptic signaling. Overall, our model predicts that a combination of MERC linkage and mitochondria size is necessary for optimal ATP production in the cytosol.
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Jaffredo M, Bertin E, Pirog A, Puginier E, Gaitan J, Oucherif S, Lebreton F, Bosco D, Catargi B, Cattaert D, Renaud S, Lang J, Raoux M. Dynamic Uni- and Multicellular Patterns Encode Biphasic Activity in Pancreatic Islets. Diabetes 2021; 70:878-888. [PMID: 33468514 DOI: 10.2337/db20-0214] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Accepted: 01/11/2021] [Indexed: 11/13/2022]
Abstract
Biphasic secretion is an autonomous feature of many endocrine micro-organs to fulfill physiological demands. The biphasic activity of islet β-cells maintains glucose homeostasis and is altered in type 2 diabetes. Nevertheless, underlying cellular or multicellular functional organizations are only partially understood. High-resolution noninvasive multielectrode array recordings permit simultaneous analysis of recruitment, of single-cell, and of coupling activity within entire islets in long-time experiments. Using this unbiased approach, we addressed the organizational modes of both first and second phase in mouse and human islets under physiological and pathophysiological conditions. Our data provide a new uni- and multicellular model of islet β-cell activation: during the first phase, small but highly active β-cell clusters are dominant, whereas during the second phase, electrical coupling generates large functional clusters via multicellular slow potentials to favor an economic sustained activity. Postprandial levels of glucagon-like peptide 1 favor coupling only in the second phase, whereas aging and glucotoxicity alter coupled activity in both phases. In summary, biphasic activity is encoded upstream of vesicle pools at the micro-organ level by multicellular electrical signals and their dynamic synchronization between β-cells. The profound alteration of the electrical organization of islets in pathophysiological conditions may contribute to functional deficits in type 2 diabetes.
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Affiliation(s)
- Manon Jaffredo
- University of Bordeaux, CNRS, Institute of Chemistry and Biology of Membranes and Nano-objects, UMR 5248, Pessac, France
| | - Eléonore Bertin
- University of Bordeaux, CNRS, Institute of Chemistry and Biology of Membranes and Nano-objects, UMR 5248, Pessac, France
| | - Antoine Pirog
- University of Bordeaux, CNRS, Institut National Polytechnique de Bordeaux, Laboratoire de l'Intégration du Matériau au Système, UMR 5218, Talence, France
| | - Emilie Puginier
- University of Bordeaux, CNRS, Institute of Chemistry and Biology of Membranes and Nano-objects, UMR 5248, Pessac, France
| | - Julien Gaitan
- University of Bordeaux, CNRS, Institute of Chemistry and Biology of Membranes and Nano-objects, UMR 5248, Pessac, France
| | - Sandra Oucherif
- University of Bordeaux, CNRS, Institute of Chemistry and Biology of Membranes and Nano-objects, UMR 5248, Pessac, France
| | - Fanny Lebreton
- Cell Isolation and Transplantation Center, Department of Surgery, Geneva University Hospitals, University of Geneva, Geneva, Switzerland
| | - Domenico Bosco
- Cell Isolation and Transplantation Center, Department of Surgery, Geneva University Hospitals, University of Geneva, Geneva, Switzerland
| | - Bogdan Catargi
- University of Bordeaux, CNRS, Institute of Chemistry and Biology of Membranes and Nano-objects, UMR 5248, Pessac, France
- University of Bordeaux, Hôpital Saint-André, Endocrinology and Metabolic Diseases, Bordeaux, France
| | - Daniel Cattaert
- University of Bordeaux, CNRS, Aquitaine Institute for Cognitive and Integrative Neuroscience, UMR 5287, Bordeaux, France
| | - Sylvie Renaud
- University of Bordeaux, CNRS, Institut National Polytechnique de Bordeaux, Laboratoire de l'Intégration du Matériau au Système, UMR 5218, Talence, France
| | - Jochen Lang
- University of Bordeaux, CNRS, Institute of Chemistry and Biology of Membranes and Nano-objects, UMR 5248, Pessac, France
| | - Matthieu Raoux
- University of Bordeaux, CNRS, Institute of Chemistry and Biology of Membranes and Nano-objects, UMR 5248, Pessac, France
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Idevall-Hagren O, Tengholm A. Metabolic regulation of calcium signaling in beta cells. Semin Cell Dev Biol 2020; 103:20-30. [PMID: 32085965 DOI: 10.1016/j.semcdb.2020.01.008] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Revised: 01/10/2020] [Accepted: 01/28/2020] [Indexed: 12/22/2022]
Abstract
The cytoplasmic Ca2+ concentration ([Ca2+]cyt) regulates a vast number of cellular functions, including insulin secretion from beta cells. The major physiological insulin secretagogue, glucose, triggers [Ca2+]cyt oscillations in beta cells. Synchronization of the oscillations among the beta cells within an islet underlies the generation of pulsatile insulin secretion. This review describes the mechanisms generating [Ca2+]cyt oscillations, the interactions between [Ca2+]cyt and cell metabolism, as well as the contribution of various organelles to the shaping of [Ca2+]cyt signals and insulin secretion. It also discusses how Ca2+ signals are coordinated and spread throughout the islets and data indicating that altered Ca2+ signaling is associated with beta cell dysfunction and development of type 2 diabetes.
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Affiliation(s)
- Olof Idevall-Hagren
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre, Box 571, SE-751 23 Uppsala, Sweden
| | - Anders Tengholm
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre, Box 571, SE-751 23 Uppsala, Sweden.
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11
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Whitticar NB, Nunemaker CS. Reducing Glucokinase Activity to Enhance Insulin Secretion: A Counterintuitive Theory to Preserve Cellular Function and Glucose Homeostasis. Front Endocrinol (Lausanne) 2020; 11:378. [PMID: 32582035 PMCID: PMC7296051 DOI: 10.3389/fendo.2020.00378] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 05/12/2020] [Indexed: 12/21/2022] Open
Abstract
Pancreatic beta-cells are the only cells in the body that can synthesize and secrete insulin. Through the process of glucose-stimulated insulin secretion, beta-cells release insulin into circulation, stimulating GLUT4-dependent glucose uptake into peripheral tissue. Insulin is normally secreted in pulses that promote signaling at the liver. Long before type 2 diabetes is diagnosed, beta-cells become oversensitive to glucose, causing impaired pulsatility and overstimulation in fasting levels of glucose. The resulting hypersecretion of insulin can cause poor insulin signaling and clearance at the liver, leading to hyperinsulinemia and insulin resistance. Continued overactivity can eventually lead to beta-cell exhaustion and failure at which point type 2 diabetes begins. To prevent or reverse the negative effects of overstimulation, beta-cell activity can be reduced. Clinical studies have revealed the potential of beta-cell rest to reverse new cases of diabetes, but treatments lack durable benefits. In this perspective, we propose an intervention that reduces overactive glucokinase activity in the beta-cell. Glucokinase is known as the glucose sensor of the beta-cell due to its high control over insulin secretion. Therefore, glycolytic overactivity may be responsible for hyperinsulinemia early in the disease and can be reduced to restore normal stimulus-secretion coupling. We have previously reported that reducing glucokinase activity in prediabetic mouse islets can restore pulsatility and enhance insulin secretion. Building on this counterintuitive finding, we review the importance of pulsatile insulin secretion and highlight how normalizing glucose sensing in the beta cell during prediabetic hyperinsulinemia may restore pulsatility and improve glucose homeostasis.
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Affiliation(s)
- Nicholas B. Whitticar
- Translational Biomedical Sciences Program, Graduate College, Ohio University, Athens, OH, United States
- Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens OH, United States
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, United States
| | - Craig S. Nunemaker
- Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens OH, United States
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, United States
- *Correspondence: Craig S. Nunemaker
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12
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Boczek T, Radzik T, Ferenc B, Zylinska L. The Puzzling Role of Neuron-Specific PMCA Isoforms in the Aging Process. Int J Mol Sci 2019; 20:ijms20246338. [PMID: 31888192 PMCID: PMC6941135 DOI: 10.3390/ijms20246338] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Revised: 12/10/2019] [Accepted: 12/13/2019] [Indexed: 01/02/2023] Open
Abstract
The aging process is a physiological phenomenon associated with progressive changes in metabolism, genes expression, and cellular resistance to stress. In neurons, one of the hallmarks of senescence is a disturbance of calcium homeostasis that may have far-reaching detrimental consequences on neuronal physiology and function. Among several proteins involved in calcium handling, plasma membrane Ca2+-ATPase (PMCA) is the most sensitive calcium detector controlling calcium homeostasis. PMCA exists in four main isoforms and PMCA2 and PMCA3 are highly expressed in the brain. The overall effects of impaired calcium extrusion due to age-dependent decline of PMCA function seem to accumulate with age, increasing the susceptibility to neurotoxic insults. To analyze the PMCA role in neuronal cells, we have developed stable transfected differentiated PC12 lines with down-regulated PMCA2 or PMCA3 isoforms to mimic age-related changes. The resting Ca2+ increased in both PMCA-deficient lines affecting the expression of several Ca2+-associated proteins, i.e., sarco/endoplasmic Ca2+-ATPase (SERCA), calmodulin, calcineurin, GAP43, CCR5, IP3Rs, and certain types of voltage-gated Ca2+ channels (VGCCs). Functional studies also demonstrated profound changes in intracellular pH regulation and mitochondrial metabolism. Moreover, modification of PMCAs membrane composition triggered some adaptive processes to counterbalance calcium overload, but the reduction of PMCA2 appeared to be more detrimental to the cells than PMCA3.
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Affiliation(s)
- Tomasz Boczek
- Department of Molecular Neurochemistry, Medical University, 92-215 Lodz, Poland; (T.B.); (T.R.); (B.F.)
- Department of Ophthalmology, Stanford University School of Medicine, Palo Alto, CA 94304, USA
| | - Tomasz Radzik
- Department of Molecular Neurochemistry, Medical University, 92-215 Lodz, Poland; (T.B.); (T.R.); (B.F.)
| | - Bozena Ferenc
- Department of Molecular Neurochemistry, Medical University, 92-215 Lodz, Poland; (T.B.); (T.R.); (B.F.)
| | - Ludmila Zylinska
- Department of Molecular Neurochemistry, Medical University, 92-215 Lodz, Poland; (T.B.); (T.R.); (B.F.)
- Correspondence: ; Tel.: +48-42-272-5680
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Santo-Domingo J, Dayon L, Wiederkehr A. Protein Lysine Acetylation: Grease or Sand in the Gears of β-Cell Mitochondria? J Mol Biol 2019; 432:1446-1460. [PMID: 31628953 DOI: 10.1016/j.jmb.2019.09.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 09/16/2019] [Accepted: 09/18/2019] [Indexed: 02/06/2023]
Abstract
Mitochondria carry out many essential functions in metabolism. A central task is the oxidation of nutrients and the generation of ATP by oxidative phosphorylation. Mitochondrial metabolism needs to be tightly regulated for the cell to respond to changes in ATP demand and nutrient supply. Here, we review how protein lysine acetylation contributes to the regulation of mitochondrial metabolism in insulin target tissues and the insulin-secreting pancreatic β-cell. We summarize recent evidence showing that in pancreatic β-cells, lysine acetylation occurs on a large number of proteins involved in metabolism. Furthermore, we give a brief overview of the molecular mechanism that controls lysine acetylation dynamics. We propose that protein lysine acetylation is an important mechanism for the fine-tuning of mitochondrial activity in β-cells during normal physiology. In contrast, nutrient oversupply, oxidative stress, or inhibition of the mitochondrial deacetylase SIRT3 leads to protein lysine hyperacetylation, which impairs mitochondrial function. By perturbing mitochondrial activity in β-cells and insulin target tissues, protein lysine hyperacetylation may contribute to the development of type 2 diabetes.
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Affiliation(s)
- Jaime Santo-Domingo
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015 Lausanne, Switzerland
| | - Loïc Dayon
- Proteomics, Nestlé Institute of Health Sciences, 1015 Lausanne, Switzerland
| | - Andreas Wiederkehr
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015 Lausanne, Switzerland.
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14
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Santo-Domingo J, Galindo AN, Cominetti O, De Marchi U, Cutillas P, Dayon L, Wiederkehr A. Glucose-dependent phosphorylation signaling pathways and crosstalk to mitochondrial respiration in insulin secreting cells. Cell Commun Signal 2019; 17:14. [PMID: 30786936 PMCID: PMC6381748 DOI: 10.1186/s12964-019-0326-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 02/08/2019] [Indexed: 01/13/2023] Open
Abstract
Background Glucose is the main secretagogue of pancreatic beta-cells. Uptake and metabolism of the nutrient stimulates the beta-cell to release the blood glucose lowering hormone insulin. This metabolic activation is associated with a pronounced increase in mitochondrial respiration. Glucose stimulation also initiates a number of signal transduction pathways for the coordinated regulation of multiple biological processes required for insulin secretion. Methods Shotgun proteomics including TiO2 enrichment of phosphorylated peptides followed by liquid chromatography tandem mass spectrometry on lysates from glucose-stimulated INS-1E cells was used to identify glucose regulated phosphorylated proteins and signal transduction pathways. Kinase substrate enrichment analysis (KSEA) was applied to identify key regulated kinases and phosphatases. Glucose-induced oxygen consumption was measured using a XF96 Seahorse instrument to reveal cross talk between glucose-regulated kinases and mitochondrial activation. Results Our kinetic analysis of substrate phosphorylation reveal the molecular mechanism leading to rapid activation of insulin biogenesis, vesicle trafficking, insulin granule exocytosis and cytoskeleton remodeling. Kinase-substrate enrichment identified upstream kinases and phosphatases and time-dependent activity changes during glucose stimulation. Activity trajectories of well-known glucose-regulated kinases and phosphatases are described. In addition, we predict activity changes in a number of kinases including NUAK1, not or only poorly studied in the context of the pancreatic beta-cell. Furthermore, we pharmacologically tested whether signaling pathways predicted by kinase-substrate enrichment analysis affected glucose-dependent acceleration of mitochondrial respiration. We find that phosphoinositide 3-kinase, Ca2+/calmodulin dependent protein kinase and protein kinase C contribute to short-term regulation of energy metabolism. Conclusions Our results provide a global view into the regulation of kinases and phosphatases in insulin secreting cells and suggest cross talk between glucose-induced signal transduction and mitochondrial activation. Electronic supplementary material The online version of this article (10.1186/s12964-019-0326-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Jaime Santo-Domingo
- Nestlé Institute of Health Sciences, Nestlé Research, EPFL Innovation Park Bâtiment G, 1015, Lausanne, Switzerland.
| | - Antonio Núñez Galindo
- Nestlé Institute of Health Sciences, Nestlé Research, EPFL Innovation Park Bâtiment G, 1015, Lausanne, Switzerland
| | - Ornella Cominetti
- Nestlé Institute of Health Sciences, Nestlé Research, EPFL Innovation Park Bâtiment G, 1015, Lausanne, Switzerland
| | - Umberto De Marchi
- Nestlé Institute of Health Sciences, Nestlé Research, EPFL Innovation Park Bâtiment G, 1015, Lausanne, Switzerland
| | - Pedro Cutillas
- Analytical Signalling Group, Centre for Cell Signalling, Queen Mary University of London, London, UK
| | - Loïc Dayon
- Nestlé Institute of Health Sciences, Nestlé Research, EPFL Innovation Park Bâtiment G, 1015, Lausanne, Switzerland
| | - Andreas Wiederkehr
- Nestlé Institute of Health Sciences, Nestlé Research, EPFL Innovation Park Bâtiment G, 1015, Lausanne, Switzerland
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15
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Chareyron I, Wall C, Thevenet J, Santo-Domingo J, Wiederkehr A. Cellular stress is a prerequisite for glucose-induced mitochondrial matrix alkalinization in pancreatic β-cells. Mol Cell Endocrinol 2019; 481:71-83. [PMID: 30476561 DOI: 10.1016/j.mce.2018.11.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Revised: 11/20/2018] [Accepted: 11/22/2018] [Indexed: 11/24/2022]
Abstract
Changes in mitochondrial and cytosolic pH alter the chemical gradient across the inner mitochondrial membrane. The proton chemical gradient contributes to mitochondrial ATP synthesis as well as the uptake and release of metabolites and ions from the organelle. Here mitochondrial pH and ΔpH were studied for the first time in human pancreatic β-cells. Adenoviruses were used for rat insulin promoter dependent expression of the pH sensor SypHer targeted to either the mitochondrial matrix or the cytosol. The matrix pH in resting human β-cells is low (pH = 7.50 ± SD 0.17) compared to published values in other cell types. Consequently, the ΔpH of β-cells mitochondria is small. Glucose stimulation consistently resulted in acidification of the matrix pH in INS-1E insulinoma cells and β-cells in intact human islets or islet monolayer cultures. We registered acidification with similar kinetics but of slightly smaller amplitude in the cytosol of β-cells, thus glucose stimulation further reduced the ΔpH. Infection of human islets with high levels of adenoviruses caused the mitochondrial pH to increase. The apoptosis inducer and broad-spectrum kinase inhibitor staurosporine had similar effects on pH homeostasis. Although staurosporine alone does not affect the mitochondrial pH, glucose slightly increases the matrix pH of staurosporine treated cells. These two cellular stressors alter the normal mitochondrial pH response to glucose in pancreatic β-cells.
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Affiliation(s)
- Isabelle Chareyron
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland
| | - Christopher Wall
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland
| | - Jonathan Thevenet
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland
| | - Jaime Santo-Domingo
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland
| | - Andreas Wiederkehr
- Mitochondrial Function, Nestlé Institute of Health Sciences, 1015, Lausanne, Switzerland.
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16
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In-vivo correlations between skin metabolic oscillations and vasomotion in wild-type mice and in a model of oxidative stress. Sci Rep 2019; 9:186. [PMID: 30655574 PMCID: PMC6336806 DOI: 10.1038/s41598-018-36970-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Accepted: 11/27/2018] [Indexed: 12/17/2022] Open
Abstract
Arterioles in the cutaneous microcirculation frequently display an oscillatory phenomenon defined vasomotion, consistent with periodic diameter variations in the micro-vessels associated with particular physiological or abnormal conditions. The cellular mechanisms underlying vasomotion and its physiological role have not been completely elucidated. Various mechanisms were demonstrated, based on cell Ca2+ oscillations determined by the activity of channels in the plasma membrane or sarcoplasmic reticulum of vascular cells. However, the possible engagement in vasomotion of cell metabolic oscillations of mitochondrial or glycolytic origin has been poorly explored. Metabolic oscillations associated with the production of ATP energy were previously described in cells, while limited studies have investigated these fluctuations in-vivo. Here, we characterised a low-frequency metabolic oscillator (MO-1) in skin from live wild-type and Nrf2−/− mice, by combination of fluorescence spectroscopy and wavelet transform processing technique. Furthermore, the relationships between metabolic and microvascular oscillators were examined during phenylephrine-induced vasoconstriction. We found a significant interaction between MO-1 and the endothelial EDHF vasomotor mechanism that was reduced in the presence of oxidative stress (Nrf2−/− mice). Our findings suggest indirectly that metabolic oscillations may be involved in the mechanisms underlying endothelium-mediated skin vasomotion, which might be altered in the presence of metabolic disturbance.
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17
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De Marchi U, Galindo AN, Thevenet J, Hermant A, Bermont F, Lassueur S, Domingo JS, Kussmann M, Dayon L, Wiederkehr A. Mitochondrial lysine deacetylation promotes energy metabolism and calcium signaling in insulin-secreting cells. FASEB J 2018; 33:4660-4674. [PMID: 30589571 DOI: 10.1096/fj.201801424r] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In pancreatic β-cells, mitochondria generate signals that promote insulin granule exocytosis. Here we study how lysine acetylation of mitochondrial proteins mechanistically affects metabolism-secretion coupling in insulin-secreting cells. Using mass spectrometry-based proteomics, we identified lysine acetylation sites in rat insulinoma cell line clone 1E cells. In cells lacking the mitochondrial lysine deacetylase sirtuin-3 (SIRT3), several matrix proteins are hyperacetylated. Disruption of the SIRT3 gene has a deleterious effect on mitochondrial energy metabolism and Ca2+ signaling. Under resting conditions, SIRT3 deficient cells are overactivated, which elevates the respiratory rate and enhances calcium signaling and basal insulin secretion. In response to glucose, the SIRT3 knockout cells are unable to mount a sustained cytosolic ATP response. Calcium signaling is strongly reduced and the respiratory response as well as insulin secretion are blunted. We propose mitochondrial protein lysine acetylation as a control mechanism in β-cell energy metabolism and Ca2+ signaling.-De Marchi, U., Galindo, A. N., Thevenet, J., Hermant, A., Bermont, F., Lassueur, S., Domingo, J. S., Kussmann, M., Dayon, L., Wiederkehr, A. Mitochondrial lysine deacetylation promotes energy metabolism and calcium signaling in insulin-secreting cells.
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Affiliation(s)
- Umberto De Marchi
- Mitochondrial Function, Nestlé Institute of Health Sciences, Lausanne, Switzerland
| | | | - Jonathan Thevenet
- Mitochondrial Function, Nestlé Institute of Health Sciences, Lausanne, Switzerland
| | - Aurélie Hermant
- Mitochondrial Function, Nestlé Institute of Health Sciences, Lausanne, Switzerland
| | - Flavien Bermont
- Mitochondrial Function, Nestlé Institute of Health Sciences, Lausanne, Switzerland
| | - Steve Lassueur
- Mitochondrial Function, Nestlé Institute of Health Sciences, Lausanne, Switzerland
| | - Jaime Santo Domingo
- Mitochondrial Function, Nestlé Institute of Health Sciences, Lausanne, Switzerland
| | - Martin Kussmann
- Liggins Institute, University of Auckland, Auckland, New Zealand
| | - Loïc Dayon
- Proteomics, Nestlé Institute of Health Sciences, Lausanne, Switzerland; and
| | - Andreas Wiederkehr
- Mitochondrial Function, Nestlé Institute of Health Sciences, Lausanne, Switzerland
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18
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Hisab AS. Effects of cyclic AMP on the differentiation and bioenergetics of rat C6 glioma cells. Int J Neurosci 2018; 129:230-244. [PMID: 30232914 DOI: 10.1080/00207454.2018.1526798] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
INTRODUCTION Elevation in the level of intracellular cAMP is known to induce astrocytic differentiation of C6 glioma cells by unknown mechanisms. METHODS Therefore, cytoskeletal protein genes (phalloidin) fluorescents to investigate morphological changes, cell proliferation assay, MTT assay, flow cytometry, western blotting, in-cell western, immune-cytochemical (protein expression and localization), and oxygen electrodes (oxygen consumption rate) after a treatment with 0.25 mM dbcAMP were conducted. RESULTS Undifferentiated cells (media without dbcAMP) showed a flat polygonal appearance, whereas those cultured in the presence of 0.25 mM dbcAMP exhibited a more differentiated astrocytic morphology. They had more numerous neurite-like thin processes. The cell proliferation of differentiated c6 glioma reduced at day 2 and then started to increase at day 3 till day 5 compared to undifferentiated c6 glioma cells. In terms of flow-cytometry data, dbcAMP had no apoptotic effect on the C6 glioma cells. There was an increase in the protein expression GFAP (specific marker for astrocytes). There was no significant effect between undifferentiated and 5-day differentiation regarding their response to glucose 10 mM. In addition, there were no significant effects of glucose on the basal of 5-day differentiation of C6 glioma cells. However, there was a significant correlation between the concentration of glucose and inhibition of the basal oxygen consumption. Finally, glucose 10 mM did not stimulate NAD (P)H levels of C6 glioma cells. CONCLUSION The above results showed that cAMP induce C6 glioma cells differentiation without affecting its bioenergetics. Therefore cAMP is considered to be the best differentiating agent.
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Affiliation(s)
- Ahmed S Hisab
- a School of life Sciences , Queens Medical Centre , Nottingham , UK.,b Department of internal medicine, Faculty of veterinary medicine , Basrah University , Basra , Iraq
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19
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Jahan I, Corbin KL, Bogart AM, Whitticar NB, Waters CD, Schildmeyer C, Vann NW, West HL, Law NC, Wiseman JS, Nunemaker CS. Reducing Glucokinase Activity Restores Endogenous Pulsatility and Enhances Insulin Secretion in Islets From db/db Mice. Endocrinology 2018; 159:3747-3760. [PMID: 30239634 PMCID: PMC6202857 DOI: 10.1210/en.2018-00589] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Accepted: 09/12/2018] [Indexed: 12/22/2022]
Abstract
An early sign of islet failure in type 2 diabetes (T2D) is the loss of normal patterns of pulsatile insulin release. Disruptions in pulsatility are associated with a left shift in glucose sensing that can cause excessive insulin release in low glucose (relative hyperinsulinemia, a hallmark of early T2D) and β-cell exhaustion, leading to inadequate insulin release during hyperglycemia. Our hypothesis was that reducing excessive glucokinase activity in diabetic islets would improve their function. Isolated mouse islets were exposed to glucose and varying concentrations of the glucokinase inhibitor d-mannoheptulose (MH) to examine changes in intracellular calcium ([Ca2+]i) and insulin secretion. Acutely exposing islets from control CD-1 mice to MH in high glucose (20 mM) dose dependently reduced the size of [Ca2+]i oscillations detected by fura-2 acetoxymethyl. Glucokinase activation in low glucose (3 mM) had the opposite effect. We then treated islets from male and female db/db mice (age, 4 to 8 weeks) and heterozygous controls overnight with 0 to 10 mM MH to determine that 1 mM MH produced optimal oscillations. We then used 1 mM MH overnight to measure [Ca2+]i and insulin simultaneously in db/db islets. MH restored oscillations and increased insulin secretion. Insulin secretion rates correlated with MH-induced increases in amplitude of [Ca2+]i oscillations (R2 = 0.57, P < 0.01, n = 10) but not with mean [Ca2+]i levels in islets (R2 = 0.05, not significant). Our findings show that correcting glucose sensing can restore proper pulsatility to diabetic islets and improved pulsatility correlates with enhanced insulin secretion.
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Affiliation(s)
- Ishrat Jahan
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
| | - Kathryn L Corbin
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
| | - Avery M Bogart
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Honors Tutorial College, Ohio University, Athens, Ohio
| | - Nicholas B Whitticar
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
| | - Christopher D Waters
- Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia
| | - Cara Schildmeyer
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Honors Tutorial College, Ohio University, Athens, Ohio
| | - Nicholas W Vann
- Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia
| | - Hannah L West
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Honors Tutorial College, Ohio University, Athens, Ohio
| | - Nathan C Law
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
| | | | - Craig S Nunemaker
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Correspondence: Craig S. Nunemaker, PhD, Department of Biomedical Sciences, 228 Irvine Hall, Ohio University Heritage College of Osteopathic Medicine, Athens, Ohio 45701. E-mail:
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20
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Skelin Klemen M, Dolenšek J, Slak Rupnik M, Stožer A. The triggering pathway to insulin secretion: Functional similarities and differences between the human and the mouse β cells and their translational relevance. Islets 2017; 9:109-139. [PMID: 28662366 PMCID: PMC5710702 DOI: 10.1080/19382014.2017.1342022] [Citation(s) in RCA: 72] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
In β cells, stimulation by metabolic, hormonal, neuronal, and pharmacological factors is coupled to secretion of insulin through different intracellular signaling pathways. Our knowledge about the molecular machinery supporting these pathways and the patterns of signals it generates comes mostly from rodent models, especially the laboratory mouse. The increased availability of human islets for research during the last few decades has yielded new insights into the specifics in signaling pathways leading to insulin secretion in humans. In this review, we follow the most central triggering pathway to insulin secretion from its very beginning when glucose enters the β cell to the calcium oscillations it produces to trigger fusion of insulin containing granules with the plasma membrane. Along the way, we describe the crucial building blocks that contribute to the flow of information and focus on their functional role in mice and humans and on their translational implications.
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Affiliation(s)
- Maša Skelin Klemen
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Jurij Dolenšek
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Marjan Slak Rupnik
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
- Institute of Physiology; Center for Physiology and Pharmacology; Medical University of Vienna; Vienna, Austria
| | - Andraž Stožer
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
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21
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Yildirim V, Vadrevu S, Thompson B, Satin LS, Bertram R. Upregulation of an inward rectifying K+ channel can rescue slow Ca2+ oscillations in K(ATP) channel deficient pancreatic islets. PLoS Comput Biol 2017; 13:e1005686. [PMID: 28749940 PMCID: PMC5549769 DOI: 10.1371/journal.pcbi.1005686] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Revised: 08/08/2017] [Accepted: 07/16/2017] [Indexed: 12/02/2022] Open
Abstract
Plasma insulin oscillations are known to have physiological importance in the regulation of blood glucose. In insulin-secreting β-cells of pancreatic islets, K(ATP) channels play a key role in regulating glucose-dependent insulin secretion. In addition, they convey oscillations in cellular metabolism to the membrane by sensing adenine nucleotides, and are thus instrumental in mediating pulsatile insulin secretion. Blocking K(ATP) channels pharmacologically depolarizes the β-cell plasma membrane and terminates islet oscillations. Surprisingly, when K(ATP) channels are genetically knocked out, oscillations in islet activity persist, and relatively normal blood glucose levels are maintained. Compensation must therefore occur to overcome the loss of K(ATP) channels in K(ATP) knockout mice. In a companion study, we demonstrated a substantial increase in Kir2.1 protein occurs in β-cells lacking K(ATP) because of SUR1 deletion. In this report, we demonstrate that β-cells of SUR1 null islets have an upregulated inward rectifying K+ current that helps to compensate for the loss of K(ATP) channels. This current is likely due to the increased expression of Kir2.1 channels. We used mathematical modeling to determine whether an ionic current having the biophysical characteristics of Kir2.1 is capable of rescuing oscillations that are similar in period to those of wild-type islets. By experimentally testing a key model prediction we suggest that Kir2.1 current upregulation is a likely mechanism for rescuing the oscillations seen in islets from mice deficient in K(ATP) channels. Pulsatile insulin secretion is important for the proper regulation of blood glucose, and disruption of this pulsatility is a hallmark of type II diabetes. An ion channel was discovered more than three decades ago that conveys the metabolic state of insulin-secreting β-cells to the plasma membrane because it is blocked by ATP and opened by ADP, and thereby controls the activity of these electrically-excitable cells on a rapid time scale according to the prevailing blood glucose level. In addition to setting the appropriate level of insulin secretion, K(ATP) channels play a key role in generating the oscillations in cellular activity that underlie insulin pulsatility. It is therefore surprising that oscillations in activity persist in islets in which the K(ATP) channels are genetically knocked out. In this combined modeling and experimental study, we demonstrate that the role played by K(ATP) current in wild-type β-cells can be taken over by an inward-rectifying K+ current which, we show here, is upregulated in β-cells from SUR1 knockout mice. This result helps to resolve a mystery in the field that has remained elusive for more than a decade, since the first studies showing oscillations in SUR1-/- islets.
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Affiliation(s)
- Vehpi Yildirim
- Department of Mathematics, Florida State University, Tallahassee, FL, United States of America
| | - Suryakiran Vadrevu
- Brehm Diabetes Center, University of Michigan Medical School, Ann Arbor, MI, United States of America
| | - Benjamin Thompson
- Brehm Diabetes Center, University of Michigan Medical School, Ann Arbor, MI, United States of America
| | - Leslie S. Satin
- Brehm Diabetes Center, University of Michigan Medical School, Ann Arbor, MI, United States of America
| | - Richard Bertram
- Department of Mathematics and Programs in Molecular Biophysics and Neuroscience, Florida State University, Tallahassee, FL, United States of America
- * E-mail:
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22
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Abstract
The pancreatic β-cell secretes insulin in response to elevated plasma glucose. This review applies an external bioenergetic critique to the central processes of glucose-stimulated insulin secretion, including glycolytic and mitochondrial metabolism, the cytosolic adenine nucleotide pool, and its interaction with plasma membrane ion channels. The control mechanisms responsible for the unique responsiveness of the cell to glucose availability are discussed from bioenergetic and metabolic control standpoints. The concept of coupling factor facilitation of secretion is critiqued, and an attempt is made to unravel the bioenergetic basis of the oscillatory mechanisms controlling secretion. The need to consider the physiological constraints operating in the intact cell is emphasized throughout. The aim is to provide a coherent pathway through an extensive, complex, and sometimes bewildering literature, particularly for those unfamiliar with the field.
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Affiliation(s)
- David G Nicholls
- Buck Institute for Research on Aging, Novato, California; and Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, Malmo, Sweden
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23
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Merrins MJ, Poudel C, McKenna JP, Ha J, Sherman A, Bertram R, Satin LS. Phase Analysis of Metabolic Oscillations and Membrane Potential in Pancreatic Islet β-Cells. Biophys J 2017; 110:691-699. [PMID: 26840733 DOI: 10.1016/j.bpj.2015.12.029] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Revised: 12/17/2015] [Accepted: 12/22/2015] [Indexed: 01/01/2023] Open
Abstract
Metabolism in islet β-cells displays oscillations that can trigger pulses of electrical activity and insulin secretion. There has been a decades-long debate among islet biologists about whether metabolic oscillations are intrinsic or occur in response to oscillations in intracellular Ca(2+) that result from bursting electrical activity. In this article, the dynamics of oscillatory metabolism were investigated using five different optical reporters. Reporter activity was measured simultaneously with membrane potential bursting to determine the phase relationships between the metabolic oscillations and electrical activity. Our experimental findings suggest that Ca(2+) entry into β-cells stimulates the rate of mitochondrial metabolism, accounting for the depletion of glycolytic intermediates during each oscillatory burst. We also performed Ca(2+) clamp tests in which we clamped membrane potential with the KATP channel-opener diazoxide and KCl to fix Ca(2+) at an elevated level. These tests confirm that metabolic oscillations do not require Ca(2+) oscillations, but show that Ca(2+) plays a larger role in shaping metabolic oscillations than previously suspected. A dynamical picture of the mechanisms of oscillations emerged that requires the restructuring of contemporary mathematical β-cell models, including our own dual oscillator model. In the companion article, we modified our model to account for these new data.
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Affiliation(s)
- Matthew J Merrins
- Division of Endocrinology, Diabetes & Metabolism, Department of Medicine and Department of Biomolecular Chemistry, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin; William S. Middleton Memorial Veterans Hospital, Madison, Wisconsin
| | - Chetan Poudel
- Division of Endocrinology, Diabetes & Metabolism, Department of Medicine and Department of Biomolecular Chemistry, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin; William S. Middleton Memorial Veterans Hospital, Madison, Wisconsin
| | - Joseph P McKenna
- Department of Mathematics and Programs in Neuroscience and Molecular Biophysics, Florida State University, Tallahassee, Florida
| | - Joon Ha
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
| | - Arthur Sherman
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
| | - Richard Bertram
- Department of Mathematics and Programs in Neuroscience and Molecular Biophysics, Florida State University, Tallahassee, Florida
| | - Leslie S Satin
- Department of Pharmacology and Brehm Diabetes Center, University of Michigan, Ann Arbor, Michigan.
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24
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Yi L, Bandak B, Wang X, Bertram R, Roper MG. Dual Detection System for Simultaneous Measurement of Intracellular Fluorescent Markers and Cellular Secretion. Anal Chem 2016; 88:10368-10373. [PMID: 27712062 DOI: 10.1021/acs.analchem.6b02404] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Glucose-stimulated insulin secretion from pancreatic β-cells within islets of Langerhans plays a critical role in maintaining glucose homeostasis. Although this process is essential for maintaining euglycemia, the underlying intracellular mechanisms that control it are still unclear. To allow simultaneous correlation between intracellular signal transduction events and extracellular secretion, an analytical system was developed that integrates fluorescence imaging of intracellular probes with high-speed automated insulin immunoassays. As a demonstration of the system, intracellular [Ca2+] ([Ca2+]i) was measured by imaging Fura-2 fluorescence simultaneously with insulin secretion from islets exposed to elevated glucose levels. Both [Ca2+]i and insulin were oscillatory during application of 10 mM glucose with temporal and quantitative profiles similar to what has been observed elsewhere. In previous work, sinusoidal glucose levels have been used to test the entrainment of islets while monitoring either [Ca2+]i or insulin levels; using this newly developed system, we show unambiguously that oscillations of both [Ca2+]i and insulin release are entrained to oscillatory glucose levels and that the temporal correlation of these are maintained throughout the experiment. It is expected that the developed analytical system can be expanded to investigate a number of other intracellular messengers in islets or other stimulus-secretion pathways in different cells.
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Affiliation(s)
- Lian Yi
- Department of Chemistry and Biochemistry, Florida State University , 95 Chieftain Way, Dittmer Building, Tallahassee, Florida 32306, United States
| | - Basel Bandak
- Department of Chemistry and Biochemistry, Florida State University , 95 Chieftain Way, Dittmer Building, Tallahassee, Florida 32306, United States
| | - Xue Wang
- Department of Chemistry and Biochemistry, Florida State University , 95 Chieftain Way, Dittmer Building, Tallahassee, Florida 32306, United States
| | - Richard Bertram
- Department of Mathematics and Program in Neuroscience, Florida State University , Tallahassee, Florida 32306, United States.,Program in Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
| | - Michael G Roper
- Department of Chemistry and Biochemistry, Florida State University , 95 Chieftain Way, Dittmer Building, Tallahassee, Florida 32306, United States.,Program in Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
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25
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Gregg T, Poudel C, Schmidt BA, Dhillon RS, Sdao SM, Truchan NA, Baar EL, Fernandez LA, Denu JM, Eliceiri KW, Rogers JD, Kimple ME, Lamming DW, Merrins MJ. Pancreatic β-Cells From Mice Offset Age-Associated Mitochondrial Deficiency With Reduced KATP Channel Activity. Diabetes 2016; 65:2700-10. [PMID: 27284112 PMCID: PMC5001174 DOI: 10.2337/db16-0432] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2016] [Accepted: 05/31/2016] [Indexed: 12/20/2022]
Abstract
Aging is accompanied by impaired glucose homeostasis and an increased risk of type 2 diabetes, culminating in the failure of insulin secretion from pancreatic β-cells. To investigate the effects of age on β-cell metabolism, we established a novel assay to directly image islet metabolism with NAD(P)H fluorescence lifetime imaging (FLIM). We determined that impaired mitochondrial activity underlies an age-dependent loss of insulin secretion in human islets. NAD(P)H FLIM revealed a comparable decline in mitochondrial function in the pancreatic islets of aged mice (≥24 months), the result of 52% and 57% defects in flux through complex I and II, respectively, of the electron transport chain. However, insulin secretion and glucose tolerance are preserved in aged mouse islets by the heightened metabolic sensitivity of the β-cell triggering pathway, an adaptation clearly encoded in the metabolic and Ca(2+) oscillations that trigger insulin release (Ca(2+) plateau fraction: young 0.211 ± 0.006, aged 0.380 ± 0.007, P < 0.0001). This enhanced sensitivity is driven by a reduction in KATP channel conductance (diazoxide: young 5.1 ± 0.2 nS; aged 3.5 ± 0.5 nS, P < 0.01), resulting in an ∼2.8 mmol/L left shift in the β-cell glucose threshold. The results demonstrate how mice but not humans are able to successfully compensate for age-associated metabolic dysfunction by adjusting β-cell glucose sensitivity and highlight an essential mechanism for ensuring the maintenance of insulin secretion.
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Affiliation(s)
- Trillian Gregg
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI Biophysics Graduate Training Program, University of Wisconsin-Madison, Madison, WI Laboratory for Optical and Computational Instrumentation, University of Wisconsin-Madison, Madison, WI
| | - Chetan Poudel
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI Laboratory for Optical and Computational Instrumentation, University of Wisconsin-Madison, Madison, WI
| | - Brian A Schmidt
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI
| | - Rashpal S Dhillon
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, WI
| | - Sophia M Sdao
- Integrated Program in Biochemistry, University of Wisconsin-Madison, Madison, WI
| | - Nathan A Truchan
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI
| | - Emma L Baar
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI
| | - Luis A Fernandez
- Department of Surgery, Division of Transplantation, University of Wisconsin-Madison, Madison, WI
| | - John M Denu
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, WI
| | - Kevin W Eliceiri
- Laboratory for Optical and Computational Instrumentation, University of Wisconsin-Madison, Madison, WI Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI
| | - Jeremy D Rogers
- Laboratory for Optical and Computational Instrumentation, University of Wisconsin-Madison, Madison, WI Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI
| | - Michelle E Kimple
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI William S. Middleton Memorial Veterans Hospital, Madison, WI
| | - Dudley W Lamming
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI William S. Middleton Memorial Veterans Hospital, Madison, WI
| | - Matthew J Merrins
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI Laboratory for Optical and Computational Instrumentation, University of Wisconsin-Madison, Madison, WI Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, WI William S. Middleton Memorial Veterans Hospital, Madison, WI
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26
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Li G, Wu B, Ward MG, Chong ACN, Mukherjee S, Chen S, Hao M. Multifunctional in vivo imaging of pancreatic islets during diabetes development. J Cell Sci 2016; 129:2865-75. [PMID: 27270669 DOI: 10.1242/jcs.190843] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 05/27/2016] [Indexed: 01/13/2023] Open
Abstract
Pancreatic islet dysfunction leading to insufficient glucose-stimulated insulin secretion triggers the clinical onset of diabetes. How islet dysfunction develops is not well understood at the cellular level, partly owing to the lack of approaches to study single islets longitudinally in vivo Here, we present a noninvasive, high-resolution system to quantitatively image real-time glucose metabolism from single islets in vivo, currently not available with any other method. In addition, this multifunctional system simultaneously reports islet function, proliferation, vasculature and macrophage infiltration in vivo from the same set of images. Applying our method to a longitudinal high-fat diet study revealed changes in islet function as well as alternations in islet microenvironment. More importantly, this label-free system enabled us to image real-time glucose metabolism directly from single human islets in vivo for the first time, opening the door to noninvasive longitudinal in vivo studies of healthy and diabetic human islets.
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Affiliation(s)
- Ge Li
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - Binlin Wu
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - Meliza G Ward
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - Angie C N Chong
- Department of Surgery, Weill Cornell Medical College, New York, NY 10065, USA
| | - Sushmita Mukherjee
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - Shuibing Chen
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA Department of Surgery, Weill Cornell Medical College, New York, NY 10065, USA
| | - Mingming Hao
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
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27
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Wills QF, Boothe T, Asadi A, Ao Z, Warnock GL, Kieffer TJ, Johnson JD. Statistical approaches and software for clustering islet cell functional heterogeneity. Islets 2016; 8:48-56. [PMID: 26909740 PMCID: PMC4878268 DOI: 10.1080/19382014.2016.1150664] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Worldwide efforts are underway to replace or repair lost or dysfunctional pancreatic β-cells to cure diabetes. However, it is unclear what the final product of these efforts should be, as β-cells are thought to be heterogeneous. To enable the analysis of β-cell heterogeneity in an unbiased and quantitative way, we developed model-free and model-based statistical clustering approaches, and created new software called TraceCluster. Using an example data set, we illustrate the utility of these approaches by clustering dynamic intracellular Ca(2+) responses to high glucose in ∼300 simultaneously imaged single islet cells. Using feature extraction from the Ca(2+) traces on this reference data set, we identified 2 distinct populations of cells with β-like responses to glucose. To the best of our knowledge, this report represents the first unbiased cluster-based analysis of human β-cell functional heterogeneity of simultaneous recordings. We hope that the approaches and tools described here will be helpful for those studying heterogeneity in primary islet cells, as well as excitable cells derived from embryonic stem cells or induced pluripotent cells.
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Affiliation(s)
- Quin F Wills
- a Wellcome Trust Center for Human Genetics, University of Oxford , Oxford , United Kingdom
- b Weatherall Institute of Molecular Medicine, University of Oxford , Oxford , United Kingdom
| | - Tobias Boothe
- c Department of Cellular and Physiological Sciences , Life Sciences Center, University of British Columbia , Vancouver , Canada
| | - Ali Asadi
- c Department of Cellular and Physiological Sciences , Life Sciences Center, University of British Columbia , Vancouver , Canada
| | - Ziliang Ao
- d Department of Surgery , University of British Columbia , Vancouver , Canada
| | - Garth L Warnock
- d Department of Surgery , University of British Columbia , Vancouver , Canada
| | - Timothy J Kieffer
- c Department of Cellular and Physiological Sciences , Life Sciences Center, University of British Columbia , Vancouver , Canada
- d Department of Surgery , University of British Columbia , Vancouver , Canada
| | - James D Johnson
- c Department of Cellular and Physiological Sciences , Life Sciences Center, University of British Columbia , Vancouver , Canada
- d Department of Surgery , University of British Columbia , Vancouver , Canada
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28
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Markwardt ML, Seckinger KM, Rizzo MA. Regulation of Glucokinase by Intracellular Calcium Levels in Pancreatic β Cells. J Biol Chem 2015; 291:3000-9. [PMID: 26698632 DOI: 10.1074/jbc.m115.692160] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Indexed: 01/01/2023] Open
Abstract
Glucokinase (GCK) controls the rate of glucose metabolism in pancreatic β cells, and its activity is rate-limiting for insulin secretion. Posttranslational GCK activation can be stimulated through either G protein-coupled receptors or receptor tyrosine kinase signaling pathways, suggesting a common mechanism. Here we show that inhibiting Ca(2+) release from the endoplasmic reticulum (ER) decouples GCK activation from receptor stimulation. Furthermore, pharmacological release of ER Ca(2+) stimulates activation of a GCK optical biosensor and potentiates glucose metabolism, implicating rises in cytoplasmic Ca(2+) as a critical regulatory mechanism. To explore the potential for glucose-stimulated GCK activation, the GCK biosensor was optimized using circularly permuted mCerulean3 proteins. This new sensor sensitively reports activation in response to insulin, glucagon-like peptide 1, and agents that raise cAMP levels. Transient, glucose-stimulated GCK activation was observed in βTC3 and MIN6 cells. An ER-localized channelrhodopsin was used to manipulate the cytoplasmic Ca(2+) concentration in cells expressing the optimized FRET-GCK sensor. This permitted quantification of the relationship between cytoplasmic Ca(2+) concentrations and GCK activation. Half-maximal activation of the FRET-GCK sensor was estimated to occur at ∼400 nm Ca(2+). When expressed in islets, fluctuations in GCK activation were observed in response to glucose, and we estimated that posttranslational activation of GCK enhances glucose metabolism by ∼35%. These results suggest a mechanism for integrative control over GCK activation and, therefore, glucose metabolism and insulin secretion through regulation of cytoplasmic Ca(2+) levels.
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Affiliation(s)
- Michele L Markwardt
- From the University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Kendra M Seckinger
- From the University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Mark A Rizzo
- From the University of Maryland School of Medicine, Baltimore, Maryland 21201
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29
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Drews G, Bauer C, Edalat A, Düfer M, Krippeit-Drews P. Evidence against a Ca(2+)-induced potentiation of dehydrogenase activity in pancreatic beta-cells. Pflugers Arch 2015; 467:2389-97. [PMID: 25893711 DOI: 10.1007/s00424-015-1707-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Revised: 03/31/2015] [Accepted: 04/01/2015] [Indexed: 02/07/2023]
Abstract
Pancreatic beta-cells respond to an unchanging stimulatory glucose concentration with oscillations in membrane potential (Vm), cytosolic Ca(2+) concentration ([Ca(2+)]c), and insulin secretion. The underlying mechanisms are largely ascertained. Some particular details, however, are still in debate. Stimulus-secretion coupling (SSC) of beta-cells comprises glucose-induced Ca(2+) influx into the cytosol and thus into mitochondria. It is suggested that this activates (mitochondrial) dehydrogenases leading to an increase in reduction equivalents and ATP production. According to SSC, a glucose-induced increase in ATP production would thus further augment ATP production, i.e. induce a feed-forward loop that is hardly compatible with oscillations. Consistently, other studies favour a feedback mechanism that drives oscillatory mitochondrial ATP production. If Ca(2+) influx activates dehydrogenases, a change in [Ca(2+)]c should increase the concentration of reduction equivalents. We measured changes in flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) autofluorescence in response to changes in glucose concentration or glucose-independent changes in [Ca(2+)]c. The FAD signal was altered by glucose but not by alterations in [Ca(2+)]c. NAD(P)H was increased by glucose but even decreased by Ca(2+) influx evoked by tolbutamide. The mitochondrial membrane potential ΔΨ was hyperpolarized by 4 mM glucose. As adding tolbutamide then depolarized ΔΨ, we deduce that Ca(2+) does not activate mitochondrial activity but by contrast even inhibits it by reducing the driving force for ATP production. Inhibition of Ca(2+) influx reversed the Ca(2+)-induced changes in ΔΨ and NAD(P)H. The results are consistent with a feedback mechanism which transiently and repeatedly reduces ATP production and explain the oscillatory activity of pancreatic beta-cells at increased glucose concentrations.
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Affiliation(s)
- Gisela Drews
- Department of Pharmacology, Institute of Pharmacy, University of Tübingen, Auf der Morgenstelle 8, 72076, Tübingen, Germany
| | - Cita Bauer
- Department of Pharmacology, Institute of Pharmacy, University of Tübingen, Auf der Morgenstelle 8, 72076, Tübingen, Germany
| | - Armin Edalat
- Department of Pharmacology, Institute of Pharmacy, University of Tübingen, Auf der Morgenstelle 8, 72076, Tübingen, Germany
- Institute of Pharmaceutical and Medicinal Chemistry, University of Münster, Corrensstraße 48, 48149, Münster, Germany
| | - Martina Düfer
- Institute of Pharmaceutical and Medicinal Chemistry, University of Münster, Corrensstraße 48, 48149, Münster, Germany
| | - Peter Krippeit-Drews
- Department of Pharmacology, Institute of Pharmacy, University of Tübingen, Auf der Morgenstelle 8, 72076, Tübingen, Germany.
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30
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Watts M, Fendler B, Merrins MJ, Satin LS, Bertram R, Sherman A. Calcium and Metabolic Oscillations in Pancreatic Islets: Who's Driving the Bus? *. SIAM JOURNAL ON APPLIED DYNAMICAL SYSTEMS 2015; 13:683-703. [PMID: 25698909 PMCID: PMC4331037 DOI: 10.1137/130920198] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Pancreatic islets exhibit bursting oscillations in response to elevated blood glucose. These oscillations are accompanied by oscillations in the free cytosolic Ca2+ concentration (Cac ), which drives pulses of insulin secretion. Both islet Ca2+ and metabolism oscillate, but there is some debate about their interrelationship. Recent experimental data show that metabolic oscillations in some cases persist after the addition of diazoxide (Dz), which opens K(ATP) channels, hyperpolarizing β-cells and preventing Ca2+ entry and Ca2+ oscillations. Further, in some islets in which metabolic oscillations were eliminated with Dz, increasing the cytosolic Ca2+ concentration by the addition of KCl could restart the metabolic oscillations. Here we address why metabolic oscillations persist in some islets but not others, and why raising Cac restarts oscillations in some islets but not others. We answer these questions using the dual oscillator model (DOM) for pancreatic islets. The DOM can reproduce the experimental data and shows that the model supports two different mechanisms for slow metabolic oscillations, one that requires calcium oscillations and one that does not.
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Affiliation(s)
- Margaret Watts
- National Institutes of Health, Bethesda, MD 20892. The first and sixth authors’ research was supported by the NIH/NIDDK Intramural Research Program
| | - Bernard Fendler
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724. This author’s research was supported by the Simons Foundation and the Starr Cancer Consortium (I3-A123)
| | - Matthew J. Merrins
- University of Michigan, Ann Arbor, MI 48105. The third author’s research was supported by the National Institutes of Health (F32-DK085960), and the fourth author’s research was supported by the National Institutes of Health (R01-DK46409)
| | - Leslie S. Satin
- University of Michigan, Ann Arbor, MI 48105. The third author’s research was supported by the National Institutes of Health (F32-DK085960), and the fourth author’s research was supported by the National Institutes of Health (R01-DK46409)
| | - Richard Bertram
- Department of Mathematics and Programs in Neuroscience and Molecular Biophysics, Florida State University, Tallahassee, FL 32306. This author’s research was supported by the National Institutes of Health (DK080714)
| | - Arthur Sherman
- National Institutes of Health, Bethesda, MD 20892. The first and sixth authors’ research was supported by the NIH/NIDDK Intramural Research Program
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31
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Pulsatile insulin secretion, impaired glucose tolerance and type 2 diabetes. Mol Aspects Med 2015; 42:61-77. [PMID: 25637831 DOI: 10.1016/j.mam.2015.01.003] [Citation(s) in RCA: 151] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Revised: 01/09/2015] [Accepted: 01/10/2015] [Indexed: 12/28/2022]
Abstract
Type 2 diabetes (T2DM) results when increases in beta cell function and/or mass cannot compensate for rising insulin resistance. Numerous studies have documented the longitudinal changes in metabolism that occur during the development of glucose intolerance and lead to T2DM. However, the role of changes in insulin secretion, both amount and temporal pattern, has been understudied. Most of the insulin secreted from pancreatic beta cells of the pancreas is released in a pulsatile pattern, which is disrupted in T2DM. Here we review the evidence that changes in beta cell pulsatility occur during the progression from glucose intolerance to T2DM in humans, and contribute significantly to the etiology of the disease. We review the evidence that insulin pulsatility improves the efficacy of secreted insulin on its targets, particularly hepatic glucose production, but also examine evidence that pulsatility alters or is altered by changes in peripheral glucose uptake. Finally, we summarize our current understanding of the biophysical mechanisms responsible for oscillatory insulin secretion. Understanding how insulin pulsatility contributes to normal glucose homeostasis and is altered in metabolic disease states may help improve the treatment of T2DM.
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32
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Wuttke A. Lipid Signalling Dynamics at the β-cell Plasma Membrane. Basic Clin Pharmacol Toxicol 2015; 116:281-90. [DOI: 10.1111/bcpt.12369] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Accepted: 12/15/2014] [Indexed: 12/26/2022]
Affiliation(s)
- Anne Wuttke
- Department of Medical Cell Biology; Uppsala University; Uppsala Sweden
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33
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Gilon P, Chae HY, Rutter GA, Ravier MA. Calcium signaling in pancreatic β-cells in health and in Type 2 diabetes. Cell Calcium 2014; 56:340-61. [DOI: 10.1016/j.ceca.2014.09.001] [Citation(s) in RCA: 116] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 08/26/2014] [Accepted: 09/01/2014] [Indexed: 12/24/2022]
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34
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In vivo tissue-wide synchronization of mitochondrial metabolic oscillations. Cell Rep 2014; 9:514-21. [PMID: 25373899 DOI: 10.1016/j.celrep.2014.09.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Revised: 06/09/2014] [Accepted: 09/11/2014] [Indexed: 11/20/2022] Open
Abstract
Little is known about the spatiotemporal coordination of mitochondrial metabolism in multicellular organisms in situ. Using intravital microscopy in live animals, we report that mitochondrial metabolism undergoes rapid and periodic oscillations under basal conditions. Notably, mitochondria in vivo behave as a network of functionally coupled oscillators, which maintain a high level of coordination throughout the tissue via the activity of gap junctions. These findings reveal a unique aspect of the relationship between tissue architecture and self-organization of mitochondrial metabolism in vivo.
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35
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Nunemaker CS, Satin LS. Episodic hormone secretion: a comparison of the basis of pulsatile secretion of insulin and GnRH. Endocrine 2014; 47:49-63. [PMID: 24610206 PMCID: PMC4382805 DOI: 10.1007/s12020-014-0212-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2014] [Accepted: 02/13/2014] [Indexed: 01/01/2023]
Abstract
Rhythms govern many endocrine functions. Examples of such rhythmic systems include the insulin-secreting pancreatic beta-cell, which regulates blood glucose, and the gonadotropin-releasing hormone (GnRH) neuron, which governs reproductive function. Although serving very different functions within the body, these cell types share many important features. Both GnRH neurons and beta-cells, for instance, are hypothesized to generate at least two rhythms endogenously: (1) a burst firing electrical rhythm and (2) a slower rhythm involving metabolic or other intracellular processes. This review discusses the importance of hormone rhythms to both physiology and disease and compares and contrasts the rhythms generated by each system.
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Affiliation(s)
- Craig S. Nunemaker
- Division of Endocrinology and Metabolism, Department of, Medicine, University of Virginia, P.O. Box 801413, Charlottesville, VA 22901, USA,
| | - Leslie S. Satin
- Pharmacology Department, University of Michigan Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
- Brehm Diabetes Research Center, University of Michigan, Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
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36
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Hodson DJ, Tarasov AI, Gimeno Brias S, Mitchell RK, Johnston NR, Haghollahi S, Cane MC, Bugliani M, Marchetti P, Bosco D, Johnson PR, Hughes SJ, Rutter GA. Incretin-modulated beta cell energetics in intact islets of Langerhans. Mol Endocrinol 2014; 28:860-71. [PMID: 24766140 PMCID: PMC4042069 DOI: 10.1210/me.2014-1038] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Accepted: 04/17/2014] [Indexed: 01/08/2023] Open
Abstract
Incretins such as glucagon-like peptide 1 (GLP-1) are released from the gut and potentiate insulin release in a glucose-dependent manner. Although this action is generally believed to hinge on cAMP and protein kinase A signaling, up-regulated beta cell intermediary metabolism may also play a role in incretin-stimulated insulin secretion. By employing recombinant probes to image ATP dynamically in situ within intact mouse and human islets, we sought to clarify the role of GLP-1-modulated energetics in beta cell function. Using these techniques, we show that GLP-1 engages a metabolically coupled subnetwork of beta cells to increase cytosolic ATP levels, an action independent of prevailing energy status. We further demonstrate that the effects of GLP-1 are accompanied by alterations in the mitochondrial inner membrane potential and, at elevated glucose concentration, depend upon GLP-1 receptor-directed calcium influx through voltage-dependent calcium channels. Lastly, and highlighting critical species differences, beta cells within mouse but not human islets respond coordinately to incretin stimulation. Together, these findings suggest that GLP-1 alters beta cell intermediary metabolism to influence ATP dynamics in a species-specific manner, and this may contribute to divergent regulation of the incretin-axis in rodents and man.
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Affiliation(s)
| | | | - Silvia Gimeno Brias
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Ryan K. Mitchell
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Natalie R. Johnston
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Shahab Haghollahi
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Matthew C. Cane
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Marco Bugliani
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Piero Marchetti
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Domenico Bosco
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Paul R. Johnson
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Stephen J. Hughes
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Guy A. Rutter
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine (D.J.H, A.I.T., S.G.B., R.K.M., N.R.J., S.H., M.C.C., G.A.R.), Imperial College London, London W12 0NN, United Kingdom; Department of Endocrinology and Metabolism (M.B., P.M.), University of Pisa, 56126 Pisa, Italy; Cell Isolation and Transplantation Center, Department of Surgery (D.B.), Geneva University Hospitals and University of Geneva, 1205 Geneva, Switzerland; Oxford Centre for Diabetes, Endocrinology, & Metabolism (P.R.J., S.J.H.), University of Oxford, Oxford OX3 7LE, United Kingdom; NIHR Oxford Biomedical Research Centre (P.R.J., S.J.H.), Churchill Hospital, Oxford OX3 7LE, United Kingdom; and Nuffield Department of Surgical Sciences (P.R.J., S.J.H.), University of Oxford, Oxford OX3 9DU, United Kingdom
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Mitochondrial matrix Ca²⁺ accumulation regulates cytosolic NAD⁺/NADH metabolism, protein acetylation, and sirtuin expression. Mol Cell Biol 2014; 34:2890-902. [PMID: 24865966 DOI: 10.1128/mcb.00068-14] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Mitochondrial calcium uptake stimulates bioenergetics and drives energy production in metabolic tissue. It is unknown how a calcium-mediated acceleration in matrix bioenergetics would influence cellular metabolism in glycolytic cells that do not require mitochondria for ATP production. Using primary human endothelial cells (ECs), we discovered that repetitive cytosolic calcium signals (oscillations) chronically loaded into the mitochondrial matrix. Mitochondrial calcium loading in turn stimulated bioenergetics and a persistent elevation in NADH. Rather than serving as an impetus for mitochondrial ATP generation, matrix NADH rapidly transmitted to the cytosol to influence the activity and expression of cytosolic sirtuins, resulting in global changes in protein acetylation. In endothelial cells, the mitochondrion-driven reduction in both the cytosolic and mitochondrial NAD(+)/NADH ratio stimulated a compensatory increase in SIRT1 protein levels that had an anti-inflammatory effect. Our studies reveal the physiologic importance of mitochondrial bioenergetics in the metabolic regulation of sirtuins and cytosolic signaling cascades.
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De Marchi U, Thevenet J, Hermant A, Dioum E, Wiederkehr A. Calcium co-regulates oxidative metabolism and ATP synthase-dependent respiration in pancreatic beta cells. J Biol Chem 2014; 289:9182-94. [PMID: 24554722 PMCID: PMC3979381 DOI: 10.1074/jbc.m113.513184] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Mitochondrial energy metabolism is essential for glucose-induced calcium signaling and, therefore, insulin granule exocytosis in pancreatic beta cells. Calcium signals are sensed by mitochondria acting in concert with mitochondrial substrates for the full activation of the organelle. Here we have studied glucose-induced calcium signaling and energy metabolism in INS-1E insulinoma cells and human islet beta cells. In insulin secreting cells a surprisingly large fraction of total respiration under resting conditions is ATP synthase-independent. We observe that ATP synthase-dependent respiration is markedly increased after glucose stimulation. Glucose also causes a very rapid elevation of oxidative metabolism as was followed by NAD(P)H autofluorescence. However, neither the rate of the glucose-induced increase nor the new steady-state NAD(P)H levels are significantly affected by calcium. Our findings challenge the current view, which has focused mainly on calcium-sensitive dehydrogenases as the target for the activation of mitochondrial energy metabolism. We propose a model of tight calcium-dependent regulation of oxidative metabolism and ATP synthase-dependent respiration in beta cell mitochondria. Coordinated activation of matrix dehydrogenases and respiratory chain activity by calcium allows the respiratory rate to change severalfold with only small or no alterations of the NAD(P)H/NAD(P)(+) ratio.
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Pedersen MG, Mosekilde E, Polonsky KS, Luciani DS. Complex patterns of metabolic and Ca²⁺ entrainment in pancreatic islets by oscillatory glucose. Biophys J 2014; 105:29-39. [PMID: 23823221 DOI: 10.1016/j.bpj.2013.05.036] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 05/10/2013] [Accepted: 05/17/2013] [Indexed: 11/29/2022] Open
Abstract
Glucose-stimulated insulin secretion is pulsatile and driven by intrinsic oscillations in metabolism, electrical activity, and Ca(2+) in pancreatic islets. Periodic variations in glucose can entrain islet Ca(2+) and insulin secretion, possibly promoting interislet synchronization. Here, we used fluorescence microscopy to demonstrate that glucose oscillations can induce distinct 1:1 and 1:2 entrainment of oscillations (one and two oscillations for each period of exogenous stimulus, respectively) in islet Ca(2+), NAD(P)H, and mitochondrial membrane potential. To our knowledge, this is the first demonstration of metabolic entrainment in islets, and we found that entrainment of metabolic oscillations requires voltage-gated Ca(2+) influx. We identified diverse patterns of 1:2 entrainment and showed that islet synchronization during entrainment involves adjustments of both oscillatory phase and period. All experimental findings could be recapitulated by our recently developed mathematical model, and simulations suggested that interislet variability in 1:2 entrainment patterns reflects differences in their glucose sensitivity. Finally, our simulations and recordings showed that a heterogeneous group of islets synchronized during 1:2 entrainment, resulting in a clear oscillatory response from the collective. In summary, we demonstrate that oscillatory glucose can induce complex modes of entrainment of metabolically driven oscillations in islets, and provide additional support for the notion that entrainment promotes interislet synchrony in the pancreas.
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40
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Abstract
In vivo gene manipulation is a cornerstone approach in modern physiology. Cre-Lox technology has been extensively used to delete genes and activate reporters in pancreatic β-cells, bringing new insight into the pathophysiology of diabetes. In all cases, it is important to understand the expression domain of the specific reporter-Cre combination in order to correctly interpret the data. In the case of targeted genes with significant expression and function in the brain, the use of Ins2 promoter driven Cre, commonly known as RIP-Cre, has been shown to confound data interpretation when appropriate controls are not present. The recent article from the Philipson group in Islets provides an important characterization of a new Cre-deleter model, referred to as MIP1-CreER, which employs the mouse Ins1 promoter. This Ins1 promoter, recapitulating the expression pattern of the endogenous Ins1 gene, does not drive significant transgene expression in the brain and therefore is highly specific for deleting genes or turning on reporters in the pancreatic β-cell. This model promises to be widely used in the field of islet biology. Here, I review recent developments in the area of in vivo gene modification and predict areas where such tools will be refined further.
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Affiliation(s)
- James D Johnson
- Department of Cellular and Physiological Sciences; University
of British Columbia; Life Sciences Centre; Vancouver, BC
Canada
- Correspondence to: James D Johnson;
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41
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Abstract
Mathematical modeling of the electrical activity of the pancreatic β-cell has been extremely important for understanding the cellular mechanisms involved in glucose-stimulated insulin secretion. Several models have been proposed over the last 30 y, growing in complexity as experimental evidence of the cellular mechanisms involved has become available. Almost all the models have been developed based on experimental data from rodents. However, given the many important differences between species, models of human β-cells have recently been developed. This review summarizes how modeling of β-cells has evolved, highlighting the proposed physiological mechanisms underlying β-cell electrical activity.
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Key Words
- ADP, adenosine diphosphate
- ATP, adenosine triphosphate
- CK, Chay-Keizer
- CRAC, calcium release-activated current
- Ca2+, calcium ions
- DOM, dual oscillator model
- ER, endoplasmic reticulum
- F6P, fructose-6-phosphate
- FBP, fructose-1,6-bisphosphate
- GLUT, glucose transporter
- GSIS, glucose-stimulated insulin secretion
- HERG, human eter à-go-go related gene
- IP3R, inositol-1,4,5-trisphosphate receptors
- KATP, ATP-sensitive K+ channels
- KCa, Ca2+-dependent K+ channels
- Kv, voltage-dependent K+ channels
- MCU, mitochondrial Ca2+ uniporter
- NCX, Na+/Ca2+ exchanger
- PFK, phosphofructokinase
- PMCA, plasma membrane Ca2+-ATPase
- ROS, reactive oxygen species
- RyR, ryanodine receptors
- SERCA, sarco-endoplasmic reticulum Ca2+-ATPase
- T2D, Type 2 Diabetes
- TCA, trycarboxylic acid cycle
- TRP, transient receptor potential
- VDCC, voltage-dependent Ca2+ channels
- Vm, membrane potential
- [ATP]i, cytosolic ATP
- [Ca2+]i, intracellular calcium concentration
- [Ca2+]m, mitochondrial calcium
- [Na+], Na+ concentration
- action potentials
- bursting
- cAMP, cyclic AMP
- calcium
- electrical activity
- ion channels
- mNCX, mitochondrial Na+/Ca2+ exchanger
- mathematical model
- β-cell
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Affiliation(s)
- Gerardo J Félix-Martínez
- Department of Electrical Engineering; Universidad
Autónoma Metropolitana-Iztapalapa; México, DF,
México
- Correspondence to: Gerardo J
Félix-Martínez;
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Transplantation of Encapsulated Pancreatic Islets as a Treatment for Patients with Type 1 Diabetes Mellitus. Adv Med 2014; 2014:429710. [PMID: 26556410 PMCID: PMC4590955 DOI: 10.1155/2014/429710] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 11/30/2013] [Indexed: 12/19/2022] Open
Abstract
Encapsulation of pancreatic islets has been proposed and investigated for over three decades to improve islet transplantation outcomes and to eliminate the side effects of immunosuppressive medications. Of the numerous encapsulation systems developed in the past, microencapsulation have been studied most extensively so far. A wide variety of materials has been tested for microencapsulation in various animal models (including nonhuman primates or NHPs) and some materials were shown to induce immunoprotection to islet grafts without the need for chronic immunosuppression. Despite the initial success of microcapsules in NHP models, the combined use of islet transplantation (allograft) and microencapsulation has not yet been successful in clinical trials. This review consists of three sections: introduction to islet transplantation, transplantation of encapsulated pancreatic islets as a treatment for patients with type 1 diabetes mellitus (T1DM), and present challenges and future perspectives.
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Nourmohammadzadeh M, Lo JF, Bochenek M, Mendoza-Elias JE, Wang Q, Li Z, Zeng L, Qi M, Eddington DT, Oberholzer J, Wang Y. Microfluidic array with integrated oxygenation control for real-time live-cell imaging: effect of hypoxia on physiology of microencapsulated pancreatic islets. Anal Chem 2013; 85:11240-9. [PMID: 24083835 DOI: 10.1021/ac401297v] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
In this article, we present a novel microfluidic islet array based on a hydrodynamic trapping principle. The lab-on-a-chip studies with live-cell multiparametric imaging allow understanding of physiological and pathophysiological changes of microencapsulated islets under hypoxic conditions. Using this microfluidic array and imaging analysis techniques, we demonstrate that hypoxia impairs the function of microencapsulated islets at the single islet level, showing a heterogeneous pattern reflected in intracellular calcium signaling, mitochondrial energetic, and redox activity. Our approach demonstrates an improvement over conventional hypoxia chambers that is able to rapidly equilibrate to true hypoxia levels through the integration of dynamic oxygenation. This work demonstrates the feasibility of array-based cellular analysis and opens up new modality to conduct informative analysis and cell-based screening for microencapsulated pancreatic islets.
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Affiliation(s)
- Mohammad Nourmohammadzadeh
- Department of Surgery/Transplant, University of Illinois at Chicago , 840 South Wood Street, Room 502, Chicago, Illinois 60612
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Merrins MJ, Van Dyke AR, Mapp AK, Rizzo MA, Satin LS. Direct measurements of oscillatory glycolysis in pancreatic islet β-cells using novel fluorescence resonance energy transfer (FRET) biosensors for pyruvate kinase M2 activity. J Biol Chem 2013; 288:33312-22. [PMID: 24100037 DOI: 10.1074/jbc.m113.508127] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Pulses of insulin released from pancreatic β-cells maintain blood glucose in a narrow range, although the source of these pulses is unclear. We and others have proposed that positive feedback mediated by the glycolytic enzyme phosphofructokinase-1 (PFK1) enables β-cells to generate metabolic oscillations via autocatalytic activation by its product fructose 1,6-bisphosphate (FBP). Although much indirect evidence has accumulated in favor of this hypothesis, a direct measurement of oscillating glycolytic intermediates has been lacking. To probe glycolysis directly, we engineered a family of inter- and intramolecular FRET biosensors based on the glycolytic enzyme pyruvate kinase M2 (PKAR; pyruvate kinase activity reporter), which multimerizes and is activated upon binding FBP. When introduced into Min6 β-cells, PKAR FRET efficiency increased rapidly in response to glucose. Importantly, however, metabolites entering downstream of PFK1 (glyceraldehyde, pyruvate, and ketoisocaproate) failed to activate PKAR, consistent with sensor activation by FBP; the dependence of PKAR on FBP was further confirmed using purified sensor in vitro. Using a novel imaging modality for monitoring mitochondrial flavin fluorescence in mouse islets, we show that slow oscillations in mitochondrial redox potential stimulated by 10 mm glucose are in phase with glycolytic efflux through PKM2, measured simultaneously from neighboring islet β-cells expressing PKAR. These results indicate that PKM2 activity in β-cells is oscillatory and are consistent with pulsatile PFK1 being the mediator of slow glycolytic oscillations.
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Affiliation(s)
- Matthew J Merrins
- From the Department of Pharmacology and Brehm Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, Michigan 48105
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45
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Li J, Shuai HY, Gylfe E, Tengholm A. Oscillations of sub-membrane ATP in glucose-stimulated beta cells depend on negative feedback from Ca(2+). Diabetologia 2013; 56:1577-86. [PMID: 23536115 PMCID: PMC3671113 DOI: 10.1007/s00125-013-2894-0] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Accepted: 03/04/2013] [Indexed: 10/27/2022]
Abstract
AIMS/HYPOTHESIS ATP links changes in glucose metabolism to electrical activity, Ca(2+) signalling and insulin secretion in pancreatic beta cells. There is evidence that beta cell metabolism oscillates, but little is known about ATP dynamics at the plasma membrane, where regulation of ion channels and exocytosis occur. METHODS The sub-plasma-membrane ATP concentration ([ATP]pm) was recorded in beta cells in intact mouse and human islets using total internal reflection microscopy and the fluorescent reporter Perceval. RESULTS Glucose dose-dependently increased [ATP]pm with half-maximal and maximal effects at 5.2 and 9 mmol/l, respectively. Additional elevations of glucose to 11 to 20 mmol/l promoted pronounced [ATP]pm oscillations that were synchronised between neighbouring beta cells. [ATP]pm increased further and the oscillations disappeared when voltage-dependent Ca(2+) influx was prevented. In contrast, K(+)-depolarisation induced prompt lowering of [ATP]pm. Simultaneous recordings of [ATP]pm and the sub-plasma-membrane Ca(2+) concentration ([Ca(2+)]pm) during the early glucose-induced response revealed that the initial [ATP]pm elevation preceded, and was temporarily interrupted by the rise of [Ca(2+)]pm. During subsequent glucose-induced oscillations, the increases of [Ca(2+)]pm correlated with lowering of [ATP]pm. CONCLUSIONS/INTERPRETATION In beta cells, glucose promotes pronounced oscillations of [ATP]pm, which depend on negative feedback from Ca(2+) . The bidirectional interplay between these messengers in the sub-membrane space generates the metabolic and ionic oscillations that underlie pulsatile insulin secretion.
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Affiliation(s)
- J. Li
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, 75123 Uppsala, Sweden
| | - H. Y. Shuai
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, 75123 Uppsala, Sweden
| | - E. Gylfe
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, 75123 Uppsala, Sweden
| | - A. Tengholm
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, 75123 Uppsala, Sweden
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Lorenz MA, El Azzouny MA, Kennedy RT, Burant CF. Metabolome response to glucose in the β-cell line INS-1 832/13. J Biol Chem 2013; 288:10923-35. [PMID: 23426361 PMCID: PMC3624472 DOI: 10.1074/jbc.m112.414961] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells is triggered by metabolism of the sugar to increase ATP/ADP ratio that blocks the KATP channel leading to membrane depolarization and insulin exocytosis. Other metabolic pathways believed to augment insulin secretion have yet to be fully elucidated. To study metabolic changes during GSIS, liquid chromatography with mass spectrometry was used to determine levels of 87 metabolites temporally following a change in glucose from 3 to 10 mM glucose and in response to increasing concentrations of glucose in the INS-1 832/13 β-cell line. U-[(13)C]Glucose was used to probe flux in specific metabolic pathways. Results include a rapid increase in ATP/ADP, anaplerotic tricarboxylic acid cycle flux, and increases in the malonyl CoA pathway, support prevailing theories of GSIS. Novel findings include that aspartate used for anaplerosis does not derive from the glucose fuel added to stimulate insulin secretion, glucose flux into glycerol-3-phosphate, and esterification of long chain CoAs resulting in rapid consumption of long chain CoAs and de novo generation of phosphatidic acid and diacylglycerol. Further, novel metabolites with potential roles in GSIS such as 5-aminoimidazole-4-carboxamide ribotide (ZMP), GDP-mannose, and farnesyl pyrophosphate were found to be rapidly altered following glucose exposure.
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Affiliation(s)
- Matthew A Lorenz
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48105, USA
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Luciani DS, White SA, Widenmaier SB, Saran VV, Taghizadeh F, Hu X, Allard MF, Johnson JD. Bcl-2 and Bcl-xL suppress glucose signaling in pancreatic β-cells. Diabetes 2013; 62:170-82. [PMID: 22933114 PMCID: PMC3526034 DOI: 10.2337/db11-1464] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
B-cell lymphoma 2 (Bcl-2) family proteins are established regulators of cell survival, but their involvement in the normal function of primary cells has only recently begun to receive attention. In this study, we demonstrate that chemical and genetic loss-of-function of antiapoptotic Bcl-2 and Bcl-x(L) significantly augments glucose-dependent metabolic and Ca(2+) signals in primary pancreatic β-cells. Antagonism of Bcl-2/Bcl-x(L) by two distinct small-molecule compounds rapidly hyperpolarized β-cell mitochondria, increased cytosolic Ca(2+), and stimulated insulin release via the ATP-dependent pathway in β-cell under substimulatory glucose conditions. Experiments with single and double Bax-Bak knockout β-cells established that this occurred independently of these proapoptotic binding partners. Pancreatic β-cells from Bcl-2(-/-) mice responded to glucose with significantly increased NAD(P)H levels and cytosolic Ca(2+) signals, as well as significantly augmented insulin secretion. Inducible deletion of Bcl-x(L) in adult mouse β-cells also increased glucose-stimulated NAD(P)H and Ca(2+) responses and resulted in an improvement of in vivo glucose tolerance in the conditional Bcl-x(L) knockout animals. Our work suggests that prosurvival Bcl proteins normally dampen the β-cell response to glucose and thus reveals these core apoptosis proteins as integrators of cell death and physiology in pancreatic β-cells.
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Affiliation(s)
- Dan S. Luciani
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Surgery, University of British Columbia, Vancouver, British Columbia, Canada
- Child & Family Research Institute, Vancouver, British Columbia, Canada
- Corresponding authors: James D. Johnson, , and Dan S. Luciani,
| | - Sarah A. White
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Surgery, University of British Columbia, Vancouver, British Columbia, Canada
- Child & Family Research Institute, Vancouver, British Columbia, Canada
| | - Scott B. Widenmaier
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Varun V. Saran
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada the
- University of British Columbia James Hogg Research Centre, St. Paul's Hospital, Vancouver, British Columbia, Canada
| | - Farnaz Taghizadeh
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Xiaoke Hu
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Michael F. Allard
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada the
- University of British Columbia James Hogg Research Centre, St. Paul's Hospital, Vancouver, British Columbia, Canada
| | - James D. Johnson
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Surgery, University of British Columbia, Vancouver, British Columbia, Canada
- Corresponding authors: James D. Johnson, , and Dan S. Luciani,
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The mitochondrial Na+/Ca2+ exchanger upregulates glucose dependent Ca2+ signalling linked to insulin secretion. PLoS One 2012; 7:e46649. [PMID: 23056385 PMCID: PMC3466326 DOI: 10.1371/journal.pone.0046649] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Accepted: 09/03/2012] [Indexed: 11/25/2022] Open
Abstract
Mitochondria mediate dual metabolic and Ca2+ shuttling activities. While the former is required for Ca2+ signalling linked to insulin secretion, the role of the latter in β cell function has not been well understood, primarily because the molecular identity of the mitochondrial Ca2+ transporters were elusive and the selectivity of their inhibitors was questionable. This study focuses on NCLX, the recently discovered mitochondrial Na+/Ca2+ exchanger that is linked to Ca2+ signalling in MIN6 and primary β cells. Suppression either of NCLX expression, using a siRNA construct (siNCLX) or of its activity, by a dominant negative construct (dnNCLX), enhanced mitochondrial Ca2+ influx and blocked efflux induced by glucose or by cell depolarization. In addition, NCLX regulated basal, but not glucose-dependent changes, in metabolic rate, mitochondrial membrane potential and mitochondrial resting Ca2+. Importantly, NCLX controlled the rate and amplitude of cytosolic Ca2+ changes induced by depolarization or high glucose, indicating that NCLX is a critical and rate limiting component in the cross talk between mitochondrial and plasma membrane Ca2+ signalling. Finally, knockdown of NCLX expression was followed by a delay in glucose-dependent insulin secretion. These findings suggest that the mitochondrial Na+/Ca2+ exchanger, NCLX, shapes glucose-dependent mitochondrial and cytosolic Ca2+ signals thereby regulating the temporal pattern of insulin secretion in β cells.
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Abstract
The importance of K(ATP) channels in stimulus-secretion coupling of β-cells is well established, although they are not indispensable for the maintenance of glycaemic control. This review article depicts a new role for K(ATP) channels by showing that genetic or pharmacological ablation of these channels protects β-cells against oxidative stress. Increased production of oxidants is a crucial factor in the pathogenesis of type 2 diabetes mellitus (T2DM). T2DM develops when β-cells can no longer compensate for the high demand of insulin resulting from excess fuel intake. Instead β-cells start to secrete less insulin and β-cell mass is diminished by apoptosis. Both, reduction of insulin secretion and β-cell mass induced by oxidative stress, are prevented by deletion or inhibition of K(ATP) channels. These findings may open up new insights into the early treatment of T2DM.
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Affiliation(s)
- G Drews
- Department of Pharmacology, Institute of Pharmacy, University of Tübingen, Tübingen, Germany.
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50
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Tarasov AI, Semplici F, Ravier MA, Bellomo EA, Pullen TJ, Gilon P, Sekler I, Rizzuto R, Rutter GA. The mitochondrial Ca2+ uniporter MCU is essential for glucose-induced ATP increases in pancreatic β-cells. PLoS One 2012; 7:e39722. [PMID: 22829870 PMCID: PMC3400633 DOI: 10.1371/journal.pone.0039722] [Citation(s) in RCA: 138] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Accepted: 05/25/2012] [Indexed: 01/09/2023] Open
Abstract
Glucose induces insulin release from pancreatic β-cells by stimulating ATP synthesis, membrane depolarisation and Ca2+ influx. As well as activating ATP-consuming processes, cytosolic Ca2+ increases may also potentiate mitochondrial ATP synthesis. Until recently, the ability to study the role of mitochondrial Ca2+ transport in glucose-stimulated insulin secretion has been hindered by the absence of suitable approaches either to suppress Ca2+ uptake into these organelles, or to examine the impact on β-cell excitability. Here, we have combined patch-clamp electrophysiology with simultaneous real-time imaging of compartmentalised changes in Ca2+ and ATP/ADP ratio in single primary mouse β-cells, using recombinant targeted (Pericam or Perceval, respectively) as well as entrapped intracellular (Fura-Red), probes. Through shRNA-mediated silencing we show that the recently-identified mitochondrial Ca2+ uniporter, MCU, is required for depolarisation-induced mitochondrial Ca2+ increases, and for a sustained increase in cytosolic ATP/ADP ratio. By contrast, silencing of the mitochondrial Na+-Ca2+ exchanger NCLX affected the kinetics of glucose-induced changes in, but not steady state values of, cytosolic ATP/ADP. Exposure to gluco-lipotoxic conditions delayed both mitochondrial Ca2+ uptake and cytosolic ATP/ADP ratio increases without affecting the expression of either gene. Mitochondrial Ca2+ accumulation, mediated by MCU and modulated by NCLX, is thus required for normal glucose sensing by pancreatic β-cells, and becomes defective in conditions mimicking the diabetic milieu.
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Affiliation(s)
- Andrei I. Tarasov
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Francesca Semplici
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Magalie A. Ravier
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
- Institut de Génomique Fonctionnelle, INSERM U661, CNRS UMR5203, Université Montpellier I et II, Montpellier, France
| | - Elisa A. Bellomo
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Timothy J. Pullen
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Patrick Gilon
- Pole of Endocrinology, Diabetes and Nutrition, Faculty of Medicine, Université Catholique de Louvain, Brussels, Belgium
| | - Israel Sekler
- Department of Physiology, Faculty of Health Sciences, Ben Gurion University, Beer-Sheva, Israel
| | - Rosario Rizzuto
- Department of Biomedical Sciences, University of Padua, Padua, Italy
| | - Guy A. Rutter
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
- * E-mail:
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