1
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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 At high glucose, this is superseded by a calcium-dependent mechanism.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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2
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Marinelli I, Parekh V, Fletcher P, Thompson B, Ren J, Tang X, Saunders TL, Ha J, Sherman A, Bertram R, Satin LS. Slow oscillations persist in pancreatic beta cells lacking phosphofructokinase M. Biophys J 2022; 121:692-704. [PMID: 35131294 PMCID: PMC8948000 DOI: 10.1016/j.bpj.2022.01.027] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 12/07/2021] [Accepted: 01/28/2022] [Indexed: 11/22/2022] Open
Abstract
Pulsatile insulin secretion by pancreatic beta cells is necessary for tight glucose control in the body. Glycolytic oscillations have been proposed as the mechanism for generating the electrical oscillations underlying pulsatile insulin secretion. The glycolytic enzyme 6-phosphofructokinase-1 (PFK) synthesizes fructose-1,6-bisphosphate (FBP) from fructose-6-phosphate. It has been proposed that the slow electrical and Ca2+ oscillations (periods of 3-5 min) observed in islets result from allosteric feedback activation of PFKM by FBP. Pancreatic beta cells express three PFK isozymes: PFKL, PFKM, and PFKP. A prior study of mice that were engineered to lack PFKM using a gene-trap strategy to delete Pfkm produced a mosaic reduction in global Pfkm expression, but the islets isolated from the mice still exhibited slow Ca2+ oscillations. However, these islets still expressed residual PFKM protein. Thus, to more fully test the hypothesis that beta cell PFKM is responsible for slow islet oscillations, we made a beta-cell-specific knockout mouse that completely lacked PFKM. While PFKM deletion resulted in subtle metabolic changes in vivo, islets that were isolated from these mice continued to exhibit slow oscillations in electrical activity, beta cell Ca2+ concentrations, and glycolysis, as measured using PKAR, an FBP reporter/biosensor. Furthermore, simulations obtained with a mathematical model of beta cell activity shows that slow oscillations can persist despite PFKM loss provided that one of the other PFK isoforms, such as PFKP, is present, even if its level of expression is unchanged. Thus, while we believe that PFKM may be the main regulator of slow oscillations in wild-type islets, PFKP can provide functional redundancy. Our model also suggests that PFKM likely dominates, in vivo, because it outcompetes PFKP with its higher FBP affinity and lower ATP affinity. We thus propose that isoform redundancy may rescue key physiological processes of the beta cell in the absence of certain critical genes.
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Affiliation(s)
- Isabella Marinelli
- Centre for Systems Modelling & Quantitative Biomedicine (SMQB), University of Birmingham, Birmingham, UK
| | - Vishal Parekh
- Department of Pharmacology and Brehm Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, Michigan
| | - Patrick Fletcher
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Bethesda
| | - Benjamin Thompson
- Department of Pharmacology and Brehm Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, Michigan
| | - Jinhua Ren
- Department of Pharmacology and Brehm Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, Michigan
| | - Xiaoqing Tang
- Department of Biological Sciences, Michigan Technological University, Houghton, Michigan
| | - Thomas L Saunders
- Division of Medical Medicine and Genetics, Department of Internal Medicine, Transgenic Animal Model Core, University of Michigan Medical School, Ann Arbor, Michigan
| | - Joon Ha
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Bethesda
| | - Arthur Sherman
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Bethesda
| | - 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 Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, Michigan.
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3
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Mikawa T, Shibata E, Shimada M, Ito K, Ito T, Kanda H, Takubo K, Shimada A, Lleonart ME, Inagaki N, Yokode M, Kondoh H. Characterization of genetically modified mice for phosphoglycerate mutase, a vitally-essential enzyme in glycolysis. PLoS One 2021; 16:e0250856. [PMID: 33914812 PMCID: PMC8084212 DOI: 10.1371/journal.pone.0250856] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Accepted: 04/15/2021] [Indexed: 01/14/2023] Open
Abstract
Glycolytic metabolism is closely involved in physiological homeostasis and pathophysiological states. Among glycolytic enzymes, phosphoglycerate mutase (PGAM) has been reported to exert certain physiological role in vitro, whereas its impact on glucose metabolism in vivo remains unclear. Here, we report the characterization of Pgam1 knockout mice. We observed that homozygous knockout mice of Pgam1 were embryonic lethal. Although we previously reported that both PGAM-1 and -2 affect global glycolytic profile of cancers in vitro, in vivo glucose parameters were less affected both in the heterozygous knockout of Pgam1 and in Pgam2 transgenic mice. Thus, the impact of PGAM on in vivo glucose metabolism is rather complex than expected before.
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Affiliation(s)
- Takumi Mikawa
- Geriatric Unit, Graduate School of Medicine, Kyoto University, Kyoto, Japan
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Eri Shibata
- Geriatric Unit, Graduate School of Medicine, Kyoto University, Kyoto, Japan
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Midori Shimada
- Joint Faculty of Veterinary Science, Yamaguchi University, Yamaguchi, Japan
| | - Ken Ito
- Geriatric Unit, Graduate School of Medicine, Kyoto University, Kyoto, Japan
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Tomiko Ito
- Geriatric Unit, Graduate School of Medicine, Kyoto University, Kyoto, Japan
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Hiroaki Kanda
- Department of Pathology, Saitama Cancer Center, Saitama, Japan
| | - Keiyo Takubo
- Department of Stem Cell Biology, Research Institute, National Center for Global Health and Medicine, Tokyo, Japan
| | | | | | - Nobuya Inagaki
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Masayuki Yokode
- Geriatric Unit, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Hiroshi Kondoh
- Geriatric Unit, Graduate School of Medicine, Kyoto University, Kyoto, Japan
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
- * E-mail:
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4
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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: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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5
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Westermeier F, Holyoak T, Asenjo JL, Gatica R, Nualart F, Burbulis I, Bertinat R. Gluconeogenic Enzymes in β-Cells: Pharmacological Targets for Improving Insulin Secretion. Trends Endocrinol Metab 2019; 30:520-531. [PMID: 31213347 DOI: 10.1016/j.tem.2019.05.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 05/14/2019] [Accepted: 05/16/2019] [Indexed: 02/06/2023]
Abstract
Pancreatic β-cells express the gluconeogenic enzymes glucose 6-phosphatase (G6Pase), fructose 1,6-bisphosphatase (FBP), and phosphoenolpyruvate (PEP) carboxykinase (PCK), which modulate glucose-stimulated insulin secretion (GSIS) through their ability to reverse otherwise irreversible glycolytic steps. Here, we review current knowledge about the expression and regulation of these enzymes in the context of manipulating them to improve insulin secretion in diabetics. Because the regulation of gluconeogenic enzymes in β-cells is so poorly understood, we propose novel research avenues to study these enzymes as modulators of insulin secretion and β-cell dysfunction, with especial attention to FBP, which constitutes an attractive target with an inhibitor under clinical evaluation at present.
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Affiliation(s)
- Francisco Westermeier
- FH JOANNEUM Gesellschaft mbH University of Applied Sciences, Institute of Biomedical Science, Eggenberger Allee 13, 8020 Graz, Austria
| | - Todd Holyoak
- Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | - Joel L Asenjo
- Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Independencia 631, 5110566 Valdivia, Chile
| | - Rodrigo Gatica
- Escuela de Veterinaria, Facultad de Ciencias, Universidad Mayor, La Pirámide 5750, 8580745 Santiago, Chile
| | - Francisco Nualart
- Centro de Microscopía Avanzada, CMA BIO, Facultad de Ciencias Biológicas, Universidad de Concepción, Casilla 160 C, 4030000 Concepción, Chile
| | - Ian Burbulis
- Department of Biochemistry and Molecular Genetics, School of Medicine, University of Virginia, Jordan Hall Room 6022, 1340 Jefferson Park Avenue, Charlottesville, VA 22908, USA; Escuela de Medicina, Universidad San Sebastián, Sede Patagonia, Lago Panguipulli 1390, 5501842 Puerto Montt, Chile
| | - Romina Bertinat
- Centro de Microscopía Avanzada, CMA BIO, Facultad de Ciencias Biológicas, Universidad de Concepción, Casilla 160 C, 4030000 Concepción, Chile.
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6
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Abstract
Insulin secretion from pancreatic islet β-cells occurs in a pulsatile fashion, with a typical period of ∼5 min. The basis of this pulsatility in mouse islets has been investigated for more than four decades, and the various theories have been described as either qualitative or mathematical models. In many cases the models differ in their mechanisms for rhythmogenesis, as well as other less important details. In this Perspective, we describe two main classes of models: those in which oscillations in the intracellular Ca2+ concentration drive oscillations in metabolism, and those in which intrinsic metabolic oscillations drive oscillations in Ca2+ concentration and electrical activity. We then discuss nine canonical experimental findings that provide key insights into the mechanism of islet oscillations and list the models that can account for each finding. Finally, we describe a new model that integrates features from multiple earlier models and is thus called the Integrated Oscillator Model. In this model, intracellular Ca2+ acts on the glycolytic pathway in the generation of oscillations, and it is thus a hybrid of the two main classes of models. It alone among models proposed to date can explain all nine key experimental findings, and it serves as a good starting point for future studies of pulsatile insulin secretion from human islets.
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Affiliation(s)
- Richard Bertram
- Department of Mathematics and Programs in Neuroscience and Molecular Biophysics, Florida State University, Tallahassee, FL
| | - Leslie S Satin
- Department of Pharmacology and Brehm Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, MI
| | - Arthur S Sherman
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
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7
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McKenna JP, Ha J, Merrins MJ, Satin LS, Sherman A, Bertram R. Ca2+ Effects on ATP Production and Consumption Have Regulatory Roles on Oscillatory Islet Activity. Biophys J 2017; 110:733-742. [PMID: 26840737 DOI: 10.1016/j.bpj.2015.11.3526] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 10/21/2015] [Accepted: 11/06/2015] [Indexed: 11/19/2022] Open
Abstract
Pancreatic islets respond to elevated blood glucose by secreting pulses of insulin that parallel oscillations in β-cell metabolism, intracellular Ca(2+) concentration, and bursting electrical activity. The mechanisms that maintain an oscillatory response are not fully understood, yet several models have been proposed. Only some can account for experiments supporting that metabolism is intrinsically oscillatory in β-cells. The dual oscillator model (DOM) implicates glycolysis as the source of oscillatory metabolism. In the companion article, we use recently developed biosensors to confirm that glycolysis is oscillatory and further elucidate the coordination of metabolic and electrical signals in the insulin secretory pathway. In this report, we modify the DOM by incorporating an established link between metabolism and intracellular Ca(2+) to reconcile model predictions with experimental observations from the companion article. With modification, we maintain the distinguishing feature of the DOM, oscillatory glycolysis, but introduce the ability of Ca(2+) influx to reshape glycolytic oscillations by promoting glycolytic efflux. We use the modified model to explain measurements from the companion article and from previously published experiments with islets.
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Affiliation(s)
- Joseph P McKenna
- Department of Mathematics, 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
| | - 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
| | - Leslie S Satin
- Department of Pharmacology and Brehm Diabetes Center, University of Michigan, Ann Arbor, Michigan
| | - 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, Florida State University, Tallahassee, Florida; Programs in Neuroscience and Molecular Biophysics, Florida State University, Tallahassee, Florida.
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8
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Koppe L, Nyam E, Vivot K, Manning Fox JE, Dai XQ, Nguyen BN, Trudel D, Attané C, Moullé VS, MacDonald PE, Ghislain J, Poitout V. Urea impairs β cell glycolysis and insulin secretion in chronic kidney disease. J Clin Invest 2016; 126:3598-612. [PMID: 27525435 DOI: 10.1172/jci86181] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Accepted: 06/24/2016] [Indexed: 12/25/2022] Open
Abstract
Disorders of glucose homeostasis are common in chronic kidney disease (CKD) and are associated with increased mortality, but the mechanisms of impaired insulin secretion in this disease remain unclear. Here, we tested the hypothesis that defective insulin secretion in CKD is caused by a direct effect of urea on pancreatic β cells. In a murine model in which CKD is induced by 5/6 nephrectomy (CKD mice), we observed defects in glucose-stimulated insulin secretion in vivo and in isolated islets. Similarly, insulin secretion was impaired in normal mouse and human islets that were cultured with disease-relevant concentrations of urea and in islets from normal mice treated orally with urea for 3 weeks. In CKD mouse islets as well as urea-exposed normal islets, we observed an increase in oxidative stress and protein O-GlcNAcylation. Protein O-GlcNAcylation was also observed in pancreatic sections from CKD patients. Impairment of insulin secretion in both CKD mouse and urea-exposed islets was associated with reduced glucose utilization and activity of phosphofructokinase 1 (PFK-1), which could be reversed by inhibiting O-GlcNAcylation. Inhibition of O-GlcNAcylation also restored insulin secretion in both mouse models. These results suggest that insulin secretory defects associated with CKD arise from elevated circulating levels of urea that increase islet protein O-GlcNAcylation and impair glycolysis.
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9
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Sun B, Brooks ED, Koeberl DD. Preclinical Development of New Therapy for Glycogen Storage Diseases. Curr Gene Ther 2016; 15:338-47. [PMID: 26122079 DOI: 10.2174/1566523215666150630132253] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2014] [Revised: 03/24/2015] [Accepted: 04/01/2015] [Indexed: 02/07/2023]
Abstract
Glycogen storage disease (GSD) consists of more than 10 discrete conditions for which the biochemical and genetic bases have been determined, and new therapies have been under development for several of these conditions. Gene therapy research has generated proof-of-concept for GSD types I (von Gierke disease) and II (Pompe disease). Key features of these gene therapy strategies include the choice of vector and regulatory cassette, and recently adeno-associated virus (AAV) vectors containing tissue-specific promoters have achieved a high degree of efficacy. Efficacy of gene therapy for Pompe disease depend upon the induction of immune tolerance to the therapeutic enzyme. Efficacy of von Gierke disease is transient, waning gradually over the months following vector administration. Small molecule therapies have been evaluated with the goal of improving standard of care therapy or ameliorating the cellular abnormalities associated with specific GSDs. The receptor-mediated uptake of the therapeutic enzyme in Pompe disease was enhanced by administration of β2 agonists. Rapamycin reduced the liver fibrosis observed in GSD III. Further development of gene therapy could provide curative therapy for patients with GSD, if efficacy from preclinical research is observed in future clinical trials and these treatments become clinically available.
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10
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Abstract
Insulin secretion is one of the most characteristic features of β-cell physiology. As it plays a central role in glucose regulation, a number of experimental and theoretical studies have been performed since the discovery of the pancreatic β-cell. This review article aims to give an overview of the mathematical approaches to insulin secretion. Beginning with the bursting electrical activity in pancreatic β-cells, we describe effects of the gap-junction coupling between β-cells on the dynamics of insulin secretion. Then, implications of paracrine interactions among such islet cells as α-, β-, and δ-cells are discussed. Finally, we present mathematical models which incorporate effects of glycolysis and mitochondrial glucose metabolism on the control of insulin secretion.
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Affiliation(s)
- Kyungreem Han
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul, South Korea
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11
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Abstract
Oscillatory phenomenon in electrical activity and cytoplasmic calcium concentration in response to glucose are intimately connected to multiple key aspects of pancreatic β-cell physiology. However, there is no single model for oscillatory mechanisms in these cells. We set out to identify possible pacemaker candidates for burst activity and cytoplasmic Ca(2+) oscillations in these cells by analyzing published hypotheses, their corresponding mathematical models, and relevant experimental data. We found that although no single pacemaker can account for the variety of oscillatory phenomena in β-cells, at least several separate mechanisms can underlie specific kinds of oscillations. According to our analysis, slowly activating Ca(2+)-sensitive K(+) channels can be responsible for very fast Ca(2+) oscillations; changes in the ATP/ADP ratio and in the endoplasmic reticulum calcium concentration can be pacemakers for both fast bursts and cytoplasmic calcium oscillations, and cyclical cytoplasmic Na(+) changes may underlie patterning of slow calcium oscillations. However, these mechanisms still lack direct confirmation, and their potential interactions raises new issues. Further studies supported by improved mathematical models are necessary to understand oscillatory phenomena in β-cell physiology.
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Affiliation(s)
- L E Fridlyand
- Dept. of Medicine, MC-1027, Univ. of Chicago, 5841 S. Maryland Ave., Chicago, IL 60637, USA.
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12
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Echigoya Y, Okabe H, Itou T, Endo H, Sakai T. Molecular characterization of glycogen synthase 1 and its tissue expression profile with type II hexokinase and muscle-type phosphofructokinase in horses. Mol Biol Rep 2011; 38:461-9. [DOI: 10.1007/s11033-010-0129-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2009] [Accepted: 03/23/2010] [Indexed: 01/07/2023]
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13
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Chehtane M, Khaled AR. Interleukin-7 mediates glucose utilization in lymphocytes through transcriptional regulation of the hexokinase II gene. Am J Physiol Cell Physiol 2010; 298:C1560-71. [PMID: 20200205 DOI: 10.1152/ajpcell.00506.2009] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The cytokine interleukin-7 (IL-7) has essential growth activities that maintain the homeostatic balance of the immune system. Little is known of the mechanism by which IL-7 signaling regulates metabolic activity in support of its vital function in lymphocytes. We observed that IL-7 deprivation caused a rapid decline in the metabolism of glucose that was attributable to loss of intracellular glucose retention. To identify the transducer of the IL-7 metabolic signal, we examined the expression of three important regulators of glucose metabolism, the glucose transporter GLUT-1 and two glycolytic enzymes, hexokinase II (HXKII) and phosphofructokinase-1 (PFK-1), using an IL-7-dependent T-cell line and primary lymphocytes. We found that in lymphocytes deprived of IL-7 loss of glucose uptake correlated with decreased expression of HXKII. Readdition of IL-7 to cytokine-deprived lymphocytes restored the transcription of the HXKII gene within 2 h, but not that of GLUT-1 or PFK-1. IL-7-mediated increases in HXKII, but not GLUT-1 or PFK-1, were also observed at the protein level. Inhibition of HXKII with 3-bromopyruvate or specific small-interfering RNA decreased glucose utilization, as well as ATP levels, in the presence of IL-7, whereas overexpression of HXKII, but not GLUT-1, restored glucose retention and increased ATP levels in the absence of IL-7. We conclude that IL-7 controls glucose utilization by regulating the gene expression of HXKII, suggesting a mechanism by which IL-7 supports bioenergetics that control cell fate decisions in lymphocytes.
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Affiliation(s)
- Mounir Chehtane
- Burnett School of Biomedical Sciences, University of Central Florida, Orlando, FL 32827, USA
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14
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Getty-Kaushik L, Viereck JC, Goodman JM, Guo Z, LeBrasseur NK, Richard AMT, Flanagan JN, Yaney GC, Hamilton JA, Tornheim K. Mice deficient in phosphofructokinase-M have greatly decreased fat stores. Obesity (Silver Spring) 2010; 18:434-40. [PMID: 19779479 PMCID: PMC2871150 DOI: 10.1038/oby.2009.295] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Synthesis of triacylglycerol requires the glucose-derived glycerol component, and glucose uptake has been viewed as the rate-limiting step in glucose metabolism in adipocytes. Furthermore, adipose tissue contains all three isoforms of the glycolytic enzyme phosphofructokinase (PFK). We here report that mice deficient in the muscle isoform PFK-M have greatly reduced fat stores. Mice with disrupted activity of the PFK-M distal promoter were obtained from Lexicon Pharmaceuticals, developed from OmniBank OST#56064. Intra-abdominal fat was measured by magnetic resonance imaging of the methylene proton signal. Lipogenesis from labeled glucose was measured in isolated adipocytes. Lipolysis (glycerol and free fatty acid release) was measured in perifused adipocytes. Intra-abdominal fat in PFK-M-deficient female mice (5-10 months old) was 17 +/- 3% of that of wild-type littermates (n = 4; P < 0.02). Epididymal fat weight in 15 animals (7-9.5 months) was 34 +/- 4% of control littermate (P < 0.002), with 10-30% lower body weight. Basal and insulin-stimulated lipogenesis in PFK-M-deficient epididymal adipocytes was 40% of the rates in cells from heterozygous littermates (n = 3; P < 0.05). The rate of isoproterenol-stimulated lipolysis in wild-type adipocytes declined approximately 10% after 1 h and 50% after 2 h; in PFK-M-deficient cells it declined much more rapidly, 50% in 1 h and 90% in 2 h, and lipolytic oscillations appeared to be damped (n = 4). These results indicate an important role for PFK-M in adipose metabolism. This may be related to the ability of this isoform to generate glycolytic oscillations, because such oscillations may enhance the production of the triacylglycerol precursor alpha-glycerophosphate.
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Affiliation(s)
- Lisa Getty-Kaushik
- Obesity Research Center, Evans Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Jason C. Viereck
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Jessie M. Goodman
- Obesity Research Center, Evans Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, USA
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Zifang Guo
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Nathan K. LeBrasseur
- Section of Endocrinology, Diabetes and Nutrition, Evans Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, USA.
| | - Ann-Marie T. Richard
- Obesity Research Center, Evans Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, USA
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, USA
| | - John N. Flanagan
- Section of Endocrinology, Diabetes and Nutrition, Evans Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, USA.
| | - Gordon C. Yaney
- Obesity Research Center, Evans Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, USA
| | - James A. Hamilton
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Keith Tornheim
- Obesity Research Center, Evans Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, USA
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, USA
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15
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Abstract
Pancreatic beta-cells possess an inherent ability to generate oscillatory signals that trigger insulin release. Coordination of the secretory activity among beta-cells results in pulsatile insulin secretion from the pancreas, which is considered important for the action of the hormone in the target tissues. This review focuses on the mechanisms underlying oscillatory control of insulin secretion at the level of the individual beta-cell. Recent studies have demonstrated that oscillations of the cytoplasmic Ca(2+) concentration are synchronized with oscillations in beta-cell metabolism, intracellular cAMP concentration, phospholipase C activity and plasma membrane phosphoinositide lipid concentrations. There are complex interdependencies between the different messengers and signalling pathways that contribute to amplitude regulation and shaping of the insulin secretory response to nutrient stimuli and neurohormonal modulators. Several of these pathways may be important pharmacological targets for improving pulsatile insulin secretion in type 2 diabetes.
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Affiliation(s)
- Anders Tengholm
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre, Box 571, SE-75123 Uppsala, Sweden.
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16
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Abstract
Mathematical modeling of pancreatic beta cells has contributed significantly to the understanding of the mechanisms involved in glucose-stimulated insulin secretion (GSIS). Early models of insulin secretion built in the 1970s were phenomenological with little biological foundation for the proposed mechanisms. In the 1980s, models focused on identifying the regulation of bursting electrical activity known to be important for insulin secretion. The main result was to reject proposed mechanisms as new data emerged, but important results of the role of cell-to-cell coupling were also established. New models have been proposed that provide possible explanations for the occurrence of various patterns of bursting and calcium oscillations. In addition, modeling has played an important role in comparing competing effects of calcium on both NADH and adenosine 3'-5'-cyclic monophosphate levels. Models including modern cell biological results of the regulation of insulin containing granules and cell heterogeneity have appeared, providing updated versions of the early models proposed in the 1970s. These models, when coupled to electrophysiological- and calcium-based ones, have the prospect to aid in understanding the overall picture of GSIS. In addition, they might be useful for estimating in vivo beta-cell functioning. Beta-cell modeling will likely move closer to clinical applications, where it can be expected to play an important role, as it has and will, in understanding the complex oscillatory phenomena observed in beta cells and islets.
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Holz GG, Heart E, Leech CA. Synchronizing Ca2+ and cAMP oscillations in pancreatic beta-cells: a role for glucose metabolism and GLP-1 receptors? Focus on "regulation of cAMP dynamics by Ca2+ and G protein-coupled receptors in the pancreatic beta-cell: a computational approach". Am J Physiol Cell Physiol 2007; 294:C4-6. [PMID: 17989206 DOI: 10.1152/ajpcell.00522.2007] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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