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Abstract
Pancreatic β cells operate with a high rate of membrane recycling for insulin secretion, yet endocytosis in these cells is not fully understood. We investigate this process in mature mouse β cells by genetically deleting dynamin GTPase, the membrane fission machinery essential for clathrin-mediated endocytosis. Unexpectedly, the mice lacking all three dynamin genes (DNM1, DNM2, DNM3) in their β cells are viable, and their β cells still contain numerous insulin granules. Endocytosis in these β cells is severely impaired, resulting in abnormal endocytic intermediates on the plasma membrane. Although insulin granules are abundant, their release upon glucose stimulation is blunted in both the first and second phases, leading to hyperglycemia and glucose intolerance in mice. Dynamin triple deletion impairs insulin granule exocytosis and decreases intracellular Ca2+ responses and granule docking. The docking defect is correlated with reduced expression of Munc13-1 and RIM1 and reorganization of cortical F-actin in β cells. Collectively, these findings uncover the role of dynamin in dense-core vesicle endocytosis and secretory capacity. Insulin secretion deficiency in the absence of dynamin-mediated endocytosis highlights the risk of impaired membrane trafficking in endocrine failure and diabetes pathogenesis.
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Affiliation(s)
- Fan Fan
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226
| | - Yumei Wu
- HHMI, Yale University School of Medicine, New Haven, CT 06510
- Departments of Neuroscience and Cell Biology, Program in Cellular Neuroscience, Neurodegeneration and Repair, Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT 06510
| | - Manami Hara
- Section of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Chicago, Chicago, IL 60637
| | - Adam Rizk
- Section of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Chicago, Chicago, IL 60637
| | - Chen Ji
- Synapses and Circuits section, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892
| | - Dan Nerad
- Emergency Medicine, Carl R. Darnall Army Medical Center, Fort Hood, TX 76544
| | - Natalia Tamarina
- Department of Medicine, The Kovler Diabetes Center, University of Chicago, Chicago, IL 60637
| | - Xuelin Lou
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226;
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2
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Fan F, Wendlick J, Tamarina N, Wu Y, Ferguson S, Philipson LH, De Camilli P, Lou X. Dynamin Function in Exocytosis and Endocytosis Coupling of Dense-Core Vesicles in Pancreatic Beta Cells. Biophys J 2020. [DOI: 10.1016/j.bpj.2019.11.2700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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3
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Bergeron V, Ghislain J, Vivot K, Tamarina N, Philipson LH, Fielitz J, Poitout V. Deletion of Protein Kinase D1 in Pancreatic β-Cells Impairs Insulin Secretion in High-Fat Diet-Fed Mice. Diabetes 2018; 67:71-77. [PMID: 29038309 PMCID: PMC5741145 DOI: 10.2337/db17-0982] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [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] [Received: 08/16/2017] [Accepted: 10/09/2017] [Indexed: 12/29/2022]
Abstract
Ββ-Cell adaptation to insulin resistance is necessary to maintain glucose homeostasis in obesity. Failure of this mechanism is a hallmark of type 2 diabetes (T2D). Hence, factors controlling functional β-cell compensation are potentially important targets for the treatment of T2D. Protein kinase D1 (PKD1) integrates diverse signals in the β-cell and plays a critical role in the control of insulin secretion. However, the role of β-cell PKD1 in glucose homeostasis in vivo is essentially unknown. Using β-cell-specific, inducible PKD1 knockout mice (βPKD1KO), we examined the role of β-cell PKD1 under basal conditions and during high-fat feeding. βPKD1KO mice under a chow diet presented no significant difference in glucose tolerance or insulin secretion compared with mice expressing the Cre transgene alone; however, when compared with wild-type mice, both groups developed glucose intolerance. Under a high-fat diet, deletion of PKD1 in β-cells worsened hyperglycemia, hyperinsulinemia, and glucose intolerance. This was accompanied by impaired glucose-induced insulin secretion both in vivo in hyperglycemic clamps and ex vivo in isolated islets from high-fat diet-fed βPKD1KO mice without changes in islet mass. This study demonstrates an essential role for PKD1 in the β-cell adaptive secretory response to high-fat feeding in mice.
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Affiliation(s)
- Valérie Bergeron
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Quebec, Canada
- Department of Medicine, Université de Montréal, Montréal, Quebec, Canada
| | - Julien Ghislain
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Quebec, Canada
| | - Kevin Vivot
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Quebec, Canada
| | | | | | - Jens Fielitz
- Experimental and Clinical Research Center, Charité-Universitätsmedizin Berlin, Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
- DZHK (German Center for Cardiovascular Research), Greifswald, Germany
- Department of Internal Medicine B, University Medicine Greifswald, Greifswald, Germany
| | - Vincent Poitout
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Quebec, Canada
- Department of Medicine, Université de Montréal, Montréal, Quebec, Canada
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4
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Rosario W, Singh I, Wautlet A, Patterson C, Flak J, Becker TC, Ali A, Tamarina N, Philipson LH, Enquist LW, Myers MG, Rhodes CJ. The Brain-to-Pancreatic Islet Neuronal Map Reveals Differential Glucose Regulation From Distinct Hypothalamic Regions. Diabetes 2016; 65:2711-23. [PMID: 27207534 PMCID: PMC5001176 DOI: 10.2337/db15-0629] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [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] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 04/06/2016] [Indexed: 12/24/2022]
Abstract
The brain influences glucose homeostasis, partly by supplemental control over insulin and glucagon secretion. Without this central regulation, diabetes and its complications can ensue. Yet, the neuronal network linking to pancreatic islets has never been fully mapped. Here, we refine this map using pseudorabies virus (PRV) retrograde tracing, indicating that the pancreatic islets are innervated by efferent circuits that emanate from the hypothalamus. We found that the hypothalamic arcuate nucleus (ARC), ventromedial nucleus (VMN), and lateral hypothalamic area (LHA) significantly overlap PRV and the physiological glucose-sensing enzyme glucokinase. Then, experimentally lowering glucose sensing, specifically in the ARC, resulted in glucose intolerance due to deficient insulin secretion and no significant effect in the VMN, but in the LHA it resulted in a lowering of the glucose threshold that improved glucose tolerance and/or improved insulin sensitivity, with an exaggerated counter-regulatory response for glucagon secretion. No significant effect on insulin sensitivity or metabolic homeostasis was noted. Thus, these data reveal novel direct neuronal effects on pancreatic islets and also render a functional validation of the brain-to-islet neuronal map. They also demonstrate that distinct regions of the hypothalamus differentially control insulin and glucagon secretion, potentially in partnership to help maintain glucose homeostasis and guard against hypoglycemia.
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Affiliation(s)
- Wilfredo Rosario
- Kovler Diabetes Center, Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Chicago, Chicago, IL
| | - Inderroop Singh
- Kovler Diabetes Center, Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Chicago, Chicago, IL
| | - Arnaud Wautlet
- Kovler Diabetes Center, Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Chicago, Chicago, IL
| | - Christa Patterson
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI
| | - Jonathan Flak
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI
| | - Thomas C Becker
- Duke Molecular Physiology Institute and Sarah W. Stedman Nutrition and Metabolism Center, Duke University, Durham, NC
| | - Almas Ali
- Kovler Diabetes Center, Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Chicago, Chicago, IL
| | - Natalia Tamarina
- Kovler Diabetes Center, Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Chicago, Chicago, IL
| | - Louis H Philipson
- Kovler Diabetes Center, Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Chicago, Chicago, IL
| | - Lynn W Enquist
- Department of Molecular Biology, Princeton University, Princeton, NJ
| | - Martin G Myers
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI
| | - Christopher J Rhodes
- Kovler Diabetes Center, Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Chicago, Chicago, IL
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5
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Campbell JE, Ussher JR, Mulvihill EE, Kolic J, Baggio LL, Cao X, Liu Y, Lamont BJ, Morii T, Streutker CJ, Tamarina N, Philipson LH, Wrana JL, MacDonald PE, Drucker DJ. TCF1 links GIPR signaling to the control of beta cell function and survival. Nat Med 2015; 22:84-90. [DOI: 10.1038/nm.3997] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Accepted: 10/26/2015] [Indexed: 12/18/2022]
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6
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Fan F, Ji C, Wu Y, Ferguson SM, Tamarina N, Philipson LH, Lou X. Dynamin 2 regulates biphasic insulin secretion and plasma glucose homeostasis. J Clin Invest 2015; 125:4026-41. [PMID: 26413867 DOI: 10.1172/jci80652] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Accepted: 08/20/2015] [Indexed: 12/18/2022] Open
Abstract
Alterations in insulin granule exocytosis and endocytosis are paramount to pancreatic β cell dysfunction in diabetes mellitus. Here, using temporally controlled gene ablation specifically in β cells in mice, we identified an essential role of dynamin 2 GTPase in preserving normal biphasic insulin secretion and blood glucose homeostasis. Dynamin 2 deletion in β cells caused glucose intolerance and substantial reduction of the second phase of glucose-stimulated insulin secretion (GSIS); however, mutant β cells still maintained abundant insulin granules, with no signs of cell surface expansion. Compared with control β cells, real-time capacitance measurements demonstrated that exocytosis-endocytosis coupling was less efficient but not abolished; clathrin-mediated endocytosis (CME) was severely impaired at the step of membrane fission, which resulted in accumulation of clathrin-coated endocytic intermediates on the plasma membrane. Moreover, dynamin 2 ablation in β cells led to striking reorganization and enhancement of actin filaments, and insulin granule recruitment and mobilization were impaired at the later stage of GSIS. Together, our results demonstrate that dynamin 2 regulates insulin secretory capacity and dynamics in vivo through a mechanism depending on CME and F-actin remodeling. Moreover, this study indicates a potential pathophysiological link between endocytosis and diabetes mellitus.
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7
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Swisa A, Granot Z, Tamarina N, Sayers S, Bardeesy N, Philipson L, Hodson DJ, Wikstrom JD, Rutter GA, Leibowitz G, Glaser B, Dor Y. Loss of Liver Kinase B1 (LKB1) in Beta Cells Enhances Glucose-stimulated Insulin Secretion Despite Profound Mitochondrial Defects. J Biol Chem 2015; 290:20934-20946. [PMID: 26139601 PMCID: PMC4543653 DOI: 10.1074/jbc.m115.639237] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2015] [Indexed: 12/25/2022] Open
Abstract
The tumor suppressor liver kinase B1 (LKB1) is an important regulator of pancreatic β cell biology. LKB1-dependent phosphorylation of distinct AMPK (adenosine monophosphate-activated protein kinase) family members determines proper β cell polarity and restricts β cell size, total β cell mass, and glucose-stimulated insulin secretion (GSIS). However, the full spectrum of LKB1 effects and the mechanisms involved in the secretory phenotype remain incompletely understood. We report here that in the absence of LKB1 in β cells, GSIS is dramatically and persistently improved. The enhancement is seen both in vivo and in vitro and cannot be explained by altered cell polarity, increased β cell number, or increased insulin content. Increased secretion does require membrane depolarization and calcium influx but appears to rely mostly on a distal step in the secretion pathway. Surprisingly, enhanced GSIS is seen despite profound defects in mitochondrial structure and function in LKB1-deficient β cells, expected to greatly diminish insulin secretion via the classic triggering pathway. Thus LKB1 is essential for mitochondrial homeostasis in β cells and in parallel is a powerful negative regulator of insulin secretion. This study shows that β cells can be manipulated to enhance GSIS to supra-normal levels even in the face of defective mitochondria and without deterioration over months.
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Affiliation(s)
- Avital Swisa
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
| | - Zvi Granot
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
| | - Natalia Tamarina
- Department of Medicine, University of Chicago, Chicago, Illinois 60637
| | - Sophie Sayers
- Section of Cell Biology and Functional Genomics, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, SW7 2AZ, London, United Kingdom
| | - Nabeel Bardeesy
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Boston, Massachusetts 02114
| | - Louis Philipson
- Department of Medicine, University of Chicago, Chicago, Illinois 60637
| | - David J Hodson
- Section of Cell Biology and Functional Genomics, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, SW7 2AZ, London, United Kingdom
| | - Jakob D Wikstrom
- Endocrinology and Metabolism Service, Department of Internal Medicine, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel; Unit of Dermatology and Venereology, Department of Medicine, Karolinska Institutet, Karolinska University Hospital, 171 77 Stockholm, Sweden
| | - Guy A Rutter
- Section of Cell Biology and Functional Genomics, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, SW7 2AZ, London, United Kingdom
| | - Gil Leibowitz
- Endocrinology and Metabolism Service, Department of Internal Medicine, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel
| | - Benjamin Glaser
- Endocrinology and Metabolism Service, Department of Internal Medicine, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel
| | - Yuval Dor
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
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8
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Smith EP, An Z, Wagner C, Lewis AG, Cohen EB, Li B, Mahbod P, Sandoval D, Perez-Tilve D, Tamarina N, Philipson LH, Stoffers DA, Seeley RJ, D'Alessio DA. The role of β cell glucagon-like peptide-1 signaling in glucose regulation and response to diabetes drugs. Cell Metab 2014; 19:1050-7. [PMID: 24836562 PMCID: PMC4109713 DOI: 10.1016/j.cmet.2014.04.005] [Citation(s) in RCA: 126] [Impact Index Per Article: 12.6] [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] [Received: 10/15/2013] [Revised: 02/18/2014] [Accepted: 03/25/2014] [Indexed: 12/19/2022]
Abstract
Glucagon-like peptide-1 (GLP-1), an insulinotropic gut peptide released after eating, is essential for normal glucose tolerance (GT). To determine whether this effect is mediated directly by GLP-1 receptors (GLP1R) on islet β cells, we developed mice with β cell-specific knockdown of Glp1r. β cell Glp1r knockdown mice had impaired GT after intraperitoneal (i.p.) glucose and did not secrete insulin in response to i.p. or intravenous GLP-1. However, they had normal GT after oral glucose, a response that was impaired by a GLP1R antagonist. β cell Glp1r knockdown mice had blunted responses to a GLP1R agonist but intact glucose lowering with a dipeptidylpeptidase 4 (DPP-4) inhibitor. Thus, in mice, β cell Glp1rs are required to respond to hyperglycemia and exogenous GLP-1, but other factors compensate for reduced GLP-1 action during meals. These results support a role for extraislet GLP1R in oral glucose tolerance and paracrine regulation of β cells by islet GLP-1.
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Affiliation(s)
- Eric P Smith
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Zhibo An
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Constance Wagner
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Alfor G Lewis
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Eric B Cohen
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Bailing Li
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Parinaz Mahbod
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Darleen Sandoval
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Diego Perez-Tilve
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Natalia Tamarina
- Department of Medicine, The Kovler Diabetes Center, University of Chicago, Chicago, IL 60637, USA
| | - Louis H Philipson
- Department of Medicine, The Kovler Diabetes Center, University of Chicago, Chicago, IL 60637, USA
| | - Doris A Stoffers
- Institute for Diabetes, Obesity and Metabolism and the Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Randy J Seeley
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - David A D'Alessio
- Division of Endocrinology, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, USA; Cincinnati Veterans Affairs Medical Center, Cincinnati, OH 45237, USA.
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9
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Kaihara KA, Dickson LM, Jacobson DA, Tamarina N, Roe MW, Philipson LH, Wicksteed B. β-Cell-specific protein kinase A activation enhances the efficiency of glucose control by increasing acute-phase insulin secretion. Diabetes 2013; 62:1527-36. [PMID: 23349500 PMCID: PMC3636652 DOI: 10.2337/db12-1013] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [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] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Acute insulin secretion determines the efficiency of glucose clearance. Moreover, impaired acute insulin release is characteristic of reduced glucose control in the prediabetic state. Incretin hormones, which increase β-cell cAMP, restore acute-phase insulin secretion and improve glucose control. To determine the physiological role of the cAMP-dependent protein kinase (PKA), a mouse model was developed to increase PKA activity specifically in the pancreatic β-cells. In response to sustained hyperglycemia, PKA activity potentiated both acute and sustained insulin release. In contrast, a glucose bolus enhanced acute-phase insulin secretion alone. Acute-phase insulin secretion was increased 3.5-fold, reducing circulating glucose to 58% of levels in controls. Exendin-4 increased acute-phase insulin release to a similar degree as PKA activation. However, incretins did not augment the effects of PKA on acute-phase insulin secretion, consistent with incretins acting primarily via PKA to potentiate acute-phase insulin secretion. Intracellular calcium signaling was unaffected by PKA activation, suggesting that the effects of PKA on acute-phase insulin secretion are mediated by the phosphorylation of proteins involved in β-cell exocytosis. Thus, β-cell PKA activity transduces the cAMP signal to dramatically increase acute-phase insulin secretion, thereby enhancing the efficiency of insulin to control circulating glucose.
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Affiliation(s)
- Kelly A. Kaihara
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
| | - Lorna M. Dickson
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
| | - David A. Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Natalia Tamarina
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
| | - Michael W. Roe
- Department of Medicine, Cell and Developmental Biology, SUNY Upstate Medical University, Syracuse, New York
| | - Louis H. Philipson
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
| | - Barton Wicksteed
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
- Corresponding author: Barton Wicksteed,
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10
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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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11
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Abstract
We have developed a detailed mathematical model of ionic flux in beta-cells that includes the most essential channels and pumps in the plasma membrane. This model is coupled to equations describing Ca2+, inositol 1,4,5-trisphosphate (IP3), ATP, and Na+ homeostasis, including the uptake and release of Ca2+ by the endoplasmic reticulum (ER). In our model, metabolically derived ATP activates inward Ca2+ flux by regulation of ATP-sensitive K+ channels and depolarization of the plasma membrane. Results from the simulations support the hypothesis that intracellular Na+ and Ca2+ in the ER can be the main variables driving both fast (2-7 osc/min) and slow intracellular Ca2+ concentration oscillations (0.3-0.9 osc/min) and that the effect of IP3 on Ca2+ leak from the ER contributes to the pattern of slow calcium oscillations. Simulations also show that filling the ER Ca2+ stores leads to faster electrical bursting and Ca2+ oscillations. Specific Ca2+ oscillations in isolated beta-cell lines can also be simulated.
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12
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Qian F, Huang P, Ma L, Kuznetsov A, Tamarina N, Philipson LH. TRP genes: candidates for nonselective cation channels and store-operated channels in insulin-secreting cells. Diabetes 2002; 51 Suppl 1:S183-9. [PMID: 11815479 DOI: 10.2337/diabetes.51.2007.s183] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [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: 11/13/2022]
Abstract
Nonselective cation channels may play a role in insulin secretion by regulating pancreatic beta-cell plasma membrane potential, Ca(2+) homeostasis, and thereby glucose signaling. Transient receptor potential channel (TRPC)-related genes encode nonselective cation channels, some of which are similar to those described for beta-cells. Some TRPC-like channels are activated via G-protein--coupled mechanisms, some have been reported to be calcium-store-operated channels (SOC), and others are activated by novel signaling molecules or are sensitive to pressure and osmotic strength. Here we report the cloning and expression of mSTRPC4 from a mouse insulinoma cDNA library. mSTRPC4 encoded a protein of 97 kd, expressed in both endocrine cells and the brain. Stable cell lines expressing mSTRPC4 showed abundant mSTRPC4 protein, but no reproducible currents could be detected. mSTRPC4 therefore probably functions as a heteromultimer. We also report that LTRPC2, a G-protein and adenosine 5'-diphosphoribose (ADPR)-activated nonselective cation channel, is also expressed in human islets. TRPC-like channels may provide a pathway for depolarization or Ca(2+) entry in beta-cells and may be interesting targets for manipulating beta-cell function.
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Affiliation(s)
- Feng Qian
- Department of Neurobiology, Physiology, and Pharmacology, the University of Chicago, Chicago, Illinois, USA
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13
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Abstract
Baculovirus transduction is a gene transfer method that uses a moth cell virus for mammalian cells in culture, which results in a high-level prolonged expression. Here we demonstrate that recombinant baculoviruses can serve as efficient gene transfer vehicles for delivering foreign genes driven by mammalian promoters into human and mouse pancreatic islet cells. Existing methods, such as various transfection and electroporation techniques, either suffer from low efficiency or cause extensive membrane damage. Viral vectors have emerged as an important tool for gene delivery and expression in mammalian cells but suffer from several drawbacks, such as lengthy construction time and expression of viral genes. The baculovirus Autographa californica multiple nuclear polyhedrosis virus is widely used as a vector for expression of foreign genes in insect cells and, more recently, in some mammalian cells. Using several green fluorescent protein- and LacZ-expressing constructs in a cytomegalovirus promoter cassette, we obtained efficient gene expression in primary human and mouse islet cells. There was no impairment of glucose-stimulated intracellular free calcium responses after baculovirus infection. The safety and the relative ease of construction and propagation of the virus makes the baculovirus system a useful tool for facilitating the transfer of foreign genes.
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Affiliation(s)
- L Ma
- Department of Medicine, Howard Hughes Medical Institute, University of Chicago, Illinois, USA
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14
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Roe MW, Worley JF, Qian F, Tamarina N, Mittal AA, Dralyuk F, Blair NT, Mertz RJ, Philipson LH, Dukes ID. Characterization of a Ca2+ release-activated nonselective cation current regulating membrane potential and [Ca2+]i oscillations in transgenically derived beta-cells. J Biol Chem 1998; 273:10402-10. [PMID: 9553098 DOI: 10.1074/jbc.273.17.10402] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Although stimulation of insulin secretion by glucose is regulated by coupled oscillations of membrane potential and intracellular Ca2+ ([Ca2+]i), the membrane events regulating these oscillations are incompletely understood. In the presence of glucose and tetraethylammonium, transgenically derived beta-cells (betaTC3-neo) exhibit coupled voltage and [Ca2+]i oscillations strikingly similar to those observed in normal islets in response to glucose. Using these cells as a model system, we investigated the membrane conductance underlying these oscillations. Alterations in delayed rectifier or Ca2+-activated K+ channels were excluded as a source of the conductance oscillations, as they are completely blocked by tetraethylammonium. ATP-sensitive K+ channels were also excluded, since the ATP-sensitive K+ channel blocker tolbutamide substituted for glucose in inducing [Ca2+]i oscillations. Thapsigargin, which depletes intracellular Ca2+ stores, and maitotoxin, an activator of nonselective cation channels, both converted the glucose-dependent [Ca2+]i oscillations into a sustained elevation. On the other hand, both SKF 96365, a blocker of Ca2+ store-operated channels, and external Na+ removal suppressed the glucose-stimulated [Ca2+]i oscillations. Maitotoxin activated a nonselective cation current in betaTC3 cells that was attenuated by removal of extracellular Na+ and by SKF 96365, in the same manner to a current activated in mouse beta-cells following depletion of intracellular Ca2+ stores. Currents similar to these are produced by the mammalian trp-related channels, a gene family that includes Ca2+ store-operated channels and inositol 1,4,5-trisphosphate-activated channels. We found several of the trp family genes were expressed in betaTC3 cells by reverse transcriptase polymerase chain reaction using specific primers, but by Northern blot analysis, mtrp-4 was the predominant message expressed. We conclude that a conductance underlying glucose-stimulated oscillations in beta-cells is provided by a Ca2+ store depletion-activated nonselective cation current, which is plausibly encoded by homologs of trp genes.
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Affiliation(s)
- M W Roe
- Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA
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Shireman PK, McCarthy WJ, Pearce WH, Patterson BK, Shively VP, Cipollone M, Tamarina N, Verrusio EN, Kwaan HC. Elevated levels of plasminogen-activator inhibitor type 1 in atherosclerotic aorta. J Vasc Surg 1996; 23:810-7; discussion 817-8. [PMID: 8667502 DOI: 10.1016/s0741-5214(96)70243-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
PURPOSE Plasminogen activator inhibitor type I (PAI-1) inhibits the plasminogen activators that convert plasminogen to plasmin. In addition to initiating fibrinolysis, plasmin activates tissue matrix metalloproteinases, which cause degradation of the extracellular matrix (ECM) in the arterial wall. Elevated levels of PAI-1 ultimately decrease plasmin formation and may lead to an accumulation of ECM and arteriosclerosis. METHODS PAI-1 was studied by four methods in atherosclerotic (aneurysmal and occlusive) and normal (organ donor) aorta: (1) PAI-1 secretion by tissue explant supernatants, including time course and inhibition studies; (2) tissue PAI-1 by protein extraction; (3) PAI-1 mRNA was quantitated by Northern analysis using glyceraldehyde-3-phosphate dehydrogenase to normalize for RNA loading; and (4) in situ hybridization was used to localize the cells that produced PAI-1 mRNA. RESULTS Supernatant PAI-1 levels at 48 hours were 776 +/- 352, ng/ml in 11 atherosclerotic aortas and 248 +/- 98 ng/ml in 8 normal aortas (p < 0.005). Tissue PAI-1 levels per 100 mg of tissue were 99 +/- 58 ng in 11 atherosclerotic aortas and 38 +/- 20 ng in 5 normal aortas (p < 0.05). PAI-1 mRNA levels by Northern analysis were 0.91 +/- 0.49 in seven atherosclerotic aortas and 0.44 +/- 0.27 in five normal aortas. Supernatant time-course experiments revealed that PAI-1 increased over time. Inhibitor studies revealed that PAI-1 decreased to approximately one third of control values when cycloheximide or actinomycin D were added to the media, indicating that active synthesis of PAI-1 had occurred. In-situ hybridization localized PAI-1 mRNA predominately to endothelial cells and a few scattered vascular smooth muscle and inflammatory cells. Subgroup analysis revealed no statistically significant differences between aneurysmal and occlusive PAI-1 levels in any of the experiments. CONCLUSION PAI-1 secretion, as measured by tissue explant supernatants, and total tissue PAI-1 in the protein extracts were significantly increased in atherosclerotic aorta. This elevation was also observed in the mRNA, which suggests that the increase is controlled at the level of transcription. PAI-1 mRNA was localized to endothelial, vascular smooth muscle, and inflammatory cells. We conclude that elevated levels of PAI-1 exist in diseased aorta. These elevated levels may lead to an accumulation of ECM, thereby contributing to the arteriosclerosis found in aortic occlusive and aneurysmal disease.
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Affiliation(s)
- P K Shireman
- Division of Vascular Surgery, Northwestern University School of Medicine, Chicago, IL, USA
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