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Rebelato E, Abdulkader F, Curi R, Carpinelli AR. Control of the intracellular redox state by glucose participates in the insulin secretion mechanism. PLoS One 2011; 6:e24507. [PMID: 21909396 PMCID: PMC3164208 DOI: 10.1371/journal.pone.0024507] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Accepted: 08/12/2011] [Indexed: 01/07/2023] Open
Abstract
BACKGROUND Production of reactive oxygen species (ROS) due to chronic exposure to glucose has been associated with impaired beta cell function and diabetes. However, physiologically, beta cells are well equipped to deal with episodic glucose loads, to which they respond with a fine tuned glucose-stimulated insulin secretion (GSIS). In the present study, a systematic investigation in rat pancreatic islets about the changes in the redox environment induced by acute exposure to glucose was carried out. METHODOLOGY/PRINCIPAL FINDINGS Short term incubations were performed in isolated rat pancreatic islets. Glucose dose- and time-dependently reduced the intracellular ROS content in pancreatic islets as assayed by fluorescence in a confocal microscope. This decrease was due to activation of pentose-phosphate pathway (PPP). Inhibition of PPP blunted the redox control as well as GSIS in a dose-dependent manner. The addition of low doses of ROS scavengers at high glucose concentration acutely improved beta cell function. The ROS scavenger N-acetyl-L-cysteine increased the intracellular calcium response to glucose that was associated with a small decrease in ROS content. Additionally, the presence of the hydrogen peroxide-specific scavenger catalase, in its membrane-permeable form, nearly doubled glucose metabolism. Interestingly, though an increase in GSIS was also observed, this did not match the effect on glucose metabolism. CONCLUSIONS The control of ROS content via PPP activation by glucose importantly contributes to the mechanisms that couple the glucose stimulus to insulin secretion. Moreover, we identified intracellular hydrogen peroxide as an inhibitor of glucose metabolism intrinsic to rat pancreatic islets. These findings suggest that the intracellular adjustment of the redox environment by glucose plays an important role in the mechanism of GSIS.
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Affiliation(s)
- Eduardo Rebelato
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Sao Paulo, Brazil.
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102
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Mathematical modeling and statistical analysis of calcium-regulated insulin granule exocytosis in β-cells from mice and humans. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:257-64. [PMID: 21839108 DOI: 10.1016/j.pbiomolbio.2011.07.012] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2011] [Revised: 07/12/2011] [Accepted: 07/28/2011] [Indexed: 11/24/2022]
Abstract
Insulin is released from pancreatic β-cells as a result of Ca²⁺-evoked exocytosis of dense-core granules. Secretion is biphasic, which has been suggested to correspond to the release of different granule pools. Here we review and carefully reanalyze previously published patch-clamp data on depolarization-evoked Ca²⁺-currents and corresponding capacitance measurements. Using a statistical mixed-effects model, we show that the data indicate that pool depletion is negligible in response to short depolarizations in mouse β-cells. We then review mathematical models of granule dynamics and exocytosis in rodent β-cells and present a mathematical description of Ca²⁺-evoked exocytosis in human β-cells, which show clear differences to their rodent counterparts. The model suggests that L- and P/Q-type Ca²⁺-channels are involved to a similar degree in exocytosis during electrical activity in human β-cells.
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103
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Abstract
Voltage-gated calcium (Ca(2+)) channels are key transducers of membrane potential changes into intracellular Ca(2+) transients that initiate many physiological events. There are ten members of the voltage-gated Ca(2+) channel family in mammals, and they serve distinct roles in cellular signal transduction. The Ca(V)1 subfamily initiates contraction, secretion, regulation of gene expression, integration of synaptic input in neurons, and synaptic transmission at ribbon synapses in specialized sensory cells. The Ca(V)2 subfamily is primarily responsible for initiation of synaptic transmission at fast synapses. The Ca(V)3 subfamily is important for repetitive firing of action potentials in rhythmically firing cells such as cardiac myocytes and thalamic neurons. This article presents the molecular relationships and physiological functions of these Ca(2+) channel proteins and provides information on their molecular, genetic, physiological, and pharmacological properties.
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Affiliation(s)
- William A Catterall
- Department of Pharmacology, University of Washington, Seattle, Washington 98195-7280, USA.
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104
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Xu S, Shimahara T, Cooke IM. Capacitance increases of dissociated tilapia prolactin cells in response to hyposmotic and depolarizing stimuli. Gen Comp Endocrinol 2011; 173:38-47. [PMID: 21549709 DOI: 10.1016/j.ygcen.2011.04.020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2010] [Revised: 04/07/2011] [Accepted: 04/19/2011] [Indexed: 11/25/2022]
Abstract
Prolactin (PRL) is the major hormonal mediator of adaptation to hyposmotic conditions. In tilapia (Oreochromis mossambicus), PRL cells are segregated to the rostral pars distalis of the anterior pituitary facilitating the nearly pure culture of dissociated PRL cells. Membrane capacitance (C(m)) was recorded at 1Hz or higher for tens of minutes as a surrogate monitor of PRL secretion by exocytosis from cells under perforated patch clamp. The study compares secretory responses to trains of depolarizing clamps (100 at 2.5 Hz, from -70 to +10 mV for 100 ms) to the physiological stimulus, exposure to hyposmotic medium, here a switch from 350 to 300 mOsm saline ([Ca²⁺] 15 mM). Two-thirds of cells tested with each stimulus responded. In response to depolarizing clamps, C(m) increased linearly at an average rate of 7.2 fF/s. The increase was also linear in response to hyposmotic perfusion, but the average rate was 0.68 fF/s. Response to depolarization was reversibly blocked in Ca²⁺-omitted saline, or in saline with 30 μM Cd²⁺. It was unaffected by 0.1 μM tetrodotoxin. By contrast, responses were reduced but not absent during perfusion of hyposmotic saline with Ca²⁺-omitted; 30 μM Cd²⁺ appeared to enhance the hyposmotic response. BAPTA-AM eliminated responses to both stimuli, confirming that secretion was dependent on increases of intracellular [Ca²⁺]. Together with previous observations from this laboratory of [Ca²⁺](i) with simultaneous collection and immunoassay of perfusate for PRL, we conclude that depolarization and hyposmotic stimuli initiate secretion by independent mechanisms.
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Affiliation(s)
- Shenghong Xu
- Békésy Laboratory of Neurobiology, University of Hawaii, Honolulu, HI 96822, USA
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105
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Andersson SA, Pedersen MG, Vikman J, Eliasson L. Glucose-dependent docking and SNARE protein-mediated exocytosis in mouse pancreatic alpha-cell. Pflugers Arch 2011; 462:443-54. [PMID: 21643653 DOI: 10.1007/s00424-011-0979-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2011] [Revised: 05/05/2011] [Accepted: 05/13/2011] [Indexed: 12/20/2022]
Abstract
The function of alpha-cells in patients with type 2 diabetes is often disturbed; glucagon secretion is increased at hyperglycaemia, yet fails to respond to hypoglycaemia. A crucial mechanism behind the fine-tuned release of glucagon relies in the exocytotic machinery including SNARE proteins. Here, we aimed to investigate the temporal role of syntaxin 1A and SNAP-25 in mouse alpha-cell exocytosis. First, we used confocal imaging to investigate glucose dependency in the localisation of SNAP-25 and syntaxin 1A. SNAP-25 was mainly distributed in the plasma membrane at 2.8 mM glucose, whereas the syntaxin 1A distribution in the plasma membrane, as compared to the cytosolic fraction, was highest at 8.3 mM glucose. Furthermore, following inclusion of an antibody against SNAP-25 or syntaxin 1A, exocytosis evoked by a train of ten depolarisations and measured as an increase in membrane capacitance was reduced by ~50%. Closer inspection revealed a reduction in the refilling of granules from the reserve pool (RP), but also showed a decreased size of the readily releasable pool (RRP) by ~45%. Disparate from the situation in pancreatic beta-cells, the voltage-dependent Ca²⁺ current was not reduced, but the Ca²⁺ sensitivity of exocytosis decreased by the antibody against syntaxin 1A. Finally, ultrastructural analysis revealed that the number of docked granules was >2-fold higher at 16.7 mM than at 1 mM glucose. We conclude that syntaxin 1A and SNAP-25 are necessary for alpha-cell exocytosis and regulate fusion of granules belonging to both the RRP and RP without affecting the Ca²⁺ current.
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Affiliation(s)
- Sofia A Andersson
- Islet Cell Exocytosis, Department of Clinical Sciences Malmö, Lund University Diabetes Centre, Lund University, Malmö, Sweden.
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106
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Seino S, Shibasaki T, Minami K. Dynamics of insulin secretion and the clinical implications for obesity and diabetes. J Clin Invest 2011; 121:2118-25. [PMID: 21633180 DOI: 10.1172/jci45680] [Citation(s) in RCA: 255] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Insulin secretion is a highly dynamic process regulated by various factors including nutrients, hormones, and neuronal inputs. The dynamics of insulin secretion can be studied at different levels: the single β cell, pancreatic islet, whole pancreas, and the intact organism. Studies have begun to analyze cellular and molecular mechanisms underlying dynamics of insulin secretion. This review focuses on our current understanding of the dynamics of insulin secretion in vitro and in vivo and discusses their clinical relevance.
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Affiliation(s)
- Susumu Seino
- Division of Diabetes and Endocrinology, Department of Internal Medicine, Kobe University Graduate School of Medicine, Kobe, Japan.
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107
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Bidaud I, Lory P. Hallmarks of the channelopathies associated with L-type calcium channels: a focus on the Timothy mutations in Ca(v)1.2 channels. Biochimie 2011; 93:2080-6. [PMID: 21664226 DOI: 10.1016/j.biochi.2011.05.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Accepted: 05/19/2011] [Indexed: 11/29/2022]
Abstract
Within the voltage-gated calcium channels (Cav channels) family, there are four genes coding for the L-type Cav channels (Cav1). The Cav1 channels underly many important physiological functions like excitation-contraction coupling, hormone secretion, neuronal excitability and gene transcription. Mutations found in the genes encoding the Cav channels define a wide variety of diseases called calcium channelopathies and all four genes coding the Cav1 channels are carrying such mutations. L-type calcium channelopathies include muscular, neurological, cardiac and vision syndromes. Among them, the Timothy syndrome (TS) is linked to missense mutations in CACNA1C, the gene that encodes the Ca(v)1.2 subunit. Here we review the important features of the Cav1 channelopathies. We also report on the specific properties of TS-Ca(v)1.2 channels, which display non-inactivating calcium current as well as higher plasma membrane expression. Overall, we conclude that both electrophysiological and surface expression properties must be investigated to better account for the functional consequences of mutations linked to calcium channelopathies.
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Affiliation(s)
- Isabelle Bidaud
- CNRS, UMR-5203, Institut de Génomique Fonctionnelle, Montpellier, France
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108
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Mourad NI, Nenquin M, Henquin JC. Metabolic amplification of insulin secretion by glucose is independent of β-cell microtubules. Am J Physiol Cell Physiol 2011; 300:C697-706. [DOI: 10.1152/ajpcell.00329.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Glucose-induced insulin secretion (IS) by β-cells is controlled by two pathways. The triggering pathway involves ATP-sensitive potassium (KATP) channel-dependent depolarization, Ca2+ influx, and rise in the cytosolic Ca2+ concentration ([Ca2+]c), which triggers exocytosis of insulin granules. The metabolic amplifying pathway augments IS without further increasing [Ca2+]c. After exclusion of the contribution of actin microfilaments, we here tested whether amplification implicates microtubule-dependent granule mobilization. Mouse islets were treated with nocodazole or taxol, which completely depolymerized and polymerized tubulin. They were then perifused to measure [Ca2+]c and IS. Metabolic amplification was studied during imposed steady elevation of [Ca2+]c by tolbutamide or KCl or by comparing [Ca2+]c and IS responses to glucose and tolbutamide. Nocodazole did not alter [Ca2+]c or IS changes induced by the three secretagogues, whereas taxol caused a small inhibition of IS that is partly ascribed to a decrease in [Ca2+]c. When [Ca2+]c was elevated and controlled by KCl or tolbutamide, the amplifying action of glucose was unaffected by microtubule disruption or stabilization. Both phases of IS were larger in response to glucose than tolbutamide, although triggering [Ca2+]c was lower. This difference, due to amplification, persisted in nocodazole- or taxol-treated islets, even when IS was augmented fourfold by microfilament disruption with cytochalasin B or latrunculin B. In conclusion, metabolic amplification rapidly augments first and second phases of IS independently of insulin granule translocation along microtubules. We therefore extend our previous proposal that it does not implicate the cytoskeleton but corresponds to acceleration of the priming process conferring release competence to insulin granules.
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Affiliation(s)
- Nizar I. Mourad
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
| | - Myriam Nenquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
| | - Jean-Claude Henquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
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109
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Sato Y, Endo H, Okuyama H, Takeda T, Iwahashi H, Imagawa A, Yamagata K, Shimomura I, Inoue M. Cellular hypoxia of pancreatic beta-cells due to high levels of oxygen consumption for insulin secretion in vitro. J Biol Chem 2011; 286:12524-32. [PMID: 21296882 DOI: 10.1074/jbc.m110.194738] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Cellular oxygen consumption is a determinant of intracellular oxygen levels. Because of the high demand of mitochondrial respiration during insulin secretion, pancreatic β-cells consume large amounts of oxygen in a short time period. We examined the effect of insulin secretion on cellular oxygen tension in vitro. We confirmed that Western blotting of pimonidazole adduct was more sensitive than immunostaining for detection of cellular hypoxia in vitro and in vivo. The islets of the diabetic mice but not those of normal mice were hypoxic, especially when a high dose of glucose was loaded. In MIN6 cells, a pancreatic β-cell line, pimonidazole adduct formation and stabilization of hypoxia-inducible factor-1α (HIF-1α) were detected under mildly hypoxic conditions. Inhibition of respiration rescued the cells from becoming hypoxic. Glucose stimulation decreased cellular oxygen levels in parallel with increased insulin secretion and mitochondrial respiration. The cellular hypoxia by glucose stimulation was also observed in the isolated islets from mice. The MIN6 cells overexpressing HIF-1α were resistant to becoming hypoxic after glucose stimulation. Thus, glucose-stimulated β-cells can become hypoxic by oxygen consumption, especially when the oxygen supply is impaired.
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Affiliation(s)
- Yoshifumi Sato
- Department of Biochemistry, Osaka Medical Center for Cancer and Cardiovascular Diseases, 1-3-3 Nakamichi, Higashinari-ku, Osaka 537-8511
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110
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Huising MO, Pilbrow AP, Matsumoto M, van der Meulen T, Park H, Vaughan JM, Lee S, Vale WW. Glucocorticoids differentially regulate the expression of CRFR1 and CRFR2α in MIN6 insulinoma cells and rodent islets. Endocrinology 2011; 152:138-50. [PMID: 21106875 PMCID: PMC3219054 DOI: 10.1210/en.2010-0791] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Urocortin 3 (Ucn 3), member of the corticotropin-releasing factor (CRF) family of peptide hormones, is released from β-cells to potentiate insulin secretion. Ucn 3 activates the CRF type-2 receptor (CRFR2) but does not activate the type-1 receptor (CRFR1), which was recently demonstrated on β-cells. While the direct actions of Ucn 3 on insulin secretion suggest the presence of cognate receptors within the islet microenvironment, this has not been established. Here we demonstrate that CRFR2α is expressed by MIN6 insulinoma cells and by primary mouse and human islets, with no detectable expression of CRFR2β. Furthermore, stimulation of MIN6 cells or primary mouse islets in vitro or in vivo with glucocorticoids (GCs) robustly and dose-dependently increases the expression of CRFR2α, while simultaneously inhibiting the expression of CRFR1 and incretin receptors. Luciferase reporters driven by the mouse CRFR1 or CRFR2α promoter in MIN6 cells confirm these differential effects of GCs. In contrast, GCs inhibit CRFR2α promoter activity in HEK293 cells and inhibit the expression of CRFR2β in A7r5 rat aortic smooth muscle cells and differentiated C2C12 myotubes. These findings suggest that the GC-mediated increase of CRFR2α depends on the cellular context of the islet and deviates from the GC-mediated suppression of CRFR1 and incretin receptors. Furthermore, GC-induced increases in CRFR2α expression coincide with increased Ucn 3-dependent activation of cAMP and MAPK pathways. We postulate that differential effect of GCs on the expression of CRFR1 and CRFR2α in the endocrine pancreas represent a mechanism to shift sensitivity from CRFR1 to CRFR2 ligands.
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Affiliation(s)
- M O Huising
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037, USA
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111
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Casamassima F, Hay AC, Benedetti A, Lattanzi L, Cassano GB, Perlis RH. L-type calcium channels and psychiatric disorders: A brief review. Am J Med Genet B Neuropsychiatr Genet 2010; 153B:1373-90. [PMID: 20886543 DOI: 10.1002/ajmg.b.31122] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Accepted: 07/28/2010] [Indexed: 01/11/2023]
Abstract
Emerging evidence from genome-wide association studies (GWAS) support the association of polymorphisms in the alpha 1C subunit of the L-type voltage-gated calcium channel gene (CACNA1C) with bipolar disorder. These studies extend a rich prior literature implicating dysfunction of L-type calcium channels (LTCCs) in the pathophysiology of neuropsychiatric disorders. Moreover, calcium channel blockers reduce Ca(2+) flux by binding to the α1 subunit of the LTCC and are used extensively for treating hypertension, preventing angina, cardiac arrhythmias and stroke. Calcium channel blockers have also been studied clinically in psychiatric conditions such as mood disorders and substance abuse/dependence, yielding conflicting results. In this review, we begin with a summary of LTCC pharmacology. For each category of disorder, this article then provides a review of animal and human data. In particular, we extensively focus on animal models of depression and clinical trials in mood disorders and substance abuse/dependence. Through examining rationale and study design of published clinical trials, we provide some of the possible reasons why we still do not have definitive evidence of efficacy of calcium-channel antagonists for mood disorders. Refinement of genetic results and target phenotypes, enrollment of adequate sample sizes in clinical trials and progress in physiologic and pharmacologic studies to synthesize tissue and isoform specific calcium channel antagonists, are all future challenges of research in this promising field. © 2010 Wiley-Liss, Inc.
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112
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Pedersen MG. Insulin secretory granules enter a highly calcium-sensitive state following palmitate-induced dissociation from calcium channels: a theoretical study. J Neuroendocrinol 2010; 22:1315-24. [PMID: 20722978 DOI: 10.1111/j.1365-2826.2010.02056.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Impaired insulin secretion is a major contributor to diabetes. Obesity is a known risk factor for the development of diabetes, and prolonged exposure of pancreatic islets to lipids results in impaired insulin secretion. Insulin is released from pancreatic β-cells as a result of Ca(2+) -induced exocytosis. Recent experiments have shown that chronic palmitate exposure results in the loss of localised Ca(2+) -influx and impaired exocytosis of insulin secretory granules in β-cells. In the present study, the roles of Ca(2+) -channel clustering disruption, and dissociation of granules from Ca(2+) -channels, in the impaired exocytotic and secretory responses from palmitate-treated β-cells, are investigated using mathematical models of Ca(2+) dynamics, granule pools, exocytosis and secretion. It is shown that either disruption of Ca(2+) -channel clusters or dissociation of granules from Ca(2+) -channels with a shift to a highly calcium-sensitive pool can explain the recent experimental findings of palmitate-induced defects of exocytosis and insulin secretion. On the basis of imaging results, it is argued that a shift to a highly calcium-sensitive state after dissociation of granules from Ca(2+) -channels is the most likely explanation for the experimental findings from β-cells exposed chronically to palmitate.
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Affiliation(s)
- M G Pedersen
- Department of Information Engineering, University of Padova, Padova, Italy.
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113
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Dzhura I, Chepurny OG, Kelley GG, Leech CA, Roe MW, Dzhura E, Afshari P, Malik S, Rindler MJ, Xu X, Lu Y, Smrcka AV, Holz GG. Epac2-dependent mobilization of intracellular Ca²+ by glucagon-like peptide-1 receptor agonist exendin-4 is disrupted in β-cells of phospholipase C-ε knockout mice. J Physiol 2010; 588:4871-89. [PMID: 21041529 DOI: 10.1113/jphysiol.2010.198424] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Calcium can be mobilized in pancreatic β-cells via a mechanism of Ca(2+)-induced Ca(2+) release (CICR), and cAMP-elevating agents such as exendin-4 facilitate CICR in β-cells by activating both protein kinase A and Epac2. Here we provide the first report that a novel phosphoinositide-specific phospholipase C- (PLC-) is expressed in the islets of Langerhans, and that the knockout (KO) of PLC- gene expression in mice disrupts the action of exendin-4 to facilitate CICR in the β-cells of these mice. Thus, in the present study, in which wild-type (WT) C57BL/6 mouse β-cells were loaded with the photolabile Ca(2+) chelator NP-EGTA, the UV flash photolysis-catalysed uncaging of Ca(2+) generated CICR in only 9% of the β-cells tested, whereas CICR was generated in 82% of the β-cells pretreated with exendin-4. This action of exendin-4 to facilitate CICR was reproduced by cAMP analogues that activate protein kinase A (6-Bnz-cAMP-AM) or Epac2 (8-pCPT-2'-O-Me-cAMP-AM) selectively. However, in β-cells of PLC- KO mice, and also Epac2 KO mice, these test substances exhibited differential efficacies in the CICR assay such that exendin-4 was partly effective, 6-Bnz-cAMP-AM was fully effective, and 8-pCPT-2'-O-Me-cAMP-AM was without significant effect. Importantly, transduction of PLC- KO β-cells with recombinant PLC- rescued the action of 8-pCPT-2'-O-Me-cAMP-AM to facilitate CICR, whereas a K2150E PLC- with a mutated Ras association (RA) domain, or a H1640L PLC- that is catalytically dead, were both ineffective. Since 8-pCPT-2'-O-Me-cAMP-AM failed to facilitate CICR in WT β-cells transduced with a GTPase activating protein (RapGAP) that downregulates Rap activity, the available evidence indicates that a signal transduction 'module' comprised of Epac2, Rap and PLC- exists in β-cells, and that the activities of Epac2 and PLC- are key determinants of CICR in this cell type.
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Affiliation(s)
- Igor Dzhura
- Department of Medicine, State University of New York Upstate Medical University, Syracuse, NY, USA
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114
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Sasai M, Tadokoro S, Hirashima N. Artificial exocytotic system that secretes intravesicular contents upon Ca2+ influx. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:14788-14792. [PMID: 20722459 DOI: 10.1021/la102737e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Exocytosis is a crucial process of secreting various signaling molecules such as neurotransmitters, hormones, and other chemical mediators into the extracellular space. Exocytotic release is caused by membrane fusion of intracellular vesicles with the plasma membrane triggered by an increase in intracellular Ca(2+). In the present study, we developed an artificial system of exocytosis that secretes intravesicular contents upon Ca(2+) influx. We prepared artificial secretory cells using cell-sized giant unilamellar liposomal vesicles (GUVs) that contain small liposomes (SUVs) that correspond to secretory vesicles. To observe exocytosis-like secretion in an artificial system, we labeled both an intra-SUV solution and an SUV membrane with a soluble fluorescent dye and a rhodamine-labeled phospholipid, respectively. To induce membrane fusion between SUVs and a GUV as observed in exocytosis, the Ca(2+) concentration of intra-GUV was elevated by incorporating ionomycin (a Ca(2+) ionophore) into the GUV membrane. We succeeded in inducing exocytosis-like secretion by Ca(2+) elevation in a GUV together with the osmolarity difference between the intra-GUV and extra-GUV solutions.
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Affiliation(s)
- Masao Sasai
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan
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115
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Ravier MA, Cheng-Xue R, Palmer AE, Henquin JC, Gilon P. Subplasmalemmal Ca(2+) measurements in mouse pancreatic beta cells support the existence of an amplifying effect of glucose on insulin secretion. Diabetologia 2010; 53:1947-57. [PMID: 20461354 PMCID: PMC3297670 DOI: 10.1007/s00125-010-1775-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2010] [Accepted: 04/07/2010] [Indexed: 10/19/2022]
Abstract
AIMS/HYPOTHESIS Glucose-induced insulin secretion is attributed to a rise of beta cell cytosolic free [Ca(2+)] ([Ca(2+)](c)) (triggering pathway) and amplification of the action of Ca(2+). This concept of amplification rests on observations that glucose can increase Ca(2+)-induced insulin secretion without further elevating an imposed already high [Ca(2+)](c). However, it remains possible that this amplification results from an increase in [Ca(2+)] just under the plasma membrane ([Ca(2+)](SM)), which escaped detection by previous measurements of global [Ca(2+)](c). This was the hypothesis that we tested here by measuring [Ca(2+)](SM). METHODS The genetically encoded Ca(2+) indicators D3-cpv (untargeted) and LynD3-cpv (targeted to plasma membrane) were expressed in clusters of mouse beta cells. LynD3-cpv was also expressed in beta cells within intact islets. [Ca(2+)](SM) changes were monitored using total internal reflection fluorescence microscopy. Insulin secretion was measured in parallel. RESULTS Beta cells expressing D3cpv or LynD3cpv displayed normal [Ca(2+)] changes and insulin secretion in response to glucose. Distinct [Ca(2+)](SM) fluctuations were detected during repetitive variations of KCl between 30 and 32-35 mmol/l, attesting to the adequate sensitivity of our system. When the amplifying pathway was evaluated (high KCl + diazoxide), increasing glucose from 3 to 15 mmol/l consistently lowered [Ca(2+)](SM) while stimulating insulin secretion approximately two fold. Blocking Ca(2+) uptake by the endoplasmic reticulum largely attenuated the [Ca(2+)](SM) decrease produced by high glucose but did not unmask localised [Ca(2+)](SM) increases. CONCLUSIONS/INTERPRETATION Glucose can increase Ca(2+)-induced insulin secretion without causing further elevation of beta cell [Ca(2+)](SM). The phenomenon is therefore a true amplification of the triggering action of Ca(2+).
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Affiliation(s)
- M. A. Ravier
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, 1200 Brussels, Belgium
| | - R. Cheng-Xue
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, 1200 Brussels, Belgium
| | - A. E. Palmer
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA
| | - J. C. Henquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, 1200 Brussels, Belgium
| | - P. Gilon
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, 1200 Brussels, Belgium
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Mourad NI, Nenquin M, Henquin JC. Metabolic amplifying pathway increases both phases of insulin secretion independently of β-cell actin microfilaments. Am J Physiol Cell Physiol 2010; 299:C389-98. [DOI: 10.1152/ajpcell.00138.2010] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Two pathways control glucose-induced insulin secretion (IS) by β-cells. The triggering pathway involves ATP-sensitive potassium (KATP) channel-dependent depolarization, Ca2+ influx, and a rise in the cytosolic Ca2+ concentration ([Ca2+]c), which triggers exocytosis of insulin granules. The metabolic amplifying pathway augments IS without further increasing [Ca2+]c. The underlying mechanisms are unknown. Here, we tested the hypothesis that amplification implicates actin microfilaments. Mouse islets were treated with latrunculin B and cytochalasin B to depolymerize actin or jasplakinolide to polymerize actin. They were then perifused to measure [Ca2+]c and IS. Metabolic amplification was studied during imposed steady elevation of [Ca2+]c by tolbutamide or KCl or by comparing the magnitude of [Ca2+]c and IS changes produced by glucose and tolbutamide. Both actin polymerization and depolymerization augmented IS triggered by all stimuli without increasing (sometimes decreasing) [Ca2+]c, which indicates a predominantly inhibitory function of microfilaments in exocytosis at a step distal to [Ca2+]c increase. When [Ca2+]c was elevated and controlled by KCl or tolbutamide, the amplifying action of glucose was facilitated by actin depolymerization and unaffected by polymerization. Both phases of IS were larger in response to high-glucose than to tolbutamide in low-glucose, although triggering [Ca2+]c was lower. This difference in IS, due to amplification, persisted when the IS rate was doubled by actin depolymerization or polymerization. In conclusion, metabolic amplification is rapid and influences the first as well as the second phase of IS. It is a late step of stimulus-secretion coupling, which does not require functional actin microfilaments and could correspond to acceleration of the priming process conferring release competence to insulin granules.
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Affiliation(s)
- Nizar I. Mourad
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
| | - Myriam Nenquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
| | - Jean-Claude Henquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
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Chen TS, Tan SS, Yeo RWY, Teh BJ, Luo R, Li G, Lim SK. Delineating biological pathways unique to embryonic stem cell-derived insulin-producing cell lines from their noninsulin-producing progenitor cell lines. Endocrinology 2010; 151:3600-10. [PMID: 20501672 DOI: 10.1210/en.2009-1418] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
To identify unique biochemical pathways in embryonic stem cell-derived insulin-producing cells as potential therapeutic targets to prevent or delay beta-cell dysfunction or death in diabetic patients, comparative genome-wide gene expression studies of recently derived mouse insulin-producing cell lines and their progenitor cell lines were performed using microarray technology. Differentially expressed genes were functionally clustered to identify important biochemical pathways in these insulin-producing cell lines. Biochemical or cellular assays were then performed to assess the relevance of these pathways to the biology of these cells. A total of 185 genes were highly expressed in the insulin-producing cell lines, and computational analysis predicted the pentose phosphate pathway (PPP), clathrin-mediated endocytosis, and the peroxisome proliferator-activated receptor (PPAR) signaling pathway as important pathways in these cell lines. Insulin-producing ERoSHK cells were more resistant to hydrogen peroxide (H(2)O(2))-induced oxidative stress. Inhibition of PPP by dehydroepiandrosterone and 6-aminonicotinamide abrogated this H(2)O(2) resistance with a concomitant decrease in PPP activity as measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Clathrin-mediated endocytosis, which is essential in maintaining membrane homeostasis in secreting cells, was up-regulated by glucose in ERoSHK but not in their progenitor ERoSH cells. Its inhibition by chlorpromazine at high glucose concentration was toxic to the cells. Troglitazone, a PPARG agonist, up-regulated expression of Ins1 and Ins2 but not Glut2. Gene expression analysis has identified the PPP, clathrin-mediated endocytosis, and the PPAR signaling pathway as the major delineating pathways in these insulin-producing cell lines, and their biological relevance was confirmed by biochemical and cellular assays.
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Affiliation(s)
- Tian Sheng Chen
- Institute of Medical Biology, Agency for Science, Technology, and Research, Singapore
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118
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Sherman A. Lessons from models of pancreatic beta cells for engineering glucose-sensing cells. Math Biosci 2010; 227:12-9. [PMID: 20580727 DOI: 10.1016/j.mbs.2010.05.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Revised: 05/13/2010] [Accepted: 05/17/2010] [Indexed: 12/31/2022]
Abstract
Mathematical models of pancreatic beta cells suggest design principles that can be applied to engineering cells to sense glucose and secrete insulin. Engineering cells can potentially both contribute to future diabetes therapies and generate new insights into beta-cell function. The focus is on ion channels, Ca(2+)handling, and elements of metabolism that combine to produce the varied oscillatory patterns exhibited by beta cells.
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Affiliation(s)
- Arthur Sherman
- National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Laboratory of Biological Modeling, Bethesda, MD 20892-5621, USA.
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Cui Z, Hou J, Chen X, Li J, Xie Z, Xue P, Cai T, Wu P, Xu T, Yang F. The Profile of Mitochondrial Proteins and Their Phosphorylation Signaling Network in INS-1 β Cells. J Proteome Res 2010; 9:2898-908. [DOI: 10.1021/pr100139z] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Ziyou Cui
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
| | - Junjie Hou
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiulan Chen
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jing Li
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhensheng Xie
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
| | - Peng Xue
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
| | - Tanxi Cai
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
| | - Peng Wu
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
| | - Tao Xu
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
| | - Fuquan Yang
- Laborotary of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, Tianjin Key Laboratory for Biomarkers of Occupational and Environmental Hazard, Medical College of CAPF, Tianjin 300162, China, National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China, and Graduate University of Chinese Academy of Sciences, Beijing 100049, China
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Loss of high-frequency glucose-induced Ca2+ oscillations in pancreatic islets correlates with impaired glucose tolerance in Trpm5-/- mice. Proc Natl Acad Sci U S A 2010; 107:5208-13. [PMID: 20194741 DOI: 10.1073/pnas.0913107107] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Glucose homeostasis is critically dependent on insulin release from pancreatic beta-cells, which is strictly regulated by glucose-induced oscillations in membrane potential (V(m)) and the cytosolic calcium level ([Ca(2+)](cyt)). We propose that TRPM5, a Ca(2+)-activated monovalent cation channel, is a positive regulator of glucose-induced insulin release. Immunofluorescence revealed expression of TRPM5 in pancreatic islets. A Ca(2+)-activated nonselective cation current with TRPM5-like properties is significantly reduced in Trpm5(-/-) cells. Ca(2+)-imaging and electrophysiological analysis show that glucose-induced oscillations of V(m) and [Ca(2+)](cyt) have on average a reduced frequency in Trpm5(-/-) islets, specifically due to a lack of fast oscillations. As a consequence, glucose-induced insulin release from Trpm5(-/-) pancreatic islets is significantly reduced, resulting in an impaired glucose tolerance in Trpm5(-/-) mice.
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121
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Jewell JL, Oh E, Thurmond DC. Exocytosis mechanisms underlying insulin release and glucose uptake: conserved roles for Munc18c and syntaxin 4. Am J Physiol Regul Integr Comp Physiol 2010; 298:R517-31. [PMID: 20053958 DOI: 10.1152/ajpregu.00597.2009] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Type 2 diabetes has been coined "a two-hit disease," as it involves specific defects of glucose-stimulated insulin secretion from the pancreatic beta cells in addition to defects in peripheral tissue insulin action required for glucose uptake. Both of these processes, insulin secretion and glucose uptake, are mediated by SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) protein core complexes composed of syntaxin, SNAP-23/25, and VAMP proteins. The SNARE core complex is regulated by the Sec1/Munc18 (SM) family of proteins, which selectively bind to their cognate syntaxin isoforms with high affinity. The process of insulin secretion uses multiple Munc18-syntaxin isoform pairs, whereas insulin action in the peripheral tissues appears to use only the Munc18c-syntaxin 4 pair. Importantly, recent reports have linked obesity and Type 2 diabetes in humans with changes in protein levels and single nucleotide polymorphisms (SNPs) of Munc18 and syntaxin isoforms relevant to these exocytotic processes, although the molecular mechanisms underlying the observed phenotypes remain incomplete (5, 104, 144). Given the conservation of these proteins in two seemingly disparate processes and the need to design and implement novel and more effective clinical interventions, it will be vitally important to delineate the mechanisms governing these conserved SNARE-mediated exocytosis events. Thus, we provide here an up-to-date historical review of advancements in defining the roles and molecular mechanisms of Munc18-syntaxin complexes in the pathophysiology of Type 2 diabetes.
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Affiliation(s)
- Jenna L Jewell
- Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA
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122
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Seino S, Shibasaki T, Minami K. Pancreatic beta-cell signaling: toward better understanding of diabetes and its treatment. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2010; 86:563-577. [PMID: 20551594 PMCID: PMC3081169 DOI: 10.2183/pjab.86.563] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Accepted: 04/14/2010] [Indexed: 05/29/2023]
Abstract
Pancreatic beta-cells play a central role in the maintenance glucose homeostasis by secreting insulin, a key hormone that regulates blood glucose levels. Dysfunction of the beta-cells and/or a decrease in the beta-cell mass are associated closely with the pathogenesis and pathophysiology of diabetes mellitus, a major metabolic disease that is rapidly increasing worldwide. Clarification of the mechanisms of insulin secretion and beta-cell fate provides a basis for the understanding of diabetes and its better treatment. In this review, we discuss cell signaling critical for the insulin secretory function based on our recent studies.
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Affiliation(s)
- Susumu Seino
- Division of Cellular and Molecular Medicine, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Hyogo, Japan.
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123
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Role of mitochondria in beta-cell function and dysfunction. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:193-216. [PMID: 20217499 DOI: 10.1007/978-90-481-3271-3_9] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Pancreatic beta-cells are poised to sense glucose and other nutrient secretagogues to regulate insulin exocytosis, thereby maintaining glucose homeostasis. This process requires translation of metabolic substrates into intracellular messengers recognized by the exocytotic machinery. Central to this metabolism-secretion coupling, mitochondria integrate and generate metabolic signals, thereby connecting glucose recognition to insulin exocytosis. In response to a glucose rise, nucleotides and metabolites are generated by mitochondria and participate, together with cytosolic calcium, to the stimulation of insulin release. This review describes the mitochondrion-dependent pathways of regulated insulin secretion. Mitochondrial defects, such as mutations and reactive oxygen species production, are discussed in the context of beta-cell failure that may participate to the etiology of diabetes.
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124
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Microscopic anatomy of the human islet of Langerhans. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:1-19. [PMID: 20217491 DOI: 10.1007/978-90-481-3271-3_1] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Human islets of Langerhans are complex micro-organs responsible for maintaining glucose homeostasis. Islets contain five different endocrine cell types, which react to changes in plasma nutrient levels with the release of a carefully balanced mixture of islet hormones into the portal vein. Each endocrine cell type is characterized by its own typical secretory granule morphology, different peptide hormone content, and specific endocrine, paracrine, and neuronal interactions. During development, a cascade of transcription factors determines the formation of the endocrine pancreas and its constituting islet cell types. Differences in ontogeny between the ventrally derived head section and the dorsally derived head, body, and tail section are responsible for differences in innervation, blood supply, and endocrine composition. Islet cells show a close topographical relationship to the islet vasculature, and are supplied with a five to tenfold higher blood flow than the exocrine compartment. Islet microanatomy is disturbed in patients with type 1 diabetes, with a marked reduction in beta-cell content and the presence of inflammatory infiltrates. Histopathological lesions in type 2 diabetes are less pathognomonic with a more limited reduction in beta-cell content and occasional deposition of amyloid in the islet interstitial space.
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125
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Silencing of the mitochondrial NADH shuttle component aspartate-glutamate carrier AGC1/Aralar1 in INS-1E cells and rat islets. Biochem J 2009; 424:459-66. [PMID: 19764902 DOI: 10.1042/bj20090729] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Transfer of reducing equivalents between cytosolic compartments and the mitochondrial matrix is mediated by NADH shuttles. Among these, the malate-aspartate shuttle has been proposed to play a major role in beta-cells for the control of glucose-stimulated insulin secretion. AGC1 or Aralar1 (aspartate-glutamate carrier 1) is a key component of the malate-aspartate shuttle. Overexpression of AGC1 increases the capacity of the malate-aspartate shuttle, resulting in enhanced metabolism-secretion coupling, both in INS-1E cells and rat islets. In the present study, knockdown of AGC1 was achieved in the same beta-cell models, using adenovirus-mediated delivery of shRNA (small-hairpin RNA). Compared with control INS-1E cells, down-regulation of AGC1 blunted NADH formation (-57%; P<0.05), increased lactate production (+16%; P<0.001) and inhibited glucose oxidation (-22%; P<0.01). This correlated with a reduced secretory response at 15 mM glucose (-25%; P<0.05), while insulin release was unchanged at intermediate 7.5 mM and basal 2.5 mM glucose. In isolated rat islets, efficient AGC1 knockdown did not alter insulin exocytosis evoked by 16.7 mM glucose. However, 4 mM amino-oxyacetate, commonly used to block transaminases of the malate-aspartate shuttle, inhibited glucose-stimulated insulin secretion to similar extents in INS-1E cells (-66%; P<0.01) and rat islets (-56%; P<0.01). These results show that down-regulation of the key component of the malate-aspartate shuttle AGC1 reduced glucose-induced oxidative metabolism and insulin secretion in INS-1E cells, whereas similar AGC1 knockdown in rat islets did not affect their secretory response.
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126
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Rosengren AH, Jokubka R, Tojjar D, Granhall C, Hansson O, Li DQ, Nagaraj V, Reinbothe TM, Tuncel J, Eliasson L, Groop L, Rorsman P, Salehi A, Lyssenko V, Luthman H, Renström E. Overexpression of alpha2A-adrenergic receptors contributes to type 2 diabetes. Science 2009; 327:217-20. [PMID: 19965390 DOI: 10.1126/science.1176827] [Citation(s) in RCA: 200] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Several common genetic variations have been associated with type 2 diabetes, but the exact disease mechanisms are still poorly elucidated. Using congenic strains from the diabetic Goto-Kakizaki rat, we identified a 1.4-megabase genomic locus that was linked to impaired insulin granule docking at the plasma membrane and reduced beta cell exocytosis. In this locus, Adra2a, encoding the alpha2A-adrenergic receptor [alpha(2A)AR], was significantly overexpressed. Alpha(2A)AR mediates adrenergic suppression of insulin secretion. Pharmacological receptor antagonism, silencing of receptor expression, or blockade of downstream effectors rescued insulin secretion in congenic islets. Furthermore, we identified a single-nucleotide polymorphism in the human ADRA2A gene for which risk allele carriers exhibited overexpression of alpha(2A)AR, reduced insulin secretion, and increased type 2 diabetes risk. Human pancreatic islets from risk allele carriers exhibited reduced granule docking and secreted less insulin in response to glucose; both effects were counteracted by pharmacological alpha(2A)AR antagonists.
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127
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Gao W, Starkov VG, He ZX, Wang QH, Tsetlin VI, Utkin YN, Lin ZJ, Bi RC. Functions, structures and Triton X-100 effect for the catalytic subunits of heterodimeric phospholipases A2 from Vipera nikolskii venom. Toxicon 2009; 54:709-16. [DOI: 10.1016/j.toxicon.2009.05.024] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Revised: 04/16/2009] [Accepted: 05/25/2009] [Indexed: 10/20/2022]
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128
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Abstract
Insulin secretion is regulated by a series of complex events generated by various intracellular signals including Ca(2+), ATP, cAMP and phospholipid-derived signals. Glucose-stimulated insulin secretion is the principal mode of insulin secretion, and the mechanism potentiating the secretion is critical for physiological responses. Among the various intracellular signals involved, cAMP is particularly important for amplifying insulin secretion. Recently, glucagon-like peptide-1 (GLP-1) analogues and dipeptidyl peptidase-IV (DPP-IV) inhibitors have been developed as new antidiabetic drugs. These drugs all act through cAMP signalling in pancreatic beta-cells. Until recently, cAMP was generally thought to potentiate insulin secretion through protein kinase A (PKA) phosphorylation of proteins associated with the secretory process. However, it is now known that in addition to PKA, cAMP has other targets such as Epac (also referred to as cAMP-GEF). The variety of the effects mediated by cAMP signalling may be linked to cAMP compartmentation in the pancreatic beta-cells.
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Affiliation(s)
- S Seino
- Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Hyogo, Japan.
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129
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Calcium-sensing beyond neurotransmitters: functions of synaptotagmins in neuroendocrine and endocrine secretion. Biosci Rep 2009; 29:245-59. [PMID: 19500075 DOI: 10.1042/bsr20090031] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Neurotransmitters, neuropeptides and hormones are released through the regulated exocytosis of SVs (synaptic vesicles) and LDCVs (large dense-core vesicles), a process that is controlled by calcium. Synaptotagmins are a family of type 1 membrane proteins that share a common domain structure. Most synaptotagmins are located in brain and endocrine cells, and some of these synaptotagmins bind to phospholipids and calcium at levels that trigger regulated exocytosis of SVs and LDCVs. This led to the proposed synaptotagmin-calcium-sensor paradigm, that is, members of the synaptotagmin family function as calcium sensors for the regulated exocytosis of neurotransmitters, neuropeptides and hormones. Here, we provide an overview of the synaptotagmin family, and review the recent mouse genetic studies aimed at understanding the functions of synaptotagmins in neurotransmission and endocrine-hormone secretion. Also, we discuss potential roles of synaptotagmins in non-traditional endocrine systems.
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130
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Deriy LV, Gomez EA, Jacobson DA, Wang X, Hopson JA, Liu XY, Zhang G, Bindokas VP, Philipson LH, Nelson DJ. The granular chloride channel ClC-3 is permissive for insulin secretion. Cell Metab 2009; 10:316-23. [PMID: 19808024 PMCID: PMC2778193 DOI: 10.1016/j.cmet.2009.08.012] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2009] [Revised: 07/06/2009] [Accepted: 08/18/2009] [Indexed: 11/29/2022]
Abstract
Insulin secretion from pancreatic beta cells is dependent on maturation and acidification of the secretory granule, processes necessary for prohormone convertase cleavage of proinsulin. Previous studies in isolated beta cells revealed that acidification may be dependent on the granule membrane chloride channel ClC-3, in a step permissive for a regulated secretory response. In this study, immuno-EM of beta cells revealed colocalization of ClC-3 and insulin on secretory granules. Clcn3(-/-) mice as well as isolated islets demonstrate impaired insulin secretion; Clcn3(-/-) beta cells are defective in regulated insulin exocytosis and granular acidification. Increased amounts of proinsulin were found in the majority of secretory granules in the Clcn3(-/-) mice, while in Clcn3(+/+) cells, proinsulin was confined to the immature secretory granules. These results demonstrate that in pancreatic beta cells, chloride channels, specifically ClC-3, are localized on insulin granules and play a role in insulin processing as well as insulin secretion through regulation of granular acidification.
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Affiliation(s)
- Ludmila V Deriy
- Department of Neurobiology, Pharmacology, and Physiology, The University of Chicago, Chicago, IL 60637, USA
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131
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Géminard C, Rulifson EJ, Léopold P. Remote control of insulin secretion by fat cells in Drosophila. Cell Metab 2009; 10:199-207. [PMID: 19723496 DOI: 10.1016/j.cmet.2009.08.002] [Citation(s) in RCA: 411] [Impact Index Per Article: 27.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/20/2009] [Revised: 07/07/2009] [Accepted: 08/11/2009] [Indexed: 01/20/2023]
Abstract
Insulin-like peptides (ILPs) couple growth, metabolism, longevity, and fertility with changes in nutritional availability. In Drosophila, several ILPs called Dilps are produced by the brain insulin-producing cells (IPCs), from which they are released into the hemolymph and act systemically. We show here that in response to nutrient deprivation, brain Dilps are no longer secreted and accumulate in the IPCs. We further demonstrate that the larval fat body, a functional homolog of vertebrate liver and white fat, couples the level of circulating Dilps with dietary amino acid levels by remotely controlling Dilp release through a TOR/RAPTOR-dependent mechanism. We finally use ex vivo tissue coculture to demonstrate that a humoral signal emitted by the fat body transits through the hemolymph and activates Dilp secretion in the IPCs. Thus, the availability of nutrients is remotely sensed in fat body cells and conveyed to the brain IPCs by a humoral signal controlling ILP release.
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Affiliation(s)
- Charles Géminard
- Institute for Developmental Biology and Cancer, CNRS/University of Nice-Sophia Antipolis, Parc Valrose, 06108 Nice, France
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132
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Karaca M, Castel J, Tourrel-Cuzin C, Brun M, Géant A, Dubois M, Catesson S, Rodriguez M, Luquet S, Cattan P, Lockhart B, Lang J, Ktorza A, Magnan C, Kargar C. Exploring functional beta-cell heterogeneity in vivo using PSA-NCAM as a specific marker. PLoS One 2009; 4:e5555. [PMID: 19440374 PMCID: PMC2679208 DOI: 10.1371/journal.pone.0005555] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Accepted: 04/15/2009] [Indexed: 11/18/2022] Open
Abstract
Background The mass of pancreatic β-cells varies according to increases in insulin demand. It is hypothesized that functionally heterogeneous β-cell subpopulations take part in this process. Here we characterized two functionally distinct groups of β-cells and investigated their physiological relevance in increased insulin demand conditions in rats. Methods Two rat β-cell populations were sorted by FACS according to their PSA-NCAM surface expression, i.e. βhigh and βlow-cells. Insulin release, Ca2+ movements, ATP and cAMP contents in response to various secretagogues were analyzed. Gene expression profiles and exocytosis machinery were also investigated. In a second part, βhigh and βlow-cell distribution and functionality were investigated in animal models with decreased or increased β-cell function: the Zucker Diabetic Fatty rat and the 48 h glucose-infused rat. Results We show that β-cells are heterogeneous for PSA-NCAM in rat pancreas. Unlike βlow-cells, βhigh-cells express functional β-cell markers and are highly responsive to various insulin secretagogues. Whereas βlow-cells represent the main population in diabetic pancreas, an increase in βhigh-cells is associated with gain of function that follows sustained glucose overload. Conclusion Our data show that a functional heterogeneity of β-cells, assessed by PSA-NCAM surface expression, exists in vivo. These findings pinpoint new target populations involved in endocrine pancreas plasticity and in β-cell defects in type 2 diabetes.
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Affiliation(s)
- Melis Karaca
- Laboratoire de Physiopathologie de la Nutrition, Université Paris Diderot, CNRS UMR 7059, Paris, France.
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Lee HS, Jeong J, Lee KJ. Characterization of Vesicles Secreted from Insulinoma NIT-1 Cells. J Proteome Res 2009; 8:2851-62. [DOI: 10.1021/pr900009y] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Hyo Sun Lee
- Center for Cell Signaling & Drug Discovery Research, College of Pharmacy and Division of Life & Pharmaceutical Sciences, Ewha Womans University, Seoul, Korea 120-750
| | - Jaeho Jeong
- Center for Cell Signaling & Drug Discovery Research, College of Pharmacy and Division of Life & Pharmaceutical Sciences, Ewha Womans University, Seoul, Korea 120-750
| | - Kong-Joo Lee
- Center for Cell Signaling & Drug Discovery Research, College of Pharmacy and Division of Life & Pharmaceutical Sciences, Ewha Womans University, Seoul, Korea 120-750
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Newcomer insulin secretory granules as a highly calcium-sensitive pool. Proc Natl Acad Sci U S A 2009; 106:7432-6. [PMID: 19372374 DOI: 10.1073/pnas.0901202106] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Insulin secretion is biphasic in response to a step in glucose stimulation. Recent experiments suggest that 2 different mechanisms operate during the 2 phases, with transient first-phase secretion due to exocytosis of docked granules but the second sustained phase due largely to newcomer granules. Another line of research has shown that there exist 2 pools of releasable granules with different Ca(2+) sensitivities. An immediately releasable pool (IRP) is located in the vicinity of Ca(2+) channels, whereas a highly Ca(2+)-sensitive pool (HCSP) resides mainly away from Ca(2+) channels. We extend a previous model of exocytosis and insulin release by adding an HCSP and show that the inclusion of this pool naturally leads to insulin secretion mainly from newcomer granules during the second phase of secretion. We show that the model is compatible with data from single cells on the HCSP and from stimulation of islets by glucose, including L- and R-type Ca(2+) channel knockouts, as well as from Syntaxin-1A-deficient cells. We also use the model to investigate the relative contribution of calcium signaling and pool depletion in controlling biphasic secretion.
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