Granule docking and cargo release in pancreatic β-cells

2008 ◽  
Vol 36 (3) ◽  
pp. 294-299 ◽  
Author(s):  
Sebastian Barg ◽  
Anders Lindqvist ◽  
Stefanie Obermüller
Keyword(s):  
Insulin Secretion ◽  
Live Cell Imaging ◽  
Cell Imaging ◽  
Fusion Pore ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Isolated Pancreatic Islets ◽  
Biphasic Insulin ◽  
Biphasic Insulin Secretion

Biphasic insulin secretion is required for proper insulin action and is observed not only in vivo, but also in isolated pancreatic islets and even single β-cells. Late events in the granule life cycle are thought to underlie this temporal pattern. In the last few years, we have therefore combined live cell imaging and electrophysiology to study insulin secretion at the level of individual granules, as they approach the plasma membrane, undergo exocytosis and finally release their insulin cargo. In the present paper, we review evidence for two emerging concepts that affect insulin secretion at the level of individual granules: (i) the existence of specialized sites where granules dock in preparation for exocytosis; and (ii) post-exocytotic regulation of cargo release by the fusion pore.

Specific Deletion of CASK in Pancreatic β Cells Affects Glucose Homeostasis and Improves Insulin Sensitivity in Obese Mice by Reducing Hyperinsulinemia Running Title: β Cell CASK Deletion Reduces Hyperinsulinemia

2021 ◽  
Author(s):  
Xingjing Liu ◽  
Peng Sun ◽  
Qingzhao Yuan ◽  
Jinyang Xie ◽  
Ting Xiao ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Insulin Secretion ◽  
Insulin Sensitivity ◽  
Glucose Homeostasis ◽  
Chow Diet ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Calcium Calmodulin Dependent ◽  
Normal Chow

Calcium/calmodulin-dependent serine protein kinase (CASK) is involved in the secretion of insulin vesicles in pancreatic β-cells. The present study revealed a new <i>in vivo </i>role of CASK in glucose homeostasis during the progression of type 2 diabetes mellitus (T2DM). A Cre-loxP system was used to specifically delete the <i>Cask </i>gene in mouse β-cells (βCASKKO), and the glucose metabolism was evaluated in <a>βCASKKO</a> mice fed a normal chow diet (ND) or a high-fat diet (HFD). ND-fed mice exhibited impaired insulin secretion in response to glucose stimulation. Transmission electron microscopy showed significantly reduced numbers of insulin granules at or near the cell membrane in the islets of βCASKKO mice. By contrast, HFD-fed βCASKKO mice showed reduced blood glucose and a partial relief of hyperinsulinemia and insulin resistance when compared to HFD-fed wildtype mice. The IRS1/PI3K/AKT signaling pathway was upregulated in the adipose tissue of HFD-βCASKKO mice. These results indicated that knockout of the <i>Cask</i> gene in β cells had a diverse effect on glucose homeostasis: reduced insulin secretion in ND-fed mice, but improves insulin sensitivity in HFD-fed mice. Therefore, CASK appears to function in the insulin secretion and contributes to hyperinsulinemia and insulin resistance during the development of obesity-related T2DM.

scholarly journals Protein Kinase CK2 Controls CaV2.1-Dependent Calcium Currents and Insulin Release in Pancreatic β-cells

2020 ◽  
Vol 21 (13) ◽  
pp. 4668
Author(s):  
Rebecca Scheuer ◽  
Stephan Ernst Philipp ◽  
Alexander Becker ◽  
Lisa Nalbach ◽  
Emmanuel Ampofo ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Calcium Currents ◽  
Insulin Biosynthesis ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Voltage Dependent ◽  
Regulatory Impact ◽  
Kinase Ck2

The regulation of insulin biosynthesis and secretion in pancreatic β-cells is essential for glucose homeostasis in humans. Previous findings point to the highly conserved, ubiquitously expressed serine/threonine kinase CK2 as having a negative regulatory impact on this regulation. In the cell culture model of rat pancreatic β-cells INS-1, insulin secretion is enhanced after CK2 inhibition. This enhancement is preceded by a rise in the cytosolic Ca2+ concentration. Here, we identified the serine residues S2362 and S2364 of the voltage-dependent calcium channel CaV2.1 as targets of CK2 phosphorylation. Furthermore, co-immunoprecipitation experiments revealed that CaV2.1 binds to CK2 in vitro and in vivo. CaV2.1 knockdown experiments showed that the increase in the intracellular Ca2+ concentration, followed by an enhanced insulin secretion upon CK2 inhibition, is due to a Ca2+ influx through CaV2.1 channels. In summary, our results point to a modulating role of CK2 in the CaV2.1-mediated exocytosis of insulin.

Tetracaine stimulates insulin secretion through the mobilization of Ca2+ from thapsigargin- and IP3-insensitive Ca2+ reservoir in pancreatic β-cells

2000 ◽  
Vol 78 (6) ◽  
pp. 462-468 ◽  
Author(s):  
José Roberto Bosqueiro ◽  
Everardo Magalhães Carneiro ◽  
Silvana Bordin ◽  
Antonio Carlos Boschero
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Islets ◽  
Isolated Islets ◽  
Inositol Triphosphate ◽  
Free Medium ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Isolated Pancreatic Islets ◽  
High Concentrations

The effect of tetracaine on 45Ca efflux, cytoplasmic Ca2+ concentration [Ca2+]i, and insulin secretion in isolated pancreatic islets and β-cells was studied. In the absence of external Ca2+, tetracaine (0.1-2.0 mM) increased the 45Ca efflux from isolated islets in a dose-dependant manner. Tetracaine did not affect the increase in 45Ca efflux caused by 50 mM K+ or by the association of carbachol (0.2 mM) and 50 mM K+. Tetracaine permanently increased the [Ca2+]i in isolated β-cells in Ca2+-free medium enriched with 2.8 mM glucose and 25 µM D-600 (methoxiverapamil). This effect was also observed in the presence of 10 mM caffeine or 1 µM thapsigargin. In the presence of 16.7 mM glucose, tetracaine transiently increased the insulin secretion from islets perfused in the absence and presence of external Ca2+. These data indicate that tetracaine mobilises Ca2+ from a thapsigargin-insensitive store and stimulates insulin secretion in the absence of extracellular Ca2+. The increase in 45Ca efflux caused by high concentrations of K+ and by carbachol indicates that tetracaine did not interfere with a cation or inositol triphosphate sensitive Ca2+ pool in β-cells.

Increased expression of GAD65 and GABA in pancreatic β-cells impairs first-phase insulin secretion

2000 ◽  
Vol 279 (3) ◽  
pp. E684-E694 ◽  
Author(s):  
Yuguang Shi ◽  
Jamil Kanaani ◽  
Virginie Menard-Rose ◽  
Yan Hui Ma ◽  
Pi-Yun Chang ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glucose Tolerance ◽  
Cell Function ◽  
Normal Glucose Tolerance ◽  
Negative Regulator ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Pancreas Perfusion ◽  
First Phase Insulin Secretion

The functional role of glutamate decarboxylase (GAD) and its product GABA in pancreatic islets has remained elusive. Mouse β-cells express the larger isoform GAD67, whereas human islets express only the smaller isoform GAD65. We have generated two lines of transgenic mice expressing human GAD65 in pancreatic β-cells (RIP7-hGAD65, Lines 1 and 2) to study the effect that GABA generated by this isoform has on islet cell function. The ascending order of hGAD65 expression and/or activity in β-cells was Line 1 heterozygotes < Line 2 heterozygotes < Line 1 homozygotes. Line 1 heterozygotes have normal glucose tolerance, whereas Line 1 homozygotes and Line 2 heterozygotes exhibit impaired glucose tolerance and inhibition of insulin secretion in vivo in response to glucose. In addition, fasting levels of blood glucose are elevated and insulin is decreased in Line 1 homozygotes. Pancreas perfusion experiments suggest that GABA generated by GAD65 may function as a negative regulator of first-phase insulin secretion in response to glucose by affecting a step proximal to or at the KATP +channel.

scholarly journals Downregulation of lncRNA TUG1 Affects Apoptosis and Insulin Secretion in Mouse Pancreatic β Cells

2015 ◽  
Vol 35 (5) ◽  
pp. 1892-1904 ◽  
Author(s):  
Dan-dan Yin ◽  
Er-bao Zhang ◽  
Liang-hui You ◽  
Ning Wang ◽  
Lin-tao Wang ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Cell Function ◽  
Annexin V ◽  
Pancreatic Tissue ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Lncrna Tug1

Background: Increasing evidence indicates that long noncoding RNAs (IncRNAs) perform specific biological functions in diverse processes. Recent studies have reported that IncRNAs may be involved in β cell function. The aim of this study was to characterize the role of IncRNA TUG1 in mouse pancreatic β cell functioning both in vitro and in vivo. Methods: qRT-PCR analyses were performed to detect the expression of lncRNA TUG1 in different tissues. RNAi, MTT, TUNEL and Annexin V-FITC assays and western blot, GSIS, ELISA and immunochemistry analyses were performed to detect the effect of lncRNA TUG1 on cell apoptosis and insulin secretion in vitro and in vivo. Results: lncRNA TUG1 was highly expressed in pancreatic tissue compared with other organ tissues, and expression was dynamically regulated by glucose in Nit-1 cells. Knockdown of lncRNA TUG1 expression resulted in an increased apoptosis ratio and decreased insulin secretion in β cells both in vitro and in vivo . Immunochemistry analyses suggested decreased relative islet area after treatment with lncRNA TUG1 siRNA. Conclusion: Downregulation of lncRNA TUG1 expression affected apoptosis and insulin secretion in pancreatic β cells in vitro and in vivo. lncRNA TUG1 may represent a factor that regulates the function of pancreatic β cells.

scholarly journals Syntaxin 4 Facilitates Biphasic Glucose-Stimulated Insulin Secretion from Pancreatic β-Cells

2006 ◽  
Vol 20 (1) ◽  
pp. 183-193 ◽  
Author(s):  
Beth A. Spurlin ◽  
Debbie C. Thurmond
Keyword(s):  
Insulin Secretion ◽  
Wild Type ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Mouse Islet ◽  
Biphasic Insulin ◽  
Syntaxin 4 ◽  
Insulin Granule ◽  
Glucose Stimulated Insulin Secretion ◽  
Interfering Rna

Abstract Numerous overexpression studies have recently implicated Syntaxin 4 as an effector of insulin secretion, although its requirement in insulin granule exocytosis is unknown. To address this, islets from Syntaxin 4 heterozygous (−/+) knockout mice were isolated and compared with islets from wild-type mice. Under static incubation conditions, Syntaxin 4 (−/+) islets showed a 60% reduction in glucose-stimulated insulin secretion compared with wild-type islets. Perifusion analyses revealed that Syntaxin 4 (−/+) islets secreted 50% less insulin during the first phase of glucose-stimulated insulin secretion and that this defect could be fully restored by the specific replenishment of recombinant Syntaxin 4. This essential role for Syntaxin 4 in secretion from the islet was localized to the β-cells because small interfering RNA-mediated depletion of Syntaxin 4 in MIN6 β-cells abolished glucose-stimulated insulin secretion. Moreover, immunofluorescent confocal microscopy revealed that Syntaxin 4 was principally localized to the β-cells and not the α-cells of the mouse islet. Remarkably, islets isolated from transgenic mice that express 2.4-fold higher levels of Syntaxin 4 relative to wild-type mice secreted approximately 35% more insulin during both phases of insulin secretion, suggesting that increased Syntaxin 4 may be beneficial for enhancing biphasic insulin secretion in a regulated manner. Taken together, these data support the notion that Syntaxin 4-based SNARE complexes are essential for biphasic insulin granule fusion in pancreatic β-cells.

scholarly journals Optogenetic control of insulin secretion by pancreatic β-cells in vitro and in vivo

Gene Therapy ◽  
2015 ◽  
Vol 22 (7) ◽  
pp. 553-559 ◽  
Author(s):  
T Kushibiki ◽  
S Okawa ◽  
T Hirasawa ◽  
M Ishihara
Keyword(s):  
Insulin Secretion ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Optogenetic Control
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