Glucose-Dependent Changes in SNARE Protein Levels in Pancreatic β-Cells

Abstract Prolonged exposure to high glucose concentration alters the expression of a set of proteins in pancreatic β-cells and impairs their capacity to secrete insulin. The cellular and molecular mechanisms that lie behind this effect are poorly understood. In this study, three either in vitro or in vivo models (cultured rat pancreatic islets incubated in high glucose media, partially pancreatectomized rats, and islets transplanted to streptozotozin-induced diabetic mice) were used to evaluate the dependence of the biological model and the treatment, together with the cell location (insulin granule or plasma membrane) of the affected proteins and the possible effect of sustained insulin secretion, on the glucose-induced changes in protein expression. In all three models, islets exposed to high glucose concentrations showed a reduced expression of secretory granule-associated vesicle-soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins synaptobrevin/vesicle-associated membrane protein 2 and cellubrevin but minor or no significant changes in the expression of the membrane-associated target-SNARE proteins syntaxin1 and synaptosomal-associated protein-25 and a marked increase in the expression of synaptosomal-associated protein-23 protein. The inhibition of insulin secretion by the L-type voltage-dependent calcium channel nifedipine or the potassium channel activator diazoxide prevented the glucose-induced reduction in islet insulin content but not in vesicle-SNARE proteins, indicating that the granule depletion due to sustained exocytosis was not involved in the changes of protein expression induced by high glucose concentration. Altogether, the results suggest that high glucose has a direct toxic effect on the secretory pathway by decreasing the expression of insulin granule SNARE-associated proteins.

Download Full-text

Protective Effect of Siegesbeckia orientalis on Pancreatic β-Cells under High Glucose-Induced Glucotoxicity

Applied Sciences ◽

10.3390/app112210963 ◽

2021 ◽

Vol 11 (22) ◽

pp. 10963

Author(s):

Chi-Chang Chang ◽

Jer-Yiing Houng ◽

Shih-Wei Wang ◽

Chin-Feng Hsuan ◽

Yung-Chuan Lu ◽

...

Keyword(s):

Oxidative Stress ◽

Antioxidant Enzymes ◽

Insulin Secretion ◽

Protective Effect ◽

Normal Level ◽

High Glucose ◽

Glucose Concentration ◽

Β Cells ◽

Pancreatic Β Cells ◽

Siegesbeckia Orientalis

The glucotoxicity caused by long-term exposure of β-cells to high glucose (HG) conditions may lead to the generation of more reactive oxygen species (ROS), reduce the activity of antioxidant enzymes, cause cell damage and apoptosis, and induce insulin secretion dysfunction. Siegesbeckia orientalis linne is a traditional folk herbal medicine used to treat snake bites, rheumatoid arthritis, allergies, and immune deficiencies. In this study, we evaluated the protective effect of S. orientalis ethanol extract (SOE) on cell death and oxidative stress in RIN-m5f pancreatic β-cells stimulated by two HG concentrations (50–100 mM). In the cell viability assay, SOE could significantly increase the survival rate of pancreatic β-cells under HG-induced conditions. For the oxidative stress induced by HG condition, the treatment of SOE effectively reduced the ROS formation, increased the content of intracellular glutathione, and up-regulated the expression of antioxidant enzymes, catalase, superoxide dismutase, and glutathione peroxidase. As a result, the SOE treatment could decrease the glucotoxicity-mediated oxidative damage on RIN-m5F β-cells. Moreover, SOE had the function of regulating insulin secretion in pancreatic β-cells under different HG-mediated conditions. It could decrease the increasing intracellular insulin secretion under the low glucose concentration to normal level; while increase the decreasing intracellular insulin secretion under the relatively high glucose concentration to normal level. Taken together, this study suggests that SOE has a protective effect on pancreatic β-cells under the HG-stimulated glucotoxic environment.

Download Full-text

Distinct glucose-dependent stress responses revealed by translational profiling in pancreatic β-cells

Journal of Endocrinology ◽

10.1677/joe.1.06898 ◽

2007 ◽

Vol 192 (1) ◽

pp. 179-187 ◽

Cited By ~ 30

Author(s):

Isabel C Greenman ◽

Edith Gomez ◽

Claire E J Moore ◽

Terence P Herbert

Keyword(s):

Stress Responses ◽

High Glucose ◽

Glucose Concentration ◽

High Glucose Concentration ◽

Cell Integrity ◽

Β Cells ◽

Pancreatic Β Cells ◽

Interacting Protein ◽

Thioredoxin Interacting Protein ◽

Specific Subset

In pancreatic β-cells, following an acute (within 1 h) increase in glucose concentration, there are rapid changes in the expression of a large subset of proteins. The change in the expression of many of these proteins is mediated by a post-transcriptional mechanism through either increases or decreases in the rate of translation from pre-existing transcripts. These proteins, whose synthesis is rapidly up- or down-regulated in response to glucose, are likely important in mounting the correct response to changes in plasma glucose concentrations. However, the vast majority of these proteins remain unidentified. Therefore, in order to identify these proteins, we analysed changes in the levels of mRNAs associated with polysomes (i.e. actively translating mRNAs) isolated from mouse insulinoma 6 cells incubated at either 0.5 or 20 mM glucose for 1 h. Changes in the levels of polysomal mRNAs in response to glucose were analysed using affymetrix oligonucleotide microarrays (translational profiling). This work revealed that, in response to a change in glucose concentration, the abundance of 313 transcripts associated with polysomes changed by more than 1.5-fold, of which the abundance of 37 changed by more than twofold. The majority of these transcripts encoded proteins associated with metabolism or gene expression. More detailed analysis showed that a number of mRNAs encoding proteins associated with the induction of oxidative stress, including thioredoxin-2 and thioredoxin-interacting protein were rapidly redistributed onto heavier polysomes at high glucose concentration, indicating an increase in their expression. At low glucose concentration, when the general rate of protein synthesis is low, a number of mRNAs encoding integrated stress response proteins, including ATF4 and CHOP10, associate with heavier polysomes, indicating that their expression is up-regulated. In conclusion, translational profiling has revealed that, at either low or at high glucose concentration, β-cells rapidly increase the synthesis of a specific subset of proteins that are likely important in maintaining β-cell integrity and survival during conditions of nutritional stress.

Download Full-text

The level of menadione redox-cycling in pancreatic β-cells is proportional to the glucose concentration: Role of NADH and consequences for insulin secretion

Toxicology and Applied Pharmacology ◽

10.1016/j.taap.2011.11.002 ◽

2012 ◽

Vol 258 (2) ◽

pp. 216-225 ◽

Cited By ~ 7

Author(s):

Emma Heart ◽

Meridith Palo ◽

Trayce Womack ◽

Peter J.S. Smith ◽

Joshua P. Gray

Keyword(s):

Insulin Secretion ◽

Glucose Concentration ◽

Redox Cycling ◽

Β Cells ◽

Pancreatic Β Cells

Download Full-text

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

Molecular Endocrinology ◽

10.1210/me.2005-0157 ◽

2006 ◽

Vol 20 (1) ◽

pp. 183-193 ◽

Cited By ~ 62

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.

Download Full-text

Crucial roles of neuronatin in insulin secretion and high glucose-induced apoptosis in pancreatic β-cells

Cellular Signalling ◽

10.1016/j.cellsig.2008.01.005 ◽

2008 ◽

Vol 20 (5) ◽

pp. 907-915 ◽

Cited By ~ 40

Author(s):

Myung Kuk Joe ◽

Hyo Jung Lee ◽

Young Ho Suh ◽

Kyu Lee Han ◽

Joo Hyun Lim ◽

...

Keyword(s):

Insulin Secretion ◽

High Glucose ◽

Β Cells ◽

Pancreatic Β Cells ◽

Induced Apoptosis

Download Full-text

High glucose concentration in T1D patients modulates apoptotic protein expression: Down regulation of BAX and FAS and up regulation of XIAP

Human Immunology ◽

10.1016/j.humimm.2012.04.020 ◽

2012 ◽

Vol 73 (8) ◽

pp. 801-804 ◽

Cited By ~ 5

Author(s):

Elizabeth Valencia ◽

Ethel Codner ◽

Francisca Salas-Pérez ◽

Carolina Pizarro ◽

Elena Carrasco P ◽

...

Keyword(s):

Protein Expression ◽

High Glucose ◽

Glucose Concentration ◽

High Glucose Concentration ◽

Down Regulation ◽

Apoptotic Protein

Download Full-text

In pancreatic β-cells myosin 1b regulates glucose-stimulated insulin secretion by modulating an early step in insulin granule trafficking from the Golgi

Molecular Biology of the Cell ◽

10.1091/mbc.e21-03-0094 ◽

2021 ◽

pp. mbc.E21-03-0094

Author(s):

Hiroshi Tokuo ◽

Shigeru Komaba ◽

Lynne M. Coluccio

Keyword(s):

Insulin Secretion ◽

Islet Cells ◽

Early Stage ◽

Secretory Granules ◽

Β Cells ◽

Pancreatic Β Cells ◽

Glucose Levels ◽

Insulin Granule ◽

Glucose Stimulated Insulin Secretion ◽

Insulinoma Cells

Pancreatic β-cells secrete insulin, which controls blood glucose levels, and defects in insulin secretion are responsible for diabetes mellitus. The actin cytoskeleton and some myosins support insulin granule trafficking and release, although a role for the class I myosin Myo1b, an actin- and membrane-associated load-sensitive motor, in insulin biology is unknown. We found by immunohistochemistry that Myo1b is expressed in islet cells of rat pancreas. In cultured rat insulinoma 832/13 cells Myo1b localized near actin patches, the trans-Golgi network (TGN) marker TGN38, and insulin granules in the perinuclear region. Myo1b depletion by siRNA in 832/13 cells reduced intracellular proinsulin and insulin content and glucose-stimulated insulin secretion (GSIS), and led to the accumulation of (pro)insulin SGs at the TGN. Using an in situ fluorescent pulse-chase strategy to track nascent proinsulin (Bearrows et al., 2019), Myo1b depletion in insulinoma cells reduced the number of (pro)insulin-containing secretory granules budding from the TGN. The studies indicate for the first time that in pancreatic β-cells Myo1b controls GSIS at least in part by mediating an early stage in insulin granule trafficking from the TGN.

Download Full-text