scholarly journals ROCK1 regulates insulin secretion from β-cells

2021 ◽  
Author(s):  
Byung-Jun Sung ◽  
Sung-Bin Lim ◽  
Jae Hyeon Kim ◽  
Won-Mo Yang ◽  
Rohit N Kulkarni ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Pyruvate Kinase ◽  
Glucose Homeostasis ◽  
Isolated Islets ◽  
Whole Body ◽  
Proximity Ligation Assay ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Glucose Stimulated Insulin Secretion

Objective: The endocrine pancreatic β-cells play a pivotal role in the maintenance of whole-body glucose homeostasis and its dysregulation is a consistent feature in all forms of diabetes. However, knowledge of intracellular regulators that modulate b-cell function remains incomplete. We investigated the physiological role of ROCK1 in the regulation of insulin secretion and glucose homeostasis. Methods: Mice lacking ROCK1 in pancreatic β-cells (RIP-Cre; ROCK1loxP/loxP, β-ROCK1-/-) were studied. Glucose and insulin tolerance tests as well as glucose-stimulated insulin secretion (GSIS) were measured. Insulin secretion response to a direct glucose or pyruvate or pyruvate kinase (PK) activator stimulation in isolated islets from β-ROCK1-/- mice or β-cell lines with knockdown of ROCK1 were also evaluated. Proximity ligation assay was performed to determine the physical interactions between PK and ROCK1. Results: Mice with a deficiency of ROCK1 in pancreatic β-cells exhibited significantly increased blood glucose levels and reduced serum insulin without changes in body weight. Interestingly, β-ROCK1-/- mice displayed progressive impairment of glucose tolerance while maintaining insulin sensitivity mostly due to impaired GSIS. Consistently, GSIS was markedly decreased in ROCK1-deficient islets and ROCK1 knockdown INS-1 cells. Concurrently, ROCK1 blockade led to a significant decrease in intracellular calcium levels, ATP levels, and oxygen consumption rates in isolated islets and INS-1 cells. Treatment of ROCK1-deficient islets or ROCK1 knockdown β-cells either with pyruvate or a PK activator rescued the impaired GSIS. Mechanistically, we observed that ROCK1 binding to PK is greatly enhanced by glucose stimulation in β-cells. Conclusions: Our findings demonstrate that β-cell ROCK1 is essential for glucose-stimulated insulin secretion and maintenance of glucose homeostasis and that ROCK1 acts as an upstream regulator of glycolytic pyruvate kinase signaling.

scholarly journals L-Arginine prevents cereblon-mediated ubiquitination of glucokinase and stimulates glucose-6-phosphate production in pancreatic β-cells

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Jaeyong Cho ◽  
Yukio Horikawa ◽  
Mayumi Enya ◽  
Jun Takeda ◽  
Yoichi Imai ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Ubiquitin Ligase ◽  
E3 Ubiquitin Ligase ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Direct Stimulation ◽  
Glucose Ratio ◽  
Glucose Stimulated Insulin Secretion

Abstract We sought to determine a mechanism by which L-arginine increases glucose-stimulated insulin secretion (GSIS) in β-cells by finding a protein with affinity to L-arginine using arginine-immobilized magnetic nanobeads technology. Glucokinase (GCK), the key regulator of GSIS and a disease-causing gene of maturity-onset diabetes of the young type 2 (MODY2), was found to bind L-arginine. L-Arginine stimulated production of glucose-6-phosphate (G6P) and induced insulin secretion. We analyzed glucokinase mutants and identified three glutamate residues that mediate binding to L-arginine. One MODY2 patient with GCKE442* demonstrated lower C-peptide-to-glucose ratio after arginine administration. In β-cell line, GCKE442* reduced L-arginine-induced insulin secretion compared with GCKWT. In addition, we elucidated that the binding of arginine protects glucokinase from degradation by E3 ubiquitin ligase cereblon mediated ubiquitination. We conclude that L-arginine induces insulin secretion by increasing G6P production by glucokinase through direct stimulation and by prevention of degradation.

scholarly journals The adaptor protein APPL2 controls glucose-stimulated insulin secretion via F-actin remodeling in pancreatic β-cells

2020 ◽  
Vol 117 (45) ◽  
pp. 28307-28315
Author(s):  
Baile Wang ◽  
Huige Lin ◽  
Xiaomu Li ◽  
Wenqi Lu ◽  
Jae Bum Kim ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Islets ◽  
Adaptor Protein ◽  
Hek293 Cells ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Actin Remodeling ◽  
Actin Depolymerization ◽  
Glucose Stimulated Insulin Secretion

Filamentous actin (F-actin) cytoskeletal remodeling is critical for glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells, and its dysregulation causes type 2 diabetes. The adaptor protein APPL1 promotes first-phase GSIS by up-regulating solubleN-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein expression. However, whether APPL2 (a close homology of APPL1 with the same domain organization) plays a role in β-cell functions is unknown. Here, we show that APPL2 enhances GSIS by promoting F-actin remodeling via the small GTPase Rac1 in pancreatic β-cells. β-cell specific abrogation of APPL2 impaired GSIS, leading to glucose intolerance in mice. APPL2 deficiency largely abolished glucose-induced first- and second-phase insulin secretion in pancreatic islets. Real-time live-cell imaging and phalloidin staining revealed that APPL2 deficiency abolished glucose-induced F-actin depolymerization in pancreatic islets. Likewise, knockdown of APPL2 expression impaired glucose-stimulated F-actin depolymerization and subsequent insulin secretion in INS-1E cells, which were attributable to the impairment of Ras-related C3 botulinum toxin substrate 1 (Rac1) activation. Treatment with the F-actin depolymerization chemical compounds or overexpression of gelsolin (a F-actin remodeling protein) rescued APPL2 deficiency-induced defective GSIS. In addition, APPL2 interacted with Rac GTPase activating protein 1 (RacGAP1) in a glucose-dependent manner via the bin/amphiphysin/rvs-pleckstrin homology (BAR-PH) domain of APPL2 in INS-1E cells and HEK293 cells. Concomitant knockdown of RacGAP1 expression reverted APPL2 deficiency-induced defective GSIS, F-actin remodeling, and Rac1 activation in INS-1E cells. Our data indicate that APPL2 interacts with RacGAP1 and suppresses its negative action on Rac1 activity and F-actin depolymerization thereby enhancing GSIS in pancreatic β-cells.

scholarly journals Neuroligin-2-derived peptide-covered polyamidoamine-based (PAMAM) dendrimers enhance pancreatic β-cells' proliferation and functions

MedChemComm ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 280-293
Author(s):  
Anna Munder ◽  
Yoni Moskovitz ◽  
Aviv Meir ◽  
Shirin Kahremany ◽  
Laura Levy ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Cellular Stress ◽  
Pamam Dendrimers ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Cell Functions ◽  
Functional Maturation ◽  
Glucose Stimulated Insulin Secretion

The nanoscale composite improved β-cell functions in terms of rate of proliferation, glucose-stimulated insulin secretion, resistance to cellular stress and functional maturation.

scholarly journals γ-Oryzanol Protects Pancreatic β-Cells Against Endoplasmic Reticulum Stress in Male Mice

Endocrinology ◽  
2015 ◽  
Vol 156 (4) ◽  
pp. 1242-1250 ◽  
Author(s):  
Chisayo Kozuka ◽  
Sumito Sunagawa ◽  
Rei Ueda ◽  
Moritake Higa ◽  
Hideaki Tanaka ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Insulin Secretion ◽  
Er Stress ◽  
High Fat Diet ◽  
Diabetic Mice ◽  
High Fat ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Glucose Stimulated Insulin Secretion

Abstract Endoplasmic reticulum (ER) stress is profoundly involved in dysfunction of β-cells under high-fat diet and hyperglycemia. Our recent study in mice showed that γ-oryzanol, a unique component of brown rice, acts as a chemical chaperone in the hypothalamus and improves feeding behavior and diet-induced dysmetabolism. However, the entire mechanism whereby γ-oryzanol improves glucose metabolism throughout the body still remains unclear. In this context, we tested whether γ-oryzanol reduces ER stress and improves function and survival of pancreatic β-cells using murine β-cell line MIN6. In MIN6 cells with augmented ER stress by tunicamycin, γ-oryzanol decreased exaggerated expression of ER stress-related genes and phosphorylation of eukaryotic initiation factor-2α, resulting in restoration of glucose-stimulated insulin secretion and prevention of apoptosis. In islets from high-fat diet-fed diabetic mice, oral administration of γ-oryzanol improved glucose-stimulated insulin secretion on following reduction of exaggerated ER stress and apoptosis. Furthermore, we examined the impact of γ-oryzanol on low-dose streptozotocin-induced diabetic mice, where exaggerated ER stress and resultant apoptosis in β-cells were observed. Also in this model, γ-oryzanol attenuated mRNA level of genes involved in ER stress and apoptotic signaling in islets, leading to amelioration of glucose dysmetabolism. Taken together, our findings demonstrate that γ-oryzanol directly ameliorates ER stress-induced β-cell dysfunction and subsequent apoptosis, highlighting usefulness of γ-oryzanol for the treatment of diabetes mellitus.

scholarly journals β-Cell-specific pyruvate dehydrogenase deficiency impairs glucose-stimulated insulin secretion

2010 ◽  
Vol 299 (6) ◽  
pp. E910-E917 ◽  
Author(s):  
Malathi Srinivasan ◽  
Cheol S. Choi ◽  
Pushpankur Ghoshal ◽  
Lioudmila Pliss ◽  
Jignesh D. Pandya ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Mouse Model ◽  
Pyruvate Dehydrogenase ◽  
Isolated Islets ◽  
Male Mice ◽  
Β Cells ◽  
Β Cell ◽  
Pyruvate Cycling ◽  
Glucose Stimulated Insulin Secretion

Glucose-stimulated insulin secretion (GSIS) by β-cells requires the generation of ATP from oxidation of pyruvate as well as generation of coupling factors involving three different pyruvate cycling shuttles. The roles of several key enzymes involved in pyruvate cycling in β-cells have been documented using isolated islets and β-cell clonal lines. To investigate the role of the pyruvate dehydrogenase (PDH) complex (PDC) in GSIS, a murine model of β-cell-specific PDH deficiency (β-PDHKO) was created. Pancreatic insulin content was decreased in 1-day-old β-PDHKO male pups and adult male mice. The plasma insulin levels were decreased and blood glucose levels increased in β-PDHKO male mice from neonatal life onward. GSIS was reduced in isolated islets from β-PDHKO male mice with about 50% reduction in PDC activity. Impairment in a glucose tolerance test and in vivo insulin secretion during hyperglycemic clamp was evident in β-PDHKO adults. No change in the number or size of islets was found in pancreata from 4-wk-old β-PDHKO male mice. However, an increase in the mean size of individual β-cells in islets of these mice was observed. These findings show a key role of PDC in GSIS by pyruvate oxidation. This β-PDHKO mouse model represents the first mouse model in which a mitochondrial oxidative enzyme deletion by gene knockout has been employed to demonstrate an altered GSIS by β-cells.

scholarly journals NAD kinase regulates the size of the NADPH pool and insulin secretion in pancreatic β-cells

2012 ◽  
Vol 303 (2) ◽  
pp. E191-E199 ◽  
Author(s):  
Joshua P. Gray ◽  
Kambiz N. Alavian ◽  
Elizabeth A. Jonas ◽  
Emma A. Heart
Keyword(s):  
Insulin Secretion ◽  
Redox Regulation ◽  
De Novo ◽  
Antioxidant Defense System ◽  
Nad Kinase ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Glucose Stimulated Insulin Secretion

NADPH is an important component of the antioxidant defense system and a proposed mediator in glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells. An increase in the NADPH/NADP+ ratio has been reported to occur within minutes following the rise in glucose concentration in β-cells. However, 30 min following the increase in glucose, the total NADPH pool also increases through a mechanism not yet characterized. NAD kinase (NADK) catalyzes the de novo formation of NADP+ by phosphorylation of NAD+. NAD kinases have been shown to be essential for redox regulation, oxidative stress defense, and survival in bacteria and yeast. However, studies on NADK in eukaryotic cells are scarce, and the function of this enzyme has not been described in β-cells. We employed INS-1 832/13 cells, an insulin-secreting rat β-cell line, and isolated rodent islets to investigate the role of NADK in β-cell metabolic pathways. Adenoviral-mediated overexpression of NADK resulted in a two- to threefold increase in the total NADPH pool and NADPH/NADP+ ratio, suggesting that NADP+ formed by the NADK-catalyzed reaction is rapidly reduced to NADPH via cytosolic reductases. This increase in the NADPH pool was accompanied by an increase in GSIS in NADK-overexpressing cells. Furthermore, NADK overexpression protected β-cells against oxidative damage by the redox cycling agent menadione and reversed menadione-mediated inhibition of GSIS. Knockdown of NADK via shRNA exerted the opposite effect on all these parameters. These data suggest that NADK kinase regulates intracellular redox and affects insulin secretion and oxidative defense in the β-cell.

scholarly journals SIRT6 protects against palmitate-induced pancreatic β-cell dysfunction and apoptosis

2016 ◽  
Vol 231 (2) ◽  
pp. 159-165 ◽  
Author(s):  
Xiwen Xiong ◽  
Xupeng Sun ◽  
Qingzhi Wang ◽  
Xinlai Qian ◽  
Yang Zhang ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Mrna Levels ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Glucose Stimulation ◽  
Cell Dysfunction ◽  
High Concentrations ◽  
Glucose Stimulated Insulin Secretion

Chronic exposure of pancreatic β-cells to abnormally elevated levels of free fatty acids can lead to β-cell dysfunction and even apoptosis, contributing to type 2 diabetes pathogenesis. In pancreatic β-cells, sirtuin 6 (SIRT6) has been shown to regulate insulin secretion in response to glucose stimulation. However, the roles played by SIRT6 in β-cells in response to lipotoxicity remain poorly understood. Our data indicated that SIRT6 protein and mRNA levels were reduced in islets from diabetic and aged mice. High concentrations of palmitate (PA) also led to a decrease in SIRT6 expression in MIN6 β-cells and resulted in cell dysfunction and apoptosis. Knockdown of Sirt6 caused an increase in cell apoptosis and impairment in insulin secretion in response to glucose in MIN6 cells even in the absence of PA exposure. Furthermore, overexpression of SIRT6 alleviated the palmitate-induced lipotoxicity with improved cell viability and increased glucose-stimulated insulin secretion. In summary, our data suggest that SIRT6 can protect against palmitate-induced β-cell dysfunction and apoptosis.

scholarly journals Hypoxylonol F Isolated from Annulohypoxylon annulatum Improves Insulin Secretion by Regulating Pancreatic β-cell Metabolism

Biomolecules ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 335 ◽  
Author(s):  
Dahae Lee ◽  
Buyng Su Hwang ◽  
Pilju Choi ◽  
Taejung Kim ◽  
Youngseok Kim ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Molecular Mechanisms ◽  
Cell Metabolism ◽  
Peroxisome Proliferator ◽  
Pancreatic Β Cell ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Peroxisome Proliferator Activated Receptor ◽  
Glucose Stimulated Insulin Secretion

Insulin plays a key role in glucose homeostasis and is hence used to treat hyperglycemia, the main characteristic of diabetes mellitus. Annulohypoxylon annulatum is an inedible ball-shaped wood-rotting fungus, and hypoxylon F is one of the major compounds of A. annulatum. The aim of this study is to evaluate the effects of hypoxylonol F isolated from A. annulatum on insulin secretion in INS-1 pancreatic β-cells and demonstrate the molecular mechanisms involved. Glucose-stimulated insulin secretion (GSIS) values were evaluated using a rat insulin ELISA kit. Moreover, the expression of proteins related to pancreatic β-cell metabolism and insulin secretion was evaluated using Western blotting. Hypoxylonol F isolated from A. annulatum was found to significantly enhance glucose-stimulated insulin secretion without inducing cytotoxicity. Additionally, hypoxylonol F enhanced insulin receptor substrate-2 (IRS-2) levels and activated the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway. Interestingly, it also modulated the expression of peroxisome proliferator-activated receptor γ (PPARγ) and pancreatic and duodenal homeobox 1 (PDX-1). Our findings showed that A. annulatum and its bioactive compounds are capable of improving insulin secretion by pancreatic β-cells. This suggests that A. annulatum can be used as a therapeutic agent to treat diabetes.

scholarly journals Formation of βTC3 and MIN6 Pseudoislets Changes the Expression Pattern of Gpr40, Gpr55, and Gpr119 Receptors and Improves Lysophosphatidylcholines-Potentiated Glucose-Stimulated Insulin Secretion

Cells ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 2062
Author(s):  
Anna Drzazga ◽  
Eliza Cichońska ◽  
Maria Koziołkiewicz ◽  
Edyta Gendaszewska-Darmach
Keyword(s):  
Endothelial Cells ◽  
Insulin Secretion ◽  
Expression Pattern ◽  
Cell Model ◽  
Spatial Arrangement ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Altered Expression ◽  
Glucose Stimulated Insulin Secretion

The impaired spatial arrangement and connections between cells creating islets of Langerhans as well as altered expression of G protein-coupled receptors (GPCRs) often lead to dysfunction of insulin-secreting pancreatic β cells and can significantly contribute to the development of diabetes. Differences in glucose-stimulated insulin secretion (GSIS) are noticeable not only in diabetic individuals but also in model pancreatic β cells, e.g., βTC3 and MIN6 β cell lines with impaired and normal insulin secretion, respectively. Now, we compare the ability of GPCR agonists (lysophosphatidylcholines bearing fatty acid chains of different lengths) to potentiate GSIS in βTC3 and MIN6 β cell models, cultured as adherent monolayers and in a form of pseudoislets (PIs) with pancreatic MS1 endothelial cells. Our aim was also to investigate differences in expression of the GPCRs responsive to LPCs in these experimental systems. Aggregation of β cells into islet-like structures greatly enhanced the expression of Gpr40, Gpr55, and Gpr119 receptors. In contrast, the co-culture of βTC3 cells with endothelial cells converted the GPCR expression pattern closer to the pattern observed in MIN6 cells. Additionally, the efficiencies of various LPC species in βTC3-MS1 PIs also shifted toward the MIN6 cell model.

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