Glucose-stimulated insulin secretion is not obligatorily linked to an increase in O2 consumption in βHC9 cells

1998 ◽  
Vol 275 (6) ◽  
pp. E1100-E1106 ◽  
Author(s):  
Klearchos K. Papas ◽  
Mary Ann C. Jarema
Keyword(s):  
Oxygen Consumption ◽  
Insulin Secretion ◽  
Nutrient Starvation ◽  
O2 Consumption ◽  
Β Cells ◽  
Β Cell ◽  
Glucose Stimulation ◽  
Cell Hyperplasia ◽  
Mouse Pancreatic Islets ◽  
Glucose Stimulated Insulin Secretion

We investigated the effects of glucose on the rates of oxygen consumption (OCR) and insulin secretion (ISR) by βHC9 cells derived from mouse pancreatic islets with β-cell hyperplasia. Our results demonstrate that the OCR by βHC9 cells incubated in nutrient-rich DMEM is unaffected by glucose (0–25 mM), is dissociated from the ISR (which increases with the addition of glucose), and is always higher than that measured in PBS. Glucose (25 mM) increases both the OCR and ISR when added to nutrient-free PBS. On the basis of results presented here, we suggest that, contrary to the current consensus, the observed increases in the OCR by β-cells upon addition of glucose to nutrient-free buffers may be unrelated to the process of glucose-stimulated insulin secretion (GSIS) and, instead, related to nutrient starvation. We believe that a reevaluation of the implication of changes in OCR upon glucose stimulation in the process of GSIS is warranted and that OCR and ISR measurements should be performed in more physiological media to avoid nutrient starvation artifacts.

scholarly journals Delineation of glutamate pathways and secretory responses in pancreatic islets with β-cell–specific abrogation of the glutamate dehydrogenase

2012 ◽  
Vol 23 (19) ◽  
pp. 3851-3862 ◽  
Author(s):  
Laurène Vetterli ◽  
Stefania Carobbio ◽  
Shirin Pournourmohammadi ◽  
Rafael Martin-del-Rio ◽  
Dorte M. Skytt ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glutamate Dehydrogenase ◽  
Secretory Response ◽  
Β Cells ◽  
Β Cell ◽  
Glucose Stimulation ◽  
Knockout Mouse Model ◽  
Glucose Stimulated Insulin Secretion ◽  
Amplifying Pathway

In pancreatic β-cells, glutamate dehydrogenase (GDH) modulates insulin secretion, although its function regarding specific secretagogues is unclear. This study investigated the role of GDH using a β-cell–specific GDH knockout mouse model, called βGlud1−/−. The absence of GDH in islets isolated from βGlud1–/– mice resulted in abrogation of insulin release evoked by glutamine combined with 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid or l-leucine. Reintroduction of GDH in βGlud1–/– islets fully restored the secretory response. Regarding glucose stimulation, insulin secretion in islets isolated from βGlud1–/– mice exhibited half of the response measured in control islets. The amplifying pathway, tested at stimulatory glucose concentrations in the presence of KCl and diazoxide, was markedly inhibited in βGlud1–/– islets. On glucose stimulation, net synthesis of glutamate from α-ketoglutarate was impaired in GDH-deficient islets. Accordingly, glucose-induced elevation of glutamate levels observed in control islets was absent in βGlud1–/– islets. Parallel biochemical pathways, namely alanine and aspartate aminotransferases, could not compensate for the lack of GDH. However, the secretory response to glucose was fully restored by the provision of cellular glutamate when βGlud1–/– islets were exposed to dimethyl glutamate. This shows that permissive levels of glutamate are required for the full development of glucose-stimulated insulin secretion and that GDH plays an indispensable role in this process.

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 Glucagon Potentiates Insulin Secretion Via β-Cell GCGR at Physiological Concentrations of Glucose

Cells ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 2495
Author(s):  
Yulin Zhang ◽  
Chengsheng Han ◽  
Wenzhen Zhu ◽  
Guoyi Yang ◽  
Xiaohong Peng ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
High Glucose ◽  
Critical Role ◽  
Β Cells ◽  
Β Cell ◽  
Glucose Stimulation ◽  
Primary Mouse ◽  
High Concentrations ◽  
Glucose Stimulated Insulin Secretion ◽  
Glucagon Receptors

Incretin-potentiated glucose-stimulated insulin secretion (GSIS) is critical to maintaining euglycemia, of which GLP-1 receptor (GLP-1R) on β-cells plays an indispensable role. Recently, α-cell-derived glucagon but not intestine-derived GLP-1 has been proposed as the critical hormone that potentiates GSIS via GLP-1R. However, the function of glucagon receptors (GCGR) on β-cells remains elusive. Here, using GCGR or GLP-1R antagonists, in combination with glucagon, to treat single β-cells, α-β cell clusters and isolated islets, we found that glucagon potentiates insulin secretion via β-cell GCGR at physiological but not high concentrations of glucose. Furthermore, we transfected primary mouse β-cells with RAB-ICUE (a genetically encoded cAMP fluorescence indicator) to monitor cAMP level after glucose stimulation and GCGR activation. Using specific inhibitors of different adenylyl cyclase (AC) family members, we revealed that high glucose concentration or GCGR activation independently evoked cAMP elevation via AC5 in β-cells, thus high glucose stimulation bypassed GCGR in promoting insulin secretion. Additionally, we generated β-cell-specific GCGR knockout mice which glucose intolerance was more severe when fed a high-fat diet (HFD). We further found that β-cell GCGR activation promoted GSIS more than GLP-1R in HFD, indicating the critical role of GCGR in maintaining glucose homeostasis during nutrient overload.

scholarly journals Ontology of the apelinergic system in mouse pancreas during pregnancy and relationship with β-cell mass

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Brenda Strutt ◽  
Sandra Szlapinski ◽  
Thineesha Gnaneswaran ◽  
Sarah Donegan ◽  
Jessica Hill ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Insulin Secretion ◽  
Glucose Transporter ◽  
Cell Mass ◽  
Elevated Serum ◽  
Pancreatic Β Cell ◽  
Β Cells ◽  
Β Cell ◽  
Glucose Transporter 2 ◽  
Glucose Stimulated Insulin Secretion

AbstractThe apelin receptor (Aplnr) and its ligands, Apelin and Apela, contribute to metabolic control. The insulin resistance associated with pregnancy is accommodated by an expansion of pancreatic β-cell mass (BCM) and increased insulin secretion, involving the proliferation of insulin-expressing, glucose transporter 2-low (Ins+Glut2LO) progenitor cells. We examined changes in the apelinergic system during normal mouse pregnancy and in pregnancies complicated by glucose intolerance with reduced BCM. Expression of Aplnr, Apelin and Apela was quantified in Ins+Glut2LO cells isolated from mouse pancreata and found to be significantly higher than in mature β-cells by DNA microarray and qPCR. Apelin was localized to most β-cells by immunohistochemistry although Aplnr was predominantly associated with Ins+Glut2LO cells. Aplnr-staining cells increased three- to four-fold during pregnancy being maximal at gestational days (GD) 9–12 but were significantly reduced in glucose intolerant mice. Apelin-13 increased β-cell proliferation in isolated mouse islets and INS1E cells, but not glucose-stimulated insulin secretion. Glucose intolerant pregnant mice had significantly elevated serum Apelin levels at GD 9 associated with an increased presence of placental IL-6. Placental expression of the apelinergic axis remained unaltered, however. Results show that the apelinergic system is highly expressed in pancreatic β-cell progenitors and may contribute to β-cell proliferation in pregnancy.

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 Inhibition of Forkhead Box O1 Protects Pancreatic β-Cells against Dexamethasone-Induced Dysfunction

Endocrinology ◽  
2009 ◽  
Vol 150 (9) ◽  
pp. 4065-4073 ◽  
Author(s):  
Xiongfei Zhang ◽  
Wei Yong ◽  
Jinghuan Lv ◽  
Yunxia Zhu ◽  
Jingjing Zhang ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Cell Types ◽  
Pancreatic Β Cell ◽  
Rinm5f Cells ◽  
Β Cells ◽  
Β Cell ◽  
Rat Islets ◽  
Cell Dysfunction ◽  
Forkhead Box ◽  
Glucose Stimulated Insulin Secretion

Abstract Forkhead Box O1 (FoxO1) is a key transcription regulator of insulin/IGF-I signaling pathway, and its activity can be increased by dexamethasone (DEX) in several cell types. However, the role of FoxO1 in DEX-induced pancreatic β-cell dysfunction has not been fully understood. Therefore, in this study, we investigated whether FoxO1 could mediate DEX-induced β-cell dysfunction and the possible underlying mechanisms in pancreatic β-cell line RINm5F cells and primary rat islet. We found that DEX markedly increased FoxO1 mRNA and protein expression and decreased FoxO1 phosphorylation through the Akt pathway, which resulted in an increase in active FoxO1 in RINm5F cells and isolated rat islets. Activated FoxO1 subsequently inhibited pancreatic duodenal homeobox-1 expression and induced nuclear exclusion of pancreatic duodenal homeobox-1. Knockdown of FoxO1 by RNA interference restored the expression of pancreatic duodenal homeobox-1 and prevented DEX-induced dysfunction of glucose-stimulated insulin secretion in rat islets. Together, the results of present study demonstrate that FoxO1 is integrally involved in DEX-induced inhibition of pancreatic duodenal homeobox-1 and glucose-stimulated insulin secretion dysfunction in pancreatic islet β-cells. Inhibition of FoxO1 can effectively protect β-cells against DEX-induced dysfunction.

scholarly journals Glucose regulates microtubule disassembly and the dose of insulin secretion via tau phosphorylation

2020 ◽  
Author(s):  
Ada Admin ◽  
Kung-Hsien Ho ◽  
Xiaodun Yang ◽  
Anna B. Osipovich ◽  
Over Cabrera ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
High Glucose ◽  
Tau Phosphorylation ◽  
Β Cells ◽  
Glucose Stimulation ◽  
Microtubule Network ◽  
Mouse Islet ◽  
Protein Tau ◽  
Basal Insulin Secretion ◽  
Glucose Stimulated Insulin Secretion

The microtubule cytoskeleton of pancreatic islet β-cells regulates glucose-stimulated insulin secretion (GSIS). We have reported that the microtubule-mediated movement of insulin vesicles away from the plasma membrane limits insulin secretion. High glucose-induced remodeling of microtubule network facilitates robust GSIS. This remodeling involves disassembly of old microtubules and nucleation of new microtubules. Here, we examine the mechanisms whereby glucose stimulation decreases microtubule lifetimes in β-cells. Using real-time imaging of photoconverted microtubules, we demonstrate that high levels of glucose induce rapid microtubule disassembly preferentially in the periphery of individual β-cells, and this process is mediated by the phosphorylation of microtubule-associated protein tau. Specifically, high glucose induces tau hyper-phosphorylation via glucose-responsive kinases GSK3, PKA, PKC, and CDK5. This causes dissociation of tau from and subsequent destabilization of microtubules. Consequently, tau-knockdown in mouse islet β-cells facilitates microtubule turnover, causing increased basal insulin secretion, depleting insulin vesicles from the cytoplasm, and impairing GSIS. More importantly, tau-knockdown uncouples microtubule destabilization from glucose stimulation. These findings suggest that tau suppresses peripheral microtubules turning-over to restrict insulin over-secretion at basal conditions and preserve the insulin pool that can be released in following stimulation; high glucose promotes tau phosphorylation to enhance microtubule disassembly to acutely enhance GSIS.

scholarly journals Microtubules and Gαo-signaling independently regulate the preferential secretion of newly synthesized insulin granules in pancreatic islet β cells

2020 ◽  
Author(s):  
Ruiying Hu ◽  
Xiaodong Zhu ◽  
Mingyang Yuan ◽  
Kung-Hsien Ho ◽  
Irina Kaverina ◽  
...  
Keyword(s):  
Pancreatic Islet ◽  
Β Cells ◽  
Β Cell ◽  
Glucose Stimulation ◽  
Potential Models ◽  
Insulin Granules ◽  
High Insulin ◽  
Underlying Mechanisms ◽  
Glucose Stimulated Insulin Secretion

AbstractFor sustainable function, each pancreatic islet β cell maintains thousands of insulin granules (IGs) at all times. Glucose stimulation induces the secretion of a small portion of these IGs and simultaneously triggers IG biosynthesis to sustain this stock. The failure of these processes, often induced by sustained high-insulin output, results in type 2 diabetes. Intriguingly, newly synthesized IGs are more likely secreted during glucose-stimulated insulin secretion. The older IGs tend to lose releasability and be degraded, which represents a futile metabolic load that can sensitize β cells to workload-induced dysfunction and even death. Here, we examine the factor(s) that allows the preferential secretion of younger IGs. We show that β cells without either microtubules (MTs) or Gαo signaling secrete a bigger portion of older IGs, which is associated with increased IG docking on plasma membrane. Yet Gαo inactivation does not alter the β-cell MT network. These findings suggest that Gαo and MT regulate the preferential release of newer IGs via parallel pathways and provide two potential models to further explore the underlying mechanisms and physiological significance of this regulation in functional β cells.

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