Increased expression of GAD65 and GABA in pancreatic  β-cells impairs 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.

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A Systematic Review of Beta Cell Function in Adults of Black African Ethnicity

Journal of Diabetes Research ◽

10.1155/2019/7891359 ◽

2019 ◽

Vol 2019 ◽

pp. 1-17 ◽

Cited By ~ 1

Author(s):

M. Ladwa ◽

O. Hakim ◽

S. A. Amiel ◽

L. M. Goff

Keyword(s):

Insulin Secretion ◽

Glucose Tolerance ◽

Beta Cell ◽

Beta Cell Function ◽

Cell Function ◽

Normal Glucose Tolerance ◽

Qualitative Synthesis ◽

Intravenous Glucose ◽

Black African

Background. Understanding ethnic differences in beta cell function has important implications for preventative and therapeutic strategies in populations at high risk of type 2 diabetes (T2D). The existing literature, largely drawn from work in children and adolescents, suggests that beta cell function in black African (BA) populations is upregulated when compared to white Europeans (WE). Methods. A systematic literature search was undertaken in June 2018 to identify comparative studies of beta cell function between adults (>age 18 years) of indigenous/diasporic BA and WE ethnicity. All categories of glucose tolerance and all methodologies of assessing beta cell function in vivo were included. Results. 41 studies were identified for inclusion into a qualitative synthesis. The majority were studies in African American populations (n=30) with normal glucose tolerance (NGT)/nondiabetes (n=25), using intravenous glucose stimulation techniques (n=27). There were fewer studies in populations defined as only impaired fasting glucose/impaired glucose tolerance (IFG/IGT) (n=3) or only T2D (n=3). Although BA broadly exhibited greater peripheral insulin responses than WE, the relatively small number of studies which measured C-peptide to differentiate between beta cell insulin secretion and hepatic insulin extraction (n=14) had highly variable findings. In exclusively IGT or T2D cohorts, beta cell insulin secretion was found to be lower in BA compared to WE. Conclusions. There is inconsistent evidence for upregulated beta cell function in BA adults, and they may in fact exhibit greater deficits in insulin secretory function as glucose intolerance develops.

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

Cellular Physiology and Biochemistry ◽

10.1159/000373999 ◽

2015 ◽

Vol 35 (5) ◽

pp. 1892-1904 ◽

Cited By ~ 68

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.

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Inhibition of Small Maf Function in Pancreatic β-Cells Improves Glucose Tolerance Through the Enhancement of Insulin Gene Transcription and Insulin Secretion

Endocrinology ◽

10.1210/en.2014-1906 ◽

2015 ◽

Vol 156 (10) ◽

pp. 3570-3580 ◽

Cited By ~ 9

Author(s):

Hiroshi Nomoto ◽

Takuma Kondo ◽

Hideaki Miyoshi ◽

Akinobu Nakamura ◽

Yoko Hida ◽

...

Keyword(s):

Insulin Secretion ◽

Glucose Tolerance ◽

High Fat Diet ◽

Cell Function ◽

High Fat ◽

Β Cells ◽

Β Cell ◽

Β Cell Function

The large-Maf transcription factor v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA) has been found to be crucial for insulin transcription and synthesis and for pancreatic β-cell function and maturation. However, insights about the effects of small Maf factors on β-cells are limited. Our goal was to elucidate the function of small-Maf factors on β-cells using an animal model of endogenous small-Maf dysfunction. Transgenic (Tg) mice with β-cell-specific expression of dominant-negative MafK (DN-MafK) experiments, which can suppress the function of all endogenous small-Mafs, were fed a high-fat diet, and their in vivo phenotypes were evaluated. Phenotypic analysis, glucose tolerance tests, morphologic examination of β-cells, and islet experiments were performed. DN-MafK-expressed MIN6 cells were also used for in vitro analysis. The results showed that DN-MafK expression inhibited endogenous small-Maf binding to insulin promoter while increasing MafA binding. DN-MafK Tg mice under high-fat diet conditions showed improved glucose metabolism compared with control mice via incremental insulin secretion, without causing changes in insulin sensitivity or MafA expression. Moreover, up-regulation of insulin and glucokinase gene expression was observed both in vivo and in vitro under DN-MafK expression. We concluded that endogenous small-Maf factors negatively regulates β-cell function by competing for MafA binding, and thus, the inhibition of small-Maf activity can improve β-cell function.

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PINK1 deficiency in β-cells increases basal insulin secretion and improves glucose tolerance in mice

Open Biology ◽

10.1098/rsob.140051 ◽

2014 ◽

Vol 4 (5) ◽

pp. 140051 ◽

Cited By ~ 24

Author(s):

Emma Deas ◽

Kaisa Piipari ◽

Asif Machhada ◽

Abi Li ◽

Ana Gutierrez-del-Arroyo ◽

...

Keyword(s):

Insulin Secretion ◽

Glucose Tolerance ◽

Cell Function ◽

Glucose Sensing ◽

Β Cells ◽

Β Cell Function ◽

Basal Insulin Secretion ◽

Low Glucose ◽

Induced Apoptosis

The Parkinson's disease (PD) gene, PARK6 , encodes the PTEN-induced putative kinase 1 (PINK1) mitochondrial kinase, which provides protection against oxidative stress-induced apoptosis. Given the link between glucose metabolism, mitochondrial function and insulin secretion in β-cells, and the reported association of PD with type 2 diabetes, we investigated the response of PINK1-deficient β-cells to glucose stimuli to determine whether loss of PINK1 affected their function. We find that loss of PINK1 significantly impairs the ability of mouse pancreatic β-cells (MIN6 cells) and primary intact islets to take up glucose. This was accompanied by higher basal levels of intracellular calcium leading to increased basal levels of insulin secretion under low glucose conditions. Finally, we investigated the effect of PINK1 deficiency in vivo and find that PINK1 knockout mice have improved glucose tolerance. For the first time, these combined results demonstrate that loss of PINK1 function appears to disrupt glucose-sensing leading to enhanced insulin release, which is uncoupled from glucose uptake, and suggest a key role for PINK1 in β-cell function.

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β-Cell-specific ablation of sirtuin 4 does not affect nutrient-stimulated insulin secretion in mice

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00170.2020 ◽

2020 ◽

Vol 319 (4) ◽

pp. E805-E813

Author(s):

Frank K. Huynh ◽

Brett S. Peterson ◽

Kristin A. Anderson ◽

Zhihong Lin ◽

Aeowynn J. Coakley ◽

...

Keyword(s):

Insulin Secretion ◽

Glucose Tolerance ◽

Cell Function ◽

Whole Body ◽

Β Cells ◽

Β Cell ◽

Direct Role ◽

Normal Glucose

Sirtuins are a family of proteins that regulate biological processes such as cellular stress and aging by removing posttranslational modifications (PTMs). We recently identified several novel PTMs that can be removed by sirtuin 4 (SIRT4), which is found in mitochondria. We showed that mice with a global loss of SIRT4 [SIRT4-knockout (KO) mice] developed an increase in glucose- and leucine-stimulated insulin secretion, and this was followed by accelerated age-induced glucose intolerance and insulin resistance. Because whole body SIRT4-KO mice had alterations to nutrient-stimulated insulin secretion, we hypothesized that SIRT4 plays a direct role in regulating pancreatic β-cell function. Thus, we tested whether β-cell-specific ablation of SIRT4 would recapitulate the elevated insulin secretion seen in mice with a global loss of SIRT4. Tamoxifen-inducible β-cell-specific SIRT4-KO mice were generated, and their glucose tolerance and glucose- and leucine-stimulated insulin secretion were measured over time. These mice exhibited normal glucose- and leucine-stimulated insulin secretion and maintained normal glucose tolerance even as they aged. Furthermore, 832/13 β-cells with a CRISPR/Cas9n-mediated loss of SIRT4 did not show any alterations in nutrient-stimulated insulin secretion. Despite the fact that whole body SIRT4-KO mice demonstrated an age-induced increase in glucose- and leucine-stimulated insulin secretion, our current data indicate that the loss of SIRT4 specifically in pancreatic β-cells, both in vivo and in vitro, does not have a significant impact on nutrient-stimulated insulin secretion. These data suggest that SIRT4 controls nutrient-stimulated insulin secretion during aging by acting on tissues external to the β-cell, which warrants further study.

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IL-1β reciprocally regulates chemokine and insulin secretion in pancreatic β-cells via NF-κB

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00153.2015 ◽

2015 ◽

Vol 309 (8) ◽

pp. E715-E726 ◽

Cited By ~ 35

Author(s):

Susan J. Burke ◽

Krisztian Stadler ◽

Danhong Lu ◽

Evanna Gleason ◽

Anna Han ◽

...

Keyword(s):

Nitric Oxide ◽

Insulin Secretion ◽

Transcriptional Activity ◽

Cell Function ◽

Inflammatory Responses ◽

Cell Mass ◽

Negative Regulator ◽

Β Cells ◽

Β Cell ◽

Pancreatic Β Cells

Proinflammatory cytokines impact islet β-cell mass and function by altering the transcriptional activity within pancreatic β-cells, producing increases in intracellular nitric oxide abundance and the synthesis and secretion of immunomodulatory proteins such as chemokines. Herein, we report that IL-1β, a major mediator of inflammatory responses associated with diabetes development, coordinately and reciprocally regulates chemokine and insulin secretion. We discovered that NF-κB controls the increase in chemokine transcription and secretion as well as the decrease in both insulin secretion and proliferation in response to IL-1β. Nitric oxide production, which is markedly elevated in pancreatic β-cells exposed to IL-1β, is a negative regulator of both glucose-stimulated insulin secretion and glucose-induced increases in intracellular calcium levels. By contrast, the IL-1β-mediated production of the chemokines CCL2 and CCL20 was not influenced by either nitric oxide levels or glucose concentration. Instead, the synthesis and secretion of CCL2 and CCL20 in response to IL-1β were dependent on NF-κB transcriptional activity. We conclude that IL-1β-induced transcriptional reprogramming via NF-κB reciprocally regulates chemokine and insulin secretion while also negatively regulating β-cell proliferation. These findings are consistent with NF-κB as a major regulatory node controlling inflammation-associated alterations in islet β-cell function and mass.

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Plasma Secretagogin is Increased in Individuals with Glucose Dysregulation

Experimental and Clinical Endocrinology & Diabetes ◽

10.1055/a-1001-2244 ◽

2019 ◽

Author(s):

Chao Yang ◽

Hua Qu ◽

Xiaolan Zhao ◽

Yingru Hu ◽

Jiayao Xiong ◽

...

Keyword(s):

Insulin Resistance ◽

Insulin Secretion ◽

Glucose Tolerance ◽

Cell Function ◽

Model Assessment ◽

Homeostasis Model Assessment ◽

Β Cells ◽

Β Cell ◽

Β Cell Function ◽

First Phase Insulin Secretion

Abstract Objective Secretagogin, a Ca2+ binding protein, is one of the most abundant proteins in pancreatic β-cells and is critical for maintaining the structural integrity and signaling competence of β-cells. This study seeks to assess the concentrations of plasma secretagogin in participants with prediabetes (pre-DM) and newly diagnosed type 2 diabetes (T2DM) and to explore its relationship to parameters of glucose and lipid metabolism, first-phase insulin secretion, insulin resistance and pancreatic β-cell function. Materials and Methods A total of 126 eligible subjects were divided into three groups: a normal glucose tolerance (NGT, n=45), a pre-DM (n=30), and a T2DM (n=51) group. An intravenous glucose tolerance test (IVGTT) was performed, and clinical and biochemical parameters were measured for all subjects. Results Plasma secretagogin levels were significantly higher in both pre-DM and T2DM patients compared with NGT subjects and were highest in the T2DM group. Correlation analysis showed that plasma secretagogin levels were positively correlated with fasting plasma glucose, postchallenge plasma glucose (2hPG), HbA1c and body mass index (BMI) but were not correlated with waist-hip ratio, blood pressure, lipid profiles, fasting serum insulin, homeostasis model assessment for insulin resistance, homeostasis model assessment for β-cell function and first-phase insulin secretion indicators. Multiple logistic regression analysis revealed that 2hPG and BMI were independent predictors for elevation of plasma secretagogin concentrations. Conclusions Increased circulating secretagogin might be a molecular predictor for early diagnosis of diabetes. Further studies are needed to confirm this finding and explore the role of secretagogin in obesity.

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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

10.2337/figshare.16797871 ◽

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 in vivo 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 Cask 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 Cask 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.

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

International Journal of Molecular Sciences ◽

10.3390/ijms21134668 ◽

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.

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