2082-P: A Negative Regulatory Role of Insulinoma Beta Cell–Derived Exosomes in Glucose-Stimulated Insulin Secretion of Beta-Cells by Upregulating Exosomal MicroRNAs-Associated Signals

Inhibition of insulin-degrading enzyme (IDE) has been proposed as a possible therapeutic target for type 2 diabetes treatment. However, many aspects of IDE's role in glucose homeostasis need to be clarified. In light of this, new preclinical models are required to elucidate the specific role of this protease in the main tissues related to insulin handling. To address this, here we generated a novel line of mice with selective deletion of the Ide gene within pancreatic beta-cells, B-IDE-KO mice, which have been characterized in terms of multiple metabolic end points, including blood glucose, plasma C-peptide, and intraperitoneal glucose tolerance tests. In addition, glucose-stimulated insulin secretion was quantified in isolated pancreatic islets and beta-cell differentiation markers and insulin secretion machinery were characterized by RT-PCR. Additionally, IDE was genetically and pharmacologically inhibited in INS-1E cells and rodent and human islets, and insulin secretion was assessed. Our results show that, in vivo, life-long deletion of IDE from beta-cells results in increased plasma C-peptide levels. Corroborating these findings, isolated islets from B-IDE-KO mice showed constitutive insulin secretion, a hallmark of beta-cell functional immaturity. Unexpectedly, we found 60% increase in Glut1 (a high-affinity/low- Km glucose transporter), suggesting increased glucose transport into the beta-cell at low glucose levels, which may be related to constitutive insulin secretion. In parallel, IDE inhibition in INS-1E and islet cells resulted in impaired insulin secretion after glucose challenge. We conclude that IDE is required for glucose-stimulated insulin secretion. When IDE is inhibited, insulin secretion machinery is perturbed, causing either inhibition of insulin release at high glucose concentrations or constitutive secretion.

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Microtubules and beta cell function: effect of colchicine on microtubules and insulin secretion in vitro by mouse beta cells.

The Journal of Cell Biology ◽

10.1083/jcb.92.2.425 ◽

1982 ◽

Vol 92 (2) ◽

pp. 425-434 ◽

Cited By ~ 55

Author(s):

A E Boyd ◽

W E Bolton ◽

B R Brinkley

Keyword(s):

Insulin Secretion ◽

Beta Cell ◽

Beta Cells ◽

Calcium Concentration ◽

Cell Function ◽

Cultured Cells ◽

Immediate Release ◽

Prolonged Release ◽

Microtubule Network

A monolayer culture system was developed to study the role of microtubules in insulin secretion. Cultured cells were obtained to study the role of microtubules in insulin secretion. Cultured cells were obtained by enzymatic digestion of pancreases from C57BL-KsJ mice 6-12 wk of age. On day 4 of culture, the medium was changed, control or treatment medium added, and frequent samples were removed for insulin assay. Microtubules and beta cells were identified by indirect immunofluorescence with monospecific antibodies to tubulin and insulin. An extensive microtubule network radiates from the perinuclear region of the beta cell to the plasma membrane. Although alterations in the calcium concentration of the medium did not affect the microtubule pattern, the absence of calcium or glucose in the medium inhibited insulin secretion (P less than 0.001). Optimum insulin release occurred at a calcium concentration of 2.5 mM. Colchicine, in concentrations of 10(-10) M, did not affect the microtubule immunofluorescent pattern, whereas concentrations of 1 and 5 x 10(-7) M decreased the number of microtubules, and microtubules could not be identified in cultures treated with 10(-6) M colchicine for 2 h. After a 2-h preincubation, the prolonged release of insulin at either 2.0 or 4.5 mg/ml of glucose was decreased by 10(-6) M colchicine (P less than 0.02). The immediate release of insulin was similar to that in control plates and occurred in cultures with no identifiable microtubules. Microtubules and insulin secretion were not altered by 10(-6) M lumicolchicine and prolonged insulin secretion recovered 24 h after removal of colchicine. These studies show that the microtubules facilitate sustained secretion of insulin but are not required for the immediate release of the hormone. Alterations in the extracellular calcium concentration which play an essential role in insulin secretion do not alter the microtubule pattern in the beta cell.

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Inherent Beta Cell Dysfunction Contributes to Autoimmune Susceptibility

Biomolecules ◽

10.3390/biom11040512 ◽

2021 ◽

Vol 11 (4) ◽

pp. 512

Author(s):

Yong Kyung Kim ◽

Lori Sussel ◽

Howard W. Davidson

Keyword(s):

Insulin Secretion ◽

Beta Cell ◽

Beta Cells ◽

Pancreatic Beta Cell ◽

Cell Loss ◽

The Body ◽

Beta Cell Dysfunction ◽

Metabolic Characteristics ◽

Cell Dysfunction ◽

Glucose Stimulated Insulin Secretion

The pancreatic beta cell is a highly specialized cell type whose primary function is to secrete insulin in response to nutrients to maintain glucose homeostasis in the body. As such, the beta cell has developed unique metabolic characteristics to achieve functionality; in healthy beta cells, the majority of glucose-derived carbons are oxidized and enter the mitochondria in the form of pyruvate. The pyruvate is subsequently metabolized to induce mitochondrial ATP and trigger the downstream insulin secretion response. Thus, in beta cells, mitochondria play a pivotal role in regulating glucose stimulated insulin secretion (GSIS). In type 2 diabetes (T2D), mitochondrial impairment has been shown to play an important role in beta cell dysfunction and loss. In type 1 diabetes (T1D), autoimmunity is the primary trigger of beta cell loss; however, there is accumulating evidence that intrinsic mitochondrial defects could contribute to beta cell susceptibility during proinflammatory conditions. Furthermore, there is speculation that dysfunctional mitochondrial responses could contribute to the formation of autoantigens. In this review, we provide an overview of mitochondrial function in the beta cells, and discuss potential mechanisms by which mitochondrial dysfunction may contribute to T1D pathogenesis.

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Role of Insulin in Glucose-Stimulated Insulin Secretion in Beta Cells

Current Diabetes Reviews ◽

10.2174/157339905774574301 ◽

2005 ◽

Vol 1 (3) ◽

pp. 309-330 ◽

Cited By ~ 6

Author(s):

H. Goren

Keyword(s):

Insulin Secretion ◽

Beta Cells ◽

Glucose Stimulated Insulin Secretion

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NMDA receptor inhibition increases, synchronizes, and stabilizes the collective pancreatic beta cell activity: Insights through multilayer network analysis

PLoS Computational Biology ◽

10.1371/journal.pcbi.1009002 ◽

2021 ◽

Vol 17 (5) ◽

pp. e1009002

Author(s):

Marko Šterk ◽

Lidija Križančić Bombek ◽

Maša Skelin Klemen ◽

Marjan Slak Rupnik ◽

Marko Marhl ◽

...

Keyword(s):

Insulin Secretion ◽

Nmda Receptor ◽

Beta Cell ◽

Nmda Receptors ◽

Beta Cells ◽

Cell Activity ◽

Calcium Waves ◽

Multilayer Network ◽

Receptor Inhibition

NMDA receptors promote repolarization in pancreatic beta cells and thereby reduce glucose-stimulated insulin secretion. Therefore, NMDA receptors are a potential therapeutic target for diabetes. While the mechanism of NMDA receptor inhibition in beta cells is rather well understood at the molecular level, its possible effects on the collective cellular activity have not been addressed to date, even though proper insulin secretion patterns result from well-synchronized beta cell behavior. The latter is enabled by strong intercellular connectivity, which governs propagating calcium waves across the islets and makes the heterogeneous beta cell population work in synchrony. Since a disrupted collective activity is an important and possibly early contributor to impaired insulin secretion and glucose intolerance, it is of utmost importance to understand possible effects of NMDA receptor inhibition on beta cell functional connectivity. To address this issue, we combined confocal functional multicellular calcium imaging in mouse tissue slices with network science approaches. Our results revealed that NMDA receptor inhibition increases, synchronizes, and stabilizes beta cell activity without affecting the velocity or size of calcium waves. To explore intercellular interactions more precisely, we made use of the multilayer network formalism by regarding each calcium wave as an individual network layer, with weighted directed connections portraying the intercellular propagation. NMDA receptor inhibition stabilized both the role of wave initiators and the course of waves. The findings obtained with the experimental antagonist of NMDA receptors, MK-801, were additionally validated with dextrorphan, the active metabolite of the approved drug dextromethorphan, as well as with experiments on NMDA receptor KO mice. In sum, our results provide additional and new evidence for a possible role of NMDA receptor inhibition in treatment of type 2 diabetes and introduce the multilayer network paradigm as a general strategy to examine effects of drugs on connectivity in multicellular systems.

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In vivo phosphoproteomics reveals pathogenic signaling changes in diabetic islets

10.1101/439638 ◽

2018 ◽

Author(s):

Francesca Sacco ◽

Anett Seelig ◽

Sean J. Humphrey ◽

Natalie Krahmer ◽

Francesco Volta ◽

...

Keyword(s):

Type 2 Diabetes ◽

Insulin Secretion ◽

Beta Cells ◽

Pancreatic Beta Cells ◽

Drug Targets ◽

High Sensitivity ◽

Glucose Stimulated Insulin Secretion

SUMMARYProgressive decline of pancreatic beta cells function is key to the pathogenesis of type 2 diabetes. Protein phosphorylation is the central mechanism controlling glucose-stimulated insulin secretion in beta cells. However, if and how signaling networks are remodeled in diabetic isletsin vivoremain unknowns. Here we applied high-sensitivity mass spectrometry-based proteomics and quantified the levels of about 6,500 proteins and 13,000 phosphopeptides in islets of obese diabetic mice and matched controls. This highlighted drastic remodeling of key kinase hubs and signaling pathways. We integrated our phosphoproteomic dataset with a literature-derived signaling network, which revealed a crucial and conserved role of GSK3 kinase in the control of the beta cells-specific transcription factor PDX1 and insulin secretion, which we functionally verified. Our resource will enable the community to investigate potential mechanisms and drug targets in type 2 diabetes.

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Stable overexpression of the glucose-6-phosphatase catalytic subunit attenuates glucose sensitivity of insulin secretion from a mouse pancreatic beta-cell line

Journal of Endocrinology ◽

10.1677/joe.0.1640307 ◽

2000 ◽

Vol 164 (3) ◽

pp. 307-314 ◽

Cited By ~ 14

Author(s):

K Iizuka ◽

H Nakajima ◽

A Ono ◽

K Okita ◽

J Miyazaki ◽

...

Keyword(s):

Insulin Secretion ◽

Beta Cell ◽

Cell Line ◽

Beta Cells ◽

Pancreatic Beta Cells ◽

Glucose Sensor ◽

Pancreatic Beta Cell ◽

Catalytic Subunit ◽

Beta Cell Line ◽

Glucose Stimulated Insulin Secretion

Glucose-6-phosphatase (G-6-Pase) hydrolyzes glucose-6-phosphate to glucose, reciprocal with the so-called glucose sensor, glucokinase, in pancreatic beta cells. To study the role of G-6-Pase in glucose-stimulated insulin secretion from beta cells, we have introduced rat G-6-Pase catalytic subunit cDNA and have established permanent clones with 3-, 7- and 24-fold G-6-Pase activity of the mouse beta-cell line, MIN6. In these clones, glucose usage and ATP production in the presence of 5.5 or 25 mM glucose were reduced, and glucose-stimulated insulin secretion was decreased in proportion to the increased G-6-Pase activity. In addition, insulin secretory capacity in response to d-fructose and pyruvate was unchanged; however, 25 mM glucose-stimulated insulin secretion and intracellular calcium response were completely inhibited. In the clone with 24-fold G-6-Pase activity, changes in intracellular NAD(P)H autofluorescence in response to 25 mM glucose were reduced, but the changes with 20 mM fructose and 20 mM pyruvate were not altered. Stable overexpression of G-6-Pase in beta cells resulted in attenuation of the overall glucose-stimulated metabolic responses corresponding to the degree of overexpression. This particular experimental manipulation shows that the possibility exists of modulating glucose-stimulated insulin release by thoroughly altering glucose cycling at the glucokinase/G-6-Pase step.

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Paired box 6 programs essential exocytotic genes in the regulation of glucose-stimulated insulin secretion and glucose homeostasis

Science Translational Medicine ◽

10.1126/scitranslmed.abb1038 ◽

2021 ◽

Vol 13 (600) ◽

pp. eabb1038

Author(s):

Wing Yan So ◽

Wai Nam Liu ◽

Adrian Kee Keong Teo ◽

Guy A. Rutter ◽

Weiping Han

Keyword(s):

Insulin Secretion ◽

Beta Cell ◽

Pancreatic Islets ◽

Beta Cells ◽

Pancreatic Beta Cells ◽

Cell Function ◽

Pancreatic Beta Cell ◽

Beta Cell Line ◽

Pathophysiological Role ◽

Glucose Stimulated Insulin Secretion

The paired box 6 (PAX6) transcription factor is crucial for normal pancreatic islet development and function. Heterozygous mutations of PAX6 are associated with impaired insulin secretion and early-onset diabetes mellitus in humans. However, the molecular mechanism of PAX6 in controlling insulin secretion in human beta cells and its pathophysiological role in type 2 diabetes (T2D) remain ambiguous. We investigated the molecular pathway of PAX6 in the regulation of insulin secretion and the potential therapeutic value of PAX6 in T2D by using human pancreatic beta cell line EndoC-βH1, the db/db mouse model, and primary human pancreatic islets. Through loss- and gain-of-function approaches, we uncovered a mechanism by which PAX6 modulates glucose-stimulated insulin secretion (GSIS) through a cAMP response element–binding protein (CREB)/Munc18-1/2 pathway. Moreover, under diabetic conditions, beta cells and pancreatic islets displayed dampened PAX6/CREB/Munc18-1/2 pathway activity and impaired GSIS, which were reversed by PAX6 replenishment. Adeno-associated virus–mediated PAX6 overexpression in db/db mouse pancreatic beta cells led to a sustained amelioration of glycemic perturbation in vivo but did not affect insulin resistance. Our study highlights the pathophysiological role of PAX6 in T2D-associated beta cell dysfunction in humans and suggests the potential of PAX6 gene transfer in preserving and restoring beta cell function.

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The Role of Fatty Acid Signaling in Islet Beta-Cell Adaptation to Normal Pregnancy

Frontiers in Endocrinology ◽

10.3389/fendo.2021.799081 ◽

2022 ◽

Vol 12 ◽

Author(s):

Jee-Hye Kim ◽

Viviane Delghingaro-Augusto ◽

Jeng Yie Chan ◽

D. Ross Laybutt ◽

Joseph Proietto ◽

...

Keyword(s):

Insulin Secretion ◽

Fatty Acid ◽

Beta Cell ◽

Liver Glycogen ◽

Oral Glucose ◽

Pregnant Rat ◽

Islet Beta Cell ◽

Glucose Stimulated Insulin Secretion ◽

Beta Cell Adaptation

BackgroundMaintenance of a normal fetal nutrient supply requires major adaptations in maternal metabolic physiology, including of the islet beta-cell. The role of lipid signaling processes in the mechanisms of islet beta-cell adaptation to pregnancy has been minimally investigated.ObjectiveTo determine the effects of pregnancy on islet fatty acid (FA) metabolic partitioning and FA augmentation of glucose-stimulated insulin secretion (GSIS).MethodsAge matched virgin, early pregnant (gestational day-11, G11) and late pregnant (G19) Sprague-Dawley rats were studied. Fasted and fed state biochemistry, oral glucose tolerance tests (OGTT), and fasted and post-OGTT liver glycogen, were determined to assess in vivo metabolic characteristics. In isolated islets, FA (BSA-bound palmitate 0.25 mmol/l) augmentation of GSIS, FA partitioning into esterification and oxidation processes using metabolic tracer techniques, lipolysis by glycerol release, triacylglycerols (TG) content, and the expression of key beta-cell genes were determined.ResultsPlasma glucose in pregnancy was lower, including during the OGTT (glucose area under the curve 0-120 min (AUC0-120); 655±24 versus 849±13 mmol.l-1.min; G19 vs virgin; P<0.0001), with plasma insulin concentrations equivalent to those of virgin rats (insulin AUC0-120; 97±7 versus 83±7 ng.ml-1.min; G19 vs virgin; not significant). Liver glycogen was depleted in fasted G19 rats with full recovery after oral glucose. Serum TG increased during pregnancy (4.4±0.4, 6.7±0.5; 17.1±1.5 mmol/l; virgin, G11, G19, P<0.0001), and islet TG content decreased (147±42, 172±27, 73±13 ng/µg protein; virgin, G11, G19; P<0.01). GSIS in isolated islets was increased in G19 compared to virgin rats, and this effect was augmented in the presence of FA. FA esterification into phospholipids, monoacylglycerols and TG were increased, whereas FA oxidation was reduced, in islets of pregnant compared to virgin rats, with variable effects on lipolysis dependent on gestational age. Expression of Ppargc1a, a key regulator of mitochondrial metabolism, was reduced by 51% in G11 and 64% in G19 pregnant rat islets compared to virgin rat islets (P<0.001).ConclusionA lowered set-point for islet and hepatic glucose homeostasis in the pregnant rat has been confirmed. Islet adaptation to pregnancy includes increased FA esterification, reduced FA oxidation, and enhanced FA augmentation of glucose-stimulated insulin secretion.

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