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Metabolism-disrupting chemicals (MDCs) are endocrine disruptors with obesogenic and/or diabetogenic action. There is mounting evidence linking exposure to MDCs to increased susceptibility to diabetes. Despite the important role of glucagon in glucose homeostasis, there is little information on the effects of MDCs on α-cells. Furthermore, there are no methods to identify and test MDCs with the potential to alter α-cell viability and function. Here, we used the mouse α-cell line αTC1-9 to evaluate the effects of MDCs on cell viability and glucagon secretion. We tested six chemicals at concentrations within human exposure (from 0.1 pM to 1 µM): bisphenol-A (BPA), tributyltin (TBT), perfluorooctanoic acid (PFOA), triphenylphosphate (TPP), triclosan (TCS), and dichlorodiphenyldichloroethylene (DDE). Using two different approaches, MTT assay and DNA-binding dyes, we observed that BPA and TBT decreased α-cell viability via a mechanism that depends on the activation of estrogen receptors and PPARγ, respectively. These two chemicals induced ROS production, but barely altered the expression of endoplasmic reticulum (ER) stress markers. Although PFOA, TPP, TCS, and DDE did not alter cell viability nor induced ROS generation or ER stress, all four compounds negatively affected glucagon secretion. Our findings suggest that αTC1-9 cells seem to be an appropriate model to test chemicals with metabolism-disrupting activity and that the improvement of the test methods proposed herein could be incorporated into protocols for the screening of diabetogenic MDCs. [ABSTRACT FROM AUTHOR]

Pancreatic α‐cells secrete glucagon to maintain energy homeostasis. Although histamine has an important role in energy homeostasis, the expression and function of histamine receptors in pancreatic α‐cells remains unknown. We found that the histamine H3 receptor (H3R) was expressed in mouse pancreatic α‐cells and αTC1.6 cells, a mouse pancreatic α‐cell line. H3R inhibited glucagon secretion from αTC1.6 cells by inhibiting an increase in intracellular Ca2+ concentration. We also found that immepip, a selective H3R agonist, decreased serum glucagon concentration in rats. These results suggest that H3R modulates glucagon secretion from pancreatic α‐cells.

Glucose-dependent insulinotropic polypepide (GIP) was first extracted from porcine gut mucosa and identified as 'incretin' decades ago. Though early studies have shown the possible GIP isoforms by gel filtration profiles from porcine or human intestinal extracts analyzed by radioimmunoassay (RIA), GIP is currently believed to consist of 42 amino acids (GIP1-42), which are released from gut K-cells and promote postprandial insulin release. In fact, GIP1-42 is usually processed from proGIP by the action of prohormone convertase (PC) 1/3 in the gut. GIP expression is occasionally found in the intestinal glucagon-like peptide-1-secreting cells, suggesting gene expression of both GIP and proglucagon can co-exist in identical cells. However, GIP1-42 immunoreactivity is rarely found in α-cells or other pancreatic endocrine cells of wild-type mammals. Interestingly, we found that short-form GIP1-30 is expressed in and released from pancreatic α-cells and a subset of enteroendocrine cells through proGIP processing by PC2. GIP1-30 is also insulinotropic and modulates glucose-stimulated insulin secretion in a paracrine manner. It is also suggested that short-form GIP1-30 possibly plays a crucial role for the islet development. It has not been well elucidated whether expression of GIP1-30 is modulated in the diabetic status, and whether GIP1-30 might have therapeutic potentials. Our preliminary data suggest that short-form GIP1-30 might play important roles in glucose metabolism. [ABSTRACT FROM AUTHOR]

Pancreatic α-cells secrete glucagon to maintain energy homeostasis. Although histamine has an important role in energy homeostasis, the expression and function of histamine receptors in pancreatic α-cells remains unknown. We found that the histamine H 3 receptor (H 3 R) was expressed in mouse pancreatic α-cells and αTC1.6 cells, a mouse pancreatic α-cell line. H 3 R inhibited glucagon secretion from αTC1.6 cells by inhibiting an increase in intracellular Ca 2+ concentration. We also found that immepip, a selective H 3 R agonist, decreased serum glucagon concentration in rats. These results suggest that H 3 R modulates glucagon secretion from pancreatic α-cells. [ABSTRACT FROM AUTHOR]

Metabolism-disrupting chemicals (MDCs) are endocrine disruptors with obesogenic and/or diabetogenic action. There is mounting evidence linking exposure to MDCs to increased susceptibility to diabetes. Despite the important role of glucagon in glucose homeostasis, there is little information on the effects of MDCs on α-cells. Furthermore, there are no methods to identify and test MDCs with the potential to alter α-cell viability and function. Here, we used the mouse α-cell line αTC1-9 to evaluate the effects of MDCs on cell viability and glucagon secretion. We tested six chemicals at concentrations within human exposure (from 0.1 pM to 1 µM): bisphenol-A (BPA), tributyltin (TBT), perfluorooctanoic acid (PFOA), triphenylphosphate (TPP), triclosan (TCS), and dichlorodiphenyldichloroethylene (DDE). Using two different approaches, MTT assay and DNA-binding dyes, we observed that BPA and TBT decreased α-cell viability via a mechanism that depends on the activation of estrogen receptors and PPARγ, respectively. These two chemicals induced ROS production, but barely altered the expression of endoplasmic reticulum (ER) stress markers. Although PFOA, TPP, TCS, and DDE did not alter cell viability nor induced ROS generation or ER stress, all four compounds negatively affected glucagon secretion. Our findings suggest that αTC1-9 cells seem to be an appropriate model to test chemicals with metabolism-disrupting activity and that the improvement of the test methods proposed herein could be incorporated into protocols for the screening of diabetogenic MDCs.

The glucagon receptor (GCGR) is a potential target for diabetes therapy. Several emerging GCGR antagonism-based therapies are under preclinical and clinical development. However, GCGR antagonism, as well as genetically engineered GCGR deficiency in animal models, are accompanied by α-cell hyperplasia and hyperglucagonemia, which may limit the application of GCGR antagonism. To better understand the physiological changes in α cells following GCGR disruption, we performed single cell sequencing of α cells isolated from control and gcgr -/- (glucagon receptor deficient) zebrafish. Interestingly, beyond the α-cell hyperplasia, we also found that the expression of gcga, gcgb, pnoca, and several glucagon-regulatory transcription factors were dramatically increased in one cluster of gcgr -/- α cells. We further confirmed that glucagon mRNA was upregulated in gcgr -/- animals by in situ hybridization and that glucagon promoter activity was increased in gcgr -/- ;Tg(gcga:GFP) reporter zebrafish. We also demonstrated that gcgr -/- α cells had increased glucagon protein levels and increased granules after GCGR disruption. Intriguingly, the increased mRNA and protein levels could be suppressed by treatment with high-level glucose or knockdown of the pnoca gene. In conclusion, these data demonstrated that GCGR deficiency not only induced α-cell hyperplasia but also increased glucagon expression in α cells, findings which provide more information about physiological changes in α-cells when the GCGR is disrupted., Competing Interests: Conflict of interest The authors declare that they have no conflicts interest with the contents of this article., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Pancreatic α-cells secrete glucagon to maintain energy homeostasis. Although histamine has an important role in energy homeostasis, the expression and function of histamine receptors in pancreatic α-cells remains unknown. We found that the histamine H3 receptor (H3R) was expressed in mouse pancreatic α-cells and αTC1.6 cells, a mouse pancreatic α-cell line. H3R inhibited glucagon secretion from αTC1.6 cells by inhibiting an increase in intracellular Ca(2+) concentration. We also found that immepip, a selective H3R agonist, decreased serum glucagon concentration in rats. These results suggest that H3R modulates glucagon secretion from pancreatic α-cells.