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Mechanisms of impaired pancreatic ??cell function in high?fat diet?induced obese mice: The role of endoplasmic reticulum stress.

ABSTRACT: The aim of the study was to examine whether there was excessive endoplasmic reticulum stress (ERs) in the islets of high?fat diet (HFD)?induced obese mice, as well as the effects of ERs on ??cell function. Male C57BL/6J mice were fed a HFD for 16 weeks. Pancreatic ??cell function was evaluated using intraperitoneal glucose tolerance and insulin release tests, and via electron microscopy. The expression of activating transcription factor 6 (ATF6) and phosphorylated (p)?eukaryotic initiation factor 2? (eIF2?) were detected via immunofluorescence staining to determine whether exposure to a HFD induced ERs in pancreatic islets. In vitro, ERs was induced by palmitate (PA) in INS?1 cells, and the protein expression of ATF6, and mRNA expression of ATF6 and insulin were examined via western blot and quantitative PCR (qPCR) analyses, respectively. The nuclear localization of ATF6 was examined by immunofluorescence. Finally, small interfering (si)RNA was used to downregulate ATF6 expression in INS?1 cells to further determine whether ATF6 mediated the ERs?induced impairment of insulin gene transcription. After 16 weeks of induction, the obese mice showed impaired glucose tolerance, insulin resistance and hyperinsulinemia. Immunohistochemistry staining showed increased p?eIF2? and ATF6 expression in pancreatic islets in the obesity group compared with the normal group. Electron microscopy indicated that the microstructures and secretory functions of ??cells were impaired. After 24 h of incubation, ATF mRNA and protein expression in the PA group was significantly higher compared with the control group. However, the insulin mRNA expression in the PA group was significantly decreased. Furthermore, qPCR showed that the insulin mRNA expression was significantly increased 24 h after PA treatment in cells transfected with ATF6?siRNA compared with the negative control group. The present suggested shows that ERs?induced activation of ATF6 may play an important role in the development of ??cell dysfunction in obese mice.

SUBMITTER: Yi X

PROVIDER: S-EPMC7115219 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Mechanisms of impaired pancreatic β‑cell function in high‑fat diet‑induced obese mice: The role of endoplasmic reticulum stress.

Yi Xiaoqing X Cai Xuan X Wang Sisi S Xiao Yanfeng Y

Molecular medicine reports 20200305 5

The aim of the study was to examine whether there was excessive endoplasmic reticulum stress (ERs) in the islets of high‑fat diet (HFD)‑induced obese mice, as well as the effects of ERs on β‑cell function. Male C57BL/6J mice were fed a HFD for 16 weeks. Pancreatic β‑cell function was evaluated using intraperitoneal glucose tolerance and insulin release tests, and via electron microscopy. The expression of activating transcription factor 6 (ATF6) and phosphorylated (p)‑eukaryotic initiation facto ...[more]

PMID: 32323766

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Project description:BACKGROUND & AIMS:Disruption to endoplasmic reticulum (ER) calcium homeostasis has been implicated in obesity, however, the ability to longitudinally monitor ER calcium fluctuations has been challenging with prior methodologies. We recently described the development of a Gaussia luciferase (GLuc)-based reporter protein responsive to ER calcium depletion (GLuc-SERCaMP) and investigated the effect of a high fat diet on ER calcium homeostasis. METHODS:A GLuc-based reporter cell line was treated with palmitate, a free fatty acid. Rats intrahepatically injected with GLuc-SERCaMP reporter were fed a cafeteria diet or high fat diet. The liver and plasma were examined for established markers of steatosis and compared to plasma levels of SERCaMP activity. RESULTS:Palmitate induced GLuc-SERCaMP release in vitro, indicating ER calcium depletion. Consumption of a cafeteria diet or high fat pellets correlated with alterations to hepatic ER calcium homeostasis in rats, shown by increased GLuc-SERCaMP release. Access to ad lib high fat pellets also led to a corresponding decrease in microsomal calcium ATPase activity and an increase in markers of hepatic steatosis. In addition to GLuc-SERCaMP, we have also identified endogenous proteins (endogenous SERCaMPs) with a similar response to ER calcium depletion. We demonstrated the release of an endogenous SERCaMP, thought to be a liver esterase, during access to a high fat diet. Attenuation of both GLuc-SERCaMP and endogenous SERCaMP was observed during dantrolene administration. CONCLUSIONS:Here we describe the use of a reporter for in vitro and in vivo models of high fat diet. Our results support the theory that dietary fat intake correlates with a decrease in ER calcium levels in the liver and suggest a high fat diet alters the ER proteome. Lay summary: ER calcium dysregulation was observed in rats fed a cafeteria diet or high fat pellets, with fluctuations in sensor release correlating with fat intake. Attenuation of sensor release, as well as food intake was observed during administration of dantrolene, a drug that stabilizes ER calcium. The study describes a novel technique for liver research and provides insight into cellular processes that may contribute to the pathogenesis of obesity and fatty liver disease.

Project description:Gut dysbiosis induced by high fat diet (HF) or obesity is a predisposing factor to develop diverse inflammatory diseases. Polyphenols and fibers, often eaten together, have been reported to have prebiotic actions, but their health promoting benefits still need to be further characterized and defined. This study attempted to understand how polyphenol rutin and polysaccharide inulin influence intestinal health in mouse model fed a HF (60 kcal%) diet. A total of 48 C57BL/6J mice were divided into four groups fed with a low fat (10% kcal%) control diet (LC), a high fat control diet (HC), a high-fat diet supplemented with rutin (HR), or a high-fat diet supplemented rutin and inulin (HRI) for 20 weeks. Rutin supplementation reduced the HF diet-induced increase of Firmicutes/Bacteroidetes (F/B) ratio, Deferribacteraceae population and plasma lipopolysaccharide (LPS) (p < 0.05); ameliorated inflammation as indicated by the decreased circulating inflammatory cytokines (p < 0.05) and the reduced expressions of intestinal inflammatory mediators (p < 0.05); and attenuated the endoplasmic reticulum (ER) stress in Paneth cells as indicated by the decreased expressions of the ER markers (p < 0.05). Compared to the rutin supplementation alone, the co-administration of rutin with inulin improved the utilization of rutin as indicated by its decreased excretion, suppressed a number of harmful bacteria including Deferribacteraceae and Desulfovibrionaceae (p < 0.05), and further reduced the expression of the key inflammatory cytokine TNF-? and increased the production of butyrate, despite the supplementation of inulin reversed the decrease of body weight induced by rutin supplementation due to an increased food intake. Taken together, our data demonstrated that rutin supplementation ameliorated the inflammatory status and ER stress in Paneth cells under a HF-induced obese state, and its co-administration with inulin further mitigated the inflammatory status, indicating the potential to combine polyphenol rutin and the polysaccharide inulin as a dietary strategy to ameliorate gut dysbiosis, to improve inflammatory status and thereby to reduce medical disorders associated with HF-induced obesity.

Dataset Information

Mechanisms of impaired pancreatic ??cell function in high?fat diet?induced obese mice: The role of endoplasmic reticulum stress.

Publications

Mechanisms of impaired pancreatic β‑cell function in high‑fat diet‑induced obese mice: The role of endoplasmic reticulum stress.

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