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GRP78 expression inhibits insulin and ER stress-induced SREBP-1c activation and reduces hepatic steatosis in mice.

ABSTRACT: Hepatic steatosis is present in insulin-resistant obese rodents and is concomitant with active lipogenesis. Hepatic lipogenesis depends on the insulin-induced activation of the transcription factor SREBP-1c. Despite prevailing insulin resistance, SREBP-1c is activated in the livers of genetically and diet-induced obese rodents. Recent studies have reported the presence of an ER stress response in the livers of obese ob/ob mice. To assess whether ER stress promotes SREBP-1c activation and thus contributes to lipogenesis, we overexpressed the chaperone glucose-regulated protein 78 (GRP78) in the livers of ob/ob mice using an adenoviral vector. GRP78 overexpression reduced ER stress markers and inhibited SREBP-1c cleavage and the expression of SREBP-1c and SREBP-2 target genes. Furthermore, hepatic triglyceride and cholesterol contents were reduced, and insulin sensitivity improved, in GRP78-injected mice. These metabolic improvements were likely mediated by restoration of IRS-2 expression and tyrosine phosphorylation. Interestingly, GRP78 overexpression also inhibited insulin-induced SREBP-1c cleavage in cultured primary hepatocytes. These findings demonstrate that GRP78 inhibits both insulin-dependent and ER stress-dependent SREBP-1c proteolytic cleavage and explain the role of ER stress in hepatic steatosis in obese rodents.

SUBMITTER: Kammoun HL

PROVIDER: S-EPMC2673873 | biostudies-literature | 2009 May

REPOSITORIES: biostudies-literature

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GRP78 expression inhibits insulin and ER stress-induced SREBP-1c activation and reduces hepatic steatosis in mice.

Kammoun Hélène L HL Chabanon Hervé H Hainault Isabelle I Luquet Serge S Magnan Christophe C Koike Tatsuro T Ferré Pascal P Foufelle Fabienne F

The Journal of clinical investigation 20090413 5

Hepatic steatosis is present in insulin-resistant obese rodents and is concomitant with active lipogenesis. Hepatic lipogenesis depends on the insulin-induced activation of the transcription factor SREBP-1c. Despite prevailing insulin resistance, SREBP-1c is activated in the livers of genetically and diet-induced obese rodents. Recent studies have reported the presence of an ER stress response in the livers of obese ob/ob mice. To assess whether ER stress promotes SREBP-1c activation and thus co ...[more]

PMID: 19363290

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Project description:BackgroundNonalcoholic fatty liver disease (NAFLD) is a common chronic liver disease worldwide, and its incidence is increasing annually, but there is currently no specific drug for treating NAFLD. Shenling Baizhu powder (SL) is a safe herbal compound commonly used in clinical practice. Our previous research has shown that SL has the effect of preventing NAFLD, but its specific mechanism has not been determined. In this study, the potential mechanism of SL on NAFLD was explored by in vivo experiments.MethodsWistar rats fed a choline-deficient amino acid-defined diet (CDAA) were treated with SL for 8 weeks. Then, serum samples were collected to obtain biochemical indicators; adipose tissue and liver samples were collected for pathological detection; a moorFLPI-2 blood flow imager was used to measure liver microcirculation blood flow, and a rat cytokine array was used to screen potential target proteins. The expression of liver adiponectin/SREBP-1c pathway-related proteins was determined by Western blotting.ResultsSL effectively reduced the liver wet weight, as well as the levels of total cholesterol (TC) and triglyceride (TG) in the liver, and ameliorated liver injury in CDAA-fed rats. Pathological examinations showed that SL markedly reduced liver lipid droplets and improved liver lipid accumulation. In addition, the detection of liver blood flow showed that SL increased liver microcirculation in CDAA-fed rats. Through the cytokine array, a differentially expressed cytokine, namely, adiponectin, was screened in the liver. Western blotting assays showed that SL increased the expression of adiponectin and phosphoacetyl-CoA Carboxylase (p-ACC) in the liver and decreased the expression of steroid regulatory element-binding protein-1c (SREBP-1c) and fatty acid synthase (FAS).ConclusionThese results suggest that SL can increase the levels of adiponectin in the liver and serum and can inhibit the expression of SREBP-1c, thereby regulating systemic lipid metabolism and reducing liver lipid accumulation.

Project description:Background/objectivesAn increasing life expectancy in society has burdened healthcare systems substantially because of the rising prevalence of age-related metabolic diseases. This study compared the effects of animal protein hydrolysate (APH) and casein on metabolic diseases using aged mice.Materials/methodsEight-week-old and 50-week-old C57BL/6J mice were used as the non-aged (YC group) and aged controls (NC group), respectively. The aged mice were divided randomly into 3 groups (NC, low-APH [LP], and high-APH [HP] and fed each experimental diet for 12 weeks. In the LP and HP groups, casein in the AIN-93G diet was substituted with 16 kcal% and 24 kcal% APH, respectively. The mice were sacrificed when they were 63-week-old, and plasma and hepatic lipid, white adipose tissue weight, hepatic glucose, lipid, and antioxidant enzyme activities, immunohistochemistry staining, and mRNA expression related to the glucose metabolism on liver and muscle were analyzed.ResultsSupplementation of APH in aging mice resulted in a significant decrease in visceral fat (epididymal, perirenal, retroperitoneal, and mesenteric fat) compared to the negative control (NC) group. The intraperitoneal glucose tolerance test and area under the curve analysis revealed insulin resistance in the NC group, which was alleviated by APH supplementation. APH supplementation reduced hepatic gluconeogenesis and increased glucose utilization in the liver and muscle. Furthermore, APH supplementation improved hepatic steatosis by reducing the hepatic fatty acid and phosphatidate phosphatase activity while increasing the hepatic carnitine palmitoyltransferase activity. Furthermore, in the APH supplementation groups, the red blood cell (RBC) thiobarbituric acid reactive substances and hepatic H2O2 levels decreased, and the RBC glutathione, hepatic catalase, and glutathione peroxidase activities increased.ConclusionsAPH supplementation reduced visceral fat accumulation and alleviated obesity-related metabolic diseases, including insulin resistance and hepatic steatosis, in aged mice. Therefore, high-quality animal protein APH that reduces the molecular weight and enhances the protein digestibility-corrected amino acid score has potential as a dietary supplement for healthy aging.

Dataset Information

GRP78 expression inhibits insulin and ER stress-induced SREBP-1c activation and reduces hepatic steatosis in mice.

Publications

GRP78 expression inhibits insulin and ER stress-induced SREBP-1c activation and reduces hepatic steatosis in mice.

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