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Hairy and enhancer of split 6 prevents hepatic lipid accumulation through inhibition of Pparg2 expression.

ABSTRACT: Peroxisome proliferator-activated receptor gamma (PPAR?) is a master regulator for white adipocyte differentiation and lipid storage. The increased level of hepatic PPAR?2 isoform reprograms liver for lipid storage and causes abnormal fat accumulation in certain pathophysiologic conditions. The current study aimed to investigate a role of transcriptional repressor hairy and enhancer of split 6 (HES6) in the regulation of Pparg2 expression and hepatic steatosis induced by diet. Liver-specific overexpression of Hes6 using adenovirus reduced Pparg2 messenger RNA levels by 90% and hepatic triglyceride accumulation by 22% compared to the levels in mice injected with an adenoviral empty vector with Western diet feeding. In sharp contrast, silencing Hes6 gene expression using short hairpin RNA increased hepatic lipid accumulation and Pparg2 messenger RNA levels by 70% and 4-fold, respectively. To locate hepatocyte nuclear factor 4 alpha (HNF4?) binding site(s), through which repressional activity of HES6 is mediated, a 2.5-kb Pparg2 promoter-driven luciferase reporter was constructed for transient transfection assays. Subsequently, chromatin immunoprecipitation and electrophoretic mobility shift assays were performed. An HNF4? binding consensus sequence was identified at 903 base pairs upstream from the transcription start site of Pparg2. Deletion or point mutation of the sequence in a luciferase reporter containing the Pparg2 promoter abolished HNF4?-mediated activation in HeLa cells. Chromatin immunoprecipitation and electrophoretic mobility shift assays further confirmed direct recruitment and binding of HNF4? to the site. Gene expression analysis with liver samples from subjects with nonalcoholic steatohepatitis suggested that the axis of the Hes6-Hnf4a-Pparg2 transcriptional cascade is also responsible for hepatic fat accumulation in humans. Conclusion: HES6 represses Pparg2 gene expression, thereby preventing hepatic lipid accumulation induced by chronic Western diet feeding or pathophysiologic conditions. (Hepatology Communications 2017;1:1085-1098).

SUBMITTER: Park JE

PROVIDER: S-EPMC5721401 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Hairy and enhancer of split 6 prevents hepatic lipid accumulation through inhibition of <i>Pparg2</i> expression.

Park Jung Eun JE Lee Mikang M Kim Seong-Chul SC Zhang Yanqiao Y Hardwick James P JP Lee Yoon Kwang YK

Hepatology communications 20171108 10

Peroxisome proliferator-activated receptor gamma (PPARγ) is a master regulator for white adipocyte differentiation and lipid storage. The increased level of hepatic PPARγ2 isoform reprograms liver for lipid storage and causes abnormal fat accumulation in certain pathophysiologic conditions. The current study aimed to investigate a role of transcriptional repressor hairy and enhancer of split 6 (HES6) in the regulation of <i>Pparg2</i> expression and hepatic steatosis induced by diet. Liver-speci ...[more]

PMID: 29404444

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Project description:Background/aimsLiver lipid accumulation induced by high-fat diet (HFD) is an early onset process of non-alcoholic fatty liver diseases (NAFLD). Protein kinase A (PKA) is known to be involved in hepatic lipid metabolism. However, the role of PKA in NAFLD has not been well tested in vivo due to the lack of optimal PKA deficient mouse model.MethodsA novel PKA-specific inhibitor gene was conditionally overexpressed in mouse (PKAi mouse) liver using LoxP/Cre system. PKA activity in the liver extract was measured with a commercial assay kit. The PKAi and control mice of 8-week age, were subjected to HFD or chow diet (CD) for 2 months. Body weight, liver index, and triglyceride in the liver were measured. RNA sequencing was performed for the liver tissues and analyzed with Gene Ontology (GO) and pathway enrichment.ResultsPKAi-GFP protein was overexpressed in the liver and the PKA activation was significantly inhibited in the liver of PKAi mouse. When fed with CD, RNA sequencing revealed 56 up-regulated and 51 down-regulated genes in PKAi mice compared with control mice, which were mainly involved in lipid metabolism though no significant differences in the body weight, liver index, triglyceride accumulation were observed between PKAi and control mice. However, when fed with HFD for 2 months, the liver was enlarged more, and the accumulation of triglyceride in the liver was more severe in PKAi mice. When comparing the transcriptomes of CD-fed and HFD-fed control mice, GO enrichment showed that the genes down-regulated by HFD were mainly enriched in immune-related GO terms, and up-regulated genes were enriched in metabolism. When comparing the transcriptomes of CD-fed and HFD-fed PKAi mice, GO analysis showed that the down-regulated genes were enriched in metabolism, while the up-regulated genes were clustered in ER stress-related pathways. When comparing HFD-fed PKAi and HFD-fed control mice, the genes with lower expression level in PKAi mice were enriched in the lipoprotein synthesis, which might explain that more TG is accumulated in PKAi liver after HFD feeding.ConclusionsReduced PKA activity could be a factor promoting the TG accumulation in the liver and the development of NAFLD.

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Hairy and enhancer of split 6 prevents hepatic lipid accumulation through inhibition of Pparg2 expression.

Publications

Hairy and enhancer of split 6 prevents hepatic lipid accumulation through inhibition of <i>Pparg2</i> expression.

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