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The transcription cofactor CRTC1 protects from aberrant hepatic lipid accumulation.

ABSTRACT: Nonalcoholic fatty liver disease (NAFLD) is a rapidly emerging global health-problem. NAFLD encompasses a range of conditions associated with hepatic steatosis, aberrant accumulation of fat in hepatocytes. Although obesity and metabolic syndrome are considered to have a strong association with NAFLD, genetic factors that predispose liver to NAFLD and molecular mechanisms by which excess hepatic lipid develops remain largely unknown. We report that the transcription cofactor CRTC1 confers broad spectrum protection against hepatic steatosis development. CRTC1 directly interferes with the expression of genes regulated by lipogenic transcription factors, most prominently liver x receptor ? (LXR?). Accordingly, Crtc1 deficient mice develop spontaneous hepatic steatosis in young age. As a cyclic AMP effector, CRTC1 mediates anti-steatotic effects of calorie restriction (CR). Notably, CRTC1 also mediates anti-lipogenic effects of bile acid signaling, whereas it is negatively regulated by miR-34a, a pathogenic microRNA upregulated in a broad spectrum of NAFLD. These patterns of gene function and regulation of CRTC1 are distinct from other CR-responsive proteins, highlighting critical protective roles that CRTC1 selectively plays against NAFLD development, which in turn provides novel opportunities for selectively targeting beneficial therapeutic effects of CR.

SUBMITTER: Kim H

PROVIDER: S-EPMC5116671 | biostudies-literature | 2016 Nov

REPOSITORIES: biostudies-literature

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The transcription cofactor CRTC1 protects from aberrant hepatic lipid accumulation.

Kim Hwijin H

Scientific reports 20161121

Nonalcoholic fatty liver disease (NAFLD) is a rapidly emerging global health-problem. NAFLD encompasses a range of conditions associated with hepatic steatosis, aberrant accumulation of fat in hepatocytes. Although obesity and metabolic syndrome are considered to have a strong association with NAFLD, genetic factors that predispose liver to NAFLD and molecular mechanisms by which excess hepatic lipid develops remain largely unknown. We report that the transcription cofactor CRTC1 confers broad s ...[more]

PMID: 27869139

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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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The transcription cofactor CRTC1 protects from aberrant hepatic lipid accumulation.

Publications

The transcription cofactor CRTC1 protects from aberrant hepatic lipid accumulation.

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