Transcriptional repression of SIRT1 by protein inhibitor of activated STAT 4 (PIAS4) in hepatic stellate cells contributes to liver fibrosis.

Lina Sun,Yaoyao Bian,Mingming Fang,Junliang Chen,Zhiwen Fan,Min Li,Xiaoyan Wu,Huihui Xu,Yong Xu,Wenfang Tian,Jing Shao

doi:10.1038/srep28432

Abstract

Interstitial fibrosis represents a key pathological process in non-alcoholic steatohepatitis (NASH). In the liver, fibrogenesis is primarily mediated by activated hepatic stellate cells (HSCs) transitioning from a quiescent state in response to a host of stimuli. The molecular mechanism underlying HSC activation is not completely understood. Here we report that there was a simultaneous up-regulation of PIAS4 expression and down-regulation of SIRT1 expression accompanying increased hepatic fibrogenesis in an MCD-diet induced mouse model of NASH. In cultured primary mouse HSCs, stimulation with high glucose activated PIAS4 while at the same time repressed SIRT1. Over-expression of PIAS4 directly repressed SIRT1 promoter activity. In contrast, depletion of PIAS4 restored SIRT1 expression in HSCs treated with high glucose. Estrogen, a known NASH-protective hormone, antagonized HSC activation by targeting PIAS4. Lentivirus-mediated delivery of short hairpin RNA (shRNA) targeting PIAS4 in mice ameliorated MCD diet induced liver fibrosis by normalizing SIRT1 expression in vivo. PIAS4 promoted HSC activation in a SIRT1-dependent manner in vitro. Mechanistically, PIAS4 mediated SIRT1 repression led to SMAD3 hyperacetylation and enhanced SMAD3 binding to fibrogenic gene promoters. Taken together, our data suggest SIRT1 trans-repression by PIAS4 plays an important role in HSC activation and liver fibrosis.

Highlights

Accompanying changes in life style and dietary choices there is a growing global pandemic of obesity and related metabolic disorders, which include non-alcoholic steatohepatitis or NASH1
We evaluated the involvement of PIAS4 in liver fibrosis employing a classic model of NASH wherein db/db mice were fed on a methionine-and-choline deficient (MCD) diet for 4 weeks[16]
Quantitative PCR (Fig. 1A) and Western blotting (Fig. 1B) analyses found that accompanying up-regulation of fibrogenic proteins such as collagen type I (Col1a1), there was a concomitant increase in PIAS4 expression and a decrease in SIRT1 expression in the livers of MCD-fed mice

Summary

Introduction

Accompanying changes in life style and dietary choices there is a growing global pandemic of obesity and related metabolic disorders, which include non-alcoholic steatohepatitis or NASH1. Trans-differentiation of quiescent HSCs to an activated state represents a key process in NASH-associated fibrosis. During NASH pathogenesis, HSCs are exposed to a plethora of nutrients (e.g., high concentrations of glucose) and become activated gaining the ability to proliferate and synthesize extracellular matrix (ECM) proteins[6]. Our laboratory has identified a pathway in which the SUMO E3 ligase PIAS4 represses SIRT1 transcription to promote cancer metastasis[14,15]. We report that PIAS4 mediates SIRT1 repression in cultured HSCs exposed to high glucose and in a mouse model of NASH-associated liver fibrosis. PIAS4 promotes HSC activation and liver fibrosis by stimulating SMAD3 acetylation and target binding in a SIRT1-dependent manner. Targeting PIAS4 might facilitate the development of novel therapeutic solutions against liver fibrosis in the context of NASH

Methods

Results

Conclusion