Activation of TWIST Transcription by Chromatin Remodeling Protein BRG1 Contributes to Liver Fibrosis in Mice.

Wenhui Dong,Yong Xu,Jun Lu,Yang Shao,Dongmei Wu,Yuwen Zhu,Junli Guo,Ming Kong

doi:10.3389/fcell.2020.00340

Abstract

Liver fibrosis is a complex pathophysiological process to which many different cell types contribute. Endothelial cells play versatile roles in the regulation of liver fibrosis. The underlying epigenetic mechanism is not fully appreciated. In the present study, we investigated the role of BRG1, a chromatin remodeling protein, in the modulation of endothelial cells in response to pro-fibrogenic stimuli in vitro and liver fibrosis in mice. We report that depletion of BRG1 by siRNA abrogated TGF-β or hypoxia induced down-regulation of endothelial marker genes and up-regulation of mesenchymal marker genes in cultured endothelial cells. Importantly, endothelial-specific BRG1 deletion attenuated CCl4 induced liver fibrosis in mice. BRG1 knockdown in vitro or BRG1 knockout in vivo was accompanied by the down-regulation of TWIST, a key regulator of endothelial phenotype. Mechanistically, BRG1 interacted with and was recruited to the TWIST promoter by HIF-1α to activate TWIST transcription. BRG1 silencing rendered a more repressive chromatin structure surrounding the TWIST promoter likely contributing to TWIST down-regulation. Inhibition of HIF-1α activity dampened liver fibrosis in mice. Similarly, pharmaceutical inhibition of TWIST alleviated liver fibrosis in mice. In conclusion, our data suggest that epigenetic activation of TWIST by BRG1 contributes to the modulation of endothelial phenotype and liver fibrosis. Therefore, targeting the HIF1α-BRG1-TWIST axis may yield novel therapeutic solutions to treat liver fibrosis.

Highlights

The liver is constantly exposed to a myriad of injurious stimuli, including pathogens, toxins, nutrients, and metabolites, which inevitably trigger the host defense mechanism (Shackel and Rockey, 2005)
We have previously shown that endothelial-specific deletion of Brahma related gene 1 (BRG1) in mice attenuates bile duct ligation (BDL) and thioacetamide induced liver fibrosis by regulating the transcription of caveolin-1 (CAV1) (Shao et al, 2020) and NADPH oxidase 4 (NOX4)
We first sought to determine the role of BRG1 in endothelial-to-mesenchymal transition (EndMT) in vitro by treating primary human vascular endothelial cells with Transforming growth factor beta (TGF-β), a prominent inducer of EndMT and fibrosis (Kovacic et al, 2012)

Summary

Introduction

The liver is constantly exposed to a myriad of injurious stimuli, including pathogens, toxins, nutrients, and metabolites, which inevitably trigger the host defense mechanism (Shackel and Rockey, 2005). Fibrogenesis is part of the evolutionarily conserved host defense/wound healing process. Fibrogenesis helps wound closure and preserve structural integrity of Abbreviations: Brg, Brahma related gene 1; ChIP, Chromatin immunoprecipitation; EndMT, Endothelial-to-mesenchymal transition; HUVEC, Human umbilical vascular endothelial cell; LSEC, Liver sinusoidal endothelial cells; KDM3A, Lysine demethylase 3A; KDM7, Lysine methyltransferase 7; qPCR, Quantitative polymerase chain reaction; TGF-β, Transforming growth factor beta. Serves to disrupt hepatic structures, severely compromises hepatic functions, and is often associated with end-stage liver diseases such as hepatocellular carcinoma and cirrhosis (Brenner et al, 2013). Irrespective of the etiologies, liver fibrogenesis is mediated by activated myofibroblasts capable of both muscle-like contraction and producing fibrillar proteins to remodel the extracellular matrix (Kisseleva, 2017)

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Conclusion