Lineage-specific Transcription Factors suppress activation of Hepatic Stellate Cells during Liver Fibrosis

Development of liver fibrosis is associated with activation of quiescent Hepatic Stellate Cells (qHSCs) into Collagen Type I-producing myofibroblasts (aHSCs). Cessation of liver injury often results in fibrosis resolution and inactivation of aHSCs/myofibroblasts into a quiescent-like state (iHSCs). To identify the molecular drivers of these HSC phenotypes, we investigated the global gene expression and epigenetic changes in H3K4me2 and H3K27ac marks of primary murine and human HSCs. Motif enrichment identified ETS1/2, GATA4/6, and IRF1/2 transcription factors (TFs) as putative regulators of the HSC lineage identity in murine and human HSCs. shRNA-knockdown of these TFs resulted in marked upregulation of fibrogenic and inflammatory genes and a loss of HSC-specific phenotype in targeted murine HSCs. In support, in vivo HSC-specific ablation of GATA4, GATA6, and ETS1, and ETS1 target genes NF1 (neurofibromin 1) and PPAR? exacerbated development of carbon tetrachloride (CCl4)-induced liver fibrosis in Lrat?GATA6, LratETS1+/-, Lrat?NF1, and Lrat?PPAR? mice (vs wt littermates), but only Lrat?GATA6, and Lrat?PPAR? mice exhibited a defect in fibrosis resolution due to the lack of HSC inactivation. Therapeutic administration of a PPAR? agonist accelerated regression of liver fibrosis in CCl4-induced wt, but not in Lrat?PPAR? mice, suggesting that PPAR? signaling in HSCs is critical for HSC inactivation and regression of liver fibrosis. Common transcription factors determine the phenotype of mouse and human HSCs. Similar to murine HSCs, human aHSCs can revert into a quiescent-like, inactivated phenotype. GATA4, GATA6, and PPAR?were identified as an important driver of human HSC inactivation. Overall design: Expression/epigenetic profiling of hepatic stellate cells by RNA-seq and ChIP-seq for H3K27ac and H3K4me2