Authors: Xiao Liu, Jun Xu, Sara Rosenthal, Ling-juan Zhang, Ryan McCubbin, Nairika Meshgin, Linshan Shang, Yukinori Koyama, Hsiao-Yen Ma, Sonia Sharma, Sven Heinz, Chris K. Glass, Chris Benner, David A. Brenner, Tatiana Kisseleva
Summary: Background & Aims: Development of liver fibrosis is associated with activation of quiescent hepatic stellate cells (qHSCs) into collagen type I-producing myofibroblasts (activated or aHSCs). Cessation of liver injury often results in fibrosis resolution and inactivation of aHSCs/myofibroblasts into a quiescent-like state (iHSCs). We aimed identify molecular features of phenotypes of HSCs from mice and humans.
Methods: We performed studies with LratCre, Ets1-floxed, Nf1-floxed, Pparγ-floxed, Gata6-floxed, Rag2–/–γc–/–, and C57/Bl6 (control) mice. Some mice were given carbon tetrachloride to induce liver fibrosis, with or without a PPARγ agonist. Livers from mice were analyzed by immunohistochemistry. qHSCs, aHSCs, and iHSCs were isolated from livers of Col1α1YFP mice and analyzed by chromatin immunoprecipitation and sequencing. Human HSCs were isolated from livers denied for transplantation. We compared changes in gene expression patterns and epigenetic modifications (H3K4me2 and H3K27ac) in primary mouse and human HSCs. Transcription factors were knocked down with small hairpin RNAs in mouse HSCs.
Results: Motif enrichment identified ETS1, ETS2, GATA4, GATA6, IRF1, and IRF2 transcription factors as regulators of the mouse and human HSC lineage. Small hairpin RNA-knockdown of these transcription factors resulted in increased expression of genes that promote fibrogenesis and inflammation, and loss of HSC phenotype. Disruption of Gata6 or Ets1, or Nf1or Pparγ (which are regulated by ETS1), increased the severity of carbon tetrachloride (CCl4)-induced liver fibrosis in mice compared to control mice. Only mice with disruption of Gata6 or Pparg had defects in fibrosis resolution after CCl4 administration was stopped, associated with persistent activation of HSCs. Administration of a PPARγ agonist accelerated regression of liver fibrosis following CCl4 administration in control mice but not in mice with disruption of Pparγ.
Conclusions: Phenotypes of HSCs from humans and mice are regulated by transcription factors including ETS1, ETS2, GATA4, GATA6, IRF1, and IRF2. Activated mouse and human HSCs can revert to a quiescent-like, inactivated phenotype. We found GATA6 and PPARγ to be required for inactivation of human HSCs and regression of liver fibrosis in mice.
Source: Gastroenterology, 2020