Epigenetics of human Hepatic Stellate Cells (HSCs) in NASH

ABSTRACT: Nonalcoholic fatty liver disease (NAFLD), is a spectrum of liver disease ranging from steatosis (nonalcoholic fatty liver, NAFL) to non-alcoholic steatohepatitis (NASH) with fibrosis. Hepatic Stellate Cells (HSCs) play a critical role in the pathogenesis of NASH. In response to chronic toxic injury, quiescent HSCs (qHSCs) activate into aHSCs/myofibroblasts, that secrete the extracellular matrix to promote liver fibrosis. The mechanism of NASH-mediated activation of human HSCs is not well understood. Phenotypic changes in HSCs occur without a change in the DNA sequence but are regulated on an epigenetic level, e.g. specific modifications in the chromatin structure, which affect DNA accessibility of the regulatory transcription factors (TFs), causing transcriptional activation or repression of their target genes. We will analyze normal, NAFL, and NASH livers that have been declined for liver transplantation. We will compare our observations in human HSCs to the well characterized foz/foz mouse model of NASH. Our proposed study will integrate state-of-the- art single-cell-based technologies, a) Single cell (sc)RNA-Seq on purified human HSCs will identify major human HSC subsets; b) Single nuclei (sn)ATAC-Seq and snRNA-Seq will be performed using whole liver tissue to capture and characterize the areas of open chromatin and matching gene expression of individual HSCs; c) Transcriptional activity of the regulatory promoter/enhancer elements will be further accessed using PLAC-Seq followed by ChIP-Seq with H3K27ac, a mark associated with cellular activation (HiChIP-Seq). The transcriptome (AIM 1) and epigenome (AIM 2) of human HSCs, the genome-wide locations of the regulatory elements and their corresponding TFs that regulate distinct HSC phenotypes and drive NAFL®NASH progression, will be determined. Motif enrichment analysis of regions exhibiting characteristics of active enhancers in combination with gene expression data will enable inference of major classes of transcription factors critical for specific subsets of human HSCs. The factors that drive human HSC activation and thereby promote NAFL progression to NASH will be identified. Selected targets (AIM 3) will be evaluated using the experimental model of NASH in Western-diet (WD)-fed foz/foz mice, using ablation of individual aHSC subsets (via overexpression of Diphtheria toxin receptor (DTR) in Col1a1+ aHSCs in a Cre-loxP-dependent manner), or HSC-specific knockout of the key TFs. Specific factors that prevent or suppress HSC activation (for example, Etv1, E3F3, Egr2, NRF1, Tal1, Atf3) will be pharmacologically targeted, and the in vivo effect of treatment on Co1a1+ aHSC activation will be monitored in live WD-fed reporter LratCol1a1-Fluc foz/foz mice (that upregulate Col- 1a1-driven Luciferase in mouse aHSCs), or humanized patient-specific xenograft Rag2-/-gc-/- mice. Overall, we anticipate identifying new targets for the antifibrotic therapy of NASH.