Alcohol directly stimulates epigenetic modifications in hepatic stellate cells

Abstract

Background and aims Alcohol is a primary cause of liver disease and an important co-morbidity factor in other causes of liver disease. A common feature of progressive liver disease is fibrosis, which results from the net deposition of fibril-forming extracellular matrix (ECM). The hepatic stellate cell (HSC) is widely considered to be the major cellular source of fibrotic ECM. We determined if HSC are responsive to direct stimulation by alcohol. Methods HSC undergoing transdifferentiation were incubated with ethanol and expression of fibrogenic genes and epigenetic regulators measured. Mechanisms responsible for recorded changes were investigated using ChIP-Seq and bioinformatics analysis. Ethanol induced changes were confirmed using HSCs isolated from mouse alcohol model, ALD patient liver and precision cut liver slices. Results HSCs responded to ethanol exposure by increasing profibrogenic and ECM gene expression including elastin. Ethanol induced altered expression of multiple epigenetic regulators indicative of a potential to modulate chromatin structure during HSC transdifferentiation. MLL1, a histone 3 lysine 4 (H3K4) methyltransferase, was induced by ethanol and recruited to the elastin gene promoter where it was associated with enriched H3K4me3, mark of active chromatin. Chromatin immunoprecipitation sequencing (ChIPseq) revealed that ethanol has broad effects on the HSC epigenome and identified 41 gene loci at which both MML1 and its H3K4me3 mark were enriched in response to ethanol. Conclusions Ethanol directly influences HSC transdifferentiation by stimulating global changes in chromatin structure resulting in increased expression of ECM proteins. The ability of alcohol to remodel epigenome during HSC transdifferentiation provides mechanisms for it to act as a comorbidity factor in liver disease.

Hepatic stellate cells as key target in liver fibrosis

“…Ethanol induces an H3K4 methyltransferase, lysine methyltransferase 2A (KMT2A), and transcriptionally activates promoter of multiple ECM genes, including elastin [264]. Ethanol can also induce H3K9 acetylation in HSCs in time- and dose-dependent manner [265]…”

Elastin in the Liver

“…Ethanol stimulates HSC transdifferentiation by causing changes in chromatin structure. The expression of ECM proteins including elastin is increased in this process (Page et al, 2015). Overexpression of miR-29a leads to downregulation of elastin and other ECM proteins in HSC (Li et al, 2011).…”

Decoding liver injury: A regulatory role for histone modifications

“…An intriguing question to ask would be whether H3K9-H3K27 methylation might have a genome-wide role in regulating HSC phenotype. Of note, a recent study implicated a panel of histone demethylases in the process of alcohol-induced HSC activation (Page et al , 2015). Combined, these data suggest a complex network of HMTs and HDMs that exerts a cumulative effect on the methylation status of histones and consequently chromatin structure of genes key to HSC activation and fibrogenesis.…”