title: Moderate, chronic ethanol feeding exacerbates carbon-tetrachloride-induced hepatic fibrosis via hepatocyte-specific hypoxia inducible factor 1α
abstract: The hypoxia-sensing transcriptional factor HIF1α is implicated in a variety of hepato-pathological conditions; however, the contribution of hepatocyte-derived HIF1α during progression of alcoholic liver injury is still controversial. HIF1α induces a variety of genes including those involved in apoptosis via p53 activation. Increased hepatocyte apoptosis is critical for progression of liver inflammation, stellate cell activation and fibrosis. Using hepatocyte-specific HIF1α-deficient mice (ΔHepHIF1α-/-), here we investigated the contribution of HIF1α to ethanol-induced hepatocyte apoptosis and its role in amplification of fibrosis after carbon tetrachloride (CCl4) exposure. Moderate ethanol feeding (11% of Kcal) induced accumulation of hypoxia-sensitive pimonidazole adducts and HIF1α expression in the liver within 4 days of ethanol feeding. Chronic CCl4treatment increased M30-positive cells, a marker of hepatocyte apoptosis in pair-fed control mice. Concomitant ethanol feeding (11% of Kcal) amplified CCl4-induced hepatocyte apoptosis in livers of wild-type mice, associated with elevated p53K386acetylation, PUMA expression and Ly6c+ cell infiltration. Subsequent to increased apoptosis, ethanol enhanced induction of pro-fibrotic markers including stellate cell activation, collagen 1 expression and extracellular matrix deposition, following CCl4exposure. Ethanol-induced exacerbation of hepatocyte apoptosis, p53K386acetylation and PUMA expression following CCl4exposure was attenuated in livers of ΔHepHIF1α-/- mice. This protection was also associated with a reduction in Ly6c+cell infiltration and decreased fibrosis in livers of ΔHepHIF1α-/- mice. In summary, these results indicate that moderate ethanol exposure leads to hypoxia/HIF1α-mediated signaling in hepatocytes and induction of p53-dependent apoptosis of hepatocytes, resulting in increased hepatic fibrosis during chronic CCl4exposure.
authors.affiliation: Center for Liver Disease Research, Department of Pathobiology, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Sanjoy
authors.initials: S
authors.lastname: Roychowdhury
authors.affiliation: Department of Gastroenterology, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Dian J
authors.initials: DJ
authors.lastname: Chiang
authors.affiliation: Center for Liver Disease Research, Department of Pathobiology, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Megan R
authors.initials: MR
authors.lastname: McMullen
authors.affiliation: Center for Liver Disease Research, Department of Pathobiology, Cleveland Clinic, Cleveland, Ohio ; Department of Gastroenterology, Cleveland Clinic, Cleveland, Ohio ; Department of Molecular Medicine, Case Western Reserve University, Cleveland, Ohio.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Nagy
keywords: Hypoxia; apoptosis; carbon tetrachloride; collagen; ethanol; fibrosis; hepatic stellate cells; hypoxia inducible factor 1α; inflammation; liver
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