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 CCl4 treatment 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 p53K386 acetylation, PUMA expression, and Ly6c+ cell infiltration. Subsequent to increased apoptosis, ethanol-enhanced induction of profibrotic markers, including stellate cell activation, collagen 1 expression, and extracellular matrix deposition following CCl4 exposure. Ethanol-induced exacerbation of hepatocyte apoptosis, p53K386 acetylation, and PUMA expression following CCl4 exposure 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 CCl4 exposure.