AbstractThe 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.
