Moderate, chronic ethanol feeding exacerbates carbon-tetrachloride-induced hepatic fibrosis via hepatocyte-specific hypoxia inducible factor 1α

Sanjoy Roychowdhury; Dian J Chiang; Megan R McMullen; Laura E Nagy

doi:10.1002/prp2.61

Moderate, chronic ethanol feeding exacerbates carbon-tetrachloride-induced hepatic fibrosis via hepatocyte-specific hypoxia inducible factor 1α

Pharmacol Res Perspect. 2014 Oct;2(5):e00061. doi: 10.1002/prp2.61.

Authors

Sanjoy Roychowdhury¹, Dian J Chiang², Megan R McMullen¹, Laura E Nagy³

Affiliations

¹ Center for Liver Disease Research, Department of Pathobiology, Cleveland Clinic, Cleveland, Ohio.
² Department of Gastroenterology, Cleveland Clinic, Cleveland, Ohio.
³ 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.

PMID: 25089199
PMCID: PMC4115456
DOI: 10.1002/prp2.61

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 p53^K386acetylation, 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 CCl₄ exposure. Ethanol-induced exacerbation of hepatocyte apoptosis, p53^K386 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.

Keywords: Hypoxia; apoptosis; carbon tetrachloride; collagen; ethanol; fibrosis; hepatic stellate cells; hypoxia inducible factor 1α; inflammation; liver.

Abstract

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