Ethanol induces transforming growth factor-alpha expression in hepatocytes, leading to stimulation of collagen synthesis by hepatic stellate cells.

BACKGROUND

Liver fibrosis often develops in alcoholic liver diseases without accompanying inflammation; however, the underlying mechanism is unclear. Using ethanol-exposed human HepG2 hepatoblastoma cells as a model for alcoholic liver diseases, we previously found that ethanol exposure causes HepG2 cells to secrete an approximately 6,000 Da nonheparin-binding polypeptide that stimulates collagen synthesis in human IMR-90 fibroblasts. The aim of the current study was to characterize and identify this factor.

METHODS

Concentration of type I procollagen peptide and transforming growth factor (TGF)-alpha was assessed by enzyme-linked immunosorbent assay. TGF-alpha protein expression was examined by Western blot. Type I collagen messenger RNA expression in rat hepatic stellate cells was assessed by reverse transcription-polymerase chain reaction.

RESULTS

The collagen-stimulating activity in conditioned media from ethanol-exposed HepG2 cells to stimulate type I procollagen peptide synthesis of IMR-90 cells was specifically inhibited by addition of anti-TGF-alpha antibodies. Western blot analysis showed increased TGF-alpha protein expression in ethanol-treated HepG2 cells. TGF-alpha in conditioned medium from ethanol-exposed HepG2 cells stimulated type-I collagen messenger RNA expression in rat hepatic stellate cells.

CONCLUSIONS

These results suggest that TGF-alpha derived from ethanol-exposed hepatocytes may contribute to the development of hepatic fibrosis in alcoholic liver diseases.