Hydrogen peroxide: A link between acetaldehyde-elicited α1(I) collagen gene up-regulation and oxidative stress in mouse hepatic stellate cells

Abstract

Ethanol induces liver fibrosis by several means that include, among others, the direct fibrogenic actions of acetaldehyde and the induction of an oxidative stress response. However, the mechanisms responsible for these activities, and the possible connections between oxidative stress and acetaldehyde-induced fibrosis are not well understood. In this communication we investigated the molecular mechanisms whereby acetaldehyde induces mouse α1(I) procollagen (col1a1) gene expression in cultured hepatic stellate cells. Transfection assays using reporter plasmids driven by different segments of the col1a1 promoter localized an acetaldehyde-responsive element (ACRE) between nucleotides -370 and -345. We also show that acetaldehyde enhances binding of a CCAAT/enhancer binding protein-β (C/EBPβ)-containing complex to this element, and that this effect is due, at least in part, to an increase in the concentration of nuclear p35C/EBPβ protein. Although this element overlaps to a previously described transforming growth factor β1 (TGF-β1)-responsive element, the stimulatory effect of acetaldehyde is not mediated through this cytokine, because addition of neutralizing anti-TGF-β1 antibodies does not prevent acetaldehyde-elicited col1a1 up-regulation. On the other hand, this effect is blocked by the addition of catalase, an H2O2 scavenger. Moreover, this ethanol metabolite stimulates production of H2O2 in stellate cells. Thus, these results suggest that acetaldehyde-induced col1a1 up-regulation is mediated, at least in part, through H2O2. Altogether, these data suggest that the -370 to -344 region of the col1a1 gene is a point of convergence of the action of numerous extracellular stimuli that ultimately leads to col1a1 up-regulation. In addition, we have established a direct connection between oxidative stress and enhanced col1a1 expression induced by acetaldehyde.