Transforming growth factor beta(1) induces the expression of alpha 1(I) procollagen mRNA by a hydrogen peroxide-C/EBP beta-dependent mechanism in rathepatic stellate cells

Oxidative stress plays a key role in liver fibrosis, Both inflammatory cell s and activated Kupffer cells produce H2O2, an oxidant involved in the acti vation of hepatic stellate cells (HSC). Increased production of reactive ox ygen intermediates (ROIs) in fibrotic livers is associated in part with the up-regulation of transforming growth factor beta (TGF-beta), and this cyto kine enhances collagen production by cultured HSC. However, the possible li nk between oxidative stress and the molecular mechanisms by which TGF-beta induces collagen gene expression in HSC remains to be elucidated. To addres s this question, we investigated whether H2O2 is a mediator of TGF-beta-eli cited alpha 1(I) collagen gene (collal) up-regulation. We demonstrated that TGF-beta induces the accumulation of H2O2, and that this oxidant is, in tu rn, directly involved in up-regulating the expression of the col1a1 gene. W hile the addition of H2O2 to HSC induced the expression of al(I) procollage n mRNA, catalase, an H2O2 enzyme scavenger, abrogated TGF-beta-mediated col lal gene up-regulation. We transfected HSC with chimeric plasmids driven by different segments of the mouse collal promoter and mapped a cis-acting el ement (-370 to -344) essential for TGF-beta responsiveness. We further show ed that TGF-beta induced the activation and binding of a C/EBP beta-contain ing transcriptional complex to this sequence, an effect that was also mimic ked by the addition of H2O2. Taken together, these data demonstrate a direc t connection between TGF-beta-mediated accumulation of H2O2 and the up-regu lation of col1a1 gene in HSC.