Intracellular signaling pathways involved in acetaldehyde-induced collagenand fibronectin gene expression in human hepatic stellate cells

Ethanol induces liver fibrosis by several means that include, among others, the direct fibrogenic action of acetaldehyde on hepatic stellate cells (HS C). However the mechanisms responsible for this effect are not well underst ood. Tn this communication we investigated signal transduction pathways tri ggered by acetaldehyde leading to upregulation of alpha2(I) collagen and fi bronectin gene expression in human HSC. Run-on assays showed that acetaldeh yde-enhanced transcription of these 2 genes as early as 2 hours, via de nov o protein synthesis-independent and -dependent mechanisms. It also stimulat ed a time-dependent induction in phosphorylation of pp70(S6K) and extracell ular-regulated kinase In (ERK1/2). These effects were completely prevented by calphostin C, a protein kinase C inhibitor. As expected, acetaldehyde-el icited ERK1/2 phosphorylation was inhibited by PD98059, a MEK inhibitor, bu t not by wortmannin, a PI3K inhibitor. On the other hand, both of these inh ibitors partially inhibited phosphorylation of pp70(S6K) induced by acetald ehyde suggesting that its activation is ERK1/2- and PI3K-dependent. Acetald ehyde-elicited fibronectin and alpha2(I) collagen upregulation was inhibite d by calphostin C. However, while PD98059, wortmannin and rapamycin (a pp70 (S6K) inhibitor) completely abrogated alpha2(I) collagen upregulation, they had no effect on fibronectin expression. Overall, these data suggest that protein kinase C is an upstream component from which acetaldehyde signals a re transduced to other pathways such as PI3K and ERK1/2. In addition, diffe rential activation of these pathways is needed for the increase in fibronec tin and alpha2(I) collagen gene expression induced by acetaldehyde in human HSC.