Leptin enhances α1(I) collagen gene expression in LX-2 human hepatic stellate cells through JAK-mediated H₂O₂-dependent MAPK pathways

Leptin, a liver profibrogenic cytokine, induces oxidative stress in hepatic stellate cells (HSCs), with increased formation of the oxidant H ₂O₂, which signals through p38 and extracellular signal-regulated kinase1/2(ERK1/2) pathways, stimulating tissue inhibitor of metalloproteinase-1 production. Since oxidative stress is a pathogenic mechanism of liver fibrosis and activation of collagen gene is a marker of fibrogenesis, we evaluated the effects of leptin on collagen I expression. We report here that, in LX-2 human HSCs, leptin enhances the levels of α1(I) collagen mRNA, promoter activity and protein. Janus kinase (JAK)1 and JAK2 were activated. H₂O₂ formation was increased; this was prevented by the JAK inhibitor AG490, suggesting a JAK-mediated process. ERK1/2 and p38 were activated, and the activation was blocked by catalase, consistent with an H₂O₂-dependent mechanism. AG490 and catalase also prevented leptin-stimulated α1(I) collagen mRNA expression. PD098059, an ERK1/2 inhibitor, abrogated ERK1/2 activation and suppressed α1(I) collagen promoter activity, resulting in mRNA down-regulation. The p38 inhibitor SB203580 and overexpression of dominant negative p38 mutants abrogated p38 activation and down-regulated the mRNA. While SB203580 had no effect on the promoter activity, it reduced the mRNA half-life from 24 to 4 h, contributing to the decreased mRNA level. We conclude that leptin stimulates collagen production through the H₂O₂-dependent and ERK1/2 and p38 pathways via activated JAK1 and JAK2. ERK1/2 stimulates α1(I) collagen promoter activity, whereas p38 stabilizes its mRNA. Accordingly, interference with leptin-induced oxidative stress by antioxidants provides an opportunity for the prevention of liver fibrosis.