n fibrogenic cells via oxygen-independent activation of hypoxia inducible actor-1 (HIF-1 ). However, the mechanisms underlying the increase in ro-angiogenic cytokines induced by leptin are poorly understood. This tudy was designed to investigate the regulation of HIF-1 and its target ene, VEGF in activated human hepatic stellate cells (HSC) in response to eptin. We employed HSC isolated from normal liver tissue, cultured on plastic nd used in their myofibroblast-like phenotype. Cytokine expression and ntracellular signalling pathways were investigated by western blot analysis. Increased expression of HIF-1 and VEGF were observed when HSC ere stimulated with leptin (200 ng/ml) or PDGF (10 ng/ml) for 24 h. xposure to leptin or PDGF enhanced phosphorylation levels of TSC2 on 1462 residues. Phosphorylation on T1462 results in dissociation of the SC1/TSC2 complex, which exerts an inhibitory action on mTOR activaion. Accordingly, leptin also up-regulated the phosphorylation of two major TOR targets, namely p70 S6 kinase and the translational inhibitor 4Einding protein-1. These data indicate the ability of leptin to activate the TOR pathway. Similar findings were observed when HSC were exposed o PDGF. To test if activation of HIF-1 and VEGF expression required TOR activation, we used the specific m-TOR inhibitor, rapamycin. In he presence of rapamycin, leptin and PDGF were no longer able to upegulate HIF or VEGF. Leptin has been shown to increase ROS generation n HSC. To explore the possible requirement of ROS for HIF-1 activation by eptin, HSC were pretreated with antioxidants such as N-acetyl cysteine, aocopherol or the NADPH oxidase inhibitor diphenylene iodonium DPI. All ntioxidant, and particularly DPI, inhibited at the protein level the expression f HIF-1 and VEGF stimulated by leptin or PDGF. We conclude that the increased expression of HIF-1 and VEGF in SC exposed to leptin or PDGF requires activation of the mTOR sigaling pathway and production of ROS, possibly generated by NADPHxidase.