Hypoxia-Inducible Factor-1alpha and MAPK Co-Regulate Activation of Hepatic Stellate Cells upon Hypoxia Stimulation

Background: Hepatic stellate cell (HSC) plays a key role in pathogenesis of liver fibrosis. During liver injury, hypoxia in local micro-environment is inevitable. Hif-1 alpha is the key transcriptional regulation factor that induces cell's adaptive responses to hypoxia. Recently, it was reported that MAPK is involved in regulation of Hif-1 alpha activity. Aims: To explore whether Hif-1 alpha regulates HSC activation upon hypoxia, and whether MAPK affects Hif-1 alpha-regulated signaling cascades, thus providing new targets for preventing liver fibrosis. Methods: Hif-1 alpha expression in livers of Schistosoma japonicum infected BALB/c mice was detected with western blot and immunohistochemistry. A rat cell line of HSC, HSC-T6, was cultured in 1% oxygen. HSC activation, including F-actin reorganization, increase of vimentin and alpha-SMA, was detected with western blot or immunocytochemistry. Cells were transfected with specific siRNA to Hif-1 alpha, expression of activation markers, transcription of fibrosis-promoting cytokines, secretion of collagen I were detected with western blot, Real Time PCR and ELISA. Lysate from HSC-T6 cells pretreated with PD98059, a specific MEK1 pharmacological inhibitor, was subjected to detect Hif-1 alpha ubiquitination and nuclear translocation with western blot and immunoprecipitation. Results and Conclusions: Hif-1 alpha apparently increased in liver tissues of Schistosoma japonicum infected mice. 1% O-2 induced F-actin reorganization, increase of Hif-1 alpha, vimentin and alpha-SMA in HSC-T6 cells. Hif-1 alpha Knockdown inhibited HSC-T6 activation, transcription of IL-6, TGF-beta and CTGF and secretion of collagen I from HSC-T6 cells upon hypoxia. Inhibition of MAPK phosphorylation enhanced Hif-1 alpha ubiquitination, and inhibited Hif-1 alpha translocation into nucleus. Conclusively, Hif-1 alpha and MAPK participate in HSC activation upon hypoxia.