Hypoxia-inducible factor 1 and ROCK1 regulate proliferation and collagen synthesis in hepatic stellate cells under hypoxia

Hypoxia serves a critical role in the pathogenesis of liver fibrosis. Hypoxia-inducible factor 1 (HIF1-) is induced when cells are exposed to low O-2 concentrations. Recently, it has been suggested that Rho-associated coiled-coil-forming kinase 1 (ROCK1) may be an important HIF1- regulator. In the present study, it was analyzed whether crosstalk between HIF1- and ROCK1 regulates cell proliferation and collagen synthesis in hepatic stellate cells (HSCs) under hypoxic conditions. For this purpose, a rat hepatic HSC line (HSC-T6) was cultured under hypoxic or normoxic conditions, and HIF1- and ROCK1 expression was measured at different time points. Additionally, HSC-T6 cells were transfected with HIF1- small interfering RNA (siHIF1-), and measured protein expression and mRNA transcript levels of -smooth muscle actin, collagen 1A1 and ROCK1. Collagen 3A1 secretion was also measured by ELISA. Cell proliferation was assessed by the MTT assay under these hypoxic conditions. The results indicated that a specific ROCK inhibitor, Y-27632, increased HIF1- and ROCK1 expression over time in HSC-T6 cells in response to hypoxia. In addition, knockdown of HIF1- inhibited HSC-T6 proliferation, suppressed collagen 1A1 expression, decreased collagen 3A1 secretion and attenuated ROCK1 expression. Notably, ROCK1 inhibition caused HSC-T6 quiescence, suppressed collagen secretion and downregulated HIF1- expression. Collectively, these findings indicated that the interplay between HIF1- and ROCK1 may be a critical factor that regulates cell proliferation and collagen synthesis in rat HSCs under hypoxia.