Inhibition of RhoA/ROCK signaling pathway ameliorates hypoxic pulmonary hypertension via HIF-1α-dependent functional TRPC channels.

Hypoxic pulmonary vasoconstriction (HPV) can be modulated by Rho/Rho kinase signaling, which can alter HPV vascular function via regulating myosin light chain phosphorylation, in a manner generally believed to be Ca2+-independent. We hypothesized that the RhoA/ROCK signaling pathway also can regulate HPV vascular function via a Ca2+-dependent mechanism, signaling through the functional transient receptor potential canonical (TRPC) channels. In this study, male BALB/c mice were exposed to normoxic or 10% oxygen (hypoxic) conditions for six weeks, after which systolic pressure and right ventricular hypertrophy were assessed. Transient intracellular calcium was monitored using a fluorescence imaging system. Muscle tension was measured with a contractile force recording system, and protein expression was assessed by immunoblotting. We found that the expressions of RhoA and ROCK were increased in mouse pulmonary arteries (PAs) under conditions of chronic hypoxia. Inhibition of the RhoA/ROCK signaling pathway prevented the development of hypoxic pulmonary hypertension (HPH), as evidenced by significantly reduced PA remodeling and pulmonary vasoconstriction. Immunoblotting results revealed that inhibition of the RhoA/ROCK signaling pathway significantly decreased the expression of HIF-1α. Knockdown of HIF-1α down-regulated the expression and function of the TRPC1 and TRPC6 channels in PASMCs under conditions of hypoxia. Contraction of the PAs and a Ca2+ influx into PASMCs through either receptor- or store-operated Ca2+ channels were also increased after hypoxia. However, RhoA/ROCK inhibitors markedly attenuated these changes. These results indicate that inhibition of the RhoA/ROCK signaling pathway ameliorates HPH via HIF-1α-dependent functional TRPCs.