Chronic hypoxia‐induced upregulation of RhoA/ROCK in adult pulmonary arteries involves ROS‐mediated covalent modification and activation of RhoA.

Abstract

In this study, we examined the effect of chronic hypoxia (CH) on cGMP‐PKG‐mediated relaxation in pulmonary arteries. Isolated ovine intrapulmonary arteries (PAs) from ewes exposed to CH (ewes kept at 12,470 ft altitude for 110days) or matched controls (ewes kept at sea level) were preconstricted with endothelin‐1 and relaxed to 8‐Bromoguanosine 3′,5′‐cyclic monophosphate (8‐Br‐cGMP), a cell membrane‐permeable analog of cGMP, or to DETA NONOate, a stable nitric oxide donor. We found that control PAs relaxed to NO through both cGMP‐dependent and ‐independent mechanisms. In CH, NO‐mediated relaxation increased significantly, suggesting that guanylyl cyclase activity may be upregulated in these vessels. We observed minimal PKG‐mediated relaxation to 8‐Br‐cGMP both in control or CH PAs. Inhibition of ROCK with a Rho‐kinase‐specific inhibitor (Y27632), induced increased relaxation of CH PAs to cGMP, but not in control PAs, suggesting the upregulation of Rho/ROCK signaling in CH. Increased nitration of cysteine (S‐nitrosylation) and tyrosine (3‐nitrotyrosine) residues as well as a significant increase in ET‐1‐induced RhoA activation was detected in CH PAs compared to controls. These effects are mimicked by the exposure of control PAs to exogenous peroxynitrite (ONOO‐). These findings suggest that altered redox balance in chronic hypoxia and the ensuing reactive species‐mediated post‐translational modification of RhoA lead to the activation and upregulation of the Rho/ROCK constriction pathway inducing sustained pulmonary vasoconstriction.