Exposure to chronic hypoxia causes pulmonary hypertension (PH), vascular remodelling, right ventricular (RV) hypertrophy and subsequent cardiac failure. Protein kinaseG Iα (PKGIα) is susceptible to oxidation, forming a disulfide homodimer associated with kinase targeting involved in vasodilation and diastolic relaxation. Here we investigated the role of pulmonary PKGIα redox state in hypoxic PH. We found that chronic hypoxia caused pulmonary PKGIα oxidation in mice, as determined at 3 or 28 days, compared to normoxia, likely due to upregulation of H2O2-producing enzymes NADPH oxidase 4 (NOX4), extracellular superoxide dismutase (SOD3), and H2S-producing enzyme cystathionine gamma-lyase (CSE) in the lungs. Increased pulmonary PKGIα oxidation, NOX4 and CSE protein expression were observed in lungs from PAH patients. Chronic CSE inhibition potentiated RV pressure and hypertrophy, and attenuated lung PKGIα oxidation, suggesting that the redox state of PKGIα may be mediated by the products of H2S oxidation such as polysulfide species.
To dissect the potential role of oxidised PKGIα in hypoxic PH we employed redox-dead Cys42Ser PKGIα knock-in (KI) mice which are resistant to PKGIα oxidation. KI mice exposed to chronic hypoxia for 28 days developed increased pulmonary vascular resistance, potentiated RV hypertrophy and pressure, greater pulmonary myosin light chain phosphorylation, as well as excessive pro-growth signalling in the lungs, vascular muscularisation and enhanced transition of pulmonary endothelial cells to myofibroblasts, compared to wild-type mice. Pulmonary vessels from the KI mice demonstrated impaired vasodilatory responses to H2O2 compared to wild-type. Polysulfide treatment during chronic hypoxia lead to alleviation of RV hypertrophy in the wild-type, but not in the KI mice. We conclude that PKGIα oxidation may serve an important intrinsic adaptive mechanism that offsets increased pulmonary vascular resistance in PH and thus limits progression to heart failure. We suggest that drug-induced PKGIα oxidation might be beneficial in the PH treatment.