PKG-1α leucine zipper domain defect increases pulmonary vascular tone: implications in hypoxic pulmonary hypertension

Pulmonary hypertension (PH) is a chronic disease characterized by a progressive increase in vasomotor tone, narrowing of the vasculature with structural remodeling, and increase in pulmonary vascular resistance. Current treatment strategies include nitric oxide therapy and methods to increase cGMP-mediated vasodilatation. cGMP-dependent protein kinases (PKG) are known mediators of nitric oxide- and cGMP-induced vasodilatation. Deletion of PKG-1 in mice has been shown to induce PH, however, the exact mechanisms by which loss of PKG-1 function leads to PH is not known. In a mouse model with a selective mutation in the NH2-terminus leucine zipper protein interaction domain of PKG-1α [leucine zipper mutant (LZM)], we found a progressive increase in right ventricular systolic pressure and right heart hypertrophy compared with wild-type (WT) mice and increased RhoA-GTPase activity in the lungs. When exposed to chronic hypoxia, LZM mice developed modestly enhanced right ventricular remodeling compared with WT mice. Tadalafil, a phosphodiesterase-5 inhibitor that increases cGMP levels, significantly attenuated hypoxia-induced cardiopulmonary remodeling in WT mice but had no effect in LZM mice. We conclude that a functional leucine zipper domain in PKG-1α is essential for maintenance of a low pulmonary vascular tone in normoxia and for cGMP-mediated beneficial effects of phosphodiesterase-5 inhibition in hypoxic cardiopulmonary remodeling.