Deficiency of NOX1/nicotinamide adenine dinucleotide phosphate, reduced form oxidase leads to pulmonary vascular remodeling.

OBJECTIVE Involvement of reactive oxygen species derived from nicotinamide adenine dinucleotide phosphate, reduced form (NADPH) oxidase has been documented in the development of hypoxia-induced model of pulmonary arterial hypertension (PAH). Because the PAH-like phenotype was demonstrated in mice deficient in Nox1 gene (Nox1(-/Y)) raised under normoxia, the aim of this study was to clarify how the lack of NOX1/NADPH oxidase could lead to pulmonary pathology. APPROACH AND RESULTS Spontaneous enlargement and hypertrophy of the right ventricle, accompanied by hypertrophy of pulmonary vessels, were demonstrated in Nox1(-/Y) 9 to 18 weeks old. Because an increased number of α-smooth muscle actin-positive vessels were observed in Nox1(-/Y), pulmonary arterial smooth muscle cells (PASMCs) were isolated and characterized by flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labeling staining. In Nox1(-/Y) PASMCs, the number of apoptotic cells was significantly reduced without any change in the expression of endothelin-1, and hypoxia-inducible factors HIF-1α and HIF-2α, factors implicated in the pathogenesis of PAH. A significant decrease in a voltage-dependent K(+) channel, Kv1.5 protein, and an increase in intracellular potassium levels were demonstrated in Nox1(-/Y) PASMCs. When a rescue study was performed in Nox1(-/Y) crossed with transgenic mice overexpressing rat Nox1 gene, impaired apoptosis and the level of Kv1.5 protein in PASMCs were almost completely recovered in Nox1(-/Y) harboring the Nox1 transgene. CONCLUSIONS These findings suggest a critical role for NOX1 in cellular apoptosis by regulating Kv1.5 and intracellular potassium levels. Because dysfunction of Kv1.5 is among the features demonstrated in PAH, inactivation of NOX1/NADPH oxidase may be a causative factor for pulmonary vascular remodeling associated with PAH.