NOX4 and pulmonary arterial hypertension: In addition, studies on PASMCs under normobaric hypoxia in both humans (Ismail et al., 2009) and animals (Mittal et al., 2007) have shown that the NADPH oxidase complex (specifically the Nox4 isoform) is overexpressed, contributing to PASMC proliferation leading to pulmonary hypertension.