NOX4 and pulmonary arterial hypertension: Although there have not been many studies showing the specific expression and activity of the Nox4 isoform related to PASMC proliferation and pulmonary hypertension under hypobaric hypoxia, however, it is important to mention that Nox4 is the principal isoform expressed in PASMCs of patients with pulmonary hypertension (Sturrock et al., 2006).