Abstract-Nonphagocytic NADPH oxidases have recently been suggested to play a major role in the regulation of physiological and pathophysiological processes, in particular, hypertrophy, remodeling, and angiogenesis in the systemic circulation. Moreover, NADPH oxidases have been suggested to serve as oxygen sensors in the lung. Chronic hypoxia induces vascular remodeling with medial hypertrophy leading to the development of pulmonary hypertension. We screened lung tissue for the expression of NADPH oxidase subunits. NOX1, NOXA1, NOXO1, p22phox, p47phox, p40phox, p67phox, NOX2, and NOX4 were present in mouse lung tissue. Comparing mice maintained for 21 days under hypoxic (10% O 2 ) or normoxic (21% O 2 ) conditions, an upregulation exclusively of NOX4 mRNA was observed under hypoxia in homogenized lung tissue, concomitant with increased levels in microdissected pulmonary arterial vessels. In situ hybridization and immunohistological staining for NOX4 in mouse lungs revealed a localization of NOX4 mRNA and protein predominantly in the media of small pulmonary arteries, with increased labeling intensities after chronic exposure to hypoxia. In isolated pulmonary arterial smooth muscle cells (PASMCs), NOX4 was localized primarily to the perinuclear space and its expression levels were increased after exposure to hypoxia. Treatment of PASMCs with siRNA directed against NOX4 decreased NOX4 mRNA levels and reduced PASMC proliferation as well as generation of reactive oxygen species. In lungs from patients with idiopathic pulmonary arterial hypertension (IPAH), expression levels of NOX4, which was localized in the vessel media, were 2.5-fold upregulated. These results support an important role for NOX4 in the vascular remodeling associated with development of pulmonary hypertension. (Circ Res.
2007;101:258-267.)Key Words: hypoxia Ⅲ hypoxic pulmonary vasoconstriction Ⅲ NADPH oxidase Ⅲ pulmonary hypertension Ⅲ vascular smooth muscle cell proliferation T he NADPH oxidases are superoxide-generating enzymes that release superoxide by electron transfer from NADPH to oxygen. The classical leukocyte NADPH oxidase plays an important role in host defense against bacterial and fungal pathogens. 1,2 This phagocytic type of NADPH oxidase consists of 2 membrane-bound subunits, gp91 phox and p22 phox which form the flavocytochrome b 558 complex, together with the cyctosolic subunits p40 phox , p47 phox , and p67 phox . Superoxide production by this complex is induced by assembly of the cytosolic and membrane-bound subunits. Such an assembly can be induced by the phosphorylation of p47 phox . 3 Rac GTPases are also involved in this activation process. Recently, several additional isoforms of the membrane-bound subunit gp91phox have been described. The first described homolog of gp91 phox , called mox1 (later NOX1), is primarily expressed in the colon and is suggested to be involved in mitogenic activity. 4 Additional homologs, including NOX3, NOX4 (Renox), NOX5, Duox1, and Duox2, were subsequently described. [5][6][7][8] According to ...
