Protective Role of Myelocytic Nitric Oxide Synthases against Hypoxic Pulmonary Hypertension in Mice

Rationale: Nitric oxide (NO), synthesized by NOSs (NO synthases), plays a role in the development of pulmonary hypertension (PH). However, the role of NO/NOSs in bone marrow (BM) cells in PH remains elusive. Objectives: To determine the role of NOSs in BM cells in PH. Methods: Experiments were performed on 36 patients with idiopathic pulmonary fibrosis and on wild- type (WT), nNOS (neuronal NOS)(-/-), iNOS (inducible NOS)(-/-), eNOS (endothelial NOS)(-/-), and n/i/eNOSs(-/-) mice. Measurements and Main Results: In the patients, there was a significant correlation between higher pulmonary artery systolic pressure and lower nitrite plus nitrate levels in the BAL fluid. In themice, hypoxiainducedPHdeteriorated significantly in then/i/eNOSs(-/-) genotype and, to a lesser extent, in the eNOS(-/-) genotype as compared with the WT genotype. In the n/i/eNOSs(-/-) genotype exposed to hypoxia, the number of circulating BM- derived vascular smooth muscle progenitor cells was significantly larger, and transplantation of green fluorescent protein- transgenic BM cells revealed the contribution of BM cells to pulmonary vascular remodeling. Importantly, n/i/eNOSs(-/-) - BM transplantation significantly aggravated hypoxia- induced PH in the WT genotype, andWT- BM transplantation significantly ameliorated hypoxia- induced PH in the n/i/eNOSs(-/-) genotype. A total of 69 and 49 mRNAs related to immunityand inflammation, respectively, were significantly upregulated in the lungs ofWTgenotypemice transplanted with n/i/eNOSs(-/-) - BM compared with those withWT- BM, suggesting the involvement of immune and inflammatorymechanisms in the exacerbation of hypoxiainduced PH caused by n/i/eNOSs(-/-) - BM transplantation. Conclusions: These results demonstrate that myelocytic n/i/eNOSs play an important protective role in the pathogenesis of PH.