Hyperoxia impairs postnatal alveolar epithelial development via NADPH oxidase in newborn mice

Abstract

Hyperoxia disrupts postnatal lung development in part through inducing inflammation. To determine the contribution of leukocyte-derived reactive oxygen species, we exposed newborn wild-type and NADPH oxidase p47 phox subunit null (p47 phox−/−) mice to air or acute hyperoxia (95% O2) for up to 11 days. Hyperoxia-induced pulmonary neutrophil influx was similar in wild-type and p47−/− mice at postnatal days (P) 7 and 11. Macrophages were decreased in wild-type hyperoxia-exposed mice compared with p47 phox−/− mice at P11. Hyperoxia impaired type II alveolar epithelial cell and bronchiolar epithelial cell proliferation, but depression of type II cell proliferation was significantly less in p47−/− mice at P3 and P7, when inflammation was minimal. We found reciprocal results for the expression of the cell cycle inhibitor p21 cip/waf in type II cells, which was induced in 95% O2-exposed wild-type mice, but significantly less in p47 phox−/− littermates at P7. Despite partial preservation of type II cell proliferation, deletion of p47 phox did not prevent the major adverse effects of hyperoxia on alveolar development estimated by morphometry at P11, but hyperoxia impairment of elastin deposition at alveolar septal crests was significantly worse in wild-type vs. p47 phox−/− mice at P11. Since we found that p47 phox is expressed in a subset of alveolar epithelial cells, its deletion may protect postnatal type II alveolar epithelial proliferation from hyperoxia through effects on epithelial as well as phagocyte-generated superoxide.