Oxygen toxicity contributes to the pathogenesis of bronchopulmonary dysplasia (BPD). Neonatal mice exposed to hyperoxia develop a simplified lung structure that resembles BPD. Sustained activation of the transcription factor NF-κB and increased expression of protective target genes attenuate hyperoxia-induced mortality in adults. However, the effect of enhancing hyperoxia-induced NF-κB activity on lung injury and development in neonatal animals is unknown. We performed this study to determine whether sustained NF-κB activation, mediated through IκBβ overexpression, preserves lung development in neonatal animals exposed to hyperoxia. Newborn wild-type (WT) and IκBβ-overexpressing (AKBI) mice were exposed to hyperoxia (>95%) or room air from day of life (DOL) 0-14, after which all animals were kept in room air. Survival curves were generated through DOL 14. Lung development was assessed using radial alveolar count (RAC) and mean linear intercept (MLI) at DOL 3 and 28 and pulmonary vessel density at DOL 28. Lung tissue was collected, and NF-κB activity was assessed using Western blot for IκB degradation and NF-κB nuclear translocation. WT mice demonstrated 80% mortality through 14 days of exposure. In contrast, AKBI mice demonstrated 60% survival. Decreased RAC, increased MLI, and pulmonary vessel density caused by hyperoxia in WT mice were significantly attenuated in AKBI mice. These findings were associated with early and sustained NF-κB activation and expression of cytoprotective target genes, including vascular endothelial growth factor receptor 2. We conclude that sustained hyperoxia-induced NF-κB activation improves neonatal survival and preserves lung development. Potentiating early NF-κB activity after hyperoxic exposure may represent a therapeutic intervention to prevent BPD.

Supplemental oxygen is frequently used in an attempt to improve oxygen delivery; however, prolonged exposure results in damage to the pulmonary endothelium and epithelium. Although NF-kB has been identified as a redox-responsive transcription factor, whether NF-kB activation exacerbates or attenuates hyperoxic lung injury is unclear. We determined that sustained NF-kB activity mediated by IkBb attenuates lung injury and prevents mortality in adult mice exposed to greater than 95% O 2 . Adult wild-type mice demonstrated evidence of alveolar protein leak and 100% mortality by 6 days of hyperoxic exposure, and showed NF-kB nuclear translocation that terminated after 48 hours. Furthermore, these mice showed increased expression of NF-kB-regulated proinflammatory and proapoptotic cytokines. In contrast, mice overexpressing the NF-kB inhibitory protein, IkBb (AKBI), demonstrated significant resistance to hyperoxic lung injury, with 50% surviving through 8 days of exposure. This was associated with NF-kB nuclear translocation that persisted through 96 hours of exposure. Although induction of NFkB-regulated proinflammatory cytokines was not different between wild-type and AKBI mice, significant up-regulation of antiapoptotic proteins (BCL-2, BCL-XL) was found exclusively in AKBI mice. We conclude that sustained NF-kB activity mediated by IkBb protects against hyperoxic lung injury through increased expression of antiapoptotic genes.Keywords: NF-kB; IkB; hyperoxic lung injury; apoptosis; inflammation Clinical RelevanceOxygen therapy is commonly employed in an attempt to improve oxygen delivery, and yet prolonged exposure results in lung injury. No pharmacologic strategies to attenuate hyperoxic lung injury have been identified. We show that enhancing hyperoxia-induced NF-kB activity attenuates lung injury, and thus represents a potential therapeutic target.The first studies demonstrating the lethal effect of inspiring high concentrations of oxygen were published over a century ago (1). Due to this toxicity, hyperoxic exposure has been widely used in animal studies to induce and study acute lung injury (2). Despite this, no pharmacologic therapies to attenuate hyperoxic lung injury have been identified.Hyperoxia induces proinflammatory cytokine expression (3), and results in pulmonary endothelial and epithelial cell death (4). Given these facts, both antiinflammatory and antiapoptotic strategies have been employed to attenuate hyperoxic lung injury. Although anti-inflammatory interventions have met variable success (5-9), increasing the expression of antiapoptotic factors in transgenic murine models results in attenuated hyperoxic lung injury (10-12). These studies suggest that preventing hyperoxia-induced apoptosis can prevent lung injury, but the transcriptional mechanism mediating expression of these factors is largely unknown.Hyperoxia-induced NF-kB activation has been documented in both pulmonary epithelial and endothelial cells (13). Whether this response is protective or injurious is unclear. Some in vivo s...