IκBβ-Mediated NF-κB Activation Confers Protection against Hyperoxic Lung Injury

Abstract

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...

Sustained hyperoxia-induced NF-κB activation improves survival and preserves lung development in neonatal mice

“…Furthermore, previous studies have shown that inflammatory stress-induced NF-B activation disrupts lung branching and lung morphogenesis (5, 10). In contrast, multiple studies have demonstrated that NF-B activity is protective against oxidative stress, demonstrated by increased injury with NF-B inhibition ( tivation have improved survival attributable to enhanced expression of NF-B regulated antiapoptotic genes (44). Of note, neonatal AKBI mice exposed to hyperoxia demonstrate early and enhanced expression of proinflammatory NF-B-regulated target genes compared with similarly exposed WT mice and previous reports (4,15,19,37,56,57).…”

“…In contrast, IB␤ has no nuclear export sequence and, once in the nucleus, acts to stabilize NF-B DNA binding and potentiate NF-B activity and downstream gene expression (47). This sustained NF-B activity protects cells from oxidant stress-induced cell death and prevents pulmonary oxygen toxicity in adult mice (44,58).…”

Differential sex-specific effects of oxygen toxicity in human umbilical vein endothelial cells

“…p65 is then released and free to associate with the p50 subunit; releasing the active NF-κB to enter the nucleus and activate gene expression [26]. Sustained activation of NF-κB has been shown to attenuate hyperoxia-induced mortality in adults and improve survival, preserve lung development and decrease hyperoxic lung injury in neonatal mice [27]. In human pulmonary epithelial cells, NF-κB pathway activation decreased hyperoxia induced cell death [28].…”

Endotoxemia Induces IκBβ/NF-κB–Dependent Endothelin-1 Expression in Hepatic Macrophages

“…Furthermore, we have previously reported that AKBI mice are resistant to oxidative stress and hyperoxic lung injury. (35, 43, 44) Given the potential interaction between oxidative stress and NFκB signaling, we assessed the expression of the two major anti-oxidant NFκB target genes, manganese superoxide dismutase (MnSOD) and ferritin heavy chain, and two major pro-oxidant NFκB target genes, xanthine oxidase/dehydrogenase (XOR) and cyclooxygenase-2 (COX-2). (45) Importantly, expression of these NFκB targets was not different between endotoxemic WT and AKBI mice (Supplemental Figure 2).…”