Hyperoxia and Interferon-γ–Induced Injury in Developing Lungs Occur via Cyclooxygenase-2 and the Endoplasmic Reticulum Stress–Dependent Pathway

Abstract

We noted a marked increase in cyclooxygenase-2 (Cox2) and the activation of the endoplasmic reticulum (ER) stress pathway in newborn murine lung on exposure to hyperoxia and IFN-g.We soughtto evaluate Cox2-mediated ER stress pathway activation in hyperoxia-induced and IFN-g-mediated injury in developing lungs. We applied in vivo genetic gain-of-function and genetic/chemical inhibition, as well as in vitro lossof-function genetic strategies. Hyperoxia-induced and IFN-g-mediated impaired alveolarization was rescued by Cox2 inhibition, using celecoxib. The use of small interfering RNA against the ER stress pathway mediator, the C/EBP homologous protein (CHOP; also known as growth arrest and DNA damage-inducible gene 153/GADD153), alleviated cell death in alveolar epithelial cells as well as in hyperoxia-induced and IFNg-mediated murine models of bronchopulmonary dysplasia (BPD). In addition, CHOP siRNA also restored alveolarization in the in vivo models. Furthermore, as evidence of clinical relevance, we show increased concentrations of Cox2 and ER stress pathway mediators in human lungs with BPD. Cox2, via CHOP, may significantly contribute to the final common pathway of hyperoxia-induced and IFN-g-mediated injury in developing lungs and human BPD.Keywords: newborn; oxygen; BPD; CHOP; cell deathIn the developing lung, injury attributable to hyperoxic exposure is an important component in the pathogenesis of bronchopulmonary dysplasia (BPD) (1, 2). The immature human lung during the saccular phase is most commonly exposed to such an exogenous insult, and is predisposed to BPD. The final result is a lung phenotype characterized by fewer and larger simplified alveoli (1-4). Hyperoxia-induced lung injury is characterized by an influx of inflammatory cells, along with endothelial and epithelial cell death (5, 6).Cell death is said to be a key initiator of the process of alveolar simplification. The activation of key caspases (3,8,9) and components of the extrinsic/death receptor and intrinsic/ mitochondrial cell death pathways underlies the molecular mechanisms of cell death (5-7). Another cell-death signaling pathway involves the endoplasmic reticulum (ER), which is the site for the folding and assembly of proteins destined for delivery to the extracellular space, plasma membrane, and the exocytic/endocytic compartments (8, 9). When cells are exposed to ER stress, malfolded or unfolded proteins accumulate in the ER lumen, giving rise to a synonymous term, the unfolded protein response (UPR) (8, 9). ER stress is sensed by three ER-resident transmembrane proteins, specifically, inositol-requiring enzyme-1 a (IRE-a), activating transcription factor-6a (ATF6a), and protein kinase regulated by RNA-like ER kinase (PERK), which are freed from binding immunoglobulin protein (BiP; also known as glucoseregulated protein-78, or GRP78) during ER stress (10). Whereas ER stress-induced cell death signaling can occur via multiple pathways, the pathway (i.e., via PERK) that induces transcription of the proapoptotic factor C/EBP homol...

Animal models of bronchopulmonary dysplasia. The term mouse models

“…This result, which was also dose dependent (23), mimics the increased susceptibility to respiratory tract infections that has been well studied in formerly preterm human infants with BPD (12). The same BPD model has also been reported by other investigators (25,50).…”

“…As such, a similar rescue effect was produced with use of the C/EBP homologous protein (which is a critical signaling molecule in the ER stress pathway) siRNA. These data further suggest that targeted inhibition of downstream pathways of IFN-␥ may ameliorate lung damage in hyperoxia (25).…”

Hyperoxic Exposure of Immature Mice Increases the Inflammatory Response to Subsequent Rhinovirus Infection: Association with Danger Signals

“…Furthermore, an analysis of tracheal aspirates from premature human infants showed that the level of prematurity positively correlated with respiratory tract Clec9a mRNA expression. Since hyperoxic exposure causes respiratory epithelial cell death (64–66), we speculate that premature infants experience greater epithelial cell death upon exposure to high oxygen tensions relative to that in utero , leading to expansion of Clec9a+ CD103+ DCs.…”

Inhibition of Regulatory-Associated Protein of Mechanistic Target of Rapamycin Prevents Hyperoxia-Induced Lung Injury by Enhancing Autophagy and Reducing Apoptosis in Neonatal Mice

“…Enhancement of autophagy by MTORC1 inhibition prevented apoptosis and improved diabetic phenotype (38). In contrast, we have recently reported that endoplasmic reticulum stress in hyperoxia-and IFNg-induced mouse models of BPD was associated with increased apoptotic cell death, although no data on autophagy were reported (39). In breast cancer lines, IFN-b induced autophagy upstream of MTORC1, whereas the proapoptotic function was significantly increased in the absence of autophagy (40).…”