In premature infants, sepsis is associated with alveolar simplification manifesting as bronchopulmonary dysplasia. The redox-dependent mechanisms underlying sepsis-induced inflammation and alveolar remodeling in the immature lung remain unclear. We developed a neonatal mouse model of sepsisinduced lung injury to investigate whether nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) regulates Toll-like receptor (TLR)-mediated inflammation and alveolar remodeling. Six-day-old NOX2 1/1 and NOX2 2/2 mice were injected with intraperitoneal LPS to induce sepsis. Lung inflammation and canonical TLR signaling were assessed 24 hours after LPS. Alveolar development was examined in 15-day-old mice after LPS on Day 6. The in vivo efficacy of a NOX2 inhibitor (NOX2-I) on NOX2 complex assembly and sepsis-induced lung inflammation were examined. Lung cytokine expression and neutrophil influx induced with sepsis in NOX2 1/1 mice was decreased by .50% in NOX2 2/2 mice. LPS-induced TLR4 signaling evident by inhibitor of NF-kB kinase-b and mitogen-activated protein kinase phosphorylation, and nuclear factor-kB/AP-1 translocation were attenuated in NOX2 2/2 mice. LPS increased matrix metalloproteinase 9 while decreasing elastin and keratinocyte growth factor levels in NOX21/1 mice. An LPS-induced increase in matrix metalloproteinase 9 and decrease in fibroblast growth factor 7 and elastin were not evident in NOX22/2 mice. An LPS-induced reduction in radial alveolar counts and increased mean linear intercepts were attenuated in NOX2 2/2 mice. LPS-induced NOX2 assembly evident by p67phox/gp91phox coimmunoprecipitation was disrupted with NOX2-I. NOX2-I also mitigated LPS-induced cytokine expression, TLR pathway signaling, and alveolar simplification. In a mouse model of neonatal sepsis, NOX2 regulates proinflammatory TLR signaling and alveolar remodeling induced by a single dose of LPS. Our results provide mechanistic insight into the regulation of sepsis-induced alveolar remodeling in the developing lung.Keywords: nicotinamide adenine dinucleotide phosphate oxidase; sepsis; Toll-like receptor signaling; neonatal lung injury; bronchopulmonary dysplasia Postnatal inflammation and tissue injury in the developing lung contribute to the disrupted alveolar development observed in premature infants with bronchopulmonary dysplasia (BPD) (1, 2). Risk factors associated with BPD, such as hyperoxia, barotrauma, and sepsis, trigger the production of reactive oxygen species (ROS) in the premature lung, which contributes to lung inflammation and matrix degradation (3-5). Multiple investigators have shown that markers of oxidant-mediated lung injury, such as 8-Oxo-29-deoxyguanosine, oxidized surfactant phospholipids, F2-isoprostanes, and nitrotyrosine, are elevated in the bronchoalveolar lavage, serum, or urine of premature infants who subsequently develop BPD (4-7). Therapies to mitigate oxidant stress, such as recombinant superoxide dismutase and vitamin A, have been used in premature infants to decrease BPD, with limited succes...

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