Increased Hyperoxia-Induced Lung Injury in Nitric Oxide Synthase 2 Null Mice Is Mediated via Angiopoietin 2

Abstract

Supplemental oxygen is frequently prescribed. However, prolonged exposure to high concentrations of oxygen causes hyperoxic acute lung injury (HALI), which manifests as acute respiratory distress syndrome in adults and leads to bronchopulmonary dysplasia in newborns (NBs). Nitric oxide (NO), NO synthases (NOSs), and angiopoietin (Ang) 2 have been implicated in the pathogenesis of HALI. However, the mechanisms of the contributions of NOS/NO and the relationship(s) between NOS/NO and Ang2 have not been addressed. In addition, the relevance of these moieties in adults and NBs has not been evaluated. To address these issues, we compared the responses in hyperoxia of wild-type (NOS [1/1]) and NOS null (2/2) young adult and NB mice. When compared with NOS21/1 adult controls, NOS2 2/2 animals manifest exaggerated alveolar-capillary protein leak and premature death. These responses were associated with enhanced levels of structural cell death, enhanced expression of proapoptotic regulatory proteins, and Ang2. Importantly, silencing RNA knockdown of Ang2 decreased the levels of cell death and the expression of proapoptotic mediators. These effects were at least partially NOS2 specific, and were development dependent, because survival was similar in adult NOS3 1/1 and NOS3 2/2 mice and NB NOS2 1/1 and NOS2 2/2 mice, respectively. These studies demonstrate that NOS2 plays an important protective role in HALI in adult animals. They also demonstrate that this response is mediated, at least in part, by the ability of NOS2 to inhibit hyperoxia-induced Ang2 production and thereby decrease Ang2-induced tissue injury.Keywords: cytokines; hyperoxia; lung Supplemental oxygen is commonly employed to counteract tissue hypoxemia. Although this is lifesaving in most circumstances, prolonged exposure to high concentrations of oxygen can lead to untoward effects. In the lung, exposure to hyperoxia is characterized by an inflammatory response (mediated by cytokines) and breakdown of the alveolar-capillary barrier, leading to pulmonary edema and endothelial and epithelial cell injury/ death (1). In adults, hyperoxic acute lung injury (HALI) causes acute respiratory distress syndrome (2). In neonates, HALI has been shown to lead to a pulmonary phenotype suggestive of bronchopulmonary dysplasia (3). Hence, HALI is a major cause of morbidity and mortality in both adult (2) and neonatal (3,4) populations.In addition, nitric oxide (NO) is known to have oxidant effects (5), and has been implicated in the pathogenesis of HALI. NO is generated via the action of NO synthases (NOSs). The inflammatory response in HALI is initiated and propagated, to a large extent, by the release of cytokines (1), which are known to induce NOS (6, 7). Most data suggest that hyperoxia exposure up-regulates inducible NOS (NOS2) and endothelial NOS (NOS3) expression in adult (8-16) and neonatal (7,(16)(17)(18)(19) lungs. In ALI and cell death, the endogenous production of NO is said to be mostly contributed by up-regulation of NOS2 in the lung (20)(21)(22).Previous work...

A Critical Regulatory Role for Macrophage Migration Inhibitory Factor in Hyperoxia-Induced Injury in the Developing Murine Lung

“…The net effect of the Ang2/Ang1 expression ratio is increased Ang2, which we speculate could be contributing to enhanced HALI and increased mortality in the MIFKO mice. Since increased Ang2 has been shown in mouse models and human subjects (including premature NB with RDS) to be associated with increased mortality and/or adverse pulmonary outcomes [25], [34], [35], we speculate that a decreased concentration of Ang2 could be playing a role in the protective response of the MIFTG mice in hyperoxia.…”

“…For example, in the context of HALI, Ang2 increases vascular permeability, while Ang1 tends to stabilize the blood vessels and decreases vascular permeability. Our previously published data [25], [34] suggest that higher levels of Ang2 in response to hyperoxia exposure in the lung are detrimental in the context of HALI. Such effects in HALI would be further compounded by decreased Ang1.…”

MIF intersubunit disulfide mutant antagonist supports activation of CD74 by endogenous MIF trimer at physiologic concentrations

“…A minimum of 200 cells were counted for the differential cell count (36). Total protein was measured using a DC Protein Assay (Bio-Rad) per the manufacturer's recommendations, as previously described (37).…”

Mending Leaky Blood Vessels: The Angiopoietin-Tie2 Pathway in Sepsis

“…They found that tumor necrosis factor-a-induced upregulation of inflammatory adhesion molecules by endothelial cells required Angpt-2 expression by those cells (Fiedler et al, 2006). Shortly thereafter, Bhandari et al (2012) reported that hyperoxia-induced acute lung injury in mice was ameliorated by genetic or small interfering RNA depletion of Angpt-2, and showed that bronchoalevolar lavage fluid from individuals with acute lung injury contained high levels of Angpt-2. Of note, the authors argued for an injurious role of Angpt-2 in the alveolar epithelial necrosis characteristic of this model.…”