Deletion of P2X7 attenuates hyperoxia-induced acute lung injury via inflammasome suppression

Abstract

-Increasing evidence shows that hyperoxia is a serious complication of oxygen therapy in acutely ill patients that causes excessive production of free radicals leading to hyperoxia-induced acute lung injury (HALI). Our previous studies have shown that P2X7 receptor activation is required for inflammasome activation during HALI. However, the role of P2X7 in HALI is unclear. The main aim of this study was to determine the effect of P2X7 receptor gene deletion on HALI. Wild-type (WT) and P2X7 knockout (P2X7 KO) mice were exposed to 100% O 2 for 72 h. P2X7 KO mice treated with hyperoxia had enhanced survival in 100% O 2 compared with the WT mice. Hyperoxia-induced recruitment of inflammatory cells and elevation of IL-1␤, TNF-␣, monocyte chemoattractant protein-1, and IL-6 levels were attenuated in P2X7 KO mice. P2X7 deletion decreased lung edema and alveolar protein content, which are associated with enhanced alveolar fluid clearance. In addition, activation of the inflammasome was suppressed in P2X7-deficient alveolar macrophages and was associated with suppression of IL-1␤ release. Furthermore, P2X7-deficient alveolar macrophage in type II alveolar epithelial cells (AECs) coculture model abolished protein permeability across mouse type II AEC monolayers. Deletion of P2X7 does not lead to a decrease in epithelial sodium channel expression in cocultures of alveolar macrophages and type II AECs. Taken together, these findings show that deletion of P2X7 is a protective factor and therapeutic target for the amelioration of hyperoxia-induced lung injury. acute lung injury; P2X7; NLRP3; inflammasome; hyperoxia ACUTE LUNG INJURY (ALI) IS a major clinical problem in the United States, accounting for one of the primary causes of in-hospital hypoxemic respiratory failure leading to morbidity and mortality (48). Prolonged exposure to hyperoxia has been conclusively demonstrated to cause ALI (22,58,62). Furthermore, numerous cardiovascular and pulmonary diseases require oxygen therapy (22, 28 -30, 58). Therefore, it is pertinent to understand the mechanism of damage in ALI, wherein the pathology manifests as alveolar damage from immune cell infiltration and pulmonary edema (31,63).Prolonged exposure to oxygen concentrations of FI O 2 Ͼ 0.8 has previously been shown to cause mortality in small animal and higher-order primate models (26). Hyperoxia-induced lung injury contributes to increasing the production of reactive oxygen species (ROS), inflammatory cytokines, as well as exudative pulmonary edema, collagen deposition, and damage to the alveolar epithelium (26, 32). Thus, using hyperoxia as a form of oxygen toxicity is clinically relevant to study the pathophysiology of ALI. In ALI, the disruption of the fine balance between proinflammatory and anti-inflammatory agents is the basic pathology with a concomitant activation of apoptotic signals (33, 59, 62). IL-1␤ was discovered to be one of the early inflammatory cytokines to appear in ALI patients and cause the release of additional cytokines (18). The caspase-1-mediated acti...

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