Endothelial FAK suppresses NADPH oxidase activity and ROS generation to prevent ALI

Abstract

Acute lung injury (ALI), characterized by capillary barrier dysfunction and increased reactive oxygen species (ROS) generation in the pulmonary vasculature, is associated with high morbidity/mortality and has no effective therapy. The role of endothelium-derived ROS and mechanisms to prevent ROS in the pulmonary vasculature remain enigmatic in the pathogenesis of ALI. Since focal adhesion kinase (FAK) maintains cell-matrix and inter-endothelial adhesion, we generated endothelial (EC) FAK deficient transgenic adult mice (EC-FAK−/−) to test that FAK controls vessel integrity and ROS production to prevent ALI. We show loss of EC-FAK causes destruction of alveolar structures, interstitial and alveolar edema, and leukocyte seepage into the interstitium and alveolar space. EC-FAK deletion augmented NADPH oxidase and peroxidase activities in lung endothelium causing increased ROS levels and EC apoptosis. Nox2 and Nox4 are the major NADPH oxidases in ECs. Impairment of FAK resulted in increased Nox2 protein expression whereas Nox4 levels remained unchanged suggesting increased ROS production in EC-FAK null lungs was due to hyperactivation of Nox2. These findings were recapitulated in FAK depleted human pulmonary ECs. EC-FAK null mice show increased mortality following sub-lethal dose of i.p. LPS. Our results reveal a novel role of FAK in suppressing Nox2 expression and ROS generation thereby preventing ALI.