Chapter 5 Arg mediates endothelial barrier disruption by impairing integrin α 5 β 1-mediated cell adhesion

Endothelial barrier disruption and vascular leakage importantly contribute to organ dysfunction during inflammation in conditions like sepsis and acute respiratory distress syndrome. We recently identified the kinase Abl-related gene (Arg/ABL2) as mediator of endothelial barrier disruption, but its relevance in vivo and the mechanisms by which Arg mediates endothelial barrier disruption remain largely unknown. Here, we report that Arg is activated in the endothelium during inflammation, both in pulmonary microvessels of septic patients, and in cultured endothelial cells exposed to barrier-disruptive agents. Genetic depletion of Arg in vivo (Arg-/-mice) and in vitro (siRNA-mediated silencing) strongly attenuated vascular leak and endothelial barrier disruption upon exposure to inflammatory conditions, without affecting monolayer integrity under resting conditions. Mechanistically, Arg is involved in internalization and spatial distribution of α 5 β 1 integrin, as Arg-depleted endothelial cells show enhanced expression of α 5 β 1 integrin at the cell membrane, which is predominantly located at the cell periphery, close to cell-cell contacts. The α 5 β 1 redistribution is paralleled by reduced force development at the cell-matrix interface and reduced cell retraction, thus limiting intercellular gap formation. Collectively, this study shows that Arg is a key mediator of inflammation-induced endothelial barrier disruption. This study identifies a novel Arg-driven mechanism of endothelial barrier disruption, in which Arg-mediated internalization of peripheral α 5 β 1 matrix adhesions contributes to cell retraction and gap formation. As several Abl kinase inhibitors are clinically available, Arg inhibition may form a suitable strategy to target vascular leak.