Absence of Integrin αvβ3 Enhances Vascular Leak in Mice by Inhibiting Endothelial Cortical Actin Formation

Rationale: Sepsis and acute lung injury (ALI) have devastatingly high mortality rates. Both are associated with increased vascular leak, a process regulated by complex molecular mechanisms. Objectives: We hypothesized that integrin alpha v beta 3 could be an important determinant of vascular leak and endothelial permeability in sepsis and ALI. Methods: beta 3 subunit knockout mice were tested for lung vascular leak after endotracheal LPS, and systemic vascular leak and mortality after intraperitoneal LPS and cecal ligation and puncture. Possible contributory effects of beta 3 deficiency in platelets and other hematopoietic cells were excluded by bone marrow reconstitution experiments. Endothelial cells treated with alpha v beta 3 antibodies were evaluated for sphingosine-1 phosphate (S1P)-mediated alterations in barrier function, cytoskeletal arrangement, and integrin localization. Measurements and Main Results: beta 3 knockout mice had increased vascular leak and pulmonary edema formation after endotracheal LPS, and increased vascular leak and mortality after intraperitoneal LPS and cecal ligation and puncture. In endothelial cells, alpha v beta 3 antibodies inhibited barrier-enhancing and cortical actin responses to S1P. Furthermore, S1P induced translocation of alpha v beta 3 from discrete focal adhesions to cortically distributed sites through Gi- and Rac1-mediated pathways. Cortical alpha v beta 3 localization after S1P was decreased by alpha v beta 3 antibodies, suggesting that ligation of the alpha v beta 3 with its extracellular matrix ligands is required to stabilize cortical alpha v beta 3 focal adhesions. Conclusions: Our studies identify a novel mechanism by which alpha v beta 3 mitigates increased vascular leak, a pathophysiologic function central to sepsis and ALI. These studies suggest that drugs designed to block alpha v beta 3 may have the unexpected side effect of intensifying sepsis- and ALI-associated vascular endothelial leak.