Sphingosine 1-phosphate promotes endothelial cell barrier integrity by Edg-dependent cytoskeletal rearrangement

Substances released by platelets during blood clotting are essential partic ipants in events that link hemostasis and angiogenesis and ensure adequate wound healing and tissue injury repair. We assessed the participation of sp hingosine 1-phosphate (Sph-1-P), a biologically active phosphorylated lipid growth factor released from activated platelets, in the regulation of endo thelial monolayer barrier integrity, which is key to both angiogenesis and vascular homeostasis. Sph-1-P produced rapid, sustained, and dose-dependent increases in transmonolayer electrical resistance (TER) across both human and bovine pulmonary artery and lung microvascular endothelial cells. This substance also reversed barrier dysfunction elicited by the edemagenic agen t thrombin. Sph-1-P-mediated barrier enhancement was dependent upon G(i alp ha)-receptor coupling to specific members of the endothelial differentiatio n gene (Edg) family of receptors (Edg-1 and Edg-3), Rho kinase and tyrosine kinase-dependent activation, and actin filament rearrangement. Sph-l-P-enh anced TER occurred in conjunction with Rac GTPase- and p21-associated kinas e-dependent endothelial cortical actin assembly with recruitment of the act in filament regulatory protein, cofilin. Platelet-released Sph-1-P, linked to Rac- and Rho-dependent cytoskeletal rearrangement, may act late in angio genesis to stabilize newly formed vessels, which often display abnormally i ncreased vascular permeability.