Endothelial cell junctions and the regulation of vascular permeability and leukocyte transmigration.

The endothelial lining of the vasculature forms the physical barrier between the blood and underlying tissues. Junctions between adjacent endothelial cells are dynamically modulated to sustain vascular homeostasis and to support the transendothelial migration of leukocytes during inflammation. A variety of factors initiate intracellular signaling pathways that regulate the opening and resealing of junctional complexes. This review focuses on three primary signaling pathways initiated within endothelial cells by the binding of vasoactive factors and leukocyte adhesion: Rho GTPases, reactive oxygen species, and tyrosine phosphorylation of junctional proteins. These pathways converge to regulate junctional permeability, either by affecting the stability of junctional proteins or by modulating their interactions. Although much progress has been made in understanding the relationships of these pathways, many questions remain to be answered. A full understanding of the signaling cascades that affect endothelial junctions should identify novel therapeutic targets for diseases that involve excessive permeability or inappropriate leukocyte infiltration into tissues.