Abstract-The lipid mediator sphingosine-1-phosphate (S1P), the product of sphingosine kinase (SPHK)-induced phosphorylation of sphingosine, is known to stabilize interendothelial junctions and prevent microvessel leakiness. Here, we investigated the role of SPHK1 activation in regulating the increase in pulmonary microvessel permeability induced by challenge of mice with lipopolysaccharide or thrombin ligation of protease-activating receptor (PAR)-1. Both lipopolysaccharide and thrombin increased mouse lung microvascular permeability and resulted in a delayed activation of SPHK1 that was coupled to the onset of restoration of permeability. In contrast to wild-type mice, Sphk1 Ϫ/Ϫ mice showed markedly enhanced pulmonary edema formation in response to lipopolysaccharide and PAR-1 activation. Using endothelial cells challenged with thrombin concentration (50 nmol/L) that elicited a transient but reversible increase in endothelial permeability, we observed that increased SPHK1 activity and decreased intracellular S1P concentration preceded the onset of barrier recovery. Thus, we tested the hypothesis that released S1P in a paracrine manner activates its receptor S1P1 to restore the endothelial barrier. Knockdown of SPHK1 decreased basal S1P production and Rac1 activity but increased basal endothelial permeability. In SPHK1-depleted cells, PAR-1 activation failed to induce Rac1 activation but augmented RhoA activation and endothelial hyperpermeability response. Knockdown of S1P1 receptor in endothelial cells also enhanced the increase in endothelial permeability following PAR-1 activation. S1P treatment of Sphk1 Ϫ/Ϫ lungs or SPHK1-deficient endothelial cells restored endothelial barrier function. Our results suggest the crucial role of activation of the SPHK13 S1P3 S1P1 signaling pathway in response to inflammatory mediators in endothelial cells in regulating endothelial barrier homeostasis. Key Words: sphingosine kinase Ⅲ lung vascular permeability Ⅲ thrombin Ⅲ PAR-1 Ⅲ RhoGTPases Ⅲ S1P1 Ⅲ S1P T he vascular endothelium forms a semipermeable barrier separating intravascular and tissue compartments. Disruption of endothelial barrier is a crucial factor in the pathogenesis of tissue inflammation, the hallmark of inflammatory diseases such as the acute respiratory distress syndrome. 1 Increased microvessel endothelial permeability leads to protein-rich alveolar edema that severely impairs oxygenation. 2 Thrombin, a serine protease, generated during sepsis and intravascular coagulation, ligates the endothelial cell surface receptor protease activating receptor 1 (PAR-1) and increases endothelial permeability. 1,[3][4][5][6] This increase in endothelial permeability is typically followed by a recovery period of Ϸ2 hours, during which barrier integrity is restored. 7,8 It has been surmised that PAR-1 signaling stimulates intrinsic repair mechanisms that restore barrier function. 7-9 Sphingosine-1-phosphate (S1P), a lipid mediator, was shown to be 1 such factor promoting endothelial barrier function. 10 -13 S1P binds to S...

The endothelial monolayer partitioning underlying tissue from blood components in the vessel wall maintains tissue fluid balance and host defense through dynamically opening intercellular junctions. Edemagenic agonists disrupt endothelial barrier function by signaling the opening of the intercellular junctions leading to the formation of protein-rich edema in the interstitial tissue, a hallmark of tissue inflammation that, if left untreated, causes fatal diseases, such as acute respiratory distress syndrome. In this review, we discuss how intercellular junctions are maintained under normal conditions and after stimulation of endothelium with edemagenic agonists. We have focused on reviewing the new concepts dealing with the alteration of adherens junctions after inflammatory stimulus.

TRPC6-dependent Ca2+ flux in endothelial cells after TLR4-induced diacylglycerol production mediates lung endothelial barrier disruption and inflammation induced by LPS.

Weber et al. identify TRPC6 as the calcium channel mediating the transient increase in endothelial cytosolic free calcium concentration required for transendothelial migration of leukocytes during the inflammatory response.