Activation of Sphingosine Kinase-1 Reverses the Increase in Lung Vascular Permeability Through Sphingosine-1-Phosphate Receptor Signaling in Endothelial Cells

Abstract

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...

Sphingosine-1-phosphate: the Swiss army knife of sphingolipid signaling

“…Lipopolysaccharide markedly enhanced pulmonary edema in SphK2 knockout mice, compared with wild-type mice. These results together with earlier studies also demonstrated that the S1P 1 receptor was required for normal endothelial barrier function and indicate a crucial role for S1P inside-out signaling in the regulation of endothelial barrier homeostasis (30).…”

“…eNOS activation and NO production induced by TNF-a also occurs through S1P generation and stimulation of its receptors leading to activation of Akt to confer cytoprotection from excitotoxic and neurotoxic agents (29). Intriguingly, lipopolysaccharide and thrombin, known to increase mouse lung microvascular permeability, also induced a delayed activation of SphK1 that was coupled to activation of S1P 1 to reverse microvessel leakiness (30). Interestingly, the SphK1/S1P/S1P 3 axis is a downstream component of protease activated receptor-1 (PAR1) signaling that regulates amplification of inflammation in sepsis syndrome.…”

“…However, it was recently demonstrated that treatment of mice with lipopolysaccharide increased lung microvascular permeability followed by activation of SphK1 that was coupled to restoration of normal permeability (30). Lipopolysaccharide markedly enhanced pulmonary edema in SphK2 knockout mice, compared with wild-type mice.…”

A Novel Function of Sphingosine Kinase 1 Suppression of JNK Activity in Preventing Inflammation and Injury

“…The two forms of sphingosine kinases (SphKs), SphK1 and SphK2, have received considerable attention because of their poorly understood functions that are distinct from their catalytic function needed for the production of S1P (43)(44)(45)(46). Although SphKs may play a role in mediating inflammation seen in asthma (43)(44)(45)(46)(47), SphK1 also has a protective function in LPS-and platelet-activating factor-induced lung inflammation (35,48,49). This function may be independent of the S1P production.…”

Fingolimod and macular edema

“…These receptors play an important role in the regulation of endothelial and epithelial barriers [9][10][11] and have been shown to increase vascular permeability. 12 Fingolimod is an S1P receptor analogue, which acts via the S1P1 receptor agonism to protect the adherence junction between the cells; it also acts via the S1P3 receptor agonism to reduce the tight junction between the endothelial cells. This reduction in the tight junctions results in the breakdown of the inner BRB, resulting in ME.…”