Rationale:: The role of sphingosine-1-phosphate (S1P) and its receptors in the pathogenesis of atherosclerosis has not been investigated. Objective:: We hypothesized that the S1P receptor 3 (S1P ₃ ) plays a causal role in the pathogenesis of atherosclerosis. Methods and Results:: We examined atherosclerotic lesion development in mice deficient for S1P ₃ and apolipoprotein (Apo)E. Although S1P ₃ deficiency did not affect lesion size after 25 or 45 weeks of normal chow diet, it resulted in a dramatic reduction of the monocyte/macrophage content in lesions of S1P ₃ ^−/− /ApoE ^−/− double knockout mice. To search for putative defects in monocyte/macrophage recruitment, we examined macrophage-driven inflammation during thioglycollate-induced peritonitis. Elicited peritoneal macrophages were reduced in S1P ₃ -deficient mice and expressed lower levels of tumor necrosis factor-α and monocyte chemoattractant protein-1. Bone marrow–derived S1P ₃ -deficient macrophages produced less MCP-1 in response to lipopolysaccharide stimulation. In vitro, S1P was chemotactic for wild-type but not S1P ₃ -deficient peritoneal macrophages. In vivo, S1P concentration increased rapidly in the peritoneal cavity after initiation of peritonitis. Treatment with the S1P analog FTY720 attenuated macrophage recruitment to the peritoneum. Studies in bone marrow chimeras showed that S1P ₃ in both hematopoietic and nonhematopoietic cells contributed to monocyte/macrophage accumulation in atherosclerotic lesions. Finally, S1P ₃ deficiency increased the smooth muscle cell content of atherosclerotic lesions and enhanced neointima formation after carotid ligation arguing for an antiproliferative/antimigratory role of S1P ₃ in the arterial injury response. Conclusions:: Our data suggest that S1P ₃ mediates the chemotactic effect of S1P in macrophages in vitro and in vivo and plays a causal role in atherosclerosis by promoting inflammatory monocyte/macrophage recruitment and altering smooth muscle cell behavior.

The biologically active sphingolipid sphingosine-1-phosphate (S1P) plays key functions in the immune, inflammatory, and cardiovascular systems. In the vasculature, S1P and its receptors are involved in vessel morphogenesis and angiogenesis during embryonic development and in the adult organism both under normal and pathological conditions. Via its actions on endothelial and smooth muscle cells, S1P regulates arterial tone, vascular permeability, and tissue perfusion. Elevated local S1P levels during inflammation induce endothelial adhesion molecules, recruit inflammatory cells, and activate dendritic cells. At the same time, S1P activates a negative feedback loop that consecutively seals endothelial cell-cell contacts, decreases vascular leakage, and inhibits cytokine-induced leukocyte adhesion. Thus S1P determines not only the build-up, magnitude, and duration of an inflammatory reaction but also the pace of its resolution. This review focuses on the role S1P plays in endothelial function, its receptors and signalling pathways, and the role its major carrier high-density lipoproteins (HDL) play in its bioavailability and transport. We will also discuss the potential of interfering with S1P-S1P receptor interactions for the treatment of endothelial disorders and vascular pathologies.

Sphingosine-1-phosphate (S1P) participates in inflammation; however, its role in leukocyte rolling is still unclear. Here we use intravital microscopy in inflamed mouse cremaster muscle venules and human endothelial cells to show that S1P contributes to P-selectin-dependent leukocyte rolling through endothelial S1P receptor 3 (S1P₃) and Gα_q, PLCβ and Ca²⁺. Intra-arterial S1P administration increases leukocyte rolling, while S1P₃deficiency or inhibition dramatically reduces it. Mast cells involved in triggering rolling also release S1P that mobilizes P-selectin through S1P₃. Histamine and epinephrine require S1P₃for full-scale effect accomplishing it by stimulating sphingosine kinase 1 (Sphk1). In a counter-regulatory manner, S1P₁inhibits cAMP-stimulated Sphk1 and blocks rolling as observed in endothelial-specificS1P₁^−/−mice. In agreement with a dominant pro-rolling effect of S1P₃, FTY720 inhibits rolling in control andS1P₁^−/−but not inS1P₃^−/−mice. Our findings identify S1P as a direct and indirect contributor to leukocyte rolling and characterize the receptors mediating its action.