Abstract
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 Gαq, PLCβ and Ca2+. Intra-arterial S1P administration increases leukocyte rolling, while S1P3 deficiency or inhibition dramatically reduces it. Mast cells involved in triggering rolling also release S1P that mobilizes P-selectin through S1P3. Histamine and epinephrine require S1P3 for full-scale effect accomplishing it by stimulating sphingosine kinase 1 (Sphk1). In a counter-regulatory manner, S1P1 inhibits cAMP-stimulated Sphk1 and blocks rolling as observed in endothelial-specific S1P1−/− mice. In agreement with a dominant pro-rolling effect of S1P3, FTY720 inhibits rolling in control and S1P1−/− but not in S1P3−/− mice. Our findings identify S1P as a direct and indirect contributor to leukocyte rolling and characterize the receptors mediating its action.
Highlights
Sphingosine-1-phosphate (S1P) participates in inflammation; its role in leukocyte rolling is still unclear
To examine whether S1P receptor 3 (S1P3) plays a role in P-selectin-dependent leukocyte rolling in vivo, we employed intravital microscopy to monitor rolling in post-capillary venules of the surgically exteriorized mouse cremaster muscle[24,25]
Profound spontaneous leukocyte rolling is induced by the surgical preparation of the cremaster, which exclusively depends on the rapid mobilization of P-selectin from endothelial Weibel–Palade bodies to the luminal surface in its initial phase (o45 min after exteriorization of the cremaster muscle)[17,26,27,28]
Summary
Sphingosine-1-phosphate (S1P) participates in inflammation; its role in leukocyte rolling is still unclear. In favour of a pro-inflammatory role, exogenous S1P induces endothelial vascular cell adhesion molecule 1 (VCAM-1) and E-selectin, while endogenous S1P mediates the stimulatory effect of tumor-necrosis factor (TNF)-a and LPS on adhesion molecules, which is suppressed by S1P1 short interfering RNA8–10. Chronic overexpression of sphingosine kinase 1 augments VCAM-1 and E-selectin expression and enhances neutrophil adhesion after TNF-a11 Both S1P and S1P1 agonists have been demonstrated to inhibit TNF-ainduced endothelial adhesion molecule expression and adherence of inflammatory cells by interfering with endothelial NF-kB and stimulating nitric oxide production[12,13,14]. Several explanations have been put forward for these apparent discrepancies such as the assumption that S1P receptors may be differentially expressed among endothelial beds, and that the wide range of S1P concentrations employed in the individual studies may have led to contrary effects as observed for S1P in other systems[15]. It is controversial if S1P in general and S1P3 in particular affect leukocyte rolling
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