Abstract
S1P is a platelet-derived angiogenic sphingolipid that activates a novel family of G-protein coupled receptors; eNOS has been implicated in angiogenic responses of vascular endothelial cells (EC). We explored whether and how S1P might regulate eNOS. We found that S1P induces robust eNOS activation to a degree comparable to those induced by classical eNOS agonists such as bradykinin or VEGF in cultured bovine aortic EC. eNOS activation by S1P is mediated via a signaling cascade comprising S1P1 (EDG-1) receptors; PTx-sensitive G-proteins; PI3-kinase β; and a protein kinase Akt, which phosphorylates eNOS at serine 1179 to activate the enzyme. VEGF was known to activate eNOS and modulate angiogenesis independently of S1P. We discovered that VEGF induces marked up-regulation of S1P1 protein/mRNA expression by 4 fold within 90 min, and thereby enhances subsequent S1P-dependent eNOS activation/S1179 phosphorylation in cultured EC as well as in intact rat mesenteric arterioles. These data indicate that VEGF specifically induces expression of S1P receptors, associated with enhanced eNOS responses to S1P. We propose that VEGF acts to sensitize the vascular endothelium to the effects of lipid mediators by promoting the induction of S1P1 receptors, representing a potentially important point of cross-talk between receptor-regulated eNOS signaling pathways. These studies establish that an angiogenic lipid mediator S1P is a novel and potent eNOS regulator in the vasculature, which modulates its specific receptors synergistically with VEGF. [Jpn J Physiol 54 Suppl:S42 (2004)]
