Abstract 618: The Sphingosine-1-phosphate Receptor 3 (S1P3) Governs Macrophage Recruitment To Atherosclerotic Lesions And Inflammation Sites
Objective- Sphingosine-1-phosphate (S1P) is a biologically active sphingolipid that regulates a multitude of physiological processes such as immunity, angiogenesis, regulation of vascular tone, inflammation and cardioprotection. S1P mediates its effects through engagement of its 5 cognate G protein-coupled receptors S1P1–5, of which only S1P1, −2, and −3 are expressed in the vasculature. As the role of S1P and its receptors in atherosclerosis is currently unknown, we examined the progression of atherosclerosis in mice deficient for S1P3 on the ApoE−/−background.
Methods and Results- Atherosclerotic lesion formation and composition was examined in 12 male ApoE−/− // S1P3−/− and 10 ApoE−/− mice fed a normal chow diet for 45 weeks. The brachiocephalic artery (BCA) was serially sectioned according to the method of Cavalieri, and lesion volume and composition were determined. While there was no difference in plaque volume, macrophage content in the lesion was reduced by 76.1% in ApoE−/− // S1P3−/− vs. ApoE−/− mice (6.6±1.1% vs. 27.3±2.7%, p< 0.001). In contrast, lesional smooth muscle cell (SMC) content was increased by 74.4% in ApoE−/− // S1P3−/− vs. ApoE−/− mice (7.3±1.0% vs. 4.2±0.6%, p<0.01). Collagen content was not altered. Serum lipid levels and peripheral blood cell counts were similar. To test if macrophage recruitment to inflammation sites was impaired by S1P3 deficiency, we used a model of sterile peritonitis caused by the irritant thioglycolate. Four days after injection, there was a dramatic decrease in macrophage cell counts in the peritoneum by 82.6% in S1P3−/− mice vs. C57BL/6 controls (2.2±1.3 vs. 12.4±2.3*106 per cavity, p<0.001). In addition, the inflammatory cytokine mRNA expression profile of the S1P3-deficient peritoneal macrophages was strongly altered: MCP-1 and TNFα gene expression were downregulated by 67% and 75%, respectively, while IFNγ gene expression was upregulated by 329%. No changes were observed in the expression of CCR-2, IL-1a, IL-6, IL-10, MIP-1α, MIP-1β, and GM-CSF.
Conclusions- The S1P3 receptor plays a major role in the recruitment of monocyte/macrophages to inflammation sites and atherosclerotic lesions by altering macrophage cytokine expression.