Abstract 3916: Hematopoietic Sphingosine-1-phosphate Receptor 4 Affects Inflammation, Migration And Atherosclerotic Lesion Formation
Background: The bioactive lipid mediator sphingosine-1-phosphate (S1P), an important component of HDL, is involved in a broad variety of cellular responses like inflammation and migration. S1P is considered antiatherogenic, mainly due to its anti-inflammatory properties upon binding to one of its designated G-protein-coupled receptors. While knowledge on S1P receptors 1–3 function is increasing, nothing is known about S1P receptor 4 (S1P4) signaling in atherosclerosis.
Aim: Our aim was to investigate the role of S1P4 in atherogenesis.
Methods & Results: Immunohistochemical staining of human atherosclerotic plaques using an S1P4 specific antibody revealed strong immunoreactivity in T-cells and monocytes/macrophages, and moderate to low staining in endothelium and smooth muscle cells. To investigate hematopoietic S1P4 signaling in atherosclerosis development, we transplanted bone marrow from newly generated S1P4−/− mice to irradiated LDL receptor deficient mice. After reconstitution, mice were fed a high fat diet for 10 weeks, after which lesion development was analyzed. S1P4−/− reconstituted mice developed significantly smaller (25%, p<0.05) atherosclerotic lesions compared to controls. Interestingly, lesions of the S1P4−/− transplanted mice exhibited a more inflammatory phenotype as characterized by a higher T-cell content (87 ± 9.5 vs. 132 ± 19 cells/mm2) and an increase in small macrophages. To assess the contribution of S1P4 signaling in macrophages in more detail in vitro experiments using bone marrow derived macrophages were performed. Interestingly, S1P4−/− macrophages exhibited a ~50% decreased migration towards S1P compared to control cells (p<0.05). Moreover, we found an augmented inflammatory response, characterized by increased IL-12 and decreased IL-10 production, in S1P4−/− macrophages upon LPS treatment. This difference became even more pronounced when cells were coincubated with LPS and S1P.
Conclusions: This is the first report to describe the presence of S1P4 in human atherosclerotic lesions. More importantly, this is the first study to describe a functional role for hematopoietic S1P4 in atherosclerosis development most likely via induction of migration and inhibition of inflammation.