The Sphingosine-1-phospate receptor 1 mediates S1P action during cardiac development

We determined, by real-time PCR analysis, that S1P1R was expressed at least 10-fold higher than other S1P receptors in the developing heart. Immunohistochemical analysis revealed S1P1R protein expression in both endothelial and myocardial cells in the developing atrium and ventricle. Using AV canal cultures, we observed that treatment with either FTY720 (an S1P1,3,4,5R agonist) or KRP203 (an S1P1R-specific agonist) caused similar effects on AV canal cultures as S1P treatment, including induction of cell rounding, inhibition of cell migration, and inhibition of EMT. In vivo, morphological analysis of embryonic hearts at E10.5 revealed that S1P1R-/- hearts were malformed with reduced myocardial tissue. In addition to reduced myocardial tissue, E12.5 S1P1R-/- hearts had disrupted morphology of the heart wall and trabeculae, with thickened and disorganized outer compact layer and reduced fibronectin (FN) deposition compared to S1P1R+/+ littermates. The reduced myocardium was accompanied by a decrease in cell proliferation but not an increase in apoptosis.These data indicate that S1P1R is the primary mediator of S1P action in AV canal cultures and that loss of S1P1R expression in vivo leads to malformed embryonic hearts, in part due to reduced fibronectin expression and reduced cell proliferation.Sphingosine-1-phosphate (S1P) is a biologically active lysophospholipid that is involved in cellular differentiation, proliferation, migration, cytoskeletal reorganization, and apoptosis [1,2]. S1P is produced by sphingosine kinase 1 and 2 (SPHK1 and SPHK2) from sphingosine in response to various cellular stimuli, including vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), tumor necrosis factor-α (TNFα), transforming growth factor-beta (TGFβ), epidermal growth factor (EGF) and cytokines [1-5]. After release from cells, S1P acts in an autocrine and paracrine manner through its cell surface receptors to influence cellular processes.S1P receptors (S1