Epicardial progenitor cells (EpiCs) which are derived from the proepicardium have the potential to differentiate into coronary vascular smooth muscle cells during development.Whether sphingosine 1-phosphate (S1P),a highly hydrophobic zwitterionic lysophospholipid in signal transduction,induces the differentiation of EpiCs is unknown.In the present study,we demonstrated that S1P significantly induced the expression of smooth muscle cell specific markers α-smooth muscle actin and myosin heavy chain 11 in the EpiCs.And the smooth muscle cells differentiated from the EpiCs stimulated by S1P were further evaluated by gel contraction assay.To further confirm the major subtype of sphingosine 1-phosphate receptors (S1PRs) involved in the differentiation of EpiCs,we used the agonists and antagonists of different S1PRs.The results showed that the S1P1/S1 P3 antagonist VPC23019 and the S1P2 antagonist JTE013 significantly attenuated EpiCs differentiation,while the S1P1 agonist SEW2871 and antagonist W146 did not affect EpiCs differentiation.These results collectively suggested that S1P,principally through its receptor S1P3,increases EpiCs differentiation into VSMCs and thus indicated the importance of S1P signaling in the embryonic coronary vasculature,while S1P2 plays a secondary role.