Selective coupling of the S1P(3) receptor subtype to S1P-mediated RhoA activation and cardioprotection.

Sphingosine-1-phosphate (S1P), a bioactive lysophospholipid, is generated and released at sites of tissue injury in the heart and can act on S1P(1), S1P(2), and S1P(3) receptor subtypes to affect cardiovascular responses. We established that S1P causes little phosphoinositide hydrolysis and does not induce hypertrophy indicating that it does not cause receptor coupling to G(q). We previously demonstrated that S1P confers cardioprotection against ischemia/reperfusion by activating RhoA and its downstream effector PKD. The S1P receptor subtypes and G proteins that regulate RhoA activation and downstream responses in the heart have not been determined. Using siRNA or pertussis toxin to inhibit different G proteins in NRVMs we established that S1P regulates RhoA activation through Gα(13) but not Gα(12), Gα(q), or Gα(i). Knockdown of the three major S1P receptors using siRNA demonstrated a requirement for S1P(3) in RhoA activation and subsequent phosphorylation of PKD, and this was confirmed in studies using isolated hearts from S1P(3) knockout (KO) mice. S1P treatment reduced infarct size induced by ischemia/reperfusion in Langendorff perfused wild-type (WT) hearts and this protection was abolished in the S1P(3) KO mouse heart. CYM-51736, an S1P(3)-specific agonist, also decreased infarct size after ischemia/reperfusion to a degree similar to that achieved by S1P. The finding that S1P(3) receptor- and Gα(13)-mediated RhoA activation is responsible for protection against ischemia/reperfusion suggests that selective targeting of S1P(3) receptors could provide therapeutic benefits in ischemic heart disease.