Selective coupling of the S1P3 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 SIP causes little phosphoinositide hydrolysis and does not induce hypertrophy indicating that it does not cause receptor coupling to Gq. We previously demonstrated that S1P confers cardioprotection against ischemia/reperfusion by activating RhoA and its downstream effector PKD. The SIP 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 Gan but not Gan, Gag, or Gte,. Knockdown of the three major SIP 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. SIP 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 SIP. The finding that S1P3 receptor- and Gan-mediated RhoA activation is responsible for protection against ischemia/reperfusion suggests that selective targeting of S1P3 receptors could provide therapeutic benefits in ischemic heart disease. (C) 2016 Elsevier Ltd. All rights reserved.