Identification of a Novel Role for Sphingolipid Signaling in TNF α and Ischemic Preconditioning Mediated Cardioprotection

TNF α administration mimics ischemic preconditioning and neutralizing antibodies to TNFα and IL-1 β abolish exercise-induced preconditioning. However, the pharmacology of TNFα ʹs cardioprotective effects and associated downstream signaling events has not been delineated. We evaluated the temporal and dose specific requirements of TNF α to function as a preconditioning mimetic. Furthermore we postulated that the preconditioning effect of TNF α might be orchestrated via sphingolipid signaling. The cardioprotective effect of TNF α and the role of sphingolipid signaling were assessed using a classical preconditioning protocol in the isolated perfused rat heart with the measurement of infarct size and contractile function modulation in response to index ischemia and reperfusion. Recombinant TNF α at an optimal dose of 0.5 ng/ml mimicked ischemic preconditioning by reducing infarct size by 60%v non-preconditioned ischemia-reperfusion controls (P<0.01). The infarct sparing effect of TNF α required a wash-out period prior to the index ischemic-reperfusion. Moreover, the classic ischemic preconditioning antagonist such as 5-hydroxydecanoate abolished TNF α preconditioning. An inhibitor of the sphingolipid signaling pathway, N-oleoylethanolamine (NOE, 1 μ m) attenuated ischemic and TNF α preconditioning. Likewise, cell-permeable C2-ceramide and sphingosine 1-phosphate (sphingolipid signaling intermediates) both reproduced the preconditioning cardioprotective phenotype. Finally, TNF α and ceramide conferred preconditioning-like cardioprotection against post-ischemic contractile dysfunction and this cardioprotective effect was attenuated by NOE. In contrast, NOE did not reverse ischemic preconditioning enhanced post-ischemic contractile function. In conclusion, TNFα activates preconditioning-like tolerance against infarction and contractile dysfunction. This cardioprotection is mediated, in part, via activation of novel sphingolipid signaling intermediates.