Interplay between the SAFE and the sphingolipid pathway for cardioprotection

Aim: Activation of both the Survivor Activating Factor Enhancement (SAFE) pathway (including Tumor Necrosis Factor-alpha (TNF-alpha) and Signal Transducer and Activator of Transcription-3 (STAT-3)) and the sphingolipid signalling pathway (including sphingosine kinase-1 (SK1) and sphingosine-1 phosphate (S1P)) play a key role in promoting cardioprotection against ischemia-reperfusion injury (IRI). We investigated whether the activation of the SAFE pathway by exogenous S1P is dependent on the activation of SK1 for cardioprotection. Materials and methods: Isolated cardiomyocytes from TNF-alpha knockout (KO) mice, cardiomyocyte-specific STAT-3 KO mice and their wild-type (WT) littermates were exposed to simulated ischemia in the presence of a trigger of the SAFE pathway (S1P) and SK1 inhibitor (SK1-I). Similarly, isolated perfused hearts from adult TNF-alpha KO, STAT-3 KO and WT mice were subjected to IRI with S1P and/or SK1-I. Cell viability, infarct size (IS) and SK1 activity were assessed. Key findings: In isolated cardiomyocytes and in isolated hearts subjected to simulated ischemia/IRI, S1P pretreatment decreased cell death in WT mice, an effect that was abrogated in the presence of SK1-I. S1P failed to reduce cell death after simulated ischemia/IRI in both cardiomyocytes or hearts isolated from TNF-alpha KO and STAT-3 KO mice. Interestingly, S1P pretreatment increased SK1 activity in WT and STAT-3 KO mice, with no changes in TNF-alpha KO mice. Significance: Our data strongly suggest SK1 as a key component to activate STAT-3 downstream of TNF-alpha in the SAFE pathway, paving the way for the development of novel cardioprotective strategies that may target SK1 to modulate the SAFE pathway and increase cell survival following IRI.