Ischaemic postconditioning protects isolated mouse hearts against ischaemia/reperfusion injury via sphingosine kinase isoform-1 activation

Aims Sphingosine-1-phosphate (S1P) plays a vital role in cytoskeletal rearrangement, development, and apoptosis. Sphingosine kinase-1 (SphK1), the key enzyme catalyzing the formation of S1P, mediates ischaemic preconditioning. Ischaemic postconditioning (POST) has been shown to protect hearts against ischaemia/reperfusion injury (IR). To date, no studies have examined the role of SphK1 in POST. Methods and results Wild-type (WT) and SphK1 null (KO) mouse hearts were subjected to IR (45 min of global ischaemia and 45 min of reperfusion) in a Langendorff apparatus. Left ventricular developed pressure (LVDP), maximum velocity of increase or decrease of LV pressure (±dP/dtmax), and LV end-diastolic pressure (LVEDP) were recorded. Infarction size was measured by 1% triphenyltetrazolium chloride staining. POST, consisting of 5 s of ischaemia and 5 s of reperfusion for three cycles after the index ischaemia, protected hearts against IR: recovery of LVDP and ±dP/dtmax were elevated; LVEDP was decreased; infarction size (% of risk area) was reduced from 40 ± 2% in the control group to 29 ± 2% of the risk area in the POST group (P < 0.05, n = 4 per group). Phosphorylation of Akt and extracellular signal-regulated kinases detected by Western blotting was increased at 10 min of reperfusion. The protection induced by POST was abolished in KO hearts. Infarction size in KO hearts (57 ± 5%) was not different from the KO control group (53 ± 5% of risk area, n = 4, P = NS). Conclusions A short period of ischaemic POST protected WT mouse hearts against IR. The cardiac protection induced by POST was abrogated in SphK1–KO mouse hearts. Thus, SphK1 is critical for successful ischaemic POST.