Early ischaemic preconditioning requires Akt- and PKA-mediated activation of eNOS via serine1176 phosphorylation.

Aims: The role of endothelial nitric oxide synthase (eNOS)/NO signalling is well documented in late ischaemic preconditioning (IPC); however, the role of eNOS and its activation in early IPC remains controversial. This study investigates the role of eNOS in early IPC and the signalling pathways and molecular interactions that regulate eNOS activation during early IPC.
Methods and Results: Rat hearts were subjected to 30-min global ischaemia and reperfusion (I/R) with or without IPC (three cycles 5-min I and 5-min R) in the presence or absence of the NOS inhibitor l-NAME, phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 (LY), and protein kinase A (PKA) inhibitor H89 during IPC induction or prior endothelial permeablization. IPC improved post-ischaemic contractile function and reduced infarction compared with I/R with this being abrogated by l-NAME or endothelial permeablization. eNOS(Ser1176), Akt(Ser473), and PKA(Thr197) phosphorylation was increased following IPC. I/R decreased eNOS(Ser1176) phosphorylation, whereas IPC increased it. Mass spectroscopy confirmed eNOS(Ser1176) phosphorylation and quantitative Western blots showed ∼24% modification of eNOS(Ser1176) following IPC. Immunoprecipitation demonstrated eNOS, Akt, and PKA complexation. Immunohistology showed IPC-induced Akt and PKA phosphorylation in cardiomyocytes and endothelium. With eNOS activation, IPC increased NO production as measured by electron paramagnetic resonance spin trapping and fluorescence microscopy. LY or H89 not only decreased Akt(Ser473) or PKA(Thr197) phosphorylation, respectively, but also abolished IPC-induced preservation of eNOS and eNOS(Ser1176) phosphorylation as well as cardioprotection.
Conclusion: Thus, Akt- and PKA-mediated eNOS activation, with phosphorylation near the C-terminus, is critical for early IPC-induced cardioprotection, with eNOS-derived NO from the endothelium serving a critical role.