Abstract 1421: Role of c-Src Tyrosine Kinase in Ischemic Preconditioning: Formation of Focal Adhesion Kinase - Paxillin Complex Confers Cardioprotection
We previously demonstrated that
intact c-Src is necessary for the development of ischemic preconditioning (IPC) (loss of IPC in c-Src+/− mice) and
targeted disruption of the c-Src gene attenuates myocardial ischemia (I)/reperfusion injury (enhanced recovery of LV function in c-Src−/− mice).
To investigate the mechanism whereby c-Src plays two apparently opposite roles in myocardial ischemia, we examined the interaction among c-Src, focal adhesion kinase (FAK), and paxillin (Pax). Hearts from wild-type (WT) and c-Src KO mice were subjected to 15 or 25 min of global I with or without IPC. Western immunoblotting was performed to assess the expression levels of c-Src, FAK, and Pax. Myocardial expression levels of c-Src in c-Src+/− were 42% of those in WT but there was no difference in FAK and Pax expression levels between WT and c-Src+/−. In WT, IPC enhanced dephosphorylation of c-Src (Tyr416), suggesting that IPC inactivated c-Src during I (Fig. A⇓). In contrast, the expression levels of phosphorylated (P) Pax (Tyr118) during I remained higher in WT IPC(+) compared with WT IPC(−) (Fig. B⇓). There was no difference in P-FAK between WT IPC(−) and WT IPC(+). In c-Src+/−, P-FAK (Tyr925) was lower than in WT at all time-points and IPC failed to maintain P-Pax levels during I. Immunoprecipitation revealed that IPC enhanced the formation of complexes between FAK and Pax in WT but not in c-Src+/−. In c-Src−/−, P-Pax levels were the lowest at baseline but were the highest during I of 3 strains. These results demonstrate that the assembly of FAK and Pax is an obligatory step during the development of IPC. Phosphorylation of Pax may be a novel therapeutic approach for the protection of ischemic myocardium.