Objective Explore cardioprotective mechanisms induced by reperfusion injury salvage kinase (ERK1/2) signal transduction pathways changes in isolated mouse hearts.
Methods Established Langendorff perfused mouse heart model, 96 C57BL mouse hearts were divided to 4 groups: 1) I/R control: 30 min global ischemia and 2 h reperfusion; 2) IPC:IPC with 3 episodes of 10 s of ischemia and 10 s reperfusion after 30 min ischemia and before 2 h reperfusion; 3) IPC+ERK1/2 inhibitor PD98059 (10–5 mol/L for 15 min); 4) I/R+ERK1/2 inhibitor PD98059 (10–5 mol/L for 15 min). The effects of IPC on Ischemic size, myocardial cell apoptosis index, phospho-protein kinase (P-ERK1/2) and phospho-protein kinase B(P-Akt) were measured. Expressions of apoptosis related proteins, including Bax, Bcl-2 and Cyt.C, in cytosolic and membrane fraction were detected by Western blot.
Results Following 180min reperfusion, infarct size was significantly reduced in postconditioning group (32.8 ± 3. 8)% compared with I/R group hearts [(48.1 ± 4.8)%, P < 0.05], and equally improved myocardial function compared with I/R group (all P < 0.05). Compared with ischemia reperfusion group, ischemic postconditioning group markedly decreased apoptotic index (AI)(P < 0.05), increased the mRNA expression of Bcl-2 gene (P < 0.05), the ratio of Bcl-2 to Bax was incidentally up-regulated (P < 0.05). Although IPC did not induce changes in the level of Bcl-2 expression in cytosolic fraction compared with I/R groups, the expression of Bcl-2 inmembrane fraction was up regulatedin IPC group compared with I/R group. The increase in the lease of mitochondrial Cyt.C into cytosol induced by I/R was significantly reduced by IPC. The histopathological changes in mitochondria and myocardium destroyed by ischemia repefusion were alleviated markedly by ischemic postconditioning. IPC significantly increased myocardial ERK1/2 phosphorylation, PD98059 inhibited the phosphorylation of ERK1/2 and abolished the cardioprotective effects induced by IPC.
Conclusions Postconditioning plays a pivotal role in reducing myocardial infarct size after ischemia/reperfusion injury. IPC right before reperfusion but not after reperfusion attenuated I/R injury of isolated mouse hearts via the upstream target, ERK1/2-MAPK signal transduction pathway which mediated the expression of Bcl-2/Bax and the release of mitochondrial Cyt.C.