The role of differential activation of p38-mitogen-activated protein kinase in preconditioned ventricular myocytes

Activation of protein kinase C (PKC) and more recently mitogen-activated protein kinases (MAPKs) have been associated with the cardioprotective effect of ischemic preconditioning. We examined the interplay between these kinases in a characterized model of ischemic preconditioning in cultured rat neonatal ventricular cardiocytes where ectopic expression of active PKC-δ results in protection. Two members of the MAPK family, p38 and p42/44, were activated transiently during preconditioning by brief simulated ischemia/reoxygenation. Overexpression of active PKC-δ, rather than augmenting, completely abolished this activation. We therefore determined whether a similar process occurred during lethal prolonged simulated ischemia. In contrast to ischemia, brief, lethal-simulated ischemia activated only p38 (2.8±0.45 vs. basal, P<0.01), which was attenuated by expression of active PKC-δ or by preconditioning (0.48±0.1 vs. ischemia, P<0.01). To determine whether reduced p38 activation was the cause or an effect of protection, we used SB203580, a p38 inhibitor. SB203580 reduced ischemic injury (CK release 38.0±3.1%, LDH release 77.3±4.0%, and MTT bioreduction 127.1±4.8% of control, n=20, P<0.05). To determine whether p38 activation was isoform selective, myocytes were infected with adenoviruses encoding wild-type p38α or p38β. Transfected p38α and β show differential activation (P<0.001) during sustained simulated ischemia, with p38α remaining activated (1.48±0.36 vs. basal) but p38β deactivated (0.36±0.1 vs. basal, P<0.01). Prior preconditioning prevented the activation of p38α (0.65±0.11 vs. ischemia, P<0.05). Moreover, cells expressing a dominant negative p38α, which prevented ischemic p38 activation, were resistant to lethal simulated ischemia (CK release 82.9±3.9% and MTT bioreduction 130.2±6.5% of control, n=8, P<0.05). Thus, inhibition of p38α activation during ischemia reduces injury and may contribute to preconditioning-induced cardioprotection in this model.