Targeted inhibition of p38 mitogen-activated protein kinase antagonizes cardiac injury and cell death following ischemia-reperfusion in vivo

The p38 branch of the mitogen-activated protein kinase (MAPK) signaling cascade has been implicated as a regulator of cardiomyocyte apoptosis in culture as well as in the adult heart. However, considerable disagreement persists as to the functional effects attributed to p38 signaling, given that both pro- and anti-apoptotic regulatory roles have been reported. To address this area of uncertainty in the literature, we investigated the cell death effects associated with p38 inactivation in both cultured neonatal cardiomyocytes and the adult heart. In vitro, adenoviral-mediated gene transfer of two different dominant-negative-encoding p38 vectors reduced apoptosis induced by 2-deoxyglucose treatment, whereas overexpression of wild-type p38alpha or an activated mitogen-activated protein kinase kinase (MKK)6 mutant each enhanced cell death. In vivo, transgenic mice expressing a dominant-negative MKK6 mutant or a dominant-negative p38alpha mutant were each significantly protected from ischemia-reperfusion injury, as assessed by infarct area measurements, DNA laddering, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling, and functional assessment of ventricular performance. Similarly, transgenic mice overexpressing the p38-inactivating dual specificity phosphatase MAPK phosphatase-1 (MKP-1) were also partially protected, whereas MKP-1 gene-targeted mice showed greater injury after ischemia-reperfusion injury. Mechanistically, inhibition of p38 signaling promoted a dramatic up-regulation of Bcl-2 in the hearts of transgenic mice. In primary neonatal cardiomyocyte cultures, adenoviral-mediated gene transfer of a p38 inhibitory mutant up-regulated Bcl-2, whereas expression of an activated p38 mutant down-regulated Bcl-2 protein levels. Collectively, these results indicate that p38 functions as a pro-death signaling effector in both cultured myocytes as well as in the intact heart.