Activation of p38
mitogen-activated
protein (MAP)
kinase (MAPK) has been implicated in the mechanism of cardiomyocyte (CMC) protection and injury. The
p38 MAPK controversy may be related to differential effects of this
kinase on apoptosis and
necrosis. We have hypothesized that
p38 MAPK-mediated
F-actin reorganization promotes apoptotic cell death, whereas it protects from osmotic stress-induced necrotic cell death. Cultured neonatal rat CMCs were subjected to 2 h of simulated
ischemia followed by reoxygenation.
p38 MAPK activity measured by phosphorylation of MAP
kinase-activated
protein (
MAPKAP) kinase 2 was increased during simulated
ischemia and reoxygenation. This was associated with translocation of
heat shock protein 27 (HSP27) from the cytosolic to the cytoskeletal fraction and
F-actin reorganization.
Cytochrome c release from mitochondria,
caspase-3 activation, and DNA fragmentation were increased during reoxygenation. Robust
lactate dehydrogenase (LDH) release was observed under hyposmotic (140 mosM) reoxygenation. The
p38 MAPK inhibitor
SB-203580 abrogated activation of
p38 MAPK, translocation of HSP27, and
F-actin reorganization and prevented
cytochrome c release,
caspase-3 activation, and DNA fragmentation. Conversely,
SB-203580 enhanced LDH release during hyposmotic reoxygenation. The
F-actin disrupting agent
cytochalasin D inhibited
F-actin reorganization and prevented
cytochrome c release,
caspase-3 activation, and DNA fragmentation, whereas it enhanced LDH release during hyposmotic reoxygenation. When CMCs were incubated under the isosmotic condition for the first 15 min of reoxygenation,
SB-203580 and
cytochalasin D increased
ATP content of CMCs and prevented LDH release after the conversion to the hyposmotic condition. These results suggest that
F-actin reorganization mediated by activation of
p38 MAPK plays a differential role in apoptosis and protection against osmotic stress-induced
necrosis during reoxygenation in neonatal rat CMCs; however, the sarcolemmal fragility caused by
p38 MAPK inhibition can be reversed during temporary blockade of physical stress during reoxygenation.