MAPKAPK-2 (MK2) is a
protein kinase activated downstream of p38-MAPK which
phosphorylates the small
heat shock proteins HSP27 and alphaB
crystallin and modulates p38-MAPK cellular distribution. p38-MAPK
activation is thought to contribute to
myocardial ischemic injury; therefore, we investigated MK2 effects on
ischemic injury and p38 cellular localization using MK2-deficient
mice (KO).
Immunoblotting of extracts from Langendorff-perfused
hearts subjected to aerobic
perfusion or global
ischemia or
reperfusion showed that the total and
phosphorylated p38 levels were significantly lower in MK2(-/-) compared to MK2(+/+)
hearts at baseline, but the ratio of
phosphorylated/total p38 was similar. These results were confirmed by
cellular fractionation and
immunoblotting for both
cytosolic and nuclear compartments. Furthermore,
HSP27 and alphaB crsytallin
phosphorylation were reduced to baseline in MK2(-/-)
hearts. On semiquantitative
immunofluorescence laser confocal microscopy of
hearts during aerobic
perfusion, the
mean total p38
fluorescence was significantly higher in the nuclear compared to extranuclear (
cytoplasmic, sarcomeric, and sarcolemmal compartments) in MK2(+/+)
hearts. However, although the increase in
phosphorylated p38
fluorescence intensity in all compartments following
ischemia in MK2(+/+)
hearts was lost in MK2(-/-)
hearts, it was basally elevated in nuclei of MK2(-/-)
hearts and was similar to that seen during
ischemia in MK2(+/+)
hearts. Despite these differences, similar
infarct volumes were recorded in
wild-type MK2(+/+) and MK2(-/-)
hearts, which were decreased by the p38 inhibitor SB203580 (1 muM) in both
genotypes. In conclusion, p38 MAPK-induced
myocardial ischemic injury is not modulated by MK2. However, the absence of MK2 perturbs the cellular distribution of p38. The preserved nuclear distribution of active p38
MAPK in MK2(-/-)
hearts and the conserved response to SB203580 suggests that
activation of p38
MAPK may contribute to
injury independently of MK2.
