The inactivation of
glycogen synthase kinase-3beta (
GSK-3beta) is proposed as the event integrating protective pathways initiated by preconditioning and other interventions. The inactivation of
GSK-3 is thought to decrease the probability of opening of the
mitochondrial permeability transition pore. The aim of this study was to verify the role of
GSK-3 using a targeted
mouse line lacking the critical
N-terminal serine within
GSK-3beta (Ser9) and the highly homologous GSK-3alpha (Ser21), which when
phosphorylated results in
kinase inactivation. Postconditioning with 10 cycles of 5 seconds of
reperfusion/5 seconds of
ischemia and preconditioning with 6 cycles of 4 minutes of
ischemia/6 minutes of
reperfusion, similarly reduced
infarction of the isolated perfused
mouse heart in response to 30 minutes of global
ischemia and 120 minutes of
reperfusion. Preconditioning caused noticeable inactivating
phosphorylation of
GSK-3. However, both preconditioning and postconditioning still protected
hearts of
homozygous GSK-3 double knockin
mice. Moreover, direct
pharmacological inhibition of
GSK-3 catalytic activity with structurally diverse inhibitors before or after
ischemia failed to recapitulate conditioning protection. Nonetheless,
cyclosporin A, a direct
mitochondrial permeability transition pore inhibitor, reduced
infarction in
hearts from both
wild-type and
homozygous GSK-3 double knockin
mice. Furthermore, in adult
cardiac myocytes from
GSK-3 double knockin
mice,
insulin exposure was still as effective as
cyclosporin A in delaying
mitochondrial permeability transition pore opening. Our results, which include a novel
genetic approach, suggest that the inhibition of
GSK-3 is unlikely to be the key determinant of cardioprotective signaling in either preconditioning or postconditioning in
the mouse.
