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.