Activation of the Akt/GSK3β signaling pathway mediates survival of vulnerable hippocampal neurons after transient global cerebral ischemia in rats

Recent studies have revealed that the phosphatidylinositol 3-kinase (PI3-K) pathway is involved in apoptotic cell death after experimental cerebral ischemia. The serine-threonine kinase, Akt, functions in the PI3-K pathway and prevents apoptosis by phosphorylation at Ser473 after a variety of cell death stimuli. After phosphorylation, activated Akt inactivates other apoptogenic factors, including glycogen synthase kinase-3 beta (GSK3 beta), thereby inhibiting cell death. However, the role of Akt/GSK3 beta signaling in the delayed death of hippocampal neurons in the CA1 subregion after transient global cerebral ischemia (tGCI) has not been clarified. Transient global cerebral ischemia for 5mins was induced by bilateral common carotid artery occlusion combined with hypotension. Western blot analysis showed a significant increase in phospho-Akt (Ser473) and phospho-GSK3 beta (Ser9) in the hippocampal CA1 subregion after tGCl. Immunohistochemistry showed that expression of phospho-Akt (Ser473) and phospho-GSK3 beta (Ser9) was markedly increased in the vulnerable CA1 subregion, but not in the ischemic-tolerant CA3 subregion. Double staining with phospho-GSK3 beta (Ser9) and terminal deoxynucleotidyl transferase-mediated uridine 5-triphosphate-biotin nick end labeling showed different cellular distributions in the CA1 subregion 3 days after tGCI. Phosphorylation of AM and GSK3 beta was prevented by LY294002, a PI3-K inhibitor, which facilitated subsequent DNA fragmentation 3 days after tGCl. Moreover, transgenic rats that overexpress copper/zinc-superoxide dismutase, which is known to be neuroprotective against delayed hippocampal CA1 injury after tGCl, had enhanced and persistent phosphorylation of both Akt and GSK3 beta after tGCl. These findings suggest that activation of the Akt/GSK3 beta signaling pathway may mediate survival of vulnerable hippocampal CA1 neurons after tGCl.