Activation of PI3-K/Akt pathway for thermal preconditioning to protect cultured cerebellar granule neurons against low potassium-induced apoptosis

Aim: This study was designed to investigate whether the activation of the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway is required for thermal preconditioning to protect rat cerebellar granule neurons (CGN) against apoptosis induced by low potassium, and to explore the possibility of a link between the upregulated heat shock protein (HSP)70 expression and Akt activation in the acquisition of neuroprotection induced by thermal preconditioning. Methods: CGN cultured for 8 d in vitro were switched to 5K medium for 24 h after thermal preconditioning (TP; 43.5 degrees C for 90 min, then 37 degrees C for 1 h). To study the role of the PI3-K/Akt pathway, a PI3-K inhibitor, LY294002 (20 mu mol/L) was added into the cultures 1 h before TP. 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay and fluorescein diacetate staining were used to determine cell viability. Hoechst 33258 staining and agar gel electrophoresis were used to test the morphological and biological characters of CGN. Western blot analysis was employed to detect the levels of phospho-Akt, phospho-glycogen synthase kinase 3 beta (GSK3 beta) Akt, GSK3 beta, and HSP70. Results: TP protected CGN against apoptosis induced by low potassium. LY294002 inhibited the neuroprotective effect on CGN induced by T P. TP induced a robust activation of Akt and the inactivation of GSK3 beta via PI3-K. Furthermore, the activation of the PI3-K/Akt pathway by TP persisted for 24 h in the 5K cultures. LY294002 (20 mu mol/L) failed to inhibit the upregulated HSP70 expression induced by TP. Conclusion: The activation of the PI3-K/Akt pathway is required for TP to protect CGN against apoptosis induced by low potassium, but the neuroprotective effect by Akt activation is not mediated through the downstream induction of HSP70 expression.