Abstract
Preconditioning of sublethal ischemia exhibits neuroprotection against subsequent ischemia‐induced neuronal death. It has been indicated that glutamate, an excitatory amino acid, is involved in the pathogenesis of ischemia‐induced neuronal death or neurodegeneration. To elucidate whether prestimulation of glutamate receptor could counter ischemia‐induced neuronal death or neurodegeneration, we examined the effect of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate (AMPA), an ionotropic subtype of glutamate receptor, on excess glutamate‐induced excitotoxicity using primary cortical neuronal cultures. We found that AMPA exerted a neuroprotective effect in a time‐ and concentration‐dependent manner. A blocker of phosphatidylinositol‐3 kinase (PI3K), LY294002 (10 μM), significantly attenuated AMPA‐induced protection. In addition, Ser473 of Akt/PKB, a downstream target of PI3K, was phosphorylated by AMPA administration (10 μM). Glycogen synthase kinase 3β (GSK3β), which has been reported to be inactivated by Akt, was phosphorylated at Ser9 by AMPA. Ser9‐phosphorylated GSK3β or inactivated form would be a key molecule for neuroprotection, insofar as lithium chloride (100 μM) and SB216763 (10 μM), inhibitors of GSK3β, also induced phosphorylation of GSK3β at Ser9 and exerted neuroprotection, respectively. Glutamate (100 μM) increased cleaved caspase‐3, an apoptosis‐related cysteine protease, and caspase‐3 inhibitor (Ac‐DEVD‐CHO; 1 μM) blocked glutamate‐induced excitotoxicity in our culture. AMPA (10 μM, 24 hr) and SB216763 (10 μM) prominently decreased glutamate‐induced caspase‐3 cleavage. These findings suggest that AMPA activates PI3K‐Akt and subsequently inhibits GSK3β and that inactivated GSK3β attenuates glutamate‐induced caspase‐3 cleavage and neurotoxicity. © 2007 Wiley‐Liss, Inc.