The inhibition of glycogen synthase kinase 3β by a metabotropic glutamate receptor 5 mediated pathway confers neuroprotection to Aβ peptides

Activation of glycogen synthase kinase 3 beta (Gsk3 beta) has been shown to be a key component in signaling pathways that underlie neurodegeneration and neurodegenerative disease. Conversely, inactivation of Gsk3 beta by phosphoinositide 3-kinase (PI3K)/Akt is an important neuroprotective mechanism. Previous studies have shown that agonist activation of group I metabotropic glutamate receptors (mGluRs) can increase neuronal survival and prevent apoptosis. However, little is known about the signaling pathways that couple mGluR5 to neuroprotection. In this report, we investigated whether activation of the PI3K/Akt/Gsk3 beta pathway, which has been shown to have an important neuroprotective mechanism, is required for mGluR5 activation mediated neuroprotection against beta-amyloid. We found that brief incubations of mouse hippocampal slices with (R,S)-3,5-dihydroxyphenylglycine (DHPG) resulted in increased phosphorylation of Akt and Gsk3 beta. The PI3K inhibitors, LY294002 and wortmannin, blocked the DHPG-induced increased phosphorylation of Akt and Gsk3 beta. Similar results were observed in rat primary hippocampal cultures. Finally, we found that the PI3K inhibitor LY294002 can block (R,S)-2-chloro-5-hydroxyphenylglycine (CHPG) mediated neuroprotection against beta-amyloid. Thus, these findings suggest that mGluR5 can modulate the PI3K/Akt/Gsk3 beta pathway in the hippocampus, and that modulation of this signaling pathway can reverse beta-amyloid-induced neuronal toxicity.