Role of GSK-3beta activation and alpha7 nAChRs in Abeta(1-42)-induced tau phosphorylation in PC12 cells

Beta-amyloid peptide 1-42 (Abeta(1-42)) and hyperphosphorylated tau are associated with neurodegeneration in Alzheimer's disease. Emerging evidence indicates that Abeta(1-42) can potentiate hyperphosphorylation of tau in cell lines and in transgenic mice, but the underlying mechanism(s) remains unclear. In this study, Abeta(1-42)-induced tau phosphorylation was investigated in differentiated PC12 cells. Treatment of cells with Abeta(1-42) increased phosphorylation of tau at serine-202 as detected by AT8 antibody. This Abeta(1-42)-induced tau phosphorylation paralleled phosphorylation of glycogen synthase kinase-3beta (GSK-3beta) at tyrosine-216 (GSK-3beta-pY216), which was partially inhibited by the GSK-3beta inhibitor, CHIR98023. Abeta(1-42)-induced tau phosphorylation and increase in GSK-3beta-pY216 phosphorylation were also partially attenuated by alpha7 nicotinic acetylcholine receptor (alpha7 nAChR) selective ligands including agonist A-582941 and antagonists methyllycaconitine and alpha-bungarotoxin. The alpha7 nAChR Agonist and the GSK-3beta inhibitor had no additive effect. These observations suggest that alpha7 nAChR modulation can influence Abeta(1-42)-induced tau phosphorylation, possibly involving GSK-3beta. This study provides evidence of nAChR mechanisms underlying Abeta(1-42) toxicity and tau phosphorylation, which, if translated in vivo, could provide additional basis for the utility of alpha7 nAChR ligands in the treatment of Alzheimer's disease.