Ginsenoside Rb1 And Rg1 Can Attenuate Beta-amyloid Protein_25-35-induced Tau Protein Hyperphosphorylation In Embryo Rat Cortical Neurons

Objective To investigate the effect and the molecular mechanism of aggregated beta-amyloid protein25-35 (Aβ25-35) on the level of tau protein phosphorylation in embryo rat cortical neurons, and to explore the protective effects of gisenoside Rb1 and gisenoside Rg1 on Aβ25-35-induced tau protein hyperphosporylation. Methods Primary cultures of cortical neurons were prepared from the embryonic day 18±2 Sprague-Dawley rats. MTT assay was used to measure the cytotoxicity of Aβ25-35 in cortical neurons, then chose an appropriate concentration of Aβ25-35. In order to detect the levels of tau phosphorylation,total tau protein and glycogen synthase kinase-3β(GSK-3β), western blot and immunocytochemical staining were performed on neurons exposed to 20μmol/L Aβ25-35 in the presence or absence of 24-hour pretreatment with several dose of ginsenoside Rb1, ginsenoside Rg1 or 10mmol/L lithium chloride (LiCl), a specific inhibitor of GSK-3β. Results Aβ25-35 treatment above the concentration of 20μmol/L resulted in decreasing of cell viability of cortical neurons in a dose-dependent manner. Aβ25-35 (20μmol/L) exposure of neurons for various periods induced tau protein hyperphorylation. The levels of tau protein phosphorylation in the sites of Ser396, Ser199/202, Thr231 and the amount of whole tau increased after 3h or 6h exposure and reached the maximum level after 12h exposure, then gradually declined after 24h exposure. Meanwhile, the expressions of the amount of whole GSK-3β and activated GSK-3β were also increased after Aβ25-35 (20μmol/L) exposure of neurons for 12h. Pretreatment with several dose of ginsenoside Rb1, ginsenoside Rg1 or 10mmol/L LiCl, a specific inhibitor of GSK-3β, markedly attenuated Aβ25-35-induced tau hyperphosphorylation and the expression of GSK-3β, and 10μmol/L Rb1 or 20μmol/L Rg1 showed the best protective effect on attenuating Aβ25-35-induced tau protein hyperphosphorylation.Conclusion GSK-3β activation by Aβ25-35 may lead to extensive tau phosphorylation. Gisenoside Rb1 and gisenoside Rg1 can attenuate Aβ25-35-induced tau protein hyperphosphorylation by inhibiting the activation of GSK-3β.