Effects of estrogen on glycogen synthase kinase-3β activity

Abstract

Objective To investigate the effects of 17β-estradiol (E2) on glycogen synthase kinase-3β (GSK-3β) activity and the possible related mechanisms. Methods E2 was added to rat primary cortical neurons and its effect on cell viability was measured by methyl thiazol tetrazolium (MTT) assays; its effect on GSK-3 activity was detected directedly. The phosphorylated (9Ser) and non-phosphorylated GSK-3β expression after drug treatment was detected by Western blotting. The effects of estrogen receptor blocker and various kinase inhibitors on GSK-3 phosphorylation and GSK-3 activity were also measured. Results As compared with control group, in a concentration range of 1, 10, 100, 200 and 500 nmol/L, E2 didn’t significantly decrease cell viability in rat primary cortical neurons (the corresponding cell viability was 98.4%, 107.5%, 105.8%, 95.6% and 82.3% respectively). At concentrations of 1, 10 and 100 nmol/L, E2 dose-dependently decreased GSK-3 activity (to 85.6%, 78.5% and 65.4% of control group respectively). Western blotting indicated that E2 also dose-dependently increased GSK-3β (9Ser) phosphorylation without significantly affecting non-phosphorylated GSK-3β expression. The effect of E2 on GSK-3β phosphorylation could be partially blocked by estrogen receptor antagonist ICI-182780. The GSK-3β phosphorylation induced by E2 could be partially reversed by mitogen-activated protein kinase (MAPK) inhibitor PD98059 and protein kinase C (PKC) inhibitor GF109203X, but not by an Akt inhibitor Akt-I. The GSK-3 activity was decreased to 65.4% (P=0.000) of control group after E2 administration, and this effect could be partially reversed by ICI, PD98059, GF109203X administration, but not by Akt-I. These data were in accordance with those of Western blotting. Conclusion E2 can decrease GSK-3 activity as indicated by increased GSK-3β (9Ser) phosphorylation in an estrogen receptor-dependent manner, and the effect of E2 on GSK-3 phosphorylation may be mediated through MAPK and PKC signaling pathways. Key words: Estrogens; Glycogen syntheses kinase-3β; Alzheimer’s disease