Testosterone prevents the heat shock-induced overactivation of glycogen synthase kinase-3β but not of cyclin-dependent kinase 5 and c-Jun NH2-terminal kinase and concomitantly abolishes hyperphosphorylation of τ:: Implications of Alzheimer's disease

We have shown previously that glycogen synthase kinase-3beta (GSK-3beta), cyclin-dependent kinase 5, and c-Jun NH2-terminal kinase become overactivated and hyperphosphorylate tau in heat-shocked female rats. This hyperphosphorylation of tau is estrogen-independent, prevented by androgens, and similar to Alzheimer's disease. In this study, ovariectomized (OVX) Sprague-Dawley rats (n = 75) received daily injections of 10 mug of 17beta-estradiol benzoate (EB), or 250 mug of testosterone propionate (TP), or both EB and TP, or sesame oil (SO) vehicle for 4-6 weeks. In kinase assays of forebrain homogenates, overactivation of GSK-3beta at 0-6 In after heat shock toward human recombinant tau, bovine tau, and phosphoglycogen synthase peptide 2 was prevented in OVX + TP and OVX + (EB + TP) but not in sham-OVX + SO, OVX + SO, and OVX + EB. Abs against inactive (pSer(9)) and activity-enhanced (pTyr(216)) GSK-3beta showed marked increase of pSer(9)- and decrease of pTyr(216)-GSK-3beta in both OVX + TP and OVX + (EB + TP) but not in sham-OVX + SO, OVX + SO, and OVX + EB. EB enhanced the overactivation of cyclin-dependent kinase 5. The activity of c-Jun NH2-terminal kinase was gonadal hormone-independent. The serum concentrations of testosterone and 17beta-estradiol were 2.53 ng/ml and 201 pg/ml in OVX + TP and OVX + EB, respectively. These findings demonstrate that testosterone prevents the hyperphosphorylation of tau by inhibiting the heat shock-induced overactivation of GSK-3beta and suggest that androgens given to aging men or, in combination with estrogens, to postmenopausal women could prevent or delay Alzheimer's disease.