Trolox and 17β-estradiol protect against amyloid β-peptide neurotoxicity by a mechanism that involves modulation of the Wnt signaling pathway

Oxidative stress is a key mechanism in amyloid beta-peptide (A beta)-mediated neurotoxicity; therefore, the protective roles of 17 beta-estradiol (E-2) and antioxidants ( Trolox and vitamin C) were assayed on hippocampal neurons. Our results show the following: 1) E-2 and Trolox attenuated the neurotoxicity mediated by A beta and H2O2 as measured by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide reduction assays, quantification of apoptotic cells, and morphological studies of the integrity of the neurite network. 2) Vitamin C failed to protect neurons from A beta toxicity. 3) A beta-mediated endoperoxide production, reported to induce cell damage, was decreased in the presence of E-2 and Trolox. 4) Two key Wnt signaling components were affected by E-2 and Trolox; in fact, the enzyme glycogen synthase kinase 3 beta was inhibited by both E-2 and Trolox, and both compounds were able to stabilize cytoplasmic beta-catenin. 5) E-2 activated the expression of the Wnt-5a and Wnt-7a ligands, and at the same time, E-2, through the alpha estrogen receptor, was able to prevent the excitotoxic A beta-induced rise in bulk-free Ca2+ as an alternative pathway to increase cell viability. 6) Finally, the Wnt-7a ligand protected against cytoplasmic calcium disturbances induced by A beta treatment. Our results suggest that control of oxidative stress, regulation of cytoplasmic calcium, and activation of Wnt signaling may prevent A beta neurotoxicity.