Genistein protects against amyloid-beta-induced toxicity in SH-SY5Y cells by regulation of Akt and Tau phosphorylation.

Alzheimer's disease is a neurodegenerative disorder characterized by extracellular deposition of amyloid-ß (Aß) peptide and hyperphosphorylation of Tau protein, which ultimately leads to the formation of intracellular neurofibrillary tangles and cell death. Increasing evidence indicates that genistein, a soy isoflavone, has neuroprotective effects against Aß-induced toxicity. However, the molecular mechanisms involved in its neuroprotection are not well understood. In this study, we have established a neuronal damage model using retinoic-acid differentiated SH-SY5Y cells treated with different concentrations of Aß25-35 to investigate the effect of genistein against Aß-induced cell death and the possible involvement of protein kinase B (PKB, also termed Akt), glycogen synthase kinase 3ß (GSK-3ß), and Tau as an underlying mechanism to this neuroprotection. Differentiated SH-SY5Y cells were pre-treated for 24 hr with genistein (1 and 10 nM) and exposed to Aß25-35 (25 µM), and we found that genistein partially inhibited Aß induced cell death, primarily apoptosis. Furthermore, the protective effect of genistein was associated with the inhibition of Aß-induced Akt inactivation and Tau hyperphosphorylation. These findings reinforce the neuroprotective effects of genistein against Aß toxicity and provide evidence that its mechanism may involve regulation of Akt and Tau proteins.