Genistein Inhibits Aβ25-35-Induced Synaptic Toxicity and Regulates CaMKII/CREB Pathway in SH-SY5Y Cells

Genistein (Gen), as a functional food in human diet, has shown many beneficial effects on neurodegenerative diseases such as Alzheimer's disease (AD). But the neuroprotective mechanism of Gen is not clear. Because synaptic failure is considered as the earliest phase in the pathogenesis of AD, we try to validate our hypothesis that synapse may be one target of Gen on protecting neurons. In this study, SH-SY5Y cells were pre-incubated with or without Gen for 2 h followed by the incubation with A beta 25-35 (25 mu mol/L) for another 24 h. Flow cytometry, Western Blots, and RT-PCR analysis were used to test the synaptic factors. The data showed that Gen pre-treatment could reverse the A beta 25-35-induced down-regulation of synaptophysin and postsynaptic marker postsynaptic density-95. In addition, the down-regulation of NR1 and NR2B induced by A beta 25-35 which are subunits of N-methyl-d-aspartate receptor also could be antagonized by pre-treatment of Gen. Moreover, the factors of CaMKII/CREB signaling pathway were detected. The results showed that mRNA and protein expressions of (Ca2+)/calmodulin(CaM), CaMKII/pCaMKII, and CREB/pCREB were significantly down-regulated by A beta 25-35, but they were all restored by the pre-treatment of Gen. Furthermore, Gen also maintained the intracellular Ca2+ concentration which was disturbed by A beta 25-35. In conclusion, these results suggested that Gen could protect synaptic dysfunction induced by A beta, and the mechanism might be associated with the regulation of synaptic markers and Ca2+ level through activating CaM/CaMK/CREB signaling pathway.