BDNF and Alzheimer disease: Next, we determined whether BDNF overexpressing existed neuroprotective effect for NSCs in AD brain, Aβ42 was added into the culture medium to mimic the microenvironment of AD in vitro. The data showed that both kinds of NSCs were damaged in a dose-dependent manner; however, BDNF gene transfer had neuroprotective effects and improved NSC viability, neuronal fate, and neurite outgrowth in response to Aβ toxicity in term of neural differentiation (Supplementary Fig. S5).