GDNF and Alzheimer disease: Not only Aβ was found and established as the cargo in astrocyte-derived exosomes isolated from AD patients, the levels of β-site amyloid precursor protein-cleaving enzyme 1 (BACE-1), γ-secretase, soluble Aβ42, soluble amyloid precursor protein (sAPP)β, sAPPα, glial-derived neurotrophic factor (GDNF), P-T181-Tau, and P-S396-Tau were all found to be higher than the normal situation, even higher than the levels in neuronal exosomes [39].