Abbreviations: CNS, central nervous system; AD, Alzheimer’s disease; PD, Parkinson’s disease; ASD, autism spectrum disorder; TBI, traumatic brain injury; MI, myocardial infarction; MSC, mesenchymal stem cell; BDNF, brain-derived neurotrophic factor; CKD, chronic kidney disease; MS, multiple sclerosis; EV, extracellular vesicle. Here, BDNF is linked to autism spectrum disorder.