BDNF and Parkinson disease: Increased passage of MSCs naturally boost secretion of BDNF; MSCs are promising delivery systems for therapeutics in various neurodegenerative disorders, such as Alzheimer’s disease and Parkinson’s disease, because of their secretomes (Rodrigues Hell et al., 2009; Harrell et al., 2021; Jalali et al., 2021; Kuo et al., 2021).