GDNF and Parkinson disease: An example is the long-term effects of HSC-based glial derived neurotrophic factor (GDNF) via exosome transfer and direct diffusion that improved motor function for up to 12 months, preserved DA neurons and selectively targeted degenerative areas in the brain of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) PD mice [264].