SNCA and Parkinson disease: In the 6-OHDA-induced PD mice injected with saline, the intensity of green fluorescence and colocalization of SN dopaminergic neurons were found to be stronger, while the expression levels of alpha-synuclein (α-syn) (pathological fibers in PD) were reduced in 6-OHDA-treated mice injected with MSC–EV–NC mimic or MSC–EV–miR-181a–2–3p mimic (Fig. 9A).