To define the role of microglial ARRBs in the PD mouse model, AAVs carrying the microglia-specific promoter F4/80 (Supplementary Fig. S4a) were used to deliver siRNA to knock down ARRB1 or ARRB2 in microglia as confirmed by immunostaining (Supplementary Fig. S4b). Here, ARRB2 is linked to Parkinson disease.