ARRB2 and Parkinson disease: We then used Arrb1−/− and Arrb2−/− mice and microglia-specific depletion of ARRBs to demonstrate that ARRB1 ablation significantly ameliorated, whereas knockout of ARRB2 exaggerated, DA neuron degeneration, microglia activation, and neuroinflammation in two PD mouse models in vivo.