TLR4 and Parkinson disease: Studies have reported decreased AP-1 expression in dopaminergic neurons, less reduction in ROS content, and improved dyskinesia in PD mice in the MPTP model of TLR4-knockout (KO) mice, suggesting that TLR4 plays a key role in the pathogenesis of PD (Campolo et al., 2019; Heidari et al., 2022).