Further, in a rotenone-induced PD mouse model, TLR4-knockout mice were protected against phagocytic, proinflammatory microglial activity, dopaminergic neuronal loss, and motor impairments, reinforcing the link between gut barrier dysfunction, microglial activity, and neuroinflammation in PD (Perez-Pardo et al., 2019). This evidence concerns the gene TLR4 and Parkinson disease.