These data further suggested that the lower TGF‐β1 level might be one of reasons in AQP4−/− mice contributed to stronger microglial activation, which might subsequently result in more dopaminergic neuronal death and more severe PD disease after MPTP intoxication, and certain other factor(s) in brain homogenates might also be responsible for the more microgliosis and neuronal damage after MPTP treatment. Here, AQP4 is linked to Parkinson disease.