AQP4 and Parkinson disease: Previous studies suggested that α‐syn plays an important role in the initiation and maintenance of inflammation in PD patients and a MPTP‐PD animal model by activating microglial cells to produce TNF‐a and IL‐1β.38, 39, 40 Since astrocytes highly express AQP4,41 we next determined whether there were any differences in the expression of α‐syn between AQP4+/+ and AQP4−/− mouse astrocytes after 1‐methyl‐4‐phenylpyridinium (MPP+, the active metabolite of MPTP) treatment.