AQP4 and Parkinson disease: The PD protein α‐syn may play a role in microglial activation in the substantia nigra in PD and the levels of MHCII, a classical pro‐inflammatory molecule.38, 55, 56 However, in this study, after MPTP treatment, AQP4+/+ mice showed significant neuronal pathology but only very low levels of α‐syn.