AQP4 and Parkinson disease: While the clearance of α-syn via the glymphatic system has not yet been investigated, Hoshi and colleagues showed a negative correlation between AQP-4 expression and α-syn deposition, suggesting that a defined population of AQP-4 proteins serves as mediators via which the glymphatic system modifies α-syn deposition in the neocortex of patients with PD (Hoshi et al., 2017).