Expression of Aquaporin 1 and Aquaporin 4 in the Temporal Neocortex of Patients with Parkinson's Disease

The astrocytic water channel proteins aquaporin 1 (AQP1) and aquaporin 4 (AQP4) are known to be altered in brains affected by several neurodegenerative disorders, including Alzheimer's disease. However, AQP expression in brains affected by Parkinson's disease (PD) has not been described in detail. Recently, it has been reported that alpha-synuclein (alpha-syn)-immunolabeled astrocytes show preferential distribution in several cerebral regions, including the neocortex, in patients with PD. Here, we investigated whether AQP expression is associated with alpha-syn deposition in the temporal neocortex of PD patients. In accordance with the consensus criteria for dementia with Lewy bodies, the patients were classified into neocortical (PDneo), limbic (PDlim), and brain stem (PDbs) groups. Expressions of alpha-syn, AQP1, and AQP4 in the temporal lobes of the individual PD patients were examined immunohistochemically. Immunohistochemical analysis demonstrated more numerous AQP4-positive and AQP1-positive astrocytes in the PDneo group than in the PDbs, PDlim, and control groups. However, in the PDneo cases, these astrocytes were not often observed in alpha-syn-rich areas, and semiquantitative analysis revealed that there was a significant negative correlation between the levels of AQP4 and alpha-syn in layers V-VI, and between those of AQP1 and alpha-syn in layers II-III. These findings suggest that a defined population of AQP4- and AQP1-expressing reactive astrocytes may modify alpha-syn deposition in the neocortex of patients with PD.