[Roles of Aquaporins in Brain Disorders].

Aquaporin (AQP) is a water channel protein that is expressed in the cell membranes. AQPs are related to several kinds of human diseases such as cataract. In the mammalian central nervous system (CNS), AQP4 is specifically expressed in the astrocyte membranes lining the perivascular and periventricular structures. AQP4 plays a role in the development of brain edema associated with certain brain disorders. Neuromyelitis optica (NMO) is a demyelinating disorder, and patients with NMO develop autoimmune antibodies against AQP4 in their serum. Therefore, AQP4 is involved in NMO pathogenesis. A new concept referred to as "glymphatic pathway" has been recently proposed to explain the lymphatic system in the CNS. Dysfunction of the "glymphatic pathway" may cause several neurodegenerative diseases and mood disorders. Importantly, AQP4 may play a role in the "glymphatic pathway". Further investigation of AQP4 in CNS disorders is necessary, and a new drug against AQP4 is expected.