Figure 1.

Figure shows representative schemes for expression and polarization/localization of AQP-4 in healthy (left) and dysfunctional (right) perivascular astrocyte. Astrocytes processes wrap the vessel forming a sheath around it. Cerebrospinal fluid (CSF) flows in the perivascular space created around the vessel. The astrocytic water channel AQP-4 is polarized, as it is densely expressed by astrocytes almost exclusively at the endfeet, in direct contact with the perivascular space, where it facilitates the interchanges of water. In aging and some pathological conditions, such as Alzheimer’s disease (AD), AQP-4 loses its polarization in reactive astrocytes and it is found diffusively expressed. Also, higher AQP-4 expression has been documented in Parkinson’s disease, cerebral ischemia, amyotrophic lateral sclerosis, and other neurological diseases (for review see Xiao and Hu, 2014; Mader and Brimberg, 2019).