AQP4 and Alzheimer disease: Moreover, in the temporal cortex of AD patients, reduced mRNA expression of the water channel aquaporin 4 (AQP4; Figure 7) and activated astrocyte marker glial fibrillary acidic protein (GFAP) in association with the severity of CAA pathology [69] and in AD-related pathology, including Aβ burden and Braak stage [70].