Water exchange across the BBB is mediated by multiple pathways including the dedicated water channel AQP4, and redistribution of AQP4 has been associated with pericyte deficiency at the early stage of BBB disruption (Warth et al., 2004; Montagne et al., 2018), as well as with the accumulation of amyloid deposits in AD (Yang et al., 2011). Here, AQP4 is linked to Alzheimer disease.