Loss of perivascular aquaporin-4 localization impairs glymphatic exchange and promotes amyloid β plaque formation in mice

Background: Slowed clearance of amyloid beta (A beta) is believed to underlie the development of A beta plaques that characterize Alzheimer's disease (AD). A beta is cleared in part by the glymphatic system, a brain-wide network of perivascular pathways that supports the exchange of cerebrospinal and brain interstitial fluid. Glymphatic clearance, or perivascular CSF-interstitial fluid exchange, is dependent on the astroglial water channel aquaporin-4 (AQP4) as deletion of Aqp4 in mice slows perivascular exchange, impairs A beta clearance, and promotes A beta plaque formation. Methods: To define the role of AQP4 in human AD, we evaluated AQP4 expression and localization in a human post mortem case series. We then used the alpha-syntrophin (Snta 1) knockout mouse model which lacks perivascular AQP4 localization to evaluate the effect that loss of perivascular AQP4 localization has on glymphatic CSF tracer distribution. Lastly, we crossed this line into a mouse model of amyloidosis (Tg2576 mice) to evaluate the effect of AQP4 localization on amyloid beta levels. Results: In the post mortem case series, we observed that the perivascular localization of AQP4 is reduced in frontal cortical gray matter of subjects with AD compared to cognitively intact subjects. This decline in perivascular AQP4 localization was associated with increasing A beta and neurofibrillary pathological burden, and with cognitive decline prior to dementia onset. In rodent studies, Snta 1 gene deletion slowed CSF tracer influx and interstitial tracer efflux from the mouse brain and increased amyloid beta levels. Conclusions: These findings suggest that the loss of perivascular AQP4 localization may contribute to the development of AD pathology in human populations.

Automated summary

This study found that the loss of perivascular localization of AQP4 is associated with the development of A beta plaques and cognitive decline in subjects with Alzheimer's disease (AD). Rodent studies also showed that loss of AQP4 localization leads to abnormal distribution of CSF tracer and increased levels of amyloid beta.