There has been a renewed focus on the role of central nervous system (CNS) fluids and barriers in neurological disorders, including in cerebral amyloid angiopathy (CAA). A body of suggestive evidence has indicated a link between impaired amyloid-β (Aβ) clearance and CAA formation, highlighting a fundamental need to improve our insights into the mechanisms of brain clearance. Nonetheless, the fluid circulation and influx/efflux routes remain largely disputed and poorly understood. In many studies, full consideration of the brain barriers that compartmentalize the CNS is lacking. Thus, we aim to provide new transgenic mouse models marking the brain barriers that will allow us to fill these critical knowledge gaps between CNS fluid clearance and CAA progression.

We have developed two novel specific dual-reporter mouse strains: one visualizing CNS vascular barrier using Claudin5-GFP (cerebral blood vessels) and Prox1-TdTom (lymphatic vessels) and one marking the brain barriers with Aqp4-mRuby3 (for astrocyte endfeet of the glia limitans) and VE-cadherin-GFP (for the leptomeninges and blood vessels). These two strains were successfully crossed with an ArcAβ transgenic mouse line, which has resulted in two novel triple-transgenic models of cerebral amyloidosis.

Aβ deposition was observed in correlation with changes of brain barrier marker fluorescent expression using ex vivo imaging at different ages. At chronic stages of the disease, brain barriers markers showed minor compromise in fluorescent expression, but astrocyte and oligodendrocyte were strongly activated. Secondly, solute drainage pathways from brain parenchyma were investigated through evaluation of tracer distribution at various timepoints after infusion into different brain regions and CSF space. Pilot tracer experiments have revealed location- and size- dependent ISF drainage pathways that do not concur with the glymphatic drainage hypothesis. The prevalence of each pathway and correlations between Aβ deposition and tracer distribution continue to be studied.

Our preliminary results demonstrate that our novel brain barrier reporter mice allow to provide new perspectives on the understanding of brain clearance in rodent CAA models. Going forward, our histological findings will be validated with multiple in vivo imaging modalities, including two-photon microscopy and synchrotron-based X-ray imaging.