Disease stage-sensitive MFSD2A-caveolae axis insigates hippocampal blood-brain barrier disruption in Alzheimer's disease

Blood-brain barrier (BBB) malfunction contributes to pathophysiology of Alzheimer's disease (AD), yet the mechanisms that confer hippocampal endotheliocytes vulnerability remain unclear. Here we identify loss of endothelial major facilitator superfamily domain-containing protein 2A (MFSD2A), a suppressor of caveolae-mediated transcytosis, as an early and hippocampus-specific feature of AD-associated vascular impairment. In post-mortem human AD brains, reduction in hippocampal MFSD2A was accompanied with increased levels of caveolin-1 and perivascular albumin extravasation. Analysis of human single-nucleus transcriptomic data further demonstrated that vascular expression of MFSD2A declined during transition from mild cognitive impairment to established AD. In APP/PS1 mice, MFSD2A loss occurred early in hippocampal microvessels and coincided with disproportionately high hippocampal BBB leakage and reductions in GLUT1 and claudin-5, despite broader amyloid deposition throughout other brain regions. Restoration of endothelial MFSD2A using an AAV-BR1-based vascular vector during early stage of amyloid pathology, reduced albumin extravasation and preserved GLUT1 and claudin-5. Early intervention also reduced amyloid plaque burden and plaque-associated neuritic dystrophy, whereas this treatment during established amyloid pathology, although modifying selected endothelial markers, failed to reverse BBB leakage, amyloid pathology, or cognitive impairment. Sustained MFSD2A restoration from the early disease stage provided the greatest protection, preserving hippocampal BBB integrity, reducing amyloid and neuritic pathology, improving long-term potentiation and ameliorating spatial learning and memory deficits. These findings define endothelial MFSD2A loss as a disease stage-sensitive mechanism of hippocampal BBB vulnerability and highlight the MFSD2A-caveolae axis as a therapeutic target for early-stage AD.