Project Summary/Abstract Cognitive dysfunction and dementia are a major health challenge for the elderly and one of the primary underlying causes, cerebral small vessel disease (CSVD), contributes to 50% of all dementias worldwide. The breakdown of blood vascular barrier and impaired lymphatic clearance associated with CSVD are considered early biomarkers of human cognitive dysfunction, and reduced cortical cerebral blood flow and microvascular leak are observed during disease onset in both dementia patients and mouse models. One classification of CSVD, amyloidal CSVD, is characterized by the increased deposition of amyloid beta (Aβ), derived from the pathologic proteolytic processing of amyloid precursor protein (APP), along and within the brain microvasculature. Amyloidal CSVD appears in nearly all elderly patients with dementia and in roughly 65-85% of the elderly without dementia. Reciprocally, impaired blood and lymphatic microvasculature undermine Aβ clearance from the brain microenvironment, exacerbating Aβ deposition and CSVD pathology. Blood and lymphatic microvascular dysfunction during amyloidal CSVD are characterized by the disintegration of vascular endothelial cell-cell adhesions and their primary mediator, vascular endothelial cadherin (VE-cadherin). However, molecular mechanisms that link Aβ to changes in blood and lymphatic vessel permeability via endothelial cell junctional instability and VE-cadherin disassembly are unknown. Recently we have identified a novel mechanism by which the proteolytic processing of the Notch1 receptor is critical for the promotion of microvascular barrier function through the enhancement of endothelial VE-cadherin junctions. Additionally, our preliminary data suggest that both Notch1 and APP required association with VE-cadherin junctions for their proper processing by γ-secretase. Here, building upon mechanistic insights uncovered by two highly complementary laboratories (Kutys and Jun labs), our research team will apply engineering and experimental approaches that span biological scales from single molecules to 3D human biomimetic microvessels to investigate our central hypothesis that increased cerebral Aβ disrupts a critical signaling balance of Notch1 and/or APP processing at VE-cadherin junctions to drive blood and lymphatic microvascular dysfunction. Together, these studies will define new homeostatic mechanisms regulating brain blood and lymphatic microvascular function, how these molecular processes may be disrupted by Aβ, and potentially identify new targets for preventative and therapeutic intervention.