beta amyloid fragments derived from activated platelets deposit in cerebrovascular endothelium: usage of a novel blood brain barrier endothelial cellmodel system

Amyloid precursor protein (A beta PP) processing results in generation of a myloid beta peptide (A beta) which deposits in the brain parenchyma and cer ebrovasculature of patients with Alzheimer b disease (AD). Evidence that th e vascular deposits derive in part from A beta PP fragments originating fro m activated platelets includes findings that individuals who have had multi ple small strokes have a higher prevalence of AD compared to individual's w ho have taken antiplatelet drugs. Thus, determination of whether platelet A beta PP fragments are capable of traversing the blood-brain barrier (BBB) is critical. We have established that activated platelets from patients wit h AD retain more surface transmembrane-bound A beta PP (mA beta PP) than co ntrol platelets. We report here that this mA beta PP can be cleaved to A be ta-containing fragments which pass through a novel BBB model system. This m odel utilizes human BBB endothelial cells (BEC) isolated from brains of pat ients with AD. These BEC, after exposure to activated platelets which have been surface-labeled with fluorescein and express surface-retained mA beta PP, cleave fluorescein-tagged surface proteins, including mA beta PP, resul ting in passage to the BEC layer. The data confirm that BEC contribute to p rocessing of platelet derived mA beta PP and show that the processing yield s A beta containing fragments which could potentially contribute to cerebro vascular A beta deposition.