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

Amyloid precursor protein (A beta PP) processing results in generation of amyloid beta peptide (A beta) which deposits in the brain parenchyma and cerebrovasculature of patients with Alzheimer b disease (AD). Evidence that the vascular deposits derive in part from A beta PP fragments originating from activated platelets includes findings that individuals who have had multiple small strokes have a higher prevalence of AD compared to individual's who 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 with AD retain more surface transmembrane-bound A beta PP (mA beta PP) than control platelets. We report here that this mA beta PP can be cleaved to A beta-containing fragments which pass through a novel BBB model system. This model utilizes human BBB endothelial cells (BEC) isolated from brains of patients 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, resulting in passage to the BEC layer. The data confirm that BEC contribute to processing of platelet derived mA beta PP and show that the processing yields A beta containing fragments which could potentially contribute to cerebrovascular A beta deposition.