Blood brain barrier endothelial cells express candidate amyloid precursor protein-cleaving secretases

Abstract

Proteolytic cleavage of the amyloid precursor protein (AβPP) results in the generation of the amyloidogenic fiagment known as amyloid βpeptide (Aβ). Deposition of Aβ in the brain parenchyma and cerebrovasculature is a feature of Alzheimer's disease (AD). To date, the process whereby A is generated and deposited remains unclear. We have previously established that activated platelets from AD patients retain more AβPP on their surface than control platelets. We report here that an endothelial cell-derived enzyme can cleave this surface platelet A PPP. Human blood brain barrier endothelial cells from brains of AD patients were assayed for potential AβPP-cleaving enzymes using synthetic peptide substrates encompassing the AβN-termi-nus cleavage site. A protease activity capable of cleaving AβPP on the surface Of AD platelets was noted. The AβPP cleavage is partially inhibited by EDTA, by ZincOV, as well as by a specgic inhibitor of the Zn metalloprotease E.C.3.4.24.15. Furthermore, the protease is recognized by an antibody directed against it, using immunohistochemis-tty, Western blot analysis and frow cytometry. The protease is not secreted, but rather resides intracellularly as well as on the surface of the endothelial cells. The data suggest that E.C.3.4.24.15 synthesized by brain endothelial cells may process the platelet-derived AβPP, yielding fiagments which could contribute to cerebrovascular Aβ deposits.