Senile plaques in cerebral amyloid angiopathy show accumulation of amyloid precursor protein without cytoskeletal abnormalities.
The abnormal neurites that surround beta-amyloid in senile plaques (SP) in Alzheimer disease contain beta-amyloid precursor protein (beta APP) or abnormal filaments which react with antibodies to tau. Occasionally, beta APP and abnormal filaments are present in the same neurite. Whether both types of abnormal neurites are reactive to the presence of beta-amyloid or they are instead independent from each other is unknown. To begin to clarify this issue, we comparatively studied beta APP and tau-epitopes in SP from cases of classical Alzheimer disease and cases of cerebral amyloid angiopathy, with SP but without neurofibrillary pathology. In subjects with cerebral amyloid angiopathy, about one-third of SP, the same percentage as in Alzheimer disease, were beta APP reactive in the absence of tau-reactivity. beta APP epitopes were ultrastructurally localized in dense bodies of probable lysosomal origin, adjacent to the core of SP. These results demonstrate that beta APP and tau-reactive cytoskeletal alterations occur independently in the neurites of SP. The presence of beta APP in dystrophic neurites of SP and the localization of beta APP in lysosomes suggest that beta APP containing dystrophic neurites may play a role in the extracellular deposition of amyloid.