Astrocytes accumulate Aβ42 and give rise to astrocytic amyloid plaques in Alzheimer disease brains

beta-Amyloid(1-42) (Abeta42), a major component of amyloid plaques, accumulates within pyramidal neurons in the brains of individuals with Alzheimer's disease (AD) and Down syndrome. In brain areas exhibiting AD pathology, Abeta42-immunopositive material is observed in astrocytes. In the present study, single- and double-label immunohistochemistry were used to reveal the origin and fate of this material in astrocytes. Our findings suggest that astrocytes throughout the entorhinal cortex of AD patients gradually accumulate Abeta42-positive material and that the amount of this material correlates positively with the extent of local AD pathology. Abeta42-positive material within astrocytes appears to be of neuronal origin, most likely accumulated via phagocytosis of local degenerated dendrites and synapses, especially in the cortical molecular layer. The co-localization of neuron-specific proteins, alpha7 nicotinic acetylcholine receptor and choline acetyltransferase, in Abeta42-burdened, activated astrocytes supports this possibility. Our results also suggest that some astrocytes containing Abeta42-positive deposits undergo lysis, resulting in the formation of astrocyte-derived amyloid plaques in the cortical molecular layer in brain regions showing moderate to advanced AD pathology. These astrocytic plaques can be distinguished from those arising from neuronal lysis by virtue of their smaller size, their nearly exclusive localization in the subpial portion of the molecular layer of the cerebrocortex, and by their intense glial fibrillary acidic protein immunoreactivity. Overall, Abeta42 accumulation and the selective:lysis of Abeta42-burdened neurons and astrocytes appear to make a major contribution to the observed amyloid plaques in AD brains. (C) 2003 Elsevier Science B.V. All rights reserved.