Protease Inhibitor Coinfusion with Amyloid beta -Protein Results in Enhanced Deposition and Toxicity in Rat Brain

Amyloid beta-protein, Abeta, is normally produced in brain and is cleared by unknown mechanisms. In Alzheimer's disease (AD), Abeta accumulates in plaque-like deposits and is implicated genetically in neurodegeneration. Here we investigate mechanisms for Abeta degradation and Abeta toxicity in...

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Bibliographic Details
Published in:The Journal of neuroscience 1998-10, Vol.18 (20), p.8311-8321
Main Authors: Frautschy, Sally A, Horn, David L, Sigel, Jason J, Harris-White, Marni E, Mendoza, John J, Yang, Fusheng, Saido, T. C, Cole, Gregory M
Format: Article
Language:English
Subjects:
Alzheimer Disease - metabolism
Alzheimer Disease - pathology
Amyloid beta-Peptides - analysis
Amyloid beta-Peptides - immunology
Amyloid beta-Peptides - metabolism
Amyloidosis - metabolism
Amyloidosis - pathology
Animals
Antibodies, Monoclonal
Aprotinin - pharmacology
Cathepsins - metabolism
Female
Frontal Lobe - metabolism
Frontal Lobe - pathology
Glial Fibrillary Acidic Protein - analysis
Gliosis - metabolism
In Situ Nick-End Labeling
Leupeptins - pharmacology
Lysosomes - chemistry
Lysosomes - physiology
Microscopy, Confocal
Neuroglia - chemistry
Neuroglia - physiology
Neurons - enzymology
Neurons - pathology
Neurotoxins - metabolism
Protease Inhibitors - pharmacology
Rats
Rats, Sprague-Dawley
Serine Proteinase Inhibitors - pharmacology
Thalamus - metabolism
Thalamus - pathology
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Summary:Amyloid beta-protein, Abeta, is normally produced in brain and is cleared by unknown mechanisms. In Alzheimer's disease (AD), Abeta accumulates in plaque-like deposits and is implicated genetically in neurodegeneration. Here we investigate mechanisms for Abeta degradation and Abeta toxicity in vivo, focusing on the effects of Abeta40, which is the peptide that accumulates in apolipoprotein E4-associated AD. Chronic intraventricular infusion of Abeta40 into rat brain resulted in limited deposition and toxicity. Coinfusion of Abeta40 with the cysteine protease inhibitor leupeptin resulted in increased extracellular and intracellular Abeta immunoreactivity. Analysis of gliosis and TUNEL in neuron layers of the frontal and entorhinal cortex suggested that leupeptin exacerbated Abeta40 toxicity. This was supported further by the neuronal staining of cathepsin B in endosomes or lysosomes, colocalizing with intracellular Abeta immunoreactivity in pyknotic cells. Leupeptin plus Abeta40 caused limited but significant neuronal phospho-tau immunostaining in the entorhinal cortex. Intriguingly, Abeta40 plus leupeptin induced intracellular accumulation of the more toxic Abeta, Abeta42, in a small group of septal neurons. Leupeptin infusion previously has been reported to interfere with lysosomal proteolysis and to result in the accumulation of lipofuscin, dystrophic neurites, tau- and ubiquitin-positive inclusions, and structures resembling paired helical filaments. Coinfusion of Abeta40 with the serine protease inhibitor aprotinin also increased diffuse extracellular deposition but reduced astrocytosis and TUNEL and was not associated with intracellular Abeta staining. Collectively, these data suggest that an age or Alzheimer's-related defect in lysosomal/endosomal function could promote Abeta deposition and DNA fragmentation in neurons and glia similar to that found in Alzheimer's disease.
ISSN:0270-6474
1529-2401
DOI:10.1523/jneurosci.18-20-08311.1998