ABSTRACT
BACKGROUND: Alzheimer's disease (AD) is characterized by the deposition of insoluble amyloid plaques in the neuropil composed of highly stable, self-assembled Amyloid-beta (Aß) fibrils. Copper has been implicated to play a role in Alzheimer's disease. Dimers of Aß have been isolated from AD brain and have been shown to be neurotoxic. RESULTS: We have investigated the formation of dityrosine cross-links in Aß42 formed by covalent ortho-ortho coupling of two tyrosine residues under conditions of oxidative stress with elevated copper and shown that dityrosine can be formed in vitro in Aß oligomers and fibrils and that these links further stabilize the fibrils. Dityrosine crosslinking was present in internalized Aß in cell cultures treated with oligomeric Aß42 using a specific antibody for dityrosine by immunogold labeling transmission electron microscopy. Results also revealed the prevalence of dityrosine crosslinks in amyloid plaques in brain tissue and in cerebrospinal fluid from AD patients. CONCLUSIONS: Aß dimers may be stabilized by dityrosine crosslinking. These results indicate that dityrosine cross-links may play an important role in the pathogenesis of Alzheimer's disease and can be generated by reactive oxygen species catalyzed by Cu2+ ions. The observation of increased Aß and dityrosine in CSF from AD patients suggests that this could be used as a potential biomarker of oxidative stress in AD.
Subject(s)
Alzheimer Disease/metabolism , Amyloid beta-Peptides/metabolism , Peptide Fragments/metabolism , Tyrosine/analogs & derivatives , Aged , Aged, 80 and over , Alzheimer Disease/pathology , Biomarkers/metabolism , Cells, Cultured , Copper/metabolism , Female , Humans , Male , Neuroblastoma , Oxidative Stress/physiology , Plaque, Amyloid/metabolism , Plaque, Amyloid/pathology , Tyrosine/metabolismABSTRACT
Aß42 [amyloid-ß peptide-(1-42)] plays a central role in Alzheimer's disease and is known to have a detrimental effect on neuronal cell function and survival when assembled into an oligomeric form. In the present study we show that administration of freshly prepared Aß42 oligomers to a neuroblastoma (SH-SY5Y) cell line results in a reduction in survival, and that Aß42 enters the cells prior to cell death. Immunoconfocal and immunogold electron microscopy reveal the path of the Aß42 with time through the endosomal system and shows that it accumulates in lysosomes. A 24 h incubation with Aß results in cells that have damaged lysosomes showing signs of enzyme leakage, accumulate autophagic vacuoles and exhibit severely disrupted nuclei. Endogenous Aß is evident in the cells and the results of the present study suggest that the addition of Aß oligomers disrupts a crucial balance in Aß conformation and concentration inside neuronal cells, resulting in catastrophic effects on cellular function and, ultimately, in cell death.
