Identification of neurotoxic cross-linked amyloid-ß dimers in the Alzheimer's brain.

ABSTRACT

The primary structure of canonical amyloid-ß-protein was elucidated more than 30 years ago, yet the forms of amyloid-ß that play a role in Alzheimer's disease pathogenesis remain poorly defined. Studies of Alzheimer's disease brain extracts suggest that amyloid-ß, which migrates on sodium dodecyl sulphate polyacrylamide gel electrophoresis with a molecular weight of ∼7 kDa (7kDa-Aß), is particularly toxic; however, the nature of this species has been controversial. Using sophisticated mass spectrometry and sensitive assays of disease-relevant toxicity we show that brain-derived bioactive 7kDa-Aß contains a heterogeneous mixture of covalently cross-linked dimers in the absence of any other detectable proteins. The identification of amyloid-ß dimers may open a new phase of Alzheimer's research and allow a better understanding of Alzheimer's disease, and how to monitor and treat this devastating disorder. Future studies investigating the bioactivity of individual dimers cross-linked at known sites will be critical to this effort.