Direct evidence for self-propagation of different amyloid-ß fibril conformations

Abstract

Background: Amyloid fibrils formed by amyloid-ß (Aß) peptides are associated with Alzheimer's disease and can occur in a range of distinct morphologies that are not uniquely determined by the Aß sequence. Whether distinct conformations of Aß fibrils can be stably propagated over multiple cycles of seeding and fibril growth has not been established experimentally. Objective: The ability of the 40-residue peptide Aß 1-40 to assemble into fibrils with the conformation of the mutant Aß 1-40 peptide containing the 'Osaka' mutation E22 was investigated. Methods: Fibril formation of highly pure, recombinant Aß 1-40 in the presence of distinct, preformed seeds in vitro was recorded with thioflavin T fluorescence, and distinct fibrillar structures were identified and distinguished by fluorescence spectroscopy and electron microscopy. Results: We propagated the specific quaternary structure of Aß 1-40 E22 fibrils with wild-type Aß 1-40 over up to seven cycles of seeding and fibril elongation. As a result of a 10 7 -fold dilution of the initially present Aß 1-40 E22 seeds, the vast majority of fibrils formed after the seventh propagation cycle with Aß 1-40 did not contain a single molecule of Aß 1-40 E22, but still retained the conformation of the initial Aß 1-40 E22 seeds. Increased critical concentrations of Aß 1-40 fibrils formed in the presence of Aß 1-40 E22 nuclei suggest that these fibrils are less stable than homolo-gously seeded Aß 1-40 fibrils, consistent with a kinetically controlled mechanism of fibril formation. Conclusion: The propagation of a distinct Aß fibril conformation over multiple cycles of seeded fibril growth demonstrates the basic ability of the Aß peptide to form amyloid strains that in turn may cause phenotypes in Alzheimer's disease.