Cu(II) mediates kinetically distinct, non-amyloidogenic aggregation of amyloid-beta peptides

Cu(II) ions are implicated in the pathogenesis of Alzheimer disease by influencing the aggregation of the amyloid-β (Aβ) peptide. Elucidating the underlying Cu(II)-induced Aβ aggregation is paramount for understanding the role of Cu(II) in the pathology of Alzheimer disease. The aim of this study was to characterize the qualitative and quantitative influence of Cu(II) on the extracellular aggregation mechanism and aggregate morphology of Aβ(1-40) using spectroscopic, microelectrophoretic, mass spectrometric, and ultrastructural techniques. We found that the Cu(II):Aβ ratio in solution has a major influence on (i) the aggregation kinetics/mechanism of Aβ, because three different kinetic scenarios were observed depending on the Cu(II):Aβ ratio, (ii) the metal:peptide stoichiometry in the aggregates, which increased to 1.4 at supra-equimolar Cu(II):Aβ ratio; and (iii) the morphology of the aggregates, which shifted from fibrillar to non-fibrillar at increasing Cu(II):Aβ ratios. We observed dynamic morphological changes of the aggregates, and that the formation of spherical aggregates appeared to be a common morphological end point independent on the Cu(II) concentration. Experiments with Aβ(1-42) were compatible with the conclusions for Aβ(1-40) even though the low solubility of Aβ(1-42) precluded examination under the same conditions as for the Aβ(1-40). Experiments with Aβ(1-16) and Aβ(1-28) showed that other parts than the Cu(II)-binding His residues were important for Cu(II)-induced Aβ aggregation. Based on this study we propose three mechanistic models for the Cu(II)-induced aggregation of Aβ(1-40) depending on the Cu(II):Aβ ratio, and identify key reaction steps that may be feasible targets for preventing Cu(II)-associated aggregation or toxicity in Alzheimer disease.