Differential toxicity, conformation and morphology of typical initial aggregation states of Abeta1-42 and Abetapy3-42 beta-amyloids.

Among the different species of water-soluble ?-peptides (A?1-42, A?1-40 and N-terminal truncated A?-peptides), A?py3-42 is thought to play a relevant role in Alzheimer's pathogenesis due to its abundance, resistance to proteolysis, fast aggregation kinetics, dynamic structure and high neurotoxicity. To evaluate the specific structural characteristics and neurotoxicity of A?py3-42, we separated different aggregation states of A?1-42 and A?py3-42 using fast protein liquid chromatography, isolating in both cases three peaks that corresponded to sa (small), ma (medium) and la (large) aggregates. Conformational analysis, by circular dichroism showed a prevailing random coil conformation for sa and ma, and typical ?-sheet conformation for la. AFM and TEM show differential structural features between the three aggregates of a given ?-peptide and among the aggregate of the two ?-peptides. The potential toxic effects of the different aggregates were evaluated using human neuroblastoma SH-SY5Y cells in the MTT reduction, in the xCELLigence System, and in the Annexin V binding experiments. In the case of A?1-42 the most toxic aggregate is la, while in the case of A?py3-42 both sa and la are equally toxic. A? aggregates were found to be internalized in the cells, as estimated by confocal immunofluorescence microscopy, with a higher effect observed for A?py3-42, showing a good correlation with the toxic effects. Together these experiments allowed the discrimination of the intermediate states more responsible of oligomer toxicity, providing new insights on the correlation between the aggregation process and the toxicity and confirming the peculiar role in the pathogenesis of Alzheimer disease of A?py3-42 peptide.