Expression in drosophila of tandem amyloid ß peptides provides insights into links between aggregation and neurotoxicity.

The generation and subsequent aggregation of amyloid ß (Aß) peptides play a crucial initiating role in the pathogenesis of Alzheimer disease (AD). The two main isoforms of these peptides have 40 (Aß(40)) or 42 residues (Aß(42)), the latter having a higher propensity to aggregate in vitro and being the main component of the plaques observed in vivo in AD patients. We have designed a series of tandem dimeric constructs of these Aß peptides to probe the manner in which changes in the aggregation kinetics of Aß affect its deposition and toxicity in a Drosophila melanogaster model system. The levels of insoluble aggregates were found to be substantially elevated in flies expressing the tandem constructs of both Aß(40) and Aß(42) compared with the equivalent monomeric peptides, consistent with the higher effective concentration, and hence increased aggregation rate, of the peptides in the tandem repeat. A unique feature of the Aß(42) constructs, however, is the appearance of high levels of soluble oligomeric aggregates and a corresponding dramatic increase in their in vivo toxicity. The toxic nature of the Aß(42) peptide in vivo can therefore be attributed to the higher kinetic stability of the oligomeric intermediate states that it populates relative to those of Aß(40) rather than simply to its higher rate of aggregation.