Aβ43 is neurotoxic and primes aggregation of Aβ40 in vivo

The involvement of Amyloid-beta (A beta) in the pathogenesis of Alzheimer's disease (AD) is well established. However, it is becoming clear that the amyloid load in AD brains consists of a heterogeneous mixture of A beta peptides, implying that a thorough understanding of their respective role and toxicity is crucial for the development of efficient treatments. Besides the well-studied A beta(40) and A beta(42) species, recent data have raised the possibility that A beta(43) peptides might be instrumental in AD pathogenesis, because they are frequently observed in both dense and diffuse amyloid plaques from human AD brains and are highly amyloidogenic in vitro. However, whether A beta(43) is toxic in vivo is currently unclear. Using Drosophila transgenic models of amyloid pathology, we show that A beta(43) peptides are mainly insoluble and highly toxic in vivo, leading to the progressive loss of photoreceptor neurons, altered locomotion and decreased lifespan when expressed in the adult fly nervous system. In addition, we demonstrate that A beta(43) species are able to trigger the aggregation of the typically soluble and non-toxic A beta(40), leading to synergistic toxic effects on fly lifespan and climbing ability, further suggesting that A beta(43) peptides could act as a nucleating factor in AD brains. Altogether, our study demonstrates high pathogenicity of A beta(43) species in vivo and supports the idea that A beta(43) contributes to the pathological events leading to neurodegeneration in AD.