RESUMO
Soluble amyloid-ß (Aß) aggregates of various sizes, ranging from dimers to large protofibrils, have been associated with neurotoxicity and synaptic dysfunction in Alzheimer's Disease (AD). To investigate the properties of biologically relevant Aß species, brain extracts from amyloid ß protein precursor (AßPP) transgenic mice and AD patients as well as synthetic Aß preparations were separated by size under native conditions with density gradient ultracentrifugation. The fractionated samples were then analyzed with atomic force microscopy (AFM), ELISA, and MTT cell viability assay. Based on AFM appearance and immunoreactivity to our protofibril selective antibody mAb158, synthetic Aß42 was divided in four fractions, with large aggregates in fraction 1 and the smallest species in fraction 4. Synthetic Aß aggregates from fractions 2 and 3 proved to be most toxic in an MTT assay. In AßPP transgenic mouse brain, the most abundant soluble Aß species were found in fraction 2 and consisted mainly of Aß40. Also in AD brains, Aß was mainly found in fraction 2 but primarily as Aß42. All biologically derived Aß from fraction 2 was immunologically discriminated from smaller species with mAb158. Thus, the predominant species of biologically derived soluble Aß, natively separated by density gradient ultracentrifugation, were found to match the size of the neurotoxic, 80-500 kDa synthetic Aß protofibrils and were equally detected with mAb158.
