Aggregation of Alzheimer's amyloid fibrils studied with atomic force microscopy

The aggregation and malformation of the Amyloid beta peptide abeta(1-40) is strongly believed to be involved in the development of Alzheimer’s disease (AD). With this thesis we hope to provide important clues to further understanding of amyloid formation in vitro, near physiological conditions. We use the Atomic Force Microscope (AFM) which provides three-dimensional images with vertical resolution down to Angstroms. Together with a previously developed add on tapping mode system we investigate the aggregation paths for abeta(1-40) in three different relevant physiological buffer solutions. The AFM system is extended with an external data acquisition system for increased image resolution. Our results show that protein aggregation can be very complex, many different intermediates with a large variety of morphologies are observed, including protofibrils and large mature fibrils. Our results also indicate that the appearance of protofibrils, i.e. an intermediate stage in the fibrillization, depends on the peptide concentration. It is also shown that pretreatment of samples are very important, there are large differences in aggregation behaviour between a freshly prepared abeta(1-40) sample and a sample that has been frozen prior to experiments, due to a degradation of peptide concentration. The addition of sodium chloride to the sample reveals an increased aggregation process, fibrils were seen two days earlier than for abeta(1-40). Also shown is that too large amounts of such [Cl] ions in the buffer solution rearranges the fibrils structure into amorphous aggregates. Aluminium has for many years been suggested as a possible cause in the development of AD. The addition of an aluminium citrate, stable at relevant pH, shows that the aggregation process towards fibrillization is increased, and these fibrils show no tendency of instability. The mature fibrils in the case of added aluminium citrate have larger heights than those observed in freshly prepared and frozen samples. This result may be important as a clue to explain AD pathogenesis, since similar fibrils previously have been shown to be toxic to neurons.Validerat; 20101217 (root