3-D structure of the transmembrane c-terminal domain of the amyloid precursor protein (C99), the immediate precursor of amyloid-β

Background: The soluble As oligomers have been proposed to be the disease causing entity in the pathogenesis of Alzheimer’s disease (AD), but the conformation and time course of the As oligomers are not well established. Genetically modified mouse models recapitulate pathological and biochemical processes involved in the pathogenesis of AD, and are instrumental in studying disease mechanisms and testing therapeutic strategies. Methods: In the present study, we investigated the As assemblies in the cortex of 4-20 months of age APPSwedish transgenic Tg2576 mouse, and compared these with the As assemblies that were detected in autopsy brain tissue from AD patients (58-88 years) (Bao et al. submitted). We serially extracted As species into TBS (soluble), TBST (detergent soluble) and GuCHl (insoluble) fractions. The conformation and level of the As species were determined by ELISA and immunoblotting with Ab-derived diffusible ligands (ADDLs) specific antibodies. Results: As assemblies ranging from dimers to hexamers were detected in all three extraction fractions in the Tg2576 mice, and showed a gradual increased level from 6 months of age. The dodecamers were detected from 6 months of age in Tg2576 mice brain extractions, and the levels remained the same in the older mice. Monomeric As was also detected in the TBST and GuHCl fractions, and interestingly a sharp increased level in the GuHCl fraction of 20 months old Tg2576 mice, which is the age known to show very high plaque load in this transgenic mice. Lower molecular weight As species were generally detected in the cerebral cortex of transgenic mice similar to those detected in AD patients carrying the same APPSwedish mutation. In contrast, no lower molecular weight As assemblies were detected in cortical brain tissue from sporadic AD patients. Conclusions: These results suggest that the soluble As assemblies in the Tg2576 mice brain were not same as the As species presented in the brain tissue from AD patients, and suggest that there may be a different As dynamic processes in this transgenic mice compare to AD patients, and it need to be taken into consideration when using this mouse model to evaluate anti-As therapy.