Analysis of Amyloid beta (Ab) protein in Amyloid precursor protein (APP) transgenic mouse models of Alzheimer’s disease (AD) and in human brains

Abstract

Soluble amyloid b-protein (Ab) aggregates have been identified in Alzheimer"s disease (AD) brain. To address the roles of soluble and dispersible Ab aggregates for neurodegeneration we analyzed two different amyloid precursor protein (APP)-transgenic mouse models. APP23 mice overexpress human mutant APP with the Swedish mutation. APP51/16 mice express high levels of human wild-type APP. Both mice develop Ab plaques. Dendritic degeneration, neuron loss, and loss of asymmetric synapses were seen in APP23 but not in APP51/16 mice. High levels of high-molecular weight Ab-oligomers, protofibrils, and fibrils (hiMWAb) were observed in the dispersible fraction of forebrain lysates from APP23 and APP51/16 mice as well as in human AD brains. The soluble/dispersible fraction was, thereby, received after centrifugation of native forebrain homogenates at 14.000 x g. Subsequent high-speed ultracentrifugation of this fraction separated the soluble, i.e. the supernatant, from the dispersible fraction, i.e. the resuspended pellet. The major difference between APP23 and APP51/16 mice was that APP23 mice exhibited higher levels of SDS-denaturable dispersible Ab oligomers, protofibrils and fibrils precipitated with oligomer (A11) and protofibril/ fibril (B10AP) specific antibodies than APP51/16 mice. Dispersible Ab oligomers, protofibrils, and fibrils were found associated with APP-C-terminal fragments (APP-CTFs). A potential relevance of these findings for AD was confirmed by similar quantitative differences between AD cases and non-demented cases with Ab pathology. HiMWAb42-oligomers and protofibrils with a molecular weight >1000 kDa predominated in the soluble fraction of AD brain homogenates when these samples were analyzed under native BN-PAGE conditions. Denaturation of the hiMWAb-aggregates by SDS resulted in the detection of Ab monomers, dimers, and hiMWAb with a molecular weight >160 kDa in SDS-PAGE analysis of AD cases but not in controls. Beruht auf Artikeln in: Journal of Cellular and Molecular Medicine, 2012,16:287-295; http://onlinelibrary.wiley.com/doi/10.1111/j.1582-4934.2011.01306.x/abstract;jsessionid=B2D2957AC49351F7E6CCBE3C9E2BC541.d03t01, sowie Neurobiology of Aging, online published 2012, http://www.sciencedirect.com/science/article/pii/S019745801100577X