The Proteome of Human Amyloid Beta Oligomers

Amyloid beta (Aβ) oligomers are thought to play an important role during development and progression of Alzheimer's disease (AD). Previously, we determined the Aβ oligomer concentrations in various AD mouse models and in human brain tissues of former AD patients. Here, we investigate which proteins are part of these Aβ oligomers, apart from Aβ itself. Because several oligomer-associated proteins have been implicated in mechanisms leading to AD pathology, identification of the Aβ oligomer proteome may provide insights into the formation of Aβ oligomers in vivo and may reveal novel targets for disease-modifying therapeutic approaches. Here, we separated different native Aβ assemblies in brain homogenates of transgenic (tg) AD mice and human AD post mortem samples by density gradient centrifugation, then isolated Aβ-containing assemblies by co-immunoprecipitation. Mass spectrometry of immunoprecipitated proteins with label-free quantification (LFQ) showed significant changes between the proteomes of Aβ oligomers from tg AD mice and wildtype (wt) mice, confirming some proteins that have been expected to bind Aβ species, like ApoE and Clusterin, but also indicating novel, so far unknown, protein content of Aβ oligomers, such as the RabGAP Tbc1d10b. Some of the hereby identified proteins, like, for example, Clusterin, were also found to be enriched in Aβ oligomers from human AD brain tissue derived homogenates as compared to brain tissue from non-demented controls (NC). Others, such as Netrin-1, were specifically enriched in Aβ oligomers in AD compared to NC samples, but not in mouse samples.