Amyloid β Proteoforms Elucidated by Quantitative LC/MS in the 5xFAD Mouse Model of Alzheimer's Disease

Numerous A beta proteoforms, identified in the human brain, possess differential neurotoxic and aggregation propensities. These proteoforms contribute in unknown ways to the conformations and resultant pathogenicity of oligomers, protofibrils, and fibrils in Alzheimer's disease (AD) manifestation owing to the lack of molecular-level specificity to the exact chemical composition of underlying protein products with widespread interrogating techniques, like immunoassays. We evaluated A beta proteoform flux using quantitative top-down mass spectrometry (TDMS) in a well-studied 5xFAD mouse model of age-dependent A beta-amyloidosis. Though the brain-derived A beta proteoform landscape is largely occupied by A beta 1-42, 25 different forms of A beta with differential solubility were identified. These proteoforms fall into three natural groups defined by hierarchical clustering of expression levels in the context of mouse age and proteoform solubility, with each group sharing physiochemical properties associated with either N/C-terminal truncations or both. Overall, the TDMS workflow outlined may hold tremendous potential for investigating proteoform-level relationships between insoluble fibrils and soluble A beta, including low-molecular-weight oligomers hypothesized to serve as the key drivers of neurotoxicity. Similarly, the workflow may also help to validate the utility of AD-relevant animal models to recapitulate amyloidosis mechanisms or possibly explain disconnects observed in therapeutic efficacy in animal models vs humans.

Automated summary

This study focuses on the role of different proteoforms of A beta in Alzheimer's disease. The authors evaluated the flux of A beta proteoforms using quantitative top-down mass spectrometry in a mouse model. They found 25 different forms of A beta with differential solubility in addition to the major A beta 1-42 form. These proteoforms were categorized into three groups based on expression levels and solubility. The findings suggest that this workflow has potential for investigating the relationship between insoluble fibrils and soluble A beta, as well as the role of low-molecular-weight oligomers in neurotoxicity. It may also help validate the use of AD-relevant animal models.