(4cv) Directing Amyloid-? Structural Polymorphism: The Relationship between Fibril Structure and Phenotype

A number of neurodegenerative diseases are characterized by the aggregation of amyloid proteins caused by the nucleation of monomeric peptides into soluble oligomers that ultimately aggregate into insoluble fibrils. While oligomers are alleged to be the neurotoxic species, several factors have motivated research in the field into understanding amyloid fibrils and their structure. A small portion of Alzheimer's Disease (AD) cases are associated with familial mutations (FAD) in the amyloid precursor protein, which have been shown to result in significant differences in structural polymorphism of the resulting Aβ fibrils. There is also increasing evidence that these mutations lead to a diverse array of disease phenotypes. The goal of this study was to evaluate the structural and phenotypic effects of cross-seeding wild-type Aβ_1-40 with various FAD mutants and isoforms. In this study, we examined both the structural and phenotypic effects of multiple generations of seeding of WT Aβ_1-40 as well as cross-seeding with FAD mutants and an Aβ isoform. Specifically, we evaluated the impact of seeding wild-type (WT) Aβ_1-40 with pre-formed fibrils of Aβ mutants, Arctic (E22G) and Osaka (E22Δ), as well as the isoform Aβ_1-42. This was determined by kinetics measurements using thioflavin T fluorescence, fibrils structural classification and 2D class-averaging with negative-stain transmission electron microscopy, and their resulting impact on cell viability through MTT assays. Our results demonstrate that after multiple generations of Aβ_1-40 seeding, a homogenous population of fibrils with a crossover distance of 30 nm is formed, which results in decreased cell viability when compared to fibrils with a longer crossover distance. Additionally, we show that structure can be faithfully passed from mutant fibrils to that of WT fibrils. This cross-seeding of WT fibrils results in a toxicity profile similar to that of the parent mutant fibrils, as evidenced by cellular assays. Our findings have significant implications for neurodegenerative diseases caused by the aggregation of monomers into fibrils, demonstrating that the interaction between different forms of fibrils may be responsible for disease pathology.

Research Interests

My research interests look to build upon the methods that I have established during my PhD to understand the relationship different amyloid structures have on human health in a systems biology and immunology scope, for the engineering of sensing and therapeutic applications. This includes further understanding structural polymorphisms using cryo-EM, expanding on cytotoxic profile measurements in addition to MTT assays, rapidly classifying polymorphs using bioinformatics and machine learning approaches, and developing more sophisticated biological environments for amyloid nucleation to better match what occurs in patients presenting amyloid diseases.