Amyloid oligomer formation and interferences

As the global population is aging, the growing prevalence of progressive neurodegenerative diseases places a huge burden on our society. A wide range of amyloid-forming proteins or peptides, such as Alzheimer's amyloid-beta (Aβ) and Parkinson's α-Synuclein, have the inherent tendency to undergo protein homeostasis collapse under the misfolding conditions, in which these proteins or peptides fail to keep native conformations, followed by self-assembling into a diverse array of aggregates including the initial oligomers or protofibrils (or early aggregates) and mature fibrils. Though one of the hallmarks of these age-related diseases is the fibrillar deposits in the brain, numerous evidence has shown that it is the soluble early aggregates rather than these fibrils that are the main contributing factors to neurotoxicity. One of the prevalently accepted mechanisms states that early aggregates interact with lipid membranes, permeabilize and disrupt the integrity of cellular membranes, resulting in uncontrolled extracellular Ca2+ influx and imbalance of other biomolecules. However, these early aggregates are structurally heterogeneous, transient, and metastable, making them difficult to characterize their biophysical properties, such as the size distributions, the structural information, the interaction with other molecules (metal ions or extracellular globular proteins), and the permeabilization with cellular membranes.
To make a deep understanding of the above conspicuous feature of the toxicity-induced amyloid aggregates in the pathogenesis of neurodegenerative diseases, in this thesis, we discussed two main aspects of the involvement of different amyloid-forming proteins, that is amyloid oligomer formation in chapters 2-4 and oligomer interference in chapters 5-6 to discuss amyloid aggregation neurotoxic mechanisms, structural features, membrane permeabilization, and intermolecular interactions. In chapter 2, we proposed that single-molecule techniques can be taken as complementary tools for the characterization of heterogeneous amyloid aggregates and provide diagnostic perspectives for neurodegenerative diseases. Additionally, we showed a structurally and functionally relevant scaffold to stabilize Aβ oligomers in chapter 3, which enable us to determine the structure in a membrane-mimic environment, and we explored the membrane permeabilization mechanism of truncated prion protein in lipid membranes in chapter 4. Moreover, our results in chapters 5-6 reveal the effects of globular proteins on amyloid protein aggregation or the dynamic influence of lipids or metal ions on binding and unbinding to lipid membranes. Our results expand our knowledge about the toxic molecular mechanisms of amyloid aggregates and present the new directions to design
or screen the oligomer-based nanobody or antibody, which can further contribute to putting forward the diagnosis and drug design for subsequent therapy of these diseases.