Optimized Ultrasonic Irradiation Finds Out Ultrastable Aβ1–40 Oligomers

Half-Time Heat Map Reveals Ultrasonic Effects on Morphology and Kinetics of Amyloidogenic Aggregation Reaction

Ultrasonication has been recently adopted in amyloid-fibril assays because of its ability to accelerate fibril formation, being promising in the early stage diagnosis of amyloidoses in clinical applications. Although applications of this technique are expanding in the field of protein science, its effects on the aggregation reactions of amyloidogenic proteins are poorly understood. In this study, we comprehensively investigated the morphology and structure of resultant aggregates, kinetics of fibril formation, and seed-detection sensitivity under ultrasonication using β₂-microglobulin and compared these characteristics under shaking, which has been traditionally adopted in amyloid-fibril assays. To discuss the ultrasonic effects on the amyloid-fibril formation, we propose the half-time heat map, which describes the phase diagram of the aggregation reaction of amyloidogenic proteins. The experimental results show that ultrasonication greatly promotes fibril formation, especially in dilute monomer solutions, induces short-dispersed fibrils, and is capable of detecting ultra-trace-concentration seeds with a detection limit of 10 fM. Furthermore, we indicate that ultrasonication highly alters the energy landscape of an aggregation reaction due to the effect of ultrasonic cavitation. These insights contribute not only to our understanding of the effects of agitation on amyloidogenic aggregation reactions but also to their effective application in the clinical diagnosis of amyloidoses.

Optimized sonoreactor for accelerative amyloid-fibril assays through enhancement of primary nucleation and fragmentation

Ultrasonication to supersaturated protein solutions forcibly forms amyloid fibrils, thereby allowing the early-stage diagnosis for amyloidoses. Previously, we constructed a high-throughput sonoreactor to investigate features of the amyloid-fibril nucleation. Although the instrument substantiated the ultrasonication efficacy, several challenges remain; the key is the precise control of the acoustic field in the reactor, which directly affects the fibril-formation reaction. In the present study, we develop the optimized sonoreactor for the amyloid-fibril assay, which improves the reproducibility and controllability of the fibril formation. Using β₂-microglobulin, we experimentally demonstrate that achieving identical acoustic conditions by controlling oscillation amplitude and frequency of each transducer results in identical fibril-formation behavior across 36 solutions. Moreover, we succeed in detecting the 100-fM seeds using the developed sonoreactor at an accelerated rate. Finally, we reveal that the acceleration of the fibril-formation reaction with the seeds is achieved by enhancing the primary nucleation and the fibril fragmentation through the analysis of the fibril-formation kinetics. These results demonstrate the efficacy of the developed sonoreactor for the diagnosis of amyloidoses owing to the accelerative seed detection and the possibility for further early-stage diagnosis even without seeds through the accelerated primary nucleation.

Time-Resolved Observation of Evolution of Amyloid-β Oligomer with Temporary Salt Crystals

The aggregation behavior of amyloid-β (Aβ) peptides remains unclarified despite the fact that it is closely related to the pathogenic mechanism of Alzheimer's disease. Aβ peptides form diverse oligomers with various diameters before nucleation, making clarification of the mechanism involved a complex problem with conventional macroscopic analysis methods. Time-resolved single-molecule level analysis in bulk solution is thus required to fully understand their early stage aggregation behavior. Here, we perform time-resolved observation of the aggregation dynamics of Aβ oligomers in bulk solution using liquid-state transmission electron microscopy. Our observations reveal previously unknown behaviors. The most important discovery is that a salt crystal can precipitate even with a concentration much lower than its solubility, and it then dissolves in a short time, during which the aggregation reaction of Aβ peptides is significantly accelerated. These findings will provide new insights in the evolution of the Aβ oligomer.

Seeding and Cross-Seeding Aggregations of Aβ40 and Its N-Terminal-Truncated Peptide Aβ11-40

In the amyloid plaques of Alzheimer's disease (AD) patients, a large number of N-terminal-truncated amyloid β (Aβ) peptides such as Aβ_11-40 have been identified in addition to the full-length Aβ peptides. However, little is known about the roles of the N-terminal-truncated peptides in AD pathological process. Herein, seeding and cross-seeding aggregations of Aβ₄₀ and its N-terminal-truncated Aβ_11-40 were investigated in the solution and on the surfaces of chips with immobilized seeds by extensive biophysical and biological analyses. The results showed that Aβ₄₀ and Aβ_11-40 aggregates could seed both homologous and heterologous aggregations of the two monomers. However, the capability and characteristics of the seeding (homologous aggregation) and cross-seeding (heterologous aggregation) were significantly different. Aβ₄₀ seeds showed stronger acceleration effects on the aggregations than Aβ_11-40 seeds and induced β-sheet-rich fibrous aggregates of similar cytotoxicities for the two monomers. This indicates that Aβ₄₀ and Aβ_11-40 had similar aggregation pathways in the seeding and cross-seeding on Aβ₄₀ seeds. By contrast, Aβ_11-40 seeds led to different aggregation pathways of Aβ₄₀ and Aβ_11-40. Pure Aβ_11-40 aggregates had higher toxicity than Aβ₄₀ aggregates, and as seeds, Aβ_11-40 seeds induced Aβ₄₀ to form aggregates of higher cytotoxicity. However, homologous Aβ_11-40 aggregates induced by Aβ_11-40 seeds showed lower cytotoxicity than pure Aβ_11-40 aggregates. The results suggest that Aβ_11-40 plays an important role in the pathological process of AD.