The Division of Amyloid Fibrils: Systematic Comparison of Fibril Fragmentation Stability by Linking Theory with Experiments

Abstract

Summary The division of amyloid protein fibrils is required for the propagation of the amyloid state and is an important contributor to their stability, pathogenicity, and normal function. Here, we combine kinetic nanoscale imaging experiments with analysis of a mathematical model to resolve and compare the division stability of amyloid fibrils. Our theoretical results show that the division of any type of filament results in self-similar length distributions distinct to each fibril type and the conditions applied. By applying these theoretical results to profile the dynamical stability toward breakage for four different amyloid types, we reveal particular differences in the division properties of disease-related amyloid formed from α-synuclein when compared with non-disease associated model amyloid, the former showing lowered intrinsic stability toward breakage and increased likelihood of shedding smaller particles. Our results enable the comparison of protein filaments' intrinsic dynamic stabilities, which are key to unraveling their toxic and infectious potentials.

Direct Demonstration of Seed Size-Dependent α-Synuclein Amyloid Amplification

“…Interestingly, fibril fragmentation, which leads to the formation of shorter fibril seeds, is demonstrated as a vital step for the amplification of protein aggregates and the spreading of prion seeds. − This may accelerate the transmission of pathological inclusions into various regions of the brain . However, under normal conditions, protein homeostasis is tightly regulated by protein folding quality control machinery, which maintains the integrity of the proteome and limits the accumulation of protein aggregates. , Hence, fragmentation can be considered as an inherent biological property of amyloid fibrils, which is modulated by numerous factors, including thermal motion, shear forces, mechanical stress, and catalytic activity of molecular chaperones in cells. − For example, fibril disassembly by the human heat shock protein 70 (HSP 70) family promotes the disaggregation of amyloids (such as α-Syn and Tau) into potent species with strong seeding ability and prion-like behavior. − Remarkably, a growing body of evidence suggests that biological attributes of amyloid fibrils can be regulated by the size of the fibrils, which is governed by the magnitude of the fragmentation events to a greater extent. ,, In this context, extensive research has been conducted to understand the correlation between the fragmentation of amyloid fibrils and their cytotoxic potential. − However, the interplay between the heterogeneity of α-Syn fibril size and the mechanism of seed size-dependent secondary nucleation pathways involved in the prion-like transmission of pathological conformers is elusive. Here, we hypothesize that apart from biological and pathological features, the heterogeneity and nanoscale differences in fibril size may regulate the progression of α-Syn pathology by dictating distinct secondary nucleation mechanisms associated with fibril amplification pathways.…”

“…In contrast, the longer fragments favor the surface-mediated secondary nucleation pathways for the amplification of α-Syn amyloid (Figure ). In the physiological scenario, fragmentation is an intrinsic property of amyloid fibrils that takes place in the living cells, which is governed by multiple cellular pathways involving a human trichaperone complex, neutrophil-derived proteases, histones, and other cellular protein quality control cross-talk mechanisms. , However, this fragmentation process cleaves amyloids into small seeding competent propagating toxic conformers, which may critically contribute to aggravating disease progression (as seen in patients with various amyloid disorders). , In this context, our study has a broad focus on deciphering how the suprastructural variabilities, particularly the nanoscale differences in α-Syn seed length, selectively control its amplification mechanism and critical events associated with the progression of PD. It will be of great interest in the future to understand the stability of α-Syn fibrils or develop strategies to make the fibrils more thermodynamically stable.…”

Amyloid particles facilitate surface-catalyzed cross-seeding by acting as promiscuous nanoparticles

“…2 B ). Additional sonication did not further alter their size distribution noticeably as would be expected due to their already small sizes ( 26 , 27 ). To further confirm the quality the Aβ42s and Sup35NMs seed samples, dynamic light scattering (DLS) was performed on these seed samples after controlled sonication ( Materials and Methods ).…”

Stability matters, too – the thermodynamics of amyloid fibril formation

“…Indeed, both the length distribution and the polymorph distribution are so strongly defined by kinetic factors that they may almost never reach equilibrium values in realistic settings, in particular in vivo. It is, however, possible to significantly accelerate the approach to equilibrium of the fibril length distribution in in vitro experiments through mechanical action, which has been shown to act differently on different types of amyloid systems 50 .…”

“…It is, however, possible to signicantly accelerate the approach to the equilibrium of the bril length distribution in in vitro experiments through mechanical action, which has been shown to act differently on different types of amyloid systems. 50 Despite the recent advances in the quantication of polymorph populations and length distributions, we will nevertheless in the following focus on the (pseudo-)equilibrium with respect to the free monomer concentration, which is the most accessible, as well as the most informative thermodynamic parameter. It should however be noted that the three characteristics with respect to which equilibrium can be dened are not fully decoupled.…”