Cross-seeding of alpha-synuclein aggregation by amyloid fibrils of food proteins

Abstract

The aggregation of the protein α-synuclein (aSyn) into amyloid fibrils in the human brain is associated with the development of several neurodegenerative diseases, including Parkinson's disease. The previously observed prion-like spreading of aSyn aggregation throughout the brain and the finding that heterologous cross-seeding of amyloid aggregation occurs in vitro for some proteins suggest that exposure to amyloids in general may pose a risk for disease development. To elucidate which protein fibril characteristics determine if and how heterologous amyloid seeding can occur, we investigated the potential of amyloid fibrils formed from proteins found in food, hen egg white lysozyme, and bovine milk β-lactoglobulin to cross-seed aSyn aggregation in the test tube. We observed that amyloid fibrils from lysozyme, but not β-lactoglobulin, potently cross-seeded the aggregation of aSyn as indicated by a significantly shorter lag phase of aSyn aggregation in the presence of lysozyme fibrils. The cross-seeding effect of lysozyme was found to be primarily driven by a surface-mediated nucleation mechanism. The differential seeding effect of lysozyme and β-lactoglobulin on aSyn aggregation could be explained on the basis of binding affinity, binding site, and electrostatic interactions. Our results indicate that heterologous seeding of proteins may occur depending on the physicochemical characteristics of the seed protein fibril. Our findings suggest that heterologous seeding has the potential to determine the pathogenesis of neurodegenerative amyloid diseases.

Secondary Nucleation and the Conservation of Structural Characteristics of Amyloid Fibril Strains

“…Indeed, secondary nucleation might only be a special case of general surface nucleation (Buell, 2017). It has been shown that fibrils of one protein can nucleate from monomer on the surface of fibrils of another protein, while the same proteins are unable to elongate each others fibrils (Koloteva-Levine et al, 2020;Vaneyck et al, 2021). This difference suggests that cross-surface nucleation has much lower requirements for sequence similarity than cross-elongation.…”

AA amyloid in human food chain is a possible biohazard

“…Cross-seeding between unrelated proteins has been shown in vivo for the murine AA model 13 , 14 . Cross-seeding between cerebral amyloid proteins has been shown in vitro 15 , 16 as well as between such proteins and non-human amyloid fibrils, e.g. originating from the gastrointestinal microbiome 17 , 18 .…”

Bioavailability and Health Impact of Ingested Amyloid‐like Protein Fibrils and their Link with Inflammatory Status: A Need for More Research?

“…[ 96,97 ] Involvement of the endosomal‐lysosomal pathway in intraneuronal transport of amyloid species was suggested by Nath et al. [ 97 ] Interestingly, recent publications have proven the in vitro cross‐seeding of αSyn and Aβ by exogenous ALF seeds derived from food proteins, [ 28,29 ] most likely through surface‐mediated secondary nucleation effects. This raises the question if aggregation of endogenous proteins in enteric neurons, upon contact with ingested ALF structures, may occur in a similar way as bacterial cross‐seeding ( Figure 3 ).…”

“…[ 77,78,93,94 ] Expansion to oral exposure studies including common food protein derived ALFs, may already provide some insight in the extent to which ALF consumption may trigger both systemic (e.g., AA amyloidosis) and localized (neurodegenerative) amyloidosis, albeit in predisposed animal models. The fact that in vitro cross‐seeding by food‐born ALF seeds was observed for neurodegenerative precursor proteins αSyn and Aβ, [ 28,29 ] supports the need for additional research and calls for awareness of both the consumer and the food industry.…”

“…Since primary nucleation is highly sequence dependent, it is more likely that potential cross-seeding events follow a secondary nucleation process whereby endogenous proteins aggregate on the surface of an existing aggregate, in this case the ALF (core). [25] Although a high degree of sequence identity is still considered to be required for efficient cross-seeding, [26] recent publications demonstrated in vitro cross-seeding of endogenous disease-related proteins [𝛼-synuclein (𝛼Syn), Amyloid-𝛽 (A𝛽)] by food protein ALF seeds, [27][28][29] highlighting the fact that crossseeding not only depends on sequence homology, but also on physicochemical properties (e.g., binding affinity, electrostatic interactions).…”