Modulation of the extent of structural heterogeneity in α-synuclein fibrils by the small molecule thioflavin T

Abstract

The transition of intrinsically disordered, monomeric α-synuclein into β-sheet-rich oligomers and fibrils is associated with multiple neurodegenerative diseases. Fibrillar aggregates possessing distinct structures that differ in toxicity have been observed in different pathological phenotypes. Understanding the mechanism of the formation of various fibril polymorphs with differing cytotoxic effects is essential for determining how the aggregation reaction could be modulated to favor nontoxic fibrils over toxic fibrils. In this study, two morphologically different α-synuclein fibrils, one helical and the other ribbon-like, are shown to form together. Surprisingly, a widely used small molecule for probing aggregation reactions, thioflavin T (ThT), was found to tune the structural heterogeneity found in the fibrils. The ribbon-like fibrils formed in the presence of ThT were found to have a longer structural core than the helical fibrils formed in the absence of ThT. The ribbon-like fibrils are also more toxic to cells. By facilitating the formation of ribbon-like fibrils over helical fibrils, ThT reduced the extent of fibril polymorphism. This study highlights the role of a small molecule such as ThT in selectively favoring the formation of a specific type of fibril by binding to aggregates formed early on one of multiple pathways, thereby altering the structural core and external morphology of the fibrils formed.

Microglial glutamate release evoked by α‐synuclein aggregates is prevented by dopamine

“…Kim et al (2013) have shown, however, that αS oligomers spontaneously secreted by a neuroblastoma cell line had the potential to activate TLR-2 in microglial cells whereas fibrils produced from recombinant αS were unable to do so. Such discrepancies may be because of structural heterogeneity of αS oligomeric and fibrillary species in between studies (Bousset et al, 2013: Kumar, Singh, Kumari, & Udgaonkar, 2017. Glutamate release induced by αSa was also significantly curtailed by JNJ, a synthetic antagonist for purinergic P2X7 receptors (Letavic et al, 2013), which is reminiscent to previous studies showing that oligomeric forms of αS bind directly to this receptor subtype .…”

“…Our result is in agreement with data reported by Gustot et al (2015) showing that αS amyloid fibrils can trigger inflammatorytype reactions through a TLR-2-dependent mechanism. Such discrepancies may be because of structural heterogeneity of αS oligomeric and fibrillary species in between studies (Bousset et al, 2013: Kumar, Singh, Kumari, & Udgaonkar, 2017. Such discrepancies may be because of structural heterogeneity of αS oligomeric and fibrillary species in between studies (Bousset et al, 2013: Kumar, Singh, Kumari, & Udgaonkar, 2017.…”

Triphala inhibits alpha-synuclein fibrillization and their interaction study by NMR provides insights into the self-association of the protein

“…Now it is known that aSyn exists in oligomeric form during the lag phase of brillization process. 56,57,[60][61][62][63][64][65][66][67][68][69][70][71][72][73][74] So then a question arises that is the disappearance of peaks for stretches of residues in the free aSyn HSQC spectrum (Fig. 3A) due to the oligomerization of the protein?…”

β‐Amyloid aggregation and heterogeneous nucleation

“…One of the defining features of amyloids is polymorphism, and it has been shown that most of this polymorphism arises during the nucleation of the fibrillization reaction . Different forms of fibrils and/or soluble oligomers (precursors of fibrils) may have different degrees of neurotoxicity or interact differently with diagnostic or therapeutic reagents (e.g., antibodies) . For these reasons, the identification of biologically relevant heterogeneous nucleators is a point of potentially great importance.…”

“…[27][28][29] Different forms of fibrils and/or soluble oligomers (precursors of fibrils) may have different degrees of neurotoxicity or interact differently with diagnostic or therapeutic reagents (e.g., antibodies). [30][31][32] For these reasons, the identification of biologically relevant heterogeneous nucleators is a point of potentially great importance.…”