Epigallocatechin-3-gallate and related phenol compounds redirect the amyloidogenic aggregation pathway of ataxin-3 towards non-toxic aggregates and prevent toxicity in neural cells and Caenorhabditis elegans animal model

Abstract

The protein ataxin-3 (ATX3) triggers an amyloid-related neurodegenerative disease when its polyglutamine stretch is expanded beyond a critical threshold. We formerly demonstrated that the polyphenol epigallocatechin-3-gallate (EGCG) could redirect amyloid aggregation of a full-length, expanded ATX3 (ATX3-Q55) towards non-toxic, soluble, SDS-resistant aggregates. Here, we have characterized other related phenol compounds, although smaller in size, i.e. (-)-epigallocatechin gallate (EGC), and gallic acid (GA). We analysed the aggregation pattern of ATX3-Q55 and of the N-terminal globular Josephin domain (JD) by assessing the time course of the soluble protein, as well its structural features by FTIR and AFM, in the presence and the absence of the mentioned compounds. All of them redirected the aggregation pattern towards soluble, SDS-resistant aggregates. They also prevented the appearance of ordered side-chain hydrogen bonding in ATX3-Q55, which is the hallmark of polyQ-related amyloids. Molecular docking analyses on the JD highlighted three interacting regions, including the central, aggregation-prone one. All three compounds bound to each of them, although with different patterns. This might account for their capability to prevent amyloidogenesis. Saturation transfer difference NMR experiments also confirmed EGCG and EGC binding to monomeric JD. ATX3-Q55 pre-incubation with any of the three compounds prevented its calcium-influx-mediated cytotoxicity towards neural cells. Finally, all the phenols significantly reduced toxicity in a transgenic Caenorhabditis elegans strain expressing an expanded ATX3. Overall, our results show that the three polyphenols act in a substantially similar manner. GA, however, might be more suitable for antiamyloid treatments due to its simpler structure and higher chemical stability.

Beneficial Effects of Green Tea Catechins on Neurodegenerative Diseases

“…Previously, EGCG was shown to redirect amyloid aggregation of a full-length, expanded ATX3 (ATX3-Q55) toward non-toxic, soluble, sodium dodecylsulfate-resistant aggregates. Visentin et al found a similar action of EGCG, EGC, and GA [ 76 ]. These three polyphenols prevented the appearance of ordered side-chain hydrogen bonding in ATX3-Q55, which is the hallmark of polyglutamic acid-related amyloids.…”

Targeting Amyloid Aggregation: An Overview of Strategies and Mechanisms

“…Current literature shows ECGC’s capability to prevent the formation of aggregates from several potentially amyloidogenic proteins or peptides, including Aβ, α-syn [ 109 ], IAPP [ 110 ], AL [ 111 ], polyglutamine (polyQ)-containing proteins, including huntingtin (htt) [ 112 ] and ATX3 [ 87 , 113 ].…”

“…Some literature is also available regarding the antiamyloid effects of smaller polyphenols structurally related to EGCG, in particular EGC and GA. In general, they also were proved to be effective antiamyloid agents, although to a somewhat lesser extent [ 113 , 119 ].…”

“…In fact, docking strategies based on classical, molecular mechanics force fields usually require that the overall structure of the receptor be little influenced by the interaction with inhibitors. When this is actually the case, as for example in the functional interaction between EGCG or related lower-weight compounds (EG, EGC) and the Josephin domain—which triggers the amyloid aggregation in expanded ATX3 variants [ 165 , 166 , 167 ]—well-established docking approaches are able to provide detailed information on the structural basis of the action of inhibitors [ 113 ]. However, simulations of thermodynamic ensembles by molecular dynamics (MD)-based modeling of Aβ42 dimers, either in the presence or the absence of EGCG, showed that Aβ-EGCG interactions lead to a significant reduction in the β-content of specific regions of the peptide [ 168 ].…”

Protein Misfolding and Aggregation as a Therapeutic Target for Polyglutamine Diseases

“…Wanker’s group also found that epigallocatechingallate (EGCG), a green tea polyphenol, modulates misfolding and oligomerization of the expanded polyQ proteins, resulting in efficient suppression of polyQ aggregation in vitro [ 79 ]. EGCG suppressed aggregation formation of the polyQ proteins and polyQ-induced cytotoxicity in HD models of yeast and Drosophila [ 79 ], and the SCA3 model of C. elegans [ 80 , 81 ]. Importantly, EGCG was shown to redirect amyloid-like fibril formation of the polyQ proteins toward less-toxic off-pathway species that are poor in β-sheet structures with increasing solubility [ 80 ].…”