Green tea polyphenol EGCG acts differentially on the end stage aggregated polymorphs of α-synuclein generated in the presence of polyol osmolytes.

Abstract

Synucleinopathies such as Parkinson's disease, multiple systems atrophy, and dementia with Lewy bodies, are characterized by the presence of α-synuclein (α-syn) aggregates. Recently, it was found that different variants of synucleinopathies are encoded by biochemically diverse aggregated polymorphs of α-syn referred to as ‘strains’. Precise structural information on the α-syn pathological aggregates is one of the few knowledge gaps that encumber the design of effective therapies against synucleinopathies. Natural polyphenolic compounds such as epigallocatechin gallate (EGCG) have shown their efficacies in inhibiting the aggregation, as well as in remodelling of preformed aggregates of α-syn. However, a comparative account of EGCG's effect on different polymorphs of α-syn aggregates is not well explored. In this work, diverse aggregated polymorphs of α-syn were generated in the presence of different polyol osmolytes used as small-molecule crowding agents. The polymorphic aggregates of α-syn thus generated were treated with EGCG and the end products were analyzed structurally. The structural distinction of these polymorphs was assessed using FTIR, CD, AFM and proteinase K digestion. We observed that EGCG differentially acts upon all the polymorphs wherein EGCG incubated species were either disintegrated or structurally altered. Interestingly, contrary to previous reports, the EGCG treated polymorphs were β-sheet rich. Our findings are relevant in assessing the efficacy of polyphenolic compounds on diverse aggregated strains of different proteins that are shown to encode different disease variants. The appearance of β-sheet rich species in this study also engenders a more detailed examination of EGCG's mode of action on diverse classes of amyloids.