Distinct neurotoxic TDP-43 fibril polymorphs can be generated by heterotypic interactions with α-synuclein

Abstract

Amyloid aggregates of specific proteins form important pathological hallmarks in many neurodegenerative diseases, defining neuronal degeneration and disease onset. Recently, increasing numbers of patients show co-morbidities and overlaps between multiple neurodegenerative diseases, presenting distinct phenotypes. Such overlaps are often accompanied by co-localizations of more than one amyloid protein, prompting the question of whether direct interactions between different amyloid proteins could generate heterotypic amyloids. To answer this question, we investigated the effect of αsynuclein (αS) on TDP43 aggregation inspired by their co-existence in pathologies such as Lewy body dementia and limbic predominant age-related TDP43 encephalopathy. We previously showed that αS and prion-like C-terminal domain (PrLD) of TDP-43 synergistically interact with one another to generate toxic heterotypic aggregates in vitro. Here, we extend these studies to investigate whether αS induces structurally and functionally distinct polymorphs of PrLD aggregates. Using αS-PrLD heterotypic aggregates generated in two different stoichiometric proportions, we show that αS can effect PrLD fibril forms. The fibril samples have distinctive residue-level structural signatures in NMR spectra, dye-binding capability, proteinase K (PK) stability, and SDS-sensitive thermal stability. By gold nanoparticle labeling and TEM, we show the presence of both αS and PrLD proteins within the same fibrils, and thus the existence of heterotypic hybrid fibrils. We also observe that S and PrLD co-localize in the cytosol of SH-SY5Y neuroblastoma cells, and show that the heterotypic PrLD fibrils selectively induce synaptic dysfunction in primary cortical neurons. These findings establish the existence of heterotypic amyloid polymorphs and provide a molecular basis for the observed overlap between synucleinopathies and TDP43 proteinopathies.