Aggregation of α-Synuclein Splice Isoforms through a Phase Separation Pathway

The conversion of α-synuclein (αSyn) from native monomers into amyloid aggregates has long been associated with the pathogenesis of Parkinson’s disease (PD) and related synucleinopathies. Considerable efforts have thus been directed at understanding the mechanisms by which αSyn aggregation takes place. Further complexity has recently been added by the discovery of a novel route leading to αSyn aggregation, known as the condensation pathway, which involves the transient formation of dense liquid intermediates. In parallel, it has been reported that different αSyn splice isoforms may be implicated in the formation of αSyn aggregates in disease. In this study, we explore the phase separation and subsequent aggregation of four αSyn splice isoforms (αSyn-140, αSyn-126, αSyn-112 and αSyn-98). Using a variety of biophysical tools including confocal microscopy, aggregation assays, chemical kinetics and microfluidic-based approaches, we find stark differences between the four systems in their propensities to undergo phase transitions. Finally, it has been reported that αSyn splice isoforms could be responsible for modulating the αSyn phase behaviour. To investigate this, we mix αSyn-112, the second most predominant isoform after αSyn-140, with αSyn-140. Thereby, we show that even relatively small amounts of αSyn-112 can affect the condensation of αSyn-140. This highlights the importance of conducting further investigations to elucidate the role of alternative αSyn splice isoforms in synucleinopathies.