Synucleinopathies are neurodegenerative diseases caused by aggregation of α-Synuclein (α-Syn). While it has been suggested that pathogenic α-Syn can spread in the whole brain like a prion protein, those molecular mechanisms are still unknown. Here, we show that RNA G-quadruplexes (G4RNAs) have an important role in α-Syn aggregation. We found that α-Syn binds to guanine-enriched RNA sequences using RNA Bind-n-seq in vitro. In addition, α-Syn preferentially formed a complex with G4RNAs than with other RNA secondary structures. Under the molecular crowding conditions, α-Syn underwent liquid-liquid phase separation (LLPS), and G4RNAs significantly facilitated liquid-to-solid transition of α-Syn. In α-Syn overexpressing cells, α-Syn preformed fibril (PFF) increased G4RNA foci and in turn formed α-Syn aggregates. Furthermore, α-Syn aggregates were colocalized with G4RNA foci in the dopaminergic neurons of α-Syn PFF-injected mice. These observations suggest that G4RNA is a key factor of α-Syn aggregation and cell-to-cell transmission under the pathological condition. We are trying to reveal the mechanisms underlying increases of G4RNA foci by cellular stress, and define endogenous G4RNA forming RNAs involved in α-Syn phase transition.
