Abstract Synucleinopathies, including Parkinson’s disease, dementia with Lewy bodies, and multiple system atrophy, are triggered by the aggregation of α-synuclein, leading to progressive neurodegeneration 1,2,3,4,5,6,7,8 . However, the intracellular mechanism of α-synuclein aggregation remains unclear. Here we show that assembly of RNA G-quadruplexes forming scaffolds for α-synuclein aggregation, contributing to neurodegeneration. Purified α-synuclein binds RNA G-quadruplexes directly through the N-terminus. RNA G-quadruplex itself undergoes phase separation and assembly by Ca 2+ , accelerating the sol–gel phase transition of α-synuclein. In α-synuclein preformed fibrils-treated neurons, RNA G-quadruplexes assembly composed of synaptic mRNAs co-aggregates with α-synuclein upon Ca 2+ excess influx into cytoplasm, eliciting synaptic dysfunction. Forced assembly of RNA G-quadruplexes using an optogenetic approach evokes α-synuclein aggregation, neuronal dysfunction and neurodegeneration. Administration of 5-aminolevulinic acid, a prodrug of protoporphyrin IX that prevents phase separation of RNA G-quadruplexes 9 , attenuating α-synuclein aggregation, neurodegeneration, and progressive motor deficits in α-synuclein preformed fibrils-injected synucleinopathy mice. Together, assembly of RNA G-quadruplexes due to dysregulation of intracellular Ca 2+ homeostasis accelerates α-synuclein phase transition and aggregation may contribute to pathogenesis of synucleinopathies.

RNA G-quadruplexes forming scaffolds for α-synuclein aggregation lead to progressive neurodegeneration