Quantum-dot-labeled synuclein seed assay identifies drugs modulating the experimental prion-like transmission

Synucleinopathies are neurodegenerative disorders including Parkinson disease (PD), dementia with Lewy body (DLB), and multiple system atrophy (MSA) that involve deposits of the protein alpha-synuclein (α-syn) in the brain. The inoculation of α-syn aggregates derived from synucleinopathy or preformed fibrils (PFF) formed in vitro induces misfolding and deposition of endogenous α-syn. This is referred to as prion-like transmission, and the mechanism is still unknown. In this study, we label α-syn PFF with quantum dots and visualize their movement directly in acute slices of brain tissue inoculated with α-syn PFF seeds. Using this system, we find that the trafficking of α-syn seeds is dependent on fast axonal transport and the seed spreading is dependent on endocytosis and neuronal activity. We also observe pharmacological effects on α-syn seed spreading; clinically available drugs including riluzole are effective in reducing the spread of α-syn seeds and this effect is also observed in vivo. Our quantum-dot-labeled α-syn seed assay system combined with in vivo transmission experiment reveals an early phase of transmission, in which uptake and spreading of seeds occur depending on neuronal activity, and a later phase, in which seeds induce the propagation of endogenous misfolded α-syn.