Extracellular α-synuclein drives sphingosine 1-phosphate receptor subtype 1 out of lipid rafts, leading to impaired inhibitory G-protein signaling.

α-Synuclein (α-Syn)-positive intracytoplasmic inclusions, known as Lewy bodies, are thought to be involved in the pathogenesis of Lewy body diseases, such as Parkinson's disease (PD). Although growing evidence suggests that cell-to-cell transmission of α-Syn is associated with the progression of PD and that extracellular α-Syn promotes formation of inclusion bodies, its precise mechanism of action in the extracellular space remains unclear. Here, as indicated by both conventional fractionation techniques and FRET-based protein-protein interaction analysis, we demonstrate that extracellular α-Syn causes expulsion of sphingosine 1-phosphate receptor subtype 1 (S1PR) from the lipid raft fractions. S1PR regulates vesicular trafficking, and its expulsion involved α-Syn binding to membrane-surface gangliosides. Consequently, the S1PR became refractory to S1P stimulation required for activating inhibitory G-protein (G) in the plasma membranes. Moreover, the extracellular α-Syn also induced uncoupling of the S1PR on internal vesicles, resulting in the reduced amount of CD63 molecule (CD63) in the lumen of multivesicular endosomes, together with a decrease in CD63 in the released exosomes from α-Syn-treated cells. Furthermore, cholesterol-depleting agent-induced S1PR expulsion from the rafts also resulted in S1PR uncoupling. Taken together, these results suggest that extracellular α-Syn-induced expulsion of S1PR from lipid rafts promotes the uncoupling of S1PR from G, thereby blocking subsequent G signals, such as inhibition of cargo sorting into exosomal vesicles in multivesicular endosomes. These findings help shed additional light on PD pathogenesis.