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

-Synuclein (-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 -Syn is associated with the progression of PD and that extracellular -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 -Syn causes expulsion of sphingosine 1-phosphate receptor subtype 1 (S1P(1)R) from the lipid raft fractions. S1P(1)R regulates vesicular trafficking, and its expulsion involved -Syn binding to membrane-surface gangliosides. Consequently, the S1P(1)R became refractory to S1P stimulation required for activating inhibitory G-protein (G(i)) in the plasma membranes. Moreover, the extracellular -Syn also induced uncoupling of the S1P(1)R 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 -Syn-treated cells. Furthermore, cholesterol-depleting agent-induced S1P(1)R expulsion from the rafts also resulted in S1P(1)R uncoupling. Taken together, these results suggest that extracellular -Syn-induced expulsion of S1P(1)R from lipid rafts promotes the uncoupling of S1P(1)R from G(i), thereby blocking subsequent G(i) signals, such as inhibition of cargo sorting into exosomal vesicles in multivesicular endosomes. These findings help shed additional light on PD pathogenesis.