Extracellular vesicle sorting of alpha-Synuclein is regulated by sumoylation

Extracellular alpha-Synuclein has been implicated in interneuronal propagation of disease pathology in Parkinson's Disease. How alpha-Synuclein is released into the extracellular space is still unclear. Here, we show that alpha-Synuclein is present in extracellular vesicles in the central nervous system. We find that sorting of alpha-Synuclein in extracellular vesicles is regulated by sumoylation and that sumoylation acts as a sorting factor for targeting of both, cytosolic and transmembrane proteins, to extracellular vesicles. We provide evidence that the SUMO-dependent sorting utilizes the endosomal sorting complex required for transport (ESCRT) by interaction with phosphoinositols. Ubiquitination of cargo proteins is so far the only known determinant for ESCRT-dependent sorting into the extracellular vesicle pathway. Our study reveals a function of SUMO protein modification as a Ubiquitin-independent ESCRT sorting signal, regulating the extracellular vesicle release of alpha-Synuclein. We deciphered in detail the molecular mechanism which directs alpha-Synuclein into extracellular vesicles which is of highest relevance for the understanding of Parkinson's disease pathogenesis and progression at the molecular level. We furthermore propose that sumo-dependent sorting constitutes a mechanism with more general implications for cell biology.