Sortilin acts as an endocytic receptor for -synuclein fibril

Cell-to-cell spreading of misfolded a-synuclein (aSYN) is supposed to play a key role in the pathological progression of Parkinson's disease (PD) and other synucleinopathies. Receptor-mediated endocytosis has been shown to contributes to the uptake of aSYN in both neuronal and glial cells. To determine the receptor involved in aSYN endocytosis on the cell surface, we performed unbiased, and comprehensive screening using a membrane protein library of the mouse whole brain combined with affinity chromatography and mass spectrometry. The candidate molecules hit in the initial screening were validated by co-immunoprecipitation using cultured cells; sortilin, a vacuolar protein sorting 10 protein family sorting receptor, exhibited the strongest binding to aSYN fibrils. Notably, the intracellular uptake of fibrillar aSYN was slightly but significantly altered, depending on the expression level of sortilin on the cell surface, and time-lapse image analyses revealed the concomitant internalization and endosomal sorting of aSYN fibrils and sortilin. Domain deletion in the extracellular portion of sortilin revealed that the ten conserved cysteines (10CC) segment of sortilin was involved in the binding and endocytosis of fibrillar aSYN; importantly, pretreatment with a 10CC domain-specific antibody significantly hindered aSYN fibril uptake. The presence of sortilin in the core structure of Lewy bodies and glial cytoplasmic inclusions in the brain of synucleinopathy patients was confirmed via immunohistochemistry, and the expression level of sortilin in mesencephalic dopaminergic neurons may be altered with disease progression. These results provide compelling evidence that sortilin acts as an endocytic receptor for pathogenic form of aSYN, and yields important insight for the development of disease-modifying targets for synucleinopathies.