Abstract Body

Alpha-synuclein (aSyn) is an intrinsically disordered protein associated with Parkinson’s disease and other synucleinopathies, where it accumulates in pathognomonic protein inclusions in the brain. However, both the physiological function and the pathological role of aSyn are still elusive. Unlike other proteins also prone to aggregation, expression of aSyn in cell models does not readily result in inclusion formation, and additional insults are required to induce aggregation. Here, we report, for the first time, a model that recapitulates the aggregation cascade of aSyn. Our study sheds light into the role of synphilin-1 (Sph1) on aSyn assembly and localization. We show that Sph1 acts as a protein-adaptor for aSyn, and that the coiled-coil domain of Sph1 is essential for inducing inclusion formation. Moreover, the interaction between Sph1 and aSyn can be modulated (genetically, via protein levels, and by heat shock proteins), and altering the expression levels of each protein affects inclusion size and number per cell. Our study highlights the importance of membrane binding for inclusion formation and the presence of lysosomes and AP-1 vesicles in the inclusions. Finally, our study demonstrates that further investigation is necessary to decipher the role of Sph1 and other aSyn-interacting proteins on its biology and pathobiology.