Internalization of α-synuclein oligomers into SH-SY5Y cells

Aggregates of misfolded alpha-synuclein are a distinctive feature of Parkinson's disease. Small oligomers of alpha-synuclein are thought to be an important neurotoxic agent, and alpha-synuclein aggregates exhibit prion-like behavior, propagating misfolding between cells. alpha-Synuclein is internalized by both passive diffusion and active uptake mechanisms, but how uptake varies with the size of the oligomer is less clear. We explored how alpha-synuclein internalization into live SH-SY5Y cells varied with oligomer size by comparing the uptake of fluorescently labeled monomers to that of engineered tandem dimers and tetramers. We found that these alpha-synuclein constructs were internalized primarily through endocytosis. Oligomer size had little effect on their internalization pathway, whether they were added individually or together. Measurements of co-localization of the alpha-synuclein constructs with fluorescent markers for early endosomes and lysosomes showed that most of the alpha-synuclein entered endocytic compartments, in which they were probably degraded. Treatment of the cells with the Pitstop inhibitor suggested that most of the oligomers were internalized by the clathrin-mediated pathway.