α-Synuclein propagates from mouse brain to grafted dopaminergic neurons and seeds aggregation in cultured human cells

Abstract

Post-mortem analyses of brains from patients with Parkinson disease who received fetal mesencephalic transplants show that α-synuclein-containing (α-syn-containing) Lewy bodies gradually appear in grafted neurons. Here, we explored whether intercellular transfer of α-syn from host to graft, followed by seeding of α-syn aggregation in recipient neurons, can contribute to this phenomenon. We assessed α-syn cell-to-cell transfer using microscopy, flow cytometry, and high-content screening in several coculture model systems. Coculturing cells engineered to express either GFP-or DsRed-tagged α-syn resulted in a gradual increase in double-labeled cells. Importantly, α-syn-GFP derived from 1 neuroblastoma cell line localized to red fluorescent aggregates in other cells expressing DsRed-α-syn, suggesting a seeding effect of transmitted α-syn. Extracellular α-syn was taken up by cells through endocytosis and interacted with intracellular α-syn. Next, following intracortical injection of recombinant α-syn in rats, we found neuronal uptake was attenuated by coinjection of an endocytosis inhibitor. Finally, we demonstrated in vivo transfer of α-syn between host cells and grafted dopaminergic neurons in mice overexpressing human α-syn. In summary, intercellularly transferred α-syn interacts with cytoplasmic α-syn and can propagate α-syn pathology. These results suggest that α-syn propagation is a key element in the progression of Parkinson disease pathology.

Distinct higher-order α-synuclein oligomers induce intracellular aggregation

“…Certain forms of α-syn located in the extracellular environment can be internalized and induce endogeneous α-syn to selfaggregate [6,18,[46][47][48][49]. This may represent a mechanism for the spread of aggregated α-syn in the PD brain.…”

Prion-Like Propagation of Protein Aggregation and Related Therapeutic Strategies

“…This concept was further tested in numerous rodent models using viral expression of human α-synclein [30,31] and transgenic mouse models of PD [32,33]. In one case, neural stem cells were transplanted into transgenic mice expressing human α-synuclein.…”

“…Conflicting data have been presented for tau, α-synuclein, and huntingtin peptides. α-synuclein uptake reportedly occurs via a temperature-sensitive mechanism that can be blocked by inhibiting endocytosis with a dominant negative dynamin mutant [32,33,64]. Proteinase K, which removes proteins from the extracellular surface, also abolishes the majority of α-synuclein uptake from the media [64].…”

Proteolytic clearance of extracellular α-synuclein as a new therapeutic approach against Parkinson disease

“…14,18,[21][22][23][24] Recent observations that the transplants grafted into the brain of PD patients displayed Lewy bodies 25,26 were considered to be connected with Braak et al's proposal that Lewy body pathology spreads from one brain area to another according to a stereotypic pattern in specific stages. 27 Consequently, more recent in vitro and in vivo experiments [28][29][30][31][32][33] have shown that α-syn aggregates released from neuronal cells can be transferred to neighboring neurons and form Lewy body-like inclusions, providing a mechanistic basis for the spread of α-syn pathology in PD patients and a hypothesis that a prion-like mechanism may underlie the progression of PD.…”