Aggregates assembled from overexpression of wild-type α-synuclein are not toxic to human neuronal cells

Filamentous α-synuclein (α-syn) aggregates form Lewy bodies (LBs), the neuropathologic hallmarks of Parkinson disease and related α-synucleinopathies. To model Lewy body-associated neurodegeneration, we generated transfectant 3D5 of human neuronal-type in which expression of human wild-type α-syn is regulated by the tetracycline off (TetOff)-inducible mechanism. Retinoic acid-elicited differentiation promoted assembly of α-syn aggregates after TetOff induction in 3D5 cells. The aggregates accumulated 14 days after TetOff induction were primarily soluble and showed augmented thioflavin affinity with concomitant phosphorylation and nitration of α-syn. Extension of the induction led to the formation of sarkosyl-insoluble aggregates that appeared concurrently with thioflavin-positive inclusions. Immunoelectron microscopy revealed that the inclusions consist of dense bundles of 8- to 12-nm α-syn fibrils that congregate in the perikarya and resemble Lewy bodies. Most importantly, accumulation of soluble and insoluble aggregates after TetOff induction for 14 and 28 days was reversible and did not compromise the viability of the cells or their subsequent survival. Thus, this chemically defined culture paradigm provides a useful means to elucidate how oxidative injuries and other insults that are associated with aging promote α-syn to self-assemble or interact with other molecules leading to neuronal degeneration in α- synucleinopathies.