Reduction of immunoreactivity against the C-Terminal region of the intracellular α-Synuclein by exogenous α-Synuclein aggregates: Possibility of conformational changes

Background: The formation of intracellular aggregates containing α-synuclein (α-syn) is a main pathological feature of Parkinson disease. The propagation of α-syn aggregation via cell-to-cell transmission has been implicated in the progression of Parkinson disease. Objective: Our aim is to clarify the molecular mechanisms underlying the formation of intracellular aggregation by extracellular α-syn. Methods: We investigated the effects of exogenous α-syn aggregates on intracellular α-syn immunoreactivity in α-synoverexpressing SH-SY5Y cells using two antibodies to distinct epitopes of α-syn. To obtain α-syn aggregates, α-syn solution was aged with continuous agitation. Results: Immunoreactivity against the acidic C-terminal domain of the intracellular α-syn was reduced by exposure to aged α-syn, whereas that against the hydrophobic non-amyloid component region was not changed. The reduction in immunoreactivity was not suppressed by protease inhibitors but was mimicked by neutralization of the negative charges on the C-terminal of the intracellular α-syn induced by spermine or extracellular acidification. Conclusions: These results suggest that the reduction in immunoreactivity is attributed not to proteolytic cleavage but to a conformational change at the C-terminus of the intracellular α-syn. The conformational change at the C-terminus of the intracellular α-syn might be involved in an initial step of fibril formation by exogenous α-syn aggregates.