Mapping of Surface-Exposed Epitopes of In Vitro and In Vivo Aggregated Species of Alpha-Synuclein

Aggregated alpha-synuclein is the main component of Lewy bodies, intraneuronal deposits observed in Parkinson's disease and dementia with Lewy bodies. The objective of the study was to identify surface-exposed epitopes of alpha-synuclein in vitro and in vivo formed aggregates. Polyclonal immunoglobulin Y antibodies were raised against short linear peptides of the alpha-synuclein molecule. An epitope in the N-terminal region (1-10) and all C-terminal epitopes (90-140) were found to be exposed in an indirect enzyme-linked immunosorbent assay (ELISA) using recombinant monomeric, oligomeric, and fibrillar alpha-synuclein. In a phospholipid ELISA, the N-terminus and mid-region of alpha-synuclein (i.e., 1-90) were associated with phosphatidylserine and thus occluded from antibody binding. The antibodies that reacted most strongly with epitopes in the in vitro aggregates (i.e., 1-10 and epitopes between positions 90-140) also labeled alpha-synuclein inclusions in brains from transgenic (Thy-1)-h[A30P] alpha-synuclein mice and Lewy bodies and Lewy neurites in brains of patients with alpha-synucleinopathies. However, differences in reactivity were observed with the C-terminal antibodies when brain tissue from human and transgenic mice was compared. Taken together, the study shows that although similar epitopes are exposed in both in vitro and in vivo formed alpha-synuclein inclusions, structural heterogeneity can be observed between different molecular species.