Annular α-synuclein species from purified multiple system atrophy inclusions

Oligodendroglial cytoplasmic inclusions composed of alpha-synuclein filamentous aggregates are the pathological hallmark of multiple system atrophy (MSA). We found that cortical tissue from MSA cases contains increased detergent-resistant high-molecular-weight alpha-synuclein species. To analyse these species, we immunopurified alpha-synuclein aggregates from pathological samples and examined their ultrastructures using scanning electron and atomic force microscopies. Purified aggregates consisted of bundles of filaments. After treatment with 1% sarcosine or 2% 3-[(3-cholamidopropyl) dimethyl-ammonio]-1-propanesulfonate (CHAPS) detergents, we observed frequent 30-50 nm annular particles, probably released from pathological aggregates due to the dissociation of filaments by the detergents. Antibody recognition imaging using a specific anti-alpha-synuclein antibody confirmed that the annular structures were positive for alpha-synuclein. In contrast to pathological alpha-synuclein, detergent treatment of recombinant alpha-synuclein yielded only smaller, 10-18 nm spherical particles. Our results demonstrate that detergent treatment of pathological MSA alpha-synuclein aggregates, but not recombinant alpha-synuclein, yields discrete alpha-synuclein-positive species with annular morphologies. The ability of the pathological alpha-synuclein to form annular aggregates may be an important factor contributing to the toxicity of the protein in disease that may have implications in designing therapeutic strategies aimed at detoxifying alpha-synuclein aggregates.