Annular α‐synuclein species from purified multiple system atrophy inclusions

Oligodendroglial cytoplasmic inclusions composed of α-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 α-synuclein species. To analyse these species, we immunopurified α-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-α-synuclein antibody confirmed that the annular structures were positive for α-synuclein. In contrast to pathological α-synuclein, detergent treatment of recombinant α-synuclein yielded only smaller, 10–18 nm spherical particles. Our results demonstrate that detergent treatment of pathological MSA α-synuclein aggregates, but not recombinant α-synuclein, yields discrete α-synuclein-positive species with annular morphologies. The ability of the pathological α-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 α-synuclein aggregates.