Aggregation-resistant alpha-synuclein tetramers are reduced in the blood of Parkinson’s patients

Synucleinopathies such as Parkinson’s disease (PD) are defined by the accumulation and aggregation of the α-synuclein protein in neurons, glia and other tissues. We have previously shown that destabilization of α-synuclein tetramers is associated with familial PD due to SNCA mutations and demonstrated brain-region specific alterations of α-synuclein multimers in sporadic PD patients following the classical Braak spreading theory. In this study, we assessed relative levels of disordered and higher-ordered multimeric forms of cytosolic α-synuclein in blood from familial PD with G51D mutations and sporadic PD patients. We used an adapted in vitro-cross-linking protocol for human EDTA-whole blood. The relative levels of higher-ordered α-synuclein tetramers were diminished in blood from familial PD and sporadic PD patients compared to controls. Interestingly, the relative amount of α-synuclein tetramers was already decreased in asymptomatic G51D carriers, supporting the hypothesis that α-synuclein multimer destabilization precedes the development of clinical PD. Our data, therefore suggest that measuring α-synuclein tetramers in blood may have potential as a facile biomarker assay for early detection and quantitative tracking of PD progression. Synopsis The α-synuclein protein exists in different structural forms primarily as monomers, dimers, and tetramers in different human tissues. In the brain, α-synuclein tetramer to monomer ratios are observed to be altered in sporadic Parkinson’s disease (sPD) and dementia with Lewy bodies (DLB). Chemical cross-linking using disuccinimidyl glutarate (DSG) and glutaraldehyde (GA), is used to stabilize α-synuclein tetramers in blood. The α-synuclein tetramer to monomer ratio is analyzed via SDS-Page and Western blotting. The α-synuclein tetramer to monomer ratios are altered in blood from sPD patients and patients with G51D α-synuclein mutations. This alteration is characterized by a reduction in tetramer to monomer ratios, indicating a disruption in the regular levels between these two physiological forms of α-synuclein. The α-synuclein protein exists in different structural forms primarily as monomers, dimers, and tetramers in different human tissues. In the brain and blood, α-synuclein tetramer to monomer ratios are observed to be altered in sporadic and familial Parkinson’s disease (sPD), and dementia with Lewy bodies (DLB).