Proteasome inhibition induces alpha-synuclein SUMOylation and aggregate formation

Abstract

Parkinson's disease (PD) and Dementia with Lewy Bodies (DLB) are characterized pathologically by intraneuronal inclusions called Lewy bodies (LBs) and Lewy neurites. A major component of these inclusions is the protein a-synuclein, which is natively unfolded but forms oligomers and insoluble fibrillar aggregates under pathological conditions. Although alpha-synuclein is known to undergo several posttranslational modifications, the contribution of SUMOylation to alpha-synuclein aggregation and the pathogenesis of alpha-synucleinopathies have not been elucidated. Here, we provide evidence that aggregates and inclusions formed as a result of impaired proteasome activity contain SUMOylated alpha-synuclein. Additionally, SUMO1 is present in the halo of LBs colocalizing with alpha-synuclein in the brains of PD and DLB patients. Interestingly. SUMOylation does not affect the ubiquitination of alpha-synuclein. These findings suggest that proteasomal dysfunction results in the accumulation of SUMOylated alpha-synuclein and subsequently its aggregation, pointing to the contribution of this posttranslational modification to the pathogenesis of inclusion formation in alpha-synucleinopathies.