N-homocysteinylation of alpha-synuclein promotes its aggregation and neurotoxicity

The aggregation of alpha-synuclein plays a pivotal role in the pathogenesis of Parkinson's disease (PD). Epidemiological evidence indicates that high level of homocysteine (Hcy) is associated with an increased risk of PD. However, the molecular mechanisms remain elusive. Here, we report that homocysteine thiolactone (HTL), a reactive thioester of Hcy, covalently modifies alpha-synuclein on the K80 residue. The levels of alpha-synuclein K80Hcy in the brain are increased in an age-dependent manner in the TgA53T mice, correlating with elevated levels of Hcy and HTL in the brain during aging. The N-homocysteinylation of alpha-synuclein stimulates its aggregation and forms fibrils with enhanced seeding activity and neurotoxicity. Intrastriatal injection of homocysteinylated alpha-synuclein fibrils induces more severe alpha-synuclein pathology and motor deficits when compared with unmodified alpha-synuclein fibrils. Increasing the levels of Hcy aggravates alpha-synuclein neuropathology in a mouse model of PD. In contrast, blocking the N-homocysteinylation of alpha-synuclein ameliorates alpha-synuclein pathology and degeneration of dopaminergic neurons. These findings suggest that the covalent modification of alpha-synuclein by HTL promotes its aggregation. Targeting the N-homocysteinylation of alpha-synuclein could be a novel therapeutic strategy against PD.