SUMOylation of Alpha-Synuclein Influences on Alpha-Synuclein Aggregation Induced by Methamphetamine

Methamphetamine (METH) is an illegal and widely abused psychoactive stimulant. METH abusers are at high risk of neurodegenerative disorders, including Parkinson's disease (PD). Previous studies have demonstrated that METH causes alpha-synuclein (alpha-syn) aggregation in the both laboratory animal and human. In this study, exposure to high METH doses increased the expression of alpha-syn and the small ubiquitin-related modifier 1 (SUMO-1). Therefore, we hypothesized that SUMOylation of alpha-syn is involved in high-dose METH-induced alpha-syn aggregation. We measured the levels of alpha-syn SUMOylation and these enzymes involved in the SUMOylation cycle in SH-SY5Y human neuroblastoma cells (SH-SY5Y cells), in cultures of C57 BL/6 primary mouse neurons and in brain tissues of mice exposure to METH. We also demonstrated the effect of alpha-syn SUMOylation on alpha-syn aggregation after METH exposure by overexpressing the key enzyme of the SUMOylation cycle or silencing SUMO-1 expression in vitro. Then, we make introduced mutations in the major SUMOylation acceptor sites of alpha-syn by transfecting a lentivirus containing the sequence of WT alpha-syn or K96/102R alpha-syn into SH-SY5Y cells and injecting an adenovirus containing the sequence of WT alpha-syn or K96/ 102R alpha-syn into the mouse striatum. Levels of the ubiquitin-proteasome system (UPS)-related makers ubiquitin (Ub) and UbE1, as well as the autophagy-lysosome pathway (ALP)-related markers LC3, P62 and lysosomal associated membrane protein 2A (LAMP2A), were also measured in SH-SY5Y cells transfected with lentivirus and mice injected with adenovirus. The results showed that METH exposure decreases the SUMOylation level of alpha-syn, although the expression of alpha-syn and SUMO-1 are increased. One possible cause is the reduction of UBC9 level. The increase in alpha-syn SUMOylation by UBC9 overexpression relieves METH-induced alpha-syn overexpression and aggregation, whereas the decrease in alpha-syn SUMOylation by SUMO-1 silencing exacerbates the same pathology. Furthermore, mutations in the major SUMOylation acceptor sites of alpha-syn also aggravate alpha-syn overexpression and aggregation by impairing degradation through the UPS and the ALP in vitro and in vivo. These results suggest that SUMOylation of alpha-syn plays a fundamental part in alpha-syn overexpression and aggregation induced by METH and could be a suitable target for the treatment of neurodegenerative diseases.