The role of autophagy in neurotoxicity caused by extracellular ASYN

Abstract

Key words:α-synuclein, autophagy, ATG7, SH-SY5Y, neurotoxicityIntroduction: The accumulation of alpha-synuclein (ASYN) in susceptible neurons is considered to be a major contributing factor in pathogenesis of Parkinson's disease. Although ASYN was considered as an intracellular protein, recent data suggest that it can be detected extracellularly. Autophagy plays an important role in ASYN degradation; therefore, impairment of autophagy could be an important contributor to ASYN accumulation. ATG (autophagy-related genes) proteins function at several physiologically continuous steps in autophagy, and ATG7 is considered as essential in autophagosome formation and maturation. Aim: The aim of this study was to investigate the role of autophagy in neurotoxicity, caused by extracellular ASYN. Material and methods: All experiments were conducted in all-trans retinoic acid-differentiated human neuroblastoma SH-SY5Y cells, that were exposed to extracellular ASYN. The presence of extracellular ASYN and the expression of autophagy markers, beclin-1 and LC3-II, were monitored using immunoblotting. Transfection, with small interfering RNA (siRNA), was used to knock down ATG7 gene. Cell viability was assessed using crystal violet dye exclusion assay. Results: Extracellular ASYN caused significant loss of viability in differentiated SH-SY5Y cells, accompanied by the increase in expression of beclin-1 and in conversion of LC3-I to autophagosome-associated LC3-II. The RNA interference-mediated knock-down of ATG7 increased the sensitivity of SH-SY5Y cells to the extracellular ASYN-induced toxicity. Conclusion: Extracellular ASYN caused loss of viability in differentiated SH-SY5Y cells accompanied by autophagy induction. Having in mind that inhibition of autophagy, through ATG7 knock-down increased cell death, we can conclude that autophagy could have a protective role in the harmful effect of extracellular ASYN.