Oxidative stress-induced posttranslational modifications of alpha-synuclein: Specific modification of alpha-synuclein by 4-hydroxy-2-nonenal increases dopaminergic toxicity

Aggregation and neurotoxicity of misfolded alpha-synuclein (alpha Syn) are crucial mechanisms for progressive dopaminergic neurodegeneration associated with Parkinson's disease (PD). Posttranslational modifications (PTMs) of alpha Syn caused by oxidative stress, including modification by 4-hydroxy-2-nonenal (HNE-alpha Syn), nitration (n-alpha Syn), and oxidation (o-alpha Syn), have been implicated to promote oligomerization of alpha Syn. However, it is yet unclear if these PTMs lead to different types of oligomeric intermediates. Moreover, little is known about which PTM-derived alpha Syn species exerts toxicity to dopaminergic cells. In this study, we directly compared aggregation characteristics of HNE-alpha Syn, n-alpha Syn, and o-alpha Syn. Generally, all of them promoted alpha Syn oligomerization. Particularly, HNE-alpha Syn and n-alpha Syn were more prone to forming oligomers than unmodified alpha Syn. Moreover, these PTMs prevented the formation of amyloid-like fibrils, although HNE-alpha Syn and o-alpha Syn were able to generate protofibrillar structures. The cellular effects associated with distinct PTMs were studied by exposing modified alpha Syn to dopaminergic Lund human mesencephalic (LUHMES) neurons. The cellular toxicity of HNE-alpha Syn was significantly higher than other PTM species. Furthermore, we tested the toxicity of HNE-alpha Syn in dopaminergicLUHMES cells and other cell types with low tyrosine hydroxylase (TH) expression, and additionally analyzed the loss of TH-immunoreactive cells in HNE-alpha Syn-treated LUHMES cells. We observed a selective toxicity of HNE-alpha Syn to neurons with higher TH expression. Further mechanistic studies showed that HNE-modification apparently increased the interaction of extracellular alpha Syn with neurons. Moreover, exposure of differentiated LUHMES cells to HNE-alpha Syn triggered the production of intracellular reactive oxygen species, preceding neuronal cell death. Antioxidant treatment effectively protected cells from the damage triggered by HNE-alpha Syn. Our findings suggest a specific pathological effect of HNE-alpha Syn on dopaminergic neurons. (C) 2013 Elsevier Inc. All rights reserved.