Comparative analysis of 1-methyl-4-phenylpyridinium (MPP+) and manganese induced neurotoxic effects on DNA methylation in dopaminergic neurons

Idiopathic Parkinson’s disease (iPD) and manganese-induced atypical Parkinsonism are characterized by movement disorder and nigrostriatal pathology. Although clinical features, brain region involved and responsiveness to L-DOPA differentiate both, the differences at the neuronal level are largely unknown. We investigated the morphological, physiological and molecular differences in dopaminergic neurons exposed to the PD toxin 1-methyl-4-phenylpyridinium ion (MPP+) and manganese (Mn). While Mn was neurotoxic at lower dose, MPP+ toxicity entailed oxidative damage, mitochondria dysfunction and glycolytic shift. Morphological analysis highlighted mitochondrial damage, while morphometric analysis indicated loss of neuronal processes in the MPP+ model and not in the Mn model. Elecrophysiological analysis demonstrated lower number of spikes and firing frequency in MPP+ treated cells, while it was unchanged in the Mn model. High throughput transcriptomic analysis revealed upregulation of 694 and 603 genes and down-regulation of 428 and 255 genes in the MPP+ and Mn models respectively. Many differentially expressed genes were unique to either models and contributed to neuroinflammation, metabolic and mitochondrial function, apoptosis and nuclear function, synaptic plasticity, neurotransmission and cytoskeletal architecture. Analysis of the JAK-STAT pathway with implications for neuritogenesis, neuronal proliferation and nuclear function revealed contrasting profile between Mn and MPP+ models. Genome-wide DNA methylation profile revealed significant differences between both models and substantiated the epigenetic basis of the difference in the JAK-STAT pathway. We conclude that iPD and atypical Parkinsonism represent a divergent neurotoxicological manifestation at the dopaminergic neuronal level with implications for pathobiology and to evolve novel therapeutics特发性帕金森病（idiopathic Parkinson’s disease, iPD）与锰诱导型非典型帕金森综合征均以运动障碍及黑质纹状体病理改变为特征。尽管二者可通过临床特征、受累脑区及对左旋多巴（L-DOPA）的反应性进行区分，但神经元层面的差异尚不明晰。本研究针对暴露于帕金森病毒素1-甲基-4-苯基吡啶离子（MPP+）与锰（Mn）的多巴胺能神经元，探究其形态、生理及分子层面的差异。其中，低剂量锰即可表现出神经毒性，而MPP+的毒性作用涉及氧化损伤、线粒体功能障碍及糖酵解转换。形态学分析显示线粒体损伤，形态计量分析则表明，MPP+模型中存在神经元突起丢失，而锰模型中未出现该现象。电生理分析证实，经MPP+处理的细胞动作电位发放数量与放电频率均降低，而锰模型中该指标无明显变化。高通量转录组分析显示，MPP+与锰模型中分别有694个、603个基因上调，428个、255个基因下调。大量差异表达基因仅存在于单一模型中，且涉及神经炎症、代谢与线粒体功能、细胞凋亡与核功能、突触可塑性、神经传递及细胞骨架结构等生物学过程。针对与神经突形成、神经元增殖及核功能相关的JAK-STAT信号通路（JAK-STAT pathway）的分析显示，锰模型与MPP+模型的通路激活模式存在显著差异。全基因组DNA甲基化谱分析证实，两种模型间存在显著差异，并为JAK-STAT通路的差异提供了表观遗传学依据。本研究结论表明，特发性帕金森病与非典型帕金森综合征在多巴胺能神经元层面呈现出截然不同的神经毒性表现，该发现对阐明二者的病理生物学机制及研发新型治疗手段具有重要意义。