Parkinson’s disease (PD) is now recognized as a neurodegenerative condition caused by a complex interplay of genetic and environmental influences. Chronic manganese (Mn) exposure has been implicated in the development of PD. Since mitochondrial dysfunction is associated with PD pathology as well as Mn neurotoxicity, we investigated whether Mn exposure augments mitochondrial dysfunction and neurodegeneration in the nigrostriatal dopaminergic system using a newly available mitochondrially defective transgenic mouse model of PD, the MitoPark mouse. This unique PD model recapitulates key features of the disease including progressive neurobehavioral changes and neuronal degeneration. We exposed MitoPark mice to a low dose of Mn (10 mg/kg, p.o.) daily for 4 weeks starting at age 8 wks and then determined the behavioral, neurochemical and histological changes. Mn exposure accelerated the rate of progression of motor deficits in MitoPark mice when compared to the untreated MitoPark group. Mn also worsened olfactory function in this model. Most importantly, Mn exposure intensified the depletion of striatal dopamine and nigral TH neuronal loss in MitoPark mice. The neurodegenerative changes were accompanied by enhanced oxidative damage in the striatum and substantia nigra (SN) of MitoPark mice treated with Mn. Furthermore, Mn-treated MitoPark mice had significantly more oligomeric protein and IBA-1-immunoreactive microglia cells, suggesting Mn augments neuroinflammatory processes in the nigrostriatal pathway. To further confirm the direct effect of Mn on impaired mitochondrial function, we also generated a mitochondrially defective dopaminergic cell model by knocking out the TFAM transcription factor by using a CRISPR-Cas9 gene-editing method. Seahorse mitochondrial bioenergetic analysis revealed that Mn decreases mitochondrial basal and ATP-linked respiration in the TFAM KO cells. Collectively, our results reveal that Mn can augment mitochondrial dysfunction to exacerbate nigrostriatal neurodegeneration and PD-related behavioral symptoms. Our study also demonstrates that the MitoPark mouse is an excellent model to study the gene-environment interactions associated with mitochondrial defects in the nigral dopaminergic system as well as to evaluate the contribution of potential environmental toxicant interactions in a slowly progressive model of Parkinsonism.

帕金森病 (PD) 现在被认为是一种由遗传和环境影响的复杂相互作用引起的神经退行性疾病。慢性锰 (Mn) 暴露与帕金森病的发生有关。由于线粒体功能障碍与帕金森病病理学以及锰神经毒性有关，因此我们使用新近获得的帕金森病线粒体缺陷转基因小鼠模型（MitoPark 小鼠）研究了锰暴露是否会加剧黑质纹状体多巴胺能系统的线粒体功能障碍和神经变性。这种独特的 PD 模型概括了该疾病的关键特征，包括进行性神经行为变化和神经元变性。我们从 MitoPark 小鼠 8 周开始，每天将其暴露于低剂量的锰（10 mg/kg，口服），持续 4 周，然后测定其行为、神经化学和组织学变化。与未治疗的 MitoPark 组相比，锰暴露加速了 MitoPark 小鼠运动缺陷的进展速度。锰还会使该模型的嗅觉功能恶化。最重要的是，Mn 暴露加剧了 MitoPark 小鼠纹状体多巴胺的消耗和黑质 TH 神经元的损失。接受锰处理的 MitoPark 小鼠的神经退行性变化伴随着纹状体和黑质 (SN) 氧化损伤的增强。此外，经锰治疗的 MitoPark 小鼠具有显着更多的寡聚蛋白和 IBA-1 免疫反应性小胶质细胞，表明锰增强了黑质纹状体通路中的神经炎症过程。为了进一步证实锰对线粒体功能受损的直接影响，我们还通过使用 CRISPR-Cas9 基因编辑方法敲除 TFAM 转录因子，生成了线粒体缺陷的多巴胺能细胞模型。海马线粒体生物能分析表明，Mn 会降低 TFAM KO 细胞中的线粒体基础呼吸和 ATP 相关呼吸。总的来说，我们的结果表明，锰可以增强线粒体功能障碍，从而加剧黑质纹状体神经变性和帕金森病相关的行为症状。我们的研究还表明，MitoPark 小鼠是研究与黑质多巴胺能系统线粒体缺陷相关的基因-环境相互作用的优秀模型，以及评估潜在环境毒物相互作用在帕金森病缓慢进展模型中的贡献。