Mitochondrial impairment and melatonin protection in parkinsonian mice do not depend of inducible or neuronal nitric oxide synthases

MPTP-mouse model constitutes a well-known model of neuroinflammation and mitochondrial failure occurring in Parkinson’s disease (PD). Although it has been extensively reported that nitric oxide (NO●) plays a key role in the pathogenesis of PD, the relative roles of nitric oxide synthase isoforms iNOS and nNOS in the nigrostriatal pathway remains, however, unclear. Here, the participation of iNOS/nNOS isoforms in the mitochondrial dysfunction was analyzed in iNOS and nNOS deficient mice. Our results showed that MPTP increased iNOS activity in substantia nigra and striatum, whereas it sharply reduced complex I activity and mitochondrial bioenergetics in all strains. In the presence of MPTP, mice lacking iNOS showed similar restricted mitochondrial function than wild type or mice lacking nNOS. These results suggest that iNOS-dependent elevated nitric oxide, a major pathological hallmark of neuroinflammation in PD, does not contribute to mitochondrial impairment. Therefore, neuroinflammation and mitochondrial dysregulation seem to act in parallel in the MPTP model of PD. Melatonin administration, with well-reported neuroprotective properties, counteracted these effects, preventing from the drastic changes in mitochondrial oxygen consumption, increased NOS activity and prevented reduced locomotor activity induced by MPTP. The protective effects of melatonin on mitochondria are also independent of its anti-inflammatory properties, but both effects are required for an effective anti-parkinsonian activity of the indoleamine as reported in this study.

MPTP小鼠模型（MPTP-mouse model）是研究帕金森病（Parkinson’s disease, PD）中神经炎症与线粒体功能衰竭的经典模型。尽管已有大量研究证实一氧化氮（nitric oxide, NO●）在帕金森病发病机制中发挥关键作用，但黑质纹状体通路内一氧化氮合酶（nitric oxide synthase, NOS）的两种同工型iNOS与nNOS的相对功能仍未明确。本研究以iNOS及nNOS缺陷小鼠为对象，分析了这两种NOS同工型在线粒体功能异常中的参与作用。实验结果显示，MPTP可提升黑质与纹状体中的iNOS活性，同时显著降低所有受试小鼠品系的复合物I活性与线粒体生物能学水平。在MPTP造模条件下，iNOS敲除小鼠的线粒体功能受限程度与野生型小鼠或nNOS敲除小鼠无明显差异。上述结果表明，作为帕金森病神经炎症的主要病理标志，iNOS依赖型一氧化氮升高并未参与线粒体损伤过程。因此，在MPTP帕金森病模型中，神经炎症与线粒体失调似乎呈平行发生的独立进程。褪黑素（melatonin）具有已被广泛报道的神经保护特性，其给药可逆转上述异常效应，阻止MPTP诱导的线粒体氧消耗剧烈变化、NOS活性升高，并改善MPTP导致的运动能力下降。本研究同时证实，褪黑素对线粒体的保护作用与其抗炎特性相互独立，但二者均是该吲哚胺类物质发挥有效抗帕金森病活性的必要条件。