Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA.
Arch Toxicol. 2020 Dec;94(12):4007-4022. doi: 10.1007/s00204-020-02879-z. Epub 2020 Aug 20.
Methylmercury (MeHg) can elicit cognitive and motor deficits due to its developmental neuro- and myotoxic properties. While previous work has demonstrated that Nrf2 antioxidant signaling protects from MeHg toxicity, in vivo tissue-specific studies are lacking. In Drosophila, MeHg exposure shows greatest developmental toxicity in the pupal stage resulting in failed eclosion (emergence of adults) and an accompanying 'myosphere' phenotype in indirect flight muscles (IFMs). To delineate tissue-specific contributions to MeHg-induced motor deficits, we investigated the potential of Nrf2 signaling in either muscles or neurons to moderate MeHg toxicity. Larva were exposed to various concentrations of MeHg (0-20 µM in food) in combination with genetic modulation of the Nrf2 homolog cap-n-collar C (CncC), or its negative regulator Keap1. Eclosion behavior was evaluated in parallel with the morphology of two muscle groups, the thoracic IFMs and the abdominal dorsal internal oblique muscles (DIOMs). CncC signaling activity was reported with an antioxidant response element construct (ARE-GFP). We observed that DIOMs are distinguished by elevated endogenous ARE-GFP expression, which is only transiently seen in the IFMs. Dose-dependent MeHg reductions in eclosion behavior parallel formation of myospheres in the DIOMs and IFMs, while also increasing ARE-GFP expression in the DIOMs. Modulating CncC signaling via muscle-specific Keap1 knockdown and upregulation gives a rescue and exacerbation, respectively, of MeHg effects on eclosion and myospheres. Interestingly, muscle-specific CncC upregulation and knockdown both induce lethality. In contrast, neuron-specific upregulation of CncC, as well as Keap1 knockdown, rescued MeHg effects on eclosion and myospheres. Our findings indicate that enhanced CncC signaling localized to either muscles or neurons is sufficient to rescue muscle development and neuromuscular function from a MeHg insult. Additionally, there may be distinct roles for CncC signaling in myo-morphogenesis.
甲基汞（MeHg）可通过其发育性神经毒性和肌肉毒性引起认知和运动功能障碍。虽然之前的研究表明 Nrf2 抗氧化信号可防止 MeHg 毒性，但体内组织特异性研究仍缺乏。在果蝇中，MeHg 暴露在蛹期表现出最大的发育毒性，导致羽化失败（成虫出现），以及间接飞行肌肉（IFM）中伴随的“肌球”表型。为了阐明 MeHg 诱导的运动障碍的组织特异性贡献，我们研究了 Nrf2 信号在肌肉或神经元中对调节 MeHg 毒性的潜在作用。幼虫在食物中暴露于不同浓度的 MeHg（0-20µM），同时遗传调节 Nrf2 同源物 cap-n-collar C（CncC）或其负调节剂 Keap1。羽化行为与两个肌肉群的形态平行评估，即胸部 IFM 和腹部背内斜肌（DIOM）。用抗氧化反应元件构建体（ARE-GFP）报告 CncC 信号活性。我们观察到，DIOMs 的特征是内源性 ARE-GFP 表达升高，而 IFMs 中仅短暂可见。DIOMs 和 IFMs 中 MeHg 剂量依赖性减少羽化行为与肌球形成平行，同时也增加了 DIOMs 中的 ARE-GFP 表达。通过肌肉特异性 Keap1 敲低和上调调节 CncC 信号分别对羽化和肌球产生挽救和加剧作用。有趣的是，肌肉特异性 CncC 上调和敲低都会引起致死性。相比之下，神经元特异性 CncC 上调以及 Keap1 敲低均可挽救 MeHg 对羽化和肌球的影响。我们的研究结果表明，增强的 CncC 信号定位于肌肉或神经元足以挽救 MeHg 损伤的肌肉发育和神经肌肉功能。此外，CncC 信号在肌母形态发生中可能具有不同的作用。
