Bioenergetic maladaptations and axonopathy are often found in the early stages of neurodegeneration. Nicotinamide adenine dinucleotide (NAD), an essential cofactor for energy metabolism, is mainly synthesized by Nicotinamide mononucleotide adenylyl transferase 2 (NMNAT2) in CNS neurons. NMNAT2 mRNA levels are reduced in the brains of Alzheimer’s, Parkinson’s, and Huntington’s disease. Here we addressed whether NMNAT2 is required for axonal health of cortical glutamatergic neurons, whose long-projecting axons are often vulnerable in neurodegenerative conditions. We also tested if NMNAT2 maintains axonal health by ensuring axonal ATP levels for axonal transport, critical for axonal function. We generated mouse and cultured neuron models to determine the impact of NMNAT2 loss from cortical glutamatergic neurons on axonal transport, energetic metabolism, and morphological integrity. In addition, we determined if exogenous NAD supplementation or inhibiting a NAD hydrolase, sterile alpha and TIR motif-containing protein 1 (SARM1), prevented axonal deficits caused by NMNAT2 loss. This study used a combination of techniques, including genetics, molecular biology, immunohistochemistry, biochemistry, fluorescent time-lapse imaging, live imaging with optical sensors, and anti-sense oligos. We provide in vivo evidence that NMNAT2 in glutamatergic neurons is required for axonal survival. Using in vivo and in vitro studies, we demonstrate that NMNAT2 maintains the NAD-redox potential to provide “on-board” ATP via glycolysis to vesicular cargos in distal axons. Exogenous NAD+ supplementation to NMNAT2 KO neurons restores glycolysis and resumes fast axonal transport. Finally, we demonstrate both in vitro and in vivo that reducing the activity of SARM1, an NAD degradation enzyme, can reduce axonal transport deficits and suppress axon degeneration in NMNAT2 KO neurons. NMNAT2 ensures axonal health by maintaining NAD redox potential in distal axons to ensure efficient vesicular glycolysis required for fast axonal transport.

中文翻译：

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NMNAT2 通过 NAD 稳态支持囊泡糖酵解，以促进快速轴突运输


生物能量适应不良和轴索病常见于神经退行性变的早期阶段。烟酰胺腺嘌呤二核苷酸 （NAD） 是能量代谢的重要辅助因子，主要由 CNS 神经元中的烟酰胺单核苷酸腺苷转移酶 2 （NMNAT2） 合成。阿尔茨海默病、帕金森病和亨廷顿病大脑中的 NMNAT2 mRNA 水平降低。在这里，我们解决了皮质谷氨酸能神经元的轴突健康是否需要 NMNAT2，其长突出的轴突在神经退行性疾病中通常很脆弱。我们还测试了 NMNAT2 是否通过确保轴突运输的轴突 ATP 水平来维持轴突健康，这对轴突功能至关重要。我们生成了小鼠和培养的神经元模型，以确定皮质谷氨酸能神经元 NMNAT2 丢失对轴突运输、能量代谢和形态完整性的影响。此外，我们确定了外源性 NAD 补充剂或抑制 NAD 水解酶、无菌含 α 和 TIR 基序的蛋白 1 （SARM1） 是否能防止由 NMNAT2 丢失引起的轴突缺陷。这项研究结合使用了多种技术，包括遗传学、分子生物学、免疫组织化学、生物化学、荧光延时成像、光学传感器实时成像和反义寡核苷酸。我们提供体内证据表明谷氨酸能神经元中的 NMNAT2 是轴突存活所必需的。使用体内和体外研究，我们证明 NMNAT2 保持 NAD 氧化还原潜力，通过糖酵解向远端轴突中的囊泡货物提供“板载”ATP。对 NMNAT2 KO 神经元的外源性 NAD+ 补充可恢复糖酵解并恢复快速轴突运输。 最后，我们在体外和体内证明，降低 NAD 降解酶 SARM1 的活性可以减少轴突运输缺陷并抑制 NMNAT2 KO 神经元中的轴突变性。NMNAT2 通过维持远端轴突中的 NAD 氧化还原电位来确保快速轴突运输所需的有效囊泡糖酵解，从而确保轴突健康。