Aging & Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.
Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
J Cachexia Sarcopenia Muscle. 2021 Dec;12(6):1582-1596. doi: 10.1002/jcsm.12768. Epub 2021 Sep 24.
Oxidative stress and damage are associated with a number of ageing phenotypes, including age-related loss of muscle mass and reduced contractile function (sarcopenia). Our group and others have reported loss of neuromuscular junction (NMJ) integrity and increased denervation as initiating factors in sarcopenia, leading to mitochondrial dysfunction, generation of reactive oxygen species and peroxides, and loss of muscle mass and weakness. Previous studies from our laboratory show that denervation-induced skeletal muscle mitochondrial peroxide generation is highly correlated to muscle atrophy. Here, we directly test the impact of scavenging muscle mitochondrial hydrogen peroxide on the structure and function of the NMJ and muscle mass and function in a mouse model of denervation-induced muscle atrophy CuZnSOD (Sod1 mice, Sod1KO).
Whole-body Sod1KO mice were crossed to mice with increased expression of human catalase (MCAT) targeted specifically to mitochondria in skeletal muscle (mMCAT mice) to determine the impact of reduced hydrogen peroxide levels on key targets of sarcopenia, including mitochondrial function, NMJ structure and function, and indices of muscle mass and function.
Female adult (12-month-old) Sod1KO mice show a number of sarcopenia-related phenotypes in skeletal muscle including reduced mitochondrial oxygen consumption and elevated reactive oxygen species generation, fragmentation, and loss of innervated NMJs (P < 0.05), a 30% reduction in muscle mass (P < 0.05), a 36% loss of force generation (P < 0.05), and a loss of exercise capacity (305 vs. 709 m in wild-type mice, P < 0.05). Muscle from Sod1KO mice also shows a 35% reduction in sarco(endo)plasmic reticulum ATPase activity (P < 0.05), changes in the amount of calcium-regulating proteins, and altered fibre-type composition. In contrast, increased catalase expression in the mMCAT × Sod1KO mice completely prevents the mitochondrial and NMJ-related phenotypes and maintains muscle mass and force generation. The reduction in exercise capacity is also partially inhibited (35%, P < 0.05), and the loss of fibre cross-sectional area is inhibited by ~50% (P < 0.05).
Together, these striking findings suggest that scavenging of mitochondrial peroxide generation by mMCAT expression efficiently prevents mitochondrial dysfunction and NMJ disruption associated with denervation-induced atrophy and weakness, supporting mitochondrial H O as an important effector of NMJ alterations that lead to phenotypes associated with sarcopenia.
氧化应激和损伤与许多衰老表型有关，包括与年龄相关的肌肉质量损失和收缩功能降低（肌肉减少症）。我们的研究小组和其他研究小组报告称，神经肌肉接头（NMJ）完整性的丧失和去神经支配是肌肉减少症的起始因素，导致线粒体功能障碍、活性氧和过氧化物的产生，以及肌肉质量和力量的丧失。我们实验室的先前研究表明，去神经支配诱导的骨骼肌线粒体过氧化物的产生与肌肉萎缩高度相关。在这里，我们直接测试了清除骨骼肌线粒体过氧化氢对 NMJ 结构和功能以及去神经诱导的肌肉萎缩模型中肌肉质量和功能的影响。
全身性 Sod1KO 小鼠与肌肉中过表达人过氧化氢酶（MCAT）的小鼠（mMCAT 小鼠）杂交，以确定减少过氧化氢水平对包括线粒体功能、NMJ 结构和功能以及肌肉质量和功能指标在内的肌肉减少症关键靶点的影响。
成年雌性 (12 个月大) Sod1KO 小鼠表现出多种与骨骼肌相关的肌肉减少症表型，包括线粒体耗氧量降低和活性氧生成增加、碎片化和失神经 NMJ（P < 0.05），肌肉质量减少 30%（P < 0.05），力生成减少 36%（P < 0.05），运动能力丧失（野生型小鼠为 305 与 709 米，P < 0.05）。Sod1KO 小鼠的肌肉也表现出肌浆网（内质网）ATP 酶活性降低 35%（P < 0.05），钙调节蛋白含量变化，以及纤维型组成改变。相比之下，mMCAT×Sod1KO 小鼠中过氧化氢酶表达的增加完全阻止了与去神经支配相关的线粒体和 NMJ 表型，并维持了肌肉质量和力的产生。运动能力的下降也部分受到抑制（35%，P < 0.05），纤维横截面积的减少也受到抑制（~50%，P < 0.05）。
综上所述，这些引人注目的发现表明，通过 mMCAT 表达清除线粒体过氧化物的生成可有效防止与去神经支配诱导的萎缩和虚弱相关的线粒体功能障碍和 NMJ 破坏，支持 H2O2 作为导致与肌肉减少症相关表型的 NMJ 改变的重要效应物。
