ROLE OF OXIDATIVE STRESS IN AGE-RELATED LOSS OF MOTOR UNITS

对于人类来说，脆弱是衰老最突出和最一致的特征之一， 代表肌肉萎缩和虚弱的影响的总和。对于老年人来说，身体虚弱 导致行动不便，跌倒的风险高，肌肉损伤的发生率增加， 生活质量下降。尽管在过去十年中作出了相当大的努力，但进展甚微 减轻问题的严重性。在我们提供支持的头五年里， 更多种类的基因敲除和转基因小鼠，该计划项目确定了Sodl^'小鼠作为一种 非常有前途的模型来测试项目1的工作假设，即年龄相关的骨骼肌 萎缩是由运动单位总数减少引起的， 超氧化物介导的神经元和肌肉中的氧化应激，例如：（i） 运动神经元的缺失，损害了存活运动神经元的轴突发芽， 神经元，并抑制神经再生;和（ii）肌肉纤维中的氧化应激抑制神经再支配 并导致受神经支配的肌纤维的收缩性降低。工作 将通过对SodfA和Sod 1 +/+小鼠、转基因Socf 7v-小鼠和Sod 1 +/+小鼠的实验来检验这一假设。 Sod 1表达仅在神经（Soc/fA（N+）小鼠）或肌肉（Soc（7~/~（M+）小鼠）中得到拯救，并且组织特异性表达在神经（Soc/fA（N+）小鼠）和肌肉（Soc（7~/~（M+）小鼠）中得到拯救。 敲除小鼠仅在神经（Sod 1A 3，4 N）或肌肉（Sod 1A 3，4 N）中缺乏CuZnSOD活性。这些 模型使我们能够测试关于全身氧化应激的贡献的假设，以及 组织特异性氧化应激对运动神经、肌肉、运动单位和 肌肉纤维转基因小鼠将在6-8个月和18-20个月进行研究，而 将在6-8、18-20和28-30个月时对Sod 1 +/+小鼠进行研究。拟议研究的独特方面是 来自Soc/f/-小鼠的透化单纤维的运动单位性质和收缩性的测定， 具有组织特异性拯救的无效小鼠和组织特异性Sodl敲除小鼠。此外，研究 神经和肌肉的变化的相对时间，以前没有在相同的 动物在建立年龄相关变化的因果关系方面尤其具有启发性 在神经肌肉系统中。沿着项目2和项目3，研究利用非常强大的鼠标 以上列出的模型将确定肌肉中超氧化物诱导的氧化应激的机制作用 和神经在与年龄相关的骨骼肌萎缩中的作用。公共卫生的重要性在于， 了解与年龄相关的骨骼肌萎缩和虚弱的机制， 卫生专业人员设计和实施科学战略的基础， 通过减少甚至消除老年人口的身体虚弱来实现“成功老龄化”。

For humans, frailty constitutes of one of the most prominent and consistent features of aging and represents the summation of the effects of muscle atrophy and weakness. For the elderly, physical frailty contributes to impaired mobility, a high risk of falling, an increased incidence of muscle injury, and a decreased quality of life. Despite considerable effort over the past decade, little progress has been made in lessening the magnitude of the problem. During our first five years of support, research on a dozen or more varieties of knockout and transgenic mice, this Program Project identified the Sodl^' mouse as a highly promising model to test the working hypothesis of Project 1 that age-related skeletal muscle atrophy results from a decrease in the total number of motor units caused by increased superoxide-mediated oxidative stress in neurons and muscles, such that: (i) oxidative stress in neurons initiates a loss of motor neurons, impairs axonal sprouting from surviving motor neurons, and inhibits nerve regeneration; and (ii) oxidative stress in muscles fibers inhibits reinnervation and contributes to decreased contractility of innervated muscle fibers. The working hypothesis will be tested through experiments on SodfA and Sod1+/+ mice, transgenic Socf7v" mice with Sod1 expression rescued only in nerves (Soc/fA(N+) mice) or muscles (Soc(7~/~(M+) mice), and tissue-specific knockout mice that lack CuZnSOD activity only in nerves (Sod1A3,4N)N) or muscles (Sod 1 A3,4^). These models allow us to test hypotheses regarding the contribution of systemic oxidative stress, as well as tissue-specific oxidative stress on the structure and function of motor nerves, muscles, motor units and muscle fibers. Genetically modified mice will be studied at 6-8 months and 18-20 months, whereas Sod1+/+ mice will be studied at 6-8, 18-20, and 28-30 months. Unique aspects of the proposed studies are the determination of motor unit properties and contractility of permeabilized single fibers from Soc/f/"mice,, null mice with tissue-specific rescue, and tissue-specific Sodl knockout mice. Furthermore, studies of the relative timing of changes in nerves and muscles that have not been undertaken previously in the same animals will be particularly illuminating for establishing cause-effect relationships of age-related changes in the neuromuscular system. Along with Projects 2 and 3, studies utilizing the very powerful mouse models listed above will determine the mechanistic role of superoxide-induced oxidative stress in muscles and nerves in age-related skeletal muscle atrophy. The Public Health significance is the necessity to understand the mechanisms underlying age-associated skeletal muscle atrophy and weakness to provide the basis for health professionals to design and implement scientifically based strategies to ensure 'successful aging' by reducing and perhaps even eliminating physical frailty in the elderly population.