Regulation of sarcopenia and muscle dysfunction by nitric oxide

描述(申请人提供)：骨质疏松症，衰老过程中肌肉质量的丧失，是衰老的必然结果，对老年人的生活质量造成极大的损害，并使老年人口容易受到进一步虚弱的伤害。骨质疏松症及相关损伤和并发症的社会成本是巨大的，随着美国人口迅速向老年人口转变，这种成本还将迅速增长。然而，由于缺乏有关骨质疏松症原因的机制知识，因此无法采取更具体的干预措施来减缓肌肉萎缩的进程。我们的发现表明，衰老的肌肉经历了神经元型一氧化氮合酶(NNOS)的急剧减少，而将nNOS恢复到衰老的肌肉可以防止小鼠的骨骼减少。我们在这项研究中的目标是确定nNOS预防石棺减少的机制。根据我们的初步研究和其他人的发现，我们提出了一个假设，即nNOS来源的NO通过两个过程减缓骨骼肌减少：1)抑制肌肉蛋白水解酶calain-1、calain-2和caspase-3，以减少肌原纤维蛋白的蛋白分解；2)抑制炎性细胞因子的产生，这些细胞因子能够促进肌肉萎缩，特别是肿瘤坏死因子-α(TNFa)。我们将在衰老小鼠模型中通过测试NO介导的S亚硝酸化是否在肌肉衰老过程中发生肌肉蛋白酶抑制来解决这一假说。抑制钙蛋白酶是否足以减少骨质疏松症，将在经过基因改造的小鼠身上进行测试，这些小鼠已经在肌肉中产生了更高水平的钙蛋白酶抑制剂，钙蛋白酶抑制素。我们还将确定由calain-2或caspase-3引起的肌原纤维中主要肌肉蛋白的特定蛋白水解性修饰。在其他实验中，我们将测试肌肉产生NO的操作是否可以减少炎性细胞因子的产生，或者炎性细胞对肌肉的侵袭。此外，我们将通过测试干扰素-伽马基因缺失小鼠的衰老、TNFa缺失突变是否减少肌肉萎缩来确定减少促炎细胞因子的产生是否足以减缓骨质疏松症。我们期待这项研究的结果可以为减少石棺减少的潜在治疗策略提供新的见解。

DESCRIPTION (provided by applicant): Sarcopenia, the loss of muscle mass during aging, is an inevitable consequence of aging that takes a tremendous toll on the quality of life of the elderly, and predisposes the aging population to injuries that can be further debilitating. Societal cost of sarcopenia and associated injuries and complications is huge, and will grow rapidly as the United States demographic rapidly shifts toward a more senior population. However, the shortage of mechanistic knowledge concerning the causes of sarcopenia has prevented more specific interventions to slow the process of muscle wasting. Our findings show that aging muscle undergoes a dramatic reduction in neuronal nitric oxide synthase (nNOS) and that restoring nNOS to aging muscle prevents sarcopenia in mice. Our goal in this investigation is to identify the mechanisms through which nNOS protects against sarcopenia. Based upon our preliminary studies and the findings of others, we have generated the hypothesis that nNOS-derived NO slows sarcopenia through two processes: 1) inhibition of muscle proteases calpain-1, calpain-2 and caspase-3, to reduce proteolysis of myofibrillar proteins, and 2) inhibition in the production of inflammatory cytokines that are able to promote muscle wasting, especially tumor necrosis factor-alpha (TNFa). We will address this hypothesis in aging mouse models by testing whether muscle protease inhibition by NO-mediated S-nitrosylation occurs during muscle aging. Whether calpain inhibition is sufficient to reduce sarcopenia will be tested in mice that have been genetically-modified to produce elevated levels of the calpain inhibitor, calpastatin, in muscle. We will also identify the specific proteolytic modifications of major muscle proteins in myofibrils that are caused by calpain-2 or caspase-3. In other experiments, we will test whether manipulations of NO production by muscle can reduce the production of inflammatory cytokines, or muscle invasion by inflammatory cells. In addition, we will determine whether reducing the production of pro-inflammatory cytokines is sufficient to slow sarcopenia by testing whether muscle wasting is reduced in aging, TNFa null mutant on interferon-gamma null mice. We anticipate that the results of this investigation can provide new insights into potential therapeutic strategies to reduce sarcopenia.