Assessing and Alleviating Skeletal Muscle Ca2+ Handling Dysfunction in Sarcopenia

项目总结 骨骼肌质量和力量的进行性丧失，一种被称为骨质疏松症的情况，可能是 最令人衰弱的与年龄相关的改变。在骨质疏松症中，肌肉力量/力量显著下降 不仅仅是肌肉质量本身，这表明受影响的是肌肉的整体质量，而不是 只有肌肉的大小或数量。当预期的体力活动不能再进行时，就会发生肌肉疲劳。 继续或被认为涉及过度努力。不幸的是，许多老年人在 体力(如行走)远低于健康年轻人引起疲劳所需的体力 人民。肌肉中的力量产生与钙离子的释放和随后的重新隔离紧密相连 肌浆网(SR)。钙离子处理过程中的功能障碍一直很强烈 在许多疲劳生产情况下牵涉到力量生产的损失，它已经被 提示Ca~(2+)处理障碍可能是骨骼肌功能衰竭的重要原因 石棺减少症。也已知，组织缺氧在老年肌肉中更严重，这可能会加剧 导致钙离子处理失败的机制。我们已经证明了存在一系列还原的氧气 能够诱导“新陈代谢适应”以维持线粒体呼吸和能量生成 (其中钙离子处理可能需要超过40%！)降低衰老肌肉中的细胞内O2水平将 导致细胞内环境更加紊乱，导致肌肉功能受损--部分原因是 对Ca~(2+)处理过程的负面影响。氧有效性与钙离子处理之间的相互作用 老年人的骨骼肌功能障碍没有得到仔细的调查，尤其是对 这一损害尚未进行分析。这项拟议研究的目的是使用鼠标 分离的完整肌肉和完整的单个骨骼肌纤维：1)检验一些假说 围绕着这样一个概念：细胞氧气(在远高于限制线粒体的水平 呼吸)引起细胞内环境的改变，从而影响老年人对钙的处理 肌肉，从而导致在低氧条件下更早出现收缩损伤。和大多数 重要的是：2)测试处理和转基因模型，影响钙离子的不同成分 试图开发对抗O2相关钙离子的治疗策略的处理过程 处理功能障碍，从而减轻一些肌肉损伤的石棺减少。我们的 实验模型允许精确控制细胞外环境和细胞内环境 可以使用非侵入性荧光成像技术仔细监测。这就是本研究的目的。 项目使用我们独特的单肌纤维模型来仔细阐明降低 衰老肌肉中的细胞PO2损害了钙离子的处理和收缩能力，并随后开发了应对策略 减少老年受试者脆弱的与钙离子相关的处理障碍。

PROJECT SUMMARY The progressive loss of skeletal muscle mass and strength, a condition known as sarcopenia, is perhaps the most debilitating age-associated alteration. In sarcopenia, muscle strength/power decrease significantly more than muscle mass itself, suggesting that it is the overall quality of the muscle that is affected and not only the size or quantity of muscle. Muscle fatigue occurs when the intended physical activity can no longer be continued or is perceived as involving excessive effort. Unfortunately, many elderly suffer from fatigue at physical efforts far less (i.e. walking) than the efforts that are required to induce fatigue in healthy young people. Force generation in muscle is tightly coupled to the release and subsequent re-sequestering of Ca2+ by the sarcoplasmic reticulum (SR). Dysfunction in the Ca2+ handling process has been strongly implicated in the loss of force production in many fatigue producing situations, and it has been suggested that Ca2+ handling impairment may significantly contribute to skeletal muscle failure in sarcopenia. It is also known that tissue hypoxia is greater in aged muscle, and this may exacerbate the mechanisms contributing to Ca2+ handling failure. We have demonstrated that there is a range of reduced O2 availability that will induce “metabolic adaptation” to maintain mitochondrial respiration and energy generation (of which Ca2+ handling may require more than 40%!). Lower intracellular O2 levels in aged muscle will result in a more perturbed intracellular milieu, resulting in an impaired muscle function--in part due to negative effects on the Ca2+ handling process. The interplay between O2 availability and Ca2+ handling on skeletal muscle dysfunction in the elderly has not been carefully investigated, and in particular, treatments for this impairment have not been analyzed. The purpose of this proposed research is to use mouse isolated whole muscle and an intact single skeletal muscle fiber to: 1) test a number of hypotheses centered around the notion that cellular O2 (at levels well above those limiting mitochondrial respiration) induce alterations in the intracellular environment that affect Ca2+ handling in aged muscle, thereby leading to an earlier onset of contractile impairment in hypoxia. And most importantly: 2) test treatments and transgenic models which affect different components of the Ca2+ handling process in an attempt to develop therapeutic strategies for combating O2-related Ca2+ handling dysfunction and thereby alleviate some of the muscle impairment in sarcopenia. Our experimental models allow precise control of the extracellular environment and the intracellular environment can be carefully monitored using non-invasive fluorescent imaging techniques. It is the goal of this research project to use our unique single myofiber model to carefully elucidate the mechanisms by which reduced cellular PO2 in aged muscle impairs Ca2+ handling and contractility, and to subsequently develop strategies to reduce frailty associated Ca2+ handling impairments in older subjects.