Assessing and Alleviating Ca2+ Handling Dysfunction in Sarcopenia

 描述(由申请人提供)：骨骼肌质量和力量的进行性丧失，一种称为骨质疏松症的情况，可能是与年龄相关的最衰弱的改变。在骨质疏松症中，肌肉力量/力量的下降明显大于肌肉质量本身，这表明受影响的是肌肉的整体质量，而不仅仅是肌肉的SZE或数量。当预期的身体活动不能再继续或被认为涉及过度努力时，就会发生肌肉疲劳。不幸的是，许多老年人在体力活动(即步行)上的疲劳感远远低于使健康的年轻人产生疲劳所需的体力活动。肌肉中的力产生与肌浆网(SR)释放和随后的钙离子重新隔离密切相关。在许多疲劳产生的情况下，钙离子处理过程中的功能障碍与力量产生的丧失密切相关，有人认为，钙离子处理功能的障碍可能是骨骼肌功能衰竭的重要原因。众所周知，衰老的肌肉组织缺氧程度更高，这可能会加剧导致钙离子处理失败的机制。我们已经证明，存在一系列氧气可获得性降低的情况，这将诱导“代谢适应”来维持线粒体的呼吸和能量产生(其中，钙离子的处理可能需要超过40%！)因此，衰老肌肉中较低的细胞内O2水平将导致细胞内环境更加混乱，从而导致肌肉功能受损--部分原因是对钙离子处理过程的负面影响。在老年人骨骼肌功能障碍中，氧气供应和钙离子处理之间的相互作用尚未被仔细研究，尤其是这种损伤的治疗方法。 没有被分析过。这项拟议的研究的目的是使用小鼠分离的整个肌肉和完整的单个骨骼肌纤维模型，在该模型中，细胞外环境可以被精确控制，细胞内环境可以使用非侵入性荧光成像技术进行仔细监测，以：1)验证围绕以下概念的一些假说：细胞氧气水平远远高于限制呼吸的水平时，会诱导细胞内环境的改变 2)测试几种新的化合物和转基因模型，它们影响钙离子处理过程的不同组成部分(释放/肌丝结合/再隔离)，试图开发出对抗氧相关的钙处理功能障碍的治疗策略，从而减轻骨骼肌减少时的部分肌肉损伤。这项研究项目的目标是使用我们独特的单一肌纤维模型来仔细阐明老年肌肉细胞PO2降低损害钙离子处理和收缩的机制，并随后开发药物策略来减少老年受试者脆弱的相关钙处理损害。

 DESCRIPTION (provided by applicant): 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 sze 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 indue 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%!) such that 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 model, in which the extracellular environment can be precisely controlled and the intracellular environment carefully monitored using non-invasive fluorescent imaging techniques, to: 1) test a number of hypotheses centered around the notion that cellular O2, at levels well above those limiting 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 several novel compounds and transgenic models which affect different components of the Ca2+ handling process (release/myofilament binding/re- sequestration) in an attempt to develop therapeutic strategies for combating O2-related Ca2+ handling dysfunction and thereby alleviate some of the muscle impairment in sarcopenia. 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 pharmacological strategies to reduce frailty associated Ca2+ handling impairments in older subjects.