Effects of insulin-like signaling, aging, and ubiquinone on C. elegans muscle

描述（由申请人提供）：肌肉减少症是发生在老年人中的肌肉质量和肌肉力量的损失。由此导致的肌肉力量丧失导致老年人身体功能受损，并成为丧失独立性、需要养老院安置和最终死亡的风险因素。目前没有治疗肌肉减少症的方法，原因也不完全清楚。因此，有必要确定新的方法来研究肌肉减少症，并确定可能适合干预的机制。在老化过程中，C.秀丽线虫发生少肌症，胰岛素/IGF-1受体DAF-2的突变延迟了少肌症的发生。我们已经发现，mvk-1，这是蠕虫的同源物甲羟戊酸激酶基因，是需要这种延迟。甲羟戊酸激酶参与甲羟戊酸向类异戊二烯、泛醌和胆固醇的转化，该酶位于常用他汀类药物靶向的代谢途径中。众所周知，他汀类药物对肌肉有毒性作用，但这些不良反应的原因仍在积极研究中。在泛醌、类异戊二烯和胆固醇中，我们已经发现泛醌是关于肌肉老化的甲羟戊酸途径所需的输出。泛醌是线粒体电子传递链复合物I和复合物II的电子受体。先前的工作已经表明，daf-2突变体具有升高的复合物I和II活性，并且与野生型动物相比，在衰老过程中，daf-2突变体中的线粒体活性更好地保留。此外，在脊椎动物的衰老过程中，肌肉和其他组织中的复合物I活性下降。这些发现使我们假设，线粒体活性是一个驱动因素， 在衰老过程中肌肉减少症的发展，并可能涉及他汀类药物的毒性。为了验证这一假设，我们建议：（1）检查野生型蠕虫、daf-2突变体和泛醌水平降低的daf-2突变体在衰老过程中的肌肉结构;（2）测试衰老和低泛醌水平是否损害线粒体ATP的产生或（3）导致衰老过程中ROS的产生增加;（4）确定直接操纵复合物I活性上下对肌肉功能的影响;以及（5）使用用于遗传线粒体疾病的药物进行试验性化合物筛选，以测试衰老期间肌肉功能的改善。我们工作的一个新的方面将是使用最近开发的荧光蛋白纵向和非侵入性测量细胞ATP水平和ROS的产生在衰老动物的肌肉。我们的项目可以一起提供对衰老过程中肌肉线粒体功能障碍的作用的见解，或者对他汀类药物等药物导致的泛醌合成受损的反应。

DESCRIPTION (provided by applicant): Sarcopenia is the loss of muscle mass and muscle strength that occurs in aging people. The resulting loss of muscle strength contributes to impairments in physical functioning in older people and serves as a risk factor for loss of independence, need for nursing home placement, and ultimately mortality. Currently there are no treatments for sarcopenia and the cause(s) are incompletely understood. Hence there is a need to identify new ways to study sarcopenia and identify mechanisms that may be amenable to intervention. During aging, C. elegans develops sarcopenia, and mutations in the insulin/IGF-1 receptor daf-2 delay the development of sarcopenia. We have found that mvk-1, which is the worm homolog of the mevalonate kinase gene, is required for this delay. Mevalonate kinase is involved in the conversion of mevalonate to isoprenoids, ubiquinone, and cholesterol, and this enzyme lies in a metabolic pathway targeted by the commonly used statin medications. Statins have well-known toxic effects on muscle, but the cause of these adverse effects is still under active study. Among ubiquinone, isoprenoids, and cholesterol, we have found ubiquinone to be the required output of the mevalonate pathway with regards to muscle aging. Ubiquinone is the electron acceptor for complex I and complex II of the mitochondrial electron transport chain. Prior work has shown that daf-2 mutants have elevated complex I and II activity, and mitochondrial activity is better preserved in the daf-2 mutants during aging compared to wild-type animals. Additionally, complex I activity in muscle and other tissues declines during aging in vertebrates. These findings led us to hypothesize that mitochondrial activity is a driver of the development of sarcopenia during aging and perhaps is involved in statin toxicity. To test this hypothesis we propose to (1) examine muscle structure during aging in wild-type worms, daf-2 mutants, and daf-2 mutants with reduced ubiquinone levels; (2) test whether aging and low ubiquinone levels impair mitochondrial ATP production or (3) lead to increased ROS production during aging; (4) determine the consequences of directly manipulating complex I activity both up and down on muscle function; and (5) conduct a pilot compound screen using drugs used for genetic mitochondrial illnesses to test for improvements in muscle function during aging. A novel aspect of our work will be the use of recently developed fluorescent proteins to longitudinally and non-invasively measure cellular ATP levels and ROS production in the muscles of aging animals. Together our project can provide insights into the roles of mitochondrial dysfunction in muscle during aging or in response to impaired ubiquinone synthesis due to medications such as statins.