Mechanism through which chronically elevated mTOR activity impairs aged muscle recovery after disuse atrophy

摘要 与普通人群相比，老年退伍军人患有慢性疾病的负担更大，因此 更频繁的住院治疗。频繁和反复住院的一个后果是 与年龄相关的骨骼肌质量和力量丧失加速(骨质疏松症)。的综合效应 由于老年人没有充分康复，骨量减少和住院会加剧肌肉功能障碍 从卧床休息让他们加速走向失去独立性的轨道。因此，这段时间 住院前后是预防残疾、丧失独立性和虚弱的关键时期 退伍军人。目前尚不清楚为什么老年人的骨骼肌在萎缩一段时间后会抵抗再生。 此外，目前促进老年骨骼肌再生的策略在很大程度上仍然无效。建议数 这项工作意义重大，因为它证明mTOR激活是故障的原因，而不是解决方案 在停用后恢复肌肉。目前的提议是创新的，因为它与目前的治疗方法背道而驰 基于幼年动物的数据；它提出了三种独立但重叠的机制；它 使用复杂的同位素标记和蛋白质组学相结合的方法来研究废弃前后的时期 萎缩。这一建议的总体假设是，老年骨骼肌中长期激活的mTOR 在停用一段时间后，损害肌肉质量/功能的恢复。为了检验这一总体假设，我们将使用 老年(28个月)F344/BN大鼠使用和不使用mTOR抑制剂(雷帕霉素(RapA))以达到三个特定目的 决定是否抑制老年肌肉中的慢性mTOR活动：1)纠正线粒体功能障碍， 在HU一段时间后损害肌肉恢复，2)改善损害肌肉恢复的蛋白平衡应激 HU治疗一段时间后，3)有助于解决HU治疗一段时间后损害肌肉恢复的纤维化。我们的 假设抑制长期活跃的mTOR活性将：1)增加选择性翻译 MRNA改善线粒体蛋白重塑，改善网络连通性恶化，以及 改善线粒体功能，2)改善RE期间的蛋白平衡维持，3)减少肌肉纤维化 改善机械转导在心脏复张中的作用。为了实现这些具体目标，我们将使用我们创新的、有针对性的和 基于发现的动态蛋白质组学以及新的(例如线粒体成像)和成熟的 二次结果，包括功能结果，以支持我们的蛋白质组结果。希望这些都是 实验将阐明老年退伍军人肌肉恢复失败的根本原因，以及我们是否 应从根本上改变方法，促进老年肌肉停用后的恢复。这一知识 可以帮助防止相当数量的老年退伍军人加速发展到残疾门槛。

SUMMARY Older Veterans have a higher burden of comorbid chronic diseases compared to the general population, resulting in more frequent inpatient hospitalizations. A consequence of frequent and recurring hospitalizations is the acceleration of age-related loss of skeletal muscle mass and strength (sarcopenia). The combined effect of sarcopenia and hospitalization exacerbates muscle dysfunction since older adults do not adequately recover from bedrest placing them on an accelerated trajectory toward loss of independence. Therefore, the period around hospitalization is a critical period to intervene to prevent disability, loss of independence, and frailty in Veterans. It is not clear why skeletal muscle in older individuals is resistant to regrowth after a period of atrophy. Further, current strategies to enhance regrowth in older skeletal muscle remain largely ineffective. The proposed work is significant because it provides evidence that mTOR activation is the cause, not the solution, to the failure to recover muscle after disuse. The current proposal is innovative in that it goes against current therapies that were based on data from young animals; it proposes three independent but overlapping mechanisms; and it uses sophisticated combined isotope labeling and proteomic approaches to study the periods around disuse atrophy. The overall hypothesis of this proposal is that that chronically activated mTOR in aged skeletal muscle impairs the recovery of muscle mass/function after a period of disuse. To test this overall hypothesis, we will use old (28 mo) F344/BN rats with and without an mTOR inhibitor (rapamycin (Rapa)) to address three specific aims that determine if inhibiting chronic mTOR activity in older muscle: 1) corrects the mitochondrial dysfunction that impairs muscle recovery after a period of HU, 2) improves the proteostatic stress that impairs muscle recovery after a period of HU, and 3) helps resolve fibrosis that impairs muscle recovery after a period of HU. Our hypotheses are that suppression of chronically active mTOR activity will: 1) increase the selective translation of mRNA to improve mitochondrial protein remodeling, improve the deterioration of network connectivity, and improve mitochondrial function, 2) improve proteostatic maintenance during RE, and 3) reduce muscle fibrosis to improve mechanotransduction during RE. For these specific aims we will use our innovative targeted and discovery-based kinetic proteomics along with novel (e.g. mitochondrial imaging) and well-established secondary outcomes, including functional outcomes, to support our proteomic outcomes. It is hoped that these experiments will clarify the underlying cause of failed recovery in muscle of older Veterans, and whether we should fundamentally change the approach to enhance recovery after disuse in aged muscle. This knowledge could help prevent the accelerated progression to a disability threshold for a significant number of older Veterans.