Activity-dependent signaling in aging skeletal muscle

描述（由申请人提供）：与年龄相关的骨骼肌质量损失与特征明确的功能限制和身体残疾相关。尽管抗阻训练可以减轻与年龄相关的肌肉损失，但引发肌肉肥大的细胞过程以及它们随年龄增长而保留的程度尚不清楚。70 kda S6蛋白激酶（p70S6K）是蛋白激酶B/哺乳动物雷帕霉素靶点（Akt/mTOR）通路的下游靶点，参与过载和废用性萎缩期间肌肉大小的调节。该激酶和Akt/mTOR通路的其他激酶通过调节翻译抑制剂如糖原合成酶激酶3 （GSK-3）、磷酸化关键核糖体蛋白和影响真核起始因子（elF）的可用性来影响蛋白质翻译。我们提出验证以下假设：1)衰老与Akt/mTOR通路激活降低有关；2)p70S6K和mTOR磷酸化降低导致elF4E-elF4G复合物数量减少和肌肉蛋白合成减少；3)由于Akt/mTOR通路激活降低，老年动物的慢性收缩活动导致肌肉肥大钝化。我们建议使用电刺激来模拟年轻和老年大鼠后肢的急性阻力运动，并通过手术消融协同肌肉来模拟慢性收缩活动的影响。具体而言，我们将1)在年轻时进行单次阻力运动后表征Akt/mTOR信号，2)评估阻力运动对年轻时可用于蛋白质翻译的受限mRNA结合位点（elF4E-elF4G）数量的影响，3)比较年轻、中年和老年大鼠对急性收缩活动的反应中Akt/mTOR的激活、elF4E-elF4G复合物的形成和蛋白质合成，4)比较Akt/mTOR的激活。elF4E-elF4G的形成，以及青年、中年和老年大鼠对协同肌肉慢性消融的蛋白质合成。在多个时间点对肌肉样品进行p70S6K、Akt、mTOR、4EBP1和GSK-3磷酸化、elF4E-elF4G复合物和骨骼肌蛋白合成分析。我们相信，在Akt/mTOR通路中发现与年龄相关的肌肉萎缩相关的分子失调，将为旨在纠正这些缺陷的研究奠定基础，并提高老年人抗阻训练和其他治疗干预的效果。

DESCRIPTION (provided by applicant): The age-related loss of skeletal muscle mass is associated with well-characterized functional limitations and physical disability. Although resistance training attenuates age-related muscle loss, the cellular processes that initiate muscle hypertrophy and the extent to which they are preserved with age are not well understood. The 70-kDa S6 protein kinase (p70S6K) is a downstream target of the protein kinase B/mammalian target of rapamycin (Akt/mTOR) pathway that has been implicated in the regulation of muscle size during overload and disuse atrophy. This and other kinases of the Akt/mTOR pathway affect protein translation by regulating translational inhibitors such as glycogen synthase kinase 3 (GSK-3), phosphorylating key ribosomal proteins, and influencing the availability of eukaryotic initiation factors (elF's). We propose to test the hypotheses that 1) aging is associated with a reduced activation of the Akt/mTOR pathway 2) the reduced phosphorylation of p70S6K and mTOR results in a decreased number of elF4E-elF4G complexes and a reduction in muscle protein synthesis, and 3) chronic contractile activity results in blunted muscle hypertrophy in older animals due to a reduced activation of the Akt/mTOR pathway. We propose to use electrical stimulation to simulate acute resistance exercise in young and old rat hindlimbs, and surgical ablation of synergistic muscles to model the effects of chronic contractile activity. Specifically, we will 1) characterize Akt/mTOR signaling after a single bout of resistance exercise at young age, 2) assess the effects of resistance exercise on the number of capped mRNA binding sites (elF4E-elF4G) available for protein translation at young age, 3) compare the activation of Akt/mTOR, formation of elF4E-elF4G complexes, and protein synthesis of young, middle aged, and old rats in response to acute contractile activity, 4) compare the activation of Akt/mTOR, formation of elF4E-elF4G, and protein synthesis of young, middle aged, and old rats in response to chronic ablation of synergistic muscles. Muscle samples at several time points will be analyzed for p70S6K, Akt, mTOR, 4EBP1, and GSK-3 phosphorylation, elF4E-elF4G complexes, and skeletal muscle protein synthesis. We believe that the identification of molecular dysregulation in the Akt/mTOR pathway associated with age-related muscle atrophy will establish the groundwork for studies aimed at correcting these deficiencies and improving the efficacy of resistance training and other therapeutic interventions in the elderly.