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明确表征的功能限制和身体残疾相关。虽然阻力训练可以减轻与年龄相关的肌肉损失，但启动肌肉肥大的细胞过程以及它们随年龄增长而保留的程度还不清楚。 70-kDa S6蛋白激酶（p70 S6 K）是蛋白激酶B/哺乳动物雷帕霉素靶（Akt/mTOR）途径的下游靶点，其涉及在过载和废用性萎缩期间调节肌肉大小。Akt/mTOR途径的这种和其它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（eIF）的可用性来影响蛋白质翻译。我们提出测试以下假设：1）衰老与Akt/mTOR途径的活化减少相关; 2）p70 S6 K和mTOR的磷酸化减少导致eIF 4 E-eIF 4G复合物的数量减少和肌肉蛋白质合成减少;以及3）由于Akt/mTOR途径的活化减少，慢性收缩活动导致老年动物中的肌肉肥大钝化。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，以及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）表征年轻时单次抗阻运动后Akt/mTOR信号传导，2）评估抗阻运动对加帽mRNA结合位点数量的影响，（eIF 4 E-eIF 4G）在年轻时可用于蛋白质翻译，3）比较年轻、中年、4）比较年轻、中年和老年大鼠对协同肌肉慢性消融的Akt/mTOR激活、eIF 4 E-eIF 4G形成和蛋白质合成。将分析几个时间点的肌肉样品的p70 S6 K、Akt、mTOR、4 EBP 1和GSK-3磷酸化、eIF 4 E-eIF 4G复合物和骨骼肌蛋白合成。我们相信，Akt/mTOR通路中与年龄相关性肌肉萎缩相关的分子失调的鉴定将为旨在纠正这些缺陷并提高抗阻训练和其他治疗干预措施在老年人中的疗效的研究奠定基础。

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.