Activity-dependent signaling in aging skeletal muscle

描述(由申请人提供)：与年龄相关的骨骼肌块减少与明显的功能限制和身体残疾有关。尽管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着年龄的增长得到保存的程度尚不清楚。70 kDa S6蛋白激酶(P70S6K)是蛋白激酶B/哺乳动物雷帕霉素靶标(Akt/mTOR)通路的下游靶点，参与了超负荷和废用性萎缩过程中肌肉大小的调节。该蛋白和Akt/mTOR途径中的其他蛋白通过调节翻译抑制物如糖原合成酶-3(GSK-3)、磷酸化关键的核糖体蛋白以及影响真核细胞起始因子(ELF)的可获得性来影响蛋白质翻译。我们提出的假设是：1)衰老与Akt/mTOR通路的激活减少有关；2)p70S6K和mTOR的磷酸化减少导致elF4E-elF4G复合体数量减少和肌肉蛋白质合成减少；3)慢性收缩活动导致老年动物肌肉肥大，这是由于Akt/mTOR通路的激活减少所致。我们建议使用电刺激来模拟青年和老年大鼠后肢的急性阻力运动，并通过外科手术消融协同肌肉来模拟慢性收缩活动的影响。具体地说，我们将1)研究年轻时单次抗阻运动后Akt/mTOR信号的特征，2)评估抗阻运动对年轻时可用于蛋白质翻译的封顶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做出的反应，Akt/mTOR的激活、elF4E-elF4G复合体的形成和蛋白质合成，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、elF4E-elF4G的形成和蛋白质合成的影响。将对几个时间点的肌肉样本进行p70S6K、Akt、mTOR、4EBP1和GSK-3磷酸化、elF4E-elF4G复合体和骨骼肌蛋白质合成的分析。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和提高老年人抵抗训练和其他治疗干预效果的研究奠定基础。

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.