BetaCatenin Regulation of Skeletal Muscle Hypertrophy

描述（申请人提供）：作为细胞的“造房”大分子，核糖体生物合成对细胞生长至关重要。尽管核糖体在细胞生长中起着重要作用，但我们对核糖体生物合成在成人骨骼肌肥大中的作用的理解仍然存在根本性的差距。我们实验室的研究提供了证据，支持核糖体生物合成增加在骨骼肌肥大中的作用。目前的建议将开始直接检查的重要性，核糖体生物合成肌肉肥大的假设，-连环蛋白是必要的肌肉肥大通过增加蛋白质合成，通过c-myc激活核糖体生物合成。为了有条件地操纵β-连环蛋白或c-myc基因在成人骨骼肌中的表达，我们产生了HSA-MerCreMer小鼠。目的1将使用在连环蛋白基因失活后的跖肌的机械过载模型来确定连环蛋白表达是否是骨骼肌肥大所必需的。目的2将确定增加的连环蛋白表达是否足以刺激骨骼肌肥大。通过使用HSA-MerCreMer菌株产生稳定形式的β-连环蛋白，β-连环蛋白将在成人骨骼肌中过表达。目的3将确定是否c-myc表达是必要的骨骼肌肥大后，在成人骨骼肌中使用HSA-MerCreMer株的c-myc的条件性失活。将通过测量形态学（肌肉重量、纤维CSA）、生物化学（总蛋白、RNA和DNA）、分子学（蛋白质印迹、RT-PCR、启动子分析、染色质免疫沉淀（ChIP）和电泳迁移率变动试验（EMSA））和代谢（蛋白质合成和降解速率）变量，评估基因失活对肥大反应的影响。这些研究的结果有望通过确定促进骨骼肌蛋白质合成和肥大的新分子靶点而具有重要的临床意义。从长远来看，操纵核糖体生物发生的能力代表了一种有前途的新策略，以减轻或改善与衰老、卧床休息和恶病质相关的肌肉萎缩。 公共卫生相关性：骨骼肌质量占健康成年人总体重的近50%，现在被认为是一个重要的健康因素。这项研究的结果有望揭示b-连环蛋白对蛋白质合成的调节是否是肌肉生长所必需的。如果得到证实，这些结果将具有药用价值，为在与不活动、癌症和衰老相关的肌肉损失期间促进肌肉生长提供新的靶点。

DESCRIPTION (provided by applicant): As the "house-building" macromolecule of the cell, ribosome biogenesis is essential for cell growth. Despite this central role in cell growth, there remains a fundamental gap in our understanding of the role of ribosome biogenesis in adult skeletal muscle hypertrophy. Studies from our laboratory have provided evidence which supports a role for increased ribosome biogenesis in skeletal muscle hypertrophy. The current proposal will begin to directly examine the importance of ribosome biogenesis to muscle hypertrophy by testing the hypothesis that -catenin is necessary for muscle hypertrophy by increasing protein synthesis through c-myc activation of ribosome biogenesis. To conditionally, manipulate -catenin or c-myc gene expression in adult skeletal muscle we generated the HSA-MerCreMer mouse. Aim 1 will determine if ¿-catenin expression is necessary for skeletal muscle hypertrophy using a mechanical overload model of the plantaris muscle following catenin gene inactivation. Aim 2 will determine if increased expression of ¿-catenin is sufficient to stimulate skeletal muscle hypertrophy. ¿-catenin will be over-expressed in adult skeletal muscle by using the HSA- MerCreMer strain to generate a stabilized form of ¿-catenin. Aim 3 will determine if c-myc expression is necessary for skeletal muscle hypertrophy following the conditional inactivation of c-myc in adult skeletal muscle using the HSA-MerCreMer strain. The effect of gene inactivation on the hypertrophic response will be assessed by measuring morphometric (muscle weight, fiber CSA), biochemical (total protein, RNA and DNA), molecular (Western blot, RT-PCR, promoter analysis, chromatin immunoprecipitation (ChIP) and electrophorectic mobility shift assay (EMSA)) and metabolic (rates of protein synthesis and degradation) variables. The results of the proposed studies are expected to have important clinical implications by identifying new molecular targets for promoting skeletal muscle protein synthesis and hypertrophy. In the long- term, the ability to manipulate ribosome biogenesis represents a promising novel strategy to attenuate or ameliorate muscle atrophy associated with aging, bed rest and cachexia. PUBLIC HEALTH RELEVANCE: Skeletal muscle mass makes up almost 50% of the total body weight in healthy adults and it is now recognized as an important health factor. The findings from the proposed research are expected to reveal whether or not b-catenin regulation of protein synthesis is necessary for muscle growth. If confirmed, such results will be of medicinal value by providing new targets for promoting muscle growth during periods of muscle loss associated with inactivity, cancer and aging.