The role of satellite cells in skeletal muscle hypertrophy with aging

项目摘要 随着年龄的增长，骨骼肌质量的损失具有临床重要性，因为它与增加的 发病率和死亡率以及生活质量的显著恶化。也有一个加剧 对鉴定负责缺乏合成代谢的细胞和分子机制的兴趣 老年肌肉对肥大刺激的反应。使用卫星细胞治疗骨骼肌质量损失 被认为是一种有前途的治疗策略，因为它们具有干细胞的特性， 纳塔尔生长和再生我们的研究结果促使我们进行机械的 分析卫星细胞的两种众所周知的功能;与肌纤维融合，为肌纤维提供额外的细胞核， 肥大生长，卫星细胞扩张的其他功能后果，发生在响应 各种外源性刺激，如运动，随着卫星细胞丰度的增加， 机械过载远远超过与肌纤维尺寸增加相关的肌纤维增生。我们报道 卫星细胞是骨骼肌长期肥大生长所必需的， 细胞外基质活化的卫星细胞通过细胞外囊泡抑制成纤维细胞胶原的生成 (EV)miR-206的传递，揭示了卫星细胞的一种以前未被认识的功能，除了提供 一种卫星细胞与肌肉内其他细胞交流的机制。我们现在在体内 来自Pax 7-tdT报告小鼠卫星细胞间通讯的单细胞（sc）RNA-seq证据 网络，其中卫星细胞与FAP/纤维化细胞和内皮细胞通信， 肥大生长目标1将检验老化对这种交流网络产生负面影响的假设 抑制细胞外基质的适当重塑，从而抑制肥大。我们还开发了 一种新的小鼠模型，使我们能够同时耗尽卫星细胞和标记常驻肌细胞核， 2将使用该模型和单肌球蛋白（smn）RNA-seq来表征年龄依赖性的变化， 常驻myc转录组，并确定机制，使短期肥大的情况下， 成年小鼠的卫星细胞，在年老时丢失。AIM 3将使用额外的新开发的报告器 一种小鼠，能够特异性和稳定地标记卫星细胞核，以确定衰老如何改变 卫星细胞衍生的肌核转录组响应肥大刺激。我们假设， 衰老的肌肉，卫星细胞衍生的肌核具有改变的转录输出， 肥大反应，卫星细胞融合受损或有缺陷的卫星细胞可能会产生负面影响， 影响导致生长受损的常驻myc转录活性。定义融合依赖 卫星细胞和年龄相关变化的独立作用对肌肉适应性产生负面影响 将确定潜在的新目标，以促进骨骼肌生长，在面对不活动，在老化和 肌肉萎缩性疾病的脸。

Project Summary The loss of skeletal muscle mass with age is of clinical importance because it is associated with increased morbidity and mortality, as well as a marked deterioration in the quality of life. There is also a heightened interest in the identification of cellular and molecular mechanisms responsible for the lack of an anabolic response of aged muscle to hypertrophic stimuli. The use of satellite cells to treat loss of skeletal muscle mass is considered a promising therapeutic strategy given their stem cell characteristics and essential role in post- natal muscle growth and regeneration. The results of our studies have prompted us to perform mechanistic analyses of both of the well-known function of satellite cells; fusion to myofibers to provide additional nuclei for hypertrophic growth, to other functional consequences of satellite cell expansion that occurs in response to various exogenous stimuli such as exercise, as the increase in satellite cell abundance in response to mechanical overload far exceeds myonuclear accretion associated with increased myofiber size. We reported satellite cells were necessary for optimal long-term hypertrophic growth of skeletal muscle by regulating the extracellular matrix. Activated satellite cells repressed fibroblast collagen production via extracellular vesicle (EV) delivery of miR-206, revealing a previously unrecognized function of satellite cells, in addition to providing a mechanism through which satellite cells communicate with other cells within muscle. We now have in vivo single-cell (sc)RNA-seq evidence from Pax7-tdT reporter mice of a satellite cell intercellular communication network in which satellite cells communicate with FAPs/fibrogenic cells and endothelial cells during hypertrophic growth. Aim 1 will test the hypothesis that aging negatively impacts this communication network inhibiting proper remodeling of the extracellular matrix thereby inhibiting hypertrophy. We have also developed a novel mouse model that allows us to simultaneously deplete satellite cells and label resident myonuclei, Aim 2 will use this model and single-myonuclear (smn)RNA-seq to characterize age-dependent changes in the resident myonuclear transcriptome and identify mechanisms that enable short term hypertrophy in the absence of satellite cells in adult mice, which is lost in old age. Aim 3 will use an additional newly developed reporter mouse that enables specific and stable labeling of satellite cell nuclei to determine how aging alters the satellite cell-derived myonuclear transcriptome in response to a hypertrophic stimulus. We hypothesize that in aged muscle, satellite cell-derived myonuclei have altered transcriptional output that does not promote a hypertrophic response, and that impaired fusion of satellite cells or defective satellite cells may negatively impact resident myonuclear transcriptional activity contributing to impaired growth. Defining fusion-dependent and -independent roles of satellite cells and age-associated changes that negatively impact muscle adaptability will identify potential new targets to promote skeletal muscle growth in the face of inactivity, during aging and in the face of muscle wasting diseases.