Effects of HGF and Myosatin on HIF-1Alpha and Satellite Cell Activation

描述（由申请人提供）：肌肉减少症，即与年龄相关的骨骼肌质量和强度损失，与老年人生活质量下降、残疾发生率增加、独立生活能力丧失和发病风险增加有关。卫星细胞的活化、增殖和分化是维持肌肉质量的必要过程，并且已经报道了卫星细胞功能的降低，包括卫星细胞活化。在这方面，卫星细胞活化是治疗干预以改善肌肉减少症的有害影响的适当目标，因此，长期目标是更好地理解卫星细胞活化。从静止到活化的进展的特征在于增加的细胞周期进入和代谢的增加。由于缺氧诱导因子-1（HIF-1）以其反式激活糖酵解代谢重要基因的能力而闻名，因此一个合理的假设是HIF-1对卫星细胞激活的增加很重要，并且可能参与随着衰老发生的卫星细胞激活减少。为了验证这些假设，肝细胞生长因子（HGF），这是众所周知的，其能力，以激活卫星细胞，和肌生长抑制素，卫星细胞活化的负调节，将被用来确定的重要性，HIF-1的活性和增加的细胞代谢卫星细胞活化，这一信息将被用来确定机制延迟卫星细胞活化与老化。本提案的具体目的是：1）确定HIF-1在HGF诱导的卫星细胞活化增加过程中的作用，2）确定HIF-1在肌生长抑制素诱导的卫星细胞活化减少过程中的作用，3）确定HIF-1在随衰老延迟的卫星细胞活化中的重要性。卫星细胞和单纤维培养，以及成年和老年动物的整个骨骼肌模型将用于实现这些目标。HGF、肌生长抑制素、MAPK/ERK、Smad和HIF-1活性将结合HIF-1依赖性启动子活性、mRNA和蛋白质测量进行药理学和/或遗传学操作。由于HIF-1在卫星细胞活化过程中的功能以前尚未确定，因此除了染色质免疫沉淀外，还将测量关键HIF-1靶基因的mRNA水平。卫星细胞（成体肌肉干细胞）的激活在衰老中受损，可能是随着衰老发生的骨骼肌质量损失的一个因素。这项研究旨在增加对两种生长因子如何影响卫星细胞激活的理解，HGF和肌肉生长抑制素，以及这些生长因子是否通过转录因子缺氧诱导因子（HIF-1）起作用。

DESCRIPTION (provided by applicant): Sarcopenia, the age-associated loss of skeletal muscle mass and strength, is linked to a decreased quality of life for, an increased incidence of disability, loss of independent living, and increased risk for morbidity for the elderly. The activation, proliferation, and differentiation of satellite cells is a necessary progression for the maintenance of muscle mass, and decreases in satellite cell function, including satellite cell activation, have been reported with aging. In this regard, satellite cell activation is an appropriate target for therapeutic interventions to ameliorate the deleterious effects of sarcopenia, therefore, the long-term objectives are to better understand satellite cell activation. The progression from quiescence to activation is characterized by increased cell cycle entry and an increase in metabolism. Since hypoxia-inducible factor-1 (HIF-1) is known for its ability to transactivate genes important for glycolytic metabolism, a plausible hypothesis is that HIF-1 is important for increased in satellite cell activation, and may be involved in decreased satellite cell activation that occurs with aging. To test these hypotheses, hepatocyte growth factor (HGF), which is well-known for its ability to activate satellite cells, and myostatin, a negative regulator of satellite cell activation, will be used to determine the importance of HIF-1 activity and increased cell metabolism in satellite cell activation, and this information will be used to determine mechanisms underlying delayed satellite cell activation with aging. The specific aims of this proposal are to 1) Determine the role of HIF-1 during HGF-induced increases in satellite cell activation, 2) Determine the role of HIF-1 during myostatin-induced decreases in satellite cell activation, and 3) Determine the importance of HIF-1 in delayed satellite cell activation with aging. Satellite cell and single fiber cultures, and whole skeletal muscle models in adult and old animals will be used to accomplish these aims. HGF, myostatin, MAPK/ERK, Smad, and HIF-1 activities will be manipulated pharmocologically and/or genetically in conjunction with HIF-1 -dependent promoter activity, mRNA, and protein measurements. Since the function of HIF-1 during satellite cell activation has not previously been determined, mRNA levels of key HIF-1 target genes will be measured in addition to chromatin immunoprecipitatioin. Satellite cell (adult muscle stem cell) activation is impaired in aging and may be a contributor to the loss of skeletal muscle mass that occurs with aging. This research is directed towards increasing the understanding how two growth factors affect satellite cell activation, HGF and myostatin, and if these growth factors work through the transcription factor hypoxia-inducible factor (HIF-1).