Thyroid Hormone Receptor Isoforms in Skeletal Muscle

描述（由申请人提供）：骨骼肌中的干细胞在出生后肌肉生长和损伤后再生中起重要作用。已经提出，骨骼肌卫星细胞的命运可以从肌生成转变为脂肪生成，并且由于这个原因，导致在几种病理状况下异位肌内脂肪积累，例如肌病、2型糖尿病、肥胖症和年龄相关性肌肉减少症。在这个建议中，我们假设甲状腺激素受体（TR）亚型调节骨骼肌卫星细胞的承诺和细胞命运的规范在体外和体内。我们的初步观察表明，甲状腺激素受体<$<$（TR <$）在体外和体内的卫星细胞的增殖，并在其分化成肌细胞和脂肪细胞系在体外具有重要的作用。此外，甲状腺激素受体（TR）在脂肪形成分化中起作用，敲低这种表达不会损害卫星细胞增殖， 分化为功能性肌纤维。为了证实和进一步开发这些初步数据，我们计划对来自携带甲状腺激素抗性（RTH）相关TR <$和TR <$突变的小鼠的原代肌肉卫星细胞进行体外研究。我们正在计划几项研究，致力于扩大我们的知识的TR亚型调节肌肉干细胞谱系分配的分子基础。我们将分析与卫星细胞自我更新和分化相关的转录因子以及与Wnt信号通路相关的基因和蛋白表达。随后，我们将评估携带TR <$或<$突变的肌肉卫星细胞移植到预损伤肌肉后的体内分化潜力。此外，我们还将利用遗传学和药理学工具研究TR在骨骼肌损伤反应中的作用。这项研究将深入了解骨骼肌干细胞的命运分配和肌内异位脂肪形成，以及TR亚型在调节这一过程中的可能作用。K 08申请提出了一个详细，全面的培训计划，使申请人能够继续与她的研究和职业目标相关的研究。一个优秀的导师团队将直接监督研究培训的各个角度和研究进展的各个方面。最终目标是申请人利用在此资助期间获得的数据成功申请R 01。这将使申请人成为一个独立资助的医生，科学家在内分泌学领域桥接干细胞研究。

DESCRIPTION (provided by applicant): Stem cells resident in the skeletal muscle play an important role in postnatal muscle growth and regeneration after injury. It has been proposed that skeletal muscle satellite cell fate can be switched from myogenesis to adipogenesis and for this reason contribute to ectopic intra-muscle fat accumulation in several pathological condition such us myopathy, type 2 diabetes, obesity, and age-related sarcopenia. In this proposal we hypothesize that thyroid hormone receptor (TR) isoforms modulate skeletal muscle satellite cell commitment and cell fate specification in vitro and in vivo. Our preliminary observations demonstrate that thyroid hormone receptor ¿ (TR¿) has an important role both in proliferation of satellite cells in vitro and in vivo and in their differentiation to myogenic and adipogenic cell lineages in vitro. In addition thyroid hormone receptor ¿ (TR¿) plays a role in adipogenic differentiation and knocking down this expression does not impair satellite cells proliferation and differentiation into functional myofibers. To confirm and further develop these preliminary data, we plan to conduct in vitro study on primary muscle satellite cells derived from mice carrying a Resistance to Thyroid Hormone (RTH)-associate mutation for TR¿ and TR¿. We are planning several studies devoted to extend our knowledge on molecular basis of TR isoform regulation of muscle stem cell lineage allocation. We will analyze gene and protein expressions associated with transcription factors for self-renewal and differentiation of satellite cell and associated wih Wnt signaling pathway. Subsequently we will evaluate the in vivo differentiation potential of muscle satellite cell carrying a TR ¿ or ¿ mutation after transplantation into preinjured muscles. In addition, we will investigate the role of TR ¿ and ¿ in skeletal muscle response to injury by utilizing both genetic and pharmacologic tools. The work proposed in this grant will provide insight into skeletal muscle stem cell fate allocation and intra-muscle ectopic adipogenesis and the possible role of TR isoforms in modulating this process. The K08 application proposed a detailed, comprehensive training plan that will allow the applicant to pursue studies related to her research and career goals. An outstanding team of mentors will directly oversee the research training in various angles and all the aspects of research in progress. The ultimate goal is for the applicant to leverage the data obtained during this grant period into a successful R01 application. This will then allow the applicant to become an independently-funded physician-scientist in the field of endocrinology bridging stem cell research.