Physiology of Thyroid Hormone-Dependent Gene Expression

 描述(申请人提供)：甲状腺激素对骨骼肌的发育、再生和功能有重要影响。甲状腺激素受体-1是肌肉T3作用的主要介导者，在转录水平上调节许多重要的基因，包括SERCAA1和A2、UCP3和GLUT 4，以及肌肉分化因子Mygenin和MyoD1.循环中的T3通过特定的转运蛋白如MCT8和10进入心肌细胞，但我们在本授权的最后一个周期中已经证明，细胞T3的很大一部分是由2型碘甲状腺原氨酸脱碘酶(D2)催化的T4在细胞内的单脱碘所产生的。虽然成熟的肌细胞是稳定的，但骨骼肌具有强大的再生机制，在损伤后明显加速。这涉及到卫星细胞、肌肉干细胞的等价物、许多不同类型的细胞的协同作用，这些细胞定位于肌肉干细胞生态位，包括常驻基质纤维/成脂前体细胞(FAP)、T调节细胞和巨噬细胞。这些细胞产生许多促进肌肉生长的细胞因子和生长因子，包括Notch、Wnt/-catenin、Sonic Hedgehog、IL-4和IL-6，以及一些转化生长因子-家族成员等。在最后一次资助期间，我们证明了局部甲状腺激素代谢介导的甲状腺激素变化在这些信号级联中起着重要作用。我们发现，肌肉损伤后，3型碘甲状腺原氨酸脱碘酶(D3)对甲状腺激素的急性失活是必要的，以促进卫星 细胞增殖和阻止过早分化，否则将导致细胞凋亡。这 紧随其后的是2型脱碘酶(D2)介导的T4激活，这对于卫星细胞分化为成熟的成肌细胞至关重要，然后是肌纤维完成正常的肌肉再生程序。在使用基因敲除小鼠模型的研究中，我们发现D2的D3的缺失显著阻碍了损伤后的肌肉修复。利用卫星细胞移植治疗的小鼠模型，我们进一步表明D2激活的局部甲状腺激素在移植的肌肉干细胞的植入中起着至关重要的作用。在这次更新中，我们建议将使用我们独特的小鼠基因敲除模型的研究与建立的特定细胞类型的FACS分类分离相结合。我们将研究为什么D2是移植的卫星细胞存活和成功形成肌管所必需的，D3和D2在损伤后卫星细胞和肌肉干细胞生态位的其他组成部分是如何变化的，肌肉干细胞生态位中其他类型细胞的协调反应是否需要脱碘酶，以及这一过程的失调如何导致纤维化。这将扩大我们对甲状腺激素对肌肉再生的贡献的认识，并为骨骼肌损伤患者的潜在治疗策略奠定基础。

 DESCRIPTION (provided by applicant): Thyroid hormone has major effects on the development, regeneration and function of skeletal muscle. Thyroid hormone receptor 1 is the predominant mediator of muscle T3 action, and transcriptionally regulates a number of important genes including SERCA A1 and A2, UCP 3 and GLUT 4, as well as the muscle differentiation factors myogenin and MyoD1. Circulating T3 enters myocytes via specific transporters such as MCT8 and 10, but we have shown in the last cycle of this grant that a significant fraction of cellular T3 is generated by the intracellular monodeiodination of T4 catalyzed by the type 2 iodothyronine deiodinase (D2). While mature myocytes are stable, skeletal muscle has a robust regenerative mechanism that is markedly accelerated following injury. This involves the concerted actions of satellite cells, the muscle stem cell equivalent, an a number of different cell types localized to the muscle stem cell niche including resident stromal fibro/adipogenic progenitors (FAPs), T-regulatory cells, and macrophages. These cells produce a number of pro-myogenic cytokines and growth factors that that are necessary to coordinate the regeneration process including Notch, Wnt/-catenin, sonic hedgehog, IL-4 and IL-6, and a number of TGF-family members among others. During the last grant period, we showed that changes in thyroid hormone mediated by local thyroid hormone metabolism play an important role in these signaling cascades. We found that after muscle injury acute inactivation of thyroid hormone by the type 3 iodothyronine deiodinase (D3) is necessary to facilitate satellite cell proliferation and block premature differentiation that otherwise would lead to apoptosis. This is followed by increased type 2 deiodinase (D2)-mediated T4 activation that is essential for the satellite cell to differentiate into mature myoblasts and then myofibers to complete the normal muscle regeneration program. In studies employing gene knockout mouse models, we have found that a loss of either D3 of D2 dramatically impedes muscle repair after injury. Using a murine model of satellite cell transplantation therapy, we further showed that local thyroid hormone activation by D2 plays a crucial role in the engraftment of transplanted muscle stem cells. In this renewal, we propose to combine studies using our unique mouse knockout models and established FACS-sorting isolation of specific cell types. We will investigate why D2 is required for engrafted satellite cell survival and successful myotube formation, how D3 and D2 change after injury in satellite cells and other components of the muscle stem cell niche, whether deiodinases are required for the coordinated responses of other cell types in the muscle stem cell niche, and how dysregulation of this process may lead to fibrosis. This will expand our knowledge of the contributions of thyroid hormone to muscle regeneration and form the basis for potential therapeutic strategies for patients with skeletal muscle injuries.