Interrelationships between age-related skeletal muscle stem cell and NMJ decline

 描述（由申请人提供）：衰老伴随着骨骼肌大小和功能的逐渐丧失，称为肌肉减少症。作为老年人福尔斯跌倒、虚弱和功能活动性丧失的一个促成因素，与肌肉减少症相关的残疾被认为是美国医疗保健系统的一项新兴成本。与年龄相关的骨骼肌衰退的原因以及因此的治疗策略仍然难以捉摸。肌肉减少骨骼肌的特征包括去神经支配和再神经支配的持续循环、功能性神经肌肉接头（NMJ）的丧失和驻留干细胞（卫星细胞）的耗尽。然而，与年龄相关的卫星细胞和NMJ下降之间的任何相互关系仍然是模糊的。因此，该建议旨在阐明卫星细胞和衍生祖细胞在随年龄退化的NMJ中的命运和作用。此外，我们提出了一种策略，以减轻与年龄相关的NMJ下降的卫星细胞的具体操作。为了实现这些目标，将使用卫星细胞特异性小鼠遗传模型和NMJ的共聚焦免疫荧光成像。我们已经产生了初步的数据，显示在NMJ的突触后肌核的损失与肌纤维类型的转换一致，在老年骨骼肌的神经肌肉中断。在平行的研究中，我们发现卫星细胞是必需的突触后肌核，肌纤维类型的属性和运动神经末梢响应实验性神经肌肉中断成人NMJ的神经支配的维护。最后，我们证明，卫星细胞特异性受体酪氨酸激酶反馈调节剂sprouty1（Spry1）的强制表达足以减弱衰老NMJ突触后肌核的下降。我们将通过评估不同年龄段骨骼肌的NMJ完整性、卫星细胞邻近性、突触后肌核和肌纤维类型特性来巩固我们的初步发现。我们还将评估卫星细胞耗竭和卫星细胞特异性Spry1强制表达对维持NMJ和肌纤维类型特性的影响。这项建议的具体目标是：1）为了鉴定突触后肌核的丧失是否是老化退化NMJ的特征，定义与NMJ衰退相关的年龄相关肌纤维表型转变的调节因子，并检查卫星细胞衍生的对老化NMJ的贡献，2）检查卫星细胞耗竭是否加速NMJ完整性和NMJ调节的肌纤维性质的年龄相关性下降，以及3）确定卫星细胞特异性强制Spry1表达是否减弱突触后肌核、NMJ完整性的丧失，并维持NMJ随年龄调节的肌纤维特性。

 DESCRIPTION (provided by applicant): Aging is accompanied by a gradual loss of skeletal muscle size and function known as sarcopenia. A contributor to falls, frailty and loss in functional mobility in the elderly, disability associated with sarcopenia is considered to be a burgeoning cost to the US healthcare system. The reasons for age-related skeletal muscle decline and hence therapeutic strategies remain elusive. Features of sarcopenic skeletal muscle include ongoing cycles of denervation and reinnervation, loss of functional neuromuscular junctions (NMJs) and depletion of resident stem cells (satellite cells). However, any interrelationship between age-related satellite cell and NMJ decline remains ambiguous. Hence, this proposal is designed to elucidate the fates and roles of satellite cells and derived progenitors at degenerating NMJs with age. In addition, we propose a strategy to attenuate age-related NMJ decline by specific manipulation of satellite cells. To accomplish these objectives satellite cell-specific mouse genetic models and confocal immunofluorescence imaging of NMJs will be used. We have generated preliminary data that show loss of post-synaptic myonuclei at NMJs together with myofiber type transitions consistent with neuromuscular disruption in aged skeletal muscle. In parallel studies, we find satellite cells are required for the maintenance of post-synaptic myonuclei, myofiber type properties and the reinnervation of adult NMJs by motor nerve terminals in response to experimental neuromuscular disruption. Finally, we demonstrate that satellite cell specific forced expression of the receptor tyrosine kinase feedback regulator sprouty1 (Spry1) is sufficient to attenuate decline of post-synaptic myonuclei at aging NMJs. We will solidify our preliminary findings through the assessment of NMJ integrity, satellite cell proximity, post-synaptic myonuclei and myofiber type properties in skeletal muscles of various ages. We will also assess the consequences of satellite cell depletion and satellite cell specific Spry1 forced expression on the maintenance of NMJs and myofiber type properties with age. The specific aims of this proposal are: 1) To identify whether loss of post-synaptic myonuclei is a feature of aged degenerated NMJs, define regulators of age-related myofiber phenotypic transitions connected to NMJ decline and examine satellite cell derived contributions at aging NMJs, 2) To examine if satellite cell depletion accelerates age-related declines in NMJ integrity and NMJ regulated myofiber properties and 3) To determine if satellite cell-specific forced Spry1 expression attenuates loss of; post-synaptic myonuclei, NMJ integrity and maintains NMJ regulated myofiber properties with age.