MECHANISMS OF MUSCLE FIBER LENGTH DURING DISTRACTION

描述(改编自申请人的摘要)：可归因于问题 肢体延长过程中对骨骼肌的影响包括肌肉收缩， 关节脱位、轴向偏差和关节刚度。最重要的是 典型的马蹄内肌挛缩症，经常发生在明显的 延长胫骨，需要广泛的日常康复。 据推测，马蹄内肌挛缩症的发生是因为马蹄内肌的纵向生长 足底屈肌的伸展速度落后于胫骨的牵张。这个 本提案的主要目标是解决以下问题的根本基础 马蹄内肌挛缩症的发展：关注以下问题 用法：S调节足底屈肌肌纤维长度的机制 胫骨牵张时的肌肉？要解决这个问题，有三个基本原则 假说将被检验：i)卫星细胞假说；ii) 转录调控假说；以及iii)IGF-1假说。这个 “卫星细胞”假说认为，肌肉纤维的纵向生长 只有在分心时才能通过激活卫星细胞发生。这 假说将在第一阶段通过分散胫骨进行检验，并制作 测量肌肉长度，肌肉纤维长度，肌节长度， 肌节数、肌核、源于卫星细胞的肌核以及 细胞体积/肌核比率。第二阶段的具体目标是测试两者 “卫星细胞”和“转录控制”假说。辐照 将被用来摧毁卫星的有丝分裂能力 细胞。因此，如果卫星细胞激活是 牵张过程中肌肉纤维的纵向生长，然后进行照射 将阻止这一过程的发生。如果纵向的增长 肌肉纤维通过转录上调(即， 转录控制假说)，那么凝胶迁移率改变分析将是 用于识别肌动蛋白启动子的潜在调控元件 对分心的反应，以及作用于这些元素的DNA结合蛋白。 第三阶段的具体目标是测试IGF-1假说，该假说 对骨骼肌施加的渐进性慢性伸展 分心会导致局部IGF-1的增加，从而调节 肌肉纤维的纵向生长，通过卫星细胞激活或 转录上调。这一假设将通过以下方式进行检验：i) 检测分心对局部IGF-1浓度的影响； 和ii)局部输注结合于 IGF-1受体并抑制IGF-1的作用。总而言之，从长远来看 这一建议的目标是提供对因素的机械性理解 牵张过程中肌纤维纵向生长的调节 可以开发干预措施来最大限度地减少所谓 痉挛。

DESCRIPTION (Adapted from the Applicant's Abstract): Problems attributable to skeletal muscle during limb lengthening include muscle contractures, joint luxation, axial deviation, and joint stiffness. Foremost is the classic equinus contracture that frequently occurs with significant lengthening of the tibia, and requires extensive daily rehabilitation. Presumably, the equinus contracture develops because the longitudinal growth of the plantar flexor muscles lags behind the distraction of the tibia. The primary objective of this proposal is to address the underlying basis for the development of the equinus contracture by focusing upon the following use: What mechanism(s) regulates muscle fiber length in the plantar flexor muscles during tibial distraction? To address this issue, three fundamental hypotheses will be tested: i) the satellite cell hypothesis; ii) the transcriptional control hypothesis; and iii) the IGF-1 hypothesis. The "satellite cell" hypothesis states that longitudinal growth of muscle fibers can only occur during distraction by activating satellite cells. This hypothesis will be tested in Phase I by distracting the tibia, and making measurements of muscle length, muscle fiber length, sarcomere length, sarcomere number, myonuclei, myonuclei derived from satellite cells, and cell volume/myonuclei ratio. The specific aim of Phase II is to test both the "satellite cell" and "transcriptional control" hypotheses. Irradiation of the hind limb will be used to destroy the mitotic capacity of satellite cells. Hence, if satellite cell activation is a prerequisite for the longitudinal growth of muscle fibers during distraction, then irradiation will prevent this process from occurring. If the longitudinal growth of muscle fibers occurs via the upregulation of transcription (i.e., the transcription control hypothesis), then gel mobility shift assays will be used to identify potential regulatory elements of the actin promoter that respond to distraction, and DNA binding proteins that act on these elements. The specific aim of Phase III is to test the IGF-1 hypothesis which states that the progressive chronic stretch imposed upon skeletal muscle by distraction will produce a local increase in IGF-1 that mediates the longitudinal growth of muscle fibers either by satellite cell activation or upregulation of transcription. This hypothesis will be tested by: i) examining the effects of distraction on the local concentrations of IGF-1; and ii) local infusion of a monoclonal antibody (MAb) that binds to the IGF-1 receptor and inhibits the action of IGF-1. In summary, the long term goal of this proposal is to provide a mechanistic understanding of factors mediating the longitudinal growth of muscle fibers during distraction so that interventions can be developed to minimize the occurrence of so-called contractures.