MECHANISMS OF MUSCLE FIBER LENGTH DURING DISTRACTION

描述（改编自申请人的摘要）：可归因的问题 包括肌肉挛缩， 关节脱位、轴向偏移和关节僵硬。 是最重要的是 典型的马蹄肌挛缩，经常发生， 胫骨延长，需要大量的日常康复。 据推测，马蹄肌挛缩的发展是因为纵向生长 足底屈肌的运动滞后于胫骨的牵引。 的 本提案的主要目标是解决以下问题的根本依据： 马蹄肌挛缩的发展，重点放在以下方面 用途：什么机制调节跖屈肌的肌纤维长度 胫骨牵引时的肌肉 为了解决这个问题，三个基本的 假设将被测试：i）卫星细胞假设; ii） 转录控制假说;和iii）IGF-1假说。 的 “卫星细胞”假说认为， 只有在分散注意力时才会激活卫星细胞 这 将在第一阶段通过牵引胫骨， 测量肌肉长度、肌纤维长度、肌节长度， 肌节数、肌核、来自卫星细胞的肌核，以及 细胞体积/肌核比。 第二阶段的具体目标是测试 “卫星细胞”和“转录控制”假说。 照射 将用于破坏卫星的有丝分裂能力 细胞 因此，如果卫星小区的激活是 牵张过程中肌纤维的纵向生长，然后照射 将阻止这一过程的发生。 如果纵向增长 肌纤维通过转录的上调发生（即，的 转录控制假说），那么凝胶迁移率变动分析将是 用于鉴定肌动蛋白启动子的潜在调控元件， 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假设， 骨骼肌受到的渐进性慢性拉伸 注意力分散会导致IGF-1的局部增加， 肌纤维的纵向生长通过卫星细胞激活或 转录上调。 该假设将通过以下方式进行检验：i） 检查分心对IGF-1局部浓度的影响; 和ii）局部输注结合所述抗体的单克隆抗体（MAb）， IGF-1受体，并抑制IGF-1的作用。 总之，长期 本提案的目的是提供一个机械的理解因素 在牵引过程中调节肌纤维的纵向生长， 可以制定干预措施，以尽量减少所谓的 挛缩

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.