Modulation of Muscle Regenerationby Growth Factors

描述(由申请人提供)：骨骼肌修复是肌肉营养不良、骨质疏松症和废用或急性损伤后肌肉康复的主要治疗目标。因为肌肉纤维是有丝分裂后的，修复必须依赖卫星细胞，卫星细胞是居住在肌肉纤维附近的类似干细胞的群体，作为补充肌肉核内容的来源。卫星细胞的增殖、分化、迁移和融合到损伤部位的能力和效率都是损伤解决的重要步骤。长期以来，IGF-I一直被认为是调节肌肉再生过程中卫星细胞活动的关键因素之一，有助于修复受损的纤维区域，并促进肌肉生长。现在人们对IGF1基因产生的其他潜在活性多肽的特征越来越感兴趣。基因的选择性剪接导致多种异构体，这些异构体保留了成熟IGF-I的相同序列，但也产生了不同的C末端序列，称为E-肽。我们实验室的最新证据表明，E-肽延伸直接调节肌肉修复的关键步骤。首先，啮齿动物的EA和EB多肽刺激培养中的肌肉细胞增殖，潜在地增加了可用于修复的卫星细胞的数量。其次，EA多肽在分化过程中促进了IGF-I的表达和分泌。第三，EB肽以独立于IGF-I的方式调节基质金属蛋白酶的表达，特别是基质金属蛋白酶-13的表达。在其他组织类型中，基质金属蛋白酶-13活性是伤口愈合、骨重塑和肿瘤侵袭的关键调节因子，也是额外基质金属蛋白酶活性的调节器。因此，基质金属蛋白酶-13可能通过促进卫星细胞在细胞外基质中的迁移，以及通过协调新形成的肌肉纤维周围的基质重塑来促进肌肉修复。对肌肉再生过程中基质金属蛋白酶-13表达的初步测量表明，在纤维开始形成后的修复后期，基质金属蛋白酶-13的表达水平升高。此外，在MDX小鼠的肌肉中，基质金属蛋白酶-13的表达更高，缺乏肌营养不良蛋白会导致退化和再生周期的增加。这些研究表明，基质金属蛋白酶-13是肌肉修复的重要组成部分。这项资助的目标是(1)确定基质金属蛋白酶-13是否可以加速与遗传病和急性损伤相关的肌肉损伤的适当解决，以及(2)了解胰岛素样生长因子-I、E肽和基质金属蛋白酶-13活性之间的功能联系。了解它们的作用机制是至关重要的，这样才能根据它们的功能开发促进修复的疗法。 公共卫生相关性：骨骼肌修复发生在急性损伤后，是与遗传性肌肉疾病相关的持续症状，特别是在肌肉营养不良症中。因此，促进肌肉再生的疗法可以使遗传病患者、肌肉损伤恢复者和老年人受益。了解肌肉再生的机制是至关重要的，这样才能开发新的药物来帮助修复过程。

DESCRIPTION (provided by applicant): Skeletal muscle repair is a central therapeutic target for the muscular dystrophies, sarcopenia, and muscle rehabilitation after disuse or acute injury. Because muscle fibers are post-mitotic, repair must rely on satellite cells, a stem cell-like population residing close to muscle fibers as a source for replenishing nuclear content of the muscle. The ability and efficiency of satellite cell proliferation, differentiation, migration, and fusion to sites of injury are all important steps in the resolution of damage. IGF-I has long been recognized as one of the critical factors for regulating satellite cell actions during muscle regeneration, helping to repair damaged regions of the fibers, and to promote muscle growth. There is now a growing interest in the characterization of additional potentially active peptides produced by the igf1 gene. Alternative splicing of the gene results in multiple isoforms that retain the identical sequence for mature IGF-I, but also give rise to divergent C-terminal sequences, called the E-peptides. Recent evidence from our lab demonstrates that the E- peptide extensions directly regulate critical steps in muscle repair. First, the rodent EA and EB peptides stimulate proliferation of muscle cells in culture, potentially increasing the number of satellite cell available for repair. Second, the EA-peptide enhances expression and secretion of IGF-I during differentiation. Third, the EB-peptide regulates expression of matrix metalloproteinases, specifically MMP-13 in an IGF-I independent manner. In other tissue types, MMP-13 activity is a key regulator of wound healing, bone remodeling, and tumor invasion, as well as a modulator of additional MMP activity. Therefore, MMP-13 may improve muscle repair by enhancing satellite cell migration through the extracellular matrix, and by coordinating matrix remodeling around newly formed muscle fibers. Preliminary measurements of MMP-13 expression during muscle regeneration show that it is elevated during later stages of repair after fibers have begun to form. Further, MMP-13 expression is higher in muscles from the mdx mouse, where the absence of dystrophin leads to increased cycles of degeneration and regeneration. These studies suggest that MMP-13 is important component of muscle repair. The goals of this grant are (1) to determine if MMP-13 can accelerate proper resolution of muscle damage associated with genetic disease and after acute injury, and (2) to understand the functional links between IGF- I, the E peptides and MMP-13 activity. The mechanisms underlying their actions are essential to understand so that repair-enhancing therapies based on their functions can be developed. PUBLIC HEALTH RELEVANCE: Skeletal muscle repair occurs after acute injury and is an ongoing symptom associated with genetic muscle disease, specifically in the muscular dystrophies. Therefore, the therapies that enhance muscle regeneration can benefit patients suffering from genetic disease, those recovering from muscle injury, and the elderly. Understanding the mechanisms underlying muscle regeneration is of primary importance so that new agents can be developed to aid in the repair process.