BCL-2 AND SKELETAL MUSCLE STEM CELLS

成熟骨骼肌的生长或修复依赖于一个小的， 一种被称为卫星细胞的肌源性细胞群特征不明确 由于它们的位置在肌纤维的外围和 周围的基底层。 由生长因子、压力或 损伤后，这些正常静止的细胞增殖、分化， 成为长寿肌肉纤维的稳定部分。 卫星细胞是 对肌肉内稳态至关重要，并对肌肉有直接影响 修复、疾病进展和衰老。 只有一小部分卫星 细胞具有肌肉干细胞的特征。 干细胞可以 两种成肌细胞，它们在有限数量的 分裂，以及更多的自我更新的干细胞，保持高水平的细胞分裂。 扩散潜力 静止的肌肉干细胞很难 由于其数量稀少和缺乏定义的生化研究， 或分子特征。 拟议研究的目的是 识别肌肉干细胞的特征，并利用这些特征 研究干细胞在肌肉生长和修复中的作用， 与肌营养不良症相关的退化。 最近 研究表明，抑制凋亡细胞死亡的蛋白质，如 Bcl-2在各种组织中发现的自我更新干细胞中表达， 组织如皮肤上皮和肠。 我们发现， 在体外生长的一小部分肌源性细胞表达Bcl-2， 与它们作为肌源性干细胞的行为模式一致。 在 此外，我们发现来自Bcl-2缺陷动物的卫星细胞 产生的肌肉群比它们的 野生型兄弟姐妹 为了扩展这些观察，肌肉细胞将被 检查，在体外和体内，以确定是否Bcl-2 表达是肌肉干细胞的特征。凋亡相关 还将在mdx小鼠中研究基因表达（Bcl-2等）， 杜氏肌营养不良症的模型，其中肌肉经历 急性期的退化，广泛的干细胞活化和修复。 转基因小鼠将被制造出来，它们表达由肌肉驱动的Bcl-2， 特异性MRF 4启动子。 这些小鼠将与mdx小鼠交配， 确定过表达的Bcl-2是否可以抑制肌肉变性， 影响患病肌肉中存在的干细胞群体的大小。 总之，结果应有助于识别肌干 细胞，并确定肌肉生长中凋亡调节因子的作用 和体内平衡。 这些信息将大大有助于我们 了解肌肉生物学，并可能导致新的治疗 治疗肌肉疾病，肌肉萎缩和更好的策略 基于肌肉的基因治疗方法。

The growth or repair of mature skeletal muscle relies upon a small, poorly characterized population of myogenic cells termed satellite cells due to their location peripheral to muscle fibers and beneath the surrounding basal lamina. Activated by growth factors, stress or injury, these normally quiescent cells proliferate, differentiate, and become a stable part of long-lived muscle fibers. Satellite cells are critical for muscle homeostasis and have a direct impact on muscle repair, disease progression, and aging. Only small subsets of satellite cells have characteristics of muscle stem cells. Stem cells give rise to both myoblasts, which differentiate after a limited number of divisions, as well as more self-renewing stem cells that maintain a high proliferation potential. Quiescent muscle stem cells are difficult to study due to their sparse number and the lack of defining biochemical or molecular features. The objective of the proposed research is to identify characteristic features of muscle stem cells, and use these to study the role of stem cells in muscle growth and repair, particularly with respect to degeneration associated with muscular dystrophy. Recent work suggests that proteins that inhibit apoptotic cell death, such as Bcl-2, are expressed in self-renewing stem cells found in various tissues such as skin epithelium and intestine. We have found that a small subset of myogenic cells grown in vitro expresses Bcl-2 in a pattern consistent with them acting as myogenic stem cells. In addition, we found that satellite cells from Bcl-2-deficient animals give rise to muscle colonies that are significantly smaller than their wild-type siblings. To extend these observations, muscle cells will be examined, both in vitro and in vivo, to determine whether Bcl-2 expression is a characteristic of muscle stem cells. Apoptosis-related gene expression (Bcl-2, and others) will also be studied in mdx mice, a model for Duchenne muscular dystrophy in which muscles undergo an acute phase of degeneration, extensive stem cell activation and repair. Transgenic mice will be made which express Bcl-2 driven by the muscle- specific MRF4 promoter. These mice will be mated with mdx mice to determine if overexpressed Bcl-2 can inhibit muscle degeneration or affect the size of stem cell populations present in diseased muscle. In summary, results should facilitate identification of muscle stem cells and determine the role of apoptosis regulators in muscle growth and homeostasis. Such information will significantly contribute to our understanding of muscle biology, and may lead to new therapeutic strategies for treatment of muscle disorders, muscle atrophy and better methods for muscle-based gene therapy.