SP cells and downstream progenitors in human and mouse muscle

描述（申请人提供）：肌卫星细胞是骨骼肌中研究最多的细胞。它们满足组织特异性干细胞的许多要求，包括自我更新和分化成多种细胞类型的能力。除了卫星细胞外，还从人类和小鼠骨骼肌中分离出了其他肌源性祖细胞。这些“替代”肌原性祖细胞与卫星细胞不同，许多与微血管或肌纤维间质间隙有关。这些“替代”的肌源性细胞群之一是所谓的“侧群”（SP）。我们在人类肌肉中的研究表明，SP细胞分泌因子（如BMP4），诱导表达这些因子受体（bmp -受体1a， BMPR1a）的肌源性祖细胞增殖。在目前的应用中，我们将阐明人类肌肉SP细胞与BMPR1a+祖细胞之间的联系，研究肌肉SP细胞中BMPR1a的强制表达是否会导致它们的激活和对肌源性谱系的承诺，研究表达Myf5或Pax3的骨骼肌祖细胞中BMPR1a+表达的缺失是否会导致肌肉病理。并在小鼠模型中确定肌肉SP细胞或BMPR1a+祖细胞是否是具有内在高复制能力的“干细胞”样细胞。这些涉及人类和小鼠细胞的研究的具体目的是：目的1：确定人类肌肉SP细胞是否是BMPR1a+肌源性祖细胞的“祖先”；目的2：评估在人肌肉SP细胞中强制表达BMPR1a是否必要且足以诱导其增殖并向肌源性谱系分化；目的3：研究BMPR1a+Myf5+或BMPR1a+Pax3+祖细胞是否对肌肉发育和参与产后肌肉再生有重要作用；目的4：利用m-TERT GFP模型鉴定骨骼肌中表达端粒酶的细胞，并确定其与肌肉SP、BMPR1a+细胞或其他肌肉“干细胞”的关系。这些研究将揭示BMPR1a在肌肉祖细胞中的表达功能，揭示人肌肉SP与BMPR1a表达细胞之间的关系。小鼠和人类研究将相互协同，以确定两种物种中每种肌生成细胞群的意义和重要性。公共卫生相关性：骨骼肌是由不分裂的大型成熟肌肉细胞（肌纤维）和具有分裂和形成新肌肉能力的单个核细胞组成的组织。近年来，人们已经清楚地认识到，肌肉中的单个核细胞是不均匀的。这些异质的单核细胞也可以通过使用特殊的信号来触发它们分裂或成为成熟肌肉的能力来相互交流。在目前的应用中，我们将研究人类肌肉中干细胞样细胞与其他肌源性祖细胞之间的联系。我们将确定其中一些单核细胞是否是其他细胞的祖先，并确定具有长期复制能力的细胞是否可以从人类和小鼠肌肉中分离出来。这些研究的广泛目标是能够识别和选择人类肌肉中的“干细胞”，这些干细胞可能对肌肉疾病的治疗有用。

DESCRIPTION (provided by applicant): Muscle satellite cells are the most studied cells in skeletal muscle. They fulfill many of the requirements of tissue-specific stem cells, including the ability to self-renew and to differentiate into multiple cell types. In addition to satellite cells, other myogenic progenitors have been isolated from both human and mouse skeletal muscle. These 'alternative' myogenic progenitors are distinct from satellite cells and many appear associated to the microvasculature or in the interstitial spaces between myofibers. One of these 'alternative' myogenic cell populations is the so-called 'side population' (SP). Our studies in human muscle have proposed that SP cells secrete factors (such as BMP4) that induce the proliferation of myogenic progenitors expressing receptors for these factors (BMP-receptor 1a, BMPR1a). In the current application, we will elucidate the ties between human muscle SP cells and BMPR1a+ progenitors, study whether forced expression of BMPR1a in muscle SP cells leads to their activation and commitment to the myogenic lineage, investigate if loss of BMPR1a+ expression in skeletal muscle progenitors expressing Myf5 or Pax3 will lead to muscle pathology, and determine in a mouse model whether muscle SP cells or BMPR1a+ progenitors are 'stem'-like cells with intrinsic high-replicative capacity. The Specific Aims of these studies, which involve both human and mouse cells, are: Aim 1: Determine if human muscle SP cells are 'ancestors' of BMPR1a+ myogenic progenitors; Aim 2: Assess if forced expression of BMPR1a in human muscle SP cells is necessary and sufficient to induce their proliferation and specification towards the myogenic lineage; Aim 3: Investigate if BMPR1a+Myf5+ or BMPR1a+Pax3+ progenitors are important for muscle development and participate in muscle regeneration in post-natal life; Aim 4: Use the m-TERT GFP model to identify telomerase-expressing cells in skeletal muscle and determine their relationship to muscle SP, BMPR1a+ cells or other muscle 'stem' cells. These studies will unveil the function of BMPR1a expression in muscle progenitors and unravel the relationship between human muscle SP and BMPR1a-expressing cells. Mouse and human studies will synergize with one another, to define the significance and importance of each myogenic cell population in both species. PUBLIC HEALTH RELEVANCE: Skeletal muscle is a tissue composed of large mature muscle cells that are non-dividing (myofibers) and of mononuclear cells, which have the ability to divide and form new muscle. In recent years, it has become clear that the mononuclear cells in muscle are not homogeneous. These heterogeneous mononuclear cells may also communicate with one another by using special signals that trigger their ability to divide or to become mature muscle. In the present application we will study the ties between stem-like cells and other myogenic progenitors in human muscle. We will define whether some of these mononuclear cells are ancestors of others, and determine if cells that have long-replicative capacity can be isolated prospectively from human and mouse muscles. The broad objective of these studies is to be able to identify and select 'stem' cells in human muscle that may be useful for therapy of muscle disorders.