Function of Fibro-Adipogenic Progenitors in Heterotopic Ossification of Skeletal Muscle

项目摘要 异位骨化（HO）是骨骼肌和相关软组织中骨的形成， 由外伤或疾病引起的。HO的最极端形式表现在罕见的常染色体- 显性遗传性疾病，进行性骨化性纤维发育不良（FOP），其中HO持续进行性 这对健康和预期寿命造成了毁灭性的影响。我们开发了一种新的基因模型 FOP基于致病BMP受体Acvr 1（R206 H）的条件表达。利用这个模型， 我们鉴定了成纤维脂肪祖细胞（FAP），一种肌肉组织中的多能间充质祖细胞， 致病细胞群。值得注意的是，我们已经表明，肌肉注射BMP 2到野生型， 小鼠也导致FAP衍生的HO，表明FOP患者中HO发病机制的相似性， 普通民众。HO的研究几乎完全集中在骨生长的机制上，但严重的 肌肉损失可能是患者发病率的重要影响因素。本组织的总体目标 研究是为了1）了解FAP编程如何被病理性骨形成破坏; 2） 了解如何在骨骼肌再生抑制HO敏感; 3）确定是否HO的 骨骼肌完全依赖于FAP。通过使用PdgrfαCreER将Acvr 1 R206 H表达靶向FAP 和Tie 2-Cre驱动程序，Aim 1将量化再生损伤，并将确定肌肉干细胞是否 （卫星细胞; SC）功能障碍是再生缺陷的原因。这些研究将量化SC增殖 和肌肉损伤后的细胞凋亡，并将定义SC mRNA转录组。目标1还将确定是否 FAP中的Acvr 1（R206 H）表达破坏FAP-SC相互作用。Aim 2将使用RNA-Seq来定义FAP 在损伤后的早期、关键时间，检测转录组，以鉴定Acvr 1（R206 H）信号传导的基因靶标。格罗塞克 （全基因组运行）分析将量化活性基因转录的变化， 调节启动子近端聚合酶暂停，并将确定潜在的增强子靶点， Acvr 1（R206 H）信号传导。谱系追踪将确定是否异常肌肉环境差异 影响正常和突变型FAP的命运。在目标3中，DTA消融方法将确定FAP是否 是肌肉中成骨细胞的唯一来源，这些信息对于评估可能的疗效至关重要 细胞特异性疗法激活素抑制最近已成为FOP的一种强大的潜在疗法。目标4 将使用谱系追踪来解决激活素阻断如何影响增殖，存活和发育能力 FAP和SC。RNA-Seq将定义激活素抑制使FAP和SC“正常化”的程度。 转录组拟议的研究将大大有助于了解细胞和细胞 负责HO的相互作用和相关的肌肉再生抑制，并可能导致 开发基于细胞的治疗策略。

Project Summary Heterotopic ossification (HO), the formation of bone in skeletal muscle and associated soft tissues, can result from traumatic injury or disease. The most extreme form of HO is manifested in the rare, autosomal- dominant genetic disorder, Fibrodysplasia ossificans progressiva (FOP), in which HO continues progressively throughout life, resulting in devastating effects on health and life expectancy. We developed a new genetic model of FOP based on conditional expression of the disease-causing BMP receptor, Acvr1(R206H). Using this model, we identified fibro-adipogenic progenitors (FAPs), a multipotent mesenchymal progenitor in muscle tissue, as the disease-causing cell population. Notably, we have shown that intramuscular injection of BMP2 into wild type mice also leads to FAP-derived HO, suggesting mechanistic similarities of HO pathogenesis in FOP patients and the general population. Studies of HO have focused almost entirely on mechanisms of bone growth, yet severe muscle loss can be a significant contributing factor to patient morbidity. The overarching objectives of this research are to 1) understand how FAP programming becomes subverted for pathological bone formation; 2) understand how regeneration is inhibited in skeletal muscle susceptible to HO; 3) determine whether HO of skeletal muscle is entirely dependent on FAPs. By targeting Acvr1R206H expression to FAPs using PdgrfαCreER and Tie2-Cre drivers, Aim 1 will quantify regeneration impairment, and will determine whether muscle stem cell (satellite cell; SC) dysfunction is responsible for regeneration deficits. These studies will quantify SC proliferation and apoptosis after muscle injury and will define the SC mRNA transcriptome. Aim 1 will also determine whether Acvr1(R206H) expression in FAPs disrupts FAP-SC interactions. Aim 2 will use RNA-Seq to define the FAP transcriptome at early, critical, times after injury to identify gene targets of Acvr1(R206H) signaling. Gro-Seq (Genome-wide Run-On) analyses will quantify changes in active gene transcription, will identify candidate genes regulated by promoter-proximal polymerase pausing, and will identify potential enhancer targets of Acvr1(R206H) signaling. Lineage tracing will determine whether the abnormal muscle environment differentially affects the fate of normal and mutant FAPs. In Aim 3, DTA ablation approaches will determine whether FAPs are the sole source of osteogenic cells in muscle, information that is essential for evaluating the possible efficacy of cell-specific therapies. Activin inhibition has recently emerged as a powerful potential therapy for FOP. Aim 4 will use lineage tracing to address how Activin blockade affects proliferation, survival and developmental capacity of FAPs and SCs. RNA-Seq will define the extent to which Activin inhibition “normalizes” FAP and SC transcriptomes. The proposed research will contribute significantly to an understanding of the cells and cellular interactions responsible for HO and associated inhibition of muscle regeneration, and may lead to the development of strategies for cell-based therapies.