Mechanobiology of Progenitor Cells in Heterotopic Ossification

摘要 虽然罕见的遗传性疾病直接影响相对较小的人群，但它们是由以下因素引起的： 基因突变具有如此重要的意义，以至于干扰的功能很少被容忍，因此提供了 对基本细胞机制的独特见解。进行性骨化性纤维发育不良 (FOP)是由细胞命运决定的错误控制导致先天性骨骼畸形 以及通常在组织反应中形成的骨骼外（异位）软骨内骨化（HO） 损伤值得注意的是，这种从头骨形成与受损的肌肉修复反应相关。我们 发现所有具有典型FOP特征的家族性和散发性病例携带相同的杂合子， ACVR 1/ALK 2（R206 H; c.617G>A）突变，ACVR 1/ALK 2是一种介导细胞信号转导的细胞表面受体， 骨形态发生蛋白（BMP）。我们的数据显示ACVR 1 R206 H突变体受体轻度地 在存在或不存在BMP配体的情况下激活BMP信号传导途径。这项建议旨在 确定ACVR 1/BMP信号传导功能的获得如何转移肌肉修复程序， 一个通常以肌肉组织恢复为高潮的过程，一个肌肉损伤导致 内源性间充质祖细胞（MSC）向软骨细胞和成骨细胞的分化， 异位骨组织的形成。先前的研究证实了突变对细胞的自主作用， 然而，当突变增强MSC软骨/成骨时，我们也发现了MSC的分化。 突变细胞不能自发分化，但需要额外的信号。以来 组织驻留祖细胞的定型和分化受来自组织的信号调节 微环境，并且组织微环境本身由这些微环境的基质产生限定。 分化的细胞，这个建议的重点是如何增强BMP通路信号在FOP改变细胞 肌肉修复过程中生物力学环境的解释和制造。根据我们初步的 显示损伤后突变骨骼肌组织改变的物理（机械）性质的数据， 该提案将首先调查和确定机制（细胞结构，基质和刚度）， ACVR 1 R206 H突变组织在对以下疾病的早期反应期间改变结缔组织微环境： 肌肉损伤（目标1）。接下来，我们将研究机械感应信号机制， 软骨/骨间充质（非肌源性）祖细胞（MSC）差异感知和解释 微环境的信号（目标2）。最后，我们将确定突变组织的影响 微环境对内源性肌源性肌肉祖细胞（MuSC，Aim 3）的影响。这些数据将 鉴定在异位骨化中控制细胞分化的新的机械调节机制， 肌肉修复，以及揭示新的目标，为治疗干预，以防止遗传和非- HO的遗传形式和工程组织用于临床应用。

Abstract Although rare genetic disorders directly impact relatively small segments of the population, they are caused by mutations in genes with such critical importance that perturbed function is rarely tolerated, and therefore offer unique insight into fundamental cellular mechanisms. One such disease, fibrodysplasia ossificans progressiva (FOP), is caused by misregulated control of cell fate decisions that leads to congenital skeletal malformations and disabling extra-skeletal (heterotopic) endochondral ossification (HO) that often forms in response to tissue injury. Notably, this de novo bone formation is associated with an impaired muscle repair response. We identified that all familial and sporadic cases with classic features of FOP carry the same heterozygous mutation in ACVR1/ALK2 (R206H; c.617G>A), a cell surface receptor that mediates signal transduction of bone morphogenetic proteins (BMPs). Our data showed that the ACVR1 R206H mutant receptors mildly activate the BMP signaling pathway in the presence or absence of BMP ligands. This proposal seeks to identify how the resulting gain of function in ACVR1/BMP signaling diverts the program of muscle repair from one that normally culminates in restoration of muscle tissue to one in which muscle injury leads to differentiation of endogenous mesenchymal progenitor cells (MSCs) to chondrocytes and osteoblasts and the formation of heterotopic bone tissue. Previous studies confirmed cell autonomous effects of the mutation on MSC differentiation, however, while the mutation enhances MSC chondro/osteogenesis, we have also established that mutant cells do not spontaneously differentiate, but require additional signals. Since commitment and differentiation of tissue-resident progenitor cells is regulated by signals from the tissue microenvironment, and the tissue microenvironment is itself defined by matrix production by these differentiating cells, this proposal focuses on how enhanced BMP pathway signaling in FOP changes cellular interpretation and fabrication of the biomechanical environment during muscle repair. Based on our preliminary data showing altered physical (mechanical) properties of mutant skeletal muscle tissue following injury, this proposal will first investigate and identify the mechanisms (cellularity, matrix, and stiffness) through which ACVR1 R206H mutant tissue alters the connective tissue microenvironment during the early response to muscle injury (Aim 1). Next, we will examine the mechano-sensing signaling mechanisms through which chondro/osseous mesenchymal (non-myogenic) progenitor cells (MSCs) differentially sense and interpret signals from their microenvironment (Aim 2). Finally, we will determine the effects of the mutant tissue microenvironment on endogenous myogenic muscle progenitor cells (MuSCs, Aim 3). Together, these data will identify novel mechano-regulatory mechanisms controlling cell differentiation in heterotopic ossification and muscle repair and as well as reveal new targets for therapeutic interventions to prevent genetic and non- genetic forms of HO and to engineer tissues for clinical application.