Mechanisms regulating normal and ectopic endochondral ossification

软骨内骨化是长骨、肋骨、椎骨和其他骨骼的过程 元素在胚胎发生和出生后形成和生长。在此过程中，前骨骼间充质 细胞凝结并分化成软骨原基，为软骨细胞提供模板和框架 未来的骨架。在这些初期结构中，软骨细胞在生长板中组织起来， 经历成熟和肥大，为软骨内骨形成铺平道路。这个关键的多 步骤过程在大多数骨折的愈合中都有体现，但也可能在以下疾病中被篡改： 异位骨化。 HO 由软骨内骨的形成组成，软骨内骨在异位形成并积累 场所并导致许多健康问题。 HO 的一种形式是常见且非遗传性的，由以下因素触发 创伤、侵入性手术和随之而来的炎症。一种先天性、严重且常常致命的 HO 形式是 由局部突发引发，并由编码 I 型骨的 ACVR1 的激活突变驱动 形态发生蛋白 (BMP) 受体 ALK2。直到最近，获得性和先天性 HO 的形式仍然是 鉴于它们都涉及初始炎症阶段和最终阶段，因此被认为遵循相同的致病级联 随后的软骨内过程。然而，其他人最近的研究表明，先天性 HO 是由 激活素 A 通常是 BMP/规范信号传导的拮抗剂，但在这种情况下，会相互作用 突变 ALK2 并引发 pSMAD1/5/8 信号传导。如果正确，数据将意味着遗传和非 HO 的遗传形式是不同的过程，可通过它们在细胞中触发的方式来区分 水平，可能需要不同的治疗方法。因为我们长期致力于遗传发病机制的研究 和非遗传形式的 HO 并具有既得利益，我们进行了初步研究以进一步评估 那些最近的研究。我们发现激活素 A 实际上在非遗传性和遗传性中大量表达 在小鼠模型中，H2O 极大地刺激野生型前骨骼间充质细胞的软骨形成，并且 促进野生型小鼠的 HO。这些数据和其他数据引出了该项目的中心前提： HO 的遗传和非遗传形式涉及激活素 A，并由激活素 A 促进。 HO 是由于突变软骨祖细胞对激活素 A 和不规则的反应性更强而导致的 突变的 ALK2 信号传导和作用，但 HO 的非遗传和遗传形式都适合 基于抗激活素 A 的治疗。我们的目标是： (1) 阐明激活素 A 的作用机制 软骨形成； (2) 测定激活素A受体组成和细胞表面动力学； (3) 至 对激活素 A 在 HO 中的作用及其作为治疗靶点的有用性进行基因测试。我们预计该项目将 为遗传性和非遗传性 HO 的发病机制提供新的见解，并提供基础研究 软骨内骨化调节的基本见解。它还将为我们提供一个跳板 对儿童和成人 HO 有效的通用疗法。

Endochondral ossification is the process by which long bones, ribs, vertebrae and other skeletal elements form and grow during embryogenesis and after birth. During this process, preskeletal mesenchymal cells condense and differentiate into cartilaginous anlaga that provide the template and framework of the future skeleton. Within these incipient structures, the chondrocytes become organized in growth plates, undergo maturation and hypertrophy, and pave the way for endochondral bone formation. This critical multi- step process is recapitulated in healing of most bone fractures, but can also be usurped in pathologies such as heterotopic ossification. HO consists of formation of endochondral bone that forms and accumulates at ectopic sites and causes many health problems. One form of HO is common and non-genetic and is triggered by trauma, invasive surgeries and ensuing inflammation. A congenital, severe and often fatal form of HO is initiated by local flare-ups and is driven by activating mutations in ACVR1 encoding the type I bone morphogenetic protein (BMP) receptor ALK2. Up until recently, the acquired and congenital forms of HO were thought to follow the same pathogenic cascade given that they both involve an initial inflammatory stage and a subsequent endochondral process. However, recent studies by others suggested that congenital HO is caused by activin A, normally an antagonist of BMP/canonical signaling that in this condition, however, would interact with mutant ALK2 and elicit pSMAD1/5/8 signaling. If correct, the data would imply that genetic and non- genetic forms of HO are distinct processes distinguishable by the manner in which they are triggered at cell level and may require distinct therapies. Because we have long been working on the pathogenesis of genetic and non-genetic forms of HO and have a vested interest, we carried out preliminary studies to further assess those recent studies. We found that activin A is actually abundantly expressed in both non-genetic and genetic HO in mouse models, greatly stimulates chondrogenesis in wild type preskeletal mesenchymal cells, and promotes HO in wild type mice. These and other data lead to the central premise of this project that both genetic and non-genetic forms of HO involve, and are promoted by, activin A. The greater severity of genetic HO would result from greater responsiveness of mutant chondrogenic progenitors to activin A and unruly mutant ALK2 signaling and action, but both non-genetic and genetic forms of HO would be amenable to an anti-activin A-based therapy. Our Aims are: (1) To clarify the mechanisms of activin A action in chondrogenesis; (2) To determine activin A receptor composition and cell surface dynamics; and (3) To genetically test the roles of activin A in HO and its usefulness as a therapy target. We anticipate this project will provide novel insights into the pathogenesis of genetic and non-genetic forms of HO and also fundamental basic insights into the regulation of endochondral ossification. It will also provide a springboard toward an effective universal therapy for HO in both children and adults.