Mechanisms regulating normal and ectopic endochondral ossification

软骨内骨化是长骨、肋骨、椎骨和其他骨骼 元素在胚胎发生和出生后形成和生长。在此过程中，前间充质 细胞凝聚并分化成软骨原纤维，为细胞的形成提供模板和框架。 未来的骷髅在这些初始结构中，软骨细胞在生长板中变得有组织， 经历成熟和肥大，并为软骨内骨形成铺平道路。这一关键的多- 在大多数骨折的愈合过程中，重复了一个渐进过程，但在病理学中， 异位骨化HO包括软骨内骨的形成，其在异位位置形成并积累， 它会导致许多健康问题。HO的一种形式是常见的和非遗传的，并且由以下因素触发： 创伤、侵入性手术和随之而来的炎症。HO是一种先天性、严重且往往致命的形式， 由局部发作引发，并由编码I型骨的ACVR 1中的激活突变驱动 形态发生蛋白（BMP）受体ALK 2。直到最近，获得性和先天性HO的形式是 认为它们遵循相同的致病级联，因为它们都涉及初始炎症阶段和炎症反应。 随后的软骨内发育过程。然而，其他人最近的研究表明，先天性HO是由 通过激活素A，通常是BMP/经典信号传导的拮抗剂，然而，在这种情况下， 与突变ALK 2结合并引发pSMAD 1/5/8信号传导。如果正确的话，这些数据将意味着遗传和非遗传 HO的遗传形式是不同的过程，可以通过它们在细胞中被触发的方式来区分。 水平，可能需要不同的治疗。因为我们长期以来一直致力于研究遗传性 和非遗传形式的HO和既得利益，我们进行了初步研究，以进一步评估 这些最近的研究。我们发现，激活素A实际上在非遗传和遗传性肿瘤中都有大量表达， 在小鼠模型中，HO极大地刺激野生型前间充质细胞中的软骨形成， 促进野生型小鼠中的HO。这些和其他数据导致这个项目的中心前提， HO的遗传和非遗传形式涉及激活素A并由激活素A促进。遗传性疾病的严重程度 HO可能是由于突变的软骨祖细胞对激活素A的反应性更强， 突变的ALK 2信号传导和作用，但HO的非遗传和遗传形式都将服从于突变的ALK 2信号传导和作用。 基于抗激活素A的治疗。我们的目的是：（1）阐明激活素A的作用机制， 软骨形成;（2）确定激活素A受体组成和细胞表面动力学;和（3） 基因测试激活素A在HO中的作用及其作为治疗靶点的有用性。我们预计该项目将 为遗传和非遗传形式的HO的发病机制提供了新的见解， 对软骨内骨化调节的基本认识。它还将提供一个跳板， 在儿童和成人中用于HO的有效通用疗法。

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.