BMP2 Regulation of Periosteal Function

摘要 骨膜是骨外表面上高度特化的组织微环境，在骨形成中具有关键作用。 确保独特的常驻干/祖细胞群体的存活和自我更新， 负责并置骨形成和骨折修复。破坏骨膜功能的损伤是 常见，在美国每年发生1200 - 1500万例骨折，导致1800万例医生就诊和结果 损失了6000万个工作日。虽然大多数骨折愈合成功，在很大程度上是由于先天性的 再生能力的骨膜，愈合缓慢，无效（不愈合）超过5%的 对于发生在负重长骨中的骨折， 对机动性至关重要。顽固性骨折的治疗具有挑战性，目前的治疗方法 不可预测的结果，每年造成近60万患者严重残疾。不可预测 在创伤或肿瘤中大面积骨缺损的修复过程中， 切除并需要骨移植;每年进行的500，000例骨移植手术中几乎有一半 随着时间的推移而失败，很大程度上是由于缺乏协调新骨形成的活骨膜细胞 成功地将移植物与宿主骨结合我们发表的工作将BMP 2鉴定为一种有效的 骨膜功能的生理调节器。在Prx 1+干/祖细胞中缺乏BMP 2表达的小鼠 在所有已知的骨膜活动中表现出严重的缺陷。在缺乏BMP 2的情况下，骨骼不能在宽度上生长。 与它们的长度增长成比例，产生结构不稳定性，导致自发断裂;一旦 骨折时，骨膜不能启动修复，不能支持骨移植物结合。此外，本发明还提供了一种方法， 用合成代谢剂如间歇性PTH或抗sclerostin抗体治疗不能刺激皮质 在没有骨膜BMP 2的情况下的骨形成。因此，我们假设， 骨膜龛内Bmp 2的时空表达模式构成了一个重要的 机制决定活跃与静止状态的骨膜在整个出生后的生活。我们 建议3旨在验证这一假设。在目标1中，我们将验证在一个 最近完成的骨膜RNAseq作为沉积过程中BMP 2信号传导的下游介质 生长和骨折修复。在目标2中，我们将研究BMP 2驻留在ECM中的要求， 附着骨生长过程中骨膜龛与骨膜细胞产生的BMP 2。在目标3中，我们 确定增加骨膜细胞产生的内源性BMP 2是否有利于骨膜功能。 这些研究的完成将导致对细胞和分子生物学的更深入的了解。 在骨膜干/祖细胞中，BMP 2信号转导协调机制，并应导致 开发用于增强骨修复的新疗法。通过这项提议获得的知识也有 增加针对骨膜的合成代谢剂的效用以预防骨折的潜力。

Abstract The periosteum, a highly specialized tissue microenvironment on the outer surface of bone, has a key role in ensuring the survival and self-renewal of a unique population of resident stem/progenitor cells that are responsible for appositional bone formation and fracture repair. Injuries that disrupt periosteal function are common, with 12-15 million fractures occurring yearly in the US that lead to 18 million doctor’s visits and result in 60 million workdays lost. Although most fractures heal successfully, due in large part to the innate regenerative capacity of the periosteum, healing is slow and ineffectual (nonunion) for more than 5% of patients, and failure to heal can be as high as 10% for fractures that occur in weight-bearing long bones that are crucial for mobility. Recalcitrant fractures are challenging to treat and current therapies produce unpredictable outcomes, leaving almost 600,000 patients each year with significant disability. Unpredictability in healing is compounded for procedures that aim to replace large areas of bone lost during trauma or tumor resection and require bone grafting; almost half of the 500,000 bone grafting surgeries performed each year fail over time, due in large part to the absence of live periosteal cells that orchestrate the new bone formation needed to successfully unite the graft to the host bone. Our published work identifies BMP2 as a potent physiological regulator of periosteal function. Mice lacking BMP2 expression in Prx1+ stem/progenitor cells exhibit severe defects in all known periosteal activities. In the absence of BMP2, bones fail to grow in width proportional to their growth in length, creating structural instability that results in spontaneous fracture; once fractured, the periosteum fails to initiate repair and cannot support bone graft incorporation. In addition, treatment with anabolic agents such as intermittent PTH or anti-sclerostin antibody fail to stimulate cortical bone formation in the absence of periosteal BMP2. As such, we hypothesize that the dynamic spatio/temporal expression pattern of Bmp2 within the periosteal niche constitutes an essential mechanism determining active versus quiescent states of the periosteum throughout postnatal life. We propose 3 aims to test this hypothesis. In Aim 1, we will validate the functional role of pathways identified in a recently completed periosteum RNAseq as downstream mediators of BMP2 signaling during appositional growth and fracture repair. In Aim 2, we will examine the requirement for BMP2 resident in the ECM of the periosteal niche versus BMP2 produced by periosteal cell during appositional bone growth. In Aim 3, we will determine if increasing endogenous BMP2 production by periosteal cells is beneficial for periosteal function. Completion of these studies will result in a more in depth understanding of the cellular and molecular mechanisms coordinated by BMP2 signaling in periosteal stem/progenitor cells, and should lead to the development of novel therapies for enhancing bone repair. Knowledge gained through this proposal also has the potential to increase the utility of anabolic agents targeted to the periosteum to prevent fractures.