BMP2 Regulation of Periosteal Function

摘要 骨膜是一种位于骨骼外表面的高度专业化的组织微环境，在 确保独特的常驻干细胞/祖细胞群体的生存和自我更新 负责对位骨形成和骨折修复。破坏骨膜功能的损伤有 很常见，在美国每年发生1200-1500万次骨折，导致1800万次医生就诊和结果 损失了6000万个工作日。尽管大多数骨折都能成功愈合，但这在很大程度上是由于先天的 骨膜再生能力，愈合缓慢和无效(骨不连)超过5% 患者，对于发生在承重的长骨上的骨折，愈合失败的比例可能高达10% 对机动性至关重要。顽固性骨折的治疗具有挑战性，目前的治疗方法产生了 不可预测的结果，导致每年有近60万名患者严重残疾。不可预测性 用于修复创伤或肿瘤中丢失的大片骨的手术中使用的复合疗法。 手术切除，需要植骨；每年进行的50万例植骨手术中，几乎有一半 随着时间的推移，失败在很大程度上是由于缺乏协调新骨形成的活的骨膜细胞 需要成功地将移植物结合到宿主骨上。我们发表的研究发现BMP2是一种有效的 骨膜功能的生理调节。PRX1+干/祖细胞中缺乏BMP2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BMP2的情况下，骨骼不能生长 与它们的长度增长成比例，造成结构不稳定，导致自发性骨折； 骨膜断裂，无法启动修复，不能支持植骨结合。此外, 间歇性甲状旁腺素或抗硬化素抗体等合成代谢药物治疗不能刺激皮质 骨膜BMP2缺失情况下的骨形成。因此，我们假设动态 骨形态发生蛋白2在骨膜窝内的时空表达模式构成了必需的 决定骨膜在出生后整个生命中处于活动状态还是静止状态的机制。我们 提案3旨在检验这一假说。在目标1中，我们将验证在 新近完成的骨膜RNAseq作为BMP2信号的下游介导物 生长和骨折修复。在目标2中，我们会研究BMP2驻留在该中心的ECM的要求。 骨膜细胞在对位骨生长过程中产生的骨膜龛与骨形态发生蛋白2的比较。在《目标3》中，我们将 确定增加骨膜细胞内源性BMP2的产生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的更深入的了解 骨膜干/祖细胞中BMP2信号协调的机制，并应导致 促进骨修复的新疗法的开发。通过这项建议获得的知识还具有 增加以骨膜为靶点的合成代谢药物预防骨折的可能性。

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.