Endogenous repair of growth plate injuries by local and sequential delivery of factors that inhibit osteogenesis and promote chondrogenesis

 描述(由申请人提供)：骨折是儿科骨科的一个重要问题。三分之一的儿童骨折涉及生长板，生长板是长骨中的一个脆弱的软骨区域，为儿童的持续发育提供信号。生长板损伤发生在高和低冲击事件中，从车辆事故到简单的跌倒。这种损伤会导致“骨条”的形成，在“骨条”中，骨组织取代正常的生长板软骨。这可能会导致受影响骨骼的角形畸形或完全停止生长。不幸的是，目前的生长板损伤治疗是侵入性的，容易感染，成功率很低。没有可用的治疗方法可以完全再生生长板，并确保正常的纵向骨生长。该项目的长期目标是开发一种临床上有用的生长板再生生物疗法。目前应用的目的是防止骨条的形成，取而代之的是一种更接近于天然生长板的软骨组织，并可能恢复正常的纵向骨生长。最近的进展阐明了影响骨条形成的机制以及促进再生的途径。已有研究表明，损伤生长板中的血管内皮生长因子(VEGF)及其相关的血管生成可触发骨条的形成。此外，有报道称，间充质干细胞(MSCs)可以渗透到损伤部位，表达成骨标志物，并参与骨条的形成。在这个项目中，我们建议通过阻断血管生成和相关的骨形成(目标1)，通过运送干细胞迁移因子(目标2)将更多的内源性MSCs招募到损伤区域(目标2)，以及通过将其暴露于软骨生成因子(目标3)来促进MSC的软骨生成而不是成骨，以防止或取代损伤生长板中的骨棒形成(目标1)。这将在生长板损伤的大鼠模型中进行测试 使用可注射的生物材料输送系统，将按顺序在局部释放三种治疗因子：(1)抗血管内皮生长因子抗体，以阻断血管生成和骨形成；(2)干细胞吸引因子，如SDF-1或CCL25，将内源性MSCs招募到损伤区域；以及(3)转化生长因子-β1，引导招募的干细胞沿软骨系而不是骨系向下。总体而言，这些研究的数据将为生长板修复的基础生物学提供新的信息，并将提供有关拟议治疗方法的翻译潜力的信息。这将为进一步开发一种新的治疗方法铺平道路，该方法不仅可以防止骨条形成，还可以促进功能性组织工程化生长板的形成，从而防止与生长板损伤相关的生长问题。

 DESCRIPTION (provided by applicant): Fractures are a significant problem in pediatric orthopedics. One third of childhood fractures involve the growth plate, a fragile, cartilaginous region in long bones that provides signaling for continued growth in children. Growth plate injuries occur from both high and low impact events, ranging from vehicular accidents to simple falls. Such injuries can result in the formation of a "bony bar" in which bony tissue replaces normal growth plate cartilage. This can result in angular deformities or complete growth cessation in the affected bone. Unfortunately, current growth plate injury treatments are invasive, prone to infections, and have low success rates. There is no treatment available that can fully regenerate the growth plate and ensure normal longitudinal bone growth. The long-term goal of this project is to develop a clinically useful biological therapy for growth plate regeneration. The objective of the current application is to prevent bony bar formation, replacing it instead with a cartilaginous tissue that more closely resembles the native growth plate and may restore normal longitudinal bone growth. Recent advances have elucidated mechanisms that affect bony bar formation as well as pathways that can promote regeneration. It has been shown that vascular endothelial growth factor (VEGF) and its associated angiogenesis in the injured growth plate can trigger bony bar formation. As well, it has been reported that mesenchymal stem cells (MSCs) infiltrate the injury site, express osteogenic markers, and participate in bony bar formation. In this project, we propose to prevent or replace bony bar formation in the injured growth plate by blocking angiogenesis and associated bone formation (Aim 1), recruiting more endogenous MSCs to the injured area by delivery of stem cell migratory factors (Aim 2), and promoting MSC chondrogenesis rather than osteogenesis by exposing them to a chondrogenic factor (Aim 3). This will be tested in a rat model of growth plate injury by using an injectable biomaterial delivery system that will sequentially release three therapeutic factors locally: (1) anti-VEGF antibody to block angiogenesis and bone formation, (2) a stem cell attracting factor such as SDF-1 or CCL25 to recruit endogenous MSCs to the injured area, and (3) TGF-β1 to direct the recruited stem cells down the cartilage lineage instead of the bone lineage. Overall, data from these studies will contribute new information to the basic biology of growth plate repair, and will also provide information on the translational potential of the proposed therapeutic approach. This will pave the way for further development of a novel treatment that not only prevents bony bar formation but also promotes formation of a functional tissue engineered growth plate that can prevent growth problems associated with growth plate injuries.