Regulators of Ischemic Fracture Healing

 描述（由申请人提供）：许多骨折显示出受损的再生-愈合缓慢（延迟愈合）或无法愈合（不愈合）。这些损伤可能会因疼痛和功能丧失而复杂化，通常需要翻修手术，并且对社会来说是一笔巨大的成本。适当的骨再生需要强大的血管反应，因此缺乏血管化是骨愈合受损的主要风险因素。因此，增强血管形成的方法将促进受损骨折的更好愈合。血小板反应蛋白1（TSP 1）及其最接近的家族成员血小板反应蛋白2（TSP 2）是细胞外基质蛋白和有效的内源性血管生成抑制剂，其在非愈合伤口中过表达。TSP 1和TSP 2在受损骨折愈合的纤维血管阶段高度表达，并且缺乏TSP 2导致缺血性骨折愈合期间血管化和骨形成增强。TSP对组织中血管再生的影响的主要机制是这些配体与CD 47受体的相互作用，CD 47受体是一种强烈影响缺血-再灌注的多效性受体。然而，TSP-CD 47相互作用在促进缺血性骨折愈合中的意义尚未研究。我们假设TSP是通过与CD 47结合的缺血性骨折愈合的内源性抑制剂。阻断TSP-CD 47结合将促进骨折血管化并增强受损骨折愈合中的骨再生。为了解决这一假设，我们提出了三个具体目标。首先，我们将通过研究TSP 1缺失、TSP 2缺失和双敲除小鼠来研究TSP 1和TSP 2对缺血性骨折愈合的贡献。同样，我们将使用腺病毒添加回TSP 2。在目标2中，我们将询问CD 47是否通过与TSP结合来调节受损骨折愈合中的骨折血管化和骨再生。我们将在CD 47缺失小鼠中检测缺血性骨折愈合，然后评估基于TSP 1的CD 47激活肽是否抑制缺血性骨折血管重建。最后，我们将询问是否中断TSP-CD 47配体-受体相互作用骨折愈合后，使用CD 47阻断剂，提供局部或全身，可以增强骨折血管化和骨再生受损愈合。 这些研究的成功完成可能对受损骨折患者具有重要的近期临床意义。

 DESCRIPTION (provided by applicant): Many bone fractures show compromised regeneration-healing slowly (delayed union) or failing to heal (non-union). These injuries can be complicated by pain and loss of function, often requiring revision surgery, and are a significant cost to society. A robust vascular response is required for proper bone regeneration, thus a lack of vascularization is a primary risk factor for compromised bone healing. Therefore, methodologies that enhance vascularization will promote greater healing of compromised fractures. Thrombospondin 1 (TSP1) and its closest family member thrombospondin 2 (TSP2) are extracellular matrix proteins and potent endogenous inhibitors of angiogenesis that are over-expressed in non-healing wounds. TSP1 and TSP2 are highly expressed during the fibrovascular phase of compromised fracture healing and an absence of TSP2 results in enhanced vascularization and bone formation during ischemic fracture healing. A dominant mechanism for the influence of TSPs on revascularization in tissues is the interaction of these ligands with the CD47 receptor, a pleiotropic receptor that strongly influences ischemia-reperfusion. However, the significance of TSP-CD47 interactions in enhancing ischemic fracture healing has not been studied. We hypothesize that TSPs are endogenous inhibitors of ischemic fracture healing by binding to CD47. Blocking TSP-CD47 binding will promote fracture vascularization and enhance bone regeneration in compromised fracture healing. To address this hypothesis we propose three specific aims. First we will examine the contribution of TSP1 and TSP2 to ischemic fracture healing by studying TSP1-null, TSP2-null, and double-knockout mice. As well, we will add back TSP2 using adenovirus. In Aim 2, we will ask whether CD47 regulates fracture vascularization and bone regeneration in compromised fracture healing by binding to TSP. We will examine ischemic fracture healing in CD47-null mice, and then evaluate whether a TSP1-based CD47 activating peptide inhibits ischemic fracture revascularization. Finally, we will ask whether disruption of TSP-CD47 ligand-receptor interaction following fracture healing using CD47 blocking agents, delivered either locally or systemically, can enhances fracture vascularization and bone regeneration in compromised healing. Successful completion of these studies could have significant near-term clinical implications for the patient with a compromised fracture.