Ephrin Therapy for Segmental Defect Repair in Bone

 描述（由申请人提供）： 长骨的颅骨骨折是一个主要的骨科问题。在这些骨折中，10- 20%的骨愈合受损，导致骨不连或延迟愈合。这对患者构成了非常显著的发病率，延长了住院时间，并给患者和社会带来了巨大的经济负担。因此，非常需要一种有效的治疗方法，以在损伤如此严重以至于不可能正常愈合的情况下，或在因健康相关的情况而受损的正常骨折愈合中促进骨愈合。强健的骨膜反应对于有效的骨愈合至关重要。我们已经开发了重要的初步证据，肝配蛋白（efn）B1信号调节骨形成，并促进大量的骨膜响应机械负荷和骨折修复。因此，我们提出efnB 1促进骨膜对负荷和损伤的反应，并且这种骨膜反应可用于增强节段性缺损损伤的愈合。我们的实验室最近还开发了一种新的小鼠股骨节段性骨损伤模型，这是一种更好的软骨内骨修复范例，与常用的闭合性骨折模型或节段性缺损的刚性外固定方法相比，与骨折愈合受损更具临床相关性。该缺损模型在本应实现骨愈合后未能良好愈合，因此代表了一种非常具有挑战性的骨修复模型，以研究efnB 1对骨愈合的调节。提出了三个具体的目标来测试efnB 1调节骨修复使用该模型。1)为了检验efnB 1调节骨修复的假设，在股骨节段性骨缺损模型的骨愈合，我们将表征受损的节段性骨缺损愈合的转基因efnB 1小鼠系，过表达efnB 1，特别是在成骨细胞谱系细胞。2)为了验证这一假设，即efnB 1增强愈合的骨修复节段性缺损模型是由efnB 1的反向信号，诱导efnB 1与其受体（Eph）接触后，我们将检查节段性缺损修复成骨细胞特异性efnB 1基因敲除小鼠，但选择性恢复正向和反向信号或只有正向信号转导适当的efnB 1基因结构。这些构建体将是能够正向和反向信号传导的全长野生型efnB 1，或具有消除反向信号传导的缺陷信号传导结构域的截短的efnB 1。3)为了验证efnB 1治疗可以促进股骨骨不连节段性缺损愈合的假设，我们将利用第二个具体目标中确定的信号调节，将efnB 1和ephB 2基因治疗应用于野生型小鼠股骨骨不连节段性缺损并评估愈合。我们提出的研究将提高我们对严重受损愈合模型中ephrin调节骨修复的理解，并评估efnB 1治疗作为改善临床挑战性损伤以及骨质疏松症等生理条件损害的骨愈合的方法。

 DESCRIPTION (provided by applicant): Skeletal fractures of the long bones are a major orthopedic problem. Skeletal healing is impaired in 10- 20% of these fractures, resulting in nonunion or delayed union healing. This constitutes a highly significant morbidity to patients, prolonged hospitalizations, and a huge economic burden for the patient and society. Thus, it is highly desirable to have an effective treatment to promote bone healing in conditions where the injury is so severe that normal healing is not possible, or in otherwise normal fracture healing impaired by health-related conditions. A robust periosteal response is critical for efficient bone healing. We have developed significant preliminary evidence that ephrin (efn) B1 signaling regulates bone formation and promotes a substantial periosteal response to mechanical loading and fracture repair. Accordingly, we have proposed that efnB1 promotes the periosteal response to loading and injury, and that this periosteal response can be used to enhance the healing of segmental defect injuries. Our laboratory has also recently developed a novel model of segmental bone injury in the mouse femur that is a better paradigm of endochondral bone repair and is more clinically relevant to impaired fracture healing than the commonly used closed fracture models or rigid external fixation approaches to segmental defects. This defect model fails to heal well after it should have achieved bony union, and therefore represents a very challenging model of bone repair to investigate efnB1 regulation of bone healing. Three specific objectives are proposed to test efnB1 regulation of bone repair using this model. 1) To test the hypothesis that efnB1 regulates bone repair in a femoral segmental defect model of bone healing, we will characterize impaired segmental defect healing in a transgenic efnB1 mouse line that overexpresses efnB1 specifically in osteoblast lineage cells. 2) To test the hypothesis that efnB1 enhancement of healing in a segmental defect model of bone repair is regulated by efnB1 reverse signaling that is induced upon efnB1 contact with its receptors (eph), we will examine segmental defect repair in osteoblast-specific efnB1 knockout mice, but selectively restore forward and reverse signaling or only forward signaling by the transduction of appropriate efnB1 gene constructs. These constructs will be either a full-length wild-type efnB1 capable of forward and reverse signaling, or a truncated efnB1 with a defective signaling domain that eliminates reverse signaling. 3) To test the hypothesis that efnB1 therapy can promote the healing of non-union femoral segmental defects, we will utilize the signaling regulation identified in the second specific objective to aply efnB1 and ephB2 gene therapy to the femoral segmental defect of wild-type mice and evaluate healing. Our proposed studies will improve our understanding of ephrin regulation of bone repair in a severely impaired model of healing and evaluate efnB1 therapy as an approach for the improvement of bone healing impaired by clinically challenging injuries, as well by physiological conditions such as osteoporosis.