Ephrin Therapy for Segmental Defect Repair in Bone

 描述(由申请人提供)： 长骨的骨骼骨折是骨科的一个主要问题。在这些骨折中，有10%-20%的骨骼愈合受损，导致骨不连或延迟愈合。这对患者构成了非常严重的发病率，延长了住院时间，给患者和社会带来了巨大的经济负担。因此，在损伤严重到不可能正常愈合的情况下，或者在因健康相关的条件而损害正常骨折愈合的情况下，非常希望有一种有效的治疗来促进骨愈合。强健的骨膜反应对于有效的骨愈合至关重要。我们已经提出了重要的初步证据，表明EPhin(EFN)B1信号调节骨形成，并促进对机械载荷和骨折修复的实质性骨膜反应。因此，我们提出EfnB1促进骨膜对负荷和损伤的反应，这种骨膜反应可用于促进节段性缺损性损伤的愈合。我们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，它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治疗节段性骨折的刚性外固定方法相比，在临床上与受损的骨折愈合更相关。该模型在本应达到骨性愈合后不能很好地愈合，因此代表了一种非常具有挑战性的骨修复模型来研究efnB1对骨愈合的调控。使用该模型提出了三个特定的目标来测试efnB1对骨修复的调节。1)为了在股骨节段性骨愈合模型中验证efnB1调节骨修复的假设，我们将研究在成骨细胞系细胞中过表达efnB1的转基因efnB1小鼠的节段性骨愈合受损的特征。2)为了验证节段性骨修复模型中efnB1促进愈合是由efnB1与其受体(Eph)接触时诱导的efnB1反向信号调节的假设，我们将研究成骨细胞特异的efnB1基因敲除小鼠的节段性缺陷修复，但通过转导合适的efnB1基因结构选择性地恢复正向和反向信号或仅恢复正向信号。这些构建物要么是能够正向和反向信令的全长野生型efnB1，要么是带有缺陷信令结构域的截短的efnB1，从而消除了反向信令。3)为了验证EfnB1基因治疗可以促进股骨节段性骨不连修复的假说，我们利用第二个特定目标中确定的信号调控机制，将EfnB1和EphB2基因治疗应用于野生型小鼠股骨节段性缺损处，并评价其愈合情况。我们所提出的研究将提高我们对严重受损的愈合模型中骨修复的肾上腺素调节的理解，并评估EfnB1疗法作为一种改善因临床挑战性损伤以及骨质疏松等生理条件而受损的骨愈合的方法。

 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.