Bone Pseudoarthrosis Dissected through the Generation of New Mouse Models

描述（由申请人提供）：骨假关节是一种骨愈合的衰弱性缺陷。骨折和假关节都是骨组织潜在的、局部的先天性疾病的副现象，它改变了骨骼生长和重塑的过程，损害了机械健全的内部结构的发展和骨骼修复的过程。假性关节的发病机制仍有待确定，以确定适合的治疗方法。骨愈合涉及四种主要的细胞类型：间充质干细胞（MSCs）、软骨细胞、成骨细胞和破骨细胞。迄今为止，有证据表明骨形成细胞中Nf1的缺乏是Nf1（神经纤维瘤病）假关节病的原因，但涉及的细胞类型仍未确定。目前的挑战是识别NF1假关节中功能受损的细胞类型，描述与NF1功能丧失相关的细胞类型的缺陷，并基于这些知识提出纠正这些缺陷的适应性策略。在本研究中，我们研究了三种特定骨细胞类型（软骨细胞、成骨细胞或其共同前体MSCs）中Nf1单倍体功能不足或Nf1功能缺失是否会损害骨愈合。为了解决这个问题，我们建议在骨修复研究中使用缺乏一个或两个Nf1拷贝的Nf1小鼠和条件小鼠模型，特别是在MSCs、软骨细胞或成骨细胞中。有了这些小鼠模型，就有可能确定一个或两个Nf1拷贝是软骨细胞形成软骨愈伤组织或骨折后成骨细胞对软骨愈伤组织的钙化和重塑所必需的（Specific Aim I和II）。基于我们之前的工作（R21AR053978-01）和PD19830和洛伐他汀纠正Nf1-/-成骨细胞缺陷的ERK抑制特性（Specific Aim III），我们还设计了旨在表征治疗骨假关节的新治疗方法的研究。本应用程序提出的研究旨在表征调节骨重塑和修复的新途径和基因，其长期目标是更好地了解骨骼疾病并提出适应疗法。我们希望我们的研究1)描述Nf1在特定骨细胞类型的骨修复的特定阶段的作用，2)描述新的治疗靶点和策略，以确定最适合该综合征的治疗方法，3)提供新的小鼠模型，可作为临床前工具。公共卫生相关性：本申请中提出的研究旨在通过生成新的小鼠模型来表征NF1骨假关节的分子缺陷，随后用作临床前模型来测试各种药理学药物对骨愈合的纠正作用。

DESCRIPTION (provided by applicant): Bone pseudoarthrosis is a debilitating defect of bone healing. Both fracture and pseudoarthrosis represent the epiphenomena of an underlying, localized congenital disorder of skeletal tissues that alters the process of bone growth and remodeling and jeopardizes both the development of a mechanically sound internal structure and the process of bone repair. The etiopathology of pseudoarthrosis remains to be defined for the establishment of adapted therapies. Bone healing involves four main cell types: mesenchymal stem cells (MSCs), chondrocytes, osteoblasts and osteoclasts. To date, evidence suggests that lack of Nf1 in bone forming cells is responsible for NF1 (neurofibromatosis) pseudoarthrosis, but the cell types involved remain unidentified. The challenges today are to identify the cell types whose function is impaired in NF1 pseudoarthrosis, to characterize the defects associated with loss of function of Nf1 in this cell type, and based on this knowledge to propose adapted strategies to correct these defects. In this proposal, we ask whether Nf1 haplo-insufficiency or Nf1 loss of function in three specific bone cell types, chondrocytes, osteoblasts or their common precursor, MSCs, impairs bone healing. To address this question, we propose to use Nf1 mice and conditional mouse models lacking one or both copies of Nf1 specifically in MSCs, chondrocytes or osteoblasts in bone repair studies. With these mouse models in hand, it will possible to determine whether one or two copies of Nf1 is required for the formation of a cartilaginous callus by chondrocytes or for the calcification and remodeling of this callus by osteoblasts following fracture (Specific Aim I and II). We also designed studies aimed at characterizing a new therapeutic approach for treating bone pseudoarthrosis, based on our previous work (R21AR053978-01) and the ERK inhibitory property of PD19830 and lovastatin to correct the defects of Nf1-/- osteoblasts (Specific Aim III). The studies proposed in this application aim at characterizing novel pathways and genes regulating bone remodeling and repair, with the long-term goals of better understanding skeleton diseases and proposing adapted therapies. We expect our studies 1) to characterize the role of Nf1 at specific stages of bone repair in specific bone cell types, 2) to characterize novel therapeutic targets and strategies to identify the most appropriate treatment for this syndrome and 3) to provide new mouse models that can be used as pre-clinical tools. PUBLIC HEALTH RELEVANCE: The studies proposed in this application aim at characterizing the molecular defects of NF1 bone pseudoarthrosis by the generation of new mouse models, subsequently used as pre-clinical models to test the corrective effect of various pharmacological agents on bone healing.