Neuronal Regulation of Skeletal Development and Repair

 描述(申请人提供)：在这个新项目中，我们将探索感觉神经在骨骼中的作用。尽管有大量间接证据表明神经在骨骼发育和修复中的重要性，但很少有研究研究神经在骨骼发育和修复中的作用，而对血管生成在骨发育中的作用的研究越来越多。这种知识差距的部分原因是难以识别钙化组织中的神经纤维，以及缺乏研究骨骼神经支配的易处理的模型系统。为了克服这些限制，我们的实验室已经验证了可视化和干扰支配骨骼的感觉神经的功能信号的小鼠模型。利用这些模型，我们证明了表达原肌球蛋白受体激酶A(TrkA)的感觉神经元从背根神经节投射到表达神经生长因子(NGF)的发育肢体软骨膜细胞与邻近软骨的早期矿化是一致的。在胚胎发育期间，这些感觉神经中TrkA激酶活性的消除会延缓轴突向内生长，并减弱新生骨矿化。胚胎发育过程中TrkA信号的中断减少了出生后骨的获取，并延缓了实验性骨折后成人骨的再生。这些观察和下文描述的其他研究为TrkA感觉神经在骨骼发育、获取和修复中的需求提供了直接证据。这项提案中概述的研究将探索感觉神经功能促进成骨的机制。我们的方法将检验这一假设，即在发育和损伤的肢体间充质中产生的神经生长因子(NGF)激活TrkA感觉神经元以促进其存活，并将其轴突引导到初级成骨中心以启动成骨细胞分化。这一假说将在骨骼发育的背景下(目标1)和在已建立的实验性骨修复模型(目标2)下进行测试。我们相信，我们的项目将对感觉神经在健康人类中的作用产生新的见解，并最终将了解与某些骨骼疾病相关的神经病理表现。

 DESCRIPTION (provided by applicant): In this new project we will explore the role of sensory nerves in bone. In contrast to increasing body of work on to the role of angiogenesis in bone development, few studies have investigated the role of nerves in bone despite a wealth of circumstantial evidence implicating the importance of innervation in skeletal development and repair. This knowledge gap is in part due the difficulty of identifying nerve fibers in calcified tissue and the lack of tractable model systems for study skeletal innervation. To overcome these limitations, our laboratory has validated mouse models for visualizing and disrupting functional signaling of sensory nerves that innervate the skeleton. Using these models we demonstrate that tropomyosin receptor kinase A (TrkA) expressing sensory neurons emanating from the dorsal root ganglion project axons to nerve growth factor (NGF) expressing perichondral cells of developing limbs coincident with incipient mineralization of adjacent cartilage. Elimination of TrkA kinase activity in these sensory nerves during embryogenesis retards axonal ingrowth and attenuates nascent bone mineralization. Disruption of TrkA signaling during embryogenesis reduces postnatal bone acquisition and retards the regeneration of adult bone in response to experimental fracture. These observations, and other studies described below, provide direct evidence for the requirement of TrkA sensory nerves in bone development, acquisition and repair. The studies outlined in this proposal will explore the mechanisms through which sensory nerves function to promote osteogenesis. Our approach will test the hypothesis that nerve growth factor (NGF) produced in the developing and injured limb mesenchyme activates TrkA sensory neurons to promote their survival and guide their axons to primary ossification centers to initiate osteoblast differentiation. This hypothesis will be tested in a setting of bone development (Aim 1) and in response to an established model of experimental bone repair (Aim 2). We believe that our project will yield new insights into the role of sensory nerves in healthy humans and will ultimately inform on the neuropathological manifestations associated with certain bone disorders.