NGF-TrkA Signaling in Load-Induced Bone Formation

项目概要/摘要 几乎所有支配骨的感觉神经都表达1型神经营养酪氨酸激酶受体（TrkA）， 神经生长因子（NGF）的高亲和力受体。在成熟的骨骼中，这些特殊的感觉神经覆盖着 骨膜呈密集的网状网络，占据生物力学信号的优先位置。 然而，NGF在成骨细胞中的调节机制以及通过成骨细胞传递到骨的信号， 感觉神经仍然未知。我们在这个项目中的主要目标是确定上游调解人， 在应变适应性骨重建过程中NGF-TrkA信号传导的下游效应物。我们的核心假设是 成熟成骨细胞中NF-κB信号的激活是NGF表达所必需的， 机械负荷，这反过来又激活TrKA感觉神经，以提供支持负荷的成骨线索- 诱导骨形成。在具体目标1中，我们将确定成骨细胞中NGF表达的调节 使用条件敲除小鼠的体外脉动流体流和体内前肢轴向压缩。在特定 目的2，我们将通过分析mRNA和mRNA水平来确定促进负荷诱导骨形成的神经源性信号， 在NGF-TrkA信号传导减弱的小鼠模型中，来自负载肢体的蛋白质，使用体外 微流控平台在具体目标3中，我们将评估这种信号通路的潜在治疗应用 增加成骨机械负荷后的骨积累而无痛觉过敏。总的来说， 本研究将确定压力下NGF-TrkA信号传导的上游介质和下游效应物， 适应性骨重建，并提供了一种潜在的治疗工具，用于利用该系统来改善骨骼 健康此外，拟议的研究与NIAMS长期计划高度一致，我们的 跨学科团队具有独特的优势来推进这些具体目标。

Project Summary/Abstract Nearly all of the sensory nerves that innervate bone express neurotrophic tyrosine kinase receptor type 1 (TrkA), the high affinity receptor for nerve growth factor (NGF). In mature bone, these specialized sensory nerves blanket the periosteum in a dense mesh-like network, occupying a preferential location for biomechanical signaling. However, the mechanism by which NGF is regulated in the osteoblast and the signals transmitted to bone by sensory nerves remain unknown. Our main objective in this project is to determine the upstream mediators and downstream effectors of NGF-TrkA signaling during strain adaptive bone remodeling. Our central hypothesis is that activation of NF-κB signaling in mature osteoblasts is required for the expression of NGF in response to mechanical load, which in turn activates TrKA sensory nerves to provide osteogenic cues that support load- induced bone formation. In Specific Aim 1, we will determine the regulation of NGF expression in osteoblasts using in vitro pulsatile fluid flow and in vivo forelimb axial compression of conditional knockout mice. In Specific Aim 2, we will identify nerve-derived signals that promote load-induced bone formation by analyzing mRNA and protein from loaded limbs in mouse models of diminished NGF-TrkA signaling, with validation using an in vitro microfluidic platform. In Specific Aim 3, we will assess a potential therapeutic application of this signaling pathway to increase bone accrual following osteogenic mechanical loading without hyperalgesia. In total, the results from this study will define the upstream mediators and downstream effectors of NGF-TrkA signaling during strain adaptive bone remodeling and provide a potential therapeutic tool for leveraging this system to improve skeletal health. Moreover, the proposed studies are highly aligned with the NIAMS Long-Range Plan, and our interdisciplinary team is uniquely positioned to advance these specific aims.