Neuronal Regulation of Skeletal Development and Repair

这是一个更新的应用程序调查的作用，感觉神经在骨。我们的研究在 第一个资助期表明，感觉神经的NGF依赖性TrkA信号传导是主要的 在发育中的股骨和颅骨中血管生成和骨生成的驱动器。在这些无血管的情况下， 间充质谱系细胞结构域中NGF的急性上调之后是伤害感受纤维向内生长， 其随后回到增殖间充质细胞的位置。感觉神经阻滞 通过抑制TrkA信号传导或破坏NGF的向内生长，延缓血管形成并破坏 股骨和颅骨形成。颅盖模型的组织学数据显示，感觉缺失 神经纤维与缝线中增殖的成骨前体数量减少有关， 缝线过早闭合。这些观察结果表明，感觉神经的功能在 发育骨骼以维持间充质干细胞的可塑性，这一概念在四肢模型中得到了很好的建立。 再生和支持最近的研究在发展小鼠股骨。我们的初步调查结果 在微流体室中检查感觉神经轴突与MSC的相互作用表明， 浸润DRG神经纤维诱导MSC增殖，但以非接触依赖性方式限制分化。 这些作用伴随着骨祖细胞有丝分裂原（例如TGF β 1）和MSC抑制剂的上调。 分化（例如卵泡抑素样1）。总之，这些数据支持TrkA+感觉神经 在骨骼发育中发挥作用，通过递送 激活促有丝分裂和抗分化信号通路的可溶性因子。 这个概念模型将在分为三个具体目标的研究中进行探讨。具体目标1将定义 TrkA+骨骼感觉神经在发育中的颅骨中的时空模式，并确定其 对骨祖细胞增殖和细胞命运影响。Specific Aim 2将确定MSC中的关键靶基因 通过使用先前验证的共培养方法的感觉神经信号的影响。具体目标3将确定 感觉轴突衍生因子调节MSC增殖和细胞命运决定。我们的结果应该能提供 对感觉神经在骨骼形态发生、稳态和修复中的基本作用的新见解， 并提供了与人类骨骼疾病相关的神经病理学表现的重要见解。

This is a renewal application of a program investigating the role of sensory nerves in bone. Our studies during the first funding period demonstrate that NGF-dependent TrkA signaling by sensory nerves is the primary driver of angiogenesis and osteogenesis in the developing femur and skull. In these avascular settings, acute up-regulation of NGF in mesenchymal lineage cell domains is followed by nociceptive fiber ingrowth, which subsequently home to locations of proliferating mesenchymal cells. Blockade of sensory nerve ingrowth, either by inhibition of TrkA signaling or disruption of NGF, retards vascularization and disrupts femoral and calvarial bone formation. Histological data in the calvaria model revealed that loss of sensory nerve fibers is associated with reduced numbers of proliferating osteogenic precursors in the sutures and premature suture closure. These observations suggest a paradigm in which sensory nerves function in developing bone to maintain mesenchymal stem cell plasticity, a concept well established in models of limb regeneration and supported by recent studies in developing mouse femur. Our preliminary findings directly examining the interaction of sensory nerve axons with MSCs in microfluidic chambers suggest that infiltrating DRG nerve fibers induce MSC proliferation, but limit differentiation in a non-contact dependent fashion. These effects are accompanied by upregulation of osteoprogenitor mitogens (e.g. TGF) and inhibitors of MSC differentiation (e.g. follistatin-like 1). Together, this data support the premise that TrkA+ sensory nerves function in developing bone to maintain stem cells in a proliferative, undifferentiated state by delivering soluble factors that activate mitogenic and anti-differentiation signaling pathways. This conceptual model will be explored in studies divided into three Specific Aims. Specific Aim 1 will define the spatiotemporal patterning of TrkA+ skeletal sensory nerves in the developing cranium, and determine their influence on osteoprogenitor proliferation and cellular fate. Specific Aim 2 will identify key target genes in MSCs impacted by sensory nerve signals using previously validated co-culture methods. Specific Aim 3 will identify sensory axon-derived factors that regulate MSC proliferation and cell fate decisions. Our results should provide new insights into the fundamental roles sensory nerves play in skeletal morphogenesis, homeostasis and repair, and provide critical insight into the neuropathological manifestations associated with bone disorders in humans.