Bone Marrow Inflammation and Bone Resorption

项目总结/摘要 来自我们的肉毒毒素A（BTxA）诱导肌肉麻痹后快速骨丢失的小鼠模型的数据 揭示了神经肌肉功能，轴外的机械负荷赤字，是一个关键的 骨稳态调节剂。与这一论点相一致，我们观察到短暂的肌肉麻痹， 在局灶性RANKL介导的发病前触发骨髓内的急性炎症信号传导 破骨细胞生成，导致严重的皮质骨和小梁骨吸收。但 负责启动急性骨髓炎症和随后的骨 再吸收尚未阐明，因此是识别将解耦的策略的障碍 骨质流失导致的神经肌肉功能障碍该途径的一个潜在引发剂是神经源性炎症， 由感觉神经快速释放神经肽触发，并由肥大细胞放大 介导的组胺释放。因此，我们进行了一系列初步研究，以评估 在肌肉麻痹后激活这一通路，发现：1）P物质，一种经典的 神经源性炎症，在小腿麻痹1天内在胫骨骨髓中上调，2）相关基因 结缔组织肥大细胞的存在和激活在肌肉麻痹后3d内升高， 肥大细胞缺陷型KitW-sh/W-sh可明显减轻肌肉麻痹引起的骨吸收 小鼠因此，我们假设：肌肉麻痹后的骨吸收是由 神经肽信号传导，并通过肥大细胞依赖性组胺释放放大。我们会追查下去 论文通过四个互补的具体目标（SA）进行，每个目标都有相应的子假设。我们 预期骨髓内的神经肽将在BTxA诱导的肌肉麻痹之前升高。 肥大细胞活化或骨吸收的证据（SA#1）。SA#2将证明， 需要拮抗原发性神经源性炎性神经肽以成功抑制骨 肌肉麻痹引起的再吸收。在SA#3中，我们将利用不依赖cKit的结缔组织肥大 细胞缺陷小鼠，以证明肥大细胞介导的组胺信号传导是造成严重的 由肌肉麻痹引起的破骨细胞生成。然后，SA#4将提供概念证明， 组胺受体拮抗剂将显着减弱肌肉麻痹引起的骨吸收。每个 所提出的信号传导途径的方面（神经源性炎症、神经肽信号传导、肥大细胞 激活，麻痹诱导的骨吸收）已经在其他情况下进行了探索，但没有整合到一个 连接肌肉、神经和骨骼生理学的细胞信号级联。重要的是，如果我们的论点是 支持，广泛的临床经验，组胺拮抗剂将使再利用批准的药物 旨在改善由瘫痪或神经肌肉损伤引起的急性骨吸收。

PROJECT SUMMARY/ABSTRACT Data from our mouse model of rapid bone loss following Botulinum Toxin A (BTxA) induced muscle paralysis has revealed that neuromuscular function, outside the axis of mechanical loading deficits, is a critical modulator of bone homeostasis. Consistent with this thesis, we have observed that transient muscle paralysis triggers acute inflammatory signaling within bone marrow that precedes the onset of focal RANKL mediated osteoclastogenesis, which results in profound cortical and trabecular bone resorption. However, the intercellular signaling responsible for initiating acute bone marrow inflammation and subsequent bone resorption has not been elucidated and is therefore a barrier to identifying strategies that would decouple neuromuscular dysfunction from bone loss. One potential initiator of this pathway is neurogenic inflammation, which is triggered by the rapid release of the neuropeptides from sensory nerves and is amplified by mast cell mediated histamine release. We therefore pursued a series of preliminary studies to assess the potential activation of this pathway following muscle paralysis and found that: 1) Substance P, a classic initiator of neurogenic inflammation, is upregulated in tibia bone marrow within 1 d of calf paralysis, 2) genes associated with connective tissue mast cell presence and activation were elevated within 3 d following muscle paralysis, and 3) muscle paralysis induced bone resorption was significantly diminished in mast cell deficient KitW-sh/W-sh mice. We therefore hypothesize that: Bone resorption following muscle paralysis is initiated by neuropeptide signaling and is amplified by mast cell dependent histamine release. We will pursue this thesis through four complementary Specific Aims (SA), each with a corresponding sub-hypothesis. We anticipate that neuropeptides within bone marrow will be elevated by BTxA induced muscle paralysis prior to evidence of mast cell activation or bone resorption (SA#1). SA#2 will demonstrate that simultaneous antagonism of primary neurogenic inflammatory neuropeptides will be required to successfully inhibit bone resorption induced by muscle paralysis. In SA#3, we will leverage a cKit independent, connective tissue mast cell deficient mouse to demonstrate that mast cell mediated histamine signaling is responsible for the profound osteoclastogenesis induced by muscle paralysis. SA#4 will then provide proof of concept that treatment with histamine receptor antagonists will significantly attenuate bone resorption caused by muscle paralysis. Each aspect of the proposed signaling pathway (neurogenic inflammation, neuropeptide signaling, mast cell activation, paralysis induced bone resorption) has been explored in other contexts, but not integrated into a cellular signaling cascade that couples muscle, nerve, and bone physiology. Importantly, if our thesis is supported, the broad clinical experience with histamine antagonists will enable repurposing of approved drugs toward the goal of ameliorating acute bone resorption precipitated by paralysis or neuromuscular impairment.