Bone Marrow Inflammation and Bone Resorption

项目摘要/摘要 我们的A型肉毒毒素(BTxA)诱导的肌肉瘫痪小鼠模型的数据显示， 机械负荷缺陷轴之外的神经肌肉功能是骨骼的关键调节器。 动态平衡。与这篇论文一致，我们观察到一过性肌肉麻痹会引发急性 RANKL介导的局灶性白血病发病前骨髓内的炎症信号 破骨细胞生成，这是造成严重的皮质和松质骨吸收的原因 模特。然而，启动急性骨髓炎和随后的细胞间信号 骨吸收尚未阐明，因此为确定翻译策略提供了障碍 这将使神经肌肉功能障碍与骨质丢失脱钩。这种快速反应的一个潜在发起者是 神经源性炎症，由感觉神经释放神经肽引发，并由 肥大细胞介导的组胺释放。因此，我们进行了一系列初步研究，以评估 肌肉麻痹后这一通路的激活，并发现：1)P物质，一种经典的 小腿瘫痪后1天内，胫骨骨髓中神经源性炎症表达上调，2)基因 与结缔组织肥大细胞活化有关的肥大细胞在肌肉瘫痪后显著升高，以及3) 在肥大细胞缺陷的KitW-sh/W-sh小鼠中，肌肉麻痹引起的骨吸收明显减少。 因此，我们假设：肌肉麻痹后的骨吸收是由神经肽启动的。 并通过肥大细胞依赖的组胺释放而被放大。我们将通过四个方面来探讨这一论题 互补的特定目标(SA)，每个目标都有对应的子假设。首先，我们预计 BTxA诱导的肌肉麻痹会使骨髓中的神经肽升高，然后才有证据表明 肥大细胞活化或骨吸收(SA#1)。然后，SA#2将展示成功对抗 这些神经肽需要抑制肥大细胞的激活和肌肉诱导的骨吸收。 瘫痪。在SA#3中，我们将利用cKit独立的结缔组织肥大细胞缺陷小鼠 证明肥大细胞介导的组胺信号转导与深刻的破骨细胞形成有关 由肌肉麻痹引起的。然后，SA#4将提供组胺受体治疗的概念证据 拮抗剂将显著减轻肌肉麻痹引起的骨吸收。从各个方面来看， 建议的信号通路(神经源性炎症、神经肽信号、肥大细胞激活、瘫痪 诱导性骨吸收)已经在其他情况下进行了探索，但尚未整合到细胞中 整合肌肉、神经和骨骼生理学的信号级联。重要的是，如果我们的论点得到支持， 组胺拮抗剂的广泛临床经验将使已批准的药物能够重新用于 改善由瘫痪或其他神经肌肉损伤引起的急性骨吸收的目标。

PROJECT SUMMARY/ABSTRACT Data from our mouse model of 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 is responsible for the profound cortical and trabecular bone resorption observed in the model. However, the intercellular signaling that initiates acute bone marrow inflammation and subsequent bone resorption has not been elucidated and therefore presents a barrier to identifying translational strategies that would decouple neuromuscular dysfunction from bone loss. One potential initiator of this rapid response is neurogenic inflammation, which is triggered by neuropeptide release from sensory nerves and is amplified by mast cell mediated histamine release. We therefore pursued a series of preliminary studies to assess activation of this pathway following muscle paralysis and found that: 1) Substance P, a classic initiator of neurogenic inflammation, was upregulated in tibia bone marrow within 1 d of calf paralysis, 2) genes associated with connective tissue mast cell activation were acutely elevated 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 via four complementary Specific Aims (SA), each with a corresponding sub-hypothesis. First, 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 then demonstrate that successful antagonism of these neuropeptides will be required to inhibit mast cell activation and 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 has not been integrated into a cellular signaling cascade that integrates 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 other neuromuscular impairments.