Bone neuro-mechanosignaling and inflammation: New players in diabetic osteopenia

项目摘要 骨丢失是一种经常被忽视的糖尿病并发症，其潜在机制至今仍未得到重视。 很好理解。我们已经提出改变骨细胞Panx1-P2X7R机械信号的调节 复合体破坏适当的负荷诱导的骨适应，并可能导致1型糖尿病的骨丢失 (T1D)。然而，负荷诱导的骨量调节不仅发生在局部骨水平，而且发生在远程。 涉及骨骼和神经系统之间的直接信号。糖尿病会影响神经系统， 尤其是感觉神经，然而，糖尿病损害负荷诱导的神经调节的程度 骨骼反应仍然是未知的。我们的研究表明，除了它在骨细胞机械信号传递中的作用外， Panx1-P2X7R还参与骨神经机械感觉信号转导，介导负荷诱导 炎症小体激活，这两个新功能也是糖尿病的靶子。神经营养减量 因子，主要是NGF，是糖尿病周围神经病变的标志。NGF及其TrkA受体是 骨骼神经-机械感觉系统的组成部分。负荷诱导的成骨细胞释放NGF已被 建议在骨感觉纤维中启动NGF-TrkA信号，这对负荷诱导的骨是必不可少的 在小鼠体内形成。我们的初步数据表明，NGF-TrkA信号在T1D秋田骨中减弱，AS 骨骼和支配后肢的背根神经节(DRG)中NGF水平较低。此外，我们 观察到负荷调节NGF-TrkA信号成分的表达，这一反应在T1D中丢失 骨头。这一发现表明，糖尿病扰乱了骨骼机械感觉的神经感觉轴。 系统，从而损害神经成分的负荷诱导的骨形成的调节。此外, 负荷诱导背根神经节Panx1-P2X7R上调的研究结果表明，它参与了 调节骨感觉神经元的兴奋性。炎症与骨质流失有关。炎性细胞因子 在小鼠T1D的早期阶段，骨骼中的蛋白被证明是增加的，这被认为是必要的 用于诱发糖尿病骨丢失。我们的初步数据表明，负荷会加重T1D的炎症 Akita，这与Panx1-P2X7R失调和炎性小体激活相一致。负载引起的张开 糖尿病骨骼中的炎症可能是由已知的NLRP3炎症体的激活剂Panx1-P2X7R驱动的。 根据我们的初步数据，我们认为(1)糖尿病周围神经病变在糖尿病的病因中起作用。 影响骨感觉纤维和改变负荷性骨神经调节的糖尿病骨量减少 Panx1-P2X7R的调节不仅在骨骼中，而且在背根节中也是负荷诱导所必需的。 糖尿病骨组织对Panx1-P2X7R的反应和骨骼适应；(3)负荷诱导的Panx1-P2X7R的异常调节 增强局部炎症反应，从而削弱骨骼合成代谢反应。为了测试这些 假设我们将使用T1D小鼠模型，胰岛素治疗，时间序列加载，分子，生化， 组织形态计量学、药理学和遗传学方法。这些研究将确定 骨神经-机械信号和炎症作为糖尿病骨量减少症的新参与者，并确定新的和 Panx1-P2X7R功能复合体在调节健康和疾病中的骨适应中的关键作用。

Project Summary Bone loss is a diabetic complication that is often overlooked and the underlying mechanisms are still not well understood. We have proposed that altered regulation of the osteocyte Panx1-P2X7R mechanosignaling complex disrupts proper load-induced bone adaptation and likely contributes to bone loss in Type 1 diabetes (T1D). However, load-induced regulation of bone mass occurs not only at the local bone level but remotely involving direct signaling between the bone and the nervous system. Diabetes affects the nervous system, particularly sensory nerves and yet, the extent to which diabetes impairs neural regulation of load-induced bone responses is still unknown. Our studies indicate that besides its role in osteocytic mechanosignaling, Panx1-P2X7R also participates in bone neuro-mechanosensory signaling and mediates load-induced inflammasome activation, two new functions that are also targeted by diabetes. Reduction in neurotrophic factors, mainly NGF, is a hallmark of diabetic peripheral neuropathy. NGF and its TrkA receptor are components of the bone neuro-mechanosensory system. Load-induced NGF release from osteoblast has been proposed to initiate NGF-TrkA signaling in bone sensory fibers that is essential for load-induced bone formation in mice. Our preliminary data indicates that NGF-TrkA signaling is attenuated in T1D Akita bones, as evidenced by lower NGF levels in bone and dorsal root ganglia (DRG) innervating the hind limbs. Moreover we observed that loading regulates expression of NGF-TrkA signaling components, a response that is lost in T1D bones. This finding suggests that diabetes disrupts the neurosensory axis of the bone mechanosensory system, thereby impairing the neural component of the load-induced regulation of bone formation. In addition, findings of load-induced Panx1-P2X7R upregulation in DRG suggest its participation in mechanisms that modulate bone sensory neurons excitability. Inflammation is associated with bone loss. Inflammatory cytokines are shown to be increased in bones at early stages of T1D in mice, which has been proposed to be necessary for induction of diabetic bone loss. Our preliminary data indicates that loading worsens inflammation in T1D Akita, which coincides with Panx1-P2X7R dysregulation and inflammasome activation. Load-induced flaring of inflammation in diabetic bone is likely driven by Panx1-P2X7R, known activators of NLRP3 inflammasome. Based on our preliminary data, we propose that (1) diabetic peripheral neuropathy contributes to the etiology of diabetic osteopenia by affecting the bone sensory fibers and altering neural regulation of load-induced bone formation; (2) Panx1-P2X7R regulation not only in the bone but also in the DRG is essential for load-induced responses and skeletal adaptation, and (3) load-induced dysregulation of Panx1-P2X7R in diabetic bone augments local inflammatory responses that contribute to impair bone anabolic responses. To test these hypotheses we will use T1D mouse models, insulin therapy, time series loading, molecular, biochemical, histomorphometric, pharmacological and genetic approaches. These studies will establish the importance of bone neuro-mechanosignaling and inflammation as new players in diabetic osteopenia and identify novel and critical roles for the Panx1-P2X7R functional complex in regulation of bone adaptation in health and disease.