Role of the sensory nervous system in subchondral bone remodeling and synovial inflammation in OA pathology

关节由降钙素基因相关肽(α-CGRP)和P物质(SP)阳性感觉神经纤维支配，有证据表明感觉神经递质具有重要的营养作用，对正常的骨代谢和骨重建至关重要。感觉神经支配的改变可能是退行性改变的部分原因，退行性改变有助于骨关节炎(OA)的发展。在骨性关节炎的发病过程中，由于感觉神经支配和神经递质环境的改变，导致软骨下骨异常改建的分子机制大多尚不清楚。在第一个资助期，我们观察到，与WT小鼠相比，两个神经肽缺陷小鼠的软骨基质降解都加速了(与WT小鼠相比，这伴随着压痕型原子力显微镜(IT-AFM)评估的AC的生物力学特性(僵硬增加)。应用µCT和高分辨率纳米CT，我们发现了明确的证据，这两种神经肽都能保护DMM诱导的软骨下骨退化/硬化和半月板异位骨形成，影响骨微结构已经处于早期OA阶段。感觉神经肽及其受体均参与小鼠巨噬细胞机械转导，影响神经肽对黏附和ROS活性的影响。综上所述，我们的结果表明，SP和αCGRP在结构和力学性质方面都具有保护骨和软骨的功能。我们假设感觉神经肽是骨细胞代谢和表型的调节器，在骨关节炎发病过程中响应异常的机械负荷，它们参与了骨关节炎关节炎症过程的调节。为此，我们想要表征感觉神经肽在DMM诱导的骨关节炎加强迫运动(小鼠)和自发性骨关节炎(WP1)发病机制中对骨细胞细胞变化的贡献。其次，我们想要表征感觉神经肽对DMM诱导的骨关节炎加强迫运动和自发性骨关节炎(WP2)后单个核细胞(即巨噬细胞)和促炎介质在滑膜组织中的渗透、活性和成熟的影响。最后，我们将测试关节腔内应用表达α-CGRP和SP的rAAV5病毒是否会对骨关节炎诱导后关节组织的病理生理变化产生影响。

The joints are innervated by calcitonin gene-related peptide (alpha-CGRP)- and substance P (SP) positive sensory nerve fibers and there is evidence that sensory neurotransmitters have crucial trophic effects which are essential for proper bone metabolism and bone remodeling. Alteration of sensory joint innervation might be partly responsible for degenerative changes, which contribute to development of osteoarthritis (OA). Underlying molecular mechanisms which add to abnormal subchondral bone remodeling during the pathogenesis of OA due to changes in sensory joint innervation and their respective neurotransmitter milieu are mostly unknown. In the first funding period we observed that cartilage matrix degradation was accelerated in both neuropeptide-deficient mouse strains) which was accompanied by altered biomechanical properties (increased stiffness) of the AC assessed by indentation-type AFM (IT-AFM) compared to WT mice. Applying µCT and high-resolution nanoCT, we found clear evidence that both neuropeptides protect from DMM-induced subchondral bone degeneration/sclerosis and ectopic bone formation in the meniscus affecting bone microarchitecture already in an early OA stage. Both sensory neuropeptides and their receptors are involved in murine macrophage mechanotransduction affecting neuropeptide impact on adhesion and ROS activity. Taken together, our results imply that both SP and αCGRP have preserving functions for bone and cartilage in the context of structural and mechanical properties.We hypothesize that sensory neuropeptides are modulators of osteocyte metabolism and phenotype in response to aberrant mechanical loading during OA pathogenesis and that they are involved in modulating inflammatory processes in the joint during OA. For that we want to characterize the contribution of sensory neuropeptides to cellular changes in osteocytes during pathogenesis of DMM induced OA plus forced exercise (mice) and during spontaneous OA (WP1). Secondly, we want to characterize the influence of sensory neuropeptides on infiltration, activity and maturation of mononuclear cells, i.e. macrophages, and pro-inflammatory mediators into synovial tissue after DMM induced OA plus forced exercise and spontaneous OA (WP2). Finally, we will test if intra-articular application of rAAV5 virus expressing alpha-CGRP and SP impacts on joint tissues pathophysiological changes after OA induction.