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

关节受降钙素基因相关肽（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，对骨代谢和骨重塑至关重要。感觉关节神经支配的改变可能是退行性改变的部分原因，这有助于骨关节炎（OA）的发展。在骨性关节炎发病过程中，由于感觉关节神经支配和它们各自的神经递质环境的改变而导致软骨下骨重构异常的潜在分子机制大多是未知的。在第一个资助期，我们观察到，与WT小鼠相比，在两种神经肽缺乏的小鼠品系中，软骨基质降解加速，伴随着压痕型AFM （IT-AFM）评估的AC生物力学特性的改变（刚度增加）。应用微CT和高分辨率纳米oct，我们发现明确的证据表明，这两种神经肽都可以保护半月板免受dmm诱导的软骨下骨变性/硬化症和异位骨形成，影响早期OA阶段的骨微结构。感觉神经肽及其受体均参与小鼠巨噬细胞的机械转导，影响神经肽对黏附和ROS活性的影响。综上所述，我们的研究结果表明SP和αCGRP在结构和力学性能方面都对骨和软骨具有保护功能。我们假设感觉神经肽是骨关节炎发病过程中异常机械负荷下骨细胞代谢和表型的调节剂，并参与骨关节炎期间关节炎症过程的调节。为此，我们想要描述感觉神经肽在DMM诱导的OA +强迫运动（小鼠）发病过程中以及自发性OA （WP1）期间骨细胞细胞变化中的作用。其次，我们想要表征感觉神经肽对DMM诱导OA +强迫运动和自发性OA后滑膜组织中单核细胞（即巨噬细胞）和促炎介质的浸润、活性和成熟的影响（WP2）。最后，我们将检测在关节内应用表达α - cgrp和SP的rAAV5病毒对OA诱导后关节组织病理生理变化的影响。

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.