MICA: Synovial fibroblast pain pathotypes: A roadmap to understanding and targeting the complexity of patient-reported joint pain in osteoarthritis

骨关节炎（OA）是一种非常痛苦的关节疾病，也是导致残疾的主要原因。目前的止痛药物只有最低限度的效果，并且长期伴有副作用。开发更有效的OA镇痛药物的挑战之一是了解OA关节疼痛的复杂潜在机制。重要的是，滑膜关节衬里组织的炎症（称为滑膜炎）与膝关节OA患者疼痛严重程度的增加有关，我们已经证明，滑膜组织内的细胞（称为滑膜成纤维细胞）通过分泌促进炎症的因子来调节关节的炎症环境。为了研究滑膜炎和OA关节疼痛之间关系的细胞和分子基础，我们对膝关节OA患者进行了一项研究，我们通过MRI绘制了滑膜炎的解剖位置，并要求患者在膝关节图上标记疼痛最严重和疼痛最少的位置。然后，我们从患者报告的疼痛部位和无疼痛部位收集滑膜组织样本。值得注意的是，滑膜炎的程度与患者报告的疼痛模式密切相关，此外，患者报告的疼痛部位的滑膜关节衬里组织含有不同的滑膜成纤维细胞群，这些细胞促进炎症和分泌促进神经细胞生长和存活的因子。由于滑膜关节衬里组织包含许多神经末梢，我们认为这些与疼痛相关的滑膜成纤维细胞的活动是OA关节疼痛的主要原因。我们假设，减少这些滑膜成纤维细胞活动的治疗方法将减轻膝关节OA患者的关节疼痛。该建议的总体目标是在更大的患者队列中绘制疼痛相关滑膜成纤维细胞的存在和位置与患者报告的疼痛和滑膜炎之间的关系，然后确定使用一种新的基因沉默疗法调节这些细胞的活性是否会降低感觉神经功能并减轻疼痛。为了实现这些目标，我们将目前的膝关节OA患者疼痛研究扩大到82例患者（41例早期OA疾病和41例终末期疾病）。关节滑膜炎的解剖位置和程度将通过MRI测量，患者报告的疼痛严重程度和疼痛位置将通过问卷调查和完成解剖疼痛图来捕获。将收集血液和关节液，并从患者报告疼痛和无疼痛的部位收集滑膜关节衬里组织。将测量与疼痛相关的滑膜成纤维细胞基因特征的表达和空间位置，并确定它们与滑膜炎、炎症和患者报告的疼痛的血液和关节液生物标志物的关系。来自疼痛和无疼痛部位的滑膜组织和成纤维细胞的基因表达数据将使用计算模型进行分析，以建立连接滑膜成纤维细胞与神经细胞活性的基因通路网络，以确定新的候选疼痛基因介质。然后，我们将设计基因沉默疗法来靶向候选疼痛基因，并在OA小鼠模型中检查这些疗法对调节神经细胞活性的影响，确定治疗对关节组织的吸收及其对减轻关节炎症和疼痛的影响。这些实验将提供第一个证据，证明针对关节中特定的疼痛相关滑膜成纤维细胞是否可以减轻关节炎症和疼痛。总之，该项目将促进我们对滑膜成纤维细胞在炎症性疼痛中的作用的理解，并为OA患者新的疼痛缓解疗法的临床开发奠定基础。

BackgroundOsteoarthritis (OA) is highly painful joint disorder and a leading cause of disability. Current pain-relief medications are only minimally effective and are associated with side effects over the long term. One of the challenges in developing a more effective pain-relieving OA drug is understanding of the complex underlying mechanisms of OA joint pain. Importantly, inflammation of the synovial joint lining tissue (termed synovitis) is associated with increased pain severity in knee OA patients, and we have shown that the cells which reside within the synovial tissue (known as synovial fibroblasts) regulate the inflammatory environment of the joint by secreting factors that promote inflammation. To investigate the cellular and molecular basis for the relationship between synovitis and OA joint pain, we involved knee OA patients in a study where we mapped the anatomical location of synovitis by MRI and of patient-reported pain by asking patients to mark on a diagram of the knee joint, where they felt most pain and where they felt least pain. We then collected synovial tissue samples from both sites of patient-reported pain and sites of no pain. Significantly, the degree of synovitis was closely associated with the pattern of patient-reported pain, and furthermore that synovial joint lining tissue at the site of patient-reported pain contained distinct populations of synovial fibroblast cells, that promoted inflammation and secreted factors that promoted the growth and survival of nerve cells. Since the synovial joint lining tissue contains numerous nerve endings we believe that the activity of these pain-associated synovial fibroblast cells is a major contributor to OA joint pain. We hypothesise that therapeutics that reduce the activity of these synovial fibroblasts will alleviate joint pain in patients with knee OA. AimThe overarching aim of the proposal is to map the relationship between the presence and location of pain-associated synovial fibroblasts with patient-reported pain and synovitis in a larger patient cohort, and then to determine whether modulating the activity of these cells using a novel gene silencing therapeutic reduces sensory nerve function and alleviates pain.Experimental PlanTo address these aims we will expand our current knee OA patient pain study to 82 patients (41 with early OA disease and 41 with end-stage disease). The anatomical location and degree of synovitis in the joint will be measured by MRI and patient-reported pain severity and pain location captured by questionnaires and completion of the anatomical pain map. Blood and joint fluid will be collected, and synovial joint lining tissue collected from sites of patient-reported pain and no pain. The expression and spatial location of pain-associated synovial fibroblast gene signatures will be measured, and their relationship mapped to synovitis, blood and joint fluid biomarkers of inflammation and patient-reported pain determined. Gene expression data of synovial tissue and fibroblast cells from sites of pain and no-pain will be analysed using computational modelling to build networks of the gene pathways that connect the activity of synovial fibroblasts with nerve cells in order to identify new candidate pain gene mediators. We will then design gene silencing therapeutics to target candidate pain genes, and examine the effect of these therapeutics on modulating nerve cell activity and in a mouse model of OA, determine the uptake of the therapeutic to the joint tissues and its effect on reducing joint inflammation and pain. These experiments will provide the first evidence of whether targeting specific pain-associated synovial fibroblast cells in the joint can alleviate joint inflammation and pain. In summary, this project will advance our understanding of the role of synovial fibroblasts in inflammatory pain and lay the groundwork for the clinical development of a new pain-relieving therapeutic for OA patients.