It has been presumed that rheumatoid arthritis (RA) joint pain is related to inflammation in the synovium; however, recent studies reveal that pain scores in patients do not correlate with synovial inflammation. We developed a machine-learning approach (graph-based gene expression module identification or GbGMI) to identify an 815-gene expression module associated with pain in synovial biopsy samples from patients with established RA who had limited synovial inflammation at arthroplasty. We then validated this finding in an independent cohort of synovial biopsy samples from patients who had early untreated RA with little inflammation. Single-cell RNA sequencing analyses indicated that most of these 815 genes were most robustly expressed by lining layer synovial fibroblasts. Receptor-ligand interaction analysis predicted cross-talk between human lining layer fibroblasts and human dorsal root ganglion neurons expressing calcitonin gene–related peptide (CGRP⁺). Both RA synovial fibroblast culture supernatant and netrin-4, which is abundantly expressed by lining fibroblasts and was within the GbGMI-identified pain-associated gene module, increased the branching of pain-sensitive murine CGRP⁺ dorsal root ganglion neurons in vitro. Imaging of solvent-cleared synovial tissue with little inflammation from humans with RA revealed CGRP⁺ pain-sensing neurons encasing blood vessels growing into synovial hypertrophic papilla. Together, these findings support a model whereby synovial lining fibroblasts express genes associated with pain that enhance the growth of pain-sensing neurons into regions of synovial hypertrophy in RA.

中文翻译：

---

滑膜成纤维细胞基因表达与类风湿性关节炎的感觉神经生长和疼痛相关

据推测，类风湿性关节炎 (RA) 关节疼痛与滑膜炎症有关。然而，最近的研究表明，患者的疼痛评分与滑膜炎症无关。我们开发了一种机器学习方法（基于图形的基因表达模块识别或 GbGMI），以识别与关节成形术中滑膜炎症有限的确诊 RA 患者的滑膜活检样本中的疼痛相关的 815 个基因表达模块。然后，我们在一组独立的滑膜活检样本中验证了这一发现，这些样本来自患有早期未治疗的 RA 且炎症很少的患者。单细胞 RNA 测序分析表明，这 815 个基因中的大多数在内层滑膜成纤维细胞中表达最为强烈。受体-配体相互作用分析预测人内衬层成纤维细胞和表达降钙素基因相关肽（CGRP ⁺ ）的人背根神经节神经元之间的串扰。 RA 滑膜成纤维细胞培养物上清液和 netrin-4（内膜成纤维细胞大量表达且位于 GbGMI 鉴定的疼痛相关基因模块内）在体外均增加了疼痛敏感小鼠 CGRP ⁺背根神经节神经元的分支。对患有 RA 的人的溶剂清除的滑膜组织进行成像，几乎没有炎症，结果显示 CGRP ⁺疼痛感应神经元包裹血管，生长成滑膜肥厚乳头。总之，这些发现支持了一个模型，即滑膜内层成纤维细胞表达与疼痛相关的基因，从而增强 RA 滑膜肥大区域的痛觉神经元的生长。