Pain from osteoarthritis (OA) is one of the top causes of disability worldwide, but effective treatment is lacking. Nociceptive factors are released by activated synovial macrophages in OA, but depletion of synovial macrophages paradoxically worsens inflammation and tissue damage in previous studies. Rather than depleting macrophages, we hypothesized that inhibiting macrophage activation may improve pain without increasing tissue damage. We aimed to identify key mechanisms mediating synovial macrophage activation and test the role of STAT signaling in macrophages on pain outcomes in experimental knee OA. We induced experimental knee OA in rats via knee destabilization surgery, and performed RNA sequencing analysis on sorted synovial tissue macrophages to identify macrophage activation mechanisms. Liposomes laden with STAT1 or STAT6 inhibitors, vehicle (control), or clodronate (depletion control) were delivered selectively to synovial macrophages via serial intra-articular injections up to 12 weeks after OA induction. Treatment effects on knee and hindpaw mechanical pain sensitivity were measured during OA development, along with synovitis, cartilage damage, and synovial macrophage infiltration using histopathology and immunofluorescence. Lastly, crosstalk between drug-treated synovial tissue and articular chondrocytes was assessed in co-culture. The majority of pathways identified by transcriptomic analyses in OA synovial macrophages involve STAT signaling. As expected, macrophage depletion reduced pain, but increased synovial tissue fibrosis and vascularization. In contrast, STAT6 inhibition in macrophages led to marked, sustained improvements in mechanical pain sensitivity and synovial inflammation without worsening synovial or cartilage pathology. During co-culture, STAT6 inhibitor-treated synovial tissue had minimal effects on healthy chondrocyte gene expression, whereas STAT1 inhibitor-treated synovium induced changes in numerous cartilage turnover-related genes. These results suggest that STAT signaling is a major mediator of synovial macrophage activation in experimental knee OA. STAT6 may be a key mechanism mediating the release of nociceptive factors from macrophages and the development of mechanical pain sensitivity. Whereas therapeutic depletion of macrophages paradoxically increases inflammation and fibrosis, blocking STAT6-mediated synovial macrophage activation may be a novel strategy for OA-pain management without accelerating tissue damage.

中文翻译：

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靶向 STAT6 介导的滑膜巨噬细胞激活可改善实验性膝骨关节炎的疼痛

骨关节炎 (OA) 引起的疼痛是全世界残疾的主要原因之一，但缺乏有效的治疗方法。OA 中活化的滑膜巨噬细胞会释放伤害感受因子，但在之前的研究中，滑膜巨噬细胞的耗竭却反而加剧了炎症和组织损伤。我们假设抑制巨噬细胞活化可以改善疼痛而不增加组织损伤，而不是耗尽巨噬细胞。我们的目的是确定介导滑膜巨噬细胞激活的关键机制，并测试巨噬细胞中 STAT 信号传导对实验性膝关节 OA 疼痛结果的作用。我们通过膝关节失稳手术诱导大鼠实验性膝关节 OA，并对分选的滑膜组织巨噬细胞进行 RNA 测序分析，以确定巨噬细胞激活机制。在 OA 诱导后长达 12 周，通过连续关节内注射将载有 STAT1 或 STAT6 抑制剂、载体（对照）或氯膦酸盐（消耗对照）的脂质体选择性递送至滑膜巨噬细胞。使用组织病理学和免疫荧光法测量 OA 发展过程中对膝关节和后爪机械疼痛敏感性的治疗效果，以及滑膜炎、软骨损伤和滑膜巨噬细胞浸润。最后，在共培养中评估药物处理的滑膜组织和关节软骨细胞之间的串扰。OA 滑膜巨噬细胞转录组分析发现的大多数通路都涉及 STAT 信号传导。正如预期的那样，巨噬细胞的消耗减轻了疼痛，但增加了滑膜组织的纤维化和血管化。相比之下，巨噬细胞中的 STAT6 抑制导致机械疼痛敏感性和滑膜炎症显着持续改善，而不会恶化滑膜或软骨病理学。在共培养过程中，STAT6抑制剂处理的滑膜组织对健康软骨细胞基因表达的影响最小，而STAT1抑制剂处理的滑膜会诱导许多软骨更新相关基因的变化。这些结果表明 STAT 信号传导是实验性膝关节 OA 滑膜巨噬细胞激活的主要介质。STAT6可能是介导巨噬细胞释放伤害性因子和机械性疼痛敏感性发展的关键机制。尽管巨噬细胞的治疗性消耗反而会增加炎症和纤维化，但阻断 STAT6 介导的滑膜巨噬细胞活化可能是治疗 OA 疼痛而不加速组织损伤的新策略。