Osteoarthritis (OA) is a painful degenerative joint disease and a leading source of years lived with disability globally due to inadequate treatment options. Neuroimmune interactions reportedly contribute to OA pain pathogenesis. Notably, in rodents, macrophages in the DRG are associated with onset of persistent OA pain. Our objective was to determine the effects of acute systemic macrophage depletion on pain-related behaviors and joint damage using surgical mouse models in both sexes. We depleted CSF1R + macrophages by treating male macrophage Fas-induced apoptosis (MaFIA) transgenic mice 8- or 16-weeks post destabilization of the medial meniscus (DMM) with AP20187 or vehicle control (10 mg/kg i.p., 1x/day for 5 days), or treating female MaFIA mice 12 weeks post partial meniscectomy (PMX) with AP20187 or vehicle control. We measured pain-related behaviors 1–3 days before and after depletion, and, 3–4 days after the last injection we examined joint histopathology and performed flow cytometry of the dorsal root ganglia (DRGs). In a separate cohort of male 8-week DMM mice or age-matched naïve vehicle controls, we conducted DRG bulk RNA-sequencing analyses after the 5-day vehicle or AP20187 treatment. Eight- and 16-weeks post DMM in male mice, AP20187-induced macrophage depletion resulted in attenuated mechanical allodynia and knee hyperalgesia. Female mice showed alleviation of mechanical allodynia, knee hyperalgesia, and weight bearing deficits after macrophage depletion at 12 weeks post PMX. Macrophage depletion did not affect the degree of cartilage degeneration, osteophyte width, or synovitis in either sex. Flow cytometry of the DRG revealed that macrophages and neutrophils were reduced after AP20187 treatment. In addition, in the DRG, only MHCII + M1-like macrophages were significantly decreased, while CD163 + MHCII- M2-like macrophages were not affected in both sexes. DRG bulk RNA-seq revealed that Cxcl10 and Il1b were upregulated with DMM surgery compared to naïve mice, and downregulated in DMM after acute macrophage depletion. Acute systemic macrophage depletion reduced the levels of pro-inflammatory macrophages in the DRG and alleviated pain-related behaviors in established surgically induced OA in mice of both sexes, without affecting joint damage. Overall, these studies provide insight into immune cell regulation in the DRG during OA.

中文翻译：

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骨关节炎小鼠急性全身性巨噬细胞耗竭可缓解疼痛相关行为，不影响关节损伤


骨关节炎 （OA） 是一种痛苦的退行性关节疾病，由于治疗方案不足，全球残疾寿命年限是主要来源。据报道，神经免疫相互作用有助于 OA 疼痛的发病机制。值得注意的是，在啮齿动物中，DRG 中的巨噬细胞与持续性 OA 疼痛的发作有关。我们的目标是使用两性的手术小鼠模型确定急性全身性巨噬细胞耗竭对疼痛相关行为和关节损伤的影响。我们通过在内侧半月板 （DMM） 不稳定后 8 周或 16 周用 AP20187 或载体对照 （10 mg/kg ip，1x/天，持续 5 天） 处理雄性巨噬细胞 Fas 诱导的细胞凋亡 （MaFIA） 转基因小鼠来消耗 CSF1R + 巨噬细胞，或在部分半月板切除术 （PMX） 后 12 周用 AP20187 或载体对照处理雌性 MaFIA 小鼠。我们测量了耗竭前后 1-3 天的疼痛相关行为，最后一次注射后 3-4 天，我们检查了关节组织病理学并进行了背根神经节 （DRG） 的流式细胞术。在单独的雄性 8 周 DMM 小鼠或年龄匹配的幼稚载体对照队列中，我们在 5 天载体或AP20187处理后进行了 DRG 批量 RNA 测序分析。雄性小鼠 DMM 后 8 周和 16 周，AP20187诱导的巨噬细胞耗竭导致机械性痛觉异常和膝关节痛觉过敏减弱。雌性小鼠在 PMX 后 12 周巨噬细胞耗竭后表现出机械性痛觉异常、膝关节痛觉过敏和负重缺陷的缓解。巨噬细胞耗竭不影响任何性别的软骨变性程度、骨赘宽度或滑膜炎。DRG 流式细胞术显示 AP20187 处理后巨噬细胞和中性粒细胞减少。 此外，在 DRG 中，只有 MHCII + M1 样巨噬细胞显著减少，而 CD163 + MHCII-M2 样巨噬细胞在两性中均未受到影响。DRG 大量 RNA-seq 显示，与幼稚小鼠相比，DMM 手术中 Cxcl10 和 Il1b 上调，而急性巨噬细胞耗竭后 DMM 中下调。急性全身性巨噬细胞耗竭降低了 DRG 中促炎巨噬细胞的水平，并减轻了两性小鼠已建立的手术诱导的 OA 中的疼痛相关行为，而不会影响关节损伤。总体而言，这些研究提供了对 OA 期间 DRG 中免疫细胞调节的见解。