Harvey Madeleine E, Shi Mingxin, Oh Yeongseok, Mitchell Debra A, Slayden Ov D, MacLean James A, Hayashi Kanako
School of Molecular Biosciences, Center for Reproductive Biology, Washington State University, 1770 NE Stadium Way, Pullman, WA, 99164, USA.
Division of Reproductive and Developmental Sciences, Oregon National Primate Research Center, Oregon Health & Science University, Beaverton, OR, 97006, USA.
bioRxiv. 2025 Jan 24:2025.01.23.634555. doi: 10.1101/2025.01.23.634555.
Endometriosis is an inflammatory disease associated with chronic pelvic pain (CPP). Growing evidence indicates that endometriotic lesions are not the sole source of pain. Instead, central nervous system (CNS) dysfunction created by prolonged peripheral and central sensitization plays a role in developing endometriosis-associated CPP. This study investigated how CPP is established using a multiple lesion induction mouse model of endometriosis, as repeated retrograde menstruation is considered underlying endometriosis pathogenesis.
We generated endometriosis-like lesions by injecting endometrial tissue fragments into the peritoneal cavity in mice. The mice received a single (1x) or multiple inductions (6x) to simulate recurrent retrograde menstruation. Lesion development, hyperalgesia by behavioral testing, signs of peripheral sensitization, chronic inflammation, and neuroinflammation were examined with lesions, peritoneal fluids, dorsal root ganglia (DRG), spinal codes, and brain.
Multiple lesion inductions increased lesion numbers and elevated abdominal and hind paw hypersensitivity compared to single induction mice. Elevated persistent glial cell activation across several brain regions and/or spinal cords was found in the multiple induction mice. Specifically, IBA1+ microglial soma size was increased in the hippocampus and thalamus. IBA1+ cells were abundant in the cortex, hippocampus, thalamus, and hypothalamus of the multiple induction mice. GFAP+ astrocytes were mainly elevated in the hippocampus. Elevated TRPV1, SP, and CGRP expressions in the DRG were persistent in the multiple induction mice. Furthermore, multiple inductions induced the severe disappearance of TIM4 MHCII residential macrophages and the influx of increased proinflammatory TIM4 MHCII macrophages in the peritoneal cavity. The single and multiple inductions elevated secreted TNFα, IL-1β, and IL-6 levels in the peritoneal cavity at 2 weeks. Elevated cytokine levels returned to the pre-induction levels in the single induction mice at 6 weeks; however, they remained elevated in the multiple induction mice.
Our results indicate that the repeatedly occurring lesion inductions (=mimic retrograde menstruation) can be a peripheral stimulus that induces nociceptive pain and creates composite chronic inflammatory stimuli to cause neuroinflammation and sensitize the CNS. The circuits of neuroplasticity and stimulation of peripheral organs via a feedback loop of neuroinflammation may mediate widespread endometriosis-associated CPP.
子宫内膜异位症是一种与慢性盆腔疼痛（CPP）相关的炎症性疾病。越来越多的证据表明，子宫内膜异位症病灶并非疼痛的唯一来源。相反，长期的外周和中枢敏化所导致的中枢神经系统（CNS）功能障碍在子宫内膜异位症相关CPP的发生中起作用。本研究使用子宫内膜异位症的多病灶诱导小鼠模型来探究CPP是如何形成的，因为反复的经血流逆行被认为是子宫内膜异位症发病机制的基础。
我们通过将子宫内膜组织碎片注射到小鼠腹腔中来生成类似子宫内膜异位症的病灶。小鼠接受单次（1x）或多次诱导（6x）以模拟反复的经血流逆行。通过对病灶、腹腔液、背根神经节（DRG）、脊髓和大脑进行检查，来观察病灶发展、行为测试中的痛觉过敏、外周敏化迹象、慢性炎症和神经炎症。
与单次诱导小鼠相比，多次病灶诱导增加了病灶数量，并提高了腹部和后爪的超敏反应。在多次诱导小鼠中，发现多个脑区和/或脊髓中持续存在胶质细胞活化升高。具体而言，海马体和丘脑中IBA1+小胶质细胞的胞体大小增加。多次诱导小鼠的皮质、海马体、丘脑和下丘脑中IBA1+细胞丰富。GFAP+星形胶质细胞主要在海马体中升高。多次诱导小鼠的DRG中TRPV1、SP和CGRP表达持续升高。此外，多次诱导导致腹腔中TIM4 MHCII驻留巨噬细胞严重消失，促炎的TIM4 MHCII巨噬细胞流入增加。单次和多次诱导在2周时均使腹腔中分泌的TNFα、IL-1β和IL-6水平升高。单次诱导小鼠在6周时细胞因子水平恢复到诱导前水平；然而，多次诱导小鼠的细胞因子水平仍保持升高。
我们的结果表明，反复发生的病灶诱导（=模拟经血流逆行）可能是一种外周刺激，可诱导伤害性疼痛并产生复合慢性炎症刺激，从而导致神经炎症并使中枢神经系统致敏。神经可塑性回路以及通过神经炎症反馈回路对外周器官的刺激可能介导广泛的子宫内膜异位症相关CPP。
