Song Xiao-Xing, Jin Lin-Yu, Li Qiang, Li Xin-Feng, Luo Yan
Department of Anesthesiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Department of Orthopedics, Shanghai Key Laboratory for Prevention and Treatment of Bone and Joint Diseases, Shanghai Institute of Traumatology and Orthopedics, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Front Cell Neurosci. 2023 Jan 23;16:1071012. doi: 10.3389/fncel.2022.1071012. eCollection 2022.
Discogenic low back pain (DLBP) is the most commonly described form of back pain. Our previous studies indicated that estrogen-dependent DLBP mechanism was mediated by estrogen receptors (ERs) in the intervertebral disc (IVD) tissue, and the IVD degeneration degree is accompanied by downregulation of ERs, particularly ERβ. However, the neuropathological mechanisms underlying ERs modulation of DLBP are still not well understood. In this study, we investigated the antinociceptive effects of selective ERβ agonists on DLBP-related behavior by regulating substance P in spinal cord and dorsal root ganglia.
Two weeks after ovariectomies, 18-week-old female mice were randomly separated into four groups: control group; DLBP sham surgery plus vehicle group; DLBP plus vehicle group; DLBP plus ERβ-specific agonist diarylpropionitrile (DPN) group. Behavioral data was collected including behavioral measures of axial back pain (grip force and tail suspension tests) and radiating hypersensitivity (mechanical sensitivity and cold sensitivity test). Dual label scanning confocal immunofluorescence microscopy was used to observe spatial colocalization of ERβ and substance P in spinal cord. Substance P changes in spinal cord and dorsal root ganglia were measured by immunohistochemistry and real-time PCR.
ERβ activation could improve both axial and radiating behavioral disorders of DLBP. DPN facilitated the decrease of the amount of time in immobility 1 week after agonist administration. At the time point of 3 weeks, DPN group spent significantly less time in immobility than the vehicle group. In the grip strength tests, starting from postoperative week 1-week 3, DPN injection DLBP mice showed more resistance to stretch than the vehicle injection DLBP mice. Significant differences of cold withdrawal latency time were observed between the DLBP plus DPN injection and DLBP vehicle injection groups at 2- and 3-week injection time point. DPN significantly reversed the paw withdrawal threshold of DLBP mice at the time point of 1, 2, and 3 weeks. Substance P colocalized with ERβ in spinal dorsal horn, mainly in laminae I and II, a connection site of pain transmission. Substance P levels in dorsal horn and dorsal root ganglia of DLBP group were distinctly increased compared with that of control and DLBP sham group. DPN therapy could decrease substance P content in the dorsal horn and the dorsal root ganglia of DLBP mice compared with that of vehicle-treated DLBP mice.
Activation of ERβ is antinociceptive in the DLBP model by controlling substance P in spinal cord and dorsal root ganglia, which might provide a therapeutic target to manage DLBP in the clinic.
椎间盘源性下腰痛（DLBP）是最常见的下腰痛形式。我们之前的研究表明，雌激素依赖性DLBP机制是由椎间盘（IVD）组织中的雌激素受体（ERs）介导的，并且IVD退变程度伴随着ERs的下调，尤其是ERβ。然而，ERs调节DLBP的神经病理机制仍未完全清楚。在本研究中，我们通过调节脊髓和背根神经节中的P物质，研究了选择性ERβ激动剂对DLBP相关行为的镇痛作用。
卵巢切除术后两周，将18周龄雌性小鼠随机分为四组：对照组；DLBP假手术加赋形剂组；DLBP加赋形剂组；DLBP加ERβ特异性激动剂二芳基丙腈（DPN）组。收集行为学数据，包括轴向背痛的行为测量（握力和尾悬测试）和放射性超敏反应（机械敏感性和冷敏感性测试）。采用双标记扫描共聚焦免疫荧光显微镜观察脊髓中ERβ和P物质的空间共定位。通过免疫组织化学和实时PCR测量脊髓和背根神经节中P物质的变化。
ERβ激活可改善DLBP的轴向和放射性行为障碍。DPN在给予激动剂1周后促进了不动时间的减少。在3周时间点，DPN组的不动时间明显少于赋形剂组。在握力测试中，从术后第1周-第3周开始，注射DPN的DLBP小鼠比注射赋形剂的DLBP小鼠表现出更强的抗拉伸能力。在注射2周和3周时间点，注射DPN的DLBP组和注射赋形剂的DLBP组之间的冷退缩潜伏期时间存在显著差异。在1周、2周和3周时间点，DPN显著逆转了DLBP小鼠的爪退缩阈值。P物质与ERβ在脊髓背角共定位，主要在I层和II层，这是疼痛传递的连接部位。与对照组和DLBP假手术组相比，DLBP组背角和背根神经节中的P物质水平明显升高。与赋形剂处理的DLBP小鼠相比，DPN治疗可降低DLBP小鼠背角和背根神经节中的P物质含量。
在DLBP模型中，激活ERβ通过控制脊髓和背根神经节中的P物质具有镇痛作用，这可能为临床治疗DLBP提供一个治疗靶点。
