Program in Neuroscience & Mental Health, Hospital for Sick Children, Toronto, ON, Canada.
Department of Physiology, University of Toronto, Toronto, ON, Canada.
Pain. 2018 Sep;159(9):1752-1763. doi: 10.1097/j.pain.0000000000001265.
Microglia-neuron signalling in the spinal cord is a key mediator of mechanical allodynia caused by peripheral nerve injury. We recently reported sex differences in microglia in pain signalling in mice: spinal mechanisms underlying nerve injury-induced allodynia are microglial dependent in male but not female mice. Whether this sex difference in pain hypersensitivity mechanisms is conserved in other species is unknown. Here, we show that in rats, the spinal mechanisms of nerve injury-induced hypersensitivity in males differ from those in females, with microglial P2X4 receptors (P2X4Rs) being a key point of divergence. In rats, nerve injury produced comparable allodynia and reactive microgliosis in both sexes. However, inhibiting microglia in the spinal cord reversed allodynia in male rats but not female rats. In addition, pharmacological blockade of P2X4Rs, by an intrathecally administered antagonist, attenuated pain hypersensitivity in male rats only. Consistent with the behavioural findings, nerve injury increased cell surface expression and function of P2X4Rs in acutely isolated spinal microglia from male rats but not from female rats. Moreover, in microglia cultured from male rats, but not in those from female rats, stimulating P2X4Rs drove intracellular signalling through p38 mitogen-activated protein kinase. Furthermore, chromatin immunoprecipitation-qPCR revealed that the transcription factor IRF5 differentially binds to the P2rx4 promoter region in female rats vs male rats. Finally, mechanical allodynia was produced in otherwise naive rats by intrathecally administering P2X4R-stimulated microglia from male rats but not those from female rats. Together, our findings demonstrate the existence of sexually dimorphic pain signalling in rats, suggesting that this sex difference is evolutionarily conserved, at least across rodent species.
脊髓中的小胶质细胞-神经元信号转导是外周神经损伤引起机械性痛觉过敏的关键介质。我们最近报道了小鼠疼痛信号中小胶质细胞存在性别差异：在雄性小鼠中，脊髓机制是神经损伤诱导的痛觉过敏的基础，而在雌性小鼠中则不是。这种疼痛敏化机制的性别差异是否在其他物种中保守尚不清楚。在这里，我们发现在大鼠中，雄性和雌性神经损伤诱导的敏感性的脊髓机制不同，其中小胶质细胞 P2X4 受体（P2X4R）是一个关键的分歧点。在大鼠中，神经损伤在两性中均产生类似的痛觉过敏和反应性小胶质细胞增生。然而，在脊髓中抑制小胶质细胞可逆转雄性大鼠的痛觉过敏，但不能逆转雌性大鼠的痛觉过敏。此外，通过鞘内给予拮抗剂抑制 P2X4R 可减轻雄性大鼠的痛觉过敏，但不能减轻雌性大鼠的痛觉过敏。与行为学发现一致，神经损伤增加了急性分离的雄性大鼠脊髓小胶质细胞表面表达和功能，但不增加雌性大鼠脊髓小胶质细胞表面表达和功能。此外，在雄性大鼠培养的小胶质细胞中，但不在雌性大鼠培养的小胶质细胞中，刺激 P2X4R 通过 p38 丝裂原活化蛋白激酶驱动细胞内信号转导。此外，染色质免疫沉淀-qPCR 显示转录因子 IRF5 在雌性大鼠与雄性大鼠的 P2rx4 启动子区域中存在差异结合。最后，通过鞘内给予雄性大鼠小胶质细胞刺激的 P2X4R 来产生机械性痛觉过敏，而不是给予雌性大鼠小胶质细胞刺激的 P2X4R 来产生机械性痛觉过敏。总之，我们的研究结果表明大鼠存在性别二态性疼痛信号转导，这表明这种性别差异至少在啮齿动物中是进化保守的。
