Chen Ouyang, Jiang Changyu, Berta Temugin, Powell Gray Bethany, Furutani Kenta, Sullenger Bruce A, Ji Ru-Rong
Department of Anesthesiology, Center for Translational Pain Medicine, Duke University Medical Center, Durham, NC, United States.
Department of Cell Biology, Duke University Medical Center, Durham, NC, United States.
Pain. 2024 Aug 1;165(8):1824-1839. doi: 10.1097/j.pain.0000000000003206. Epub 2024 Mar 6.
Secreted microRNAs (miRNAs) have been detected in various body fluids including the cerebrospinal fluid, yet their direct role in regulating synaptic transmission remains uncertain. We found that intrathecal injection of low dose of let-7b (1 μg) induced short-term (<24 hours) mechanical allodynia and heat hyperalgesia, a response that is compromised in Tlr7-/- or Trpa1-/- mice. Ex vivo and in vivo calcium imaging in GCaMP6-report mice revealed increased calcium signal in spinal cord afferent terminals and doral root ganglion/dorsal root ganglia neurons following spinal perfusion and intraplantar injection of let-7b. Patch-clamp recordings also demonstrated enhanced excitatory synaptic transmission (miniature excitatory postsynaptic currents [EPSCs]) in spinal nociceptive neurons following let-7b perfusion or optogenetic activation of axonal terminals. The elevation in spinal calcium signaling and EPSCs was dependent on the presence of toll-like receptor-7 (TLR7) and transient receptor potential ion channel subtype A1 (TRPA1). In addition, endogenous let-7b is enriched in spinal cord synaptosome, and peripheral inflammation increased let-7b in doral root ganglion/dorsal root ganglia neurons, spinal cord tissue, and the cerebrospinal fluid. Notably, let-7b antagomir inhibited inflammatory pain and inflammation-induced synaptic plasticity (EPSC increase), suggesting an endogenous role of let-7b in regulating pain and synaptic transmission. Furthermore, intrathecal injection of let-7b, at a higher dose (10 μg), induced persistent mechanical allodynia for >2 weeks, which was abolished in Tlr7-/- mice. The high dose of let-7b also induced microgliosis in the spinal cord. Of interest, intrathecal minocycline only inhibited let-7b-induced mechanical allodynia in male but not female mice. Our findings indicate that the secreted microRNA let-7b has the capacity to provoke pain through both neuronal and glial signaling, thereby establishing miRNA as an emerging neuromodulator.
在包括脑脊液在内的各种体液中都检测到了分泌型微小RNA（miRNA），但其在调节突触传递中的直接作用仍不确定。我们发现，鞘内注射低剂量的let-7b（1微克）会诱发短期（<24小时）机械性异常性疼痛和热痛觉过敏，Tlr7-/-或Trpa1-/-小鼠对这种反应不敏感。在表达GCaMP6的小鼠中进行的体外和体内钙成像显示，在脊髓灌注和足底注射let-7b后，脊髓传入神经末梢以及背根神经节/背根神经节神经元中的钙信号增加。膜片钳记录还表明，在let-7b灌注或轴突末梢的光遗传学激活后，脊髓伤害性神经元中的兴奋性突触传递（微小兴奋性突触后电流[EPSC]）增强。脊髓钙信号和EPSC的升高依赖于Toll样受体7（TLR7）和瞬时受体电位离子通道A1亚型（TRPA1）的存在。此外，内源性let-7b在脊髓突触体中富集，外周炎症会增加背根神经节/背根神经节神经元、脊髓组织和脑脊液中的let-7b。值得注意的是，let-7b拮抗剂可抑制炎性疼痛和炎症诱导的突触可塑性（EPSC增加），表明let-7b在调节疼痛和突触传递中具有内源性作用。此外，鞘内注射较高剂量（10微克）的let-7b会诱发持续超过2周的持续性机械性异常性疼痛，而在Tlr7-/-小鼠中这种疼痛消失。高剂量的let-7b还会诱导脊髓中的小胶质细胞增生。有趣的是，鞘内注射米诺环素仅在雄性小鼠中抑制let-7b诱导的机械性异常性疼痛，而在雌性小鼠中则无此作用。我们的研究结果表明，分泌型微小RNA let-7b能够通过神经元和神经胶质信号传导引发疼痛，从而确立了miRNA作为一种新兴的神经调节剂。
