Objectives: Trigeminal neuralgia (TN) is a common neuropathic pain. Voltage-gated potassium channel (Kv) has been confirmed to be involved in the occurrence and development of TN, but the specific mechanism is still unclear. MicroRNA may be involved in neuropathic pain by regulating the expression of Kv channels and neuronal excitability in trigeminal ganglion (TG). This study aims to explore the relationship between Kv1.1 and miR-21-5p in TG with a TN model, evaluate whether miR-21-5p has a regulatory effect on Kv1.1, and to provide a new target and experimental basis for the treatment of TN.
Methods: A total of 48 SD rats were randomly divided into 6 groups: 1) a sham group (n=12), the rats were only sutured at the surgical incision without nerve ligation; 2) a sham+agomir NC group (n=6), the sham rats were microinjected with agomir NC through stereotactic brain injection in the surgical side of TG; 3) a sham+miR-21-5p agomir group (n=6), the sham rats were microinjected with miR-21-5p agomir via stereotactic brain injection in the surgical side of TG; 4) a TN group (n=12), a TN rat model was constructed using the chronic constriction injury of the distal infraorbital nerve (dIoN-CCI) method with chromium intestinal thread; 5) a TN+antagonist NC group (n=6), TN rats were microinjected with antagonist NC through stereotactic brain injection method in the surgical side of TG; 6) a TN+miR-21-5p antagonist group (n=6), TN rats were microinjected with miR-21-5p antagonist through stereotactic brain injection in the surgical side of TG. The change of mechanical pain threshold in rats of each group after surgery was detected. The expressions of Kv1.1 and miR-21-5p in the operative TG of rats were detected by Western blotting and real-time reverse transcription polymerase chain reaction. Dual luciferase reporter genes were used to determine whether there was a target relationship between Kv1.1 and miR-21-5p and whether miR-21-5p directly affected the 3'-UTR terminal of KCNA1. The effect of brain stereotaxic injection was evaluated by immunofluorescence assay, and then the analogue of miR-21-5p (agomir) and agomir NC were injected into the TG of rats in the sham group by brain stereotaxic apparatus to overexpress miR-21-5p. The miR-21-5p inhibitor (antagomir) and antagomir NC were injected into TG of rats in the TN group to inhibit the expression of miR-21-5p. The behavioral changes of rats before and after administration were observed, and the expression changes of miR-21-5p and Kv1.1 in TG of rats after intervention were detected.
Results: Compared with the baseline pain threshold, the facial mechanical pain threshold of rats in the TN group was significantly decreased from the 5th to 15th day after the surgery (P<0.05), and the facial mechanical pain threshold of rats in the sham group was stable at the normal level, which proved that the dIoN-CCI model was successfully constructed. Compared with the sham group, the expression of Kv1.1 mRNA and protein in TG of the TN group was down-regulated (both P<0.05), and the expression of miR-21-5p was up-regulated (P<0.05). The results of dual luciferase report showed that the luciferase activity of rno-miR-21-5p mimics and KCNA1 WT transfected with 6 nmol/L or 20 nmol/L were significantly decreased compared with those transfected with mimic NC and wild-type KCNA1 WT, respectively (P<0.001). Compared with low dose rno-miR-21-5p mimics (6 nmol/L) co-transfection group, the relative activity of luciferase in the high dose rno-miR-21-5p mimics (20 nmol/L) cotransfection group was significantly decreased (P<0.001). The results of immunofluorescence showed that drugs were accurately injected into TG through stereotaxic brain. After the expression of miR-21-5p in the TN group, the mechanical pain threshold and the expression of Kv1.1 mRNA and protein in TG were increased. After overexpression of miR-21-5p in the sham group, the mechanical pain threshold and the expression of Kv1.1 mRNA and protein in TG were decreased.
Conclusions: Both Kv1.1 and miR-21-5p are involved in TN and miR-21-5p can regulate Kv1.1 expression by binding to the 3'-UTR of KCNA1.
目的: 三叉神经痛(trigeminal neuralgia，TN)是一种临床上常见的神经病理性疼痛。电压门控性钾通道(voltage-gated potassium channel，Kv)已被证实参与TN的发生、发展，但具体机制仍不明确。微RNA(microRNA，miR)可通过调节三叉神经节(trigeminal ganglion，TG)上Kv通道的表达及神经元兴奋性，参与神经病理性疼痛。本研究旨在探索TN模型中TG上Kv1.1和miR-21-5p的关系，评估miR-21-5p是否对Kv1.1有调控作用，为TN的治疗提供新的靶点。方法: 将48只SD大鼠随机分为6组：1)假手术组(sham组，n=12)，大鼠仅在术侧切口缝合，不结扎神经；2)Sham+agomir NC组(n=6)，sham大鼠通过脑立体定位注射方法于术侧TG微量注射agomir NC；3)Sham+miR-21-5p agomir 组(n=6)，sham大鼠通过脑立体定位注射方法于术侧TG微量注射miR-21-5p agomir；4)TN组(n=12)，采用铬肠线慢性缩窄性眶下远端神经损伤(chronic constriction injury of the distal infraorbital nerve，dIoN-CCI)法构建TN大鼠模型；5)TN+antagomir NC组(n=6)，TN大鼠通过脑立体定位注射方法于术侧TG微量注射antagomir NC；6)TN+miR-21-5p antagomir组(n=6)，TN大鼠通过脑立体定位注射方法于术侧TG微量注射miR-21-5p antagomir。检测术后各组大鼠面部机械痛阈变化。采用蛋白质印迹法和实时反转录聚合酶链反应检测术后大鼠术侧TG中Kv1.1和miR-21-5p的表达情况。利用双荧光素酶报告基因确定Kv1.1和miR-21-5p是否存在靶标关系，即miR-21-5p是否可以直接影响KCNA1的3'端非翻译区(3'-untranslated region，3'-UTR)。通过免疫荧光法测定，对脑立体定位注射的效果进行评价，随后分别将miR-21-5p的类似物(agomir)和agomir NC通过脑立体定位仪注射至sham组大鼠TG内，使miR-21-5p过表达；向TN组大鼠TG内分别注射miR-21-5p的抑制剂(antagomir)和antagomir NC，抑制miR-21-5p表达。观察给药前后大鼠行为学变化，检测干预后大鼠TG内miR-21-5p和Kv1.1表达的变化。结果: 与基础痛阈值相比，TN组大鼠在术后第5至15天，面部机械痛阈值显著降低(P<0.05)，sham组大鼠面部机械痛阈值稳定在正常水平，证明dIoN-CCI模型构建成功。与sham组相比，TN组TG中Kv1.1 mRNA和蛋白质表达均下调(均P<0.05)，miR-21-5p的表达上调 (P<0.05)。双荧光素酶报告结果显示：与转染mimic NC和野生型KCNA1(KCNA1 WT)组相比，共转染6 nmol/L或 20 nmol/L的rno-miR-21-5p mimics的KCNA1 WT组的荧光素酶活性显著降低(P<0.001)；与6 nmol/L rno-miR-21-5p mimics共转染组相比，较大剂量(20 nmol/L)的rno-miR-21-5p mimics共转染组的荧光素酶相对活性显著降低(P<0.001)。免疫荧光法结果显示通过脑立体定位可以将药物准确注入TG。TN组抑制miR-21-5p表达后，大鼠面部机械痛阈升高，TG中Kv1.1 mRNA及蛋白质的表达水平升高；sham组过表达miR-21-5p后，大鼠面部机械痛阈降低，TG中Kv1.1 mRNA及蛋白质的表达降低。结论: Kv1.1和miR-21-5p均参与TN的发生、发展，miR-21-5p可以通过结合KCNA1 3'-UTR来调控Kv1.1的表达，进而影响TN。.
Keywords: miR-21-5p; trigeminal ganglion; trigeminal neuralgia; voltage-gated potassium channel.