Department of Neurological Surgery, University of Southern California, 2011 Zonal Ave, HMR 414, Los Angeles, CA 90033, USA.
Department of Spine Surgery, Changzheng Hospital, Second Military Medical University, 415 Fengyang Rd, Shanghai, China.
Spine J. 2020 Jul;20(7):1138-1151. doi: 10.1016/j.spinee.2020.02.019. Epub 2020 Mar 4.
Acute spinal cord injury (SCI) is a devastating condition for which spine decompression and stabilization of injury remains the only therapy available in the clinical setup. However, fibrous scar formation during the healing process significantly impairs full recovery. MicroRNAs (miRs) are small noncoding RNAs that regulate gene expression by binding to target mRNA(s) and initiating translational repression or mRNA degradation. It has been reported that microRNA-133b (miR133b) is highly expressed in regenerating neurons following a SCI in zebrafish, and lentiviral delivery of miR133b at the time of SCI in mice resulted in improved functional recovery.
The aim of this study was to investigate whether intravenous delivery of miR133b enhances spinal cord recovery when administered 24 hours following a cervical contusion injury in mice.
This is an experimental animal study of acute SCI, investigating the effect of miR133b on spinal cord recovery by targeting scar lesion formation. The approach involved setting an acute SCI in mice, which was followed 24 hours later by intravenous co-delivery of miR133b and Argonaute 2 (Ago2), a protein involved in miRNA stabilization. Readouts of the impact of this intervention included analysis of RNA and protein expression at the lesion site, in particular with regard to markers of scar tissue formation, and determination of motor function recovery by the grip strength meter task.
C57BL6 female mice between 6 and 8 weeks of age were tested. The injury model employed was a unilateral moderate contusion at the cervical fifth level. Twenty-four hours following the injury, the authors co-delivered miR133b, or scrambled miRNA as negative control, along with Ago2 for 3 consecutive days, one dose per day via tail-vein injection. They first investigated the level of miR133b in the spinal cord and in spinal cord lesion after a single dose of injection. Next, they determined the efficacy of miR133b and/or Ago2 delivery in regulating gene and protein expression at the lesion site. Finally, they established the role of miR133b and/or Ago2 in enhancing forelimb gripping recovery as assessed by the grip strength meter task for 8 weeks post-SCI.
Intravenous delivery of miR133b and/or Ago2 targeted the microenvironment at the lesion site and prevented the increased expression of certain extracellular matrix proteins (ECM), in particular collagen type 1 alpha 1 and tenascin N, which are known to have a key role in scar formation. It also reduced microglia and/or macrophage recruitment to the lesion site. Functional recovery in mice treated with miR133b and/or Ago2 started around 2 weeks postinjury and continued to improve over time, whereas mice in the control group displayed significantly poorer recovery.
Our data indicate therapeutic activity of intravenous miR133b and/or Ago2 treatment, possibly via decreasing ECM protein expression and macrophage recruitment at the lesion site, thereby minimizing detrimental fibrous scar formation.
There is an urgent medical need for better treatments of SCIs. Based on our findings in a preclinical model, the miR133b and/or Ago2 system specifically targets fibrous scar formation, a barrier in neuronal regrowth, by remodeling ECM molecules at the injury site. Prevention of scar formation is critical to improved outcomes of treatment. Of note, delivery of miR133b and/or Ago2 was initiated 24 hours after traumatic impact, thus indicating a fairly long window of opportunity providing more time and flexibility for therapeutic intervention. Intravenous miR133b may become a beneficial therapeutic strategy to treat patients with acute SCI.
急性脊髓损伤（SCI）是一种破坏性疾病，目前在临床环境中，唯一的治疗方法是脊柱减压和损伤稳定。然而，在愈合过程中纤维瘢痕的形成极大地阻碍了完全康复。微小 RNA（miRs）是通过与靶 mRNA（s）结合并启动翻译抑制或 mRNA 降解来调节基因表达的小非编码 RNA。据报道，miR133b 在斑马鱼 SCI 后的再生神经元中高度表达，并且在 SCI 时通过慢病毒递送 miR133b 可导致小鼠的功能恢复改善。
本研究旨在探讨在小鼠颈段挫伤伤后 24 小时静脉内递送 miR133b 是否能增强脊髓恢复。
这是一项急性 SCI 的实验动物研究，通过靶向瘢痕病变形成来研究 miR133b 对脊髓恢复的影响。该方法包括建立小鼠急性 SCI，然后在 24 小时后静脉共递送 miR133b 和 Argonaute 2（Ago2），Ago2 是一种参与 miRNA 稳定的蛋白质。该干预措施的影响包括分析病变部位的 RNA 和蛋白质表达，特别是与瘢痕组织形成相关的标志物，以及通过握力计任务确定运动功能恢复情况。
在 6-8 周龄的 C57BL6 雌性小鼠中进行测试。使用的损伤模型是颈 5 水平的单侧中度挫伤。损伤后 24 小时，作者通过尾静脉注射连续 3 天，每天 1 次，共同递 miR133b 或作为阴性对照的 scrambled miRNA 与 Ago2。他们首先研究了单次注射后脊髓和脊髓损伤部位 miR133b 的水平。接下来，他们确定了 miR133b 和/或 Ago2 递送在调节病变部位基因和蛋白质表达方面的功效。最后，他们通过握力计任务确定了 miR133b 和/或 Ago2 在增强 SCI 后 8 周的前肢抓握恢复中的作用。
静脉内递送 miR133b 和/或 Ago2 靶向病变部位的微环境，并防止某些细胞外基质蛋白（ECM）的表达增加，特别是胶原蛋白 1 型 alpha 1 和 tenascin N，这两种蛋白已知在瘢痕形成中起关键作用。它还减少了小胶质细胞和/或巨噬细胞向病变部位的募集。用 miR133b 和/或 Ago2 治疗的小鼠的功能恢复在损伤后约 2 周开始，并随着时间的推移继续改善，而对照组的小鼠恢复明显较差。
我们的数据表明静脉内 miR133b 和/或 Ago2 治疗具有治疗活性，可能通过减少 ECM 蛋白表达和病变部位的巨噬细胞募集，从而最大限度地减少有害的纤维瘢痕形成。
迫切需要更好的 SCI 治疗方法。基于我们在临床前模型中的发现，miR133b 和/或 Ago2 系统通过重塑损伤部位的 ECM 分子，专门针对纤维瘢痕形成，这是神经元再生的障碍。预防瘢痕形成对于改善治疗效果至关重要。值得注意的是，miR133b 和/或 Ago2 的递送是在创伤性撞击后 24 小时开始的，这表明有一个相当长的治疗机会窗口，为治疗干预提供了更多的时间和灵活性。静脉内 miR133b 可能成为治疗急性 SCI 患者的有益治疗策略。
