Toll-like receptor 4 antagonist protects against Wallerian degeneration after peripheral nerve injury

Xiong Le; Zhang Bei; Shen Ruo-wu; Ji Ai-yu; Sun Guang-qiang; Bian Hong-lin; Zhang Feng-yu; Wang Yi; Huang Heng; Li Hua-qiao; Zhou Shan-yu; Shen Zhao-kang; Wang Zhong

doi:10.3969/j.issn.2095-4344.2016.42.012

Abstract：BACKGROUND:The mechanism underlying Wal erian degeneration fol owing peripheral nerve injury is complex. Immune regulation on Wal erian degeneration is beneficial for early repair of perpheral nerve injury. <br> OBJECTIVE:To investigate the effects of Tol-like receptor 4 (TLR4) antagonist on Wal erian degeneration and axonal regeneration after early peripheral nerve injury in rats. <br> METHODS:Fifty male Wistar rats were recruited and randomly divided into treatment group (n=20), model group (n=20) and sham group (n=10). The right sciatic nerves of rats in treatment and model groups were cut and sutured end-to-end, while the sciatic nerves of rats in sham group were only exposed. In the treatment group rats were intravenously injected with 0.15 mg/kg TAK-242 via tail vein 1 hour preoperatively and 7 days postoperatively, and the rats in the other two groups were given intravenous injection of the same volume of normal saline. The sciatic nerves were removed at 24 hours, 3, 4 and 7 days after surgery. <br> RESULTS AND CONCLUSION:Real-time PCR indicated that the mRNA expressions of interleukin-1βand monocyte chemoattractant-1 were significantly increased in the model group compared with the sham group at 24 hours after surgery (both P<0.001), while the expressions were significantly decreased after TAK-242 injection (both P<0.001). Immunofluorescence showed that compared with the model group, down-regulated expression of CD68+and iba1+cel s appeared in the treatment group at 3 days after surgery (P<0.01, P<0.05). Luxol fast blue staining revealed that demyelination at the sciatic nerve stump appeared in both model and treatment groups at postoperative 7 days, but myelin debris clearance in the treatment group was significantly reduced compared with the model group (P<0.05). Hematoxylin-eosin staining showed that a lot of inflammatory cel s, Schwann cells and regenerated nerve fibers at the sciatic nerve stump were found in the model group, while there were few inflammatory cells, Schwann cel s and regenerated nerve fibers in the treatment group at 7 days after surgery. Immunohistochemistry found that the expression of growth-associated protein-43 in the treatment group was significantly lower than that in the model group at 4 days postoperatively (P<0.05). Besides, compared with the model group, a significantly decreased sciatic functional index was found in the treatment group at 20, 30 and 40 days after surgery (P<0.05). These results show that TLR4 antagonists delay early nerve regeneration in rats after sciatic nerve injury probably by inhibiting the TLR4 signaling pathway.