MiR-92b-5p inhibitor suppresses IL-18 mediated inflammatory amplification after spinal cord injury via IL-18BP up-regulation

X.-L. Lin, J. Zhu, L.-M. Wang, F. Yan, W.-P. Sha, H.-L. Yang

Department of Orthopaedic Surgery, The First Affiliated Hospital of Soochow University, Suzhou, China. suzhouspine@163.com

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• Orthopedics

OBJECTIVE: The aim of this study was to investigate the effects of miR-92b-5p inhibitor and interleukin-18-binding protein (IL-18BP) on interleukin-18 (IL-18)-mediated inflammatory response after spinal cord injury (SCI).

MATERIALS AND METHODS: In this work, microglia was isolated from the newborn C57/B6J mice spinal cord to in vitro culture. The expression of IL-18BP and IL-18 was measured by the quantitative Real Time-Polymerase Chain Reaction (qRT-PCR) after transfection of miR-92b-5p into activated microglia. The expression of IL-18BP and IL-18 was determined following miR-92b-5p inhibitor treatment. In addition, the spinal cord injury model was established in mice. The expressions of miR-92b-5p, IL-18BP, and IL-18 were measured by qRT-PCR, and the expressions of inducible nitric oxide synthase (iNOS), tumor necrosis factor (TNF-α) and interleukin-1 β (IL-1 β) were determined by Western blot. After intrathecal injection of miR-92b-5p inhibitor, the mRNA expression of miR-92b-5p, IL-18BP, and IL-18 and the expression of iNOS, TNF-α, and IL-1 β in the injured area of the spinal cord of mice were measured. Basso Mouse Scale (BMS) was used to determine the recovery of locomotor function after spinal cord injury and miR-92b-5p inhibition.

RESULTS: After miR-92b-5p transfection, the expression of IL-18BP was significantly decreased compared with that of untransfected microglia cells, whereas the level of IL-18 mRNA was significantly increased. However, the level of IL-18BP elevated significantly and the level of IL-18 reduced markedly after treatment with corresponding inhibitors. In addition, compared with the sham operation group (Sham), the RNA level of miR-92b-5p in the SCI group was significantly higher than that in the Sham, but the expression of IL-18BP was evidently declined and the expression of IL-18 was significantly increased in the SCI group. Meanwhile, the expression of miR-92b-5p in miR-92b-5p inhibitor intrathecal injection mice was remarkably lower than that in SCI group, the expression level of IL-18BP was significantly increased, and the RNA expression of IL-18 was weakened accordingly. Moreover, the protein expression of iNOS, TNF-α, and IL-1 β in miR-92b-5p inhibitor-treated mice was significantly lower than that in the SCI group. The locomotor evaluation of miR-92b-5p inhibitor group was dramatically higher than that of the SCI group.

CONCLUSIONS: Suppressing the expression of miR-92b-5p after SCI can effectively intensify the level of IL-18BP, reduce the expanded inflammatory effect of IL-18, decline the release of iNOS, TNF-α, and IL-1 β, thus alleviate the neuronal injury and improve the locomotor function after SCI.

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