TLR4/NF-κB axis signaling pathway-dependent up-regulation of miR-625-5p contributes to human intervertebral disc degeneration by targeting .

The activation of the toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) signaling pathway has been found to play a critical role in many inflammatory diseases by controlling the expression of many cytokines. However, this pathway's role in the pathological process of intervertebral disc degeneration (IDD) has not been reported to date. In the present study, we found universal activation of the TLR4/NF-κB signaling pathway and elevated levels of pro-inflammatory cytokines in IDD patients. The analyses in human nucleus pulposus cells (hNPC) and annulus fibrosus cells (hAFC) also indicated that Lipopolysaccharide (LPS) treatment could activate TLR4/NF-κB signaling and induce pro-inflammatory cytokine levels. By comparing the results of two microRNA (miRNA)-based microarrays, we identified 15 miRNAs that were dysregulated in both IDD tissues and LPS-treated cells. Of these miRNAs, the most prominently up-regulated was miR-625-5p, which was predicted to bind to the three prime untranslated region (3'-UTR) of collagen type I alpha 1 (). overexpression or down-regulation of miR-625-5p was able to repress or induce the expression of , respectively. The analyses showed that treatment with LPS, recombinant IL-6 or TNF-α could induce miR-625-5p levels but decrease expression. In contrast, the treatments with their corresponding inhibitors, CLI095, siltuximab and D2E7, respectively, resulted in the exact opposite effects. Taken together, our results suggest that activation of the TLR4/NF-κB signaling pathway induces pro-inflammatory cytokines, which further up-regulates the expression of miR-625-5p, resulting in the down-regulation of and eventually contributing to the pathological process of IDD.