MiR-140-5p inhibits synovial fibroblasts proliferation and inflammatory cytokines secretion through targeting TLR4

Objectives: This study was aimed to investigate the effects of miR-140-5p on the proliferation and inflammatory cytokines secretion of rheumatoid arthritis synovial fibroblasts (RASFs). Methods: Synovial tissue samples from 23 rheumatoid arthritis (RA) patients and 18 normal synovial tissue samples were collected. The RASFs were isolated and cultured. Then, miR-140-5p and TLR4 expression in both synovial tissue and RASFs were detected using the quantitative real-time PCR (qPCR) and western blot. Dual luciferase reporter gene assay was employed to evaluate the interaction between miR-140-5p and 3'UTR of TLR4. Western blotting and qPCR were used to examine TLR2 expression after upregulation or downregulation of miR-140-5p in RASFs. After RASFs co-infected with TLR4 overexpression lentivirus and lentivirus containing miR-140-5p or miR-control respectively, the cellular proliferation and secretion of IL-6 and IL-8 level were detected through the MTS assay and enzyme-linked immunosorbent assay, respectively. Results: MiR-140-5p was significantly down-regulated, and TLR4 was significantly up-regulated in synovial tissue samples from 23 RA patients and RASFs. Dual luciferase activity assay showed that miR-140-5p could specifically bind to the 3'UTR of TLR4. Down-regulation or up-regulation of miR-140-5p not only significantly increased or decreased the expression of TLR4, but also could promote or inhibit RASF proliferation and secretion of IL-6, and IL-8 in RASFs. Furthermore, overexpression of TLR4 can reverse the inhibitory effects of miR-140-5p on proliferation and inflammatory cytokines release of RASFs. Conclusions: MiR-140-5p could inhibit the proliferation and secretion of IL-6 and IL-8 through regulation of TLR4 expression.