Functional role of MIR-140 and MIR-146A in inflammation and catabolic processes in osteoarthritis

Purpose: Osteoarthritis (OA) is a whole-joint disorder that is characterized by the loss of articular cartilage of synovial joints, synovial inflammation, subchondral bone remodelling and ligament fibrosis. MicroRNAs (miRNAs) play a prominent role in skeletal development and their abnormal expression has been suggested to contribute to pathogenic alterations of the OA joint. MiR-140 and miR-146a are expressed in cartilage tissue and control the extracellular matrix remodeling and inflammation responses in articular cartilage through genes’ regulation participating in signaling pathways, such as the Toll-like receptor 4 (TLR-4). TLR-4 signaling pathway is over activated in OA resulting in MMPs and cytokines upregulation and subsequent cartilage degradation. The aim of the present study was to investigate the functional role of miR-140 and miR-146a in inflammation and catabolic processes contributing to OA pathogenesis. Methods: Articular osteoarthritic and normal cartilage were obtained from 20 patients with primary osteoarthritis and 12 individuals with no history of joint disease, respectively. MiR-140 and miR-146a expression levels were investigated using quantitative real-time PCR. Bioinformatics analysis was used to investigate the target genes of the above microRNAs and their involved pathways. OA cultured chondrocytes were treated with miR-140 and/or miR-146a mimic and the expression levels of TLR-4, IRAK-1, TRAF-6, IL-1β, IL-6, IL-8, TNF-a, ADAMTS-5 and MMP-13 were evaluated using quantitative real-time PCR. Results: We observed that miR-140 and miR-146a expression levels were significantly reduced in OA compared with normal chondrocytes. Bioinformatics analysis revealed that the target genes of miR-140 and miR-146 are involved in common signaling pathways associated with OA, including inflammatory pathways, such as the TLR signaling. In TLR signaling, miR-140 regulates TLR-4 expression, whereas miR-146a participates in regulation of TLR-4 signaling though targeting IRAK-1 and TRAF-6. In addition, we confirmed the regulation of TLR-4 signaling by miR-140 and miR-146a at the cellular level, as we observed down-regulation of TLR-4 expression in OA chondrocytes after miR-140 treatment, whereas a significant reduction in IRAK-1 and TRAF-6 expression was found in miR-146a-treated OA chondrocytes compared to untreated. Moreover, we found that IL-6, IL-8, ADAMTS-5 and MMP-13, all targets of TLR-4 signaling, were decreased in miR-140 and miR-146a co-treated OA chondrocytes compared to untreated. Conclusions: Our study demonstrated, for the first time, the synergistic role of miR-140 and miR-146a in OA pathogenesis through targeting the TLR-4 signaling and modulating IL-6, IL-8, ADAMTS-5 and MMP-13 expression involved in inflammation and cartilage catabolism. As miR-140 and miR-146a are crucial regulators of processes involved in OA pathogenesis, modulation of their expression in OA may be a new strategy for treating osteoarthritic patients.