Objective To explore the latent pathogenesis of circRNAs in osteoarthritis (OA), as well as their function mechanism. Methods The murine chondrocytes with and without OA were involved and used for in-depth sequencing. Herein, we carried out subsequent bioinformatics analysis to disclose the expression pattern, characteristics of circRNAs based on gene ontology, and the KEGG pathway analyses. Then sequencing data were used to deduce the interaction between circRNA and miRNA. The potential miRNA response elements for the annotated circRNAs and relevant target genes were forecasted on the basis of TargetScan and miRanda. For chondrocytes, the effect of the overexpression of the screened circRNA for apoptosis was spotted by flow cytometry as well as Western Blot. Results 466 diverse circRNAs in the 23,787 spotted circRNAs were both significantly and differentially transcribed. CircKMT2E was upregulated more than two folds in chondrocytes with OA compared with normal tissues, exhibiting an expression trend opposite to miR-140-5p. We disclosed that circKMT2E could possess mutual effect with miR-140-5p by way of AGO proteins. Thus, circKMT2E was verified to have functioned as a molecular sponge targeting miR-140-5p. Therefore, circKMT2E may be at work in the pathogenesis of OA. Further, the sponge connection between circKMT2E and miR-140-5p was proved on the basis of a dual-luciferase reporter assay. Besides, miR-140-5p was speculated can bind TLR4 by bioinformatics analysis. Further PCR analysis found the relative expression level of TLR4, caspase-3, and Bax in the OA groups presented significant upregulation. Overexpression of circKMT2E can promote apoptosis of chondrocytes. Conclusion The upregulation of circKMT2E is involved in the chondrocyte apoptosis of the pathogenesis of OA through activation of TLR4 by the sponge function of miR-140-5p.

Background Post-traumatic osteoarthritis (PTOA) is closely related to the inflammatory response caused by mechanical injury, leading to joint degeneration. Herein, we aim to evaluate the role and the underlying mechanism of NUMB in PTOA progression. Methods Anterior cruciate ligament transection (ACLT)-induced rats and LPS-treated chondrocytes were used as in vivo and in vitro models of PTOA, respectively. NUMB overexpression plasmid (pcDNA-NUMB) were administered by intra-articular injection in PTOA model rats, and safranin O-fast green staining, the Osteoarthritis Research Society International (OARSI) Scoring System, and HE staining were used to evaluate the severity of cartilage damage. The secretion of inflammatory cytokines (TNF-α, IL-1β, IL-6) and chondrocyte-specific markers (MMP13, COL2A1) was detected by ELISA. Cell viability and apoptosis were evaluated by MTT assay and TUNEL staining. Results The expression of NUMB was lower expressed in ACLT-induced PTOA rats and LPS-treated chondrocytes. NUMB overexpression enhanced cell viability and reduced cell apoptosis, inflammation and cartilage degradation in chondrocytes stimulated by IL-1β. NUMB bound with BTRC to inhibiting p-IκBα expression, resulting in NF-κB pathway inactivation. BTRC overexpression reversed the promoting effect of NUMB overexpression on cell viability and the inhibitory effects of NUMB overexpression on apoptosis, inflammation and cartilage degradation in LPS-induced chondrocytes. Besides, overexpression of NUMB alleviated articular cartilage damage by repression of inflammation and cartilage degradation in ACLT-induced PTOA rats. Conclusion Our data indicated that NUMB negatively regulates BTRC regulated PTOA progression by BTRC/NF-κB pathway, which may be a viable therapeutic target in PTOA.