CDK6 and miR-320c Co-Regulate Chondrocyte Catabolism Through NF-B Signaling Pathways

Background/Aims: Cyclin-dependent kinase 6 (CDK6) regulates inflammatory response and cell differentiation. This study sought to determine whether CDK6 and miR-320c co-regulate chondrogenesis and inflammation. Methods: Utilizing quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC), CDK6 and miR-320c expression were assessed in a micromass culture of human bone mesenchymal stem cells that underwent chondrogenesis in vitro as well as in chondrocytes from E16.5 mouse forelimbs. Normal chondrocytes were transfected with miR-320c mimic, miR-320c inhibitor, or CDK6-siRNA. Luciferase reporter assay results confirmed that miR-320c directly targets CDK6 by interacting with the 3-untranslated region (3-UTR) of its mRNA. qRT-PCR, Western blotting, and Cell Counting Kit-8 were subsequently used to evaluate the effects of miR-320c overexpression and CDK6 inhibition on inflammatory factor expression, as well as to investigate the effects of NF-kB and MAPK signaling pathway activation on IL-1-induced chondrocyte inflammation. Results: Our results show that miR-320c expression increased during the middle stage and decreased during the late stage of hBMSC chondrogenic differentiation. In contrast, CDK6 expression decreased during the middle stage and increased during the late stage of hBMSC chondrogenic differentiation. Moreover, CDK6 expression increased in severe OA cartilage and in hypertrophic chondrocytes of mouse forelimbs at E16.5. Results of the luciferase reporter assay showed that miR-320c modulated CDK6 expression by binding to the 3-UTR of its mRNA. miR-320c overexpression and CDK6 inhibition repressed IL-1-induced expression of inflammatory factors and regulated the NF-kB signaling pathway. Conclusion: CDK6 and miR-320c co-regulate hBMSC chondrogenesis and IL-1-induced chondrocyte inflammation through the NF-kB signaling pathway, suggesting that miR-320c and CDK6 inhibitors can be used to repress catabolism in human chondrocytes.