Circular RNAs (circRNAs) are involved in the development of various diseases, 
but there is little knowledge of circRNAs in osteoarthritis (OA). The aim of 
study was to identify circRNA expression in articular cartilage and to explore 
the function of chondrocyte extracellular matrix (ECM)-related circRNAs 
(circRNA-CER) in cartilage. To identify circRNAs that are specifically expressed 
in cartilage, we compared the expression of circRNAs in OA cartilage with that 
in normal cartilage. Bioinformatics was employed to predict the interaction of 
circRNAs and mRNAs in cartilage. Loss-of-function and rescue experiments for 
circRNA-CER were performed in vitro. A total of 71 circRNAs were differentially 
expressed in OA and normal cartilage. CircRNA-CER expression increased with 
interleukin-1 and tumor necrosis factor levels in chondrocytes. Silencing of 
circRNA-CER using small interfering RNA suppressed MMP13 expression and 
increased ECM formation. CircRNA-CER could compete for miR-136 with MMP13. Our 
results demonstrated that circRNA-CER regulated MMP13 expression by functioning 
as a competing endogenous RNA (ceRNA) and participated in the process of 
chondrocyte ECM degradation. We propose that circRNA-CER could be used as a 
potential target in OA therapy.