Emerging Roles of circRNA Related to the Mechanical Stress in Human Cartilage Degradation of Osteoarthritis
Circular RNAs (circRNAs) are involved in the development of various diseases; however, knowledge on circRNAs in osteoarthritis (OA) is limited. This study aims to identify circRNA expression in different regions affected by OA and to explore the function of mechanical stress-related circRNAs (circRNAs-MSR) in cartilage. Bioinformatics was employed to predict the interaction of circRNAs and mRNAs in the cartilage. Loss-of-function experiments for circRNAs-MSR were performed in vitro. A total of 104 circRNAs were differentially expressed in damaged versus intact cartilage. Of these circRNAs, 44 and 60 were upregulated and downregulated, respectively, in the damaged tissue. circRNA-MSR expression increased under mechanical stress in chondrocytes. circRNAs-MSR were silenced using small interfering RNA, and knockdown of circRNAs-MSR could suppress tumor necrosis factor alpha (TNF-α) expression and increase extracellular matrix (ECM) formation. Our results demonstrated that circRNAs-MSR regulated TNF-α expression and participated in the chondrocyte ECM degradation process. We propose that the inhibition of circRNAs-MSR could inhibit the degradation of chondrocyte ECM and knockdown of circRNAs-MSR could be a potential therapeutic target for OA.The cartilage was assessed by histologic examination, and the histologic scores were graded according to a modified Mankin scale. The score of <4 points was considered intact cartilage and a score of >6 represented damaged cartilage. Hierarchical clustering revealed the circRNA expression in the cartilage samples (Figure 1A). The scatter and volcano plots showed varied circRNA expressions between the damaged and intact cartilage samples (Figures 1B and 1C). We identified 104 differentially expressed circRNAs in the damaged cartilage compared to the intact cartilage. Of these circRNAs, 44 were upregulated and 60 were downregulated in the damaged tissue samples (Table S1). To validate the circRNA microarray results, we performed qPCR to analyze the changes in expression among the differentially expressed circRNAs. The data confirmed that circRNA_000598, circRNA_103387, circRNA_101975, and circRNA_100226 (circRNAs-MSR) were overexpressed in the damaged region compared with the intact region of the cartilage in OA (Figure 2A).OA cartilage was isolated from the knee joints of 30 patients undergoing total knee arthroplasty. Joint tissue was immediately shock-frozen in liquid nitrogen, and the articular cartilage was isolated within 24 hr from the condyles and tibia plateaus with the use of a surgical blade. The tissues were examined histologically. All tissue donors included in this study provided their informed consent. The study was approved by the Human Ethics Committee of the Peking University Third Hospital (China).This work was supported by grants from the National Natural Science Foundation of China (90919022, 81101390, and 81330040), Specialized Research Fund for the Doctoral Program of Higher Education (20110001130001), and National Natural Science Foundation of Beijing (7154248).Supplemental Information includes two figures and one table and can be found with this article online at http://dx.doi.org/10.1016/j.omtn.2017.04.004.