Low expression of CircRNA HIPK3 promotes osteoarthritis chondrocyte apoptosis by serving as a sponge of miR-124 to regulate SOX8

OBJECTIVE: CircRNA, a type of circular RNA, has recently been shown to be a potential target for osteoarthritis (OA). Circular RNA HIPK3 (CircHIPK3) is reported to be abnormally expressed in various disease tissues and affects the occurrence and development of the disease. However, the role and underlying mechanism of CircRNA HIPK3 in osteoarthritis are still unclear. The purpose of this study is to explore the effect of CircRNA HIPK3 on osteoarthritis and analyze its regulatory mechanism. PATIENTS AND METHODS: We took human OA tissues, normal knee cartilage, human OA chondrocytes and normal chondrocytes as the research objects. Real Time-quantitative Polymerase Chain Reaction (RT-qPCR) was used to detect CircHIPK3 expression level, its target gene miRNA 124 (miR-124) and downstream target molecule SOX8. Flow cytometry analysis was applied to discover the apoptosis of CircHIPK3 and miR-124 on OA cartilage in different transfection situations. Moreover, Western blot and RT-qPCR were used to detect the expression of caspase-3 in OA chondrocytes. The binding site of CircRNA HIPK3 and miR-124, miR-124, and SOX8 were verified by using Dual-Luciferase assay. RESULTS: High expressed CircHIPK3 and low expressed miR-124 were found in OA tissues and OA chondrocytes. In addition, the Dual-Luciferase report showed CircHIPK3 acted as a sponge of miR-124 in OA chondrocytes. CircHIPK3 and miR-124 expression in OA tissue were confirmed to be negatively correlated. To our surprise, knocking down CircHIPK3 and transfected miR-124 mimics both inhibited the apoptosis of OA chondrocytes. Further experiments verified that the downstream target molecule of miR-124 was SOX8 in OA chondrocytes. Besides, miR-124 inhibitors reversed the knockdown of CircHIPK3 while si-SOX8 reversed the miR-124 inhibitors effect of apoptosis on OA chondrocytes. CONCLUSIONS: Our results demonstrated that CircHIPK3 was significantly upregulated in OA cartilage tissue and cells. Low expression of CircHIPK3 promoted the apoptosis of OA chondrocytes by promoting miR-124 to suppress SOX8 expression. The molecular mechanism of CircHIPK3 in present study is expected to provide new ideas for the treatment of osteoarthritis.