Expression and function of CCN2-derived circRNAs in chondrocytes

Cellular communication network factor 2 (CCN2) molecules promote endochondral ossification and articular cartilage regeneration, and circular RNAs (circRNAs), which arise from various genes and regulate gene expression by adsorbing miRNAs, are known to be synthesized from CCN2 in human vascular endothelial cells and other types of cells. However, in chondrocytes, not only the function but also the presence of CCN2 -derived circRNA remains completely unknown. In the present study, we investigated the expression and function of CCN2 -derived circRNAs in chondrocytes. Amplicons smaller than those from known CCN2 -derived circRNAs were observed using RT-PCR analysis that could specifically amplify CCN2 -derived circRNAs in human chondrocytic HCS-2/8 cells. The nucleotide sequences of the PCR products indicated novel circRNAs in the HCS-2/8 cells that were different from known CCN2 -derived circRNAs. Moreover, the expression of several Ccn2 -derived circRNAs in murine chondroblastic ATDC5 cells was confirmed and observed to change alongside chondrocytic differentiation. Next, one of these circRNAs was knocked down in HCS-2/8 cells to investigate the function of the human CCN2 -derived circRNA. As a result, CCN2 -derived circRNA knockdown significantly reduced the expression of aggrecan mRNA and proteoglycan synthesis. Our data suggest that CCN2 -derived circRNAs are expressed in chondrocytes and play a role in chondrogenic differentiation. Graphical abstract Production and role of CCN2-derived RNAs in chondrocytes