Knockdown of miR-1271 expression reverses the CircSERPINE2-induced cartilage degradation in HC cells. (A) Downregulation of both CircSERPINE2 and miR-1271 resulted in fewer apoptotic HCs than those observed with the inhibition of CircSERPINE2 alone. Apoptosis rates were determined with annexin V-FITC/PI staining and FACS. n = 3 (three different donors). *p<0.05. (B) The expression of MMP3, MMP13, ADAMTS4, SOX9, aggrecan and COL2A1 in HC cells was detected by WB. Cells were co-infected with sh-CircSERPINE2 and miR-1271 sponge adenovirus or control virus. n = 3 (three different donors). (C) The expression of MMP13, ADAMTS4, aggrecan and COL2A1 in HC cells was detected by IF analysis. Cells were infected with control virus or sh-CircSERPINE2 with or without miR-1271 sponge adenovirus. n = 3 (three different donors). Scale bars=50 µm. (D) mRNA expression of CircSERPINE2, MMP3, MMP13, ADAMTS4, SOX9, aggrecan and COL2A1 in HC cells was detected by RT-qPCR analysis. Cells were infected with control virus or sh-CircSERPINE2 with or without miR-1271 sponge adenovirus. n=9 (three different donors for three different experiments). *p<0.05, cells co-infected with miR-1271 sponge and sh-CircSERPINE2 adenovirus versus cells infected with sh-CircSERPINE2 adenovirus only. FACS, fluorescence-activated cell sorting; FITC, fluorescein isothiocyanate; HCs, human chondrocytes; IF, immunofluorescence; PI, propidium iodide; RT-qPCR, real-time quantitative PCR; WB, western blotting.