ObjectiveTo investigate the regulatory effect of circular RNA circ_0120051 on the fibrotic phenotype of cardiac fibroblasts and the potential mechanism involved. MethodsThe expression of circ_0120051 and its host gene of solute carrier family 8 member A1（SLC8A1） mRNA in the myocardium of healthy organ donors （n=24） and heart failure （HF） patients （n=21） were assessed by real-time quantitative polymerase chain reaction （RT-qPCR） assay. RNA stability of circ_0120051 was identified by RNase R exonuclease digestion assay. The cytoplasmic and nuclear distribution of circ_0120051 in human cardiomyocyte AC16 was detected by RT-qPCR assay. The expression of fibrosis-related genes in mouse cardiac fibroblasts （mCFs） with adenovirus-mediated overexpression of circ_0120051 was detected by RT-qPCR and Western blot assay， respectively. The effect of overexpression of circ_0120051 on the migration activity of mCFs was evaluated by wound-healing assay. RNA co-immunoprecipitation （RIP） was conducted to detect the interaction between circ_0120051 and miR-144-3p. The binding site of miR-144-3p in the 3'-UTR of isocitrate dehydrogenase 2 （Idh2） mRNA was identified by the dual luciferase reporter gene assay. ResultsCirc_0120051 was significantly up-regulated in the myocardium of HF patients， while the mRNA expression of its host gene SLC8A1 was not changed. Circ_0120051 was mainly located in the cytoplasm of human AC16 cells. Results of RNase R exonuclease digestion revealed that circ_0120051 possesses the characteristic stability of circular RNA compared to the linear SLC8A1 mRNA. Overexpression of circ_0120051 could inhibit the expression of fibrosis-related gene in mCFs and mCFs migration. RIP assay confirmed the specific interaction between circ_0120051 and miR-144-3p. Transfection of miR-144-3p mimic could efficiently promote the expression of fibrosis-related genes in mCFs and reverse the inhibitory effect of circ_0120051 on the fibrotic phenotype of mCFs. Results of the dual luciferase reporter gene assay confirmed the interaction between miR-144-3p and the 3'-UTR of Idh2. Transfection of miR-144-3p transcriptionally inhibited Idh2 expression， and overexpression of circ_0120051 enhanced IDH2 expression in mCFs. MiR-144-3p mimic and Idh2 small interfering RNA （siRNA） could consistently reverse the inhibitory effects of circ_0120051 on fibrosis-related genes expression in mCFs and mCFs migration. ConclusionsCirc_0120051 inhibits the fibrotic phenotype of cardiac fibroblasts via sponging miR-144-3p to enhance the target gene of IDH2 expression.