MicroRNA‐503 promotes angiotensin II‐induced cardiac fibrosis by targeting Apelin‐13

Cardiac fibrosis is a major cause of heart failure. MicroRNAs (miRs) are important epigenetic regulators of cardiac function and cardiovascular diseases, including cardiac fibrosis. This study aimed to explore the role of miR-503 and its mechanisms in regulating cardiac fibrosis. miR-503 was found up-regulated in the mouse LV tissues subjected to transverse aortic constriction (TAC) and in neonatal cardiac fibroblasts (CFs) cultured with Angiotension II. The role of miR-503 in regulating CF cell proliferation and/or collagen production in mice neonatal CFs were determined using an MTT assay and RT-PCR respectively. Forced expression of miR-503 increased the cellular proliferation and collagen production in mice neonatal CFs. The effects were abrogated by cotransfection with AMO-503 (a specific inhibitor of miR-503). Injection of antagomiR-503 elevated cardiac function and inhibited the expression of connective tissue growth factor (CTGF) and transforming growth factor (TGF)-β in the TAC mice. Additional analysis revealed that Apelin-13 is a direct target of miR-503, as the overexpression of miR-503 decreased the protein and mRNA expression levels of Apelin-13. In the CFs with pre-treatment of AngII, we transfected AMO-503 into the cells treated with siRNA-APLN. siRNA-APLN abolished the effects of AMO-503 on the production of collagen I and III and the expression of TGF-β and CTGF. Furthermore, pre-treatment of CFs with Apelin-13 (1-100 nmol/l) inhibited angiotensin II-mediated collagen production and activation of CTGF and TGF-β. So we conclude that miR-503 promotes cardiac fibrosis via miR-503-Apelin-13-TGF-β-CTGF-collagen production pathway. Thus, miR-503 is a promising therapeutic target for reducing cardiac fibrosis.