Background/Aims: Cardiac fibrosis is a major cause of diverse cardiovascular diseases. MicroRNAs have recently been proven a novel class of regulators of cardiac fibrosis. In this study, we sought to investigate the role of miR-323a-3p and its mechanisms in regulating cardiac fibrosis. Methods: The transverse aortic constriction (TAC) mice model was induced and neonatal cardiac fibroblasts (CFs) were cultured. -yl]-2, 5-diphenyltetrazolium bromide) assay was used to detect the cell viability.

more »

... hocardiography was used to evaluate cardiac function. Masson's Trichrome stain was used to evaluate the development of fibrosis. Luciferase activity assay was performed to confirm the miRNA's binding site. Real-time PCR and Western blot were used to evaluate the level of mRNA and protein. Results: MiR-323a-3p was found up-regulated in myocardial tissues subjected to TAC and in CFs cultured with Angiotensin Ⅱ (Ang Ⅱ). Overexpression of miR-323a-3p significantly increased the mRNA levels of collagen Ⅰ, collagen Ⅲ, MMP2 and MMP9, while inhibition of miR-323a-3p prevented the proliferation, collagen production and the protein level of transforming growth factor (TGF-β) in rat neonatal CFs. Strikingly, injection of antagomiR-323a-3p elevated cardiac function and inhibited the expression of TGF-β in the TAC mice. TIMP3 was a direct target of miR-323a-3p, as the overexpression of miR-323a-3p decreased the protein and mRNA levels of TIMP3. In the CFs with pre-treatment of Ang Ⅱ, siRNA-TIMP abolished the effects of AMO-323a-3p on the inhibition of the proliferation of CFs, the down-regulation of collagen Ⅰ and collagen Ⅲ, and the expression of TGF-β. Conclusion: Our findings provide evidence that miR-323a-3p promotes cardiac fibrosis via miR-323a-3p-TIMP3-TGF-β pathway. miR-323a-3p may be a new marker for cardiac fibrosis progression and that inhibition of miR-323a-3p may be a promising therapeutic target for the treatment of cardiac fibrosis.