Mechanism Research Of Micro RNA-21 Modulates Atrial Fibrillation Myocardial Fibrosis And Cardiac Fibroblasts Proliferation In Rats

Objective Atrial fibrillation is one of the most common clinical type of fast arrhythmias, the mechanism for the occurrence and the development of atrial fibrillation has been a hot topic in the field of cardiovascular and abroad. Existing studies have shown that there is a certain correlation between myocardial fibrosis and micro RNAs. This study was designed to investigate the change of micro RNA-21 and its regulatory protein SMAD 7 expression in rat atrial tissue during atrial fibrillation, to investigate the effect of micro RNA-21 mimics and inhibitors on proliferation and activation of cardiac fibroblasts in rats, to evaluate the micro RNA-21 molecular mechanism in the process of myocardial fibrosis during atrial fibrillation.Methods The model of myocardial fibrosis was induced by isoprenaline(ISO), 60 male SD rats were randomly divided into the blank control group and the model group. The model group was treated subcutaneously with 5 mg/kg?d ISO daily for 14 days, at the same time, the blank control group was given the same amount of normal saline. The rats were killed after 14 days, and obtained myocardial tissue specimens for each group respectively. Transfection cardiac fibroblasts with micro RNA-21 mimics, inhibitors and their negative control by using Lipofectamine? 2000 Reagent, and then detection the index after 24~48 h. HE staining and Masson staining fibrosis and calculate myocardial tissue collagen volume fraction(CVF); q RT-PCR was applied to assess the expression of micro RNA-21 and the m RNA of TGF-β1 and Smad 7; Western blot was used to determine the expression of TGF-β1 and Smad 7; MTT assay was usedto determine the proliferation influence of the transfected cardiac fibroblasts by using micro RNA-21 mimics, inhibitors and their negative control.Results HE and Masson staining showed myocardial tissue in model group appeared obviously collagen fiber hyperplasia, and compared with the blank control group, myocardial interstitial collagen volume fraction(CVF) increased significantly. Compared with the normal group, micro RNA-21, TGF-β1 was upregulated and Smad 7 was down-regulated in atrial fibrillation tissue. The cardiac fibroblasts transfected with micro RNA-21 mimics exhibited over-expression micro RNA-21 enhanced TGF-β1 m RNA expression and attenuated Smad 7 m RNA expression. Nevertheless, the cardiac fibroblasts transfected with micro RNA-21 inhibitors obtained the opposite expression result. The cardiac fibroblasts proliferation activity increased significantly after transfected micro RNA-21 mimics. The cardiac fibroblasts proliferation activity obtained the opposite expression result after transfected with micro RNA-21 inhibitors.Conclusion Atrial fibrillation and obvious myocardial fibrosis can be induced by subcutaneous injection of ISO in rats. Atrial micro RNA-21 over-expression accelerates atrial fibrosis via the TGF-β1/Smad signaling pathway by decrease Smad 7 expression, micro RNA-21 mimics can obviously enhance myocardial fibroblasts proliferation activity, micro RNA-21 inhibitors can suppress the proliferation activity of cardiac fibroblasts significantly. Implicating micro RNA-21 as an important signaling molecule for the AF-substrate and a potential target for cardiac fibroblasts activation and proliferation, pointing out that this result can provide new way of thinking of interventions designed to prevent the myocardial fibrosis occurrence and development.