Abstract 18626: A Novel Inhibitory Role of MicroRNA-1 in Cardiac Fibroblast Proliferation and Differentiation
Fibroblasts play a key role in cardiac remodeling by differentiating into myofibroblasts, proliferating and producing excess extracellular matrix. MicroRNAs (miRs) are important regulators in cardiac development and disease. To date, miR analyses have been performed mostly in myocytes and cardiac tissue; little is known about miRs in cardiac fibroblasts. Using miR arrays, we determined the expression and regulation of miRs in adult rat ventricular fibroblasts in a culture model that mimics the phenotypic and functional changes of fibroblasts in diseased heart. Among miRs that were dynamically regulated, we found that miR-1, a muscle-enriched miR that has so far been extensively studied in myocytes, is expressed in fibroblasts and markedly downregulated (~10-fold) upon activation. MiR-1 downregulation was also observed in fibroblasts stimulated with angiotensin II or TGFβ for 48 hours. Gain-of-function studies in cultured rat ventricular fibroblasts showed a dose-dependent inhibitory effect of miR-1 on fibroblast proliferation (3- and 26-fold overexpression led to a 13% and 34% reduction, respectively). In contrast, fibroblast proliferation was significantly increased by 20% when endogenous miR-1 was only knocked down by 40%. Similar changes were observed in fibroblasts subjected to angiotensin II and TGFβ. Using immunostaining, we found a marked reduction of α-smooth muscle actin expression by miR-1, indicating an inhibitory effect of miR-1 on fibroblast differentiation. Mechanistic studies showed miR-1-dependent regulation of protein expression of several putative miR-1 targets that are involved in initiation of cell cycle progression (e.g., cyclin D2, CDK6) and fibrosis development (e.g., PKCε, HDAC4), some of which have been confirmed for miR-1 targeting by 3’-UTR luciferase reporter assays. Together, we show dynamic regulation of miRs in cardiac fibroblasts upon activation and demonstrate a novel inhibitory role of miR-1 in cardiac fibroblast proliferation and differentiation. Our data suggest a potential anti-fibrotic effect of miR-1 overexpression in fibroblasts and highlight the importance of cell type-specific miR-1 modulation, given the potential for arrhythmia induction reported for miR-1 overexpression in myocytes.
- © 2013 by American Heart Association, Inc.