Abstract 11375: miR-145 Is a Key Regulator of Cardiac Myofibroblast Differentiation
Introduction: Restoration of ventricular function following myocardial infarction (MI) requires infarct contracture by myofibroblasts (MFs) during the healing process. Previous studies suggested that the miR-143/-145 cluster plays a critical role in smooth muscle cell (SMC) differentiation. We evaluated whether miR-145 would promote MF differentiation and improve recovery from an MI.
Results: We found that endogenously expressed miR-145 was initially downregulated in the mouse myocardium in response to MI when compared to sham-operated controls and then recovered at 1 week. Real-time PCR demonstrated that miR-145 expression was 1.5- to 2.5-fold higher in cultured cardiac fibroblasts than cardiomyocytes or SMCs. In addition, miR-145 was downregulated in cardiac fibroblasts, but not cardiomyocytes, in response to hypoxia. We assessed the number of α-smooth muscle actin (SMA) positive cells in fibroblast cultures exposed to a miR-145 mimic and showed a 73.5% increase compared to scrambled miRNA. Ultrastructural analysis of SMA stress fibers revealed that ~95% of SMA+ cells in the miR-145 group had oriented actin-filament bundles vs. 15% in the scrambled miRNA group. Cell migration and gel contraction assays demonstrated that miR-145 induced a myofibroblast phenotype similar to the effects of TGF-β. Exposure to miR-145 produced a 12-fold increase in collagen I expression in cardiac fibroblasts compared with scrambled miRNA, a 90% reduction in p190 expression (downstream target of miR-145), and a subsequent 67% increase in Rho/ROCK activity, the central signaling pathway controlling SMA stress fiber formation. Treatment of cardiac fibroblasts with miR-145 also induced a dramatic decrease in KLF5 expression (downstream target of miR-145), releasing its inhibition of myocardin and promoting differentiation toward MFs. In vivo, the transient decrease in miR-145 expression 3 days post-MI was associated with an increase in KLF5, a decrease in myocardin expression, and differentiation toward MFs.
Conclusion: We describe a novel association between miR-145 and fibroblast differentiation toward MFs. miRNA therapy offers a new approach to promote endogenous scar healing and contracture after an extensive MI.
- © 2012 by American Heart Association, Inc.