Differential microRNA-21 and microRNA-221 Upregulation in the Biventricular Failing Heart Reveals Distinct Stress Responses of Right Versus Left Ventricular Fibroblasts

Background: The failing right ventricle (RV) does not respond like the left ventricle (LV) to guideline-directed medical therapy of heart failure, perhaps due to interventricular differences in their molecular pathophysiology. Methods: Using the canine tachypacing-induced biventricular heart failure (HF) model, we tested the hypothesis that interventricular differences in microRNAs (miRs) expression distinguish failing RV from failing LV. Results: Severe RV dysfunction was indicated by elevated end-diastolic pressure (11.3±2.5 versus 5.7±2.0 mm Hg; P<0.0001) and diminished fractional area change (24.9±7.1 versus 48.0±3.6%; P<0.0001) relative to prepacing baselines. Microarray analysis of ventricular tissue revealed that miR-21 and miR-221, 2 activators of profibrotic and proliferative processes, increased the most, at 4- and 2-fold, respectively, in RV-HF versus RV-Control. Neither miR-21 or miR-221 was statistically significantly different in LV-HF versus LV-Control. These changes were accompanied by more extensive fibrosis in RV-HF than LV-HF. To test whether miR-21 and miR-221 upregulation is specific to RV cellular response to mechanical and hormonal stimuli associated with HF, we subjected fibroblasts and cardiomyocytes isolated from normal canine RV and LV to cyclic overstretch and aldosterone. These 2 stressors markedly upregulated miR-21 and miR-221 in RV fibroblasts but not in LV fibroblasts nor cardiomyocytes of either ventricle. Furthermore, miR-21/221 knockdown significantly attenuated RV but not LV fibroblast proliferation. Conclusions: We identified a novel, biological difference between RV and LV fibroblasts that might underlie distinctions in pathological remodeling of the RV in biventricular HF.