Mir-21 Is A Biomarker For Fibrosis And The Progression To Right Ventricular Systolic Failure In A Model Of Pulmonary Volume And Pressure Overload

Introduction: Severe pulmonary insufficiency (PI) in combination with moderate pulmonary stenosis (PS) is a common long-term complication after repair of congenital heart diseases such as tetralogy of Fallot, causing progressive right ventricular (RV) dilation and failure. We characterize the physiologic and molecular characteristics of the first murine model of combined RV volume and pressure overload (PI/PS). Methods: Physiologic data was compared between sham controls and PI/PS at 1 and 3 mos. Histopathology and gene, microRNA (miR) and protein expression were assessed in the RV free wall. Plasma miR expression was assessed in children with severe PI/moderate PS vs controls (n=4). Results: Data are presented as sham vs. PI/PS at 1 and 3 mos (*p<0.05). Mice developed diastolic heart failure at 1 mo progressing to systolic heart failure by 3 mos: restrictive RV filling (E/A ratio) (0.7±0.1 vs. 2.1±0.9 and 1.9±0.4*) and elevated RV end-diastolic pressure (2.7±0.3 vs. 7.8±2, and 8.5±2 mmHg*); followed by decreased RV outflow tract shortening (44±2 vs. 39±6 and 29±6%*) and exercise capacity (32±1.1 vs. 28±1.6 and 22±1.9 min*). RV fibrosis increased over time (0 vs. 4.0±2, 3.9±0.2%* sham vs 1 and 3 mos) along with pSMAD/total SMAD expression (0.2±0.1 vs. 0.4±0.1 and 0.6±0.1*), ANP expression (25±15 and 60±27* fold at 1 and 3 mos) and tissue miR-21 expression (2.7±0.3 and 2.9±0.6 fold). However, plasma miR-21 was upregulated with diastolic heart failure and switched to being downregulated with the development of systolic heart failure (2.6±1 and -1.8 ±0.2 fold). Finally, plasma miR-21 expression from children with severe PI/moderate PS at the time of pulmonary valve replacement was downregulated compared to controls (FC -3.6±1.2). Conclusion: We describe a novel murine model of chronic RV volume and pressure overload which recapitulates many aspects of the clinical disease. Gene and protein expression changes suggest enhanced miR-21 and TGF-β signaling as a mediator of RV fibrosis. miR-21 may serve as a novel biomarker of RV fibrosis, with a decline in expression heralding the need for valve replacement. This model provides investigators with a new tool for further evaluation of a form of RV failure unique to children with repaired congenital heart disease.