Molecular and Physiologic Characterization of Rv Remodeling in a Murine Model of Pulmonary Stenosis

Right ventricular (RV) dysfunction is a common long-term complication in patients after repair of congenital heart disease. Previous investigators have examined the cellular and molecular mechanisms of left ventricular (LV) remodeling, but little is known about the stressed RV. Our purpose was to provide a detailed physiologic characterization of a model of RV hypertrophy and failure, including RV-LV interaction, and to compare gene alterations between afterloaded RV vs LV. Pulmonary artery constriction (PAC) was performed in 86 mice. Mice with mild and moderate pulmonary stenosis (PS) developed stable hypertrophy without decompensation. Mice with severe PS developed edema, decreased RV function, and high mortality. Tissue Doppler Imaging (TDI) demonstrated septal dyssynchrony and deleterious RV-LV interaction in the severe PS group. Microarray analysis showed 196 genes with increased expression and 1114 with decreased expression. Several transcripts were differentially increased in the afterloaded RV but not in the afterloaded LV, including Clusterin, Nbl1, Dkk3, Sfrp2, Fnbp4, Annexin A7, and LOX. We have characterized a murine model of RV hypertrophy and failure, providing a platform for studying the physiologic and molecular events of RV remodeling. Although the molecular responses of the RV and LV to afterload stress are mostly concordant, there are key several differences, which may represent targets for RV failure-specific therapy. Urashima et al. Page 3 The right ventricle is uniquely at risk in patients with complex congenital heart disease involving right-sided obstructive lesions (e.g. tetralogy of Fallot, tetralogy/pulmonary atresia) and in patients with systemic right ventricles (1, 40, 46). Increased stress on the right ventricle in the form of increased hemodynamic loading (pressure and/or volume) may result in abnormalities in cardiac structure, function, metabolism, coronary perfusion, neurohormonal activation, and molecular signaling. These stresses lead to both adaptive and maladaptive structural and molecular remodeling of the right ventricle, deleterious effects on the left ventricle through ventricular-ventricular interaction, and may limit long-term survival (3, 7, 29, 42). For many of these patients, detrimental conditions for the right ventricle exist throughout life, even after successful repair or palliation. As surgical techniques for primary repair of complex forms of congenital heart disease improve, long-term survival and quality of life will depend on our ability to preserve long-term right ventricular function. Decisions regarding the ideal time for surgical re-intervention will need to be based on more quantitative rather than qualitative measures. Developing a better understanding of the molecular mechanisms of right ventricular remodeling will assist in developing new therapeutic modalities to diagnose, prevent and treat right ventricular dysfunction. Although there are considerable data on the molecular events underlying afterload-induced left ventricular remodeling, there is little information for the right ventricle and some evidence to suggest that the stress responses of the right and left ventricles may be different. In the past, it was believed that differences in global structure and loading conditions represented the main differences between the right and left ventricles. However, recent work has shown increasing divergence in the anterior and primary heart field pathways leading to the differentiation of right vs. left ventricular cardiomyocytes during early development (46), and chamber-specific differences in cell signaling and calcium handling, suggesting fundamental differences between the right and left ventricles at the cellular level as well (10, 32, 34, 54, 72). Recent studies suggest that standard pharmacotherapies used to treat left ventricular dysfunction may not be as effective in patients with dysfunction of a systemic right ventricle (18). The development and characterization of a murine model of the afterloaded right ventricle will add significantly to our knowledge of chamber-specific molecular responses to stress, and provide the basis for further dissection of molecular pathways using the wide range of transgenic and gene knockouts for specific signaling components. Urashima et al. Page 4 We utilized a murine model of right ventricular pressure overload hypertrophy and right ventricular failure using pulmonary arterial constriction (PAC). The purpose of the current study was first, to provide a detailed physiologic characterization of this model, including a documentation of the effects of RV-LV interaction using Tissue-Doppler imaging (TDI). TDI has emerged as a leading technique for the assessment of ventricular dyssynchrony using data obtained from myocardial motion (17, 57). TDI-derived strain has been shown to be an excellent index of regional myocardial function because it is less influenced by overall cardiac motion (24, 25, 61). Although the usefulness of TDI has been shown in the assessment of LV function in mice (58), data on RV function are lacking. Second, we also sought to provide the first evaluation of genome-wide transcriptional alterations associated with RV pressure loading as well as a preliminary comparison of gene changes in the afterloaded RV vs. LV. Urashima et al. Page 5