Diwakar Turaga

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is a relatively rare but debilitating diagnosis in the pediatric population, and patients with end-stage HCM require heart transplantation. Here, we have examined the transcriptome in ventricular tissue from this patient group to identify cell states and underlying cellular processes unique to pediatric HCM. METHODS: We performed single-nucleus RNA sequencing (snRNA-seq) on explanted hearts at transplant in 3 pediatric patients with end-stage HCM and compared findings to pediatric control and adult HCM. RESULTS: We identified distinct underlying cellular processes in cardiomyocytes, fibroblasts, endothelial cells, and myeloid cells compared with controls. Pediatric HCM was enriched in cardiomyocytes exhibiting stressed myocardium gene signatures and underlying pathways associated with cardiac hypertrophy; cardiac fibroblasts exhibited activation signatures and compared with adult patients, exhibited heightened downstream processes associated with fibrosis and a unique, myofibroblast-like cluster with increased metabolic stress and antiapoptotic properties. We noted depletion of tissue-resident macrophages and increased vascular remodeling in endothelial cells in pediatric HCM. CONCLUSIONS: Our analysis provides the first snRNA-seq analysis focused on end-stage pediatric HCM. Fibroblast-mediated cellular processes were the most prominent in pediatric HCM, which had more downstream processes associated with fibrosis than did adult HCM.

Hypertrophic cardiomyopathy (HCM) is a relatively rare but debilitating diagnosis in the pediatric population and patients with end-stage HCM require heart transplantation. In this study, we performed single-nucleus RNA sequencing on pediatric HCM and control myocardium. We identified distinct underling cellular processes in pediatric, end-stage HCM in cardiomyocytes, fibroblasts, endothelial cells, and myeloid cells, compared to controls. Pediatric HCM was enriched in cardiomyocytes exhibiting “stressed” myocardium gene signatures and underlying pathways associated with cardiac hypertrophy. Cardiac fibroblasts exhibited clear activation signatures and heightened downstream processes associated with fibrosis, more so than adult counterparts. There was notable depletion of tissue-resident macrophages, and increased vascular remodeling in endothelial cells. Our analysis provides the first single nuclei analysis focused on end-stage pediatric HCM.

The right ventricle (RV) is one of the four pumping chambers of the heart, pumping blood to the lungs. In severe forms of congenital heart disease and pulmonary hypertension, the RV is made to pump into the systemic circulation. Such systemic RVs typically display early failure due to pressure overload. In rare cases a systemic RV persists into later decades of life – colloquially called a ‘Super RV’. Here we present the single-nucleus transcriptome of a systemic RV from a 60-year-old with congenitally corrected transposition of great arteries (ccTGA). Our data shows two specific signaling pathways enriched in the ccTGA RV myocardium. First, we show increased insulin like growth factor (IGF1) signaling within the systemic RV myocardium: there is increased expression of the main receptor IGFR1 within the cardiomyocytes, and IGF1 ligands within the cardiofibroblasts and macrophages. Second, we find increased VEGF and Wnt9 ligand expression in cardiomyocytes and increased VEGF1R and Wnt9 receptors in endothelial cells, which are implicated in angiogenesis. We show that increased insulin and angiogenesis signaling are potentially beneficial RV adaptations to increased pressure overload. This study of an adult systemic RV provides an important framework for understanding RV remodeling to systemic pressures in congenital heart disease and pulmonary hypertension.