Intrinsic Endocardial Defects Contribute to Hypoplastic Left Heart Syndrome

Abstract

Hypoplastic left heart syndrome (HLHS) is a complex congenital heart disease characterized by abnormalities in the left ventricle, associated valves, and ascending aorta. Studies have shown intrinsic myocardial defects but do not sufficiently explain developmental defects in the endocardial-derived cardiac valve, septum, and vasculature. Here, we identify a developmentally impaired endocardial population in HLHS through single-cell RNA profiling of hiPSC-derived endocardium and human fetal heart tissue with an underdeveloped left ventricle. Intrinsic endocardial defects contribute to abnormal endothelial-to-mesenchymal transition, NOTCH signaling, and extracellular matrix organization, key factors in valve formation. Endocardial abnormalities cause reduced cardiomyocyte proliferation and maturation by disrupting fibronectin-integrin signaling, consistent with recently described de novo HLHS mutations associated with abnormal endocardial gene and fibronectin regulation. Together, these results reveal a critical role for endocardium in HLHS etiology and provide a rationale for considering endocardial function in regenerative strategies.

Decoding Genetics of Congenital Heart Disease Using Patient-Derived Induced Pluripotent Stem Cells (iPSCs)

“…Single-cell RNA-seq analysis of human and mouse hearts has provided unprecedented resources on the trajectory of cardiac development in vivo at single-cell resolution and revealed a blueprint on how normal cell fate determination is altered under genetic perturbation and pathological conditions such as CHD ( Cui et al, 2019 ; De Soysa et al, 2019 ; Litvinukova et al, 2020 ; Paik et al, 2020 ). Single-cell transcriptional profiling of healthy and diseased iPSCs during cardiac differentiation would decipher how a given genetic variant affects cardiac differentiation and developmental trajectories, and uncover new molecular insights in the pathogenesis of CHD ( Churko et al, 2018 ; Kathiriya et al, 2020 ; Lam et al, 2020 ; Miao et al, 2020 ; Paige et al, 2020 ). As heart development is dependent on interaction among multiple cell types in the embryo, cardiac organoids and 3D bio-printing may serve as another tier of disease modeling using patient iPSCs ( Lee et al, 2019 ; Nugraha et al, 2019 ).…”

“…Human iPSCs are promising models for studying genetic mechanisms of isolated CHD caused by single-gene defects. In addition to cell-autonomous inherited cardiac disease such as long QT syndrome ( Moretti et al, 2010 ; Itzhaki et al, 2011 ), ventricular tachycardia ( Zhang et al, 2014 ; Sleiman et al, 2020 ) and dilated cardiomyopathy ( Sun et al, 2012 ; Hinson et al, 2015 ), patient iPSCs have been employed to model several types of CHD, including BAV and calcific aortic valve disease (CAVD) ( Theodoris et al, 2015 ), supravalvular aortic stenosis (SVAS) ( Ge et al, 2012 ), cardiac septal defects ( Ang et al, 2016 ), Barth syndrome ( Wang et al, 2014 ), and HLHS ( Hrstka et al, 2017 ; Yang et al, 2017 ; Miao et al, 2020 ; Table 2 ). Human iPSCs can be differentiated to the desired cardiovascular cell types relevant for studying different CHD ( Protze et al, 2019 ), though the immaturity of iPSC-derived cardiomyocytes (iPSC-CMs) continues to be a challenge for recapitulating the physiological scenarios in the heart ( Karbassi et al, 2020 ; Zhao et al, 2020b ).…”

“…This study is consistent with the congenital cardiac abnormalities observed in Notch1 +/− ; Nos3 –/– transgenic mice and demonstrates that interaction between NO pathway and NOTCH signaling is required for proper development of the left-sided cardiac structures including the aortic valve ( Bosse et al, 2013 ; Koenig et al, 2016 ). Recently, Miao et al (2020) have highlighted the contribution of endocardial defects to the pathogenesis of HLHS using patient iPSCs and single-cell RNA sequencing of human fetuses with under developed left ventricles. Although the genetic causes of these HLHS iPSCs are unclear, endocardial defects lead to abnormal endothelial-to-mesenchymal transition, reduced cardiomyocyte proliferation and maturation, and disrupted fibronectin-integrin signaling.…”

Ex uno, plures–From One Tissue to Many Cells: A Review of Single-Cell Transcriptomics in Cardiovascular Biology

“…Furthermore, single-cell transcriptomic data revealed that the expression of Gdf15, a cardiac-produced hormone and marker of cardiac dysfunction, was regulated by distinct cell-type-specific networks. More recently, two studies have used 10x Chromium technologies to investigate different models of congenital heart defects [ 55 , 56 , 57 , 58 ]. The first study [ 55 ] profiled the cardiogenic region of wild-type versus Hand2 null mouse embryos over three phases of cardiac development (E7.75, E8.5, E9.25).…”

“…Further, scRNAseq has been employed to analyze patient-derived hiPSC and dissect the cellular basis of cardiomyopathy associated with Duchenne muscular dystrophy (DMD) [ 71 ] and the defective cardiac development in Hypoplastic Left Heart Syndrome (HLHS) [ 56 ] and a type of Hypoplastic Right Heart Syndrome (HRHS) [ 58 ]. DMD is the most common form of muscular dystrophy, it is caused by mutation in the DMD gene, and it generally leads to dilated cardiomyopathy (DCM).…”