Abnormal Differentiation and Proliferation of Coronary Arterial Endothelium in Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a severe form of single ventricle congenital heart disease characterized by an underdevelopment of the left ventricle. Early serial postmortem examinations revealed high rate of coronary artery abnormalities in HLHS fetal hearts, which may impact ventricular development and intra-cardiac hemodynamics, leading to a poor prognosis after surgical palliations. Previous study reported that endothelial cells (ECs) lining the coronary vessels showed DNA damage in the left ventricle of human fetal heart with HLHS, indicating that EC dysfunction may contribute to the coronary abnormalities in HLHS. To investigate the underlying mechanism of HLHS coronary artery abnormalities, we profiled both human fetal heart with an underdeveloped left ventricle (ULV) and ECs differentiated from induced pluripotent stem cells (iPSCs) derived from HLHS patients at single cell resolution. CD144+/NPR3- vascular ECs were selected and further classified as venous EC (NR2F2high), arterial EC (EFNB2high) and late arterial EC (GJA5high) subclusters based on previously reported marker genes. To study the arterial phenotype, we specifically generated iPSC-arterial ECs (AECs, CD34+CDH5+CXCR4+NT5E-/low) derived from three HLHS patients and three age-matched healthy controls to further dissect the phenotype of HLHS-AECs. As compared to normal human heart and control iPSC-ECs respectively, ULV late arterial EC subcluster and HLHS iPSC-EC arterial clusters showed significantly reduced expression of arterial genes GJA5, DLL4, and HEY1. Pathway enrichment analysis based on differentially expressed genes revealed several defects in late AEC cluster from ULV compared to normal human heart, such as impaired endothelial proliferation, development and Notch signaling. HLHS iPSCs exhibited impaired AEC differentiation as evidenced by the significantly reduced CXCR4+NT5E-/low AEC progenitor population. Consistent with human heart transcriptomic data, matured HLHS iPSC-AECs also showed a lower expression of the arterial genes such as GJA5, DLL4, HEY1 which are also downstream of NOTCH signaling. Additionally, matured HLHS iPSC-AECs showed significantly decreased expression of cell proliferation marker Ki67 and G1/S transition genes (CCND1, CCND2) compared with controls. Interestingly, NOTCH ligand Jag1 treatment significantly rescued this cell proliferation defect in HLHS AECs, accompanied by upregulation of various G1/S transition genes. In summary, we found that coronary AECs from HLHS showed impaired arterial development and proliferation downstream of NOTCH signaling. These functional defects in HLHS coronary AECs could contribute to the vascular structure malformation and impaired ventricular development.