Single-Cell RNA-Seq and Patient-Specific iPSCs Reveal Endocardial Abnormalities in Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is one of the most devastating forms of congenital heart defects. Previous studies have only focused on intrinsic defects in the myocardium. However, this does not sufficiently explain the abnormal development of the cardiac valve, septum, and vasculature, which are known to originate from the endocardium. Here, using single-cell RNA profiling, induced pluripotent stem cells, and fetal heart tissue with an underdeveloped left ventricle, we identified a developmentally impaired endocardial cell population in HLHS. The intrinsic endocardial deficits contributed to abnormal endothelial to mesenchymal transition, NOTCH signaling, and extracellular matrix organization, all of which are key factors in valve formation. Consequentially, endocardial abnormalities conferred reduced proliferation and maturation of cardiomyocytes through a disrupted fibronectin-integrin interaction. Several known HLHS de novo mutations all contributed to the abnormal endocardial gene expression through the alteration of promoter/enhancer activities. These mechanistic discoveries provide an alternative angle for early intervention and heart regeneration in HLHS.

左心发育不全综合征（Hypoplastic left heart syndrome, HLHS）是最具破坏性的先天性心脏缺陷类型之一。既往研究仅聚焦于心肌的内在缺陷，但这无法充分解释心脏瓣膜、心间隔与脉管系统的异常发育——而上述结构均被证实源自心内膜。本研究借助单细胞RNA表达谱分析（single-cell RNA profiling）、诱导多能干细胞（induced pluripotent stem cells）以及左心室发育不全的胎儿心脏组织，在HLHS样本中鉴定出了发育受损的心内膜细胞群。心内膜的内在缺陷会引发内皮间质转化（endothelial to mesenchymal transition）、NOTCH信号通路以及细胞外基质组织异常，而这些均为心脏瓣膜形成的关键调控因素。进而，心内膜异常会通过紊乱的纤连蛋白-整合素相互作用，导致心肌细胞的增殖能力与成熟水平受损。目前已明确的数种HLHS新发突变，均可通过改变启动子/增强子的活性，诱导心内膜基因表达出现异常。上述机制层面的发现为HLHS的早期干预与心脏再生研究提供了全新视角。