Differential Requirement for DICER1 Activity during the Development of Mitral and Tricuspid Vlaves

Mitral and tricuspid valves are essential for unidirectional blood flow in the heart. They are derived from similar cell sources, and yet congenital dysplasia affecting both valves is clinically rare, suggesting the presence of differential regulatory mechanisms underlying their development. We specifically inactivated Dicer1 in the endocardium during cardiogenesis and found that Dicer1-deletion caused congenital mitral valve stenosis and regurgitation, while it had no impact on other valves. We showed that hyperplastic mitral valves were caused by abnormal condensation and extracellular matrix (ECM) remodeling. Our single-cell RNA Sequencing analysis revealed impaired maturation of mesenchymal cells and abnormal expression of ECM genes in mutant mitral valves. Furthermore, expression of a set of miRNAs that target ECM genes was significantly lower in tricuspid valves compared to mitral valves, consistent with the idea that the miRNAs are differentially required for mitral and tricuspid valve development. We thus reveal miRNA-mediated gene regulation as a novel molecular mechanism that differentially regulates mitral and tricuspid valve development, thereby enhancing our understanding of the non-association of inborn mitral and tricuspid dysplasia observed clinically.二尖瓣与三尖瓣是维持心脏内血液单向流动的关键结构。二者起源于相似的细胞谱系，但临床中同时累及两种瓣膜的先天性发育异常却极为罕见，这提示二者的发育过程存在差异化的调控机制。本研究在心脏发生阶段特异性地于心内膜中失活Dicer1基因，结果发现Dicer1缺失会导致先天性二尖瓣狭窄与反流，但对其他瓣膜无显著影响。我们证实，二尖瓣增生是由异常的细胞凝聚与细胞外基质（extracellular matrix, ECM）重塑所导致的。我们的单细胞RNA测序分析显示，突变小鼠的二尖瓣中，间充质细胞成熟受损且细胞外基质相关基因表达异常。此外，相较于二尖瓣，三尖瓣中靶向细胞外基质基因的一组微小RNA（miRNAs）的表达水平显著降低，这与“二尖瓣与三尖瓣发育对微小RNA的需求存在差异”的观点相符。综上，本研究揭示了微小RNA介导的基因调控是差异化调控二尖瓣与三尖瓣发育的全新分子机制，从而加深了我们对临床中先天性二尖瓣与三尖瓣发育异常不同时发生这一现象的理解。