Differential Requirement of DICER1 Activity during Development of Mitral and Tricuspid Valves

Abstract

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 unexpectedly 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. Our study thus reveals 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. Summary statementAlthough mitral and tricuspid heart valves are both derived from same cell sources in the atrioventricular region through similar initiation and remodeling processes, congenital dysplasia simultaneously affecting both valves is clinically uncommon. We show that DICER1 activity is only essential for mitral valve development whereas it is dispensable for other valves. Our study thus reveals miRNA-mediated gene regulation as a novel molecular mechanism that is differentially required to regulate mitral and tricuspid valve development, thereby enhancing our understanding of the non-association of inborn mitral and tricuspid dysplasia observed clinically.