Lincoln, J. | bioRxiv Science

bioRxiv2022

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

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.

developmental biology↗

bioRxiv2020

Nitric oxide prevents aortic valve calcification by S-nitrosylation of USP9X to activate NOTCH signaling

Calcific aortic valve disease (CAVD) is an increasingly prevalent condition and endothelial dysfunction is implicated in its etiology. We previously identified nitric oxide (NO) as a calcification inhibitor by its activation of NOTCH1, which is genetically linked to human CAVD. Here, we show that NO rescues calcification by a S-nitrosylation-mediated mechanism in porcine aortic valve interstitial cells (pAVICs) and single cell RNA-seq demonstrated regulation of NOTCH pathway by NO. A unbiased proteomic approach to identify S-nitrosylated proteins in valve cells found enrichment of the ubiquitin proteasome pathway and implicated S-nitrosylation of USP9X in NOTCH regulation during calcification. Furthermore, S-nitrosylated USP9X was shown to deubiquitinate and stabilize MIB1 for NOTCH1 activation. Consistent with this, genetic deletion of Usp9x in mice demonstrated aortic valve disease and human calcified aortic valves displayed reduced S-nitrosylation of USP9X. These results demonstrate a novel mechanism by which S-nitrosylation dependent regulation of ubiquitin-associated pathway prevents CAVD.

cell biology↗