Abstract Body: Introduction
RNA helicases are emerging regulators of gene expression during development and disease. Recent studies show that mutation of DDX21 disrupts endothelial cell function and causes developmental defects. However, whether DDX21 regulates development of the muscular compartment of the cardiovascular system, including cardiomyocytes and vascular smooth muscle cells, remains unknown.
Hypothesis
We hypothesize that DDX21 regulates gene expression programs required for cardiovascular morphogenesis within the muscular compartment of the cardiovascular system.
Methods
Public RNA-seq datasets were analyzed to evaluate associations between Ddx21 expression and congenital heart disease (CHD). To investigate its in vivo function, Ddx21 floxed mice were crossed with SM22α/Tagln-Cre mice to delete Ddx21 in the cardiovascular muscular lineage. Timed matings were used to collect embryos at multiple developmental stages for histological and molecular analyses. In parallel, human iPSC-derived cardiomyocytes were used to examine transcriptomic changes following Ddx21 knockdown by siRNA.
Results
RNA-seq analysis revealed a positive association between DDX21 expression and CHD linked to dysregulated cardiomyocyte proliferation. Conditional knockout (cKO) of DDX21 in the SM22α/Tagln lineage caused developmental cardiac abnormalities. Although embryos appeared grossly normal at earlier stages, histological analysis revealed early defects in cardiac morphogenesis. Interventricular septal hypoplasia was detectable at E13.5, the earliest stage examined. Beginning at E14.5, when the compact myocardium expands rapidly, cKO hearts exhibited markedly reduced ventricular compaction compared with controls. Overt embryonic abnormalities became evident at E18.5. Heterozygous littermates were indistinguishable from wild type, indicating haploinsufficiency does not disrupt development. CKO embryos were recovered at the normal Mendelian ratio through E18.5. However, newborn cKO exhibited marked pallor and died within 12 hours (P0.5), suggesting severe circulatory defects. Mechanistically, DDX21 regulates expression of WDR62, a recently identified CHD susceptibility gene, and modulates YAP activity, a key Hippo pathway regulator of cardiomyocyte proliferation.
Conclusion
These findings identify DDX21 as a previously unrecognized regulator of cardiac development and ventricular compaction, linking RNA helicase-mediated gene regulation to congenital heart disease.