Abstract 2162: Endocardial Fibroelastosis in Hypoplastic Left Heart Syndrome is Caused by Aberrant Endothelial to Mesenchymal Transition
Introduction: Hypoplastic left heart syndrome (HLHS) occurs in approximately 0.03% of all live births and is the leading cause of congenital heart disease in babies. Histopathologically endocardial fibrosis (syn. Endocardial fibroelastosis, EFE) is the hallmark of HLHS, but little is yet known about the underlying mechanisms of fibrogenesis in HLHS. Endothelial to mesenchymal transition (EndMT) is a mechanism by which endothelial cells can acquire a mesenchymal phenotype and contribute to the pool of fibroblasts, the main mediators of fibrogenesis.
Methods: We established a new mouse model of endocardial fibrosis and left ventricular hypoplasia which allows for genetic endothelial lineage tracing. In this model the hearts of newborn Tie1-cre;R26Rosa-STOP-YFP mice were unloaded by means of heterotopic transplantation onto the abdominal vessels of C57BL/76 wildtype recipient mice. Because endothelial cells in the donor hearts are irreversibly labeled by YFP expression irrespective of their phenotype, this model allows for analysis of EndMT within EFE. Furthermore, we analyzed 13 endocardial tissues which were obtained during surgery form children with HLHS for incidence of EndMT by double immunofluorescence-labeling using antibodies to CD31 (endothelial cell marker) and S100A4 (fibroblast marker).
Results: To gain insights into possible EndMT in HLHS we utilized a new mouse model of heterotopic transplanation of hearts from newborn Tie1-cre;R26Rosa-STOP-YFP mice into adult C57BL/6 mice. In the transplanted hearts fibroblasts in the fibrotic endocardium were positive for both YFP (endothelial cell lineage) demonstrating that these fibroblasts originate from endothelail cells via EndMT. In addition confocal analysis revealed presence of CD31+S100A4+ double-positive cells in 11 out of 13 endocardial tissues from children with HLHS but not in non-fibrotic control tissues, suggesting that these cells undergo active EndMT with an intermediate phenotype.
Conclusion: Our data suggests that aberrant EndMT is a major contributor to endocardial fibrosis in HLHS and that inhibiting EndMT could potentially be a new therapeutic strategy for children with HLHS.
This research has received full or partial funding support from the American Heart Association, Founders Affiliate (Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, Vermont).