The Role of Cell Tracing and Fate Mapping Experiments in Cardiac Outflow Tract Development, New Opportunities through Emerging Technologies

Whilst knowledge regarding the pathophysiology of congenital heart disease (CHDs) has advanced greatly in recent years, the underlying developmental processes affecting the cardiac outflow tract (OFT) such as bicuspid aortic valve, tetralogy of Fallot and transposition of the great arteries remain poorly understood. Common among CHDs affecting the OFT, is a large variation in disease phenotypes. Even though the different cell lineages contributing to OFT development have been studied for many decades, it remains challenging to relate cell lineage dynamics to the morphologic variation observed in OFT pathologies. We postulate that the variation observed in cellular contribution in these congenital heart diseases might be related to underlying cell lineage dynamics of which little is known. We believe this gap in knowledge is mainly the result of technical limitations in experimental methods used for cell lineage analysis. The aim of this review is to provide an overview of historical fate mapping and cell tracing techniques used to study OFT development and introduce emerging technologies which provide new opportunities that will aid our understanding of the cellular dynamics underlying OFT pathology.

Shorter Periconception Maternal Telomere Length and the Risk of Congenital Cardiac Outflow Defects in the Offspring: a case control study

Objective: Congenital cardiac outflow defects (COD) are the largest group of congenital heart defects, with ventricular septal defect (VSD) as the most prevalent phenotype. Increased maternal age, excessive oxidative stress and inflammation are involved in the pathophysiology and enhance telomere length (TL) shortening. We aim to study the association between periconception maternal TL, as future predictive biomarker, and the risk of having a child with COD. Design: HAVEN-study, a multicenter case-control triad study conducted in the Netherlands. Setting and population: 306 case mothers of a child with COD and 424 control mothers of a child without a congenital malformation were selected. Methods: TL was estimated, on DNA from venous blood samples, by qPCR. Multivariable logistic regression was used to compute crude and adjusted odds ratios (OR) per standard deviation (SD) decrease between maternal T/S ratio and COD and VSD risk. Main outcome measures: The risk of COD in offspring. Results: A significant association was shown between maternal TL shortening (per standard deviation) and a 29% increased risk of VSD in offspring (OR 1.29(95% CI 1.04-1.61), P= 0,02), which remained significant after additional adjustment for maternal age (adjOR 1.25(95% CI 1.01-1.55), P= 0,04). No association between maternal TL and the risk of overall COD in offspring was observed. Conclusion: Shortening of maternal TL, due to maternal conditions including age, is associated with an approximately 1.3-fold increased risk, per SD in TL-shortening, of VSD in the offspring. These findings need further confirmation in other studies on the predictive value of maternal TL.

Endothelial TGF-β signaling instructs smooth muscle cell development in the cardiac outflow tract

The development of the cardiac outflow tract (OFT), which connects the heart to the great arteries, relies on a complex crosstalk between endothelial (ECs) and smooth muscle (SMCs) cells. Defects in OFT development can lead to severe malformations, including aortic aneurysms, which are frequently associated with impaired TGF-β signaling. To better understand the role of TGF-β signaling in OFT formation, we generated zebrafish lacking the TGF-β receptor Alk5 and found a strikingly specific dilation of the OFT: alk5-/- OFTs exhibit increased EC numbers as well as extracellular matrix (ECM) and SMC disorganization. Surprisingly, endothelial-specific alk5 overexpression in alk5-/- rescues the EC, ECM, and SMC defects. Transcriptomic analyses reveal downregulation of the ECM gene fibulin-5, which when overexpressed in ECs ameliorates OFT morphology and function. These findings reveal a new requirement for endothelial TGF-β signaling in OFT morphogenesis and suggest an important role for the endothelium in the etiology of aortic malformations.