Buffering Mechanism in Aortic Arch Artery Formation and Congenital Heart Disease.

BACKGROUND: The resiliency of embryonic development to genetic and environmental perturbations has been long appreciated; however, little is known about the mechanisms underlying the robustness of developmental processes. Aberrations resulting in neonatal lethality are exemplified by congenital heart disease arising from defective morphogenesis of pharyngeal arch arteries (PAAs) and their derivatives. METHODS: Mouse genetics, lineage tracing, confocal microscopy, and quantitative image analyses were used to investigate mechanisms of PAA formation and repair. RESULTS: The second heart field (SHF) gives rise to the PAA endothelium. Here, we show that the number of SHF-derived endothelial cells (ECs) is regulated by VEGFR2 (vascular endothelial growth factor receptor 2) and Tbx1. Remarkably, when the SHF-derived EC number is decreased, PAA development can be rescued by the compensatory endothelium. Blocking such compensatory response leads to embryonic demise. To determine the source of compensating ECs and mechanisms regulating their recruitment, we investigated 3-dimensional EC connectivity, EC fate, and gene expression. Our studies demonstrate that the expression of VEGFR2 by the SHF is required for the differentiation of SHF-derived cells into PAA ECs. The deletion of 1 VEGFR2 allele (VEGFR2SHF-HET) reduces SHF contribution to the PAA endothelium, while the deletion of both alleles (VEGFR2SHF-KO) abolishes it. The decrease in SHF-derived ECs in VEGFR2SHF-HET and VEGFR2SHF-KO embryos is complemented by the recruitment of ECs from the nearby veins. Compensatory ECs contribute to PAA derivatives, giving rise to the endothelium of the aortic arch and the ductus in VEGFR2SHF-KO mutants. Blocking the compensatory response in VEGFR2SHF-KO mutants results in embryonic lethality shortly after mid-gestation. The compensatory ECs are absent in Tbx1+/- embryos, a model for 22q11 deletion syndrome, leading to unpredictable arch artery morphogenesis and congenital heart disease. Tbx1 regulates the recruitment of the compensatory endothelium in an SHF-non-cell-autonomous manner. CONCLUSIONS: Our studies uncover a novel buffering mechanism underlying the resiliency of PAA development and remodeling.

Molecular Pathways and Animal Models of Atrial Septal Defect.

The relative simplicity of the clinical presentation and management of an atrial septal defect belies the complexity of the developmental pathogenesis. Here, we describe the anatomic development of the atrial septum and the venous return to the atrial chambers. Experimental models suggest how mutations and naturally occurring genetic variation could affect developmental steps to cause a defect within the oval fossa, the so-called secundum defect, or other interatrial communications, such as the sinus venosus defect or ostium primum defect.

Parental Impressions and Perspectives of Efficacy in Prenatal Counseling for Single Ventricle Congenital Heart Disease.

Although commonly performed, optimal techniques, strategies, and content to achieve the most effective prenatal counseling have not been explored. We investigate the efficacy of prenatal counseling via survey feedback of parents of children with prenatally diagnosed single ventricle. Grades of counseling using a Likert scale (1-5) were solicited to assess: (1) overall impression of quantity of counseling, (2) explanation of the heart defect, (3) preparation for heart surgery, (4) preparation for hospital course and care, (5) preparation for complications and outcomes of a Fontan circulation, and (6) preparation for neurological, school-related, or behavioral problems. Impressions were solicited concerning specific providers. A comprehensive fetal counseling score was calculated for each participant. Burden of care including length of hospitalization was explored as impacting prenatal counseling grades. There were 59 survey respondents. Average age of the children at the time of survey was 4.6 ± 3.3 years (range 1-10 years). Highest grades were for explanation of the heart condition, with lowest grades for preparation for neurological, school-related, or behavioral problems. Cardiac surgeon received the highest with social worker lowest grade for provider. Negative correlation was found between the composite fetal counseling score and parental recollection of length of hospitalization (Pearson r = - 0.357, p < 0.01). Prenatal counseling for neurological, school-related, and behavioral problems in single ventricle is deficient. Further studies analyzing prenatal counseling techniques and content can help improve upon the delivery of this important aspect of prenatal care.

Identification of novel buffering mechanisms in aortic arch artery development and congenital heart disease.

Rationale: The resiliency of embryonic development to genetic and environmental perturbations has been long appreciated; however, little is known about the mechanisms underlying the robustness of developmental processes. Aberrations resulting in neonatal lethality are exemplified by congenital heart disease (CHD) arising from defective morphogenesis of pharyngeal arch arteries (PAA) and their derivatives. Objective: To uncover mechanisms underlying the robustness of PAA morphogenesis. Methods and Results: The second heart field (SHF) gives rise to the PAA endothelium. Here, we show that the number of SHF-derived ECs is regulated by VEGFR2 and Tbx1 . Remarkably, when SHF-derived EC number is decreased, PAA development can be rescued by the compensatory endothelium. Blocking such compensatory response leads to embryonic demise. To determine the source of compensating ECs and mechanisms regulating their recruitment, we investigated three-dimensional EC connectivity, EC fate, and gene expression. Our studies demonstrate that the expression of VEGFR2 by the SHF is required for the differentiation of SHF-derived cells into PAA ECs. The deletion of one VEGFR2 allele (VEGFR2 SHF-HET ) reduces SHF contribution to the PAA endothelium, while the deletion of both alleles (VEGFR2 SHF-KO ) abolishes it. The decrease in SHF-derived ECs in VEGFR2 SHF-HET and VEGFR2 SHF-KO embryos is complemented by the recruitment of ECs from the nearby veins. Compensatory ECs contribute to PAA derivatives, giving rise to the endothelium of the aortic arch and the ductus in VEGFR2 SHF-KO mutants. Blocking the compensatory response in VEGFR2 SHF-KO mutants results in embryonic lethality shortly after mid-gestation. The compensatory ECs are absent in Tbx1 +/- embryos, a model for 22q11 deletion syndrome, leading to unpredictable arch artery morphogenesis and CHD. Tbx1 regulates the recruitment of the compensatory endothelium in an SHF-non-cell-autonomous manner. Conclusions: Our studies uncover a novel buffering mechanism underlying the resiliency of PAA development and remodeling. Nonstandard Abbreviations and Acronyms in Alphabetical Order: CHD - congenital heart disease; ECs - endothelial cells; IAA-B - interrupted aortic arch type B; PAA - pharyngeal arch arteries; RERSA - retro-esophageal right subclavian artery; SHF - second heart field; VEGFR2 - Vascular endothelial growth factor receptor 2.