Tetralogy of Fallot: Physiological and morphological changes in conditional Jagged1 mutant mice

Abstract

The Notch signaling pathway is an evolutionarily conserved intercellular signaling mechanism essential for embryonic development in mammals. Mutations in the human Jagged1 (Jag1) gene, which encodes a ligand for the Notch, cause the autosomal dominant disorder Alagille syndrome. Symptoms of this inherited disease may include various forms of Tetralogy of Fallot.Here, we generated Jag1flox/flox Islet1Cre/+ mice with targeted Jagged1 gene conditional deletion in the cardiac outflow tract to investigate the impact of Jagged1 mutations on cardiac morphology and physiology at different developmental stages.Mice with conditional deletion exhibited severe cardiac malformations typical for Tetralogy of Fallot. Main defect was double outlet right ventricle, where aorta and pulmonary trunk are connected to the right ventricle. This abnormality is associated with ventricular septal defect, which was found in 100% of homozygotes. We also observed changes in atrioventricular and semilunar valve morphology. Mostly defects include myxomatous mitral valve or changes in the number of leaflets or leaflet bifurcation, they are typical for Notch deletion.Islet1 is also express in sinoatrial node and atrioventricular node, therefore we used the optical mapping for the visualization of cardiac conductive system. The analysis of E14.5, E16.5 embryos and adult mice showed changes in the activation pattern. In controls, we showed maturated activation from apex to base with two separate activation centres from both ventricles. Homozygous and heterozygous embryonic hearts optical maps revealed activation only from the left ventricle, indicating a perturbed function of the right bundle branch. In mutant adult mice, activation occurred at additional activation centres in both ventricles and posterior site, distinguishing them from controls where excitation is conducted from a single site at the apex.For the physiological analysis we used Vevo ultrasound imaging. Analysis was performed only on adult heterozygotes, because of the postnatal mortality of the homozygotes. Most of the monitored hemodynamical parameters did not show significant differences. However, spackle-based strain analysis revealed vulnerable areas of contractile defect that generate mechanical dyssynchrony pronounced mostly at anterior wall.In our study, we demonstrated morphological and electrophysiological alterations resulting from conditional deletion of Jag1 in heterozygous and homozygous embryos, as well as in heterozygous adults. Embryonic mice exhibited malformations and irregular activation patterns, suggesting right bundle branch disruption. Severe malformations were less prevalent in adult mice, primarily due to the survival of heterozygotes and an increased mortality rate among mice displaying severe congenital defects. Nevertheless, surviving animals exhibited abnormal electrophysiological changes along with physiological alterations resulting in dyssynchronous myocardial contractions observed during strain analysis.