Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Pharmacology and Toxicology

Supervisor

Dr. Qingping Feng

Abstract

Congenital heart disease (CHD) is the most common birth defect in infants. Identifying factors that are critical to embryonic heart development or CHDs in general could further our understanding of the disease and may lead to new strategies of its prevention and treatment. Endothelial nitric oxide synthase (NOS3/eNOS) is known for many important biological functions including vasodilation, vascular homeostasis and angiogenesis. Previous studies have shown that deficiency in NOS3 results in congenital septal defects, cardiac hypertrophy and postnatal heart failure. In addition, NOS3 is pivotal to morphogenesis of aortic valve and myocardial capillary development. The aim of my thesis was to investigate the role of NOS3 in the embryonic and adult heart. I discovered that NOS3 deficiency resulted in coronary artery hypoplasia in fetal mice and spontaneous myocardial infarction in postnatal hearts. Coronary artery diameters, vessel density and volume were significantly decreased in NOS3-/- mice at postnatal day 0. Lack of NOS3 also down-regulated the expression of Gata4, Wilms tumor-1, vascular endothelial growth factor, basic fibroblast growth factor and erythropoietin in the embryonic heart at E12.5, and inhibited migration of epicardial cells into the myocardium. In addition, my data show that the overall size and length of mitral and tricuspid valves were decreased in NOS3-/- compared with WT mice. Echocardiographic assessment showed significant regurgitation of mitral and tricuspid valves during systole in NOS3-/- mice. Immunostaining of Snail1 was performed in the embryonic heart. Snail1 positive and total mesenchymal cells in the AV cushion were decreased in NOS3-/- compared with WT mice at E10.5 and E12.5. Finally, in the adult aortic valves, NOS3 is important in inhibition of thrombosis formation. Deficiency in NOS3 leads to aortic valve thrombosis and calcification. At 12 months old, 72% (13/18) of NOS3-/- mice showed severe spontaneous aortic valve thrombosis compared with WT mice (0/12). Ex vivo culture of aortic valves showed that platelet aggregation and adhesion were significantly increased in NOS3-/- aortic valves compared with WT aortic valves. There was also a significant regurgitation of the aortic valve during systole in the NOS3-/- compared with WT mice. In addition, NOS3 deficiency resulted in significant aortic valve stenosis, calcification and fibrosis. In summary, these data suggest NOS3 plays a critical role in embryonic heart development and morphogenesis of coronary arteries and inhibits thrombosis formation in the adult aortic valves.


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