Congenital heart defects (CHDs) arise from perturbations in complex molecular and cellular processes underlying normal embryonic heart development. CHDs are the most common congenital malformation, occurring in 1 to 5% of live births, and are the leading cause of pediatric mortality. Adverse genetic and environmental factors can impede normal cardiogenesis and increase the likelihood of CHDs. Pregestational maternal diabetes increases the risk of CHDs in children by more than four-fold. As the prevalence of diabetes rapidly rises among women of childbearing age, there is a need to investigate the mechanisms and potential preventative strategies for these defects. The aim of this thesis was to explore the pathogenesis of pregestational diabetes-induced CHDs and coronary artery malformations (CAMs), while testing the efficacy of two clinically relevant pharmacotherapies. To this end, using a mouse model of pregestational diabetes, I examined the impact of hyperglycemia-induced elevations in oxidative stress and miR-122 on heart development, concurrently determining the preventative capabilities of sapropterin or antimiR-122 treatment. I confirmed that pregestational diabetes results in spectrum of CHDs, CAMs and cardiac function deficits, and that their incidence is significantly lowered with either sapropterin or antimiR-122. Specifically, sapropterin treatment lowered the incidence of CHDs and CAMs from 59% and 50% to 27% and 21%, respectively. Similarly, antimiR-122 therapy reduced this incidence of CHDs from 57% to 23%. These morphological malformations range in severity, and include septal and outflow defects (OFT), myocardium deficiencies, and hypoplastic coronary arteries. Lineage tracing experiments revealed a diminished commitment of second heart field progenitors to the OFT, endocardial cushions and ventricular myocardium in embryonic hearts from diabetic dams. In addition, deficits in cardiogenic gene expression, enzyme activity, cell proliferation, and epicardial EMT, induced by pregestational diabetes, contribute to these defects, and were prevented by both treatments. Specifically, sapropterin treatment reestablished the functional eNOS dimer and restored its phosphorylation in embryonic hearts of diabetic dams, leading to normal cardiovascular development. Conversely, antimiR-122 attenuated the targeting and inhibition of key genes responsible for cardiogenesis by miR-122. These results suggest that sapropterin and antimiR-122 may have therapeutic potential in preventing CHDs in children of women with pregestational diabetes
