186 - The Effect of Maternal Hyperglycemia-induced Oxidative Stress on Endocardial and Endocardial-derived Cells during Cardiovascular Development

Congenital heart defects (CHD) affect 1% of all live births and are the leading cause of birth defect-related mortality. The etiology of CHD is multifactorial as genomic variation and environmental factors act as contributors. Among the environmental teratogens, maternal pre-gestational diabetes mellitus and its concurrent maternal hyperglycemia (matHG) is associated with a ~5-fold increased risk of CHD. Oxidative stress (Ox-Stress) due to the generation of excess reactive oxygen species is routinely observed in embryonic hearts exposed to matHG, but its teratogenic effect on cardiac development is not fully understood. Along with increased Ox-Stress, we have observed murine embryonic hearts exposed to matHG have reduced expression of Notch1, which is highly expressed in endocardial cells (EC) and critical for normal cardiac development, and reported a gene-environment interaction between matHG and Notch1 haploinsufficiency that results in CHD in mice. We hypothesize that matHG-induced Ox-Stress leads to the downregulation of endocardial Notch signaling and aberrant EC function leading to CHD.

Objective:

To investigate the effect of matHG-induced Ox-Stress on endocardial Notch signaling and its downstream effect on EC-derived cardiovascular structures. We also investigate whether modulating intracellular levels of Ox-Stress can rescue the CHD phenotype observed with matHG exposure.

Design/Methods:

We generated mouse embryos exposed to matHG with conditional deletion of Notch1 in EC and examined the cardiac phenotype. We also utilized Rosa lineage tracing to detect differences in EC-derived structures in hyperglycemia and normoglycemia-exposed embryonic hearts. Lastly, we generated mouse embryos with overexpression of the antioxidant gene, SOD1, to determine whether this can reduce Ox-Stress and rescue the matHG-associated CHD.

Results:

We show that conditional deletion of endocardial Notch1 in embryos exposed to matHG leads to highly penetrant CHD. Further, we found reduced number of EC-derived mesenchymal cells and increased Ox-Stress in endocardial cushions of mouse hearts exposed to matHG. Finally, both wildtype and Notch1^+/- embryos with SOD1 overexpression have reduced Ox-Stress and decreased incidence of CHD compared to non-SOD1 overexpressing littermates.

Conclusion(s):

This works shows that matHG-induced Ox-Stress may be associated with aberrant EC and EC-derived cell function via disruption of Notch signaling. Mitigating Ox-Stress during cardiac development may lead to rescue of Notch signaling and EC function to reduce CHD incidence from matHG exposure.