Genetic and Developmental Modulation of Cardiac Deficits in Prenatal Alcohol Exposure

Abstract

Background: Increasing evidence demonstrates that genetic background is an important modulator of alcohol's effects on the developing fetus. Such effects are separable from maternal ethanol metabolism. Here, we study ethanol's effects on cardiogenesis in an avian model that shows strong cell death within neuronal and neural crest precursors following ethanol exposure. Methods: The study design tested the hypothesis that ethanol-induced losses of cardiac neural crest populations would disrupt outflow tract development and thus contribute to the valvuloseptal deficits observed in prenatal alcohol exposure. Three chick strains were exposed to alcohol at gestational windows between gastrulation and early heart septation (day 3 incubation), and then hearts were examined at the completion of morphogenesis (day 10 incubation). Results: Ethanol's impact on cardiac development was influenced by fetal genetics. The B300 X Hampshire Red cross exhibited pronounced cell death within cardiac neural crest populations but had normal development of the heart and aortic arches. Neural crest migration and differentiation into the distal outflow tract were also normal in these embryos, which suggested a capacity to repair earlier losses. The DeKalb White X Hampshire Red cross also did not exhibit cardiac defects. Hearts of the B300 strain had a unique phenotype with respect to ethanol exposure and exhibited a thin ventricular compact layer, dilatation, and reduced myosin/deoxyribonucleic acid and myosin/protein content, a phenotype that indicates disrupted myocardial maturation and inductive cues. The deficit was only observed when ethanol exposure occurred at stages 15 or 18 and apparently was independent of neural crest cell death. Such ventricular thinning might go undetected in the absence of extensive screening. Conclusions: Results add to the increasing evidence that genetic background strongly modulates the effects of prenatal alcohol exposure. The results also suggest that embryos have a varying capacity to repair and recover from earlier neural crest losses.