Abstract 319: Adrenergic Hormones Regulate Cardiac Metabolic Health During Embryogenesis
The adrenergic hormones, norepinephrine (NE) and epinephrine (EPI), are critically important during embryogenesis and cardiovascular development, yet their specific mechanisms of action remain mysterious. Disruption of the dopamine β-hydroxylase (Dbh) gene results in an inability to produce NE and EPI, which leads to death in utero between embryonic days 10.5 (E10.5) and E15.5 from apparent heart failure. To determine genes differentially expressed by the loss of adrenergic hormones, Affymetrix® GeneChip microarray analysis revealed 23 genes (of the 22,000 analyzed) that are significantly altered 2-fold or greater in E10.5 Dbh-/- hearts. Of these altered genes, 31% (7 of 23) are linked to metabolic regulation. The gene encoding for NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 2, Ndufb2, for example, is a subunit of the mitochondrial complex 1, and displayed a 2.1-fold change in Dbh-/- embryonic hearts. This led us to investigate the metabolic health of these Dbh-/- embryos. Initially, we measured adenosine triphosphate (ATP) and adenosine diphosphate (ADP) levels in E9.5, E10.5, and E11.5 embryos from Dbh-/-, Dbh+/-, and Dbh+/+ mice. At E9.5, ATP concentrations were similar in Dbh-/-, Dbh+/-, and Dbh+/+ embryos (p>0.7, n=6), but began to decline in the Dbh-/- embryos at E10.5 compared to Dbh+/- and Dbh+/+ embryos (p<0.02, n=5). By E11.5, ATP concentrations were markedly decreased in Dbh-/- embryos, while ADP levels were increased 5-fold relative to Dbh+/+ controls. This resulted in a significant (p<0.01, n=4) and drastic (nearly 50-fold) difference in ATP/ADP ratio (0.4 ± 0.1) in Dbh-/- compared with Dbh+/+ control embryos (20.7 ± 4.1) at E11.5. Despite this dramatic difference in energy levels, all embryos appeared grossly normal, had similar heart rates, and displayed no significant differences in caspase 3 or 7 cleavage activity. Thus, the energy deficiency observed in Dbh-/- embryos did not appear to be associated with preceding signs of distress or demise. These results suggest that adrenergic hormones play an important role in regulating energy production during a critical phase of early development that roughly coincides with the transition from embryonic to fetal stages when increased energy utilization is needed.
- © 2012 by American Heart Association, Inc.