Impaired cardiac energy metabolism in embryos lacking adrenergic stimulation

Abstract

As development proceeds from the embryonic to fetal stages, cardiac energy demands increase substantially, and oxidative phosphorylation of ADP to ATP in mitochondria becomes vital. Relatively little, however, is known about the signaling mechanisms regulating the transition from anaerobic to aerobic metabolism that occurs during the embryonic period. The main objective of this study was to test the hypothesis that adrenergic hormones provide critical stimulation of energy metabolism during embryonic/fetal development. We examined ATP and ADP concentrations in mouse embryos lacking adrenergic hormones due to targeted disruption of the essential dopamine β-hydroxylase (Dbh) gene. Embryonic ATP concentrations decreased dramatically, whereas ADP concentrations rose such that the ATP/ADP ratio in the adrenergic-deficient group was nearly 50-fold less than that found in littermate controls by embryonic day 11.5. We also found that cardiac extracellular acidification and oxygen consumption rates were significantly decreased, and mitochondria were significantly larger and more branched in adrenergic-deficient hearts. Notably, however, the mitochondria were intact with well-formed cristae, and there was no significant difference observed in mitochondrial membrane potential. Maternal administration of the adrenergic receptor agonists isoproterenol or l-phenylephrine significantly ameliorated the decreases in ATP observed in Dbh-/- embryos, suggesting that α- and β-adrenergic receptors were effective modulators of ATP concentrations in mouse embryos in vivo. These data demonstrate that adrenergic hormones stimulate cardiac energy metabolism during a critical period of embryonic development.

Metabolomics reveals critical adrenergic regulatory checkpoints in glycolysis and pentose–phosphate pathways in embryonic heart

“…Exvivo delivery of pyruvate to adrenergic-deficient embryonic hearts substantially improved OCR and steady-state ATP levels, demonstrating that apparent metabolic starvation could be overcome by addition of the appropriate substrate(s). We previously showed that adrenergic-deficient embryos have larger and more elongated mitochondria compared to controls, consistent with a "starvation" phenotype (12,64,65). Taken together, these results suggest that mitochondrial metabolism is capable of functioning in adrenergic-deficient embryos, but impaired GAPDH activity may limit the amount of pyruvate substrate entering mitochondria to fuel aerobic respiration.…”

“…All procedures and handling of mice were conducted in accordance with and approved by the University of Central Florida Institutional Animal Care and Use Committee and the guidelines established by the National Institutes of Health (NIH) for vertebrate animal research (66,67). The Dbh mouse colony was kindly provided by the Palmiter laboratory (University of Washington, Seattle, WA) (8) and maintained as described previously (11,12,68). Timed pregnancies were determined by the presence of a vaginal plug at E0.5.…”

“…All samples were centrifuged at 6000g for 5 min at 4°C. Supernatant was collected and neutralized with 1X Tris-acetate, as described previously (12,69). ATP measurements were performed with the ATPlite Bioluminescence Assay (Perkin Elmer) according to the manufacturer's protocol.…”

“…To gain insight into transcriptional changes between Dbh +/+ and Dbh -/-, a genomic-wide expression screen showed that the largest set of differentially expressed genes are involved in metabolism (11). Further evidence demonstrated that Dbh -/-embryos are energy-depleted with >95% ATP/ADP reduction by E11.5 (12). Oxygen consumption rates (OCR), an indicator of mitochondrial respiration, are established in E10.5 hearts; however, Dbh -/-hearts lag behind by ~24 hours later compared to age-matched littermate controls.…”

A modified method for isolation of human cardiomyocytes to model cardiac diseases

“…Alterations in myocardial energy substrate metabolism is known to occur in heart failure, switching from fatty acid oxidation toward predominantly glycolysis [ 28 ], providing opportunity for potential intervention [ 29 ]. There is compelling evidence indicating that aerobic metabolism in the mitochondria becomes increasingly important as the heart energy transitions, which can be measured via oxygen consumption rate (OCR) [ 30 ]. We successfully determined the OCR in the cardiomyocytes isolated using our method.…”