A hypoxic episode during cardiogenesis downregulates the adenosinergic system and alters the myocardial anoxic tolerance

Abstract

Robin E, Marcillac F, Raddatz E. A hypoxic episode during cardiogenesis downregulates the adenosinergic system and alters the myocardial anoxic tolerance. Am J Physiol Regul Integr Comp Physiol 308: R614 -R626, 2015. First published January 28, 2015 doi:10.1152/ajpregu.00423.2014.-To what extent hypoxia alters the adenosine (ADO) system and impacts on cardiac function during embryogenesis is not known. Ectonucleoside triphosphate diphosphohydrolase (CD39), ecto-5=-nucleotidase (CD73), adenosine kinase (AdK), adenosine deaminase (ADA), equilibrative (ENT1,3,4), and concentrative (CNT3) transporters and ADO receptors A 1, A2A, A2B, and A3 constitute the adenosinergic system. During the first 4 days of development chick embryos were exposed in ovo to normoxia followed or not followed by 6 h hypoxia. ADO and glycogen content and mRNA expression of the genes were determined in the atria, ventricle, and outflow tract of the normoxic (N) and hypoxic (H) hearts. Electrocardiogram and ventricular shortening of the N and H hearts were recorded ex vivo throughout anoxia/reoxygenation Ϯ ADO. Under basal conditions, CD39, CD73, ADK, ADA, ENT1,3,4, CNT3, and ADO receptors were differentially expressed in the atria, ventricle, and outflow tract. In H hearts ADO level doubled, glycogen decreased, and mRNA expression of all the investigated genes was downregulated by hypoxia, except for A 2A and A3 receptors. The most rapid and marked downregulation was found for ADA in atria. H hearts were arrhythmic and more vulnerable to anoxia-reoxygenation than N hearts. Despite downregulation of the genes, exposure of isolated hearts to ADO 1) preserved glycogen through activation of A1 receptor and Akt-GSK3␤-GS pathway, 2) prolonged activity and improved conduction under anoxia, and 3) restored QT interval in H hearts. Thus hypoxia-induced downregulation of the adenosinergic system can be regarded as a coping response, limiting the detrimental accumulation of ADO without interfering with ADO signaling.anoxia-reoxygenation; arrhythmias; glycogen metabolism; hypoxia; adenosine signaling LOW OXYGEN LEVEL is a prerequisite for normal embryonic and fetal growth including the cardiovascular system. However, hypoxia-induced imbalance between O 2 supply and demand impacts gene expression, metabolism, growth, and function (13,17,20,21,33,45,48,50,53,56). Oxygen deprivation during critical periods of embryogenesis impairs heart development and function with hemodynamic disturbances resulting in fetal growth retardation and increasing the risk of cardiovascular disease in adulthood, the so-called "fetal programming" (8,12,26,38,47,57,59). Maternal hypoxemia, reduction in umbilical blood flow, or placental insufficiency can rapidly lead to acute or chronic ischemia and/or hypoxia, which exacerbates ATP-derived adenosine (ADO) production. Since ADO represents an important regulator of the embryonic cardiovascular function (35), the present study focuses on the modulation of the adenosinergic system by hypoxia and its functional consequences in the d...

Role of adenosine signaling in coordinating cardiomyocyte function and coronary vascular growth in chronic fetal anemia

“…Thus, transcriptional regulation in myocardia of the anemic (hypoxemic) fetus is shifted to increase interstitial adenosine and adenosine signal transduction. Our findings of upregulated adenosine signaling following many days of hypoxemic stress in the late-term (85% development) fetal sheep are in contrast to a previous report of downregulated adenosinergic genes following 6 h of acute hypoxia in the early (20% development) embryonic chick heart (33). However, our findings are consistent with the majority of the field, in which hypoxia and HIF-1␣ are found to increase interstitial adenosine and intracellular adenosine signaling in many tissues, including heart, through transcriptional regulation (30).…”

Oxygen regulation in biological systems

“…Importantly, chronic hypoxia led to impaired cardiac systolic and diastolic function in the chick embryo prehatching (12). Furthermore, even relatively brief exposure to hypoxia during cardiogenesis in the chicken embryo can render the embryonic heart susceptible to later hypoxia, perhaps in part due to alterations in adenosinergic signaling pathways (34). These findings demonstrate the utility of the chicken for investigation of developmental programming of cardiac structure and function, particularly in terms of teasing out the direct effects of embryonic hypoxia.…”

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