Gene expression of atrial natriuretic factor in ovine fetal heart during development

Targeted sequencing identifies novel GATA6 variants in a large cohort of patients with conotruncal heart defects

Studies have highlighted the critical role of GATA6 in conotruncal heart defects (CTDs). Nevertheless, relationship between GATA6 variants and different CTDs remains largely unknown. Here GATA6 gene was screened in 542 patients with CTDs using targeted sequencing. Variant frequency was 2.0% (11/542). Three novel variants: c.86C>A (p.A29E), c.296T>A (p.V99D) and c.1254delC (p.S418fs) were identified in patients with transposition of the great arteries, double outlet right ventricle and persistent truncus arteriosus, respectively, but in none of the 400 controls. Western blot revealed that A29E and V99D mutant protein had similar expression pattern with wild-type GATA6 protein, but S418fs mutant protein appeared as a truncated doublet. Reporter gene assay demonstrated that A29E and V99D mutant protein retained the ability to activate BNP and ANF promoter, whereas S418fs mutant protein failed to transactivate both of them, compared with wild-type. Subcellular localization of wild-type, A29E and V99D mutant protein were in the nucleus, while S418fs mutant protein was expressed both in the nucleus and cytoplasm. In conclusion, GATA6 variant frequency in sporadic CTDs patients was higher than that in other congenital heart diseases. Variant c.1254delC was a pathogenic variant associated with CTDs, especially PTA, whereas c.86C>A and c.296T>A should be considered as likely pathogenic variants.

Maturing human pluripotent stem cell-derived cardiomyocytes in human engineered cardiac tissues

Engineering functional human cardiac tissue that mimics the native adult morphological and functional phenotype has been a long held objective. In the last 5 years, the field of cardiac tissue engineering has transitioned from cardiac tissues derived from various animal species to the production of the first generation of human engineered cardiac tissues (hECTs), due to recent advances in human stem cell biology. Despite this progress, the hECTs generated to date remain immature relative to the native adult myocardium. In this review, we focus on the maturation challenge in the context of hECTs, the present state of the art, and future perspectives in terms of regenerative medicine, drug discovery, preclinical safety testing and pathophysiological studies.

Importance of Endogenous Atrial and Brain Natriuretic Peptides in Murine Embryonic Vascular and Organ Development

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) bind to the receptor guanylyl cyclase (GC)-A, leading to diuresis, natriuresis, and blood vessel dilation. In addition, ANP and BNP have various angiogenic properties in ischemic tissue. When breeding mice devoid of GC-A, we noted significant skewing of the Mendelian ratio in the offspring, suggesting embryonic lethality due to knockout of GC-A. Consequently, we here investigated the roles of endogenous ANP and BNP in embryonic neovascularization and organ morphogenesis. Embryos resulting from GC-A(-/-) × GC-A(+/-) crosses developed hydrops fetalis (HF) beginning at embryonic day (E)14.5. All embryos with HF had the genotype GC-A(-/-). At E17.5, 33.3% (12 of 36) of GC-A(-/-) embryos had HF, and all GC-A(-/-) embryos with HF were dead. Beginning at E16.0, HF-GC-A(-/-) embryos demonstrated poorly developed superficial vascular vessels and sc hemorrhage, the fetal side of the placenta appeared ischemic, and vitelline vessels on the yolk sac were poorly developed. Furthermore, HF-GC-A(-/-) embryos also showed abnormal constriction of umbilical cord vascular vessels, few cardiac trabeculae and a thin compact zone, hepatic hemorrhage, and poor bone development. Electron microscopy of E16.5 HF-GC-A(-/-) embryos revealed severe vacuolar degeneration in endothelial cells, and the expected 3-layer structure of the smooth muscle wall of the umbilical artery was indistinct. These data demonstrate the importance of the endogenous ANP/BNP-GC-A system not only in the neovascularization of ischemic tissues but also in embryonic vascular development and organ morphogenesis.

Acclimatization to chronic hypobaric hypoxia is associated with a differential transcriptional profile between the right and left ventricle

Acute hypobaric hypoxia induces a transient reactivation of the fetal-metabolic gene program in the rat heart. Although chronic hypobaric hypoxia causes alterations in metabolism and cardiac function, little is known about the transcriptional profile associated with acclimatization to chronic hypoxia. Because in chronic hypoxia only the right ventricle is exposed to pressure overload (pulmonary hypertension), we hypothesized that chronic hypobaric hypoxia induces a differential transcriptional profile in the right and left ventricle. Male Wistar rats were exposed to a hypobaric environment (11% O2) for 4, 10, and 12 weeks. Right and left ventricular tissue was isolated for histology and candidate gene expression. Chronic hypobaric hypoxia induced right ventricular hypertrophy without fibrosis. In the right ventricle, changes in metabolic gene expression suggested a downregulation of fatty acid metabolism and an increase in glucose metabolism, while left ventricular metabolic gene expression suggested restoration of fatty acid metabolism. While myosin heavy chain isoform transcript levels in the right ventricle indicated a progressive reactivation of the fetal iso-gene pattern, there was normalization of myosin iso-gene expression in the left ventricle. Similarly, sarcoendoplasmic reticulum ATPase 2a (SERCA2a) transcript levels in the right ventricle decreased by 12 weeks of chronic hypoxia exposure, whereas, left ventricular SERCA2a expression was unchanged. In conclusion, acclimatization to chronic hypobaric hypoxia induced a differential transcriptional response between the right and left ventricle. We speculate that reactivation of the fetal-metabolic program in the right ventricle is adaptive to pressure overload.

Minireview: natriuretic peptides during development of the fetal heart and circulation

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones, secreted by the atria and ventricles, respectively, in the normal adult heart. They participate in the regulation of blood pressure and body fluid homeostasis and modify growth and development of cardiovascular tissues and bone. Levels of ANP are higher in the fetal circulation than in adults, and fetal ventricles express higher levels of ANP and BNP than adult ventricles. The reappearance of ventricular ANP expression in adults is recognized as a marker of the induction of the embryonic gene program in ventricular hypertrophy. The natriuretic peptide system appears to be functional by midgestation, to respond to volume stimuli, and to regulate blood pressure and salt and water balance in the developing embryo. In addition, the natriuretic peptides may help regulate the blood supply to the fetus, acting as vasodilators in the placental vasculature. Peaks of ANP and BNP expression during gestation coincide with significant events in cardiac organogenesis, suggesting a role for ANP/BNP in the formation of the heart. In knockout mice lacking the natriuretic peptide receptor (NPR)-A gene (Npr1(-/-)), survival is reduced, with hearts enlarged at birth and possible cardiac developmental abnormalities. Surviving adult Npr1(-/-) mice have elevated blood pressure and marked cardiac hypertrophy and fibrosis, indicating that the ANP/BNP system is an important regulator of myocyte growth during development.

Regulation of amniotic fluid volume by intramembranous absorption in sheep: role of passive permeability and vascular endothelial growth factor

OBJECTIVE

During long-term intravascular fluid infusion in the ovine fetus, a large increase in fetal urinary flow rate occurs while amniotic fluid volume increases only slightly because of increased intramembranous absorption. The current study tested the hypotheses that passive intramembranous permeability increases in response to fetal intravascular saline solution infusion and that the increased intramembranous absorption occurs in parallel with an increase in vascular endothelial growth factor gene expression in the amnion, chorion, and placenta.

STUDY DESIGN

Chronically catheterized fetal sheep that average 126 +/- 1 (SE) days of gestation either were infused intravascularly with 7 L of normal saline solution over 3 days (n = 8 sheep) or served as time controls (n = 6 sheep). Amniotic fluid volume and fetal urinary flow rate were measured daily. Intramembranous diffusional permeability was estimated daily as being equal to the clearance of intra-amniotically injected technetium 99m. Vascular endothelial growth factor messenger RNA abundance in the amnion, chorion, and placenta was determined by Northern blot analysis. Statistical analyses included analysis of variance.

RESULTS

In the infused fetuses, amniotic fluid volume and urinary flow increased (P <.01) by 891 +/- 144 mL and 3488 +/- 487 mL per day, respectively, on infusion day 3 compared with no changes over time in the control fetuses. In the infused fetuses, estimated intramembranous absorption increased by 4276 +/- 499 mL during the 3-day infusion. Intramembranous technetium 99m permeability was similar over time in the two groups. In the infused group, vascular endothelial growth factor messenger RNA levels in the amnion, chorion, and placenta increased 2- to 4-fold compared with the control group (P <.001).

CONCLUSION

The up-regulation of vascular endothelial growth gene expression may mediate the increase in the intramembranous absorption that is induced by volume-loading diuresis; however, this does not occur by passive mechanisms. We speculate that vascular endothelial growth mediates the increased intramembranous absorption by increasing vesicular transport.

Preterm premature rupture of membranes: vascular endothelial growth factor and its association with histologic chorioamnionitis

OBJECTIVE

We hypothesize that vascular endothelial growth factor, a known angiogenic and permeability factor that is locally expressed in fetal membranes and decidua, may be the primary regulator in the pathway that eventually leads to preterm premature rupture of membranes. Our objective was to test the hypothesis that, both in the presence and in the absence of histologic chorioamnionitis, there is an increased expression of the vascular endothelial growth factor gene and its receptor Flt-1 in the human fetal membranes.

STUDY DESIGN

Membranes were sampled from a region that was distinct as the rupture site from three groups of patients with preterm premature rupture of membranes. Groups 1 and 2 differed only in the length of the latency period from rupture of the membranes to delivery. Group 3 included preterm patients with intact membranes, who acted as control subjects. All patients who were selected for the study lacked clinical signs of chorioamnionitis and were delivered by cesarean delivery. Tissue samples were analyzed for interleukin-6 gene expression by Northern blot analysis and for the presence of interleukin-6 protein by immunocytochemistry. The expression of vascular endothelial growth factor and Flt-1 genes was analyzed by in situ hybridization.

RESULTS

All tissue samples from group 1 and five tissue samples from group 2 (designated as group 2A) showed expression of the interleukin-6 gene and the presence of interleukin-6 protein in the fetal membranes (P <.001) and were therefore identified as inflamed. Five tissue samples from the patients in group 2 (designated as group 2B) and all control tissue samples showed neither evidence of interleukin-6 gene expression nor the presence of its protein and therefore were identified as not inflamed. Vascular endothelial growth factor and Flt-1 gene expression were increased significantly in the fetal membrane and decidua samples that were obtained from the noninflamed tissues from group 2B (P <.005) yet showed further enhancement in expression in the inflamed tissues.

CONCLUSION

The expression patterns of vascular endothelial growth factor and Flt-1 genes are indicative of a molecular pathologic condition of fetal membranes, regardless of their inflammatory status, which suggests their role as a primary regulator of preterm premature rupture of membranes.

Natriuretic peptide system in fetal heart and circulation

Atrial natriuretic peptide, brain natriuretic peptide and C-type natriuretic peptide belong to a family of hormones that have diuretic, natriuretic and vasodepressor activity and play a part in pressure and volume homeostasis in adults. As little is known about the natriuretic peptides during cardiac maturation, this review summarizes current knowledge about the early expression of components of the natriuretic peptide system in the heart during embryonic and fetal development. The data indicate a functional importance of the fetal natriuretic peptide system, especially under pathophysiological conditions. Thus, in the fetus, the system fulfils important beneficial compensatory roles in cardiovascular disease, rather than in day-to-day pressure and volume homeostasis. In comparison with data on the relevance of natriuretic peptides in adults, those summarized here indicate a functional maturation of the natriuretic peptide system during ontogeny in mammals.

Fetal esophageal ligation induces expression of vascular endothelial growth factor messenger ribonucleic acid in fetal membranes

OBJECTIVE

Obstruction of the fetal esophagus does not always produce the expected polyhydramnios. This is because of increased intramembranous absorption of amniotic fluid into the fetal circulation. A possible mediator for this increased absorption is vascular endothelial growth factor (VEGF). The present objective was to explore whether VEGF gene expression and action would be induced in fetal membranes and placentas of ovine fetuses after esophageal ligation.

STUDY DESIGN

Five late-gestation fetal sheep underwent esophageal ligation and 5 served as control animals. On postoperative day 9, amnion, chorion, and placenta were collected for cellular localization and quantitation of VEGF messenger ribonucleic acid by in situ hybridization and Northern blot analysis. Reverse-transcription polymerase chain reaction was used to identify the VEGF molecular forms. Immunostaining with Ki-67 antibody was used to determine the proliferation of vascular endothelium in the fetal membranes and placentas.

RESULTS

VEGF messenger ribonucleic acid was localized in amniotic epithelium, chorionic cytotrophoblast, and cytotrophoblast of the placenta. VEGF164 was the major transcript expressed in these tissues. The abundance of VEGF messenger ribonucleic acid in the amnion and chorion, but not in the placenta, was significantly increased in the ligated fetuses in comparison with the control fetuses. The proliferation of the intramembranous blood vessel endothelium was greater in the ligated fetuses than in the control fetuses.

CONCLUSION

The levels of VEGF messenger ribonucleic acid and the proliferation of vascular endothelium in the amnion and chorion increased after fetal esophageal ligation. This provides a possible mechanism for the enhanced intramembranous absorption of amniotic fluid through increased vascularity and permeability of the fetal membranes, thus ameliorating the development of polyhydramnios. We speculate that the signal(s) that mediate the increase in VEGF expression is present in either the fetal urine or the fetal lung secretions, or both.

Effect of three hours of hypoxia on atrial natriuretic factor gene expression in the ovine fetal heart

OBJECTIVES

The current study investigated the effects of 3 hours of hypoxia on atrial natriuretic factor gene expression and peptide content in each of the four cardiac chambers of the near-term ovine fetus.

STUDY DESIGN

Twenty-three chronically catheterized ovine fetuses at 125 to 129 days' gestation (term 145 days) were used for this study. Fetal hypoxia was induced for 3 hours in 12 fetuses by infusion of nitrogen into the maternal trachea. The remaining fetuses were used as controls. Fetal arterial PO2 and plasma atrial natriuretic factor concentrations were measured during hypoxia. At the end of the hypoxic period atrial natriuretic factor peptide contents and messenger ribonucleic acid levels in each cardiac chamber were determined by radioimmunoassay and Northern blot analysis, respectively.

RESULTS

With infusion of nitrogen into the maternal trachea, fetal arterial PO2 was reduced within 30 minutes by an average of 8.0 +/- 0.3 (SEM) mm Hg (p < 0.0001) and remained reduced at this level throughout the entire hypoxic period. Plasma atrial natriuretic factor concentrations increased by 1152 +/- 212 pg/ml (p < 0.003) and the increase was sustained for the duration of hypoxia. Atrial natriuretic factor peptide and messenger ribonucleic acid levels were much higher in the atria than in the ventricles. Hypoxia did not result in alterations of atrial natriuretic factor peptide content or messenger ribonucleic acid abundance in each cardiac chamber.

CONCLUSIONS

In the near-term ovine fetus, 3 hours of hypoxia resulted in greatly elevated plasma atrial natriuretic factor concentrations; this response was sustained for the duration of hypoxia. However, the increase was not associated with a detectable change in atrial natriuretic factor peptide content or an induction of atrial natriuretic factor gene expression in the atria and ventricles.

Regulation of atrial natriuretic factor secretion and expression in the ovine fetus

The cardiac hormone atrial natriuretic factor (ANF) is present in the fetal circulation at high concentrations and exceeds that in the maternal circulation. Administration of exogenous ANF into the near-term ovine fetus lowers arterial pressure and reduces blood volume. The fetal kidney responds to ANF with a diuresis and natriuresis. The physiological stimuli which modulate ANF secretion in the fetus include vascular volume expansion, hyperosmolality and hypoxia, with hypoxia being the most potent stimulus. In addition, endothelin administration into the fetus increases plasma ANF concentrations. The fetal atria appears to be the primary site of ANF synthesis, although the ventricles also produce ANF. The expression of ANF peptide and its messenger RNA in the fetal atria and ventricles demonstrate a developmental pattern. Thus, the secretion of ANF may be mediated by factors such as endothelin and may be augmented by stimuli such as hypoxia which acts through induction of cardiac ANF gene expression.