Immunolocalization of N-CAM in the heart of the early developing rat embryo

Developmental defects of coronary vasculature in rat embryos administered bis-diamine

BACKGROUND

Conotruncal anomalies are often associated with abnormal coronary arteries. Although bis-diamine is known to induce conotruncal defects, its pathological effects on coronary vascular development have not been demonstrated. This study sought to assess the teratogenic effects of bis-diamine on coronary vascular development and the pathogenesis of this anomalous association.

METHODS AND RESULTS

A single 200 mg dose of bis-diamine was administered to pregnant Wistar rats at 10.5 days of gestation. Fifty-two embryos from 10 mother rats underwent morphological analysis of the coronary arteries. Three embryos each were removed from four mothers on embryonic days (ED) 14.5, 15.5, 16.5, and 17.5 and used for immunohistochemical studies using the anti-vascular cell adhesion molecule (VCAM)-1 antibody. Conotruncal anomalies were detected in 48 of 52 embryos, and an aplastic or hypoplastic left coronary artery was found in all of them. In control embryos at ED 16.5, VCAM-1-positive epicardial cells were transformed into mesenchymal cells in vascular plexus, which appeared to differentiate into the endothelial cells of coronary vasculature. In the heart at ED 17.5, coronary vasculature was well developed and connected with coronary ostia near the aorta. However, poor epicardial-mesenchymal transformation and subsequent differentiation was revealed in bis-diamine-treated embryos at EDs 16.5 and 17.5, causing abnormal development of the coronary vasculature and incomplete connections with coronary ostia of the aorta.

CONCLUSIONS

Anomalous coronary arteries in the bis-diamine-treated embryos are induced by the disruption of epicardial-mesenchymal transformation and subsequent poor development of coronary vasculature. Incomplete hatching of the coronary ostium is associated with abnormal truncal division.

Maternal diabetes induces congenital heart defects in mice by altering the expression of genes involved in cardiovascular development

Background

Congenital heart defects are frequently observed in infants of diabetic mothers, but the molecular basis of the defects remains obscure. Thus, the present study was performed to gain some insights into the molecular pathogenesis of maternal diabetes-induced congenital heart defects in mice.

Methods and results

We analyzed the morphological changes, the expression pattern of some genes, the proliferation index and apoptosis in developing heart of embryos at E13.5 from streptozotocin-induced diabetic mice. Morphological analysis has shown the persistent truncus arteriosus combined with a ventricular septal defect in embryos of diabetic mice. Several other defects including defective endocardial cushion (EC) and aberrant myofibrillogenesis have also been found. Cardiac neural crest defects in experimental embryos were analyzed and validated by the protein expression of NCAM and PGP 9.5. In addition, the protein expression of Bmp4, Msx1 and Pax3 involved in the development of cardiac neural crest was found to be reduced in the defective hearts. The mRNA expression of Bmp4, Msx1 and Pax3 was significantly down-regulated (p < 0.001) in the hearts of experimental embryos. Further, the proliferation index was significantly decreased (p < 0.05), whereas the apoptotic cells were significantly increased (p < 0.001) in the EC and the ventricular myocardium of the experimental embryos.

Conclusion

It is suggested that the down-regulation of genes involved in development of cardiac neural crest could contribute to the pathogenesis of maternal diabetes-induced congenital heart defects.

Increased NCAM expression and vascular development in trisomy 16 mouse embryos: relationship with nuchal translucency

Increased nuchal translucency in the human fetus is associated with chromosomal abnormalities, enlarged jugular lymphatic sacs, cardiac defects and changed flow through the ductus venosus. The developmental background of this nuchal edema in relation to the associated anomalies remains elusive. We studied the morphologic correlation between neurogenesis and vasculogenesis in neck, heart, and ductus venosus region of wild type and trisomy 16 mice embryos (E10- E18), using an antibody against Neural Cell Adhesion Molecule (NCAM). Trisomy 16 mice are a model for the above described human phenotype. From E12 trisomy 16 mice showed an altered arrangement of cranial nerves IX, X and XI, which are positioned between the carotid artery, jugular vein and enlarged lymphatic sac. The vagal nerve was significantly smaller, compared with wild type embryos. NCAM was over expressed in both neuronal and cardiovascular structures in trisomy 16 mice, being particularly prominent in the 4th and 6th pharyngeal arch arteries, and the ductus venosus. In the 4th and 6th pharyngeal arch arteries, NCAM over expression was located to the part of the vessel wall that is closely related to the vagal and recurrent nerve. In case of 4th pharyngeal arch artery abnormalities NCAM expression, on the other hand, was reduced. In conclusion, the interaction between neurogenesis and vasculogenesis is disturbed in the trisomy 16 mouse model, and might be a common denominator in the spectrum of anomalies associated with increased nuchal translucency.

Morphological differences in cardiovascular anomalies induced by bis-diamine between Sprague-Dawley and Wistar rats

It is known that animals show different responses to the same teratogen between different strains. We examined cardiac malformations in Sprague-Dawley (SD) and Wistar rats induced by bis-diamine, which produced conotruncal anomalies and aortic arch malformations in embryos when administered to the dams, to elucidate the morphological differences and pathogenesis in the two strains. Two hundred milligrams of bis-diamine dissolved in 1% gum-tragacanth was administered to pregnant rats on embryonic day (ED) 9.5, 10.5 and 11.5 in each strain. The embryos were removed on ED 20.5. External appearances, cardiovascular morphology and associated anomalies were examined under a dissecting microscope. An immunohistological study with an anti-N-CAM antibody, an excellent marker for neural crest cells, was performed on ED 12.5 embryos. Isolated aortic arch anomalies were common features of malformations induced by bis-diamine in SD rats and intracardiac defects were found in a small number of the embryos. Wistar rats showed more serious cardiovascular anomalies, such as persistent truncus arteriosus and tetralogy of Fallot, especially when dams were treated on ED 10.5 and isolated arch anomalies were significantly less prevalent than in SD rats. Immunohistology demonstrated that there were fewer N-CAM positive cells in the conotruncal region in Wistar rats than in SD rats. Bis-diamine induced more critical cardiovascular malformations in Wistar rats because neural crest cells, which play an important role in conotruncal septation, were more extensively damaged. Different susceptibility to bis-diamine and/or different time of neural crest cell emigration from the hindbrain might explain those morphological differences.

Bone morphogenetic protein-2 can mediate myocardial regulation of atrioventricular cushion mesenchymal cell formation in mice

Transformation of endocardial endothelial cells into invasive mesenchyme is a critical antecedent of cardiac cushion tissue formation. The message for bone morphogenetic protein (BMP)-2 is known to be expressed in myocardial cells in a manner consistent with the segmental pattern of cushion formation [Development 109(1990) 833]. In the present work, we localized BMP-2 protein in atrioventricular (AV) myocardium in mice at embryonic day (ED) 8.5 (12 somite stage) before the onset of AV mesenchymal cell formation at ED 9.5. BMP-2 protein expression was absent from ventricular myocardium throughout the stages examined. After cellularization of the AV cushion at ED 10.5, myocardial BMP-2 protein expression was diminished in AV myocardium, whereas cushion mesenchymal cells started expressing BMP protein. Expression of BMP-2 in cushion mesenchyme persisted during later stages of development, ED 13.5-16, during valuvulogenesis. Intense expression of BMP-2 persisted in the valve tissue in adult mice. Based on the expression pattern, we performed a series of experiments to test the hypothesis that BMP-2 mediates myocardial regulation of cardiac cushion tissue formation in mice. When BMP-2 protein was added to the 16-18 somite stage (ED 9.25) AV endocardial endothelium in culture, cushion mesenchymal cells were formed in the absence of AV myocardium, which invaded into collagen gels and expressed the mesenchymal marker, smooth muscle (SM) alpha-actin; whereas the endothelial marker, PECAM-1, was lost from the invaded cells. In contrast, when noggin, a specific antagonist to BMPs, was applied together with BMP-2 to the culture medium, AV endothelial cells remained as an epithelial monolayer with little expression of SM alpha-actin, and expression of PECAM-1 was retained in the endocardial cells. When noggin was added to AV endothelial cells cocultured with associated myocardium, it blocked endothelial transformation to mesenchyme. AV endothelium treated with BMP-2 expressed elevated levels of TGFbeta-2 in the absence of myocardium, as observed in the endothelium cocultured with myocardium. BMP-2-supported elevation of TGFbeta-2 expression in endocardial cells was abolished by noggin treatment. These data indicated that BMP signaling is required in and BMP-2 is sufficient for myocardial segmental regulation of AV endocardial cushion mesenchymal cell formation in mice.

Overexpression of neural cell adhesion molecule in Chagas' myocarditis

The expression of the neural cell adhesion molecule (NCAM) was studied in normal human myocardium and in Chagas' disease myocarditis. We found that NCAM is expressed in the conduction system as well as the myocardium in the fetal heart, but its expression is restricted to the conduction system and absent in the adult myocardium. Chagas' disease is an American endemic disease caused by the Trypanosoma cruzi parasite, which produces myocarditis and a blockade of the conduction system, resulting in cardiac dysfunction. We studied the expression of NCAM in paraffin-embedded human heart tissues from 34 autopsies of patients with Chagas' myocarditis and from murine and canine experimental acute Chagas' myocarditis, using a polyclonal anti-NCAM antibody and immunohistochemistry. Our results show a dramatic upregulation of NCAM expression in the intercalated discs of cardiomyocytes in acute and chronic Chagas' myocarditis. Surprisingly, the NCAM signal was detected in intracellular nests of amastigote forms of the parasite, within infected cardiomyocytes of human and experimental Chagas' myocarditis. In contrast, cardiac cell-cell adhesion proteins, N-cadherin and beta-catenin, were found in intercalated discs distorted by the infection but absent from the amastigote nests. Proteins reactive to several antibodies against NCAM were detected by Western immunoblotting in cultured T cruzi parasites and in trypomastigote forms of T cruzi extracted from the blood of infected mice. The upregulation of NCAM in Chagas' myocarditis and the expression of NCAM or a NCAM-like protein by T cruzi suggest that NCAM may act as a receptor for tissue targeting and cellular invasion by T cruzi in Chagas' disease.

Teratogenic effects of bis-diamine on early embryonic rat heart: an in vitro study

BACKGROUND

Bis-diamine induces cardiac defects, including conotruncal anomalies in rat embryos when the agent is administered to the mother. To evaluate the teratogenic effects and mechanism of bis-diamine, we performed morphological and immunohistochemical analyses of early rat embryos cultured in medium containing bis-diamine.

METHODS

The embryos were removed from mother rats on gestational day 10.5 and cultured in medium containing 1 mg of bis-diamine for 6 hr. The embryos were then cultured in medium only for another 6, 12, 18, and 42 hr, corresponding to embryonic day (ED) 11.0, 11.25, 11.5, and 12.5, respectively. Some embryos from the same mothers were used as controls and were cultured in medium only for the corresponding periods to the embryos exposed to bis-diamine. Some mother rats were given a single oral dose of 200 mg of bis-diamine on gestational day 10.5. Embryos from these pregnant rats were removed 6 hr after the oral administration of bis-diamine, and were also cultured in medium only for 6, 12, 18, and 42 hr.

RESULTS

No cardiac abnormalities were detected in the controls at any stage of development. Thirty-three of 51 (65%) embryos exposed to bis-diamine and 15 of 20 (75%) embryos removed from bis-diamine-administered mothers showed abnormal cardiac development, including dilated ventricle, elongation of outflow tract, and pericardial defect on ED 11.5. Four of six (67%) embryos exposed to bis-diamine, and five of seven (71%) removed from bis-diamine-administered mothers also presented almost the same cardiac abnormalities on ED 12.5. No cardiac abnormalities were detected in bis-diamine-treated embryos before ED 11.5. In addition, the expression of neural cell adhesion molecule (N-CAM) was examined using immunohistochemical methods. Fewer N-CAM immunoreactive cells were detected in the third and fourth aortic arches in the bis-diamine-treated embryos than in controls on ED 11.5. However, more N-CAM immunoreactive cells were detected in the bis-diamine-treated embryos than in controls on ED 12.5.

CONCLUSIONS

These results suggest that bis-diamine induces cardiac anomalies by delaying the migration of neural crest cells into the heart and by disturbing the proliferation of pericardial precursor during early cardiac development.

Differential expression of PSA-NCAM and HNK-1 epitopes in the developing cardiac conduction system of the chick

Although the critical role of the His-Purkinje system (HPS) in the propagation of cardiac action potentials from the atria to the ventricular myocardium in the mature heart is well appreciated, its functional and anatomical development are not well understood. The embryonic heart begins beating early in development devoid of a mature conduction system, and the HPS cannot be identified by conventional histochemical analysis until the seventh embryonic day of chicken development. Although many biochemical markers have been found that apparently identify HPS precursors, little is known about how these biochemical markers function in the maturation of the cardiac conduction system. Using immunohistological techniques, we demonstrated that the maturation of the HPS may be observed by the expression of two distinct populations of conduction system precursors, identified by the expression of cell surface carbohydrates PSA-NCAM (PSA) and HNK-1, both of which are known to participate in cell-cell and cell-substrate interactions in the development of the nervous system. By stage 25, PSA was detected in ventricular trabeculae and the interventricular septum (IVS) in a pattern that resembles bundle branches and Purkinje fibers. Beginning at stage 28, HNK-1 epitope expression in the IVS was observed in myocardium just superior to the PSA-positive bundles in a pattern that resembles the common His bundle. This junctional region was also positive for atrial myosin heavy chain (alpha MHC), another marker for the HPS. These data suggest that a complex, coordinated process of biochemical and morphological change governs the development of the cardiac conduction system.

Immunolocalization of vinculin in the heart of the early developing rat embryo

BACKGROUND

The interaction of cells and extracellular matrix (ECM) components is important in the morphogenesis of the developing heart and is thought be mediated in part by adhesion plaques associated with vinculin, paxillin, talin, integrin, and other proteins. We investigated the patterns of expression of vinculin in the early embryonic rat heart to evaluate the role of vinculin in cardiac morphogenesis.

METHODS

Vinculin expression was studied immunohistochemically in developing Sprague-Dawley embryonic rat hearts between days 11.5 and 15.5.

RESULTS

Vinculin expression was transient and specific in the aorticopulmonary septum on day 13.5 and in the conal septum on day 14.5, when the respective septations were complete. Less vinculin immunoreactivity was detected in the atrioventricular cushion or ventricular septum, where obvious morphological alteration takes place.

CONCLUSIONS

Sites that were immunoreactive for vinculin in the present study are reportedly associated with the distribution of neural cell adhesion molecules (N-CAM) or of soluble tropoelastin. Thus vinculin appears to play a key role in aorticopulmonary septation, where neural crest cells are transformed into ectomesenchyme. Vinculin appears to be involved in elastogenesis and is contributed by ectomesenchyme derived from the neural crest cells.