tretinoin and Endocardial-Cushion-Defects

The progress of molecular genetics has enabled us to identify the genes responsible for congenital heart malformations. However, recent studies suggest that congenital heart diseases are induced not only by mutations in certain genes, but also by abnormal maternal factors. A high concentration of maternal retinoic acid (RA), the active derivative of vitamin A, is well known as a teratogenic agent that can cause developmental defects. Our previous studies have shown that the maternal administration of RA to mice within a narrow developmental window induces outflow tract (OFT) septum defects, a condition that closely resembles human transposition of the great arteries (TGA), although the responsible factors and pathogenic mechanisms of the TGA induced by RA remain unknown. We herein demonstrate that the expression of Tbx2 in the OFT myocardium is responsive to RA, and its downregulation is associated with abnormal OFT development. We found that RA could directly downregulate the Tbx2 expression through a functional retinoic acid response element (RARE) in the Tbx2 promoter region, which is also required for the initiation of Tbx2 transcription during OFT development. Tgfb2 expression was also downregulated in the RA-treated OFT region and was upregulated by Tbx2 in a culture system. Moreover, defective epithelial-mesenchymal transition caused by the excess RA was rescued by the addition of Tgfβ2 in an organ culture system. These data suggest that RA signaling participates in the Tbx2 transcriptional mechanism during OFT development and that the Tbx2-Tgfβ2 cascade is one of the key pathways involved in inducing the TGA phenotype.

Topics: Animals; Chromatin Immunoprecipitation; DNA Primers; Endocardial Cushion Defects; Female; Galactosides; Gene Expression Regulation, Developmental; Immunohistochemistry; In Situ Hybridization; Indoles; Luciferases; Maternal-Fetal Exchange; Mice; Microarray Analysis; Myocardium; Pregnancy; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; T-Box Domain Proteins; Transforming Growth Factor beta2; Tretinoin

Retinoic acid has been associated with a number of cardiac defects, some of which seem to be related to changes in the endocardial cushions. Studies in mice and older chick embryos have suggested that these defects may be associated with a decrease in mesenchymal cell formation within the cushion. In a previous report we showed that retinoic acid lowered the number of mesenchymal cells in a culture bioassay of mesenchyme formation and that this response was due to retinoic acid modifying the production of particulate matrix from the myocardium. In this study, we have extended these observations to the embryo by implanting a retinoic acid coated bead into the embryo and examined the effect on cardiac mesenchyme formation and in the production of the particulate matrix. In all cases the addition of retinoic acid resulted in a decrease in the number of mesenchymal cells invading the endocardial cushions. In addition retinoic acid increased the production of hLAMP-1 and fibronectin but not transferrin, confirming our earlier report. Finally, we measured the volume of the cushion and calculated the cell density of both the inferior and superior cushions. The results suggest that the superior cushion is more sensitive to retinoic acid treatment than the inferior cushion. Collectively, these results support our earlier work that suggests that the mechanism of retinoic acid cardiac abnormalities involves a disruption in the production of particulate matrix from the myocardium and a subsequent decrease in cardiac mesenchyme cells that results in a malformed cardiac cushions.

Topics: Abnormalities, Drug-Induced; Animals; Cell Count; Chick Embryo; Endocardial Cushion Defects; Endocardium; Enzyme-Linked Immunosorbent Assay; Extracellular Matrix; Extracellular Matrix Proteins; Fibronectins; Heart; Mesoderm; Microscopy, Fluorescence; Microscopy, Video; Transferrin; Tretinoin

Visceroatrial heterotaxy syndrome is characterized by abnormality of visceral laterality and complex cardiovascular anomalies usually involving both the outflow and inflow tract. Morishima et al. (1995) showed that mouse embryos treated with all-trans retinoic acid at embryonic day 6.5 (primitive streak stage) induces this syndrome.. To investigate the morphogenetic process of visceroatrial heterotaxy syndrome, we examined retinoic acid-treated mouse embryos at embryonic days 9-15 using scanning electron microscopy.. The sinoatrial connection was first distinguished for the determination of situs as early as at embryonic day 10.5. Normal visceroatrial situs was found in 57% of all treated embryos, and the rest had abnormal situs, in which right isomerism was found in 81%. In the right-isomeric mouse, the cardiac morphology was characterized by abnormal looping together with dysplasia of the inflow and outflow tract cushion; that is, the primitive right ventricle was usually deviated cranially to various degrees, the atrioventricular cushion appeared trilobed in a half of them, and unilateral ventricular hypoplasia was noted in about one-third of them after embryonic day 14.5.. An anomalous relation between the atrioventricular cushions and the interventricular septum appeared to have caused a restrictive inflow to the unilateral ventricle, leading to ventricular chamber hypoplasia on the ipsilateral side. Thus, we clarified that retinoic-acid treatment at the primitive streak stage disturbed cardiac looping and formation of atrioventricular cushion development, which secondarily influenced ventricular chamber development.

Topics: Abnormalities, Drug-Induced; Animals; Endocardial Cushion Defects; Female; Fetal Heart; Gastrula; Heart Atria; Heart Defects, Congenital; Heart Septal Defects, Ventricular; Heart Ventricles; Male; Mice; Microscopy, Electron, Scanning; Morphogenesis; Tretinoin

In a previous study retinoic acid treatment of chicken hearts has resulted in a spectrum of looping disturbances. Because of a decrease in contraction force of these hearts, the myocardial volume was hypothesized to be altered. Because retinoic acid has been suggested to influence endocardial cushion volumes, these were estimated as well.. The previously studied hearts were used for estimating the absolute volumes of the atrial and ventricular myocardium and of the endocardial cushions by means of Cavalieri's principle. To measure the surface density of the trabeculations according to the isector method, we used retinoic acid treated hearts, which were perfusion fixed and in which the sections were isotropic uniform random. The volumes and surface densities found in the three morphologically distinguished groups, i.e., intact septum, isolated ventricular septal defect and double outlet right ventricle, were compared with those in shams.. A significant volume decrease was found in the right ventricular free wall myocardium of the double outlet right ventricle. No significant differences were found in the surface densities of the trabeculae. The volume of the atrioventricular cushion tissue in the double outlet right ventricle hearts was significantly increased. The morphological spectrum observed previously was also expressed in the right ventricular myocardial volume, which appeared to decrease from the least to the most malformed hearts, and in the volume of the atrioventricular cushion tissue, which appeared to increase.. Several studies have shown pathology in myocardial and cushion tissue after retinoic acid treatment. In this study we have found a decreased growth of the right ventricular myocardium and an increased growth of the atrioventricular cushion tissue. We suggest that the previously found looping disturbance causes changed hemodynamics, as reported elsewhere, and that these result in changes in growth. We cannot exclude a direct effect of retinoic acid on the myocardium, which has to explain the looping disturbance.

Topics: Animals; Cardiac Volume; Chick Embryo; Endocardial Cushion Defects; Heart; Heart Ventricles; Tretinoin

It has been reported that all-trans retinoic acid induces transposition of the great arteries (TGA) at 80-90% in ICR mice. The authors revealed that retinoic acid affects the initial formation of the conus cushions leading to a loss of spirality in the cardiac outflow tract. However, the aberrant process of septation has not been precisely defined. In this study, we observed the hearts of live embryos using a video system followed by scanning electron microscopic examination. First, we found that, in the retinoic acid-treated embryos, the proximal outflow tract cushions, in addition to hypoplasia and dysplasia, did not establish the continuity with the distal outflow tract cushions and could not contribute to the outflow septation. Second, the distal outflow tract did not rotate counter-clockwise, retaining the outflow septum anlage in the superoinferior position. Third, a tongue-like mesenchymal tissue had developed on the right anterior rim of the muscular interventricular septum and was incorporated into the interventricular septum. Altogether, these processes contributed to establishing a reversed relationship between the outflow septum anlage and the ventricular septum anlage. On the other hand, right-ward deviation of one or both of the distal outflow tract cushions, relative to the mesenchymal tissue, gave rise to variable degrees of overriding of the pulmonary artery orifice. We conclude that, due to hypoplasia and dysplasia of the proximal outflow tract cushions and lack of distal outflow tract rotation, the outflow septum anlage took an inverted relationship with the ventricular septum anlage. Various types of rightward shift of the outflow tract cushions produced a morphological spectrum of TGA-type cono-truncal anomalies.

Topics: Animals; Cardiac Output; Coronary Circulation; Embryonic and Fetal Development; Endocardial Cushion Defects; Female; Heart; Heart Septum; Male; Mice; Mice, Inbred ICR; Microscopy, Electron, Scanning; Morphogenesis; Myocardium; Pregnancy; Transposition of Great Vessels; Tretinoin; Ventricular Function, Left; Videotape Recording

The major morphologic change associated with retinoic acid (RA)-induced complete transposition of the great arteries (TGA), a congenital malformation of the heart, was investigated in a mouse model in which TGA was found in 80% of surviving fetuses.. Corrosion casts of embryonic hearts with or without prior exposure to retinoic acid were observed under a scanning electron microscope.. In control hearts, indentations caused by expanded parietal and septal ridges in the outflow tract established right ventricle-to-left ventral pulmonic and left ventricle-to-right dorsal aortic routes before the aorticopulmonary septum completion. In RA-treated hearts, indentations of proximal regions of the parietal and septal ridges were small in the proximal outflow tract, whereas those in the distal regions developed well. These morphological features in the RA-treated hearts elicited right ventricle-to-right ventral aortic and left ventricle-to-left dorsal pulmonic routes in the TGA morphology.. Hypoplasticity of the proximal regions of parietal and septal ridges in the outflow tract is one of the primary morphological abnormalities of the RA-induced TGA.

Topics: Animals; Aorta; Corrosion Casting; Endocardial Cushion Defects; Endocardium; Female; Heart; Mice; Mice, Inbred ICR; Microscopy, Electron, Scanning; Pregnancy; Transposition of Great Vessels; Tretinoin