Hyperplastic conotruncal endocardial cushions and transposition of great arteries in perlecan-null mice.

Perlecan is a heparan-sulfate proteoglycan abundantly expressed in pericellular matrices and basement membranes during development. Inactivation of the perlecan gene in mice is lethal at two developmental stages: around E10 and around birth. We report a high incidence of malformations of the cardiac outflow tract in perlecan-deficient embryos. Complete transposition of great arteries was diagnosed in 11 out of 15 late embryos studied (73%). Three of these 11 embryos also showed malformations of semilunar valves. Mesenchymal cells in the outflow tract were abnormally abundant in mutant embryos by E9.5, when the endocardial-mesenchymal transformation starts in wild-type embryos. At E10.5, mutant embryos lacked well-defined spiral endocardial ridges, and the excess of mesenchymal cells obstructed sometimes the outflow tract lumen. Most of this anomalous mesenchyme expressed the smooth muscle cell-specific alpha-actin isoform, a marker of the neural crest in the outflow tract of the mouse. In wild-type embryos, perlecan is present in the basal surface of myocardium and endocardium, as well as surrounding presumptive neural crest cells. We suggest that the excess of mesenchyme at the earlier stages of conotruncal development precludes the formation of the spiral ridges and the rotation of the septation complex in order to achieve a concordant ventriculoarterial connection. The observed mesenchymal overpopulation might be due to an uncontrolled migration of neural crest cells, which would arrive prematurely to the heart. Thus, perlecan is involved in the control of the outflow tract mesenchymal population size, underscoring the importance of the extracellular matrix in cardiac morphogenesis.

Antiangiogenic activity of aeroplysinin-1, a brominated compound isolated from a marine sponge.

(+)-aeroplysinin-1, an antibacterial brominated compound produced by certain sponges, was selected during a blind high-throughput screening for new potential antiangiogenic compounds obtained from marine organisms. In a variety of experimental systems, representing the sequential events of the angiogenic process, aeroplysinin-1 treatment of endothelial cells resulted in strong inhibitory effects. Aeroplysinin-1 inhibited the growth of endothelial cells in culture and induced endothelial cell apoptosis. Capillary tube formation on Matrigel was completely abrogated by addition of aeroplysinin-1 at the low micromolar range. Aeroplysinin-1 also exhibited a clear inhibitory effect on the migration capabilities of endothelial cells. Zymographic assays showed that aeroplysinin-1 treatment produced a decrease in the concentration of matrix metalloproteinase-2 and urokinase in conditioned medium from endothelial cells. Finally, aeroplysinin-1 exhibited a dose-dependent inhibitory effect on the in vivo chorioallantoic membrane assay, showing potent apoptosis-inducing activity in the developing endothelium. The in vivo inhibition of angiogenesis by aeroplysinin-1 was confirmed by the Matrigel plug assay. Together, our data indicate that aeroplysinin-1 is a compound that interferes with key events in angiogenesis, making it a promising drug for further evaluation in the treatment of angiogenesis-related pathologies.

Origin of coronary endothelial cells from epicardial mesothelium in avian embryos.

It has been established that coronary vessels develop through self-assembly of mesenchymal vascular progenitors in the subepicardium. Mesenchymal precursors of vascular smooth muscle cells and fibroblasts are known to originate from an epithelial-to-mesenchymal transformation of the epicardial mesothelium, but the origin of the coronary endothelium is still obscure. We herein report that at least part of the population of the precursors of the coronary endothelium are epicardially-derived cells (EPDCs). We have performed an EPDC lineage study through retroviral and fluorescent labelling of the proepicardial and epicardial mesothelium of avian embryos. In all the experiments onlythe surface mesothelium was labelled after 3 h of reincubation. However, endothelial cells from subepicardial vessels were labelled after 24-48 h and endothelial cells of intramyocardial vessels were also labelled after 48-96 h of reincubation. In addition, the development of the coronary vessels was studied in quail-chick chimeras, obtaining results which also support a mesothelial origin for endothelial and smooth muscle cells. Finally, quail proepicardial explants cultured on Matrigel showed colocalization of cytokeratin and QH1 (mesothelial and endothelial markers, respectively) after 24 h. These results, taken together, suggest that EPDC show similar competence to that displayed by bipotential vascular progenitor cells [Yamashita et al., Nature 408: 92-96 (2000)] which are able to differentiate into endothelium or smooth muscle depending on their exposure to VEGF or PDGF-BB. It is conceivable that the earliest EPDC differentiate into endothelial cells in response to myocardially-secreted VEGF, while further EPDC would be recruited by the nascent capillaries via PDGFR-beta signalling, giving rise to mural cells.

Cellular precursors of the coronary arteries.

Coronary vessels develop from a primary vascular network that differentiates in the subepicardium through a process of vasculogenesis, that is, self-assembly of mesenchymal vascular progenitors. Further growth of the subepicardial vascular plexus through a complex process of angiogenesis, vascular remodeling, and arterialization of specific branches gives rise to the definitive coronary system. This report is intended to summarize current knowledge on the origin of the coronary vascular progenitors and to provide new insights suggested by recent findings. It has been established that the mesenchymal precursors of the vascular smooth muscle cells and the adventitial fibroblasts originate from an epithelial-mesenchymal transformation of the epicardial mesothelium. We report herein experimental evidence that the precursors of the coronary endothelium are also epicardium-derived cells (EPDCs). The evidence shown includes co-localization of mesothelial and endothelial molecular markers as well as cell lineage studies performed through direct labeling of the epicardial cells. If this proposal is confirmed, the early EPDCs might be found to have a competence similar to that shown by the recently discovered bipotential vascular progenitor cells, which are able to differentiate into endothelium or smooth muscle depending on their exposure to VEGF or PDGF-BB. It is conceivable that the earliest EPDCs differentiate into endothelial cells in response to myocardially secreted VEGF, while subsequent EPDCs, recruited by the nascent capillaries via PDGFRbeta signaling, differentiate into percytes and smooth muscle cells.

[The epicardium and epicardial-derived cells: multiple functions in cardiac development]. / El epicario y las células derivadas del epicardio: múltiples funciones en el desarrollo cardíaco.

The epicardium develops from an extracardiac primordium, the proepicardium, which is constituted by a cluster of mesothelial cells located on the cephalic and ventral surface of the liver-sinus venosus limit (avian embryos) or on the pericardial side of the septum transversum (mammalian embryos). The proepicardium contacts the myocardial surface and gives rise to a mesothelium, which grows and progressively lines the myocardium. The epicardium generates, through a process of epithelial-mesenchymal transition, a population of epicardial-derived cells (EPDC). EPDC contribute to the development of cardiac connective tissue, fibroblasts, and the smooth muscle of cardiac vessels. Recent data suggest that EPDC can also differentiate into endothelial cells of the primary subepicardial vascular plexus. If this is confirmed, EPDC would show the same developmental properties that characterize the stem-cell-derived bipotential vascular progenitors recently described, whose differentiation into endothelium and smooth muscle is regulated by exposure to VEGF and PDGF-BB, respectively. Aside from their function in the development of cardiac connective and vascular tissue, EPDC also play an essential modulating role in the differentiation of the compact ventricular layer of the myocardium, a role which might be regulated by the transcription factor WT1 and the production of retinoic acid.

A modified chorioallantoic membrane assay allows for specific detection of endothelial apoptosis induced by antiangiogenic substances.

Current in vivo angiogenesis assays allow for the assessment of vascular growth inhibition induced by a test substance, but they usually do not provide information about the mechanisms underlying such an inhibition. A potential antiangiogenic mechanism is the triggering of endothelial apoptosis in the growing vessels. Apoptogenic substances can be of interest for antiangiogenic therapy specially if they specifically perform their action on the angiogenic endothelium. We have developed a modification of the chorioallantoic membrane (CAM) assay using embryos of quail ( Coturnix coturnix japonica ). This novel assay allows to elucidate whether an antiangiogenic substance is specifically triggering an apoptotic response in endothelial cells. We have used a quail-specific monoclonal endothelial marker (QH1), a standard TUNEL technique of apoptotic cell labelling together with a general nuclear counterstaining with propidium iodide. Through laser confocal microscopy, paraffin sections of chorioallantoic membranes treated with test substances are stained in three colours: red for normal cell nuclei, yellow-green for apoptotic nuclei and blue for endothelial cells and endothelial progenitors. In a test experience, our assay showed significant differences in the apoptogenic properties of two antiangiogenic substances, camptothecin and aeroplysinin-1.

Study of puupehenone and related compounds as inhibitors of angiogenesis.

Puupehenone, a sesquiterpene produced by certain sponges, was selected in the course of a blind screening for new potential inhibitors of angiogenesis. In our study, we compare the potential anti-angiogenic activities of puupehenone and another 11 related compounds that were either natural products from marine origin or their synthetic derivatives. The effects of these compounds were determined with cell growth and differentiation assays on bovine aorta endothelial cells. Our results show that these compounds are weak inhibitors to cell growth and are not selective for endothelial cells. However, contrary to cell growth, the differentiation of endothelial cells into tubular structures was completely inhibited by 7 of these compounds at concentrations equal or lower than 3 microM. Three of these compounds, isozonarol, 8-epipuupehedione and 8 epi-9,11-dihydropuupehedione, completely inhibited the in vivo angiogenesis in the CAM assay at doses equal or lower than 30 nmol/egg. Further characterisation showed that these 3 terpenes also inhibited endothelial cell production of urokinase and invasion. One compound (8-epipuupehedione) inhibited endothelial cell migration in a dose-dependent manner. The anti-angiogenic properties of the selected compounds, the simplicity of their structures and the feasibility of their synthesis make them attractive drugs for further evaluation in the treatment of angiogenesis-related pathologies.

El epicardio y las células derivadas del epicardio: múltiples funciones en el desarrollo cardíaco / The epicardium and epicardial-derived ells: multiple functions in cardiac development

Durante el desarrollo cardíaco, el epicardio deriva de un primordio externo al corazón, denominado proepicardio, que está formado por un acúmulo de células mesoteliales situado en la superficie ventral y cefálica del límite hígado-seno venoso (aves) o en la cara pericárdica del septo transverso (mamíferos). El proepicardio entra en contacto con la superficie miocárdica y da lugar a un mesotelio que crece y recubre progresivamente al miocardio. El epicardio genera, por un proceso localizado de transición epitelio-mesénquima, una población de células mesenquimáticas, las células derivadas de epicardio (CDEP). Las CDEP contribuyen al desarrollo del tejido conectivo del corazón y también dan lugar a los fibroblastos y las células musculares lisas de los vasos coronarios. Existen evidencias que sugieren la diferenciación de las CDEP en células endoteliales del plexo subepicárdico primitivo. De confirmarse esto, las CDEP mostrarían propiedades similares a los precursores vasculares bipotenciales derivados de células madre recientemente descritos, cuya diferenciación en endotelio y músculo liso se regula por exposición a VEGF y PDGF-BB, respectivamente. Además de las funciones señaladas en la formación de los tejidos vascular y conectivo del corazón, las CDEP podrían desempeñar un papel modulador esencial para la formación de la capa compacta ventricular del miocardio, un papel que podría estar regulado por el factor de transcripción WT1 y la producción de ácido retinoico (AU)