Vascular patterning of the quail coronary system during development

Myocardial development in crocodylians

BACKGROUND

Recent reports confirmed the notion that there exists a rudimentary cardiac conduction system (CCS) in the crocodylian heart, and development of its ventricular part is linked to septation. We thus analyzed myocardial development with the emphasis on the CCS components and vascularization in two different crocodylian species.

RESULTS

Using optical mapping and HNK-1 immunostaining, pacemaker activity was localized to the right-sided sinus venosus. The atrioventricular conduction was restricted to dorsal part of the atrioventricular canal. Within the ventricle, the impulse was propagated from base-to-apex initially by the trabeculae, later by the ventricular septum, in which strands of HNK-1 positivity were temporarily observed. Completion of ventricular septation correlated with transition of ventricular epicardial activation pattern to mature apex-to-base direction from two periapical foci. Despite a gradual thickening of the ventricular wall, no morphological differentiation of the Purkinje network was observed. Thin-walled coronary vessels with endothelium positive for QH1 obtained a smooth muscle coat after septation. Intramyocardial vessels were abundant especially in the rapidly thickening left ventricular wall.

CONCLUSIONS

Most of the CCS components present in the homeiotherm hearts can be identified in the developing crocodylian heart, with a notable exception of the Purkinje network distinct from the trabeculae carneae.

Vegfaa instructs cardiac muscle hyperplasia in adult zebrafish

During heart development and regeneration, coronary vascularization is tightly coupled with cardiac growth. Although inhibiting vascularization causes defects in the innate regenerative response of zebrafish to heart injury, angiogenic signals are not known to be sufficient for triggering regeneration events. Here, by using a transgenic reporter strain, we found that regulatory sequences of the angiogenic factor vegfaa are active in epicardial cells of uninjured animals, as well as in epicardial and endocardial tissue adjacent to regenerating muscle upon injury. Additionally, we find that induced cardiac overexpression of vegfaa in zebrafish results in overt hyperplastic thickening of the myocardial wall, accompanied by indicators of angiogenesis, epithelial-to-mesenchymal transition, and cardiomyocyte regeneration programs. Unexpectedly, vegfaa overexpression in the context of cardiac injury enabled ectopic cardiomyogenesis but inhibited regeneration at the site of the injury. Our findings identify Vegfa as one of a select few known factors sufficient to activate adult cardiomyogenesis, while also illustrating how instructive factors for heart regeneration require spatiotemporal control for efficacy.

Anatomy of the coronary artery and cardiac vein in the quail ventricle: patterns are distinct from those in mouse and human hearts

Coronary vessel development has been investigated in avian and mouse embryonic hearts. Quail embryos are a useful tool to examine vascular development, particularly because the QH1 antibody and transgenic quail line, Tg (tie1:H2B-eYFP), are useful to trace endothelial cells. However, there are only a few descriptions of the quail coronary vessels. Using ink injection coronary angiography, we examined the course of coronary vessels in the fetal quail heart. The major coronary arteries were the right and left septal arteries, which, respectively, branched off from the right and left coronary stems. The right septal artery ran posteriorly (dorsally) and penetrated the ventricular free wall to distribute to the posterior surface of the ventricles. The left septal artery ran anteriorly (ventrally) and penetrated the ventricular free wall to distribute to the anterior surface of the ventricles. The right and left circumflex arteries were directed posteriorly along the atrioventricular sulci. The cardiac veins consisted of three major tributaries: the middle, great, and anterior cardiac veins. The middle cardiac vein ascended along the posterior interventricular sulcus and emptied into the right atrium. The great cardiac vein ran along the anterior interventricular sulcus, entered the space between the left atrium and conus arteriosus and emptied into the right atrium behind the aortic bulb. The anterior cardiac vein drained the anterior surface of the right ventricle and connected to the anterior base of the right atrium. The course of coronary vessels in the quail heart was basically the same as that observed in chick but was different from those of mouse and human.

Avian embryonic coronary arterio-venous patterning involves the contribution of different endothelial and endocardial cell populations

BACKGROUND

Coronary vasculature irrigates the myocardium and is crucial to late embryonic and adult heart function. Despite the developmental significance and clinical relevance of these blood vessels, the embryonic origin and the cellular and molecular mechanisms that regulate coronary arterio-venous patterning are not known in detail. In this study, we have used the avian embryo to dissect the ontogenetic origin and morphogenesis of coronary vasculature.

RESULTS

We show that sinus venosus endocardial sprouts and proepicardial angioblasts pioneer coronary vascular formation, invading the developing heart simultaneously. We also report that avian ventricular endocardium has the potential to contribute to coronary vessels, and describe the incorporation of cardiac distal outflow tract endothelial cells to the peritruncal endothelial plexus to participate in coronary vascular formation. Finally, our findings indicate that large sinus venosus-independent sections of the forming coronary vasculature develop without connection to the systemic circulation and that coronary arterio-venous shunts form a few hours before peritruncal arterial endothelium connects to the aortic root.

CONCLUSIONS

Embryonic coronary vasculature is a developmental mosaic, formed by the integration of vascular cells from, at least, four different embryological origins, which assemble in a coordinated manner to complete coronary vascular development. Developmental Dynamics 247:686-698, 2018. © 2017 Wiley Periodicals, Inc.

Coronary stem development in wild-type and Tbx1 null mouse hearts

BACKGROUND

Coronary artery (CA) stems connect the ventricular coronary tree with the aorta. Defects in proximal CA patterning are a cause of sudden cardiac death. In mice lacking Tbx1, common arterial trunk is associated with an abnormal trajectory of the proximal left CA. Here we investigate CA stem development in wild-type and Tbx1 null embryos.

RESULTS

Genetic lineage tracing reveals that limited outgrowth of aortic endothelium contributes to proximal CA stems. Immunohistochemistry and fluorescent tracer injections identify a periarterial vascular plexus present at the onset of CA stem development. Transplantation experiments in avian embryos indicate that the periarterial plexus originates in mesenchyme distal to the outflow tract. Tbx1 is required for the patterning but not timing of CA stem development and a Tbx1 reporter allele is expressed in myocardium adjacent to the left but not right CA stem. This expression domain is maintained in Sema3c(-/-) hearts with a common arterial trunk and leftward positioned CA. Ectopic myocardial differentiation is observed on the left side of the Tbx1(-/-) common arterial trunk.

CONCLUSIONS

A periarterial plexus bridges limited outgrowth of the aortic endothelium with the ventricular plexus during CA stem development. Molecular differences associated with left and right CA stems provide new insights into the etiology of CA patterning defects.

Induction of the Proepicardium

The proepicardium is a transient extracardiac embryonic tissue that gives rise to the epicardium and a number of coronary vascular cell lineages. This important extracardiac tissue develops through multiple steps of inductive events, from specification of multiple cell lineages to morphogenesis. This article will review our current understanding of inductive events involved in patterning of the proepicardium precursor field, specification of cell types within the proepicardium, and their extension and attachment to the heart.

Expression of lymphatic markers during avian and mouse cardiogenesis

The adult heart has been reported to have an extensive lymphatic system, yet the development of this important system during cardiogenesis is still largely unexplored. The nuclear-localized transcription factor Prox-1 identified a sheet of Prox-1-positive cells on the developing aorta and pulmonary trunk in avian and murine embryos just before septation of the four heart chambers. The cells coalesced into a branching lymphatic network that spread within the epicardium to cover the heart. These vessels eventually expressed the lymphatic markers LYVE-1, VEGFR-3, and podoplanin. Before the Prox-1-positive cells were detected in the mouse epicardium, LYVE-1, a homologue of the CD44 glycoprotein, was primarily expressed in individual epicardial cells. Similar staining patterns were observed for CD44 in avian embryos. The proximity of these LYVE-1/CD44-positive mesenchymal cells to Prox-1-positive vessels suggests that they may become incorporated into the lymphatics. Unexpectedly, we detected LYVE-1/PECAM/VEGFR-3-positive vessels within the embryonic and adult myocardium, which remained Prox-1/podoplanin-negative. Lymphatic markers were surprisingly found in adult rat and embryonic mouse epicardial cell lines, with Prox-1 also exhibiting nuclear-localized expression in primary cultures of embryonic avian epicardial cells. Our data identified three types of cells in the embryonic heart expressing lymphatic markers: (1) Prox-1-positive cells from an extracardiac source that migrate within the serosa of the outflow tract into the epicardium of the developing heart, (2) individual LYVE-1-positive cells in the epicardium that may be incorporated into the Prox-1-positive lymphatic vasculature, and (3) LYVE-1-positive cells/vessels in the myocardium that do not become Prox-1-positive even in the adult heart.

Altered hypoxia-inducible factor-1 alpha expression levels correlate with coronary vessel anomalies

The outflow tract myocardium and other regions corresponding to the location of the major coronary vessels of the developing chicken heart, display a high level of hypoxia as assessed by the hypoxia indicator EF5. The EF5-positive tissues were also specifically positive for nuclear-localized hypoxia inducible factor-1 alpha (HIF-1alpha), the oxygen-sensitive component of the hypoxia inducible factor-1 (HIF-1) heterodimer. This led to our hypothesis that there is a "template" of hypoxic tissue that determines the stereotyped pattern of the major coronary vessels. In this study, we disturbed this template by altering ambient oxygen levels (hypoxia 15%; hyperoxia 75-40%) during the early phases of avian coronary vessel development, in order to alter tissue hypoxia, HIF-1alpha protein expression, and its downstream target genes without high mortality. We also altered HIF-1alpha gene expression in the embryonic outflow tract cardiomyocytes by injecting an adenovirus containing a constitutively active form of HIF-1alpha (AdCA5). We assayed for coronary anomalies using anti-alpha-smooth muscle actin immunohistology. When incubated under abnormal oxygen levels or injected with a low titer of the AdCA5, coronary arteries displayed deviations from their normal proximal connections to the aorta. These deviations were similar to known clinical anomalies of coronary arteries. These findings indicated that developing coronary vessels may be subject to a level of regulation that is dependent on differential oxygen levels within cardiac tissues and subsequent HIF-1 regulation of gene expression.

VESGEN 2D: automated, user-interactive software for quantification and mapping of angiogenic and lymphangiogenic trees and networks

Quantification of microvascular remodeling as a meaningful discovery tool requires mapping and measurement of site-specific changes within vascular trees and networks. Vessel density and other critical vascular parameters are often modulated by molecular regulators as determined by local vascular architecture. For example, enlargement of vessel diameter by vascular endothelial growth factor (VEGF) is restricted to specific generations of vessel branching (Parsons-Wingerter et al., Microvascular Research72: 91, 2006). The averaging of vessel diameter over many successively smaller generations is therefore not particularly useful. The newly automated, user-interactive software VESsel GENeration Analysis (VESGEN) quantifies major vessel parameters within two-dimensional (2D) vascular trees, networks, and tree-network composites. This report reviews application of VESGEN 2D to angiogenic and lymphangiogenic tissues that includes the human and murine retina, embryonic coronary vessels, and avian chorioallantoic membrane. Software output includes colorized image maps with quantification of local vessel diameter, fractal dimension, tortuosity, and avascular spacing. The density of parameters such as vessel area, length, number, and branch point are quantified according to site-specific generational branching within vascular trees. The sole user input requirement is a binary (black/white) vascular image. Future applications of VESGEN will include analysis of 3D vascular architecture and bioinformatic dimensions such as blood flow and receptor localization. Branching analysis by VESGEN has demonstrated that numerous regulators including VEGF(165), basic fibroblast growth factor, transforming growth factor beta-1, angiostatin and the clinical steroid triamcinolone acetonide induce 'fingerprint' or 'signature' changes in vascular patterning that provide unique readouts of dominant molecular signaling.

Catheter selection for coronary angiography and intervention in anomalous right coronary arteries

BACKGROUND

An anomalous origin of the right coronary artery (ARCA) from the left sinus of Valsalva (LSOV) has been reported in 6-27% of patients with coronary anomalies. The unusual location and course of this anomaly poses a technical challenge for the interventionalist. Appropriate guiding catheter selection is critical to ensure successful angiography and percutaneous intervention (PCI). We report our experience in 24 patients with an anomalous RCA originating from the LSOV.

METHODS

Twenty-four angiograms of ARCA-LSOV were reviewed by two independent interventionalists with attention to the origin and take off of the RCA within the aortic root. The origin was adjudicated with a scheme based on anatomical landmarks as described-A: origin from the aorta above the sinotubular plane; B: origin just below the ostium of the left coronary artery (LCA); C: origin below the sinotubular plane between the midline and the LCA; D: origin along the midline.

RESULTS

The distribution of various takeoffs of the RCA was as follows: For type A (N = 4) the FL3.0 and FCL3.0 catheters were successful in three and one cases, respectively. For type B (N = 5) the FCL3.0 or 3.5 was successful in four out of the five cases. For type C (N = 9) the VL catheter was successful in eight (VL3.5 = 5:VL 3.0 = 3) cases. The AL catheter was successful in five cases of type D (N = 6) RCAs (AL1 = 3:AL2 = 1:AL3 = 1).

CONCLUSIONS

The classification method and catheter selection provide a useful framework to successfully engage ARCA-LSOV and may reduce contrast and radiation exposure.

New morphological aspects of blood islands formation in the embryonic mouse hearts

Vasculogenesis in embryonic hearts proceeds by formation of aggregates consisting of erythroblasts and endothelial cells. These aggregates are called blood-islands or blood-island-like structures. We aimed to characterize blood islands in mouse embryonic hearts at stages spanning from 11 dpc through 13 dpc, i.e. prior to the establishment of the coronary circulation. Our observations suggested that there are two types of blood islands. One formed by migrating nucleated erythroblasts, which associated with migrating endothelial cell and the second by in situ emergence of two kinds of cells belonging to separate populations: one resembling an erythroblast progenitor and the second resembling an endothelial-cell progenitor. The subepicardial blood islands contain nucleated erythroblasts, undifferentiated mesenchymal cells, platelets, and early lymphocytes. The subepicardial blood islands resemble vesicles with protruding prongs directed toward the myocardium. Ahead of the prongs, angiogenic sprouting and degradation of fibronectin is observed. Vesicles gradually change their shape from spherical to tubular at 13 dpc and grow and extend along the interventricular sulcuses forming vascular tubes. We presume that the vascular tubes located within the interventricular sulcuses are precursors of coronary veins. Our data seems to indicate that embryonic heart vasculogenesis is accompanied by hematopoiesis.

Temporally expressed PDGF and FGF-2 regulate embryonic coronary artery formation and growth

OBJECTIVE

PDGF and FGF-2 are important regulators of vascular wall assembly. We tested the hypothesis that their embryonic temporal expression facilitates 2 specific events: (1) the endothelial invasion of the aortic root to form the coronary artery stems and (2) the subsequent growth and development of the arterial tree.

METHODS AND RESULTS

Addition of FGF-2 and PDGF-BB proteins to embryonic quail heart explants stimulated a 3- and 7-fold increase, respectively, in tubulogenesis, whereas neutralizing antibodies to these growth factors attenuated tubulogenesis by 40%. Anti-FGF-2 and anti-PDGF neutralizing antibodies were then introduced in ovo via the vitelline vein at various embryonic (E) days. When injections occurred before coronary ostial formation, the embryos usually developed only 1 coronary artery or lacked coronary arteries. When 1 or both major coronary arteries formed: (1) their branches had a thinner tunica media, and (2) smooth muscle investment did not progress as far distally as in shams. Other anomalies included smaller diameter coronary artery stems in some hearts. Inhibition of VEGF via injections of aflibercept (VEGF-Trap, a VEGFR-1 and -2 chimera), previously shown to be essential for coronary stem formation, limited development of the coronary arteries even though introduced after formation of coronary ostia (at E9 or EI0).

CONCLUSIONS

Our data (1) document a role for FGF-2 and PDGF in the temporal regulation of coronary artery stem formation and growth of the coronary arterial tree and (2) reveal that VEGF expression is required for normal artery/arterial formation, even after coronary artery stem formation.

Epicardial development in lamprey supports an evolutionary origin of the vertebrate epicardium from an ancestral pronephric external glomerulus

The epicardium is the outer layer of the vertebrate heart. Both the embryonic epicardium and its derived mesenchyme are critical to heart development, contributing to the coronary vasculature and modulating the proliferation of the ventricular myocardium. The embryonic epicardium arises from an extracardiac, originally paired progenitor tissue called the proepicardium, a proliferation of coelomic cells found at the limit between the liver and the sinus venosus. Proepicardial cells attach to and spread over the cardiac surface giving rise to the epicardium. Invertebrate hearts always lack of epicardium, and no hypothesis has been proposed about the origin of this tissue and its proepicardial progenitor in vertebrates. We herein describe the epicardial development in a representative of the most basal living lineage of vertebrates, the agnathan Petromyzon marinus (lamprey). The epicardium in lampreys develops by migration of coelomic cells clustered in a paired structure at the roof of the coelomic cavity, between the pronephros and the gut. Later on, these outgrowths differentiate into the pronephric external glomerulus (PEG), a structure composed of capillary networks, mesangial cells, and podocytes. This observation is consistent with the conclusion that the primordia of the most anterior pair of PEG in agnathans have been retained and transformed into the proepicardium in gnathostomes. Glomerular progenitor cells are highly vasculogenic and probably allowed for the vascularization of a cardiac tube primarily devoid of coronary vessels. This new hypothesis accounts for the striking epicardial expression of Wt1 and Pod1, two transcription factors essential for development of the excretory system.

A 3-D model of coronary vessel development

Coronary vascular disease is one of the leading causes of mortality and morbidity in the United States. Therefore, a mechanistic understanding of coronary vessel morphogenesis would aid in the innovation of new therapies targeting vascular disorders. Moreover, a functionally equivalent in vitro model system allows for the delineation of the molecular mechanisms that regulate coronary vessel development. In this study, we present a novel in vitro model system. This three-dimensional (3-D) model system consists of a tubular scaffold, which is engineered from type-I collagen and has been optimized to support the growth of embryonic cardiac tissues. In this report, proepicardial (PE) cells, the developmental precursors of coronary vessels, have been isolated from several model species and cultured on this scaffold. In this model system, the PE cells were able to recapitulate several aspects of coronary vessel morphogenesis including epicardial formation, the epicardial to mesenchymal transformation, and de novo coronary vessel development or vasculogenesis. The differentiation of PE cells was characterized using a variety of specific protein markers. The potential uses of this novel coronary developmental model are discussed.