Extension of Endocardium-Derived Vessels Generate Coronary Arteries in Neonates

Background: Unraveling how new coronary arteries develop may provide critical information for establishing novel therapeutic approaches to treating ischemic cardiac diseases. There are two distinct coronary vascular populations derived from different origins in the developing heart. Understanding the formation of coronary arteries may provide insights into new ways of promoting coronary artery formation after myocardial infarction. Methods: To understand how intramyocardial coronary arteries are generated to connect these two coronary vascular populations, we combined genetic lineage tracing, light-sheet microscopy, fluorescence micro-optical sectioning tomography, and tissue-specific gene knockout approaches to understand their cellular and molecular mechanisms. Results: We show that a subset of intramyocardial coronary arteries form by angiogenic extension of endocardium-derived vascular tunnels in the neonatal heart. Three-dimensional whole-mount fluorescence imaging showed that these endocardium-derived vascular tunnels or tubes adopt an arterial fate in neonates. Mechanistically, we implicate Mettl3 and Notch signaling in regulating endocardium-derived intramyocardial coronary artery formation. Functionally, these intramyocardial arteries persist into adulthood and play a protective role after myocardial infarction. Conclusions: A subset of intramyocardial coronary arteries form by extension of endocardium-derived vascular tunnels in the neonatal heart.

Perinatal angiogenesis from pre-existing coronary vessels via DLL4-NOTCH1 signalling

New coronary vessels are added to the heart around birth to support postnatal cardiac growth. Here we show that, in late fetal development, the embryonic coronary plexus at the inner myocardium of the ventricles expresses the angiogenic signalling factors VEGFR3 and DLL4 and generates new coronary vessels in neonates. Contrary to a previous model in which the formation of new coronary vessels in neonates from ventricular endocardial cells was proposed, we find that late fetal and neonatal ventricular endocardial cells lack angiogenic potential and do not contribute to new coronary vessels. Instead, we show using lineage-tracing as well as gain- and loss-of-function experiments that the pre-existing embryonic coronary plexus at the inner myocardium undergoes angiogenic expansion through the DLL4-NOTCH1 signalling pathway to vascularize the expanding myocardium. We also show that the pre-existing coronary plexus revascularizes the regenerating neonatal heart through a similar mechanism. These findings provide a different model of neonatal coronary angiogenesis and regeneration, potentially informing cardiovascular medicine.

Expression Profile of Genes Encoding Proteins Involved in Regulation of Vasculature Development and Heart Muscle Morphogenesis-A Transcriptomic Approach Based on a Porcine Model

Despite significant advances in treatment of acute coronary syndromes (ACS) many subjects still develop heart failure due to significantly reduced ejection fraction. Currently, there are no commonly available treatment strategies that replace the infarcted/dysfunctional myocardium. Therefore, understanding the mechanisms that control the regeneration of the heart muscle is important. The development of new coronary vessels plays a pivotal role in cardiac regeneration. Employing microarray expression assays and RT-qPCR validation expression pattern of genes in long-term primary cultured cells isolated form the right atrial appendage (RAA) and right atrium (RA) was evaluated. After using DAVID software, it indicated the analysis expression profiles of genes involved in ontological groups such as: “angiogenesis”, “blood vessel morphogenesis”, “circulatory system development”, “regulation of vasculature development”, and “vasculature development” associated with the process of creation new blood vessels. The performed transcriptomic comparative analysis between two different compartments of the heart muscle allowed us to indicate the presence of differences in the expression of key transcripts depending on the cell source. Increases in culture intervals significantly increased expression of SFRP2, PRRX1 genes and some other genes involved in inflammatory process, such as: CCL2, IL6, and ROBO1. Moreover, the right atrial appendage gene encoding lysyl oxidase (LOX) showed much higher expression compared to the pre-cultivation state.

Pathological Process of Prompt Connection between Host and Donor Tissue Vasculature Causing Rapid Perfusion of the Engineered Donor Tissue after Transplantation

The shortage of donors for transplantation therapy is a serious issue worldwide. Tissue engineering is considered a potential solution to this problem. Connection and perfusion in engineered tissues after transplantation is vital for the survival of the transplanted tissue, especially for tissues requiring blood perfusion to receive nutrients, such as the heart. A myocardial cell sheet containing an endothelial cell network structure was fabricated in vitro using cell sheet technology. Transplantation of the three-dimensional (3D) tissue by layering myocardial sheets could ameliorate ischemic heart disease in a rat model. The endothelial cell network in the 3D tissue was able to rapidly connect to host vasculature and begin perfusion within 24 h after transplantation. In this review, we compare and discuss the engineered tissue⁻host vasculature connection process between tissue engineered constructs with hydrogels and cell sheets by histological analysis. This review provides information that may be useful for further improvements of in vivo engineered tissue vascularization techniques.

Non-muscle myosin IIB (Myh10) is required for epicardial function and coronary vessel formation during mammalian development

The coronary vasculature is an essential vessel network providing the blood supply to the heart. Disruptions in coronary blood flow contribute to cardiac disease, a major cause of premature death worldwide. The generation of treatments for cardiovascular disease will be aided by a deeper understanding of the developmental processes that underpin coronary vessel formation. From an ENU mutagenesis screen, we have isolated a mouse mutant displaying embryonic hydrocephalus and cardiac defects (EHC). Positional cloning and candidate gene analysis revealed that the EHC phenotype results from a point mutation in a splice donor site of the Myh10 gene, which encodes NMHC IIB. Complementation testing confirmed that the Myh10 mutation causes the EHC phenotype. Characterisation of the EHC cardiac defects revealed abnormalities in myocardial development, consistent with observations from previously generated NMHC IIB null mouse lines. Analysis of the EHC mutant hearts also identified defects in the formation of the coronary vasculature. We attribute the coronary vessel abnormalities to defective epicardial cell function, as the EHC epicardium displays an abnormal cell morphology, reduced capacity to undergo epithelial-mesenchymal transition (EMT), and impaired migration of epicardial-derived cells (EPDCs) into the myocardium. Our studies on the EHC mutant demonstrate a requirement for NMHC IIB in epicardial function and coronary vessel formation, highlighting the importance of this protein in cardiac development and ultimately, embryonic survival.

DACH1 stimulates shear stress-guided endothelial cell migration and coronary artery growth through the CXCL12-CXCR4 signaling axis

Sufficient blood flow to tissues relies on arterial blood vessels, but the mechanisms regulating their development are poorly understood. Many arteries, including coronary arteries of the heart, form through remodeling of an immature vascular plexus in a process triggered and shaped by blood flow. However, little is known about how cues from fluid shear stress are translated into responses that pattern artery development. Here, we show that mice lacking endothelial Dach1 had small coronary arteries, decreased endothelial cell polarization, and reduced expression of the chemokine Cxcl12 Under shear stress in culture, Dach1 overexpression stimulated endothelial cell polarization and migration against flow, which was reversed upon CXCL12/CXCR4 inhibition. In vivo, DACH1 was expressed during early arteriogenesis but was down in mature arteries. Mature artery-type shear stress (high, uniform laminar) specifically down-regulated DACH1, while the remodeling artery-type flow (low, variable) maintained DACH1 expression. Together, our data support a model in which DACH1 stimulates coronary artery growth by activating Cxcl12 expression and endothelial cell migration against blood flow into developing arteries. This activity is suppressed once arteries reach a mature morphology and acquire high, laminar flow that down-regulates DACH1. Thus, we identified a mechanism by which blood flow quality balances artery growth and maturation.

[Increased vascular density with indirect myocardial revascularization in normal rat hearts]

BACKGROUND

The aim of this study was to identify if the interaction of myocardial revascularization methods increases the functional vascular area.

METHODS

A 4x3 factorial design was performed in 11 groups, five rats per group, ten samples per rat, evaluated at 45 days postoperative, with different surgical combinations. The magnitude of the interaction was evaluated by immunoexpression of vascular endothelium-derived growth factor, fibroblast growth factor and tyrosine receptor, to allow the activity of vascular endothelium-derived growth factor, fibroblast growth factor and thrombin (Flk-1), as well as vascular area measurement; Both measures were performed by computerized morphometry.

RESULTS

An increase in immunohistochemical expression and vascular area in direct proportion to the interaction was identified; It can be affirmed (ANOVA p < 0.0001), that with the interaction of all the maneuvers the maximum effect is achieved.

CONCLUSIONS

It is demonstrated that indirect myocardial revascularization has a specific weight within the integral myocardial revascularization with a real impact on cost-benefit and cost-effectiveness.

Comparative Quantitative Studies on the Microvasculature of the Heart of a Highly Selected Meat-Type and a Wild-Type Turkey Line

In this study the macroscopic and microscopic structure of the heart of a fast growing, meat-type turkey line (British United turkeys BUT Big 6) and a wild-type turkey line (Canadian Wild turkey) were compared. At 8 and 16 weeks of age, 10 birds of each genotype and sex were sampled. The body mass and heart mass of the meat-type turkey both increased at a faster rate than those of the wild-type turkey. However in both turkey lines, the relative heart mass decreased slightly with age, the decrease was statistically significant only in the male turkeys. Furthermore meat-type turkeys had a significantly (p < 0.01) lower relative heart mass and relative thickness of the left ventricle compared to the wild-type turkeys of the same age. The wild-type turkeys showed no significant change in the size of cardiomyocytes (cross sectional area and diameter) from 8 weeks to 16 weeks. In contrast, the size of cardiomyocytes increased significantly (p < 0.001) with age in the meat-type turkeys. The number of capillaries in the left ventricular wall increased significantly (p < 0.001) in wild-type turkeys from 2351 per mm² at the age of 8 weeks to 2843 per mm² at 16 weeks. However, in the meat-type turkeys there were no significant changes, capillary numbers being 2989 per mm² at age 8 weeks and 2915 per mm² at age 16 weeks. Correspondingly the area occupied by capillaries in the myocardium increased in wild-type turkeys from 8.59% at the age of 8 weeks to 9.15% at 16 weeks, whereas in meat-type turkeys this area decreased from 10.4% at 8 weeks to 9.95% at 16 weeks. Our results indicate a mismatch in development between body mass and heart mass and a compromised cardiac capillary density and architecture in the meat-type turkeys in comparison to the wild-type turkeys.

Cellular and molecular mechanisms of coronary vessel development

Development of coronary vessels is a complex process in developmental biology and it may have clinical implications. Although coronary vessels develop as a form of vasculogenesis followed by angiogenesis, the cells of the entire coronary system do not arise from the developing heart. The key events of the coronary system formation include the generation of primordium and proepicardial organ; formation of epicardium; generation of subepicardial mesenchymal cells, and the formation, remodeling and maturation of the final vascular plexus. These events represent a complex regulation of the cell fate determination, cellular migration, epicardial/mesenchymal transformation, and patterning of vasculatures. Recent studies suggest that several transcription factors, adhesion molecules, growth factors and signaling molecules play essential roles in these events. This article reviews the literature on the development of coronary vessels, and discusses current advances and controversies of molecular and cellular mechanisms, thereby directing future investigations.

Notch-independent RBPJ controls angiogenesis in the adult heart

Increasing angiogenesis has long been considered a therapeutic target for improving heart function after injury such as acute myocardial infarction. However, gene, protein and cell therapies to increase microvascularization have not been successful, most likely because the studies failed to achieve regulated and concerted expression of pro-angiogenic and angiostatic factors needed to produce functional microvasculature. Here, we report that the transcription factor RBPJ is a homoeostatic repressor of multiple pro-angiogenic and angiostatic factor genes in cardiomyocytes. RBPJ controls angiogenic factor gene expression independently of Notch by antagonizing the activity of hypoxia-inducible factors (HIFs). In contrast to previous strategies, the cardiomyocyte-specific deletion of Rbpj increased microvascularization of the heart without adversely affecting cardiac structure or function even into old age. Furthermore, the loss of RBPJ in cardiomyocytes increased hypoxia tolerance, improved heart function and decreased pathological remodelling after myocardial infarction, suggesting that inhibiting RBPJ might be therapeutic for ischaemic injury.

Growth, ageing and scaling laws of coronary arterial trees

Despite the well-known design principles of vascular systems, it is unclear whether the vascular arterial tree obeys some scaling constraints during normal growth and ageing in a given species. Based on the micro-computed tomography measurements of coronary arterial trees in mice at different ages (one week to more than eight months), we show a constant exponent of 3/4, but age-dependent scaling coefficients in a length-volume scaling law (Lc=K(length-volume) · Vc³/⁴; Lc is the crown length, Vc is the crown volume, K(length-volume) is the age-dependent scaling coefficient) during normal growth and ageing. The constant 3/4 exponent represents the self-similar fractal-like branching pattern (i.e. basic mechanism to regulate the development of vascular trees within a species), whereas the age-dependent scaling coefficients characterize the structural growth or resorption of vascular trees during normal growth or ageing, respectively. This study enhances the understanding of age-associated changes in vascular structure and function.

Hypertrophy, hyperplasia and structural dilatation of the human heart

The human heart can exceed the critical heart weight of 500 g in the course of pathological structural adaptation. This abnormal growth is performed not only by an increase in size (hypertrophy) but also in number (hyperplasia) of cardiac muscle cells. Coronary insufficiency, dilatation and chronic heart failure are noted frequently in hearts above this critical heart weight. Chronic heart failure is not a direct consequence of local destruction and scar formation following coronary insufficiency. Unlike acute cardiac dilatation with failure, chronic dilatation is not associated with stretching or overstretching of cardiac muscle cells. Starling's law is not applicable for explaining heart failure in these chronic cases. Chronic dilatation is a structural dilatation (Gefugedilatation) produced by sliding displacements (slippage) of heart muscle cells leading to a decrease in the number of muscle layers in the ventricular wall. Chronic heart failure in man therefore is rather a physical consequence of structural dilatation which severely impairs the working conditions, the efficiency and the effectiveness of the heart muscle cells than an immediate result of coronary insufficiency of inflammation with local metabolic alterations, which, of course, additionally impair the quality of the myocardium and the conducting system.

BAF200 is required for heart morphogenesis and coronary artery development

ATP-dependent SWI/SNF chromatin remodeling complexes utilize ATP hydrolysis to non-covalently change nucleosome-DNA interactions and are essential in stem cell development, organogenesis, and tumorigenesis. Biochemical studies show that SWI/SNF in mammalian cells can be divided into two subcomplexes BAF and PBAF based on the subunit composition. ARID2 or BAF200 has been defined as an intrinsic subunit of PBAF complex. However, the function of BAF200 in vivo is not clear. To dissect the possible role of BAF200 in regulating embryogenesis and organ development, we generated BAF200 mutant mice and found they were embryonic lethal. BAF200 mutant embryos exhibited multiple cardiac defects including thin myocardium, ventricular septum defect, common atrioventricular valve, and double outlet right ventricle around E14.5. Moreover, we also detected reduced intramyocardial coronary arteries in BAF200 mutants, suggesting that BAF200 is required for proper migration and differentiation of subepicardial venous cells into arterial endothelial cells. Our work revealed that PBAF complex plays a critical role in heart morphogenesis and coronary artery angiogenesis.

Disease-related growth factor and embryonic signaling pathways modulate an enhancer of TCF21 expression at the 6q23.2 coronary heart disease locus

Coronary heart disease (CHD) is the leading cause of mortality in both developed and developing countries worldwide. Genome-wide association studies (GWAS) have now identified 46 independent susceptibility loci for CHD, however, the biological and disease-relevant mechanisms for these associations remain elusive. The large-scale meta-analysis of GWAS recently identified in Caucasians a CHD-associated locus at chromosome 6q23.2, a region containing the transcription factor TCF21 gene. TCF21 (Capsulin/Pod1/Epicardin) is a member of the basic-helix-loop-helix (bHLH) transcription factor family, and regulates cell fate decisions and differentiation in the developing coronary vasculature. Herein, we characterize a cis-regulatory mechanism by which the lead polymorphism rs12190287 disrupts an atypical activator protein 1 (AP-1) element, as demonstrated by allele-specific transcriptional regulation, transcription factor binding, and chromatin organization, leading to altered TCF21 expression. Further, this element is shown to mediate signaling through platelet-derived growth factor receptor beta (PDGFR-β) and Wilms tumor 1 (WT1) pathways. A second disease allele identified in East Asians also appears to disrupt an AP-1-like element. Thus, both disease-related growth factor and embryonic signaling pathways may regulate CHD risk through two independent alleles at TCF21.

[Evaluation of coronary artery diameter in normal children by echocardiography and its clinical significance]

OBJECTIVE

To obtain normal range of coronary artery diameter with body surface area (BSA) dynamic changes in normal children at different age.

METHOD

The left main coronary artery (LCA), left anterior descending artery (LAD), left circumflex artery (LCX) and the right coronary artery (RCA) diameter were measured in 400 normal subjects from Chinese population aged 0 d to 18 years [(6.43 ± 4.45) years], using HP Sonos 5500 color Doppler ultrasonic system, according to the standard method of measuring the coronary artery diameter.

RESULT

(1) The diameters of LCA, LAD, LCX and RCA in different age groups (0 d-12 months, -3 years, -6 years, -9 years, -12 years, -18 years) had significant differences (F = 61.688, 51.343, 46.375, 50.192, P < 0.01,all groups mean differences had significant differences, there was significant difference between every two groups, P < 0.05), there were no significant differences between male and female subjects (P > 0.05). (2) The correlation analyses showed that the diameter of LCA, LAD, LCX and RCA had significant linear correlations with age, height, weight and BSA (r ranged from 0.71 to 0.85, P < 0.01 ). (3) The regression analyses were respectively performed on the diameters of LCA, LAD, LCX and RCA with BSA to establish seven regression models. The coefficients were compared for each model, the best model was chosen to create a Z score calculator, tracing out the Z value curve, through clinical practice,we chose Z score within ± 2 as the coronary artery diameter's normal range for Chinese children.

CONCLUSION

Coronary artery diameter's Z score curve is effective and reliable, it provide objective basis for clinicians and sonographers to accurately and quickly diagnose the anomalies in diameter of coronary artery.

Endothelium-derived microparticles inhibit angiogenesis in the heart and enhance the inhibitory effects of hypercholesterolemia on angiogenesis

Therapeutic angiogenesis remains unsuccessful in coronary artery disease. It is known that plasma endothelium-derived microparticles (EMPs) are increased in coronary artery disease and that hypercholesterolemia can inhibit angiogenesis. We evaluated the relationship between EMPs and hypercholesterolemia in the impairment of angiogenesis. EMPs isolated from human umbilical vein endothelial cells were injected into low-density lipoprotein receptor-null (LDLr(-/-)) mice fed a Western diet for 2 wk and C57BL6 mice for 6 h or were directly added to the tissue culture media. Hearts isolated from mice were sectioned and cultured, and endothelial tube formation was measured. The expression and phosphorylation of endothelial NO synthase (eNOS) and the generation of NO in the hearts were determined. Angiogenesis was inhibited by pathophysiological concentrations of EMPs but not physiological concentrations of EMPs in hearts from C57BL6 mice. However, angiogenesis was inhibited by EMPs at both physiological and pathophysiological concentrations of EMPs in hearts from hypercholesterolemic LDLr(-/-) mice. Pathophysiological concentrations of EMPs decreased eNOS phosphorylation at Ser(1177) and NO generation without altering eNOS expression in hearts from C57BL6 mice. Both physiological and pathophysiological concentrations of EMPs decreased not only eNOS phosphorylation at Ser(1177) and NO generation, but eNOS expression in hypercholesterolemic hearts from LDLr(-/-) mice. These data demonstrated that pathophysiological concentrations of EMPs could inhibit angiogenesis in hearts by decreasing eNOS activity. EMPs and hypercholesterolemia mutually enhanced their inhibitory effect of angiogenesis by inducing eNOS dysfunction. Our findings suggest a novel mechanism by which hypercholesterolemia impairs angiogenesis.

Bioactive scaffolds for engineering vascularized cardiac tissues

Functional vascularization is a key requirement for the development and function of most tissues, and most critically cardiac muscle. Rapid and irreversible loss of cardiomyocytes during cardiac infarction directly results from the lack of blood supply. Contractile cardiac grafts, engineered using cardiovascular cells in conjunction with biomaterial scaffolds, are an actively studied method for cardiac repair. In this article, we focus on biomaterial scaffolds designed to mediate the development and maturation of vascular networks, by immobilized growth factors. The interactive effects of multiple vasculogenic factors are discussed in the context of cardiac tissue engineering.

Resveratrol, a red wine constituent, blocks the antimitogenic effects of estradiol on human female coronary artery smooth muscle cells

CONTEXT

Antimitogenic effects of estradiol on vascular smooth muscle cells (VSMCs) may be cardioprotective, and these effects are mediated by estrogen receptor-alpha-dependent and -independent mechanisms, with the latter involving the conversion of estradiol to 2-hydroxyestradiol/2-methoxyestradiol by CYP450. Because resveratrol inhibits CYP450 and is an estrogen-receptor-alpha antagonist, resveratrol may abrogate the antimitogenic effects of estradiol.

OBJECTIVE

The objective of the study was to examine the interaction of pharmacologically relevant concentrations of resveratrol with estradiol, 2-hydroxyestradiol, and 2-methoxyestradiol in human female coronary artery VSMCs.

METHODS AND RESULTS

In human female coronary VSMCs, resveratrol (0.1-10 microm) alone did not influence serum-induced DNA or collagen synthesis or cell proliferation or migration; however, resveratrol abrogated the inhibitory effects of estradiol, but not 2-hydroxyestradiol or 2-methoxyestradiol, on these responses. Resveratrol also abrogated the inhibitory effects of estradiol on positive growth regulators (cyclin A, cyclin D, MAPK phosphorylation) and the stimulatory effects of estradiol on negative growth regulators (p21, p27). In microsomes and cells, dietarily relevant levels of resveratrol (0.001-1 microm) inhibited the metabolism of estradiol to 2-hydroxestradiol/2-methoxyestradiol. Propylpyrazoletriol (estrogen receptor-alpha agonist, 100 nmol/liter), but not diarylpropionitrile (estrogen receptor-beta agonist, 10 nmol/liter), inhibited VSMC mitogenesis, and this effect was blocked by resveratrol (5 micromol/liter). Higher concentrations (>25-50 microm) of resveratrol, never attainable in vivo, inhibited VSMC growth, an effect blocked by GW9662 (peroxisomal proliferator-activated receptor-gamma antagonist).

CONCLUSION

In conclusion, dietarily relevant levels of resveratrol abrogate the antimitogenic effects of estradiol by inhibiting CYP450-mediated estradiol metabolism and blocking estrogen receptor-alpha.

The role of interleukin-6 in the formation of the coronary vasculature

The formation and the patterning of the coronary vasculature are critical to the development and pathology of the heart. Alterations in cytokine signaling and biomechanical load can alter the vascular distribution of the vessels within the heart. Changes in the physical patterning of the vasculature can have significant impacts on the relationships of the pressure-flow network and distribution of critical growth and survival factors to the tissue. Interleukin-6 (IL-6) is a pleiotropic cytokine that regulates several biological processes, including vasculogenesis. Using both immunohistological and cardioangiographic analyses, we tested the hypothesis that IL-6-loss will result in decreased vessel density, along with changes in vascular distribution. Moreover, given the impact of vascular patterning on pressure-flow and distribution mechanics, we utilized non-Euclidean geometrical fractal analysis to quantify the changes in patterning resulting from IL-6-loss. Our analyses revealed that IL-6-loss results in a decreased capillary density and increase in intercapillary distances, but does not alter vessel size or diameter. We also observed that the IL-6-/- coronary vasculature had a marked increase in fractal dimension (D value), indicating that IL-6-loss alters vascular patterning. Characterization of IL-6-loss on coronary vasculature may lend insight into the role of IL-6 in the formation and patterning of the vascular bed.

Vascular Endothelial Growth Factor Response in Porcine Coronary and Peripheral Arteries Using Nonsurgical Occlusion Model, Local Delivery, and Liposome-Mediated Gene Transfer

Angiogenesis and arteriogenesis play an important role in advanced vascular occlusive diseases. Whether angiogenesis or arteriogenesis predominate depends on the preexisting collateral vessel network, the type and location of occlusion, and different developmental origin of the arteries. Angiogenesis and arteriogenesis were investigated following vascular endothelial growth factor (VEGF) treatment in different arteries important in occlusive arterial diseases using a newly developed porcine arterial occlusion model. Porcine coronary and peripheral arteries were occluded interventionally using blinded stent grafts. Gene transfer was performed using a needle injection catheter and cationic lipid DOCSPER as gene carrier. DNA and gene expression in arterial tissue was examined using polymerase chain reaction (PCR) and reverse transcriptase (RT)-PCR. Vessel development was determined by angiography, immunohistochemistry, and measurement of capillary density. The transfected gene and its expression were found 3 months following application. In tissue adjacent to coronary arteries, there was significantly enhanced capillary density but no increase in angiographic score. In contrast, tissue surrounding peripheral arteries demonstrated no enhancement of capillary density but an enhancement in angiographic score. These results demonstrate differential responses to VEGF treatment in coronary and peripheral arteries resulting predominantly in either angiogenesis or arteriogenesis. Further investigation of VEGF signaling pathway is necessary for better understanding of the processes of vascular development, which may have potential impact on the design of cardiovascular therapeutics.

Shared circuitry: developmental signaling cascades regulate both embryonic and adult coronary vasculature

Ischemic heart disease is the most common cause of heart failure and is among the leading causes of mortality worldwide. Therapies used for the treatment of this disease aim to restore blood flow to severely narrowed or occluded coronary arteries by either catheter-based or surgical means. Although these strategies prove efficacious for many patients, a substantial number of individuals fail to improve following these procedures. Recently, a noninvasive strategy has been proposed, focusing on the use of endogenous growth factors that trigger the growth of new coronary arteries. Using the developing heart as a model, several groups have identified some of the key pathways that not only govern the development of the coronary vascular system but also promote the growth of the adult coronary vasculature. Here, we review the major morphological events and signaling cascades that mediate the formation of the coronary vasculature in the embryo. We further describe the mechanism by which many of these same pathways also regulate the adult coronary vasculature and their potential use in the treatment of ischemic heart disease.

STAT3: a critical transcription activator in angiogenesis

Angiogenesis, the formation of new blood vessels from the pre-existing vasculature, is a complex multistage process regulated by a number of signal transduction pathways. Accumulating evidence suggests that signal transducer and activator of transcription (STATs), mainly STAT3, play an important role in angiogenesis under both physiological and pathological conditions in addition to cell survival, proliferation, differentiation, and oncogenesis. STAT3, as a critical multifunctional mediator, regulates many aspects of angiogenesis at the transcriptional level. This review will highlight the pivotal role of STAT3 in well-studied tumorous angiogenesis and cardiac angiogenesis, and summarize various potential mechanisms utilized by STAT3 to regulate the transcriptional activation of VEGF.

Effect of glucometabolic disorders on the formation of coronary collaterals in occlusive coronary artery disease

OBJECTIVE

The primary aim of this study was to assess the effect of glucometabolic disorders on coronary collateral vessels in patients with occlusive coronary artery disease.

METHODS AND RESULTS

Hundred and ninety-five consecutive patients with at least single-vessel occlusion were enrolled in this study prospectively. The standard oral glucose tolerance test was performed according to the criteria of the World Health Organization. Collateral circulation was graded according to the Rentrop classification. The mean Rentrop scores in normal glucose tolerance (NGT), impaired glucose tolerance (IGT), and diabetes were 1.40 +/- 1.02, 1.05 +/- 0.84, 1.00 +/- 0.98, respectively (P = 0.043). The percentage of patients without collateral circulation (Rentrop-0) was greatest in the diabetic group (44.4%), while the percentage was 21.8% in the IGT group and 22.0% in the NGT group. Ninety-five patients with at least one totally occluded coronary artery were analysed as a subgroup. In the totally occluded artery subgroup postprandial glycaemia was the only parameter that was associated with the Rentrop score in the univariate analysis (r = -0.34, P = 0.002)

CONCLUSIONS

In conclusion, our study results, which are in agreement with previous results, indicate that not only diabetic glucose tolerance but also impaired glucose tolerance has an adverse impact on the development of coronary collaterals.

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.

Regional and global protective effects of tissue kallikrein gene delivery to the peri-infarct myocardium

BACKGROUND

The kallikrein-kinin system participates in the maintenance of the cardiovascular phenotype. We previously demonstrated that human tissue kallikrein gene (hTK) transfer promotes the healing of ischemic limbs. The present investigation aimed to test the original hypothesis that hTK delivery to the peri-infarct myocardium would prevent post-ischemic heart failure.

METHODS AND RESULTS

Myocardial infarction (MI) was induced in anesthetized mice by permanently occluding the left coronary descendant. hTK was delivered to the peri-infarct myocardium via an adenoviral vector (Ad.hTK). Controls received Ad.Null or saline. Survival rate was similar among groups. Ad.hTK increased the number of circulating endothelial progenitor cells and promoted the growth of capillaries and arterioles in the peri-infarct myocardium. In addition, Ad.hTK increased the abundance of cardiac progenitor cells (CPCs) in the peri-infarct and suppressed the apoptotic death of peri-infarct cardiomyocytes in vivo and ex vivo. As a consequence of these beneficial effects, at 5 weeks from MI, hTK-transduced hearts were protected from post-MI ventricular dilatation and showed better systolic and diastolic functions.

CONCLUSIONS

Ad.hTK benefits the neovascularization and viability of peri-infarct myocardium and increases CPC abundance, thereby decreasing ventricular dysfunction. Our study significantly adds to the knowledge of the protective effects of TK gene transfer on ischemic diseases and opens new avenues for the treatment of post-MI cardiac failure.

Thymosin beta-4 is essential for coronary vessel development and promotes neovascularization via adult epicardium

Ischemic heart disease leading to myocardial infarction causes irreversible cell loss and scarring and is a major cause of morbidity and mortality in humans. Significant effort in the field of cardiovascular medicine has been invested in the search for adult cardiac progenitor cells that may replace damaged muscle cells and/or contribute to new vessel formation (neovascularization) and in the identification of key factors, which may induce such progenitor cells to contribute to myocardial repair and collateral vessel growth. We recently demonstrated that the actin monomer-binding protein, thymosin beta-4 (Tbeta-4), when secreted from the myocardium provides a paracrine stimulus to the cells of the epicardium-derived cells (EPDCs) to promote their inward migration and differentiation into endothelial and smooth muscle cells to form the coronary vasculature. Translating this essential role for Tbeta-4 in coronary vessel development to the adult, we found that treatment of cultured adult explants with Tbeta-4 stimulated extensive outgrowth of epicardin-positive epicardial cells, which, as they migrated away from the explant, differentiated into procollagen type I, SMalphaA, and Flk1-positive cells indicative of fibroblasts, smooth muscle, and endothelial cells; thus releasing the adult epicardium from a quiescent state and restoring pluripotency. The ability of Tbeta-4 to promote coronary vessel development and potentially induce new vasculature in the adult is essential for cardiomyocyte survival and could contribute significantly toward the reported Tbeta4-induced cardioprotection and repair in the adult heart. Tbeta-4 is currently subject to multicenter phase 1 clinical trials for treatment of cardiovascular disease (http://www.regenerx.com), therefore, insight into the repair mechanism(s) induced by Tbeta-4 is an essential step toward harnessing therapeutic survival, migration, and repair properties of the peptide in the context of acute myocardial damage.

Rebuilding the coronary vasculature: hedgehog as a new candidate for pharmacologic revascularization

Myocardial infarction and ischemic heart disease are among the most common causes of morbidity and mortality in the industrial world. Surgical and percutaneous intravascular approaches are commonly used to treat these diseases. Regrettably, a significant number of patients are either ineligible or demonstrate suboptimal responses to these therapies. In an attempt to provide such patients improved therapeutic options, much effort has been spent developing noninvasive approaches to restore coronary vascular perfusion. One such strategy, termed therapeutic revascularization or angiogenesis, involves administration of proangiogenic factors, which improve coronary perfusion by promoting growth of the coronary vasculature. Thus far, two potential proangiogenic factors have been intensively examined, fibroblast growth factor and vascular endothelial growth factor. Unfortunately, despite their apparent efficacy in animal models, neither factor has performed adequately in the clinic to date. Within the past year a new factor, hedgehog, has been shown to effectively promote the growth of the coronary vasculature and thus has been proposed as a novel candidate for therapeutic revascularization. In this review, we discuss the discovery of the hedgehog pathway as an essential regulator of the development of the coronary vasculature, as an inducer of adult coronary vascular growth, and as a therapeutic in the treatment of ischemic heart disease.

Capillary Perfusion and Wall Shear Stress Are Restored in the Coronary Circulation of Hypertrophic Right Ventricle

It has been shown that right ventricle (RV) hypertrophy involves significant compensatory vascular growth and remodeling. The objective of the present study was to determine the functional implications of the vascular growth and remodeling through a full flow analysis of arterial tree down to first capillary segments. A computer reconstruction of RV branches including the proximal right coronary artery to the posterior descending artery was established based on measured morphometric data in arrested, vasodilated porcine heart. The flows were computed throughout the reconstructed trees based on conservation of mass and momentum and appropriate pressure boundary conditions. It was found that the flow rate was significantly increased in large epicardial coronary arteries in hypertrophic as compared with control hearts but normalized in the intramyocardial coronary arteries and smaller vessels in RV hypertrophy primarily because of the significant increase in number of arterioles. Furthermore, the wall shear stress was restored to nearly homeostatic levels throughout most of the vasculature after 5 weeks of RV hypertrophy. The compensatory remodeling in RV hypertrophy functionally restores the perfusion at the arteriolar and capillary level and wall shear stress in most of larger vessels. This is the first full analysis of coronary arterial tree, with millions of vessels, in cardiac hypertrophy that reveals the compensatory adaptation of structure to function.

A volumetric model for growth of arterial walls with arbitrary geometry and loads

Stress and deformation in arterial wall tissue are factors which may influence significantly its response and evolution. In this work we develop models based on nonlinear elasticity and finite element numerical solutions for the mechanical behaviour and the remodelling of the soft tissue of arteries, including anisotropy induced by the presence of collagen fibres. Remodelling and growth in particular constitute important features in order to interpret stenosis and atherosclerosis. The main object of this work is to model accurately volumetric growth, induced by fluid shear stress in the intima and local wall stress in arteries with patient-specific geometry and loads. The model is implemented in a nonlinear finite element setting which may be applied to realistic 3D geometries obtained from in vivo measurements. The capabilities of this method are demonstrated in several examples. Firstly a stenotic process on an idealised geometry induced by a non-uniform shear stress distribution is considered. Following the growth of a right coronary artery from an in vivo reconstructed geometry is presented. Finally, experimental measurements for growth under hypertension for rat carotid arteries are modelled.

The future of therapeutic myocardial angiogenesis

Despite improvements in its medical and surgical management, ischemic coronary disease remains responsible for significant morbidity, mortality, and economic burden in developed nations. Therapeutic myocardial angiogenesis is an attractive treatment option for patients with end-stage coronary disease who have failed percutaneous and surgical methods of revascularization. Over the past decade, our understanding of the biology of new blood vessel formation has improved significantly, and consequently, the use of growth factors to induce myocardial angiogenesis has been attempted in preclinical and clinical trials. Although growth factor therapy had demonstrated tremendous success in animal models, clinical trials have shown limited benefit in patients with coronary disease. Vascular endothelial growth factors and fibroblast growth factors are perhaps the most potent inducers of angiogenesis that have been used in animal models, and the only ones that have been used in clinical trials. This review outlines the biology of new vessel formation and the effects of these growth factors in the context of myocardial angiogenesis with an emphasis on the effects on the endothelium. It also provides a brief overview of delivery strategies and summarizes the preclinical and clinical evidence relating to exogenous growth factor delivery for myocardial angiogenesis. Lastly, we discuss the limitations and future challenges of angiogenic therapy.

Reactive oxygen species drives myocardial angiogenesis?

Neovascularization, the natural physiological process of formation of new blood vessels, is extremely important for ameliorating the function of the heart that undergoes ischemic stress. This process is potentially important for the treatment of ischemic heart and limb diseases, which includes formation of capillaries (angiogenesis) and collateral arteries. Ischemia or coronary artery occlusion induces vascular endothelial growth factor (VEGF) in the experimental rat myocardial infarction model, and this molecule encourages development of coronary collateral circulation and retention of the blood supply to the ischemic area. Restoration of the blood supply to the ischemic area prevents cardiomyocyte death and cardiac remodeling. Among the various triggers and enhancers of angiogenesis, hypoxic or ischemic preconditioning, as well as pharmacologic agents such as statin and resveratrol, have been identified as important stimuli for the induction of new vessel growth. It has already been demonstrated that the VEGF family and its receptor system is the fundamental regulator in the redox cell signaling of angiogenesis. This review article will focus on the role of reactive oxygen species in the process of myocardial angiogenesis.

Compensatory growth of coronary arterioles in postinfarcted heart: regional differences in DNA synthesis and growth factor/receptor expression patterns

Previous studies have not addressed regional differences in adaptive arteriolar growth in the surviving left ventricular (LV) myocardium after infarction in appropriately aged animals, namely middle-aged or older. Accordingly, we examined the adaptive postinfarction growth of arterioles in two distinct regions, i.e., the LV free wall (LVFW) and septum, of middle-aged rats. We induced a myocardial infarction (MI) in 12-mo-old rats to analyze 1) protein expression in VEGF/Flt-1/Flk-1 and angiopoietin (Ang)-1/Ang-2/Tie-2 systems, 2) the arteriolar DNA synthesis, 3) the extent of the arteriolar bed, and 4) the alteration in minimal coronary vascular resistance. In both regions, arteriolar DNA synthesis was activated between days 4 and 7 after MI. Whereas in the LVFW the degree of DNA synthesis declined between days 11 and 14 post-MI, it continued to rise in the septum, and at day 14, the percentage of the arterioles undergoing DNA synthesis was comparable in the LVFW and the septum (9.7 ± 1.6 and 7 ± 2.1%, respectively). Arteriolar DNA synthesis was mainly associated with upregulation of Ang-2 and Tie-2 in both LV regions. Although 4 wk after MI the arteriolar beds in the LVFW and the septum expanded to the size of sham-operated rats, this growth did not compensate for the greater minimal coronary vascular resistance in the former. Thus our findings suggest that 1) the dynamics in adaptive arteriolar growth were similar between the two regions, despite a delay in the septum; and 2) the perfusion deficit in post-MI rats cannot be accounted for by inadequate adaptive growth of arterioles.

Intravenous administration of vascular endothelial growth factor improves cardiac performance and inhibits cardiomyocyte apoptosis

This study investigated the effects of vascular endothelial growth factor (VEGF) intravenous administration on cardiac performance and cardiomyocyte apoptosis in a rat model of acute myocardial infarction. Left coronary artery ligation produced extensive myocardial infarction in 48 rats and sham operated in 24 animals. Twenty-four hours after surgery, the rats were randomized to receive VEGF165-heparin (treated group) or heparin-saline (control group) treatment. The sham-operated animals were also to receive VEGF165-heparin (sham group) treatment. VEGF165 (2 microg/ml) with heparin (50 U) or heparin-saline (50 U/ml) was administered daily via the tail vein for 7 and 14 days. Fifty-eight rats survived and included in the study. There were not significant effects of VEGF on hemodynamic parameters in sham animals. As compared with control animals at 9 days after ligation (with 10 rats for each group), rats treated with VEGF had significantly higher maximum rate of left ventricular pressure rise (+ dP/dtmax) or fall ( - dP/dtmax) and microvessel counts, and significantly lower left ventricular end-diastolic pressure (LVEDP) and infarct size. At 16 days after surgery (12, 7 and 9 rats in sham, control and treated groups; respectively), VEGF treatment significantly increased mean arterial pressure (MAP), left ventricular systolic pressure (LVSP), +/- dP/dtmax and microvessel counts, and significantly decreased LVEDP and infarct size. VEGF treatment significantly inhibited cardiomyocyte apoptosis and the expression of p53, Fas and Bax protein, and increased the expression of Bcl-2 protein in myocardium at 9 days after myocardial infarction.

Method for inducing the growth of new arteries in the myocardium

OBJECTIVE

The creation of new coronary arteries has long been an objective of cardiac research. I describe a method for creating new blood vessels in the myocardium of the left ventricular wall in animals.

METHODS

The myocardium was pierced by a fistula. Then a biodegradable hydrogel fiber with antithrombogenic and nonadhesive properties was inserted into the fistula with a venous catheter. Nine dogs were used. Three fibers were inserted in each heart, and two additional punctures were made and left empty as controls.

RESULTS

During absorption of the fiber, the luminal surface of the fistula became lined with endothelial cells and developed many openings to capillary blood vessels of the myocardium naturally. Three straight fibers were inserted so they intersected in the myocardium. They created a new branched vessel. The fistulas had connections to original coronary arteries and worked as new arteries to supply blood to the area where they were created.

CONCLUSIONS

It was possible to create new blood vessels in the myocardium in animals.

Fibroblast growth factor signals regulate a wave of Hedgehog activation that is essential for coronary vascular development

Myocardial infarction and ischemic heart disease are the leading cause of death in the industrial world. Therapies employed for treating these diseases are aimed at promoting increased blood flow to cardiac tissue. Pharmacological induction of new coronary growth has recently been explored, however, clinical trials with known proangiogenic factors have been disappointing. To identify novel therapeutic targets, we have explored signaling pathways that govern embryonic coronary development. Using a combination of genetically engineered mice and an organ culture system, we identified novel roles for fibroblast growth factor (FGF) and Hedgehog (HH) signaling in coronary vascular development. We show that FGF signals promote coronary growth indirectly by signaling to the cardiomyoblast through redundant function of Fgfr1 and Fgfr2. Myocardial FGF signaling triggers a wave of HH activation that is essential for vascular endothelial growth factor (Vegf)-A, Vegf-B, Vegf-C, and angiopoietin-2 (Ang2) expression. We demonstrate that HH is necessary for coronary vascular development and activation of HH signaling is sufficient to promote coronary growth and to rescue coronary defects due to loss of FGF signaling. These studies implicate HH signaling as an essential regulator of coronary vascular development and as a potential therapeutic target for coronary neovascularization. Consistent with this, activation of HH signaling in the adult heart leads to an increase in coronary vessel density.

Effect of maternal protein restriction in rats on cardiac fibrosis and capillarization in adulthood

This study examines the effect of maternal protein restriction in rats on levels of cardiac fibrosis, myocardial capillarization, and media:lumen ratio of intramyocardial arteries in adult offspring. Female Wistar Kyoto rats were fed either a normal protein diet (NPD; 20% casein) or a low-protein diet (LPD; 8.7% casein) during pregnancy and lactation. Female offspring (seven per group) were weaned at 4 wk of age and grown to adulthood. At 24 wk of age, the offspring were perfusion fixed. Cardiac fibrosis and media:lumen ratio of intramyocardial arterioles was assessed using image analysis and cardiac capillarization was stereologically investigated. Body weights at 2 and 24 wk of age were significantly reduced (31% and 8%, respectively) in the LPD offspring; however, heart size was not different at 24 wk. Importantly by adulthood, there was a significant 15% increase in left ventricular interstitial fibrosis in LPD offspring. There were no differences in levels of perivascular fibrosis, myocardial capillarization, or in the media:lumen ratio of intramyocardial arteries between groups. Because cardiac fibrosis is associated with impaired cardiac contractility and arrhythmia, our results suggest that induction of interstitial fibrosis may contribute to the increased cardiac disease in adult subjects who were exposed to an adverse intrauterine environment.

Improvement of contractility accompanies angiogenesis rather than arteriogenesis in chronic myocardial ischemia

INTRODUCTION

Growth factor therapy provides a therapeutic alternative for "no option" patients with coronary disease. Fibroblast Growth Factor-2 (FGF-2) predominantly stimulates angiogenesis, the growth of new capillaries, whereas Monocyte Chemoattractant Protein-1 (MCP-1) is considered an arteriogenic agent. We hypothesised a synergetic effect of FGF-2 and MCP-1 in ischemic myocardium.

METHODS

A severe coronary stenosis was created in pigs. After one week, chronic ischemia was confirmed by angiography, echocardiography, reduced ejection fraction, and increase of marker enzymes. FGF-2, MCP-1, both, or vector only were then injected intramyocardially as plasmid DNA in the impaired area. Regional contractility and number of capillaries and arterial vessels were evaluated after three months.

RESULTS

FGF-2, FGF-2+MCP-1, and vector, but not MCP-1 alone improved regional contractility at rest, whereas only FGF-2 alone ameliorated function under stress conditions. Angiogenesis in the ischemic area was stimulated by FGF-2 compared to MCP-1. In contrast, MCP-1 induced arteriogenesis relative to FGF-2.

CONCLUSION

Differences for vessel growth and regional function were apparent between FGF-2 and MCP-1. This contrast could allow the speculation that development of a flow reserve in chronically ischemic myocardium is linked to angiogenesis rather than to arteriogenesis. No additional benefits were seen following combined therapy.

Vascular tenascin‐C regulates cardiac endothelial phenotype and neovascularization

Microenvironmental cues mediate postnatal neovascularization via modulation of endothelial cell and bone marrow-derived endothelial progenitor cell (EPC) activity. Numerous signals regulate the activity of both of these cell types in response to vascular injury, which suggests that parallel mechanisms regulate angiogenesis in the vascular beds of both the heart and bone marrow. To identify mediators of such shared pathways, in vivo bone marrow/cardiac phage display biopanning was performed and led to the identification of tenascin-C as a candidate protein. Functionally, tenascin-C inhibits cardiac endothelial cell spreading and enhances migration in response to angiogenic growth factors. Analysis of human coronary thrombi revealed tenascin-C protein expression colocalized with the endothelial cell/EPC marker Tie-2 in intrathrombi vascular channels. Immunostains in the rodent heart demonstrated that tenascin-C also colocalizes with EPCs homing to sites of cardiac angiogenic induction. To determine the importance of tenascin-C in cardiac neovascularization, we used an established cardiac transplantation model and showed that unlike wild-type mice, tenascin-C-/- mice fail to vascularize cardiac allografts. This demonstrates for the first time that tenascin-C is essential for postnatal cardiac angiogenic function. Together, our data highlight the role of tenascin-C as a microenvironmental regulator of cardiac endothelial/EPC activity.

Flow inhibits inward remodeling in cannulated porcine small coronary arteries

The mechanisms of flow-induced vascular remodeling are poorly understood, especially in the coronary microcirculation. We hypothesized that application of flow in small coronary arteries in organoid culture would cause a nitric oxide (NO)-mediated dilation and inhibit inward remodeling. We developed an organoid culture setup to drive a flow through cannulated arterioles at constant luminal pressure via a pressure gradient between the pipettes. Subepicardial porcine coronary arterioles with diameter at full dilation and 60 mmHg ( D0) of 168 ± 10 (SE) μm were cannulated. Vessels treated with Nω-nitro-l-arginine (l-NNA) to block NO production and untreated vessels were pressurized at 60 mmHg for 3 days with and without flow. Endothelium-dependent dilation to 10−7M bradykinin was preserved in all groups. Tone was significantly less in vessels cultured under flow conditions in the last half of the culture period. Untreated and l-NNA-treated vessels regulated their diameter to yield shear stresses of 10.3 ± 2.1 and 14.0 ± 2.4 (SE) dyn/cm2, respectively (not significantly different). Without l-NNA, passive pressure-diameter curves at the end of the culture period revealed inward remodeling in the control group [to 92.3 ± 1.3% of D0(SE)] and no remodeling in the vessels cultured under flow conditions (100.2 ± 1.3% of D0); with l-NNA, the group subjected to flow showed inward remodeling (92.1 ± 2.5% of D0). We conclude that pressurized coronary resistance arteries could be maintained in culture for several days with flow. Vessels cultured under flow conditions remained more dilated when NO synthesis was blocked. Inward remodeling occurred in vessels cultured under no-flow conditions and was inhibited by flow-dependent NO synthesis.

Formation of the coronary vasculature during development

The formation of the coronary vasculature involves a series of carefully regulated temporal events that include vasculogenesis, angiogenesis, arteriogenesis and remodeling. This review explores these events, which begin with the migration of proepicardial cells to form the epicardium and end with postnatal growth and remodeling. Coronary endothelial, smooth muscle and fibroblast cells differentiate via epithelial-mesenchymal transformation; these cells delaminate from the epicardium. Following the formation of a tubular network by endothelial cells, an aortic ring of endothelial cells penetrates the aorta at the left and right aortic cusps to form the two ostia. Smooth muscle cell recruitment occurs rapidly and the coronary artery network begins forming as blood flow is established. Recent studies have identified a number of regulatory molecules that play key roles in epicardial formation and the transformation of its component cells into mesenchyme. Moreover, we are finally gaining some understanding regarding the interplay of angiogenic growth factors in the complex process of establishing the coronary vascular tree. Understanding coronary embryogenesis is important for interventions regarding adult cardiovascular diseases as well as those necessary to correct congenital defects.

Vascular Endothelial Growth Factor Is Required for Coronary Collateral Growth in the Rat

Background— The goal of this study was to determine whether the expression of vascular endothelial growth factor (VEGF) is critical for coronary collateral growth. Previous studies have provided an association between coronary collateral growth and VEGF, but none have allowed determination of a causal role.

Methods and Results— We measured coronary collateral growth in rats subjected to repetitive episodes of myocardial ischemia (RI; one 40-second occlusion every 20 minutes for 2 hours 40 minutes, followed by 5 hours 20 minutes of rest, with this 8-hour cycle repeated 3 times per day for 10 days). Collateral growth was measured from blood flow (radioactive microspheres), visualization of arterial-arterial anastomoses (x-ray micro-CT), and maintenance of function during complete coronary occlusion in 3 groups of animals: sham (received instrumentation but no RI), experimental (subjected to RI), and anti–vascular endothelial growth factor (RI+anti-VEGF 0.6 mg/100 g per day) to block the endogenous actions of VEGF. In the 3 groups, native collateral flow (measurement for RI or sham protocol) averaged 0.2 to 0.3 mL · min −1 · g −1 of tissue. In the sham group, collateral flow did not increase during the protocol. Collateral flow in the control RI group increased by ≈6-fold to 1.63 mL · min −1 · g −1 tissue, but in the anti-VEGF group, collateral flow did not increase after the RI protocol (0.22 mL · min −1 · g −1 ). In acute experiments, collateral flow was unchanged during vasodilation with dipyridamole, indicating the increases in collateral flow are due to collateral growth and not vasodilation. X-ray micro-CT analysis revealed a 3-fold increase (versus sham group) in the number of arterial-arterial anastomoses per heart after RI, which was prevented by treatment with anti-VEGF. The growth of the collateral circulation was functional in the RI group because complete coronary occlusion did not induce any untoward effects on hemodynamics or arrhythmias. In the sham or anti-VEGF groups, coronary occlusion at the end of the protocol induced many arrhythmias and deterioration of function.

Conclusions— From these results, we conclude that the expression of VEGF is critical to the growth of coronary collaterals.

Nicorandil Promotes Myocardial Capillary and Arteriolar Growth in the Failing Heart of Dahl Salt-Sensitive Hypertensive Rats

Long-term administration of vasodilators increases shear stress, which is thought to be important for vascular growth in the heart. Nicorandil, an activator of ATP-sensitive potassium channels with a nitrate-like action, is a potent vasodilator. We have now investigated the effects of nicorandil on vascular growth and gene expression in the failing heart of Dahl salt-sensitive (DS) hypertensive rats. DS rats fed a high-salt diet from 6 weeks of age develop concentric cardiac hypertrophy secondary to hypertension at 11 weeks, followed by heart failure at 18 weeks. DS rats on such a diet were treated with a nonantihypertensive oral dose of nicorandil (6 mg/kg per day) or vehicle from 11 to 18 weeks of age. Treatment of DS rats with nicorandil improved cardiac function and attenuated the development of heart failure. Myocardial capillary and arteriolar densities did not differ between vehicle-treated DS rats and age-matched controls. The abundance of mRNAs for endothelial NO synthase (eNOS), vascular endothelial growth factor (VEGF), the VEGF receptor Flt-1, and basic fibroblast growth factor (bFGF) in the myocardium was markedly reduced in vehicle-treated DS rats compared with controls. Treatment of DS rats with nicorandil greatly increased capillary and arteriolar densities and inhibited the downregulation of eNOS, VEGF, fms-like tyrosin kinase-1, and bFGF gene expression. This, nicorandil stimulates coronary capillary and arteriolar growth and thereby likely suppresses the development of heart failure in DS rats. Nicorandil may prove beneficial for the treatment of hypertensive heart failure as well as of ischemic heart disease.

Impaired coronary collateral vessel development in patients with metabolic syndrome

BACKGROUND

The development of coronary collateral vessels is the physiological response of myocardial tissue to hypoxia or ischemia, which results in an increase in blood supply to the tissue. However, a lack of collateral vessels or the presence of poor collateralization in some patients despite the presence of significant coronary stenosis or obstruction and evidence of myocardial ischemia suggest that some other factors may affect the development of collateral circulation. In the present study we aimed to evaluate coronary collateral circulation in patients with metabolic syndrome with advanced coronary artery disease and compare the results with those of patients without metabolic syndrome.

METHOD

The study population comprised 102 patients with metabolic syndrome and advanced coronary artery disease (>or=90% diameter stenosis in at least one major epicardial coronary artery) and 102 control participants without metabolic syndrome who also had >or=90% diameter stenosis in at least one major epicardial coronary artery. The diagnosis of metabolic syndrome was based on the National Cholesterol Education Program Adult Treatment Panel III clinical definition. Coronary collateral vessels were analysed according to the Cohen and Rentrop grading system. Both groups were also divided into two additional groups according to the Rentrop collateral score as patients with poor collateral circulation (Rentrop score 0-1) and good collateral circulation (Rentrop score 2-3).

RESULTS

The mean Rentrop collateral score for patients with metabolic syndrome was significantly lower than for those without metabolic syndrome (1.38+/-0.79 compared with 1.99+/-1.08, respectively, P<0.001). When two groups were compared with respect to poor and good collateral circulation, poor collateral circulation was found to be significantly higher in the metabolic syndrome group (70% compared with 32%, respectively, P<0.001). Moreover, multivariate logistic regression analysis revealed a significant relationship between poor collateral circulation and metabolic syndrome (odds ratio=4.29, 95% confidence interval=1.73-10.69, P=0.002).

CONCLUSION

We have shown for the first time that the development of coronary collateral vessels is poorer in patients with metabolic syndrome with advanced ischemic heart disease than in control participants without metabolic syndrome. Thus, it can be suggested that metabolic syndrome is one of the significant factors affecting the development of coronary collateral vessels adversely.

Hesr, a Mediator of the Notch Signaling, Functions in Heart and Vessel Development

Hesr genes are members of the hairy and enhancer of split-related (hesr) gene family of basic helix-loop-helix-type transcriptional repressors. hesr genes have been implicated in cardiovascular development as the primary targets of Notch signaling. Functional analysis of hesr2 knockout mice revealed abnormal cardiac hemodynamics, such as atrioventricular valve regurgitation and reduced left ventricular systolic function, caused by hypoplastic AV valves and abnormal cardiomyocytes. Recent evidence demonstrates that hesr1 and hesr2 function redundantly in epithelial-to-mesenchymal transformation during atrioventricular valve formation and maintenance of trabecular cells in the heart ventricles, and in arterial-venous differentiation of blood vessels. This review highlights the many functions of the hesr gene family in heart and vessel development.

STAT3-Mediated Activation of Myocardial Capillary Growth

Proper perfusion and vessel integrity are key requisites for myocardial homeostasis. In this regard, myocardial angiogenesis occurs in physiologic and pathologic conditions. Failure in this process and the resulting deficient oxygen supply induce loss and degeneration of cardiomyocytes, atrophy, and interstitial fibrosis and are viewed as a primary cause of myocardial dysfunction and heart failure. In this review, signal transducer and activator of transcription 3 (STAT3) is highlighted as a regulator of proangiogenic circuits promoting vessel formation in the adult heart under physiologic and pathophysiologic conditions. Specifically, STAT3 regulates proangiogenic vascular endothelial growth factor (VEGF) expression and activity in the postnatal heart and suppresses an antiangiogenic and profibrotic gene program by controlling autocrine and paracrine circuits. In addition, signaling through STAT3 represents a necessary survival pathway for cardiomyocytes and endothelial cells and seems to promote cytokine-mediated cardiac angiogenesis. In contrast, STAT3 seems not to be required for differentiation processes of embryonic or adult endothelial progenitor cells. In summary, the properly timed expression and activation of STAT3 play a critical role on cardiac angiogenesis and involve the subtle control of paracrine and autocrine mechanisms regulating angiogenic circuits and survival pathways of cardiomyocytes and endothelial cells.