Transforming Growth Factor β–SMAD2 Signaling Regulates Aortic Arch Innervation and Development

Molecular Pathways and Animal Models of Semilunar Valve and Aortic Arch Anomalies

The great arteries of the vertebrate carry blood from the heart to the systemic circulation and are derived from the pharyngeal arch arteries. In higher vertebrates, the pharyngeal arch arteries are a symmetrical series of blood vessels that rapidly remodel during development to become the asymmetric aortic arch arteries carrying oxygenated blood from the left ventricle via the outflow tract. At the base of the aorta, as well as the pulmonary trunk, are the semilunar valves. These valves each have three leaflets and prevent the backflow of blood into the heart. During development, the process of aortic arch and valve formation may go wrong, resulting in cardiovascular defects, and these may, at least in part, be caused by genetic mutations. In this chapter, we will review models harboring genetic mutations that result in cardiovascular defects affecting the great arteries and the semilunar valves.

Modeling cardiac fibroblast heterogeneity from human pluripotent stem cell-derived epicardial cells

Cardiac fibroblasts play an essential role in the development of the heart and are implicated in disease progression in the context of fibrosis and regeneration. Here, we establish a simple organoid culture platform using human pluripotent stem cell-derived epicardial cells and ventricular cardiomyocytes to study the development, maturation, and heterogeneity of cardiac fibroblasts under normal conditions and following treatment with pathological stimuli. We demonstrate that this system models the early interactions between epicardial cells and cardiomyocytes to generate a population of fibroblasts that recapitulates many aspects of fibroblast behavior in vivo, including changes associated with maturation and in response to pathological stimuli associated with cardiac injury. Using single cell transcriptomics, we show that the hPSC-derived organoid fibroblast population displays a high degree of heterogeneity that approximates the heterogeneity of populations in both the normal and diseased human heart. Additionally, we identify a unique subpopulation of fibroblasts possessing reparative features previously characterized in the hearts of model organisms. Taken together, our system recapitulates many aspects of human cardiac fibroblast specification, development, and maturation, providing a platform to investigate the role of these cells in human cardiovascular development and disease.

Smooth Muscle Heterogeneity and Plasticity in Health and Aortic Aneurysmal Disease

Vascular smooth muscle cells (VSMCs) are the predominant cell type in the medial layer of the aorta, which plays a critical role in the maintenance of aortic wall integrity. VSMCs have been suggested to have contractile and synthetic phenotypes and undergo phenotypic switching to contribute to the deteriorating aortic wall structure. Recently, the unprecedented heterogeneity and diversity of VSMCs and their complex relationship to aortic aneurysms (AAs) have been revealed by high-resolution research methods, such as lineage tracing and single-cell RNA sequencing. The aortic wall consists of VSMCs from different embryonic origins that respond unevenly to genetic defects that directly or indirectly regulate VSMC contractile phenotype. This difference predisposes to hereditary AAs in the aortic root and ascending aorta. Several VSMC phenotypes with different functions, for example, secreting VSMCs, proliferative VSMCs, mesenchymal stem cell-like VSMCs, immune-related VSMCs, proinflammatory VSMCs, senescent VSMCs, and stressed VSMCs are identified in non-hereditary AAs. The transformation of VSMCs into different phenotypes is an adaptive response to deleterious stimuli but can also trigger pathological remodeling that exacerbates the pathogenesis and development of AAs. This review is intended to contribute to the understanding of VSMC diversity in health and aneurysmal diseases. Papers that give an update on VSMC phenotype diversity in health and aneurysmal disease are summarized and recent insights on the role of VSMCs in AAs are discussed.

Cardiac Neural Crest

Cardiac neural crest (CNC) cells are pluripotent cells derived from the dorsal neural tube that migrate and contribute to the remodeling of pharyngeal arch arteries and septation of the cardiac outflow tract (OFT). Numerous molecular cascades regulate the induction, specification, delamination, and migration of the CNC. Extensive analyses of the CNC ranging from chick ablation models to molecular biology studies have explored the mechanisms of heart development and disease, particularly involving the OFT and aortic arch (AA) system. Recent studies focus more on reciprocal signaling between the CNC and cells originated from the second heart field (SHF), which are essential for the development of the OFT myocardium, providing new insights into the molecular mechanisms underlying congenital heart diseases (CHDs) and some human syndromes.

Importance of endothelial Hey1 expression for thoracic great vessel development and its distal enhancer for Notch-dependent endothelial transcription

Thoracic great vessels such as the aorta and subclavian arteries are formed through dynamic remodeling of embryonic pharyngeal arch arteries (PAAs). Previous work has shown that loss of a basic helix-loop-helix transcription factor Hey1 in mice causes abnormal fourth PAA development and lethal great vessel anomalies resembling congenital malformations in humans. However, how Hey1 mediates vascular formation remains unclear. In this study, we revealed that Hey1 in vascular endothelial cells, but not in smooth muscle cells, played essential roles for PAA development and great vessel morphogenesis in mouse embryos. Tek-Cre-mediated Hey1 deletion in endothelial cells affected endothelial tube formation and smooth muscle differentiation in embryonic fourth PAAs and resulted in interruption of the aortic arch and other great vessel malformations. Cell specificity and signal responsiveness of Hey1 expression were controlled through multiple cis-regulatory regions. We found two distal genomic regions that had enhancer activity in endothelial cells and in the pharyngeal epithelium and somites, respectively. The novel endothelial enhancer was conserved across species and was specific to large-caliber arteries. Its transcriptional activity was regulated by Notch signaling in vitro and in vivo, but not by ALK1 signaling and other transcription factors implicated in endothelial cell specificity. The distal endothelial enhancer was not essential for basal Hey1 expression in mouse embryos but may likely serve for Notch-dependent transcriptional control in endothelial cells together with the proximal regulatory region. These findings help in understanding the significance and regulation of endothelial Hey1 as a mediator of multiple signaling pathways in embryonic vascular formation.

Systematic Analysis of the Smooth Muscle Wall Phenotype of the Pharyngeal Arch Arteries During Their Reorganization into the Great Vessels and Its Association with Hemodynamics

Early outflow morphogenesis is a critical event in cardiac development. Understanding mechanical and molecular based morphogenetic relationships at early stages of cardiogenesis is essential for the advancement of cardiovascular technology related to congenital heart defects. In this study, we pair molecular changes in pharyngeal arch artery (PAA) vascular smooth muscle cells (VSMCs) with hemodynamic changes over the course of the same period. We focus on Hamburger Hamilton stage 24-36 chick embryos, using both Doppler ultrasound and histological sections to phenotype PAA VSMCs, and establish a relationship between hemodynamics and PAA composition. Our findings show that PAA VSMCs transition through a synthetic, intermediate, and contractile phenotype over time. Wall shear stress magnitude per arch varies throughout development. Despite distinct hemodynamic and fractional expression trends, no strong correlation was found between the two, indicating that WSS magnitude is not the main driver of PAA wall remodeling and maturation. While WSS magnitude was not found to be a major driver, this work provides a basic framework for investigating relationships between hemodynamic forces and tunica media during a critical period of development. Anat Rec, 302:153-162, 2019. © 2018 Wiley Periodicals, Inc.

Asymmetry in Mechanosensitive Gene Expression during Aortic Arch Morphogenesis

Embryonic aortic arches (AA) are initially bilaterally paired, transitional vessels and failures in remodeling based on hemodynamic and growth-related adaptations cause a spectrum of congenital heart disease (CHD) anatomies. Identifying regulatory mechanisms and cross-talk between the genetic elements of these vessels are critical to understand the ethiology of CHD and refine predictive computational models. This study aims to screen expression profiles of fundamental biological pathways in AA at early stages of chick embryo morphogenesis and correlate them with our current understanding of growth and mechanical loading. Reverse transcription-quantitative PCR (RT-qPCR) was followed by correlation and novel peak expression analyses to compare the behaviour and activation period of the genes. Available protein networks were also integrated to investigate the interactions between molecules and highlight major hierarchies. Only wall shear stress (WSS) and growth-correlated expression patterns were investigated. Effect of WSS was seen directly on angiogenesis as well on structural and apoptosis-related genes. Our time-resolved network suggested that WSS-correlated genes coordinate the activity of critical growth factors. Moreover, differential gene expression of left and right AA might be an indicator of subsequent asymmetric morphogenesis. These findings may further our understanding of the complex processes of cardiac morphogenesis and errors resulting in CHD.

Incidental finding of pulmonary arterial sling during patent ductus arteriosus surgery in a patient with Mowat-Wilson syndrome

Mowat-Wilson syndrome is a genetic condition due to a mutation in the ZEB2 gene; it affects many systems including the cardiovascular system. The pulmonary arterial sling originates from a failure of development of the proximal portion of the left sixth aortic arch, resulting in an anomalous left pulmonary artery origin from the posterior wall of the right pulmonary artery and the left pulmonary artery crossing to the left lung between the trachea and the oesophagus. We present a 4-month-old infant with Mowat-Wilson syndrome and left pulmonary arterial sling, and discuss the association of these two rare conditions. Pulmonary arterial sling is significantly more frequent in patients with Mowat-Wilson syndrome than in the general population.

Patent ductus arteriosus coexisting with a left brachiocephalic artery originating from the descending aorta: A case report

RATIONAL

Patent ductus arteriosus (PDA) and a coexisting left brachiocephalic artery originating from the descending aorta is an extremely rare anomaly of unknown etiology.

PATIENT CONCERNS

Herein we report a 3-year-old female who was found to have this condition during intervention process to close PDA.

DIAGNOSIS

The patient was diagnosed with PDA coexisting with left brachiocephalic artery through angiography.

INTERVENTION

Intervention involved transcatheter closure of the pulmonary side of PDA with coils.

OUTCOMES

At 6-months follow up, the patient was well, with no symptoms and normal flow through the left carotid artery.

LESSONS

PDA coexisting with left brachiocephalic artery originating from the descending aorta is a very rare anomaly. When this variety of PDA is closed, it is important to avoid affecting the blood flow in the left brachiocephalic trunk. For this reason, closure on the side of the pulmonary artery may be the best solution.

Pharyngeal arch artery defects and lethal malformations of the aortic arch and its branches in mice deficient for the Hrt1/Hey1 transcription factor

The aortic arch and major branch arteries are formed from the three pairs of pharyngeal arch arteries (PAAs) during embryonic development. Their morphological defects are clinically observed as isolated diseases, as a part of complicated cardiovascular anomalies or as a manifestation of multi-organ syndromes such as 22q11.2 deletion syndrome. Although numerous genes have been implicated in PAA formation and remodeling, detailed mechanisms remain poorly understood. Here we report that the mice null for Hrt1/Hey1, a gene encoding a downstream transcription factor of Notch and ALK1 signaling pathways, show perinatal lethality on the C57BL/6N, C57BL/6N × C57BL/6J or C57BL/6N × 129X1/SvJ background. Hrt1/Hey1 null embryos display abnormal development of the fourth PAA (PAA4), which results in congenital vascular defects including right-sided aortic arch, interruption of the aortic arch and aberrant origin of the right subclavian artery. Impaired vessel formation occurs randomly in PAA4 of Hrt1/Hey1 null embryos, which likely causes the variability of congenital malformations. Endothelial cells in PAA4 of null embryos differentiate normally but are structurally disorganized at embryonic day 10.5 and 11.5. Vascular smooth muscle cells are nearly absent in the structurally-defective PAA4, despite the appropriate migration of cardiac neural crest cells into the fourth pharyngeal arches. Endothelial expression of Jag1 is down-regulated in the structurally-defective PAA4 of null embryos, which may be one of the mechanisms underlying the suppression of vascular smooth muscle cell differentiation. While the direct downstream phenomena of the Hrt1/Hey1 deficiency remain to be clarified, we suggest that Hrt1/Hey1-dependent transcriptional regulation has an important role in PAA formation during embryonic development.

Growth and hemodynamics after early embryonic aortic arch occlusion

The majority of severe clinically significant forms of congenital heart disease (CHD) are associated with great artery lesions, including hypoplastic, double, right or interrupted aortic arch morphologies. While fetal and neonatal interventions are advancing, their potential ability to restore cardiac function, optimal timing, location, and intensity required for intervention remain largely unknown. Here, we combine computational fluid dynamics (CFD) simulations with in vivo experiments to test how individual pharyngeal arch artery hemodynamics alter as a result of local interventions obstructing individual arch artery flow. Simulated isolated occlusions within each pharyngeal arch artery were created with image-derived three-dimensional (3D) reconstructions of normal chick pharyngeal arch anatomy at Hamburger-Hamilton (HH) developmental stages HH18 and HH24. Acute flow redistributions were then computed using in vivo measured subject-specific aortic sinus inflow velocity profiles. A kinematic vascular growth-rendering algorithm was then developed and implemented to test the role of changing local wall shear stress patterns in downstream 3D morphogenesis of arch arteries. CFD simulations predicted that altered pressure gradients and flow redistributions were most sensitive to occlusion of the IVth arches. To evaluate these simulations experimentally, a novel in vivo experimental model of pharyngeal arch occlusion was developed and implemented using two-photon microscopy-guided femtosecond laser-based photodisruption surgery. The right IVth arch was occluded at HH18, and resulting diameter changes were followed for up to 24 h. Pharyngeal arch diameter responses to acute hemodynamic changes were predicted qualitatively but poorly quantitatively. Chronic growth and adaptation to hemodynamic changes, however, were predicted in a subset of arches. Our findings suggest that this complex biodynamic process is governed through more complex forms of mechanobiological vascular growth rules. Other factors in addition to wall shear stress or more complex WSS rules are likely important in the long-term arterial growth and patterning. Combination in silico/experimental platforms are essential for accelerating our understanding and prediction of consequences from embryonic/fetal cardiovascular occlusions and lay the foundation for noninvasive methods to guide CHD diagnosis and fetal intervention.

α5 and αv integrins cooperate to regulate vascular smooth muscle and neural crest functions in vivo

The RGD-binding α5 and αv integrins have been shown to be key regulators of vascular smooth muscle cell (vSMC) function in vitro. However, their role on vSMCs during vascular development in vivo remains unclear. To address this issue, we have generated mice that lack α5, αv or both α5 and αv integrins on their vSMCs, using the SM22α-Cre transgenic mouse line. To our surprise, neither α5 nor αv mutants displayed any obvious vascular defects during embryonic development. By contrast, mice lacking both α5 and αv integrins developed interrupted aortic arches, large brachiocephalic/carotid artery aneurysms and cardiac septation defects, but developed extensive and apparently normal vasculature in the skin. Cardiovascular defects were also found, along with cleft palates and ectopically located thymi, in Wnt1-Cre α5/αv mutants, suggesting that α5 and αv cooperate on neural crest-derived cells to control the remodelling of the pharyngeal arches and the septation of the heart and outflow tract. Analysis of cultured α5/αv-deficient vSMCs suggests that this is achieved, at least in part, through proper assembly of RGD-containing extracellular matrix proteins and the correct incorporation and activation of latent TGF-β.

Heterogeneity in the Segmental Development of the Aortic Tree: Impact on Management of Genetically Triggered Aortic Aneurysms

An extensive search of the medical literature examining the development of the thoracic aortic tree reveals that the thoracic aorta does not develop as one unit or in one stage: the oldest part of the thoracic aorta is the descending aorta with the aortic arch being the second oldest, developing under influence from the neural crest cell. Following in chronological order are the proximal ascending aorta and aortic root, which develop from a conotruncal origin. Different areas of the thoracic aorta develop under the influence of different gene sets. These parts develop from different cell lineages: the aortic root (the conotruncus), developing from the mesoderm; the ascending aorta and aortic arch, developing from the neural crest cells; and the descending aorta from the mesoderm. Findings illustrate that the thoracic aorta is not a single entity, in developmental terms. It develops from three or four distinct areas, at different stages of embryonic life, and under different sets of genes and signaling pathways. Genetically triggered thoracic aortic aneurysms are not a monolithic group but rather share a multi-genetic origin. Identification of therapeutic targets should be based on the predilection of certain genes to cause aneurysmal disease in specific aortic segments.

The functional diversity of essential genes required for mammalian cardiac development

Genes required for an organism to develop to maturity (for which no other gene can compensate) are considered essential. The continuing functional annotation of the mouse genome has enabled the identification of many essential genes required for specific developmental processes including cardiac development. Patterns are now emerging regarding the functional nature of genes required at specific points throughout gestation. Essential genes required for development beyond cardiac progenitor cell migration and induction include a small and functionally homogenous group encoding transcription factors, ligands and receptors. Actions of core cardiogenic transcription factors from the Gata, Nkx, Mef, Hand, and Tbx families trigger a marked expansion in the functional diversity of essential genes from midgestation onwards. As the embryo grows in size and complexity, genes required to maintain a functional heartbeat and to provide muscular strength and regulate blood flow are well represented. These essential genes regulate further specialization and polarization of cell types along with proliferative, migratory, adhesive, contractile, and structural processes. The identification of patterns regarding the functional nature of essential genes across numerous developmental systems may aid prediction of further essential genes and those important to development and/or progression of disease. genesis 52:713–737, 2014.

Bicuspid aortic valve morphology and associated cardiovascular abnormalities in fetal Turner syndrome: a pathomorphological study

INTRODUCTION

Bicuspid aortic valve (BAV) is common in Turner syndrome (TS). In adult TS, 82-95% of BAVs have fusion of the right and left coronary leaflets. Data in fetal stages are scarce. The purpose of this study was to gain insight into aortic valve morphology and associated cardiovascular abnormalities in a fetal TS cohort with adverse outcome early in development.

MATERIAL AND METHODS

We studied post-mortem heart specimens of 36 TS fetuses and 1 TS newborn.

RESULTS

BAV was present in 28 (76%) hearts. BAVs showed fusion of the right and left coronary leaflet (type 1 BAV) in 61%, and fusion of the right coronary and non-coronary leaflet (type 2 BAV) in 39%. There were no significant differences in occurrence of additional cardiovascular abnormalities between type 1 and type 2 BAV. However, all type 2 BAV hearts showed ascending aorta hypoplasia and tubular hypoplasia of the B segment, as opposed to only 55 and 64% of type 1 BAV hearts, respectively.

DISCUSSION

The proportion of type 2 BAV seems higher in TS fetuses than in adults. Fetal type 2 BAV hearts all had severe aortic pathology, possibly contributing to a worse prognosis of type 2 than type 1 BAV in TS.

Systematic analysis of the development of the ductus venosus in wild type mouse and human embryos

BACKGROUND

Doppler flow velocities of the ductus venosus are increasingly used to assess fetal increased nuchal translucency, growth-restriction and monochorionic twins, and might contribute to screening for cardiac defects. It is disputed whether a sphincter at the ductus venosus inlet actively regulates blood flow.

AIMS

This study aims to define the morphogenesis of the developing mouse and human ductus venosus and to address the existence of a sphincter.

STUDY DESIGN

The presence of endothelium, smooth muscle, elastic fibers and nerves in the ductus venosus of E10.5-15.5 mouse embryos and in three corresponding human embryos (CS16, CS19 and CS23) was examined using immunohistochemistry. Three-dimensional reconstructions of the ductus venosus of E11.5-15.5 mouse and CS14-23 human embryos were generated and examined.

RESULTS

The ductus venosus lumen was narrowed from ventral-caudal to dorsal-cranial in E13.5-15.5 mouse and CS16-23 human embryos. Mouse embryos showed positive endothelial Pecam1 expression from E11.5-15.5 and smooth muscle actin staining in the ventral-caudal part of the ductus venosus from E12.5-15.5. At all developmental stages, elastic fiber and nerve marker expression was not detected in the ductus venosus (Fig. 2). In human embryos endothelial Pecam1 and smooth muscle actin expression was found in the ductus venosus from CS16 and CS19 onwards. Elastic fiber and nerve marker expression was not detected in all stages (Fig. 4). Morphogenesis and staining results of the ductus venosus were similar in both species.

CONCLUSIONS

The ductus venosus lacks a sphincter at its inlet as no accumulation of smooth muscle cells, elastic fibers or nerve innervation was found in mouse embryos from E11.5-15.5 and in human embryos from CS14-23.

Requirement for integrin-linked kinase in neural crest migration and differentiation and outflow tract morphogenesis

BACKGROUND

Neural crest defects lead to congenital heart disease involving outflow tract malformation. Integrin-linked-kinase (ILK) plays important roles in multiple cellular processes and embryogenesis. ILK is expressed in the neural crest, but its role in neural crest and outflow tract morphogenesis remains unknown.

RESULTS

We ablated ILK specifically in the neural crest using the Wnt1-Cre transgene. ILK ablation resulted in abnormal migration and overpopulation of neural crest cells in the pharyngeal arches and outflow tract and a significant reduction in the expression of neural cell adhesion molecule (NCAM) and extracellular matrix components. ILK mutant embryos exhibited an enlarged common arterial trunk and ventricular septal defect. Reduced smooth muscle differentiation, but increased ossification and neurogenesis/innervation were observed in ILK mutant outflow tract that may partly be due to reduced transforming growth factor β2 (TGFβ2) but increased bone morphogenetic protein (BMP) signaling. Consistent with these observations, microarray analysis of fluorescence-activated cell sorting (FACS)-sorted neural crest cells revealed reduced expression of genes associated with muscle differentiation, but increased expression of genes of neurogenesis and osteogenesis.

CONCLUSIONS

Our results demonstrate that ILK plays essential roles in neural crest and outflow tract development by mediating complex crosstalk between cell matrix and multiple signaling pathways. Changes in these pathways may collectively result in the unique neural crest and outflow tract phenotypes observed in ILK mutants.

Smad2 and myocardin-related transcription factor B cooperatively regulate vascular smooth muscle differentiation from neural crest cells

RATIONALE

Vascular smooth muscle cell (VSMC) differentiation from neural crest cells (NCCs) is critical for cardiovascular development, but the mechanisms remain largely unknown.

OBJECTIVE

Transforming growth factor-β (TGF-β) function in VSMC differentiation from NCCs is controversial. Therefore, we determined the role and mechanism of a TGF-β downstream signaling intermediate Smad2 in NCC differentiation to VSMCs.

METHODS AND RESULTS

By using Cre/loxP system, we generated a NCC tissue-specific Smad2 knockout mouse model and found that Smad2 deletion resulted in defective NCC differentiation to VSMCs in aortic arch arteries during embryonic development and caused vessel wall abnormality in adult carotid arteries where the VSMCs are derived from NCCs. The abnormalities included 1 layer of VSMCs missing in the media of the arteries with distorted and thinner elastic lamina, leading to a thinner vessel wall compared with wild-type vessel. Mechanistically, Smad2 interacted with myocardin-related transcription factor B (MRTFB) to regulate VSMC marker gene expression. Smad2 was required for TGF-β-induced MRTFB nuclear translocation, whereas MRTFB enhanced Smad2 binding to VSMC marker promoter. Furthermore, we found that Smad2, but not Smad3, was a progenitor-specific transcription factor mediating TGF-β-induced VSMC differentiation from NCCs. Smad2 also seemed to be involved in determining the physiological differences between NCC-derived and mesoderm-derived VSMCs.

CONCLUSIONS

Smad2 is an important factor in regulating progenitor-specific VSMC development and physiological differences between NCC-derived and mesoderm-derived VSMCs.

Critical transitions in early embryonic aortic arch patterning and hemodynamics

Transformation from the bilaterally symmetric embryonic aortic arches to the mature great vessels is a complex morphogenetic process, requiring both vasculogenic and angiogenic mechanisms. Early aortic arch development occurs simultaneously with rapid changes in pulsatile blood flow, ventricular function, and downstream impedance in both invertebrate and vertebrate species. These dynamic biomechanical environmental landscapes provide critical epigenetic cues for vascular growth and remodeling. In our previous work, we examined hemodynamic loading and aortic arch growth in the chick embryo at Hamburger-Hamilton stages 18 and 24. We provided the first quantitative correlation between wall shear stress (WSS) and aortic arch diameter in the developing embryo, and observed that these two stages contained different aortic arch patterns with no inter-embryo variation. In the present study, we investigate these biomechanical events in the intermediate stage 21 to determine insights into this critical transition. We performed fluorescent dye microinjections to identify aortic arch patterns and measured diameters using both injection recordings and high-resolution optical coherence tomography. Flow and WSS were quantified with 3D computational fluid dynamics (CFD). Dye injections revealed that the transition in aortic arch pattern is not a uniform process and multiple configurations were documented at stage 21. CFD analysis showed that WSS is substantially elevated compared to both the previous (stage 18) and subsequent (stage 24) developmental time-points. These results demonstrate that acute increases in WSS are followed by a period of vascular remodeling to restore normative hemodynamic loading. Fluctuations in blood flow are one possible mechanism that impacts the timing of events such as aortic arch regression and generation, leading to the variable configurations at stage 21. Aortic arch variations noted during normal rapid vascular remodeling at stage 21 identify a temporal window of increased vulnerability to aberrant aortic arch morphogenesis with the potential for profound effects on subsequent cardiovascular morphogenesis.

Tbx1 genetically interacts with the transforming growth factor-β/bone morphogenetic protein inhibitor Smad7 during great vessel remodeling

RATIONALE

Growth and remodeling of the pharyngeal arch arteries are vital for the development of a mature great vessel system. Dysmorphogenesis of the fourth arch arteries can result in interruption of the aortic arch type B, typically found in DiGeorge syndrome. Tbx1 haploinsufficient embryos, which model DiGeorge syndrome, display fourth arch artery defects during formation of the vessels. Recovery from such defects is a documented yet unexplained phenotype in Tbx1 haploinsufficiency.

OBJECTIVE

To understand the nature of fourth arch artery growth recovery in Tbx1 haploinsufficiency and its underlying genetic control.

METHODS AND RESULTS

We categorized vessel phenotypes of Tbx1 heterozygotes as hypoplastic or aplastic at the conclusion of pharyngeal artery formation and compared these against the frequency of vessel defects scored at the end of great vessel development. The frequency of hypoplastic vessels decreased during embryogenesis, whereas no reduction of vessel aplasia was seen, implying recovery is attributable to remodeling of hypoplastic vessels. We showed that Smad7, an inhibitory Smad within the transforming growth factor-β pathway, is regulated by Tbx1, is required for arch artery remodeling, and genetically interacts with Tbx1 in this process. Tbx1 and Tbx1;Smad7 haploinsufficiency affected several remodeling processes; however, concurrent haploinsufficiency particularly impacted on the earliest stage of vascular smooth muscle cell vessel coverage and subsequent fibronectin deposition. Conditional reconstitution of Smad7 with a Tbx1Cre driver indicated that the interaction between the 2 genes is cell autonomous.

CONCLUSIONS

Tbx1 acts upstream of Smad7 controlling vascular smooth muscle and extracellular matrix investment of the fourth arch artery.

Myocardin-like protein 2 regulates TGFβ signaling in embryonic stem cells and the developing vasculature

The molecular mechanisms that regulate and coordinate signaling between the extracellular matrix (ECM) and cells contributing to the developing vasculature are complex and poorly understood. Myocardin-like protein 2 (MKL2) is a transcriptional co-activator that in response to RhoA and cytoskeletal actin signals physically associates with serum response factor (SRF), activating a subset of SRF-regulated genes. We now report the discovery of a previously undescribed MKL2/TGFβ signaling pathway in embryonic stem (ES) cells that is required for maturation and stabilization of the embryonic vasculature. Mkl2(-/-) null embryos exhibit profound derangements in the tunica media of select arteries and arterial beds, which leads to aneurysmal dilation, dissection and hemorrhage. Remarkably, TGFβ expression, TGFβ signaling and TGFβ-regulated genes encoding ECM are downregulated in Mkl2(-/-) ES cells and the vasculature of Mkl2(-/-) embryos. The gene encoding TGFβ2, the predominant TGFβ isoform expressed in vascular smooth muscle cells and embryonic vasculature, is activated directly via binding of an MKL2/SRF protein complex to a conserved CArG box in the TGFβ2 promoter. Moreover, Mkl2(-/-) ES cells exhibit derangements in cytoskeletal organization, cell adhesion and expression of ECM that are rescued by forced expression of TGFβ2. Taken together, these data demonstrate that MKL2 regulates a conserved TGF-β signaling pathway that is required for angiogenesis and ultimately embryonic survival.

Cellular decisions in cardiac outflow tract and coronary development: an act by VEGF and NOTCH

Congenital cardiac abnormalities are, due to their relatively high frequency and severe impact on quality of life, an important focus in cardiovascular research. Recently, various human studies have revealed a high coincidence of VEGF and NOTCH polymorphisms with cardiovascular outflow tract anomalies, such as bicuspid aortic valves and Tetralogy of Fallot, next to predisposition for cardiovascular pathologies, including atherosclerosis and aortic valve calcification. This genetic association between VEGF/NOTCH mutations and congenital cardiovascular defects in humans has been supported by substantial proof from animal models, revealing interaction of both pathways in cellular processes that are crucial for cardiac development. This review focuses on the role of VEGF and NOTCH signaling and their interplay in cardiogenesis with special interest to coronary and outflow tract development. An overview of the association between congenital malformations and VEGF/NOTCH polymorphisms in humans will be discussed along with their potential mechanisms and processes as revealed by transgenic mouse models. The molecular and cellular interaction of VEGF and subsequent Notch-signaling in these processes will be highlighted.

The neural crest in cardiac congenital anomalies

This review discusses the function of neural crest as they relate to cardiovascular defects. The cardiac neural crest cells are a subpopulation of cranial neural crest discovered nearly 30 years ago by ablation of premigratory neural crest. The cardiac neural crest cells are necessary for normal cardiovascular development. We begin with a description of the crest cells in normal development, including their function in remodeling the pharyngeal arch arteries, outflow tract septation, valvulogenesis, and development of the cardiac conduction system. The cells are also responsible for modulating signaling in the caudal pharynx, including the second heart field. Many of the molecular pathways that are known to influence specification, migration, patterning and final targeting of the cardiac neural crest cells are reviewed. The cardiac neural crest cells play a critical role in the pathogenesis of various human cardiocraniofacial syndromes such as DiGeorge, Velocardiofacial, CHARGE, Fetal Alcohol, Alagille, LEOPARD, and Noonan syndromes, as well as Retinoic Acid Embryopathy. The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but are involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. Thus many of the human syndromes linking defects in the heart, face and brain can be better understood when considered within the context of a single cardiocraniofacial developmental module with the neural crest being a key cell type that interconnects the regions.

TGFβ signaling and congenital heart disease: Insights from mouse studies

Transforming growth factor β (TGFβ) regulates one of the major signaling pathways that control tissue morphogenesis. In vitro experiments using heart explants indicated the importance of this signaling pathway for the generation of cushion mesenchymal cells, which ultimately contribute to the valves and septa of the mature heart. Recent advances in mouse genetics have enabled in vivo investigation into the roles of individual ligands, receptors, and coreceptors of this pathway, including investigation of the tissue specificity of these roles in heart development. This work has revealed that (1) cushion mesenchyme can form in the absence of TGFβ signaling, although mesenchymal cell numbers may be misregulated; (2) TGFβ signaling is essential for correct remodeling of the cushions, particularly those of the outflow tract; (3) TGFβ signaling also has a role in ensuring accurate remodeling of the pharyngeal arch arteries to form the mature aortic arch; and (4) mesenchymal cells derived from the epicardium require TGFβ signaling to promote their differentiation to vascular smooth muscle cells to support the coronary arteries. In addition, a mouse genetics approach has also been used to investigate the disease pathogenesis of Loeys-Dietz syndrome, a familial autosomal dominant human disorder characterized by a dilated aortic root, and associated with mutations in the two TGFβ signaling receptor genes, TGFBR1 and TGFBR2. Further important insights are likely as this exciting work progresses.

Transforming growth factor beta2 is negatively regulated by endogenous retinoic acid during early heart morphogenesis

Vitamin A-deficient (VAD) quail embryos lack the vitamin A-active form, retinoic acid (RA) and are characterized by a phenotype that includes a grossly abnormal cardiovascular system that can be rescued by RA. Here we report that the transforming growth factor, TGFbeta2 is involved in RA-regulated cardiovascular development. In VAD embryos TGFbeta2 mRNA and protein expression are greatly elevated. The expression of TGFbeta receptor II is also elevated in VAD embryos but is normalized by treatment with TGFbeta2-specific antisense oligonucleotides (AS). Administration of this AS or an antibody specific for TGFbeta2 to VAD embryos normalizes posterior heart development and vascularization, while the administration of exogenous active TGFbeta2 protein to normal quail embryos mimics the excessive TGFbeta2 status of VAD embryos and induces VAD cardiovascular phenotype. In VAD embryos pSmad2/3 and pErk1 are not activated, while pErk2 and pcRaf are elevated and pSmad1/5/8 is diminished. We conclude that in the early avian embryo TGFbeta2 has a major role in the retinoic acid-regulated posterior heart morphogenesis for which it does not use Smad2/3 pathways, but may use other signaling pathways. Importantly, we conclude that retinoic acid is a critical negative physiological regulator of the magnitude of TGFbeta2 signals during vertebrate heart formation.

TGFβ2-mediated production of hyaluronan is important for the induction of epicardial cell differentiation and invasion

In the developing heart, the epicardium is a major source of progenitor cells that contribute to the formation of the coronary vessel system. These epicardial progenitors give rise to the different cellular components of the coronary vasculature by undergoing a number of morphological and physiological changes collectively known as epithelial to mesenchymal transformation (EMT). However, the specific signaling mechanisms that regulate epicardial EMT are yet to be delineated. In this study we investigated the role of TGFβ2 and hyaluronan (HA) during epicardial EMT and how signals from these two molecules are integrated during this important process. Here we show that TGFβ2 induces MEKK3 activation, which in turn promotes ERK1/2 and ERK5 phosphorylation. TGFβ2 also increases Has2 expression and subsequent HA production. Nevertheless, inhibition of MEKK3 kinase activity, silencing of ERK5 or pharmacological disruption of ERK1/2 activation significantly abrogates this response. Thus, TGFβ2 promotes Has2 expression and HA production through a MEKK3/ERK1/2/5-dependent cascade. Furthermore, TGFβ2 is able to induce epicardial cell invasion and differentiation but not proliferation. However, inhibition of MEKK3-dependent pathways, degradation of HA by hyaluronidases or blockade of CD44, significantly impairs the biological response to TGFβ2. Taken together, these findings demonstrate that TGFβ2 activation of MEKK3/ERK1/2/5 signaling modulates Has2 expression and HA production leading to the induction of EMT events. This is an important and novel mechanism showing how TGFβ2 and HA signals are integrated to regulate changes in epicardial cell behavior.

Abnormal Shh and FOXC2 expression correlates with aberrant lymphatic development in human fetuses with increased nuchal translucency

OBJECTIVE

Previous research in fetuses with increased nuchal translucency (NT) showed abnormal lymphatic endothelial differentiation characteristics, including increased vascular endothelial growth factor (VEGF)-A expression, and aberrant smooth muscle cells (SMCs) surrounding enlarged jugular lymphatic sacs (JLS). We hypothesized that abnormal Sonic hedgehog (Shh) expression would result in altered VEGF-A signaling in the lymphatic endothelial cells of the JLS and that aberrant acquisition of SMCs could be caused by downregulation of forkhead transcription factor FOXC2 and upregulation of platelet-derived growth factor (PDGF)-B in the lymphatic endothelial cells of the JLS.

METHODS

Five trisomy 21 fetuses and four controls were investigated using immunohistochemistry for Shh, VEGF-A, FOXC2 and PDGF-B expression in the lymphatic endothelial cells of the JLS.

RESULTS

An increased Shh, VEGF-A and PDGF-B expression, and decreased FOXC2 expression were shown in the lymphatic endothelial cells of the JLS of the trisomic fetuses.

CONCLUSIONS

Increased Shh and VEGF-A expression is correlated with an aberrant lymphatic endothelial differentiation in trisomy 21 fetuses. The SMCs surrounding the JLS can possibly be explained by an increase of PDGF-B-induced SMC recruitment and/or differentiation. This underscores earlier findings that indicate the loss of lymphatic identity in trisomy 21 fetuses and a shift towards a blood vessel wall phenotype.

Focal adhesion kinase is required for neural crest cell morphogenesis during mouse cardiovascular development

Neural crest cells (NCCs) participate in the remodeling of the cardiac outflow tract and pharyngeal arch arteries during cardiovascular development. Focal adhesion kinase (FAK) mediates signal transduction by integrin and growth factor receptors, each of which is important for normal cardiovascular development. To investigate the role of FAK in NCC morphogenesis, we deleted it in murine NCCs using Wnt1cre, yielding craniofacial and cardiovascular malformations resembling those observed in individuals with DiGeorge syndrome. In these mice, we observed normal cardiac NCC migration but reduced differentiation into smooth muscle within the aortic arch arteries and impaired cardiac outflow tract rotation, which resulted in a dextroposed aortic root. Moreover, within the conotruncal cushions, Fak-deficient NCCs formed a less organized mesenchyme, with reduced expression of perlecan and semaphorin 3C, and exhibited disorganized F-actin stress fibers within the aorticopulmonary septum. Additionally, absence of Fak resulted in reduced in vivo phosphorylation of Crkl and Erk1/2, components of a signaling pathway essential for NCC development. Consistent with this, both TGF-beta and FGF induced FAK and Crkl phosphorylation in control but not Fak-deficient NCCs in vitro. Our results indicate that FAK plays an essential role in cardiac outflow tract development by promoting the activation of molecules such as Crkl and Erk1/2.

Possible association between genetic polymorphisms in transforming growth factor beta receptors, serum transforming growth factor beta1 concentration and abdominal aortic aneurysm

BACKGROUND

Previous studies have suggested a role for transforming growth factor (TGF) beta and its receptor in thoracic aortic aneurysm, but their role in abdominal aortic aneurysm (AAA) is unknown. This study examined the possible association between TGF-beta receptor 1 and 2 (TGFBR-1 and -2) single nucleotide polymorphisms (SNPs) and serum TGF-beta1 with AAA.

METHODS

Serum concentrations of TGF-beta1 and 58 SNPs for TGFBR-1 and -2 were examined in 1003 and 1711 men respectively from the Health In Men Study. Validation of SNPs was examined in a second referral cohort of 1043 subjects from New Zealand, of whom 654 had an AAA.

RESULTS

Serum TGF-beta1 was not associated with AAA. Only one SNP in TGFBR-2 was weakly associated with AAA; TGFBR2 g.42917C > T, SNP ID rs1078985CC; odds ratio 0.64 (95 per cent confidence interval (c.i.) 0.45 to 0.93); P = 0.020 uncorrected; but this association did not hold after adjusting for multiple testing and was not validated in the New Zealand cohort: odds ratio 0.98 (95 per cent c.i. 0.50 to 1.94); P = 0.960.

CONCLUSION

These findings suggest there is no important role of genetic polymorphisms in the main receptors for TGF-beta and circulating TGF-beta1 in AAA in older individuals. (c) 2009 British Journal of Surgery Society Ltd.

Specific local cardiovascular changes of Nepsilon-(carboxymethyl)lysine, vascular endothelial growth factor, and Smad2 in the developing embryos coincide with maternal diabetes-induced congenital heart defects

OBJECTIVE

Embryos exposed to a diabetic environment in utero have an increased risk to develop congenital heart malformations. The mechanism behind the teratogenicity of diabetes still remains enigmatic. Detrimental effects of glycation products in diabetic patients have been well documented. We therefore studied a possible link between glycation products and the development of congenital cardiovascular malformations. Furthermore, we investigated other possible mechanisms involved in this pathogenesis: alterations in the levels of vascular endothelial growth factor (VEGF) or phosphorylated Smad2 (the latter can be induced by both glycation products and VEGF).

RESEARCH DESIGN AND METHODS

We examined the temporal spatial patterning of the glycation products Nepsilon(carboxymethyl)lysine (CML) and methylglyoxal (MG) adducts, VEGF expression, and phosphorylated Smad2 during cardiovascular development in embryos from normal and diabetic rats.

RESULTS

Maternal diabetes increased the CML accumulation in the areas susceptible to diabetes-induced congenital heart disease, including the outflow tract of the heart and the aortic arch. No MG adducts could be detected, suggesting that CML is more likely to be indicative for increased oxidative stress than for glycation. An increase of CML in the outflow tract of the heart was accompanied by an increase in phosphorylated Smad2, unrelated to VEGF. VEGF showed a time-specific decrease in the outflow tract of embryos from diabetic dams.

CONCLUSIONS

From our results, we can conclude that maternal diabetes results in transient and localized alterations in CML, VEGF expression, and Smad2 phosphorylation overlapping with those regions of the developing heart that are most sensitive to diabetes-induced congenital heart disease.

Influence of genetic background on genetically engineered mouse phenotypes

The history of mouse genetics, which involves the study of strain-dependent phenotype variability, makes it clear that the genetic background onto which a gene-targeted allele is placed can cause considerable variation in genetically engineered mouse (GEM) phenotype. This variation can present itself as completely different phenotypes, as variations in penetrance of phenotype, or as variable expressivity of phenotype. In this chapter we provide examples from gene-targeting literature showing each of these types of phenotype variation. We discuss ways in which modifier genes can affect the phenotype of a mouse with a mutant gene, and we give examples of modifier locus identification. We also review approaches to minimize gene polymorphism and flanking gene differences between experimental animals, and between them and their controls. In addition, we discuss the advantages and disadvantages of performing the first analysis of a knockout mouse on a mixed genetic background. We conclude that a mixed background provides the quickest preview of possible strain-dependent phenotypes (1 , 2). Finally, we review recent approaches to improving genetic diversity by generating new inbred strains that encompass a broader range of alleles within the mouse species.

PDGF-B signaling is important for murine cardiac development: its role in developing atrioventricular valves, coronaries, and cardiac innervation

We hypothesized that PDGF-B/PDGFR-beta-signaling is important in the cardiac contribution of epicardium-derived cells and cardiac neural crest, cell lineages crucial for heart development. We analyzed hearts of different embryonic stages of both Pdgf-b-/- and Pdgfr-beta-/- mouse embryos for structural aberrations with an established causal relation to defective contribution of these cell lineages. Immunohistochemical staining for alphaSMA, periostin, ephrinB2, EphB4, VEGFR-2, Dll1, and NCAM was performed on wild-type and knockout embryos. We observed that knockout embryos showed perimembranous and muscular ventricular septal defects, maldevelopment of the atrioventricular cushions and valves, impaired coronary arteriogenesis, and hypoplasia of the myocardium and cardiac nerves. The abnormalities correspond with models in which epicardial development is impaired and with neuronal neural crest-related innervation deficits. This implies a role for PDGF-B/PDGFR-beta-signaling specifically in the contribution of these cell lineages to cardiac development.

Smad signaling in the neural crest regulates cardiac outflow tract remodeling through cell autonomous and non-cell autonomous effects

Neural crest cells (NCCs) are indispensable for the development of the cardiac outflow tract (OFT). Here, we show that mice lacking Smad4 in NCCs have persistent truncus arteriosus (PTA), severe OFT cushion hypoplasia, defective OFT elongation, and mispositioning of the OFT. Cardiac NCCs lacking Smad4 have increased apoptosis, apparently due to decreased Msx1/2 expression. This contributes to the reduction of NCCs in the OFT. Unexpectedly, mutants have MF20-expressing cardiomyocytes in the splanchnic mesoderm within the second heart field (SHF). This may result from abnormal differentiation or defective recruitment of differentiating SHF cells into OFT. Alterations in Bmp4, Sema3C, and PlexinA2 signals in the mutant OFT, SHF, and NCCs, disrupt the communications among different cell populations. Such disruptions can further affect the recruitment of NCCs into the OFT mesenchyme, causing severe OFT cushion hypoplasia and OFT septation failure. Furthermore, these NCCs have drastically reduced levels of Ids and MT1-MMP, affecting the positioning and remodeling of the OFT. Thus, Smad-signaling in cardiac NCCs has cell autonomous effects on their survival and non-cell autonomous effects on coordinating the movement of multiple cell lineages in the positioning and the remodeling of the OFT.

High glucose-induced thioredoxin-interacting protein in renal proximal tubule cells is independent of transforming growth factor-beta1

Hyperglycemia is a causative factor in the pathogenesis of diabetic nephropathy. Here, we demonstrate the transcriptional profiles of the human proximal tubule cell line (HK-2 cells) exposed to high glucose using cDNA microarray analysis. Thioredoxin-interacting protein (Txnip) was the gene most significantly increased among 10 strongly up-regulated and 15 down-regulated genes. Txnip, heat shock proteins 70 and 90, chemokine (C-C motif) ligand 20, and matrix metalloproteinase-7 were chosen for verification of gene expression. Real-time reverse transcriptase-polymerase chain reaction confirmed the mRNA expression levels of these five genes, consistent with microarray analysis. The increased protein expression of Txnip, CCL20, and MMP7 were also verified by Western blotting and enzyme-linked immunosorbent assay. Increased expression of Txnip and of nitrotyrosine, as a marker of oxidative stress, were confirmed in vivo in diabetic Ren-2 rats. Subsequent studies focused on the dependence of Txnip expression on up-regulation of transforming growth factor (TGF)-beta1 under high-glucose conditions. Overexpression of Txnip and up-regulation of Txnip promoter activity were observed in cells in which the TGF-beta1 gene was silenced in HK-2 cells using short interfering RNA technology. High glucose further increased both Txnip expression and its promoter activity in TGF-beta1 silenced cells compared with wild-type cells exposed to high glucose, suggesting that high glucose induced Txnip through a TGF-beta1-indepen-dent pathway.

Pathogenic sequence for dissecting aneurysm formation in a hypomorphic polycystic kidney disease 1 mouse model

OBJECTIVE

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a multi-system disorder characterized by progressive cyst formation in the kidneys. Serious complications of ADPKD are intracranial and aortic aneurysms. The condition is mainly caused by mutations in the PKD1 or PKD2 gene. We have carefully analyzed vascular remodeling in hypomorphic Pkd1(nl/nL) mouse model with dissecting aneurysms in the aorta.

METHODS AND RESULTS

Quantitative real-time polymerase chain reaction revealed that in the aorta the expression of normal Pkd1 is reduced to approximately 26%. Using (immuno)histochemistry we have characterized the pathogenetic sequence for dissecting aneurysm formation. The aorta shows regions with accumulation of matrix components between the elastin lamellae. This is followed by increased numbers of smooth muscle cells and locally weakening of the media. In the intima, accumulation of matrix components and detachment of endothelial cells from the elastin lamellae results in a tear. The combination of weak media and a tear in the intima leads to rupture of the vessel wall resulting in intramural bleeding.

CONCLUSIONS

The Pkd1(nl/nl) mouse reveals that polycystin1 is implicated in maintenance of the vessel wall structural integrity, and it is a useful model for dissecting aneurysm formation studies.

SOST expression is restricted to the great arteries during embryonic and neonatal cardiovascular development

Spatial-temporal regulation of bone morphogenetic protein (BMP) and Wnt activity is essential for normal cardiovascular development, and altered activity of these growth factors causes maldevelopment of the cardiac outflow tract and great arteries. In the present study, we show that SOST, a Dan family member reported to antagonize BMP and Wnt activity, is expressed within the medial vessel wall of the great arteries containing smooth muscle cells. The ascending aorta, aortic arch, brachiocephalic artery, common carotids, and pulmonary trunk were all associated with SOST expressing smooth muscle cells, while the heart itself, including the valves, and more distal arteries, that is, pulmonary arteries, subclavian arteries, and descending aorta, were negative. SOST was expressed from embryonic day 15.5 up to the neonatal period. SOST expression, however, did not correspond with inhibition of Smad-dependent BMP activity or beta-catenin-dependent Wnt activity in the great arteries. Activity of both signaling pathways was already down-regulated before induction of SOST expression.

Persistent ductus arteriosus in the Brown-Norway inbred rat strain

Persistent ductus arteriosus (PDA) is a common cardiovascular anomaly in children caused by the pathologic persistence of the left sixth pharyngeal arch artery. The inbred Brown-Norway (BN) rat presents with increased vascular fragility due to an aortic elastin deficit resulting from decreased elastin synthesis. The strikingly high prevalence of PDA in BN rats in a pilot study led us to investigate this vascular anomaly in 12 adolescent BN rats. In all BN rats, a PDA was observed macroscopically, whereas a ligamentum arteriosum was found in adult controls. The macroscopic appearance of the PDA was tubular (n = 2), stenotic (n = 8), or diverticular (n = 2). The PDA had the structure of a muscular artery with intimal thickening. In the normal closing ductus of the neonatal controls, the media consisted of layers of smooth muscle cells (SMCs) intermingled with layers of elastin. The intima was thin and poor in elastin. By contrast, the media of PDA in BN rats elastin lamellae were absent and the intima contained many elastic fibers. The abnormal distribution of elastin in the PDA of BN rats suggests that impaired elastin metabolism is related to the persistence of the ductus and implicates a genetically determined factor that may link the PDA with aortic fragility.

Hepatic stellate cells do not derive from the neural crest

BACKGROUND/AIMS

Hepatic stellate cells (HSC) have been hypothesised to derive from the neural crest, based on their expression of multiple neural/neuroendocrine features and their contacts with autonomic nerve endings.

METHODS

We studied the emergence of HSC in the liver during embryonic development in a transgenic mouse line expressing yellow fluorescent protein (YFP) in all neural crest cells and their derivatives. Cellular YFP expression in these mice was compared with desmin expression between embryonic day (E) 11.5 and adulthood.

RESULTS

YFP was abundantly expressed in neural crest cells delaminating from the neural tube and in all known neural crest-derived structures and cell populations. In particular, YFP expressing cells perfectly mimicked the spatial and temporal pattern of enteric nervous system development from neural crest cells migrating from the postotic region. Cells within the adrenal medulla were also YFP positive. Analysis of the liver showed that desmin-expressing, stellate-shaped, perisinusoidally located HSC were evident from E11.5 onwards. However, no detectable YFP expression was seen in the developing liver or in HSC, from E11.5 until adulthood.

CONCLUSIONS

These findings suggest HSC do not descend from the neural crest, and therefore may derive from the septum transversum mesenchyme, from endoderm or from the mesothelial liver capsule.

Transforming growth factor-beta1 differentially mediates fibronectin and inflammatory cytokine expression in kidney tubular cells

Transforming growth factor-beta(1) (TGF-beta(1)) is not only an important fibrogenic but also immunomodulatory cytokine in the human kidney. We have recently demonstrated that TGF-beta(1) induces interleukin-8 (IL-8), macrophage chemoattractant protein-1 (MCP-1), and fibronectin production in renal proximal tubular (HK-2) cells. However, the unique dependence of IL-8, MCP-1, and fibronectin on TGF-beta(1) expression is unknown. The TGF-beta(1) gene was effectively silenced in HK-2 cells using small-interference (si) RNA. Basal secretion of IL-8 and MCP-1 decreased (both P < 0.05) but, paradoxically, fibronectin increased (P < 0.05) in TGF-beta(1)-silenced cells compared with cells transfected with nonspecific siRNA. Significant increases were observed in mRNA for the TGF-beta(2) (P < 0.05), TGF-beta(3) (P < 0.05) isoforms and pSmad2 (P < 0.05), which were reflected in protein expression. Concurrent exposure to pan-specific TGF-beta antibody reversed the observed increase in fibronectin expression, suggesting that TGF-beta(2) and TGF-beta(3) isoforms mediate the increased fibronectin expression in TGF-beta(1)-silenced cells. An increase in the DNA binding activity of activator protein-1 (AP-1; P < 0.05) was also observed in TGF-beta(1)-silenced cells. In contrast, nuclear factor-kappaB (NF-kappaB) DNA binding activity was significantly decreased (P < 0.0005). These studies demonstrate that TGF-beta(1) is a key regulator of IL-8 and MCP-1, whereas fibronectin expression is regulated by a complex interaction between the TGF-beta isoforms in the HK-2 proximal tubular cell line. Decreased expression of TGF-beta(1) reduces chemokine production in association with reduced NF-kappaB DNA binding activity, suggesting that immunomodulatory pathways in the kidney are specifically dependent on TGF-beta(1). Conversely, decreased expression of TGF-beta(1) results in increased TGF-beta(2), TGF-beta(3), AP-1, and pSmad2 that potentially mediates the observed increase in fibronectin.

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

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