Molecular identity of arteries, veins, and lymphatics

Molecular determinants of cross-species transmission in emerging viral infections

SUMMARYSeveral examples of high-impact cross-species transmission of newly emerging or re-emerging bat-borne viruses, such as Sudan virus, Nipah virus, and severe acute respiratory syndrome coronavirus 2, have occurred in the past decades. Recent advancements in next-generation sequencing have strengthened ongoing efforts to catalog the global virome, in particular from the multitude of different bat species. However, functional characterization of these novel viruses and virus sequences is typically limited with regard to assessment of their cross-species potential. Our understanding of the intricate interplay between virus and host underlying successful cross-species transmission has focused on the basic mechanisms of entry and replication, as well as the importance of host innate immune responses. In this review, we discuss the various roles of the respective molecular mechanisms underlying cross-species transmission using different recent bat-borne viruses as examples. To delineate the crucial cellular and molecular steps underlying cross-species transmission, we propose a framework of overall characterization to improve our capacity to characterize viruses as benign, of interest, or of concern.

Direct male development in chromosomally ZZ zebrafish

The genetics of sex determination varies across taxa, sometimes even within a species. Major domesticated strains of zebrafish (Danio rerio), including AB and TU, lack a strong genetic sex determining locus, but strains more recently derived from nature, like Nadia (NA), possess a ZZ male/ZW female chromosomal sex-determination system. AB fish pass through a juvenile ovary stage, forming oocytes that survive in fish that become females but die in fish that become males. To understand mechanisms of gonad development in NA zebrafish, we studied histology and single cell transcriptomics in developing ZZ and ZW fish. ZW fish developed oocytes by 22 days post-fertilization (dpf) but ZZ fish directly formed testes, avoiding a juvenile ovary phase. Gonads of some ZW and WW fish, however, developed oocytes that died as the gonad became a testis, mimicking AB fish, suggesting that the gynogenetically derived AB strain is chromosomally WW. Single-cell RNA-seq of 19dpf gonads showed similar cell types in ZZ and ZW fish, including germ cells, precursors of gonadal support cells, steroidogenic cells, interstitial/stromal cells, and immune cells, consistent with a bipotential juvenile gonad. In contrast, scRNA-seq of 30dpf gonads revealed that cells in ZZ gonads had transcriptomes characteristic of testicular Sertoli, Leydig, and germ cells while ZW gonads had granulosa cells, theca cells, and developing oocytes. Hematopoietic and vascular cells were similar in both sex genotypes. These results show that juvenile NA zebrafish initially develop a bipotential gonad; that a factor on the NA W chromosome, or fewer than two Z chromosomes, is essential to initiate oocyte development; and without the W factor, or with two Z doses, NA gonads develop directly into testes without passing through the juvenile ovary stage. Sex determination in AB and TU strains mimics NA ZW and WW zebrafish, suggesting loss of the Z chromosome during domestication. Genetic analysis of the NA strain will facilitate our understanding of the evolution of sex determination mechanisms.

Direct Male Development in Chromosomally ZZ Zebrafish

The genetics of sex determination varies across taxa, sometimes even within a species. Major domesticated strains of zebrafish ( Danio rerio ), including AB and TU, lack a strong genetic sex determining locus, but strains more recently derived from nature, like Nadia (NA), possess a ZZ male/ZW female chromosomal sex-determination system. AB strain fish pass through a juvenile ovary stage, forming oocytes that survive in fish that become females but die in fish that become males. To understand mechanisms of gonad development in NA zebrafish, we studied histology and single cell transcriptomics in developing ZZ and ZW fish. ZW fish developed oocytes by 22 days post-fertilization (dpf) but ZZ fish directly formed testes, avoiding a juvenile ovary phase. Gonads of some ZW and WW fish, however, developed oocytes that died as the gonad became a testis, mimicking AB fish, suggesting that the gynogenetically derived AB strain is chromosomally WW. Single-cell RNA-seq of 19dpf gonads showed similar cell types in ZZ and ZW fish, including germ cells, precursors of gonadal support cells, steroidogenic cells, interstitial/stromal cells, and immune cells, consistent with a bipotential juvenile gonad. In contrast, scRNA-seq of 30dpf gonads revealed that cells in ZZ gonads had transcriptomes characteristic of testicular Sertoli, Leydig, and germ cells while ZW gonads had granulosa cells, theca cells, and developing oocytes. Hematopoietic and vascular cells were similar in both sex genotypes. These results show that juvenile NA zebrafish initially develop a bipotential gonad; that a factor on the NA W chromosome or fewer than two Z chromosomes is essential to initiate oocyte development; and without the W factor or with two Z doses, NA gonads develop directly into testes without passing through the juvenile ovary stage. Sex determination in AB and TU strains mimics NA ZW and WW zebrafish, suggesting loss of the Z chromosome during domestication. Genetic analysis of the NA strain will facilitate our understanding of the evolution of sex determination mechanisms.

Impact Assessment of Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) and Hemostatic Sponge on Vascular Anastomosis Regeneration in Rats

The proper regeneration of vessel anastomoses in microvascular surgery is crucial for surgical safety. Pituitary adenylate cyclase-activating polypeptide (PACAP) can aid healing by decreasing inflammation, apoptosis and oxidative stress. In addition to hematological and hemorheological tests, we examined the biomechanical and histological features of vascular anastomoses with or without PACAP addition and/or using a hemostatic sponge (HS). End-to-end anastomoses were established on the right femoral arteries of rats. On the 21st postoperative day, femoral arteries were surgically removed for evaluation of tensile strength and for histological and molecular biological examination. Effects of PACAP were also investigated in tissue culture in vitro to avoid the effects of PACAP degrading enzymes. Surgical trauma and PACAP absorption altered laboratory parameters; most notably, the erythrocyte deformability decreased. Arterial wall thickness showed a reduction in the presence of HS, which was compensated by PACAP in both the tunica media and adventitia in vivo. The administration of PACAP elevated these parameters in vitro. In conclusion, the application of the neuropeptide augmented elastin expression while HS reduced it, but no significant alterations were detected in collagen type I expression. Elasticity and tensile strength increased in the PACAP group, while it decreased in the HS decreased. Their combined use was beneficial for vascular regeneration.

Sinus venosus adaptation models prolonged cardiovascular disease and reveals insights into evolutionary transitions of the vertebrate heart

How two-chambered hearts in basal vertebrates have evolved from single-chamber hearts found in ancestral chordates remains unclear. Here, we show that the teleost sinus venosus (SV) is a chamber-like vessel comprised of an outer layer of smooth muscle cells. We find that in adult zebrafish nr2f1a mutants, which lack atria, the SV comes to physically resemble the thicker bulbus arteriosus (BA) at the arterial pole of the heart through an adaptive, hypertensive response involving smooth muscle proliferation due to aberrant hemodynamic flow. Single cell transcriptomics show that smooth muscle and endothelial cell populations within the adapting SV also take on arterial signatures. Bulk transcriptomics of the blood sinuses flanking the tunicate heart reinforce a model of greater equivalency in ancestral chordate BA and SV precursors. Our data simultaneously reveal that secondary complications from congenital heart defects can develop in adult zebrafish similar to those in humans and that the foundation of equivalency between flanking auxiliary vessels may remain latent within basal vertebrate hearts.

New strategy of using double-network hydrogel extravascular stent for preventing venous graft restenosis after coronary artery bypass grafting

OBJECTIVE

Effective therapies for the prevention of vein graft failure, which frequently occurs in coronary artery bypass grafting (CABG) due to intimal hyperplasia (IH), are still lacking. Here, we investigated the effects of the perivenous application of double-network hydrogel on vein grafts in carotid artery bypass grafting in a rabbit model.

METHODS

Healthy New Zealand white rabbits were randomized into the following groups: no graft, graft, or graft + Double-network hydrogel external stent (DNHES). The rabbits' carotid artery was bypassed via the jugular vein. Double-network hydrogel external stent was wrapped around the jugular graft after the anastomoses were completed. Blood flow parameters and tissue histology of the vein grafts were evaluated.

RESULTS

Compared with the untreated vein grafts at 12 weeks after the surgery, the DNHES significantly improved graft flow, attenuated intimal and medial thickening, reduced the anti-proliferating cell nuclear antigen proliferation index of the vein grafts, decreased the mRNA and protein expression of Mitogen-Activated Protein Kinase (MAPK) and Transforming Growth Factor-β (TGF-β), and increased the mRNA and protein expression of endothelial Nitric Oxide Synthase (eNOS).

CONCLUSION

The perivenous application of DNHES exerts beneficial effects on vein grafts, reduces the inflammatory response in carotid artery bypass grafting in a rabbit model, and appears to be a safe and promising strategy to prevent vein graft failure.

Administration of a new nano delivery system coated with Tirofiban to prevent early thrombosis of vein graft

OBJECTIVE

To verify the administration of a new nano delivery system coated with Tirofiban on preventing early thrombosis in vein graft.

METHODS

Forty New Zealand white rabbits were randomly divided into five groups with eight rabbits in each group. The rabbits of all groups underwent jugular vein transplantation, except group I with only neck opening and closing operation. Vein grafts of group II were preprocessed by intravenous injection of normal saline; group III were preprocessed by tirofiban alone; group IV were preprocessed by unloaded nanoparticles of PLGA-PEG; group V were preprocessed by PLGA-PEG coated with tirofiban. Coagulation and platelet function of peripheral and vein graft blood were detected at 1, 2, 4, 12 h and 1, 3, 7, 10, 14 days after operation. Patency rate of vein graft and blood flow index were measured by vascular ultrasound at third, seventh, 10th, and 14th days after operation; two rabbits in each group were randomly sacrificed at the corresponding time of detection. Pathological differences of vein grafts were observed by HE stainin.

RESULTS

The patency rate of vein grafts in group V was significantly higher than that in group II to IV. The platelet and platelet aggregation rate in group V were inhibited in vein graft blood significantly. The post-operative PT and APTT in vein graft blood in group V were increased obviously while the FBG, D-dimer and FDP were significantly inhibited. Except group I, the lumen loss rate of vein grafts in group V was significantly lower than that in other groups, and vein graft blood in group V had a significant lower expression of platelet P-selectin and GP IIb/IIIa receptor than that in other groups.

CONCLUSION

This study proves that PEG-PLGA coated with tirofiban can effectively prevent early vein graft stenosis from thrombosis by inhibition of platelet function, coagulation function.

Integrative single-cell analysis of cardiogenesis identifies developmental trajectories and non-coding mutations in congenital heart disease

To define the multi-cellular epigenomic and transcriptional landscape of cardiac cellular development, we generated single-cell chromatin accessibility maps of human fetal heart tissues. We identified eight major differentiation trajectories involving primary cardiac cell types, each associated with dynamic transcription factor (TF) activity signatures. We contrasted regulatory landscapes of iPSC-derived cardiac cell types and their in vivo counterparts, which enabled optimization of in vitro differentiation of epicardial cells. Further, we interpreted sequence based deep learning models of cell-type-resolved chromatin accessibility profiles to decipher underlying TF motif lexicons. De novo mutations predicted to affect chromatin accessibility in arterial endothelium were enriched in congenital heart disease (CHD) cases vs. controls. In vitro studies in iPSCs validated the functional impact of identified variation on the predicted developmental cell types. This work thus defines the cell-type-resolved cis-regulatory sequence determinants of heart development and identifies disruption of cell type-specific regulatory elements in CHD.

Sex differences in arterial identity correlate with neointimal hyperplasia after balloon injury

BACKGROUND

Endovascular treatment of atherosclerotic arterial disease exhibits sex differences in clinical outcomes including restenosis. However, sex-specific differences in arterial identity during arterial remodeling have not been described. We hypothesized that sex differences in expression of the arterial determinant erythropoietin-producing hepatocellular receptor interacting protein (Ephrin)-B2 occur during neointimal proliferation and arterial remodeling.

METHODS AND RESULTS

Carotid balloon injury was performed in female and male Sprague-Dawley rats without or 14 days after gonadectomy; the left common carotid artery was injured and the right carotid artery in the same animal was used as an uninjured control. Arterial hemodynamics were evaluated in vivo using ultrasonography pre-procedure and post-procedure at 7 and 14 days and wall composition examined using histology, immunofluorescence and Western blot at 14 days after balloon injury. There were no significant baseline sex differences. 14 days after balloon injury, there was decreased neointimal thickness in female rats with decreased smooth muscle cell proliferation and decreased type I and III collagen deposition, as well as decreased TNFα- or iNOS-positive CD68+ cells and increased CD206- or TGM2-positive CD68+ cells. Female rats also showed less immunoreactivity of VEGF-A, NRP1, phosphorylated EphrinB2, and increased Notch1, as well as decreased phosphorylated Akt1, p38 and ERK1/2. These differences were not present in rats pretreated with gonadectomy.

CONCLUSIONS

Decreased neointimal thickness in female rats after carotid balloon injury is associated with altered arterial identity that is dependent on intact sex hormones. Alteration of arterial identity may be a mechanism of sex differences in neointimal proliferation after arterial injury.

The Etiology and Molecular Mechanism Underlying Smooth Muscle Phenotype Switching in Intimal Hyperplasia of Vein Graft and the Regulatory Role of microRNAs

Mounting evidence suggests that the phenotypic transformation of venous smooth muscle cells (SMCs) from differentiated (contractile) to dedifferentiated (proliferative and migratory) phenotypes causes excessive proliferation and further migration to the intima leading to intimal hyperplasia, which represents one of the key pathophysiological mechanisms of vein graft restenosis. In recent years, numerous miRNAs have been identified as specific phenotypic regulators of vascular SMCs (VSMCs), which play a vital role in intimal hyperplasia in vein grafts. The review sought to provide a comprehensive overview of the etiology of intimal hyperplasia, factors affecting the phenotypic transformation of VSMCs in vein graft, and molecular mechanisms of miRNAs involved in SMCs phenotypic modulation in intimal hyperplasia of vein graft reported in recent years.

Epigenetic Regulation of Endothelial Cell Lineages During Zebrafish Development-New Insights From Technical Advances

Epigenetic regulation is integral in orchestrating the spatiotemporal regulation of gene expression which underlies tissue development. The emergence of new tools to assess genome-wide epigenetic modifications has enabled significant advances in the field of vascular biology in zebrafish. Zebrafish represents a powerful model to investigate the activity of cis-regulatory elements in vivo by combining technologies such as ATAC-seq, ChIP-seq and CUT&Tag with the generation of transgenic lines and live imaging to validate the activity of these regulatory elements. Recently, this approach led to the identification and characterization of key enhancers of important vascular genes, such as gata2a, notch1b and dll4. In this review we will discuss how the latest technologies in epigenetics are being used in the zebrafish to determine chromatin states and assess the function of the cis-regulatory sequences that shape the zebrafish vascular network.

Mapping the developing human cardiac endothelium at single-cell resolution identifies MECOM as a regulator of arteriovenous gene expression

AIMS

Coronary vasculature formation is a critical event during cardiac development, essential for heart function throughout perinatal and adult life. However, current understanding of coronary vascular development has largely been derived from transgenic mouse models. The aim of this study was to characterize the transcriptome of the human foetal cardiac endothelium using single-cell RNA sequencing (scRNA-seq) to provide critical new insights into the cellular heterogeneity and transcriptional dynamics that underpin endothelial specification within the vasculature of the developing heart.

METHODS AND RESULTS

We acquired scRNA-seq data of over 10 000 foetal cardiac endothelial cells (ECs), revealing divergent EC subtypes including endocardial, capillary, venous, arterial, and lymphatic populations. Gene regulatory network analyses predicted roles for SMAD1 and MECOM in determining the identity of capillary and arterial populations, respectively. Trajectory inference analysis suggested an endocardial contribution to the coronary vasculature and subsequent arterialization of capillary endothelium accompanied by increasing MECOM expression. Comparative analysis of equivalent data from murine cardiac development demonstrated that transcriptional signatures defining endothelial subpopulations are largely conserved between human and mouse. Comprehensive characterization of the transcriptional response to MECOM knockdown in human embryonic stem cell-derived EC (hESC-EC) demonstrated an increase in the expression of non-arterial markers, including those enriched in venous EC.

CONCLUSIONS

scRNA-seq of the human foetal cardiac endothelium identified distinct EC populations. A predicted endocardial contribution to the developing coronary vasculature was identified, as well as subsequent arterial specification of capillary EC. Loss of MECOM in hESC-EC increased expression of non-arterial markers, suggesting a role in maintaining arterial EC identity.

Discovery and Characterization of Intercondylar Transphyseal Complexes and their Oncological Significance in Transphyseal Extension of Pediatric Osteosarcoma

Objective

To explore whether there exist undiscovered transphyseal vasculature‐canal compound structures in immature femurs and tibias, and reveal their potential oncological impact.

Methods

This investigation was divided into a morphological study and a clinical study. In the morphological part, a new‐identified anatomic structure was investigated by using radiographical, anatomical, and histological methodologies. Twenty‐eight 1‐mm‐slice thickness magnetic resonance images of pediatric knees were generated and 10 pediatric knees were dissected to verify the existence and universality, observe the radiographic and anatomic characteristics, and determined the located region of this structure. Hematoxylin–eosin staining, immunofluorescence, and angiography procedures were performed to illustrate its histological feature, molecular identification, and vascular origination, respectively. In the clinical part, 38 pediatric osteosarcoma patients were enrolled from January 2014 to December 2020. A descriptive clinical study including 13 typical participants was conducted to investigate the oncological significance of this new‐identified structure. Meanwhile, the discrepancy in transphyseal osteosarcoma extension between different physeal regions was evaluated in a cross‐sectional study.

Results

In the morphological study, we discovered a new‐found vasculature‐canal compound structure, intercondylar transphyseal complex (ITC), which originated from the middle genicular vessels, traversed the whole epiphysis, and breached the intact open physis in the immature proximal tibia or distal femur. The components of ITC included the juxta‐articular, epiphyseal, and transphyseal segments of vessels, the canals that traverse the entire epiphysis and physis and enclosed the vessels, vascular foramina on articular facet and foramina‐covered synovium. Depending on the location, ITCs can be divided into three types: femoral ITC, anterior tibial ITC, and posterior tibial ITC. Clinically, the ITC may facilitate intercondylar transphyseal sarcomatous dissemination without damaging the adjacent physeal cartilage. Compared to bilateral condylar physes, more osteosarcomas transgressed the open growth plates through intercondylar regions in which ITC was located (P = 0.022).

Conclusion

As the “gap” on intact open physis, ITC, which is a new‐identified compound structure in intercondylar regions of immature femur or tibia, may promote intercondylar transphyseal tumor extension. Moreover, the identification and characterization of ITC subvert some traditional comprehensions about physis and may provide novel perspectives for pediatric osteosarcomas.

Acute shear stress and vein graft disease

The long saphenous vein is commonly used in cardiac surgery to bypass occluded coronary arteries. Its use is complicated by late stenosis and occlusion due to the development of intimal hyperplasia. It is accepted that intimal hyperplasia is a multifactorial inflammatory process that starts immediately after surgery. The role of acute changes in haemodynamic conditions when the vein is implanted into arterial circulation, especially shear stress, is not fully appreciated. This review provides an overview of intimal hyperplasia and the effect of acute shear stress changes on the activation of pro-inflammatory mediators.

The versatility and paradox of BMP signaling in endothelial cell behaviors and blood vessel function

Blood vessels expand via sprouting angiogenesis, and this process involves numerous endothelial cell behaviors, such as collective migration, proliferation, cell–cell junction rearrangements, and anastomosis and lumen formation. Subsequently, blood vessels remodel to form a hierarchical network that circulates blood and delivers oxygen and nutrients to tissue. During this time, endothelial cells become quiescent and form a barrier between blood and tissues that regulates transport of liquids and solutes. Bone morphogenetic protein (BMP) signaling regulates both proangiogenic and homeostatic endothelial cell behaviors as blood vessels form and mature. Almost 30 years ago, human pedigrees linked BMP signaling to diseases associated with blood vessel hemorrhage and shunts, and recent work greatly expanded our knowledge of the players and the effects of vascular BMP signaling. Despite these gains, there remain paradoxes and questions, especially with respect to how and where the different and opposing BMP signaling outputs are regulated. This review examines endothelial cell BMP signaling in vitro and in vivo and discusses the paradox of BMP signals that both destabilize and stabilize endothelial cell behaviors.

Pro-angiogenic activity and vasculogenic mimicry in the tumor microenvironment by leptin in cancer

The acquired ability to induce the formation of a functional vasculature is a hallmark of cancer. Blood vessels in tumors are formed through various mechanisms, among the most important in cancer biology, angiogenesis, and vasculogenic mimicry have been described. Leptin is one of the main adipokines secreted by adipocytes in normal breast tissue and the tumor microenvironment. Here, we provide information on the relationship between leptin and the development of angiogenesis and vasculogenic mimicry in different types of cancer. Here, we report that leptin activates different pathways such as JAK-STAT3, MAPK/ERK, PKC, JNK, p38, and PI3K-Akt to induce the expression of various angiogenic factors and vasculogenic mimicry. In vivo models, leptin induces blood vessel formation through the PI3K-Akt-mTOR pathway. Interestingly, the relationship between leptin and vasculogenic mimicry was more significant in breast cancer. The information obtained suggests that leptin could be playing an essential role in tumor survival and metastasis through the induction of vascular mechanisms such as angiogenesis and vasculogenic mimicry; thus, leptin-induced pathways could be suggested as a promising therapeutic target.

From remodeling to quiescence: The transformation of the vascular network

The vascular system is essential for embryogenesis, healing, and homeostasis. Dysfunction or deregulated blood vessel function contributes to multiple diseases, including diabetic retinopathy, cancer, hypertension, or vascular malformations. A balance between the formation of new blood vessels, vascular remodeling, and vessel quiescence is fundamental for tissue growth and function. Whilst the major mechanisms contributing to the formation of new blood vessels have been well explored in recent years, vascular remodeling and quiescence remain poorly understood. In this review, we highlight the cellular and molecular mechanisms responsible for vessel remodeling and quiescence during angiogenesis. We further underline how impaired remodeling and/or destabilization of vessel networks can contribute to vascular pathologies. Finally, we speculate how addressing the molecular mechanisms of vascular remodeling and stabilization could help to treat vascular-related disorders.

Exploring the choroidal vascular labyrinth and its molecular and structural roles in health and disease

The choroid is a key player in maintaining ocular homeostasis and plays a role in a variety of chorioretinal diseases, many of which are poorly understood. Recent advances in the field of single-cell RNA sequencing have yielded valuable insights into the properties of choroidal endothelial cells (CECs). Here, we review the role of the choroid in various physiological and pathophysiological mechanisms, focusing on the role of CECs. We also discuss new insights regarding the phenotypic properties of CECs, CEC subpopulations, and the value of measuring transcriptomics in primary CEC cultures derived from post-mortem eyes. In addition, we discuss key phenotypic, structural, and functional differences that distinguish CECs from other endothelial cells such as retinal vascular endothelial cells. Understanding the specific clinical and molecular properties of the choroid will shed new light on the pathogenesis of the broad clinical range of chorioretinal diseases such as age-related macular degeneration, central serous chorioretinopathy and other diseases within the pachychoroid spectrum, uveitis, and diabetic choroidopathy. Although our knowledge is still relatively limited with respect to the clinical features and molecular pathways that underlie these chorioretinal diseases, we summarise new approaches and discuss future directions for gaining new insights into these sight-threatening diseases and highlight new therapeutic strategies such as pluripotent stem cell‒based technologies and gene therapy.

EPHB4 mutation causes adult and adolescent-onset primary lymphedema

Primary lymphedema results from the anomalous development of the lymphatic system and typically presents during infancy, childhood, or adolescence. Adult-onset primary lymphedema is rare and mutations associated with this condition have not been identified. The purpose of this investigation was to search for variants that cause adult-onset primary lymphedema. We discovered an autosomal dominant EPHB4 mutation in a patient who developed unilateral leg lymphedema at age 39 years; the same mutation affected his son who presented with the disease at 14 years of age.

Activation of EphrinB2 Signaling Promotes Adaptive Venous Remodeling in Murine Arteriovenous Fistulae

BACKGROUND

Arteriovenous fistulae (AVF) are the preferred mode of vascular access for hemodialysis. Before use, AVF remodel by thickening and dilating to achieve a functional conduit via an adaptive process characterized by expression of molecular markers characteristic of both venous and arterial identity. Although signaling via EphB4, a determinant of venous identity, mediates AVF maturation, the role of its counterpart EphrinB2, a determinant of arterial identity, remains unclear. We hypothesize that EphrinB2 signaling is active during AVF maturation and may be a mechanism of venous remodeling.

METHODS

Aortocaval fistulae were created or sham laparotomy was performed in C57Bl/6 mice, and specimens were examined on Days 7 or 21. EphrinB2 reverse signaling was activated with EphB4-Fc applied periadventitially in vivo and in endothelial cell culture medium in vitro. Downstream signaling was assessed using immunoblotting and immunofluorescence.

RESULTS

Venous remodeling during AVF maturation was characterized by increased expression of EphrinB2 as well as Akt1, extracellular signal-regulated kinases 1/2 (ERK1/2), and p38. Activation of EphrinB2 with EphB4-Fc increased phosphorylation of EphrinB2, endothelial nitric oxide synthase, Akt1, ERK1/2, and p38 and was associated with increased diameter and wall thickness in the AVF. Both mouse and human endothelial cells treated with EphB4-Fc increased phosphorylation of EphrinB2, endothelial nitric oxide synthase, Akt1, ERK1/2, and p38 and increased endothelial cell tube formation and migration.

CONCLUSIONS

Activation of EphrinB2 signaling by EphB4-Fc was associated with adaptive venous remodeling in vivo while activating endothelial cell function in vitro. Regulation of EphrinB2 signaling may be a new strategy to improve AVF maturation and patency.

Directed Differentiation of Hemogenic Endothelial Cells from Human Pluripotent Stem Cells

Blood vessels are ubiquitously distributed within all tissues of the body and perform diverse functions. Thus, derivation of mature vascular endothelial cells, which line blood vessel lumens, from human pluripotent stem cells is crucial for a multitude of tissue engineering and regeneration applications. In vivo, primordial endothelial cells are derived from the mesodermal lineage and are specified toward specific subtypes, including arterial, venous, capillary, hemogenic, and lymphatic. Hemogenic endothelial cells are of particular interest because, during development, they give rise to hematopoietic stem and progenitor cells, which then generate all blood lineages throughout life. Thus, creating a system to generate hemogenic endothelial cells in vitro would provide an opportunity to study endothelial-to-hematopoietic transition, and may lead to ex vivo production of human blood products and reduced reliance on human donors. While several protocols exist for the derivation of progenitor and primordial endothelial cells, generation of well-characterized hemogenic endothelial cells from human stem cells has not been described. Here, a method for the derivation of hemogenic endothelial cells from human embryonic stem cells in approximately 1 week is presented: a differentiation protocol with primitive streak cells formed in response to GSK3β inhibitor (CHIR99021), then mesoderm lineage induction mediated by bFGF, followed by primordial endothelial cell development promoted by BMP4 and VEGF-A, and finally hemogenic endothelial cell specification induced by retinoic acid. This protocol yields a well-defined population of hemogenic endothelial cells that can be used to further understand their molecular regulation and endothelial-to-hematopoietic transition, which has the potential to be applied to downstream therapeutic applications.

Tmem100-BAC-EGFP mice to selectively mark and purify embryonic endothelial cells of large caliber arteries in mid-gestational vascular formation

Embryonic vascular development is achieved through the complex arrays of differentiation, proliferation, migration and mutual interaction of different cell types, and visualization as well as purification of unique cell populations are fundamental in studying its detailed mechanisms using in vivo experimental models. We previously demonstrated that Tmem100 was a novel endothelial gene encoding a small transmembrane protein, and that Tmem100 null mice showed embryonic lethality due to severe impairment of vascular formation. In the present study, we generated an EGFP reporter mouse line using a 216 kb genomic region containing mouse Tmem100 gene. A novel line designated as Tmem100-BAC-EGFP mice precisely recapitulated the Tmem100 expression profile at the mid-gestational stage, which was highly enriched in endothelial cells of large caliber arteries in mouse embryos. FACS experiments demonstrated that Tmem100-BAC-EGFP mice served to selectively purify a specific population of arterial endothelial cells, indicating their usefulness not only for the research concerning Tmem100 expression and function but also for comparative analysis of multiple endothelial cell subgroups in embryonic vascular development.

Candidate Glycoprotein Biomarkers for Canine Visceral Hemangiosarcoma and Validation Using Semi-Quantitative Lectin/Immunohistochemical Assays

Visceral hemangiosarcoma (HSA) is one of the more frequent cancers in dogs and has a high metastatic rate and poor prognosis, as clinical signs only become apparent in advanced stages of tumor development. In order to improve early and differential diagnostic capabilities and hence, prognosis for dogs with HSA, two types of biomarker are needed: a point-of-care diagnostic biomarker and a prognostic biomarker—preferentially based on samples obtained with minimally invasive methods. In this study, we applied a lectin magnetic bead array-coupled tandem mass spectrometry (LeMBA-MS/MS) workflow through discovery and validation phases to discover serum glycoprotein biomarker candidates for canine HSA. By this approach, we found that Datura stramonium (DSA), wheat germ agglutinin (WGA), Sambucus nigra (SNA), and Pisum sativum (PSA) lectins captured the highest number of validated candidate glycoproteins. Secondly, we independently validated serum LeMBA-MS/MS results by demonstrating the in situ relationship of lectin-binding with tumor cells. Using lectin-histochemistry and immunohistochemistry (IHC) for key proteins on tissues with HSA and semi-quantitation of the signals, we demonstrate that a combination of DSA histochemistry and IHC for complement C7 greatly increases the prospect of a more specific diagnosis of canine HSA.

Selection of different endothelialization modes and different seed cells for tissue-engineered vascular graft

Tissue-engineered vascular grafts (TEVGs) have enormous potential for vascular replacement therapy. However, thrombosis and intimal hyperplasia are important problems associated with TEVGs especially small diameter TEVGs (<6 mm) after transplantation. Endothelialization of TEVGs is a key point to prevent thrombosis. Here, we discuss different types of endothelialization and different seed cells of tissue-engineered vascular grafts. Meanwhile, endothelial heterogeneity is also discussed. Based on it, we provide a new perspective for selecting suitable types of endothelialization and suitable seed cells to improve the long-term patency rate of tissue-engineered vascular grafts with different diameters and lengths.

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The material, diameter and length of tissue-engineered vascular graft are all key factors affecting its long-term patency.

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Endothelialization strategies should consider the different diameters and lengths of tissue-engineered vascular grafts.

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Cell heterogeneity and tissue heterogeneity should be considered in the application of seed cells.

Potential Utilization of Lymphoscintigraphy in Patients With Klippel-Trenaunay Syndrome

PURPOSE

Klippel-Trenaunay syndrome (KTS) is a rare disease that was characterized by vascular malformation. Lymphatic malformation was also commonly associated with KTS. However, the application of lymphoscintigraphy in the management of patients with KTS was rarely described. The purpose of this study is to assess whether the findings of lymphoscintigraphy can aid the management of the patients with KTS.

METHODS

A total of 28 patients with known KTS who underwent Tc-dextran lymphoscintigraphy with lower extremity tracer injection were included in this retrospective analysis. The images from lymphoscintigraphy were reviewed for any abnormalities in the body with the attention on the region of left subclavian-jugular venous angle.

RESULTS

In addition to abnormal activity in the other regions, abnormal activity in the left subclavian-jugular venous angle was visualized in over half of the patients (53.6%, 15/28). Based on the findings of the lymphoscintigraphy, 7 patients with left subclavian-jugular venous angle activity underwent thoracic duct decompression. In 4 patients with postsurgery follow-up, 3 achieved significant, measurable symptomatic relief.

CONCLUSIONS

Lymphoscintigraphy can be used to assess potential candidates for thoracic duct decompression to alleviate the symptoms in patients with KTS.

Genes and phenotypes in vascular malformations

Vascular malformations (VMs) are caused by localized defects of vascular development. Most VMs are due to sporadic, postzygotic mutations, while some are the result of autosomal dominant germline mutations. Genotype-phenotype correlation is influenced by many factors. Individual genes can induce different phenotypes (pleiotropy), and similar phenotypes can be due to different genes/mutations (redundancy). The phenotypic spectrum of somatic mutations is wide, and depends on variant allele frequency, timing during embryogenesis, cell type(s) involved and type of mutation. The phenotype of germline mutations is determined by penetrance and expressivity, and is influenced by epigenetic factors (DNA methylation, histone modification) or 'second-hit' somatic mutations. Except for disorders with pathognomonic phenotypes such as Proteus syndrome or a characteristic constellation of symptoms such as CLOVES [congenital lipomatous (fatty) overgrowth, vascular malformations, epidermal naevi and scoliosis/skeletal/spinal anomalies] or PIK3CA-related overgrowth spectrum syndrome, differential diagnosis of VM is therefore difficult. It will be greatly facilitated with increasing analytic sensitivity of sequencing techniques such as next-generation sequencing. High-sensitivity molecular techniques are a prerequisite for targeted pharmacotherapy, i.e. selective therapeutic inhibition of activating mutations underlying VM, which has shown promising results in preliminary studies.

Intrinsic Endocardial Defects Contribute to Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a complex congenital heart disease characterized by abnormalities in the left ventricle, associated valves, and ascending aorta. Studies have shown intrinsic myocardial defects but do not sufficiently explain developmental defects in the endocardial-derived cardiac valve, septum, and vasculature. Here, we identify a developmentally impaired endocardial population in HLHS through single-cell RNA profiling of hiPSC-derived endocardium and human fetal heart tissue with an underdeveloped left ventricle. Intrinsic endocardial defects contribute to abnormal endothelial-to-mesenchymal transition, NOTCH signaling, and extracellular matrix organization, key factors in valve formation. Endocardial abnormalities cause reduced cardiomyocyte proliferation and maturation by disrupting fibronectin-integrin signaling, consistent with recently described de novo HLHS mutations associated with abnormal endocardial gene and fibronectin regulation. Together, these results reveal a critical role for endocardium in HLHS etiology and provide a rationale for considering endocardial function in regenerative strategies.

EphB4 signaling maintains the contractile phenotype of adult venous smooth muscle cells

BACKGROUND

Autologous vein grafting remains the gold standard for surgical bypass grafts. However, vein bypasses still have significant incidence of failure. Ephrin type-B receptor 4 (EphB4), the embryonic venous determinant, may modulate vein graft adaptation. Although EphB4 is expressed in venous endothelial and smooth muscle cells (SMCs), it is not known whether EphB4 is functional in human SMCs.

MATERIALS AND METHODS

Human adult venous SMCs were obtained from the inferior vena cava of an adult human liver donor. Primary SMCs were stimulated with EphrinB2/Fc or transfected with an EphB4-expression vector (GV219-EphB4). Expression of SMC phenotype markers, migration, and proliferation were evaluated.

RESULTS

Activation of EphB4 with EphrinB2/Fc increased the mRNA and protein expression of the venous SMC contractile markers alpha actin, calponin-1, SM22, and MYH11, while decreasing the expression of the synthetic marker osteopontin. EphrinB2/Fc treatment inhibited SMC migration, but not proliferation. In addition, overexpression of EphB4 increased mRNA expression of SMC contractile markers, while decreasing expression of the apoptosis marker caspase-9.

CONCLUSIONS

EphB4 was present and functional in adult human venous SMCs. Stimulation of EphB4 increased expression of contractile SMC phenotypic markers and decreased SMC migration in vitro, functioning to retain the contractile phenotype of SMCs. EphB4 activation, therefore, recapitulates changes observed during vein graft adaptation to the arterial environment in vivo. EphB4 represents a new strategy to inhibit neointimal hyperplasia during vein graft adaption.

Harnessing the Power of Eph/ephrin Biosemiotics for Theranostic Applications

Comprehensive basic biological knowledge of the Eph/ephrin system in the physiologic setting is needed to facilitate an understanding of its role and the effects of pathological processes on its activity, thereby paving the way for development of prospective therapeutic targets. To this end, this review briefly addresses what is currently known and being investigated in order to highlight the gaps and possible avenues for further investigation to capitalize on their diverse potential.

Targeting connexin37 alters angiogenesis and arteriovenous differentiation in the developing mouse retina

Connexin37 (Cx37) forms intercellular channels between endothelial cells (EC), and contributes to coordinate the motor tone of vessels. We investigated the contribution of this protein during physiological angiogenesis. We show that, compared to WT littermates, mice lacking Cx37 (Cx37-/- ) featured (i) a decreased extension of the superficial vascular plexus during the first 4 days after birth; (ii) an increased vascular density at the angiogenic front at P6, due to an increase in the proliferative rate of EC and in the sprouting of the venous compartment, as well as to a somewhat displaced position of tip cells; (iii) a decreased coverage of newly formed arteries and veins by mural cells; (iv) altered ERK-dependent endothelial cells proliferation through the EphB4 signaling pathway, which is involved in the specification of veins and arteries. In vitro studies documented that, in the absence of Cx37, human venous EC (HUVEC) released less platelet-derived growth factor (PDGF) and more Angiopoietin-2, two molecules involved in the recruitment of mural cells. Treatment of mice with DAPT, an inhibitor of the Notch pathway, decreased the expression of Cx37, and partially mimicked in WT retinas, the alterations observed in Cx37-/- mice. Thus, Cx37 contributes to (i) the early angiogenesis of retina, by interacting with the Notch pathway; (ii) the growth and maturation of neo-vessels, by modulating tip, stalk, and mural cells; (iii) the regulation of arteriovenous specification, thus, representing a novel target for treatments of retina diseases.

Adult Human Vein Grafts Retain Plasticity of Vessel Identity

BACKGROUND

The spiral saphenous vein graft is an excellent choice for venous reconstruction after periphery vein injury, but only few cases have been reported. We implanted a segment of a single saphenous vein into both the popliteal vein as a venous vein graft and into the popliteal artery as an arterial vein graft at the same time in a trauma patient; we then had an extraordinary opportunity to harvest and examine both patent venous and arterial vein grafts at 2 weeks after implantation.

METHODS

A spiral saphenous vein graft was made as previously described and implanted into the popliteal vein and artery as interposition grafts; because of the patient's serious injuries, an amputation was performed at day 18 after vascular reconstruction. The grafts were harvested, fixed, and examined using histology and immunohistochemistry.

RESULTS

Both grafts were patent, and there was a larger neointimal area in the venous graft compared to the arterial graft. There were CD31- and vWF-positive cells on both neointimal endothelia, with subendothelial deposition of α-actin-, CD3-, CD45-, and CD68-positive cells. There were fewer cells in the venous graft neointima compared to the arterial graft neointima; however, there were more inflammatory cells in the neointima of the venous graft. Some of the neointimal cells were PCNA-positive, whereas very few cells were cleaved caspase-3 positive. The venous graft neointimal endothelial cells were Eph-B4 and COUP-TFII positive, while the arterial graft neointimal endothelial cells were dll-4 and Ephrin-B2 positive.

CONCLUSIONS

The spiral saphenous vein graft remains a reasonable choice for vessel reconstruction, especially in the presence of diameter mismatch. Both the venous and arterial grafts showed similar re-endothelialization and cellular deposition; the venous graft had more neointimal hyperplasia and inflammation. At an early time, endothelial cells showed venous identity in the venous graft, whereas endothelial cells showed arterial identity in the arterial graft.

CLINICAL RELEVANCE

Veins can be used as venous or arterial vein grafts but venous grafts have more neointimal hyperplasia and inflammation; vein grafts acquire different vessel identity depending on the environment into which they are implanted.

Genomic Characterization of Endothelial Enhancers Reveals a Multifunctional Role for NR2F2 in Regulation of Arteriovenous Gene Expression

RATIONALE

Significant progress has revealed transcriptional inputs that underlie regulation of artery and vein endothelial cell fates. However, little is known concerning genome-wide regulation of this process. Therefore, such studies are warranted to address this gap.

OBJECTIVE

To identify and characterize artery- and vein-specific endothelial enhancers in the human genome, thereby gaining insights into mechanisms by which blood vessel identity is regulated.

METHODS AND RESULTS

Using chromatin immunoprecipitation and deep sequencing for markers of active chromatin in human arterial and venous endothelial cells, we identified several thousand artery- and vein-specific regulatory elements. Computational analysis revealed that NR2F2 (nuclear receptor subfamily 2, group F, member 2) sites were overrepresented in vein-specific enhancers, suggesting a direct role in promoting vein identity. Subsequent integration of chromatin immunoprecipitation and deep sequencing data sets with RNA sequencing revealed that NR2F2 regulated 3 distinct aspects related to arteriovenous identity. First, consistent with previous genetic observations, NR2F2 directly activated enhancer elements flanking cell cycle genes to drive their expression. Second, NR2F2 was essential to directly activate vein-specific enhancers and their associated genes. Our genomic approach further revealed that NR2F2 acts with ERG (ETS-related gene) at many of these sites to drive vein-specific gene expression. Finally, NR2F2 directly repressed only a small number of artery enhancers in venous cells to prevent their activation, including a distal element upstream of the artery-specific transcription factor, HEY2 (hes related family bHLH transcription factor with YRPW motif 2). In arterial endothelial cells, this enhancer was normally bound by ERG, which was also required for arterial HEY2 expression. By contrast, in venous endothelial cells, NR2F2 was bound to this site, together with ERG, and prevented its activation.

CONCLUSIONS

By leveraging a genome-wide approach, we revealed mechanistic insights into how NR2F2 functions in multiple roles to maintain venous identity. Importantly, characterization of its role at a crucial artery enhancer upstream of HEY2 established a novel mechanism by which artery-specific expression can be achieved.

Promoting Roles of Embryonic Signals in Embryo Implantation and Placentation in Cooperation with Endocrine and Immune Systems

Embryo implantation in the uterus is an essential process for successful pregnancy in mammals. In general, the endocrine system induces sufficient embryo receptivity in the endometrium, where adhesion-promoting molecules increase and adhesion-inhibitory molecules decrease. Although the precise mechanisms remain unknown, it is widely accepted that maternal–embryo communications, including embryonic signals, improve the receptive ability of the sex steroid hormone-primed endometrium. The embryo may utilize repulsive forces produced by an Eph–ephrin system for its timely attachment to and subsequent invasion through the endometrial epithelial layer. Importantly, the embryonic signals are considered to act on maternal immune cells to induce immune tolerance. They also elicit local inflammation that promotes endometrial differentiation and maternal tissue remodeling during embryo implantation and placentation. Additional clarification of the immune control mechanisms by embryonic signals, such as human chorionic gonadotropin, pre-implantation factor, zona pellucida degradation products, and laeverin, will aid in the further development of immunotherapy to minimize implantation failure in the future.

Venous Mechanical Properties After Arteriovenous Fistulae in Mice

BACKGROUND

An arteriovenous fistula (AVF) exposes the outflow vein to arterial magnitudes and frequencies of blood pressure and flow, triggering molecular pathways that result in venous remodeling and AVF maturation. It is unknown, however, how venous remodeling, that is lumen dilation and wall thickening, affects venous mechanical properties. We hypothesized that a fistula is more compliant compared with a vein because of altered contributions of collagen and elastin to the mechanical properties.

METHODS

Ephb4^+/- and littermate wild-type (WT) male mice were treated with sham surgery or needle puncture to create an abdominal aortocaval fistulae. The thoracic inferior vena cava was harvested 3 wk postoperatively for mechanical testing and histological analyses of collagen and elastin.

RESULTS

Mechanical testing of the thoracic inferior vena cava from Ephb4^+/- and WT mice showed increased distensibility and increased compliance of downstream veins after AVF compared with sham. Although Ephb4^+/- veins were thicker than WT veins at the baseline, after AVF, both Ephb4^+/- and WT veins showed similar wall thickness as well as similar collagen and elastin area fractions, but increased collagen undulation compared with sham.

CONCLUSIONS

Fistula-induced remodeling of the outflow vein results in circumferentially increased distensibility and compliance, likely due to post-translational modifications to collagen.

COUP-TFII in Health and Disease

The nuclear receptors (NRs) belong to a vast family of evolutionary conserved proteins acting as ligand-activated transcription factors. Functionally, NRs are essential in embryogenesis and organogenesis and in adulthood they are involved in almost every physiological and pathological process. Our knowledge of NRs action has greatly improved in recent years, demonstrating that both their expression and activity are tightly regulated by a network of signaling pathways, miRNA and reciprocal interactions. The Chicken Ovalbumin Upstream Promoter Transcription Factor II (COUP-TFII, NR2F2) is a NR classified as an orphan due to the lack of a known natural ligand. Although its expression peaks during development, and then decreases considerably, in adult tissues, COUP-TFII is an important regulator of differentiation and it is variably implicated in tissues homeostasis. As such, alterations of its expression or its transcriptional activity have been studied and linked to a spectrum of diseases in organs and tissues of different origins. Indeed, an altered COUP-TFII expression and activity may cause infertility, abnormality in the vascular system and metabolic diseases like diabetes. Moreover, COUP-TFII is actively investigated in cancer research but its role in tumor progression is yet to be fully understood. In this review, we summarize the current understanding of COUP-TFII in healthy and pathological conditions, proposing an updated and critical view of the many functions of this NR.

Molecular Targets for Improving Arteriovenous Fistula Maturation and Patency

The increasing prevalence of chronic and end-stage renal disease creates an increased need for reliable vascular access, and although arteriovenous fistulae (AVF) are the preferred mode of hemodialysis access, 60% fail to mature and only 50% remain patent at one year. Fistulae mature by diameter expansion and wall thickening; this outward remodeling of the venous wall in the fistula environment relies on a delicate balance of extracellular matrix (ECM) remodeling, inflammation, growth factor secretion, and cell adhesion molecule upregulation in the venous wall. AVF failure occurs via two distinct mechanisms with early failure secondary to lack of outward remodeling, that is insufficient diameter expansion or wall thickening, whereas late failure occurs with excessive wall thickening due to neointimal hyperplasia (NIH) and insufficient diameter expansion in a previously functional fistula. In recent years, the molecular basis of AVF maturation and failure are becoming understood in order to develop potential therapeutic targets to aide maturation and prevent access loss. Erythropoietin-producing hepatocellular carcinoma (Eph) receptors, along with their ligands, ephrins, determine vascular identity and are critical for vascular remodeling in the embryo. Manipulation of Eph receptor signaling in adults, as well as downstream pathways, is a potential treatment strategy to improve the rates of AVF maturation and patency. This review examines our current understanding of molecular changes occurring following fistula creation, factors predictive of fistula success, and potential areas of intervention to decrease AVF failure.

Surface markers: An identity card of endothelial cells

All endothelial cells have the common characteristic that they line the vessels of the blood circulatory system. However, endothelial cells display a large degree of heterogeneity in the function of their location in the vascular tree. In this article, we have summarized the expression patterns of a number of well-accepted endothelial surface markers present in normal microvascular endothelial cells, arterial and venous endothelial cells, lymphatic endothelial cells, tumor endothelial cells, and endothelial precursor cells.

Molecular regulation of arteriovenous endothelial cell specification

The systemic circulation depends upon a highly organized, hierarchal blood vascular network that requires the successful specification of arterial and venous endothelial cells during development. This process is driven by a cascade of signaling events (including Hedgehog, vascular endothelial growth factor (VEGF), Notch, connexin (Cx), transforming growth factor-beta (TGF- β), and COUP transcription factor 2 (COUP-TFII)) to influence endothelial cell cycle status and expression of arterial or venous genes and is further regulated by hemodynamic flow. Failure of endothelial cells to properly undergo arteriovenous specification may contribute to vascular malformation and dysfunction, such as in hereditary hemorrhagic telangiectasia (HHT) and capillary malformation-arteriovenous malformation (CM-AVM) where abnormal vessel structures, such as large shunts lacking clear arteriovenous identity and function, form and compromise peripheral blood flow. This review provides an overview of recent findings in the field of arteriovenous specification and highlights key regulators of this process.

Molecular changes associated with vascular malformations

Vascular anomalies are typically classified into two major categories, vascular tumors and vascular malformations. Most vascular malformations are caused sporadically by somatic mosaic gene mutations, and genetic analyses have advanced our understanding of the biomolecular mechanisms involved in their pathogenesis. Culprit gene mutations typically involve two major signaling pathways; the RAS/MAPK/ERK pathway is typically involved in fast-flow arteriovenous malformations, whereas the PI3K/AKT/mTOR pathway is typically mutated in slow-flow venous and lymphatic malformations. These findings suggest new therapeutic approaches to vascular malformations, focusing on targeting the etiologic mutated pathways. This review summarizes the currently available literature reflecting the updated International Society for Study of Vascular Anomalies classification system with emphasis on potential therapeutic targets that will provide vascular surgeons with an updated perspective on the etiologic basis of vascular malformations, allowing improved multidisciplinary collaboration.