Signaling pathways in the specification of arteries and veins

Panorama of artery endothelial cell dysfunction in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a fatal lung disease characterized by progressive pulmonary vascular remodeling. The initial cause of pulmonary vascular remodeling is the dysfunction of pulmonary arterial endothelial cells (PAECs), manifested by changes in the categorization of cell subtypes, endothelial programmed cell death, such as apoptosis, necroptosis, pyroptosis, ferroptosis, et al., overproliferation, senescence, metabolic reprogramming, endothelial-to-mesenchymal transition, mechanosensitivity, and regulation ability of peripheral cells. Therefore, it is essential to explore the mechanism of endothelial dysfunction in the context of PAH. This review aims to provide a comprehensive understanding of the molecular mechanisms underlying endothelial dysfunction in PAH. We highlight the developmental process of PAECs and changes in PAH and summarise the latest classification of endothelial dysfunction. Our review could offer valuable insights into potential novel EC-specific targets for preventing and treating PAH.

Another Notch in the Belt of Rheumatoid Arthritis

Notch ligands and receptors, including JAG1/2, DLL1/4, and Notch1/3, are enriched on macrophages (MΦs), fibroblast-like synoviocytes (FLS), and/or endothelial cells in rheumatoid arthritis (RA) compared with normal synovial tissues (ST). Power Doppler ultrasound-guided ST studies reveal that the Notch family is highly involved in early active RA, especially during neovascularization. In contrast, the Notch family is not implicated during the erosive stage, evidenced by their lack of correlation with radiographic damage in RA ST. Toll-like receptors and tumor necrosis factor (TNF) are the common inducers of Notch expression in RA MΦs, FLS, and endothelial cells. Among Notch ligands, JAG1 and/or DLL4 are most inducible by inflammatory responses in RA MΦs or endothelial cells and transactivate their receptors on RA FLS. TNF plays a central role on Notch ligands, as anti-TNF good responders display JAG1/2 and DLL1/4 transcriptional downregulation in RA ST myeloid cells. In in vitro studies, TNF increases Notch3 expression in MΦs, which is further amplified by RA FLS addition. Specific disease-modifying antirheumatic drugs reduced JAG1 and Notch3 expression in MΦ and RA FLS cocultures. Organoids containing FLS and endothelial cells have increased expression of JAG1 and Notch3. Nonetheless, Methotrexate, interleukin-6 receptor (IL-6R) antibodies, and B cell blockers are mostly ineffective at decreasing Notch family expression. NF-κB, MAPK, and AKT pathways are involved in Notch signaling, whereas JAK/STATs are not. Although Notch blockade has been effective in RA preclinical studies, its small molecule inhibitors have failed in phase I and II studies, suggesting that alternative strategies may be required to intercept their function.

Pathophysiology in Brain Arteriovenous Malformations: Focus on Endothelial Dysfunctions and Endothelial-to-Mesenchymal Transition

Brain arteriovenous malformations (bAVMs) substantially increase the risk for intracerebral hemorrhage (ICH), which is associated with significant morbidity and mortality. However, the treatment options for bAVMs are severely limited, primarily relying on invasive methods that carry their own risks for intraoperative hemorrhage or even death. Currently, there are no pharmaceutical agents shown to treat this condition, primarily due to a poor understanding of bAVM pathophysiology. For the last decade, bAVM research has made significant advances, including the identification of novel genetic mutations and relevant signaling in bAVM development. However, bAVM pathophysiology is still largely unclear. Further investigation is required to understand the detailed cellular and molecular mechanisms involved, which will enable the development of safer and more effective treatment options. Endothelial cells (ECs), the cells that line the vascular lumen, are integral to the pathogenesis of bAVMs. Understanding the fundamental role of ECs in pathological conditions is crucial to unraveling bAVM pathophysiology. This review focuses on the current knowledge of bAVM-relevant signaling pathways and dysfunctions in ECs, particularly the endothelial-to-mesenchymal transition (EndMT).

Endothelial cell diversity: the many facets of the crystal

Endothelial cells (ECs) form the inner lining of blood vessels and play crucial roles in angiogenesis. While it has been known for a long time that there are considerable differences among ECs from lymphatic and blood vessels, as well as among arteries, veins and capillaries, the full repertoire of endothelial diversity is only beginning to be elucidated. It has become apparent that the role of ECs is not just limited to their exchange functions. Indeed, a multitude of organ-specific functions, including release of growth factors, regulation of immune functions, have been linked to ECs. Recent years have seen a surge into the identification of spatiotemporal molecular and functional heterogeneity of ECs, supported by technologies such as single-cell RNA sequencing (scRNA-seq), lineage tracing and intersectional genetics. Together, these techniques have spurred the generation of epigenomic, transcriptomic and proteomic signatures of ECs. It is now clear that ECs across organs and in different vascular beds, but even within the same vessel, have unique molecular identities and employ specialized molecular mechanisms to fulfil highly specialized needs. Here, we focus on the molecular heterogeneity of the endothelium in different organs and pathological conditions.

Vascular development, remodeling and maturation

The development of the vascular system is crucial in supporting the growth and health of all other organs in the body, and vascular system dysfunction is the major cause of human morbidity and mortality. This chapter discusses three successive processes that govern vascular system development, starting with the differentiation of the primitive vascular system in early embryonic development, followed by its remodeling into a functional circulatory system composed of arteries and veins, and its final maturation and acquisition of an organ specific semi-permeable barrier that controls nutrient uptake into tissues and hence controls organ physiology. Along these steps, endothelial cells forming the inner lining of all blood vessels acquire extensive heterogeneity in terms of gene expression patterns and function, that we are only beginning to understand. These advances contribute to overall knowledge of vascular biology and are predicted to unlock the unprecedented therapeutic potential of the endothelium as an avenue for treatment of diseases associated with dysfunctional vasculature.

A Preliminary Study of the Role of Endothelial-Mesenchymal Transitory Factor SOX 2 and CD147 in the Microvascularization of Oral Squamous Cell Carcinoma

INTRODUCTION

The aim of this study was to detect the possible endothelial expression of embryonic-type cancer stem cells (CSC) marker SOX2 and the stemness-type CSC marker CD147 in oral potential malignant disorders (OPMDs), oral leukoplakia (OL) in particular, and oral squamous cell carcinoma (OSCC).

METHODS

This study focuses on the immunohistochemical pattern of expression of CSC protein-biomarkers SOX2 and CD147 in paraffin-embedded samples of 21 OSCCs of different grades of differentiation and 30 cases of OLs with different grades of dysplasia, compared to normal oral mucosa.

RESULTS

The protein biomarker SOX2 was expressed in the endothelial cells, but without establishing any statistically significant correlation among OSCC, OL, and normal tissue specimens. However, SOX endothelial staining was noticed in 7/30 (23.3%) cases of OL (one non-dysplastic, one mildly dysplastic, one moderately dysplastic, and four severely dysplastic cases) and 5/21 (23.8%) cases of OSCC (two well-differentiated, one moderately differentiated, and two poorly differentiated cases). Although CD147 is expressed in normal oral epithelium, OL, and OSCC neoplastic cells, its vascular-endothelial expression was noticed in only 2/5 (40%) cases of normal oral epithelium, 1/30 (3.3%) cases of OL (one severely dysplastic case), and 4/21 (19%) cases of OSCC (two well-differentiated, one moderately differentiated, and one poorly differentiated case). Therefore, no statistically significant correlation among OSCC, OL, and normal tissue specimens was established.

CONCLUSION

The endothelial presence of SOX2 both in oral potentially malignant and malignant lesions suggests that SOX2 may be implicated in the microvascularization process and associated with the degree of dysplasia in OL. The expression of CD147 may be attributed both to local inflammation and tumorigenesis. The implementation of CD147 in larger groups of tissue samples will shed some light on its role in cancer and inflammation. The evidence so far supports the need for more studies, which may support the clinical significance of these novel cancer stem cell biomarkers.

Applications and Considerations for Microfluidic Systems To Model the Blood-Brain Barrier

In a myriad of developmental and degenerative brain diseases, characteristic pathological biomarkers are often associated with cerebral blood flow and vasculature. However, the relationship between vascular dysfunction and markers of brain disease is not well-defined. Additionally, it is difficult to deliver effective therapeutics to the brain due to the highly regulated blood-brain barrier (BBB) at the microvasculature interface of the brain. This Review first covers the need for modeling the BBB and the challenges of modeling the BBB. In vitro models of the BBB enable the study of the relationship between vascular dysfunction, BBB function, and disease progression and can serve as a platform to screen therapeutics. In particular, microfluidic-based in vitro BBB models are useful for studying brain vasculature as they support cell culture within the presence of continuous perfusion, which mirrors the in vivo flow and associated stress conditions in the brain. Early microfluidic models of the BBB created the most simplistic models possible that still displayed some functional aspects of the in vivo BBB. Therefore, this Review also discusses the emerging unique ways in which microfluidics in tandem with recent advancements in cell culture, biomaterials, and in vitro modeling can be used to develop more complex and physiologically relevant models of the BBB. Finally, we discuss the current and future state-of-the-art application of microfluidic BBB models for drug development and disease modeling, and the ongoing areas of needed innovation in this field.

CD82 expression marks the endothelium to hematopoietic transition at the onset of blood specification in human

During embryonic development, all blood progenitors are initially generated from endothelial cells that acquire a hemogenic potential. Blood progenitors emerge through an endothelial-to-hematopoietic transition regulated by the transcription factor RUNX1. To date, we still know very little about the molecular characteristics of hemogenic endothelium and the molecular changes underlying the transition from endothelium to hematopoiesis. Here, we analyzed at the single cell level a human embryonic stem cell-derived endothelial population containing hemogenic potential. RUNX1-expressing endothelial cells, which harbor enriched hemogenic potential, show very little molecular differences to their endothelial counterpart suggesting priming toward hemogenic potential rather than commitment. Additionally, we identify CD82 as a marker of the endothelium-to-hematopoietic transition. CD82 expression is rapidly upregulated in newly specified blood progenitors then rapidly downregulated as further differentiation occurs. Together our data suggest that endothelial cells are first primed toward hematopoietic fate, and then rapidly undergo the transition from endothelium to blood.

Mathematical models of developmental vascular remodelling: A review

Over the past 40 years, there has been a strong focus on the development of mathematical models of angiogenesis, while developmental remodelling has received little such attention from the mathematical community. Sprouting angiogenesis can be seen as a very crude way of laying out a primitive vessel network (the raw material), while remodelling (understood as pruning of redundant vessels, diameter control, and the establishment of vessel identity and hierarchy) is the key to turning that primitive network into a functional network. This multiscale problem is of prime importance in the development of a functional vasculature. In addition, defective remodelling (either during developmental remodelling or due to a reactivation of the remodelling programme caused by an injury) is associated with a significant number of diseases. In this review, we discuss existing mathematical models of developmental remodelling and explore the important contributions that these models have made to the field of vascular development. These mathematical models are effectively used to investigate and predict vascular development and are able to reproduce experimentally observable results. Moreover, these models provide a useful means of hypothesis generation and can explain the underlying mechanisms driving the observed structural and functional network development. However, developmental vascular remodelling is still a relatively new area in mathematical biology, and many biological questions remain unanswered. In this review, we present the existing modelling paradigms and define the key challenges for the field.

Insights gained from single-cell RNA analysis of murine endothelial cells in aging hearts

Aging is the strongest risk factor for cardiovascular disease, with progressive decline in the function of vascular endothelial cells (ECs) with age. Systematic analyses of the effects of aging on different cardiac EC types remain limited. Here, we constructed a scRNA atlas of EC transcriptomes in young and old mouse hearts. We identified 10 EC subclusters. The multidimensionally differential genes (DEGs) analysis across different EC clusters shows molecular changes with aging, showing the increase in the overall inflammatory microenvironment and the decrease in angiogenesis and cytoskeletal support capacity of aged ECs. And we performed an in-depth analysis of 3 special ECs, Immunology, Proliferating and Angiogenic. The Immunology EC seems highly associated with some immune regulatory functions, which decline with aging at different degrees. Analysis of two types of neovascular ECs, Proliferating, Angiogenic, implied that Angiogenic ECs can differentiate into multiple EC directions after initially originating from proliferating ECs. And aging leads to a decrease in the ability of vascular angiogenesis and differentiation. Finally, we summarized the effects of aging on cell signaling communication between different EC clusters. This cardiac EC atlas offers comprehensive insights into the molecular regulations of cardiovascular aging, and provides new directions for the prevention and treatment of age-related cardiovascular disease.

Extracellular matrix cues regulate the differentiation of pluripotent stem cell-derived endothelial cells

The generation of endothelial cells (ECs) from human pluripotent stem cells (PSCs) has been a promising approach for treating cardiovascular diseases for several years. Human PSCs, particularly induced pluripotent stem cells (iPSCs), are an attractive source of ECs for cell therapy. Although there is a diversity of methods for endothelial cell differentiation using biochemical factors, such as small molecules and cytokines, the efficiency of EC production varies depending on the type and dose of biochemical factors. Moreover, the protocols in which most EC differentiation studies have been performed were in very unphysiological conditions that do not reflect the microenvironment of native tissue. The microenvironment surrounding stem cells exerts variable biochemical and biomechanical stimuli that can affect stem cell differentiation and behavior. The stiffness and components of the extracellular microenvironment are critical inducers of stem cell behavior and fate specification by sensing the extracellular matrix (ECM) cues, adjusting the cytoskeleton tension, and delivering external signals to the nucleus. Differentiation of stem cells into ECs using a cocktail of biochemical factors has been performed for decades. However, the effects of mechanical stimuli on endothelial cell differentiation remain poorly understood. This review provides an overview of the methods used to differentiate ECs from stem cells by chemical and mechanical stimuli. We also propose the possibility of a novel EC differentiation strategy using a synthetic and natural extracellular matrix.

Vascular endothelial cell development and diversity

Vascular endothelial cells form the inner layer of blood vessels where they have a key role in the development and maintenance of the functional circulatory system and provide paracrine support to surrounding non-vascular cells. Technical advances in the past 5 years in single-cell genomics and in in vivo genetic labelling have facilitated greater insights into endothelial cell development, plasticity and heterogeneity. These advances have also contributed to a new understanding of the timing of endothelial cell subtype differentiation and its relationship to the cell cycle. Identification of novel tissue-specific gene expression patterns in endothelial cells has led to the discovery of crucial signalling pathways and new interactions with other cell types that have key roles in both tissue maintenance and disease pathology. In this Review, we describe the latest findings in vascular endothelial cell development and diversity, which are often supported by large-scale, single-cell studies, and discuss the implications of these findings for vascular medicine. In addition, we highlight how techniques such as single-cell multimodal omics, which have become increasingly sophisticated over the past 2 years, are being utilized to study normal vascular physiology as well as functional perturbations in disease.

Role of angiogenic transdifferentiation in vascular recovery

Tissue repair requires the orchestration of multiple processes involving a multiplicity of cellular effectors, signaling pathways, and cell-cell communication. The regeneration of the vasculature is a critical process for tissue repair and involves angiogenesis, adult vasculogenesis, and often arteriogenesis, which processes enable recovery of perfusion to deliver oxygen and nutrients to the repair or rebuild of the tissue. Endothelial cells play a major role in angiogenesis, whereas circulating angiogenic cells (primarily of hematopoietic origin) participate in adult vasculogenesis, and monocytes/macrophages have a defining role in the vascular remodeling that is necessary for arteriogenesis. Tissue fibroblasts participate in tissue repair by proliferating and generating the extracellular matrix as the structural scaffold for tissue regeneration. Heretofore, fibroblasts were not generally believed to be involved in vascular regeneration. However, we provide new data indicating that fibroblasts may undergo angiogenic transdifferentiation, to directly expand the microvasculature. Transdifferentiation of fibroblasts to endothelial cells is initiated by inflammatory signaling which increases DNA accessibility and cellular plasticity. In the environment of under-perfused tissue, the activated fibroblasts with increased DNA accessibility can now respond to angiogenic cytokines, which provide the transcriptional direction to induce fibroblasts to become endothelial cells. Periphery artery disease (PAD) involves the dysregulation of vascular repair and inflammation. Understanding the relationship between inflammation, transdifferentiation, and vascular regeneration may lead to a new therapeutic approach to PAD.

Non-cardiomyocytes in the heart in embryo development, health, and disease, a single-cell perspective

Recent single-cell atlases of the heart gave unprecedented details about the diversity of cell types and states during heart development in health and disease conditions. Beyond a profiling tool, researchers also use single-cell analyses to dissect the mechanism of diseases in animal models. The new knowledge from these studies revealed that beating cardiomyocytes account for less than 50% of the total heart cell population. In contrast, non-cardiomyocytes (NCMs), such as cardiac fibroblasts, endothelial cells, and immune cells, make up the remaining proportion and have indispensable roles in structural support, homeostasis maintenance, and injury repair of the heart. In this review, we categorize the composition and characteristics of NCMs from the latest single-cell studies of the heart in various contexts and compare the findings from both human samples and mouse models. This information will enrich our understanding of the cellular basis of heart development and diseases and provide insights into the potential therapeutic targets in NCMs to repair the heart.

Quantification and Visualization of Reliable Hemodynamics Evaluation Based on Non-Contact Arteriovenous Fistula Measurement

The condition of arteriovenous fistula (AVF) blood flow is typically checked by using auscultation; however, auscultation should require a qualitative judgment dependent on the skills of doctors, and further attention to contact infection is required. For these reasons, this study developed a non-contact and non-invasive medical device to measure the pulse wave of AVFs by applying optical imaging technology. As a first step toward realization of the quantification judgment based on non-contact AVF measurement, we experimentally validated the developed system, whereby the hemodynamics of 168 subjects were visually and quantitatively evaluated based on clinical tests. Based on the evaluation results, the fundamental statistical characteristics of the non-contact measurement, including the average and median values, and distribution of measured signal-to-noise power ratio, were demonstrated. The clinical test results contributed to the future construction of quantified criteria for the AVF condition with the non-contact measurement.

Notch signaling pathway: architecture, disease, and therapeutics

The NOTCH gene was identified approximately 110 years ago. Classical studies have revealed that NOTCH signaling is an evolutionarily conserved pathway. NOTCH receptors undergo three cleavages and translocate into the nucleus to regulate the transcription of target genes. NOTCH signaling deeply participates in the development and homeostasis of multiple tissues and organs, the aberration of which results in cancerous and noncancerous diseases. However, recent studies indicate that the outcomes of NOTCH signaling are changeable and highly dependent on context. In terms of cancers, NOTCH signaling can both promote and inhibit tumor development in various types of cancer. The overall performance of NOTCH-targeted therapies in clinical trials has failed to meet expectations. Additionally, NOTCH mutation has been proposed as a predictive biomarker for immune checkpoint blockade therapy in many cancers. Collectively, the NOTCH pathway needs to be integrally assessed with new perspectives to inspire discoveries and applications. In this review, we focus on both classical and the latest findings related to NOTCH signaling to illustrate the history, architecture, regulatory mechanisms, contributions to physiological development, related diseases, and therapeutic applications of the NOTCH pathway. The contributions of NOTCH signaling to the tumor immune microenvironment and cancer immunotherapy are also highlighted. We hope this review will help not only beginners but also experts to systematically and thoroughly understand the NOTCH signaling pathway.

Brain Vascular Microenvironments in Cancer Metastasis

Primary tumours, particularly from major solid organs, are able to disseminate into the blood and lymphatic system and spread to distant sites. These secondary metastases to other major organs are the most lethal aspect of cancer, accounting for the majority of cancer deaths. The brain is a frequent site of metastasis, and brain metastases are often fatal due to the critical role of the nervous system and the limited options for treatment, including surgery. This creates a need to further understand the complex cell and molecular biology associated with the establishment of brain metastasis, including the changes to the environment of the brain to enable the arrival and growth of tumour cells. Local changes in the vascular network, immune system and stromal components all have the potential to recruit and foster metastatic tumour cells. This review summarises our current understanding of brain vascular microenvironments, fluid circulation and drainage in the context of brain metastases, as well as commenting on current cutting-edge experimental approaches used to investigate changes in vascular environments and alterations in specialised subsets of blood and lymphatic vessel cells during cancer spread to the brain.

Heterogeneity in endothelial cells and widespread venous arterialization during early vascular development in mammals

Arteriogenesis rather than unspecialized capillary expansion is critical for restoring effective circulation to compromised tissues in patients. Deciphering the origin and specification of arterial endothelial cells during embryonic development will shed light on the understanding of adult arteriogenesis. However, during early embryonic angiogenesis, the process of endothelial diversification and molecular events underlying arteriovenous fate settling remain largely unresolved in mammals. Here, we constructed the single-cell transcriptomic landscape of vascular endothelial cells (VECs) during the time window for the occurrence of key vasculogenic and angiogenic events in both mouse and human embryos. We uncovered two distinct arterial VEC types, the major artery VECs and arterial plexus VECs, and unexpectedly divergent arteriovenous characteristics among VECs that are located in morphologically undistinguishable vascular plexus intra-embryonically. Using computational prediction and further lineage tracing of venous-featured VECs with a newly developed Nr2f2CrexER mouse model and a dual recombinase-mediated intersectional genetic approach, we revealed early and widespread arterialization from the capillaries with considerable venous characteristics. Altogether, our findings provide unprecedented and comprehensive details of endothelial heterogeneity and lineage relationships at early angiogenesis stages, and establish a new model regarding the arteriogenesis behaviors of early intra-embryonic vasculatures.

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.

A census of the lung: CellCards from LungMAP

The human lung plays vital roles in respiration, host defense, and basic physiology. Recent technological advancements such as single-cell RNA sequencing and genetic lineage tracing have revealed novel cell types and enriched functional properties of existing cell types in lung. The time has come to take a new census. Initiated by members of the NHLBI-funded LungMAP Consortium and aided by experts in the lung biology community, we synthesized current data into a comprehensive and practical cellular census of the lung. Identities of cell types in the normal lung are captured in individual cell cards with delineation of function, markers, developmental lineages, heterogeneity, regenerative potential, disease links, and key experimental tools. This publication will serve as the starting point of a live, up-to-date guide for lung research at https://www.lungmap.net/cell-cards/. We hope that Lung CellCards will promote the community-wide effort to establish, maintain, and restore respiratory health.

Human Induced Pluripotent Stem Cell-Derived Vascular Cells: Recent Progress and Future Directions

Human induced pluripotent stem cells (hiPSCs) hold great promise for cardiovascular regeneration following ischemic injury. Considerable effort has been made toward the development and optimization of methods to differentiate hiPSCs into vascular cells, such as endothelial and smooth muscle cells (ECs and SMCs). In particular, hiPSC-derived ECs have shown robust potential for promoting neovascularization in animal models of cardiovascular diseases, potentially achieving significant and sustained therapeutic benefits. However, the use of hiPSC-derived SMCs that possess high therapeutic relevance is a relatively new area of investigation, still in the earlier investigational stages. In this review, we first discuss different methodologies to derive vascular cells from hiPSCs with a particular emphasis on the role of key developmental signals. Furthermore, we propose a standardized framework for assessing and defining the EC and SMC identity that might be suitable for inducing tissue repair and regeneration. We then highlight the regenerative effects of hiPSC-derived vascular cells on animal models of myocardial infarction and hindlimb ischemia. Finally, we address several obstacles that need to be overcome to fully implement the use of hiPSC-derived vascular cells for clinical application.

Spatiotemporal and Functional Heterogeneity of Hematopoietic Stem Cell-Competent Hemogenic Endothelial Cells in Mouse Embryos

Hematopoietic stem cells (HSCs) are derived from hemogenic endothelial cells (HECs) during embryogenesis. The HSC-primed HECs increased to the peak at embryonic day (E) 10 and have been efficiently captured by the marker combination CD41^-CD43^-CD45^-CD31⁺CD201⁺Kit⁺CD44⁺ (PK44) in the aorta-gonad-mesonephros (AGM) region of mouse embryos most recently. In the present study, we investigated the spatiotemporal and functional heterogeneity of PK44 cells around the time of emergence of HSCs. First, PK44 cells in the E10.0 AGM region could be further divided into three molecularly different populations showing endothelial- or hematopoietic-biased characteristics. Specifically, with the combination of Kit, the expression of CD93 or CD146 could divide PK44 cells into endothelial- and hematopoietic-feature biased populations, which was further functionally validated at the single-cell level. Next, the PK44 population could also be detected in the yolk sac, showing similar developmental dynamics and functional diversification with those in the AGM region. Importantly, PK44 cells in the yolk sac demonstrated an unambiguous multilineage reconstitution capacity after in vitro incubation. Regardless of the functional similarity, PK44 cells in the yolk sac displayed transcriptional features different from those in the AGM region. Taken together, our work delineates the spatiotemporal characteristics of HECs represented by PK44 and reveals a previously unknown HSC competence of HECs in the yolk sac. These findings provide a fundamental basis for in-depth study of the different origins and molecular programs of HSC generation in the future.

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.

Therapeutic Potential of Endothelial Progenitor Cells in Pulmonary Diseases

Compromised alveolar development and pulmonary vascular remodeling are hallmarks of pediatric lung diseases such as bronchopulmonary dysplasia (BPD) and alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). Although advances in surfactant therapy, corticosteroids, and anti-inflammatory drugs have improved clinical management of preterm infants, still those who suffer with severe vascular complications lack viable treatment options. Paucity of the alveolar capillary network in ACDMPV causes respiratory distress and leads to mortality in a vast majority of ACDMPV infants. The discovery of endothelial progenitor cells (EPCs) in 1997 brought forth the paradigm of postnatal vasculogenesis and hope for promoting vascularization in fragile patient populations, such as those with BPD and ACDMPV. The identification of diverse EPC populations, both hematopoietic and nonhematopoietic in origin, provided a need to identify progenitor cell selective markers which are linked to progenitor properties needed to develop cell-based therapies. Focusing to the future potential of EPCs for regenerative medicine, this review will discuss various aspects of EPC biology, beginning with the identification of hematopoietic, nonhematopoietic, and tissue-resident EPC populations. We will review knowledge related to cell surface markers, signature gene expression, key transcriptional regulators, and will explore the translational potential of EPCs for cell-based therapy for BPD and ACDMPV. The ability to produce pulmonary EPCs from patient-derived induced pluripotent stem cells (iPSCs) in vitro, holds promise for restoring vascular growth and function in the lungs of patients with pediatric pulmonary disorders.

Emerging Approaches to Understanding Microvascular Endothelial Heterogeneity: A Roadmap for Developing Anti-Inflammatory Therapeutics

The endothelium is the inner layer of all blood vessels and it regulates hemostasis. It also plays an active role in the regulation of the systemic inflammatory response. Systemic inflammatory disease often results in alterations in vascular endothelium barrier function, increased permeability, excessive leukocyte trafficking, and reactive oxygen species production, leading to organ damage. Therapeutics targeting endothelium inflammation are urgently needed, but strong concerns regarding the level of phenotypic heterogeneity of microvascular endothelial cells between different organs and species have been expressed. Microvascular endothelial cell heterogeneity in different organs and organ-specific variations in endothelial cell structure and function are regulated by intrinsic signals that are differentially expressed across organs and species; a result of this is that neutrophil recruitment to discrete organs may be regulated differently. In this review, we will discuss the morphological and functional variations in differently originated microvascular endothelia and discuss how these variances affect systemic function in response to inflammation. We will review emerging in vivo and in vitro models and techniques, including microphysiological devices, proteomics, and RNA sequencing used to study the cellular and molecular heterogeneity of endothelia from different organs. A better understanding of microvascular endothelial cell heterogeneity will provide a roadmap for developing novel therapeutics to target the endothelium.

Developmental Perspectives on Arterial Fate Specification

Blood vessel acquisition of arterial or venous fate is an adaptive phenomenon in response to increasing blood circulation during vascular morphogenesis. The past two decades of effort in this field led to development of a widely accepted paradigm of molecular regulators centering on VEGF and Notch signaling. More recent findings focused on shear stress-induced cell cycle arrest as a prerequisite for arterial specification substantially modify this traditional understanding. This review aims to summarize key molecular mechanisms that work in concert to drive the acquisition of arterial fate in two distinct developmental settings of vascular morphogenesis: de novo vasculogenesis of the dorsal aorta and postnatal retinal angiogenesis. We will also discuss the questions and conceptual controversies that potentially point to novel directions of investigation and possible clinical relevance.

Shifting osteogenesis in vascular calcification

Transitions between cell fates commonly occur in development and disease. However, reversing an unwanted cell transition in order to treat disease remains an unexplored area. Here, we report a successful process of guiding ill-fated transitions toward normalization in vascular calcification. Vascular calcification is a severe complication that increases the all-cause mortality of cardiovascular disease but lacks medical therapy. The vascular endothelium is a contributor of osteoprogenitor cells to vascular calcification through endothelial-mesenchymal transitions, in which endothelial cells (ECs) gain plasticity and the ability to differentiate into osteoblast-like cells. We created a high-throughput screening and identified SB216763, an inhibitor of glycogen synthase kinase 3 (GSK3), as an inducer of osteoblastic-endothelial transition. We demonstrated that SB216763 limited osteogenic differentiation in ECs at an early stage of vascular calcification. Lineage tracing showed that SB216763 redirected osteoblast-like cells to the endothelial lineage and reduced late-stage calcification. We also found that deletion of GSK3β in osteoblasts recapitulated osteoblastic-endothelial transition and reduced vascular calcification. Overall, inhibition of GSK3β promoted the transition of cells with osteoblastic characteristics to endothelial differentiation, thereby ameliorating vascular calcification.

Selective Endothelial Hyperactivation of Oncogenic KRAS Induces Brain Arteriovenous Malformations in Mice

OBJECTIVE

Brain arteriovenous malformations (bAVMs) are a leading cause of hemorrhagic stroke and neurological deficits in children and young adults, however, no pharmacological intervention is available to treat these patients. Although more than 95% of bAVMs are sporadic without family history, the pathogenesis of sporadic bAVMs is largely unknown, which may account for the lack of therapeutic options. KRAS mutations are frequently observed in cancer, and a recent unprecedented finding of these mutations in human sporadic bAVMs offers a new direction in the bAVM research. Using a novel adeno-associated virus targeting brain endothelium (AAV-BR1), the current study tested if endothelial KRAS^G12V mutation induces sporadic bAVMs in mice.

METHODS

Five-week-old mice were systemically injected with either AAV-BR1-GFP or -KRAS^G12V . At 8 weeks after the AAV injection, bAVM formation and characteristics were addressed by histological and molecular analyses. The effect of MEK/ERK inhibition on KRAS^G12V -induced bAVMs was determined by treatment of trametinib, a US Food and Drug Administration (FDA)-approved MEK/ERK inhibitor.

RESULTS

The viral-mediated KRAS^G12V overexpression induced bAVMs, which were composed of a tangled nidus mirroring the distinctive morphology of human bAVMs. The bAVMs were accompanied by focal angiogenesis, intracerebral hemorrhages, altered vascular constituents, neuroinflammation, and impaired sensory/cognitive/motor functions. Finally, we confirmed that bAVM growth was inhibited by trametinib treatment.

INTERPRETATION

Our innovative approach using AAV-BR1 confirms that KRAS mutations promote bAVM development via the MEK/ERK pathway, and provides a novel preclinical mouse model of bAVMs which will be useful to develop a therapeutic strategy for patients with bAVM. ANN NEUROL 2021;89:926-941.

Wilms' Tumor 1-Associated Protein Contributes to Chemo-Resistance to Cisplatin Through the Wnt/β-Catenin Pathway in Endometrial Cancer

BACKGROUND

Cisplatin remains the mainstay of endometrial cancer (EC) chemotherapy. Wilms' tumor 1-associated protein (WTAP), playing a critical role in transcriptional and post-transcriptional regulation, has been reported as an oncogene, and its expression is elevated in multiple types of human tumors. Recent evidence has shown that the increased expression of WTAP is also closely related to chemo-resistance. However, its specific role in the susceptibility of human EC cells to cisplatin remains largely unexplored.

METHODS

WTAP over-expression and WTAP depletion cell lines as well as their corresponding controls were constructed by transfection with lentivirus. Western blotting analysis and quantitative real-time polymerase chain reaction (qRT-PCR) were employed to detect the expression of WTAP. Cell proliferation assay, colony formation assay, cell cycle assay, and apoptosis analysis were adopted to evaluate the effect of WTAP on the chemo-sensitivity of EC cells to cisplatin as well as its underlying mechanism. Immunofluorescence staining was used to assess the translocation of β-catenin. Moreover, a subcutaneous xenograft tumor model was established to assess the effect of WTAP on tumor growth after cisplatin treatment.

RESULTS

Depletion of WTAP in RL95-2 cells significantly enhanced the chemo-susceptibility of cells to cisplatin and increased the cell apoptosis, while WTAP over-expression in ARK-2 cells exhibited the opposite effects. Additionally, WTAP depletion significantly suppressed xenograft-tumor growth and enhanced sensitivity and apoptosis of tumor cells in vivo. Mechanistic analysis exhibited that WTAP over-expression facilitated the cytoplasm-to-nucleus translocation of β-catenin and enhanced the GSK3β phosphorylation at Ser9, while WTAP depletion revealed the opposite results, indicating that WTAP rendered chemo-resistance of EC cells to cisplatin by promoting the Wnt/β-catenin pathway.

CONCLUSIONS

WTAP might promote the chemo-resistance of EC cells to cisplatin through activating the Wnt/β-catenin pathway. Collectively, our findings offered novel insights into EC treatment.

Development and Application of Endothelial Cells Derived From Pluripotent Stem Cells in Microphysiological Systems Models

The vascular endothelium is present in all organs and blood vessels, facilitates the exchange of nutrients and waste throughout different organ systems in the body, and sets the tone for healthy vessel function. Mechanosensitive in nature, the endothelium responds to the magnitude and temporal waveform of shear stress in the vessels. Endothelial dysfunction can lead to atherosclerosis and other diseases. Modeling endothelial function and dysfunction in organ systems in vitro, such as the blood-brain barrier and tissue-engineered blood vessels, requires sourcing endothelial cells (ECs) for these biomedical engineering applications. It can be difficult to source primary, easily renewable ECs that possess the function or dysfunction in question. In contrast, human pluripotent stem cells (hPSCs) can be sourced from donors of interest and renewed almost indefinitely. In this review, we highlight how knowledge of vascular EC development in vivo is used to differentiate induced pluripotent stem cells (iPSC) into ECs. We then describe how iPSC-derived ECs are being used currently in in vitro models of organ function and disease and in vivo applications.

Endothelial dysfunction and cardiovascular risk in lupus nephritis: New roles for old players?

In systemic lupus erythematosus (SLE) patients, most of the clinical manifestation share a vascular component triggered by endothelial dysfunction. Endothelial cells (ECs) activation occurs both on the arterial and venous side, and the high vascular density of kidneys accounts for the detrimental outcomes of SLE through lupus nephritis (LN). Kidney damage, in turn, exerts a negative feedback on the cardiovascular (CV) system aggravating risk factors for CV diseases such as hypertension, stroke and coronary syndrome among others. Despite the intensive investigation on SLE and LN, the role of endothelial dysfunction, as well as the underlying mechanisms, remains to be fully understood, with no specifically targeted pharmacological treatment. It is not known, in fact, if the activation pathway(s) in venous ECs are similar to the one in arterial ECs and doubts persist on the shared manifestation of microcirculation compared to macrocirculation. In this work, we aim to review the recent literature about the role of endothelial activation and dysfunction in the development of CV complications in SLE and LN patients. We, therefore, focus on arteriovenous similarities and differences and on specific pathways of great vessels compared to capillaries. Critically summarising the available data is of pivotal importance for both basic researchers and clinicians in order to develop and test new pharmacological approaches in the treatment of basic components of SLE and LN.

Location, Location, Location: How Vascular Specialization Influences Hematopoietic Fates During Development

During embryonic development, sequential waves of hematopoiesis give rise to blood-forming cells with diverse lineage potentials and self-renewal properties. This process must accomplish two important yet divergent goals: the rapid generation of differentiated blood cells to meet the needs of the developing embryo and the production of a reservoir of hematopoietic stem cells to provide for life-long hematopoiesis in the adult. Vascular beds in distinct anatomical sites of extraembryonic tissues and the embryo proper provide the necessary conditions to support these divergent objectives, suggesting a critical role for specialized vascular niche cells in regulating disparate blood cell fates during development. In this review, we will examine the current understanding of how organ- and stage-specific vascular niche specialization contributes to the development of the hematopoietic system.

PRL-2 phosphatase is required for vascular morphogenesis and angiogenic signaling

Protein tyrosine phosphatases are essential modulators of angiogenesis and have been identified as novel therapeutic targets in cancer and anti-angiogenesis. The roles of atypical Phosphatase of Regenerative Liver (PRL) phosphatases in this context remain poorly understood. Here, we investigate the biological function of PRL phosphatases in developmental angiogenesis in the postnatal mouse retina and in cell culture. We show that endothelial cells in the retina express PRL-2 encoded by the Ptp4a2 gene, and that inducible endothelial and global Ptp4a2 mutant mice exhibit defective retinal vascular outgrowth, arteriovenous differentiation, and sprouting angiogenesis. Mechanistically, PTP4A2 deletion limits angiogenesis by inhibiting endothelial cell migration and the VEGF-A, DLL-4/NOTCH-1 signaling pathway. This study reveals the importance of PRL-2 as a modulator of vascular development.

Cells of the adult human heart

Cardiovascular disease is the leading cause of death worldwide. Advanced insights into disease mechanisms and therapeutic strategies require a deeper understanding of the molecular processes involved in the healthy heart. Knowledge of the full repertoire of cardiac cells and their gene expression profiles is a fundamental first step in this endeavour. Here, using state-of-the-art analyses of large-scale single-cell and single-nucleus transcriptomes, we characterize six anatomical adult heart regions. Our results highlight the cellular heterogeneity of cardiomyocytes, pericytes and fibroblasts, and reveal distinct atrial and ventricular subsets of cells with diverse developmental origins and specialized properties. We define the complexity of the cardiac vasculature and its changes along the arterio-venous axis. In the immune compartment, we identify cardiac-resident macrophages with inflammatory and protective transcriptional signatures. Furthermore, analyses of cell-to-cell interactions highlight different networks of macrophages, fibroblasts and cardiomyocytes between atria and ventricles that are distinct from those of skeletal muscle. Our human cardiac cell atlas improves our understanding of the human heart and provides a valuable reference for future studies.

P130Cas/bcar1 mediates zebrafish caudal vein plexus angiogenesis

P130CAS/BCAR1 belongs to the CAS family of adaptor proteins, with important regulatory roles in cell migration, cell cycle control, and apoptosis. Previously, we and others showed that P130CAS mediates VEGF-A and PDGF signalling in vitro, but its cardiovascular function in vivo remains relatively unexplored. We characterise here a novel deletion model of P130CAS in zebrafish. Using in vivo microscopy and transgenic vascular reporters, we observed that while bcar1−/− zebrafish showed no arterial angiogenic or heart defects during development, they strikingly failed to form the caudal vein plexus (CVP). Endothelial cells (ECs) within the CVP of bcar1−/− embryos produced fewer filopodial structures and did not detach efficiently from neighbouring cells, resulting in a significant reduction in ventral extension and overall CVP area. Mechanistically, we show that P130Cas mediates Bmp2b-induced ectopic angiogenic sprouting of ECs in the developing embryo and provide pharmacological evidence for a role of Src family kinases in CVP development.

Cancer Stem Cells, Quo Vadis? The Notch Signaling Pathway in Tumor Initiation and Progression

The Notch signaling pathway regulates cell proliferation, cytodifferentiation and cell fate decisions in both embryonic and adult life. Several aspects of stem cell maintenance are dependent from the functionality and fine tuning of the Notch pathway. In cancer, Notch is specifically involved in preserving self-renewal and amplification of cancer stem cells, supporting the formation, spread and recurrence of the tumor. As the function of Notch signaling is context dependent, we here provide an overview of its activity in a variety of tumors, focusing mostly on its role in the maintenance of the undifferentiated subset of cancer cells. Finally, we analyze the potential of molecules of the Notch pathway as diagnostic and therapeutic tools against the various cancers.

Transcriptome analysis of common and diverged circulating miRNAs between arterial and venous during aging

Circulating miRNAs have received extensive attention as non-invasive biomarkers for prediction and diagnosis of disease. However, most samples have been obtained from peripheral venous blood. To evaluate whether peripheral venous miRNAs represent circulating miRNAs from all blood vessels under a given condition, such as aging, we compared the miRNA profiles of venous and arterial plasma between young and aged rats by Illumina next-generation sequencing. The DEseq2 tool was used to obtain differentially-expressed miRNAs. We observed 105 aging-related deregulated miRNAs in vein and 62 in artery, which were highly associated with cell survival and inflammation, respectively. On the other hand, the young and aged groups exhibited a unique arterial-venous bias. There were 54 differentially-expressed miRNAs in the young group and 42 in the aged group; only 8 miRNAs were shared. Further transcriptional factors enrichment analysis found that the shared miRNAs could be partially upregulated by NF-κB and SIRT1. These transcriptional factors could be organ-specific and/or regulated in physiological and aging states as possible causal factors. This study suggested the potential application of circulating miRNAs, which reflect the systematic response to certain conditions, such as aging, and the importance of origin selection for candidate circulating miRNAs.

The Importance of Mechanical Forces for in vitro Endothelial Cell Biology

Blood and lymphatic vessels are lined by endothelial cells which constantly interact with their luminal and abluminal extracellular environments. These interactions confer physical forces on the endothelium, such as shear stress, stretch and stiffness, to mediate biological responses. These physical forces are often altered during disease, driving abnormal endothelial cell behavior and pathology. Therefore, it is critical that we understand the mechanisms by which endothelial cells respond to physical forces. Traditionally, endothelial cells in culture are grown in the absence of flow on stiff substrates such as plastic or glass. These cells are not subjected to the physical forces that endothelial cells endure in vivo, thus the results of these experiments often do not mimic those observed in the body. The field of vascular biology now realize that an intricate analysis of endothelial signaling mechanisms requires complex in vitro systems to mimic in vivo conditions. Here, we will review what is known about the mechanical forces that guide endothelial cell behavior and then discuss the advancements in endothelial cell culture models designed to better mimic the in vivo vascular microenvironment. A wider application of these technologies will provide more biologically relevant information from cultured cells which will be reproducible to conditions found in the body.

Wilms' tumour 1-associating protein inhibits endothelial cell angiogenesis by m6A-dependent epigenetic silencing of desmoplakin in brain arteriovenous malformation

Brain arteriovenous malformations (AVMs) are congenital vascular abnormality in which arteries and veins connect directly without an intervening capillary bed. So far, the pathogenesis of brain AVMs remains unclear. Here, we found that Wilms' tumour 1‐associating protein (WTAP), which has been identified as a key subunit of the m6A methyltransferase complex, was down‐regulated in brain AVM lesions. Furthermore, the lack of WTAP could inhibit endothelial cell angiogenesis in vitro. In order to screen for downstream targets of WTAP, we performed RNA transcriptome sequencing (RNA‐seq) and Methylated RNA Immunoprecipitation Sequencing technology (MeRIP‐seq) using WTAP‐deficient and control endothelial cells. Finally, we determined that WTAP regulated Desmoplakin (DSP) expression through m6A modification, thereby affecting angiogenesis of endothelial cells. In addition, an increase in Wilms' tumour 1 (WT1) activity caused by WTAP deficiency resulted in substantial degradation of β‐catenin, which might also inhibit angiogenesis of endothelial cells. Collectively, our findings revealed the critical function of WTAP in angiogenesis and laid a solid foundation for the elucidation of the pathogenesis of brain AVMs.

Impaired SMAD1/5 Mechanotransduction and Cx37 (Connexin37) Expression Enable Pathological Vessel Enlargement and Shunting

OBJECTIVE

Impaired ALK1 (activin receptor-like kinase-1)/Endoglin/BMP9 (bone morphogenetic protein 9) signaling predisposes to arteriovenous malformations (AVMs). Activation of SMAD1/5 signaling can be enhanced by shear stress. In the genetic disease hereditary hemorrhagic telangiectasia, which is characterized by arteriovenous malformations, the affected receptors are those involved in the activation of mechanosensitive SMAD1/5 signaling. To elucidate how genetic and mechanical signals interact in AVM development, we sought to identify targets differentially regulated by BMP9 and shear stress. Approach and Results: We identify Cx37 (Connexin37) as a differentially regulated target of ligand-induced and mechanotransduced SMAD1/5 signaling. We show that stimulation of endothelial cells with BMP9 upregulated Cx37, whereas shear stress inhibited this expression. This signaling was SMAD1/5-dependent, and in the absence of SMAD1/5, there was an inversion of the expression pattern. Ablated SMAD1/5 signaling alone caused AVM-like vascular malformations directly connecting the dorsal aorta to the inlet of the heart. In yolk sacs of mouse embryos with an endothelial-specific compound heterozygosity for SMAD1/5, addition of TNFα (tumor necrosis factor-α), which downregulates Cx37, induced development of these direct connections bypassing the yolk sac capillary bed. In wild-type embryos undergoing vascular remodeling, Cx37 was globally expressed by endothelial cells but was absent in regions of enlarging vessels. TNFα and endothelial-specific compound heterozygosity for SMAD1/5 caused ectopic regions lacking Cx37 expression, which correlated to areas of vascular malformations. Mechanistically, loss of Cx37 impairs correct directional migration under flow conditions.

CONCLUSIONS

Our data demonstrate that Cx37 expression is differentially regulated by shear stress and SMAD1/5 signaling, and that reduced Cx37 expression is permissive for capillary enlargement into shunts.

Single Cell Analysis in Vascular Biology

The ability to quantify DNA, RNA, and protein variations at the single cell level has revolutionized our understanding of cellular heterogeneity within tissues. Via such analyses, individual cells within populations previously thought to be homogeneous can now be delineated into specific subpopulations expressing unique sets of genes, enabling specialized functions. In vascular biology, studies using single cell RNA sequencing have revealed extensive heterogeneity among endothelial and mural cells even within the same vessel, key intermediate cell types that arise during blood and lymphatic vessel development, and cell-type specific responses to disease. Thus, emerging new single cell analysis techniques are enabling vascular biologists to elucidate mechanisms of vascular development, homeostasis, and disease that were previously not possible. In this review, we will provide an overview of single cell analysis methods and highlight recent advances in vascular biology made possible through single cell RNA sequencing.

Cell Death Pathways in Ischemic Stroke and Targeted Pharmacotherapy

Ischemic stroke is one of the significant causes of morbidity and mortality, affecting millions of people across the globe. Cell injury in the infarct region is an inevitable consequence of focal cerebral ischemia. Subsequent reperfusion exacerbates the harmful effect and increases the infarct volume. These cellular injuries follow either a regulated pathway involving tightly structured signaling cascades and molecularly defined effector mechanisms or a non-regulated pathway, also known as accidental cell death, where the process is biologically uncontrolled. Classical cell death pathways are long established and well reported in several articles that majorly define apoptotic cell death. A recent focus on cell death study also considers investigation on non-classical pathways that are tightly regulated, may or may not involve caspases, but non-apoptotic. Pathological cell death is a cardinal feature of different neurodegenerative diseases. Although ischemia cannot be classified as a neurodegenerative disease, it is a cerebrovascular event where the infarct region exhibits aberrant cell death. Over the past few decades, several therapeutic options have been implicated for ischemic stroke. However, their use has been hampered owing to the number of limitations that they possess. Ischemic penumbral neurons undergo apoptosis and become dysfunctional; however, they are salvageable. Thus, understanding the role of different cell death pathways is crucial to aid in the modern treatment of protecting apoptotic neurons.

Embryonic endothelial evolution towards first hematopoietic stem cells revealed by single-cell transcriptomic and functional analyses

Hematopoietic stem cells (HSCs) in adults are believed to be born from hemogenic endothelial cells (HECs) in mid-gestational embryos. Due to the rare and transient nature, the HSC-competent HECs have never been stringently identified and accurately captured, let alone their genuine vascular precursors. Here, we first used high-precision single-cell transcriptomics to unbiasedly examine the relevant EC populations at continuous developmental stages with intervals of 0.5 days from embryonic day (E) 9.5 to E11.0. As a consequence, we transcriptomically identified two molecularly different arterial EC populations and putative HSC-primed HECs, whose number peaked at E10.0 and sharply decreased thereafter, in the dorsal aorta of the aorta-gonad-mesonephros (AGM) region. Combining computational prediction and in vivo functional validation, we precisely captured HSC-competent HECs by the newly constructed Neurl3-EGFP reporter mouse model, and realized the enrichment further by a combination of surface markers (Procr⁺Kit⁺CD44⁺, PK44). Surprisingly, the endothelial-hematopoietic dual potential was rarely but reliably witnessed in the cultures of single HECs. Noteworthy, primitive vascular ECs from E8.0 experienced two-step fate choices to become HSC-primed HECs, namely an initial arterial fate choice followed by a hemogenic fate conversion. This finding resolves several previously observed contradictions. Taken together, comprehensive understanding of endothelial evolutions and molecular programs underlying HSC-primed HEC specification in vivo will facilitate future investigations directing HSC production in vitro.

State-of-the-Art Strategies for the Vascularization of Three-Dimensional Engineered Organs

Engineering three-dimensional (3D) implantable tissue constructs is a promising strategy for replacing damaged or diseased tissues and organs with functional replacements. However, the efficient vascularization of new 3D organs is a major scientific and technical challenge since large tissue constructs or organs require a constant blood supply to survive in vivo. Current approaches to solving this problem generally fall into the following three major categories: (a) cell-based, (b) angiogenic factor-based, and (c) scaffold-based. In this review, we summarize state-of-the-art technologies that are used to develop complex, stable, and functional vasculature for engineered 3D tissue constructs and organs; additionally, we have suggested directions for future research.

RNA Sequencing Reveals the Activation of Wnt Signaling in Low Flow Rate Brain Arteriovenous Malformations

Background

The blood flow rate of brain arteriovenous malformations (bAVMs) is an important clinical characteristic closely associated with the hemorrhage risk and radiosurgery obliteration rate of bAVMs. However, the underlying molecular properties remain unclear. To identify potential key molecules, signaling pathways, and vascular cell types involved, we compared gene expression profiles between bAVMs with high flow rates and low flow rates (LFR) and validated the functions of selected key molecules in vitro.

Methods and Results

We performed RNA‐sequencing analysis on 51 samples, including 14 high flow rate bAVMs and 37 LFR bAVMs. Functional pathway analysis was performed to identify potential signals influencing the flow rate phenotype of bAVMs. Candidate genes were investigated in bAVM specimens by immunohistochemical staining. Migration, tube formation, and proliferation assays were used to test the effects of candidate genes on the phenotypic properties of cultured human umbilical vein endothelial cells and human brain vascular smooth muscle cells. We identified 250 upregulated and 118 downregulated genes in LFR bAVMs compared with high flow rate bAVMs. Wnt signaling was activated in the LFR group via upregulation of FZD10 and MYOC. Immunohistochemical staining showed that vascular endothelial and smooth muscle cells of LFR bAVMs exhibited increased FZD10 and MYOC expression. Experimentally elevating these genes promoted human umbilical vein endothelial cells and migration and tube formation by activating canonical Wnt signaling in vitro.

Conclusions

Our results suggest that canonical Wnt signaling mediated by FZD10 and MYOC is activated in vascular endothelial and smooth muscle cells in LFR bAVMs.

Integrative bioinformatics analysis of miRNA and mRNA expression profiles and identification of associated miRNA-mRNA network in aortic dissection

BACKGROUND

Aortic dissection (AD) is one of the most lethal cardiovascular diseases. The aim of this study was to identify core genes and pathways revealing pathogenesis in AD.

METHODS

We screened differentially expressed mRNAs and miRNAs using mRNA and miRNA expression profile data of AD from Gene Expression Omnibus. Then functional and pathway enrichment analyses of differential expression genes (DEGs) was performed utilizing the database for annotation, visualization, and integrated discovery (DAVID). Target genes with differential expression miRNAs (DEMIs) were predicted using the miRWalk database, and the intersection between these predictions and DEGs was selected as differentially expressed miRNA-target genes. In addition, a protein-protein interaction (PPI) network and miRNA-mRNA regulatory network were constructed.

RESULTS

In total, 130 DEGs and 47 DEMIs were identified from mRNA and miRNA microarray, respectively, and 45 DEGs were DEMI-target genes. The PPI and miRNA-mRNA network included 79 node genes and 74 node genes, respectively, while 23 hub genes and 2 hub miRNAs were identified. The DEGs, PPI and modules differential expression miRNA-target genes were all mainly enriched in cell cycle, cell proliferation and cell apoptosis signaling pathways.

CONCLUSION

Taken above, the study reveals some candidate genes and pathways potentially involving molecular mechanisms of AD. These findings provide a new insight for research and treatment of AD.

SOX Transcription Factors in Endothelial Differentiation and Endothelial-Mesenchymal Transitions

The SRY (Sex Determining Region Y)-related HMG box of DNA binding proteins, referred to as SOX transcription factors, were first identified as critical regulators of male sex determination but are now known to play an important role in vascular development and disease. SOX7, 17, and 18 are essential in endothelial differentiation and SOX2 has emerged as an essential mediator of endothelial-mesenchymal transitions (EndMTs), a mechanism that enables the endothelium to contribute cells with abnormal cell differentiation to vascular disease such as calcific vasculopathy. In the following paper, we review published information on the SOX transcription factors in endothelial differentiation and hypothesize that SOX2 acts as a mediator of EndMTs that contribute to vascular calcification.

Veins and Arteries Build Hierarchical Branching Patterns Differently: Bottom-Up versus Top-Down

A tree-like hierarchical branching structure is present in many biological systems, such as the kidney, lung, mammary gland, and blood vessels. Most of these organs form through branching morphogenesis, where outward growth results in smaller and smaller branches. However, the blood vasculature is unique in that it exists as two trees (arterial and venous) connected at their tips. Obtaining this organization might therefore require unique developmental mechanisms. As reviewed here, recent data indicate that arterial trees often form in reverse order. Accordingly, initial arterial endothelial cell differentiation occurs outside of arterial vessels. These pre-artery cells then build trees by following a migratory path from smaller into larger arteries, a process guided by the forces imparted by blood flow. Thus, in comparison to other branched organs, arteries can obtain their structure through inward growth and coalescence. Here, new information on the underlying mechanisms is discussed, and how defects can lead to pathologies, such as hypoplastic arteries and arteriovenous malformations.

Building and Regenerating the Lung Cell by Cell

The unique architecture of the mammalian lung is required for adaptation to air breathing at birth and thereafter. Understanding the cellular and molecular mechanisms controlling its morphogenesis provides the framework for understanding the pathogenesis of acute and chronic lung diseases. Recent single-cell RNA sequencing data and high-resolution imaging identify the remarkable heterogeneity of pulmonary cell types and provides cell selective gene expression underlying lung development. We will address fundamental issues related to the diversity of pulmonary cells, to the formation and function of the mammalian lung, and will review recent advances regarding the cellular and molecular pathways involved in lung organogenesis. What cells form the lung in the early embryo? How are cell proliferation, migration, and differentiation regulated during lung morphogenesis? How do cells interact during lung formation and repair? How do signaling and transcriptional programs determine cell-cell interactions necessary for lung morphogenesis and function?