NRP1 acts cell autonomously in endothelium to promote tip cell function during sprouting angiogenesis

A proteomics approach to isolating neuropilin-dependent α5 integrin trafficking pathways: neuropilin 1 and 2 co-traffic α5 integrin through endosomal p120RasGAP to promote polarised fibronectin fibrillogenesis in endothelial cells

Integrin trafficking to and from membrane adhesions is a crucial mechanism that dictates many aspects of a cell's behaviour, including motility, polarisation, and invasion. In endothelial cells (ECs), the intracellular traffic of α5 integrin is regulated by both neuropilin 1 (NRP1) and neuropilin 2 (NRP2), yet the redundancies in function between these co-receptors remain unclear. Moreover, the endocytic complexes that participate in NRP-directed traffic remain poorly annotated. Here we identify an important role for the GTPase-activating protein p120RasGAP in ECs, promoting the recycling of α5 integrin from early endosomes. Mechanistically, p120RasGAP enables transit of endocytosed α5 integrin-NRP1-NRP2 complexes to Rab11+ recycling endosomes, promoting cell polarisation and fibronectin (FN) fibrillogenesis. Silencing of both NRP receptors, or p120RasGAP, resulted in the accumulation of α5 integrin in early endosomes, a loss of α5 integrin from surface adhesions, and attenuated EC polarisation. Endothelial-specific deletion of both NRP1 and NRP2 in the postnatal retina recapitulated our in vitro findings, severely impairing FN fibrillogenesis and polarised sprouting. Our data assign an essential role for p120RasGAP during integrin traffic in ECs and support a hypothesis that NRP receptors co-traffic internalised cargoes. Importantly, we utilise comparative proteomics analyses to isolate a comprehensive map of NRP1-dependent and NRP2-dependent α5 integrin interactions in ECs.

DNA G-Quadruplex in NRP1 Promoter Facilitates SARS-CoV-2 Infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection continues to raise concerns worldwide. Numerous host factors involved in SARS-CoV-2 infection have been identified, but the regulatory mechanisms of these host factor remain unclear. Here, we report the role of G-quadruplexes (G4s) located in the host factor promoter region in SARS-CoV-2 infection. Using bioinformatics, biochemical, and biological assays, we provide evidence for the presence of G4 structures in the promoter regions of SARS-CoV-2 host factors NRP1. Specifically, we focus on two representative G4s in the NRP1 promoter and highlight its importance in SARS-CoV-2 pathogenesis. The presence of the G4 structure greatly increases NRP1 expression, facilitating SARS-CoV-2 entry into cells. Utilizing published single-cell RNA sequencing data obtained from simulated SARS-CoV-2 infection in human bronchial epithelial cells (HBECs), we found that ciliated cells with high levels of NRP1 are prominently targeted by the virus during infection. Furthermore, our study identifies E2F1 act as a transcription factor that binds to G4s. These findings uncover a previously unknown mechanism underlying SARS-CoV-2 infection and suggest that targeting G4 structures could be a potential strategy for COVID-19 prevention and treatment.

HTATIP2 regulates arteriogenic activity in monocytes from patients with limb ischemia

Use of autologous cells isolated from elderly patients with multiple comorbidities may account for the modest efficacy of cell therapy in patients with chronic limb threatening ischemia (CLTI). We aimed to determine whether proarteriogenic monocyte/macrophages (Mo/MΦs) from patients with CLTI were functionally impaired and to demonstrate the mechanisms related to any impairment. Proarteriogenic Mo/MΦs isolated from patients with CLTI were found to have an impaired capacity to promote neovascularization in vitro and in vivo compared with those isolated from healthy controls. This was associated with increased expression of human HIV-1 TAT interactive protein-2 (HTATIP2), a transcription factor known to suppress angiogenesis/arteriogenesis. Silencing HTATIP2 restored the functional capacity of CLTI Mo/MΦs, which was associated with increased expression of arteriogenic regulators Neuropilin-1 and Angiopoietin-1, and their ability to enhance angiogenic (endothelial tubule formation) and arteriogenic (smooth muscle proliferation) processes in vitro. In support of the translational relevance of our findings, silencing HTATIP2 in proarteriogenic Mo/MΦs isolated from patients with CLTI rescued their capacity to enhance limb perfusion in the ischemic hindlimb by effecting greater angiogenesis and arteriogenesis. Ex vivo modulation of HTATIP2 may offer a strategy for rescuing the functional impairment of pro-angio/arteriogenic Mo/MΦs prior to autologous delivery and increase the likelihood of clinical efficacy.

Tamoxifen exacerbates morbidity and mortality in male mice receiving medetomidine anaesthesia

Tamoxifen-induced CreER-LoxP recombination is often used to induce spatiotemporally controlled gene deletion in genetically modified mice. Prior work has shown that tamoxifen and tamoxifen-induced CreER activation can have off-target effects that should be controlled. However, it has not yet been reported whether tamoxifen administration, independently of CreER expression, interacts adversely with commonly used anaesthetic drugs such as medetomidine or its enantiomer dexmedetomidine in laboratory mice (Mus musculus). Here, we report a high incidence of urinary plug formation and morbidity in male mice on a mixed C57Bl6/J6 and 129/SvEv background when tamoxifen treatment was followed by ketamine-medetomidine anaesthesia. Medetomidine is therefore contra-indicated for male mice after tamoxifen treatment. As dexmedetomidine causes morbidity and mortality in male mice at higher rates than medetomidine even without tamoxifen treatment, our findings suggest that dexmedetomidine is not a suitable alternative for anaesthesia of male mice after tamoxifen treatment. We conclude that the choice of anaesthetic drug needs to be carefully evaluated in studies using male mice that have undergone tamoxifen treatment for inducing CreER-LoxP recombination.

Infection of liver sinusoidal endothelial cells with Muromegalovirus muridbeta1 involves binding to neuropilin-1 and is dynamin-dependent

Liver sinusoidal endothelial cells (LSEC) are scavenger cells with a remarkably high capacity for clearance of several blood-borne macromolecules and nanoparticles, including some viruses. Endocytosis in LSEC is mainly via the clathrin-coated pit mediated route, which is dynamin-dependent. LSEC can also be a site of infection and latency of betaherpesvirus, but mode of virus entry into these cells has not yet been described. In this study we have investigated the role of dynamin in the early stage of muromegalovirus muridbeta1 (MuHV-1, murid betaherpesvirus 1, murine cytomegalovirus) infection in mouse LSECs. LSEC cultures were freshly prepared from C57Bl/6JRj mouse liver. We first examined dose- and time-dependent effects of two dynamin-inhibitors, dynasore and MitMAB, on cell viability, morphology, and endocytosis of model ligands via different LSEC scavenger receptors to establish a protocol for dynamin-inhibition studies in these primary cells. LSECs were challenged with MuHV-1 (MOI 0.2) ± dynamin inhibitors for 1h, then without inhibitors and virus for 11h, and nuclear expression of MuHV-1 immediate early antigen (IE1) measured by immune fluorescence. MuHV-1 efficiently infected LSECs in vitro. Infection was significantly and independently inhibited by dynasore and MitMAB, which block dynamin function via different mechanisms, suggesting that initial steps of MuHV-1 infection is dynamin-dependent in LSECs. Infection was also reduced in the presence of monensin which inhibits acidification of endosomes. Furthermore, competitive binding studies with a neuropilin-1 antibody blocked LSEC infection. This suggests that MuHV-1 infection in mouse LSECs involves virus binding to neuropilin-1 and occurs via endocytosis.

Mitochondria in endothelial cells angiogenesis and function: current understanding and future perspectives

Endothelial cells (ECs) angiogenesis is the process of sprouting new vessels from the existing ones, playing critical roles in physiological and pathological processes such as wound healing, placentation, ischemia/reperfusion, cardiovascular diseases and cancer metastasis. Although mitochondria are not the major sites of energy source in ECs, they function as important biosynthetic and signaling hubs to regulate ECs metabolism and adaptations to local environment, thus affecting ECs migration, proliferation and angiogenic process. The understanding of the importance and potential mechanisms of mitochondria in regulating ECs metabolism, function and the process of angiogenesis has developed in the past decades. Thus, in this review, we discuss the current understanding of mitochondrial proteins and signaling molecules in ECs metabolism, function and angiogeneic signaling, to provide new and therapeutic targets for treatment of diverse cardiovascular and angiogenesis-dependent diseases.

Overexpression of NRP1 is Associated with Poor Prognosis via Accelerating Immunosuppression in Head and Neck Squamous Cell Carcinoma

Background

Neuropilin-1 (NRP1) is a significant molecular structure that participates in many diseases progress including malignant tumors. However, its role in head and neck squamous cell carcinoma (HNSCC) remains to be uncovered. In this study, we determined the function of NRP1 as a crucial biomarker in proliferation, metastasis and immunosuppression in HNSCC.

Methods

We collected samples of normal tissues (n = 18) and HNSCC tissues (n = 202) for immunohistochemical staining of NRP1 and evaluated its correlation to clinical prognostic characteristics. Furthermore, we enrolled 37 HNSCC patients received immune checkpoint blockade (ICB) treatment with defined therapeutic effects records. The biological process, signal pathways, and immune infiltration relevance to NRP1 were analyzed utilized transcriptome data from The Cancer Genome Atlas (TCGA).

Results

The NRP1 protein expression was significantly upregulated in HNSCC tissue and was associated with T stage, N stage, histological differentiation, recurrence and NRP1 expression. The high expression of NRP1 indicated poor survival rate and was found to be an independent prognosis factor. Enrichment analysis showed that NRP1 was associated with cell adhesion, extracellular matrix organization, homophilic cell adhesion via plasma membrane in biological process and neuroactive ligand-receptor interaction, protein digestion and absorption, calcium signal pathways. Moreover, NRP1 mRNA level was found positively correlated to cancer associated fibroblast cells, Treg cells and macrophage/monocyte cells.

Conclusion

NRP1 might be likely to develop into a potential immunoregulation target as well as a predictive biomarker in HNSCC immune treatment.

Mesenchymal Stromal Cells Facilitate Tip Cell Fusion Downstream of BMP-Mediated Venous Angiogenesis-Brief Report

BACKGROUND

The goal of this study was to identify and characterize cell-cell interactions that facilitate endothelial tip cell fusion downstream of BMP (bone morphogenic protein)-mediated venous plexus formation.

METHODS

High resolution and time-lapse imaging of transgenic reporter lines and loss-of-function studies were carried out to study the involvement of mesenchymal stromal cells during venous angiogenesis.

RESULTS

BMP-responsive stromal cells facilitate timely and precise fusion of venous tip cells during developmental angiogenesis.

CONCLUSIONS

Stromal cells are required for anastomosis of venous tip cells in the embryonic caudal hematopoietic tissue.

SIRT1 attenuates blood-spinal cord barrier disruption after spinal cord injury by deacetylating p66Shc

Disruption of the blood-spinal cord barrier (BSCB) leads to inflammatory cell infiltration and neural cell death, thus, contributing to poor functional recovery after spinal cord injury (SCI). Previous studies have suggested that Sirtuin 1 (SIRT1), an NAD⁺-dependent class III histone deacetylase, is abundantly expressed in endothelial cells and promotes endothelial homeostasis. However, the role of SIRT1 in BSCB function after SCI remains poorly defined. Here, we report that SIRT1 is highly expressed in spinal cord endothelial cells, and its expression significantly decreases after SCI. Using endothelial cell-specific SIRT1 knockout mice, we observed that endothelial cell-specific knockout of SIRT1 aggravated BSCB disruption, thus, resulting in widespread inflammation, neural cell death and poor functional recovery after SCI. In contrast, activation of SIRT1 by the agonist SRT1720 had beneficial effects. In vitro, knockdown of SIRT1 exacerbated IL-1β-induced endothelial barrier disruption in bEnd.3 cells, whereas overexpression of SIRT1 was protective. Using RNA-seq and IP/MS analysis, we identified p66Shc, a redox protein, as the potential target of SIRT1. Further studies demonstrated that SIRT1 interacts with and deacetylates p66Shc, thereby attenuating oxidative stress and protecting endothelial barrier function. Overall, our results indicate that SIRT1 decreases endothelial ROS production and attenuates BSCB disruption by deacetylating p66Shc after SCI, and suggest that SIRT1 activation has potential as a therapeutic approach to promote functional recovery against BSCB disruption following SCI.

Shaping the brain vasculature in development and disease in the single-cell era

The CNS critically relies on the formation and proper function of its vasculature during development, adult homeostasis and disease. Angiogenesis - the formation of new blood vessels - is highly active during brain development, enters almost complete quiescence in the healthy adult brain and is reactivated in vascular-dependent brain pathologies such as brain vascular malformations and brain tumours. Despite major advances in the understanding of the cellular and molecular mechanisms driving angiogenesis in peripheral tissues, developmental signalling pathways orchestrating angiogenic processes in the healthy and the diseased CNS remain incompletely understood. Molecular signalling pathways of the 'neurovascular link' defining common mechanisms of nerve and vessel wiring have emerged as crucial regulators of peripheral vascular growth, but their relevance for angiogenesis in brain development and disease remains largely unexplored. Here we review the current knowledge of general and CNS-specific mechanisms of angiogenesis during brain development and in brain vascular malformations and brain tumours, including how key molecular signalling pathways are reactivated in vascular-dependent diseases. We also discuss how these topics can be studied in the single-cell multi-omics era.

Potassium Dehydroandrograpolide Succinate Targets NRP1 Mediated VEGFR2/VE-Cadherin Signaling Pathway to Promote Endothelial Barrier Repair

Impairment of vascular endothelial integrity is associated with various vascular diseases. Our previous studies demonstrated that andrographolide is critical to maintaining gastric vascular homeostasis, as well as to regulating pathological vascular remodeling. Potassium dehydroandrograpolide succinate (PDA), a derivative of andrographolide, has been clinically used for the therapeutic treatment of inflammatory diseases. This study aimed to determine whether PDA promotes endothelial barrier repair in pathological vascular remodeling. Partial ligation of the carotid artery in ApoE^-/- mice was used to evaluate whether PDA can regulate pathological vascular remodeling. A flow cytometry assay, BRDU incorporation assay, Boyden chamber cell migration assay, spheroid sprouting assay and Matrigel-based tube formation assay were performed to determine whether PDA can regulate the proliferation and motility of HUVEC. A molecular docking simulation and CO-immunoprecipitation assay were performed to observe protein interactions. We observed that PDA induced pathological vascular remodeling characterized by enhanced neointima formation. PDA treatment significantly enhanced the proliferation and migration of vascular endothelial cells. Investigating the potential mechanisms and signaling pathways, we observed that PDA induced endothelial NRP1 expression and activated the VEGF signaling pathway. Knockdown of NRP1 using siRNA transfection attenuated PDA-induced VEGFR2 expression. The interaction between NRP1 and VEGFR2 caused VE-Cad-dependent endothelial barrier impairment, which was characterized by enhanced vascular inflammation. Our study demonstrated that PDA plays a critical role in promoting endothelial barrier repair in pathological vascular remodeling.

Cre toxicity in mouse models of cardiovascular physiology and disease

The Cre-LoxP system provides a widely used method for studying gene requirements in the mouse as the main mammalian genetic model organism. To define the molecular and cellular mechanisms that underlie cardiovascular development, function and disease, various mouse strains have been engineered that allow Cre-LoxP-mediated gene targeting within specific cell types of the cardiovascular system. Despite the usefulness of this system, evidence is accumulating that Cre activity can have toxic effects in cells, independently of its ability to recombine pairs of engineered LoxP sites in target genes. Here, we have gathered published evidence for Cre toxicity in cells and tissues relevant to cardiovascular biology and provide an overview of mechanisms proposed to underlie Cre toxicity. Based on this knowledge, we propose that each study utilising the Cre-LoxP system to investigate gene function in the cardiovascular system should incorporate appropriate controls to account for Cre toxicity.

Neuropilin 1 and its inhibitory ligand mini-tryptophanyl-tRNA synthetase inversely regulate VE-cadherin turnover and vascular permeability

The formation of a functional blood vessel network relies on the ability of endothelial cells (ECs) to dynamically rearrange their adhesive contacts in response to blood flow and guidance cues, such as vascular endothelial growth factor-A (VEGF-A) and class 3 semaphorins (SEMA3s). Neuropilin 1 (NRP1) is essential for blood vessel development, independently of its ligands VEGF-A and SEMA3, through poorly understood mechanisms. Grounding on unbiased proteomic analysis, we report here that NRP1 acts as an endocytic chaperone primarily for adhesion receptors on the surface of unstimulated ECs. NRP1 localizes at adherens junctions (AJs) where, interacting with VE-cadherin, promotes its basal internalization-dependent turnover and favors vascular permeability initiated by histamine in both cultured ECs and mice. We identify a splice variant of tryptophanyl-tRNA synthetase (mini-WARS) as an unconventionally secreted extracellular inhibitory ligand of NRP1 that, by stabilizing it at the AJs, slows down both VE-cadherin turnover and histamine-elicited endothelial leakage. Thus, our work shows a role for NRP1 as a major regulator of AJs plasticity and reveals how mini-WARS acts as a physiological NRP1 inhibitory ligand in the control of VE-cadherin endocytic turnover and vascular permeability.

SARS-CoV-2: An Overview of the Genetic Profile and Vaccine Effectiveness of the Five Variants of Concern

With the onset of the COVID-19 pandemic, enormous efforts have been made to understand the genus SARS-CoV-2. Due to the high rate of global transmission, mutations in the viral genome were inevitable. A full understanding of the viral genome and its possible changes represents one of the crucial aspects of pandemic management. Structural protein S plays an important role in the pathogenicity of SARS-CoV-2, mutations occurring at this level leading to viral forms with increased affinity for ACE2 receptors, higher transmissibility and infectivity, resistance to neutralizing antibodies and immune escape, increasing the risk of infection and disease severity. Thus, five variants of concern are currently being discussed, Alpha, Beta, Gamma, Delta and Omicron. In the present review, a comprehensive summary of the following critical aspects regarding SARS-CoV-2 has been made: (i) the genomic characteristics of SARS-CoV-2; (ii) the pathological mechanism of transmission, penetration into the cell and action on specific receptors; (iii) mutations in the SARS-CoV-2 genome; and (iv) possible implications of mutations in diagnosis, treatment, and vaccination.

Neuropilin-1 deficiency in vascular smooth muscle cells is associated with hereditary hemorrhagic telangiectasia arteriovenous malformations

Patients with hereditary hemorrhagic telangiectasia (HHT) have arteriovenous malformations (AVMs) with genetic mutations involving the activin-A receptor like type 1 (ACVRL1 or ALK1) and endoglin (ENG). Recent studies have shown that Neuropilin-1 (NRP-1) inhibits ALK1. We investigated the expression of NRP-1 in livers of patients with HHT and found that there was a significant reduction in NRP-1 in perivascular smooth muscle cells (SMCs). We used Nrp1^SM22KO mice (Nrp1 was ablated in SMCs) and found hemorrhage, increased immune cell infiltration with a decrease in SMCs, and pericyte lining in lungs and liver in adult mice. Histologic examination revealed lung arteriovenous fistulas (AVFs) with enlarged liver vessels. Evaluation of the retina vessels at P5 from Nrp1^SM22KO mice demonstrated dilated capillaries with a reduction of pericytes. In inflow artery of surgical AVFs from the Nrp1^SM22KO versus WT mice, there was a significant decrease in Tgfb1, Eng, and Alk1 expression and phosphorylated SMAD1/5/8 (pSMAD1/5/8), with an increase in apoptosis. TGF-β1–stimulated aortic SMCs from Nrp1^SM22KO versus WT mice have decreased pSMAD1/5/8 and increased apoptosis. Coimmunoprecipitation experiments revealed that NRP-1 interacts with ALK1 and ENG in SMCs. In summary, NRP-1 deletion in SMCs leads to reduced ALK1, ENG, and pSMAD1/5/8 signaling and reduced cell death associated with AVM formation.

Quantifying and Characterizing Angiogenesis Using the Postnatal Mouse Retina

Angiogenesis refers to the expansion of blood vessels from a preexisting vascular plexus, and it is a fundamental process for organ development, the female reproductive system, and wound healing, but it is also a common denominator in several diseases such as cancer and neovascular eye disease. For these reasons, shedding light on the molecular and cellular mechanisms of angiogenesis has the potential to devise new therapeutic strategies to refrain pathological vessel growth or even promote new vessel formation in ischemic conditions and organ grafts. The mouse postnatal retina provides an excellent and widely adopted model to study physiological angiogenesis in vivo, and this chapter outlines a detailed protocol for its dissection, staining, and analysis of the vasculature.

The Embryonic Mouse Hindbrain Model to Study Sprouting Angiogenesis In Vivo

Blood vessel growth is a fundamental process for organ development and wound healing but is also associated with ischemic diseases and cancer. The growth of new blood vessels from preexisting vasculature, termed sprouting angiogenesis, is the predominant mode of blood vessel growth in central nervous system vascularization and pathological vessel growth. Accordingly, studying the molecular and cellular mechanisms of angiogenesis holds the promise to find novel therapeutic targets to stimulate new vessel formation in ischemic tissues or inhibit pathological vessel growth in disease. The embryonic mouse hindbrain provides an excellent model to study sprouting angiogenesis in vivo by histochemical or fluorescent wholemount immunolabeling, thus allowing high-resolution image capture of nascent vasculature and subsequent quantification of relevant angiogenic parameters. This chapter describes how to use the mouse embryonic hindbrain as a model to study physiological angiogenesis, including detailed protocols for hindbrain dissection, wholemount staining, and angiogenic parameters analysis.

The Embryonic Mouse Hindbrain and Postnatal Retina as In Vivo Models to Study Angiogenesis

Angiogenesis, the growth of new blood vessels from pre-existing ones, is a fundamental process for organ development, exercise-induced muscle growth, and wound healing, but is also associated with different diseases such as cancer and neovascular eye disease. Accordingly, elucidating the molecular and cellular mechanisms of angiogenesis has the potential to identify new therapeutic targets to stimulate new vessel formation in ischemic tissues or inhibit pathological vessel growth in disease. This chapter describes the mouse embryo hindbrain and postnatal retina as models to study physiological angiogenesis and provides detailed protocols for tissue dissection, sample staining and analysis.

HIF‑1α in cerebral ischemia (Review)

Cerebral ischemic injury may lead to a series of serious brain diseases, death or different degrees of disability. Hypoxia-inducible factor-1α (HIF-1α) is an oxygen-sensitive transcription factor, which mediates the adaptive metabolic response to hypoxia and serves a key role in cerebral ischemia. HIF-1α is the main molecule that responds to hypoxia. HIF-1α serves an important role in the development of cerebral ischemia by participating in numerous processes, including metabolism, proliferation and angiogenesis. The present review focuses on the endogenous protective mechanism of cerebral ischemia and elaborates on the role of HIF-1α in cerebral ischemia. In addition, it focuses on cerebral ischemia interventions that act on the HIF-1α target, including biological factors, non-coding RNA, hypoxic-ischemic preconditioning and drugs, and expands upon the measures to strengthen the endogenous compensatory response to support HIF-1α as a therapeutic target, thus providing novel suggestions for the treatment of cerebral ischemia.

Neuropilin 1 regulates bone marrow vascular regeneration and hematopoietic reconstitution

Ionizing radiation and chemotherapy deplete hematopoietic stem cells and damage the vascular niche wherein hematopoietic stem cells reside. Hematopoietic stem cell regeneration requires signaling from an intact bone marrow (BM) vascular niche, but the mechanisms that control BM vascular niche regeneration are poorly understood. We report that BM vascular endothelial cells secrete semaphorin 3 A (SEMA3A) in response to myeloablation and SEMA3A induces p53 - mediated apoptosis in BM endothelial cells via signaling through its receptor, Neuropilin 1 (NRP1), and activation of cyclin dependent kinase 5. Endothelial cell - specific deletion of Nrp1 or Sema3a or administration of anti-NRP1 antibody suppresses BM endothelial cell apoptosis, accelerates BM vascular regeneration and concordantly drives hematopoietic reconstitution in irradiated mice. In response to NRP1 inhibition, BM endothelial cells increase expression and secretion of the Wnt signal amplifying protein, R spondin 2. Systemic administration of anti - R spondin 2 blocks HSC regeneration and hematopoietic reconstitution which otherwise occurrs in response to NRP1 inhibition. SEMA3A - NRP1 signaling promotes BM vascular regression following myelosuppression and therapeutic blockade of SEMA3A - NRP1 signaling in BM endothelial cells accelerates vascular and hematopoietic regeneration in vivo.

Hierarchical imaging and computational analysis of three-dimensional vascular network architecture in the entire postnatal and adult mouse brain

The formation of new blood vessels and the establishment of vascular networks are crucial during brain development, in the adult healthy brain, as well as in various diseases of the central nervous system. Here, we describe a step-by-step protocol for our recently developed method that enables hierarchical imaging and computational analysis of vascular networks in postnatal and adult mouse brains. The different stages of the procedure include resin-based vascular corrosion casting, scanning electron microscopy, synchrotron radiation and desktop microcomputed tomography imaging, and computational network analysis. Combining these methods enables detailed visualization and quantification of the 3D brain vasculature. Network features such as vascular volume fraction, branch point density, vessel diameter, length, tortuosity and directionality as well as extravascular distance can be obtained at any developmental stage from the early postnatal to the adult brain. This approach can be used to provide a detailed morphological atlas of the entire mouse brain vasculature at both the postnatal and the adult stage of development. Our protocol allows the characterization of brain vascular networks separately for capillaries and noncapillaries. The entire protocol, from mouse perfusion to vessel network analysis, takes ~10 d.

VEGFR1 signaling in retinal angiogenesis and microinflammation

Five vascular endothelial growth factor receptor (VEGFR) ligands (VEGF-A, -B, -C, -D, and placental growth factor [PlGF]) constitute the VEGF family. VEGF-A binds VEGF receptors 1 and 2 (VEGFR1/2), whereas VEGF-B and PlGF only bind VEGFR1. Although much research has been conducted on VEGFR2 to elucidate its key role in retinal diseases, recent efforts have shown the importance and involvement of VEGFR1 and its family of ligands in angiogenesis, vascular permeability, and microinflammatory cascades within the retina. Expression of VEGFR1 depends on the microenvironment, is differentially regulated under hypoxic and inflammatory conditions, and it has been detected in retinal and choroidal endothelial cells, pericytes, retinal and choroidal mononuclear phagocytes (including microglia), Müller cells, photoreceptor cells, and the retinal pigment epithelium. Whilst the VEGF-A decoy function of VEGFR1 is well established, consequences of its direct signaling are less clear. VEGFR1 activation can affect vascular permeability and induce macrophage and microglia production of proinflammatory and proangiogenic mediators. However the ability of the VEGFR1 ligands (VEGF-A, PlGF, and VEGF-B) to compete against each other for receptor binding and to heterodimerize complicates our understanding of the relative contribution of VEGFR1 signaling alone toward the pathologic processes seen in diabetic retinopathy, retinal vascular occlusions, retinopathy of prematurity, and age-related macular degeneration. Clinically, anti-VEGF drugs have proven transformational in these pathologies and their impact on modulation of VEGFR1 signaling is still an opportunity-rich field for further research.

Progress in understanding of the stalk and tip cells formation involvement in angiogenesis mechanisms

Vascular sprouting is a key process of angiogenesis and mainly related to the formation of stalk and tip cells. Many studies have found that angiogenesis has a great clinical significance in promoting the functional repair of impaired tissues and anti-angiogenesis is a key to treatment of many tumors. Therefore, how the pathways regulate angiogenesis by regulating the formation of stalk and tip cells is an urgent problem for researchers. This review mainly summarizes the research progress of pathways affecting the formation of stalk and tip cells during angiogenesis in recent years, including the main signaling pathways (such as VEGF-VEGFR-Dll4-Notch signaling pathway, ALK-Smad signaling pathway,CCN1-YAP/YAZ signaling pathway and other signaling pathways) and cellular actions (such as cellular metabolisms, intercellular tension and other actions), aiming to further give the readers an insight into the mechanism of regulating the formation of stalk and tip cells during angiogenesis and provide more targets for anti-angiogenic drugs.

Aflibercept, a VEGF (Vascular Endothelial Growth Factor)-Trap, Reduces Vascular Permeability and Stroke-Induced Brain Swelling in Obese Mice

Background and Purpose

Brain edema is an important underlying pathology in acute stroke, especially when comorbidities are present. VEGF (Vascular endothelial growth factor) signaling is implicated in edema. This study investigated whether obesity impacts VEGF signaling and brain edema, as well as whether VEGF inhibition alters stroke outcome in obese subjects.

Methods

High-fat diet-induced obese mice were subjected to a transient middle cerebral artery occlusion. VEGF-A and VEGFR2 (receptor) expression, infarct volume, and swelling were measured 3 days post-middle cerebral artery occlusion. To validate the effect of an anti-VEGF strategy, we used aflibercept, a fusion protein that has a VEGF-binding domain and acts as a decoy receptor, in human umbilical vein endothelial cells stimulated with rVEGF (recombinant VEGF; 50 ng/mL) for permeability and tube formation. In vivo, aflibercept (10 mg/kg) or IgG control was administered in obese mice 3 hours after transient 30 minutes middle cerebral artery occlusion. Blood-brain barrier integrity was assessed by IgG staining and dextran extravasation in the postischemic brain. A separate cohort of nonobese (lean) mice was subjected to 40 minutes middle cerebral artery occlusion to test the effect of aflibercept on malignant infarction.

Results

Compared with lean mice, obese mice had increased mortality, infarct volume, swelling, and blood-brain barrier disruption. These outcomes were also associated with increased VEGF-A and VEGFR2 expression. Aflibercept reduced VEGF-A-stimulated permeability and tube formation in human umbilical vein endothelial cells. Compared with the IgG-treated controls, mice treated with aflibercept had reduced mortality rates (40% versus 17%), hemorrhagic transformation (43% versus 27%), and brain swelling (28% versus 18%), although the infarct size was similar. In nonobese mice with large stroke, aflibercept neither improved nor exacerbated stroke outcomes.

Conclusions

The study demonstrates that aflibercept selectively attenuates stroke-induced brain edema and vascular permeability in obese mice. These findings suggest the repurposing of aflibercept to reduce obesity-enhanced brain edema in acute stroke.

Endothelial cell mechanics and blood flow forces in vascular morphogenesis

The vertebrate cardiovascular system is made up by a hierarchically structured network of highly specialised blood vessels. This network emerges during early embryogenesis and evolves in size and complexity concomitant with embryonic growth and organ formation. Underlying this plasticity are actin-driven endothelial cell behaviours, which allow endothelial cells to change their shape and move within the vascular network. In this review, we discuss the cellular and molecular mechanisms involved in vascular network formation and how these intrinsic mechanisms are influenced by haemodynamic forces provided by pressurized blood flow. While most of this review focusses on in vivo evidence from zebrafish embryos, we also mention complementary findings obtained in other experimental systems.

Proteomic analysis of bone marrow-derived mesenchymal stem cell extracellular vesicles from healthy donors: implications for proliferation, angiogenesis, Wnt signaling, and the basement membrane

Background

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have shown therapeutic potential in various in vitro and in vivo studies in cutaneous wound healing. Furthermore, there are ubiquitous studies highlighting the pro-regenerative effects of BM-MSC extracellular vesicles (BM-MSC EVs). The similarities and differences in BM-MSC EV cargo among potential healthy donors are not well understood. Variation in EV protein cargo is important to understand, as it may be useful in identifying potential therapeutic applications in clinical trials. We hypothesized that the donors would share both important similarities and differences in cargo relating to cell proliferation, angiogenesis, Wnt signaling, and basement membrane formation—processes shown to be critical for effective cutaneous wound healing.

Methods

We harvested BM-MSC EVs from four healthy human donors who underwent strict screening for whole bone marrow donation and further Good Manufacturing Practices-grade cell culture expansion for candidate usage in clinical trials. BM-MSC EV protein cargo was determined via mass spectrometry and Proteome Discoverer software. Corresponding proteomic networks were analyzed via the UniProt Consortium and STRING consortium databases.

Results

More than 3000 proteins were identified in each of the donors, sharing > 600 proteins among all donors. Despite inter-donor variation in protein identities, there were striking similarities in numbers of proteins per biological functional category. In terms of biologic function, the proteins were most associated with transport of ions and proteins, transcription, and the cell cycle, relating to cell proliferation. The donors shared essential cargo relating to angiogenesis, Wnt signaling, and basement membrane formation—essential processes in modulating cutaneous wound repair.

Conclusions

Healthy donors of BM-MSC EVs contain important similarities and differences among protein cargo that may play important roles in their pro-regenerative functions. Further studies are needed to correlate proteomic signatures to functional outcomes in cutaneous repair.

An Essential NRP1-Mediated Role for Tagln2 in Gastric Cancer Angiogenesis

Knowledge about the precise biological role and underlying mechanism of Tagln2 in tumor progression is relatively limited, especially in angiogenesis focused on tumor derived endothelial cells (ECs) has rarely been reported. Here, the function, molecular mechanism and potential clinical value of Tagln2 in gastric cancer (GC) angiogenesis were investigated. GC tissue microarrays were used to assess the expression of Tagln2 in ECs. The relationships between expression and clinicopathological features were analyzed to evaluate the clinical value of Tagln2. Gain- and loss-of-function approaches were performed in ECs to investigate the functions of Tagln2 in angiogenesis. A combination of angiogenesis antibody array, RNA-Seq analyses and a series of in vitro experiments were performed to reveal the proangiogenic mechanism mediated by NRP1. Immunohistochemistry performed on an independent tissue chip (n=75) revealed significant upregulation of Tagln2 in tumor-derived ECs which were specifically immunolabeled with CD34. Additionally, high Tagln2 levels correlated significantly with the presence of lymph node as well as distant metastases. Gain- and loss-of-function approaches highlighted the function of Tagln2 in promoting EC proliferation, motility, and capillary-like tube formation and in reducing apoptosis. Tagln2 upregulation led to significantly increased mRNA and protein levels of NRP1 and subsequently activated the NRP1/VEGFR2 and downstream MAPK signaling pathways. These data indicate the importance of Tagln2 in angiogenesis, as a potential therapeutic target, and as a candidate prognostic marker in GC.

Use of NanoBiT and NanoBRET to monitor fluorescent VEGF-A binding kinetics to VEGFR2/NRP1 heteromeric complexes in living cells

BACKGROUND AND PURPOSE

VEGF-A is a key mediator of angiogenesis, primarily signalling via VEGF receptor 2 (VEGFR2). Endothelial cells also express the co-receptor neuropilin-1 (NRP1) that potentiates VEGF-A/VEGFR2 signalling. VEGFR2 and NRP1 had distinct real-time ligand binding kinetics when monitored using BRET. We previously characterised fluorescent VEGF-A isoforms tagged at a single site with tetramethylrhodamine (TMR). Here, we explored differences between VEGF-A isoforms in living cells that co-expressed both receptors.

EXPERIMENTAL APPROACH

Receptor localisation was monitored in HEK293T cells expressing both VEGFR2 and NRP1 using membrane-impermeant HaloTag and SnapTag technologies. To isolate ligand binding pharmacology at a defined VEGFR2/NRP1 complex, we developed an assay using NanoBiT complementation technology whereby heteromerisation is required for luminescence emissions. Binding affinities and kinetics of VEGFR2-selective VEGF165 b-TMR and non-selective VEGF165 a-TMR were monitored using BRET from this defined complex.

KEY RESULTS

Cell surface VEGFR2 and NRP1 were co-localised and formed a constitutive heteromeric complex. Despite being selective for VEGFR2, VEGF165 b-TMR had a distinct kinetic ligand binding profile at the complex that largely remained elevated in cells over 90 min. VEGF165 a-TMR bound to the VEGFR2/NRP1 complex with kinetics comparable to those of VEGFR2 alone. Using a binding-dead mutant of NRP1 did not affect the binding kinetics or affinity of VEGF165 a-TMR.

CONCLUSION AND IMPLICATIONS

This NanoBiT approach enabled real-time ligand binding to be quantified in living cells at 37°C from a specified complex between a receptor TK and its co-receptor for the first time.

Myeloid-resident neuropilin-1 promotes choroidal neovascularization while mitigating inflammation

Age-related macular degeneration (AMD) in its various forms is a leading cause of blindness in industrialized countries. Here, we provide evidence that ligands for neuropilin-1 (NRP1), such as Semaphorin 3A and VEGF-A, are elevated in the vitreous of patients with AMD at times of active choroidal neovascularization (CNV). We further demonstrate that NRP1-expressing myeloid cells promote and maintain CNV. Expression of NRP1 on cells of myeloid lineage is critical for mitigating production of inflammatory factors such as IL6 and IL1β. Therapeutically trapping ligands of NRP1 with an NRP1-derived trap reduces CNV. Collectively, our findings identify a role for NRP1-expressing myeloid cells in promoting pathological angiogenesis during CNV and introduce a therapeutic approach to counter neovascular AMD.

Neuropilin 1 Regulation of Vascular Permeability Signaling

The vascular endothelium acts as a selective barrier to regulate macromolecule exchange between the blood and tissues. However, the integrity of the endothelium barrier is compromised in an array of pathological settings, including ischemic disease and cancer, which are the leading causes of death worldwide. The resulting vascular hyperpermeability to plasma molecules as well as leukocytes then leads to tissue damaging edema formation and inflammation. The vascular endothelial growth factor A (VEGFA) is a potent permeability factor, and therefore a desirable target for impeding vascular hyperpermeability. However, VEGFA also promotes angiogenesis, the growth of new blood vessels, which is required for reperfusion of ischemic tissues. Moreover, edema increases interstitial pressure in poorly perfused tumors, thereby affecting the delivery of therapeutics, which could be counteracted by stimulating the growth of new functional blood vessels. Thus, targets must be identified to accurately modulate the barrier function of blood vessels without affecting angiogenesis, as well as to develop more effective pro- or anti-angiogenic therapies. Recent studies have shown that the VEGFA co-receptor neuropilin 1 (NRP1) could be playing a fundamental role in steering VEGFA-induced responses of vascular endothelial cells towards angiogenesis or vascular permeability. Moreover, NRP1 is involved in mediating permeability signals induced by ligands other than VEGFA. This review therefore focuses on current knowledge on the role of NRP1 in the regulation of vascular permeability signaling in the endothelium to provide an up-to-date landscape of the current knowledge in this field.

The Role of Heparan Sulfate and Neuropilin 2 in VEGFA Signaling in Human Endothelial Tip Cells and Non-Tip Cells during Angiogenesis In Vitro

During angiogenesis, vascular endothelial growth factor A (VEGFA) regulates endothelial cell (EC) survival, tip cell formation, and stalk cell proliferation via VEGF receptor 2 (VEGFR2). VEGFR2 can interact with VEGFR2 co-receptors such as heparan sulfate proteoglycans (HSPGs) and neuropilin 2 (NRP2), but the exact roles of these co-receptors, or of sulfatase 2 (SULF2), an enzyme that removes sulfate groups from HSPGs and inhibits HSPG-mediated uptake of very low density lipoprotein (VLDL), in angiogenesis and tip cell biology are unknown. In the present study, we investigated whether the modulation of binding of VEGFA to VEGFR2 by knockdown of SULF2 or NRP2 affects sprouting angiogenesis, tip cell formation, proliferation of non-tip cells, and EC survival, or uptake of VLDL. To this end, we employed VEGFA splice variant 121, which lacks an HSPG binding domain, and VEGFA splice variant 165, which does have this domain, in in vitro models of angiogenic tip cells and vascular sprouting. We conclude that VEGFA₁₆₅ and VEGFA₁₂₁ have similar inducing effects on tip cells and sprouting in vitro, and that the binding of VEGFA₁₆₅ to HSPGs in the extracellular matrix does not seem to play a role, as knockdown of SULF2 did not alter these effects. Co-binding of NRP2 appears to regulate VEGFA–VEGFR2-induced sprout initiation, but not tip cell formation. Finally, as the addition of VLDL increased sprout formation but not tip cell formation, and as VLDL uptake was limited to non-tip cells, our findings suggest that VLDL plays a role in sprout formation by providing biomass for stalk cell proliferation.

Classical and alternative receptors for SARS-CoV-2 therapeutic strategy

Understanding the molecules that are essential for severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) entry can provide insights into viral infection and dissemination. Recently, it has been identified from several studies that angiotensin‐converting enzyme 2 receptor and transmembrane serine protease 2 are the main entry molecules for the SARS‐CoV‐2, which produced the pandemic of Covid‐19. However, additional evidence showed several other viral receptors and cellular proteases that are also important in facilitating viral entry and transmission in the target cells. In this review, we summarized the types of SARS‐CoV‐2 entry molecules and discussed their crucial roles for virus binding, protein priming and fusion to the cellular membrane important for SARS‐CoV‐2 infection.

Targeting neuropilin-1 interactions is a promising anti-tumor strategy

ABSTRACT

Neuropilins (NRP1 and NRP2) are multifunctional receptor proteins that are involved in nerve, blood vessel, and tumor development. NRP1 was first found to be expressed in neurons, but subsequent studies have demonstrated its surface expression in cells from the endothelium and lymph nodes. NRP1 has been demonstrated to be involved in the occurrence and development of a variety of cancers. NRP1 interacts with various cytokines, such as vascular endothelial growth factor family and its receptor and transforming growth factor β1 and its receptor, to affect tumor angiogenesis, tumor proliferation, and migration. In addition, NRP1+ regulatory T cells (Tregs) play an inhibitory role in tumor immunity. High numbers of NRP1+ Tregs were associated with cancer prognosis. Targeting NRP1 has shown promise, and antagonists against NRP1 have had therapeutic efficacy in preliminary clinical studies. NRP1 treatment modalities using nanomaterials, targeted drugs, oncolytic viruses, and radio-chemotherapy have gradually been developed. Hence, we reviewed the use of NRP1 in the context of tumorigenesis, progression, and treatment.

Complement C4A Regulates Autoreactive B Cells in Murine Lupus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease mediated by pathogenic autoantibodies. While complement protein C4 is associated with SLE, its isoforms (C4A and C4B) are not equal in their impact. Despite being 99% homologous, genetic studies identified C4A as more protective than C4B. By generating gene-edited mouse strains expressing either human C4A or C4B and crossing these with the 564lgi lupus strain, we show that, overall, C4A-like 564Igi mice develop less humoral autoimmunity than C4B-like 564Igi mice. This includes a decrease in the number of GCs, autoreactive B cells, autoantibodies, and memory B cells. The higher efficiency of C4A in inducing self-antigen clearance is associated with the follicular exclusion of autoreactive B cells. These results explain how the C4A isoform is protective in lupus and suggest C4A as a possible replacement therapy in lupus.

Simoni et al. address a long-standing question about how complement C4A and C4B isoforms differ in function in vivo in autoimmunity. They find that C4A leads to an increased protection in humoral autoimmunity relative to C4B. Autoantibody diversity is likewise dependent on the C4 protein isotype.

Regeneration of the pulmonary vascular endothelium after viral pneumonia requires COUP-TF2

Acute respiratory distress syndrome is associated with a robust inflammatory response that damages the vascular endothelium, impairing gas exchange. While restoration of microcapillaries is critical to avoid mortality, therapeutic targeting of this process requires a greater understanding of endothelial repair mechanisms. Here, we demonstrate that lung endothelium possesses substantial regenerative capacity and lineage tracing reveals that native endothelium is the source of vascular repair after influenza injury. Ablation of chicken ovalbumin upstream promoter-transcription factor 2 (COUP-TF2) (Nr2f2), a transcription factor implicated in developmental angiogenesis, reduced endothelial proliferation, exacerbating viral lung injury in vivo. In vitro, COUP-TF2 regulates proliferation and migration through activation of cyclin D1 and neuropilin 1. Upon influenza injury, nuclear factor κB suppresses COUP-TF2, but surviving endothelial cells ultimately reestablish vascular homeostasis dependent on restoration of COUP-TF2. Therefore, stabilization of COUP-TF2 may represent a therapeutic strategy to enhance recovery from pathogens, including H1N1 influenza and SARS-CoV-2.

Endothelial sprouting, proliferation, or senescence: tipping the balance from physiology to pathology

Therapeutic modulation of vascular cell proliferation and migration is essential for the effective inhibition of angiogenesis in cancer or its induction in cardiovascular disease. The general view is that an increase in vascular growth factor levels or mitogenic stimulation is beneficial for angiogenesis, since it leads to an increase in both endothelial proliferation and sprouting. However, several recent studies showed that an increase in mitogenic stimuli can also lead to the arrest of angiogenesis. This is due to the existence of intrinsic signaling feedback loops and cell cycle checkpoints that work in synchrony to maintain a balance between endothelial proliferation and sprouting. This balance is tightly and effectively regulated during tissue growth and is often deregulated or impaired in disease. Most therapeutic strategies used so far to promote vascular growth simply increase mitogenic stimuli, without taking into account its deleterious effects on this balance and on vascular cells. Here, we review the main findings on the mechanisms controlling physiological vascular sprouting, proliferation, and senescence and how those mechanisms are often deregulated in acquired or congenital cardiovascular disease leading to a diverse range of pathologies. We also discuss alternative approaches to increase the effectiveness of pro-angiogenic therapies in cardiovascular regenerative medicine.

Effects of NRP1 on angiogenesis and vascular maturity in endothelial cells are dependent on the expression of SEMA4D

Angiogenesis and vascular maturation play important roles in tumorigenesis and tumor development. The expression of neuropilin 1 (NRP1) is closely associated with angiogenesis in tumors; however, the molecular mechanisms of action in angiogenesis and tumor maturation, as well as the potential clinical value of NRP1 remain unclear. The importance of NRP1 expression in tumor progression was determined using The Cancer Genome Atlas (TCGA) database analysis. Gain- and loss-of-function experiments of NRP1 were performed in vascular endothelial cells (ECs) to investigate the functions in angiogenesis. CCK-8, flow cytometry, Transwell experiments and a series of in vitro experiments were used to detect cell functions. A combination of angiogenesis antibody arrays and RNA-Seq analyses were performed to reveal the proangiogenic mechanisms of action. The function of semaphorin 4D (SEMA4D) was also investigated separately. NRP1 mRNA levels were significantly increased in primary tumors compared with normal tissues based on TCGA data (P<0.01) and were associated with tumor development in patients. Gain- and loss-of-function experiments highlighted the function of NRP1 in promoting EC proliferation, motility and capillary-like tube formation and in reducing apoptosis. NRP1 overexpression led to significantly decreased EC markers (PECAM-1, angiogenin, PIGF and MMP-9) expression levels and reduced the vascular maturity. MAPK7, TPM1, RRBP1, PTPRK, HSP90A, PRKD2, PFKFB3, RGS4 and SPARC were revealed to play important roles in this process. SEMA4D was revealed to be a key protein associated with NRP1 in ECs. These data indicated that NRP1-promoted angiogenesis may be induced at the cost of reducing maturity of the ECs. NRP1 may also be a therapeutic target for antiangiogenic strategies and a candidate prognostic marker for tumors.

Lymphatic Endothelial Cell Junctions: Molecular Regulation in Physiology and Diseases

Lymphatic endothelial cells (LECs) lining lymphatic vessels develop specialized cell-cell junctions that are crucial for the maintenance of vessel integrity and proper lymphatic vascular functions. Successful lymphatic drainage requires a division of labor between lymphatic capillaries that take up lymph via open "button-like" junctions, and collectors that transport lymph to veins, which have tight "zipper-like" junctions that prevent lymph leakage. In recent years, progress has been made in the understanding of these specialized junctions, as a result of the application of state-of-the-art imaging tools and novel transgenic animal models. In this review, we discuss lymphatic development and mechanisms governing junction remodeling between button and zipper-like states in LECs. Understanding lymphatic junction remodeling is important in order to unravel lymphatic drainage regulation in obesity and inflammatory diseases and may pave the way towards future novel therapeutic interventions.

Neuropilin: Handyman and Power Broker in the Tumor Microenvironment

Neuropilin-1 and neuropilin-2 form a small family of transmembrane receptors, which, due to the lack of a cytosolic protein kinase domain, act primarily as co-receptors for various ligands. Performing at the molecular level both the executive and organizing functions of a handyman as well as of a power broker, they are instrumental in controlling the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. In this setting, the various neuropilin ligands and interaction partners on various cells of the tumor microenvironment, such as cancer cells, endothelial cells, cancer-associated fibroblasts, and immune cells, are surveyed. The suitability of various neuropilin-targeting substances and the intervention in neuropilin-mediated interactions is considered as a possible building block of tumor therapy.

Involvement of Heparanase in Endothelial Cell-Cardiomyocyte Crosstalk

Traditionally, the management of diabetes has focused mainly on controlling high blood glucose levels. Unfortunately, despite valiant efforts to normalize this blood glucose, poor medication management predisposes these patients to heart failure. Following diabetes, how the heart utilizes different sources of fuel for energy is key to the development of heart failure. The diabetic heart switches from using both glucose and fats, to predominately using fats as an energy resource for maintaining its activities. This transformation to using fats as an exclusive source of energy is helpful in the initial stages of the disease and is tightly controlled. However, over the progression of diabetes, there is a loss of this controlled supply and use of fats, which ultimately has terrible consequences since the uncontrolled use of fats produces toxic by-products which weaken heart function and cause heart disease. Heparanase is a key player that directs how much fats are provided to the heart and does so in association with several partners like LPL and VEGFs. Together, they regulate the amount of fats supplied, and their subsequent breakdown to provide energy. Following diabetes, there is a disruption in this network resulting in fat oversupply and cell death. Understanding how the heparanase-LPL-VEGFs "ensemble" cooperates, and its dysfunction in the diabetic heart would be useful in restoring metabolic equilibrium and limiting diabetes-related cardiac damage.

Epidermal autonomous VEGFA/Flt1/Nrp1 functions mediate psoriasis-like disease

Psoriasis is a common chronic skin disorder characterized by keratinocyte hyperproliferation with altered differentiation accompanied by inflammation and increased angiogenesis. It remains unclear whether the first events that initiate psoriasis development occur in keratinocytes or inflammatory cells. Here, using different psoriasis mouse models, we showed that conditional deletion of Flt1 or Nrp1 in epidermal cells inhibited psoriasis mediated by Vegfa overexpression or c-Jun/JunB deletion. Administration of anti-Nrp1 antibody reverted the psoriasis phenotype. Using transcriptional and chromatin profiling of epidermal cells following Vegfa overexpression together with Flt1 or Nrp1 deletion, we identified the gene regulatory network regulated by Vegfa/Nrp1/Flt1 during psoriasis development and uncovered a key role of Fosl1 in regulating the chromatin remodeling mediated by Vegfa overexpression in keratinocytes. In conclusion, our study identifies an epidermal autonomous function of Vegfa/Nrp1/Flt1 that mediates psoriatic-like disease and demonstrates the clinical relevance of blocking Vegfa/Nrp1/Flt1 axis in psoriasis.

Tumor angiogenesis: causes, consequences, challenges and opportunities

Tumor vascularization occurs through several distinct biological processes, which not only vary between tumor type and anatomic location, but also occur simultaneously within the same cancer tissue. These processes are orchestrated by a range of secreted factors and signaling pathways and can involve participation of non-endothelial cells, such as progenitors or cancer stem cells. Anti-angiogenic therapies using either antibodies or tyrosine kinase inhibitors have been approved to treat several types of cancer. However, the benefit of treatment has so far been modest, some patients not responding at all and others acquiring resistance. It is becoming increasingly clear that blocking tumors from accessing the circulation is not an easy task to accomplish. Tumor vessel functionality and gene expression often differ vastly when comparing different cancer subtypes, and vessel phenotype can be markedly heterogeneous within a single tumor. Here, we summarize the current understanding of cellular and molecular mechanisms involved in tumor angiogenesis and discuss challenges and opportunities associated with vascular targeting.

Long noncoding RNA SNHG16 silencing inhibits the aggressiveness of gastric cancer via upregulation of microRNA-628-3p and consequent decrease of NRP1

Background

MicroRNA-628-3p (miR-628) has been reported to play important roles in the progression of multiple human cancer types. Nonetheless, whether the expression profile of miR-628 is altered in gastric cancer remains unclear and whether its aberrant expression plays a crucial part in the aggressiveness of gastric cancer is yet to be determined. Therefore, in this study, we systematically investigated the involvement of miR-628 in gastric cancer progression.

Materials and methods

MiR-628 expression in gastric cancer tissues and cell lines were determined via reverse transcription-quantitative polymerase chain reaction (RT-qPCR). A CCK-8 assay, flow-cytometric analysis, Transwell assays, and a xenograft model experiment were performed to evaluate the influence of miR-628 overexpression on gastric cancer cells. Notably, the mechanisms underlying the tumor-suppressive activity of miR-628 in gastric cancer cells were explored by bioinformatics analysis, a luciferase reporter assay, RT-qPCR, and Western blotting.

Results

MiR-628 expression was low in gastric cancer tissue samples and cell lines. The low expression of miR-628 was closely associated with the lymph node metastasis, invasive depth and TNM stage among patients with gastric cancer. Further clinical analysis indicated that patients with gastric cancer underexpressing miR-628 had a worse prognosis than did the patients with high miR-628 expression in the tumor. Overexpressed miR-628 restrained proliferation, migration, and invasion; induced apoptosis; and impaired tumor growth of gastric cancer cells. In addition, neuropilin 1 (NRP1) mRNA was validated as the direct target of miR-628 in gastric cancer. Long noncoding RNA small nucleolar RNA host gene 16 (SNHG16) was demonstrated to sponge miR-628 in gastric cancer. Moreover, miR-628 knockdown abrogated the influence of SNHG16 silencing on gastric cancer cells.

Conclusion

Our findings elucidate how the SNHG16–miR-628–NRP1 pathway serves as a regulatory network playing crucial roles in gastric cancer progression, suggesting that this pathway may be a novel target of anticancer therapy.

Loss of the transcription factor RBPJ induces disease-promoting properties in brain pericytes

Sufficient vascular supply is indispensable for brain development and function, whereas dysfunctional blood vessels are associated with human diseases such as vascular malformations, stroke or neurodegeneration. Pericytes are capillary-associated mesenchymal cells that limit vascular permeability and protect the brain by preserving blood-brain barrier integrity. Loss of pericytes has been linked to neurodegenerative changes in genetically modified mice. Here, we report that postnatal inactivation of the Rbpj gene, encoding the transcription factor RBPJ, leads to alteration of cell identity markers in brain pericytes, increases local TGFβ signalling, and triggers profound changes in endothelial behaviour. These changes, which are not mimicked by pericyte ablation, imperil vascular stability and induce the acquisition of pathological landmarks associated with cerebral cavernous malformations. In adult mice, loss of Rbpj results in bigger stroke lesions upon ischemic insult. We propose that brain pericytes can acquire deleterious properties that actively enhance vascular lesion formation and promote pathogenic processes.

Pericytes are perivascular cells essential for blood-brain barrier maintenance. Here Diéguez-Hurtado et al. show that depletion of the transcription factor RBPJ in pericytes affects their molecular identity and disturbs endothelial cell behaviour, inducing the formation of vascular lesions in the brain.

Sec14l3 potentiates VEGFR2 signaling to regulate zebrafish vasculogenesis

Vascular endothelial growth factor (VEGF) regulates vasculogenesis by using its tyrosine kinase receptors. However, little is known about whether Sec14-like phosphatidylinositol transfer proteins (PTP) are involved in this process. Here, we show that zebrafish sec14l3, one of the family members, specifically participates in artery and vein formation via regulating angioblasts and subsequent venous progenitors’ migration during vasculogenesis. Vascular defects caused by sec14l3 depletion are partially rescued by restoration of VEGFR2 signaling at the receptor or downstream effector level. Biochemical analyses show that Sec14l3/SEC14L2 physically bind to VEGFR2 and prevent it from dephosphorylation specifically at the Y¹¹⁷⁵ site by peri-membrane tyrosine phosphatase PTP1B, therefore potentiating VEGFR2 signaling activation. Meanwhile, Sec14l3 and SEC14L2 interact with RAB5A/4A and facilitate the formation of their GTP-bound states, which might be critical for VEGFR2 endocytic trafficking. Thus, we conclude that Sec14l3 controls vasculogenesis in zebrafish via the regulation of VEGFR2 activation.

The growth factor VEGF is known to regulate vasculogenesis but the downstream pathways activated are unclear. Here, the authors report that Sec14l3, a member of the PITP (phosphatidyl inositol transfer proteins) family regulates the formation of zebrafish vasculature by promoting VEGFR2 endocytic trafficking.

The endothelial tip-stalk cell selection and shuffling during angiogenesis

Angiogenesis is a critical, fine-tuned, multi-staged biological process. Tip-stalk cell selection and shuffling are the building blocks of sprouting angiogenesis. Accumulated evidences show that tip-stalk cell selection and shuffling are regulated by a variety of physical, chemical and biological factors, especially the interaction among multiple genes, their products and environments. The classic Notch-VEGFR, Slit-Robo, ECM-binding integrin, semaphorin and CCN family play important roles in tip-stalk cell selection and shuffling. In this review, we outline the progress and prospect in the mechanism and the roles of the various molecules and related signaling pathways in endothelial tip-stalk cell selection and shuffling. In the future, the regulators of tip-stalk cell selection and shuffling would be the potential markers and targets for angiogenesis.

Neuropilins in the Context of Tumor Vasculature

Neuropilin-1 and Neuropilin-2 form a small family of plasma membrane spanning receptors originally identified by the binding of semaphorin and vascular endothelial growth factor. Having no cytosolic protein kinase domain, they function predominantly as co-receptors of other receptors for various ligands. As such, they critically modulate the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. This review highlights the diverse neuropilin ligands and interacting partners on endothelial cells, which are relevant in the context of the tumor vasculature and the tumor microenvironment. In addition to tumor cells, the latter contains cancer-associated fibroblasts, immune cells, and endothelial cells. Based on the prevalent neuropilin-mediated interactions, the suitability of various neuropilin-targeted substances for influencing tumor angiogenesis as a possible building block of a tumor therapy is discussed.

EGFL7 regulates sprouting angiogenesis and endothelial integrity in a human blood vessel model

Elucidating the mechanisms underlying sprouting angiogenesis and permeability should enable the development of more effective therapies for various diseases, including retinopathy, cancer, and other vascular disorders. We focused on epidermal growth factor-like domain 7 (EGFL7) which plays an important role in NOTCH signaling and in the organization of angiogenic sprouts. We developed an EGFL7-knockdown in vitro microvessel model and investigated the effect of EGFL7 at a tissue level. We found EGFL7 knockdown suppressed VEGF-A-induced sprouting angiogenesis accompanied by an overproduction of endothelial filopodia and reduced collagen IV deposition at the basal side of endothelial cells. We also observed impaired barrier function which reflected an inflammatory condition. Furthermore, our results showed that proper formation of adherens junctions and phosphorylation of VE-cadherin was disturbed. In conclusion, by using a 3D microvessel model we identified novel roles for EGFL7 in endothelial function during sprouting angiogenesis.

Transmembrane protein 215 promotes angiogenesis by maintaining endothelial cell survival

Sprouting angiogenesis is a major form of neovascularization of tissues suffering from hypoxia and other related stress. Endothelial cells (ECs) undergo proliferation, differentiation, programmed death, and migration during angiogenic sprouting, but the underlying molecular mechanisms regulating ECs in angiogenesis have been incompletely elucidated. Here we report that the transmembrane protein 215 (TMEM215) is involved in angiogenesis by regulating EC survival. The murine TMEM215 gene, which possesses two transcriptional starting sites as determined by 5′‐rapid amplification of complementary DNA (cDNA) ends (RACE), encodes a two‐pass TMEM. The TMEM215 transcripts were detected in ECs in addition to other tissues by quantitative reverse transcription‐polymerase chain reaction. Immunofluorescence showed that TMEM215 was expressed in the vasculature in retina, liver, and tumor, and colocalized with EC markers. We show that knockdown of TMEM215 in ECs induced strong cell death of ECs in vitro without affecting cell proliferation and migration, suggesting that TMEM215 was required for EC survival. Downregulation of TMEM215 expression compromised lumen formation and sprouting capacities of ECs in vitro. Moreover, intravitreous injection of TMEM215 small interfering RNA resulted in delayed and abnormal development of retinal vasculature with poor perfusion. These results identified TMEM215 as a novel molecule involved in angiogenesis by regulating the survival of ECs.

Knockdown of HIF-1α impairs post-ischemic vascular reconstruction in the brain via deficient homing and sprouting bmEPCs

Although the critical role of hypoxia inducible factor-1α (HIF-1α) in cerebral neovascularization after stroke has been well characterized, the details regarding the regulation of endothelial progenitor cell (EPC)-dependent neovascularization by HIF-1α are not completely understood. Using lentiviral shRNA to knockdown HIF-1α, we showed that HIF-1α plays a central role in bone marrow-derived EPC (bmEPC) homing and sprouting in the post-acute stage of ischemic Sprague Dawley (SD) rat brains. First, knockdown of HIF-1α decreased the homing of both endogenous and exogenous bmEPCs to the ischemic brain. Additionally, the knockdown impaired the incorporation and sprouting of bmEPCs in the ischemic brain. In vitro, knockdown of HIF-1α inhibited the spheroid sprouting and tube formation of bmEPCs. Mechanically, the HIF-1α-dependent recruitment of bmEPCs to the ischemic brain was relative to the CXCL12/CXCR4 axis and HMGB1, which were relative to astrocytes. In addition, the loss of HIF-1α resulted in deficient expression levels of VEGF-A, Flk-1, NRP1, and Dll4 in the ischemic brains, bmEPCs, and astrocytes. These findings suggested that HIF-1α implicates in bmEPC homing via CXCL12/CXCR4 and HMGB1 and that it promotes bmEPC sprouting via VEGF-A/flk1-NRP1/Dll4.