The neuropilin 1 cytoplasmic domain is required for VEGF-A-dependent arteriogenesis

Therapeutic Angiogenesis Mediated by Traditional Chinese Medicine: Advances in Cardiovascular Disease Treatment

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese Medicine (TCM) shows growing potential as an adjunct or alternative therapy for vascular occlusion diseases (e.g., stroke, peripheral artery disease) by promoting therapeutic angiogenesis to restore blood flow in ischemic regions while minimizing side effects.

AIMS OF THE STUDY

This review examines TCM-mediated angiogenesis mechanisms and therapeutic advances in vascular occlusion management, establishing a theoretical foundation for clinical translation and precision medicine development.

MATERIALS AND METHODS

We systematically analyzed PubMed articles on TCM-induced angiogenesis in vascular occlusion diseases, focusing on herbal formulations, single herbs, bioactive compounds, and their associated signaling pathways. Search PubMed for studies investigating the role of Chinese herbal medicine (TCM), natural compounds, and herbal medicine in angiogenesis, while excluding research related to cancer, tumor, or oncological contexts.

RESULTS

TCM formulas, individual herbs, and monomeric compounds enhance endothelial cell proliferation, migration, and tube formation via pathways such as HIF/VEGF, PI3K/AKT, NOTCH, BMP/ALK, and Apelin/APJ, improving ischemic blood flow.

CONCLUSION

This review highlights angiogenesis as a novel strategy for vascular occlusive diseases and underscores TCM's efficacy through multi-target angiogenic regulation mechanism.However, further research using modern medical technologies is needed to optimize clinical application and advance precision medicine.

Neuropilin-1: A Multifaceted Target for Cancer Therapy

Neuropilin-1 (NRP1), initially identified as a neuronal guidance protein, has emerged as a multifaceted regulator in cancer biology. Beyond its role in axonal guidance and angiogenesis, NRP1 is increasingly recognized for its significant impact on tumor progression and therapeutic outcomes. This review explores the diverse functions of NRP1 in cancer, encompassing its influence on tumor cell proliferation, migration, invasion, and metastasis. NRP1 interacts with several key signaling pathways, including vascular endothelial growth factor (VEGF), semaphorins, and transforming growth factor-beta (TGF-β), modulating the tumor microenvironment and promoting angiogenesis. Moreover, NRP1 expression correlates with poor prognosis in various malignancies, underscoring its potential as a prognostic biomarker. Therapeutically, targeting NRP1 holds promise as a novel strategy to inhibit tumor growth and enhance the efficacy of regular treatments such as chemotherapy and radiotherapy. Strategies involving NRP1-targeted therapies, including monoclonal antibodies, small molecule inhibitors, and gene silencing techniques, are being actively investigated in preclinical and clinical settings. Despite challenges in specificity and delivery, advances in understanding NRP1 biology offer new avenues for personalized cancer therapy. Although several types of cancer cells can express NRPs, the role of NRPs in tumor pathogenesis is largely unknown. Future investigations are needed to enhance our understanding of the effects and mechanisms of NRPs on the proliferation, apoptosis, and migration of neuronal, endothelial, and cancer cells. The novel frameworks or multi-omics approaches integrate data from multiple databases to better understand cancer's molecular and clinical features, develop personalized therapies, and help identify biomarkers. This review highlights the pivotal role of NRP1 in cancer pathogenesis and discusses its implications for developing targeted therapeutic approaches to improve patient outcomes, highlighting the role of OMICS in targeting cancer patients for personalized therapy.

DCBLD1 Modulates Angiogenesis by Regulation of the VEGFR-2 Endocytosis in Endothelial Cells

BACKGROUND

Unwanted angiogenesis is involved in the progression of various malignant tumors and cardiovascular diseases, and the factors that regulate angiogenesis are potential therapeutic targets. We tested the hypothesis that DCBLD1 (discoidin, CUB, and LCCL domain-containing protein 1) is a coreceptor of VEGFR-2 (vascular endothelial growth factor receptor-2) and modulates angiogenesis in endothelial cells.

METHODS

A carotid artery ligation model and retinal angiogenesis assay were used to study angiogenesis using globe knockout or endothelial cell-specific conditional Dcbld1 knockout mice in vivo. Immunoblotting, immunofluorescence staining, plasma membrane subfraction isolation, Coimmunoprecipitation, and mass spectrum assay were performed to clarify the molecular mechanisms.

RESULTS

Loss of Dcbld1 impaired VEGF (vascular endothelial growth factor) response and inhibited VEGF-induced endothelial cell proliferation and migration. Dcbld1 deletion interfered with adult and developmental angiogenesis. Mechanistically, DCBLD1 bound to VEGFR-2 and regulated the formation of VEGFR-2 complex with negative regulators: protein tyrosine phosphatases, E3 ubiquitin ligases (neuronal precursor cell-expressed developmentally downregulated gene 4, Nedd4 and c-Casitas B-lineage lymphoma, c-Cbl), and also Dcbld1 knockdown promoted lysosome-mediated VEGFR-2 degradation in endothelial cells.

CONCLUSION

These findings demonstrated the essential role of endothelial DCBLD1 in regulating VEGF signaling and provided evidence that DCBLD1 promotes VEGF-induced angiogenesis by limiting the dephosphorylation, ubiquitination, and lysosome degradation after VEGFR-2 endocytosis. We proposed that endothelial DCBLD1 is a potential therapeutic target for ischemic cardiovascular diseases by the modulation of angiogenesis through regulation of the VEGFR-2 endocytosis.

Reassessment of arterial versus venous perfusion of diabetic retinal neovascularization using ultrawide-field fluorescein angiography

PURPOSE

The purpose of this study was to assess whether diabetic NV is perfused by the arterial or the venous circulation.

METHODS

This is a retrospective, consecutive case series evaluating patients with proliferative diabetic retinopathy (PDR) imaged with ultrawide-field (UWF) fluorescein angiography (FA). Areas of neovascularization elsewhere (NVE) and neovascularization of the disc (NVD) were assessed. Perfusion was defined as arterial, arteriovenous, or venous if the area of diabetic neovascularization (NV) began to hyperfluoresce either prior, during, or after laminar venous flow, respectively.

RESULTS

A total of 180 eyes from 176 patients with 928 NV were identified (830 NVE, 98 NVD). Of those, 5.1% of NVE were classified as arterial and 58.2% of NVD were classified as arterial. The remaining NV were classified as arteriovenous except for a small subset (6.1%) which were indeterminate. None of the NV were classified as venous. Noteworthy examples demonstrated NV that nearly fully perfused prior to any detectable fluorescence within nearby veins as well as clear shunting of blood from a feeding artery to a draining vein.

CONCLUSIONS

UWF FA images suggest that some NV is perfused by retinal arteries. This may be useful in devising strategies for early detection and treatment of NV precursors.

KEY MESSAGES

What is known • Diabetic retinal neovascularization has long been thought to be perfused by the retinal venous circulation. • Vascular endothelial growth factor has been shown to play key roles in both angiogenesis and arteriogenesis. What is new • Ultrawide-field fluorescein angiography demonstrates that at least some diabetic neovascularization is perfused by the retinal arterial circulation. • This supports the hypothesis that diabetic neovascularization may arise from arterially-perfused intraretinal microvascular abnormalities in the capillary bed.

Neuropilin-1 controls vascular permeability through juxtacrine regulation of endothelial adherens junctions

Neuropilin-1 (NRP1) regulates endothelial cell (EC) biology through modulation of vascular endothelial growth factor receptor 2 (VEGFR2) signalling by presenting VEGFA to VEGFR2. How NRP1 impacts VEGFA-mediated vascular hyperpermeability has however remained unresolved, described as exerting either a positive or a passive function. Using EC-specific Nrp1 knock-out mice, we discover that EC-expressed NRP1 exerts an organotypic role. In the ear skin, VEGFA/VEGFR2-mediated vascular leakage was increased following loss of EC NRP1, implicating NRP1 in negative regulation of VEGFR2 signalling. In contrast, in the back skin and trachea, loss of EC NRP1 decreased vascular leakage. In accordance, phosphorylation of vascular endothelial (VE)-cadherin was increased in the ear skin but suppressed in the back skin of Nrp1 iECKO mice. NRP1 expressed on perivascular cells has been shown to impact VEGF-mediated VEGFR2 signalling. Importantly, expression of NRP1 on perivascular cells was more abundant in the ear skin than in the back skin. Global loss of NRP1 resulted in suppressed VEGFA-induced vascular leakage in the ear skin, implicating perivascular NRP1 as a juxtacrine co-receptor of VEGFA in this compartment. Altogether, we demonstrate that perivascular NRP1 is an active participant in EC VEGFA/VEGFR2 signalling and acts as an organotypic modifier of EC biology.

Physiological and tumor-associated angiogenesis: Key factors and therapy targeting VEGF/VEGFR pathway

Cancer remains one of the leading causes of death worldwide and poses a significant challenge to effective treatment due to its complexity. Angiogenesis, the formation of new blood vessels, is one of the cancer hallmarks and is a critical process in tumor growth and metastasis. The pivotal role of angiogenesis in cancer development has made antiangiogenic treatment a promising strategy for cancer therapy. To develop an effective therapy, it is essential to understand the basics of the physiological and tumor angiogenesis process. This review presents the primary factors related to physiological and tumor angiogenesis and the mechanisms of angiogenesis in tumors. We summarize potential molecular targets for cancer treatment by focusing on the vasculature, with the VEGF/VEGFR pathway being one of the most important and well-studied. Additionally, we present the advantages and limitations of currently used clinical protocols for cancer treatment targeting the VEGF/VEGFR pathway.

NRP1 promotes osteo/odontogenic differentiation via shroom3 in dental pulp stem cells

Neuropilin-1 (NRP1) is a single transmembrane glycoprotein involved in a variety of physiological events. However, the exact mechanisms by which NRP1 regulates dental pulp stem cells (DPSCs) to differentiate toward an osteo/odontogenic phenotype are poorly understood. Here, we determined the significantly increased expression of full-length NRP1 and glycosaminoglycan (GAG)-modified NRP1 during osteo/odontogenesis in DPSCs. NRP1 was confirmed to promote alkaline phosphatase (ALP) activity, mineralized nodule deposition, protein and mRNA expression of Runx2, DSPP and DMP1 in DPSCs via the loss-of-function and gain-of-function approaches. Further, a non-GAG-modified NRP1 mutant (NRP1 S612A) was generated and the suppression of osteo/odontogenic differentiation was observed in the NRP1 S612A overexpression cells. Knockdown of the adaptor protein shroom3 resulted in the inhibition of osteo/odontogenesis. The protein-protein interaction network, the protein-protein docking and confocal analyses indicated the interactions between NRP1 and shroom3. Furthermore, immunoprecipitation followed by western analysis confirmed the binding of NRP1 to shroom3, but overexpression of NRP1 S612A greatly influenced the recruitment of shroom3 by NRP1. These results provide strong evidence that NRP1 is a critical regulator for osteo/odontogenesis through interacting with shroom3. Moreover, our results indicate that NRP1 S612A attenuates osteo/odontogenesis, suggesting that GAG modification is essential for NRP1 in DPSCs.

Role of endothelial Raptor in abnormal arteriogenesis after lower limb ischaemia in type 2 diabetes

AIMS

Proper arteriogenesis after tissue ischaemia is necessary to rebuild stable blood circulation; nevertheless, this process is impaired in type 2 diabetes mellitus (T2DM). Raptor is a scaffold protein and a component of mammalian target of rapamycin complex 1 (mTORC1). However, the role of the endothelial Raptor in arteriogenesis under the conditions of T2DM remains unknown. This study investigated the role of endothelial Raptor in ischaemia-induced arteriogenesis during T2DM.

METHODS AND RESULTS

Although endothelial mTORC1 is hyperactive in T2DM, we observed a marked reduction in the expression of endothelial Raptor in two mouse models and in human vessels. Inducible endothelial-specific Raptor knockout severely exacerbated impaired hindlimb perfusion and arteriogenesis after hindlimb ischaemic injury in 12-week high-fat diet fed mice. Additionally, we found that Raptor deficiency dampened vascular endothelial growth factor receptor 2 (VEGFR2) signalling in endothelial cells (ECs) and inhibited VEGF-induced cell migration and tube formation in a PTP1B-dependent manner. Furthermore, mass spectrometry analysis indicated that Raptor interacts with neuropilin 1 (NRP1), the co-receptor of VEGFR2, and mediates VEGFR2 trafficking by facilitating the interaction between NRP1 and Synectin. Finally, we found that EC-specific overexpression of the Raptor mutant (loss of mTOR binding) reversed impaired hindlimb perfusion and arteriogenesis induced by endothelial Raptor knockout in high-fat diet fed mice.

CONCLUSION

Collectively, our study demonstrated the crucial role of endothelial Raptor in promoting ischaemia-induced arteriogenesis in T2DM by mediating VEGFR2 signalling. Thus, endothelial Raptor is a novel therapeutic target for promoting arteriogenesis and ameliorating perfusion in T2DM.

Neuropilin invites reoviruses into neurons

In this issue of Cell Host & Microbe, Shang et al. identify murine neuropilin 1 as a host factor that binds reovirus particles, directing cell entry and contributing to viral dissemination and neurovirulence. This study highlights the reovirus model system to investigate host receptors and their significance in viral pathogenesis.

Vascular Endothelial Growth Factor (VEGF) and Its Role in the Cardiovascular System

Cardiovascular diseases remain the leading cause of death worldwide, with ischemic heart disease (IHD) as the most common. Ischemia-induced angiogenesis is a process in which vascular endothelial growth factor (VEGF) plays a crucial role. To conduct research in the field of VEGF's association in cardiovascular diseases, it is vital to understand its role in the physiological and pathological processes in the heart. VEGF-based therapies have demonstrated a promising role in preclinical studies. However, their potential in human therapies is currently under discussion. Furthermore, VEGF is considered a potential biomarker for collateral circulation assessment and heart failure (HF) mortality. Additionally, as VEGF is involved in angiogenesis, there is a need to elucidate the impact of VEGF-targeted therapies in terms of cardiovascular side effects.

Defining the Functional Influence of Endothelial Cell-Expressed Oncogenic Activating Mutations on Vascular Morphogenesis and Capillary Assembly

This study sought to define key molecules and signals controlling major steps in vascular morphogenesis, and how these signals regulate pericyte recruitment and pericyte-induced basement membrane deposition. The morphogenic impact of endothelial cell (EC) expression of activating mutants of Kirsten rat sarcoma virus (kRas), mitogen-activated protein kinase 1 (Mek1), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), Akt serine/threonine kinase 1 (Akt1), Ras homolog enriched in brain (Rheb) Janus kinase 2 (Jak2), or signal transducer and activator of transcription 3 (Stat3) expression versus controls was evaluated, along with EC signaling events, pharmacologic inhibitor assays, and siRNA suppression experiments. Primary stimulators of EC lumen formation included kRas, Akt1, and Mek1, whereas PIK3CA and Akt1 stimulated a specialized type of cystic lumen formation. In contrast, the key drivers of EC sprouting behavior were Jak2, Stat3, Mek1, PIK3CA, and mammalian target of rapamycin (mTor). These conclusions are further supported by pharmacologic inhibitor and siRNA suppression experiments. EC expression of active Akt1, kRas, and PIK3CA led to markedly dysregulated lumen formation coupled to strongly inhibited pericyte recruitment and basement membrane deposition. For example, activated Akt1 expression in ECs excessively stimulated lumen formation, decreased EC sprouting behavior, and showed minimal pericyte recruitment with reduced mRNA expression of platelet-derived growth factor-BB, platelet-derived growth factor-DD, and endothelin-1, critical EC-derived factors known to stimulate pericyte invasion. The study identified key signals controlling fundamental steps in capillary morphogenesis and maturation and provided mechanistic details on why EC activating mutations induced a capillary deficiency state with abnormal lumens, impaired pericyte recruitment, and basement deposition: predisposing stimuli for the development of vascular malformations.

Endothelial Neuropilin-1: a multifaced signal transducer with an emerging role in inflammation and atherosclerosis beyond angiogenesis

Neuropilin-1 (NRP1) is a transmembrane glycoprotein expressed by several cell types including, neurons, endothelial cells (ECs), smooth muscle cells, cardiomyocytes and immune cells comprising macrophages, dendritic cells and T cell subsets. Since NRP1 discovery in 1987 as an adhesion molecule in the frog nervous system, more than 2300 publications on PubMed investigated the function of NRP1 in physiological and pathological contexts. NRP1 has been characterised as a coreceptor for class 3 semaphorins and several members of the vascular endothelial growth factor (VEGF) family. Because the VEGF family is the main regulator of blood and lymphatic vessel growth in addition to promoting neurogenesis, neuronal patterning, neuroprotection and glial growth, the role of NRP1 in these biological processes has been extensively investigated. It is now established that NRP1 promotes the physiological growth of new vessels from pre-existing ones in the process of angiogenesis. Furthermore, several studies have shown that NRP1 mediates signalling pathways regulating pathological vascular growth in ocular neovascular diseases and tumour development. Less defined are the roles of NRP1 in maintaining the function of the quiescent established vasculature in an adult organism. This review will focus on the opposite roles of NRP1 in regulating transforming growth factor β signalling pathways in different cell types, and on the emerging role of endothelial NRP1 as an atheroprotective, anti-inflammatory factor involved in the response of ECs to shear stress.

Dual Pigment Epithelium-derived Factor and Hepatocyte Growth Factor Overexpression: A New Therapy for Pulmonary Hypertension

Pulmonary hypertension (PH) is a disease characterized by advanced pulmonary vasculature remodeling that is thought to be curable only through lung transplantation. The application of angiogenic hepatocyte growth factor (HGF) is reported to be protective in PH through its anti-vascular remodeling effect, but excessive HGF-mediated immature neovascularization is not conducive to the restoration of pulmonary perfusion because of apparent vascular leakage. As a canonical antiangiogenic molecule, pigment epithelium-derived factor (PEDF) inhibits angiogenesis and reduces vascular permeability in a variety of diseases. However, the effect of PEDF on HGF-based PH treatment remains to be determined. In this study, monocrotaline-induced PH rats and endothelial cells isolated from rat and human PH lung tissues were used. We assessed PH progression, right cardiac function, and pulmonary perfusion in HGF- and/or PEDF-treated rats with PH. Additionally, the receptor and mechanism responsible for the role of PEDF in HGF-based PH therapy were investigated. In this study, we found that HGF and PEDF jointly prevent PH development and improve right cardiac function in rats with PH. Moreover, PEDF delivery increases the pulmonary perfusion in PH lungs and inhibits immature angiogenesis and vascular endothelial (VE)-cadherin junction disintegration induced by HGF without affecting the therapeutic inhibition of pulmonary vascular remodeling by HGF. Mechanistically, PEDF targets VE growth factor receptor 2 and suppresses its phosphorylation at Y951 and Y1175 but not Y1214. Finally, VE growth factor receptor 2/VE protein tyrosine phosphatase/VE-cadherin complex formation and Akt and Erk1/2 inactivation were observed in rat and human PH lung endothelial cells. Collectively, our data indicate that PEDF additively enhances the efficacy of HGF against PH, which may provide new insights into treatment strategies for clinical PH.

Neuropilin-1 interacts with VE-cadherin and TGFBR2 to stabilize adherens junctions and prevent activation of endothelium under flow

Linear and disturbed flow differentially regulate gene expression, with disturbed flow priming endothelial cells (ECs) for a proinflammatory, atheroprone expression profile and phenotype. Here, we investigated the role of the transmembrane protein neuropilin-1 (NRP1) in ECs exposed to flow using cultured ECs, mice with an endothelium-specific knockout of NRP1, and a mouse model of atherosclerosis. We demonstrated that NRP1 was a constituent of adherens junctions that interacted with VE-cadherin and promoted its association with p120 catenin, stabilizing adherens junctions and inducing cytoskeletal remodeling in alignment with the direction of flow. We also showed that NRP1 interacted with transforming growth factor-β (TGF-β) receptor II (TGFBR2) and reduced the plasma membrane localization of TGFBR2 and TGF-β signaling. NRP1 knockdown increased the abundance of proinflammatory cytokines and adhesion molecules, resulting in increased leukocyte rolling and atherosclerotic plaque size. These findings describe a role for NRP1 in promoting endothelial function and reveal a mechanism by which NRP1 reduction in ECs may contribute to vascular disease by modulating adherens junction signaling and promoting TGF-β signaling and inflammation.

A Novel Blood-Brain Barrier-Penetrating and Vascular-Targeting Chimeric Peptide Inhibits Glioma Angiogenesis

The high vascularization of glioma highlights the potential value of anti-angiogenic therapeutics for glioma treatment. Previously, we designed a novel vascular-targeting and blood-brain barrier (BBB)-penetrating peptide, TAT-AT7, by attaching the cell-penetrating peptide TAT to a vascular-targeting peptide AT7, and we demonstrated that TAT-AT7 could target binding to the vascular endothelial growth factor receptor 2 (VEGFR-2) and Neuropilin-1 (NRP-1), which are both highly expressed in endothelial cells. TAT-AT7 has been proven to be a good targeting peptide which could effectively deliver the secretory endostatin gene to treat glioma via the TAT-AT7-modified polyethyleneimine (PEI) nanocomplex. In the current study, we further explored the molecular binding mechanisms of TAT-AT7 to VEGFR-2 and NRP-1 and its anti-glioma effects. Accordingly, TAT-AT7 was proven to competitively bind to VEGFR-2 and NRP-1 and prevent VEGF-A165 binding to the receptors by the surface plasmon resonance (SPR) assay. TAT-AT7 inhibited endothelial cells' proliferation, migration, invasion, and tubule formation, as well as promoted endothelial cells' apoptosis in vitro. Further research revealed that TAT-AT7 inhibited the phosphorylation of VEGFR-2 and its downstream PLC-γ, ERK1/2, SRC, AKT, and FAK kinases. Additionally, TAT-AT7 significantly inhibited angiogenesis of zebrafish embryo. Moreover, TAT-AT7 had a better penetrating ability and could penetrate the BBB into glioma tissue and target glioma neovascularization in an orthotopic U87-glioma-bearing nude mice model, and exhibited the effect of inhibiting glioma growth and angiogenesis. Taken together, the binding and function mechanisms of TAT-AT7 were firstly revealed, and TAT-AT7 was proven to be an effective and promising peptide for the development of anti-angiogenic drugs for targeted treatment of glioma.

Extracellular Matrix Regulation of Vascular Morphogenesis, Maturation, and Stabilization

The extracellular matrix represents a critical regulator of tissue vascularization during embryonic development and postnatal life. In this perspective, we present key information and concepts that focus on how the extracellular matrix controls capillary assembly, maturation, and stabilization, and, in addition, contributes to tissue stability and health. In particular, we present and discuss mechanistic details underlying (1) the role of the extracellular matrix in controlling different steps of vascular morphogenesis, (2) the ability of endothelial cells (ECs) and pericytes to coassemble into elongated and narrow capillary EC-lined tubes with associated pericytes and basement membrane matrices, and (3) the identification of specific growth factor combinations ("factors") and peptides as well as coordinated "factor" and extracellular matrix receptor signaling pathways that are required to form stabilized capillary networks.

KIF13B mediates VEGFR2 recycling to modulate vascular permeability

Excessive vascular endothelial growth factor-A (VEGF-A) signaling induces vascular leakage and angiogenesis in diseases. VEGFR2 trafficking to the cell surface, mediated by kinesin-3 family protein KIF13B, is essential to respond to VEGF-A when inducing angiogenesis. However, the precise mechanism of how KIF13B regulates VEGF-induced signaling and its effects on endothelial permeability is largely unknown. Here we show that KIF13B-mediated recycling of internalized VEGFR2 through Rab11-positive recycling vesicle regulates endothelial permeability. Phosphorylated VEGFR2 at the cell-cell junction was internalized and associated with KIF13B in Rab5-positive early endosomes. KIF13B mediated VEGFR2 recycling through Rab11-positive recycling vesicle. Inhibition of the function of KIF13B attenuated phosphorylation of VEGFR2 at Y951, SRC at Y416, and VE-cadherin at Y685, which are necessary for endothelial permeability. Failure of VEGFR2 trafficking to the cell surface induced accumulation and degradation of VEGFR2 in lysosomes. Furthermore, in the animal model of the blinding eye disease wet age-related macular degeneration (AMD), inhibition of KIF13B-mediated VEGFR2 trafficking also mitigated vascular leakage. Thus, the present results identify the fundamental role of VEGFR2 recycling to the cell surface in mediating vascular permeability, which suggests a promising strategy for mitigating vascular leakage associated with inflammatory diseases.

Single-Molecule Imaging of Membrane Proteins on Vascular Endothelial Cells

Transporting substances such as gases, nutrients, waste, and cells is the primary function of blood vessels. Vascular cells use membrane proteins to perform crucial endothelial functions, including molecular transport, immune cell infiltration, and angiogenesis. A thorough understanding of these membrane receptors from a clinical perspective is warranted to gain insights into the pathogenesis of vascular diseases and to develop effective methods for drug delivery through the vascular endothelium. This review summarizes state-of-the-art single-molecule imaging techniques, such as super-resolution microscopy, single-molecule tracking, and protein-protein interaction analysis, for observing and studying membrane proteins. Furthermore, recent single-molecule studies of membrane proteins such as cadherins, integrins, caveolins, transferrin receptors, vesicle-associated protein-1, and vascular endothelial growth factor receptor are discussed.

Endothelial ARHGEF26 is an angiogenic factor promoting VEGF signalling

AIMS

Genetic studies have implicated the ARHGEF26 locus in the risk of coronary artery disease (CAD). However, the causal pathways by which DNA variants at the ARHGEF26 locus confer risk for CAD are incompletely understood. We sought to elucidate the mechanism responsible for the enhanced risk of CAD associated with the ARHGEF26 locus.

METHODS AND RESULTS

In a conditional analysis of the ARHGEF26 locus, we show that the sentinel CAD-risk signal is significantly associated with various non-lipid vascular phenotypes. In human endothelial cell (EC), ARHGEF26 promotes the angiogenic capacity, and interacts with known angiogenic factors and pathways. Quantitative mass spectrometry showed that one CAD-risk coding variant, rs12493885 (p.Val29Leu), resulted in a gain-of-function ARHGEF26 that enhances proangiogenic signalling and displays enhanced interactions with several proteins partially related to the angiogenic pathway. ARHGEF26 is required for endothelial angiogenesis by promoting macropinocytosis of Vascular Endothelial Growth Factor Receptor 2 (VEGFR2) on cell membrane and is crucial to Vascular Endothelial Growth Factor (VEGF)-dependent murine vessel sprouting ex vivo. In vivo, global or tissue-specific deletion of ARHGEF26 in EC, but not in vascular smooth muscle cells, significantly reduced atherosclerosis in mice, with enhanced plaque stability.

CONCLUSIONS

Our results demonstrate that ARHGEF26 is involved in angiogenesis signaling, and that DNA variants within ARHGEF26 that are associated with CAD risk could affect angiogenic processes by potentiating VEGF-dependent angiogenesis.

Involvement of transmembrane protein 184a during angiogenesis in zebrafish embryos

Angiogenesis, the outgrowth of new blood vessels from existing vasculature, is critical during development, tissue formation, and wound healing. In response to vascular endothelial growth factors (VEGFs), endothelial cells are activated to proliferate and move towards the signal, extending the vessel. These events are directed by VEGF-VEGF receptor (Vegfr2) signal transduction, which in turn is modulated by heparan sulfate proteoglycans (HSPGs). HSPGs are glycoproteins covalently attached to HS glycosaminoglycan chains. Transmembrane protein 184a (Tmem184a) has been recently identified as a heparin receptor, which is believed to bind heparan sulfate chains in vivo. Therefore, Tmem184a has the potential to fine-tune interactions between VEGF and HS, modulating Vegfr2-dependent angiogenesis. The function of Tmem184a has been investigated in the regenerating zebrafish caudal fin, but its role has yet to be evaluated during developmental angiogenesis. Here we provide insights into how Tmem184a contributes to the proper formation of the vasculature in zebrafish embryos. First, we find that knockdown of Tmem184a causes a reduction in the number of intact intersegmental vessels (ISVs) in the zebrafish embryo. This phenotype mimics that of vegfr2b knockout mutants, which have previously been shown to exhibit severe defects in ISV development. We then test the importance of HS interactions by removing the binding domain within the Tmem184a protein, which has a negative effect on angiogenesis. Tmem184a is found to act synergistically with Vegfr2b, indicating that the two gene products function in a common pathway to modulate angiogenesis. Moreover, we find that knockdown of Tmem184a leads to an increase in endothelial cell proliferation but a decrease in the amount of VE-cadherin present. Together, these findings suggest that Tmem184a is necessary for ISVs to organize into mature, complete vessels.

VEGFR endocytosis: Implications for angiogenesis

The binding of vascular endothelial growth factor (VEGF) superfamily to VEGF receptor tyrosine kinases (VEGFRs) and co-receptors regulates vasculogenesis, angiogenesis and lymphangiogenesis. A recurring theme is that dysfunction in VEGF signaling promotes pathological angiogenesis, an important feature of cancer and pro-inflammatory disease states. Endocytosis of basal (resting) or activated VEGFRs facilitates signal attenuation and endothelial quiescence. However, increasing evidence suggest that activated VEGFRs can continue to signal from intracellular compartments such as endosomes. In this chapter, we focus on the evolving link between VEGFR endocytosis, signaling and turnover and the implications for angiogenesis. There is much interest in how such understanding of VEGFR dynamics can be harnessed therapeutically for a wide range of human disease states.

ESCPE-1 mediates retrograde endosomal sorting of the SARS-CoV-2 host factor Neuropilin-1

Endosomal sorting maintains cellular homeostasis by recycling transmembrane proteins and associated proteins and lipids (termed "cargoes") from the endosomal network to multiple subcellular destinations, including retrograde traffic to the trans-Golgi network (TGN). Viral and bacterial pathogens subvert retrograde trafficking machinery to facilitate infectivity. Here, we develop a proteomic screen to identify retrograde cargo proteins of the endosomal SNX-BAR sorting complex promoting exit 1 (ESCPE-1). Using this methodology, we identify Neuropilin-1 (NRP1), a recently characterized host factor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, as a cargo directly bound and trafficked by ESCPE-1. ESCPE-1 mediates retrograde trafficking of engineered nanoparticles functionalized with the NRP1-interacting peptide of the SARS-CoV-2 spike (S) protein. CRISPR-Cas9 deletion of ESCPE-1 subunits reduces SARS-CoV-2 infection levels in cell culture. ESCPE-1 sorting of NRP1 may therefore play a role in the intracellular membrane trafficking of NRP1-interacting viruses such as SARS-CoV-2.

KANK4 Promotes Arteriogenesis by Potentiating VEGFR2 Signaling in a TALIN-1-Dependent Manner

BACKGROUND

Arteriogenesis plays a critical role in maintaining adequate tissue blood supply and is related to a favorable prognosis in arterial occlusive diseases. Strategies aimed at promoting arteriogenesis have thus far not been successful because the factors involved in arteriogenesis remain incompletely understood. Previous studies suggest that evolutionarily conserved KANK4 (KN motif and ankyrin repeat domain-containing proteins 4) might involve in vertebrate vessel development. However, how the KANK4 regulates vessel function remains unknown. We aim to determine the role of endothelial cell-specifically expressed KANK4 in arteriogenesis.

METHODS

The role of KANK4 in regulating arteriogenesis was evaluated using Kank4^-/- and KANK4^iECOE mice. Molecular mechanisms underlying KANK4-potentiated arteriogenesis were investigated by employing RNA transcriptomic profiling and mass spectrometry analysis.

RESULTS

By analyzing Kank4-EGFP reporter mice, we showed that KANK4 was specifically expressed in endothelial cells. In particular, KANK4 displayed a dynamic expression pattern from being ubiquitously expressed in all endothelial cells of the developing vasculature to being explicitly expressed in the endothelial cells of arterioles and arteries in matured vessels. In vitro microfluidic chip-based vascular morphology analysis and in vivo hindlimb ischemia assays using Kank4^-/- and KANK4^iECOE mice demonstrated that deletion of KANK4 impaired collateral artery growth and the recovery of blood perfusion, whereas KANK4 overexpression leads to increased vessel caliber and blood perfusion. Bulk RNA sequencing and Co-immunoprecipitation/mass spectrometry (Co-IP/MS) analysis identified that KANK4 promoted EC proliferation and collateral artery remodeling through coupling VEGFR2 (vascular endothelial growth factor receptor 2) to TALIN-1, which augmented the activation of the VEGFR2 signaling cascade.

CONCLUSIONS

This study reveals a novel role for KANK4 in arteriogenesis in response to ischemia. KANK4 links VEGFR2 to TALIN-1, resulting in enhanced VEGFR2 activation and increased EC proliferation, highlighting that KANK4 is a potential therapeutic target for promoting arteriogenesis for arterial occlusive diseases.

The β8 integrin cytoplasmic domain activates extracellular matrix adhesion to promote brain neurovascular development

In the developing mammalian brain, neuroepithelial cells interact with blood vessels to regulate angiogenesis, blood-brain barrier maturation and other key neurovascular functions. Genetic studies in mice have shown that neurovascular development is controlled, in part, by Itgb8, which encodes the neuroepithelial cell-expressed integrin β8 subunit. However, these studies have involved complete loss-of-function Itgb8 mutations, and have not discerned the relative roles for the β8 integrin extracellular matrix (ECM) binding region versus the intracellular signaling tail. Here, Cre/lox strategies have been employed to selectively delete the cytoplasmic tail of murine Itgb8 without perturbing its transmembrane and extracellular domains. We report that the β8 integrin cytoplasmic domain is essential for inside-out modulation of adhesion, including activation of latent-TGFβs in the ECM. Quantitative sequencing of the brain endothelial cell transcriptome identifies TGFβ-regulated genes with putative links to blood vessel morphogenesis, including several genes linked to Wnt/β-catenin signaling. These results reveal that the β8 integrin cytoplasmic domain is essential for the regulation of TGFβ-dependent gene expression in endothelial cells and suggest that cross-talk between TGFβs and Wnt pathways is crucial for neurovascular development.

VEGFA, B, C: Implications of the C-Terminal Sequence Variations for the Interaction with Neuropilins

Vascular endothelial growth factors (VEGFs) are the key regulators of blood and lymphatic vessels’ formation and function. Each of the proteins from the homologous family VEGFA, VEGFB, VEGFC and VEGFD employs a core cysteine-knot structural domain for the specific interaction with one or more of the cognate tyrosine kinase receptors. Additional diversity is exhibited by the involvement of neuropilins–transmembrane co-receptors, whose b1 domain contains the binding site for the C-terminal sequence of VEGFs. Although all relevant isoforms of VEGFs that interact with neuropilins contain the required C-terminal Arg residue, there is selectivity of neuropilins and VEGF receptors for the VEGF proteins, which is reflected in the physiological roles that they mediate. To decipher the contribution made by the C-terminal sequences of the individual VEGF proteins to that functional differentiation, we determined structures of molecular complexes of neuropilins and VEGF-derived peptides and examined binding interactions for all neuropilin-VEGF pairs experimentally and computationally. While X-ray crystal structures and ligand-binding experiments highlighted similarities between the ligands, the molecular dynamics simulations uncovered conformational preferences of VEGF-derived peptides beyond the C-terminal arginine that contribute to the ligand selectivity of neuropilins. The implications for the design of the selective antagonists of neuropilins’ functions are discussed.

Endothelial k-RasV12 Expression Induces Capillary Deficiency Attributable to Marked Tube Network Expansion Coupled to Reduced Pericytes and Basement Membranes

OBJECTIVE

We sought to determine how endothelial cell (EC) expression of the activating k-Ras (kirsten rat sarcoma 2 viral oncogene homolog) mutation, k-RasV12, affects their ability to form lumens and tubes and interact with pericytes during capillary assembly Approach and Results: Using defined bioassays where human ECs undergo observable tubulogenesis, sprouting behavior, pericyte recruitment to EC-lined tubes, and pericyte-induced EC basement membrane deposition, we assessed the impact of EC k-RasV12 expression on these critical processes that are necessary for proper capillary network formation. This mutation, which is frequently seen in human ECs within brain arteriovenous malformations, was found to markedly accentuate EC lumen formation mechanisms, with strongly accelerated intracellular vacuole formation, vacuole fusion, and lumen expansion and with reduced sprouting behavior, leading to excessively widened tube networks compared with control ECs. These abnormal tubes demonstrate strong reductions in pericyte recruitment and pericyte-induced EC basement membranes compared with controls, with deficiencies in fibronectin, collagen type IV, and perlecan deposition. Analyses of signaling during tube formation from these k-RasV12 ECs reveals strong enhancement of Src (Src proto-oncogene, non-receptor tyrosine kinase), Pak2 (P21 [RAC1 (Rac family small GTPase 1)] activated kinase 2), b-Raf (v-raf murine sarcoma viral oncogene homolog B1), Erk (extracellular signal-related kinase), and Akt (AK strain transforming) activation and increased expression of PKCε (protein kinase C epsilon), MT1-MMP (membrane-type 1 matrix metalloproteinase), acetylated tubulin and CDCP1 (CUB domain-containing protein 1; most are known EC lumen regulators). Pharmacological blockade of MT1-MMP, Src, Pak, Raf, Mek (mitogen-activated protein kinase) kinases, Cdc42 (cell division cycle 42)/Rac1, and Notch markedly interferes with lumen and tube formation from these ECs.

CONCLUSIONS

Overall, this novel work demonstrates that EC expression of k-RasV12 disrupts capillary assembly due to markedly excessive lumen formation coupled with strongly reduced pericyte recruitment and basement membrane deposition, which are critical pathogenic features predisposing the vasculature to develop arteriovenous malformations.

Cysteine oxidation of copper transporter CTR1 drives VEGFR2 signalling and angiogenesis

VEGFR2 (KDR/Flk1) signaling in endothelial cells (ECs) is essential for developmental and reparative angiogenesis. Reactive oxygen species (ROS) and copper (Cu) are also involved.in these processes. However, their inter-relationship is poorly understood. The role of endothelial Cu importer CTR1 in VEGFR2 signaling and angiogenesis in vivo is hitherto unknown. Here we show that CTR1 functions as a previously unrecognized redox sensor to promote angiogenesis in ECs. CTR1-depleted ECs showed reduced VEGF-induced VEGFR2 signaling and angiogenic responses. Mechanistically, CTR1 was rapidly sulfenylated at Cys189 in cytosolic C-terminus upon VEGF stimulation, which induced CTR1-VEGFR2 disulfide bond formation and their co-internalization to early endosomes, driving sustained VEGFR2 signaling. In vivo, EC-specific Ctr1-deficient mice or CRISPR/Cas9-generated “redox-dead” Cys to Ala Ctr1 knock-in mutant mice had impaired developmental and reparative angiogenesis. Thus, oxidation of CTR1 at Cys189 promotes VEGFR2 internalization and signaling to enhance angiogenesis. Our study uncovers an important mechanism for ROS sensing through CTR1 to drive neovascularization.

Molecular basis for pericyte-induced capillary tube network assembly and maturation

Here we address the functional importance and role of pericytes in capillary tube network assembly, an essential process that is required for vascularized tissue development, maintenance, and health. Healthy capillaries may be directly capable of suppressing human disease. Considerable advances have occurred in our understanding of the molecular and signaling requirements controlling EC lumen and tube formation in 3D extracellular matrices. A combination of SCF, IL-3, SDF-1α, FGF-2 and insulin ("Factors") in conjunction with integrin- and MT1-MMP-induced signaling are required for EC sprouting behavior and tube formation under serum-free defined conditions. Pericyte recruitment to the abluminal EC tube surface results in elongated and narrow tube diameters and deposition of the vascular basement membrane. In contrast, EC tubes in the absence of pericytes continue to widen and shorten over time and fail to deposit basement membranes. Pericyte invasion, recruitment and proliferation in 3D matrices requires the presence of ECs. A detailed analysis identified that EC-derived PDGF-BB, PDGF-DD, ET-1, HB-EGF, and TGFβ1 are necessary for pericyte recruitment, proliferation, and basement membrane deposition. Blockade of these individual factors causes significant pericyte inhibition, but combined blockade profoundly interferes with these events, resulting in markedly widened EC tubes without basement membranes, like when pericytes are absent.

Characterization of protein isoform diversity in human umbilical vein endothelial cells via long-read proteogenomics

Endothelial cells (ECs) comprise the lumenal lining of all blood vessels and are critical for the functioning of the cardiovascular system. Their phenotypes can be modulated by alternative splicing of RNA to produce distinct protein isoforms. To characterize the RNA and protein isoform landscape within ECs, we applied a long read proteogenomics approach to analyse human umbilical vein endothelial cells (HUVECs). Transcripts delineated from PacBio sequencing serve as the basis for a sample-specific protein database used for downstream mass-spectrometry (MS) analysis to infer protein isoform expression. We detected 53,863 transcript isoforms from 10,426 genes, with 22,195 of those transcripts being novel. Furthermore, the predominant isoform in HUVECs does not correspond with the accepted "reference isoform" 25% of the time, with vascular pathway-related genes among this group. We found 2,597 protein isoforms supported through unique peptides, with an additional 2,280 isoforms nominated upon incorporation of long-read transcript evidence. We characterized a novel alternative acceptor for endothelial-related gene CDH5, suggesting potential changes in its associated signalling pathways. Finally, we identified novel protein isoforms arising from a diversity of RNA splicing mechanisms supported by uniquely mapped novel peptides. Our results represent a high-resolution atlas of known and novel isoforms of potential relevance to endothelial phenotypes and function.[Figure: see text].

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.

Sphingolipids in Lung Pathology in the Coronavirus Disease Era: A Review of Sphingolipid Involvement in the Pathogenesis of Lung Damage

Sphingolipids are bioactive lipids involved in the regulation of cell survival, proliferation, and the inflammatory response. The SphK/S1P/S1PR pathway (S1P pathway) is a driver of many anti-apoptotic and proliferative processes. Pro-survival sphingolipid sphingosine-1-phosphate (S1P) initiates its signaling cascade by interacting with various sphingosine-1-phosphate receptors (S1PR) through which it is able to exert its pro-survival or inflammatory effects. Whereas sphingolipids, including ceramides and sphingosines are pro-apoptotic. The pro-apoptotic lipid, ceramide, can be produced de novo by ceramide synthases and converted to sphingosine by way of ceramidases. The balance of these antagonistic lipids and how this balance manifests is the essence of the sphingolipid rheostat. Recent studies on SARS-CoV-2 have implicated the S1P pathway in the pathogenesis of novel coronavirus disease COVID-19-related lung damage. Accumulating evidence indicates that an aberrant inflammatory process, known as "cytokine storm" causes lung injury in COVID-19, and studies have shown that the S1P pathway is involved in signaling this hyperinflammatory response. Beyond the influence of this pathway on cytokine storm, over the last decade the S1P pathway has been investigated for its role in a wide array of lung pathologies, including pulmonary fibrosis, pulmonary arterial hypertension (PAH), and lung cancer. Various studies have used S1P pathway modulators in models of lung disease; many of these efforts have yielded results that point to the potential efficacy of targeting this pathway for future treatment options. Additionally, they have emphasized S1P pathway's significant role in inflammation, fibrosis, and a number of other endothelial and epithelial changes that contribute to lung damage. This review summarizes the S1P pathway's involvement in COVID-19 and chronic lung diseases and discusses the potential for targeting S1P pathway as a therapeutic option for these diseases.

Activation of Smad2/3 signaling by low fluid shear stress mediates artery inward remodeling

Endothelial cell (EC) sensing of wall fluid shear stress (FSS) from blood flow governs vessel remodeling to maintain FSS at a specific magnitude or set point in healthy vessels. Low FSS triggers inward remodeling to restore normal FSS but the regulatory mechanisms are unknown. In this paper, we describe the signaling network that governs inward artery remodeling. FSS induces Smad2/3 phosphorylation through the type I transforming growth factor (TGF)-β family receptor Alk5 and the transmembrane protein Neuropilin-1, which together increase sensitivity to circulating bone morphogenetic protein (BMP)-9. Smad2/3 nuclear translocation and target gene expression but not phosphorylation are maximal at low FSS and suppressed at physiological high shear. Reducing flow by carotid ligation in rodents increases Smad2/3 nuclear localization, while the resultant inward remodeling is blocked by the EC-specific deletion of Alk5. The flow-activated MEKK3/Klf2 pathway mediates the suppression of Smad2/3 nuclear translocation at high FSS, mainly through the cyclin-dependent kinase (CDK)-2-dependent phosphosphorylation of the Smad linker region. Thus, low FSS activates Smad2/3, while higher FSS blocks nuclear translocation to induce inward artery remodeling, specifically at low FSS. These results are likely relevant to inward remodeling in atherosclerotic vessels, in which Smad2/3 is activated through TGF-β signaling.

Endocytosis and Transcytosis of SARS-CoV-2 Across the Intestinal Epithelium and Other Tissue Barriers

Since 2003, the world has been confronted with three new betacoronaviruses that cause human respiratory infections: SARS-CoV, which causes severe acute respiratory syndrome (SARS), MERS-CoV, which causes Middle East respiratory syndrome (MERS), and SARS-CoV-2, which causes Coronavirus Disease 2019 (COVID-19). The mechanisms of coronavirus transmission and dissemination in the human body determine the diagnostic and therapeutic strategies. An important problem is the possibility that viral particles overcome tissue barriers such as the intestine, respiratory tract, blood-brain barrier, and placenta. In this work, we will 1) consider the issue of endocytosis and the possibility of transcytosis and paracellular trafficking of coronaviruses across tissue barriers with an emphasis on the intestinal epithelium; 2) discuss the possibility of antibody-mediated transcytosis of opsonized viruses due to complexes of immunoglobulins with their receptors; 3) assess the possibility of the virus transfer into extracellular vesicles during intracellular transport; and 4) describe the clinical significance of these processes. Models of the intestinal epithelium and other barrier tissues for in vitro transcytosis studies will also be briefly characterized.

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.

TET2 Protects Against Vascular Smooth Muscle Cell Apoptosis and Intimal Thickening in Transplant Vasculopathy

BACKGROUND

Coronary allograft vasculopathy (CAV) is a devastating sequela of heart transplant in which arterial intimal thickening limits coronary blood flow. There are currently no targeted therapies to prevent or reduce this pathology that leads to transplant failure. Vascular smooth muscle cell (VSMC) phenotypic plasticity is critical in CAV neointima formation. TET2 (TET methylcytosine dioxygenase 2) is an important epigenetic regulator of VSMC phenotype, but the role of TET2 in the progression of CAV is unknown.

METHODS

We assessed TET2 expression and activity in human CAV and renal transplant samples. We also used the sex-mismatched murine aortic graft model of graft arteriopathy (GA) in wild-type and inducible smooth muscle-specific Tet2 knockout mice; and in vitro studies in murine and human VSMCs using knockdown, overexpression, and transcriptomic approaches to assess the role of TET2 in VSMC responses to IFNγ (interferon γ), a cytokine elaborated by T cells that drives CAV progression.

RESULTS

In the present study, we found that TET2 expression and activity are negatively regulated in human CAV and renal transplant samples and in the murine aortic graft model of GA. IFNγ was sufficient to repress TET2 and induce an activated VSMC phenotype in vitro. TET2 depletion mimicked the effects of IFNγ, and TET2 overexpression rescued IFNγ-induced dedifferentiation. VSMC-specific TET2 depletion in aortic grafts, and in the femoral wire restenosis model, resulted in increased VSMC apoptosis and medial thinning. In GA, this apoptosis was tightly correlated with proliferation. In vitro, TET2-deficient VSMCs undergo apoptosis more readily in response to IFNγ and expressed a signature of increased susceptibility to extrinsic apoptotic signaling. Enhancing TET2 enzymatic activity with high-dose ascorbic acid rescued the effect of GA-induced VSMC apoptosis and intimal thickening in a TET2-dependent manner.

CONCLUSIONS

TET2 is repressed in CAV and GA, likely mediated by IFNγ. TET2 serves to protect VSMCs from apoptosis in the context of transplant vasculopathy or IFNγ stimulation. Promoting TET2 activity in vivo with systemic ascorbic acid reduces VSMC apoptosis and intimal thickening. These data suggest that promoting TET2 activity in CAV may be an effective strategy for limiting CAV progression.

A Genetically Engineered Mouse Model of Venous Anomaly and Retinal Angioma-like Vascular Malformation

Characterization of key regulators in vein development will advance our understanding of mechanisms underlying venous anomalies and provide therapeutic targets for the treatment of vascular malformations. Here, we provide a detailed protocol for the generation of genetically engineered mouse models targeting the Tek gene for the analysis of vein formation and vein-associated vascular diseases at the embryonic and postnatal stages. It includes steps involved in the whole-mount processing of mouse skin, mesentery, and retina for the examination of vascular malformation during embryonic and postnatal development.

NRP1 and MMP9 are dual targets of RNA-binding protein QKI5 to alter VEGF-R/ NRP1 signalling in trophoblasts in preeclampsia

Preeclampsia (PE) is characterized by placental ischemia and hypoxia, resulting in abnormal casting of the uterine spiral artery, which is mainly caused by insufficient trophoblastic cell infiltration. A reduction in levels of growth factor-based signalling via Neuropilin-1 (NRP1) has been shown to contribute to dysfunctional trophoblast development. In this study, we showed that the RNA-binding protein, QKI5, regulated NRP1 expression and significantly improved trophoblast proliferation in vitro and in vivo. QKI5 and NRP1 expressions were significantly reduced in human PE placentas and in trophoblasts during hypoxia. Overexpression of these factors significantly improved cell proliferation and migration in vitro, in contrast to a decrease upon siRNA knockdown of QKI5 and NRP1 in HTR-8/SVneo cells. Using RIP and RNA pull-down assays, we further showed that QKI5 directly interacted with the 3'-UTR region of NRP1, to mediate cell proliferation and migration via matrix metalloprotease-9. Further, similar to NRP1, QKI5 also targets matrix metalloproteinase 9 (MMP9) involved in secretion of growth factors and its effects can be counteracted by NRP1 overexpression. In vivo studies using a PE mouse model revealed that QKI5 overexpression alleviated PE-related symptoms such as elevated blood pressure and proteinuria. Taken together, we found that QKI5 was a novel regulator, of VEGF-R/NRP1 signalling pathway functioning in trophoblast proliferation and migration, resulting in major contributors to the pathogenesis of PE. While careful evaluation of the broad implications of QKI5 expression is still necessary, this study identified QKI5 as a promising target for treatment strategies in acute PE patients.

The endosomal RIN2/Rab5C machinery prevents VEGFR2 degradation to control gene expression and tip cell identity during angiogenesis

Sprouting angiogenesis is key to many pathophysiological conditions, and is strongly regulated by vascular endothelial growth factor (VEGF) signaling through VEGF receptor 2 (VEGFR2). Here we report that the early endosomal GTPase Rab5C and its activator RIN2 prevent lysosomal routing and degradation of VEGF-bound, internalized VEGFR2 in human endothelial cells. Stabilization of endosomal VEGFR2 levels by RIN2/Rab5C is crucial for VEGF signaling through the ERK and PI3-K pathways, the expression of immediate VEGF target genes, as well as specification of angiogenic 'tip' and 'stalk' cell phenotypes and cell sprouting. Using overexpression of Rab mutants, knockdown and CRISPR/Cas9-mediated gene editing, and live-cell imaging in zebrafish, we further show that endosomal stabilization of VEGFR2 levels is required for developmental angiogenesis in vivo. In contrast, the premature degradation of internalized VEGFR2 disrupts VEGF signaling, gene expression, and tip cell formation and migration. Thus, an endosomal feedforward mechanism maintains receptor signaling by preventing lysosomal degradation, which is directly linked to the induction of target genes and cell fate in collectively migrating cells during morphogenesis.

Molecular Mechanisms Associated with ROS-Dependent Angiogenesis in Lower Extremity Artery Disease

Currently, atherosclerosis, which affects the vascular bed of all vital organs and tissues, is considered as a leading cause of death. Most commonly, atherosclerosis involves coronary and peripheral arteries, which results in acute (e.g., myocardial infarction, lower extremities ischemia) or chronic (persistent ischemia leading to severe heart failure) consequences. All of them have a marked unfavorable impact on the quality of life and are associated with increased mortality and morbidity in human populations. Lower extremity artery disease (LEAD, also defined as peripheral artery disease, PAD) refers to atherosclerotic occlusive disease of the lower extremities, where partial or complete obstruction of peripheral arteries is observed. Decreased perfusion can result in ischemic pain, non-healing wounds, and ischemic ulcers, and significantly reduce the quality of life. However, the progressive atherosclerotic changes cause stimulation of tissue response processes, like vessel wall remodeling and neovascularization. These mechanisms of adapting the vascular network to pathological conditions seem to play a key role in reducing the impact of the changes limiting the flow of blood. Neovascularization as a response to ischemia induces sprouting and expansion of the endothelium to repair and grow the vessels of the circulatory system. Neovascularization consists of three different biological processes: vasculogenesis, angiogenesis, and arteriogenesis. Both molecular and environmental factors that may affect the process of development and growth of blood vessels were analyzed. Particular attention was paid to the changes taking place during LEAD. It is important to consider the molecular mechanisms underpinning vessel growth. These mechanisms will also be examined in the context of diseases commonly affecting blood vessel function, or those treatable in part by manipulation of angiogenesis. Furthermore, it may be possible to induce the process of blood vessel development and growth to treat peripheral vascular disease and wound healing. Reactive oxygen species (ROS) play an important role in regulation of essential cellular signaling pathways such as cell differentiation, proliferation, migration and apoptosis. With regard to the repair processes taking place during diseases such as LEAD, prospective therapeutic methods have been described that could significantly improve the treatment of vessel diseases in the future. Summarizing, regenerative medicine holds the potential to transform the therapeutic methods in heart and vessel diseases treatment.

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.

Decreased inspired oxygen stimulates de novo formation of coronary collaterals in adult heart

RATIONALE

Collateral vessels lessen myocardial ischemia when acute or chronic coronary obstruction occurs. It has long been assumed that although native (pre-existing) collaterals enlarge in obstructive disease, new collaterals do not form in the adult. However, the latter was recently shown to occur after coronary artery ligation. Understanding the signals that drive this process is challenged by the difficulty in studying collateral vessels directly and the complex milieu of signaling pathways, including cell death, induced by ligation. Herein we show that hypoxemia alone is capable of inducing collateral vessels to form and that the novel gene Rabep2 is required.

OBJECTIVE

Hypoxia stimulates angiogenesis during embryonic development and in pathological states. We hypothesized that hypoxia also stimulates collateral formation in adult heart by a process that involves RABEP2, a recently identified protein required for formation of collateral vessels during development.

METHODS AND RESULTS

Exposure of mice to reduced FiO2 induced collateral formation that resulted in smaller infarctions following LAD ligation and that reversed on return to normoxia. Deletion of Rabep2 or knockdown of Vegfa inhibited formation. Hypoxia upregulated Rabep2, Vegfa and Vegfr2 in heart and brain microvascular endothelial cells (HBMVECs). Knockdown of Rabep2 impaired migration of HBMVECs. In contrast to systemic hypoxia, deletion of Rabep2 did not affect collateral formation induced by ischemic injury caused by LAD ligation.

CONCLUSIONS

Hypoxia induced formation of coronary collaterals by a process that required VEGFA and RABEP2, proteins also required for collateral formation during development. Knockdown of Rabep2 impaired cell migration, providing one potential mechanism for RABEP2's role in collateral formation. This appears specific to hypoxia, since formation after acute ischemic injury was unaffected in Rabep2-/- mice. These findings provide a novel model for studying coronary collateral formation, and demonstrate that hypoxia alone can induce new collaterals to form in adult heart.

Defining an Upstream VEGF (Vascular Endothelial Growth Factor) Priming Signature for Downstream Factor-Induced Endothelial Cell-Pericyte Tube Network Coassembly

OBJECTIVE

In this work, we have sought to define growth factor requirements and the signaling basis for different stages of human vascular morphogenesis and maturation. Approach and Results: Using a serum-free model of endothelial cell (EC) tube morphogenesis in 3-dimensional collagen matrices that depends on a 5 growth factor combination, SCF (stem cell factor), IL (interleukin)-3, SDF (stromal-derived factor)-1α, FGF (fibroblast growth factor)-2, and insulin (factors), we demonstrate that VEGF (vascular endothelial growth factor) pretreatment of ECs for 8 hours (ie, VEGF priming) leads to marked increases in the EC response to the factors which includes; EC tip cells, EC tubulogenesis, pericyte recruitment and proliferation, and basement membrane deposition. VEGF priming requires VEGFR2, and the effect of VEGFR2 is selective to the priming response and does not affect factor-dependent tubulogenesis in the absence of priming. Key molecule and signaling requirements for VEGF priming include RhoA, Rock1 (Rho-kinase), PKCα (protein kinase C α), and PKD2 (protein kinase D2). siRNA suppression or pharmacological blockade of these molecules and signaling pathways interfere with the ability of VEGF to act as an upstream primer of downstream factor-dependent EC tube formation as well as pericyte recruitment. VEGF priming was also associated with the formation of actin stress fibers, activation of focal adhesion components, upregulation of the EC factor receptors, c-Kit, IL-3Rα, and CXCR4 (C-X-C chemokine receptor type 4), and upregulation of EC-derived PDGF (platelet-derived growth factor)-BB, PDGF-DD, and HB-EGF (heparin-binding epidermal growth factor) which collectively affect pericyte recruitment and proliferation.

CONCLUSIONS

Overall, this study defines a signaling signature for a separable upstream VEGF priming step, which can activate ECs to respond to downstream factors that are necessary to form branching tube networks with associated mural cells.

RNase A Treatment Interferes With Leukocyte Recruitment, Neutrophil Extracellular Trap Formation, and Angiogenesis in Ischemic Muscle Tissue

Background: RNase A (the bovine equivalent to human RNase 1) and RNase 5 (angiogenin) are two closely related ribonucleases. RNase 5 is described as a powerful angiogenic factor. Whether RNase A shares the same angiogenic characteristic, or interferes with vessel growth as demonstrated for arteriogenesis, has never been investigated and is the topic of this present study.

Methods and Results: To investigate whether RNase A shows a pro‐ or anti-angiogenic effect, we employed a murine hindlimb model, in which femoral artery ligation (FAL) results in arteriogenesis in the upper leg, and, due to provoked ischemia, in angiogenesis in the lower leg. C57BL/6J male mice underwent unilateral FAL, whereas the contralateral leg was sham operated. Two and seven days after the surgery and intravenous injection of RNase A (50 μg/kg dissolved in saline) or saline (control), the gastrocnemius muscles of mice were isolated from the lower legs for (immuno-) histological analyses. Hematoxylin and Eosin staining evidenced that RNase A treatment resulted in a higher degree of ischemic tissue damage. This was, however, associated with reduced angiogenesis, as evidenced by a reduced capillary/muscle fiber ratio. Moreover, RNase A treatment was associated with a significant reduction in leukocyte infiltration as shown by CD45⁺ (pan-leukocyte marker), Ly6G⁺ or MPO⁺ (neutrophils), MPO⁺/CitH₃⁺ [neutrophil extracellular traps (NETs)], and CD68⁺ (macrophages) staining. CD68/MRC1 double staining revealed that RNase A treated mice showed a reduced percentage of M1-like polarized (CD68⁺/MRC1⁻) macrophages whereas the percentage of M2-like polarized (CD68⁺/MRC1⁺) macrophages was increased.

Conclusion: In contrast to RNase 5, RNase A interferes with angiogenesis, which is linked to reduced leukocyte infiltration and NET formation.

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.

Sphingosine-1-Phosphate Receptor 1 Activity Promotes Tumor Growth by Amplifying VEGF-VEGFR2 Angiogenic Signaling

The vascular endothelial growth factor-A (VEGF-A)-VEGFR2 pathway drives tumor vascularization by activating proangiogenic signaling in endothelial cells (ECs). Here, we show that EC-sphingosine-1-phosphate receptor 1 (S1PR1) amplifies VEGFR2-mediated angiogenic signaling to enhance tumor growth. We show that cancer cells induce S1PR1 activity in ECs, and thereby, conditional deletion of S1PR1 in ECs (EC-S1pr1^−/− mice) impairs tumor vascularization and growth. Mechanistically, we show that S1PR1 engages the heterotrimeric G-protein Gi, which amplifies VEGF-VEGFR2 signaling due to an increase in the activity of the tyrosine kinase c-Abl1. c-Abl1, by phosphorylating VEGFR2 at tyrosine-951, prolongs VEGFR2 retention on the plasmalemma to sustain Rac1 activity and EC migration. Thus, S1PR1 or VEGFR2 antagonists, alone or in combination, reverse the tumor growth in control mice to the level seen in EC-S1pr1^−/− mice. Our findings suggest that blocking S1PR1 activity in ECs has the potential to suppress tumor growth by preventing amplification of VEGF-VEGFR2 signaling.

Vijay Avin et al. demonstrate an essential role of endothelial cell (EC)-S1PR1 signaling in amplifying VEGFR2-mediated tumor growth. S1PR1 by Gi and c-Abl1 phosphorylates VEGFR2 at Y951, which retains VEGFR2 at EC plasmalemma, thus enabling EC migration, tumor angiogenesis, and growth.

Signalling, Metabolic Pathways and Iron Homeostasis in Endothelial Cells in Health, Atherosclerosis and Alzheimer's Disease

Endothelial cells drive the formation of new blood vessels in physiological and pathological contexts such as embryonic development, wound healing, cancer and ocular diseases. Once formed, all vessels of the vasculature system present an endothelial monolayer (the endothelium), lining the luminal wall of the vessels, that regulates gas and nutrient exchange between the circulating blood and tissues, contributing to maintaining tissue and vascular homeostasis. To perform their functions, endothelial cells integrate signalling pathways promoted by growth factors, cytokines, extracellular matrix components and signals from mechanosensory complexes sensing the blood flow. New evidence shows that endothelial cells rely on specific metabolic pathways for distinct cellular functions and that the integration of signalling and metabolic pathways regulates endothelial-dependent processes such as angiogenesis and vascular homeostasis. In this review, we provide an overview of endothelial functions and the recent advances in understanding the role of endothelial signalling and metabolism in physiological processes such as angiogenesis and vascular homeostasis and vascular diseases. Also, we focus on the signalling pathways promoted by the transmembrane protein Neuropilin-1 (NRP1) in endothelial cells, its recently discovered role in regulating mitochondrial function and iron homeostasis and the role of mitochondrial dysfunction and iron in atherosclerosis and neurodegenerative diseases.

New insights into the role of co-receptor neuropilins in tumour angiogenesis and lymphangiogenesis and targeted therapy strategies

Local tumour sites lead to pathological angiogenesis and lymphangiogenesis due to malignant conditions such as hypoxia. Although VEGF and VEGFR are considered to be the main anti-tumour treatment targets, the problems of limited efficacy and observable side effects of some drugs relevant to this target still remain to be solved. Therefore, it is necessary to identify new therapeutic targets for angiogenesis or lymphangiogenesis. The neuropilin family is a class of single transmembrane glycoprotein receptors, including neuropilin1 (NRP1) and neuropilin2 (NRP2), which could act as co-receptors of VEGFA-165 and VEGFC and play a key role in promoting tumour proliferation, invasion and metastasis. In this review, we introduced the schematic diagram to visually reveal the function of NRP1 and NRP2 in enhancing the binding affinity of VEGFR2 to VEGFA-165 and VEGFR3 to VEGFC, respectively. We also discussed the signalling pathways that depend on the co-receptors NRP1 and NRP2 and some existing targeted therapeutic strategies, such as monoclonal antibodies, targeted peptides, microRNAs and small molecule inhibitors. It will contribute a vital foundation for the future research and development of new drugs targeting NRPs. HIGHLIGHTS NRP1 acts as a co-receptor with VEGFR2 and the pro-angiogenic factor VEGFA-165 to up-regulate tumour angiogenesis by promoting endothelial cells proliferation, survival, migration, invasion and by preventing of apoptosis. NRP2 acts as a co-receptor with VEGFR3 and the pro-lymphogenic factor VEGFC to facilitate tumour metastasis by promoting lymphangiogenesis. Although NRP1 and NRP2 do not have enzymatic signalling activity, the affinity of VEGFR2 for VEGFA-165 and VEGFR3 for VEGFC can increase in a co-receptor manner, as detailed in the schematic. The exclusive roles of NRP1 and NRP2 in signalling pathways are specifically described to emphasise the molecular regulatory mechanisms involved in co-receptors. Various studies have shown that the co-receptors NRP1 and NRP2 can be directly or indirectly targeted by different methods to prevent tumour angiogenesis and lymphangiogenesis. Therapeutic strategies targeting NRPs look promising soon as evidenced by preclinical and clinical studies.

Conformationally active integrin endocytosis and traffic: why, where, when and how?

Spatiotemporal control of integrin-mediated cell adhesion to the extracellular matrix (ECM) is critical for physiological and pathological events in multicellular organisms, such as embryonic development, angiogenesis, platelet aggregation, leukocytes extravasation, and cancer cell metastatic dissemination. Regulation of integrin adhesive function and signaling relies on the modulation of both conformation and traffic. Indeed, integrins exist in a dynamic equilibrium between a bent/closed (inactive) and an extended/open (active) conformation, respectively endowed with low and high affinity for ECM ligands. Increasing evidence proves that, differently to what hypothesized in the past, detachment from the ECM and conformational inactivation are not mandatory for integrin to get endocytosed and trafficked. Specific transmembrane and cytosolic proteins involved in the control of ECM proteolytic fragment-bound active integrin internalization and recycling exist. In the complex masterplan that governs cell behavior, active integrin traffic is key to the turnover of ECM polymers and adhesion sites, the polarized secretion of endogenous ECM proteins and modifying enzymes, the propagation of motility and survival endosomal signals, and the control of cell metabolism.

Neuron-derived VEGF contributes to cortical and hippocampal development independently of VEGFR1/2-mediated neurotrophism

Vascular endothelial growth factor (VEGF) is a potent mitogen critical for angiogenesis and organogenesis. Deletion or inhibition of VEGF during development not only profoundly suppresses vascular outgrowth, but significantly affects the development and function of various organs. In the brain, VEGF is thought to not only promote vascular growth, but also directly act on neurons as a neurotrophic factor by activating VEGF receptors. In the present study, we demonstrated that deletion of VEGF using hGfap-Cre line, which recombines genes specifically in cortical and hippocampal neurons, severely impaired brain organization and vascularization of these regions. The mutant mice had motor deficits, with lethality around the time of weaning. Multiple reporter lines indicated that VEGF was highly expressed in neurons, but that its cognate receptors, VEGFR1 and 2 were exclusive to endothelial cells in the brain. In accordance, mice lacking neuronal VEGFR1 and VEGFR2 did not exhibit neuronal deformities or lethality. Taken together, our data suggest that neuron-derived VEGF contributes to cortical and hippocampal development likely through angiogenesis independently of direct neurotrophic effects mediated by VEGFR1 and 2.