Neuropilin-1 regulates vascular endothelial growth factor-mediated endothelial permeability

Tumour-specific activation of a tumour-blood transport improves the diagnostic accuracy of blood tumour markers in mice

BACKGROUND

The accuracy of blood-based early tumour recognition is compromised by signal production at non-tumoral sites, low amount of signal produced by small tumours, and variable tumour production. Here we examined whether tumour-specific enhancement of vascular permeability by the particular tumour homing peptide, iRGD, which carries dual function of binding to integrin receptors overexpressed in the tumour vasculature and is known to promote extravasation via neuropilin-1 receptor upon site-specific cleavage, might be useful to improve blood-based tumour detection by inducing a yet unrecognised vice versa tumour-to-blood transport.

METHODS

To detect an iRGD-induced tumour-to-blood transport, we examined the effect of intravenously injected iRGD on blood levels of α-fetoprotein (AFP) and autotaxin in several mouse models of hepatocellular carcinoma (HCC) or in mice with chronic liver injury without HCC, and on prostate-specific antigen (PSA) levels in mice with prostate cancer.

FINDINGS

Intravenously injected iRGD rapidly and robustly elevated the blood levels of AFP in several mouse models of HCC, but not in mice with chronic liver injury. The effect was primarily seen in mice with small tumours and normal basal blood AFP levels, was attenuated by an anti-neuropilin-1 antibody, and depended on the concentration gradient between tumour and blood. iRGD treatment was also able to increase blood levels of autotaxin in HCC mice, and of PSA in mice with prostate cancer.

INTERPRETATION

We conclude that iRGD induces a tumour-to-blood transport in a tumour-specific fashion that has potential of improving diagnosis of early stage cancer.

FUNDING

Deutsche Krebshilfe, DKTK, LOEWE-Frankfurt Cancer Institute.

SP-8356 inhibits acute lung injury by suppressing inflammatory cytokine production and immune cell infiltration

This study investigated the anti-inflammatory and protective properties of SP-8356, a synthetic derivative of (1S)-(-)-verbenone, in a mouse model of LPS-induced acute lung injury (ALI). By targeting intracellular signaling pathways and inflammatory responses, SP-8356 demonstrated a potent ability to attenuate deleterious effects of proinflammatory stimuli. Specifically, SP-8356 effectively inhibited the activation of crucial signaling molecules such as NF-κB and Akt, and subsequently dampened the expression of inflammatory cytokines in various lung cellular components. Intervention with SP-8356 treatment also preserved the structural integrity of the epithelial and endothelial barriers. By reducing immune cell infiltration into inflamed lung tissue, SP-8356 exerted a broad protective effect against ALI. These findings position SP-8356 as a promising therapeutic candidate for pulmonary inflammatory diseases that cause ALI.

Downregulation of Nrp1 transcription promotes blood-brain barrier disruption following experimental cerebral ischemia-reperfusion

Disruption of the blood-brain barrier (BBB) following cerebral ischemia-reperfusion injury (CIRI) is a major factor in the pathophysiology of stroke. Endothelial cell-cell communication is essential for maintaining BBB integrity. By analyzing GSE227651 data, we found that a decrease in endothelial cell-cell communication mediated by Sema3/Nrp1 may be due to the downregulation of Nrp1 transcription, which could contribute to BBB breakdown after CIRI. We confirmed this hypothesis by using western blot analysis to show a reduction in Nrp1 protein levels in penumbra endothelial cells after CIRI in mice. We then overexpressed Nrp1 specifically in brain endothelial cells using adeno-associated virus in mice. Furthermore, Nrp1 overexpression had a protective effect on BBB integrity, as evidenced by a decrease in IgG and albumin leakage caused by CIRI in mice. Finally, we found that Nrp1 overexpression also reduced brain cell death and neurological deficits induced by cerebral ischemia-reperfusion in mice. Our findings suggest that Nrp1 downregulation may be a key factor in the breakdown of endothelial cell-cell communication and subsequent BBB disruption following CIRI. Targeting Nrp1-mediated pathways may be a promising approach for mitigating BBB damage and alleviating neurological consequences in stroke patients.

Is neuropilin-1 the neuroimmune initiator of multi-system hyperinflammation in COVID-19?

A major immunopathological feature of Coronavirus disease-2019 (COVID-19) is excessive inflammation in the form of "cytokine storm". The storm is characterized by injurious levels of cytokines which form a complicated network damaging different organs, including the lungs and the brain. The main starter of "cytokine network" hyperactivation in COVID-19 has not been discovered yet. Neuropilins (NRPs) are transmembrane proteins that act as neuronal guidance and angiogenesis modulators. The crucial function of NRPs in forming the nervous and vascular systems has been well-studied. NRP1 and NRP2 are the two identified homologs of NRP. NRP1 has been shown as a viral entry pathway for SARS-CoV2, which facilitates neuroinvasion by the virus within the central or peripheral nervous systems. These molecules directly interact with various COVID-19-related molecules, such as specific regions of the spike protein (major immune element of SARS-CoV2), vascular endothelial growth factor (VEGF) receptors, VEGFR1/2, and ANGPTL4 (regulator of vessel permeability and integrity). NRPs mainly play a role in hyperinflammatory injury of the CNS and lungs, and also the liver, kidney, pancreas, and heart in COVID-19 patients. New findings have suggested NRPs good candidates for pharmacotherapy of COVID-19. However, therapeutic targeting of NRP1 in COVID-19 is still in the preclinical phase. This review presents the implications of NRP1 in multi-organ inflammation-induced injury by SARS-CoV2 and provides insights for NRP1-targeting treatments for COVID-19 patients.

VEGFA Isoforms as Pro-Angiogenic Therapeutics for Cerebrovascular Diseases

Therapeutic angiogenesis has long been considered a viable treatment for vasculature disruptions, including cerebral vasculature diseases. One widely-discussed treatment method to increase angiogenesis is vascular endothelial growth factor (VEGF) A. In animal models, treatment with VEGFA proved beneficial, resulting in increased angiogenesis, increased neuronal density, and improved outcome. However, VEGFA administration in clinical trials has thus far failed to replicate the promising results seen in animal models. The lack of beneficial effects in humans and the difficulty in medicinal translation may be due in part to administration methods and VEGFA's ability to increase vascular permeability. One solution to mitigate the side effects of VEGFA may be found in the VEGFA isoforms. VEGFA is able to produce several different isoforms through alternative splicing. Each VEGFA isoform interacts differently with both the cellular components and the VEGF receptors. Because of the different biological effects elicited, VEGFA isoforms may hold promise as a tangible potential therapeutic for cerebrovascular diseases.

Molecular mimicry of host short linear motif-mediated interactions utilised by viruses for entry

Viruses are obligate intracellular parasites that depend on host cellular machinery for performing even basic biological functions. One of the many ways they achieve this is through molecular mimicry, wherein the virus mimics a host sequence or structure, thereby being able to hijack the host's physiological interactions for its pathogenesis. Such adaptations are specific recognitions that often confer tissue and species-specific tropisms to the virus, and enable the virus to utilise previously existing host signalling networks, which ultimately aid in further steps of viral infection, such as entry, immune evasion and spread. A common form of sequence mimicry utilises short linear motifs (SLiMs). SLiMs are short-peptide sequences that mediate transient interactions and are major elements in host protein interaction networks. This work is aimed at providing a comprehensive review of current literature of some well-characterised SLiMs that play a role in the attachment and entry of viruses into host cells, which mimic physiological receptor-ligand interactions already present in the host. Considering recent trends in emerging diseases, further research on such motifs involved in viral entry can help in the discovery of previously unknown cellular receptors utilised by viruses, as well as help in the designing of targeted therapeutics such as vaccines or inhibitors directed towards these interactions.

Morphological and functional findings in COVID-19 lung disease as compared to Pneumonia, ARDS, and High-Altitude Pulmonary Edema

Coronavirus disease-2019 (COVID-19) may severely affect respiratory function and evolve to life-threatening hypoxia. The clinical experience led to the implementation of standardized protocols assuming similarity to severe acute respiratory syndrome (SARS-CoV-2). Understanding the histopathological and functional patterns is essential to better understand the pathophysiology of COVID-19 and then develop new therapeutic strategies. Epithelial and endothelial cell damage can result from the virus attack, thus leading to immune-mediated response. Pulmonary histopathological findings show the presence of Mallory bodies, alveolar coating cells with nuclear atypia, reactive pneumocytes, reparative fibrosis, intra-alveolar hemorrhage, moderate inflammatory infiltrates, micro-abscesses, microthrombus, hyaline membrane fragments, and emphysema-like lung areas. COVID-19 patients may present different respiratory stages from silent to critical hypoxemia, are associated with the degree of pulmonary parenchymal involvement, thus yielding alteration of ventilation and perfusion relationships. This review aims to: discuss the morphological (histopathological and radiological) and functional findings of COVID-19 compared to acute interstitial pneumonia, acute respiratory distress syndrome (ARDS), and high-altitude pulmonary edema (HAPE), four entities that share common clinical traits, but have peculiar pathophysiological features with potential implications to their clinical management.

Vascular and lymphatic regulation of gastrointestinal function and disease risk

The vascular and lymphatic systems in the gut regulate lipid transport while restricting transfer of commensal gut microbiota and directing immune cell trafficking. Increased permeability of the endothelial systems in the intestine associates with passage of antigens and microbiota from the gut into the bloodstream leading to tissue inflammation, the release of pro-inflammatory mediators and ultimately to abnormalities of systemic metabolism. Recent studies show that lipid metabolism maintains homeostasis and function of intestinal blood and lymphatic endothelial cells, BECs and LECs, respectively. This review highlights recent progress in this area, and information related to the contribution of the lipid transporter CD36, abundant in BECs and LECs, to gastrointestinal barrier integrity, inflammation, and to gut regulation of whole body metabolism. The potential role of endothelial lipid delivery in epithelial tissue renewal after injury and consequently in the risk of gastric and intestinal diseases is also discussed.

MicroRNA-150 (miR-150) and Diabetic Retinopathy: Is miR-150 Only a Biomarker or Does It Contribute to Disease Progression?

Diabetic retinopathy (DR) is a chronic disease associated with diabetes mellitus and is a leading cause of visual impairment among the working population in the US. Clinically, DR has been diagnosed and treated as a vascular complication, but it adversely impacts both neural retina and retinal vasculature. Degeneration of retinal neurons and microvasculature manifests in the diabetic retina and early stages of DR. Retinal photoreceptors undergo apoptosis shortly after the onset of diabetes, which contributes to the retinal dysfunction and microvascular complications leading to vision impairment. Chronic inflammation is a hallmark of diabetes and a contributor to cell apoptosis, and retinal photoreceptors are a major source of intraocular inflammation that contributes to vascular abnormalities in diabetes. As the levels of microRNAs (miRs) are changed in the plasma and vitreous of diabetic patients, miRs have been suggested as biomarkers to determine the progression of diabetic ocular diseases, including DR. However, few miRs have been thoroughly investigated as contributors to the pathogenesis of DR. Among these miRs, miR-150 is downregulated in diabetic patients and is an endogenous suppressor of inflammation, apoptosis, and pathological angiogenesis. In this review, how miR-150 and its downstream targets contribute to diabetes-associated retinal degeneration and pathological angiogenesis in DR are discussed. Currently, there is no effective treatment to stop or reverse diabetes-caused neural and vascular degeneration in the retina. Understanding the molecular mechanism of the pathogenesis of DR may shed light for the future development of more effective treatments for DR and other diabetes-associated ocular diseases.

Neuropilin Is a New Player in the Pathogenesis of COVID-19

Abstract—A family of glycoproteins called neuropilins is gaining attention as a new contributor to the pathogenesis of COVID-19. The concept of penetration of SARS-CoV-2 into host cells is traditionally associated with the receptor role of the ACE2 protein. New evidence suggests that it is possible to enhance pulmonary viral infection by involvement of neuropilins. Neuropilins have two prominent features: (a) a wide range of participation in cellular and tissue processes; (b) a concomitant enhancement of effects associated with the co-reception of regulatory proteins. These features determine the special role of functionally disseminated neuropilins in the pathogenesis of vascular system damage, immunothrombosis, and organ damage with comorbid manifestations during COVID-19. However, the presentation of neuropilins as a generalized therapeutic target that has a corrective effect on the affected areas is an ambiguous approach and requires a selective strategy.

Angiogenesis, Lymphangiogenesis, and Inflammation in Chronic Obstructive Pulmonary Disease (COPD): Few Certainties and Many Outstanding Questions

Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation, predominantly affecting the lung parenchyma and peripheral airways, that results in progressive and irreversible airflow obstruction. COPD development is promoted by persistent pulmonary inflammation in response to several stimuli (e.g., cigarette smoke, bacterial and viral infections, air pollution, etc.). Angiogenesis, the formation of new blood vessels, and lymphangiogenesis, the formation of new lymphatic vessels, are features of airway inflammation in COPD. There is compelling evidence that effector cells of inflammation (lung-resident macrophages and mast cells and infiltrating neutrophils, eosinophils, basophils, lymphocytes, etc.) are major sources of a vast array of angiogenic (e.g., vascular endothelial growth factor-A (VEGF-A), angiopoietins) and/or lymphangiogenic factors (VEGF-C, -D). Further, structural cells, including bronchial and alveolar epithelial cells, endothelial cells, fibroblasts/myofibroblasts, and airway smooth muscle cells, can contribute to inflammation and angiogenesis in COPD. Although there is evidence that alterations of angiogenesis and, to a lesser extent, lymphangiogenesis, are associated with COPD, there are still many unanswered questions.

Non-coding RNAs in the regulation of blood–brain barrier functions in central nervous system disorders

The blood–brain barrier (BBB) is an essential component of the neurovascular unit that controls the exchanges of various biological substances between the blood and the brain. BBB damage is a common feature of different central nervous systems (CNS) disorders and plays a vital role in the pathogenesis of the diseases. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long non-coding RNA (lncRNAs), and circular RNAs (circRNAs), are important regulatory RNA molecules that are involved in almost all cellular processes in normal development and various diseases, including CNS diseases. Cumulative evidences have demonstrated ncRNA regulation of BBB functions in different CNS diseases. In this review, we have summarized the miRNAs, lncRNAs, and circRNAs that can be served as diagnostic and prognostic biomarkers for BBB injuries, and demonstrated the involvement and underlying mechanisms of ncRNAs in modulating BBB structure and function in various CNS diseases, including ischemic stroke, hemorrhagic stroke, traumatic brain injury (TBI), spinal cord injury (SCI), multiple sclerosis (MS), Alzheimer's disease (AD), vascular cognitive impairment and dementia (VCID), brain tumors, brain infections, diabetes, sepsis-associated encephalopathy (SAE), and others. We have also discussed the pharmaceutical drugs that can regulate BBB functions via ncRNAs-related signaling cascades in CNS disorders, along with the challenges, perspective, and therapeutic potential of ncRNA regulation of BBB functions in CNS diseases.

A widespread viral entry mechanism: The C-end Rule motif-neuropilin receptor interaction

Many phylogenetically distant animal viruses, including the new coronavirus severe acute respiratory syndrome coronavirus 2, have surface proteins with polybasic sites that are cleaved by host furin and furin-like proteases. Other than priming certain viral surface proteins for fusion, cleavage generates a carboxy-terminal RXXR sequence. This C-end Rule (CendR) motif is known to bind to neuropilin (NRP) receptors on the cell surface. NRPs are ubiquitously expressed, pleiotropic cell surface receptors with important roles in growth factor signaling, vascular biology, and neurobiology, as well as immune homeostasis and activation. The CendR–NRP receptor interaction promotes endocytic internalization and tissue spreading of different cargo, including viral particles. We propose that the interaction between viral surface proteins and NRPs plays an underappreciated and prevalent role in the transmission and pathogenesis of diverse viruses and represents a promising broad-spectrum antiviral target.

The disruption and hyperpermeability of blood-labyrinth barrier mediates cisplatin-induced ototoxicity

The ototoxic mechanisms of cisplatin on the organ of Corti and spiral ganglion neurons have been extensively studied, while few studies have been focused on the stria vascularis (SV). Herein, we verified the functional and morphological impairment in SV induced by a single injection of cisplatin (12 mg/kg, I.P.), represented by a reduction in Endocochlear Potentials (EP) and strial atrophy, and explored underlying mechanisms. Our results revealed increased extravasation of chromatic tracers (Evans blue dye and FITC-dextran) around microvessels after cisplatin exposure. The increased vascular permeability could be attributed to changes of pericytes (PCs) and perivascular-resident macrophage-like melanocytes (PVM/Ms) in number or morphology, as well as the enhanced level of HIF-1α and downstream VEGF. This capillary leakage led to a high accumulation of cisplatin in the perivascular space in SV, and disrupted the integrity of blood-labyrinth barrier (BLB). Also, tight junction (ZO-1) loosening and Na⁺, K⁺-ATPase damage was considered to be other critical contributors of BLB breakdown, which resulted in EP drop and consequent hearing loss. This study explored the role of stria vascularis in cisplatin-induced ototoxicity in terms of BLB hyperpermeability and pointed to a novel therapeutic target for the prevention of cisplatin-related hearing loss.

Mechanisms of Immunothrombosis by SARS-CoV-2

SARS-CoV-2 contains certain molecules that are related to the presence of immunothrombosis. Here, we review the pathogen and damage-associated molecular patterns. We also study the imbalance of different molecules participating in immunothrombosis, such as tissue factor, factors of the contact system, histones, and the role of cells, such as endothelial cells, platelets, and neutrophil extracellular traps. Regarding the pathogenetic mechanism, we discuss clinical trials, case-control studies, comparative and translational studies, and observational studies of regulatory or inhibitory molecules, more specifically, extracellular DNA and RNA, histones, sensors for RNA and DNA, as well as heparin and heparinoids. Overall, it appears that a network of cells and molecules identified in this axis is simultaneously but differentially affecting patients at different stages of COVID-19, and this is characterized by endothelial damage, microthrombosis, and inflammation.

The BMP Pathway in Blood Vessel and Lymphatic Vessel Biology

Bone morphogenetic proteins (BMPs) were originally identified as the active components in bone extracts that can induce ectopic bone formation. In recent decades, their key role has broadly expanded beyond bone physiology and pathology. Nowadays, the BMP pathway is considered an important player in vascular signaling. Indeed, mutations in genes encoding different components of the BMP pathway cause various severe vascular diseases. Their signaling contributes to the morphological, functional and molecular heterogeneity among endothelial cells in different vessel types such as arteries, veins, lymphatic vessels and capillaries within different organs. The BMP pathway is a remarkably fine-tuned pathway. As a result, its signaling output in the vessel wall critically depends on the cellular context, which includes flow hemodynamics, interplay with other vascular signaling cascades and the interaction of endothelial cells with peri-endothelial cells and the surrounding matrix. In this review, the emerging role of BMP signaling in lymphatic vessel biology will be highlighted within the framework of BMP signaling in the circulatory vasculature.

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.

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.

miR-24 targets SARS-CoV-2 co-factor Neuropilin-1 in human brain microvascular endothelial cells: Insights for COVID-19 neurological manifestations

Neuropilin-1 is a transmembrane glycoprotein that has been implicated in several processes including angiogenesis and immunity. Recent evidence has also shown that it is implied in the cellular internalization of the severe acute respiratory syndrome coronavirus (SARS-CoV-2), which causes the coronavirus disease 2019 (COVID-19). We hypothesized that specific microRNAs can target Neuropilin-1. By combining bioinformatic and functional approaches, we identified miR-24 as a regulator of Neuropilin-1 transcription. Since Neuropilin-1 has been shown to play a key role in the endothelium-mediated regulation of the blood-brain barrier, we validated miR-24 as a functional modulator of Neuropilin-1 in human brain microvascular endothelial cells (hBMECs), which are the most suitable cell line for an in vitro bloodâ€"brain barrier model.

miR-24 Targets the Transmembrane Glycoprotein Neuropilin-1 in Human Brain Microvascular Endothelial Cells

Neuropilin-1 is a transmembrane glycoprotein that has been implicated in several processes including angiogenesis and immunity. Recent evidence has also shown that it is implied in the cellular internalization of the severe acute respiratory syndrome coronavirus (SARS-CoV-2), which causes the coronavirus disease 2019 (COVID-19). We hypothesized that specific microRNAs can target Neuropilin-1. By combining bioinformatic and functional approaches, we identified miR-24 as a regulator of Neuropilin-1 transcription. Since Neuropilin-1 has been shown to play a key role in the endothelium-mediated regulation of the blood-brain barrier, we validated miR-24 as a functional modulator of Neuropilin-1 in human brain microvascular endothelial cells (hBMECs), which are the most suitable cell line for an in vitro blood-brain barrier model.

The Diagnostic and Therapeutic Value of Multimarker Analysis in Heart Failure. An Approach to Biomarker-Targeted Therapy

Background: Heart failure is a pathophysiological state, which is still associated with high morbidity and mortality despite established therapies. Diverse well-known biomarkers fail to assess the variety of individual pathophysiology in the context of heart failure.

Methods: An analysis of prospective, multimarker-specific therapeutic approaches to heart failure based on studies in current literature was performed. A total of 159 screened publications in the field of biomarkers in heart failure were hand-selected and found to be eligible for this study by a team of experts.

Results: Established biomarkers of the inflammatory axis, matrix remodeling, fibrosis and oxidative stress axis, as well as potential therapeutic interventions were investigated. Interaction with end organs, such as cardio-hepatic, cardio-renal and cardio-gastrointestinal interactions show the complexity of the syndrome and could be of further therapeutic value. MicroRNAs are involved in a wide variety of physiologic and pathophysiologic processes in heart failure and could be useful in diagnostic as well as therapeutic setting.

Conclusion: Based on our analysis by a biomarker-driven approach in heart failure therapy, patients could be treated more specifically in long term with a consideration of different aspects of heart failure. New studies evaluating a multimarker – based therapeutic approach could lead in a decrease in the morbidity and mortality of heart failure patients.

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.

Emerging Roles for Neuropilin-2 in Cardiovascular Disease

Cardiovascular disease, the leading cause of death worldwide, is predominantly associated with atherosclerosis. Atherosclerosis is a chronic inflammatory disease characterised by the narrowing of large to medium-sized arteries due to a build-up of plaque. Atherosclerotic plaque is comprised of lipids, extracellular matrix, and several cell types, including endothelial, immune, and vascular smooth muscle cells. Such narrowing of the blood vessels can itself restrict blood flow to vital organs but most severe clinical complications, including heart attacks and strokes, occur when lesions rupture, triggering the blood to clot and obstructing blood flow further down the vascular tree. To circumvent such obstructions, percutaneous coronary intervention or bypass grafts are often required; however, re-occlusion of the treated artery frequently occurs. Neuropilins (NRPs), a multifunctional family of cell surface co-receptors, are expressed by endothelial, immune, and vascular smooth muscle cells and are regulators of numerous signalling pathways within the vasculature. Here, we review recent studies implicating NRP2 in the development of occlusive vascular diseases and discuss how NRP2 could be targeted for therapeutic intervention.

Role of VEGFs/VEGFR-1 Signaling and its Inhibition in Modulating Tumor Invasion: Experimental Evidence in Different Metastatic Cancer Models

The vascular endothelial growth factor (VEGF) family members, VEGF-A, placenta growth factor (PlGF), and to a lesser extent VEGF-B, play an essential role in tumor-associated angiogenesis, tissue infiltration, and metastasis formation. Although VEGF-A can activate both VEGFR-1 and VEGFR-2 membrane receptors, PlGF and VEGF-B exclusively interact with VEGFR-1. Differently from VEGFR-2, which is involved both in physiological and pathological angiogenesis, in the adult VEGFR-1 is required only for pathological angiogenesis. Besides this role in tumor endothelium, ligand-mediated stimulation of VEGFR-1 expressed in tumor cells may directly induce cell chemotaxis and extracellular matrix invasion. Furthermore, VEGFR-1 activation in myeloid progenitors and tumor-associated macrophages favors cancer immune escape through the release of immunosuppressive cytokines. These properties have prompted a number of preclinical and clinical studies to analyze VEGFR-1 involvement in the metastatic process. The aim of the present review is to highlight the contribution of VEGFs/VEGFR-1 signaling in the progression of different tumor types and to provide an overview of the therapeutic approaches targeting VEGFR-1 currently under investigation.

Angiopoietin-like 4 binds neuropilins and cooperates with VEGF to induce diabetic macular edema

The majority of patients with diabetic macular edema (DME), the most common cause of vision loss in working-age Americans, do not respond adequately to current therapies targeting VEGFA. Here, we show that expression of angiopoietin-like 4 (ANGPTL4), a HIF-1-regulated gene product, is increased in the eyes of diabetic mice and patients with DME. We observed that ANGPTL4 and VEGF act synergistically to destabilize the retinal vascular barrier. Interestingly, while ANGPTL4 modestly enhanced tyrosine phosphorylation of VEGF receptor 2, promotion of vascular permeability by ANGPTL4 was independent of this receptor. Instead, we found that ANGPTL4 binds directly to neuropilin 1 (NRP1) and NRP2 on endothelial cells (ECs), leading to rapid activation of the RhoA/ROCK signaling pathway and breakdown of EC-EC junctions. Treatment with a soluble fragment of NRP1 (sNRP1) prevented ANGPTL4 from binding to NRP1 and blocked ANGPTL4-induced activation of RhoA as well as EC permeability in vitro and retinal vascular leakage in diabetic animals in vivo. In addition, sNRP1 reduced the stimulation of EC permeability by aqueous fluid from patients with DME. Collectively, these data identify the ANGPTL4/NRP/RhoA pathway as a therapeutic target for the treatment of DME.

Glycocalyx regulation of vascular endothelial growth factor receptor 2 activity

We have previously shown that knockdown of endomucin (EMCN), an integral membrane glycocalyx glycoprotein, prevents VEGF-induced proliferation, migration, and tube formation in vitro and angiogenesis in vivo. In the endothelium, VEGF mediates most of its angiogenic effects through VEGF receptor 2 (VEGFR2). To understand the role of EMCN, we examined the effect of EMCN depletion on VEGFR2 endocytosis and activation. Results showed that although VEGF stimulation promoted VEGFR2 internalization in control endothelial cells (ECs), loss of EMCN prevented VEGFR2 endocytosis. Cell surface analysis revealed a decrease in VEGFR2 following VEGF stimulation in control but not siRNA directed against EMCN-transfected ECs. EMCN depletion resulted in heightened phosphorylation following VEGF stimulation with an increase in total VEGFR2 protein. These results indicate that EMCN modulates VEGFR2 endocytosis and activity and point to EMCN as a potential therapeutic target.-LeBlanc, M. E., Saez-Torres, K. L., Cano, I., Hu, Z., Saint-Geniez, M., Ng, Y.-S., D'Amore, P. A. Glycocalyx regulation of vascular endothelial growth factor receptor 2 activity.

Gold Cube-in-Cube Based Oxygen Nanogenerator: A Theranostic Nanoplatform for Modulating Tumor Microenvironment for Precise Chemo-Phototherapy and Multimodal Imaging

Engineering a versatile oncotherapy nanoplatform integrating both diagnostic and therapeutic functions has always been an intractable challenge in targeted cancer treatment. Herein, to actualize the theme of precise medicine, a nanoplatform is developed by anchoring Mn-Cdots to doxorubicin (DOX)-loaded mesoporous silica-coated gold cube-in-cubes core/shell nanocomposites and further conjugating them to a Arg-Gly-Asp (RGD) peptide (denoted as RGD-CCmMC/DOX) to achieve an active-targeting effect. Under 635 nm irradiation, the nanoplatform acts as oxygen nanogenerator that produces O₂ in situ and amplifies the content of singlet oxygen (¹O₂) in the hypoxic tumor microenvironment (TME), which has been demonstrated to attenuate tumor hypoxia and synchronously enhance photodynamic efficacy. Moreover, the gold cube-in-cube core in this work has been proven as a photothermal agent for hyperthermia, which exhibits a favorable photothermal effect with a 65.6% calculated photothermal conversion efficiency under 808 nm irradiation. In addition, the nanoplatform achieves heat- and pH-sensitive drug release with precise control to specific-tumor sites, executing combined chemo-phototherapy functions. Besides, it functions as a multimodal bioimaging agent of photothermal, fluorescence, and magnetic resonance imaging for the accurate diagnosis and guidance of therapy. As validated by in vivo and in vitro assays, the TME-responsive nanoplatform is highly biocompatible and effectively obliterates 4T1 tumor xenografts on nude mice after triple-synergetic treatment. This work presents a rational design of versatile nanoplatforms, which modulate the TME to enable high therapeutic performance and multiplexed imaging, which provides an innovative paradigm for targeted tumor therapy.

Modulation of Receptor Tyrosine Kinase Activity through Alternative Splicing of Ligands and Receptors in the VEGF-A/VEGFR Axis

Vascular endothelial growth factor A (VEGF-A) signaling is essential for physiological and pathological angiogenesis. Alternative splicing of the VEGF-A pre-mRNA gives rise to a pro-angiogenic family of isoforms with a differing number of amino acids (VEGF-A_xxxa), as well as a family of isoforms with anti-angiogenic properties (VEGF-A_xxxb). The biological functions of VEGF-A proteins are mediated by a family of cognate protein tyrosine kinase receptors, known as the VEGF receptors (VEGFRs). VEGF-A binds to both VEGFR-1, largely suggested to function as a decoy receptor, and VEGFR-2, the predominant signaling receptor. Both VEGFR-1 and VEGFR-2 can also be alternatively spliced to generate soluble isoforms (sVEGFR-1/sVEGFR-2). The disruption of the splicing of just one of these genes can result in changes to the entire VEGF-A/VEGFR signaling axis, such as the increase in VEGF-A₁₆₅a relative to VEGF-A₁₆₅b resulting in increased VEGFR-2 signaling and aberrant angiogenesis in cancer. Research into this signaling axis has recently focused on manipulating the splicing of these genes as a potential therapeutic avenue in disease. Therefore, further research into understanding the mechanisms by which the splicing of VEGF-A/VEGFR-1/VEGFR-2 is regulated will help in the development of drugs aimed at manipulating splicing or inhibiting specific splice isoforms in a therapeutic manner.

The Intestinal Lymphatic System: Functions and Metabolic Implications

The lymphatic system of the gut plays important roles in the transport of dietary lipids, as well as in immunosurveillance and removal of interstitial fluid. Historically, despite its crucial functions in intestinal homeostasis, the lymphatic system has been poorly studied. In the last 2 decades, identification of specific molecular mediators of lymphatic endothelial cells (LECs) growth together with novel genetic approaches and intravital imaging techniques, have advanced our understanding of the mechanisms regulating intestinal lymphatic physiology in health and disease. As its metabolic implications are gaining recognition, intestinal lymphatic biology is currently experiencing a surge in interest. This review describes current knowledge related to molecular control of intestinal lymphatic vessel structure and function. We discuss regulation of chylomicron entry into lymphatic vessels by vascular endothelial growth factors (VEGFs), hormones, transcription factors and the specific signaling pathways involved. The information covered supports the emerging role of intestinal lymphatics in etiology of the metabolic syndrome and their potential as a therapeutic target.

Neuropilin-1 Controls Endothelial Homeostasis by Regulating Mitochondrial Function and Iron-Dependent Oxidative Stress

The transmembrane protein neuropilin-1 (NRP1) promotes vascular endothelial growth factor (VEGF) and extracellular matrix signaling in endothelial cells (ECs). Although it is established that NRP1 is essential for angiogenesis, little is known about its role in EC homeostasis. Here, we report that NRP1 promotes mitochondrial function in ECs by preventing iron accumulation and iron-induced oxidative stress through a VEGF-independent mechanism in non-angiogenic ECs. Furthermore, NRP1-deficient ECs have reduced growth and show the hallmarks of cellular senescence. We show that a subcellular pool of NRP1 localizes in mitochondria and interacts with the mitochondrial transporter ATP-binding cassette B8 (ABCB8). NRP1 loss reduces ABCB8 levels, resulting in iron accumulation, iron-induced mitochondrial superoxide production, and iron-dependent EC senescence. Treatment of NRP1-deficient ECs with the mitochondria-targeted antioxidant compound mitoTEMPO or with the iron chelator deferoxamine restores mitochondrial activity, inhibits superoxide production, and protects from cellular senescence. This finding identifies an unexpected role of NRP1 in EC homeostasis.

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A subcellular pool of NRP1 localizes in the mitochondria of endothelial cells (ECs)

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NRP1 regulates mitochondrial function via ABCB8 transporter

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NRP1 loss induces iron accumulation and iron-dependent oxidative stress in ECs

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NRP1 protects ECs from iron-dependent premature cellular senescence

Vascular endothelial growth factor signaling in development and disease

Vascular endothelial growth factors (VEGFs) are best known for their involvement in orchestrating the development and maintenance of the blood and lymphatic vascular systems. VEGFs are secreted by a variety of cells and they bind to their cognate tyrosine kinase VEGF receptors (VEGFRs) in endothelial cells to elicit various downstream effects. In recent years, there has been tremendous progress in elucidating different VEGF/VEGFR signaling functions in both the blood and lymphatic vascular systems. Here, and in the accompanying poster, we present key elements of the VEGF/VEGFR pathway and highlight the classical and newly discovered functions of VEGF signaling in blood and lymphatic vessel development and pathology.

Molecular Pharmacology of VEGF-A Isoforms: Binding and Signalling at VEGFR2

Vascular endothelial growth factor-A (VEGF-A) is a key mediator of angiogenesis, signalling via the class IV tyrosine kinase receptor family of VEGF Receptors (VEGFRs). Although VEGF-A ligands bind to both VEGFR1 and VEGFR2, they primarily signal via VEGFR2 leading to endothelial cell proliferation, survival, migration and vascular permeability. Distinct VEGF-A isoforms result from alternative splicing of the Vegfa gene at exon 8, resulting in VEGFxxxa or VEGFxxxb isoforms. Alternative splicing events at exons 5⁻7, in addition to recently identified posttranslational read-through events, produce VEGF-A isoforms that differ in their bioavailability and interaction with the co-receptor Neuropilin-1. This review explores the molecular pharmacology of VEGF-A isoforms at VEGFR2 in respect to ligand binding and downstream signalling. To understand how VEGF-A isoforms have distinct signalling despite similar affinities for VEGFR2, this review re-evaluates the typical classification of these isoforms relative to the prototypical, “pro-angiogenic” VEGF165a. We also examine the molecular mechanisms underpinning the regulation of VEGF-A isoform signalling and the importance of interactions with other membrane and extracellular matrix proteins. As approved therapeutics targeting the VEGF-A/VEGFR signalling axis largely lack long-term efficacy, understanding these isoform-specific mechanisms could aid future drug discovery efforts targeting VEGF receptor pharmacology.

Co-administration of iRGD with peptide HPRP-A1 to improve anticancer activity and membrane penetrability

To improve the specificity and penetration of anticancer peptides against tumors, in this study, we examined the effects of co-administration of the membrane-active peptide HPRP-A1 and the tumor homing/penetrating peptide iRGD. iRGD peptide is widely recognized as an efficient cell membrane penetration peptide targeting to αvβ3 integrins and neuropilin-1 (NRP-1) receptors, which show high expression in many tumor cells. The anticancer activity, cancer specificity and penetration activity in vitro and in vivo of the co-administered peptides were examined on 2D monolayer cells, 3D multi-cellular spheroids (MCS) and xenograft nude mice. Co-administration of iRGD and HPRP-A1 exhibited stronger anticancer activity and tumor specificity against A549 non-small cell lung cancer cells with NRP-1 receptor overexpression compared with HPRP-A1 alone. A549 cells showed uptake of the peptide combination and destruction of the integrity of the cell membrane, as well as adherence to the mitochondrial net, resulting in induction of apoptosis by a caspase-dependent pathway. The iRGD peptide dramatically increased the penetration depth of HPRP-A1 on A549 MCS and anticancer efficacy in an A549 xenograft mouse model. Our results suggest that the co-administration strategy of anticancer and penetrating peptides could be a potential therapeutic approach for cancer treatment in clinical practice.

Regulation of human feto-placental endothelial barrier integrity by vascular endothelial growth factors: competitive interplay between VEGF-A165a, VEGF-A165b, PIGF and VE-cadherin

The human placenta nourishes and protects the developing foetus whilst influencing maternal physiology for fetal advantage. It expresses several members of the vascular endothelial growth factor (VEGF) family including the pro-angiogenic/pro-permeability VEGF-A₁₆₅a isoform, the anti-angiogenic VEGF-A₁₆₅b, placental growth factor (PIGF) and their receptors, VEGFR1 and VEGFR2. Alterations in the ratio of these factors during gestation and in complicated pregnancies have been reported; however, the impact of this on feto-placental endothelial barrier integrity is unknown. The present study investigated the interplay of these factors on junctional occupancy of VE-cadherin and macromolecular leakage in human endothelial monolayers and the perfused placental microvascular bed. Whilst VEGF-A₁₆₅a (50 ng/ml) increased endothelial monolayer albumin permeability (P<0.0001), equimolar concentrations of VEGF-A₁₆₅b (P>0.05) or PlGF (P>0.05) did not. Moreover, VEGF-A₁₆₅b (100 ng/ml; P<0.001) but not PlGF (100 ng/ml; P>0.05) inhibited VEGF-A₁₆₅a-induced permeability when added singly. PlGF abolished the VEGF-A₁₆₅b-induced reduction in VEGF-A₁₆₅a-mediated permeability (P>0.05); PlGF was found to compete with VEGF-A₁₆₅b for binding to Flt-1 at equimolar affinity. Junctional occupancy of VE-cadherin matched alterations in permeability. In the perfused microvascular bed, VEGF-A₁₆₅b did not induce microvascular leakage but inhibited and reversed VEGF-A₁₆₅a-induced loss of junctional VE-cadherin and tracer leakage. These results indicate that the anti-angiogenic VEGF-A₁₆₅b isoform does not increase permeability in human placental microvessels or HUVEC primary cells and can interrupt VEGF-A₁₆₅a-induced permeability. Moreover, the interplay of these isoforms with PIGF (and s-flt1) suggests that the ratio of these three factors may be important in determining the placental and endothelial barrier in normal and complicated pregnancies.

Occludin downregulation in high glucose is regulated by SSTR2 via the VEGF/NRP1/Akt signaling pathway in RF/6A cells

Occludin is a tight junction protein that forms the permeability barrier, which is typically disturbed in ischemic associated diseases. The aim of the present study was to determine whether somatostatin receptor 2 (SSTR₂) in RF/6A cells is involved in the modulation of the downregulation of occludin induced by high glucose, and to evaluate the implicated molecules. RF/6A cells were maintained in Dulbecco's modified Eagle medium and treated with 0 or 30 mM D-glucose. SSTR₂ agonist octreotide (OCT), OCT with SSTR₂ antagonist cycle-somatostatin (c-SOM) and neuropilin 1 (NRP1) inhibitor ATWLPPR, respectively, were administered to RF/6A cells under high glucose conditions. Cell apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labeling. Western blot analysis was used to detect the protein expression level of SSTR₂, occludin, vascular endothelial growth factor (VEGF), protein kinase B (Akt), phosphorylated Akt (p-Akt), extracellular signal-related kinases (ERK) and p-ERK proteins. The amount of VEGF released was determined by ELISA. Notably, the level of occludin reduced significantly under high glucose conditions. The results indicated that the administration of OCT prevented the reduction of occludin induced by high glucose, and co-administration with c-SOM reversed the effect of OCT. Increased VEGF secretion and expression of VEGF, p-Akt and p-ERK in RF/6A cells induced by high glucose were inhibited by OCT. ATWLPPR also prevented the downregulation of occludin, but did not inhibit p-Akt and p-ERK levels under high glucose conditions. The current study concluded that the activation of SSTR₂ prevents high glucose-induced occludin downregulation in RF/6A cells, and VEGF, NRP1, p-Akt and p-ERK were implicated in this process. The pharmacological effects of SSTR₂ targeting to endothelium may be used to assess the role of resistance of permeability and anti-inflammation.

VEGF isoforms have differential effects on permeability of human pulmonary microvascular endothelial cells

BACKGROUND

Alternative splicing of Vascular endothelial growth factor-A mRNA transcripts (commonly referred as VEGF) leads to the generation of functionally differing isoforms, the relative amounts of which have potentially significant physiological outcomes in conditions such as acute respiratory distress syndrome (ARDS). The effect of such isoforms on pulmonary vascular permeability is unknown. We hypothesised that VEGF₁₆₅a and VEGF₁₆₅b isoforms would have differing effects on pulmonary vascular permeability caused by differential activation of intercellular signal transduction pathways.

METHOD

To test this hypothesis we investigated the physiological effect of VEGF₁₆₅a and VEGF₁₆₅b on Human Pulmonary Microvascular Endothelial Cell (HPMEC) permeability using three different methods: trans-endothelial electrical resistance (TEER), Electric cell-substrate impedance sensing (ECIS) and FITC-BSA passage. In addition, potential downstream signalling pathways of the VEGF isoforms were investigated by Western blotting and the use of specific signalling inhibitors.

RESULTS

VEGF₁₆₅a increased HPMEC permeability using all three methods (paracellular and transcellular) and led to associated VE-cadherin and actin stress fibre changes. In contrast, VEGF₁₆₅b decreased paracellular permeability and did not induce changes in VE-cadherin cell distribution. Furthermore, VEGF₁₆₅a and VEGF₁₆₅b had differing effects on both the phosphorylation of VEGF receptors and downstream signalling proteins pMEK, p42/44MAPK, p38 MAPK, pAKT and peNOS. Interestingly specific inhibition of the pMEK, p38 MAPK, PI3 kinase and eNOS pathways blocked the effects of both VEGF₁₆₅a and VEGF₁₆₅b on paracellular permeability and the effect of VEGF₁₆₅a on proliferation/migration, suggesting that this difference in cellular response is mediated by an as yet unidentified signalling pathway(s).

CONCLUSION

This study demonstrates that the novel isoform VEGF₁₆₅a and VEGF₁₆₅b induce differing effects on permeability in pulmonary microvascular endothelial cells.

Endothelial cAMP deactivates ischemia-reperfusion-induced microvascular hyperpermeability via Rap1-mediated mechanisms

Approaches to reduce excessive edema due to the microvascular hyperpermeability that occurs during ischemia-reperfusion (I/R) are needed to prevent muscle compartment syndrome. We tested the hypothesis that cAMP-activated mechanisms actively restore barrier integrity in postischemic striated muscle. We found, using I/R in intact muscles and hypoxia-reoxygenation (H/R, an I/R mimic) in human microvascular endothelial cells (HMVECs), that hyperpermeability can be deactivated by increasing cAMP levels through application of forskolin. This effect was seen whether or not the hyperpermeability was accompanied by increased mRNA expression of VEGF, which occurred only after 4 h of ischemia. We found that cAMP increases in HMVECs after H/R, suggesting that cAMP-mediated restoration of barrier function is a physiological mechanism. We explored the mechanisms underlying this effect of cAMP. We found that exchange protein activated by cAMP 1 (Epac1), a downstream effector of cAMP that stimulates Rap1 to enhance cell adhesion, was activated only at or after reoxygenation. Thus, when Rap1 was depleted by small interfering RNA, H/R-induced hyperpermeability persisted even when forskolin was applied. We demonstrate that 1) VEGF mRNA expression is not involved in hyperpermeability after brief ischemia, 2) elevation of cAMP concentration at reperfusion deactivates hyperpermeability, and 3) cAMP activates the Epac1-Rap1 pathway to restore normal microvascular permeability. Our data support the novel concepts that 1) different hyperpermeability mechanisms operate after brief and prolonged ischemia and 2) cAMP concentration elevation during reperfusion contributes to deactivation of I/R-induced hyperpermeability through the Epac-Rap1 pathway. Endothelial cAMP management at reperfusion may be therapeutic in I/R injury.NEW & NOTEWORTHY Here, we demonstrate that 1) stimulation of cAMP production deactivates ischemia-reperfusion-induced hyperpermeability in muscle and endothelial cells; 2) VEGF mRNA expression is not enhanced by brief ischemia, suggesting that VEGF mechanisms do not activate immediate postischemic hyperpermeability; and 3) deactivation mechanisms operate via cAMP-exchange protein activated by cAMP 1-Rap1 to restore integrity of the endothelial barrier.

VEGF165-induced vascular permeability requires NRP1 for ABL-mediated SRC family kinase activation

Fantin et al. show that the VEGF isoform VEGF165 signals through a complex of VEGFR2 and NRP1, in which the NRP1 cytoplasmic domain promotes the ABL-mediated activation of SRC family kinases to evoke a hyperpermeability response, a known cause of pathological edema.

The vascular endothelial growth factor (VEGF) isoform VEGF165 stimulates vascular growth and hyperpermeability. Whereas blood vessel growth is essential to sustain organ health, chronic hyperpermeability causes damaging tissue edema. By combining in vivo and tissue culture models, we show here that VEGF165-induced vascular leakage requires both VEGFR2 and NRP1, including the VEGF164-binding site of NRP1 and the NRP1 cytoplasmic domain (NCD), but not the known NCD interactor GIPC1. In the VEGF165-bound receptor complex, the NCD promotes ABL kinase activation, which in turn is required to activate VEGFR2-recruited SRC family kinases (SFKs). These results elucidate the receptor complex and signaling hierarchy of downstream kinases that transduce the permeability response to VEGF165. In a mouse model with choroidal neovascularisation akin to age-related macular degeneration, NCD loss attenuated vessel leakage without affecting neovascularisation. These findings raise the possibility that targeting NRP1 or its NCD interactors may be a useful therapeutic strategy in neovascular disease to reduce VEGF165-induced edema without compromising vessel growth.

A genetic variant in NRP1 is associated with worse response to ranibizumab treatment in neovascular age-related macular degeneration

OBJECTIVE

The aim of the study was to investigate the role of single-nucleotide polymorphisms (SNPs) located in the neuropilin-1 (NRP1) gene in treatment response to antivascular endothelial growth factor (VEGF) therapy for neovascular age-related macular degeneration (nvAMD).

METHODS

Four SNPs in the NRP1 gene (rs2229935, rs2247383, rs2070296, and rs2804495) were genotyped in a study cohort of 377 nvAMD patients who received the loading dose of three monthly ranibizumab injections. Treatment response was assessed as the change in visual acuity after three monthly loading injections compared with baseline.

RESULTS

SNP rs2070296 was associated with change in visual acuity after 3 months of treatment. Patients carrying the GA or AA genotypes performed significantly worse than individuals carrying the GG genotype (P=0.01). A cumulative effect of rs2070296 in the NRP1 gene and rs4576072 located in the VEGF receptor 2 (VEGFR2 or KDR) gene, previously associated with treatment response, was observed. Patients carrying two risk alleles performed significantly worse than patients carrying zero or one risk allele (P=0.03), and patients with more than two risk alleles responded even worse to the therapy (P=3×10). The combined effect of these two SNPs on the response was also seen after 6 and 12 months of treatment.

CONCLUSION

This study suggests that genetic variation in NRP1, a key molecule in VEGFA-driven neovascularization, influences treatment response to ranibizumab in nvAMD patients. The results of this study may be used to generate prediction models for treatment response, which in the future may help tailor medical care to individual needs.

Neuropilin-1 modulates interferon-γ-stimulated signaling in brain microvascular endothelial cells

Inflammatory response of blood-brain barrier (BBB) endothelial cells plays an important role in pathogenesis of many central nervous system inflammatory diseases, including multiple sclerosis; however, the molecular mechanism mediating BBB endothelial cell inflammatory response remains unclear. In this study, we first observed that knockdown of neuropilin-1 (NRP1), a co-receptor of several structurally diverse ligands, suppressed interferon-γ (IFNγ)-induced C-X-C motif chemokine 10 expression and activation of STAT1 in brain microvascular endothelial cells in a Rac1-dependent manner. Moreover, endothelial-specific NRP1-knockout mice, VECadherin-Cre-ERT2/NRP1^flox/flox mice, showed attenuated disease progression during experimental autoimmune encephalomyelitis, a mouse neuroinflammatory disease model. Detailed analysis utilizing histological staining, quantitative PCR, flow cytometry and magnetic resonance imaging demonstrated that deletion of endothelial NRP1 suppressed neuron demyelination, altered lymphocyte infiltration, preserved BBB function and decreased activation of the STAT1-CXCL10 pathway. Furthermore, increased expression of NRP1 was observed in endothelial cells of acute multiple sclerosis lesions. Our data identify a new molecular mechanism of brain microvascular endothelial inflammatory response through NRP1-IFNγ crosstalk that could be a potential target for intervention of endothelial cell dysfunction in neuroinflammatory diseases.

Recent updates in experimental protocols for endothelial cells

Scleroderma (systemic sclerosis, SSc) is a multisystem autoimmune disease of unknown etiology. The disease is characterized by vascular disorder, activation of the immune system, and excessive deposition of matrix proteins in the skin and involved organs. The vascular disorder is believed to play a crucial role in disease pathogenesis. Endothelial injury and dysfunction, subsequent capillary loss and arteriolar wall thickness, are well documented in all involved organs. The resulting tissue hypoxia and ischemia fail to initiate new vessel formation leading to progressive loss of vasculature with no apparent replenishment. Issues related to endothelial injury/activation, dysfunction and failure of angio/vasculogenesis are central to the understanding of SSc vasculopathy. Isolation of endothelial cells and cells involved in the genesis of new vessels is enormously important in the investigation of mechanisms involved in SSc vasculopathy. Nevertheless, this goal has been difficult to achieve in view of the charac­teristic slow growth of endothelial cells, the high demand for growth factors and rapid growth of contaminating cells and the scarcity of circulating cells involved in angio/vasculogenesis hampered this line of investigation. Nonetheless, recent technologic progress in the last decade provided us with the tools to isolate vascular cells with an acceptable purity based on unique cell surface markers using immunoselection methods. The purpose of this review is to update the readers on current technical state-of-the-art methods of isolation and propagation of vascular cells. We wish that this review will spark interest in more investigations of this crucial phase of SSc pathogenesis.

A modified thymosin alpha 1 inhibits the growth of breast cancer both in vitro and in vivo: suppressment of cell proliferation, inducible cell apoptosis and enhancement of targeted anticancer effects

Thymosin alpha 1 (Tα1) is commonly used for treating several diseases; however its usage has been limited because of poor penetration of the target tissue, such as tumor cells. In the present study, Tα1-iRGD, a peptide by conjugating Tα1 with the iRGD fragment, was evaluated its performance in MCF-7 and MDA-MB-231 human breast cancer cells. Compared with the wild-type peptide, Tα1-iRGD was more selective in binding tumor cells in the cell attachment assay. Furthermore, the MTT assay confirmed that Tα1-iRGD proved more effective in significantly inhibiting the growth of MCF-7 cells in contrast to the general inhibition displayed by Tα1. Further, conjugation of Tα1 with iRGD preserved the immunomodulatory activity of the drug by increasing the proliferation of mouse spleen lymphocytes. Further, compared with Tα1 treatment, Tα1-iRGD treatment of MCF-7 cells considerably increased the number of cells undergoing apoptosis, resulting in a dose-dependent inhibition of cancer cell growth, which was associated with a much better effect on up-regulation of the expression of BCL2-associated X protein (Bax), caspase 9, etc. More importantly, treatment with Ta1-iRGD was more efficacious than treatment with Ta1 in vivo. This study highlights the importance of iRGD on enhancement of cell penetration and tumor accumulation. In summary, our findings demonstrate that the novel modified Tα1 developed in this study has the potential to be used for treating breast cancer.

Deletion of miR-150 Exacerbates Retinal Vascular Overgrowth in High-Fat-Diet Induced Diabetic Mice

Diabetic retinopathy (DR) is the leading cause of blindness among American adults above 40 years old. The vascular complication in DR is a major cause of visual impairment, making finding therapeutic targets to block pathological angiogenesis a primary goal for developing DR treatments. MicroRNAs (miRs) have been proposed as diagnostic biomarkers and potential therapeutic targets for various ocular diseases including DR. In diabetic animals, the expression levels of several miRs, including miR-150, are altered. The expression of miR-150 is significantly suppressed in pathological neovascularization in mice with hyperoxia-induced retinopathy. The purpose of this study was to investigate the functional role of miR-150 in the development of retinal microvasculature complications in high-fat-diet (HFD) induced type 2 diabetic mice. Wild type (WT) and miR-150 null mutant (miR-150-/-) male mice were given a HFD (59% fat calories) or normal chow diet. Chronic HFD caused a decrease of serum miR-150 in WT mice. Mice on HFD for 7 months (both WT and miR-150-/-) had significant decreases in retinal light responses measured by electroretinograms (ERGs). The retinal neovascularization in miR-150-/--HFD mice was significantly higher compared to their age matched WT-HFD mice, which indicates that miR-150 null mutation exacerbates chronic HFD-induced neovascularization in the retina. Overexpression of miR-150 in cultured endothelial cells caused a significant reduction of vascular endothelial growth factor receptor 2 (VEGFR2) protein levels. Hence, deletion of miR-150 significantly increased the retinal pathological angiogenesis in HFD induced type 2 diabetic mice, which was in part through VEGFR2.

Neuropilin-1 mediates vascular permeability independently of vascular endothelial growth factor receptor-2 activation

Neuropilin-1 (NRP1) regulates developmental and pathological angiogenesis, arteriogenesis, and vascular permeability, acting as a coreceptor for semaphorin 3A (Sema3A) and the 165-amino acid isoform of vascular endothelial growth factor A (VEGF-A165). NRP1 is also the receptor for the CendR peptides, a class of cell- and tissue-penetrating peptides with a specific R-x-x-R carboxyl-terminal motif. Because the cytoplasmic domain of NRP1 lacks catalytic activity, NRP1 is mainly thought to act through the recruitment and binding to other receptors. We report here that the NRP1 intracellular domain mediates vascular permeability. Stimulation with VEGF-A165, a ligand-blocking antibody, and a CendR peptide led to NRP1 accumulation at cell-cell contacts in endothelial cell monolayers, increased cellular permeability in vitro and vascular leakage in vivo. Biochemical analyses, VEGF receptor-2 (VEGFR-2) silencing, and the use of a specific VEGFR blocker established that the effects induced by the CendR peptide and the antibody were independent of VEGFR-2. Moreover, leakage assays in mice expressing a mutant NRP1 lacking the cytoplasmic domain revealed that this domain was required for NRP1-induced vascular permeability in vivo. Hence, these data define a vascular permeability pathway mediated by NRP1 but independent of VEGFR-2 activation.

NRP1 function and targeting in neurovascular development and eye disease

Neuropilin 1 (NRP1) is expressed by neurons, blood vessels, immune cells and many other cell types in the mammalian body and binds a range of structurally and functionally diverse extracellular ligands to modulate organ development and function. In recent years, several types of mouse knockout models have been developed that have provided useful tools for experimental investigation of NRP1 function, and a multitude of therapeutics targeting NRP1 have been designed, mostly with the view to explore them for cancer treatment. This review provides a general overview of current knowledge of the signalling pathways that are modulated by NRP1, with particular focus on neuronal and vascular roles in the brain and retina. This review will also discuss the potential of NRP1 inhibitors for the treatment for neovascular eye diseases.

Complex regulation of HSC emergence by the Notch signaling pathway

Hematopoietic stem cells are formed during embryonic development, and serve as the foundation of the definitive blood program for life. Notch signaling has been well established as an essential direct contributor to HSC specification. However, several recent studies have indicated that the contribution of Notch signaling is complex. HSC specification requires multiple Notch signaling inputs, some received directly by hematopoietic precursors, and others that occur indirectly within neighboring somites. Of note, proinflammatory signals provided by primitive myeloid cells are needed for HSC specification via upregulation of the Notch pathway in hemogenic endothelium. In addition to multiple requirements for Notch activation, recent studies indicate that Notch signaling must subsequently be repressed to permit HSC emergence. Finally, Notch must then be reactivated to maintain HSC fate. In this review, we discuss the growing understanding of the dynamic contributions of Notch signaling to the establishment of hematopoiesis during development.

Impedance analysis of GPCR-mediated changes in endothelial barrier function: overview and fundamental considerations for stable and reproducible measurements

The past 20 years has seen significant growth in using impedance-based assays to understand the molecular underpinning of endothelial and epithelial barrier function in response to physiological agonists and pharmacological and toxicological compounds. Most studies on barrier function use G protein-coupled receptor (GPCR) agonists which couple to fast and transient changes in barrier properties. The power of impedance-based techniques such as electric cell-substrate impedance sensing (ECIS) resides in its ability to detect minute changes in cell layer integrity label-free and in real-time ranging from seconds to days. We provide a comprehensive overview of the biophysical principles, applications, and recent developments in impedance-based methodologies. Despite extensive application of impedance analysis in endothelial barrier research, little attention has been paid to data analysis and critical experimental variables, which are both essential for signal stability and reproducibility. We describe the rationale behind common ECIS data presentation and interpretation and illustrate practical guidelines to improve signal intensity by adapting technical parameters such as electrode layout, monitoring frequency, or parameter (resistance versus impedance magnitude). Moreover, we discuss the impact of experimental parameters, including cell source, liquid handling, and agonist preparation on signal intensity and kinetics. Our discussions are supported by experimental data obtained from human microvascular endothelial cells challenged with three GPCR agonists, thrombin, histamine, and sphingosine-1-phosphate.

Decreased expression of neuropilin-1 as a novel key factor contributing to peripheral microvasculopathy and defective angiogenesis in systemic sclerosis

OBJECTIVES

In systemic sclerosis (SSc), vascular involvement is characterised by vascular endothelial growth factor (VEGF)-A/VEGF receptor (VEGFR) system disturbances. Neuropilin-1 (NRP1), a receptor for both class-3 semaphorins (Sema3s) and VEGF-A, is required for optimal VEGF-A/VEGFR-2 signalling. Here, we investigated the possible involvement of Sema3A/NRP1 axis in SSc.

METHODS

Circulating Sema3A and soluble NRP1 (sNRP1) were measured in patients with SSc and controls. NRP1 and Sema3A expression in skin biopsies was evaluated by immunofluorescence and western blotting. NRP1 expression was assessed in SSc and healthy dermal microvascular endothelial cells (SSc-MVECs and H-MVECs), and in SSc and control endothelial progenitor cell (EPC)-derived endothelial cells (ECs). The possible impact of transcription factor Friend leukaemia integration 1 (Fli1) deficiency on endothelial NRP1 expression was investigated by gene silencing. The binding of Fli1 to NRP1 gene promoter was evaluated using chromatin immunoprecipitation. Capillary morphogenesis was performed on Matrigel.

RESULTS

Decreased sNRP1 levels in SSc were associated with active and late nailfold videocapillaroscopy patterns and digital ulcers. No difference in Sema3A was found between patients and controls. NRP1 was significantly decreased in SSc-MVECs both ex vivo and in vitro. NRP1 and Fli1 significantly decreased in H-MVECs challenged with SSc sera, while they were not different in SSc and control EPC-derived ECs. Fli1 occupied the NRP1 gene promoter and Fli1 gene silencing reduced NRP1 expression in H-MVECs. NRP1 gene silencing in H-MVECs resulted in a significantly impaired angiogenic capacity comparable to that of cells treated with SSc sera.

CONCLUSION

In SSc, NRP1 deficiency may be an additional factor in the perturbed VEGF-A/VEGFR-2 system contributing to peripheral microvasculopathy and defective angiogenesis.

Neuropilin regulation of angiogenesis

Blood vessel formation during vertebrate development relies on a process called angiogenesis and is essential for organ growth and tissue viability. In addition, angiogenesis leads to pathological blood vessel growth in diseases with tissue ischaemia, such as neovascular eye disease and cancer. Neuropilin 1 (NRP1) is a transmembrane protein that serves as a receptor for the VEGF₁₆₅ isoform of the vascular endothelial growth factor (VEGF) to enhance cell migration during angiogenesis via VEGF receptor 2 (VEGFR2), and it is also essential for VEGF-induced vascular permeability and arteriogenesis. In addition, NRP1 activation affects angiogenesis independently of VEGF signalling by activating the intracellular kinase ABL1. NRP1 also acts as a receptor for the class 3 semaphorin (SEMA3A) to regulate vessel maturation during tumour angiogenesis and vascular permeability in eye disease. In the present paper, we review current knowledge of NRP1 regulation during angiogenesis and vascular pathology.