Angiopoietin-2 stimulation of endothelial cells induces alphavbeta3 integrin internalization and degradation

Microvascular destabilization and intricated network of the cytokines in diabetic retinopathy: from the perspective of cellular and molecular components

Microvascular destabilization is the primary cause of the inner blood-retinal barrier (iBRB) breakdown and increased vascular leakage in diabetic retinopathy (DR). Microvascular destabilization results from the combinational effects of increased levels of growth factors and cytokines, involvement of inflammation, and the changed cell-to-cell interactions, especially the loss of endothelial cells and pericytes, due to hyperglycemia and hypoxia. As the manifestation of microvascular destabilization, the fluid transports via paracellular and transcellular routes increase due to the disruption of endothelial intercellular junctional complexes and/or the altered caveolar transcellular transport across the retinal vascular endothelium. With diabetes progression, the functional and the structural changes of the iBRB components, including the cellular and noncellular components, further facilitate and aggravate microvascular destabilization, resulting in macular edema, the neuroretinal damage and the dysfunction of retinal inner neurovascular unit (iNVU). Although there have been considerable recent advances towards a better understanding of the complex cellular and molecular network underlying the microvascular destabilization, some still remain to be fully elucidated. Recent data indicate that targeting the intricate signaling pathways may allow to against the microvascular destabilization. Therefore, efforts have been made to better clarify the cellular and molecular mechanisms that are involved in the microvascular destabilization in DR. In this review, we discuss: (1) the brief introduction of DR and microvascular destabilization; (2) the cellular and molecular components of iBRB and iNVU, and the breakdown of iBRB; (3) the matrix and cell-to-cell contacts to maintain microvascular stabilization, including the endothelial glycocalyx, basement membrane, and various cell-cell interactions; (4) the molecular mechanisms mediated cell-cell contacts and vascular cell death; (5) the altered cytokines and signaling pathways as well as the intricate network of the cytokines involved in microvascular destabilization. This comprehensive review aimed to provide the insights for microvascular destabilization by targeting the key molecules or specific iBRB cells, thus restoring the function and structure of iBRB and iNVU, to treat DR.

Vascular leak in sepsis: physiological basis and potential therapeutic advances

Sepsis is a life-threatening condition characterised by endothelial barrier dysfunction and impairment of normal microcirculatory function, resulting in a state of hypoperfusion and tissue oedema. No specific pharmacological therapies are currently used to attenuate microvascular injury. Given the prominent role of endothelial breakdown and microcirculatory dysfunction in sepsis, there is a need for effective strategies to protect the endothelium. In this review we will discuss key mechanisms and putative therapeutic agents relevant to endothelial barrier function.

Gastrointestinal bleeding in von Willebrand patients: special diagnostic and management considerations

INTRODUCTION

Severe and recurrent gastrointestinal (GI) bleeding caused by angiodysplasia is a significant problem in patients with von Willebrand disease (VWD) and in those with acquired von Willebrand syndrome (AVWS). At present, angiodysplasia-related GI bleeding is often refractory to standard treatment including replacement therapy with von Willebrand factor (VWF) concentrates and continues to remain a major challenge and cause of significant morbidity in patients despite advances in diagnostics and therapeutics.

AREAS COVERED

This paper reviews the available literature on GI bleeding in VWD patients, examines the molecular mechanisms implicated in angiodysplasia-related GI bleeding, and summarizes existing strategies in the management of bleeding GI angiodysplasia in patients with VWF abnormalities. Suggestions are made for further research directions.

EXPERT OPINION

Bleeding from angiodysplasia poses a significant challenge for individuals with abnormal VWF. Diagnosis remains a challenge and may require multiple radiologic and endoscopic investigations. Additionally, there is a need for enhanced understanding at a molecular level to identify effective therapies. Future studies of VWF replacement therapies using newer formulations as well as other adjunctive treatments to prevent and treat bleeding will hopefully improve care.

Integrin-Dependent Cell-Matrix Adhesion in Endothelial Health and Disease

The endothelium is a dynamic, semipermeable layer lining all blood vessels, regulating blood vessel formation and barrier function. Proper composition and function of the endothelial barrier are required for fluid homeostasis, and clinical conditions characterized by barrier disruption are associated with severe morbidity and high mortality rates. Endothelial barrier properties are regulated by cell-cell junctions and intracellular signaling pathways governing the cytoskeleton, but recent insights indicate an increasingly important role for integrin-mediated cell-matrix adhesion and signaling in endothelial barrier regulation. Here, we discuss diseases characterized by endothelial barrier disruption, and provide an overview of the composition of endothelial cell-matrix adhesion complexes and associated signaling pathways, their crosstalk with cell-cell junctions, and with other receptors. We further present recent insights into the role of cell-matrix adhesions in the developing and mature/adult endothelium of various vascular beds, and discuss how the dynamic regulation and turnover of cell-matrix adhesions regulates endothelial barrier function in (patho)physiological conditions like angiogenesis, inflammation and in response to hemodynamic stress. Finally, as clinical conditions associated with vascular leak still lack direct treatment, we focus on how understanding of endothelial cell-matrix adhesion may provide novel targets for treatment, and discuss current translational challenges and future perspectives.

Special considerations in GI bleeding in VWD patients

Gastrointestinal (GI) bleeding is an important cause of morbidity and mortality in von Willebrand disease (VWD). It has been noted that GI bleeding caused by angiodysplasia is overrepresented in VWD patients compared to other causes. The bleeding from angiodysplasia is notoriously difficult to treat; recurrences and rebleeds are common. A growing body of basic science evidence demonstrates that von Willebrand factor negatively regulates angiogenesis through multiple pathways. VWD is clinically highly associated with angiodysplasia. The predisposition to angiodysplasia likely accounts for many of the clinical difficulties related to managing GI bleeding in VWD patients. Diagnosis and treatment are challenging with the current tools available, and much further research is needed to further optimize care for these patients with regard to acute treatment, prophylaxis, and adjunctive therapies. In this review we provide an overview of the available literature on GI bleeding in VWD and explore the molecular underpinnings of angiodysplasia-related GI bleeding. Considerations for diagnostic effectiveness are discussed, as well as the natural history and recurrence of these lesions and which therapeutic options are available for acute and prophylactic management.

Angiopoietin-2-induced lymphatic endothelial cell migration drives lymphangiogenesis via the β1 integrin-RhoA-formin axis

Lymphangiogenesis is an essential physiological process but also a determining factor in vascular-related pathological conditions. Angiopoietin-2 (Ang2) plays an important role in lymphatic vascular development and function and its upregulation has been reported in several vascular-related diseases, including cancer. Given the established role of the small GTPase RhoA on cytoskeleton-dependent endothelial functions, we investigated the relationship between RhoA and Ang2-induced cellular activities. This study shows that Ang2-driven human dermal lymphatic endothelial cell migration depends on RhoA. We demonstrate that Ang2-induced migration is independent of the Tie receptors, but dependent on β1 integrin-mediated RhoA activation with knockdown, pharmacological approaches, and protein sequencing experiments. Although the key proteins downstream of RhoA, Rho kinase (ROCK) and myosin light chain, were activated, blockade of ROCK did not abrogate the Ang2-driven migratory effect. However, formins, an alternative target of RhoA, were identified as key players, and especially FHOD1. The Ang2-RhoA relationship was explored in vivo, where lymphatic endothelial RhoA deficiency blocked Ang2-induced lymphangiogenesis, highlighting RhoA as an important target for anti-lymphangiogenic treatments.

A hitchhiker's guide through the COVID-19 galaxy

Numerous reviews have summarized the epidemiology, pathophysiology and the various therapeutic aspects of Coronavirus disease 2019 (COVID-19), but a practical guide on "how to treat whom with what and when" based on an understanding of the immunological background of the disease stages remains missing. This review attempts to combine the current knowledge about the immunopathology of COVID-19 with published evidence of available and emerging treatment options. We recognize that the information about COVID-19 and its treatment is rapidly changing, but hope that this guide offers those on the frontline of this pandemic an understanding of the host response in COVID-19 patients and supports their ongoing efforts to select the best treatments tailored to their patient's clinical status.

The Manifold Cellular Functions of von Willebrand Factor

The plasma glycoprotein von Willebrand factor (VWF) is exclusively synthesized in endothelial cells (ECs) and megakaryocytes, the precursor cells of platelets. Its primary function lies in hemostasis. However, VWF is much more than just a "fishing hook" for platelets and a transporter for coagulation factor VIII. VWF is a true multitasker when it comes to its many roles in cellular processes. In ECs, VWF coordinates the formation of Weibel-Palade bodies and guides several cargo proteins to these storage organelles, which control the release of hemostatic, inflammatory and angiogenic factors. Leukocytes employ VWF to assist their rolling on, adhesion to and passage through the endothelium. Vascular smooth muscle cell proliferation is supported by VWF, and it regulates angiogenesis. The life cycle of platelets is accompanied by VWF from their budding from megakaryocytes to adhesion, activation and aggregation until the end in apoptosis. Some tumor cells acquire the ability to produce VWF to promote metastasis and hide in a shell of VWF and platelets, and even the maturation of osteoclasts is regulated by VWF. This review summarizes the current knowledge on VWF's versatile cellular functions and the resulting pathophysiological consequences of their dysregulation.

A systems biology model of junctional localization and downstream signaling of the Ang-Tie signaling pathway

The Ang–Tie signaling pathway is an important vascular signaling pathway regulating vascular growth and stability. Dysregulation in the pathway is associated with vascular dysfunction and numerous diseases that involve abnormal vascular permeability and endothelial cell inflammation. The understanding of the molecular mechanisms of the Ang–Tie pathway has been limited due to the complex reaction network formed by the ligands, receptors, and molecular regulatory mechanisms. In this study, we developed a mechanistic computational model of the Ang–Tie signaling pathway validated against experimental data. The model captures and reproduces the experimentally observed junctional localization and downstream signaling of the Ang–Tie signaling axis, as well as the time-dependent role of receptor Tie1. The model predicts that Tie1 modulates Tie2’s response to the context-dependent agonist Ang2 by junctional interactions. Furthermore, modulation of Tie1’s junctional localization, inhibition of Tie2 extracellular domain cleavage, and inhibition of VE-PTP are identified as potential molecular strategies for potentiating Ang2’s agonistic activity and rescuing Tie2 signaling in inflammatory endothelial cells.

Targeting RGD-binding integrins as an integrative therapy for diabetic retinopathy and neovascular age-related macular degeneration

Integrins are a class of transmembrane receptors that are involved in a wide range of biological functions. Dysregulation of integrins has been implicated in many pathological processes and consequently, they are attractive therapeutic targets. In the ophthalmology arena, there is extensive evidence suggesting that integrins play an important role in diabetic retinopathy (DR), age-related macular degeneration (AMD), glaucoma, dry eye disease and retinal vein occlusion. For example, there is extensive evidence that arginyl-glycyl-aspartic acid (Arg-Gly-Asp; RGD)-binding integrins are involved in key disease hallmarks of DR and neovascular AMD (nvAMD), specifically inflammation, vascular leakage, angiogenesis and fibrosis. Based on such evidence, drugs that engage integrin-linked pathways have received attention for their potential to block all these vision-threatening pathways. This review focuses on the pathophysiological role that RGD-binding integrins can have in complex multifactorial retinal disorders like DR, diabetic macular edema (DME) and nvAMD, which are leading causes of blindness in developed countries. Special emphasis will be given on how RGD-binding integrins can modulate the intricate molecular pathways and regulate the underlying pathological mechanisms. For instance, the interplay between integrins and key molecular players such as growth factors, cytokines and enzymes will be summarized. In addition, recent clinical advances linked to targeting RGD-binding integrins in the context of DME and nvAMD will be discussed alongside future potential for limiting progression of these diseases.

Angiopoietin 2 stimulates trophoblast invasion via a mechanism associated with JNK signaling

Extravillous trophoblast cell (EVT) invasion is tightly controlled, and its dysregulation can lead to altered spiral artery remodeling and contribute to a number of different pregnancy complications. Angiopoietin-2 (Ang-2) is expressed by trophoblast cells and various cells in the decidua, and trophoblast cells express its receptor, Tie2. Ang-2 has been shown to play roles in tumor progression and metastasis but it is not known if it also regulates EVT invasion. Here, we show that both the HTR-8/SVneo cell line and primary isolates of human EVT expressed various integrins and the Tie2 receptor, and Ang-2 stimulated their migration and/or invasion. Ang-2 increased expression of matrix metalloproteinase (MMP)2 and MMP9, altered the cytoskeleton of HTR-8/SVneo cells and also induced phosphorylation of Tie2, JNK and c-Jun. Inhibition of p-JNK (using SP600125) blocked the Ang-2 induced invasion of HTR-8/SVneo cells. In addition, inhibition of Tie2 (pexmetinib) and integrin signaling (RGDS and ATN-161) also blocked Ang-2-induced invasion. In conclusion, we demonstrate that Ang-2 can stimulate EVT invasion via a mechanism associated with activation of both the Tie2 receptor and integrins, which appear to work through different pathways; Tie2 through the JNK/c-JUN pathway and integrins through an as yet unidentified pathway(s). We therefore propose that any alterations in Ang-2 expression in the decidua would lead to an imbalance in pro- and anti-invasive factors, disrupting regulation of EVT invasion and spiral artery remodeling and thereby contribute to the etiology of several complications of pregnancy.

Chemosensitizing activity of peptide from Lentinus squarrosulus (Mont.) on cisplatin-induced apoptosis in human lung cancer cells

The limitations of cisplatin, a standard chemotherapy for lung cancer, have been documented with serious adverse effects and drug resistance. To address the need for novel therapy, this study firstly reveals the potential of peptide from Lentinus squarrosulus (Mont.) as a chemotherapeutic adjuvant for cisplatin treatment. The purified peptide from L. squarrosulus aqueous extracts was obtained after eluting with 0.4 M NaCl through FPLC equipped with anion exchange column. Preincubation for 24 h with 5 µg/mL of the peptide at prior to treatment with 5 µM cisplatin significantly diminished %cell viability in various human lung cancer cells but not in human dermal papilla and proximal renal cells. Flow cytometry indicated the augmentation of cisplatin-induced apoptosis in lung cancer cells pretreated with peptide from L. squarrosulus. Preculture with the peptide dramatically inhibited colony formation in lung cancer cells derived after cisplatin treatment. Strong suppression on integrin-mediated survival was evidenced with the diminution of integrins (β1, β3, β5, α5, αV) and down-stream signals (p-FAK/FAK, p-Src/Src, p-Akt/Akt) consequence with alteration of p53, Bax, Blc-2 and Mcl-1 in cisplatin-treated lung cancer cells preincubated with peptide from L. squarrosulus. These results support the development of L. squarrosulus peptide as a novel combined chemotherapy with cisplatin for lung cancer treatment.

THE ANGIOPOIETIN/TIE PATHWAY IN RETINAL VASCULAR DISEASES: A Review

PURPOSE

To provide a concise overview for ophthalmologists and practicing retina specialists of available clinical evidence of manipulating the angiopoietin/tyrosine kinase with immunoglobulin-like and endothelial growth factor-like domains (Tie) pathway and its potential as a therapeutic target in retinal vascular diseases.

METHODS

A literature search for articles on the angiopoietin/Tie pathway and molecules targeting this pathway that have reached Phase 2 or 3 trials was undertaken on PubMed, Association for Research in Vision and Ophthalmology meeting abstracts (2014-2019), and ClinicalTrials.gov databases. Additional information on identified pipeline drugs was obtained from publicly available information on company websites.

RESULTS

The PubMed and Association for Research in Vision and Ophthalmology meeting abstract search yielded 462 results, of which 251 publications not relevant to the scope of the review were excluded. Of the 141 trials related to the angiopoietin/Tie pathway on ClinicalTrials.gov, seven trials focusing on diseases covered in this review were selected. Vision/anatomic outcomes from key clinical trials on molecules targeting the angiopoietin/Tie pathway in patients with retinal vascular diseases are discussed.

CONCLUSION

Initial clinical evidence suggests a potential benefit of targeting the angiopoietin/Tie pathway and vascular endothelial growth factor-A over anti-vascular endothelial growth factor-A monotherapy alone, in part due to of the synergistic nature of the pathways.

The effects of sepsis on endothelium and clinical implications

ABSTRACT

Sepsis accounts for nearly 700 000 deaths in Europe annually and is caused by an overwhelming host response to infection resulting in organ failure. The endothelium is an active contributor to sepsis and as such represents a major target for therapy. During sepsis, endothelial cells amplify the immune response and activate the coagulation system. They are both a target and source of inflammation and serve as a link between local and systemic immune responses. In response to cytokines produced by immune cells, the endothelium expresses adhesion molecules and produces vasoactive compounds, inflammatory cytokines, and chemoattractants, thus switching from an anticoagulant to procoagulant state. These responses contribute to local control of infection, but systemic activation can lead to microvascular thrombosis, capillary permeability, hypotension, tissue hypoxia, and ultimately tissue damage. This review focuses on the role of the endothelium in leucocyte adhesion and transmigration as well as production of reactive oxygen and nitrogen species, microRNAs and cytokines, formation of signalling microparticles, and disseminated intravascular coagulation. We also discuss alterations in endothelial permeability and apoptosis. Finally, we review the diagnostic potential of endothelial markers and endothelial pathways as therapeutic targets for this devastating disease.

Vanucizumab mode of action: Serial biomarkers in plasma, tumor, and skin-wound-healing biopsies

Vanucizumab is a novel bispecific antibody inhibiting vascular endothelial growth factor (VEGF-A) and angiopoietin-2 (Ang-2) that demonstrated safety and anti-tumor activity in part I of a phase I study of 42 patients with advanced solid tumors. Part II evaluated the pharmacodynamic effects of vanucizumab 30 or 15 mg/kg every 2 weeks in 32 patients. Serial plasma samples, paired tumor, and skin-wound-healing biopsies were taken over 29 days to evaluate angiogenic markers. Vanucizumab was associated with marked post-infusion reductions in circulating unbound VEGF-A and Ang-2. By day 29, tumor samples revealed mean reductions in density of microvessels (-32.2%), proliferating vessels (-47.9%) and Ang-2 positive vessels (-62.5%). Skin biopsies showed a mean reduction in density of microvessels (-49.0%) and proliferating vessels (-25.7%). Gene expression profiling of tumor samples implied recruitment and potential activation of lymphocytes. Biopsies were safely conducted. Vanucizumab demonstrated a consistent biological effect on vascular-related biomarkers, confirming proof of concept. Skin-wound-healing biopsies were a valuable surrogate for studying angiogenesis-related mechanisms.

Association of Low Tumor Endothelial Cell pY397-Focal Adhesion Kinase Expression With Survival in Patients With Neoadjuvant-Treated Locally Advanced Breast Cancer

IMPORTANCE

Determining the risk of relapse after neoadjuvant chemotherapy in patients with locally advanced breast cancer is required to offer alternative therapeutic strategies.

OBJECTIVE

To examine whether endothelial cell phosphorylated-focal adhesion kinase (EC-pY397-FAK) expression in patients with treatment-naive locally advanced breast cancer is a biomarker for chemotherapy sensitivity and is associated with survival after neoadjuvant chemotherapy.

DESIGN, SETTING, AND PARTICIPANTS

In this prognostic study, expression levels of EC-pY397-FAK and tumor cell (TC)-pY397-FAK were determined by immunohistochemistry in prechemotherapy core biopsies from 82 female patients with locally advanced breast cancer treated with anthracycline-based combination neoadjuvant chemotherapy at Nottingham City Hospital in Nottingham, UK. Median follow-up time was 67 months. The study was conducted from December 1, 2010, to September 28, 2019, and data analysis was performed from October 2, 2019, to March 31, 2020.

EXPOSURES

All women underwent surgery followed by adjuvant radiotherapy and, if tumors were estrogen receptor-positive, 5-year tamoxifen treatment.

MAIN OUTCOMES AND MEASURES

Outcomes were pathologic complete response and 5-year relapse-free survival examined using Kaplan-Meier, univariable logistic, multivariable logistic, and Cox proportional hazards models.

RESULTS

A total of 82 women (age, 29-76 years) with locally advanced breast cancer (stage IIA-IIIC) were included. Of these, 21 women (26%) had high EC-pY397-FAK expression that was associated with estrogen receptor positivity (71% vs 46%; P = .04), progesterone receptor positivity (67% vs 39%; P = .03), high Ki67 (86% vs 41%; P < .001), 4-immunohistochemically stained luminal-B (52% vs 8%; P < .001), higher tumor category (T3/T4 category: 90% vs 59%; P = .01), high lymph node category (N2-3 category: 43% vs 5%; P < .001), and high tumor node metastasis stage (IIIA-IIIC: 90% vs 66%; P = .03). Of 21 patients with high EC-pY397-FAK expression levels, none showed pathologic complete response, compared with 11 of 61 patients with low EC-pY397-FAK expression levels who showed pathologic complete response (odds ratio, 0.70; 95% CI, 0.61-0.82; P = .04). High EC-pY397-FAK expression levels and high blood vessel density (BVD) were associated with shorter 5-year relapse-free survival compared with those with low EC-pY397-FAK expression levels (hazard ratio [HR], 2.21; 95% CI, 1.17-4.20; P = .01) and low BVD (HR, 2.2; 95% CI, 1.15-4.35; P = .02). High TC-pY397-FAK expression levels in 15 of 82 women (18%) were not associated significantly with pathologic complete response or 5-year relapse-free survival. A multivariable Cox regression model for 5-year relapse-free survival indicated that high EC-pY397-FAK expression levels was an independent poor prognostic factor after controlling for other validated prognostic factors (HR, 3.91; 95% CI, 1.42-10.74; P = .01). Combined analysis of EC-pY397-FAK expression levels, TC-pY397-FAK expression levels, and BVD improved prognostic significance over individually tested features.

CONCLUSIONS AND RELEVANCE

The findings of this study suggest that low EC-pY397-FAK expression levels are associated with chemotherapy sensitivity and improved 5-year relapse-free survival after systemic therapy. Combined analysis of high EC-pY397-FAK expression levels, high TC-pY397-FAK expression levels, and high BVD appeared to identify a high-risk population.

Angiopoietin Level Trajectories in Toddlers With Severe Sepsis and Septic Shock and Their Effect on Capillary Endothelium

OBJECTIVE

Angiopoietins are postulated diagnostic biomarkers in children and adults with severe sepsis and septic shock. The diagnostic value of angiopoietins in children less than 5 years old has not been established, nor has their effect on permeability in the capillary microvasculature. We aim to determine if levels of angiopoietin-1 or -2 (angpt-1, -2) are diagnostic for severe sepsis/shock in young children and whether they affect the permeability of cultured human dermal microvascular endothelial cells (HDMEC).

DESIGN

Prospective observational study of children < 5 years old. Patients were classified as non-systemic inflammatory response syndrome (SIRS), SIRS/sepsis and severe sepsis/septic shock.

SETTING

Tertiary care pediatric hospitals.

PATIENTS

Critically ill children.

INTERVENTIONS

None.

MEASUREMENTS

Plasma angpt-1 and -2 levels were measured with enzyme-linked immunoassays. Expression of angpt-2 in endothelial cells was assessed with quantitative polymerase chain reaction. Permeability changes in cultured HDMECs were assessed with transendothelial electrical resistance measurements.

RESULTS

Angpt-1 levels were significantly higher in younger children compared with levels found in previous study of older children across disease severity (all P < 0.001). Angpt-2 was significantly higher in this cohort with severe sepsis/septic shock compared with children without SIRS and SIRS/sepsis (all P < 0.003). Angpt-2/1 ratio was also elevated in children with severe sepsis/septic shock but an order of magnitude less than older children (P < 0.02, P = 0.002). Angpt-1 and -2 did not affect basal HDMEC permeability or modulate leak in isolation or in the presence of tumor necrosis factor (TNF).

CONCLUSIONS

Angpt-2 levels and the angpt-2/1 ratio are appropriate diagnostic biomarkers of severe sepsis/septic shock in children less than 5 years old. Neither angpt-1 nor -2 affects basal HDMEC permeability alone or modulates TNF induced capillary leak.

Colicin N Mediates Apoptosis and Suppresses Integrin-Modulated Survival in Human Lung Cancer Cells

The inherent limitations, including serious side-effects and drug resistance, of current chemotherapies necessitate the search for alternative treatments especially for lung cancer. Herein, the anticancer activity of colicin N, bacteria-produced antibiotic peptide, was investigated in various human lung cancer cells. After 24 h of treatment, colicin N at 5-15 µM selectively caused cytotoxicity detected by MTT assay in human lung cancer H460, H292 and H23 cells with no noticeable cell death in human dermal papilla DPCs cells. Flow cytometry analysis of annexin V-FITC/propidium iodide indicated that colicin N primarily induced apoptosis in human lung cancer cells. The activation of extrinsic apoptosis evidenced with the reduction of c-FLIP and caspase-8, as well as the modulation of intrinsic apoptosis signaling proteins including Bax and Mcl-1 were observed via Western blot analysis in lung cancer cells cultured with colicin N (10-15 µM) for 12 h. Moreover, 5-15 µM of colicin N down-regulated the expression of activated Akt (p-Akt) and its upstream survival molecules, integrin β1 and αV in human lung cancer cells. Taken together, colicin N exhibits selective anticancer activity associated with suppression of integrin-modulated survival which potentiate the development of a novel therapy with high safety profile for treatment of human lung cancer.

C16 Peptide Promotes Vascular Growth and Reduces Inflammation in a Neuromyelitis Optica Model

The goal of this study was to elucidate the mechanism of action of C16, a laminin-1 peptide that competes with αvβ3 for integrin binding, in treating neuromyelitis optica (NMO). A NMO rat model was established and specific inhibitors were used to investigate the effect of Tie2 kinase, integrin, and PI3K/Akt signaling pathways on C16 function in NMO using histological, immunohistochemical, immunofluorescence, Western blot, and ELISA assays. A total of 150 rats were divided into five groups: a control untreated group (n = 18) and four test groups (n = 33 per group) including vehicle-treated control, C16, Tie2 kinase inhibitor + C16, and PI3K/Akt inhibitor LY294002 + C16. We found that inhibiting Tie2 kinase resulted in partial loss of C16 peptide-mediated effects, while suppressing PI3K/Akt signaling reduced C16 peptide-mediated effects. In addition, activation of the αvβ3 integrin axis and Tie2 kinase promoted PI3K/Akt signaling. Our study showed that the Tie2-PI3K/Akt, Tie2 integrin, and integrin-PI3K/Akt signaling pathways regulate C16 peptide function in vascular growth and stabilization as well as inflammation in NMO.

Alternative trafficking of Weibel-Palade body proteins in CRISPR/Cas9-engineered von Willebrand factor-deficient blood outgrowth endothelial cells

BACKGROUND

Synthesis of the hemostatic protein von Willebrand factor (VWF) drives formation of endothelial storage organelles called Weibel-Palade bodies (WPBs). In the absence of VWF, angiogenic and inflammatory mediators that are costored in WPBs are subject to alternative trafficking routes. In patients with von Willebrand disease (VWD), partial or complete absence of VWF/WPBs may lead to additional bleeding complications, such as angiodysplasia. Studies addressing the role of VWF using VWD patient-derived blood outgrowth endothelial cells (BOECs) have reported conflicting results due to the intrinsic heterogeneity of patient-derived BOECs.

OBJECTIVE

To generate a VWF-deficient endothelial cell model using clustered regularly interspaced short palindromic repeats (CRISPR) genome engineering of blood outgrowth endothelial cells.

METHODS

We used CRISPR/CRISPR-associated protein 9 editing in single-donor cord blood-derived BOECs (cbBOECs) to generate clonal VWF -/- cbBOECs. Clones were selected using high-throughput screening, VWF mutations were validated by sequencing, and cells were phenotypically characterized.

RESULTS

Two VWF -/- BOEC clones were obtained and were entirely devoid of WPBs, while their overall cell morphology was unaltered. Several WPB proteins, including CD63, syntaxin-3 and the cargo proteins angiopoietin (Ang)-2, interleukin (IL)-6, and IL-8 showed alternative trafficking and secretion in the absence of VWF. Interestingly, Ang-2 was relocated to the cell periphery and colocalized with Tie-2.

CONCLUSIONS

CRISPR editing of VWF provides a robust method to create VWF- deficient BOECs that can be directly compared to their wild-type counterparts. Results obtained with our model system confirmed alternative trafficking of several WPB proteins in the absence of VWF and support the theory that increased Ang-2/Tie-2 interaction contributes to angiogenic abnormalities in VWD patients.

Substrate stiffness directs diverging vascular fates

Embryonic stem cells (ESC) are excellent cell culture systems for elucidating developmental signals that may be part of the stem cell niche. Although stem cells are traditionally induced using predominately soluble signals, the mechanical environment of the niche can also play a role in directing cells towards differential cell lineages. Interested in diverging vascular fates, we set out to examine to what extent mechanical signaling played a role in endothelial cell and/or smooth muscle fate. Using chemically-defined staged vascular differentiation methods, vascular progenitor cells (VPC) fate was examined on single stiffness polyacrylamide hydrogels of 10 kPa, 40 kPa and >0.1 GPa. Emergence of vascular cell populations aligned with corresponding hydrogel stiffness: EC-lineages favoring the softer material and SMC lineages favoring the stiffest material. Statistical significance was observed on both cell lines on almost all days. Transcriptome analysis indicated that the populations on the varying stiffness emerge in distinct categories. Lastly, blocking studies show that αvβ1, and not αvβ6, activation mediates stiffness-directed vascular differentiation. Overall, these studies indicate that softer materials direct VPCs into a more EC-like fate compared to stiffer materials. STATEMENT OF SIGNIFICANCE: Although stem cells are traditionally induced using predominately soluble signals, the mechanical environment of the niche also plays a role in directing cell fate. Several studies have examined the stiffness-induced cell fate from mesenchymal stem cells (MSCs) and undifferentiated embryonic stem cells (ESCs). This is the first study that rigorously examines the role of matrix stiffness in diverging vascular fates from a purified population of vascular progenitor cells (VPCs). We show that the emergence of endothelial cell (EC) versus smooth muscle cell (SMC) populations corresponds with hydrogel stiffness: EC-lineages favoring the softness material and SMC lineages favoring the stiffest material, and that αvβ1 activation mediates this stiffness-directed vascular differentiation.

Tumor Angiogenesis Is Differentially Regulated by Phosphorylation of Endothelial Cell Focal Adhesion Kinase Tyrosines-397 and -861

Expression of focal adhesion kinase (FAK) in endothelial cells (EC) is essential for angiogenesis, but how FAK phosphorylation at tyrosine-(Y)397 and Y861 regulate tumor angiogenesis in vivo is unknown. Here, we show that tumor growth and angiogenesis are constitutively reduced in inducible, ECCre+;FAKY397F/Y397F -mutant mice. Conversely, ECCre+;FAKY861F/Y861F mice exhibit normal tumor growth with an initial reduction in angiogenesis that recovered in end-stage tumors. Mechanistically, FAK-Y397F ECs exhibit increased Tie2 expression, reduced Vegfr2 expression, decreased β1 integrin activation, and disrupted downstream FAK/Src/PI3K(p55)/Akt signaling. In contrast, FAK-Y861F ECs showed decreased Vegfr2 and Tie2 expression with an enhancement in β1 integrin activation. This corresponds with a decrease in Vegfa-stimulated response, but an increase in Vegfa+Ang2- or conditioned medium from tumor cell-stimulated cellular/angiogenic responses, mimicking responses in end-stage tumors with elevated Ang2 levels. Mechanistically, FAK-Y861F, but not FAK-Y397F ECs showed enhanced p190RhoGEF/P130Cas-dependent signaling that is required for the elevated responses to Vegfa+Ang2. This study establishes the differential requirements of EC-FAK-Y397 and EC-FAK-Y861 phosphorylation in the regulation of EC signaling and tumor angiogenesis in vivo. SIGNIFICANCE: Distinct motifs of the focal adhesion kinase differentially regulate tumor blood vessel formation and remodeling.

Role of Angiopoietin-2 in Vascular Physiology and Pathophysiology

Angiopoietins 1–4 (Ang1–4) represent an important family of growth factors, whose activities are mediated through the tyrosine kinase receptors, Tie1 and Tie2. The best characterized are angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2). Ang1 is a potent angiogenic growth factor signaling through Tie2, whereas Ang2 was initially identified as a vascular disruptive agent with antagonistic activity through the same receptor. Recent data demonstrates that Ang2 has context-dependent agonist activities. Ang2 plays important roles in physiological processes and the deregulation of its expression is characteristic of several diseases. In this review, we summarize the activity of Ang2 on blood and lymphatic endothelial cells, its significance in human physiology and disease, and provide a current view of the molecular signaling pathways regulated by Ang2 in endothelial cells.

Differential Effects of Ang-2/VEGF-A Inhibiting Antibodies in Combination with Radio- or Chemotherapy in Glioma

Antiangiogenic strategies have not shown striking antitumor activities in the majority of glioma patients so far. It is unclear which antiangiogenic combination regimen with standard therapy is most effective. Therefore, we compared anti-VEGF-A, anti-Ang2, and bispecific anti-Ang-2/VEGF-A antibody treatments, alone and in combination with radio- or temozolomide (TMZ) chemotherapy, in a malignant glioma model using multiparameter two-photon in vivo microscopy in mice. We demonstrate that anti-Ang-2/VEGF-A lead to the strongest vascular changes, including vascular normalization, both as monotherapy and when combined with chemotherapy. The latter was accompanied by the most effective chemotherapy-induced death of cancer cells and diminished tumor growth. This was most probably due to a better tumor distribution of the drug, decreased tumor cell motility, and decreased formation of resistance-associated tumor microtubes. Remarkably, all these parameters where reverted when radiotherapy was chosen as combination partner for anti-Ang-2/VEGF-A. In contrast, the best combination partner for radiotherapy was anti-VEGF-A. In conclusion, while TMZ chemotherapy benefits most from combination with anti-Ang-2/VEGF-A, radiotherapy does from anti-VEGF-A. The findings imply that uninformed combination regimens of antiangiogenic and cytotoxic therapies should be avoided.

Anti-angiogenic Targets: Angiopoietin and Angiopoietin Receptors

Tumor blood vessel formation (angiogenesis) is essential for tumor growth and metastasis. Two main endothelial ligand–receptor pathways regulating angiogenesis are vascular endothelial growth factor (VEGF) receptor and angiopoietin-TIE receptor pathways. The angiopoietin-TIE pathway is required for the remodeling and maturation of the blood and lymphatic vessels during embryonic development after VEGF and VEGF-C mediated development of the primary vascular plexus. Angiopoietin-1 (ANGPT1) stabilizes the vasculature after angiogenic processes, via tyrosine kinase with immunoglobulin-like and EGF-like domains 2 (TIE2) activation. In contrast, ANGPT2 is upregulated at sites of vascular remodeling. ANGPT2 is secreted by activated endothelial cells in inflammation, promoting vascular destabilization. ANGPT2 has been found to be expressed in many human cancers. Intriguingly, in preclinical models inhibition of ANGPT2 has provided promising results in preventing tumor angiogenesis, tumor growth, and metastasis, making it an attractive candidate to target in tumors. However, until now the first ANGPT2 targeting therapies have been less effective in clinical trials than in experimental models. Additionally, in preclinical models combined therapy against ANGPT2 and VEGF or immune checkpoint inhibitors has been superior to monotherapies, and these pathways are also targeted in early clinical trials. In order to improve current anti-angiogenic therapies and successfully exploit ANGPT2 as a target for cancer treatment, the biology of the angiopoietin-TIE pathway needs to be profoundly clarified.

Antithrombotic therapy in ventricular assist device (VAD) management: From ancient beliefs to updated evidence. A narrative review

Platelets play a key role in the pathogenesis of ventricular assist device (VAD) thrombosis; therefore, antiplatelet drugs are essential, both in the acute phase and in the long-term follow-up in VAD management. Aspirin is the most used agent and still remains the first-choice drug for lifelong administration after VAD implantation. Anticoagulant drugs are usually recommended, but with a wide range of efficacy targets. Dual antiplatelet therapy, targeting more than one pathway of platelet activation, has been used for patients developing a thrombotic event, despite an increased risk of bleeding complications. Although different strategies have been attempted, bleeding and thrombotic events remain frequent and there are no uniform strategies adopted for pharmacological management in the short and mid- or long-term follow up. The aim of this article is to provide an overview of the evidence from randomized clinical trials and observational studies with a focus on the pathophysiologic mechanisms underlying bleeding and thrombosis in VAD patients and the best antithrombotic regimens available.

Targeting the Tie2-αvβ3 integrin axis with bi-specific reagents for the inhibition of angiogenesis

BACKGROUND

Increased activity of the receptor tyrosine kinase Tie2 has been implicated in the promotion of pathological angiogenesis. This activity is mainly mediated through angiopoietin (Ang)1- and Ang2-dependent activation of integrins by Tie2, rendering the Ang/Tie2/integrin axis an attractive putative target for cancer therapeutics.

RESULTS

To target this axis, we developed single domain, non-immunoglobulin high-affinity bi-specific protein inhibitors against both Tie2 and αvβ3 integrin. We have previously engineered the Ang2-binding domain of Tie2 (Ang2-BD) as a Tie2 inhibitor. Here, we engineered an exposed loop in Ang2-BD to generate variants that include an integrin-binding Arg-Gly-Asp (RGD) motif and used flow cytometry screening of a yeast-displayed Ang2-BD RGD loop library to identify the integrin antagonists. The bi-specific antagonists targeting both Tie2 and αvβ3 integrin inhibited adhesion and proliferation of endothelial cells cultured together with the αvβ3 integrin ligand vitronectin, as well as endothelial cell invasion and tube formation. The bi-specific reagents inhibited downstream signaling by Tie2 intracellularly in response to its agonist Ang1 more effectively than the wild-type Ang2 BD that binds Tie2 alone.

CONCLUSIONS

Collectively, this study-the first to describe inhibitors targeting all the known functions resulting from Tie2/integrin αvβ3 cross-talk-has created new tools for studying Tie2- and integrin αvβ3-dependent molecular pathways and provides the basis for the rational and combinatorial engineering of ligand-Tie2 and ligand-integrin αvβ3 receptor interactions. Given the roles of these pathways in cancer angiogenesis and metastasis, this proof of principle study paves the route to create novel Tie2/integrin αvβ3-targeting proteins for clinical use as imaging and therapeutic agents.

Platelet-Activation Mechanisms and Vascular Remodeling

This overview article for the Comprehensive Physiology collection is focused on detailing platelets, how platelets respond to various stimuli, how platelets interact with their external biochemical environment, and the role of platelets in physiological and pathological processes. Specifically, we will discuss the four major functions of platelets: activation, adhesion, aggregation, and inflammation. We will extend this discussion to include various mechanisms that can induce these functional changes and a discussion of some of the salient receptors that are responsible for platelets interacting with their external environment. We will finish with a discussion of how platelets interact with their vascular environment, with a special focus on interactions with the extracellular matrix and endothelial cells, and finally how platelets can aid and possibly initiate the progression of various vascular diseases. Throughout this overview, we will highlight both the historical investigations into the role of platelets in health and disease as well as some of the more current work. Overall, the authors aim for the readers to gain an appreciation for the complexity of platelet functions and the multifaceted role of platelets in the vascular system. © 2017 American Physiological Society. Compr Physiol 8:1117-1156, 2018.

Abnormal angiogenesis in blood outgrowth endothelial cells derived from von Willebrand disease patients

: Bleeding associated with angiodysplasia is a common, often intractable complication in patients with von Willebrand disease (VWD). von Willebrand factor (VWF), the protein deficient or defective in VWD, is a negative regulator of angiogenesis, which may explain the pathologic blood vessel growth in VWD. This study explores the normal range of angiogenesis in blood outgrowth endothelial cells (BOECs) derived from healthy donors and compares this to angiogenesis in BOECs from VWD patients of all types and subtypes. BOECs were assessed for VWF and angiopoietin-2 (Ang-2) gene expression, secretion, and storage. To explore angiogenic potential, we characterized cellular proliferation, matrix protein adhesion, migration, and tubule formation. We found great angiogenic variability in VWD BOECs with respect to each of the angiogenesis parameters. However, type 1 and 3 VWD BOECs had higher Ang-2 secretion associated with impaired endothelial cell migration velocity and enhanced directionality. Type 2A and 2B BOECs were the most proliferative and multiple VWD BOECs had impaired tubule formation in Matrigel. This study highlights the angiogenic variability in BOECs derived from VWD patients. Abnormal cell proliferation, migration, and increased Ang-2 secretion are common features of VWD BOECs. Despite the many abnormalities of VWD BOECs, significant heterogeneity among individual VWD phenotypes precludes a simple description of relationship between VWD type and in vitro surrogates for angiodysplasia.

Integrins as therapeutic targets in the organ-specific metastasis of human malignant melanoma

Integrins are a large family of adhesion molecules that mediate cell-cell and cell-extracellular matrix interactions. Among the 24 integrin isoforms, many have been found to be associated with tumor angiogenesis, tumor cell migration and proliferation, and metastasis. Integrins, especially αvβ3, αvβ5 and α5β1, participate in mediating tumor angiogenesis by interacting with the vascular endothelial growth factor and angiopoietin-Tie signaling pathways. Melanoma patients have a poor prognosis when the primary tumor has generated distant metastases, and the melanoma metastatic site is an independent predictor of the survival of these patients. Different integrins on the melanoma cell surface preferentially direct circulating melanoma cells to different organs and promote the development of metastases at specific organ sites. For instance, melanoma cells expressing integrin β3 tend to metastasize to the lungs, whereas those expressing integrin β1 preferentially generate lymph node metastases. Moreover, tumor cell-derived exosomes which contain different integrins may prepare a pre-metastatic niche in specific organs and promote organ-specific metastases. Because of the important role that integrins play in tumor angiogenesis and metastasis, they have become promising targets for the treatment of advanced cancer. In this paper, we review the integrin isoforms responsible for angiogenesis and organ-specific metastasis in malignant melanoma and the inhibitors that have been considered for the future treatment of metastatic disease.

Cooperation between AlphavBeta3 integrin and the fibroblast growth factor receptor enhances proliferation of Hox-overexpressing acute myeloid leukemia cells

A poor prognosis subtype of acute myeloid leukemia (AML) is characterized by increased expression of a set of homeodomain (HD) transcription factors, including HoxA9, HoxA10 and Cdx4. This encompasses AML with MLL1 gene translocations, because Mll1-fusion proteins aberrantly activate HOX transcription. We previously identified FGF2 (Fibroblast Growth Factor 2) as a target gene for HoxA9 and HoxA10 that was indirectly activated by Mll-Ell (an Mll1-fusion protein). Autocrine stimulation of Mll-Ell⁺ myeloid progenitor cells by Fgf2 stabilized βcatenin and increased expression of βcatenin target genes, including CDX4. Since HOXA9 and HOXA10 are Cdx4 target genes, Fgf2 indirectly augmented direct effects of Mll-Ell on these genes. ITGB3, encoding β3 integrin, is another HoxA10 target gene. In the current studies, we found activation of ITGB3 transcription in Mll-Ell⁺ myeloid progenitor cells via HoxA9 and HoxA10. Increased expression of αvβ3 integrin increased Syk-activation; contributing to cytokine hypersensitivity. However, inhibiting Fgf-R partly reversed αvβ3 activity in Mll-Ell⁺ progenitor cells by decreasing ITGB3 promoter activity in a βcatenin- and Cdx4-dependent manner. Inhibitors of Fgf-R or Syk impaired proliferation of CD34⁺ bone marrow cells from AML subjects with increased Hox-expression; with a greater combined effect. These studies identified a rational therapeutic approach to this AML subtype.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

Vimentin knockout results in increased expression of sub-endothelial basement membrane components and carotid stiffness in mice

Intermediate filaments are involved in stress-related cell mechanical properties and in plasticity via the regulation of focal adhesions (FAs) and the actomyosin network. We investigated whether vimentin regulates endothelial cells (ECs) and vascular smooth muscle cells (SMCs) and thereby influences vasomotor tone and arterial stiffness. Vimentin knockout mice (Vim^−/−) exhibited increased expression of laminin, fibronectin, perlecan, collagen IV and VE-cadherin as well as von Willebrand factor deposition in the subendothelial basement membrane. Smooth muscle (SM) myosin heavy chain, α-SM actin and smoothelin were decreased in Vim^−/− mice. Electron microscopy revealed a denser endothelial basement membrane and increased SM cell-matrix interactions. Integrin α_v, talin and vinculin present in FAs were increased in Vim^−/− mice. Phosphorylated FA kinase and its targets Src and ERK1/2 were elevated in Vim^−/− mice. Knockout of vimentin, but not of synemin, resulted in increased carotid stiffness and contractility and endothelial dysfunction, independently of blood pressure and the collagen/elastin ratio. The increase in arterial stiffness in Vim^−/− mice likely involves vasomotor tone and endothelial basement membrane organization changes. At the tissue level, the results show the implication of FAs both in ECs and vascular SMCs in the role of vimentin in arterial stiffening.

New insights into the non-hemostatic role of von Willebrand factor in endothelial protection

During exposure to ischemia-reperfusion (I/R) insult, angiotensin II (AngII)-induced endothelin-1 (ET-1) upregulation in endothelial cells progressively impairs nitric oxide (NO) bioavailability while increasing levels of superoxide anion (O₂^-) and leading to the onset of endothelial dysfunction. Moreover, the overexpression of ET-1 increases the endothelial and circulating levels of von Willebrand factor (vWF), a glycoprotein with a crucial role in arterial thrombus formation. Nowadays, the non-hemostatic role of endothelial vWF is emerging, although we do not yet know whether its increased expression is cause or consequence of endothelial dysfunction. Notably, the vWF blockade or depletion leads to endothelial protection in cultured cells, animal models of vascular injury, and patients as well. Despite the recent efforts to develop an effective pharmacological strategy, the onset of endothelial dysfunction is still difficult to prevent and remains closely related to adverse clinical outcome. Unraveling the non-hemostatic role of endothelial vWF in the onset of endothelial dysfunction could provide new avenues for protection against vascular injury mediated by AngII.

Angiopoietin-Tie signalling in the cardiovascular and lymphatic systems

Endothelial cells that form the inner layer of blood and lymphatic vessels are important regulators of vascular functions and centrally involved in the pathogenesis of vascular diseases. In addition to the vascular endothelial growth factor (VEGF) receptor pathway, the angiopoietin (Ang)-Tie system is a second endothelial cell specific ligand-receptor signalling system necessary for embryonic cardiovascular and lymphatic development. The Ang-Tie system also regulates postnatal angiogenesis, vessel remodelling, vascular permeability and inflammation to maintain vascular homoeostasis in adult physiology. This system is implicated in numerous diseases where the vasculature has an important contribution, such as cancer, sepsis, diabetes, atherosclerosis and ocular diseases. Furthermore, mutations in the TIE2 signalling pathway cause defects in vascular morphogenesis, resulting in venous malformations and primary congenital glaucoma. Here, we review recent advances in the understanding of the Ang-Tie signalling system, including cross-talk with the vascular endothelial protein tyrosine phosphatase (VE-PTP) and the integrin cell adhesion receptors, focusing on the Ang-Tie system in vascular development and pathogenesis of vascular diseases.

Angiodysplasia in von Willebrand Disease: Understanding the Clinical and Basic Science

Severe and intractable gastrointestinal bleeding caused by angiodysplasia is a debilitating problem for up to 20% of patients with von Willebrand disease (VWD). Currently, the lack of an optimal treatment for this recurrent problem presents an ongoing challenge for many physicians in their management of affected patients. Over the past few years, studies have pointed to a regulatory role for the hemostatic protein, von Willebrand factor (VWF), in angiogenesis, providing a novel target for the modulation of vessel development. This article will review the clinical implications and molecular pathology of angiodysplasia in VWD.

Angiopoietin-2 impairs collateral artery growth associated with the suppression of the infiltration of macrophages in mouse hindlimb ischaemia

Background

Angiopoietin-2 (Ang-2), a ligand of the Tie-2 receptor, plays an important role in maintaining endothelial cells and in destabilizing blood vessels. Collateral artery growth (arteriogenesis) is a key adaptive response to arterial occlusion. It is unknown whether the destabilization of blood vessels by Ang-2 can affect arteriogenesis and modulate mononuclear cell function. This study aimed to investigate the effects of Ang-2 on collateral artery growth.

Methods

Hindlimb ischaemia model was produced in C57BL/6 mice by femoral artery ligation. Blood flow perfusion was measured using a laser Doppler perfusion imager quantitative RT-PCR analysis was applied to identify the level of angiogenic factors.

Results

After the induction of hindlimb ischaemia, blood flow recovery was impaired in mice treated with recombinant Ang-2 protein; this was accompanied by a reduction of peri-collateral macrophage infiltration. In addition, quantitative RT-PCR analysis revealed that Ang-2 treatment decreased monocyte chemotactic protein-1 (MCP-1), platelet-derived growth factor-BB (PDGF-BB) mRNA levels in ischaemic adductor muscles. Ang-2 can lead to macrophage M1/M2 polarization shift inhibition in the ischaemic muscles. Furthermore, Ang-2 reduced the in vitro inflammatory response in macrophages and vascular cells involved in arteriogenesis.

Conclusions

Our results demonstrate that Ang-2 is essential for efficient arteriogenesis, which controls macrophage infiltration.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1055-x) contains supplementary material, which is available to authorized users.

Constitutive Association of Tie1 and Tie2 with Endothelial Integrins is Functionally Modulated by Angiopoietin-1 and Fibronectin

Functional cross-talk between Tie2 and Integrin signaling pathways is essential to coordinate endothelial cell adhesion and migration in response to the extracellular matrix, yet the mechanisms behind this phenomenon are unclear. Here, we examine the possibility that receptor cross-talk is driven through uncharacterized Tie-integrin interactions on the endothelial surface. Using a live cell FRET-based proximity assay, we monitor Tie-integrin receptor recognition and demonstrate that both Tie1 and Tie2 readily associate with integrins α₅ß₁ and α_Vß₃ through their respective ectodomains. Although not required, Tie2-integrin association is significantly enhanced in the presence of the extracellular component and integrin ligand fibronectin. In vitro binding assays with purified components reveal that Tie-integrin recognition is direct, and further demonstrate that the receptor binding domain of the Tie2 ligand Ang-1, but not the receptor binding domain of Ang-2, can independently associate with α₅ß₁ or α_Vß₃. Finally, we reveal that cooperative Tie/integrin interactions selectively stimulate ERK/MAPK signaling in the presence of both Ang-1 and fibronectin, suggesting a molecular mechanism to sensitize Tie2 to extracellular matrix. We provide a mechanistic model highlighting the role of receptor localization and association in regulating distinct signaling cascades and in turn, the angiogenic switch.

Effects of amelogenins on angiogenesis-associated processes of endothelial cells

OBJECTIVE

To study the effects of an amelogenin mixture on integrin-dependent adhesion, DNA synthesis and apoptosis of cultured human dermal microvascular endothelial cells and angiogenesis in an organotypic assay.

METHOD

Immobilised antibodies against specific integrins (alpha-1, alpha-2, alpha-3, alpha-4, alpha-5, alpha-v, ß1, ß2, ß3, ß4, ß6, alpha-vß3, alpha-vß5 and alpha-5ß1) were used to capture treated human dermal microvascular endothelial cells, which were detected colourimetrically. DNA synthesis of the cells was monitored by 5-bromo-2'- deoxyuridine incorporation and apoptosis by a TdT-mediated dUTP nick-end labelling technique. Tubule formation from aortic arches of 13-d-old chick embryos were followed over 48h.

RESULTS

The amelogenin mixture increased microvessel outgrowth by 76% (p < 0.01, n=12) from the aortic explants. Also, amelogenins increased the adhesion (p < 0.01, n = 5) by multiple angiogenesis associated integrin subunits and alpha-vß3, alpha-vß5 and alpha-5ß1 heterodimers on human dermal microvascular endothelial cells at a non-mitogenic concentration (100 µg/ml). Conversely, amelogenins at 1,000 µg/ml decreased microvessel formation possibly due to attenuation of corresponding integrins despite increasing (p < 0.001, n = 8) DNA synthesis. No significant apoptosis was detected in human dermal microvascular endothelial cells cultured on Matrigel with and without amelogenins.

CONCLUSION

Increased surface expression of integrins on endothelial cells may contribute to the proangiogenic property of amelogenins.

Angiogenesis in malignant melanoma

Despite the development of novel therapies, the therapy of malignant melanoma remains challenging. Various studies have shown the vascular system to be pivotal for metastasis in melanoma. Consequently, the effect of various antiangiogenic therapies has been and is being investigated in preclinical and clinical trials. While most studies focus on inhibition of vascular endothelial growth factor (VEGF) signaling, others are aimed at determining the effect of multikinase inhibitors or the inhibition of angiogenic integrin activity. However, overall survival rates have not significantly improved in clinical trials with antiangiogenic agents. Resistance to anti-VEGF monotherapy has been observed in several studies, especially in malignant melanoma. Angiopoietin-2 (Ang-2) represents a promising candidate molecule for antiangiogenic therapy and the effect of Ang-2 inhibitors is currently being explored in first trials. In melanoma, Ang-2 has been shown to be a marker for metastasis formation and represents an interesting therapeutic target molecule. Future studies are required to analyze the effect of a combined approach, using anti-VEGF and anti-Ang-2, as therapy for malignant melanoma.

microRNA miR-142-3p Inhibits Breast Cancer Cell Invasiveness by Synchronous Targeting of WASL, Integrin Alpha V, and Additional Cytoskeletal Elements

MicroRNAs (miRNAs, micro ribonucleic acids) are pivotal post-transcriptional regulators of gene expression. These endogenous small non-coding RNAs play significant roles in tumorigenesis and tumor progression. miR-142-3p expression is dysregulated in several breast cancer subtypes. We aimed at investigating the role of miR-142-3p in breast cancer cell invasiveness. Supported by transcriptomic Affymetrix array analysis and confirmatory investigations at the mRNA and protein level, we demonstrate that overexpression of miR-142-3p in MDA-MB-231, MDA-MB-468 and MCF-7 breast cancer cells leads to downregulation of WASL (Wiskott-Aldrich syndrome-like, protein: N-WASP), Integrin-αV, RAC1, and CFL2, molecules implicated in cytoskeletal regulation and cell motility. ROCK2, IL6ST, KLF4, PGRMC2 and ADCY9 were identified as additional targets in a subset of cell lines. Decreased Matrigel invasiveness was associated with the miR-142-3p-induced expression changes. Confocal immunofluorescence microscopy, nanoscale atomic force microscopy and digital holographic microscopy revealed a change in cell morphology as well as a reduced cell volume and size. A more cortical actin distribution and a loss of membrane protrusions were observed in cells overexpressing miR-142-3p. Luciferase activation assays confirmed direct miR-142-3p-dependent regulation of the 3’-untranslated region of ITGAV and WASL. siRNA-mediated depletion of ITGAV and WASL resulted in a significant reduction of cellular invasiveness, highlighting the contribution of these factors to the miRNA-dependent invasion phenotype. While knockdown of WASL significantly reduced the number of membrane protrusions compared to controls, knockdown of ITGAV resulted in a decreased cell volume, indicating differential contributions of these factors to the miR-142-3p-induced phenotype. Our data identify WASL, ITGAV and several additional cytoskeleton-associated molecules as novel invasion-promoting targets of miR-142-3p in breast cancer.

Regulation of signaling interactions and receptor endocytosis in growing blood vessels

Blood vessels and the lymphatic vasculature are extensive tubular networks formed by endothelial cells that have several indispensable functions in the developing and adult organism. During growth and tissue regeneration but also in many pathological settings, these vascular networks expand, which is critically controlled by the receptor EphB4 and the ligand ephrin-B2. An increasing body of evidence links Eph/ephrin molecules to the function of other receptor tyrosine kinases and cell surface receptors. In the endothelium, ephrin-B2 is required for clathrin-dependent internalization and full signaling activity of VEGFR2, the main receptor for vascular endothelial growth factor. In vascular smooth muscle cells, ephrin-B2 antagonizes clathrin-dependent endocytosis of PDGFRβ and controls the balanced activation of different signal transduction processes after stimulation with platelet-derived growth factor. This review summarizes the important roles of Eph/ephrin molecules in vascular morphogenesis and explains the function of ephrin-B2 as a molecular hub for receptor endocytosis in the vasculature.

Angiopoietin-4 increases permeability of blood vessels and promotes lymphatic dilation

The angiopoietin (Ang) ligands are potential therapeutic targets for lymphatic related diseases, which include lymphedema and cancer. Ang-1 and Ang-2 functions are established, but those of Ang-4 are poorly understood. We used intravital fluorescence microscopy to characterize Ang-4 actions on T241 murine fibrosarcoma-associated vessels in mice. The diameters of lymphatic vessels draining Ang-4- or VEGF-C (positive control)-expressing tumors increased to 123 and 135 μm, respectively, and parental, mock-transduced (negative controls) and tumors expressing Ang-1 or Ang-2 remained at baseline (∼60 μm). Ang-4 decreased human dermal lymphatic endothelial cell (LEC) monolayer permeability by 27% while increasing human dermal blood endothelial cell (BEC) monolayer permeability by 200%. In vivo, Ang-4 stimulated a 4.5-fold increase in tumor-associated blood vessel permeability compared with control when measured using intravital quantitative multiphoton microscopy. Ang-4 activated receptor signaling in both LECs and BECs, evidenced by tyrosine kinase with Ig and endothelial growth factor homology domains-2 (TIE2) receptor, protein kinase B, and Erk1,2 phosphorylation detectable by immunoblotting. These data suggest that Ang-4 actions are mediated through cell-type-specific networks and that lymphatic vessel dilation occurs secondarily to increased vascular leakage. Ang-4 also promoted survival of LECs. Thus, blocking Ang-4 may prune the draining lymphatic vasculature and decrease interstitial fluid pressure (IFP) by reducing vascular permeability.

The roles of ADAMTS in angiogenesis and cancer

Angiogenesis is an indispensable mechanism involved in both physiological processes and various pathological conditions, such as inflammation, aberrant wound healing, tumor progression, and metastasis. Among many angiogenic stimulators and inhibitors, vascular endothelial growth factor (VEGF) is regarded as one of the most important members of the signaling protein family involved in blood vessel formation and maturation. The a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs) proteins are a family of multifunctional proteinases. Such proteolytic enzymes are associated with various physiological processes, such as collagen maturation, organogenesis, angiogenesis, and reproduction. Importantly, deficiency or overexpression of certain ADAMTS proteinases has been shown to be directly involved in a number of serious diseases, including tumor progression and metastasis. This review explores in-depth the connections between ADAMTS proteinases as positive/negative mediators during angiogenesis and VEGF.

Aggressive primary cutaneous B-cell lymphomas show increased Angiopoietin-2-induced angiogenesis

Primary cutaneous large B-cell lymphomas, leg type (PCLBCL/LT) are primary cutaneous B-cell lymphoma (PCBCL) with an intermediate prognosis. Therefore, antracycline-based polychemotherapy combined with rituximab has been recommended as first-line treatment. Yet, despite this regimen, the 5-year survival rate remains 50-66% only. Angiogenesis, the formation of a vascular network, is essential for the pathogenesis of nodal lymphomas. So far, no study has analysed angiogenesis and its key factors in PCLBCL/LT. The present study was aimed at characterizing angiogenesis in PCLBCL/LT to identify the angiogenic molecules as potential therapeutic targets. The intra-tumoral microvessel density (MVD) was assessed by immunohistochemical studies of CD20 and CD31. The MVD was higher in PCLBCL/LT compared with indolent PCBCL. Analyses of open-source microarray data showed correlation between the angiogenic molecule angiopoietin-2 (Ang-2) and pan-endothelial cell markers. ELISA studies determined a shift between Ang-2 and Ang-1 towards Ang-2 in the peripheral blood of PCLBCL/LT patients. Immunofluorescence costainings against the Ang receptor Tie2/angiogenic integrins/CD34 revealed that the vasculature in both aggressive and indolent PCBCL tumors harbours an endothelial cell subpopulation with reduced expression of Tie2. In contrast, the alternative Ang-2 binding partners, angiogenic integrins, are strongly expressed in PCBCL. In line with these findings, downstream targets of Ang-2-integrin signalling, that is phosphorylation of focal adhesion kinase at Tyr397, and sprouting angiogenesis are enhanced in PCLBCL/LT. Our data present Ang-2 as a promising therapeutic target and anti-angiogenic therapy as a new line in treatment of PCLBCL/LT as a hitherto intractable disease.

The TIE Receptor Family

The endothelial TIE1 and TIE2 receptor tyrosine kinases form a distinct subfamily characterized by their unique extracellular domains. Together with the angiopoietin growth factors (ANGPT1, ANGPT2, ANGPT4, also abbreviated as ANG), the TIE receptors form an endothelial specific signaling pathway with important functions in the regulation of lymphatic and cardiovascular development and vascular homeostasis. Angiopoietins exist in multimeric forms that activate the TIE receptors via unique mechanism. In endothelial cell–cell contacts, angiopoietins induce the formation of homomeric in trans TIE receptor complexes extending across the cell junctions, whereas matrix-bound angiopoietin-1 (ANG1) activates the TIE receptors in a cis configuration. In comparison to the vascular endothelial growth factor receptors, the TIE receptors undergo little ubiquitin-mediated degradation after activation, whereas TIE2 signaling is negatively regulated by the vascular endothelial protein tyrosine phosphatase, VE-PTP. ANG1 activation of TIE2 supports vascular stabilization, whereas angiopoietin-2 (ANG2), a context-dependent weak TIE2 agonist/antagonist, promotes pathological tumor angiogenesis, vascular permeability, and inflammation. Recently, ANG2 has been found to mediate some of its vascular destabilizing and angiogenic functions via integrin signalling. The circulating levels of ANG2 are increased in cancer, and in several human diseases associated with inflammation and vascular leak, for example, in sepsis. Blocking of ANG2 has emerged as a potential novel therapeutic strategy for these diseases. In addition, preclinical results demonstrate that genetic TIE1 deletion in mice inhibits the vascularization and growth of tumor isografts and protects from atherosclerosis, with little effect on normal vascular homeostasis in adult mice. The ability of the ANG-TIE pathway to control vessel stability and angiogenesis makes it an interesting vascular target for the treatment of the various diseases.

Endothelial destabilization by angiopoietin-2 via integrin β1 activation

Angiopoietins regulate vascular homeostasis via the endothelial Tie receptor tyrosine kinases. Angiopoietin-1 (Ang1) supports endothelial stabilization via Tie2 activation. Angiopoietin-2 (Ang2) functions as a context-dependent Tie2 agonist/antagonist promoting pathological angiogenesis, vascular permeability and inflammation. Elucidating Ang2-dependent mechanisms of vascular destablization is critical for rational design of angiopoietin antagonists that have demonstrated therapeutic efficacy in cancer trials. Here, we report that Ang2, but not Ang1, activates β1-integrin, leading to endothelial destablization. Autocrine Ang2 signalling upon Tie2 silencing, or in Ang2 transgenic mice, promotes β1-integrin-positive elongated matrix adhesions and actin stress fibres, regulating vascular endothelial-cadherin-containing cell–cell junctions. The Tie2-silenced monolayer integrity is rescued by β1-integrin, phosphoinositide-3 kinase or Rho kinase inhibition, and by re-expression of a membrane-bound Tie2 ectodomain. Furthermore, Tie2 silencing increases, whereas Ang2 blocking inhibits transendothelial tumour cell migration in vitro. These results establish Ang2-mediated β1-integrin activation as a promoter of endothelial destablization, explaining the controversial vascular functions of Ang1 and Ang2.

Angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) have opposing effects on vascular stability through their receptor Tie2, but there is evidence for Tie2-independent functions of Ang2. Here, Hakanpaa et al. show that Ang2 directly activates β1-integrin, leading to rearrangement of the actin cytoskeleton and decreased VE-cadherin in cell–cell junctions.