ENDOGLIN is dispensable for vasculogenesis, but required for vascular endothelial growth factor-induced angiogenesis

Targeting BMP2 for therapeutic strategies against hepatocellular carcinoma

OBJECTIVES

This study aimed to investigate the role of BMP2 in hepatocellular carcinoma (HCC) growth and metastasis using a dual approach combining single-cell RNA sequencing (scRNA-seq) and bulk RNA-seq.

METHODS

scRNA-seq data from the GEO database and bulk RNA-seq data from the TCGA database were analyzed. Differentially expressed marker genes of endothelial cells were identified and analyzed using enrichment analysis, PPI analysis, correlation analysis, and GSEA. In vitro, experiments were conducted using the Huh-7 HCC cell line, and in vivo, models of HCC growth and metastasis were established by knocking down BMP2.

RESULTS

The scRNA-seq analysis identified BMP2 as a key marker gene in endothelial cells of HCC samples. Elevated BMP2 expression correlated with poor prognosis in HCC. In vitro experiments showed that silencing BMP2 inhibited the proliferation, migration, and invasion of liver cancer cells. In vivo studies confirmed increased BMP2 expression in HCC tissues, promoting angiogenesis and HCC growth.

CONCLUSION

This study highlights the role of BMP2 in tumor angiogenesis and HCC progression. Targeting BMP2 could be a promising therapeutic strategy against HCC.

Exploring the tumor micro-environment in primary and metastatic tumors of different ovarian cancer histotypes

Ovarian cancer is a highly heterogeneous disease consisting of at least five different histological subtypes with varying clinical features, cells of origin, molecular composition, risk factors, and treatments. While most single-cell studies have focused on High grade serous ovarian cancer, a comprehensive landscape of the constituent cell types and their interactions within the tumor microenvironment are yet to be established in the different ovarian cancer histotypes. Further characterization of tumor progression, metastasis, and various histotypes are also needed to connect molecular signatures to pathological grading for personalized diagnosis and tailored treatment. In this study, we leveraged high-resolution single-cell RNA sequencing technology to elucidate the cellular compositions on 21 solid tumor samples collected from 12 patients with six ovarian cancer histotypes and both primary (ovaries) and metastatic (omentum, rectum) sites. The diverse collection allowed us to deconstruct the histotypes and tumor site-specific expression patterns of cells in the tumor, and identify key marker genes and ligand-receptor pairs that are active in the ovarian tumor microenvironment. Our findings can be used in improving precision disease stratification and optimizing treatment options.

Defining the clinical validity of genes reported to cause pulmonary arterial hypertension

PURPOSE

Pulmonary arterial hypertension (PAH) is a rare, progressive vasculopathy with significant cardiopulmonary morbidity and mortality. Genetic testing is currently recommended for adults diagnosed with heritable, idiopathic, anorexigen-, hereditary hemorrhagic telangiectasia-, and congenital heart disease-associated PAH, PAH with overt features of venous/capillary involvement, and all children diagnosed with PAH. Variants in at least 27 genes have putative evidence for PAH causality. Rigorous assessment of the evidence is needed to inform genetic testing.

METHODS

An international panel of experts in PAH applied a semi-quantitative scoring system developed by the NIH Clinical Genome Resource to classify the relative strength of evidence supporting PAH gene-disease relationships based on genetic and experimental evidence.

RESULTS

Twelve genes (BMPR2, ACVRL1, ATP13A3, CAV1, EIF2AK4, ENG, GDF2, KCNK3, KDR, SMAD9, SOX17, and TBX4) were classified as having definitive evidence and 3 genes (ABCC8, GGCX, and TET2) with moderate evidence. Six genes (AQP1, BMP10, FBLN2, KLF2, KLK1, and PDGFD) were classified as having limited evidence for causal effects of variants. TOPBP1 was classified as having no known PAH relationship. Five genes (BMPR1A, BMPR1B, NOTCH3, SMAD1, and SMAD4) were disputed because of a paucity of genetic evidence over time.

CONCLUSION

We recommend that genetic testing includes all genes with definitive evidence and that caution be taken in the interpretation of variants identified in genes with moderate or limited evidence. Genes with no known evidence for PAH or disputed genes should not be included in genetic testing.

SERUM SOLUBLE ENDOGLIN IN PEDIATRIC SEPTIC SHOCK-ASSOCIATED MULTIPLE ORGAN DYSFUNCTION SYNDROME

ABSTRACT

Background: Endothelial activation is a key driver of multiple organ dysfunction syndrome (MODS). Soluble endoglin (sENG) is expressed by mature and progenitor endothelial cells and thought to have angiogenic properties. We sought to determine the association between sENG and pediatric sepsis-associated MODS. Methods: Prospective observational study of pediatric septic shock. Primary outcome of interest was complicated course-a composite of death by (or) MODS on day 7 of illness. Secondary outcomes included individual organ dysfunctions. Endothelial biomarkers including sENG were measured using multiplex Luminex assays among patients with existing data on the Pediatric Sepsis Biomarker Risk Model (PERSEVERE-II) data. Multivariable regression was used to test the independent association between sENG and clinical outcomes. Serum sENG concentrations across PERSEVERE-II mortality risk strata and correlations with established markers of endothelial dysfunction were determined. Results: Three hundred six critically ill children with septic shock were included. Serum sENG concentrations were higher among those with primary and secondary outcomes of interest, with the exception of acute neurological dysfunction. Soluble endoglin was independently associated with increased odds of complicated course (adjusted odds ratio, 1.53; 95% confidence interval, 1.02-2.27; P = 0.038) and acute renal dysfunction (adjusted odds ratio, 1.84; 95% confidence interval, 1.18-2.876; P = 0.006). Soluble endoglin demonstrated graded responses across PERSEVERE-II risk strata and was positively correlated with endothelial biomarkers, except angiopoietin-1. Conclusions: Serum sENG is independently associated with complicated course and acute renal dysfunction in pediatric septic shock. Future studies are required to validate our observational data, and mechanistic studies are necessary to elucidate whether endoglin plays an organ-specific role in the development or resolution of acute renal dysfunction in sepsis.

Antiangiogenic potential of Lepista nuda extract suppressing MAPK/p38 signaling-mediated developmental angiogenesis in zebrafish and HUVECs

The medicinal properties of natural/edible plant products and their use are popular in traditional practice owing to their nutritional contents with little to no side effects. Lepista nuda (L. nuda), an edible mushroom (Clitocybe nuda, commonly known as blewit), has attracted researchers to evaluate its contents and the mechanism of its activities. In the current study, we focused on evaluating the antiangiogenic effects of L. nuda water extract on zebrafish development and in vitro human umbilical vein endothelial cell (HUVEC) tube formation. Bioactive components such as ergothioneine, eritadenine, and adenosine were identified and quantified by HPLC analysis. The L. nuda extract showed antiangiogenic properties and inhibited intersegmental vessel (ISV), caudal vein plexus (CVP), hyaloid vessel (HV), and subintestinal vessel (SIV) development in Tg (fli1: EGFP) zebrafish embryos. The expression of angiogenesis-related genes (vegfaa, kdrl, vegfba, flt1, kdr) was affected following L. nuda extract treatment. L. nuda extract attenuated in vitro HUVEC tube formation, migration, and invasion. Furthermore, inhibition of MAPK/p38 signaling and depletion of proangiogenic genes, including growth factors (fgf, ang2, and vegfa); primary and accessory receptors (tie2, vegfr2, and eng); MMPs (mmp1 and mmp2); and cytokines (il-1α, il-1β, il-6, and tnf-α) was observed in HUVECs following L. nuda treatment. An in vivo zebrafish xenograft assay showed that L. nuda extract inhibited HuCCT1 cell-induced SIV sprouting in HuCCT1-injected embryos. Collectively, the results suggest that L. nuda could be a potential inhibitor of angiogenesis limiting cancer progression.

Timely Wound Healing is Dependent upon Endothelial but not Hair Follicle Stem Cell Toll-like Receptor 2 Signaling

As a part of innate immunity, Toll-like receptor 2 (TLR2) plays an important function in most defensive responses of the organism, including but not limited to infections. Cutaneous injury, one of the most common challenges for mammals, mobilizes a number of cell types, including epithelial, immune, and vascular cells for timely tissue repair. However, in contrast to immune cells, little is known about TLR2 function on non-immune cells during skin regeneration. Here, we used two tissue-specific conditional TLR2 knockout mouse lines to address the impact of TLR2 in endothelial and hair follicle stem cells (HFSCs) on cutaneous wound healing. The loss of TLR2 on endothelial cells diminishes their ability to migrate, sprout, and proliferate in response to specific TLR2 ligands, and also reduces the secretion of key pro-angiogenic factors. Lack of TLR2 on endothelial cells prolongs wound healing due to diminished angiogenesis. TLR2 is expressed in key structures of hair follicle including HFSCs, secondary hair germ, and dermal papilla. Despite the prominent role for HFSCs in skin regeneration, excision of TLR2 from HFSCs has no impact on their proliferation or wound healing potential. Our study demonstrates that timely tissue regeneration after skin injury is dependent upon endothelial TLR2 for robust angiogenesis, while HFSC TLR2 is dispensable.

Cerebral Hemorrhage: Pathophysiology, Treatment, and Future Directions

Intracerebral hemorrhage (ICH) is a devastating form of stroke with high morbidity and mortality. This review article focuses on the epidemiology, cause, mechanisms of injury, current treatment strategies, and future research directions of ICH. Incidence of hemorrhagic stroke has increased worldwide over the past 40 years, with shifts in the cause over time as hypertension management has improved and anticoagulant use has increased. Preclinical and clinical trials have elucidated the underlying ICH cause and mechanisms of injury from ICH including the complex interaction between edema, inflammation, iron-induced injury, and oxidative stress. Several trials have investigated optimal medical and surgical management of ICH without clear improvement in survival and functional outcomes. Ongoing research into novel approaches for ICH management provide hope for reducing the devastating effect of this disease in the future. Areas of promise in ICH therapy include prognostic biomarkers and primary prevention based on disease pathobiology, ultra-early hemostatic therapy, minimally invasive surgery, and perihematomal protection against inflammatory brain injury.

Endoglin Modulates TGFβR2 Induced VEGF and Proinflammatory Cytokine Axis Mediated Angiogenesis in Prolonged DEHP-Exposed Breast Cancer Cells

Angiogenesis is the process of vascular network development and plays a crucial role in cancer growth, progression, and metastasis. Phthalates are a class of environmental pollutants that have detrimental effects on human health and are reported to increase cancer risk. However, the interplay between phthalate exposure and angiogenesis has not been investigated thoroughly. In this study, we investigated the effect of prolonged di (2-ethylhexyl) phthalate (DEHP) treatment on the angiogenic potential of triple-negative breast cancer. MDA-MB-231 cells were exposed to physiological concentrations of DEHP for more than three months. Prolonged DEHP exposure induced angiogenesis in breast cancer cells. Endoglin (ENG)/CD105 is a membrane glycoprotein and an auxiliary receptor of the TGFβ receptor complex. In endothelial cells, ENG is highly expressed and it is a prerequisite for developmental angiogenesis. A literature review highlights endoglin as a well-known mesenchymal stem cell marker responsible for vascular development and angiogenesis. NGS analysis showed that endoglin overexpression in DEHP-exposed MDA-MB-231 cells correlated with tumor development and growth. An in vivo zebrafish xenograft assay showed that VEGFA induced sprouting of the subintestinal vein (SIV) in embryos injected with DEHP-exposed cells. Endoglin knockdown reduced SIV sprouting and VEGFA expression in zebrafish embryos. An in vitro HUVEC tube formation assay showed that endoglin depletion reversed DEHP-induced VEGF-mediated HUVEC tube formation in coculture. DEHP-induced endoglin activated TGFβ/SMAD3/VEGF and MAPK/p38 signaling in MDA-MB-231 cells. A cytokine angiogenesis antibody array showed induced expression of the inflammatory cytokines IL1α, IL1β, IL6, and IL8, along with GMCSF and VEGF. Endoglin knockdown reversed DEHP-induced activation of the TGFβ/SMAD3/VEGF signaling axis, MAPK/p38 signaling, and cytokine regulation, limiting angiogenesis potential both in vivo and in vitro. Targeting endoglin might serve as a potential alternative treatment to control angiogenesis, leading to metastasis and limiting cancer progression.

Safety and Tolerability of Intravitreal Carotuximab (DE-122) in Patients With Persistent Exudative Age-Related Macular Degeneration: A Phase I Study

Purpose

Carotuximab (DE-122) is a novel endoglin antibody that exhibits potent anti-angiogenic activity. The aim of this study was to evaluate the safety and tolerability of a single intravitreal injection of four ascending doses of carotuximab in patients with persistent exudative age-related macular degeneration (AMD).

Methods

In an open-label, dose-escalating, sequential cohort study, patients with persistent exudative AMD were assigned to an intravitreal injection of carotuximab 0.5 mg, 1.0 mg, 2.0 mg, or 4.0 mg (n = 3 per group). Safety and change in central subfield thickness (CST), as measured by spectral domain–optical coherence tomography, were assessed from baseline until day 90. Rescue therapy with an anti-vascular endothelial growth factor medication was allowed on days 8, 30, and 60.

Results

Seven patients (58%) experienced at least one adverse event (AE), including five patients (41.7%) who experienced one or more AEs in the study eye and two patients (16.7%) who experienced one or more non-ocular AEs. Posterior eye deposits were reported in one patient 2 days after receiving 1.0 mg, but they resolved spontaneously by day 43. A >50-µm reduction in CST on two consecutive visits was observed in four patients (33%), including one patient in each dose cohort.

Conclusions

In this study, carotuximab was generally well tolerated, with no serious AEs reported, when administered as a single intravitreal injection to patients with persistent exudative AMD.

Translational Relevance

Further characterization of the safety and efficacy of carotuximab will be needed to determine what role it may have in the treatment of exudative AMD.

Endoglin deficiency impairs VEGFR2 but not FGFR1 or TIE2 activation and alters VEGF-mediated cellular responses in human primary endothelial cells

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disease characterized by vascular dysplasia. Mutations of the endoglin (ENG) gene that encodes a co-receptor of the transforming growth factor β1 signaling pathway cause type I HHT. ENG is primarily expressed in endothelial cells (ECs), but its interaction with other key angiogenic pathways to control angiogenesis has not been well addressed. The aim of this study is to investigate ENG interplay with VEGFR2, FGFR1 and TIE2 in primary human ECs. ENG was knocked-down with siRNA in human umbilical vein ECs (HUVECs) and human lung microvascular ECs (HMVEC-L). Gene expression was measured by RT-qPCR and Western blotting. Cell signaling pathway activation was analyzed by detecting phosphor-ERK and phosphor-AKT levels. Cell migration and apoptosis were assessed using the Boyden chamber assay and the CCK-8 Kit, respectively. Loss of ENG in HUVECs led to significantly reduced expression of VEGFR2 but not TIE2 or FGFR1, which was also confirmed in HMVEC-L. HUVECs lacking ENG had significantly lower levels of active Rac1 and a substantial reduction of the transcription factor Sp1, an activator of VEGFR2 transcription, in nuclei. Furthermore, VEGF- but not bFGF- or angiopoietin-1-induced phosphor-ERK and phosphor-AKT were suppressed in ENG deficient HUVECs. Functional analysis revealed that ENG knockdown inhibited cell migratory but enhanced anti-apoptotic activity induced by VEGF. In contrast, bFGF, angiopoietin-1 and -2 induced HUVEC migration and anti-apoptotic activities were not affected by ENG knockdown. In conclusion, ENG deficiency alters the VEGF/VEGFR2 pathway, which may play a role in HHT pathogenesis.

3D Collagen Hydrogel Promotes In Vitro Langerhans Islets Vascularization through ad-MVFs Angiogenic Activity

Adipose derived microvascular fragments (ad-MVFs) consist of effective vascularization units able to reassemble into efficient microvascular networks. Because of their content in stem cells and related angiogenic activity, ad-MVFs represent an interesting tool for applications in regenerative medicine. Here we show that gentle dissociation of rat adipose tissue provides a mixture of ad-MVFs with a length distribution ranging from 33–955 μm that are able to maintain their original morphology. The isolated units of ad-MVFs that resulted were able to activate transcriptional switching toward angiogenesis, forming tubes, branches, and entire capillary networks when cultured in 3D collagen type-I hydrogel. The proper involvement of metalloproteases (MMP2/MMP9) and serine proteases in basal lamina and extracellular matrix ECM degradation during the angiogenesis were concurrently assessed by the evaluation of alpha-smooth muscle actin (αSMA) expression. These results suggest that collagen type-I hydrogel provides an adequate 3D environment supporting the activation of the vascularization process. As a proof of concept, we exploited 3D collagen hydrogel for the setting of ad-MVF–islet of Langerhans coculture to improve the islets vascularization. Our results suggest potential employment of the proposed in vitro system for regenerative medicine applications, such as the improving of the islet of Langerhans engraftment before transplantation.

PS1 FAD mutants decrease ephrinB2-regulated angiogenic functions, ischemia-induced brain neovascularization and neuronal survival

Microvascular pathology and ischemic lesions contribute substantially to neuronal dysfunction and loss that lead to Alzheimer disease (AD). To facilitate recovery, the brain stimulates neovascularization of damaged tissue via sprouting angiogenesis, a process regulated by endothelial cell (EC) sprouting and the EphB4/ephrinB2 system. Here, we show that in cultures of brain ECs, EphB4 stimulates the VE-cadherin/Rok-α angiogenic complexes known to mediate sprouting angiogenesis. Importantly, brain EC cultures expressing PS1 FAD mutants decrease the EphB4-stimulated γ-secretase cleavage of ephrinB2 and reduce production of the angiogenic peptide ephrinB2/CTF2, the VE-cadherin angiogenic complexes and EC sprouting and tube formation. These data suggest that FAD mutants may attenuate ischemia-induced brain angiogenesis. Supporting this hypothesis, ischemia-induced VE-cadherin angiogenic complexes, levels of neoangiogenesis marker Endoglin, vascular density, and cerebral blood flow recovery, are all decreased in brains of mouse models expressing PS1 FAD mutants. Ischemia-induced brain neuronal death and cognitive deficits also increase in these mice. Furthermore, a small peptide comprising the C-terminal sequence of peptide ephrinB2/CTF2 rescues angiogenic functions of brain ECs expressing PS1 FAD mutants. Together, our data show that PS1 FAD mutations impede the EphB4/ephrinB2-mediated angiogenic functions of ECs and impair brain neovascularization, neuronal survival and cognitive recovery following ischemia. Furthermore, our data reveal a novel brain angiogenic mechanism targeted by PS1 FAD mutants and a potential therapeutic target for ischemia-induced neurodegeneration. Importantly, FAD mutant effects occur in absence of neuropathological hallmarks of AD, supporting that such hallmarks may form downstream of mutant effects on neoangiogenesis and neuronal survival.

Pulmonary Vascular Complications in Hereditary Hemorrhagic Telangiectasia and the Underlying Pathophysiology

In this review, we discuss the role of transforming growth factor-beta (TGF-β) in the development of pulmonary vascular disease (PVD), both pulmonary arteriovenous malformations (AVM) and pulmonary hypertension (PH), in hereditary hemorrhagic telangiectasia (HHT). HHT or Rendu-Osler-Weber disease is an autosomal dominant genetic disorder with an estimated prevalence of 1 in 5000 persons and characterized by epistaxis, telangiectasia and AVMs in more than 80% of cases, HHT is caused by a mutation in the ENG gene on chromosome 9 encoding for the protein endoglin or activin receptor-like kinase 1 (ACVRL1) gene on chromosome 12 encoding for the protein ALK-1, resulting in HHT type 1 or HHT type 2, respectively. A third disease-causing mutation has been found in the SMAD-4 gene, causing a combination of HHT and juvenile polyposis coli. All three genes play a role in the TGF-β signaling pathway that is essential in angiogenesis where it plays a pivotal role in neoangiogenesis, vessel maturation and stabilization. PH is characterized by elevated mean pulmonary arterial pressure caused by a variety of different underlying pathologies. HHT carries an additional increased risk of PH because of high cardiac output as a result of anemia and shunting through hepatic AVMs, or development of pulmonary arterial hypertension due to interference of the TGF-β pathway. HHT in combination with PH is associated with a worse prognosis due to right-sided cardiac failure. The treatment of PVD in HHT includes medical or interventional therapy.

A novel method for visualizing and tracking endogenous mRNA in a specific cell population in pathological neovascularization

Diabetic retinopathy, retinopathy of prematurity and retinal vein occlusion are potentially blinding conditions largely due to their respective neovascular components. The development of real-time in vivo molecular imaging methods, to assess levels of retinal neovascularization (NV), would greatly benefit patients afflicted with these conditions. mRNA hybridization techniques offer a potential method to image retinal NV. The success of these techniques hinges on the selection of a target mRNA whose tissue levels and spatial expression patterns correlate closely with disease burden. Using a model of oxygen-induced retinopathy (OIR), we previously observed dramatic increases in retinal endoglin that localized to neovascular structures (NV), directly correlating with levels of neovascular pathology. Based on these findings, we have investigated Endoglin mRNA as a potential marker for imaging retinal NV in OIR mice. Also of critical importance, is the application of innovative technologies capable of detecting mRNAs in living systems with high sensitivity and specificity. To detect and visualize endoglin mRNA in OIR mice, we have designed and synthesized a novel imaging probe composed of short-hairpin anti-sense (AS) endoglin RNA coupled to a fluorophore and black hole quencher (AS-Eng shRNA). This assembly allows highly sensitive fluorescence emission upon hybridization of the AS-Eng shRNA to cellular endoglin mRNA. The AS-Eng shRNA is further conjugated to a diacyl-lipid (AS-Eng shRNA–lipid referred to as probe). The lipid moiety binds to serum albumin facilitating enhanced systemic circulation of the probe. OIR mice received intraperitoneal injections of AS-Eng shRNA–lipid. Ex vivo imaging of their retinas revealed specific endoglin mRNA dependent fluorescence superimposed on neovascular structures. Room air mice receiving AS-Eng shRNA–lipid and OIR mice receiving a non-sense control probe showed little fluorescence activity. In addition, we found that cells in neovascular lesions labelled with endoglin mRNA dependent fluorescence, co-labelled with the macrophage/microglia-associated marker IBA1. Others have shown that cells expressing macrophage/microglia markers associate with retinal neovascular structures in proportion to disease burden. Hence we propose that our probe may be used to image and to estimate the levels of retinal neovascular disease in real-time in living systems.

Endoglin Targeting: Lessons Learned and Questions That Remain

Approximately 30 years ago, endoglin was identified as a transforming growth factor (TGF)-β coreceptor with a crucial role in developmental biology and tumor angiogenesis. Its selectively high expression on tumor vessels and its correlation with poor survival in cancer patients led to the exploration of endoglin as a therapeutic target for cancer. The endoglin neutralizing antibody TRC105 (Carotuximab^®, Tracon Pharmaceuticals (San Diego, CA, USA) was subsequently tested in a wide variety of preclinical cancer models before being tested in phase I-III clinical studies in cancer patients as both a monotherapy and in combination with other chemotherapeutic and anti-angiogenic therapies. The combined data of these studies have revealed new insights into the role of endoglin in angiogenesis and its expression and functional role on other cells in the tumor microenvironment. In this review, we will summarize the preclinical work, clinical trials and biomarker studies of TRC105 and explore what these studies have enabled us to learn and what questions remain unanswered.

Targeting Endoglin-Expressing Regulatory T Cells in the Tumor Microenvironment Enhances the Effect of PD1 Checkpoint Inhibitor Immunotherapy

PURPOSE

Endoglin is a coreceptor for TGFβ ligands that is highly expressed on proliferating endothelial cells and other cells in the tumor microenvironment. Clinical studies have noted increased programmed cell death (PD)-1 expression on cytotoxic T cells in the peripheral blood of patients with cancer treated with TRC105, an endoglin-targeting antibody. In this study, we investigated the combination of endoglin antibodies (TRC105 and M1043) with an anti-PD1 antibody.

EXPERIMENTAL DESIGN

The combination anti-endoglin/anti-PD1 antibodies was tested in four preclinical mouse models representing different stages of cancer development. To investigate the underlying mechanism, Fc-receptor-knockout mice were used complemented with depletion of multiple immune subsets in mice. Tumor growth and the composition of immune infiltrate were analyzed by flow cytometry. Finally, human colorectal cancer specimens were analyzed for presence of endoglin-expressing regulatory T cells (Treg).

RESULTS

In all models, the combination of endoglin antibody and PD1 inhibition produced durable tumor responses, leading to complete regressions in 30% to 40% of the mice. These effects were dependent on the presence of Fcγ receptors, indicating the involvement of antibody-dependent cytotoxic responses and the presence of CD8⁺ cytotoxic T cells and CD4⁺ Th cells. Interestingly, treatment with the endoglin antibody, TRC105, significantly decreased the number of intratumoral Tregs. Endoglin-expressing Tregs were also detected in human colorectal cancer specimens.

CONCLUSIONS

Taken together, these data provide a rationale for combining TRC105 and anti-PD1 therapy and provide additional evidence of endoglin's immunomodulatory role.

Pathogenic variants in the ABCC6 gene are associated with an increased risk for ischemic stroke

Ischemic stroke causes a high mortality and morbidity worldwide. It results from a complex interplay of incompletely known environmental and genetic risk factors. We investigated the ABCC6 gene as a candidate risk factor for ischemic stroke because of the increased ischemic stroke incidence in the autosomal recessive disorder pseudoxanthoma elasticum, caused by biallelic pathogenic ABCC6 variants, the higher cardiovascular risk in heterozygous carriers and the established role of ABCC6 dysfunction in myocardial ischemia. We established segregation of a known pathogenic ABCC6 variant (p.[Arg1314Gln]) in 11/19 family members of an ischemic stroke patient in a large multigenerational family suffering from ischemic stroke and/or cardiovascular disease at a relatively young age. In an independent case-control study in 424 ischemic stroke patients and 250 healthy controls, pathogenic ABCC6 variants were 4.9 times more frequent (P = 0.036; 95% CI 1.11-21.33) in the ischemic stroke patient cohort. To study cellular consequences of ABCC6 deficiency in the brain, immunostaining of brain sections in Abcc6-deficient mice and wild-type controls were performed. An upregulation of Bmp4 and Eng and a downregulation of Alk2 was identified in Abcc6-/- mice, suggesting an increase in apoptosis and angiogenesis. As both of these processes are induced in ischemia, we propose that a pro-ischemic state may explain the higher risk to suffer from ischemic stroke in patients carrying a pathogenic ABCC6 variant, as this may lower the threshold to develop acute ischemic events in these patients. In conclusion, this study identified heterozygous ABCC6 variants as a risk factor for ischemic stroke. Further, dysregulation of Bmp (Bmp4, Alk2) and Tgfβ (Eng) signaling in the brain of Abcc6-/- mice could lead to a pro-ischemic state, lowering the threshold to develop acute ischemic events. These data demonstrate the importance of a molecular analysis of the ABCC6 gene in patients diagnosed with cryptogenic ischemic stroke.

Effects of Oral Anticoagulant Therapy on Gene Expression in Crosstalk between Osteogenic Progenitor Cells and Endothelial Cells

Direct oral anti-coagulants (DOACs) are employed in clinical practice for the prevention and treatment of recurrent venous thromboembolism and for the prevention of stroke in non-valvular atrial fibrillation. DOACs directly and reversibly inhibit activated factor X or thrombin and can interfere with other pathophysiological processes such as inflammation, lipid metabolism, and bone turnover. We aimed to evaluate the possible effects of DOACs on osteogenesis and angiogenesis. We treated 34 patients affected by cardiovascular disorders with DOACs; biochemical and molecular analyses were performed before and after three months of treatment. Circulating progenitors (CPs; CD34⁻, CD45⁻, CD14⁻, CD73⁺, CD105⁺), which share typical bone marrow stem cell (MSCs) features, were harvested from peripheral blood of the study subjects to monitor the expression of osteogenesis-related genes RUNX2 and SPARC. Human umbilical vein endothelial cells (HUVECs) were used to probe angiogenesis-related VEGF, CD31, and CD105 gene expression. We performed co-culture experiments using a commercial human mesenchymal stem cells line (hMSCs) obtained from bone marrow and HUVECs. Clinical parameters related to bone metabolism, coagulation, renal and liver function, and the lipid profile were evaluated. Values of the C-terminal telopeptide type I collagen (CTX) increased after the treatment. We found a significant increase in osteogenesis marker gene expression in CPs after three months of anticoagulant therapy. An increase in the RUNX2 expression determinant alone was detected instead in hMSCs co-cultured with HUVECs in the presence of treated patients’ sera. The VEGF, CD31, and CD105 marker genes appeared to be significantly upregulated in HUVECs co-cultured with hMSCs in the presence of treated patients’ sera. Under these conditions, new vessel formation increased as well. Our results highlight an unexpected influence of DOAC therapy on osteogenic commitment and vascular endothelial function promotion.

Cardiac Progenitor Cell-Derived Extracellular Vesicles Reduce Infarct Size and Associate with Increased Cardiovascular Cell Proliferation

Cell transplantation studies have shown that injection of progenitor cells can improve cardiac function after myocardial infarction (MI). Transplantation of human cardiac progenitor cells (hCPCs) results in an increased ejection fraction, but survival and integration are low. Therefore, paracrine factors including extracellular vesicles (EVs) are likely to contribute to the beneficial effects. We investigated the contribution of EVs by transplanting hCPCs with reduced EV secretion. Interestingly, these hCPCs were unable to reduce infarct size post-MI. Moreover, injection of hCPC-EVs did significantly reduce infarct size. Analysis of EV uptake showed cardiomyocytes and endothelial cells primarily positive and a higher Ki67 expression in these cell types. Yes-associated protein (YAP), a proliferation marker associated with Ki67, was also increased in the entire infarcted area. In summary, our data suggest that EV secretion is the driving force behind the short-term beneficial effect of hCPC transplantation on cardiac recovery after MI.

Molecular signature of progenitor cells isolated from young and adult human hearts

The loss of endogenous cardiac regenerative capacity within the first week of postnatal life has intensified clinical trials to induce cardiac regeneration in the adult mammalian heart using different progenitor cell types. We hypothesized that donor age-related phenotypic and functional characteristics of cardiac progenitor cells (CPC) account for mixed results of cell-based cardiac repair. We compared expression profiles and cell turnover rates of human heart-derived c-kit^pos progenitors (c-kit^pos CPC) and cardiosphere-derived cells (CDC) from young and adult donor origin and studied their in vitro angiogenic and cardiac differentiation potential, which can be relevant for cardiac repair. We report that 3-dimensional CDC expansion recapitulates a conducive environment for growth factor and cytokine release from adult donor cells (aCDC) that optimally supports vascular tube formation and vessel sprouting. Transdifferentiation capacity of c-kit^pos CPCs and CDCs towards cardiomyocyte-like cells was modest, however, most notable in young c-kit^pos cells and adult CDCs. Progenitors isolated with different methods thus show cell- and donor-specific characteristics that may account for variable contributions in functional myocardial recovery.

Exploring the in situ expression of vascular endothelial growth factor and endoglin in pemphigus foliaceus variants and pemphigus vulgaris

BACKGROUND

Erythroderma is a severe manifestation of pemphigus foliaceus (PF), a blistering disease mediated by IgG autoantibodies against desmoglein 1. Increasing evidence supports the contribution of angiogenic mediators in the pathogenesis of erythroderma.

OBJECTIVE

To evaluate the in situ expression of vascular endothelial growth factor (VEGF) and endoglin in patients with PF with erythroderma.

METHODS

Formalin-fixed paraffin-embedded skin samples obtained from patients with erythrodermic PF (n = 19; 12 patients with endemic PF), non-erythrodermic PF (n = 17), pemphigus vulgaris (PV; n = 10), psoriasis (n = 10) and healthy individuals (HI; n = 10) were processed in an automated immunohistochemistry platform utilizing anti-VEGF and anti-endoglin as primary antibodies. Reactivity was evaluated both manually (0 = negative; 1+ = mild; 2+ = intense) and through an automated microvessel analysis algorithm.

RESULTS

Vascular endothelial growth factor expression in erythrodermic PF was higher than in non-erythrodermic PF (P = 0.034) and in HI (P = 0.004), and similar to psoriasis (P = 0.667) and PV (P = 0.667). In non-erythrodermic PF, VEGF positivity was similar to HI (P = 0.247), and lower than psoriasis (P = 0.049) and PV (P = 0.049). Both erythrodermic and non-erythrodermic PF presented similar endoglin expression (P = 0.700). In addition, endoglin positivity during erythrodermic PF was similar to psoriasis (P = 0.133) and lower than PV (P = 0.0009). Increased expression of in situVEGF suggests that healing processes are triggered in response to tissue damage led by autoantibodies in PF, especially during erythroderma. Reduced endoglin positivity suggests that an unbalanced angiogenesis may occur during erythrodermic PF. Further studies may help to confirm if the regulation of VEGF and endoglin expression in patients with PF can contribute to control the healing process and enable disease remission.

CONCLUSION

Overexpression of VEGF in erythrodermic PF as well as in PV and psoriasis points out a dysregulated repair process in severe forms of these diseases and suggests VEGF and endoglin could act as prognostic markers and future therapeutic targets to enable proper healing in PF.

Cardiosphere-Derived Cells Require Endoglin for Paracrine-Mediated Angiogenesis

Clinical trials of stem cell therapy to treat ischemic heart disease primarily use heterogeneous stem cell populations. Small benefits occur via paracrine mechanisms that include stimulating angiogenesis, and increased understanding of these mechanisms would help to improve patient outcomes. Cardiosphere-derived-cells (CDCs) are an example of these heterogeneous stem cell populations, cultured from cardiac tissue. CDCs express endoglin, a co-receptor that binds specific transforming growth factor β (TGFβ) family ligands, including bone morphogenetic protein 9 (BMP9). In endothelial cells endoglin regulates angiogenic responses, and we therefore hypothesized that endoglin is required to promote the paracrine pro-angiogenic properties of CDCs. Cre/LoxP technology was used to genetically manipulate endoglin expression in CDCs, and we found that the pro-angiogenic properties of the CDC secretome are endoglin dependent both in vitro and in vivo. Importantly, BMP9 pre-treatment of endoglin-depleted CDCs restores their pro-angiogenic paracrine properties. As BMP9 signaling is normally required to maintain endoglin expression, we propose that media containing BMP9 could be critical for therapeutic CDC preparation.

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It is essential to understand how stem cell populations generate paracrine benefit

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Endoglin is necessary for the pro-angiogenic properties of the CDC secretome

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Pro-angiogenic defects of endoglin-depleted CDCs can be rescued by BMP9

TGF-β Signaling in Control of Cardiovascular Function

Genetic studies in animals and humans indicate that gene mutations that functionally perturb transforming growth factor β (TGF-β) signaling are linked to specific hereditary vascular syndromes, including Osler-Rendu-Weber disease or hereditary hemorrhagic telangiectasia and Marfan syndrome. Disturbed TGF-β signaling can also cause nonhereditary disorders like atherosclerosis and cardiac fibrosis. Accordingly, cell culture studies using endothelial cells or smooth muscle cells (SMCs), cultured alone or together in two- or three-dimensional cell culture assays, on plastic or embedded in matrix, have shown that TGF-β has a pivotal effect on endothelial and SMC proliferation, differentiation, migration, tube formation, and sprouting. Moreover, TGF-β can stimulate endothelial-to-mesenchymal transition, a process shown to be of key importance in heart valve cushion formation and in various pathological vascular processes. Here, we discuss the roles of TGF-β in vasculogenesis, angiogenesis, and lymphangiogenesis and the deregulation of TGF-β signaling in cardiovascular diseases.

Endoglin interacts with VEGFR2 to promote angiogenesis

Endoglin, a TGF-β coreceptor predominantly expressed in endothelial cells, plays an important role in vascular development and tumor-associated angiogenesis. However, the mechanism by which endoglin regulates angiogenesis, especially during tip cell formation, remains largely unknown. In this study, we report that endoglin promoted VEGF-induced tip cell formation. Mechanistically, endoglin interacted with VEGF receptor (VEGFR)-2 in a VEGF-dependent manner, which sustained VEGFR2 on the cell surface and prevented its degradation. Endoglin mutants deficient in the ability to interact with VEGFR2 failed to sustain VEGFR2 on the cell surface and to promote VEGF-induced tip cell formation. Further, an endoglin-targeting monoclonal antibody (mAb), TRC105, cooperated with a VEGF-A targeting mAb, bevacizumab, to inhibit VEGF signaling and tip cell formation in vitro and to inhibit tumor growth, metastasis, and tumor-associated angiogenesis in a murine tumor model. This study demonstrate a novel mechanism by which endoglin initiates and regulates VEGF-driven angiogenesis while providing a rationale for combining anti-VEGF and anti-endoglin therapy in patients with cancer.-Tian, H., Huang, J. J., Golzio, C., Gao, X., Hector-Greene, M., Katsanis, N., Blobe, G. C. Endoglin interacts with VEGFR2 to promote angiogenesis.

Inhibiting DPP4 in a mouse model of HHT1 results in a shift towards regenerative macrophages and reduces fibrosis after myocardial infarction

AIMS

Hereditary Hemorrhagic Telangiectasia type-1 (HHT1) is a genetic vascular disorder caused by haploinsufficiency of the TGFβ co-receptor endoglin. Dysfunctional homing of HHT1 mononuclear cells (MNCs) towards the infarcted myocardium hampers cardiac recovery. HHT1-MNCs have elevated expression of dipeptidyl peptidase-4 (DPP4/CD26), which inhibits recruitment of CXCR4-expressing MNCs by inactivation of stromal cell-derived factor 1 (SDF1). We hypothesize that inhibiting DPP4 will restore homing of HHT1-MNCs to the infarcted heart and improve cardiac recovery.

METHODS AND RESULTS

After inducing myocardial infarction (MI), wild type (WT) and endoglin heterozygous (Eng+/-) mice were treated for 5 days with the DPP4 inhibitor Diprotin A (DipA). DipA increased the number of CXCR4+ MNCs residing in the infarcted Eng+/- hearts (Eng+/- 73.17±12.67 vs. Eng+/- treated 157.00±11.61, P = 0.0003) and significantly reduced infarct size (Eng+/- 46.60±9.33% vs. Eng+/- treated 27.02±3.04%, P = 0.03). Echocardiography demonstrated that DipA treatment slightly deteriorated heart function in Eng+/- mice. An increased number of capillaries (Eng+/- 61.63±1.43 vs. Eng+/- treated 74.30±1.74, P = 0.001) were detected in the infarct border zone whereas the number of arteries was reduced (Eng+/- 11.88±0.63 vs. Eng+/- treated 6.38±0.97, P = 0.003). Interestingly, while less M2 regenerative macrophages were present in Eng+/- hearts prior to DipA treatment, (WT 29.88±1.52% vs. Eng+/- 12.34±1.64%, P<0.0001), DPP4 inhibition restored the number of M2 macrophages to wild type levels.

CONCLUSIONS

In this study, we demonstrate that systemic DPP4 inhibition restores the impaired MNC homing in Eng+/- animals post-MI, and enhances cardiac repair, which might be explained by restoring the balance between the inflammatory and regenerative macrophages present in the heart.

Altered angiogenesis as a common mechanism underlying preterm birth, small for gestational age, and stillbirth in women living with HIV

Background

Angiogenic processes in the placenta are critical regulators of fetal growth and impact birth outcomes, but there are limited data documenting these processes in HIV-infected women or women from low-resource settings.

Objective

We sought to determine whether angiogenic factors are associated with adverse birth outcomes in HIV-infected pregnant women started on antiretroviral therapy.

Study Design

This is a secondary analysis of samples collected as part of a clinical trial randomizing pregnant women and adolescents infected with HIV to lopinavir/ritonavir-based (n = 166) or efavirenz-based (n = 160) antiretroviral therapy in Tororo, Uganda. Pregnant women living with HIV were enrolled between 12-28 weeks of gestation. Plasma samples were evaluated for angiogenic biomarkers (angiopoietin-1, angiopoietin-2, vascular endothelial growth factor, soluble fms-like tyrosine kinase-1, placental growth factor, and soluble endoglin) by enzyme-linked immunosorbent assay between: 16-<20, 20-<24, 24-<28, 28-<32, 32-<36, 36-<37 weeks of gestation. The primary outcome was preterm birth.

Results

In all, 1115 plasma samples from 326 pregnant women and adolescents were evaluated. There were no differences in angiogenic factors according to antiretroviral therapy group (P > .05 for all). The incidence of adverse birth outcomes was 16.9% for spontaneous preterm births, 25.6% for small-for-gestational-age births, and 2.8% for stillbirth. We used linear mixed effect modelling to evaluate longitudinal changes in angiogenic factor concentrations between birth outcome groups adjusting for gestational age at venipuncture, maternal age, body mass index, gravidity, and the interaction between treatment arm and gestational age. Two angiogenic factors–soluble endoglin and placental growth factor–were associated with adverse birth outcomes. Significantly higher concentrations of soluble endoglin throughout gestation were found in study participants destined to deliver preterm [likelihood ratio test, χ²(1) = 12.28, P < .0005] and in those destined to have stillbirths [χ²(1) = 5.67, P < .02]. By contrast, significantly lower concentrations of placental growth factor throughout gestation were found in those destined to have small-for-gestational-age births [χ²(1) = 7.89, P < .005] and in those destined to have stillbirths [χ²(1) = 21.59, P < .0001].

Conclusion

An antiangiogenic state in the second or third trimester is associated with adverse birth outcomes, including stillbirth in women and adolescents living with HIV and receiving antiretroviral therapy.

The roles of endoglin gene in cerebrovascular diseases

Endoglin (ENG, also known as CD105) is a transforming growth factor β (TGFβ) associated receptor and is required for both vasculogenesis and angiogenesis. Angiogenesis is important in the development of cerebral vasculature and in the pathogenesis of cerebral vascular diseases. ENG is an essential component of the endothelial nitric oxide synthase activation complex. Animal studies showed that ENG deficiency impairs stroke recovery. ENG deficiency also impairs the regulation of vascular tone, which contributes to the pathogenesis of brain arteriovenous malformation (bAVM) and vasospasm. In human, functional haploinsufficiency of ENG gene causes type I hereditary hemorrhagic telangiectasia (HHT1), an autosomal dominant disorder. Compared to normal population, HHT1 patients have a higher prevalence of AVM in multiple organs including the brain. Vessels in bAVM are fragile and tend to rupture, causing hemorrhagic stroke. High prevalence of pulmonary AVM in HHT1 patients are associated with a higher incidence of paradoxical embolism in the cerebral circulation causing ischemic brain injury. Therefore, HHT1 patients are at risk for both hemorrhagic and ischemic stroke. This review summarizes the possible mechanism of ENG in the pathogenesis of cerebrovascular diseases in experimental animal models and in patients.

Endoglin and alk1 as therapeutic targets for hereditary hemorrhagic telangiectasia

INTRODUCTION

Hereditary Haemorrhagic Telangiectasia (HHT) is as an autosomal dominant trait characterized by frequent nose bleeds, mucocutaneous telangiectases, arteriovenous malformations (AVMs) of the lung, liver and brain, and gastrointestinal bleedings due to telangiectases. HHT is originated by mutations in genes whose encoded proteins are involved in the transforming growth factor β (TGF-β) family signalling of vascular endothelial cells. In spite of the great advances in the diagnosis as well as in the molecular, cellular and animal models of HHT, the current treatments remain just at the palliative level. Areas covered: Pathogenic mutations in genes coding for the TGF-β receptors endoglin (ENG) (HHT1) or the activin receptor-like kinase-1 (ACVRL1 or ALK1) (HHT2), are responsible for more than 80% of patients with HHT. Therefore, ENG and ALK1 are the main potential therapeutic targets for HHT and the focus of this review. The current status of the preclinical and clinical studies, including the anti-angiogenic strategy, have been addressed. Expert opinion: Endoglin and ALK1 are attractive therapeutic targets in HHT. Because haploinsufficiency is the pathogenic mechanism in HHT, several therapeutic approaches able to enhance protein expression and/or function of endoglin and ALK1 are keys to find novel and efficient treatments for the disease.

Beyond organoids: In vitro vasculogenesis and angiogenesis using cells from mammals and zebrafish

The ability to culture complex organs is currently an important goal in biomedical research. It is possible to grow organoids (3D organ-like structures) in vitro; however, a major limitation of organoids, and other 3D culture systems, is the lack of a vascular network. Protocols developed for establishing in vitro vascular networks typically use human or rodent cells. A major technical challenge is the culture of functional (perfused) networks. In this rapidly advancing field, some microfluidic devices are now getting close to the goal of an artificially perfused vascular network. Another development is the emergence of the zebrafish as a complementary model to mammals. In this review, we discuss the culture of endothelial cells and vascular networks from mammalian cells, and examine the prospects for using zebrafish cells for this objective. We also look into the future and consider how vascular networks in vitro might be successfully perfused using microfluidic technology.

Endoglin prevents vascular malformation by regulating flow-induced cell migration and specification through VEGFR2 signalling

Loss-of-function (LOF) mutations in the endothelial cell (EC) enriched gene endoglin (ENG) causes the human disease hereditary haemorrhagic telangiectasia-1, characterized by vascular malformations promoted by vascular endothelial growth factor A (VEGFA). How ENG deficiency alters EC behaviour to trigger these anomalies is not understood. Mosaic ENG deletion in the postnatal mouse rendered Eng LOF ECs insensitive to flow-mediated venous to arterial migration. Eng LOF ECs retained within arterioles acquired venous characteristics and secondary ENG-independent proliferation resulting in arterio-venous malformation (AVM). Analysis following simultaneous Eng LOF and overexpression (OE) revealed that ENG OE ECs dominate tip cell positions and home preferentially to arteries. ENG knock-down altered VEGFA-mediated VEGFR2 kinetics and promoted AKT signalling. Blockage of PI3K/AKT partly normalised flow-directed migration of ENG LOF ECs in vitro and reduced the severity of AVM in vivo. This demonstrates the requirement of ENG in flow-mediated migration and modulation of VEGFR2 signalling in vascular patterning.

The role of endoglin in post-ischemic revascularization

Following arterial occlusion, blood vessels respond by forming a new network of functional capillaries (angiogenesis), by reorganizing preexisting capillaries through the recruitment of smooth muscle cells to generate new arteries (arteriogenesis) and by growing and remodeling preexisting collateral arterioles into physiologically relevant arteries (collateral development). All these processes result in the recovery of organ perfusion. The importance of endoglin in post-occlusion reperfusion is sustained by several observations: (1) endoglin expression is increased in vessels showing active angiogenesis/remodeling; (2) genetic endoglin haploinsufficiency in humans causes deficient angiogenesis; and (3) the reduction of endoglin expression by gene disruption or the administration of endoglin-neutralizing antibodies reduces angiogenesis and revascularization. However, the precise role of endoglin in the several processes associated with revascularization has not been completely elucidated and, in some cases, the function ascribed to endoglin by different authors is controversial. The purpose of this review is to organize in a critical way the information available for the role of endoglin in several phenomena (angiogenesis, arteriogenesis and collateral development) associated with post-ischemic revascularization.

Increased Wnt5a in squamous cell lung carcinoma inhibits endothelial cell motility

BACKGROUND

Angiogenesis is important both in normal tissue function and disease and represents a key target in lung cancer (LC) therapy. Unfortunately, the two main subtypes of non-small-cell lung cancers (NSCLC) namely, adenocarcinoma (AC) and squamous cell carcinoma (SCC) respond differently to anti-angiogenic e.g. anti-vascular endothelial growth factor (VEGF)-A treatment with life-threatening side effects, often pulmonary hemorrhage in SCC. The mechanisms behind such adverse reactions are still largely unknown, although peroxisome proliferator activator receptor (PPAR) gamma as well as Wnt-s have been named as molecular regulators of the process. As the Wnt microenvironments in NSCLC subtypes are drastically different, we hypothesized that the particularly high levels of non-canonical Wnt5a in SCC might be responsible for alterations in blood vessel growth and result in serious adverse reactions.

METHODS

PPARgamma, VEGF-A, Wnt5a, miR-27b and miR-200b levels were determined in resected adenocarcinoma and squamous cell carcinoma samples by qRT-PCR and TaqMan microRNA assay. The role of PPARgamma in VEGF-A expression, and the role of Wnts in overall regulation was investigated using PPARgamma knock-out mice, cancer cell lines and fully human, in vitro 3 dimensional (3D), distal lung tissue aggregates. PPARgamma mRNA and protein levels were tested by qRT-PCR and immunohistochemistry, respectively. PPARgamma activity was measured by a PPRE reporter system. The tissue engineered lung tissues expressing basal level and lentivirally delivered VEGF-A were treated with recombinant Wnts, chemical Wnt pathway modifiers, and were subjected to PPARgamma agonist and antagonist treatment.

RESULTS

PPARgamma down-regulation and VEGF-A up-regulation are characteristic to both AC and SCC. Increased VEGF-A levels are under direct control of PPARgamma. PPARgamma levels and activity, however, are under Wnt control. Imbalance of both canonical (in AC) and non-canonical (in SCC) Wnts leads to PPARgamma down-regulation. While canonical Wnts down-regulate PPARgamma directly, non-canonical Wnt5a increases miR27b that is known regulator of PPARgamma.

CONCLUSION

During carcinogenesis the Wnt microenvironment alters, which can downregulate PPARgamma leading to increased VEGF-A expression. Differences in the Wnt microenvironment in AC and SCC of NSCLC lead to PPARgamma decrease via mechanisms that differentially alter endothelial cell motility and branching which in turn can influence therapeutic response.

Modulation of endoglin expression in islets of langerhans by VEGF reveals a novel regulator of islet endothelial cell function

BACKGROUND

Endoglin/CD105 is an auxiliary receptor for transforming growth factor-β with established roles in vascular remodelling. It has recently been shown that heterozygous endoglin deficiency in mice decreases insulin secretion in an animal model of obesity, highlighting a potential role for endoglin in the regulation of islet function. We have previously identified two different populations of endoglin expressing cells in human and mouse islets which are: (i) endothelial cells (ECs) and (ii) islet mesenchymal stromal cells. The contribution of islet EC endoglin expression to islet development and sensitivity to VEGF is unknown and is the focus of this study.

RESULTS

In vitro culture of mouse islets with VEGF164 for 48 h increased endoglin mRNA levels above untreated controls but VEGF did not modulate VEGFR2, CD31 or CD34 mRNA expression or islet viability. Removal of EC-endoglin expression in vivo reduced islet EC area but had no apparent effect on islet size or architecture.

CONCLUSION

EC-specific endoglin expression in islets is sensitive to VEGF and plays partial roles in driving islet vascular development, however such regulation appears to be distinct to mechanisms required to modulate islet viability and size.

Mutational and clinical analysis of the ENG gene in patients with pulmonary arterial hypertension

Background

Pulmonary arterial hypertension (PAH) is a rare vascular disorder characterized by a capillary wedge pressure ≤ 15 mmHg and a mean pulmonary arterial pressure ≥ 25 mmHg at rest. PAH can be idiopathic, heritable or associated with other conditions. The aim of this study was to analyze the Endoglin (ENG) gene and assess the influence of the c.572G > A (p.G191D) mutation in patients with idiopathic or associated PAH. The correlation between the pathogenic mutations and clinical and functional parameters was further analyzed.

Results

Sixteen different changes in the ENG gene were found in 44 out of 57 patients. After in silico analysis, we classified eight mutations as pathogenic in 16 of patients. The c.572G>A (p.G191D) variation was observed in ten patients, and the analysis for the splicing process using hybrid minigenes, with pSPL3 vector to assess splicing alterations, do not generate a new transcript. Age at diagnosis (p = 0.049) and the 6-min walking test (p = 0.041) exhibited statistically significant differences between carriers and non-carriers of pathogenic mutations. Patients with pathogenic mutations exhibited disease symptoms 8 years before non-carriers. Five patients with pathogenic mutations were carriers of another mutation in the BMPR2 or ACVRL1 genes.

Conclusions

We present a series of PAH patients with mutations in the ENG gene, some of them not previously described, exhibiting clinical and hemodynamic alterations suggesting that the presence of these mutations may be associated with the severity of the disease. Moreover, genetic analysis in patients with PAH may be of clinical relevance and indicates the complexity of the genetic background.

Genetic risk factors for spontaneous intracerebral haemorrhage

Intracerebral haemorrhage (ICH) is associated with the greatest morbidity and mortality of all stroke subtypes. Established risk factors for ICH include hypertension, alcohol use, current cigarette smoking, and use of oral anticoagulants and/or antiplatelet agents. Familial aggregation of ICH has been observed, and the heritability of ICH risk has been estimated at 44%. Few genes have been found to be associated with ICH at the population level, and much of the evidence for genetic risk factors for ICH comes from single studies conducted in relatively small and homogenous populations. In this Review, we summarize the current knowledge of genetic variants associated with primary spontaneous ICH. Two variants of the gene encoding apolipoprotein E (APOE) - which also contributes to the pathogenesis of cerebral amyloid angiopathy - are the most likely candidates for variants that increase the risk of ICH. Other promising candidates for risk alleles in ICH include variants of the genes ACE, PMF1/SLC25A44, COL4A2, and MTHFR. Other genetic variants, related to haemostasis, lipid metabolism, inflammation, and the CNS microenvironment, have been linked to ICH in single candidate gene studies. Although evidence for genetic contributions to the risk of ICH exists, we do not yet fully understand how and to what extent this information can be utilized to prevent and treat ICH.

Functional and Biological Role of Endothelial Precursor Cells in Tumour Progression: A New Potential Therapeutic Target in Haematological Malignancies

It was believed that vasculogenesis occurred only during embryo life and that postnatal formation of vessels arose from angiogenesis. Recent findings demonstrate the existence of Endothelial Precursor Cells (EPCs), which take partin postnatal vasculogenesis. EPCs are recruited from the bone marrow under the stimulation of growth factors and cytokines and reach the sites of neovascularization in both physiological and pathological conditions such as malignancies where they contribute to the “angiogenic switch” and tumor progression. An implementation of circulating EPCs in the bloodstream of patients with haematological malignancies has been demonstrated. This increase is strictly related to the bone marrow microvessel density and correlated with a poor prognosis. The EPCs characterization is a very complex process and still under investigation. This literature review aims to provide an overview of the functional and biological role of EPCs in haematological malignancies and to investigate their potential as a new cancer therapeutic target.

The great escape; the hallmarks of resistance to antiangiogenic therapy

The concept of antiangiogenic therapy in cancer treatment has led to the approval of different agents, most of them targeting the well known vascular endothelial growth factor pathway. Despite promising results in preclinical studies, the efficacy of antiangiogenic therapy in the clinical setting remains limited. Recently, awareness has emerged on resistance to antiangiogenic therapies. It has become apparent that the intricate complex interplay between tumors and stromal cells, including endothelial cells and associated mural cells, allows for escape mechanisms to arise that counteract the effects of these targeted therapeutics. Here, we review and discuss known and novel mechanisms that contribute to resistance against antiangiogenic therapy and provide an outlook to possible improvements in therapeutic approaches.

VEGF, Notch and TGFβ/BMPs in regulation of sprouting angiogenesis and vascular patterning

The blood vasculature is constantly adapting to meet the demand from tissue. In so doing, branches may form, reorganize or regress. These complex processes employ integration of multiple signalling cascades, some of them being restricted to endothelial and mural cells and, hence, suitable for targeting of the vasculature. Both genetic and drug targeting experiments have demonstrated the requirement for the vascular endothelial growth factor (VEGF) system, the Delta-like-Notch system and the transforming growth factor β (TGFβ)/bone morphogenetic protein (BMP) cascades in vascular development. Although several of these signalling cascades in part converge into common downstream components, they differ in temporal and spatial regulation and expression. For example, the pro-angiogenic VEGFA is secreted by cells in need of oxygen, presented to the basal side of the endothelium, whereas BMP9 and BMP10 are supplied via the bloodstream in constant interaction with the apical side to suppress angiogenesis. Delta-like 4 (DLL4), on the other hand, is provided as an endothelial membrane bound ligand. In the present article, we discuss recent data on the integration of these pathways in the process of sprouting angiogenesis and vascular patterning and malformation.

Noninvasive detection of trophoblast protein signatures linked to early pregnancy loss using trophoblast retrieval and isolation from the cervix (TRIC)

OBJECTIVE

To examine the expression pattern of biomarker proteins in extravillous trophoblast (EVT) cells obtained noninvasively by trophoblast retrieval and isolation from the cervix (TRIC) in patients with early pregnancy loss compared with control patients with uncomplicated term delivery.

DESIGN

Case-control study.

SETTING

Academic medical center.

PATIENT(S)

Women with either early pregnancy loss (EPL, n = 10) or an uncomplicated term delivery (N = 10).

INTERVENTION(S)

Endocervical specimens obtained from ongoing pregnancies at gestational ages of 5-10 weeks to generate an archive of EVT cells isolated by TRIC, with medical records examined to select specimens matched for gestational age at the time of endocervical sampling.

MAIN OUTCOME MEASURE(S)

Known serum biomarkers for adverse pregnancy outcome that are expressed by EVT cells were evaluated by semiquantitative immunocytochemistry, using antibodies against endoglin (ENG), FMS-like tyrosine kinase-1 (FLT-1), α-fetoprotein (AFP), pregnancy-associated plasma protein-A (PAPP-A), galectin-13 (LGALS13), galectin-14 (LGALS14), and placental growth factor (PGF).

RESULT(S)

The EVT purity was over 95% in all specimens, based on chorionic gonadotropin expression; however, the number of EVT cells obtained was significantly lower in women with EPL than the control group. There was a statistically significant elevation of AFP, ENG, and FLT-1, and statistically significant reduction of PAPP-A, LGALS14, and PGF in the EPL group compared with controls.

CONCLUSION(S)

In this pilot study, EVT cells isolated by TRIC early in gestation exhibited altered protein expression patterns before an EPL compared with uncomplicated term pregnancies.

Macro- and microvascular disease in systemic sclerosis

Vasculopathy is common in patients with connective tissue disease and can be directly implicated in the pathogenesis of the disease. Systemic sclerosis is an auto-immune multiorgan connective tissue disorder characterized by fibrosis of the skin and visceral organs and vascular disease. Micro- and macro-vessels are a direct target of the disease. In this review, we present the various clinical manifestations of the vasculopathy that can be present in SSc patients, and then discuss the various aspects of the pathophysiology of the vascular disorders.

Decreasing matrix modulus of PEG hydrogels induces a vascular phenotype in human cord blood stem cells

Adult and congenital cardiovascular diseases are significant health problems that are often managed using surgery. Bypass grafting is a principal therapy, but grafts fail at high rates due to hyperplasia, fibrosis, and atherosclerosis. Biocompatible, cellularized materials that attenuate these complications and encourage healthy microvascularization could reduce graft failure, but an improved understanding of biomaterial effects on human stem cells is needed to reach clinical utility. Our group investigates stem-cell-loaded biomaterials for placement along the adventitia of at-risk vessels and grafts. Here, the effects of substrate modulus on human CD34+ stem cells from umbilical cord blood were evaluated. Cells were isolated by immunomagnetic separation and encapsulated in 3, 4, and 6 weight% PEG hydrogels containing 0.032% gelatin and 0.0044% fibronectin. Gels reached moduli of 0.34, 4.5, and 9.1 kPa. Cell viability approached 100%. Cell morphologies appeared similar across gels, but proliferation was significantly lower in 6 wt% gels. Expression profiling using stem cell signaling arrays indicated enhanced self-renewal and differentiation into vascular endothelium among cells in the lower weight percent gels. Thus, modulus was associated with cell proliferation and function. Gels with moduli in the low kilopascal range may be useful in stimulating cell engraftment and microvascularization of graft adventitia.

CD105 expression in oral capillary hemangiomas and cavernous hemangiomas

Capillary hemangioma (capillary lobular hemangioma) and cavernous hemangioma (venous malformation) are relatively common oral tumors/malformations and are characterized by increased numbers of normal and abnormal blood vessels. However, the causes of these lesions are not well understood. CD105 (endoglin) is predominantly expressed in proliferating blood endothelial cells (ECs). We analyzed expressions of CD105, CD34, von Willebrand factor, Ki-67, cyclooxygenase-2 (COX-2), and vascular endothelial growth factor (VEGF)-A in 31 capillary hemangiomas and 34 cavernous hemangiomas. Staining scores were calculated as the product of the proportion score and intensity score. Morphologically normal oral mucosa specimens (n = 10) were simultaneously evaluated as normal controls. As compared with cavernous hemangiomas and normal controls, capillary hemangiomas had higher staining scores for CD105, VEGF-A, and COX-2. The Ki-67 labeling index was significantly higher in capillary hemangiomas than in cavernous hemangiomas and normal controls (P < 0.01). These findings suggest that the biological characteristics of capillary and cavernous hemangiomas are quite different. The ECs of capillary hemangiomas actively proliferated and were generally regulated by VEGF-A. In contrast, the ECs of cavernous hemangiomas lacked proliferative activity. These results suggest that angiogenesis and vasodilatation of pre-existing blood vessels are important in the development of capillary hemangioma and cavernous hemangioma, respectively.

Mononuclear cells and vascular repair in HHT

Hereditary hemorrhagic telangiectasia (HHT) or Rendu–Osler–Weber disease is a rare genetic vascular disorder known for its endothelial dysplasia causing arteriovenous malformations and severe bleedings. HHT-1 and HHT-2 are the most prevalent variants and are caused by heterozygous mutations in endoglin and activin receptor-like kinase 1, respectively. An undervalued aspect of the disease is that HHT patients experience persistent inflammation. Although endothelial and mural cells have been the main research focus trying to unravel the mechanism behind the disease, wound healing is a process with a delicate balance between inflammatory and vascular cells. Inflammatory cells are part of the mononuclear cells (MNCs) fraction, and can, next to eliciting an immune response, also have angiogenic potential. This biphasic effect of MNC can hold a promising mechanism to further elucidate treatment strategies for HHT patients. Before MNC are able to contribute to repair, they need to home to and retain in ischemic and damaged tissue. Directed migration (homing) of MNCs following tissue damage is regulated by the stromal cell derived factor 1 (SDF1). MNCs that express the C-X-C chemokine receptor 4 (CXCR4) migrate toward the tightly regulated gradient of SDF1. This directed migration of monocytes and lymphocytes can be inhibited by dipeptidyl peptidase 4 (DPP4). Interestingly, MNC of HHT patients express elevated levels of DPP4 and show impaired homing toward damaged tissue. Impaired homing capacity of the MNCs might therefore contribute to the impaired angiogenesis and tissue repair observed in HHT patients. This review summarizes recent studies regarding the role of MNCs in the etiology of HHT and vascular repair, and evaluates the efficacy of DPP4 inhibition in tissue integrity and repair.

Vascular biomarkers and correlation with peripheral vasculopathy in systemic sclerosis

Vascular disease is a hallmark of systemic sclerosis (SSc). It is present in every patient, being responsible both for the earliest clinical manifestations and the major life-threatening complications of the disease, and thus determining important morbidity and mortality. In SSc, progressive vascular injury leads to vascular tone dysfunction and reduced capillary blood flow, with consequent tissue ischemia and chronic hypoxia. These phenomena are often accompanied by abnormal levels of vascular factors. Microangiopathy in SSc may be easily assessed by nailfold videocapillaroscopy. The variety of derangements detected in the nailfold capillaries is accompanied by abnormal levels of different vascular mediators and appears to be the best evaluable predictor of the development of peripheral vascular complications, such as digital ulcers. The purpose of this review is to summarize in SSc the most relevant vascular biomarkers and the main associations between vascular biomarkers and capillaroscopic parameters and/or the presence of digital ulcers. Vascular biomarkers could become useful predictive factors of vascular damage in SSc, allowing an earlier management of vascular complications.

Endoglin promotes angiogenesis in cell- and animal-based models of retinal neovascularization

PURPOSE

We investigated endoglin expression in hypoxic microvascular endothelial cells and retinal endoglin expression in rats that develop experimental oxygen-induced retinopathy (OIR). We also tested neutralizing antibodies (Abs) against endoglin (anti-CD105 Ab) and VEGF (anti-VEGF Ab) either alone or in combination for efficacy against serum-induced retinal microvascular endothelial cell proliferation and retinal neovascularization (NV) in OIR rats. To our knowledge, this marks the first time that a biologic agent has been used to target retinal endoglin and modulate retinal neovascularization.

METHODS

Induction of endoglin by hypoxia was measured by immunohistochemical analysis and ELISA. Proliferation was quantified using a colorimetric 5-bromo-2-deoxyuridine ELISA. Western blots were used to measure endoglin levels in retinas of OIR rats. Immunohistochemical staining was also preformed in OIR rats using anti-CD105 and fluorescein isothiocyanate-conjugated isolectin B4 antibodies.

RESULTS

Anti-CD105 Ab and Anti-VEGF Ab, administered alone or in combination, reduced serum-induced retinal microvascular endothelial cell proliferation. Additionally, in a rat model of oxygen-induced retinopathy, retinal endoglin was significantly increased at 14(2), 14(3), 14(4) and 14(6) compared with retinal levels in control rats. At 14(2), immunohistochemical analysis demonstrated that endoglin was elevated in newly developed vessels at the peripheral extent of major veins, precisely where NV is expected to develop in OIR rats. Neutralizing anti-CD105 reduced retinal NV in OIR rats.

CONCLUSIONS

Our data support other studies showing that reduction of endoglin expression inhibits retinal NV. Our findings demonstrate that retinal endoglin immunolocalization overlaps with nascent neovascular structures in OIR rats. Therefore, endoglin may serve as a useful predictor of incipient neovascular disease.

Activin A is anti-lymphangiogenic in a melanoma mouse model

Melanoma spreads primarily to the sentinel lymph nodes, and its risk correlates with lymphangiogenesis, which is mainly driven by vascular endothelial growth factor (VEGF)-C. However, anti-lymphangiogenic factors are poorly characterized. We have shown in a melanoma model that Wnt1 reduces lymphangiogenesis by reducing VEGF-C expression. Screening this model for additional potentially anti-lymphangiogenic factors identified increased activin A expression and reduced expression of the antagonist, follistatin (FST), in Wnt1(+) cells. Activin A is known to reduce blood vessel formation, but the effects on lymphangiogenesis are unknown. Here we show that human primary melanoma expresses significantly higher levels of activin A and lower levels of FST compared with nevi and melanoma metastasis. Using our mouse model with melanoma cells overexpressing Wnt1, FST, Wnt1/FST, or the inhibin βA subunit (INHBA, resulting in activin A expression), we found both activin A and Wnt1 to reduce lymphangiogenesis. Whereas Wnt1 also reduced metastasis, this was not seen with activin A. In vitro, activin A phosphorylated SMAD2 in both melanoma and lymphatic endothelium but, although it reduced sprouting of lymphatic endothelium, it enhanced the migration of melanoma cells. In conclusion, activin A is an anti-lymphangiogenic factor, but because of its pleiotropic effects on cell mobility it appears not suitable as a pharmacological target.