Hot and Cold Tumors: Is Endoglin (CD105) a Potential Target for Vessel Normalization?

Tumors are complex masses formed by malignant but also by normal cells. The interaction between these cells via cytokines, chemokines, growth factors, and enzymes that remodel the extracellular matrix (ECM) constitutes the tumor microenvironment (TME). This TME can be determinant in the prognosis and the response to some treatments such as immunotherapy. Depending on their TME, two types of tumors can be defined: hot tumors, characterized by an immunosupportive TME and a good response to immunotherapy; and cold tumors, which respond poorly to this therapy and are characterized by an immunosuppressive TME. A therapeutic strategy that has been shown to be useful for the conversion of cold tumors into hot tumors is vascular normalization. In this review we propose that endoglin (CD105) may be a useful target of this strategy since it is involved in the three main processes involved in the generation of the TME: angiogenesis, inflammation, and cancer-associated fibroblast (CAF) accumulation. Moreover, the analysis of endoglin expression in tumors, which is already used in the clinic to study the microvascular density and that is associated with worse prognosis, could be used to predict a patient's response to immunotherapy.

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.

The Role of Endoglin in Hepatocellular Carcinoma

Endoglin (CD105) is a type-1 integral transmembrane glycoprotein and coreceptor for transforming growth factor-β (TGF-β) ligands. The endoglin/TGF-β signaling pathway regulates hemostasis, cell proliferation/migration, extracellular matrix (ECM) synthesis and angiogenesis. Angiogenesis contributes to early progression, invasion, postoperative recurrence, and metastasis in hepatocellular carcinoma (HCC), one of the most widespread malignancies globally. Endoglin is overexpressed in newly formed HCC microvessels. It increases microvessel density in cirrhotic and regenerative HCC nodules. In addition, circulating endoglin is present in HCC patients, suggesting potential for use as a diagnostic or prognostic factor. HCC angiogenesis is dynamic and endoglin expression varies by stage. TRC105 (carotuximab) is an antibody against endoglin, and three of its clinical trials were related to liver diseases. A partial response was achieved when combining TRC105 with sorafenib. Although antiangiogenic therapy still carries some risks, combination therapy with endoglin inhibitors or other targeted therapies holds promise.

Endoglin in the Spotlight to Treat Cancer

A spotlight has been shone on endoglin in recent years due to that fact of its potential to serve as both a reliable disease biomarker and a therapeutic target. Indeed, endoglin has now been assigned many roles in both physiological and pathological processes. From a molecular point of view, endoglin mainly acts as a co-receptor in the canonical TGFβ pathway, but also it may be shed and released from the membrane, giving rise to the soluble form, which also plays important roles in cell signaling. In cancer, in particular, endoglin may contribute to either an oncogenic or a non-oncogenic phenotype depending on the cell context. The fact that endoglin is expressed by neoplastic and non-neoplastic cells within the tumor microenvironment suggests new possibilities for targeted therapies. Here, we aimed to review and discuss the many roles played by endoglin in different tumor types, as well as the strong evidence provided by pre-clinical and clinical studies that supports the therapeutic targeting of endoglin as a novel clinical strategy.

Impact of CD105 Flow-Cytometric Expression on Childhood B-Acute Lymphoblastic Leukemia

Background

CD105 (Endoglin) is a receptor of the transforming growth factor-Beta (TGF- β) superfamily. It is expressed in angiogenic endothelial cells and is considered a powerful marker of angiogenesis and a potential main player in the pathogenesis of vascular diseases as well as tumor progression. CD105 expression was correlated with poor prognosis in many types of solid malignancies, however, its influence on hematological neoplasms is still an area of interest.

Purpose

To assess the flow-cytometric expression of CD105 in childhood B-acute lymphoblastic leukemia (B-ALL) and its relation to disease response after the induction chemotherapy.

Subjects and Methods

Eighty children newly diagnosed with B-ALL were screened for flow-cytometric expression of CD105 at time of diagnosis, then they were followed up to detect their response to induction therapy.

Results

CD105 was expressed in 41.2% of B-ALL patients. Higher expression of CD105 was observed in high and very high-risk groups. The multivariate analysis considered CD105 positivity as an independent prognostic marker for response to induction therapy. Values higher than 2.5 Specific fluorescence indices (SFIs) and 35% expression were sensitive predictors to induction failure.

Conclusion

CD105 can be considered as a potential prognostic marker for the detection of response to induction therapy in childhood B-ALL, and it can serve to optimize treatment decisions.

Pressure Overload-Mediated Sustained PKR2 (Prokineticin-2 Receptor) Signaling in Cardiomyocytes Contributes to Cardiac Hypertrophy and Endotheliopathies

[Figure: see text].

BMP Receptor Inhibition Enhances Tissue Repair in Endoglin Heterozygous Mice

Hereditary hemorrhagic telangiectasia type 1 (HHT1) is a severe vascular disorder caused by mutations in the TGFβ/BMP co-receptor endoglin. Endoglin haploinsufficiency results in vascular malformations and impaired neoangiogenesis. Furthermore, HHT1 patients display an impaired immune response. To date it is not fully understood how endoglin haploinsufficient immune cells contribute to HHT1 pathology. Therefore, we investigated the immune response during tissue repair in Eng+/- mice, a model for HHT1. Eng+/- mice exhibited prolonged infiltration of macrophages after experimentally induced myocardial infarction. Moreover, there was an increased number of inflammatory M1-like macrophages (Ly6Chigh/CD206-) at the expense of reparative M2-like macrophages (Ly6Clow/CD206+). Interestingly, HHT1 patients also showed an increased number of inflammatory macrophages. In vitro analysis revealed that TGFβ-induced differentiation of Eng+/- monocytes into M2-like macrophages was blunted. Inhibiting BMP signaling by treating monocytes with LDN-193189 normalized their differentiation. Finally, LDN treatment improved heart function after MI and enhanced vascularization in both wild type and Eng+/- mice. The beneficial effect of LDN was also observed in the hind limb ischemia model. While blood flow recovery was hampered in vehicle-treated animals, LDN treatment improved tissue perfusion recovery in Eng+/- mice. In conclusion, BMPR kinase inhibition restored HHT1 macrophage imbalance in vitro and improved tissue repair after ischemic injury in Eng+/- mice.

Endoglin Level Is Critical for Cartilage Tissue Formation In Vitro by Passaged Human Chondrocytes

Transforming growth factor beta (TGFβ) signaling is required for in vitro chondrogenesis. In animal models of osteoarthritis (OA), TGFβ receptor alterations are detected in chondrocytes in severe OA cartilage. It is not known whether such changes are dependent on the grade of human OA and if they affect chondrogenesis. Thus, the purpose of this study was to determine if human OA chondrocytes obtained from low-grade or high-grade disease could form cartilage tissue and to assess the role of the co-receptors, endoglin (ENG) and TGFβ receptor 3 (TGFBRIII), in the regulation of this tissue generation in vitro. We hypothesized that the grade of OA disease would not affect the ability of cells to form cartilage tissue and that the TGFβ co-receptor, ENG, would be critical to regulating tissue formation. Chondrocytes isolated from low-grade OA or high-grade OA human articular cartilage (AC) were analyzed directly (P0) or passaged in monolayer to P2. Expression of the primary TGFβ receptor ALK5, and the co-receptors ENG and TGFβRIII, was assessed by image flow cytometry. To assess the ability to form cartilaginous tissue, cells were placed in three-dimensional culture at high density and cultured in chondrogenic media containing TGFβ3. ENG knockdown was used to determine its role in regulating tissue formation. Overall, grade-specific differences in expression of ALK5, ENG, and TGFβRIII in primary or passaged chondrocytes were not detected; however, ENG expression increased significantly after passaging. Despite the presence of ALK5, P0 cells did not form cartilaginous tissue. In contrast, P2 cells derived from low-grade and high-grade OA AC formed hyaline-like cartilaginous tissues of similar quality. Knockdown of ENG in P2 cells inhibited cartilaginous tissue formation compared to controls indicating that the level of ENG protein expression is critical for in vitro chondrogenesis by passaged articular chondrocytes. This study demonstrates that it is not the grade of OA, but the levels of ENG in the presence of ALK5 that influences the ability of human passaged articular chondrocytes to form cartilaginous tissue in vitro in 3D culture. This has implications for cartilage repair therapies. Impact statement These findings are important clinically, given the limited availability of osteoarthritis (OA) cartilage tissue. Being able to use cells from all grades of OA will increase our ability to obtain sufficient cells for cartilage repair. In addition, it is possible that endoglin (ENG) levels, in the presence of ALK5 expression, may be suitable to use as biomarkers to identify cells able to produce cartilage.

Endoglin Expression and Microvessel Density as Prognostic Factors in Pediatric Rhabdomyosarcoma

(1) Background: The study proposed to analyze microvessel density (MVD) in rhabdomyosarcoma (RMS) based on the expression of angiogenesis markers and define its prognostic role in this group of patients. (2) Methods: The study included forty-nine pediatric patients diagnosed with RMS. Tumor tissue expression of CD31, CD34, and CD105 was analyzed. MVD was calculated and correlated with clinical RMS prognostic parameters. (3) Results: CD31, CD34, and CD105 are expressed in all RMS cases. MVD/CD105 was significantly higher in the RMS group than in the control group. The mean and median values of MVD/CD105 in RMS were lower than MVD/CD31 and MVD/CD34. MVD/CD105 was significantly higher in patients with alveolar RMS and those with metastatic disease. Patients with higher levels of MVD/CD105 had a higher risk of death (HR = 1.009). (4) Conclusion: CD105 is a relevant angiogenesis marker in pediatric RMS, and MVD/CD105 is an independent risk factor of short overall survival in children with RMS.

Biomarkers of angiogenesis in twin gestations and the risk of preeclampsia - review of the current literature

Twin pregnancy is one of the key risk factors for the development of preeclampsia. Soluble fms-like tyrosine kinase-1, placental growth factor, and soluble endoglin are molecules involved in the process of angiogenesis with a proven role in the pathogenesis of preeclampsia. The aim of the review was to summarize available data on maternal serum levels of the biomarkers of angiogenesis and their usefulness in predicting preeclampsia in twin pregnancies. Most of available data suggest biomarkers concentrations differ between singleton and twin gestation and are related to chorionicity of twin pregnancy. Several algorithms including biomarkers of angiogenesis in prediction of PE in twin pregnancy are available and seem promising, however more large prospective surveys are necessary to assess their usefulness in general clinic use.

Placental expression of endoglin, placental growth factor, leptin, and hypoxia-inducible factor-1 in diabetic pregnancy and pre-eclampsia

OBJECTIVE

To evaluate a level of expression of endoglin (Eng), leptin (Lep), placental growth factor (PlGF), and hypoxia-inducible factor-1alpha (HIF-1α) in placenta among women with pre-eclampsia and diabetes mellitus (DM), considering the method of glycemia correction and preconception care.

MATERIALS AND METHODS

A retrospective cohort study was conducted. A total of 124 women were divided into following groups: type 1 DM (n = 40), type 2DM (n = 31), gestational DM (n = 33), pre-eclampsia without DM (PE) (n = 10) and the control group (n = 10). The histochemical study was performed by using primary monoclonal antibodies to Eng, PlGF, Lep, and HIF-1α (Abcam, UK).

RESULTS

The highest level of placental expression of Eng was observed in the PE group (20.34%). The same trend was also typical for T1DM (not planned) and insulin-treated groups: T2DM and GDM. An amount of cell with an PlGF expression was significantly higher in the control group (12.2%), while the lowest was observed in the pre-eclampsia group (1.18%) and T1DM (not planned) (1.26%). The placental leptin expression within each DM group was increased among the patients with unplanned pregnancy and those who received insulin therapy. We observed the lowest Lep expression in the PE group (6.3%). High level of HIF-1α expression was detected in T1DM (not planned) (30.44%) and PE (29.64%) as compared to the control group (11.62%). In T2DM and GDM insulin groups, the HIF-1α expression was significantly higher as compared to diet groups.

CONCLUSION

The obtained data show that DM and pre-eclampsia are associated with changes in angiogenic and metabolic placental factor expressions. The degree of changes depends on preconception care and the control of glycemia level during pregnancy.

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.

Association of Exosomal miR-34a with Markers of Dyslipidemia and Endothelial Dysfunction in Children and Adolescents with T1DM

OBJECTIVE

Dyslipidemia and endothelial dysfunction are common disorders and major causative factors for atherosclerosis in patients with type 1 diabetes mellitus (T1DM). However, their pathophysiology in young patients with T1DM is still under evaluated. We aimed, for the first time, to assess the expression of exosomal micro-RNA 34a (miR-34a) in serum of children and adolescents with T1DM and correlate this expression with markers of dyslipidemia and endothelial dysfunction.

METHODS

The study included 120 T1DM patients and 100 control subjects. Assessment of miR-34a was performed using quantitative real-time polymerase chain reaction. Lipid profile was assessed on an automated analyzer and serum endoglin and intracellular adhesion molecule (ICAM) concentrations were measured using immunometric methods.

RESULTS

Relative expression of miR-34a and serum endoglin and ICAM concentrations were higher in patients than controls (p=0.001) and in patients with dyslipidemia (42 patients) compared to patients without dyslipidemia (78 patients) (p=0.01). Linear regression analysis revealed a strong independent association between exosomal miR-34a expression and total cholesterol, low-density lipoprotein, serum endoglin and serum ICAM after adjustment for other cofactors. The utility of miR-34a as an indicator for associated dyslipidemia was tested using receiver operator characteristic curve analysis which revealed area under the curve: 0.73 with confidence interval: 0.63-0.83 and p=0.001.

CONCLUSION

This was the first study to show the altered expression of exosomal miR-34a among children and adolescents with T1DM. Moreover, association of miR-34a with markers of dyslipidemia and endothelial dysfunction was identified, suggesting that it could play a role in regulation of lipid metabolism and endothelial function in T1DM.

Soluble Endoglin as a Potential Biomarker of Nonalcoholic Steatohepatitis (NASH) Development, Participating in Aggravation of NASH-Related Changes in Mouse Liver

Nonalcoholic steatohepatitis (NASH) is characterized by hepatic steatosis with inflammation and fibrosis. Membrane endoglin (Eng) expression is shown to participate in fibrosis, and plasma concentrations of soluble endoglin (sEng) are increased in patients with hypercholesterolemia and type 2 diabetes mellitus. We hypothesize that NASH increases both hepatic Eng expression and sEng in blood and that high levels of sEng modulate cholesterol and bile acid (BA) metabolism and affect NASH progression. Three-month-old transgenic male mice overexpressing human sEng and their wild type littermates are fed for six months with either a high-saturated fat, high-fructose high-cholesterol (FFC) diet or a chow diet. Evaluation of NASH, Liquid chromatography-mass spectrometry (LC/MS) analysis of BA, hepatic expression of Eng, inflammation, fibrosis markers, enzymes and transporters involved in hepatic cholesterol and BA metabolism are assessed using Real-Time Quantitative Reverse Transcription Polymerase Chain reaction (qRT-PCR) and Western blot. The FFC diet significantly increases mouse sEng levels and increases hepatic expression of Eng. High levels of human sEng results in increased hepatic deposition of cholesterol due to reduced conversion into BA, as well as redirects the metabolism of triglycerides (TAG) to its accumulation in the liver, via reduced TAG elimination by β-oxidation combined with reduced hepatic efflux. We propose that sEng might be a biomarker of NASH development, and the presence of high levels of sEng might support NASH aggravation by impairing the essential defensive mechanism protecting NASH liver against excessive TAG and cholesterol accumulation, suggesting the importance of high sEng levels in patients prone to develop NASH.

Potential Second-Hits in Hereditary Hemorrhagic Telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant genetic disorder that presents with telangiectases in skin and mucosae, and arteriovenous malformations (AVMs) in internal organs such as lungs, liver, and brain. Mutations in ENG (endoglin), ACVRL1 (ALK1), and MADH4 (Smad4) genes account for over 95% of HHT. Localized telangiectases and AVMs are present in different organs, with frequencies which differ among affected individuals. By itself, HHT gene heterozygosity does not account for the focal nature and varying presentation of the vascular lesions leading to the hypothesis of a “second-hit” that triggers the lesions. Accumulating research has identified a variety of triggers that may synergize with HHT gene heterozygosity to generate the vascular lesions. Among the postulated second-hits are: mechanical trauma, light, inflammation, vascular injury, angiogenic stimuli, shear stress, modifier genes, and somatic mutations in the wildtype HHT gene allele. The aim of this review is to summarize these triggers, as well as the functional mechanisms involved.

Endoplasmic Reticulum Associated Protein Degradation (ERAD) in the Pathology of Diseases Related to TGFβ Signaling Pathway: Future Therapeutic Perspectives

The transforming growth factor signaling pathway (TGFβ) controls a wide range of cellular activities in adulthood as well as during embryogenesis including cell growth, differentiation, apoptosis, immunological responses and other cellular functions. Therefore, germline mutations in components of the pathway have given rise to a heterogeneous spectrum of hereditary diseases with variable phenotypes associated with malformations in the cardiovascular, muscular and skeletal systems. Our extensive literature and database searches revealed 47 monogenic diseases associated with germline mutations in 24 out of 41 gene variant encoding for TGFβ components. Most of the TGFβ components are membrane or secretory proteins and they are therefore expected to pass through the endoplasmic reticulum (ER), where fidelity of proteins folding is stringently monitored via the ER quality control machineries. Elucidation of the molecular mechanisms of mutant proteins’ folding and trafficking showed the implication of ER associated protein degradation (ERAD) in the pathogenesis of some of the diseases. For example, hereditary hemorrhagic telangiectasia types 1 and 2 (HHT1 and HHT2) and familial pulmonary arterial hypertension (FPAH) associated with mutations in Endoglin, ALK1 and BMPR2 components of the signaling pathway, respectively, have all exhibited loss of function phenotype as a result of ER retention of some of their disease-causing variants. In some cases, this has led to premature protein degradation through the proteasomal pathway. We anticipate that ERAD will be involved in the mechanisms of other TGFβ signaling components and therefore warrants further research. In this review, we highlight advances in ER quality control mechanisms and their modulation as a potential therapeutic target in general with particular focus on prospect of their implementation in the treatment of monogenic diseases associated with TGFβ components including HHT1, HHT2, and PAH. In particular, we emphasis the need to establish disease mechanisms and to implement such novel approaches in modulating the molecular pathway of mutant TGFβ components in the quest for restoring protein folding and trafficking as a therapeutic approach.

Endoglin Promotes Myofibroblast Differentiation and Extracellular Matrix Production in Diabetic Nephropathy

Diabetic nephropathy (DN) is a complication of diabetes mellitus that can lead to proteinuria and a progressive decline in renal function. Endoglin, a co-receptor of TGF-β, is known primarily for regulating endothelial cell function; however, endoglin is also associated with hepatic, cardiac, and intestinal fibrosis. This study investigates whether endoglin contributes to the development of interstitial fibrosis in DN. Kidney autopsy material from 80 diabetic patients was stained for endoglin and Sirius Red and scored semi-quantitatively. Interstitial endoglin expression was increased in samples with DN and was correlated with Sirius Red staining (p < 0.001). Endoglin expression was also correlated with reduced eGFR (p = 0.001), increased creatinine (p < 0.01), increased systolic blood pressure (p < 0.05), hypertension (p < 0.05), and higher IFTA scores (p < 0.001). Biopsy samples from DN patients were also co-immunostained for endoglin together with CD31, CD68, vimentin, or α-SMA Endoglin co-localized with both the endothelial marker CD31 and the myofibroblast marker α-SMA. Finally, we used shRNA to knockdown endoglin expression in a human kidney fibroblast cell line. We found that TGF-β1 stimulation upregulated SERPINE1, CTGF, and ACTA2 mRNA and α-SMA protein, and that these effects were significantly reduced in fibroblasts after endoglin knockdown. Taken together, these data suggest that endoglin plays a role in the pathogenesis of interstitial fibrosis in DN.

Raloxifene and n-Acetylcysteine Ameliorate TGF-Signalling in Fibroblasts from Patients with Recessive Dominant Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin disease caused by mutation of the COL7A1 gene. RDEB is associated with high levels of TGF-β1, which is likely to be involved in the fibrosis that develops in this disease. Endoglin (CD105) is a type III coreceptor for TGF-β1 and its overexpression in fibroblasts deregulates physiological Smad/Alk1/Alk5 signalling, repressing the synthesis of TGF-β1 and extracellular matrix (ECM) proteins. Raloxifene is a specific estrogen receptor modulator designated as an orphan drug for hereditary hemorrhagic telangiectasia, a rare vascular disease. Raloxifene stimulates endoglin synthesis, which could attenuate fibrosis. By contrast, the antioxidant N-acetylcysteine may have therapeutic value to rectify inflammation, fibrosis and endothelial dysfunction. Thus, we present here a repurposing strategy based on the molecular and functional screening of fibroblasts from RDEB patients with these drugs, leading us to propose the repositioning of these two well-known drugs currently in clinical use, raloxifene and N-acetylcysteine, to counteract fibrosis and inflammation in RDEB. Both compounds modulate the profibrotic events that may ultimately be responsible for the clinical manifestations in RDEB, suggesting that these findings may also be relevant for other diseases in which fibrosis is an important pathophysiological event.

Differential Expression of Circulating Plasma miRNA-370 and miRNA-10a from Patients with Hereditary Hemorrhagic Telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant, vascular disorder that presents with telangiectases and arteriovenous malformations. HHT is a genetically heterogeneous disorder, involving mutations in endoglin (ENG; HHT1) and activin receptor-like kinase 1 (ACVRL1/ALK1; HHT2) genes that account for over 85% of all HHT patients. The current diagnosis of HHT patients remains at the clinical level, but many suspected patients do not have a clear HHT diagnosis or do not show pathogenic mutations in HHT genes. This situation has prompted the search for biomarkers to help in the early diagnosis of the disease. We have analyzed the plasma levels in HHT patients of selected micro-RNAs (miRNAs), small single-stranded RNAs that regulate gene expression at the transcriptional level by interacting with specific RNA targets. A total of 16 HHT1 and 17 HHT2 plasma samples from clinically confirmed patients and 16 controls were analyzed in this study. Total RNA was purified from plasma, and three selected miRNAs (miRNA-10a, miRNA-214, and miRNA-370), related to the pathobiology of cardiovascular diseases and potentially targeting ENG or ALK1, were measured by quantitative polymerase chain reaction. Compared with controls, levels of miRNA-370, whose putative target is ENG, were significantly downregulated in HHT1, but not in HHT2, whereas the levels of miRNA-10a, whose putative target is ALK1, were significantly upregulated in HHT2, but not in HHT1. In addition, the levels of miRNA-214, potentially targeting ENG and ALK1, did not change in either HHT1 or HHT2 patients versus control samples. While further studies are warranted, these results suggest that dysregulated plasma levels of miRNA-370 or miRNA-10a could help to identify undiagnosed HHT1 or HHT2 patients, respectively.

Overexpression of Activin Receptor-Like Kinase 1 in Endothelial Cells Suppresses Development of Arteriovenous Malformations in Mouse Models of Hereditary Hemorrhagic Telangiectasia

RATIONALE

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disease caused by mutations in ENG, ALK1, or SMAD4. Since proteins from all 3 HHT genes are components of signal transduction of TGF-β (transforming growth factor β) family members, it has been hypothesized that HHT is a disease caused by defects in the ENG-ALK1-SMAD4 linear signaling. However, in vivo evidence supporting this hypothesis is scarce.

OBJECTIVE

We tested this hypothesis and investigated the therapeutic effects and potential risks of induced-ALK1 or -ENG overexpression (OE) for HHT.

METHODS AND RESULTS

We generated a novel mouse allele (ROSA26^Alk1) in which HA (human influenza hemagglutinin)-tagged ALK1 and bicistronic eGFP expression are induced by Cre activity. We examined whether ALK1-OE using the ROSA26^Alk1 allele could suppress the development of arteriovenous malformations (AVMs) in wounded adult skin and developing retinas of Alk1- and Eng-inducible knockout (iKO) mice. We also used a similar approach to investigate whether ENG-OE could rescue AVMs. Biochemical and immunofluorescence analyses confirmed the Cre-dependent OE of the ALK1-HA transgene. We could not detect any pathological signs in ALK1-OE mice up to 3 months after induction. ALK1-OE prevented the development of retinal AVMs and wound-induced skin AVMs in Eng-iKO as well as Alk1-iKO mice. ALK1-OE normalized expression of SMAD and NOTCH target genes in ENG-deficient endothelial cells (ECs) and restored the effect of BMP9 (bone morphogenetic protein 9) on suppression of phosphor-AKT levels in these endothelial cells. On the other hand, ENG-OE could not inhibit the AVM development in Alk1-iKO models.

CONCLUSIONS

These data support the notion that ENG and ALK1 form a linear signaling pathway for the formation of a proper arteriovenous network during angiogenesis. We suggest that ALK1 OE or activation can be an effective therapeutic strategy for HHT. Further research is required to study whether this therapy could be translated into treatment for humans.

Usefulness of the sFlt-1/PlGF (Soluble fms-Like Tyrosine Kinase-1/Placental Growth Factor) Ratio in Diagnosis or Misdiagnosis in Women With Clinical Diagnosis of Preeclampsia

Preeclampsia is characterized by angiogenic imbalance (AI), sFlt-1 (soluble fms-like tyrosine kinase-1)/PlGF (placental growth factor) is useful for its diagnosis and prediction of adverse outcomes, but the relationship among the degrees of AI as assessed by this ratio with the correct diagnosis, clinical characteristics, and outcomes in women with clinical diagnosis of preeclampsia are unclear. We studied 810 women with clinical diagnosis of preeclampsia. Patients were divided into 3 groups based on their degree of AI, evaluated by the sFlt-1/PlGF ratio: no AI (≤38), mild AI (>38-<85), and severe AI (≥85). Patients with no AI were more likely to have comorbidities and false significant proteinuria compared with patients with mild and severe AI (P<0.001). The rates of preterm delivery, delivery within 14 days, and small-for-gestational-age infant were higher among patients with severe AI than in patients with no and mild AI (P<0.001) and in patients with mild AI that in those with no AI (P≤0.01). The occurrence of any adverse maternal outcome (HELLP syndrome, elevated liver enzymes, thrombocytopenia, placental abruption, acute kidney injury) was only present in patients with severe AI. Interestingly, the frequency of misdiagnosis of preeclampsia was progressively lower as the degrees of AI increased (no AI: 100%, mild AI: 88.2%, and severe AI: 15.6%). We concluded that in women with clinical diagnosis of preeclampsia, severe AI is characterized by high frequency of true preeclampsia and preeclampsia-related adverse outcomes, in contrast, no and mild AI, are characterized by unnecessary early deliveries, often due to misdiagnosis.

The relation of serum endocan and soluble endoglin levels with metabolic control in children and adolescents with type 1 diabetes mellitus

Objectives Endothelial dysfunction is an early marker of vascular disease in Type 1 diabetes mellitus (T1DM). In the present study, we aimed to investigate serum endocan and soluble endoglin (S-endoglin) levels, and their relation with metabolic control in children with T1DM, which was not previously assessed. Methods A total of 64 T1DM subjects and 64 healthy subjects were included in this study. Their anthropometric features, arterial blood pressures, pubertal status, insulin doses were recorded. Glycated hemoglobin, serum endocan and S-endoglin levels were measured and compared to each other. Results Serum endocan and S-endoglin levels were higher in children with T1DM than those of healthy group (p<0.01). Significant positive correlation was detected between both endocan and S-endoglin (r=0.579, p<0.001); and HbA1c and endocan (r=0.296, p=0.01). Compared to patients with good metabolic control, those with poorer metabolic control (HbA1c > 8%) had an older age, longer duration of diabetes, higher number of pubertal children. Also, patients with poorer metabolic control had higher endocan and S-endoglin levels than those of healthy group, but this finding did not reach statistical significance. There was no correlation between the endocan/S-endoglin levels and age, duration of diabetes and insulin dose. Conclusion Serum levels of endocan and S-endoglin which are novel biomarkers of endothelial dysfunction are high in children with T1DM. Elevated serum endocan and endoglin levels in children with T1DM without microvascular complications indicates endothelial damage in very early stages of the disease.

Transforming Growth Factor-Beta 1 and Endoglin Levels in Congenital Solitary Functioning Kidney

Introduction:

Glomerular hyperfiltration leads to hypertension, microalbuminuria, and impaired renal function in children with congenital solitary functioning kidney (cSFK). The purpose of this study was to investigate the associations between serum transforming growth factor β-1 (TGF) and endoglin levels and hypertension, renal function or microalbuminuria in children with cSFK.

Materials and Methods:

63 patients and 36 controls were included in the study. Serum endoglin and TGF-β1 level was measured using ELISA commercial kits.

Results:

Serum TGF-β1 and endoglin levels were higher in patients than those of controls (P = 0.04 and P < 0.001, respectively). The prevalence of hypertension was found to be 45.6%. There was a positive association between endoglin levels and the presence of masked hypertension (odds ratio: 1.121, P = 0.04). TGF-β1 and endoglin levels were positively associated with microalbuminuria (OR: 1.17, P = 0.04; OR: 1.836, P = 0.01). ROC curve analysis showed that serum endoglin and TGF-β1 levels had predictive value for microalbuminuria (cut-off value: 4.86 ng/mL, sensitivity: 94.7%, specificity: 54.5%, area under the curve ± standard error [AUC ± SE]: 0.888 ± 0.025, P = 0.01 for endoglin; cut-off value 561.24 pg/mL, sensitivity: 89.5%, specificity: 73%, AUC ± SE: 0.995 ± 0.334, P = 0.02 for TGF-β1). There were no significant relationships between glomerular filtration rate and serum TGF-β1 or endoglin levels.

Conclusions:

Endoglin and TGF-β1 may play an important role in the pathophysiology of microalbuminuria in cSFK. Endoglin may have a role in the development of hypertension in children with cSFK.

Review of Pharmacological Strategies with Repurposed Drugs for Hereditary Hemorrhagic Telangiectasia Related Bleeding

The diagnosis of hereditary hemorrhagic telangiectasia (HHT) is based on the Curaçao criteria: epistaxis, telangiectases, arteriovenous malformations in internal organs, and family history. Genetically speaking, more than 90% of HHT patients show mutations in ENG or ACVRL1/ALK1 genes, both belonging to the TGF-β/BMP9 signaling pathway. Despite clear knowledge of the symptoms and genes of the disease, we still lack a definite cure for HHT, having just palliative measures and pharmacological trials. Among the former, two strategies are: intervention at "ground zero" to minimize by iron and blood transfusions in order to counteract anemia. Among the later, along the last 15 years, three different strategies have been tested: (1) To favor coagulation with antifibrinolytic agents (tranexamic acid); (2) to increase transcription of ENG and ALK1 with specific estrogen-receptor modulators (bazedoxifene or raloxifene), antioxidants (N-acetylcysteine, resveratrol), or immunosuppressants (tacrolimus); and (3) to impair the abnormal angiogenic process with antibodies (bevacizumab) or blocking drugs like etamsylate, and propranolol. This manuscript reviews the main strategies and sums up the clinical trials developed with drugs alleviating HHT.

Potential Role of Circulating Endoglin in Hypertension via the Upregulated Expression of BMP4

Endoglin is a membrane glycoprotein primarily expressed by the vascular endothelium and involved in cardiovascular diseases. Upon the proteolytic processing of the membrane-bound protein, a circulating form of endoglin (soluble endoglin, sEng) can be released, and high levels of sEng have been observed in several endothelial-related pathological conditions, where it appears to contribute to endothelial dysfunction. Preeclampsia is a multisystem disorder of high prevalence in pregnant women characterized by the onset of high blood pressure and associated with increased levels of sEng. Although a pathogenic role for sEng involving hypertension has been reported in several animal models of preeclampsia, the exact molecular mechanisms implicated remain to be identified. To search for sEng-induced mediators of hypertension, we analyzed the protein secretome of human endothelial cells in the presence of sEng. We found that sEng induces the expression of BMP4 in endothelial cells, as evidenced by their proteomic signature, gene transcript levels, and BMP4 promoter activity. A mouse model of preeclampsia with high sEng plasma levels (sEng⁺) showed increased transcript levels of BMP4 in lungs, stomach, and duodenum, and increased circulating levels of BMP4, compared to those of control animals. In addition, after crossing female wild type with male sEng⁺ mice, hypertension appeared 18 days after mating, coinciding with the appearance of high plasma levels of BMP4. Also, serum levels of sEng and BMP4 were positively correlated in pregnant women with and without preeclampsia. Interestingly, sEng-induced arterial pressure elevation in sEng⁺ mice was abolished in the presence of the BMP4 inhibitor noggin, suggesting that BMP4 is a downstream mediator of sEng. These results provide a better understanding on the role of sEng in the physiopathology of preeclampsia and other cardiovascular diseases, where sEng levels are increased.

Resveratrol Promotes Tumor Microvessel Growth via Endoglin and Extracellular Signal-Regulated Kinase Signaling Pathway and Enhances the Anticancer Efficacy of Gemcitabine against Lung Cancer

The synergistic anticancer effect of gemcitabine (GEM) and resveratrol (RSVL) has been noted in certain cancer types. However, whether the same phenomenon would occur in lung cancer is unclear. Here, we uncovered the molecular mechanism by which RSVL enhances the anticancer effect of GEM against lung cancer cells both in vitro and in vivo. We established human lung adenocarcinoma HCC827 xenografts in nude mice and treated them with GEM and RSVL to detect their synergistic effect in vivo. Tumor tissue sections from nude mice were subjected to hematoxylin and eosin staining for blood vessel morphological observation, and immunohistochemistry was conducted to detect CD31-positive staining blood vessels. We also established the HCC827-human umbilical vein endothelial cell (HUVEC) co-culture model to observe the tubule network formation. Human angiogenesis antibody array was used to screen the angiogenesis-related proteins in RSVL-treated HCC827. RSVL suppressed the expression of endoglin (ENG) and increased tumor microvessel growth and blood perfusion into tumor. Co-treatment of RSVL and GEM led to more tumor growth suppression than treatment of GEM alone. Mechanistically, using the HCC827-HUVEC co-culture model, we showed that RSVL-suppressed ENG expression was accompanied with augmented levels of phosphorylated extracellular signal-regulated kinase (ERK) 1/2 and increased tubule network formation, which may explain why RSVL promoted tumor microvessel growth in vivo. RSVL promoted tumor microvessel growth via ENG and ERK and enhanced the anticancer efficacy of GEM. Our results suggest that intake of RSVL may be beneficial during lung cancer chemotherapy.

Dexamethasone causes defective glucose-6-phosphate dehydrogenase dependent antioxidant barrier through endoglin in pregnant and nonpregnant rats

Glucocorticoid therapy has been associated with adverse cardiometabolic effects during pregnancy. Inflammation-mediated cardiac dysfunction, an independent risk factor for morbidity and mortality, has been linked to defective glucose-6-phosphate dehydrogenase (G6PD) dependent antioxidant defenses and increased endoglin expression. We therefore sought to investigate the effects of dexamethasone (DEX) on cardiac endoglin and G6PD-dependent antioxidant defense. Twenty-four rats were randomly assigned to nonpregnant (PRE(-)), DEX-exposed nonpregnant (PRE(-) + DEX), pregnant (PRE(+)), and DEX-exposed pregnant (PRE(+) + DEX) rats, respectively (n = 6 per group). PRE(-) and PRE(+) rats received vehicle (per oral (po)), while PRE(-) + DEX and PRE(+) + DEX groups were administered DEX (0.2 mg/kg po) between gestational days 14 and 19, respectively. Results showed that DEX caused increased cardiac pro-inflammatory markers (adenosine deaminase (ADA) activity, endoglin, vascular cell adhesion molecule-1 (VCAM-1), tissue injury markers (LDH, GGT, AST, ALT, and ALP), metabolic disturbances (elevated fasting plasma glucose, free fatty acid (FFA), lactate, cardiac FFA, and lactate) and depressed G6PD-dependent antioxidant defenses (G6PD activity, reduced glutathione/oxidized glutathione ratio, and nitric oxide) in pregnant and nonpregnant rats. The present study demonstrates that DEX led to increased cardiac endoglin and VCAM-1 that is accompanied by defective G6PD-dependent antioxidant defenses but not cardiac lipid accumulation in both pregnant and nonpregnant rats.

Role of activin receptor-like kinase 1 in vascular development and cerebrovascular diseases

Activin receptor-like kinase 1 (ALK1) is a transmembrane serine/threonine receptor kinase of the transforming growth factor beta (TGFβ) receptor superfamily. ALK1 is specifically expressed in vascular endothelial cells, and its dynamic changes are closely related to the proliferation of endothelial cells, the recruitment of pericytes to blood vessels, and functional differentiation during embryonic vascular development. The pathophysiology of many cerebrovascular diseases is today understood as a disorder of endothelial cell function and an imbalance in the proportion of vascular cells. Indeed, mutations in ALK1 and its co-receptor endoglin are major genetic risk factors for vascular arteriovenous malformation. Many studies have shown that ALK1 is closely related to the development of cerebral aneurysms, arteriovenous malformations, and cerebral atherosclerosis. In this review, we describe the various roles of ALK1 in the regulation of angiogenesis and in the maintenance of cerebral vascular homeostasis, and we discuss its relationship to functional dysregulation in cerebrovascular diseases. This review should provide new perspectives for basic research on cerebrovascular diseases and offer more effective targets and strategies for clinical diagnosis, treatment, and prevention.

Soluble Endoglin (sCD105) as a Novel Biomarker for Detecting Aggressive Prostate Cancer

BACKGROUND/AIM

We have previously found elevated levels of endoglin (CD105) in the prostate cancer (PC) tissue of men with poor prognosis, compared to men with indolent disease. Herein, we examined whether plasma levels of the soluble form of CD105 (sCD105) differ according to the PC grade at diagnosis.

PATIENTS AND METHODS

We measured sCD105 in 73 subjects with biopsy-confirmed PC at the Durham, North Carolina, Veteran Affairs Health System. The association between sCD105 and intermediate/high-grade PC risk [Gleason Group (GG) 2-5 vs. 1] was examined using regression models.

RESULTS

Of 73 men, 27 had low-grade PC and 46 high-grade PC. Higher GG was linked to lower sCD105 (GG1: 6938 pg/ml, GG2-3: 6150 pg/ml, GG4-5: 5554 pg/ml; p=0.012). On multivariable analysis, lower sCD105 was associated with increased high-grade PC risk (OR_{per 1000 units}=1.33, p=0.028).

CONCLUSION

Lower sCD105 levels were associated with intermediate and high-risk PC. Further investigation is warranted in a larger PC cohort.

Amniotic fluid concentrations of soluble endoglin and endothelial cell-specific molecule-1 in pregnancies complicated with neural tube defects

Objective To determine the concentrations of soluble endoglin (sCD105) and endothelial cell-specific molecule-1 (ESM-1) in the amniotic fluid (AF) of pregnant women, and to investigate the relationship between these concentrations and neural tube defects (NTDs). Methods AF concentrations of sCD105 and ESM-1 were measured in the study group, which included 60 pregnant women complicated with NTDs, and 64 pregnant women with unaffected healthy fetuses (control group). The AF concentrations of sCD105 and ESM-1 in both groups were measured using enzyme-linked immunosorbent assay and compared. Results There were no significant differences in terms of the mean AF concentrations of sCD105 and ESM-1 between the groups (P=0.141, P=0.084, respectively). There was a significant difference between the AF sCD105 concentrations in those with gestational age <24 weeks (n=101) and ≥24 weeks (n=23) (X̅<24=76.35±126.62 vs. X≥24=39.87±58.32, P=0.041). AF ESM-1 concentrations were found to be statistically significant in the gestational age <22 weeks (n=90) and ≥22 weeks (n=34) groups (X̅<22=135.91±19.26 vs. X̅≥22=148.56±46.85, P=0.035). A positive and low-level relation at a statistically significant level was determined between the gestational age and AF ESM-1 concentration in the study group (r=0.257; P=0.048). Conclusion AF concentrations of sCD105 and ESM-1 were not associated with the development of NTDs. Unlike studies that reported that ESM-1 concentrations decreased in maternal plasma with increased gestational age, we determined an increase that was proportionate to gestational age in AF.

Novel Biomarkers for Evaluation of Endothelial Dysfunction

Endothelial dysfunction is one of the earliest indicators of cardiovascular (CV) dysfunction, and its evaluation would be of considerable importance to stratify CV risk of many diseases and to assess the efficacy of atheroprotective treatments. Flow-mediated dilation is the most widely used method to study endothelial function. However, it is operator-dependent and can be influenced by physiological variations. Circulating biomarkers are a promising alternative. Due to the complexity of endothelial function, many of the biomarkers studied do not provide consistent information about the endothelium when measured alone. New circulating markers are being explored and some of them are thought to be suitable for the clinical setting. In this review, we focus on novel biomarkers of endothelial dysfunction, particularly endothelial microparticles, endocan, and endoglin, and discuss whether they fulfill the criteria to be applied in clinical practice.

Maternal Serum Placental Growth Factor, Soluble Fms-Like Tyrosine Kinase-1, and Soluble Endoglin in Twin Gestations and the Risk of Preeclampsia-A Systematic Review

Multiple gestation is one of the key risk factors for the occurrence of preeclampsia (PE). Soluble fms-like tyrosine kinase-1, placental growth factor, and soluble endoglin are molecules involved in the process of angiogenesis with a proven role in the pathogenesis of PE. The aim of the review was to summarize available data on maternal serum levels of the above-mentioned factors and their usefulness in predicting PE in twin pregnancies. Only original research articles written in English were considered eligible. Reviews, chapters, case studies, conference papers, experts’ opinions, editorials, and letters were excluded from the analysis. No publication date limitations were imposed. The systematic literature search using PubMed/MEDLINE, Scopus, Embase, and Cochrane Library databases identified 338 articles, 10 of which were included in the final qualitative analyses. The included studies showed significant differences in maternal serum levels of the discussed factors between women with twin pregnancies with PE and those who did not develop PE, and their promising performance in predicting PE, alone or in combination with other factors. The identification of the most effective algorithms, their prompt introduction to the clinical practice, and further assessment of the real-life performance should become a priority.

Soluble CD105 is prognostic of disease recurrence in prostate cancer patients

While the overall 5-year survival rate for prostate cancer is near 100%, up to 35% of patients will develop recurrent disease. At the time of prostatectomy, prostate-specific antigen (PSA) is used to guide primary therapy with the goal of curative intervention. It can be valuable to know when primary therapy may not in fact be curative, so that subsequent adjuvant therapy can be administered at an early stage to limit progression. We examined prostate cancer patients with PSA ≤10 ng/mL that were all subjected to prostatectomy with at least 5 years of follow-up (n = 181). Based on data that endoglin (CD105) signaling in the tumor can contribute to prostate cancer progression, we examined the expression of soluble CD105 (sCD105) in the patient plasma. To determine the relation of plasma sCD105 measures to cellular CD105 in tissues, we tested an independent set of prostate cancer tissues and paired plasma (n = 31). Elevated sCD105 was found to be associated with recurrence-free survival of prostate cancer patients. Further, sCD105 levels in patient plasma were inversely correlated with cellular CD105 expression. This translational study supported preclinical data demonstrating the pro-tumorigenic capacity of cellular CD105 and provide a blood-based biomarker, sCD105, for prostate cancer recurrence in prostatectomy patients with PSA levels ≤10 ng/mL.

Loss of Endothelial Endoglin Promotes High-Output Heart Failure Through Peripheral Arteriovenous Shunting Driven by VEGF Signaling

RATIONALE

ENG (endoglin) is a coreceptor for BMP (bone morphogenetic protein) 9/10 and is strongly expressed in endothelial cells. Mutations in ENG lead to the inherited vascular disorder hereditary hemorrhagic telangiectasia characterized by local telangiectases and larger arteriovenous malformations (AVMs); but how ENG functions to regulate the adult vasculature is not understood.

OBJECTIVE

The goal of the work was to determine how ENG maintains vessel caliber in adult life to prevent AVM formation and thereby protect heart function.

METHODS AND RESULTS

Genetic depletion of endothelial Eng in adult mice led to a significant reduction in mean aortic blood pressure. There was no evidence of hemorrhage, anemia, or AVMs in major organs to explain the reduced aortic pressure. However, large AVMs developed in the peripheral vasculature intimately associated with the pelvic cartilaginous symphysis-a noncapsulated cartilage with a naturally high endogenous expression of VEGF (vascular endothelial growth factor). The increased blood flow through these peripheral AVMs explained the drop in aortic blood pressure and led to increased cardiac preload, and high stroke volumes, ultimately resulting in high-output heart failure. Development of pelvic AVMs in this region of high VEGF expression occurred because loss of ENG in endothelial cells leads to increased sensitivity to VEGF and a hyperproliferative response. Development of AVMs and associated progression to high-output heart failure in the absence of endothelial ENG was attenuated by targeting VEGF signaling with an anti-VEGFR2 (VEGF receptor 2) antibody.

CONCLUSIONS

ENG promotes the normal balance of VEGF signaling in quiescent endothelial cells to maintain vessel caliber-an essential function in conditions of increased VEGF expression such as local hypoxia or inflammation. In the absence of endothelial ENG, increased sensitivity to VEGF drives abnormal endothelial proliferation in local regions of high VEGF expression, leading to AVM formation and a rapid injurious impact on heart function.

Structural biology of betaglycan and endoglin, membrane-bound co-receptors of the TGF-beta family

Betaglycan and endoglin, membrane-bound co-receptors of the TGF-β family, are required to mediate the signaling of a select subset of TGF-β family ligands, TGF-β2 and InhA, and BMP-9 and BMP-10, respectively. Previous biochemical and biophysical methods suggested alternative modes of ligand binding might be responsible for these co-receptors to selectively recognize and potentiate the functions of their ligands, yet the molecular details were lacking. Recent progress determining structures of betaglycan and endoglin, both alone and as bound to their cognate ligands, is presented herein. The structures reveal relatively minor, but very significant structural differences that lead to entirely different modes of ligand binding. The different modes of binding nonetheless share certain commonalities, such as multivalency, which imparts the co-receptors with very high affinity for their cognate ligands, but at the same time provides a mechanism for release by stepwise binding of the signaling receptors, both of which are essential for their functions.

Identification of an Endoglin Variant Associated With HCV-Related Liver Fibrosis Progression by Next-Generation Sequencing

Despite the astonishing progress in treating chronic hepatitis C virus (HCV) infection with direct-acting antiviral agents, liver fibrosis remains a major health concern in HCV infected patients, in particular due to the treatment cost and insufficient HCV screening in many countries. Only a fraction of patients with chronic HCV infection develop liver fibrosis. While there is evidence that host genetic factors are involved in the development of liver fibrosis, the common variants identified so far, in particular by genome-wide association studies, were found to have limited effects. Here, we conducted an exome association study in 88 highly selected HCV-infected patients with and without fibrosis. A strategy focusing on TGF-β pathway genes revealed an enrichment in rare variants of the endoglin gene (ENG) in fibrosis patients. Replication studies in additional cohorts (617 patients) identified one specific ENG variant, Thr5Met, with an overall odds ratio for fibrosis development in carriers of 3.04 (1.39-6.69). Our results suggest that endoglin, a key player in TGF-β signaling, is involved in HCV-related liver fibrogenesis.

Endoglin Protein Interactome Profiling Identifies TRIM21 and Galectin-3 as New Binding Partners

Endoglin is a 180-kDa glycoprotein receptor primarily expressed by the vascular endothelium and involved in cardiovascular disease and cancer. Heterozygous mutations in the endoglin gene (ENG) cause hereditary hemorrhagic telangiectasia type 1, a vascular disease that presents with nasal and gastrointestinal bleeding, skin and mucosa telangiectases, and arteriovenous malformations in internal organs. A circulating form of endoglin (alias soluble endoglin, sEng), proteolytically released from the membrane-bound protein, has been observed in several inflammation-related pathological conditions and appears to contribute to endothelial dysfunction and cancer development through unknown mechanisms. Membrane-bound endoglin is an auxiliary component of the TGF-β receptor complex and the extracellular region of endoglin has been shown to interact with types I and II TGF-β receptors, as well as with BMP9 and BMP10 ligands, both members of the TGF-β family. To search for novel protein interactors, we screened a microarray containing over 9000 unique human proteins using recombinant sEng as bait. We find that sEng binds with high affinity, at least, to 22 new proteins. Among these, we validated the interaction of endoglin with galectin-3, a secreted member of the lectin family with capacity to bind membrane glycoproteins, and with tripartite motif-containing protein 21 (TRIM21), an E3 ubiquitin-protein ligase. Using human endothelial cells and Chinese hamster ovary cells, we showed that endoglin co-immunoprecipitates and co-localizes with galectin-3 or TRIM21. These results open new research avenues on endoglin function and regulation.

Endoglin Trafficking/Exosomal Targeting in Liver Cells Depends on N-Glycosylation

Injury of the liver involves a wound healing partial reaction governed by hepatic stellate cells and portal fibroblasts. Individual members of the transforming growth factor-β (TGF-β) superfamily including TGF-β itself and bone morphogenetic proteins (BMP) exert diverse and partially opposing effects on pro-fibrogenic responses. Signaling by these ligands is mediated through binding to membrane integral receptors type I/type II. Binding and the outcome of signaling is critically modulated by Endoglin (Eng), a type III co-receptor. In order to learn more about trafficking of Eng in liver cells, we investigated the membranal subdomain localization of full-length (FL)-Eng. We could show that FL-Eng is enriched in Caveolin-1-containing sucrose gradient fractions. Since lipid rafts contribute to the pool of exosomes, we could consequently demonstrate for the first time that exosomes isolated from cultured primary hepatic stellate cells and its derivatives contain Eng. Moreover, via adenoviral overexpression, we demonstrate that all liver cells have the capacity to direct Eng to exosomes, irrespectively whether they express endogenous Eng or not. Finally, we demonstrate that block of N-glycosylation does not interfere with dimerization of the receptor, but abrogates the secretion of soluble Eng (sol-Eng) and prevents exosomal targeting of FL-Eng.

Soluble Endoglin As a Marker for Preeclampsia, Its Severity, and the Occurrence of Adverse Outcomes

Preeclampsia is characterized by an imbalance in angiogenic factors, including sEng (soluble endoglin). However, the relationship of sEng with the severity of preeclampsia, clinical, and laboratory parameters, and the occurrence of adverse outcomes are not fully elucidated. We studied 1002 women with preeclampsia. Serum concentrations of sEng were measured by ELISA. Serum sEng levels were significantly different (P<0.001) in patients with preeclampsia than in healthy pregnancy. In addition, these factors were markedly different in patients with hemolysis, elevated liver enzymes, low platelet count syndrome and eclampsia than in patients with preeclampsia with or without severe features (P<0.001) and in patients with preeclampsia with severe features than in those without severe features (P<0.001). sEng correlated positively with blood pressure, proteinuria, and levels of creatinine, uric acid, aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase; and inversely with gestational age, infant's birth weight, and platelets counts (P<0.001 for all). The risk of combined and specific adverse outcomes (pulmonary edema, acute renal failure, placental abruption, hepatic hematoma or rupture, maternal death, cerebral hemorrhage, thrombocytopenia, elevated liver enzymes, preterm delivery, small for gestational age infant, and need for endotracheal intubation, positive inotropic drug support, and hemodialysis) was higher in patients with sEng values in the highest quartile (odds ratio ≥3.1) compared with the lowest quartile. Patients in the highest quartile of sEng were more likely to deliver early compared with those in the lowest quartile (HR, 2.33; 95% CI, 1.91-2.84). We concluded that circulating concentrations of sEng seem to be a suitable marker to assess the severity of preeclampsia and are associated with increased risk of adverse outcomes.

CD105 as a tool for assessing microvessel density in renal cell carcinoma

Background

Angiogenesis plays an essential role in both tumor growth and metastasis. CD105 expression was correlated with prognosis in many tumors, but its value in renal cell carcinoma (RCC) is still questionable.

Materials and Methods

The aim of this study was to evaluate microvessel density (MVD) by using CD105 marker, in 95 cases of renal cell carcinoma.

Results

CD105 showed positivity in 93 cases. The mean MVD value was significantly higher in clear cell carcinoma compared to papillary and chromophobe subtypes (P = 0.000). We noticed a significant correlation between MVD and ISUP grade (P = 0.007). The highest MVD value was observed in tumors with ISUP grade 1 and 2, while the lowest MVD value was noted in ISUP grade 3 tumors. A high vessel density was identified in tumors with a low Fuhrman grade, compared to those with a high grade (P = 0.010). MVD value was lower in tumors with a larger diameter, compared to small ones (P = 0.026).

Conclusion

In conclusion, CD105 expression (MVD) is inversely related to tumor aggressiveness in clear cell RCC and can be used as a favorable prognosis marker. The vascularity differences between histological subtypes of RCCs could be useful for a better selection of patients that may benefit from anti-angiogenic therapies.

BMP9 directly induces rapid GSK3-β phosphorylation in a Wnt-independent manner through class I PI3K-Akt axis in osteoblasts

Bone morphogenetic protein (BMP)9 has been reported to be the most potent BMP to induce bone formation. However, the details of BMP9-transduced intracellular signaling remain ambiguous. Here, we have investigated signal transduction mechanisms of BMP9 in comparison to BMP2, another potent inducer of bone formation, in osteoblasts. In a mouse osteoblast cell line, BMP9 induced higher mRNA levels of alkaline phosphatase (ALP) and runt-related transcription factor 2 (Runx2) than BMP2 within 2 h. Unlike BMP2, BMP9 induced rapid phosphorylation of glycogen synthase kinase 3-β (GSK3-β) and protein kinase B (Akt) and increased the cellular protein content of β-catenin. BMP9 moderately increased mRNA levels of several canonical Wingless-related integration site to lower degrees than BMP2. Furthermore, BMP9-induced GSK3-β phosphorylation was not inhibited by pretreatment with actinomycin D, cycloheximide, or Brefeldin A, indicating it is independent of Wnt protein secretion. BMP9-induced GSK3-β phosphorylation was abrogated by Akt or class I PI3K-specific inhibitors. Moreover, inactivation of GSK3-β by LiCl did not further promote ALP and Runx2 mRNA induction by BMP9 as significantly as that by BMP2. Notably, BMP9-induced GSK3-β phosphorylation was inhibited by small interfering RNA against endoglin and GIPC PDZ domain-containing family, member 1. Taken together, our present findings have indicated that BMP9 directly activates GSK3β-β-catenin signaling pathway through class I PI3K-Akt Axis in osteoblasts, which may be essential for the potent osteoinductive activity of BMP9.-Eiraku, N., Chiba, N., Nakamura, T., Amir, M. S., Seong, C.-H., Ohnishi, T., Kusuyama, J., Noguchi, K., Matsuguchi, T. BMP9 directly induces rapid GSK3-β phosphorylation in a Wnt-independent manner through class I PI3K-Akt axis in osteoblasts.

Structural Adaptation in Its Orphan Domain Engenders Betaglycan with an Alternate Mode of Growth Factor Binding Relative to Endoglin

Betaglycan (BG) and endoglin (ENG), homologous co-receptors of the TGF-β family, potentiate the signaling activity of TGF-β2 and inhibin A, and BMP-9 and BMP-10, respectively. BG exists as monomer and forms 1:1 growth factor (GF) complexes, while ENG exists as a dimer and forms 2:1 GF complexes. Herein, the structure of the BG orphan domain (BG_O) reveals an insertion that blocks the region that the endoglin orphan domain (ENG_O) uses to bind BMP-9, preventing it from binding in the same manner. Using binding studies with domain-deleted forms of TGF-β and BG_O, as well as small-angle X-ray scattering data, BG_O is shown to bind its cognate GF in an entirely different manner compared with ENG_O. The alternative interfaces likely engender BG and ENG with the ability to selectively bind and target their cognate GFs in a unique temporal-spatial manner, without interfering with one another or other TGF-β family GFs.

MMP-12, Secreted by Pro-Inflammatory Macrophages, Targets Endoglin in Human Macrophages and Endothelial Cells

Upon inflammation, monocyte-derived macrophages (MΦ) infiltrate blood vessels to regulate several processes involved in vascular pathophysiology. However, little is known about the mediators involved. Macrophage polarization is crucial for a fast and efficient initial response (GM-MΦ) and a good resolution (M-MΦ) of the inflammatory process. The functional activity of polarized MΦ is exerted mainly through their secretome, which can target other cell types, including endothelial cells. Endoglin (CD105) is a cell surface receptor expressed by endothelial cells and MΦ that is markedly upregulated in inflammation and critically involved in angiogenesis. In addition, a soluble form of endoglin with anti-angiogenic activity has been described in inflammation-associated pathologies. The aim of this work was to identify components of the MΦ secretome involved in the shedding of soluble endoglin. We find that the GM-MΦ secretome contains metalloprotease 12 (MMP-12), a GM-MΦ specific marker that may account for the anti-angiogenic activity of the GM-MΦ secretome. Cell surface endoglin is present in both GM-MΦ and M-MΦ, but soluble endoglin is only detected in GM-MΦ culture supernatants. Moreover, MMP-12 is responsible for the shedding of soluble endoglin in vitro and in vivo by targeting membrane-bound endoglin in both MΦ and endothelial cells. These data demonstrate a direct correlation between GM-MΦ polarization, MMP-12, and soluble endoglin expression and function. By targeting endothelial cells, MMP-12 may represent a novel mediator involved in vascular homeostasis.

Synergistic Anti-Angiogenic Effects Using Peptide-Based Combinatorial Delivery of siRNAs Targeting VEGFA, VEGFR1, and Endoglin Genes

Angiogenesis is a process of new blood vessel formation, which plays a significant role in carcinogenesis and the development of diseases associated with pathological neovascularization. An important role in the regulation of angiogenesis belongs to several key pathways such as VEGF-pathways, TGF-β-pathways, and some others. Introduction of small interfering RNA (siRNA) against genes of pro-angogenic factors is a promising strategy for the therapeutic suppression of angiogenesis. These siRNA molecules need to be specifically delivered into endothelial cells, and non-viral carriers modified with cellular receptor ligands can be proposed as perspective delivery systems for anti-angiogenic therapy purposes. Here we used modular peptide carrier L1, containing a ligand for the CXCR4 receptor, for the delivery of siRNAs targeting expression of VEGFA, VEGFR1 and endoglin genes. Transfection properties of siRNA/L1 polyplexes were studied in CXCR4-positive breast cancer cells MDA-MB-231 and endothelial cells EA.Hy926. We have demonstrated the efficient down-regulation of endothelial cells migration and proliferation by anti-VEGFA, anti-VEGFR1, and anti-endoglin siRNA-induced silencing. It was found that the efficiency of anti-angiogenic treatment can be synergistically improved via the combinatorial delivery of anti-VEGFA and anti-VEGFR1 siRNAs. Thus, this approach can be useful for the development of therapeutic angiogenesis inhibition.

Elevated Expressions of Survivin and Endoglin in Patients with Hepatic Carcinoma

OBJECTIVE

To investigate expression profiles of survivin and endoglin in patients with hepatic carcinoma.

MATERIALS AND METHODS

Cancerous tissues (hepatic carcinoma group) of 48 patients with hepatic carcinoma and adjacent noncancerous hepatic tissues (control group) were used as objects of study. Histopathological staining [hematoxylin & eosin (H&E) staining] was used to study the pathological differences in hepatic tissues between hepatic carcinoma group and control group. Moreover, survivin and endoglin protein expressions in hepatic tissues in hepatic carcinoma group and control group were detected via western blotting. Finally, Statistical Product and Service Solutions 17.0 statistical software was used to analyze the differences in survivin and endoglin expressions in hepatic tissues between hepatic carcinoma group and control group.

RESULTS

H&E staining showed that histopathological features in hepatic carcinoma group were significantly different from those in control group. Compared with those in control group, the cell structure in hepatic carcinoma group was damaged, karyopyknosis was obvious, and the hepatic injury was serious. Reverse transcription-polymerase chain reaction showed that survivin and endoglin mRNA expression levels in hepatic carcinoma group were significantly increased compared with those in control group. Besides, immunofluorescence method and western blotting revealed the low expressions of survivin and endoglin proteins in tissues in control group, which were obviously lower than those in hepatic tissues in hepatic carcinoma group. Results of analyses of variance showed that the expressions of survivin and endoglin in normal hepatic tissues and cancerous tissues had statistically significant differences (p < 0.01). Furthermore, expressions of survivin and endoglin were significantly associated with histological grade, tumor size, and tumor, node, metastasis (TNM) stage.

CONCLUSION

Elevated expressions of survivin and endoglin are associated with histological grade, tumor size, and TNM stage in patients with hepatic carcinoma, indicating that survivin and endoglin might be involved in the pathogenesis of hepatic carcinoma and therapeutic targeting them might be a novel approach for the treatment of hepatic carcinoma.

Decreased sEng plasma levels in hypertensive patients with endothelial dysfunction under chronic treatment with Perindopril

Purpose: Endoglin is a transmembrane glycoprotein which plays an important role in maintaining cardiovascular homeostasis. One of its forms, soluble endoglin (sEng), a molecule with antiangiogenic properties, has been found overexpressed in patients suffering from hypercholesterolemia, diabetes mellitus and hypertension, and is proposed as a marker of endothelial damage. Accordingly, we aimed to quantify the efficacy of various antihypertensive regimens on sEng levels, in hypertensive patients with endothelial dysfunction.

Patients and methods: 323 patients were enrolled, and there were 99 patients with normal blood pressure values, 106 hypertensive patients under chronic treatment with different types of antihypertensive molecules (beta blockers, calcium channel blockers, and diuretics) in monotherapy, and 118 hypertensive patients under chronic treatment with perindopril. sEng plasma levels were quantified and were correlated with classical methods of assessing the endothelial damage.

Results: Patients under chronic treatment with perindopril had lower sEng plasma levels compared with the other group of hypertensive patients under different regimens of antihypertensive treatment (sEng: 4.73±1.39 versus 5.63±2.33, p<0.01).

Conclusion: Decreased sEng plasma levels were found in patients under chronic treatment with perindopril, when compared with other antihypertensive regimens of treatment (beta blockers, calcium channel blockers, and/or diuretics).

Endoglin is a conserved regulator of vasculogenesis in zebrafish - implications for hereditary haemorrhagic telangiectasia

Hereditary haemorrhagic telangiectasia (HHT) is a progressive vascular disease with high mortality and prevalence. There is no effective treatment of HHT due to the lack of comprehensive knowledge of its underlying pathological mechanisms. The majority of HHT1 patients carry endoglin (ENG) mutations. Here, we used Danio rerio (zebrafish) as an in vivo model to investigate the effects of endoglin knockdown on vascular development. According to phylogenetic analyses and amino acid sequence similarity analyses, we confirmed that endoglin is conserved in vertebrates and descended from a single common ancestor. Endoglin is highly expressed in the vasculature beginning at the segmentation period in zebrafish. Upon endoglin knockdown by morpholinos, we observed disruption in the intersegmental vessels (ISVs) and decreased expression of several vascular markers. RNA sequencing (RNA-Seq) results implied that the BMP-binding endothelial regulator (bmper) is a gene affected by endoglin knockdown. Rescue experiments demonstrated that overexpression of bmper significantly increased the number of endothelial cells (ECs) and reduced the defects at ISVs in zebrafish. Moreover, there was enhanced tube formation in ENG mutant ECs derived from a HHT patient after human recombinant BMPER (hrBMPER) stimulation. Taken together, our results suggest that bmper, a potential downstream gene of ENG, could be targeted to improve vascular integrity in HHT.

Bioreactor-Controlled Physoxia Regulates TGF-β Signaling to Alter Extracellular Matrix Synthesis by Human Chondrocytes

Culturing articular chondrocytes under physiological oxygen tension exerts positive effects on their extracellular matrix synthesis. The underlying molecular mechanisms which enhance the chondrocytic phenotype are, however, still insufficiently elucidated. The TGF-β superfamily of growth factors, and the prototypic TGF-β isoforms in particular, are crucial in maintaining matrix homeostasis of these cells. We employed a feedback-controlled table-top bioreactor to investigate the role of TGF-β in microtissues of human chondrocytes over a wider range of physiological oxygen tensions (i.e., physoxia). We compared 1%, 2.5%, and 5% of partial oxygen pressure (pO₂) to the ‘normoxic’ 20%. We confirmed physoxic conditions through the induction of marker genes (PHD3, VEGF) and oxygen tension-dependent chondrocytic markers (SOX9, COL2A1). We identified 2.5% pO₂ as an oxygen tension optimally improving chondrocytic marker expression (ACAN, COL2A1), while suppressing de-differentiation markers (COL1A1,COL3A1). Expression of TGF-β isoform 2 (TGFB2) was, relatively, most responsive to 2.5% pO₂, while all three isoforms were induced by physoxia. We found TGF-β receptors ALK1 and ALK5 to be regulated by oxygen tension on the mRNA and protein level. In addition, expression of type III co-receptors betaglycan and endoglin appeared to be regulated by oxygen tension as well. R-Smad signaling confirmed that physoxia divergently regulated phosphorylation of Smad1/5/8 and Smad2/3. Pharmacological inhibition of canonical ALK5-mediated signaling abrogated physoxia-induced COL2A1 and PAI-1 expression. Physoxia altered expression of hypertrophy markers and that of matrix metalloproteases and their activity, as well as expression ratios of specific proteins (Sp)/Krüppel-like transcription factor family members SP1 and SP3, proving a molecular concept of ECM marker regulation. Keeping oxygen levels tightly balanced within a physiological range is important for optimal chondrocytic marker expression. Our study provides novel insights into transcriptional regulations in chondrocytes under physoxic in vitro conditions and may contribute to improving future cell-based articular cartilage repair strategies.

Human epithelial ovarian cancer cells expressing CD105, CD44 and CD106 surface markers exhibit increased invasive capacity and drug resistance

The high rate of mortality associated with ovarian cancer (OC) is due in part to the development of resistance to chemotherapy, which allows the resistant tumour cells to invade and metastasise. Clarifying the mechanistic basis for drug resistance may reveal novel avenues for treatment. The present study investigated the mechanism of paclitaxel (PTX) resistance in human epithelial OC by evaluating the expression of stem cell-associated cell surface markers endoglin (CD105), CD44 antigen and vascular cell adhesion molecule 1 (CD106), in association with the malignant potential of the human OC OVCAR3 cell line and its PTX-resistant derivative OC3/TAX300. The expression of CD105, CD44 and CD106 was detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR) and flow cytometry, and cell invasion was evaluated using a Transwell invasion assay. CD105, CD44 and CD106 levels were increased in OC3/TAX300 cells compared with the OVCAR3 cells, as determined by flow cytometry (P<0.01) and RT-qPCR (P<0.05). Additionally, the number of invading cells was increased in the OC3/TAX300 group compared with the OVCAR3 group (54.7±6.65 vs. 31.8±6.55; P<0.01). A western blot analysis of cell surface marker expression in 80 clinical epithelial OC tissue samples, differing in terms of sensitivity to drug treatments, disease stage and degree of differentiation, revealed that high CD105, CD44 or CD106 expression was associated with drug resistance, advanced disease stage, poor differentiation and high rate of recurrence. These data indicated that exposure to high doses of PTX enhanced the stem-like properties of OC cells, which are associated with drug resistance and invasion and lead to poor prognosis due to induced chemoresistance and/or metastasis. Therefore, CD105, CD44 and CD106 may serve as potential stem cell-associated cell surface and prognostic markers, and therapeutic targets, in OC.