Human Endoglin Research Articles

High soluble endoglin levels do not induce endothelial dysfunction in mouse aorta.

Increased levels of a soluble form of endoglin (sEng) circulating in plasma have been detected in various pathological conditions related to cardiovascular system. High concentration of sEng was also proposed to contribute to the development of endothelial dysfunction, but there is no direct evidence to support this hypothesis. Therefore, in the present work we analyzed whether high sEng levels induce endothelial dysfunction in aorta by using transgenic mice with high expression of human sEng. Transgenic mice with high expression of human sEng on CBAxC57Bl/6J background (Sol-Eng +) and age-matched transgenic littermates that do not develop high levels of human soluble endoglin (control animals in this study) on chow diet were used. As expected, male and female Sol-Eng + transgenic mice showed higher levels of plasma concentrations of human sEng as well as increased blood arterial pressure, as compared to control animals. Functional analysis either in vivo or ex vivo in isolated aorta demonstrated that the endothelium-dependent vascular function was similar in Sol-Eng + and control mice. In addition, Western blot analysis showed no differences between Sol-Eng + and control mice in the protein expression levels of endoglin, endothelial NO-synthase (eNOS) and pro-inflammatory ICAM-1 and VCAM-1 from aorta. Our results demonstrate that high levels of soluble endoglin alone do not induce endothelial dysfunction in Sol-Eng + mice. However, these data do not rule out the possibility that soluble endoglin might contribute to alteration of endothelial function in combination with other risk factors related to cardiovascular disorders.

Soluble Endoglin Specifically Binds Bone Morphogenetic Proteins 9 and 10 via Its Orphan Domain, Inhibits Blood Vessel Formation, and Suppresses Tumor Growth

Endoglin (CD105), a transmembrane protein of the transforming growth factor β superfamily, plays a crucial role in angiogenesis. Mutations in endoglin result in the vascular defect known as hereditary hemorrhagic telangiectasia (HHT1). The soluble form of endoglin was suggested to contribute to the pathogenesis of preeclampsia. To obtain further insight into its function, we cloned, expressed, purified, and characterized the extracellular domain (ECD) of mouse and human endoglin fused to an immunoglobulin Fc domain. We found that mouse and human endoglin ECD-Fc bound directly, specifically, and with high affinity to bone morphogenetic proteins 9 and 10 (BMP9 and BMP10) in surface plasmon resonance (Biacore) and cell-based assays. We performed a function mapping analysis of the different domains of endoglin by examining their contributions to the selectivity and biological activity of the protein. The BMP9/BMP10 binding site was localized to the orphan domain of human endoglin composed of the amino acid sequence 26-359. We established that endoglin and type II receptors bind to overlapping sites on BMP9. In the in vivo chick chorioallantoic membrane assay, the mouse and the truncated human endoglin ECD-Fc both significantly reduced VEGF-induced vessel formation. Finally, murine endoglin ECD-Fc acted as an anti-angiogenic factor that decreased blood vessel sprouting in VEGF/FGF-induced angiogenesis in in vivo angioreactors and reduced the tumor burden in the colon-26 mouse tumor model. Together our findings indicate an important role of soluble endoglin ECD in the regulation of angiogenesis and highlight efficacy of endoglin-Fc as a potential anti-angiogenesis therapeutic agent.

Preeclampsia, a disease of the maternal endothelium: the role of antiangiogenic factors and implications for later cardiovascular disease.

Preeclampsia is a clinical syndrome defined as the new onset of hypertension and proteinuria during the second half of pregnancy.1 It afflicts 3% to 5% of pregnancies and is a leading cause of maternal mortality, especially in developing countries.2,3 Because the only known remedy is delivery of the placenta, in developed countries preeclampsia is an important cause of premature delivery, usually medically indicated for the benefit of the mother. This results in infant morbidity and substantial healthcare expenditure.4 Despite the considerable morbidity and mortality, the cause of preeclampsia has remained enigmatic. Both hypertension and proteinuria implicate the endothelium as the target of the disease. The hypertension of preeclampsia is characterized by peripheral vasoconstriction and decreased arterial compliance.5,6 The proteinuria of preeclampsia is associated with a pathognomonic renal lesion known as glomerular endotheliosis, in which the endothelial cells of the glomerulus swell and endothelial fenestrations are lost.7,8 Podocyturia has been recently associated with preeclampsia during clinical disease9; however, whether this is the cause or effect of proteinuria is unknown. The glomerular filtration rate is decreased compared with normotensive pregnant women; in rare cases, acute renal failure may develop. Preeclampsia is a systemic vascular disorder that may also affect the liver and the brain in the mothers. When the liver is involved, women may present with abdominal pain, nausea, vomiting, and elevated liver enzymes. Pathological examination of the liver reveals periportal and sinusoidal fibrin deposition and, in more extreme cases, hemorrhage and necrosis.10 The severe preeclampsia variant HELLP syndrome (hemolysis, elevated liver enzymes, low platelets) occurs in ≈20% of women with severe preeclampsia,11 and is named not only for the liver involvement, but also for the disorder of the coagulation system that develops.12 Approximately 20% of …

Endoglin Upregulation in the Liver after Bile Duct Ligation in Rats

Background: Transforming growth factor beta 1 (TGF- 1) has been implicated in the stimulation of extracellu- lar matrix synthesis in acute and chronic liver disease. Endoglin (CD-105) is a membrane glycoprotein that binds TGF- 1 with high affinity. Endoglin is overexpressed in several model of fibrosis. The goal of the present study was to evaluate the effect of bile duct ligation (BDL) on endoglin expression and the effect of endoglin overexpression on liver fibrosis in rats. Methods: Rat livers were transfected with a vector containing full length human endoglin (h-end) or an empty vector (mock) and 48 hours after were subjected to either BDL or sham operation (SO). Eighteen days after, a blood sample was obtained and bilirubin and serum enzyme activities were measured to assess liver damage. Liver fibrosis was quantified by a computer-assisted image analysis of Sirius red stained livers and by liver hydroxyproline content. Endoglin expres- sion in the liver tissue was assessed by Western blot and immunohystochemistry. Results: Both immunohistochemistry and Western blot reveals endoglin upregulation after BDL in rats. In addition, these techniques also reveal effective human endoglin transfection in the rat's liver. After BDL, liver fibrosis and plasma levels of enzymes were similar in h-end transfected and mock-transfected rats. Western blots showed higher endoglin expression after BDL in h-end transfected and mock-transfected rats. Conclusions: The present study provides clear evidence that endoglin is upregulated in the liver of rats with BDL. h-end overexpression did not improve liver fibrosis after BDL in rats.

Dynamic expression of Endoglin, a TGF-beta co-receptor, during pre-circulation vascular development in chick

Mutations in the human Endoglin gene, encoding a dimeric TGF-beta co-receptor, lead to type 1 hereditary hemorrhagic telangiectasia. Studies in mice have revealed important roles of Endoglin in endothelial cell proliferation, differentiation and integrity. Endoglin(-/-) mouse embryos die at mid-gestation due to cardiac defects and vessel rupture. Its role during early vasculogenesis is unclear, as the initial phase of vascular endothelial cell formation appears unaffected in Endoglin(-/-) embryos. In order to understand possible roles of Endoglin in early vascular development, we used the chick model and analyzed the temporal and spatial expression pattern of Endoglin during vasculogenesis in pre-circulation stage chick embryos. Weak Endoglin expression was detected at HH4 in the node and in the extraembryonic mesoderm. The node-specific expression is transitory and disappears after HH5. Strong up-regulation of Endoglin expression is seen at HH8 in all endothelial progenitors undergoing morphological changes to become endothelial cells. Most extraembryonic splanchnopleural vascular endothelial cells down-regulate Endoglin after their morphological differentiation, whereas lateral plate and cardiac endothelial cells remain positive until HH12, followed by a clear drop after circulation starts at HH13. Progenitors for the pronephric duct are positive from HH10 to HH12, but down-regulate Endoglin after epithelialization of duct cells. Overall, these data reveal a dynamic expression pattern of Endoglin in pre-circulation chick development and indicate that Endoglin may play an important role in the transition from endothelial progenitors to functional endothelial cells during early vascular development.

Endoglin is dispensable for angiogenesis, but required for endocardial cushion formation in the midgestation mouse embryo

Vascular patterning depends on precisely coordinated timing of endothelial cell differentiation and onset of cardiac function. Endoglin is a transmembrane receptor for members of the TGF-beta superfamily that is expressed on endothelial cells from early embryonic gestation to adult life. Heterozygous loss of function mutations in human ENDOGLIN cause Hereditary Hemorrhagic Telangiectasia Type 1, a vascular disorder characterized by arteriovenous malformations that lead to hemorrhage and stroke. Endoglin null mice die in embryogenesis with numerous lesions in the cardiovascular tree including incomplete yolk sac vessel branching and remodeling, vessel dilation, hemorrhage and abnormal cardiac morphogenesis. Since defects in multiple cardiovascular tissues confound interpretations of these observations, we performed in vivo chimeric rescue analysis using Endoglin null embryonic stem cells. We demonstrate that Endoglin is required cell autonomously for endocardial to mesenchymal transition during formation of the endocardial cushions. Endoglin null cells contribute widely to endothelium in chimeric embryos rescued from cardiac development defects, indicating that Endoglin is dispensable for angiogenesis and vascular remodeling in the midgestation embryo, but is required for early patterning of the heart.

Production and Characterization of a High-Affinity Nanobody Against Human Endoglin

Abstract Antibodies or antibody fragments are almost exclusively applied in human therapy and diagnosis. The high affinity and specificity of antibodies makes them suitable for these applications. Nanobody, the variable domain of Camelidae heavy chain antibodies, have superior properties compared with conventional antibodies in that they are small, non-immunogenic, very stable, highly soluble, and easy to produce in large quantities. In the present study, we report the isolation and characterization of a high-affinity binder against human endoglin retrieved from camels' nanobody gene library. Endoglin (CD105), an accessory protein of the transforming growth factor beta receptor complex, has become an attractive molecule for the targeting of the tumor vasculature. Upregulation of endoglin on proliferating endothelial cells is associated with tumor neovascularization. Here, we generated two nanobody gene libraries displayed on phage particles. Some single-domain antibody fragments have been isolated that specifically recognize the recombinant extracellular domain of human endoglin. The other selected anti-endoglin nanobody (AR1-86) showed strong binding to human endoglin expressing endothelial cells (HUVECs), while no binding was observed with the endoglin-negative cell line (HEK293). This high-affinity single-domain antibody could be a good candidate for the generation of vascular or tumor targeting agents in cancer therapy.

Structural Model of Human Endoglin, a Transmembrane Receptor Responsible for Hereditary Hemorrhagic Telangiectasia

Endoglin is a type I membrane protein expressed as a disulphide-linked homodimer on human vascular endothelial cells whose haploinsufficiency is responsible for the dominant vascular dysplasia known as hereditary hemorrhagic telangiectasia (HHT). Structurally, endoglin belongs to the zona pellucida (ZP) family of proteins that share a ZP domain of ∼260 amino acid residues at their extracellular region. Endoglin is a component of the TGF-β receptor complex, interacts with the TGF-β signalling receptors types I and II, and modulates cellular responses to TGF-β. Here, we have determined for the first time the three-dimensional structure of the ∼140 kDa extracellular domain of endoglin at 25 Å resolution, using single-particle electron microscopy (EM). This reconstruction provides the general architecture of endoglin, which arranges as a dome made of antiparallel oriented monomers enclosing a cavity at one end. A high-resolution structure of endoglin has also been modelled de novo and found to be consistent with the experimental reconstruction. Each subunit comprises three well-defined domains, two of them corresponding to ZP regions, organised into an open U-shaped monomer. This domain arrangement was found to closely resemble the overall structure derived experimentally and the three modelled de novo domains were tentatively assigned to the domains observed in the EM reconstruction. This molecular model was further tested by tagging endoglin's C terminus with an IgG Fc fragment visible after 3D reconstruction of the labelled protein. Combined, these data provide the structural framework to interpret endoglin's functional domains and mutations found in HHT patients.

In vitro characterization of binding and stability of single-chain Fv Ni-NTA-liposomes

Recently, we presented a new method for the generation of single-chain Fv (scFv) immunoliposomes, which circumvents the necessity to introduce additional reactive groups in the protein. This method is based on immobilizing scFv fragments via their C-terminal hexahistidyl-tag on liposomes containing nickel-complexed dioleoyl-glycero-succinyl-nitrilotriacetic acid (Ni-NTA-DOGS) as an anchor lipid within the lipid bilayer. Here, we have extended this approach to various other scFv fragments and further demonstrate strong and selective binding of these liposomes to target cells in vitro. In order to evaluate suitability for in vivo applications, we investigated the influence of human plasma on stability and binding behaviour of scFv Ni-NTA-liposomes in vitro using scFv A5 directed against human endoglin (CD105) as a model antibody. We could show that the binding activity to target cells is rapidly lost in the presence of human plasma. Incorporation of polyethylene glycol (PEG) chains into the lipid bilayer did not protect against loss of binding capability. Further studies showed that loss of binding is mainly due to displacement of Ni-NTA-bound scFv fragments caused by plasma proteins. In conclusion, the system allows for a rapid and flexible generation of target cell specific immunoliposomes for in vitro applications but lacks stability for in vivo applications.

Endoglin Controls Cell Migration and Composition of Focal Adhesions: FUNCTION OF THE CYTOSOLIC DOMAIN

Mutations in the human endoglin gene result in hereditary hemorrhagic telangiectasia type 1, a vascular disorder characterized by multisystemic vascular dysplasia, arteriovenous malformations, and focal dilatation of postcapillary venules. Previous studies have implicated endoglin in the inhibition of cell migration in vivo and in vitro. In the course of studies to address the relationship of the conserved cytosolic domain to endoglin function, we identified zyxin, a LIM domain protein that is concentrated at focal adhesions, as an interactor with endoglin in human umbilical vein vascular endothelial cells. This interaction is localized within the 47-amino acid carboxyl-terminal cytosolic domain of endoglin, and maps within zyxin residues 326-572. The endoglin-zyxin interaction was found to be largely mediated by the third LIM domain of zyxin, and is specific for endoglin because the homologous cytosolic domain of the transforming growth factor-beta type III receptor, betaglycan, fails to interact with zyxin. Expression of endoglin is associated with reduction of zyxin, as well as its interacting proteins p130(cas) and CrkII, from a focal adhesion protein fraction, and this reduction is correlated with inhibition of cell migration. We also show that endoglin-dependent: (i) inhibition of cell migration, (ii) reduction of focal adhesion-associated p130(cas)/CrkII protein levels, (iii) tyrosine phosphorylation of p130(cas), and (iv) focal adhesion-associated endoglin levels are mediated by the cytosolic domain of endoglin. These results suggest a novel mechanism of endoglin function involving its interaction with LIM domain-containing proteins, and associated adapter proteins, affecting sites of focal adhesion.

Targeting of immunoliposomes to endothelial cells using a single-chain Fv fragment directed against human endoglin (CD105)

We generated immunoliposomes targeting proliferating endothelial cells by chemically coupling a single-chain Fv fragment (scFv A5) directed against human endoglin to the liposomal surface. For this purpose, we introduced an additional cysteine residue at the C-terminus of the scFv fragment. This scFv′ fragment was expressed in soluble form in bacteria and allowed for a site-directed coupling to sulfhydryl-reactive lipids incorporated into the lipid bilayer. The immunoliposomes (ILA5) showed rapid and strong binding to human endoglin-expressing endothelial cells (HUVEC, HDMEC), while no binding was observed with various endoglin-negative cell lines and blood lymphocytes. In vitro, ILA5 were stable for several hours in serum- or plasma-containing medium. Incubation of endothelial cells with ILA5 at 37 °C led to increased binding and internalisation of the liposomes as evidenced by a perinuclear accumulation. In vitro, doxorubicin-loaded ILA5 showed an increased cytotoxicity towards endothelial cells compared to untargeted liposomes and free doxorubicin. Since the vasculature of tumours is easily accessible to drug carrier systems, the described endothelial cell-specific immunoliposomes may be useful for the development of efficacious and safe vascular targeting agents in cancer therapy.

Targeting of immunoliposomes to endothelial cells using a single-chain Fv fragment directed against human endoglin (CD105)

We generated immunoliposomes targeting proliferating endothelial cells by chemically coupling a single-chain Fv fragment (scFv A5) directed against human endoglin to the liposomal surface. For this purpose, we introduced an additional cysteine residue at the C-terminus of the scFv fragment. This scFv′ fragment was expressed in soluble form in bacteria and allowed for a site-directed coupling to sulfhydryl-reactive lipids incorporated into the lipid bilayer. The immunoliposomes (ILA5) showed rapid and strong binding to human endoglin-expressing endothelial cells (HUVEC, HDMEC), while no binding was observed with various endoglin-negative cell lines and blood lymphocytes. In vitro, ILA5 were stable for several hours in serum- or plasma-containing medium. Incubation of endothelial cells with ILA5 at 37 °C led to increased binding and internalisation of the liposomes as evidenced by a perinuclear accumulation. In vitro, doxorubicin-loaded ILA5 showed an increased cytotoxicity towards endothelial cells compared to untargeted liposomes and free doxorubicin. Since the vasculature of tumours is easily accessible to drug carrier systems, the described endothelial cell-specific immunoliposomes may be useful for the development of efficacious and safe vascular targeting agents in cancer therapy.

Isolation of endothelial cell-specific human antibodies from a novel fully synthetic scFv library

We have isolated single-chain Fv fragments directed against human endothelial cells from a novel fully synthetic human scFv library (scFv 479). This library was constructed using the variable germline segments DP47 and DPκ9 as scaffolds. Complementarity determining regions 3 (CDR) of the variable heavy and light chain were introduced with a length of 9 amino acid residues. In total, 16 amino acid positions of all six CDRs exposed in the antigen-binding site were randomized and the library was produced from synthetic oligonucleotides encoding the entire scFv fragment. From this library endothelial-specific scFv fragments were either selected using the recombinant extracellular domain of human endoglin (CD105) or by cell selections with human dermal microvascular endothelial cells (HDMEC). These scFv fragments might be useful for the generation of vascular or tumor targeting agents in cancer therapy.

Bispecific single-chain diabody-mediated killing of endoglin-positive endothelial cells by cytotoxic T lymphocytes.

We present a novel vascular tumor therapy approach based on lysing endothelial cells by cytotoxic T lymphocytes (CTLs). Retargeting of CTLs is achieved by a recombinant bispecific antibody molecule (bispecific single-chain diabody) directed against human endoglin (CD105, EDG) and the T-cell coreceptor CD3 (scDb EDGCD3). Bacterially expressed scDb EDGCD3 was able to bind to endoglin-expressing endothelial cells as well as CD3-expressing T lymphocytes. The single-chain diabody mediated killing of endothelial cells (HUVEC, HMEC) by activated cytotoxic T lymphocytes at picomolar concentrations, and cells not expressing endoglin were not affected. Because endoglin is up-regulated in the vasculature of many solid tumors, this antibody molecule should be capable of lysing tumor endothelial cells and thus destroying the vascular bed of the tumor.

Endoglin Expression Regulates Basal and TGF-β1-induced Extracellular Matrix Synthesis in Cultured L6E9 Myoblasts

Background/aims: TGF-β1 plays a major role in extracellular matrix (ECM) accumulation in tissue fibrosis. Connective tissue growth factor appears to play a critical role in this effect. Endoglin is a component of the transforming growth factor b (TGF-β) receptor complex. Endoglin is upregulated by TGF-β1, but its functional role in ECM regulation is unknown. Using rat myoblasts as a model system, we have assessed the role of endoglin on regulating CTGF expression and ECM synthesis and accumulation in the presence or absence of TGF-β1. Methods: L6E9 myoblast cell line was transfected with human endoglin, and collagen, fibronectin and CTGF production was assessed by Western blot and by proline incorporation to collagen proteins. Results: Northern blot analysis revealed that parental rat myoblasts L₆E₉ do not express endogenous endoglin. Upon endoglin transfection, endoglin-expressing cells displayed a decreased CTGF expression and decreased collagen and fibronectin accumulation respect to mock transfectants. Northern blot analysis also revealed a decreased α ₂ (I) procollagen mRNA expression in endoglin transfectants. TGF-β1 treatment induced an increase in CTGF expression and collagen synthesis and accumulation in L6E9 myoblasts. This effect was significantly lower in endoglin-transfected than in mock-transfected cells. Conclusion: These results demonstrate that endoglin expression negatively regulates basal and TGF-β1-induced CTGF and collagen expression and synthesis.

Inducible expression of human endoglin during inflammation and wound healing in vivo.

Because angiogenesis and inflammation are intimately associated and endoglin is required for angiogenesis, we wished to determine whether it also plays a role in inflammation. Using an immunohistochemical approach, we examined spatial and temporal changes in endoglin expression during inflammation and angiogenesis. We found low levels of endoglin expression in quiescent endothelium in a range of normal adult human tissues. However, constitutive levels of expression are higher in dermal capillaries surrounding hair follicles and in alveolar capillaries as well as in the high endothelial cells of lymph tissue. During inflammatory disease, endoglin expression is strongly upregulated and is consistently associated with an infiltrate of inflammatory cells. For the first time, we have determined the relative changes in endoglin expression from the normal quiescent state through the inflammatory changes and angiogenesis that occur during dermal wound healing in vivo using a timed human wound healing model. Endoglin expression increases rapidly, reaching a peak of expression co-incident with maximal T cell infiltrate and persisting at an elevated level for at least 28 days in both activated and proliferating endothelial cells. Enhanced endoglin expression is not limited to angiogenesis, it is also associated with inflammation.

Lack of specificity of endoglin expression for tumor blood vessels.

A monoclonal antibody (MAb; A11) has been raised following mouse immunization with cultured human microvascular endothelial cells. The MAb showed a strong positivity within tumor vessels in glioblastoma and breast carcinoma samples, and the distribution was consistent with antigen association with vascular endothelial cells. A purification procedure of the antigen was developed starting from DG-RSV-LT-2, an immortalized human endothelial cell line. Molecular mass, N-terminal sequence of the purified antigen and localization on endothelial cell surface allowed identification with human endoglin (CD105). Flow cytometry analysis of a group of normal and transformed cell lines showed that, besides endothelial cells and myelocytic leukemia cells already shown to be positive, fetal fibroblasts, choriocarcinoma, fibrosarcoma and rhabdomyosarcoma cell lines were also positive for this antigen. Immunohistochemic analysis of several normal adult tissues revealed a more extensive presence of the antigen in normal vessels compared to that described with previously characterized antibodies. In fact, even though the staining was weaker than in tumor tissues, all tissues were found to be positive, at least in microvessels, except for normal breast. Moreover, in some tissues (glands and reproductive tract) a positive reaction was observed in the stroma. Since endoglin has been proposed as a possible target for antiangiogenic therapy in tumor patients and our data demonstrate a sizable amount of endoglin in normal vessels and stroma, its clinical use should be carefully reevaluated.

Comparative Sequence Analysis of the Human and Rat Endoglin Promoter

Comparative Sequence Analysis of the Human and Rat Endoglin Promoter

Targeting of adenovirus to endothelial cells by a bispecific single-chain diabody directed against the adenovirus fiber knob domain and human endoglin (CD105).

The use of adenoviruses for antivascular cancer gene therapy is limited by their low transduction efficiency for endothelial cells. We have developed a recombinant bispecific antibody as a molecular bridge, linking the adenovirus capsid to the endothelial cell surface protein endoglin, for vascular targeting of adenoviruses. Endoglin (CD105), a component of the transforming growth factor beta receptor complex, represents a promising target for antivascular cancer therapy. Endoglin is expressed predominantly on endothelial cells and is upregulated in angiogenic areas of tumors. We isolated single-chain Fv fragments directed against human endoglin from a human semisynthetic antibody library. One of the isolated scFv fragments (scFv C4) bound specifically to various proliferating primary endothelial cells or cell lines including HUVEC, HDMEC, HMVEC, and HMEC. ScFv C4 was therefore used to construct a bispecific single-chain diabody directed against endoglin and the adenovirus fiber knob domain (scDb EDG-Ad). This bispecific molecule mediated enhanced and selective adenovirus transduction of HUVECs, which was independent from binding to the coxsackievirus and adenovirus receptor (CAR) and alpha(v)-integrins. Thus, adenovirus infection was redirected to a new cellular receptor (CD105) and cell entry pathway. These results demonstrate the utility of bispecific single-chain diabodies, which can be produced in large quantities in bacteria, for the retargeting of adenoviruses in cancer gene therapy.

Vascular gene transfer driven by endoglin and ICAM-2 endothelial-specific promoters.

The involvement of the vascular endothelium in a large number of diseases supports the importance of vascular-specific gene delivery for their treatment. The hereditary hemorrhagic telangiectasia type 1 is an example of a vascular inherited disease (OMIM 187300). This is an autosomal dominant vascular disorder originated by mutations in the endoglin gene and associated with frequent epistaxis, telangiectases, gastrointestinal bleedings, and arteriovenous malformations in brain, lung and liver. Here, we address for the first time the possibility of using in vivo gene transfer to target endoglin expression to the vasculature. The promoter of the endothelial gene, ICAM-2, was used to generate transgenic animals which demonstrated endothelial expression of endoglin. Next, the promoters of the human endothelial genes, endoglin and ICAM-2, were inserted upstream of the human endoglin cDNA, and the resulting constructs were systemically or locally delivered, demonstrating endoglin expression in the vessel walls of liver, lung and skin. These gene transfer experiments represent an initial step in the treatment of the hereditary hemorrhagic telangiectasia type 1 by gene therapy, and suggest that endoglin and ICAM-2 promoters can be used to deliver other genes to the endothelium specifically.