Biomedical subjects

Michelle Letarte

Publications and source records attributed to Michelle Letarte.

At least 19 recordsLinked to original sources

PubMed2006

Endoglin regulates cyclooxygenase-2 expression and activity.

The endoglin heterozygous (Eng(+/-)) mouse, which serves as a model of hereditary hemorrhagic telangiectasia (HHT), was shown to express reduced levels of endothelial NO synthase (eNOS) with impaired activity. Because of intricate changes in vasomotor function in the Eng(+/-) mice and the potential interactions between the NO- and prostaglandin-producing pathways, we assessed the expression and function of cyclooxygenase (COX) isoforms. A specific upregulation of COX-2 in the vascular endothelium and increased urinary excretion of prostaglandin E(2) were observed in the Eng(+/-) mice. Specific COX-2 inhibition with parecoxib transiently increased arterial pressure in Eng(+/-) but not in Eng(+/+) mice. Transfection of endoglin in L6E9 myoblasts, shown previously to stimulate eNOS expression, led to downregulation of COX-2 with no change in COX-1. In addition, COX-2 promoter activity and protein levels were inversely correlated with endoglin levels, in doxycyclin-inducible endothelial cells. Chronic NO synthesis inhibition with N(omega)-nitro-l-arginine methyl ester induced a marked increase in COX-2 only in the normal Eng(+/+) mice. N(omega)-nitro-l-arginine methyl ester also increased COX-2 expression and promoter activity in doxycyclin-inducible endoglin expressing endothelial cells, but not in control cells. The level of COX-2 expression following transforming growth factor-beta1 treatment was less in endoglin than in mock transfected L6E9 myoblasts and was higher in human endothelial cells silenced for endoglin expression. Our results indicate that endoglin is involved in the regulation of COX-2 activity. Furthermore, reduced endoglin levels and associated impaired NO production may be responsible, at least in part, for augmented COX-2 expression and activity in the Eng(+/-) mice.

Animals↗

PubMed2006

Soluble endoglin contributes to the pathogenesis of preeclampsia.

Preeclampsia is a pregnancy-specific hypertensive syndrome that causes substantial maternal and fetal morbidity and mortality. Maternal endothelial dysfunction mediated by excess placenta-derived soluble VEGF receptor 1 (sVEGFR1 or sFlt1) is emerging as a prominent component in disease pathogenesis. We report a novel placenta-derived soluble TGF-beta coreceptor, endoglin (sEng), which is elevated in the sera of preeclamptic individuals, correlates with disease severity and falls after delivery. sEng inhibits formation of capillary tubes in vitro and induces vascular permeability and hypertension in vivo. Its effects in pregnant rats are amplified by coadministration of sFlt1, leading to severe preeclampsia including the HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome and restriction of fetal growth. sEng impairs binding of TGF-beta1 to its receptors and downstream signaling including effects on activation of eNOS and vasodilation, suggesting that sEng leads to dysregulated TGF-beta signaling in the vasculature. Our results suggest that sEng may act in concert with sFlt1 to induce severe preeclampsia.

Adult↗

PubMed2006

Reduced angiogenic responses in adult Endoglin heterozygous mice.

OBJECTIVE: To determine if angiogenesis is altered in adult Endoglin heterozygous (Eng(+/-)) mice, the animal model for the vascular disorder hereditary hemorrhagic telangiectasia type 1 (HHT1). METHODS: Primary cultures of endothelial cells were generated from Eng(+/-) and Eng(+/+) mice and analyzed for proliferation, migration, and ability to form capillary-like tubes. Endothelial cells derived from umbilical veins of newborns (HUVEC) with an HHT1 genotype were also tested for capillary formation. Two in vivo models of angiogenesis were tested in the Eng(+/-) and Eng(+/+) mice: Matrigel implant-dependent angiogenesis and reperfusion following hindlimb ischemia. RESULTS: The Eng(+/-) endothelial cells displayed significantly reduced proliferation and migration, increased collagen production, and decreased NO synthase expression and vascular endothelial growth factor (VEGF) secretion. They also showed impaired capillary tube formation in vitro, as did the HHT1 HUVEC. These endothelial cell-specific abnormalities were associated with impaired Matrigel-dependent capillary tube formation in vivo and delayed reperfusion following hindlimb ischemia. CONCLUSIONS: Although vascular development is normal in Eng(+/-) mice, angiogenic abnormalities were observed in the adult mice and their isolated endothelial cells. These results suggest that a normal level of endoglin is required for full angiogenic activity.

Animals↗

PubMed2006

Symptomatic children with hereditary hemorrhagic telangiectasia: a pediatric center experience.

OBJECTIVE: To assess the clinical and genetic characteristics of symptomatic children with hereditary hemorrhagic telangiectasia (HHT). DESIGN: Cross-sectional study. SETTING: The HHT clinics in Toronto. PARTICIPANTS: All children with symptomatic HHT treated from April 1, 1996, through December 31, 2002. INTERVENTIONS: Participants were screened for visceral arteriovenous malformations (AVMs). Molecular testing was performed in the children or their affected family members. MAIN OUTCOME MEASURES: Prevalence of epistaxis, telangiectases, pulmonary and cerebral AVMs, and genetic characteristics. RESULTS: Fourteen children presented with manifestations of HHT. Seven had cardiorespiratory symptoms related to pulmonary AVMs. Three had neurological symptoms secondary to bleeding from spinal or cerebral AVMs. Two were referred because of skin telangiectases and 2, because of multiple episodes of epistaxis. Screening results revealed a cerebral AVM in 1 of 11 neurologically asymptomatic children. Of the children without respiratory symptoms, 1 was diagnosed as having definite and 1, suspected pulmonary AVMs. Four children with pulmonary AVMs carried an endoglin gene mutation (HHT type 1), and 1 carried an activin receptor-like kinase 1 gene mutation (HHT type 2). The 2 children with spinal AVMs belong to the same HHT type 2 family. No mutation was found in 1 child with pulmonary and 1 with cerebral AVMs. CONCLUSIONS: Visceral AVMs and mucosal telangiectases are present in children with HHT and can lead to life-threatening events. Failure to identify a disease-associated mutation for each child suggests complex mutations or novel HHT genes.

Adolescent↗

PubMed2005

Reduced endothelial secretion and plasma levels of transforming growth factor-beta1 in patients with hereditary hemorrhagic telangiectasia type 1.

OBJECTIVE: To determine if patients with hereditary hemorrhagic telangiectasia (HHT) show alterations in transforming growth factor (TGF)-beta and its pathways. METHODS: Blood samples were obtained from HHT patients and controls, while endothelial cells were derived from umbilical veins of newborns (HUVEC) from HHT families. TGF-beta1 in plasma, or secreted by HUVEC, and plasma endoglin levels were measured by ELISA. Cellular levels of endoglin and receptor Smad proteins were tested by metabolic labeling and immunoprecipitation, mRNA levels for endoglin and TGF-beta1 by real-time PCR, and receptor Smad phosphorylation by Western blotting. RESULTS: TGF-beta1 and endoglin plasma levels analyzed in 197 individuals showed an inverse correlation with age. Circulating levels of TGF-beta1 were reduced in HHT1 patients (with Endoglin mutations) compared to control, but not in HHT2 patients (with ALK1 mutations). Endoglin levels were unchanged in plasma but decreased in activated monocytes and HUVEC with an HHT1 genotype. These HUVEC also expressed reduced levels of endoglin and TGF-beta1 mRNA, secreted less TGF-beta1, and showed normal receptor Smad expression and phosphorylation. CONCLUSIONS: Decreased plasma TGF-beta1 levels in HHT1 patients correlate with reduced production by endothelial cells. The lower endoglin expression in these cells may alter the regulation of TGF-beta1 via Smad-independent pathways.

Antigens, CD↗

PubMed2005

Cost comparison of genetic and clinical screening in families with hereditary hemorrhagic telangiectasia.

Endoglin (ENG) and ALK-1 mutations cause hereditary hemorrhagic telangiecstasia (HHT), an autosomal dominant disorder leading to vascular dysplasia in the form of mucocutaneous telangiectasia and visceral arteriovenous malformations (AVMs). We proposed to compare two alternative strategies for management of HHT: screening HHT families with molecular diagnostic tests followed by targeted clinical screening versus conventional clinical screening. A decision analytic model was constructed to compare screening strategies for a hypothetical HHT family. The family consists of 1 index case and 13 relatives. The clinical screening protocol in use at the Canadian HHT Center in Toronto was assumed to be the standard of care. Unit costs for clinical screening (in Canadian dollars) were obtained from the 2003 Ontario Health Insurance Schedule of Benefits. Genetic screening costs were estimated for quantitative multiplex PCR and sequencing of Endoglin (ENG) and ALK-1 genes, as performed at HHT Solutions, Toronto. The genetic screening strategy resulted in a net cost of $4,060 per individual versus $5,975 for the clinical screening strategy. The genetic screening strategy would save $1,915 per family member or $26,810 saved per family. Sensitivity analyses revealed that the genetic screening strategy was cost saving over all plausible ranges of input variables for all hypothetical families tested. We concluded that a genetic screening strategy with targeted clinical screening is more economically attractive than conventional clinical screening and results in a reduction in the number of clinical tests for family members who do not have HHT.

Adolescent↗

PubMed2005

Characterization of murine S-endoglin isoform and its effects on tumor development.

Endoglin is a transmembrane glycoprotein that acts as an auxiliary receptor for transforming growth factor-beta (TGF-beta) and modulates cellular responses to this pleiotropic cytokine. Endoglin is strongly expressed in endothelial cells, where it appears to exert a crucial role in vascular development and angiogenesis. Two endoglin isoforms (L and S), differing in their cytoplasmic domains, have been previously characterized in human tissues. We now demonstrate the existence of similar L- and S-endoglin variants in murine tissues with 47 and 35 amino acids, respectively, in their cytoplasmic tail. RT-PCR analysis showed that L is the predominant endoglin isoform expressed in mouse tissues, although S-endoglin mRNA is significantly expressed in liver and lung, as well as in endothelial cell lines. Furthermore, a protein of size equivalent to recombinant S-endoglin expressed in mammalian cells was detected in mouse endothelial cells by Western blot analysis. L- and S-endoglin isoforms can form disulfide-linked heterodimers, as demonstrated by cotransfection of L- and S-endoglin constructs. To address the role of S-endoglin in vivo, an S-Eng(+) transgenic mouse model that targets S-endoglin expression to the endothelium was generated. The lethal phenotype of endoglin-null (Eng(-/-)) mice was not rescued by breeding S-Eng(+) transgenic mice into the endoglin-null background. S-Eng(+) mice exhibited reduced tumor growth and neovascularization after transplantation of Lewis lung carcinoma cells. In addition, S-Eng(+) mice showed a drastic inhibition of benign papilloma formation when subjected to two-stage chemical skin carcinogenesis. These results point to S-endoglin as an antiangiogenic molecule, in contrast to L-endoglin which is proangiogenic. Oncogene (2005) 24, 4450-4461. doi:10.1038/sj.onc.1208644 Published online 4 April 2005.

Amino Acid Sequence↗

PubMed2005

TGF-{beta} signaling of human T cells is modulated by the ancillary TGF-{beta} receptor endoglin.

Transforming growth factor beta (TGF-beta) inhibits T cell activation and alters differentiation of naive T cells into effector cells. Although four main cell-surface proteins can interact with TGF-beta, only the signaling receptors type I (TGF-betaR type I) and type II (TGF-betaR type II) have so far been described on T cells. The aim of the present study was to investigate the expression of the ancillary receptor endoglin (CD105) by T cells and its role in TGF-beta-mediated signal transduction and function. CD105 expression was analyzed on resting and activated human CD4(+) T cells by flow cytometry, western blot, immunoprecipitation, proliferation and SMAD-responsive reporter gene assays. CD4(+) T cells constitutively expressed CD105 in memory T cells and partially also in naive T cells; however, surface expression is regulated and is increased following TCR engagement, which induced serine/threonine phosphorylation of CD105. In contrast to the suppressive signal mediated by the TGF-beta, cross-linking of CD105 substantially enhanced T cell proliferation, indicating that CD105 by itself mediates signal transduction. Furthermore, CD105 cross-linking induced SMAD-independent signaling via ERK kinase phosphorylation. The present study demonstrates that CD105 is expressed on the surface by activated CD4(+) T cells and CD3 regulated by post-translational means. Furthermore, CD105 acts as a regulatory receptor, counteracting TGF-beta-mediated suppression.

Activin Receptors, Type I↗

PubMed2005

Endoglin null endothelial cells proliferate faster and are more responsive to transforming growth factor beta1 with higher affinity receptors and an activated Alk1 pathway.

Endoglin is an accessory receptor for transforming growth factor beta (TGFbeta) in endothelial cells, essential for vascular development. Its pivotal role in angiogenesis is underscored in Endoglin null (Eng-/-) murine embryos, which die at mid-gestation (E10.5) from impaired yolk sac vessel formation. Moreover, mutations in endoglin and the endothelial-specific TGFbeta type I receptor, ALK1, are linked to hereditary hemorrhagic telangiectasia. To determine the role of endoglin in TGFbeta pathways, we derived murine endothelial cell lines from Eng+/+ and Eng-/- embryos (E9.0). Whereas Eng+/+ cells were only partially growth inhibited by TGFbeta, Eng-/- cells displayed a potent anti-proliferative response. TGFbeta-dependent Smad2 phosphorylation and Smad2/3 translocation were unchanged in the Eng-/- cells. In contrast, TGFbeta treatment led to a more rapid activation of the Smad1/5 pathway in Eng null cells that was apparent at lower TGFbeta concentrations. Enhanced activity of the Smad1 pathway in Eng-/- cells was reflected in higher expression of ALK1-dependent genes such as Id1, Smad6, and Smad7. Analysis of cell surface receptors revealed that the TGFbeta type I receptor, ALK5, which is required for ALK1 function, was increased in Eng-/- cells. TGFbeta receptor complexes were less numerous but displayed a higher binding affinity. These results suggest that endoglin modulates TGFbeta signaling in endothelial cells by regulating surface TGFbeta receptors and suppressing Smad1 activation. Thus an altered balance in TGFbeta receptors and downstream Smad pathways may underlie defects in vascular development and homeostasis.

Active Transport, Cell Nucleus↗

PubMed2005

Analysis of leukocyte membrane protein interactions using protein microarrays.

BACKGROUND: Protein microarrays represent an emerging class of proteomic tools to investigate multiple protein-protein interactions in parallel. A sufficient proportion of immobilized proteins must maintain an active conformation and an orientation that allows for the sensitive and specific detection of antibody and ligand binding. In order to establish protein array technology for the characterization of the weak interactions between leukocyte membrane proteins, we selected the human leukocyte membrane protein CD200 (OX2) and its cell surface receptor (hCD200R) as a model system. As antibody-antigen reactions are generally of higher affinity than receptor-ligand binding, we first analyzed the reactivity of monoclonal antibodies (mAb) to normal and mutant forms of immobilized CD200R. RESULTS: Fluorescently labelled mAb DX147, DX136 and OX108 were specifically reactive with immobilized recombinant hCD200R extracellular region, over a range of 0.1-40 microg ml(-1) corresponding to a limit of sensitivity of 0.01-0.05 femtomol per spot. Orientating hCD200R using capture antibodies, showed that DX147 reacts with an epitope spatially distinct from the more closely related DX136 and OX108 epitopes. A panel of soluble recombinant proteins with mutations in hCD200R domain 1 produced by transiently transfected cells, was arrayed directly without purification and screened for binding to the three mAb. Several showed decreased binding to the blocking mAb DX136 and OX108, suggesting close proximity of these epitopes to the CD200 binding site. Binding of hCD200 to directly immobilized rat, mouse, and hCD200R was achieved with multimeric ligands, in the form of biotinylated-hCD200 coupled to FITC-labelled avidin coated beads. CONCLUSION: We have achieved sensitive, specific and reproducible detection of immobilized CD200R with different antibodies and mapped antigenic epitopes for two mAb in the vicinity of the ligand binding site using protein microarrays. We also detected CD200 binding to its receptor, a low affinity interaction, using beads presenting multivalent ligands. Our results demonstrate the quantitative aspects of protein arrays and their potential use in detecting simultaneously multiple protein-protein interactions and in particular the weak interactions found between leukocyte membrane proteins.

Animals↗

PubMed2005

A role for endoglin in coupling eNOS activity and regulating vascular tone revealed in hereditary hemorrhagic telangiectasia.

Decreased endothelial NO synthase (eNOS)-derived NO bioavailability and impaired vasomotor control are crucial factors in cardiovascular disease pathogenesis. Hereditary hemorrhagic telangiectasia type 1 (HHT1) is a vascular disorder associated with ENDOGLIN (ENG) haploinsufficiency and characterized by venous dilatations, focal loss of capillaries, and arteriovenous malformations (AVMs). We report that resistance arteries from Eng+/- mice display an eNOS-dependent enhancement in endothelium-dependent dilatation and impairment in the myogenic response, despite reduced eNOS levels. We have found that eNOS is significantly reduced in endoglin-deficient endothelial cells because of decreased eNOS protein half-life. We demonstrate that endoglin can reside in caveolae and associate with eNOS, suggesting a stabilizing function of endoglin for eNOS. After Ca2+-induced activation, endoglin-deficient endothelial cells have reduced eNOS/Hsp90 association, produce less NO, and generate more eNOS-derived superoxide (O2-), indicating that endoglin also facilitates eNOS/Hsp90 interactions and is an important regulator in the coupling of eNOS activity. Treatment with an O2- scavenger reverses the vasomotor abnormalities in Eng(+/-) arteries, suggesting that uncoupled eNOS and resulting impaired myogenic response represent early events in HHT1 pathogenesis and that the use of antioxidants may provide a novel therapeutic modality.

Acetylcholine↗

PubMed2005

Novel mutations and polymorphisms in genes causing hereditary hemorrhagic telangiectasia.

Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal dominant vascular disorder caused by mutations in Endoglin (ENG) or activin receptor-like kinase-1 (ALK1, ACVRL1) genes. We performed molecular characterization in clinically affected probands of 31 HHT families and detected a total of 28 different mutations in the two genes, including four shared by more than one family. Twelve mutations were identified in the ENG gene, six of which were novel and comprised two nonsense mutations in exons 6 and 8, deletions in exons 5 and 11, and splice site mutations in exon 12 and intron 8. Eleven of sixteen mutations identified in the ALK1 gene were novel single base pair substitutions in exons 4, 7, 8, and 9. We also describe the first de novo ALK1 mutation that causes a previously unreported c.1133C>A substitution of a highly conserved residue (p.P378H). The proband and his two daughters, who also carried the familial mutation, all suffered from gastrointestinal (GI) bleeding. In addition, we report seven newly identified polymorphisms and summarize all known ones in both genes.

Activin Receptors, Type II↗

PubMed2005

Multivalent recombinant proteins for probing functions of leucocyte surface proteins such as the CD200 receptor.

CD200 (OX2) is a membrane glycoprotein that interacts with a structurally related receptor (CD200R) involved in the regulation of macrophage function. The interaction is of low affinity (K(D) approximately 1 microm) but can be detected using CD200 displayed in a multivalent form on beads or with dimeric fusion proteins consisting of the extracellular region of CD200 and immunoglobulin Fc regions. We prepared putative pentamers and trimers of mouse CD200 with sequences from cartilage oligomeric matrix protein (COMP) and surfactant protein D (SP-D), respectively. The COMP protein gave high-avidity binding and was a valuable tool for showing the interaction whilst the SP-D protein gave weak binding. In vivo experiments showed that an agonistic CD200R monoclonal antibody caused some amelioration in a model of experimental autoimmune encephalomyelitis but the COMP protein was cleared rapidly and had minimal effect. Pentameric constructs also allowed detection of the rat CD48/CD2 interaction, which is of much lower affinity (K(D) approximately 70 microm). These reagents may have an advantage over Fc-bearing hybrid molecules for probing cell surface proteins without side-effects due to the Fc regions. The CD200-COMP gave strong signals in protein microarrays, suggesting that such reagents may be valuable in high throughput detection of weak interactions.

Animals↗

PubMed2003

Expression of the TGF-beta coreceptor endoglin in epidermal keratinocytes and its dual role in multistage mouse skin carcinogenesis.

Endoglin is an integral membrane glycoprotein primarily expressed in the vascular endothelium, but also found on macrophages and stromal cells. It binds several members of the transforming growth factor (TGF)-beta family of growth factors and modulates TGF-beta(1)-dependent cellular responses. However, it lacks cytoplasmic signaling motifs and is considered as an auxiliary receptor for TGF-beta. We show here that endoglin is expressed in mouse and human epidermis and in skin appendages, such as hair follicles and sweat glands, as determined by immunohistochemistry. In normal interfollicular epidermis, endoglin was restricted to basal keratinocytes and absent in differentiating cells of suprabasal layers. Follicular expression of endoglin was high in hair bulb keratinocytes, but decreased in parts distal from the bulb. To address the role of endoglin in skin carcinogenesis in vivo, Endoglin heterozygous mice were subjected to long-term chemical carcinogenesis treatment. Reduction in endoglin had a dual effect during multistage carcinogenesis, by inhibiting the early appearance of benign papillomas, but increasing malignant progression to highly undifferentiated carcinomas. Our results are strikingly similar to those previously reported for transgenic mice overexpressing TGF-beta(1) in the epidermis. These data suggest that endoglin might attenuate TGF-beta(1) signaling in normal epidermis and interfere with progression of skin carcinogenesis.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2003

Loss of coordinated androgen regulation in nonmalignant ovarian epithelial cells with BRCA1/2 mutations and ovarian cancer cells.

Epidemiological studies have implicated androgens in the etiology/progression of epithelial ovarian cancer. Because normal and malignant ovarian epithelial cells are growth inhibited by transforming growth factor (TGF) beta, we tested the ability of 5alpha-dihydrotestosterone (DHT) to modulate this response and the expression of TGF-beta receptor types I and II. Cells derived from the ovarian surface epithelium of women undergoing oophorectomy (n = 7) for nonovarian indications or with a germ-line BRCA1 or 2 mutation (n = 9), and from the ascitic fluid of patients with primary ovarian cancer (n = 8) were cultured with and without DHT. Cell proliferation after TGF-beta1 or vehicle treatment was determined, and transcripts for TGF-beta receptors were measured by quantitative reverse transcription-PCR. As low levels of androgen receptor were observed in the cultures, we also measured transcript levels for steroid receptor coactivators SRC-1, ARA70, and AIB1. TGF-beta1 inhibited growth in 12 of 13 cultures tested, and DHT generally reversed this effect, demonstrating that androgens can block TGF-beta-induced growth inhibition in both malignant and nonmalignant ovarian epithelial cells. Transcripts for TGF-beta receptors, SRC-1, and ARA70 were found to be coordinately regulated by androgen in control cells, but not in either malignant or BRCA1/2-positive cell cultures. These findings raise the possibility that by modulating steroid receptor coactivator expression, androgen might affect other hormonal responses and contribute to the initiation of ovarian cancer.

Activin Receptors, Type I↗

PubMed2003

Cerebral vascular abnormalities in a murine model of hereditary hemorrhagic telangiectasia.

BACKGROUND AND PURPOSE: Hereditary hemorrhagic telangiectasia type 1 (HHT1) is an autosomal dominant vascular dysplasia caused by mutations in the endoglin gene and characterized by dilated vessels and arteriovenous malformations (AVMs). To understand the etiology of this disorder, we evaluated the cerebral vasculature of endoglin heterozygous (Eng+/-) mice, which represent the only animal model of HHT1. METHODS: The cerebral vasculature of Eng+/- and Eng+/+ mice from C57BL/6 (B6) and 129/Ola (129) strains with a differential susceptibility to HHT1 was studied with corrosion casting. Casts were observed by scanning electron microscopy to detect malformations and evaluate arterial diameters and orientation of endothelial nuclei. Measurements were taken to assess relative constriction at arteriolar branching points and downstream relative dilatation. RESULTS: Three of 10 Eng+/- mice demonstrated abnormal vascular findings including AVMs, while none of 15 Eng+/+ mice did. The incidence of relative constriction at arteriolar branching points was significantly less in both Eng+/- groups than in their Eng+/+ counterparts. The occurrence of relative dilatation was significantly greater in B6-Eng+/- than in B6-Eng+/+ mice. Endothelial nuclei were significantly rounder and deviated more from the direction of blood flow in Eng+/- than in Eng+/+ mice. CONCLUSIONS: Eng+/- mice showed significant structural alterations in cerebral blood vessels, indicating that the level of endoglin on endothelium is critical for maintenance of normal vasculature. Since endoglin haploinsufficiency is associated with HHT1, such changes in arteriolar structures might occur in HHT1 patients and predispose them to AVMs and their sequelae.

Animals↗

PubMed2003

Characterization of 17 novel endoglin mutations associated with hereditary hemorrhagic telangiectasia.

Hereditary hemorrhagic telangiectasia type 1 (HHT1) is a vascular dysplasia caused by mutations in the endoglin (ENG) gene and associated with epistaxis, telangiectases, and a high incidence of pulmonary arteriovenous malformations. To efficiently detect deletions and insertions, we optimized a quantitative multiplex polymerase chain reaction (QMPCR) analysis. We report 17 novel mutations, of which six were detected by QMPCR. Three deletions occurring in intronic sequences were associated with a single copy of exons 9a-14, exon 5, and exons 7-8, respectively. A transient 70kDa monomeric mutant protein resulted from the in-frame deletion of exons 7 and 8 but no mutant protein was present in the other cases. Deletion (in exon 10) or insertion (in exon 7) of two nucleotides, as well as a 1-bp deletion in the small exon 9a were found by QMPCR. Sequencing was required to detect single nucleotide deletions/insertions in exons 2, 5, 6, and 8. No mutant proteins were associated with these frame shift mutations. Two novel splice site mutations resulted in skipping of exons 2 and 4, respectively, while a previously reported intron 3 splice mutant was observed as a de novo mutation. We also report five novel nonsense and missense mutations, including one de novo. Review of the 80 HHT1 families reported to date indicates that 10% would not be resolved by sequencing and that an additional 25% could be revealed by QMPCR performed prior to sequencing. Thus the use of QMPCR accelerates genetic screening for HHT1 and resolves mutations affecting whole exons.

Adolescent↗

PubMed2003

Disease-associated mutations in conserved residues of ALK-1 kinase domain.

Activin receptor-like kinase-1 (ALK-1), the gene mutated in HHT type 2 (HHT2), is a serine/threonine kinase receptor type I of the TGF-beta superfamily, specifically expressed on endothelial cells. We established an HHT2 genotype in 16 families and report nine novel mutations. These include insertions and deletions of single base pairs in exons 3, 8 and 9, as well as nonsense mutations in exons 4 and 8 of ALK-1, which would lead to premature truncation and unstable mRNA or protein. Three novel missense mutations were identified in exons 7 and 8 of the kinase domain. Five previously reported substitutions were also observed in the families analyzed. Our results bring to 36, the number of mutations associated with HHT2, and are mostly found in exons 8 and 3 followed by exons 4 and 7. To ascertain the potential functional implications of the missense mutations in the ALK-1 kinase domain, we generated a model based on the three-dimensional structure of the homologous ALK-5 kinase domain. Our data reveal that the 11 missense mutations modify residues conserved among type I receptors and alter the polarity, charge, hydrophobicity and/or size of the substituted amino-acid and likely lead to misfolded and nonfunctional proteins.

Activin Receptors, Type I↗