Vascular defects associated with hereditary hemorrhagic telangiectasia revealed in patient-derived isogenic iPSCs in 3D vessels on chip.

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disease characterized by weak blood vessels. HHT1 is caused by mutations in the ENDOGLIN (ENG) gene. Here, we generated induced pluripotent stem cells (hiPSCs) from a patient with rare mosaic HHT1 with tissues containing both mutant (ENGc.1678C>T) and normal cells, enabling derivation of isogenic diseased and healthy hiPSCs, respectively. We showed reduced ENG expression in HHT1 endothelial cells (HHT1-hiPSC-ECs), reflecting haploinsufficiency. HHT1c.1678C>T-hiPSC-ECs and the healthy isogenic control behaved similarly in two-dimensional (2D) culture, forming functionally indistinguishable vascular networks. However, when grown in 3D organ-on-chip devices under microfluidic flow, lumenized vessels formed in which defective vascular organization was evident: interaction between inner ECs and surrounding pericytes was decreased, and there was evidence for vascular leakage. Organs on chip thus revealed features of HHT in hiPSC-derived blood vessels that were not evident in conventional 2D assays.

Genetic variation in the functional ENG allele inherited from the non-affected parent associates with presence of pulmonary arteriovenous malformation in hereditary hemorrhagic telangiectasia 1 (HHT1) and may influence expression of PTPN14.

HHT shows clinical variability within and between families. Organ site and prevalence of arteriovenous malformations (AVMs) depend on the HHT causative gene and on environmental and genetic modifiers. We tested whether variation in the functional ENG allele, inherited from the unaffected parent, alters risk for pulmonary AVM in HHT1 mutation carriers who are ENG haploinsufficient. Genetic association was found between rs10987746 of the wild type ENG allele and presence of pulmonary AVM [relative risk = 1.3 (1.0018-1.7424)]. The rs10987746-C at-risk allele associated with lower expression of ENG RNA in a panel of human lymphoblastoid cell lines (P = 0.004). Moreover, in angiogenically active human lung adenocarcinoma tissue, but not in uninvolved quiescent lung, rs10987746-C was correlated with expression of PTPN14 (P = 0.004), another modifier of HHT. Quantitative TAQMAN expression analysis in a panel of normal lung tissues from 69 genetically heterogeneous inter-specific backcross mice, demonstrated strong correlation between expression levels of Eng, Acvrl1, and Ptpn14 (r2 = 0.75-0.9, P < 1 × 10(-12)), further suggesting a direct or indirect interaction between these three genes in lung in vivo. Our data indicate that genetic variation within the single functional ENG gene influences quantitative and/or qualitative differences in ENG expression that contribute to risk of pulmonary AVM in HHT1, and provide correlative support for PTPN14 involvement in endoglin/ALK1 lung biology in vivo. PTPN14 has been shown to be a negative regulator of Yap/Taz signaling, which is implicated in mechanotransduction, providing a possible molecular link between endoglin/ALK1 signaling and mechanical stress. EMILIN2, which showed suggestive genetic association with pulmonary AVM, is also reported to interact with Taz in angiogenesis. Elucidation of the molecular mechanisms regulating these interactions in endothelial cells may ultimately provide more rational choices for HHT therapy.

Genetic variants of Adam17 differentially regulate TGFß signaling to modify vascular pathology in mice and humans.

Outcome of TGFß1 signaling is context dependent and differs between individuals due to germ-line genetic variation. To explore innate genetic variants that determine differential outcome of reduced TGFß1 signaling, we dissected the modifier locus Tgfbm3, on mouse chromosome 12. On a NIH/OlaHsd genetic background, the Tgfbm3b(C57) haplotype suppresses prenatal lethality of Tgfb1(-/-) embryos and enhances nuclear accumulation of mothers against decapentaplegic homolog 2 (Smad2) in embryonic cells. Amino acid polymorphisms within a disintegrin and metalloprotease 17 (Adam17) can account, at least in part, for this Tgfbm3b effect. ADAM17 is known to down-regulate Smad2 signaling by shedding the extracellular domain of TGFßRI, and we show that the C57 variant is hypomorphic for down-regulation of Smad2/3-driven transcription. Genetic variation at Tgfbm3 or pharmacological inhibition of ADAM17, modulates postnatal circulating endothelial progenitor cell (CEPC) numbers via effects on TGFßRI activity. Because CEPC numbers correlate with angiogenic potential, this suggests that variant Adam17 is an innate modifier of adult angiogenesis, acting through TGFßR1. To determine whether human ADAM17 is also polymorphic and interacts with TGFß signaling in human vascular disease, we investigated hereditary hemorrhagic telangiectasia (HHT), which is caused by mutations in TGFß/bone morphogenetic protein receptor genes, ENG, encoding endoglin (HHT1), or ACVRL1 encoding ALK1 (HHT2), and considered a disease of excessive abnormal angiogenesis. HHT manifests highly variable incidence and severity of clinical features, ranging from small mucocutaneous telangiectases to life-threatening visceral and cerebral arteriovenous malformations (AVMs). We show that ADAM17 SNPs associate with the presence of pulmonary AVM in HHT1 but not HHT2, indicating genetic variation in ADAM17 can potentiate a TGFß-regulated vascular disease.

Mouse and human strategies identify PTPN14 as a modifier of angiogenesis and hereditary haemorrhagic telangiectasia.

Hereditary haemorrhagic telangiectasia (HHT) [corrected] is a vascular dysplasia syndrome caused by mutations in transforming growth factor-ß/bone morphogenetic protein pathway genes, ENG and ACVRL1. HHT [corrected] shows considerable variation in clinical manifestations, suggesting environmental and/or genetic modifier effects. Strain-specific penetrance of the vascular phenotypes of Eng(+/-) and Tgfb1(-/-) mice provides further support for genetic modification of transforming growth factor-ß pathway deficits. We previously identified variant genomic loci, including Tgfbm2, which suppress prenatal vascular lethality of Tgfb1(-/-) mice. Here we show that human polymorphic variants of PTPN14 within the orthologous TGFBM2 locus influence clinical severity of HHT, [corrected] as assessed by development of pulmonary arteriovenous malformation. We also show that PTPN14, ACVRL1 and EFNB2, encoding EphrinB2, show interdependent expression in primary arterial endothelial cells in vitro. This suggests an involvement of PTPN14 in angiogenesis and/or arteriovenous fate, acting via EphrinB2 and ACVRL1/activin receptor-like kinase 1. These findings contribute to a deeper understanding of the molecular pathology of HHT [corrected] in particular and to angiogenesis in general.

Endoglin has a crucial role in blood cell-mediated vascular repair.

BACKGROUND: Endoglin, an accessory receptor for transforming growth factor-beta in vascular endothelial cells, is essential for angiogenesis during mouse development. Mutations in the human gene cause hereditary hemorrhagic telangiectasia type 1 (HHT1), a disease characterized by vascular malformations that increase with age. Although haploinsufficiency is the underlying cause of the disease, HHT1 individuals show great heterogeneity in age of onset, clinical manifestations, and severity. METHODS AND RESULTS: In situ hybridization and immunohistochemical analysis of mouse and human hearts revealed that endoglin is upregulated in neoangiogenic vessels formed after myocardial infarction. Microvascularity within the infarct zone was strikingly lower in mice with reduced levels of endoglin (Eng+/-) compared with wild-type mice, which resulted in a greater deterioration in cardiac function as measured by magnetic resonance imaging. This did not appear to be because of defects in host inflammatory cell numbers in the infarct zone, which accumulated to a similar extent in wild-type and heterozygous mice. However, defects in vessel formation and heart function in Eng+/- mice were rescued by injection of mononuclear cells from healthy human donors but not by mononuclear cells from HHT1 patients. CONCLUSIONS: These results establish defective vascular repair as a significant component of the origin of HHT1. Because vascular damage or inflammation occurs randomly, it may also explain disease heterogeneity. More generally, the efficiency of vascular repair may vary between individuals because of intrinsic differences in their mononuclear cells.

A pulmonary right-to-left shunt in patients with hereditary hemorrhagic telangiectasia is associated with an increased prevalence of migraine.

INTRODUCTION: Hereditary hemorrhagic telangiectasia (HHT) is a rare autosomal-dominant vascular dysplasia with a high prevalence of pulmonary arteriovenous malformation (PAVM). Recent studies report an increased prevalence of migraine in patients with a cardiac right-to-left shunt. The aim of our study was to evaluate whether there is also an increased prevalence of migraine in patients with a pulmonary right-to-left shunt (PAVM). METHODS: All patients with HHT referred to our hospital till April 2004 with or without PAVM and with or without migraine were included in the study. RESULTS: In total, 538 HHT patients (41.6% men; mean age +/- SD, 39.3 +/- 18.6 years) could be included. PAVM was present in 208 patients (38.7%; mean age, 39.3 +/- 17.6 years). Significantly more women were present in the PAVM subgroup compared to the non-PAVM subgroup, 65.4% vs 53.9% (p = 0.009). Migraine occurred in 88 patients with HHT, a prevalence of 16.4%. The prevalence of migraine in women with HHT was significantly higher compared to men, 19.4% vs 12.1%, respectively (p = 0.03) The prevalence of migraine in patients with PAVM was 21.2%, which was significantly higher then in patients without PAVM, 13.3% (p = 0.02). The occurrence of PAVM in the patients with migraine is significantly higher than in those without migraine, 50.0% vs 36.4%, respectively (p = 0.02). CONCLUSION: This study showed a higher prevalence of PAVM in patients with migraine and HHT. The right-to-left shunt due to the PAVM might play a causal role in the pathogenesis of migraine in patients with HHT. This needs to be determined in further studies.

Embolotherapy of pulmonary arteriovenous malformations: long-term results in 112 patients.

PURPOSE: To evaluate the long-term results of embolotherapy of pulmonary arteriovenous malformations (PAVMs) in a large group of patients. MATERIALS AND METHODS: Between July 1988 and August 2001, 134 consecutive patients underwent embolotherapy of PAVMs with feeding arteries larger than 3 mm or that had previously caused bleeding or systemic complications. The mean follow-up was 62.2 months. The primary endpoints of the study were the efficacy of embolotherapy, decrease in right-to-left shunt, and increase in partial arterial oxygen pressure (PaO(2)); the secondary endpoint was the prevalence of complications. Standard follow-up consisted of yearly history, chest radiography, and arterial blood gas measurement. RESULTS: Follow-up was available in 112 patients. Initially, 296 PAVMs were embolized in these patients. Nineteen patients (17%) underwent a second procedure and four patients underwent a third procedure because of recanalization of originally occluded feeding arteries (25 PAVMs, 8%) or interval enlargement of untreated PAVMs (53 PAVMs). In total, 349 PAVMs were embolized in 157 sessions. The mean diameter of occluded vessels was 4.7 mm. The long-term outcomes of embolotherapy were successful in 83% of patients overall and in 96% of patients in whom all angiographically visible PAVMs were embolized. Recanalization occurred in 12 of 16 patients who underwent repeat treatment because of enlargement of nonembolized PAVMs. Postprocedural pleurisy occurred after 14 of 157 sessions (9%). Periprocedural complications occurred in 12 sessions (8%) and included migration of an embolic device, transient ischemic attack (TIA), angina pectoris, and early cerebral infarction after embolization. Three patients experienced TIA and two patients experienced a cerebral abscess during follow-up after embolotherapy. CONCLUSIONS: Embolotherapy of PAVMs is efficacious and durable in the majority of patients. Patients should remain under regular review because recanalization of PAVMs or enlargement of untreated PAVMs can occur years after treatment.

A combined syndrome of juvenile polyposis and hereditary haemorrhagic telangiectasia associated with mutations in MADH4 (SMAD4).

BACKGROUND: Juvenile polyposis and hereditary haemorrhagic telangiectasia are autosomal dominant disorders with distinct and non-overlapping clinical features. The former, an inherited gastrointestinal malignancy predisposition, is caused by mutations in MADH4 (encoding SMAD4) or BMPR1A, and the latter is a vascular malformation disorder caused by mutations in ENG (endoglin) or ACVRL1 (ALK1). All four genes encode proteins involved in the transforming-growth-factor-beta signalling pathway. Although there are reports of patients and families with phenotypes of both disorders combined, the genetic aetiology of this association is unknown. METHODS: Blood samples were collected from seven unrelated families segregating both phenotypes. DNA from the proband of each family was sequenced for the ACVRL1, ENG, and MADH4 genes. Mutations were examined for familial cosegregation with phenotype and presence or absence in population controls. Findings No patient had mutations in the ENG or ACVRL1 genes; all had MADH4 mutations. Three cases of de-novo MADH4 mutations were found. In one, the mutation was passed on to a similarly affected child. Each mutation cosegregated with the syndromic phenotype in other affected family members. INTERPRETATION: Mutations in MADH4 can cause a syndrome consisting of both juvenile polyposis and hereditary haemorrhagic telangiectasia phenotypes. Since patients with these disorders are generally ascertained through distinct medical specialties, genetic testing is recommended for patients presenting with either phenotype to identify those at risk of this syndrome. Patients with juvenile polyposis who have an MADH4 mutation should be screened for the vascular lesions associated with hereditary haemorrhagic telangiectasia, especially occult arteriovenous malformations in visceral organs that may otherwise present suddenly with serious medical consequences.

Hereditary hemorrhagic telangiectasia: an update on transforming growth factor beta signaling in vasculogenesis and angiogenesis.

Hereditary hemorrhagic telangiectasia (HHT) is a vascular disorder in humans which has been mapped to two genes, endoglin and activin receptor-like kinase-1 (ALK-1) both of which mediate signaling by transforming growth factor beta ligands in vascular endothelial cells. Animal models have shown that these receptors are not only important for maintaining vascular integrity but also for angiogenesis both during embryonic development and during tumor growth. Here, we review the current status of reported mutations in the context of the clinical manifestations and the effects on the vessel wall both in patients and in animal models of the disease.

The prevalence and manifestations of hereditary hemorrhagic telangiectasia in the Afro-Caribbean population of the Netherlands Antilles: a family screening.

Hereditary hemorrhagic telangiectasia (HHT) has been reported rarely in people of African descent. The prevalence in the Afro-Caribbean population of the Netherlands Antilles is suspected to be high. A family screening in this population was done to arrive at a point prevalence and to identify patients with pulmonary involvement. By clinical history and physical examination, 219 persons over age twelve with a first-degree relative with HHT were screened. The diagnosis was based on the new diagnostic criteria [Shovlin et al., 2000]. Chest-roentgenogram and pulse-oximetry or measurement of arterial oxygen pressure were used to detect pulmonary involvement. HHT was diagnosed in 112 individuals (51%), with at least a point prevalence of 1 in 1,331 inhabitants of Curaçao and Bonaire older than twelve years. The diagnosis was uncertain in 27; this was partly due to the new stringent criteria. Epistaxis was present in 98% and telangiectases in 99%. Facial telangiectases were relatively rare due to pigmented skin. Pulmonary involvement was found in 28% with serious-mainly neurological-complications in 48%. The point-prevalence of HHT in the Afro-Caribbean population of the Netherlands Antilles is the highest known in the world. Pulmonary involvement in this population is not rare and causes serious complications.

Quantification of right-to-left shunt with (99m)Tc-labelled albumin macroaggregates and 100% oxygen in patients with hereditary haemorrhagic telangiectasia.

Pulmonary arteriovenous malformations (PAVMs) are often associated with hereditary haemorrhagic telangiectasia (HHT). The quantification of right-to-left shunts in patients with PAVMs is important in diagnosis and follow up. Traditionally, this shunt is measured by the 100% oxygen method, in which the value for the arteriovenous difference in oxygen content, Cao(2)-CVO(2) (where Cao(2) is the oxygen content of arterial blood and CVO(2) is the oxygen content of mixed venous blood) is estimated. Alternative methods consist of measurement of the systemic or renal uptake of (99m)Tc-labelled macroaggregates of albumin (MAA), which are trapped in pulmonary capillaries, but pass through PAVMs. We first measured Cao(2)-CVO(2) in 12 HHT patients before and after embolization of PAVMs. We obtained a mean value of 4.4 ml/100 ml, instead of the usual 5 ml/100 ml. Subsequently, we measured right-to-left shunt in 21 HHT patients using the 100% oxygen method and with two different methods involving (99m)Tc. We used the kidney-lung method (K/L method), in which it is assumed that the right kidney receives 10% of the cardiac output, and we also used a method with two tracers (HSA/MAA method): (1) (99m)Tc-labelled human serum albumin (HSA) (which passes through pulmonary capillaries) to measure the fraction of the cardiac output perfusing the kidneys, and (2) MAA to measure the shunt fraction. In 35 shunt measurements we evaluated this new technique and the K/L method, by comparing the results with those from the 100% oxygen method. There was poor agreement between the 100% oxygen method and the K/L method, with 95% limits of agreement for the shunt fraction of -15.2% to +15.2%. There was moderate agreement between the 100% oxygen method and the HSA/MAA method, with limits of agreement of -8.3% to +7.7%. We conclude that the different methods cannot replace each other, because the limits of agreement are too wide for clinical use.