94

ACVRL1

ACVRLK1|ALK-1|ALK1|HHT|HHT2|ORW2|SKR3|TSR-I;activin A receptor type II-like 1;ACVRL1;activin A receptor type II-like 1

TGF-B superfamily receptor type I|activin A receptor, type II-like kinase 1|serine/threonine-protein kinase receptor R3

12q13.13

protein-coding

Count: ACVRL1; 94

BACKGROUND: Most patients with familial primary pulmonary hypertension have defects in the gene for bone morphogenetic protein receptor II (BMPR2), a member of the transforming growth factor beta (TGF-beta) superfamily of receptors. Because patients with hereditary hemorrhagic telangiectasia may have lung disease that is indistinguishable from primary pulmonary hypertension, we investigated the genetic basis of lung disease in these patients. METHODS: We evaluated members of five kindreds plus one individual patient with hereditary hemorrhagic telangiectasia and identified 10 cases of pulmonary hypertension. In the two largest families, we used microsatellite markers to test for linkage to genes encoding TGF-beta-receptor proteins, including endoglin and activin-receptor-like kinase 1 (ALK1), and BMPR2. In subjects with hereditary hemorrhagic telangiectasia and pulmonary hypertension, we also scanned ALK1 and BMPR2 for mutations. RESULTS: We identified suggestive linkage of pulmonary hypertension with hereditary hemorrhagic telangiectasia on chromosome 12q13, a region that includes ALK1. We identified amino acid changes in activin-receptor-like kinase 1 that were inherited in subjects who had a disorder with clinical and histologic features indistinguishable from those of primary pulmonary hypertension. Immunohistochemical analysis in four subjects and one control showed pulmonary vascular endothelial expression of activin-receptor-like kinase 1 in normal and diseased pulmonary arteries. CONCLUSIONS: pulmonary hypertension in association with hereditary hemorrhagic telangiectasia can involve mutations in ALK1. These mutations are associated with diverse effects, including the vascular dilatation characteristic of hereditary hemorrhagic telangiectasia and the occlusion of small pulmonary arteries that is typical of primary pulmonary hypertension.

BACKGROUND: mutations of the transforming growth factor beta (TGFbeta) receptor components ENDOGLIN and ALK-1 cause the autosomal dominant vascular disorder hereditary haemorrhagic telangiectasia (HHT). Heterozygous mutations of the type II receptor BMPR2 underlie familial primary pulmonary hypertension. OBJECTIVE: To investigate kindreds presenting with both pulmonary hypertension and HHT. METHODS: Probands and families were identified by specialist pulmonary hypertension centres in five countries. DNA sequence analysis of ALK-1, ENDOGLIN, and BMPR2 was undertaken. Cellular localisation was investigated by heterologous overexpression of mutant constructs in both BAEC and HeLa cells. The impact of a novel sequence variant was assessed through comparative analysis and computer modelling. RESULTS: Molecular analysis of 11 probands identified eight missense mutations of ALK-1, one of which was observed in two families. mutations were located within exons 5 to 10 of the ALK-1 gene. The majority of ALK-1 mutant constructs appeared to be retained within the cell cytoplasm, in the endoplasmic reticulum. A novel GS domain mutation, when overexpressed, reached the cell surface but is predicted to disrupt conformational changes owing to loss of a critical hydrogen bond. Two novel missense mutations were identified in ENDOGLIN. CONCLUSIONS: The association of pulmonary arterial hypertension and HHT identifies an important disease complication and appears most common among subjects with defects in ALK-1 receptor signalling. Future studies should focus on detailed molecular analysis of the common cellular pathways disrupted by mutations of ALK-1 and BMPR2 that cause inherited pulmonary vascular disease.

BACKGROUND: pulmonary arterial hypertension (PAH) is a potentially fatal vasculopathy that can develop at any age. Adult-onset disease has previously been associated with mutations in BMPR2 and ALK-1. Presentation in early life may be associated with congenital heart disease but frequently is idiopathic. METHODS AND RESULTS: We performed mutation analysis in genes encoding receptor members of the transforming growth factor-beta cell-signaling pathway in 18 children (age at presentation <6 years) with PAH. Sixteen children were initially diagnosed with idiopathic PAH and 2 with PAH in association with congenital heart defects. Germ-line mutations were observed in 4 patients (22%) (age at disease onset, 1 month to 6 years), all of whom presented with idiopathic PAH. The BMPR2 mutations (n=2, 11%) included a partial gene deletion and a nonsense mutation, both arising de novo in the proband. Importantly, a missense mutation of ALK-1 and a branch-site mutation of endoglin were also detected. Presenting clinical features or progression of pulmonary hypertension did not distinguish between patients with mutations in the different genes or between those without mutations. CONCLUSIONS: The cause of PAH presenting in childhood is heterogeneous in nature, with genetic defects of transforming growth factor-beta receptors playing a critical role.

BACKGROUND: Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder characterized by the presence of telangiectases and arteriovenous malformations. In some families in whom a form of idiopathic pulmonary arterial hypertension cosegregated with HHT, mutations in the ACVRL1 gene were present. PURPOSE: We noninvasively measured the pulmonary artery systolic pressure (PASP) in a group of patients with HHT. METHODS: Doppler transthoracic echocardiography and mutation analysis by direct sequencing were used. RESULTS: We studied 68 patients (age 19-84 years, mean 50.75 + 15.11; 32 females) and PASP measurement was possible in 44 (64. 7%); in addition, 9 of them (20.5%) showed elevated values. Molecular analysis identified mutations in the ACVRL1 gene in 7 of these 9 subjects. Even on exclusion of relatives of the single case with known pulmonary hypertension, 5 of 37 patients (13.5%) still showed values higher than those of controls. CONCLUSION: The data indicate that elevated PASP values are a frequent and previously unrecognized complication of HHT. Because clinically significant pulmonary artery hypertension (a relevant cause of morbidity and mortality) may subsequently develop in these patients, we propose that the measurement of PASP should be included among the parameters recorded for all patients undergoing Doppler transthoracic echocardiography during routine clinical screening.

BACKGROUND: mutations of the bone morphogenetic protein receptor II gene (BMPR2), and 1 mutation of the activin receptor-like kinase 1 gene (ALK1) have been reported in patients with pulmonary arterial hypertension (PAH). METHODS AND RESULTS: A genomic study of ALK1 and BMPR2 was conducted in 21 PAH probands under 16 years of age to study the relationship between the clinical features of the patients and these genes. In all 4 familial aggregates of PAH, 3 ALK1 or 1 BMPR2 mutations were identified. Among 17 probands aged between 4 and 14 years with idiopathic PAH, 2 ALK1 mutations (2/17: 11.8%) and 3 BMPR2 mutations (3/17: 17.6%; 5 mutations in total: 5/17: 29.4%) were found. CONCLUSION: Each proband with the ALK1 mutation developed PAH, as did the probands with the BMPR2 mutation. Hence, it is proposed that ALK1 plays as notable a role as BMPR2 in the etiology of PAH. Furthermore, asymptomatic carriers with the ALK1 mutation within the serine - threonine kinase domain are at risk of developing PAH and hereditary hemorrhagic telangiectasia, so close follow-up is recommended for those individuals.

Up to 30% of adult patients with sickle cell disease (SCD) will develop pulmonary hypertension (pHTN), a complication associated with significant morbidity and mortality. To identify genetic factors that contribute to risk for pHTN in SCD, we performed association analysis with 297 single nucleotide polymorphisms (SNPs) in 49 candidate genes in patients with sickle cell anemia (Hb SS) who had been screened for pHTN by echocardiography (n = 111). Evidence of association was primarily identified for genes in the TGFbeta superfamily, including activin A receptor, type II-like 1 (ACVRL1), bone morphogenetic protein receptor 2 (BMPR2), and bone morphogenetic protein 6 (BMP6). The association of pHTN with ACVRL1 and BMPR2 corroborates the previous association of these genes with primary pHTN. Moreover, genes in the TGFbeta pathway have been independently implicated in risk for several sickle cell complications, suggesting that this gene pathway is important in overall sickle cell pathophysiology. Genetic variation in the beta-1 adrenergic receptor (ADRB1) was also associated with pHTN in our dataset. A multiple regression model, which included age and baseline hemoglobin as covariates, retained SNPs in ACVRL1, BMP6, and ADRB1 as independently contributing to pHTN risk. These findings may offer new promise for identifying patients at risk for pHTN, developing new therapeutic targets, and reducing the occurrence of this life-threatening SCD complication.

mutations of the bone morphogenetic protein receptor II gene (BMPR2) have been reported in patients with pulmonary arterial hypertension (PAH). In hereditary hemorrhagic telangiectasia (HHT) patients with PAH, missense mutations of the activin receptor-like kinase 1 gene (ALK1) located in the serine-threonine kinase domain. Recently, the mutations of ALK1 in the serine-threonine kinase domain were observed in PAH patients. ALK1 mutations play a critical role in PAH without HHT as well as in PAH with HHT. Because only 10-20% carriers with BMPR2 mutations develop PAH, the existence of environmental factors or modifier genes as 5-HTT(serotonin transporter) and ACE (angiotensin converting enzyme) is highly probable.

mutations in transforming growth factor-beta (TGF-beta) receptor superfamily members underlie conditions characterized by vascular dysplasia. mutations in endoglin and activin-like kinase receptor 1 (ALK1) cause hereditary hemorrhagic telangiectasia, whereas bone morphogenetic protein type II receptor (BMPR-II) mutations underlie familial pulmonary arterial hypertension. To understand the functional roles of these receptors, we examined their relative contributions to BMP signaling in human pulmonary artery endothelial cells (HPAECs). BMP9 potently and selectively induced Smad1/5 phosphorylation and Id gene expression in HPAECs. Contrary to expectations, BMP9 also stimulated Smad2 activation. Furthermore, BMP9 induced the expression of interleukin 8 and E-selectin. Using small interfering RNA, we demonstrate that the type I receptor, ALK1, is essential for these responses. However, small interfering RNA and inhibitor studies showed no involvement of ALK5 or endoglin. We further demonstrate that, of the candidate type II receptors, BMPR-II predominantly mediated IL-8 and E-selectin induction and mitogenic inhibition by BMP9. Conversely, activin receptor type II (ActR-II) contributed more to BMP9-mediated Smad2 activation. Only abolition of both type II receptors significantly reduced the Smad1/5 and Id responses. Both ALK1 and BMPR-II contributed to growth inhibition of HPAECs, whereas ActR-II was not involved. Taken together, our findings demonstrate the critical role of type II receptors in balancing BMP9 signaling via ALK1 and emphasize the essential role for BMPR-II in a subset of BMP9 responses (interleukin 8, E-selectin, and proliferation). This differential signaling may contribute to the contrasting pathologies of hereditary hemorrhagic telangiectasia and pulmonary arterial hypertension.

RATIONALE: Activin A receptor type II-like kinase-1 (ACVRL1, also known as ALK1) mutation is a cause of hereditary hemorrhagic telangiectasia (HHT) and/or heritable pulmonary arterial hypertension (PAH). OBJECTIVES: To describe the characteristics of patients with PAH carrying an ACVRL1 mutation. METHODS: We reviewed clinical, functional, and hemodynamic characteristics of 32 patients with PAH carrying an ACVRL1 mutation, corresponding to 9 patients from the French PAH Network and 23 from literature analysis. These cases were compared with 370 patients from the French PAH Network (93 with a bone morphogenetic protein receptor type 2 [BMPR2] mutation and 277 considered as idiopathic cases without identified mutation). Distribution of mutations in the ACVRL1 gene in patients with PAH was compared with the HHT mutation Database. MEASUREMENTS AND MAIN RESULTS: At diagnosis, ACVRL1 mutation carriers were significantly younger (21.8 +/- 16.7 yr) than BMPR2 mutation carriers and noncarriers (35.7 +/- 14.9 and 47.6 +/- 16.3 yr, respectively; P < 0.0001). In seven of the nine patients from the French PAH Network, PAH diagnosis preceded manifestations of HHT. ACVRL1 mutation carriers had better hemodynamic status at diagnosis, but none responded to acute vasodilator challenge and they had shorter survival when compared with other patients with PAH despite similar use of specific therapies. ACVRL1 mutations in exon 10 were more frequently observed in patients with PAH, as compared with what was observed in the HHT mutation Database (33.3 vs. 5%; P < 0.0001). CONCLUSIONS: ACVRL1 mutation carriers were characterized by a younger age at PAH diagnosis. Despite less severe initial hemodynamics and similar management, these patients had worse prognosis compared with other patients with PAH, suggesting more rapid disease progression.

mutations in the bone morphogenetic protein receptor type 2 (BMPR2) gene and the activin receptor-like kinase 1 (ALK1) gene have been reported in heritable pulmonary arterial hypertension (HPAH) and idiopathic pulmonary arterial hypertension (IPAH). However, the relation between clinical characteristics and each gene mutation in IPAH and HPAH is still unclear, especially in childhood. The aim of this study was to determine, in a retrospective study, the influence and clinical outcomes of gene mutations in childhood IPAH and HPAH. Fifty-four patients with IPAH or HPAH whose onset of disease was at <16 years of age were included. Functional characteristics, hemodynamic parameters, and clinical outcomes were compared in BMPR2 and ALK1 mutation carriers and noncarriers. Overall 5-year survival for all patients was 76%. Eighteen BMPR2 mutation carriers and 7 ALK1 mutation carriers were detected in the 54 patients with childhood IPAH or HPAH. Five-year survival was lower in BMPR2 mutation carriers than mutation noncarriers (55% vs 90%, hazard ratio 12.54, p = 0.0003). ALK1 mutation carriers also had a tendency to have worse outcome than mutation noncarriers (5-year survival rate 64%, hazard ratio 5.14, p = 0.1205). In conclusion, patients with childhood IPAH or HPAH with BMPR2 mutation have the poorest clinical outcomes. ALK1 mutation carriers tended to have worse outcomes than mutation noncarriers. It is important to consider aggressive treatment for BMPR2 or ALK1 mutation carriers.CI - Copyright (c) 2012 Elsevier Inc. All rights reserved.

BACKGROUND: Idiopathic pulmonary arterial hypertension (IPAH) continues to be one of the most serious intractable diseases that might start with activation of several triggers representing the genetic susceptibility of a patient. To elucidate what essentially contributes to the onset and progression of IPAH, we investigated factors playing an important role in IPAH by searching discrepant or controversial expression patterns between our murine model and those previously published for human IPAH. We employed the mouse model, which induced muscularization of pulmonary artery leading to hypertension by repeated intratracheal injection of Stachybotrys chartarum, a member of nonpathogenic and ubiquitous fungus in our envelopment. METHODS: Microarray assays with ontology and pathway analyses were performed with the lungs of mice. A comparison was made of the expression patterns of biological pathways between our model and those published for IPAH. RESULTS: Some pathways in our model showed the same expression patterns in IPAH, which included bone morphogenetic protein (BMP) signaling with down-regulation of BMP receptor type 2, activin-like kinase type 1, and endoglin. On the other hand, both Wnt/planar cell polarity (PCP) signaling and its downstream Rho/ROCK signaling were found alone to be activated in IPAH and not in our model. CONCLUSIONS: Activation of Wnt/PCP signaling, in upstream positions of the pathway, found alone in lungs from end stage IPAH may play essential roles in the pathogenesis of the disease.

BACKGROUND: Aim of this prospective study was to compare clinical and genetic findings in children with idiopathic or heritable pulmonary arterial hypertension (I/HPAH) with children affected with congenital heart defects associated PAH (CHD-APAH). METHODS: Prospectively included were 40 consecutive children with invasively diagnosed I/HPAH or CHD-APAH and 117 relatives. Assessment of family members, pedigree analysis and systematic screening for mutations in TGFss genes were performed. RESULTS: Five mutations in the bone morphogenetic protein type II receptor (BMPR2) gene, 2 Activin A receptor type II-like kinase-1 (ACVRL1) mutations and one Endoglin (ENG) mutation were found in the 29 I/HPAH children. Two mutations in BMPR2 and one mutation in ACVRL1 and ENG, respectively, are described for the first time. In the 11 children with CHD-APAH one BMPR2 gene mutation and one Endoglin gene mutation were found. Clinical assessment of relatives revealed familial aggregation of the disease in 6 children with PAH (HPAH) and one CHD-APAH patient. Patients with mutations had a significantly lower PVR. CONCLUSION: mutations in different TGFss genes occurred in 8/29 (27.6%) I/HPAH patients and in 2/11 (18.2%) CHD-APAH patients and may influence the clinical status of the disease. Therefore, genetic analysis in children with PAH, especially in those with I/HPAH, may be of clinical relevance and shows the complexity of the genetic background.

Activin receptor-like kinase 1 (Acvrl1; Alk1) is a type I receptor for transforming growth factor-beta (TGF-beta). ALK1 plays a pivotal role in vascular development and is involved in the development of hereditary hemorrhagic telangiectasia 2 (HHT2), a dominantly inherited vascular disorder, and pulmonary hypertension. We have previously shown that Alk1 is expressed predominantly in arterial endothelial cells (ECs). Despite recent discoveries of a number of artery-specific genes, the regulatory elements of these genes have not been characterized. To investigate the cis-acting elements essential for the artery-specific Alk1 expression, we have generated a series of transgenic constructs with various lengths and regions of Alk1 genomic fragments connected to a LacZ reporter gene, and analyzed the reporter gene expression in transgenic mice. We found that a 9.2-kb genomic fragment, which includes 2.7-kb promoter region and the entire intron 2, is sufficient to drive arterial endothelium-specific expression. The defined regulatory region, as well as the transgenic mouse lines, would be invaluable resources in studying the mechanisms underlying angiogenesis, arteriogenesis, and vascular disorders, such as HHT and pulmonary hypertension. The full text of this article is available online at http://circres.ahajournals.org.

Arteriovenous malformations (AVMs) are direct connections between arteries and veins associated with loss of the intervening capillary bed. In the lungs, pulmonary AVMs can result in right to left shunts and severe cyanosis and dyspnoea. However, the cellular and molecular mechanisms underlying AVM formation are poorly understood. One important clue comes from the fact that pulmonary AVMs frequently occur in the familial disease hereditary haemorrhagic telangiectasia (HHT), which is associated with mutations in one of two receptors involved in transforming growth factor-beta family signalling, either endoglin (ENG) or activin receptor-like kinase 1 (ACVRL1, also known as ALK1). To elucidate the potential link between ENG or ACVRL1 deficiency and AVM formation in HHT, we performed a comprehensive study of Acvrl1 and Eng expression in wild-type and Eng-deficient (Eng+/-) mouse lungs using a combination of immunohistochemistry and RT-PCR from laser-microdissected arteries, veins and capillaries. We found that Eng and Acvrl1 have distinct expression profiles in the pulmonary vasculature and are only co-expressed in the distal (pre-capillary) arteries, distal veins and capillaries, consistent with the tendency for pulmonary AVMs to form in the distal pulmonary vessels in HHT. Downstream pSmad1/5/8 activity was found in the distal arteries and was specifically reduced in Eng+/- mice, consistent with previous in vitro data showing that Eng promotes Acvrl1-mediated Smad1/5/8 phosphorylation. Eng was more widely expressed than Acvrl1 in the lungs, as Eng alone was found in pulmonary veins, potentially explaining the increased frequency of AVMs in HHT1 patients. Furthermore, the association of ACVRL1 mutations with a second vascular disease, familial pulmonary artery hypertension, underlines the importance of ACVRL1 expression in the distal arteries that are affected in this disorder.

AIMS: mutations in the ALK1 gene, coding for an endothelial-specific receptor of the transforming growth factor-beta superfamily, are the underlying cause of hereditary haemorrhagic telangiectasia type 2, but are also associated with familial pulmonary hypertension (PH). We assessed the lung vasculature of mice with a heterozygous deletion of Alk1 (Alk1(+/-)) for disease manifestations and levels of reactive O(2) species (ROS) implicated in both disorders. METHODS AND RESULTS: Several signs of PH, including elevated right ventricular (RV) systolic pressure leading to RV hypertrophy, reduced vascular density, and increased thickness and outward remodelling of pulmonary arterioles, were observed in 8- to 18-week-old Alk1(+/-) mice relative to wild-type littermate controls. Higher ROS lung levels were also documented. At 3 weeks, Alk1(+/-) mice were indistinguishable from controls and were prevented from subsequently developing PH when treated with the anti-oxidant Tempol for 6 weeks, confirming a role for ROS in pathogenesis. Levels of NADPH oxidases and superoxide dismutases were higher in adults than newborns, but unchanged in Alk1(+/-) mice vs. controls. Prostaglandin metabolites were also normal in adult Alk1(+/-) lungs. In contrast, NO production was reduced, while endothelial NO synthase (eNOS)-dependent ROS production was increased in adult Alk1(+/-) mice. Pulmonary near resistance arteries from adult Alk1(+/-) mice showed less agonist-induced force and greater acetylcholine-induced relaxation; the later was normalized by catalase or Tempol treatment. CONCLUSION: The increased pulmonary vascular remodelling in Alk1(+/-) mice leads to signs of PH and is associated with eNOS-dependent ROS production, which is preventable by anti-oxidant treatment.