Molecular and functional analysis identifies ALK-1 as the predominant cause of pulmonary hypertension related to hereditary haemorrhagic telangiectasia

BMP signaling in vascular biology and dysfunction

The vascular system is critical for developmental growth, tissue homeostasis and repair but also for tumor development. Bone morphogenetic protein (BMP) signaling has recently emerged as a fundamental pathway of the endothelium by regulating cardiovascular and lymphatic development and by being causative for several vascular dysfunctions. Two vascular disorders have been directly linked to impaired BMP signaling: pulmonary arterial hypertension and hereditary hemorrhagic telangiectasia. Endothelial BMP signaling critically depends on the cellular context, which includes among others vascular heterogeneity, exposure to flow, and the intertwining with other signaling cascades (Notch, WNT, Hippo and hypoxia). The purpose of this review is to highlight the most recent findings illustrating the clear need for reconsidering the role of BMPs in vascular biology.

Pulmonary Arterial Hypertension: A Current Perspective on Established and Emerging Molecular Genetic Defects

Pulmonary arterial hypertension (PAH) is an often fatal disorder resulting from several causes including heterogeneous genetic defects. While mutations in the bone morphogenetic protein receptor type II (BMPR2) gene are the single most common causal factor for hereditary cases, pathogenic mutations have been observed in approximately 25% of idiopathic PAH patients without a prior family history of disease. Additional defects of the transforming growth factor beta pathway have been implicated in disease pathogenesis. Specifically, studies have confirmed activin A receptor type II-like 1 (ACVRL1), endoglin (ENG), and members of the SMAD family as contributing to PAH both with and without associated clinical phenotypes. Most recently, next-generation sequencing has identified novel, rare genetic variation implicated in the PAH disease spectrum. Of importance, several identified genetic factors converge on related pathways and provide significant insight into the development, maintenance, and pathogenetic transformation of the pulmonary vascular bed. Together, these analyses represent the largest comprehensive compilation of BMPR2 and associated genetic risk factors for PAH, comprising known and novel variation. Additionally, with the inclusion of an allelic series of locus-specific variation in BMPR2, these data provide a key resource in data interpretation and development of contemporary therapeutic and diagnostic tools.

Management of pulmonary arterial hypertension

Pulmonary hypertension (PH) is common and may result from a number of disorders, including left heart disease, lung disease, and chronic thromboembolic disease. Pulmonary arterial hypertension (PAH) is an uncommon disease characterized by progressive remodeling of the distal pulmonary arteries, resulting in elevated pulmonary vascular resistance and, eventually, in right ventricular failure. Over the past decades, knowledge of the basic pathobiology of PAH and its natural history, prognostic indicators, and therapeutic options has exploded. A thorough evaluation of a patient is critical to correctly characterize the PH. Cardiac studies, including echocardiography and right heart catheterization, are key elements in the assessment. Given the multitude of treatment options currently available for PAH, assessment of risk and response to therapy is critical in long-term management. This review also underscores unique situations, including perioperative management, intensive care unit management, and pregnancy, and highlights the importance of collaborative care of the PAH patient through a multidisciplinary approach.

Functional and splicing defect analysis of 23 ACVRL1 mutations in a cohort of patients affected by Hereditary Hemorrhagic Telangiectasia

Hereditary Hemorrhagic Telangiectasia syndrome (HHT) or Rendu-Osler-Weber (ROW) syndrome is an autosomal dominant vascular disorder. Two most common forms of HHT, HHT1 and HHT2, have been linked to mutations in the endoglin (ENG) and activin receptor-like kinase 1 (ACVRL1or ALK1) genes respectively. This work was designed to examine the pathogenicity of 23 nucleotide variations in ACVRL1 gene detected in more than 400 patients. Among them, 14 missense mutations and one intronic variant were novels, and 8 missense mutations were previously identified with questionable implication in HHT2. The functionality of missense mutations was analyzed in response to BMP9 (specific ligand of ALK1), the maturation of the protein products and their localization were analyzed by western blot and fluorescence microscopy. The splicing impairment of the intronic and of two missense mutations was examined by minigene assay. Functional analysis showed that 18 out of 22 missense mutations were defective. Splicing analysis revealed that one missense mutation (c.733A>G, p.Ile245Val) affects the splicing of the harboring exon 6. Similarly, the intronic mutation outside the consensus splicing sites (c.1048+5G>A in intron 7) was seen pathogenic by splicing study. Both mutations induce a frame shift creating a premature stop codon likely resulting in mRNA degradation by NMD surveillance mechanism. Our results confirm the haploinsufficiency model proposed for HHT2. The affected allele of ACVRL1 induces mRNA degradation or the synthesis of a protein lacking the receptor activity. Furthermore, our data demonstrate that functional and splicing analyses together, represent two robust diagnostic tools to be used by geneticists confronted with novel or conflicted ACVRL1 mutations.

Selective enhancement of endothelial BMPR-II with BMP9 reverses pulmonary arterial hypertension

Genetic evidence implicates the loss of bone morphogenetic protein type II receptor (BMPR-II) signaling in the endothelium as an initiating factor in pulmonary arterial hypertension (PAH). However, selective targeting of this signaling pathway using BMP ligands has not yet been explored as a therapeutic strategy. Here, we identify BMP9 as the preferred ligand for preventing apoptosis and enhancing monolayer integrity in both pulmonary arterial endothelial cells and blood outgrowth endothelial cells from subjects with PAH who bear mutations in the gene encoding BMPR-II, BMPR2. Mice bearing a heterozygous knock-in allele of a human BMPR2 mutation, R899X, which we generated as an animal model of PAH caused by BMPR-II deficiency, spontaneously developed PAH. Administration of BMP9 reversed established PAH in these mice, as well as in two other experimental PAH models, in which PAH develops in response to either monocrotaline or VEGF receptor inhibition combined with chronic hypoxia. These results demonstrate the promise of direct enhancement of endothelial BMP signaling as a new therapeutic strategy for PAH.

Selective enhancement of endothelial BMPR-II with BMP9 reverses pulmonary arterial hypertension

Genetic evidence implicates the loss of bone morphogenetic protein type II receptor (BMPR-II) signaling in the endothelium as an initiating factor in pulmonary arterial hypertension (PAH). However, selective targeting of this signaling pathway using BMP ligands has not yet been explored as a therapeutic strategy. Here, we identify BMP9 as the preferred ligand for preventing apoptosis and enhancing monolayer integrity in both pulmonary arterial endothelial cells and blood outgrowth endothelial cells from subjects with PAH who bear mutations in the gene encoding BMPR-II, BMPR2. Mice bearing a heterozygous knock-in allele of a human BMPR2 mutation, R899X, which we generated as an animal model of PAH caused by BMPR-II deficiency, spontaneously developed PAH. Administration of BMP9 reversed established PAH in these mice, as well as in two other experimental PAH models, in which PAH develops in response to either monocrotaline or VEGF receptor inhibition combined with chronic hypoxia. These results demonstrate the promise of direct enhancement of endothelial BMP signaling as a new therapeutic strategy for PAH.

Accurate genetic diagnosis of Finnish pulmonary arterial hypertension patients using oligonucleotide-selective sequencing

The genetic basis of pulmonary arterial hypertension (PAH) among Finnish PAH patients is poorly understood. We adopted a novel-targeted next-generation sequencing (NGS) approach called Oligonucleotide-Selective Sequencing (OS-Seq) and developed a custom data analysis and interpretation pipeline to identify pathogenic base substitutions, insertions, and deletions in seven genes associated with PAH (BMPR2, BMPR1B, ACVRL1, ENG, SMAD9, CAV1, and KCNK3) from Finnish PAH patients. This study represents the first clinical study with OS-Seq technology on patients suffering from a rare genetic disorder. We analyzed DNA samples from 21 Finnish PAH patients, whose BMPR2 and ACVRL1 mutation status had been previously studied using Sanger sequencing. Our sequencing panel covered 100% of the targeted base pairs with >15× sequencing depth. Pathogenic base substitutions were identified in the BMPR2 gene in 29% of the Finnish PAH cases. Two of the pathogenic variant-positive patients had been previously tested negative using Sanger sequencing. No clinically significant variants were identified in the six other PAH genes. Our study validates the use of targeted OS-Seq for genetic diagnostics of PAH and revealed pathogenic variants that had been previously missed using Sanger sequencing.

Pulmonary arterial hypertension associated with congenital heart disease and Eisenmenger syndrome: current practice in pediatrics

Pulmonary arterial hypertension (PAH) is an uncommon but serious disease characterized by severe pulmonary vascular disease and significant morbidity and mortality. PAH associated with congenital heart disease (APAH-CHD) is one etiology of PAH that has innate characteristics delineating it from other forms of PAH. The patient with APAH-CHD presents with unique challenges consisting of not only pulmonary vascular disease but also the complexity of the cardiac lesion. Eisenmenger syndrome (ES) represents the severe end of the spectrum for disease in APAH-CHD. Over time, systemic-to-pulmonary shunting through cardiac defects increases pulmonary vascular resistance to levels significant enough to reverse shunting across the defect. Historically, ES patients have been reported to have better outcomes than IPAH despite similarities in pulmonary vascular disease. However, recent studies are challenging this notion. Nonetheless, APAH-CHD survival has improved with the advent of modern PAH targeted therapies. New therapeutic options have allowed us to reconsider the dogma of inoperability in APAH-CHD patients with unrepaired defects. Certainly advances have been made, however, investigators must continue to advance the field through controlled clinical trials in both adult and pediatric APAH-CHD patients.

Cardiopulmonary exercise testing demonstrates maintenance of exercise capacity in patients with hypoxemia and pulmonary arteriovenous malformations

BACKGROUND

Patients with pulmonary arteriovenous malformations (PAVMs) are unusual because hypoxemia results from right-to-left shunting and not airway or alveolar disease. Their surprisingly well-preserved exercise capacity is not generally appreciated.

METHODS

To examine why exercise tolerance is preserved, cardiopulmonary exercise tests were performed while breathing room air in 21 patients with radiologically proven PAVMs, including five restudied 3 to 12 months after embolization when their PAVMs had regressed. Where physiologic matching was demonstrable, comparisons were made with 12 healthy control subjects.

RESULTS

The majority of patients achieved their predicted work rate despite a resting arterial oxygen saturation (SaO₂) of 80% to 96%. Peak work rate and oxygen consumption (VO₂) were no lower in patients with more hypoxemia. Despite higher SaO₂ following embolization (median, 96% and 90%; P = .009), patients achieved similar work rates and similar peak VO₂. Strikingly, treated patients reset to virtually identical peak oxygen pulses (ie, VO₂ per heart beat) and in many cases to the same point on the peak oxygen pulse/work rate plot. The 21 patients had increased minute ventilation (VE) for given increases in CO₂ production (VE/VCO₂ slope), but perceived dyspnea was no greater than in the 12 control subjects or in the same patients before compared to after embolization comparison. Overall, work rate and peak VO₂ were associated not with oxygenation parameters but with VE/VCO₂ slope, BMI, and anaerobic threshold.

CONCLUSIONS

Patients with hypoxemia and PAVMs can maintain normal oxygen delivery/VO₂ during peak exercise. Following improvement of SaO₂ by embolization, patients appeared to reset compensatory mechanisms and, as a result, achieved similar peak VO₂ per heart beat and peak work rates.

The economic burden of pulmonary arterial hypertension (PAH) in the US on payers and patients

BACKGROUND

Pulmonary arterial hypertension (PAH) is a rare condition that can ultimately lead to right heart failure and death. In this study we estimated the health care costs and resource utilization associated with PAH in a large US managed care health plan.

METHODS

Subjects with claims-based evidence of PAH from 1/1/2004 to 6/30/2010 (identification period) were selected. To be included in the final PAH study sample, subjects were required to have ≥2 claims with a primary PH diagnosis; ≥2 claims with a PAH related-diagnosis (connective tissue diseases, congenital heart diseases, portal hypertension); and ≥1 claim with evidence of a PAH-indicated medication. The earliest date of a claim with evidence of PAH-indicated medication during the identification period was set as the index date. Health care costs and resource utilization were compared between an annualized baseline period and a 12 month follow-up period.

RESULTS

504 PAH subjects were selected for the final study cohort. Estimated average total health care costs were approximately 16% lower in the follow-up period compared to the baseline period (follow-up costs = $98,243 [SD = 110,615] vs. baseline costs = $116,681 [SD = 368,094], p < 0.001), but substantively high in each period relative to costs reported for other chronic diseases. Pharmacy costs were significantly higher in the follow-up period vs. the baseline period, ($38,514 [SD = 34,817] vs. $6,440 [SD = 12,186], p < 0.001) but medical costs were significantly lower in the follow-up vs. baseline ($59,729 [SD = 106,683] vs. $110,241 [SD = 368,725], p < 0.001). These costs were mirrored in health-care resource utilization estimates. The average counts of ambulatory visits and inpatient stays were lower in the follow-up vs. the baseline (both p < 0.001). Results varied in exploratory analyses when less restrictive subject identification algorithms were used.

CONCLUSIONS

Subjects with evidence of PAH had substantively high health care costs. Medical costs appeared to decrease following PAH medication use, but with a concomitant increase in pharmacy costs.

Targeted delivery of genes to endothelial cells and cell- and gene-based therapy in pulmonary vascular diseases

Pulmonary arterial hypertension (PAH) is a devastating disease that, despite significant advances in medical therapies over the last several decades, continues to have an extremely poor prognosis. Gene therapy is a method to deliver therapeutic genes to replace defective or mutant genes or supplement existing cellular processes to modify disease. Over the last few decades, several viral and nonviral methods of gene therapy have been developed for preclinical PAH studies with varying degrees of efficacy. However, these gene delivery methods face challenges of immunogenicity, low transduction rates, and nonspecific targeting which have limited their translation to clinical studies. More recently, the emergence of regenerative approaches using stem and progenitor cells such as endothelial progenitor cells (EPCs) and mesenchymal stem cells (MSCs) have offered a new approach to gene therapy. Cell-based gene therapy is an approach that augments the therapeutic potential of EPCs and MSCs and may deliver on the promise of reversal of established PAH. These new regenerative approaches have shown tremendous potential in preclinical studies; however, large, rigorously designed clinical studies will be necessary to evaluate clinical efficacy and safety.

Regulation of bone morphogenetic protein 9 (BMP9) by redox-dependent proteolysis

BMP9, a member of the TGFβ superfamily, is a homodimer that forms a signaling complex with two type I and two type II receptors. Signaling through high-affinity activin receptor-like kinase 1 (ALK1) in endothelial cells, circulating BMP9 acts as a vascular quiescence factor, maintaining endothelial homeostasis. BMP9 is also the most potent BMP for inducing osteogenic signaling in mesenchymal stem cells in vitro and promoting bone formation in vivo. This activity requires ALK1, the lower affinity type I receptor ALK2, and higher concentrations of BMP9. In adults, BMP9 is constitutively expressed in hepatocytes and secreted into the circulation. Optimum concentrations of BMP9 are essential to maintain the highly specific endothelial-protective function. Factors regulating BMP9 stability and activity remain unknown. Here, we showed by chromatography and a 1.9 Å crystal structure that stable BMP9 dimers could form either with (D-form) or without (M-form) an intermolecular disulfide bond. Although both forms of BMP9 were capable of binding to the prodomain and ALK1, the M-form demonstrated less sustained induction of Smad1/5/8 phosphorylation. The two forms could be converted into each other by changing the redox potential, and this redox switch caused a major alteration in BMP9 stability. The M-form displayed greater susceptibility to redox-dependent cleavage by proteases present in serum. This study provides a mechanism for the regulation of circulating BMP9 concentrations and may provide new rationales for approaches to modify BMP9 levels for therapeutic purposes.

Bone Morphogenetic Protein (BMP) signaling in development and human diseases

Bone Morphogenetic Proteins (BMPs) are a group of signaling molecules that belongs to the Transforming Growth Factor-β (TGF-β) superfamily of proteins. Initially discovered for their ability to induce bone formation, BMPs are now known to play crucial roles in all organ systems. BMPs are important in embryogenesis and development, and also in maintenance of adult tissue homeostasis. Mouse knockout models of various components of the BMP signaling pathway result in embryonic lethality or marked defects, highlighting the essential functions of BMPs. In this review, we first outline the basic aspects of BMP signaling and then focus on genetically manipulated mouse knockout models that have helped elucidate the role of BMPs in development. A significant portion of this review is devoted to the prominent human pathologies associated with dysregulated BMP signaling.

Pulmonary arterial hypertension: the clinical syndrome

Pulmonary arterial hypertension is a progressive disorder in which endothelial dysfunction and vascular remodeling obstruct small pulmonary arteries, resulting in increased pulmonary vascular resistance and pulmonary pressures. This leads to reduced cardiac output, right heart failure, and ultimately death. In this review, we attempt to answer some important questions commonly asked by patients diagnosed with pulmonary arterial hypertension pertaining to the disease, and aim to provide an explanation in terms of classification, diagnosis, pathophysiology, genetic causes, demographics, and prognostic factors. Furthermore, important molecular pathways that are central to the pathogenesis of pulmonary arterial hypertension are reviewed, including nitric oxide, prostacyclin, endothelin-1, reactive oxygen species, and endothelial and smooth muscle proliferation.

The genetics of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease for which there is an ever-expanding body of genetic and related pathophysiological information on disease pathogenesis. Many germline gene mutations have now been described, including mutations in the gene coding bone morphogenic protein receptor type 2 (BMPR2) and related genes. Recent advanced gene-sequencing methods have facilitated the discovery of additional genes with mutations among those with and those without familial forms of PAH (CAV1, KCNK3, EIF2AK4). The reduced penetrance, variable expressivity, and female predominance of PAH suggest that genetic, genomic, and other factors modify disease expression. These multi-faceted variations are an active area of investigation in the field, including but not limited to common genetic variants and epigenetic processes, and may provide novel opportunities for pharmacological intervention in the near future. They also highlight the need for a systems-oriented multi-level approach to incorporate the multitude of biological variations now associated with PAH. Ultimately, an in-depth understanding of the genetic factors relevant to PAH provides the opportunity for improved patient and family counseling about this devastating disease.

[Pulmonary hypertension: definition, diagnostic and new classification]

Pulmonary hypertension (PH): mean pulmonary arterial pressure (mPAP) ≥ 25 mm Hg on right heart catheterization at rest. Pulmonary arterial hypertension (PAH): mPAP ≥ 25 mm Hg, pulmonary capillary wedge pressure (PCWP) ≤ 15 mm Hg and pulmonary vascular resistances (PVR) >3 Wood units. Patients with compatible symptoms (exertional dyspnea, syncopes, signes of right heart failure) can show signs of PH on cardiac echography and therefore need to be investigated in search of the cause of PH. After ruling out the frequent causes of PH (left heart and chronic respiratory diseases), the V/Q lung scan is used to screen for patients with post-embolic PH, that need to be further investigated hemodynamically and radiologically in order to decide operability. For the rest of the patients, only right heart catheterization can identify patients with precapillary PH and these patients must be further evaluated (clinically, by blood samples and by imaging techniques) in order to be classified in one the PH groups of the classification. For the future the discovery of novel risk factors and understanding the mechanism involved with the already known ones represent two major points of research.

BMPR2 gene mutation in pulmonary arteriovenous malformation and pulmonary hypertension: a case report

The transforming growth factor-β superfamily signaling pathway is thought to be involved in the pathogenesis of pulmonary arteriovenous malformation (PAVM). However, the association between bone morphogenetic protein receptor type 2 (BMPR2) gene mutations and PAVM remains unclear. We present a case of concurrent PAVM and pulmonary arterial hypertension (PAH), with a deletion mutation in exon 6 and exon 7 of the BMPR2 gene. Drug treatment for PAH improved the patient's hemodynamics and exercise capacity, but worsened oxygenation. This case suggests that BMPR2 gene mutation may be associated with the complex presentation of PAVM combined with PAH.

Mutations of NOTCH3 in childhood pulmonary arterial hypertension

Mutations of BMPR2 and other TGF-β superfamily genes have been reported in pulmonary arterial hypertension (PAH). However, 60-90% of idiopathic PAH cases have no mutations in these genes. Recently, the expression of NOTCH3 was shown to be increased in the pulmonary artery smooth muscle cells of PAH patients. We sought to investigate NOTCH3 and its target genes in PAH patients and clarify the role of NOTCH3 signaling. We screened for mutations in NOTCH3, HES1, and HES5 in 41 PAH patients who had no mutations in BMPR2, ALK1, endoglin, SMAD1/4/8, BMPR1B, or Caveolin-1. Two novel missense mutations (c.2519 G>A p.G840E, c.2698 A>C p.T900P) in NOTCH3 were identified in two PAH patients. We performed functional analysis using stable cell lines expressing either wild-type or mutant NOTCH3. The protein-folding chaperone GRP78/BiP was colocalized with wild-type NOTCH3 in the endoplasmic reticulum, whereas the majority of GRP78/BiP was translocated into the nuclei of cells expressing mutant NOTCH3. Cell proliferation and viability were higher for cells expressing mutant NOTCH3 than for those expressing wild-type NOTCH3. We identified novel NOTCH3 mutations in PAH patients and revealed that these mutations were involved in cell proliferation and viability. NOTCH3 mutants induced an impairment in NOTCH3-HES5 signaling. The results may contribute to the elucidation of PAH pathogenesis.

Genetics and genomics of pulmonary arterial hypertension

Major discoveries have been obtained within the last decade in the field of hereditary predisposition to pulmonary arterial hypertension (PAH). Among them, the identification of bone morphogenetic protein receptor type 2 (BMPR2) as the major predisposing gene and activin A receptor type II-like kinase-1 (ACVRL1, also known as ALK1) as the major gene when PAH is associated with hereditary hemorrhagic telangiectasia. The mutation detection rate for the known genes is approximately 75% in familial PAH, but the mutation shortfall remains unexplained even after careful molecular investigation of these genes. To identify additional genetic variants predisposing to PAH, investigators harnessed the power of next-generation sequencing to successfully identify additional genes that will be described in this report. Furthermore, common genetic predisposing factors for PAH can be identified by genome-wide association studies and are detailed in this paper. The careful study of families and routine genetic diagnosis facilitated natural history studies based on large registries of PAH patients to be set up in different countries. These longitudinal or cross-sectional studies permitted the clinical characterization of PAH in mutation carriers to be accurately described. The availability of molecular genetic diagnosis has opened up a new field for patient care, including genetic counseling for a severe disease, taking into account that the major predisposing gene has a highly variable penetrance between families. Molecular information can be drawn from the genomic study of affected tissues in PAH, in particular, pulmonary vascular tissues and cells, to gain insight into the mechanisms leading to the development of the disease. High-throughput genomic techniques, on the basis of next-generation sequencing, now allow the accurate quantification and analysis of ribonucleic acid, species, including micro-ribonucleic acids, and allow for a genome-wide investigation of epigenetic or regulatory mechanisms, which include deoxyribonucleic acid methylation, histone methylation, and acetylation, or transcription factor binding.

Pulmonary arterial hypertension as the first manifestation in a patient with hereditary hemorrhagic telangiectasia

A 17-year-old Japanese girl visited our hospital for an evaluation of exertional dyspnea. A diagnosis of pulmonary arterial hypertension (PAH) was confirmed based on the findings of right heart catheterization. Detailed questioning revealed a family history of hereditary hemorrhagic telangiectasia (HHT), and a genetic mutation analysis disclosed a mutation in the activin receptor-like kinase 1 gene (ACVRL1). The patient was finally diagnosed with HHT according to the Curaçao diagnostic criteria eight years after the diagnosis of PAH. This case supports previous reports indicating that signs of PAH can be the first manifestation of disease in ACVRL1 mutation carriers.

Clinical and molecular genetic features of hereditary pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disorder that may be hereditary (HPAH), idiopathic (IPAH), or associated with either drug-toxin exposures or other medical conditions. Familial cases have long been recognised and are usually due to mutations in the bone morphogenetic protein receptor type 2 gene (BMPR2), or, much less commonly, two other members of the transforming growth factor-β superfamily, activin-like kinase-type 1 (ALK1), and endoglin (ENG), which are associated with hereditary hemorrhagic telangiectasia. In addition, approximately 20% of patients with IPAH carry mutations in BMPR2. Clinical testing for BMPR2 mutations is available and may be offered to HPAH and IPAH patients but should be preceded by genetic counselling, since lifetime penetrance is only 10% to 20%, and there are currently no known effective preventative measures. Identification of a familial mutation can be valuable in reproductive planning and identifying family members who are not mutation carriers and thus will not require lifelong surveillance. With advances in genomic technology and with international collaborative efforts, genome-wide association studies will be conducted to identify additional genes for HPAH, genetic modifiers for BMPR2 penetrance, and genetic susceptibility to IPAH. In addition, collaborative studies of BMPR2 mutation carriers should enable identification of environmental modifiers, biomarkers for disease development and progression, and surrogate markers for efficacy end points in clinical drug development, thereby providing an invaluable resource for trials of PAH prevention.

Physiological and pathological angiogenesis in the adult pulmonary circulation

Angiogenesis occurs during growth and physiological adaptation in many systemic organs, for example, exercise-induced skeletal and cardiac muscle hypertrophy, ovulation, and tissue repair. Disordered angiogenesis contributes to chronic inflammatory disease processes and to tumor growth and metastasis. Although it was previously thought that the adult pulmonary circulation was incapable of supporting new vessel growth, over that past 10 years new data have shown that angiogenesis within this circulation occurs both during physiological adaptive processes and as part of the pathogenic mechanisms of lung diseases. Here we review the expression of vascular growth factors in the adult lung, their essential role in pulmonary vascular homeostasis and the changes in their expression that occur in response to physiological challenges and in disease. We consider the evidence for adaptive neovascularization in the pulmonary circulation in response to alveolar hypoxia and during lung growth following pneumonectomy in the adult lung. In addition, we review the role of disordered angiogenesis in specific lung diseases including idiopathic pulmonary fibrosis, acute adult distress syndrome and both primary and metastatic tumors of the lung. Finally, we examine recent experimental data showing that therapeutic enhancement of pulmonary angiogenesis has the potential to treat lung diseases characterized by vessel loss.

Right ventricle in pulmonary hypertension

During heart development chamber specification is controlled and directed by a number of genes and a fetal heart gene expression pattern is revisited during heart failure. In the setting of chronic pulmonary hypertension the right ventricle undergoes hypertrophy, which is likely initially adaptive, but often followed by decompensation, dilatation and failure. Here we discuss differences between the right ventricle and the left ventricle of the heart and begin to describe the cellular and molecular changes which characterize right heart failure. A prevention and treatment of right ventricle failure becomes a treatment goal for patients with severe pulmonary hypertension it follows that we need to understand the pathobiology of right heart hypertrophy and the transition to right heart failure.

Genomics and proteomics of pulmonary vascular disease

Study of RNA and proteins in cells of both normal and diseased tissues is providing researchers with new knowledge of disease pathologies. While still in its early stages, high-throughput expression analysis is improving our understanding of the pathogenesis of pulmonary arterial hypertension (PAH). While many studies have used microarray and proteomic analyses as "hypothesis-generating" tools, the technologies also have potential to identify and quantify biomarkers of disease. To date, many of the published studies have examined gene expression profiles of tissue biopsies, others have utilized cells from peripheral blood. Microarray technology has been employed successfully in the investigation of a diverse array of human diseases. The potential of high-throughput expression analysis to improve our understanding of the pathogenesis of PAH is highlighted in this review. Proteomic studies of PAH and pulmonary vascular diseases in general have been little utilized thus far. To date, such studies are few and no consistent biomarker has emerged from studies of either plasma or blood cells from idiopathic pulmonary arterial hypertension (IPAH) patients. The studies of both lung tissue and lymphocytes are perhaps more revealing and suggest that changes in the cytoskeletal machinery may play a role in the pathogenesis of idiopathic pulmonary arterial hypertension. The oncology literature has demonstrated the utility of gene microarray analysis to predict important outcomes such as response to therapy and survival. It is likely that in the near future, gene microarrays and proteomic analyses will also be employed in a pharmacogenomics approach in PAH, helping to identify the most appropriate therapies for individual patients.

Correction of nonsense BMPR2 and SMAD9 mutations by ataluren in pulmonary arterial hypertension

Heritable pulmonary arterial hypertension (HPAH) is a serious lung vascular disease caused by heterozygous mutations in the bone morphogenetic protein (BMP) pathway genes, BMPR2 and SMAD9. One noncanonical function of BMP signaling regulates biogenesis of a subset of microRNAs. We have previously shown that this function is abrogated in patients with HPAH, making it a highly sensitive readout of BMP pathway integrity. Ataluren (PTC124) is an investigational drug that permits ribosomal readthrough of premature stop codons, resulting in a full-length protein. It exhibits oral bioavailability and limited toxicity in human trials. Here, we tested ataluren in lung- or blood-derived cells from patients with HPAH with nonsense mutations in BMPR2 (n = 6) or SMAD9 (n = 1). Ataluren significantly increased BMP-mediated microRNA processing in six of the seven cases. Moreover, rescue was achieved even for mutations exhibiting significant nonsense-mediated mRNA decay. Response to ataluren was dose dependent, and complete correction was achieved at therapeutic doses currently used in clinical trials for cystic fibrosis. BMP receptor (BMPR)-II protein levels were normalized and ligand-dependent phosphorylation of downstream target Smads was increased. Furthermore, the usually hyperproliferative phenotype of pulmonary artery endothelial and smooth muscle cells was reversed by ataluren. These results indicate that ataluren can effectively suppress a high proportion of BMPR2 and SMAD9 nonsense mutations and correct BMP signaling in vitro. Approximately 29% of all HPAH mutations are nonsense point mutations. In light of this, we propose ataluren as a potential new personalized therapy for this significant subgroup of patients with PAH.

Update on pediatric pulmonary arterial hypertension. Differences and similarities to adult disease

Children and adults with pulmonary arterial hypertension (PAH) have similarities and differences in their background characteristics, hemodynamics, and clinical manifestations. Regarding genetic background, mutations in BMPR2-related pathways seem to be pivotal; however, it is likely that other modifier genes and bioactive mediators have roles in the various forms of PAH in children and adults. In pediatric PAH, there are no clear sex differences in incidence, age at onset, disease severity, or prognosis but, as compared with adults, syncope incidence, pulmonary vascular resistance, and mean pulmonary artery pressure are higher, and vasoreactivity to acute drug testing is more frequent, among children. Nevertheless, the pharmacokinetic effects of 3 major pulmonary vasodilators appear to be similar in children and adults with PAH. This review focuses on the specific pathophysiologic features of PAH in children.

Heritable forms of pulmonary arterial hypertension

Tremendous progress has been made in understanding the genetics of heritable pulmonary arterial hypertension (HPAH) since its description in the 1950s. Germline mutations in the gene coding bone morphogenetic receptor type 2 (BMPR2) are detectable in the majority of cases of HPAH, and in a small proportion of cases of idiopathic pulmonary arterial hypertension (IPAH). Recent advancements in gene sequencing methods have facilitated the discovery of additional genes with mutations among those with and without familial PAH (CAV1, KCNK3). HPAH is an autosomal dominant disease characterized by reduced penetrance, variable expressivity, and female predominance. These characteristics suggest that genetic and nongenetic factors modify disease expression, highlighting areas of active investigation. The reduced penetrance makes genetic counseling complex, as the majority of carriers of PAH-related mutations will never be diagnosed with the disease. This issue is increasingly important, as clinical testing for BMPR2 and other mutations is now available for the evaluation of patients and their at-risk kin. The possibilities to avoid mutation transmission, such as the rapidly advancing field of preimplantation genetic testing, highlight the need for all clinicians to understand the genetic features of PAH risk.

A novel channelopathy in pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension is a devastating disease with high mortality. Familial cases of pulmonary arterial hypertension are usually characterized by autosomal dominant transmission with reduced penetrance, and some familial cases have unknown genetic causes.

METHODS

We studied a family in which multiple members had pulmonary arterial hypertension without identifiable mutations in any of the genes known to be associated with the disease, including BMPR2, ALK1, ENG, SMAD9, and CAV1. Three family members were studied with whole-exome sequencing. Additional patients with familial or idiopathic pulmonary arterial hypertension were screened for the mutations in the gene that was identified on whole-exome sequencing. All variants were expressed in COS-7 cells, and channel function was studied by means of patch-clamp analysis.

RESULTS

We identified a novel heterozygous missense variant c.608 G→A (G203D) in KCNK3 (the gene encoding potassium channel subfamily K, member 3) as a disease-causing candidate gene in the family. Five additional heterozygous missense variants in KCNK3 were independently identified in 92 unrelated patients with familial pulmonary arterial hypertension and 230 patients with idiopathic pulmonary arterial hypertension. We used in silico bioinformatic tools to predict that all six novel variants would be damaging. Electrophysiological studies of the channel indicated that all these missense mutations resulted in loss of function, and the reduction in the potassium-channel current was remedied by the application of the phospholipase inhibitor ONO-RS-082.

CONCLUSIONS

Our study identified the association of a novel gene, KCNK3, with familial and idiopathic pulmonary arterial hypertension. Mutations in this gene produced reduced potassium-channel current, which was successfully remedied by pharmacologic manipulation. (Funded by the National Institutes of Health.)

Pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a chronic and progressive disease leading to right heart failure and ultimately death if untreated. The first classification of PH was proposed in 1973. In 2008, the fourth World Symposium on PH held in Dana Point (California, USA) revised previous classifications. Currently, PH is devided into five subgroups. Group 1 includes patients suffering from idiopathic or familial PAH with or without germline mutations. Patients with a diagnosis of PAH should systematically been screened regarding to underlying mutations of BMPR2 gene (bone morphogenetic protein receptor type 2) or more rarely of ACVRL1 (activine receptor-like kinase type 1), ENG (endogline) or Smad8 genes. Pulmonary veno occusive disease and pulmonary capillary hemagiomatosis are individualized and designated as clinical group 1'. Group 2 'Pulmonary hypertension due to left heart diseases' is divided into three sub-groups: systolic dysfonction, diastolic dysfonction and valvular dysfonction. Group 3 'Pulmonary hypertension due to respiratory diseases' includes a heterogenous subgroup of respiratory diseases like PH due to pulmonary fibrosis, COPD, lung emphysema or interstitial lung disease for exemple. Group 4 includes chronic thromboembolic pulmonary hypertension without any distinction of proximal or distal forms. Group 5 regroup PH patients with unclear multifactorial mechanisms. Invasive hemodynamic assessment with right heart catheterization is requested to confirm the definite diagnosis of PH showing a resting mean pulmonary artery pressure (mPAP) of ≥ 25 mmHg and a normal pulmonary capillary wedge pressure (PCWP) of ≤ 15 mmHg. The assessment of PCWP may allow the distinction between pre-capillary and post-capillary PH (PCWP > 15 mmHg). Echocardiography is an important tool in the management of patients with underlying suspicion of PH. The European Society of Cardiology and the European Respiratory Society (ESC-ERS) guidelines specify its role, essentially in the screening proposing criteria for estimating the presence of PH mainly based on tricuspid regurgitation peak velocity and systolic artery pressure (sPAP). The therapy of PAH consists of non-specific drugs including oral anticoagulation and diuretics as well as PAH specific therapy. Diuretics are one of the most important treatment in the setting of PH because right heart failure leads to fluid retention, hepatic congestion, ascites and peripheral edema. Current recommendations propose oral anticoagulation aiming for targeting an International Normalized Ratio (INR) between 1.5-2.5. Target INR for patients displaying chronic thromboembolic PH is between 2–3. Better understanding in pathophysiological mechanisms of PH over the past quarter of a century has led to the development of medical therapeutics, even though no cure for PAH exists. Several specific therapeutic agents were developed for the medical management of PAH including prostanoids (epoprostenol, trepoprostenil, iloprost), endothelin receptor antagonists (bosentan, ambrisentan) and phosphodiesterase type 5 inhibitors (sildenafil, tadalafil). This review discusses the current state of art regarding to epidemiologic aspects of PH, diagnostic approaches and the current classification of PH. In addition, currently available specific PAH therapy is discussed as well as future treatments.

Integrating molecular genetics and systems approaches to pulmonary vascular diseases

There is incredible potential to advance our understanding of disease pathogenesis, enhance our diagnostic capability, and revolutionize our treatment modalities with the advent of advanced systems approaches to genetic, genomic, and epigenetic discoveries. Investigation using these technologies is beginning to impact our understanding of pulmonary arterial hypertension (PAH). The following review details work to date on single gene mutations in PAH, and expression array analysis in the disease. The wider use of DNA-based arrays for genome wide association studies (GWAS) and copy number alterations is examined. The impact of epigenomic modulation in the pathobiology of PAH and its therapeutic implications is investigated. Finally, a summary of the capabilities and promises for next-generation sequencing is discussed. A framework for studies of the future is proposed.

Signal transduction in the development of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a unique disease. Properly speaking, it is not a disease of the lung. It can be seen more as a microvascular disease occurring mainly in the lungs and affecting the heart. At the cellular level, the PAH paradigm is characterized by inflammation, vascular tone imbalance, pulmonary arterial smooth muscle cell proliferation and resistance to apoptosis and the presence of in situ thrombosis. At a clinical level, the aforementioned abnormal vascular properties alter physically the pulmonary circulation and ventilation, which greatly influence the right ventricle function as it highly correlates with disease severity. Consequently, right heart failure remains the principal cause of death within this cohort of patients. While current treatment modestly improve patients' conditions, none of them are curative and, as of today, new therapies are lacking. However, the future holds potential new therapies that might have positive influence on the quality of life of the patient. This article will first review the clinical presentation of the disease and the different molecular pathways implicated in the pathobiology of PAH. The second part will review tomorrow's future putative therapies for PAH.

High prevalence of pulmonary hypertension in patients with hereditary hemorrhagic telangiectasia

OBJECTIVE

Hereditary hemorrhagic telangiectasia (HHT) is a vascular disorder causing mucocutaneous telangiectases and visceral arteriovenous malformations (AVMs). Pulmonary hypertension (PH) is considered an uncommon complication of HHT whose impact on the survival of these patients is currently unknown.

METHODS

From January 1995 to December 2008, 29 hospitalized patients with definite HHT were included and followed until January 2011. Data on demographics, clinical symptoms and survival were recorded. PH was classified according to echocardiographic probability.

RESULTS

A CT angiogram was performed in 24 of the 29 patients with HHT and AVMs were detected in 16 of them (67%): hepatic in 58%, pulmonary in 33% and spinal in 3%; 37% had both pulmonary and hepatic AVMs. Transthoracic Doppler echocardiography (TTE) was performed in 21 patients. PH was considered possible in 4 (14%) and probable in 9 (31%). The mean age at diagnosis was lower in patients with PH than in patients without PH (54±16.5 years vs 73±8.8 years, p=0.002). PH was more prevalent in patients with AVMs (56 vs. 23%, p=0.036). The mean follow-up of the entire cohort was 6±4.4 years (range: 2 months-17 years), during this time 18 patients died (62%; mean age 73±8.1 years). Patients with PH died at a younger age (68±8.4 vs. 79±2.7 years, p=0.015) than those without PH.

CONCLUSIONS

PH is a severe condition that significantly reduces survival on HHT patients. PH should be suspected in all HHT patients with dyspnea and hepatic AVMs.

Transforming growth factor-β inhibition and endothelin receptor blockade in rats with monocrotaline-induced pulmonary hypertension

Transforming growth factor-β (TGF-β) inhibition is an investigational therapy for pulmonary arterial hypertension with promising results in experimental studies. The present work compared this approach with endothelin-receptor blockade and evaluated the effects of combined administration. Pulmonary arterial hypertension was induced by single monocrotaline injection (60 mg/kg) in 75 Wistar rats and 15 rats served as controls. Intervention groups consisted of treatment with an antibody against TGF-β-ligand, bosentan, both or none, initiated four weeks after monocrotaline injection. Right ventricular systolic pressure, pulmonary vascular remodeling, and exercise tolerance were evaluated eight weeks after monocrotaline injection. Either treatment, alone or in combination, lowered mortality. Comparable efficacy was found in the three treatment groups in terms of right ventricular systolic pressure (~45% decrease) and hypertrophy (~30% decrease), as well as exercise capacity. The three treatment groups equally ameliorated pulmonary vascular remodeling, evidenced by decreased vessel-wall thickness (in vessels 50-200 μm) and a smaller number of pre-capillary arterioles (< 50 μm) with a muscularized media. Treatment either with an antibody against TGF-β or with endothelin receptor blockade are equally effective in experimental pulmonary hypertension. Their combination provides no added benefit, indicating common mechanisms of action.

Pulmonary hypertension: biomarkers

Physicians look to biomarkers to inform the management of pulmonary hypertension (PH) at all stages, from assessing susceptibility through screening, diagnosis, and risk stratification to drug selection and monitoring. PH is a heterogeneous disorder and currently there are no accepted blood biomarkers specific to any manifestation of the condition. Brain natriuretic peptide and its N-terminal peptide have been most widely studied. Other candidate prognostic biomarkers in patients with pulmonary arterial hypertension (PAH) include growth and differentiation factor-15, red cell distribution width, uric acid, creatinine, inflammatory markers such as interleukin-6, angiopoietins, and microRNAs. Combining the measurement of biomarkers reflecting different components of the pathology with other modalities may enable better molecular characterisation of PH subtypes and permit improved targeting of therapeutic strategies and disease monitoring.

Molecular pathogenesis of pulmonary arterial hypertension

Recent clinical and experimental studies are redefining the cellular and molecular bases of pulmonary arterial hypertension (PAH). The genetic abnormalities first identified in association with the idiopathic form of PAH--together with a vast increase in our understanding of cell signaling, cell transformation, and cell-cell interactions; gene expression; microRNA processing; and mitochondrial and ion channel function--have helped explain the abnormal response of vascular cells to injury. Experimental and clinical studies now converge on the intersection and interactions between a genetic predisposition involving the BMPR2 signaling pathway and an impaired metabolic and chronic inflammatory state in the vessel wall. These deranged processes culminate in an exuberant proliferative response that occludes the pulmonary arterial (PA) lumen and obliterates the most distal intraacinar vessels. Here, we describe emerging therapies based on preclinical studies that address these converging pathways.

Genetics and pharmacogenomics in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an uncommon disease in the general population, but a disease with significant morbidity and mortality. The prevalence of heritable PAH (HPAH) remains unknown. The reason for incomplete penetrance of HPAH is not well understood. A patient's clinical response to disease-specific therapy is complex, involving the severity of the patient's disease, other comorbidities, appropriateness of the prescribed therapy, and patient compliance. Warfarin is often used as an adjuvant therapy in patients with PAH.

Outcomes of childhood pulmonary arterial hypertension in BMPR2 and ALK1 mutation carriers

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.

ANG-1 TIE-2 and BMPR signalling defects are not seen in the nitrofen model of pulmonary hypertension and congenital diaphragmatic hernia

BACKGROUND

Pulmonary hypertension (PH) is a lethal disease that is associated with characteristic histological abnormalities of the lung vasculature and defects of angiopoetin-1 (ANG-1), TIE-2 and bone morphogenetic protein receptor (BMPR)-related signalling. We hypothesized that if these signalling defects cause PH generically, they will be readily identifiable perinatally in congenital diaphragmatic hernia (CDH), where the typical pulmonary vascular changes are present before birth and are accompanied by PH after birth.

METHODS

CDH (predominantly left-sided, LCDH) was created in Sprague-Dawley rat pups by e9.5 maternal nitrofen administration. Left lungs from normal and LCDH pups were compared at fetal and postnatal time points for ANG-1, TIE-2, phosphorylated-TIE-2, phosphorylated-SMAD1/5/8 and phosphorylated-ERK1/2 by immunoprecipitation and Western blotting of lung protein extracts and by immunohistochemistry on lung sections.

RESULTS

In normal lung, pulmonary ANG-1 protein levels fall between fetal and postnatal life, while TIE-2 levels increase. Over the corresponding time period, LCDH lung retained normal expression of ANG-1, TIE-2, phosphorylated-TIE-2 and, downstream of BMPR, phosphorylated-SMAD1/5/8 and phosphorylated-p44/42.

CONCLUSION

In PH and CDH defects of ANG-1/TIE-2/BMPR-related signalling are not essential for the lethal vasculopathy.

Pulmonary hypertension: chapters of innovation and tribulation

As can be seen by the mounting literature, there has been immense progress in the field of pulmonary hypertension (PH) over the last three decades, illustrated by several important milestones including improved understanding of disease pathogenesis, new classifications of disease, advances in screening and diagnostic techniques, and new rules for staging and follow-up, which have subsequently led to improvements in patient outcomes. The objectives of this manuscript are to not only highlight these very recent advances but also point out areas of deficiencies or gaps in our knowledge that may serve a focal point for future discussion and investigation.

TGFβ signaling and cardiovascular diseases

Transforming growth factor β (TGFβ) family members are involved in a wide range of diverse functions and play key roles in embryogenesis, development and tissue homeostasis. Perturbation of TGFβ signaling may lead to vascular and other diseases. In vitro studies have provided evidence that TGFβ family members have a wide range of diverse effects on vascular cells, which are highly dependent on cellular context. Consistent with these observations genetic studies in mice and humans showed that TGFβ family members have ambiguous effects on the function of the cardiovascular system. In this review we discuss the recent advances on TGFβ signaling in (cardio)vascular diseases, and describe the value of TGFβ signaling as both a disease marker and therapeutic target for (cardio)vascular diseases.