Heterogeneity of pathologic lesions in familial primary pulmonary hypertension

Phosphoproteomic analysis of lung tissue from patients with pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disorder associated with high morbidity and mortality despite currently available treatments. We compared the phosphoproteome of lung tissue from subjects with idiopathic PAH (iPAH) obtained at the time of lung transplant with control lung tissue. The mass spectrometry-based analysis found 60,428 phosphopeptide features from which 6622 proteins were identified. Within the subset of identified proteins there were 1234 phosphopeptides with q < 0.05, many of which are involved in immune regulation, angiogenesis, and cell proliferation. Most notably there was a marked relative increase in phosphorylated (S378) IKZF3 (Aiolos), a zinc finger transcription factor that plays a key role in lymphocyte regulation. In vitro phosphorylation assays indicated that GSK3 alpha and/or GSK3 beta could phosphorylate IKZF3 at S378. Western blot analysis demonstrated increased pIKZF3 in iPAH lungs compared to controls. Immunohistochemistry demonstrated phosphorylated IKZF3 in lymphocytes surrounding severely hypertrophied pulmonary arterioles. In situ hybrization showed gene expression in lymphocyte aggregates in PAH samples. A BCL2 reporter assay showed that IKZF3 increased BCL2 promoter activity and demonstrated the potential role of phosphorylation of IKZF3 in the regulation of BCL mediated transcription. Kinase network analysis demonstrated potentially important regulatory roles of casein kinase 2, cyclin-dependent kinase 1 (CDK1), mitogen-associated protein kinases (MAPKs), and protein kinases (PRKs) in iPAH. Bioinformatic analysis demonstrated enrichment of RhoGTPase signaling and the potential importance of cGMP-dependent protein kinase 1 (PRKG). In conclusion, this unbiased phosphoproteomic analysis demonstrated several novel targets regulated by kinase networks in iPAH, and reinforced the potential role of immune regulation in the pathogenesis of iPAH. The identified up- and down-regulated phosphoproteins have potential to serve as biomarkers for PAH and to provide new insights for therapeutic strategies.

Platelets, extracellular vesicles and coagulation in pulmonary arterial hypertension

Pulmonary arterial hypertension is a rare disease of the pulmonary vasculature, characterised pathologically by proliferation, remodelling and thrombosis in situ. Unfortunately, existing therapeutic interventions do not reverse these findings and the disease continues to result in significant morbidity and premature mortality. A number of haematological derangements have been described in pulmonary arterial hypertension which may provide insights into the pathobiology of the disease and opportunities to explore new therapeutic pathways. These include quantitative and qualitative platelet abnormalities, such as thrombocytopaenia, increased mean platelet volume and altered platelet bioenergetics. Furthermore, a hypercoagulable state and aberrant negative regulatory pathways can be observed, which could contribute to thrombosis in situ in distal pulmonary arteries and arterioles. Finally, there is increasing interest in the role of extracellular vesicle autocrine and paracrine signalling in pulmonary arterial hypertension, and their potential utility as biomarkers and novel therapeutic targets. This review focuses on the potential role of platelets, extracellular vesicles and coagulation pathways in the pathobiology of pulmonary arterial hypertension. We highlight important unanswered clinical questions and the implications of these observations for future research and pulmonary arterial hypertension-directed therapies.

Plexogenic arteriopathy in broiler lungs: Evaluation of line, age, and sex influences

Plexiform lesions form in the terminal pulmonary arterioles of human patients suffering from prolonged pulmonary arterial hypertension. Plexiform lesions also develop in broiler lungs, but lesion incidences are not strongly correlated with sustained pulmonary hypertension as reflected by right to total ventricular weight (RVTV) ratios. The present study was conducted to assess plexiform lesion incidences in broiler lines that have been divergently selected for susceptibility or resistance to pulmonary hypertension. Broilers from susceptible (SUS) and resistant (RES) lines were reared together and only clinically healthy (nonascitic, noncyanotic) individuals were evaluated to minimize potential line differences in cardiopulmonary hemodynamics. The objective was to determine if an innate genetic predisposition for plexogenic arteriopathy would be exposed in SUS broilers when compared with RES broilers in the absence of extreme differences in cardiopulmonary hemodynamics. Broilers up to 12 wk age from the SUS and RES lines had essentially equivalent BW, indices of cardiopulmonary function (left ventricle + septum weight, total ventricle weight, and RVTV ratios), and lung volumes within a sex. Average RVTV ratios for broilers from both lines were indicative of normal pulmonary arterial pressures at all ages sampled. Nevertheless, plexiform lesions were detected in SUS and RES broiler lungs immediately posthatch and thereafter at all ages sampled. Lesion incidences were consistently low and did not differ between the lines within any of the sampling ages. This evidence demonstrates that plexiform lesions develop extremely rapidly in broiler chicks, apparently without the prerequisite for vascular stress caused by severe, prolonged pulmonary arterial hypertension. No innate genetic predisposition for complex vascular lesion development appeared to exist in the SUS line when compared with the RES line.

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.

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.

Potential Interventions Against BMPR2-Related Pulmonary Hypertension

For more than 60 years, researchers have sought to understand the molecular basis of idiopathic pulmonary arterial hypertension (PAH). Recognition of the heritable form of the disease led to the creation of patient registries in the 1980s and 1990s, and discovery of BMPR2 as the cause of roughly 80% of heritable PAH in 2000. With discovery of the disease gene came opportunity for intervention, with focus on 2 alternative approaches. First, it may be possible to correct the effects of BMPR2 mutation directly through interventions targeted at correction of trafficking defects, increasing expression of the unmutated allele, and correction of splicing defects. Second, therapeutic interventions are being targeted at the signaling consequences of BMPR2 mutation. In particular, therapies targeting cytoskeletal and metabolic defects caused by BMPR2 mutation are currently in trials, or will be ready for human trials in the near future. Translation of these findings into therapies is the culmination of decades of research, and holds great promise for treatment of the underlying molecular bases of disease.

The molecular genetics and cellular mechanisms underlying pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an incurable disorder clinically characterised by a sustained elevation of mean arterial pressure in the absence of systemic involvement. As the adult circulation is a low pressure, low resistance system, PAH represents a reversal to a foetal state. The small pulmonary arteries of patients exhibit luminal occlusion resultant from the uncontrolled growth of endothelial and smooth muscle cells. This vascular remodelling is comprised of hallmark defects, most notably the plexiform lesion. PAH may be familial in nature but the majority of patients present with spontaneous disease or PAH associated with other complications. In this paper, the molecular genetic basis of the disorder is discussed in detail ranging from the original identification of the major genetic contributant to PAH and moving on to current next-generation technologies that have led to the rapid identification of additional genetic risk factors. The impact of identified mutations on the cell is examined, particularly, the determination of pathways disrupted in disease and critical to pulmonary vascular maintenance. Finally, the application of research in this area to the design and development of novel treatment options for patients is addressed along with the future directions PAH research is progressing towards.

Pulmonary vascular disease in Gaucher disease: clinical spectrum, determinants of phenotype and long-term outcomes of therapy

Pulmonary arterial hypertension (PAH) and hepatopulmonary syndrome (HPS) are rare pulmonary vascular complications of type 1 Gaucher disease (GD1). We examined GBA1 genotype, spleen status, Severity Score Index (SSI), and other patient characteristics as determinants of GD/PAH-HPS phenotype. We also examined the long-term outcomes of imiglucerase enzyme replacement therapy (ERT) +/- adjuvant therapies in 14 consecutive patients. We hypothesized a role of BMPR2 and ALK1 as genetic modifiers underlying GD/PAH-HPS phenotype. Median age at diagnosis of GD1 was 5 yrs (2-22); PAH was diagnosed at median 36 yrs (22-63). There was a preponderance of females (ratio 5:2). ERT was commenced at median 36.5 yrs (16-53) and adjuvant therapy at 36 yrs (24-57). GBA1 genotype was N370S homozygous in two patients, N370S heteroallelic in 12. Median SSI was 15 (7-20). All patients had undergone splenectomy at median age 12 yrs (2-30). In three patients, HPS was the initial presentation, and PAH developed after its resolution; in these three, HPS responded dramatically to ERT. In seven patients, sequencing of the coding regions of BMPR2 and ALK1 was undertaken: 3/7 were heterozygous for BMPR2 polymorphisms; none harbored ALK1 variants. With ERT (± adjuvant therapy), 5/14 improved dramatically, five remained stable, two worsened, and two died prematurely. In this largest series of GD/PAH-HPS patients, there is preponderance of females and N370S heteroallelic GBA1 genotype. Splenectomy appears essential to development of this phenotype. In some patients, HPS precedes PAH. BMPR2 and ALK1 appear not be modifier genes for this rare phenotype of GD. ERT +/- adjuvant therapy improves prognosis of this devastating GD phenotype.

Pulmonary arterial hypertension: a comparison between children and adults

The characteristics of pulmonary arterial hypertension (PAH), including pathology, symptoms, diagnosis and treatment are reviewed in children and adults. The histopathology seen in adults is also observed in children, although children have more medial hypertrophy at presentation. Both populations have vascular and endothelial dysfunction. Several unique disease states are present in children, as lung growth abnormalities contribute to pulmonary hypertension. Although both children and adults present at diagnosis with elevations in pulmonary vascular resistance and pulmonary artery pressure, children have less heart failure. Dyspnoea on exertion is the most frequent symptom in children and adults with PAH, but heart failure with oedema occurs more frequently in adults. However, in idiopathic PAH, syncope is more common in children. Haemodynamic assessment remains the gold standard for diagnosis, but the definition of vasoreactivity in adults may not apply to young children. Targeted PAH therapies approved for adults are associated with clinically meaningful effects in paediatric observational studies; children now survive as long as adults with current treatment guidelines. In conclusion, there are more similarities than differences in the characteristics of PAH in children and adults, resulting in guidelines recommending similar diagnostic and therapeutic algorithms in children (based on expert opinion) and adults (evidence-based).

BMPR2 mutation alters the lung macrophage endothelin-1 cascade in a mouse model and patients with heritable pulmonary artery hypertension

Macrophage derived-endothelin-1 (ET-1) has been suggested to contribute to a number of chronic lung diseases. Whether the ET-1 cascade from non-vascular sources (inflammatory cells) also contributes to pulmonary artery hypertension (PAH) and in particular to heritable PAH (HPAH) with known bone morphogenetic protein type 2 receptor (BMPR2) mutations is not known. We tested this notion using bone marrow-derived macrophages (BMDM; precursors of tissue macrophages) isolated from ROSA26rtTAXTetO(7)-tet-BMPR2(R899X) mice (model of PAH with universal expression of a mutated BMPR2 gene) with and without activation by LPS and in human lung tissue from HPAH with BMPR2 mutations and idiopathic PAH (IPAH). At baseline ET(A) and ET(B) receptors and endothelin converting enzyme (ECE) gene expression was reduced in BMPR2 mutant BMDM compared with controls. In control BMDM, LPS resulted in increased ppET-1 gene expression and ET-1 in culture media, whereas ET(A) and ET(B) receptor and ECE gene expression was decreased. These findings were more severe in BMPR2 mutant BMDM. Antagonism of the ET(B) receptor resulted in increased ET-1 in the media, suggesting that decreased ET-1 uptake by the ET(B) receptor contributes to the elevation. While ET-1 expression was demonstrated in lung macrophages from controls and IPAH and HPAH patients, ET(A) and ET(B) expression was decreased in the HPAH, but not IPAH, patients compared with controls. We conclude that reduced expression of macrophage ET-1 receptors in HPAH increases lung ET-1 and may contribute to the pathogenesis and maintenance of HPAH. This is the first description of protein expression that distinguishes HPAH from IPAH in patients.

Pulmonary arterial hypertension: current therapeutic strategies

The treatment of pulmonary arterial hypertension--once a lethal condition--has evolved considerably over the past few years as the number of therapeutic options available to treat this disease has increased. In this Review we attempt to summarize the current knowledge of the pathogenesis of pulmonary hypertension, in relation to the therapies presently available and those that could become available in the near future. The use of prostacyclin and its analogs, calcium-channel blockers, endothelin-receptor antagonists and phosphodiesterase type 5 inhibitors is reviewed. Newer concepts, such as the use of combination therapy, and the potential for long-term disease amelioration and improvement of outcomes, are also discussed. The role of supportive care and medications not specific to pulmonary hypertension is also examined. In addition, we review the novel emerging therapies, such as imatinib, fasudil, simvastatin, ghrelin and vasoactive intestinal peptide, which hold therapeutic potential for disease modification as well as treatment of symptoms.

Standard therapies for pulmonary arterial hypertension

After half a century of clinical experience and research, management of pulmonary arterial hypertension remains a challenge. Currently, data to support the use of standard therapies for pulmonary arterial hypertension (oxygen supplementation, diuretics, digoxin, anticoagulation, and calcium channel blockers) are mostly retrospective, uncontrolled prospective, or derived from other diseases with similar but not identical manifestations. In the absence of any further prospective, controlled studies, it is reasonable to use these therapies when they are tolerated. When these therapies are poorly tolerated, however, the threshold for discontinuation should be low.

Moderate Pulmonary Arterial Hypertension in Male Mice Lacking the Vasoactive Intestinal Peptide Gene

Background— Vasoactive intestinal peptide (VIP), a pulmonary vasodilator and inhibitor of vascular smooth muscle proliferation, has been reported absent in pulmonary arteries from patients with idiopathic pulmonary arterial hypertension (PAH). We have tested the hypothesis that targeted deletion of the VIP gene may lead to PAH with pulmonary vascular remodeling.

Methods and Results— We examined VIP knockout (VIP −/− ) mice for evidence of PAH, right ventricular (RV) hypertrophy, and pulmonary vascular remodeling. Relative to wild-type control mice, VIP −/− mice showed moderate RV hypertension, RV hypertrophy confirmed by increased ratio of RV to left ventricle plus septum weight, and enlarged, thickened pulmonary artery and smaller branches with increased muscularization and narrowed lumen. Lung sections also showed perivascular inflammatory cell infiltrates. No systemic hypertension and no arterial hypoxemia existed to explain the PAH. The condition was associated with increased mortality. Both the vascular remodeling and RV remodeling were attenuated after a 4-week treatment with VIP.

Conclusions— Deletion of the VIP gene leads to spontaneous expression of moderately severe PAH in mice during air breathing. Although not an exact model of idiopathic PAH, the VIP −/− mouse should be useful for studying molecular mechanisms of PAH and evaluating potential therapeutic agents. VIP replacement therapy holds promise for the treatment of PAH, and mutations of the VIP gene may be a factor in the pathogenesis of idiopathic PAH.

Genetics and mediators in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an uncommon disorder of the pulmonary vasculature characterized by remodeling of the smallest pulmonary arteries, leading to a progressive increase in pulmonary vascular resistance. Various forms of PAH exist, including familial (FPAH) and idiopathic (IPAH) forms and associated conditions. FPAH transmits as an autosomal dominant trait that exhibits genetic anticipation but also markedly reduced penetrance (20%). The primary genetic defect of FPAH, identifiable in more than 70% of cases of FPAH, is a mutation in the gene encoding bone morphogenetic protein receptor type 2 (BMPR2), a member of the transforming growth factor beta superfamily. The true prevalence of BMPR2 mutations in IPAH is unknown, with reports ranging from 10% to 40% of patients. The cause of the variable phenotypic expression of PAH among carriers of mutated BMPR2 genes and patients is unclear, and likely related to environmental and genetic modifiers of disease not yet fully elucidated. Although BMPR2-related pathways seem to be pivotal, many other mediator pathways participate in the pathogenesis of different forms of PAH and are being actively investigated, both independently and in combination. As understanding of the molecular basis of this devastating disease improves, opportunities for earlier diagnosis, additional therapeutic regimens, and perhaps disease prevention will emerge.

Relationship of BMPR2 Mutations to Vasoreactivity in Pulmonary Arterial Hypertension

Background— Vasoreactivity tests are fundamental in evaluating pulmonary arterial hypertension (PAH). Mutations of the transforming growth factor-β type II receptor gene, BMPR2 , predispose to the development of pulmonary hypertension and may alter the response to vasodilators. Previous investigations have not examined the relationship of BMPR2 mutations to vasoreactivity.

Methods and Results— We identified 133 consecutive unrelated patients with either idiopathic or familial PAH. Sixty-six patients were excluded because we lacked either DNA samples (n=18) or complete data from a vasoreactivity test (n=48). The remaining 67 patients were screened for BMPR2 DNA sequence variations, and specific variations were confirmed by gene sequencing. The vasoreactivity of patients with nonsynonymous BMPR2 variations was compared with that of patients without nonsynonymous BMPR2 variations. We found nonsynonymous BMPR2 variations in 27 of 67 patients with idiopathic (n=16 of 52) or familial (n=11 of 15) PAH. Vasoreactivity was identified in 3.7% of 27 patients with nonsynonymous BMPR2 variations and in 35% of 40 patients without nonsynonymous BMPR2 variations ( P =0.003). Five of the 27 nonsynonymous variations occur commonly in healthy individuals. None of the remaining 22 patients with BMPR2 variations demonstrated vasoreactivity, and the analysis remained unchanged when we assumed that nonsynonymous BMPR2 variations were present in all 15 patients with familial PAH.

Conclusions— Patients with familial or idiopathic PAH and nonsynonymous BMPR2 variations are unlikely to demonstrate vasoreactivity. Further trials are required to determine whether long-term therapy can be directed by tests for BMPR2 variations.

Mediators and modulators of pulmonary arterial hypertension

Pulmonary hypertension (PH), defined as a mean pulmonary arterial (PA) pressure of >25 mmHg at rest or >30 mmHg during exercise, is characterized by a progressive and sustained increase in pulmonary vascular resistance that eventually leads to right ventricular failure. Clinically, PH may result from a variety of underlying diseases (Table 1 and Refs. 50, 113, 124). Pulmonary arterial hypertension (PAH) may be familial (FPAH) or sporadic (idiopathic, IPAH), formerly known as primary pulmonary hypertension, i.e., for which there is no demonstrable cause. More often, PAH is due to a variety of identifiable diseases including scleroderma and other collagen disorders, liver disease, human immunodeficiency virus, and the intake of appetite-suppressant drugs such as phentermine and fenfluramine (72). Other, more common, causes of PAH include left ventricular failure (perhaps the most common cause), valvular lesions, chronic pulmonary diseases, sleep-disordered breathing, and prolonged residence at high altitude. This classification, now widely accepted, was first proposed at a meeting in Evian, France, in 1998, and modified in Venice, Italy, in 2003 (124).

Gender issues in pulmonary vascular disease

Gender differences in pulmonary vascular diseases, as exemplified by primary pulmonary hypertension and scleroderma-related pulmonary hypertension, are not well-explained; however, in general terms, they seem to be related to a combination of genetic predispositions and gender-specific environmental triggers. More information is needed in both areas with respect to mechanisms of disease. More information also is needed about possible gender differences in disease presentation,course, and response to treatments.

Primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a rare disorder characterised by raised pulmonary-artery pressure in the absence of secondary causes. Precapillary pulmonary arteries are affected by medial hypertrophy, intimal fibrosis, microthrombosis, and plexiform lesions. Most individuals present with dyspnoea or evidence of right heart failure. Echocardiography is the best non-invasive test to screen for suspected pulmonary hypertension. The discovery of mutations in the coding region of the gene for bone morphogenetic protein receptor 2 in patients with familial and sporadic PPH may help not only to elucidate pathogenesis but also to direct future treatment options. The pathogenesis is not completely understood, but recent investigations have revealed many possible candidate modifier genes. Without treatment, the disorder progresses in most cases to right heart failure and death. With current therapies such as epoprostenol, progression of disease is slowed, but not halted. Many promising new therapeutic options, including prostacyclin analogues, endothelin-1-receptor antagonists, and phosphodiesterase inhibitors, improve clinical function and haemodynamic measures and may prolong survival.

Primary pulmonary hypertension and cor pulmonale

Primary pulmonary hypertension and cor pulmonale represent forms of precapillary pulmonary hypertension due to intrinsic lung disease. In the case of primary pulmonary hypertension, this is due to disease of the pulmonary vasculature while cor pulmonale is related to diseases of the pulmonary vasculature, airways, or interstitium. Patients present with signs and symptoms of right ventricular dysfunction and low cardiac output including dyspnea, chest pain and peripheral edema. Therapy is directed at the underlying disease and may include supplemental oxygen for diseases causing chronic hypoxemia and anticoagulation for thrombotic disease. Vasodilator therapy has variable efficacy for pulmonary vascular disorders. Postacyclin by continuous infusion has been a major advance in the therapy of primary pulmonary hypertension and has prolonged survival and delayed the need for lung transplantation. Bosentan, an endothelin receptor blocking agent is the first oral medication approved for the therapy of pulmonary hypertension.

Recent advances in pulmonary vascular disease

There have been remarkable advances in our understanding of the pathobiology of pulmonary hypertension. A region on chromosome 2 encoding bone morphogenetic receptor type 2 has been identified to underlie familial and many cases of sporadic primary pulmonary arterial hypertension. The vasoactive mediators, discovered and defined by vascular biologists, have been translated into promising treatments of human disease. Prostacyclin, endothelin receptor blockers, sildenafil, and nitric oxide have been applied therapeutically to limit, and occasionally reverse, the inexorable damage to the pulmonary circulation initiated by recently identified genetic and environmental triggers of pulmonary arterial hypertension.

Genetic aspects of pulmonary arterial hypertension

This paper concentrates on the genetic aspects of pulmonary arterial hypertension (PAH), a diagnostically based subclass of pulmonary hypertension that includes primary pulmonary hypertension (PPH). During the past year, patients with familial and sporadic PPH were found to have germline heterozygous missense, nonsense and frameshift mutations in bone morphogenetic protein receptor II (BMPR2). Mutations in BMPR2, a member of the transforming growth factor-beta (TGF-beta) receptor superfamily, are predicted to interrupt the bone morphogenetic protein (BMP) signalling pathway, resulting in proliferation, rather than apoptosis of cells within small arterioles. Mechanistically, haploinsufficiency was found by using in vitro gene expression experiments, but a dominant-negative mechanism has not been excluded. The failure to find BMPR2 mutations in all families with familial PPH and in all patients with sporadic PPH suggests that other genes remain to be identified. Mutations in ALK1, a TGF-beta type 1 receptor, previously known to cause type 2 hereditary haemorrhagic telangiectasia (HHT), have also been reported in a few HHT families with clinical and histological features of PPH. The clinical development of PPH, as in neoplasia, appears to require 'two hits' The two hits can be provided either by genetic or environmental factors.

Pathobiology of pulmonary hypertension. The role of platelets and thrombosis

With the rare exceptions of PAH associated with antiphospholipid antibodies, genetic platelet dysfunction, or inherited deficiencies of antithrombotic pathways, the thrombotic lesions are secondary, but frequently occurring, in most cases of primary or secondary PAH. Pulmonary arterial hypertension is associated with thrombotic lesions and persistent vasoconstriction and structural remodeling of PA. Activated platelets interact with the PA wall and may contribute to the functional and structural alterations of pulmonary vessels by releasing vasoactive factors and mitogenic mediators.

Genetics of primary pulmonary hypertension

Familial primary pulmonary hypertension (FPPH) is a well described clinical entity in which the disease occurs in at least two first degree relatives. It is clinically and pathologically indistinguishable from sporadic PPH. Mutations in the gene which encodes bone morphogenetic receptor 2 have recently been discovered in familial and sporadic PPH. This review discusses the basic clinical and genetic features of FPPH, and describes the research that led to the discovery of the disease-causing gene. Potential mechanisms of disease are also discussed, as well as implications for future investigations.

The pathology of pulmonary artery hypertension

The pathologic features of primary pulmonary hypertension (PPH) are well known but its pathogenesis remains uncertain. In the first section, this chapter outlines the characteristic structural changes of PPH. The second section deals with the pathogenesis of these changes drawing on animal models of chronic pulmonary hypertension. The third section deals with phenotypic alterations in cells from the wall of the pulmonary artery of hypertensive animals. The recent identification of a germlike mutation in the BMPR2 gene in patients with PPH provides a novel opportunity to further our understanding of the pathogenesis of this disease.

Gene expression patterns in the lungs of patients with primary pulmonary hypertension: a gene microarray analysis

Primary pulmonary hypertension (PPH) is a disease of unknown etiology characterized by lumen-obliterating endothelial cell proliferation and vascular smooth muscle hypertrophy of the small precapillary pulmonary arteries. Because the vascular lesions are homogeneously distributed throughout the entire lung, we propose that a tissue fragment of the lung is representative of the whole lung. RNA extracted from the fragments is likely to provide meaningful information regarding the changes in gene expression pattern in PPH when compared with structurally normal lung tissue. We hypothesize that the lung tissue gene expression pattern of patients with PPH has a characteristic profile when compared with the gene expression pattern of structurally normal lungs and that this characteristic gene expression profile provides new insights into the pathobiology of PPH. Using oligonucleotide microarray technology, we characterized the expression pattern in the lung tissue obtained from 6 patients with primary pulmonary hypertension (PPH)-including 2 patients with the familial form of PPH (FPPH)-and from 6 patients with histologically normal lungs. For the data analysis, gene clusters were generated and the gene expression pattern differences between PPH and normal lung tissue and between PPH and FPPH lung tissue were compared. All PPH lung tissue samples showed a decreased expression of genes encoding several kinases and phosphatases, whereas several oncogenes and genes coding for ion channel proteins were upregulated in their expression. Importantly, we could distinguish by pattern comparison between sporadic PPH and FPPH, because alterations in the expression of transforming growth factor-beta receptor III, bone morphogenic protein 2, mitogen-activated protein kinase kinase 5, RACK 1, apolipoprotein C-III, and the gene encoding the laminin receptor 1 were only found in the samples from patients with sporadic PPH, but not in FPPH samples. We conclude that the microarray gene expression technique is a new and useful molecular tool that provides novel information pertinent to a better characterization and understanding of the pathobiology of the distinct clinical phenotypes of pulmonary hypertension.

Sporadic primary pulmonary hypertension is associated with germline mutations of the gene encoding BMPR-II, a receptor member of the TGF-beta family

BACKGROUND

Primary pulmonary hypertension (PPH), resulting from occlusion of small pulmonary arteries, is a devastating condition. Mutations of the bone morphogenetic protein receptor type II gene (BMPR2), a component of the transforming growth factor beta (TGF-beta) family which plays a key role in cell growth, have recently been identified as causing familial PPH. We have searched for BMPR2 gene mutations in sporadic PPH patients to determine whether the same genetic defect underlies the more common form of the disorder.

METHODS

We investigated 50 unrelated patients, with a clinical diagnosis of PPH and no identifiable family history of pulmonary hypertension, by direct sequencing of the entire coding region and intron/exon boundaries of the BMPR2 gene. DNA from available parent pairs (n=5) was used to assess the occurrence of spontaneous (de novo) mutations contributing to sporadic PPH.

RESULTS

We found a total of 11 different heterozygous germline mutations of the BMPR2 gene in 13 of the 50 PPH patients studied, including missense (n=3), nonsense (n=3), and frameshift (n=5) mutations each predicted to alter the cell signalling response to specific ligands. Parental analysis showed three occurrences of paternal transmission and two of de novo mutation of the BMPR2 gene in sporadic PPH.

CONCLUSION

The sporadic form of PPH is associated with germline mutations of the gene encoding the receptor protein BMPR-II in at least 26% of cases. A molecular classification of PPH, based upon the presence or absence of BMPR2 mutations, has important implications for patient management and screening of relatives.

Distribution of obstructive intimal lesions and their cellular phenotypes in chronic pulmonary hypertension. A morphometric and immunohistochemical study

We investigated the distribution of pulmonary arteriopathy in chronic pulmonary hypertension (PH) in a quantitative histopathologic study, using computer-assisted image analysis. We also examined the histologic manifestations and cellular phenotypes of various obstructive intimal lesions in PH with an immunohistochemical method. A total of 53 lungs removed at autopsy or explantation were obtained for the study from 51 documented cases of moderate to severe PH (15 cases of primary pulmonary hypertension [PPH], eight cases of Eisenmenger's syndrome [EISEN], 22 cases of chronic major-vessel thromboembolic disease [CTED], and three cases of PH associated with other known causes), and two unused donor lungs served as normal controls. Intimal thickening in PPH was most prominent in small pulmonary arteries and arterioles less than 200 micrometer in diameter. Plexiform lesions in PPH were associated with significantly smaller arteries than in EISEN. Arteries larger than 400 micrometer showed a significant intimal thickening only in CTED. Obstructive intimal lesions in PH comprised a morphologic spectrum with frequent intermediate forms between plexiform and thrombotic lesions. Most cells within various intimal lesions showed an immunoprofile of myofibroblasts that were positive for vimentin and alpha-smooth muscle actin, but negative for desmin and endothelial markers including Factor VIII, clonal designator (CD)31, and CD34. Endothelial markers were positive only in the single layer of cells lining slitlike lumens, when the latter were present. In conclusion, major types of PH had characteristic distribution patterns of obstructive intimal lesions, showing mainly a myofibroblastic phenotype and variable endothelial/vascular differentiation.

Primary pulmonary hypertension: insights into pathogenesis from epidemiology

Primary pulmonary hypertension (PPH) is a rare disease that affects young people predominantly of female gender. Early epidemiologic studies have shown that the diagnosis is usually made 1 to 2 years after symptoms onset, and the mean survival is reduced to 2 to 3 years thereafter. New insights into the pathogenesis of PPH by epidemiologic studies may be obtained through the utilization of informatic technologies coupled to a clear definition of the disease. Early stages of precapillary pulmonary hypertension could be identified through screening tests like echocardiography in populations with higher incidence, such as familial PPH and the conditions associated with pulmonary hypertension. These latter conditions are hemodynamically and pathologically similar to the primary form, and they can give insight into several possible aspects of the pathogenesis of PPH. Prospective registries are very useful in coordinating the collection of epidemiologic data, and new technologies, such as informatics, may improve the management and the continuous updating of the databases.

Lipid mediator dysregulation in primary pulmonary hypertension

The characteristic arteriopathy of primary pulmonary hypertension (PPH) with attendant endothelial dysfunction provides an opportunity for enhanced cellular activation in the lung. Data from many laboratories support the concept of altered eicosanoid metabolism in PPH. Rigorously quantitative measurements of the excretion of metabolites of thromboxane A2 and prostacyclin support persistent platelet activation and inadequate endothelial response in patients with PPH. Recent studies measuring excretion of prostaglandin D2 metabolites suggest that additional cell sources, such as activated tissue macrophages, may also play a role in the observed elevation in thromboxane excretion and possibly in the pathogenesis of the vascular remodeling. Additional research examining in vivo cell activation in patients receiving therapy with long-term infusion of prostacyclin may further our understanding of the pathogenesis of PPH.

Genetics and immunogenetic aspects of primary pulmonary hypertension

Primary pulmonary hypertension (PPH), also referred to as unexplained or idiopathic pulmonary hypertension, is the clinical term used to describe a condition in patients for which we can find no underlying cause. Patients with PPH not uncommonly also have evidence of immune dysregulation: autoimmune disorders, drug therapy, or HIV infections. We will review these associations and possible relevant abnormalities in immune regulation with regard to how they may play a role in the pathogenesis of PPH. Autoantibody-HLA correlations have been observed in several subsets of PPH patients. In addition, a familial form of PPH has been described and characterized with linkage to chromosome 2q31-q32. The identification of a specific gene for PPH and the subsequent understanding of its effects will help us identify the basic cause of PPH. Furthering our understanding regarding the role(s) and significance of immunogenetic as well as genetic aspects of the pathogenesis and pathophysiology of PPH should also lead to improved therapeutic modalities for PPH.

Clinical insights into the pathogenesis of primary pulmonary hypertension

Because of the lack of adequate animal models, much of our knowledge of the pathogenesis of primary pulmonary hypertension has come from clinical experiences. The clinical response to vasodilators, prostenoids, and anticoagulants as treatments appear to correlate with the pathologic changes of medial hypertrophy, intimal proliferation, and thrombosis. Endothelial dysfunction, as a primary abnormality in primary pulmonary hypertension, provides an explanation for the pathologic and clinical expression of the disease in its various forms. Other clinical features of the disease, such as age of onset and rapidity of progression, may be influenced by triggers of the disease process and underlying individual genetic susceptibility. As we have been able to correlate the spectrum of clinical observations with advances in vascular biology, newer, more focused and effective therapies should begin to emerge.

Abnormalities in circulating von Willebrand factor and survival in pulmonary hypertension

BACKGROUND

Changes in circulating von Willebrand factor (vWF) have been widely used for evaluating the severity of endothelial dysfunction in vascular disorders. In pulmonary hypertension, quantitative and structural abnormalities in circulating von Willebrand factor have been identified. We therefore hypothesized that these abnormalities could have prognostic implications.

PATIENTS AND METHODS

We studied 30 consecutive medically treated patients with primary (n = 11) or secondary precapillary pulmonary hypertension associated with congenital heart disease (n = 16) or schistosomiasis (n = 3). Plasma antigenic activity of vWF (vWF:Ag) was measured by electroimmunodiffusion. The relative concentration of low molecular weight vWF multimers (vWF:LMW/Total) was determined by Western immunoblotting. Results of initial evaluation were analyzed at the end of the first and third years of follow-up.

RESULTS

Baseline vWF:Ag activity (P <0.0002) and the vWF: LMW/Total ratio (P <0.005) were higher in patients who died during the first year than in survivors. All patients with vWF:Ag activity >250% or a vWF:LMW/Total ratio >70% died in the first year. All 7 patients with vWF:Ag activity <100% were alive at the end of 3 years of follow-up. A vWF:LMW/Total ratio >68% was 67% sensitive and 95% specific for 1-year mortality, with an overall predictive value of 80%. Both vWF:Ag levels and mortality were greater in the patients with primary pulmonary hypertension than in patients with secondary pulmonary hypertension.

CONCLUSION

Patients with pulmonary hypertension who have abnormalities in circulating vWF have reduced 1-year survival. This might affect decisions such as patient assignment to lung transplantation.

Continuous infusion of prostacyclin normalizes plasma markers of endothelial cell injury and platelet aggregation in primary pulmonary hypertension

BACKGROUND

Primary pulmonary hypertension (PPH) is characterized by vascular injury of pulmonary arterioles, in which endothelial dysfunction may play a major role. Although continuous infusion of prostacyclin (prostaglandin I2, a potent vasodilator released by vascular endothelial cells) improves the clinical status and survival in PPH, its mechanism or mechanisms of action remain unclear.

METHODS AND RESULTS

We measured endothelium-derived clotting factors and assayed platelet aggregation in 64 patients (26 adults and 38 children) with PPH before long-term PGI2 therapy. Repeat studies were performed in 42 patients (18 adults, 24 children) after one year of PGI2 therapy. At baseline, 87% of adults and 79% of children had abnormal platelet aggregation. In addition, factor VIII, von Willebrand (vW) antigen, and ristocetin cofactor levels were abnormally high in 92%, 72%, and 52%, respectively, of the adults versus 29%, 16%, and 16%, respectively, of the children (P<.005 adults versus children). With long-term PGI2, platelet aggregation normalized in 83% of the adults and 80% of the children who had platelet aggregation abnormalities at baseline (P<.01). Factor VIII, vW antigen, and ristocetin cofactor also decreased with long-term PGI2 in both groups (P<.02). The ratio of ristocetin cofactor to vW antigen, which may reflect biological activity of vW factor, increased with long-term PGI2 in adults from an abnormally low level (0.6+/-0.2) to normal level (1.10+/-0.4), and in children the ratio increased from 0.8+/-0.3 to 1.3+/-0.4 (normal, 0.8 to 1.4).

CONCLUSIONS

Alterations in the coagulation system may contribute to the pathogenesis of PPH; the normalization of these endothelial markers concomitant with improvement in hemodynamic parameters with long-term PGI2 suggests that long-term PGI2 remodels the pulmonary vascular bed with subsequent decreases in endothelial cell injury and hypercoagulability.

Pulmonary hypertension in systemic autoimmune disease

Rare in occurrence, insidious in onset, and relentless in its course, pulmonary hypertension in systemic autoimmune disease remains one of the most challenging entities to diagnose and treat today. The subtlety and nonspecificity of its symptoms and signs, the lack of availability of sensitive, noninvasive, accurate diagnostic tests, the rudimentary understanding we have of its pathogenesis, the multiplicity of findings on histopathologic survey, and the paucity of data from large-scale therapeutic trials in this population all pose many frustrations for patient and physician. Although supportive, symptomatic therapy remains the mainstay of treatment, we continue to await the results of carefully conducted clinical trials investigating antiinflammatory drugs and vasodilators. Careful scrutiny of the histologic lesions seen in pulmonary hypertension has shown striking similarity with the changes of PPH in some patients, and close follow-up of patients diagnosed with PPH has shown that some of them later develop evidence of a specific autoimmune disease like scleroderma. A natural tendency to extrapolate the use of therapeutic modalities of PPH to patients with autoimmune disease-associated pulmonary hypertension then results. We are thus encouraged by the lessons learned from the past about PPH; studies of patients with PPH have identified a subset of them who enjoy a distinct survival advantage with use of vasodilators or transplantation. We remain hopeful that future investigations in the treatment of autoimmune disease-associated pulmonary hypertension will yield similar information, and that we will be able to provide afflicted individuals some long-awaited improvements in quality and duration of life.

Pathogenesis and evolution of plexiform lesions in pulmonary hypertension associated with scleroderma and human immunodeficiency virus infection

Patients with primary pulmonary hypertension develop vascular lesions characterized by proliferated blood channels, the so-called plexiform lesions. These lesions are often associated with concentric intimal obliteration of pulmonary vessels. We report that the lungs of three patients with scleroderma-associated pulmonary hypertension showed a predominance of obliterative-concentric lesions, with relatively few plexiform or combined lesions. In contrast, plexiform lesions predominated in the lungs obtained from three patients with human immunodeficiency virus (HIV)-associated pulmonary hypertension; pure obliterative-concentric lesions were infrequent. Both plexiform and concentric obliterative lesions stained strongly positive for the endothelial cell marker factor VIII-related antigen. Muscle-specific actin immunostaining highlighted the smooth muscle cells of the tunica media of plexiform vessels, but not the luminal layers of the concentric-obliterative lesions. Proliferating cells, as determined by immunostaining with the MIB-1 antibody, were only detected in the plexiform vascular lesions. We postulate that concentric-obliterative lesions and plexiform lesions are temporally and etiologically related. A scaffolding of proliferating endothelial cells could be the common denominator of both lesions. Our hypothesis that there exists a chronological continuum, proceeding from early, proliferative plexiform lesions to late, nonproliferative concentric-obliterative lesions in primary and secondary pulmonary hypertension, may lead to better targeted treatment strategies and disease classification.

Localization of the gene for familial primary pulmonary hypertension to chromosome 2q31-32

Primary pulmonary hypertension (PPH), an often fatal disease, is characterized by elevated pulmonary artery pressures in the absence of a secondary cause. Endovascular occlusion in the smallest pulmonary arteries occurs by proliferation of cells and matrix, with thrombus and vasospasm. Diagnosis is often delayed because the initial symptoms of fatigue and dyspnea on exertion are nonspecific and definitive diagnosis requires invasive procedures. The average life expectancy after diagnosis is two to three years with death usually due to progressive right heart failure. The aetiology of the disease is unknown. Although most cases appear to be sporadic, approximately 6% of cases recorded in the NIH Primary Pulmonary Hypertension Registry are inherited in an autosomal dominant manner with reduced penetrance. Following a genome-wide search using a set of highly polymorphic short tandem repeat (STR) markers and 19 affected individuals from six families, initial evidence for linkage was obtained with two chromosome 2q markers. We subsequently genotyped patients and all available family members for 19 additional markers spanning approximately 40 centiMorgans (cM) on the long arm of chromosome 2. We obtained a maximum two-point lod score of 6.97 at theta = 0 with the marker D2S389; multipoint linkage analysis yielded a maximum lod score of 7.86 with the marker D2S311. Haplotype analysis established a minimum candidate interval of approximately 25 cM.

Coagulation and fibrinolytic profiles in patients with severe pulmonary hypertension

STUDY OBJECTIVES

Although in situ thrombosis is a prominent finding in lung vessels from patients with primary and secondary pulmonary hypertension, to our knowledge, plasma coagulation factors that might contribute to a hypercoagulable state have not been fully investigated. We hypothesized that the local coagulation environment in the lung vasculature is important to progression if not initiation of pulmonary hypertension.

DESIGN

Quasi-experimental cross-sectional design with concurrent controls.

SETTING

Referral clinics and inpatient services of a University Hospital and a Veterans Administration Medical Center.

PARTICIPANTS

To investigate the role of plasma coagulation factors in severe pulmonary hypertension, we sampled plasma from patients with primary pulmonary hypertension, patients with pulmonary hypertension secondary to a discernible etiology, and normal adult control subjects.

RESULTS

We detected abnormalities of the thrombomodulin/protein C anticoagulant system, evidenced by a decrease in soluble thrombomodulin, in patients with primary pulmonary hypertension. In the patients with primary pulmonary hypertension, we found impaired fibrinolytic activity, with a rise in the fibrinolytic inhibitor plasminogen activator 1 and elevated euglobulin lysis time. Lower fibrinolytic activity correlated with high mean pulmonary artery pressure. In contrast, in patients with secondary pulmonary hypertension, von Willebrand factor antigen and fibrinogen levels were increased, and fibrinolytic activity decreased.

CONCLUSIONS

Different patterns of coagulation and fibrinolytic abnormalities are apparent in plasma from patients with primary and secondary pulmonary hypertension. Although we are unable to address causality with this study, we speculate that abnormalities of these coagulation mechanisms may initiate or play a role in perpetuation of pulmonary hypertension.

Coancestry in apparently sporadic primary pulmonary hypertension

OBJECTIVE

To examine sporadic cases of primary pulmonary hypertension of coancestry.

DESIGN

An epidemiologic study of families of patients with primary pulmonary hypertension.

SETTING

A university-affiliated referral population.

PARTICIPANTS

Family members of 13 patients with primary pulmonary hypertension.

MEASUREMENTS

Family pedigrees involving grandparents, parents, siblings, and children were supplemented by genealogic records. Coefficients of kinship (Ck) were calculated for the patients with primary pulmonary hypertension who demonstrated coancestry and compared with 500 sets of controls drawn at random from genealogic records.

RESULTS

Two patients with sporadic primary pulmonary hypertension demonstrated coancestry. The great-great grandfather and great-great grandmother of one patient were the great-grandfather and great-grandmother of the other patient. No other cases of primary pulmonary hypertension were identified in these two families. The CK of the affected individuals (CK = 10.02 x 10(-5)) suggests strongly that the observed relationship did not occur by chance alone. Among 500 random sets of matched controls, only two sets yielded CK of 10.02 x 10(-5) or greater (p = 0.004). Coancestry could not be identified for the other five families of patients with sporadic primary pulmonary hypertension for whom genealogic records were available.

CONCLUSIONS

The finding of coancestry in patients with sporadic primary pulmonary hypertension suggests that a genetic basis exists for some patients with apparently sporadic primary pulmonary hypertension. Familial primary pulmonary hypertension may be more common than previously recognized.

Genetic anticipation and abnormal gender ratio at birth in familial primary pulmonary hypertension

The genetic basis of familial primary pulmonary hypertension (FPPH) is unknown, but the clinical and pathologic features are the same as in sporadically occurring primary pulmonary hypertension (PPH). Because few families with this disease have been reported, the mode of inheritance and genetic features have not been clearly established. We previously reported a tendency for decreasing age of onset in subsequent generations of affected families. The purpose of this study was to examine the pattern of inheritance in a large number of families in an attempt to find clues to pathogenesis. From 24 families we studied 429 members, 124 of whom were known to carry the gene for disease. We constructed cumulative mortality curves for each gender of the 99 affected individuals. We analyzed gender ratios of progeny of affected members and carriers and compared age at death of affected members by generation. More females (160) than males (122) were born to persons carrying the gene, p < 0.01, suggesting selective wastage of male fetuses or an abnormal primary sex ratio. Genetic anticipation was confirmed; the age at death was 45.6 +/- 14.5 versus 36.3 +/- 12.6 versus 24.2 +/- 11 standard deviation (SD) years in successive generations, p < 0.05. Five cases of male-to-male transmission were observed, excluding X-linkage. Age at death was the same for males and females. More females had the gene (84 females, 40 males) and more females with the gene developed disease (72 of 84 females [86%] versus 27 of 40 males [68%]). The disease has highly variable penetrance among families.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary plexogenic pulmonary hypertension shows imperfect formation of the internal elastic lamina of the pulmonary arteries

Lung tissue from subjects dying from primary plexogenic pulmonary hypertension (PPH) has shown defects of elastin formation of the lung arteries. Lung vessels from 5 cases of PPH were compared with those of 9 age-matched normal subjects, and 24 individuals having secondary pulmonary hypertension (2 degrees PH). PPH cases and those with 2 degrees PH due to congenital heart disease with left-to-right shunts (2 degrees PH, LRS), showed active proliferation of medial smooth muscle cells (SMC) through defects of the internal elastic lamina (IEL) into the arterial lumen to form typical plexiform lesions. Larger arteries showed accelerated intimal thickening similar to normal aging. Plexiform lesions were not seen in normal subjects or in those developing high pulmonary pressures later in life. The observations showed that the development of discontinuities of the IEL of the pulmonary arteries and intimal thickening is accelerated in normal subjects by high pulmonary artery pressure, especially when this is established at a very young age. They suggest that such discontinuities occur in PPH due to inherent abnormality of the elastin of the arterial walls, with advanced early proliferation of medial SMC and obstruction of the pulmonary arterial circulation.