Heterozygous germline mutations in BMPR2, encoding a TGF-beta receptor, cause familial primary pulmonary hypertension

Pulmonary Hypertension in Transgenic Mice Expressing a Dominant-Negative BMPRII Gene in Smooth Muscle

Bone morphogenetic peptides (BMPs), a family of cytokines critical to normal development, were recently implicated in the pathogenesis of familial pulmonary arterial hypertension. The type-II receptor (BMPRII) is required for recognition of all BMPs, and targeted deletion of BMPRII in mice results in fetal lethality before gastrulation. To overcome this limitation and study the role of BMP signaling in postnatal vascular disease, we constructed a smooth muscle–specific transgenic mouse expressing a dominant-negative BMPRII under control of the tetracycline gene switch (SM22-tet-BMPRII delx4+ mice). When the mutation was activated after birth, mice developed increased pulmonary artery pressure, RV/LV+S ratio, and pulmonary arterial muscularization with no increase in systemic arterial pressure. Studies with SM22-tet-BMPRII delx4+ mice support the hypothesis that loss of BMPRII signaling in smooth muscle is sufficient to produce the pulmonary hypertensive phenotype.

Bone morphogenetic protein receptor-II mutation Arg491Trp causes malignant phenotype of familial primary pulmonary hypertension

A four-generation pedigree of familial primary pulmonary hypertension (FPPH) with 14 alive members was collected. In the family, three of the 14 alive familial members were diagnosed as FPPH. Mutations in bone morphogenetic protein receptor-II (BMPR-II) gene were screened by using sequencing analysis. A C-to-T transition at position 1471 in exon 11 of the BMPR-II gene was identified, resulting in an Arg491Trp mutation. We confirmed segregation of the mutation within the family and excluded the presence of the mutations in a panel of 240 chromosomes from normal individuals. No mutations were found in BMPR-II gene in other 10 patients with sporadic primary pulmonary hypertension. The Arg491Trp mutation is located in the kinase domain and predicted to disturb the kinase activity of BMPR-II. Total 7 familial members died at age 8-45 years with various symptoms, indicating other genetic or environmental modifiers involved in the modification of the clinical phenotype.

Serotonin-induced smooth muscle hyperplasia in various forms of human pulmonary hypertension

Hyperplasia of pulmonary artery smooth muscle cells (PA-SMCs) is a hallmark pathological feature of pulmonary hypertension (PH). Serotonin (5-HT) is involved in the hyperplasia through its interactions with specific receptors and internalization by a specific plasma membrane transporter. We investigated the expression and role of the 5-HT transporter (5-HTT) and 5-HT1B, 5-HT2A, and 5-HT2B receptors in lungs and isolated PA-SMCs from patients with primary PH (n=14), pulmonary veno-occlusive disease (n=4), or secondary PH (SPH, n=8) and nonpulmonary hypertensive control subjects. Whereas strong immunostaining for the three receptor types and 5-HTT was seen in remodeled pulmonary vessels from patients in all PH categories, only 5-HTT expression was increased in lungs and cultured PA-SMCs from patients versus controls. The increased growth response of PA-SMCs from patients with primary PH, pulmonary veno-occlusive disease, or SPH to 5-HT or serum was entirely attributable to 5-HTT overexpression, because 5-HTT inhibitors but not 5-HT receptor antagonists abolished 5-HT mitogenic activity and reduced the serum-induced growth response to similar levels in patients as in controls. The L-allelic variant of the 5-HTT gene promoter, which is associated with 5-HTT overexpression, was present homozygously in 14 of 25 (56%) lung transplantation patients with SPH but in only 27% of controls. Polymorphism of the 5-HTT gene promoter was only partly responsible for the increased 5-HTT expression in PH, because PA-SMCs from patients exhibited higher 5-HTT levels than same-genotype cells from controls and no additional promoter sequence alterations were found. We conclude that 5-HTT overexpression is a common pathogenic mechanism in various forms of PH.

Overexpression of Smurf1 negatively regulates mouse embryonic lung branching morphogenesis by specifically reducing Smad1 and Smad5 proteins

Early embryonic lung branching morphogenesis is regulated by many growth factor-mediated pathways. Bone morphogenetic protein 4 (BMP4) is one of the morphogens that stimulate epithelial branching in mouse embryonic lung explant culture. To further understand the molecular mechanisms of BMP4-regulated lung development, we studied the biological role of Smad-ubiquitin regulatory factor 1 (Smurf1), an ubiquitin ligase specific for BMP receptor-regulated Smads, during mouse lung development. The temporo-spatial expression pattern of Smurf1 in mouse embryonic lung was first determined by quantitative real-time PCR and immunohistochemistry. Overexpression of Smurf1 in airway epithelial cells by intratracheal introduction of recombinant adenoviral vector dramatically inhibited embryonic day (E) 11.5 lung explant growth in vitro. This inhibition of lung epithelial branching was restored by coexpression of Smad1 or by addition of soluble BMP4 ligand into the culture medium. Studies at the cellular level show that overexpression of Smurf1 reduced epithelial cell proliferation and differentiation, as documented by reduced PCNA-positive cell index and by reduced mRNA levels for surfactant protein C and Clara cell protein 10 expression. Further studies found that overexpression of Smurf1 reduced BMP-specific Smad1 and Smad5, but not Smad8, protein levels. Thus overexpression of Smurf1 specifically promotes Smad1 and Smad5 ubiquitination and degradation in embryonic lung epithelium, thereby modulating the effects of BMP4 on embryonic lung growth.

Activation of K+ channels: an essential pathway in programmed cell death

Cell apoptosis and proliferation are two counterparts in sharing the responsibility for maintaining normal tissue homeostasis. In recent years, the process of the programmed cell death has gained much interest because of its influence on malignant cell growth and other pathological states. Apoptosis is characterized by a distinct series of morphological and biochemical changes that result in cell shrinkage, DNA breakdown, and, ultimately, phagocytic death. Diverse external and internal stimuli trigger apoptosis, and enhanced K+ efflux has been shown to be an essential mediator of not only early apoptotic cell shrinkage, but also of downstream caspase activation and DNA fragmentation. The goal of this review is to discuss the role(s) played by K+ transport or flux across the plasma membrane in the regulation of the apoptotic volume decrease and apoptosis. Attention has also been paid to the role of inner mitochondrial membrane ion transport in the regulation of mitochondrial permeability and apoptosis. We provide specific examples of how deregulation of the apoptotic process contributes to pulmonary arterial medial hypertrophy, a major pathological feature in patients with pulmonary arterial hypertension. Finally, we discuss the targeting of K+ channels as a potential therapeutic tool in modulating apoptosis to maintain the balance between cell proliferation and cell death that is essential to the normal development and function of an organism.

A new animal model for pulmonary hypertension based on the overexpression of a single gene, angiopoietin-1

BACKGROUND

Angiopoietin-1 gene expression in human pulmonary hypertensive lungs is directly proportional to increasing pulmonary vascular resistance. We hypothesized that targeted overexpresssion of angiopoietin-1 in the lung would cause persistent pulmonary hypertension in an animal model.

METHODS

We injected 2 x 10(10) genomic particles of adeno-associated virus-angiopoietin-1 (AAV-Ang-1) into the right ventricular outflow tract of 30 Fischer rats while using adeno-associated virus-lacZ (AAV-lacZ) injected rats and carrier-injected rats as our control groups. All animals underwent survival surgery and were sacrificed at serial timepoints postgene delivery. At each timepoint, pulmonary artery pressures were measured and pulmonary angiography using the Microfil polymer perfusion technique was performed. The lungs were harvested for pathologic analysis, mRNA analysis, Western blot assays, and in situ RNA hybridization to localize gene expression.

RESULTS

Pulmonary artery pressures of AAV-Ang-1 injected rats were significantly increased compared with the control groups (p < 0.01) at all timepoints. Pathologic analysis of AAV-Ang-1 lung specimens demonstrated increased smooth muscle cell proliferation within the medial layer of arterioles with obliteration of small vessels similar to that seen in human pulmonary hypertension. Angiograms of AAV-Ang-1 injected lungs showed blunting of small peripheral arterioles consistent with advanced pulmonary hypertension. In situ RNA hybridization localized angiopoietin-1 expression to the vascular wall of small-caliber pulmonary vessels. Protein and mRNA assays confirmed persistent angiopoietin-1 expression in the lung for up to 60 days postgene delivery.

CONCLUSIONS

Overexpression of angiopoietin-1 using an adeno-associated virus vector causes pulmonary hypertension in rats. These data provide a novel physiologic animal model for pulmonary hypertension.

Malignant infantile osteopetrosis and primary pulmonary hypertension: a new combination?

Malignant infantile osteopetrosis (MIOP), a rare genetic disorder of the osteoclast, is fatal without hematopoietic stem cell transplantation. Primary pulmonary hypertension (PPH), a rare progressive disorder of the pulmonary circulation, is predominantly fatal in the absence of successful therapy. A clinical association between these two disorders has not been recognized and a pathophysiologic link between osteoclast function and pulmonary vascular pressure as a rationale for such an association is not readily apparent. Here, we report five infants with MIOP, without cardiac abnormalities, who were found to have PPH after undergoing stem cell transplantation. We suggest that PPH may be linked to a specific variant of MIOP and recognizing the potential for pulmonary hypertension in children with MIOP may lead to a more rapid diagnosis and life-saving intervention.

Synergy and antagonism between Notch and BMP receptor signaling pathways in endothelial cells

Notch and bone morphogenetic protein signaling pathways are important for cellular differentiation, and both have been implicated in vascular development. In many cases the two pathways act similarly, but antagonistic effects have also been reported. The underlying mechanisms and whether this is caused by an interplay between Notch and BMP signaling is unknown. Here we report that expression of the Notch target gene, Herp2, is synergistically induced upon activation of Notch and BMP receptor signaling pathways in endothelial cells. The synergy is mediated via RBP-Jkappa/CBF-1 and GC-rich palindromic sites in the Herp2 promoter, as well as via interactions between the Notch intracellular domain and Smad that are stabilized by p/CAF. Activated Notch and its downstream effector Herp2 were found to inhibit endothelial cell (EC) migration. In contrast, BMP via upregulation of Id1 expression has been reported to promote EC migration. Interestingly, Herp2 was found to antagonize BMP receptor/Id1-induced migration by inhibiting Id1 expression. Our results support the notion that Herp2 functions as a critical switch downstream of Notch and BMP receptor signaling pathways in ECs.

Effect of 5-lipoxygenase on the development of pulmonary hypertension in rats

5-Lipoxygenase (5-LO) and its downstream leukotriene products have been implicated in the development of pulmonary hypertension. In this study, we examined the effects of 5-LO overexpression in rat lungs on pulmonary hypertension using a recombinant adenovirus expressing 5-LO (Ad5-LO). Transthoracic echocardiography and right heart catheterization data showed that 5-LO overexpression in the lung did not cause pulmonary hypertension in normal rats; however, it markedly accelerated the progression of pulmonary hypertension in rats treated with monocrotaline (MCT). An increase in pulmonary artery pressure occurred earlier in the rats treated with MCT + Ad5-LO (7-10 days) compared with those treated with control vector, MCT + adenovirus expressing green fluorescent protein (AdGFP), or MCT alone (15-18 days). The weight ratio of the right ventricle to left ventricle plus septum was higher in the MCT + Ad5-LO group than that of the MCT + AdGFP or MCT group (0.45 +/- 0.08 vs. 0.35 +/- 0.03 or 0.33 +/- 0.06). Lung tissue histological sections from MCT + Ad5-LO rats exhibited more severe inflammatory cell infiltration and pulmonary vascular muscularization than those from MCT + AdGFP- or MCT-treated rats. Administration of 5-LO inhibitors, zileuton or MK-886, to either MCT- or MCT + Ad5-LO-treated rats prevented the development of pulmonary hypertension. These data suggest that 5-LO plays a critical role in the progression of pulmonary hypertension in rats and that the detrimental effect of 5-LO is manifest only in the setting of pulmonary vascular endothelial cell dysfunction.

Novel Insertional Mutation in the Bone Morphogenetic Protein Receptor Type II Associated With Sporadic Primary Pulmonary Hypertension

Primary pulmonary hypertension (PPH), which results 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 and sporadic PPH. The first case of BMPR2 mutation found in Japan is reported here in a 19-year-old woman with a clinical diagnosis of PPH and no identifiable family history of pulmonary hypertension. Direct sequencing of the entire coding region and intron/exon boundaries of BMPR2 revealed a frameshift mutation predicted to alter the cell signaling response to specific ligands. A molecular classification of PPH, based upon the presence or absence of BMPR2 mutations, might have important implications for patient management and screening of relatives.

TGF-beta receptor kinase inhibitor enhances growth and integrity of embryonic stem cell-derived endothelial cells

Recent findings have shown that embryonic vascular progenitor cells are capable of differentiating into mural and endothelial cells. However, the molecular mechanisms that regulate their differentiation, proliferation, and endothelial sheet formation remain to be elucidated. Here, we show that members of the transforming growth factor (TGF)-β superfamily play important roles during differentiation of vascular progenitor cells derived from mouse embryonic stem cells (ESCs) and from 8.5–days postcoitum embryos. TGF-β and activin inhibited proliferation and sheet formation of endothelial cells. Interestingly, SB-431542, a synthetic molecule that inhibits the kinases of receptors for TGF-β and activin, facilitated proliferation and sheet formation of ESC-derived endothelial cells. Moreover, SB-431542 up-regulated the expression of claudin-5, an endothelial specific component of tight junctions. These results suggest that endogenous TGF-β/activin signals play important roles in regulating vascular growth and permeability.

From developmental disorder to heritable cancer: it's all in the BMP/TGF-beta family

Transforming growth factor-beta (TGF-beta) regulates many cellular processes through complex signal-transduction pathways that have crucial roles in normal development. Disruption of these pathways can lead to a range of diseases, including cancer. Mutations in the genes that encode members of the TGF-beta pathway are involved in vascular diseases as well as gastrointestinal neoplasia. More recently, they have been implicated in Cowden syndrome, which is normally associated with mutations in the phosphatase and tensin homologue gene PTEN. Molecular studies of TGF-beta signalling are now showing why mutations in genes that encode components of this pathway result in inherited cancer and developmental diseases.

A new recessive syndrome with VATER-like defects, pulmonary hypertension, abnormal ears, blue sclera, laryngeal webs, and persistent growth deficiency

VATER association is a term frequently used to describe children with multiple malformations. However, occasionally these children have malformations that are not typical of VATER defects and may represent unique multiple malformation syndromes with specific prognoses and recurrence risks. Two siblings with a heretofore previously undescribed multiple malformation syndrome are presented whose features include vertebral defects, cardiac abnormalities, pulmonary hypertension, laryngeal webs, blue sclerae, and persistent growth deficiency. Autosomal recessive inheritance is suggested. These cases suggest that other individuals labeled VATER association with multiple other defects should be reviewed more closely to give accurate prognosis and recurrence risk information to families.

Sequence analysis of bone morphogenetic protein receptor type II mRNA from ascitic and nonascitic commercial broilers

Ascites syndrome, also known as pulmonary hypertension syndrome (PHS), is a common metabolic disorder in rapidly growing meat-type chickens. Environmental factors, such as cold, altitude, and diet, play significant roles in development of the disease, but there is also an important genetic component to PHS susceptibility. The human disease familial primary pulmonary hypertension (FPPH) is similar to PHS in broilers both genetically and physiologically. Several recent studies have shown that mutations in the bone morphogenetic protein receptor type II (BMPR2) gene are a cause of FPPH in humans. To determine whether mutations in the chicken BMPR2 gene play a similar role in PHS susceptibility, BMPR-II mRNA from ascitic and nonascitic commercial broilers were sequenced and compared with the published Leghorn chicken BMPR-II mRNA sequence. Fourteen single nucleotide polymorphisms (SNP) were identified in the commercial broiler BMPR-II mRNA. No mutations unique to ascites-susceptible broilers were present in the coding, 5' untranslated or 3' untranslated regions of BMPR-II mRNA. The twelve SNP present within the coding region of BMPR-II mRNA were synonymous substitutions and did not alter the BMPR-II protein sequence. In addition, analysis of BMPR2 gene expression by reverse transcriptase-PCR indicated that there were no differences in BMPR-II mRNA levels in ascitic and nonascitic birds. Therefore, it appears unlikely that mutations in the BMPR2 gene were responsible for susceptibility to PHS in these commercial broilers.

Mutations in bone morphogenetic protein receptor 1B cause brachydactyly type A2

Brachydactyly (BD) type A2 is an autosomal dominant hand malformation characterized by shortening and lateral deviation of the index fingers and, to a variable degree, shortening and deviation of the first and second toes. We performed linkage analysis in two unrelated German families and mapped a locus for BD type A2 to 4q21-q25. This interval includes the gene bone morphogenetic protein receptor 1B (BMPR1B), a type I transmembrane serinethreonine kinase. In one family, we identified a T599 --> A mutation changing an isoleucine into a lysine residue (I200K) within the glycine/serine (GS) domain of BMPR1B, a region involved in phosphorylation of the receptor. In the other family we identified a C1456 --> T mutation leading to an arginine-to-tryptophan amino acid change (R486W) in a highly conserved region C-terminal of the BMPR1B kinase domain. An in vitro kinase assay showed that the I200K mutation is kinase-deficient, whereas the R486W mutation has normal kinase activity, indicating a different pathogenic mechanism. Functional analyses with a micromass culture system revealed a strong inhibition of chondrogenesis by both mutant receptors. Overexpression of mutant chBmpR1b in vivo in chick embryos by using a retroviral system resulted either in a BD phenotype with shortening and/or missing phalanges similar to the human phenotype or in severe hypoplasia of the entire limb. These findings imply that both mutations identified in human BMPR1B affect cartilage formation in a dominant-negative manner.

Simvastatin rescues rats from fatal pulmonary hypertension by inducing apoptosis of neointimal smooth muscle cells

BACKGROUND

Pulmonary vascular injury by toxins can induce neointimal formation, pulmonary arterial hypertension (PAH), right ventricular failure, and death. We showed previously that simvastatin attenuates smooth muscle neointimal proliferation and pulmonary hypertension in pneumonectomized rats injected with the alkaloid toxin monocrotaline. The present study was undertaken to investigate the efficacy of simvastatin and its mechanism of reversing established neointimal vascular occlusion and pulmonary hypertension.

METHODS AND RESULTS

Pneumonectomized rats injected with monocrotaline at 4 weeks demonstrated severe PAH at 11 weeks (mean pulmonary artery pressure [mPAP]=42 versus 17 mm Hg in normal rats) and death by 15 weeks. When rats with severe PAH received simvastatin (2 mg x kg(-1) x d(-1) by gavage) from week 11, there was 100% survival and reversal of PAH after 2 weeks (mPAP=36 mm Hg) and 6 weeks (mPAP=24 mm Hg) of therapy. Simvastatin treatment reduced right ventricular hypertrophy and reduced proliferation and increased apoptosis of pathological smooth muscle cells in the neointima and medial walls of pulmonary arteries. Longitudinal transcriptional profiling revealed that simvastatin downregulated the inflammatory genes fos, jun, and tumor necrosis factor-alpha and upregulated the cell cycle inhibitor p27Kip1, endothelial nitric oxide synthase, and bone morphogenetic protein receptor type 1a.

CONCLUSIONS

Simvastatin reverses pulmonary arterial neointimal formation and PAH after toxic injury.

Expression of human herpesvirus 8 in primary pulmonary hypertension

BACKGROUND

Severe pulmonary hypertension constitutes a group of diseases characterized by complex, lumen-occluding vascular lesions that develop in genetically susceptible persons. The only viral infection associated with severe pulmonary hypertension has been that due to human immunodeficiency virus type 1, but neither the viral genome nor viral antigens have been demonstrated in pathologic lesions.

METHODS

We examined lung-tissue samples from 16 patients with sporadic primary pulmonary hypertension and 14 patients with secondary pulmonary hypertension for evidence of infection with human herpesvirus 8 (HHV-8). HHV-8 infection was ascertained immunohistochemically with use of an antibody directed against latency-associated nuclear antigen 1 (LANA-1), and a polymerase-chain-reaction (PCR) assay was performed on lung DNA to detect the viral cyclin gene of HHV-8. Sequence analysis was also performed.

RESULTS

In lung tissue from 10 of 16 patients with primary pulmonary hypertension (62 percent), cells within the plexiform lesions as well as cells outside the lesions were positive for LANA-1 on immunohistochemical analysis. Tissue from the same 10 patients contained viral cyclin on PCR analysis. No LANA-1 was detected in lung tissue from patients with secondary pulmonary hypertension, although one such patient had PCR evidence of viral cyclin. Plexiform lesions from patients with primary pulmonary hypertension had a histologic and immunohistochemical resemblance to cutaneous Kaposi's sarcoma lesions.

CONCLUSIONS

The spectrum of trigger factors and molecular mechanisms leading to severe pulmonary hypertension and the formation of plexiform lesions is apparently wide, including both genetic and epigenetic factors. Our data suggest that infection with the vasculotropic virus HHV-8 may have a pathogenetic role in primary pulmonary hypertension.

Direct signaling by the BMP type II receptor via the cytoskeletal regulator LIMK1

Bone morphogenetic proteins (BMPs) regulate multiple cellular processes, including cell differentiation and migration. Their signals are transduced by the kinase receptors BMPR-I and BMPR-II, leading to Smad transcription factor activation via BMPR-I. LIM kinase (LIMK) 1 is a key regulator of actin dynamics as it phosphorylates and inactivates cofilin, an actin depolymerizing factor. During a search for LIMK1-interacting proteins, we isolated clones encompassing the tail region of BMPR-II. Although the BMPR-II tail is not involved in BMP signaling via Smad proteins, mutations truncating this domain are present in patients with primary pulmonary hypertension (PPH). Further analysis revealed that the interaction between LIMK1 and BMPR-II inhibited LIMK1's ability to phosphorylate cofilin, which could then be alleviated by addition of BMP4. A BMPR-II mutant containing the smallest COOH-terminal truncation described in PPH failed to bind or inhibit LIMK1. This study identifies the first function of the BMPR-II tail domain and suggests that the deregulation of actin dynamics may contribute to the etiology of PPH.

Bone morphogenetic proteins induce apoptosis in human pulmonary vascular smooth muscle cells

Pulmonary vascular medial hypertrophy in primary pulmonary hypertension (PPH) is mainly caused by increased proliferation and decreased apoptosis in pulmonary artery smooth muscle cells (PASMCs). Mutations of the bone morphogenetic protein (BMP) receptor type II (BMP-RII) gene have been implicated in patients with familial and sporadic PPH. The objective of this study was to elucidate the apoptotic effects of BMPs on normal human PASMCs and to examine whether BMP-induced effects are altered in PASMCs from PPH patients. Using RT-PCR, we detected six isoforms of BMPs (BMP-1 through -6) and three subunits of BMP receptors (BMP-RIa, -RIb, and -RII) in PASMCs. Treatment of normal PASMCs with BMP-2 or -7 (100-200 nM, 24-48 h) markedly increased the percentage of cells undergoing apoptosis. The BMP-2-mediated apoptosis in normal PASMCs was associated with a transient activation or phosphorylation of Smad1 and a marked downregulation of the antiapoptotic protein Bcl-2. In PASMCs from PPH patients, the BMP-2- or BMP-7-induced apoptosis was significantly inhibited compared with PASMCs from patients with secondary pulmonary hypertension. These results suggest that the antiproliferative effect of BMPs is partially due to induction of PASMC apoptosis, which serves as a critical mechanism to maintain normal cell number in the pulmonary vasculature. Inhibition of BMP-induced PASMC apoptosis in PPH patients may play an important role in the development of pulmonary vascular medial hypertrophy in these patients.

Genetic studies of pulmonary arterial hypertension

These genetic studies of primary pulmonary hypertension (PPH) initially tried to define immunogenetic subsets. Because only small subsets could be classified when defined by HLA/autoantibody associations and the familial form of PPH failed to segregate with the HLA class II locus, the focus shifted to a genome scan of families with PPH (FPPH). This approach identified a gene on chromosome 2q33,34 called PPH1. Mutations in this gene, now known to be bone morphogenetic protein receptor 2 (BMPR2), can cause PPH. Mutations in a second gene, ALK-1, present in families with hereditary hemorrhagic telangiectasia type 2, also causes PPH. Both genes, involved in TGF-B signaling, provide exciting clues for defining the pathogenesis of PPH.

Fibroblast-specific expression of a kinase-deficient type II transforming growth factor beta (TGFbeta) receptor leads to paradoxical activation of TGFbeta signaling pathways with fibrosis in transgenic mice

To better understand the role of disrupted transforming growth factor beta (TGFbeta) signaling in fibrosis, we have selectively expressed a kinase-deficient human type II TGFbeta receptor (TbetaRIIDeltak) in fibroblasts of transgenic mice, using a lineage-specific expression cassette subcloned from the pro-alpha2(I) collagen gene. Surprisingly, despite previous studies that characterized TbetaRIIDeltak as a dominant negative inhibitor of TGFbeta signaling, adult mice expressing this construct demonstrated TGFbeta overactivity and developed dermal and pulmonary fibrosis. Compared with wild type cells, transgenic fibroblasts proliferated more rapidly, produced more extracellular matrix, and showed increased expression of key markers of TGFbeta activation, including plasminogen activator inhibitor-1, connective tissue growth factor, Smad3, Smad4, and Smad7. Smad2/3 phosphorylation was increased in transgenic fibroblasts. Overall, the gene expression profile of explanted transgenic fibroblasts using cDNA microarrays was very similar to that of littermate wild type cells treated with recombinant TGFbeta1. Despite basal up-regulation of TGFbeta signaling pathways, transgenic fibroblasts were relatively refractory to further stimulation with TGFbeta1. Thus, responsiveness of endogenous genes to TGFbeta was reduced, and TGFbeta-regulated promoter-reporter constructs transiently transfected into transgenic fibroblasts showed little activation by recombinant TGFbeta1. Responsiveness was partially restored by overexpression of wild type type II TGFbeta receptors. Activation of MAPK pathways by recombinant TGFbeta1 appeared to be less perturbed than Smad-dependent signaling. Our results show that expression of TbetaRIIDeltak selectively in fibroblasts leads to paradoxical ligand-dependent activation of downstream signaling pathways and causes skin and lung fibrosis. As well as confirming the potential for nonsignaling receptors to regulate TGFbeta activity, these findings support a direct role for perturbed TGFbeta signaling in fibrosis and provide a novel genetically determined animal model of fibrotic disease.

Growth factor signaling in lung morphogenetic centers: automaticity, stereotypy and symmetry

Lung morphogenesis is stereotypic, both for lobation and for the first several generations of airways, implying mechanistic control by a well conserved, genetically hardwired developmental program. This program is not only directed by transcriptional factors and peptide growth factor signaling, but also co-opts and is modulated by physical forces. Peptide growth factors signal within repeating epithelial-mesenchymal temporospatial patterns that constitute morphogenetic centers, automatically directing millions of repetitive events during both stereotypic branching and nonstereotypic branching as well as alveolar surface expansion phases of lung development. Transduction of peptide growth factor signaling within these centers is finely regulated at multiple levels. These may include ligand expression, proteolytic activation of latent ligand, ligand bioavailability, ligand binding proteins and receptor affinity and presentation, receptor complex assembly and kinase activation, phosphorylation and activation of adapter and messenger protein complexes as well as downstream events and cross-talk both inside and outside the nucleus. Herein we review the critical Sonic Hedgehog, Fibroblast Growth Factor, Bone Morphogenetic Protein, Vascular Endothelial Growth Factor and Transforming Growth Factorbeta signaling pathways and propose how they may be functionally coordinated within compound, highly regulated morphogenetic gradients that drive first stereotypic and then non-stereotypic, automatically repetitive, symmetrical as well as asymmetrical branching events in the lung.

Primary pulmonary hypertension may be a heterogeneous disease with a second locus on chromosome 2q31

OBJECTIVES

The aim of our study was to identify genetic causes of primary pulmonary hypertension (PPH), to estimate the proportion of families with mutations in the BMPR2 (bone morphogenetic protein receptor type 2) gene, and to examine whether genetic heterogeneity might play a role.

BACKGROUND

The BMPR2 mutations have been identified in a substantial portion of patients with familial or sporadic PPH. However, the genetic cause of PPH remains unclear in at least 45% of families.

METHODS

We investigated 130 members of 10 families with at least 1 PPH patient, recruited without selection for familial disease. Manifest PPH was documented in 21 individuals. An increase in pulmonary artery systolic pressure (PASP) above 40 mm Hg during supine bicycle exercise was found in 46 healthy individuals. Their PASP increased from 21.0 +/- 4.6 mm Hg at rest to 54.0 +/- 9.8 mm Hg during exercise. In 51 relatives, PASP values were normal at rest and during exercise, and 12 members were classified as status unknown.

RESULTS

Two families showed a mutation in the BMPR2 gene. Three families with no BMBR2 mutation showed evidence for linkage to a more proximal location on chromosome 2q31 (odds ratio [OR] for linkage 1.1.10(6):1). This locus, designated PPH2, maps in-between the markers D2S335 and D2S2314. We obtained significant support for heterogeneity in PPH with an OR of 2.8.10(11).

CONCLUSIONS

We conclude that PPH may be a genetically heterogeneous disorder with at least two-and possibly more-causative genes.

Insights into the genetic and molecular basis of primary pulmonary hypertension

The pathogenesis of primary pulmonary hypertension (PPH) remains poorly understood. Molecular genetic studies have identified that mutations within the gene BMPR2 on the long arm of chromosome 2 underlie familial PPH. This review explores the significance of the PPH gene identification and examines additional genetic determinants, emphasizing the immediate implications for assessment and management of patients and their relatives.

The endothelin system in pulmonary hypertension

Pulmonary hypertension (PH) may result from numerous clinical entities affecting the pulmonary circulation primarily or secondarily. It is recognized that vascular endothelial dysfunction contributes to the development and perpetuation of PH by creating an imbalance between vasodilating and antiproliferative forces and between vasoconstrictive and proliferative forces. In that context, endothelin-1 (ET-1) overproduction was rapidly targeted as a plausible contributor to the pathogenesis of PH. The lung is recognized as the major site for ET production and clearance. In all animal models of PH studied, circulating plasma ET-1 levels are elevated, accompanied by an increase in lung tissue expression of the peptide. The use of selective ETA and dual ETA-ETB receptor antagonists in these models both in prevention and in therapeutic studies have confirmed the contribution of ET-1 to the rise in pulmonary vascular tone, pulmonary medial hypertrophy, and right ventricular hypertrophy. This is found consistently in models affecting the pulmonary circulation primarily or producing PH secondarily. Recent clinical trials in patients with pulmonary arterial hypertension have confirmed the therapeutic effectiveness of ET-receptor antagonists in humans. We offer a systematic review of the pathogenic role of the ET system in the development of PH as well as the rationale behind the preclinical and ongoing clinical trials with this new class of agents.

Peroxisome proliferator-activated receptor gamma (PPARgamma) expression is decreased in pulmonary hypertension and affects endothelial cell growth

PPARgamma is a member of a family of nuclear receptors/ligand-dependent transcription factors, which bind to hormone response elements on target gene promoters. An antiproliferative and proapoptotic action profile of PPARgamma has been described and PPARgamma may function as a tumor suppressor gene, but little is known about the role of PPARgamma in vascular remodeling. One group of human diseases that shows impressive vascular remodeling exclusively in the lungs is the group of severe pulmonary hypertensive disorders, which is characterized by complex, endothelial cell-proliferative lesions of lung precapillary arterioles composed of clusters of phenotypically altered endothelial cells that occlude the vessel lumen and contribute to the elevation of the pulmonary arterial pressure and reduce local lung tissue blood flow. In the present study, we report the ubiquitous PPARgamma expression in normal lungs, and in contrast, a reduced lung tissue PPARgamma gene and protein expression in the lungs from patients with severe PH and loss of PPARgamma expression in their complex vascular lesions. We show that fluid shear stress reduces PPARgamma expression in ECV304 endothelial cells, that ECV304 cells that stably express dominant-negative PPARgamma (DN-PPARgamma ECV304) form sprouts when placed in matrigel and that DN-PPARgamma ECV304 cells, after tail vein injection in nude mice, form lumen-obliterating lung vascular lesions. We conclude that fluid shear stress decreases the expression of PPARgamma in endothelial cells and that loss of PPARgamma expression characterizes an abnormal, proliferating, apoptosis-resistant endothelial cell phenotype.

Prognostic factors for survival in human immunodeficiency virus-associated pulmonary arterial hypertension

We report a large monocentric case series of 82 patients with human immunodeficiency virus-associated pulmonary arterial hypertension (PAH). No germline mutations of the PPH1 gene (bone morphogenetic protein receptor-II) were found in any of the 19 patients tested. PAH was the direct cause of death in 72% of cases. Survival rates of the overall population at 1, 2, and 3 years were 73, 60, and 47%, respectively. Survival was significantly poorer in patients in New York Heart Association functional class III-IV at the time of diagnosis, as compared with those in functional class I-II with respective rates of 60, 45, and 28% versus 100, 90, 84% at 1, 2, and 3 years (p < 0.0001). Subsequently, we analyzed prognostic factors in patients in functional class III-IV. Univariate analysis indicated that CD4 lymphocyte count of more than 212 cells mm(-3), the use of combination antiretroviral therapy (CART), and epoprostenol infusion were related with a better survival. On multivariate analysis only CD4 lymphocyte count was an independent predictor of survival, presumably because CART and epoprostenol infusion were strongly linked in our patient population. These results suggest that patients with severe human immunodeficiency virus-associated PAH should be considered for long-term epoprostenol infusion in association with CART.

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.

Pulmonary hypertension: new perspectives

The World Health Organization symposium offers a new treatment-oriented classification of pulmonary hypertension based on an improved understanding of its pathophysiology. Regardless of the etiology, severe or unrelieved pulmonary hypertension leads to right heart failure. Symptoms and signs of pulmonary hypertension are often subtle and nonspecific. As a result, a significant delay between the onset of symptoms and the diagnosis of pulmonary hypertension is common. Echocardiography with Doppler flow is the most useful study to evaluate patients suspected of having pulmonary hypertension. The suspected diagnosis of pulmonary hypertension should then be confirmed by right heart catheterization. If present, further evaluation may include oxygen assessment, pulmonary function testing, high resolution computed tomography of the chest, and ventilation-perfusion lung scanning. Treatment of pulmonary hypertension requires uncommon expertise. General measures include correction of the underlying cause, reversal of hypoxemia and judicious use of diuretics. Advances in vasodilator therapy have increased treatment options beyond calcium channel blockers and intravenous epoprostenol. Lung transplantation remains an option for select patients with pulmonary hypertension not responding to medical management.

Systemic sclerosis: the susceptible host (genetics and environment)

It is becoming evident that several genetic factors participate in modulating susceptibility to SSc and its clinical manifestations. Some genes that specifically affect ECM metabolism and vascular function may be unique to SSc and scleroderma-related disorders; others, such as those genes involved in regulating immune tolerance, are likely shared with other autoimmune diseases. The effect of genetic variations (or polymorphisms) that are found in most of these genes taken individually will likely have only a small or modest effect on disease risk; only a few genetic variations are expected to be highly penetrant. Moreover, genetic studies in SSc have to deal with the additional issues of heterogeneous phenotypes, low disease prevalence in the general population, and an even greater paucity of multiplex families that makes traditional linkage studies difficult, if not impossible. Alternative approaches include allelic association studies, but conventional case-controls designs may be subject to selection bias and will require large sample sizes if the genes that are under investigation confer only modest (OR = 1.5-2.0) disease risk (Fig. 2). The simultaneous examination of several genes that are biologically relevant to a specific disease process to attain higher aggregate ORs, is one approach that was used in several reports that were cited in this review. The use of family-based controls, such as in the transmission-disequilibrium test (based on assessment of the transmitted or nontransmitted alleles that are associated with disease from heterozygous parents to affected offspring), would provide more robustness to spurious associations from population stratification, but is actually less powerful and efficient than case-control designs. Furthermore, for many late adult-onset diseases the effort required to obtain samples from living parents are for a variety of reasons not trivial. The success of these allelic association-based approaches depends on the identification of likely candidate disease genes (or at least markers in disequilibrium with disease genes), careful definition/ascertainment of disease phenotypes to minimize genetic heterogeneity, and for case-control designs, strategies to account for population stratification or admixture. The identification of candidate genes will be aided by rapid progress in the Human Genome Project and other genome efforts that will eventually identify all human genetic variations. Although this will lead to better understanding of the genes that might be involved in complex diseases, much work is required to understand the basic biology of how disease genotypes become clinical phenotypes. This is especially daunting in complex diseases, such as SSc, where the phenotype (including disease susceptibility and clinical presentation) is influenced by dynamic interactions between genetic variations and environment. Multi-center collaborative efforts with research paradigms that integrate genetic and environmental factors (including sociodemographic variables) will be required to elucidate the contribution of environment and genetics in the pathogenesis of SSc.

Pulmonary hypertension in systemic sclerosis

Pulmonary arterial hypertension occurs in up to 15% of patients who have systemic sclerosis (SSc) and has a high mortality. It can develop as an isolated complication or secondary to pulmonary fibrosis. There have been significant advances in assessment and therapy for this complication. Patients should be screened regularly by Doppler-echocardiography and pulmonary function tests. Right heart catheterization provides important diagnostic and prognostic information. Drawing from experience with treating primary pulmonary hypertension, treatment in the context of SSc is now possible. Patients should receive oral anticoagulation and oxygen supplementation. Calcium channel blockers are rarely effective, but parenteral prostacyclin analogs improve functional capacity and pulmonary hemodynamics. The oral endothelin-receptor blocker, bosentan, was shown to be an effective therapy for established symptomatic pulmonary hypertension in SSc. The next major challenge is to improve diagnosis and treatment of early stage or presymptomatic pulmonary hypertension with the goal of preventing this important cause of premature SSc-related mortality.

An assessment of the role of the inhibitory gamma subunit of the retinal cyclic GMP phosphodiesterase and its effect on the p42/p44 mitogen-activated protein kinase pathway in animal and cellular models of pulmonary hypertension

1. We have previously reported that the inhibitory gamma subunit of the rod photoreceptor type 6 cyclic GMP phosphodiesterase (PDEgamma) is expressed in nonretinal tissues and is involved in the stimulation of the p42/p44 mitogen-activated protein kinase (MAPK) pathway by growth factors and G-protein-coupled receptor agonists. We have now investigated whether PDEgamma plays a role in modulating chronic hypoxic-dependent mitogenic signalling pathways in pulmonary smooth muscle from rats with pulmonary hypertension (PHT). 2. We show for the first time that PDEgamma is expressed in rat main, first, intrapulmonary and resistance pulmonary arteries. Moreover, its expression is increased in all the arteries to varying extents by chronic hypoxia. The extent of the increased expression of PDEgamma is correlated with an enhanced activation of p42/p44 MAPK in these vessels. 3. We also report that PDEgamma translation from mRNA transcript is increased in cultured human pulmonary artery smooth muscle cells subjected to chronic hypoxia for 14 days. This was correlated with hypoxic-dependent increase in p42/p44 MAPK activation. 4. In conclusion, our studies identify for the first time a major chronic hypoxic-dependent change in the phenotypic expression of an intermediate protein regulating mitogenic signalling in pulmonary arteries. This may have a significant effect on arterial remodelling in PHT. Future studies will focus on strategies designed to knockout rod PDEgamma to assess whether this rescues rats from chronic hypoxic-dependent changes in arterial remodelling and PHT.

Krüppel-like factor 4 (KLF4/GKLF) is a target of bone morphogenetic proteins and transforming growth factor beta 1 in the regulation of vascular smooth muscle cell phenotype

Vascular smooth muscle cell (VSMC) differentiation and phenotypic modulation is characterized by changes in mRNA expression for smooth muscle (SM) marker contractile proteins such as alpha-SM actin and SM22 alpha. Transforming growth factor beta1 (TGF-beta 1) is a potent VSMC differentiation factor; however, it is not known if other TGF-beta-superfamily members, in particular the bone morphogenetic proteins (BMPs), modulate VSMC phenotype. Here we demonstrate that a large subset of TGF-beta-superfamily members and their type I receptors are differentially co-expressed as VSMC phenotype changes during fetal/neonatal development and that BMP2, -4, and -6 reciprocally regulate SM-marker mRNA and protein expression in vitro. BMP2 and BMP6 decrease expression of the SM markers alpha-SM actin, SM22alpha, and calponin in rat VSMCs, whereas BMP4 increases their expression. The effects of BMP-2, -4, and -6 on SM marker gene transcription are mediated through a consensus TGF-beta-controlling element, the TCE, which is common to regulatory regions of SM-marker genes. Moreover, co-treatment experiments revealed that BMP-2, -4, and -6 each inhibit TGF-beta 1-modulated increases in SM22alpha reporter gene activity. Regardless of whether they positively or negatively regulate SM marker expression, TGF-beta 1 and BMP-2, -4, and -6 all induced binding of the Krüppel-like transcription factor, GKLF/KLF4, to the TGF-beta control element. Induction of KLF4 was confirmed by immunocytochemistry and Western blotting, which revealed that a lower molecular weight KLF4 protein is induced after treatment with TGF-beta-superfamily members. Taken together, our results demonstrate that multiple members of the TGF-beta superfamily act in concert to modulate VSMC phenotype.

Pulmonary veno-occlusive disease caused by an inherited mutation in bone morphogenetic protein receptor II

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary hypertension in which the vascular changes originate in the small pulmonary veins and venules. The pathogenesis is unknown and any link with primary pulmonary hypertension (PPH) has been speculative. Mutations in the bone morphogenetic protein receptor II (BMPR2) gene have been identified in at least 50% of familial cases and in 25% of sporadic cases of PPH. We report a patient with documented PVOD whose mother had severe pulmonary hypertension. Sequencing of the patient's BMPR2 coding region revealed a del44C mutation in Exon 1 that is predicted to encode for a truncated protein. Analysis of DNA from family members suggests that this mutation was transmitted by the proband's mother to two of her four children. The finding of PVOD associated with a BMPR2 mutation reveals a possible pathogenetic connection with PPH.

Pathophysiology of pulmonary hypertension due to lung disease

Pulmonary hypertension (PH) often complicates the course of patients with advanced lung disease, and it is associated with a worse prognosis. Per the recent classification of pulmonary hypertensive disorders, PH due to lung disease is considered as a separate category within a group of disorders that was previously referred to as "secondary" PH. Among the lung diseases associated with PH, the incidence and clinical course of PH is best known for patients with COPD. Per studies in patients with COPD and other lung disorders, it is evident that the pathophysiology and treatment of these disorders is generally distinct from that of pulmonary arterial hypertensive disorders. Changes in the pulmonary vasculature that accompany elevations in pulmonary vascular pressure are generally referred to as pulmonary vascular remodeling. Chronic hypoxia is well known to cause pulmonary vascular remodeling and PH, and it is the major mechanism implicated for the development of PH in patients with lung disease. Other mediators have also been implicated in the pathogenesis of PH in animal models and patients with PH, including patients with pulmonary diseases. General features of pulmonary vascular remodeling are discussed with particular emphasis on those changes that have been described in patients with lung diseases. Recent discoveries in these areas are also reviewed, and findings in pulmonary arterial hypertensive diseases are contrasted with those found in patients with PH due to lung diseases. Some of these discoveries have already led to new treatment strategies for patients with the most severe forms of PH. PH due to lung diseases shares some common pathophysiologic features with pulmonary arterial hypertension. Therefore, it is likely that these discoveries and new treatments will also be extended to benefit patients with PH due to lung disease.

Signaling molecules in nonfamilial pulmonary hypertension

BACKGROUND

Biochemical, genetic, and clinical evidence indicates that smooth-muscle proliferation around small pulmonary vessels is an essential part of the pathogenesis of pulmonary hypertension. Mutations in the bone morphogenetic protein receptor type 2 (BMPR2) have been linked to familial cases of pulmonary hypertension, but the molecular basis of the common nonfamilial forms is unknown.

METHODS

We evaluated the pattern of expression of angiopoietin-1, a protein involved in the recruitment of smooth-muscle cells around blood vessels; TIE2, the endothelial-specific receptor for angiopoietin-1; and bone morphogenetic protein receptor type 1A (BMPR1A) and BMPR2 in lung-biopsy specimens from patients with pulmonary hypertension and from normotensive control patients. The effect of angiopoietin-1 on the modulation of BMPR expression was also evaluated in subcultures of human pulmonary arteriolar endothelial cells.

RESULTS

The expression of angiopoietin-1 messenger RNA and the protein itself and the phosphorylation of TIE2 were strongly up-regulated in the lungs of patients with various forms of pulmonary hypertension, correlating directly with the severity of disease. A mechanistic link between familial and acquired pulmonary hypertension was demonstrated by the finding that angiopoietin-1 shuts off the expression of BMPR1A, a transmembrane protein required for BMPR2 signaling, in pulmonary arteriolar endothelial cells. Similarly, we found that the expression of BMPR1A was severely reduced in the lungs of patients with various forms of acquired as well as primary nonfamilial pulmonary hypertension.

CONCLUSIONS

These findings suggest that all forms of pulmonary hypertension are linked by defects in the signaling pathway involving angiopoietin-1, TIE2, BMPR1A, and BMPR2 and consequently identify specific molecular targets for therapeutic intervention.

The NO − K+ Channel Axis in Pulmonary Arterial Hypertension

The prognosis of patients with pulmonary arterial hypertension (PAH) is poor. Available therapies (Ca(++)-channel blockers, epoprostenol, bosentan) have limited efficacy or are expensive and associated with significant complications. PAH is characterized by vasoconstriction, thrombosis in-situ and vascular remodeling. Endothelial-derived nitric oxide (NO) activity is decreased, promoting vasoconstriction and thrombosis. Voltage-gated K+ channels (Kv) are downregulated, causing depolarization, Ca(++)-overload and PA smooth muscle cell (PASMC) contraction and proliferation. Augmenting the NO and Kv pathways should cause pulmonary vasodilatation and regression of PA remodeling. Several inexpensive oral treatments may be able to enhance the NO axis and/or K+ channel expression/function and selectively decrease pulmonary vascular resistance (PVR). Oral L-Arginine, NOS' substrate, improves NO synthesis and functional capacity in humans with PAH. Most of NO's effects are mediated by cyclic guanosine-monophosphate (c-GMP). cGMP causes vasodilatation by activating K+ channels and lowering cytosolic Ca++. Sildenafil elevates c-GMP levels by inhibiting type-5 phosphodiesterase, thereby opening BK(Ca). channels and relaxing PAs. In PAH, sildenafil (50 mg-po) is as effective and selective a pulmonary vasodilator as inhaled NO. These benefits persist after months of therapy leading to improved functional capacity. 3) Oral Dichloroacetate (DCA), a metabolic modulator, increases expression/function of Kv2.1 channels and decreases remodeling and PVR in rats with chronic-hypoxic pulmonary hypertension, partially via a tyrosine-kinase-dependent mechanism. These drugs appear safe in humans and may be useful PAH therapies, alone or in combination.

BMP signaling is required for septation of the outflow tract of the mammalian heart

Bone morphogenetic proteins (BMPs) constitute a family of approximately 20 growth factors involved in a tremendous variety of embryonic inductive processes. BMPs elicit dose-dependent effects on patterning during gastrulation and gradients of BMP activity are thought to be established through regulation of the relative concentrations of BMP receptors, ligands and antagonists. We tested whether later developmental events also are sensitive to reduced levels of BMP signaling. We engineered a knockout mouse that expresses a BMP type II receptor that lacks half of the ligand-binding domain. This altered receptor is expressed at levels comparable with the wild-type allele, but has reduced signaling capability. Unlike Bmpr2-null mice, mice homozygous for this hypomorphic receptor undergo normal gastrulation, providing genetic evidence of the dose-dependent effects of BMPs during mammalian development. Mutants, however, die at midgestation with cardiovascular and skeletal defects, demonstrating that the development of these tissues requires wild-type levels of BMP signaling. The most striking defects occur in the outflow tract of the heart, with absence of septation of the conotruncus below the valve level and interrupted aortic arch, a phenotype known in humans as persistent truncus arteriosus (type A4). In addition, semilunar valves do not form in mutants, while the atrioventricular valves appear unaffected. Abnormal septation of the heart and valve anomalies are the most frequent forms of congenital cardiac defects in humans; however, most mouse models display broad defects throughout cardiac tissues. The more restricted spectrum of cardiac anomalies in Bmpr2(deltaE2) mutants makes this strain a key murine model to understand the embryonic defects of persistent truncus arteriosus and impaired semilunar valve formation in humans.

Operative classification of thromboembolic disease determines outcome after pulmonary endarterectomy

OBJECTIVE

We sought to determine whether type and location of thromboembolic disease in the pulmonary vascular tree predicts the hemodynamic result and clinical outcome in patients undergoing pulmonary endarterectomy.

METHODS

From 1998 to 2000, 202 patients with pulmonary hypertension and pulmonary vascular resistance ranging from 194 to 2950 dynes-s-cm(-5) underwent pulmonary endarterectomy. Preoperative and postoperative tricuspid valve function, pulmonary artery pressure, and pulmonary vascular resistance were determined by means of transthoracic echocardiography and measurements with a Swan-Ganz catheter (Edwards Lifesciences, Irvine, Calif), respectively. Patients underwent intraoperative classification of thromboembolism as follows: type 1 (76 patients), fresh thrombus in the main-lobar pulmonary arteries; type 2 (81 patients), intimal thickening and fibrosis proximal to the segmental arteries; type 3 (38 patients), disease within distal segmental arteries only; and type 4 (7 patients), distal arteriolar vasculopathy without visible thromboembolic disease.

RESULTS

Overall perioperative mortality was 4.5% (9/202 patients). By means of univariate analysis, patients with type 3 or 4 disease (distal pulmonary vasculopathy) had more residual postoperative tricuspid regurgitation (P <.0001), higher postoperative pulmonary artery systolic pressure (P <.0001), and greater postoperative pulmonary vascular resistance (P <.0001) compared with that seen in patients with type 1 or 2 disease, in whom thromboembolic disease was more surgically accessible. Factors such as severity of preoperative tricuspid regurgitation, patient age, and circulatory arrest time had no correlation with postoperative hemodynamic improvement. Patients with distal thromboembolic disease (type 3-4) had higher perioperative mortality, required longer inotropic support, and had longer hospital stays compared with patients with type 1 or 2 thromboembolic disease.

CONCLUSION

The degree of improvement in pulmonary hypertension and tricuspid regurgitation after pulmonary endarterectomy is determined by the type and location of pulmonary thromboembolic disease. Classification of thromboembolism is useful for predicting patient outcome after pulmonary endarterectomy.

Genetic analysis of the mammalian transforming growth factor-beta superfamily

Members of the TGF-beta superfamily, which includes TGF-betas, growth differentiation factors, bone morphogenetic proteins, activins, inhibins, and glial cell line-derived neurotrophic factor, are synthesized as prepropeptide precursors and then processed and secreted as homodimers or heterodimers. Most ligands of the family signal through transmembrane serine/threonine kinase receptors and SMAD proteins to regulate cellular functions. Many studies have reported the characterization of knockout and knock-in transgenic mice as well as humans or other mammals with naturally occurring genetic mutations in superfamily members or their regulatory proteins. These investigations have revealed that TGF-beta superfamily ligands, receptors, SMADs, and upstream and downstream regulators function in diverse developmental and physiological pathways. This review attempts to collate and integrate the extensive body of in vivo mammalian studies produced over the last decade.

Genetics and pulmonary hypertension

Primary pulmonary hypertension (PPH) is a serious pulmonary vascular disease occurring mostly in adult women. Although its occurrence in families was reported within a few years after the original clinical report, PPH was formerly believed rarely to have a genetic basis. Recent progress has not only clarified a basic molecular mechanism for PPH in families, but has also identified mutations of the same gene in many sporadic PPH patients, suggesting that its basis is commonly genetic. Extensive investigations in many centers are now in progress to provide a complete dissection of all the pathogenetic mechanisms of PPH.

Simvastatin attenuates smooth muscle neointimal proliferation and pulmonary hypertension in rats

Hypertensive pulmonary vascular disease is characterized by abnormal proliferation of vascular endothelial and smooth muscle cells, leading to occlusion of pulmonary arterioles, pulmonary hypertension, right ventricular failure, and death. Compounds with antiproliferative effects on vascular endothelial and smooth muscle cells, such as 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, may prevent the development of experimental hypertensive pulmonary vascular disease. Pneumonectomized rats injected with monocrotaline at 7 days develop severe hypertensive pulmonary vascular disease with neointimal formation. Rats were randomized to receive either vehicle or treatment with the HMG-CoA reductase inhibitor simvastatin (2 mg/kg per day). By Day 35, rats that received vehicle had higher mean pulmonary arterial pressures (53 +/- 2 mm Hg) and right ventricular hypertrophy (right ventricle/[left ventricle plus septum] [RV/LV+S] = 0.78 +/- 0.09) than rats in Group PMS5-35 that received simvastatin from Day 5 to 35 (mean pulmonary arterial pressure = 27 +/- 3 mm Hg, RV/LV+S = 0.34 +/- 0.08; p < or = 0.001). Pulmonary vascular remodeling with neointimal formation consisting of vascular smooth muscle cells was more severe in vehicle-treated rats (vascular occlusion score, 1.98 +/- 0.02) than in Group PMS5-35 (vascular occlusion score, 0.59 +/- 0.46; p < 0.001). In addition, lung endothelial nitric oxide synthase gene expression was decreased in vehicle-treated animals but was restored toward normal levels in simvastatin-treated animals. Simvastatin attenuates monocrotaline-induced pulmonary vascular remodeling with neointimal formation, pulmonary arterial hypertension, and right ventricular hypertrophy in rats.

Molecular and cellular basis of pulmonary vascular remodeling in pulmonary hypertension

Clinical pulmonary hypertension is characterized by a sustained elevation in pulmonary arterial pressure. Pulmonary vascular remodeling involves structural changes in the normal architecture of the walls of pulmonary arteries. The process of vascular remodeling can occur as a primary response to injury, or stimulus such as hypoxia, within the resistance vessels of the lung. Alternatively, the changes seen in more proximal vessels may arise secondary to a sustained increase in intravascular pressure. To withstand the chronic increase in intraluminal pressure, the vessel wall becomes thickened and stronger. This "armouring" of the vessel wall with extra-smooth muscle and extracellular matrix leads to a decrease in lumen diameter and reduced capacity for vasodilatation. This maladaptive response results in increased pulmonary vascular resistance and consequently, sustained pulmonary hypertension. The process of pulmonary vascular remodeling involves all layers of the vessel wall and is complicated by the finding that cellular heterogeneity exists within the traditional compartments of the vascular wall: intima, media, and adventitia. In addition, the developmental stage of the organism greatly modifies the response of the pulmonary circulation to injury. This review focuses on the latest advances in our knowledge of these processes as they relate to specific forms of pulmonary hypertension and particularly in the light of recent genetic studies that have identified specific pathways involved in the pathogenesis of severe pulmonary hypertension.