Severe pulmonary hypertension after the discovery of the familial primary pulmonary hypertension gene

Treatment with anti-gremlin 1 antibody ameliorates chronic hypoxia/SU5416-induced pulmonary arterial hypertension in mice

The expression of the bone morphogenetic protein antagonist, Gremlin 1, was recently shown to be increased in the lungs of pulmonary arterial hypertension patients, and in response to hypoxia. Gremlin 1 released from the vascular endothelium may inhibit endogenous bone morphogenetic protein signaling and contribute to the development of pulmonary arterial hypertension. Here, we investigate the impact of Gremlin 1 inhibition in disease after exposure to chronic hypoxia/SU5416 in mice. We investigated the effects of an anti-Gremlin 1 monoclonal antibody in the chronic hypoxia/SU5416 murine model of pulmonary arterial hypertension. Chronic hypoxic/SU5416 exposure of mice induced upregulation of Gremlin 1 mRNA in lung and right ventricle tissue compared with normoxic controls. Prophylactic treatment with an anti-Gremlin 1 neutralizing mAb reduced the hypoxic/SU5416-dependent increase in pulmonary vascular remodeling and right ventricular hypertrophy. Importantly, therapeutic treatment with an anti-Gremlin 1 antibody also reduced pulmonary vascular remodeling and right ventricular hypertrophy indicating a role for Gremlin 1 in the progression of the disease. We conclude that Gremlin 1 plays a role in the development and progression of pulmonary arterial hypertension in the murine hypoxia/SU5416 model, and that Gremlin 1 is a potential therapeutic target for pulmonary arterial hypertension.

Effects of vascular endothelial growth factor on endothelin-1 production by human lung microvascular endothelial cells in vitro

AIMS

Increased endothelin-1 (ET-1) is a hallmark of pulmonary arterial hypertension (PAH), and contributes to its pathogenesis. The factors controlling ET-1 in PAH are poorly understood. Combined with other stimuli, vascular endothelial growth factor (VEGF) blockade results in PAH-like lesions in animal models, and has been associated with PAH in humans. The effects of VEGF on ET-1 production by human lung blood microvascular endothelial cells (HMVEC-LBl) are unknown.

MAIN METHODS

We exposed HMVEC-LBl in-vitro to human VEGF-121 (40 ng/mL) in serum-free medium for 7h, in the absence or presence of the VEGF receptor antagonist, SU5416 (3 and 10 μM). ET-1 production was measured in the supernatant. Phosphorylation of VEGF receptor 2 (VEGFR2) was measured by Western blotting after exposure to VEGF without or with SU5416 for 5 and 10 min.

KEY FINDINGS

VEGF effectively caused VEGFR2 phosphorylation, which was blocked by SU5416. VEGF decreased ET-1 production by at least 29%. In the absence of VEGF, SU5416 increased ET-1 production, by 16% at 10 μM, and SU5416 was able to completely abolish the VEGF effect on ET-1 production.

SIGNIFICANCE

VEGF may promote vascular health by decreasing ET-1 production in HVMEC-LBl. Blockade of VEGF signaling by SU5416 increases ET-1 levels. The role of VEGF in modulating endothelin production in PAH deserves further study.

Inhibition of vascular endothelial growth factor receptor under hypoxia causes severe, human-like pulmonary arterial hypertension in mice: potential roles of interleukin-6 and endothelin

AIMS

Severe pulmonary arterial hypertension (PAH) is an incurable disease whose exact mechanisms remain unknown. However, growing evidence highlights the role of inflammation and endothelin (ET) signaling. The lack of reliable models makes it difficult to investigate the pathophysiology of this disease. Our aim was therefore to develop a mouse model of severe PAH closely mimicking the human condition to explore the role of interleukin-6 (IL-6), and ET signaling in advanced PAH progression.

MAIN METHODS

Young male SV129 mice received vascular endothelial growth factor receptor inhibitor (SU5416) three times a week and were exposed to hypoxia (10% O2) for three weeks. Molecular analysis and histological assessment were examined using real-time PCR, Western blot and immunostaining, respectively.

KEY FINDINGS

The developed murine model presented important characteristics of severe PAH in human: concentric neointimal wall thickening, plexogenic lesions, recruitment of macrophages, and distal arteriolar wall muscularization. We detected an increase of IL-6 production and a stronger macrophage recruitment in adventitia of remodeled arterioles developing plexogenic lesions. Moreover, ET-1 and ET receptor A were up-regulated in lung lysates and media of remodeled arterioles. Recombinant IL-6 stimulated the proliferation and regulated endothelial cells in increasing ET-1 and decreasing ET receptor B.

SIGNIFICANCE

These data describe a murine model, which displays the most important features of human severe PAH. We assume that inflammation, particularly IL-6 regulating ET signaling, plays a crucial role in forming plexogenic lesions. This model is thus reliable and might be used for a better understanding of severe PAH progression and treatment.

Endothelial progenitor cell-based therapy for pulmonary arterial hypertension

A growing body of evidence in animal models and clinical studies supports the concept that endothelial progenitor cell (EPC)-mediated therapy ameliorates pulmonary arterial hypertension (PAH) and thus may represent a novel approach to treat it. Conversely, several experimental findings suggest that EPCs may be involved in PAH pathogenesis and disease progression. These discrepant results confuse the application of EPC transplantation as an effective treatment strategy for PAH. To improve the study of EPC transplantation in PAH therapy, it is high time that we resolve this dilemma. In this review, we examine the pathobiological changes of PAH, the characteristics of EPCs, and the underlying mechanisms of EPC effects on PAH.

Involvement of BMPR2 in the protective effect of fluoxetine against monocrotaline-induced endothelial apoptosis in rats

Mutations in bone morphogenetic protein (BMP) receptor II (BMPR2) are associated with the apoptosis of the pulmonary artery endothelial cells and the loss of the pulmonary small vessels. The present study was designed to investigate the involvement of BMPR2 in the protective effect of fluoxetine against monocrotaline (MCT)-induced endothelial apoptosis in rats. Models of pulmonary arterial hypertension in rats were established by a single intraperitoneal injection of MCT (60 mg/kg). Fluoxetine (2 and 10 mg/kg) was intragastrically administered once a day. After 21 days, MCT caused pulmonary hypertension, right ventricular hypertrophy, and pulmonary vascular remodeling and significantly reduced the BMPR2 expression in lungs and pulmonary arteries. Fluoxetine dose-dependently inhibited MCT-induced pulmonary arterial hypertension and effectively protected the lungs against MCT-induced endothelial apoptosis, reduction in the number of alveolar sacs, and loss of the pulmonary small vessels. Fluoxetine reversed the expression of cyclic guanosine 3',5'-monophosphate-dependent kinase І, BMPR2, phospho-Smad1, β-catenin, and reduced the expression of caspase 3 in rat lungs. These findings suggest that BMPR2 is probably involved in the protective effect of fluoxetine against MCT-induced endothelial apoptosis in rats.

Genomics of pulmonary arterial hypertension: implications for therapy

Pulmonary arterial hypertension (PAH) remains a vexing clinical disease with no cure. Despite advances and the discovery of a gene (BMPR2) associated with many of the hereditary forms of the disease, and some cases not previously known to be inherited, the reasons for mutations in this gene as a cause remain somewhat elusive. Clearly, a complex interplay exists between genetic alterations, environmental exposures (including infections), and disease development. This article addresses the advances in the genetics of PAH, including the identification of genetic etiologies and modulators, and the role of genetics in predicting disease progression and targeting therapeutics.

Propylthiouracil attenuates monocrotaline-induced pulmonary arterial hypertension in rats

BACKGROUND

Propylthiouracil (PTU) enhances nitric oxide production and inhibits smooth muscle cell proliferation, suggesting a possible role in the prevention of pulmonary arterial hypertension (PAH).

METHODS AND RESULTS

The 30 male Sprague-Dawley rats were randomized to receive saline injection only (group 1), monocrotaline (MCT) (70 mg/kg) only (group 2) or MCT + 0.1% PTU in drinking water (group 3) given on day 5 after MCT administration. By day 35, western blot showed lower connexin43 (Cx43) and membranous protein kinase C-epsilon expressions in the right ventricle (RV) of group 2 animals than in the other groups (all P<0.05). Conversely, Cx43 expression in the lung was higher in group 2 than in other groups (all P<0.02). Additionally, mRNA expressions of matrix metalloproteinase-9, tissue necrotic factor-alpha, and caspase-3 were higher, whereas Bcl-2 and endothelial nitric oxide synthase were lower, in the lungs and RV of group 2 rats than in the other groups (all P<0.05). Moreover, the numbers of alveolar sacs and lung arterioles were also reduced in group 2 than in other groups (all P<0.05), and RV systolic pressure and RV weight were increased in group 2 compared with other groups (all P<0.001).

CONCLUSIONS

PTU effectively attenuates complications associated with MCT-induced PAH.

Role of the TGF-beta/Alk5 signaling pathway in monocrotaline-induced pulmonary hypertension

RATIONALE

Pulmonary arterial hypertension is a progressive disease characterized by an elevation in the mean pulmonary artery pressure leading to right heart failure and a significant risk of death. Alterations in two transforming growth factor (TGF) signaling pathways, bone morphogenetic protein receptor II and the TGF-beta receptor I, Alk1, have been implicated in the pathogenesis of pulmonary hypertension (PH). However, the role of TGF-beta family signaling in PH and pulmonary vascular remodeling remains unclear.

OBJECTIVES

To determine whether inhibition of TGF-beta signaling will attenuate and reverse monocrotaline-induced PH (MCT-PH).

METHODS

We have used an orally active small-molecule TGF-beta receptor I inhibitor, SD-208, to determine the functional role of this pathway in MCT-PH.

MEASUREMENTS AND MAIN RESULTS

The development of MCT-PH was associated with increased vascular cell apoptosis, which paralleled TGF-beta signaling as documented by psmad2 expression. Inhibition of TGF-beta signaling with SD-208 significantly attenuated the development of the PH and reduced pulmonary vascular remodeling. These effects were associated with decreased early vascular cell apoptosis, adventitial cell proliferation, and matrix metalloproteinase expression. Inhibition of TGF-beta signaling with SD-208 in established MCT-PH resulted in a small but significant improvement in hemodynamic parameters and medial remodeling.

CONCLUSIONS

These findings provide evidence that increased TGF-beta signaling participates in the pathogenesis of experimental severe PH.

The critical role of vascular endothelial growth factor in pulmonary vascular remodeling after lung injury

The pulmonary vascular endothelial cell plays a crucial role in the regulation of the pulmonary vascular tone and in the maintenance of the barrier function and integrity of the alveolar-capillary membrane. It also plays a major role in coagulation, fibrinolysis, and angiogenesis and participates in inflammatory reactions. Vascular endothelial growth factor (VEGF) is a central growth and survival factor for the endothelial cell. Particularly high levels of VEGF are expressed in the lungs, reflecting the critical role of VEGF for lung development and structural integrity of the adult lung. Vascular endothelial growth factor exerts a variety of physiological and pathophysiological actions in the lung. Recent evidence suggests its involvement in the pathogenesis of lung diseases such as bronchopulmonary dysplasia, acute lung injury, emphysema, and pulmonary hypertension. To summarize the critical effects of VEGF on the pulmonary endothelial cell in the pathogenesis of these diseases, the purposes of this review are to (1) discuss the biological activities and intracellular signaling pathways of VEGF in the lung; (2) summarize the regulatory mechanisms involved in VEGF expression; (3)address the effects of VEGF on endothelial cells in hyperoxia-induced and other forms of lung injury; (4) highlight the endothelial effects of VEGF in the pathogenesis of emphysema; and (5) explore the role of VEGF in the pathogenesis of pulmonary arterial hypertension.

Pathology of pulmonary hypertension

The secondary role of pathology in the present clinical management of pulmonary hypertension (PH) reflects to some extent the limitations of the current understanding of the disease. Ample room exists for the diagnostic translation of the pathobiologic studies, with the goal of improving the diagnostic and prognostic power of the pathologic assessment of pulmonary vascular remodeling. This article seeks to show the complementarities of the pathology and pathobiology of PH.

Rho kinase-mediated vasoconstriction is important in severe occlusive pulmonary arterial hypertension in rats

Vascular remodeling, rather than vasoconstriction, is believed to account for high vascular resistance in severe pulmonary arterial hypertension (PAH). We have found previously that acute Rho kinase inhibition nearly normalizes PAH in chronically hypoxic rats that have no occlusive neointimal lesions. Here we examined whether Rho kinase-mediated vasoconstriction was also important in a rat model of severe occlusive PAH. Adult rats were exposed to chronic hypoxia ( approximately 10% O(2)) after subcutaneous injection of the vascular endothelial growth factor receptor inhibitor SUGEN 5416. Hemodynamic measurements were made in anesthetized rats after 2 weeks of hypoxia (early group) and 3 weeks of hypoxia plus 2 weeks of normoxia (late group). Both groups developed PAH, with greater severity in the late group. In the early group, intravenous fasudil was more effective than intravenous bradykinin, inhaled NO, or intravenous iloprost in reducing right ventricular systolic pressure. Despite more occlusive vascular lesions, fasudil also markedly reduced right ventricular systolic pressure in late-stage rats. Blood-perfused lungs from late-stage rats showed spontaneous vasoconstriction, which was reversed partially by the endothelin A receptor blocker BQ123 and completely by fasudil or Y-27632. Phosphorylation of MYPT1, a downstream target of Rho kinase, was increased in lungs from both groups of rats, and fasudil (intravenous) reversed the increased phosphorylation in the late group. Thus, in addition to structural occlusion, Rho kinase-mediated vasoconstriction is an important component of severe PAH in SUGEN 5416/hypoxia-exposed rats, and PAH can be significantly reduced in the setting of a severely remodeled lung circulation if an unconventional vasodilator is used.

Vascular endothelial growth factor in the lung

Vascular endothelial growth factor (VEGF) is a pluripotent growth and permeability factor that has a broad impact on endothelial cell function. The lung tissue is very rich in this protein; many different lung cells produce VEGF and also respond to VEGF. VEGF is critical for the development of the lung and serves as a maintenance factor during adult life. In addition to the physiological functions of this protein, there is increasing evidence that VEGF also plays a role in several acute and chronic lung diseases, such as acute lung injury, severe pulmonary hypertension, and emphysema. Here we provide a comprehensive overview of the rapidly expanding literature.

Impaired transforming growth factor-beta signaling in idiopathic pulmonary arterial hypertension

Mutations in transforming growth factor-beta family receptor-II, bone morphogenetic protein receptor-2, and activin-like kinase-1 have been associated with pulmonary hypertension. In the present study, we determined that pulmonary arteries in normal lungs and in lungs of patients with emphysema and idiopathic pulmonary arterial hypertension comparably expressed transforming growth factor-beta receptors I and II, Smad(1, 5, 8), Smad2, Smad3, Smad4, phosphorylated Smad(1, 5, 8), and phosphorylated Smad2 (the latter two both indicative of active in vivo signaling) in endothelial cells, as assessed by immunohistochemistry and quantitative morphometry. Medial or intimal smooth muscle cells had weak or absent expression of these molecules. In clear contrast to endothelial cell expression in pulmonary arteries and in endothelial cells lining incipient vessels within plexiform lesions of hypertensive lungs, endothelial cells present in the core of the lesions lacked expression of all examined members of the signaling molecules. These findings were made irrespective of the mutation status of bone morphogenetic protein receptor-2 in hypertensive patients. Our findings suggest that pulmonary artery endothelial cells in both normal and severely hypertensive lungs have active transforming growth factor-beta family signaling, and that loss of signaling might contribute to the abnormal growth of endothelial cells in plexiform lesions in idiopathic pulmonary arterial hypertension.

Pathology of pulmonary hypertension

This article briefly discusses the traditional concepts of severe pulmonary hypertension and then details how the concept of severe pulmonary hypertension has moved from a vasoconstrictive to an angioproliferative disorder.

Oxidative stress in severe pulmonary hypertension

Severe pulmonary hypertension (PH) occurs in a primary or "unexplained" form and in a group of secondary forms associated with a number of diseases. Because the lung tissue from patients with severe PH demonstrates complex vascular lesions, which contain inflammatory cells, we wondered whether the lung tissue from patients with severe PH was "under oxidative stress." We used immunohistochemistry to localize nitrotyrosine and 8-hydroxy guanosine in the lung tissue sections from patients with primary and secondary PH. In some lung tissue extracts, the eicosanoid metabolites 5-oxo-eicosatetraenoic acid, leukotriene B4 5-hydroxyeicosatetraenoic acid (HETE), 12-HETE, and 15-HETE were measured using mass spectroscopy, and superoxide dismutase amount and activity were measured. Nitrotyrosine expression was ubiquitous in all PH lungs, and 5-oxo-eicosatetraenoic acid and HETE levels were elevated in the lungs of patients with severe PH but not in those lungs that were from the patients with severe PH treated chronically with prostacyclin. We conclude that indeed the lungs from patients with severe PH are under oxidative stress and that chronic prostacyclin infusion has an antiinflammatory effect on the lung tissue.

Angiogenesis and pulmonary hypertension: a unique process in a unique disease

Severe pulmonary hypertension is a fatal condition associated with marked alterations of the cellular components of pulmonary arteries. In this review, we discuss the component of endothelial cell proliferation present in pulmonary arteries in patients with severe pulmonary hypertension. Because these proliferated endothelial cells exhibit markers of angiogenesis, we have named this process as "disordered or misguided angiogenesis." We also discuss the recent evidence that germline or somatic inactivating mutations in tumor suppressor or proapoptotic genes may play a significant role in the abnormal proliferation of pulmonary endothelial cells. The unraveling of the pathobiology of severe pulmonary hypertension may lead us to novel therapies and approaches to better diagnose the disease.

Identification of differentially expressed genes in pulmonary adenocarcinoma by using cDNA array

No clear patterns in molecular changes underlying the malignant processes in lung cancer of different histological types have been found so far. To identify critical genes in lung cancer progression we compared the expression profile of cancer related genes in 14 pulmonary adenocarcinoma patients with normal lung tissue by using the cDNA array technique. Principal component analyses (PCA) and permutation test were used to detect the differentially expressed genes. The expression profiles of 10 genes were confirmed by semi-quantitative real-time RT-PCR. In tumour samples, as compared to normal lung tissue, the up-regulated genes included such known tumour markers as CCNB1, PLK, tenascin, KRT8, KRT19 and TOP2A. The down-regulated genes included caveolin 1 and 2, and TIMP3. We also describe, for the first time, down-regulation of the interesting SOCS2 and 3, DOC2 and gravin. We show that silencing of SOCS2 is not caused by methylation of exon 1 of the gene. In conclusion, by using the cDNA array technique we were able to reveal marked differences in the gene expression level between normal lung and tumour tissue and find possible new tumour markers for pulmonary adenocarcinoma.

Janus face of vascular endothelial growth factor: the obligatory survival factor for lung vascular endothelium controls precapillary artery remodeling in severe pulmonary hypertension

Vascular endothelial growth factor (VEGF) plays a central role in the life and death of pulmonary vascular endothelial cells. Treatment of neonatal or adult rats with a VEGF receptor blocker destroys lung capillaries by inducing endothelial cell apoptosis and causes emphysema. Human lung tissue samples from patients with endstage emphysema have decreased levels of VEGF messenger RNA and protein and have decreased expression of kinase insert domain-containing receptor (VEGF receptor II). These decreases are associated with a high rate of alveolar septal cell apoptosis, indicating perhaps that decreased VEGF and kinase insert domain-containing receptor expression impairs endothelial cell survival in emphysematous lungs. Combination of VEGF receptor blockade with chronic hypoxia (3-wk exposure) results in obliteration of small precapillary pulmonary arteries by proliferating endothelial cells, severe pulmonary hypertension, and death caused by right-side heart failure. We propose that 1) VEGF receptor blockade causes endothelial cell apoptosis, 2) hypoxic vasoconstriction (shear stress) selects apoptosis-resistant endothelial cells that proliferate and obliterate the lumen, and 3) the vascular remodeling observed is relevant to the structural alterations that characterize severe pulmonary hypertension (including primary pulmonary hypertension) in humans. The endovascular cell growth in human disease and in our model exhibits some similarities with neoplastic cell growth. Chemotherapy strategies can now be employed in the animal model in an attempt to treat established vascular-obliterative lung disease.