Molecular and cellular basis of pulmonary vascular remodeling in pulmonary hypertension

Pulmonary arterial hypertension

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

The potential efficacy of R8-modified paclitaxel-loaded liposomes on pulmonary arterial hypertension

PURPOSE

In this paper, a novel liposomal formulation of paclitaxel modified with octaarginine (R8) was fabricated and the therapeutic efficacy of it on pulmonary arterial hypertension was evaluated.

METHODS

Octaarginine-modified stealth liposomes loaded with PTX (R8-PTX-LIP) were prepared and characterized. Vector cytoxicity and anti-proliferation ability of different formulations on primary cultured VSMCs were determined with MTT assay. The uptake capacity of VSMCs on different formulations were evaluated by flow cytometry, and the influences on cytoskeletons of liposomes were investigated by cytoskeleton staining with rhodamine-phalloidin. The biodistribution of liposomes were imaged by a CCD camera using a near-infrared fluorophore DiD. The therapeutic efficacy of different PTX-formulations of PAH was evaluated by hemodynamic measurement, right ventricular hypertrophic parameters and vessel diameters.

RESULTS

The cellular uptake of R8 modified liposomes (R8-LIP) was improved noticeably compared with other groups. All liposomes did not exert cytotoxicity on VSMCs in 24 h. R8-PTX-LIP exhibited the strongest inhibitory effect on the proliferation of VSMCs among all the formulations (p < 0.001). R8-PTX-LIP could reverse the phenotype transformation, and inhibit cell migration. mPAP, (RV/LV+S) and the wall thickness of small distal pulmonary arteries of rats treated with R8-PTX-LIP were significantly lower than those from other groups (p < 0.001).

CONCLUSIONS

In conclusion, the drug delivery system of R8-modified paclitaxel-loaded liposomes we established showed pronounced inhibitory effect over VSMCs proliferation and cytoskeleton formation in vitro, a stronger pulmonary delivery ability in vivo, and was effective on PAH, showing the potential for pulmonary drug delivery system for PAH treatment.

In vitro assessment of clevidipine using the profilin1 hypertensive mouse model

Hypertension represents a major risk factor for cardiovascular events, associating with vascular hypertrophy and dysfunction in resistance vessels. Clevidipine is a novel antihypertensive drug working as a selective calcium channel antagonist with an ultra-short half-life that lowers arterial blood pressure by reducing systemic arterial resistance. The aim was to assess the effect of clevidipine on the hypertrophic vessels of profilin1 hypertensive transgenic mice compared to sodium nitroprusside (SNP) and labetalol using wire myograph techniques. The effects of clevidipine, SNP and labetalol on the hypertrophic vessels were studied on mesenteric arterial function from 8 profilin1 hypertrophic mice and eight non-transgenic controls. Our results showed a significant difference between the effects of the three drugs on the hypertrophic mesenteric arteries of transgenic profilin1 mice compared to the non-transgenic controls. The half maximal effective concentration (EC50) of clevidipine, SNP and labetalol in profilin1 mice (1.90 ± 0.05, 0.97 ± 0.07, 2.80 ± 0.05 nM, respectively) were significantly higher than the EC50 in non-transgenic controls (0.91 ± 0.06, 0.32 ± 0.06, 0.80 ± 0.09 nM, respectively). Moreover, the increase in the EC50 for clevidipine (2-fold) to produce the same effect on both normal and hypertrophic arteries was less than that of SNP (3-fold) and labetalol (3.5-fold). Therefore, we concluded clevidipine exhibited the lowest dose shift to relax the hypertrophic vessels compared to SNP and labetalol in the profilin1 hypertrophic animal mouse model.

MicroRNA in the Diseased Pulmonary Vasculature: Implications for the Basic Scientist and Clinician

Since the first descriptions of their active functions more than ten years ago, small non-coding RNA species termed microRNA (miRNA) have emerged as essential regulators in a broad range of adaptive and maladaptive cellular processes. With an exceptionally rapid pace of discovery in this field, the dysregulation of many individual miRNAs has been implicated in the development and progression of various cardiovascular diseases. MiRNA are also expected to play crucial regulatory roles in the progression of pulmonary vascular diseases such as pulmonary hypertension (PH), yet direct insights in this field are only just emerging. This review will provide an overview of pulmonary hypertension and its molecular mechanisms, tailored for both basic scientists studying pulmonary vascular biology and physicians who manage PH in their clinical practice. We will describe the pathobiology of pulmonary hypertension and mechanisms of action of miRNA relevant to this disease. Moreover, we will summarize the potential roles of miRNA as biomarkers and therapeutic targets as well as future strategies for defining the cooperative actions of these powerful effectors in pulmonary vascular disease.

Chloroquine prevents progression of experimental pulmonary hypertension via inhibition of autophagy and lysosomal bone morphogenetic protein type II receptor degradation

RATIONALE

Pulmonary arterial hypertension (PAH) is characterized by excessive proliferation and apoptosis resistance in pulmonary artery smooth muscle cells (PASMCs).

OBJECTIVE

We reasoned that chloroquine, based on its ability to inhibit autophagy and block lysosomal degradation of the bone morphogenetic protein type II receptor (BMPR-II), might exert beneficial effects in this disease.

METHODS AND RESULTS

PAH was induced in male Sprague-Dawley rats by administering monocrotaline. The induction of PAH was associated with changes in lung expression of LC3B-II, ATG5, and p62, consistent with increased autophagy, and decreased BMPR-II protein expression. Administration of chloroquine prevented the development of PAH, right ventricular hypertrophy, and vascular remodelling after monocrotaline, and prevented progression of established PAH in this model. Similar results were obtained with hydroxychloroquine. Chloroquine treatment increased whole lung and PASMC p62 protein levels consistent with inhibition of autophagy, and increased levels of BMPR-II protein. Chloroquine inhibited proliferation and increased apoptosis of PASMCs in vivo. In cultured rat PASMCs we confirmed that chloroquine both inhibited autophagy pathways and increased expression of BMPR-II protein via lysosomal inhibition. Consistent with the in vivo findings, chloroquine inhibited the proliferation and stimulated apoptosis of rat PASMCs in vitro, with no effect on endothelial cell proliferation or survival. Moreover, direct inhibition of autophagy pathways by ATG5 small interfering RNA knockdown inhibited proliferation of rat PASMCs.

CONCLUSIONS

Chloroquine and hydroxychloroquine exert beneficial effects in experimental PAH. The mechanism of action includes inhibition of autophagy pathways and inhibition of lysosomal degradation of BMPR-II.

Pulmonary hypertension in rheumatic diseases: epidemiology and pathogenesis

The focus of this review is to increase awareness of pulmonary arterial hypertension (PAH) in patients with rheumatic diseases. Epidemiology and pathogenesis of PAH in rheumatic diseases is reviewed, with recommendations for early screening and diagnosis and suggestion of possible role of immunosuppressive therapy in treatment for PAH in rheumatic diseases. A MEDLINE search for articles published between January 1970 and June 2012 was conducted using the following keywords: pulmonary hypertension, scleroderma, systemic sclerosis, pulmonary arterial hypertension, connective tissues disease, systemic lupus erythematosus, mixed connective tissue disease, rheumatoid arthritis, Sjogren's syndrome, vasculitis, sarcoidosis, inflammatory myopathies, dermatomyositis, ankylosing spondylitis, spondyloarthropathies, diagnosis and treatment. Pathogenesis and disease burden of PAH in rheumatic diseases was highlighted, with emphasis on early consideration and workup of PAH. Screening recommendations and treatment were touched upon. PAH is most commonly seen in systemic sclerosis and may be seen in isolation or in association with interstitial lung disease. Several pathophysiologic processes have been identified including an obliterative vasculopathy, veno-occlusive disease, formation of microthrombi and pulmonary fibrosis. PAH in systemic lupus erythematosus is associated with higher prevalence of antiphospholipid and anticardiolipin antibodies and the presence of Raynaud's phenomenon. Endothelial proliferation with vascular remodeling, abnormal coagulation with thrombus formation and immune-mediated vasculopathy are the postulated mechanisms. Improvement with immunosuppressive medications has been reported. Pulmonary fibrosis, extrinsic compression of pulmonary arteries and granulomatous vasculitis have been reported in patients with sarcoidosis. Intimal and medial hyperplasia with luminal narrowing has been observed in Sjogren's syndrome, mixed connective tissue disease and inflammatory myopathies. Pulmonary arterial hypertension (PAH) associated with rheumatic diseases carries a particularly grim prognosis with faster progression of disease and poor response to therapy. Though largely associated with systemic sclerosis, it is being increasingly recognized in other rheumatic diseases. An underlying inflammatory component may explain the poor response to therapy in patients with rheumatic diseases and is a rationale for consideration of immunosuppressive therapy in conjunction with vasodilator therapy in treatment for PAH. Further studies identifying pathogenetic pathways and possible targets of therapy, especially the role of immunomodulatory medications, are warranted.

Hypoxia-induced mitogenic factor (HIMF/FIZZ1/RELMα) in chronic hypoxia- and antigen-mediated pulmonary vascular remodeling

Background

Both chronic hypoxia and allergic inflammation induce vascular remodeling in the lung, but only chronic hypoxia appears to cause PH. We investigate the nature of the vascular remodeling and the expression and role of hypoxia-induced mitogenic factor (HIMF/FIZZ1/RELMα) in explaining this differential response.

Methods

We induced pulmonary vascular remodeling through either chronic hypoxia or antigen sensitization and challenge. Mice were evaluated for markers of PH and pulmonary vascular remodeling throughout the lung vascular bed as well as HIMF expression and genomic analysis of whole lung.

Results

Chronic hypoxia increased both mean pulmonary artery pressure (mPAP) and right ventricular (RV) hypertrophy; these changes were associated with increased muscularization and thickening of small pulmonary vessels throughout the lung vascular bed. Allergic inflammation, by contrast, had minimal effect on mPAP and produced no RV hypertrophy. Only peribronchial vessels were significantly thickened, and vessels within the lung periphery did not become muscularized. Genomic analysis revealed that HIMF was the most consistently upregulated gene in the lungs following both chronic hypoxia and antigen challenge. HIMF was upregulated in the airway epithelial and inflammatory cells in both models, but only chronic hypoxia induced HIMF upregulation in vascular tissue.

Conclusions

The results show that pulmonary vascular remodeling in mice induced by chronic hypoxia or antigen challenge is associated with marked increases in HIMF expression. The lack of HIMF expression in the vasculature of the lung and no vascular remodeling in the peripheral resistance vessels of the lung is likely to account for the failure to develop PH in the allergic inflammation model.

Assessment of the endothelial functions in monocrotaline-induced pulmonary hypertension

Pulmonary hypertension (PH) is a life-threatening disease that causes endothelial dysfunction in the pulmonary vascular bed. Systemic endothelial dysfunction has also been reported in PH. This study compared the systemic and pulmonary vascular responses and some blood biomarkers of endothelial function in monocrotaline (MCT)-induced PH of rats. It also investigated the effect of sildenafil and iloprost treatment. MCT application induced elevation in the right ventricular pressures of the rat heart that had been reversed by sildenafil and iloprost treatment. Acetylcholine-induced endothelium-dependent relaxations of the isolated pulmonary artery were decreased in the PH group and this failure was reversed by sildenafil and iloprost treatment. Acetylcholine-induced endothelium-dependent relaxations of the isolated thoracic aorta were similar in all groups. Serotonin-induced contractions of the pulmonary artery were augmented by PH. In the isolated aorta, serotonin-stimulated contraction was not different in the control and MCT groups, but sildenafil and iloprost treatment decreased serotonin responses. The nitric oxide (NO) level in systemic circulation was not significantly changed by PH. However, sildenafil and iloprost treatments caused a decrease in the plasma level of NO. Asymmetric dimethylarginine levels in plasma were significantly decreased after MCT application and were not recovered by sildenafil and iloprost treatment. Total antioxidant capacity and H2S level of plasma were similar in all groups. Results of this study showed that MCT-induced PH caused specific toxic effects on pulmonary vasculature without any functional effects on the aorta. In addition, it was also demonstrated that sildenafil and iloprost treatments were effective in the MCT-induced PH.

A role for miR-145 in pulmonary arterial hypertension: evidence from mouse models and patient samples

RATIONALE

Despite improved understanding of the underlying genetics, pulmonary arterial hypertension (PAH) remains a severe disease. Extensive remodeling of small pulmonary arteries, including proliferation of pulmonary artery smooth muscle cells (PASMCs), characterizes PAH. MicroRNAs (miRNAs) are noncoding RNAs that have been shown to play a role in vascular remodeling.

OBJECTIVE

We assessed the role of miR-145 in PAH.

METHODS AND RESULTS

We localized miR-145 in mouse lung to smooth muscle. Using quantitative PCR, we demonstrated increased expression of miR-145 in wild-type mice exposed to hypoxia. PAH was evaluated in miR-145 knockout and mice treated with anti-miRs via measurement of systolic right ventricular pressure, right ventricular hypertrophy, and percentage of remodeled pulmonary arteries. miR-145 deficiency and anti-miR-mediated reduction resulted in significant protection from the development of PAH. In contrast, miR-143 anti-miR had no effect. Furthermore, we observed upregulation of miR-145 in lung tissue of patients with idiopathic and heritable PAH compared with unaffected control subjects and demonstrated expression of miR-145 in SMC of remodeled vessels from such patients. Finally, we show elevated levels of miR-145 expression in primary PASMCs cultured from patients with BMPR2 mutations and also in the lungs of BMPR2-deficient mice.

CONCLUSIONS

miR-145 is dysregulated in mouse models of PAH. Downregulation of miR-145 protects against the development of PAH. In patient samples of heritable PAH and idiopathic PAH, miR-145 is expressed in remodeled vessels and mutations in BMPR2 lead to upregulation of miR-145 in mice and PAH patients. Manipulation of miR-145 may represent a novel strategy in PAH treatment.

Osteopontin is an endogenous modulator of the constitutively activated phenotype of pulmonary adventitial fibroblasts in hypoxic pulmonary hypertension

Increased cell proliferation and migration, of several cell types are key components of vascular remodeling observed in pulmonary hypertension (PH). Our previous data demonstrate that adventitial fibroblasts isolated from pulmonary arteries of chronically hypoxic hypertensive calves (termed PH-Fibs) exhibit a "constitutively activated" phenotype characterized by high proliferative and migratory potential. Osteopontin (OPN) has been shown to promote several cellular activities including growth and migration in cancer cells. We thus tested the hypothesis that elevated OPN expression confers the "activated" highly proproliferative and promigratory/invasive phenotype of PH-Fibs. Our results demonstrate that, both in vivo and ex vivo, PH-Fibs exhibited increased expression of OPN, as well as its cognate receptors, α(V)β(3) and CD44, compared with control fibroblasts (CO-Fibs). Augmented OPN expression in PH-Fibs corresponded to their high proliferative, migratory, and invasive properties and constitutive activation of ERK1/2 and AKT signaling. OPN silencing via small interfering RNA or sequestering OPN production by specific antibodies led to decreased proliferation, migration, invasion, and attenuated ERK1/2, AKT phosphorylation in PH-Fibs. Furthermore, increasing OPN levels in CO-Fibs via recombinant OPN resulted in significant increases in their proliferative, migratory, and invasive capabilities to the levels resembling those of PH-Fibs. Thus our data suggest OPN as an essential contributor to the activated (highly proliferative, migratory, and proinvasive) phenotype of pulmonary adventitial fibroblasts in hypoxic PH.

Pharmacologic agents elevating cAMP prevent arginase II expression and proliferation of pulmonary artery smooth muscle cells

Arginase II has been shown to be involved in the hypoxia-induced proliferation of human pulmonary artery smooth muscle cells (hPASMCs). The signal transduction pathways responsible for the induction of arginase II are poorly understood. Cyclic AMP is involved in many intracellular processes, and cAMP levels are regulated by a balance between production via adenylate cyclases and degradation via phosphodiesterases. The purpose of this study was to determine the effects of cAMP on hypoxia-induced arginase expression, activity, and proliferation in hPASMCs. We found that the cAMP analog 8-Bromo-cAMP (8-Br-cAMP), the adenylate cyclase activator forskolin, and the phosphodiesterase 3 inhibitor cilostamide prevented the hypoxic induction of arginase II mRNA and protein expression in hPASMCs. The inhibition of arginase II protein was found to be mediated by exchange protein directly activated by cAMP. Arginase activity was decreased by 8-Br-cAMP, as evidenced by significantly lower V(max) for arginase in normoxia and hypoxia. The hypoxia-induced hPASMC proliferation was completely prevented by the addition of 8-Br-cAMP, forskolin, or cilostamide. These data are the first to describe the inhibitory effect of cAMP on arginase activity, expression, and resultant proliferation of hypoxic hPASMCs.

Mechanics and Function of the Pulmonary Vasculature: Implications for Pulmonary Vascular Disease and Right Ventricular Function

The relationship between cardiac function and the afterload against which the heart muscle must work to circulate blood throughout the pulmonary circulation is defined by a complex interaction between many coupled system parameters. These parameters range broadly and incorporate system effects originating primarily from three distinct locations: input power from the heart, hydraulic impedance from the large conduit pulmonary arteries, and hydraulic resistance from the more distal microcirculation. These organ systems are not independent, but rather, form a coupled system in which a change to any individual parameter affects all other system parameters. The result is a highly nonlinear system which requires not only detailed study of each specific component and the effect of disease on their specific function, but also requires study of the interconnected relationship between the microcirculation, the conduit arteries, and the heart in response to age and disease. Here, we investigate systems-level changes associated with pulmonary hypertensive disease progression in an effort to better understand this coupled relationship.

Hypoxia induces downregulation of PPAR-γ in isolated pulmonary arterial smooth muscle cells and in rat lung via transforming growth factor-β signaling

Chronic hypoxia activates transforming growth factor-β (TGF-β) signaling and leads to pulmonary vascular remodeling. Pharmacological activation of peroxisome proliferator-activated receptor-γ (PPAR-γ) has been shown to prevent hypoxia-induced pulmonary hypertension and vascular remodeling in rodent models, suggesting a vasoprotective effect of PPAR-γ under chronic hypoxic stress. This study tested the hypothesis that there is a functional interaction between TGF-β/Smad signaling pathway and PPAR-γ in isolated pulmonary artery small muscle cells (PASMCs) under hypoxic stress. We observed that chronic hypoxia led to a dramatic decrease of PPAR-γ protein expression in whole lung homogenates (rat and mouse) and hypertrophied pulmonary arteries and isolated PASMCs. Using a transgenic model of mouse with inducible overexpression of a dominant-negative mutant of TGF-β receptor type II, we demonstrated that disruption of TGF-β pathway significantly attenuated chronic hypoxia-induced downregulation of PPAR-γ in lung. Similarly, in isolated rat PASMCs, antagonism of TGF-β signaling with either a neutralizing antibody to TGF-β or the selective TGF-β receptor type I inhibitor SB431542 effectively attenuated hypoxia-induced PPAR-γ downregulation. Furthermore, we have demonstrated that TGF-β1 treatment suppressed PPAR-γ expression in PASMCs under normoxia condition. Chromatin immunoprecipitation analysis showed that TGF-β1 treatment significantly increased binding of Smad2/3, Smad4, and the transcriptional corepressor histone deacetylase 1 to the PPAR-γ promoter in PASMCs. Conversely, treatment with the PPAR-γ agonist rosiglitazone attenuated TGF-β1-induced extracellular matrix molecule expression and growth factor in PASMCs. These data provide strong evidence that activation of TGF-β/Smad signaling, via transcriptional suppression of PPAR-γ expression, mediates chronic hypoxia-induced downregulation of PPAR-γ expression in lung.

Transgenic expression of human matrix metalloproteinase-1 attenuates pulmonary arterial hypertension in mice

PAH (pulmonary arterial hypertension) is a debilitating and life-threatening disease, often affecting young people. We specifically expressed human MMP-1 (matrix metalloproteinase-1) in mouse macrophages and examined its effects in attenuating the decompensating features of MCT (monocrotaline)-induced PAH. Measurement of RV (right ventricular) pressure revealed a 2.5-fold increase after treatment with MCT, which was reduced to 1.5-fold in MMP-1 transgenic mice. There was conspicuous pulmonary inflammation with chronic infiltration of mononuclear cells after the administration of MCT, which was significantly diminished in transgenic mice. Furthermore, transgenic mice showed decreased collagen deposition compared with WT (wild-type). Staining for Mac-3 (macrophage-3) and α-SMA (α-smooth muscle actin) revealed extensive infiltration of macrophages and medial hypertrophy of large pulmonary vessels with complete occlusion of small arteries respectively. These changes were markedly reduced in MMP-1 transgenic mice compared with WT. Western blotting for molecules involved in cell multiplication and proliferation depicted a significant decrease in the lung tissue of transgenic mice after the treatment with MCT. In conclusion, the present study demonstrated that transgenic expression of human MMP-1 decreased proliferation of smooth muscle cells and prevented excessive deposition of collagen in the pulmonary arterial tree. Our results indicate that up-regulation of MMP-1 could attenuate the debilitation of human PAH and provide an option for therapeutic intervention.

Repeated exposure to Aspergillus fumigatus conidia results in CD4+ T cell-dependent and -independent pulmonary arterial remodeling in a mixed Th1/Th2/Th17 microenvironment that requires interleukin-4 (IL-4) and IL-10

Pulmonary arterial remodeling is a pathological process seen in a number of clinical disease states, driven by inflammatory cells and mediators in the remodeled artery microenvironment. In murine models, Th2 cell-mediated immune responses to inhaled antigens, such as purified Aspergillus allergen, have been reported to induce remodeling of pulmonary arteries. We have previously shown that repeated intranasal exposure of healthy C57BL/6 mice to viable, resting Aspergillus fumigatus conidia leads to the development of chronic pulmonary inflammation and the coevolution of Th1, Th2, and Th17 responses in the lungs. Our objective was to determine whether repeated intranasal exposure to Aspergillus conidia would induce pulmonary arterial remodeling in this mixed Th inflammatory microenvironment. Using weekly intranasal conidial challenges, mice developed robust pulmonary arterial remodeling after eight exposures (but not after two or four). The process was partially mediated by CD4+ T cells and by interleukin-4 (IL-4) production, did not require eosinophils, and was independent of gamma interferon (IFN-γ) and IL-17. Furthermore, remodeling could occur even in the presence of strong Th1 and Th17 responses. Rather than serving an anti-inflammatory function, IL-10 was required for the development of the Th2 response to A. fumigatus conidia. However, in contrast to previous studies of pulmonary arterial remodeling driven by the A. fumigatus allergen, viable conidia also stimulated pulmonary arterial remodeling in the absence of CD4+ T cells. Remodeling was completely abrogated in IL-10-/- mice, suggesting that a second, CD4+ T cell-independent, IL-10-dependent pathway was also driving pulmonary arterial remodeling in response to repeated conidial exposure.

MicroRNA and vascular remodelling in acute vascular injury and pulmonary vascular remodelling

Vascular remodelling is an integral pathological process central to a number of cardiovascular diseases. The complex interplay between distinct cell populations in the vessel wall following vascular injury leads to inflammation, cellular dysfunction, pro-growth signals in the smooth muscle cell (SMC) compartment, and the acquisition of a synthetic phenotype. Although the signals for vascular remodelling are diverse in different pathological contexts, SMC proliferation and migration are consistently observed. It is therefore critical to elucidate key mechanisms central to these processes. MicroRNAs (miRNAs) are small non-coding sequences of RNA that have the capacity to regulate many genes, pathways, and complex biological networks within cells, acting either alone or in concert with one another. In diseases such as cancer and cardiac disease, the role of miRNA in disease pathogenesis has been documented in detail. In contrast, despite a great deal of interest in miRNA, relatively few studies have directly assessed the role of miRNA in vascular remodelling. The potential for modulation of miRNA to achieve therapeutic benefits in this setting is attractive. Here, we focus on the role of miRNA in vascular inflammation and remodelling associated with acute vascular injury (vein graft disease, angioplasty restenosis, and in-stent restenosis) as well as in vascular remodelling associated with the development of pulmonary arterial hypertension.

Human immunodeficiency virus transgenic rats exhibit pulmonary hypertension

Human immunodeficiency virus (HIV)-associated pulmonary arterial hypertension (PAH) is a serious noninfectious disease involving an aberrant increase in pressure in the blood vessels of the lung, which leads to right ventricular (RV) heart failure and can eventually result in death. A lack of viable animal models of HIV-PAH has limited the identification of signaling pathways involved in HIV-mediated onset and progression of PAH. To determine whether the HIV-1 transgenic (HIV Tg) rat displays pathophysiological end points associated with PAH, we evaluated peak RV systolic pressure (RVSP), RV hypertrophy, pulmonary vessel remodeling, and alterations in gene expression by real-time PCR and microarray. RVSP was measured by RV catheterization via the right jugular vein in 3- and 9-mo-old HIV Tg and age-matched Fischer 344 (control) male rats while under 2% isoflurane anesthesia. RVSP was elevated in the HIV Tg rats (34.2 ± 2.5 mmHg) compared with the F344 controls (21.2 ± 2.5 mmHg), with more significant elevations in the 9-mo-old HIV Tg rats (42.5 ± 3.7 mmHg). We observed significant increases in RV wall thickness in HIV Tg rats compared with controls, both histologically and by echocardiograph measurement. HIV Tg rats also show increased thickening of the pulmonary artery and remodeling of small pulmonary arteries, as well as altered expression of gene pathways associated with PAH. These data represent the first analysis of PAH in HIV Tg rats and suggest that this model will be useful for investigating pathways and identifying potential therapies for HIV-PAH.

Epigenetic regulation of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is diagnosed as a sustained elevation of pulmonary arterial pressure to more than 25 mm Hg at rest or to more than 30 mm Hg with exercise. PAH is an intrinsic disease of the pulmonary vascular smooth muscle and endothelial cells in association with plexiform lesions, medial thickening, concentric laminar intimal fibrosis and thrombotic lesions. Pulmonary vascular remodeling is the characteristic pathological change of PAH. The pathogenesis of PAH has been studied at the level of smooth muscle and endothelial cells. Existing research does not adequately explain susceptibility to the disease, and recent evidence reveals that epigenetic alterations may be involved in PAH. Epigenetics refers to all heritable changes in phenotype or in gene expression states, including chromatin remodeling, DNA methylation, histone modification and RNA interference, which are not involved in the DNA sequence itself. This review will focus on recent advances in epigenetics related to PAH, including epigenetic changes of superoxide dismutase, endothelial nitric oxide synthase and the bone morphogenetic protein signaling pathway. This will provide new insight for improved treatment and prevention of PAH. Future work aimed at specific epigenetic treatments may prove to be an effective therapy for patients with PAH.

Transgenic expression of human matrix metalloproteinase-9 augments monocrotaline-induced pulmonary arterial hypertension in mice

OBJECTIVES

Pulmonary arterial hypertension (PAH) is characterized by intimal lesions, right ventricular hypertrophy, and adventitial thickening of pulmonary arteries with progressive pulmonary hypertension. This investigation was aimed to examine the effects of transgenic expression of human matrix metalloproteinase-9 (MMP-9) in the pathogenesis of PAH.

METHODS

PAH was induced using serial subcutaneous administration of monocrotaline (MCT). Right ventricular pressure was measured through the right jugular vein using a 1.4F Millar Mikro-tip catheter-transducer. Zymography, western blotting, and quantitative reverse transcription PCR (qRT-PCR) were carried out for MMP-9. Immunohistochemistry was performed for α-smooth muscle actin (α-SMA) and Mac-3 antigen.

RESULTS

Measurement of right ventricular pressure demonstrated 2.5-fold and 3.7-fold elevation after the administration of MCT in wild-type and MMP-9 transgenic mice, respectively. Zymography, western blotting, and qRT-PCR depicted increased activity and expression of MMP-9 after treatment with MCT, which were augmented in transgenic mice. There was marked pulmonary inflammation with extensive infiltration of mononuclear cells, which was more intense in MMP-9 transgenic mice. SMA and Mac-3 staining demonstrated hypertrophy of pulmonary arteries with occlusion of precapillary vessels and extensive infiltration of macrophages, respectively. All these changes were aggravated in MCT-treated MMP-9 transgenic mice when compared to normal littermates.

CONCLUSION

Our study demonstrated that the MCT-induced PAH in mouse is a reproducible and potentially valuable animal model for the human disease. Our results further demonstrated that MMP-9 plays a significant role in the pathogenesis of PAH and effective blocking of MMP-9 could provide an option in the therapeutic intervention of human PAH.

Is peroxisome proliferator-activated receptor gamma (PPARγ) a therapeutic target for the treatment of pulmonary hypertension?

Pulmonary hypertension (PH), a progressive disorder associated with significant morbidity and mortality, is caused by complex pathways that culminate in structural and functional alterations of the pulmonary circulation and increases in pulmonary vascular resistance and pressure. Diverse genetic, pathological, or environmental triggers stimulate PH pathogenesis culminating in vasoconstriction, cell proliferation, vascular remodeling, and thrombosis. We conducted a thorough literature review by performing MEDLINE searches via PubMed to identify articles pertaining to PPARγ as a therapeutic target for the treatment of PH. This review examines basic and preclinical studies that explore PPARγ and its ability to regulate PH pathogenesis. Despite the current therapies that target specific pathways in PH pathogenesis, including prostacyclin derivatives, endothelin-receptor antagonists, and phosphodiesterase type 5 inhibitors, morbidity and mortality related to PH remain unacceptably high, indicating the need for novel therapeutic approaches. Consequently, therapeutic targets that simultaneously regulate multiple pathways involved in PH pathogenesis have gained attention. This review focuses on peroxisome proliferator-activated receptor gamma (PPARγ), a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors. While the PPARγ receptor is best known as a master regulator of lipid and glucose metabolism, a growing body of literature demonstrates that activation of PPARγ exerts antiproliferative, antithrombotic, and vasodilatory effects on the vasculature, suggesting its potential efficacy as a PH therapeutic target.

Pulmonary vascular disease related to hemodynamic stress in the pulmonary circulation

Hemodynamic stress in the pulmonary vessel is directly linked to the development of vascular remodeling and dysfunction, ultimately leading to pulmonary hypertension. Recently, some advances have been made in our molecular understanding of the exogenous upstream stimuli that initiate hemodynamic pertubations as well as the downstream vasoactive effectors that control these responses. However, much still remains unknown regarding how these complex signaling pathways connect in order to result in these characteristic pathophysiological changes. This chapter will describe our current understanding of and needed areas of research into the clinical, physiological, and molecular changes associated with pressure/volume overload in the pulmonary circulation.

Spleen tyrosine kinase modulates the proliferation and phenotypes of vascular smooth muscle cells induced by platelet-derived growth factor

Platelet-derived growth factor BB (PDGF-BB) regulates vascular smooth muscle cells (VSMCs) by activating signaling cascades that promote vasoconstriction and growth, but the underlying mechanisms remain incompletely characterized. In this study, we aimed at investigating the role of spleen tyrosine kinase (Syk) in the proliferation and phenotypes in rat pulmonary arterial VSMCs. Our results demonstrate that PDGF-BB or Syk-adenovirus led to a substantial increase of proliferation of VSMCs and cytoskeleton rearrangement in rat VSMCs. Consistently, these cells underwent phenotype changes. Notably, Syk inhibitor piceatannol significantly inhibited those biological effects induced by PDGF-BB. Thus, we conclude that Syk plays an important role in vascular remodeling through the modulation of proliferation and phenotypes of VSMCs.

The role of collagen in extralobar pulmonary artery stiffening in response to hypoxia-induced pulmonary hypertension

Hypoxic pulmonary hypertension (HPH) causes extralobar pulmonary artery (PA) stiffening, which potentially impairs right ventricular systolic function. Changes in the extracellular matrix proteins collagen and elastin have been suggested to contribute to this arterial stiffening. We hypothesized that vascular collagen accumulation is a major cause of extralobar PA stiffening in HPH and tested our hypothesis with transgenic mice that synthesize collagen type I resistant to collagenase degradation (Col1a1(R/R)). These mice and littermate controls that have normal collagen degradation (Col1a1(+/+)) were exposed to hypoxia for 10 days; some were allowed to recover for 32 days. In vivo PA pressure and isolated PA mechanical properties and collagen and elastin content were measured for all groups. Vasoactive studies were also performed with U-46619, Y-27632, or calcium- and magnesium-free medium. Pulmonary hypertension occurred in both mouse strains due to chronic hypoxia and resolved with recovery. HPH caused significant PA mechanical changes in both mouse strains: circumferential stretch decreased, and mid-to-high-strain circumferential elastic modulus increased (P < 0.05 for both). Impaired collagen type I degradation prevented a return to baseline mechanical properties with recovery and, in fact, led to an increase in the low and mid-to-high-strain moduli compared with hypoxia (P < 0.05 for both). Significant changes in collagen content were found, which tended to follow changes in mid-to-high-strain elastic modulus. No significant changes in elastin content or vasoactivity were observed. Our results demonstrate that collagen content is important to extralobar PA stiffening caused by chronic hypoxia.

PPARgamma as a potential therapeutic target in pulmonary hypertension

Pulmonary hypertension (PH) is a progressive disorder of the pulmonary circulation associated with significant morbidity and mortality. The pathobiology of PH involves a complex series of derangements causing endothelial dysfunction, vasoconstriction and abnormal proliferation of pulmonary vascular wall cells that lead to increases in pulmonary vascular resistance and pressure. Recent evidence indicates that the ligand-activated transcription factor, peroxisome proliferator-activated receptor gamma (PPARgamma) can have a favorable impact on a variety of pathways involved in the pathogenesis of PH. This review summarizes PPARgamma biology and the emerging evidence that therapies designed to activate this receptor may provide novel approaches to the treatment of PH. Mediators of PH that are regulated by PPARgamma are reviewed to provide insights into potential mechanisms underlying therapeutic effects of PPARgamma ligands in PH.

Urotensin II-induced signaling involved in proliferation of vascular smooth muscle cells

The urotensin II receptor, bound by the ligand urotensin II, generates second messengers, ie, inositol triphosphate and diacylglycerol, which stimulate the subsequent release of calcium (Ca²⁺) in vascular smooth muscle cells. Ca²⁺ influx leads to the activation of Ca²⁺-dependent kinases (CaMK) via calmodulin binding, resulting in cellular proliferation. We hypothesize that urotensin II signaling in pulmonary arterial vascular smooth muscle cells (Pac1) and primary aortic vascular smooth muscle cells (PAVSMC) results in phosphorylation of Ca²⁺/calmodulin-dependent kinases leading to cellular proliferation. Exposure of Pac1 cultures to urotensin II increased intracellular Ca²⁺, subsequently activating Ca²⁺/calmodulin-dependent kinase kinase (CaMKK), and Ca²⁺/calmodulin-dependent kinase Type I (CaMKI), extracellular signal-regulated kinase (ERK 1/2), and protein kinase D. Treatment of Pac1 and PAVSMC with urotensin II increased proliferation as measured by ³H-thymidine uptake. The urotensin II-induced increase in ³H-thymidine incorporation was inhibited by a CaMKK inhibitor. Taken together, our results demonstrate that urotensin II stimulation of smooth muscle cells leads to a Ca²⁺/calmodulin-dependent kinase-mediated increase in cellular proliferation.

Tanshinone IIA modulates pulmonary vascular response to agonist and hypoxia primarily via inhibiting Ca2+ influx and release in normal and hypoxic pulmonary hypertension rats

The present study was designed to investigate the vascular effects and underlying mechanisms of tanshinone IIA on isolated rat pulmonary artery. Isometric tension was recorded in the arteries from normal and hypoxic pulmonary hypertension rats under normoxia or hypoxia condition. The results showed that tanshinone IIA exerted a biphasic effect on rat pulmonary artery. The constriction was attenuated by endothelium-denudation but was enhanced by inhibition of nitric oxide synthase. Pretreatment with tetraethylammonium (Ca2+-activated K+ channel inhibitor) upward shifted the concentration-response curve without affecting the maximum dilatation. Pretreatment with zinc protoporphyrin IX (heme oxygenase-1 inhibitor), 4-aminopyridine (KV channel inhibitor), glibenclamide (KATP channel inhibitor) or BaCl2 (inwardly rectifying K+ channel inhibitor) did not affect the vasoreactivity. Meanwhile, tanshinone IIA almost abolished vasoconstriction induced by extracellular Ca2+. Under hypoxia condition, tanshinone IIA eliminated acute hypoxia-induced initial contraction, potentiated following vasorelaxation, attenuated and reversed sustained contraction to relaxation in pulmonary artery from normal rats, and reversed phenylephrine-induced sustained constriction to sustained relaxation in remodeled pulmonary artery from hypoxic pulmonary hypertension rats. We concluded that the mild constrictive effect induced by tanshinone IIA was affected by integrity of endothelium and production of nitric oxide, while the potent dilative effect was endothelium-independent and produced primarily by inhibiting extracellular Ca2+ influx and partially by inhibiting intracellular Ca2+ release, as well as activating Ca2+-activated K+ channels. The modulation of tanshinone IIA on pulmonary vasoreactivity under both acute and chronic hypoxia condition may provide a new insight for curing hypoxic pulmonary hypertension.

Deficiency of lung antioxidants in idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is associated with lower levels of the pulmonary vasodilator nitric oxide (NO) and its biochemical reaction products (nitrite [NO(2) (-)], nitrate [NO(3) (-)]), in part, due to the reduction in pulmonary endothelial NO synthesis. However, NO levels are also determined by consumptive reactions, such as with superoxide to form peroxynitrite, which subsequently may generate stable products of nitrotyrosine (Tyr-NO(2)) and/or NO(3) (-). In this context, superoxide dismutase (SOD) preserves NO in vivo by scavenging superoxide and preventing the consumptive reactions. Here, we hypothesized that reactive oxygen species (ROS) consumption of NO may contribute to the low NO level and development of pulmonary hypertension. To test this, nitrotyrosine and antioxidants glutathione (GSH), glutathione peroxidase (GPx), catalase, and SOD were evaluated in IPAH patients and healthy controls. SOD and GPx activities were decreased in IPAH lungs (all p < 0.05), while catalase and GSH activities were similar among the groups (all p > 0.2). SOD activity was directly related to exhaled NO (eNO) (R(2)= 0.72, p= 0.002), and inversely related to bronchoalveolar lavage (BAL) NO(3) (-) (R(2)=-0.73, p= 0.04). Pulmonary artery pressure (PAP) could be predicted by a regression model incorporating SOD, GPx, and NO(3) values (R(2)= 0.96, p= 0.01). These findings suggest that SOD and GPx are associated with alterations in NO and PAP in IPAH.

Pulmonary arterial hypertension in systemic sclerosis

Pulmonary arterial hypertension (PAH) in systemic sclerosis (SSc) is a complex clinical situation resulting from restricted flow through the pulmonary arterial circulation ending in increased pulmonary vascular resistance and right heart failure. PAH is a common and life-threatening complication in connective tissue diseases, specifically in SSc if not treated rapidly and adequately. Based on the emerging knowledge in SSc epidemiology by large scale patient cohorts such as EUSTAR, of PAH pathophysiology and advances in cardiopulmonary diagnostic techniques, several novel treatment approaches have been examined and have proceeded to licensing and daily use in the clinical practice. Amongst them are different endothelin receptor antagonists and PDE-5 inhibitors, but several other ideas are being currently pursued to improve the long-term outcome of the affected patients.

Effects of electro-acupuncture on endothelium-derived endothelin-1 and endothelial nitric oxide synthase of rats with hypoxia-induced pulmonary hypertension

Pulmonary hypertension (PH) is characterized by elevated pulmonary artery pressure (PAP), pulmonary vascular remodeling and right ventricular hypertrophy, which are mainly due to endothelial dysfunction. Electro-acupuncture has shown beneficial effects on cardiovascular homeostasis, but little evidence has been obtained on pulmonary effects. The goal of the present study was to investigate whether electro-acupuncture on bladder-13 and -15 points can protect against chronic hypoxia-induced PH by regulating endothelium-derived endothelin (ET)-1 and endothelial nitric oxide synthase (eNOS). Male Wistar rats were exposed to hypoxia to induce PH. Hemodynamic analysis revealed that mean PAP was similar under normoxic conditions. Chronic hypoxia increased mean PAP to 37 ± 3 mmHg, and electro-acupuncture attenuated it to 29 ± 3 mmHg. Absolute right ventricular weight was ameliorated by electro-acupuncture from 0.288 ± 0.048 g to 0.228 ± 0.029 g under hypoxic conditions. Hypoxia-induced right ventricular hypertrophy index decreased from 0.477 ± 0.069 to 0.378 ± 0.053 with electro-acupuncture treatment. Histological examination revealed that hypoxic rats showed increased medial pulmonary artery wall thickness as well as muscularization. However, these alternations by chronic hypoxia were attenuated by electro-acupuncture. There was no difference in eNOS or ET-1 between groups under normoxic conditions. Electro-acupuncture treatment significantly improved the circulating eNOS concentration (365.36 ± 31.51 pg/mL) compared with only hypoxia exposure (247.60 ± 30.64 pg/mL). In lung homogenate, levels of eNOS under hypoxia increased from 684.96 ± 117.90 to 869.86 ± 197.61 pg/mg by electro-acupuncture treatment. Levels of ET-1 changed oppositely to eNOS in response to electro-acupuncture (ET-1 in plasma, 29.44 ± 2.09 versus 20.70 ± 2.37 pg/mL; ET-1 in lung homogenate, 120.51 ± 3.03 versus 110.60 ± 4.04 pg/mg). In conclusion, these results indicated that treatment with electro-acupuncture can protect against hypoxia-induced PH, possibly by regulating the balance of endothelium-derived vasoconstrictors and vasodilators.

Pulmonary hypertension is ameliorated in mice deficient in thrombin-activatable fibrinolysis inhibitor

BACKGROUND

The fibrinolytic system has been implicated in the pathogenesis of pulmonary hypertension (PH). Thrombin-activatable fibrinolysis inhibitor (TAFI) inhibits fibrinolysis and therefore its absence would be expected to increase fibrinolysis and ameliorate PH.

OBJECTIVE

The objective of the present study was to evaluate the effect of TAFI deficiency on pulmonary hypertension in the mouse.

METHODS AND RESULTS

PH was induced in C57/Bl6 wild-type (WT) or TAFI-deficient (KO) mice by weekly subcutaneous treatment with 600 mg kg(-1) monocrotaline (MCT) for 8 weeks. PH was inferred from right heart hypertrophy measured using the ratio of right ventricle-to-left ventricle-plus-septum weight [RV/(LV+S)]. Pulmonary vascular remodeling was analyzed by morphometry. TAFI-deficient MCT-treated and wild-type MCT-treated mice suffered similar weight loss. TAFI-deficient MCT-treated mice had reduced levels of total protein and tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), transforming growth factor-beta (TGF-beta) and monocyte chemoattractant protein-1 (MCP-1) in bronchial alveolar lavage compared with wild-type MCT-treated mice. The ratio of RV to (LV+S) weight was significantly higher in WT/MCT than in KO/MCT mice. The pulmonary artery wall area and vascular stenosis were both greater in MCT-treated WT mice compared with MCT-treated TAFI-deficient mice.

CONCLUSIONS

TAFI-deficient MCT-treated mice had less pulmonary hypertension, vascular remodeling and reduced levels of cytokines compared with MCT-treated WT animals, possibly as a result of reduced coagulation activation.

Involvement of the bone morphogenetic protein system in endothelin- and aldosterone-induced cell proliferation of pulmonary arterial smooth muscle cells isolated from human patients with pulmonary arterial hypertension

Recent genetic studies have uncovered a link between familial and idiopathic pulmonary arterial hypertension (PAH) and germline mutations in the bone morphogenetic protein type-II receptor (BMPRII). The pathology of PAH is characterized by remodeling of the pulmonary arteries due to pulmonary artery smooth muscle cell (PASMC) hyperproliferation. Although increased endothelial injury and impaired suppression of PASMC proliferation are both critical for the cellular pathogenesis of PAH, a detailed molecular mechanism underlying PAH has yet to be elucidated. In the present study, we investigated the roles of the BMP system and other vasoactive factors associated with PAH (including endothelin (ET), angiotensin II (Ang II) and aldosterone) in the mitotic actions of PASMCs isolated from idiopathic and secondary PAH lungs. ET1 and aldosterone stimulated PASMC proliferation of idiopathic PAH more effectively than secondary PAH, whereas Ang II and ET3 failed to activate mitosis in either of the PASMC cell type. The effects of ET1 and aldosterone were blocked by bosentan, an ET type-A/B receptor (ETA/BR) antagonist, and eplerenone, a selective mineralocorticoid receptor (MR) blocker, respectively. Among the BMP ligands examined, BMP-2 and BMP-7, but not BMP-4 or BMP-6, significantly increased cell mitosis in both PASMC cell types. Notably, ET1- and aldosterone-induced mitosis and mitogen-activated protein kinase phosphorylation were significantly increased in the presence of BMP-2 and BMP-7 in PASMCs isolated from idiopathic PAH, although additive effects were not observed in PASMCs isolated from secondary PAH. Inhibition of extracellular signal-regulated kinase 1 (ERK1)/ERK2 signaling suppressed basal-, ET1- and aldosterone-induced PASMC mitosis more potently than that of stress-activated protein kinase/c-Jun NH2-terminal kinase inhibition. Given the fact that BMP-2 and BMP-7 upregulated ETA/BR and MR expression and that BMP-2 decreased 11betaHSD2 (11beta-hydroxysteroid dehydrogenase type 2) levels in PASMCs isolated from idiopathic PAH, BMPR-Smad signaling may have a key role in amplifying the ETA/BR and/or MR-ERK signaling in PASMCs of the PAH lung. Collectively, the functional link between BMP and ET and/or the MR system may be involved in the progress of PASMC mitosis, ultimately leading to the development of clinical PAH.

Right ventricular heart failure from pulmonary embolism: key distinctions from chronic pulmonary hypertension

BACKGROUND

The right ventricle normally operates as a low pressure, high-flow pump connected to a high-capacitance pulmonary vascular circuit. Morbidity and mortality in humans with pulmonary hypertension (PH) from any cause is increased in the presence of right ventricular (RV) dysfunction, but the differences in pathology of RV dysfunction in chronic versus acute occlusive PH are not widely recognized.

METHODS AND RESULTS

Chronic PH that develops over weeks to months leads to RV concentric hypertrophy without inflammation that may progress slowly to RV failure. In contrast, pulmonary embolism (PE) results in an abrupt vascular occlusion leading to increased pulmonary artery pressure within minutes to hours that causes immediate deformation of the RV. RV injury is secondary to mechanical stretch, shear force, and ischemia that together provoke a cytokine and chemokine-mediated inflammatory phenotype that amplifies injury.

CONCLUSIONS

This review will briefly describe causes of pulmonary embolism and chronic PH, models of experimental study, and pulmonary vascular changes, and will focus on mechanisms of right ventricular dysfunction, contrasting mechanisms of RV adaptation and injury in these 2 settings.

Effects of sulfur dioxide on hypoxic pulmonary vascular structural remodeling

Hypoxic pulmonary hypertension is a pathophysiological process important in the development of various cardiopulmonary diseases. Recently, we found that sulfur dioxide could be produced endogenously by pulmonary vessels, and that it showed vascular regulatory capabilities. In this paper, we examined the role of sulfur dioxide in hypoxic pulmonary vascular structural remodeling (HPVSR). A total of 48 Wistar rats were divided into six groups. Rats in the hypoxic group, hypoxic+sulfur dioxide group, and hypoxic+hydroxamate group were left under hypoxic conditions, whereas the control group, control+sulfur dioxide group, and control+hydroxamate group rats were left in room air. For each group, we measured the pulmonary arterial pressure, sulfur dioxide content in plasma and lung tissue, glutamate oxaloacetate transaminase 1 and 2 mRNAs, micro- and ultra-structural changes in pulmonary arteries, proliferation of pulmonary smooth muscle cells, vascular collagen metabolism, pulmonary endothelial cell inflammatory response, and pulmonary vascular endothelin-1 production in the rats. In hypoxic rats, the content of sulfur dioxide in plasma and lung tissue decreased significantly in comparison with those in the control groups, and significant pulmonary hypertension, pulmonary vascular structural remodeling, and increased vascular inflammatory response were also observed in hypoxic rats. Sulfur dioxide donor significantly downregulated Raf-1, mitogen-activated protein kinase kinase-1 (MEK-1) and p-ERK/ERK, and inhibited pulmonary vascular smooth muscle cell proliferation, collagen remodeling and pulmonary vascular endothelial cell nuclear factor-kappaB (NF-kappaB), and intercellular adhesion molecule 1 (ICAM-1) expressions. It also prevented pulmonary hypertension and pulmonary vascular structural remodeling in association with the upregulated sulfur dioxide/glutamate oxaloacetate transaminase pathway. Hydroxamate, however, advanced pulmonary hypertension, pulmonary vascular structural remodeling, and inflammatory response of the pulmonary artery in association with a downregulated sulfur dioxide/glutamate oxaloacetate transaminase pathway. The results suggested that sulfur dioxide markedly inhibited Raf-1, MEK-1, and the phosphorylation of extracellular signal-regulated kinase (ERK), and then inhibited pulmonary arterial smooth muscle cell (PASMC) proliferation induced by hypoxia. The downregulated sulfur dioxide/glutamate oxaloacetate transaminase pathway may be involved in the mechanisms responsible for pulmonary hypertension and pulmonary vascular structural remodeling.

Nuclear autoantigen CENP-B transactivation of the epidermal growth factor receptor via chemokine receptor 3 in vascular smooth muscle cells

OBJECTIVE

We have previously found that the CENP-B nuclear autoantigen, which is specifically targeted by autoantibodies in the limited cutaneous form of systemic sclerosis, behaved as a potent migratory factor for human pulmonary artery smooth muscle cells (PASMCs). Other recent studies have shown that several disease-associated autoantigens induced cell migration by interacting with various chemokine receptors. Prompted by this hypothesis, we undertook this study to determine whether CENP-B interacts with chemokine receptors on the surface of human PASMCs, to explore the relevant signaling pathways, and to characterize the effects of anti-CENP-B binding on SMC stimulation.

METHODS

To demonstrate the expression of specific chemokine receptors by human PASMCs at both the messenger RNA and protein levels, reverse transcription-polymerase chain reaction, immunoblotting, and flow cytometry analyses were performed. Desensitization studies and specific inhibitors were used to further identify the CENP-B target on the surface of human PASMCs.

RESULTS

Our data strongly suggested that CENP-B used chemokine receptor 3 (CCR3) to mediate human PASMCs signaling. Moreover, several lines of evidence indicated that CENP-B binding subsequently stimulated the cross-talk between CCR3 and epidermal growth factor receptor (EGFR) via a matrix metalloprotease-dependent mechanism that involved the processing of heparin-binding EGF-like growth factor. Transactivation of the EGFR through CCR3 was found to be a critical pathway that elicits MAP kinase activation and secretion of cytokines such as interleukin-8. Finally, anti-CENP-B autoantibodies were found to abolish this signaling pathway, thus preventing CENP-B from transactivating EGFR and exerting its cytokine-like activities toward vascular smooth muscle cells.

CONCLUSION

The identification of CENP-B as a CCR3 ligand opens up new perspectives for the study of the pathogenic role of anti-CENP-B autoantibodies.

Hypoxia promotes human pulmonary artery smooth muscle cell proliferation through induction of arginase

Vascular remodeling and smooth muscle cell proliferation are hallmark pathogenic features of pulmonary artery hypertension (PAH). Alterations in the metabolism of l-arginine via arginase and nitric oxide synthase play a critical role in the endothelial dysfunction seen in PAH. l-arginine metabolism by arginase produces l-ornithine and urea. l-ornithine is a precursor for polyamine and proline synthesis, ultimately leading to an increase in cellular proliferation. Given the integral role of the smooth muscle layer in the pathogenesis of hypoxia-induced PAH, we hypothesized that hypoxia would increase cellular proliferation via arginase induction in human pulmonary artery smooth muscle cells (hPASMC). We found that arginase II mRNA and protein expression were significantly increased in cultured hPASMC exposed to 1% O(2) for 24 and 48 h, which coincided with an increase in arginase activity at 48 h. There were no hypoxia-induced changes in levels of arginase I mRNA or protein in cultured hPASMC. Exposure to hypoxia resulted in more than one and a half times as many viable cells after 120 h than normoxic exposure. The addition of the arginase inhibitor, S-(2-boronoethyl)-l-cysteine, completely prevented both the hypoxia-induced increase in arginase activity and proliferation in hPASMC. Furthermore, transfection of small interfering RNA (siRNA) targeting arginase II in hPASMC resulted in knockdown of arginase II protein levels and complete prevention of the hypoxia-induced cellular proliferation. These data support our hypothesis that hypoxia increases proliferation of hPASMC through the induction of arginase II.

Sustained hypoxia leads to the emergence of cells with enhanced growth, migratory, and promitogenic potentials within the distal pulmonary artery wall

All forms of chronic pulmonary hypertension (PH) are characterized by structural remodeling of the pulmonary artery (PA) media, a process previously attributed solely to changes in the phenotype of resident smooth muscle cells (SMC). However, recent experimental evidence in both systemic and pulmonary circulations suggests that other cell types, including circulating and local progenitors, contribute significantly to this process. The goal of this study was to determine if hypoxia-induced remodeling of distal PA (dPA) media involves the emergence of cells with phenotypic and functional characteristics distinct from those of resident dPA SMC and fibroblasts. In vivo, in contrast to the phenotypically uniform SMC composition of dPA media in control calves, the remodeled dPA media of neonatal calves with severe hypoxia-induced PH comprised cells exhibiting a distinct phenotype, including the expression of hematopoetic (CD45), leukocytic/monocytic (CD11b, CD14), progenitor (cKit), and motility-associated (S100A4) cell markers. Consistent with these in vivo observations, primary cell cultures isolated from dPA media of hypertensive calves yielded not only differentiated SMC, but also smaller, morphologically rhomboidal (thus termed here "R") cells that transiently expressed CD11b, constitutively expressed the mesenchymal cell marker type I procollagen, expressed high mRNA levels of progenitor cell markers cKit, CD34, CD73, as well as for inflammatory mediators, IL-6 and MCP-1, and, with time in culture, gained expression of a myofibroblast marker, alpha-SM-actin. R cells exhibited highly augmented proliferative, migratory, invasive, and potent promitogenic capabilities, which were due, at least in part, to the production of PDGFs, SDF-1/CXCL12, and S100A4. These data suggest that the cellular mechanisms of dPA remodeling include the emergence of cells with phenotypic and functional characteristics markedly distinct from those of resident dPA cells.

Endothelial-Mesenchymal Transition Occurs during Embryonic Pulmonary Artery Development

Pulmonary vascular remodeling is a process generally associated with pulmonary hypertension that involves intimal thickening, medial hyperthrophy, and plexiform lesions. Morphological studies during pulmonary hypertension have indicated that intimal thickening consists of immature smooth muscle cells (SMCs) associated with determined extracellular matrix components, suggesting an important role for these cells in vascular lesions. Controversy exists regarding the nature and origin of the cells conforming the intimal thickenings. In this study, the authors characterized the in vivo phenotype of the cells located in the pulmonary artery wall during the advanced stages of chicken embryo development and examined whether intimal thickenings are present in such stages. Immunolabeling of cryosections demonstrated presence of intimal thickenings composed of mesenchymal cells that may arise from the endothelium. These cells persist either as nonmuscle throughout the development, or possibly convert to cells expressing alpha -smooth muscle actin (alpha-SM actin). To determine whether pulmonary endothelial cells undergo a transition to mesenchymal cells, the authors used pulmonary artery explants from 10- to 11-day-old chicken embryos and found that explanted endothelial cells detached from the monolayer and acquired mesenchymal characteristics. Some of these cells maintained immunoreactivity for von Willebrand factor (vWF), whereas other jointly lost vWF and gained alpha -SM actin expression (transitional cells), suggesting conversion to SMCs. Therefore, these findings strongly support the authors' in vivo observations and demonstrate that embryonic pulmonary endothelial cells undergo a transition to mesenchymal cells and participate in intimal thickening formation and pulmonary vascular remodeling.

Treatment of pediatric pulmonary hypertension

Pulmonary hypertension was once thought to be a rare condition and only managed in specialized centers. Now however, with the advent of echocardiography, it is found in many clinical scenarios, in the neonate with chronic lung disease, in the acute setting in the intensive care unit, in connective tissue disease and in cardiology pre- and postoperatively. We have a better understanding of the pathological process and have a range of medication which is starting to be able to palliate this previously fatal condition. This review describes the areas that are known in this condition and those that are less familiar. The basic physiology behind pulmonary hypertension and pulmonary vascular disease is explained. The histopathologic process and the various diagnostic tools are described and are followed by the current and future therapy at our disposal.

VEGF ameliorates pulmonary hypertension through inhibition of endothelial apoptosis in experimental lung fibrosis in rats

Idiopathic pulmonary fibrosis (IPF) can lead to the development of secondary pulmonary hypertension (PH) and ultimately death. Despite this known association, the precise mechanism of disease remains unknown. Using a rat model of IPF, we explored the role of the proangiogenic and antiapoptotic growth factor VEGF in the vascular remodeling that underlies PH. In this model, adenoviral delivery of active TGF-beta1 induces pulmonary arterial remodeling, loss of the microvasculature in fibrotic areas, and increased pulmonary arterial pressure (PAP). Immunohistochemistry and mRNA analysis revealed decreased levels of VEGF and its receptor, which were inversely correlated with PAP and endothelial cell apoptosis in both the micro- and macrovasculature. Treatment of IPF rats with adenoviral delivery of VEGF resulted in reduced endothelial apoptosis, increased vascularization, and improved PAP due to reduced remodeling but worsened PF. These data show that experimental pulmonary fibrosis (PF) leads to loss of the microvasculature through increased apoptosis and to remodeling of the pulmonary arteries, with both processes resulting in PH. As administration of VEGF ameliorated the PH in this model but concomitantly aggravated the fibrogenic process, VEGF-based therapies should be used with caution.

WNT signaling in lung disease: a failure or a regeneration signal?

The WNT family of signaling proteins is essential to organ development in general and lung morphogenesis in particular. Originally identified as a developmentally active signaling pathway, the WNT pathway has recently been linked to the pathogenesis of important lung diseases, in particular lung cancer and pulmonary fibrosis. This review summarizes our current understanding about WNT signaling in lung development and disease, and is structured into three chapters. The first chapter presents an introduction to WNT signaling, outlining WNT proteins, their receptors and signaling intermediates, as well as the regulation of this complex pathway. The second chapter focuses on the role of WNT signaling in the normal embryonic and adult lung, and highlights recent findings of altered WNT signaling in lung diseases, such as lung cancer, pulmonary fibrosis, or pulmonary arterial hypertension. In the last chapter, we will discuss novel data and ideas about the biological effects of WNT signaling on the cellular level, highlighting pleiotropic effects induced by WNT ligands on distinct cell types, and how these cellular effects may be relevant to the pathogenesis of the aforementioned diseases.

Hypotonic activation of volume-sensitive outwardly rectifying anion channels (VSOACs) requires coordinated remodeling of subcortical and perinuclear actin filaments

Cell volume regulation requires activation of volume-sensitive outwardly rectifying anion channels (VSOACs). The actin cytoskeleton may participate in the activation of VSOACs but the roles of the two major actin pools remain undefined. We hypothesized that structural reorganization of both subcortical and perinuclear actin filaments (F-actin) contributes to the hypotonic activation of VSOACs. Hypotonic stress of pulmonary artery smooth muscle cells (PASMCs) was associated with reorganization of both peripheral and perinuclear F-actin, and with activation of VSOACs. Preincubation with cytochalasin D caused prominent dissociation of perinuclear, but not of subcortical F-actin. Cytochalasin D failed to induce isotonic activation and delayed the hypotonic activation of VSOACs. F-actin stabilization by phalloidin delayed both the hypotonic stress-induced dissociation of membrane-associated actin filaments and the activation kinetics of VSOACs. PKCepsilon, which was proposed to phosphorylate and inhibit VSOACs, colocalized primarily with F-actin and the net kinase activity remained unchanged during hypotonic cell swelling. In conclusion, normal hypotonic activation of VSOACs requires disruption of peripheral F-actin but intact perinuclear F-actin; interference with this pattern of actin reorganization delays the activation kinetics of VSOACs. The cell swelling-induced peripheral actin dissociation may underlie the observed translocation of PKCepsilon, which leads to a net decrease of PKCepsilon inhibitory activity in submembranous sites. Thus, reorganization of actin and PKCepsilon may establish conditions for mechano- and/or signal transduction-mediated activation of VSOACs.