Vascular remodeling in pulmonary hypertension

Right atrial to left atrial volume index ratio is associated with increased mortality in patients with pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) is characterized by increased pulmonary vascular resistance leading to right heart failure. Elevated right atrial (RA) pressure reflects right ventricular (RV) pressure overload and is an established risk factor for mortality in PH. We hypothesized that PH patients with an increased ratio of RA to LA volume index (RAVI/LAVI), would have increased mortality.

METHODS

We evaluated the association of RAVI/LAVI with mortality in 124 patients seen at a single academic center's PH clinic after adjusting for the REVEAL risk score, an established risk score in PH. LA and RA volume indices were measured in the four-and two-chamber views by two independent researchers. Multivariable logistic regression was used to model the independent association of RAVI/LAVI with survival.

RESULTS

Among 124 patients (mean age 62 ± 12.7 years, 68.6% female), each unit increase in RAVI/LAVI was associated with a nearly twofold increase in mortality (OR: 1.91, 95% CI: 1.20-3.04). In a multivariable logistic regression, each unit increase in RAVI/LAVI was associated with a nearly twofold increase in mortality (OR: 1.73, 95% CI: 1.003-2.998). Furthermore, RAVI/LAVI in the highest quartile (>1.42) was significantly associated with elevated right atrial pressure (RAP) to pulmonary artery wedge pressure ratio (RAP/PAWP) (0.76 ± 0.41, P = 0.02) compared with the lowest quartile (<0.77), suggesting an interaction between invasive hemodynamic data, atrial structural changes, and mortality in PH.

CONCLUSIONS

Increased RAVI/LAVI in PH is associated with decreased survival and accounts for atrial structural remodeling related to invasive hemodynamics. These findings support further study of this index in predicting outcomes in PH.

Ventilation-induced changes correlate to pulmonary vascular response and VEGF, VEGFR-1/2, and eNOS expression in the rat model of postnatal hypoxia

Neonatal asphyxia occurs due to reduction in oxygen supply to vital organs in the newborn. Rapid restoration of oxygen to the lungs after a long period of asphyxia can cause lung injury and decline of respiratory function, which result from the activity of molecules that induce vascular changes in the lung such as nitric oxide (NO) and vascular endothelial growth factors (VEGF). In this study, we evaluated the pulmonary and vascular morphometry of rats submitted to the model of neonatal asphyxia and mechanical ventilation, their expression of pulmonary VEGF, VEGF receptors (VEGFR-1/VEGFR-2), and endothelial NO synthase (eNOS). Neonate Sprague-Dawley rats (CEUA #043/2011) were divided into four groups (n=8 each): control (C), control submitted to ventilation (CV), hypoxia (H), and hypoxia submitted to ventilation (HV). The fetuses were harvested at 21.5 days of gestation. The morphometric variables measured were body weight (BW), total lung weight (TLW), left lung weight (LLW), and TLW/BW ratio. Pulmonary vascular measurements, VEGFR-1, VEGFR-2, VEGF, and eNOS immunohistochemistry were performed. The morphometric analysis showed decreased TLW and TLW/BW ratio in HV compared to C and H (P<0.005). Immunohistochemistry showed increased VEGFR-2/VEGF and decreased VEGFR-1 expression in H (P<0.05) and lower eNOS expression in H and HV. Median wall thickness was increased in H, and the expression of VEGFR-1, VEGFR-2, VEGF, and eNOS was altered, especially in neonates undergoing H and HV. These data suggested the occurrence of arteriolar wall changes mediated by NO and VEGF signaling in neonatal hypoxia.

Oxidative stress and bronchopulmonary dysplasia

With the progress of modern medicine, oxygen therapy has become a crucial measure for the treatment of premature infants. As an environmental stimulus, in the normal development of lungs, oxygen plays a very important regulatory role. However, the problem is that long-term exposure to hyperoxia can interfere with the development of lungs, leading to irreversible developmental abnormalities. Now, the incidence of bronchopulmonary dysplasia (BPD) is increasing year by year. The existing related research shows that although BPD is a multi-factor triggered disease, its main risk factors are the premature exposure to hyperoxia and the role of reactive oxygen species (ROS). As for premature infants, especially very premature babies and those with very low birth weight, prolonged exposure to high oxygen can affect and alter the normal developmental trajectories of lung tissue and vascular beds, triggering developmental disorders, such as BPD. In the relevant studies about human BPD, a large number of them support that ROS is associated with impaired lung development. Neonates, due to the damage in the development of alveolar, are specific to hyperoxia-induced inflammatory damage. This review while focusing on the role of oxidative stress in the pathogenesis of BPD, suggests that antioxidant measures may be effective to guard against BPD of preterm infants.

Transition from post-capillary pulmonary hypertension to combined pre- and post-capillary pulmonary hypertension in swine: a key role for endothelin

Key points

Passive, isolated post‐capillary pulmonary hypertension (PH) secondary to left heart disease may progress to combined pre‐ and post‐capillary or ‘active’ PH

This ‘activation’ of post‐capillary PH significantly increases morbidity and mortality, and is still incompletely understood.

In this study, pulmonary vein banding gradually produced post‐capillary PH with structural and functional microvascular remodelling in swine.

Ten weeks after banding, the pulmonary endothelin pathway was upregulated, likely contributing to pre‐capillary aspects in the initially isolated post‐capillary PH.

Inhibition of the endothelin pathway could potentially stop the progression of early stage post‐capillary PH.

Abstract

Passive, isolated post‐capillary pulmonary hypertension (IpcPH) secondary to left heart disease may progress to combined pre‐ and post‐capillary or ‘active’ PH (CpcPH) characterized by chronic pulmonary vascular constriction and remodelling. The mechanisms underlying this ‘activation’ of passive pulmonary hypertension (PH) remain incompletely understood. Here we investigated the role of the vasoconstrictor endothelin‐1 (ET) in the progression from IpcPH to CpcPH in a swine model for post‐capillary PH. Swine underwent pulmonary vein banding (PVB; n = 7) or sham‐surgery (Sham; n = 6) and were chronically instrumented 4 weeks later. Haemodynamics were assessed for 8 weeks, at rest and during exercise, before and after administration of the ET receptor antagonist tezosentan. After sacrifice, the pulmonary vasculature was investigated by histology, RT‐qPCR and myograph experiments. Pulmonary arterial pressure and resistance increased significantly over time. mRNA expression of prepro‐endothelin‐1 and endothelin converting enzyme‐1 in the lung was increased, while ET_A expression was unchanged and ET_B expression was downregulated. This was associated with increased plasma ET levels from week 10 onward and a more pronounced vasodilatation to in vivo administration of tezosentan at rest and during exercise. Myograph experiments showed decreased endothelium‐dependent vasodilatation to Substance P and increased vasoconstriction to KCl in PVB swine consistent with increased muscularization observed with histology. Moreover, maximal vasoconstriction to ET was increased whereas ET sensitivity was decreased. In conclusion, PVB swine gradually developed PH with structural and functional vascular remodelling. From week 10 onward, the pulmonary ET pathway was upregulated, likely contributing to pre‐capillary activation of the initially isolated post‐capillary PH. Inhibition of the ET pathway could thus potentially provide a pharmacotherapeutic target for early stage post‐capillary PH.

Passive, isolated post‐capillary pulmonary hypertension (PH) secondary to left heart disease may progress to combined pre‐ and post‐capillary or ‘active’ PH

This ‘activation’ of post‐capillary PH significantly increases morbidity and mortality, and is still incompletely understood.

In this study, pulmonary vein banding gradually produced post‐capillary PH with structural and functional microvascular remodelling in swine.

Ten weeks after banding, the pulmonary endothelin pathway was upregulated, likely contributing to pre‐capillary aspects in the initially isolated post‐capillary PH.

Inhibition of the endothelin pathway could potentially stop the progression of early stage post‐capillary PH.

Aryl Hydrocarbon Receptor Nuclear Translocator in Vascular Smooth Muscle Cells Is Required for Optimal Peripheral Perfusion Recovery

BACKGROUND

Limb ischemia resulting from peripheral vascular disease is a common cause of morbidity. Vessel occlusion limits blood flow, creating a hypoxic environment that damages distal tissue, requiring therapeutic revascularization. Hypoxia-inducible factors (HIFs) are key transcriptional regulators of hypoxic vascular responses, including angiogenesis and arteriogenesis. Despite vascular smooth muscle cells' (VSMCs') importance in vessel integrity, little is known about their functional responses to hypoxia in peripheral vascular disease. This study investigated the role of VSMC HIF in mediating peripheral ischemic responses.

METHODS AND RESULTS

We used ArntSMKO mice with smooth muscle-specific deletion of aryl hydrocarbon receptor nuclear translocator (ARNT, HIF-1β), required for HIF transcriptional activity, in a femoral artery ligation model of peripheral vascular disease. ArntSMKO mice exhibit impaired perfusion recovery despite normal collateral vessel dilation and angiogenic capillary responses. Decreased blood flow manifests in extensive tissue damage and hypoxia in ligated limbs of ArntSMKO mice. Furthermore, loss of aryl hydrocarbon receptor nuclear translocator changes the proliferation, migration, and transcriptional profile of cultured VSMCs. ArntSMKO mice display disrupted VSMC morphologic features and wrapping around arterioles and increased vascular permeability linked to decreased local blood flow.

CONCLUSIONS

Our data demonstrate that traditional vascular remodeling responses are insufficient to provide robust peripheral tissue reperfusion in ArntSMKO mice. In all, this study highlights HIF responses to hypoxia in arteriole VSMCs critical for the phenotypic and functional stability of vessels that aid in the recovery of blood flow in ischemic peripheral tissues.

Interleukin-6 trans-signaling contributes to chronic hypoxia-induced pulmonary hypertension

Interleukin-6 (IL-6) is a pleotropic cytokine that signals through the membrane-bound IL-6 receptor (mIL-6R) to induce anti-inflammatory (“classic-signaling”) responses. This cytokine also binds to the soluble IL-6R (sIL-6R) to promote inflammation (“trans-signaling”). mIL-6R expression is restricted to hepatocytes and immune cells. Activated T cells release sIL-6R into adjacent tissues to induce trans-signaling. These cellular actions require the ubiquitously expressed membrane receptor gp130. Reports show that IL-6 is produced by pulmonary arterial smooth muscle cells (PASMCs) exposed to hypoxia in culture as well as the medial layer of the pulmonary arteries in mice exposed to chronic hypoxia (CH), and IL-6 knockout mice are protected from CH-induced pulmonary hypertension (PH). IL-6 has the potential to contribute to a broad array of downstream effects, such as cell growth and migration. CH-induced PH is associated with increased proliferation and migration of PASMCs to previously non-muscularized vessels of the lung. We tested the hypothesis that IL-6 trans-signaling contributes to CH-induced PH and arterial remodeling. Plasma levels of sgp130 were significantly decreased in mice exposed to CH (380 mmHg) for five days compared to normoxic control mice (630 mmHg), while sIL-6R levels were unchanged. Consistent with our hypothesis, mice that received the IL-6 trans-signaling-specific inhibitor sgp130Fc, a fusion protein of the soluble extracellular portion of gp130 with the constant portion of the mouse IgG1 antibody, showed attenuation of CH-induced increases in right ventricular systolic pressure, right ventricular and pulmonary arterial remodeling as compared to vehicle (saline)-treated control mice. In addition, PASMCs cultured in the presence of IL-6 and sIL-6R showed enhanced migration but not proliferation compared to those treated with IL-6 or sIL-6R alone or in the presence of sgp130Fc. These results indicate that IL-6 trans-signaling contributes to pulmonary arterial cell migration and CH-induced PH.

Pentose Shunt, Glucose-6-Phosphate Dehydrogenase, NADPH Redox, and Stem Cells in Pulmonary Hypertension

Redox signaling plays a critical role in the pathophysiology of cardiovascular diseases. The pentose phosphate pathway is a major source of NADPH redox in the cell. The activities of glucose-6-phosphate dehydrogenase (the rate-limiting enzyme in the pentose shunt) and glucose flux through the shunt pathway is increased in various lung cells including, the stem cells, in pulmonary hypertension. This chapter discusses the importance of the shunt pathway and glucose-6-phosphate dehydrogenase in the pathogenesis of pulmonary artery remodeling and occlusive lesion formation within the hypertensive lungs.

High Spatial Resolution Multi-Organ Finite Element Modeling of Ventricular-Arterial Coupling

While it has long been recognized that bi-directional interaction between the heart and the vasculature plays a critical role in the proper functioning of the cardiovascular system, a comprehensive study of this interaction has largely been hampered by a lack of modeling framework capable of simultaneously accommodating high-resolution models of the heart and vasculature. Here, we address this issue and present a computational modeling framework that couples finite element (FE) models of the left ventricle (LV) and aorta to elucidate ventricular-arterial coupling in the systemic circulation. We show in a baseline simulation that the framework predictions of (1) LV pressure-volume loop, (2) aorta pressure-diameter relationship, (3) pressure-waveforms of the aorta, LV, and left atrium (LA) over the cardiac cycle are consistent with the physiological measurements found in healthy human. To develop insights of ventricular-arterial interactions, the framework was then used to simulate how alterations in the geometrical or, material parameter(s) of the aorta affect the LV and vice versa. We show that changing the geometry and microstructure of the aorta model in the framework led to changes in the functional behaviors of both LV and aorta that are consistent with experimental observations. On the other hand, changing contractility and passive stiffness of the LV model in the framework also produced changes in both the LV and aorta functional behaviors that are consistent with physiology principles.

Novel imaging approaches for small animal models of lung disease (2017 Grover Conference series)

Imaging in small animal models of lung disease is challenging, as existing technologies are limited either by resolution or by the terminal nature of the imaging approach. Here, we describe the current state of small animal lung imaging, the technological advances of laboratory-sourced phase contrast X-ray imaging, and the application of this novel technology and its attendant image analysis techniques to the in vivo imaging of the large airways and pulmonary vasculature in murine models of lung health and disease.

Dysregulated expression of microRNAs and mRNAs in pulmonary artery remodeling in ascites syndrome in broiler chickens

Ascites syndrome (AS), also known as pulmonary artery hypertension, remains a challenging disease that severely affects both humans and broiler chickens. Pulmonary artery remodeling presents a key step in the development of AS. In this study, we obtained pulmonary artery tissues from broilers with and without AS to perform miRNA sequencing analysis, miRNA-mRNA association analysis and pathological examinations. 29 significantly differentially expressed miRNAs were found both in known and novel miRNAs with 18 up-regulated and 11 down-regulated miRNAs. Their predicted potential targets were involved in a wide range of functional clusters as indicated via GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses. The upregulation of miR-155, miR-23b-3p, miR-146b-5p and miR-146b-3p were found closely associated with the pathogenesis of pulmonary artery remodeling in AS progression. The association analysis for the miRNAs-mRNAs showed that these 29 significantly differentially expressed miRNAs regulate 162 differentially expressed target genes. Among them, 20 miRNAs correlated with 18 predicted target genes that appear to be involved in pulmonary artery remodeling, mainly in three broad physiological processes: the hypoxia sensing response (HIF1α, NHE1, STAT5 and STAT3), endothelial permeability dysfunction (CD44, TRAF2, CDK2AP1, LZTFL1, JAZF1, PEBP1, LRP1B, RPS14 and THBS2) and inflammation (MEOX2, STAT5, STAT3, IRF8, MAP3K8, IL-1BETA and TNFRSF1B). Pathological pulmonary artery remodeling in the AS broilers was consistently observed in the present study. Taken together, the current analysis further illuminates the molecular mechanism of pulmonary artery remodeling underlying AS progression.

Aging and anatomical variations in lung tissue stiffness

Lung function is inherently mechanical in nature and depends on the capacity to conduct air and blood to and from the gas exchange regions. Variations in the elastic properties of the human lung across anatomical compartments and with aging are likely important determinants of lung function but remain relatively poorly characterized. Here we applied atomic force microscopy microindentation to characterize human lung tissue from subjects ranging in age from 11 to 60 yr old. We observed striking anatomical variations in elastic modulus, with the airways (200- to 350-µm diameter) the stiffest and the parenchymal regions the most compliant. Vessels (diameter < 100 µm) represented an intermediate mechanical environment and displayed diameter-dependent trends in elastic modulus. Binning our samples into younger (11-30 yr old) and older (41-60 yr old) groups, we observed significant age-related increases in stiffness in parenchymal and vessel compartments, with the most pronounced changes in the vessels. To investigate cellular mechanisms that might contribute to vascular stiffening with aging, we studied primary human pulmonary artery smooth muscle cells from subjects ranging in age from 11 to 60 yr old. While we observed no change in the mechanical properties of the cells themselves, we did observe trends toward increases in traction forces and extracellular matrix deposition with aging. These results demonstrate age-related changes in tissue mechanical properties that likely contribute to impaired lung function with aging and underscore the potential to identify mechanisms that contribute to mechanical tissue remodeling through the study of human cells and tissues from across the aging spectrum.

Arginase and α-smooth muscle actin induction after hyperoxic exposure in a mouse model of bronchopulmonary dysplasia

The L-arginine/NO pathway is an important regulator of pulmonary hypertension, the leading cause of mortality in patients with the chronic lung disease of prematurity, bronchopulmonary dysplasia. L-arginine can be metabolized by NO synthase (NOS) to form L-citrulline and NO, a potent vasodilator. Alternatively, L-arginine can be metabolized by arginase to form urea and L-ornithine, a precursor to collagen and proline formation important in vascular remodelling. In the current study, we hypothesized that C3H/HeN mice exposed to prolonged hyperoxia would have increased arginase expression and pulmonary vascular wall cell proliferation. C3H/HeN mice were exposed to 14 days of 85% O₂ or room air and lung homogenates analyzed by western blot for protein levels of arginase I, arginase II, endothelial NOS (eNOS), ornithine decarboxylase (ODC), ornithine aminotransferase (OAT), and α-smooth muscle actin (α-SMA). Hyperoxia did not change arginase I or eNOS protein levels. However, arginase II protein levels were 15-fold greater after hyperoxia exposure than in lungs exposed to room air. Greater protein levels of ODC and OAT were found in lungs following hyperoxic exposure than in room air animals. α-SMA protein levels were found to be 7-fold greater in the hyperoxia exposed lungs than in room air lungs. In the hyperoxia exposed lungs there was evidence of greater pulmonary vascular wall cell proliferation by α-SMA immunohistochemistry than in room air lungs. Taken together, these data are consistent with a more proliferative vascular phenotype, and may explain the propensity of patients with bronchopulmonary dysplasia to develop pulmonary hypertension.

NOD2 deficiency exacerbates hypoxia-induced pulmonary hypertension and enhances pulmonary vascular smooth muscle cell proliferation

Expression of nucleotide-binding oligomerization domain protein 2 (NOD2) is upregulated in pulmonary artery smooth muscle cells (PASMCs) during hypoxia. To investigate the involvement of NOD2 in the pulmonary vascular response to hypoxia, we subjected wild-type and NOD2-deficient mice to chronic normobaric hypoxic conditions. Compared to wild-type mice, NOD2-deficient mice developed severe pulmonary hypertension with exaggerated elevation of right ventricular systolic pressure, profound right ventricular hypertrophy and striking vascular remodeling after exposure to hypoxia. Pulmonary vascular remodeling in NOD2-deficient mice was characterized by increased PASMC proliferation. Furthermore, hypoxia-inducible factor-1α expression and Akt phosphorylation were upregulated in PASMCs from NOD2-deficient mice exposed to hypoxia. Our findings revealed that the absence of NOD2 exacerbated hypoxia-induced PASMC proliferation, pulmonary hypertension and vascular remodeling, but had no effect on PASMC migration or contractility.

Image-based computational assessment of vascular wall mechanics and hemodynamics in pulmonary arterial hypertension patients

Pulmonary arterial hypertension (PAH) is a disease characterized by an elevated pulmonary arterial (PA) pressure. While several computational hemodynamic models of the pulmonary vasculature have been developed to understand PAH, they are lacking in some aspects, such as the vessel wall deformation and its lack of calibration against measurements in humans. Here, we describe a computational modeling framework that addresses these limitations. Specifically, computational models describing the coupling of hemodynamics and vessel wall mechanics in the pulmonary vasculature of a PAH patient and a normal subject were developed. Model parameters, consisting of linearized stiffness E of the large vessels and Windkessel parameters for each outflow branch, were calibrated against in vivo measurements of pressure, flow and vessel wall deformation obtained, respectively, from right-heart catheterization, phase-contrast and cine magnetic resonance images. Calibrated stiffness E of the proximal PA was 2.0 and 0.5 MPa for the PAH and normal models, respectively. Calibrated total compliance C_T and resistance R_T of the distal vessels were, respectively, 0.32 ml/mmHg and 11.3 mmHg∗min/l for the PAH model, and 2.93 ml/mmHg and 2.6 mmHg∗min/l for the normal model. These results were consistent with previous findings that the pulmonary vasculature is stiffer with more constricted distal vessels in PAH patients. Individual effects on PA pressure due to remodeling of the distal and proximal compartments of the pulmonary vasculature were also investigated in a sensitivity analysis. The analysis suggests that the remodeling of distal vasculature contributes more to the increase in PA pressure than the remodeling of proximal vasculature.

The Role of Nicotinamide Adenine Dinucleotide Phosphate Oxidases in Lung Architecture Remodeling

Chronic lung disorders, such as pulmonary artery hypertension (PAH), chronic obstructive pulmonary disease (COPD), asthma and neonatal bronchopulmonary dysplasia (BPD), are characterized by airway and/or vascular remodeling. Despite differences in the pathology, reactive oxygen species (ROS) have been highlighted as a critical contributor to the initiation and development of airway and vascular remodeling. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox) appear to play a pivotal role in lung signaling, leading to marked changes in pulmonary airway and vascular cell phenotypes, including proliferation, hypertrophy and apoptosis. In this review, we summarized the current literature regarding the role of Nox in the airway and vascular remodeling.

Hypoxia-induced microRNA-26b inhibition contributes to hypoxic pulmonary hypertension via CTGF

The objective of this study was to explore the role of miRNAs in the control of HPH as well as molecular mechanism underlying. Computational analysis and luciferase assay were carried out to search the target gene of miR-26b. Luciferase assay, RT-PCR and western-blot analysis was performed to test interaction among hypoxia, miR-26b, SRF and CTGF. MiR-26b was significantly downregulated; meanwhile, CTGF and SRF were significantly upregulated in HPH rat model. Using computational analysis, CTGF was found to be a virtual target gene of miR-26b, and only cell transfected with vectors containing wild-type CTGF 3'UTR and miR-26b showed a lower luciferase activity than scramble control. Hypoxia significantly inhibited miR-26b promoter, and promoted SRF promoter. Meanwhile, hypoxia had no effect on CTGF promoter. In addition, SRF promoted the promoter of CTGF. MiR-26b was significantly downregulated; meanwhile, CTGF and SRF were upregulated in PASMCs exposed to hypoxia. In addition, miR-26b and SRF siRNA, but not CTGF siRNA, significantly inhibited SRF expression. Meanwhile, miR-26b, SRF siRNA, and CTGF siRNA significantly inhibited CTGF expression in hypoxia-treated cell. PASMCs treated with hypoxia showed higher cell viability and higher percentage cells in S phase than the control, which could be reversed by miR-26b, SRF siRNA, and CTGF siRNA transfection. These findings suggested that hypoxia induced miR-26b inhibition and SRF and CTGF upregulation in HPH rat model. CTGF mediated hypoxia-induced regulation of miR-26b and SRF in proliferation of PASMCs, which indicated that hypoxia-induced miR-26b inhibition contributed to the pathogenesis of HPH via CTGF.

Aquaporin 1-mediated changes in pulmonary arterial smooth muscle cell migration and proliferation involve β-catenin

Exposure to hypoxia induces migration and proliferation of pulmonary arterial smooth muscle cells (PASMCs), leading to vascular remodeling and contributing to the development of hypoxic pulmonary hypertension. The mechanisms controlling PASMC growth and motility are incompletely understood, although aquaporin 1 (AQP1) plays an important role. In tumor, kidney, and stem cells, AQP1 has been shown to interact with β-catenin, a dual function protein that activates the transcription of crucial target genes (i.e., c-Myc and cyclin D1) related to cell migration and proliferation. Thus the goal of this study was to examine mechanisms by which AQP1 mediates PASMC migration and proliferation, with a focus on β-catenin. Using primary rat PASMCs from resistance level pulmonary arteries infected with adenoviral constructs containing green fluorescent protein (control; AdGFP), wild-type AQP1 (AdAQP1), or AQP1 with the COOH-terminal tail deleted (AdAQP1M), we demonstrated that increasing AQP1 expression upregulated β-catenin protein levels and the expression (mRNA and protein) of the known β-catenin targets c-Myc and cyclin D1. In contrast, infection with AdAQP1M had no effect on any of these variables. Using silencing approaches to reduce β-catenin levels prevented both hypoxia- and AQP1-induced migration and proliferation of PASMCs, as well as induction of c-Myc and cyclin D1 by AQP1. Thus our results indicate that elevated AQP1 levels upregulate β-catenin protein levels, via a mechanism requiring the AQP1 COOH-terminal tail, enhancing expression of β-catenin targets and promoting PASMC proliferation and migration.

Wnt5a is elevated in heart failure and affects cardiac fibroblast function

Wnt signaling is dysregulated in heart failure (HF) and may promote cardiac hypertrophy, fibrosis, and inflammation. Blocking the Wnt ligand Wnt5a prevents HF in animal models. However, the role of Wnt5a in human HF and its functions in cardiac cells remain unclear. Here, we investigated Wnt5a regulation in HF patients and its effects on primary mouse and human cardiac fibroblasts. Serum Wnt5a was elevated in HF patients and associated with hemodynamic, neurohormonal, and clinical measures of disease severity. In failing human hearts, Wnt5a protein correlated with interleukin (IL)-6 and tissue inhibitor of metalloproteinase (TIMP)-1. Wnt5a messenger RNA (mRNA) levels were markedly upregulated in failing myocardium and both mRNA and protein levels declined following left ventricular assist device therapy. In primary mouse and human cardiac fibroblasts, recombinant Wnt5a dose-dependently upregulated mRNA and protein release of IL-6 and TIMP-1. Wnt5a did not affect β-catenin levels, but activated extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. Importantly, inhibition of ERK1/2 activation attenuated Wnt5a-induced release of IL-6 and TIMP-1. In conclusion, our results show that Wnt5a is elevated in the serum and myocardium of HF patients and is associated with measures of progressive HF. Wnt5a induces IL-6 and TIMP-1 in cardiac fibroblasts, which might promote myocardial inflammation and fibrosis, and thereby contribute to HF progression.

KEY MESSAGES

• Wnt5a is elevated in serum and myocardium of HF patients and is associated with measures of progressive HF. • In cardiac fibroblasts, Wnt5a upregulates interleukin (IL)-6 and tissue inhibitor of metalloproteinase (TIMP)-1 through the ERK pathway. • Wnt5a-mediated effects might promote myocardial inflammation and fibrosis, and thereby contribute to HF progression.

Quercetin Inhibits Pulmonary Arterial Endothelial Cell Transdifferentiation Possibly by Akt and Erk1/2 Pathways

This study aimed to investigate the effects and mechanisms of quercetin on pulmonary arterial endothelial cell (PAEC) transdifferentiation into smooth muscle-like cells. TGF-β1-induced PAEC transdifferentiation models were applied to evaluate the pharmacological actions of quercetin. PAEC proliferation was detected with CCK8 method and BurdU immunocytochemistry. Meanwhile, the identification and transdifferentiation of PAECs were determined by FVIII immunofluorescence staining and α-SMA protein expression. The related mechanism was elucidated based on the levels of Akt and Erk1/2 signal pathways. As a result, quercetin effectively inhibited the TGF-β1-induced proliferation and transdifferentiation of the PAECs and activation of Akt/Erk1/2 cascade in the cells. In conclusion, quercetin is demonstrated to be effective for pulmonary arterial hypertension (PAH) probably by inhibiting endothelial transdifferentiation possibly via modulating Akt and Erk1/2 expressions.

Exosomes Derived from Human Pulmonary Artery Endothelial Cells Shift the Balance between Proliferation and Apoptosis of Smooth Muscle Cells

Background: The overproliferation of pulmonary vascular cells is noted in pulmonary hypertension. The role of exosomes from pulmonary artery endothelial cells (PAEC) in the proliferation and apoptosis of pulmonary artery smooth muscle cells (PASMC) remains unclear. Methods: Exosomes were isolated and purified from the culture medium of PAEC using a commercial kit. Lipopolysaccharide (LPS), hypoxia, and hydrogen peroxide were utilized to induce PAEC injury. Coculture of PAEC and PASMC was conducted using Transwell plates, and GW4869 was applied to inhibit exosome release. The proliferation and apoptosis level of PASMC was assayed by MTT assay, apoptosis staining, and cleaved caspase-3 immunoblotting. Plasma exosomes were isolated by differential ultracentrifugation. Results: LPS or hypoxia enhance exosome release from PAEC. Release of PAEC-derived exosomes positively correlates with LPS concentration. The coculture of LPS-disposed PAEC with PASMC leads to overproliferation and apoptosis resistance in PASMC, and the exosome inhibitor GW4869 can partly cancel out this effect. Exosomes derived from PAEC could be internalized into PASMC, and thus promote proliferation and induce apoptosis resistance in PASMC. Idiopathic pulmonary arterial hypertension patients exhibit a higher circulation level of endothelium-derived exosomes. Conclusions: Inflammation and hypoxia could induce PAEC to release exosomes. PAEC- derived exosomes are involved in overproliferation and apoptosis resistance in PASMC, by which they may contribute to the pathogenesis of pulmonary hypertension.

Modulation of Intersectin-1s Lung Expression Induces Obliterative Remodeling and Severe Plexiform Arteriopathy in the Murine Pulmonary Vascular Bed

Murine models of pulmonary arterial hypertension (PAH) that recapitulate the plexiform and obliterative arteriopathy seen in PAH patients and help in defining the molecular mechanisms involved are missing. Herein, we investigated whether intersectin-1s (ITSN) deficiency and prolonged lung expression of an ITSN fragment with endothelial cell (EC) proliferative potential (EH_ITSN), present in the lungs of PAH animal models and human patients, induce formation of plexiform/obliterative lesions and defined the molecular mechanisms involved. ITSN-deficient mice (knockout/heterozygous and knockdown) were subjected to targeted lung delivery of EH_ITSN via liposomes for 20 days. Immunohistochemistry and histological and morphometric analyses revealed a twofold increase in proliferative ECs and a 1.35-fold increase in proliferative α-smooth muscle actin-positive cells in the lungs of ITSN-deficient mice, transduced with the EH_ITSN relative to wild-type littermates. Treated mice developed severe medial wall hypertrophy, intima proliferation, and various forms of obliterative and plexiform-like lesions in pulmonary arteries, similar to PAH patients. Hemodynamic measurements indicated modest increases in the right ventricular systolic pressure and right ventricle hypertrophy. Transcriptional and protein assays of lung tissue indicated p38^MAPK-dependent activation of Elk-1 transcription factor and increased expression of c-Fos gene. This unique murine model of PAH-like plexiform/obliterative arteriopathy induced via a two-hit pathophysiological mechanism without hypoxia provides novel druggable targets to ameliorate and, perhaps, reverse the EC plexiform phenotype in severe human PAH.

Reactive Oxygen Species in COPD-Related Vascular Remodeling

The pathogenesis of chronic obstructive pulmonary disease (COPD) is a multifaceted process involving the alteration of pulmonary vasculature. Such vascular remodeling can be associated with inflammation, shear stress, and hypoxia-conditions commonly seen in patients with lung diseases. Particularly, the overproduction of reactive oxygen species (ROS) in the diseased lungs contributes greatly to pulmonary vascular remodeling. ROS play an important role in vascular homeostasis, yet excessive ROS can alter pulmonary vasculature and impair lung function, as implicated in COPD at all stages. Increased inflammatory cell infiltration and endothelial dysfunction both correspond to the severity of COPD. As a byproduct of vascular remodeling, pulmonary hypertension negatively affects the long-term survival rate of COPD patients. While there is currently no cure for COPD, several treatment options have focused on alleviating COPD symptoms. Interventions such as long-term oxygen therapy, endothelium-targeted treatment, and pharmacological therapies show promising results in improving the life span of COPD patients and attenuating the progression of pulmonary hypertension. In this chapter, we aim to discuss the contributing factors of pulmonary vascular remodeling in COPD with an emphasis on the ROS, as well as potential redox treatments for COPD-related vascular remodeling.

The role of MIF, cyclinD1 and ERK in the development of pulmonary hypertension in broilers

Pulmonary hypertension (PH) is a major disease in the broiler breeding industry. During PH, the pulmonary artery undergoes remodelling, which is caused by pulmonary vascular smooth muscle cell proliferation. CyclinD1 regulates cell proliferation. This study investigated the role of cyclinD1 in the development of PH in broilers, and which bioactivators and signalling pathway are involved in the pathological process. The PH group contained 3-4-week-old broilers with clinical PH, and the healthy group broilers from the same flock without PH. Histopathology indicated pulmonary arterial walls were thicker in the PH group compared with the healthy group. Target gene expressions of macrophage migration inhibitory factor (MIF), extracellular signal-regulated kinase (ERK), and cyclinD1 detected by quantitative real-time PCR were upregulated in the PH group compared with the healthy group. Immunohistochemistry showed MIF, phosphorylated ERK (p-ERK) and cyclinD1 were present on pulmonary vascular walls; MIF was present in the cytoplasm of arterial endothelial cells and smooth muscle cells; p-ERK and cyclinD1 were present in smooth muscle cell cytoplasm. Western blotting demonstrated that MIF, p-ERKand cyclinD1 levels were significantly higher (P < 0.01) in the PH group compared with the healthy group. In summary, increased MIF in PH broiler pulmonary arteries upregulated cyclinD1 via the ERK signalling pathway to induce pulmonary vascular smooth muscle cell proliferation, causing pulmonary artery remodelling and hypertension.

Soluble Guanylate Cyclase Stimulators and Activators: Novel Therapies for Pulmonary Vascular Disease or a Different Method of Increasing cGMP?

Pulmonary arterial hypertension (PAH) is a progressively worsening disorder characterized by increased pulmonary vascular resistance leading to increased afterload, right ventricular hypertrophy, and ultimately right heart failure and death. Current pharmacologic treatments primarily act to reduce pulmonary vascular resistance (PVR) and provide some benefit but do not cure PAH. Canonical vasodilator therapy involving the nitric oxide (NO)-soluble guanylate cyclase (sGC)-cGMP pathway has demonstrated efficacy, but in pathologic states, endothelial dysfunction within the pulmonary vasculature leads to the reduced synthesis and bioavailability of NO. Acting downstream of NO, sGC stimulators and activators restore the endogenous functions of NO and exploit the positive effects of sGC stimulation on various organ systems, including the heart. Riociguat (BAY 63-2521) is the first agent in a class of sGC stimulators to receive FDA approval for the treatment of PAH and chronic thromboembolic hypertension (CTEPH). Riociguat has demonstrated significant benefit as assessed by 6MWD, PVR, N-terminal pro-brain natriuretic peptide (NT-proBNP) levels, time to clinical worsening, World Health Organization (WHO) functional class, and other quality of life measures in clinical trials as a monotherapy and in combination with endothelin receptor antagonists or non-intravenous prostanoids. Riociguat is the first FDA-approved treatment option for inoperable or persistent CTEPH and adds a new effective drug to available treatment options for pulmonary hypertension (PH). The question of whether riociguat is superior to other available treatment options is unanswered at the present time and requires further study.

Hypertension-linked mechanical changes of rat gut

Hypertension is the most prevalent risk factor for cardiovascular disease caused by a persistent increase in arterial blood pressure that has lasting effects on the mechanical properties of affected tissues like myocardium and blood vessels. Our group recently discovered that gut dysbiosis is linked to hypertension in several animal models and humans; however, whether hypertension influences the gut's mechanical properties remains unknown. In this study, we evaluated the hypothesis that hypertension increases fibrosis and thus mechanical properties of the gut. A custom indentation system was used to test colon samples from Wistar Kyoto (WKY) normotensive rats and Spontaneously Hypertensive Rats (SHR). Using force-displacement data, we derived an steady-state modulus metric to quantify mechanical properties of gastrointestinal tissue. We observed that SHR proximal colon has a mean steady-state modulus almost 3 times greater than WKY control rat colon (5.11±1.58kPa and 18.17±11.45kPa, respectively). These increases were associated with increase in vascular smooth muscle cells layer and collagen deposition in the intestinal wall in the SHR.

STATEMENT OF SIGNIFICANCE

Mechanical characterization of biological materials can provide insight into health and disease of tissue. Recent investigations into a variety of cardiovascular pathologies show coincident changes in the microbiome and pathology of the gut. In this study, we sought to quantify changes in the gut in hypertension through mechanical characterization. Our methods and simple models for characterization, adapted from Hertz indentation models, prove useful to identify a meaningful steady-state modulus metric for small and irregular tissues from laboratory animals. Our data, for the first time, establish a stiffening of the gut wall in Spontaneously Hypertensive Rats. This observation suggests significant structural and functional changes in the gut correlate with hypertension, and future experiments are warranted to explore the specific causal relationship between dysbiosis, fibrosis, and stiffening in the gut during the development and maintenance of hypertension.

Update on novel targets and potential treatment avenues in pulmonary hypertension

Pulmonary hypertension (PH) is a condition marked by a combination of constriction and remodeling within the pulmonary vasculature. It remains a disease without a cure, as current treatments were developed with a focus on vasodilatory properties but do not reverse the remodeling component. Numerous recent advances have been made in the understanding of cellular processes that drive pathologic remodeling in each layer of the vessel wall as well as the accompanying maladaptive changes in the right ventricle. In particular, the past few years have yielded much improved insight into the pathways that contribute to altered metabolism, mitochondrial function, and reactive oxygen species signaling and how these pathways promote the proproliferative, promigratory, and antiapoptotic phenotype of the vasculature during PH. Additionally, there have been significant advances in numerous other pathways linked to PH pathogenesis, such as sex hormones and perivascular inflammation. Novel insights into cellular pathology have suggested new avenues for the development of both biomarkers and therapies that will hopefully bring us closer to the elusive goal: a therapy leading to reversal of disease.

Role of noncoding RNA in vascular remodelling

PURPOSE OF REVIEW

Noncoding RNAs (ncRNAs), such as microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) are becoming fundamentally important in the pathophysiology relating to injury-induced vascular remodelling. We highlight recent studies that demonstrate the involvement of ncRNAs in vein graft disease, in in-stent restenosis and in pulmonary arterial hypertension, with a particular focus on endothelial cell and vascular smooth muscle cell function. We also briefly discuss the emerging role of exosomal-derived ncRNAs and how this mechanism impacts on vascular function.

RECENT FINDINGS

ncRNAs have been described as novel regulators in the pathophysiology of vascular injury, inflammation, and vessel wall remodelling. In particular, several studies have demonstrated that manipulation of miRNAs can reduce the burden of pathological vascular remodelling. Such studies have also shown that exosomal miRNA-mediated, cell-to-cell communication between endothelial cells and vascular smooth muscle cells is critical in the disease process. In addition to miRNAs, lncRNAs are emerging as regulators of vascular function in health and disease. Although lncRNAs are complex in both their sheer numbers and mechanisms of action, identifying their contribution to vascular disease is essential.

SUMMARY

Given the important roles of ncRNAs in vascular injury and remodelling together will their capacity for cell-to-cell communication, manipulating ncRNA might provide novel therapeutic interventions.

The Na+/H+ exchanger contributes to increased smooth muscle proliferation and migration in a rat model of pulmonary arterial hypertension

Increased muscularity of small pulmonary vessels, involving enhanced proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs), is a key component of the vascular remodeling underlying the development of pulmonary hypertension (PH). Stimuli such as growth factors and hypoxia induce PASMC alkalinization, proliferation, and migration through upregulation of the Na⁺/H⁺ exchanger (NHE), inhibition of which prevents the development of hypoxia‐induced vascular remodeling and PH. We wanted to explore whether NHE was also necessary for pathologic PASMC proliferation and migration in a model of pulmonary arterial hypertension (PAH), a severe form of PH not associated with persistent hypoxia. PASMCs were isolated from rats exposed to SU5416‐hypoxia (SuHx) followed by return to normoxia and from vehicle controls. We measured resting intracellular pH (pH_i) and NHE activity using the pH‐sensitive fluorescent dye BCECF‐AM. PASMC proliferation and migration were assessed using BrdU incorporation and transwell filters, respectively. NHE activity was increased in SuHx PASMCs, although resting pH_i was unchanged. SuHx PASMCs also exhibited increased proliferation and migration relative to controls, which was attenuated in the setting of pharmacologic inhibition of NHE. Our findings suggest that increased NHE activity contributes to pathologic PASMC function in the SuHx model of PAH, although this effect does not appear to be mediated by global changes in pH_i homeostasis.

Role of Endogenous Sulfur Dioxide in Regulating Vascular Structural Remodeling in Hypertension

Sulfur dioxide (SO₂), an emerging gasotransmitter, was discovered to be endogenously generated in the cardiovascular system. Recently, the physiological effects of endogenous SO₂ were confirmed. Vascular structural remodeling (VSR), an important pathological change in many cardiovascular diseases, plays a crucial role in the pathogenesis of the diseases. Here, the authors reviewed the research progress of endogenous SO₂ in regulating VSR by searching the relevant data from PubMed and Medline. In spontaneously hypertensive rats (SHRs) and pulmonary hypertensive rats, SO₂/aspartate aminotransferase (AAT) pathway was significantly altered. SO₂ inhibited vascular smooth muscle cell (VSMC) proliferation, promoted apoptosis, inhibited the synthesis of extracellular collagen but promoted its degradation, and enhanced antioxidative capacity, thereby playing a significant role in attenuating VSR. However, the detailed mechanisms needed to be further explored. Further studies in this field would be important for the better understanding of the pathogenesis of systemic hypertension and pulmonary hypertension. Also, clinical trials are needed to demonstrate if SO₂ would be a potential therapeutic target in cardiovascular diseases.

Smooth muscle cell progenitors are primed to muscularize in pulmonary hypertension

Excess and ectopic smooth muscle cells (SMCs) are central to cardiovascular disease pathogenesis, but underlying mechanisms are poorly defined. For instance, pulmonary hypertension (PH) or elevated pulmonary artery blood pressure is a devastating disease with distal extension of smooth muscle to normally unmuscularized pulmonary arterioles. We identify novel SMC progenitors that are located at the pulmonary arteriole muscular-unmuscular border and express both SMC markers and the undifferentiated mesenchyme marker platelet-derived growth factor receptor-β (PDGFR-β). We term these cells "primed" because in hypoxia-induced PH, they express the pluripotency factor Kruppel-like factor 4 (KLF4), and in each arteriole, one of them migrates distally, dedifferentiates, and clonally expands, giving rise to the distal SMCs. Furthermore, hypoxia-induced expression of the ligand PDGF-B regulates primed cell KLF4 expression, and enhanced PDGF-B and KLF4 levels are required for distal arteriole muscularization and PH. Finally, in PH patients, KLF4 is markedly up-regulated in pulmonary arteriole smooth muscle, especially in proliferating SMCs. In sum, we have identified a pool of SMC progenitors that are critical for the pathogenesis of PH, and perhaps other vascular disorders, and therapeutic strategies targeting this cell type promise to have profound implications.

Endothelial and Smooth Muscle Cell Interactions in the Pathobiology of Pulmonary Hypertension

In the pulmonary vasculature, the endothelial and smooth muscle cells are two key cell types that play a major role in the pathobiology of pulmonary vascular disease and pulmonary hypertension. The normal interactions between these two cell types are important for the homeostasis of the pulmonary circulation, and any aberrant interaction between them may lead to various disease states including pulmonary vascular remodeling and pulmonary hypertension. It is well recognized that the endothelial cell can regulate the function of the underlying smooth muscle cell by releasing various bioactive agents such as nitric oxide and endothelin-1. In addition to such paracrine regulation, other mechanisms exist by which there is cross-talk between these two cell types, including communication via the myoendothelial injunctions and information transfer via extracellular vesicles. Emerging evidence suggests that these nonparacrine mechanisms play an important role in the regulation of pulmonary vascular tone and the determination of cell phenotype and that they are critically involved in the pathobiology of pulmonary hypertension.

2-AMINOETHYLDIPHENYLBORINATE MODIFIES THE PULMONARY CIRCULATION IN PULMONARY HYPERTENSIVE NEWBORN LAMBS WITH PARTIAL GESTATION AT HIGH ALTITUDE

Calcium signaling through store operated channels (SOC) is involved in hypoxic pulmonary hypertension. We determined whether a treatment with 2-aminoethyldiphenylborinate (2-APB), a compound with SOC blocker activity, reduces pulmonary hypertension and vascular remodeling. Twelve newborn lambs exposed to perinatal chronic hypoxia were studied, 6 of them received a 2-APB treatment and the other 6 received vehicle treatment, for 10 days in both cases. Throughout this period, we recorded cardiopulmonary variables and on day 11 we evaluated the response to an acute hypoxic challenge. Additionally, we assessed the vasoconstrictor and vasodilator function in isolated pulmonary arteries as well as their remodeling in lung slices. 2-APB reduced pulmonary arterial pressure at the third and tenth days, cardiac output between the fourth and eighth days, and pulmonary vascular resistance at the tenth day of treatment. The pulmonary vasoconstrictor response to acute hypoxia was reduced by the end of treatment. 2-APB also decreased maximal vasoconstrictor response to the thromboxane mimetic U46619 and endothelin-1 and increased maximal relaxation to 8-Br-cGMP. The maximal relaxation and potency to phosphodiesterase-5 and Rho-kinase inhibition with sildenafil and fasudil respectively, were also increased. Finally, 2-APB reduced the medial and adventitial layers' thickness, the expression of α-actin and the percentage of Ki67+ nuclei of small pulmonary arteries. Taken together, our results indicate that 2-APB reduces pulmonary hypertension, vasoconstrictor responses and pathological remodeling in pulmonary hypertensive lambs. We conclude that SOC targeting may be a useful strategy for the treatment of neonatal pulmonary hypertension, however, further testing of specific blockers is needed.

Peroxisome Proliferator-Activated Receptor γ-Mediated Inhibition on Hypoxia-Triggered Store-Operated Calcium Entry. A Caveolin-1-Dependent Mechanism

Our previous publication demonstrated that peroxisome proliferator-activated receptor γ (PPARγ) inhibits the pathogenesis of chronic hypoxia (CH)-induced pulmonary hypertension by targeting store-operated calcium entry (SOCE) in rat distal pulmonary arterial smooth muscle cells (PASMCs). In this study, we aim to determine the role of a membrane scaffolding protein, caveolin-1, during the suppressive process of PPARγ on SOCE. Adult (6-8 weeks) male Wistar rats (200-250 g) were exposed to CH (10% O2) for 21 days to establish CH-induced pulmonary hypertension. Primary cultured rat distal PASMCs were applied for the molecular biological experiments. First, hypoxic exposure led to 2.5-fold and 1-fold increases of caveolin-1 protein expression in the distal pulmonary arteries and PASMCs, respectively. Second, effective knockdown of caveolin-1 significantly reduced hypoxia-induced SOCE for 58.2% and 41.5%, measured by Mn(2+) quenching and extracellular Ca(2+) restoration experiments, respectively. These results suggested that caveolin-1 acts as a crucial regulator of SOCE, and hypoxia-up-regulated caveolin-1 largely accounts for hypoxia-elevated SOCE in PASMCs. Then, by using a high-potency PPARγ agonist, GW1929, we detected that PPARγ activation inhibited SOCE and caveolin-1 protein for 62.5% and 59.8% under hypoxia, respectively, suggesting that caveolin-1 also acts as a key target during the suppressive process of PPARγ on SOCE in PASMCs. Moreover, by using effective small interfering RNAs against PPARγ and caveolin-1, and PPARγ antagonist, T0070907, we observed that PPARγ plays an inhibitory role on caveolin-1 protein by promoting its lysosomal degradation, without affecting the messenger RNA level. PPARγ inhibits SOCE, at least partially, by suppressing cellular caveolin-1 protein in PASMCs.

Lung Circulation

The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.

Protective effects of drag-reducing polymers in a rat model of monocrotaline-induced pulmonary hypertension

OBJECTIVES

Drag-reducing polymers (DRPs) are blood-soluble macromolecules which may increase blood flow and reduce vascular resistance. The purpose of the present study was to observe the effect of DRPs on monocrotaline-induced pulmonary hypertension (PH) in the rat model.

METHODS

A total of 64 male Wistar rats were randomly divided into four groups: Group I (pulmonary hypertension model + DRP treatment); Group II (pulmonary hypertension model + saline treatment); Group III (control + DRP treatment); Group IV (control + saline treatment). After five weeks, comparisons were made of the following indices: survival rate, body weight, blood pressure, right ventricular systolic pressure, right ventricular hypertrophy, wall thickness of pulmonary arteries, the internal diameter of small pulmonary arteries, plasma IL-1β and IL-6.

RESULTS

The survival rate after 5 weeks varied significantly across all groups (P=0.013), but the survival rates of Groups I and II were not statistically significantly different. Administration of DRP (intravenous injection twice weekly) attenuated the PH-induced increase in right ventricular systolic pressure and suppressed the increases in right ventricular (RV) weight and the ratio of right ventricular weight to left ventricle plus septum weight (RV/LV + S). DRP treatment also significantly decreased the wall thickness of pulmonary arteries, augmented the internal diameter of small pulmonary arteries, and suppressed increases in the plasma levels of IL-1β and IL-6.

CONCLUSIONS

DRP treatment with intravenous injection effectively inhibited the development of monocrotaline-induced pulmonary hypertension in the rat model. DRPs may have potential application for the treatment of pulmonary hypertension.

Endothelial cell regulation of pulmonary vascular tone, inflammation, and coagulation

The pulmonary endothelium represents a heterogeneous cell monolayer covering the luminal surface of the entire lung vasculature. As such, this cell layer lies at a critical interface between the blood, airways, and lung parenchyma, and must act as a selective barrier between these diverse compartments. Lung endothelial cells are able to produce and secrete mediators, display surface receptor, and cellular adhesion molecules, and metabolize circulating hormones to influence vasomotor tone, both local and systemic inflammation, and coagulation functions. In this review, we will explore the role of the pulmonary endothelium in each of these systems, highlighting key regulatory functions of the pulmonary endothelial cell, as well as novel aspects of the pulmonary endothelium in contrast to the systemic cell type. The interactions between pulmonary endothelial cells and both leukocytes and platelets will be discussed in detail, and wherever possible, elements of endothelial control over physiological and pathophysiological processes will be examined.

Resolvin E1 normalizes contractility, Ca2+ sensitivity and smooth muscle cell migration rate in TNF-α- and IL-6-pretreated human pulmonary arteries

Pulmonary hypertension (PH) is a rare disease in which pathophysiology is characterized by an increase in proinflammatory mediators, chronic endothelial dysfunctions, and a high migration rate of smooth muscle cells (SMC). Over the course of the last decade, various treatments have been proposed to relax the pulmonary arteries, none of which have been effective in resolving PH. Our hypothesis is that artery-relaxing drugs are not the long-term solution, but rather the inhibition of tissue inflammation, which underlies human pulmonary artery (HPA) dysfunctions that lead to abnormal vasoconstriction. The goal of the present study was to assess the anti-inflammatory effects of resolvin E1 (RvE1) with concomitant effects on SMC migration and on HPA reactivity. The role and mode of action of RvE1 and its precursor, monoacylglyceride eicosapentaenoic acid were assessed on HPA under proinflammatory conditions, involving a combined pretreatment with 10 ng/ml TNF-α and 10 ng/ml IL-6. Our results show that TNF-α and IL-6 treatment induced hyperreactivity and Ca2+ hypersensitivity in response to pharmaco-mechanical stimuli, including 80 mM KCl, 1 μM phorbol 12–13-dibutyrate, and 30 nM U-46619. Furthermore, the proinflammatory treatment increased the migration rate of SMC isolated from HPA. The phosphorylation level of regulatory contractile proteins (CPI-17, MYPT-1), and proinflammatory signaling pathways (c-Fos, c-Jun, NF-κB) were also significantly increased compared with control conditions. Conversely, 300 nM RvE1 was able to normalize all of the above abnormal events triggered by proinflammation. In conclusion, RvE1 can resolve human arterial hyperreactivity via the resolution of inflammatory markers.

A case of diffuse panbronchiolitis, associated with severe pulmonary hypertension, managed with bilateral lung transplantation from a brain-dead donor

Diffuse panbronchiolitis (DPB) is a chronic respiratory disease that mainly involves the respiratory bronchioles, and has historically been associated with a very poor prognosis. The development of long-term low dose macrolide therapy in the 1980s has dramatically improved the prognosis of DPB. Nevertheless, some cases are resistant to macrolide therapy, and ultimately develop severe respiratory failure and pulmonary hypertension; in such cases lung transplantation is a viable treatment option. Here we report the case of a 40-year-old patient with a 20-year history of DPB, who underwent bilateral lung transplantation due to severe respiratory failure with pulmonary hypertension.

Compartment-specific expression of collagens and their processing enzymes in intrapulmonary arteries of IPAH patients

Alterations in extracellular matrix (ECM) have been implicated in the pathophysiology of pulmonary hypertension. Here, we have undertaken a compartment-specific study to elucidate the expression profile of collagens and their processing enzymes in donor and idiopathic pulmonary arterial hypertension (IPAH) pulmonary arteries. Predominant intimal, but also medial and perivascular, remodeling and reduced lumen diameter were detected in IPAH pulmonary arteries. Two-photon microscopy demonstrated accumulation of collagen fibers. Quantification of collagen in pulmonary arteries revealed collagen accumulation mainly in the intima of IPAH pulmonary arteries compared with donors. Laser capture-microdissected pulmonary artery profiles (intima+media and perivascular tissue) were analyzed by real-time PCR for ECM gene expression. In the intima+media of IPAH vessels, collagens (COL4A5, COL14A1, and COL18A1), matrix metalloproteinase (MMP) 19, and a disintegrin and metalloprotease (ADAM) 33 were higher expressed, whereas MMP10, ADAM17, TIMP1, and TIMP3 were less abundant. Localization of COLXVIII, its cleavage product endostatin, and MMP10, ADAM33, and TIMP1 was confirmed in pulmonary arteries by immunohistochemistry. ELISA for collagen XVIII/endostatin demonstrated significantly elevated plasma levels in IPAH patients compared with donors, whereas circulating MMP10, ADAM33, and TIMP1 levels were similar between the two groups. Endostatin levels were correlated with pulmonary arterial wedge pressure, and established prognostic markers of IPAH, right atrial pressure, cardiac index, 6-min walking distance, NH2-terminal pro-brain natriuretic peptide, and uric acid. Expression of unstudied collagens, MMPs, ADAMs, and TIMPs were found to be significantly altered in IPAH intima+media. Elevated levels of circulating collagen XVIII/endostatin are associated with markers of a poor prognosis.