Vascular remodeling in pulmonary hypertension

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.

Transdifferentiation of endothelial cells to smooth muscle cells play an important role in vascular remodelling

Pulmonary artery remodelling it is a major feature of pulmonary hypertension (PH). It is characterised by cellular and structural changes of the pulmonary arteries causing higher pulmonar vascular resistance and right ventricular failure. Abnormal deposition of smooth muscle-like (SM-like) cells in normally non-muscular, small diameter vessels and a deregulated control of endothelial cells are considered pathological features of PH. The origin of the SM-like cells and the mechanisms underlying the development and progression of this remodelling process are not understood. Endothelial cells within the intima may migrate from their organised layer of cells and transition to mesenchymal or SM-like phenotype in a process called endothelial-mesenchymal transition (EnMT). Traditionally, Waddington's epigenetic landscape illustrates that fates of somatic cells are progressively determined to compulsorily follow a downhill differentiation pathway. EnMT induces the transformation of cells with stem cell traits, therefore contrasting Waddington's theory and confirming that cell fate seems to be far more flexible than previously thought. The prospect of therapeutic inhibition of EnMT to delay or prevent PH may represent a promising new treatment modality.

Modulation of miRNAs in Pulmonary Hypertension

MicroRNAs (miRNAs) have emerged as a new class of posttranscriptional regulators of many cardiac and vascular diseases. They are a class of small, noncoding RNAs that contributes crucial roles typically through binding of the 3′-untranslated region of mRNA. A single miRNA may influence several signaling pathways associated with cardiac remodeling by targeting multiple genes. Pulmonary hypertension (PH) is a rare disorder characterized by progressive obliteration of pulmonary (micro) vasculature that results in elevated vascular resistance, leading to right ventricular hypertrophy (RVH) and RV failure. The pathology of PH involves vascular cell remodeling including pulmonary arterial endothelial cell (PAEC) dysfunction and pulmonary arterial smooth muscle cell (PASMC) proliferation. There is no cure for this disease. Thus, novel intervention pathways that govern PH induced RVH may result in new treatment modalities. Current therapies are limited to reverse the vascular remodeling. Recent studies have demonstrated the roles of various miRNAs in the pathogenesis of PH and pulmonary disorders. This review provides an overview of recent discoveries on the role of miRNAs in the pathogenesis of PH and discusses the potential for miRNAs as therapeutic targets and biomarkers of PH at clinical setting.

Intrapulmonary Activation of the Angiotensin-Converting Enzyme Type 2/Angiotensin 1-7/G-Protein-Coupled Mas Receptor Axis Attenuates Pulmonary Hypertension in Ren-2 Transgenic Rats Exposed to Chronic Hypoxia

The present study was performed to evaluate the role of intrapulmonary activity of the two axes of the renin-angiotensin system (RAS): vasoconstrictor angiotensin-converting enzyme (ACE)/angiotensin II (ANG II)/ANG II type 1 receptor (AT1) axis, and vasodilator ACE type 2 (ACE2)/angiotensin 1-7 (ANG 1-7)/Mas receptor axis, in the development of hypoxic pulmonary hypertension in Ren-2 transgenic rats (TGR). Transgene-negative Hannover Sprague-Dawley (HanSD) rats served as controls. Both TGR and HanSD rats responded to two weeks´ exposure to hypoxia with a significant increase in mean pulmonary arterial pressure (MPAP), however, the increase was much less pronounced in the former. The attenuation of hypoxic pulmonary hypertension in TGR as compared to HanSD rats was associated with inhibition of ACE gene expression and activity, inhibition of AT1 receptor gene expression and suppression of ANG II levels in lung tissue. Simultaneously, there was an increase in lung ACE2 gene expression and activity and, in particular, ANG 1-7 concentrations and Mas receptor gene expression. We propose that a combination of suppression of ACE/ANG II/AT1 receptor axis and activation of ACE2/ANG 1-7/Mas receptor axis of the RAS in the lung tissue is the main mechanism explaining attenuation of hypoxic pulmonary hypertension in TGR as compared with HanSD rats.

EP3 receptor deficiency attenuates pulmonary hypertension through suppression of Rho/TGF-β1 signaling

Pulmonary arterial hypertension (PAH) is commonly associated with chronic hypoxemia in disorders such as chronic obstructive pulmonary disease (COPD). Prostacyclin analogs are widely used in the management of PAH patients; however, clinical efficacy and long-term tolerability of some prostacyclin analogs may be compromised by concomitant activation of the E-prostanoid 3 (EP3) receptor. Here, we found that EP3 expression is upregulated in pulmonary arterial smooth muscle cells (PASMCs) and human distal pulmonary arteries (PAs) in response to hypoxia. Either pharmacological inhibition of EP3 or Ep3 deletion attenuated both hypoxia and monocrotaline-induced pulmonary hypertension and restrained extracellular matrix accumulation in PAs in rodent models. In a murine PAH model, Ep3 deletion in SMCs, but not endothelial cells, retarded PA medial thickness. Knockdown of EP3α and EP3β, but not EP3γ, isoforms diminished hypoxia-induced TGF-β1 activation. Expression of either EP3α or EP3β in EP3-deficient PASMCs restored TGF-β1 activation in response to hypoxia. EP3α/β activation in PASMCs increased RhoA-dependent membrane type 1 extracellular matrix metalloproteinase (MMP) translocation to the cell surface, subsequently activating pro-MMP-2 and promoting TGF-β1 signaling. Activation or disruption of EP3 did not influence PASMC proliferation. Together, our results indicate that EP3 activation facilitates hypoxia-induced vascular remodeling and pulmonary hypertension in mice and suggest EP3 inhibition as a potential therapeutic strategy for pulmonary hypertension.

Inhibition of NOX/VPO1 pathway and inflammatory reaction by trimethoxystilbene in prevention of cardiovascular remodeling in hypoxia-induced pulmonary hypertensive rats

Recent studies show that resveratrol exerts beneficial effects on prevention of pulmonary hypertension. This study is performed to explore the effects of trimethoxystilbene, a novel resveratrol analog, on rat pulmonary vascular remodeling and right ventricular hypertrophy in hypoxia-induced pulmonary arterial hypertension (PAH) and the underlying mechanisms. Sprague-Dawley rats were placed in a chamber and exposed to 10% O(2) continuously for 4 weeks to induce PAH. The effects of trimethoxystilbene (5 or 10 mg/kg per day, intragastric [i.g.]) and resveratrol (as a positive control, 25 mg/kg per day, i.g.) on hypoxia-induced PAH vascular remodeling and right ventricle hypertrophy were evaluated. At the end of experiments, the index for pulmonary vascular remodeling and right ventricle hypertrophy, inflammatory cell infiltration in lung tissue, the plasma levels and lung tissue contents of hydrogen peroxide (H(2)O(2)), the mRNA and protein levels for NADPH oxidases (NOX2, NOX4) and vascular peroxidase 1 (VPO1) in pulmonary artery or right ventricle were measured. The results showed that trimethoxystilbene treatment significantly attenuated hypoxia-induced pulmonary vascular remodeling (such as decrease in the ratio of wall thickness to vessel external diameter) and right ventricle hypertrophy (such as decrease in the ratio of right ventricle weight to the length of the tibia), accompanied by downregulation of NOX2, NOX4, and VPO1 expression in pulmonary artery or right ventricle, decrease in H(2)O(2) production and inflammatory cell infiltration in lung tissue. Trimethoxystilbene is able to prevent pulmonary vascular remodeling and right ventricle hypertrophy in hypoxia-induced rat model of PAH, which is related to inhibition of the NOX/VPO1 pathway-mediated oxidative stress and the inflammatory reaction.

Hemodynamics and right-ventricle functional characteristics of a swine carotid artery-jugular vein shunt model of pulmonary arterial hypertension: An 18-month experimental study

The continuous changes in pulmonary hemodynamic properties and right ventricular (RV) function in pulmonary arterial hypertension (PAH) have not been fully characterized in large animal model of PAH induced by a carotid artery-jugular vein shunt. A minipig model of PAH was induced by a surgical anastomosis between the left common carotid artery and the left jugular vein. The model was validated by catheter examination and pathologic analyses, and the hemodynamic features and right-ventricle functional characteristics of the model were continuously observed by Doppler echocardiography. Of the 45 minipigs who received the surgery, 27 survived and were validated as models of PAH, reflected by mean pulmonary artery pressure ≥25 mmHg, and typical pathologic changes of pulmonary arterial remodeling and RV fibrosis. Non-invasive indices of pulmonary hemodynamics (pulmonary artery accelerating time and its ratio to RV ventricular ejection time) were temporarily increased, then reduced later, similar to changes in tricuspid annular displacement. The Tei index of the RV was elevated, indicating a progressive impairment in RV function. Surgical anastomosis between carotid artery and jugular vein in a minipig is effective to establish PAH, and non-invasive hemodynamic and right-ventricle functional indices measured by Doppler echocardiography may be used as early indicators of PAH.

Antioxidant mechanism of Rutin on hypoxia-induced pulmonary arterial cell proliferation

Reactive oxygen species (ROS) are involved in the pathologic process of pulmonary arterial hypertension as either mediators or inducers. Rutin is a type of flavonoid which exhibits significant scavenging properties on oxygen radicals both in vitro and in vivo. In this study, we proposed that rutin attenuated hypoxia-induced pulmonary artery smooth muscle cell (PASMC) proliferation by scavenging ROS. Immunofluorescence data showed that rutin decreased the production of ROS, which was mainly generated through mitochondria and NADPH oxidase 4 (Nox4) in pulmonary artery endothelial cells (PAECs). Western blot results provided further evidence on rutin increasing expression of Nox4 and hypoxia-inducible factor-1α (HIF-1α). Moreover, cell cycle analysis by flow cytometry indicated that proliferation of PASMCs triggered by hypoxia was also repressed by rutin. However, N-acetyl-L-cysteine (NAC), a scavenger of ROS, abolished or diminished the capability of rutin in repressing hypoxia-induced cell proliferation. These data suggest that rutin shows a potential benefit against the development of hypoxic pulmonary arterial hypertension by inhibiting ROS, subsequently preventing hypoxia-induced PASMC proliferation.

Aging in blood vessels. Medicinal agents FOR systemic arterial hypertension in the elderly

Aging impairs blood vessel function and leads to cardiovascular disease. The mechanisms underlying the age-related endothelial, smooth muscle and extracellular matrix vascular dysfunction are discussed. Vascular dysfunction is caused by: (1) Oxidative stress enhancement. (2) Reduction of nitric oxide (NO) bioavailability, by diminished NO synthesis and/or augmented NO scavenging. (3) Production of vasoconstrictor/vasodilator factor imbalances. (4) Low-grade pro-inflammatory environment. (5) Impaired angiogenesis. (6) Endothelial cell senescence. The aging process in vascular smooth muscle is characterized by: (1) Altered replicating potential. (2) Change in cellular phenotype. (3) Changes in responsiveness to contracting and relaxing mediators. (4) Changes in intracellular signaling functions. Systemic arterial hypertension is an age-dependent disorder, and almost half of the elderly human population is hypertensive. The influence of hypertension on the aging cardiovascular system has been studied in models of hypertensive rats. Treatment for hypertension is recommended in the elderly. Lifestyle modifications, natural compounds and hormone therapies are useful for initial stages and as supporting treatment with medication but evidence from clinical trials in this population is needed. Since all antihypertensive agents can lower blood pressure in the elderly, therapy should be based on its potential side effects and drug interactions.

Distinct differences in gene expression patterns in pulmonary arteries of patients with chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis with pulmonary hypertension

RATIONALE

The development of pulmonary hypertension (PH) in patients with idiopathic pulmonary fibrosis (IPF) or chronic obstructive pulmonary disease (COPD) is associated with increased morbidity.

OBJECTIVES

To elucidate whether vascular remodeling in a well-characterized PH-COPD and PH-IPF patient cohort results from similar or divergent molecular changes.

METHODS

Vascular remodeling of donor, PH-COPD, and PH-IPF pulmonary arteries was assessed. Laser capture microdissected pulmonary artery profiles in combination with whole genome microarrays were performed.

MEASUREMENTS AND MAIN RESULTS

Pulmonary arteries from patients with COPD and IPF with PH exhibited remodeling of vascular layers and reduction of lumen area. Pathway analyses comparing normalized gene expression profiles obtained from patients with PH-IPF or PH-COPD revealed the retinol and extracellular matrix (ECM) receptor interaction to be the most perturbed processes. Within the ECM-receptor pathway, differential regulation of 5 out of the top 10 results (collagen, type III, α-1; tenascin C; collagen, type VI, α-3; thrombospondin 2; and von Willebrand factor) were verified by real-time polymerase chain reaction and immunohistochemical staining.

CONCLUSIONS

Despite clinical and histologic vascular remodeling in all patients with PH-COPD and PH-IPF, differential gene expression pattern was present in pulmonary artery profiles. Several genes involved in retinol metabolism and ECM receptor interaction enable discrimination of vascular remodeling in PH-IPF or PH-COPD. This suggests that pulmonary arterial remodeling in PH-COPD and PH-IPF is caused by different molecular mechanisms and may require specific therapeutic options.

The aquaporin 1 C-terminal tail is required for migration and growth of pulmonary arterial myocytes

Pulmonary arterial smooth muscle cell (PASMC) proliferation and migration are important contributors to the vascular remodeling that occurs during development of pulmonary hypertension. We previously demonstrated that aquaporin (AQP)1, a member of the water channel family of proteins, was expressed in PASMCs and was necessary for hypoxia-induced migration; however, the mechanism by which AQP1 controls this response is unclear. The C-terminal tail of AQP1 contains putative calcium (EF-hand) and protein binding sites. Thus, we wanted to explore whether the C-terminal tail or the EF-hand motif of AQP1 was required for migration and proliferation. Rat PASMCs were isolated from distal pulmonary arteries, and proliferation and migration were measured using BrdU incorporation and transwell filters, respectively. To deplete AQP1, PASMCs were transfected with AQP1 small interference RNA (siRNA) or nontargeting siRNA. Knockdown of AQP1 reduced basal proliferation and hypoxia-induced migration and proliferation in PASMCs. In subsequent experiments, wild-type AQP1, AQP1 lacking the entire cytoplasmic C-terminal tail, or AQP1 with a mutation in the EF-hand motif were expressed in PASMCs using adenoviral constructs. For all AQP1 constructs, infection increased AQP1 protein levels, water permeability, and the change in cell volume induced by hypotonic challenge. Infection with wild-type and EF-hand mutated AQP1, but not C-terminal-deleted AQP1, increased PASMC migration and proliferation. Our results suggest that AQP1 controls proliferation and migration in PASMCs and that the mechanism requires the C-terminal tail of the protein but is independent of water transport or the EF-hand motif.

Simulated microgravity induces an inflammatory response in the common carotid artery of rats

Post-spaceflight orthostatic intolerance is one of the most important adverse effects after exposure to space microgravity, and there are still no effective countermeasures. It has been considered that arterial remodeling may play an important role in the occurrence of post-spaceflight orthostatic intolerance, but the cellular mechanisms remain unknown. In this study, we investigated whether an inflammatory response exists in the common carotid artery of rats exposed to simulated microgravity. For this, Sprague-Dawley rats were subjected to 4 weeks of hindlimb unweighting to simulate microgravity. The expression levels of the adhesion molecules E-selectin and vascular cell adhesion molecule-1 (VCAM-1), and the cytokine monocyte chemoattractant protein-1 (MCP-1) in the common carotid artery of simulated microgravity rats were evaluated by immunohistochemical staining, quantitative RT-PCR, and Western blot analyses. The recruitment of monocytes in the common carotid artery of rats exposed to simulated microgravity was investigated by en face immunofluorescence staining and monocyte binding assays. Our results provided convincing evidence that there is an inflammatory response in the common carotid artery of rats exposed to simulated microgravity. Our work suggests that the inflammatory response may be a novel cellular mechanism that is responsible for the arterial remodeling that occurs during exposure to microgravity.

Endothelin ETA receptor antagonism in cardiovascular disease

Since the discovery of the endothelin system in 1988, it has been implicated in numerous physiological and pathological phenomena. In the cardiovascular system, endothelin-1 (ET-1) acts through intracellular pathways of two endothelin receptors (ETA and ETB) located mainly on smooth muscle and endothelial cells to regulate vascular tone and provoke mitogenic and proinflammatory reactions. The endothelin ETA receptor is believed to play a pivotal role in the pathogenesis of several cardiovascular disease including systemic hypertension, pulmonary arterial hypertension (PAH), dilated cardiomyopathy, and diabetic microvascular dysfunction. Growing evidence from recent experimental and clinical studies indicates that the blockade of endothelin receptors, particularly the ETA subtype, grasps promise in the treatment of major cardiovascular pathologies. The simultaneous blockade of endothelin ETB receptors might not be advantageous, leading possibly to vasoconstriction and salt and water retentions. This review summarizes the role of ET-1 in cardiovascular modulation and the therapeutic potential of endothelin receptor antagonism.

Clinical analysis of risk factors of the patency of the descending branch of the lateral circumflex femoral artery

Many studies have provided anatomical statistics of the descending branch of lateral circumflex femoral artery (LCFA) through its use as the pedicle of anterolateral thigh (ALT) flaps. However, most of the results from these studies were acquired during surgeries or from cadavers. Therefore, this study has studied the descending branch of LCFA in patients with underlying diseases or risk factors using lower extremity angiography, and how such risk factors and the degree of stenosis in other arteries affect the patency and stability of the descending branch. The subjects of retrospective study were 89 legs from 49 patients who had received lower extremity angiography. Risk factors included age, BMI, diabetes, hypertension, tobacco use, hyperlipidemia, cardiac status, carotid status, renal disease, pulmonary status, and history of lower limb amputation. Analysis of the degree of stenosis in the descending branch of LCFA in regard to each risk factor have shown that hypertension, pulmonary function, history of lower limb amputation, and the total score of 11 risk factors were statistically significant. Also, in the correlation study of lower limb arteries, there was a significant correlation with the degree of stenosis in the posterior tibial artery, but not so in others. Therefore, when planning a flap surgery using the descending branch of LCFA, one needs to run imaging tests such as angiography to check arterial patency in patients with hypertension, impaired pulmonary function, and history of lower limb amputation.

Tumor necrosis factor alpha induces a serotonin dependent early increase in ciliary beat frequency and epithelial transport velocity in murine tracheae

The tracheal epithelium prevents via its highly effective clearance mechanism the contamination of the lower airways by pathogens. This mechanism is driven by ciliary bearing cells which are not only in contact with the gas phase; in addition they are also influenced by inflammatory mediators. These mediators can alter the protective function of the epithelium. Since the pro-inflammatoric cytokine tumor necrosis factor-α (TNF-α) plays a pivotal role within the inflammatory cascade, we investigated its effect onto the tracheal epithelium measured by its ciliary beat frequency and the particle transport velocity. In organ explant experiments the ciliary beat frequency and the particle transport velocity were measured under the application of TNF-α using tracheae from male C57BL6J mice. We observed a dose dependent TNF-α induced increase of both particle transport velocity and ciliary beat frequency. Knock out mice experiments made evident that the increase was depended on the expression of tumor necrosis factor receptor 1 (TNF-R1). The increases in ciliary beat frequency as well as the accelerated particle transport velocity were either inhibited by the unspecific serotonin antagonist methysergide or by cyproheptadine a specific 5-HT2 receptor antagonist. Thus, acetylcholine antagonists or nitric oxide synthase (NOS) inhibitors failed to inhibit the TNF-α induced activation. In conclusion, TNF-α may play a pivotal role in the protection of lower airways by inducing ciliary activity and increase in particle transport velocity via TNF-R1 and 5-HT2 receptor.

Recapitulation of developing artery muscularization in pulmonary hypertension

Excess smooth muscle accumulation is a key component of many vascular disorders, including atherosclerosis, restenosis, and pulmonary artery hypertension, but the underlying cell biological processes are not well defined. In pulmonary artery hypertension, reduced pulmonary artery compliance is a strong independent predictor of mortality, and pathological distal arteriole muscularization contributes to this reduced compliance. We recently demonstrated that embryonic pulmonary artery wall morphogenesis consists of discrete developmentally regulated steps. In contrast, poor understanding of distal arteriole muscularization in pulmonary artery hypertension severely limits existing therapies that aim to dilate the pulmonary vasculature but have modest clinical benefit and do not prevent hypermuscularization. Here, we show that most pathological distal arteriole smooth muscle cells, but not alveolar myofibroblasts, derive from pre-existing smooth muscle. Furthermore, the program of distal arteriole muscularization encompasses smooth muscle cell dedifferentiation, distal migration, proliferation, and then redifferentiation, thereby recapitulating many facets of arterial wall development.

Dynamic blood flow and wall shear stress in pulmonary hypertensive disease

This study provides new model of pulsatile flow in the pulmonary circulation in health and pulmonary hypertensive disease. Structural vascular remodeling typical of pulmonary hypertensive disease was implemented in the model by progressively altering the mechanical properties of the arterial geometry and progressively increasing the inlet pulse pressure (PP). The transmission of PP throughout the tree was shown to increase in advanced stages of disease, creating the potential for a `vicious-cycle' of damage to vasculature. Wall shear stress (WSS) was shown to be highest in the terminal arteries of the model and increased significantly with disease. A further trend observed in WSS results was that high WSS values began to `climb' the arterial tree towards the proximal vessels as disease progressed. This suggests a link between WSS and distal remodeling in pulmonary hypertensive disease, which initiates in the small muscular arteries and arterioles and spreads into larger arteries as the disease progresses.

HIF and pulmonary vascular responses to hypoxia

In the lung, acute reductions in oxygen lead to hypoxic pulmonary vasoconstriction, whereas prolonged exposures to hypoxia result in sustained vasoconstriction, pulmonary vascular remodeling, and the development of pulmonary hypertension. Data from both human subjects and animal models implicate a role for hypoxia-inducible factors (HIFs), oxygen-sensitive transcription factors, in pulmonary vascular responses to both acute and chronic hypoxia. In this review, we discuss work from our laboratory and others supporting a role for HIF in modulating hypoxic pulmonary vasoconstriction and mediating hypoxia-induced pulmonary hypertension, identify some of the downstream targets of HIF, and assess the potential to pharmacologically target the HIF system.