Vascular remodeling in the circulations of the lung

Role of Optical Coherence Tomography in Vasculitis-Associated Pulmonary Hypertension and Chronic Thromboembolic Pulmonary Hypertension

BACKGROUND

Identifying and understanding the microstructural changes within the wall of the pulmonary artery (PA) is crucial for elucidating disease mechanisms and guiding treatment strategies. We assessed the utility of optical coherence tomography (OCT) in identifying such changes within segmental/subsegmental PAs and compared the morphological variations in WHO group 4 pulmonary hypertension associated with Behcet Disease (BD), Takayasu arteritis (TA) and chronic thromboembolic pulmonary hypertension (CTEPH). Idiopathic pulmonary arterial hypertension (IPAH) patients served as controls.Methods and Results: A total of 197 cross-sectional images were analyzed from 20 consecutive patients. BD patients exhibited lower %wall area and mean wall thickness (MWT) compared with CTEPH, TA and, IPAH patients. TA patients showed a notably higher %wall area, which was significant in IPAH and BD patients. Variations in %wall area measurements were observed across distinct cross-sectional segments of the PA within individual patients (22% in CTEPH, 19% in BD, 16% in TA, 23% in IPAH patients). Intravascular webs, bands, and thrombi were observed in BD and CTEPH patients. OCT provided clear delineation of vascular wall calcifications and adventitial vasa vasorum. No procedure-related complications were observed.

CONCLUSIONS

PA involvement differs among the various etiologies of PH, with the PA being heterogeneously affected. OCT offers promise in elucidating microstructural vascular wall changes and providing insights into disease mechanisms and treatment effects.

The role of vasculature and angiogenesis in respiratory diseases

In European countries, nearly 10% of all hospital admissions are related to respiratory diseases, mainly chronic life-threatening diseases such as COPD, pulmonary hypertension, IPF or lung cancer. The contribution of blood vessels and angiogenesis to lung regeneration, remodeling and disease progression has been increasingly appreciated. The vascular supply of the lung shows the peculiarity of dual perfusion of the pulmonary circulation (vasa publica), which maintains a functional blood-gas barrier, and the bronchial circulation (vasa privata), which reveals a profiled capacity for angiogenesis (namely intussusceptive and sprouting angiogenesis) and alveolar-vascular remodeling by the recruitment of endothelial precursor cells. The aim of this review is to outline the importance of vascular remodeling and angiogenesis in a variety of non-neoplastic and neoplastic acute and chronic respiratory diseases such as lung infection, COPD, lung fibrosis, pulmonary hypertension and lung cancer.

Advances for Pulmonary Functional Imaging: Dual-Energy Computed Tomography for Pulmonary Functional Imaging

Dual-energy computed tomography (DECT) can improve the differentiation of material by using two different X-ray energy spectra, and may provide new imaging techniques to diagnostic radiology to overcome the limitations of conventional CT in characterizing tissue. Some techniques have used dual-energy imaging, which mainly includes dual-sourced, rapid kVp switching, dual-layer detectors, and split-filter imaging. In iodine images, images of the lung's perfused blood volume (PBV) based on DECT have been applied in patients with pulmonary embolism to obtain both images of the PE occluding the pulmonary artery and the consequent perfusion defects in the lung's parenchyma. PBV images of the lung also have the potential to indicate the severity of PE, including chronic thromboembolic pulmonary hypertension. Virtual monochromatic imaging can improve the accuracy of diagnosing pulmonary vascular diseases by optimizing kiloelectronvolt settings for various purposes. Iodine images also could provide a new approach in the area of thoracic oncology, for example, for the characterization of pulmonary nodules and mediastinal lymph nodes. DECT-based lung ventilation imaging is also available with noble gases with high atomic numbers, such as xenon, which is similar to iodine. A ventilation map of the lung can be used to image various pulmonary diseases such as chronic obstructive pulmonary disease.

Isolation of vasa vasorum endothelial cells from pulmonary artery adventitia: Implementation to vascular biology research

Isolated endothelial cells are valuable in vitro model for vascular research. At present, investigation of disease-relevant changes in vascular endothelium at the molecular level requires established endothelial cell cultures, preserving vascular bed-specific phenotypic characteristics. Vasa vasorum (VV) form a microvascular network around large blood vessels, in both the pulmonary and systemic circulations, that are critically important for maintaining the integrity and oxygen supply of the vascular wall. However, despite the pathophysiological significance of the VV, methods for the isolation and culture of vasa vasorum endothelial cells (VVEC) have not yet been reported. In our prior studies, we demonstrated the presence of hypoxia-induced angiogenic expansion of the VV in the pulmonary artery (PA) of neonatal calves; an observation which has been followed by a series of in vitro studies on isolated PA VVEC. Here we present a detailed protocol for reproducible isolation, purification, and culture of PA VVEC. We show these cells to express generic endothelial markers, (vWF, eNOS, VEGFR2, Tie1, and CD31), as well as progenitor markers (CD34 and CD133), bind lectin Lycopersicon Esculentum, and incorporate acetylated low-density lipoproteins labeled with acetylated LDL (DiI-Ac-LDL). qPCR analysis additionally revealed the expression of CD105, VCAM-1, ICAM-1, MCAM, and NCAM. Ultrastructural electron microscopy and immunofluorescence staining demonstrated that VVEC are morphologically characterized by a developed actin and microtubular cytoskeleton, mitochondrial network, abundant intracellular vacuolar/secretory system, and cell-surface filopodia. VVEC exhibit exponential growth in culture and can be mitogenically activated by multiple growth factors. Thus, our protocol provides the opportunity for VVEC isolation from the PA, and potentially from other large vessels, enabling advances in VV research.

The substitution of SERCA2 redox cysteine 674 promotes pulmonary vascular remodeling by activating IRE1α/XBP1s pathway

Pulmonary hypertension (PH) is a life-threatening disease characterized by pulmonary vascular remodeling, in which hyperproliferation of pulmonary artery smooth muscle cells (PASMCs) plays an important role. The cysteine 674 (C674) in the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2 (SERCA2) is the critical redox regulatory cysteine to regulate SERCA2 activity. Heterozygous SERCA2 C674S knock-in mice (SKI), where one copy of C674 was substituted by serine to represent partial C674 oxidative inactivation, developed significant pulmonary vascular remodeling resembling human PH, and their right ventricular systolic pressure modestly increased with age. In PASMCs, substitution of C674 activated inositol requiring enzyme 1 alpha (IRE1α) and spliced X-box binding protein 1 (XBP1s) pathway, accelerated cell cycle and cell proliferation, which reversed by IRE1α/XBP1s pathway inhibitor 4μ8C. In addition, suppressing the IRE1α/XBP1s pathway prevented pulmonary vascular remodeling caused by substitution of C674. Similar to SERCA2a, SERCA2b is also important to restrict the proliferation of PASMCs. Our study articulates the causal effect of C674 oxidative inactivation on the development of pulmonary vascular remodeling and PH, emphasizing the importance of C674 in restricting PASMC proliferation to maintain pulmonary vascular homeostasis. Moreover, the IRE1α/XBP1s pathway and SERCA2 might be potential targets for PH therapy.

Systemic-pulmonary collateral supply associated with clinical severity of chronic thromboembolic pulmonary hypertension: a study using intra-aortic computed tomography angiography

OBJECTIVES

To assess whether systemic-pulmonary collaterals are associated with clinical severity and extent of pulmonary perfusion defects in chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

This prospective study was approved by a local ethics committee. Twenty-four patients diagnosed with inoperable CTEPH were enrolled between July 2014 and February 2017. Systemic-pulmonary collaterals were detected using pulmonary vascular enhancement on intra-aortic computed tomography (CT) angiography. The pulmonary enhancement parameters were calculated, including (1) Hounsfield unit differences (HUdiff) between pulmonary trunks and pulmonary arteries (PAs) or veins (PVs), namely HUdiff-PA and HUdiff-PV, on the segmental base; (2) the mean HUdiff-PA, mean HUdiff-PV, numbers of significantly enhanced PAs and PVs, on the patient base. Pulmonary perfusion defects were recorded and scored using the lung perfused blood volume (PBV) based on intravenous dual-energy CT (DECT) angiography. Pearson's or Spearman's correlation coefficients were used to evaluate correlations between the following: (1) segment-based intra-aortic CT and intravenous DECT parameters (2) patient-based intra-aortic CT parameters and clinical severity parameters or lung PBV scores. Statistical significance was set at p < 0.05.

RESULTS

Segmental HUdiff-PV was correlated with the segmental perfusion defect score (r = 0.45, p < 0.01). The mean HUdiff-PV was correlated with the mean pulmonary arterial pressure (PAP) (r = 0.52, p < 0.01), cardiac output (rho = - 0.41, p = 0.05), and lung PBV score (rho = 0.43, p = 0.04). And the number of significantly enhanced PVs was correlated with the mean PAP (r = 0.54, p < 0.01), pulmonary vascular resistance (r = 0.54, p < 0.01), and lung PBV score (rho = 0.50, p = 0.01).

CONCLUSIONS

PV enhancement measured by intra-aortic CT angiography reflects clinical severity and pulmonary perfusion defects in CTEPH.

KEY POINTS

• Intra-aortic CT angiography demonstrated heterogeneous enhancement within the pulmonary vasculature, showing collaterals from the systemic arteries to the pulmonary circulation in CTEPH. • The degree of systemic-pulmonary collateral development was significantly correlated with the clinical severity of CTEPH and may be used to evaluate disease progression. • The distribution of systemic-pulmonary collaterals is positively correlated with perfusion defects in the lung segments in CTEPH.

Cyclo-VEGI inhibits bronchial artery remodeling in a murine model of chronic asthma

Purpose/Aim: In the context of asthma, airway bronchial remodeling and angiogenesis in the bronchial mucosa are well established. Cyclopeptidic-vascular endothelial growth inhibitor (cyclo-VEGI) is an inhibitor of the vascular endothelial growth factor (VEGF) receptor that increases the proliferation of endothelial cells and the formation of new vessels. However, changes in the bronchial arteries of patients with asthma have not been clearly elucidated. We investigated whether structural changes occurred in bronchial arteries, as well as the effects of cyclo-VEGI in a mouse model of chronic asthma (in vivo) and human fibroblasts (in vitro). Materials and Methods: A validated mouse model of allergic airway inflammation with ovalbumin (OVA) as the causative allergen was used for the study. Mice were treated with cyclo-VEGI or fluticasone during OVA challenge. In vitro experiments were conducted to determine whether fibroblasts proliferated following elastin exposure and the effects of cyclo-VEGI on them. Results: OVA sensitization and challenge led to greater perivascular smooth muscle area, more elastic fibers, and elevated expression of vascular cell adhesion molecule (VCAM)-1 antigen. These phenomena indicated changes to bronchial arteries. Cyclo-VEGI and fluticasone treatment both inhibited airway hyper-responsiveness and inflammation. Cyclo-VEGI-treated mice exhibited decreased perivascular smooth muscle area, elastin fibers, and VCAM-1 expression. Fluticasone-treated mice exhibited reductions in perivascular smooth muscle but not in perivascular elastin or VCAM-1 expression. In vitro, fibroblast proliferation was enhanced by elastin treatment, which was inhibited by cyclo-VEGI treatment. Eotaxin expression was elevated in elastin-treated fibroblasts and decreased with cyclo-VEGI treatment. Conclusions: Vascular remodeling occurred in our mouse model of chronic asthma. Cyclo-VEGI could reduce airway inflammation and hyper-responsiveness by inhibiting VCAM-1 expression and elastin deposition around the bronchial arteries.

Anti-angiogenic Properties of Bevacizumab Improve Respiratory System Inflammation in Ovalbumin-Induced Rat Model of Asthma

Studies on the bronchial vascular bed have revealed that the number of blood vessels in the lamina propria and under the mucosa of the lung tissue increases in patients suffering from mild to severe asthma. Thus, in this study, a new strategy was employed in respiratory system disorders by angiogenesis inhibition in an ovalbumin (OVA)-induced rat model of asthma. Twenty-one male Wistar albino rats, 8 weeks old, were randomly divided into three groups (n = 7 in each group), including (1) control group, (2) OVA-treated group, and (3) OVA + Bmab (bevacizumab drug). On days 1 and 8, 1 mg of OVA and aluminum hydroxide in sterile phosphate-buffered saline (PBS) were intraperitoneally injected to rats in groups 2 and 3. The control group was only subject to intraperitoneal injection of saline on days 1 and 8. One week after the last injection, the rats (groups 2 and 3) were exposed to OVA inhalation for 30 min at 2-day intervals from days 15 to 25. After sensitization and challenge with OVA, the OVA + Bmab group (group 3) were treated with a 5 mg/kg bevacizumab drug. Genes and protein expression of IL-1β and TNF-α and the expression of vascular endothelial growth factor (VEGF) protein were assessed by real-time PCR and immunohistochemistry respectively, in lung tissue. OVA exposure increased mucosal secretion and inflammatory cell populations in lung tissue and OVA-specific IgE level in serum. Also, VEGF and cytokine factor expression were significantly elevated in the OVA-induced asthma model (p ≤ 0.05). However, rats in OVA + Bmab group showed significantly a decrease in VEGF and IL-1β and TNF-α genes as well as proteins (p ≤ 0.05). The results showed that bevacizumab efficiently diminished bronchial inflammation via downregulation of VEGF expression, followed by inflammatory cells population and cytokines reduction. Angiogenesis inhibition in rats with induced asthma not only suppresses the inflammatory process through blocking VEGF expression but also inhibits the development of new blood vessels and progressing asthmatic attacks.

Depiction of mosaic perfusion in chronic thromboembolic pulmonary hypertension (CTEPH) on C-arm computed tomography compared to computed tomography pulmonary angiogram (CTPA)

To evaluate mosaic perfusion patterns and vascular lesions in patients with chronic thromboembolic pulmonary hypertension (CTEPH) using C-Arm computed tomography (CACT) compared to computed tomography pulmonary angiography (CTPA). We included 41 patients (18 female; mean age 59.9 ± 18.3 years) with confirmed CTEPH who underwent CACT and CTPA within 21 days (average 5.3 ± 5.2). Two readers (R1; R2) independently evaluated datasets from both imaging techniques for mosaic perfusion patterns and presence of CTEPH-typical vascular lesions. The number of pulmonary arterial segments with typical findings was evaluated and the percentage of affected segments was calculated and categorized: < 25%; 25–49%; 50–75%; < 75% of all pulmonary arterial segments affected by thromboembolic vascular lesions. Inter-observer agreement was calculated for both modalities using the intraclass-correlation-coefficient (ICC). Based on consensus reading the inter-modality agreement (CACT_cons vs. CTPA_cons) was calculated using the ICC. Inter-observer agreement was excellent for central vascular lesions (ICC > 0.87) and the percentage of affected segments (ICC > 0.76) and good for the perceptibility of mosaic perfusion (ICC > 0.6) and attribution of the pattern of mosaic perfusion (ICC > 0.6) for both readers on CACT and CTPA. Inter-modality agreement was excellent for the perceptibility of mosaic perfusion (ICC = 1), the present perfusion pattern (ICC = 1) and central vascular lesions (ICC = 1). However, inter-modality agreement for the percentage of affected segments was fair (ICC = 0.50), with a greater proportion of identified affected segments on CACT_cons. CACT demonstrates a high agreement with CTPA regarding the detection of mosaic perfusion. CACT detects a higher number of peripheral vascular lesions compared to CTPA.

P2Y Purinergic Receptors, Endothelial Dysfunction, and Cardiovascular Diseases

Purinergic G-protein-coupled receptors are ancient and the most abundant group of G-protein-coupled receptors (GPCRs). The wide distribution of purinergic receptors in the cardiovascular system, together with the expression of multiple receptor subtypes in endothelial cells (ECs) and other vascular cells demonstrates the physiological importance of the purinergic signaling system in the regulation of the cardiovascular system. This review discusses the contribution of purinergic P2Y receptors to endothelial dysfunction (ED) in numerous cardiovascular diseases (CVDs). Endothelial dysfunction can be defined as a shift from a “calm” or non-activated state, characterized by low permeability, anti-thrombotic, and anti-inflammatory properties, to a “activated” state, characterized by vasoconstriction and increased permeability, pro-thrombotic, and pro-inflammatory properties. This state of ED is observed in many diseases, including atherosclerosis, diabetes, hypertension, metabolic syndrome, sepsis, and pulmonary hypertension. Herein, we review the recent advances in P2Y receptor physiology and emphasize some of their unique signaling features in pulmonary endothelial cells.

Poor Subpleural Perfusion Predicts Failure After Balloon Pulmonary Angioplasty for Nonoperable Chronic Thromboembolic Pulmonary Hypertension

BACKGROUND

Poor subpleural perfusion (PSP) in the capillary phase of pulmonary angiography predicts worse outcomes following pulmonary endarterectomy in operable chronic thromboembolic pulmonary hypertension (CTEPH). Balloon pulmonary angioplasty (BPA) has emerged as a treatment for nonoperable CTEPH. The goal of the present article was to assess the association between PSP and BPA failure.

METHODS

Subpleural perfusion was classified as poor (defined as subpleural spaces either not perfused or minimally perfused in all segments) or normal. We retrospectively reviewed PSP and hemodynamic variables of 101 consecutive patients who underwent BPA from February 2014 to August 2016. The total cross-sectional area of bronchial arteries was also measured by using CT scanning. Patients were categorized according to hemodynamic results after the last BPA: a failure group (defined as mean pulmonary arterial pressure > 30 mm Hg and a decrease in pulmonary vascular resistance < 30% [n = 15]) or a success group (n = 86).

RESULTS

Although baseline hemodynamic variables were similar between the two groups, PSP was observed in 46.7% of patients in the failure group vs 13.9% in the success group (P = .003). Multivariate analysis revealed that PSP was the only predictor of BPA failure (OR, 4.02 [95% CI, 1.17-13.89]; P = .028). Patients with PSP exhibited poorly developed bronchial arteries compared with patients with normal perfusion (7.0 [5.8-9.6] mm² vs 8.7 [6.9-11.3] mm²; P = .032).

CONCLUSIONS

PSP in the capillary phase, suggesting the presence of small vessel disease with diffuse distal thrombosis, is a predictor of BPA failure. PSP was also associated with less developed bronchial arteries, which suggests a key role of bronchial-pulmonary anastomoses in maintaining the pulmonary capillary bed open downstream of the pulmonary arterial obstruction. PSP affected approximately 15% of patients with nonoperable CTEPH who underwent BPA.

Clinical Significance of Late Phase of Lung Perfusion Blood Volume (Lung Perfusion Blood Volume) Quantified by Dual-Energy Computed Tomography in Patients With Pulmonary Thromboembolism

PURPOSE

Using dual-energy computed tomography (DECT), we quantified the lung perfusion blood volume (PBV) in the late phase, which may reflect both the pulmonary artery and systemic collateral flow. We then investigated the clinical significance of late-phase lung PBV values.

MATERIALS AND METHODS

We retrospectively studied 206 patients (266 scans) who underwent early-phase and late-phase DECT. The patients were divided into 2 groups depending on whether or not they had pulmonary thromboembolism (PTE) (n=94 and 112). Patients with PTE were further divided into 2 subgroups, depending on whether they had acute PTE or chronic PTE (n=66 and 28). Pulmonary artery enhancement (PAenh) was measured on DECT. We then calculated the [lung PBV/PAenh] ratio in all patients during both the early and late phases for adjustment of timing.

RESULTS

The [late-phase lung PBV/PAenh] ratio was 0.092±0.029 in the group with PTE and 0.108±0.030 in the group without PTE, showing a significant difference between the 2 groups (P<0.0001). The [early-phase lung PBV values/PAenh]/[late-phase lung PBV values/PAenh] ratio was 0.68±0.19 and 0.84±0.20, respectively, also showing a significant difference between the 2 groups (P<0.0001). Finally, the [early-phase lung PBV/PAenh]/[late-phase lung PBV/PAenh] ratio was 0.71±0.19 in patients with acute PTE and 0.56±0.16 in patients with chronic PTE, and there was a significant difference between these 2 subgroups (P=0.0004).

CONCLUSIONS

It may be useful to determine late-phase lung PBV values in patients with PTE, because this parameter may reflect the systemic collateral flow, which is increased in chronic PTE.

A novel mouse model of high flow-induced pulmonary hypertension-surgically induced by right pulmonary artery ligation

BACKGROUND

This study sought to establish a new model of high-flow pulmonary hypertension (PH) in mice. This model may be useful for studies seeking to reduce the pulmonary vascular resistance and delay the development of PH caused by congenital heart disease.

MATERIALS AND METHODS

The right pulmonary artery was ligated via a right posterolateral thoracotomy. Pulmonary hemodynamics was evaluated by right heart catheterization immediately after ligation and at 2, 4, 8, and 12 wk postoperatively. The right ventricle (RV) and the left ventricle (LV) with septum (S) were weighed to calculate the RV/(LV + S) ratio as an index of right ventricular hypertrophy. Morphologic changes in the left lungs were analyzed, and percentages of muscularized pulmonary vessels were assessed by hematoxylin and eosin, elastica van Gieson and alpha-smooth muscle actin staining. All the study data were compared with data from a model of PH generated by hypoxic stimulation.

RESULTS

A pulmonary hypertensive state was successfully induced by 2 wk after surgery. However, the morphologic analysis demonstrated that pulmonary vascular muscularization, as evaluated using right ventricular systolic pressure and RV/(LV + S), was not significantly increased until 4 wk postoperatively. When mice from the new model and the hypoxic model were compared, no significant differences were observed in any of the evaluated indices.

CONCLUSIONS

High-flow PH can be induced within 4 wk after ligation of the right pulmonary artery, which is easily performed in mice. Such mice can be used as a model of high-flow PH.

Dynamic (4D) CT perfusion offers simultaneous functional and anatomical insights into pulmonary embolism resolution

OBJECTIVE

Resolution and long-term functional effects of pulmonary emboli are unpredictable. This study was carried out to assess persisting vascular bed perfusion abnormalities and resolution of arterial thrombus in patients with recent pulmonary embolism (PE).

METHODS AND MATERIALS

26 Patients were prospectively evaluated by dynamic (4D) contrast enhanced CT perfusion dynamic pulmonary CT perfusion. Intermittent volume imaging was performed every 1.5-1.7s during breath-hold and perfusion values were calculated by maximum-slope technique. Thrombus load (modified Miller score; MMS) and ventricular diameter were determined. Perfusion maps were visually scored and correlated with residual endoluminal filling defects.

RESULTS

The mean initial thrombus load was 13.1±4.6 MMS (3-16), and 1.2±2.1 MMS (0-8) at follow up. From the 24 CTPs with diagnostic quality perfusion studies, normal perfusion was observed in 7 (29%), and mildly-severely abnormal in 17 (71%). In 15 patients with no residual thrombus on follow up CTPA, normal perfusion was observed in 6, and abnormal perfusion in 9. Perfusion was abnormal in all patients with residual thrombus on follow up CTPA. Pulmonary perfusion changes were classified as reduced (n=4), delayed (systemic circulation pattern; n=5), and absent (no-flow; n=5). The right ventricle was dilated in 12/25 (48%) at presentation, and normal in all 26 follow up scans. Weak correlation was found between initial ventricular dilatation and perfusion abnormality at follow up (r=0.15).

CONCLUSIONS

Most patients had substantial perfusion abnormality at 3-6 months post PE. Abnormal perfusion patterns were frequently observed in patients and in regions with no corresponding evidence of residual thrombus on CTPA. Some defects exhibit delayed, presumed systemic, enhancement (which we have termed 'stunned' lung). CT perfusion provides combined anatomical and functional information about PE resolution.

Microvascular disease in chronic thromboembolic pulmonary hypertension: a role for pulmonary veins and systemic vasculature

Limited numbers of operated patients with chronic thromboembolic pulmonary hypertension (CTEPH) are refractory to pulmonary endarterectomy (PEA) and experience persistent pulmonary hypertension (PH).

We retrospectively assessed lung histology available from nine patients with persistent PH (ineffective PEA (inPEA) group) and from eight patients transplanted for distal CTEPH inaccessible by PEA (noPEA group). Microscopically observed peculiarities were compared with the histology of a recently developed CTEPH model in piglets. Pre-interventional clinical/haemodynamic data and medical history of patients from the inPEA and noPEA groups were collected and analysed.

Conspicuous remodelling of small pulmonary arteries/arterioles, septal veins and pre-septal venules, including focal capillary haemangiomatosis, as well as pronounced hypertrophy and enlargement of bronchial systemic vessels, were the predominant pattern in histology from both groups. Most findings were reproduced in our porcine CTEPH model. Ink injection experiments unmasked abundant venular involvement in so-called small vessel or microvascular disease, as well as post-capillary bronchopulmonary shunting in human and experimental CTEPH.

Microvascular disease is partly due to post-capillary remodelling in human and experimental CTEPH and appears to be related to bronchial-to-pulmonary venous shunting. Further studies are needed to clinically assess the functional importance of this finding.

Angiogenesis and vascular remodeling in chronic airway diseases

Asthma and chronic obstructive pulmonary disease remain a global health problem, with increasing morbidity and mortality. Despite differences in the causal agents, both diseases exhibit various degrees of inflammatory changes, structural alterations of the airways leading to airflow limitation. The existence of transient disease phenotypes which overlap both diseases and which progressively decline the lung function has complicated the search for an effective therapy. Important characteristics of chronic airway diseases include airway and vascular remodeling, of which the molecular mechanisms are complex and poorly understood. Recently, we and others have shown that airway smooth muscle (ASM) cells are not only structural and contractile components of airways, rather they bear capabilities of producing large number of pro-inflammatory and mitogenic factors. Increase in size and number of blood vessels both inside and outside the smooth muscle layer as well as hyperemia of bronchial vasculature are contributing factors in airway wall remodeling in patients with chronic airway diseases, proposing for the ongoing mechanisms like angiogenesis and vascular dilatation. We believe that vascular changes directly add to the airway narrowing and hyper-responsiveness by exudation and transudation of proinflammatory mediators, cytokines and growth factors; facilitating trafficking of inflammatory cells; causing oedema of the airway wall and promoting ASM accumulation. One of the key regulators of angiogenesis, vascular endothelial growth factor in concerted action with other endothelial mitogens play pivotal role in regulating bronchial angiogenesis. In this review article we address recent advances in pulmonary angiogenesis and remodelling that contribute in the pathogenesis of chronic airway diseases.

Neutrophil dependence of vascular remodeling after Mycoplasma infection of mouse airways

Vascular remodeling is a feature of sustained inflammation in which capillaries enlarge and acquire the phenotype of venules specialized for plasma leakage and leukocyte recruitment. We sought to determine whether neutrophils are required for vascular remodeling in the respiratory tract by using Mycoplasma pulmonis infection as a model of sustained inflammation in mice. The time course of vascular remodeling coincided with the influx of neutrophils during the first few days after infection and peaked at day 5. Depletion of neutrophils with antibody RB6-8C5 or 1A8 reduced neutrophil influx and vascular remodeling after infection by about 90%. Similarly, vascular remodeling after infection was suppressed in Cxcr2(-/-) mice, in which neutrophils adhered to the endothelium of venules but did not extravasate into the tissue. Expression of the venular adhesion molecule P-selectin increased in endothelial cells from day 1 to day 3 after infection, as did expression of the Cxcr2-receptor ligands Cxcl1 and Cxcl2. Tumor necrosis factor α (TNFα) expression increased more than sixfold in the trachea of wild-type and Cxcr2(-/-) mice, but intratracheal administration of TNFα did not induce vascular remodeling similar to that seen in infection. We conclude that neutrophil influx is required for remodeling of capillaries into venules in the airways of mice with Mycoplasma infection and that TNFα signaling is necessary but not sufficient for vascular remodeling.

High proliferative potential endothelial colony-forming cells contribute to hypoxia-induced pulmonary artery vasa vasorum neovascularization

Angiogenic expansion of the vasa vasorum (VV) is an important contributor to pulmonary vascular remodeling in the pathogenesis of pulmonary hypertension (PH). High proliferative potential endothelial progenitor-like cells have been described in vascular remodeling and angiogenesis in both systemic and pulmonary circulations. However, their role in hypoxia-induced pulmonary artery (PA) VV expansion in PH is not known. We hypothesized that profound PA VV neovascularization observed in a neonatal calf model of hypoxia-induced PH is due to increased numbers of subsets of high proliferative cells within the PA adventitial VV endothelial cells (VVEC). Using a single cell clonogenic assay, we found that high proliferative potential colony-forming cells (HPP-CFC) comprise a markedly higher percentage in VVEC populations isolated from the PA of hypoxic (VVEC-Hx) compared with control (VVEC-Co) calves. VVEC-Hx populations that comprised higher numbers of HPP-CFC also demonstrated markedly higher expression levels of CD31, CD105, and c-kit than VVEC-Co. In addition, significantly higher expression of CD31, CD105, and c-kit was observed in HPP-CFC vs. the VVEC of the control but not of hypoxic animals. HPP-CFC exhibited migratory and tube formation capabilities, two important attributes of angiogenic phenotype. Furthermore, HPP-CFC-Co and some HPP-CFC-Hx exhibited elevated telomerase activity, consistent with their high replicative potential, whereas a number of HPP-CFC-Hx exhibited impaired telomerase activity, suggestive of their senescence state. In conclusion, our data suggest that hypoxia-induced VV expansion involves an emergence of HPP-CFC populations of a distinct phenotype with increased angiogenic capabilities. These cells may serve as a potential target for regulating VVEC neovascularization.

The adventitia: Essential role in pulmonary vascular remodeling

A rapidly emerging concept is that the vascular adventitia acts as a biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. It is the most complex compartment of the vessel wall and comprises a variety of cells including fibroblasts, immunomodulatory cells, resident progenitor cells, vasa vasorum endothelial cells, and adrenergic nerves. In response to vascular stress or injury, resident adventitial cells are often the first to be activated and reprogrammed to then influence tone and structure of the vessel wall. Experimental data indicate that the adventitial fibroblast, the most abundant cellular constituent of adventitia, is a critical regulator of vascular wall function. In response to vascular stresses such as overdistension, hypoxia, or infection, the adventitial fibroblast is activated and undergoes phenotypic changes that include proliferation, differentiation, and production of extracellular matrix proteins and adhesion molecules, release of reactive oxygen species, chemokines, cytokines, growth factors, and metalloproteinases that, collectively, affect medial smooth muscle cell tone and growth directly and that stimulate recruitment and retention of circulating inflammatory and progenitor cells to the vessel wall. Resident dendritic cells also participate in "sensing" vascular stress and actively communicate with fibroblasts and progenitor cells to simulate repair processes that involve expansion of the vasa vasorum, which acts as a conduit for further delivery of inflammatory/progenitor cells. This review presents the current evidence demonstrating that the adventitia acts as a key regulator of pulmonary vascular wall function and structure from the "outside in."

Different perfusion pattern between acute and chronic pulmonary thromboembolism: evaluation with two-phase dual-energy perfusion CT

OBJECTIVE

The purpose of this study was to evaluate whether two-phase dual-energy CT can differentiate between lung perfusion patterns of patients with chronic pulmonary thromboembolism (PTE) and those of patients with acute PTE.

SUBJECTS AND METHODS

A total of 114 patients clinically suspected to have PTE were prospectively enrolled. All patients underwent dual-energy CT at pulmonary artery (PA) and delayed phases. Of 68 patients diagnosed with PTE on CT, 42 were finally included. Iodine-related attenuation values (IRAs) were measured in PA and delayed phases for each lung segment, and IRA change ratios were calculated using the formula 100% × [(IRA of delayed phase) - (IRA of PA phase)]/(IRA of PA phase).

RESULTS

Among the 42 patients (19 men and 23 women; mean age, 60.3 ± 13.2 years; range, 28-82 years), 24 had a diagnosis of acute PTE and 18 of chronic PTE. Those segments with both perfusion and filling defects (n = 143) in patients with acute PTE showed no significant changes of mean IRA between PA and delayed phases, whereas the segments from patients with chronic PTE (n = 94) showed significantly increased IRA on delayed phase as compared with PA phase. The mean IRA change ratios in acute and chronic PTE were -3.14% and 191.9%, respectively (p < 0.0001).

CONCLUSION

Chronic PTE segments were significantly more enhanced on the delayed phase of two-phase dual-energy CT images than were acute PTE segments, possibly resulting from more extensive systemic collateral formation in chronic PTE. Two-phase dual-energy CT can be used to differentiate distinct regional perfusion patterns between acute and chronic PTE.

Fatty acid binding protein 4 regulates VEGF-induced airway angiogenesis and inflammation in a transgenic mouse model: implications for asthma

Neovascularization of the airways occurs in several inflammatory lung diseases, including asthma. Vascular endothelial growth factor (VEGF) plays an important role in vascular remodeling in the asthmatic airways. Fatty acid binding protein 4 (FABP4 or aP2) is an intracellular lipid chaperone that is induced by VEGF in endothelial cells. FABP4 exhibits a proangiogenic function in vitro, but whether it plays a role in modulation of angiogenesis in vivo is not known. We hypothesized that FABP4 promotes VEGF-induced airway angiogenesis and investigated this hypothesis with the use of a transgenic mouse model with inducible overexpression of VEGF165 under a CC10 promoter [VEGF-TG (transgenic) mice]. We found a significant increase in FABP4 mRNA levels and density of FABP4-expressing vascular endothelial cells in mouse airways with VEGF overexpression. FABP4(-/-) mouse airways showed a significant decrease in neovessel formation and endothelial cell proliferation in response to VEGF overexpression. These alterations in airway vasculature were accompanied by attenuated expression of proinflammatory mediators. Furthermore, VEGF-TG/FABP4(-/-) mice showed markedly decreased expression of endothelial nitric oxide synthase, a well-known mediator of VEGF-induced responses, compared with VEGF-TG mice. Finally, the density of FABP4-immunoreactive vessels in endobronchial biopsy specimens was significantly higher in patients with asthma than in control subjects. Taken together, these data unravel FABP4 as a potential target of pathologic airway remodeling in asthma.

The adventitia: essential regulator of vascular wall structure and function

The vascular adventitia acts as a biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. It is the most complex compartment of the vessel wall and is composed of a variety of cells, including fibroblasts, immunomodulatory cells (dendritic cells and macrophages), progenitor cells, vasa vasorum endothelial cells and pericytes, and adrenergic nerves. In response to vascular stress or injury, resident adventitial cells are often the first to be activated and reprogrammed to influence the tone and structure of the vessel wall; to initiate and perpetuate chronic vascular inflammation; and to stimulate expansion of the vasa vasorum, which can act as a conduit for continued inflammatory and progenitor cell delivery to the vessel wall. This review presents the current evidence demonstrating that the adventitia acts as a key regulator of vascular wall function and structure from the outside in.

Targeting the adventitial microenvironment in pulmonary hypertension: A potential approach to therapy that considers epigenetic change

Experimental data indicate that the adventitial compartment of blood vessels, in both the pulmonary and systemic circulations, like the connective tissue stroma in tissues throughout the body, is a critical regulator of vessel wall function in health and disease. It is clear that adventitial cells, and in particular the adventitial fibroblast, are activated early following vascular injury, and play essential roles in regulating vascular wall structure and function through production of chemokines, cytokines, growth factors, and reactive oxygen species (ROS). The recognition of the ability of these cells to generate and maintain inflammatory responses within the vessel wall provides insight into why vascular inflammatory responses, in certain situations, fail to resolve. It is also clear that the activated adventitial fibroblast plays an important role in regulating vasa vasorum growth, which can contribute to ongoing vascular remodeling by acting as a conduit for delivery of inflammatory and progenitor cells. These functions of the fibroblast clearly support the idea that targeting chemokine, cytokine, adhesion molecule, and growth factor production in activated fibroblasts could be helpful in abrogating vascular inflammatory responses and thus in ameliorating vascular disease. Further, the recent observations that fibroblasts in vascular and fibrotic diseases may maintain their activated state through epigenetic alterations in key inflammatory and pro-fibrotic genes suggests that current therapies used to treat pulmonary hypertension may not be sufficient to induce apoptosis or to inhibit key inflammatory signaling pathways in these fibroblasts. New therapies targeted at reversing changes in the acetylation or methylation status of key transcriptional networks may be needed. At present, therapies specifically targeting abnormalities of histone deacytelase (HDAC) activity in fibroblast-like cells appear to hold promise.

Is length an appropriate estimator to characterize pulmonary alveolar capillaries? A critical evaluation in the human lung

Stereological estimations of total capillary length have been used to characterize changes in the alveolar capillary network (ACN) during developmental processes or pathophysiological conditions. Here, we analyzed whether length estimations are appropriate to describe the 3D nature of the ACN. Semi-thin sections of five human lungs, previously investigated by Gehr et al. (Respir Physiol 1978; 32:121-140), were used to estimate alveolar capillary length using a "design-based" or a "model-based" stereological approach. The design-based approach involves counting of capillary profiles related to a defined area of the reference space. The model-based approach bases on the assumption that capillaries are round tubes and length was calculated from capillary volume and surface area. The model-based approach provided a mean of 6,950 km (SD: 3,108 km) for total capillary length, the design-based approach resulted in a mean of 2,746 km (SD: 722 km). Because of the geometry of the ACN both approaches carry an unpredictable bias. The bias incurred by the design-based approach is proportional to the ratio between radius and length of the capillary segments in the ACN, the number of branching points and the winding of the capillaries. The model-based approach is biased because of the real noncylindrical shape of capillaries and the network structure. In conclusion, the estimation of the total length of capillaries in the ACN cannot be recommended as the geometry of the ACN does not fulfill the requirements for stereological length estimation. Until new methods are being developed, the unbiased estimates of capillary volume, and surface area should be preferred.

Targeting abnormal airway vascularity as a therapeutical strategy in asthma

Asthma is a chronic inflammatory disease of airways, characterized by airway hyperresponsiveness and airflow limitation with acute bronchoconstriction, swelling of the airway wall, chronic mucus plug formation and airway wall remodelling. Functional and structural changes in the vasculature of asthmatic airways have been documented, and the signalling mechanisms are complex and have recently attracted much attention. The vascular changes may affect inflammatory cell recruitment, airway hyperresponsiveness and the regulation of airway calibre, and further, the level of disease control. Many critical factors are involved in the pathophysiological regulation of vascular changes in bronchial asthma, and the actions of these factors must be very carefully orchestrated. By better understanding the complicated actions of each factor, we may be able to advance further in asthma treatment.

Pulmonary periarterial inflammation in fatal asthma

BACKGROUND

To date, little information has been available about pulmonary artery pathology in asthma. The pulmonary artery supplies the distal parts of the lungs and likely represents a site of immunological reaction in allergic inflammation. The objective of this study was to describe the inflammatory cell phenotype of pulmonary artery adventitial inflammation in lung tissue from patients who died of asthma.

METHODS

We quantified the different inflammatory cell types in the periarterial region of small pulmonary arteries in lung tissue from 22 patients who died of asthma [fatal asthma (FA)] and 10 control subjects. Using immunohistochemistry and image analysis, we quantified the cell density for T lymphocytes (CD3, CD4, CD8), B lymphocytes (CD20), eosinophils, mast cells (chymase and tryptase), and neutrophils in the adventitial layer of pulmonary arteries with a diameter smaller than 500 microm.

RESULTS

Our data (median/interquartile range) demonstrated increased cell density of mast cells [FA=271.8 (148.7) cells/mm2; controls=177.0 (130.3) cells/mm2, P=0.026], eosinophils [FA=23.1 (58.6) cells/mm2; controls=0.0 (2.3) cells/mm2, P=0.012], and neutrophils [FA=50.4 (85.5) cells/mm2; controls=2.9 (30.5) cells/mm2, P=0.009] in the periarterial space in FA. No significant differences were found for B and T lymphocytes or CD4+ or CD8+ subsets. Chymase/tryptase positive (MCCT) mast cells predominated over tryptase (MCT) mast cells in the perivascular arterial space in both asthma patients and controls [MCCT/(MCCT+MCT)=0.91 (0-1) in FA and 0.75 (0-1) in controls, P=0.86].

CONCLUSIONS

Our results show that the adventitial layer of the pulmonary artery participates in the inflammatory process in FA, demonstrating increased infiltration of mast cells, eosinophils, and neutrophils, but not of T and B lymphocytes.

A protocol for a lung neovascularization model in rodents

By providing insight into the cellular events of vascular injury and repair, experimental model systems seek to promote timely therapeutic strategies for human disease. The goal of many current studies of neovascularization is to identify cells critical to the process and their role in vascular channel assembly. We propose here a protocol to analyze, in an in vivo rodent model, vessel and capillary remodeling (reorganization and growth) in the injured lung. Sequential analyses of stages in the assembly of vascular structures, and of relevant cell types, provide further opportunities to study the molecular and cellular determinants of lung neovascularization.

Brothers and sisters: molecular insights into arterial-venous heterogeneity

The molecular differences between arteries and veins are genetically predetermined and are evident even before the first embryonic heart beat. Although ephrinB2 and EphB4 are expressed in cells that will ultimately differentiate into arteries and veins, respectively, many other genes have been shown to play a significant role in cell fate determination. The expression patterns of ephrinB2 and EphB4 are restricted to arterial-venous boundaries, and Eph/ephrin signaling provides repulsive cues at arterial-venous boundaries that are thought to prevent intermixing of arterial- and venous-fated cells. However, the maintenance of arterial-venous fate is susceptible to some degree of plasticity. Thus, in response to signals from the ambient microenvironment and shear stress, there is flow-mediated intercalation of the arteries and veins that ultimately leads to the formation of a functional, closed-loop circulation. In addition, cells in the blood vessels of each organ undergo epigenetic, morphological, and functional adaptive changes that are specific to the proximate function of their cognate organ(s). These adaptive changes result in an interorgan and intraorgan vessel heterogeneity that manifest clinically in a disparate response of different organs to identical risk factors and injury in the same animal. In this review, we focus on the molecular and physiological factors influencing arterial-venous heterogeneity between and within different organ(s). We explore arterial-venous differences in selected organs, as well as their respective endothelial cell architectural organization that results in their inter- and intraorgan heterogeneity.

Dilatation of bronchial arteries correlates with extent of central disease in patients with chronic thromboembolic pulmonary hypertension

BACKGROUND

Dilatation of the bronchial arteries is a well-recognized feature in patients with chronic thromboembolic pulmonary hypertension (CTEPH). The purpose of the current study was to use computed tomography (CT) to assess the relationship between dilated bronchial arteries and the extent of thrombi, and to evaluate the predictive value of the former for surgical outcome.

METHODS AND RESULTS

Fifty-nine patients with CTEPH and 16 with pulmonary arterial hypertension (PAH) were retrospectively evaluated. The total cross-sectional area of bronchial arteries was measured by CT and its relationship with the central extent of thrombi or surgical outcome was assessed. The total area of the bronchial arteries in CTEPH patients was significantly larger than that in PAH patients (median [range], 6.9 [1.7-29.5] mm(2) vs 3.2 [0.8-9.4] mm(2)), with the total area of bronchial arteries correlating with the central extent of thrombi. In patients who had undergone pulmonary thromboendarterectomy (PTE) (n=22), the change in PaO(2) after surgery had a tendency to correlate with the total area of the bronchial arteries.

CONCLUSION

The total cross-sectional area of the bronchial arteries correlated with the extent of central disease in patients with CTEPH, and it might predict gas exchange improvement after PTE.

Morphogenetic lung defects of JSAP1-deficient embryos proceeds via the disruptions of the normal expressions of cytoskeletal and chaperone proteins

Recent studies have shown that JNK/stress-activated protein kinase-associated protein 1 (JSAP1)-deficient mice die from respiratory failure shortly after birth. To understand the underlying mechanism, we investigated the histological appearances and cell type changes in developing jsap1(-/-) lungs between E12.5 and E18.5. At the light microscopic level, no overt abnormality was detected in jsap1(-/-) until E16.5. However, alveoli and airway formations that normally occur after E16.5 were poorly advanced in jsap1(-/-). Despite these morphological defects, surfactant secreting cells labeled by anti-SP-B or anti-SP-C were present in normal ranges in jsap1(-/-) lungs. Smooth muscle alpha-actin expressing cells were also developed in jsap1(-/-) lungs, although actin expression was decreased. The expressions of transcriptional factors, such as, nuclear factor Ib (Nfib), N-myc, and octamer transcriptional factor 1 (Oct-1), which play a critical role in lung morphogenesis, were found to be down-regulated, whereas signal transducer and activator of transcription 3 (Stat3), sonic hedgehog (Shh), and smoothened (Smo) were up-regulated, in jsap1(-/-) lungs at E17.5-E18.5 compared with those in jsap1(+/+) lungs. Proteomics analysis of E17.5 lung identified 39 proteins with altered expressions, which included actin, tropomyosin, myosin light chain, vimentin, heat shock protein (Hsp27), and Hsp84. These results suggest that JSAP1 is required for the normal expressions of cytoskeletal and chaperone proteins in the developing lung, and that impaired expressions of these proteins might cause morphogenetic defects observed in jsap1(-/-) lungs.

MIP-2 causes differential activation of RhoA in mouse aortic versus pulmonary artery endothelial cells

Previously, we have shown that endothelial cell chemotaxis to the proangiogenic chemokine MIP-2 (macrophage inflammatory protein-2) is much greater in mouse aortic endothelial cells (EC) than pulmonary arterial endothelial cells (PA EC). This was true despite the observation that both cell types display comparable levels of the ligand receptor, CXCR(2) (8). Since the systemic arterial circulation is proangiogenic in the adult lung and the pulmonary circulation is relatively resistant to neovascularization, we questioned whether the observed functional heterogeneity is related to inherent differences in cell signaling cascades of the two EC subtypes. Specifically, we measured activation of Rac1 and RhoA, both thought to be involved in EC cell migration. Rac1 showed inconsistent and minimal changes in both cell types after MIP-2 treatment (p>0.05). However, activated RhoA was increased upon exposure to MIP-2 only in aortic EC (61% increase; p<0.05). Decreased RhoA activation after treatment of aortic EC with specific siRNA for RhoA resulted in a functional decrease in EC chemotaxis to MIP-2 (17% increase; p<0.05). Additionally, increased RhoA activation in PA EC with adenoviral infection of RhoA caused an increase in PA EC chemotaxis to MIP-2 (46% increase; p<0.05). Inhibition of RhoA activity with the Rho kinase inhibitor, Y27632, blocked aortic EC chemotaxis and stress fiber formation. Thus, RhoA activation is increased after MIP-2 treatment in mouse aortic endothelial cells but not in pulmonary artery endothelial cells. We conclude that RhoA is part of a signaling pathway essential for aortic cell migration after CXCR(2) ligation. This result provides one explanation for the difference in chemotaxis observed in these two endothelial subtypes that express similar levels of CXCR(2).

Pulmonary vascular remodeling

The maladaptive response of the pulmonary vasculature that occurs in patients with congenital diaphragmatic hernia significantly impacts outcome. Muscularized distal pulmonary arterioles inhibit the ability of the neonate to adjust to extrauterine circulation, resulting in severe pulmonary hypertension. This review summarizes the current state of knowledge regarding normal and abnormal development of the lung vascular system and identifies current and potential therapies directed toward preserving or restoring proper pulmonary vascular function.

Phenotypic heterogeneity of the endothelium: II. Representative vascular beds

Endothelial cells, which form the inner cellular lining of blood vessels and lymphatics, display remarkable heterogeneity in structure and function. This is the second of a 2-part review on the phenotypic heterogeneity of blood vessel endothelial cells. The first part discusses the scope, the underlying mechanisms, and the diagnostic and therapeutic implications of phenotypic heterogeneity. Here, these principles are applied to an understanding of organ-specific phenotypes in representative vascular beds including arteries and veins, heart, lung, liver, and kidney. The goal is to underscore the importance of site-specific properties of the endothelium in mediating homeostasis and focal vascular pathology, while at the same time emphasizing the value of approaching the endothelium as an integrated system.

Molecular mechanisms of pulmonary vascular development

In this era of rapidly advancing vascular biology research, a vast array of growth factors and signaling molecules have been recognized as key players in the mechanisms that control lung vascular development. In the lung, vascular development is a complex, multistep process that includes specialization of primitive cells to vascular progenitors; formation of primitive vascular networks; remodeling with local regression and branching; specialization toward arteries, veins, and lymphatics; stabilization of vessels by matrix production and recruitment of supporting cells; and maintenance of the vascular structure. This complex, highly organized process requires exquisite orchestration of the regulatory activity of multiple molecules in a specific temporospatial order. Most of these molecules are members of 3 major growth factor families that have been recently identified. They are the vascular endothelial growth factor, angiopoietin, and ephrin families. Understanding the functional reach of several members of these growth factor families is integral to an appreciation of the etiology and pathogenesis of developmental lung vascular disorders affecting newborns. This review summarizes recent advances in the molecular bases of lung vascular development and some of the pulmonary diseases resulting from aberrant vascular growth, including bronchopulmonary dysplasia, alveolar capillary dysplasia, congenital cystic pulmonary disorders, congenital pulmonary hemangiomatosis, and lung hypoplasia.

Tracheal occlusion: A review of obstructing fetal lungs to make them grow and mature

Fetal lung growth and functional differentiation are affected strongly by the extent that pulmonary tissue is distended (expanded) by liquid that naturally fills developing future airspaces. Methods that prevent normal egress of this lung fluid through the trachea magnify mechanical stretching of lung parenchymal cells, thereby promoting lung development. Indeed, experimental observations demonstrate that in utero tracheal occlusion (TO) performed on fetuses during the late canalicular-early saccular stage potently stimulates pulmonary growth and maturation. In this review, we present the four principle non-human animal models of TO/obstruction and discuss them in relation to their utility in elucidating lung development, in remedying congenital diaphragmatic hernia (CDH) as well as in investigating the stretching effects on growth and remodeling of the fine vasculature.

Cell-cell adhesion in lung endothelium

Homotypic cell-cell adhesion is essential for tissue and organ development, remodeling, regeneration, and physiological function. Whereas a significant number of homotypic cell-cell adhesion molecules have been identified, much more is known about those concentrated in epithelia than in endothelia. Among the endothelial cell-cell adhesion molecules, very little is known that is specific to endothelium in the pulmonary and bronchial circulations. This review focuses primarily on homotypic cell-cell adhesion molecules that are or are likely to be important in lung endothelium.

Hypoxia-induced mitogenic factor has proangiogenic and proinflammatory effects in the lung via VEGF and VEGF receptor-2

From a mouse model of hypoxia-induced pulmonary hypertension, we previously found a highly upregulated protein in the lung that we named hypoxia-induced mitogenic factor (HIMF), also known as found in inflammatory zone 1 (FIZZ1), and resistin-like molecule alpha (RELMalpha). However, the mechanisms of HIMF in the pulmonary vascular remodeling remain unknown. We now demonstrate that HIMF promoted cell proliferation, migration, and the production of vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1) in pulmonary endothelial cells as well as the production of reactive oxygen species in murine monocyte/macrophage cells. HIMF-induced CD31-positive cell infiltrate in in vivo Matrigel plugs was significantly suppressed by VEGF receptor-2 (VEGFR2) blockade. In ex vivo studies, HIMF stimulated the production of VEGF, MCP-1, and stromal cell-derived factor-1 (SDF-1) in the lung resident cells, and VEGFR2 neutralization significantly suppressed HIMF-induced MCP-1 and SDF-1 production. Furthermore, intravenous injection of HIMF showed marked increase of CD68-positive inflammatory cells in the lungs, and these events were attenuated by VEGFR2 neutralization. Intravenous injection of HIMF also downregulated the expression of VEGFR2 in the lung. These results suggest that HIMF plays critical roles in pulmonary inflammation as well as angiogenesis.

Vascular perfusion of human lung cancer in a rat orthotopic model using dynamic contrast-enhanced magnetic resonance imaging

Lung cancer is the leading cause of death among cancers. Early detection and diagnosis present a major goal in the efforts to improve survival rates of lung cancer patients. Changes in angiogenic activity and microvascular perfusion properties in cancers can serve as markers of malignancy. The aim of this study was to employ MRI means to measure the microvascular perfusion parameters of orthotopic nonsmall cell lung cancer, using the experimental rat model. Anatomical and dynamic contrast-enhanced lung images were acquired at high spatial resolution, and registered and analyzed, pixel by pixel and globally, by means of a model-based algorithm. The MRI output yielded color-coded parametric images of the influx and efflux transcapillary transfer constants that indicated rapid microvascular perfusion. The transfer constants were about 1 order of magnitude higher than those found in other tumors or in nonorthotopic lung cancer, with the influx constant median value of 0.42 min(-1) and the efflux constant median value of 1.61 min(-1). The rapid perfusion was in accord with the immunostaining of the capillaries, which suggested the tumor exploitation of the existing alveolar vessels. The results showed that high resolution, dynamic, contrast-enhanced MRI is an effective tool for the quantitative measurement of spatial and temporal changes in lung cancer perfusion and vasculature.

Pulmonary artery adventitial fibroblasts cooperate with vasa vasorum endothelial cells to regulate vasa vasorum neovascularization: a process mediated by hypoxia and endothelin-1

The precise cellular and molecular mechanisms regulating adventitial vasa vasorum neovascularization, which occurs in the pulmonary arterial circulation in response to hypoxia, remain unknown. Here, using a technique to isolate and culture adventitial fibroblasts (AdvFBs) and vasa vasorum endothelial cells (VVECs) from the adventitia of pulmonary arteries, we report that hypoxia-activated pulmonary artery AdvFBs exhibited pro-angiogenic properties and influenced the angiogenic phenotype of VVEC, in a process of cell-cell communication involving endothelin-1 (ET-1). We demonstrated that AdvFBs, either via co-culture or conditioned media, stimulated VVEC proliferation and augmented the self-assembly and integrity of cord-like networks that formed when VVECs where cultured on Matrigel. In addition, hypoxia-activated AdvFBs produced ET-1, suggesting a paracrine role for this pro-angiogenic molecule in these processes. When co-cultured on Matrigel, AdvFBs and VVECs self-assembled into heterotypic cord-like networks, a process augmented by hypoxia but attenuated by either selective endothelin receptor antagonists or oligonucleotides targeting prepro-ET-1 mRNA. From these observations, we propose that hypoxia-activated AdvFBs exhibit pro-angiogenic properties and, as such, communicate with VVECs, in a process involving ET-1, to regulate vasa vasorum neovascularization occurring in the adventitia of pulmonary arteries in response to chronic hypoxia.

Growth of pulmonary microvasculature in ventilated preterm infants

RATIONALE

Density-based morphometric studies have demonstrated decreased capillary density in infants with bronchopulmonary dysplasia (BPD) and in BPD-like animal models, leading to the prevailing view that microvascular development is disrupted in BPD.

OBJECTIVE

To perform a comprehensive analysis of the early and late effects of ventilation on pulmonary microvascular growth in preterm infants.

METHODS

Postmortem lung samples were collected from ventilated preterm infants who died between 23 and 29 wk ("short-term ventilated") or between 36 and 39 wk ("long-term ventilated") corrected postmenstrual age. Results were compared with age-matched infants or stillborn infants ("early" and "late" control subjects). Microvascular growth was studied by anti-platelet endothelial cell adhesion molecule (PECAM)-1 immunohistochemistry, quantitative stereology, analysis of endothelial cell proliferation, and Western blot analysis of pulmonary PECAM-1 protein levels.

MEASUREMENTS

Measurements were made of capillary density, volume of air-exchanging parenchyma, volume of microvascular endothelial cells, Ki67 labeling index of endothelial cells, and PECAM-1/actin protein levels.

MAIN RESULTS

Lungs of long-term ventilated infants showed a significant (more than twofold) increase in volume of air-exchanging parenchyma and a 60% increase in total pulmonary microvascular endothelial volume compared with late control subjects, associated with 60% higher pulmonary PECAM-1 protein levels. The marked expansion of the pulmonary microvasculature in ventilated lungs was, at least partly, attributable to brisk endothelial cell proliferation. The microvasculature of ventilated lungs appeared immature, retaining a saccular architectural pattern.

CONCLUSIONS

The pulmonary microvasculature of ventilated preterm infants displayed marked angiogenesis, nearly proportionate to the growth of the air-exchanging lung parenchyma. These results challenge the paradigm of microvascular growth arrest as a major pathogenic factor in BPD.

Role of CXCR2/CXCR2 ligands in vascular remodeling during bronchiolitis obliterans syndrome

Angiogenesis and vascular remodeling support fibroproliferative processes; however, no study has addressed the importance of angiogenesis during fibro-obliteration of the allograft airway during bronchiolitis obliterans syndrome (BOS) that occurs after lung transplantation. The ELR(+) CXC chemokines both mediate neutrophil recruitment and promote angiogenesis. Their shared endothelial cell receptor is the G-coupled protein receptor CXC chemokine receptor 2 (CXCR2). We found that elevated levels of multiple ELR(+) CXC chemokines correlated with the presence of BOS. Proof-of-concept studies using a murine model of BOS not only demonstrated an early neutrophil infiltration but also marked vascular remodeling in the tracheal allografts. In addition, tracheal allograft ELR(+) CXC chemokines were persistently expressed even in the absence of significant neutrophil infiltration and were temporally associated with vascular remodeling during fibro-obliteration of the tracheal allograft. Furthermore, in neutralizing studies, treatment with anti-CXCR2 Abs inhibited early neutrophil infiltration and later vascular remodeling, which resulted in the attenuation of murine BOS. A more profound attenuation of fibro-obliteration was seen when CXCR2(-/-) mice received cyclosporin A. This supports the notion that the CXCR2/CXCR2 ligand biological axis has a bimodal function during the course of BOS: early, it is important for neutrophil recruitment and later, during fibro-obliteration, it is important for vascular remodeling independent of neutrophil recruitment.