Exposure to hyperoxia decreases the expression of vascular endothelial growth factor and its receptors in adult rat lungs

Combination of pioglitazone, a PPARγ agonist, and synthetic surfactant B-YL prevents hyperoxia-induced lung injury in adult mice lung explants

INTRODUCTION

Hyperoxia-induced lung injury is characterized by acute alveolar injury, disrupted epithelial-mesenchymal signaling, oxidative stress, and surfactant dysfunction, yet currently, there is no effective treatment. Although a combination of aerosolized pioglitazone (PGZ) and a synthetic lung surfactant (B-YL peptide, a surfactant protein B mimic) prevents hyperoxia-induced neonatal rat lung injury, whether it is also effective in preventing hyperoxia-induced adult lung injury is unknown.

METHOD

Using adult mice lung explants, we characterize the effects of 24 and 72-h (h) exposure to hyperoxia on 1) perturbations in Wingless/Int (Wnt) and Transforming Growth Factor (TGF)-β signaling pathways, which are critical mediators of lung injury, 2) aberrations of lung homeostasis and injury repair pathways, and 3) whether these hyperoxia-induced aberrations can be blocked by concomitant treatment with PGZ and B-YL combination.

RESULTS

Our study reveals that hyperoxia exposure to adult mouse lung explants causes activation of Wnt (upregulation of key Wnt signaling intermediates β-catenin and LEF-1) and TGF-β (upregulation of key TGF-β signaling intermediates TGF-β type I receptor (ALK5) and SMAD 3) signaling pathways accompanied by an upregulation of myogenic proteins (calponin and fibronectin) and inflammatory cytokines (IL-6, IL-1β, and TNFα), and alterations in key endothelial (VEGF-A and its receptor FLT-1, and PECAM-1) markers. All of these changes were largely mitigated by the PGZ + B-YL combination.

CONCLUSION

The effectiveness of the PGZ + B-YL combination in blocking hyperoxia-induced adult mice lung injury ex-vivo is promising to be an effective therapeutic approach for adult lung injury in vivo.

Umbilical cord blood exosomes from very preterm infants with bronchopulmonary dysplasia aggravate lung injury in mice

Bronchopulmonary dysplasia (BPD) is characterized by abnormal development of the blood vessels and alveoli in lungs, which largely occurs in premature infants. Exosomes (EXO) from very preterm infants (VPI) with BPD (BPD-EXO) impair angiogenic activities of human umbilical vein endothelial cells (HUVECs) via EXO-miRNAs cargo. This study aimed to determine whether and how BPD-EXO affect the development of BPD in a mouse model. We showed that treating BPD mice with BPD-EXO chronically and irreversibly aggravated lung injury. BPD-EXO up-regulated 139 and down-regulated 735 genes in the mouse lung tissue. These differentially expressed genes were enriched to the MAPK pathway (e.g., Fgf9 and Cacna2d3), which is critical to angiogenesis and vascular remodeling. BPD-EXO suppressed expression of Fgf9 and Cacna2d3 in HUVECs and inhibited migration, tube formation, and increased cell apoptosis in HUVECs. These data demonstrate that BPD-EXO aggravate lung injury in BPD mice and impair lung angiogenesis, plausibly leading to adverse outcomes of VPI with BPD. These data also suggest that BPD-EXO could serve as promising targets for predicting and treating BPD.

NOX4 Mediates Epithelial Cell Death in Hyperoxic Acute Lung Injury Through Mitochondrial Reactive Oxygen Species

Management of acute respiratory distress involves O2 supplementation, which is lifesaving, but causes severe hyperoxic acute lung injury (HALI). NADPH oxidase (NOX) could be a major source of reactive oxygen species (ROS) in hyperoxia (HO). Epithelial cell death is a crucial step in the development of many lung diseases. Alveolar type II (AT2) cells are the metabolically active epithelial cells of alveoli that serve as a source of AT1 cells following lung injury. The aim of this study was to determine the possible role of AT2 epithelial cell NOX4 in epithelial cell death from HALI. Wild type (WT), Nox4 fl/fl (control), and Nox4 -/- Spc-Cre mice were exposed to room air (NO) or 95% O2 (HO) to investigate the structural and functional changes in the lung. C57BL/6J WT animals subjected to HO showed increased expression of lung NOX4 compared to NO. Significant HALI, increased bronchoalveolar lavage cell counts, increased protein levels, elevated proinflammatory cytokines and increased AT2 cell death seen in hyperoxic Nox4 fl/fl control mice were attenuated in HO-exposed Nox4 -/- Spc-Cre mice. HO-induced expression of NOX4 in MLE cells resulted in increased mitochondrial (mt) superoxide production and cell apoptosis, which was reduced in NOX4 siRNA silenced cells. This study demonstrates a novel role for epithelial cell NOX4 in accelerating lung epithelial cell apoptosis from HALI. Deletion of the Nox4 gene in AT2 cells or silencing NOX4 in lung epithelial cells protected the lungs from severe HALI with reduced apoptosis and decreased mt ROS production in HO. These results suggest NOX4 as a potential target for the treatment of HALI.

Capillary Changes Precede Disordered Alveolarization in a Mouse Model of Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD), the most common sequela of preterm birth, is a severe disorder of the lung that is often associated with long-lasting morbidity. A hallmark of BPD is the disruption of alveolarization, whose pathogenesis is incompletely understood. Here, we tested the vascular hypothesis that disordered vascular development precedes the decreased alveolarization associated with BPD. Neonatal mouse pups were exposed to 7, 14, or 21 days of normoxia (21% O₂) or hyperoxia (85% O₂) with n = 8-11 for each group. The right lungs were fixed by vascular perfusion and investigated by design-based stereology or three-dimensional reconstruction of data sets obtained by serial block-face scanning EM. The alveolar capillary network of hyperoxia-exposed mice was characterized by rarefaction, partially altered geometry, and widening of capillary segments as shown by three-dimensional reconstruction. Stereology revealed that the development of alveolar epithelium and capillary endothelium was decreased in hyperoxia-exposed mice; however, the time course of these effects was different. That the surface area of the alveolar epithelium was smaller in hyperoxia-exposed mice first became evident at Day 14. In contrast, the surface area of the endothelium was reduced in hyperoxia-exposed mouse pups at Day 7. The thickness of the air-blood barrier decreased during postnatal development in normoxic mice, whereas it increased in hyperoxic mice. The endothelium and the septal connective tissue made appreciable contributions to the thickened septa. In conclusion, the present study provides clear support for the idea that the stunted alveolarization follows the disordered microvascular development, thus supporting the vascular hypothesis of BPD.

Effect of low VEGF on lung development and function

Vascular endothelial growth factor (VEGF) is important for lung development and function but ideal mouse models are limited to decipher the quantitative relationship between VEGF expression levels and its proper development and pathogenesis. Human SPC promoter has been used to faithfully express genes or cDNAs in the pulmonary epithelium in many transgenic mouse models. In the study, a mouse model of lung-specific and reversible VEGF repression (hspc-rtTR^tg/+/Vegf^tetO/tetO) was generated. Human SPC promoter was used to drive lung-specific rtTR expression, a cDNA coding for doxycycline-regulated transcription repression protein. By crossing with Vegf^tetO/tetO mice, that has tetracycline operator sequences insertion in 5'-UTR region, it allows us to reversibly inhibit lung VEGF transcription from its endogenous level through doxycycline food, water or injection. The tissue-specific inhibition of VEGF is used to mimic abnormal expression levels of VEGF in lung. Reduced VEGF expression in lung is confirmed by quantitative real time PCR and immunoblotting. Lung development and structure was analyzed by histology analysis and found significantly affected under low VEGF. The pulmonary epithelium and alveolarization are found abnormal with swelling alveolar septum and enlargement of air space. Genome-wide gene expression analysis identified that immune activities are involved in the VEGF-regulated lung functions. The transgenic mouse model can be used to mimic human pulmonary diseases. The mouse model confirms the important regulatory roles of epithelial expressed VEGF in lung development and function. This mouse model is valuable for studying VEGF-regulated lung development, pathogenesis and drug screening under low VEGF expression.

Assessment of the Alveolar Capillary Network in the Postnatal Mouse Lung in 3D Using Serial Block-Face Scanning Electron Microscopy

The alveolar capillary network (ACN) has a large surface area that provides the basis for an optimized gas exchange in the lung. It needs to adapt to morphological changes during early lung development and alveolarization. Structural alterations of the pulmonary vasculature can lead to pathological functional conditions such as in bronchopulmonary dysplasia and various other lung diseases. To understand the development of the ACN and its impact on the pathogenesis of lung diseases, methods are needed that enable comparative analyses of the complex three-dimensional structure of the ACN at different developmental stages and under pathological conditions. In this study a newborn mouse lung was imaged with serial block-face scanning electron microscopy (SBF-SEM) to investigate the ACN and its surrounding structures before the alveolarization process begins. Most parts but not all of the examined ACN contain two layers of capillaries, which were repeatedly connected with each other. A path from an arteriole to a venule was extracted and straightened to allow cross-sectional visualization of the data along the path within a plane. This allows a qualitative characterization of the structures that erythrocytes pass on their way through the ACN. One way to define regions of the ACN supplied by specific arterioles is presented and used for analyses. Pillars, possibly intussusceptive, were found in the vasculature but no specific pattern was observed in regard to parts of the saccular septa. This study provides 3D information with a resolution of about 150 nm on the microscopic structure of a newborn mouse lung and outlines some of the potentials and challenges of SBF-SEM for 3D analyses of the ACN.

Comparison of Mean VEGF-A Expression Between Acute Ischemic Stroke Patients and Non-Ischemic Stroke Subjects

BACKGROUND

Glucose and oxygen supply to neurons are disrupted during acute ischemic stroke, resulting in hypoxia. This event, in turn, activates the transcription of hypoxia-inducible factor (HIF-1), which is responsible for activating genes responsible for angiogenesis, including vascular endothelial growth factor (VEGF). VEGF and their receptor systems exert complex mechanisms of angiogenesis, including the stimulator, inhibitors, angiogenic and modulator. VEGF-A is the primary regulator of angiogenesis, both during physiological and pathological conditions. Nevertheless, the role of VEGF on the prognosis of hypoxia remains controversial.

AIM

The purpose of this study was to address if there is any difference between the mean expression of VEGF-A between acute ischemic patients and non-ischemic stroke subjects.

METHODS

This was an observational study with a cross-sectional design, the population in this research is the acute ischemic stroke patients and non-ischemic stroke subjects, which were admitted on Emergency Room and later treated in the Stroke Unit, Dr Sardjito General Hospital, Yogyakarta, Indonesia. Subjects were recruited using the purposive method, yielding a total of 64 subjects on both groups. Diagnosis of acute ischemic stroke was established using a head CT scan. Patients who meet the inclusion criteria and willing to participate in the study were asked to provide informed consent. Laboratory analysis was conducted during the first 24 hours after being treated at Stroke Unit, Dr Sardjito General Hospital, Yogyakarta, Indonesia, with venous blood was withdrawn VEGF-A levels between acute ischemic stroke and non-ischemic stroke subjects were subsequently compared. Categorical variables (including gender) were tested using either chi-square or Fisher exact test. Interval data was examined using student t-test if data distribution was normal.

RESULTS

As many as 35 acute ischemic stroke and 35 non-ischemic stroke patients were included in the study, among whom were 18 men (51.43%) and 17 women (48.57%) among stroke patients and 21 (60%) men and 14 (40%) women among subjects without stroke. The average of the subject's age on stroke and non-ischemic stroke group was 58.51 and 48.57 years old. VEGF-A levels were significantly higher in the non-stroke group (561.77 ± 377.92) compared with stroke group (397.78 ± 181.53) with p = 0.02.

CONCLUSION

expression of VEGF-A in acute ischemic stroke group was lower when compared with the non-stroke group.

Mechanical ventilation strategies alter cardiovascular biomarkers in an infant rat model

Mechanical ventilation (MV) is routinely used in pediatric general anesthesia and critical care, but may adversely affect the cardiocirculatory system. Biomarkers are increasingly measured to assess cardiovascular status and improve clinical treatment decision-making. As the impact of mechanical ventilation strategies on cardiovascular biomarkers in ventilated infants is largely unknown, we conducted this retrospective study in a healthy in vivo infant rat ventilation model using 14-days old Wistar rats. We hypothesized that 2 h of mechanical ventilation with high and low positive end-expiratory pressure (PEEP), hyperoxemia, hypoxemia, hypercapnia, and hypocapnia would significantly impact B-type natriuretic peptide (BNP), vascular endothelial growth factor (VEGF), and endothelin-1 (ET-1). We found BNP to be driven by both high (9 cmH₂ O) and low (1 cmH₂ O) PEEP compared to ventilated control animals (P < 0.05). VEGF concentrations were associated with high PEEP, hyperoxemia, hypoxemia, and hypocapnia (P < 0.05), whereas ET-1 levels were changed only in response to hypoxemia (P < 0.05). In conclusion, the mode of mechanical ventilation alters plasma biomarker concentrations. Moreover, BNP and VEGF might serve as surrogate parameters for ventilation induced cardiovascular compromise and lung tissue damage. Furthermore, our data support the hypothesis, that sudden onset of hyperoxemia may trigger a quick VEGF release as a possible cellular survival reflex.

Recent developments in 3-D reconstruction and stereology to study the pulmonary vasculature

Alterations of the pulmonary vasculature are an important feature of human lung diseases such as chronic obstructive pulmonary disease, pulmonary hypertension, and bronchopulmonary dysplasia. Experimental studies to investigate the pathogenesis or a therapeutic intervention in animal models of these diseases often require robust, meaningful, and efficient morphometric data that allow for appropriate statistical testing. The gold standard for obtaining such data is design-based stereology. However, certain morphological characteristics of the pulmonary vasculature make the implementation of stereological methods challenging. For example, the alveolar capillary network functions according to the sheet flow principle, thus making unbiased length estimations impossible and requiring other strategies to obtain mechanistic morphometric data. Another example is the location of pathological changes along the branches of the vascular tree. For developmental defects like in bronchopulmonary dysplasia or for pulmonary hypertension, it is important to know whether certain segments of the vascular tree are preferentially altered. This cannot be overcome by traditional stereological methods but requires the combination of a three-dimensional data set and stereology. The present review aims at highlighting the great potential while discussing the major challenges (such as time consumption and data volume) of this combined approach. We hope to raise interest in the potential of this approach and thus stimulate solutions to overcome the existing challenges.

Effects of trauma, hemorrhagic shock, and chronic stress on lung vascular endothelial growth factor

BACKGROUND

Vascular endothelial growth factor (VEGF) and its receptors (VEGFR-1 and VEGFR-2) regulate vascular permeability and endothelial cell survival. We hypothesized that hemorrhagic shock (HS) and chronic stress (CS) would increase expression of lung VEGF and its receptors, potentiating pulmonary edema in lung tissue.

MATERIALS AND METHODS

Male Sprague-Dawley rats aged 8-9 wk were randomized: naïve control, lung contusion (LC), LC followed by HS (LCHS), and LCHS with CS in a restraint cylinder for 2 h/d (LCHS/CS). Animals were sacrificed on days 1 and 7. Expressions of lung VEGF, VEGFR-1, and VEGFR-2 were determined by polymerase chain reaction. Lung Injury Score (LIS) was graded on light microscopy by inflammatory cell counts, interstitial edema, pulmonary edema, and alveolar integrity (range: 0 = normal; 8 = severe injury).

RESULTS

Seven days after LC, lung VEGF and VEGFR-1 were increased, and lung tissue healed (LIS: 0.8 ± 0.8). However, 7 d after LCHS and LCHS/CS, lung VEGF and VEGFR-1 expressions were decreased. VEGFR-2 was also decreased after LCHS/CS. LIS was elevated 7 d after LCHS and LCHS/CS (6.5 ± 1.0 and 8.2 ± 0.8). Increased LIS after LCHS and LCHS/CS was because of higher inflammatory cell counts, increased interstitial edema, and loss of alveolar integrity, whereas pulmonary edema was unchanged.

CONCLUSIONS

Elevation of lung VEGF and VEGFR-1 expressions after LC alone was associated with healing of injured lung tissue. Expressions of VEGF, VEGFR-1, and VEGFR-2 were reduced after LCHS and LCHS/CS, and injured lung tissue did not heal. Persistent lung injury after severe trauma was because of inflammation rather than pulmonary edema.

Vascular Endothelial Growth Factor Expression (VEGF) in Salivary Glands of Young and Old Hyperoxic Rats

The aim of this study is to evaluate whether hyperoxia and age can influence the expression of vascular endothelial growth factor (VEGF) in the salivary glands of rats. Our study was carried out on four groups of male Wistar rats (total 24 rats). One group was composed of 6 young rats (3 months old); another group by 6 old rats (24 months old). The rats belonging to the first two groups were exposed to hyperoxia (98–100% O2) for a period of 60–65 hours in a large Plexiglas chamber; the other two groups were control groups. The rats were then anaesthetized with Nembutal (30 mg/kg) intraperitoneally and then killed. The submandibular glands were removed and processed for immunohistochemical analysis of VEGF. The exposure to hyperoxia decreased salivary gland VEGF expression in rats. The tissues analyzed (nervous tissue, vascular endothelium, myoepithelial cells, ductal endothelium, mucinous glands) always expressed VEGF, thus demonstrating that not only vascular endothelial cells, but also the other elements evaluated, have a role in the neoangiogenesis. Only in the serous glands, in both normoxic and hyperoxic young and old rats, was the VEGF expression constantly negative and it did not influence the neoangiogenesis. The vascular growth is a fundamental part of normal salivary gland development, so we speculated that strategies aimed at preservation or promotion of salivary gland VEGF expression may mitigate or attenuate hyperoxia-induced gland microvascular injury. Further studies specifically aimed at investigating these prospects are warranted.

Sequestration of Vascular Endothelial Growth Factor (VEGF) Induces Late Restrictive Lung Disease

Rationale

Neonatal respiratory distress syndrome is a restrictive lung disease characterized by surfactant deficiency. Decreased vascular endothelial growth factor (VEGF), which demonstrates important roles in angiogenesis and vasculogenesis, has been implicated in the pathogenesis of restrictive lung diseases. Current animal models investigating VEGF in the etiology and outcomes of RDS require premature delivery, hypoxia, anatomically or temporally limited inhibition, or other supplemental interventions. Consequently, little is known about the isolated effects of chronic VEGF inhibition, started at birth, on subsequent developing lung structure and function.

Objectives

To determine whether inducible, mesenchyme-specific VEGF inhibition in the neonatal mouse lung results in long-term modulation of AECII and whole lung function.

Methods

Triple transgenic mice expressing the soluble VEGF receptor sFlt-1 specifically in the mesenchyme (Dermo-1/rtTA/sFlt-1) were generated and compared to littermate controls at 3 months to determine the impact of neonatal downregulation of mesenchymal VEGF expression on lung structure, cell composition and function. Reduced tissue VEGF bioavailability has previously been demonstrated with this model.

Measurements and Main Results

Triple transgenic mice demonstrated restrictive lung pathology. No differences in gross vascular development or protein levels of vascular endothelial markers was noted, but there was a significant decrease in perivascular smooth muscle and type I collagen. Mutants had decreased expression levels of surfactant protein C and hypoxia inducible factor 1-alpha without a difference in number of type II pneumocytes.

Conclusions

These data show that mesenchyme-specific inhibition of VEGF in neonatal mice results in late restrictive disease, making this transgenic mouse a novel model for future investigations on the consequences of neonatal RDS and potential interventions.

Transplacental Administration of Rosiglitazone Attenuates Hyperoxic Lung Injury in a Preterm Rabbit Model

INTRODUCTION

Continuous improvements in perinatal care have allowed the survival of increasingly more prematurely born infants. The establishment of respiration in an extremely immature yet still developing lung results in chronic lung injury with significant mortality and morbidity. We experimentally evaluated a novel medical strategy to prevent hyperoxia-induced lung injury by prenatal rosiglitazone.

MATERIALS AND METHODS

Pregnant rabbits were injected with saline or rosiglitazone (3 mg/kg) 48 and 24 h prior to preterm delivery at 28 days of gestation (term = 31 days). The pups were held in normoxia (21% O2) or hyperoxia (>95% O2), and assessment was done at three different time points (1 h, 24 h and 7 days).

RESULTS

The administration of rosiglitazone resulted in a significant decrease in tissue damping (resistance) on day 7. Furthermore, significantly increased expression of vascular endothelial growth factor, fetal liver kinase 1 and surfactant protein B immediately after delivery was noted by immunohistochemistery. On day 7, there was a more mature lung parenchymal architecture in rosiglitazone-exposed pups.

DISCUSSION

In a preterm rabbit model, prenatal maternal administration of rosiglitazone attenuates neonatal hyperoxic lung injury and results in a more mature pulmonary parenchyma.

The role of vascular endothelial growth factor receptor-1 signaling in compensatory contralateral lung growth following unilateral pneumonectomy

Compensatory lung growth models have been widely used to investigate alveolization because the remaining lung can be kept intact and volume loss can be controlled. Vascular endothelial growth factor (VEGF) plays an important role in blood formation during lung growth and repair, but the precise mechanisms involved are poorly understood; therefore, the aim of this study was to investigate the role of VEGF signaling in compensatory lung growth. After left pneumonectomy, the right lung weight was higher in VEGF transgenic mice than wild-type (WT) mice. Compensatory lung growth was suppressed significantly in mice injected with a VEGF neutralizing antibody and in VEGF receptor-1 tyrosine kinase-deficient mice (TK(-/-) mice). The mobilization of progenitor cells expressing VEGFR1(+) cells from bone marrow and the recruitment of these cells to lung tissue were also suppressed in the TK(-/-) mice. WT mice transplanted with bone marrow from TK(-/-)transgenic GFP(+) mice had significantly lower numbers of GFP(+)/aquaporin 5(+), GFP(+)/surfactant protein A(+), and GFP(+)/VEGFR1(+) cells than WT mice transplanted with bone marrow from WTGFP(+) mice. The GFP(+)/VEGFR1(+) cells also co-stained for aquaporin 5 and surfactant protein A. Overall, these results suggest that VEGF signaling contributes to compensatory lung growth by mobilizing VEGFR1(+) cells.

Role of microRNA-150 and glycoprotein nonmetastatic melanoma protein B in angiogenesis during hyperoxia-induced neonatal lung injury

Glycoprotein nonmetastatic melanoma protein B (GPNMB), a transmembrane protein, has been reported to have an important role in tissue repair and angiogenesis. Recently, we have demonstrated that hyperoxia exposure down-regulates microRNA (miR)-150 expression and concurrent induction of its target gene, GPNMB, in neonatal rat lungs. This study aimed to test the hypothesis that soluble GPNMB (sGPNMB) promotes angiogenesis in the hyperoxic neonatal lungs. Wild-type (WT) or miR-150 knockout (KO) neonates, exposed to 95% O2 for 3, 6, and 10 days, were evaluated for lung phenotypes, GPNMB protein expression in the lungs, and sGPNMB levels in the bronchoalveolar lavage. Angiogenic effects of sGPNMB were examined both in vitro and in vivo. After a 6-day exposure, similar analyses were performed in WT and miR-150 KO neonates during recovery at 7, 14, and 21 days. miR-150 KO neonates displayed an increased capillary network, decreased inflammation, and less alveolar damage compared with WT neonates after hyperoxia exposure. The early induction of GPNMB and sGPNMB were found in miR-150 KO neonates. The recombinant GPNMB, which contained a soluble portion of GPNMB, promoted endothelial tube formation in vitro and enhanced angiogenesis in vivo. The increased capillaries in the hyperoxic lungs of miR-150 KO neonates appeared dysmorphic. They were abnormally enlarged in size and occasionally laid at subepithelial regions in the alveoli. However, the lung architecture returned to normal during recovery, suggesting that abnormal vascularity during hyperoxia does not affect postnatal lung development. GPNMB plays an important role in angiogenesis during hyperoxia injury. Treatment with GPNMB may offer a novel therapeutic approach in reducing pathologic complications in bronchopulmonary dysplasia.

Postnatal hyperoxia exposure differentially affects hepatocytes and liver haemopoietic cells in newborn rats

Premature newborns are frequently exposed to hyperoxic conditions and experimental data indicate modulation of liver metabolism by hyperoxia in the first postnatal period. Conversely, nothing is known about possible modulation of growth factors and signaling molecules involved in other hyperoxic responses and no data are available about the effects of hyperoxia in postnatal liver haematopoiesis. The aim of the study was to analyse the effects of hyperoxia in the liver tissue (hepatocytes and haemopoietic cells) and to investigate possible changes in the expression of Vascular Endothelial Growth Factor (VEGF), Matrix Metalloproteinase 9 (MMP-9), Hypoxia-Inducible Factor-1α (HIF-1α), endothelial Nitric Oxide Synthase (eNOS), and Nuclear Factor-kB (NF-kB). Experimental design of the study involved exposure of newborn rats to room air (controls), 60% O₂ (moderate hyperoxia), or 95% O₂ (severe hyperoxia) for the first two postnatal weeks. Immunohistochemical and Western blot analyses were performed. Severe hyperoxia increased hepatocyte apoptosis and MMP-9 expression and decreased VEGF expression. Reduced content in reticular fibers was found in moderate and severe hyperoxia. Some other changes were specifically produced in hepatocytes by moderate hyperoxia, i.e., upregulation of HIF-1α and downregulation of eNOS and NF-kB. Postnatal severe hyperoxia exposure increased liver haemopoiesis and upregulated the expression of VEGF (both moderate and severe hyperoxia) and eNOS (severe hyperoxia) in haemopoietic cells. In conclusion, our study showed different effects of hyperoxia on hepatocytes and haemopoietic cells and differential involvement of the above factors. The involvement of VEGF and eNOS in the liver haemopoietic response to hyperoxia may be hypothesized.

Multiple wall in-folds sub-divide single segments during capillary regression in hyperoxic acute lung injury

The present study provides further insight into the structural processes that remodel pulmonary capillaries in the injured adult lung. Early in hyperoxia acute lung injury (HALI), many sub-dividing segments are present throughout the capillary network before segment occlusion and loss predominate and capillary density decreases later in the period. A second segment sub-division triggered in regenerating capillaries after air breathing (post-HALI) demonstrates a similar mechanism of organization at a time of contrasting change in the capillary density. As we have previously reported, the process of segment sub-division includes in-folding of the endothelial-epithelial surface (alveolar-capillary membrane) to form inter-luminal structures (ILSs) and loops, with loop separation increasing segment number. Unexpectedly, the findings support remodeling of the capillary density by wall in-folding in acute lung injury, demonstrating a similar mechanism in capillary regression as well as in regeneration in the adult lung.

Alveolar oxygen tension and angio-architecture of the distal adult lung

The present study demonstrates the fine structure of pulmonary capillaries first injured and then undergoing growth in response to a change in the ambient alveolar oxygen tension. Breathing a high fraction of inspired oxygen (FiO2 0.75) triggers restriction by endothelial cell injury and effacement leading to segment narrowing and shortening and segment loss as demonstrated by a fall in density. Subsequently, breathing a relatively low fraction (FiO2 0.21) triggers capillary assembly (angiogenesis), which reverses the changes. The data underscore the structural reprogramming (reduction and restoration) of pulmonary capillaries in response to significant shifts in oxygen tension.

Hypoxia-induced expression of VEGF splice variants and protein in four retinal cell types

The purpose of this study was to investigate the hypoxia-induced Vegf120, Vegf164 and Vegf188 mRNA expression profiles in rat Müller cells (MC), astrocytes, retinal pigmented epithelial cells (RPE) and retinal microvascular endothelial cells (RMEC) and correlate these findings to VEGF secreted protein. Cultured cells were exposed to normoxia or hypoxia. Total RNA was isolated from cell lysates and Vegf splice variant mRNA copy numbers were assayed by a validated qRT-PCR external calibration curve method. mRNA copy numbers were normalized to input total RNA. Conditioned medium was collected from cells and assayed for total VEGF protein by ELISA. Hypoxia increased total Vegf mRNA and secreted protein in all the retinal cell types, with the highest levels observed in MC and astrocytes ranking second. Total Vegf mRNA levels in hypoxic RPE and RMEC were comparable; however, the greatest hypoxic induction of each Vegf splice variant mRNA was observed in RMEC. RPE and RMEC ranked 3rd and 4th respectively, in terms of secreted total VEGF protein in hypoxia. The Vegf120, Vegf164 and Vegf188 mRNA splice variants were all increased in hypoxic cells compared to normoxic controls. In normoxia, the relative Vegf splice variant mRNA levels ranked from highest to lowest for each cell type were Vegf164 > Vegf120 > Vegf188. Hypoxic induction did not alter this ranking, although it did favor an increased stoichiometry of Vegf164 mRNA over the other two splice variants. MC and astrocytes are likely to be the major sources of total Vegf, Vegf164 splice variant mRNAs, and VEGF protein in retinal hypoxia.

Mesenchymal stem cells protect against neonatal rat hyperoxic lung injury

OBJECTIVES

Bronchopulmonary dysplasia (BPD) is a significant global health problem and currently lacks effective therapy. We established a neonatal rat model of BPD to investigate therapeutic potential of bone marrow-derived mesenchymal stem cells (BMSCs) in neonatal hyperoxic lung injury.

METHODS

BMSCs were isolated, identified, and transfected by lentiviral vector carrying green fluorescent protein gene in vitro. Neonatal Sprague-Dawley rats were injected intravenously with either BMSCs or phosphate-buffered saline following 95% oxygen exposure, and assessed for the survival rate and alveolar injury during recovery.

RESULTS

Treatment with BMSCs after oxygen exposure for 7 days improved survival of neonatal rat during recovery. BMSCs protected against neonatal rat hyperoxic lung injury during recovery as demonstrated by enhanced expression of AQP5 and SP-C, likely due to the suppression of alveolar cell apoptosis and lung inflammation responses to oxygen with up-regulation of the expression of BCL-2 gene and down-regulation of the expression of BAX gene and stimulation of vascular endothelial growth factor and so on.

CONCLUSIONS

BMSCs protect against O2-mediated injury partially through stimulation of potent mediators that participate in tissue repair.

Prenatal hypoxia downregulates the expression of pulmonary vascular endothelial growth factor and its receptors in fetal mice

BACKGROUND

Previous reports showed that prenatal hypoxia delays the process of lung maturation. Vascular endothelial growth factor (VEGF) and its receptors were important for lung development. However, the role of VEGF and VEGF receptors in altered fetal lung development and maturation induced by prenatal hypoxia remains unknown.

OBJECTIVES

To elucidate the role of VEGF and VEGF receptors in altered fetal lung development and maturation induced by prenatal hypoxia.

METHODS

Lung sections of control and maternal hypoxic fetal mice were used for the determination of lung development and total RNA isolated from lung homogenates were used for determination of the expression patterns of VEGF, Flt-1, Flk-1, hypoxia-inducible factor (HIF)-1α, HIF-2α, surfactant protein (SP)-A, SP-B, SP-C, and SP-D by quantitative real-time RT-PCR.

RESULTS

Prenatal hypoxia resulted in fetal mice body weight gain impairment, delayed fetal pulmonary aeration and maturation. Pulmonary SP-A, SP-B, SP-C, and SP-D mRNA were all decreased in the prenatal hypoxia group. In addition, we demonstrated that prenatal hypoxia inhibited the developmental increase of pulmonary HIF-1α and HIF-2α expression and resulted in decreasing VEGF and its receptors (Flt-1 and Flk-1) at the mRNA expression level and VEGF protein level in fetal lungs. These inhibitory effects persisted and progressed even when the dams were returned to air.

CONCLUSIONS

We suggest that prenatal hypoxia insults, at least in late gestation, influence pulmonary VEGF and VEGF receptor expression through the down-regulation of HIF pathways and impair fetal lung growth and maturation.

Exogenous surfactant protects against endotoxin induced acute respiratory distress syndrome in rodents via vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor which is abundantly expressed in the normal lung and is released by numerous cell types. Using a bacteria-induced lung injury model and surfactant therapy in rats, VEGF expression in lung was investigated. Sprague Dawley male rats were divided into four groups: buffer controls; rats challenged with LPS (055:B5 E. coli); challenged with LPS and treated with porcine surfactant (P-SF); and challenged with LPS and treated with synthetic surfactant (S-SF). The expressions of VEGF, PCNA, and BrdU were studied. VEGF protein expression was decreased in comparison to the control rats, as seen by both Western immunoblot and immunohistochemistry. Protein expression of PCNA and proliferation index as determined by both PCNA and BrdU immunostaining were also seen to be decreased in the LPS-treated animals, and with the surfactant treatment the expression was increased. The downregulation of VEGF in the alveolar space may reflect the recovery from acute lung injury, which leads to the limited endothelial permeability, and may participate in the decrease in capillary number, as observed during acute respiratory distress syndrome with potentially significant clinical consequences.

Neonatal hyperoxia causes pulmonary vascular disease and shortens life span in aging mice

Bronchopulmonary dysplasia is a chronic lung disease observed in premature infants requiring oxygen supplementation and ventilation. Although the use of exogenous surfactant and protective ventilation strategies has improved survival, the long-term pulmonary consequences of neonatal hyperoxia are unknown. Here, we investigate whether neonatal hyperoxia alters pulmonary function in aging mice. By 67 weeks of age, mice exposed to 100% oxygen between postnatal days 1 to 4 showed significantly a shortened life span (56.6% survival, n = 53) compared to siblings exposed to room air as neonates (100% survival, n = 47). Survivors had increased lung compliance and decreased elastance. There was also right ventricular hypertrophy and pathological evidence for pulmonary hypertension, defined by reduction of the distal microvasculature and the presence of numerous dilated arterioles expressing von Willebrand factor and α-smooth muscle actin. Consistent with recent literature implicating bone morphogenetic protein (BMP) signaling in pulmonary vascular disease, BMP receptors and downstream phospho-Smad1/5/8 were reduced in lungs of aging mice exposed to neonatal oxygen. BMP signaling alterations were not observed in 8-week-old mice. These data suggest that loss of BMP signaling in aged mice exposed to neonatal oxygen is associated with a shortened life span, pulmonary vascular disease, and associated cardiac failure. People exposed to hyperoxia as neonates may be at increased risk for pulmonary hypertension.

The chitinase-like proteins breast regression protein-39 and YKL-40 regulate hyperoxia-induced acute lung injury

RATIONALE

Prolonged exposure to 100% O(2) causes hyperoxic acute lung injury (HALI), characterized by alveolar epithelial cell injury and death. We previously demonstrated that the murine chitinase-like protein, breast regression protein (BRP)-39 and its human homolog, YKL-40, inhibit cellular apoptosis. However, the regulation and roles of these molecules in hyperoxia have not been addressed.

OBJECTIVES

We hypothesized that BRP-39 and YKL-40 (also called chitinase-3-like 1) play important roles in the pathogenesis of HALI.

METHODS

We characterized the regulation of BRP-39 during HALI and the responses induced by hyperoxia in wild-type mice, BRP-39-null (-/-) mice, and BRP-39(-/-) mice in which YKL-40 was overexpressed in respiratory epithelium. We also compared the levels of tracheal aspirate YKL-40 in premature newborns with respiratory failure.

MEASUREMENTS AND MAIN RESULTS

These studies demonstrate that hyperoxia inhibits BRP-39 in vivo in the murine lung and in vitro in epithelial cells. They also demonstrate that BRP-39(-/-) mice have exaggerated permeability, protein leak, oxidation, inflammatory, chemokine, and epithelial apoptosis responses, and experience premature death in 100% O(2). Lastly, they demonstrate that YKL-40 ameliorates HALI, prolongs survival in 100% O(2), and rescues the exaggerated injury response in BRP-39(-/-) animals. In accord with these findings, the levels of tracheal aspirate YKL-40 were lower in premature infants treated with hyperoxia for respiratory failure who subsequently experienced bronchopulmonary dysplasia or death compared with those that did not experience these complications.

CONCLUSIONS

These studies demonstrate that hyperoxia inhibits BRP-39/YKL-40, and that BRP-39 and YKL-40 are critical regulators of oxidant injury, inflammation, and epithelial apoptosis in the murine and human lung.

The 'new' bronchopulmonary dysplasia: challenges and commentary

Lung development is orchestrated by highly integrated morphogenic programs of interrelated patterns of gene and protein expression. Injury to the developing lung in the canalicular and saccular phases of lung development alters subsequent alveolar and vascular development resulting in simplified alveolar structures, dysmorphic capillary configuration, variable interstitial cellularity and fibroproliferation that are characteristic of the 'new' bronchopulmonary dysplasia (BPD). Fetal and neonatal infection, abnormal stretch of the developing airways and alveoli, altered expression of surfactant proteins (or genetically altered proteins), polymorphisms of genes encoding for vascular endothelial growth factors, and reactive oxygen species result in imparied gas exchange in the developing lung. However, the 'new' BPD represents only one form of neonatal chronic lung disease and the consistent use of both the physiologic definition and severity scale would provide greater accuracy in determining the impact of the disease currently defined by its treatment. Our present labelling of the clinical state of oxygen supplementation and/or ventilatory support at 36 weeks' postmenstrual age and the histopathologic severity of alveolar arrest and vascular 'simplification' may not always be predictive of the degree of altered lung development and thus longer-term pulmonary function evaluations are needed to determine the impact of this disorder in specific infants. The proposed role of novel molecular therapies, and the combined effects of currently established therapies, as well as exogenous surfactant and inhaled nitric oxide or repetitive surfactant dosing, on the severity and incidence of new BPD hold considerable promise for reducing the long-term pulmonary morbidity among infants delivered prematurely.

Neonatal oxygen adversely affects lung function in adult mice without altering surfactant composition or activity

Despite its potentially adverse effects on lung development and function, supplemental oxygen is often used to treat premature infants in respiratory distress. To understand how neonatal hyperoxia can permanently disrupt lung development, we previously reported increased lung compliance, greater alveolar simplification, and disrupted epithelial development in adult mice exposed to 100% inspired oxygen fraction between postnatal days 1 and 4. Here, we investigate whether oxygen-induced changes in lung function are attributable to defects in surfactant composition and activity, structural changes in alveolar development, or both. Newborn mice were exposed to room air or 40%, 60%, 80%, or 100% oxygen between postnatal days 1 and 4 and allowed to recover in room air until 8 wk of age. Lung compliance and alveolar size increased, and airway resistance, airway elastance, tissue elastance, and tissue damping decreased, in mice exposed to 60-80% oxygen; changes were even greater in mice exposed to 100% oxygen. These alterations in lung function were not associated with changes in total protein content or surfactant phospholipid composition in bronchoalveolar lavage. Moreover, surface activity and total and hydrophobic protein content were unchanged in large surfactant aggregates centrifuged from bronchoalveolar lavage compared with control. Instead, the number of type II cells progressively declined in 60-100% oxygen, whereas levels of T1alpha, a protein expressed by type I cells, were comparably increased in mice exposed to 40-100% oxygen. Thickened bundles of elastin fibers were also detected in alveolar walls of mice exposed to > or = 60% oxygen. These findings support the hypothesis that changes in lung development, rather than surfactant activity, are the primary causes of oxygen-altered lung function in children who were exposed to oxygen as neonates. Furthermore, the disruptive effects of oxygen on epithelial development and lung mechanics are not equivalently dose dependent.

Vascular endothelial growth factor receptor and coreceptor expression in human acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is characterized by the development of noncardiogenic pulmonary edema, which has been related to the bioactivity of vascular endothelial growth factor (VEGF). Vascular endothelial growth factor receptors and coreceptors regulate this bioactivity. We hypothesized VEGF receptors 1 and 2 (VEGFR1, VEGFR2) and coreceptor neuropilin-1 (NRP-1) would be expressed in human lung tissue with a significant change in expression in ARDS lung.

METHODS

Archival "normal" (no lung pathology and non-ARDS), "early" (within 48 hours), and "later" (after day 7) ARDS lung-tissue sections (n = 5) were immunostained for VEGFR1, VEGFR2, and NRP-1 from human subjects (n = 4). Staining was assessed densitometrically using Histometrix software.

RESULTS

VEGFR1, VEGFR2, and NRP-1 were expressed on both sides of the alveolar-capillary membrane in both normal and ARDS human lung tissue. In later ARDS, there was a significant up-regulation of VEGFR1 and VEGFR2 versus normal and early ARDS (P < .0001). Neuropilin-1 was down-regulated in early ARDS versus normal lung (P < .05), with normalization in later ARDS (P < .001).

CONCLUSION

Differential temporal VEGFR1, VEGFR2, and NRP-1 up-regulation occurs in human ARDS, providing evidence of further functional regulation of VEGF bioactivity via VEGFR2 consistent with a protective role for VEGF in lung injury recovery. The mechanisms behind these observations remain to be clarified.

VEGF in biological control

Vascular endothelial growth factor A (VEGF-A) belongs to a family of heparin binding growth factors that include VEGF-B, VEGF-C, VEGF-D, and placental-like growth factor (PLGF). First discovered for its ability to regulate vascular endothelial cell permeability, VEGF is a well-known angiogenic factor that is important for vascular development and maintenance in all mammalian organs. The development of molecular tools and pharmacological agents to selectively inhibit VEGF function and block angiogenesis and/or vascular permeability has led to great promise in the treatment of various cancers, macular degeneration, and wound healing. However, VEGF is also important in animals for the regulation of angiogenesis, stem cell and monocyte/macrophage recruitment, maintenance of kidney and lung barrier functions and neuroprotection. In addition to its role in regulating endothelial cell proliferation, migration, and cell survival, VEGF receptors are also located on many non-endothelial cells and act through autrocrine pathways to regulate cell survival and function. The following review will discuss the role of VEGF in physiological angiogenesis as well as its role in non-angiogenic processes that take place in adult organs.

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.

Early inhaled nitric oxide treatment decreases apoptosis of endothelial cells in neonatal rat lungs after vascular endothelial growth factor inhibition

Vascular endothelial growth factor (VEGF) receptor blockade impairs lung growth and decreases nitric oxide (NO) production in neonatal rat lungs. Inhaled NO (iNO) treatment after VEGF inhibition preserves lung growth in infant rats by unknown mechanisms. We hypothesized that neonatal VEGF inhibition disrupts lung growth by causing apoptosis in endothelial cells, which is attenuated by early iNO treatment. Three-day-old rats received SU-5416, an inhibitor of VEGF receptor, or its vehicle and were raised in room air with or without iNO (10 ppm). SU-5416 reduced alveolar counts and lung vessel density by 28% ( P < 0.005) and 21% ( P < 0.05), respectively, as early as at 7 days of age. SU-5416 increased lung active caspase-3 protein by 60% at 5 days of age ( P < 0.05), which subsided by 7 days of age, suggesting a transient increase in lung apoptosis after VEGF blockade. Apoptosis primarily colocalized to lung vascular endothelial cells, and SU-5416 increased endothelial cell apoptotic index by eightfold at 5 days of age ( P <0.0001). iNO treatment after SU-5416 prevented the increases in lung active caspase-3 and in endothelial cell apoptotic index. There was no difference in alveolar type 2 cell number between control and SU-5416-treated rats. We conclude that neonatal VEGF receptor inhibition causes transient apoptosis in pulmonary endothelium, which is followed by persistently impaired lung growth. Early iNO treatment after VEGF inhibition reduces endothelial cell apoptosis in neonatal lungs. We speculate that enhancing endothelial cell survival after lung injury may preserve neonatal lung growth in bronchopulmonary dysplasia.

Epidermal growth factor-like domain 7 protects endothelial cells from hyperoxia-induced cell death

Hyperoxia is one of the major contributors to the development of bronchopulmonary dysplasia (BPD), a chronic lung disease in premature infants. Emerging evidence suggests that the arrested lung development of BPD is associated with pulmonary endothelial cell death and vascular dysfunction resulting from hyperoxia-induced lung injury. A better understanding of the mechanism of hyperoxia-induced endothelial cell death will provide critical information for the pathogenesis and therapeutic development of BPD. Epidermal growth factor-like domain 7 (EGFL7) is a protein secreted from endothelial cells. It plays an important role in vascular tubulogenesis. In the present study, we found that Egfl7 gene expression was significantly decreased in the neonatal rat lungs after hyperoxic exposure. The Egfl7 expression was returned to near normal level 2 wk after discounting oxygen exposure during recovery period. In cultured human endothelial cells, hyperoxia also significantly reduced Egfl7 expression. These observations suggest that diminished levels of Egfl7 expression might be associated with hyperoxia-induced endothelial cell death and lung injury. When we overexpressed human Egfl7 (hEgfl7) in EA.hy926 human endothelial cell line, we found that hEgfl7 overexpression could partially block cytochrome c release from mitochondria and decrease caspase-3 activation. Further Western blotting analyses showed that hEgfl7 overexpression could reduce expression of a proapoptotic protein, Bax, and increase expression of an antiapoptotic protein, Bcl-xL. Theses findings indicate that hEGFL7 may protect endothelial cell from hyperoxia-induced apoptosis by inhibition of mitochondria-dependent apoptosis pathway.

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

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

Intrauterine pulmonary hypertension impairs angiogenesis in vitro: role of vascular endothelial growth factor nitric oxide signaling

RATIONALE

Mechanisms that impair angiogenesis in neonatal persistent pulmonary hypertension (PPHN) are poorly understood.

OBJECTIVES

To determine if PPHN alters fetal pulmonary artery endothelial cell (PAEC) phenotype and impairs growth and angiogenesis in vitro, and if altered vascular endothelial growth factor-nitric oxide (VEGF-NO) signaling contributes to this abnormal phenotype.

METHODS

Proximal PAECs were harvested from fetal sheep that had undergone partial ligation of the ductus arteriosus in utero (PPHN) and age-matched control animals. Growth and tube formation +/- VEGF and NO stimulation and inhibition were studied in normal and PPHN PAECs. Western blot analysis was performed for VEGF, VEGF receptor-2 (VEGF-R2), and endothelial NO synthase (eNOS) protein content. NO production with VEGF administration was measured in normal and PPHN PAECs.

MEASUREMENTS AND MAIN RESULTS

PPHN PAECs demonstrate decreased growth and tube formation in vitro. VEGF and eNOS protein expression were decreased in PPHN PAECs, whereas VEGF-R2 protein expression was not different. VEGF and NO increased PPHN PAEC growth and tube formation to values achieved in normal PAECs. VEGF inhibition decreased growth and tube formation in normal and PPHN PAECs. NOS inhibition decreased growth in normal and PPHN PAECs, but tube formation was only reduced in normal PAECs. NO reversed the inhibitory effects of VEGF-R2 inhibition on tube formation in normal and PPHN PAECs. VEGF increased NO production in normal and PPHN PAECs.

CONCLUSIONS

PPHN in utero causes sustained impairment of PAEC phenotype in vitro, with reduced PAEC growth and tube formation and down-regulation of VEGF and eNOS protein. VEGF and NO enhanced growth and tube formation of PPHN PAECs.

Hyperoxia enhances VEGF release from A549 cells via post-transcriptional processes

Exposure of animals to hyperoxia decreases lung VEGF mRNA expression concomitant with an acute increase in VEGF protein within the epithelial lining fluid (ELF). The VEGF concentration in ELF is in excess of that found in the plasma, leading to the hypothesis that hyperoxia stimulates the release of VEGF protein from stores within the extracellular matrix. To test this hypothesis in a cell culture system, we exposed A549 cells to 95% O(2) (Ox) for 48 h followed by recovery in room air (RA) for 24 h. We found that Ox increased VEGF protein two- to threefold within the medium at 48 h of exposure and during recovery. Heparin clearing revealed the medium to contain a 50/50 mixture of the heparin-binding (VEGF(165)) and heparin-nonbinding (VEGF(121)) proteins and that Ox increased both proteins equally. Transcriptional activation of VEGF seems unlikely to explain the increase in VEGF protein, as expression of full-length and splice variant VEGF mRNA was unchanged by hyperoxia. Analysis of cell-associated VEGF proteins found that Ox increased the expression of VEGF(121) and VEGF(165) proteins. Blocking binding sites with exogenous heparin enhanced VEGF protein in the medium from RA-grown cells, whereas heparinase digestion of bound VEGF revealed a greater reserve of VEGF protein in RA cells. Collectively these findings indicate that hyperoxia enhances the expression of VEGF(121/165) proteins and facilitates the release of VEGF(165) from cell-associated stores. Increases in VEGF in ELF may represent an adaptive response fostering cell survival and type II cell proliferation in O(2)-induced lung injury.

Key developmental regulators change during hyperoxia-induced injury and recovery in adult mouse lung

Developmentally important genes have recently been linked to tissue regeneration and epithelial cell repair in neonatal and adult animals in several organs, including liver, skin, prostate, and musculature. We hypothesized that developmentally important genes play roles in lung injury repair in adult mice. Although there is considerable information known about these processes, the specific molecular pathways that mediate injury and regulate tissue repair are not fully elucidated. Using a hyperoxic injury model to study these mechanisms of lung injury and tissue repair, we selected the following genes based upon their known or putative roles in lung development and organogenesis: TTF-1, FGF9, FGF10, BMP4, PDGF-A, VEGF, Ptc, Shh, Sca-1, BCRP, CD45, and Cyclin-D2. Our findings demonstrate that several developmentally important genes (Sca-1, Shh, PDGF-A, VEGF, BCRP, CD45, BMP4, and Cyclin-D2) change during hyperoxic injury and normoxic recovery in mice, suggesting that adult lung may reactivate key developmental regulatory pathways for tissue repair. The mRNA for one gene (TTF-1), unchanged during hyperoxia, was upregulated late in recovery phase. These novel findings provide the basis for testing the efficacy of post-injury lung repair in animals genetically modified to inactivate or express individual molecules.

VEGF-induced heme oxygenase-1 confers cytoprotection from lethal hyperoxia in vivo

Prolonged exposure to hyperoxia results in hyperoxic acute lung injury (HALI). Vascular endothelial growth factor (VEGF) has been shown to have cytoprotective effects and prolong survival in an in vivo model of HALI. Heme oxygenase-1 (HO-1) has protective effects in hyperoxia; therefore, we hypothesized that induction of HO-1 would be an important contributor to VEGF-induced cytoprotection. Using inducible, lung-specific VEGF overexpressing transgenic mice, we demonstrated that VEGF is a potent inducer of HO-1 mRNA and protein in mouse lung. To evaluate the effect of inhibition of HO-1 on injury, VEGF transgenic mice were treated with HO-1 short interfering RNA (HO-1 siRNA) and exposed to hyperoxia. Total lung lavage protein concentration, TUNEL staining, lipid peroxidation, and wet-to-dry ratio were all increased, consistent with increased injury. These findings were corroborated by survival studies in which inhibition of HO-1 function using tin-protoporphryin or silencing of HO-1 with lentiviral HO-1 short hairpin RNA (ShRNA) significantly decreased survival in hyperoxia. We conclude from these data that VEGF-induced HO-1 is an important contributor to cytoprotection in this in vivo model of acute lung injury and that alterations in VEGF function in the lung are likely to be important determinants of the outcome of acute lung injury.

Vascular endothelial growth factor accelerates compensatory lung growth after unilateral pneumonectomy

We hypothesize that compensatory lung growth after unilateral pneumonectomy in a murine model is, in part, angiogenesis dependent and can be altered using angiogenic agents, possibly through regulation of endothelial cell proliferation and apoptosis. Left pneumonectomy was performed in mice. Mice were then treated with proangiogenic factors [vascular endothelial growth factor (VEGF); basic fibroblast growth factor (bFGF)], VEGF receptor antibodies (MF-1, DC101), and VEGF receptor small molecule chemical inhibitors. Lung volume and mass were measured. The lungs were analyzed using immunohistochemistry by CD31 staining, terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling, type II pneumocytes staining, and proliferating cell nuclear antigen. Compensatory lung growth was complete by postoperative day 10 and was associated with diffuse apoptosis of endothelial cells and pneumocytes. This process was accelerated by VEGF, such that growth was complete by postoperative day 4 with similar associated apoptosis. bFGF had no effect on lung growth. MF-1 and DC101 had no effect. The VEGF receptor small molecule chemical inhibitors also had no effect. VEGF, but not bFGF, accelerates growth. VEGF receptor inhibitors do not block growth, suggesting that other proangiogenic factors play a role or can compensate for VEGF receptor blockade. Diffuse apoptosis, endothelial cell and pneumocyte, occurs at cessation of both normal compensatory and VEGF-accelerated growth. Angiogenesis modulators may control growth via regulation of endothelial cell proliferation and apoptosis, although the exact relationship between endothelial cells and pneumocytes has yet to be determined. The fact that bFGF did not accelerate growth in our model when it did accelerate regeneration in the liver model suggests that angiogenesis during organ regeneration is regulated in an organ-specific manner.

The cellular basis for diverse responses to oxygen

Mammalian cells have divergent responses to varying oxygen levels. Cells exposed to low oxygen levels (hypoxia) activate the transcription factor hypoxia-inducible factor-1 (HIF-1) as an adaptive response. Cells exposed to hypoxia do not undergo senescence or cell death and do not diminish ATP levels. By contrast, cells exposed to high oxygen levels (hyperoxia) undergo senescence and cell death and decrease their ATP levels, yet do not activate HIF-1. Despite these divergent responses with respect to senescence, cell death, metabolism, and gene expression, the signaling events in both systems are mediated by the generation of mitochondrial-derived reactive oxygen species (ROS). This perspective reviews the role of signaling through mitochondrial ROS in hypoxic and hyperoxic environments.

PDGF and microvessel wall remodeling in adult lung: imaging PDGF-Rbeta and PDGF-BB molecules in progenitor smooth muscle cells developing in pulmonary hypertension

Smooth muscle cells are relatively rare cells in the microvessels of the normal adult lung but develop in high numbers in the clinical pulmonary hypertensions (PHs). Understanding this cellular response has profound implications for determining the pathogenesis of PH, and for the development of therapeutic strategies, yet little is known of the angiogenic molecules responsible. The authors have previously shown that interstitial fibroblasts, and intermediate cells, are the progenitors of smooth muscle cells developing in adult lung microvessels in an in vivo model of experimental PH. The present study evaluates PDGF-Rbeta/PDGF-BB, an important angiogenic signaling pathway, using antibodies linked to protein A-gold (pA-AU) and quantitative high-resolution imaging techniques to detect expression by these cells. Each progenitor cell type in the control lung expressed PDGF-Rbeta and PDGF-BB. In the hypertensive lung, PDGF-Rbeta was highly expressed by fibroblasts developing as perivascular cells, the mean number of pA-AU labeled antigenic sites per cell profile, and their density (microm(-2)), increasing with time: in intermediate cells the mean number of sites per cell profile, although not their density (microm(-2)), also increased with time but less so than in the fibroblasts. In clear contrast to the RTK, constitutive expression levels of PDGF-BB were low in each progenitor cell type and remained restricted in the hypertensive lung.

Recombinant human VEGF treatment transiently increases lung edema but enhances lung structure after neonatal hyperoxia

Recent studies suggest that VEGF may worsen pulmonary edema during acute lung injury (ALI), but, paradoxically, impaired VEGF signaling contributes to decreased lung growth during recovery from ALI due to neonatal hyperoxia. To examine the diverse roles of VEGF in the pathogenesis of and recovery from hyperoxia-induced ALI, we hypothesized that exogenous recombinant human VEGF (rhVEGF) treatment during early neonatal hyperoxic lung injury may increase pulmonary edema but would improve late lung structure during recovery. Sprague-Dawley rat pups were placed in a hyperoxia chamber (inspired O(2) fraction 0.9) for postnatal days 2-14. Pups were randomized to daily intramuscular injections of rhVEGF(165) (20 microg/kg) or saline (controls). On postnatal day 14, rats were placed in room air for a 7-day recovery period. At postnatal days 3, 14, and 21, rats were killed for studies, which included body weight and wet-to-dry lung weight ratio, morphometric analysis [including radial alveolar counts (RAC), mean linear intercepts (MLI), and vessel density], and lung endothelial NO synthase (eNOS) protein content by Western blot analysis. Compared with room air controls, hyperoxia increased pulmonary edema by histology and wet-to-dry lung weight ratios at postnatal day 3, which resolved by day 14. Although treatment with rhVEGF did not increase edema in control rats, rhVEGF increased wet-to-dry weight ratios in hyperoxia-exposed rats at postnatal days 3 and 14 (P < 0.01). Compared with room air controls, hyperoxia decreased RAC and increased MLI at postnatal days 14 and 21. Treatment with VEGF resulted in increased RAC by 181% and decreased MLI by 55% on postnatal day 14 in the hyperoxia group (P < 0.01). On postnatal day 21, RAC was increased by 176% and MLI was decreased by 58% in the hyperoxia group treated with VEGF. rhVEGF treatment during hyperoxia increased eNOS protein on postnatal day 3 by threefold (P < 0.05). We conclude that rhVEGF treatment during hyperoxia-induced ALI transiently increases pulmonary edema but improves lung structure during late recovery. We speculate that VEGF has diverse roles in hyperoxia-induced neonatal lung injury, contributing to lung edema during the acute stage of ALI but promoting repair of the lung during recovery.

Cytokines in tolerance to hyperoxia-induced injury in the developing and adult lung

Cytokines are peptides that are produced by virtually every nucleated cell type in the body, possess overlapping biological activities, exert different effects at different concentrations, can either synergize or antagonize the effects of other cytokines, are regulated in a complex manner, and function via cytokine cascades. Hyperoxia-induced acute lung injury (HALI) is characterized by an influx of inflammatory cells, increased pulmonary permeability, and endothelial and epithelial cell injury/death. Some of these effects are orchestrated by cytokines. There are significant differences in the response of the developing versus the adult lung to hyperoxia. We review here cytokines (and select growth factors) that are involved in tolerance toward HALI in animal models. Increased cytokine expression and release have a cascade effect in HALI. IL-1 precedes the increase in IL-6 and CINC-1/IL-8 and this seems to predate the influx of inflammatory cells. Inflammatory cells in the alveolar space amplify the lung damage. Other cytokines that are primarily involved in this inflammatory response include IFN-gamma, MCP-1, and MIP-2. Certain cytokines (and growth factors) seem to ameliorate HALI by affecting cell death pathways. These include GM-CSF, KGF, IL-11, IL-13, and VEGF. There are significant differences in the type and temporal sequence of cytokine expression and release in the adult and newborn lung in response to hyperoxia. The newborn lung is greatly resistant to hyperoxia compared to the adult. The delayed increase in lung IL-1 and IL-6 in the newborn could induce protective factors that would help in the resolution of hyperoxia-induced injury. Designing a therapeutic approach to counteract oxygen toxicity in the adult and immature lung first needs understanding of the unique responses in each scenario.

Vascular endothelial growth factor (VEGF) in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS): paradox or paradigm?

Acute respiratory distress syndrome (ARDS), the most severe form of acute lung injury (ALI), remains a devastating condition with a high mortality. It is characterised by alveolar injury and increased pulmonary vascular permeability. Vascular endothelial cell growth factor (VEGF) was identified by its properties to increase permeability and act as a cellular growth factor, hence its potential for a key role in the pathogenesis of ALI/ARDS. This review describes the basic biology of VEGF and its receptors as an essential prerequisite to discussing the available and sometimes paradoxical published data, before considering a paradigm for the role of VEGF in the human lung.

Vascular endothelial growth factor in the lung

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