Changes in fetal lung distension alter expression of vascular endothelial growth factor and its isoforms in developing rat lung

Biomarkers of lung alveolarization and microvascular maturation in response to intermittent hypoxia and/or early antioxidant/fish oil supplementation in neonatal rats

OBJECTIVE

Extremely preterm infants experience frequent intermittent hypoxia (IH) episodes during oxygen therapy which causes significant damage to the lungs and curtails important signaling pathways that regulate normal lung alveolarization and microvascular maturation. We tested the hypothesis that early supplementation with fish oil and/or antioxidants in rats exposed to neonatal IH improves expression of lung biomarkers of alveolarization and microvascular maturation, and reduces IH-induced lung injury.

STUDY DESIGN/METHODS

From birth (P0) to P14, rat pups were exposed to room air (RA) or neonatal IH during which they received daily oral supplementation with either: (1) olive oil (OO) (control); (2) Coenzyme Q10 (CoQ10) in OO; (3) fish oil; (4) glutathione nanoparticles (nGSH); or (5) fish oil +CoQ10. At P14 pups were placed in RA until P21 with no further treatment. RA controls were similarly treated. Lung growth and alveolarization, histopathology, apoptosis, oxidative stress and biomarkers of alveolarization and microvascular maturation were determined.

RESULTS

Neonatal IH was associated with reduced lung weights and severe histopathological outcomes. These effects were curtailed with fish oil and nGSH. nGSH was also protective against apoptosis, while CoQ10 prevented IH-induced ROS production. Of all treatments, nGSH and CoQ10 + fish oil-induced vascular endothelial growth factor165 and CD31 (Platelet endothelial cell adhesion molecule-1), which are associated with angiogenesis. CoQ10 + fish oil improved alveolarization in RA and IH despite evidence of hemorrhage.

CONCLUSIONS

The benefits of nGSH and CoQ10 + fish oil suggest an antioxidant effect which may be required to curtail IH-induced lung injury. Further clinical assessment of the effectiveness of nGSH is warranted.

The Cellular and Molecular Effects of Fetoscopic Endoluminal Tracheal Occlusion in Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a complex disease associated with pulmonary hypoplasia and pulmonary hypertension. Great strides have been made in our ability to care for CDH patients, specifically in the prenatal improvement of lung volume and morphology with fetoscopic endoluminal tracheal occlusion (FETO). While the anatomic effects of FETO have been described in-depth, the changes it induces at the cellular and molecular level remain a budding area of CDH research. This review will delve into the cellular and molecular effects of FETO in the developing lung, emphasize areas in which further research may improve our understanding of CDH, and highlight opportunities to optimize the FETO procedure for improved postnatal outcomes.

Pulmonary hypoplasia correlates with the length of anhydramnios in patients with early pregnancy renal anhydramnios (EPRA)

BACKGROUND

Early pregnancy renal anhydramanios (EPRA) occurs when the fetus is anuric before 22 weeks gestational age (GA) and is considered universally lethal. Serial amnioinfusions have successfully ameliorated the lethal pulmonary hypoplasia associated with EPRA and have resulted in cases of neonatal survival, peritoneal dialysis, and renal transplant.

OBJECTIVE

We sought to evaluate the lung pathology of untreated fetuses and neonates that had EPRA.

STUDY DESIGN

This is a retrospective case series of all fetuses and neonates diagnosed with isolated EPRA that underwent autopsy at a single tertiary care center between 1987 and 2018. Autopsy data were correlated with ultrasound findings and GA at delivery. Fetal weights, lung weights, and lung developmental stage were recorded.

RESULTS

Nineteen cases met criteria for analysis and ranged from 16 to 38 weeks GA at termination or birth. The observed-to-expected (O/E) lung-to-body-weight ratio was significantly associated with GA (r = -0.51, p = 0.03), such that as GA increased the O/E ratio decreased. When limited to patients >22 weeks, this relationship strengthened (r = -0.75, p = 0.01). Importantly, overall O/E body weight had no relationship with GA.

CONCLUSION

This study shows that the degree of pulmonary hypoplasia in EPRA increases with the length of anhydramnios. This suggests that amnioinfusions are likely to be of most benefit the soonest they can feasibly be initiated.

VEGFR1-tyrosine kinase signaling in pulmonary fibrosis

Vascular endothelial growth factor (VEGF) is not only an important factor for angiogenesis but also lung development and homeostasis. VEGF-A binds three tyrosine kinase (TK) receptors VEGFR1–3. Idiopathic pulmonary fibrosis (IPF) is one of the poor prognoses of lung diseases. The relationship of VEGF and IPF remains to be clarified. Treatment with nintedanib used for the treatment of IPF reduced fibroblast proliferation, inhibited TK receptors, platelet-derived growth factor receptor (PDGFR), fibroblast growth factor receptor (FGFR), and VEGFR. Because the effect of that treatment is still not satisfactory, the emergence of new therapeutic agents is needed. This review describes the enhancement of pulmonary fibrosis by VEGFR1-TK signal and suggests that the blocking of the VEGFR1-TK signal may be useful for the treatment of pulmonary fibrosis.

Emerging antenatal therapies for congenital diaphragmatic hernia-induced pulmonary hypertension in preclinical models

Congenital diaphragmatic hernia (CDH)-related deaths are the largest contributor to in-hospital neonatal deaths in children with congenital malformations. Morbidity and mortality in CDH are directly related to the development of pulmonary hypertension (PH). Current treatment consists of supportive measures. To date, no pharmacotherapy has been shown to effectively reverse the hallmark finding of pulmonary vascular remodeling that is associated with pulmonary hypertension in CDH (CDH-PH). As such, there is a great need for novel therapies to effectively manage CDH-PH. Our review aims to evaluate emerging therapies, and specifically focuses on those that are still under investigation and not approved for clinical use by the Food and Drug Administration. Therapies were categorized into antenatal pharmacotherapies or antenatal regenerative therapies and assessed on their method of administration, safety profile, the effect on pulmonary vascular pathophysiology, and overall efficacy. In general, emerging antenatal pharmaceutical and regenerative treatments primarily aim to alleviate pulmonary vascular remodeling by restoring normal function and levels of key regulatory factors involved in pulmonary vascular development and/or in promoting angiogenesis. Overall, while these emerging therapies show great promise for the management of CDH-PH, most require further assessment of safety and efficacy in preclinical models before translation into the clinical setting. IMPACT: Emerging antenatal therapies for congenital diaphragmatic hernia-induced pulmonary hypertension (CDH-PH) show promise to effectively mitigate vascular remodeling in preclinical models. Further investigation is needed in preclinical and human studies to evaluate safety and efficacy prior to translation into the clinical arena. This review offers a comprehensive and up-to-date summary of emerging therapies currently under investigation in experimental animal models. There is no cure for CDH-PH. This review explores emerging therapeutic options for the treatment of CDH-PH and evaluates their impact on key molecular pathways and clinical markers of disease to determine efficacy in the preclinical stage.

Transamniotic Stem Cell Therapy for Experimental Congenital Diaphragmatic Hernia: Structural, Transcriptional, and Cell Kinetics Analyses in the Nitrofen Model

PURPOSE

We examined select pulmonary effects and donor cell kinetics after transamniotic stem cell therapy (TRASCET) in a model of congenital diaphragmatic hernia (CDH).

METHODS

Pregnant dams (n = 58) received nitrofen on gestational day 9.5 (E9) to induce fetal CDH. Fetuses (n = 681) were divided into 4 groups: untreated (n = 99) and 3 groups receiving volume-matched intra-amniotic injections on E17 of either saline (n = 142), luciferase-labeled amniotic fluid-derived mesenchymal stem cells (afMSCs; n = 299), or acellular recombinant luciferase (n = 141). Pulmonary morphometry, quantitative gene expression of pulmonary vascular tone mediators, or screening for labeled afMSCs were performed at term (E22). Statistical comparisons were by Mann-Whitney U-test, nested ANOVA, and Wald test.

RESULTS

TRASCET led to significant downregulation of endothelial nitric oxide synthase and endothelin receptor-A expressions compared to both untreated and saline groups (both p < 0.001). TRASCET also led to a significant decrease in arteriole wall thickness compared to the untreated group (p < 0.001) but not the saline group (p = 0.180). Donor afMSCs were identified in the bone marrow and umbilical cord (p = 0.035 and 0.015, respectively, vs. plain luciferase controls).

CONCLUSIONS

The effects of TRASCET in experimental CDH appear to be centered on the pulmonary vasculature and to derive from circulating donor cells.

Intra-Amniotic Sildenafil Treatment Promotes Lung Growth and Attenuates Vascular Remodeling in an Experimental Model of Congenital Diaphragmatic Hernia

BACKGROUND

Defective lung development resulting in lung hypoplasia and an attenuated and hypermuscularized pulmonary vasculature contributes to significant postnatal mortality in congenital diaphragmatic hernia (CDH). We hypothesize that deficient embryonic pulmonary blood flow contributes to defective lung development in CDH, which may therefore be ameliorated via enhancement of embryonic pulmonary blood flow.

METHODS

The mouse nitrofen model of CDH was utilized to measure embryonic pulmonary blood flow by in utero intracardiac injection of FITC-labeled tomato lectin and color-flow Doppler ultrasound. The effect of prenatal intra-amniotic treatment with sildenafil on survival, lung growth, and vascular morphology in the nitrofen model was determined.

RESULTS

Nitrofen-treated embryos exhibited decreased blood flow in the lung periphery compared to controls, and intra-amniotic sildenafil significantly improved embryonic pulmonary blood flow. Similar to nitrofen alone, pups delivered after nitrofen treatment and intra-amniotic injection of dextrose control exhibited respiratory distress and never survived beyond 6 h. Intra-amniotic sildenafil ameliorated respiratory distress in nitrofen-treated pups and improved postnatal survival to 82%. Following intra-amniotic sildenafil treatment at embryonic day (E)10.5, nitrofen-treated P0 lungs were larger with increased left lobe weight, reduced small pulmonary arterial wall muscularization, and increased airway branching complexity compared to controls. Intra-amniotic sildenafil treatment later at E15.5 also resulted in improved survival, lung growth, and attenuation of vascular remodeling in nitrofen-treated embryos.

CONCLUSIONS

Defective embryonic pulmonary blood flow may contribute to lung maldevelopment in CDH. Enhancement of embryonic pulmonary blood flow via intra-amniotic sildenafil results in lung growth and attenuation of pulmonary vascular remodeling and may have therapeutic potential for CDH.

Congenital diaphragmatic hernia as a potential target for transamniotic stem cell therapy

PURPOSE

We sought to determine whether TRASCET could impact congenital diaphragmatic hernia (CDH).

METHODS

Twelve pregnant dams received Nitrofen on gestational day 9.5 (E9; term = 22 days) to induce fetal CDH. Fetuses were divided into three groups: untreated (n = 31) and two groups receiving volume-matched intraamniotic injections of either saline (n = 37) or a suspension of 2 × 10⁶ cells/mL of amniotic fluid-derived mesenchymal stem cells (afMSCs; n = 65) on E17. Animals were euthanized at term. Expression of fibroblast growth factor-10 (FGF-10), vascular endothelial growth factor-A (VEGF-A), and surfactant protein-C (SPC) was quantified by qRT-PCR. Statistical analysis was by the Mann-Whitney U test with Bonferroni adjusted criterion (p ≤ 0.01).

RESULTS

Among survivors with CDH (n = 27/133), the TRASCET group showed significant downregulation of FGF-10 and VEGF-A gene expressions compared to the untreated (p < 0.001 for both) and saline groups (p = 0.005 and p = 0.004, respectively). SPC expression was higher in the TRASCET group compared to the untreated group (p = 0.01), but not the saline group (p = 0.043). Lung laterality had minimal impact on these comparisons.

CONCLUSIONS

Transamniotic stem cell therapy affects select processes of lung development in experimental congenital diaphragmatic hernia. Further scrutiny into this novel therapy as a potential component of the prenatal management of this disease is warranted.

LEVEL OF EVIDENCE

N/A (animal and laboratory study).

Pulmonary hypertension secondary to congenital diaphragmatic hernia: factors and pathways involved in pulmonary vascular remodeling

Congenital diaphragmatic hernia (CDH) is a severe birth defect that is characterized by pulmonary hypoplasia and pulmonary hypertension (PHTN). PHTN secondary to CDH is a result of vascular remodeling, a structural alteration in the pulmonary vessel wall that occurs in the fetus. Factors involved in vascular remodeling have been reported in several studies, but their interactions remain unclear. To help understand PHTN pathophysiology and design novel preventative and treatment strategies, we have conducted a systematic review of the literature and comprehensively analyzed all factors and pathways involved in the pathogenesis of pulmonary vascular remodeling secondary to CDH in the nitrofen model. Moreover, we have linked the dysregulated factors with pathways involved in human CDH. Of the 358 full-text articles screened, 75 studies reported factors that play a critical role in vascular remodeling secondary to CDH. Overall, the impairment of epithelial homeostasis present in pulmonary hypoplasia results in altered signaling to endothelial cells, leading to endothelial dysfunction. This causes an impairment of the crosstalk between endothelial cells and pulmonary artery smooth muscle cells, resulting in increased smooth muscle cell proliferation, resistance to apoptosis, and vasoconstriction, which clinically translate into PHTN.

The mechanosensitive ion channel TRPV4 is a regulator of lung development and pulmonary vasculature stabilization

Introduction –

Clinical observations and animal models suggest a critical role for the dynamic regulation of transmural pressure and peristaltic airway smooth muscle contractions for proper lung development. However, it is currently unclear how such mechanical signals are transduced into molecular and transcriptional changes at the cell level. To connect these physical findings to a mechanotransduction mechanism, we identified a known mechanosensor, TRPV4, as a component of this pathway.

Methods –

Embryonic mouse lung explants were cultured on membranes and in submersion culture to modulate explant transmural pressure. Time-lapse imaging was used to capture active changes in lung biology, and whole-mount images were used to visualize the organization of the epithelial, smooth muscle, and vascular compartments. TRPV4 activity was modulated by pharmacological agonism and inhibition.

Results –

TRPV4 expression is present in the murine lung with strong localization to the epithelium and major pulmonary blood vessels. TRPV4 agonism and inhibition resulted in hyper- and hypoplastic airway branching, smooth muscle differentiation, and lung growth, respectively. Smooth muscle contractions also doubled in frequency with agonism and were reduced by 60% with inhibition demonstrating a functional role consistent with levels of smooth muscle differentiation. Activation of TRPV4 increased the vascular capillary density around the distal airways, and inhibition resulted in a near complete loss of the vasculature.

Conclusions –

These studies have identified TRPV4 as a potential mechanosensor involved in transducing mechanical forces on the airways to molecular and transcriptional events that regulate the morphogenesis of the three essential tissue compartments in the lung.

Efficacy of Bosentan in patients after Fontan procedures: a double-blind, randomized controlled trial

Fontan surgery is a widely used palliative procedure that significantly improves the survival period of patients with complex congenital heart disease (CHD). However, it does not decrease postoperative complication rate. Previous studies suggested that elevated mean pulmonary artery pressure (mPAP) and vascular resistance lead to decreased exercise tolerance and myocardial dysfunction. Therapy with endothelial receptor antagonists (Bosentan) has been demonstrated to improve the patients' prognosis. A double-blind, randomized controlled trial was performed to explore the efficacy of Bosentan in treating patients who underwent the Fontan procedure. Eligible participants were randomly divided into Bosentan group and control group. Liver function was tested at a local hospital and the results were reported to the phone inspector every month. If the results suggested abnormal liver function, treatment would be adjusted or terminated. All the participants finished the follow-up study, with no patients lost to follow-up. Unblinding after 2-year follow-up, no mortality was observed in either group. However, secondary end-points were found to be significantly different in the comparable groups. The cardiac function and 6-min walking distance in the Bosentan group were significantly superior to those in the control group (P=0.018 and P=0.027). Bosentan could improve New York Heart Association (NYHA) functional status and improve the results of the 6-min walking test (6MWT) in Fontan patients post-surgery, and no other benefits were observed. Furthermore, a primary meta-analysis study systematically reviewed all the similar clinical trails worldwide and concluded an overall NYHA class improvement in Fontan patients who received Bosentan treatments.

Aberrant Pulmonary Vascular Growth and Remodeling in Bronchopulmonary Dysplasia

In contrast to many other organs, a significant portion of lung development occurs after birth during alveolarization, thus rendering the lung highly susceptible to injuries that may disrupt this developmental process. Premature birth heightens this susceptibility, with many premature infants developing the chronic lung disease, bronchopulmonary dysplasia (BPD), a disease characterized by arrested alveolarization. Over the past decade, tremendous progress has been made in the elucidation of mechanisms that promote postnatal lung development, including extensive data suggesting that impaired pulmonary angiogenesis contributes to the pathogenesis of BPD. Moreover, in addition to impaired vascular growth, patients with BPD also frequently demonstrate alterations in pulmonary vascular remodeling and tone, increasing the risk for persistent hypoxemia and the development of pulmonary hypertension. In this review, an overview of normal lung development will be presented, and the pathologic features of arrested development observed in BPD will be described, with a specific emphasis on the pulmonary vascular abnormalities. Key pathways that promote normal pulmonary vascular development will be reviewed, and the experimental and clinical evidence demonstrating alterations of these essential pathways in BPD summarized.

Cord blood-derived endothelial colony-forming cell function is disrupted in congenital diaphragmatic hernia

Vascular growth is necessary for normal lung development. Although endothelial progenitor cells (EPCs) play an important role in vascularization, little is known about EPC function in congenital diaphragmatic hernia (CDH), a severe neonatal condition that is associated with pulmonary hypoplasia. We hypothesized that the function of endothelial colony-forming cells (ECFCs), a type of EPC, is impaired in CDH. Cord blood (CB) was collected from full-term CDH patients and healthy controls. We assessed CB progenitor cell populations as well as plasma vascular endothelial growth factor (VEGF) and stromal cell-derived factor 1α (SDF1α) levels. CB ECFC clonogenicity; growth kinetics; migration; production of VEGF, SDF1α, and nitric oxide (NO); vasculogenic capacity; and mRNA expression of VEGF-A, fms-related tyrosine kinase 1 (FLT1), kinase insert domain receptor (KDR), nitric oxide synthase (NOS) 1-3, SDF1, and chemokine (C-X-C motif) receptor 4 (CXCR4) were also assessed. Compared with controls, CB ECFCs were decreased in CDH. CDH ECFCs had reduced potential for self-renewal, clonogenicity, proliferation, and migration. Their capacity for NO production was enhanced but their response to VEGF was blunted in CDH ECFCs. In vivo potential for de novo vasculogenesis was reduced in CDH ECFCs. There was no difference in CB plasma VEGF and SDF1α concentrations, VEGF and SDF1α production by ECFCs, and ECFC mRNA expression of VEGF-A, FLT1, KDR, NOS1-3, SDF1, and CXCR4 between CDH and control subjects. In conclusion, CB ECFC function is disrupted in CDH, but these changes may be caused by mechanisms other than alteration of VEGF-NO and SDF1-CXCR4 signaling.

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.

Plasma vascular endothelial growth factor A and placental growth factor: novel biomarkers of pulmonary hypertension in congenital diaphragmatic hernia

Pulmonary hypertension (PH) due to abnormal pulmonary vascular development is an important determinant of illness severity in congenital diaphragmatic hernia (CDH). Vascular endothelial growth factor A (VEGFA) and placental growth factor (PLGF) may be important mediators of pulmonary vascular development in health and disease. This prospective study investigated the relationship between plasma VEGFA and PLGF and measures of pulmonary artery pressure, oxygenation, and cardiac function in CDH. A cohort of 10 infants with CDH consecutively admitted to a surgical neonatal intensive care unit (NICU) was recruited. Eighty serial plasma samples were obtained and analyzed by multiplex immunoassay to quantify VEGFA and PLGF. Concurrent assessment of pulmonary artery pressure (PAP) and cardiac function were made by echocardiography. Plasma VEGFA was higher and PLGF was lower in CDH compared with existing normative data. Combined plasma VEGFA:PLGF ratio correlated positively with measures of PAP, diastolic ventricular dysfunction, and oxygenation index. Nonsurvivors had higher VEGFA:PLGF ratio than survivors at days 3–4 of life and in the second week of life. These findings suggest that increased plasma VEGFA and reduced PLGF correlate with clinical severity of pulmonary vascular disease and may be associated with adverse outcome in CDH. This potential role for combined plasma VEGFA and PLGF in CDH as disease biomarkers, pathogenic mediators, and therapeutic targets merits further investigation.

VEGF receptor expression decreases during lung development in congenital diaphragmatic hernia induced by nitrofen

Changes in vascular endothelial growth factor (VEGF) in pulmonary vessels have been described in congenital diaphragmatic hernia (CDH) and may contribute to the development of pulmonary hypoplasia and hypertension; however, how the expression of VEGF receptors changes during fetal lung development in CDH is not understood. The aim of this study was to compare morphological evolution with expression of VEGF receptors, VEGFR1 (Flt-1) and VEGFR2 (Flk-1), in pseudoglandular, canalicular, and saccular stages of lung development in normal rat fetuses and in fetuses with CDH. Pregnant rats were divided into four groups (n=20 fetuses each) of four different gestational days (GD) 18.5, 19.5, 20.5, 21.5: external control (EC), exposed to olive oil (OO), exposed to 100 mg nitrofen, by gavage, without CDH (N-), and exposed to nitrofen with CDH (CDH) on GD 9.5 (term=22 days). The morphological variables studied were: body weight (BW), total lung weight (TLW), left lung weight, TLW/BW ratio, total lung volume, and left lung volume. The histometric variables studied were: left lung parenchymal area density and left lung parenchymal volume. VEGFR1 and VEGFR2 expression were determined by Western blotting. The data were analyzed using analysis of variance with the Tukey-Kramer post hoc test. CDH frequency was 37% (80/216). All the morphological and histometric variables were reduced in the N- and CDH groups compared with the controls, and reductions were more pronounced in the CDH group (P<0.05) and more evident on GD 20.5 and GD 21.5. Similar results were observed for VEGFR1 and VEGFR2 expression. We conclude that N- and CDH fetuses showed primary pulmonary hypoplasia, with a decrease in VEGFR1 and VEGFR2 expression.

Changes in the expression of vascular endothelial growth factor after fetal tracheal occlusion in an experimental model of congenital diaphragmatic hernia

Introduction. Vascular endothelial growth factor (VEGF), an angiogenic factor secreted by type II pneumocytes, could play a role in congenital diaphragmatic hernia (CDH) pathogenesis. Animal studies suggest that VEGF accelerates lung growth. Aim. To quantify VEGF on fetal lungs in a nitrofen rat model for CDH and to analyze the effect of tracheal occlusion (TO) in VEGF in fetal lung rats after nitrofen and in control rats not exposed to nitrofen. Methods. Pregnant rats received nitrofen on day 9.5 of gestation. Fetuses were divided into 2 groups: those that underwent TO on day 20 and those that did not. On day 21, fetuses were delivered, and the lungs were dissected for subsequent VEGF quantification. Results. CDH was detected in 43% of the fetuses that received nitrofen. Fetuses with CDH showed significantly reduced lung weight/fetal weight ratio and lower VEGF levels than the remainder. A higher VEGF value was observed after TO. Conclusions. VEGF protein was significantly lower in fetuses with CDH. TO induced a significant increase in VEGF compared to the fetuses that did not undergo TO. Although not statistically significant, we observed higher VEGF levels in fetuses with CDH and TO compared to fetuses with CDH and no further intervention.

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.

Low urine vascular endothelial growth factor levels are associated with mechanical ventilation, bronchopulmonary dysplasia and retinopathy of prematurity

BACKGROUND

Organ-specific vascular endothelial growth factor (VEGF) expression is decreased during the pathogenesis of bronchopulmonary dysplasia (BPD) and retinopathy of prematurity (ROP) several weeks before either disease can be diagnosed. Early measurement of organ-specific tissue VEGF levels might allow identification of infants at high risk for these diseases, but is not clinically feasible. Urine VEGF is easily measured and useful in early diagnosis of several diseases.

OBJECTIVES

Our aims were to assess the correlation of urine VEGF levels measured in the first postnatal month with subsequent BPD or ROP diagnosis and to determine whether various infant characteristics influence urine VEGF levels.

METHODS

106 subjects born at <29 weeks' gestation and surviving to 36 weeks' postmenstrual age were selected from an existing database and biorepository. Urine VEGF and total protein were measured in 2-3 samples per subject.

RESULTS

Urine VEGF/protein levels increased by 72% per week (p < 0.0001) during the first postnatal month. In multivariable analysis controlling for postnatal age, lower VEGF/protein was associated with higher levels of mechanical respiratory support (p = 0.006), male gender (p = 0.001) and early sepsis (p = 0.003) but not with fraction of inspired oxygen. Lower urine VEGF/protein and mechanical ventilation were each associated with BPD and ROP. In analyses adjusted for respiratory support, lower urine VEGF/protein and ROP remained associated but urine VEGF/protein and BPD did not.

CONCLUSIONS

Low urine VEGF/protein levels in the first postnatal month are associated with mechanical ventilation, BPD, and ROP.

Prenatal retinoic acid improves lung vascularization and VEGF expression in CDH rat

OBJECTIVE

We sought to investigate the effects of antenatal retinoic acid on the pulmonary vasculature and vascular endothelial growth factor (VEGF) and VEGF receptors (VEGFR) expression in a nitrofen-induced congenital diaphragmatic hernia (CDH) model.

STUDY DESIGN

Rat fetuses were exposed to nitrofen at gestational day 9.5 and/or all-trans retinoic acid (ATRA) at gestational days 18.5-20.5. We assessed lung growth, airway, and vascular morphometry. VEGF, VEGFR1, and VEGFR2 expression was analyzed by Western blotting and immunohistochemistry. Continuous data were analyzed by analysis of variance and Kruskal-Wallis test.

RESULTS

CDH decreased lung to body weight ratio, increased mean linear intercept and mean transection length/airspace, and decreased mean airspace cord length. ATRA did not affect lung growth or morphometry. CDH increased proportional medial wall thickness of arterioles while ATRA reduced it. ATRA recovered expression of VEGF and receptors, which were reduced in CDH.

CONCLUSION

Retinoic acid and VEGF may provide pathways for preventing pulmonary hypertension in CDH.

Expression of hypoxia-inducible factors, regulators, and target genes in congenital diaphragmatic hernia patients

Congenital diaphragmatic hernia (CDH) is associated with lung hypoplasia and pulmonary hypertension and has high morbidity and mortality rates. The cause and pathophysiology of CDH are not fully understood. However, impaired angiogenesis appears to play an important role in the pathophysiology of CDH. Therefore, we examined different components of an important pathway in angiogenesis: hypoxia-inducible factors (HIFs); HIF regulators von Hippel-Lindau (VHL) and prolyl 3-hydroxylase (PHD3); and HIF target genes vascular endothelial growth factor A ( VEGF-A ) and vascular endothelial growth factor receptor 2 ( VEGFR-2 ). Quantitative polymerase chain reaction of lung tissue showed a significantly decreased expression of VEGF-A mRNA in the alveolar stage of lung development in CDH patients compared with matched control patients. In the canalicular stage, no differences for VEGF-A were seen between the lungs of CDH patients and those of control patients. Other components of angiogenesis (VHL, HIF-1α, HIF-2α, HIF-3α, VEGFR-2 mRNA, PHD3 protein) that were analyzed showed no differences in expression between CDH and control patients, independent of the developmental stage. A lower expression of VEGF mRNA in CDH patients in the alveolar stage, possibly as a result of downregulation of HIF-2α might indicate a role for these factors in the pathophysiology of CDH.

Antenatal sildenafil treatment attenuates pulmonary hypertension in experimental congenital diaphragmatic hernia

BACKGROUND

Lung hypoplasia and persistent pulmonary hypertension of the newborn limit survival in congenital diaphragmatic hernia (CDH). Unlike other diseases resulting in persistent pulmonary hypertension of the newborn, infants with CDH are refractory to inhaled nitric oxide (NO). Nitric oxide mediates pulmonary vasodilatation at birth in part via cyclic GMP production. Phosphodiesterase type 5 (PDE5) limits the effects of NO by inactivation of cyclic GMP. Because of the limited success in postnatal management of CDH, we hypothesized that antenatal PDE5 inhibition would attenuate pulmonary artery remodeling in experimental nitrofen-induced CDH.

METHODS AND RESULTS

Nitrofen administered at embryonic day 9.5 to pregnant rats resulted in a 60% incidence of CDH in the offspring and recapitulated features seen in human CDH, including structural abnormalities (lung hypoplasia, decreased pulmonary vascular density, pulmonary artery remodeling, right ventricular hypertrophy), and functional abnormalities (decreased pulmonary artery relaxation in response to the NO donor 2-(N,N-diethylamino)-diazenolate-2-oxide). Antenatal sildenafil administered to the pregnant rat from embryonic day 11.5 to embryonic day 20.5 crossed the placenta, increased fetal lung cyclic GMP and decreased active PDE5 expression. Antenatal sildenafil improved lung structure, increased pulmonary vessel density, reduced right ventricular hypertrophy, and improved postnatal NO donor 2-(N,N-diethylamino)-diazenolate-2-oxide-induced pulmonary artery relaxation. This was associated with increased lung endothelial NO synthase and vascular endothelial growth factor protein expression. Antenatal sildenafil had no adverse effect on retinal structure/function and brain development.

CONCLUSIONS

Antenatal sildenafil improves pathological features of persistent pulmonary hypertension of the newborn in experimental CDH and does not alter the development of other PDE5-expressing organs. Given the high mortality/morbidity of CDH, the potential benefit of prenatal PDE5 inhibition in improving the outcome for infants with CDH warrants further studies.

Regulation of the Pulmonary Circulation in the Fetus and Newborn

During the development of the pulmonary vasculature in the fetus, many structural and functional changes occur to prepare the lung for the transition to air breathing. The development of the pulmonary circulation is genetically controlled by an array of mitogenic factors in a temporo-spatial order. With advancing gestation, pulmonary vessels acquire increased vasoreactivity. The fetal pulmonary vasculature is exposed to a low oxygen tension environment that promotes high intrinsic myogenic tone and high vasocontractility. At birth, a dramatic reduction in pulmonary arterial pressure and resistance occurs with an increase in oxygen tension and blood flow. The striking hemodynamic differences in the pulmonary circulation of the fetus and newborn are regulated by various factors and vasoactive agents. Among them, nitric oxide, endothelin-1, and prostaglandin I2 are mainly derived from endothelial cells and exert their effects via cGMP, cAMP, and Rho kinase signaling pathways. Alterations in these signaling pathways may lead to vascular remodeling, high vasocontractility, and persistent pulmonary hypertension of the newborn.

Antenatal steroid and tracheal occlusion restore vascular endothelial growth factor receptors in congenital diaphragmatic hernia rat model

OBJECTIVE

Investigate the effects of antenatal steroids and tracheal occlusion on pulmonary expression of vascular endothelial growth factor receptors in rats with nitrofen-induced congenital diaphragmatic hernia.

STUDY DESIGN

Fetuses were exposed to nitrofen at embryonic day 9.5. Subgroups received dexamethasone or were operated on for tracheal occlusion, or received combined treatment. Morphologic variables were recorded. To analyze vascular endothelial growth factor receptor 1 and vascular endothelial growth factor receptor 2 expression, we performed Western blotting and immunohistochemistry. Morphologic variables were analyzed by analysis of variance and immunohistochemistry by Kruskal-Wallis test.

RESULTS

Congenital diaphragmatic hernia decreased body weight, total lung weight, and lung-to-body weight ratio. Tracheal occlusion increased total lung weight and lung-to-body weight ratio (P < .05). Fetuses with congenital diaphragmatic hernia had reduced vascular endothelial growth factor receptor 1 and vascular endothelial growth factor receptor 2 expression, whereas steroids and tracheal occlusion increased their expression. Combined treatment increased expression of receptors, but had no additive effect.

CONCLUSION

Vascular endothelial growth factor signaling disruption may be associated with pulmonary hypertension in congenital diaphragmatic hernia. Tracheal occlusion and steroids provide a pathway for restoring expression of vascular endothelial growth factor receptors.

Cloning, large-scale production, and purification of active dimeric rat vascular endothelial growth factor (rrVEGF-164)

Large-scale production of recombinant rat vascular endothelial growth factor (rrVEGF-164) is desirable for angiogenic studies. In this study, biologically active recombinant rat vascular endothelial growth factor (rrVEGF-164) was cloned and expressed in the yeast Pichia pastoris, and large-scale production was performed by fermentation. cDNA encoding VEGF-164 was prepared from embryonic rat tissue RNA, and a recombinant pPIC9HV/rVEGF-164 plasmid, containing an AOX1 promoter, was constructed. The methylotrophic P. pastoris was used as the eukaryotic expression system. After transformation, rrVEGF-164 was produced by fermentation ( approximately 124mg/L) and purified by heparin affinity chromatography. SDS-PAGE indicated that rrVEGF-164 was produced as a disulphide-bridged dimer of 48kDa which was purified to near homogeneity by heparin affinity chromatography in a large quantity. A bioassay indicated a three- to fivefold increase in endothelial cell proliferation after 3days, due to the addition of the produced rrVEGF-164. The produced rrVEGF-164 showed a higher biological activity than a commercially available, mouse cell line-based, growth factor. In conclusion, using the P. pastoris expression system we were able to produce biologically active rat VEGF-164 in high quantities and this may provide a powerful tool for basic and applied life sciences.

Congenital diaphragmatic hernia: current status and review of the literature

Treatment of congenital diaphragmatic hernia (CDH) challenges obstetricians, pediatric surgeons, and neonatologists. Persistent pulmonary hypertension (PPHT) associated with lung hypoplasia in CDH leads to a high mortality rate at birth. PPHT is principally due to an increased muscularization of the arterioles. Management of CDH has been greatly improved by the introduction of prenatal surgical intervention with tracheal obstruction (TO) and by more appropriate postnatal care. TO appears to accelerate fetal lung growth and to increase the number of capillary vessels and alveoli. Improvement of postnatal care over the last years is mainly due to the avoidance of lung injury by applying low peak inflation pressure during ventilation. The benefits of other drugs or technical improvements such as the use of inhaled nitric oxide or extracorporeal membrane oxygenation (ECMO) are still being debated and no single strategy is accepted worldwide. Despite intensive clinical and experimental research, the treatment of newborn with CDH remains difficult.

Vascular endothelial growth factor isoform and receptor expression during compensatory lung growth

BACKGROUND

Vascular endothelial growth factor (VEGF) is required for blood vessel formation during lung growth and repair. Alteration of VEGF isoform expression has been demonstrated in response to fetal tracheal occlusion and in models of lung injury. The purpose of this study was to investigate VEGF expression during compensatory lung growth in the mouse.

METHODS

Under general anesthesia, adult mice underwent left thoracotomy with (n = 5) or without (sham, n = 5) pneumonectomy. The right lungs were harvested at 1, 3, and 7 d after the operation. Lung-to-body weight ratio as well as total DNA and protein content were measured. VEGF protein expression was analyzed by Western blot and ELISA. VEGF isoform expression was evaluated using semi-quantitative PCR followed by Imagequant optical densitometry. Values were compared by Student's t-test and ANOVA using Fisher's protected least significant difference post-hoc test where appropriate.

RESULTS

Compensatory lung growth was observed as measured by increases in right lung-to-body weight ratio and in DNA and protein content. Total VEGF RNA and protein expression did not change after pneumonectomy. However, on post-operative day 1, there was a decrease in the relative percentage of VEGF188 mRNA (P < 0.01), and an increase in the relative percentage of VEGF164 mRNA (P = 0.05). At 3 d postpneumonectomy, low relative VEGF188 expression persisted (P < 0.05), VEGF164 expression normalized, and relative VEGF120 expression increased (P < 0.01). Isoform expression in the pneumonectomy animals was identical to sham animals by the seventh d. There were no differences observed in VEGF receptor expression.

CONCLUSION

During compensatory lung growth, we have observed an early postoperative reversion of VEGF isoform expression to the pattern seen during fetal lung development and in lung injury models.

Increased distension stimulates distal capillary growth as well as expression of specific angiogenesis genes in fetal mouse lungs

Tracheal occlusion (TO) performed surgically in utero near the end of gestation causes a rapid increase in the distension of future airspaces, resulting in accelerated lung development. The authors hypothesize that TO stimulates microvascular growth concomitant with a rapid increase in the expression of genes implicated in angiogenesis. Mouse fetuses underwent in utero surgery (TO or sham-TO surgery) at 16.5 days of gestation, whereupon development was allowed to continue for a further 1 or 24 hours. Microvascular changes were assessed by immunohistochemical staining of fetal lung sections for platelet endothelial cell adhesion molecule-1. Levels of vascular endothelial growth factor-A (VEGF-A; isoforms 120, 164 and 188), VEGF receptors 1 and 2 (VEGFR-1 and -2), angiopoietins 1 and 2, and Tie2 mRNAs were determined by quantitative real-time polymerase chain reaction (PCR). The authors observed more intercapillary interconnection, less isolated capillaries, and a more extended capillary network inside septa of lungs that underwent 24 h of TO versus sham-TO. Moreover, the authors observed a significant increase in mRNA levels of VEGF 188 and VEGFR-1 as early as 1 hour following TO and of VEGFR-1 and angiopoietin 1 after 24 hours. Together, these results suggest that surgically applied stretching quickly enhances the expression of specific angiogenesis and vessel maintenance genes, which seems to result in the maturation and organization of a more extensive and complex capillary network.

Spatiotemporal expression of flk-1 in pulmonary epithelial cells during lung development

Vascular endothelial growth factor-A (VEGF-A) responsive effects mediated via the receptors fetal liver kinase-1 (flk-1) and fms-like tyrosine kinase (flt-1), are key processes of pulmonary vascular development. Flk-1 has been shown to be involved in early embryonic lung epithelial to endothelial crosstalk and branching morphogenesis. Recent reports suggested a role of VEGF-A in lung epithelial cell function. Based on these observations, we hypothesize that epithelial flk-1 has a unique function in pulmonary development. Thus, the aim of this study is to elucidate spatiotemporal expression of flk-1 during lung development with respect to the epithelial system. Embryonic lungs were screened for flk-1 messenger RNA and protein at daily intervals, including postnatal stages. From Embryonic Day (ED) 12.5 through ED 15.5, flk-1 expression was restricted to the early vascular primitive network, while from ED 16.5 on flk-1 was detectable in the epithelial system and persisted there postnatally. At postnatal stages, flk-1 expression was increasingly restricted to individual cells in the alveolar septa. Isolation and in vitro cultivation of alveolar epithelial cells confirmed flk-1 expression and showed VEGF secretion into the supernatant. To our knowledge, this is the first murine study characterizing epithelial flk-1 expression at different stages throughout lung organogenesis until birth and at postnatal stages. To confirm epithelial flk-1 expression, we performed reporter gene analysis of the flk-1 promoter in vivo. Investigations on transgenic mouse strains, containing either a complete or incomplete flk-1 promoter driving expression of the lacZ reporter gene, suggested differential flk-1 regulation in endothelial and epithelial cells.

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.

Decreased lung fibroblast growth factor 18 and elastin in human congenital diaphragmatic hernia and animal models

RATIONALE

Lung hypoplasia in congenital diaphragmatic hernia (CDH) seems to involve impaired alveolar septation. We hypothesized that disturbed deposition of elastin and expression of fibroblast growth factor 18 (FGF18), an elastogenesis stimulus, occurs in CDH.

OBJECTIVES

To document FGF18 and elastin in human CDH and ovine surgical and rat nitrofen models and to use models to evaluate the benefit of treatments.

METHODS

Human CDH and control lungs were collected post mortem. Diaphragmatic hernia was created in sheep at 85 days; fetal lungs were collected at 139 days (term = 145 days). Pregnant rats received nitrofen at 12 days; fetal lungs were collected at 21 days (term = 22 days). Some of the sheep fetuses with hernia underwent tracheal occlusion (TO); some of the nitrofen-treated pregnant rats received vitamin A. Both treatments are known to promote lung growth.

MEASUREMENTS AND MAIN RESULTS

Coincidental with the onset of secondary septation, FGF18 protein increased threefold in control human lungs, which failed to occur in CDH. FGF18 labeling was found in interstitial cells of septa. Elastin staining demonstrated poor septation and markedly decreased elastin density in CDH lungs. Consistently, lung FGF18 transcripts were diminished 60 and 83% by CDH in sheep and rats, respectively, and elastin density and expression were diminished. TO and vitamin A restored FGF18 and elastin expression in sheep and rats, respectively. TO restored elastin density.

CONCLUSIONS

Impaired septation in CDH is associated with decreased FGF18 expression and elastic fiber deposition. Simultaneous correction of FGF18 and elastin defects by TO and vitamin A suggests that defective elastogenesis may result, at least partly, from FGF18 deficiency.

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.

Prenatal intervention for isolated congenital diaphragmatic hernia

PURPOSE OF REVIEW

We aim to review the recent literature regarding early prenatal prediction of outcome in babies diagnosed with isolated congenital diaphragmatic hernia, as well as results of fetal therapy for this condition.

RECENT FINDINGS

Current survival rates in population-based studies are around 55-70%. Highly specialized centers report 80% and more, but discount the hidden mortality, mainly in the antenatal period. Fetuses presenting with liver herniation and a lung-to-head ratio of less than 1.0 measured in midgestation have a poor prognosis. Other volumetric techniques are being evaluated for use in midtrimester. Recently, a randomized trial failed to show benefit from prenatal therapy, but lacked power to document the potential advantage of prenatal therapy in severe cases. We proposed percutaneous fetal endoluminal tracheal occlusion with a balloon at 26-28 weeks through a 3.3 mm incision. In severe cases, fetal endoluminal tracheal occlusion increased lung size as well as survival, with an early (7 day) survival, late neonatal (28 day) survival and survival at discharge of 75, 58 and 50%, respectively, comparing favorably with 9% in contemporary controls. Airways can be restored prior to birth improving neonatal survival (83.3% compared with 33.3%). The procedure carries a risk for preterm prelabour rupture of the fetal membranes, although that may decrease with experience.

SUMMARY

Fetuses with severe congenital diaphragmatic hernia can be identified in the second trimester. Fetal endoluminal tracheal occlusion can be considered as a minimally invasive fetal therapy, improving outcome in such highly selected cases.

DNA microarray reveals novel genes induced by mechanical forces in fetal lung type II epithelial cells

Mechanical forces are essential for normal fetal lung development. However, the cellular and molecular mechanisms regulating this process are still poorly defined. In this study, we used oligonucleotide microarrays to investigate gene expression in cultured embryonic d 19 rat fetal lung type II epithelial cells exposed to a level of mechanical strain similar to the developing lung. Significance Analysis of Microarrays (SAM) identified 92 genes differentially expressed by strain. Interestingly, several members of the solute carrier family of amino acid transporter (Slc7a1, Slc7a3, Slc6a9, and tumor-associated protein 1) genes involved in amino acid synthesis (Phgdh, Psat1, Psph, Cars, and Asns), as well as the amiloride-sensitive epithelial sodium channel gene (Scnn1a) were up-regulated by the application of force. These results were confirmed by quantitative real-time PCR (qRT-PCR). Thus, this study identifies genes induced by strain that may be important for amino acid signaling pathways and protein synthesis in fetal type II cells. In addition, these data suggest that mechanical forces may contribute to facilitate lung fluid reabsorption in preparation for birth. Taken together, the present investigation provides further insights into how mechanical forces may modulate fetal lung development.

Pleiotropic role of VEGF-A in regulating fetal pulmonary mesenchymal cell turnover

Tight regulation of VEGF-A production and signaling is important for the maintenance of lung development and homeostasis. VEGF null mice have provided little insight into the role of VEGF during the later stages of lung morphogenesis. Therefore, we examined the in vitro effects of autocrine and paracrine VEGF-A production and the inhibition of VEGF-A signaling on a Flk-1-negative subset of fetal pulmonary mesenchymal cells (pMC). We hypothesized that VEGF-A receptor signaling regulates turnover of fetal lung mesenchyme in a cell cycle-dependent manner. VEGF receptor blockade with SU-5416 caused cell spreading and decreased proliferation and bcl-2 localization. Nuclear expression of the cell cycle inhibitory protein, p21, was increased with SU-5416 treatment, and p27 was absent. Autocrine VEGF production by pMC resulted in proliferation and p21/p27-dependent contact inhibition. In contrast, exogenous VEGF-A increased cell progression through the cell cycle. Selective activation of Flt by placental growth factor demonstrated the importance of this receptor/kinase in the VEGF-A responsiveness of pMC. The expression and localization of the survival factor bcl-2 was dependent on VEGF. These results provide evidence that VEGF-A plays a critical role in the regulation of fetal pulmonary mesenchymal proliferation, survival, and the subsequent development of normal lung architecture through bcl-2 and p21/p27-dependent cell cycle control.