Vascular Endothelial Growth Factor Gene Expression in Human Fetal Lung In Vitro

Abstract

Neonatal respiratory function depends on the development of a well-formed pulmonary capillary bed. Vascular endothelial growth factor (VEGF) is a potent inducer of endothelial cell growth and angiogenesis. High levels of VEGF protein and messenger RNA (mRNA) have been detected in the developing lung, suggesting that VEGF plays a role in the development of the pulmonary capillary bed. To begin to understand the role of VEGF in human lung development, we explored the regulation of VEGF gene expression and the localization of VEGF protein and mRNA in a model of the developing human lung. VEGF protein and mRNA were detected in midtrimester human fetal lung tissue, and their levels increased with time in explant culture. VEGF protein and mRNA were increased by the maintenance of human fetal lung explants in 2% O2 environments compared with 20% O2 environments. VEGF mRNA levels were found to be increased by cyclic adenosine monophosphate (cAMP) in explants that were incubated in 20% O2, but not in those incubated in 2% O2. Immunostaining for VEGF protein demonstrated localization primarily in airway epithelial cells in midtrimester human fetal lung tissue. Immunostaining for VEGF increased with incubation of human fetal lung explants in 2% and 20% O2. Interestingly, VEGF protein was localized primarily in the basement membrane subjacent to airway epithelial cells after 4 d of incubation in 20% O2. Incubation of tissues in the presence of dibutyryl cAMP resulted in an increase in immunostaining for VEGF, primarily in the basement membranes of prealveolar ducts in 20% O2-treated tissues. In situ hybridization studies indicated that VEGF mRNA was present in both mesenchymal cells and airway epithelial cells. These data suggest that VEGF gene expression is regulated by both oxygen and cAMP in the developing human lung. The detection of VEGF mRNA and protein in distal airway epithelial cells and the detection of VEGF protein in the basement membrane subjacent to the airway epithelial cells suggest that translocation of VEGF protein occurs after its synthesis in the epithelium. Localization of VEGF to the basement membrane of airway epithelial cells may be important for directing capillary development in the human lung.

Adenylate Cyclase/Protein Kinase A Signaling Pathway Enhances Angiogenesis Through Induction of Vascular Endothelial Growth Factor In Vivo

“…In that paper, Rp-cAMP, a cAMP antagonist, suppressed VEGF expression induced by PGE2 (23). cAMPdependent increase in VEGF expression was also observed in isolated organs such as perfused rat lungs and human fetal lung explants (24,25).…”

Effects of vascular endothelial growth factor on isolated fetal alveolar type II cells

“…In the lung, alveolar type II cells are the major source of VEGF (1,19,25,33), the epithelial cells that secrete surfactant and maintain alveolar epithelial renewal (11). VEGF production by type II cells is upregulated by hypoxia (27).…”

Effects of Oxidative Stress and Antenatal Corticosteroids on the Pulmonary Expression of Vascular Endothelial Growth Factor (VEGF) and Alveolarization

“…It has also been shown that oxidative stress inactivates the survival signal of VEGF in endothelial cells through the action of peroxynitrite (Acarregui et al, 1999) .…”

“…In an in vitro study of human foetal lungs, Acarregui et al (Acarregui et al, 1999) found increased levels of VEGF mRNA when the lung tissue was maintained in dexamethasone for 4 days as from the onset of incubation in 0.20 FiO 2 . However, when the epithelium was first incubated in FiO 2 0.20 and then treated with dexamethasone, mRNA levels were not increased.…”

“…The different experimental models used, or the fact that the effect of dexamethasone on the differentiation of type II cells might lead to a relative increase in VEGF mRNA (Acarregui et al, 1999) could explain the discrepancies found in the effect of dexamethasone on VEGF expression.…”