Vascular endothelial growth factor gene expression in human fetal lung in vitro

Neonatal respiratory function depends on the development of a well-formed p ulmonary capillary bed. Vascular endothelial growth factor (VEGF) is a pote nt 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 cap illary bed. To begin to understand the role of VEGF in human lung developme nt, 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 pro tein and mRNA were detected in midtrimester human fetal lung tissue, and th eir levels increased with time in explant culture. VEGF protein and mRNA we re increased by the maintenance of human fetal lung explants in 2% O-2 envi ronments compared with 20% O-2 environments. VEGF mRNA levels were found to be increased by cyclic adenosine monophosphate (cAMP) in explants that wer e incubated in 20% O-2, but not in those incubated in 2% O-2. Immunostainin g for VEGF protein demonstrated localization primarily in airway epithelial cells in midtrimester human fetal lung tissue. Immunostaining for VEGF inc reased with incubation of human fetal lung explants in 2% and 20% O-2. Inte restingly, VEGF protein was localized primarily in the basement membrane su bjacent to airway epithelial cells after 4 d of incubation in 20% O-2. Incu bation of tissues in the presence of dibutyryl cAMP resulted in an increase in immunostaining for VEGF, primarily in the basement membranes of prealve olar ducts in 20% O-2-treated tissues. In Situ hybridization studies indica ted that VEGF mRNA was present in both mesenchymal cells and airway epithel ial cells. These data suggest that VEGF gene expression is regulated by bot h 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 pro tein in the basement membrane subjacent to the airway epithelial cells sugg est that translocation of VEGF protein occurs after its synthesis in the ep ithelium. Localization of VEGF to the basement membrane of airway epithelia l cells may be important for directing capillary development in the human l ung.