Acarregui M J, Penisten S T, Goss K L, Ramirez K, Snyder J M
Department of Pediatrics, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
Am J Respir Cell Mol Biol. 1999 Jan;20(1):14-23. doi: 10.1165/ajrcmb.20.1.3251.
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.
新生儿呼吸功能取决于发育良好的肺毛细血管床的形成。血管内皮生长因子（VEGF）是内皮细胞生长和血管生成的强效诱导剂。在发育中的肺中已检测到高水平的VEGF蛋白和信使核糖核酸（mRNA），这表明VEGF在肺毛细血管床的发育中起作用。为了开始了解VEGF在人类肺发育中的作用，我们在发育中的人类肺模型中探索了VEGF基因表达的调控以及VEGF蛋白和mRNA的定位。在孕中期人胎儿肺组织中检测到VEGF蛋白和mRNA，并且它们在器官培养中的水平随时间增加。与20%氧气环境相比，将人胎儿肺器官维持在2%氧气环境中可使VEGF蛋白和mRNA增加。发现在20%氧气中孵育的器官中，环磷酸腺苷（cAMP）可增加VEGF mRNA水平，但在2%氧气中孵育的器官中则不然。VEGF蛋白的免疫染色显示主要定位于孕中期人胎儿肺组织的气道上皮细胞中。将人胎儿肺器官在2%和20%氧气中孵育后，VEGF的免疫染色增加。有趣的是，在20%氧气中孵育4天后，VEGF蛋白主要定位于气道上皮细胞下方的基底膜中。在二丁酰cAMP存在下孵育组织导致VEGF免疫染色增加，主要在20%氧气处理的组织中的肺泡前导管基底膜中。原位杂交研究表明，VEGF mRNA存在于间充质细胞和气道上皮细胞中。这些数据表明，在发育中的人类肺中，VEGF基因表达受氧气和cAMP的调控。在远端气道上皮细胞中检测到VEGF mRNA和蛋白，以及在气道上皮细胞下方的基底膜中检测到VEGF蛋白，这表明VEGF蛋白在其上皮合成后发生转运。VEGF定位于气道上皮细胞的基底膜可能对指导人类肺中的毛细血管发育很重要。
