title: Hypoxia-inducible factors in the first trimester human lung.
abstract: Lung development takes place in a relatively low-oxygen environment, which is beneficial for lung organogenesis, including vascular development. Hypoxia-inducible factor (HIF)-1 plays an important role in mediating oxygen-regulated events. HIF-1 is stable and initiates gene transcription under hypoxia, whereas in normoxia, interaction with the von Hippel-Lindau (VHL) tumor suppressor protein leads to rapid degradation of the HIF-1alpha subunit. Interaction with VHL requires hydroxylation of HIF-1alpha proline residues by prolyl hydroxylases (PHDs). We investigated the expression of the various components regulating HIF-1alpha stability in first trimester (8-14 weeks) human lungs. Spatial expression was assessed by immunohistochemistry and temporal expression by quantitative PCR. Immunoreactivity for PHD1, PHD3, and seven in absentia homolog (SIAH)1 was noted in the pulmonary epithelium. PHD2 was not expressed in the airway epithelium, but in the lung parenchyma. HIF-1alpha and vascular endothelial growth factor (VEGF) immunoreactivity were primarily detected in the branching epithelium. HIF-2alpha and ARNT proteins localized to the developing epithelium as well as mesenchymal, most likely vascular, structures in the parenchyma. VEGF receptor 2 (VEGFR2) was found in the subepithelium as well as in vascular structures of the mesenchyme. All components of the VEC complex (VHL, NEDD8, and Cullin2) were found in the epithelium. Quantitative PCR analysis demonstrated that VEGF, VEGFR1, HIF-1alpha, HIF-2alpha, ARNT, PHD1, PHD2, PHD3, and SIAH1 gene expression was constant during early pulmonary organogenesis. Cumulatively, the data suggest that the lung develops in a low-oxygen environment that allows for proper vascular development through HIF-regulated pathways.
authors.affiliation: Canadian Institute of Health Research Group in Lung Development, Hospital for Sick Children Research Institute, Department of Pediatrics, University of Toronto, Toronto, ON, Canada
authors.forename: Frederick
authors.initials: F
authors.lastname: Groenman
authors.forename: Martin
authors.initials: M
authors.lastname: Rutter
authors.forename: Isabella
authors.initials: I
authors.lastname: Caniggia
authors.forename: Dick
authors.initials: D
authors.lastname: Tibboel
authors.forename: Martin
authors.initials: M
authors.lastname: Post
mesh_terms: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000235:genetics / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins; D049308:Dioxygenases / Q000235:genetics / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D007150:Immunohistochemistry; D008168:Lung / Q000737:chemistry / Q000196:embryology / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011393:Procollagen-Proline Dioxygenase / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000235:genetics / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000235:genetics / Q000378:metabolism; D000098563:Seven in Absentia Proteins; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D049308:Dioxygenases; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D009687:Nuclear Proteins; D011393:Procollagen-Proline Dioxygenase; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases; D042461:Vascular Endothelial Growth Factor A; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2; D000098563:Seven in Absentia Proteins; D000099162:Endothelial PAS Domain-Containing Protein 1; C497396:ARNT protein, human; C497442:HIF1A protein, human; C490190:EGLN1 protein, human; C488894:EGLN3 protein, human