Low oxygen tension stimulates collagen synthesis and COL1A1 transcription through the action of TGF-beta1.
Recent findings point to low oxygen tension (hypoxia) as an important mechanism for the expression of several eukaryotic genes. We have previously shown that hypoxia (2% O2), when compared to standard oxygen tension (20% O2), upregulates the mRNA levels of the human alpha1(I) (COL1A1) procollagen gene and transforming growth factor-beta1 (TGF-beta1) in human dermal fibroblasts. In this report, we determined the effect of hypoxia on collagen synthesis and transcription. Exposure of human dermal fibroblasts to hypoxia for 24-72 h led to a threefold, dose-dependent increase in collagenous protein (P < 0.0001; r = 0.9794) and to enhanced type I procollagen deposition, as shown by direct immunofluorescence. Transient transfections with a series of luciferase- and CAT-promoter constructs of the human COL1A1 gene (spanning from -2.5 kb to +113 bp) showed that hypoxia increases the transcriptional activity of constructs having 5' endpoints between -804 bp and -107 bp, with loss of stimulation at -84 bp. Maximal increase in promoter activity in hypoxia was observed between -190 and -174 bp of the proximal promoter, once a cKrox repressor site (-199 to -224 bp) was deleted. Upregulation of COL1A1 mRNA levels in hypoxia was blocked by a TGF-beta1 anti-sense oligonucleotide, and failed to occur in fibroblasts from TGF-beta1 knock-out mice. Co-transfection and overexpression with a Smad7 construct abrogated the increase in COL1A1 promoter activity observed in hypoxia. Upregulated transcriptional activity of the TGF-beta1 promoter in hypoxia was found to be maximal between -453 and -175 bp from the transcriptional start site. Since hypoxia is a critical feature of the early phases of wound repair, we conclude that it may act as a potent physiologic stimulus for collagen synthesis. TGF-beta1 appears to be a critical component of this response.
Falanga
Vincent
V
Department of Dermatology and Skin Surgery, Roger Williams Medical Center, Boston University School of Medicine, Providence, Rhode Island 02908, USA. vfalanga@bu.edu
Zhou
Linda
L
Yufit
Tatyana
T
D000328:Adult; D000818:Animals; D002478:Cells, Cultured; D003094:Collagen / Q000096:biosynthesis* / Q000235:genetics*; D024042:Collagen Type I; D000090602:Collagen Type I, alpha 1 Chain; D004268:DNA-Binding Proteins / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D007231:Infant, Newborn; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D010100:Oxygen / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000502:physiology; D012867:Skin / Q000378:metabolism / Q000473:pathology; D051906:Smad7 Protein; D015534:Trans-Activators / Q000494:pharmacology; D014158:Transcription, Genetic / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000502:physiology*; D053773:Transforming Growth Factor beta1
D024042:Collagen Type I; D000090602:Collagen Type I, alpha 1 Chain; D004268:DNA-Binding Proteins; C497806:SMAD7 protein, human; D051906:Smad7 Protein; C497807:Smad7 protein, mouse; C508960:TGFB1 protein, human; C508961:Tgfb1 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D003094:Collagen; D010100:Oxygen