Low oxygen tension stimulates collagen synthesis and COL1A1 transcription through the action of TGF‐β1

Abstract

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.

Loss of myeloid cell-derived vascular endothelial growth factor accelerates fibrosis

“…Hypoxia has been shown to increase the production of collagen as well as profibrogenic factors like plasminogen activator inhibitor-1, tissue inhibitor of metalloproteinase-1, and connective tissue growth factor through an HIF-mediated transcriptional response (33)(34)(35). Furthermore, hypoxia and TGF-β have been shown to synergize with regard to the production of certain collagens in fibroblasts (36,37). Here, we observed an increase in HIF proteins and in the hypoxia and HIF-regulated marker protein CA-IX after treatment with bleomycin; this increase is much more pronounced in Mut animals.…”

Akt Mediates Mechanical Strain-Induced Collagen Production by Mesangial Cells

“…MC were stretched in the presence or absence of the PI3K inhibitor LY294002 (20 mol, 30 min pre-incubation). (A) Transcriptional activation of the col 1A1 gene was studied using a reporter construct in which the full-length promoter of the col 1A1 gene is placed upstream of the luciferase gene (28). MC were transfected with col 1A1-luc and pCMV-␤-gal as described in Materials and Methods, stretched for 18 h, and luciferase and ␤-gal activities were assayed as described.…”

Provisional Matrix Deposition in Hemostasis and Venous Insufficiency: Tissue Preconditioning for Nonhealing Venous Ulcers

“…However, exposure to prolonged culture in hypoxic conditions ( > 1 week), thus, mimicking an ischemic dermal environment, did not support these processes. 112 Similarly, other studies using dermal fibroblasts have reported up-regulated expression of pro-a1 (I) 113 and (III) collagens 114,115 after acute exposure to hypoxic conditions in vitro, followed by decreased expression in response to prolonged hypoxia. 114,115 Under hypoxic conditions dermal fibroblastproduced collagen cannot be synthesized or crosslinked effectively, since the enzymes required for collagen polymerization and crosslinking, prolyl hydroxylase, lysyl hydroxylase, and lysyl oxidase, all require molecular oxygen as a cofactor to perform their biological function in the collagen synthesis and maturation pathway.…”