title: Hypoxia inducible factor-1α directly induces the expression of receptor activator of nuclear factor-κB ligand in periodontal ligament fibroblasts.
abstract: During orthodontic tooth movement, local hypoxia and enhanced osteoclastogenesis are observed in the compression side of periodontal tissues. The receptor activator of nuclear factor-κB ligand (RANKL) is an osteoblast/stromal cell-derived factor that is essential for osteoclastogenesis. In this study, we examined the effect of hypoxia on RANKL expression in human periodontal ligament fibroblasts (PDLFs) to investigate the relationship between local hypoxia and enhanced osteoclastogenesis in the compression side of periodontal tissues. Hypoxia significantly enhanced the levels of RANKL mRNA and protein as well as hypoxia inducible factor-1α (HIF-1α) protein in PDLFs. Constitutively active HIF-1α alone significantly increased the levels of RANKL expression in PDLFs under normoxic conditions, whereas dominant negative HIF-1α blocked hypoxia-induced RANKL expression. To investigate further whether HIF-1α directly regulates RANKL transcription, a luciferase reporter assay was performed using the reporter vector containing the RANKL promoter sequence. Exposure to hypoxia or overexpression of constitutively active HIF-1α significantly increased RANKL promoter activity, whereas dominant negative HIF-1α blocked hypoxia-induced RANKL promoter activity. Furthermore, mutations of putative HIF-1α binding elements in RANKL promoter prevented hypoxia-induced RANKL promoter activity. The results of chromatin immunoprecipitation showed that hypoxia or constitutively active HIF-1α increased the DNA binding of HIF-1α to RANKL promoter. These results suggest that HIF-1α mediates hypoxia-induced up-regulation of RANKL expression and that in compression side periodontal ligament, hypoxia enhances osteoclastogenesis, at least in part, via an increased RANKL expression in PDLFs.
authors.affiliation: Department of Molecular Genetics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, 110-749, Korea.
authors.forename: Hyun-Jung
authors.initials: HJ
authors.lastname: Park
authors.forename: Kyung Hwa
authors.initials: KH
authors.lastname: Baek
authors.forename: Hye-Lim
authors.initials: HL
authors.lastname: Lee
authors.forename: Arang
authors.initials: A
authors.lastname: Kwon
authors.forename: Hyo Rin
authors.initials: HR
authors.lastname: Hwang
authors.forename: Abdul S
authors.initials: AS
authors.lastname: Qadir
authors.forename: Kyung Mi
authors.initials: KM
authors.lastname: Woo
authors.forename: Hyun-Mo
authors.initials: HM
authors.lastname: Ryoo
authors.forename: Jeong-Hwa
authors.initials: JH
authors.lastname: Baek
mesh_terms: D015687:Cell Hypoxia; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D005347:Fibroblasts / Q000378:metabolism*; D017930:Genes, Reporter; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D049410:Luciferases, Renilla / Q000096:biosynthesis / Q000235:genetics; D010513:Periodontal Ligament / Q000166:cytology* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D053245:RANK Ligand / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D053245:RANK Ligand; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D049410:Luciferases, Renilla