title: Hypoxia triggers a HIF-mediated differentiation of peripheral blood mononuclear cells into osteoclasts.
abstract: BACKGROUND
  The source and mechanisms leading to osteoclast (OC) generation during tooth movement are not clearly understood. We hypothesized that during tooth movement, OC differentiate from peripheral blood mononuclear cells (PBMNC) downstream of the global hypoxia-inducible transcription factor hypoxia-inducible factor (HIF)-1α.
  
  
  OBJECTIVE
  The objective of this study was to demonstrate up-regulation of OC growth factors from osteoblasts (OB) and subsequent conversion of PBMNC into functional OC under hypoxic stress.
  
  
  METHODS
  Human primary PBMNC were cocultured with/without OB and subjected to either hypoxia (2.5% O2) or normoxia (21% O2) over 14 days. Levels of HIF, vascular endothelial growth factor (VEGF) and receptor activator for nuclear factor kappa-β ligand (RANKL) were measured. Conversion of PBMNC into OC was measured using resorption and TRAP assays.
  
  
  RESULTS
  Functional OC were only observed in response to hypoxia during coculture of PBMNC and OB and only after up-regulation of HIF, VEGF and RANKL in the hypoxic conditions. YC-1, a HIF inhibitor, reduced OC formation in response to hypoxia.
  
  
  CONCLUSIONS
  Hypoxia triggers the differentiation of PBMNC into functional OC in the presence of OB in a HIF-dependent manner as would occur during orthodontic loading of the periodontal ligament space.
authors.affiliation: Department of Orthodontics, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73162, USA. tdandajena@msn.com
authors.forename: T C
authors.initials: TC
authors.lastname: Dandajena
authors.forename: M A
authors.initials: MA
authors.lastname: Ihnat
authors.forename: B
authors.initials: B
authors.lastname: Disch
authors.forename: J
authors.initials: J
authors.lastname: Thorpe
authors.forename: G F
authors.initials: GF
authors.lastname: Currier
mesh_terms: D000135:Acid Phosphatase / Q000032:analysis; D015415:Biomarkers / Q000032:analysis; D015153:Blotting, Western; D016723:Bone Remodeling / Q000502:physiology; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology*; D049109:Cell Proliferation; D002470:Cell Survival / Q000502:physiology; D018920:Coculture Techniques; D004797:Enzyme-Linked Immunosorbent Assay; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000032:analysis / Q000037:antagonists & inhibitors / Q000502:physiology*; D007191:Indazoles / Q000494:pharmacology; D007527:Isoenzymes / Q000032:analysis; D007963:Leukocytes, Mononuclear / Q000502:physiology*; D010006:Osteoblasts / Q000502:physiology; D010010:Osteoclasts / Q000187:drug effects / Q000502:physiology*; D053245:RANK Ligand / Q000032:analysis; D000071681:Tartrate-Resistant Acid Phosphatase; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000032:analysis
chemical_list: D015415:Biomarkers; D005452:Fluoresceins; D005456:Fluorescent Dyes; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007191:Indazoles; D007527:Isoenzymes; D053245:RANK Ligand; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; C027780:carboxyfluoresceindiacetate; C090937:3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase