title: Hypoxia promotes the production and inhibits the destruction of human articular cartilage.
abstract: OBJECTIVE
  To determine the effects of hypoxia on both anabolic and catabolic pathways of metabolism in human articular cartilage and to elucidate the roles played by hypoxia-inducible factors (HIFs) in these responses.
  
  
  METHODS
  Normal human articular cartilage from a range of donors was obtained at the time of above-the-knee amputations due to sarcomas not involving the joint space. Fresh cartilage tissue explants and isolated cells were subjected to hypoxia and treatment with interleukin-1α. Cell transfections were performed on isolated human chondrocytes.
  
  
  RESULTS
  Using chromatin immunoprecipitation, we found that hypoxia induced cartilage production in human tissue explants through direct binding of HIF-2α to a specific site in the master-regulator gene SOX9. Importantly, hypoxia also suppressed spontaneous and induced destruction of human cartilage in explant culture. We found that anticatabolic responses were predominantly mediated by HIF-1α. Manipulation of the hypoxia-sensing pathway through depletion of HIF-targeting prolyl hydroxylase-containing protein 2 (PHD-2) further enhanced cartilage responses as compared to hypoxia alone. Hypoxic regulation of tissue-specific metabolism similar to that in human cartilage was observed in pig, but not mouse, cartilage.
  
  
  CONCLUSIONS
  We found that resident chondrocytes in human cartilage are exquisitely adapted to hypoxia and use it to regulate tissue-specific metabolism. Our data revealed that while fundamental regulators, such as SOX9, are key molecules both in mice and humans, the way in which they are controlled can differ. This is all the more important since it is upstream regulators such as this that need to be directly targeted for therapeutic benefit. HIF-specific hydroxylase PHD-2 may represent a relevant target for cartilage repair.
authors: Kennedy Institute of Rheumatology and University of Oxford, London, UK.
authors: Brendan L
authors: BL
authors: Thoms
authors: Katarzyna A
authors: KA
authors: Dudek
authors: Jérôme E
authors: JE
authors: Lafont
authors: Christopher L
authors: CL
authors: Murphy
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000293:Adolescent; D000328:Adult; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D001665:Binding Sites; D002358:Cartilage, Articular / Q000378:metabolism* / Q000473:pathology; D015687:Cell Hypoxia / Q000502:physiology; D002478:Cells, Cultured; D002648:Child; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D053582:Interleukin-1alpha / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008875:Middle Aged; D011393:Procollagen-Proline Dioxygenase / Q000172:deficiency; D055758:SOX9 Transcription Factor / Q000378:metabolism; D013552:Swine; D014162:Transfection; D055815:Young Adult; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D053582:Interleukin-1alpha; D011393:Procollagen-Proline Dioxygenase; D055758:SOX9 Transcription Factor; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human; C527932:SOX9 protein, human; C490190:EGLN1 protein, human