title: Hypoxia potentiates the BMP-2 driven COL2A1 stimulation in human articular chondrocytes via p38 MAPK.
abstract: OBJECTIVE
  Since the biological effect of cartilage mediators is generally studied in a non-physiologic environment of 21% O2, we investigated the effects of a chronic hypoxia on the capability of articular chondrocytes to respond to one anabolic stimulation.
  
  
  METHODS
  Human Articular Chondrocytes (HACs) were cultured under hypoxia and stimulated with the chondrogenic growth factor BMP-2. The phenotype of the chondrocytes was studied by RT-PCR, and the cartilage-specific type II collagen production and deposition were also examined by western immunoblot and immunofluorescence. The Bone Morphogenetic protein (BMP) signalling pathway was also analysed.
  
  
  RESULTS
  BMP-2 is much more efficient to stimulate the expression of the cartilage-specific gene COL2A1 by HACs when cultured under hypoxia (1%O2) compared to normoxia (21%O2). Analysis of the BMP-activated signalling shows that the Smad pathway is inhibited under hypoxia, whereas p38 MAPK is activated, and is involved in a synergy between hypoxia and BMP signalling, thus contributing to the enhanced anabolic response.
  
  
  CONCLUSIONS
  Our study shows that hypoxia interplays with a chondrogenic factor and enhances the overall anabolic activity of the HACs. Alternatively to Hypoxia-Inducible Factor (HIF) signalling, and through a cross-talk with the BMP signalling which involves the p38 pathway, hypoxic stimulation markedly increases the capability of chondrocytes to produce the cartilage-specific type II collagen. Therefore our study provides new evidences of the multilayered effects of hypoxia in the anabolic functions of chondrocytes. This understanding may help promoting the anabolic function of articular chondrocytes, and thus improving their manipulation for cell therapy.
authors.affiliation: Institute for Biology and Chemistry of Proteins, CNRS, UMR 5305 Laboratory of Tissue Biology and Therapeutic Engineering, Université Claude Bernard-Lyon 1 and University of Lyon, France. Electronic address: jerome.lafont@ibcp.fr.
authors.forename: J E
authors.initials: JE
authors.lastname: Lafont
authors.affiliation: Institute for Biology and Chemistry of Proteins, CNRS, UMR 5305 Laboratory of Tissue Biology and Therapeutic Engineering, Université Claude Bernard-Lyon 1 and University of Lyon, France.
authors.forename: F-A
authors.initials: FA
authors.lastname: Poujade
authors.affiliation: Institute for Biology and Chemistry of Proteins, CNRS, UMR 5305 Laboratory of Tissue Biology and Therapeutic Engineering, Université Claude Bernard-Lyon 1 and University of Lyon, France.
authors.forename: M
authors.initials: M
authors.lastname: Pasdeloup
authors.affiliation: Orthopaedic Surgery Department, Hôpital de la Croix-Rousse, 103 grande rue de la Croix-Rousse, 69317 Lyon Cedex 04, France.
authors.forename: P
authors.initials: P
authors.lastname: Neyret
authors.affiliation: Institute for Biology and Chemistry of Proteins, CNRS, UMR 5305 Laboratory of Tissue Biology and Therapeutic Engineering, Université Claude Bernard-Lyon 1 and University of Lyon, France.
authors.forename: F
authors.initials: F
authors.lastname: Mallein-Gerin
mesh_terms: D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology*; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism*; D015687:Cell Hypoxia / Q000502:physiology*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism*; D020219:Chondrogenesis / Q000187:drug effects; D024042:Collagen Type I / Q000378:metabolism; D024043:Collagen Type II / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D015398:Signal Transduction / Q000187:drug effects; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; C499177:COL2A1 protein, human; D024042:Collagen Type I; D024043:Collagen Type II; D048051:p38 Mitogen-Activated Protein Kinases
keywords: Anabolism; BMP signalling; Hypoxia; Type II collagen production