title: p38gamma mitogen-activated protein kinase suppresses chondrocyte production of MMP-13 in response to catabolic stimulation.
abstract: OBJECTIVE
  The signaling protein p38 mitogen-activated protein kinase is required for inflammatory signaling in chondrocytes that regulates matrix metalloproteinase (MMP) production. We sought to determine the role of specific p38 isoforms in chondrocyte catabolic signaling in response to IL-1beta and fibronectin fragments (Fn-f).
  
  
  METHODS
  Human articular chondrocytes isolated from normal ankle cartilage from tissue donors or from osteoarthritic knee cartilage obtained during knee replacement were stimulated with IL-1beta or Fn-f, with or without pretreatment with p38 inhibitors (SB203580 or BIRB796) or growth factors (IGF-1 and OP-1). p38 isoform phosphorylation was measured by antibody array and immunoblotting. MMP-13 expression was measured by real-time polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and immunoblotting. Chondrocytes were transfected with plasmids expressing constitutively active (CA) p38gamma or with adenovirus expressing dominant negative (DN) p38gamma.
  
  
  RESULTS
  Stimulation of chondrocytes with either IL-1beta or Fn-f led to enhanced phosphorylation of p38alpha and p38gamma, with little phosphorylation of p38beta or p38delta isoforms. p38alpha localized to the nucleus and p38gamma to the cytosol. Inhibition of both p38alpha and p38gamma with BIRB796 resulted in less inhibition of MMP-13 production in response to IL-1beta or FN-f than did inhibition of only p38alpha with SB203580. Transfection with CA p38gamma resulted in decreased MMP-13 production while transduction with DN p38gamma resulted in increased MMP-13 production. IGF-1 and OP-1 pretreatment inhibited p38alpha phosphorylation but not p38gamma phosphorylation.
  
  
  CONCLUSIONS
  p38gamma is activated by catabolic stimulation of human articular chondrocytes, but interestingly suppresses MMP-13 production. Treatments that increase p38gamma activation may be of therapeutic benefit in reducing chondrocyte production of MMP-13.
authors.affiliation: Department of Internal Medicine, The Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Long
authors.forename: R F
authors.initials: RF
authors.lastname: Loeser
mesh_terms: D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism*; D019902:Chondrocytes / Q000187:drug effects* / Q000378:metabolism*; D015536:Down-Regulation; D005353:Fibronectins / Q000494:pharmacology; D006801:Humans; D007249:Inflammation / Q000378:metabolism; D053583:Interleukin-1beta / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism / Q000494:pharmacology*; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism*; D048291:Mitogen-Activated Protein Kinase 12 / Q000378:metabolism / Q000494:pharmacology*; D010003:Osteoarthritis / Q000378:metabolism; D010446:Peptide Fragments / Q000494:pharmacology
chemical_list: D005353:Fibronectins; D053583:Interleukin-1beta; D047908:Intracellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D048291:Mitogen-Activated Protein Kinase 12; D053509:Matrix Metalloproteinase 13