title: Enhanced suppressor of cytokine signaling 3 in arthritic cartilage dysregulates human chondrocyte function.
abstract: OBJECTIVE
  To determine the expression of suppressor of cytokine signaling 3 (SOCS-3) in human articular chondrocytes and its functional consequences.
  
  
  METHODS
  Chondrocytes were isolated from the cartilage of patients with osteoarthritis (OA), patients with rheumatoid arthritis (RA), and trauma patients and from the healthy cartilage of patients with a femoral neck fracture. The human chondrocyte cell line G6 and primary bovine chondrocytes were used in validation experiments. SOCS-3 messenger RNA (mRNA) expression was measured by quantitative polymerase chain reaction, and SOCS-3 protein levels were determined by Western blotting and immunohistochemical analysis. To ascertain the role of SOCS-3 in the chondrocyte response to interleukin-1β (IL-1β) or lipopolysaccharide (LPS), the expression of SOCS3 was either reduced by small interfering RNA or enhanced by viral transduction.
  
  
  RESULTS
  The expression of SOCS-3 mRNA (but not that of SOCS-1 mRNA) was significantly enhanced in chondrocytes obtained from OA cartilage (mean ± SD ΔC(t)  3.4 ± 1.0) and RA cartilage (ΔC(t)  3.4 ± 1.4) compared with cartilage obtained from patients with femoral neck fracture (ΔC(t)  5.3 ± 1.2). The expression of SOCS3 correlated significantly with that of other genes known to be expressed in arthritic chondrocytes, such as MMP13 (r = 0.743), ADAMTS4 (r = 0.779), and ADAMTS5 (r = 0.647), and an inverse relationship was observed with COL2A1 (r = -0.561). Up-regulation of SOCS-3 by IL-1 in G6 chondrocytes and its spontaneous expression in OA chondrocytes were reduced by mithramycin, a specific inhibitor of transcription factor Sp-1. Overexpression of SOCS-3 in bovine chondrocytes reduced IL-1- and LPS-induced nitric oxide production and insulin-like growth factor 1-induced proteoglycan synthesis. Interestingly, a similar impairment of function was observed in OA chondrocytes, which was partially restored by SOCS-3 gene knockdown.
  
  
  CONCLUSIONS
  This study demonstrated that both SOCS-3 mRNA and SOCS-3 protein are expressed in human arthritic chondrocytes and affect cellular responses involved in cartilage pathology.
authors.affiliation: Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. a.vandeloo@reuma.umcn.nl
authors.forename: Fons A J
authors.initials: FA
authors.lastname: van de Loo
authors.forename: Sharon
authors.initials: S
authors.lastname: Veenbergen
authors.forename: Ben
authors.initials: B
authors.lastname: van den Brand
authors.forename: Miranda B
authors.initials: MB
authors.lastname: Bennink
authors.forename: Esmeralda
authors.initials: E
authors.lastname: Blaney-Davidson
authors.forename: Onno J
authors.initials: OJ
authors.lastname: Arntz
authors.forename: Henk M
authors.initials: HM
authors.lastname: van Beuningen
authors.forename: Peter M
authors.initials: PM
authors.lastname: van der Kraan
authors.forename: Wim B
authors.initials: WB
authors.lastname: van den Berg
mesh_terms: D051722:ADAM Proteins / Q000235:genetics / Q000378:metabolism; D000071121:ADAMTS4 Protein; D000071116:ADAMTS5 Protein; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D002417:Cattle; D002460:Cell Line; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D008297:Male; D053509:Matrix Metalloproteinase 13 / Q000235:genetics / Q000378:metabolism; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D020370:Osteoarthritis, Knee / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D011348:Procollagen N-Endopeptidase / Q000235:genetics / Q000378:metabolism; D011509:Proteoglycans / Q000378:metabolism; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D007375:Interleukin-1; D011509:Proteoglycans; C106644:SOCS3 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D051722:ADAM Proteins; D000071116:ADAMTS5 Protein; C121532:ADAMTS5 protein, human; D053509:Matrix Metalloproteinase 13; D011348:Procollagen N-Endopeptidase; D000071121:ADAMTS4 Protein; C000603918:ADAMTS4 protein, human