title: Connexin43 enhances the expression of osteoarthritis-associated genes in synovial fibroblasts in culture.
abstract: BACKGROUND
  Recent work has shown that the gap junction protein connexin43 (Cx43) is upregulated in cells of the joint during osteoarthritis (OA). Here we examined if the OA-associated increase in Cx43 expression impacts the function of synovial fibroblasts by contributing to the production of catabolic and inflammatory factors that exacerbate joint destruction in arthritic disease.
  
  
  METHODS
  Using rabbit and human synovial fibroblast cell lines, we examined the effects of Cx43 overexpression and Cx43 siRNA-mediated knockdown on the gene expression of OA-associated matrix metalloproteinases (MMP1 and MMP13), aggrecanases (ADAMTS4 and ADAMTS5), and inflammatory factors (IL1, IL6 and PTGS2) by quantitative real time RT-PCR. We examined collagenase activity in conditioned media of cultured synovial cells following Cx43 overexpression. Lastly, we assessed the interplay between Cx43 and the NFκB cascade by western blotting and gene expression studies.
  
  
  RESULTS
  Increasing Cx43 expression enhanced the gene expression of MMP1, MMP13, ADAMTS4, ADAMTS5, IL1, IL6 and PTGS2 and increased the secretion of collagenases into conditioned media of cultured synovial fibroblasts. Conversely, knockdown of Cx43 decreased expression of many of these catabolic and inflammatory genes. Modulation of Cx43 expression altered the phosphorylation of the NFκB subunit, p65, and inhibition of NFκB with chemical inhibitors blocked the effects of increased Cx43 expression on the mRNA levels of a subset of these catabolic and inflammatory genes.
  
  
  CONCLUSIONS
  Increasing or decreasing Cx43 expression alone was sufficient to alter the levels of catabolic and inflammatory genes expressed by synovial cells. The NFκB cascade mediated the effect of Cx43 on the expression of a subset of these OA-associated genes. As such, Cx43 may be involved in joint pathology during OA, and targeting Cx43 expression or function may be a viable therapeutic strategy to attenuate the catabolic and inflammatory environment of the joint during OA.
authors.forename: Aditi
authors.initials: A
authors.lastname: Gupta
authors.forename: Corinne
authors.initials: C
authors.lastname: Niger
authors.forename: Atum M
authors.initials: AM
authors.lastname: Buo
authors.forename: Eric R
authors.initials: ER
authors.lastname: Eidelman
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Chen
authors.affiliation: Department of Orthopaedics, University of Maryland School of Medicine, 100 Penn Street, Allied Health Building, Room 540E, Baltimore, MD 21201, USA. jstai002@umaryland.edu.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Stains
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D018031:Connexin 43 / Q000096:biosynthesis* / Q000235:genetics*; D005347:Fibroblasts / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D010003:Osteoarthritis / Q000235:genetics* / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D013583:Synovial Membrane / Q000378:metabolism*
chemical_list: D018031:Connexin 43; D018836:Inflammation Mediators