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Involvement of ADAM8 in osteoclastogenesis and pathological bone destruction
  1. Mari Ainola (mari.ainola{at}helsinki.fi)
  1. University of Helsinki, Finland
    1. Tian-Fang Li (tianfangl{at}yahoo.com)
    1. University of Rochester, United States
      1. Jami Mandelin (jami.mandelin{at}gmail.com)
      1. University of Helsinki, Finland
        1. Mika Hukkanen (mika.hukkanen{at}helsinki.fi)
        1. University of Helsinki, Finland
          1. Sun Jin Choi (sjchoi{at}nidcr.nih.gov)
          1. University of Rochester Medical Center, United States
            1. Jari Salo (jari.salo{at}hus.fi)
            1. Helsinki University Central Hospital, Finland
              1. Yrjö T. Konttinen (yrjo.konttinen{at}helsinki.fi)
              1. Institute of Clinical Medicine, Helsinki University, Finland

                Abstract

                Objectives: The eventual role of ADAM8 (a disintegrin and a metalloproteinase) in osteoclastogenesis was studied in erosive rheumatoid arthritis (RA) and in vitro.

                Methods: ADAM8 protein and mRNA expression was measured in RA pannus and synovitis and compared to osteoarthritic (OA) synovial membrane. Human monocytes were isolated and stimulated with pro-inflammatory cytokines and their ADAM8 expression and surface ADAM8 were measured. Human peripheral blood monocytes and RAW 264.7 mouse monocyte/macrophage cells were stimulated to osteclast like-cells, and their expression of ADAM8 and osteoclastic markers (calcitonin receptor, integrin beta 3, cathepsin K, TRAP) were analyzed. Transfection and siRNA were used to assess the role of ADAM8 in formation of polykaryons.

                Results: Increased numbers of ADAM8 positive cells were shown particularly in the pannus-cartilage/bone junction close or adjoining to TRAP positive multinucleate cells under formation (60 ± 2 % in pannus, 47 ± 2 % in synovitis vs. 10 ± 1 % in OA, p < 0.001). Human pannus contained high ADAM8 mRNA copy numbers (23 ± 7 in pannus, 14 ± 4 in synovitis vs. 1.7 ± 0.3 in OA, p < 0.001). Functional studies in vitro disclosed ADAM8 mRNA and protein, which was first converted to a proteolytically active and then to fusion-active form. Gene transfection and siRNA experiments enhanced and inhibited, respectively, expression of osteoclast markers and maturation of multinuclear cells.

                Conclusions: ADAM8 may be involved in bone destruction in RA because it is upregulated in RA pannus adjacent to developing erosions and enhances maturation of osteoclast-like cells.

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