Osteoclastic Bone Degradation and the Role of Different Cysteine Proteinases and Matrix Metalloproteinases: Differences Between Calvaria and Long Bone

Authors

  • Vincent Everts PhD,

    Corresponding author
    1. Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam (ACTA), Universiteit van Amsterdam and Vrije Universiteit, Amsterdam, The Netherlands
    • Department of Oral Cell Biology, ACTA, Vrije Universiteit, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
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  • Wolf Korper,

    1. Department of Cell Biology and Histology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
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  • Kees A Hoeben,

    1. Department of Cell Biology and Histology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
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  • Ineke DC Jansen,

    1. Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam (ACTA), Universiteit van Amsterdam and Vrije Universiteit, Amsterdam, The Netherlands
    2. Department of Periodontology, ACTA, Universiteit van Amsterdam and Vrije Universiteit, Amsterdam, The Netherlands
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  • Dieter Bromme,

    1. Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, Canada
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  • Kitty BJM Cleutjens,

    1. Department of Pathology, Cardiovascular Research Institute Maastricht (CARIM), University of Maastricht, Maastricht, The Netherlands
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  • Sylvia Heeneman,

    1. Department of Pathology, Cardiovascular Research Institute Maastricht (CARIM), University of Maastricht, Maastricht, The Netherlands
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  • Christoph Peters,

    1. Institut für Molekulare Medizin und Zellforschung, Albert-Ludwigs-Universität, Freiburg, Germany
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  • Thomas Reinheckel,

    1. Institut für Molekulare Medizin und Zellforschung, Albert-Ludwigs-Universität, Freiburg, Germany
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  • Paul Saftig,

    1. Biochemisches Institut, University of Kiel, Kiel, Germany
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  • Wouter Beertsen

    1. Department of Periodontology, ACTA, Universiteit van Amsterdam and Vrije Universiteit, Amsterdam, The Netherlands
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  • The authors state that they have no conflicts of interest.

Abstract

Osteoclastic bone degradation involves the activity of cathepsin K. We found that in addition to this enzyme other, yet unknown, cysteine proteinases participate in digestion. The results support the notion that osteoclasts from different bone sites use different enzymes to degrade the collagenous bone matrix.

Introduction: The osteoclast resorbs bone by lowering the pH in the resorption lacuna, which is followed by secretion of proteolytic enzymes. One of the enzymes taken to be essential in resorption is the cysteine proteinase, cathepsin K. Some immunolabeling and enzyme inhibitor data, however, suggest that other cysteine proteinases and/or proteolytic enzymes belonging to the group of matrix metalloproteinases (MMPs) may participate in the degradation. In this study, we investigated whether, in addition to cathepsin K, other enzymes participate in osteoclastic bone degradation.

Materials and Methods: In bones obtained from mice deficient for cathepsin K, B, or L or a combination of K and L, the bone-resorbing activity of osteoclasts was analyzed at the electron microscopic level. In addition, bone explants were cultured in the presence of different selective cysteine proteinase inhibitors and an MMP inhibitor, and the effect on resorption was assessed. Because previous studies showed differences in resorption by calvarial osteoclasts compared with those present in long bones, in all experiments, the two types of bone were compared. Finally, bone extracts were analyzed for the level of activity of cysteine proteinases and the effect of inhibitors hereupon.

Results: The analyses of the cathepsin-deficient bone explants showed that, in addition to cathepsin K, calvarial osteoclasts use other cysteine proteinases to degrade bone matrix. It was also shown that, in the absence of cathepsin K, long bone osteoclasts use MMPs for resorption. Cathepsin L proved to be involved in the MMP-mediated resorption of bone by calvarial osteoclasts; in the absence of this cathepsin, calvarial osteoclasts do not use MMPs for resorption. Selective inhibitors of cathepsin K and other cysteine proteinases showed a stronger effect on calvarial resorption than on long bone resorption.

Conclusions: Our findings suggest that (1) cathepsin K–deficient long bone osteoclasts compensate the lack of this enzyme by using MMPs in the resorption of bone matrix; (2) cathepsin L is involved in MMP-mediated resorption by calvarial osteoclasts; (3) in addition to cathepsin K, other, yet unknown, cysteine proteinases are likely to participate in skull bone degradation; and finally, (4) the data provide strong additional support for the existence of functionally different bone-site specific osteoclasts.

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