The Bone Lining Cell: Its Role in Cleaning Howship's Lacunae and Initiating Bone Formation

Authors

  • V. Everts,

    Corresponding author
    1. Department of Cell Biology and Histology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
    2. Department of Periodontology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam, Amsterdam, The Netherlands
    • Department of Cell Biology and Histology Academic Medical Centre University of Amsterdam P.O. Box 22700 1100 DE Amsterdam, The Netherlands
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  • J. M. Delaissé,

    1. OsteoPro/Center for Clinical and Basic Research, Herlev/Ballerup, Denmark
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  • W. Korper,

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

    1. Department of Periodontology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam, Amsterdam, The Netherlands
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  • W. Tigchelaar-Gutter,

    1. Department of Cell Biology and Histology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
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  • P. Saftig,

    1. Department of Biochemistry, University of Goettingen, Goettingen, Germany
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  • W. Beertsen

    1. Department of Periodontology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam, Amsterdam, The Netherlands
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Abstract

In this study we investigated the role of bone lining cells in the coordination of bone resorption and formation. Ultrastructural analysis of mouse long bones and calvariae revealed that bone lining cells enwrap and subsequently digest collagen fibrils protruding from Howship's lacunae that are left by osteoclasts. By using selective proteinase inhibitors we show that this digestion depends on matrix metalloproteinases and, to some extent, on serine proteinases. Autoradiography revealed that after the bone lining cells have finished cleaning, they deposit a thin layer of a collagenous matrix along the Howship's lacuna, in close association with an osteopontin-rich cement line. Collagenous matrix deposition was detected only in completely cleaned pits. In bone from pycnodysostotic patients and cathepsin K-deficient mice, conditions in which osteoclastic bone matrix digestion is greatly inhibited, bone matrix leftovers proved to be degraded by bone lining cells, thus indicating that the bone lining cell “rescues” bone remodeling in these anomalies. We conclude that removal of bone collagen left by osteoclasts in Howship's lacunae is an obligatory step in the link between bone resorption and formation, and that bone lining cells and matrix metalloproteinases are essential in this process.

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