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Osteoclasts secrete osteopontin into resorption lacunae during bone resorption

Authors
  • Luukkonen, Jani
  • Hilli, Meeri
  • Nakamura, Miho
  • Ritamo, Ilja
  • Valmu, Leena
  • Kauppinen, Kyösti
  • Tuukkanen, Juha
  • Lehenkari, Petri
Type
Published Article
Journal
Histochemistry and Cell Biology
Publisher
Springer Berlin Heidelberg
Publication Date
Jan 14, 2019
Volume
151
Issue
6
Pages
475–487
Identifiers
DOI: 10.1007/s00418-019-01770-y
Source
Springer Nature
Keywords
License
Green

Abstract

Osteopontin (OPN) is a non-collagenous extracellular sialylated glycoprotein located in bone. It is believed to be one of the key components in osteoclast attachment to bone during resorption. In this study, we characterized OPN and other glycoproteins found in the resorption lacunae to confirm the role of osteoclasts in OPN secretion using electron microscopy and mass spectrometry. Additionally, we examined the glycan epitopes of resorption pits and the effects of different glycan epitopes on the differentiation and function of osteoclasts. Osteoarthritic femoral heads were examined by immunohistochemistry to reveal the presence of OPN in areas of increased bone metabolism in vivo. Our results demonstrate that human osteoclasts secrete OPN into resorption lacunae on native human bone and on carbonated hydroxyapatite devoid of natural OPN. OPN is associated with an elevated bone turnover in osteoarthritic bone under experimental conditions. Our data further confirm that osteoclasts secrete OPN into the resorption pit where it may function as a chemokine for subsequent bone formation. We show that α2,3- and α2,6-linked sialic acids have a role in the process of osteoclast differentiation. OPN is one of the proteins that has both of the above sialic residues, hence we propose that de-sialylation can effect osteoclast differentiation in bone.

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