University of Oulu

Luukkonen J, Pascual LM, Patlaka C, Lång P, Turunen S, Halleen J, et al. (2017) Increased amount of phosphorylated proinflammatory osteopontin in rheumatoid arthritis synovia is associated to decreased tartrate-resistant acid phosphatase 5B/5A ratio. PLoS ONE 12(8): e0182904. https://doi.org/10.1371/journal.pone.0182904

Increased amount of phosphorylated proinflammatory osteopontin in rheumatoid arthritis synovia is associated to decreased tartrate-resistant acid phosphatase 5B/5A ratio

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Author: Luukkonen, Jani1; Mira Pascual, Laia2; Patlaka, Christina2;
Organizations: 1Department of Anatomy, Medical Research Center Oulu, University of Oulu, Oulu, Finland
2Department of Laboratory Medicine, Division of Pathology, Karolinska Institutet, Stockholm, Sweden
3Pharmatest Services Ltd., Itäinen Pitkäkatu 4, FI, Turku, Finland
4Department of Surgery, University of Oulu Hospital, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 9 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2017101150051
Language: English
Published: Public Library of Science, 2017
Publish Date: 2017-10-11
Description:

Abstract

Background: Osteopontin (OPN) is an immunoregulatory protein which production increases in both rheumatoid arthritis (RA) and osteoarthritis (OA). Phosphorylated osteopontin (Phospho-OPN) is known to increase macrophage and osteoclast activation, this process is controlled by extracellular tartrate-resistant acid phosphatase (TRAcP), also a biomarker for RA. Here, we evaluated the phosphorylation status of OPN in RA and OA synovia, as well as its correlation with TRAcP isoforms.

Methods: Synovial tissue and fluid were obtained from 24 RA (14 seropositive and 10 seronegative) and 24 OA patients. Western blotting was used to analyze the extent of OPN phosphorylation. TRAcP isoforms were measured in synovial fluid using ELISA; immunohistochemistry assessed the distribution of OPN and TRAcP expressing cells in the synovial tissue, especially distinguishing between the TRAcP isoforms.

Results: Full-length OPN was more phosphorylated in RA than in OA (p<0.05). The thrombin cleaved C-terminal end of OPN was also more phosphorylated in RA (p<0.05). RA patients had a lower concentration of TRAcP 5B and higher concentration of less active 5A in their synovial fluid compared to OA patients. The TRAcP 5B/5A ratio was decreased in RA and correlated negatively with the amount of phospho-OPN (p<0.05). TRAcP positive cells for both isoforms were found all along the synovial lining; OPN antibody staining was localized in the extracellular matrix.

Conclusions: Our data suggests that in RA the synovial fluid contains insufficient amounts of TRAcP 5B which increase levels of the proinflammatory phospho-OPN. This may lead to increased macrophage and osteoclast activation, resulting in the increased local inflammation and bone resorption present in RA joints.

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Series: PLoS ONE
ISSN: 1932-6203
ISSN-E: 1932-6203
ISSN-L: 1932-6203
Volume: 12
Issue: 8
Article number: e0182904
DOI: 10.1371/journal.pone.0182904
OADOI: https://oadoi.org/10.1371/journal.pone.0182904
Type of Publication: A1 Journal article – refereed
Field of Science: 3111 Biomedicine
Subjects:
Copyright information: © 2017 Luukkonen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
  https://creativecommons.org/licenses/by/4.0/