Peptidyl arginine deiminase type 2 (PAD-2) and PAD-4 but not PAD-1, PAD-3, and PAD-6 are expressed in rheumatoid arthritis synovium in close association with tissue inflammation

Authors

  • Céline Foulquier,

    1. Unité Mixte de Recherche 5165, CNR–Université Toulouse III, Institut Fédératif de Recherche 30 (IFR30), Toulouse, France
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  • Mireille Sebbag,

    1. Unité Mixte de Recherche 5165, CNR–Université Toulouse III, Institut Fédératif de Recherche 30 (IFR30), Toulouse, France
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  • Cyril Clavel,

    1. Unité Mixte de Recherche 5165 CNRS–Université Toulouse III and Laboratory of Cell Biology and Cytology, Institut Fédératif de Biologie, CHU de Toulouse, IFR30, Toulouse, France
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  • Sabine Chapuy-Regaud,

    1. Unité Mixte de Recherche 5165, CNR–Université Toulouse III, Institut Fédératif de Recherche 30 (IFR30), Toulouse, France
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  • Roula Al Badine,

    1. Unité Mixte de Recherche 5165, CNR–Université Toulouse III, Institut Fédératif de Recherche 30 (IFR30), Toulouse, France
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  • Marie-Claire Méchin,

    1. Unité Mixte de Recherche 5165, CNR–Université Toulouse III, Institut Fédératif de Recherche 30 (IFR30), Toulouse, France
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  • Christian Vincent,

    1. Laboratory of Cell Biology and Cytology, Institut Fédératif de Biologie, CHU de Toulouse, IFR30, Toulouse, France
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  • Rachida Nachat,

    1. Unité Mixte de Recherche 5165, CNR–Université Toulouse III, Institut Fédératif de Recherche 30 (IFR30), Toulouse, France
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  • Michiyuki Yamada,

    1. Yokohama City University, Yokohama, Japan
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  • Hidenari Takahara,

    1. Ibaraki University, Ibaraki, Japan
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  • Michel Simon,

    1. Unité Mixte de Recherche 5165, CNR–Université Toulouse III, Institut Fédératif de Recherche 30 (IFR30), Toulouse, France
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  • Marina Guerrin,

    1. Unité Mixte de Recherche 5165 CNRS–Université Toulouse III and Laboratory of Cell Biology and Cytology, Institut Fédératif de Biologie, CHU de Toulouse, IFR30, Toulouse, France
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  • Guy Serre

    Corresponding author
    1. Unité Mixte de Recherche 5165 CNRS–Université Toulouse III and Laboratory of Cell Biology and Cytology, Institut Fédératif de Biologie, CHU de Toulouse, IFR30, Toulouse, France
    • Unité “Différenciation Épidermique et Auto-immunité Rhumatoïde,” UMR 5165 CNRS-Université Paul Sabatier, Hôpital Purpan, Place du Dr Baylac, TSA 400 31, 31059 Toulouse Cedex 9, France
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Abstract

Objective

Autoantibodies to citrullinated proteins (ACPAs) are specific for rheumatoid arthritis (RA) and probably are involved in its pathophysiology. Citrullyl residues, posttranslationally generated by peptidyl arginine deiminase (PAD), are indispensable components of ACPA-targeted epitopes. The aim of this study was to identify which PAD isotypes are expressed in the synovial tissue (ST) of patients with RA and are involved in the citrullination of fibrin, the major synovial target of ACPAs.

Methods

Expression of all PAD isotypes, including the recently described PAD type 6 (PAD-6), was explored by reverse transcription–polymerase chain reaction and immunoblotting, first in blood-derived mononuclear leukocytes from healthy donors, then in ST samples from 16 patients with RA and 11 control patients (4 with other arthritides and 7 with osteoarthritis [OA]). In ST samples from patients with RA, PADs were localized by immunohistochemistry.

Results

In lymphocytic and monocytic cells and, similarly, in ST samples from patients with RA, the PAD-2, PAD-4, and PAD-6 genes were found to be transcribed, but only PAD-2 and PAD-4 enzymes were detected. PAD-2 was also expressed in ST from control patients, including those with OA, while PAD-4 was preferentially expressed in ST from patients with other arthritides. In RA, the expression levels of PAD-2 and PAD-4 were correlated with the intensity of inflammation (cell infiltration, hypervascularization, and synovial lining hyperplasia), and both enzymes were demonstrable within or in the vicinity of citrullinated fibrin deposits.

Conclusion

PAD-2 and PAD-4 are the only PAD isotypes expressed in the ST of patients with RA and those with other arthritides. Inflammatory cells are a major source, but PAD-4 also comes from hyperplastic synoviocytes. Both isotypes are probably involved in the citrullination of fibrin.

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