title: Peptidylarginine deiminase 2 is required for tumor necrosis factor alpha-induced citrullination and arthritis, but not neutrophil extracellular trap formation.
abstract: Citrullination, the post-translational conversion of arginines to citrullines, may contribute to rheumatoid arthritis development given the generation of anti-citrullinated protein antibodies (ACPAs). However, it is not known which peptidylarginine deiminase (PAD) catalyzes the citrullination seen in inflammation. PAD4 exacerbates inflammatory arthritis and is critical for neutrophil extracellular traps (NETs). NETs display citrullinated antigens targeted by ACPAs and thus may be a source of citrullinated protein. However, PAD4 is not required for citrullination in inflamed lungs. PAD2 is important for citrullination in healthy tissues and is present in NETs, but its role in citrullination in the inflamed joint, NETosis and inflammatory arthritis is unknown. Here we use mice with TNFα-induced inflammatory arthritis, a model of rheumatoid arthritis, to identify the roles of PAD2 and PAD4 in citrullination, NETosis, and arthritis. In mice with TNFα-induced arthritis, citrullination in the inflamed ankle was increased as determined by western blot. This increase was unchanged in the ankles of mice that lack PAD4. In contrast, citrullination was nearly absent in the ankles of PAD2-deficient mice. Interestingly, PAD2 was not required for NET formation as assessed by immunofluorescence or for killing of Candida albicans as determined by viability assay. Finally, plasma cell numbers as assessed by flow cytometry, IgG levels quantified by ELISA, and inflammatory arthritis as determined by clinical and pathological scoring were all reduced in the absence of PAD2. Thus, PAD2 contributes to TNFα-induced citrullination and arthritis, but is not required for NETosis. In contrast, PAD4, which is critical for NETosis, is dispensable for generalized citrullination supporting the possibility that NETs may not be a major source of citrullinated protein in arthritis.
authors.affiliation: Department of Medicine, University of Wisconsin, Madison, WI, USA.
authors.forename: Mandar
authors.initials: M
authors.lastname: Bawadekar
authors.affiliation: Department of Medicine, University of Wisconsin, Madison, WI, USA.
authors.forename: Daeun
authors.initials: D
authors.lastname: Shim
authors.affiliation: Department of Medicine, University of Wisconsin, Madison, WI, USA.
authors.forename: Chad J
authors.initials: CJ
authors.lastname: Johnson
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Wisconsin, Madison, WI, USA.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Warner
authors.affiliation: Department of Medicine, University of Wisconsin, Madison, WI, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Rebernick
authors.affiliation: Institute for Inflammation Research, Center for Rheumatology and Spine Diseases, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Dres
authors.initials: D
authors.lastname: Damgaard
authors.affiliation: Institute for Inflammation Research, Center for Rheumatology and Spine Diseases, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Claus H
authors.initials: CH
authors.lastname: Nielsen
authors.affiliation: Institute for Molecules and Materials and Radboud Institute for Molecular Life Sciences, Radboud University, Nijmegen, The Netherlands.
authors.forename: Ger J M
authors.initials: GJM
authors.lastname: Pruijn
authors.affiliation: Department of Medicine, University of Wisconsin, Madison, WI, USA; Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Jeniel E
authors.initials: JE
authors.lastname: Nett
authors.affiliation: Department of Medicine, University of Wisconsin, Madison, WI, USA; William S. Middleton Memorial Veterans Hospital, Madison, WI, USA. Electronic address: mshelef@medicine.wisc.edu.
authors.forename: Miriam A
authors.initials: MA
authors.lastname: Shelef
mesh_terms: D000818:Animals; D000075422:Anti-Citrullinated Protein Antibodies / Q000378:metabolism; D001169:Arthritis, Experimental / Q000235:genetics / Q000276:immunology*; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D000076302:Citrullination; D065206:Extracellular Traps / Q000378:metabolism; D006801:Humans; D006867:Hydrolases / Q000235:genetics / Q000378:metabolism*; D007074:Immunoglobulin G / Q000378:metabolism; D007249:Inflammation / Q000276:immunology*; D007596:Joints / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010950:Plasma Cells / Q000502:physiology; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases / Q000235:genetics / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics
chemical_list: D000075422:Anti-Citrullinated Protein Antibodies; D007074:Immunoglobulin G; D014409:Tumor Necrosis Factor-alpha; D006867:Hydrolases; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases; C552151:peptidylarginine deiminase 4, mouse
keywords: Citrullination; Murine model; Neutrophil extracellular trap; Peptidylarginine deiminase; Rheumatoid arthritis; TNFα