ARTHRITIS & RHEUMATOLOGY Vol. 67, No. 12, December 2015, pp 3135–3145 DOI 10.1002/art.39313 VC 2015 The Authors. Arthritis & Rheumatolgy published by Wiley Periodicals, Inc. on behalf of the American College of Rheumatology. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Release of Active Peptidyl Arginine Deiminases by Neutrophils Can Explain Production of Extracellular Citrullinated Autoantigens in Rheumatoid Arthritis Synovial Fluid Julia Spengler,1 Bozo Lugonja,1 A. Jimmy Ytterberg,2 Roman A. Zubarev,3 Andrew J. Creese,4 Mark J. Pearson,1 Melissa M. Grant,4 Michael Milward,4 Karin Lundberg,2 Christopher D. Buckley,5 Andrew Filer,6 Karim Raza,5 Paul R. Cooper,4 Iain L. Chapple,4 and Dagmar Scheel-Toellner1 Objective. In the majority of patients with rheu- citrullinated autoantigens that are generated by peptidy- matoid arthritis (RA), antibodies specifically recognize larginine deiminases (PADs). Neutrophils express high levels of PAD and accumulate in the synovial fluid (SF) The views expressed in this publication are those of the of RA patients during disease flares. This study was authors and not necessarily those of the National Health Service, the National Institute for Health Research, or the Department of Health. undertaken to test the hypothesis that neutrophil cell Supported by the European Union Seventh Framework Pro- death, induced by either NETosis (extrusion of genomic gramme (project Gums and Joints; HEALTH-2010-261460 and project DNA–protein complexes known as neutrophil extracellu- EuroTEAM; HEALTH-F2-2012-305549) and by the NIHR Wellcome Trust Clinical Research Facility at University Hospitals Birmingham lar traps [NETs]) or necrosis, can contribute to produc- NHS Foundation Trust. Dr. Filer’s work was supported by an Arthritis tion of autoantigens in the inflamed joint. Research UK Clinician Scientist Award (18547). Dr. Scheel-Toellner’s Methods. Extracellular DNA was quantified in the work was supported by a Medical Research Council Confidence in Concepts grant (MC_PC_12011), a Medical Research Council Develop- SF of patients with RA, patients with osteoarthritis (OA), mental Pathway Funding Scheme grant (MR/M007669/1), and a Uni- and patients with psoriatic arthritis (PsA). Release of versity Hospital Birmingham Charities grant (17-3-690). The Arthritis PAD from neutrophils was investigated by Western blot- Research UK Rheumatoid Arthritis Pathogenesis Centre of Excellence (RACE) is funded in part by Arthritis Research UK (grant 20298). ting, mass spectrometry, immunofluorescence staining, 1Julia Spengler, Dipl Hum Biol, Bozo Lugonja, MSc, Mark J. and PAD activity assays. PAD2 and PAD4 protein expres- Pearson, PhD, Dagmar Scheel-Toellner, PhD: Arthritis Research UK sion, as well as PAD enzymatic activity, were assessed in Centre of Excellence for Rheumatoid Arthritis Pathogenesis and Uni- versity of Birmingham, Birmingham, UK; 2A. Jimmy Ytterberg, PhD, the SF of patients with RA and those with OA. Karin Lundberg, PhD: Karolinska University Hospital and Karolinska Results. Extracellular DNA was detected at sig- 3 Institutet, Stockholm, Sweden; Roman A. Zubarev, PhD: Karolinska nificantly higher levels in RA SF than in OA SF (P < Institutet, Stockholm, Sweden; 4Andrew J. Creese, PhD, Melissa M. Grant, PhD, Michael Milward, PhD, Paul R. Cooper, PhD, Iain L. Chapple, 0.001) or PsA SF (P < 0.05), and its expression levels PhD: University of Birmingham, Birmingham, UK; 5Christopher D. correlated with neutrophil concentrations and PAD Buckley, DPhil, Karim Raza, PhD: Arthritis Research UK Centre of activity in RA SF. Necrotic neutrophils released less Excellence for Rheumatoid Arthritis Pathogenesis, University of Birmingham, and Sandwell and West Birmingham Hospitals NHS soluble extracellular DNA compared to NETotic cells in Trust, Birmingham, UK; 6Andrew Filer, PhD: Arthritis Research UK vitro (P < 0.05). Higher PAD activity was detected in Centre of Excellence for Rheumatoid Arthritis Pathogenesis, Univer- sity of Birmingham, and University Hospitals NHS Foundation Trust, RA SF than in OA SF (P < 0.05). The citrullinated pro- Birmingham, UK. teins PAD2 and PAD4 were found attached to NETs and Address correspondence to Dagmar Scheel-Toellner, PhD, also freely diffused in the supernatant. PAD enzymatic Rheumatology Research Group, Arthritis Research UK Centre of Excellence for Rheumatoid Arthritis Pathogenesis, College of Medical activity was detected in supernatants of neutrophils un- and Dental Sciences, University of Birmingham Research Laborato- dergoing either NETosis or necrosis. ries, Queen Elizabeth Hospital, Birmingham B15 2WD, UK. E-mail: Conclusion. Release of active PAD isoforms into [email protected]. Submitted for publication January 26, 2015; accepted in the SF by neutrophil cell death is a plausible explanation revised form July 30, 2015. for the generation of extracellular autoantigens in RA. 3135 3136 SPENGLER ET AL The synovial cavity of patients with rheumatoid localization of PAD within the cells, the levels of PAD arthritis (RA) is infiltrated by large numbers of neutro- activity in SF from patients with different arthritides, and phils. Once activated, neutrophils augment disease devel- the levels of PAD activity in relation to evidence of neutro- opment and progression through the generation of phil infiltration and NETosis were examined. reactive oxygen species, proteolytic enzymes, and proin- flammatory cytokines (1). Several forms of neutrophil PATIENTS AND METHODS cell death have been described (2), such as apoptosis, necrosis, and a novel pathway involving extrusion of Patient selection and sample collection. RA patients fulfilled the American College of Rheumatology 1987 classifica- genomic DNA–protein complexes known as neutrophil tion criteria for RA (13). Osteoarthritis (OA) of the knee and extracellular traps (NETs), termed NETosis (3). This psoriatic arthritis (PsA) were diagnosed according to established complex process involves the active release of genomic criteria (14,15). SF samples were aspirated from the joints of all DNA into the extracellular space. The resulting network patients under manual palpation or ultrasound guidance. Synovi- of DNA and associated proteins (e.g., histones, myelo- al tissue was obtained by ultrasound-guided synovial biopsy (16). peroxidase, and neutrophil elastase), or NETs, is pre- Ethics approval was obtained and all participants gave their writ- sent in the joints of RA patients (4,5). NETosis involves ten informed consent. Details on the demographic and clinical characteristics of the patients are shown in Table 1. activation of peptidylarginine deiminase 4 (PAD4). The Reagents. For immunofluorescence staining, we used importance of this enzyme to NETosis is underlined by antibodies to neutrophil elastase (ab21595; Abcam), combined the observation that neutrophils in PAD4-deficient mice with an Alexa Fluor 647–conjugated goat anti-rabbit IgG anti- do not generate NETs upon stimulation (6). body (Jackson ImmunoResearch), and antibodies to PAD4 PAD4 belongs to a family of 5 PAD isoforms (ab128086; Abcam), combined with a streptavidin–Alexa Fluor whose enzymatic activity leads to deimination of argi- 488–conjugated (Jackson ImmunoResearch) goat anti-mouse IgG2a biotin antibody (Southern Biotech). Anti-human PAD2 nine side chains, resulting in protein citrullination. PAD antibodies (ab50257; Abcam) were revealed with an Alexa isoforms are highly homologous and functionally simi- Fluor 488–conjugated donkey anti-rabbit IgG antibody (Life lar, but differ in their expression pattern throughout Technologies). Antibodies to CD15 (clone MEM-158; Immu- various organ systems and cell types (7). Neutrophils notools) or to citrullinated histone H3 (ab5103; Abcam) were express PAD2, which is ubiquitously expressed, and combined with a donkey anti-mouse IgM antibody (Jackson PAD4, which is mainly expressed by myeloid cells (7). ImmunoResearch) or an Alexa Fluor 647–conjugated donkey Activation of PAD isoforms is relevant to RA, as spe- anti-rabbit IgG antibody (Jackson ImmunoResearch), respec- tively. All stainings included concentration-, species-, and cific autoimmunity to citrullinated proteins has been isotype-matched control antibodies. observed in ;60% of RA patients (8,9), and this charac- For Western blotting, antibodies specific for neutro- teristic defines a group of patients with more aggressive phil elastase (ab21595; Abcam), antibodies specific for PAD2 disease and distinct genetic associations. (ab50257; Abcam), and 2 monoclonal antibodies to PAD4 Anti–citrullinated protein antibodies (ACPAs) (H00023569-M01 from Novus Biologicals and ab128086 bind a diverse range of citrullinated proteins, and B cell from Abcam) were used. All 3 PAD isoform antibodies were tested to exclude cross-reactivity. Human recombinant PAD4 responses to these modified proteins have been observed was purchased from Cayman Chemical (item no. 10500). Sytox in the rheumatoid joint (10). It is not yet clear whether Green was purchased from Invitrogen. Other reagents used neutrophils in the synovial fluid (SF) contribute to the included DNase I (AM2235; Ambion, Applied Biosystems), pool of available extracellular PAD and whether PADs placental DNA (D4642; Sigma-Aldrich), and protease inhibi- are enzymatically active. In this context, it is also important tor cocktail (P8340; Sigma-Aldrich). Neutrophil isolation