title: Rheumatoid arthritis antigens homocitrulline and citrulline are generated by local myeloperoxidase and peptidyl arginine deiminases 2, 3 and 4 in rheumatoid nodule and synovial tissue.
abstract: Seropositive rheumatoid arthritis (RA) is characterized by autoantibodies binding to citrullinated and homocitrullinated proteins. We wanted to study the expression patterns of these disease-associated protein forms and if the rheumatoid nodule and synovial tissue itself contain biologically active levels of citrullinating peptidyl arginine deiminases 2, 3 and 4 and homocitrullination-facilitating neutrophil enzyme myeloperoxidase.
  
  
  
  Total of 195 synovial samples from metatarsal joints from five ACPA/RF-positive RA patients (n = 77), synovial samples from knees of eight seropositive RA (n = 60), seven seronegative RA (n = 33) and five osteoarthritis (n = 25) patients were analyzed for citrulline and homocitrulline contents using HPLC. The location of citrulline- and homocitrulline-containing proteins, PAD 2, 3, 4 and myeloperoxidase were shown by immunostaining. Myeloperoxidase and citrulline- or homocitrulline-containing proteins were stained on Western blot.
  
  
  
  Overall, necrosis was frequent in metatarsals of seropositive RA and absent in seronegative RA and osteoarthritis patients. In histological analysis, there was a significant local patterning and variation in the citrulline and homocitrulline content and it was highest in metatarsal synovial tissues of seropositive RA patients. We found peptidyl arginine deiminase 2, 3 and 4 in the lining and sublining layers of intact synovial tissue. Myeloperoxidase was found locally around necrotic areas. The tissues with necrosis contained the highest levels of citrulline and homocitrulline.
  
  
  
  Rheumatoid nodules and synovia contain significant amount of PAD2, 3 and 4 and myeloperoxidase enzymes. These enzymes could explain the levels of citrulline and homocitrulline in seropositive RA synovial and rheumatoid nodule tissues especially around necrotic tissue.
authors.affiliation: Department of Anatomy and Cell Biology, Cancer and Translational Medicine Research Unit, University of Oulu, P.O. Box 5000, 90014, Oulu, Finland. sanna.turunen@oulu.fi.
authors.forename: Sanna
authors.identifier: 0000-0003-1526-5784
authors.initials: S
authors.lastname: Turunen
authors.affiliation: Department of Anatomy and Cell Biology, Cancer and Translational Medicine Research Unit, University of Oulu, P.O. Box 5000, 90014, Oulu, Finland.|Division of Rheumatology, Department of Internal Medicine, Oulu University Hospital, Oulu, Finland.
authors.forename: Johanna
authors.initials: J
authors.lastname: Huhtakangas
authors.affiliation: Division of Orthopedic Surgery, Oulu University Hospital, Oulu, Finland.
authors.forename: Tomi
authors.initials: T
authors.lastname: Nousiainen
authors.affiliation: Division of Orthopedic Surgery, Oulu University Hospital, Oulu, Finland.
authors.forename: Maarit
authors.initials: M
authors.lastname: Valkealahti
authors.affiliation: Department of Pathology, Cancer and Translational Medicine Research Unit, University of Oulu and Oulu University Hospital, Oulu, Finland.
authors.forename: Jukka
authors.initials: J
authors.lastname: Melkko
authors.affiliation: Department of Clinical Chemistry, Cancer and Translational Medicine Research Unit, University of Oulu, Oulu, Finland.|Northern Finland Laboratory Centre NordLab, Oulu University Hospital, Oulu, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Risteli
authors.affiliation: Department of Anatomy and Cell Biology, Cancer and Translational Medicine Research Unit, University of Oulu, P.O. Box 5000, 90014, Oulu, Finland.|Division of Orthopedic Surgery, Oulu University Hospital, Oulu, Finland.
authors.forename: Petri
authors.initials: P
authors.lastname: Lehenkari
mesh_terms: D000368:Aged; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000378:metabolism*; D001324:Autoantigens / Q000276:immunology* / Q000378:metabolism*; D015153:Blotting, Western; D002851:Chromatography, High Pressure Liquid; D002956:Citrulline / Q000031:analogs & derivatives / Q000276:immunology / Q000378:metabolism; D005260:Female; D006801:Humans; D006867:Hydrolases / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D009195:Peroxidase / Q000378:metabolism; D000080064:Protein-Arginine Deiminase Type 2; D000076342:Protein-Arginine Deiminases
chemical_list: D001324:Autoantigens; C001352:homocitrulline; D002956:Citrulline; D009195:Peroxidase; D006867:Hydrolases; C000620352:PADI2 protein, human; D000080064:Protein-Arginine Deiminase Type 2; D000076342:Protein-Arginine Deiminases
keywords: Citrulline; Homocitrulline; Myeloperoxidase; Necrosis; Peptidyl arginine deiminase; Rheumatoid arthritis; Synovial tissue