title: Potential protein targets of the peptidylarginine deiminase 2 and peptidylarginine deiminase 4 enzymes in rheumatoid synovial tissue and its possible meaning.
abstract: OBJECTIVE
  The molecular mechanism of citrullination involves the calcium-dependent peptidylarginine deiminase (PAD) family of enzymes. These enzymes induce a stereochemical modification of normal proteins and transform them into autoantigens, which in rheumatoid arthritis trigger a complex cascade of joint inflammatory events followed by chronic synovitis, pannus formation, and finally, cartilage destruction. By hypothesizing that PAD2 and PAD4 enzymes produce autoantigens, we investigated five possible synovial protein targets of PAD enzymes.
  
  
  METHODS
  We measured PAD2, PAD4, and citrullinated proteins in 10 rheumatoid and 10 osteoarthritis synovial biopsies and then assessed the post-translational modifications of fibrinogen, cytokeratin, tubulin, IgG, and vimentin proteins using a double-fluorescence assay with specific antibodies and an affinity-purified anti-citrullinated peptide (CCP) antibody. The degree of co-localization was analyzed, and statistical significance was determined by ANOVA, Fisher's exact test, and regression analysis.
  
  
  RESULTS
  The principal results of this study demonstrated that citrullinated proteins, such as fibrinogen, IgG, and other probed proteins, were targets of PAD2 and PAD4 activity in rheumatoid synovial biopsies, whereas osteoarthritis biopsies were negative for this enzyme (p<0.0001). An analysis of citrullination sites using the UniProtKB/Swiss-Prot data bank predicts that the secondary structure of the analyzed proteins displays most of the sites for citrullination; a discussion regarding its possible meaning in terms of pathogenesis is made.
  
  
  CONCLUSIONS
  Our results support the conclusion that the synovial citrullination of proteins is PAD2 and PAD4 dependent. Furthermore, there is a collection of candidate proteins that can be citrullinated.
authors.affiliation: Department of Immunology, Unidad Académica de Ciencias Biológicas, Universidad Autónoma de Zacatecas, Zacatecas, México.
authors.forename: Martha Adriana
authors.initials: MA
authors.lastname: Badillo-Soto
authors.affiliation: Department of Immunology, Unidad Académica de Ciencias Biológicas, Universidad Autónoma de Zacatecas, Zacatecas, México.
authors.forename: Mayra
authors.initials: M
authors.lastname: Rodríguez-Rodríguez
authors.affiliation: Department of Immunology, Unidad Académica de Ciencias Biológicas, Universidad Autónoma de Zacatecas, Zacatecas, México.
authors.forename: María Elena
authors.initials: ME
authors.lastname: Pérez-Pérez
authors.affiliation: Unidad Médica de Alta Especialidad (UMAE) T1, Instituto Mexicano del Seguro Social (IMSS), León, Guanajuato, México.
authors.forename: Leonel
authors.initials: L
authors.lastname: Daza-Benitez
authors.affiliation: Department of Immunology, Unidad Académica de Ciencias Biológicas, Universidad Autónoma de Zacatecas, Zacatecas, México.
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Bollain-Y-Goytia
authors.affiliation: Servicio de Traumatología y Ortopedia, HGZMF del IMSS, Zacatecas, México.
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Carrillo-Jiménez
authors.affiliation: Department of Immunology, Unidad Académica de Ciencias Biológicas, Universidad Autónoma de Zacatecas, Zacatecas, México.
authors.forename: Esperanza
authors.initials: E
authors.lastname: Avalos-Díaz
authors.affiliation: Department of Immunology, Unidad Académica de Ciencias Biológicas, Universidad Autónoma de Zacatecas, Zacatecas, México.
authors.forename: Rafael
authors.initials: R
authors.lastname: Herrera-Esparza
keywords: Peptidylarginine deiminase 2; peptidylarginine deiminase 4; rheumatoid arthritis; synovial membrane