title: Upregulation of immunoproteasome subunits in myositis indicates active inflammation with involvement of antigen presenting cells, CD8 T-cells and IFNΓ.
abstract: OBJECTIVE
  In idiopathic inflammatory myopathies (IIM) infiltration of immune cells into muscle and upregulation of MHC-I expression implies increased antigen presentation and involvement of the proteasome system. To decipher the role of immunoproteasomes in myositis, we investigated individual cell types and muscle tissues and focused on possible immune triggers.
  
  
  METHODS
  Expression of constitutive (PSMB5, -6, -7) and corresponding immunoproteasomal subunits (PSMB8, -9, -10) was analyzed by real-time RT-PCR in muscle biopsies and sorted peripheral blood cells of patients with IIM, non-inflammatory myopathies (NIM) and healthy donors (HD). Protein analysis in muscle biopsies was performed by western blot. Affymetrix HG-U133 platform derived transcriptome data from biopsies of different muscle diseases and from immune cell types as well as monocyte stimulation experiments were used for validation, coregulation and coexpression analyses.
  
  
  RESULTS
  Real-time RT-PCR revealed significantly increased expression of immunoproteasomal subunits (PSMB8/-9/-10) in DC, monocytes and CD8+ T-cells in IIM. In muscle biopsies, the immunosubunits were elevated in IIM compared to NIM and exceeded levels of matched blood samples. Proteins of PSMB8 and -9 were found only in IIM but not NIM muscle biopsies. Reanalysis of 78 myositis and 20 healthy muscle transcriptomes confirmed these results and revealed involvement of the antigen processing and presentation pathway. Comparison with reference profiles of sorted immune cells and healthy muscle confirmed upregulation of PSMB8 and -9 in myositis biopsies beyond infiltration related changes. This upregulation correlated highest with STAT1, IRF1 and IFNγ expression. Elevation of T-cell specific transcripts in active IIM muscles was accompanied by increased expression of DC and monocyte marker genes and thus reflects the cell type specific involvement observed in peripheral blood.
  
  
  CONCLUSIONS
  Immunoproteasomes seem to indicate IIM activity and suggest that dominant involvement of antigen processing and presentation may qualify these diseases exemplarily for the evolving therapeutic concepts of immunoproteasome specific inhibition.
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Khetam
authors.initials: K
authors.lastname: Ghannam
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Lorena
authors.initials: L
authors.lastname: Martinez-Gamboa
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Lydia
authors.initials: L
authors.lastname: Spengler
authors.affiliation: Friedrich Baur Institute, Ludwig Maximilians University, Munich, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Krause
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Biljana
authors.initials: B
authors.lastname: Smiljanovic
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Bonin
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Salyan
authors.initials: S
authors.lastname: Bhattarai
authors.affiliation: German Arthritis Research Center, Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Grützkau
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Gerd-R
authors.initials: GR
authors.lastname: Burmester
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Häupl
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Eugen
authors.initials: E
authors.lastname: Feist
mesh_terms: D000328:Adult; D000368:Aged; D018414:CD8-Positive T-Lymphocytes / Q000201:enzymology / Q000276:immunology* / Q000473:pathology; D003713:Dendritic Cells / Q000201:enzymology / Q000276:immunology* / Q000473:pathology; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000276:immunology*; D006801:Humans; D050856:Interferon Regulatory Factor-1 / Q000276:immunology / Q000378:metabolism; D007371:Interferon-gamma / Q000096:biosynthesis / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000096:biosynthesis / Q000276:immunology; D009220:Myositis / Q000201:enzymology / Q000276:immunology* / Q000473:pathology; D046988:Proteasome Endopeptidase Complex / Q000096:biosynthesis / Q000276:immunology*; D050794:STAT1 Transcription Factor / Q000276:immunology / Q000378:metabolism; D015854:Up-Regulation / Q000276:immunology
chemical_list: C573415:IFNG protein, human; C494257:IRF1 protein, human; D050856:Interferon Regulatory Factor-1; D009124:Muscle Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D007371:Interferon-gamma; D046988:Proteasome Endopeptidase Complex
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