title: The immunoreceptor tyrosine-based activation motif (ITAM) -related factors are increased in synovial tissue and vasculature of rheumatoid arthritic joints.
abstract: BACKGROUND
  The immunoreceptor tyrosine-based activation motif (ITAM) pathway provides osteoclast co-stimulatory signals and regulates proliferation, survival and differentiation of effector immune cells. In the osteoclast, the receptors Triggering Receptor Expressed on Myeloid cells 2 (TREM2) and Osteoclast Associated Receptor (OSCAR) and their respective adaptor proteins, DAP12 and FcRγ mediate ITAM signals and induce calcium signaling and the crucial transcription factor, NFATc1. In rheumatoid arthritis (RA), OSCAR expression by monocytes is inversely correlated with disease activity. Additionally, serum levels of OSCAR are reduced in RA patients versus healthy controls suggesting that expression and secretion or cleavage of soluble (s) OSCAR is immune modulated. Recent data suggest that endothelial cells may also be a source of OSCAR.
  
  
  METHODS
  ITAM receptors, their adaptor proteins, and NFATc1 and cathepsin K were detected in human synovial tissues by immunohistochemistry. Synovial tissues from patients with active RA were compared with tissue from patients in remission, osteoarthritis (OA) patients and healthy individuals. OSCAR was measured by immunoassay in synovial fluids recovered from active RA and OA patients. Endothelial cells were cultured with or without 5 ng/mL TNF-α or IL-1β over 72 hours. Temporal expression of OSCAR mRNA was assessed by qRT PCR and OSCAR protein in the supernatant was measured by ELISA.
  
  
  RESULTS
  Significantly higher (P < 0.05) NFATc1-positive inflammatory cell aggregates were found in active RA tissues than in healthy synovial tissue. Similarly, the percentage of OSCAR, FcRγ, DAP12 and TREM2 positive cells was significantly higher in active RA tissues compared to the healthy synovial tissue. Notably, OSCAR was strongly expressed in the microvasculature of the active RA tissues (9/9), inactive RA (8/9) weakly in OA (4/9) but only in the lumen of healthy synovial tissue (0/8). OSCAR levels were detected in synovial fluids from both RA (47 to 152 ng/mL) and OA (112 to 145 ng/mL) patients. Moreover, OSCAR mRNA expression and soluble OSCAR release was stimulated by TNF-α and IL1-β in cultured endothelial cells.
  
  
  CONCLUSIONS
  Increased levels of ITAM related factors were present in synovial tissue from active RA joints compared to OA and healthy joints. OSCAR was strongly expressed by the vasculature of active RA patients and membrane bound and soluble OSCAR was stimulated by inflammatory mediators in endothelial cells in vitro.
authors.forename: Tania N
authors.initials: TN
authors.lastname: Crotti
authors.forename: Anak A S S K
authors.initials: AA
authors.lastname: Dharmapatni
authors.forename: Ekram
authors.initials: E
authors.lastname: Alias
authors.forename: Andrew C W
authors.initials: AC
authors.lastname: Zannettino
authors.forename: Malcolm D
authors.initials: MD
authors.lastname: Smith
authors.forename: David R
authors.initials: DR
authors.lastname: Haynes
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018501:Antirheumatic Agents / Q000627:therapeutic use; D001172:Arthritis, Rheumatoid / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D053583:Interleukin-1beta / Q000494:pharmacology; D007596:Joints / Q000098:blood supply / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008875:Middle Aged; D050778:NFATC Transcription Factors / Q000235:genetics / Q000378:metabolism; D053244:Osteoprotegerin / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D011961:Receptors, Fc / Q000235:genetics / Q000378:metabolism; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013583:Synovial Membrane / Q000098:blood supply / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018501:Antirheumatic Agents; D053583:Interleukin-1beta; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D050778:NFATC Transcription Factors; C494003:NFATC1 protein, human; C512828:OSCAR protein, human; D053244:Osteoprotegerin; D011956:Receptors, Cell Surface; D011961:Receptors, Fc; D011971:Receptors, Immunologic; C498715:TREM2 protein, human; C110546:TYROBP protein, human; D014409:Tumor Necrosis Factor-alpha