title: Comparison of cathepsins K and S expression within the rheumatoid and osteoarthritic synovium.
abstract: OBJECTIVE
  To determine and compare the expression of cathepsins K and S proteins in joints with rheumatoid arthritis (RA) and osteoarthritis (OA) and to determine the effect of interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) on the expression of cathepsin K in fibroblast-like synoviocytes.
  
  
  METHODS
  Expression and localization of cathepsins K and S were determined by immunohistochemistry in the synovium of 10 RA- and 8 OA-affected joints. Northern and Western blot analyses were performed to analyze cathepsin K and S expression in primary fibroblast-like synoviocyte cultures from RA and OA patients. The effect of IL-1 beta and TNF alpha on the expression and secretion of cathepsin K in primary cultures of synoviocytes was determined by real-time polymerase chain reaction and Western blot analysis. Staining of in situ activity was used to identify active cathepsin K enzyme in primary synovial fibroblast cultures.
  
  
  RESULTS
  Cathepsin K and S protein expression was identified in the synovium from patients with RA and OA. Cathepsin K protein was localized in synovial fibroblasts, stromal multinucleated giant cells, and, to a lesser degree, in CD68+ macrophage-like synoviocytes. Of note is the expression of cathepsin K in synovial fibroblasts and mononuclear macrophage-like cells at sites of cartilage erosion in RA and in interdigitating cells of lymphocyte-rich areas. In contrast, cathepsin S expression was restricted to CD68+ macrophage-like synoviocytes, interdigitating cells, and endothelial cells of blood vessels. Cathepsin K protein expression in the interstitial areas and perivascular regions of RA-derived synovial specimens was 2-5 times higher than in OA samples (P < 0.001), whereas the expression of cathepsin S did not significantly differ in these diseases. Cathepsin K expression levels in normal synovium were low and restricted to fibroblast-like cells. Of note, cathepsin K also was expressed in repairing fibrocartilage in 1 OA specimen. Primary cell cultures of RA- and OA-derived synovial fibroblasts expressed comparable amounts of cathepsin K at the transcript and protein levels. Both cell cultures secreted mature cathepsin K as well as procathepsin K, and expressed active cathepsin K in cytosolic vesicles. In contrast, neither RA- nor OA-derived fibroblasts expressed detectable levels of cathepsin S. IL-1 beta and TNF alpha stimulated the transcript (7-8-fold) and protein expression (2-fold) of cathepsin K (P < 0.05) in primary synovial fibroblast cultures, without differences in expression between RA- and OA-derived synovial fibroblasts.
  
  
  CONCLUSIONS
  The presence of cathepsin K polypeptide in synovial fibroblasts and macrophage-like cells in normal, OA, and RA synovia suggests a constitutive expression of this protease and a role in synovial remodeling. The comparable increase in cathepsin K expression after stimulation of RA- and OA-derived synovial fibroblasts with IL-1 beta and TNF alpha further suggests that the expression of cathepsin K is independent of cellular alterations leading to the invasive phenotype of RA-synovial fibroblasts. However, the overexpression of cathepsin K in RA synovia due to an increase in the number of cathepsin K-expressing cells identifies this enzyme as a candidate protease for the pathologic degradation of articular cartilage. Cathepsin S expression in macrophage-like synoviocytes suggests dual activity in antigen presentation and matrix degradation in the inflamed synovia.
authors.affiliation: Mount Sinai School of Medicine, New York, New York 10029, USA.
authors.forename: Wu-Shiun
authors.initials: WS
authors.lastname: Hou
authors.forename: Weijie
authors.initials: W
authors.lastname: Li
authors.forename: Gernot
authors.initials: G
authors.lastname: Keyszer
authors.forename: Ekkehard
authors.initials: E
authors.lastname: Weber
authors.forename: Roger
authors.initials: R
authors.lastname: Levy
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Klein
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Gravallese
authors.forename: Steven R
authors.initials: SR
authors.lastname: Goldring
authors.forename: Dieter
authors.initials: D
authors.lastname: Brömme
mesh_terms: D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D056657:Cathepsin K; D002403:Cathepsins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D010450:Endopeptidases / Q000378:metabolism; D005260:Female; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D007596:Joints / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000378:metabolism; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D007375:Interleukin-1; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D002403:Cathepsins; D010450:Endopeptidases; C028217:cathepsin S; C534130:CTSK protein, human; D056657:Cathepsin K