title: Stimulation of fibrotic processes by the infrapatellar fat pad in cultured synoviocytes from patients with osteoarthritis: a possible role for prostaglandin f2α.
abstract: OBJECTIVE
  Stiffening of the joint is a feature of knee osteoarthritis (OA) that can be caused by fibrosis of the synovium. The infrapatellar fat pad (IPFP) present in the knee joint produces immune-modulatory and angiogenic factors. The goal of the present study was to investigate whether the IPFP can influence fibrotic processes in synovial fibroblasts, and to determine the role of transforming growth factor β (TGFβ) and prostaglandin F2α (PGF2α ) in these processes.
  
  
  METHODS
  Batches of fat-conditioned medium (FCM) were made by culturing pieces of IPFP obtained from the knees of 13 patients with OA. Human OA fibroblast-like synoviocytes (FLS) (from passage 3) were cultured in FCM with or without inhibitors of TGFβ/activin receptor-like kinase 5 or PGF2α for 4 days. The FLS were analyzed for production of collagen and expression of the gene for procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2; encoding lysyl hydroxylase 2b, an enzyme involved in collagen crosslinking) as well as the genes encoding α-smooth muscle actin and type I collagen α1 chain. In parallel, proliferation and migration of the synoviocytes were analyzed.
  
  
  RESULTS
  Collagen production and PLOD2 gene expression by the FLS were increased 1.8-fold (P < 0.05) and 6.0-fold (P < 0.01), respectively, in the presence of FCM, relative to control cultures without FCM. Moreover, the migration and proliferation of synoviocytes were stimulated by FCM. Collagen production was positively associated with PGF2α levels in the FCM (R = 0.89, P < 0.05), and inhibition of PGF2α levels reduced the extent of FCM-induced collagen production and PLOD2 expression. Inhibition of TGFβ signaling had no effect on the profibrotic changes.
  
  
  CONCLUSIONS
  These results indicate that the IPFP can contribute to the development of synovial fibrosis in the knee joint by increasing collagen production, PLOD2 expression, cell proliferation, and cell migration. In addition, whereas the findings showed that TGFβ is not involved, the more recently discovered profibrotic factor PGF2α appears to be partially involved in the regulation of profibrotic changes.
authors.affiliation: Erasmus MC University Medical Center, Rotterdam, The Netherlands. y.bastiaansen@erasmusmc.nl
authors.forename: Yvonne M
authors.initials: YM
authors.lastname: Bastiaansen-Jenniskens
authors.forename: Wu
authors.initials: W
authors.lastname: Wei
authors.forename: Carola
authors.initials: C
authors.lastname: Feijt
authors.forename: Jan H
authors.initials: JH
authors.lastname: Waarsing
authors.forename: Jan A N
authors.initials: JA
authors.lastname: Verhaar
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Zuurmond
authors.forename: Roeland
authors.initials: R
authors.lastname: Hanemaaijer
authors.forename: Reinout
authors.initials: R
authors.lastname: Stoop
authors.forename: Gerjo J V M
authors.initials: GJ
authors.lastname: van Osch
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism / Q000473:pathology*; D000368:Aged; D000369:Aged, 80 and over; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000494:pharmacology; D015237:Dinoprost / Q000378:metabolism*; D005260:Female; D005355:Fibrosis; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000378:metabolism / Q000473:pathology*; D010329:Patella; D008240:Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase / Q000235:genetics / Q000378:metabolism; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D016212:Transforming Growth Factor beta / Q000378:metabolism
chemical_list: D017077:Culture Media, Conditioned; D016212:Transforming Growth Factor beta; D003094:Collagen; D015237:Dinoprost; C479138:PLOD2 protein, human; D008240:Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase