title: Co-culture with infrapatellar fat pad differentially stimulates proteoglycan synthesis and accumulation in cartilage and meniscus tissues.
abstract: OBJECTIVE
  Although osteoarthritis is widely viewed as a disease of the whole joint, relatively few studies have focused on interactions among joint tissues in joint homeostasis and degeneration. In particular, few studies have examined the effects of the infrapatellar fat pad (IFP) on cartilaginous tissues. The aim of this study was to test the hypothesis that co-culture with healthy IFP would induce degradation of cartilage and meniscus tissues.
  
  
  METHODS
  Bovine articular cartilage, meniscus, and IFP were cultured isolated or as cartilage-fat or meniscus-fat co-cultures for up to 14 days. Conditioned media were assayed for sulfated glycosaminoglycan (sGAG) content, nitrite content, and matrix metalloproteinase (MMP) activity, and explants were assayed for sGAG and DNA contents.
  
  
  RESULTS
  Co-cultures exhibited increased cumulative sGAG release and sGAG release rates for both cartilage and meniscus, and the cartilage (but not meniscus) exhibited a substantial synergistic effect of co-culture (sGAG release in co-culture was significantly greater than the summed release from isolated cartilage and fat). Fat co-culture did not significantly alter the sGAG content of either cartilage or meniscus explants, indicating that IFP co-culture stimulated net sGAG production by cartilage. Nitrite release was increased relative to isolated tissue controls in co-cultured meniscus, but not the cartilage, with no synergistic effect of co-culture. Interestingly, MMP-2 production was decreased by co-culture for both cartilage and meniscus.
  
  
  CONCLUSIONS
  This study demonstrates that healthy IFP may modulate joint homeostasis by stimulating sGAG production in cartilage. Counter to our hypothesis, healthy IFP did not promote degradation of either cartilage or meniscus tissues.
authors.affiliation: a Department of Mechanical Engineering , Stanford University , Stanford , CA , USA.
authors.forename: James F
authors.initials: JF
authors.lastname: Nishimuta
authors.affiliation: b Department of Electrical Engineering , Stanford University , Stanford , CA , USA.
authors.forename: Monica F
authors.initials: MF
authors.lastname: Bendernagel
authors.affiliation: a Department of Mechanical Engineering , Stanford University , Stanford , CA , USA.
authors.forename: Marc E
authors.initials: ME
authors.lastname: Levenston
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D002417:Cattle; D018920:Coculture Techniques; D000072600:Meniscus / Q000378:metabolism* / Q000473:pathology; D020370:Osteoarthritis, Knee / Q000378:metabolism* / Q000473:pathology; D011509:Proteoglycans / Q000096:biosynthesis*
chemical_list: D011509:Proteoglycans
keywords: Cartilage; co-culture; fat; infrapatellar fat pad; meniscus