title: Human knee and ankle cartilage explants: catabolic differences.
abstract: The prevalence of osteoarthritis (OA) is lower in some joints, i.e., the ankle, than in the knee. We have compared the cartilages from these two joints of the same limb in adult donors (matched pairs). Our data to date suggest that there are metabolic, biochemical and biomechanical differences between the cartilages of the two joints. The current study has focused on extending the metabolic studies comparing the response of chondrocytes to Interleukin-1beta (IL-1beta) and osteogenic protein 1 (OP-1) by analyzing changes in sulfate incorporation into glycosaminoglycans (GAGs) as a measure of proteoglycan (PG) synthesis. Human adult chondrocytes from normal knees (tibiofemoral) and ankles (talocrural) joints cultured as explants both responded to IL-1beta after 72 h by decreasing PG synthesis; however, the IC50 for the knee chondrocytes was 6.2 pg/ml, while that for the ankle was 35 pg/ml. When the explants were incubated for 72 h with IL-1beta and allowed to rebound without IL-1beta, synthesis of PG was significantly elevated by ankle chondrocytes within five days; knee chondrocytes were unable to significantly increase synthesis even after eight days. However, in both knee and ankle, application of OP-I enhanced PG synthesis in the rebound phase. In response to IL-1, an upregulation of proteinase activity was detectable by an increase in the neoepitopes proteolytically-generated by both aggrecanase and matrix metalloproteinases (MMPs), in the deep zone of the knee cartilage. Stromelysin and collagenase were upregulated as well. The data emerging from these studies confirm that the ankle is less responsive to catabolic stimulation and more responsive to anabolic stimulation following IL-1 removal. These differences in metabolic activity between the cartilages of the two joints could in part help to explain their differences in susceptibility to OA.
authors.affiliation: Department of Orthopaedic Surgery, Wichernhaus at Rummelsberg Hospital, Schwarzenbruck/Nürnberg, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Eger
authors.forename: Barbara L
authors.initials: BL
authors.lastname: Schumacher
authors.forename: Jürgen
authors.initials: J
authors.lastname: Mollenhauer
authors.forename: Klaus E
authors.initials: KE
authors.lastname: Kuettner
authors.forename: Ada A
authors.initials: AA
authors.lastname: Cole
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000378:metabolism*; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism; D046508:Culture Techniques; D010450:Endopeptidases / Q000096:biosynthesis; D006025:Glycosaminoglycans / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D006651:Histocytochemistry; D006801:Humans; D007150:Immunohistochemistry; D007375:Interleukin-1 / Q000494:pharmacology; D007719:Knee Joint / Q000378:metabolism*; D011509:Proteoglycans / Q000096:biosynthesis; D016212:Transforming Growth Factor beta
chemical_list: C525819:BMP7 protein, human; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D006025:Glycosaminoglycans; D007375:Interleukin-1; D011509:Proteoglycans; D016212:Transforming Growth Factor beta; D010450:Endopeptidases