Abstract 36

Biochemical aspects of degenerative cartilage in osteoarthritis

Y. Xiao², PhD, M.E. Forsythe ¹ FRCSC, R. Crawford^1,3 DPhil (Oxon)

¹The Department of Orthopaedic Surgery, The Prince Charles Hospital, Brisbane, Queensland, Australia

²TissueBioRegeneration and Integration, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia

³Medical Engineering Department, Queensland University of Technology, Brisbane, Queensland, Australia

The exact etiology and pathophysiology of osteoarthritis (OA) remains elusive, although it is characterized by degeneration of articular (hyaline) cartilage. A primary role for subchondral bone in the etiopathogenesis has been proposed with possible communication between the subchondral bone and deep cartilage. The purpose of our study was to analyze molecular changes during the progression in cartilage degeneration and to reveal the molecular alterations to histological changes. Five patients with radiographic Grade IV osteoarthritis of the medial compartment undergoing total knee replacement were included in this study. Osteochondral samples from the tibiae were obtained from the arthritic and relatively normal compartments of the knee joints for comparison. Samples were decalcified and prepared for immunohistochemistry and chondrocytes were isolated and cultured for the mRNA expression of type I collagen, osteocalcin, osteopontin, alkaline phosphatase, bone sialoprotein and bone morphogenitic protein 2 and 4, et al. The most significant finding on immunohistochemical analysis was strong expression of molecules for mineralization in the chondrocytes in Grate IV OA in the deep layers of cartilage except type I collagen. Up-regulated expression of bone matrix protein genes were found during the osteo-differentiation of chondrocytes from OA patent. The appearance of the chondrocytes and the staining distribution suggest that during the progress of OA chondrocytes differentially produce matrix proteins like osteocalcin and bone sialoprotein, which induces articular cartilage mineralization and subsequent replacement of articular cartilage by subcondral bone tissue through the change of collagen type.

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