Degeneration of articular cartilage occurs with aging and accelerated in osteoarthritis (OA). However, the mechanisms responsible for these changes are currently unknown. The focus of this project is the member of the bone morphogenetic protein (BMP) family, BMP-7 or osteogenic protein-1 (OP-1), that has an ability to induce anabolic processes in cartilage. Previously, we showed for the first time that OP-1 message and protein are expressed in adult human articular cartilage and that their levels declined with aging and cartilage degeneration. Our hypothesis is that, with aging, human articular cartilage exhibits a decrease in endogenous OP-1 content, synthesis and metabolism. This may lead to an elevated susceptibility of the chondrocytes to catabolic processes thus contributing/promoting cartilage degeneration. The long-term objective is to understand the biological function and regulation of endogenous OP-1 in aging human articular cartilage in comparison to OA. The uniqueness of this project is that we have unlimited access to human cartilages from organ donors collected through the Regional Organ Bank of Illinois. We can distinguish between normal (no-pathologically) and pathologically progressive (degenerative) aging by documenting changes in a joint that rarely develops OA (ankle joint) compared to changes in a joint with the higher prevalence of OA (knee joint). The objectives of the present study will be tested by three specific aims: 1) Assess the response of articular cartilage to catabolic stimuli (IL-1 and mechanical injury) by studying cartilage endogenous OP-1 and investigate whether this response is different between normal and pathologically progressive aging; 2) Investigate the metabolism of endogenous OP-1 at its near steady state and under exposure to catabolic stimuli (IL-1 and mechanical injury) in adult articular cartilage of different ages; 3) Study whether changes in endogenous OP-1 have a causative role in impairing cartilage homeostasis in normal and pathologically progressive aging. We intend to perturb OP-1 function or expressing using specific neutralizing antibody, binding proteins, and/or antisense oligonucleotides. In order to accomplish these specific aims, a novel sensitive ELISA method has been developed by us. This method allows us to analyze the concentrations of OP-1 protein in cartilage extracts and culture medium. Also a new neoepitope antibody to the specific cleavage site between pro- and mature domains of OP-1 has been developed and characterized. This antibody is critical, since both forms of OP-1 (pro- and mature) have been identified in human articular cartilage and the neoepitope antibody will provide a tool to assess changes in processing and activation of endogenous OP-1 under different experimental conditions. This study will contribute to the understanding of the mechanisms of cartilage repair/anabolism.
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