Osteoarthritis (OA) is among the most common diseases that develop as a function of advancing age. Age-related changes in chondroctes may increase susceptibility to the development of OA. Additional factors initiate remodeling of articular cartilage which is characteristic of OA and trigger an inflammatory response. This project previously analyzed chondrocyte proliferation in aging. We showed that TGFbeta is the most potent stimulus of chondrocyte proliferation, and as a function of aging the proliferative response to TGFbeta decreases markedly. We also showed that chondrocytes are the major intraaticular cell source of nitric oxide. Nitric oxide inhibits chondrocyte proliferation and induces apoptosis in those calls. These studies also suggested an apparent similarity between apototic bodies that are generated in chondrocyte cultures exposed to nitric oxide in vitro and matrix vesicles isolated from articular cartilage. We now propose the following hypothesis for the development of OA: as a function of aging cartilage cellularity decreases, in part because of the reduced ability of the calls to replicate and in part due to cell death. Chondrocyto death results in the formation of apoptotic bodies which accumulate in cartilage since this organ does not contain phagocytic cells. This constitutes one of the age-related risk factors for OA. We will (I) Analyze cartilage cellularity and the presence of apoptotic bodies in normal human articular cartilage from donors age 20-100. Isolate matrix vesicles from human articular cartilage and examine their ultrastructural, biochemical and functional properties relative to apoptotic bodies generated from chondrocytes in vitro. (ii) Determine cartilage cellularity, the presence of apoptotic bodies and matrix vesicles in cartilage from osteoporosis patients and assess functional properties of chondrocytes and matrix vesicles from osteoporosis patients. (iii) Examine chondrocytes from donors age 20-100 for their response to TGFB with respect to PPI formation and DNA synthesis. (iv) Define the effect of cell cycle status and in vitro senescence on TGFB induced PPi formation. It is proposed that PPi production is a function of non-cycling but not of proliferating cells and that senescent cells produce more PPi. (v) Analyze TGFB activated kinases and kinase inhibitors which regulate cell cycle progression versus secretory gene expression during in vivo aging and in vitro senescence.
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