MATRIX ASSEMBLY BY ARTICULAR CARTILAGE

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The maintenance of healthy cartilage depends on balancing the synthetic and degradative processes of tissue turnover, processes controlled by the resident cartilage cells, the chondrocytes. Another vital process is the control of proper assembly of matrix once new synthesis occurs. Although the macromolecules which make up the extracellular matrix have a significant capacity for cell-free self assembly, most assembly occurs immediately adjacent to the chondrocyte cell surface, within a zone termed the cell-associated or pericellular matrix. This proximity most likely proves the chondrocytes a means to control or catalyze the assembly process. Many of the cell-matrix interactions which are involved in initial matrix assembly occur via interaction of matrix macromolecules with cell surface receptors or high affinity binding proteins. Our preliminary data suggest that the interaction of hyaluronan (HA) with chondrocyte cell surfaces, via an HA-receptor, is essential for the assembly of a cell-associated matrix. We propose that once assembled, this HA matrix serves as a nucleating template for most distant extracellular matrix organization. Further, aberrations in HA receptor or other matrix binding receptors during aging or disease result in faulty cell-associated matrix assembly and loss of cartilage integrity. Therefore, the aims of this proposal are to explore the mechanisms of chondrocyte cell-matrix interactions, how various macromolecules are directly or indirectly anchored to the chondrocyte cell surface, and how these parameters are likely to change with aging or disease. Although several receptors are likely present on chondrocytes participating in cell-associated matrix assembly, this proposal focuses on two receptors in particular; the HA-receptor and the anchorin CII collagen receptor. Use of these two receptors will provide a well-rounded initial approach to the study of receptor-mediated mechanisms of chondrocyte matrix assembly. The degree of structural changes in HA and proteoglycan which hinder or prevent normal matrix assembly will also be determined. The chondrocytes to be studied in this proposal will be derived from normal adult bovine and later from human articular cartilage, and grown in an alginate bead culture system. this system allows accessibility to the cell-associated pericellular matrix while maintaining the phenotype of the chondrocyte.