The resiliency and physical-chemical properties of articular cartilage, necessary for its load-bearing functions, depend on the content and organization of the specific proteoglycans and collagens of the extracellular matrix. Since the chondrocytes (cartilage cells) are responsible for both synthesis and catabolism of the matrix, they directly determine the biochemical composition and biophysical properties of the tissue. In healthy cartilage, a finely regulated balance must be maintained between anabolism and catabolism of the specific extra cellular matrix macromolecules by teh chondrocytes. There is good evidence that progressive degeneration of articular cartilage, such as may occur in osteoarthritis, is at least partly the result of excessive chondrocytic catabolism which is not matched by appropriate biosynthesis of new matrix. Articular cartilage is not a homogeneous tissue, but rather is stratified; both the morphology of the chondrocytes and the biochemical composition of the extracellular matrix show characteristic variation at different depths from the articular surface. It is not known what specific roles the chondrocytes in different zones play in maintaining the integrity of normal articular cartilage, nor whether they respond differently under pathological conditions. In a novel approach to these questions, in recent studies in this laboratory, sub-populations of articular chondrocytes were isolated from different depths of the tissue and maintained in culture in order to make direct comparative studies of their metabolic potential. In this way we have demonstrated that articular chondrocytes derived from different depths of cartilage show striking differences, and continue to exhibit morphological and metabolic characteristics in keeping with their original anatomical location and the biochemical nature of the matrix which surrounded them in vivo. The primary purpose of this project is to study such sub-populations of chondrocytes in more detail, in order to analyze those metabolic differences which form the basis of the heterogeneity of normal tissue, and which may also influence the course of pathological deterioration of articular cartilage. A further goal is to determine how closely the metabolism of specific sub-populations of cultured chondrocytes corresponds to that of cells within slices of fresh tissues. In addition, sub-populations of articular chondrocytes will be tested for any differential responses to a variety of important modulators of chondrocytic metabolism, such as Interleukin 1 and insulin-like growth factor (IGF-1). Techniques of analytical biochemistry, immunohistochemistry, and molecular biology will be applied in order to characterize the proteoglycans and collagens produced, and to determine the biosysynthetic capacities of the different groups of chondrocytes.
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