This project aims to clarify the mechanisms by which structure and composition of cartilage extracellular matrix are altered during senescence. The structural modifications are thought to lead to impairment of the basic functional property of cartilage; resilience - a property that renders cartilage suitable for its biomechanical function in joints and other elastic body structures. Specifically, the present project aims to learn more about the mechanisms in cartilage cells that regulate biosynthesis and secretion of cartilage matrix components, including high and low molecular weight proteoglycans, Type II collagen, link proteins, and 60Kd protein. Biochemical experiments will uncover further structural differences in proteoglycans that may distinguish embryonic from adult and senescent cartilage. Pulse-chase experiments will monitor the kinetics of synthesis of the protein moiety of the various matrix components, and the average rates with which each of them moves from the rough ER to the extracellular millieu. Enzymatic assays will determine the activity of some Golgi complex-associated pathways effecting post-translational modifications of matrix components, to uncover a possible coordinate regulation between such activity and synthesis of matrix component protein moiety. Immunological approaches will study (a) intracellular distribution of precursor forms of matrix components in order to define common and distinct intracellular routes of elaboration, and (b) extracellular distribution of completed components as a function of age. These concerted research lines will shed light on how the cellular regulatory mechanisms are altered in senescent cartilage cells as to possibly account for the drastic age-related changes in matrix structure and composition, and on whether topographical distribution of matrix components is altered with age. The resulting information will prove useful in designing future attempts to restore normal homeostatic mechanisms in senescent cartilage.
