BONE-CELLS AND BONE REMODELING

Recent data have shown that bone remodeling is a complex process, invo lving multiple components. These include cells of various origin, a ca lcified extracellular matrix and numerous factors regulating cellular activities, tissue formation and degradation. Bone resorption and form ation activities are regulated at various levels during the course of bone cell differentiation. These activities are ensured by various hor mones, many of them having indirect effects on bone cells through the production of local factors. Various cytokines and growth factors have been shown to affect bone cells proliferation and differentiation and these effects are modulated by many hormones. Cells of the osteoblast ic lineage may play an important role in the regulation of bone remode ling as they synthesize a number of local factors affecting osteoclast s. These cells are also involved in the first steps of matrix degradat ion, allowing thus osteoclast attachment to the bone matrix. Some loca l growth factors are incorporated into the bone matrix and may serve a s coupling agents between bone resorption and formation. The precise c ontribution of these factors during the process of bone remodeling in normal conditions and ageing is, however, unclear.