Morphological study on cell-cell interaction between osteoclasts and osteoblasts

We reviewed morphological characteristics in cell-cell interaction between osteoclasts and the cells of osteoblast lineage. Heparan sulfate proteoglycans (HSPG) are localized in the intercellular space between osteoblasts and osteoclasts. HSPG is involved in reservation of heparin binding growth factors (HBGF), protection from proteolysis of HBGF, and ligand-receptor interaction in the case of fibroblast growth factors. HSPG may play an important role in cell-cell interaction between osteoblasts and osteoclasts by reserving HBGF and heparin binding adhesion molecules such as fibronectin. On the other hand, CD44, a hyaluronate receptor, and moesin are colocalized in the basolateral plasma membrane of osteoclasts. Calcitonin changes their localization in osteoclasts, suggesting that the CD44-moesin-actin filament system is engaged in the regulation of cell polarity. Although hyaluronates colocalize with CD44 in the basolateral membrane of osteoclasts, the precise intracellular signaling mechanism needs to be clarified in further research. Bone metabolism may be regulated by cell-cell and cell-matrix interaction among bone cells via adhesion molecule, extracellular matrices and cytokines.