CYTOSKELETAL CHANGES IN OSTEOCLASTS DURING THE RESORPTION CYCLE

Osteoclasts are large, multinucleated cells which change their shape a nd polarity according to their resorptive activity. At least in vitro, nonresorbing osteoclasts move on the bone surface and do not show cle ar evidence of apical-basolateral polarity. When stimulated for resorp tion, osteoclasts undergo a rapid reorganization of the cytoskeleton a nd appear clearly polarized. The detailed nature of different membrane domains in polarized osteoclasts is still far from clear, but a remar kable feature is the formation of a tight sealing zone between the ruf fled border and the rest of the cell membrane. Characteristic organiza tion of F-actin into a belt or ring-like structure with a double circl e of vinculin around it is needed for the formation of the sealing zon e. This type of microfilament organization is typical only for resorbi ng osteoclasts and can thus be used as a marker for resorbing cells. T hese characteristic changes in the molecular organization of the cytos keleton in osteoclasts during the resorption cycle offer several poten tial targets to inhibit bone resorption, perhaps cell-specific. (C) 19 96 Wiley-Liss, Inc.