Journey Across the Osteoclast

Abstract
Living bone is continuously remodeled. Certain bone cells, osteoblasts, build bone, even as other bone cells, osteoclasts, degrade it. In this week9s issue, Salo et al. (p. 270) and Nesbitt et al. (p. 266) show that the bone matrix, degraded in a compartment under the osteoclast, is transferred through the cell for release into the extracellular space by transcytosis. In their Perspective, Mostov and Werb discuss the similarities of bone transcytosis to membrane-trafficking processes in other cells and argue that transcytosis is not just a degradation pathway, but may also be a critical regulatory step in bone remodeling and thus a potential target for therapy.