Osteoclasts, macrophages, and the molecular mechanisms of bone resorption.

The osteoclast is a physiological polykaryon and the major if not exclusive resorptive cell of bone. It participates in bone remodeling, repair, and growth and mobilization of mineral to meet homeostatic demands. Most importantly, osteoporosis, a disease endemic in Western society and Asia, is always a reflection of enhanced osteoclastic activity relative to bone formation by osteoblasts. In fact, all forms of anti-osteoporosis therapy proven successful involve inhibition of osteoclastic bone resorption. Bone resorption is regulated either by altering recruitment of osteoclast precursors into fully differentiated resorptive polykaryons or modulating the rate at which mature osteoclasts degrade bone. With this in mind, our laboratory has focused on the molecular mechanisms of osteoclast differentiation and the means by which the cell degrades bone matrix.