Osteoclast: Origin and Differentiation

Summary of Chapter I in Bone Resorption (edited by Felix Bronner, Mary C. Farach-Carson and Janet Rubin, published by Springer-Verlag London Limited, 2005: Osteoclast was recognized in 1873. It arose from hematogenous stem cells. Osteoclast precursors appear early macrophage characteristics, such as the ability to fuse with like cells and the abiligy to phagocytose. The essential effect of M-CSF on osteoclastogenesis support that osteoclasts and macrophages share a common origin.Osteoclastogenesis in vivo in a microenvinorment that other cells could close contact with osteoclast precursors. The critical factor contributed by bone stromal cells for terminal osteoclast differentiation is RANKL. Osteoclast differentiation undergo three steps: early differentiation, where hematopoietic stem cells proliferate within the macrophage lineage; progression into the early osteoclast precursor step with expression of calcitonin receptor and TRAP; and a later stage where fusion occurs.