Figure 1
From: Bone loss: Factors that regulate osteoclast differentiation - an update
New members of the TNF receptor ligand family: role of RANKL (ODF, TRANCE, OPGL) and its receptor RANK in osteoclast differentiation. RANKL, a membrane-bound TNF-related factor, is expressed by osteoblast/stromal cells and is upregulated by osteotropic factors such as 1,25(OH)2D3, PTH, IL-6 or IL-11. Osteoclast (OC) precursors express RANK, a membrane-bound TNF receptor, that recognizes RANKL through cell-cell interaction with osteoblast/stromal cells. This interaction enables osteoclast precursors to differentiate in the presence of M-CSF. Osteoprotegerin (OPG) is a member of the TNF receptor family that lacks a transmembrane domain and represents a secreted TNF receptor. OPG recognizes RANKL, and this decoy receptor blocks the interaction between RANK and RANKL, leading to inhibition of osteoclast differentiation and activation.