Figure 1

Key steps in bone remodelling. 1) Osteocytes send signals to the fluid part, activating pre-osteoblasts (Pb) and pre-osteoclasts (Pc). 2) Pb s express RANKL and Pc s express the RANK receptor. 3) RANK/RANKL binding induces Pc s' proliferation. Pc s enlarge and fuse, forming mature osteoclasts which start the bone resorption process. 4) Mature osteoblasts express the decoy receptor OPG and start the bone formation process. RANKL/OPG binding inhibits RANKL, thus protecting bone from excessive resorption. 5) During the mineralization process, osteoids secreted by osteoblasts calcify. 6) Finally in the resting phase, the initial situation is re-established.