Fig. 1.

Osteoblast–osteoclast communication in bone remodeling. The basic RANKL-RANK communication system is influenced by hormones like PTH and 1,25(OH)₂D₃, Wnt signaling, growth factors, including BMPs, TGFβ1, IGF-1, PDGF-BB and others. Following bone resorption, growth factors released from the ECM influence differentiation of bone marrow stromal cells or directly act on osteoblasts. PTH can act via newly discovered couplin. In combination with 1,25(OH)₂D₃, BMPs upregulate cathepsin K and anhydrase II to promote bone resorption