Figure 6
(a–d) Contribution of sFRP4 to bone remodeling. Wnt signals derived from osteoblasts (bold green arrows) promote osteoblast proliferation and differentiation (arrows indicate positive effects) and repress osteoclast formation (red T-shaped bars indicate inhibitory effects). sFRP4 produced in osteoblasts and osteoclasts (bold blue arrows) fine-tunes the balance between bone deposition and resorption through the functional blocking of Wnt ligands. (a) Bone remodeling is controlled by balanced amounts of Wnt ligands and sFRP4. (b) Functional loss of sFRP4 causes a synergistic enhancement of bone deposition by increasing osteoblast activity and repressing osteoclast formation. (c) Bone resorption develops as a result of reduced osteoblastic expression of Wnt ligands and elevated sFRP4 expression that blocks the inhibitory effect of Wnt signal on osteoclast formation. (d) Functional loss of sFRP4 in aged bone (“Loss of sFRP4 in Aging”) prevents age-related bone loss by recovering the Wnt signal activity for osteoblast and osteoclast formation.
