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. 2013 Jan 16;123(2):666–681. doi: 10.1172/JCI64840

Figure 13. Schematic representation of bone remodeling and the coupling process in controls and Ctsk-deficient mice.

Figure 13

(A) Under normal circumstance, osteoclasts secrete clastokines, including osteoanabolic factors such as S1P, for the regulation of bone formation. Additionally, osteoclasts resorb bone, thus releasing MDGFs to enhance bone formation. (B) Absence of cathepsin K increases S1P released by osteoclasts and may increase intact MDGFs (11). Furthermore, S1P induces an increase in the production of RANKL by osteoblasts (20), leading to increased osteoclast differentiation. An overall increase in the level of S1P stimulates bone formation. OC-pre, osteoclast precursor.