Fig. 4.

Schematic representation of the bone remodeling process. When Fas is defective, a greater amount of S1P is released by osteoclasts (grey arrows) and this leads to increased production of RANKL by osteoblasts (black arrow). As a result, greater stimulation of osteoblasts and the migration of osteoclast precursor cells occurs, and differentiation of osteoclasts is enhanced. S1P that is produced by osteoclasts serves to recruit osteoblasts to bone resorption sites as an initial step in the process to replace lost bone. An overall increase in the level of S1P then stimulates bone formation.