Figure 1.

Schematic model of eldecalcitol action on bone cells. Eldecalcitol enhances differentiation of RANKL-rich preosteoblasts to RANKL-poor mature osteoblasts. As a result, the number of RANKL-rich cells is reduced in bone surface. RANKL suppresses the expression of S1PR1 in preosteoclasts. Reduction in RANKL expression by eldecalcitol induces S1PR1. Eldecalcitol also suppresses the expression of S1PR2 in preosteoclasts, and an increase in S1PR1 by eldecalcitol cooperatively stimulates the mobilization of preosteoclasts from bone marrow to blood circulation where S1P concentration is high.