Figure 3.

1α,25(OH)₂D₃ inhibits RANKL-induced terminal differentiation into osteoclasts. (A) Osteoclast precursor cells were isolated from the bone marrow of WT C57BL/6J mice. These cells were cultured in the presence of 30 ng/ml M-CSF without or with increasing doses of 1α,25(OH)₂D₃ for 3 days, and cell proliferation was assessed as described in Methods. (B) Bone marrow cells were cultured with M-CSF for the first 3 days (1st period) and then with RANKL in addition to M-CSF for the latter 3 days (2nd period). The presence of 1α,25(OH)₂D₃ at 10^–8 M is indicated by “+”. Note that the presence of 1α,25(OH)₂D₃ only in the latter period was sufficient to inhibit the formation of TRAP-positive multinucleate cells, whereas its presence in the former M-CSF–dependent cell growth period failed to inhibit osteoclastogenesis.