1,25-dihydroxyvitamin D-3 inhibits directly human osteoclastogenesis by down-regulation of the c-Fms and RANK expression

Abstract

Objective: 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3) is a key molecule to maintain calcium homeostasis and bone metabolism. It was recently reported that 1,25(OH)(2)D-3 directly inhibited osteoclast differentiation in mouse bone marrow cells and human bone marrow-derived colony-forming unit granulocyte macrophage (CFU-GM) cells. However, the direct effects of 1,25(OH)(2)D-3 and its affecting mechanisms on the osteoclast differentiation of human osteoclast precursors remain largely unknown. In this study, we examined the direct effects of 1,25(OH)(2)D-3 on the osteoclastogenesis of human peripheral blood (PB) osteoclast precursors. Methods: In vitro osteoclastogenesis assays were performed using osteoclast precursors from normal PB. The gene expressions were analyzed using real-time PCR. The cell surface proteins, including c-Fms and RANK, were measured by flow cytometry. Results: 1,25(OH)(2)D-3 strongly inhibited osteoclast differentiation and it suppressed the expression of RANK in the human PB osteoclast precursors. One mechanism of RANK inhibition by 1,25(OH)(2)D-3 is down-regulation of the M-CSF receptor c-Fms, which is required for the expression of RANK. In contrast to the previous reports on mouse osteoclast precursors, 1,25(OH)(2)D-3 did not affect the expression of c-Fos. Parallel to the inhibition of osteoclastogenesis, 1,25(OH)(2)D-3 increased the expression and phosphorylation of CCAAT enhancer-binding protein beta (C/EBP beta), which is a recently discovered inhibitor of osteoclastogenesis. Conclusions: Our results show that 1,25(OH)(2)D-3 inhibits human osteoclastogenesis by decreasing the RANK+ osteoclast precursors, and we suggest that 1,25(OH)(2)D-3 may be a powerful therapeutic agent for treating inflammation-induced bone disease that shows excessive osteoclast activation. (C) 2012 Societe francaise de rhumatologie. Published by Elsevier Masson SAS. All rights reserved.