Primary human bone marrow adipocytes support TNF-α-induced osteoclast differentiation and function through RANKL expression

Purpose: In previous reports, it was demonstrated that bone marrow adipocytes were related to steroid osteoporosis through osteoclastogenesis induced by Receptor Activator of Nuclear factor kappa-B Ligand (RANKL) expression. The purpose of this study was to evaluate the effect of Tumor necrosis factor-alpha (TNF-alpha) on RANKL expression in bone marrow adipocytes, and osteoclast differentiation supported by human bone marrow adipocytes. Methods: RANKL, osteoprotegerin (OPG), and macrophage-colony stimulating factor (M-CSF) mRNA expression in bone marrow adipocytes and their regulation by TNF-alpha treatment were measured by real-time RT-PCR. Co-cultures of bone marrow adipocytes and osteoclast precursors were performed with or without TNF-alpha, and osteoclast differentiation was evaluated morphologically and functionally. Results: RANKL expression and an increase in the RANKL/OPG ratio in bone marrow adipocytes were stimulated by TNF-alpha treatment. In co-culture of bone marrow adipocytes and osteoclast precursors with TNF-alpha, the number of TRAP-positive multinuclear cells and resorption cavity formations of calcium phosphate film were increased. Osteoclast differentiation was suppressed by anti-RANKL antibody treatment. In co-culture with non-cell-contact conditions, no TRAP-positive cells or resorption cavity formations were observed. Conclusions: TNF-alpha increased RANKL expression in primary human bone marrow adipocytes. TNF-alpha induced the ability of bone marrow adipocytes to promote osteoclast differentiation and activity in a manner directly related to RANKL expression. (C) 2011 Elsevier Ltd. All rights reserved.