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 κ-B Ligand (RANKL) expression. The purpose of this study was to evaluate the effect of Tumor necrosis factor-alpha (TNF-α) 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-α treatment were measured by real-time RT-PCR. Co-cultures of bone marrow adipocytes and osteoclast precursors were performed with or without TNF-α, 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-α treatment. In co-culture of bone marrow adipocytes and osteoclast precursors with TNF-α, 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-α increased RANKL expression in primary human bone marrow adipocytes. TNF-α induced the ability of bone marrow adipocytes to promote osteoclast differentiation and activity in a manner directly related to RANKL expression.