Human bone marrow adipocytes support dexamethasone-induced osteoclast differentiation and function through RANKL expression

The TNF-family molecule, Receptor Activator of Nuclear factor kappa B Ligand (RANKL) is known as a key regulator for bone remodeling, and is essential for the development and activation of osteoclasts. In this study, we examined the regulation of RANKL in primary human bone marrow adipocytes and the relationship between bone marrow adipocytes and bone metabolism. RANKL expression and the RANKL/osteoprotegerin (OPG) mRNA ratio in marrow adipocytes increased following dexamethasone treatment. In co-cultures of human osteoclast precursors and bone marrow adipocytes with dexamethasone, osteoclast precursors differentiated to TRAP-positive multinuclear cells. Moreover, the ability of bone resorption was confirmed in co-culture in flasks coated with calcium phosphate film. Osteoclast precursor differentiation and bone resorption were blocked by RANKL antibody pretreatment. TRAP-positive multinuclear cells did not form in co-culture without cell-to-cell contact conditions. We conclude that primary human bone marrow adipocytes have the ability to promote osteoclast differentiation and activities, similar to osteoblasts and other RANKL-expressing cells.