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

Abstract

The TNF-family molecule, Receptor Activator of Nuclear factor κ 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 coculture 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.There are various hypotheses about the function of bone marrow adipocytes, which are present in large quantities in the choke marrow space. Some hold that bone marrow adipocytes function as 1) a spacer between hematopoietic cells and bone tissue, 2) a fat metabolism organ, 3) an energy storehouse, or 4) support cells of hematopoiesis and bone metabolism (14). In contrast, it is clear that subcutaneous and visceral fats are not only simple spacers, but also energy storehouses. Subcutaneous and visceral fats also serve as metabolic organs secreting physiologically active substances named adipokines, which are associated with hypertension and metabolic syndrome (23). The adipokines, such as leptin, adiponectin, and TNF-α, act on osteoclasts and osteoblasts that are associated with bone metabolism (1,8,10,17,22). However, their function has not yet been fully elucidated.It is known that with aging, the composition of the bone marrow shifts to favor the presence of adipocytes, and osteoclast activity increases while osteoblast function declines, resulting in osteoporosis (14). Several reports have described the relationship between bone marrow adipocytes and bone metabolism. The BMS2 adipocyte cell line from murine bone marrow stromal cells promotes the differentiation of osteoclast-like cells in the presence of vitamin D (7). C3 protein, which is secreted during the initial stage of adipogenesis in murine bone marrow stromal cells, enhances osteoclast differentiation (15). Receptor Activator of Nuclear factor κ B Ligand (RANKL) is an essential molecule in osteoclast differentiation, as is the decoy receptor molecule os-

Adipocytes regulate the bone marrow microenvironment in a mouse model of obesity

“…Halade et al (16) reported that OPG secretion decreased and RANKL expression increased in osteoblasts stimulated with adipocyte-secreted factors. By contrast, Goto et al (20) demonstrated that adipocyte-secreted cytokines upregulated RANKL mRNA expression in osteoblasts, consistent with osteoclast differentiation in vitro. These observations are in agreement with those of this study and demonstrate that adipocytes increase osteoclastogenesis via the OPG/RANKL/RANK system in the bone microenvironment.…”

“…Oshima et al (19) demonstrated that adiponectin induced by cytokines secreted by adipocytes directly suppresses bone-resorption activity by inhibiting osteoclastogenesis. However, observations of Goto et al (20) demonstrate that primary human bone marrow adipocytes promote osteoclast differentiation and activities. Leptin, an adipocyte-derived cytokine, has been found to function as a negative regulator of bone mass in a mouse model (21).…”

Potentiation of osteoclastogenesis by adipogenic conversion of bone marrowderivedmesenchymal stem cells

“…Considering that BMSCs are the precursors of osteoblasts, adipogenesis in the bone marrow limits the pool of osteoblasts, however, recent studies have indicated that it also potentiates bone metabolism through secretion of the factors such as insulin, insulin-like growth factor, and leptin (5,17,18,24). In fact, our previous observations demonstrated that bone marrow-derived adipocytes expressed the RANKL gene transcripts, whose level was up-regulated by TNF-α and dexamethasone (10,11,15). Therefore, in the present study, we aimed to examine the role of adipogenic conversion of BMSCs in osteoclastogenesis in vitro, focusing on the production of RANKL.…”

“…Total protein concentration was determined by the BCA protein assay (Pierce, Rockford, IL). Proteins (8 or 16 μg) were electrophoresed through an SDSpolyacrylamide gel and were electrophoretically is mediated by augmented expression of RANKL in adipocytes (10,11,15). These lines of evidence also suggest that adipogenic differentiation of BMSCs in the bone marrow might stimulate osteoclastogenesis.…”

<b>Steroid changes adipokine concentration in the blood and bone marrow </b><b>fluid </b>

“…In the bone marrow space, there is a large quantity of mature adipocytes that are possible candidates for adipokine secretion. Considering the enclosed nature of the bone marrow space, intramedullary adipocytes may be involved in bone metabolism, as we previously reported that bone marrow adipocytes express receptor activator of nuclear factor kappa-B ligand (RANKL) and support osteoclast differentiation (5,8). Plasminogen activator inhibitor-1 (PAI-1), one of the adipokines secreted by adipocytes (1), suppresses fibrinolysis by binding tissue-type plasminogen activator (t-PA), and a relationship between PAI-1 and thrombosis or hypercoagulation has been suggested.…”