BMSC-derived MCP-1 enhances osteoclastogenesis.

<p>TRAP staining showing increased numbers of multinuclear TRAP⁺ OCs generated from cocultures of monocytes with BMSCs and either primary MM cells (PtMM) isolated from six MM patients (<b>A</b>) or ARP-1 cells (<b>B</b>) in medium with RANKL, compared with those in cultures with MM cells only or with BMSCs only. BMSCs were generated from bone marrow aspirates of MM patients or generated from human healthy fetal bones. Similar results were obtained for cocultures with MM.1S and other MM cell lines. (<b>C</b>) The levels of secreted MCP-1 in conditioned medium from cocultures of ARP-1 cells and BMSCs were higher than those from cultures of ARP-1 cells alone or cultures of BMSCs alone. Similar results were obtained for conditioned medium from cocultures of MM.1S cells and BMSCs. The numbers of multinuclear TRAP⁺ OCs per well of 24-well plate as determined by TRAP staining (<b>D</b>) and the expression levels of OC-associated proteins CTSK and TRAP, determined by real-time PCR, in OCs generated from cocultures of monocytes with ARP-1 cells and BMSCs in medium containing RANKL (<b>E</b>) were higher than those in cocultures of monocytes with ARP-1 cells only or with BMSCs only. The numbers of OCs (<b>D</b>) and the expression levels of CTSK and TRAP in OCs generated from cocultures of ARP-1 and BMSCs with the addition of RANKL and neutralizing antibodies against MCP-1 (αMCP-1) (<b>E</b>) were lower than with those from cocultures containing control IgG (Ctrl IgG). Similar results were obtained for cocultures of monocytes with BMSCs and MM.1S cells. Representative results from four independent experiments are shown. **<i>P</i> ≤ 0.01.