Stroma cells and Monocytes make Multiple Myeloma Cells Active In Bone Marrow Microenviroment

The Bone marrow (BM) microenvironment plays crucial role in pathogenesis of multiple myeloma　(MM). Paracrine secretion of cytokines in BM stromal cells promotes multiple myeloma cell proliferation and protects against drug-induced cytotoxicity. In current study, monocytes, component of BM cells, can directly promote mesenchymal stem cells osteogenic differentiation through cell contact interactions. Down-regulation of inhibitors such as DKK1 drives the differentiation of mesechymal stem cells into osteoblasts. In this study, we examined the role of monocytes as a potential niche component that supports myeloma cells. We investigated the proliferation of MM cell lines cultured alone or co-cultured with BM stromal cells, monocytes, or a combination of BM stromal cells and monocytes. Consistently, we observed increased proliferation of MM cell lines in the presence of either BM stromal cells or monocytes compared to cell line-only control. Furthermore, the co-culture of BM stromal cells plus monocytes induced the greatest degree of proliferation of myeloma cells. In addition to increased proliferation, BMSCs and monocytes decreased the rate of apoptosis of myeloma cells. Our results therefore suggest that highlights the role of monocyte as an important component of the BM microenvironment.