The effects of conditioned media generated by polarized macrophages on the cellular behaviours of bone marrow mesenchymal stem cells

Macrophages (M phi s) are involved in a variety of physiological and pathological events including wound healing and tissue regeneration, in which they play both positive and negative roles depending on their polarization state. In this study, we investigated the cellular behaviours of bone marrow mesenchymal stem cells (BMMSCs) after incubation in different conditioned media (CMs) generated by unpolarized M phi s (M0) or polarized M phi s (M1 and M2). M phi polarization was induced by stimulation with various cytokines, and CMs were obtained from in vitro M phi cultures termed CM0, CM1 and CM2 based on each M phi phenotype. We found that CM1 supported the proliferation and adipogenic differentiation of BMMSCs, whereas CM0 had a remarkable effect on cell osteogenic differentiation. To a certain degree, CM2 also facilitated BMMSC osteogenesis; in particular, cells incubated with CM2 exhibited an enhanced capacity to form robust stem cell sheets. Although incubation with CM1 also increased production of extracellular matrix components, such as fibronectin, COL-1 and integrin 1during sheet induction, the sheets generated by CM2-incubated cells were thicker than those generated by CM1-incubated cells (P < 0.001). Our data suggest that each M phi phenotype has a unique effect on BMMSCs. Fine-tuning M phi polarization following transplantation may serve as an effective method to modulate the therapeutic potential of BMMSCs.