Interplay between mesenchymal stem cells and macrophages: Promoting bone tissue repair

Figure 2 The dialogue between mesenchymal stem cells and macrophages in mediating the immune environment and bone tissue. Multiple inflammatory factors secreted by M1 macrophages can promote the differentiation of osteoclast precursors into osteoclasts. When the inflammatory factors accumulate to a certain extent, the differentiation of osteoclasts is inhibited by the action of osteogenic factors secreted by M2 macrophages and mesenchymal stem cells (MSCs). Macrophages can promote the secretion of various osteogenic induction factors by MSCs through direct contact or by secreting various bioactive factors indirectly, inducing further differentiation of osteogenic precursor cells into osteoblasts. MSC: Mesenchymal stem cell; RANK: Receptor activator of nuclear factor kappa-B; RANKL: Receptor activator of nuclear factor kappa-B ligand; NF-κB: Nuclear factor kappa-B; TRAF6: Tumor necrosis factor receptor-associated factor 6; NFATc1: Transcription factor nuclear factor of activated T cells; OPG: Osteoprotegerin; OSM: Oncostatin-M; OSMR: Oncostatin-M receptor; RUNX2: Runt-related transcription factor 2; OCN: Osteocalcin; Osx: Osterix; OPN: Osteopontin; ALPL: Alkaline phosphatase; BMP-2: Bone morphogenetic protein-2; TNF: Tumor necrosis factor; IL: Interleukin; IFN: Interferon; TGF-β: Transforming growth factor beta; IGF-1: Insulin-like growth factor-1.