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

Figure 1 Bidirectional interaction between mesenchymal stem cells and macrophages. Mesenchymal stem cells (MSCs) can facilitate the proliferation and infiltration of macrophages, enhance their phagocytic capabilities, and promote the polarization of macrophages phenotypes. Macrophages are capable of activating MSCs, boosting their proliferation and migration abilities, influencing the immune regulatory microenvironment of MSCs, and promoting the multilineage differentiation of MSCs through the secretion of inflammatory-related factors, chemokines, and osteogenic-related factors. MSC: Mesenchymal stem cell; CCL2: C-C motif chemokine ligand 2; CCR2: C-C motif chemokine receptor 2; VEGF-A: Vascular endothelial growth factor-A; PEG2: Prostaglandin E2; IL: Interleukin; IFN: Interferon; TGF-β: Transforming growth factor beta; FoxO1: Forkhead box transcription factor O1; NF-κB: Nuclear factor kappa-B; MyD88: Myeloid differentiation primary response gene 88; TIRAP: Toll-interleukin-1 receptor domain-containing adaptor protein; TIR: Toll-interleukin-1 receptor; SR: Scavenger receptor; AKT: Protein kinase B; PTN: Pleiotropic hormones; TLR4: Toll-like receptor 4; THBS-1: Thrombospondin-1; BMP-2: Bone morphogenetic protein-2; OSM: Oncostatin-M; IDO: Indoleamine 2,3-dioxygenase; HGF: Hepatocyte growth factor; miRNA: MicroRNA; ROS: Reactive oxygen species; NO: Nitric oxide.