MSC-secreted TGF-β regulates lipopolysaccharide-stimulated macrophage M2-like polarization via the Akt/FoxO1 pathway

Background An uncontrolled inflammatory response is a critical pathophysiological feature of sepsis. Mesenchymal stem cells (MSCs) induce macrophage phenotype polarization and reduce inflammation in sepsis. MSC-secreted transforming growth factor beta (TGF-beta) participated in the immune modulatory function of MSCs. However, the underlying mechanism of MSC-secreted TGF-beta was not fully elucidated in regulation macrophage M2-like polarization. Methods The paracrine effects of MSCs on macrophage polarization were studied using a co-culture protocol with LPS-stimulated RAW264.7 cells/mouse peritoneal macrophages and MSCs. The effect of TGF-beta in the co-culture system was blocked by the TGF-beta receptor inhibitor. To determine the role of MSC-secreted TGF-beta, we used recombinant TGF-beta to culture with LPS-stimulated RAW264.7 cells. In addition, we employed antibody microarray analysis to determine the mechanisms of MSC secreted TGF-beta on LPS-stimulated RAW264.7 cell/mouse peritoneal macrophage M2-like polarization. Furthermore, we used an Akt inhibitor and a FoxO1 inhibitor to inhibit the Akt/FoxO1 pathway. The nuclear translocation of FoxO1 was detected by Western blot. Results MSCs induced LPS-stimulated RAW264.7 cell/mouse peritoneal macrophage polarization towards the M2-like phenotype and significantly reduced pro-inflammatory cytokine levels via paracrine, which was inhibited by TGF-beta receptor inhibitor. Furthermore, we found that MSC-secreted TGF-beta enhanced the macrophage phagocytic ability. The antibody microarray analysis and Western blot verified that TGF-beta treatment activated the Akt/FoxO1 pathway in LPS-stimulated macrophages, TGF-beta-induced FoxO1 nuclear translocation and obviously expressed in the cytoplasm, the effects of TGF-beta regulatory effects on LPS-stimulated macrophage were inhibited by pre-treatment with Akt inhibitor and FoxO1 inhibitor. Conclusions TGF-beta secreted by MSCs could skew LPS-stimulated macrophage polarization towards the M2-like phenotype, reduce inflammatory reactions, and improve the phagocytic ability via the Akt/FoxO1 pathway, providing potential therapeutic strategies for sepsis.