Human Umbilical Cord Mesenchymal Stem Cell-derived Exosomes Induce Macrophage M2 Polarization by Antagonizing LPS-mediated Stimulation of the NF-κB and STAT3 Pathways.

Background: Many studies have documented the protective effects of regulating macrophage M1/M2 polarization in inflammatory diseases characterized by their imbalance state. In pathological diseases associated with inflammation, mesenchymal stem cells (MSCs) regulate macrophages, thereby having anti-inflammatory and tissue regenerative effects. Exosomes have been suggested as an alternative mechanism that underlies the paracrine function of MSCs. Thus, this study explored the anti-inflammatory impact of human umbilical cord MSCssecreted exosomes (hucMSCs-EX) by influencing macrophage polarization in normal and inflammatory environments in vitro.

Methods: In this study, hucMSCs-conditioned medium (hucMSCs-CM) and hucMSCs- EX were used to treat RAW264.7 macrophages with or without LPS. The expressions of TNF- α, IL-10, IL-6, IL-1β, and Arg-1 were quantified by qPCR. The expressions of IL-6 and IL-10 were evaluated by ELISAs. Western blots (WB) were performed to observe the expressions of CD206, NF-κB P65, NF-κB p-p65, p-STAT3, STAT3, and NF-κB phosphorylation. The number of cells expressing CD206 and the fluorescence intensity were measured via flow cytometry (FC) and immunofluorescence staining. Cell propagation and migration were examined via MTT and transwell assays, respectively.

Results: The inhibition of LPS-induced inflammatory polarization by hucMSCs-EX or hucMSCs- CM led to increases in IL-10 and arginase (Arg) levels and decreases in those of IL-6 and TNF-α. Moreover, hucMSCs-EX enhanced the CD206 expression in RAW264.7 cells and accelerated the propagation and migration of LPS-induced cells. The suppressive impact of hucMSCs-EX on the LPS-induced phenotypic polarization of M1 macrophages was linked with the reduction of NF-κB signaling. They stimulated the transition of M2 macrophages by enhancing the activity of STAT3 in RAW264.7 cells.

Conclusion: This study indicated that hucMSCs-EX enhances the macrophage transition into the M2 phenotype by inhibiting the NF-κB p65 axis and stimulating that of STAT3.