Axl Involved in Mineral Trioxide Aggregate Induces Macrophage Polarization

In this study, we examined the effect of mineral trioxide aggregate (MTA) on macrophage polarization and the potential involvement of Axl/nuclear factor kappa B (NF-κB) signaling in mediating the effect of MTA.

The human monocyte cell line THP-1 was cultured with MTA solution for 1, 2, or 3 days, and the population change of M2 macrophages was analyzed by flow cytometry. Expression of M2 cytokines was examined by enzyme-linked immunosorbent assay. Phagocytosis and angiogenesis-induction ability were also assayed. The involvement of Axl/NF-κB signaling in MTA-treated cells was examined by analyzing phosphorylation status of Axl, Akt, IKKα/β, and IκBα. Specific inhibitors for Axl/Akt/NF-κB signaling were added to MTA-treated THP-1 cells, and their cytokine expression change was examined.

Flow cytometry analysis showed that MTA treatment increased CD206＋ cells in a time-dependent way. After MTA treatment, the expression of M2-related cytokines was up-regulated. MTA also enhanced phagocytic ability and the ability of THP-1 cells to induce angiogenesis. Treatment of MTA led to activate Axl/Akt/NF-kB signal axis by phosphorylation of Axl, Akt, IKKα/β, IκBα, and p65. In addition, MTA-induced interleukin 10, transforming growth factor beta, and vascular endothelial growth factor expression was suppressed as specific inhibitors were added.

Our findings indicate that MTA is able to induce macrophage polarization toward the M2 phenotype, with up-regulation of interleukin 10, transforming growth factor beta, and vascular endothelial growth factor, and that Axl/Akt/NF-κB signaling participates in this process. These results provide the cellular and molecular basis of MTA's anti-inflammatory action in clinical applications.