miR-155 Regulates Immune Modulatory Properties of Mesenchymal Stem Cells by Targeting TAK1-binding Protein 2

MSCs possess potent immunosuppressive capacity. We have reported that mouse MSCs inhibit T cell proliferation and function via nitric oxide. This immune regulatory capacity of MSCs is induced by the inflammatory cytokines IFN gamma together with either TNF alpha or IL-1 beta. This effect of inflammatory cytokines on MSCs is extraordinary; logarithmic increases in the expression of iNOS and chemokines are often observed. To investigate the molecular mechanisms underlying this robust effect of cytokines, we examined the expression of microRNAs in MSCs before and after cytokine treatment. We found that miR-155 is most significantly up-regulated. Furthermore, our results showed that miR-155 inhibits the immunosuppressive capacity of MSCs by reducing iNOS expression. We further demonstrated that miR-155 targets TAK1-binding protein 2 (TAB2) to regulate iNOS expression. Additionally, knockdown of TAB2 reduced iNOS expression. In summary, our study demonstrated that miR-155 inhibits the immunosuppressive capacity of MSCs by reducing iNOS expression by targeting TAB2. Our data revealed a novel role of miR-155 in regulating the immune modulatory activities of MSCs.