It has been demonstrated that progesterone has immune suppressive properties and can inhibit Toll-like receptor 4 (TLR4)-triggered immune response. Multiple microRNAs are induced in innate immune cells, among them miR-155, miR-146a and miR-21 are particularly ubiquitous. In this study, we investigated the potential roles of miR-155 in progesterone-mediated regulation of innate immune responses. We found that progesterone pre-treatment suppressed LPS- and poly(I:C)-induced miR-155 expression in macrophages. Increasing the activity of miR-155, significantly attenuated the progesterone's inhibition on LPS-induced IL-6 as well as LPS- and poly(I:C)-induced IFN-β expression in macrophages. Furthermore, we demonstrated that progesterone up-regulated LPS-induced SOCS1 expression while overexpression of miR-155 inhibited SOCS1 expression. In conclusion, the present study has demonstrated that progesterone suppresses TLRs-triggered immune response by regulating miR-155, and the decreased miR-155 contributes to inhibit TLR-induced IL-6 and IFN-β via increased SOCS1 expression.
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