Activation of Gonadotropin-releasing Hormone Receptor Impedes the Immunosuppressive Activity of Decidual Regulatory T Cells via Deactivating the Mechanistic Target of Rapamycin Signaling

Understanding maternal immune tolerance is crucial for the development of therapeutics for immunological pregnancy complications. Decidual regulatory T cells (Tregs) play a pivotal role in the maintenance of maternal immune tolerance. Using a murine allogeneic pregnancy model in the current study, we identified the up-regulation of gonadotropin-releasing hormone receptor (GnRHR) in decidual T cell subsets including CD4(+) conventional T cells, CD8(+) T cells, and CD4(+)Foxp3(+) Tregs. Using a lentivirus-mediated GnRHR overexpression system and a GnRHR agonist, we found that GnRHR activation decreased the expression of Treg functional molecules such as IL10 (IL-10), IL-35 subunit EBI3 (Ebi3), IL2RA (CD25), TNFRSF18 (GITR), ICOS, and Treg master regulator FOXP3. The functional analysis indicated that GnRHR activation impairs the ability of Tregs to inhibit conventional T cell proliferation. We also revealed that GnRHR activation suppressed the mechanistic target of rapamycin (mTOR) signaling in GnRHR-overexpressing splenic Tregs (Wild type C57BL/6 J background) and decidual Tregs. MHY1485, a potent mTOR activator, effectively abolished the effect of the GnRHR agonist and promoted the immunosuppressive capability of Tregs. Furthermore, in an adoptive transfer model, Treg-specific GnRHR knockdown increased Foxp3 expression in decidual Tregs while decreasing the production of IFN-gamma and IL-17 in decidual effector CD4(+) T cells and reducing the production of IFN-gamma in decidual effector CD8(+) T cells. Taken together, the present study unveils a novel mechanism by which the immunosuppressive function of decidual Tregs is modulated, and deepens our understanding of maternal immune tolerance.