Estradiol Suppresses TLR4-triggered Apoptosis of Decidual Stromal Cells and Drives an Anti-inflammatory TH2 Shift by Activating SGK1

A pro-inflammatory cytokine profile at the feto-maternal interface may predispose immune maladaptation notably in early miscarriages. We investigated the involvement of estradiol (E-2)-activated serum-glucocorticoid regulated kinase 1 (SGK1) in preserving the tolerogenic and pro-survival intrauterine microenvironment beneficial to gestation maintenance. Decidual SGK1 was down-regulated in early miscarriage, consistent with the lower serum E-2 concentration seen in pregnancy loss. Lipopolysaccharide (LPS)/Toll-like receptors 4 (TLR4) signaling induced apoptosis and the pro-inflammatory T helper type (T-H) 1 response of decidual stromal cells (DSCs) were associated with miscarriage. SGK1 activation was suppressed by LPS/TLR4 signaling and would be rescued by E-2 administration via the PI3K signaling pathway in DSCs. SGK1 activation attenuated TLR4-mediated cell apoptosis, while promoting cell viability of DSCs by up-regulating the pro-survival genes BCL2 and XIAP, and enhancing the phosphorylation of FOXO1. Furthermore, E-2-induced SGK1 activation reduced the secretion of pro-inflammatory T(H)1 cytokines, and promoted the generation of T(H)2 cytokines and elevated IRF4 mRNA and protein levels in LPS-incubated DSCs. Pharmacologic inhibition of SGK1 or suppression by small interfering (si) RNA increased the phosphorylation and nuclear translocation of NF-.B to reverse the pro-T(H)2 and anti-inflammatory effects of E-2 pretreatment, leading to compromised pregnancy. These findings suggest that the E-2-mediated SGK1 activation suppressed LPS-mediated apoptosis and promoted the anti-inflammatory T(H)2 responses in DSCs, ultimately contributing to a successful pregnancy.