Extracellular Vesicle-Mediated Secretion of HLA-E by Trophoblasts Maintains Pregnancy by Regulating the Metabolism of Decidual NK Cells

Extracellular vesicles derived from trophoblasts (T-EVs) play an important role in pregnancy, but the mechanism is not entirely clear. In this study, we found that HLA-E, which is mostly confined to the cytoplasm of trophoblast cells, was secreted by T-EVs. The level of HLA-E in T-EVs from unexplained recurrent spontaneous abortion (URSA) patients was lower than that in normal pregnancy (NP) and RSA patients who had an abnormal embryo karyotype (AK-RSA). T-EVs promoted secretion of IFN-gamma and VEGF alpha by decidual NK (dNK) cells from URSA patients via HLA-E, VEGF alpha was necessary for angiogenesis and trophoblast growth, and IFN-gamma inhibited Th17 induction. Glycolysis and oxidative phosphorylation (OxPhos) were involved in this process. Glycolysis but not OxPhos of dNK cells facilitated by T-EVs was dependent on mTORC1 activation. Inhibition of T-EV production in vivo increased the susceptibility of mice to embryo absorption, which was reversed by transferring exogenous Qa-1(+)T-EVs. T-EVs promoted secretion of IFN-gamma and VEGF alpha by dNK cells to maintain pregnancy via Qa-1 in abortion-prone mouse models. This study reveals a new mechanism of pregnancy maintenance mediated by HLA-E via T-EVs.