Trophoblasts regulate natural killer cells via control of interleukin-15 receptor signaling

Research progress on the STAT signaling pathway in pregnancy and pregnancy-associated disorders

Signal transducer and activator of transcription (STAT) proteins, pivotal regulators of signaling cascades, undergo activation in response to the stimulation of cytokines and growth factors, and participate in biological processes, including inflammation, immune responses, cell proliferation, and differentiation. During the process of pregnancy, STAT signaling is involved in regulating embryonic implantation, endometrial decidualization, and establishing and maintaining maternal-fetal immune tolerance. Increasing evidence suggests that aberrant STAT signaling contributes to the occurrence and development of pregnancy disorders, including repeated implantation failure (RIF), preeclampsia (PE), recurrent spontaneous abortion (RSA), preterm birth (PTB) and gestational diabetes mellitus (GDM). Elucidating the molecular mechanisms of the STAT signaling pathway holds promise for further understanding the establishment and maintenance of normal pregnancy, and thereby providing potent targets and strategic avenues for the prevention and management of ailments associated with pregnancy. In this review, we summarized the roles of the STAT signaling pathway and its related regulatory function in embryonic implantation, endometrial decidualization, and maternal-fetal immune tolerance. In conclusion, in-depth research on the mechanism of the STAT signaling pathway not only enhances our understanding of normal pregnancy processes but also offers STAT-based therapeutic approaches to protect women from the burden of pregnancy-related disorders.

Natural Killer Cell Derived Microvesicles Affect the Function of Trophoblast Cells

The interaction of natural killer (NK) and trophoblast cells underlies the formation of immune tolerance in the mother-fetus system and the maintenance of the physiological course of pregnancy. In addition, NK cells affect the function of trophoblast cells, interacting with them via the receptor apparatus and through the production of cytokines. Microvesicles (MVs) derived from NK cells are able to change the function of target cells. However, in the overall pattern of interactions between NK cells and trophoblasts, the possibility that both can transmit signals to each other via MVs has not been taken into account. Therefore, the aim of this study was to assess the effect of NK cell-derived MVs on the phenotype, proliferation, and migration of trophoblast cells and their expression of intracellular messengers. We carried out assays for the detection of content transferred from MV to trophoblasts. We found that NK cell-derived MVs did not affect the expression of CD54, CD105, CD126, CD130, CD181, CD119, and CD120a receptors in trophoblast cells or lead to the appearance of CD45 and CD56 receptors in the trophoblast membrane. Further, the MVs reduced the proliferation but increased the migration of trophoblasts with no changes to their viability. Incubation of trophoblast cells in the presence of MVs resulted in the activation of STAT3 via pSTAT3(Ser727) but not via pSTAT3(Tyr705). The treatment of trophoblasts with MVs did not result in the phosphorylation of STAT1 and ERK1/2. The obtained data indicate that NK cell-derived MVs influence the function of trophoblast cells, which is accompanied by the activation of STAT3 signaling.

NK-92 cells change their phenotype and function when cocultured with IL-15, IL-18 and trophoblast cells

NK cell development is affected by their cellular microenvironment and cytokines, including IL-15 and IL-18. NK cells can differentiate in secondary lymphoid organs, liver and within the uterus in close contact with trophoblast cells. The aim was to evaluate changes in the NK cell phenotype and function in the presence of IL-15, IL-18 and JEG-3, a trophoblast cell line. When cocultured with JEG-3 cells, IL-15 caused an increase in the number of NKG2D+ NK-92 cells and the intensity of CD127 expression. IL-18 stimulates an increase in the amount of NKp44+ NK-92 cells and in the intensity of NKp44 expression by pNK in the presence of trophoblast cells. NK-92 cell cytotoxic activity against JEG-3 cells increased only in presence of IL-18. Data on changes in the cytotoxic activity of NK-92 cells against JEG-3 cells in the presence of IL-15 and IL-18 indicate the modulation of NK cell function both by the cytokine microenvironment and directly by target cells. IL-15 and IL-18 were present in conditioned media (CM) from 1st and 3rd trimester placentas. In the presence of 1st trimester CM and JEG-3 cells, NK-92 cells showed an increase in the intensity of NKG2D expression. In the presence of 3rd trimester CM and JEG-3 cells, a decrease in the expression of NKG2D by NK-92 cells was observed. Thus, culturing of NK-92 cells with JEG-3 trophoblast cells stimulated a pronounced change in the NK cell phenotype, bringing it closer to the decidual NK cell-like phenotype.

MiR-519d-3p in Trophoblastic Cells: Effects, Targets and Transfer to Allogeneic Immune Cells via Extracellular Vesicles

Members of the placenta-specific miRNA cluster C19MC, including miR-519d, are secreted by fetal trophoblast cells within extracellular vesicles (EVs). Trophoblast-derived EVs can be internalized by the autologous trophoblast and surrounding maternal immune cells, resulting in coordination of cellular responses. The study of functions and targets of placental miRNAs in the donor and recipient cells may contribute to the understanding of the immune tolerance essential in pregnancy. Here, we report that miR-519d-3p levels correlate positively with cell proliferation and negatively with migration in trophoblastic cell lines. Inhibition of miR-519d-3p in JEG-3 cells increases caspase-3 activation and apoptosis. PDCD4 and PTEN are targeted by miR-519d-3p in a cell type-specific manner. Transfection of trophoblastic cell lines with miR-519d mimic results in secretion of EVs containing elevated levels of this miRNA (EV_miR-519d). Autologous cells enhance their proliferation and decrease their migration ability when treated with EV_miR-519d. NK92 cells incorporate EV-delivered miR-519d-3p at higher levels than Jurkat T cells. EV_miR-519d increases the proliferation of Jurkat T cells but decreases that of NK92 cells. Altogether, miR-519d-3p regulates pivotal trophoblast cell functions, can be transferred horizontally via EVs to maternal immune cells and exerts functions therein. Vesicular miRNA transfer from fetal trophoblasts to maternal immune cells may contribute to the immune tolerance in pregnancy.

Innate Immune Cells and Toll-like Receptor-Dependent Responses at the Maternal-Fetal Interface

During pregnancy, the placenta, the mother and the fetus exploit several mechanisms in order to avoid fetal rejection and to maintain an immunotolerant environment throughout nine months. During this time, immune cells from the fetal and maternal compartments interact to provide an adequate defense in case of an infection and to promote a tolerogenic milieu for the fetus to develop peacefully. Trophoblasts and decidual cells, together with resident natural killer cells, dendritic cells, Hofbauer cells and other macrophages, among other cell types, contribute to the modulation of the uterine environment to sustain a successful pregnancy. In this review, the authors outlined some of the various roles that the innate immune system plays at the maternal-fetal interface. First, the cell populations that are recruited into gestational tissues and their immune mechanisms were examined. In the second part, the Toll-like receptor (TLR)-dependent immune responses at the maternal-fetal interface was summarized, in terms of their specific cytokine/chemokine/antimicrobial peptide expression profiles throughout pregnancy.

Changes in expression of Ki-67, CD16 and CD56 by natural killer cells from peripheral blood mononuclear cells in the setting of recurrent miscarriage after in vitro culturing in the presence of trophoblast cells and IL-2

The aim of this research was to assess the proliferative activity of Natural Killer Cells (NK cells) from Peripheral Blood Mononuclear Cells (PBMCs) in the presence of trophoblast cells in women with a history of recurrent miscarriages. We examined the peripheral blood of women with recurrent miscarriage in the proliferative (n = 12) or secretory (n = 13) phase of their menstrual cycle, and pregnant women with a history of recurrent miscarriage at 6-7 weeks of their current pregnancy (n = 14). Controls were fertile non-pregnant women in the proliferative (n = 11) or secretory (n = 13) phase of their menstrual cycle, and pregnant women at 6-7 weeks of a physiologically normal pregnancy (n = 20). We used IL-2 as a factor maintaining PBMCs viability during long-term culturing. We established that culturing in the presence of IL-2 contributed to an increase in the number of CD56+CD16- NK cells and to a decrease in the number of CD56+CD16+ NK cells from PBMCs compared with these numbers before culturing in both healthy women and in women with recurrent miscarriage. After culturing of PBMCs in the presence of trophoblast cells and IL-2 (compared with culturing without trophoblast cells), the intensity of Ki-67 expression by NK cells was reduced in the whole NK cell population (CD3-CD56+), and in the CD56+CD16- and CD56+CD16+ populations of NK cells in women with recurrent miscarriage and in healthy controls. The intensity of CD56 expression was reduced in the presence of trophoblast cells and IL-2 in non-pregnant women with recurrent miscarriage in the secretory versus the proliferative phase of the menstrual cycle.

Interaction of NK Cells, Trophoblast, and Endothelial Cells during Angiogenesis

We studied changes in angiogenesis during contact interaction of natural killer cells and endothelial cells in the presence of secretory products of trophoblast cells activated by various cytokines. Activated trophoblast regulates angiogenesis by producing soluble factors that affect endothelial cells either directly or indirectly through activation of proangiogenic activity of natural killer cells. A stimulating effect of the trophoblast supernatants activated by IL-1β and an inhibitory effect of trophoblast supernatants activated by IL-6 and TGFβ for the formation of tube-like structures by endothelial cells were revealed. During contact culturing, natural killer cells increased the length of tube-like structures formed by endothelial cells. The trophoblast activated by IL-1β affects angiogenesis both directly through the production of proangiogenic factors and indirectly through activation of the proangiogenic potential of natural killer cells. Trophoblast activated by IFNγ affects angiogenesis only by stimulating the proangiogenic potential of natural killer cells. Under conditions of contact interaction of natural killer cells and endothelial cells, soluble factors of trophoblast activated by IL-6 or TGFβ attenuated the angiogenesis-stimulating effect of natural killer cells.