Udo R. Markert

A pivotal role for galectin-1 in fetomaternal tolerance

A successful pregnancy requires synchronized adaptation of maternal immune-endocrine mechanisms to the fetus. Here we show that galectin-1 (Gal-1), an immunoregulatory glycan-binding protein, has a pivotal role in conferring fetomaternal tolerance. Consistently with a marked decrease in Gal-1 expression during failing pregnancies, Gal-1–deficient (Lgals1−/−) mice showed higher rates of fetal loss compared to wild-type mice in allogeneic matings, whereas fetal survival was unaffected in syngeneic matings. Treatment with recombinant Gal-1 prevented fetal loss and restored tolerance through multiple mechanisms, including the induction of tolerogenic dendritic cells, which in turn promoted the expansion of interleukin-10 (IL-10)–secreting regulatory T cells in vivo. Accordingly, Gal-1s protective effects were abrogated in mice depleted of regulatory T cells or deficient in IL-10. In addition, we provide evidence for synergy between Gal-1 and progesterone in the maintenance of pregnancy. Thus, Gal-1 is a pivotal regulator of fetomaternal tolerance that has potential therapeutic implications in threatened pregnancies.

Trophoblast invasion: the role of intracellular cytokine signalling via signal transducer and activator of transcription 3 (STAT3)

Trophoblast cells display a very unique capability: they physiologically invade into the surrounding tissue. This capability is widely associated with tumours, and, indeed, the invasive behaviour of both is rather similar. The imposing difference is that trophoblast cell invasion is temporally and locally controlled in contrast to unlimited tumour invasion. It initiates immediately after embryo implantation into the endometrium. Parallel to tumours, trophoblasts secrete proteases, such as matrix metalloproteinases, which dissolve the extracellular matrix and the surrounding tissue. Thereby, these proteases prepare and allow true invasion of trophoblasts. The invasive capacities of trophoblasts are positively and negatively regulated by numerous cytokines including leukaemia inhibitory factor (LIF), interleukin-6, hepatocyte growth factor, granulocyte macrophage-colony stimulating factor and others. They interact via specific receptors with the trophoblast cells, in which they activate intracellular signalling cascades. These will then induce expression of invasion relevant genes. One of these signalling pathways is the Janus kinase/signal transducers and activators of transcription (STAT) pathway. Especially phosphorylated STAT3 enhances invasiveness of tumours and trophoblast cells, where it is mainly activated by LIF. One of its most efficient physiological antagonists is suppressor of cytokine signalling 3. The balance of these two intracellular molecules seems to be a key regulator of tumour and trophoblast invasion.

MicroRNA expression profiles of trophoblastic cells.

BACKGROUND MicroRNAs (miRNAs) are small single-stranded RNA molecules working as post-transcriptional modulators of gene expression. Trophoblast cells are a heterogenous group of fetal cells forming the feto-maternal interface and displaying a wide spectrum of functions. The regulation of their behavior may partly underly the control through miRNAs. Therefore, we aimed to compare the miRNA profile of primary first and third trimester trophoblast cells with that of different trophoblastic cell lines. MATERIAL AND METHODS Total RNA was obtained from isolated cytotrophoblast cells from healthy term and first trimester placentae and the cell lines HTR-8/SVneo (immortalized trophoblast cells), JEG-3 (choriocarcinoma), ACH-3P and AC1-M59, which are choriocarcinoma cells fused with first and third trimester trophoblast cells, respectively. The expression level of 762 different miRNAs was quantitatively analyzed by using a TaqMan Human MicroRNA Array. For testing the reproducibility of the array technique, the expression of 9 selected miRNAs has been re-analyzed by individual qPCR. RESULTS The analyzed cell types share many similar patterns of miRNAs, but are significantly distinct in the expression of three miRNA clusters: chromosome 19 miRNA cluster (C19MC; containing 54 different miRNAs), C14MC (34 miRNAs) and a minor cluster (miRNA-371 to miRNA-373 cluster), also located on chromosome 19. Expression of miRNAs within C19MC increases significantly from first to third trimester trophoblast while that of C14MC members decreases. MiRNAs within the miR-371-3 cluster augment slightly. C19MC and the miR-371-3 cluster are not expressed by HTR-8/SVneo cells whilst C14MC is almost not detectable in the choriocarcinoma-derived cell lines complete array data available at NCBI Gene Expression Omnibus accession number GSE32346: http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE32346). Beside the miRNAs within the mentioned clusters, further 27 miRNAs are differentially expressed (>100 fold) between term and first trimester trophoblast cells. The placenta-specific miRNAs miR-141 and miR-21 as well as let-7g are expressed in all tested cells with the highest expression in primary trophoblast cells. CONCLUSION Primary first trimester and term trophoblast cells and trophoblastic cell lines display major differences in their miRNA fingerprints which may be involved in their different behavior and characteristics.

Pregnancy-associated miRNA-clusters

MicroRNAs (miRNAs) are expressed in the placenta and can be detected in maternal plasma. An increasing number of studies have been published on the cellular origin, distribution and function of miRNAs in pregnancy. Specific miRNA profiles have been described for the placenta, maternal plasma and several pregnancy disorders. It has been observed that numerous miRNAs, which are predominantly or exclusively expressed during pregnancy, are clustered in chromosomal regions, may be controlled by the same promoters, may have similar seed regions and targets, and work synergistically. The three most eminent clusters are the chromosome 19 miRNA cluster (C19MC), C14MC and miR-371-3 cluster, which is also localized on chromosome 19. MiRNA members of these clusters are not only detected in the placenta, but also in other compartments, e.g. in serum where they have the potential to become novel biomarkers of pregnancy disorders. Additionally, some members are also expressed in a variety of tumors. Antagonism of selected miRNAs or their targets may lead to novel strategies for the development of new drug classes in pregnancy disorders or other diseases. This review summarizes current knowledge on the pregnancy-related miRNA clusters - the C19MC, C14MC and miR-371-3 cluster - in regard to pregnancy and also other, mostly pathological circumstances.

MicroRNAs in pregnancy.

Since the discovery of non-coding RNAs, several families of small regulatory molecules have been described including small nucleolar RNAs, piwi-interacting RNAs and microRNAs (miRNAs). MiRNAs are small single-stranded RNA molecules which play an important role in the regulation of gene expression at the transcriptional level. Recent studies demonstrated that about 30% of human genes are regulated by miRNAs and their deregulation has been associated with malignancies and poor outcome. Therefore, it is not surprising that profiling of miRNAs expression and studies on their regulation became a great field of interest in the last decade. However, miRNA-mediated regulation in pregnancy remains poorly investigated although several independent processes associated with placenta development have been shown to be miRNA-regulated. This review provides a general overview of the current data on profiles and functions of microRNAs in the peri-implantation period, embryonic stem cells, placentation and pregnancy, as well as in several pregnancy-related pathologies. We conclude that miRNAs present in the maternal circulation may provide a new promising diagnostic tool for pregnancy disorders.

Placental Trophoblast from Successful Human Pregnancies Expresses the Tolerance Signaling Molecule, CD200 (OX-2)*

Problem: Th1 cytokine‐dependent abortions in the CBA × DBA/2 mouse model have been linked to down‐regulation of expression of the CD200 (OX‐2) ‘tolerance’ signal on trophoblast and in decidua prior to onset of the abortion process. Abortions could be prevented by administration of a soluble CD200. Is CD200 expressed on trophoblast in successful human pregnancy?

Signal Transduction in Trophoblast Invasion

During the first trimester of pregnancy, well-differentiated primary cells of the placenta known as trophoblast cells grow in an invasive and destructive fashion similar to malignancies, but limited in space and time. The comparison of trophoblast cells with their malignant counterpart, human choriocarcinoma cells, offers an attractive model to understand the origin or development of malignant growth. Several cytokines and growth factors are known to influence trophoblast migration (e.g. EGF, IGF-2, HGF), proliferation (e.g. leptin, HGF, GM-CSF) and/or invasion (e.g. leukemia inhibitory factor, LIF), each factor utilizing at least one pathway for intracellular signaling in the trophoblast. Two pathways that are crossed especially often mediate the signals of these factors and are simultaneously well established in terms of tumor invasion: the Janus kinase-signal transducers and activators of transcription (Jak-Stat) and receptor-associated tyrosine kinase-mitogen-activated protein kinase (RTK-MAPK) pathways. These two pathways are detrimental for reproduction in general, and in part for placenta development, as a series of knockout experiments demonstrate. Aspects of each pathway are also implicated to be involved in trophoblast invasion, e.g. STAT3 is constitutively activated in invasive first trimester trophoblast cells, and activated ERK is detectable in intermediate trophoblast cells, an invasive phenotype. Interaction at several intersection points between the pathways has been described in several cell systems so that the same would seem to be possible in trophoblast cells. In this review, some of the possible areas of interaction are alluded to.

mTOR mediates human trophoblast invasion through regulation of matrix-remodeling enzymes and is associated with serine phosphorylation of STAT3

The intracellular signaling molecule mammalian target of rapamycin (mTOR) is essential for cell growth and proliferation. It is involved in mouse embryogenesis, murine trophoblast outgrowth and linked to tumor cell invasiveness. In order to assess the role of mTOR in human trophoblast invasion we analyzed the in vitro invasiveness of HTR-8/SVneo immortalized first-trimester trophoblast cells in conjunction with enzyme secretion upon mTOR inhibition and knockdown of mTOR protein expression. Additionally, we also tested the capability of mTOR to trigger signal transducer and activator of transcription (STAT)-3 by its phosphorylation status. Rapamycin inhibited mTOR kinase activity as demonstrated with a lower phosphorylation level of the mTOR substrate p70 S6 kinase (S6K). With the use of rapamycin and siRNA-mediated mTOR knockdown we could show that cell proliferation, invasion and secretion of matrix-metalloproteinases (MMP)-2 and -9, urokinase-like plasminogen activator (uPA) and its major physiological uPA inhibitor (PAI)-1 were inhibited. While tyrosine phosphorylation of STAT3 was unaffected by mTOR inhibition and knockdown, serine phosphorylation was diminished. We conclude that mTOR signaling is one major mechanism in a tightly regulated network of intracellular signal pathways including the JAK/STAT system to regulate invasion in human trophoblast cells by secretion of enzymes that remodel the extra-cellular matrix (ECM) such as MMP-2, -9, uPA and PAI-1. Dysregulation of mTOR may contribute to pregnancy-related pathologies caused through impaired trophoblast invasion.

Evidence for a Correlation between Trophoblast Invasiveness and STAT3 Activity

Problem: Extravillous trophoblast cells are capable of invading decidual tissue during early pregnancy. This property is reminiscent of cancer cells. The invasiveness of trophoblasts, however, extends only to a well‐regulated limit. Signal transduction processes underlying this phenomenon are as yet poorly characterized. Many factors involved in trophoblast invasiveness are known to trigger intracellular signaling cascades in other cell types that ultimately lead to the activation of signal transducers and activators of transcription (STATs). STAT3 activity was recently found related to the malignant phenotype of different tumor cells and potentially contributes to their invasive properties.

Governing the invasive trophoblast: current aspects on intra- and extracellular regulation.

Citation Fitzgerald JS, Germeyer A, Huppertz B, Jeschke U, Knöfler M, Moser G, Scholz C, Sonderegger S, Toth B, Markert UR. Governing the invasive trophoblast: current aspects on intra‐ and extracellular regulation. Am J Reprod Immunol 2010