Role of GnRH–GnRH receptor signaling at the maternal-fetal interface

Role of gonadotropin-releasing hormone 2 and its receptor in human reproductive cancers

Gonadotropin-releasing hormone (GnRH1) and its receptor (GnRHR1) drive reproduction by regulating gonadotropins. Another form, GnRH2, and its receptor (GnRHR2), also exist in mammals. In humans, GnRH2 and GnRHR2 genes are present, but coding errors in the GnRHR2 gene are predicted to hinder full-length protein production. Nonetheless, mounting evidence supports the presence of a functional GnRHR2 in humans. GnRH2 and its receptor have been identified throughout the body, including peripheral reproductive tissues like the ovary, uterus, breast, and prostate. In addition, GnRH2 and its receptor have been detected in a wide number of reproductive cancer cells in humans. Notably, GnRH2 analogues have potent anti-proliferative, pro-apoptotic, and/or anti-metastatic effects on various reproductive cancers, including endometrial, breast, placental, ovarian, and prostate. Thus, GnRH2 is an emerging target to treat human reproductive cancers.

Paternal obesity induces epigenetic aberrations and gene expression changes in placenta and fetus

Paternal epigenome regulates placental and fetal growth. However, the effect of paternal obesity on placenta and its subsequent effect on the fetus via sperm remains unknown. We previously discovered abnormal methylation of imprinted genes involved in placental and fetal development in the spermatozoa of obese rats. In the present study, elaborate epigenetic characterization of sperm, placenta, and fetus was performed. For 16 weeks, male rats were fed either control or a high-fat diet. Following mating studies, sperm, placenta, and fetal tissue were collected. Significant changes were observed in placental weights, morphology, and cell populations. Methylation status of imprinted genes-Igf2, Peg3, Cdkn1c, and Gnas in spermatozoa, correlated with their expression in the placenta and fetus. Placental DNA methylating enzymes and 5-methylCytosine levels increased. Furthermore, in spermatozoa, DNA methylation of a few genes involved in pathways associated with placental endocrine function-gonadotropin-releasing hormone, prolactin, estrogen, and vascular endothelial growth factor, correlated with their expression in placenta and fetus. Changes in histone-modifying enzymes were also observed in the placenta. Histone marks H3K4me3, H3K9me3, and H4ac were downregulated, while H3K27me3 and H3ac were upregulated in placentas derived from obese male rats. This study shows that obesity-related changes in sperm methylome translate into abnormal expression in the F1-placenta fathered by the obese male, presumably affecting placental and fetal development.

How neuroactive factors mediates immune responses during pregnancy: An interdisciplinary view

Pregnancy, from insemination to parturition, is a highly complex but well-orchestrated process that requires various organs and systems to participate. Immune system and neuroendocrine system are important regulators in healthy pregnancy. Dozens of neuroactive factors have been detected in human placenta, whether they are locally secreted or circulated. Among them, some are vividly studied such as corticotropin-releasing hormone (CRH), human chorionic gonadotropin (hCG), transforming growth factor-β (TGF-β), progesterone and estrogens, while others are relatively lack of research. Though the neuroendocrine-immune interactions are demonstrated in some diseases for decades, the roles of neuroactive factors in immune system and lymphocytes during pregnancy are not fully elucidated. This review aims to provide an interdisciplinary view on how the neuroendocrine system mediate immune system during pregnancy process.

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-γ and IL-17 in decidual effector CD4⁺ T cells and reducing the production of IFN-γ 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.

No significant long-term complications from inadvertent exposure to gonadotropin-releasing hormone agonist during early pregnancy in mothers and offspring: a retrospective analysis

BACKGROUND

Administration of gonadotropin-releasing hormone agonist (GnRH-a) in the luteal phase is commonly used for pituitary suppression during in vitro fertilisation (IVF). There is an ineluctable risk of inadvertent exposure of spontaneous pregnancy to GnRH-a. However, little is known about the pregnancy complications and repregnancy outcomes of the affected women and the neurodevelopmental outcomes of the GnRH-a-exposed children.

METHODS

Retrospective analysis was used to determine obstetric and repregnancy outcomes after natural conception in 114 women who naturally conceived while receiving GnRH-a during their early pregnancy over the past 17 years. The GnRH-a-exposed children were evaluated to determine their neonatal characteristics and long-term neurodevelopmental outcomes. The outcomes were compared to those of relevant age-matched control groups.

RESULTS

Sixty-five women had 66 live births. The neonatal health outcomes and the incidence of maternal complications were similar in the GnRH-a-exposed and control groups. Thirty-one GnRH-a-exposed children, aged 2-8 years, were available for investigation of neurodevelopment. Except for one case of autism spectrum disorder, the full-scale intelligence quotient score was within the normal range and similar to that of the control group. Most mothers with successful pregnancies and about one-third of the women who had spontaneous abortions were subsequently able to conceive naturally again. IVF is recommended for repregnancy in women who have experienced ectopic pregnancies.

CONCLUSIONS

Accidental exposure to GnRH-a in early pregnancy might be safe. Reproductive treatment suggestions for repregnancy should be made with consideration of the outcomes of the previously GnRH-a-exposed spontaneous pregnancy.

Conditional loss of ERK1 and ERK2 results in abnormal placentation and delayed parturition in the mouse

Extracellular-signal-regulated kinases (ERK) 1 and 2 regulate many aspects of the hypothalamic-pituitary-gonadal axis. We sought to understand the role of ERK1/2 signaling in cells expressing a Cre allele regulated by the endogenous GnRHR promoter (GRIC-ERKdko). Adult female GRIC-ERKdko mice were hypogonadotropic and anovulatory. Gonadotropin administration and mating led to pregnancy in one-third of the ERKdko females. Litters from ERKdko females and pup weights were reduced coincident with delayed parturition and 100% neonatal mortality. Based on this, we examined Cre expression in implantation sites as a potential mechanism. GnRHR mRNA levels at e10.5 and e12.5 were comparable to pituitary levels from adult female mice at proestrus and GnRHR mRNA in decidua was enriched compared to whole implantation site. In vivo studies confirmed recombination in decidua, and GRIC-ERKdko placentas showed reduced ERK2 expression. Histopathology revealed abnormalities in placental architecture in the GRIC-ERKdko animals. Regions of apoptosis at the decidual/uterine interface at e18.5 were observed in control animals but apoptotic tone in these regions was reduced in ERKdko animals. These studies support a potential model of ERK-dependent signaling within the implantation site leading to loss of placental architecture and mis-regulation of apoptotic events at parturition occurring coincident with prolonged gestation and neonatal mortality.

Gonadotropin-releasing hormone and gonadotropin-releasing hormone receptor are expressed at tubal ectopic pregnancy implantation sites

OBJECTIVE

To investigate whether gonadotropin-releasing hormone (GnRH) and GnRH receptor (GnRHR) are expressed at tubal ectopic pregnancy sites, and to study the potential role of GnRH signaling in regulating immortalized human trophoblast cell viability.

DESIGN

Immunohistochemical and experimental studies.

SETTING

Academic research laboratory.

PATIENT(S)

Fallopian tube implantation sites (n = 25) were collected from women with ectopic pregnancy. First-trimester human placenta biopsies (n = 5) were obtained from elective terminations of pregnancy.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

GnRH and GnRHR expression was examined by means of immunohistochemistry and histoscoring. Trophoblastic BeWo choriocarcinoma and immortalized extravillous trophoblast (HTR-8/SVneo) cell viability was examined by means of cell counting after incubation with GnRH and/or GnRH antagonist (Antide).

RESULT(S)

GnRH and GnRHR immunoreactivity was detected in cytotrophoblast, syncytiotrophoblast, and extravillous trophoblast in all women with tubal pregnancy. GnRH immunoreactivity was higher and GnRHR immunoreactivity lower in syncytiotrophoblast compared with cytotrophoblast. GnRH and GnRHR immunoreactivity was detected in adjacent fallopian tube epithelium. Whereas neither GnRH nor Antide altered HTR-8/SVneo cell viability, treatment with GnRH significantly increased the overall cell viability of BeWo cells at 48 and 72 hours, and these effects were abolished by pretreatment with Antide.

CONCLUSION(S)

GnRH and GnRHR are expressed in trophoblast cell populations and fallopian tube epithelium at tubal ectopic pregnancy sites. GnRH increases BeWo cell viability, an effect mediated by the GnRHR. Further work is required to investigate the potential role of GnRH signaling in ectopic pregnancy.

Neuroendocrinology of pregnancy and parturition

During pregnancy, the maternal brain drives a series of adaptive mechanisms that are fundamental for allowing fetal growth and development, protecting both mother and fetus from adverse programming and timing of parturition. This neuroendocrine concept is even more complex as fetal brain and placenta also participate as regulators of maternal-placental-fetal physiology. The placenta is now seen as a neuroendocrine organ, acting as a source of several neuroactive factors that may exert their biologic effects either locally or by entering maternal and fetal circulation, thus acting in an autocrine, paracrine, and endocrine manner. A variety of hypothalamic neurohormones (GnRH, GHRH, somatostatin, CRH, oxytocin) are expressed in the placenta. When stress occurs during pregnancy, the maternal, fetal, and placental hypothalamic-pituitary-adrenal (HPA) axes are activated to stimulate a series of responses contributing to maintain physiologic conditions while at the same time avoiding the adverse effects of stress on the mother and offspring. However, when stress is excessive, a number of obstetric complications may occur, such as preterm birth, pre-eclampsia and intrauterine growth restriction, related to an impairment of the placental adaptive response.

Neuroendocrine aspects of placenta and pregnancy

Placenta plays a central role in the regulation of physiological mechanisms of pregnancy, and in particular is the organ of communication between mother and fetus. This action is also related to its ability to produce hormones, growth factors and cytokines during the progression of pregnancy, and in response to stimuli such as stress and inflammation/infection. In the last years the understanding of the physiological and pathological functions of human placenta revealed the hypersecretion of hormones in presence of gestational diseases and raised the question whether this mechanism is cause of disorders of pregnancy, or part of an adaptive response of placenta to resolve adverse conditions. However, there are evidences indicating that changes of placental hormone secretion may have clinical usefulness, since they are measurable in biological fluids, and may be used as predictive markers or prognostic tools. Of particular interest is the role of corticotropin releasing hormone, urocortins and activins in the maintaining physiological pregnancy and in the pathogenesis of diseases (preterm birth and preeclampsia).

Gonadotropin-releasing hormone/gonadotropin-releasing hormone receptor signaling in the placenta

PURPOSE OF REVIEW

This review summarizes our current understanding of the role of gonadotropin-releasing hormone (GnRH)/GnRH receptor (GnRHR) signaling at the maternal-fetal interface.

RECENT FINDINGS

Several isoforms of GnRH and GnRHR are described. The hypothalamic decapeptide, GnRH-I, binds to the anterior pituitary and induces the synthesis and secretion of luteinizing hormone and follicle-stimulating hormone. It is also found in extrahypothalamic sites. A second isoform, GnRH-II, acts both in the hypothalamus and other organ systems, including placenta, breast, endometrium, and ovary. Although several putative isoforms of GnRHR have been identified, it is clear that, in humans, both GnRH-I and GnRH-II signal through a single receptor, GnRHR-I. GnRH-I, GnRH-II, and GnRHR-I mRNA and protein have been identified in placenta and regulate the β-subunit of human chorionic gonadotropin production, which is essential for the maintenance of early pregnancy. They may also play a role in the autocrine/paracrine regulation of trophoblast invasion through extracellular matrix remodeling.

SUMMARY

GnRH-I and GnRH-II have multiple extrapituitary roles. In placenta, they bind to GnRHR-I to stimulate the production of β-subunit of human chorionic gonadotropin. They may also play a role in trophoblast invasion. A better understanding of the molecular mechanisms involved in GnRH/GnRHR signaling at the maternal-fetal interface may identify novel roles for GnRH agonists/antagonists in the prevention or treatment of hormonally mediated diseases.