Peroxisome proliferator-activated receptors and retinoid X receptor-alpha in term human gestational tissues: tissue specific and labour-associated changes

Homeobox genes in the human placenta: Twists and turns on the path to find novel targets

Fetal growth restriction (FGR) is a clinically important human pregnancy disorder that is thought to originate early in pregnancy and while its aetiology is not well understood, the disorder is associated with placental insufficiency. Currently treatment for FGR is limited by increased surveillance using ultrasound monitoring and premature delivery, or corticosteroid medication in the third trimester to prolong pregnancy. There is a pressing need for novel strategies to detect and treat FGR at its early stage. Homeobox genes are well established as master regulators of early embryonic development and increasing evidence suggests they are also important in regulating early placental development. Most important is that specific homeobox genes are abnormally expressed in human FGR. This review focusses on identifying the molecular pathways controlled by homeobox genes in the normal and FGR-affected placenta. This information will begin to address the knowledge gap in the molecular aetiology of FGR and lay the foundation for identifying potential diagnostic and therapeutic targets.

Role of Transcription Factors in the Management of Preterm Birth: Impact on Future Treatment Strategies

Preterm birth is defined as the birth of a neonate before 37 weeks of gestation and is considered as a leading cause of the under five deaths of neonates. Neonates born preterm are known to have higher perinatal mortality and morbidity with associated risks of low birth weight, respiratory distress syndrome, gastrointestinal, immunologic, central nervous system, hearing, and vision problems, cerebral palsy, and delayed development. India leads the list of countries with the greatest number of preterm births. The studies focusing on the molecular mechanisms related to the etiology of preterm birth have described the role of different transcription factors. With respect to this, transcription factors like peroxisome proliferator activated receptors (PPAR), nuclear factor kappa β (NF-kβ), nuclear erythroid 2-related factor 2 (Nrf2), and progesterone receptor (PR) are known to be associated with preterm labor. All these transcription factors are linked together with a common cascade involving inflammatory processes. Thus, the current review describes the possible cross-talk between these transcription factors and their therapeutic potential to prevent or manage preterm labor.

NURR1 Alterations in Perinatal Stress: A First Step towards Late-Onset Diseases? A Narrative Review

Perinatal life represents a delicate phase of development where stimuli of all sorts, coming to or from the mother, can influence the programming of the future baby's health. These stimuli may have consequences that persist throughout adulthood. Nuclear receptor related 1 protein (NURR1), a transcription factor with a critical role in the development of the dopaminergic neurons in the midbrain, mediates the response to stressful environmental stimuli in the perinatal period. During pregnancy, low-grade inflammation triggered by maternal obesity, hyperinsulinemia or vaginal infections alters NURR1 expression in human gestational tissues. A similar scenario is triggered by exposure to neurotoxic compounds, which are associated with NURR1 epigenetic deregulation in the offspring, with potential intergenerational effects. Since these alterations have been associated with an increased risk of developing late-onset diseases in children, NURR1, alone, or in combination with other molecular markers, has been proposed as a new prognostic tool and a potential therapeutic target for several pathological conditions. This narrative review describes perinatal stress associated with NURR1 gene deregulation, which is proposed here as a mediator of late-onset consequences of early life events.

Rosiglitazone augments antioxidant response in the human trophoblast and prevents apoptosis†

Insufficient perfusion of the trophoblast by maternal blood is associated with an increased generation of reactive oxygen species and complications of the placenta. In this study, we first examined whether rosiglitazone, an agonist of the peroxisome proliferator-activated receptor-γ (PPARγ), protects the human trophoblast from oxidative injury by regulating key antioxidant proteins, catalase (CAT) and the superoxide dismutases (SOD1 and SOD2). In first trimester placental explants, localization of CAT was limited to cytotrophoblasts, whereas SOD1 was expressed in both the cyto- and syncytiotrophoblasts. In first trimester placental explants, hypoxia decreased the expression of both SOD1 and SOD2, and increased apoptosis. Treatment with rosiglitazone dose-dependently upregulated anti-oxidative CAT and SOD2, and rescued hypoxic injury in first trimester villous explants and JEG-3 cells, strongly suggesting the involvement of the PPARγ in regulating their expressions. Rosiglitazone facilitated transcription activity of PPARγ, and enhanced promotor binding, increased transcriptional activity at the CAT promoter, and elevated protein expression/activity. Treatment of hypoxic JEG-3 cells with rosiglitazone resulted in mitochondrial membrane potential increase and a reduction of caspase 9 and caspase 3 activity which is consistent with improved cell survival. To complement PPARγ activation data, we also utilized the antagonist (SR-202) and siRNA to suppress PPARγ expression and demonstrate the specific role of PPARγ in reducing ROS and oxidative stress. Ex vivo examination of term human placenta revealed lower expression of antioxidant proteins in pathologic compared to healthy placental tissues, which could be rescued by rosiglitazone, indicating that rosiglitazone can improve survival of the trophoblast under pathological conditions. These findings provide evidence that the PPARγ pathway directly influences cellular antioxidants production and the pathophysiology of placental oxidative stress.

Effect of spontaneous term labour on the expression of the NR4A receptors nuclear receptor related 1 protein (Nurr1), neuron-derived clone 77 (Nur77) and neuron-derived orphan receptor 1 (NOR1) in human fetal membranes and myometrium

Inflammation has been implicated in the mechanisms responsible for human labour. Emerging evidence indicates that nuclear receptor subfamily 4A (NR4A) receptors regulate the transcription of genes involved in inflammation. The aim of the present study was to determine the effect of spontaneous term labour, Toll-like receptor (TLR) ligands and nucleotide-binding oligomerisation domain-containing (NOD) ligands on the expression of nuclear receptor related 1 protein (Nurr1), neuron-derived clone 77 (Nur77) and neuron-derived orphan receptor 1 (NOR1) in human fetal membranes and myometrium. Human fetal membranes and myometrium were collected from term non-labouring women and women after spontaneous labour onset. Tissue explants were used to determine the effect of the bacterial products lipopolysaccharide (LPS; TLR4 ligand), flagellin (TLR5 ligand), fibroblast-stimulating lipopeptide (FSL-1) (TLR2 ligand), γ-D-glutamyl-meso-diaminopimelic acid (iE-DAP) (NOD1 ligand) or minimal peptidoglycan muramyl dipeptide (MDP; NOD2 ligand) on Nurr1, Nur77 and NOR1 expression. Term labour was associated with significantly higher Nurr1 and Nur77, but not NOR1, expression in fetal membranes and myometrium. LPS and MDP increased Nurr1, Nur77 and NOR in fetal membranes; flagellin increased Nurr1 in fetal membranes and the myometrium, as well as NOR1 in the myometrium; and FSL-1 increased Nurr1 expression in fetal membranes. In summary, human labour and bacterial products increase Nurr1, Nur77 and/or NOR1 expression in human fetal membranes and myometrium. This increase in NR4A receptors may contribute to the expression of proinflammatory and pro-labour genes associated with fetal membrane rupture and myometrial contractions.

Nuclear retinoid receptors and pregnancy: placental transfer, functions, and pharmacological aspects

Animal models of vitamin A (retinol) deficiency have highlighted its crucial role in reproduction and placentation, whereas an excess of retinoids (structurally or functionally related entities) can cause toxic and teratogenic effects in the embryo and foetus, especially in the first trimester of human pregnancy. Knock-out experimental strategies-targeting retinoid nuclear receptors RARs and RXRs have confirmed that the effects of vitamin A are mediated by retinoic acid (especially all-trans retinoic acid) and that this vitamin is essential for the developmental process. All these data show that the vitamin A pathway and metabolism are as important for the well-being of the foetus, as they are for that of the adult. Accordingly, during this last decade, extensive research on retinoid metabolism has yielded detailed knowledge on all the actors in this pathway, spurring the development of antagonists and agonists for therapeutic and research applications. Natural and synthetic retinoids are currently used in clinical practice, most often on the skin for the treatment of acne, and as anti-oncogenic agents in acute promyelocytic leukaemia. However, because of the toxicity and teratogenicity of retinoids during pregnancy, their pharmacological use needs a sound knowledge of their metabolism, molecular aspects, placental transfer, and action.

Expression of 15-Hydroxyprostaglandin Dehydrogenase in Human Chorion Is Associated with Peroxisome Proliferator-Activated Receptor Isoform Expression in Term Labor

Chorionic NAD-dependent 15-hydroxy prostaglandin dehydrogenase (PGDH) plays a pivotal role in controlling the amount of prostaglandins in the uterus. Peroxisome proliferator-activated receptors (PPARs) are implicated to be involved in parturition. In this study, we investigated whether PPARs are involved in control of PGDH expression in chorion. The chorionic tissues were collected from the following groups of the women with singleton pregnancy: term no labor (TNL), term labor (TL) and preterm labor (PTL). Chorionic trophoblasts were isolated and cultured in vitro. Immunocytochemistry analysis showed that PPARα, PPARβ, and PPARγ were localized to trophoblasts in chorion. The protein levels of PGDH, PPARβ, and PPARγ were localized to trophoblasts in chorion. The protein levels of PPARα, PPARβ, and PPARγ were reduced in TL tissues compared to that of TNL group. PPARα, PPARβ, and PPARγ expression correlated to PGDH in TNL tissues, whereas only PPARγ expression correlated to PGDH in TL chorion tissues. PGDH expression was decreased in PTL tissues compared with TL group, whereas the expression of PPARs was not significantly different between TL and PTL groups. The agonists of three PPARs dose-dependently stimulated PGDH activity, mRNA, and protein expression in cultured chorionic cells. PPARs did not affect the stability of PGDH mRNA but stimulated the transcriptional activity of HPGD gene. Our results suggest that PPARs play pivotal roles in maintenance of PGDH expression in chorion during human pregnancy.

An M1-like Macrophage Polarization in Decidual Tissue during Spontaneous Preterm Labor That Is Attenuated by Rosiglitazone Treatment

Decidual macrophages are implicated in the local inflammatory response that accompanies spontaneous preterm labor/birth; however, their role is poorly understood. We hypothesized that decidual macrophages undergo a proinflammatory (M1) polarization during spontaneous preterm labor and that PPARγ activation via rosiglitazone (RSG) would attenuate the macrophage-mediated inflammatory response, preventing preterm birth. In this study, we show that: 1) decidual macrophages undergo an M1-like polarization during spontaneous term and preterm labor; 2) anti-inflammatory (M2)-like macrophages are more abundant than M1-like macrophages in decidual tissue; 3) decidual M2-like macrophages are reduced in preterm pregnancies compared with term pregnancies, regardless of the presence of labor; 4) decidual macrophages express high levels of TNF and IL-12 but low levels of peroxisome proliferator-activated receptor γ (PPARγ) during spontaneous preterm labor; 5) decidual macrophages from women who underwent spontaneous preterm labor display plasticity by M1↔M2 polarization in vitro; 6) incubation with RSG reduces the expression of TNF and IL-12 in decidual macrophages from women who underwent spontaneous preterm labor; and 7) treatment with RSG reduces the rate of LPS-induced preterm birth and improves neonatal outcomes by reducing the systemic proinflammatory response and downregulating mRNA and protein expression of NF-κB, TNF, and IL-10 in decidual and myometrial macrophages in C57BL/6J mice. In summary, we demonstrated that decidual M1-like macrophages are associated with spontaneous preterm labor and that PPARγ activation via RSG can attenuate the macrophage-mediated proinflammatory response, preventing preterm birth and improving neonatal outcomes. These findings suggest that the PPARγ pathway is a new molecular target for future preventative strategies for spontaneous preterm labor/birth.

Labor inhibits placental mechanistic target of rapamycin complex 1 signaling

INTRODUCTION

Labor induces a myriad of changes in placental gene expression. These changes may represent a physiological adaptation inhibiting placental cellular processes associated with a high demand for oxygen and energy (e.g., protein synthesis and active transport) thereby promoting oxygen and glucose transfer to the fetus. We hypothesized that mechanistic target of rapamycin complex 1 (mTORC1) signaling, a positive regulator of trophoblast protein synthesis and amino acid transport, is inhibited by labor.

METHODS

Placental tissue was collected from healthy, term pregnancies (n = 15 no-labor; n = 12 labor). Activation of Caspase-1, IRS1/Akt, STAT, mTOR, and inflammatory signaling pathways was determined by Western blot. NFĸB p65 and PPARγ DNA binding activity was measured in isolated nuclei.

RESULTS

Labor increased Caspase-1 activation and mTOR complex 2 signaling, as measured by phosphorylation of Akt (S473). However, mTORC1 signaling was inhibited in response to labor as evidenced by decreased phosphorylation of mTOR (S2448) and 4EBP1 (T37/46 and T70). Labor also decreased NFĸB and PPARγ DNA binding activity, while having no effect on IRS1 or STAT signaling pathway.

DISCUSSION AND CONCLUSION

Several placental signaling pathways are affected by labor, which has implications for experimental design in studies of placental signaling. Inhibition of placental mTORC1 signaling in response to labor may serve to down-regulate protein synthesis and amino acid transport, processes that account for a large share of placental oxygen and glucose consumption. We speculate that this response preserves glucose and oxygen for transfer to the fetus during the stressful events of labor.

Fine-mapping an association of FSHR with preterm birth in a Finnish population

Preterm birth is a complex disorder defined by gestations of less than 37 weeks. While preterm birth is estimated to have a significant genetic component, relative few genes have been associated with preterm birth. Polymorphism in one such gene, follicle-stimulating hormone receptor (FSHR), has been associated with preterm birth in Finnish and African American mothers but not other populations. To refine the genetic association of FSHR with preterm birth we conducted a fine-mapping study at the FSHR locus in a Finnish cohort. We sequenced a total of 44 kb, including protein-coding and conserved non-coding regions, in 127 preterm and 135 term mothers. Overall, we identified 288 single nucleotide variants and 65 insertion/deletions of 1-2 bp across all subjects. While no common SNPs in protein-coding regions were associated with preterm birth, including one previously associated with timing of fertilization, multiple SNPs spanning the first and second intron showed the strongest associations. Analysis of the associated SNPs revealed that they form both a protective (OR = 0.50, 95% CI = 0.25-0.93) as well as a risk (OR = 1.89, 95% CI = 1.08-3.39) haplotype with independent effects. In these haplotypes, two SNPs, rs12052281 and rs72822025, were predicted to disrupt ZEB1 and ELF3 transcription factor binding sites, respectively. Our results show that multiple haplotypes at FSHR are associated with preterm birth and we discuss the frequency and structure of these haplotypes outside of the Finnish population as a potential explanation for the absence of FSHR associations in some populations.

The effect of omega-3 polyunsaturated fatty acids on the inflammatory response of the amnion

OBJECTIVE

To investigate the effect of omega-3 PUFAs, eicosapentanoic acid (EPA) and docosohexanoic acid (DHA) on inflammatory cytokine production in the amnion.

STUDY DESIGN

Amnion explants were obtained at elective caesarean sections and cultured in vitro with EPA and DHA. IL-8 and IL-6 secretion was determined by ELISA, the role of PPARγ was investigated using specific agonists and antagonists and activity of MMP assessed by gelatin zymography.

RESULTS

A combination of EPA and DHA significantly reduced the concentration of IL-8 and IL-6 released into the supernatant compared to untreated controls (p<0.001). Stimulation of PPARγ with troglitazone reduced IL-8 production, and the PPARγ antagonist GW9662 partially reversed this effect. The activity of MMP-9 was also significantly reduced by treatment with EPA and DHA in combination compared to untreated control (p<0.05).

CONCLUSION

The omega-3 PUFAs EPA and DHA decrease the inflammatory response of the amnion, and this may be partially mediated through PPARγ.

PLAC1 Expression Decreases in Chorionic Villi in Response to Labor

PLAC1 (Placenta-Specific 1) is a recently described, trophoblast-expressed gene essential for normal placental development. The protein localizes to the microvillus membrane surface of the syncytiotrophoblast in direct proximity to the maternal compartment. Although its role has not been defined, increased circulating levels of human PLAC1 mRNA in maternal blood are associated with preeclampsia. Furthermore, PLAC1-null mice exhibit decreased viability in the peripartum period suggesting a role in pregnancy maintenance late in gestation. We examined PLAC1 gene expression in the human placenta during normal pregnancy and pregnancies associated with maternal diabetes and preeclampsia using quantitative, real time PCR (q-RT-PCR). Although there was no apparent difference in PLAC1 gene expression among human pregnancies complicated by diabetes or preeclampsia, an unexpected effect of labor was noted at term. PLAC1 expression in placentae delivered vaginally following induced or spontaneous labor was significantly reduced compared to placentae not exposed to labor making it one of only a few placental genes influenced by labor. The significance of this finding is unknown. Viewed in the context of its importance in placental development, however, these findings are consistent with a role for PLAC1 in the maintenance of the maternal-fetal interface.

Homeobox genes and down-stream transcription factor PPARγ in normal and pathological human placental development

The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface is controlled by nuclear transcription factors including homeobox genes. Here we summarize current knowledge regarding the expression and function of homeobox genes in the placenta. We also describe the identification of target transcription factors including PPARγ, biological pathways regulated by homeobox genes and their role in placental development. The role of the nuclear receptor PPARγ, ligands and target genes in human placental development is also discussed. A better understanding of these pathways will improve our knowledge of placental cell biology and has the potential to reveal new molecular targets for the early detection and diagnosis of pregnancy complications including human fetal growth restriction.

Expression and Function of PPARs in Placenta

Peroxisome proliferator-activated receptors (PPAR) are members of the superfamily of nuclear hormone receptors involved in embryonic development and differentiation of several tissues including placenta, which respond to specific ligands such as polyunsaturated fatty acids by altering gene expression. Three subtypes of this receptor have been discovered, each evolving to achieve different biological functions. The PPARs also control a variety of target genes involved in lipid homeostasis. Similar to other nuclear receptors, the transcriptional activity of PPARs is affected not only by ligand-stimulation but also by crosstalk with other molecules. For example, both PPARs and the RXRs are ligand-activated transcription factors that coordinately regulate gene expression. In addition, several mechanisms underlying negative regulation of gene expression by PPARs have been shown. It is suggested that PPARs are key messengers responsible for the translation of nutritional stimuli into changes in gene expression pathways for placental development.

Peroxisome proliferator-activated receptor alpha expression changes in human pregnant myometrium

Peroxisome proliferator-activated receptor alpha (PPARα) has been demonstrated to exhibit anti-inflammatory activities that are hypothesized to play a key role in labor suppression and maintenance of uterine quiescence. The aim of this study was to identify pregnancy- and labor-associated changes in PPARα in human myometrium. For this investigation, human myometrium was obtained from premenopausal women, and the study participants were categorized into the following 4 groups: nonpregnant (NP; n = 10), preterm not in labor (PNL; n = 10, gestation range 20-35 weeks), term not in labor (TNL; n = 20, gestation range 37-41 weeks), and term in labor (TL; n = 20, gestation range 37-41 weeks). Immunohistochemistry was used to locate and confirm the expression of PPARα. Relative quantitative real-time polymerase chain reaction (PCR) and Western blotting were employed to study the expression of anti-inflammatory PPARα and proinflammatory interleukin 1β (IL-1β). Immunohistochemistry indicated that PPARα was located in the nucleus of uterine smooth muscle cells. Compared to other groups, in PNL group, the PPARα messenger RNA (mRNA) and protein increased significantly. Decreased PPARα mRNA and protein expressions in myometrium were associated with labor while IL-1β increased remarkably. There were negative correlations between PPARα and IL-1β on mRNA (r = -.765, P < .01) and protein (r = -.624, P < .01) levels analyzed using Pearson test. In conclusion, human pregnancy is associated with changes in expression of PPARα and IL-1β in myometrium. The changes observed suggest that PPARα may play a role in maintaining pregnancy or initiating labor through inhibiting the expression of IL-1β in human myometrium.