Decreased tryptophan catabolism by placental indoleamine 2,3-dioxygenase in preeclampsia

OBJECTIVE: Tryptophan degradation and depletion resulting from activation of indoleamine 2,3-dioxygenase is characteristic of inflammatory reactions and may control their intensity. Normal third-trimester pregnancy is characterized by a maternal systemic inflammatory response, which is more intense in preeclampsia. Therefore, we studied tryptophan metabolism in pregnant women, with or without preeclampsia, as well as expression and function of placental indoleamine 2,3-dioxygenase. STUDY DESIGN: Plasma concentrations of tryptophan and kynurenine in women with preeclampsia, appropriately matched women with normal pregnancy, and healthy nonpregnant women were measured. Placental enzymatic activity and messenger RNA (mRNA) expression level of indoleamine 2,3-dioxygenase were determined from the same placental material. Peripheral blood mononuclear cell proliferation was determined in medium conditioned by prior culture with villous tissue. RESULTS: The plasma ratio of kynurenine to tryptophan, an in vivo index of enzyme activity, was significantly increased compared with nonpregnant controls in normal pregnancy but not in preeclampsia. The activity and mRNA expression level of indoleamine 2,3-dioxygenase in term placentas were significantly lower in preeclampsia. Medium conditioned by culture of villous tissue explants of preeclampsia was less effective in inhibiting peripheral blood mononuclear cell proliferation compared with that of normal pregnancy. CONCLUSION: These observations suggest that in preeclampsia, reduced placental indoleamine 2,3-dioxygenase activity (and relatively elevated plasma tryptophan) could cause dysregulation of the inflammatory response that is intrinsic to normal pregnancy. This may contribute to the pathogenesis of the maternal syndrome of preeclampsia.     

Expression of indoleamine 2,3-dioxygenase in the rhesus monkey and common marmoset

Indoleamine 2,3-dioxygenase (IDO) catalyzes the initial and rate-limiting step of tryptophan degradation along the kynurenine pathway, and is hypothesized to limit tryptophan availability at embryo implantation and prevent maternal T cell activation at the maternal–fetal interface. To determine if nonhuman primates are suitable models for investigating the role of IDO during pregnancy, we defined the expression of IDO in the rhesus monkey and common marmoset with particular attention to the female reproductive tract and placenta. IDO mRNA was detected by RT-PCR in the rhesus monkey term placenta, lung, small intestine, spleen, lymph node and nonpregnant uterus, and also in the common marmoset placenta. Immunohistochemical analysis of rhesus monkey tissues localized IDO to glandular epithelium of nonpregnant endometrium and first trimester decidua, vessel endothelium of nonpregnant myometrium, first trimester decidua and term decidua, and villous vessel endothelium and syncytiotrophoblast of term placenta. Western blot analysis confirmed IDO in rhesus monkey term placenta. In the common marmoset, IDO was detected in glandular epithelium of the nonpregnant uterus and in the decidua at day 60 and day 128 of gestation. IDO activity was higher in rhesus monkey and common marmoset decidua and placentas than in other tissues. Confirmation of IDO expression in rhesus monkey and common marmoset uterine and placental tissues supports the hypothesis that this enzyme regulates immune activation at the maternal–fetal interface and demonstrates that nonhuman primates may provide models with distinct similarities to human placentation to study the role of IDO in maternal–fetal immune dialogue.     

Expression of indoleamine 2,3-dioxygenase in the rhesus monkey and common marmoset

Indoleamine 2,3-dioxygenase (IDO) catalyzes the initial and rate-limiting step of tryptophan degradation along the kynurenine pathway, and is hypothesized to limit tryptophan availability at embryo implantation and prevent maternal T cell activation at the maternal-fetal interface. To determine if nonhuman primates are suitable models for investigating the role of IDO during pregnancy, we defined the expression of IDO in the rhesus monkey and common marmoset with particular attention to the female reproductive tract and placenta. IDO mRNA was detected by RT-PCR in the rhesus monkey term placenta, lung, small intestine, spleen, lymph node and nonpregnant uterus, and also in the common marmoset placenta. Immunohistochemical analysis of rhesus monkey tissues localized IDO to glandular epithelium of nonpregnant endometrium and first trimester decidua, vessel endothelium of nonpregnant myometrium, first trimester decidua and term decidua, and villous vessel endothelium and syncytiotrophoblast of term placenta. Western blot analysis confirmed IDO in rhesus monkey term placenta. In the common marmoset, IDO was detected in glandular epithelium of the nonpregnant uterus and in the decidua at day 60 and day 128 of gestation. IDO activity was higher in rhesus monkey and common marmoset decidua and placentas than in other tissues. Confirmation of IDO expression in rhesus monkey and common marmoset uterine and placental tissues supports the hypothesis that this enzyme regulates immune activation at the maternal-fetal interface and demonstrates that nonhuman primates may provide models with distinct similarities to human placentation to study the role of IDO in maternal-fetal immune dialogue.     

Trophoblast debris modulates the expression of immune proteins in macrophages: a key to maternal tolerance of the fetal allograft?

Interactions between maternal immune cells and the placenta are of substantial interest since diseases of pregnancy, such as recurrent miscarriage, villitis of unknown etiology and preeclampsia may arise due to inadequate adaptation of the maternal immune system. During normal pregnancy trophoblast debris is shed from the placenta into the maternal blood in large quantities. This trophoblast debris is then rapidly cleared from the maternal circulation. In this study, we exposed trophoblast debris generated from an in vitro placental explant model to peripheral blood-derived macrophages and quantified a variety of molecules that are important in immune responses by ELISA or flow cytometry. Phagocytosis of trophoblast debris resulted in reduced cell-surface expression of MHC-II molecules, the costimulatory molecules (CD80, CD86, CD40 and B7H3), monocyte chemoattractant protein-1 (MCP-1), inter-cellular adhesion molecule 1 (ICAM-1) and IL-8 receptors in macrophages while the expression of programmed death-1 ligand 1 (PD-L1) was upregulated. In addition, phagocytosis of trophoblast debris induced the secretion of the anti-inflammatory cytokines IL-10, IL6 and IL1Ra and decreased the secretion of pro-inflammatory cytokines IL-1β, IL12p70 and IL-8 by macrophages. Phagocytosis of trophoblast debris also increased macrophage expression of the immunosuppressive enzyme indoleamine 2,3-dioxygenase (IDO). We have shown that phagocytosis of trophoblast debris from normal placentae alters the phenotype of macrophages such that they are likely to deviate maternal immune responses towards tolerance and away from inflammation. This may be one of the mechanisms that allow the human fetal allograft to survive in direct contact with the maternal immune system.     

Localisation of indoleamine 2,3-dioxygenase and kynurenine hydroxylase in the human placenta and decidua: implications for role of the kynurenine pathway in pregnancy

Indoleamine 2,3-dioxygenase (IDO) has been implicated in contributing to immunotolerance in early pregnancy, but the presence in the term placenta of mRNAs for enzymes that produce other biologically active kynurenine end-products suggests other functions for kynurenine pathway metabolites. The aim of this study was to investigate the localisation of two key enzymes - IDO and kynurenine hydroxylase (KYN-OHase) - in first trimester decidua and in the human placenta across pregnancy. Using immunocytochemistry, it was shown that there was strong expression of IDO and KYN-OHase in stromal and glandular epithelial cells of first trimester decidua. In first and second trimester placenta, IDO and KYN-OHase were localised to the syncytiotrophoblast, stroma and macrophages. IDO and KYN-OHase mRNAs were also identified, and the enzymes appear to be functional because kynurenine and 3-hydroxy-anthranilic acid (respective products of the activity of these enzyme) were released into the medium when first trimester placental explants were maintained in culture for 48h. In term placenta, both IDO and KYN-OHase immunoreactivities were confined mainly to vascular endothelial cells of villous blood vessels, and to macrophages within the fetal villus, whereas syncytial staining was very weak or absent. The shift of expression of these enzymes away from the syncytiotrophoblast to fetal endothelial cells in terminal villi suggests that the function of the enzymes may change from a role in immunosuppression at the maternal-fetal interface in early pregnancy, to one associated with regulation of fetoplacental blood flow or placental metabolism in late gestation.     

The effects of apoptotic,deported human placental trophoblast on macrophages: Possible consequences for pregnancy

During pregnancy, trophoblasts are shed into maternal blood from the placenta as they die. Trophoblasts are fetal cells and are therefore immunologically foreign to the maternal immune system, but the effects of shed trophoblasts on the maternal immune system are poorly characterized. We have used an in vitro villous explant model to harvest shed trophoblasts. These shed trophoblasts consist of multinucleated syncytial knots as well as mononuclear cells, and approximately 90% are apoptotic as determined by immunostaining with antibodies recognizing activated caspase-3 and the M30 cytokeratin neoepitope. U937 cells phagocytosed the shed apoptotic trophoblasts and, subsequently, secretion of the anti-inflammatory cytokine IL-10 was increased. In contrast, secretion of the proinflammatory cytokine Il-1β by U937 cells was decreased after phagocytosis of apoptotic trophoblasts and the changes in both IL-10 and IL-1β secretion were blocked by co-incubation with the phagocytosis inhibitor cytochalasin B. Shed trophoblasts caused a significant increase also in expression of the, immunosuppressive, tryptophan-metabolizing enzyme indoleamine 2,3-dioxygenase. We speculate that the shedding of trophoblasts may not be simply a mechanism the fetus uses to dispose of aged trophoblasts but rather shed apoptotic trophoblasts may provide a chronic source of tolerizing paternally derived antigens to regulate maternal immune responses to the fetus.     

The effects of apoptotic, deported human placental trophoblast on macrophages: possible consequences for pregnancy

During pregnancy, trophoblasts are shed into maternal blood from the placenta as they die. Trophoblasts are fetal cells and are therefore immunologically foreign to the maternal immune system, but the effects of shed trophoblasts on the maternal immune system are poorly characterized. We have used an in vitro villous explant model to harvest shed trophoblasts. These shed trophoblasts consist of multinucleated syncytial knots as well as mononuclear cells, and approximately 90% are apoptotic as determined by immunostaining with antibodies recognizing activated caspase-3 and the M30 cytokeratin neoepitope. U937 cells phagocytosed the shed apoptotic trophoblasts and, subsequently, secretion of the anti-inflammatory cytokine IL-10 was increased. In contrast, secretion of the proinflammatory cytokine Il-1beta by U937 cells was decreased after phagocytosis of apoptotic trophoblasts and the changes in both IL-10 and IL-1beta secretion were blocked by co-incubation with the phagocytosis inhibitor cytochalasin B. Shed trophoblasts caused a significant increase also in expression of the, immunosuppressive, tryptophan-metabolizing enzyme indoleamine 2,3-dioxygenase. We speculate that the shedding of trophoblasts may not be simply a mechanism the fetus uses to dispose of aged trophoblasts but rather shed apoptotic trophoblasts may provide a chronic source of tolerizing paternally derived antigens to regulate maternal immune responses to the fetus.     

Indoleamine 2,3-dioxygenase (IDO) expression in invasive extravillous trophoblast supports role of the enzyme for materno-fetal tolerance

It is still not understood how the fetus escapes from being attacked by the maternal immune system. Recent reports based on mouse and in vitro models have suggested that the enzyme indoleamine 2,3-dioxygenase (IDO) is important for materno-fetal tolerance. IDO activity in the human placenta is known to be high and might lead to inhibition of T-cell proliferation, thus preventing fetal tissue from rejection by the maternal immune system. In an attempt to elucidate the precise location of IDO at the feto-maternal junctional zone, we investigated human placental and decidual tissue of first and third trimester of pregnancy using an immunohistochemical approach. In placental tissues, only syncytiotrophoblast and endothelial cells showed moderate expression of IDO. This pattern was observed regardless of whether first or third trimester tissue was investigated. In early and term decidua, cells with the typical morphology of invasive extravillous trophoblast (EVT) were strongly positive for IDO. Blocking immunohistochemical experiments with cytokeratin and IDO antibodies identified invasive EVT as the location of predominant IDO expression. Since EVT are the fetal cells with the closest contact to the maternal immune system, our results suggest that it is EVT which protects the fetus from rejection by downregulating local maternal T-cell responses.     

Novel model of placental tissue explants infected by cytomegalovirus reveals different permissiveness in early and term placentae and inhibition of indoleamine 2,3-dioxygenase activity

Human cytomegalovirus (HCMV) is the most common cause of viral intrauterine infection. Placental infection suggests hematogenous spread and permissiveness may vary according to the age of pregnancy. We set up and investigate permissivity of early and term placenta to HCMV with an ex vivo model of placental histocultures and evaluate the activity profile of IDO. Fourteen first trimester placentae were obtained following elective abortion and twelve term placentae after elective caesarean section. Fresh placental chorionic villi were isolated, washed and distributed on collagen sponge gels after overnight incubation with the virus. The culture medium was collected and fresh medium renewed regularly. Histology and immunohistochemistry showed preserved villous integrity in cultured placental histocultures. Infection could be seen in tissue sections of both early and term placentae, although early placentae were more permissive. Indoleamine 2,3-dioxygenase (IDO) is highly expressed in the placenta and is known to prevent maternal immune rejection. Constitutive IDO activity was higher in early, compared to term placentae and HCMV infection inhibited IDO activity in early placentae. IFN-γ-induced IDO activity was suppressed by HCMV in both early and term placentae. Our work shows a novel method of placenta organ culture. Our findings suggest that HCMV infects early placentae more strongly than term placentae. Early placental dysfunction through the inhibition of IDO activity may reveal a possible mechanism for miscarriages.     

Mouse model for allogeneic immune reaction against fetus recapitulates human pre-eclampsia

AIM: We have previously demonstrated that mRNA expression and enzyme activity levels of placental indoleamine 2,3-dioxygenase (IDO), which degrades L-tryptophan and blocks the proliferation of T cells, are significantly low in patients with severe pre-eclampsia. From this observation, we hypothesized that induction of maternal allogeneic immune reaction by reduced IDO activity is one of the causes of pre-eclampsia. METHODS: To examine this hypothesis, we administered an IDO inhibitor to pregnant female mice carrying allogeneic concepti. Since administration of an IDO inhibitor to pregnant mice starting at E4.5 is already reported to cause allogeneic fetal rejection, we modified the regimen and started the administration at E6.5 when the fetus and placenta have already been established. RESULTS: Pregnant mice treated with an IDO inhibitor developed high blood pressure and proteinuria in addition to local circulation impairment in the placenta, which is analogous to the lesions that are characteristic of human pre-eclampsia. In contrast, pregnant mice carrying syngeneic concepti did not manifest such symptoms. CONCLUSIONS: Our findings reveal a pivotal role for IDO activity in the etiology of pre-eclampsia. These data also lend support to the current hypothesis that pre-eclampsia is one of the possible manifestations of a maternal immunological reaction against an allogeneic fetus.     

NFκB-dependent increase of kynurenine pathway activity in human placenta: inhibition by sulfasalazine

Catabolism of tryptophan via the kynurenine pathway is up-regulated in the human placenta by infection, resulting in the release of pro-inflammatory and neuroactive metabolites into the fetal circulation. In this study we determined if activation of NFκB is involved in the inflammation-induced increase of kynurenine pathway activity in the human placenta. Placentae obtained after elective caesarian section at 37-40 weeks gestation (n=8), and explants (35-40 mg) prepared from terminal villi were incubated under standard conditions in the presence of 10 μg/ml LPS for 24 or 48 h; duplicates of each explant were incubated either with or without 5mM sulfasalazine added to the medium. Expression of mRNAs for key kynurenine-forming enzymes, indoleamine 2,3-dioxygrenase (IDO) and tryptophan 2,3-doalxygenase (TDO) and the inflammatory cytokines TNFα and IL6 was studied by RT-PCR. Kynurenine output by explants was measured in samples in the incubation medium by absorbance at 363nm after separation from other metabolites using an HPLC technique. Expression of IDO, TDO, TNFα and IL6 mRNAs was increased with LPS treatment, a response mitigated by the presence of sulfasalazine (P<0.01, P<0.01, P=0.03 &P=0.04). Kynurenine output into the culture medium increased with LPS treatment but this was also prevented by sulfasalazine at 24h (mean ± SEM; 412.1 ± 40 vs. 147.7 ± 48.9 nM/mg, P=0.01) and 48 h (636 ± 39.1 vs. 135.5 ± 29.8 nM/mg, P=0.001, respectively). Sulfasalazine inhibited the LPS induction of both the kynurenine pathway and pro-inflammatory cytokines in the placenta, implicating NFκB in the LPS effect. Direct measurement of NFκB activity showed that sulfasalazine decreased NFκB activation under both control and LPS-treated conditions. These observations show that kynurenine pathway activity in the human placenta is increased by a NFκB dependent pathway, and suggests a new therapeutic strategy for the management of pregnancies with in utero infection.     

Indoleamine 2,3-dioxygenase,immunosuppression and pregnancy

Pharmacologic inhibition of indoleamine 2,3-dioxygenase (IDO) activity during murine pregnancy results in maternal T-cell-mediated rejection of allogeneic but not syngeneic conceptuses. Increased risk of allogeneic pregnancy failure induced by exposure to IDO inhibitor is strongly correlated with maternal C3 deposition at the maternal-fetal interface. Here we review evidence that cells expressing IDO contribute to immunosuppression by inhibiting T-cell responses to tumor antigens and tissue allografts, as well as fetal tissues.     

Abnormal expression of HLA-DR antigen in the placenta of a patient with pemphigoid gestationis

The villous stroma and fetal endothelium in chorionic villi adjacent to maternal decidua in a placenta of a woman suffering from pemphigoid gestationis were found to have abnormal expression of HLA-DR antigen. This aberrant DR expression may be a reflection of an immune attack on the placenta.     

Localization of the extracellular Ca(2+)-sensing receptor in the human placenta

We have demonstrated using immunohistochemistry and in situ hybridization that the calcium-sensing receptor (CaR) is expressed in both villous and extravillous regions of the human placenta. CaR expression was detected in both first trimester and term placentas. In the villous region of the placenta, the CaR was detected in syncytiotrophoblasts and at lower levels in cytotrophoblasts. Local expression of the CaR in the brush border of syncytiotrophoblasts suggests a role for maternal Ca(2+) concentration in the control of transepithelial transport between the mother and fetus. In the extravillous region of the placenta, the CaR was detected in cells forming trophoblast columns in anchoring villi, in close proximity to maternal blood vessels and in transitional cytotrophoblasts. Given the importance of extravillous cytotrophoblasts in the process of uterine invasion and maintenance of placental immune privilege, the CaR represents a possible target by which the maternal extracellular Ca(2+) concentration could promote or maintain placentation. Thus, the results support hypotheses that the CaR contributes to the local control of transplacental calcium transport and to the regulation of placental development.     

Immunosuppression by placental indoleamine 2,3-dioxygenase: a role for mesenchymal stem cells

BACKGROUND/OBJECTIVES: Mesenchymal stem cells (MSC) can be isolated from human placenta and have the potential to contribute to the immunosuppressive properties of placental tissue. The objectives of this study were to investigate the phenotype and differentiation characteristics of MSC derived from human placenta and evaluate the role of the tryptophan degrading enzyme, indoleamine 2,3 dioxygenase (IDO), in mediating their immunosuppressive affect. METHODS: MSC obtained from placental tissue (pMSC) were characterised using flow cytometry and tested for multipotency by determining differentiation into all mesenchymal lineages. The immunosuppressive properties of pMSC were tested in allogeneic mixed lymphocyte reactions and IDO expression and activity were measured by semi-quantitative real-time PCR and HPLC respectively. RESULTS: Multipotent stem cells were isolated from placenta and displayed chondrogenic, osteogenic and limited adipogenic differentiation. Cell surface antigen expression of pMSC was similar to bone marrow MSC (bMSC) with lack of the haematopoietic and common leukocyte markers (CD34, CD45), and expression of adhesion (CD29, CD166, CD44) and stem cell (CD 90, CD105, CD73) markers. Placental MSC were suppressive of allogeneic T-cell proliferation, an effect which was intensified following IDO induction by IFN-gamma. Replenishment of tryptophan or treatment with the IDO-blocker, 1-methyl-tryptophan (1-MT), attenuated the immunosuppressive action of pMSC. CONCLUSIONS: These results suggest that placental tissue contains MSC, which are phenotypically and functionally similar to bMSC, and that IDO is a key mediator of their immunosuppressive effect. Further investigation is needed to determine if pMSC function effects pregnancy outcome.     

Apoptosis and its role in the trophoblast

During early placentation the trophoblast of the human placenta differentiates to the villous and extravillous types of trophoblast. Villous trophoblast provides the epithelial cover of the placental villous trees in direct contact to maternal blood. Extravillous trophoblast invades maternal uterine tissues thus directly contacting maternal stromal and immune cells. A subset of extravillous trophoblast, endovascular trophoblast initially occludes the lumen of spiral arteries and comes into direct contact with maternal blood. In recent years apoptosis has been described in both types of trophoblast and the importance of this cascade for the normal function of the trophoblast has become obvious. One feature of serious conditions such as preeclampsia or intrauterine growth restriction is changes in apoptosis regulation in villous and/or extravillous trophoblast resulting in altered trophoblast invasion and/or shedding into the maternal circulation. This review summarizes recent findings on trophoblast apoptosis in normal and pathologic pregnancies.     

Villous explant culture: characterization and evaluation of a model to study trophoblast invasion.

The mechanisms that control invasion of cytotrophoblast (CTB) cells into the maternal decidua and myometrium with transformation of the maternal spiral arteries are not fully understood, but oxygen is thought to be a key factor. We carried out a semiquantitative evaluation of an explant culture model for use in the study of trophoblast proliferation and invasion. Explants of human villous tissue (6-9 weeks of gestation) cultured on Matrigel in both standard culture conditions (18% O2) and in a low oxygen environment (2% O2) produced regions of outgrowth, of cytotrophoblast cells from villous tips and migration of cells into the Matrigel. The number of sites of outgrowth and migration, area of outgrowth, and extent of migration of cells into the Matrigel tended to increase throughout the culture period (144 h) but varied between explants from the same placenta and those from different placentas. There were no significant differences in the number of sites of outgrowth or migration scores in explants cultured in a low oxygen environment compared to those cultured in standard conditions. This study highlights the importance of careful validation, design and interpretation of experiments using in vitro culture systems, particularly those investigating the regulatory role of oxygen.     

Placental and trophoblastic in vitro models to study preventive and therapeutic agents for preeclampsia

In the field of preeclampsia, enormous efforts are ongoing to identify biomarkers predicting the syndrome already in the first trimester of pregnancy. At the same time, there is the need for in vitro models to test such biomarkers prior to their use in clinical trials. In addition, in vitro models may accelerate the development and evaluation of the benefit of any putative therapeutics. Therefore, in vitro systems have been established to evaluate the release of biomarkers and measure the effect of putative therapeutics using placental villous explants as well as the choriocarcinoma cell line BeWo. For explants, a cryogenic method to freeze, transport and thaw villous explants was developed to use such tissues for a multi-site tissue culture evaluation.Here we focus on three out of many in vitro models that have been established for human placental trophoblast. (1) Choriocarcinoma cell lines such as BeWo, Jeg-3 and Jar cells (2) isolated primary trophoblast cells, and (2) villous explants from normal placentas delivered at term. Cell lines were used to assess the effect of differentiation and fusion on the expression and release of a preeclampsia marker (placental protein 13; PP13) and beta-hCG. Moreover, cell lines were used to study the effect of putative preeclampsia therapeutics such as vitamins C and E, heparin and aspirin on marker release and viability. Cryopreservation of villous explants enabled shipment to a remote laboratory and testing of parameters in different countries using explants from one and the same placenta.Recently published data make it tempting to speculate that the choriocarcinoma cell line BeWo as well as fresh and cryogenically stored placental villous explants may well serve as in vitro models to study preventive and therapeutic agents in the field of preeclampsia.     

Differential expression and the anti-apoptotic effect of human placental neurotrophins and their receptors

Neurotrophin (NT) is important in the survival, maintenance and differentiation of neuronal tissue, and functions in follicle maturation, tumor growth, angiogenesis and immunomodulation; however, the expression of NT and its receptors (NTR) in human placenta and their influence on fetal growth are unclear. Here we investigated the correlation of NT and NTR in human placenta with uterine environment and fetal growth. TrkB, a NTR, mRNA was expressed on decidual and villous tissue and increased with gestational age, localizing in the trophoblast layer and endothelium by immunohistochemistry. Villous TrkB mRNA was significantly increased in preeclampsia (PE) than in controls and was higher in the normotensive small for gestational age (SGA) placenta, although it was not significant. It was also significantly increased in the small twin of discordant twin pregnancies. Brain-derived neurotrophic factor (BDNF), the main ligand of TrkB, was expressed in membranous chorion and villous tissue and was significantly higher in maternal plasma in normotensive SGA and PE than in controls. TrkB mRNA expression was up-regulated on cultured villous tissue explants and on JEG-3, a choriocarcinoma cell line, by H₂O₂ treatment. BDNF decreased apoptotic cells in H₂O₂-treated JEG-3, indicating that BDNF/TrkB signaling had anti-apoptotic effects against oxidative stress in JEG-3, suggesting a protective role of BDNF/TrkB in human villous tissue under unfavorable conditions in utero.     

Soluble epoxide hydrolase in the human placenta throughout gestation

ObjectiveTo investigate the spatial and temporal changes of soluble epoxide hydrolase (sEH) in the human placenta throughout gestation and to study the effects of hypoxia-reoxygenation (HR) on the expression of sEH in villous explants in vitro.Materials and methodsPlacental samples were obtained from women of different gestation and grouped as early (8–12 weeks, n = 10), mid- (16–28 weeks, n = 6), and late gestation (38–39 weeks, n = 10) according to gestational age. Immunohistochemistry, western blot, and real-time quantitative PCR were used to assess the cellular distribution and temporal changes of sEH. Villous explant cultures were used to study the effect of HR (8 h at 2% oxygen, followed by 16 h at 8% oxygen, two cycles) on the expression of sEH.ResultsUsing a mouse monoclonal antibody against human sEH, immunoreactivity of sEH was observed mainly localized in the cytotrophoblasts and, to a lesser extent, the syncytiotrophoblast in the villous tissues throughout gestation. Compared to villous tissues of early gestation, the levels of sEH mRNA and protein were significantly increased in villous samples of mid- and late gestation. Furthermore, villous explants subjected to HR had significantly higher levels of sEH mRNA and protein compared to villous tissues kept at 8% oxygen throughout the experiment.ConclusionOur results indicate that sEH is likely to play an essential role in the development of human placenta and HR is a possible factor regulating the expression of sEH in the placenta.