Interferon-tau suppresses prostaglandin F2alpha secretion independently of the mitogen-activated protein kinase and nuclear factor kappa B pathways

Expression of nuclear factor kappa B components in the ovine maternal liver in early pregnancy periods

There is a systemic immunological adaptation to maintaining tolerance towards the allogeneic fetus, and the liver participates in the adaptive immune tolerance during normal pregnancy. Nuclear factor kappa B (NF-κB) signalings contribute to immune regulation and liver homoeostasis. The objective of this study is to explore the effects of early pregnancy on expression of NF-κB components in the maternal liver in sheep. The maternal livers were sampled on Day 16 of the estrous cycle, and Days 13, 16, and 25 of gestation, and the expression of NF-κB components, including NF-κB1 (p50), NF-κB2 (p52), RelA (p65), RelB, and c-Rel, was detected by quantitative real-time polymerase chain reaction (PCR), Western blot analysis, and immunohistochemical analysis. Our data revealed that early pregnancy inhibited the expression of NF-κB1 and c-Rel, but the expression of NF-κB1 and c-Rel was increased during early pregnancy. However, early pregnancy enhanced the expression of NF-κB2, RelA, and RelB with the pregnancy progress. In conclusion, early pregnancy regulates the expression of NF-κB components in the maternal livers, which may contribute to maintaining maternal liver homeostasis and immune tolerance during early pregnancy in sheep.

Modification of endometrial fatty acid concentrations by the pre-implantation conceptus in pasture-fed dairy cows

The current study determined whether the pre-implantation conceptus modified endometrial fatty acid concentrations. Oestrus was synchronized in 14 mature lactating cows and embryos were transferred on day 7. Cows were slaughtered 10 d later, with each uterine horn flushed, the pre-implantation conceptus located, and inter-caruncular endometrial tissue collected from the gravid horn (containing the pre-implantation conceptus) and non-gravid horn. Endometrial fatty acid concentrations in the gravid and non-gravid horn were compared using linear models in restricted maxiumum likelihood. Investigations of the correlations among selected fatty acids and trophoblast weight or uterine fluid interferon-tau (IFN-τ) concentrations were also undertaken. The presence of the pre-implantation conceptus had relatively minor effects on endometrial fatty acid concentrations, but the ω6:ω3 ratio was greater and concentrations of stearic and oleic acid were slightly increased in the gravid horn. In the gravid horn, a negative linear relationship between the concentration of arachidonic acid and conceptus weight and IFN-τ concentration in the uterine luminal fluid were observed. In contrast, there was a positive relationship between concentrations of dihomo-γ-linolenic acid in the non-gravid horn and conceptus weight. In conclusion, the presence of the pre-implantation conceptus appears to modulate endometrial fatty acids, as indicated by the differences in endometrial fatty acid concentrations in the gravid and non-gravid uterine horns. The physiological implication of these local effects of the pre-implantation conceptus, on reproductive success requires further investigation.

Phospholipase A2 regulation of bovine endometrial (BEND) cell prostaglandin production

BACKGROUND

Prostaglandins (PG), produced by the uterine endometrium, are key regulators of several reproductive events, including estrous cyclicity, implantation, pregnancy maintenance and parturition. Phospholipase A2 (PLA2) catalyzes the release of arachidonic acid from membrane phospholipids, the rate-limiting step in PG biosynthesis. The bovine endometrial (BEND) cell line has served as a model system for investigating regulation of signaling mechanisms involved in uterine PG production but information concerning the specific PLA2 enzymes involved and their role in regulation of this process is limited. The objectives of this investigation were to evaluate the expression and activities of calcium-dependent group IVA (PLA2G4A) and calcium-independent group VI (PLA2G6) enzymes in the regulation of BEND cell PG production.

METHODS

Cells were grown to near-confluence and treated with phorbol 12, 13 dibutyrate (PDBu), interferon-tau (IFNT), the PLA2G4A inhibitor pyrrolidine-1 (PYR-1), the PLA2G6 inhibitor bromoenol lactone (BEL) and combinations of each. Concentrations of PGF2alpha and PGE2 released into the medium were determined. Western blot analysis was performed on cellular protein to determine effects of treatment on expression of PLA2G4A, PLA2G6 and PLA2G4C. PLA2 assays were performed on intact cells by measuring arachidonic acid and linoleic acid release and group-specific PLA2 activity assays were performed on cell lysates.

RESULTS

BEND cells produced about 10-fold more PGE2 than PGF2alpha under resting conditions. Production of both PGs increased significantly in response to PDBu-stimulation. PYR-1 significantly diminished production of both PGs by resting cells and abolished the stimulatory effect of PDBu. BEL stimulated production of both PGs. IFNT reduced both PGE2 and PGF2alpha production by resting cells and diminished PDBu stimulation of PG production. Conversely, IFNT did not significantly reduce BEL stimulation of PG production. Cellular expression of PLA2G4A was enhanced by PDBu and this response was diminished by IFNT. Expression of PLA2G6 was not observed to be affected by treatments and no PLA2G4C expression was observed. Arachidonic acid release from intact cells was significantly increased by PDBu and this effect was attenuated by PYR-1 but not by BEL. Release of linoleic acid from intact cells was stimulated by PDBu and inhibited by BEL but not PYR-1. Group specific PLA2-activity assays demonstrated both PLA2G4A and PLA2G6 activity.

CONCLUSION

Results from this study demonstrate that PGE2 and PGF2-alpha production by BEND cells is mediated by the activity and expression of PLA2G4A. Interferon-tau treatment diminished expression of PLA2G4A and PG production. BEND cells were shown to express PLA2G6 but, unlike primary or early passage luminal bovine endometrial cells, stimulation of PLA2G6 activity was not associated with increased PG production.

Acid sphingomyelinase involvement in tumor necrosis factor alpha-regulated vascular and steroid disruption during luteolysis in vivo

TNF is well known for its role in inflammation, including direct effects on the vasculature. TNF also is implicated in the regulation of reproduction by its actions to affect ovarian steroidogenic cells and to induce apoptosis of corpus luteum (CL)-derived endothelial cells in vitro. We hypothesized that the disruption of TNF signaling would postpone the regression of the highly vascularized CL in vivo, and this effect could be replicated in mutant mouse models lacking TNF receptor (TNFRI(-/-)) and/or a critical enzyme of TNF signaling, acid sphingomyelinase (ASMase(-/-)). In the current study, the treatment of pseudopregnant mice with the luteolytic mediator prostaglandin F2-alpha (PGF) significantly increased TNF in the ovaries when compared with saline-treated controls. Treatment with PGF also reduced serum progesterone (P4) concentrations and caused involution of the CL. However, pretreatment of pseudopregnant mice with Etanercept (ETA), a TNF-neutralizing antibody, inhibited the PGF-induced decrease in P4 and delayed luteal regression. A similar outcome was evident in pseudopregnant TNFRI(-/-) animals. Treatment of luteal microvascular endothelial cells (MVECs) with TNF provoked a significant increase in ASMase activity when compared with the corresponding controls. Furthermore, TNF-induced MVEC death was inhibited in the ASMase(-/-) mice. The ASMase(-/-) mice displayed no obvious evidence of luteal regression 24 h after treatment with PGF and were resistant to the PGF-induced decrease in P4. Together these data provide evidence that TNF plays an active role in luteolysis. Further studies are required to determine the deleterious effects of anti-inflammatory agents on basic ovarian processes.

A microarray analysis for genes regulated by interferon-tau in ovine luminal epithelial cells

Interferon-tau (IFNT) is released by preimplantation conceptuses of ruminant species and prepares the mother for pregnancy. Although one important function is to protect the corpus luteum from the luteolytic activity of prostaglandin-F 2alpha, IFNT most likely regulates a range of other physiological processes in endometrium. Here, an immortalized cell line from ovine uterine luminal epithelial cells was treated with IFNT for either 8 or 24 h. RNA was subjected to cDNA microarray analysis, with RNA from untreated cells as the reference standard. Of 15 634 genes, 1274 (8%) were IFNT responsive at P<0.01 and 585 at P<0.001 to at least one treatment. Of the latter, 356 were up-regulated and 229 down-regulated. Increasing IFNT concentrations from 10 ng/ml to 10 microg/ml had minor effects, and most genes up- or down-regulated at 8 h were regulated similarly at 24 h. Although IFNT influences many genes implicated in antiviral activity and apoptosis, its action also likely regulates prostaglandin metabolism, growth factors and their receptors, apoptosis and the nuclear factor (NF)-kappaB cascade, extracellular matrix accretion, angiogenesis, blood coagulation, and inflammation. In particular, it increased mRNA concentrations of genes related to the vascular endothelial growth factor R2 pathway of angiogenesis and down-regulated ones associated with hypoxia. Two genes implicated in the antiluteolytic actions of IFNT (encoding cyclooxygenase-2 and the oxytocin receptor respectively) were down-regulated in response to all treatments. IFNT targets a complex range of physiological processes during the establishment of pregnancy.

Pleiotropy and Redundancy of STAT Proteins in Early Pregnancy

Signal transducers and activators of transcription (STATs) are a group of proteins involved in signal transduction from numerous bioactive substances. Hormones and cytokines such as leukaemia inhibitory factor, interferon-tau and prolactin, which play key roles during early pregnancy, activate the Janus kinase (JAK)/STAT signalling pathway. The STATs are thus involved in the regulation of implantation, establishing uterine receptivity and regulation of the maternal immune response. It seems that STATs can orchestrate signals from hormones and cytokines in different cell types and may therefore generate numerous biological effects, despite the relatively small number of receptors activating the JAK/STAT pathway. This review summarizes the participation of STATs in the main processes of early pregnancy, especially regarding their pleiotropy and redundancy.

The abortifacient effects from the seeds of Coix lachryma-jobi L. var. ma-yuen Stapf

This study evaluated the abortifacient effects of the extracts of seeds of Coix lachryma-jobi L. var. ma-yuen Stapf (adlay) in pregnant rats. Pregnant rats were treated with oral administration of adlay seed extracts on d 6 of pregnancy and their fetuses were examined for growth and malformations on d 20 of pregnancy. Following oral administration of 1 g/kg body weight of water extracts but not methanolic extracts, fetal resorptions were significantly increased and mortality of postimplantation was increased. There were no significant differences in the uterine and fetal weight compared to control. Fetal malformations were not observed in the adlay seed extracts-treated pregnant rats. The contractile activity of uteri isolated from rats on d 20 of pregnancy was assessed. The spontaneous uterine contractions were significantly enhanced in rats treated with water extracts of adlay seeds (1 g/kg body weight). Immunoblotting of uteri from rats treated with water extracts of adlay seeds demonstrated an induction of cyclooxygenase-2 (COX-2) protein expression. The water extracts of adlay seeds also enhanced extracellular signal-regulated protein kinase (ERK) 1/2 phosphorylation and protein kinase C (PKC)-alpha translocation from cytosolic to particulate fractions in uteri. These results indicate that the water extracts of adlay seeds are capable of inducing embryotoxicity and enhancing uterine contractility during pregnancy. The enhanced activities of PKC-alpha, ERK1/2, and COX-2 may contribute to these responses.

Interaction of stress-activated protein kinase-interacting protein-1 with the interferon receptor subunit IFNAR2 in uterine endometrium

During early pregnancy in ruminants, a type I interferon (IFN-tau) signals from the conceptus to the mother to ensure the functional survival of the corpus luteum. IFN-tau operates through binding to the type I IFN receptor (IFNR). Here we have explored the possibility that IFNAR2, one of the two subunits of the receptor, might interact with hitherto unknown signal transduction factors in the uterus that link IFN action to pathways other than the well established Janus kinase-signal transducer and activator of transcription pathways. A yeast two-hybrid screen of an ovine (ov) endometrial cDNA library with the carboxyl-terminal 185 amino acids of ovIFNAR2 as bait identified stress-activated protein kinase-interacting protein 1 (ovSin1) as a protein that bound constitutively through its own carboxyl terminus to the receptor. ovSin1 is a little studied, 522-amino acid-long polypeptide (molecular weight, 59,200) that is highly conserved across vertebrates, but has identifiable orthologs in Drosophila and yeast. It appears to be expressed ubiquitously in mammals, although in low abundance, in a wide range of mammalian tissues in addition to endometrium. Sin1 mRNA occurs in at least two alternatively spliced forms, the smaller of which lacks a 108-bp internal exon. ovSin1, although not exhibiting features of a membrane-spanning protein, such as IFNAR2, is concentrated predominantly in luminal and glandular epithelial cells of the uterine endometrium. When ovSin1 and ovIFNAR2 are coexpressed, the two proteins can be coimmunoprecipitated and colocalized to the plasma membrane and to perinuclear structures. Sin1 provides a possible link among type I IFN action, stress-activated signaling pathways, and control of prostaglandin production.

Inhibition of phorbol ester-induced PGF2alpha secretion by IFN-tau is not through regulation of protein kinase C

Inhibitory effect of IFN-tau on phorbol ester (PdBu)-induced PGF2alpha secretion was hypothesized to be manifested by the regulation of protein kinase C (PKC) in bovine endometrial (BEND) cells. Following 12 h stimulation with PdBu, cells were unresponsive to freshly added PdBu. Pretreatment of cells with a PKC inhibitor abolished PGF2alpha secretion in response to PdBu. Therefore, PdBu induction of PGF2alpha secretion is through activation of PKC. The alpha, epsilon, iota and lambda isotypes of the PKC family were identified by Western blotting. Cells were then treated with medium alone (control), PdBu or PdBu + IFN-tau for 3 or 6 h. The PdBu-induced secretion of PGF2alpha was suppressed by IFN-tau. At 3 and 6 h, PKCalpha and PKCepsilon were detected both in the cytosolic and membrane fractions of unstimulated cells. There was a clear reduction of PKCalpha in the cytoplasm induced by PdBu and PdBu + IFN-tau at 3 and 6 h. The total abundance (cytoplasm and membrane fractions) of PKCalpha was lower in the PdBu + IFN-tau than PdBu alone. These temporal responses indicate a PKCalpha responsiveness of BEND cells to PdBu and PDBu + INF-tau with some evidence that IFN-tau causes a slight but detectable reduction in PKCalpha when added with PdBu. However, IFN-tau-induced decrease in the total abundance of PKCalpha was not enough to affect negatively the translocation of the PKCalpha to the membrane. Therefore, IFN-tau's ability to suppress secretion of PGF2alpha is unlikely due to an interference with the PdBu-induced activity of PKC.

Interferon-τ Induces Degradation of Prostaglandin H Synthase-2 Messenger RNA in Bovine Endometrial Cells Through a Transcription-Dependent Mechanism1

A series of experiments were undertaken to examine the effects of interferon (IFN)-tau on regulation of prostaglandin H synthase (PGHS)-2 mRNA in bovine endometrial (BEND) cells as a means to elucidate the actions of IFN-tau to maintain pregnancy. The objective was to determine if IFN-tau mediates posttranscriptional regulation of PGHS-2 mRNA. Cells were treated with phorbol 12,13-dibutyrate (PdBu) for 3 h to induce PGHS-2 mRNA expression. Actinomycin D (0 or 1 microg/ml) or the p38 mitogen-activated protein kinase (MAPK) inhibitor, SB203580 (1 microM), were added at 3 h, followed by addition of IFN-tau (0 or 50 ng/ml) at 3.5 h and extraction of RNA at 4.5 h. The concentrations of PGHS-2 mRNA were stable between 3 and 4.5 h regardless of actinomycin D. Simultaneous treatment of PdBu-treated cells with actinomycin D and SB203580 (1 microM) decreased PGHS-2 mRNA. Addition of IFN-tau (50 ng/ml) reduced PGHS-2 mRNA, which was not observed when actinomycin D was present. Concurrent treatments of cells with SB203580 and IFN-tau (5 ng/ml) decreased concentrations of PGHS-2 mRNA in an additive manner. Although IFN-tau reduced PGHS-2 mRNA concentrations, phosphorylation of p38 MAPK was induced by IFN-tau, PdBu, and PdBu combined with IFN-tau after 10 min of treatment. Both the p38 MAPK inhibitor and IFN-tau decreased prostaglandin F(2alpha) secretion, and decreases were additive when the two were given together. In summary, activation of p38 MAPK by PdBu is required for continued presence of PGHS-2 mRNA and secretion of prostaglandin F(2alpha) in BEND cells. Interferon-tau mediates a transcription-dependent mechanism, which induces degradation of PGHS-2 mRNA. However, the consequences of an IFN-tau-induced activation of p38 MAPK warrant further investigation, because inhibition of p38 MAPK caused a degradation of PGHS-2 mRNA.

Differential Effects of Interferon-τ on the Prostaglandin Synthetic Pathway in Bovine Endometrial Cells Treated with Phorbol Ester

Rationale for these experiments was to evaluate the dose effects of bovine interferon-tau (IFN-tau) on the prostaglandin secretory pathway of immortalized bovine endometrial (BEND) cells in response to phorbol 12, 13-dibutyrate (PdBu) and to characterize similar responses in primary bovine uterine epithelial cells as a biomonitor of embryo-induced antiluteolytic effects on the endometrium. The BEND cells were treated with PdBu (0 or 100 ng/mL) and IFN-tau (0 or 50 ng/mL) for 6 h. The PdBu stimulated secretions of PGF2alpha and prostaglandin E2 (PGE2). Co-treatment of cells with IFN-tau blocked PdBu-induced secretion of both PGF2alpha and PGE2. Treatment with PdBu for 6 h induced expression of prostaglandin H synthase-2 mRNA, prostaglandin H synthase-2 protein, and prostaglandin E synthase mRNA, which were blocked with concurrent addition of IFN-tau. Doses of IFN-tau (0.05, 0.5, 1, 5, 10, and 20 microg/mL) were used with PdBu (0 and 100 ng/mL). The IFN-tau alone failed to stimulate secretion of PGF2alpha and PGE2, whereas IFN-tau doses <5 microg/mL suppressed PdBu-stimulated secretions of PGF2alpha and PGE2. Uterine epithelial cells were isolated from cows at d 17 after estrus and were cultured to confluence in serum-free medium. Cells were treated with IFN-tau (0, 50, or 500 ng/mL) and PdBu (0 or 100 ng/mL) before media were collected after 24 h for PGF2alpha and PGE2 analyses. Treatment of primary uterine epithelial cells with PdBu induced PGF2alpha secretion, and IFN-tau (50 and 500 ng/mL) caused a reduction in PGF2alpha secretion induced by PdBu. In the absence of PdBu, IFN-tau increased basal secretion of PGF2alpha. Concentrations of PGE2 increased in response to PdBu, and the 50-ng/mL dose of IFN-tau had a stimulatory effect on PGE2 concentrations compared with the 500-ng/mL dose in the absence of PdBu. Phorbol ester-induced gene transcription as related to prostaglandin synthesis is regulated by IFN-tau in vitro.

Interferon-tau blocks the stimulatory effect of tumor necrosis factor-alpha on prostaglandin F2alpha synthesis by bovine endometrial stromal cells

Tumor necrosis factor-alpha (TNFalpha) has been shown to be a potent stimulator of prostaglandin (PG) F2alpha synthesis in bovine endometrial stromal cells. The aims of the present study were to determine the effect of interferon-tau (IFNtau) on TNFalpha-stimulated PGF2alpha synthesis and the intracellular mechanisms of TNFalpha and IFNtau action in the stromal cells. When cultured bovine stromal cells were exposed to TNFalpha (0.006-0.6 nM) for 24 h, the production of PGF2alpha and cyclooxygenase (COX)-2 gene expression were stimulated by TNFalpha (0.06-0.6 nM, P < 0.05). Moreover, a specific COX-2 inhibitor (NS-398; 5 nM) blocked the stimulatory effect of TNFalpha on PGF2alpha production (P < 0.05). Although IFNtau (0.03-30 ng/ml) did not stimulate basal PGF2alpha production in the stromal cells, it suppressed TNFalpha action in PGF2alpha production dose dependently (P < 0.05). Moreover, the stimulatory effect of TNFalpha (0.6 nM) on COX-2 gene expression was completely blocked by IFNtau (30 ng/ml; P < 0.05), although the gene expression of COX-2 was not influenced by IFNtau. The overall results indicate that the stimulatory effect of TNFalpha on PGF2alpha production is mediated by the up-regulation of COX-2 gene expression and suggest that one of the mechanisms of the inhibitory effect of IFNtau on luteolysis is the inhibition of TNFalpha action in PGF2alpha production in the stromal cells by the down-regulation of COX-2 gene expression stimulated by TNFalpha.

Influence of different isoforms of recombinant trophoblastic interferons on prostaglandin production in cultured bovine endometrial cells

In ruminants, interferon produced by the trophectoderm (IFN-tau) is recognized as the embryonic signal responsible for maternal recognition of pregnancy. IFN-tau is believed to act by down-regulating estrogen receptors, thus preventing appearance of oxytocin receptors responsible for the release of prostaglandin F(2alpha) (PGF(2alpha)) by the endometrium. The present study was undertaken to determine in vitro the biological activities of different IFN-tau isoforms and document putative alternate luteotrophic mechanisms. Endometrial cells in primary cultures were treated with five different rIFN-tau isoforms: two ovine isoforms (ro-4 and ro-11) and three bovine isoforms (rb-1a, rb-2b and rb-3b). Their effect was quantified by measurement of PGE(2) and PGF(2alpha) production by ELISA and induction of cyclooxygenase (COX-2) by Western and Northern analysis and correlated with antiviral activity previously reported. The overall pattern of response to the IFNs tested suggests that low concentrations (<1 microg/ml) reduced the production of both PGs and higher concentrations (>1 microg/ml) stimulated preferentially PGE(2); however, exceptions were noted. Isoform rb-2b with high antiviral activity inhibited PG production in both cell types at all concentrations tested. IFNs rb-1a and ro-11 had similar antiviral activities, inhibiting PG at low concentrations and stimulating them at high concentrations. Isoform rb-3b stands out relative to the other IFNs tested because it induced a variable non-dose-dependent effect on PG production and low antiviral activity. An increase in COX-2 protein expression and messenger was correlated with increased PG production. The results showing two distinct responses to IFN-tau depending on its concentration and/or isoform and the absence of correlation with antiviral activity suggest that complex transduction mechanisms are involved.

Secretion of monocyte chemoattractant protein-1 by endothelial cells of the bovine corpus luteum: regulation by cytokines but not prostaglandin F2alpha

Information regarding the regulation of monocyte chemoattractant protein-1 (MCP-1) in regression of the corpus luteum (CL) is limited. This study tested the hypothesis that endothelial cells derived from bovine CL are a source of MCP-1, and that proinflammatory cytokines, prostaglandin F2alpha (PGF2alpha), and progesterone regulate MCP-1 expression. Endothelial cells were treated without (Control) or with PGF2alpha (1 micro M), TNFalpha (100 ng/ml), interferon-gamma (IFNgamma, 200 IU/ml), and TNFalpha + IFNgamma for 24 and 48 h in the absence or presence of progesterone (P4, 250 ng/ml). Increases in MCP-1 mRNA and protein were observed in response to TNFalpha within 24 and 48 h of culture, respectively (P < 0.05). Interferon-gamma stimulated (P < 0.05) both MCP-1 mRNA and protein after 24 h of culture, and this effect was also sustained through 48 h of culture (P < 0.05). Cotreatment of cultures with TNFalpha + IFNgamma lead to further increases (P < 0.05) in MCP-1 in both 24- and 48-h cultures. Surprisingly, neither PGF2alpha nor P4 affected MCP-1 production. Subsequent experiments revealed that the endothelial cells lacked prostaglandin F2alpha receptor mRNA, and the MAPK pathway, although present and responsive to growth factor stimulation, was unresponsive to PGF2alpha stimulation. In summary, endothelial cells derived from bovine CL respond to TNFalpha and IFNgamma stimulation with an increase in MCP-1 secretion. In contrast, neither PGF2alpha nor P4 directly influenced endothelial expression of MCP-1. These results suggest that cytokines stimulate the synthesis of MCP-1 observed during PGF2alpha-induced luteal regression.

Regulation of endometrial prostaglandin F(2alpha) synthesis during luteolysis and early pregnancy in cattle

Luteal regression is caused by a pulsatile release of prostaglandin (PG) F(2alpha) from the uterus in the late luteal phase in most mammals including cattle. Although it has been proposed in ruminants that pulsatile PGF(2alpha) secretion is generated by a positive feedback loop between luteal and/or hypophyseal oxytocin and uterine PGF(2alpha), the bovine endometrium may possess other mechanisms for initiation of luteolytic PGF(2alpha) secretion. It has been recently demonstrated that tumor necrosis factor-alpha (TNF-alpha) stimulates PGF(2alpha) output from bovine endometrial tissue not only during the follicular phase but also during the late luteal phase, suggesting that TNF-alpha is a factor in the initiation of luteolysis in cattle. Furthermore, our recent study has shown that IFN-tau suppresses the action of TNF-alpha on PGF(2alpha) synthesis by the bovine endometrium in vitro, suggesting that IFN-tau plays a luteoprotective role by inhibiting TNF-alpha-induced PGF(2alpha) production in early pregnancy. On the other hand, factors other than oxytocin or TNF-alpha have also been suggested to be involved in the regulation of PGF(2alpha) synthesis by bovine endometrium. The purpose of this review is to summarize our current understanding of the endocrine mechanisms that regulate the timing and pattern of uterine PGF(2alpha) secretion during the estrous cycle and early pregnancy.

Uterine-conceptus interactions and reproductive failure in cattle

The dialogue between trophectoderm cells of the conceptus and epithelial cells of the endometrium is critical to CL maintenance and embryo survival. The signal transduction mechanisms by which bovine interferon (IFN)-tau regulates cyclooxygenase (COX)-2 expression and secretion of prostaglandin F2alpha (PGF2alpha) in bovine endometrial (BEND) cells is examined. Stimulation of Protein Kinase C with a phorbol ester (phorbol 12, 13 dibutyrate [PDBu]) activates COX-2 gene expression and PGF2alpha secretion via the mitogen-activated protein kinase (MAPK) pathway. Interferon-tau attenuates PDBu activation of PGF2alpha secretion, but this inhibitory effect appears to be independent of the MAPK pathway. Embryonic IFN-tau, acting through a Type I IFN receptor, activates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway resulting in activation or repression of interferon-stimulated genes. Experimental evidence is provided that IFN-tau regulation of STATs regulates gene expression of COX-2 in a manner that decreases secretion of PGF2alpha. Maternal regulation of the antiluteolytic pathway is discussed relative to the ability of the polyunsaturated fatty acid, eicosapentaenoic (EPA), to decrease endometrial secretion of PGF2alpha and progesterone to increase both conceptus development and IFN-tau secretion.

Aromatic hydrocarbon receptor-driven Bax gene expression is required for premature ovarian failure caused by biohazardous environmental chemicals

Polycyclic aromatic hydrocarbons (PAHs) are toxic chemicals released into the environment by fossil fuel combustion. Moreover, a primary route of human exposure to PAHs is tobacco smoke. Oocyte destruction and ovarian failure occur in PAH-treated mice, and cigarette smoking causes early menopause in women. In many cells, PAHs activate the aromatic hydrocarbon receptor (Ahr), a member of the Per-Arnt-Sim family of transcription factors. The Ahr is also activated by dioxin, one of the most intensively studied environmental contaminants. Here we show that an exposure of mice to PAHs induces the expression of Bax in oocytes, followed by apoptosis. Ovarian damage caused by PAHs is prevented by Ahr or Bax inactivation. Oocytes microinjected with a Bax promoter-reporter construct show Ahr-dependent transcriptional activation after PAH, but not dioxin, treatment, consistent with findings that dioxin is not cytotoxic to oocytes. This difference in the action of PAHs versus dioxin is conveyed by a single base pair flanking each Ahr response element in the Bax promoter. Oocytes in human ovarian biopsies grafted into immunodeficient mice also accumulate Bax and undergo apoptosis after PAH exposure in vivo. Thus, Ahr-driven Bax transcription is a novel and evolutionarily conserved cell-death signaling pathway responsible for environmental toxicant-induced ovarian failure.