Expression of interferon receptor subunits, IFNAR1 and IFNAR2, in the ovine uterus

Interferon-tau, a Type 1 interferon involved in maternal recognition of pregnancy

Interferon-tau is a major product of ovine and bovine conceptuses during the period before the trophoblast makes firm attachment to the uterine wall and begins to form a placenta. Its primary function is in preventing a return to ovarian cyclicity and hence ensuring the pregnancy continues, although it undoubtedly has other roles in ensuring receptivity of the maternal endometrium. Despite having properties similar to those of other Type 1, IFN-tau is not virally inducible and functions in a constitutive process unrelated to pathogenesis. The genes for IFN-tau (IFNT), which are confined to ruminant ungulate species, would appear to be the most recently evolved mammalian Type 1 gene family and are primarily under the transcriptional control of Ets2 and signal transduction pathways that target that transcription factor. The IFNT provide an illustration of how a gene control region can be commandeered and then refined to provide a radically changed pattern of expression.

Antiviral activity of bovine uterus and placenta induced by Newcastle disease virus

The antiviral activity profile of the uterus and fetal membranes from bovine placenta, induced by the Newcastle disease virus (NDV) throughout gestation, was investigated. Explants of the endometrium and caruncles were collected from the uterus, and amniochorion, allantochorion and cotyledons, from fetal placenta. Tissue cultures were induced with ~6.0 hemagglutinating units (HU) of NDV. Supernatants were concentrated 20 fold, filtered in 100kDa cut-off membranes and antiviral activity was titrated in MDBK x VSV system. Tissues of the uterus did not exhibit antiviral activity, while allantochorion and amniochorion produced antiviral factors throughout gestation. Antiviral factors were not related with IFN-alpha, gamma, tau or TNF-alpha. The antiviral activity pattern observed showed to be related with the development of fetal membranes and increased at the end of pregnancy. Such data suggest that IFN genes inducible by virus are present in fetal membranes of the cow placenta and their expression is dependent on the age of gestation.

Pregnancy recognition and conceptus implantation in domestic ruminants: roles of progesterone, interferons and endogenous retroviruses

The present review highlights new information on pregnancy recognition and conceptus development and implantation in sheep with respect to regulation by progesterone, interferons and endogenous retroviruses. After formation of the corpus luteum, progesterone acts on the endometrium and stimulates blastocyst growth and elongation to a filamentous conceptus (embryo/fetus and associated extra-embryonic membranes). The envelope of endogenous retroviruses related to Jaagsiekte sheep retroviruses appears to intrinsically regulate mononuclear trophectoderm cell proliferation and differentiation into trophoblast giant binucleate cells. The mononuclear trophectoderm cells of elongating sheep conceptuses secrete interferon-tau, which acts on the endometrium to prevent development of the luteolytic mechanism by inhibiting transcription of the gene for the oestrogen receptor alpha in the luminal and superficial ductal glandular epithelia. These actions prevent oestrogen-induced transcription of the oxytocin receptor gene and, therefore, oxytocin-induced luteolytic pulses of prostaglandin F2alpha. Progesterone down regulation of its receptors in luminal and glandular epithelia correlates temporally with a reduction in anti-adhesive mucin land induction of secreted galectin 15 (LGALSI5) and secreted phosphoprotein 1, which are proposed to regulate trophectoderm proliferation and adhesion. Interferon-c acts on the endometrial lumenal epithelium to induce WNT7A and to stimulate LGALS 15, cathepsin L and cystatin C, which are candidate regulators of conceptus development and implantation. The number of potential contributors to maternal recognition and establishment of pregnancy continues to grow and this highlights our limited appreciation of the complexity of the key molecules and signal transduction pathways that intersect during these key developmental processes. The goal of improving reproductive efficiency by preventing embryonic losses that occur during the peri-implantation period of pregnancy in domestic ruminants provides the challenge to increase our knowledge of endometrial function and conceptus development.

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.

Conceptus signals for establishment and maintenance of pregnancy

Establishment and maintenance of pregnancy results from signaling by the conceptus (embryo/fetus and associated extraembryonic membranes) and requires progesterone produced by the corpus luteum (CL). In most mammals, hormones produced by the trophoblast maintain progesterone production by acting directly or indirectly to maintain the CL. In domestic animals (ruminants and pigs), hormones from the trophoblast are antiluteolytic in that they act on the endometrium to prevent uterine release of luteolytic prostaglandin F2 alpha (PGF). In cyclic and pregnant sheep, progesterone negatively autoregulates expression of the progesterone receptor (PR) gene in the endometrial luminal (LE) and superficial glandular epithelium (GE). Available evidence in cyclic sheep indicates that loss of the PR is closely followed by increases in epithelial estrogen receptors (ER) and then oxytocin receptors (OTR), allowing oxytocin to induce uterine release of luteolytic PGF pulses. In pregnant sheep, the conceptus trophoblast produces interferon tau (IFN tau) that acts on the endometrium to inhibit transcription of the ER alpha gene directly and the OTR gene indirectly to abrogate development of the endometrial luteolytic mechanism. Subsequently, sequential, overlapping actions of progesterone, IFN tau, placental lactogen (PL) and growth hormone (GH) comprise a hormonal servomechanism that regulates endometrial gland morphogenesis and terminal differentiated function to maintain pregnancy in sheep. In pigs, the conceptus trophoblast produces estrogen that alters the direction of PGF secretion from an endocrine to exocrine direction, thereby sequestering luteolytic PGF within the uterine lumen. Conceptus estrogen also increases expression of fibroblast growth factor 7 (FGF-7) in the endometrial LE that, in turn, stimulates proliferation and differentiated functions of the trophectoderm, which expresses the FGF-7 receptor. Strategic manipulation of these physiological mechanisms can offer therapeutic schemes to improve uterine capacity, conceptus survival and reproductive health.

Identification of interferon-tau isoforms expressed by the peri-implantation goat (Capra hircus) conceptus

Interferon-tau (IFN-tau) is the maternal recognition of pregnancy factor in pecoran ruminants. The aims of this study were to identify the various IFN-tau transcripts in the peri-implantation caprine (ca) conceptus and to compare these nucleotide sequences phylogenetically with established mRNA sequences from the goat. Conceptuses (n = 5) were collected from Boer crossbred and Angora female goats by laparotomy at days 17 and 18 of pregnancy. Total cellular RNA was extracted and RT-PCR was performed by standard procedures using a DNA polymerase with proofreading activity and gene-specific primers complimentary to non-coding regions of the published caIFN-tau sequence. Nine distinct nucleotide sequences were isolated that encode five distinct caIFN-tau proteins. These caIFN-tau have greater sequence homology with ovine IFN-tau (94-96% nucleotide identity; 90-93% amino acid identity) than with bovine IFN-tau (<92% nucleotide identity; <85% amino acid identity). The novel caIFN-tau isoforms contained pronounced nucleotide and amino acid sequence identity with one another (97-99% nucleotide identity; 94-99% amino acid identity) but only moderate sequence identity with the previously identified caIFN-tau (94-96% nucleotide identity; 87-90% amino acid identity). In conclusion, multiple caIFN-tau mRNA species are expressed during peri-implantation conceptus development and distinct clusters of caIFN-tau genes appear to have evolved in this species.

Conceptus signals for establishment and maintenance of pregnancy

Establishment and maintenance of pregnancy results from signaling by the conceptus (embryo/fetus and associated extraembryonic membranes) and requires progesterone produced by the corpus luteum. In most mammals, hormones produced by the trophoblast maintain progesterone production by acting directly or indirectly to maintain the corpus luteum. In domestic animals (ruminants and pigs), hormones from the trophoblast are antiluteolytic in that they act on the endometrium to prevent uterine release of luteolytic prostaglandin F2alpha. In cyclic and pregnant sheep, progesterone negatively autoregulates progesterone receptor gene expression in the endometrial luminal and superficial glandular epithelium. In cyclic sheep, loss of the progesterone receptor is closely followed by increases in epithelial estrogen receptors and then oxytocin receptors, allowing oxytocin to induce uterine release of luteolytic prostaglandin F2alpha pulses. In pregnant sheep, the conceptus trophoblast produces interferon tau that acts on the endometrium to inhibit transcription of the estrogen receptor alpha gene directly and the oxytocin receptor gene indirectly to abrogate development of the endometrial luteolytic mechanism. Subsequently, sequential, overlapping actions of progesterone, interferon tau, placental lactogen, and growth hormone comprise a hormonal servomechanism that regulates endometrial gland morphogenesis and terminal differentiated function to maintain pregnancy in sheep. In pigs, the conceptus trophoblast produces estrogen that alters the direction of prostaglandin F2alpha secretion from an endocrine to exocrine direction, thereby sequestering luteolytic prostaglandin F2alpha within the uterine lumen. Conceptus estrogen also increases expression of fibroblast growth factor 7 in the endometrial lumenal epithelium that, in turn, stimulates proliferation and differentiated functions of the trophectoderm, which expresses the fibroblast growth factor 7 receptor. Strategic manipulation of these physiological mechanisms may improve uterine capacity, conceptus survival, and reproductive health.

Expression of Cyclooxygenase-2 and Granulocyte-Macrophage Colony-Stimulating Factor in the Endometrial Epithelium of the Cow Is Up-Regulated During Early Pregnancy and in Response to Intrauterine Infusions of Interferon-τ1

On the basis of results obtained in vitro, we previously proposed a model in which signals from the conceptus, namely interferon-tau (IFN-tau) and prostaglandin E2, increase the expression of cyclooxygenase (COX)-2 or granulocyte-macrophage colony-stimulating factor (GM-CSF) in immune and nonimmune cells of the bovine endometrium. Two experiments were conducted to verify the validity of this hypothesis in vivo. In experiment 1, the in vivo expression of COX-2 and GM-CSF during early pregnancy was monitored. Uteri from heifers were collected at different days (d) of the estrous cycle and pregnancy (P). In experiment 2, the effects of intrauterine infusions of IFN-tau on the expression of COX-2 and GM-CSF were analyzed. Immunohistochemistry was performed on uterine sections, and image analysis was used to evaluate the staining intensity in the conceptus, the luminal epithelium (LE), and the subepithelial stroma. In experiment 1, staining for COX-2 was maximal between d18P and d24P, both in the LE and in the conceptus, whereas staining for GM-CSF reached a plateau between d18P and d30P in the LE. In experiment 2, in response to IFN-tau, COX-2 was up-regulated in the LE of the ipsilateral horn, whereas GM-CSF was enhanced in both uterine horns. The current report supports the view that the conceptus, through its secretion of IFN-tau, stimulates maternal epithelial expression of COX-2 and GM-CSF during the peri-attachment period in the cow.

Identification of genes in the ovine endometrium regulated by interferon tau independent of signal transducer and activator of transcription 1

Interferon tau (IFNtau), a type I IFN produced by the conceptus trophectoderm, increases many type I IFN-stimulated genes (ISGs) in the ovine uterine endometrial stroma and glandular epithelium (GE) using signal transducer and activator of transcription 1 (STAT1)-dependent pathways. Most ISGs are not induced or increased by IFNtau in the STAT1-negative endometrial luminal epithelium (LE). The objective was to identify genes regulated by IFNtau in a STAT1-independent manner using DNA microarray and human cell lines. The RNA from human 2fTGH and U3A (STAT1 null 2fTGH) cell lines, stimulated for 24 h with nothing or recombinant ovine IFNtau, was profiled using an Affymetrix human genome U95Av2 microarray. In 2fTGH cells, IFNtau increased the expression of 101 genes at least 2-fold, including IFN-inducible 56-kDa protein (IFI56), ISG12 or p27, and guanylate binding protein isoform I (GBP-2). In U3A cells, IFNtau increased expression of 66 genes at least 2-fold, including Wnt7a. Steady-state levels of IFI56, ISG12, GBP-2, and Wnt7a mRNAs increased in the ovine uterine endometrium between d 10 and 16 of pregnancy but not during the estrous cycle. GBP-2 and IFI56 mRNAs were expressed only in endometrial stroma, ISG12 in both LE and GE, and Wnt7a only in LE of the ovine uterus. Intrauterine infusion of ovine IFNtau increased expression of all four genes in the endometrium of cyclic ewes. Therefore, IFNtau does regulate genes independent of STAT1 in the endometrial LE and U3A cells and dependent on STAT1 in the endometrial stroma and 2fTGH cells. These IFNtau -stimulated genes may be important in establishment of uterine receptivity to the embryo and conceptus implantation given their stage-specificity in endometrium across diverse species.

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.

Pregnancy and interferon tau regulate major histocompatibility complex class I and beta2-microglobulin expression in the ovine uterus

Major histocompatibility complex (MHC) class I molecules, consisting of an alpha chain and beta2-microglobulin (beta2MG), play an important role in immune rejection responses by discriminating self and nonself and are increased by type I interferons during antiviral responses. Interferon tau (IFNtau), the pregnancy-recognition signal in ruminants, is a type I interferon produced by the ovine conceptus between Days 11 and 21 of gestation. In study 1, expression of MHC class I alpha chain and beta2MG mRNA and protein was detected primarily in endometrial luminal epithelium (LE) and glandular epithelium (GE) on Days 10 and 12 of the estrous cycle and pregnancy. On Days 14-20 of pregnancy, MHC class I and beta2MG expression increased only in endometrial stroma and GE and, concurrently, was absent in LE and superficial ductal GE (sGE). Although neither MHC class I nor beta2MG proteins were detected in Day 20 trophectoderm, beta2MG mRNA was detected in conceptus trophectoderm. In study 2, cyclic ewes were ovariectomized on Day 5, treated daily with progesterone to Day 16, received intrauterine infusions between Days 11 and 16 of either control serum proteins or recombinant ovine IFNtau, and were hysterectomized on Day 17. The IFNtau increased MHC class I and beta2MG expression only in endometrial stroma and GE. During pregnancy, MHC class I and beta2MG gene expression is inhibited in endometrial LE and sGE but, paradoxically, is stimulated by IFNtau in the stroma and GE. The silencing of MHC class I alpha chain and beta2MG genes in the endometrial LE and sGE during pregnancy recognition and establishment may be a critical mechanism preventing immune rejection of the conceptus allograft.