Dynamic regulation of expression of colony-stimulating factor 1 in the reproductive tract of cattle during the estrous cycle and in pregnancy

Dickkopf-1 expression during early bovine placentation and its down-regulation in somatic cell nuclear transfer (SCNT) pregnancies

The precise role of Dickkopf-1 (Dkk-1) during early bovine trophoblast development and subsequent placentation is not fully understood. Using somatic cell nuclear transfer (SCNT) generated pregnancies as a model of poor placentation we have found that mean levels of Dkk-1 mRNA were 1.5 fold lower in SCNT fetal cotyledon tissue at Day 50 of gestation than those resulting from artificial insemination (AI) and 2 fold lower at Days 100 and 150 (P<0.004). Dkk-1 expression in cotyledon tissue was localized by in situ hybridization to fetal binucleate cells (BNCs). Examining conceptuses from blastocyst stage we show that Dkk-1 mRNA was first evident between Days 15-20 of gestation in trophoblast tissue (when BNCs first appear) prior to the initial expression of the BNC specific bovine placental lactogen (bPL) on Day 20. Dkk-1 mRNA levels were higher than bPL in trophoblast tissue throughout the pre-attachment period (Days 24-31), however, this reversed during cotyledon development with only a subset of the bPL immunoreactive BNCs also containing Dkk-1 protein, suggesting a specific role for Dkk-1 during early placentation. One function of Dkk-1 is as an antagonist of the Wnt signaling pathway and, although Wnt5A and Wnt7A mRNAs were expressed in Day 50 bovine cotyledons, their expression levels were similar between AI and SCNT. In addition, the nuclear localization of beta-catenin, which is an indicator of activation of the Wnt pathway, was also similar between AI and SCNT cotyledon tissue. Transcriptional control of Dkk-1 was not due to changes in DNA methylation levels in the promoter region as methylation levels were no different when comparing AI and SCNT tissues. The decreased expression of Dkk-1 in SCNT cotyledons that are prone to abnormal placentation suggests a role in cotyledon formation but the mechanism and regulatory control is yet to be revealed.

Bovine endometrial legumain and TIMP-2 regulation in response to presence of a conceptus

The precise mechanism of placentation in the bovine species where a restricted trophoblast invasion occurs to form the synepitheliochorial placenta is not fully understood. This study initially investigated the conceptus-maternal interactions in the peri-attachment period by comparing the proteins present at Days 16 and 18 in uterine luminal fluid (ULF) of pregnant with nonpregnant cows using 2-D gel electrophoresis. Nine protein spots were identified that were present in greater amounts in pregnant compared to nonpregnant ULF: carbonic anhydrase, ezrin, heat shock protein 70, isocitrate dehydrogenase, nucleoside diphosphate kinase, peroxiredoxin 1, purine nucleoside phosphorylase, thioredoxin and triosephosphate isomerase and four proteins that were less abundant in ULF from the gravid compared to the nongravid horns or nonpregnant uteri: cystatin E/M, legumain, retinol-binding protein (RBP) and tissue inhibitor of matrix metalloproteinase 2 (TIMP-2). Successful placentation requires the remodelling of the endometrial surface therefore uterine mRNA and protein expression of legumain, a protease activator, and TIMP-2, a protease inhibitor, was examined in detail during the oestrous cycle and from Days 13 to 31 of pregnancy. Both mRNAs were up-regulated in the endometrium during the luteal phase of the oestrous cycle and during early pregnancy. Although legumain and TIMP-2 mRNA expression levels were similar between uterine horns at the same day of pregnancy, the amount of protein differed between gravid and nongravid horns possibly modulated by interferon-tau or by other factors produced by the conceptus. These events at the conceptus-maternal interface may provide localised control of protease activity necessary for controlling trophoblast invasion of the endometrium.

Colony-stimulating factor-1-dependent macrophage functions regulate the maternal decidua immune responses against Listeria monocytogenes infections during early gestation in mice

The association between extreme-prematurity births and intrauterine infection emphasizes the importance of understanding the host immune responses against uterine-invading microbes during early pregnancy to the prevention of preterm births. Listeria monocytogenes, a clinically relevant intracellular bacterium, has a predilection for replication at the maternofetal interface during pregnancy. Here, using mice carrying the recessive null osteopetrotic mutation in the colony-stimulating factor-1 (CSF-1) gene, we show that CSF-1-dependent macrophage functions are required for the maternal decidua immune responses against L. monocytogenes infections during early gestation in mice. In the absence of CSF-1, pregnant mice were more susceptible to uterine infection by L. monocytogenes; their inability to control the expansion of colonized bacteria in the pregnant uterus led to decidual cell death, tissue disintegration, and resorption of the developing embryo. However, CSF-1-deficient mice were able to produce significant levels of both Th1 cytokines and neutrophil chemoattractants and to recruit neutrophils to the decidual tissue in response to Listeria infection. Depletion of macrophages in hormonally induced pseudopregnant mice resulted in higher uterine bacterial levels after L. monocytogenes infection. These data suggest that the anti-Listeria responses in the maternal decidual tissue are dependent on CSF-1-regulated macrophages.

Combinatorial roles of protein kinase A, Ets2, and 3',5'-cyclic-adenosine monophosphate response element-binding protein-binding protein/p300 in the transcriptional control of interferon-tau expression in a trophoblast cell line

In ruminants, conceptus interferon-tau (IFNT) production is necessary for maintenance of pregnancy. We examined the role of protein kinase A (PKA) in regulating IFNT expression through the activation of Ets2 in JAr choriocarcinoma cells. Although overexpression of the catalytic subunit of PKA or the addition of 8-bromo-cAMP had little ability to up-regulate boIFNT1 reporter constructs on their own, coexpression with Ets2 led to a large increase in gene expression. Progressive truncation of reporter constructs indicated that the site of PKA/Ets2 responsiveness lay in a region of the promoter between -126 and -67, which lacks a cAMP response element but contains the functional Ets2-binding site and an activator protein 1 (AP1) site. Specific mutation of the former reduced the PKA/Ets2 effects by more than 98%, whereas mutation of an AP1-binding site adjacent to the Ets2 site or pharmacological inhibition of MAPK kinase 2 led to a doubling of the combined Ets2/PKA effects, suggesting there is antagonism between the Ras/MAPK pathway and the PKA signal transduction pathway. Although Ets2 is not a substrate for PKA, lowering the effective concentrations of the coactivators, cAMP response element-binding protein-binding protein (CBP)/p300, known PKA targets, reduced the ability of PKA to synergize with Ets2, suggesting that PKA effects on IFNT regulation might be mediated through CBP/p300 coactivation, particularly as CBP and Ets2 occupy the proximal promoter region of IFNT in bovine trophoblast CT-1 cells. The up-regulation of IFNT in the elongating bovine conceptus is likely due to the combinatorial effects of PKA, Ets2, and CBP/p300 and triggered via growth factors released from maternal endometrium.

Immunoendocrine aspects of endometrial function and implantation

Effective ovarian and uterine function relies on a complex interplay between the endocrine and immune systems. It is generally accepted that in reproductive tissues, oestradiol and progesterone have pro- and anti-inflammatory activities respectively and, in this regard, the paracrine effects of the sex steroids on the ovary are similar to the endocrine effects on the uterus. Ovarian leukocyte recruitment and cytokine release are central to follicle development, ovulation and corpus luteum function. At the uterine level, the cyclical changes in sex steroids regulate the number and distribution of endometrial and decidual immune cells as well as other immune signalling and surveillance factors. The uterine mucosa is unique, in that it must tolerate sperm and the allogeneic blastocyst in a way that does not compromise uterine immune surveillance against bacteria, yeast and viruses. Crosstalk between the sex steroids and immune mediators (systemic and local) are central to these functions, and this article will review these mechanisms and their importance for successful reproductive function and pregnancy success.

Effects of implantation and early pregnancy on the expression of cytokines and vascular surface molecules in the sheep endometrium

Successful implantation is a highly coordinated process involving changes in cytokines, adhesion molecules, hormones, enzymes and growth factors. This study examines the expression of key cytokines and vascular surface molecules in the pregnant uterus of sheep around the time of implantation. Uterine tissues and uterine washings were collected from non-pregnant and pregnant sheep at 17-19 days post-coitus (dpc), 26-27 and 34-36 dpc. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of caruncular/placentomal tissues revealed that cytokines IL-2, IL-4 and IL-8, which were not detected in non-pregnant uterus, were induced more strongly at 26-27 dpc than at other stages of pregnancy tested. Cytokines LIF, IL-6, IL-10, TNF-alpha were also most highly expressed at 26-27 dpc, expression of them being lower at other time-points during early pregnancy and non-pregnancy. The cytokines IL-1beta, IFN-gamma and TGF-beta were expressed in all non-pregnant and pregnant tissues examined. Enzyme-linked immunosorbent assay (ELISA) performed on uterine washings clearly detected the presence of IL-1alpha protein at 26-27 and 34-36 dpc. Immunohistochemistry revealed that expression of vascular adhesion molecule VCAM-1 in endometrial endothelium was strongly induced at 26-27 dpc in the pregnant endometrium. Expression of CD5 on vascular endothelium was not induced in placentomal tissues until 26-27 dpc and was further increased by 34-36 dpc. These results demonstrate a dynamic change in a wide range of cytokines during early stages of pregnancy, with a critical period around 26-27 dpc. In addition, at 26-27 dpc, expression of the surface/adhesion molecules, CD5 and VCAM-1, is induced on vascular endothelium of the sheep endometrium, possibly as a direct consequence of the changed cytokine environment, and may be involved in directing the changes in leucocyte migration observed during pregnancy.

Animal models of implantation

Implantation is an intricately timed event necessary in the process of viviparous birth that allows mammals to nourish and protect their young during early development. Human implantation begins when the blastocyst both assumes a fixed position in the uterus and establishes a more intimate relationship with the endometrium. Due to the impracticalities of studying implantation in humans, animal models are necessary to decipher the molecular and mechanical events of this process. This review will discuss the differences in implantation between different animal models and describe how these differences can be utilized to investigate discrete implantation stages. In addition, factors that have been shown to be involved in implantation in the human and other various animal models including growth factors, cytokines, modulators of cell adhesion, and developmental factors will be discussed, and examples from each will be given.