301. LEUKEMIA INHIBITORY FACTOR IS A CRITICAL REGULATOR OF DECIDUALIZATION OF ENDOMETRIAL STROMAL CELLS IN HUMANS AND MICE

Decidualization is the differentiation of endometrial stromal cells into decidual cells. It is a critical process in embryo implantation, placentation and the establishment of pregnancy. Inadequate decidualization can lead to infertility, abnormal placentation and recurrent miscarriage. Endometrial leukemia inhibitory factor (LIF) is indispensible in blastocyst implantation in mice and dysregulated in infertile women. LIF is produced by 1st trimester decidual cells but its role in decidualization is not known. This study aimed to examine the role of LIF in human and mouse decidualization. Primary human endometrial stomal cells (HESC) were isolated and decidualized (D) by treatment with estradiol (E) +medroxyprogesterone acetate (MPA) for 14 days. HESC were also treated with E+MPA+/–LIF (0.5, 5, 50, 100 and 200 ng/mL) for 14 days. Prolactin secretion was used to assess the extent of decidualization (n = 6). D and non-D HESC were also treated with LIF (0.5, 5, 50, 100 and 200 ng/mL +/– LIF inhibitor) for 15min and the phosphorylation (p) of signal transducer and activator of transcription (STAT)3/STAT3 abundance was detected by Western blot (n = 4). RNA was isolated for analysis of LIF and LIF receptor (R) mRNA expression during decidualization (n = 4). HESC treated with E+MPA+LIF (50, 100 and 200 ng/mL) secreted more prolactin compared to cells treated with E+MPA alone (P < 0.05). LIF increased pSTAT3/STAT3 abundance in D and non-D cells while LIF+LIF inhibitor abolished pSTAT3/STAT3. LIF mRNA was downregulated while LIF-R mRNA increased during decidualization. In vivo, mated mice (n = 5) were injected intraperitoneally with a unique long acting LIF inhibitor post-implantation at day 4.5 of pregnancy and resulted in reduced decidualization compared to control. This is the first study to demonstrate that LIF promoted decidualization of HESC possibly via pSTAT3. It further suggested that LIF regulated decidualization in mice demonstrating a newly identified critical role for LIF in the establishment of pregnancy.

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P–322 Addressing progesterone and cAMP signalling pathways for decidualization induction of endometrial stromal cells of patients with endometriosis

Human Reproduction ◽

10.1093/humrep/deab130.321 ◽

2021 ◽

Vol 36 (Supplement_1) ◽

Author(s):

J Moyer ◽

D Dunj. Baston-Buest ◽

G Wennemuth ◽

A Bielfeld ◽

R Grümmer

Keyword(s):

Stromal Cells ◽

Day Treatment ◽

Embryo Implantation ◽

Flow Cytometric Analysis ◽

Prolactin Secretion ◽

In Vivo Model ◽

Endometrial Stromal Cells ◽

Simultaneous Application

Abstract Study question Which compounds/compound combinations are most effective in decidualization induction of endometrial stromal cells (ESCs) of patients with and without endometriosis? Summary answer Combination of compounds addressing different steps in the signalling cascade of decidualization induce decidualization more effectively than application of the individual compounds alone. What is known already Decidualization is the monthly recurring differentiation process of the ESCs in preparation for embryo implantation in human. Undifferentiated ESCs reveal an increased potential to proliferate and invade after retrograde menstruation. This may lead to the formation of ectopic lesions and the manifestation of the chronic gynaecological disease of endometriosis due to an impairment of the decidualization process. Study design, size, duration Compounds and compound combinations addressing the progesterone receptor- or the cAMP-mediated pathway were evaluated with regard to their own and their synergistic potential to induce decidualization of ESCs from women with (n = 10) and without (n = 10) endometriosis during a 6-day treatment. Participants/materials, setting, methods Human primary ESCs were isolated via enzymatic-mechanic digestion from eutopic endometrium from women with and without endometriosis and treated for 6 days in vitro with different progestins (progesterone, medoxyprogesterone acetate (MPA)), 8-Br-cAMP, forskolin, or phosphodiesterase (PDE)-inhibitor (Rolipram) alone or in combination. The degree of decidualization induction was quantified by morphological, biochemical (prolactin) and molecular (HAND2, FOXO1) parameters by means of ELISA, flow cytometric analysis, Realtime PCR and Western blot analysis. Main results and the role of chance After 6 days of treatment, decidualization was induced by forskolin as well as by 8-Br-cAMP whereas progestins or PDE alone hardly induced prolactin secretion by ESCs as a marker of decidualization. A change of morphology from undifferentiated fibroblast-like cells to rounded cells could be observed in parallel with the secretion of prolactin. Forskolin and 8-Br-cAMP-induced decidualization was significantly enhanced by MPA but not by progesterone. These effects were similar in ESCs from women with and without endometriosis. Moreover, forskolin-induced decidualization was significantly enhanced by simultaneous application of PDE. Interestingly, this effect was higher in cells of patients with endometriosis. An induction of decidualization in ESCs was associated with a parallel increase of the process-associated transcription factors HAND2 and FOXO1. This rise of transcription was markedly increased in combination with MPA but not with progesterone. Limitations, reasons for caution Endometrial tissue was obtained from women undergoing infertility treatment and thus may differ from the endometrium of fertile women. Results obtained from primary cells in vitro may not cover the in vivo situation in all respects. Wider implications of the findings: The results of this study provide baseline data for the development of a possible therapeutical approach to induce decidualization as a treatment option for endometriosis. Further research is required to determine the effectiveness of the in vitro tested compound combinations in an in vivo model. Trial registration number Not applicable

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P-322 Addressing progesterone and cAMP signalling pathways for decidualization induction of endometrial stromal cells of patients with endometriosis

Human Reproduction ◽

10.1093/humrep/deab127.077 ◽

2021 ◽

Vol 36 (Supplement_1) ◽

Author(s):

J Moyer ◽

D Dunja Baston-Buest ◽

G Wennemuth ◽

A Bielfeld ◽

R Grümmer

Keyword(s):

Stromal Cells ◽

Day Treatment ◽

Embryo Implantation ◽

Flow Cytometric Analysis ◽

Prolactin Secretion ◽

In Vivo Model ◽

Endometrial Stromal Cells ◽

Simultaneous Application

Abstract Study question Which compounds/compound combinations are most effective in decidualization induction of endometrial stromal cells (ESCs) of patients with and without endometriosis? Summary answer Combination of compounds addressing different steps in the signalling cascade of decidualization induce decidualization more effectively than application of the individual compounds alone. What is known already Decidualization is the monthly recurring differentiation process of the ESCs in preparation for embryo implantation in human. Undifferentiated ESCs reveal an increased potential to proliferate and invade after retrograde menstruation. This may lead to the formation of ectopic lesions and the manifestation of the chronic gynaecological disease of endometriosis due to an impairment of the decidualization process. Study design, size, duration Compounds and compound combinations addressing the progesterone receptor- or the cAMP-mediated pathway were evaluated with regard to their own and their synergistic potential to induce decidualization of ESCs from women with (n = 10) and without (n = 10) endometriosis during a 6-day treatment. Participants/materials, setting, methods Human primary ESCs were isolated via enzymatic-mechanic digestion from eutopic endometrium from women with and without endometriosis and treated for 6 days in vitro with different progestins (progesterone, medoxyprogesterone acetate (MPA)), 8-Br-cAMP, forskolin, or phosphodiesterase (PDE)-inhibitor (Rolipram) alone or in combination. The degree of decidualization induction was quantified by morphological, biochemical (prolactin) and molecular (HAND2, FOXO1) parameters by means of ELISA, flow cytometric analysis, Realtime PCR and Western blot analysis. Main results and the role of chance After 6 days of treatment, decidualization was induced by forskolin as well as by 8-Br-cAMP whereas progestins or PDE alone hardly induced prolactin secretion by ESCs as a marker of decidualization. A change of morphology from undifferentiated fibroblast-like cells to rounded cells could be observed in parallel with the secretion of prolactin. Forskolin and 8-Br-cAMP-induced decidualization was significantly enhanced by MPA but not by progesterone. These effects were similar in ESCs from women with and without endometriosis. Moreover, forskolin-induced decidualization was significantly enhanced by simultaneous application of PDE. Interestingly, this effect was higher in cells of patients with endometriosis. An induction of decidualization in ESCs was associated with a parallel increase of the process-associated transcription factors HAND2 and FOXO1. This rise of transcription was markedly increased in combination with MPA but not with progesterone. Limitations, reasons for caution Endometrial tissue was obtained from women undergoing infertility treatment and thus may differ from the endometrium of fertile women. Results obtained from primary cells in vitro may not cover the in vivo situation in all respects. Wider implications of the findings The results of this study provide baseline data for the development of a possible therapeutical approach to induce decidualization as a treatment option for endometriosis. Further research is required to determine the effectiveness of the in vitro tested compound combinations in an in vivo model. Trial registration number not applicable

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The actions of resveratrol in decidualizing endometrium: acceleration or inhibition?†

Biology of Reproduction ◽

10.1093/biolre/ioaa172 ◽

2020 ◽

Vol 103 (6) ◽

pp. 1152-1156

Author(s):

Keiji Kuroda ◽

Asako Ochiai ◽

Jan J Brosens

Keyword(s):

Stromal Cells ◽

Ovarian Function ◽

Embryo Implantation ◽

Clinical Effects ◽

Polyphenolic Compound ◽

Endometrial Stromal Cells ◽

Decidual Cells ◽

Multistep Process ◽

Drug Interventions

Abstract Resveratrol, a natural polyphenolic compound, is widely studied for its anti-inflammatory and antisenescent properties. Recently, two studies reported seemingly conflicting findings on the actions of resveratrol on decidualization of human endometrial stromal cells (HESCs). One study by Ochiai et al. demonstrated that resveratrol inhibits decidual transformation of primary cultured HESCs. The other study by Mestre Citrinovitz et al., showed that resveratrol enhances decidualization of HESCs in culture. At a glance, the reason for these opposing observations seems puzzling. However, recent studies demonstrated that decidualization is a multistep process, which starts with an acute proinflammatory stress response that lasts for several days and is followed by the emergence of stress-resistant decidual cells as well as senescent decidual cells. The balance between these decidual subpopulations may determine if the cycling endometrium can successfully transition into the decidua of pregnancy upon embryo implantation. Here, we explore the importance of timing of drugs aimed at modulating the decidual response. We posit that resveratrol treatment during the initial proinflammatory decidual phase, i.e., coinciding with the implantation window in vivo, inhibits decidual transformation of the endometrium. However, when given after the initial phase, resveratrol may promote decidualization by inhibiting decidual senescence. Further, if restricted to the proliferative phase, resveratrol may promote ovarian function without adversely impacting on embryo implantation or decidualization. Thus, failure to align drug interventions with the correct phase of the menstrual cycle may negate beneficial clinical effects and results in adverse reproductive outcomes.

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Leukemia Inhibitory Factor: Roles in Embryo Implantation and in Nonhormonal Contraception

The Scientific World JOURNAL ◽

10.1155/2014/201514 ◽

2014 ◽

Vol 2014 ◽

pp. 1-10 ◽

Cited By ~ 33

Author(s):

Naguib Salleh ◽

Nelli Giribabu

Keyword(s):

Leukemia Inhibitory Factor ◽

Growth And Development ◽

Immune Modulation ◽

Embryo Implantation ◽

Critical Role ◽

Inhibitory Factor ◽

Trophoblast Invasion ◽

Leukaemia Inhibitory Factor ◽

Multiple Processes

Leukaemia inhibitory factor (LIF) plays an indispensible role in embryo implantation. Aberrant LIF production is linked to implantation failure. LIF regulates multiple processes prior to and during implantation such as uterine transformation into a receptive state, decidualization, blastocyst growth and development, embryo-endometrial interaction, trophoblast invasion, and immune modulation. Due to its critical role, LIF has been a target for a nonhormonal contraception. In this review, we summarize up-to-date information on the role of LIF in implantation and its role in contraception.

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The Role of Decidual Subpopulations in Implantation, Menstruation and Miscarriage

Frontiers in Reproductive Health ◽

10.3389/frph.2021.804921 ◽

2021 ◽

Vol 3 ◽

Author(s):

Joanne Muter ◽

Chow-Seng Kong ◽

Jan J. Brosens

Keyword(s):

Stromal Cells ◽

Acute Stress ◽

Embryo Implantation ◽

Recurrence Risk ◽

Tissue Remodelling ◽

Endometrial Stromal Cells ◽

Decidual Cells ◽

Unk Cells ◽

Acute Stress Response

In each menstrual cycle, the endometrium becomes receptive to embryo implantation while preparing for tissue breakdown and repair. Both pregnancy and menstruation are dependent on spontaneous decidualization of endometrial stromal cells, a progesterone-dependent process that follows rapid, oestrogen-dependent proliferation. During the implantation window, stromal cells mount an acute stress response, which leads to the emergence of functionally distinct decidual subsets, reflecting the level of replication stress incurred during the preceding proliferative phase. Progesterone-dependent, anti-inflammatory decidual cells (DeC) form a robust matrix that accommodates the conceptus whereas pro-inflammatory, progesterone-resistant stressed and senescent decidual cells (senDeC) control tissue remodelling and breakdown. To execute these functions, each decidual subset engages innate immune cells: DeC partner with uterine natural killer (uNK) cells to eliminate senDeC, while senDeC co-opt neutrophils and macrophages to assist with tissue breakdown and repair. Thus, successful transformation of cycling endometrium into the decidua of pregnancy not only requires continuous progesterone signalling but dominance of DeC over senDeC, aided by recruitment and differentiation of circulating NK cells and bone marrow-derived decidual progenitors. We discuss how the frequency of cycles resulting in imbalanced decidual subpopulations may determine the recurrence risk of miscarriage and highlight emerging therapeutic strategies.

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Downregulation of decidual SKP2 is associated with human recurrent miscarriage

10.21203/rs.3.rs-260689/v1 ◽

2021 ◽

Author(s):

Shijian Lv ◽

Mei Liu ◽

Lizhen Xu ◽

Cong Zhang

Keyword(s):

Stromal Cells ◽

Recurrent Miscarriage ◽

Aerobic Glycolysis ◽

Critical Role ◽

Protein S ◽

Pcr Analysis ◽

Endometrial Stromal Cells ◽

Downstream Target ◽

F Box Protein

Abstract Background: Recurrent miscarriage (RM) is a very frustrating problem for both couples and clinicians. To date, the etiology of RM remains poorly understood. Decidualization plays a critical role in implantation and the maintenance of pregnancy, and its deficiency is closely correlated with RM. The F-box protein S-phase kinase associated protein 2 (SKP2) is a key component of the SCF-type E3 ubiquitin ligase complex, which is critically involved in ErbB family-induced Akt ubiquitination, aerobic glycolysis and tumorigenesis. SKP2 is pivotal for reproduction, and SKP2-deficient mice show impaired ovarian development and reduced fertility.Methods: Here, we investigated the expression and function of SKP2 in human decidualization and its relation with RM. A total of 40 decidual samples were collected. Quantitative PCR analysis, western blot analysis and immunohistochemistry analysis were performed to analyze the differential expression of SKP2 between RM and control cells. For in vitro induction of decidualization, both HESCs (human endometrial stromal cells) cell line and primary ESCs (endometrial stromal cells) were used to analyze the effects of SKP2 on decidualization via siRNA transfection.Results: Compared to normal pregnant women, the expression of SKP2 was reduced in the decidual tissues from individuals with RM. After in vitro induction of decidualization, knockdown of SKP2 apparently attenuated the decidualization of HESCs and resulted in the downregulation of HOXA10 and FOXM1, which are essential for normal human decidualization. Moreover, our experiments demonstrated that SKP2 silencing reduced the expression of its downstream target GLUT1.Conclusions: Our study indicates a functional role of SKP2 in RM: downregulation of SKP2 in RM leads to impaired decidualization and downregulation of GLUT1 and consequently predisposes individuals to RM.

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Loss of imprinting control of the lncRNA H19-fetal mitogen IGF2 gene cluster in the decidual microenvironment of patients with idiopathic spontaneous miscarriages

10.21203/rs.3.rs-1044267/v1 ◽

2021 ◽

Author(s):

Xue Wen ◽

Qi Zhang ◽

Lei Zhou ◽

Zhaozhi Li ◽

Xue Wei ◽

...

Keyword(s):

Stromal Cells ◽

Noncoding Rna ◽

Recurrent Miscarriage ◽

Critical Role ◽

Ctcf Binding ◽

Ctcf Binding Site ◽

Monoallelic Expression ◽

Endometrial Stromal Cells ◽

Control Center ◽

Loss Of Imprinting

Abstract Miscarriage, the spontaneous loss of a pregnancy before the fetus achieves viability, is a common complication of pregnancy. Decidualization plays a critical role in the implantation of the embryo. To search for molecular factors underlying miscarriage, we explored the role of long noncoding RNAs (lncRNAs) in the decidual microenvironment, where the molecular crosstalk at the feto–maternal interface occurs. By integrating RNA-seq data from recurrent miscarriage patients and decidualized endometrial stromal cells, we identified H19 , a noncoding RNA that exhibits paternally imprinted monoallelic expression in normal tissues, as the most upregulated lncRNA associated with miscarriage. Aberrant upregulation of H19 lncRNA was observed in decidual tissues derived from patients with spontaneous miscarriage as well as decidualized endometrial stromal cells. The maternally imprinted fetal mitogen Igf2, which is usually reciprocally co-regulated with H19 in the same imprinting cluster, was also upregulated. Notably, both genes underwent loss of imprinting, as H19 and IGF2 were actively transcribed from both parental alleles in decidual tissues. Mechanistically, this loss of imprinting in decidual tissues was associated with the loss of the H3K27m3 suppression marker in the IGF2 promoter, CpG hypomethylation at the central CTCF binding site in the imprinting control center (ICR) that is located between IGF2 and H19 , and the loss of CTCF-mediated intrachromosomal looping. These data provide the first evidence that aberrant control of the ICR epigenotype-intrachromosomal looping- H19/IGF2 imprinting pathway may be a critical epigenetic risk factor in the abnormal decidualization related to miscarriage.

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211. Proteomic identification of caldesmon as one of the physiological substrates of proprotein convertase 6 during decidualisation

Reproduction Fertility and Development ◽

10.1071/srb08abs211 ◽

2008 ◽

Vol 20 (9) ◽

pp. 11

Author(s):

B. M. Hardman ◽

L. M. Kilpatrick ◽

A. N. Stephens ◽

J. I. C. Chen ◽

P. Stanton ◽

...

Keyword(s):

Stromal Cells ◽

Hypoxia Inducible Factor ◽

Immunohistochemical Analysis ◽

Spectrometric Analysis ◽

Structural Protein ◽

Proprotein Convertase ◽

Endometrial Stromal Cells ◽

Decidual Cells

We have previously demonstrated that proprotein convertase 5/6 (PC6), a member of the proprotein convertase (PC) family, is a critical endometrial factor for implantation. PC6 is upregulated in the endometrium specifically at implantation in association with epithelial differentiation (in human and monkey) and stromal cell decidualisation (in the mouse, human and monkey). Knockdown of endometrial PC6 during early pregnancy in mice in vivo led to complete failure of implantation, while blocking of PC6 production in human endometrial stromal cells in vitro inhibited decidualisation. PCs convert a range of precursor proteins of important functions into their bioactive forms; they are thus regarded as critical ‘master switch’ molecules. We hypothesise that PC6 exerts its roles in the endometrium by regulating proteins of diverse functions essential for implantation. In this study, we utilised proteomic technology and aimed to identify proteins that are specifically cleaved by PC6 in human endometrial stromal cells (HESC) during decidualisation. HESC were decidualised with cyclic AMP, the cell lysates were treated with and without recombinant human PC6-A (rPC6-A), and the 2D Differential in Gel Electrophoresis (2D DiGE) protein profiles were compared between the two treatments. We identified several proteins which were differentially cleaved following the addition of rPC6-A. Mass spectrometric analysis confirmed that the most abundant of these were caldesmon, tropomyosin-2, tropomyosin-4, hypoxia Inducible factor-1 and chloride intracellular channel-1. These proteins showed spot shifts in hPC6-A treated HESC lysates consistent with hPC6-A cleavage. western blot analysis confirmed the specific cleavage of caldesmon by PC6 in HESCs, and immunohistochemical analysis showed co-localisation of caldesmon and PC6 in decidual cells in human endometrial tissue. Given that caldesmon is a structural protein previously found to be involved in actin filament reorganisation, our results strongly suggest that PC6 is a mediator of structural remodelling of stromal cells during decidualisation in the endometrium.

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Implantation Failure in Female Kiss1−/− Mice Is Independent of Their Hypogonadic State and Can Be Partially Rescued by Leukemia Inhibitory Factor

Endocrinology ◽

10.1210/en.2013-1916 ◽

2014 ◽

Vol 155 (8) ◽

pp. 3065-3078 ◽

Cited By ~ 32

Author(s):

Michele Calder ◽

Yee-Ming Chan ◽

Renju Raj ◽

Macarena Pampillo ◽

Adrienne Elbert ◽

...

Keyword(s):

Leukemia Inhibitory Factor ◽

Hypogonadotropic Hypogonadism ◽

Embryo Implantation ◽

Critical Role ◽

Inhibitory Factor ◽

Implantation Failure ◽

Mouse Uterus ◽

Female Mice ◽

Wild Type Female ◽

Neuroendocrine Axis

The hypothalamic kisspeptin signaling system is a major positive regulator of the reproductive neuroendocrine axis, and loss of Kiss1 in the mouse results in infertility, a condition generally attributed to its hypogonadotropic hypogonadism. We demonstrate that in Kiss1−/− female mice, acute replacement of gonadotropins and estradiol restores ovulation, mating, and fertilization; however, these mice are still unable to achieve pregnancy because embryos fail to implant. Progesterone treatment did not overcome this defect. Kiss1+/− embryos transferred to a wild-type female mouse can successfully implant, demonstrating the defect is due to maternal factors. Kisspeptin and its receptor are expressed in the mouse uterus, and we suggest that it is the absence of uterine kisspeptin signaling that underlies the implantation failure. This absence, however, does not prevent the closure of the uterine implantation chamber, proper alignment of the embryo, and the ability of the uterus to undergo decidualization. Instead, the loss of Kiss1 expression specifically disrupts embryo attachment to the uterus. We observed that on the day of implantation, leukemia inhibitory factor (Lif), a cytokine that is absolutely required for implantation in mice, is weakly expressed in Kiss1−/− uterine glands and that the administration of exogenous Lif to hormone-primed Kiss1−/− female mice is sufficient to partially rescue implantation. Taken together, our study reveals that uterine kisspeptin signaling regulates glandular Lif levels, thereby identifying a novel and critical role for kisspeptin in regulating embryo implantation in the mouse. This study provides compelling reasons to explore this role in other species, particularly livestock and humans.

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227.An inhibitor of leukemia inhibitory factor signalling blocks embryo implantation in the mouse

Reproduction Fertility and Development ◽

10.1071/srb04abs227 ◽

2004 ◽

Vol 16 (9) ◽

pp. 227

Author(s):

E. Dimitriadis ◽

C. Stoikos ◽

M. Baca ◽

W. Fairlie ◽

A. D. Uboldi ◽

...

Keyword(s):

Early Pregnancy ◽

Leukemia Inhibitory Factor ◽

Embryo Implantation ◽

Uterine Horn ◽

Inhibitory Factor ◽

Luminal Epithelium ◽

Pregnant Uterus ◽

Implantation Sites ◽

Post Implantation

Embryo implantation is a critical step in the establishment of pregnancy. Endometrial leukemia inhibitory factor (LIF) is essential for embryo implantation in the mouse (1). Uterine LIF is expressed in the luminal epithelium on Day 3 of pregnancy (D3) (D0�=�day of plug detection) and signals via activation of signal transducer and activator of transcription (Stat) 3 (2). We examined the effect of a novel LIF signalling inhibitor on the phosphorylation (p) of Stat3 during early pregnancy and on embryo implantation in the mouse. We injected LIF inhibitor into one uterine horn and PBS into the other uterine horn of the mouse at D3 and examined the effect on pStat3 immunostaining in the luminal epithelium between 30 and 360�min later. We found no immunoreactive pStat3 in luminal epithelium following treatment with LIF inhibitor at 60 and 90�min but variable staining at other time points. The PBS-treated uterine horn showed intense immunostaining at all times. LIF inhibitor (1mg/kg body weight per day) or PBS was administered to mice (a) subcutaneously, (b) intraperitoneally, at 8-hourly intervals for 3�days from D2, or (c) continuously into the peritoneal cavity via Alzet pumps from D2. No effect was seen on implantation at D6. When LIF antagonist (3.5mg/kg/day) or PBS were administered by Alzet pumps from D2 together with ip injections, 4-hourly from D3 for 36�h, there were no implantation sites in the uteri of treated mice (n�=�5) while the control mice (n�=�4) had 3.6��0.5�sites (P�<�0.001). Histologically, the uteri of the treated mice resembled non-pregnant uterus, while the control uterus resembled post-implantation uterus. The results demonstrate that treatment of mice during early pregnancy with a novel LIF inhibitor blocks LIF action in vivo and embryo implantation. This knowledge is important for development of novel contraceptives. (1) Stewart, C. L., Kaspar, P., Brunet, L. J., Bhatt, H., Gadi, I., Kontgen, F., Abbondanzo, S. J. (1992) Nature 359, 76–79. (2) Cheng, J. G., Chen, J. R., Hernandez, L., Alvord, W. G., Stewart, C. L. (2001) Proc. Natl Acad. Sci. USA 98, 8680–8685.

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