Cytochrome P450 26A1 regulates the clusters and killing activity of NK cells during the peri-implantation period.

Cytochrome P450 26A1 (CYP26A1) plays a vital role in early pregnancy in mice. Our previous studies have found that CYP26A1 affects embryo implantation by modulating natural killer (NK) cells, and that there is a novel population of CYP26A1+ NK cells in the uteri of pregnant mice. The aim of this study was to investigate the effects of CYP26A1 on the subsets and killing activity of NK cells. Through single-cell RNA sequencing (scRNA-seq), we identified four NK cell subsets in the uterus, namely, conventional NK (cNK), tissue-resident NK (trNK) 1 and 2, and proliferating trNK (trNKp). The two most variable subpopulations after uterine knockdown of CYP26A1 were trNKp and trNK2 cells. CYP26A1 knockdown significantly downregulated the expression of the NK cell function-related genes Cd44, Cd160, Vegfc, and Slamf6 in trNK2 cells, and Klra17 and Ogn in trNKp cells. Both RNA-seq and cytotoxicity assays confirmed that CYP26A1+ NK cells had low cytotoxicity. These results indicate that CYP26A1 may affect the immune microenvironment at the maternal-foetal interface by regulating the activity of NK cells.

Cytochrome P450 26A1 Modulates the Polarization of Uterine Macrophages During the Peri-Implantation Period.

Uterine M1/M2 macrophages activation states undergo dynamic changes throughout pregnancy, and inappropriate macrophages polarization can cause adverse pregnancy outcomes, especially during the peri-implantation period. Our previous studies have confirmed that Cytochrome P450 26A1 (CYP26A1) can affect embryo implantation by regulating uterine NK cells and DCs. The aim of this study was to investigate whether CYP26A1 regulates the polarization of uterine macrophages in early pregnancy. Here, we observed that Cyp26a1 was significantly upregulated in M1 as compared with M2 of uterine macrophages, Raw264.7 and iBMDM. Knockdown of CYP26A1 in mice uterine significantly decreased the number of embryo implantation sites and the proportion of CD45+F4/80+CD206 - M1-like uterine macrophages. Primary uterine macrophages treated with anti-CYP26A1 antibody expressed significantly lower levels of M1 markers Nos2, Il1b, Il6 and Tnf-a. In CYP26A1 knockout Raw264.7 cells, the protein levels of M1 markers TNF-α, IL-6 and CD86 were significantly decreased as compared with the wild type cells. Moreover, CYP26A1 deficiency decreased the ability to produce nitric oxide and increased the phagocytosis capacity of Raw264.7 cells under M1 stimulation state. The re-introduction of CYP26A1 partially reversed the polarization levels of M1 in CYP26A1 knockout Raw264.7 cells. CYP26A1 may regulate the polarization of uterine macrophages to M1 through Stap1 and Slc7a2. In summary, these results indicate that CYP26A1 plays a significant role in macrophage polarization, and knockdown of CYP26A1 can cause insufficient M1 polarization during the peri-implantation period, which has adverse effects on blastocyst implantation.

A novel Cytochrome P450 26A1 expressing NK cell subset at the mouse maternal-foetal interface.

Cyp26a1 had important roles in mouse embryo implantation and was highly expressed in some of NK cells at the human maternal-foetal interface in early pregnancy. However, the regulatory effect of Cyp26a1 on NK cells remains poorly understood. Through qPCR and flow cytometric assays, we found that Cyp26a1 was expressed by mouse uterine NK cells but not spleen NK cells during the peri-implantation period and there was a group of NK cells that highly expressed Cyp26a1, that is Cyp26a1+ NK cell subset. single cell-population transcriptome sequencing on Cyp26a1+ NK and Cyp26a1- NK cell subsets was performed. We found that there were 3957 differentially expressed genes in the Cyp26a1+ NK cell subset with a cut-off of fold change ≥2 and FDR < 0.01, 2509 genes were up-regulated and 1448 genes were down-regulated in Cyp26a1+ NK cell subset. Moreover, cytokine-cytokine receptor interaction signalling pathway and natural killer cell-mediated cytotoxicity signalling pathway were enriched according to KEGG pathway enrichment analysis. We further found that the expression of Gzma and Klrg1 was significantly increased and Fcgr4 was significantly decreased when inhibiting Cyp26a1. Our experimental results show that there is a novel NK cell subset of Cyp26a1+ NK cells in mouse uterus and Cyp26a1 can regulate the gene expression of Gzma, Klrg1 and Fcgr4 in the Cyp26a1+ NK cells.

Cytochrome P450 26A1 modulates uterine dendritic cells in mice early pregnancy.

Cytochrome P450 26A1 (CYP26A1) plays important roles in the mice peri-implantation period. Inhibiting its expression or function leads to pregnancy failure. However, little is known about the underlying mechanisms involved, especially the relationship between CYP26A1 and immune cells. In this study, using Cyp26a1-specific antisense morpholigos (Cyp26a1-MO) knockdown mice model and pCR3.1-Cyp26a1 vaccine mice model, we found that the number of uterine CD45+ CD11c+ MHCIIlo-hi F4/80- dendritic cells (DCs) was significantly decreased in the treated mice. The percentage of mature DCs (CD86hi ) was obviously lower and the percentage of immature DCs (CD86lo ) was remarkably higher in uterine DCs in the treatment group than that of the control group. Further experiments found that ID2, a transcription factor associated with DCs development, and CD86, a DC mature marker molecule, were both significantly reduced in mice uteri in the treated group. In vitro, ID2 and CD86 also decreased in bone marrow-derived DCs under Cyp26a1-MO treatment. These findings provide novel information that CYP26A1 might affect the embryo implantation via modulating the differentiation and maturation of uterine DCs.

Cytochrome P450 26A1 modulates natural killer cells in mouse early pregnancy.

Cytochrome P450 26A1 (CYP26A1) has a spatiotemporal expression pattern in the uterus, with a significant increase in mRNA and protein levels during peri-implantation. Inhibiting the function or expression of CYP26A1 can cause pregnancy failure, suggesting an important regulatory role of CYP26A1 in the maintenance of pregnancy. However, little is known about the exact mechanism involved. In this study, using a pCR3.1-cyp26a1 plasmid immunization mouse model and a Cyp26a1-MO (Cyp26a1-specific antisense oligos) knockdown mouse model, we report that the number of Dolichos biflorus agglutinin (DBA) lectin-positive uterine natural killer (uNK) cells was reduced in pCR3.1-cyp26a1 plasmid immunized and Cyp26a1-MO-treated mice. In contrast, the percentage of CD3- CD49b+ NK cells in the uteri from the treatment group was significantly higher than that of the control group in both models. Similarly, significantly up-regulated expression of CD49b (a pan-NK cell marker), interferon gamma, CCL2, CCR2 (CCL2 receptor) and CCL3 were detected in the uteri of pCR3.1-cyp26a1- and Cyp26a1-MO-treated mice. Transcriptome analysis suggested that CYP26A1 might regulate NK cells through chemokines. In conclusion, the present data suggest that silencing CYP26A1 expression/function can decrease the number of uNK cells and significantly increase the percentage of CD3- CD49b+ NK cells in the uteri of pregnant mice. These findings provide a new line of evidence correlating the deleterious effects of blocking CYP26A1 in pregnancy with the aberrant regulation of NK cells in the uterus.

The Balance between Conventional DCs and Plasmacytoid DCs Is Pivotal for Immunological Tolerance during Pregnancy in the Mouse.

Dendritic cells (DCs), which can shape their functions depending on the microenvironment, are crucial for the delicate balance of immunity and tolerance during pregnancy. However, the mechanism underlying the microenvironment-educated plasticity of DC differentiation during pregnancy remains largely unclear. Here, we found that the differentiation of conventional DCs (cDCs) and plasmacytoid DCs (pDCs) is regulated in a tissue-specific manner during pregnancy. The ratio of cDCs and pDCs remained constant in the spleen. However, the ratio changed in the para-aortic lymph nodes (LNs), where cDC percentages were significantly reduced concurrent with an increase in pDCs from E8.5 to E16.5. Moreover, the expansion of pDCs and T regulatory (Treg) cells was correlated in the para-aortic LNs, and pDCs had more potential to induce regulatory T cells (Tregs) compared with cDCs (independent of IDO expression). Notably, the balance between cDCs and pDCs is disrupted in IFN-γ-induced abnormal pregnancy, accompanied by lower Treg percentages in the para-aortic LNs and decidua. To further identify the underlying mechanism, we found that elevated IFN-γ can increase the levels of GM-CSF to alter the differentiation of pDCs into cDCs in vivo. Therefore, we provide a novel regulatory mechanism underlying pregnancy-related immune tolerance that involves the balance of DC subsets, which may offer a new target for the prevention of human spontaneous abortion.

Seminal plasma induces inflammation in the uterus through the γδ T/IL-17 pathway.

After insemination, a large number of leukocytes migrate into the uterus, which is accompanied by intense inflammation. However, the details of how seminal plasma interacts with the uterus are still not very clear. Here, we present that neutrophils migrate and accumulate around the uterine epithelium following insemination, which is accompanied by an increase in interleukin (IL) 17A levels. Additionally, we find that γδ T cells are the major source of IL-17A, and the seminal plasma could induce the γδ T cells to secret IL-17A. Blocking IL-17A could reduce the number of neutrophils in the uterus and prevent them from migrating to the epithelium by decreasing the chemokines CXCL1, CXCL2 and CXCL5. Blocking IL-17A did not affect the Th1/Th2 balance but actually diminished the inflammation in the uterus by reducing the expression of IL-1ß and TNF-α. In summary, we found a new mechanism by which seminal plasma could influence the inflammation in the uterus through the γδ T/IL-17 pathway to regulate the expression of various chemokines and cytokines.

IFN-γ modulates Ly-49 receptors on NK cells in IFN-γ-induced pregnancy failure.

We have previously shown that interferon gamma (IFN-γ) induces aberrant CD49b(+) natural killer (NK) cell recruitment by regulating CX3CL1 and eventually provokes foetal loss. In this study, we show that IFN-γ also modulates Ly-49 receptors on NK cells during pregnancy failure. The percentages of Ly-49A(+) and Ly-49G2(+) NK cells in the uteri of the IFN-γ-treated group were significantly lower than those observed in the control group. Moreover, the median fluorescence intensity (MFI) values of Ly-49A and Ly-49G2 expression on NK cells in the uteri of the IFN-γ-treated group were significantly lower than those of the control group. Using isolated spleen leucocytes, we further found that IFN-γ significantly reduced the percentage of Ly-49A(+) NK cells in vitro. However, CX3CL1 was not involved in the modulation of Ly-49 receptors, and the expression of CX3CR1 was not regulated by IFN-γ in spleen leucocytes. Collectively, our data indicate that IFN-γ can modulate Ly-49 receptors on NK cells and this process may play a role in IFN-γ-induced pregnancy failure. Thus, we provide a new line of evidence correlating the deleterious effects of IFN-γ with its role in regulating NK cell Ly-49 receptors during pregnancy failure.

Regulation of cyp26a1 on Th17 cells in mouse peri-implantation.

Cytochrome P450 26A1 (cyp26a1) is expressed in the mouse uterus during peri-implantation. The repression of this protein is closely associated with a reduction in implantation sites, suggesting a specific role for cyp26a1 in pregnancy and prompting questions concerning how a metabolic enzyme can generate this distinct outcome. To explore the effective downstream targets of cyp26a1 and confirm if its role in peri-implantation depends on its metabolic substrate RA (retinoic acid), we characterized the changes in the peripheral blood, spleen and uterine implantation sites using the cyp26a1 gene vaccine constructed before. Flow cytometry results showed a significant increase in CD4(+) RORγt(+) Th17 cells in both the peripheral blood and spleen in the experimental group. The expression of RORγt and IL-17 presented the Th17 cells reduction in uterus followed by the suppression of cyp26a1 expression. For greater certainty, cyp26a1 antibody blocking model and RNA interference model were constructed to determine the precise target immune cell group. High performance liquid chromatography results showed a significant increase in uterine at-RA followed by the immunization of cyp26a1 gene vaccine. Both the ascertain by measuring RARα protein levels in peri-implantation uterus after gene vaccine immunization and researches using the specific agonist and antagonist against RARα suggested that RARα may be the main RA receptor for signal transduction. These results provided more evidence for the signal messenger role of RA in cyp26a1 regulation from the other side. Here, we showed that the cyp26a1-regulated Th17 cells are dependent on at-RA signalling, which is delivered through RARα in mouse peri-implantation.

High-dose interferon-γ promotes abortion in mice by suppressing Treg and Th17 polarization.

As a classic type I cytokine, interferon-gamma (IFN-γ) is known to manifest a miscarriage-inducing effect, although the specific mechanism is still unclear. To determine whether immune cells such as regulatory T (Treg) and Th17 cells are involved in these abortions, syngeneically pregnant (BALB/c×BALB/c) mice were subjected to intravaginal IFN-γ administration (5 × 10(3) IU/mouse on D3 of gestation). These mice experienced significant fetal loss on D7/D8 of pregnancy, and a remarkable drop in the Treg cell ratio was observed in the peripheral blood and the spleen by flow cytometry. In situ detection of the uterine tissue peri-implantation revealed that IFN-γ treatment also caused statistically significant reductions in forkhead box P3, RAR-related orphan receptor gamma, and IL-17 levels, which indicated local decreases in Treg and Th17 cells at uterine implantation sites. The IFN-γ receptor alpha (IFN-γRα) level was also lowered in the uterus. These results demonstrate that in murine pregnancy, a supraphysiological dose of IFN-γ could induce peri-implantation failure. Moreover, in this study, the decreases in both Treg and Th17-type cells, which may be relevant to the role of IFN-γRα, may be one of the main reasons that IFN-γ causes abortion.

A novel role of IGFBP7 in mouse uterus: regulating uterine receptivity through Th1/Th2 lymphocyte balance and decidualization.

Previously we have screened out Insulin-like Growth Factor Binding Protein 7 (IGFBP7) as a differentially expressed gene in post-implantation uterus versus pre-implantation uterus by suppressive subtractive hybridation. However its function in uterus was not clearly identified. In this research, the expression and function of IGFBP7 during post-implantation were studied. We found that IGFBP7 was mainly located in the glandular epithelium and the stroma, and was upregulated after embryo implantation. The vector pCR3.1-IGFBP7-t expressing partial IGFBP7 was constructed. Inhibition of IGFBP7 by specific DNA immunization induced significant reduction of implanted embryos and pregnancy rate. The number of implanted embryos (5.68 ± 0.46) was significantly reduced after immunization with pCR3.1-IGFBP7-t, as compared with that of the mice immunized with the control vector (12.29 ± 0.36) or saline (14.58 ± 0.40) (p<0.01). After specific inhibition of IGFBP7, the T helper type 1 (Th1) cytokine IFNγ, was significantly elevated (p<0.05) and the Th2 cytokines IL-4 and IL-10, were reduced in uteri (p<0.05). The increase of Tbet and the decrease of Gata3 were found in mice peripheral lymphocytes by flow cytometry. The expression of decidualization marker IGFBP1 and angiogenesis regulator VEGF were declined in uteri (p<0.05). The expression of apoptosis-associated proteins, caspase3 and Bcl-2, were also declined (p<0.05). These results showed that inhibition of IGFBP7 induced pregnancy failure by shifting uterine cytokines to Th1 type dominance and repressing uterine decidualization.

Retinoic acid synthesis and metabolism are concurrent in the mouse uterus during peri-implantation.

Vitamin A (retinol) and its active metabolite, retinoic acid (RA), serve dual roles in the female reproductive tract. Cytochrome P450 26A1 (Cyp26a1), an RA-metabolizing enzyme, is involved in mammalian early pregnancy. In order to investigate the role of RA synthesis and metabolism during embryo implantation, we first investigated the spatiotemporal expression of RA-signal in the mouse uterus during the peri-implantation period. RA-signal-related molecules, including binding proteins, synthesizing enzymes, catabolizing enzymes and receptors, were all expressed in the mouse uterus during embryo implantation. The locations of the RA synthetic system (Aldh1a1, Aldh1a2, CRBP1) and catabolizing enzyme (Cyp26a1) were distinctive in the mouse uterus during the peri-implantation period. Aldh1a1 was located in the gland epithelium, whereas Aldh1a2 and CRBP1 were located in the stroma and Cyp26a1 was expressed in the luminal and glandular epithelium. These results demonstrate that RA synthesis occurs in the stroma, whereas RA metabolism takes place in the endometrial epithelium. When endometrial epithelial cells were isolated on day 4.5 of pregnancy and treated with E(2) (17beta-estradiol) or a combination of E(2) and progesterone, all-trans-RA (10 µM) significantly down-regulated the expression of LIF, HB-EF and CSF-1 in these cells in vitro. Taken together, these results suggest that the accumulation of RA in the stroma during mouse embryo implantation has an inhibitory effect on the expression of the three implantation-essential genes, LIF, HB-EGF and CSF-1. Therefore, the expression of Cyp26a1 in luminal and glandular epithelium might block the adverse effect of RA in order to promote successful embryo implantation.

Insulin-like growth factor binding protein 7 modulates estrogen-induced trophoblast proliferation and invasion in HTR-8 and JEG-3 cells.

Previous research has reported that IGFBP7 functions as a tumor suppressor gene in different tumors, but its role in the trophoblast has not been elucidated. In this research, we studied the regulation mechanism of IGFBP7 in trophoblast proliferation and invasion in HTR-8 and JEG-3 cell lines. We found that IGFBP7 was abundantly expressed in normal human syncytiotrophoblast tissue samples but that this was lacking in hydatidiform moles. The proliferation and invasion capacities of HTR-8 and JEG-3 cells were significantly inhibited by recombinant IGFBP7. Estrogen (E2) stimulated the expression of IGFBP7 at a concentration of 5-10 ng/mL. This stimulation was inhibited by the estrogen receptor antagonist Fulvestrant (ICI182.780) and a TGFß-neutralizing antibody. In conclusion, our data reveals that estrogen stimulates the expression of IGFBP7 through estrogen receptors and TGFß. The expression of IGFBP7 could be stimulated by TGFß in a dose-dependent manner and inhibited by IFNγ in HTR-8 and JEG-3 cells. IGFBP7 could also inhibit the phosphorylation of ERK and the expression of PCNA, MMP2 and MMP9 in HTR-8 and JEG-3 cells. These findings suggest that IGFBP7 is a key regulator of E2-induced trophoblast proliferation and invasion.

The antitumor immunopreventive effects of a DNA vaccine against CYP26a1 on mouse breast carcinoma.

BACKGROUND: CYP26a1, which functioned mainly as a retinoic acid (RA) catabolic enzyme, has been shown to be oncogenic and to support cell survival in many breast carcinoma cells. OBJECTIVES: The purpose of the study was to investigate the antitumor effect of a DNA vaccine targeting CYP26a1 on breast tumors development in mice which highly express CYP26a1 and to further clarify its potential mechanism. METHODS: After three times immunization of the DNA vaccine, the BALB/c mice were inoculated with the engineered 4T1 breast cancer cells expressing CYP26a1. Primary tumors were measured every 4 days after tumor cell inoculation. The primary tumors were surgically removed and weighted after 30 days of inoculation. The anti-CYP26a1 antibody titer of the antiserum was measured by an enzyme-linked immunosorbent assay (ELISA). The effect of the vaccine on apoptosis of the primary tumor was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). Apoptosis-related proteins in primary tumor were detected by Western blotting. The expression of the Th1 and Th2 type cytokines was detected by RT-PCR. RESULTS: The vaccine could elicit the production of anti-CYP26a1 antibody and significantly inhibit the growth of the primary tumor compared to the control groups (p<0.05). The vaccine induced the apoptosis of the primary tumor with the increase in expression of apoptosis-related proteins p53, Caspase3 and Fas. Furthermore, the vaccine increased the expression of the Th1 cytokine, but not the expression of Th2 cytokine. CONCLUSION: Our study shows that the vaccine targeting CYP26a1 significantly inhibits the primary tumor growth and progression by activating the apoptosis pathway and by eliciting both humoral and cellular immune responses.

Evidence for the inhibition of fertilization in vitro by anti-ZP3 antisera derived from DNA vaccine.

Previously we have found that DNA vaccine, pCMV4-rZPC' can generate specific antibodies against rabbit ZPC (amino acid 263-415, rZPC'), which binds to ovarian ZP and leads to a significant reduction of fertility in vivo. The purpose of this study was to evaluate the effect of antisera from pCMV4-rZPC(')-immunized mice on sperm-oocyte interaction in vitro. The effect of antisera from DNA vaccine-immunized mice on fertilization and early embryonic development was studied using an in vitro fertilization system. The results showed that the antisera supplemented in fertilization medium (10%, v/v) significantly decreased the rate of fertilization compared to that of control groups (P<0.05); whereas the antisera showed no significant effect on the rate of fertilization when ZP-free eggs were used. Moreover, the antisera pre-neutralized with mouse soluble zona pellucida lost the capacity to inhibit fertilization when compared with that of control groups. In addition, the antisera showed no detrimental effect on early developmental potential of mouse embryos in vitro. Taken together, our study provided herein direct evidence showing that antisera generated by DNA vaccine can block sperm-egg recognition during fertilization via targeting the oocyte ZP proteins.

Estradiol-regulated proline-rich acid protein 1 is repressed by class I histone deacetylase and functions in peri-implantation mouse uterus.

Secretory protein proline-rich acid protein 1 (PRAP1) is abundantly expressed in late pregnant uterus. However, regulation and function of PRAP1 in pregnant uterus is still elusive. We firstly reported differential expression of PRAP1 in peri-implantation uteri and its localization in endometrial epithelia. Expression of PRAP1 in uterus was induced by 17ß-estradiol and its expression showed a negative correlation with that of class Ihistone deacetylases (HDACs) in isolated endometrial epithelia. PRAP1 was increased by HDACs inhibitor sodium butyrate treatment, while decreased significantly by estrogen receptor inhibitor ICI182,780 via up-regulating class IHDACs. Number of implanted embryos was decreased in mice immunized with pCR3.1-PRAP1 or injected with rabbit anti-PRAP1 antibody. DNA immunization or antibody injection could affect apoptosis and expression of cytokines (IL-4, IFN-γ). In conclusion, both 17ß-estradiol and class IHDACs are involved in modulating PRAP1 expression in peri-implantation uteri. Preliminary functional research indicates that neutralizing PRAP1 protein causes reduction of implanted embryos.

Retinoic acid metabolizing enzyme CYP26A1 is implicated in rat embryo implantation.

BACKGROUND: The retinoic acid metabolizing enzyme Cyp26a1 plays a pivotal role in vertebrate embryo development. Cyp26a1 was characterized previously as a differentially expressed gene in peri-implantation rat uteri via suppressive subtracted hybridization analysis. However, the role of Cyp26a1 in rat embryo implantation remained elusive. METHODS: The expression of Cyp26a1 in the uteri of early pregnancy, pseudopregnancy and artificial decidualization was detected by northern blotting, real time-PCR, in situ hybridization, western blotting and immunofluorescent staining. The effect of Cyp26a1 on apoptosis of endometrial stromal cells (ESCs) isolated from rat uteri was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and Hoechst staining. Apoptosis-related proteins in ESCs were detected by western blotting. RESULTS: Cyp26a1 showed distinctive expression patterns in embryos and uteri during the peri-implantation period, with a remarkable increase (P < 0.01 versus Days 4-5) in mRNA and protein in the implantation phase (Days 5.5-6.5 of pregnancy). CYP26A1 was specifically localized in glandular epithelium, luminal epithelium and decidua basalis. The level of CYP26A1 protein was significantly increased in uteri of artificial decidualization (P < 0.01 versus control). Forced Cyp26a1 overexpression significantly reduced the sensitivity of ESCs to etoposide-induced apoptosis, with reductions in p53 (P < 0.01) and Fas (P < 0.05) proteins versus control, while in contrast, FasL (P < 0.01) and proliferating cell nuclear antigen (P < 0.05) proteins increased. CONCLUSIONS: Cyp26a1 is spatiotemporally expressed in the uterus during embryo implantation and decidualization. Overexpression of Cyp26a1 attenuates the process of uterine stromal cell apoptosis, probably via down-regulating the expression of p53 and FasL.

Role of secretory protease inhibitor SPINK3 in mouse uterus during early pregnancy.

Successful embryo implantation depends on intricate epithelial-stromal cross-talk. However, molecular modulators involved in this cellular communication remain poorly elucidated. Using multiple approaches, we have investigated the spatiotemporal expression and regulation of serine protease inhibitor Kazal type 3 (SPINK3) in mouse uterus during the estrous cycle and early pregnancy. In cycling mice, both SPINK3 mRNA and protein are only expressed during proestrus. In the pregnant mouse, the expression levels of both SPINK3 mRNA and protein increase on days 5-8 and then decline. Spink3 mRNA is expressed exclusively in the uterine glandular epithelium, whereas SPINK3 protein is localized on the surface of both luminal and glandular epithelium and in the decidua. Moreover, SPINK3 in the decidua has been observed in the primary decidual zone on day 6 and the secondary decidual zone on days 7-8; this is tightly associated with the progression of decidualization. SPINK3 has also been found in decidual cells of the artificially decidualized uterine horn but not control horn, whereas Spink3 mRNA localizes in the glands of both horns. The expression of endometrial Spink3 is not regulated by the blastocyst according to its expression pattern during pseudopregnancy and delayed implantation but is induced by progesterone and further augmented by a combination of progesterone and estrogen in ovariectomized mice. Thus, uterine-gland-derived SPINK3, as a new paracrine modulator, might play an important role in embryo implantation through its influence on stromal decidualization in mice.

Retinoic acid-metabolizing enzyme cytochrome P450 26a1 (cyp26a1) is essential for implantation: functional study of its role in early pregnancy.

Vitamin A (VA) is required for normal fetal development and successful pregnancy. Excessive VA intake during pregnancy may lead to adverse maternal and fetal effects. Cytochrome P450 26A1 (cyp26a1), a retinoic acid (RA)-metabolizing enzyme, is involved in VA metabolism. It has been shown that cyp26a1 is expressed in female reproductive tract, especially in uterus. In order to investigate the role of cyp26a1 during pregnancy, we constructed a recombinant plasmid DNA vaccine encoding cyp26a1 protein and immunized mice with the plasmid. Compared to control groups, the pregnancy rate of the cyp26a1 plasmid-immunized mice were significantly decreased (P < 0.01). Further results showed that both cyp26a1 mRNA and protein were specifically induced in the uterus during implantation period and localized in the uterine luminal epithelium. Importantly, the number of implantation sites was also significantly reduced (P < 0.05) after the uterine injection of cyp26a1-specific antisense oligos or anti-cyp26a1 antibody on day 3 of pregnancy. Accordingly, the expression of RA-related cellular retinoic acid binding protein 1 and tissue transglutaminase was markedly increased (P < 0.05) in the uterine luminal epithelium after intrauterine injection treatments. These data demonstrate that uterine cyp26a1 activity is important for the maintenance of pregnancy, especially during the process of blastocyst implantation.

Effects of TGF beta-1 on mouse embryo implantation and expression of H2-D1 and H2-DM.

We investigated the mechanism that TGF-beta1 influences the immuno-environment at maternal-fetal interface and affects embryo implantation, using mouse uterine horn injection model. The expression of MHC I antigen (H2-D1) and the chaperone of MHC II antigen (H2-DM) after anti-TGF-beta1 antibody or hrTGF-beta1 treated pregnant mice were examined by real-time PCR, western blotting and immunohistochemistry. The results showed that the number of implanted embryos of anti-TGF-beta1 antibody-treated mice was decreased compared with the control. The expression of H2-D1 and H2-DM on days 6 and 7 treated uteri was increased both at mRNA and protein levels. In hrTGF-beta1 treated group, the expression of H2-D1 and H2-DM protein was decreased, and the number of implanted embryos was slightly increased. Immunohistochemical studies revealed that H2-D1 and H2-DM were mainly localized to the primary decidual zone. The anti-TGF-beta1 antibody and exogenous hrTGF-beta1 treatment altered the intensity of H2-D1 and H2-DM signal but did not change their localization. These observations suggested that injection of anti-TGF-beta1 antibody affected the number of mouse embryo implantation, and regulated the expression of H2-DM and H2-Q10.