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

Pet Wellness and Vitamin A: A Narrative Overview

The health of companion animals, particularly dogs and cats, is significantly influenced by nutrition, with vitamins playing a crucial role. Vitamin A, in particular, is indispensable, with diverse roles ranging from vision to immune modulation and reproduction. Despite its importance, the metabolism and dietary requirements of vitamin A in companion animals remain complex and not fully understood. This review provides a comprehensive overview of the historical perspective, the digestion, the metabolism, the physiological roles, the deficiency, the excess, and the interactions with other micronutrients of vitamin A in companion animals. Additionally, it highlights future research directions and gaps in our understanding. Insights into the metabolism of vitamin A in companion animals, personalized nutrition strategies based on genetic variability, longitudinal studies tracking the status of vitamin A, and investigations into its immunomodulatory effects are crucial for optimizing pet health and wellness. Furthermore, understanding the stability and bioavailability of vitamin A in pet food formulations is essential for ensuring the provision of adequate micronutrients. Overall, this review underscores the importance of vitamin A in companion animal nutrition and the need for further research to enhance our understanding and to optimize dietary recommendations for pet health and well-being.

Establishment of Murine Pregnancy Requires the Promyelocytic Leukemia Zinc Finger Transcription Factor

Using an established human primary cell culture model, we previously demonstrated that the promyelocytic leukemia zinc finger (PLZF) transcription factor is a direct target of the progesterone receptor (PGR) and is essential for progestin-dependent decidualization of human endometrial stromal cells (HESCs). These in vitro findings were supported by immunohistochemical analysis of human endometrial tissue biopsies, which showed that the strongest immunoreactivity for endometrial PLZF is detected during the progesterone (P4)-dominant secretory phase of the menstrual cycle. While these human studies provided critical clinical support for the important role of PLZF in P4-dependent HESC decidualization, functional validation in vivo was not possible due to the absence of suitable animal models. To address this deficiency, we recently generated a conditional knockout mouse model in which PLZF is ablated in PGR-positive cells of the mouse (Plzf d/d). The Plzf d/d female was phenotypically analyzed using immunoblotting, real-time PCR, and immunohistochemistry. Reproductive function was tested using the timed natural pregnancy model as well as the artificial decidual response assay. Even though ovarian activity is not affected, female Plzf d/d mice exhibit an infertility phenotype due to an inability of the embryo to implant into the Plzf d/d endometrium. Initial cellular and molecular phenotyping investigations reveal that the Plzf d/d endometrium is unable to develop a transient receptive state, which is reflected at the molecular level by a blunted response to P4 exposure with a concomitant unopposed response to 17-β estradiol. In addition to a defect in P4-dependent receptivity, the Plzf d/d endometrium fails to undergo decidualization in response to an artificial decidual stimulus, providing the in vivo validation for our earlier HESC culture findings. Collectively, our new Plzf d/d mouse model underscores the physiological importance of the PLZF transcription factor not only in endometrial stromal cell decidualization but also uterine receptivity, two uterine cellular processes that are indispensable for the establishment of pregnancy.

Attenuated retinoic acid signaling is among the early responses in mouse uterus approaching embryo attachment

The uterus is transiently receptive for embryo implantation. It remains to be understood why the uterus does not reject a semi-allogeneic embryo (to the biological mother) or an allogeneic embryo (to a surrogate) for implantation. To gain insights, we examined uterine early response genes approaching embryo attachment on day 3 post coitum (D3) at 22 hours when blue dye reaction, an indication of embryo attachment, had not manifested in mice. C57BL/6 pseudo-pregnant (control) and pregnant mouse uteri were collected on D3 at 22 hours for microarray analysis. The self-assembling-manifold (SAM) algorithm identified 21,858 unique probesets. Principal component analysis indicated a clear separation between the pseudo-pregnant and pregnant groups. There were 106 upregulated and five downregulated protein-coding genes in the pregnant uterus with fold change (fc) >1.5 and q value <5%. Gene ontology (GO) analysis of the 106 upregulated genes revealed 38 significant GO biological process (GOBP) terms (P <0.05), and 32 (84%) of them were associated with immune responses, with a dominant natural killer (NK) cell activation signature. Among the top eight upregulated protein-coding genes, Cyp26a1 inactivates retinoic acid (RA) while Lrat promotes vitamin A storage, both of which are expected to attenuate RA bioavailability; Atp6v0d2 and Gjb2 play roles in ion transport and transmembrane transport; Gzmb, Gzmc, and Il2rb are involved in immune responses; and Tdo2 is important for kynurenine pathway. Most of these genes or their related pathways have functions in immune regulations. RA signaling has been implicated in immune tolerance and immune homeostasis, and uterine NK cells have been implicated in immunotolerance at the maternal-fetal interface in the placenta. The mechanisms of immune responses approaching embryo attachment remain to be elucidated. The coordinated effects of the early response genes may hold the keys to the question of why the uterus does not reject an implanting embryo.

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.

Molecules and Prostaglandins Related to Embryo Tolerance

It is generally understood that the entry of semen into the female reproductive tract provokes molecular and cellular changes facilitating conception and pregnancy. We show a broader picture of the participation of prostaglandins in the fertilization, implantation and maintenance of the embryo. A large number of cells and molecules are related to signaling networks, which regulate tolerance to implantation and maintenance of the embryo and fetus. In this work, many of those cells and molecules are analyzed. We focus on platelets, polymorphonuclear leukocytes, and group 2 innate lymphoid cells involved in embryo tolerance in order to have a wider view of how prostaglandins participate. The combination of platelets and neutrophil extracellular traps (Nets), uterine innate lymphoid cells (uILC), Treg cells, NK cells, and sex hormones have an important function in immunological tolerance. In both animals and humans, the functions of these cells can be regulated by prostaglandins and soluble factors in seminal plasma to achieve an immunological balance, which maintains fetal-maternal tolerance. Prostaglandins, such as PGI2 and PGE2, play an important role in the suppression of the previously mentioned cells. PGI2 inhibits platelet aggregation, in addition to IL-5 and IL-13 expression in ILC2, and PGE2 inhibits some neutrophil functions, such as chemotaxis and migration processes, leukotriene B4 (LTB4) biosynthesis, ROS production, and the formation of extracellular traps, which could help prevent trophoblast injury and fetal loss. The implications are related to fertility in female when seminal fluid is deposited in the vagina or uterus.

Endometrial Decidualization: The Primary Driver of Pregnancy Health

Interventions to prevent pregnancy complications have been largely unsuccessful. We suggest this is because the foundation for a healthy pregnancy is laid prior to the establishment of the pregnancy at the time of endometrial decidualization. Humans are one of only a few mammalian viviparous species in which decidualization begins during the latter half of each menstrual cycle and is therefore independent of the conceptus. Failure to adequately prepare (decidualize) the endometrium hormonally, biochemically, and immunologically in anticipation of the approaching blastocyst—including the downregulation of genes involved in the pro- inflammatory response and resisting tissue invasion along with the increased expression of genes that promote angiogenesis, foster immune tolerance, and facilitate tissue invasion—leads to abnormal implantation/placentation and ultimately to adverse pregnancy outcome. We hypothesize, therefore, that the primary driver of pregnancy health is the quality of the soil, not the seed.

Uterine function in the mouse requires speckle-type poz protein

Speckle-type poz protein (SPOP) is an E3-ubiquitin ligase adaptor for turnover of a diverse number of proteins involved in key cellular processes such as chromatin remodeling, transcriptional regulation, and cell signaling. Genomic analysis revealed that SPOP somatic mutations are found in a subset of endometrial cancers, suggesting that these mutations act as oncogenic drivers of this gynecologic malignancy. These studies also raise the question as to the role of wild-type SPOP in normal uterine function. To address this question, we generated a mouse model (Spopd/d) in which SPOP is ablated in uterine cells that express the PGR. Fertility studies demonstrated that SPOP is required for embryo implantation and for endometrial decidualization. Molecular analysis revealed that expression levels of the PGR at the protein and transcript level are significantly reduced in the Spopd/d uterus. While this result was unexpected, this finding explains in part the dysfunctional phenotype of the Spopd/d uterus. Moderate increased levels of the ESR1, GATA2, and SRC2 were detected in the Spopd/d uterus, suggesting that SPOP is required to maintain the proteome for normal uterine function. With age, the Spopd/d endometrium exhibits large glandular cysts with foci of epithelial proliferation, further supporting a role for SPOP in maintaining a healthy uterus. Collectively, studies on the Spopd/d mouse support an important role for SPOP in normal uterine function and suggest that this mouse model may prove useful to study the role of SPOP-loss-of-function mutations in the etiopathogenesis of endometrial cancer.

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⁺MHCII^lo‐hiF4/80⁻ dendritic cells (DCs) was significantly decreased in the treated mice. The percentage of mature DCs (CD86^hi) was obviously lower and the percentage of immature DCs (CD86^lo) 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.

Uterine responses to early pre-attachment embryos in the domestic dog and comparisons with other domestic animal species

In the dog, there is no luteolysis in the absence of pregnancy. Thus, this species lacks any anti-luteolytic endocrine signal as found in other species that modulate uterine function during the critical period of pregnancy establishment. Nevertheless, in the dog an embryo-maternal communication must occur in order to prevent rejection of embryos. Based on this hypothesis, we performed microarray analysis of canine uterine samples collected during pre-attachment phase (days 10-12) and in corresponding non-pregnant controls, in order to elucidate the embryo attachment signal. An additional goal was to identify differences in uterine responses to pre-attachment embryos between dogs and other mammalian species exhibiting different reproductive patterns with regard to luteolysis, implantation, and preparation for placentation. Therefore, the canine microarray data were compared with gene sets from pigs, cattle, horses, and humans. We found 412 genes differentially regulated between the two experimental groups. The functional terms most strongly enriched in response to pre-attachment embryos related to extracellular matrix function and remodeling, and to immune and inflammatory responses. Several candidate genes were validated by semi-quantitative PCR. When compared with other species, best matches were found with human and equine counterparts. Especially for the pig, the majority of overlapping genes showed opposite expression patterns. Interestingly, 1926 genes did not pair with any of the other gene sets. Using a microarray approach, we report the uterine changes in the dog driven by the presence of embryos and compare these results with datasets from other mammalian species, finding common-, contrary-, and exclusively canine-regulated genes.

Reprogramming of the retinoic acid pathway in decidualizing human endometrial stromal cells

Upon breaching of the endometrial surface epithelium, the implanting embryo embeds in the decidualizing stroma. Retinoic acid (RA), a metabolite of vitamin A, is an important morphogen during embryonic and fetal development, although the role of the RA pathway in the surrounding decidual cells is not understood. Here we show that decidual transformation of human endometrial stromal cells (HESCs) results in profound reprogramming of the RA signaling and metabolism pathways. Differentiating HESCs downregulate the intracellular carrier proteins CRABP2 and FABP5, responsible for transfer and binding of RA to the nuclear receptors RAR and PPARβ/δ, respectively. Furthermore, the expression of RAR, the receptor that mediates the pro-apoptotic effects of RA, was also inhibited. By contrast, PPARβ/δ, which transduces the differentiation responses of RA, was upregulated. Decidualization was also associated with increased expression of retinol-binding protein 4 (RBP4) and various enzymes involved in the metabolism of RA and its precursor, retinaldehyde (Rald), including CYP26A1, DHRS3, and RDH12. Exposure of differentiating HESCs to RA or Rald reversed the inhibition of the CRABP2-RAR pathway, perturbed the expression of decidual marker genes and triggered cell death. Taken together, the data demonstrate that decidualizing HESCs silence RA signaling by downregulating key cytoplasmic binding proteins and by increasing retinoid metabolism. However, excessive RA exposure is toxic for decidual cells and triggers a response that may lead to pregnancy failure.

Retinoic acid signaling determines the fate of uterine stroma in the mouse Müllerian duct

The Müllerian duct develops into the oviduct, uterus, and vagina, all of which are quite distinct in their morphology and function. The epithelial fate of these female reproductive organs in developing mice is determined by factors secreted from the stroma; however, how stromal differentiation occurs in the female reproductive organs derived from the Müllerian duct is still unclear. In the present study, roles of retinoic acid (RA) signaling in developing female reproductive tracts were investigated. Retinol dehydrogenase 10 (RDH10) and aldehyde dehydrogenase family 1 subfamily A2 (ALDH1A2) mRNAs and proteins and transactivation activity of endogenous RA were found in the stroma of proximal Müllerian ducts and gradually decreased from the proximal to caudal regions in fetal mice. In organ-cultured Müllerian ducts, retinaldehyde or RA treatment induced uterine epithelial differentiation, defined as a layer of columnar epithelial cells negative for oviductal and vaginal epithelial markers. In contrast, inhibition of RA receptor (RAR) signaling induced vaginal epithelial differentiation, characterized as vaginal epithelial marker genes-positive stratified epithelium. Grafting experiments of the organ-cultured Müllerian duct revealed irreversible epithelial fate determination. Although RAR did not directly bind to the homeobox A10 (Hoxa10) promoter region, RA-RAR signaling stimulated Hoxa10 expression. Thus, RA-RAR signaling in the Müllerian duct determines the fate of stroma to form the future uterus and vagina.

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.

Uterine selection of human embryos at implantation

Human embryos frequently harbor large-scale complex chromosomal errors that impede normal development. Affected embryos may fail to implant although many first breach the endometrial epithelium and embed in the decidualizing stroma before being rejected via mechanisms that are poorly understood. Here we show that developmentally impaired human embryos elicit an endoplasmic stress response in human decidual cells. A stress response was also evident upon in vivo exposure of mouse uteri to culture medium conditioned by low-quality human embryos. By contrast, signals emanating from developmentally competent embryos activated a focused gene network enriched in metabolic enzymes and implantation factors. We further show that trypsin, a serine protease released by pre-implantation embryos, elicits Ca²⁺ signaling in endometrial epithelial cells. Competent human embryos triggered short-lived oscillatory Ca²⁺ fluxes whereas low-quality embryos caused a heightened and prolonged Ca²⁺ response. Thus, distinct positive and negative mechanisms contribute to active selection of human embryos at implantation.

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.

Elevated periimplantation uterine natural killer cell density in human endometrium is associated with impaired corticosteroid signaling in decidualizing stromal cells

BACKGROUND

Decidualizing human endometrial stromal cells (HESCs) profoundly up-regulate 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1), the enzyme that converts inert cortisone to active cortisol. We postulated that the induction of a cortisol gradient upon decidualization of the periimplantation endometrium may impact on the uterine natural killer (uNK) cell population and on local expression of corticosteroid-dependent target genes.

METHODS

Midluteal endometrial biopsies (n = 55) were processed for uNK cell (CD56) analysis and primary HESC cultures. The cultures remained either untreated or were decidualized for 4 or 8 days. A tissue microarray was constructed from endometria with normal (n = 18) and elevated uNK cell (n = 18) scores. An abnormal uNK cell test was defined as greater than 5% CD56(+) cells in the subluminal stroma.

RESULTS

Increased uNK cell density was associated with lower endometrial expression of 11βHSD1 and mineralocorticoid receptor (MR) but not glucocorticoid receptor in vivo. Elevated uNK cell density also corresponded to impaired induction of key decidual markers (11βHSD1, prolactin, and insulin-like growth factor binding protein-1) and MR-dependent enzymes (dehydrogenase/reductase member 3 and retinol saturase) in differentiating HESC cultures. Increased uNK cell density in vivo was not associated with increased in vitro expression of either IL-15 or IL-11, two cytokines implicated in uNK cell regulation.

CONCLUSIONS

Elevated levels of uNK cells in the stroma underlying the surface epithelium are associated with inadequate cortisol biosynthesis by resident decidualizing cells and suboptimal induction of key MR-dependent enzymes involved in lipid biogenesis and the retinoid transport pathway. Our observations suggest that uNK cell testing identifies those women at risk of reproductive failure due to relative uterine cortisol deficiency.

Differential gene expression profiling of mouse uterine luminal epithelium during periimplantation

Uterine luminal epithelium (LE) is critical for establishing uterine receptivity. Microarray analysis of gestation day 3.5 (D3.5, preimplantation) and D4.5 (postimplantation) LE from natural pregnant mice identified 382 upregulated and 245 downregulated genes in the D4.5 LE. Gene Ontology annotation grouped 186 upregulated and 103 downregulated genes into 22 and 15 enriched subcategories, respectively, in regulating DNA-dependent transcription, metabolism, cell morphology, ion transport, immune response, apoptosis, signal transduction, and so on. Signaling pathway analysis revealed 99 genes in 21 significantly changed signaling pathways, with 14 of these pathways involved in metabolism. In situ hybridization confirmed the temporal expression of 12 previously uncharacterized genes, including Atp6v0a4, Atp6v0d2, F3, Ggh, Tmprss11d, Tmprss13, Anpep, Fxyd4, Naip5, Npl, Nudt19, and Tpm1 in the periimplantation uterus. This study provides a comprehensive picture of the differentially expressed genes in the periimplantation LE to help understand the molecular mechanism of LE transformation upon establishment of uterine receptivity.

Changes in mouse uterine transcriptome in estrus and proestrus

Changes in the CD-1 mouse uterine transcriptome during proestrus and estrus were investigated to help elucidate mechanisms of uterine tissue remodeling during the estrus cycle and their regulation by estrogen and progesterone in preparation of the uterus for pregnancy. Mice were staged beginning at 6 weeks of age, and uterine horns were harvested after monitoring two estrus cycles. Microarray analysis of whole uterine horn RNA identified 2428 genes differentially expressed in estrus compared to proestrus, indicating there is extensive remodeling of mouse uterus during the estrus cycle, affecting ~10% of all protein-encoding genes. Many (~50%) of these genes showed the same differential expression in independent analyses of isolated uterine lumenal epithelial cells. Changes in gene expression associated with structural alterations of the uterus included remodeling of the extracellular matrix, changes in cell keratins and adhesion molecules, activation of mitosis and changes in major histocompatibility complex class II (MHCII) presentation, complement and coagulation cascades, and cytochrome P450 expression. Signaling pathways regulated during the estrus cycle, involving ligand-gated channels, Wnt and hedgehog signaling, and transcription factors with poorly understood roles in reproductive tissues, included several genes and gene networks that have been implicated in pathological states. Many of the molecular pathways and biological functions represented by the genes differentially expressed from proestrus to estrus are also altered during the human menstrual cycle, although not necessarily at the corresponding phases of the cycle. These findings establish a baseline for further studies in the mouse model to dissect mechanisms involved in uterine tissue response to endocrine disruptors and the development of reproductive tract diseases.

Toxicological effects of the different substances in tobacco smoke on human embryonic development by a systems chemo-biology approach

The physiological and molecular effects of tobacco smoke in adult humans and the development of cancer have been well described. In contrast, how tobacco smoke affects embryonic development remains poorly understood. Morphological studies of the fetuses of smoking pregnant women have shown various physical deformities induced by constant fetal exposure to tobacco components, especially nicotine. In addition, nicotine exposure decreases fetal body weight and bone/cartilage growth in addition to decreasing cranial diameter and tibia length. Unfortunately, the molecular pathways leading to these morphological anomalies are not completely understood. In this study, we applied interactome data mining tools and small compound interaction networks to elucidate possible molecular pathways associated with the effects of tobacco smoke components during embryonic development in pregnant female smokers. Our analysis showed a relationship between nicotine and 50 additional harmful substances involved in a variety of biological process that can cause abnormal proliferation, impaired cell differentiation, and increased oxidative stress. We also describe how nicotine can negatively affect retinoic acid signaling and cell differentiation through inhibition of retinoic acid receptors. In addition, nicotine causes a stress reaction and/or a pro-inflammatory response that inhibits the agonistic action of retinoic acid. Moreover, we show that the effect of cigarette smoke on the developing fetus could represent systemic and aggressive impacts in the short term, causing malformations during certain stages of development. Our work provides the first approach describing how different tobacco constituents affect a broad range of biological process in human embryonic development.

Signal transducer and activator of transcription-3 (Stat3) plays a critical role in implantation via progesterone receptor in uterus

Recent studies have shown that activation of the signal transducer and activator of transcription-3 (Stat3) is required for decidualization, interacting with progesterone receptor (PR) in uterus. Based on previous reports, we hypothesized that crosstalk between STAT3 and PR signaling is required for successful implantation. To identify the interaction between STAT3 and PR isoforms, we performed immunoprecipitation following transient cotransfection and found that STAT3 physically interacted with PR-A, which is known to be important for uterine development and function, but not with PR-B. To further investigate the role of Stat3 in uterine function, Stat3 was conditionally ablated only in the PR-positive cells (PR(cre/+) Stat3(f/f); Stat3(d/d)). Our studies revealed that ovarian function and uterine development of Stat3(d/d) mice were normal. However, Stat3(d/d) female mice were infertile due to defective embryo implantation. Unlike Stat3(f/f) mice, Stat3(d/d) mice exhibited an unclosed uterine lumen. Furthermore, uteri of Stat3(d/d) mice were unable to undergo a well-characterized hormonally induced decidual reaction. The expression of stromal PR was decreased during decidualization and preimplantation period in Stat3(d/d) mice, and PR target genes were significantly down-regulated after progesterone induction. Our results suggest that STAT3 and PR crosstalk is required for successful implantation in the mouse uterus.

Induction of 11β-HSD 1 and activation of distinct mineralocorticoid receptor- and glucocorticoid receptor-dependent gene networks in decidualizing human endometrial stromal cells

The actions of glucocorticoids at the feto-maternal interface are not well understood. Here, we show that decidualization of human endometrial stromal cells (HESCs) in response to progesterone and cAMP signaling is associated with a strong induction of 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) expression and enzyme activity. Decidualization also triggered a gradual decrease in glucocorticoid receptor (GR) expression and reciprocal increase in mineralocorticoid receptor (MR) levels. Gene expression profiling of differentiating HESCs after small interfering RNA (siRNA)-mediated knockdown of either GR or MR identified 239 and 167 significantly regulated genes, respectively. Interestingly, GR-repressed genes were enriched for Krüppel-associated box domain containing zinc-finger proteins, transcriptional repressors involved in heterochromatin formation. In agreement, GR knockdown was sufficient to enhance trimethylated H3K9 levels in decidualizing cells. Conversely, we identified several MR-dependent genes implicated in lipid droplet biogenesis and retinoid metabolism. For example, the induction in differentiating HESCs of DHRS3, encoding a highly conserved enzyme that catalyzes the oxidation/reduction of retinoids and steroids, was enhanced by aldosterone, attenuated in response to MR knockdown, and abolished upon treatment with the MR antagonist RU26752. Furthermore, we demonstrate that decidualization is associated with dynamic changes in the abundance and distribution of cytoplasmic lipid droplets, the formation of which was blocked by RU26752. In summary, progesterone drives local cortisol biosynthesis by decidual cells through induction of 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1), leading to transcriptional regulation of distinct GR and MR gene networks involved in epigenetic programming and lipid and retinoid metabolism, respectively.

Smoothelin-like 1 protein is a bifunctional regulator of the progesterone receptor during pregnancy

During pregnancy, uterine smooth muscle (USM) coordinately adapts its contractile phenotype in order to accommodate the developing fetus and then prepare for delivery. Herein we show that SMTNL1 plays a major role in pregnancy to promote adaptive responses in USM and that this process is specifically mediated through interactions of SMTNL1 with the steroid hormone receptor PR-B. In vitro and in vivo SMTNL1 selectively binds PR and not other steroid hormone receptors. The physiological relationship between the two proteins was also established in global gene expression and transcriptional reporter studies in pregnant smtnl1(-/-) mice and by RNA interference in progesterone-sensitive cell lines. We show that the contraction-associated and progestin-sensitive genes (oxytocin receptor, connexin 43, and cyclooxygenase-2) and prolactins are down-regulated in pregnant smtnl1(-/-) mice. We suggest that SMTNL1 is a bifunctional co-regulator of PR-B signaling and thus provides a molecular mechanism whereby PR-B is targeted to alter gene expression patterns within USM cells to coordinately promote alterations in USM function during pregnancy.

Bioinformatic detection of E47, E2F1 and SREBP1 transcription factors as potential regulators of genes associated to acquisition of endometrial receptivity

BACKGROUND

The endometrium is a dynamic tissue whose changes are driven by the ovarian steroidal hormones. Its main function is to provide an adequate substrate for embryo implantation. Using microarray technology, several reports have provided the gene expression patterns of human endometrial tissue during the window of implantation. However it is required that biological connections be made across these genomic datasets to take full advantage of them. The objective of this work was to perform a research synthesis of available gene expression profiles related to acquisition of endometrial receptivity for embryo implantation, in order to gain insights into its molecular basis and regulation.

METHODS

Gene expression datasets were intersected to determine a consensus endometrial receptivity transcript list (CERTL). For this cluster of genes we determined their functional annotations using available web-based databases. In addition, promoter sequences were analyzed to identify putative transcription factor binding sites using bioinformatics tools and determined over-represented features.

RESULTS

We found 40 up- and 21 down-regulated transcripts in the CERTL. Those more consistently increased were C4BPA, SPP1, APOD, CD55, CFD, CLDN4, DKK1, ID4, IL15 and MAP3K5 whereas the more consistently decreased were OLFM1, CCNB1, CRABP2, EDN3, FGFR1, MSX1 and MSX2. Functional annotation of CERTL showed it was enriched with transcripts related to the immune response, complement activation and cell cycle regulation. Promoter sequence analysis of genes revealed that DNA binding sites for E47, E2F1 and SREBP1 transcription factors were the most consistently over-represented and in both up- and down-regulated genes during the window of implantation.

CONCLUSIONS

Our research synthesis allowed organizing and mining high throughput data to explore endometrial receptivity and focus future research efforts on specific genes and pathways. The discovery of possible new transcription factors orchestrating the CERTL opens new alternatives for understanding gene expression regulation in uterine function.