Nuclear Progesterone Receptor Research Articles

Progesterone Antagonist Therapy in a Pelizaeus-Merzbacher Mouse Model

Pelizaeus-Merzbacher disease (PMD) is a severe hypomyelinating disease, characterized by ataxia, intellectual disability, epilepsy, and premature death. In the majority of cases, PMD is caused by duplication of PLP1 that is expressed in myelinating oligodendrocytes. Despite detailed knowledge of PLP1, there is presently no curative therapy for PMD. We used a Plp1 transgenic PMD mouse model to test the therapeutic effect of Lonaprisan, an antagonist of the nuclear progesterone receptor, in lowering Plp1 mRNA overexpression. We applied placebo-controlled Lonaprisan therapy to PMD mice for 10 weeks and performed the grid slip analysis to assess the clinical phenotype. Additionally, mRNA expression and protein accumulation as well as histological analysis of the central nervous system were performed. Although Plp1 mRNA levels are increased 1.8-fold in PMD mice compared to wild-type controls, daily Lonaprisan treatment reduced overexpression at the RNA level to about 1.5-fold, which was sufficient to significantly improve the poor motor phenotype. Electron microscopy confirmed a 25% increase in the number of myelinated axons in the corticospinal tract when compared to untreated PMD mice. Microarray analysis revealed the upregulation of proapoptotic genes in PMD mice that could be partially rescued by Lonaprisan treatment, which also reduced microgliosis, astrogliosis, and lymphocyte infiltration.

Progesterone increases ex vivo testosterone production and decreases the expression of progestin receptors and steroidogenic enzymes in the fathead minnow (Pimephales promelas) ovary

Progesterone (P4) is a metabolic precursor for a number of steroids, including estrogens and androgens. P4 also has diverse roles within the vertebrate ovary that include oocyte growth and development. The objectives of this study were to measure the effects of P4 on testosterone (T) and 17β-estradiol (E2) production in the fathead minnow (FHM) ovary and on the mRNA abundance of transcripts involved in steroidogenesis and steroid receptor signaling. Ovary explants were treated with P4 (10−6M) for 6 and 12h. P4 administration significantly increased T production ∼3-fold at both 6 and 12h, whereas E2 production was not affected, consistent with the hypothesis that excess P4 is not converted to terminal estrogens in the mature ovary. Nuclear progesterone receptor mRNA was decreased at 6h and membrane progesterone receptor gamma-2 mRNA was significantly down-regulated at both 6 and 12h; however there was no change in membrane progesterone receptor alpha or beta mRNA levels. Androgen receptor (ar) and estrogen receptor 2a (esr2a) mRNA were significantly reduced at 6h with P4 treatment, but there was no change in esr2b mRNA at either time point. Transcripts for enzymes in the steroid pathway (star, hsd11b2) were significantly lower at 6h compared to controls, whereas cyp17a and cyp19a mRNA abundance did not change with treatments at either time point. These data suggest that P4 incubation can lead to increased T production in the FHM ovary without a concomitant change in E2, and that the membrane bound progestin receptors are differentially regulated by P4 in the teleost ovary. As environmental progestins have received increased attention due to their suspected role as endocrine disruptors, mechanistic data on the role of exogenous P4 treatments in the male and female gonad is warranted.

Increased progesterone receptor A expression in labouring human myometrium is associated with decreased promoter occupancy by the histone demethylase JARID1A

Progesterone regulates female reproductive function predominantly through two nuclear progesterone receptors (PRs), PR-A and PR-B. During human parturition myometrial PR expression is altered to favour PR-A, which activates pro-labour genes. We have previously identified histone H3 lysine 4 trimethylation (H3K4me3) as an activator of myometrial PR-A expression at labour. To further elucidate the mechanisms regulating PR isoform expression in the human uterus at labour, we have (i) determined the methylation profile of the cytosine-guanine dinucleotides (CpG) island in the promoter region of the PR gene and (ii) identified the histone-modifying enzymes that target the H3K4me3 mark at the PR promoters in term and preterm human myometrial tissues obtained before and after labour onset. Bisulphite sequencing showed that despite overall low levels of PR CpG island methylation, there was a significant decrease in methylated CpGs with labour in both preterm (P < 0.05) and term (P < 0.01) groups downstream of the PR-B transcription start site. This methylation change was not associated with altered PR-B expression, but may contribute to the increase in PR-A expression with labour. Chromatin immunoprecipitation revealed that the histone methyltransferase, SET and MYND domain-containing protein 3 (SMYD3), bound to the PR gene at significantly higher levels at the PR-A promoter compared with the PR-B promoter (P < 0.010), with no labour-associated changes observed. The H3K4 demethylase, Jumonji AT-rich interactive domain 1A (JARID1A), also bound to the PR-A, but not to the PR-B promoter prior to term labour, and decreased significantly at the onset of labour (P = 0.014), providing a mechanism for the previously reported increase in H3K4me3 level and PR-A expression with labour. Our studies suggest that epigenetic changes mediated by JARID1A, SMYD3 and DNA methylation may be responsible, at least in part, for the functional progesterone withdrawal that precipitates human labour.

Expression of a Mitochondrial Progesterone Receptor (PR-M) in Leiomyomata and Association With Increased Mitochondrial Membrane Potential

Clinical evidence supports a role for progestins in the growth of leiomyomata (fibroids). The mechanism(s) for this is thought to involve gene regulation via the nuclear progesterone receptors. Recently a mitochondrial progesterone receptor (PR-M) has been identified with evidence of a progesterone/progestin-dependent increase in cellular respiration. This observation raises a possible new mechanism whereby progesterone/progestin may affect the growth of fibroids. The goals of this research were to determine differential expression of PR-M in normal myometrium compared with the edge of a fibroid within the same uterus, to demonstrate a progestin-dependent increase in mitochondria membrane potential using an immortalized human myometrial cell line and to examine mitochondrial membrane potential in transfected cells expressing the complete coding sequence of PR-M. Protein levels of PR-M, PR-B, PR-A, mitochondrial porin, and glyceraldehyde-3-phosphate dehydrogenase were determined in the myometrium and adjacent edge of a fibroid in 10 subjects undergoing hysterectomy for benign indications. Mitochondrial membrane potential was determined by fluorescent emission of 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolecarbocyanide iodine in hTERT-HM cells treated with R5020 and in transfected hTERT-HM cells determined by the fluorescent emission of tetramethylrhodamine methyl ester. Higher levels of PR-M and mitochondrial porin were found in the fibroid edge compared with adjacent myometrium. Progestin increased mitochondrial membrane potential in hTERT-HM cells, which was not affected by a translation inhibitor. This effect was exaggerated in hTERT-HM cells expressing PR-M after transient transfection. These studies suggest a mechanism whereby progesterone/progestin may affect the growth of fibroids by altering mitochondrial activity.

Enhancement of Cell Surface Expression and Receptor Functions of Membrane Progestin Receptor α (mPRα) by Progesterone Receptor Membrane Component 1 (PGRMC1): Evidence for a Role of PGRMC1 as an Adaptor Protein for Steroid Receptors

A variety of functions have been proposed for progesterone receptor membrane component 1 (PGRMC1), including acting as a component of a membrane progestin receptor and as an adaptor protein. Here we show that stable overexpression of human PGRMC1 in nuclear progesterone receptor (PR)-negative breast cancer cell lines causes increased expression of PGRMC1 and membrane progesterone receptor α (mPRα) on cell membranes that is associated with increased specific [(3)H]progesterone binding. The membrane progestin binding affinity and specificity were characteristic of mPRα, with a Kd of 4.7 nM and high affinity for the mPR-specific agonist, Org OD 02-0, and low affinity for corticosteroids. Progestin treatment caused activation of G proteins, further evidence for increased expression of functional mPRs on PGRMC1-transfected cell membranes. Immunocytochemical and coimmunoprecipitation studies showed a close association of PGRMC1 with mPRα in cell membranes. Transfection of PGRMC1 into spontaneously immortalized rat granulosa cells was associated with membrane expression of PGRMC1 and mPRα as well as antiapoptotic effects of progestins that were abolished after cotransfection with small interfering RNA for mPRα. These data demonstrate that PGRMC1 can act as an adaptor protein, transporting mPRα to the cell surface, and that the progestin binding and apoptotic functions previously ascribed to PGRMC1 are dependent on cell surface expression of mPRα. Collectively, the results suggest PGRMC1 and mPRα are components of a membrane progesterone receptor protein complex. Increased expression of estrogen receptor β was also observed in the membranes of PGRMC1-transfected cells, suggesting that PGRMC1 can act as an adaptor protein for multiple classes of steroid receptors.

Abstract P6-05-01: Basal and induced receptor profiles cluster cell lines into subtypes and predict drug response in a panel of breast cancer lines

Abstract Molecular subtype is a critical determinant of therapeutic approaches in breast cancer. The subtype is based on the expression of three receptors: The Her2/ErbB2 receptor tyrosine kinase (RTK), whose over-expression defines the HER2amp subtype, and the estrogen or progesterone nuclear hormone receptors, whose over-expression defines the HR+ subtype. Triple negative breast cancers (TNBCs) express low levels of all three receptors. HER2amp status serves as a biomarker for therapy with anti-Her2/ErbB2 antibodies such as trastuzumab or pertuzumab and HR+ status is a biomarker for therapy with hormone receptor antagonists such as tamoxifen. TNBCs are usually treated with cytotoxic chemotherapy. However, breast cancer subtypes are heterogeneous, clinical and mRNA subtypes are not identical, and even the best available biomarker, HER2amp status, correctly predicts response to trastuzumab in only a subset of patients. Projects such as the Cancer Cell Line Encyclopedia aim to identify drug response determinants by relating dose-response profiles for multiple compounds to genomic features across cancer cell collections. Recent studies have suggested that measures of target activity such as phosphorylation are more correlated with drug response than mutation status or gene expression, and steady-state protein data is becoming available for tumors and cell lines. However, few studies have tried to relate the biochemistry of signal transduction to drug response on a large scale, mainly because the measurements are demanding and the utility of the approach is unproven. In this work, we ask whether measurement of the basal and perturbed states of immediate-to-early signaling proteins in serum-starved cells, a robust measurement that can be collected with relatively little biological variability, is predictive of tumor subtype as well as of drug response. We measured the abundance and basal phosphorylation state of nuclear and cell surface receptors and of downstream signaling kinases in the standardized NCI-ICBP43 cell line collection. Because perturbation reveals features of signal transduction that are not apparent by steady state profiling, and because biological ligands present in the microenvironment can alter drug sensitivity, we also collected response profiles by exposing cells to a diverse set of growth factors and cytokines and measuring the activities of downstream signaling kinases before and after ligand addition. We present how the resulting set of ∼3×105 receptor and cell response measurements segregated with clinical subtype and how these proteomic measurements predict the sensitivity of cells to a range of targeted anti-cancer drugs. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-05-01.

114 PROGESTERONE CONCENTRATIONS DURING IVM AFFECT BOVINE OOCYTE QUALITY AT THE MOLECULAR LEVEL

Progesterone (P4) is important for the developmental competence of cumulus–oocyte complexes (COC) used for in vitro maturation (IVM). In a recent study, we were able to show that circulating P4 concentrations had an effect on the molecular quality of COC recovered during repeated ovum pickup sessions, which might affect further development. (Schlüter et al. 2013 Reprod. Fertil. Dev. 25, 250). The aim of the present study was to determine the influence of different P4 concentrations during IVM on the molecular quality of bovine COC. The COC were collected from slaughterhouse ovaries and cultured as described recently (Stinshoff et al. 2011 Theriogenology 76, 1433–1441). The IVM medium was supplemented with 0, 50, 150, 300, and 450 ng mL–1 P4. Ethanol served as vehicle control. After IVF with a bull of proven fertility, the presumptive zygotes were cultured in SOF under 5% oxygen (Stinshoff et al. 2011). Cleavage and developmental rates were determined at Day 3 and Day 7/8 (Day 0: IVF). Additionally, maturation rates were assessed. For mRNA analysis, immature and matured denuded COC (n = 5) were individually frozen at –80°C to analyse the relative transcript abundance using RT-qPCR. The transcripts studied play important roles during oocyte development [growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), glucose transporter 1 (SCL2A1), hypoxia inducible factor 2α (HIF2α), nuclear progesterone receptor (PGR), progestin and adipoQ receptor 5 (PAQR5), progesterone receptor membrane component 1 and 2 (PGRMC1, PGRMC2)]. Data were tested using ANOVA followed by multiple pairwise comparisons using Tukey's test. A P-value of &lt;0.05 was considered significant. The percentage of oocytes that reached the MII stage was similar in oocytes from all treatment groups (82.2–88.1%). Despite similar cleavage rates across all groups, the developmental rates did show significant differences. More embryos developed to the blastocyst stage stemming from oocytes cultured without any supplement or cultured only with alcohol compared to oocytes stemming from the group cultured with less than 50 ng mL–1 P4 (25.4 ± 5.7 and 27.9 ± 7.2 v. 15.8 ± 2.6). The relative abundance of SCL2A1, BMP15, and PGRMC1transcripts in single oocytes did not show differences related to the supplementation of the IVM medium, whereas GDF9, HIF2α, and PAQR5 mRNA was reduced in oocytes of all groups compared with immature ones. The PGR and PGRMC2 transcripts were increased in matured oocytes of the control group and the vehicle control group (PGRMC2). In summary, supplementation of the IVM medium with different P4 concentrations had an effect on the molecular quality of oocytes after IVM, which might affect further development. The financial support of the FBF (Förderverein Biotechnologieforschung) e.V. is gratefully acknowledged.

No direct nuclear effect of progesterone in the inner ear: other possible pathways

Conclusion: No nuclear progesterone receptors were found in human or rat stria vascularis, organ of Corti or spiral ganglion with immunohistochemistry or polymerase chain reaction (PCR). Progesterone receptor B (PR-B) was found with Western blot in the cochlea, probably representing the staining in the cochlear bone. The effect of progesterone on hearing is therefore most likely not due to a direct action on the inner ear. Objectives: Studies suggest that progesterone as a component in hormone replacement therapy has a negative effect on hearing thresholds and otoacoustic emissions in pre- and postmenopausal women and mice. This study was designed to examine the presence of PRs in the cochlea of humans and rats. Methods: Immunohistochemical staining of PR protein in humans and rats, PCR of PR-B mRNA expression, and Western blot of PR-A and PR-B protein in rats was performed. Results: No nuclear staining could be found for any PR in human or rat inner ear except the PR-B staining in the cochlear bone. No mRNA expression was detected by PCR. PR-B could be detected in Western blot performed on the whole cochlea including bone.

Differential impact of the expression of the androgen receptor by age in estrogen receptor–positive breast cancer

We evaluated the expression of the androgen receptor (AR) to determine its significance in breast cancer. AR expression levels were analyzed in 250 invasive breast cancers by immunohistochemistry and any association with the clinicopathological features was evaluated. AR expression was higher in estrogen receptor (ER)-positive cases than in ER-negative cases (P < 0.0001). AR expression was associated with ER level, and it increased with age in ER-positive cases. The cut-off value was determined to be 75% (Cancer Res. 2009;69:6131–6140), and AR expression was considered to be high in 155 (62%) cases. High AR expression significantly correlated with lower nuclear grade (P < 0.0001), ER and progesterone receptor (PR) positivity (P < 0.0001 and P = 0.0022), HER2 negativity (P = 0.0113), lower Ki67 index (P < 0.0001) and a longer disease-free survival (DFS) and distant metastasis-free survival (DMFS) (P = 0.0003 and 0.0107). This association between a high AR expression and a good DFS and DMFS was significant for ER-positive tumors (P < 0.0001 and P = 0.0018); however, no association existed between AR expression and prognosis for ER-negative tumors. In patients ≤51 years old, a high AR expression level significantly correlated with a better prognosis, but this was not significant in patients who were 50 or younger. Multivariate Cox hazard analyses revealed AR expression to be independently associated with a good prognosis in overall patients (HR 0.46, P = 0.0052) and in the ER-positive cohort (HR 0.34, P = 0.0009). AR expression is associated with a less aggressive phenotype and a good prognosis in patients with ER-positive breast cancer. This is considered to be a specific phenomenon for postmenopausal breast cancer patients.

Increased AKT or MEK1/2 Activity Influences Progesterone Receptor Levels and Localization in Endometriosis

Endometriosis is characterized by progesterone resistance and hyperactivity of the AKT and MAPK pathways. Kinases can cause posttranslational modifications of the progesterone receptor (PR) to influence cellular localization and protein stability. The objective of this study was to determine whether the increased AKT or MAPK kinase-1/2 (MEK1/2) activity observed in endometriotic stromal cells (OSIS) from ovarian endometriomas influences levels of PR protein. In turn, the effects of inhibiting AKT or MEK1/2 in the presence of the progestin R5020 on cell viability were investigated. Inhibiting AKT with MK-2206 or MEK1/2 with U0126 for 24 hours in the absence of R5020 increased total and nuclear PRA and PRB protein levels in OSIS but not in eutopic endometrial stromal cells from disease-free patients from disease-free patients. MK-2206 and R5020 decreased OSIS viability and increased apoptosis. Trends toward decreased volumes of sc grafted endometriosis tissues were demonstrated with MK-2206 and progesterone. Inhibition of AKT or MEK1/2 increased total and nuclear PR protein in OSIS. MK-2206 and R5020 decreased OSIS viability and increased apoptosis. The AKT and MAPK pathways may be potential molecular targets for the treatment of endometriosis.

Progesterone receptors induce FOXO1-dependent senescence in ovarian cancer cells

Loss of nuclear progesterone receptors (PR) and low circulating progesterone levels are associated with increased ovarian cancer (OC) risk. However, PR are abundantly expressed in a significant percentage of serous and endometrioid ovarian tumors; patients with PR+ tumors typically experience longer progression-free survival relative to those with PR-null tumors. The molecular mechanisms of these protective effects are poorly understood. To study PR action in OC in the absence of added estrogen (i.e., needed to induce robust PR expression), we created ES-2 OC cells stably expressing vector control or GFP-tagged PR-B (GFP-PR). Progestin (R5020) stimulation of ES-2 cells stably expressing GFP-PR induced cellular senescence characterized by altered cellular morphology, prolonged survival, senescence-associated β-galactosidase activity, G1 cell cycle arrest and upregulation of the cell cycle inhibitor, p21, as well as the Forkhead-box transcription factor, FOXO1; these results repeated in unmodified ER+/PR+ PEO4 OC cells. PR-B and FOXO1 were detected within the same PRE-containing regions of the p21 upstream promoter. Knockdown of p21 resulted in molecular compensation via FOXO1-dependent upregulation of numerous FOXO1 target genes (p15, p16, p27) and an increased rate of senescence. Inhibition of FOXO1 (with AS1842856) or stable FOXO1 knockdown inhibited progestin-induced p21 expression and blocked progestin-induced senescence. Overall, these findings support a role for PR as a tumor suppressor in OC cells, which exhibits inhibitory effects by inducing FOXO1-dependent cellular senescence. Clinical “priming” of the PR-FOXO1-p21 signaling pathway using PR agonists may provide a useful strategy to induce irreversible cell cycle arrest and thereby sensitize OC cells to existing chemotherapies as part of combination “two-step” therapies.

Implication of nuclear progesterone receptor on respiratory control in newborn mice.

We tested the hypothesis that nuclear progesterone receptors (PR) contribute to respiratory control development by studying newborn mice lacking PR expression (PRKO) or wild type controls (WT) at 1 and 4 postnatal days (P1 – P4). Minute ventilation was assessed under normoxia and in response to hypoxia (FiO2=14%, 12%, 10%, 20 min each) using whole body plethysmography. Hypoxic ventilatory response (HVR) was expressed as percentage changes from normoxia, apnea frequency was evaluated under normoxia. In P1 and P4 PRKO mice HVR was 2–3 times lower than in WT for the whole range of FiO2, during the early (peak response) and late (steady state) phase of HVR. In P1, the frequency of spontaneous apnea was lower in PRKO than in WT, while the frequency of post‐sigh apnea frequency was similar. In P4, the frequency of spontaneous and post‐sigh apnea was higher in PRKO than in WT. We conclude that the nuclear progesterone receptor plays a prominent role in respiratory regulation in newborn mice. Both phases of HVR (early and late) are disrupted in PRKO mice, likely indicating effects on peripheral chemoreceptors and central integration. Supported by CIHR.

Progesterone enhances respiratory frequency and reduces apnea frequency during sleep in mice KO for the nuclear progesterone receptor

We used adult female mice knocked‐out for the nuclear progesterone receptor gene (PRKO) and wild‐type (WT) controls to record breathing pattern and apnea frequency across sleep/wake states (determined by EEG/EMG analysis). Respiratory frequency (fR) was similar in WT and PRKO mice during quiet wakefulness. During nREM and REM sleep, fR declined respectively by 31 ± 3 % and 27 ± 5 % in PRKO mice and by 17 ± 7 % and 11 ± 15 % in WT mice (p&lt;0.0001 sleep state effect: p=0.03 group effect). Apnea frequency during sleep (nREM+REM) was 13.8 ± 6 h−1 in WT and 30.4 ± 18 h−1 in PRKO mice. A group of PRKO female mice was treated with progesterone for 7 days (eq. 4mg/kg/day ‐ subcutaneous pump), and compared to the PRKO and WT females treated with vehicle. After progesterone treatment in PRKO mice, fR values were 12 ± 5 % and 7 ± 5 % lower during nREM and REM sleep compared to wakefulness (no significant sleep state effect). Apnea frequency during sleep in PRKO mice treated with progesterone was 2.8 ± 2 h−1, markedly lower than in PRKO mice treated with vehicle. We conclude that deletion of the nuclear progesterone receptor aggravates the respiratory depression during sleep and enhances apnea frequency. Since progesterone treatment in PRKO mice enhances fR and reduces apnea frequency during sleep, progesterone also acts on the respiratory control system through other signalling pathways. Founded by CIHR.

Comparative breast cancer research, lessons from companion animals.

Comparative breast cancer research, lessons from companion animals.

Approaches to the design of selective ligands for membrane progesterone receptor alpha

A number of progesterone derivatives were assayed in terms of their affinity for recombinant human membrane progesterone receptor alpha (mPRα) in comparison with nuclear progesterone receptor (nPR). The 16α,17α-cycloalkane group diminished an affinity of steroids for mPRα without significant influence on affinity for nPR, thus rendering a prominent selectivity of ligands for nPR. On the contrary, substitution of methyl at C10 for ethyl or methoxy group moderately increased the affinity for mPRα and significantly lowered the affinity for nPR. A similar but even more prominent effect was observed upon substitution of the 3-oxo group for the 3-O-methoxyimino group. A significant preference towards mPRα was also rendered by the 17α-hydroxy group and additional C6-C7-double bond. The data suggest that the modes of ligand interaction with mPRα and nPR in the C3 region of the steroid molecule are different. One can speculate that combination of the above substitutions at C17, C10, C6, and C3 may give ligand(s) with high specificity towards mPRα over nPR.

Immunohistochemical analysis of breast tissue microarray images using contextual classifiers

Background: Tissue microarrays (TMAs) are an important tool in translational research for examining multiple cancers for molecular and protein markers. Automatic immunohistochemical (IHC) scoring of breast TMA images remains a challenging problem. Methods: A two-stage approach that involves localization of regions of invasive and in-situ carcinoma followed by ordinal IHC scoring of nuclei in these regions is proposed. The localization stage classifies locations on a grid as tumor or non-tumor based on local image features. These classifications are then refined using an auto-context algorithm called spin-context. Spin-context uses a series of classifiers to integrate image feature information with spatial context information in the form of estimated class probabilities. This is achieved in a rotationally-invariant manner. The second stage estimates ordinal IHC scores in terms of the strength of staining and the proportion of nuclei stained. These estimates take the form of posterior probabilities, enabling images with uncertain scores to be referred for pathologist review. Results: The method was validated against manual pathologist scoring on two nuclear markers, progesterone receptor (PR) and estrogen receptor (ER). Errors for PR data were consistently lower than those achieved with ER data. Scoring was in terms of estimated proportion of cells that were positively stained (scored on an ordinal scale of 0-6) and perceived strength of staining (scored on an ordinal scale of 0-3). Average absolute differences between predicted scores and pathologist-assigned scores were 0.74 for proportion of cells and 0.35 for strength of staining (PR). Conclusions: The use of context information via spin-context improved the precision and recall of tumor localization. The combination of the spin-context localization method with the automated scoring method resulted in reduced IHC scoring errors.

The role of progesterone in implantation and trophoblast invasion

With its genomic and non-genomic actions, progesterone plays a role in preparing the endometrium for implantation and also in regulating trophoblast invasion and migration. The genomic actions of progesterone are mediated by the classical nuclear progesterone receptors, PR-A and PR-B. In addition to their genomic actions, nuclear progesterone receptors may also trigger rapid cytoplasmic signalling events. Membrane-bound progesterone receptors have been implicated in the rapid non-genomic actions of progesterone. Both genomic and extra-nuclear actions of progesterone are crucial for adequate decidualisation and implantation. Progesterone plays a role in establishing uterine receptivity by blocking the proliferative effect of oestrogen, by inducing genes that allow the endometrium to permit embryo attachment, and also acts as a negative regulator of trophoblast invasion by controlling matrix metalloproteinase (MMP) activity.

Progesterone Is Essential for Protecting against LPS-Induced Pregnancy Loss. LIF as a Potential Mediator of the Anti-inflammatory Effect of Progesterone

Lipopolysaccharide (LPS) administration to mice on day 7 of gestation led to 100% embryonic resorption after 24 h. In this model, nitric oxide is fundamental for the resorption process. Progesterone may be responsible, at least in part, for a Th2 switch in the feto-maternal interface, inducing active immune tolerance against fetal antigens. Th2 cells promote the development of T cells, producing leukemia inhibitory factor (LIF), which seems to be important due to its immunomodulatory action during early pregnancy. Our aim was to evaluate the involvement of progesterone in the mechanism of LPS-induced embryonic resorption, and whether LIF can mediate hormonal action. Using in vivo and in vitro models, we provide evidence that circulating progesterone is an important component of the process by which infection causes embryonic resorption in mice. Also, LIF seems to be a mediator of the progesterone effect under inflammatory conditions. We found that serum progesterone fell to very low levels after 24 h of LPS exposure. Moreover, progesterone supplementation prevented embryonic resorption and LPS-induced increase of uterine nitric oxide levels in vivo. Results show that LPS diminished the expression of the nuclear progesterone receptor in the uterus after 6 and 12 h of treatment. We investigated the expression of LIF in uterine tissue from pregnant mice and found that progesterone up-regulates LIF mRNA expression in vitro. We observed that LIF was able to modulate the levels of nitric oxide induced by LPS in vitro, suggesting that it could be a potential mediator of the inflammatory action of progesterone. Our observations support the view that progesterone plays a critical role in a successful pregnancy as an anti-inflammatory agent, and that it could have possible therapeutic applications in the prevention of early reproductive failure associated with inflammatory disorders.

Protective actions of progesterone in the cardiovascular system: Potential role of membrane progesterone receptors (mPRs) in mediating rapid effects

The protective functions of progesterone in the cardiovascular system have received little attention even though evidence has accumulated that progesterone lowers blood pressure, inhibits coronary hyperactivity and has powerful vasodilatory and natriuretic effects. One possible reason why potential beneficial actions of progesterone on cardiovascular functions have not been extensively studied is that divergent effects to those of progesterone have been observed in many clinical trials with synthetic progestins such as medroxyprogesterone acetate which are associated with increased risk of coronary disease. Evidence that progesterone exerts protective effects on cardiovascular functions is briefly reviewed. The finding that progesterone administration decreases blood vessel vasoconstriction in several animal models within a few minutes suggests that rapid, nongenomic progesterone mechanisms are of physiological importance in regulating vascular tone. Rapid activation of second messenger pathways by progesterone has been observed in vascular endothelial and smooth muscle cells, resulting in alterations in endothelial nitric oxide synthase (eNOS) activity and calcium influx, respectively. Both nuclear progesterone receptors (PRs) and novel membrane progesterone receptors (mPRs) are candidates for the intermediaries in these rapid, cell-surface initiated progesterone actions in endothelial and smooth muscle vascular cells. PRs have been detected in both cell types. New data are presented showing mPRα, mPRβ and mPRγ are also present in human endothelial and smooth muscle vascular cells. Preliminary evidence suggests mPRs mediate rapid progestin signaling in these endothelial cells, resulting in down-regulation of cAMP production and increased nitric oxide synthesis. The role of mPRs in progesterone regulation of cardiovascular functions warrants further investigation.

Expression of progesterone receptor membrane component (PGRMC) 1 and 2, serpine mRNA binding protein 1 (SERBP1) and nuclear progesterone receptor (PGR) in the bovine endometrium during the estrous cycle and the first trimester of pregnancy

Progesterone (P4) is involved in the regulation of essential reproductive functions affecting the target cells through both nuclear progesterone receptors (PGRs) and membrane progesterone receptors. The aim of this study was to determine the mRNA and protein expression for PGRMC1, PGRMC2, SERBP1 and PGR within the bovine endometrium during the estrous cycle and the first trimester of pregnancy. There were no changes in PGRMC1 and PGRMC2 mRNA and protein expression during the estrous cycle, however, mRNA levels of PGRMC1 and PGRMC2 were increased (P<0.001) in pregnant animals. SERBP1 mRNA expression was increased (P<0.05), while the level of this protein was decreased (P<0.05) on days 11–16 of the estrous cycle. The expression of PGR mRNA was higher (P<0.01) on days 17–20 compared to days 6–10 and 11–16 of the estrous cycle and pregnancy. PGR-A and PGR-B protein levels were elevated on days 1–5 and 17–20 of the estrous cycle as compared to other stages of the cycle and during pregnancy. In conclusion, our results indicate that P4 may influence endometrial cells through both genomic and nongenomic way. This mechanism may contribute to the regulation of the estrous cycle and provide protection during pregnancy.