Progesterone receptor-Src kinase signaling pathway mediates neuroprogesterone induction of the luteinizing hormone surge in female rats

Neural circuits in female rats are exposed to sequential estradiol and progesterone to regulate the release of luteinizing hormone (LH) and ultimately ovulation. Estradiol induces progesterone receptors (PGRs) in anteroventral periventricular nucleus (AVPV) kisspeptin neurons, and as estradiol reaches peak concentrations, neuroprogesterone (neuroP) synthesis is induced in hypothalamic astrocytes. This local neuroP signals to PGRs expressed in kisspeptin neurons to trigger the LH surge. We tested the hypothesis that neuroP-PGR signaling through Src family kinase (Src) underlies the LH surge. As observed in vitro, PGR and Src are co-expressed in AVPV neurons. Estradiol treatment increased the number of PGR immunopositive cells and PGR and Src colocalization. Furthermore, estradiol treatment increased the number of AVPV cells that had extranuclear PGR and Src in close proximity (< 40 nm). Infusion of the Src inhibitor (PP2) into the AVPV region of ovariectomized/adrenalectomized (ovx/adx) rats attenuated the LH surge in trunk blood collected 53 h post-estradiol (50 µg) injection that induced neuroP synthesis. Although PP2 reduced the LH surge in estradiol benzoate treated ovx/adx rats, activation of either AVPV PGR or Src in 2 µg estradiol-primed animals significantly elevated LH concentrations compared to dimethyl sulfoxide infused rats. Finally, antagonism of either AVPV PGR or Src blocked the ability of PGR or Src activation to induce an LH surge in estradiol-primed ovx/adx rats. These results indicate that neuroP, which triggers the LH surge, signals through an extranuclear PGR-Src signaling pathway.

Progesterone Receptors in AVPV Kisspeptin Neurons Are Sufficient for Positive Feedback Induction of the LH Surge

Kisspeptin, encoded by Kiss1, stimulates gonadotropin-releasing hormone neurons to govern reproduction. In female rodents, estrogen-sensitive kisspeptin neurons in the rostral anteroventral periventricular (AVPV) hypothalamus are thought to mediate estradiol (E2)-induced positive feedback induction of the preovulatory luteinizing hormone (LH) surge. AVPV kisspeptin neurons coexpress estrogen and progesterone receptors (PGRs) and are activated during the LH surge. While E2 effects on kisspeptin neurons have been well studied, progesterone's regulation of kisspeptin neurons is less understood. Using transgenic mice lacking PGR exclusively in kisspeptin cells (termed KissPRKOs), we previously demonstrated that progesterone action specifically in kisspeptin cells is essential for ovulation and normal fertility. Unlike control females, KissPRKO females did not generate proper LH surges, indicating that PGR signaling in kisspeptin cells is required for positive feedback. However, because PGR was knocked out from all kisspeptin neurons in the brain, that study was unable to determine the specific kisspeptin population mediating PGR action on the LH surge. Here, we used targeted Cre-mediated adeno-associated virus (AAV) technology to reintroduce PGR selectively into AVPV kisspeptin neurons of adult KissPRKO females, and tested whether this rescues occurrence of the LH surge. We found that targeted upregulation of PGR in kisspeptin neurons exclusively in the AVPV is sufficient to restore proper E2-induced LH surges in KissPRKO females, suggesting that this specific kisspeptin population is a key target of the necessary progesterone action for the surge. These findings further highlight the critical importance of progesterone signaling, along with E2 signaling, in the positive feedback induction of LH surges and ovulation.

Cell-type specific analysis of physiological action of estrogen in mouse oviducts

One of the endogenous estrogens, 17β-estradiol (E2 ) is a female steroid hormone secreted from the ovary. It is well established that E2 causes biochemical and histological changes in the uterus. However, it is not completely understood how E2 regulates the oviductal environment in vivo. In this study, we assessed the effect of E2 on each oviductal cell type, using an ovariectomized-hormone-replacement mouse model, single-cell RNA-sequencing (scRNA-seq), in situ hybridization, and cell-type-specific deletion in mice. We found that each cell type in the oviduct responded to E2 distinctively, especially ciliated and secretory epithelial cells. The treatment of exogenous E2 did not drastically alter the transcriptomic profile from that of endogenous E2 produced during estrus. Moreover, we have identified and validated genes of interest in our datasets that may be used as cell- and region-specific markers in the oviduct. Insulin-like growth factor 1 (Igf1) was characterized as an E2 -target gene in the mouse oviduct and was also expressed in human fallopian tubes. Deletion of Igf1 in progesterone receptor (Pgr)-expressing cells resulted in female subfertility, partially due to an embryo developmental defect and embryo retention within the oviduct. In summary, we have shown that oviductal cell types, including epithelial, stromal, and muscle cells, are differentially regulated by E2 and support gene expression changes, such as growth factors that are required for normal embryo development and transport in mouse models. Furthermore, we have identified cell-specific and region-specific gene markers for targeted studies and functional analysis in vivo.

Progesterone Receptor Serves the Ovary as a Trigger of Ovulation and a Terminator of Inflammation

Ovulation is triggered by the gonadotropin surge that induces the expression of two key genes, progesterone receptor (Pgr) and prostaglandin-endoperoxide synthase 2 (Ptgs2), in the granulosa cells of preovulatory follicles. Their gene products PGR and PTGS2 activate two separate pathways that are both essential for successful ovulation. Here, we show that the PGR plays an additional essential role: it attenuates ovulatory inflammation by diminishing the gonadotropin surge-induced Ptgs2 expression. PGR indirectly terminates Ptgs2 expression and PGE2 synthesis in granulosa cells by inhibiting the nuclear factor κB (NF-κB), a transcription factor required for Ptgs2 expression. When the expression of PGR is ablated in granulosa cells, the ovary undergoes a hyperinflammatory condition manifested by excessive PGE2 synthesis, immune cell infiltration, oxidative damage, and neoplastic transformation of ovarian cells. The PGR-driven termination of PTGS2 expression may protect the ovary from ovulatory inflammation.

Involvement of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) in mPRα (PAQR7)-mediated progesterone induction of vascular smooth muscle relaxation

Progesterone acts directly on vascular smooth muscle cells (VSMCs) through activation of membrane progesterone receptor α (mPRα)-dependent signaling to rapidly decrease cytosolic Ca²⁺ concentrations and induce muscle relaxation. However, it is not known whether this progesterone action involves uptake of Ca²⁺ by the sarco/endoplasmic reticulum (SR) and increased sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) activity. The present results show that treatment of cultured human VSMCs with progesterone and the selective mPR agonist Org OD-02-0 (OD 02-0) but not with the nuclear PR agonist R5020 increased SERCA protein expression, which was blocked by knockdown of mPRα with siRNA. Moreover, treatments with progesterone and OD 02-0, but not with R5020, increased phospholamban (PLB) phosphorylation, which would result in disinhibition of SERCA function. Progesterone and OD 02-0 significantly increased Ca²⁺ levels in the SR and caused VSMC relaxation. These effects were blocked by pretreatment with cyclopiazonic acid (CPA), a SERCA inhibitor, and by knockdown of SERCA2 with siRNA, suggesting that SERCA2 plays a critical role in progesterone induction of VSMC relaxation. Treatment with inhibitors of inhibitory G proteins (Gi, NF023), MAP kinase (AZD 6244), Akt/Pi3k (wortmannin), and a Rho activator (calpeptin) blocked the progesterone- and OD 02-0-induced increase in Ca²⁺ levels in the SR and SERCA expressions. These results suggest that the rapid effects of progesterone on cytosolic Ca²⁺ levels and relaxation of VSMCs through mPRα involve regulation of the functions of SERCA2 and PLB through Gi, MAP kinase, and Akt signaling pathways and downregulation of RhoA activity.NEW & NOTEWORTHY The rapid effects of progesterone on cytosolic Ca²⁺ levels and relaxation of VSMCs through mPRα involve regulation of the functions of SERCA2 and PLB through Gi, MAP kinase, and Akt signaling pathways and downregulation of RhoA activity.

Progesterone's Effects on Cognitive Performance of Male Mice Are Independent of Progestin Receptors but Relate to Increases in GABAA Activity in the Hippocampus and Cortex

Progestogens' (e.g., progesterone and its neuroactive metabolite, allopregnanolone), cognitive effects and mechanisms among males are not well-understood. We hypothesized if progestogen's effects on cognitive performance are through its metabolite allopregnanolone, and not actions via binding to traditional progestin receptors (PRs), then progesterone administration would enhance performance in tasks mediated by the hippocampus and cortex, coincident with increasing allopregnanolone concentrations, brain derived neurotrophic factor (BDNF) and/or muscimol binding of PR knock out (PRKO) and wild-type PR replete mice. Experiment 1: Progesterone (4 mg/kg, subcutaneously (SC; n = 12/grp), or oil vehicle control, was administered to gonadally-intact adult male mice PRKO mice and their wild-type counterparts and cognitive behaviors in object recognition, T-maze and water maze was examined. Progesterone, compared to vehicle, when administered post-training increased time investigating novel objects by the PRKO and wild-type mice in the object recognition task. In the T-maze task, progesterone administration to wild-type and PRKO mice had significantly greater number of spontaneous alternations compared to their vehicle-administered counterparts. In the water maze task, PRKO mice administered vehicle spent significantly fewer seconds in the quadrant associated with the escape platform on testing compared to all other groups. Experiment 2: Progesterone administered to wild-type and PRKO mice increased plasma progesterone and allopregnanolone levels (n = 5/group). PRKO mice had higher allopregnanolone levels in plasma and hippocampus, but not cortex, when administered progesterone and compared to wild-type mice. Experiment 3: Assessment of PR binding revealed progesterone administered wild-type mice had significantly greater levels of PRs in the hippocampus and cortex, compared to all other groups (n = 5/group). Wild-type mice administered progesterone, but not vehicle, had increased BDNF levels in the hippocampus, but not the cortex, compared to PRKOs. Wild-type as well as PRKO mice administered progesterone experienced significant increases in maximal GABAA agonist, muscimol, binding in hippocampus and cortex, compared to their vehicle-administered counterparts. Thus, adult male mice can be responsive to progesterone for cognitive performance, and such effects may be independent of PRs trophic actions of BDNF levels in the hippocampus and/or increases in GABAA activity in the hippocampus and cortex.

Involvement of progesterone and estrogen receptors in the ram sperm acrosome reaction

The steroid hormones 17-β estradiol (E2) and progesterone (P4) can regulate capacitation, hyperactive motility, and the acrosome reaction (AR) during the sperm transit through the female tract. Moreover, exogenous P4 and E2 can induce the AR in ovine spermatozoa, and progesterone receptor (PR) and estrogen receptors (ERα and ERβ) are present in these cells. Thus, to investigate whether the effects both steroid hormones in ram sperm capacitation and AR are receptor-mediated, we incubated them with receptor agonists (tanaproget 1 μM and 5 μM for PR or resveratrol 5 μM and 10 μM for ER) or antagonists (mifepristone 4 μM and 40 μM for PR or tamoxifen 5 μM and 10 μM for ER) in capacitating conditions. The addition of receptor modulators did not affect sperm viability or total motility, although changes in progressive motility were detected. The incubation with both receptor agonists increased the percentage of acrosome-reacted spermatozoa, evaluated by chlortetracycline staining, when compared with the capacitated nontreated sample (Cap-C, P < 0.001). Moreover, the ER agonist resveratrol 10 μM provoked a greater AR than E2 (P < 0.01). Furthermore, the incubation with the receptor antagonists prevented the induction of the AR by P4 or E2, as the antagonists-treated spermatozoa presented a similar CTC pattern to that of Cap-C. In conclusion, these results confirm that P4 and E2 can induce the AR in ram spermatozoa and that this effect is receptor-mediated.

Clozapine Induced Disturbances in Hepatic Glucose Metabolism: The Potential Role of PGRMC1 Signaling

Newly emerging evidence has implicated that progesterone receptor component 1 (PGRMC1) plays a novel role not only in the lipid disturbance induced by atypical antipsychotic drugs (AAPD) but also in the deterioration of glucose homoeostasis induced by clozapine (CLZ) treatment. The present study aimed to investigate the role of PGRMC1 signaling on hepatic gluconeogenesis and glycogenesis in male rats following CLZ treatment (20 mg/kg daily for 4 weeks). Recombinant adeno-associated viruses (AAV) were constructed for the knockdown or overexpression of hepatic PGRMC1. Meanwhile, AG205, the specific inhibitor of PGRMC1 was also used for functional validation of PGRMC1. Hepatic protein expressions were measured by western blotting. Meanwhile, plasma glucose, insulin and glucagon, HbA1c and hepatic glycogen were also determined by assay kits. Additionally, concentrations of progesterone (PROG) in plasma, liver and adrenal gland were measured by a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Our study demonstrated that CLZ promoted the process of gluconeogenesis and repressed glycogenesis, respectively mediated by PI3K-Akt-FOXO1 and GSK3β signaling via inhibition of PGRMC1-EGFR/GLP1R in rat liver, along with an increase in fasting blood glucose, HbA1c levels and a decrease in insulin and hepatic glycogen levels. Furthermore, through PGRMC1-EGFR/GLP1R-PI3K-Akt pathway, knockdown or inhibition (by AG205) of PGRMC1 mimics, whereas its overexpression moderately alleviates CLZ-induced glucose disturbances. Potentially, the PGRMC1 target may be regarded as a novel therapeutic strategy for AAPD-induced hepatic glucose metabolism disorder.

Inhibition of progesterone receptor activity during development increases reelin-immunoreactivity in Cajal-Retzius cells, alters synaptic innervation in neonatal dentate gyrus, and impairs episodic-like memory in adulthood

Progesterone receptor (PR) is expressed in Cajal-Retzius (CR) cells of the dentate gyrus (DG) molecular layer during the postnatal period (P1-28), a critical stage of development for the dentate gyrus and its circuitry. CR cells secrete the glycoprotein, reelin, which is required for typical development of the DG and its connections, particularly afferent input from the perforant path. This pathway regulates the processing of sensory information arriving from entorhinal cortex and integrates this information to form episodic memories. To assess the potential role of PR activity on the development of these connections and associated behavior, rats were treated daily from P1 to 7 with the PR antagonist, RU486. RU486 treatment increased the number of reelin-ir cells, suggesting an accumulation of reelin, and implicating PR in the regulation of a principle developmental function of CR cells. RU486 also altered the synaptic bouton marker, synaptophysin-ir, in a sex-specific manner, suggesting a role for PR activity in the development of perforant path innervation of the molecular layer (MOL). Finally, both control and RU486 treated rats spent significantly more time with a temporally distant object in the Relative Recency task, suggesting an intact associative memory for object identity and temporal order in both groups. In contrast, the same RU486 treated rats were impaired in an episodic-like memory task compared to controls, failing to integrate object identity ('what'), time ('when'), and object position ('where'). These findings reveal a novel role for PR in regulating CR cell function within the MOL, thereby altering development of DG connectivity and behavioral function.

Progesterone receptor membrane component 1 promotes the growth of breast cancers by altering the phosphoproteome and augmenting EGFR/PI3K/AKT signalling

BACKGROUND

Increased expression of the progesterone receptor membrane component 1 (PGRMC1) has been linked to multiple cancers, including breast cancer. Despite being a regulatory receptor and a potential therapeutic target, the oncogenic potential of PGRMC1 has not been studied.

METHODS

The impact of PGRMC1 on breast cancer growth and progression was studied following chemical inhibition and alteration of PGRMC1 expression, and evaluated by using online-based gene expression datasets of human breast cancer tissue. MTS, flow cytometry, qPCR, Western blotting, confocal microscopy and phosphoproteome analysis were performed.

RESULTS

We observed higher PGRMC1 levels in both ER-positive ZR-75-1 and TNBC MDA-MB-468 cells. Both chemical inhibition and silencing decreased cell proliferation, induced cell-cycle arrest, promoted apoptosis and reduced the migratory and invasive capabilities of ZR-75-1 and MDA-MB-468 cells. Further, phosphoproteome analysis demonstrated an overall decrease in activation of proteins involved in PI3K/AKT/mTOR and EGFR signalling pathways. In contrast, overexpression of PGRMC1 in non-malignant MCF10A cells resulted in increased cell proliferation, and enhanced activity of PI3K/AKT/mTOR and EGFR signalling pathways.

CONCLUSIONS

Our data demonstrate that PGRMC1 plays a prominent role in regulating the growth of cancer cells by altering the PI3K/AKT/mTOR and EGFR signalling mechanisms in both ER-positive and TNBC cells.

PGRMC1/2 promotes luteal vascularization and maintains the primordial follicles of mice

To determine whether conditional depletion of progesterone receptor membrane component (PGRMC) 1 and PGRMC2 affected ovarian follicle development, follicle distribution was assessed in ovaries of young (≈3-month-old) and middle-aged (≈6-month-old) control (Pgrmc1/2fl/fl) and double conditional PGRMC1/2-knockout (Pgrmc1/2d/d) mice. This study revealed that the distribution of primary, preantral and antral follicles was not altered in Pgrmc1/2d/d mice, regardless of the age. Although the number of primordial follicles was similar at ≈3 months of age, their numbers were reduced by ≈80% in 6-month-old Pgrmc1/2d/d mice compared to age-matched Pgrmc1/2fl/fl mice. The Pgrmc1/2d/d mice were generated using Pgr-cre mice, so ablation of Pgrmc1 and Pgrmc2 in the ovary was restricted to peri-ovulatory follicles and subsequent corpora lutea (CL). In addition, the vascularization of CL was attenuated in Pgrmc1/2d/d mice, although mRNA levels of vascular endothelial growth factor A (Vegfa) were elevated. Moreover, depletion of Pgrmc1 and Pgrmc2 altered the gene expression profile in the non-luteal component of the ovary such that Vegfa expression, a stimulator of primordial follicle growth, was elevated; Kit Ligand expression, another stimulator of primordial follicle growth, was suppressed and anti-Mullerian hormone, an inhibitor of primordial follicle growth, was enhanced compared to Pgrmc1/2fl/fl mice. These data reveal that luteal cell depletion of Pgrmc1 and 2 alters the expression of growth factors within the non-luteal component of the ovary, which could account for the premature demise of the adult population of primordial follicles. In summary, the survival of adult primordial follicles is dependent in part on progesterone receptor membrane component 1 and 2.

Roles of progesterone receptor membrane component 1 and membrane progestin receptor alpha in regulation of zebrafish oocyte maturation

Although previous studies suggest membrane progesterone receptor alpha (mPRα/Paqr7) mediates 17, 20β-dihydroxy-4-pregnen-3-one (DHP) induction of oocyte maturation (OM) in zebrafish, critical information needed to establish mPRα as the receptor mediating OM is lacking. The relative potencies of progestins and specific mPRα agonists in inducing OM matched their relative binding affinities for zebrafish mPRα, supporting its role in OM. Microinjection of pertussis toxin blocked DHP induction of OM and the progestin-induced decrease in cyclic AMP levels, suggesting mPRα activates an inhibitory G protein (Gi). Microinjection of morpholino antisense oligonucleotides to zebrafish pgrmc1 blocked induction of OM by DHP which was accompanied by decreased levels of Pgrmc1 and mPRα on the oocyte plasma membranes. Similarly, treatment of denuded oocytes with a PGRMC1 inhibitor, AG205, blocked the gonadotropin-induced increase in plasma membrane mPRα levels and attenuated DHP induction of OM. Co-incubation with two inhibitors of epidermal growth factor Erbb2, ErbB2 inhibitor II and AG 879, prevented induction of OM by DHP, indicating the likely involvement of Erbb2 in mPRα-mediated signaling. Treatment with AG205 reversed the inhibitory effects of the Erbb2 inhibitors on OM and also inhibited insulin-like growth factor-1 induction of OM. Close associations between Pgrmc1 and mPRα, and between Pgrmc1 and Erbb2 were detected in zebrafish oocytes with in situ proximity ligation assays. The results suggest progestin induction of OM in zebrafish is mediated through an mPRα/Gi/Erbb2 signaling pathway that requires Pgrmc1 for expression of mPRα on oocyte membranes and that Pgrmc1 also is required for induction of OM through Erbb2.

Lordosis facilitated by GPER-1 receptor activation involves GnRH-1, progestin and estrogen receptors in estrogen-primed rats

The present study assessed the participation of membrane G-protein coupled estrogen receptor 1 (GPER-1) and gonadotropin releasing hormone 1 (GnRH-1) receptor in the display of lordosis induced by intracerebroventricular (icv) administration of G1, a GPER-1 agonist, and by unesterified 17β-estradiol (free E₂). In addition, we assessed the participation of both estrogen and progestin receptors in the lordosis behavior induced by G1 in ovariectomized (OVX), E₂-benzoate (EB)-primed rats. In Experiment 1, icv injection of G1 induced lordosis behavior at 120 and 240min. In Experiment 2, icv injection of the GPER-1 antagonist G15 significantly reduced lordosis behavior induced by either G1 or free E₂. In addition, Antide, a GnRH-1 receptor antagonist, significantly depressed G1 facilitation of lordosis behavior in OVX, EB-primed rats. Similarly, icv injection of Antide blocked the stimulatory effect of E₂ on lordosis behavior. In Experiment 3, systemic injection of either tamoxifen or RU486 significantly reduced lordosis behavior induced by icv administration of G1 in OVX, EB-primed rats. The results suggest that GnRH release activates both estrogen and progestin receptors and that this activation is important in the chain of events leading to the display of lordosis behavior in response to activation of GPER-1 in estrogen-primed rats.

Progesterone-Mediated Non-Classical Signaling

Progesterone is essential for pregnancy maintenance and menstrual cycle regulation. Hormone action has been primarily ascribed to the well-characterized classical signaling pathway involving ligand binding, activation of nuclear progesterone receptors (PRs), and subsequent activation of genes containing progesterone response elements (PREs). Recent studies have revealed progesterone actions via non-classical signaling pathways, often mediated by non-genomic signaling. Progesterone signaling, in conjunction with growth factor signaling, impacts on the function of growth factors and regulates important physiological actions such as cell growth and remodeling, as well as apoptosis. This review focuses on non-classical progesterone signaling pathways, both including and excluding PR, and highlights how research in this area will provide a better understanding of progesterone actions and may inform novel therapeutic strategies.

α-Estrogen and Progesterone Receptors Modulate Kisspeptin Effects on Prolactin: Role in Estradiol-Induced Prolactin Surge in Female Rats

Kisspeptin (Kp) regulates prolactin (PRL) in an estradiol-dependent manner. We investigated the interaction between ovarian steroid receptors and Kp in the control of PRL secretion. Intracerebroventricular injections of Kp-10 or Kp-234 were performed in ovariectomized (OVX) rats under different hormonal treatments. Kp-10 increased PRL release and decreased 3,4-dihydroxyphenylacetic acid levels in the median eminence (ME) of OVX rats treated with estradiol (OVX+E), which was prevented by tamoxifen. Whereas these effects of Kp-10 were absent in OVX rats, they were replicated in OVX rats treated with selective agonist of estrogen receptor (ER)α, propylpyrazole triol, but not of ERβ, diarylpropionitrile. Furthermore, the Kp-10-induced increase in PRL was two times higher in OVX+E rats also treated with progesterone (OVX+EP), which was associated with a reduced expression of both tyrosine hydroxylase (TH) and Ser40-phosphorylated TH in the ME. Kp-10 also reduced dopamine levels in the ME of OVX+EP rats, an effect blocked by the progesterone receptor (PR) antagonist RU486. We also determined the effect of Kp antagonism with Kp-234 on the estradiol-induced surges of PRL and luteinizing hormone (LH), using tail-tip blood sampling combined with ultrasensitive enzyme-linked immunosorbent assay. Kp-234 impaired the early phase of the PRL surge and prevented the LH surge in OVX+E rats. Thus, we provide evidence that Kp stimulation of PRL release requires ERα and is potentiated by progesterone via PR activation. Moreover, alongside its essential role in the LH surge, Kp seems to play a role in the peak phase of the estradiol-induced PRL surge.

Potential contribution of progesterone receptors to the development of sexual behavior in male and female mice

We previously showed that estradiol can have both defeminizing and feminizing effects on the developing mouse brain. Pre- and early postnatal estradiol defeminized the ability to show lordosis in adulthood, whereas prepubertal estradiol feminized this ability. Furthermore, we found that estradiol upregulates progesterone receptors (PR) during development, inducing both a male-and female-typical pattern of PR expression in the mouse hypothalamus. In the present study, we took advantage of a newly developed PR antagonist (ZK 137316) to determine whether PR contributes to either male- or female-typical sexual differentiation. Thus groups of male and female C57Bl/6j mice were treated with ZK 137316 or OIL as control: males were treated neonatally (P0-P10), during the critical period for male sexual differentiation, and females were treated prepubertally (P15-P25), during the critical period for female sexual differentiation. In adulthood, mice were tested for sexual behavior. In males, some minor effects of neonatal ZK treatment on sexual behavior were observed: latencies to the first mount, intromission and ejaculation were decreased in neonatally ZK treated males; however, this effect disappeared by the second mating test. By contrast, female mice treated with ZK during the prepubertal period showed significantly less lordosis than OIL-treated females. Mate preferences were not affected in either males or females treated with ZK during development. Taken together, these results suggest a role for PR and thus perhaps progesterone in the development of lordosis behavior in female mice. By contrast, no obvious role for PR can be discerned in the development of male sexual behavior.

Conditional Ablation of Progesterone Receptor Membrane Component 2 Causes Female Premature Reproductive Senescence

The nonclassical progesterone receptors progesterone receptor membrane component (PGRMC) 1 and PGRMC2 have been implicated in regulating cell survival of endometrial and ovarian cells in vitro and are abundantly expressed in these cell types. The objective of this study was to determine if Pgrmc1 and Pgrmc2 are essential for normal female reproduction. To accomplish this objective, Pgrmc1 and/or Pgrmc2 floxed mice (Pgrmc2fl/fl and Pgrmc1/2fl/fl) were crossed with Pgr-cre mice, which resulted in the conditional ablation of Pgrmc1 and/or Pgrmc2 from female reproductive tissues (i.e.,Pgrmc2d/d and Pgrmc1/2d/d mice). A breeding trial revealed that conditional ablation of Pgrmc2 initially led to subfertility, with Pgrmc2d/d female mice producing 47% fewer pups/litter than Pgrmc2fl/fl mice (P = 0.001). Pgrmc2d/d mice subsequently underwent premature reproductive senescence by parities 2 to 5, producing 37.8% fewer litters overall during the trial compared with Pgrmc2fl/fl mice (P = 0.020). Similar results were observed with Pgrmc1/2d/d mice. Based on ovarian morphology and serum P4, the subfertility/infertility was not due to faulty ovulation or luteal insufficiency. Rather an analysis of midgestation implantation sites revealed that postimplantation embryonic death was the major cause of the subfertility/infertility. As with our previous report of Pgrmc1d/d mice, Pgrmc2d/d and Pgrmc1/2d/d mice developed endometrial cysts consistent with accelerated aging of this tissue. Given the timing of postimplantation embryonic demise, uterine decidualization may be disrupted in mice deficient in PGRMC2 or PGRMC1/2. Overall, this study revealed that Pgrmc1 and/or Pgrmc2 are required for the maintenance of uterine histoarchitecture and normal female reproductive lifespan.

Estrogen-dependent estrous behavior in rabbits is antagonized by the antiprogestin RU486

Estrogen receptor-alpha (ERα) dimerizes with unliganded progesterone receptor (PR) in target tissues to trigger genomic and non-genomic effects. In ovariectomized rats the antiprogestin RU486 or antisense nucleotides against PR antagonize estradiol-induced sexual receptivity. We determined the relevance of unliganded PR for the expression of estrogen-dependent scent-marking (chinning) and sexual receptivity by injecting RU486 to: a) ovariectomized (ovx) rabbits given estradiol benzoate (EB; 5μg/day); b) intact rabbits. Chinning and lordosis were quantified in ovx animals before (5days; baseline) and during hormonal treatments: EB+RU486 (20mg/day; n=18) or EB+vehicle (n=18). On treatment day 4 LQ (lordosis quotient) increased in both groups, relative to baseline (mean±se): LQ=1±5 (baseline) vs 25±21 (EB+RU486) and 2±6 (baseline) vs 37±29 (EB+vehicle). On day 9 LQ values were: 22±23 (EB+RU486) and 54±39 (EB+vehicle). Chinning increased only in the EB+vehicle group (day 9=55±46 vs baseline=17±20 marks/10min). In intact rabbits one RU486 injection: reduced the LQ from 72±7to 36±8 five hrs later, increased the latency to receive first ejaculation from 45 to 98s, and decreased the number of ejaculations received in the test from 3 to 2 but did not modify mounting latency or chinning. Results support a participation of unliganded PR for the induction (ovx) and maintenance (intact) of rabbit estrous behavior by estrogens.

Pushing estrogen receptor around in breast cancer

The estrogen receptor-α (herein called ER) is a nuclear sex steroid receptor (SSR) that is expressed in approximately 75% of breast cancers. Therapies that modulate ER action have substantially improved the survival of patients with ER-positive breast cancer, but resistance to treatment still remains a major clinical problem. Treating resistant breast cancer requires co-targeting of ER and alternate signalling pathways that contribute to resistance to improve the efficacy and benefit of currently available treatments. Emerging data have shown that other SSRs may regulate the sites at which ER binds to DNA in ways that can powerfully suppress the oncogenic activity of ER in breast cancer. This includes the progesterone receptor (PR) that was recently shown to reprogram the ER DNA binding landscape towards genes associated with a favourable outcome. Another attractive candidate is the androgen receptor (AR), which is expressed in the majority of breast cancers and inhibits growth of the normal breast and ER-positive tumours when activated by ligand. These findings have led to the initiation of breast cancer clinical trials evaluating therapies that selectively harness the ability of SSRs to 'push' ER towards anti-tumorigenic activity. Our review will focus on the established and emerging clinical evidence for activating PR or AR in ER-positive breast cancer to inhibit the tumour growth-promoting functions of ER.

Aging-Related Changes in Ovarian Hormones, Their Receptors, and Neuroendocrine Function

Ovarian steroid hormones exert a broad range of effects on the body and brain. In the nervous system, estrogen and progesterone have crucial feedback actions on the hypothalamic neurons that drive the reproductive axis. In addition, hormones exert a variety of actions on other traditionally nonreproductive functions such as cognition, learning and memory, neuroprotection, mood and affective behavior, and locomotor activity. The actions of hormones on the hypothalamus are largely mediated by their nuclear hormone receptors, the two estrogen receptors, ERα and ERβ, and the two progesterone receptor isoforms, PR-A and PR-B. Thus, changes in the circulating concentrations of estrogens and progestins during the life cycle can result in differential activation of their receptors. Furthermore, changes in the numbers, activity, and distribution of hypothalamic ERs and PRs can occur as a function of developmental age. The purpose of this article is to review the literature on the causes and consequences of alterations in steroid hormones, their neural receptors, and their interactions on reproductive senescence. We have also discussed several important experimental design considerations, focusing on rodent models in current use for understanding the mechanisms of menopause in women.

Exploring Flexibility of Progesterone Receptor Ligand Binding Domain Using Molecular Dynamics

Progesterone receptor (PR), a member of nuclear receptor (NR) superfamily, plays a vital role for female reproductive tissue development, differentiation and maintenance. PR ligand, such as progesterone, induces conformation changes in PR ligand binding domain (LBD), thus mediates subsequent gene regulation cascades. PR LBD may adopt different conformations upon an agonist or an antagonist binding. These different conformations would trigger distinct transcription events. Therefore, the dynamics of PR LBD would be of general interest to biologists for a deep understanding of its structure-function relationship. However, no apo-form (non-ligand bound) of PR LBD model has been proposed either by experiments or computational methods so far. In this study, we explored the structural dynamics of PR LBD using molecular dynamics simulations and advanced sampling tools in both ligand-bound and the apo-forms. Resolved by the simulation study, helix 11, helix 12 and loop 895–908 (the loop between these two helices) are quite flexible in antagonistic conformation. Several residues, such as Arg899 and Glu723, could form salt-bridging interaction between helix 11 and helix 3, and are important for the PR LBD dynamics. And we also propose that helix 12 in apo-form PR LBD, not like other NR LBDs, such as human estrogen receptor α (ERα) LBD, may not adopt a totally extended conformation. With the aid of umbrella sampling and metadynamics simulations, several stable conformations of apo-form PR LBD have been sampled, which may work as critical structural models for further large scale virtual screening study to discover novel PR ligands for therapeutic application.

Central obesity increases risk of breast cancer irrespective of menopausal and hormonal receptor status in women of South Asian Ethnicity

BACKGROUND

Current evidence suggests that the relationship between obesity and breast cancer (BC) risk may vary between ethnic groups.

METHODS

A total of 1633 BC cases and 1504 controls were enrolled in hospital-based case-control study in Mumbai, India, from 2009 to 2013. Along with detailed questionnaire, we collected anthropometric measurements on all participants. We used unconditional logistic regression models to estimate odds ratios (ORs) and 95% confidence interval (CI) for BC risk associated with anthropometry measurements, stratified on tumour subtype and menopausal status.

RESULTS

Waist-to-hip ratio (WHR) of ≥0.95 was strongly associated with risk of BC compared to WHR ≤0.84 in both premenopausal (OR = 4.3; 95% CI: 2.9-6.3) and postmenopausal women (OR = 3.4; 95% CI: 2.4-4.8) after adjustment for body mass index (BMI). Premenopausal women with a BMI ≥30 were at lower risk compared to women with normal BMI (OR = 0.5; 95% CI: 0.4-0.8). A similar protective effect was observed in women who were postmenopausal for <10 years (OR = 0.6; 95% CI: 0.4-0.9) but not in women who were postmenopausal for ≥10 years (OR = 1.8; 95% CI: 1.1-3.3). Overweight and obese women (BMI: 25-29.9 and ≥ 30 kg/m(2), respectively) were at increased BC risk irrespective of menopausal status if their WHR ≥0.95. Central obesity (measured in terms of WC and WHR) increased the risk of both premenopausal and postmenopausal BCs irrespective of hormone receptor (HR) status.

CONCLUSIONS

Central obesity appears to be a key risk factor for BC irrespective of menopausal or HR status in Indian women with no history of hormone replacement therapy.

Conditional Ablation of Progesterone Receptor Membrane Component 1 Results in Subfertility in the Female and Development of Endometrial Cysts

Progesterone (P4) is essential for female fertility. The objective of this study was to evaluate the functional requirement of the nonclassical P4 receptor (PGR), PGR membrane component 1, in regulating female fertility. To achieve this goal, the Pgrmc1 gene was floxed by insertion of loxP sites on each side of exon 2. Pgrmc1 floxed (Pgrmc1(fl/fl)) mice were crossed with Pgr(cre) or Amhr2(cre) mice to delete Pgrmc1 (Pgrmc1(d/d)) from the female reproductive tract. A 6-month breeding trial revealed that conditional ablation of Pgrmc1 with Pgr(cre/+) mice resulted in a 40% reduction (P = .0002) in the number of pups/litter. Neither the capacity to ovulate in response to gonadotropin treatment nor the expression of PGR and the estrogen receptor was altered in the uteri of Pgrmc1(d/d) mice compared with Pgrmc1(fl/fl) control mice. Although conditional ablation of Pgrmc1 from mesenchymal tissue using Amhr2(cre/+) mice did not reduce the number of pups/litter, the total number of litters born in the 6-month breeding trial was significantly decreased (P = .041). In addition to subfertility, conditional ablation of Pgrmc1 using either Amhr2(cre/+) or Pgr(cre/+) mice resulted in the development of endometrial cysts starting around 4 months of age. Interestingly, pregnancy attenuated the formation of these uterine cysts. These new findings demonstrate that PGR membrane component 1 plays an important role in female fertility and uterine tissue homeostasis.

Myometrial Progesterone responsiveness and the Control of Human Parturition

OBJECTIVE

The goal of this review is to assess the body of literature addressing the mechanism of progesterone withdrawal in the control of human parturition and in particular the recent advances in testing the hypothesis that human parturition is initiated by decreased myometrial responsiveness to progesterone, ie, functional progesterone withdrawal.

METHODS

Published studies of progesterone responsiveness of the pregnant human myometrium in the context of parturition control were reviewed.

RESULTS

Advances in understanding the molecular basis for progesterone receptor (PR)-mediated control of progesterone responsiveness has led to the hypothesis that functional progesterone withdrawal in human parturition is mediated by specific changes in myometrial PR expression, function, or both. The human PR exists as two major subtypes, PR-A and PR-B. As PR-A represses progesterone actions mediated by PR-B, the extent of progesterone responsiveness is inversely related to the PR-A/PR-B expression ratio. In women, the onset of term labor is associated with a significant increase in the myometrial PR-A/PR-B expression ratio that may facilitate functional progesterone withdrawal. Interestingly, expression of the estrogen receptor-alpha (ERalpha) increases concordantly with the PR-A/PR-B expression ratio in nonlaboring myometrium. This finding indicates that functional estrogen activation and functional progesterone withdrawal are linked.

CONCLUSION

Functional progesterone withdrawal in human parturition is likely mediated by an increase in the myometrial PR-A/PR-B expression ratio and possibly by modulation of coactivator and corepressor proteins. Functional progesterone withdrawal appears to induce functional estrogen activation. Thus, for most of pregnancy, progesterone may decrease myometrial estrogen responsiveness by inhibiting ERalpha expression. Such an interaction would explain why the human myometrium is refractory to the high levels of circulating estrogens for most of pregnancy. At term, functional progesterone withdrawal removes the suppression of ERalpha expression leading to an increase in ERalpha and a concomitant increase in myometrial estrogen responsiveness. Estrogen can then act to transform the myometrium to a contractile phenotype. This model explains why disruption of progesterone action alone triggers the full parturition cascade. The link between functional progesterone withdrawal and functional estrogen activation may be a critical mechanism for the endocrine control of human parturition.

Immunomodulatory and Transcriptional Effects of Progesterone Through Progesterone A and B Receptors in Hec50co Poorly Differentiated Endometrial Cancer Cells

OBJECTIVE

Derivatives of progesterone, progestins, are used to treat endometrial cancer; however, the pathways activated by the hormone have not been fully investigated. Progesterone acts through two receptor isoforms, progesterone receptors A and B (PRA and PRB), transcription factors that control the expression of downstream genes leading to endometrial differentiation. The purpose of this study was to perform an expression analysis to identify the mechanisms underlying progesterone's growth suppressive and immunomodulatory effects in endometrial cancer.

METHODS

To study the molecular effects of progesterone, PRs were introduced into Hec50co cells. Expression array analyses followed by confirmatory semiquantitive reverse-transcriptase polymerase chain reaction (RT-PCR) experiments were performed.

RESULTS

Expression analysis demonstrated a significant effect of progesterone after 12 hours of treatment on a number of genes, including cell signaling, DNA remodeling, apoptotic, tumor-suppressor, and transcription factors. Of particular interest was the consistent modulation of cytokines, which generally predicted for a powerful anti-inflammatory effect of progesterone through PR. Specifically, pro-inflammatory genes such as TNFalpha, IL-1beta, and MCP-1/MCAF-1 were down-regulated and anti-inflammatory genes such as TRAP1 and SMAD4 were induced.

CONCLUSION

We have discovered that progesterone has a modulatory effect on inflammation and many other important cellular functions. These effects likely underlie the inhibitory effects of progesterone on tumor growth and invasion.

Progestins inhibit calcitriol-induced CYP24A1 and synergistically inhibit ovarian cancer cell viability: An opportunity for chemoprevention

OBJECTIVES

Previously we have shown in endometrial cells that progesterone (P4) and calcitriol (CAL, 1,25(OH)2D3) synergistically promote apoptosis and that progestins induce expression of the vitamin D receptor. In the current study we examined the progestin/vitamin D combination in ovarian cells and searched for other progestin-related effects on vitamin D metabolism that may underlie the novel interaction between progestins and vitamin D, including whether progestins inhibit CYP24A1, the enzyme that renders CAL inactive.

METHODS

We investigated the impact of P4 on CAL-induced CYP24A1 expression in cancer cell lines expressing progesterone receptors (PRs), [OVCAR-5, OVCAR-3-PGR (PR-transfected OVCAR-3 ovarian line), and T47D-WT, T47D-A and T47D-B (breast lines expressing PRs or individual PR isoforms)] or lines that do not express PRs (OVCAR-3 and T47D-Y). We examined CYP24A1 expression using RT-PCR and western blotting, and apoptosis by TUNEL. We also investigated P4 inhibition of Cyp24a1 in ovaries from CAL-treated mice.

RESULTS

CAL treatment induced CYP24A1 expression. When co-treated with P4, cell lines expressing PRs showed marked inhibition of CYP24A1 expression (p<0.001), along with increased apoptosis (p<0.01); cells not expressing PRs did not. Mouse ovaries showed a significant reduction in CAL-induced Cyp24a1 mRNA (p<0.001) and protein (p<0.01) in response to P4.

CONCLUSIONS

We show for the first time that progestins and vitamin D synergistically reduce cell viability and induce apoptosis in ovarian cells and that progestins PR-dependently inhibit CAL-induced CYP24A1, thus extending CAL activity. The combination of progestins and vitamin D deserves further consideration as a strategy for inhibiting ovarian carcinogenesis.

Inverse Relationship between Progesterone Receptor and Myc in Endometrial Cancer

Endometrial cancer, the most common gynecologic malignancy, is a hormonally-regulated disease. Response to progestin therapy positively correlates with hormone receptor expression, in particular progesterone receptor (PR). However, many advanced tumors lose PR expression. We recently reported that the efficacy of progestin therapy can be significantly enhanced by combining progestin with epigenetic modulators, which we term “molecularly enhanced progestin therapy.” What remained unclear was the mechanism of action and if estrogen receptor α (ERα), the principle inducer of PR, is necessary to restore functional expression of PR via molecularly enhanced progestin therapy. Therefore, we modeled advanced endometrial tumors that have lost both ERα and PR expression by generating ERα-null endometrial cancer cell lines. CRISPR-Cas9 technology was used to delete ERα at the genomic level. Our data demonstrate that treatment with a histone deacetylase inhibitor (HDACi) was sufficient to restore functional PR expression, even in cells devoid of ERα. Our studies also revealed that HDACi treatment results in marked downregulation of the oncogene Myc. We established that PR is a negative transcriptional regulator of Myc in endometrial cancer in the presence or absence of ERα, which is in contrast to studies in breast cancer cells. First, estrogen stimulation augmented PR expression and decreased Myc in endometrial cancer cell lines. Second, progesterone increased PR activity yet blunted Myc mRNA and protein expression. Finally, overexpression of PR by adenoviral transduction in ERα-null endometrial cancer cells significantly decreased expression of Myc and Myc-regulated genes. Analysis of the Cancer Genome Atlas (TCGA) database of endometrial tumors identified an inverse correlation between PR and Myc mRNA levels, with a corresponding inverse correlation between PR and Myc downstream transcriptional targets SRD5A1, CDK2 and CCNB1. Together, these data reveal a previously unanticipated inverse relationship between the tumor suppressor PR and the oncogene Myc in endometrial cancer.

Progesterone receptor membrane component-1 regulates hepcidin biosynthesis

Iron homeostasis is tightly regulated by the membrane iron exporter ferroportin and its regulatory peptide hormone hepcidin. The hepcidin/ferroportin axis is considered a promising therapeutic target for the treatment of diseases of iron overload or deficiency. Here, we conducted a chemical screen in zebrafish to identify small molecules that decrease ferroportin protein levels. The chemical screen led to the identification of 3 steroid molecules, epitiostanol, progesterone, and mifepristone, which decrease ferroportin levels by increasing the biosynthesis of hepcidin. These hepcidin-inducing steroids (HISs) did not activate known hepcidin-inducing pathways, including the BMP and JAK/STAT3 pathways. Progesterone receptor membrane component-1 (PGRMC1) was required for HIS-dependent increases in hepcidin biosynthesis, as PGRMC1 depletion in cultured hepatoma cells and zebrafish blocked the ability of HISs to increase hepcidin mRNA levels. Neutralizing antibodies directed against PGRMC1 attenuated the ability of HISs to induce hepcidin gene expression. Inhibiting the kinases of the SRC family, which are downstream of PGRMC1, blocked the ability of HISs to increase hepcidin mRNA levels. Furthermore, HIS treatment increased hepcidin biosynthesis in mice and humans. Together, these data indicate that PGRMC1 regulates hepcidin gene expression through an evolutionarily conserved mechanism. These studies have identified drug candidates and potential therapeutic targets for the treatment of diseases of abnormal iron metabolism.

The mammary stem cell hierarchy: a looking glass into heterogeneous breast cancer landscapes

The mammary gland is a dynamic organ that undergoes extensive morphogenesis during the different stages of embryonic development, puberty, estrus, pregnancy, lactation and involution. Systemic and local cues underlie this constant tissue remodeling and act by eliciting an intricate pattern of responses in the mammary epithelial and stromal cells. Decades of studies utilizing methods such as transplantation and lineage-tracing have identified a complex hierarchy of mammary stem cells, progenitors and differentiated epithelial cells that fuel mammary epithelial development. Importantly, these studies have extended our understanding of the molecular crosstalk between cell types and the signaling pathways maintaining normal homeostasis that often are deregulated during tumorigenesis. While several questions remain, this research has many implications for breast cancer. Fundamental among these are the identification of the cells of origin for the multiple subtypes of breast cancer and the understanding of tumor heterogeneity. A deeper understanding of these critical questions will unveil novel breast cancer drug targets and treatment paradigms. In this review, we provide a current overview of normal mammary development and tumorigenesis from a stem cell perspective.

The role of steroid hormones in breast cancer stem cells

Breast cancer stem cells (BCSCs) are potent tumor-initiating cells in breast cancer, the most common cancer among women. BCSCs have been suggested to play a key role in tumor initiation which can lead to disease progression and formation of metastases. Moreover, BCSCs are thought to be the unit of selection for therapy-resistant clones since they survive conventional treatments, such as chemotherapy, irradiation, and hormonal therapy. The importance of the role of hormones for both normal mammary gland and breast cancer development is well established, but it was not until recently that the effects of hormones on BCSCs have been investigated. This review will discuss recent studies highlighting how ovarian steroid hormones estrogen and progesterone, as well as therapies against them, can regulate BCSC activity.

A functional progesterone receptor is required for immunomodulation, reduction of reactive gliosis and survival of oligodendrocyte precursors in the injured spinal cord

The anti-inflammatory effects of progesterone have been increasingly recognized in several neuropathological models, including spinal cord inflammation. In the present investigation, we explored the regulation of proinflammatory factors and enzymes by progesterone at several time points after spinal cord injury (SCI) in male rats. We also demonstrated the role of the progesterone receptor (PR) in inhibiting inflammation and reactive gliosis, and in enhancing the survival of oligodendrocyte progenitors cells (OPC) in injured PR knockout (PRKO) mice receiving progesterone. First, after SCI in rats, progesterone greatly attenuated the injury-induced hyperexpression of the mRNAs of interleukin 1β (IL1β), IL6, tumor necrosis factor alpha (TNFα), inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2), all involved in oligodendrocyte damage. Second, the role of the PR was investigated in PRKO mice after SCI, in which progesterone failed to reduce the high expression of IL1β, IL6, TNFα and IκB-α mRNAs, the latter being considered an index of reduced NF-κB transactivation. These effects occurred in a time framework coincident with a reduction in the astrocyte and microglial responses. In contrast to wild-type mice, progesterone did not increase the density of OPC and did not prevent apoptotic death of these cells in PRKO mice. Our results support a role of PR in: (a) the anti-inflammatory effects of progesterone; (b) the modulation of astrocyte and microglial responses and (c) the prevention of OPC apoptosis, a mechanism that would enhance the commitment of progenitors to the remyelination pathway in the injured spinal cord.

Progesterone attenuates Aβ(25-35)-induced neuronal toxicity via JNK inactivation and progesterone receptor membrane component 1-dependent inhibition of mitochondrial apoptotic pathway

Progesterone, which acts as a neurosteroid in nervous system, has been shown to have neuroprotective effects in different experiments in vitro and in vivo. Our previous study demonstrates that progesterone exerts neuroprotections in Alzheimer's disease-like rats. Present study attempted to evaluate the protective effects of progesterone on Aβ-treated neurons and potential mechanisms involved in neuroprotection. Results showed that treatment with progesterone protected primary cultured rat cortical neurons against Aβ(25-35)-induced apoptosis. Furthermore, we observed that progesterone alleviated mitochondrial dysfunction by rescuing mitochondrial membrane potential under Aβ challenge. Moreover, progesterone could also attenuate Bax/Bcl-2 proteins ratio upregulation and inhibit the activation of caspase-3 in Aβ-treated neurons. These indicate that progesterone attenuates Aβ(25-35)-induced neuronal toxicity by inhibiting mitochondria-associated apoptotic pathway. Both classic progesterone receptors (classic PR) and progesterone receptor membrane component 1 (PGRMC1), a special progesterone membrane receptor, are broadly expressed throughout the brain. The protective effect of progesterone was partially abolished by PGRMC1 inhibitor AG205 rather than classic PR antagonist RU486 in this study. Additionally, progesterone protected neurons by inhibiting Aβ-induced activation of JNK, which was an upstream signaling component in Aβ-induced mitochondria-associated apoptotic pathway. But this process was independent of PGRMC1. Taken together, these results suggest that progesterone exerts a protective effect against Aβ(25-35)-induced insults at least in part by two complementary pathways: (1) progesterone receptor membrane component 1-dependent inhibition of mitochondrial apoptotic pathway, and (2) blocking Aβ-induced JNK activation. The present study provides new insights into the mechanism by which progesterone brings neuroprotection. This article is part of a Special Issue entitled 'Steroids & Nervous System'.

Inactivation of the Progesterone Receptor in Mx1+ Cells Potentiates Osteogenesis in Calvaria but Not in Long Bone

The effect of progesterone on bone remains elusive. We previously reported that global progesterone receptor (PR) knockout mice displayed high bone mass phenotype, suggesting that PR influences bone growth and modeling. Recently, Mx1+ cells were characterized to be mesenchymal stem cell-like pluripotent Cells. The aim of this study was to evaluate whether the PR in Mx1+ cells regulates osteogenesis. Using the Mx1-Cre;mT/mG reporter mouse model, we found that the calvarial cells exhibited minimal background Mx1-Cre activity prior to Cre activation by IFNα treatment as compared to the bone marrow stromal cells. IFNα treatment significantly activated Mx1-Cre in the calvarial cells. When the PR gene was deleted in the Mx1-Cre;PR-flox calvarial cells in vitro, significantly higher levels of expression of osteoblast maturation marker genes (RUNX2, Osteocalcin, and Dmp1) and osteogenic potential were detected. The PR-deficient calvariae exhibited greater bone volume, especially in the males. Although Mx1-Cre activity could be induced on the bone surface in vivo, the Mx1+ cells did not differentiate into osteocytes in long bones. Bone volumes at the distal femurs and the bone turnover marker serum Osteocalcin were similar between the Mx1-Cre;PR-flox mutant mice and the corresponding wild types in both sexes. In conclusion, our data demonstrates that blocking progesterone signaling via PRs in calvarial Mx1+ cells promoted osteoblast differentiation in the calvaria. Mx1+ was expressed by heterogeneous cells in bone marrow and did not differentiate into osteocyte during long bone development in vivo. Selectively inactivating the PR gene in Mx1+ cells affected the membrane bone formation but did not affect peripheral skeletal homeostasis.

Targeting female hormone receptors as cervical cancer therapy

While preventive methods for cervical cancer are effective, available therapies for advanced cervical cancers are ineffective. New experimental evidence points to weaknesses of prior studies and provides fresh molecular insights on the opposing roles of estrogen receptor alpha (ERα) and the progesterone receptor (PR) that may be translated into valuable treatments for a subset of cervical cancers.

Cell-based assay of nongenomic actions of progestins revealed inhibitory G protein coupling to membrane progestin receptor α (mPRα)

Previously, we established cell lines stably producing goldfish membrane progestin receptor α (goldfish mPRα) proteins, which mediate steroidal nongenomic actions. In this study, we transfected these cell lines (MDA-MD-231) with cDNAs encoding a recombinant luciferase gene (GloSensor). These cells can be used for monitoring the effects of ligands that bind to mPR by means of luminescence, the intensity of which reflects intracellular cyclic adenosine monophosphate (cAMP) levels. Luminescence intensity of the cells increased significantly when cells were treated with forskolin, strong activator of adenylyl cyclase. Then, we established a strategy to measure changes in luminescence that correlated with the actions of the ligands. The actions of ligands were measurable by the prevention of stimulation caused by forskolin after ligand stimulation. The studies using these cell lines indicated that cAMP concentrations were decreased specifically by the mPR ligands 17α,20β-dihydroxy-4-pregnen-3-one, diethylstilbestrol and progesterone. Furthermore, pertussis toxin inhibited the decrease in cAMP levels caused by mPR ligands. These results support evidence from previous results that mPRα is coupled to an inhibitory G protein.

Progesterone regulation of tissue factor depends on MEK1/2 activation and requires the proline-rich site on progesterone receptor

To characterize the molecular mechanism and map the response element used by progesterone (P) to upregulate tissue factor (TF) in breast cancer cells. TF expression and mRNA levels were analyzed in breast cancer ZR-75 and T47D cells, using Western blot and real-time PCR, respectively. Mapping of the TF promoter was performed using luciferase vectors. Progesterone receptor (PR) and specificity protein 1 (Sp1) binding to the TF promoter were analyzed by chromatin immuno precipitation assay. Specific or selective inhibitors were used for the MEK1/2 and the c-Src pathways (UO126 and PP2, respectively). TF mRNA increase peaks at 18 h following P treatment in ZR-75 and T47D cells. P upregulation occurs via a transcriptional mechanism that depends on PR and MEK1/2 activation, PR and Sp1 transcription factors bind to a region in the TF promoter that contains three Sp1 sites. TF mRNA upregulation requires an intact PR proline-rich site (mPRO), but it is independent from c-Src. TF upregulation by P is mediated by Sp1 sites in the TF promoter region. Transcriptional upregulation in breast cancer cells occurs via a new mechanism that requires MEK1/2 activation and the mPRO site but independent of c-Src activity. PR Phosphorylation at serine 294 and 345 is not essential.

Blocking of progestin action disrupts spermatogenesis in Nile tilapia (Oreochromis niloticus)

In vitro studies have indicated that the maturation-inducing hormone 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP, DHP), probably through nuclear progestin receptor (Pgr), might be involved in the proliferation of spermatogonial cells and the initiation of meiosis in several fish species. However, further in vivo evidence is required to elucidate the role of DHP in spermatogenesis during sexual differentiation in teleosts. In this study, we cloned pgr and analyzed its expression in Nile tilapia (Oreochromis niloticus) and treated XY fish with RU486 (a synthetic Pgr antagonist) from 5 days after hatching (dah) to determine the role of DHP in spermatogenesis. Sequence and phylogenetic analyses revealed that the Pgr identified in tilapia is a genuine Pgr. Pgr was found to be expressed in the Sertoli cells surrounding spermatogonia and spermatids in the testis of tilapia. Real-time PCR analysis revealed that the expression of pgr in the testis was significantly upregulated from 10 dah, further increased at 50 dah, and persisted until adulthood in fish. In the testis of RU486-treated fish, the transcript levels of germ cell markers and a meiotic marker were substantially reduced. However, the expression of markers in Sertoli cells remained unchanged. Moreover, the production of 11-ketotestosterone and the expression of genes encoding various steroidogenic enzymes were also not altered. In contrast, the expression of cyp17a2, encoding one of the critical steroidogenic enzymes involved in DHP biosynthesis, declined significantly, possibly indicating the inhibition of DHP production by RU486. RU486 treatment given for 2 months did not affect spermatogenesis; however, treatment given for more than 3 months resulted in a decrease in spermatogonial cell numbers and depletion of later-phase spermatogenic cells. Simultaneous excessive DHP supplementation restored spermatogenesis in RU486-treated XY fish. Taken together, our data further indicated that DHP, possibly through Pgr, might be essential for spermatogonial cell proliferation and spermatogenesis in fish.

Genomic and non-genomic actions of progestogens in the breast

Evidence is growing that progestogens may enhance breast cancer risk under hormone therapy in the postmenopause or hormonal contraception. However, differences may exist within the progestogen class and certain progestogens may have a higher potency in terms of breast cancer risk. The mechanism(s) by which these progestogens might influence breast cancer risk appear to be mediated via genomic and/or non-genomic effects triggered by activated progestogen receptors. In general, regulation of gene expression by progestogen receptors seems to be a multifactorial process involving both actions which often converge. In the present review, we describe the known genomic and non-genomic effects in the breast, especially focusing on the progestins. This article is part of a Special Issue entitled 'Menopause'.

CRISPLD2 is a target of progesterone receptor and its expression is decreased in women with endometriosis

Endometriosis, defined as the presence of endometrial cells outside of the uterine cavity, is a major cause of infertility and pelvic pain, afflicting more than 10% of reproductive age women. Endometriosis is a chronic inflammatory disease and lipopolysaccharide promotes the proliferation and invasion of endometriotic stromal cells. Cysteine-rich secretory protein LCCL domain-containing 2 (CRISPLD2) has high affinity for lipopolysaccharide and plays a critical role in defense against endotoxin shock. However, the function of CRISPLD2 has not been studied in endometriosis and uterine biology. Herein, we examined the expression of CRISPLD2 in endometrium from patients with and without endometriosis using immunohistochemistry. The expression of CRISPLD2 was higher in the secretory phase in human menstrual cycle compared to proliferative phase. The expression of CRISPLD2 was significantly decreased in the endometrium of women with endometriosis in the early secretory phase compared to women without endometriosis. The increase of CRISPLD2 expression at the early secretory and dysregulation of its expression in endometriosis suggest progesterone (P4) regulation of CRISPLD2. To investigate whether CRISPLD2 is regulated by P4, we examined the expression of the CRISPLD2 in the uteri of wild-type and progesterone receptor knock out (PRKO) mice. The expression of CRISPLD2 was significantly increased after P4 treatment in the wild-type mice. However, CRISPLD2 expression was significantly decreased in the (PRKO) mice treated with P4. During early pregnancy, the expression of CRISPLD2 was increased in decidua of implantation and post-implantation stages. CRISPLD2 levels were also increased in cultured human endometrial stromal cells during in vitro decidualization. These results suggest that the CRISPLD2 is a target of the progesterone receptor and may play an important role in pathogenesis of endometriosis.

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.

Hormonal therapy in epithelial ovarian cancer

The ovary is an endocrine and end organ. Hormones and their receptors have been associated with ovarian cancer and may be related to its causation. Some data suggest that hormonal therapies may have an effect on ovarian cancer in palliative settings. The most well studied anticancer drugs are tamoxifen, megestrol acetate, medroxyprogesterone acetate, leuprolide acetate, anastrozole and letrozole. Presently, no hormonal therapy is approved by the US FDA for the treatment of any type of ovarian malignancy or is listed as an active agent by any of the authoritative compendia. Owing to the endocrine associations with ovarian cancer, the minimal side effects of hormonal therapy and the demonstrated activity of hormonal therapies in other endocrine organ-associated malignancies, further study of hormonal therapies for ovarian cancer is warranted.

Pregnane xenobiotic receptors and membrane progestin receptors: role in neurosteroid-mediated motivated behaviours

Progestogens have actions in the midbrain ventral tegmental area (VTA) to mediate motivated behaviours, such as those involved in reproductive processes, among female rodents. In the VTA, the formation and actions of one progestogen, 5α-pregnan-3α-ol-20-one (3α,5α-THP), are necessary and sufficient to facilitate sexual responding (measured by lordosis) of female rodents. Although 3α,5α-THP can be produced after metabolism of ovarian progesterone, 3α,5α-THP is also a neurosteroid produced de novo in brain regions, such as the VTA. There can be dynamic changes in 3α,5α-THP production associated with behavioural experience, such as mating. Questions of interest are the sources and targets of 3α,5α-THP. Regarding sources, the pregnane xenobiotic receptor (PXR) may be a novel factor involved in 3α,5α-THP metabolism in the VTA (as well as a direct target of 3α,5α-THP). We have identified PXR in the midbrain of female rats, and manipulating PXR in this region reduces 3α,5α-THP synthesis and alters lordosis, as well as affective and social behaviours. Regarding targets, recent studies have focused on the role of membrane progestin receptors (mPRs). We have analysed the expression of two of the common forms of these receptors (mPRα/paqr7 and mPRβ/paqr8) in female rats. The expression of mPRα was observed in peripheral tissues and brain areas, including the hypothalamus and midbrain. The expression of mPRβ was only observed in brain tissues and was abundant in the midbrain and hypothalamus. To our knowledge, studies of these receptors in mammalian models have been limited to expression and regulation, instead of function. One question that was addressed was the functional effects of progestogens via mPRα and mPRβ in the midbrain of hormone-primed rats for lordosis. Studies to date suggest that mPRβ may be an important target of progestogens in the VTA for lordosis. Taken together, the result of these studies demonstrate that PXR is involved in the production of 3α,5α-THP in the midbrain VTA. Moreover, mPRs may be a target for the actions of progestogens in the VTA for lordosis.

Nonclassical progesterone signalling molecules in the nervous system

Progesterone (P4) regulates a wide range of cognitive, neuroendocrine, neuroimmune and neuroprotective functions. Therefore, it is not surprising that this ovarian hormone acts through multiple receptors. Ever since the 1980s, studies investigating the neural effects of P4 have focused mainly on genomic and nongenomic actions of the classical progestin receptor (PGR). More recently, two groups of nonclassical P4 signalling molecules have been identified: (i) the class II progestin and adipoQ receptor (PAQR) family, which includes PAQR 5, 6, 7, 8 and 9, also called membrane progestin receptor α (mPRα; PAQR7), mPRβ (PAQR8), mPRγ (PAQR5), mPRδ (PAQR6) and mPRε (PAQR9), and (ii) the b5-like haeme/steroid-binding protein family, which includes progesterone receptor membrane component 1 (Pgrmc1), Pgrmc2, neudesin and neuferricin. In this review, we describe the structures, neuroanatomical localisation and signalling mechanisms of these molecules. We also discuss gonadotrophin-releasing hormone regulation as an example of a physiological function regulated by multiple progesterone receptors but through different mechanisms.

Membrane progestin receptors in the midbrain ventral tegmental area are required for progesterone-facilitated lordosis of rats

Progesterone (P₄) and its metabolites, rapidly facilitate lordosis of rats partly through actions in the ventral tegmental area (VTA). The study of membrane progestin receptors (mPRs), of the Progestin and AdipoQ Receptor (PAQR) superfamily, has been limited to expression and regulation, instead of function. We hypothesized that if mPRs are required for progestin-facilitated lordosis in the VTA, then mPRs will be expressed in this region and knockdown will attenuate lordosis. First, expression of mPR was examined by reverse-transcriptase polymerase chain reaction (RT-PCR) in brain and peripheral tissues of proestrous Long-Evans rats. Expression of mPRα (paqr7) was observed in peripheral tissues and brain areas, including hypothalamus and midbrain. Expression of mPRβ (paqr8) was observed in brain tissues and was abundant in the midbrain and hypothalamus. Second, ovariectomized rats were estrogen (E₂; 0.09 mg/kg, SC), and P₄ (4 mg/kg, SC) or vehicle-primed, and infused with antisense oligodeoxynucleotides (AS-ODNs) targeted against mPRα and/or mPRβ intracerebroventricularly or to the VTA. Rats were assessed for motor (open field), anxiety (elevated plus maze), social (social interaction), and sexual (lordosis) behavior. P₄-facilitated lordosis was significantly reduced with administration of AS-ODNs for mPRα, mPRβ, or co-administration of mPRα and mPRβ to the lateral ventricle, compared to vehicle. P₄-facilitated lordosis was reduced, compared to vehicle, by administration of mPRβ AS-ODNs, or co-administration of mPRα and mPRβ AS-ODNs, but not mPRα AS-ODNs alone, to the VTA. No differences were observed for motor, anxiety, or social behaviors. Thus, mPRs in the VTA are targets of progestin-facilitated lordosis of rats.

Breast cancer among nurses: is the intensity of night work related to hormone receptor status?

The aim of this study was to investigate whether night work is related to breast cancer receptor status. The effect of night work on the risk of estrogen receptor- and progesterone receptor-defined breast cancers was evaluated in 513 nurses diagnosed with breast cancer between 1996 and 2007 and in 757 frequency-matched controls, all of whom were selected from a cohort of Norwegian nurses. Odds ratios for the exposure "duration of work with a minimum of 6 consecutive night shifts" were compared for tumor subgroups with respect to the common control group through the use of polytomous logistic regression. Statistically significant associations were observed between breast cancer and work durations of ≥ 5 years with ≥ 6 consecutive night shifts, with the highest risk observed for progesterone receptor-positive tumors (odds ratio = 2.4, 95% confidence interval: 1.3, 4.3; P-trend = 0.01). When the exposure variable was dichotomized (ever/never worked ≥ 6 consecutive night shifts), a borderline statistically significant heterogeneity (P = 0.05) was seen between progesterone receptor-positive and progesterone receptor-negative tumors in postmenopausal women. The association observed between consecutive night shifts and progesterone receptor-positive cancers suggests that progesterone could play an important role in the detrimental effects of night work.

The classical progesterone receptor mediates the rapid reduction of fallopian tube ciliary beat frequency by progesterone

BACKGROUND

The transport of gametes as well as the zygote is facilitated by motile cilia lining the inside of the fallopian tube. Progesterone reduces the ciliary beat frequency within 30 minutes in both cows and mice. This rapid reduction suggest the involvement of a non-genomic signaling mechanism, although it is not known which receptors that are involved. Here we investigated the possible involvement of the classical progesterone receptor in this process.

METHOD

The ciliary beat frequency of mice fallopian tube was measured ex vivo using an inverted bright field microscope and a high speed camera. The effects of the agonists progesterone and promegestone and an antagonist, mifeprestone, were investigated in wildtype mice. The effect of progesterone was also investigated in mice lacking the classical progesterone receptor.

RESULTS

Progesterone, as well as the more specific PR agonist promegestone, significantly reduced the CBF at concentrations of 10-100 nanomolar within 10-30 minutes. In the absence of progesterone, the PR antagonist mifeprestone had no effect on the ciliary beat frequency at a concentration of 1 micromolar. When ciliated cells were pre-incubated with 1 micromolar mifeprestone, addition of progesterone did not reduce the ciliary beat frequency. Accordingly, in ciliated cells from mice not expressing the classical progesterone receptor, exposure to 100 nanomolar progesterone did not reduce the ciliary beat frequency.

CONCLUSIONS

This is the first study to provide comprehensive evidence that the classical progesterone receptor mediates the rapid reduction of the tubal ciliary beat frequency by progesterone.

Progesterone and neuroprotection

Numerous studies aimed at identifying the role of estrogen on the brain have used the ovariectomized rodent as the experimental model. And while estrogen intervention in these animals has, at least partially, restored cholinergic, neurotrophin and cognitive deficits seen in the ovariectomized animal, it is worth considering that the removal of the ovaries results in the loss of not only circulating estrogen but of circulating progesterone as well. As such, the various deficits associated with ovariectomy may be attributed to the loss of progesterone as well. Similarly, one must also consider the fact that the human menopause results in the precipitous decline of not just circulating estrogens, but in circulating progesterone as well and as such, the increased risk for diseases such as Alzheimer's disease during the postmenopausal period could also be contributed by this loss of progesterone. In fact, progesterone has been shown to exert neuroprotective effects, both in cell models, animal models and in humans. Here, we review the evidence that supports the neuroprotective effects of progesterone and discuss the various mechanisms that are thought to mediate these protective effects. We also discuss the receptor pharmacology of progesterone's neuroprotective effects and present a conceptual model of progesterone action that supports the complementary effects of membrane-associated and classical intracellular progesterone receptors. In addition, we discuss fundamental differences in the neurobiology of progesterone and the clinically used, synthetic progestin, medroxyprogesterone acetate that may offer an explanation for the negative findings of the combined estrogen/progestin arm of the Women's Health Initiative-Memory Study (WHIMS) and suggest that the type of progestin used may dictate the outcome of either pre-clinical or clinical studies that addresses brain function.

Progesterone action in endometrial cancer, endometriosis, uterine fibroids, and breast cancer

Progesterone receptor (PR) mediates the actions of the ovarian steroid progesterone, which together with estradiol regulates gonadotropin secretion, prepares the endometrium for implantation, maintains pregnancy, and differentiates breast tissue. Separation of estrogen and progesterone actions in hormone-responsive tissues remains a challenge. Pathologies of the uterus and breast, including endometrial cancer, endometriosis, uterine fibroids, and breast cancer, are highly associated with estrogen, considered to be the mitogenic factor. Emerging evidence supports distinct roles of progesterone and its influence on the pathogenesis of these diseases. Progesterone antagonizes estrogen-driven growth in the endometrium, and insufficient progesterone action strikingly increases the risk of endometrial cancer. In endometriosis, eutopic and ectopic tissues do not respond sufficiently to progesterone and are considered to be progesterone-resistant, which contributes to proliferation and survival. In uterine fibroids, progesterone promotes growth by increasing proliferation, cellular hypertrophy, and deposition of extracellular matrix. In normal mammary tissue and breast cancer, progesterone is pro-proliferative and carcinogenic. A key difference between these tissues that could explain the diverse effects of progesterone is the paracrine interactions of PR-expressing stroma and epithelium. Normal endometrium is a mucosa containing large quantities of distinct stromal cells with abundant PR, which influences epithelial cell proliferation and differentiation and protects against carcinogenic transformation. In contrast, the primary target cells of progesterone in the breast and fibroids are the mammary epithelial cells and the leiomyoma cells, which lack specifically organized stromal components with significant PR expression. This review provides a unifying perspective for the diverse effects of progesterone across human tissues and diseases.

Activation of enteroendocrine membrane progesterone receptors promotes incretin secretion and improves glucose tolerance in mice

Glucagon-like peptide-1 (GLP-1) secretion is classically regulated by ingested nutrients. To identify novel molecular targets controlling incretin secretion, we analyzed enteroendocrine cell pathways important for hormone biosynthesis and secretion. We demonstrate that progesterone increases GLP-1 secretion and extracellular signal-related kinase 1/2 (ERK1/2) phosphorylation in enteroendocrine GLUTag cells via mechanisms sensitive to the mitogen-activated protein kinase inhibitor U0126. The stimulatory effects of progesterone (P4) or the synthetic progestin R5020 on ERK1/2 phosphorylation were independent of the classical progesterone receptor antagonist RU486. Furthermore, a cell-impermeable BSA-progesterone conjugate rapidly increased ERK1/2 phosphorylation and GLP-1 secretion. Knockdown of the membrane progesterone receptors Paqr5 or Paqr7 in GLUTag cells eliminated the stimulatory effect of R5020 and progesterone on GLP-1 secretion. Enteral progesterone administration increased plasma levels of GLP-1, glucose-dependent insulinotropic polypeptide (GIP), and insulin, and improved oral glucose tolerance in an RU486-insensitve manner in mice: however, systemic progesterone exposure did not improve glucose homeostasis. Unexpectedly, the glucoregulatory actions of enteral progesterone did not require classical incretin receptor signaling and were preserved in Glp1r(-/-) and Glp1r(-/-):Gipr(-/-) mice. Intestine-restricted activation of membrane progesterone receptors may represent a novel approach for stimulation of incretin hormone secretion and control of glucose homeostasis.

The pathogenesis of endometrial polyps: a systematic semi-quantitative review

The pathogenesis and natural history of endometrial polyps are not very clear. The objective of this study was to assess the opinions of international medical literature regarding the factors involved in the pathogenesis of endometrial polyps and to organize the results consistently with what is known about endometrial physiology.

MATERIALS AND METHODS

A systematic review was carried out with the following search engines: PubMed, OVID, Scopus, SCIELO, and AJOL. Two hundreds forty-six abstracts were selected from the literature; of these abstracts, 58 factors were extracted and set as causative, non-causative, unclear or protective link with endometrial polyps. This relation is described through a correspondence analysis and tested with a main effect hierarchical log-linear model.

RESULTS

The log-linear model resulted significant for the correspondence found with the following factors: (i) causative link (ageing, bcl-2 protein, excess weight/obesity, tamoxifen regardless of timing, relationship between estrogen receptors and prog-estinics, unbalanced estrogen therapy, estrogen-like effect, and unbalance between estrogens and progestinics), (ii) protective link (progestinics, antiestrogenic action), (iii) unclear link (menopause, ki-67 protein, angiogenesis, tamoxifen for a short time, tamoxifen for a long time, hormone replacement therapy (HRT), endometritis/inflammation), and (iv) non-causative link (none of the factors specifically).

DISCUSSION

Subsequently to a review of the physiology of the endometrium, the onsetting of endometrial polyps was suggested through estrogen-related and non-estrogen related ways; the two ways can overlap. The most implied factors in the development of endometrial polyps are linked with one of these or both ways.