Characterization and regulation of a mRNA encoding the prostaglandin F2alpha receptor in the rat ovary

Expression patterns of chemokine (C-C motif) ligand 2, prostaglandin F2A receptor and immediate early genes at mRNA level in the bovine corpus luteum after intrauterine treatment with a low dose of prostaglandin F2A

The present study evaluated expression patterns of chemokine (C-C motif) ligand 2 gene/Monocyte chemoattractant protein-1 gene (CCL2/MCP-1), prostaglandin F2 alpha receptor gene (PTGFR) and immediate early genes including nuclear receptor subfamily 4, group A, member 1 (NR4A1), early growth response 1 (EGR1) and FBJ murine osteosarcoma viral oncogene homolog (FOS) in cells of the bovine corpus luteum after intrauterine infusion of a low dose of prostaglandin F2α (PGF2A) aimed at enhancing our understanding of the mechanisms of luteolysis. Holstein dairy cows were superovulated (>6 corpora lutea [CL]) and on day 9 of the estrous cycle were infused with a low dose of PGF2A (0.5 mg PGF2A in 0.25 ml phosphate buffered saline) into the greater curvature of the uterine horn ipsilateral to the CL. Ultrasound-guided biopsy samples of different CL were collected at 0 min, 15 min, 30 min, 1h, 2h and 6h after PGF2A infusion. Expression profiles and localization of mRNA for PTGFR, CCL2/MCP-1, and immediate early genes (NR4A1, EGR1 and FOS), were investigated by using qPCR and in situ hybridization. The concentrations of early response genes including FOS, NR4A1, and EGR1 exhibited the greatest increase at 30 min after PGF2A, compared to other time points. Expression profile of CCL2 mRNA increased gradually after intrauterine infusion of PGF2A with maximal up-regulation for CCL2 at 6h. Abundance of PTGFR mRNA only increased at 15 min and significantly decreased at 6h, compared to 0 min. Cellular localizations of all studied genes except CCL2 (primarily localized to apparent immune cells) were predominantly visualized in large luteal cells. Interestingly, early response genes demonstrated a changing profile in cellular localization with initial responses appearing to be in both large luteal cells and endothelial cells, although no staining for PTGFR mRNA was observed in endothelial cells. Later, sustained responses, were only observed in large luteal cells, although PTGFR mRNA was decreasing in large luteal cells over time after PGF2A. The involvement of the immune system was also highlighted by the immediate increases in CCL2 mRNA that became much greater over time as there was an apparent influx of CCL2-positive immune cells. Thus, the temporal and cell-specific localization patterns for the studied mRNA demonstrate the complex pathways that are responsible for initiation of luteolysis in the bovine CL.

Luteolysis and the Auto-, Paracrine Role of Cytokines From Tumor Necrosis Factor α and Transforming Growth Factor β Superfamilies

Successful pregnancy establishment demands optimal luteal function in mammals. Nonetheless, regression of the corpus luteum (CL) is absolutely necessary for normal female cyclicity. This dichotomy relies on intricate molecular signals and rapidly activated biological responses, such as angiogenesis, extracellular matrix (ECM) remodeling, or programmed cell death. The CL establishment and growth after ovulation depend not only on the luteinizing hormone-mediated endocrine signal but also on a number of auto-, paracrine interactions promoted by cytokines and growth factors like fibroblast growth factor 2, vascular endothelial growth factor A, and tumor necrosis factor α (TNF), which coordinate vascularigenesis and ECM reorganization as well as steroidogenesis. With the organ fully developed, the release of the uterine prostaglandin F2α activates luteolysis, an intricate process supported by intraluteal interactions that ensure the loss of steroidogenic function (functional luteolysis) and the involution of the organ (structural luteolysis). This chapter provides an overview of the local action of cytokines during luteal function, with particular emphasis on the role of TNF and transforming growth factor β superfamilies during luteolysis.

Prostaglandin F receptor expression in intrauterine tissues of pregnant rats

In this investigation, we studied the expression and localization of rat prostaglandin F (FP) receptor in uterine tissues of rats on gestational Days 10, 15, 18, 20, 21, 21.5 and postpartal Days 1 and 3 using Western blotting analysis, real-time PCR, and immunohistochemistry. A high level of immunoreactivity was observed on gestational Days 20, 21, and 21.5 with the most significant signals found on Day 20. FP receptor protein was expressed starting on gestational Day 15, and a fluctuating unsteady increase was observed until delivery. Uterine FP receptor mRNA levels were low between Days 10 and 18 of gestation (p < 0.05). The transcript level increased significantly on Day 20 and peaked on Day 21.5 just before labor (p < 0.05). There was a positive correlation between FP receptor mRNA expression and serum estradiol levels (rs = 0.78; p < 0.01) along with serum estradiol/progesterone ratios (rs = 0.79; p < 0.01). In summary, we observed an increase FP receptor expression in rat uterus with advancing gestation, a marked elevation of expression at term, and a concominant decrease during the postpartum period. These findings indicate a role for uterine FP receptors in the mediation of uterine contractility at term.

Patterns of gene expression in the bovine corpus luteum following repeated intrauterine infusions of low doses of prostaglandin F2alpha

Natural luteolysis involves multiple pulses of prostaglandin F2alpha (PGF) released by the nonpregnant uterus. This study investigated expression of 18 genes from five distinct pathways, following multiple low-dose pulses of PGF. Cows on Day 9 of the estrous cycle received four intrauterine infusions of 0.25 ml of phosphate-buffered saline (PBS) or PGF (0.5 mg of PGF in 0.25 ml of PBS) at 6-h intervals. A luteal biopsy sample was collected 30 min after each PBS or PGF infusion. There were four treatment groups: Control (n = 5; 4 PBS infusions), 4XPGF (4 PGF infusions; n = 5), 2XPGF-non-regressed (2 PGF infusions; n = 5; PGF-PBS-PGF-PBS; no regression after treatments), and 2XPGF-regressed (PGF-PBS-PGF-PBS; regression after treatments; n = 5). As expected, the first PGF pulse increased mRNA for the immediate early genes JUN, FOS, NR4A1, and EGR1 but unexpectedly also increased mRNA for steroidogenic (STAR) and angiogenic (VEGFA) pathways. The second PGF pulse induced immediate early genes and genes related to immune system activation (IL1B, FAS, FASLG, IL8). However, mRNA for VEGFA and STAR were decreased by the second PGF infusion. After the third and fourth PGF pulses, a distinctly luteolytic pattern of gene expression was evident, with inhibition of steroidogenic and angiogenic pathways, whereas, there was induction of pathways for immune system activation and production of PGF. The pattern of PGF-induced gene expression was similar in corpus luteum not destined for luteolysis (2X-non-regressed) after the first PGF pulse but was very distinct after the second PGF pulse. Thus, although the initial PGF pulse induced mRNA for many pathways, the second and later pulses of PGF appear to have set the distinct pattern of gene expression that result in luteolysis.

Evidence suggesting multiple promoting roles of luteal group IVA phospholipase A(2) in prostaglandin F(2alpha)-induced regression in pseudopregnant rats

We evaluated effects of local administration of selective inhibitors of group IVA phospholipase A(2) (GIVA PLA(2)) and cyclooxygenase (COX) on exogenous prostaglandin (PG) F(2alpha)-induced luteal regression in pseudopregnant rats. Intra-bursal treatment with a GIVA PLA(2) inhibitor AACOCF(3) just prior to PGF(2alpha) (30microg, subcutaneously) on day 6 of pseudopregnancy (PSP6) prevented a decline in circulating progesterone and inhibited TUNEL-positive reactions of steroidogenic cell. Its treatment on PSP9 failed to inhibit functional regression, but reduced significantly apoptosis of steroidogenic cells and vascular endothelial cells, and suppressed the infiltration of macrophages. A COX-2-selective inhibitor NS398 inhibited the decline of progesterone and apoptosis of steroidogenic cells on PSP6 but not on PSP9. A COX-1 inhibitor SC560 exerted insignificant anti-luteolytic effects. Overall data suggest that luteal GIVA PLA(2) plays multiple promoting roles in PGF(2alpha)-induced luteal regression at least partly by a COX-2 activity-related mechanism in pseudopregnant rats.

Food deprivation stimulates the luteolytic capacity in the gilt

The aims of this study were to study the effects of fasting on progesterone (P4) production in the pig and to verify whether fasting influences luteal expression of PGF(2alpha) receptor (FPr) and prostaglandin secretion. Superovulated prepubertal gilts were used; half of them were fasted for 72h starting on day 2 (F2) or 9 (F9) of the induced estrous cycle, respectively, while two groups (C2 and C9) served as respective controls. Plasma P4 and PGFM concentrations were determined by RIA while FPr mRNA expression in CLs collected at the end of fasting period was measured by real-time PCR. In experiment 1, plasma P4 concentrations in fasted gilts were significantly (P<0.01) higher than in controls starting from day 3 (F2; n=6) and 10 (F9; n=6). FPr mRNA expression was similar in F2 and C2 (n=6) CLs while it was significantly (P<0.05) higher in F9 than in C9 (n=6) CLs. In experiment 2, cloprostenol administered on day 12 significantly (P<0.05) increased FPr mRNA expression in CLs from both F9 (n=6) and C9 (n=6) gilts. At the time of cloprostenol injection PGFM levels were significantly higher (P<0.05) in the fasted group and cloprostenol-induced luteolysis in fasted but not in normally fed gilts. Results from this study indicate that fasting in prepubertal gilts induced to ovulate stimulates luteal P4 and PGFM production as well as FPr mRNA expression, thus increasing luteolytic susceptibility.

Hypothyroidism prolongs corpus luteum function in the pregnant rat

It has been shown that hypothyroidism in the rat produces a prolongation of pregnancy associated with a delay in the fall of circulating progesterone (P4) at term. The aim of the present work is to determine whether the delayed P4 decline in hypothyroid mother rats is due to a retarded induction of P4 degradation to 20alphaOH P4 or to a stimulation of its synthesis, and to investigate the possible mechanisms that may underlie the altered luteal function. We determined by RIA the circulating profile of the hormones (TSH, PRL, LH, P4, PGF2alpha, and PGE2) involved in luteal regulation at the end of pregnancy and, by semiquantitative RT-PCR, the expression of factors involved in P4 synthesis (CytP450scc, StAR, 3betaHSD, PRLR) and metabolism (20alphaHSD, PGF2alphaR, iNOS and COX2). Our results show that the delay in P4 decline and parturition is the resultant of retarded luteal regression, caused by a combination of decreases in luteolytic factors, mainly luteal PGF2alpha, iNOS mRNA expression and also circulating LH, and increased synthesis or action of luteotrophic factors, such as luteal and circulating PGE2 and circulating PRL. All these changes may be direct causes of the decreased 20alphaHSD mRNA and protein (measured by western blot analysis) expression, which in the presence of unchanged expression of the factors involved in P4 synthesis results in elevated luteal and circulating P4 that prolonged pregnancy and also may favor longer survival of the corpus luteum.

Changes in steady-state concentrations of messenger ribonucleic acids in luteal tissue during prostaglandin F2α induced luteolysis in mares

Transvaginal ultrasound-guided luteal biopsy was used to evaluate the effects of prostaglandin (PG)F2alpha on steady-state concentrations of mRNA for specific genes that may be involved in regression of the corpus luteum (CL). Eight days after ovulation (Hour 0), mares (n=8/group) were randomized into three groups: control (no treatment or biopsy), saline+biopsy (saline treatment at Hour 0 and luteal biopsy at Hour 12), or PGF2alpha+biopsy (5mg PGF2alpha at Hour 0 and luteal biopsy at Hour 12). The effects of biopsy on CL were compared between the controls (no biopsy) and saline+biopsy group. At Hour 24 (12h after biopsy) there was a decrease in circulating progesterone in saline group to 56% of pre-biopsy values, indicating an effect of biopsy on luteal function. Mean plasma progesterone concentrations were lower (P<0.001) at Hour 12 in the PG group compared to the other two groups. The relative concentrations of mRNA for different genes in luteal tissue at Hour 12 was quantified by real time PCR. Compared to saline-treated mares, treatment with PGF2alpha increased mRNA for cyclooxygenase-2 (Cox-2, 310%, P<0.006), but decreased mRNA for LH receptor to 44% (P<0.05), steroidogenic acute regulatory protein to 22% (P<0.001), and aromatase to 43% (P<0.1) of controls. There was no difference in mRNA levels for PGF2alpha receptor between PG and saline-treated groups. Results indicated that luteal biopsy alters subsequent luteal function. However, the biopsy approach was effective for collecting CL tissue for demonstrating dynamic changes in steady-state levels of mRNAs during PGF2alpha-induced luteolysis. Increased Cox-2 mRNA concentrations suggested that exogenous PGF2alpha induced the synthesis of intraluteal PGF2alpha. Thus, the findings are consistent with the concept that an intraluteal autocrine loop augments the luteolytic effect of uterine PGF2alpha in mares.

Expression, localization and function of prostaglandin receptors in myometrium

Prostaglandins (PGs) play a role in the initiation and maintenance of labor, acting via specific relaxatory or contractile receptors on myometrium. Myometrial response to addition of PGs may be determined by the type and concentration of receptor expressed. Autoradiographic and ligand binding studies suggest a topographic distribution of receptors between fundus, lower segment, and cervix, and that hormonally regulated changes in expression occur with advancing gestation and labor. These receptors have now been cloned and sequenced allowing molecular studies. Current dogma suggests functional regionalization of the pregnant human uterus occurs with the lower segment displaying a contractile phenotype throughout gestation changing to a relaxatory phenotype at labor to allow passage of the fetal head whereas the upper segment has a relaxatory phenotype throughout most of gestation to accommodate the growing fetus and adopts a contractile phenotype for expulsion at labor. Studies to determine the role of PG receptors in this phenomenon are currently underway.

Treatment with prostaglandin F2alpha increases expression of prostaglandin synthase-2 in the rat corpus luteum

Recent studies indicate that the corpus luteum (CL) may be a source of prostaglandin F2alpha (PGF2alpha) for regression. We investigated expression of mRNA and protein for prostaglandin G/H synthase (PGHS) in the CL of immature superovulated rats following administration of PGF2alpha. We observed an increase in mRNA for PGHS-2, the induced isoform, at 1 h and protein at 8 and 24 h after treatment. One hour after PGF2alpha, there was also a progressive decrease in plasma progesterone concentration. There were no changes, however, in expression of PGHS-1, the constitutive isoform, over the 24 h sampling period. These results indicate that PGHS-2 increases following PGF2alpha treatment and that expression of this enzyme in the rat CL may contribute to the luteolytic mechanism.

Expression and localization of the contractile prostaglandin F receptor in pregnant rat myometrium in late gestation, labor, and postpartum

A polyclonal antibody was raised against amino acids 7-18 in the first extracellular loop of rat prostaglandin F (FP) receptor to monitor expression and localization in pregnant rat myometrium at Gestational Days 16, 18, 20, 21, 21.5, 22 (delivery), and 23 (1-day postpartum; n = 5 per group). The antibody recognized a protein of approximately 43 kDa on Western blot analysis in both membrane (soluble and nonsoluble) and cytosolic fractions of myometrium on each day of gestation. Expression of FP protein increased significantly (P < 0.05) during late gestation in both soluble membrane and cytosolic fractions, being significantly greater at Day 21.5 than at Day 20 of gestation in the soluble membrane fraction and in the cytosolic fraction of tissues collected during labor compared with those obtained before labor. The total concentration of FP receptor in the membrane (soluble plus nonsoluble) remained high throughout late gestation and fell significantly (P < 0.05) in the postpartum period. The FP receptor in the soluble membrane fraction (compared to the total membrane FP receptor) was significantly (P < 0.05) higher in late gestation than earlier, whereas the ratio of FP protein in cytosolic to that in the total membrane was significantly (P < 0.05) higher on Day 23 than earlier in gestation, suggesting a dynamic movement of FP with advancing gestational age. Immunoreactive FP receptor localized to circular and longitudinal smooth muscle at all gestational ages, but changes in intracellular localization were observed in late gestation with a staining pattern similar to alpha-actin, suggesting an association with myofibrils. Our study suggests an increase in FP-receptor protein in myometrium with advancing gestation and a marked elevation at term. This supports a role for uterine FP receptors in mediation of uterine contractility at term.

Prostaglandin F(2alpha) receptor in the corpus luteum: recent information on the gene, messenger ribonucleic acid, and protein

The prostaglandin (PG) F(2alpha) receptor (FPr) in the corpus luteum is essential for maintaining normal reproductive cyclicity in many species. Activation of this seven-transmembrane spanning receptor at the end of the cycle leads to a decrease in progesterone and the demise of the corpus luteum (luteolysis). Recently, the gene structure of the FPr in three mammalian species has been elucidated; however, promoter regulation of the gene is still poorly understood. The FPr mRNA is extremely low in steroidogenic follicular cells (theca or granulosa) but is expressed at high levels in the corpus luteum, particularly in the large luteal cells. Treatment with PGF(2alpha) decreased FPr mRNA expression in luteal cells in most species that have been studied. Key amino acids have been suggested to be critical for binding of FPr to PGF(2alpha) based on three-dimensional modeling and comparisons with other G-protein-coupled receptors. Moieties of the PGF(2alpha) molecule that are essential for binding or specificity of binding to the FPr have been identified by radioreceptor binding studies. In this article, recent information is reviewed on the structure of the FPr gene, regulation of luteal FPr mRNA, and receptor/ligand interaction requirements for the FPr protein.

Actions of prostaglandin F2alpha and prolactin on intercellular adhesion molecule-1 expression and monocyte/macrophage accumulation in the rat corpus luteum

Expression of intercellular adhesion molecule-1 (ICAM-1) and the accumulation of monocytes/macrophages are inflammatory events that occur during PRL (PRL)-induced regression of the rat corpus luteum. Here we have compared the ability of prostaglandin F2alpha (PGF) and PRL to induce, in rat corpora lutea, inflammatory events thought to perpetuate luteal regression. Immature rats were ovulated with eCG-hCG and then hypophysectomized (Day 0), which resulted in a single cohort of persistent, functional corpora lutea. On Days 9-11, the rats received twice daily injections of saline, PGF (Lutalyse, 250 microg/injection), or PRL (312 microg/injection) to induce luteal regression. Surprisingly, luteal weight and plasma progestin concentrations (progesterone and 20alpha-dihydroprogesterone) did not differ between PGF-treated rats and controls; whereas both luteal weight and plasma progestins declined significantly in PRL-treated rats. Furthermore, corpora lutea of PGF-treated rats and controls contained relatively minimal ICAM-1 staining and few monocytes/macrophages. In contrast, but as expected, corpora lutea of PRL-treated rats stained intensely for ICAM-1 and contained numerous monocytes/macrophages. In an additional experiment, there was no indication that luteal prostaglandin F2alpha receptor mRNA diminished as a result of hypophysectomy. These findings suggest that prolactin, not PGF, induces the inflammatory events that accompany regression of the rat corpus luteum.

Prostaglandin F2alpha-induced expression of 20alpha-hydroxysteroid dehydrogenase involves the transcription factor NUR77

Prostaglandin F(2)alpha (PGF(2)alpha) binding to its receptor on the rat corpus luteum triggers various signal transduction pathways that lead to the activation of a steroidogenic enzyme, 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), which in turn catabolizes progesterone. The molecular mechanism underlying PGF(2)alpha-induced 20alpha-HSD enzyme activity has not yet been explored. In this report we show, using mice lacking PGF(2)alpha receptor and pregnant rats, that PGF(2)alpha is responsible for the rapid and massive expression of the 20alpha-HSD gene at the end of pregnancy leading to a decrease in progesterone secretion. We also present evidence that PGF(2)alpha enhances 20alpha-HSD promoter activity. We have determined a region upstream of the -1590 position in the 20alpha-HSD promoter that confers regulation by PGF(2)alpha in ovarian primary cells. This region encompasses a unique transcription factor-binding site with a sequence of a NUR77 response element. Deletion of this motif or overexpression of a NUR77 dominant negative protein caused a complete loss of 20alpha-HSD promoter activation by PGF(2)alpha. NUR77 also transactivated the 20alpha-HSD promoter in transient transfection experiments in corpus luteum-derived cells (GG-CL). This induction required the NUR77-transactivating domain. We also show that PGF(2)alpha induces a very rapid expression of NUR77 that binds to a distal response element located at -1599/-1606 but does not interact with another proximal putative NUR77 response element located downstream in the promoter. A rapid increase in NUR77 mRNA was observed in mice corpora lutea just before parturition at a time when 20alpha-HSD becomes expressed. This increase in the expression of both genes was not seen in PGF(2)alpha receptor knockout mice. By using cyclosporin A and PGF(2)alpha treatment, we established that inhibition of NUR77 DNA binding in vivo prevents PGF(2)alpha induction of the 20alpha-HSD gene in the corpus luteum. Taken together, our results demonstrate, for the first time, that PGF(2)alpha induces in the corpus luteum the expression of the nuclear orphan receptor and transcription factor, NUR77, which in turn leads to the transcriptional stimulation of 20alpha-HSD, triggering the decrease in serum progesterone essential for parturition.

Effect of oxytocin receptor blockade on rat myometrial responsiveness to prostaglandin f(2)(alpha)

In the present study we have shown that the genetic expression of prostaglandin (PG)F(2alpha) receptor (R) and cyclooxygenase (COX)-2 increases in laboring rat myometrium. This finding was associated with a relatively weak contractile in vitro response (E:(max)) of isolated uterine strips when challenged with PGF(2alpha). Five days postpartum PGF(2alpha)-R mRNA values exceeded those during labor while COX-2 mRNA was reduced to preparturient values. Maximal contractility of isolated strips stimulated with PGF(2alpha) at this time was enhanced and E:C(50) decreased. Oxytocin treatment of estrogen-primed nonpregnant rats down-regulated uterine contractile responsiveness to PGF(2alpha), leaving mRNA values for this receptor unchanged, whereas oxytocin receptor blockade with atosiban (an oxytocin receptor antagonist) left E:(max) unaltered. In contrast, atosiban treatment of pregnant rats resulted in a 2.5-fold increase in E:(max) and a considerably reduced EC(50) during labor when compared to untreated delivering rats. The increased contractile ability was associated with a threefold increase in PGF(2alpha)-R mRNA production, indicating that the regulation by atosiban of the PGF(2alpha)-induced response is exerted at the genetic level. Based on the present data we suggest that 1) PGF(2alpha)-R stimulation may not primarily exert a contracting role in the normally delivering myometrium, and 2) the presence of the PGF(2alpha)-R system in rat myometrium may explain the apparent functional redundancy of the oxytocinergic system during the process of birth in animals lacking oxytocin or where the oxytocin receptor is blocked. In this context PGF(2alpha) receptor stimulation may, in the absence of oxytocin receptor stimulation, exert the contractile forces needed for proper propulsion of the fetus.

Pregnancy and exogenous steroid treatments modulate the expression of relaxant EP(2) and contractile FP receptors in the rat uterus

Prostaglandins (PGs) interact with specific receptors on plasma membranes to regulate myometrial activity in many species. The present study examined whether the expression of relaxant prostaglandin E receptor subtype two (EP(2)) and contractile prostaglandin F receptor (FP) mRNA in the rat uterus is changed during various states of pregnancy and regulated by steroid hormones. Expression of mRNA for EP(2) and FP receptors in the full-thickness uteri was analyzed by reverse transcription-polymerase chain reaction using specific primers. Abundance of receptor mRNA was expressed relative to beta-actin mRNA. Results showed that 1) mRNA for EP(2) receptors in the rat uterus was substantially increased during pregnancy (320%) compared with the nonpregnant state (100%, P < 0.01), and declined during labor at term (36% vs. 100% in control, P < 0.01); 2) mRNA expression for FP receptors in rat uterus was increased during pregnancy (333% vs. 100% in nonpregnant rats, P < 0. 01) and reached maximal levels during labor (515% vs. 100% in control, P < 0.01); 3) upon RU-486 treatment on Day 19 of pregnancy, uterine EP(2) receptor mRNA levels were decreased (18% vs. 100% in control, P < 0.01), and FP mRNA levels were increased (357% vs. 100% in control, P < 0.01); 4) with ICI 164384 (an antiestrogen) treatment on Day 19 of gestation, uterine FP receptor mRNA levels were decreased without effects on EP(2) receptors; 5) in ovariectomized (ovx) rats, progesterone increased EP(2) (163% vs. 100% in control, P < 0.01) and had no effects on FP receptor mRNA expression in the rat uterus; 6) estradiol increased FP receptor mRNA levels (358% vs. 100% in control, P < 0.01) and had no effects on EP(2) mRNA in the ovx rat uterus. Therefore, we conclude that steroid hormones modulate the mRNA for relaxant EP(2) and contractile FP receptors for PGs in the uterus and thus regulate uterine activity during pregnancy and labor.

A putative stimulatory role of progesterone acting via progesterone receptors in the steroidogenic cells of the human corpus luteum

To further explore the proposed auto-regulatory role of progesterone action in the human corpus luteum (CL), the expression and functional roles of progesterone receptor (PR) isoforms A and B during the luteal phase (LP) of the menstrual cycle were investigated. A total of 27 otherwise healthy patients previously scheduled for surgery were recruited after informed consent. An LH rise was detected, and CL were grouped according to age (Days 2-5 post-LH-rise, early LP; Days 6-10, mid LP; Days 11-14, late LP). Using a semiquantitative reverse transcription-polymerase chain reaction assay, the PR-B mRNA levels, which were 100- to 1000-fold lower than PR-A/B mRNA, were 46% lower (P < 0.05, n = 24) in mid LP, compared to early and late LP. CL tissue levels of progesterone and PR-A/B protein levels were inversely correlated to increasing CL age; i.e., significantly reduced levels were observed in the late LP (r(2) = 0.34, P < 0.01, n = 23). Expression of PR-A/B mRNA as well as PR-A/B protein were detected by in situ hybridization and immunohistochemistry, respectively. Both methods revealed a clear and distinct localization to cells in the steroidogenic layer of the CL. Freshly obtained mid-luteal CL cells were cultured in vitro, and media were analyzed for progesterone concentrations after treatment by incremental doses of hCG and the stable PR antagonist mifepristone, alone or in combination. Mifepristone did not per se alter progesterone synthesis, but when it was added in conjunction with hCG, a dose-related inhibitory response was seen, with a maximal 47% reduction in progesterone output at a 10 microM addition (P < 0.05, n = 3). Collectively, these data implicate a stimulatory role of progesterone receptor-mediated action in the steroidogenic cells of the human CL, which may serve as an important pathway for maintaining functional homeostasis during early pregnancy.

Distinct expression of gelatinase A [matrix metalloproteinase (MMP)-2], collagenase-3 (MMP-13), membrane type MMP 1 (MMP-14), and tissue inhibitor of MMPs type 1 mediated by physiological signals during formation and regression of the rat corpus luteum

The corpus luteum (CL) is a transient endocrine organ that secretes progesterone to support pregnancy. The CL is formed from an ovulated follicle in a process that involves extensive angiogenesis and tissue remodeling. If fertilization does not occur or implantation is unsuccessful, the CL will undergo regression, which involves extensive tissue degradation. Extracellular proteases, such as serine proteases and matrix metalloproteinases (MMPs), are thought to play important roles in both the formation and regression of the CL. In this study, we have examined the physiological regulation pattern and cellular distribution of messenger RNAs coding for gelatinase A (MMP-2), collagenase-3 (MMP-13), membrane type MMP 1 (MT1-MMP, MMP-14), and the major MMP inhibitor, tissue inhibitor of MMPs type 1 (TIMP-1) in the CL of adult pseudopregnant (psp) rat. Northern blot and in situ hybridization analyses revealed that gelatinase A messenger RNA was mainly expressed during luteal development, indicating that gelatinase A may be associated with the neovascularization and tissue remodeling that takes place during CL formation. Collagenase-3 had a separate expression pattern and was only expressed in the regressing CL, suggesting that this MMP may be related with luteal regression. MT1-MMP that in vitro can activate progelatinase A and procollagenase-3 was constitutively expressed during the formation, function, and regression of the CL and may therefore be involved in the activation of these MMPs. TIMP-1 was induced during both the formation and regression of the CL, suggesting that this inhibitor modulates MMP activity during these processes. To test whether the induction of collagenase-3 and TIMP-1 is coupled with luteal regression, we prolonged the luteal phase by performing hysterectomies, and induced premature luteal regression by treating the pseudopregnant rats with a PGF2alpha analog, cloprostenol. In both treatments, collagenase-3 and TIMP-1 were induced only after the serum level of progesterone had decreased, suggesting that collagenase-3 and TIMP-1 are induced by physiological signals, which initiate functional luteolysis to play a role in tissue degradation during structural luteolysis. In conclusion, our data suggest that gelatinase A, collagenase-3, and MT1-MMP may have separate functions during the CL life span: gelatinase A mainly takes part in CL formation, whereas collagenase-3 mainly takes part in luteal regression; MT1-MMP is constitutively expressed during the CL life span and may therefore serve as an in vivo activator of both gelatinase A and collagenase-3. TIMP-1 is up-regulated both during the formation and regression of the CL and may therefore regulate MMP activity during both processes.

Changes in expression of contractile FP and relaxatory EP2 receptors in pregnant rat myometrium during late gestation, at labor, and postpartum

Prostaglandins synthesized at parturition may act via specific myometrial receptors as mediators of uterine contractions. Several isoforms of eicosanoid (prostaglandin) receptors, identified by pharmacological means, are linked to contractile (FP, EP1, EP3) or relaxatory (EP2, EP4, IP, DP) intracellular pathways. Changes in mRNA expression of the contractile FP and the relaxatory EP2 receptor were measured in myometrium throughout gestation, at parturition, and postpartum. Timed pregnant rats were killed at 0900 h on Day 16, 18, 20, 21, 21.5, or 22 (parturition) of pregnancy or one day postpartum (n = 5 animals/group). A longitudinal section of myometrium was removed, total RNA was extracted, and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was performed for glyceraldehyde phosphate dehydrogenase (GAPDH), calponin, EP2, and FP receptor mRNA expression. Complementary DNA products were run on agarose gels and visualized, and the quantity of cDNA product was measured against a DNA mass ladder. RT-PCR product identity was confirmed by restriction enzyme cleavage. EP2 receptor mRNA expression was highest at Day 16 and declined significantly to Day 21.5 and one day postpartum (p < 0.05, Student-Newman-Keuls procedure). Expression of FP receptor mRNA was low at Day 16 of gestation and increased significantly until delivery (p < 0.05, ANOVA) at Day 22, then fell to prepartum levels at one day postpartum. Myometrial activity at parturition may change from an active quiescent to an active contractile state in concert with a decline in expression of the relaxatory EP2 receptors and up-regulation of contractile FP receptors.