Role of progesterone receptor activation in pituitary adenylate cyclase activating polypeptide gene expression in rat ovary

PACAP: A regulator of mammalian reproductive function

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an ancestral molecule that was isolated from sheep hypothalamic extracts based on its action to stimulate cAMP production by pituitary cell cultures. PACAP is one of a number of ligands that coordinate with GnRH to control reproduction. While initially viewed as a hypothalamic releasing factor, PACAP and its receptors are widely distributed, and there is growing evidence that PACAP functions as a paracrine/autocrine regulator in the CNS, pituitary, gonads and placenta, among other tissues. This review will summarize current knowledge concerning the expression and function of PACAP in the hypothalamic-pituitary-gonadal axis with special emphasis on its role in pituitary function in the fetus and newborn.

Ovulation: Parallels With Inflammatory Processes

The midcycle surge of LH sets in motion interconnected networks of signaling cascades to bring about rupture of the follicle and release of the oocyte during ovulation. Many mediators of these LH-induced signaling cascades are associated with inflammation, leading to the postulate that ovulation is similar to an inflammatory response. First responders to the LH surge are granulosa and theca cells, which produce steroids, prostaglandins, chemokines, and cytokines, which are also mediators of inflammatory processes. These mediators, in turn, activate both nonimmune ovarian cells as well as resident immune cells within the ovary; additional immune cells are also attracted to the ovary. Collectively, these cells regulate proteolytic pathways to reorganize the follicular stroma, disrupt the granulosa cell basal lamina, and facilitate invasion of vascular endothelial cells. LH-induced mediators initiate cumulus expansion and cumulus oocyte complex detachment, whereas the follicular apex undergoes extensive extracellular matrix remodeling and a loss of the surface epithelium. The remainder of the follicle undergoes rapid angiogenesis and functional differentiation of granulosa and theca cells. Ultimately, these functional and structural changes culminate in follicular rupture and oocyte release. Throughout the ovulatory process, the importance of inflammatory responses is highlighted by the commonalities and similarities between many of these events associated with ovulation and inflammation. However, ovulation includes processes that are distinct from inflammation, such as regulation of steroid action, oocyte maturation, and the eventual release of the oocyte. This review focuses on the commonalities between inflammatory responses and the process of ovulation.

Cellular and molecular mechanisms of the preovulatory follicle differenciation and ovulation: What do we know in the mare relative to other species

Terminal follicular differentiation and ovulation are essential steps of reproduction. They are induced by the increase in circulating LH, and lead to the expulsion from the ovary of oocytes ready to be fertilized. This review summarizes our current understanding of cellular and molecular pathways that control ovulation using a broad mammalian literature, with a specific focus to the mare, which is unique in some aspects of ovarian function in some cases. Essential steps and key factors are approached. The first part of this review concerns LH, receptors and signaling, addressing the description of the equine gonadotropin and cloning, signaling pathways that are activated following the binding of LH to its receptors, and implication of transcription factors which better known are CCAAT-enhancer-binding proteins (CEBP) and cAMP response element-binding protein (CREB). The second and major part is devoted to the cellular and molecular actors within follicular cells during preovulatory maturation. We relate to 1) molecules involved in vascular permeability and vasoconstriction, 2) involvement of neuropeptides, such as kisspeptin, neurotrophins and neuronal growth factor, neuropeptide Y (NPY), 3) the modification of steroidogenesis, steroids intrafollicular levels and enzymes activity, 4) the local inflammation, with the increase in prostaglandins synthesis, and implication of leukotrienes, cytokines and glucocorticoids, 5) extracellular matrix remodelling with involvement of proteases, antiproteases and inhibitors, as well as relaxin, and finaly 6) the implication of oxytocine, osteopontin, growth factors and reactive oxygen species. The third part describes our current knowledge on molecular aspect of in vivo cumulus-oocyte-complexe maturation, with a specific focus on signaling pathways, paracrine factors, and intracellular regulations that occur in cumulus cells during expansion, and in the oocyte during nuclear and cytoplasmic meiosis resumption. Our aim was to give an overall and comprehensive map of the regulatory mechanisms that intervene within the preovulatory follicle during differentiation and ovulation.

Spatiotemporal expression analysis of nuclear estrogen receptors in the zebrafish ovary and their regulation in vitro by endocrine hormones and paracrine factors

Estradiol (E2) stimulates luteinizing hormone receptor (lhcgr) expression via nuclear estrogen receptors (nERs) in the zebrafish ovary. We have demonstrated that endocrine hormones such as gonadotropin (hCG) and paracrine factors such as epidermal growth factor (EGF) and pituitary adenylate cyclase-activating peptide (PACAP) can modulate E2-induced lhcgr expression in vitro. These observations raised a question on whether these hormones and factors exert their effects via regulating the expression of nERs. In this study, we first characterized the spatiotemporal expression profiles of three nER subtypes in the zebrafish ovary, including esr1 (ERα), esr2a (ERβ2) and esr2b (ERβ1). All three nERs increased their expression at the pre-vitellogenic stage and peaked at mid- (esr1 and esr2a) or late vitellogenic (esr2b) stage, followed by a significant decline at the full-grown stage. RT-PCR analysis showed that esr1 and esr2b were exclusively expressed in the follicle layer while esr2a was expressed in both compartments. We then examined how E2, hCG, PACAP and EGF regulated the expression of nERs in cultured zebrafish follicle cells. E2 quickly increased esr1 but reduced esr2a and esr2b expression from 1.5 to 12h of treatment. Similarly, EGF down-regulated esr2a significantly at 1.5h and this effect was further intensified at 24h. hCG decreased the expression of all three nER subtypes with similar potency throughout the 24-h time-course. Interestingly, PACAP exerted a biphasic regulation on esr2a. Our present study suggests that nERs, especially esr2a, provide potential target points for other hormones and factors to modulate E2 activity during folliculogenesis in the zebrafish.

Balance between cAMP and Ca(2+) signals regulates expression levels of pituitary adenylate cyclase-activating polypeptide gene in neurons

Mice lacking the gene encoding pituitary adenylate cyclase-activating polypeptide (PACAP) or its specific receptor, PAC1, show abnormal behaviors related to schizophrenia. However, the regulation of PACAP expression in neurons remains unclear. Here, we report that Pacap mRNA levels are regulated transcriptionally and post-transcriptionally by cAMP and Ca(2+) signals in cultured rat cortical cells. Pacap mRNA levels decreased proportionately with the intensity of cAMP signaling, and this decrease was accelerated by N-methyl-D-aspartate (NMDA) receptor blockade, suggesting that cAMP signaling enhances the degradation of Pacap mRNA, whereas NMDA receptor-mediated signals inhibit its degradation. However, depolarization (which produced a robust increase in Ca(2+) signals) together with cAMP signaling resulted in a synergistic induction of Pacap mRNA through calcineurin and its substrate, cAMP-response element-binding protein (CREB)-regulated transcription coactivator 1. These results strongly support the concept that while cAMP signaling can accelerate the degradation of Pacap mRNA, it can also synergistically enhance Ca(2+) signaling-induced transcriptional activation of Pacap. Taken together, our findings suggest that a balance between Ca(2+) and cAMP signals regulates PACAP levels in neurons and that a perturbation of this balance may result in psychiatric disorders, such as schizophrenia.

X-linked lymphocyte regulated gene 5c-like (Xlr5c-like) is a novel target of progesterone action in granulosa cells of periovulatory rat ovaries

Progesterone (P4), acting through its nuclear receptor (PGR), plays an essential role in ovulation by mediating the expression of genes involved in ovulation and/or luteal formation. To identify ovulatory specific PGR-regulated genes, a preliminary microarray analysis was performed using rat granulosa cells treated with hCG ± RU486 (PGR antagonist). The transcript most highly down-regulated by RU486 was an EST (expressed sequence tag) sequence (gb: BI289578.1) that matches with predicted sequence for Xlr5c-like mRNA. Since nothing is known about Xlr5c-like, we first characterized the expression pattern of Xlr5c-like mRNA in the rat ovary. The level of mRNA for Xlr5c-like is transiently up-regulated in granulosa cells of periovulatory follicles after hCG stimulation in PMSG-primed rat ovaries. The transient induction of Xlr5c-like mRNA was mimicked by hCG treatment in cultured granulosa cells from preovulatory ovaries. We further demonstrated that the LH-activated PKA, MEK, PI3K, and p38 signaling is involved in the increase in Xlr5c-like mRNA. The increase in Xlr5c-like mRNA was abolished by RU486. The inhibitory effect of RU486 was reversed by MPA (synthetic progestin), but not by dexamethasone (synthetic glucocorticoid). Furthermore, mutation of SP1/SP3 and PGR response element sites in the promoter region of Xlr5c-like decreased Xlr5c-like reporter activity. RU486 also inhibited Xlr5c-like reporter activity. ChIP assay verified the binding of PGR and SP3 to the Xlr5c-like promoter in periovulatory granulosa cells. Functionally, siRNA-mediated Xlr5c-like knockdown in granulosa cell cultures resulted in reduced levels of mRNA for Snap25, Cxcr4, and Adamts1. Recombinant Xlr5c-like protein expressed using an adenoviral approach was localized predominantly to the nucleus and to a lesser extent to the cytoplasm of rat granulosa cells. In conclusion, this is the first report showing the spatiotemporally regulated expression of Xlr5c-like mRNA by hCG in rat periovulatory ovaries. P4/PGR mediates the LH-induced increase in Xlr5c-like mRNA. In turn, Xlr5c-like is involved in regulating the expression of specific ovulatory genes such as Snap25, Cxcr4, and Adamts1, possibly acting in the nucleus of periovulatory granulosa cells.

Investigation of the possible functions of PACAP in human trophoblast cells

Pituitary adenylate cyclase activating polypeptide (PACAP) is an endogenous neuropeptide having a widespread distribution both in the nervous system and peripheral organs including the female reproductive system. Both the peptide and its receptors have been shown in the placenta but its role in placental growth, especially its human aspects, remains unknown. The aim of the present study was to investigate the effects of PACAP on invasion, proliferation, cell survival, and angiogenesis of trophoblast cells. Furthermore, cytokine production was investigated in human decidual and peripheral blood mononuclear cells. For in vitro studies, human invasive proliferative extravillous cytotrophoblast (HIPEC) cells and HTR-8/SVneo human trophoblast cells were used. Both cell types were used for testing the effects of PACAP on invasion and cell survival in order to investigate whether the effects of PACAP in trophoblasts depend on the examined cell type. Invasion was studied by standardized invasion assay. PACAP increased proliferation in HIPEC cells, but not in HTR-8 cells. Cell viability was examined using MTT test, WST-1 assay, and annexin V/propidium iodide flow cytometry assay. Survival of HTR-8/SVneo cells was studied under oxidative stress conditions induced by hydrogen peroxide. PACAP as pretreatment, but not as co-treatment, significantly increased the number of surviving HTR-8 cells. Viability of HIPEC cells was investigated using methotrexate (MTX) toxicity, but PACAP1-38 could not counteract its toxic effect. Angiogenic molecules were determined both in the supernatant and the cell lysate by angiogenesis array. In the supernatant, we found that PACAP decreased the secretion of various angiogenic markers, such as angiopoietin, angiogenin, activin, endoglin, ADAMTS-1, and VEGF. For the cytokine assay, human decidual and peripheral blood lymphocytes were separated and treated with PACAP1-38. Th1 and Th2 cytokines were analyzed with CBA assay and the results showed that there were no significant differences in control and PACAP-treated cells. In summary, PACAP seems to play various roles in human trophoblast cells, depending on the cell type and microenvironmental influences.

GATA augments GNRH-mediated increases in Adcyap1 gene expression in pituitary gonadotrope cells

Pituitary adenylate cyclase-activating polypeptide 1 (PACAP or ADCYAP1) regulates gonadotropin biosynthesis and secretion, both alone and in conjunction with GNRH. Initially identified as a hypothalamic-releasing factor, ADCYAP1 subsequently has been identified in pituitary gonadotropes, suggesting it may act as an autocrine-paracrine factor in this tissue. GNRH has been shown to increase pituitary Adcyap1 gene expression through the interaction of CREB and jun/fos with CRE/AP1 cis-elements in the proximal promoter. In these studies, we were interested in identifying additional transcription factors and cognate cis-elements which regulate Adcyap1 gene promoter activity and chose to focus on the GATA family of transcription factors known to be critical for both pituitary cell differentiation and gonadotropin subunit expression. By transient transfection and electrophoretic mobility shift assay analysis, we demonstrate that GATA2 and GATA4 stimulate Adcyap1 promoter activity via a GATA cis-element located at position -191 in the rat Adcyap1 gene promoter. Furthermore, we show that addition of GATA2 or GATA4 significantly augments GNRH-mediated stimulation of Adcyap1 gene promoter activity in the gonadotrope LβT2 cell line. Conversely, blunting GATA expression with specific siRNA inhibits the ability of GNRH to stimulate ADCYAP1 mRNA levels in these cells. These data demonstrate a complex interaction between GNRH and GATA on ADCYAP1 expression, providing important new insights into the regulation of gonadotrope function.

Role of PACAP in Female Fertility and Reproduction at Gonadal Level - Recent Advances

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic neuropeptide, first isolated from hypothalamic extracts, but later shown in peripheral organs, such as endocrine glands, gastrointestinal system, cardiovascular system, and reproductive organs. PACAP plays a role in fertility and reproduction. Numerous studies report on the gonadal regulatory effects of PACAP at hypothalamo-hypophyseal levels. However, the local effects of PACAP at gonadal levels are also important. The present review summarizes the effects of PACAP in the ovary. PACAP and its receptors are present in the ovary, and PACAP plays a role in germ cell migration, meiotic division, follicular development, and atresia. The autocrine-paracrine hormonal effects seem to play a regulatory role in ovulation, luteinization, and follicular atrophy. Altogether, PACAP belongs to the ovarian regulatory peptides.

Control of oocyte release by progesterone receptor-regulated gene expression

The progesterone receptor (PGR) is a nuclear receptor transcription factor that is essential for female fertility, in part due to its control of oocyte release from the ovary, or ovulation. In all mammals studied to date, ovarian expression of PGR is restricted primarily to granulosa cells of follicles destined to ovulate. Granulosa cell expression of PGR is induced by the pituitary Luteinizing Hormone (LH) surge via mechanisms that are not entirely understood, but which involve activation of Protein Kinase A and modification of Sp1/Sp3 transcription factors on the PGR promoter. Null mutations for PGR or treatment with PGR antagonists block ovulation in all species analyzed, including humans. The cellular mechanisms by which PGR regulates ovulation are currently under investigation, with several downstream pathways having been identified as PGR-regulated and potentially involved in follicular rupture. Interestingly, none of these PGR-regulated genes has been demonstrated to be a direct transcriptional target of PGR. Rather, in ovarian granulosa cells, PGR may act as an inducible coregulator for constitutively bound Sp1/Sp3 transcription factors, which are key regulators for a discrete cohort of ovulatory genes.

Initiation of the expression of peroxisome proliferator-activated receptor gamma (PPAR gamma) in the rat ovary and the role of FSH

PPARgamma is highly expressed in granulosa cells by 23 days post-partum (pp) and is down-regulated in response to the LH surge. We tested the hypothesis that high levels of FSH during the neonatal period trigger the expression of PPARgamma. To determine when PPARgamma expression is initiated, ovaries were collected from neonatal rats. Messenger RNA for PPARgamma was undetectable on day 1, low from days 5-14, and increased by day 19 pp (p < 0.05). PPARgamma was detected in select granulosa cells in primary/early secondary follicles. Messenger RNA for the FSH receptor was detected as early as day 1 and remained steady throughout day 19 pp. The FSH receptor was detected by immunoblot analysis in ovaries collected 1, 2, and 5-9 days pp. In a subsequent experiment, neonatal rats were treated with acyline (GnRH antagonist) which significantly reduced FSH (p < 0.05) but not levels of mRNA for PPARgamma. The role of FSH in the induction of PPARgamma expression was further assessed in ovarian tissue from FORKO mice. Both mRNA and protein for PPARgamma were identified in ovarian tissue from FORKO mice. In summary, the FSH/FSH receptor system is present in granulosa cells prior to the onset of expression of PPARgamma. Reducing FSH during the neonatal period, or the ability to respond to FSH, did not decrease expression of mRNA for PPARgamma. These data indicate that FSH is not a primary factor initiating the expression of PPARgamma and that other agents play a role in activating its expression in the ovary.

Control of ovulation in mice by progesterone receptor-regulated gene networks

The mid-cycle surge of luteinizing hormone (LH) induces ovulation, a process during which a fertilizable oocyte is released from a mature ovarian follicle. Although ovulation is a physiologically well-characterized event, the underlying molecular pathways remain poorly understood. Progesterone receptor (PGR), which mediates the biological effects of the steroid hormone progesterone, has emerged as a key regulator of ovulation in mice. The development of a progesterone-receptor-null (Pgr-null) mouse model confirmed a critical role of this hormone in ovulation because in these mutant mice, mature pre-ovulatory follicles fail to release the oocytes. This animal model has thus presented a unique opportunity to study the molecular pathways underlying ovulation. Gene-expression profiling experiments by several groups, using the ovaries of Pgr-null mice, revealed novel gene networks, which act downstream of PGR to control ovulation. These genes encode diverse molecules such as proteases, transcription factors, cell-adhesion molecules, modulators of vascular activities and regulators of inflammation. Functional analyses using gene-knockout mouse models have confirmed that some of these factors play critical roles during ovulation. The knowledge gained from these studies has helped us to understand better the molecular mechanisms that facilitate the release of oocytes from pre-ovulatory follicles. Further analysis of the role of molecular regulators of ovulation will help identify useful molecular targets that would allow the development of improved contraceptives and new therapeutics for anovulatory infertility.

GnRH stimulates expression of PACAP in the pituitary gonadotropes via both the PKA and PKC signaling systems

Recent studies have demonstrated a clear role for pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of gonadotropin biosynthesis and secretion, both alone and in conjunction with GnRH. First defined as a hypothalamic releasing factor, PACAP subsequently has been identified in the gonadotrope subpopulation of the anterior pituitary gland, suggesting that PACAP may act as an autocrine-paracrine factor in this tissue. In initial studies, we determined that GnRH markedly stimulated endogenous PACAP mRNA levels and promoter-reporter activity in the mature gonadotrope cell line, LbetaT2. GnRH-stimulated rat PACAP promoter activity was blunted with deletion from position -915 to -402 and eliminated with further truncation to position -77 relative to the transcriptional start site. Site-directed mutagenesis demonstrated a functional requirement for a cAMP response element (CRE)-like site at position -205 and an activating protein-1 (AP-1)-like site at position -275, both of which bound CRE binding protein and AP-1 family members on EMSA. Treatment with pharmacological activators or inhibitors of second messenger signaling pathways implicated the protein kinase A, protein kinase C, and MAPK pathways in the GnRH response. In support of these in vitro data, we demonstrate that JunB binds to the rat PACAP gene promoter by chromatin immunoprecipitation assay and that small interfering RNA knockdown of JunB, cFos, and CRE binding protein factors blunts PACAP expression. In summary, these results further elucidate the complex functional interactions between PACAP and GnRH in the anterior pituitary. Specifically, these studies demonstrate that GnRH-stimulated PACAP gene expression is mediated via multiple signaling pathways acting on CRE/AP-1 sites in the proximal gene promoter. Because both PACAP and GnRH regulate gonadotropin biosynthesis and secretion, these results provide important insight into the critical fine tuning of gonadotrope function and, thereby, the maintenance of normal reproductive function.

Role of hypoxia in the regulation of periovulatory EDN2 expression in the mouse

We have previously proposed endothelin-2 (EDN2) as a granulosa cell-derived contractile signal that facilitates ovulation. Spatially, Edn2 mRNA expression is restricted to granulosa cells of periovulatory follicles. Temporally, mRNA for this contractile peptide is expressed immediately before follicle rupture. The primary objective of this study was to test the hypothesis that hypoxia mediates EDN2 expression in granulosa cells at ovulation, and if it does, to determine the region within the promoter responsible for this effect. To determine the effect of hypoxia on mRNA expression, immature mice were treated with 5 IU of PMSG followed 48 h later by 5 IU of human chorionic gonadotropin (hCG). Granulosa cells were isolated at 9 h after hCG, cultured under normal or hypoxic conditions, and the expression level of mRNA was compared. mRNA expression was increased when granulosa cells were cultured in a hypoxic environment (p<0.05). Subsequent promoter analysis found that the 5' upstream region of the EDN2 promoter (between -1894 bp and -1407 bp) was responsible for hypoxia-mediated changes in EDN2 expression. This promoter region contains multiple sites for potential transcriptional regulation, including that by hypoxia-inducible factor 1 (HIF-1, ACGTG) at -1297 bp. The second objective of this study was to determine whether the progesterone receptor (PR) or cyclooxygenase-2 (COX-2), two key regulators of periovulatory events, controlled EDN2 expression. To accomplish this, gonadotropin-primed mice were treated with RU-486 or indomethacin and expression of mRNA for Edn2 was determined in ovaries collected at 12 h after hCG. Treatment with RU-486 or indomethacin did not affect expression of mRNA for Edn2 (p>0.05). Taken together, we believe that hypoxia, but not the PR or COX-2, regulate gonadotropin-induced EDN2 expression in the periovulatory follicle.

Luteinizing hormone-induced RUNX1 regulates the expression of genes in granulosa cells of rat periovulatory follicles

The LH surge induces specific transcription factors that regulate the expression of a myriad of genes in periovulatory follicles to bring about ovulation and luteinization. The present study determined 1) the localization of RUNX1, a nuclear transcription factor, 2) regulation of Runx1 mRNA expression, and 3) its potential function in rat ovaries. Up-regulation of mRNA and protein for RUNX1 is detected in preovulatory follicles after human chorionic gonadotropin (hCG) injection in gonadotropin-treated immature rats as well as after the LH surge in cycling animals by in situ hybridization and immunohistochemical and Western blot analyses. The regulation of Runx1 mRNA expression was investigated in vitro using granulosa cells from rat preovulatory ovaries. Treatments with hCG, forskolin, or phorbol 12 myristate 13-acetate stimulated Runx1 mRNA expression. The effects of hCG were reduced by inhibitors of protein kinase A, MAPK kinase, or p38 kinase, indicating that Runx1 expression is regulated by the LH-initiated activation of these signaling mediators. In addition, hCG-induced Runx1 mRNA expression was inhibited by a progesterone receptor antagonist and an epidermal growth factor receptor tyrosine kinase inhibitor, whereas amphiregulin stimulated Runx1 mRNA expression, demonstrating that the expression is mediated by the activation of the progesterone receptor and epidermal growth factor receptor. Finally, knockdown of Runx1 mRNA by small interfering RNA decreased progesterone secretion and reduced levels of mRNA for Cyp11a1, Hapln1, Mt1a, and Rgc32. The hormonally regulated expression of Runx1 in periovulatory follicles, its involvement in progesterone production, and regulation of preovulatory gene expression suggest important roles of RUNX1 in the periovulatory process.

Pituitary Adenylate Cyclase Activating Polypeptide Messenger RNA in the Paraventricular Nucleus and Anterior Pituitary During the Rat Estrous Cycle1

The neuropeptide pituitary adenylate cyclase activating polypeptide (ADCYAP 1, or PACAP) has been demonstrated to enhance gonadotropin-releasing hormone (GnRH)-induced gonadotropin secretion and regulate gonadotropin subunit gene expression in cultures of anterior pituitary cells. In the present study, we used in situ hybridization and real-time polymerase chain reaction to examine the expression of Pacap mRNA within the paraventricular nucleus (PVN) and anterior pituitary throughout the estrous cycle of the rat. Levels of luteinizing hormone in serum and pituitary gonadotropin subunit mRNAs were evaluated and displayed cyclic fluctuations similar to those reported previously. Pacap mRNA expression in the PVN and pituitary varied significantly during the estrous cycle, with the greatest changes occurring on the day of proestrus. Pacap mRNA levels in the PVN declined significantly on the morning of diestrus. During proestrus, PVN Pacap mRNA levels significantly increased 3 h before the gonadotropin surge and then declined. Pituitary expression of Pacap mRNA also varied on the afternoon of proestrus with a moderate decline at the time of the gonadotropin surge and a significant increase later in the evening. Expression of the mRNA species encoding the 288 amino acid form of follistatin increased significantly following the rise in pituitary Pacap mRNA, at the termination of the secondary surge in follicle-stimulating hormone beta (Fshb) gene expression. These results suggest that PACAP is involved in events before and following the gonadotropin surge, perhaps through increased gonadotroph sensitivity to GnRH and suppression of Fshb subunit expression through increased follistatin, as previously observed in vitro.

Regulation of Matrix Metalloproteinase-19 Messenger RNA Expression in the Rat Ovary1

Matrix metalloproteinases (MMPs) are instrumental in the constant tissue remodeling in the ovary. An induction of MMP-19 mRNA in periovulatory follicles has been reported in mouse ovaries. However, little is known about MMP-19 expression during the follicular and luteal periods or about the ovarian regulation of MMP-19 mRNA expression. We examined the expression pattern of MMP-19 mRNA during various reproductive phases and the periovulatory regulation of MMP-19 mRNA in the rat ovary. In gonadotropin-primed, immature rat ovaries, levels of MMP-19 mRNA transiently increased during both follicular growth and ovulation. The MMP-19 mRNA was localized to the theca-interstitial layer of growing follicles and to the granulosa and theca-interstitial layers of periovulatory follicles. A similar expression pattern of MMP-19 mRNA in periovulatory follicles was observed in ovaries from naturally cycling adult rats. Accumulation of MMP-19 mRNA was detected in regressing corpus luteum. The regulation of MMP-19 mRNA expression during the periovulatory period was investigated via in vivo studies and through in vitro culture studies on follicular cells. The hCG-induction of MMP-19 mRNA was mimicked by treating granulosa cells, but not theca-interstitial cells, from preovulatory follicles with LH or activators of the protein kinase (PK) A or PKC pathways. Cycloheximide blocked the LH- or forskolin-induced MMP-19 mRNA expression, demonstrating the requirement for new protein synthesis. In contrast, blocking activation of the progesterone receptor or prostaglandin synthesis had no effect on the increase in MMP-19 mRNA expression. In conclusion, the induction of MMP-19 mRNA suggests an important role of this proteinase during follicular growth, ovulation, and luteal regression.

Development and application of a rat ovarian gene expression database

The pituitary gonadotropins play a key role in follicular development and ovulation through the induction of specific genes. To identify these genes, we have constructed a genome-wide rat ovarian gene expression database (rOGED). The database was constructed from total RNA isolated from intact ovaries, granulosa cells, or residual ovarian tissues collected from immature pregnant mare serum gonadotropin (PMSG)/human chorionic gonadotropin-treated rats at 0 h (no PMSG), 12 h, and 48 h post PMSG, as well as 6 and 12 h post human chorionic gonadotropin. The total RNA was used for DNA microarray analysis using Affymetrix Rat Expression Arrays 230A and 230B (Affymetrix, Santa Clara, CA). The microarray data were compiled and used for display of individual gene expression profiles through specially developed software. The final rOGED provides immediate analysis of temporal gene expression profiles for over 28,000 genes in intact ovaries, granulosa cells, and residual ovarian tissue during follicular growth and the preovulatory period. The accuracy of the rOGED was validated against the gene profiles for over 20 known genes. The utility of the rOGED was demonstrated by identifying six genes that have not been described in the rat periovulatory ovary. The mRNA expression patterns and cellular localization for each of these six genes (estrogen sulfotransferase, synaptosomal-associated protein 25 kDa, runt-related transcription factor, calgranulin B, alpha1-macroglobulin, and MAPK phosphotase-3) were confirmed by Northern blot analyses and in situ hybridization, respectively. The current findings demonstrate that the rOGED can be used as an instant reference for ovarian gene expression profiles, as well as a reliable resource for identifying important yet, to date, unknown ovarian genes.

Progesterone-receptor antagonists and statins decrease de novo cholesterol synthesis and increase apoptosis in rat and human periovulatory granulosa cells in vitro

Progesterone-receptor (PR) stimulation promotes survival in rat and human periovulatory granulosa cells. To investigate the mechanisms involved, periovulatory rat granulosa cells were incubated in vitro with or without the PR-antagonist Org 31710. Org 31710 caused the expected increase in apoptosis, and expression profiling using cDNA microarray analysis revealed regulation of several groups of genes with functional and/or metabolic connections. This regulation included decreased expression of genes involved in follicular rupture, increased stress responses, decreased angiogenesis, and decreased cholesterol synthesis. A decreased cholesterol synthesis was verified in experiments with both rat and human periovulatory granulosa cells treated with the PR-antagonists Org 31710 or RU 486 by measuring incorporation of [14C]acetate into cholesterol, cholesterol ester, and progesterone. Correspondingly, specific inhibition of cholesterol synthesis in periovulatory rat granulosa cells using 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (lovastatin, mevastatin, or simvastatin) increased apoptosis, measured as DNA fragmentation and caspase-3/7 activity. The increase in apoptosis caused by simvastatin was reversed by addition of the cholesterol synthesis-intermediary mevalonic acid. These results show that PR antagonists reduce cholesterol synthesis in periovulatory granulosa cells and that cholesterol synthesis is important for granulosa cell survival.

Pituitary adenylate cyclase-activating peptide: a pivotal modulator of steroid-induced reproductive behavior in female rodents

Pituitary adenylate cyclase-activating polypeptide (PACAP) regulates the secretion of GnRH into the hypothalamic hypophysial portal system and sensitizes the pituitary for release of hormones that trigger ovulation. Because reproductive behavior is synchronized with GnRH release, the present study was undertaken to determine whether PACAP in the ventromedial nucleus (VMN) plays a role in receptivity. To this end, we used rat and mouse reproductive behavioral models to determine the biological relationship between PACAP and steroid receptor function in females. We provide evidence for the requirement of PACAP in the VMN for progesterone (P)-dependent sexual behavior in estrogen (E)-primed females. We clarify the biological and molecular mechanisms of PACAP activity by showing 1) that inhibition of endogenous PACAP suppresses P receptor (PR)-dependent sexual behavior facilitated by the steroid P or D1-like agonist SKF38393 and 2) that PR, steroid receptor coactivators-1 and -2, and new protein synthesis are essential for ligand independent PACAP-facilitated behavior. These findings are consistent with convergence of PACAP-mediated cellular signals on PR for genomic activation and subsequent behavioral changes. Further, we show that steroids regulate both endogenous PACAP mRNA in the VMN and immunoreactive PACAP in the medial basal hypothalamus and cerebral spinal fluid for ligand-dependent, steroid receptor-dependent receptivity. The present findings delineate a novel, steroid-dependent mechanism within the female hypothalamus by which the neuropeptide PACAP acts as a feed-forward, paracrine, and/or autocrine factor for synchronization of behavior coordinate with hypothalamic control of ovulation.

Phosphodiesterase regulation is critical for the differentiation and pattern of gene expression in granulosa cells of the ovarian follicle

Feedback regulations are integral components of the cAMP signaling required for most cellular processes, including gene expression and cell differentiation. Here, we provide evidence that one of these feedback regulations involving the cyclic nucleotide phosphodiesterase PDE4D plays a critical role in cAMP signaling during the differentiation of granulosa cells of the ovarian follicle. Gonadotropins induce PDE4D mRNA and increase the cAMP hydrolyzing activity in granulosa cells, demonstrating that a feedback regulation of cAMP is operating in granulosa cells in vivo. Inactivation of the PDE4D by homologous recombination is associated with an altered pattern of cAMP accumulation induced by the gonadotropin LH/human chorionic gonadotropin (hCG), impaired female fertility, and a markedly decreased ovulation rate. In spite of a disruption of the cAMP response, LH/hCG induced P450 side chain cleavage expression and steroidogenesis in a manner similar to wild-type controls. Morphological examination of the ovary of PDE4D-/- mice indicated luteinization of antral follicles with entrapped oocytes. Consistent with the morphological finding of unruptured follicles, LH/hCG induction of genes involved in ovulation, including cyclooxygenase-2, progesterone receptor, and the downstream genes, is markedly decreased in the PDE4D-/- ovaries. These data demonstrate that PDE4D regulation plays a critical role in gonadotropin mechanism of action and suggest that the intensity and duration of the cAMP signal defines the pattern of gene expression during the differentiation of granulosa cells.

Follicle-stimulating hormone suppresses cytosolic 3,5,3'-triiodothyronine-binding protein messenger ribonucleic acid expression in rat granulosa cells

FSH plays crucial roles in differentiation of granulosa cells and development of follicles. Considering the broad scope of FSH effects, a large number of genes are likely responsive to the hormone. However, only a limited number of genes have been identified as FSH-regulated genes, particularly during the preantral stage. In an attempt to better define genes involved in follicular development, we examined primary granulosa cell cultures, an undifferentiated rat ovarian granulosa cell line and rat ovaries, using differential display, quantitative RT-PCR, Northern blot analysis, and in situ hybridization. We report, for the first time, that nicotinamide adenine dinucleotide phosphate-dependent cytosolic T(3)-binding protein mRNA is expressed in the ovary, particularly in the granulosa cell layer of preantral and early antral follicles, but not in large preovulatory follicles. Its expression markedly declines in response to FSH, which is dependent on the period of the exposure. This FSH-responsive down-regulation is dependent on granulosa cell differentiation and follicular development. FSH down-regulates the mRNA via the adenylyl cyclase/cAMP pathway, and the down-regulation requires de novo synthesis of a regulatory protein(s). The cytosolic T(3)-binding protein may play a significant role in the regulation of steroidogenesis and follicular development in the mammalian ovary.

Uterine-ovarian biochemical and developmental interactions to the postimplantation treatment with a butadiene metabolite, diepoxybutane, in pregnant rats

An industrial chemical used in synthetic rubber production, 1,3-butadiene, is toxic to reproduction in rats and mice. Bioactivation of butadiene to reactive intermediates, i.e. diepoxybutane and other metabolites, is responsible for this toxicity. The present study examines the biochemical and developmental mechanisms of diepoxybutane at the feto-maternal placental axis during gestation. Female Sprague-Dawley rats were administered four daily intraperitoneal doses of diepoxybutane in groups (0.25, 0.30, 0.35, or 0.40 mmol in sesame oil per kg body weight, n = 6/group) during postimplantation (gestation days 5-8) and euthanized on gestation day 9 or 12 for retrieval of uterine and ovarian tissues, and serum for assays. The results demonstrate that this timely diepoxybutane treatment significantly decreased placental levels of pituitary adenylate cyclase-activating polypeptide mRNA expression that was measured by reverse transcription-polymerase chain reaction and of matrix metalloproteinase-9 activity that was determined by gelatin zymography, and serum progesterone levels on gestation days 9 and 12. From a developmental standpoint, fetal growth and viability were reduced in correlation with treatment-related effects of diepoxybutane on implantation losses and fetal resorptions on gestation day 9. Additionally, fetal mortality was maximally increased due to significantly pronounced, dose-independent effects on these parameters on gestation day 12. This trend towards more severe embryolethal treatment effects from gestation day 9 to 12 suggests that fetal metabolism in the gravid uteri of rats may be more sensitive to diepoxybutane exposure as pregnancy progresses. The inhibitory actions of diepoxybutane on placental pituitary adenylate cyclase-activating polypeptide expression and matrix metalloproteinase activity may contribute towards altering placental molecular support for fetal development and viability. Moreover, the reproductive toxicity of diepoxybutane in rats appears to be linked to progesterone action.

Follicle-stimulating hormone-responsive cytoskeletal genes in rat granulosa cells: class I beta-tubulin, tropomyosin-4, and kinesin heavy chain

FSH regulates gene expression for granulosa cell differentiation and follicular development. Therefore, FSH-responsive genes are crucial, but only a few genes have been identified for the early stage of follicular development. In particular, little is known about cytoskeletal genes, which likely play essential roles in the morphological changes such as the antrum formation, a major landmark. FSH is also known to induce the differentiation of an immature, undifferentiated rat ovary granulosa (ROG) cell line. Our data show that FSH induced massive yet distinct reorganization of microtubules and the actin cytoskeletons as well as morphological changes. To identify those genes responding to FSH during the differentiation, differential display was performed on ROG cells. Of the 80 FSH-responsive genes identified, there were three cytoskeleton-related genes (class I beta-tubulin, tropomyosin 4, and kinesin heavy chain), which are crucial for intracellular morphogenesis, transport, and differentiation. Northern blots show that the level of these gene transcripts reached a peak at 6 h after FSH treatment and subsided at 24 h. FSH induced the similar temporal expression not only in granulosa cells isolated from immature rats, but also in vivo. For instance, in situ hybridization showed that beta-tubulin mRNA was transiently expressed in the granulosa cells of large preantral and early antral follicles. Despite the same temporal expression, the regulatory mechanisms of the three genes were strikingly different. As an example, cycloheximide blocked the beta-tubulin mRNA expression, whereas it increased tropomyosin-4 (TM4) mRNA. Yet, it did not impact kinesin heavy chain (Khc) mRNA. In conclusion, FSH induces the massive reorganization of the cytoskeletons and morphological changes by the selective regulation of the gene expression, protein synthesis, and rearrangement of the cytoskeletal proteins in the ROG cells and probably, specific follicles and granulosa cells.

Temporal and spatial patterns of ovarian gene transcription following an ovulatory dose of gonadotropin in the rat

In recent years, there have been a number of efforts to identify genes that are expressed in mature ovarian follicles in response to an ovulatory dose of LH or its homologue hCG. This review keys on 20 ovulation-specific genes that we have identified by the molecular procedure known as differential display. The objective is to use this sampling of genes to illustrate the diversity in the temporal and spatial patterns of expression of genes in the ovary following the stimulus of this gonadal target tissue by a single glycoprotein hormone. The specific genes that are surveyed include 5-aminolevulinate synthase; early growth response protein-1; gamma-glutamylcysteine synthetase; cyclooxygenase-2; epiregulin; pituitary adenylate cyclase-activating polypeptide; tumor necrosis factor-stimulated gene-6; regulator of G-protein signaling protein-2; adrenodoxin; steroidogenic acute regulatory protein; 3alpha-hydroxysteroid dehydrogenase; CD63, a disintegrin and metalloproteinase with thrombospondin motifs; tissue inhibitor of metalloproteinase-1; carbonyl reductase, a G-protein-coupled receptor; pancreatitis-associated protein-III; glutathione S-transferase; and metallothionein-1. The ovulatory expression of these different genes is predominantly within the granulosa layer of mature follicles. However, there were also instances of expression in the thecal and stromal tissue of the ovary, as well as in vascular endothelial cells and in luteal tissue. The overwhelming impression is that the molecular events of ovulation are far more complex, and therefore more highly ordered, than originally imagined.

Stage-dependent regulation of ovarian pituitary adenylate cyclase-activating polypeptide mRNA levels by GnRH in cultured rat granulosa cells

The present study was designed to test whether GnRH regulates pituitary adenylate cyclase-activating polypeptide mRNA levels in a stage-dependent manner during follicle development in the rat ovary. The granulosa cells of preovulatory and immature follicles obtained from PMSG- and estrogen-treated rats, respectively, were cultured in serum-free conditions in the presence of various hormones. GnRH receptor mRNA expression was detected in both preovulatory and immature granulosa cells and was down-regulated by gonadotropins. Treatment of preovulatory granulosa cells with GnRH agonist stimulated pituitary adenylate cyclase-activating polypeptide mRNA levels in a dose-dependent manner. In situ hybridization analysis of cultured preovulatory follicles revealed that GnRH-induced pituitary adenylate cyclase- activating polypeptide signals were detected in granulosa cells, but not thecal cells. In immature granulosa cells, cotreatment with GnRH agonist suppressed FSH-stimulated pituitary adenylate cyclase-activating polypeptide mRNA levels in a dose-dependent manner, whereas treatment with GnRH alone had no effect. Furthermore, treatment with GnRH antagonist inhibited LH-induced pituitary adenylate cyclase-activating polypeptide gene expression in preovulatory granulosa cells, whereas it stimulated FSH-induced pituitary adenylate cyclase-activating polypeptide gene expression in immature granulosa cells. Interestingly, GnRH-stimulated pituitary adenylate cyclase-activating polypeptide mRNA levels in preovulatory granulosa cells was inhibited by arachidonyltri fluoromethyl ketone, an inhibitor of phospholipase A(2), but not by an inhibitor of protein kinase A or C. Lastly, treatment of preovulatory follicles with pituitary adenylate cyclase-activating polypeptide antagonist suppressed GnRH-stimulated progesterone production during 6--9 h of culture. Taken together, these results demonstrate the stage-dependent regulation of pituitary adenylate cyclase-activating polypeptide mRNA levels by GnRH, the stimulatory and inhibitory effect in granulosa cells of preovulatory and immature follicles, respectively.

Developmental regulation of mitogen-activated protein kinase-activated kinases-2 and -3 (MAPKAPK-2/-3) in vivo during corpus luteum formation in the rat

The current study investigates the activation in vivo and regulation of the expression of components of the p38 mitogen-activated protein kinase (MAPK) pathway during gonadotropin-induced formation and development of the rat corpus luteum, employing a sequential PMSG/human CG (hCG) treatment paradigm. We postulated that the p38 MAPK pathway could serve to promote phosphorylation of key substrates during luteal maturation, since maturing luteal cells, thought to be cAMP-nonresponsive, nevertheless maintain critical phosphoproteins. Both p38 MAPK and its upstream activator MAPK kinase-6 (MKK6) were found to be chronically activated during the luteal maturation phase, with activation detected by 24 h post hCG and maintained through 4 days post hCG. The p38 MAPK downstream protein kinase target termed MAPK-activated protein kinase-3 (MAPKAPK-3) was newly induced at both mRNA and protein levels during luteal formation and maturation, while mRNA and protein expression of the closely related MAPKAPK-2 diminished. Two potential substrates for MAPKAPKs, the small heat shock protein HSP-27 and the cAMP regulatory element binding protein CREB, were monitored in vivo for phosphorylation. HSP-27 phosphorylation was not modulated during luteal maturation. In contrast, we observed sustained luteal-phase CREB phosphorylation in vivo, consistent with upstream MKK6/p38 MAPK activation and MAPKAPK-3 induction. MAPKAPK-3-specific immune complex kinase assays provided direct evidence that MAPKAPK-3 was in an activated state during luteal maturation in vivo. Cellular inhibitor studies indicated that an intact p38 MAPK path was required for CREB phosphorylation in a cellular model of luteinization, as treatment of luteinized granulosa cells with the p38 MAPK inhibitor SB 203580 strongly inhibited CREB phosphorylation. Transient transfection studies provided direct evidence that MAPKAPK-3 was capable of signaling to activate CREB transcriptional activity, as assessed by means of GAL4-CREB fusion protein construct coexpressed with GAL4-luciferase reporter construct. Introduction of wild-type, but not kinase-dead mutant, MAPKAPK-3 cDNA, into a mouse ovarian cell line stimulated GAL4-CREB- dependent transcriptional activity approximately 3-fold. Thus MAPKAPK-3 is indeed uniquely poised to support luteal maturation through the phosphorylation and activation of the nuclear transcription factor CREB.

Expression of an intracisternal A-particle-like element in rat ovary

We have isolated a rat intracisternal-A particle element (IAP)-like element (IAP-LE) from ovarian granulosa cells that appears to be identical to the rat EST clone AA964260. The compiled cDNA sequences contain several putative in-frame translation initiation codons with the largest capable of encoding a 365 amino acid protein with a reverse transcriptase domain in the N-terminus as well as a bipartite nuclear localization signal sequence in the middle. Northern blotting shows a major approximately 7 Kb transcript and a minor approximately 5 Kb transcript that are abundantly expressed in the ovary. In situ hybridization histochemistry using ovaries from gonadotropin-treated immature rats and regularly cycling adult rats show that this transcript is predominantly localized to granulosa cells of all healthy follicles, including primary follicles, and to newly-formed and healthy corpora lutea. This cell-specific expression pattern of the IAP-LE gene is distinct from those of the several known retroviral elements, suggesting the potentially novel functional importance of the IAP-LE gene. Taken together, our results demonstrate abundant and cell-specific expression of a novel IAP-LE in rat granulosa cells.

Progesterone receptor activation mediates LH-induced type-I pituitary adenylate cyclase activating polypeptide receptor (PAC(1)) gene expression in rat granulosa cells

We have previously reported that the pituitary adenylate cyclase activating polypeptide (PACAP) gene is regulated in ovarian granulosa cells by the autocrine and/or paracrine interaction between progesterone and its nuclear receptor progesterone receptor (PR). To initiate studies on the functional significance of the progesterone-induced PACAP production in luteinizing granulosa cells, we sought to determine the expression and hormonal regulation of PACAP receptors in the rat ovary. The relative mRNA levels of three known PACAP receptor subtypes (PAC(1), VPAC(1), and VPAC(2)) were determined in ovaries of immature rats treated with gonadotropins, by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) assays. Results show that all PAC(1), VPAC(1), and VPAC(2) transcripts are expressed at a detectable level in immature rat ovaries. Importantly, the ovarian level of PAC(1), but not VPAC(1) or VPAC(2), mRNA notably changes during gonadotropin challenges. Ovarian PAC(1) mRNA expression decreases during the pregnant mare's serum gonadotropin (PMSG)-induced follicular phase but substantially increases during the human chorionic gonadotropin (hCG)-induced periovulatory period. Because the hCG-induced increase in ovarian PAC(1) mRNA expression is attributable to the hormone-induced PAC(1) mRNA expression in granulosa cells of the preovulatory follicles, we next examined whether hCG regulates PAC(1) mRNA expression by directly acting on granulosa cells. When granulosa cells isolated from PMSG (40 h)-primed immature rats were challenged with hCG (or forskolin), PAC(1), but not VPAC(1) or VPAC(2), mRNA expression significantly increased within 6 h. Because the LH-induced PAC(1) mRNA expression (6 h) proceeds PR activation (3 h) in granulosa cells as the LH-induced PACAP mRNA expression (6 h) does, we further determined the cause-effect relationship among LH, PR activation and PAC(1) receptor gene expression, by examining the effect of PR antagonist, ZK98299, on the ability of LH to increase PAC(1) mRNA levels in luteinizing granulosa cells. Results show that ZK98299 inhibited the stimulatory effect of hCG (or forskolin) on PAC(1) mRNA expression, at the level of all known splice variants of PAC(1) mRNA in granulosa cells. In summary, our results demonstrating that PR activation is critical for the LH-induced PAC(1) gene expression in luteinizing granulosa cells suggest that PR activation regulates the finely tuned expression of the PACAP/PACAP receptor genes in luteinizing granulosa cells and thus dictates the timing of the autocrine and/or paracrine function of PACAP in preovulatory follicles.