EGF-like factor epiregulin and amphiregulin expression is regulated by gonadotropins/cAMP in human ovarian follicular cells

Gonadotropins up-regulate the expression of enolase 2, but not enolase 1, in the rat ovary

It has been demonstrated that the glycolytic enzymes, enolase 1 (ENO1) and enolase 2 (ENO2), are expressed in the rat ovary. In the present study, we found that mRNA levels of ovarian ENO2 but not ENO1 in normal cycling adult female rats changed significantly during the estrous cycle: ovarian ENO2 mRNA levels at metestrus were lower than those at estrus. Single injection of human CG (hCG) or equine CG (eCG) into immature (3 week old) rats up-regulated ovarian expression of ENO2. hCG mainly increased ENO2 expression in oocytes and theca cells of preantral and antral follicles, and eCG did in theca cells of these follicles. In contrast, hCG and eCG did not affect the expression of ENO1, which was mainly expressed in granulosa cells. These results suggest that endogenous gonadotropins up-regulate expression of ENO2 in oocytes and theca cells of preantral and antral follicles, which would activate glycolysis in these cells. It is also suggested that the activated glycolysis is necessary for ovarian functions such as follicle growth and maturation, and hormone production.

A new hypothesis regarding ovarian follicle development: ovarian rigidity as a regulator of selection and health

The mammalian ovary consists of a large number of dormant immature follicles, each containing a single oocyte and located on the periphery of the ovary. With each reproductive cycle, a group of immature follicles is sequentially activated to resume growth, and pituitary gonadotropins and ovarian steroid and peptide hormones cooperate to ensure further growth and development. A single dominant follicle eventually emerges, ovulates, and then involutes to allow the selection of the next group of follicles. While hormones are known to control the later stages of folliculogenesis, little is known about the pathways that activate individual immature primordial follicles in the dormant follicle pool. We advance a new hypothesis: that follicle activation is dependent on the physical environment of the ovary in addition to well-established hormonal cues. This novel perspective on ovarian function may provide new avenues to study follicle dynamics and identify therapeutic targets for ovarian dysfunction.

Endothelin-1 (ET-1) increases the expression of remodeling genes in vascular smooth muscle through linked calcium and cAMP pathways: role of a phospholipase A(2)(cPLA(2))/cyclooxygenase-2 (COX-2)/prostacyclin receptor-dependent autocrine loop

Several important genes that are involved in inflammation and tissue remodeling are switched on by virtue of CRE response elements in their promoters. The upstream signaling mechanisms that inflammatory mediators use to activate cAMP response elements (CREs) are poorly understood. Endothelin (ET) is an important vasoactive mediator that plays roles in inflammation, vascular remodeling, angiogenesis, and carcinogenesis by activating 7 transmembrane G protein-coupled receptors (GPCR). Here we characterized the mechanisms ET-1 uses to regulate CRE-dependent remodeling genes in pulmonary vascular smooth muscle cells. These studies revealed activation pathways involving a cyclooxygenase-2 (COX-2)/prostacyclin receptor (IP receptor) autocrine loop and an interlinked calcium-dependent pathway. We found that ET-1 activated several CRE response genes in vascular smooth muscle cells, particularly COX-2, amphiregulin, follistatin, inhibin-beta-A, and CYR61. ET-1 also activated two other genes epiregulin and HB-EGF. Amphiregulin, follistatin, and inhibin-beta-A and epiregulin were activated by an autocrine loop involving cPLA2, arachidonic acid release, COX-2-dependent PGI(2) synthesis, and IP receptor-linked elevation of cAMP leading to CRE transcription activation. In contrast COX-2, CYR61, and HB-EGF transcription were regulated in a calcium-dependent, COX-2 independent, manner. Observations with IP receptor antagonists and COX-2 inhibitors were confirmed with IP receptor or COX-2-specific small interfering RNAs. ET-1 increases in intracellular calcium and gene transcription were dependent upon ET(a) activation and calcium influx through T type voltage-dependent calcium channels. These studies give important insights into the upstream signaling mechanisms used by G protein-coupled receptor-linked mediators such as ET-1, to activate CRE response genes involved in angiogenesis, vascular remodeling, inflammation, and carcinogenesis.

Human oocyte maturation is dependent on LH-stimulated accumulation of the epidermal growth factor-like growth factor, amphiregulin

BACKGROUND

The LH surge promotes ovulation via activation of multiple signaling networks in the ovarian follicle. Studies in animal models have shown the importance of LH-induced activation of the epidermal growth factor (EGF)signaling network in critical peri-ovulatory events. We investigated the biological significance of regulatory mechanisms mediated by EGF-like growth factors during LH stimulation in humans.

METHODS

We characterized the EGF signaling network in mature human ovarian follicles using in vivo and in vitro approaches. Amphiregulin (AREG) levels were measured in 119 follicular fluid (FF) samples from IVF/ICSI patients. Biological activity of human FF was assessed using in vitro oocyte maturation, cumulus expansion and cell mitogenic assays.

RESULTS

AREG is the most abundant EGF-like growth factor accumulating in the FF of mature follicles of hCG-stimulated patients. No AREG was detected before the LH surge or before hCG stimulation of granulosa cells in vitro, demonstrating that the accumulation of AREG requires gonadotrophin stimulation. Epiregulin and betacellulin mRNA were detected in both human mural and cumulus granulosa cells, although at significantly lower levels than AREG. FF from stimulated follicles causes cumulus expansion and oocyte maturation in a reconstitution assay. Immunodepletion of AREG abolishes the ability of FF to stimulate expansion (P < 0.0001) and oocyte maturation (P < 0.05), confirming the biological activity of AREG. Conversely, mitogenic activity of FF remained after depletion of AREG, indicating that other mitogens accumulate in FF. FF from follicles yielding an immature germinal vesicle oocyte or from an oocyte that develops into an aberrant embryo contains lower AREG levels than that from follicles yielding a healthy oocyte (P = 0.008).

CONCLUSIONS

EGF-like growth factors play a role in critical peri-ovulatory events in humans, and AREG accumulation is a useful marker of gonadotrophin stimulation and oocyte competence.

Human ovarian follicular development: from activation of resting follicles to preovulatory maturation

By integrating morphometrical and endocrinological data, as well as biological effects of various molecules synthesized by the human follicle, we propose a dynamic view of the follicle growth within the human ovary. Folliculogenesis starts with entry of resting follicles into the growth phase, a process where the kit system plays a key role. Several months are required for a new growing follicle to reach the preantral stage (0.15mm), then 70 additional days to reach the size of 2mm. Early growing follicle growth is regulated by subtle interactions between follicle-stimulating hormone (FSH) and local factors produced by theca and granulosa cells (GCs), as well as the oocyte. From the time they enter the selectable stage during the late luteal phase, follicles become sensitive to cyclic changes of FSH in terms of granulosa cell proliferation. During the early follicular phase, the early selected follicle grows very quickly and estradiol is present in the follicular fluid. However, the total steroid production remains moderate. From the mid-follicular phase, the preovulatory follicle synthesizes high quantities of estradiol, then after the mid-cycle gonadotropin surge, very large amounts of progesterone. At this stage of development, the responsiveness of the follicle to gonadotropins is maximum, especially to luteinizing hormone (LH) that triggers granulosa wall dissociation and cumulus expansion as well as oocyte nuclear maturation. Thus, as the follicle develops, its responsiveness to gonadotropins progressively increases under the control of local factors acting in an autocrine/paracrine fashion.

Role for cumulus cell-produced EGF-like ligands during primate oocyte maturation in vitro

The developmental competence of in vitro-matured (IVM) rhesus macaque cumulus oocyte complexes (COCs) is deficient compared with in vivo-matured (IVM) oocytes. To improve oocyte quality and subsequent embryo development following IVM, culture conditions must be optimized. A series of experiments was undertaken to determine the role of epidermal growth factor (EGF) during IVM of rhesus macaque COCs. The addition of Tyrphostin AG-1478 (a selective inhibitor of the EGF receptor EGFR) to the IVM medium yielded fewer oocytes maturing to metaphase II of meiosis II (MII), decreased cumulus expansion, and a lower percentage of embryos that developed to the blastocyst stage compared with untreated IVM controls, indicating that EGFR activation is important for IVM maturation in the rhesus macaque. However, the addition of recombinant human EGF (r-hEGF) to the IVM medium did not enhance outcome. The expression of mRNAs encoding the EGF-like factors amphiregulin, epiregulin, and betacellulin in cumulus cells indicates that these factors produced by cumulus cells may be responsible for maximal EGFR activation during oocyte maturation, precluding any further effect of exogenous r-hEGF. Additionally, these results illustrate the potential futility of exogenous supplementation of IVM medium without prior knowledge of pathway activity.

Luteinizing hormone-induced up-regulation of ErbB-2 is insufficient stimulant of growth and invasion in ovarian cancer cells

The effects of luteinizing hormone (LH), a gonadotropic hormone implicated in the development of ovarian cancer, are mediated by specific binding to its G protein-coupled receptor, the LH receptor (LHR). Activated LHR initiates second messenger responses, including cyclic AMP (cAMP) and inositol phosphate. Because cAMP increases expression of ErbB-2, a receptor tyrosine kinase whose overexpression in cancers correlates with poor survival, we hypothesized that LH may regulate ErbB-2 expression. Cell surface LHR expression in stable transformants of the ErbB-2-overexpressing ovarian cancer cell line SKOV3 was confirmed by PCR and whole-cell ligand binding studies. Second messenger accumulation in the LHR-expressing cells confirmed signaling through Gs and Gq. Western blots of total protein revealed that LHR introduction up-regulated ErbB-2 protein expression 2-fold and this was further up-regulated in a time- and dose-dependent manner in response to LH. Forskolin and 8Br-cAMP also up-regulated ErbB-2 in both LHR-expressing and mock-transfected cells, indicating that regulation of ErbB-2 is a cAMP-mediated event. Kinase inhibitor studies indicated the involvement of protein kinase A-mediated, protein kinase C-mediated, epidermal growth factor receptor-mediated, and ErbB-2-mediated mechanisms. The LH-induced up-regulation of ErbB-2 was insufficient to overcome the negative effects of LH on proliferation, invasion, and migration. A molecular signature for this nonaggressive phenotype was determined by Taqman array to include increased and decreased expression of genes encoding adhesion proteins and metalloproteinases, respectively. These data establish a role for LH and LHR in the regulation of ErbB-2 expression and suggest that, in some systems, ErbB-2 up-regulation alone is insufficient in producing a more aggressive phenotype.

Epidermal growth factor-like growth factors in the follicular fluid: role in oocyte development and maturation

The growth and maturation of the ovarian follicle requires the coordinate function of somatic cells and the oocyte. Over the past three decades, numerous growth factors involved in the bidirectional signals between the somatic and germ cells have been identified. A possible function of epidermal growth factor (EGF) signaling at selected stages of follicle maturation had been proposed early on and is supported by many observations of in vitro effects of this growth factor on steroidogenesis, oocyte maturation, and cumulus expansion. However, attempts to link EGF levels in the follicular fluid with the state of follicle and oocyte maturation have been inconclusive. More recently, data generated using mouse genetic models perturbing ovulation and fertility indicate that EGF-like growth factors, rather than EGF itself, accumulate in the follicle at the time of ovulation. EGF-like growth factor mRNA is regulated by the luteinizing hormone surge, and corresponding proteins are detected in the follicle. The EGF-like growth factors amphiregulin, epiregulin, and betacellulin are potent stimulators of oocyte maturation and cumulus expansion, and perturbation of this EGF network in vivo impairs ovulation. Similar findings in species other than the mouse confirm an important physiological role for this network at the time of ovulation. Whether this network also plays a critical role in humans and whether it can be used as a biological marker of follicle development or for the improvement of fertility remains to be determined. This review summarizes the most recent findings on the EGF network during ovulation and the potential clinical applications of manipulating this intercellular communication pathway in the control of fertility.

Characterization, expression, and functional activity of pituitary adenylate cyclase-activating polypeptide and its receptors in human granulosa-luteal cells

CONTEXT

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are found in the ovary of mammalian species, although nothing is known about the possible role of PACAP and VIP in the human ovary.

OBJECTIVE

We investigated the expression of PACAP and PACAP/VIP receptors in human granulosa-luteal (GL) cells obtained from consenting in vitro fertilization patients attending a private fertility clinic and assessed a possible antiapoptotic effect of these molecules.

MAIN OUTCOME MEASURES

We measured the expression of PACAP and PACAP/VIP receptor mRNAs in GL cells in response to FSH or LH, as well as the effects of PACAP and VIP on apoptosis. We also evaluated the levels of procaspase-3 in GL cells cultured in the absence of serum.

RESULTS

After 7 d in culture, GL cells displayed increased responsiveness to FSH and LH (100 ng/ml). FSH and LH promoted PACAP expression, LH doing so in a time-dependent fashion. VIP receptor (VPAC1-R and VPAC2-R) mRNAs were also induced by gonadotropin stimulation. Although PACAP receptor (PAC1-R) mRNA was barely detectable, Western blot analysis revealed its presence. The apoptotic effect of serum withdrawal from the culture environment was reverted by both PACAP and VIP. Both peptides showed the ability to reverse a decrease in procaspase-3 levels induced by culture in the absence of serum.

CONCLUSIONS

PACAP and VIP appear to play a role in maintenance of follicle viability as a consequence of the antiapoptotic effect. Further studies are warranted to evaluate the respective roles of PACAP and VIP in ovarian physiology and to identify their mechanism of action.

The luteinizing hormone receptor-activated extracellularly regulated kinase-1/2 cascade stimulates epiregulin release from granulosa cells

We examine the pathways involved in the luteinizing hormone receptor (LHR)-dependent activation of the epidermal growth factor (EGF) network using cocultures of LHR-positive granulosa cells and LHR-negative test cells expressing an EGF receptor (EGFR)-green fluorescent protein fusion protein. Activation of the LHR in granulosa cells results in the release of EGF-like growth factors that are detected by measuring the phosphorylation of the EGFR-green fluorescent protein expressed only in the LHR-negative test cells. Using neutralizing antibodies and real-time PCR, we identified epiregulin as the main EGF-like growth factor produced upon activation of the LHR expressed in immature rat granulosa cells, and we show that exclusive inhibition or activation of the ERK1/2 cascade in granulosa cells prevents or enhances epiregulin release, respectively, with little or no effect on epiregulin expression. These results show that the LHR-stimulated ERK1/2 pathway stimulates epiregulin release.

Amphiregulin as a novel target for breast cancer therapy

Amphiregulin, an EGF family growth factor, binds and activates the epidermal growth factor receptor (EGFR or ErbB1). Activation of the EGFR by amphiregulin can occur through autocrine, paracrine and juxtacrine mechanisms. Amphiregulin plays a role in several biological processes including nerve regeneration, blastocyst implantation, and bone formation. Amphiregulin also plays an important role in mammary duct formation as well as the outgrowth and branching of several other human tissues such as the lung, kidney and prostate. This effect is most likely due to the induction of genes involved in invasion and migration such as cytokines and matrix metalloproteases. Clinical studies have suggested that amphiregulin also plays a role in human breast cancer progression and its expression has been associated with aggressive disease. Therefore, amphiregulin may be a novel and effective target for the treatment of breast cancer and could represent an alternative to targeting the EGFR.

Identification of potential markers of oocyte competence expressed in bovine cumulus cells matured with follicle-stimulating hormone and/or phorbol myristate acetate in vitro

Oocyte competence is the ability of the oocyte to complete maturation, undergo successful fertilization, and reach the blastocyst stage. Cumulus cells are indispensable for this process. Their removal significantly affects the blastocyst rates. Moreover, the properties and functions of cumulus cells are regulated by the oocyte. They also reflect the oocyte's degree of maturation. Our study was aimed at identifying markers of oocyte competence that are expressed in bovine cumulus cells. In a previous study in our laboratory, the blastocyst yield following FSH or phorbol myristate acetate (PMA) treatment was 45%%. Therefore, we tested four sets of conditions during the first 6 h of in vitro maturation (IVM): FSH (0.1 microg/ml), PMA (0.1 microM), FSH ++ PMA, and negative control. Extracts from each IVM treatment were hybridized against the same negative control on a microarray containing a partial library of differentially expressed transcripts in the cumulus of competent oocytes collected at 6 h after LH in vivo. Common positive clones between diffrentially treated cells were selected, and 15 candidates were validated by real-time PCR. Based on this, the main candidates expressed in cumulus cells and that could be valuable and indirect markers of oocyte competence are hyaluronan synthase 2 (HAS2), inhibin betaA (INHBA), epidermal growth factor receptor (EGFR), gremlin 1 (GREM1), betacellulin (BTC), CD44, tumor necrosis factor-induced protein 6 (TNFAIP6), and prostaglandin-endoperoxide synthase 2 (PTGS2). These biomarkers could be potential candidates to predict oocyte competence and to select higher-quality embryos for transfer. Additionally, these indirect predictors of oocyte competence and follicular health could improve our knowledge of gene expression patterns in the cumulus and yield insights into the molecular pathways controlling oocyte competence.

Amphiregulin is much more abundantly expressed than transforming growth factor-alpha and epidermal growth factor in human follicular fluid obtained from patients undergoing in vitro fertilization-embryo transfer

OBJECTIVE

To identify the most important epidermal growth factor (EGF) receptor ligand in the LH or hCG signal pathway in human ovary.

DESIGN

A retrospective clinical study.

SETTING

Tertiary university hospital.

PATIENT(S)

Ninety-eight infertile patients who underwent IVF-embryo transfer.

INTERVENTION(S)

Sera and follicular fluid were collected at the time of oocyte retrieval. The levels of EGF, transforming growth factor-alpha (TGFalpha), and amphiregulin (AR) were measured in follicular fluid and sera by using ELISA.

MAIN OUTCOME MEASURE(S)

The relationships between the level of AR and level of hCG, fertilization rate, and embryo quality.

RESULT(S)

Amphiregulin was abundantly expressed in follicular fluid after hCG stimulation. Although large differences were found between AR and both EGF and TGFalpha in follicular fluid, no significant difference was detected in the levels of the three EGF receptor ligands in sera. The level of AR was inversely correlated with the fertilization rate and hCG level, whereas little significant association was observed between the level of AR and embryo quality.

CONCLUSION(S)

Amphiregulin was expressed most dominantly among EGF receptor ligands tested and may mediate the hCG signal in human oocyte maturation. Elaborate interaction between AR and hCG may be required for an optimal oocyte maturation.

EGF-like peptides mediate FSH-induced maturation of cumulus cell-enclosed mouse oocytes

This study was carried out to examine the participation of epidermal growth factor (EGF)-like peptides in the induction of germinal vesicle breakdown (GVB) in mouse cumulus cell-enclosed oocytes (CEO). The EGF-like peptide, amphiregulin (AR), dose-dependently stimulated meiotic resumption in CEO, but not denuded oocytes (DO) maintained in meiotic arrest with 300 microM dbcAMP. The EGF receptor (EGFR) kinase inhibitor, AG1478, blocked meiotic resumption induced by FSH and AR in CEO, but had no effect in DO. FSH-induced maturation was also suppressed by antisera to both EGFR and EGF. Maturation occurred with slightly faster kinetics in AR-stimulated CEO when compared to FSH-stimulated CEO. When CEO were maintained in meiotic arrest with a low level of dbcAMP, FSH was initially inhibitory to maturation and later stimulatory; the stimulatory phase was prevented by AG1478, indicating mediation by EGF-like peptides. Pulsing CEO with high levels of dbcAMP also stimulated GVB and could be blocked by AG1478. Treatment of arrested CEO with PKC agonists stimulated maturation and this was prevented with AG1478 as well as antibodies to EGFR. FSH-induced maturation of dbcAMP-arrested CEO was blocked by bisindolylmaleimide I (BIM-I), an inhibitor of PKC, implicating PKC in FSH action. EGF-stimulated CEO failed to resume maturation in the presence of glycerrhetinic acid, a gap junction inhibitor, suggesting transfer of positive signal through the cell-cell coupling pathway. These data support the idea that EGF-like peptides provide a common pathway mediating the meiosis-inducing influence of FSH, cAMP pulsing, and PKC activation in mouse CEO by a gap junction-dependent process.

The kinetics of the hydrogen/deuterium exchange of epidermal growth factor receptor ligands

Five highly homologous epidermal growth factor receptor ligands were studied by mass spectral analysis, hydrogen/deuterium (H/D) exchange via attenuated total reflectance Fourier transform-infrared spectroscopy, and two-dimensional correlation analysis. These studies were performed to determine the order of events during the exchange process, the extent of H/D exchange, and associated kinetics of exchange for a comparative analysis of these ligands. Furthermore, the secondary structure composition of amphiregulin (AR) and heparin-binding-epidermal growth factor (HB-EGF) was determined. All ligands were found to have similar contributions of 3(10)-helix and random coil with varying contributions of beta-sheets and beta-turns. The extent of exchange was 40%, 65%, 55%, 65%, and 98% for EGF, transforming growth factor-alpha (TGF-alpha), AR, HB-EGF, and epiregulin (ER), respectively. The rate constants were determined and classified as fast, intermediate, and slow: for EGF the 0.20 min(-1) (Tyr), 0.09 min(-1) (Arg, beta-turns), and 1.88 x 10(-3) min(-1) (beta-sheets and 3(10)-helix); and for TGF-alpha 0.91 min(-1) (Tyr), 0.27 min(-1) (Arg, beta-turns), and 1.41 x 10(-4) min(-1) (beta-sheets). The time constants for AR 0.47 min(-1) (Tyr), 0.04 min(-1) (Arg), and 1.00 x 10(-4) min(-1) (buried 3(10)-helix, beta-turns, and beta-sheets); for HB-EGF 0.89 min(-1) (Tyr), 0.14 min(-1) (Arg and 3(10)-helix), and 1.00 x 10(-3) min(-1) (buried 3(10)-helix, beta-sheets, and beta-turns); and for epiregulin 0.16 min(-1) (Tyr), 0.03 min(-1) (Arg), and 1.00 x 10(-4) min(-1) (3(10)-helix and beta-sheets). These results provide essential information toward understanding secondary structure, H/D exchange kinetics, and solvation of these epidermal growth factor receptor ligands in their unbound state.

Luteinizing hormone signaling in preovulatory follicles involves early activation of the epidermal growth factor receptor pathway

LH activates a cascade of signaling events that are propagated throughout the ovarian preovulatory follicle to promote ovulation of a mature egg. Critical to LH-induced ovulation is the induction of epidermal growth factor (EGF)-like growth factors and transactivation of EGF receptor (EGFR) signaling. Because the timing of this transactivation has not been well characterized, we investigated the dynamics of LH regulation of the EGF network in cultured follicles. Preovulatory follicles were cultured with or without recombinant LH and/or specific inhibitors. EGFR and MAPK phosphorylation were examined by immunoprecipitation and Western blot analyses. By semiquantitative RT-PCR, increases in amphiregulin and epiregulin mRNAs were detected 30 min after recombinant LH stimulation of follicles and were maximal after 2 h. LH-induced EGFR phosphorylation also increased after 30 min and reached a maximum at 2 h. EGFR activation precedes oocyte maturation and is cAMP dependent, because forskolin similarly activated EGFR. LH-induced EGFR phosphorylation was sensitive to AG1478, an EGFR kinase inhibitor, and to inhibitors of matrix metalloproteases GM6001 and TNFalpha protease inhibitor-1 (TAPI-1), suggesting the involvement of EGF-like growth factor shedding. LH- but not amphiregulin-induced oocyte maturation and EGFR phosphorylation were sensitive to protein synthesis inhibition. When granulosa cells were cultured with a combination of neutralizing antibodies against amphiregulin, epiregulin, and betacellulin, EGFR phosphorylation and MAPK activation were inhibited. In cultured follicles, LH-induced MAPK activation was partially inhibited by AG1478 and GM6001, indicating that this pathway is regulated in part by the EGF network but also involves additional pathways. Thus, complex mechanisms are involved in the rapid amplification and propagation of the LH signal within preovulatory follicles and include the early activation of the EGF network.

Interactive actions of prostaglandin and epidermal growth factor to enhance proliferation of granulosa cells from chicken prehierarchical follicles

The interactive actions of prostaglandin (PG) and epidermal growth factor (EGF) on proliferation of granulosa cells was investigated in prehierarchical small yellow follicles (SYF) of laying hens. The granulosa layers were dispersed into single cells by 12.5 microg/ml collagenase. After 16 h pre-incubation in 0.5% fetal calf serum-supplemented medium, the medium was replaced with serum-free medium. Immunocytochemical staining showed that granulosa cells expressed EGF and its receptor, and their expression was increased by PGE(1) (1-100 ng/ml) or forskolin (10(-7) to 10(-5)M) treatments. EGF receptor was also induced by its ligand EGF. The specific prostaglandin synthase inhibitors SC560 (for COX-1) and NS398 (for COX-2) suppressed EGF-stimulated increase of the granulosa cell number. Furthermore, the effect of EGF was confirmed by the immunocytochemical staining of the proliferating cell nuclear antigen in granulosa cells. Though EGF promoted the expression of both COX-1 and COX-2, the rescue experiment indicated that combined treatment of PGE(1) showed better rescuing effect on NS398 inhibition than SC560 at 10(-6)M, which implies COX-2 plays the predominant role in mediating EGF action. The above results indicate that reciprocal stimulation of intracellular PG and EGF production may enhance proliferation of granulosa cells, hence to facilitate development of chicken prehierarchical follicles.

Regulation of granulosa cell proliferation and EGF-like ligands during the periovulatory interval in monkeys

BACKGROUND

This study seeks to clarify cell cycle dynamics of granulosa cells following hCG and elucidate the expression of epidermal growth factor (EGF)-like ligands during luteinization.

METHODS

Granulosa cells were obtained from rhesus macaques undergoing controlled ovarian stimulation protocols before or after an ovulatory hCG bolus. Cell cycle characteristics were determined by flow cytometry and levels of EGF receptor (EGFR), amphiregulin (AREG), epiregulin (EREG) and betacellulin (BTC) mRNAs were measured by real-time RT-PCR.

RESULTS

The proportion of cells in S-phase was 7.5% prior to hCG and did not decline until 24 h after hCG (3.1%). EGFR protein and BTC mRNA did not change following hCG, whereas AREG and EREG mRNA increased starting at 3 and 12 h post-hCG, respectively, and remained elevated thereafter.

CONCLUSIONS

Cell cycle transit of macaque granulosa cells does not change until 24 h after an ovulatory stimulus, whereas the EGF-like ligands EREG and AREG are increased rapidly. This suggests that luteinizing granulosa cells are refractory to mitogenic stimulation by EGFR ligands.

Molecular mechanisms of ovulation: co-ordination through the cumulus complex

Successful ovulation requires that developmentally competent oocytes are released with appropriate timing from the ovarian follicle. Somatic cells of the follicle sense the ovulatory stimulus and guide resumption of meiosis and release of the oocyte, as well as structural remodelling and luteinization of the follicle. Complex intercellular communication co-ordinates critical stages of oocyte maturation and links this process with release from the follicle. To achieve these outcomes, ovulation is controlled through multiple inputs, including endocrine hormones, immune and metabolic signals, as well as intrafollicular paracrine factors from the theca, mural and cumulus granulosa cells and the oocyte itself. This review focuses on the recent advances in understanding of molecular mechanisms that commence after the gonadotrophin surge and culminate with release of the oocyte. These mechanisms include intracellular signalling, gene regulation and remodelling of tissue structure in each of the distinct ovarian compartments. Most critical ovulatory mediators exert effects through the cumulus cell complex that surrounds and connects with the oocyte. The convergence of ovulatory signals through the cumulus complex co-ordinates the key mechanistic processes that mediate and control oocyte maturation and ovulation.

Luteinizing hormone-dependent activation of the epidermal growth factor network is essential for ovulation

In the preovulatory ovarian follicle, mammalian oocytes are maintained in prophase meiotic arrest until the luteinizing hormone (LH) surge induces reentry into the first meiotic division. Dramatic changes in the somatic cells surrounding the oocytes and in the follicular wall are also induced by LH and are necessary for ovulation. Here, we provide genetic evidence that LH-dependent transactivation of the epidermal growth factor receptor (EGFR) is indispensable for oocyte reentry into the meiotic cell cycle, for the synthesis of the extracellular matrix surrounding the oocyte that causes cumulus expansion, and for follicle rupture in vivo. Mice deficient in either amphiregulin or epiregulin, two EGFR ligands, display delayed or reduced oocyte maturation and cumulus expansion. In compound-mutant mice in which loss of one EGFR ligand is associated with decreased signaling from a hypomorphic allele of the EGFR, LH no longer signals oocyte meiotic resumption. Moreover, induction of genes involved in cumulus expansion and follicle rupture is compromised in these mice, resulting in impaired ovulation. Thus, these studies demonstrate that LH induction of epidermal growth factor-like growth factors and EGFR transactivation are essential for the regulation of a critical physiological process such as ovulation and provide new strategies for manipulation of fertility.

A delayed gonadotropin-dependent and growth factor-mediated activation of the extracellular signal-regulated kinase 1/2 cascade negatively regulates aromatase expression in granulosa cells

Human chorionic gonadotropin and human FSH (hFSH) elicit a transient increase in ERK1/2 phosphorylation lasting less than 60 min in immature granulosa cells expressing a low density of gonadotropin receptors. In cells expressing a high density of receptors, human chorionic gonadotropin and human FSH elicit this fast transient increase in ERK1/2 phosphorylation and also a delayed and more sustained increase that is detectable after 6-9 h. Both the early and delayed increases in ERK1/2 phosphorylation can be blocked with inhibitors of protein kinase A, the epidermal growth factor receptor kinase, metalloproteases, and MAPK kinase. The delayed effect, but not the early effect, can also be blocked with an inhibitor of protein kinase C. Because the delayed increase in ERK1/2 phosphorylation correlates with low aromatase expression in response to gonadotropins, we tested the effects of these inhibitors on aromatase expression. These inhibitors had little or no effect on gonadotropin-induced aromatase expression in cells expressing a low density of receptors, but they enhanced gonadotropin-induced aromatase expression in cells expressing a high density of receptors. Phorbol esters also induced a prolonged increase in ERK1/2 phosphorylation and, when added together with hFSH, blocked the induction of aromatase expression by hFSH in cells expressing a low density of hFSH receptor. A MAPK kinase inhibitor reversed the inhibitory effect of the phorbol ester on aromatase induction. We conclude that the effects of gonadotropins on ERK1/2 phosphorylation are mediated by epidermal growth factor-like growth factors and that the delayed effect is partially mediated by protein kinase C and acts as a negative regulator of aromatase expression.

PGE2 up-regulates EGF-like growth factor biosynthesis in human granulosa cells: new insights into the coordination between PGE2 and LH in ovulation

LH and prostaglandin E(2) (PGE(2)) share many similar effects on the pre-ovulatory follicle. They can induce independently cumulus expansion, the resumption of meiosis and progesterone production. However, cyclooxygenase-2 (COX-2) inhibitors were found to hinder most of the LH-induced effects. Recently, EGF-like growth factors amphiregulin (Ar) and epiregulin (Ep) were found to be produced in response to LH stimulation and to induce cumulus expansion and oocyte maturation. We aimed at evaluating whether PGE(2) induces Ar and Ep syntheses in human granulosa cells and whether the inhibition of PGE(2) production by selective COX-2 inhibitor, nimesulide, affects LH-induced Ar and Ep biosynthesis. Ar and Ep mRNA levels increased following PGE(2) stimulation, in a dose- and time-dependent manner, which resembled those of LH. The blockade of protein kinase A (PKA) (by H89) and mitogen-activated protein kinase (MAPK) (by UO126) reduced the expression of PGE(2)-induced Ar and Ep biosynthesis. Although the stimulation of the cells with LH in the presence of nimesulide did not change the progesterone levels, it resulted in a significant reduction of Ar and Ep biosynthesis. In conclusion, PGE(2) may mimic LH action, at least in part, by the induction of Ar and Ep biosynthesis, which involves cAMP/PKA and MAPK pathways. The negative effect of nimesulide on the ovulatory process may be due to the reduction of Ar and Ep biosynthesis, which implies a possible collaborative role between PGE(2) and LH on their induction.

Epidermal growth factor receptor in adult retinal neurons of rat, mouse, and human

During development, the epidermal growth factor receptor (EGFR) regulates proliferation and differentiation of many types of cells, including precursors of neurons and glia. In the adult, EGFR continues to drive the growth and differentiation of epithelial cells but is absent from glia in the CNS. However, the localization and functions of EGFR in adult neurons are not well defined. By using immunohistochemistry and Western blotting, we have identified EGFR and its ligands in adult retinal ganglion cells in the normal rat, mouse, and human retina. EGFR and its ligands were also present in certain other adult retinal neurons, for example, horizontal cells and amacrine cells, and had different distribution patterns among these species. In addition, we found that EGFR was expressed in the rat retinal ganglion cell line RGC-5. One of the EGFR ligands, EGF, caused a cell shape change and increased neurofilament phosphorylation in RGC-5 cells. The expression of EGFR in postmitotic, terminally differentiated adult retinal neurons suggests that EGFR has pleiotropic functions. In addition to the conventional mitogenic role in adult epithelial cells, EGFR must serve a different, nonmitogenic function in adult neurons. Our work localizes EGFR and its ligands in the adult retinas of several species as a step toward investigating the nonmitogenic functions of EGFR in adult neurons.

Differential expression of genes coding for EGF-like factors and ADAMTS1 following gonadotropin stimulation in normal and transformed human granulosa cells

We have demonstrated previously that the synthesis of epiregulin and amphiregulin, of the EGF-like growth factor family, is stimulated by luteinizing hormone in human follicular (granulosa) cells obtained from in vitro fertilization program. In the present work, we demonstrate that H89, a PKA inhibitor, attenuated the expression of these growth factors both in the mRNA and the protein levels, suggesting PKA involvement in this signaling pathway. SV40-transformed human granulosa cells showed higher basal levels of epiregulin and amphiregulin than normal cells, which were still elevated following cAMP stimulation by Forskolin. Cleavage by a disintegrin and metalloproteinases (ADAMs) is essential for activation of these growth factors, allowing their interaction with EGF receptor. Expression of ADAMTS1 and ADAM12 was downregulated by cAMP in normal, but not in SV40-transformed cells, suggesting that in normal cells epiregulin and amphiregulin activity is downregulated by a feedback mechanism that may be lost in SV40-transformed cells and their loss of downregulation may be involved in the development of ovarian tumors.

G-protein-coupled receptor signaling and the EGF network in endocrine systems

The epidermal growth factor (EGF) network is composed of a complex array of growth factors synthesized as precursors and expressed on the cell surface. These latent growth factors are activated by cleavage and shedding from the cell surface and act by binding to various homo- and hetero-dimers of the EGF receptors (ErbBs). Although the exact molecular steps are poorly understood, ligand binding to G-protein-coupled receptors as diverse as the beta-adrenoceptors or the lysophosphatidic acid receptors leads to shedding of EGF growth factors and activation of EGF receptors. Recent observations from the pituitary and in the ovary are providing new insight into the role of this network in endocrine systems.

Role of the epidermal growth factor network in ovarian follicles

The LH surge causes major remodeling of the ovarian follicle in preparation for the ovulatory process. These changes include reprogramming of granulosa cells to differentiate into luteal cells, changes in cumulus cell secretory properties, and oocyte maturation. This review summarizes published data in support of the concept that LH stimulation of ovarian follicles involves activation of a local epidermal growth factor (EGF) network. A model describing this property of LH signaling and its branching to other signaling modules is discussed. According to this model, LH activation of mural granulosa cells stimulates cAMP signaling, which, in turn, induces the expression of the EGF-like growth factors epiregulin, amphiregulin, and betacellulin. These growth factors function by activating EGF receptors in either an autocrine/juxtacrine fashion within the mural layer, or they diffuse to act on cumulus cells. Activation of EGF receptor signaling in cumulus cells, together with cAMP priming, triggers oocyte nuclear maturation and acquisition of developmental competence as well as cumulus expansion. This model has important implications for ovarian physiology and for the development of new strategies for the pharmacological control of ovulation and for gamete maturation in vitro.