Cholesterol transport and steroidogenesis by the corpus luteum

Global gene expression in the bovine corpus luteum is altered after stimulatory and superovulatory treatments

Equine chorionic gonadotrophin (eCG) has been widely used in superovulation and artificial insemination programmes and usually promotes an increase in corpus luteum (CL) volume and stimulates progesterone production. Therefore, to identify eCG-regulated genes in the bovine CL, the transcriptome was evaluated by microarray analysis and the expression of selected genes was validated by qPCR and western blot. Eighteen Nelore crossbred cows were divided into control (n = 5), stimulated (n = 6) and superovulated groups (n = 7). Ovulation was synchronised using a progesterone device-based protocol. Stimulated animals received 400 IU of eCG at device removal and superovulated animals received 2000 IU of eCG 4 days prior. Corpora lutea were collected 7 days after gonadotrophin-releasing hormone administration. Overall, 242 transcripts were upregulated and 111 transcripts were downregulated in stimulated cows (P ≤ 0.05) and 111 were upregulated and 113 downregulated in superovulated cows compared to the control animals (1.5-fold, P ≤ 0.05). Among the differentially expressed genes, many were involved in lipid biosynthesis and progesterone production, such as PPARG, STAR, prolactin receptors and follistatin. In conclusion, eCG modulates gene expression differently depending on the treatment, i.e. stimulatory or superovulatory. Our data contribute to the understanding of the pathways involved in increased progesterone levels observed after eCG treatment.

Effects of exposure to nanoparticle-rich diesel exhaust on pregnancy in rats

Pollutants from burning of diesel fuel are hazardous to human health. Nanoparticles in diesel exhaust potentially have profound impact on fetal development and maternal endocrine function during pregnancy due to their ability to penetrate deeply into the body. To investigate the effects of nanoparticle-rich diesel exhaust (NR-DE) on pregnancy, pregnant rats were exposed to NR-DE, filtered diesel exhaust (F-DE) or clean air for 19 days of gestation. Relative weights of maternal liver and spleen to body weight were significantly lower in the NR-DE and F-DE groups than those in the control group. The serum concentration of maternal progesterone was significantly lower, while those of luteinizing hormone (LH) and corticosterone were significantly higher in the NR-DE and F-DE groups than those in the control group. The serum concentration of estradiol-17β was significantly higher in the F-DE group than that in the control group. The levels of cytochrome P450 side-chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase and LH receptor mRNA in the corpus luteum were significantly lower in the NR-DE and F-DE groups than those in the control. In fetuses, body weight and crown-rump length were significantly greater and shorter, respectively, in both males and females in the NR-DE and F-DE groups than those in the control group. These results demonstrate that exposure of pregnant rats to NR-DE and F-DE suppresses the function of corpora lutea and stimulates the function of the adrenal cortex, suggesting a risk of spontaneous abortion associated with maternal hormonal changes.

Roles of antioxidant enzymes in corpus luteum rescue from reactive oxygen species-induced oxidative stress

Progesterone produced by the corpus luteum (CL) regulates the synthesis of various endometrial proteins required for embryonic implantation and development. Compromised CL progesterone production is a potential risk factor for prenatal development. Reactive oxygen species (ROS) play diverse roles in mammalian reproductive biology. ROS-induced oxidative damage and subsequent adverse developmental outcomes constitute important issues in reproductive medicine. The CL is considered to be highly exposed to locally produced ROS due to its high blood vasculature and steroidogenic activity. ROS-induced apoptotic cell death is involved in the mechanisms of CL regression that occurs at the end of the non-fertile cycle. Luteal ROS production and propagation depend upon several regulating factors, including luteal antioxidants, steroid hormones and cytokines, and their crosstalk. However, it is unknown which of these factors have the greatest contribution to the maintenance of CL integrity and function during the oestrous/menstrual cycle. There is evidence to suggest that antioxidants play important roles in CL rescue from luteolysis when pregnancy ensues. As luteal phase defect impacts fertility by preventing implantation and early conceptus development in livestock and humans, this review attempts to address the importance of ROS-scavenging antioxidant enzymes in the control of mammalian CL function and integrity. The corpus luteum (CL) is a transient endocrine organ that develops after ovulation from the ovulated follicle during each reproductive cycle. The main function of the CL is the production and secretion of progesterone which is necessary for embryonic implantation and development. Compromised CL progesterone production is a potential risk factor for prenatal development and pregnancy outcomes. Reactive oxygen species (ROS), which are natural by-products of cellular respiration and metabolism, play diverse roles in mammalian reproductive biology. ROS-induced oxidative damage and subsequent development of adverse pregnancy outcomes constitute important issues in reproductive medicine. Before the end of the first trimester, a high rate of human and animal conceptions end in spontaneous abortion and most of these losses occur at the time of implantation in association with ROS-induced oxidative damage. Every cell in the body is normally able to defend itself against the oxidative damage caused by the ROS. The cellular antioxidant enzymes constitute the first line of defence against the toxic effects of ROS. The CL is considered to be highly exposed to locally produced ROS due to its high blood vasculature and metabolic activity. There is now evidence to suggest that cellular antioxidants play important roles in CL rescue from regression when pregnancy ensues. As defective CL function impacts fertility by preventing implantation and early conceptus development in livestock and humans, this review attempts to address the importance of antioxidant enzymes in the control of mammalian CL function and integrity.

Cylindrospermopsin, a blue-green algal toxin, inhibited human luteinised granulosa cell protein synthesis in vitro

The blue-green algal toxin cylindrospermopsin (CYN) inhibits protein synthesis, and CYP450 enzymes metabolise CYN to cytotoxic endproducts. Human chorionic gonadotrophin (hCG) stimulates the de novo synthesis of StAR and CYP450 aromatase. Human IVF-derived granulosa cells (GC) (n=7) were exposed to 0-5μM CYN±1IU/ml hCG for 2-24h. After 24h pre-culture GC responded to hCG by increasing estradiol 17β (E(2)) and progesterone (P(4)) synthesis. Three micromolar of CYN±1IU/ml hCG for 24h was not cytotoxic and did not affect basal or hCG-stimulated E(2) or P(4) production, but did inhibit protein synthesis (p<0.05, n=4). hCG-stimulated steroidogenesis was not reduced by CYN, suggesting a lack of effect on StAR or CYP450 aromatase protein synthesis. hCG enhanced the effects of CYN on GC protein synthesis. Twenty four hours exposure to 0.1μM CYN did not affect GC, supporting the establishment of a 0.0024μM Guideline level for CYN in public water supplies.

Fractalkine is expressed in the human ovary and increases progesterone biosynthesis in human luteinised granulosa cells

BACKGROUND

Recent evidence from rodent ovaries has demonstrated expression of fractalkine and the existence of fractalkine receptor, and showed that there is a significant increase in steroidogenesis in response to fractalkine, yet the role of fractalkine and CX3CR1 in the human ovary is still unknown. This study aimed to determine the expression levels of fractalkine and CX3CR1 in the human ovary and to investigate their roles in sexual hormone biosynthesis by human luteinising granulosa cells. This is the first detailed report of fractalkine and CX3CR1 expression and function in the human ovary.

METHODS

Fractalkine and CX3CR1 expression levels were measured by immunohistochemistry using ovarian tissue from pathological specimens from five individuals. Granulosa cells were obtained from patients during IVF treatment. They were cultured and treated with increasing doses of hCG with or without fractalkine. Media were collected to detect estradiol and progesterone by chemiluminescence. StAR, 3-βHSD and CYP11A expression were determined in granulosa cells treated with or without fractalkine by real-time RT-PCR.

RESULTS

Fractalkine and CX3CR1 were expressed in the human ovary and in luteinising granulosa cells. However, fractalkine expression was stronger in luteinising granulosa cells. Treatment with fractalkine augmented hCG stimulation of progesterone production in a dose-dependent manner with concomitant increases in transcript levels for key steroidogenic enzymes (StAR, 3-βHSD and CYP11A) but had no effect on estradiol biosynthesis (P<0.05).

CONCLUSIONS

Fractalkine and CX3CR1 were found to express in human ovary and luteinising granulosa cells. Fractalkine can increase the biosynthesis of progesterone in a dose-dependent manner by enhancing transcript levels of key steroidogenic enzymes.

Luteinizing hormone stimulates mammalian target of rapamycin signaling in bovine luteal cells via pathways independent of AKT and mitogen-activated protein kinase: modulation of glycogen synthase kinase 3 and AMP-activated protein kinase

LH stimulates the production of cAMP in luteal cells, which leads to the production of progesterone, a hormone critical for the maintenance of pregnancy. The mammalian target of rapamycin (MTOR) signaling cascade has recently been examined in ovarian follicles where it regulates granulosa cell proliferation and differentiation. This study examined the actions of LH on the regulation and possible role of the MTOR signaling pathway in primary cultures of bovine corpus luteum cells. Herein, we demonstrate that activation of the LH receptor stimulates the phosphorylation of the MTOR substrates ribosomal protein S6 kinase 1 (S6K1) and eukaryotic translation initiation factor 4E binding protein 1. The actions of LH were mimicked by forskolin and 8-bromo-cAMP. LH did not increase AKT or MAPK1/3 phosphorylation. Studies with pathway-specific inhibitors demonstrated that the MAPK kinase 1 (MAP2K1)/MAPK or phosphatidylinositol 3-kinase/AKT signaling pathways were not required for LH-stimulated MTOR/S6K1 activity. However, LH decreased the activity of glycogen synthase kinase 3Beta (GSK3B) and AMP-activated protein kinase (AMPK). The actions of LH on MTOR/S6K1 were mimicked by agents that modulated GSK3B and AMPK activity. The ability of LH to stimulate progesterone secretion was not prevented by rapamycin, a MTOR inhibitor. In contrast, activation of AMPK inhibited LH-stimulated MTOR/S6K1 signaling and progesterone secretion. In summary, the LH receptor stimulates a unique series of intracellular signals to activate MTOR/S6K1 signaling. Furthermore, LH-directed changes in AMPK and GSK3B phosphorylation appear to exert a greater impact on progesterone synthesis in the corpus luteum than rapamycin-sensitive MTOR-mediated events.

Estrogens and androgens affect human luteal cell function

OBJECTIVE

To evaluate estrogens (Es)--E2, estrone (E1), and estriol--and androgens--T and androstendione (A)-effect on P, prostaglandin (PG) F2α, PGE2, and vascular endothelial growth factor (VEGF) release and on VEGF expression in human luteal cells. To elucidate whether androgens effects were direct or mediated by their conversion in Es, an aromatase inhibitor was used. Finally, the luteal effect of the non-aromatizable dihydrotestosterone was evaluated.

DESIGN

Prospective laboratory study.

SETTING

University hospital.

PATIENT(S)

Corpora lutea (CLs) were obtained from 36 normally menstruating patients in the midluteal phase of the menstrual cycle.

INTERVENTION(S)

The human luteal cells were isolated from CLs and primary cultures were established.

MAIN OUTCOME MEASURE(S)

P and PG release were assayed by enzyme immunoassay; VEGF secretion by ELISA; VEGF messenger RNA (mRNA) expression by real-time polymerase chain reaction (PCR).

RESULT(S)

P and PGF2α secretion were decreased by Es and androgens. The VEGF release was increased by Es and androgens, whereas VEGF mRNA expression was not. The aromatase inhibitor counteracted T and A luteal effects.

CONCLUSION(S)

Both Es and androgens could participate in the regulation of human luteal function. The effect of T and A seems to be mediated by their conversion to Es, whereas for dihydrotestosterone, both direct androgenic and indirect estrogenic luteal effects could coexist.

Expression of Npc1 in glial cells corrects sterility in Npc1(-/-) mice

Niemann-Pick type C1 (NPC) disease is an autosomal recessive neurodegenerative disorder. One feature of the mouse model of NPC1 is it's infertility. We have made transgenic mice which express the Npc1 protein exclusively in fibrillary astrocytes, using the glial fibrillary acidic protein (GFAP) promoter. This selective expression of Npc1 corrects sterility in GFAP-Npc1(-/-), Npc1(-/-) mice. Counts of acidophils in the pituitary of GFAP-Npc1E, Npc1(-/-) mice, as compared Npc1(-/-) mice, and measurements of dopamine D2 receptor (DRD2) mRNA in the pituitary, suggest mechanisms for fertility enhancement. We conclude that the correction of sterility in GFAP-Npc1E, Npc1(-/-) mice is a result of restoring hypothalamic control of the pituitary.

High-density lipoprotein metabolism and the human embryo

BACKGROUND

High-density lipoprotein (HDL) appears to be the dominant lipoprotein particle in human follicular fluid (FF). The reported anti-atherogenic properties of HDL have been attributed in part to reverse cholesterol transport. The discoveries of the scavenger receptor class B type I (SR-BI) and the ATP-binding cassette A1 lipid (ABCA1) transporter have generated studies aimed at unraveling the pathways of HDL biogenesis, remodeling and catabolism. The production of SR-BI and ABCA1 knockout mice as well as other lipoprotein metabolism-associated mutants has resulted in reduced or absent fertility, leading us to postulate the existence of a human hepatic-ovarian HDL-associated axis of fertility. Here, we review an evolving literature on the role of HDL metabolism on mammalian fertility and oocyte development.

METHODS

An extensive online search was conducted of published articles relevant to the section topics discussed. All relevant English language articles contained in Pubmed/Medline, with no specific time frame for publication, were considered for this narrative review. Cardiovascular literature was highly cited due to the wealth of relevant knowledge on HDL metabolism, and the dearth thereof in the reproductive field.

RESULTS

Various vertebrate models demonstrate a role for HDL in embryo development and fertility. In our clinical studies, FF levels of HDL cholesterol and apolipoprotein AI levels were negatively associated with embryo fragmentation, but not with embryo cell cleavage rate. However, the HDL component, paraoxonase 1 arylesterase activity, was positively associated with embryo cell cleavage rate.

CONCLUSIONS

HDL contributes to intra-follicular cholesterol homeostasis which appears to be important for successful oocyte and embryo development.

Effects of menstrual cycle phase on metabolomic profiles in premenopausal women

BACKGROUND

Characterization of the normal degree of physiological variation in the metabolomic profiles of healthy humans is a necessary step in the development of metabolomics as both a clinical research and diagnostic tool. This study investigated the effects of the menstrual cycle on (1)H nuclear magnetic resonance (NMR) derived metabolomic profiles of urine and plasma from healthy women.

METHODS

In this study, 34 healthy women were recruited and a first void urine and fasting blood sample were collected from each woman at four different time points during one menstrual cycle. Serum hormone levels were used in combination with the menstrual calendar to classify the urine and plasma samples into five different phases i.e. menstrual, follicular, periovulatory, luteal and premenstrual. The urine and plasma samples were analysed using (1)H NMR spectroscopy and subsequent data were analysed using principal component analysis (PCA) and partial least squares discriminant analysis.

RESULTS

PCA of the urine spectra showed no separation of samples based on the phases of the menstrual cycle. Multivariate analysis of the plasma spectra showed a separation of the menstrual phase and the luteal phase samples (R(2) = 0.61, Q(2) = 0.41). Subsequent analysis revealed a significant decrease in levels of glutamine, glycine, alanine, lysine, serine and creatinine and a significant increase in levels of acetoacetate and very low density lipoprotein (VLDL CH(2)) during the luteal phase.

CONCLUSIONS

These results establish a need to control for metabolic changes that occur in plasma due to the menstrual cycle in the design of future metabolomic studies involving premenopausal women.

Female infertility due to anovulation and defective steroidogenesis in NPC2 deficient mice

Niemann Pick C2 (NPC2) and NPC1 proteins function cooperatively to catalyze cholesterol efflux from lysosomes. NPC1 is expressed in ovarian cells and female NPC1 mice are infertile. This work addressed for the first time the localization and function of murine NPC2 protein in the ovary. Ovarian NPC2 was localized to theca and luteal cells, which use cholesterol as a substrate to produce estradiol and progesterone, respectively. NPC2 deficient (NPC2-/-) females had abnormal estrous cycles and were infertile, with normal folliculogenesis until the antral stage, but a complete absence of corpora lutea and many zonae pellucidae remnants, indicative of anovulation. Serum estradiol was reduced and ovarian cholesterol was accumulated in NPC2-/- mice, suggesting a defect in cholesterol export from intracellular stores. After superovulation, NPC2-/- mice ovulated less eggs than their wild type littermates, showed ovaries with less corpora lutea and numerous unruptured follicles, and lower serum progesterone concentration. Together, these results suggest that NPC2 participates in the traffic of ovarian cholesterol required to provide the substrate for steroid synthesis and support follicle maturation, ovulation and luteinization.

Human corpus luteum physiology and the luteal-phase dysfunction associated with ovarian stimulation

The human corpus luteum is a temporary endocrine gland that develops after ovulation from the ruptured follicle during the luteal phase. It is an important contributor of steroid hormones, particularly progesterone, and is critical for the maintenance of early pregnancy. Luteal-phase dysfunction can result in premature regression of the gland, with a subsequent shift to an infertile cycle. Understanding the mechanism of steroidogenesis during corpus luteum growth and regression is crucial for evaluating the normal physiology and pathophysiology of reproductive cycles. The rate-limiting step in corpus luteum steroidogenesis is the transport of cholesterol to the site of steroid production. Steroidogenic acute regulatory protein is a key player in this process and is positively correlated with progesterone concentrations throughout the early and mid-luteal phase. Changes in the endocrine environment brought on by the gonadotrophins used for ovarian stimulation are thought to underlie the corpus luteum dysfunction associated with IVF cycles. While ovarian hyperstimulation syndrome is associated with human chorionic gonadotrophin (HCG), studies suggest that exogenous progesterone provides necessary luteal support in patients undergoing IVF. The current trend towards simple stimulation protocols and the use of single-embryo transfers provide further opportunity to revisit HCG administration as luteal support.

Gonadal function, first cases of pregnancy, and child delivery in a woman with lipoid congenital adrenal hyperplasia

CONTEXT

Mutations in the steroidogenic acute regulatory protein (StAR) gene often cause lipoid congenital adrenal hyperplasia (LCAH). In this disorder an impairment of steroid synthesis leads to adrenal and gonadal insufficiencies with a particular female genital phenotype in both human karyotypes. Pregnancy in LCAH has not been yet reported.

OBJECTIVE

We describe the first cases of pregnancy in a LCAH female patient bearing the L275P mutation in the StAR gene.

DESIGN

We studied the gonadal function, pubertal development, and apply the appropriate hormonal therapy to support pregnancies.

PATIENT

A 46,xx patient of French Canadian descent was diagnosed with LCAH at the age of 4.5 months. Substitution therapy with glucocorticoids and mineralocorticoids led to normal growth and development. Progressive pubertal development started at the age of 11 7/12 yr. Menarche occurred at 14 2/12 yr with normal regular menstruations thereafter but without ovulation.

RESULTS

Clomiphene stimulation induced the first pregnancy at 25 4/12 yr of age. Spontaneous abortion occurred after 6 wk gestation. The second pregnancy (with clomiphene stimulation) was induced at the age of 26 yr. Progesterone (Prog) therapy was added at the 17th day of the cycle to protect pregnancy. Vaginal delivery of dichorionic-diamniotic twin pregnancy occurred at 30 wk gestation (two normal weight male babies). Two years later, again under clomiphene stimulation, she underwent another successful singleton pregnancy and delivered a normal weight female baby at 36 wk. The pregnancies were almost uncomplicated.

CONCLUSION

Despite the dysfunctional StAR, pregnancy is possible under the proper therapeutic strategy.

Expression of scavenger receptor-BI and low-density lipoprotein receptor and differential use of lipoproteins to support early steroidogenesis in luteinizing macaque granulosa cells

An ovulatory hCG stimulus to rhesus macaques undergoing controlled ovarian stimulation protocols results in a rapid and sustained increase in progesterone synthesis. The use of lipoproteins as a substrate for progesterone synthesis remains unclear, and the expression of lipoprotein receptors [very-low-density lipoprotein receptor (VLDLR), low-density lipoprotein receptor (LDLR), and scavenger receptor-BI (SR-BI)] soon after human chorionic gonadotropin (hCG) (<12 h) has not been characterized. This study investigated lipoprotein receptor expression and lipoprotein (VLDL, LDL, and HDL) support of steroidogenesis during luteinization of macaque granulosa cells. Granulosa cells were aspirated from rhesus monkeys undergoing controlled ovarian stimulation before or up to 24 h after an ovulatory hCG stimulus. The expression of VLDLR decreased within 3 h of hCG, whereas LDLR and SR-BI increased at 3 and 12 h, respectively. Granulosa cells isolated before hCG were cultured for 24 h in the presence of FSH or FSH plus hCG with or without VLDL, LDL, or HDL. Progesterone levels increased in the presence of hCG regardless of lipoprotein addition, although LDL, but not HDL, further augmented hCG-induced progesterone. Other cells were cultured with FSH or FSH plus hCG without an exogenous source of lipoprotein for 24 h, followed by an additional 24 h culture with or without lipoproteins. Cells treated with hCG in the absence of any lipoprotein were unable to maintain progesterone levels through 48 h, whereas LDL (but not HDL) sustained progesterone synthesis. These data suggest that an ovulatory stimulus rapidly mobilizes stored cholesterol esters for use as a progesterone substrate and that as these are depleted, new cholesterol esters are obtained through an LDLR- and/or SR-BI-mediated mechanism.

Activation of Cl- channels by human chorionic gonadotropin in luteinized granulosa cells of the human ovary modulates progesterone biosynthesis

Chloride permeability pathways and progesterone (P4) secretion elicited by human chorionic gonadotropin (hCG) in human granulosa cells were studied by electrophysiological techniques and single-cell volume, membrane potential and Ca2+i measurements. Reduction in extracellular Cl(-) and equimolar substitution by the membrane-impermeant anions glutamate or gluconate significantly increased hCG-stimulated P4 accumulation. A similar result was achieved by exposing the cells to hCG in the presence of a hypotonic extracellular solution. Conversely, P4 accumulation was drastically reduced in cells challenged with hCG exposed to a hypertonic solution. Furthermore, conventional Cl(-) channel inhibitors abolished hCG-mediated P4 secretion. In contrast, 25-hydroxycholesterol-mediated P4 accumulation was unaffected by Cl(-) channel blockers. In human granulosa cells, hCG triggered the activation of a tamoxifen-sensitive outwardly rectifying Cl(-) current comparable to the volume-sensitive outwardly rectifying Cl(-) current. Exposure of human granulosa cells to hCG induced a rapid 4,4'-diisothiocyanatostilbene-2,2-disulphonic acid-sensitive cell membrane depolarization that was paralleled with an approximately 20% decrease in cell volume. Treatment with hCG evoked oscillatory and nonoscillatory intracellular Ca2+ signals in human granulosa cells. Extracellular Ca2+ removal and 4,4'-diisothiocyanatostilbene-2,2-disulphonic acid abolished the nonoscillatory component while leaving the Ca2+ oscillations unaffected. It is concluded that human granulosa cells express functional the volume-sensitive outwardly rectifying Cl(-) channels that are activated by hCG, which are critical for plasma membrane potential changes, Ca2+ influx, and P4 production.

Effect of estrogen on the expression of luteinizing hormone-human chorionic gonadotropin receptor messenger ribonucleic acid in cultured rat granulosa cells

Estrogen has been considered to enhance FSH actions in the ovary, including the induction of the LH receptor (LHR). In this study, we elucidated the mechanism underlying the effect of estrogen on the induction of LHR by FSH in rat granulosa cells. Estradiol clearly enhanced the FSH-induced LHR mRNA increase in a time- and dose-dependent manner, with a maximum increase of approximately 3.5-fold at 72 h, compared with the level of LHR mRNA solely induced by FSH. We then investigated whether the effect of estrogen on LHR mRNA was due to increased transcription and/or altered mRNA stability. A luciferase assay with the plasmid containing the LHR 5'-flanking region did not show that estradiol increased the promoter activity induced by FSH. In contrast, the decay curves for LHR mRNA showed a significant increase in half-life with FSH and estradiol, suggesting that the increased stability of LHR mRNA is at least responsible for the regulation of LHR mRNA by estrogen. Recently mevalonate kinase (Mvk) was identified as a trans-factor that binds to LHR mRNA and alters LHR mRNA stability in the ovary. We found that estradiol, with FSH, decreased Mvk mRNA levels in rat granulosa cell culture, resulting in up-regulation of LHR mRNA that was inversely correlated to Mvk mRNA expression. Furthermore, the augmentation of FSH-induced LHR expression in the presence of estrogen was erased with the overexpression of Mvk by transient transfection. Taken together, these data indicate that LHR mRNA is up-regulated due to increased stability when estrogen negatively controls Mvk.

Changes in the proteome of functional and regressing corpus luteum during pregnancy and lactation in the rat

The corpus luteum (CL) is an exquisitely regulated transitory endocrine gland necessary for the onset and maintenance of pregnancy in mammals. Most of the data on the mechanisms of CL differentiation at the molecular level come from genomic studies, but direct protein data are scarce. Here we have undertaken a differential expression proteomic approach to identify, in an unbiased way, those proteins whose levels change significantly in the rat CL as it evolves from functionality during pregnancy to regression after parturition. Moreover, we have compared the regressing CL with the newly formed functional CL that coexist during lactation under the same endocrine environment. We have defined a "proteomic signature" of CL functionality, which is constituted by a set of 24 proteins with a few differences between pregnancy and lactation. Most of these markers are new and are involved in microtubule assembly, retinoic acid transport, and Raf kinase signaling cascade; 10 are enzymes that define a ketogenic metabolic landscape, demonstrating, for the first time, the prevalence of de novo cholesterol synthesis in luteal cells. The "proteomic signature of regression," on the other hand, is composed of nine proteins, one of which is 20alpha-hydroxysteroid dehydrogenase and two, ferritin and gamma-actin, are new. The discovery of unpredictable new actors in the differentiation process of CL reported here will contribute to new hypotheses that explain the complex female reproductive function at the protein level. It will also open new doors to research on each identified protein by relating them to cellular differentiation.

Regulation of human luteinizing hormone receptor in the ovary

The luteinizing hormone receptor (LHR) is essential for elevated levels of progesterone to maintain pregnancy during the first trimester; the maintenance of the expression of LHR is a key factor controlling the duration of luteal function. Therefore, as the expression of LHR is most likely to be regulated by the stability of the receptor mRNA at the luteal phase of the human menstrual cycle, we focused on studies examining the stability of mRNA rather than the production of mRNA. In addition, LHR (exon 9), one of the splice variants of human LHR (hLHR), was cloned in the corpus luteum of a patient with a regular menstrual cycle. The results of Western blots using Percoll gradient fractionation indicated that hLHR formed complexes with hLHR (exon 9), which are transferred to the lysosome, where they are eventually degraded, instead of being translocated from the endoplasmic reticulum to the transducing organelle. These results showed that hLHR (exon 9) caused a reduction in the expression of functional receptor number and affected the signaling condition of wild-type hLHR. As the luteal phase progressed hLHR (exon 9) increased relative to hLHR, demonstrating that hLHR (exon 9) was expressed more than hLHR in the late luteal phase. This work reveals the essential function of the regulatory and structural elements involved in human LH receptor splicing, and that hLHR (exon 9) can negatively control the function of wild-type receptors. Moreover, this finding presented a novel mechanism of regulation of LHR in the human corpus luteum. (Reprod Med Biol 2008; 7: 11-16).

Features of natural and gonadotropin-releasing hormone antagonist-induced corpus luteum regression and effects of in vivo human chorionic gonadotropin

CONTEXT

The natural process of luteolysis and luteal regression is induced by withdrawal of gonadotropin support.

OBJECTIVE

The objectives of this study were: 1) to compare the functional changes and apoptotic features of natural human luteal regression and induced luteal regression; 2) to define the ultrastructural characteristics of the corpus luteum at the time of natural luteal regression and induced luteal regression; and 3) to examine the effect of human chorionic gonadotropin (hCG) on the steroidogenic response and apoptotic markers within the regressing corpus luteum.

DESIGN

Twenty-three women with normal menstrual cycles undergoing tubal ligation donated corpus luteum at specific stages in the luteal phase. Some women received a GnRH antagonist prior to collection of corpus luteum, others received an injection of hCG with or without prior treatment with a GnRH antagonist.

MAIN OUTCOME MEASURE

Main outcome measures were plasma hormone levels and analysis of excised luteal tissue for markers of apoptosis, histology, and ultrastructure.

RESULTS

The progesterone and estradiol levels, corpus luteum DNA, and protein contents in induced luteal regression resembled those of natural luteal regression. hCG treatment raised progesterone and estradiol in both natural luteal regression and induced luteal regression. The increase in apoptosis detected in induced luteal regression by cytochrome c in the cytosol, activated caspase-3, and nuclear DNA fragmentation, was similar to that observed in natural luteal regression. The antiapoptotic protein Bcl-2 was significantly lower during natural luteal regression. The proapoptotic proteins Bax and Bak were at a constant level. Apoptotic and nonapoptotic death of luteal cells was observed in natural luteal regression and induced luteal regression at the ultrastructural level. hCG prevented apoptotic cell death, but not autophagy.

CONCLUSION

The low number of apoptotic cells disclosed and the frequent autophagocytic suggest that multiple mechanisms are involved in cell death at luteal regression. hCG restores steroidogenic function and restrains the apoptotic process, but not autophagy.

Tumor necrosis factor-alpha activates nuclear factor-kappaB but does not regulate progesterone production in cultured human granulosa luteal cells

BACKGROUND

The role of tumor necrosis factor-alpha (TNF-alpha) in granulosa luteal cell function and steroidogenesis is still controversial. Our aim was to examine the steroidogenic response, together with the simultaneous expression and activation of nuclear factor-kappaB (NF-kappaB), in cultured human granulosa luteal cells (GLCs) following administration of TNF-alpha.

MATERIALS AND METHODS

This prospective controlled study was conducted in the Human Reproduction Division at the Institute of Maternal and Child Research, Faculty of Medicine, University of Chile and the San Borja Arriarán Hospital, National Health Service, Santiago, Chile. GLCs were obtained from aspirates of follicles from women undergoing in vitro fertilization (IVF). Thirty-two women undergoing IVF for tubal-factor and/or male-factor infertility participated in this study. Protein levels of NF-kappaB, the NF-kappaB inhibitor IkappaBalpha and steroidogenic acute regulatory protein (StAR) were determined by Western blot and localization of NF-kappaB was studied by indirect immunofluorescence. Progesterone production was determined by radioimmunoassay.

RESULTS

TNF-alpha did not affect the expression of StAR protein or the synthesis of progesterone. NF-kappaB was expressed in the GLCs and activated by TNF-alpha, resulting in degradation of IkappaBalpha and mobilization of the p65 NF-kappaB subunit into the nucleus.

CONCLUSIONS

These results indicate that TNF-alpha did not modulate steroidogenesis in cultured human GLCs. However, NF-kappaB was activated by TNF-alpha. Therefore the activation of NF-kappaB via the TNF-alpha pathway is likely associated with other preovulatory granulosa cell processes important for human ovarian function.

Inhibition of progesterone production in human luteinized granulosa cells treated with LXR agonists

Progesterone production by luteal cells is dependent on the supply of cholesterol by lipoproteins. The aim of this study was to determine whether the liver X receptors (LXRs) contribute to cholesterol homeostasis and progesterone secretion in human luteinized granulosa cells. Cells were isolated from follicular aspirates of patients undergoing in vitro fertilization. Luteinization was induced by a 7-day treatment with human chorionic gonadotrophin. LXR beta was expressed at higher levels than LXR alpha in granulosa cells and its expression was increased during luteinization. Treatment of luteinized granulosa cells by LXR agonists induced a significant time- and dose-dependent reduction in progesterone secretion (50% reductions after a 7-day treatment with 1-microM of either GW3965 or T0901317). mRNA levels of steroidogenic genes including steroidogenic acute regulatory protein and P450 side-chain cleavage were only moderately affected by LXR activation, with a significant reduction that was observed at 10 microM agonist concentration. Cellular cholesterol was markedly reduced after treatment with LXR agonists as a result of an increased cholesterol efflux that was related to the induction of LXR target genes (ABCA1, ABCG1, apo E, PLTP). Our study identifies LXRs as new, key actors contributing to regulation of cholesterol metabolism and steroidogenesis in luteinized granulosa cells.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

Can luteal regression be reversed?

The corpus luteum is an endocrine gland whose limited lifespan is hormonally programmed. This debate article summarizes findings of our research group that challenge the principle that the end of function of the corpus luteum or luteal regression, once triggered, cannot be reversed. Overturning luteal regression by pharmacological manipulations may be of critical significance in designing strategies to improve fertility efficacy.

Effects of hepatic expression of the high-density lipoprotein receptor SR-BI on lipoprotein metabolism and female fertility

The etiology of human female infertility is often uncertain. The sterility of high-density lipoprotein (HDL) receptor-negative (SR-BI(-/-)) female mice suggests a link between female infertility and abnormal lipoprotein metabolism. SR-BI(-/-) mice exhibit elevated plasma total cholesterol [with normal-sized and abnormally large HDL and high unesterified to total plasma cholesterol (UC:TC) ratio]. We explored the influence of hepatic SR-BI on female fertility by inducing hepatic SR-BI expression in SR-BI(-/-) animals by adenovirus transduction or stable transgenesis. For transgenes, we used both wild-type SR-BI and a double-point mutant, Q402R/Q418R (SR-BI-RR), which is unable to bind to and mediate lipid transfer from wild-type HDL normally, but retains virtually normal lipid transport activities with low-density lipoprotein. Essentially wild-type levels of hepatic SR-BI expression in SR-BI(-/-) mice restored to nearly normal the HDL size distribution and plasma UC:TC ratio, whereas approximately 7- to 40-fold overexpression dramatically lowered plasma TC and increased biliary cholesterol secretion. In contrast, SR-BI-RR overexpression had little effect on SR-BI(+/+) mice, but in SR-BI(-/-) mice, it substantially reduced levels of abnormally large HDL and normalized the UC:TC ratio. In all cases, hepatic transgenic expression restored female fertility. Overexpression in SR-BI(-/-) mice of lecithin:cholesterol acyl transferase, which esterifies plasma HDL cholesterol, did not normalize the UC:TC ratio, probably because the abnormal HDL was a poor substrate, and did not restore fertility. Thus, hepatic SR-BI-mediated lipoprotein metabolism influences murine female fertility, raising the possibility that dyslipidemia might contribute to human female infertility and that targeting lipoprotein metabolism might complement current assisted reproductive technologies.

Prochloraz: an imidazole fungicide with multiple mechanisms of action

Prochloraz is an imidazole fungicide that is widely used in Europe, Australia, Asia and South America within gardening and agriculture. Screening studies have shown that prochloraz elicits multiple mechanisms of action in vitro, as it antagonizes the androgen and the oestrogen receptor, agonizes the Ah receptor and inhibits aromatase activity. In vivo prochloraz acts as an antiandrogen in the Hershberger assay by reducing weights of reproductive organs, affecting androgen-regulated gene expressions in the prostate and increasing luteinizing hormone levels. In order to investigate the developmental effects of prochloraz, pregnant Wistar dams were dosed perinatally with 30 mg/kg prochloraz. Results showed that prochloraz significantly reduced plasma and testicular testosterone levels in gestational day 21 male foetuses, whereas testicular progesterone was increased. Gestational length was increased by prochloraz. In male pups a significant increase in nipple retention was found, and the weight of the bulbourethral glands was decreased. Behavioural studies showed that the activity level and sweet preference of adult males were significantly increased, indicating that exposure during gestation and lactation causes permanent effects in adulthood. Overall, these results indicate that prochloraz feminizes the male offspring after perinatal exposure, and that these effects are due, at least in part, to diminished fetal steroidogenesis. Thus, a novel endocrine disruptor has been identified that is mechanistically interesting as it elicits dual mechanisms of action and acts as an antiandrogen both by blocking the androgen receptor and by inhibiting fetal steroidogenesis. That a fungicide with such effects is so widely used is a cause for concern, and its use should be reduced, thereby minimizing the risk of human exposure.

17β-Hydroxysteroid dehydrogenase type 7 (Hsd17b7) reverts cholesterol auxotrophy in NS0 cells

NS0 is a host cell line widely used for the production of recombinant therapeutic proteins. In this work, we investigated the cholesterol-dependent phenotype of NS0 cells. Growth response to different precursors and comparative transcript analyses pointed to deficiency of 17beta-hydroxysteroid dehydrogenase type 7 (Hsd17b7) in NS0 cells. Hsd17b7 was previously shown to encode for an enzyme involved in estrogenic steroid biosynthesis. Its recent cloning into a yeast mutant deficient in ERG27 led to its functional characterization as the 3-ketoreductase of the cholesterol biosynthesis pathway. To ascertain that its cholesterol biosynthesis is blocked at the reduction reaction catalyzed by Hsd17b7, we genetically engineered NS0 cells to over express Hsd17b7. The stable transfectants of Hsd17b7 were able to grow independent of cholesterol. The results affirm the role of Hsd17b7 in the cholesterol biosynthesis pathway in mammals. Further, the findings allow for rational engineering of this industrially important cell line to alleviate their cholesterol dependence.

Perinatal Exposure to the Fungicide Prochloraz Feminizes the Male Rat Offspring

Prochloraz is a commonly used fungicide that has shown multiple mechanisms of action in vitro. It antagonizes the androgen and the estrogen receptors, agonizes the Ah receptor, and inhibits aromatase activity. In vivo prochloraz acts antiandrogenically in the Hershberger assay by reducing weights of reproductive organs, affecting androgen-regulated gene expressions, and increasing luteinizing hormone (LH) levels. The purpose of this study was to investigate reproductive toxic effects after exposure during gestation and lactation to prochloraz alone and a mixture of five pesticides (deltamethrin, methiocarb, prochloraz, simazine, and tribenuron-methyl). Prochloraz (30 mg/kg/day) or the mixture (20 mg/kg/day) was dosed to pregnant Wistar dams from gestational day (GD) 7 until postnatal day (PND) 16. Some dams were taken for cesarean section at GD 21, and others were allowed to give birth. Results showed that prochloraz and the mixture significantly reduced plasma and testicular testosterone levels in GD 21 male fetuses, whereas testicular progesterone was increased. Gestational length was increased by prochloraz. Chemical analysis of the rat breast milk showed that prochloraz was transferred to the milk. In males a significant increase of nipple retention was found, and the bulbourethral gland weight was decreased, whereas other reproductive organs were unaffected. In addition cytochrome P450 (CYP)1A activities in livers were induced by prochloraz, possibly as a result of Ah receptor activation. Behavioral studies showed that the activity level and sweet preference of adult males were significantly increased. Overall these results strongly indicate that prochloraz feminizes the male offspring after perinatal exposure, and that these effects are due, at least in part, to diminished fetal steroidogenesis.

Large-Scale Generation and Analysis of Expressed Sequence Tags from Porcine Ovary1

One method to identify the factors that control ovarian function is to characterize the genes that are expressed in ovary. In the present study, cDNA libraries from fetal, neonatal, and prepubertal porcine ovaries, pubertal ovaries on different days of the estrous cycle (Days 0 [follicle], 5, and 12 [follicle and corpus luteum]), and follicles isolated from weaned sows (diameter, 2, 4, 6, and 8 mm) were constructed and sequenced. A total of 22 176 cDNAs were sequenced, of which 15 613 were of sufficient quality for clustering. Clustering of cDNAs resulted in 8507 contigs, 6294 (74%) of which were comprised of a single sequence. Sixty-eight percent of the contigs had consensus sequences that were homologous to existing Tentative Consensus (TC) sequences or mature transcripts (ET) in The Institute for Genomic Research Porcine Gene Index. The consensus sequences were classified according to the Gene Ontology Index. Most cDNA-encoded proteins were components of the nucleus, ribosome, or mitochondrion. The proteins primarily functioned in binding, catalysis, and transport. Nearly 75% of the proteins were involved in metabolism and cell growth and/or maintenance. Analysis of the cDNA frequency across different libraries demonstrated differential gene expression within different-size follicles, between follicles and corpora lutea, and across developmental time-points. The expression of selected genes (analyzed by ribonuclease protection assay and Northern blotting) was consistent with the frequency of their respective cDNA in the individual libraries. This porcine ovary unigene set will be useful for identifying factors and mechanisms controlling ovarian follicular development in a variety of species.

Regulation of steroidogenesis by p53 in macaque granulosa cells and H295R human adrenocortical cells

Ovulation and formation of a functional corpus luteum in primates involve cascades of events, including increased progesterone synthesis and changes in granulosa cell proliferation. However, critical gaps remain in our understanding of how an ovulatory gonadotropin surge initiates these processes. To more fully elucidate changes in the cell cycle during luteal formation, the actions of the tumor suppressor p53 were examined. Rhesus macaque granulosa cells were isolated during controlled ovarian stimulation protocols before (nonluteinized) or after (luteinized) an ovulatory gonadotropin stimulus. Phosphorylated p53 protein was detected in the cytoplasm of granulosa cells before and after human chorionic gonadotropin (hCG) treatment, whereas granulosa cells from hormonally controlled rats did not express p53 before or after hCG. Treatment of nonluteinized macaque granulosa cells with hCG and the p53 inhibitor pifithrin-alpha (PFT) in vitro did not alter markers of the cell cycle, including proliferating cell nuclear antigen, p21, and human double minute (HDM)-2 expression compared with hCG alone. Levels of pregnenolone and progesterone increased 2- and 4-fold, respectively, within 6 h of hCG treatment, whereas PFT completely blocked this hCG-induced effect. Estradiol was increased transiently (>10-fold) by hCG plus PFT relative to levels after hCG alone. PFT also inhibited hCG-induced increases in steroidogenic acute regulatory protein and 3beta-hydroxysteroid dehydrogenase mRNAs. Similar results were obtained using the human adrenocortical cell line H295R, suggesting that p53 may have a general function in primate steroidogenesis. These data indicate that p53 plays a key role in luteinization of the primate ovarian follicle though the regulation of steroidogenic enzymes leading to progesterone synthesis.