Dynamic changes in gene expression that occur during the period of spontaneous functional regression in the rhesus macaque corpus luteum

Prostaglandin F2α regulates mitochondrial dynamics and mitophagy in the bovine corpus luteum

Prostaglandins are arachidonic acid-derived lipid mediators involved in numerous physiological and pathological processes. PGF2α analogues are therapeutically used for regulating mammalian reproductive cycles and blood pressure, inducing term labor, and treating ocular disorders. PGF2α exerts effects via activation of calcium and PKC signaling, however, little is known about the cellular events imposed by PGF2α signaling. Here, we explored the early effects of PGF2α on mitochondrial dynamics and mitophagy in the bovine corpus luteum employing relevant and well characterized in vivo and in vitro approaches. We identified PKC/ERK and AMPK as critical protein kinases essential for activation of mitochondrial fission proteins, DRP1 and MFF. Furthermore, we report that PGF2α elicits increased intracellular reactive oxygen species and promotes receptor-mediated activation of PINK-Parkin mitophagy. These findings place the mitochondrium as a novel target in response to luteolytic mediator, PGF2α. Understanding intracellular processes occurring during early luteolysis may serve as a target for improving fertility.

Immunofluorescent Evidence for Nuclear Localization of Aromatase in Astrocytes in the Rat Central Nervous System

Estrogens regulate a variety of neuroendocrine, reproductive and also non-reproductive brain functions. Estradiol biosynthesis in the central nervous system (CNS) is catalyzed by the enzyme aromatase, which is expressed in several brain regions by neurons, astrocytes and microglia. In this study, we performed a complex fluorescent immunocytochemical analysis which revealed that aromatase is colocalized with the nuclear stain in glial fibrillary acidic protein (GFAP) positive astrocytes in cell cultures. Confocal immunofluorescent Z-stack scanning analysis confirmed the colocalization of aromatase with the nuclear DAPI signal. Nuclear aromatase was also detectable in the S100β positive astrocyte subpopulation. When the nuclear aromatase signal was present, estrogen receptor alpha was also abundant in the nucleus. Immunostaining of frozen brain tissue sections showed that the nuclear colocalization of the enzyme in GFAP-positive astrocytes is also detectable in the adult rat brain. CD11b/c labelled microglial cells express aromatase, but the immunopositive signal was distributed only in the cytoplasm both in the ramified and amoeboid microglial forms. Immunostaining of rat ovarian tissue sections and human granulosa cells revealed that aromatase was present only in the cytoplasm. This novel observation suggests a new unique mechanism in astrocytes that may regulate certain CNS functions via estradiol production.

Increased 27-hydroxycholesterol production during luteolysis may mediate the progressive decline in progesterone secretion

STUDY QUESTION

Does 27-hydroxycholesterol (27OH) actively facilitate the progression of luteolysis?

SUMMARY ANSWER

There is increased mRNA expression of the enzyme that produces 27OH during luteolysis in vivo in rhesus macaques and sheep, and 27OH reduces progesterone secretion from human luteinized granulosa cells.

WHAT IS KNOWN ALREADY

There is an increase in mRNA expression of liver x receptor (LXR) and a decrease in sterol regulatory element binding protein 2 (SREBP2) target genes during spontaneous luteolysis in primates, which could result in reduced cholesterol availability for steroidogenesis. Concentrations of 27OH are also increased in primate corpora lutea (CL) during luteolysis, and 27OH is a dual LXR agonist and SREBP2 inhibitor.

STUDY DESIGN SIZE, DURATION

This was an in vitro study using primary human luteinized granulosa cells in a control versus treatment(s) design. Analyses of CL from sheep undergoing induced or spontaneous luteolysis were also performed, along with database mining of microarray data from rhesus macaque CL.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Primary luteinizing granulosa cells were obtained from 37 women aged 24-44 who were undergoing oocyte donation or IVF for male factor or idiopathic infertility, and cells were further luteinized in vitro using human chorionic gonadotropin. Three approaches to test the effect of 27OH produced via CYP27A1 (cytochrome p450, family 27, subfamily A, polypeptide 1) on luteinized granulosa cells were used: (i) direct 27OH supplementation, (ii) induction of endogenous CYP27A1 activity via pharmacologic inhibition of steroidogenesis, and (iii) siRNA-mediated knockdown to directly inhibit CYP27A1 as well as cholesterol transport into the mitochondria via the steroidogenic acute regulatory protein (STAR). Endpoints included: progesterone (P4) secretion into culture media determined by enzyme immunoassay, cholesterol efflux and uptake assays using fluorescent lipid analogs, and mRNA expression determined via semi-quantitative real-time PCR (QPCR). An additional experiment involved QPCR analysis of 40 CL collected from ewes undergoing induced or spontaneous luteolysis, as well as database mining of microarray data generated from 16 rhesus macaque CL collected during spontaneous luteolysis and 13 macaque CL collected during a luteinizing hormone ablation and replacement protocol.

MAIN RESULTS AND THE ROLE OF CHANCE

The mRNA expression of CYP27A1 was significantly increased during luteolysis in rhesus macaques and sheep in vivo, and CYP27A1 transcription was suppressed by luteinizing hormone and hCG. There was a significant decrease in hCG-stimulated P4 secretion from human luteinized granulosa cells caused by 27OH treatment, and a significant increase in basal and hCG-stimulated P4 synthesis when endogenous 27OH production was inhibited via CYP27A1 knockdown, indicating that 27OH inhibits steroidogenesis. Pharmacologic inhibition of steroidogenesis by aminoglutethimide significantly induced LXR and inhibited SREBP2 target gene mRNA expression, indicating that increased oxysterol production occurs when steroidogenesis is suppressed. Inhibiting cholesterol delivery into the mitochondria via knockdown of STAR resulted in reduced SREBP2 target gene mRNA expression, indicating that STAR function is necessary to maintain SREBP2-mediated transcription. The effects of 27OH treatment on markers of LXR and SREBP2 activity were moderate, and knockdown of CYP27A1 did not prevent aminoglutethimide-induced changes in LXR and SREBP2 target gene mRNA expression. These observations indicate that 27OH inhibits P4 secretion partially via mechanisms separate from its role as an LXR agonist and SREBP2 inhibitor, and also demonstrate that other oxysterols are involved in modulating LXR and SREBP2-mediated transcription when steroidogenesis is suppressed.

LARGE SCALE DATA

None.

LIMITATIONS REASONS FOR CAUTION

Luteinized granulosa cells may differ from luteal cells, and the effect on luteal function in vivo was not directly tested. The mechanisms that cause the initial rise in CYP27A1 mRNA expression during luteolysis are also not clear.

WIDER IMPLICATIONS OF THE FINDINGS

The factors causing luteolysis in primates have not yet been determined. This study provides functional evidence of a novel mechanism via increased 27OH synthesis during luteolysis, which subsequently represses progesterone secretion. Increased 27OH may also facilitate the progression of luteolysis in domestic animal species.

STUDY FUNDING AND COMPETING INTEREST(S)

The authors have nothing to disclose. Support was provided by the Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD) of the National Institutes of Health (NIH), award number R00HD067678 to R.L.B.

Ovarian Lipid Metabolism Modulates Circulating Lipids in Premenopausal Women

CONTEXT

The premenopausal circulating lipid profile may be linked to the hormonal profile and ovarian lipid metabolism.

OBJECTIVE

Assess how estradiol, progesterone, and ovarian lipid metabolism contributes to the premenopausal lipid profile; and evaluate the acute effects of a common hormonal oral contraceptive (OC) on circulating lipids.

DESIGN

Experimental crossover with repeated measures.

SETTING

Academic hospitals.

PATIENTS

Eight healthy, regularly menstruating women.

INTERVENTIONS

Participants underwent periodic serum sampling during a normal menstrual cycle; a standard 21-day, monophasic combined hormonal OC cycle (30 µg of ethinyl estradiol and 150 µg of levonorgestrel per day); menopause simulated by leuprolide acetate (22.5-mg depot); and an artificial menstrual cycle achieved via transdermal estradiol (50 to 300 µg/d) and vaginal micronized progesterone (100 to 300 mg/d).

MAIN OUTCOME MEASURES

Primary outcomes included evaluation of total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein cholesterol, triglycerides, and the total cholesterol to HDL cholesterol ratio. To estimate the effect of estradiol, progesterone, and ovarian lipid metabolism, all specimens except those from the OC cycle were analyzed. Subgroup analysis was conducted on the follicular and luteal phases. In a separate analysis, the effect of the OC was evaluated relative to the normal menstrual cycle.

RESULTS

Estradiol was significantly associated with increased levels of HDL cholesterol throughout the menstrual cycle and in the follicular phase. Ovarian effects were associated with reduced lipid levels, especially during the luteal phase. The OC was associated with an increased total cholesterol to HDL cholesterol ratio and triglycerides.

CONCLUSION

Previously unappreciated factors including ovarian lipid metabolism may contribute to the premenopausal lipid profile.

Changes in immune cell distribution and their cytokine/chemokine production during regression of the rhesus macaque corpus luteum

Our previous flow cytometry results demonstrated a significant increase in neutrophils, macrophages/monocytes, and natural killer (NK) cells in dispersed rhesus monkey corpora lutea (CL) after progesterone (P4) levels had fallen below 0.3 ng/ml for ≥3 days during the natural menstrual cycle. In this study, immunohistochemistry revealed the CD11b+ cells (neutrophils, macrophages/monocytes) present in the CL after luteal P4 synthesis ceased were distributed throughout the tissue. CD16+ cells (presumptive NK cells) were observed mainly near the vasculature in functional CL, until their numbers increased and they became widely distributed in regressing CL. To determine if the immune cells that enter luteal tissue during structural regression are functionally different from those that are present during peak function, CD11b+ or CD16+ populations were enriched from mid-late stage (functional) and regressing (days 1.8 ± 0.3 postmenses) CL using antibody-conjugated magnetic microbeads. Flow cytometry analyses revealed the majority of CD11b+ cells expressed CD14, a protein mainly produced by macrophages/monocytes. The antibody-enriched and depleted fractions were cultured for 24 h, and the media then analyzed for the production of 29 cytokines/chemokines. From the mid-late CL, the CD11b+-enriched fraction produced three cytokines/chemokines, whereas CD16+-enriched cells only produced the chemokine CCL2. However, CD11b +-enriched cells isolated from regressed CL produced eight cytokines/chemokines. The CD16+-enriched cells isolated from regressing CL produced significant levels of only three cytokines. Thus, the CD11b+ cells that appear in the rhesus macaque CL after functional regression produce several cytokines/chemokines that likely play a role in orchestrating structural regression.

Gene expression profiling of bovine ovarian follicular and luteal cells provides insight into cellular identities and functions

After ovulation, somatic cells of the ovarian follicle (theca and granulosa cells) become the small and large luteal cells of the corpus luteum. Aside from known cell type-specific receptors and steroidogenic enzymes, little is known about the differences in the gene expression profiles of these four cell types. Analysis of the RNA present in each bovine cell type using Affymetrix microarrays yielded new cell-specific genetic markers, functional insight into the behavior of each cell type via Gene Ontology Annotations and Ingenuity Pathway Analysis, and evidence of small and large luteal cell lineages using Principle Component Analysis. Enriched expression of select genes for each cell type was validated by qPCR. This expression analysis offers insight into cell-specific behaviors and the differentiation process that transforms somatic follicular cells into luteal cells.

Corpus luteum as a novel target of weight changes that contribute to impaired female reproductive physiology and function

Obesity and malnutrition are associated with decreased fecundity in women. Impaired reproductive capacity in obese women is often attributed to anovulation. However, obese women with ovulatory cycles also have reduced fertility, but the etiology of their impaired reproduction is only partially understood. Accumulating evidence suggests that obesity directly impairs oocyte and embryo quality as well as endometrial receptivity. In obese women, urinary progesterone metabolite excretion is decreased, but in excess of what can be explained by suppressed gonadotropin secretion, suggesting that apart from its central effect obesity may directly affect progesterone (P4) production. These observations have led to the novel hypothesis that obesity directly affects corpus luteum (CL) function. Similarly, we hypothesize that weight loss may contribute to luteal dysfunction. Here, we propose a non-human primate model, the vervet monkey, to examine the effect of weight gain and loss on menstrual cycle parameters and CL gene expression. In this model, weight gain and loss did not significantly alter menstrual cyclicity; however, both induced alterations in the CL transcriptome. In the weight gain monkey, we observed that impaired mid-luteal P4 secretion was associated with downregulation of steroidogenic pathways in CL. Collectively, these preliminary findings support our hypothesis that weight gain and loss may contribute to CL dysfunction. The vervet model described and preliminary observations provide a basis for a larger study to address this important question. Understanding the mechanisms by which weight gain and loss contribute to reproductive dysfunction can assist in the development of targeted treatments to enhance women's reproductive capability when it is desired.

ABBREVIATIONS

CL: corpus luteum; P4: progesterone; E2: estradiol; PDG: pregnanediol 3-glucoronide; LH: luteinizing hormone; FSH: follicle-stimulating hormone; GnRH: gonadotropin releasing hormone; BMI: body mass index; qrtPCR: quantitative real-time PCR; PGR: progesterone receptor; ART: assisted reproductive technology; IVF: in vitro fertilization; HPO: hypothalamic-pituitary-ovarian axis; MMPs: matrix metalloproteinases Gene symbols: LH receptor (LHGCR); cholesterol side-chain cleavage enzyme (CYP11A1); 3 beta-hydroxysteroid dehydrogenase type II (HSD3B2); steroidogenic acute regulatory protein (STAR); LDL receptor (LDLR); scavenger receptor B1 (SCARB1); ATP-binding cassette sub-family A member 1 (ABCA1); ATP-binding cassette sub-family G member 1 (ABCG1); apolipoprotein A (APOA1); 24 dehydrocholesterol reductase (DHCR24); 3-hydroxy-3-methylglytaryl-CoA reductase (HMGCR); vascular endothelial growth factor A (VEGFA); vascular endothelial growth factor C (VEGFC); vascular endothelial growth factor receptor 1 (VEGFR1); and TIMP metallopeptidase inhibitor 1 (TIMP1); amphiregulin (AREG); epiregulin (EREG); CCAAT/enhancer binding protein alpha (CEBPBA); cAMP responsive element binding protein 3-like 1 (CREB3L1); ADAM metallopeptidase with thrombospodin type 1 motif 1 (ADAMTS1); matrix metallopeptidase 9 (MMP9); cytochrome b-245 beta polypeptide (CYBB or NOX2); NADH oxidase (NCF2 or NOXA2); Fc fragment of IgG receptor IIb (FCGR2B); Fc fragment of IgG receptor IIb (FCGR2C); ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1); RAB27A member RAS oncofamily (RAB27A); hydroxyprostaglandin dehydrogenase (HPGD); prostaglandin-endoperoxidase synthase 1 (PTGS1); integrin B2 (ITGB2); leukotriene A4 hydrolase (LTA4H); radixin (RDX); ezrin (EZR); nuclear receptor subfamily 5 group A member 2 (NR5A2).

Western-style diet, with and without chronic androgen treatment, alters the number, structure, and function of small antral follicles in ovaries of young adult monkeys

OBJECTIVE

To examine the small antral follicle (SAF) cohort in ovaries of adult rhesus monkeys after consumption of a Western-style diet (WSD), with or without chronically elevated androgen levels since before puberty.

DESIGN

Cholesterol or T (n = 6 per group) implants were placed SC in female rhesus macaques beginning at 1 year of age (prepubertal), with addition of a WSD (high fat/fructose) at 5.5 years (menarche approximately 2.6 years). Ovaries were collected at 7 years of age. One ovary per female was embedded in paraffin for morphologic and immunohistochemical analyses. The SAFs (<2.5 mm) were dissected from the other ovary obtained at or near menses in a subgroup of females (n = 3 per group) and processed for microarray analyses of the SAF transcriptome. Ovaries of adult monkeys consuming a standard macaque diet (low in fats and sugars) were obtained at similar stages of the menstrual cycle and used as controls for all analyses.

SETTING

Primate research center.

ANIMAL(S)

Adult, female rhesus monkeys (Macaca mulatta).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURES

Histologic analyses, SAF counts and morphology, protein localization and abundance in SAFs, transcriptome in SAFs (messenger RNAs [mRNAs]).

RESULT(S)

Compared with controls, consumption of a WSD, with and without T treatment, increased the numbers of SAFs per ovary, owing to the presence of more atretic follicles. Numbers of granulosa cells expressing cellular proliferation markers (pRb and pH3) was greater in healthy SAFs, whereas numbers of cells expressing the cell cycle inhibitor (p21) was higher in atretic SAFs. Intense CYP17A1 staining was observed in the theca cells of SAFs from WSD with or without T groups, compared with controls. Microarray analyses of the transcriptome in SAFs isolated from WSD and WSD plus T-treated females and controls consuming a standard diet identified 1,944 genes whose mRNA levels changed twofold or more among the three groups. Further analyses identified several gene pathways altered by WSD and/or WSD plus T associated with steroid, carbohydrate, and lipid metabolism, plus ovarian processes. Alterations in levels of several SAF mRNAs are similar to those observed in follicular cells from women with polycystic ovary syndrome.

CONCLUSION(S)

These data indicate that consumption of a WSD high in fats and sugars in the presence and absence of chronically elevated T alters the structure and function of SAFs within primate ovaries.

Dynamics of Immune Cell Types Within the Macaque Corpus Luteum During the Menstrual Cycle: Role of Progesterone

The goal of the current study was to characterize the immune cell types within the primate corpus luteum (CL). Luteal tissue was collected from rhesus females at discrete intervals during the luteal phase of the natural menstrual cycle. Dispersed cells were incubated with fluorescently labeled antibodies specific for the immune cell surface proteins CD11b (neutrophils and monocytes/macrophages), CD14 (monocytes/macrophages), CD16 (natural killer [NK] cells), CD20 (B-lymphocytes), and CD3epsilon (T-lymphocytes) for analysis by flow cytometry. Numbers of CD11b-positive (CD11b(+)) and CD14(+) cells increased significantly 3 to 4 days after serum progesterone (P4) concentrations declined below 0.3 ng/ml. CD16(+) cells were the most abundant immune cell type in CL during the mid and mid-late luteal phases and were 3-fold increased 3 to 4 days after serum P4 decreased to baseline levels. CD3epsilon(+) cells tended to increase 3 to 4 days after P4 decline. To determine whether immune cells were upregulated by the loss of luteotropic (LH) support or through loss of LH-dependent steroid milieu, monkeys were assigned to 4 groups: control (no treatment), the GnRH antagonist Antide, Antide plus synthetic progestin (R5020), or Antide plus the estrogen receptor agonists diarylpropionitrile (DPN)/propyl-pyrazole-triol (PPT) during the mid-late luteal phase. Antide treatment increased the numbers of CD11b(+) and CD14(+) cells, whereas progestin, but not estrogen, replacement suppressed the numbers of CD11b(+), CD14(+), and CD16(+) cells. Neither Antide nor steroid replacement altered numbers of CD3epsilon(+) cells. These data suggest that increased numbers of innate immune cells in primate CL after P4 synthesis declines play a role in onset of structural regression of primate CL.

Age-Specific Gene Expression Profiles of Rhesus Monkey Ovaries Detected by Microarray Analysis

The biological function of human ovaries declines with age. To identify the potential molecular changes in ovarian aging, we performed genome-wide gene expression analysis by microarray of ovaries from young, middle-aged, and old rhesus monkeys. Microarray data was validated by quantitative real-time PCR. Results showed that a total of 503 (60 upregulated, 443 downregulated) and 84 (downregulated) genes were differentially expressed in old ovaries compared to young and middle-aged groups, respectively. No difference in gene expression was found between middle-aged and young groups. Differentially expressed genes were mainly enriched in cell and organelle, cellular and physiological process, binding, and catalytic activity. These genes were primarily associated with KEGG pathways of cell cycle, DNA replication and repair, oocyte meiosis and maturation, MAPK, TGF-beta, and p53 signaling pathway. Genes upregulated were involved in aging, defense response, oxidation reduction, and negative regulation of cellular process; genes downregulated have functions in reproduction, cell cycle, DNA and RNA process, macromolecular complex assembly, and positive regulation of macromolecule metabolic process. These findings show that monkey ovary undergoes substantial change in global transcription with age. Gene expression profiles are useful in understanding the mechanisms underlying ovarian aging and age-associated infertility in primates.

Joint MiRNA/mRNA expression profiling reveals changes consistent with development of dysfunctional corpus luteum after weight gain

Obese women exhibit decreased fertility, high miscarriage rates and dysfunctional corpus luteum (CL), but molecular mechanisms are poorly defined. We hypothesized that weight gain induces alterations in CL gene expression. RNA sequencing was used to identify changes in the CL transcriptome in the vervet monkey (Chlorocebus aethiops) during weight gain. 10 months of high-fat, high-fructose diet (HFHF) resulted in a 20% weight gain for HFHF animals vs. 2% for controls (p = 0.03) and a 66% increase in percent fat mass for HFHF group. Ovulation was confirmed at baseline and after intervention in all animals. CL were collected on luteal day 7-9 based on follicular phase estradiol peak. 432 mRNAs and 9 miRNAs were differentially expressed in response to HFHF diet. Specifically, miR-28, miR-26, and let-7b previously shown to inhibit sex steroid production in human granulosa cells, were up-regulated. Using integrated miRNA and gene expression analysis, we demonstrated changes in 52 coordinately regulated mRNA targets corresponding to opposite changes in miRNA. Specifically, 2 targets of miR-28 and 10 targets of miR-26 were down-regulated, including genes linked to follicular development, steroidogenesis, granulosa cell proliferation and survival. To the best of our knowledge, this is the first report of dietary-induced responses of the ovulating ovary to developing adiposity. The observed HFHF diet-induced changes were consistent with development of a dysfunctional CL and provide new mechanistic insights for decreased sex steroid production characteristic of obese women. MiRNAs may represent novel biomarkers of obesity-related subfertility and potential new avenues for therapeutic intervention.

Activation of Adenosine Monophosphate-Activated Protein Kinase Is an Additional Mechanism That Participates in Mediating Inhibitory Actions of Prostaglandin F2Alpha in Mature, but Not Developing, Bovine Corpora Lutea

Elevated cytosolic calcium and protein kinase C are well-established mediators of luteolytic actions of prostaglandin F2alpha (PGF2alpha). The objectives of this study were to determine 1) if calcium/calmodulin-dependent kinase kinase 2 (CAMKK2) participates in mediating PGF2alpha actions in developing (Day [d]-4) and mature (d-10) bovine corpus luteum (CL), 2) distal targets of CAMKK2, 3) developmental expression of adenosine monophosphate-activated protein kinase (AMPK), and 4) effects of AMPK activation on progesterone (P4) production. Expression of AMPK increased as the CL matured. Activation of the prostaglandin receptor (FP) induced rapid phosphorylation of AMPK, which was blocked by a CAMKK2 inhibitor. Changes in basal P4 secretion in vitro were determined in response to AMPK activation via metformin (met) or 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) in d-4 and d-10 CL. Production of P4 in d-10 CL decreased with met or AICAR compared to control, similar to activation by PGF2alpha. Therefore, potential distal targets of AMPK in d-10 CL were examined during induced functional regression via exogenous PGF2alpha. Serum and luteal P4 decreased at 2 and 4 h after administration of PGF2alpha. Protein expression of LDLR decreased at 2 and 4 h, while those of ACAT1 and STAR increased 4 h after PGF2alpha. During induced regression, alterations of cholesterol transport proteins contributed to decreased luteal and serum P4. Therefore, developmental differences in signal transduction associated with FP, specifically CAMKK2 and AMPK, partially contribute to differences in the ability of PGF2alpha to induce regression in mature, but not developing, bovine CL. Multiple cholesterol transport proteins, including LDLR, were altered by PGF2alpha and could be potential AMPK targets.

Decreased cholesterol uptake and increased liver x receptor-mediated cholesterol efflux pathways during prostaglandin F2 alpha-induced and spontaneous luteolysis in sheep

In nonprimate species, it has been well established that prostaglandin F2 alpha (PGF2alpha) initiates luteolysis. Changes in intracellular cholesterol concentrations caused by modulation of cholesterol uptake and efflux may mediate PGF2alpha-induced luteolysis. These changes in cholesterol efflux and uptake are controlled, in part, by the liver x receptors (LXR) alpha (NR1H3) and beta (NR1H2), nuclear receptors that increase expression of genes necessary for cholesterol efflux or limiting cholesterol uptake. Therefore, we hypothesized that PGF2alpha reduces expression of cholesterol uptake and increases expression of cholesterol efflux genes, mediated in part by enhanced LXR activity. To test this hypothesis, an induced luteolysis model was used whereby ewes were treated during their midluteal phase with saline or PGF2alpha and corpora lutea (CL) collected 12, 24, or 48 h later for determination of mRNA and protein concentrations by quantitative real-time PCR and Western blot analysis, respectively. As a complementary approach, CL undergoing spontaneous luteolysis were compared to midluteal phase CL. The lipoprotein receptors responsible for cholesterol uptake were significantly decreased in both luteolysis models. Expression of the LXR target gene ATP binding cassette subfamily A1 (ABCA1), an important mediator of cholesterol efflux, was significantly increased in both experimental models. Chromatin immunoprecipitation confirmed that PGF2alpha treatment resulted in enhanced NR1H3 and NR1H2 binding to the ABCA1 promoter. Qualitative changes in lipid droplet distribution were also observed following PGF2alpha treatment. These data support the hypothesis that reduced cholesterol uptake and increased efflux mediate luteolysis in sheep, which is partially controlled by PGF2alpha stimulation of LXR activity.

Effects of steroid ablation and progestin replacement on the transcriptome of the primate corpus luteum during simulated early pregnancy

Previous microarray analyses indicated that a portion of the transcriptome in the macaque corpus luteum (CL) of the menstrual cycle was regulated indirectly by luteinizing hormone via the local actions of steroid hormones, notably progesterone (P). The current study was designed to investigate this concept in the CL of early pregnancy by analyzing chorionic gonadotrophin (CG)-regulated genes that are dependent versus independent of local steroid action. Exogenous human chorionic gonadotropin treatment simulating early pregnancy (SEP) began on Day 9 of the luteal phase in female rhesus monkeys with and without concurrent administration of the 3-β-hydroxysteroid dehydrogenase inhibitor trilostane (TRL) with or without the synthetic progestin R5020. Compared with SEP treatment alone, TRL altered 50 mRNA transcripts on Day 10, rising to 95 on Day 15 (P<0.05, ≥2-fold change in gene expression). Steroid-sensitive genes were validated; notably effects of steroid ablation and P replacement varied by day. Expression of some genes previously identified as P-regulated in the macaque CL during the menstrual cycle were not significantly altered by steroid ablation and P replacement during CG exposure in SEP. These data indicate that the majority of CG-regulated luteal transcripts are differentially expressed independently of local steroid actions. However, the steroid-regulated genes in the macaque CL may be essential during early pregnancy, based on previous reports that TRL treatment initiates premature structural regression of the CL during SEP. These data reinforce the concept that the structure, function and regulation of the rescued CL in early pregnancy differs from the CL of the menstrual cycle in primates.

Involvement of miRNAs in ovarian follicular and luteal development

Although much progress has been made in the genetic dissection of biological networks involved in follicular/luteal development in the mammalian ovary, the gene regulation mechanisms involved are still poorly understood. Over the last 10 years, miRNAs have emerged as master regulators of tissue growth and differentiation in animals. However, compared with other body tissues, little is still known about the functional involvement of miRNAs in the ovary. Several studies have identified miRNA populations specifically associated with the development of follicles and corpora lutea, particularly in relation to the follicular-luteal transition, and the functional involvement of some of these miRNAs has been characterised in vitro and/or in vivo. Specifically, three different miRNAs, miR-224, miR-378 and miR-383, have shown to be involved in regulating aromatase expression during follicle development. In addition, miR-21 has been identified as promoting follicular cell survival during ovulation, and pro-angiogenic miR-17-5p and let-7b were shown to be necessary for normal development of the corpus luteum. Experimental evidence for the involvement of several other miRNAs in different aspects of follicle/luteal development has also been obtained. In addition, many of these studies exemplify the challenges associated with identifying physiologically relevant targets of ovarian miRNAs. Continuous advances in this field will be considerably facilitated by progress in understanding miRNA physiology in other body systems and will eventually lead to a much better understanding of the control of follicular/luteal development. In turn, through the potential offered by miRNA diagnostics and miRNA therapeutics, this new knowledge should bring considerable benefits to reproductive medicine.

Liver x receptor modulation of gene expression leading to proluteolytic effects in primate luteal cells

The expressions of genes involved in cholesterol efflux increase, whereas those involved in extracellular cholesterol uptake decrease, during spontaneous functional regression of the primate corpus luteum (CL). This may result from liver x receptor (LXR) alpha (official symbol NR1H3) and/or beta (official symbol NR1H2) control of luteal gene transcription, because these nuclear receptor superfamily members are key regulators of cellular cholesterol homeostasis. Therefore, studies were conducted to assess endogenous LXR ligands in the primate CL through the luteal phase, and to determine the effect of synthetic or natural LXR ligands on cholesterol efflux and uptake in functional primate luteal cells. Using high-performance liquid chromatography tandem mass spectrometry, three LXR ligands were identified and quantified in the rhesus macaque CL, including 22R-hydroxycholesterol (22ROH), 27-hydroxycholesterol (27OH), and desmosterol. Levels of 22ROH paralleled serum progesterone concentrations, whereas mean levels of 27OH tended to be higher following the loss of progesterone synthesis. Desmosterol was present throughout the luteal phase. Functional macaque luteal cells treated with the synthetic LXR agonist T0901317 or physiologically relevant concentrations of the endogenous luteal ligands 22ROH, 27OH, and desmosterol had increased expression of various known LXR target genes and greater cholesterol efflux. Additionally, T0901317 reduced low-density lipoprotein receptor protein and extracellular low-density lipoprotein uptake, whereas 27OH decreased low-density lipoprotein receptor protein, most likely via a posttranslational mechanism. Collectively, these data support the hypothesis that LXR activation causes increased cholesterol efflux and decreased extracellular cholesterol uptake. In theory, these effects could deplete the primate CL of cholesterol needed for steroidogenesis, ultimately contributing to functional regression.

Microarray analysis of the primate luteal transcriptome during chorionic gonadotrophin administration simulating early pregnancy

To explore chorionic gonadotrophin (CG)-regulated gene expression in the primate corpus luteum (CL), adult female rhesus macaques were treated in a model of simulated early pregnancy (SEP). Total RNA was isolated from individual CL after specific intervals of exposure (1, 3, 6 and 9 days) to recombinant hCG in vivo and hybridized to Affymetrix™ GeneChip Rhesus Macaque Genome Arrays. The mRNA levels of 1192 transcripts changed ≥2-fold [one-way ANOVA, false discovery rate (FDR) correction; P< 0.05] during SEP when compared with Day 10 untreated controls. Real-time PCR validation indicated that 15 of 17 genes matched in expression pattern between PCR and microarray. Protein levels of three genes identified as CG-sensitive, CYP19A1 (aromatase), PGRMC1 (progestin-binding protein) and STAR (steroidogenic acute regulatory protein) were quantified by western blot analysis. To further analyze global changes in gene expression induced by CG exposure, luteal gene expression was compared between SEP (rescued) and regressing CL, utilizing previously banked GeneChip data from the luteal phase of the menstrual cycle. Expression patterns and mRNA levels were analyzed between time-matched intervals. Transcripts for 7677 mRNAs differed in expression patterns ≥2-fold (one-way ANOVA, FDR correction; P< 0.05) between the hCG-exposed (SEP) CL and regressing CL. Regressed CL (at menses) were most unlike all other CL. Pathway analysis of significantly affected transcripts was performed; the pathway most impacted by CG exposure was steroid biosynthesis. Further comparisons of the genome-wide changes in luteal gene expression during CG rescue and luteolysis in the natural menstrual cycle should identify additional key regulatory pathways promoting primate fertility.

Deciphering the luteal transcriptome: potential mechanisms mediating stage-specific luteolytic response of the corpus luteum to prostaglandin F2α

The objective of this study was to identify prostaglandin F2α (PG)-induced changes in the transcriptome of bovine corpora lutea (CL) that are specific to mature, PG-responsive (day 11) CL vs. developing (day 4) CL, which do not undergo luteolysis in response to PG administration. CL were collected at 0, 4, and 24 h after PG injection on days 4 and 11 of the estrous cycle ( n = 5 per day and time point), and microarray analysis was performed with GeneChip Bovine Genome Arrays. Data normalization was performed with affy package and significance testing with maanova from Bioconductor. Significance (relative to 0 h time point) was declared at fold change >2.0 or <0.5 and false discovery rate of <5%. At 4 and 24 h after PG, 221 (day 4) and 661 (day 11) and 248 (day 4) and 1,421 (day 11) regulated genes, respectively, were identified. The accentuated gene expression response in day 11 CL was accompanied by specific enrichment of PG-regulated genes in distinctive gene ontology categories (immune related and other), particularly at 24 h after injection. Specificity in putative transcription factor binding sites was observed among PG-regulated genes on day 11 vs. day 4, including a potential association of ETS transcription factors with acute PG-induced gene expression specific to day 11 CL. Temporal and PG-induced regulation of abundance of mRNA for ETS transcription factor family members linked to the stage-specific response to PG was not observed. Increased abundance of protein and/or mRNA for six PG-regulated putative ETS-responsive genes was noted in day 11 but not day 4 CL. Results reveal insight into stage-specific gene expression in bovine CL in response to PG and potential transcriptional mediators of luteolysis.

Analysis of microarray data from the macaque corpus luteum; the search for common themes in primate luteal regression

The factors and processes involved in regression of the primate corpus luteum (CL) are complex and not fully understood. Systemic identification of those genes that are differentially expressed utilizing macaque model systems of luteal regression could help clarify some of the important molecular events involved in loss of primate luteal structure and function during luteolysis. In addition, examining gene pathways involved in luteal regression may help elucidate novel approaches for overcoming infertility or designing ovary-based contraceptives. This review provides an overview of the current published microarray experiments evaluating the transcriptome of the macaque CL, and compares and contrasts the data from spontaneous, GnRH antagonist and prostaglandin F2α-induced luteal regression. In addition, further uses of these databases are discussed, as well as limitations of both array technology and the rhesus macaque genome array.

The reverse cholesterol transport system as a potential mediator of luteolysis in the primate corpus luteum

The cessation of progesterone (P(4)) production (i.e. functional regression), arguably the key event in luteolysis of the primate corpus luteum (CL), is poorly understood. Previously, we found that genes encoding proteins involved in cholesterol uptake decreased, while those involved in cholesterol efflux (reverse cholesterol transport, RCT) increased in expression during spontaneous functional regression of the rhesus macaque CL, thereby potentially depleting the cholesterol reserves needed for steroidogenesis. Therefore, a comprehensive analysis of the components necessary for RCT was performed. RCT components were expressed (mRNA and/or protein) in the macaque CL including cholesterol sensors (liver X receptors alpha or NR1H3; and beta or NR1H2), efflux proteins (ATP-binding cassette subfamilies A1 (ABCA1) and G1), acceptors (apolipoproteins A1 or APOA1; and E or APOE), and plasma proteins facilitating high-density lipoprotein formation (lecithin:cholesterol acyltransferase or LCAT; phospholipid transfer protein or PLTP). ABCA1, APOE, PLTP, and NR1H3 increased, while lipoprotein receptors decreased, in expression (mRNA and/or protein) through the period of functional regression. The expression of APOA1 and APOE, as well as NR1H3, was greatest in the CL and tissues involved in regulating cholesterol homeostasis. Immunolocalization studies revealed that RCT proteins and lipoprotein receptors were expressed in large luteal cells, which possess intracellular cholesterol reserves during periods of P(4) synthesis. Lipid staining revealed changes in luteal cholesterol ester/lipid distribution that occurred following functional regression. These results indicate that decreased cholesterol uptake and increased RCT may be critical for the initiation of primate luteolysis by limiting intracellular cholesterol pools required for steroidogenesis.