Retinoic acid (RA) represses follicle stimulating hormone (FSH)-induced luteinizing hormone (LH) receptor in rat granulosa cells

Retinoic acid (all-trans) presents antioxidant properties within human ovary and reduces progesterone production by human granulosa cells

Both vitamin A and E support female reproduction and embryonic development. These vitamins have been associated with decreased fertility or failure to end the pregnancy in animals. An observational study was conducted on follicular fluid (FF) samples to determine the concentrations of fat-soluble vitamins of women undergoing in vitro fertilization and its correlation with assisted reproductive technology characteristics and pregnancy outcomes. Moreover, the effects of all-trans-retinoic acid (atRA) and alpha-tocopherol on granulosa cell viability, apoptosis, autophagy and hormonal production were evaluated. No association was identified between fat-soluble vitamin concentrations in FF and infertility aetiology, body mass index or woman's age. There were differences in follicular antioxidant profiles and ovarian response stimulation. In vitro evaluation of atRA and alpha-tocopherol reveals that, at physiological concentrations, both compounds may affect the viability of granulosa cells. In addition, these compounds are able to protect granulosa cells from oxidative stress, as well as to affect estradiol and progesterone production. Our data suggest that atRA and alpha-tocopherol levels should be well controlled as they may have implications in the function and viability of granulosa cells and highlights retinol as a marker of the oxidative defenses within ovary environment.

Nuclear receptors: Key regulators of somatic cell functions in the ovulatory process

The development of the ovarian follicle to its culmination by ovulation is an essential element of fertility. The final stages of ovarian follicular growth are characterized by granulosa cell proliferation and differentiation, and steroid synthesis under the influence of follicle-stimulating hormone (FSH). The result is a population of granulosa cells poised to respond to the ovulatory surge of luteinizing hormone (LH). Members of the nuclear receptor superfamily of transcription factors play indispensable roles in the regulation of these events. The key regulators of the final stages of follicular growth that precede ovulation from this family include the estrogen receptor beta (ESR2) and the androgen receptor (AR), with additional roles for others, including steroidogenic factor-1 (SF-1) and liver receptor homolog-1 (LRH-1). Following the LH surge, the mural and cumulus granulosa cells undergo rapid changes that result in expansion of the cumulus layer, and a shift in ovarian steroid hormone biosynthesis from estradiol to progesterone production. The nuclear receptor best associated with these events is LRH-1. Inadequate cumulus expansion is also observed in the absence of AR and ESR2, but not the progesterone receptor (PGR). The terminal stages of ovulation are regulated by PGR, which increases the abundance of the proteases that are directly responsible for rupture. It further regulates the prostaglandins and cytokines associated with the inflammatory-like characteristics of ovulation. LRH-1 regulates PGR, and is also a key regulator of steroidogenesis, cellular proliferation, and cellular migration, and cytoskeletal remodeling. In summary, nuclear receptors are among the panoply of transcriptional regulators with roles in ovulation, and several are necessary for normal ovarian function.

Retinoic acid signaling in ovarian folliculogenesis and steroidogenesis

Retinoids are essential for reproduction. Most research has focused on the role of retinoic acid signaling in the regulation of meiosis during early fetal germ cell development. However, less attention has been paid to the possible effects of retinoic acid signaling in adult female gonads. Retinoic acid, its receptors, and the key enzymes required for retinoic acid synthesis are expressed in the ovaries and they are involved in the regulation of folliculogenesis and steroidogenesis. Exposure to compounds that can interfere with normal retinoic acid signaling is associated with adverse ovarian outcomes, including altered steroidogenesis and reduction in indicators of ovarian reserve in women and laboratory animal models. These observations call for more attention to retinoids as regulators of adult ovarian physiology and as possible targets of endocrine disruption by environmental chemicals. In this review, we summarize the current knowledge of retinoids in folliculogenesis and steroidogenesis in post-pubertal mammalian ovaries.

Retinoic acid signaling is dispensable for somatic development and function in the mammalian ovary

Retinoic acid (RA) is a potent inducer of cell differentiation and plays an essential role in sex-specific germ cell development in the mammalian gonad. RA is essential for male gametogenesis and hence fertility. However, RA can also disrupt sexual cell fate in somatic cells of the testis, promoting transdifferentiation of male Sertoli cells to female granulosa-like cells when the male sexual regulator Dmrt1 is absent. The feminizing ability of RA in the Dmrt1 mutant somatic testis suggests that RA might normally play a role in somatic cell differentiation or cell fate maintenance in the ovary. To test for this possibility we disrupted RA signaling in somatic cells of the early fetal ovary using three genetic strategies and one pharmaceutical approach. We found that deleting all three RA receptors (RARs) in the XX somatic gonad at the time of sex determination did not significantly affect ovarian differentiation, follicle development, or female fertility. Transcriptome analysis of adult triple mutant ovaries revealed remarkably little effect on gene expression in the absence of somatic RAR function. Likewise, deletion of three RA synthesis enzymes (Aldh1a1-3) at the time of sex determination did not masculinize the ovary. A dominant-negative RAR transgene altered granulosa cell proliferation, likely due to interference with a non-RA signaling pathway, but did not prevent granulosa cell specification and oogenesis or abolish fertility. Finally, culture of fetal XX gonads with an RAR antagonist blocked germ cell meiotic initiation but did not disrupt sex-biased gene expression. We conclude that RA signaling, although crucial in the ovary for meiotic initiation, is not required for granulosa cell specification, differentiation, or reproductive function.

Endogenous acetaldehyde toxicity during antral follicular development in the mouse ovary

The biosynthesis of androgens requires multiple steps and during the conversion of pregnenolone to 17α-hydroxypregnenolone and dehydroepiandrosterone (DHEA) by CYP17a1. Acetaldehyde is potentially formed as a by-product in theca cells during antral follicular development. In this study, acetaldehyde level was significantly increased after eCG stimulation and reached a maximum level at 36-h post-eCG. By 48 h, the level of acetaldehyde decreased in association with the induction of aldehyde dehydrogenase (ALDH) type 1 family members. When immature mice were co-injected with the ALDH inhibitor, cyanamide, and eCG, the expression of genes involved in the differentiations of granulosa cells was suppressed and the number of ovulated oocytes was reduced. The in vitro studies showed that ALDH inhibitors prevented FSH-induced granulosa cell differentiation. These results indicate that acetaldehyde is generated as a by-product during steroidogenesis and can exert toxic effects to impair the differentiation of granulosa cells, reduce ovulation and decrease oocyte quality.

Autoantigens in ovarian autoimmunity associated with unexplained infertility and premature ovarian failure

OBJECTIVE

To identify ovarian autoantigens associated with ovarian autoantibodies.

DESIGN

Hypothesis-generating prospective study.

SETTING

Urban infertility referral centers and academic research institution.

PATIENT(S)

Seventy-four patients with infertility, 19 patients with premature ovarian failure (POF), and 16 healthy control women.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Identification of autoantigens.

RESULT(S)

To identify major antigens for ovarian autoimmunity, sera from 74 women with unexplained infertility were screened for ovarian autoantibodies (AOAs) by immunoassay and one-dimensional Western blot. The majority of sera had immunoreactions at 50-56 kDa. Six representative positive infertility sera were used to identify antigens between 40 and 60 kD by two-dimensional Western blot and mass spectrometry. Antigens included aldehyde (retinal) dehydrogenases (ALDH1A1, ALDH1A2, and ALDH7A1), protein disulfide isomerase A3, vimentin, α-enolase, phosphoglycerate dehydrogenase, and selenium-binding protein 1 (SBP1). Sixty percent (24 out of 40) of infertility and POF sera were positive for recombinant ALDH1A1, SBP1, or enolase; 80.7% (21 out of 26) of AOA-positive sera had antibodies to one or more of the three antigens, and only 7% (1 out of 14) of AOA-negative sera had antibodies to recombinant proteins.

CONCLUSION(S)

ALDH1A1 and SBP1 are unique to ovarian autoimmunity associated with infertility and POF, and may provide the basis for specific tests to identify patients with ovarian autoimmunity.

Bovine Early Embryonic Development and Vitamin A

Vitamin A and its derivatives, collectively termed as retinoids, have been paid attention in recent years because of their effects in bovine reproduction. However, the role of retinoids in the pre-implantation period continues to be largely unexplored, in contrast to later stages of development. Retinoids control cell growth, differentiation and death through binding to specific nuclear receptors by retinoic acid and other active metabolites. This paper reviews how retinoids can influence early embryonic development in cattle through their influence on the follicle, the extrafollicular oocyte and the pre-implantation embryo itself.

The Roles of Vitamin A for Cytoplasmic Maturation of Bovine Oocytes

Vitamin A is one of the micronutrients which have been implicated in cattle reproduction. In cattle, ingested vitamin A, mainly as beta-carotene (BC) from forages and retinol ester from formula feed, is metabolized and transported to the oocytes and cumulus-granulosa cells in ovarian follicles through binding to various interacting molecules. The active form of vitamin A, retinoic acid (RA), functions as a regulator of gene expression in these targets. Early research showed the positive effects of vitamin A supplementation on bovine fertility in artificial insemination, and several studies on effects of vitamin A metabolites used in other artificial reproductive techniques (ART), including superovulation, ovum pick up, and in vitro maturation culture have provided evidence for the specific roles of vitamin A in oocyte cytoplasmic maturation (acquisition of developmental competence of oocytes during their meiotic maturation period for the embryonic development after fertilization). BC may enhance cytoplasmic maturation by its antioxidant properties which cannot be replaced by RA. Furthermore, RA may promote cytoplasmic maturation of bovine oocytes via its modulatory effects on the gene expression of gonadotrophin receptors, midkine, cyclooxygenase-2, and nitric oxide synthase in cumulus-granulosa cells.

The molecular signature of polycystic ovary syndrome (PCOS) theca cells defined by gene expression profiling

Polycystic ovary syndrome (PCOS) is characterized by increased ovarian androgen secretion, anovulatory infertility due to arrested folliculogenesis, and is frequently found in association with insulin resistance and obesity. Characterization of PCOS theca cells demonstrated that elevated expression of the steroidogenic enzymes 17alpha hydroxylase/17,20 lyase (CYP17) and P450 side chain cleavage enzyme (CYP11A1) play a role in increased androgen production by 3beta-hydroxysteroid dehydrogenase in the PCOS theca cell. However, the gene networks and signal transduction pathways which cause the altered expansion of the steroid enzymes remain to be determined. In order to identify these gene networks and/or signaling pathways, we carried out global gene expression profiling of normal and PCOS theca cells using subtractive suppressive hybridization and oligonucleotide microarray analysis. These analyses demonstrated that approximately 2% of genes expressed in the theca cell exhibit altered mRNA abundance in PCOS. Characterization of these genes revealed that retinoic acid synthesis and Wnt signal transduction are altered in the PCOS theca cell. In addition, the transcription factor GATA6, which regulates the promoter activity of CYP17 and CYP11A, was increased in the PCOS compared to normal theca cells. Thus, global gene expression profiling has identified potential pathways which may determine the PCOS theca cell phenotype.

The molecular phenotype of polycystic ovary syndrome (PCOS) theca cells and new candidate PCOS genes defined by microarray analysis

Polycystic ovary syndrome (PCOS) affects 5% of reproductive aged women and is the leading cause of anovulatory infertility. A hallmark of PCOS is excessive theca cell androgen secretion, which is directly linked to the symptoms of PCOS. Our previous studies demonstrated that theca cells from PCOS ovaries maintained in long term culture persistently secrete significantly greater amounts of androgens than normal theca cells, suggesting an intrinsic abnormality. Furthermore, previous studies suggested that ovarian hyperandrogenemia is inherited as an autosomal dominant trait. However, the genes responsible for ovarian hyperandrogenemia of PCOS have not been identified. In this present study, we carried out microarray analysis to define the gene networks involved in excess androgen synthesis by the PCOS theca cells in order to identify candidate PCOS genes. Our analysis revealed that PCOS theca cells have a gene expression profile that is distinct from normal theca cells. Included in the cohort of genes with increased mRNA abundance in PCOS theca cells were aldehyde dehydrogenase 6 and retinol dehydrogenase 2, which play a role in all-trans-retinoic acid biosynthesis and the transcription factor GATA6. We demonstrated that retinoic acid and GATA6 increased the expression of 17alpha-hydroxylase, providing a functional link between altered gene expression and intrinsic abnormalities in PCOS theca cells. Thus, our analyses have 1) defined a stable molecular phenotype of PCOS theca cells, 2) suggested new mechanisms for excess androgen synthesis by PCOS theca cells, and 3) identified new candidate genes that may be involved in the genetic etiology of PCOS.