Differential expression of two estrogen receptor beta isoforms in the human fetal testis during the second trimester of pregnancy

β-estradiol promotes the growth of primary human fetal spermatogonial stem cells via the induction of stem cell factor in Sertoli cells

BACKGROUND

Mammalian spermatogenesis is responsible for male fertility and is supported by the self-renewal and differentiation of spermatogonial stem cells (SSCs). Sertoli cells provide a supportive microenvironment for SSCs, in part by the production of stem cell factor (SCF), which is a potent regulator of spermatogonia proliferation and survival.

METHODS

We investigated the novel role of β-estradiol in modulating the proliferation and apoptosis of fetal SSCs via the regulation of SCF secretion in Sertoli cells isolated from human fetal testes. The proliferation of SSCs in the co-culture system was determined by colony formation and BrdU incorporation assays. TUNEL assay was used to measure SSC apoptosis in co-culture in response to treatment with control, β-estradiol, or the combination of β-estradiol and the estrogen receptor inhibitor ICI 182780.

RESULTS

In the system with purified human fetal Sertoli cells (MIS+/c-Kit-/AP-), β-estradiol upregulated the production of SCF in a dose- and time-dependent manner. In the co-culture system of primary human fetal SSCs (c-Kit+/SSEA-4+/Oct-4+/AP+) and Sertoli cells (MIS+), β-estradiol markedly increased the proliferation of SSCs. Moreover, SSC apoptosis was significantly inhibited by β-estradiol and was completely reversed by the combination of β-estradiol and ICI 182780.

CONCLUSION

Here we report, for the first time, that β-estradiol can induce the increase of SCF expression in human fetal Sertoli cells and regulates the growth and survival of human fetal SSCs. These novel findings provide new perspectives on the current understanding of the role of estrogen in human spermatogenesis.

Estrogens and development of the rete testis, efferent ductules, epididymis and vas deferens

Estrogen has always been considered the female hormone and testosterone the male hormone. However, estrogen's presence in the testis and deleterious effects of estrogen treatment during development have been known for nearly 90 years, long before estrogen receptors (ESRs) were discovered. Eventually it was learned that testes actually synthesize high levels of estradiol (E2) and sequester high concentrations in the reproductive tract lumen, which seems contradictory to the overwhelming number of studies showing reproductive pathology following exogenous estrogen exposures. For too long, the developmental pathology of estrogen has dominated our thinking, even resulting in the "estrogen hypothesis" as related to the testicular dysgenesis syndrome. However, these early studies and the development of an Esr1 knockout mouse led to a deluge of research into estrogen's potential role in and disruption of development and function of the male reproductive system. What is new is that estrogen action in the male cannot be divorced from that of androgen. This paper presents what is known about components of the estrogen pathway, including its synthesis and target receptors, and the need to achieve a balance between androgen- and estrogen-action in male reproductive tract differentiation and adult functions. The review focuses on what is known regarding development of the male reproductive tract, from the rete testis to the vas deferens, and examines the expression of estrogen receptors and presence of aromatase in the male reproductive system, traces the evidence provided by estrogen-associated knockout and transgenic animal models and discusses the effects of fetal and postnatal exposures to estrogens. Hopefully, there will be enough here to stimulate discussions and new investigations of the androgen:estrogen balance that seems to be essential for development of the male reproductive tract.

Bisphenols Threaten Male Reproductive Health via Testicular Cells

Male reproductive function and health are largely dependent on the testes, which are strictly regulated by their major cell components, i. e., Sertoli, Leydig, and germ cells. Sertoli cells perform a crucial phagocytic function in addition to supporting the development of germ cells. Leydig cells produce hormones essential for male reproductive function, and germ cell quality is a key parameter for male fertility assessment. However, these cells have been identified as primary targets of endocrine disruptors, including bisphenols. Bisphenols are a category of man-made organic chemicals used to manufacture plastics, epoxy resins, and personal care products such as lipsticks, face makeup, and nail lacquers. Despite long-term uncertainty regarding their safety, bisphenols are still being used worldwide, especially bisphenol A. While considerable attention has been paid to the effects of bisphenols on health, current bisphenol-related reproductive health cases indicate that greater attention should be given to these chemicals. Bisphenols, especially bisphenol A, F, and S, have been reported to elicit various effects on testicular cells, including apoptosis, DNA damage, disruption of intercommunication among cells, mitochondrial damage, disruption of tight junctions, and arrest of proliferation, which threaten male reproductive health. In addition, bisphenols are xenoestrogens, which alter organs and cells functions via agonistic or antagonistic interplay with hormone receptors. In this review, we provide in utero, in vivo, and in vitro evidence that currently available brands of bisphenols impair male reproductive health through their action on testicular cells.

Estrogens in Human Male Gonadotropin Secretion and Testicular Physiology From Infancy to Late Puberty

Several reports in humans as well as transgenic mouse models have shown that estrogens play an important role in male reproduction and fertility. Estrogen receptor alpha (ERα) and beta (ERβ) are expressed in different male tissues including the brain. The estradiol-binding protein GPER1 also mediates estrogen action in target tissues. In human testes a minimal ERα expression during prepuberty along with a marked pubertal up-regulation in germ cells has been reported. ERβ expression was detected mostly in spermatogonia, primary spermatocytes, and immature spermatids. In Sertoli cells ERβ expression increases with age. The aromatase enzyme (cP450arom), which converts androgens to estrogens, is widely expressed in human tissues (including gonads and hypothalamus), even during fetal life, suggesting that estrogens are also involved in human fetal physiology. Moreover, cP450arom is expressed in the early postnatal testicular Leydig cells and spermatogonia. Even though the aromatase complex is required for estrogen synthesis, its biological relevance is also related to the regulation of the balance between androgens and estrogens in different tissues. Knockout mouse models of aromatase (ArKO) and estrogen receptors (ERKOα, ERKOβ, and ERKOαβ) provide an important tool to study the effects of estrogens on the male reproductive physiology including the gonadal axis. High basal serum FSH levels were reported in adult aromatase-deficient men, suggesting that estrogens are involved in the negative regulatory gonadotropin feedback. However, normal serum gonadotropin levels were observed in an aromatase-deficient boy, suggesting a maturational pattern role of estrogen in the regulation of gonadotropin secretion. Nevertheless, the role of estrogens in primate testis development and function is controversial and poorly understood. This review addresses the role of estrogens in gonadotropin secretion and testicular physiology in male humans especially during childhood and puberty.

Molecular mechanism of endocrine-disruptive effects induced by Bisphenol A: The role of transmembrane G-protein estrogen receptor 1 and integrin αvβ3

Bisphenol A (BPA) is one of the highest volume industrial products worldwide and has been widely used to make various products as the intermediates of polycarbonate plastics and epoxy resins. Inevitably, general population has been widely exposed to BPA due to extensive use of BPA-containing products. BPA has similar chemical structure with the natural estrogen and has been shown to induce a variety of estrogen-like endocrine effects on organism in vivo or in vitro. High doses of BPA tend to act as antagonist of estrogen receptors (ERs) by directly regulating the genomic transcription. However, BPA at environmentally relevant low-dose always disrupt the biological function via a non-genomic manner mediated by membrane receptors, rather than ERs. Although some studies had investigated the non-genomic effects of low-dose BPA, the exact molecular mechanism still remains unclear. Recently, we found that membrane G protein-coupled estrogen receptor 1 and integrin αvβ3 and its relative signal pathways participate in the induction of male germ cell proliferation and thyroid transcription disruption by the low-dose BPA. A profound understanding for the mechanism of action of the environmentally relevant BPA exposure not only contributes to objectively evaluate and predict the potential influence to human health, but also provides theoretical basis and methodological support for assessing health effects trigged by other estrogen-like environmental endocrine disruptors. Based mainly on our recent findings, this review outlines the research progress of molecular mechanism on endocrine disrupting effects of environmental low-dose BPA, existing problems and some consideration for future studies.

Origin and Differentiation of Androgen-Producing Cells in the Gonads

Sexual reproduction is dependent on the activity of androgenic steroid hormones to promote gonadal development and gametogenesis. Leydig cells of the testis and theca cells of the ovary are critical cell types in the gonadal interstitium that carry out steroidogenesis and provide key androgens for reproductive organ function. In this chapter, we will discuss important aspects of interstitial androgenic cell development in the gonad, including: the potential cellular origins of interstitial steroidogenic cells and their progenitors; the molecular mechanisms involved in Leydig cell specification and differentiation (including Sertoli-cell-derived signaling pathways and Leydig-cell-related transcription factors and nuclear receptors); the interactions of Leydig cells with other cell types in the adult testis, such as Sertoli cells, germ cells, peritubular myoid cells, macrophages, and vascular endothelial cells; the process of steroidogenesis and its systemic regulation; and a brief discussion of the development of theca cells in the ovary relative to Leydig cells in the testis. Finally, we will describe the dynamics of steroidogenic cells in seasonal breeders and highlight unique aspects of steroidogenesis in diverse vertebrate species. Understanding the cellular origins of interstitial steroidogenic cells and the pathways directing their specification and differentiation has implications for the study of multiple aspects of development and will help us gain insights into the etiology of reproductive system birth defects and infertility.

Changes in Estrogen Receptor ERβ (ESR2) Expression without Changes in the Estradiol Levels in the Prostate of Aging Rats

Although the prostate is androgen-dependent, it is also influenced by estrogens, which act via the estrogen receptors ERα and ERβ. In the prostate, ERβ is highly expressed in the epithelium and appears to participate in the regulation of cell proliferation, apoptosis and differentiation. Evidence shows that ERβ is decreased in malignant prostate, suggesting that it plays an important role in protecting this tissue. Despite the relationship between reductions in ERβ and abnormal growth of the gland, little is known about the age-dependent variation of this receptor. Therefore, we aimed to investigate ERβ expression in the prostatic lobes of aging Wistar rats (3 to 24 months). Histopathological alterations, including hyperplasia, intraluminal concretions, nuclear atypia and prostate intraepithelial neoplasias (PIN), were observed in the prostates of aging rats. Epithelial proliferation led to cribriform architecture in some acini, especially in the ventral prostate (VP). In the VP, areas of epithelial atrophy were also observed. Furthermore, in the lateral prostate, there was frequent prostatitis. Immunohistochemistry revealed that the expression of ERβ is reduced in specific areas related to PIN, atrophic abnormalities and cellular atypia in the prostate epithelium of senile rats. Corroborating the involvement of the receptor with proliferative activity, the punctual reduction in ERβ paralleled the increase in cell proliferation especially in areas of PIN and nuclear atypies. The decrease in ERβ reactivity occurred in a hormonal milieu characterized by a constant concentration of estradiol and decreased plasmatic and tissue DHT. This paper is a pioneering study that reveals focal ERβ reduction in the prostate of aging rats and indicates a potential disorder in the ERβ pathway. These data corroborate previous data from humans and dogs that silencing of this receptor may be associated with premalignant or malignant conditions in the prostate.

Nuclear receptors and endocrine disruptors in fetal and neonatal testes: a gapped landscape

During the last decades, many studies reported that male reproductive disorders are increasing among humans. It is currently acknowledged that these abnormalities can result from fetal exposure to environmental chemicals that are progressively becoming more concentrated and widespread in our environment. Among the chemicals present in the environment (air, water, food, and many consumer products), several can act as endocrine disrupting compounds (EDCs), thus interfering with the endocrine system. Phthalates, bisphenol A (BPA), and diethylstilbestrol (DES) have been largely incriminated, particularly during the fetal and neonatal period, due to their estrogenic and/or anti-androgenic properties. Indeed, many epidemiological and experimental studies have highlighted their deleterious impact on fetal and neonatal testis development. As EDCs can affect many different genomic and non-genomic pathways, the mechanisms underlying the adverse effects of EDC exposure are difficult to elucidate. Using literature data and results from our laboratory, in the present review, we discuss the role of classical nuclear receptors (genomic pathway) in the fetal and neonatal testis response to EDC exposure, particularly to phthalates, BPA, and DES. Among the nuclear receptors, we focused on some of the most likely candidates, such as peroxisome-proliferator activated receptor (PPAR), androgen receptor (AR), estrogen receptors (ERα and β), liver X receptors (LXR), and small heterodimer partner (SHP). First, we describe the expression and potential functions (based on data from studies using receptor agonists and mouse knockout models) of these nuclear receptors in the developing testis. Then, for each EDC studied, we summarize the main evidences indicating that the reprotoxic effect of each EDC under study is mediated through a specific nuclear receptor(s). We also point-out the involvement of other receptors and nuclear receptor-independent pathways.

Man is not a big rat: concerns with traditional human risk assessment of phthalates based on their anti-androgenic effects observed in the rat foetus

Phthalates provide one of the most documented example evidencing how much we must be cautious when using the traditional paradigm based on extrapolation of experimental data from rodent studies for human health risk assessment of endocrine disruptors (EDs). Since foetal testis is known as one of the most sensitive targets of EDs, phthalate risk assessment is routinely based on the capacity of such compounds to decrease testosterone production by the testis or to impair masculinization in the rat during foetal life. In this paper, the well-established inhibiting effects of phthalates of the foetal Leydig cells function in the rat are briefly reviewed. Then, data obtained in humans and other species are carefully analysed. Already in January 2009, using the organotypic culture system named Fetal Testis Assay (FeTA) that we developed, we reported that phthalates might not affect testosterone production in human foetal testes. Several recent experimental studies using xenografts confirm the absence of detectable anti-androgenic effect of phthalates in the human foetal testes. Epidemiological studies led to contradictory results. Altogether, these findings suggest that phthalates effects on foetal Leydig cells are largely species-specific. Consequently, the phthalate threshold doses that disturb foetal steroidogenesis in rat testes and that are presently used to define the acceptable daily intake levels for human health protection must be questioned. This does not mean that phthalates are safe because these compounds have many deleterious effects upon germ cell development that may be common to the different studied species including human. More generally, the identification of common molecular, cellular or/and phenotypic targets in rat and human testes should precede the choice of the toxicological endpoint in rat to accurately assess the safety threshold of any ED in humans.

The dynamics of nuclear receptors and nuclear receptor coregulators in the pathogenesis of endometriosis

BACKGROUND

Endometriosis is defined as the colonization and growth of endometrial tissue at anatomic sites outside the uterine cavity. Up to 15% of reproductive-aged women in the USA suffer from painful symptoms of endometriosis, such as infertility, pelvic pain, menstrual cycle abnormalities and increased risk of certain cancers. However, many of the current clinical treatments for endometriosis are not sufficiently effective and yield unacceptable side effects. There is clearly an urgent need to identify new molecular mechanisms that critically underpin the initiation and progression of endometriosis in order to develop more specific and effective therapeutics which lack the side effects of current therapies. The aim of this review is to discuss how nuclear receptors (NRs) and their coregulators promote the progression of endometriosis. Understanding the pathogenic molecular mechanisms for the genesis and maintenance of endometriosis as modulated by NRs and coregulators can reveal new therapeutic targets for alternative endometriosis treatments.

METHODS

This review was prepared using published gene expression microarray data sets obtained from patients with endometriosis and published literature on NRs and their coregulators that deal with endometriosis progression. Using the above observations, our current understanding of how NRs and NR coregulators are involved in the progression of endometriosis is summarized.

RESULTS

Aberrant levels of NRs and NR coregulators in ectopic endometriosis lesions are associated with the progression of endometriosis. As an example, endometriotic cell-specific alterations in gene expression are correlated with a differential methylation status of the genome compared with the normal endometrium. These differential epigenetic regulations can generate favorable cell-specific NR and coregulator milieus for endometriosis progression. Genetic alterations, such as single nucleotide polymorphisms and insertion/deletion polymorphisms of NR and coregulator genes, are frequently detected in ectopic lesions compared with the normal endometrium. These genetic variations impart new molecular properties to NRs and coregulators to increase their capacity to stimulate progression of endometriosis. Finally, post-translational modifications of NR coregulators, such as proteolytic processing, generate endometriosis-specific isoforms. Compared with the unmodified coregulators, these coregulator isoforms have unique functions that enhance the pathogenesis of endometriosis.

CONCLUSIONS

Epigenetic/genetic variations and posttranslational modifications of NRs and coregulators alter their original function so that they become potent 'drivers' of endometriosis progression.

Concerns about the widespread use of rodent models for human risk assessments of endocrine disruptors

Fetal testis is a major target of endocrine disruptors (EDs). During the last 20 years, we have developed an organotypic culture system that maintains the function of the different fetal testis cell types and have used this approach as a toxicological test to evaluate the effects of various compounds on gametogenesis and steroidogenesis in rat, mouse and human testes. We named this test rat, mouse and human fetal testis assay. With this approach, we compared the effects of six potential EDs ((mono-(2-ethylhexyl) phthalate (MEHP), cadmium, depleted uranium, diethylstilboestrol (DES), bisphenol A (BPA) and metformin) and one signalling molecule (retinoic acid (RA)) on the function of rat, mouse and human fetal testis at a comparable developmental stage. We found that the response is similar in humans and rodents for only one third of our analyses. For instance, RA and MEHP have similar negative effects on gametogenesis in the three species. For another third of our analyses, the threshold efficient concentrations that disturb gametogenesis and/or steroidogenesis differ as a function of the species. For instance, BPA and metformin have similar negative effects on steroidogenesis in human and rodents, but at different threshold doses. For the last third of our analyses, the qualitative response is species specific. For instance, MEHP and DES affect steroidogenesis in rodents, but not in human fetal testis. These species differences raise concerns about the extrapolation of data obtained in rodents to human health risk assessment and highlight the need of rigorous comparisons of the effects in human and rodent models, when assessing ED risk.

Diethylstilboestrol exposure does not reduce testosterone production in human fetal testis xenografts

In rodents, in utero exposure to exogenous estrogens including diethylstilboestrol (DES) results in major suppression of steroidogenesis in fetal testes. Whether similar effects occur in the human fetal testis is equivocal. Based on the results of the rodent studies, we hypothesised that exposure of human fetal testes to DES would result in a reduction in testosterone production. We show, using a xenograft approach, that testosterone production is not reduced in human fetal testis following DES exposure. Human fetal testes (15–19 weeks’ gestation, n = 6) were xenografted into castrate male nude mice which were then treated for 35 days with vehicle or 100 µg/kg DES three times a week. For comparison, similar treatment was applied to pregnant rats from e13.5–e20.5 and effects on fetal testes evaluated at e21.5. Xenograft testosterone production was assessed by measuring host seminal vesicle (SV) weights as an indirect measure over the entire grafting period, and single measurement of serum testosterone at termination. Human fetal testis xenografts showed similar survival in DES and vehicle-exposed hosts. SV weight (44.3 v 26.6 mg, p = 0.01) was significantly increased in DES compared to vehicle-exposed hosts, respectively, indicating an overall increase in xenograft testosterone production over the grafting period, whilst serum testosterone at termination was unchanged. In contrast intra-testicular testosterone levels were reduced by 89%, in fetal rats exposed to DES. In rats, DES effects are mediated via Estrogen Receptor α (ESR1). We determined ESR1 protein and mRNA expression in human and rat fetal testis. ESR1 was expressed in rat, but not in human, fetal Leydig cells. We conclude that human fetal testis exposure to DES does not impair testosterone production as it does in rats, probably because ESR1 is not expressed in human fetal Leydig cells. This indicates that DES exposure is likely to pose minimal risk to masculinization of the human fetus.

Differential effects of bisphenol A and diethylstilbestrol on human, rat and mouse fetal leydig cell function

Endocrine disruptors (ED) have been incriminated in the current increase of male reproductive alterations. Bisphenol A (BPA) is a widely used weak estrogenic environmental ED and it is debated whether BPA concentrations within the average internal exposure are toxic. In the present study we investigated the effects of 10(-12) to 10(-5) M BPA concentrations on fetal Leydig cell function, as fetal life is a critical period of sensitivity to ED effects on male reproductive function. To this aim, fetal testes from human at 6.5-10.5 gestational weeks (GW) or from rat and mouse at a comparable critical period of development (14.5 days post-coitum (dpc) for rat and 12.5 dpc for mouse) were explanted and cultured using our validated organotypic culture system in the presence or absence of BPA for 1-3 days. BPA concentrations as low as 10(-8) M reduced testosterone secretion by human testes from day 1 of culture onwards, but not by mouse and rat testes where concentrations equal to 10(-5) M BPA were required. Similarly, 10(-8) M BPA reduced INSL3 mRNA levels only in human cultured testes. On the contrary, 10(-5) and 10(-6) M diethylstilbestrol (DES), a classical estrogenic compound, affected testosterone secretion only in rat and mouse testis cultures, but not in human testis cultures. Lastly, contrarily to the DES effect, the negative effect of BPA on testosterone produced by the mouse fetal testis was maintained after invalidation of estrogen receptor α (ERα). In conclusion, these results evidenced i) a deleterious effect of BPA on fetal Leydig cells function in human for concentrations from 10(-8) M upwards, ii) species-specific differences raising concerns about extrapolation of data from rodent studies to human risk assessment, iii) a specific signaling pathway for BPA which differs from the DES one and which does not involve ERα.

Low concentrations of bisphenol A induce mouse spermatogonial cell proliferation by G protein-coupled receptor 30 and estrogen receptor-α

BACKGROUND

Bisphenol A (BPA) is one of the most prevalent chemicals in daily-use materials; therefore, human exposure to BPA is ubiquitous. The estrogenicity of BPA is generally mediated by nuclear estrogen receptors (ERs). However, low concentrations of BPA stimulate seminoma cell proliferation by an uncertain mechanism that does not involve activation of ERs.

OBJECTIVE

We investigated the possible promoting effects of low-concentration BPA and the possible mechanism(s) using the murine ER-β negative spermatogonial GC-1 cell line.

METHODS AND RESULTS

Using the specific signaling inhibitor, BPA at test concentrations ranging from 10-10 to 10-8 M markedly induced proliferation of GC-1 cells by activating both cGMP-dependent protein kinase (PKG) and epidermal growth factor receptor (EGFR) extracellular regulated kinase (ERK) pathways. BPA stimulated a rapid (15-min) phosphorylation of the transcription factor cAMP response element binding protein (CREB) and the cell cycle regulator retinoblastoma protein (Rb). Interestingly, ER-α phosphorylation is involved in the proliferation, whereas BPA does not directly transactivate ER-α in gene reporter assays. Using specific agonists and gene silencing, we further observed that BPA mediates the proliferation and fos gene expression of GC-1 cells by G protein-coupled receptor 30 (GPR30) and ER-α.

CONCLUSIONS

Our data suggest that low concentrations of BPA activate the PKG and EGFR/ERK/c-fos pathways through a cross-talk between GPR30 and ER-α, which in turn stimulates GC-1 cell proliferation. The present study provides a novel insight regarding the potential role of GPR30 and ER-α in mediating the proliferative effects of BPA in male germ cells.

Oestrogens and spermatogenesis

The role of oestrogens in male reproductive tract physiology has for a long time been a subject of debate. The testis produces significant amounts of oestrogenic hormones, via aromatase, and oestrogen receptors (ERs)alpha (ESR1) and ERbeta (ESR2) are selectively expressed in cells of the testis as well as the epididymal epithelium, depending upon species. This review summarizes the current knowledge concerning the presence and activity of aromatase and ERs in testis and sperm and the potential roles that oestrogens may have in mammalian spermatogenesis. Data show that physiology of the male gonad is in part under the control of a balance of androgens and oestrogens, with aromatase serving as a modulator.

Developmental exposures of male rats to soy isoflavones impact Leydig cell differentiation

Testicular Leydig cells, which are the predominant source of the male sex steroid hormone testosterone, express estrogen receptors (ESRs) and are subject to regulation by estrogen. Following ingestion, the two major isoflavones in soybeans, genistin and daidzin, are hydrolyzed by gut microflora to form genistein and daidzein, which have the capacity to bind ESRs and affect gene expression. Thus, the increasing use of soy-based products as nondairy sources of protein has raised concerns about the potential of these products to cause reproductive toxicity. In the present study, perinatal exposure of male rats to isoflavones induced proliferative activity in Leydig cells. Isoflavones have the capacity to act directly as mitogens in Leydig cells, because genistein treatment induced Leydig cell division in vitro. Genistein action regulating Leydig cell division involved ESRs, acting in concert with signaling molecules in the transduction pathway mediated by protein kinase B (AKT) and mitogen-activated protein kinase (MAPK). Enhanced proliferative activity in the prepubertal period increased Leydig cell numbers, which alleviated deficits in androgen biosynthesis and/or augmented serum and testicular testosterone concentrations in adulthood. Together, these observations indicate that the perinatal exposures of male rats to isoflavones affected Leydig cell differentiation, and they imply that including soy products in the diets of neonates has potential implications for testis function.

Application of laser-assisted microdissection for gene expression analysis of mammalian germ cells

Laser-assisted microdissection (LAM) is an important method to provide new significant insights into many embryological processes. To understand these processes, it is important to obtain specific populations of cells from complex tissue in an efficient and precise manner and to combine with many different molecular biological methods. During the last few years, the sophistication of the techniques of LAM has increased significantly and made the procedure easy to use. New micro-extraction protocols for DNA, RNA and proteins now allow broad downstream applications in the fields of genomics, transcriptomics and proteomics. In this review, we give a short overview of the application of LAM in combination with quantitative qPCR for the analysis of gene expression in mammalian germ cells.

Effects of resveratrol analogs on steroidogenesis and mitochondrial function in rat Leydig cells in vitro

Resveratrol and its analogs are considered to be a promising drug candidate for treatment of cancer and different age-associated diseases. In the present study we have investigated the effects of resveratrol and its synthetic analogs on steroidogenesis and mitochondrial function in primary cultures of rat Leydig cells. Our findings indicate that resveratrol and its analogs structure-dependently attenuated hCG-activated steroidogenesis in Leydig cells through suppression of the expression of steroidogenic acute regulatory protein and cytochrome P450c17. 3,5-Diacetyl resveratrol was observed to modulate mitochondrial function in Leydig cells, suppressing polarization of inner mitochondrial membrane, and 3,4,4'-trimethoxystilbene stimulated the overall activity of intracellular reductases involved in the reduction of WST-1 to formazan. Thus, the inhibitory actions of resveratrol analogs on steroidogenesis in Leydig cells indicate novel mechanisms of action of these compounds, which may be of potential therapeutic interest, where suppression of androgen action is needed.

Steroidogenesis in the fetal testis and its susceptibility to disruption by exogenous compounds

Masculinization depends on adequate production of testosterone by the fetal testis within a specific "masculinization programming window." Disorders resulting from subtle deficiencies in this process are common in humans, and environmental exposures/lifestyle could contribute causally because common therapeutic and environmental compounds can affect steroidogenesis. This evidence derives mainly from rodent studies, but because there are major species differences in regulation of steroidogenesis in the fetal testis, this may not always be a guide to potential effects in the human. In addition to direct study of the effects of compounds on steroidogenesis, information also derives from study of masculinization disorders that result from mutations in genes in pathways regulating steroidogenesis. This review addresses this issue by critically reviewing the comparative timing of production and regulation of steroidogenesis in the fetal testis of humans and of rodents and its susceptibility to disruption; where there is limited information for the fetus, evidence from effects on steroidogenesis in the adult testis is considered. There are a number of fundamental regulatory differences between the human and rodent fetal testis, most notably in the importance of paracrine vs. endocrine drives during masculinization such that inactivating LH receptor mutations block masculinization in humans but not in rodents. Other large differences involve the steroidogenic response to estrogens and GnRH analogs and possibly phthalates, whereas for other compounds there may be differences in sensitivity to disruption (ketoconazole). This comparison identifies steroidogenic targets that are either vulnerable (mitochondrial cholesterol transport, CYP11A, CYP17) or not (cholesterol uptake) to chemical interference.

Estrogen receptors and function in the male reproductive system

A substantial advance in our understanding on the estrogen signaling occurred in the last decade. Estrogens interact with two receptors, ESR1 and ESR2, also known as ERα and ERβ, respectively. ESR1 and ESR2 belong to the nuclear receptor family of transcription factors. In addition to the well established transcriptional effects, estrogens can mediate rapid signaling, triggered within seconds or minutes. These rapid effects can be mediated by ESRs or the G protein-coupled estrogen receptor GPER, also known as GPR30. The effects of estrogen on cell proliferation, differentiation and apoptosis are often mediated by growth factors. The understanding of the cross-talk between androgen, estrogen and growth factors signaling pathways is therefore essential to understand the physiopathological mechanisms of estrogen action. In this review we focused on recent discoveries about the nature of the estrogen receptors, and on the signaling and function of estrogen in the male reproductive system.

Oestrogen receptor splice variants in the pathogenesis of disease

The full-length oestrogen receptor (ER) exists in most vertebrates as two separately encoded isoforms. ER splice variants represent truncated or otherwise modified versions of the full-length alpha or beta isoforms of the parent receptor. ERalpha is found on chromosome 6q and encodes a 595 amino acid protein, while ERbeta is found on chromosome 14q and encodes a 530 amino acid protein. These receptors possess differing ligand affinities, are differentially expressed in a tissue-specific fashion and may act antagonistically. Their altered expression has been implicated in the pathophysiology of a diverse range of conditions from cancer progression in hormone-responsive tissues to neurodegenerative disease. Variously co-expressed with full-length ERs, ER splice variants may have a positive or negative influence on transcription either by modifying the effect of the parent receptor or through their own intrinsic activity. To date, the vast majority of studies have used generic primers or antibodies against the full-length receptors and would not distinguish ER-mediated effects associated with various splice variants. Thus the evidence base of the influence of ER splice variants in normal developmental physiology and in the pathogenesis of disease is weak and greater understanding of their role will undoubtedly lead to new therapeutic strategies for disease intervention and treatment. This review aims to compile the current evidence for the presence of ER splice variants in humans, their physiological roles and clinical sequelae.

The hypogonadal (hpg) mouse as a model to investigate the estrogenic regulation of spermatogenesis

The hypogonadal (hpg) mouse is an excellent animal model in which to investigate the mechanism of action of estrogens on spermatogenesis because it has arrested reproductive development without the need for surgical, endocrine, pharmacological or immunological intervention. Hpg mice are hypogonadotrophic and fail to show normal postnatal testicular development due to the congenital inability to synthesize gonadotropin-releasing hormone in the hypothalamus. The hpg testis remains responsive to gonadotropins and androgens in that fertility can be induced by treatment with these hormones. Surprisingly, chronic treatment with low concentrations of estradiol alone induces qualitatively normal spermatogenesis. The induction of testicular development by estradiol in hpg mice is accompanied by a paradoxical increase in FSH production. The actions of estradiol in hpg mice appear to be via genomic estrogen receptors, as concurrent treatment with estrogen-receptor antagonist ICI182,780 completely blocks these pituitary and testis responses. Concurrent treatment with the androgen receptor antagonist bicalutamide does not affect the estradiol-induced increase in pituitary FSH content, but markedly attenuates the estradiol-induced increase in testicular weight. Western blot analyses and immunohistochemistry provide evidence for estrogen-receptor alpha and beta expression in both pituitary gland and testis of the hpg mouse. Estradiol may therefore exert direct actions within the testes and/or indirect neuroendocrine actions via the release of FSH or other hormones from the pituitary gland, but its actions are dependent upon the availability of low levels of androgen within the testis.

Low doses of bisphenol A promote human seminoma cell proliferation by activating PKA and PKG via a membrane G-protein-coupled estrogen receptor

BACKGROUND

Fetal exposure to environmental estrogens may contribute to hypofertility and/or to testicular germ cell cancer. However, many of these xenoestrogens have only a weak affinity for the classical estrogen receptors (ERs,) which is 1,000-fold less potent than the affinity of 17beta-estradiol (E(2)). Thus, several mechanisms have been suggested to explain how they could affect male germ cell proliferation at low environmental relevant concentrations.

OBJECTIVES

In this study we aimed to explore the possible promoting effect of bisphenol A (BPA) on human testicular seminoma cells. BPA is a well-recognized estrogenic endocrine disruptor used as a monomer to manufacture poly carbonate plastic and released from resin-lined food or beverage cans or from dental sealants.

METHODS AND RESULTS

BPA at very low concentrations (10(-9) to 10(-12) M) similar to those found in human fluids stimulated JKT-1 cell proliferation in vitro. BPA activated both cAMP-dependent protein kinase and cGMP-dependent protein kinase pathways and triggered a rapid (15 min) phosphorylation of the transcription factor cAMP response-element-binding protein (CREB) and the cell cycle regulator retinoblastoma protein (Rb). This nongenomic activation did not involve classical ERs because it could not be reversed by ICI 182780 (an ER antagonist) or reproduced either by E(2) or by diethylstilbestrol (a potent synthetic estrogen), which instead triggered a suppressive effect. This activation was reproduced only by E(2) coupled to bovine serum albumin (BSA), which is unable to enter the cell. As with E(2)-BSA, BPA promoted JKT-1 cell proliferation through a G-protein-coupled nonclassical membrane ER (GPCR) involving a Galpha(s) and a Galpha(i)/Galpha(q) subunit, as shown by the reversible effect observed by the corresponding inhibitors NF449 and pertussis toxin.

CONCLUSION

This GPCR-mediated nongenomic action represents--in addition to the classical ER-mediated effect--a new basis for evaluating xenoestrogens such as BPA that, at low doses and with a high affinity for this GPCR, could interfere with the developmental programming of fetal germ cell proliferation and/or differentiation when they cross the placenta.

Identification of ERbeta1 and ERbeta2 in human seminoma, in embryonal carcinoma and in their adjacent intratubular germ cell neoplasia

BACKGROUND

Estrogens exert a role on germ cell physiology of normal human testis through the mediation of the estrogen receptor (ER) beta subtypes. Epidemiological studies evidenced an increased incidence of testicular germ cell cancer after elevated pre-natal estrogen exposure but the expression of estrogen receptors in these testicular neoplasms has not been well elucidated.

METHODS

Immunohistochemistry and Western blot analysis were used to investigate the expression of three distinct ER isoforms, ERalpha, ERbeta1, and ERbeta2 in paraffin-embedded tissues from seminomas and embryonal carcinomas, which are the most common testicular germ cell tumours.

RESULTS

Neoplastic cells of all specimens revealed a positive ERbeta1 and ERbeta2 immunoreactivity, while the ERalpha signal was undetectable. A similar pattern of estrogen receptor immunostaining was also observed in the malignant germ cells of intratubular germ cell neoplasia, adjacent to testicular cancers. Western blot analysis of tumour extracts revealed two immunoreactive bands, a 59 kDa band for ERbeta1 and a 53 kDa band for ERbeta2.

CONCLUSION

A variable ERbeta expression was previously reported in testicular germ cell tumours and, particularly, an ERbeta down-regulation was evidenced in seminoma and embryonal carcinoma. Conversely, the current study has clearly identified ERbeta1 and ERbeta2 in the neoplastic cells of seminoma and embryonal carcinoma, as well as in the malignant cells of their common pre-invasive precursor, intratubular germ cell neoplasia. Therefore, our findings suggest that ERbeta1, together with a possible ERbeta2 contribute, can mediate estrogen action in both early and late neoplastic testicular germ cells, not confirming the previously hypothesized antiproliferative effect of ERbeta on male gonadal cells.

Distribution of estrogen receptors (ERalpha and ERbeta) and androgen receptor in the testis of big fruit-eating bat Artibeus lituratus is cell- and stage-specific and increases during gonadal regression

The testis is a classical target for androgens, especially testosterone, acting via androgen receptor (AR). Alternatively, androgens can be aromatized to produce estrogens which act via specific receptors ERalpha and ERbeta. Although estrogen action is essential for maintenance of male fertility, studies regarding the expression of ERalpha and ERbeta in testis are restricted to a few species of rodent and domestic animals, but rarely in wild species. To our knowledge, there are no studies in Chiroptera species. Chiroptera represent one of the largest and most diversified orders of mammals, which possess several interesting reproductive features, including higher affinity of SHBG for estrogens than androgens. Therefore, we thought that bats would constitute a good model for investigation of the role of estrogens in the male. In this study, the distribution of ERalpha, ERbeta and AR were evaluated in the testis of the big fruit-eating bat Artibeus lituratus and their levels were compared during reproductive and regressive periods. The results showed that ERalpha and AR were restricted to the somatic cells of the testis, whereas ERbeta was widely distributed in both somatic and spermatogenic cells in a cellular and stage-specific fashion. We demonstrated for the first time by immunohistochemistry, and confirmed by Western blotting, that ERbeta and AR increased during regression. The localization of ERalpha, ERbeta and AR in a seasonal, cell and stage-specific fashion in the testis of A. lituratus suggests that these receptors may play important roles in testis function during reproductive and non-reproductive periods.

Testicular dysgenesis syndrome and the estrogen hypothesis: a quantitative meta-analysis

Male reproductive tract abnormalities such as hypospadias and cryptorchidism, and testicular cancer have been proposed to comprise a common syndrome together with impaired spermatogenesis with a common etiology resulting from the disruption of gonadal development during fetal life, the testicular dysgenesis syndrome (TDS). The only quantitative summary estimate of the link between prenatal exposure to estrogenic agents and testicular cancer was published over 10 years ago; other reviews of the link between estrogenic compounds, other than the potent pharmaceutical estrogen diethylstilbestrol (DES), and TDS end points have remained inconclusive. We conducted a quantitative meta-analysis of the association between the end points related to TDS and prenatal exposure to estrogenic agents. Inclusion in this analysis was based on mechanistic criteria, and the plausibility of an estrogen receptor (ER)-alpha-mediated mode of action was specifically explored. Eight studies were included, investigating the etiology of hypospadias and/or cryptorchidism that had not been identified in previous systematic reviews. Four additional studies of pharmaceutical estrogens yielded a statistically significant updated summary estimate for testicular cancer. Results of the subset analyses point to the existence of unidentified sources of heterogeneity between studies or within the study population.

Application of laser-capture microdissection to analysis of gene expression in the testis

The isolation and molecular analysis of highly purified cell populations from complex, heterogeneous tissues has been a challenge for many years. Spermatogenesis in the testis is a particularly difficult process to study given the unique multiple cellular associations within the seminiferous epithelium, making the isolation of specific cell types difficult. Laser-capture microdissection (LCM) is a recently developed technique that enables the isolation of individual cell populations from complex tissues. This technology has enhanced our ability to directly examine gene expression in enriched testicular cell populations by routine methods of gene expression analysis, such as real-time RT-PCR, differential display, and gene microarrays. The application of LCM has however introduced methodological hurdles that have not been encountered with more conventional molecular analyses of whole tissue. In particular, tissue handling (i.e. fixation, storage, and staining), consumables (e.g. slide choice), staining reagents (conventional H&E vs. fluorescence), extraction methods, and downstream applications have all required re-optimisation to facilitate differential gene expression analysis using the small amounts of material obtained using LCM. This review will discuss three critical issues that are essential for successful procurement of cells from testicular tissue sections; tissue morphology, capture success, and maintenance of molecular integrity. The importance of these issues will be discussed with specific reference to the two most commonly used LCM systems; the Arcturus PixCell IIe and PALM systems. The rat testis will be used as a model, and emphasis will be placed on issues of tissue handling, processing, and staining methods, including the application of fluorescence techniques to assist in the identification of cells of interest for the purposes of mRNA expression analysis.

Estrogens promote human testicular germ cell cancer through a membrane-mediated activation of extracellular regulated kinase and protein kinase A

Clinical and experimental studies have suggested that estrogens, the archetype of female hormones, participate in the control of male germ cell proliferation and that fetal exposure to environmental estrogens may contribute to hypofertility and/or to testicular germ cell cancer. However, the underlying mechanisms remain to be elucidated. 17beta-Estradiol (E2) conjugated to BSA was able to stimulate human testicular seminoma cell proliferation by triggering a rapid, nongenomic, membrane-mediated activation of ERK1/2 and cAMP-dependent protein kinase A (PKA). Both ERK1/2 and PKA participated in this promoting effect. This activation was associated with phosphorylation of the transcription factor cAMP response element-binding protein and the nuclear factor retinoblastoma protein. Enhanced proliferation together with ERK activation could be reversed by pertussis toxin, a G protein inhibitor. Estrogen receptors (ERs) in JKT-1 were characterized by immunofluorescence, subcellular fractioning, and Western blot. JKT-1 cells did not express ERalpha but ERbeta, which localized to the mitochondria and the nucleus but not to the membrane. Moreover, neither ICI-182,780, a classical ER antagonist, nor tamoxifen, a selective ER modulator, could reverse the 17beta-estradiol-BSA-induced promoting effect. Estrogens contribute to human testicular germ cell cancer proliferation by rapid activation of ERK1/2 and PKA through a membrane nonclassical ER. This nongenomic effect represents a new basis for understanding the estrogenic control of spermatogenesis and evaluating the role of fetal exposure to xenoestrogens during malignant transformation of testicular germ stem cells.

Testicular dysgenesis syndrome and the estrogen hypothesis: a quantitative meta-analysis

BACKGROUND

Male reproductive tract abnormalities such as hypospadias and cryptorchidism, and testicular cancer have been proposed to comprise a common syndrome together with impaired spermatogenesis with a common etiology resulting from the disruption of gonadal development during fetal life, the testicular dysgenesis syndrome (TDS). The hypothesis that in utero exposure to estrogenic agents could induce these disorders was first proposed in 1993. The only quantitative summary estimate of the association between prenatal exposure to estrogenic agents and testicular cancer was published over 10 years ago, and other systematic reviews of the association between estrogenic compounds, other than the potent pharmaceutical estrogen diethylstilbestrol (DES), and TDS end points have remained inconclusive.

OBJECTIVES

We conducted a quantitative meta-analysis of the association between the end points related to TDS and prenatal exposure to estrogenic agents. Inclusion in this analysis was based on mechanistic criteria, and the plausibility of an estrogen receptor (ER)-alpha-mediated mode of action was specifically explored.

RESULTS

We included in this meta-analysis eight studies investigating the etiology of hypospadias and/or cryptorchidism that had not been identified in previous systematic reviews. Four additional studies of pharmaceutical estrogens yielded a statistically significant updated summary estimate for testicular cancer.

CONCLUSIONS

The doubling of the risk ratios for all three end points investigated after DES exposure is consistent with a shared etiology and the TDS hypothesis but does not constitute evidence of an estrogenic mode of action. Results of the subset analyses point to the existence of unidentified sources of heterogeneity between studies or within the study population.

17beta-estradiol induces the translocation of the estrogen receptors ESR1 and ESR2 to the cell membrane, MAPK3/1 phosphorylation and proliferation of cultured immature rat Sertoli cells

The aim of the present study was to determine the mechanisms involved in estrogen actions in cultured rat Sertoli cells. RT-PCR detected transcripts for the estrogen receptors ESR1 and ESR2 in cultured immature Sertoli cells and in the testis of 15-, 28-, and 120-day-old rats. The expression of ESR1 and ESR2 was confirmed in Sertoli cells by immunofluorescence and Western blot. Immunohistochemistry with cryosections of testes from immature and adult rats revealed that ESR1 is present in Sertoli, Leydig, and some peritubular myoid cells, and ESR2 is present in multiple cell types, including germ cells. Treatment of Sertoli cells with 17beta-estradiol (E(2)) induced a translocation of ESR1 and ESR2 to the plasma membrane and a concomitant phosphorylation of MAPK3/1. Both effects reached a maximum after 10 min and were blocked by PP2, an inhibitor of the SRC family of protein tyrosine kinases, and by the antiestrogen ICI 182,780 (ICI). MAPK3/1 phosphorylation was also decreased in the presence of AG 1478, an inhibitor of the epidermal growth factor receptor (EGFR) kinase, and in the presence of MAP2K1/2 inhibitor UO126. Treatment with E(2) for 24 h increased the incorporation of [methyl-(3)H]thymidine, which was blocked by ICI. These results indicate that E(2) activates an SRC-mediated translocation of estrogen receptors to the plasma membrane, which results in the activation of EGFR and the mitogen-activated protein kinase signaling pathway. In addition, activation of ESR1 and/or ESR2 by E(2) is involved in proliferation of immature Sertoli cells. The estrogen actions in Sertoli cells might be a key step mediating cellular events important for spermatogenesis and fertility.

Expression of aromatase, estrogen receptor alpha and beta, androgen receptor, and cytochrome P-450scc in the human early prepubertal testis

The expression of aromatase, estrogen receptor alpha (ERalpha) and beta (ERbeta), androgen receptor (AR), and cytochrome P-450 side chain cleavage enzyme (cP450scc) was studied in prepubertal testis. Samples were divided in three age groups (GRs): GR1, newborns (1- to 21-d-old neonates, n = 5); GR2, postnatal activation stage (1- to 7-mo-old infants, n = 6); GR3, childhood (12- to 60-mo-old boys, n = 4). Absent or very poor detection of ERalpha by immunohistochemistry in all cells and by mRNA expression was observed. Leydig cells (LCs) of GR1 and GR2 showed strong immunostaining of aromatase and cP450scc but weak staining of ERbeta and AR. Interstitial cells (ICs) and Sertoli cells (SCs) expressed ERbeta, particularly in GR1 and GR2. Strong expression of AR was found in peritubular cells (PCs). For all markers, expression in GR3 was the weakest. In germ cells (GCs), i.e. gonocytes and spermatogonia, aromatase and ERbeta were immunoexpressed strongly whereas no expression of ERalpha, AR, or cP450scc was detected. It is proposed that in newborn and infantile testis, testosterone acting on PCs might modulate infant LC differentiation, whereas the absence of AR in SCs prevents development of spermatogenesis. The role of estrogen is less clear, but it could modulate the preservation of an adequate pool of precursor LCs and GCs.

Oestrogen receptor beta and neoadjuvant therapy with tamoxifen: prediction of response and effects of treatment

In order to elucidate the relative importance of oestrogen receptor (ER)α, ERβ and an ERβ variant (ERβ2/βcx) in the response of breast cancers to tamoxifen, tumour levels of each receptor were assessed in 36 patients before and after 3 months of neoadjuvant treatment with tamoxifen (20 mg daily). All patients were postmenopausal women presenting with large ERα-positive breast cancers. Clinical response to treatment was assessed by tumour volume changes as determined from sequential ultrasounds and pathological response by comparison of the tumour morphology before and after treatment. Of 33 cases, 23 (70%) were classified as having a clinical response and 16 (48%) as having a response pathologically. All tumours stained positively for ERα and ERβ and 15 out of 33 (45%) for ERβ2/βcx. There were no significant differences in quantitative expression of any receptor between tumours that subsequently responded and that did not, whether response was assessed clinically or pathologically. Tamoxifen treatment was associated with a decrease in ERα, but an increase was the most frequent change (17 out of 33) in ERβ, and no consistent change was evident in staining of the ERβ2/βcx variant. In summary, ERβ1 and ERβ2/βcx variant protein are detected in ERα-positive breast tumours but their expression is not associated with a response to tamoxifen. Differential changes in ERα and ERβ were seen with treatment.

Developmental model for the pathogenesis of testicular carcinoma in situ: genetic and environmental aspects

Carcinoma in situ testis (CIS), also known as intratubular germ cell neoplasia (ITGCN), is a pre-invasive precursor of testicular germ cell tumours, the commonest cancer type of male adolescents and young adults. In this review, evidence supporting the hypothesis of developmental origin of testicular germ cell cancer is summarized, and the current concepts regarding aetiology and pathogenesis of this disease are critically discussed. Comparative studies of cell surface proteins (e.g. PLAP and KIT), some of the germ cell-specific markers (e.g. MAGEA4, VASA, TSPY and NY-ESO-1), supported by studies of regulatory elements of the cell cycle (e.g. p53, CHK2 and p19-INK4d) demonstrated a close similarity of CIS to primordial germ cells and gonocytes, consistent with the pre-meiotic origin of CIS. Recent gene expression profiling studies showed that CIS cells closely resemble embryonic stem cells (ESCs). The abundance of factors associated with pluripotency (NANOG and OCT-3/4) and undifferentiated state (AP-2gamma) may explain the remarkable pluripotency of germ cell neoplasms, which are capable of differentiating to various somatic tissue components of teratomas. Impaired gonadal development resulting in the arrest of gonocyte differentiation and retention of its embryonic features, associated with an increasing genomic instability, is the most probable model for the pathogenesis of CIS. Genomic amplification of certain chromosomal regions, e.g. 12p, may facilitate survival of CIS and further invasive progression. Genetic studies, have so far not identified gene polymorphisms predisposing to the most common non-familial testicular cancer, but this research has only recently begun. Association of CIS with other disorders, such as congenital genital malformations and some forms of impaired spermatogenesis, all rising in incidence in a synchronous manner, led to the hypothesis that CIS might be a manifestation of testicular dysgenesis syndrome (TDS). The aetiology of TDS including testicular cancer remains to be elucidated, but epidemiological trends suggest a primary role for environmental factors, probably combined with genetic susceptibility.

Estrogen regulation of testicular function

Evidence supporting a role for estrogen in male reproductive tract development and function has been collected from rodents and humans. These studies fall into three categories: i) localization of aromatase and the target protein for estrogen (ER-alpha and ER-beta) in tissues of the reproductive tract; ii) analysis of testicular phenotypes in transgenic mice deficient in aromatase, ER-alpha and/or ER-beta gene; and, iii) investigation of the effects of environmental chemicals on male reproduction. Estrogen is thought to have a regulatory role in the testis because estrogen biosynthesis occurs in testicular cells and the absence of ERs caused adverse effects on spermatogenesis and steroidogenesis. Moreover, several chemicals that are present in the environment, designated xenoestrogens because they have the ability to bind and activate ERs, are known to affect testicular gene expression. However, studies of estrogen action are confounded by a number of factors, including the inability to dissociate estrogen-induced activity in the hypothalamus and pituitary from action occurring directly in the testis and expression of more than one ER subtype in estrogen-sensitive tissues. Use of tissue-specific knockout animals and administration of antiestrogens and/or aromatase inhibitors in vivo may generate additional data to advance our understanding of estrogen and estrogen receptor biology in the developing and mature testis.

ERbeta protein expression in female cynomolgus monkey and CF-1 mouse brain: Western analysis

In humans and rodents, multiple ERbeta variants with sizes ranging from 477-549 amino acids (aa) have been described. The identification of these variants in target tissues has important implications for estrogen signaling and cellular responsiveness. Western blot analysis using two anti-ERbeta antibodies specific for mammalian ERbeta sequences (PA1-310B and PA1-311) was employed to examine ERbeta protein expression in neural tissues from ovariectomized (OVX) cynomolgus macaques and CF-1 mice as well as to assess potential regulatory effects of acute and extended estradiol (E(2)) treatment. In hypothalamic extracts from both species, a single ERbeta immunoreactive (ERbeta-ir) band was detected at approximately 54 kDa, corresponding to the expected molecular weight for ERbeta477 and/or 485. In cynomolgus females, oral E(2) administration for 16 weeks had no apparent effect on hypothalamic ERbeta protein expression. In mouse, a single injection of E(2) did not change hypothalamic ERbeta protein levels 1.5, 4, 8, 16, or 24 h after injection. Extending the hormonal treatment to 4 or 21 days in OVX female mice also had no effect on the level of hypothalamic ERbeta protein. Additional regional analyses in female mouse brain with PA1-310B antibody showed that a second, 59 kDa ERbeta-ir band was present in cortex, striatum, hippocampus, and amygdala that could represent one or both of the larger ERbeta variants (530 and 549aa). The expression level of the second ERbeta isoform exhibited regional variation, with the strongest immunoreactivity detected in cortex and amygdala. Elucidating the functions of these ERbeta isoforms in the CNS will facilitate our understanding of the tissue- and promoter-specific actions of estrogen.

Differential expression of estrogen receptors (ERalpha/ERbeta) in testis of mature and immature pigs

High affinity estrogen receptors (ERs) mediate estrogen action in male reproductive tissues. The objective of the present study was the immunolocalization of estrogen receptor alpha and estrogen receptor beta in immature and mature testes of pig, a species in which the role of estrogens on gonadal function is scarcely known. Testes from 3 and 18 month-old pigs were investigated. Immunohistochemistry was performed on paraffin embedded-tissues using both mouse anti-human monoclonal IgG ERalpha and IgG ERbeta 1 isoform. Western blot analysis demonstrated antibody specificity. ERalpha staining was not observed in immature testes, but it was detected in spermatogonia, spermatocytes and in the most Leydig cells of mature testes. ERbeta immunoreactivity was observed in spermatogonia and Leydig cells of immature gonads, while it was clearly detected in spermatogonia and in spermatocytes of adult pig testes. The differential ERalpha/ERbeta expression in germ and somatic cells of the gonads suggest a role of estrogens in function and in development of pig testis.

Transcription Factor AP-2γ Is a Developmentally Regulated Marker of Testicular CarcinomaIn situand Germ Cell Tumors

PURPOSE

Transcription factor activator protein-2gamma (TFAP2C, AP-2gamma) was reported previously in extraembryonic ectoderm and breast carcinomas but not in the testis. In our recent gene expression study we detected AP-2gamma in carcinoma in situ testis (CIS, or intratubular germ cell neoplasia), precursor of testicular germ cell tumors. In this study we aimed to investigate the expression pattern of AP-2gamma and to shed light on this factor in germ cell differentiation and the pathogenesis of germ cell neoplasia.

EXPERIMENTAL DESIGN

We analyzed expression pattern of AP-2gamma at the RNA and protein level in normal human tissues and a panel of tumors and tumor-derived cell lines. In the gonads, we established the ontogeny of expression of AP-2gamma in normal and dysgenetic samples. We also investigated the regulation of AP-2gamma by steroids and retinoic acid.

RESULTS

We detected abundant AP-2gamma in testicular CIS and in testicular germ cell tumors of young adults and confirmed differential expression of AP-2gamma in somatic tumors. We found that AP-2gamma expression was regulated by retinoic acid in an embryonal carcinoma cell line (NT2). The investigation of ontogeny of AP-2gamma protein expression in fetal gonads revealed that it was confined to oogonia/gonocytes and was down-regulated with germ cell differentiation. In some prepubertal intersex cases, AP-2gamma was detected outside of the normal window of expression, probably marking neoplastic transformation of germ cells.

CONCLUSIONS

AP-2gamma is developmentally regulated and associated with the undifferentiated phenotype in germ cells. This transcription factor may be involved in self-renewal and survival of immature germ cells and tissue-specific stem cells. AP-2gamma is a novel marker of testicular CIS and CIS-derived tumors.

Estrogen Receptor β Expression and Apoptosis of Spermatocytes of Mice Overexpressing a Rat Androgen-Binding Protein Transgene1

Progression of the first meiotic division in male germ cells is regulated by a variety of factors, including androgens and possibly estrogens. When this regulation fails, meiosis is arrested and primary spermatocytes degenerate by apoptosis. Earlier studies showed that overexpression of rat androgen-binding protein (ABP) in the testis of transgenic mice results in a partial meiotic arrest and apoptosis of pachytene spermatocytes. In view of the recent localization of estrogen receptor beta (ERbeta) in primary spermatocytes and data suggesting the ability of ERbeta to repress cellular proliferation, we tested the hypothesis that variations in the testicular steroid microenvironment caused by excess ABP produce changes in ERbeta expression in this cellular type that could be associated to the meiotic arrest and, eventually, to the induction of germ cell apoptosis observed in the ABP transgenic mice. Increased levels of ERbeta mRNA and protein were demonstrated in the testis of rat ABP transgenic mice compared with nontransgenic littermates by reverse transcriptase-polymerase chain reaction (RT-PCR) experiments, Northern blotting, and Western Blotting. The major differences were found when isolated germ cells of transgenic and nontransgenic littermates were analyzed by RT-PCR. In keeping with this finding, ERbeta was strongly immunolabeled in pachytene spermatocytes of rat ABP transgenic mice and localized in tubular stages in which TUNEL labeling was maximal. Confocal microscopy analysis of a fluorescent TUNEL assay and ERbeta immunohistochemistry revealed that degenerating pachytene spermatocytes overexpressed ERbeta. The present results are consistent with the interpretation that ERbeta is associated with the events that regulate negatively the progression of meiosis or that lead to spermatocyte apoptosis.

Prenatal estrogen exposure differentially affects estrogen receptor-associated proteins in rat testis gonocytes

We previously reported that gonocytes from 3-day-old rat testes proliferate in response to estradiol. In the present study, we found that purified gonocytes contained the mRNAs of estrogen receptor beta (ERbeta) and the chaperones Hsp90, p23, and Cyp40, but no inducible Hsp70. Immunoblot analysis showed high levels of ERbeta, Hsp90, p23, Cyp40, and the constitutive Hsc70 in gonocytes. Prenatal exposure to the estrogenic compounds diethylstilbestrol, bisphenol A, genistein, and coumestrol led to significantly increased Hsp90 mRNA levels in testis, but not p23 and Cyp40. In situ hybridization analysis indicated that Hsp90 mRNA was prominent in gonocytes, where it was increased following phytoestrogen exposure, whereas bisphenol A induced a more generalized increase throughout the testis. Immunoblot analysis of testicular extracts demonstrated that Hsp90 protein levels were significantly increased following estrogen exposure, and immunohistochemical analysis indicated that this increase occurred predominantly in gonocytes. By contrast, no change was observed in the expression of Cyp40, p23, and ERbeta, whereas Hsc70 was increased by bisphenol A only. Using an antibody and reverse transcriptase-polymerase chain reaction probes specific for Hsp90alpha, we subsequently confirmed that Hsp90alpha was primarily expressed in gonocytes, and that it was increased following estrogen exposure. Hsp90 immunolocalization in fetal and prepubertal testes showed an increased expression in fetal gonocytes upon estrogen exposure, but no difference in the subsets of Hsp90-positive germ cells in prepubertal testes. These results demonstrate that prenatal estrogen exposure specifically affects Hsp90 expression in gonocytes. Considering the interaction of Hsp90 with several signaling molecules, changes in its expression levels may lead to subsequent changes in gonocyte development.

Small nuclear RING finger protein expression during gonad development: regulation by gonadotropins and estrogen in the postnatal ovary

Small nuclear RING finger protein (SNURF/RNF4) is a steroid receptor coregulator that is down-regulated in testicular germ cell cancer. In this work, we examined SNURF expression during murine fetal gonad development and postnatal ovarian folliculogenesis by in situ hybridization and immunohistochemical staining. SNURF mRNA was detectable in gonads of both sexes from embryonic 10.5 days post conception onward. SNURF protein localized to gonocytes and somatic Leydig and Sertoli cells of fetal testis and in oogonia and supporting cells of fetal ovary. In murine postnatal ovary, SNURF mRNA and protein were expressed throughout folliculogenesis, peaking in the oocytes of preantral follicles. Lower amounts of SNURF mRNA and protein were also present in granulosa cells of secondary, antral, and preovulatory follicles and in luteal glands. Exposure of immature female mice and rats to gonadotropin from pregnant mare serum and human chorionic gonadotropin did not change dramatically SNURF mRNA levels in ovary. SNURF mRNA expression was increased in ovaries of immature mice treated with diethylstilbestrol, an effect that was blocked by the pure antiestrogen ICI 182,780. SNURF protein was constitutively expressed in oocytes of hypophysectomized rats, and its content was augmented by estradiol in granulosa cells. In granulosa cell culture, SNURF mRNA accumulation was transiently increased by treatment with the LH agonists phorbol myristate and forskolin at 4 h after treatment and at 48 h in differentiated cells expressing markers of the preovulatory phenotype. These results suggest a role for SNURF in fetal germ cell development as well as in oocyte and granulosa cell maturation in an estrogen- and gonadotropin-regulated fashion.

Expression of Estrogen Receptors α and β in the Fetal Baboon Testisand Epididymis1

Although studies in transgenic mice suggest that estrogen is important for development of the testis, very little is known about the potential role of estrogen in maturation of the primate fetal testis. Therefore, as a first step to determine whether estrogen regulates maturation of the fetal primate testis, we used immunocytochemistry to determine estrogen receptor (ER) alpha and beta expression in the fetal baboon testis. Second, we established methods to quantify ERbeta mRNA levels by competitive reverse transcription-polymerase chain reaction in Sertoli cells isolated by laser capture microdissection (LCM) from the fetal baboon testis. ERbeta protein expression was abundant in the nuclei of Sertoli, peritubular, and interstitial cells in baboon fetuses at mid (Day 100) and late (Day 165) gestation (term is 184 days). ERbeta mRNA level was 0.03 attomole/femtomole 18S rRNA in Sertoli cell nuclei and associated cytoplasm isolated by LCM. ERalpha was expressed in low level in seminiferous tubules and in moderate level in peritubular cells on Day 165. Germ cells expressed very little ERalpha or ERbeta protein, whereas the baboon fetal epididymis exhibited extensive ERalpha and ERbeta immunostaining at mid- and late gestation. In contrast to the robust expression of ERbeta, androgen receptor protein was not demonstrable within the cells of the seminiferous cords but was abundantly expressed in epididymal epithelial cells of the fetal baboon. In summary, the results of this study show that the fetal baboon testis and epididymis expressed the ERalpha and ERbeta, and we suggest that our nonhuman primate baboon model can be used to study the potential role of estrogen on maturation of the fetal testis.

Inhibition of testicular steroidogenesis by the xenoestrogen bisphenol A is associated with reduced pituitary luteinizing hormone secretion and decreased steroidogenic enzyme gene expression in rat Leydig cells

Exposure of humans to bisphenol A (BPA), a monomer in polycarbonate plastics and a constituent of resins used in food packaging and dentistry, is significant. In this report exposure of rats to 2.4 microg/kg.d (a dose that approximates BPA levels in the environment) from postnatal d 21-35 suppressed serum LH (0.21 +/- 0.05 ng/ml; vs. control, 0.52 +/- 0.04; P < 0.01) and testosterone (T) levels (1.62 +/- 0.16 ng/ml; vs. control, 2.52 +/- 0.21; P < 0.05), in association with decreased LHbeta and increased estrogen receptor beta pituitary mRNA levels as measured by RT-PCR. Treatment of adult Leydig cells with 0.01 nm BPA decreased T biosynthesis by 25% as a result of decreased expression of the steroidogenic enzyme 17alpha-hydroxylase/17-20 lyase. BPA decreased serum 17beta-estradiol levels from 0.31 +/- 0.02 ng/ml (control) to 0.22 +/- 0.02, 0.19 +/- 0.02, and 0.23 +/- 0.03 ng/ml in rats exposed to 2.4 microg, 10 microg, or 100 mg/kg.d BPA, respectively, from 21-35 d of age (P < 0.05) due to its ability to inhibit Leydig cell aromatase activity. Exposures of pregnant and nursing dams, i.e. from gestation d 12 to postnatal d 21, decreased T levels in the testicular interstitial fluid from 420 +/- 34 (control) to 261 +/- 22 (P < 0.05) ng/ml in adulthood, implying that the perinatal period is a sensitive window of exposure to BPA. As BPA has been measured in several human populations, further studies are warranted to assess the effects of BPA on male fertility.