Ontogenesis of the in vitro response of rat testis to gonadotropin-releasing hormone

Six Decades of Research on Human Fetal Gonadal Steroids

Human fetal gonads acquire endocrine steroidogenic capabilities early during their differentiation. Genetic studies show that this endocrine function plays a central role in the sexually dimorphic development of the external genitalia during fetal development. When this endocrine function is dysregulated, congenital malformations and pathologies are the result. In this review, we explain how the current knowledge of steroidogenesis in human fetal gonads has benefited from both the technological advances in steroid measurements and the assembly of detailed knowledge of steroidogenesis machinery and its expression in human fetal gonads. We summarise how the conversion of radiolabelled steroid precursors, antibody-based assays, mass spectrometry, ultrastructural studies, and the in situ labelling of proteins and mRNA have all provided complementary information. In this review, our discussion goes beyond the debate on recommendations concerning the best choice between the different available technologies, and their degrees of reproducibility and sensitivity. The available technologies and techniques can be used for different purposes and, as long as all quality controls are rigorously employed, the question is how to maximise the generation of robust, reproducible data on steroid hormones and their crucial roles in human fetal development and subsequent functions.

Determination of Endocrine Disruption Potential of Bisphenol A Alternatives in Food Contact Materials Using In Vitro Assays: State of the Art and Future Challenges

Alternatives to bisphenol A (BPA) are developed for food contact materials as a result of increasing evidence of exposure-correlated harmful effects of BPA. In vitro assays provide the fast, affordable, and mechanism insightful ways to screen endocrine disruption (ED), which is a major concern of new BPA alternatives. In this review, we summarize the safety and regulation information on the alternatives to BPA, review the state of the art of in vitro assays for ED evaluation, highlight their advantages and limitations, and discuss the challenges and future research needs. Our review shows that ligand binding, reporter gene, cell proliferation, and steroidogenesis are four commonly used in vitro assays to determine the ED at the response of receptor, gene transcription, and whole cell level. Major challenges are found from in vitro-in vivo translation and identification of ED chemicals in polymers. More studies on these areas are needed in the future.

The effects of perfluorooctanoic acid (PFOA) on fetal and adult rat testis

Perfluorooctanoic acid (PFOA) is a widely dispersed synthetic chemical, which accumulates in living organisms and has been connected with male reproductive disorders. To monitor the effects of PFOA, fetal rat testes or seminiferous tubule segments (stage VII-VIII) of adult rats were cultured in 0-100 μg/ml PFOA for 24 h. Afterwards, cAMP, progesterone, testosterone and StAR protein levels were measured from the fetal testes culture. Measurements were combined with immunohistochemistry, immunofluorescence, TUNEL and flow cytometric analysis to monitor cell death in somatic and germ cells. This study shows that the levels of cAMP, progesterone, testosterone and expression of StAR decreased significantly in PFOA 50 and 100 μg/ml. PFOA affected cell populations significantly by decreasing the amount of diploid, proliferating, meiotic I and G2/M-phase cells in adult rat testis. However, PFOA did not affect fetal, proliferating or adult rat Sertoli cells but an increased tendency of apoptosis in fetal Leydig cells was observed.

Do G-protein coupled estrogen receptor and bisphenol A analogs influence on Leydig cell epigenetic regulation in immature boar testis ex vivo?

Organotypic culture of testicular fragments from 7-day-old male pigs (Polish White Large) was used. Tissues were treated with an antagonist of G-protein coupled estrogen receptor (GPER) (G-15; 10 nM), and bisphenol A (BPA), and its analogs (TBBPA, TCBPA; 10 nM) alone or in combination and analyzed using electron and light (stainings for collagen fibers, lipid droplet and autophagy markers) microscopes. In addition, mRNA and protein abundances and localization of molecules required for miRNA biogenesis and function (Drosha, Exportin 5; EXPO5, Dicer, and Argonaute 2; AGO2) were assessed together with calcium ion (Ca²⁺) and estradiol concentrations. Regardless of GPER blockade and/or treatment with BPA, TBBPA and TCBPA, there were no changes in Leydig cell morphology. Also, there were no changes in lipid droplet content and distribution but there were changes in lipid and autophagy protein abundance. In the interstitial tissue, there was an increase of collagen content, especially after treatment with BPA analogs and G-15 + BPA. Independent of the treatment, there was downregulation of EXPO5 and Dicer genes but the Drosha and AGO2 genes were markedly upregulated as a result of treatment with G-15 + BPA and TCBPA, respectively. There was always a lesser abundance of EXPO5 and AGO2 proteins regardless of treatment. There was markedly greater abundances of Drosha after G-15 + BPA treatment, and this also occurred for Dicer after treatment with G-15 + TCBPA. Immunolocalization of miRNA proteins indicated there was a cytoplasmic-nuclear pattern in control and treated cells. There was an increase of Ca²⁺ concentrations after treatment with G-15 and BPA analogs. Estradiol secretion decreased after antagonist and chemical treatments when these were administered alone, however, there was an increase in estradiol secretion after treatment with combinations of these compounds.

Identifying Greener and Safer Plasticizers: A 4-Step Approach

The health and economic burden of endocrine disrupting chemicals, such as the plasticizer di(2-ethylhexyl) phthalate (DEHP), is prompting industry to develop alternatives. However, the absence of requirements for manufacturers to ensure the safety of these alternatives has led to the generation of replacements that may have similar or worse effects than the original chemicals. Consequently, there is increasing recognition by scientists, regulators and industry that proactive approaches are needed to develop safe chemical substitutes. We propose a 4-step approach for the design, characterization and toxicological testing of responsible alternative chemicals that we illustrate with our ongoing studies on DEHP replacements. Our approach is comprised of: (1) the design and characterization of alternative chemicals based on innovative chemical structures and environmental considerations; (2) large-scale in vitro cell-based high throughput and selective ex vivo studies to preselect the most innocuous alternatives; (3) an acute toxicity in vivo study to rule out overt toxicity of the selected candidates; and (4) an in utero and lactational exposure study comparing the effects of selected candidates to those currently in use, emphasizing commonly described phenotypes after exposure to the latter. Using this 4-step approach, we have identified 2 alternative chemicals displaying good plasticizing properties, better biodegradability, and less leaching than DEHP without any apparent toxicity in vivo. This process has thus far proven useful in the proactive identification of responsible chemical replacements for DEHP.

Effects of environmental Bisphenol A exposures on germ cell development and Leydig cell function in the human fetal testis

BACKGROUND

Using an organotypic culture system termed human Fetal Testis Assay (hFeTA) we previously showed that 0.01 μM BPA decreases basal, but not LH-stimulated, testosterone secreted by the first trimester human fetal testis. The present study was conducted to determine the potential for a long-term antiandrogenic effect of BPA using a xenograft model, and also to study the effect of BPA on germ cell development using both the hFETA and xenograft models.

METHODS

Using the hFeTA system, first trimester testes were cultured for 3 days with 0.01 to 10 μM BPA. For xenografts, adult castrate male nude mice were injected with hCG and grafted with first trimester testes. Host mice received 10 μM BPA (~ 500 μg/kg/day) in their drinking water for 5 weeks. Plasma levels of total and unconjugated BPA were 0.10 μM and 0.038 μM respectively. Mice grafted with second trimester testes received 0.5 and 50 μg/kg/day BPA by oral gavage for 5 weeks.

RESULTS

With first trimester human testes, using the hFeTA model, 10 μM BPA increased germ cell apoptosis. In xenografts, germ cell density was also reduced by BPA exposure. Importantly, BPA exposure significantly decreased the percentage of germ cells expressing the pluripotency marker AP-2γ, whilst the percentage of those expressing the pre-spermatogonial marker MAGE-A4 significantly increased. BPA exposure did not affect hCG-stimulated androgen production in first and second trimester xenografts as evaluated by both plasma testosterone level and seminal vesicle weight in host mice.

CONCLUSIONS

Exposure to BPA at environmentally relevant concentrations impairs germ cell development in first trimester human fetal testis, whilst gonadotrophin-stimulated testosterone production was unaffected in both first and second trimester testis. Studies using first trimester human fetal testis demonstrate the complementarity of the FeTA and xenograft models for determining the respective short-term and long term effects of environmental exposures.

An Initial Investigation of an Alternative Model to Study rat Primordial Germ Cell Epigenetic Reprogramming

BACKGROUND

Primordial germ cells (PGC) are the precursors of the gametes. During pre-natal development, PGC undergo an epigenetic reprogramming when bulk DNA demethylation occurs and is followed by sex-specific de novo methylation. The de novo methylation and the maintenance of the methylation patterns depend on DNA methyltransferases (DNMTs). PGC reprogramming has been widely studied in mice but not in rats. We have previously shown that the rat might be an interesting model to study germ cell development. In face of the difficulties of getting enough PGC for molecular studies, the aim of this study was to propose an alternative method to study rat PGC DNA methylation. Rat embryos were collected at 14, 15 and 19 days post-coitus (dpc) for the analysis of 5mC, 5hmC, DNMT1, DNMT3a and DNMT3b expression or at 16dpc for treatment 5-Aza-CdR, a DNMT inhibitor, in vitro.

METHODS

Once collected, the gonads were placed in 24-well plates previously containing 45μm pore membrane and medium with or without 5-Aza-CdR. The culture was kept for five days and medium was changed daily. The gonads were either fixed or submitted to RNA extraction.

RESULTS

5mC and DNMTs labelling suggests that PGC are undergoing epigenetic reprogramming around 14/15dpc. The in vitro treatment of rat embryonic gonads with 1 μM of 5-Aza-CdR lead to a loss of 5mC labelling and to the activation of Pax6 expression in PGC, but not in somatic cells, suggesting that 5-Aza-CdR promoted a PGC-specific global DNA hypomethylation.

CONCLUSIONS

This study suggests that the protocol used here can be a potential method to study the wide DNA demethylation that takes place during PGC reprogramming.

Effects of daidzein on testosterone secretion in cultured immature mouse testis

Background: Daidzein is a major isoflavone in soybeans. Several in vivo studies have showed that daidzein can affect immature male testosterone production. However, whether daidzein has direct action on immature male testis is unknown.

Objective: We investigated the effects of daidzein on testosterone secretion in 3-day-old and 21-day-old mouse Leydig cells with organotypic culture model.

Materials and Methods: The testes were exposed to different concentrations (10-7 to 10-4 M) of daidzein for 72 h with medium changed every 24 h. From 72 to 75 h of culture, 100 ng/ml human chorionic gonadotropin (hCG) was added. The testosterone production was determined, and the related mechanisms of daidzein action were also evaluated by measuring the mRNA levels of steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (P450scc), and 3β-hydroxysteroid dehydrogenase (3β-HSD-1) involved in testosterone biosynthesis.

Results: The results revealed that in the presence of 100 ng/ml hCG, 10-7 to 10-5 M daidzein had no significant effect on testosterone secretion in cultured 3-day-old mouse testis. But 10-4 M daidzein significantly increased testosterone concentration (p < 0.05). Daidzein in range of studied doses had no obvious influence on testosterone production in cultured 21-day-old mouse testis. RT-PCR results showed that 10-4 M daidzein had obvious influence on the mRNA levels of StAR, P450scc and 3β-HSD-1 in cultured 3-day-old mouse testis (p < 0.05).

Conclusion: These results suggest that daidzein mainly influences neonatal mouse testis function, and the influence is partially related to the upregulation of StAR, P450scc, and 3β-HSD-1 mRNA levels.

Adverse effects of endocrine disruptors on the foetal testis development: focus on the phthalates

There are great concerns about the increasing incidence of abnormalities in male reproductive function. Human sperm counts have markedly dropped and the rate of testicular cancer has clearly augmented over the past four decades. Moreover, the prevalence rates of cryptorchidism and hypospadias are also probably increasing. It has been hypothesized that all these adverse trends in male reproduction result from abnormalities in the development of the testis during foetal and neonatal life. Furthermore, many recent epidemiological, clinical and experimental data suggest that these male reproductive disorders could be due to the effects of xenobiotics termed endocrine disruptors, which are becoming more and more concentrated and prevalent in our environment. Among these endocrine disruptors, we chose to focus this review on the phthalates for different reasons: 1) they are widespread in the environment; 2) their concentrations in many human biological fluids have been measured; 3) the experimental data using rodent models suggesting a reprotoxicity are numerous and are the most convincing; 4) their deleterious effects on the in vivo and in vitro development and function of the rat foetal testis have been largely studied; 5) some epidemiological data in humans suggest a reprotoxic effect at environmental concentrations at least during neonatal life. However, the direct effects of phthalates on human foetal testis have never been explored. Thus, as we did for the rat in the 1990s, we recently developed and validated an organ culture system which allows maintenance of the development of the different cell types of human foetal testis. In this system, addition of 10-4 M MEHP (mono-2-ethylhexyl phthalate), the most produced phthalate, had no effect on basal or LH-stimulated production of testosterone, but it reduced the number of germ cells by increasing their apoptosis, without modification of their proliferation. This is the first experimental demonstration that phthalates alter the development of the foetal testis in humans. Using our organotypic culture system, we and others are currently investigating the effect of MEHP in the mouse and the rat, and it will be interesting to compare the results between these species to analyse the relevance of toxicological tests based on rodent models.

A new chapter in the bisphenol A story: bisphenol S and bisphenol F are not safe alternatives to this compound

Bisphenol A (BPA) is a widely studied typical endocrine-disrupting chemical, and one of the major new issues is the safe replacement of this commonly used compound. Bisphenol S (BPS) and bisphenol F (BPF) are already or are planned to be used as BPA alternatives. With the use of a culture system that we developed (fetal testis assay [FeTA]), we previously showed that 10 nmol/L BPA reduces basal testosterone secretion of human fetal testis explants and that the susceptibility to BPA is at least 100-fold lower in rat and mouse fetal testes. Here, we show that addition of LH in the FeTA system considerably enhances BPA minimum effective concentration in mouse and human but not in rat fetal testes. Then, using the FeTA system without LH (the experimental conditions in which mouse and human fetal testes are most sensitive to BPA), we found that, as for BPA, 10 nmol/L BPS or BPF is sufficient to decrease basal testosterone secretion by human fetal testes with often nonmonotonic dose-response curves. In fetal mouse testes, the dose-response curves were mostly monotonic and the minimum effective concentrations were 1,000 nmol/L for BPA and BPF and 100 nmol/L for BPS. Finally, 10,000 nmol/L BPA, BPS, or BPF reduced Insl3 expression in cultured mouse fetal testes. This is the first report describing BPS and BPF adverse effects on a physiologic function in humans and rodents.

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.

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.

Integrative rodent models for assessing male reproductive toxicity of environmental endocrine active substances

In the present review, we first summarize the main benefits, limitations and pitfalls of conventional in vivo approaches to assessing male reproductive structures and functions in rodents in cases of endocrine active substance (EAS) exposure from the postulate that they may provide data that can be extrapolated to humans. Then, we briefly present some integrated approaches in rodents we have recently developed at the organism level. We particularly focus on the possible effects and modes of action (MOA) of these substances at low doses and in mixtures, real-life conditions and at the organ level, deciphering the precise effects and MOA on the fetal testis. It can be considered that the in vivo experimental EAS exposure of rodents remains the first choice for studies and is a necessary tool (together with the epidemiological approach) for understanding the reproductive effects and MOA of EASs, provided the pitfalls and limitations of the rodent models are known and considered. We also provide some evidence that classical rodent models may be refined for studying the multiple consequences of EAS exposure, not only on the reproductive axis but also on various hormonally regulated organs and tissues, among which several are implicated in the complex process of mammalian reproduction. Such models constitute an interesting way of approaching human exposure conditions. Finally, we show that organotypic culture models are powerful complementary tools, especially when focusing on the MOA. All these approaches have contributed in a combinatorial manner to a better understanding of the impact of EAS exposure on human reproduction.

Rat Gnrhr promoter directs species-specific gene expression in the pituitary and testes of transgenic mice

The GnRH receptor (GnRHR) is expressed in several non-pituitary tissues, notably in gonads. However, mechanisms underlying the gonad-specific expression of Gnrhr are not well understood. Here, Gnrhr expression was analysed in the developing testes and pituitaries of rats and transgenic mice bearing the human placental alkaline phosphatase reporter gene (ALPP) under the control of the rat Gnrhr promoter. We showed that the 3.3 kb, but not the pituitary-specific 1.1 kb promoter, directs ALPP expression exclusively to testis Leydig cells from embryonic day 12 onwards. Real-time PCR analysis revealed that promoter activity displayed the same biphasic profile as marker genes in Leydig cells, i.e. abrupt declines after birth followed by progressive rises after a latency phase, in coherence with the differentiation and evolution of foetal and adult Leydig cell lineages. Interestingly, the developmental profile of transgene expression showed high similarity with the endogenous Gnrhr profile in the rat testis, while mouse Gnrhr was only poorly expressed in the mouse testis. In the pituitary, both transgene and Gnrhr were co-expressed at measurable levels with similar ontogenetic profiles, which were markedly distinct from those in the testis. Castration that induced pituitary Gnrhr up-regulation in rats did not affect the mouse Gnrhr. However, it duly up-regulated the transgene. In addition, in LβT2 cells, the rat, but not mouse, Gnrhr promoter was sensitive to GnRH agonist stimulation. Collectively, our data highlight inter-species variations in the expression and regulation of Gnrhr in two different organs and reveal that the rat promoter sequence contains relevant genetic information that dictates rat-specific gene expression in the mouse context.

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.

Effect of mono-(2-ethylhexyl) phthalate on human and mouse fetal testis: In vitro and in vivo approaches

The present study was conducted to determine whether exposure to the mono-(2-ethylhexyl) phthalate (MEHP) represents a genuine threat to male human reproductive function. To this aim, we investigated the effects on human male fetal germ cells of a 10⁻⁵ M exposure. This dose is slightly above the mean concentrations found in human fetal cord blood samples by biomonitoring studies. The in vitro experimental approach was further validated for phthalate toxicity assessment by comparing the effects of in vitro and in vivo exposure in mouse testes. Human fetal testes were recovered during the first trimester (7-12 weeks) of gestation and cultured in the presence or not of 10⁻⁵ M MEHP for three days. Apoptosis was quantified by measuring the percentage of Caspase-3 positive germ cells. The concentration of phthalate reaching the fetal gonads was determined by radioactivity measurements, after incubations with ¹⁴C-MEHP. A 10⁻⁵ M exposure significantly increased the rate of apoptosis in human male fetal germ cells. The intratesticular MEHP concentration measured corresponded to the concentration added in vitro to the culture medium. Furthermore, a comparable effect on germ cell apoptosis in mouse fetal testes was induced both in vitro and in vivo. This study suggests that this 10⁻⁵ M exposure is sufficient to induce changes to the in vivo development of the human fetal male germ cells.

Mono-(2-ethylhexyl) phthalate directly alters the expression of Leydig cell genes and CYP17 lyase activity in cultured rat fetal testis

Exposure to phthalates in utero alters fetal rat testis gene expression and testosterone production, but much remains to be done to understand the mechanisms underlying the direct action of phthalate within the fetal testis. We aimed to investigate the direct mechanisms of action of mono-(2-ethylhexyl) phthalate (MEHP) on the rat fetal testis, focusing on Leydig cell steroidogenesis in particular. We used an in vitro system based on the culture for three days, with or without MEHP, of rat fetal testes obtained at 14.5 days post-coitum.Exposure to MEHP led to a dose-dependent decrease in testosterone production. Moreover, the production of 5 alpha-dihydrotestosterone (5α-DHT) (-68%) and androstenedione (-54%) was also inhibited by 10 µM MEHP, whereas 17 alpha-hydroxyprogesterone (17α-OHP) production was found to increase (+41%). Testosterone synthesis was rescued by the addition of androstenedione but not by any of the other precursors used. Thus, the hormone data suggested that steroidogenesis was blocked at the level of the 17,20 lyase activity of the P450c17 enzyme (CYP17), converting 17α-OHP to androstenedione. The subsequent gene expression and protein levels supported this hypothesis. In addition to Cyp17a1, microarray analysis showed that several other genes important for testes development were affected by MEHP. These genes included those encoding insulin-like factor 3 (INSL3), which is involved in controlling testicular descent, and Inha, which encodes the alpha subunit of inhibin B.These findings indicate that under in vitro conditions known to support normal differentiation of the fetal rat testis, the exposure to MEHP directly inhibits several important Leydig cell factors involved in testis function and that the Cyp17a1 gene is a specific target to MEHP explaining the MEHP-induced suppression of steroidogenesis observed.

Many putative endocrine disruptors inhibit prostaglandin synthesis

BACKGROUND

Prostaglandins (PGs) play key roles in development and maintenance of homeostasis of the adult body. Despite these important roles, it remains unclear whether the PG pathway is a target for endocrine disruption. However, several known endocrine-disrupting compounds (EDCs) share a high degree of structural similarity with mild analgesics.

OBJECTIVES AND METHODS

Using cell-based transfection and transduction experiments, mass spectrometry, and organotypic assays together with molecular modeling, we investigated whether inhibition of the PG pathway by known EDCs could be a novel point of endocrine disruption.

RESULTS

We found that many known EDCs inhibit the PG pathway in a mouse Sertoli cell line and in human primary mast cells. The EDCs also reduced PG synthesis in ex vivo rat testis, and this reduction was correlated with a reduced testosterone production. The inhibition of PG synthesis occurred without involvement of canonical PG receptors or the peroxisome proliferator-activated receptors (PPARs), which have previously been described as targets of EDCs. Instead, our results suggest that the compounds may bind directly into the active site of the cyclooxygenase (COX) enzymes, thereby obstructing the conversion of arachidonic acid to PG precursors without interfering with the expression of the COX enzymes. A common feature of the PG inhibitory EDCs is the presence of aromatic groups that may stabilize binding in the hydrophobic active site of the COX enzymes.

CONCLUSION

Our findings suggest a hitherto unknown mode of action by EDCs through inhibition of the PG pathway and suggest new avenues to investigate effects of EDCs on reproductive and immunological disorders that have become increasingly common in recent decades.

Altérations environnementales du développement du testicule foetal: zoom sur les phtalates

L’augmentation de plusieurs anomalies de la fonction de reproduction masculine suscite de grandes inquiétudes. Au cours des quatre dernières décennies, le nombre de spermatozoïdes chez l’homme a nettement diminué, et l’incidence du cancer testiculaire a doublé. De plus, les cas de cryptorchidie et d’hypospadias sont également en augmentation. L’hypothèse la plus couramment admise est que tous ces effets néfastes sur la fonction reproductive masculine résulteraient d’anomalies survenant lors du développement du testicule pendant la vie foetale et néonatale. En outre, de nombreuses données épidémiologiques, cliniques et expérimentales suggèrent que ces troubles pourraient être dus aux effets de xénobiotiques appelés perturbateurs endocriniens qui sont de plus en plus concentrés et présents dans notre environnement. Parmi les perturbateurs endocriniens, nous avons choisi de focaliser cette revue sur les phtalates pour diverses raisons: 1) ils sont très répandus dans l’environnement; 2) leurs concentrations dans de nombreux fluides biologiques humains ont été mesurées y compris pendant la grossesse; 3) les données expérimentales utilisant le modèle rat et suggérant une reprotoxicité sont nombreuses et pertinentes; 4) les effets délétères des phtalates sur le développement et sur les fonctions du testicule foetal de rat ont largement été étudiés; 5) quelques données épidémiologiques humaines suggèrent un effet reprotoxique des phtalates aux concentrations retrouvées dans l’environnement, au moins durant la vie néonatale. Cependant, les effets directs des phtalates sur le testicule foetal humain n’avaient jamais été étudiés. Comme nous l’avions fait chez le rat dans les années 1990, nous avons récemment développé et validé un système de culture organotypique de testicule foetal humain qui permet de maintenir in vitro le développement des différents types cellulaires. Dans ce système, l’ajout de 10−4 M de MEHP (mono-2-éthylhexyl phtalate), le phtalate le plus répandu, n’a aucun effet sur la production de testostérone basale ou stimulée par l’hormone lutéinisante (LH), mais il réduit le nombre de cellules germinales en augmentant leur apoptose et sans modifier leur prolifération. Nos données constituent la première donnée expérimentale montrant que les phtalates altèrent le développement du testicule foetal humain. En outre, en utilisant le même système de culture organotypique, il est intéressant de comparer la réponse au MEHP chez l’Homme et chez les rongeurs pour analyser la pertinence des tests toxicologiques basés sur le modèle rongeur.

Intrauterine exposure to mild analgesics is a risk factor for development of male reproductive disorders in human and rat

BACKGROUND

More than half of pregnant women in the Western world report intake of mild analgesics, and some of these drugs have been associated with anti-androgenic effects in animal experiments. Intrauterine exposure to anti-androgens is suspected to contribute to the recent increase in male reproductive problems, and many of the anti-androgenic compounds are like the mild analgesics potent inhibitors of prostaglandin synthesis. Therefore, it appears imperative to further investigate the potential endocrine disrupting properties of mild analgesics.

METHODS

In a prospective birth cohort study, 2297 Danish and Finnish pregnant women completed a questionnaire and 491 of the Danish mothers participated in a telephone interview, reporting on their use of mild analgesics during pregnancy. The testicular position of newborns was assessed by trained paediatricians. In rats, the impact of mild analgesics on anogenital distance (AGD) after intrauterine exposure was examined together with the effect on ex vivo gestational day 14.5 testes.

RESULTS

In the Danish birth cohort, the use of mild analgesics was dose-dependently associated with congenital cryptorchidism. In particular, use during the second trimester increased the risk. This risk was further increased after the simultaneous use of different analgesics. The association was not found in the Finnish birth cohort. Intrauterine exposure of rats to paracetamol led to a reduction in the AGD and mild analgesics accordingly reduced testosterone production in ex vivo fetal rat testes.

CONCLUSION

There was an association between the timing and the duration of mild analgesic use during pregnancy and the risk of cryptorchidism. These findings were supported by anti-androgenic effects in rat models leading to impaired masculinization. Our results suggest that intrauterine exposure to mild analgesics is a risk factor for development of male reproductive disorders.

Cadmium increases human fetal germ cell apoptosis

BACKGROUND

Cadmium (Cd) is a common environmental pollutant and a major constituent of tobacco smoke. Adverse effects of this heavy metal on reproductive function have been identified in adults; however, no studies have examined its effects on human reproductive organs during development.

OBJECTIVES

Using our previously developed organ culture system, we investigated the effects of cadmium chloride on human gonads at the beginning of fetal life, a critical stage in the development of reproductive function.

METHODS

Human fetal gonads were recovered during the first trimester (711 weeks postconception) and cultured with or without Cd. We used different concentrations of Cd and compared results with those obtained with mouse fetal gonads at similar stages.

RESULTS

Cd, at concentrations as low as 1 microM, significantly decreased the germ cell density in human fetal ovaries. This correlated with an increase in germ cell apoptosis, but there was no effect on proliferation. Similarly, in the human fetal testis, Cd (1 microM) reduced germ cell number without affecting testosterone secretion. In mouse fetal gonads, Cd increased only female germ cell apoptosis.

CONCLUSIONS

This is the first experimental demonstration that Cd, at low concentrations, alters the survival of male and female germ cells in humans. Considering data demonstrating extensive human exposure, we believe that current environmental levels of Cd could be deleterious to early gametogenesis.

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.

Time- and dose-related effects of di-(2-ethylhexyl) phthalate and its main metabolites on the function of the rat fetal testis in vitro

BACKGROUND

Endocrine-disrupting effects of phthalates are understood primarily from in utero exposures within the fetal rat testis. Nevertheless, their path of action, dose-response character, and cellular target(s) within the fetal testis are not known.

OBJECTIVES

In this study we investigated the effects of di-(2-ethylhexyl) phthalate (DEHP), mono-(2-ethylhexyl) phthalate (MEHP), and several of their metabolites on the development of organo-cultured testes from rat fetus.

METHODS

We removed testes from 14.5-day-old rat fetuses and cultured them for 1-3 days with or without DEHP, MEHP, and the metabolites.

RESULTS

DEHP (10(-5) M) produced a proandrogenic effect after 3 days of culture, whereas MEHP disrupted testis morphology and function. Leydig cells were the first affected by MEHP, with a number of them being inappropriately located within some seminiferous tubules. Additionally, we found a time- and dose-dependent reduction of testosterone. By 48 hr, gonocyte proliferation had decreased, whereas apoptosis increased. Sertoli cell number was unaffected, although some cells appeared vacuolated, and production of anti-Müllerian hormone decreased in a time- and dose-dependent manner. The derived metabolite mono-(2-ethyl-5-hydroxyhexyl) phthalate was the only one to cause deleterious effects to the rat fetal testis in vitro.

CONCLUSION

We hope that this in vitro method will facilitate the study of different phthalate esters and other endocrine disruptors for direct testicular effects.

Phthalates impair germ cell development in the human fetal testis in vitro without change in testosterone production

BACKGROUND

Several studies have described an increasing frequency of male reproductive disorders, which may have a common origin in fetal life and which are hypothesized to be caused by endocrine disruptors. Phthalate esters represent a class of environmental endocrine-active chemicals known to disrupt development of the male reproductive tract by decreasing testosterone production in the fetal rat.

OBJECTIVES

Using the organ culture system we developed previously, we investigated the effects on the development of human fetal testis of one phthalate--mono-2-ethylhexyl phthalate (MEHP)--an industrial chemical found in many products, which has been incriminated as a disruptor of male reproductive function.

METHODS

Human fetal testes were recovered during the first trimester (7-12 weeks) of gestation, a critical period for testicular differentiation, and cultured for 3 days with or without MEHP in basal conditions or stimulated with luteinizing hormone (LH).

RESULTS

Whatever the dose, MEHP treatment had no effect on basal or LH-stimulated testosterone produced by the human fetal testis in vitro, although testosterone production can be modulated in our culture system. MEHP (10(-4) M) did not affect proliferation or apoptosis of Sertoli cells, but it reduced the mRNA expression of anti-Müllerian hormone. MEHP (10(-4) M) reduced the number of germ cells by increasing their apoptosis, measured by the detection of caspase-3-positive germ cells, without modification of their proliferation.

CONCLUSIONS

This is the first experimental demonstration that phthalates alter the development of the germ cell lineage in humans. However, in contrast to results observed in the rat, phthalates did not affect steroidogenesis.

Functional in vitro model to examine cancer therapy cytotoxicity in maturing rat testis

Childhood cancer treatment can lead to infertility. Organ culture of early postnatal testicular tissue might provide a valuable approach to the study of acute testicular toxicity. The aim of the present study was to develop a functional in vitro organ culture method, in order to identify sensitive target cells to doxorubicin-induced cytotoxicity in immature rat testis during germ cell migration prior initiation of the first wave of spermatogenesis. Testicular tissue fragments from 5-day-old Sprague-Dawley rats were cultured in the absence or presence of doxorubicin (40 and 100ng/ml) and morphology, apoptosis, proliferation and testosterone secretion was analyzed. Postnatal testicular development proceeded normally in control samples for 48h in vitro. In these untreated culture conditions germ and Sertoli cell numbers and germ cell migration were comparable to in vivo. Germ cells were the primary, most sensitive targets for in vitro-induced doxorubicin (100ng/ml) toxicity and their death was not associated with any morphological defects in the Sertoli cells. Organ culture which reduces the need of animal experimentation can be used to study the cytotoxic effects of doxorubicin on the immature testis.

[Development and regulations of testicular functions in the human foetus]

Two major functions are assumed by the testis: the production of male gametes (that is, spermatozoa) and the production of steroid hormones. Both two functions are established during fetal life and are essential to the adult fertility and the masculinization of the internal tract and genitalia. For many years, our laboratory has been interested in the ontogeny of those two functions in rodents and, since 2003, in collaboration with gynecology and obstetrics service of professor R. Frydman in Antoine-Béclère hospital, we have studied them in human. The first aim of this work was to improve the global knowledge of the human fetal testis development by using both our experimental data and the literature. Then, we focused on the different defects that can occur during the fetal testis development. Indeed, male reproductive abnormalities have been steadily increasing since the last decades and are thought to be related to the concomitant increase of the concentration of contaminants and particularly of endocrine disruptors in the environment. Thus, we decided to study the effect of endocrine disruptors on human fetal testis and, more particularly, the effect of phthalates, by using an organ culture system developed for human. In contrast to the data obtained in rat, mono (ethylhexyl)-phthalate (MEHP), an active metabolite of the most widespread phthalate in the environment, does not disturb the steroidogenic function. On the other hand, it has a negative effect on the male germ cells number. This study is the first experimental demonstration of a negative effect of phthalates directly on human fetal testis.

High radiosensitivity of germ cells in human male fetus

CONTEXT

Germ cells formed during human fetal life are essential for fertility of the adult, and several studies have described an increasing frequency of male reproductive disorders, which may have a common origin in fetal life and which are hypothesized to be caused by endocrine disruptors. However, factors inducing a genotoxic stress may also be implicated.

OBJECTIVES

We investigated the effect of gamma-irradiation on the functions of human fetal testis during the first trimester of gestation by using an organ culture system. Then we focused on the role of the p53 pathway in the observed effects.

RESULTS

Germ cells were highly sensitive to irradiation even at doses as low as 0.1 and 0.2 Gy. Indeed, for these doses, one third of germ cells died by apoptosis. Other germ cells were blocked in their cycle, but no repair seemed to occur, and longer culture with the highest dose used showed that they were destined to die. Sertoli cells were less affected, although their proliferation and the level of anti-Müllerian hormone were reduced. Irradiation had no effect on testosterone secretion or on the expression of steroidogenic enzymes by Leydig cells. After irradiation, p53 phosphorylated on serine 15 was detected from 1-24 h in all cell types. This activation of p53 was accompanied by an increase in mRNA levels of proapoptotic factors Bax and Puma, whereas that of antiapoptotic Bcl-2 remained unchanged. P21, which is responsible for cell cycle arrest, was also up-regulated 6, 30, and 72 h after irradiation. Finally, when we added pifithrin-alpha, a specific inhibitor of p53 functions, a significant decrease in irradiation-induced apoptosis in both germ and Sertoli cells was observed, indicating the involvement of the p53 pathway in irradiation-induced apoptosis.

CONCLUSIONS

This study demonstrated here for the first time the great sensitivity of human fetal germ cells to genotoxic stress caused by ionizing radiation.

p63 expression pattern in foetal and neonatal gonocytes after irradiation and role in the resulting apoptosis by using p63 knockout mice

PURPOSE

To investigate the role of p63, a member of the p53 family, in gonocyte apoptosis after radiation exposure.

MATERIALS AND METHODS

Wild-type (WT) and p63 knock-out (KO) testes were exposed in vivo or in vitro to a 3 Gy dose of 137Cesium (137Cs) gamma-rays at day 18.5 post-conception (p.c.). p63 whole expression was studied in neonatal testes by immunohistochemistry, whereas TAp63 and DeltaNp63 isoforms were studied by Reverse-transcribed Polymerase Chain Reaction (RT-PCR). Gonocyte apoptosis was analysed by immunohistochemistry (cleaved caspase 3) and In Situ End labelling (ISEL).

RESULTS

Such foetal irradiation leads to a strong increase of gonocyte apoptosis in newborns. It also induces the up-regulation of the TAp63alpha isoform and the down-regulation of the DeltaNp63alpha isoform. Moreover, in control p63KO testis, a significant increase in the number of gonocytes was associated with a strong reduction of their apoptosis compared with the control wild-type testis. Unexpectedly, after irradiation this increase of the number of apoptotic gonocytes was seen in p63KO testis, which was comparable to that in irradiated p63WT testis.

CONCLUSION

We demonstrate that p63 is able to trigger gonocyte apoptosis in control testis but is not necessarily required in their radio-induced apoptosis.

A new method for toxicity assays on human and mouse fetal testis

Exposure to environmental pollutants (EP) is associated with a wide range of toxic effects, in particular in testis development. Uranium is a potential pollutant of nuclear industry and over the last few years, its environmental concentrations have increased. In animals, the current procedures for evaluating the potential developmental toxicity of uranium are based on in vivo studies. These methods do not allow to know the direct effects on testicular cells and are obviously excluded for human experiments. Consequently, we have developed an in vitro culture system of the whole testis. In the present study we characterized and validated this organ culture system in both mouse fetal testes and human fetal testes recovered during the first trimester (6-12 weeks) of gestation. We compared the histological aspect, the number of germ cells and the testosterone production, before and after culture. Testicular architecture and intercellular communications were preserved, and organ culture appears as a powerful method for studying the early development of testicular gametogenesis and steroidogenesis in both species. Thus by using this method we will be able to investigate the effects of uranium on mouse and human developing testis. The mouse model will allow us to determine the dose range of interest without restriction of material.

Organotypic culture, a powerful model for studying rat and mouse fetal testis development

The key role of the fetal testis in the masculinization of genital organs has been known for a long time. More recently, the observed increases in male reproductive disorders has been postulated to be the result of changes in fetal and neonatal testis development in response to increasing environmental pollution. However, few tools are available for studying fetal testis development and the effects of physiological or toxic substances. We have developed an organ culture system in which rat fetal testis is grown on a filter floating on a synthetic medium containing no serum, hormones or biological factors. In this study, we have compared the long-term morpho-functional development of the various testicular cell types in this system with that observed in vivo and have extended this system to the mouse. Rat Leydig, Sertoli and germ cells and macrophages develop normally over a period of 1-2 weeks in this system. Fewer cells are produced than in vivo but the level of differentiated function is similar. Germ cells, which are difficult to culture in vitro, resume mitosis after a quiescent period, at the same time as in vivo. Similar results have been obtained with mouse fetuses, except that Leydig cells dedifferentiate in vitro if the testis is explanted after 13.5 days post conception. Testicular architecture and intercellular communication are sufficiently preserved for the development of the main fetal and neonatal testicular cell types in vitro with no added factors. Our floating-filter organotypic culture system in synthetic medium therefore allows the morpho-functional development of somatic and germ cells in fetal testis explants taken at all developmental stages in rat and at early stages in mouse. This method is potentially useful for studies of the effects of various factors, and of xenobiotics, in particular.

Le testicule fœtal est-il en danger ?

Estrogens are classically known to play a major role in female reproduction, but there is now compelling evidence that they may also be involved in the regulation of male reproductive function. In humans, a decrease in sperm count and an increase in the incidences of testicular cancer, cryptorchidism and hypospadia have been observed in many countries over the last 50 years. Male reproductive alterations were also observed in wildlife. Such male reproductive disorders have been attributed to the increase in concentration of xenobiotics, and of xenoestrogens in particular, in the environment and in food. Epidemiological, clinical and experimental studies have suggested that excessive exposure to estrogens during fetal/neonatal life can lead to reproductive disorders in adulthood. Using an in vitro model, we showed that estrogens directly affected the development of the fetal testis. Lastly, we clearly demonstrated that the fetal and neonatal testis is very sensitive to estrogens since the invalidation of estrogen receptor alpha leads to an increase of steroidogenesis and the invalidation of estrogen receptor beta enhances the development of the germ cell lineage in the male.

Endogenous estrogens inhibit mouse fetal Leydig cell development via estrogen receptor alpha

It is now accepted that estrogens play a role in male fertility and that exposure to exogenous estrogens during fetal/neonatal life can lead to reproductive disorders in the male. However, the estrogen receptor (ER)-mediated processes involved in the regulation of male reproduction during fetal and neonatal development are still largely unclear. We previously reported that ER beta deficiency affects gametogenesis in mice but changes neither the number nor the differentiated functions of fetal Leydig cells. We show here that ER alpha-deficient mice (ER alpha-/-) display higher levels of testicular testosterone secretion than wild-type mice from fetal d 13.5 onwards. This results from higher levels of steroidogenic activity per fetal Leydig cell, as indicated by the hypertrophy of these cells and the higher levels of mRNA for StAR, P450c17 and P450scc in the testis, for a similar number of Leydig cells. Because LH is not produced on fetal d 13.5 and because no change in plasma LH concentration was observed in 2-d-old ER alpha-deficient mice, LH is probably not involved in the effects of estrogens on testicular steroidogenesis in fetal and early neonatal Leydig cells. Furthermore, inactivation of ER beta did not change the effect of ER alpha inactivation on steroidogenesis. Lastly, in an organ culture system, 1 mum diethylstilbestrol decreased the testosterone secretion of wild-type fetal and neonatal testes but not of ER alpha-/- testes. Thus, this study shows that endogenous estrogens physiologically inhibit steroidogenesis via ER alpha by acting directly on the testis early in fetal and neonatal development.

Estrogen receptor beta-mediated inhibition of male germ cell line development in mice by endogenous estrogens during perinatal life

Epidemiological, clinical, and experimental studies have suggested that excessive exposure to estrogens during fetal/neonatal life can lead to reproductive disorders and sperm abnormalities in adulthood. However, it is unknown whether endogenous concentrations of estrogens affect the establishment of the male fetal germ cell lineage. We addressed this question by studying the testicular development of mice in which the estrogen receptor (ER) beta or the ERalpha gene was inactivated. The homozygous inactivation of ERbeta (ERbeta-/-) increased the number of gonocytes by 50% in 2- and 6-d-old neonates. The numbers of Sertoli and Leydig cells and the level of testicular testosterone production were unaffected, suggesting that estrogens act directly on the gonocytes. The increase in the number of gonocytes did not occur during fetal life but instead occurred just after birth, when gonocytes resumed mitosis and apoptosis. It seems to result from a decrease in the apoptosis rate evaluated by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling method and cleaved caspase-3 immunohistochemical detection. Last, mice heterozygous for the ERbeta gene inactivation behaved similarly to their ERbeta-/- littermates in terms of the number of gonocytes, apoptosis, and mitosis, suggesting that these cells are highly sensitive to the binding of estrogens to ERbeta. ERalpha inactivation had no effect on the number of neonatal gonocytes and Sertoli cells. In conclusion, this study provides the first demonstration that endogenous estrogens can physiologically inhibit germ cell growth in the male. This finding may have important implications concerning the potential action of environmental estrogens.

Retinoid-Sensitive Steps in Steroidogenesis in Fetal and Neonatal Rat Testes: In Vitro and In Vivo Studies

Retinoic acid (RA) was recently shown to modify testosterone secretion of the fetal testis in vitro. We characterized this effect by culturing rat testes explanted at various ages, from Fetal Day 14.5 to Postnatal Day 3. In basal medium, RA inhibited, in a dose-dependent manner, both basal and acute LH-stimulated testosterone secretion by testes explanted on Fetal Days 14.5, 15.5, and 16.5. It had no effect on testes from older animals. The negative effect of RA did not result from a diminution in the number of Leydig cells but from a decrease in P450c17 mRNA levels and in LH-stimulated cAMP production. However, the RA-induced decrease in P450C17 mRNA levels was also observed with neonatal testes, suggesting that this enzymatic step is no longer rate limiting at this developmental stage. To study the physiological relevance of RA effects, we used fetuses and neonates issued from mothers fed a vitamin A-deficient (VAD) diet, resulting in a threefold decrease of plasma retinol concentration. On Fetal Day 18.5 and on Posnatal Day 3, testosterone secretion by the testis ex vivo was significantly increased in VAD animals. This shows that the endogenous retinol inhibits differentiation and/or function of fetal Leydig cells before Fetal Day 18.5 and is required for the normal regression of fetal Leydig cell function that occurs after Fetal Day 18.5. In conclusion, our results show that retinoids play a negative role on the steroidogenic activity during the differentiation of rat fetal Leydig cells.

Development of the foetal and neonatal testis

The foetal testis originates from a proliferation of the mesonephric and the coelomic epithelia which are colonized by the primordial germ cells. In the foetal testis, the development and functions of the three main cell type precursors (Leydig, Sertoli and germ cells) do not depend upon gonadotropins. Numerous intra- and extra-testicular factors are candidates for the control of its development and functions. To study the potential involvement of these factors, we developed an organotypic culture system. In absence of any growth factors or hormone, this system allows a development of the three main cell types which mimics that observed in vivo. The effects of different regulators (gonadotropin-releasing hormone, follicle-stimulating hormone, transforming growth factor-beta, insulin-like growth factor-I, anti-Mullerian hormone, retinoic acid, oestrogens) were tested in this system. Whether or not some of the effects observed in vitro have a physiological relevance was evaluated using appropriate transgenic mice. It is concluded that the foetal testis cannot be considered as an adult mini-testis since it has a specific physiology which largely differs from that of the immature or adult testis.

Prenatal testosterone and luteinizing hormone levels in male rats exposed during pregnancy to 2,3,7,8-tetrachlorodibenzo-p-dioxin and diethylstilbestrol

Changes in the perinatal testosterone surge have been related to demasculinization of the central nervous system and androgen-dependent growth of the reproductive organs in male mammals. Earlier reports suggest that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) interferes with androgen production, but the perinatal effects have remained elusive. In the present study we explored in utero-effects of TCDD (0.05, 0.1, 0.5, and 1.0 microg/kg), introduced on day 13.5 of pregnancy, on prenatal (day 19.5 post-conception [p.c.]) testosterone (T) surge and pituitary luteinizing hormone (LH) production in TCDD-resistant Han/Wistar (H/W) and TCDD-sensitive Long-Evans (L-E) rats. To elucidate estrogenic effects on T and LH production, Sprague-Dawley (S-D) fetuses with previously known DES-sensitivity were exposed in utero to diethylstilbestrol (DES, 100-300 microg/kg) on days 13.5, 15.5, and 17.5 p.c. For comparison, H/W fetuses that responded to TCDD treatments were exposed to DES at concentration of 100 microg/kg. It was found that TCDD has a stimulatory effect on testicular T synthesis in the H/W fetuses and that their circulating T concentrations increased significantly. The effect was not seen in the inbred L-E fetuses, which throughout the study showed considerably low testicular T levels. Pituitary LH concentrations also increased in the H/W fetuses exposed to TCDD. Effects of TCDD (1.0 microg/kg) in the H/W fetuses could be confirmed in vitro by human chorionic gonadotropin (hCG) stimulation assay showing the highest response rate in the TCDD exposed testes. Stimulation of cyclic AMP (adenosine-3', 5'-cyclic monophosphate[cAMP]) production was not considerably altered by in utero TCDD exposure. A significant depression in testicular and plasma T content was seen in the DES-exposed S-D and H/W fetuses, but pituitary LH levels did not alter considerably. In the presence of hCG, DES-exposed testes showed lower in vitro T and cAMP production rates compared to the untreated testes. TCDD (1.0 microg/kg) increased and DES decreased the male body weight gain, but the changes were not sex-dependent. It is concluded that TCDD may increase the amplitude of the prenatal testosterone surge in male rats by stimulating pituitary LH production and enhancing the sensitivity of the fetal testis to LH. DES, on the contrary, apparently impairs testicular steroidogenesis and pituitary function.

Retinoid receptors involved in the effects of retinoic acid on rat testis development

We have previously shown that retinoic acid (RA) is able to act on the development of Leydig, Sertoli, and germ cells in the testis in culture (Livera et al., Biol Reprod 2000; 62:1303-1314). To identify which receptors mediate these effects, we have now added selective agonists and antagonists of retinoic acid receptors (RARs) or retinoid X receptors (RXRs) in the same organotypic culture system. The RAR alpha agonist mimicked most of the effects of RA on the cultured fetal or neonatal testis, whereas the RAR beta, gamma, and pan RXR agonists did not. The RAR alpha agonist decreased the testosterone production, the number of gonocytes, and the cAMP response to FSH of fetal testis explanted at 14.5 days postconception (dpc). The RAR alpha agonist disorganized the cords of the 14.5-dpc cultured testis and increased the cord diameter in cultured 3-days-postpartum (dpp) testis in the same way as RA. All these RA effects could be reversed by an RAR alpha antagonist and were unchanged by an RAR beta/gamma antagonist. The RAR beta agonist, however, increased Sertoli cell proliferation in the 3-dpp testis in the same way as RA, and this effect was blocked by an RAR beta antagonist. The RAR gamma and the pan RXR agonists had no selective effect. These results suggest that all the effects of RA on development of the fetal and neonatal testis are mediated via RAR alpha, except for its effect on Sertoli cell proliferation, which involves RAR beta.

Luteinizing hormone-dependent activity and luteinizing hormone-independent differentiation of rat fetal Leydig cells

Addition of 5x10(-2) U/ml recombinant luteinizing hormone (LH) to testes from fetuses at 16.5 day post conception (dpc) cultured for 5 days increased the number of Leydig cells by 34% and the acute LH-stimulated testosterone production by 600%. To determine whether these positive effects of LH in vitro are physiologically relevant in vivo, fetuses were decapitated on days 16.5 pc (before the onset of LH expression in the hypophysis) or 18.5 pc (before the surge of LH in the fetal plasma) and removed at 21.5 dpc. The number of fetal Leydig cells per testis and the acute LH-stimulated testosterone production by the testes ex vivo were unaltered by decapitation. Since, in all groups, the number of Leydig cells doubled between 16.5 and 18.5 dpc and between 18.5 and 21.5 dpc, these results suggest that neither the appearance of new fully differentiated fetal Leydig cells nor the maintenance of differentiated functions in existing fetal Leydig cells depend on LH during late fetal life, although this hormone is present in the plasma. Decapitation reduced the testosterone concentrations in the plasma (-56%) and in the testis in vivo (-67%) and the basal testosterone secretion of the testis ex vivo (-70%). This suggests that LH is required to maintain the physiological activity of the Leydig cell during late fetal life. However, the decrease of the in vivo testosterone production after decapitation was not sufficient to impair the growth of the Wolffian ducts and the lengthening of the anogenital distance. In conclusion, during late fetal life in the rat, Leydig cells are LH-independent for their functional differentiation and LH-dependent for their activity.

Multiple effects of retinoids on the development of Sertoli, germ, and Leydig cells of fetal and neonatal rat testis in culture

We investigated the effect of retinoids on the development of Sertoli, germ, and Leydig cells using 3-day culture of testes from fetuses 14.5 and 18.5 days post-conception (dpc) and from neonates 3 days postpartum (dpp). Addition of 10(-6) M and 3.10(-8) M retinoic acid (RA) caused a dose-dependent disruption of the seminiferous cords in 14.5-day-old fetal testes, without any change in the 5-bromo-2'-deoxyuridine (BrdU) labeling index of the Sertoli cells. RA caused no disorganization of older testes, but it did cause hyperplasia of the Sertoli cells in 3-dpp testes. Fragmentation of the Sertoli cell DNA was not detected in control or RA-treated testes at any age studied. The cAMP produced in response to FSH was significantly decreased in RA-treated testes for all studied ages. Both 10(-6) M and 3.10(-8) M RA dramatically reduced the number of gonocytes per 14.5-dpc testis. This resulted from a high increase in apoptosis, which greatly exceeded the slight increase of mitosis. RA caused no change in the number of gonocytes in testes explanted on 18.5 dpc (the quiescent period), whereas it increased this number in testes explanted on 3 dpp (i.e., when gonocyte mitosis and apoptosis resume). Lastly, RA and retinol (RE) reduced both basal and acute LH-stimulated testosterone secretion by 14.5-dpc testis explants, without change in the number of 3beta-hydroxysteroid dehydrogenase-positive cells per testis. Retinoids had no effect on basal or LH-stimulated testosterone production by older testes. In conclusion, RE and RA are potential regulators of the development of the testis and act mainly negatively during fetal life and positively during the neonatal period on the parameters we have studied.

Apoptosis and mitosis in gonocytes of the rat testis during foetal and neonatal development

This study was undertaken to determine the extent of apoptosis and mitosis in the various testicular cell types throughout rat development from foetal day 14.5 to postnatal days 9-10. Apoptotic activity was studied by detecting DNA fragmentation (TUNEL method) in situ. A TUNEL-positive reaction was detected in gonocytes, while none of the other testicular cells were labelled. The morphology of the TUNEL-positive gonocytes was characteristic of apoptotic cells and was different from that observed in experimentally induced necrosis. The percentage of stained gonocytes peaked on day 15.5-16.5 post-conception (dpc), decreased thereafter and no TUNEL-positive gonocytes were found from foetal day 18.5 onwards. On postnatal day 2, apoptosis resumed and increased to reach a maximum on day 7. Mitosis in the gonocytes, as evaluated by the immunodetection of 5-bromo-2'-deoxyuridine (BrdU) incorporation, was present during the same developmental periods but the ratio of BrdU-positive/TUNEL-positive gonocytes was much greater in the foetal period than in the neonatal period. In an organotypic culture system, the changes in the apoptotic and mitotic activities of the gonocytes in testicular explants from foetuses on days 18.5 and 20.5 or from neonates on day 3, cultured for two days were similar to those observed in vivo. Addition of LH or FSH did not influence either apoptosis or mitosis in the germ cells. These results suggest that both apoptosis and mitosis of gonocytes are independent of gonadotrophins and are mainly controlled by intratesticular factors.

mRNA expression of gonadotropin-releasing hormones (GnRHs) and GnRH receptor in goldfish

In goldfish (Carassius auratus), two distinct forms of gonadotropin-releasing hormone (GnRH), namely, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), have been identified in the brain using chromatographic, immunological, and molecular cloning approaches. These two native GnRHs act on specific receptors in the anterior pituitary to stimulate the synthesis and release of gonadotropins and growth hormone in goldfish. To evaluate the potential roles of sGnRH and cGnRH-II in both neural and reproductive tissues in goldfish, we studied the mRNA expression of sGnRH, cGnRH-II, and GnRH receptor (GnRH-R) in discrete brain areas, pituitary, ovary, and testis by a combined reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot analysis. Total RNA was extracted from various tissues of sexually recrudescent male and female goldfish and RT-PCR was performed with primers specific for GnRH-R complementary DNA (cDNA), sGnRH cDNA, cGnRH-II cDNA-1, and cDNA-2. Results showed that GnRHs and GnRH-R mRNAs are differentially distributed in the brain. In the goldfish brain, sGnRH mRNA was predominantly expressed in the forebrain areas (olfactory bulb, telencephalon, and hypothalamus) whereas cGnRH-II mRNA-1 were expressed in all brain areas including olfactory bulbs and optic tectum-thalamus. The expression level of cGnRH-II mRNA-2 was much lower than that of cGnRH-II mRNA-1 in the brain. On the other hand, GnRH-R mRNA was expressed in all brain regions and pituitary. In the ovary and testis, GnRH-R mRNA, sGnRH mRNA, and cGnRH-II mRNA-1, but not cGnRH-II mRNA-2, are expressed. Sequence analysis of the PCR products showed that nucleotide sequences of GnRH-R in gonads are identical with that in the brain and pituitary. The coexistence of GnRHs and GnRH-R mRNAs in both neural and gonadal tissues supports the notion that sGnRH and cGnRH-II may act as neurotransmitters and/or neuromodulators in the brain and as autocrine and/or paracrine hormones in gonadal tissues in addition to their established neuroendocrine roles at the pituitary of goldfish.

Expression and regulation of transforming growth factor beta1 mRNA and protein in rat fetal testis in vitro

The expression and secretion of Transforming Growth Factor beta1 (TGFbeta1) by cultured testes of day 20.5 rat fetuses were investigated. The testes were found to express two TGFbeta1 mRNA transcripts of 2.5 and 1.8 kb. By using mink lung epithelial cell bioassay based on the measurement of the inhibition of tritiated thymidine incorporation in response to TGFbeta1 immunoreactive material, the fetal testes were shown to secrete TGFbeta1 protein in organ culture. This secretion was positively regulated by dibutyryl cyclic AMP or by LH and FSH together, but not by LH alone and very slightly by FSH alone, which suggests interactions between Leydig and Sertoli cells for the control of TGFbeta1 production. These regulations probably take place at a posttranscriptional step since no concomitant increase of TGFbeta1 mRNA levels was observed. Such a positive regulation of TGFbeta1 secretion by gonadotropins could be a characteristic of the rat fetal testis.

Transforming growth factor beta1 inhibits steroidogenesis in dispersed fetal testicular cells in culture

TGF beta1 has been detected by immunohistochemistry in the rat fetal testis. Therefore, we attempted to determine whether this factor can act as a local regulator of Leydig cell function during fetal development. An inhibitory effect of TGF beta1 on basal and luteinizing hormone (LH)-stimulated testosterone secretion by fetal testes in vitro was observed only with testes from 13.5 day-old fetuses and not with testes from older stages. The lack of effect of exogenous TGF beta1 in organ culture after day 13.5 might be related to an elevated intratesticular concentration that would already exert maximal biological effect. On the contrary, in a model of dispersed testicular cells in culture, TGF beta1 was able to inhibit LH-stimulated testosterone production by fetal Leydig cells from 16.5 and 20.5 day-old fetuses. This inhibition of LH-stimulated testosterone production was dose- and time-dependent and was maximal after 48 h of treatment with 1 ng/ml TGF beta1, with testosterone secretion being reduced to 25% of control values. Inhibition of testosterone secretion was also observed in basal and dbcAMP-stimulated conditions, suggesting that one site of action of TGF beta1 is located after the production of cAMP. However, TGF beta1 was also able to inhibit LH-induced cAMP production. As demonstrated by the transformation of steroidogenic precursors into testosterone, TGF beta1 did not significantly alter 3beta-hydroxysteroid dehydrogenase (3beta HSD) activity but induced a strong inhibition of cytochrome P450 17alpha-hydroxylase/C17-20 lyase (P450C17) activity which was associated with a marked diminution of cytochrome P450C17 mRNA levels (26% of control values) but not of cytochrome P450scc mRNA. In addition to its effect on steroidogenesis, TGF beta1 exhibited morphogenic actions on the fetal testicular cells, inducing spreading when the cells were adherent and aggregation when the cells were cultured in conditions of lesser adherence and without any significant effect on either total cell number or 3beta HSD positive cells. Taken together these results suggest that TGF beta1 likely plays a morphogenic and physiological role very early in the fetal testis via paracrine/autocrine mechanisms.