Expression and localization of aromatase during fetal mouse testis development

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.

Pubertal exposure to tebuconazole increases testosterone production via inhibiting testicular aromatase activity in rats

Tebuconazole is a triazole compound used agriculturally to treat plant pathogenic fungi. However, whether pubertal exposure to tebuconazole affects Leydig cell development remains unknown. Here, we exposed male Sprague-Dawley rats at 35 days of age to 0, 25, 50, or 100 mg kg^-1 day^-1 tebuconazole for 21 days. Tebuconazole exposure increased serum testosterone level but lowered estradiol level at a dose of 100 mg kg^-1, without affecting serum luteinizing hormone and follicle-stimulating hormone concentrations. Tebuconazole up-regulated the expression of testicular Cyp11a1, Hsd11b1, and Fshr genes as well as their proteins at a dose of 100 mg kg^-1. However, tebuconazole did not stimulate the proliferation of Leydig cells. Tebuconazole in vitro inhibits aromatase activity in primary rat Leydig cells with IC₅₀ value of 40 μmol/L. In conclusion, tebuconazole exposure stimulates pubertal Leydig cell differentiation via inhibiting aromatase activity.

Short-Term Fasting Reveals Amino Acid Metabolism as a Major Sex-Discriminating Factor in the Liver

Sex impacts on liver physiology with severe consequences for energy metabolism and response to xenobiotic, hepatic, and extra-hepatic diseases. The comprehension of the biology subtending sex-related hepatic differences is therefore very relevant in the medical, pharmacological, and dietary perspective. The extensive application of metabolomics paired to transcriptomics here shows that, in the case of short-term fasting, the decision to maintain lipid synthesis using amino acids (aa) as a source of fuel is the key discriminant for the hepatic metabolism of male and female mice. Pharmacological and genetic interventions indicate that the hepatic estrogen receptor (ERα) has a key role in this sex-related strategy that is primed around birth by the aromatase-dependent conversion of testosterone into estradiol. This energy partition strategy, possibly the result of an evolutionary pressure enabling mammals to tailor their reproductive capacities to nutritional status, is most important to direct future sex-specific dietary and medical interventions.

Steroidogenic enzymes, their products and sex steroid receptors during testis development and spermatogenesis in the domestic cat (Felis catus)

In the present study we comprehensively characterize intratesticular sex steroid production, metabolism and receptors in the domestic cat to elucidate the role of testosterone, estradiol and progesterone in testis development, steroid synthesis and spermatogenesis. There is a great demand for new concepts of fertility control in domestic (feral) cats and wild felids. The acquired knowledge will help to understand the regulation of spermatogenesis in felids, and may reveal new target points for male contraception. Progesterone and androgens are produced throughout all stages of testicular development; their synthesizing enzymes are mainly expressed in Leydig cells, and to a much lesser extent also in tubular cells. Aromatase (CYP19A1), the estrogen synthesizing enzyme, is only present in the tubuli and is first detectable in spermatocytes and round spermatids at puberty. As shown by elevated expression of the enzymes steroid 5-α-reductase type 1 (SRD5A) and aldo-keto-reductase family 1 member C3 (AKR1C3), the capacity to metabolize particular steroids increases during testis development. Apparently, this refers to a decreasing intra-testicular testosterone concentration per mg tissue with increasing testis weight during postpuberty. The increasing potential of sulfation of E2 by estrogen sulfotransferase (SULT1E1) with ongoing development might be responsible for the low level of unconjugated intratesticular estradiol in all stages of development probably due to facilitated excretion of conjugated estrogens. For the first time, expression of the progesterone membrane receptor components 1 and 2 (PGRMC1, PGRMC2) was studied in mammalian testis tissue. Both of these and also the progesterone receptor (PGR) are expressed depending on the developmental stage and cell type, suggesting an important regulatory role of progesterone in the testis. Androgen receptor (AR) is present in almost all cell types except for some spermatogenic cells. The co-localization of aromatase with estrogen receptor alpha (ESR1) in spermatocytes and round spermatids of domestic cat testis indicates an auto-/paracrine function of estrogen in spermatogenesis. In summary, the testis of the domestic cat is an important source of sex steroids. All of them could act within the testis but additionally, at least androgens and estrogens are likely secreted by the testis, partly as conjugated steroids.

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.