Relationships between liver testosterone receptor isoforms and aromatase activity in female green frog, Rana esculenta

Decreased attractivity in female garter snakes treated with an aromatase inhibitor

Most experimental studies on sexual signal regulation via hormone manipulation have focused on male signals, yet female signals demonstrate substantial phenotypic variation and hormone-dependent expression. Female red-sided garter snakes (Thamnophis sirtalis parietalis) produce a skin-based sex pheromone used by males in mate selection. The principle female sex steroid, 17 β-estradiol, controls pheromone production in snakes, but studies manipulating female garter snakes have produced conflicting results, relied on behavioral tests with males in the laboratory, and did not quantify pheromone expression. Because aromatase is the terminal enzyme in estradiol biosynthesis, we hypothesized that female garter snakes rely on aromatase to ultimately control pheromone production during the annual cycle of this species. To test this, we used a known pharmacological inhibitor of aromatase, fadrozole (FAD). Wild-caught female garter snakes were chronically treated via subcutaneous injections of either FAD (1.0 mg kg^-1 ) or saline (control) for six months in the laboratory during the active period of the annual cycle then hibernated. In two separate field bioassays the next spring at the den site, FAD females received approximately 50% less courtship from wild, sexually active male garter snakes compared to SHAM females. Pheromone analysis revealed that four of the largest, unsaturated methyl ketones were specifically downregulated in FAD females, indicating that aromatase action is a crucial, permissive step in the maintenance of female attractivity.

Celebrating 50+ years of research on the reproductive biology and endocrinology of the green frog: An overview

This issue is dedicated to the late Professor Giovanni Chieffi, and this article is an overview of the research on Comparative Endocrinology of reproduction using Rana esculenta (alias Pelophylax esculentus) as a model system. Starting from the early 1970s till today, a large quantity of work have been conducted both in the fields of experimental endocrinology and in the definition of the diffuse neuroendocrine system, with a major focus on the increasing role of regulatory peptides. The various aspects investigated concerned the histological descriptions of principal endocrine glands of the hypothalamic-pituitary-gonadal (HPG) axis, the localization and distribution in the HPG of several different substances (i.e. neurosteroids, hypothalamic peptide hormones, pituitary gonadotropins, gonadal sex steroids, and other molecules), the determination of sex hormone concentrations in both serum and tissues, the hormone manipulations, as well as the gene and protein expression of steroidogenic enzymes and their respective receptors. All together these researches, often conducted considering different periods of the annual reproductive cycle of the green frog, allowed to understand the mechanism of cascade control/regulation of the HPG axis of R. esculenta, characterizing the role of different hormones in the two sexes, and testing the hypotheses about the function of single hormones in different target organs. It becomes evident from the review that, in their simplest form, several features of this species are specular as compared to those of other vertebrate species and that reproduction in this frog species is either under endogenous multi-hormonal control or by a wide array of different factors. Our excursus of this research, spanning almost five decades, shows that R. esculenta has been intensively and successfully used as an animal model in reproductive endocrinology as well as several field studies such as those involving environmental concerns that focus on the effects of endocrine disruptors and other environmental contaminants.

Effects of elevated dissolved carbon dioxide and perfluorooctane sulfonic acid, given singly and in combination, on steroidogenic and biotransformation pathways of Atlantic cod

In the aquatic environments, the predicted changes in water temperature, pO2 and pCO2 could result in hypercapnic and hypoxic conditions for aquatic animals. These conditions are thought to affect several basic cellular and physiological mechanisms. Yet, possible adverse effects of elevated CO2 (hypercapnia) on teleost fish, as well as combined effects with emerging and legacy environmental contaminants are poorly investigated. In this study, juvenile Atlantic cod (Gadus morhua) were divided into groups and exposed to three different water bath PFOS exposure regimes (0 (control), 100 and 200 μg L(-1)) for 5 days at 1h/day, followed by three different CO2-levels (normocapnia, moderate (0.3%) and high (0.9%)). The moderate CO2 level is the predicted near future (within year 2300) level, while 0.9% represent severe hypercapnia. Tissue samples were collected at 3, 6 and 9 days after initiated CO2 exposure. Effects on the endocrine and biotransformation systems were examined by analyzing levels of sex steroid hormones (E2, T, 11-KT) and transcript expression of estrogen responsive genes (ERα, Vtg-α, Vtg-β, ZP2 and ZP3). In addition, transcripts for genes encoding xenobiotic metabolizing enzymes (cyp1a and cyp3a) and hypoxia-inducible factor (HIF-1α) were analyzed. Hypercapnia alone produced increased levels of sex steroid hormones (E2, T, 11-KT) with concomitant mRNA level increase of estrogen responsive genes, while PFOS produced weak and time-dependent effects on E2-inducible gene transcription. Combined PFOS and hypercapnia exposure produced increased effects on sex steroid levels as compared to hypercapnia alone, with transcript expression patterns that are indicative of time-dependent interactive effects. Exposure to hypercapnia singly or in combination with PFOS produced modulations of the biotransformation and hypoxic responses that were apparently concentration- and time-dependent. Loading plots of principal component analysis (PCA) produced a significant grouping of individual scores according to the exposure scenarios at day 6 and 9. Overall, the PCA analysis produced a unique clustering of variables that signifies a positive correlation between exposure to high PFOS concentration and mRNA expression of E2 responsive genes. Notably, this pattern was not evident for individuals exposed to PFOS concentrations in combination with elevated CO2 scenarios. To our knowledge, the present study is the first of its kind, to evaluate such effects using combined exposure to a perfluoroalkyl sulfonate and elevated levels of CO2 saturation, representative of future oceanic climate change, in any fish species or lower vertebrate.

D-Aspartic acid implication in the modulation of frog brain sex steroid levels

There is evidence that D-aspartate (D-Asp) modulates sex hormone levels in frog testis by regulating the activity of P450 aromatase (P450 aro), the key enzyme which converts Testosterone (T) in 17ß-Estradiol (E2). Here we report, for the first time, that there is a direct correlation among brain levels of D-Asp, P450 aro, E2 and Estradiol Receptor (ERα) in the male frogs during the reproductive as well as the post-reproductive phases of the breeding cycle, with highest levels being observed in the post-reproductive period. D-Asp i.p. administration to frogs ready for reproduction, induced an increase of brain P450 aro protein expression with concomitant enhancement of both E2 levels and ERα expression; at the same time, brain T levels and Androgen receptor expression decreased. In contrast, in the post-reproductive frogs, D-Asp treatment did not modify any of these parameters. Taken together, these results imply that the regulation of P450 aro expression by D-Asp could be an important step in the control of E2 levels in the frog brain.

Peroxisome proliferator-activated receptors, estrogenic responses and biotransformation system in the liver of salmon exposed to tributyltin and second messenger activator

The mechanisms by which organotin compounds produce modulations of the endocrine systems and other biological responses are not fully understood. In this study, juvenile salmon were force-fed diet containing TBT (0: solvent control, 0.1, 1 and 10mg/kg fish) for 72 h. Subsequently, fish exposed to solvent control and 10mg TBT were exposed to waterborne concentration (200 microg/l) of the adenylate cyclase (AC) stimulator, forskolin for 2 and 4h. The overall aim of the study was to explore whether TBT endocrine disruptive effects involve second messenger activation. Liver was sampled from individual fish (n=8) at the end of the exposures. The transcription patterns of peroxisome proliferator-activated receptor (PPAR) isotype and acyl-coenzyme A oxidase 1 (ACOX1), aromatase isoform, estrogen receptor-alpha (ER alpha), pregnane X receptor (PXR), CYP3A and glutathione S-transferase (GST) genes were measured by quantitative polymerase chain reaction (qPCR). Our data showed a consistent increase in PPAR alpha, PPAR beta and PPAR gamma mRNA and protein expression after TBT exposure that were inversely correlated with ACOX1 mRNA levels. Forskolin produced PPAR isotype-specific mRNA and protein effects that were modulated by TBT. ACOX1 expression was decreased (at 2h) and increased (at 4h) by forskolin and the presence of TBT potentiated these effects. TBT apparently increased mRNA and protein levels of cyp19a, compared to the solvent control, whereas cyp19b mRNA levels were unaffected by TBT treatment. Combined TBT and forskolin exposure produced respective decrease and increase of mRNA levels of cyp19a and cyp19b, compared with control. TBT decreased ER alpha mRNA at low dose (1mg/kg) and forskolin exposure alone produced a consistent decrease of ER alpha mRNA levels that were not affected by the presence of TBT. Interestingly, PXR and CYP3A mRNA levels were differentially affected, either decreased or increased, after exposure to TBT and forskolin, singly and also in combination. GST mRNA was increased by TBT exposure. Exposure to forskolin alone increased GST expression with time, and combined exposure with TBT potentiated these respective effects. Overall, the present study demonstrates multiple biological effects of TBT given singly or in combination with cAMP activator. There are no studies known to us that have evaluated the endocrine disruptive effects of TBT in the presence of a second messenger activator, and our data suggest that TBT may exert endocrine, biotransformation and lipid peroxidative effects through modulation of cAMP/PKA second messenger signaling with overt physiological consequences.

Vitellogenin synthesis via androgens in primary cultures of tilapia hepatocytes

Involvement of androgens in vitellogenin (VTG) synthesis was investigated using the primary hepatocyte cultures of tilapia, Oreochromis mossambicus. Concentration of VTG in the medium was assessed by enzyme-linked immunosorbent assay. When the hepatocytes of females were treated with testosterone (T), 17 alpha-methyltestosterone (MT) and 5 alpha-dihydrotestosterone (DHT), VTG concentration in the medium slightly increased or maintained. DHT, but not T and MT, increased VTG in the medium of male hepatocyte cultures. However, VTG production in the male hepatocytes, which were previously treated with estradiol-17 beta (E(2)), maintained high level by treatment of T. Similarly, co-treatment of E(2) and the androgens to the male hepatocytes enhanced VTG concentration in the medium. These results suggest that the androgens have some roles in VTG synthesis in the hepatocytes. Tamoxifen, a nonsteroidal antiestrogen, reduced VTG synthesis by the androgens. On the other hand, co-treatment of T and fadrozole, an aromatase inhibitor, failed to inhibit the effect of VTG synthesis by T alone. Analysis with RT-PCR did not demonstrate expression of the brain and the ovarian types of aromatase mRNA in the liver. These results suggest that the possibility of local aromatization of the androgens in the tilapia liver is low and that androgens bind estrogen receptor and, consequently, exert estrogenic action. Treatment of cyproterone acetate, an antiandrogen reagent, increased production of VTG with DHT. Involvement of androgens might not be ignored in regulation of VTG synthesis in the liver.

Aromatase activity in the European sea bass (Dicentrarchus labrax L.) brain. Distribution and changes in relation to age, sex, and the annual reproductive cycle

Cytochrome P450 aromatase activity (AA) was measured in different tissues of the sea bass (Dicentrarchus labrax L.) using a tritiated water release assay that was previously optimized and validated for this species. In adult fish entering the reproductive season, AA was highest on a per mg protein basis, in the brain (2.04+/-0.4 pmol/mg prot/h; mean+/-SEM), followed by the ovary (0.59+/-0.1) and was detectable in visceral fat (0.21+/-0.05), liver (0.08+/-0.009), and head kidney (0.03+/-0.004). However, AA was negligible in the rest of the tissues tested: heart, testis, muscle, and spleen. Consistent with results obtained in other species, dissection of the brain into its major constitutive parts revealed that AA was concentrated in areas implicated in the control of reproduction, including the olfactory bulb, telencephalon, and hypothalamus (range: 2.6-16.2 pmol/mg prot/h), as well as the pituitary gland (6.2-9.3 pmol/mg prot/h). Lower AA was noted in the optic bulb, cerebellum, and medulla. However, in contrast to some previously published reports concerning the content and distribution of neural aromatase in fish, males consistently exhibited higher AA than females. In one-year-old juvenile fish completing the process of gonadal sex differentiation, brain AA (0.63 pmol/mg prot/h) was similar in both sexes and ten times lower than that measured in the brain of first time spawners (6.52 pmol/mg prot/h), in this case with males showing an overall higher (24%) activity than females. When surveyed throughout the year, brain AA dramatically changed during the reproductive cycle. Maximum average values of approximately 7 pmol/mg prot/h were obtained that coincided with the spawning season. The peak in brain AA was preceded by two and one months by the peak of plasma testosterone and the peak of the gonadosomatic index, respectively. This is the first measurement of the distribution of the activity of a steroidogenic enzyme in the sea bass, an established model in comparative endocrinology. Together, these results demonstrate sex- and seasonally-related variations in AA and establish the basis for further comparative studies of certain androgen-mediated actions through locally formed estrogen in both central and peripheral targets.

Amphibians as a model for the study of endocrine disruptors

Evidence shows that environmental compounds can interfere with the endocrine systems of wildlife and humans. The main sink of such substances, called endocrine disruptors (EDs), which are mainly of anthropogenic origin, is surface water; thus, aquatic vertebrates such as fishes and amphibians are most endangered. Despite numerous reports on EDs in fishes, information about EDs in amphibians is scarce, and this paucity of information is of particular concern in view of the worldwide decline of amphibians. EDs could contribute to changes of amphibian populations via adverse effects on reproduction and the thyroid system. In amphibians, EDs can affect reproduction by (anti)estrogenic and (anti)androgenic modes of action that produce severe effects including abnormal sexual differentiation. ED actions on the thyroid system cause acceleration or retardation of metamorphosis, which may also affect population levels. Our broad knowledge of amphibian biology and endocrinology indicates that amphibians are very suitable models for the study of EDs. In particular, effects of EDs on the thyroid system triggering metamorphosis can be determined easily and most sensitively in amphibians compared to other vertebrates. A new classification of EDs according to their biological modes of action is proposed because EDs have quite heterogeneous chemical structures, which do not allow prediction of their biological effects. Methods and strategies are proposed for identification and risk assessment of EDs, whether as pure test substances or as mixtures from environmental samples. Effects of EDs on the thyroid system of amphibians can be assessed by a single animal model (Xenopus laevis), whereas the various types of reproduction need comparative studies to investigate whether general endocrine principles do exist among several species of anurans and urodeles. Thus, at least one anuran and one urodelean model are needed to determine ED interference with reproduction.

Sexually dimorphic expression of steroidogenic factor 1 (SF-1) in developing gonads of the American bullfrog, Rana catesbeiana

Genetic sex determination leads to gonadal differentiation and ultimately the differences between the sexes in steroid hormone secretion. Gonadal steroidogenesis is critical for the development of a sexually dimorphic phenotype and adult reproductive function. Control of gonadal development and steroidogenesis is under the regulation, at least in part, of steroidogenic factor-1 (SF-1). We have begun to characterize SF-1 expression in an amphibian to determine the role of this protein in development and reproduction. We have detected a putative SF-1 protein from several tissues in the American bullfrog, Rana catesbeiana, that co-migrates with mouse SF-1 on a Western blot. Our results show that bullfrog SF-1 protein is expressed in steroidogenic and other reproductive tissues in a manner similar to that reported for other species, with high expression in the brain, pituitary, gonad, liver, and interrenal, but little or no expression in non-reproductive tissues such as skin and intestine. Using a quantitative Western blot analysis system, we documented changes in SF-1 protein in the gonads of developing tadpoles. Our results indicate that there is sexually dimorphic expression of SF-1 protein that becomes evident at the time of sexual differentiation of the gonads. In males, the expression of SF-1 decreases following testicular formation and in females the expression increases with the formation of ovaries. This is the first study to investigate changes in SF-1 during development at the protein level. The expression is similar to that reported for changes in SF-1 mRNA expression in chickens and alligators, however, opposite to that seen in mammals and turtles. These results indicate that SF-1 may play a pivotal role in development of the reproductive system in amphibians as it does in other vertebrate groups.

Estrogen therapy for hepatectomy patients with poor liver function?

Estrogen is well known to promote liver regeneration after partial hepatectomy. Administration of estradiol prior to partial hepatectomy also induces increased activity of DNA synthesis. Endogenous aromatase plays a key role in the conversion of testosterone to estradiol. The aromatase activity was induced by IL-6, which is a key factor for liver regeneration. It has been reported that IL-6 interacts with gp80/130 receptor and regulates the STAT1/3 pathway to induce DNA synthesis in hepatocyte. The IL-6 induced aromatase activity results in increased serum estradiol level. This corresponded well with observation that estradiol was elevated after partial hepatectomy. Therefore, it is very likely that estradiol and IL-6 synergize in stimulation of hepatocyte proliferation during liver regeneration. We propose that a short-term estradiol treatment may be beneficial for patients with poor liver function after hepatectomy.