Tissue-specific suppression of estrogen, androgen and glucocorticoid receptor gene expression in feral vitellogenic male Mozambique tilapia

Sex-specific responses to growth hormone and luteinizing hormone in a model teleost, the Mozambique tilapia

Across the vertebrate lineage, sexual dimorphism in body size is a common phenomenon that results from trade-offs between growth and reproduction. To address how key hormones that regulate growth and reproduction interact in teleost fishes, we studied Mozambique tilapia (Oreochromis mossambicus) to determine whether the activities of luteinizing hormone (Lh) are modulated by growth hormone (Gh), and conversely, whether targets of Gh are affected by the presence of Lh. In particular, we examined how gonadal morphology and specific gene transcripts responded to ovine GH (oGH) and/or LH (oLH) in hypophysectomized male and female tilapia. Hypophysectomized females exhibited a diminished gonadosomatic index (GSI) concomitant with ovarian follicular atresia. The combination of oGH and oLH restored GSI and ovarian morphology to conditions observed in sham-operated controls. A similar pattern was observed for GSI in males. In control fish, gonadal gh receptor (ghr2) and estrogen receptor β (erβ) expression was higher in females versus males. A combination of oGH and oLH restored erβ and arβ in females. In males, testicular insulin-like growth factor 3 (igf3) expression was reduced following hypophysectomy and subsequently restored to control levels by either oGH or oLH. By contrast, the combination of both hormones was required to recover ovarian igf3 expression in females. In muscle, ghr2 expression was more responsive to oGH in males versus females. In the liver of hypophysectomized males, igf2 expression was diminished by both oGH and oLH; there was no effect of hypophysectomy, oGH, or oLH on igf2 expression in females. Collectively, our results indicate that gene transcripts associated with growth and reproduction exhibit sex-specific responses to oGH and oLH. These responses reflect, at least in part, how hormones mediate trade-offs between growth and reproduction, and thus sexual dimorphism, in teleost fishes.

Reproductive health and endocrine disruption in smallmouth bass (Micropterus dolomieu) from the Lake Erie drainage, Pennsylvania, USA

Smallmouth bass Micropterus dolomieu were sampled from three sites within the Lake Erie drainage (Elk Creek, Twentymile Creek, and Misery Bay, an embayment in Presque Isle Bay). Plasma, tissues for histopathological analyses, and liver and testes preserved in RNALater® were sampled from 30 smallmouth bass (of both sexes) at each site. Liver and testes samples were analyzed for transcript abundance with Nanostring nCounter® technology. Evidence of estrogenic endocrine disruption was assessed by the presence and severity of intersex (testicular oocytes; TO) and concentrations of plasma vitellogenin in male fish. Abundance of 17 liver transcripts associated with reproductive function, endocrine activity, and contaminant detoxification pathways and 40 testes transcripts associated with male and female reproductive function, germ cell development, and steroid biosynthesis were also measured. Males with a high rate of TO (87-100%) and plasma vitellogenin were noted at all sites; however, TO severity was greatest at the site with the highest agricultural land cover. Numerous transcripts were differentially regulated among the sites and patterns of transcript abundance were used to better understand potential risk factors for estrogenic endocrine disruption. The results of this study suggest endocrine disruption is prevalent in this region and further research would benefit to identify the types of contaminants that may be associated with the observed biological effects.

Endocrine disruption in the sub Antarctic fish Patagonotothen tessellata (Perciformes, Notothenidae) from Beagle Channel associated to anthropogenic impact

Situated in the sub-Antarctic region, Beagle Channel represents a unique marine ecosystem due to the connection between the Pacific and the Atlantic Oceans, and its proximity to the Antarctic Peninsula. Ushuaia city, the biggest settlement on the channel, exerts an increasing anthropogenic pressure by discharges of urban and industrial effluents. In the present work, we use Patagonotothen tessellata, one of the most abundant and widespread species in the channel, as a bioindicator species in order to evidence anthropic impact from Ushuaia Bay and surrounding areas. We first analyzed and characterized real time gene expression of androgen receptor, estrogen receptor and different forms of vitellogenin (VTG), under laboratory conditions. This was achieved by induction with estradiol of P. tessellata males. Then, the selected genes were used as biomarkers for an environmental biomonitoring study. Morphometric indices and circulating sex steroids (estradiol and testosterone) were also quantified in male fish collected from different sites. The qPCR analysis showed that vtgAb form is more inducible than vtgAa or vtgC forms after estrogen induction. The field survey revealed the up-regulation of vtgAb and the androgen receptor in fish from sites with higher anthropogenic influence. Sex steroids followed seasonal variations according to their reproductive cycle, with higher levels of estradiol and testosterone in winter and summer seasons. The use of biomarkers such as gene expression of VTG demonstrates that fish from Ushuaia Bay are likely to be exposed to endocrine disrupting compounds. To our knowledge, this research is the first attempt to assess the endocrine disruption associated to anthropic impact in a widespread fish of the Beagle Channel and contributes to a better understanding of the reproductive physiology of sub Antarctic ichthyofauna.

Biomonitoring the effects of urban-stream waters on the health status of pale chub (Zacco platypus): A comparative analysis of biological indexes and biomarker levels

The objective of this study was to biomonitor the effects of potential environmental pollutants in urban-stream waters, on fish health. Pale chub (Zacco platypus), a dominant species in the Korea urban stream waters, was chosen and biomonitoring indicators for the different spatial characteristics were tailored in an urban watershed. Biological responses including biotic-somatic index as well as gonadal development phase and plasma steroids levels, and the biochemical responses, ethoxyresorufin-o-deethylase (EROD) and acetylcholinesterase (AChE) activities, were measured. No significant difference was observed in the length-weight relationship between the up-stream waters and the down-stream waters. However, changes in the gonad-somatic index (GSI) levels, plasma 17β-estradiol (E2) levels, and mature oocyte frequencies in the female fish collected during the spawning season were observed in the down-stream waters at each monitoring site. Moreover, intersex condition (testis-ova) in the male fish in down-stream waters was recorded, even if it was just one fish. Although no significant difference was observed in the EROD and AChE activities between the up-stream waters and the down-stream waters, changes in the reproductive biomarker levels, including the GSI levels, plasma E2 levels, and gonadal maturation, lead to variable biomonitoring endpoints between the spatial different sites. These results imply that exposure to the down-stream waters can cause reproductive impairment in wild Z. platypus, individual variability in the biological responses further indicate the reproductive health was affected more by the down-stream waters than the up-stream waters. The finding from this study can provide the biomonitoring endpoint on the wild fish health in urban watershed that is crucial to the early risk assessment of its biological impacts. More multi-biomarkers studies reflecting the variation in the biological organization of wild fish and, therefore, the effects of urban-stream waters in the fish health are warranted.

Experimental Approaches for Characterizing the Endocrine-Disrupting Effects of Environmental Chemicals in Fish

Increasing industrial and agricultural activities have led to a disturbing increase of pollutant discharges into the environment. Most of these pollutants can induce short-term, sustained or delayed impacts on developmental, physiological, and behavioral processes that are often regulated by the endocrine system in vertebrates, including fish, thus they are termed endocrine-disrupting chemicals (EDCs). Physiological impacts resulting from the exposure of these vertebrates to EDCs include abnormalities in growth and reproductive development, as many of the prevalent chemicals are capable of binding the receptors to sex steroid hormones. The approaches employed to investigate the action and impact of EDCs is largely dependent on the specific life history and habitat of each species, and the type of chemical that organisms are exposed to. Aquatic vertebrates, such as fish, are among the first organisms to be affected by waterborne EDCs, an attribute that has justified their wide-spread use as sentinel species. Many fish species are exposed to these chemicals in the wild, for either short or prolonged periods as larvae, adults, or both, thus, studies are typically designed to focus on either acute or chronic exposure at distinct developmental stages. The aim of this review is to provide an overview of the approaches and experimental methods commonly used to characterize the effects of some of the environmentally prevalent and emerging EDCs, including 17 α-ethinylestradiol, nonylphenol, BPA, phthalates, and arsenic; and the pervasive and potential carriers of EDCs, microplastics, on reproduction and growth. In vivo and in vitro studies are designed and employed to elucidate the direct effects of EDCs at the organismal and cellular levels, respectively. In silico approaches, on the other hand, comprise computational methods that have been more recently applied with the potential to replace extensive in vitro screening of EDCs. These approaches are discussed in light of model species, age and duration of EDC exposure.

Early-life exposure to 17β-estradiol and 4-nonylphenol impacts the growth hormone/insulin-like growth-factor system and estrogen receptors in Mozambique tilapia, Oreochromis mossambicus

It is widely recognized that endocrine disrupting chemicals (EDCs) released into the environment through anthropogenic activities can have short-term impacts on physiological and behavioral processes and/or sustained or delayed long-term developmental effects on aquatic organisms. While numerous studies have characterized the effects of EDCs on temperate fishes, less is known on the effects of EDCs on the growth and reproductive physiology of tropical species. To determine the long-term effects of early-life exposure to common estrogenic chemicals, we exposed Mozambique tilapia (Oreochromis mossambicus) yolk-sac fry to 17β-estradiol (E2) and nonylphenol (NP) and subsequently characterized the expression of genes involved in growth and reproduction in adults. Fry were exposed to waterborne E2 (0.1 and 1 μg/L) and NP (10 and 100 μg/L) for 21 days. After the exposure period, juveniles were reared for an additional 112 days until males were sampled. Gonadosomatic index was elevated in fish exposed to E2 (0.1 μg/L) while hepatosomatic index was decreased by exposure to NP (100 μg/L). Exposure to E2 (0.1 μg/L) induced hepatic growth hormone receptor (ghr) mRNA expression. The high concentration of E2 (1 μg/L), and both concentrations of NP, increased hepatic insulin-like growth-factor 1 (igf1) expression; E2 and NP did not affect hepatic igf2 and pituitary growth hormone (gh) levels. Both E2 (1 μg/L) and NP (10 μg/L) induced hepatic igf binding protein 1b (igfbp1b) levels while only NP (100 μg/L) induced hepatic igfbp2b levels. By contrast, hepatic igfbp6b was reduced in fish exposed to E2 (1 μg/L). There were no effects of E2 or NP on hepatic igfbp4 and igfbp5a expression. Although the expression of three vitellogenin transcripts was not affected, E2 and NP stimulated hepatic estrogen receptor (erα and erβ) mRNA expression. We conclude that tilapia exposed to E2 and NP as yolk-sac fry exhibit subsequent changes in the endocrine systems that control growth and reproduction during later life stages.

Androgen receptor-beta mRNA levels in different tissues in breeding and post-breeding male and female sticklebacks, Gasterosteus aculeatus

BACKGROUND

Androgens induce male characters by activating androgen receptors (AR). Previous quantitative studies on AR in fishes have been limited to few tissues and/or a single season/reproductive state. The aim of this investigation was to study the possible role of AR-beta expression levels in the control of male traits in the three-spined stickleback. To that end, AR-beta expression levels in major tissues in breeding and post-breeding male and female sticklebacks were examined.

METHODS

AR-beta mRNA levels were quantified in ten tissues; eye, liver, axial muscle, heart, brain, intestine, ovary, testis, kidney and pectoral muscle in six breeding and post-breeding males and females using reverse transcription quantitative PCR.

RESULTS

Breeding in contrast to post-breeding males built nests and showed secondary sexual characters (e.g. kidney hypertrophy) and elevated androgen levels. Post-breeding females had lower ovarian weights and testosterone levels than breeding females. AR-beta was expressed in all studied tissues in both sexes and reproductive states with the highest expression in the gonads and in the kidneys. The kidney is an androgen target organ in sticklebacks, from which breeding males produce the protein spiggin, which is used in nest-building. There was also high AR-beta expression in the intestine, an organ that appears to take over hyperosmo-regulation in fresh water when the kidney hypertrophies in mature males and largely loses this function. The only tissue that showed effects of sex or reproductive state on AR-beta mRNA levels was the kidneys, where post-breeding males displayed higher AR-beta mRNA levels than breeding males.

CONCLUSION

The results indicate that changes in AR-beta mRNA levels play no or little role in changes in androgen dependent traits in the male stickleback.

Characterization of androgen receptor structure and nucleocytoplasmic shuttling of the rice field eel

Androgen receptor (AR) plays a critical role in prostate cancer and male sexual differentiation. We have identified AR from a primitive vertebrate with a sex reversal characteristic, the rice field eel. AR of this species (eAR) is distinct from human AR, especially in the ligand binding domain (LBD), and its expression in gonads shows an increasing tendency during gonadal transformation from ovary via ovotestis to testis. eAR has a restricted androgen-dependent transactivation function after a nuclear translocation upon dihydrotestosterone exposure. A functional nuclear localization signal was further identified in the DNA binding domain and hinge region. Although nuclear export is CRM1-independent, eAR has a novel nuclear export signal, which is negatively charged, indicating that a nuclear export pathway may be mediated by electrostatic interaction. Further, our studies have identified critical sequences for ligand binding in the C terminus. A structure of three α-helices in the LBD has been conserved from eels to humans during vertebrate evolution, despite a distinct amino acid sequence. Mutation analysis confirmed that the LBD is essential for dihydrotestosterone-induced nuclear import of eAR and following transactivation function in the nucleus. In addition, eAR interacts with both Sox9a1 and Sox9a2, and their interaction regulates transactivation of eAR. Our data suggest that the primitive species conserves and especially acquires key novel domains, the nuclear export signal and LBD, for the eAR function in spite of a rapid sequence evolution.

Alterations in mRNA expression of steroid receptors and heat shock proteins in the liver of rare minnow (Grobiocypris rarus) exposed to atrazine and p,p'-DDE

The chaperon role of heat shock proteins (HSPs) throughout the life cycle of steroid receptors have been demonstrated in vitro. However, the actions of HSPs in steroid pathways in animals especially in fish were unclear. In this study, sexually mature rare minnows (Gobiocypris rarus) were exposed to typical endocrine disruptors (atrazine and p,p'-DDE). Hypertrophy of hepatocytes at the 333 microg/l atrazine treatment and atrophy of hepatocytes in all p,p'-DDE treatments were observed. The expression of liver hsp70 and hsp90 in atrazine treatments were significantly up-regulated. Moreover, remarkable increases in the expression of androgen receptor (ar) and estrogen receptor (er) were observed, while alterations of the glucoticorcoid receptor (gr) expression was not significant in atrazine exposed fish. The expression of ar, er, gr, hsp70 and hsp90 were significantly suppressed following p,p'-DDE exposure. These results demonstrate that the expression of hsp70 and hsp90 is altered along with changes of steroid receptors in vivo. Therefore, the results are consistent with the possibility that in fish heat shock proteins (HSPs) play chaperon roles for the steroid receptors in vivo, which also concurs with previous in vitro mammalian studies.

Isolation and characterization of three estrogen receptor transcripts in Oreochromis mossambicus (Peters)

Exposure of aquatic organisms to 17beta-estradiol (E(2)) induces a variety of estrogen-responsive genes, including vitellogenin (vtg)-the precursor protein of egg yolk in oviparous animals and to date the single most used gene product in screening for estrogenic endocrine disruption. Transcription regulation of vtg by E(2) is dependent on binding of the ligand (E(2)) to a specific nuclear receptor (estrogen receptor, ESR) which in turn binds to an estrogen responsive element (ERE) in the promoter of vtg. Since a local tilapiine, Oreochromis mossambicus (Peters), is targeted as a model for estrogenic endocrine disruption in Southern Africa, a platform of knowledge is necessary for the ontogenic and tissue specific behavior of ESR in this species before vtg levels can be interpreted in relation to such endocrine disruption. Therefore, three ESR cDNA sequences (ESR1, ESR2a and ESR2b) in O. mossambicus were isolated and QPCR protocols were developed to ascertain their quantitative transcript levels in adult brain, gonadal and hepatic tissues. ESR1 transcript levels were highest in female liver tissue compared to males and other tissues, whereas the levels for ESR2a and b were not statistically significantly different between male and female tissues. Quantitative gene levels during development demonstrated a sharp increase in ESR1 during the stage of gonad differentiation (50-60 days post-fertilization) in this species. Finally, an induction experiment in adult male liver tissue confirms the upregulation of ESR1 by E(2).

The effects of 17beta-estradiol on various reproductive parameters in the hermaphrodite fish Kryptolebias marmoratus

The effect of a single injection of 17beta-estradiol (E2) was evaluated in the hermaphrodite fish Kryptolebias marmoratus. The fish [average body weight (BW), 0.15+/-0.01 g] were injected with either two concentrations of E2 (1 and 100 microg/g BW) once intraperitoneally. They were sampled at intervals of 7, 15, and 30 days after a single E2 injection. Gonadosomatic index (GSI), hepatosomatic index (HSI), the frequency of gonadal development, number of ovulated eggs, and plasma steroids levels were measured. The transcript abundances of vitellogenin (VTG) and estrogen receptors (ERalpha and beta) mRNA in the liver were also analyzed using quantitative real time polymerase chain reaction (real time PCR). GSI and the frequency of mature oocytes in the 100-microg E2-exposed group decreased compared to that of the control group during the experiment, and the number of ovulated eggs in the 100-microg E2-exposed group was lower when compared to the other groups. However, plasma E2 and 11-ketotestosterone (11-KT) levels were not significantly different between the experimental groups. On the other hand, plasma testosterone level and VTG mRNA abundance in the 100-microg E2-exposed group were significantly lower than the control group after 30 days. These results indicate that E2 stimulation at high concentration interferes with reproductive phenomena through delayed response. In addition, HSI in the 100-microg E2-exposed group and ERalpha mRNA abundance in the 1-microg E2-exposed group were significantly higher than the control group at 7 days after E2 injection, although there was no significant difference in HSI and ERalpha mRNA between all groups at 30 days. These results indicate temporal responses in reproductive parameters following high-dose E2 exposure in the hermaphrodite fish K. marmoratus.

Measuring multiple hormones from a single water sample using enzyme immunoassays

Many aquatic species, such as teleosts, release into the water and detect multiple bioactive substances to assist in schooling, migration, alarm reactions, and to stimulate behavioral and physiological responses during reproduction and in parent-offspring interactions. Understanding the complex relationship between hormones, behavior and their function in communication requires the simultaneous examination of multiple circulating hormones. However, repeated blood sampling within a short time period is not possible in smaller animals without impacting the very behaviors under investigation. The non-invasive technique of collecting and measuring hormone values in holding water using either radioimmunoassay (RIA) or enzyme immunoassay (EIA) is becoming widely used in teleost research. Commercial assay kits in particular enable rapid and reliable data generation, yet their assay buffers are often specific and potentially incompatible with each other, which can hinder measuring multiple hormones from the same sample. We present here the validation and application of a "nested" elution technique we developed that allows for repeated sampling of multiple reproductive hormones - testosterone (T), 17beta-estradiol (E2), progesterone (P), prostaglandin F(2 alpha) (PGF) and 11-ketotestosterone (11KT) - from individual samples of animal holding water by using commercial EIA systems. Our results show that when using appropriate controls to account for possible technical and biological confounds, this technique provides a powerful new tool for research in aquatic endocrinology and physiology.

Induction of vitellogenin production in male tilapia (Oreochromis mossambicus) by commercial fish diets

Mozambique tilapia, (Oreochromis mossambicus), are a euryhaline teleost and an important biological model species. Captive male tilapia frequently have high levels of the estrogen-induced yolk precursor protein vitellogenin (Vg), a common indicator of exposure to estrogenic compounds. Sex steroids are found in commercial fish diets, but relatively few studies have examined the relationship between commercial diets and Vg production. In a fasting experiment to ascertain a dietary role in male Vg production, plasma Vg was reduced to negligible levels after 2 weeks of fasting, while no change in estrogen receptor (ER) expression was seen. When male tilapia were fed a squid-based diet that replaced the commercial trout diet, plasma Vg was reduced to undetectable levels over 40 days, concomitant with significant reductions in hepatic expression of Vgs A, B, and C, and ERbeta, compared with control fish fed commercial trout diet. Female tilapia fed the squid-based for 20 days had no change in these parameters. When male tilapia were fed a defined, soy-based diet, plasma Vg reduced to 20% of levels in fish given either commercial trout diet or a defined, fishmeal-based diet. Overall, results from these studies suggest that estrogens in a commercial trout diet induce vitellogenin production by increasing expression of Vg, but not ER genes in male tilapia.

Temporal expression of two cytochrome P450 aromatase isoforms during development in Oreochromis mossambicus, in association with histological development

Oreochromis mossambicus is targeted as a sentinel species for assay development to detect disruption of estrogen-dependent pathways in Southern Africa. Aromatase--an enzyme encoded by either of two cytochrome P450 19 (cyp19) genes in O. mossambicus is the only enzyme able to catalyze the aromatization of androgens to estrogens. As part of background studies relating to evaluating the use of early life stages of O. mossambicus as an endocrine disruptor screen, we investigated the tissue specificity and temporal expression of cyp19 transcripts, cyp19a (ovarian cyp19) and cyp19b (brain cyp19) during development and estrogen exposure. The cyp19a transcript was detected only in the ovaries of adults, and expression during development reflected this result as induction of cyp19a coincides with histological development of putative ovaries. Using primers that only identify the ovarian transcript, cyp19a transcript levels demonstrated a typical reflection of puberty - after an initial surge in cyp19a, juveniles expressed very low levels, which increased again at the time histologically discernable vitellogenic ovaries were detected. Moreover, we found evidence of putative alternate transcript of cyp19a whose function is currently unknown. cyp19b transcripts were expressed in brain and muscle tissue of both male and female adults, in addition to ovaries in females. During development, cyp19b transcript levels were increased coincidental with cyp19a at 20 days post fertilization but the expression pattern was distinct from that observed for cyp19a. These studies set the foundation for utilizing this native species as a possible indicator of endocrine disruption and accentuates the importance of understanding "normal" basal levels of transcript levels and the nature of amplification of QPCR targets.

Salmeterol with fluticasone enhances the suppression of IL-8 release and increases the translocation of glucocorticoid receptor by human neutrophils stimulated with cigarette smoke

The combination of inhaled corticosteroids and long-acting beta2-adrenoceptor agonists is increasingly used in chronic obstructive pulmonary disease (COPD). Recently, we have demonstrated that combination of salmeterol and fluticasone propionate (FP) additionally suppress the production of IL-8 by human monocyte. In this study, the molecular mechanism behind the effectiveness of this combination therapy is investigated in human neutrophils. Human neutrophils were preincubated with salmeterol or FP or the combination. The amount of interleukin-8 (IL-8), elastase and matrix metalloproteinases (MMP)-2 and -9 releases, and reactive oxygen species (ROS) generation and expression of MAP kinase phosphatase (MKP-1) and glucocorticoid receptor (GR) were determined. Cigarette smoke medium (CSM) induces an increased expression of CXC receptors and the production of ROS that may explain the strong production of IL-8 by neutrophils. The expression of CXC receptors, the production of ROS, and the release of elastase and MMP-2 and -9 were not influenced by salmeterol, FP, or the combination. Interestingly, the combination therapy had an additive suppressive effect on the CSM-induced production of IL-8. The latter could be explained by an increased mRNA expression of MKP-1, the GR and an increased translocation of the GR to the nucleus. This leads eventually to suppression of both the NF-kappaB and MAPK pathways and, hence, to less IL-8 production by the neutrophil. These data are in support for the use of a combination therapy in COPD patients.