Regulation of ovarian steroidogenesis in vitro by IGF-I and insulin in common carp, Cyprinus carpio: stimulation of aromatase activity and P450arom gene expression

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.

The insulin-like growth factor 1 stimulates ovarian steroidogenesis and oocyte maturation in spotted steed Hemibarbus maculatus

The insulin-like growth factor 1 (IGF1) plays important roles in fish reproduction. To understand the role of IGF1 in steroidogenesis and oocyte maturation, we investigated expression pattern and functions of Igf1 during in vitro maturation of spotted steed (Hemibarbus maculatus) oocytes. Igf1 expression quantified by qPCR and western blotting revealed that both Igf1 mRNA and protein was significantly increased in mature follicles. The immunofluorescence analyses showed IGF1 protein signal was detected in the theca cells of ovarian follicles during vitellogenesis stage, and in both theca cells and granulosa cells of matured oocytes. Incubation of ovarian follicles with recombinant IGF1 (rIGF1) significantly enhanced the rate of spotted steed oocyte germinal vesicle breakdown (GVBD), a marker of oocyte maturation. qPCR analysis showed that the transcription of steroidogenesis-related genes (3β-hsd, 20β-hsd, Cyp17a and Cyp19a1a) were influenced after IGF1 treatment. In addition, the expression profiles of receptors of Igf1, Fsh and Lh indicated that a cross talk response to IGF1 induced oocyte maturation. Furthermore, IGF1 treatment did not affect ERK protein expression but significantly upregulated CyclinB and AKT protein expression. All together, these findings help us to understand the molecular mechanism of IGF1 in regulation ovarian steroidogenesis and oocyte maturation of spotted steed.

sox19 regulates ovarian steroidogenesis in common carp

In teleost, ovarian steroidogenesis governed by the neuroendocrine system is also regulated by several transcription factors of gonadal origin. Investigating the synchronized interactions between the transcriptional and the hormonal factors is vital to comprehend the mechanisms that lead to gonadal differentiation. This study signifies the role of sry-related box (sox) 19 in ovarian steroidogenesis regulation of the common carp, Cyprinus carpio. Analysis of tissue distribution displayed higher sox19 expression in brain and ovary, and gonadal ontogeny showed higher expression of sox19 at 80 days post hatch (dph). Higher sox19 mRNA expression during spawning and increase of sox19 post human chorionic gonadotropin induction substantiate gonadotropin dependency. Estradiol-17β treatment but not 17α-methyl-di-hydroxy-testosterone to 50 dph common carp for inducing mono-sex, elevated sox19 expression substantially. Sox19 protein was observed in granulosa cells of the follicular layer in common carp ovary. Higher sox19 expression was detected in isolated granulosa and theca cells, in vitro. Transient gene silencing with sox19-siRNA caused downregulation of various ovary-related genes including those specific to activator protein-1 factors, fibroblast growth factors, wnt-signaling, steroidogenic genes along with certain transcription factors. Serum 17α, 20β-dihydroxy-4-pregnen-3-one and estradiol-17β reduced significantly post sox19 silencing, in vivo. Concomitantly, a decrease in aromatase activity was detected post sox19-siRNA treatment, in vivo. This study demonstrates the impact of sox19 in the regulation of common carp ovarian growth and steroidogenesis.

Igf3: a novel player in fish reproduction†

As in other vertebrates, fish reproduction is tightly controlled by gonadotropin signaling. One of the most perplexing aspects of gonadotropin action on germ cell biology is the restricted expression of gonadotropin receptors in somatic cells of the gonads. Therefore, the identification of factors conveying the action of gonadotropins on germ cells is particularly important for understanding the mechanism of reproduction. Insulin-like growth factors (Igfs) are recognized as key factors in regulating reproduction by triggering a series of physiological processes in vertebrates. Recently, a novel member of Igfs called Igf3 has been identified in teleost. Different from the conventional Igf1 and Igf2 that are ubiquitously expressed in a majority of tissues, Igf3 is solely or highly expressed in the fish gonads. The role of Igf3 in mediating the action of gonadotropin through Igf type 1 receptor on several aspects of oogenesis and spermatogenesis have been demonstrated in several fish species. In this review, we will summarize existing data on Igf3. This new information obtained from Igf3 provides insight into elucidating the molecular mechanism of fish reproduction, and also highlights the importance of Igf system in mediating the action of gonadotropin signaling on animal reproduction.

Participation of Phosphatidylinositol-3 Kinase Signalling in Human Chorionic Gonadotropin, Bovine Insulin (B-Insulin) and Human-Insulin-Like Growth Factor-I Induced Oocyte Maturation and Steroidogenesis in the Grey Mullet, Mugil Cephalus

CONTEXT

The grey mullet, Mugil cephalus, is an edible fish of high economic importance. Breeding biology with reference to hormonal/growth factor regulation of oocyte maturation needs to be known for its commercial production.

OBJECTIVE

The present study was conducted to examine the potency of maturation inducing hormones, chorionic gonadotropin (hCG), bovine-insulin, and insulin like growth factor1 (h-IGF-1) I on ovarian steroidogenesis and oocyte maturation.

DESIGN

The role of hormones and growth factors on steroidogenesis and oocyte maturation was investigated using specific inhibitors, Wortmannin for phosphatidylinositol-3 (PI3) kinase, trilostane for 3β-hydroxysteroid dehydrogenase, 1-octanol and 1-heptanol for gap junctions, actinomycin D for transcription and cycloheximide for translation of signal molecules.

METHODS

Actions of hormonal and growth factors were examined for steroidogenesis, by radioimmunoassay and oocyte maturation by germinal vesicle breakdown (GVBD). Specific inhibitors were used to determine the cell signaling pathways, PI3 kinase.

RESULTS

All the inhibitors attenuated the hCG-induced oocyte maturation (GVBD%), steroidogenesis including transcription, translation, gap junctions and PI3 kinase signaling. These inhibitors failed to inhibit h-IGF-I and b-insulin-induced oocyte maturation, steroidogenesis, translation and PI3 kinase signaling.

CONCLUSION

hCG induces oocyte maturation via steroid dependent pathway involving gap junctions, transcription, translation and PI3 kinase signaling, unlike h-IGF-I and b-insulin in the mullet.

Insulin-like growth factors 1 and 2 regulate gene expression and enzymatic activity of cyp17a1 in ovarian follicles of the yellowtail, Seriola quinqueradiata

There is accumulating evidence that insulin-like growth factors (IGFs), primary mediators of somatic growth, play an important role in fish reproduction. Previously, we showed that IGF-1 and IGF-2 are expressed in the ovarian follicle cells of the yellowtail (Seriola quinqueradiata) during the vitellogenic phase, suggesting that IGFs may be involved in ovarian steroidogenesis. In this study, we examined the effects of IGF-1 and IGF-2 on gene expression and activity of steroidogenic enzymes in yellowtail ovary in vitro. IGF-1 and IGF-2 had no effect on mRNA levels of several steroidogenesis-related genes (star, cyp11a1, hsd3b, cyp17a2, and cyp19a1). However, both IGFs enhanced the transcription of cyp17a1 in vitellogenic ovaries, although such up-regulation was not found in the ovary at the pre-vitellogenic stage. The stage-dependent effects of IGFs were correlated with changes in ovarian cyp17a1 mRNA levels during the reproductive cycle: transcript abundances increased in conjunction with ovarian development. In addition, IGF-induced cyp17a1 gene expression was significantly inhibited by wortmannin, suggesting that PI3 kinase plays an essential role in IGF-mediated ovarian steroidogenesis. Furthermore, IGF-1 and IGF-2 promoted the conversion of both progesterone and 17α-hydroxyprogesterone to androstenedione in vitellogenic ovaries, suggesting that both IGFs stimulated 17α-hydroxylase and C_17-20 lyase activities. Taken together, these findings suggest that IGF-1 and IGF-2 act directly on follicle cells to stimulate steroid production through an increase in gene expression and enzymatic activity of cyp17a1 via induction of PI3 kinase.

Effects of bisphenol A (BPA) on brain-specific expression of cyp19a1b gene in swim-up fry of Labeo rohita

Estrogen regulates numerous developmental and physiological processes and effects are mediated mainly by estrogenic receptors (ERs), which function as ligand-regulated transcription factor. ERs can be activated by many different types endocrine disrupting chemicals (EDCs) and interfere with behaviour and reproductive potential of living organism. Estrogenic regulation of membrane associated G protein-coupled estrogen receptor, GPER activity has also been reported. Bisphenol A (BPA), a ubiquitous endocrine disruptor is present in many household products, has been linked to many adverse effect on sexual development and reproductive potential of wild life species. The present work is aimed to elucidate how an environmentally pervasive chemical BPA affects in vivo expression of a known estrogen target gene, cyp19a1b in the brain, and a known estrogenic biomarker, vitellogenin (Vg) in the whole body homogenate of 30 days post fertilization (dpf) swim-up fry of Labeo rohita. We confirm that, like estrogen, the xenoestrogen BPA exposure for 5-15 days induces strong overexpression of cyp19a1b, but not cyp19a1a mRNA in the brain and increase concentration of vitellogenin in swim-up fry. BPA also induces strong overexpression of aromatase B protein and aromatase activity in brain. Experiments using selective modulators of classical ERs and GPER argue that this induction is largely through nuclear ERs, not through GPER. Thus, BPA has the potential to elevate the levels of aromatase and thereby, levels of endogenous estrogen in developing brain. These results indicate that L. rohita swim-up fry can be used to detect environmental endocrine disruptors either using cyp19a1b gene expression or vitellogenin induction.

Molecular mechanism of mercury-induced reproductive impairments in banded gourami, Trichogaster fasciata

Mercury is one of the key pollutants responsible for the degradation of natural aquatic ecosystems. Among the different forms of mercury that exist in the environment, mercuric chloride (HgCl₂) is the dominant pollutant for freshwater environments as it is used as an ingredient in antiseptics, disinfectants and preservatives, insecticides, batteries and in metallurgical and photographic operations. Pollutant may exert their action on organisms or populations by affecting their normal endocrine function as well as reproduction. Thus, the present study tried to understand the effect of mercuric chloride (HgCl₂) on reproductive function and to decipher the molecular mechanism of Hg-induced reproductive impairments of female Trichogaster fasciata. Both in vivo and in vitro experiments were performed by using ecologically relevant doses of HgCl₂ and the resulting effects on follicular development, steroidogenic potentiality, aromatase activity, aromatase gene expression and steroidogenic factor-1 (SF-1) expression pattern were analysed. In vivo exposure to HgCl₂ caused reproductive impairments as shown by the inhibitory role of HgCl₂ on follicular development, steroid biosynthesis and SF-1 activity. In vitro experiments revealed that aromatase activity, steroidogenesis, aromatase and SF-1 expression were blocked by HgCl₂. The results obtained from this study contribute to understand the molecular mechanism of HgCl₂-induced reproductive impairment of T. fasciata.

Estrogen-regulated expression of cyp19a1a and cyp19a1b genes in swim-up fry of Labeo rohita

P450 aromatase is the terminal enzyme in the steroidogenic pathway and catalyzes the conversion of androgens to estrogens. The expression of cyp19a1 genes in brain and gonad of Indian major carp, Labeo rohita swim-up fry was measured by quantitative real-time polymerase chain-reaction. Results demonstrated that cyp19a1b and cyp19a1a predominate in brain and gonad respectively. Treatment of fry with an aromatase inhibitor fadrozole for 6days attenuated brain cyp19a1b expression, but not cyp19a1a of gonad. Fadrozole also attenuated brain aromatase activity. Treatment with 17β-estradiol (E2) for 6days resulted in up-regulation of brain cyp19a1b transcripts in a dose- and time-dependent manner, but not cyp19a1a. Whole-body concentration of vitellogenin also increased in response to E2. Altogether, these results indicate L. rohita swim-up fry can be used to detect environmental estrogens either using vitellogenin induction or cyp19a1b gene expression.

Membrane receptor cross talk in gonadotropin-, IGF-I-, and insulin-mediated steroidogenesis in fish ovary: An overview

Gonadal steroidogenesis is critical for survival and reproduction of all animals. The pathways that regulate gonadal steroidogenesis are therefore conserved among animals from the steroidogenic enzymes to the intracellular signaling molecules and G protein-coupled receptors (GPCRs) that mediate the activity of these enzymes. Regulation of fish ovarian steroidogenesis in vitro by gonadotropin (GtH) and GPCRs revealed interaction between adenylate cyclase and calcium/calmodulin-dependent protein kinases (CaMKs) and also MAP kinase pathway. Recent studies revealed another important pathway in GtH-induced fish ovarian steroidogenesis: cross talk between GPCRs and membrane receptor tyrosine kinases. Gonadotropin binding to Gαs-coupled membrane receptor in fish ovary leads to production of cAMP which in turn trans-activate the membrane-bound epidermal growth factor receptor (EGFR). This is followed by activation of ERK1/2 signaling that promotes steroid production. Interestingly, GtH-induced trans-activation of EGFR in the fish ovary uniquely requires matrix-metalloproteinase-mediated release of EGF. Inhibition of these proteases blocks GtH-induced steroidogenesis. Increased cAMP production in fish ovarian follicle upregulate follicular cyp19a1a mRNA expression and aromatase activity leading to increased biosynthesis of 17β-estradiol (E2). Evidence for involvement of SF-1 protein in inducing cyp19a1a mRNA and aromatase activity has also been demonstrated. In addition to GtH, insulin-like growth factor (IGF-I) and bovine insulin can alone induced steroidogenesis in fish ovary. In intact follicles and isolated theca cells, IGF-I and insulin had no effect on GtH-induced testosterone and 17a,hydroxysprogeaterone production. GtH-stimulated E2 and 17,20bdihydroxy-4-pregnane 3-one production in granulosa cells however, was significantly increased by IGF-I and insulin. Both IGF-I and insulin mediates their signaling via receptor tyrosine kinases leading to activation of PI3 kinase/Akt and MAP kinase. These kinase signals then activates steroidogenic enzymes which promotes steroid production. PI3 kinase, therefore considered to be an initial component of the signal transduction pathways which precedes MAP kinase in IGF-1 and insulininduced steroidogenesis in fish ovary. Thus, investigation on the mechanism of signal transduction regulating fish ovarian steroidogenesis have shown that multiple, apparently independent signal transduction pathways are needed to convey the message of single hormone or growth factor.

Expression and functional characterization of intrafollicular GH-IGF system in the zebrafish ovary

The somatotrophic axis plays important roles in influencing reproduction. All key members of this axis including growth hormone (GH, gh), GH receptors (ghra and ghrb), insulin-like growth factors (IGFs, igf1, igf2 and igf3) and IGF receptors (igf1ra and igf1rb) were detected in the zebrafish ovary. GH was exclusively expressed in the full-grown oocytes, while its receptors were detectable in both the follicle cells and oocytes. The IGFs and their receptors were all expressed in both compartments except igf3, which was expressed in the follicle cells only. During folliculogenesis, there was a sharp decrease of gh expression at follicle activation; however, the expression of its receptors increased significantly. The expression profiles of igf1, igf2a, and igf2b were similar to that of fshr, whereas igf3 expression was close to lhcgr, suggesting differential roles for different forms of IGFs in follicle development. To examine if the ovarian GH-IGF system is regulated by gonadotropins (e.g., hCG) and GH, we performed in vitro experiments using cultured zebrafish follicle cells. The expression of igf1 and igf1ra, but not others, was down-regulated by hCG (LH analog), whereas recombinant zebrafish GH stimulated igf1 expression. In addition, GH also increased the expression of activin βA subunit (inhbaa). In agreement with this, the stimulatory effect of GH but not IGF-I on oocyte maturation could be abolished by follistatin. In conclusion, the present study revealed an intrafollicular network involving GH-IGF mini-axis in the zebrafish ovary; however, it might not work in the same way as that of the systemic somatotrophic axis.

Changes in gene expression and cellular localization of insulin-like growth factors 1 and 2 in the ovaries during ovary development of the yellowtail, Seriola quinqueradiata

A method of controlling the somatic growth and reproduction of yellowtail fish (Seriola quinqueradiata) is needed in order to establish methods for the efficient aquaculture production of the species. However, little information about the hormonal interactions between somatic growth and reproduction is available for marine teleosts. There is accumulating evidence that insulin-like growth factor (IGF), a major hormone related somatic growth, plays an important role in fish reproduction. As the first step toward understanding the physiological role of IGF in the development of yellowtail ovaries, we characterized the expression and cellular localization of IGF-1 and IGF-2 in the ovary during development. We histologically classified the maturity of two-year-old females with ovaries at various developmental stages into the perinucleolar (Pn), yolk vesicle (Yv), primary yolk (Py), secondary yolk and tertiary yolk (Ty) stages, according to the most advanced type of oocyte present. The IGF-1 gene expression showed constitutively high levels at the different developmental stages, although IGF-1 mRNA levels tended to increase from the Py to the Ty stage with vitellogenesis, reaching maximum levels during the Ty stage. The IGF-2 mRNA levels increased as ovarian development advanced. Using immunohistochemistry methods, immunoreactive IGF-1 was mainly detected in the theca cells of ovarian follicles during late secondary oocyte growth, and in part of the granulosa cells of Ty stage oocytes. IGF-2 immunoreactivity was observed in all granulosa cells in layer in Ty stage oocytes. These results indicate that follicular IGFs may be involved in yellowtail reproduction via autocrine/paracrine mechanisms.

G-protein coupled estrogen receptor (GPER) inhibits final oocyte maturation in common carp, Cyprinus carpio

GPR-30, now named as GPER (G protein-coupled estrogen receptor) was first identified as an orphan receptor and subsequently shown to be required for estrogen-mediated signaling in certain cancer cells. Later studies demonstrated that GPER has the characteristics of a high affinity estrogen membrane receptor on Atlantic croaker and zebra fish oocytes and mediates estrogen inhibition of oocyte maturation in these two distantly related teleost. To determine the broad application of these findings to other teleost, expression of GPER mRNA and its involvement in 17β-estradiol mediated inhibition of oocyte maturation in other cyprinid, Cyprinus carpio was investigated. Carp oocytes at pre-vitellogenic, late-vitellogenic and post-vitellogenic stages of development contained GPER mRNA and its transcribed protein with a maximum at late-vitellogenic oocytes. Ovarian follicular cells did not express GPER mRNA. Carp oocytes GPER mRNA was essentially identical to that found in other perciformes and cyprinid fish oocytes. Both spontaneous and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P)-induced oocyte maturation in carp was significantly decreased when they were incubated with either E2, or GPER agonist G-1. On the other hand spontaneous oocyte maturation was significantly increased when carp ovarian follicles were incubated with an aromatase inhibitor, fadrozole, GPER antagonist, G-15 and enzymatic removal of the ovarian follicle cell layers. This increase in oocyte maturation was partially reversed by co-treatment with E2. Consistent with previous findings with human and fish GPR30, E2 treatment in carp oocytes caused increase in cAMP production and simultaneously decrease in oocyte maturation, which was inhibited by the addition of 17,20β-P. The results suggest that E2 and GPER play a critical role in regulating re-entry in to meiotic cell cycle in carp oocytes.

Steroid-induced oocyte maturation in Indian shad Tenualosa ilisha (Hamilton, 1822) is dependent on phosphatidylinositol 3 kinase but not MAP kinase activation

Fully grown fish and amphibian oocytes exposed to a maturation-inducing steroid (MIS) activates multiple signal transduction pathways, leading to formation and activation of maturation-promoting factor (MPF) and induction of germinal vesicle breakdown (GVBD). The present study was to investigate if phosphatidylinositol 3 kinase (PI3 kinase) and mitogen-activated protein kinase (MAP kinase) activation are required for naturally occurring MIS, 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P)-induced cdc2 activation and oocyte maturation (OM) in Tenualosa ilisha. We observed that 17,20β-P-induced OM was significantly inhibited by PI3 kinase inhibitors Wortmannin and LY29400. 17,20 β-P was shown to activate PI3 kinase maximally at 90 min and cdc2 kinase at 16 h of treatment. Relative involvement of PI3 kinase, MAP kinase and cdc2 kinase in 17,20β-P-induced OM was examined. MAP kinase was rapidly phosphorylated and activated (60-120 min) after MIS treatment and this response preceded the activation of cdc2 kinase by several hours. A selective inhibitor of MAP kinase (MEK), PD98059, sufficiently blocked the phosphorylation and activation of MAP kinase. Inhibition of MAP kinase activity using PD98059 however, had no effect on MIS-induced cdc2 kinase activation and GVBD. These results demonstrate that activation of the PI3 kinase is required for 17,20β-P-induced cdc2 kinase activation and OM in T. ilisha. MAP kinase although was activated in response to 17,20β-P and PI3 kinase activation, it is not necessary for cdc2 activation and OM in this species.

Molecular and cellular effects of chemicals disrupting steroidogenesis during early ovarian development of brown trout (Salmo trutta fario)

A range of chemicals found in the aquatic environment have the potential to influence endocrine function and affect sexual development by mimicking or antagonizing the effects of hormones, or by altering the synthesis and metabolism of hormones. The aim of this study was to evaluate whether the effects of chemicals interfering with sex hormone synthesis may affect the regulation of early ovarian development via the modulation of sex steroid and insulin-like growth factor (IGF) systems. To this end, ex vivo ovary cultures of juvenile brown trout (Salmo trutta fario) were exposed for 2 days to either 1,4,6-androstatriene-3,17-dione (ATD, a specific aromatase inhibitor), prochloraz (an imidazole fungicide), or tributyltin (TBT, a persistent organic pollutant). Further, juvenile female brown trout were exposed in vivo for 2 days to prochloraz or TBT. The ex vivo and in vivo ovarian gene expression of the aromatase (CYP19), responsible for estrogen production, and of IGF1 and 2 were compared. Moreover, 17β-estradiol (E2) and testosterone (T) production from ex vivo ovary cultures was assessed. Ex vivo exposure to ATD inhibited ovarian E2 synthesis, while T levels accumulated. However, ATD did not affect ex vivo expression of cyp19, igf1, or igf2. Ex vivo exposure to prochloraz inhibited ovarian E2 production, but did not affect T levels. Further prochloraz up-regulated igf1 expression in both ex vivo and in vivo exposures. TBT exposure did not modify ex vivo synthesis of either E2 or T. However, in vivo exposure to TBT down-regulated igf2 expression. The results indicate that ovarian inhibition of E2 production in juvenile brown trout might not directly affect cyp19 and igf gene expression. Thus, we suggest that the test chemicals may interfere with both sex steroid and IGF systems in an independent manner, and based on published literature, potentially lead to endocrine dysfunction and altered sexual development.

Neuroendocrine mechanisms in athletes

Athletic activity may be associated with alterations in various neuroendocrine axes depending on the state of energy availability. In addition, genetic factors and an underlying predilection for polycystic ovarian syndrome (PCOS) may predispose some athletes to develop functional hypothalamic amenorrhea earlier than other athletes. In conditions of low energy availability associated with athletic activity, changes that occur in various neuroendocrine axes are primarily adaptive, and aim to either conserve energy for the most essential functions, or allow the body to draw on its reserves to meet energy needs. These hormonal changes, however, then lead to changes in body composition and bone metabolism. Impaired bone accrual in younger athletes and low bone density in older athletes constitutes the major pathologic consequence of neuroendocrine changes associated with low energy availability. The female athlete triad of low energy availability, menstrual dysfunction, and low bone density is prevalent in certain kinds of sports and activities, particularly endurance sports, gymnastics, and ballet. It is essential to screen for this condition in athletes at every preparticipation physical and during office visits, and to put in place an effective treatment team to manage the triad early, in order to optimize outcomes.

Effect of phenol on ovarian secretion of 17β-estradiol in common carp Cyprinus carpio

Phenol is a common substance present in many industrial wastewaters and in nonspecific pesticides. Due to its solubility and volatility phenol is often found in marine and freshwater environment. It is lipophilic compound and has a high potential for accumulating along the trophic chain. Phenol thus is not only a threat to natural environment but also to human health. The effects of phenol on the secretion of 17β-estradiol were examined in female common carp Cyprinus carpio. Vitellogenic stage fish were exposed to physiological safe dose of phenol for 0, 24, 48 and 96 h. In the in vitro experiments, vitellogenic follicles were incubated with phenol and dose- and time-course effects on leuteinising hormone (LH) induced steroid production were examined. Exposure of fish with phenol gradually attenuated serum and ovarian 17β-estradiol levels with increasing time and maximum inhibition was noticed after 96 h. Administration of phenol significantly inhibited LH-induced secretion of 17β-estradiol by the ovarian follicles in vitro. To clarify the mechanism of attenuated production of 17β-estradiol in phenol-treated follicles, stimulated by LH, in vitro effect phenol and LH on aromatase activity (conversion of testosterone to 17β-estradiol) and cytochrome P450arom gene expression in carp ovarian follicles were investigated. Physiological safe dose of phenol significantly inhibited LH-stimulated aromatase activity and P450arom gene expression in ovarian follicles. The present study further demonstrated that LH-induced activation of ovarian steroidogenic factor-1 (SF-1) is strongly inhibited by phenol treatment. These results suggest that physiological safe dose of phenol as endocrine disruption (ED) potential and the effect can be mediated via several cellular pathways including the inhibition of SF-1 activity, aromatase activity and P450arom gene expression.

Involvement of PI3 kinase and MAP kinase in IGF-I and insulin-induced ovarian steroidogenesis in common carp Cyprinus carpio

Previously, we observed that in vitro steroidogenesis in intact ovarian follicles of common carp Cyprinus carpio can alone be induced by recombinant human insulin-like growth factor (IGF-I) and bovine insulin (b-insulin) and this induction was gonadotropin-independent. To investigate early signal transduction components involved in this process, the possible role of phosphatidylinositol 3-kinase (PI3 kinase) during ovarian steroidogenesis was examined. IGF-I and b-insulin induced testosterone and 17β-estradiol production in carp ovarian theca and granulosa cells in short-term coincubation and this induction was significantly inhibited by Wortmannin and LY294002, two mechanistically different specific inhibitors of PI3 kinase. IGF-I and b-insulin were shown to activate PI3 kinase from 30 min onwards with a maximum at 90 min. In this study, we found the involvement of mitogen-activated protein kinase (MAP kinase) in the regulation of IGF-I- and b-insulin-induced steroidogenesis in carp ovary. An antagonist of mitogen-activated protein kinase kinase1/2 (MEK1/2) markedly attenuated IGF-I- and b-insulin-induced steroid production. Cells treated with IGF-I and b-insulin stimulated ERK1/2-dependent phosphorylation of extracellular signal regulated protein kinase1/2 (ERKs1/2) in a time-dependent manner, which was significantly attenuated in presence of MEK1/2 inhibitor. PI3 kinase inhibitors strongly attenuated phosphorylation and activation of MAP kinase, which was increased during IGF-I and b-insulin-induced steroidogenesis. Taken together, these results suggest that PI3 kinase is an initial component of the signal transduction pathway which precedes the MAP kinase during IGF-I- and b-insulin-induced steroidogenesis in C. carpio ovarian follicles.

Effect of cadmium chloride on secretion of 17β-estradiol by the ovarian follicles of common carp, Cyprinus carpio

Cadmium (Cd(2+)) is a common environmental pollutant present in wastes associated with mining, smelting and electroplating. It is a major constituent of the tobacco smoke. Exposure of this heavy metal has been linked to wide range of detrimental effects on mammalian reproduction particularly on ovarian steroidogenesis. Low doses of Cd(2+) are reported to stimulate ovarian luteal progesterone synthesis whereas high doses inhibited it. Cd(2+) exposure is also reported to inhibit gonadal function in fish. In the present study the effects of cadmium chloride (CdCl(2)) on the secretion of gonadotropin-induced 17β-estradiol was examined in female common carp Cyprinus carpio. Vitellogenic stage fish were exposed to physiological safe dose of CdCl(2) for 0, 24, 48 and 96 h and serum and ovarian 17β-estradiol levels were estimated. In the in vitro experiments, vitellogenic follicles were incubated with CdCl(2) and a dose- and time-dependent effects on steroid production were estimated induced by LH. Exposure of fish with CdCl(2) gradually attenuated serum and ovarian 17β-estradiol levels with increasing time and maximum inhibition was noticed after 96 h. Administration of CdCl(2) to the incubations significantly inhibited LH-induced release of 17β-estradiol in vitro. To clarify the mechanism of attenuated production of 17β-estradiol, in vitro effects of CdCl(2) on LH induced P450 aromatase activity (conversion of testosterone to 17β-estradiol) and cytochrome P450arom gene expression in carp ovarian follicles were evaluated. Results show that LH-stimulated P450 aromatase activity and P450arom gene expression in ovarian follicles were significantly inhibited by CdCl(2). The present study further demonstrated that LH-induced stimulation of ovarian steroidogenic factor-1 (SF-1) which activates aromatase enzyme, is strongly inhibited by cadmium chloride treatment.

Expression of LH receptor in nonpregnant mouse endometrium: LH induction of 3β-HSD and de novo synthesis of progesterone

In mouse uterus, at the late diestrus stage LH binding sites have previously been described. The aim of our study was to confirm the existence of LH receptor (Lhr (Lhcgr)) mRNA and its protein in mouse endometrium. Endometrium at all stages of the estrous cycle contained Lhr mRNA, essentially identical to that found in mouse ovary. Endometrium also contained a 72  kDa immunoreactive receptor protein that bound to mouse anti-LHR antibody in western blot. Both receptor mRNA and protein were maximally expressed in the endometrium at metestrus and LH caused a significant increase in their expression levels. Endometrium also contained 3β-hydroxy steroid dehydrogenase (3β-hsd) mRNA and 3β-HSD protein. LH addition elevated their expression and activity as evident from increased conversion of labeled pregnenolone to progesterone (P(4)) and de novo P(4) synthesis. LH-induced endometrial P(4) synthesis is mediated through expression of steroidogenic acute regulatory (Star) gene. Results demonstrated that LH-induced P(4) synthesis in endometrium is possibly mediated through the cAMP pathway. Involvement of a MAPK pathway was also evident. Gonadotropin-stimulated endometrial P(4) synthesis was markedly attenuated by an antagonist of MEK1/2, PD98059. LH-stimulated MEK1/2-dependent phosphorylation of ERK1/2 in a concentration- and time-dependant manner in cultured endometrial tissues. Moreover, involvement of cAMP in LH-stimulated activation of ERK1/2 was also evident. It is therefore possible that the major signaling pathways regulating endometrial steroidogenesis in mouse, including the adenylate cyclase and MAP kinase pathways, converge at a point distal to activation of protein kinase A and ERK1/2.

Development of an in vitro system for functional studies of ovarian follicular cells in European sea bass (Dicentrarchus labrax)

The layers of follicular cells surrounding the oocyte and the interactions among them and the germ cells are critical for the successful maintenance of the ovarian functions. We have set up the isolation procedure and culture conditions of sea bass ovarian follicular cells. Their behaviour at three different physiological temperatures (25, 18 and 15 °C) was evaluated by verifying their steroidogenic capacity along time together with the expression of follicular specific genes (cyp19a1, fshr, lhr and star). These characteristics revealed this culture as a good in vitro alternative to short term in vivo studies at the level of the ovarian follicle. Moreover, to evaluate the suitability of this system for gene function studies conditions for transient transfection of plasmid DNA were optimized. Finally, the characteristics of the follicular culture were not affected by freezing and thawing cycles what facilitates the performance of experiments independently of the reproductive season. In conclusion, we have developed an in vitro homologous system that enables functional and gene expression studies and resembles the in vivo situation in the ovarian follicle.

Insulin-like growth factor 3 regulates expression of genes encoding steroidogenic enzymes and key transcription factors in the Nile tilapia gonad

Insulin-like growth factors (Igfs) are implicated in a wide variety of physiological roles in teleost gonadal development and reproduction. In the present study, igf3 mRNA expression in the tilapia ovary was found to be higher than in the testis from 5 to 40 days after hatching (dah) but was lower than that in testis from 50 to 70 dah. Consistently, Igf3 protein signal was detected in the somatic cells of XX and XY gonads from 10 dah until adulthood by immunohistochemistry, using a specific Igf3 polyclonal antibody. Incubation of ovarian and testicular cells in primary culture with recombinant Igf3 significantly increased nr5a1, foxl2, dmrt1, cyp19a1a, cyp11a1, cyp11b2, hsd3b2 , and cyp17a1 expression in a time- and dose-dependent manner. Promoter analysis using luciferase assays in HEK293 cells revealed that igf3 promoter activity was directly activated by Nr5a1 (Sf1) and further enhanced by Foxl2, Nr0b1a (Dax1), and Nr0b1b (Dax2) but repressed by Dmrt1 and estrogen receptor (Esr1, Esr2a, or Esr2b) along with 17beta-estradiol treatment. In addition, igf3 promoter activity was increased slightly by forskolin treatment alone but synergistically up-regulated by transfection with nr5a1. These in vitro results correlated well with the expression profile of igf3 during early gonad differentiation. Our results indicated that igf3 is involved in fish gonad steroidogenesis because of its ability to regulate the expression of foxl2, dmrt1, and nr5a1 and steroidogenic enzymes. The expression of igf3 is in turn regulated by transcription factors Foxl2, Dmrt1, and Nr5a1, as well as by 17beta-estradiol treatment.

Regulation and actions of insulin-like growth factors in the ovary of zebrafish (Danio rerio)

Insulin-like growth factors (Igf) are known paracrine/autocrine regulators of ovarian development in teleosts. Initial studies investigated the hormonal and intracellular signalling cascades involved in regulating the expression of ovarian-derived Igfs in zebrafish (Danio rerio). Quantitative real-time PCR was used to quantify the expression of igf3, igf2a, and igf2b in full grown immature (FG; 0.57-0.65 mm) and mid-vitellogenic (MV; 0.45-0.56 mm) follicles. Addition of the gonadotropin analogue human chorionic gonadotropin (hCG) and the adenylate cyclase activator forskolin increased igf3 expression in FG and MV follicles, but had no effect on igf2a or igf2b expression. The effects of hCG on igf3 expression were blocked by the addition of the protein kinase A inhibitor H-89. Pituitary adenylate cyclase activating peptide also stimulated a small increase in igf3 expression in FG follicles, while growth hormone and salmon gonadotropin releasing hormone had no effect on igf3, igf2a, or igf2b expression. Secondary studies investigated the involvement of ovarian-derived Igfs in mediating the ovarian actions of gonadotropins on cell survival and steroidogenesis. Treatment of FG follicles with recombinant human IGF1, hCG, or forskolin inhibited the induction of caspase-3/7 activity, which was used as a measure of apoptosis. The effects of hCG and forskolin on caspase-3/7 were attenuated by co-treatment with NVP-AEW54, an IGF1 receptor antagonist. In other studies, hCG was shown to increase the production of the maturation-inducing steroid 17,20β-dihydroxy-4-pregnen-3-one, but this action was not affected by co-treatment with NVP-AEW54. These results suggest there is a high degree of hormonal specificity in regulating Igfs in the zebrafish ovary and the ovarian-derived Igfs, presumably Igf3, are downstream mediators of gonadotropin-dependent cell survival, but are not involved in gonadotropin-induced steroidogenesis.

Ovarian steroidogenesis and the role of sex steroid hormones on ovarian growth and maturation of the Japanese eel

Three sex steroid hormones, estradiol-17β (E2), 11-ketotestosterone (11-KT), and 17α,20β-dihydroxy-4-pregnen-3-one (DHP), are well established as primary estrogen, androgen, and progestin, respectively, in teleost fish. Japanese eel, Anguilla japonica, would be a suitable candidate to study ovarian steroid physiology of fish because the ovarian growth and steroidogenesis is dormant under laboratory condition but can be induced by administration of exogenous gonadotropic reagents. In this review, we summarized our work on the function and production of sex steroid hormones in the ovary of the Japanese eel during ovarian growth and oocyte maturation artificially induced by treatment with extract of salmon pituitary. In vitro and in vivo assays suggest that 11-KT and E2 play primary roles in previtellogenic and vitellogenic growth of oocytes, respectively, whereas DHP is essential for induction of final oocyte maturation. We also reviewed the correlation between ovarian steroidogenesis to produce these sex steroid hormones, serum titers and gene expression.

Disruption of the salmon reproductive endocrine axis through prolonged nutritional stress: changes in circulating hormone levels and transcripts for ovarian genes involved in steroidogenesis and apoptosis

Mechanisms regulating the normal progression of ovarian follicular growth versus onset of atresia in fishes are poorly understood. To gain a better understanding of these processes, we exposed immature female coho salmon (Oncorhynchus kisutch) to prolonged fasting to induce follicular atresia and monitored body growth, development of the ovarian follicles, changes in reproductive hormones, and transcripts for ovarian genes. Prolonged fasting reduced body and ovary weight and increased the appearance of atretic follicles relative to normally fed controls. Endocrine analyses showed that fasting reduced plasma insulin-like growth factor 1 (IGF1), estradiol-17β (E2), and pituitary, but not plasma, levels of follicle-stimulating hormone (FSH). Transcripts for ovarian fsh receptor (fshr) and steroidogenesis-related genes, such as steroidogenic acute regulatory protein (star), 3β-hydroxysteroid dehydrogenase (hsd3b), and P450 aromatase (cyp19a1a) were significantly lower in fasted fish. Ovarian expression of apoptosis-related genes, such as Fas-associated death domain (fadd), caspase 8 (casp8), caspase 3 (casp3), and caspase 9 (casp9) were significantly elevated in fasted fish compared to fed fish, indicating that apoptosis is involved in the process of atresia in this species. Interestingly, some genes such as fadd, casp8, casp3, and hsd3b, were differentially expressed prior to increases in the number of atretic follicles and reductions in hormone levels induced by fasting, and may therefore have potential as early indicators of atresia. Together these results suggest that prolonged nutritional stress may disrupt the reproductive system and induce follicular atresia in part via reductions in ovarian IGF and FSH signaling, and downstream effects on steroidogenesis-related genes and E2 production.