Effects of castration and chronic steroid treatments on hypothalamic gonadotropin-releasing hormone content and pituitary gonadotropins in male wild-type and estrogen receptor-alpha knockout mice

Elevated Risk of Thyroid Malignancy in Biological Males Taking Estrogen Hormone Therapy

OBJECTIVE

The role of estrogen in developing thyroid malignancy is poorly understood. Epidemiological studies have shown exogenous estrogen is associated with increased risk in females. Still, no studies to date have investigated this association among biological males undergoing estrogen hormone therapy.

STUDY DESIGN

Retrospective cohort study.

SETTING

TriNetX Research Network.

METHODS

Biologically male patients prescribed estrogen with at least 5 years of follow-up were queried from the database. Rates of diagnosis of malignant neoplasm of the thyroid gland within 5 years of estrogen hormone therapy prescription were determined, and statistics were conducted within the TriNetX platform.

RESULTS

We identified 6394 biologically male patients from 65 health care organizations prescribed estrogen hormone treatment. The average age was 44.4 years. When balanced for demographic factors as well as known risk factors for thyroid malignancy, the estrogen treatment cohort had a 0.64% risk for diagnosis of thyroid malignancy within 5 years, compared to a 0.27% risk among patients not taking estrogen (relative risk: 2.35, 95% confidence interval: 1.34-4.15, P = .002).

CONCLUSION

We found a higher risk of developing thyroid cancer in biologically male patients prescribed estrogen hormone therapy. This is the first association found between estrogen and thyroid malignancy in this group.

Developmental Delay and Male-Biased Sex Ratio in esr2b Knockout Zebrafish

The estrogen receptor signaling pathway plays an important role in vertebrate embryonic development and sexual differentiation. There are four major estrogen receptors in zebrafish: esr1, esr2a, esr2b and gper. However, the specific role of different estrogen receptors in zebrafish is not clear. To investigate the role of esr2b in zebrafish development and reproduction, this study utilized TALENs technology to generate an esr2b knockout homozygous zebrafish line. The number of eggs laid by esr2b knockout female zebrafish did not differ significantly from that of wild zebrafish. The embryonic development process of wild-type and esr2b knockout zebrafish was observed, revealing a significant developmental delay in the esr2b knockout zebrafish. Additionally, mortality rates were significantly higher in esr2b knockout zebrafish than in their wild-type counterparts at 24 hpf. The reciprocal cross experiment between esr2b knockout zebrafish and wild-type zebrafish revealed that the absence of esr2b resulted in a decline in the quality of zebrafish oocytes, while having no impact on sperm cells. The knockout of esr2b also led to an abnormal sex ratio in the adult zebrafish population, with a female-to-male ratio of approximately 1:7. The quantitative PCR (qPCR) and in situ hybridization results demonstrated a significant downregulation of cyp19ab1b expression in esr2b knockout embryos compared to wild-type embryos throughout development (at 2 dpf, 3 dpf and 4 dpf). Additionally, the estrogen-mediated induction expression of cyp19ab1b was attenuated, while the estradiol-induced upregulated expression of vtg1 was disrupted. These results suggest that esr2b is involved in regulating zebrafish oocyte development and sex differentiation.

Unraveling Hypothalamus-Pituitary dysregulation: Hypergonadotropism in F1 progeny due to prenatal exposure to hexavalent chromium

The endocrine disruptor hexavalent chromium [Cr(VI)] is a proven reproductive toxicant. We recently demonstrated that prenatal Cr(VI) exposure causes testicular resistance to gonadotropins, resulting in hypergonadotropic hypoandrogenism in F1 rats. However, the mechanism driving hypergonadotropism in F1 rats exposed to Cr(VI) prenatally remains an enigma. Therefore, we hypothesized that 'Prenatal Cr(VI) exposure may disrupt steroid hormones-mediated negative feedback regulation of the hypothalamic GnRH, and its receptor in the pituitary of F1 rats, leading to hypergonadotropism.' We administered potassium dichromate (50, 100, or 200 mg/L) to pregnant rats through drinking water between days 9 and 14, and their male F1 offspring were euthanized at 60 days of age. Prenatal Cr(VI) exposure in F1 rats resulted in the accumulation of Cr in the hypothalamus and pituitary. Western blot detected decreased hypothalamic GnRH, Kisspeptin1, and its receptor GPR54, along with diminished ERα, AR, aromatase, and 5α reductase, and GnRH regulatory transcription factors Pit-1 and GATA-4 proteins. Immunohistochemical studies revealed increased immunopositivity of GnRH receptor, AR, 5α reductase, ERα, ERβ, and aromatase proteins in the pituitary, whereas decreased Kisspeptin1, GPR54, and inhibin β. Our findings imply that Cr(VI) exposure during the prenatal period disrupts the hypothalamic Kisspeptin-GPR54-Pit-1/GATA4-GnRH network, boosting the pituitary GnRH receptor. We conclude that prenatal exposure to Cr(VI) alters GnRH expression in the hypothalamus and its receptor in the pituitary of F1 progeny through interfering with the negative feedback effect of androgens and estrogens.

Role of Estrogen Receptor α in Aging and Chronic Disease

Estrogen receptor alpha (ERα) plays a crucial role in reproductive function in both sexes. It also mediates cellular responses to estrogens in multiple nonreproductive organ systems, many of which regulate systemic metabolic homeostasis and inflammatory processes in mammals. The loss of estrogens and/or ERα agonism during aging is associated with the emergence of several comorbid conditions, particularly in females undergoing the menopausal transition. Emerging data also suggests that male mammals likely benefit from ERα agonism if done in a way that circumvents feminizing characteristics. This has led us, and others, to speculate that tissue-specific ERα agonism may hold therapeutic potential for curtailing aging and chronic disease burden in males and females that are at high-risk of cancer and/or cardiovascular events with traditional estrogen replacement therapies. In this mini-review, we emphasize the role of ERα in the brain and liver, summarizing recent evidence that indicates these two organs systems mediate the beneficial effects of estrogens on metabolism and inflammation during aging. We also discuss how 17α-estradiol administration elicits health benefits in an ERα-dependent manner, which provides proof-of-concept that ERα may be a druggable target for attenuating aging and age-related disease burden.

The effects of androgen deprivation on working memory and quality of life in prostate cancer patients: The roles of hypothalamic connectivity

BACKGROUND

Androgen deprivation therapy (ADT) has been associated with adverse effects on the brain. ADT alters testosterone levels via its action on the hypothalamus-pituitary-gonadal axis and may influence hypothalamic functions. Given the wide regional connectivity of the hypothalamus and its role in regulating cognition and behavior, we assessed the effects of ADT on hypothalamic resting state functional connectivity (rsFC) and their cognitive and clinical correlates.

METHODS

In a prospective observational study, 22 men with nonmetastatic prostate cancer receiving ADT and 28 patients not receiving ADT (controls), matched in age, years of education, and Montreal Cognitive Assessment score, participated in N-back task and quality of life (QoL) assessments and brain imaging at baseline and at 6 months. Imaging data were processed with published routines and the results of a group by time flexible factorial analysis were evaluated at a corrected threshold.

RESULTS

ADT and control groups did not differ in N-back performance or QoL across time points. Relative to controls, patients receiving ADT showed significantly higher hypothalamus-right mid-cingulate cortex (MCC) and precentral gyrus (PCG) rsFC during follow-up versus baseline. Further, the changes in MCC and PCG rsFC were correlated positively with the change in QoL score and 0-back correct response rate, respectively, in patients with undergoing ADT.

CONCLUSION

Six-month ADT affects hypothalamic functional connectivity with brain regions critical to cognitive motor and affective functions. Elevated hypothalamic MCC and PCG connectivity likely serve to functionally compensate for the effects of ADT and sustain attention and overall QoL. The longer-term effects of ADT remain to be investigated.

Consumption of soy isoflavones during the prepubertal phase delays puberty and causes hypergonadotropic hypogonadism with disruption of hypothalamic-pituitary gonadotropins regulation in male rats

Isoflavones are phytoestrogens with recognized estrogenic activity but may also affect testosterone, corticosterone and thyroid hormone levels in experimental models. However, the molecular mechanisms involved in these alterations are still unclear. Isoflavones are present in soy-based infant formula, in breast milk after the consumption of soy by the mother and are widely used for the preparation of beverages consumed by toddlers and teenagers. In this sense, we proposed to investigate the effects of soy isoflavone exposure during the prepubertal period, a recognized window of sensitivity for endocrine disruption, over the hypothalamic-pituitary-testicular (HPT) axis. For this, 42 3-week-old male Wistar rats were exposed to 0.5, 5 or 50 mg of soy isoflavones/kg from postnatal day (PND) 23 to PND60. We evaluated body growth, age at puberty, serum concentrations of LH, FSH, testosterone and estradiol, and the expression of the transcripts (mRNA) of genes encoding key genes controlling the hypothalamic-pituitary-testicular (HPT) axis. In the hypothalamus, we observed an increase in Esr1 mRNA expression (0.5 and 5 mg). In the pituitary, we observed an increase in Gnrhr mRNA expression (50 mg), a reduction in Lhb mRNA expression (0.5 mg), and a reduction in Ar mRNA expression. In the testis, we observed an increase in Lhcgr mRNA expression (50 mg) and a reduction in Star mRNA expression (0.5 and 5 mg). The serum levels of LH (5 and 50 mg) and FSH (0.5 mg) were increased, while testosterone and estradiol were reduced. Puberty was delayed in all groups. Taken together, these results suggest that prepubertal consumption of relevant levels of soy isoflavones disrupts the HPT axis, causing hypergonadotropic hypogonadism and altered expression levels of key genes regulating the axis.

Transcription factor GATA2 may potentiate follicle-stimulating hormone production in mice via induction of the BMP antagonist gremlin in gonadotrope cells

Mammalian reproduction depends on the gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone, which are secreted by pituitary gonadotrope cells. The zinc-finger transcription factor GATA2 was previously implicated in FSH production in male mice; however, its mechanisms of action and role in females were not determined. To directly address GATA2 function in gonadotropes, we generated and analyzed gonadotrope-specific Gata2 KO mice using the Cre-lox system. We found that while conditional KO (cKO) males exhibited ∼50% reductions in serum FSH levels and pituitary FSHβ subunit (Fshb) expression relative to controls, FSH production was apparently normal in cKO females. In addition, RNA-seq analysis of purified gonadotropes from control and cKO males revealed a profound decrease in expression of gremlin (Grem1), a bone morphogenetic protein (BMP) antagonist. We show Grem1 was expressed in gonadotropes, but not other cell lineages, in the adult male mouse pituitary. Furthermore, Gata2, Grem1, and Fshb mRNA levels were significantly higher in the pituitaries of WT males relative to females but decreased in males treated with estradiol and increased following ovariectomy in control but not cKO females. Finally, we found that recombinant gremlin stimulated Fshb expression in pituitary cultures from WT mice. Collectively, the data suggest that GATA2 promotes Grem1 expression in gonadotropes and that the gremlin protein potentiates FSH production. The mechanisms of gremlin action have not yet been established but may involve attenuation of BMP binding to activin type II receptors in gonadotropes, facilitating induction of Fshb transcription by activins or related ligands.

Hypothalamic connectivities predict individual differences in ADT-elicited changes in working memory and quality of life in prostate cancer patients

Androgen deprivation therapy (ADT) has been associated with adverse effects on cognition. However, we currently lack understanding of the neurobiology and prognostic markers of these effects. Given that ADT acts via the hypothalamus-pituitary-gonadal axis, we assessed whether baseline hypothalamic resting state functional connectivity (rsFC) could predict changes in working memory and quality of life in prostate cancer patients following androgen deprivation. In a prospective observational study, 28 men with non-metastatic prostate cancer receiving ADT and 38 patients not receiving ADT (controls), matched in age, years of education and Montreal Cognitive Assessment score, participated in brain imaging at baseline, and N-back task and quality-of-life (QoL) assessments at baseline and at 6 months follow-up. Imaging data were processed with published routines and evaluated at a corrected threshold. ADT and control groups did not differ in N-back performance or QoL across time points. In ADT, the changes in 0-back correct response rate (follow-up-baseline) were correlated with baseline hypothalamus-precentral gyrus rsFC; the changes in 1-back correct response rate and reaction time were each correlated with hypothalamus-middle frontal gyrus and superior parietal lobule rsFC. The changes in physical well-being subscore of QoL were correlated with baseline hypothalamus-anterior cingulate and cuneus rsFC. The hypothalamus rsFCs predicted N-back and QoL change with an area under the receiver operating characteristic curve of 0.93 and 0.73, respectively. Baseline hypothalamus-frontoparietal and salience network rsFC's predict inter-subject variations in the changes in working-memory and QoL following 6 months of ADT. Whether and how hypothalamic rsFCs may predict the cognitive and QoL effects with longer-term ADT remain to be investigated.

Growth Hormone Pulses and Liver Gene Expression Are Differentially Regulated by the Circadian Clock Gene Bmal1

In this study, we found that loss of the circadian clock gene Bmal1 causes disruptions throughout the growth hormone (GH) axis, from hepatic gene expression to production of urinary pheromones and pheromone-dependent behavior. First, we show that Bmal1 knockout (KO) males elicit reduced aggressive responses from wild-type (WT) males and secrete lower levels of major urinary proteins (MUPs); however, we also found that a liver-specific KO of Bmal1 (liver-Bmal1-KO) produces a similar reduction in MUP secretion without a defect in aggressive behavior, indicating that the decrease in elicited aggression arises from another factor. We then shifted our investigation to determine the cause of MUP dysregulation in Bmal1 KO animals. Because the pulse pattern of GH drives sexually dimorphic expression of hepatic genes including MUPs, we examined GH pulsatility. We found that Bmal1 KO males have a female-like pattern of GH release, whereas liver-Bmal1-KO mice are not significantly different from either WT or Bmal1 KO. Since differential patterns of GH release regulate the transcription of many sexually dimorphic genes in the liver, we then examined hepatic gene transcription in Bmal1 KO and liver-Bmal1-KO mice. We found that while some female-predominant genes increase in the Bmal1 KO, there was no decrease in male-predominant genes, and little change in the liver-Bmal1-KO. We also found disrupted serum insulin growth factor 1 (IGF-1) and liver Igf1 messenger RNA in the Bmal1 KO mice, which may underlie the disrupted GH release. Overall, our findings differentiate between GH-pulse-driven and circadian-driven effects on hepatic genes, and the functional consequences of altered GH pulsatility.

Lack of AR in LepRb Cells Disrupts Ambulatory Activity and Neuroendocrine Axes in a Sex-Specific Manner in Mice

Disorders of androgen imbalance, such as hyperandrogenism in females or hypoandrogenism in males, increase risk of visceral adiposity, type 2 diabetes, and infertility. Androgens act upon androgen receptors (AR) which are expressed in many tissues. In the brain, AR are abundant in hypothalamic nuclei involved in regulation of reproduction and energy homeostasis, yet the role of androgens acting via AR in specific neuronal populations has not been fully elucidated. Leptin receptor (LepRb)-expressing neurons coexpress AR predominantly in hypothalamic arcuate and ventral premammillary nuclei (ARH and PMv, respectively), with low colocalization in other LepRb neuronal populations, and very low colocalization in the pituitary gland and gonads. Deletion of AR from LepRb-expressing cells (LepRbΔAR) has no effect on body weight, energy expenditure, and glucose homeostasis in male and female mice. However, LepRbΔAR female mice show increased body length later in life, whereas male LepRbΔAR mice show an increase in spontaneous ambulatory activity. LepRbΔAR mice display typical pubertal timing, estrous cycles, and fertility, but increased testosterone levels in males. Removal of sex steroid negative feedback action induced an exaggerated rise in luteinizing hormone in LepRbΔAR males and follicle-stimulating hormone in LepRbΔAR females. Our findings show that AR can directly affect a subset of ARH and PMv neurons in a sex-specific manner and demonstrate specific androgenic actions in the neuroendocrine hypothalamus.

Pituitary Hyperplasia, Hormonal Changes and Prolactinoma Development in Males Exposed to Estrogens-An Insight From Translational Studies

Estrogen signaling plays an important role in pituitary development and function. In sensitive rat or mice strains of both sexes, estrogen treatments promote lactotropic cell proliferation and induce the formation of pituitary adenomas (dominantly prolactin or growth-hormone-secreting ones). In male patients receiving estrogen, treatment does not necessarily result in pituitary hyperplasia, hyperprolactinemia or adenoma development. In this review, we comprehensively analyze the mechanisms of estrogen action upon their application in male animal models comparing it with available data in human subjects. Sex-specific molecular targets of estrogen action in lactotropic (PRL) cells are highlighted in the context of their proliferative and secretory activity. In addition, putative effects of estradiol on the cellular/tumor microenvironment and the contribution of postnatal pituitary progenitor/stem cells and transdifferentiation processes to prolactinoma development have been analyzed. Finally, estrogen-induced morphological and hormone-secreting changes in pituitary thyrotropic (TSH) and adrenocorticotropic (ACTH) cells are discussed, as well as the putative role of the thyroid and/or glucocorticoid hormones in prolactinoma development, based on the current scarce literature.

The role of adrenal derived androgens in castration resistant prostate cancer

Castration resistant prostate cancer (CRPC) remains androgen dependant despite castrate levels of circulating testosterone following androgen deprivation therapy, the first line of treatment for advanced metstatic prostate cancer. CRPC is characterized by alterations in the expression levels of steroidgenic enzymes that enable the tumour to derive potent androgens from circulating adrenal androgen precursors. Intratumoral androgen biosynthesis leads to the localized production of both canonical androgens such as 5α-dihydrotestosterone (DHT) as well as less well characterized 11-oxygenated androgens, which until recently have been overlooked in the context of CRPC. In this review we discuss the contribution of both canonical and 11-oxygenated androgen precursors to the intratumoral androgen pool in CRPC. We present evidence that CRPC remains androgen dependent and discuss the alterations in steroidogenic enzyme expression and how these affect the various pathways to intratumoral androgen biosynthesis. Finally we summarize the current treatment strategies for targeting adrenal derived androgen biosynthesis.

Neurochemical Characterization of Neurons Expressing Estrogen Receptor β in the Hypothalamic Nuclei of Rats Using in Situ Hybridization and Immunofluorescence

Estrogens play an essential role in multiple physiological functions in the brain, including reproductive neuroendocrine, learning and memory, and anxiety-related behaviors. To determine these estrogen functions, many studies have tried to characterize neurons expressing estrogen receptors known as ERα and ERβ. However, the characteristics of ERβ-expressing neurons in the rat brain still remain poorly understood compared to that of ERα-expressing neurons. The main aim of this study is to determine the neurochemical characteristics of ERβ-expressing neurons in the rat hypothalamus using RNAscope in situ hybridization (ISH) combined with immunofluorescence. Strong Esr2 signals were observed especially in the anteroventral periventricular nucleus (AVPV), bed nucleus of stria terminalis, hypothalamic paraventricular nucleus (PVN), supraoptic nucleus, and medial amygdala, as previously reported. RNAscope ISH with immunofluorescence revealed that more than half of kisspeptin neurons in female AVPV expressed Esr2, whereas few kisspeptin neurons were found to co-express Esr2 in the arcuate nucleus. In the PVN, we observed a high ratio of Esr2 co-expression in arginine-vasopressin neurons and a low ratio in oxytocin and corticotropin-releasing factor neurons. The detailed neurochemical characteristics of ERβ-expressing neurons identified in the current study can be very essential to understand the estrogen signaling via ERβ.

Nonclassical actions of estradiol-17beta are not detectable in the alphaT3-1 and LbetaT2 immortalized gonadotrope cell lines†

The immortalized mouse gonadotrope cell lines alphaT3-1 and LbetaT2 cells have been a substitute model for primary gonadotropes. These cell lines have provided a homogeneous cell population, as compared to the dissociated anterior pituitaries, which contain a heterogeneous population of cells potentially responsive to estradiol-17beta (E2). Nonclassical actions of E2 assumed to occur through the plasma membrane estrogen receptor 1 (ESR1, also known as ERalpha). These actions have included inhibition of gonadotropin-releasing hormone (GnRH)-induced increases in intracellular calcium concentrations and phosphorylation of p44/42 mitogen-activated protein kinase (ERK-1/2) in ovine pituitaries including primary gonadotropes in vitro. The objective of the present experiment was to determine if alphaT3-1 and LbetaT2 are cell models with limitations to examine the nonclassical actions of E2 occurring in gonadotropes. Experiments were conducted to determine if the cells have ESR1 at the plasma membrane using biotinylation cell and isolation of surface protein and staining with a fluorescently labeled E2 conjugate. The alphaT3-1 cells contain ESR1 associated with but not enriched within lipid rafts of the plasma membrane and do not translocate to lipid rafts upon binding of E2. In contrast, LbetaT2 cells lack ESR1 associated with the plasma membrane. Pretreatment with E2 did not cause inhibition of GnRH-stimulated increases in intracellular concentrations of calcium for either cell type. Phosphorylation of ERK-1/2 was not stimulated by E2 in either cell type. Although these cells lines have been used extensively to study GnRH signaling, in vitro or in vivo effects of nonclassical actions of E2 cannot be replicated in either cell line.

Impact of estrogens in males and androgens in females

Androgens and estrogens are known to be critical regulators of mammalian physiology and development. While these two classes of steroids share similar structures (in general, estrogens are derived from androgens via the enzyme aromatase), they subserve markedly different functions via their specific receptors. In the past, estrogens such as estradiol were thought to be most important in the regulation of female biology, while androgens such as testosterone and dihydrotestosterone were believed to primarily modulate development and physiology in males. However, the emergence of patients with deficiencies in androgen or estrogen hormone synthesis or actions, as well as the development of animal models that specifically target androgen- or estrogen-mediated signaling pathways, have revealed that estrogens and androgens regulate critical biological and pathological processes in both males and females. In fact, the concept of "male" and "female" hormones is an oversimplification of a complex developmental and biological network of steroid actions that directly impacts many organs. In this Review, we will discuss important roles of estrogens in males and androgens in females.

Immunohistomorphometric Changes of The Pituitary Gonadotropic Cells After Testosterone Application in a Rat Model of the Andropause

Andropause, the culminating phase of male ageing, is characterized by deregulation of the hypothalamic-pituitarygonadal axis and low circulating free testosterone. The aim of this study was to investigate the immunohistomorphometric characteristics of the pituitary gonadotropic i.e. follicle-stimulating hormone (FSH) and the luteinizing hormone (LH) producing cells after testosterone application in a rat model of the andropause. Middle-aged Wistar rats were divided into orchidectomized (ORX; n=8) and testosterone treated orchidectomized (ORX+T; n=8) groups. Testosterone propionate (5 mg/kg b.m./day) was administered for three weeks, while the ORX group received the vehicle alone. Immunohistochemically stained FSH and LH cells underwent morphometric and optical density-related analysis, while circulating concentrations of the sex steroids were measured by immunoassays. Serum concentrations of testosterone and estradiol were significantly (p<0.05) increased by 24 and 2.7 fold respectively, compared to the ORX group. The volume of FSH and LH cells was significantly (p<0.05) decreased by 51.3% and 56.6% respectively, in comparison with ORX rats. Relative volume density of FSH and LH cells was also significantly (p<0.05) decreased by 54.0% and 72.8% respectively, compared to the ORX group. Results related to the optical density of gonadotropic cells (reflecting their hormonal content) were in line with the morphometric findings i.e. this parameter of FSH and LH cells was significantly (p<0.05) decreased by 25.7% and 16.2% respectively, in comparison with ORX rats. Conclusion: In conclusion, applied testosterone increased the serum concentrations of sex steroids, as well as it decreased morphometric parameters and optical density of gonadotropic cells in ORX rats.

Mapping GABA and glutamate inputs to gonadotrophin-releasing hormone neurones in male and female mice

Gonadotrophin-releasing hormone (GnRH) neurone function is dependent upon gonadal steroid hormone feedback, which is communicated in large part through an afferent neuronal network. The classical neurotransmitters GABA and glutamate are important regulators of GnRH neurone activity and are implicated in mediating feedback signals. In the present study, we aimed to determine whether GABAergic or glutamatergic input to GnRH neurones differs between males and females and/or exhibits morphological plasticity in response to steroid hormone feedback in females. Tissue collected from GnRH-green fluorescent protein (GFP) male and female mice in dioestrus underwent immunofluorescence labelling of GFP and either the vesicular GABA transporter (VGAT) or the vesicular glutamate transporter 2 (VGLUT2). No differences in the densities or absolute numbers of VGAT-immunoreactive (-IR) or VGLUT2-IR puncta apposed to GnRH neurones were identified between males and females. The most significant input from either neurotransmitter was to the proximal dendritic region and 80% of VGAT-IR puncta apposed to GnRH neurones co-localised with synaptophysin. Putative inputs were also assessed in ovariectomised (OVX) female mice treated with negative (OVX+E) or positive (OVX+E+E) feedback levels of oestrogen, and OVX+E+E mice were killed during the expected GnRH/luteinising hormone surge. No differences in VGLUT2-IR contacts to GnRH neurones were identified between animals under the negative-feedback influence of oestrogen (OVX+E) or the positive influence of oestrogen (OVX+E+E), regardless of cFos activation status. By contrast, a significant elevation in putative GABAergic inputs to GnRH neurones at the time of the preovulatory surge was found in the cFos-negative subset of GnRH neurones, both at the level of the soma and at the proximal dendrite. Taken together, these data suggest that, although GABAergic and glutamatergic innervation of GnRH neurones is not sexually differentiated, cyclic fluctuations in steroid hormone feedback over the female oestrous cycle result in plastic changes in GABAergic inputs to a subpopulation of GnRH neurones.

Soy Phytoestrogens Do Not Fully Reverse Changes in Rat Pituitary Castration Cells: Unbiased Stereological Study

The aim of the study was to examine the potential of the principal soy isoflavones, genistein and daidzein, or isoflavone rich soy extract to recover pituitary castration cells in orchidectomized adult male rats in comparison with the effects of estradiol. Two weeks post orchidectomy (Orx), animals received estradiol-dipropionate, genistein, daidzein or soy extract subcutaneously for 3 weeks. Control sham-operated (So) and Orx rats received just the vehicle. Changes in the volumes of pars distalis, of individual follicle-stimulating hormone (FSH) and luteinizing hormone (LH) containing cells, their volume, numerical density and number were determined by unbiased design-based stereology. The intracellular content of βFSH and βLH was estimated by relative intensity of fluorescence (RIF). Orchidectomy increased all examined stereological parameters and RIF. Compared to Orx, estradiol increased the volume of pars distalis, but reversed RIF and all morphometric parameters of gonadotropes to the level of So rats, except their number. Treatments with purified isoflavones and soy extract decreased RIF to the control So level, expressing an estradiol-like effect. However, the histological appearance and morphometrical features of gonadotropes did not follow this pattern. Genistein increased the volume of pars distalis, decreased the volume density of LH-labeled cells and raised the number of gonadotropes. Daidzein decreased the cell volume of gonadotropic cells but increased their number and numerical density. Soy extract induced an increase in number and numerical density of FSH-containing cells. Therefore, it can be concluded that soy phytoestrogens do not fully reverse the Orx-induced changes in pituitary castration cells. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.

The hypothalamic-pituitary-testicular axis and the testicular function are modulated after silver nanoparticle exposure

Silver nanoparticles (AgNPs) are widely used in industrial and medical applications and humans may be exposed through different routes, increasing the risk of toxicity. We investigated the transcript expression of genes involved in the regulation of the hypothalamic-pituitary-testicular (HPT) axis and the parameters associated with sperm functionality after prepubertal exposure. AgNPs modulated the transcript expression of genes involved in the control of the HPT axis and spermatogenesis in the groups treated with lower doses, while the functional parameters related to sperm and puberty were affected in the groups administered higher doses. These results suggest that the HPT axis is disrupted by AgNPs during the prepubertal and pubertal periods, which are highly susceptible windows for the endocrine-disrupting chemical activity.

17β-estradiol (E2) promotes growth and stability of new dendritic spines via estrogen receptor β pathway in intact mouse cortex

The steroid hormone 17β-estradiol (E2) remodels neural circuits at the synaptic level in the mammalian hippocampus and cortex. However, the underlying mechanism of synapse dynamics remains unclear. To elucidate the mechanism, we traced individual dendritic spines on layer V pyramidal neurons of the primary sensory cortex in adult female mice under E2 intervention using two-photon in vivo imaging microscopy. We confirmed the increase of the spine density upon E2 treatment in the intact mouse cortex. Furthermore, we found that this increase is due to the promotion of spine formation and the stability of newly formed spines. E2 treatment doesn't alter the elimination rate of pre-existing spines. Our results also indicate that the activation of the estrogen receptor β (ERβ) mimics the effects of E2 administration on spine dynamics. Taken together, our findings suggest that estrogen promotes growth and stability of new dendritic spines via the ERβ pathway in the intact cortex of female mice.

Control of lupus nephritis by changes of gut microbiota

BACKGROUND

Systemic lupus erythematosus, characterized by persistent inflammation, is a complex autoimmune disorder with no known cure. Immunosuppressants used in treatment put patients at a higher risk of infections. New knowledge of disease modulators, such as symbiotic bacteria, can enable fine-tuning of parts of the immune system, rather than suppressing it altogether.

RESULTS

Dysbiosis of gut microbiota promotes autoimmune disorders that damage extraintestinal organs. Here we report a role of gut microbiota in the pathogenesis of renal dysfunction in lupus. Using a classical model of lupus nephritis, MRL/lpr, we found a marked depletion of Lactobacillales in the gut microbiota. Increasing Lactobacillales in the gut improved renal function of these mice and prolonged their survival. We used a mixture of 5 Lactobacillus strains (Lactobacillus oris, Lactobacillus rhamnosus, Lactobacillus reuteri, Lactobacillus johnsonii, and Lactobacillus gasseri), but L. reuteri and an uncultured Lactobacillus sp. accounted for most of the observed effects. Further studies revealed that MRL/lpr mice possessed a "leaky" gut, which was reversed by increased Lactobacillus colonization. Lactobacillus treatment contributed to an anti-inflammatory environment by decreasing IL-6 and increasing IL-10 production in the gut. In the circulation, Lactobacillus treatment increased IL-10 and decreased IgG2a that is considered to be a major immune deposit in the kidney of MRL/lpr mice. Inside the kidney, Lactobacillus treatment also skewed the Treg-Th17 balance towards a Treg phenotype. These beneficial effects were present in female and castrated male mice, but not in intact males, suggesting that the gut microbiota controls lupus nephritis in a sex hormone-dependent manner.

CONCLUSIONS

This work demonstrates essential mechanisms on how changes of the gut microbiota regulate lupus-associated immune responses in mice. Future studies are warranted to determine if these results can be replicated in human subjects.

Effects of active immunization against GnRH versus surgical castration on hypothalamic-pituitary function in boars

The objective was to compare effects of anti-GnRH immunization (immunocastration) versus surgical castration on hypothalamic-pituitary function in boars. Thirty-six boars were randomly divided into three groups (n = 12/group): control, surgically castrated, or immunized against GnRH at 10 wk of age (boostered 8 wk later). Compared to intact boars, immunocastration reduced (P < 0.05) serum concentrations of LH, FSH, testosterone and inhibin B and caused severe testicular atrophy, whereas surgical castration increased (P < 0.05) serum concentrations of LH and FSH. Both immunocastration and surgical castration consistently reduced hypothalamic GnRH synthesis, with decreased (P < 0.05) mRNA expressions of GnRH, GnRH up-stream gatekeeper genes kiss1 and its receptor (GPR54), and androgen receptor in the hypothalamic arcuate nucleus (ARC) and anteroventral periventricular nucleus (AVPV), as well as GnRH content in the median eminence. Inconsistently, mRNA expressions of gonadotropin-inhibitory hormone (GnIH) in ARC and AVPV as well as its receptor (GPR147) in pituitary were selectively reduced (P < 0.05), but mRNA expressions of estrogen receptor alpha and aromatase (CPY17A1) in pituitary were selectively increased (P < 0.05) in surgical castrates. In response to selectively attenuated suppressive signaling from GnIH and testosterone, mRNA expressions of GnRH receptor (GnRHR), LH-β and FSH-β in pituitary were increased (P < 0.05) in surgical castrates, whereas these pituitary gene expressions were decreased (P < 0.05) in immunocastrates, due to loss of hypothalamic GnRH signaling. We concluded that immunocastration and surgical castration consistently reduced hypothalamic GnRH synthesis due to a testosterone deficiency disrupting testosterone-Kisspeptin-GPR54-GnRH signaling pathways. Furthermore, selectively attenuated GnIH and testosterone signaling in the pituitary increased gonadotropin production in surgical castrates.

The Bone Sparing Effects of 2-Methoxyestradiol Are Mediated via Estrogen Receptor-α in Male Mice

2-Methoxyestradiol (2ME2), a metabolite of 17β-estradiol (E2), exerts bone sparing effects in animal models. We hypothesized that the underlying mechanism is back conversion of 2ME2 to E2, which subsequently acts via estrogen receptor (ER)α. We measured serum E2 levels in orchidectomized wild-type (WT) mice treated with 2ME2 66.6 μg/d or placebo. In placebo-treated animals, E2 was below the detection limit. In 2ME2-treated mice, the serum E2 level was 4.97 ± 0.68 pg/mL. This corresponds to the level found in diesterus in cycling female mice. Next, we investigated bone parameters in orchidectomized WT and ERα knockout mice treated with 2ME2 or placebo for 35 days. 2ME2 (6.66 μg/d) preserved trabecular and cortical bone in WT mice. Trabecular volumetric-bone mineral density was 64 ± 20%, and trabecular bone volume/total volume was 60 ± 20% higher in the metaphyseal region of the femur in the 2ME2 group, compared with placebo (P < .01). Both trabecular number and trabecular thickness were increased (P < .01). Cortical bone mineral content in the diaphyseal region of the femur was 31 ± 3% higher in the 2ME2 group, compared with placebo (P < .001). This was due to larger cortical area (P < .001). Three-point bending showed an increased bone strength in WT 2ME2-treated animals compared with placebo (maximum load [Fmax] +19±5% in the 2ME2 group, P < .05). Importantly, no bone parameter was affected by 2ME2 treatment in ERα knockout mice. In conclusion, 2ME2 treatment of orchidectomized mice results in increased serum E2. ERα mediates the bone sparing effects of 2ME2. The likely mediator of this effect is E2 resulting from back conversion of 2ME2.

Membrane-Localized Estrogen Receptor 1 Is Required for Normal Male Reproductive Development and Function in Mice

Estrogen receptor 1 (ESR1) mediates major reproductive functions of 17β-estradiol (E2). Male Esr1 knockout (Esr1KO) mice are infertile due to efferent ductule and epididymal abnormalities. The majority of ESR1 is nuclear/cytoplasmic; however, a small fraction is palmitoylated at cysteine 451 in mice and localized to cell membranes, in which it mediates rapid E2 actions. This study used an Esr1 knock-in mouse containing an altered palmitoylation site (C451A) in ESR1 that prevented cell membrane localization, although nuclear ESR1 was expressed. These nuclear-only estrogen receptor 1 (NOER) mice were used to determine the roles of membrane ESR1 in males. Epididymal sperm motility was reduced 85% in 8-month-old NOER mice compared with wild-type controls. The NOER mice had decreased epididymal sperm viability and greater than 95% of sperm had abnormalities, including coiled midpieces and tails, absent heads, and folded tails; this was comparable to 4-month Esr1KO males. At 8 months, daily sperm production in NOER males was reduced 62% compared with controls. The NOER mice had histological changes in the rete testes, efferent ductules, and seminiferous tubules that were comparable with those previously observed in Esr1KO males. Serum T was increased in NOER males, but FSH, LH, and E2 were unchanged. Critically, NOER males were initially subfertile, becoming infertile with advancing age. These findings identify a previously unknown role for membrane ESR1 in the development of normal sperm and providing an adequate environment for spermatogenesis.

Pituitary Aromatase P450 May Be Involved in Maintenance of the Population of Luteinizing Hormone-Positive Pituitary Cells in Mice

As aromatase P450 is located in several pituitary cells, testosterone can be transformed into 17β-estradiol in the gland by the enzyme. The possible role of this transformation in pituitary function remains to be elucidated, but some evidence suggests a physiological and pathophysiological role for pituitary aromatase. To determine its relevance in the modulation of pituitary function, mainly associated with reproduction, luteinizing hormone (LH)-positive cells in the hypophysis of female and male aromatase knockout (ArKO) mice were studied. In all LH-positive cells, significant increases in the cellular (p < 0.01) and nuclear (p < 0.05) areas were found in the ArKO mice compared to the wild-type mice. In the ArKO mice, LH-positive cells were more abundant (p < 0.01); they were characterized by a stronger cytoplasmic reaction and the cells were more polygonal and exhibited more short, thick cytoplasmic prolongations than those in the wild-type mice. Moreover, LH-positive cells showed a greater proliferation rate in the ArKO mice compared to the wild-type mice (p < 0.01). These findings suggest that the local production of estradiol mediated by pituitary aromatase is necessary for the regulation of LH-positive gonadotropic cells, exerting an autoparacrine inhibitory regulation. These results could underlie the higher pituitary aromatase expression observed in male versus female mice. Similar effects were found in ArKO male and female mice, suggesting that in both sexes the effects of estrogens on maintenance of the LH-positive pituitary cell population could be related to the local aromatization of testosterone to estradiol inside the hypophysis. Therefore, aromatase could modulate pituitary LH-positive cells in males through local estradiol synthesis.

Disruptions in the hypothalamic-pituitary-gonadal axis in rat offspring following prenatal maternal exposure to lipopolysaccharide

Postnatal treatment with bacterial endotoxin lipopolysaccharide (LPS) changes the activity of the hypothalamic-pituitary-gonadal (HPG) axis and the gonadotropin-releasing hormone (GnRH) surge in rats. Exposure to an immune challenge in the critical periods of development has profound and long-lasting effects on the stress response, immune, metabolic, and reproductive functions. Prenatal LPS treatment delays the migration of GnRH neurons associated with increased cytokine release in maternal and fetal compartments. We investigated the effects of a single maternal exposure to LPS (18 μg/kg, i.p.) on day 12 (embryonic day (E)12) of pregnancy on reproductive parameters in rat offspring. Hypothalamic GnRH content, plasma luteinizing hormone (LH), testosterone, and estradiol concentrations were measured in both male and female offsprings at different stages of postnatal development by RIA and ELISA (n = 10 each per group). Body weight and in females day of vaginal opening (VO) were recorded. In offspring exposed to LPS prenatally, compared with controls, body weight was decreased in both sexes at P5 and P30; in females, VO was delayed; hypothalamic GnRH content was decreased at postnatal days 30-60 (P30-P60) in both sexes; plasma LH concentration was decreased at P14-P60 in females; plasma concentrations of testosterone/estradiol were increased at P14 in females, and plasma estradiol was increased at P14 in males. Hence activation of the maternal immune system by LPS treatment at a prenatal critical period leads to decreased GnRH and LH levels in pre- and postpubertal life and sex steroid imbalance in the prepubertal period, and delayed sexual maturation of female offspring.

Prenatal Exposures of Male Rats to the Environmental Chemicals Bisphenol A and Di(2-Ethylhexyl) Phthalate Impact the Sexual Differentiation Process

The increasing incidence of reproductive anomalies, described as testicular dysgenesis syndrome, is thought to be related to the exposure of the population to chemicals in the environment. Bisphenol A (BPA) and di(2-ethylhexyl)phthalate (DEHP), which have hormonal and antihormonal activity, have attracted public attention due to their presence in consumer products. The present study investigated the effects of BPA and DEHP on reproductive development. Timed-pregnant female rats were exposed to BPA and DEHP by gavage from gestational days 12 to 21. Results showed that prenatal exposures to test chemicals exerted variable effects on steroidogenic factor 1 and GATA binding protein 4 protein expression and increased (P < .05) sex-determining region Y-box 9 and antimüllerian hormone protein in the infantile rat testis compared with levels in the control unexposed animals. Pituitary LHβ and FSHβ subunit protein expression was increased (P < .05) in BPA- and DEHP-exposed prepubertal male rats but were decreased (P < .05) in adult animals relative to control. Exposure to both BPA and DEHP in utero inhibited (P < .05) global DNA hydroxymethylation in the adult testis in association with altered DNA methyltransferase protein expression. Together the present data suggest that altered developmental programming in the testes associated with chemical exposures are related to the disruption of sexual differentiation events and DNA methylation patterns. The chemical-induced effects impact the development of steroidogenic capacity in the adult testis.

Population pharmacokinetic/pharmacodynamic assessment of pharmacological effect of a selective estrogen receptor β agonist on total testosterone in healthy men

BACKGROUND

LY500307 is a highly selective estrogen receptor β (ERβ) agonist, which loses its selectivity at high dose and leads to undesirable suppression of total testosterone (TT) concentration. The objective of the present analysis was to define the LY500307 dose with minimal effect on TT METHODS: LY500307 and TT concentrations were obtained from a single ascending-dose study in a total of 30 healthy male subjects. LY500307 (in the range of 0.5 to 500 mg) or placebo was administered orally as a single dose on 2 occasions with a 3-week washout period. A population pharmacokinetics/pharmacodynamics (PK/PD) model that integrated Fourier series in an indirect response model was developed to describe the circadian rhythm of TT and the exposure-response relationship of LY500307 on TT.

RESULTS

The maximum TT suppression (Emax ) was approximately 28.6%. The potency (EC50 ) of LY500307 on TT suppression was approximately 1.69 ng/mL with a 95%CI of 0.871 to 4.44 ng/mL. This model could provide inferences on LY500307 dose levels that would result in various magnitudes of TT suppression.

CONCLUSIONS

Population PK/PD modeling is a highly sensitive tool to detect exposure-response relationships on top of the complicated and highly variable circadian rhythm of TT.

Homeodomain Transcription Factor Msx-2 Regulates Uterine Progenitor Cell Response to Diethylstilbestrol

The fate of mouse uterine epithelial progenitor cells is determined between postnatal days 5 to 7. Around this critical time window, exposure to an endocrine disruptor, diethylstilbestrol (DES), can profoundly alter uterine cytodifferentiation. We have shown previously that a homeo domain transcription factor MSX-2 plays an important role in DES-responsiveness in the female reproductive tract (FRT). Mutant FRTs exhibited a much more severe phenotype when treated with DES, accompanied by gene expression changes that are dependent on Msx2. To better understand the role that MSX-2 plays in uterine response to DES, we performed global gene expression profiling experiment in mice lacking Msx2 By comparing this result to our previously published microarray data performed on wild-type mice, we extracted common and differentially regulated genes in the two genotypes. In so doing, we identified potential downstream targets of MSX-2, as well as genes whose regulation by DES is modulated through MSX-2. Discovery of these genes will lead to a better understanding of how DES, and possibly other endocrine disruptors, affects reproductive organ development.

Pituitary androgen receptor signalling regulates prolactin but not gonadotrophins in the male mouse

Production of the androgen testosterone is controlled by a negative feedback loop within the hypothalamic-pituitary-gonadal (HPG) axis. Stimulation of testicular Leydig cells by pituitary luteinising hormone (LH) is under the control of hypothalamic gonadotrophin releasing hormone (GnRH), while suppression of LH secretion by the pituitary is controlled by circulating testosterone. Exactly how androgens exert their feedback control of gonadotrophin secretion (and whether this is at the level of the pituitary), as well as the role of AR in other pituitary cell types remains unclear. To investigate these questions, we exploited a transgenic mouse line (Foxg1^Cre/+; AR^fl/y) which lacks androgen receptor in the pituitary gland. Both circulating testosterone and gonadotrophins are unchanged in adulthood, demonstrating that AR signalling is dispensable in the male mouse pituitary for testosterone-dependent regulation of LH secretion. In contrast, Foxg1^Cre/+; AR^fl/y males have a significant increase in circulating prolactin, suggesting that, rather than controlling gonadotrophins, AR-signalling in the pituitary acts to suppress aberrant prolactin production in males.

Adult exposure to bisphenol A (BPA) in Wistar rats reduces sperm quality with disruption of the hypothalamic-pituitary-testicular axis

Reproductive physiology involves complex biological processes that can be disrupted by exposure to environmental contaminants. The effects of bisphenol A (BPA) on spermatogenesis and sperm quality is still unclear. The objective of this study was to investigate the reproductive toxicity of BPA at dosages considered to be safe (5 or 25mg BPA/kg/day). We assessed multiple sperm parameters, the relative expression of genes involved in the central regulation of the hypothalamic-pituitary-testicular axis, and the serum concentrations of testosterone, estradiol, LH and FSH. BPA exposure reduced sperm production, reserves and transit time. Significant damage to the acrosomes and the plasma membrane with reduced mitochondrial activity and increased levels of defective spermatozoa may have compromised sperm function and caused faster movement through the epididymis. BPA exposure reduced the serum concentrations of testosterone, LH and FSH and increased the concentration of estradiol. The relative gene expression revealed an increase in gonadotropin releasing hormone receptor (Gnrhr), luteinizing hormone beta (Lhb), follicle stimulating hormone beta (Fshb), estrogen receptor beta (Esr2) and androgen receptor (Ar) transcripts in the pituitary and a reduction in estrogen receptor alpha (Esr1) transcripts in the hypothalamus. In this study, we demonstrated for the first time that adult male exposure to BPA caused a reduction in sperm production and specific functional parameters. The corresponding pattern of gene expression is indicative of an attempt by the pituitary to reestablish normal levels of LH, FSH and testosterone serum concentrations. In conclusion, these data suggest that at dosages previously considered nontoxic to reproductive function, BPA compromises the spermatozoa and disrupts the hypothalamic-pituitary-gonadal axis, causing a state of hypogonadotropic hypogonadism.

Aromatase (Cyp19a1b) in the pituitary is dynamically involved in the upregulation of lhb but not fshb in the vitellogenic female ricefield eel Monopterus albus

Aromatase, encoded by Cyp19a1, is expressed in the pituitary of vertebrates; however, its physiological relevance remains poorly defined. In teleosts, the duplicated cyp19a1b is preferentially expressed in the pituitary where LH and FSH are synthesized in distinct gonadotropes. Our present study demonstrated that Cyp19a1b is colocalized with Lhb, but not Fshb, during vitellogenesis in female ricefield eels. The immunoreactive levels of Cyp19a1b and Lhb, as well as their colocalization frequency, increased during vitellogenesis toward maturation. The expression of lhb but not fshb in the pituitary fragments of female ricefield eels was induced by both estradiol (E2) and testosterone (T). In agreement, the promoter of lhb but not fshb was activated by both E2 and T. T is more potent than E2 in inducing lhb expression, whereas E2 is much more effective in activating the lhb promoter. T-induced lhb expression in the pituitary fragments was abolished by the estrogen receptor (Esr) antagonist fulvestrant and suppressed by the aromatase inhibitor letrozole, suggesting that the effect of T on lhb expression at the pituitary is largely mediated by E2. Furthermore, Lhb was shown to colocalize with Esr1 but not Esr2a. Taken together, results of the present study suggest that Cyp19a1b in LH cells may greatly upregulate lhb expression during vitellogenesis, possibly via E2 and Esr1 in an intracrine manner. The absence of Cyp19a1b in FSH cells and the insensitivity of fshb to sex steroids may contribute to the differential expression of lhb and fshb in ricefield eels and possibly other vertebrates as well.

Estrogen receptor β expression in the mouse forebrain: age and sex differences

Estrogen receptors regulate multiple brain functions, including stress, sexual, and memory-associated behaviors as well as controlling neuroendocrine and autonomic function. During development, estrogen signaling is involved in programming adult sex differences in physiology and behavior. Expression of estrogen receptor α changes across development in a region-specific fashion. By contrast, estrogen receptor β (ERβ) is expressed in many brain regions, yet few studies have explored sex and developmental differences in its expression, largely because of the absence of selective reagents for anatomical localization of the protein. This study utilized bacterial artificial chromosome transgenic mice expressing ERβ identified by enhanced green fluorescent protein (EGFP) to compare expression levels and distribution of ERβ in the male and female mouse forebrain on the day of birth (P0), on postnatal day 4 (P4), and on P21. By using qualitative analysis, we mapped the distribution of ERβ-EGFP and found developmental alterations in ERβ expression within the cortex, hippocampus, and hypothalamic regions including the arcuate, ventromedial, and paraventricular nuclei. We also report a sex difference in ERβ in the bed nucleus of the stria terminalis, with males showing greater expression at P4 and P21. Another sex difference was found in the anteroventral periventricular nucleus of P21, but not P0 or P4, mice, in which ERβ-EGFP-immunoreactive cells were densely clustered near the third ventricle in females but not males. These developmental changes and sex differences in ERβ indicate a mechanism through which estrogens might differentially affect brain functions or program adult physiology at select times during development.

Initiation of active immunization against testosterone during early puberty alters negative feedback regulation of the hypothalamic-pituitary-testicular axis in rabbits

To investigate the effects of antitestosterone immunization, initiated during early puberty, on hypothalamic-pituitary-testicular feedback in rabbits, 16 early pubertal male rabbits were randomly allocated into 2 groups (n = 8), control or immunized against testosterone-3(O-carboxymethyl)oxime-BSA in Freund adjuvant at 4 mo of age (with a booster immunization 4 wk later). Blood samples (for antibody titers and hormone concentrations) were collected at 2- or 4-wk intervals after immunization. Compared with controls, antitestosterone immunization triggered: a substantial and sustained antibody response (P < 0.01); increases in serum concentrations of luteinizing hormone (LH) and testosterone and testis weight and volume (P < 0.05); hyperplasia of testicular interstitial tissue with clustered and hypertrophic Leydig cells; and greater (P < 0.05) enzyme protein and messenger RNA (mRNA) expression levels for testicular cholesterol side-chain cleavage cytochrome P-450, 17α-hydroxylase cytochrome P-450, and 3β-dydroxysteroid dehydrogenase. Furthermore, immunoneutralization of testosterone upregulated mRNA expressions for genes in sex steroid negative feedback loops, including androgen receptor (AR), estrogen receptor alpha (ER-α), kisspeptin encoded gene (kiss-1) and kisspeptin receptor (G-coupled receptor 54) and gonadotropin-releasing hormone (GnRH) in the hypothalamic arcuate nucleus, GnRH receptor and LH-β in pituitary, and AR, inhibin-α and βA subunits in testes (P < 0.05). However, immunization did not affect mRNA expressions for follicle-stimulating hormone β, AR, and ER-α in pituitary, or ER-α in testes. We concluded that antitestosterone immunization in male rabbits, initiated during early puberty, increased GnRH mRNA expression, and in turn LH synthesis by reducing testicular feedback signaling. Reduction of direct steroidal effects on the testis may also have increased testosterone secretion. Consequently, there was an accelerated testicular development during puberty and enhanced testicular function after puberty, which likely conferred prolonged reproductive advantages.

A critical point of male gonad development: neuroendocrine correlates of accelerated testicular growth in rats during early life

Testis growth during early life is important for future male fertility and shows acceleration during the first months of life in humans. This acceleration coincides with the peak in gonadotropic hormones in the blood, while the role of hypothalamic factors remains vague. Using neonatal rats to assess this issue, we found that day 9 of life is likely critical for testis development in rats. Before this day, testicular growth was proportional to body weight gain, but after that the testes showed accelerated growth. Hypothalamic kisspeptin and its receptor mRNA levels begin to elevate 2 days later, at day 11. A significant increase in the mRNA levels for gonadotropin-releasing hormone (GnRH) receptors in the hypothalamus between days 5 and 7 was followed by a 3-fold decrease in GnRH mRNA levels in this brain region during the next 2 days. Starting from day 9, hypothalamic GnRH mRNA levels increased significantly and positively correlated with accelerated testicular growth. Triptorelin, an agonist of GnRH, at a dose that had no effect on testicular growth during “proportional” period, increased testis weights during the period of accelerated growth. The insensitivity of testicular growth to GnRH during “proportional” period was supported by inability of a 2.5-fold siRNA knockdown of GnRH expression in the hypothalamus of the 7-day-old animals to produce any effect on their testis weights. GnRH receptor blockade with cetrorelix was also without effect on testis weights during “proportional” period but the same doses of this GnRH antagonist significantly inhibited “accelerated” testicular growth. GnRH receptor mRNA levels in the pituitary as well as plasma LH concentrations were higher during “accelerated” period of testicular growth than during “proportional” period. In general, our data defined two distinct periods in rat testicular development that are primarily characterized by different responses to GnRH signaling.

Effects and therapeutic potentials of kisspeptin analogs: regulation of the hypothalamic-pituitary-gonadal axis

The hypothalamic peptide kisspeptin (metastin), the endogenous ligand of the G protein-coupled receptor KISS1R, plays a critical role in controlling GnRH release from hypothalamic GnRH neurons and thereby regulates hypothalamic-pituitary-gonadal functions. Although the therapeutic potential of kisspeptin is attractive, its susceptibility to proteolytic degradation limits its utility. To overcome this, KISS1R agonists or antagonists as peptide analogs or small molecules have been investigated. Kisspeptin analogs have been most extensively studied by reducing the length of the peptide from the original 54 amino acids to 10 amino acids or less and by substituting key amino acid residues. Also, 2 investigational kisspeptin agonist analogs have been evaluated in clinical studies in men; in agreement with animal studies, abrupt elevations in gonadotropin and testosterone levels were observed as an acute effect, followed by rapid reductions in these hormones as a chronic effect. Some studies of small-molecule KISS1R antagonists have also been published. In this review, we present a brief overview on kisspeptin/KISS1R physiology in reproductive functions and summarize the available knowledge of both agonists and antagonists. We also focus on the kisspeptin agonist analogs by summarizing key pharmacological findings from both clinical and preclinical studies, and discuss their potential therapeutic utility.

Role of estrogen receptors and g protein-coupled estrogen receptor in regulation of hypothalamus-pituitary-testis axis and spermatogenesis

Male reproductive function is under the control of both gonadotropins and androgens through a negative feedback loop that involves the hypothalamus, pituitary, and testis known as hypothalamus-pituitary-gonadal axis (HPG). Indeed, estrogens also play an important role in regulating HPG axis but the study on relative contribution to the inhibition of gonadotropins secretion exerted by the amount of estrogens produced within the hypothalamus and/or the pituitary or by the amount of circulating estrogens is still ongoing. Moreover, it is known that the maintenance of spermatogenesis is controlled by gonadotropins and testosterone, the effects of which are modulated by a complex network of locally produced factors, including estrogens. Physiological effects of estrogens are mediated by the classical nuclear estrogen receptor alpha and estrogen receptor beta, which mediate both genomic and rapid signaling events. In addition, estrogens induce rapid non-genomic responses through a membrane-associated G protein-coupled estrogen receptor (GPER). Ours and other studies reported that, in the testis, GPER is expressed in both normal germ cells and somatic cells and it is involved in mediating the estrogen action in spermatogenesis controlling proliferative and/or apoptotic events. Interestingly, GPER expression has been revealed also in the hypothalamus and pituitary. However, its role in mediating estrogen rapid actions in this context is under investigation. Recent studies indicate that GPER is involved in modulating gonadotropin-releasing hormone (GnRH) release as well as gonadotropins secretion. In this review, we will summarize the current knowledge concerning the role of estrogen/estrogen receptors molecular pathways in regulating GnRH, follicle-stimulating hormone, and luteinizing hormone release at the hypothalamic and pituitary levels in males as well as in controlling specific testicular functions such as spermatogenesis, focusing our attention mainly on estrogen signaling mediated by GPER.

GnRH-Induced Ca(2+) Signaling Patterns and Gonadotropin Secretion in Pituitary Gonadotrophs. Functional Adaptations to Both Ordinary and Extraordinary Physiological Demands

PITUITARY GONADOTROPHS ARE A SMALL FRACTION OF THE ANTERIOR PITUITARY POPULATION, YET THEY SYNTHESIZE GONADOTROPINS: luteinizing (LH) and follicle-stimulating (FSH), essential for gametogenesis and steroidogenesis. LH is secreted via a regulated pathway while FSH release is mostly constitutive and controlled by synthesis. Although gonadotrophs fire action potentials spontaneously, the intracellular Ca(2+) rises produced do not influence secretion, which is mainly driven by Gonadotropin-Releasing Hormone (GnRH), a decapeptide synthesized in the hypothalamus and released in a pulsatile manner into the hypophyseal portal circulation. GnRH binding to G-protein-coupled receptors triggers Ca(2+) mobilization from InsP3-sensitive intracellular pools, generating the global Ca(2+) elevations necessary for secretion. Ca(2+) signaling responses to increasing (GnRH) vary in stereotyped fashion from subthreshold to baseline spiking (oscillatory), to biphasic (spike-oscillatory or spike-plateau). This progression varies somewhat in gonadotrophs from different species and biological preparations. Both baseline spiking and biphasic GnRH-induced Ca(2+) signals control LH/FSH synthesis and exocytosis. Estradiol and testosterone regulate gonadotropin secretion through feedback mechanisms, while FSH synthesis and release are influenced by activin, inhibin, and follistatin. Adaptation to physiological events like the estrous cycle, involves changes in GnRH sensitivity and LH/FSH synthesis: in proestrus, estradiol feedback regulation abruptly changes from negative to positive, causing the pre-ovulatory LH surge. Similarly, when testosterone levels drop after orquiectomy the lack of negative feedback on pituitary and hypothalamus boosts both GnRH and LH secretion, gonadotrophs GnRH sensitivity increases, and Ca(2+) signaling patterns change. In addition, gonadotrophs proliferate and grow. These plastic changes denote a more vigorous functional adaptation in response to an extraordinary functional demand.

Effects of castration on androgen receptors and gonadotropins in the pituitary of adult male viscachas

The aims of the present study were to determine whether castration results in quantitative immunohistochemical changes in androgen receptors (AR), LH-immunoreactive (IR) cells and FSH-IR cells, and to analyse the colocalisation of AR and gonadotropins in the pituitary pars distalis (PD) of viscachas. Pituitaries were processed for light and electron microscopy. AR-IR, LH-IR and FSH-IR cells were detected by immunohistochemistry. In morphometric studies, the percentage of AR-IR, LH-IR, FSH-IR, LH-IR/AR-IR and FSH-IR/AR-IR cells was determined. In intact viscachas, AR were distributed throughout the PD; they were numerous at the caudal end, with intense immunostaining. LH-IR cells and FSH-IR cells were found mainly in the ventral region and at the rostral end of the PD. Approximately 45%-66% of LH-IR cells and 49%-57% of FSH-IR cells expressed AR in the different zones of the PD. In castrated viscachas, there was a significant decrease in the percentage of AR-IR, LH-IR, FSH-IR, and FSH-IR/AR-IR cells. Some pituitary cells from castrated viscachas also exhibited ultrastructural changes. These results provide morphological evidence that gonadal androgens are directly related to the immunolabelling of AR, LH and FSH. Moreover, the colocalisation of AR and FSH is most affected by castration, suggesting the existence of a subpopulation of gonadotrophs with different regulatory mechanisms for hormonal synthesis, storage and secretion.

Castration-induced modifications of GnRH-elicited [Ca2+](i) signaling patterns in male mouse pituitary gonadotrophs in situ: studies in the acute pituitary slice preparation

Gonadotropin-releasing hormone (GnRH) binds to pituitary gonadotroph receptors and initiates [Ca(2+)](i) signals and gonadotropin secretion. Here, we recorded GnRH-induced Ca(2+) signals in acute pituitary slices from both intact and castrated male mice 15 and 45 days after orchiectomy (GnX). Cells responding with "noncanonical" sequences of Ca(2+) signaling to increasing GnRH concentrations ([GnRH]; oscillatory responses at a given [GnRH] and transient responses at both lower and higher concentrations) were augmented significantly in the castrated mice. Also, 15 days after GnX the number and size of gonadotrophs were augmented, confirming earlier anatomical studies. Hypertrophied gonadotrophs after 15 days after GnX tended to display GnRH-induced Ca(2+) responses of greater amplitude. Furthermore, median effective dose (ED50) for GnRH decreased from 0.17 nM (control) to ~0.07 nM after GnX, suggesting increased GnRH responsiveness of the gonadotroph population. The progression of Ca(2+) response patterns reported in control male rat gonadotrophs (oscillations declining and spike-plateau responses dominating at increasing [GnRH]) was less conspicuous in mouse gonadotrophs in situ. Also, GnX-induced alterations in rat gonadotrophs (persistence of Ca(2+) oscillations even at [GnRH] >100 nM) were not mirrored by mouse gonadotrophs in situ. Contrary to observations in intact and 15-day castrated mice, after 45 days of GnX the hump component diminished and oscillations were augmented with increasing [GnRH], but Ca(2+) response patterns of gonadotrophs in situ remained virtually unchanged in response to [GnRH]s >1 nM, suggesting dose discrimination failure at high [GnRH]s. This study underscores the notion that GnRH responsiveness and the effects of testosterone deficiency may not be equal in pituitary gonadotrophs across species.

Testosterone deficiency accompanied by testicular and epididymal abnormalities in TMF(-/-) mice

TMF/ARA160 is a Golgi-associated protein, which is essential for spermiogenesis. In this study, we show that lack of TMF/ARA160 leads to defects in both the testis and the epididymis. In the testis, spermatid retention and extensive proliferation of Leydig cells were observed. Concomitantly, the serum levels of luteinizing hormone (LH), a stimulator of Leydig cell proliferation, were significantly increased in TMF(-/-) mice. Structural and functional defects were also seen in the epididymis. These included apoptosis of epithelial epididymal cells and sperm stasis in the cauda. Notably, the serum testosterone levels of TMF(-/-) mice were significantly lower than those of wt mice, and external testosterone administration decreased the number of apoptotic epithelial epididymal cells in TMF(-/-) animals. In summary, we show here for the first time that TMF/ARA160 participates in the control of serum testosterone levels in males, and its absence results in major testicular and epididymal defects.

Transactivating function (AF) 2-mediated AF-1 activity of estrogen receptor α is crucial to maintain male reproductive tract function

Estrogen receptor alpha (ERα) is a ligand-dependent transcription factor containing two transcriptional activation function (AF) domains. AF-1 is in the N terminus of the receptor protein, and AF-2 activity is dependent on helix 12 of the C-terminal ligand-binding domain. We recently showed that two point mutations converting leucines 543 and 544 to alanines in helix 12 (AF2ER) minimized estrogen-dependent AF-2 transcriptional activation. A characteristic feature of AF2ER is that the estrogen antagonists ICI182780 and tamoxifen (TAM) act as agonists through intact AF-1, but not through mutated AF-2. Here we report the reproductive phenotype of male AF2ER knock-in (AF2ERKI) mice and demonstrate the involvement of ERα in male fertility. The AF2ERKI male homozygotes are infertile because of seminiferous tubular dysmorphogenesis in the testis, similar to ERα KO males. Sperm counts and motility did not differ at age 6 wk in AF2ERKI and WT mice, but a significant testis defect was observed in adult AF2ERKI male mice. The expression of efferent ductal genes involved in fluid reabsorption was significantly lower in AF2ERKI males. TAM treatment for 3 wk beginning at age 21 d activated AF-2-mutated ERα (AF2ER) and restored expression of efferent ductule genes. At the same time, the TAM treatment reversed AF2ERKI male infertility compared with the vehicle-treated group. These results indicate that the ERα AF-2 mutation results in male infertility, suggesting that the AF-1 is regulated in an AF-2-dependent manner in the male reproductive tract. Activation of ERα AF-1 is capable of rescuing AF2ERKI male infertility.

ERα/E2 signaling suppresses the expression of steroidogenic enzyme genes via cross-talk with orphan nuclear receptor Nur77 in the testes

Estrogen receptor alpha (ERα) has been reported to affect steroidogenesis in testicular Leydig cells, but its molecular mechanism remains unclear. Here, we investigate the effect of estrogen and ERα on Nur77, a major transcription factor that regulates the expression of steroidogenic enzyme genes. In MA-10 Leydig cells, estradiol (E2) treatment, and interestingly ERα overexpression, suppressed the cAMP-induced and Nur77-activated promoter activity of steroidogenic enzyme genes via the suppression of Nur77 transactivation. ERα physically interacted with Nur77 and inhibited its DNA binding activity. In addition, ERα/E2 signaling decreased Nur77 protein levels. Consistent with the above results, the testicular testosterone level was higher in Leydig cell-specific ERα knock-out mice (ERα(flox/flox)Cyp17iCre) than in wild-type mice (ERα(flox/flox)). Taken together, these results suggest that ERα/E2 signaling controls the Nur77-mediated expression of steroidogenic enzyme genes in Leydig cells. These findings may provide a mechanistic explanation for the local regulation of testicular steroidogenesis by estrogenic compounds and ERα.

Serum cholinesterases are differentially regulated in normal and dystrophin-deficient mutant mice

The cholinesterases, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE) (pseudocholinesterase), are abundant in the nervous system and in other tissues. The role of AChE in terminating transmitter action in the peripheral and central nervous system is well understood. However, both knowledge of the function(s) of the cholinesterases in serum, and of their metabolic and endocrine regulation under normal and pathological conditions, is limited. This study investigates AChE and BChE in sera of dystrophin-deficient mdx mutant mice, an animal model for the human Duchenne muscular dystrophy (DMD) and in control healthy mice. The data show systematic and differential variations in the concentrations of both enzymes in the sera, and specific changes dictated by alteration of hormonal balance in both healthy and dystrophic mice. While AChE in mdx-sera is elevated, BChE is markedly diminished, resulting in an overall cholinesterase decrease compared to sera of healthy controls. The androgen testosterone (T) is a negative modulator of BChE, but not of AChE, in male mouse sera. T-removal elevated both BChE activity and the BChE/AChE ratio in mdx male sera to values resembling those in healthy control male mice. Mechanisms of regulation of the circulating cholinesterases and their impairment in the dystrophic mice are suggested, and clinical implications for diagnosis and treatment are considered.

Evaluation of the effects of testosterone and luteinizing hormone on regulation of β-amyloid in male 3xTg-AD mice

During normal aging, men experience a significant decline in testosterone levels and a compensatory elevation in levels of gonadotropin luteinizing hormone (LH). Both low testosterone and elevated LH have been identified as significant risk factors for the development of Alzheimer's disease (AD) in men. It is unclear whether changes in testosterone or LH primarily underlie the relationship with AD, and therefore may be a more suitable therapeutic target. To examine this issue, we compared levels of β-amyloid (Aβ) immunoreactivity in male 3xTg-AD mice under varying experimental conditions associated with relatively low or high levels of testosterone and/or LH. In gonadally intact mice, Aβ accumulation increased after treatment with the gonadotropin-releasing hormone agonist leuprolide, which inhibits the hypothalamic-pituitary-gonadal (HPG) axis and reduces both testosterone and LH levels. In gonadectomized (GDX) mice with low testosterone and high LH, we also observed increased Aβ levels. Treatment of GDX mice with testosterone significantly reduced Aβ levels. In contrast, leuprolide did not significantly decrease Aβ levels and moreover, inhibited the Aβ-lowering effect of testosterone. Evaluation of hippocampal-dependent behavior revealed parallel findings, with performance in GDX mice improved by testosterone but not leuprolide. These data suggest that Aβ-lowering actions of testosterone are mediated directly by androgen pathways rather than indirectly via regulation of LH and the HPG axis. These findings support the clinical evaluation of androgen therapy in the prevention and perhaps treatment of AD in hypogonadal men.

Estrogen receptor-α mediates diethylstilbestrol-induced feminization of the seminal vesicle in male mice

BACKGROUND

Studies have shown that perinatal exposure to the synthetic estrogen diethylstilbestrol (DES) leads to feminization of the seminal vesicle (SV) in male mice, as illustrated by tissue hyperplasia, ectopic expression of the major estrogen-inducible uterine secretory protein lactoferrin (LF), and reduced expression of SV secretory protein IV (SVS IV).

OBJECTIVES

The present study was designed to evaluate the role of the estrogen receptor (ER) in this action by using ER-knockout (ERKO) mice.

METHODS

Wild-type (WT), ERα-null (αERKO), and ERβ-null (βERKO) male mice were treated with either vehicle or DES (2 μg/day) on neonatal days 1-5. These mice were divided into two groups: In the first group, intact mice were sacrificed at 10 weeks of age; in the second group, mice were castrated at 10 weeks of age, allowed to recover for 10 days, treated with dihydrotestosterone (DHT) or placebo, and sacrificed 2 weeks later. Body weights and SV weights were recorded, and mRNA expression levels of Ltf (lactoferrin), Svs4, and androgen receptor (Ar) were assessed.

RESULTS

In DES-treated intact mice, SV weights were reduced in WT and βERKO mice but not in αERKO mice. DES-treated WT and βERKO males, but not αERKO males, exhibited ectopic expression of LF in the SV. DES treatment resulted in decreased SVS IV protein and mRNA expression in WT males, but no effect was seen in αERKO mice. In addition, DES-treated βERKO mice exhibited reduced Svs4 mRNA expression but maintained control levels of SVS IV protein. In DES-treated castrated mice, DHT implants restored SV weights to normal levels in αERKO mice but not in WT mice, suggesting full androgen responsiveness in αERKO mice.

CONCLUSIONS

These data suggest that DES-induced SV toxicity and feminization are primarily mediated by ERα; however, some aspects of androgen response may require the action of ERβ.

Androgen rather than estrogen up-regulates brain-type cytochrome P450 aromatase (cyp19a1b) gene via tissue-specific promoters in the hermaphrodite teleost ricefield eel Monopterus albus

CYP19A1 in the brain and pituitary of vertebrates is important for reproductive and non-reproductive processes. In teleosts, it is broadly accepted that estradiol (E(2)) up-regulates cyp19a1b gene via a positive autoregulatory loop. Our present study, however, showed that E(2) did not up-regulate ricefield eel cyp19a1b in the hypothalamus and pituitary, whereas dihydrotestosterone (DHT) or testosterone (T) stimulated cyp19a1b expression only in the pituitary. Two tissue-specific promoters, namely promoter I and II directing the expression in the brain and pituitary respectively, were identified. Promoter I contained a non-consensus estrogen response element (ERE), and consequently did not respond to E(2). Promoter II contained an androgen response element (ARE) and consequently responded to DHT. Taken together, these results demonstrated a novel steroidal regulation of cyp19a1b gene expression and an alternative usage of tissue-specific cyp19a1b promoters in the brain and pituitary of a teleost species, the ricefield eel.

Estrogenic regulation of the GnRH neuron

Reproductive function is regulated by the secretion of luteinizing hormone (LH) and follicle-stimulating hormone from the pituitary and the steroid hormones from the gonads. The dynamic changes in the levels of the reproductive hormones regulate secondary sex characteristics, gametogenesis, cellular function, and behavior. Hypothalamic GnRH neurons, with cell bodies located in the basal hypothalamus, represent the final common pathway for neuronally derived signals to the pituitary. As such, they serve as integrators of a dizzying array of signals including sensory inputs mediating information about circadian, seasonal, behavioral, pheromonal, and emotional cues. Additionally, information about peripheral physiological function may also be included in the integrative signal to the GnRH neuron. These signals may communicate information about metabolic status, disease, or infection. Gonadal steroid hormones arguably exert the most important effects on GnRH neuronal function. In both males and females, the gonadal steroid hormones exert negative feedback regulation on axis activity at both the level of the pituitary and the hypothalamus. These negative feedback loops regulate homeostasis of steroid hormone levels. In females, a cyclic reversal of estrogen feedback produces a positive feedback loop at both the hypothalamic and pituitary levels. Central positive feedback results in a dramatic increase in GnRH secretion (Moenter et al., 1992; Xia et al., 1992; Clarke, 1993; Sisk et al., 2001). This is coupled with an increase in pituitary sensitivity to GnRH (Savoy-Moore et al., 1980; Turzillo et al., 1995), which produces the massive surge in secretion of LH that triggers ovulation. While feedback regulation of the axis in males is in part mediated by estrogen receptors (ER), there is not a clear consensus as to the relative role of ER versus AR signaling in males (Lindzey et al., 1998; Wersinger et al., 1999). Therefore, this review will focus on estrogenic signaling in the female.

Regulation of NKB pathways and their roles in the control of Kiss1 neurons in the arcuate nucleus of the male mouse

Kisspeptin (Kiss1) and neurokinin B (NKB) (encoded by the Kiss1 and Tac2 genes, respectively) are indispensable for reproduction. In the female of many species, Kiss1 neurons in the arcuate nucleus (ARC) coexpress dynorphin A and NKB. Such cells have been termed Kiss1/NKB/Dynorphin (KNDy) neurons, which are thought to mediate the negative feedback regulation of GnRH/LH secretion by 17β-estradiol. However, we have less knowledge about the molecular physiology and regulation of Kiss1/Kiss1-expressing neurons in the ARC of the male. Our work focused on the adult male mouse, where we sought evidence for coexpression of these neuropeptides in cells in the ARC, assessed the role of Kiss1 neurons in negative feedback regulation of GnRH/LH secretion by testosterone (T), and investigated the action of NKB on KNDy and GnRH neurons. Results showed that 1) the mRNA encoding Kiss1, NKB, and dynorphin are coexpressed in neurons located in the ARC; 2) Kiss1 and dynorphin A mRNA are regulated by T through estrogen and androgen receptor-dependent pathways; 3) senktide, an agonist for the NKB receptor (neurokinin 3 receptor, encoded by Tacr3), stimulates gonadotropin secretion; 4) KNDy neurons express Tacr3, whereas GnRH neurons do not; and 5) senktide activates KNDy neurons but has no discernable effect on GnRH neurons. These observations corroborate the putative role for KNDy neurons in mediating the negative feedback effects of T on GnRH/LH secretion and provide evidence that NKB released from KNDy neurons is part of an auto-feedback loop that generates the pulsatile secretion of Kiss1 and GnRH in the male.