Opposite roles of estrogen receptor (ER)-alpha and ERbeta in the modulation of luteinizing hormone responses to kisspeptin in the female rat: implications for the generation of the preovulatory surge

Vasoactive intestinal peptide excites GnRH neurons via KCa3.1, a potential player in the slow afterhyperpolarization current

Vasoactive intestinal peptide (VIP) is an important component of the suprachiasmatic nucleus (SCN) which relays circadian information to neuronal populations, including GnRH neurons. Human and animal studies have shown an impact of disrupted daily rhythms (chronic shift work, temporal food restriction, clock gene disruption) on both male and female reproduction and fertility. To date, how VIP modulates GnRH neurons remains unknown. Calcium imaging and electrophysiology on primary GnRH neurons in explants and adult mouse brain slice, respectively, were used to address this question. We found VIP excites GnRH neurons via the VIP receptor, VPAC2. The downstream signaling pathway uses both Gs protein/adenylyl cyclase/protein kinase A (PKA) and phospholipase C/phosphatidylinositol 4,5-bisphosphate (PIP2) depletion. Furthermore, we identified a UCL2077-sensitive target, likely contributing to the slow afterhyperpolarization current (IAHP), as the PKA and PIP2 depletion target, and the KCa3.1 channel as a specific target. Thus, VIP/VPAC2 provides an example of Gs protein-coupled receptor-triggered excitation in GnRH neurons, modulating GnRH neurons likely via the slow IAHP. The possible identification of KCa3.1 in the GnRH neuron slow IAHP may provide a new therapeutical target for fertility treatments.

The molecular phenotype of kisspeptin neurons in the medial amygdala of female mice

Reproduction is regulated through the hypothalamic-pituitary-gonadal (HPG) axis, largely via the action of kisspeptin neurons in the hypothalamus. Importantly, Kiss1 neurons have been identified in other brain regions, including the medial amygdala (MeA). Though the MeA is implicated in regulating aspects of both reproductive physiology and behavior, as well as non-reproductive processes, the functional roles of MeA Kiss1 neurons are largely unknown. Additionally, besides their stimulation by estrogen, little is known about how MeA Kiss1 neurons are regulated. Using a RiboTag mouse model in conjunction with RNA-seq, we examined the molecular profile of MeA Kiss1 neurons to identify transcripts that are co-expressed in MeA Kiss1 neurons of female mice and whether these transcripts are modulated by estradiol (E₂) treatment. RNA-seq identified >13,800 gene transcripts co-expressed in female MeA Kiss1 neurons, including genes for neuropeptides and receptors implicated in reproduction, metabolism, and other neuroendocrine functions. Of the >13,800 genes co-expressed in MeA Kiss1 neurons, only 45 genes demonstrated significantly different expression levels due to E₂ treatment. Gene transcripts such as Kiss1, Gal, and Oxtr increased in response to E₂ treatment, while fewer transcripts, such as Esr1 and Cyp26b1, were downregulated by E₂. Dual RNAscope and immunohistochemistry was performed to validate co-expression of MeA Kiss1 with Cck and Cartpt. These results are the first to establish a profile of genes actively expressed by MeA Kiss1 neurons, including a subset of genes regulated by E₂, which provides a useful foundation for future investigations into the regulation and function of MeA Kiss1 neurons.

The role of kisspeptin in the pathogenesis of a polycystic ovary syndrome

Hypothalamic-pituitary gonadal (HPG) axis is responsible for the development and regulation of the female reproductive system. In polycystic ovary syndrome (PCOS), there is a disturbance in the HPG axis. Kisspeptin, a neuropeptide produced by the KISS1 gene, plays a vital role in the regulation of HPG axis by binding with its receptors KISS1R/GPR54, and stimulates gonadotropin secretion from the hypothalamus into pituitary to release luteinizing hormone (LH) and follicle stimulating hormone (FSH). Polymorphisms or mutations in the KISS1 gene can cause disturbance in the kisspeptin signaling pathway and is thought to disrupt HPG axis. Altered signaling of kisspeptin can cause abnormal secretion of GnRH pulse, which leads to increased LH/FSH ratio, thereby affecting androgen levels and ovulation. The increased levels of androgen worsen the symptoms of PCOS. In the present article, we review the molecular physiology and pathology of kisspeptin and how it is responsible for the development of PCOS. The goal of this review article is to provide an overview and metabolic profile of kisspeptin in PCOS patients and the expression of kisspeptin in PCOS animal models. In the present article, we also review the molecular physiology and pathology of kisspeptin and how it is responsible for the development of PCOS.

Hypothalamic Expression of Estrogen Receptor Isoforms Underlies Estradiol Control of Luteinizing Hormone in Female Rats

Luteinizing hormone (LH) secretion during the ovarian cycle is governed by fluctuations in circulating estradiol (E2) that oppositely regulate kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) of the hypothalamus. However, how these effects are orchestrated to achieve fertility is unknown. Here, we have tested the hypothesis that AVPV and ARC neurons have different sensitivities to E2 to coordinate changes in LH secretion. Cycling and ovariectomized rats with low and high E2 levels were used. As an index of E2 responsiveness, progesterone receptor (PR) was expressed only in the AVPV of rats with high E2, showing the preovulatory LH surge. On the other hand, kisspeptin neurons in the ARC responded to low E2 levels sufficient to suppress LH release. Notably, the Esr1/Esr2 ratio of gene expression was higher in the ARC than AVPV, regardless of E2 levels. Accordingly, the selective pharmacological activation of estrogen receptor α (ERα) required lower doses to induce PR in the ARC. The activation of ERβ, in turn, amplified E2-induced PR expression in the AVPV and the LH surge. Thus, ARC and AVPV neurons are differently responsive to E2. Lower E2 levels activate ERα in the ARC, whereas ERβ potentiates the E2 positive feedback in the AVPV, which appears related to the differential Esr1/Esr2 ratio in these 2 brain areas. Our findings provide evidence that the distinct expression of ER isoforms in the AVPV and ARC plays a key role in the control of periodic secretion of LH required for fertility in females.

Kisspeptin Neurons and Estrogen-Estrogen Receptor α Signaling: Unraveling the Mystery of Steroid Feedback System Regulating Mammalian Reproduction

Estrogen produced by ovarian follicles plays a key role in the central mechanisms controlling reproduction via regulation of gonadotropin-releasing hormone (GnRH) release by its negative and positive feedback actions in female mammals. It has been well accepted that estrogen receptor α (ERα) mediates both estrogen feedback actions, but precise targets had remained as a mystery for decades. Ever since the discovery of kisspeptin neurons as afferent ERα-expressing neurons to govern GnRH neurons, the mechanisms mediating estrogen feedback are gradually being unraveled. The present article overviews the role of kisspeptin neurons in the arcuate nucleus (ARC), which are considered to drive pulsatile GnRH/gonadotropin release and folliculogenesis, in mediating the estrogen negative feedback action, and the role of kisspeptin neurons located in the anteroventral periventricular nucleus-periventricular nucleus (AVPV-PeN), which are thought to drive GnRH/luteinizing hormone (LH) surge and consequent ovulation, in mediating the estrogen positive feedback action. This implication has been confirmed by the studies showing that estrogen-bound ERα down- and up-regulates kisspeptin gene (Kiss1) expression in the ARC and AVPV-PeN kisspeptin neurons, respectively. The article also provides the molecular and epigenetic mechanisms regulating Kiss1 expression in kisspeptin neurons by estrogen. Further, afferent ERα-expressing neurons that may regulate kisspeptin release are discussed.

Advances in the Regulation of Mammalian Follicle-Stimulating Hormone Secretion

Simple Summary

The reproduction of mammals is regulated by the hypothalamic-pituitary-gonadal axis. Follicle stimulating hormone, as one of the gonadotropins secreted by the pituitary gland, plays an immeasurable role. This article mainly reviews the molecular basis and classical signaling pathways that regulate the synthesis and secretion of follicle stimulating hormone, and summarizes its internal molecular mechanism, which provides a certain theoretical basis for the research of mammalian reproduction regulation and the application of follicle stimulating hormone in production practice.

Abstract

Mammalian reproduction is mainly driven and regulated by the hypothalamic-pituitary-gonadal (HPG) axis. Follicle-stimulating hormone (FSH), which is synthesized and secreted by the anterior pituitary gland, is a key regulator that ultimately affects animal fertility. As a dimeric glycoprotein hormone, the biological specificity of FSH is mainly determined by the β subunit. As research techniques are being continuously innovated, studies are exploring the underlying molecular mechanism regulating the secretion of mammalian FSH. This article will review the current knowledge on the molecular mechanisms and signaling pathways systematically regulating FSH synthesis and will present the latest hypothesis about the nuclear cross-talk among the various endocrine-induced pathways for transcriptional regulation of the FSH β subunit. This article will provide novel ideas and potential targets for the improved use of FSH in livestock breeding and therapeutic development.

Ghrelin antagonist overrides the mRNA expression of NPY in hypothalamus in feed restricted ewes

A negative energy balance (NEB) is detrimental to reproduction in animals. A suggested link between NEB and reproductive failure is the gastrointestinal hormone ghrelin, because of the association between ghrelin and the hypothalamo-pituitary-gonadal axis. The [D-Lys3]-Growth Hormone Releasing Peptide-6 ([D-Lys3]-GHRP-6) is a ghrelin antagonist that acts on ghrelin receptors (GHS-R1). The objective of this study was to evaluate the effect of [D-Lys3]-GHRP-6 on reproduction variables in feed restricted ewes. Two experiments were conducted. Experiment I was conducted for 30 days; and Experiment II for 13 days. In both experiments the ewes (n = 18) were randomly assigned to: Control (CO): fed to meet maintenance requirements; Feed restriction (FR): 80% of maintenance restriction; or Ghrelin antagonist (GA): feed restricted and daily subcutaneous of 7.5μg/kg of [D-Lys3]-GHRP-6. Plasma was collected to measure hormones and metabolite concentration. In Experiment II, the hypothalamus and ovaries were collected on day 13. In both Experiments, sheep allocated to the FR and GA treatments decreased their body weight compared with sheep in the CO group (P < 0.06); progesterone however, did not differ between treatments (P > 0.10). Experiment I: Plasma ghrelin concentration was greater (P < 0.01) in FR and GA compared with CO ewes. Plasma non-esterified fatty acids concentration was greater (P < 0.01) in GA and FR than CO. Experiment II: Kisspeptin1-Receptor (Kiss1-R) mRNA expression was greater in FR (P < 0.01) and tended to be greater in GA (P = 0.10) compared with CO ewes. The neuro peptide-Y (NPY) mRNA expression was greater (P = 0.03) in FR than CO; and tended to be greater (P = 0.06) compared with GA ewes. Growth hormone releasing hormone (GhRH) mRNA expression was greater in GA (P = 0.04) and tended to be greater in FR (P = 0.07) compared with CO ewes. Feed restriction increased GhRH, NPY, and Kiss-R mRNA expression in hypothalamus without affecting reproductive variables.Ghrelin antagonist may prevent an increase inNPY expression in ewes.

The content of gonadotropin-releasing hormone (GnRH), kisspeptin, and estrogen receptors (ERα/ERβ) in the anteromedial hypothalamus displays daily variations throughout the rat estrous cycle

The content of gonadotropin-releasing hormone (GnRH), its mRNA, and estrogen receptor alpha (ERα) and beta (ERβ) in the hypothalamus varies throughout the estrous cycle. Furthermore, the abundance of these molecules displays asymmetry between the right and left side. In the present study, we investigated the changes in the content of ERα, ERβ, kisspeptin, and GnRH by western blot in the left and right anteromedial hypothalamus, at four different times during each stage of the rat estrous cycle. The serum levels of the follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were also measured. ERα and ERβ levels changed depending on the stage of the estrous cycle, meanwhile that of kisspeptin was modified according to both the hour of the day and the stage of the cycle. Except in estrus day, ERβ was higher in the right hypothalamus, while ERα was similar in both sides. During both proestrus and estrus, the content of kisspeptin and GnRH was higher in the right hypothalamus. The highest levels of FSH and LH occurred at 17:00 h of proestrus. But at estrus, the highest FSH levels were observed at 08:00 h and the lowest at 17:00 h. Thus, the current results show that the content of ERα, ERβ, kisspeptin, and GnRH in the anteromedial hypothalamus are regulated as a function of the stage of the estrous cycle and the hour of the day. Furthermore, the content of these proteins is regularly higher in the right anteromedial hypothalamus, regardless of the stage of the cycle or time of the day.

Clock control of mammalian reproductive cycles: Looking beyond the pre-ovulatory surge of gonadotropins

Several aspects of the physiology and behavior of organisms are expressed rhythmically with a 24-h periodicity and hence called circadian rhythms. Such rhythms are thought to be an adaptive response that allows to anticipate cyclic events in the environment. In mammals, the circadian system is a hierarchically organized net of endogenous oscillators driven by the hypothalamic suprachiasmatic nucleus (SCN). This system is synchronized by the environment throughout afferent pathways and in turn it organizes the activity of tissues by means of humoral secretions and neuronal projections. It has been shown that reproductive cycles are regulated by the circadian system. In rodents, the lesion of the SCN results on alterations of the estrous cycle, sexual behavior, tonic and phasic secretion of gonadotropin releasing hormone (GnRH)/gonadotropins and in the failure of ovulation. Most of the studies regarding the circadian control of reproduction, in particular of ovulation, have only focused on the participation of the SCN in the triggering of the proestrus surge of gonadotropins. Here we review aspects of the evolution and organization of the circadian system with particular focus on its relationship with the reproductive cycle of laboratory rodents. Experimental evidence of circadian control of neuroendocrine events indispensable for ovulation that occur prior to proestrus are discussed. In order to offer a working model of the circadian regulation of reproduction, its participation on aspects ranging from gamete production, neuroendocrine regulation, sexual behavior, mating coordination, pregnancy and deliver of the product should be assessed experimentally.

Neonatal and juvenile exposure to perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS): Advance puberty onset and kisspeptin system disturbance in female rats

Perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) are widespread and persistent chemicals in the environment, and limited data about their effects on puberty development are available. In order to explore the effects of neonatal and juvenile PFOA/PFOS exposure on puberty maturation, female rats were injected with PFOA or PFOS at 0.1, 1 and 10 mg/kg/day during postnatal day (PND) 1-5 or 26-30. The day of vaginal opening (VO) and first estrus were significantly advanced in 10 mg/kg PFOA, 1 and 10 mg/kg PFOS groups after neonatal and juvenile exposure. Besides, neonatal PFOA/PFOS exposure increased body weight and anogenital distance (AGD) in a non-dose-dependent manner. Estradiol and luteinizing hormone levels were also increased with more frequent occurrences of irregular estrous cycles in 0.1 and 1 mg/kg PFOA/PFOS exposure groups. Although no altered ovarian morphology was observed, follicles numbers were reduced in neonatal groups. Kiss1, Kiss1r and ERα mRNA expressions were downregulated after two periods' exposure in the hypothalamic anteroventral periventricular (AVPV) and arcuate (ARC) nuclei. PFOA/PFOS exposure also suppressed kisspeptin fiber intensities, especially at the high dose. In conclusion, neonatal and juvenile are critical exposure periods, during which puberty maturation may be vulnerable to environmental exposure of PFOA/PFOS, and kisspeptin system plays a key role during these processes.

mTOR signaling in the arcuate nucleus of the hypothalamus mediates the anorectic action of estradiol

Current evidence suggests that estradiol (E2), the main ovarian steroid, modulates energy balance by regulating both feeding and energy expenditure at the central level, through the energy sensor AMP-activated protein kinase (AMPK). We hypothesized that the hypothalamic mechanistic target of rapamycin (mTOR) pathway, a well-established nutrient sensor and modulator of appetite and puberty, could also mediate the anorectic effect of E2. Our data showed that ovariectomy (OVX) elicited a marked downregulation of the mTOR signaling in the arcuate nucleus of the hypothalamus (ARC), an effect that was reversed by either E2 replacement or central estrogen receptor alpha (ERα) agonism. The significance of this molecular signaling was given by the genetic inactivation of S6 kinase B1 (S6K1, a key downstream mTOR effector) in the ARC, which prevented the E2-induced hypophagia and weight loss. Overall, these data indicate that E2 induces hypophagia through modulation of mTOR pathway in the ARC.

Estradiol-Dependent and -Independent Stimulation of Kiss1 Expression in the Amygdala, BNST, and Lateral Septum of Mice

Kisspeptin, encoded by Kiss1, activates reproduction by stimulating GnRH neurons. Although most Kiss1 neurons are located in the hypothalamus, smaller Kiss1 populations also reside in the medial amygdala (MeA), bed nucleus of the stria terminalis (BnST), and lateral septum (LS). However, very little is known about the regulation and function of these extra-hypothalamic Kiss1 neurons. This study focused on the roles and interactions of two signaling factors, estradiol (E2) and GABA, known to stimulate and inhibit, respectively, extra-hypothalamic Kiss1 expression. First, using estrogen receptor (ER)α knockout (KO) and βERKO mice, we demonstrated that Kiss1 in both the BnST and LS is stimulated by E2, as occurs in the MeA, and that this E2 upregulation occurs via ERα, but not ERβ. Second, using GABABR KO and wild-type mice, we determined that whereas E2 normally increases extra-hypothalamic Kiss1 levels, such upregulation by E2 is further enhanced by the concurrent absence of GABABR signaling in the MeA and LS, but not the BnST. Third, we demonstrated that when GABABR signaling is absent, the additional removal of gonadal sex steroids does not abolish Kiss1 expression in the MeA and BnST, and in some cases the LS. Thus, Kiss1 expression in these extra-hypothalamic regions is not solely dependent on E2 stimulation. Finally, we demonstrated a significant positive correlation between Kiss1 levels in the MeA, BnST, and LS, but not between these regions and the hypothalamus (anteroventral periventricular nucleus/periventricular nucleus). Collectively, our findings indicate that both E2 and GABA independently regulate all three extra-hypothalamic Kiss1 populations, but their regulatory interactions may vary by brain region and additional yet-to-be-identified factors are likely involved.

The role of G-protein-coupled membrane estrogen receptor in mouse Leydig cell function-in vivo and in vitro evaluation

In this study, G-coupled estrogen receptor (GPER) was inactivated, by treatment with antagonist (G-15), in testes of C57BL/6 mice: immature (3 weeks old), mature (3 months old) and aged (1.5 years old) (50 μg/kg bw), as well as MA-10 mouse Leydig cells (10 nM/24 h) alone or in combination with 17β-estradiol or antiestrogen (ICI 182,780). In G-15-treated mice, overgrowth of interstitial tissue was found in both mature and aged testes. Depending on age, differences in structure and distribution of various Leydig cell organelles were observed. Concomitantly, modulation of activity of the mitochondria and tubulin microfibers was revealed. Diverse and complex GPER regulation at the mRNA level and protein of estrogen signaling molecules (estrogen receptor α and β; ERα, ERβ and cytochrome P450 aromatase; P450arom) in G-15 Leydig cells was found in relation to age and the experimental system utilized (in vivo and in vitro). Changes in expression patterns of ERs and P450arom, as well as steroid secretion, reflected Leydig cell heterogeneity to estrogen regulation throughout male life including cell physiological status.We show, for the first time, GPER with ERs and P450arom work in tandem to maintain Leydig cell architecture and supervise its steroidogenic function by estrogen during male life. Full set of estrogen signaling molecules, with involvement of GPER, is crucial for proper Leydig cell function where each molecule acts in a specific and/or complementary manner. Further understanding of the mechanisms by which GPER controls Leydig cells with special regard to male age, cell of origin and experimental system used is critical for predicting and preventing testis steroidogenic disorders based on perturbations in estrogen signaling.

Pubertal Escape From Estradiol Negative Feedback in Ewe Lambs Is Not Accounted for by Decreased ESR1 mRNA or Protein in Kisspeptin Neurons

In this study, we investigated whether decreased sensitivity to estradiol negative feedback is associated with reduced estrogen receptor α (ESR1) expression in kisspeptin neurons as ewe lambs approach puberty. Lambs were ovariectomized and received no implant (OVX) or an implant containing estradiol (OVX+E). In the middle arcuate nucleus (mARC), ESR1 messenger RNA (mRNA) was greater in OVX than OVX+E lambs but did not differ elsewhere. Post hoc analysis of luteinizing hormone (LH) secretion from OVX+E lambs revealed three patterns of LH pulsatility: low [1 to 2 pulses per 12 hours; low frequency (LF), n = 3], moderate [6 to 7 pulses per 12 hours; moderate frequency (MF), n = 6], and high [>10 pulses per 12 hours; high frequency (HF), n = 5]. The percentage of kisspeptin neurons containing ESR1 mRNA in the preoptic area did not differ among HF, MF, or LF groups. However, the percentage of kisspeptin neurons containing ESR1 mRNA in the mARC was greater in HF (57%) than in MF (36%) or LF (27%) lambs and did not differ from OVX (50%) lambs. A higher percentage of kisspeptin neurons contained ESR1 protein in all regions of the arcuate nucleus (ARC) in OVX compared with OVX+E lambs. There were no differences in ESR1 protein among the HF, MF, or LF groups in the preoptic area or ARC. Contrary to our hypothesis, increases in LH pulsatility were associated with enhanced ESR1 mRNA abundance in kisspeptin neurons in the ARC, and absence of estradiol increased the percentage of kisspeptin neurons containing ESR1 protein in the ARC. Therefore, changes in the expression of ESR1, particularly in kisspeptin neurons in the ARC, do not explain the pubertal escape from estradiol negative feedback in ewe lambs.

Hypothalamic transcriptional expression of the kisspeptin system and sex steroid receptors differs among polycystic ovary syndrome rat models with different endocrine phenotypes

OBJECTIVES:

Polycystic ovary syndrome is a heterogeneous endocrine disorder that affects reproductive-age women. The mechanisms underlying the endocrine heterogeneity and neuroendocrinology of polycystic ovary syndrome are still unclear. In this study, we investigated the expression of the kisspeptin system and gonadotropin-releasing hormone pulse regulators in the hypothalamus as well as factors related to luteinizing hormone secretion in the pituitary of polycystic ovary syndrome rat models induced by testosterone or estradiol.

METHODS:

A single injection of testosterone propionate (1.25 mg) (n=10) or estradiol benzoate (0.5 mg) (n=10) was administered to female rats at 2 days of age to induce experimental polycystic ovary syndrome. Controls were injected with a vehicle (n=10). Animals were euthanized at 90-94 days of age, and the hypothalamus and pituitary gland were used for gene expression analysis.

RESULTS:

Rats exposed to testosterone exhibited increased transcriptional expression of the androgen receptor and estrogen receptor-β and reduced expression of kisspeptin in the hypothalamus. However, rats exposed to estradiol did not show any significant changes in hormone levels relative to controls but exhibited hypothalamic downregulation of kisspeptin, tachykinin 3 and estrogen receptor-α genes and upregulation of the gene that encodes the kisspeptin receptor.

CONCLUSIONS:

Testosterone- and estradiol-exposed rats with different endocrine phenotypes showed differential transcriptional expression of members of the kisspeptin system and sex steroid receptors in the hypothalamus. These differences might account for the different endocrine phenotypes found in testosterone- and estradiol-induced polycystic ovary syndrome rats.

α-Estrogen and Progesterone Receptors Modulate Kisspeptin Effects on Prolactin: Role in Estradiol-Induced Prolactin Surge in Female Rats

Kisspeptin (Kp) regulates prolactin (PRL) in an estradiol-dependent manner. We investigated the interaction between ovarian steroid receptors and Kp in the control of PRL secretion. Intracerebroventricular injections of Kp-10 or Kp-234 were performed in ovariectomized (OVX) rats under different hormonal treatments. Kp-10 increased PRL release and decreased 3,4-dihydroxyphenylacetic acid levels in the median eminence (ME) of OVX rats treated with estradiol (OVX+E), which was prevented by tamoxifen. Whereas these effects of Kp-10 were absent in OVX rats, they were replicated in OVX rats treated with selective agonist of estrogen receptor (ER)α, propylpyrazole triol, but not of ERβ, diarylpropionitrile. Furthermore, the Kp-10-induced increase in PRL was two times higher in OVX+E rats also treated with progesterone (OVX+EP), which was associated with a reduced expression of both tyrosine hydroxylase (TH) and Ser40-phosphorylated TH in the ME. Kp-10 also reduced dopamine levels in the ME of OVX+EP rats, an effect blocked by the progesterone receptor (PR) antagonist RU486. We also determined the effect of Kp antagonism with Kp-234 on the estradiol-induced surges of PRL and luteinizing hormone (LH), using tail-tip blood sampling combined with ultrasensitive enzyme-linked immunosorbent assay. Kp-234 impaired the early phase of the PRL surge and prevented the LH surge in OVX+E rats. Thus, we provide evidence that Kp stimulation of PRL release requires ERα and is potentiated by progesterone via PR activation. Moreover, alongside its essential role in the LH surge, Kp seems to play a role in the peak phase of the estradiol-induced PRL surge.

Circulating Estradiol Regulates Brain-Derived Estradiol via Actions at GnRH Receptors to Impact Memory in Ovariectomized Rats

Systemic estradiol treatment enhances hippocampus-dependent memory in ovariectomized rats. Although these enhancements are traditionally thought to be due to circulating estradiol, recent data suggest these changes are brought on by hippocampus-derived estradiol, the synthesis of which depends on gonadotropin-releasing hormone (GnRH) activity. The goal of the current work is to test the hypothesis that peripheral estradiol affects hippocampus-dependent memory through brain-derived estradiol regulated via hippocampal GnRH receptor activity. In the first experiment, intracerebroventricular infusion of letrozole, which prevents the synthesis of estradiol, blocked the ability of peripheral estradiol administration in ovariectomized rats to enhance hippocampus-dependent memory in a radial-maze task. In the second experiment, hippocampal infusion of antide, a long-lasting GnRH receptor antagonist, blocked the ability of peripheral estradiol administration in ovariectomized rats to enhance hippocampus-dependent memory. In the third experiment, hippocampal infusion of GnRH enhanced hippocampus-dependent memory, the effects of which were blocked by letrozole infusion. Results indicate that peripheral estradiol-induced enhancement of cognition is mediated by brain-derived estradiol via hippocampal GnRH receptor activity.

Kisspeptin signalling and its roles in humans

Kisspeptins are a group of peptide fragments encoded by the KISS1 gene in humans. They bind to kisspeptin receptors with equal efficacy. Kisspeptins and their receptors are expressed by neurons in the arcuate and anteroventral periventricular nuclei of the hypothalamus. Oestrogen mediates negative feedback of gonadotrophin-releasing hormone secretion via the arcuate nucleus. Conversely, it exerts positive feedback via the anteroventral periventricular nucleus. The sexual dimorphism of these nuclei accounts for the differential behaviour of the hypothalamic-pituitary-gonadal axis between genders. Kisspeptins are essential for reproductive function. Puberty is regulated by the maturation of kisspeptin neurons and by interactions between kisspeptins and leptin. Hence, kisspeptins have potential diagnostic and therapeutic applications. Kisspeptin agonists may be used to localise lesions in cases of hypothalamic-pituitary-gonadal axis dysfunction and evaluate the gonadotrophic potential of subfertile individuals. Kisspeptin antagonists may be useful as contraceptives in women, through the prevention of premature luteinisation during in vitro fertilisation, and in the treatment of sex steroid-dependent diseases and metastatic cancers.

Estrogen Stimulation of Kiss1 Expression in the Medial Amygdala Involves Estrogen Receptor-α But Not Estrogen Receptor-β

The neuropeptide kisspeptin, encoded by Kiss1, regulates reproduction by stimulating GnRH secretion. Neurons synthesizing kisspeptin are predominantly located in the hypothalamic anteroventral periventricular (AVPV) and arcuate nuclei, but smaller kisspeptin neuronal populations also reside in extrahypothalamic brain regions, such as the medial amygdala (MeA). In adult rodents, estradiol (E₂) increases Kiss1 expression in the MeA, as in the AVPV. However, unlike AVPV and arcuate nuclei kisspeptin neurons, little else is currently known about the development, regulation, and function of MeA Kiss1 neurons. We first assessed the developmental onset of MeA Kiss1 expression in males and found that MeA Kiss1 expression is absent at juvenile ages but significantly increases during the late pubertal period, around postnatal day 35, coincident with increases in circulating sex steroids. We next tested whether developmental MeA Kiss1 expression could be induced early by E₂ exposure prior to puberty. We found that juvenile mice given short-term E₂ had greatly increased MeA Kiss1 expression at postnatal day 18. Although MeA Kiss1 neurons are known to be E₂ up-regulated, the specific estrogen receptor (ER) pathway(s) mediating this stimulation are unknown. Using adult ERα knockout and ERβ knockout mice, we next determined that ERα, but not ERβ, is required for maximal E₂-induced MeA Kiss1 expression in both sexes. These results delineate both the developmental time course of MeA Kiss1 expression and the specific ER signaling pathway required for E₂-induced up-regulation of Kiss1 in this extrahypothalamic brain region. These findings will help drive future studies ascertaining the potential functions of this understudied kisspeptin population.

Evaluation of Immortalized AVPV- and Arcuate-Specific Neuronal Kisspeptin Cell Lines to Elucidate Potential Mechanisms of Estrogen Responsiveness and Temporal Gene Expression in Females

In females, ovarian estradiol modulates kisspeptin (Kiss-1) synthesis to act as an obligatory regulator of downstream gonadotropin release in vivo, via stimulation of GnRH neurons. Changes in the ovarian condition are relayed to the neuroendocrine hypothalamus via two sexually dimorphic Kiss-1 populations, located in the anteroventral periventricular (AVPV) and arcuate nuclei, conveying estradiol-positive and -negative feedback, respectively. To elucidate how differential responsiveness to estradiol is mediated in these populations, we generated two kisspeptin-secreting cell lines from an adult kiss1-green fluorescent protein (GFP) female mouse. These lines recapitulate in vivo responsiveness to estradiol, with KTaV-3 (AVPV) cells demonstrating significantly increased kiss1 expression under high physiological estradiol exposure, whereas KTaR-1 (arcuate) cells exhibit kiss1 suppression after lower estradiol exposure. Baseline expression of estrogen receptor-α (esr1) differs significantly between KTaV-3 and KTaR-1 cells, with KTaR-1 cells demonstrating higher basal expression of esr1. Estradiol stimulation of kiss1 expression in KTaV-3 cells is modulated in a dose-dependent manner up to 25.0 pM, with less responsiveness observed at higher doses (>50.0 pM). In contrast, KTaR-1 kiss1 attenuates at lower estradiol doses (2.0-5.0 pM), returning to baseline levels at 25.0 pM and greater. Furthermore, the expression of the core clock genes bmal1 and per2 show normal rhythms in KTaV-3 cells, regardless of estradiol treatment. Conversely, KTaR-1 antiphasic transcription of bmal1 and per2 is phase delayed by low estradiol treatment. Strikingly, estradiol induces circadian rhythms of kiss1 expression only in KTaV-3 cells. Further exploration into estradiol responsiveness will reveal mechanisms responsible for the differential expression pattern demonstrated in vivo between these cell types.

Kisspeptin across the human lifespan:evidence from animal studies and beyond

Since its first description in 1996, the KISS1 gene and its peptide products, kisspeptins, have increasingly become recognised as key regulators of reproductive health. With kisspeptins acting as ligands for the kisspeptin receptor KISS1R (previously known as GPR54 or KPR54), recent work has consistently shown that administration of kisspeptin across a variety of species stimulates gonadotrophin release through influencing gonadotrophin-releasing hormone secretion. Evidence from both animal and human studies supports the finding that kisspeptins are crucial for ensuring healthy development, with knockout animal models, as well as proband genetic testing in human patients affected by abnormal pubertal development, corroborating the notion that a functional kisspeptin receptor is required for appropriate gonadotrophin secretion. Given the large body of evidence that exists surrounding the influence of kisspeptin in a variety of settings, this review summarises our physiological understanding of the role of these important peptides and their receptors, before proceeding to describe the varying role they play across the reproductive lifespan.

Direct Actions of Kisspeptins on GnRH Neurons Permit Attainment of Fertility but are Insufficient to Fully Preserve Gonadotropic Axis Activity

Kisspeptins, ligands of the receptor, Gpr54, are potent stimulators of puberty and fertility. Yet, whether direct kisspeptin actions on GnRH neurons are sufficient for the whole repertoire of their reproductive effects remains debatable. To dissect out direct vs. indirect effects of kisspeptins on GnRH neurons in vivo, we report herein the detailed reproductive/gonadotropic characterization of a Gpr54 null mouse line with selective re-introduction of Gpr54 expression only in GnRH cells (Gpr54^−/−Tg; rescued). Despite preserved fertility, adult rescued mice displayed abnormalities in gonadal microstructure, with signs of precocious ageing in females and elevated LH levels with normal-to-low testosterone secretion in males. Gpr54^−/−Tg rescued mice showed also altered gonadotropin responses to negative feedback withdrawal, while luteinizing hormone responses to various gonadotropic regulators were variably affected, with partially blunted relative (but not absolute) responses to kisspeptin-10, NMDA and the agonist of tachykinin receptors, NK2R. Our data confirm that direct effects of kisspeptins on GnRH cells are sufficient to attain fertility. Yet, such direct actions appear to be insufficient to completely preserve proper functionality of gonadotropic axis, suggesting a role of kisspeptin signaling outside GnRH cells.

Trichostatin A reduces GnRH mRNA expression with a concomitant increase in retinaldehyde dehydrogenase in GnRH-producing neurons

Trichostatin A (TSA) is a selective inhibitor of mammalian histone deacetylase and is widely used to modify the ability of DNA transcription factors to bind DNA within chromatin by interfering with histone deacetylation. In the GnRH-producing neuronal cell line GT1-7, TSA significantly reduced expression of GnRH mRNA. Kisspeptin, a known regulator of GnRH release, failed to increase GnRH mRNA expression and did not modify TSA-induced reduction of GnRH expression. TSA, but not kisspeptin, increased histone acetylation in whole-cell lysates and significantly stimulated the expression of retinaldehyde dehydrogenase (RALDH), a retinoic acid (RA)-synthesizing enzyme that is known to be involved in cell differentiation. In addition, treatment of the GT1-7 cells with RA dose-dependently inhibited the expression of GnRH mRNA. Whereas, TSA-induced reduction of GnRH mRNA was not modulated by treatment with the pan-RA receptor inverse agonist BMS493 or the RA metabolism inhibitor liarozole. Our current results suggest that the RALDH and RA might not be directly involved in the reduction of GnRH expression induced by TSA, however these substances could be a novel regulator of GnRH.

Regulation of kisspeptin and gonadotropin-releasing hormone expression in rat placenta: study using primary cultures of rat placental cells

BACKGROUND

Gonadotropin-releasing hormone (GnRH) and kisspeptin in the hypothalamus are thought to be crucial components of the hypothalamic-pituitary-gonadal (HPG) axis and maintain reproductive function. These neuropeptides are also expressed in the placenta, where they may contribute to placental physiology. In this study, we examined how these peptides are regulated within the placenta.

METHODS

We used primary cultures of placental tissue from rats of 16-18 days gestation. After stimulation with estradiol, GnRH, kisspeptin, and neurokinin B (NKB), changes in placental GnRH, kisspeptin, and human chorionic gonadotropin (hCG) mRNA expression were evaluated by real-time quantitative RT-PCR analysis.

RESULTS

Immunocytochemical analysis showed that rat placental cells contained cells expressing kisspeptin or GnRH. GnRH and kisspeptin mRNA expression was significantly increased in placental cells in the presence of estradiol; NKB mRNA expression was also stimulated by estradiol. Stimulation of the cells with kisspeptin failed to stimulate GnRH mRNA expression. Conversely, both GnRH itself and NKB increased GnRH mRNA expression. Kisspeptin mRNA expression was not increased by kisspeptin itself; however, GnRH and NKB significantly increased kisspeptin mRNA expression. hCG expression was increased in the presence of estradiol. In addition, kisspeptin, GnRH, and NKB could stimulate the expression of hCG mRNA in placental cells.

CONCLUSIONS

Our experiments using primary cultures of rat placental cells showed that GnRH, kisspeptin, and NKB expression was enhanced by estradiol, and unlike in the hypothalamus, kisspeptin did not control the expression of GnRH in placental cells. NKB might be located upstream of kisspeptin and GnRH, and these neuropeptides might be involved in the induction of hCG expression in placental cells.

Kisspeptin Induces Dynamic Chromatin Modifications to Control GnRH Gene Expression

In vitro studies have demonstrated an increase in GnRH gene expression associated with an elevated secretory response to kisspeptin administration, suggesting that kisspeptin mediates GnRH expression at both the secretory and pretranslational levels. However, the kisspeptin-mediated intracellular mechanisms associated with the dynamic chromatin modifications modulating GnRH gene expression are unclear. The studies in this manuscript describe specific histone modifications on the enhancer and promoter of the mouse GnRH (mGnRH) gene induced by kisspeptin in GnRH neuronal cell lines (GT1-7 cells). ChIP assays followed by quantitative real-time PCR (qPCR) demonstrate that 15 and 45 min of 10(-9) M kisspeptin significantly increased histone 3 acetylation (H3Ac) at the kisspeptin response element (KsRE) contained between -3446 and -2806 bp of the mGnRH enhancer (GnRHen) in GT1-7 cells, while no changes were observed in the downstream neuron-specific element (NSE). Moreover, kisspeptin specifically induced acetylation of H3AcK14 and K27 and trimethylation of H3 lysine 4 at the KsRE (markers of active chromatin) and no changes in dimethylation of H3K9 (a marker associated with gene repression). Occupancy of RNA Pol II (RNAPII) and a differential carboxyl-terminal domain (CTD) phosphorylation pattern was observed. An interaction between the NSE and the KsRE via a chromatin loop in the mGnRH gene by kisspeptin was detected by the chromosome conformation capture assay (3C). In conclusion, these results demonstrate that kisspeptin induces histone acetylation/methylation and consequently enhances the formation of a chromatin loop in the mGnRH gene which results in known increase in kisspeptin-dependent mGnRH expression.

Disparate changes in kisspeptin and neurokinin B expression in the arcuate nucleus after sex steroid manipulation reveal differential regulation of the two KNDy peptides in rats

Kisspeptin, neurokinin B (NKB) and dynorphin A are coexpressed in a population of neurons in the arcuate nucleus (ARC), termed KNDy neurons, which were recently recognized as important elements for the generation of GnRH pulses. However, the topographic distribution of these peptides and their regulated expression by sex steroids are still not well understood. In this study, detailed examination of NKB and kisspeptin immunoreactivity in the rat ARC was carried out, including comparison between sexes, with and without sex steroid replacement. Neurons expressing kisspeptin and NKB were more prominent in the caudal ARC of females, whereas neurons expressing NKB, but not kisspeptin, were the most abundant in the male. Sex steroid manipulation revealed differential regulation of kisspeptin and NKB; although kisspeptin immunoreactive (ir) cells increased in response to gonadectomy, NKB remained unchanged. Furthermore, the number of NKB-ir cells increased upon sex steroid replacement compared with gonadectomy, whereas kisspeptin did not, suggesting that sex steroids differently regulate these peptides. In addition, only in females did the density of kisspeptin- and NKB-ir fibers in the ARC increase upon sex steroid replacement in relation to sham and ovariectomy, respectively, suggesting sex-specific regulation of release. In conclusion, our observations reveal sex differences in the number of kisspeptin- and NKB-ir cells, which are more prominent in the caudal ARC. The divergent regulation of kisspeptin and NKB peptide contents in the ARC as a function of sex and steroid milieu enlarge our understanding on how these neuropeptides are posttranscriptionally regulated in KNDy neurons.

Estradiol regulates brown adipose tissue thermogenesis via hypothalamic AMPK

Estrogens play a major role in the modulation of energy balance through central and peripheral actions. Here, we demonstrate that central action of estradiol (E2) inhibits AMP-activated protein kinase (AMPK) through estrogen receptor alpha (ERα) selectively in the ventromedial nucleus of the hypothalamus (VMH), leading to activation of thermogenesis in brown adipose tissue (BAT) through the sympathetic nervous system (SNS) in a feeding-independent manner. Genetic activation of AMPK in the VMH prevented E2-induced increase in BAT-mediated thermogenesis and weight loss. Notably, fluctuations in E2 levels during estrous cycle also modulate this integrated physiological network. Together, these findings demonstrate that E2 regulation of the VMH AMPK-SNS-BAT axis is an important determinant of energy balance and suggest that dysregulation in this axis may account for the common changes in energy homeostasis and obesity linked to dysfunction of the female gonadal axis.

Effects of neuron-specific estrogen receptor (ER) α and ERβ deletion on the acute estrogen negative feedback mechanism in adult female mice

The negative feedback mechanism through which 17β-estradiol (E2) acts to suppress the activity of the GnRH neurons remains unclear. Using inducible and cell-specific genetic mouse models, we examined the estrogen receptor (ER) isoforms expressed by neurons that mediate acute estrogen negative feedback. Adult female mutant mice in which ERα was deleted from all neurons in the neonatal period failed to exhibit estrous cycles or negative feedback. Adult mutant female mice with neonatal neuronal ERβ deletion exhibited normal estrous cycles, but a failure of E2 to suppress LH secretion was seen in ovariectomized mice. Mutant mice with a GnRH neuron-selective deletion of ERβ exhibited normal cycles and negative feedback, suggesting no critical role for ERβ in GnRH neurons in acute negative feedback. To examine the adult roles of neurons expressing ERα, an inducible tamoxifen-based Cre-LoxP approach was used to ablate ERα from neurons that express calmodulin kinase IIα in adults. This resulted in mice with no estrous cycles, a normal increase in LH after ovariectomy, but an inability of E2 to suppress LH secretion. Finally, acute administration of ERα- and ERβ-selective agonists to adult ovariectomized wild-type mice revealed that activation of ERα suppressed LH secretion, whereas ERβ agonists had no effect. This study highlights the differences in adult reproductive phenotypes that result from neonatal vs adult ablation of ERα in the brain. Together, these experiments expand previous global knockout studies by demonstrating that neurons expressing ERα are essential and probably sufficient for the acute estrogen negative feedback mechanism in female mice.

Estrogen in the fetus

Estradiol and other estrogens are important modulators of fetal and maternal physiology in pregnancy. Much is known about the biosynthesis of estrogens in fetus and mother, and much is known about the role that estrogen plays in labor and delivery. However, much less is known about the regulation of estrogen biosynthesis throughout the latter half of gestation, and the role that estrogen plays in homeostatic and neuroendocrine control in the fetus. This review focuses on the biosynthesis and actions of estrogen in the fetal circulation, the role that it plays in the development of the fetus in the latter half of gestation, and the role that is played by the estrogen milieu in the control of the timing of birth. Estrogen circulates in fetal blood in both unconjugated and conjugated molecular forms, with the conjugated steroids far more abundant than the unconjugated steroids. This review therefore also addresses the biological significance of the variety of molecular forms of estrogen circulating in fetal and maternal blood.

Genetic mechanisms mediating kisspeptin regulation of GnRH gene expression

Kisspeptins (Kiss) have been shown to be key components in the regulation of gonadotropin-releasing hormone (GnRH) secretion. In vitro studies have demonstrated an increase in GnRH gene expression by Kiss suggesting regulation of GnRH at both the secretory and pretranslational levels. Here, we define genetic mechanisms that mediate Kiss action on target gene expression. In vitro, sequential deletions of the mouse GnRH (mGnRH) gene promoter fused to the luciferase (LUC) reporter gene localized at kisspeptin-response element (KsRE) between -3446 and -2806 bp of the mGnRH gene. In vivo, transgenic mice bearing sequential deletions of the mGnRH gene promoter linked to the LUC reporter localized an identical KsRE. To define the mechanism of regulation, Kiss was first shown to induce nucleosome-depleted DNA within the KsRE, and a potential binding site for the transcription factor, Otx-2, was revealed. Furthermore, increased Otx-2 mRNA, protein, and binding to the KsRE after Kiss treatment were demonstrated. In conclusion, this work identified elements in GnRH-neuronal cell lines and in transgenic mice that mediate positive regulation of GnRH by Kiss. In addition, we show for the first time that Otx-2 is regulated by Kiss, and plays a role in mediating the transcriptional response of mGnRH gene.

Sex steroid regulation of kisspeptin circuits

Kisspeptin cells appear to be the "missing link," bridging the divide between levels of gonadal steroids and feedback control of gonadotropin-releasing hormone (GnRH) secretion. Kisspeptin neurons are important in the generation of both sex steroid negative and estrogen positive feedback signals to GnRH neurons, the former being involved in the tonic regulation of GnRH secretion in males and females and the latter governing the preovulatory GnRH/luteinizing hormone (LH) surge in females. In rodents, kisspeptin-producing cells populate the anteroventral periventricular nucleus (AVPV) and the arcuate nucleus (ARC), and estrogen regulation of kisspeptin has been extensively studied in these regions. Kisspeptin cells in the ARC appear to receive and forward signals applicable to negative feedback regulation of GnRH. In the female rodent AVPV, kisspeptin cells are important for positive feedback regulation of GnRH and the preovulatory LH surge. In sheep and primates, a rostral population of kisspeptin cells is located in the dorsolateral preoptic area (POA) as well as the ARC. Initial studies showed kisspeptin cells in the latter were involved in both the positive and negative feedback regulation of GnRH. Interestingly, further studies now suggest that kisspeptin cells in the ovine POA may also play an important role in generating estrogen positive feedback. This chapter discusses the current consensus knowledge regarding the interaction between sex steroids and kisspeptin neurons in mammals.

Kisspeptin and the hypothalamic control of reproduction: lessons from the human

The hypothalamic hormone GnRH is a central driver of pituitary gonadotropin secretion, controlling pulsatile gonadotropin secretion, modulating gonadal steroid feedback, and bringing about full fertility in the adult. Thus, understanding GnRH neuronal regulation is essential to understanding the neurohumoral control of human reproduction. Genetic tools were used in patients with GnRH deficiency (i.e. idiopathic hypogonadotropic hypogonadism), a clinical syndrome that results from the failure of a normal pattern of pulsatile GnRH, to discover upstream modulators of GnRH secretion (1). In 2003, homozygosity mapping of two consanguineous pedigrees led to the identification of loss of function mutations in KISS1R (a G protein coupled receptor) by two groups (2, 3). In parallel, the Kiss1r(-/-) mouse was shown to be a phenocopy of the human GnRH-deficient state, demonstrating that the function of KISS1R/Kiss1r is conserved across mammalian species (4). Just before these human genetic discoveries, the ligand for kisspeptin-1 receptor [KISS1R; also known as G protein coupled receptor 54 (GPR54)], was discovered to be kisspeptin. Soon thereafter a large array of experimental studies began assembling genetic, expression, physiologic, transgenic, knockdown, and electrophysiological data to characterize the physiology of kisspeptin and its seminal role in modulating GnRH release.

Kisspeptins and Reproduction: Physiological Roles and Regulatory Mechanisms

Procreation is essential for survival of species. Not surprisingly, complex neuronal networks have evolved to mediate the diverse internal and external environmental inputs that regulate reproduction in vertebrates. Ultimately, these regulatory factors impinge, directly or indirectly, on a final common pathway, the neurons producing the gonadotropin-releasing hormone (GnRH), which stimulates pituitary gonadotropin secretion and thereby gonadal function. Compelling evidence, accumulated in the last few years, has revealed that kisspeptins, a family of neuropeptides encoded by the Kiss1 gene and produced mainly by neuronal clusters at discrete hypothalamic nuclei, are pivotal upstream regulators of GnRH neurons. As such, kisspeptins have emerged as important gatekeepers of key aspects of reproductive maturation and function, from sexual differentiation of the brain and puberty onset to adult regulation of gonadotropin secretion and the metabolic control of fertility. This review aims to provide a comprehensive account of the state-of-the-art in the field of kisspeptin physiology by covering in-depth the consensus knowledge on the major molecular features, biological effects, and mechanisms of action of kisspeptins in mammals and, to a lesser extent, in nonmammalian vertebrates. This review will also address unsolved and contentious issues to set the scene for future research challenges in the area. By doing so, we aim to endow the reader with a critical and updated view of the physiological roles and potential translational relevance of kisspeptins in the integral control of reproductive function.

Opposing roles of ERα and ERβ in the genesis and progression of adenocarcinoma in the rat ventral prostate

BACKGROUND

Prostate cancer is a common malignancy in men and although hormone ablation therapy is effective, men develop hormone resistance. There is need for therapies applicable earlier, such as treatment of prostatic intraepithelial neoplasia (PIN). Estrogens besides androgens play a role in prostate cancer pathogenesis via two receptors ERα and ERβ and both receptors are thought to play different, opposing, roles with ERα having proliferative properties and ERβ having anti-proliferative properties. To differentiate between the roles both receptors play in prostate cancer an ERα and an ERβ agonist, ERA-45 and ERB-26, have been tested in a rodent model for prostate carcinogenesis.

METHODS

The influence of ERα on prostate cancer progression was studied in intact male rats treated with testosterone in combination with the ERα agonist, ERA-45 for either a long-term (20-week) period or a shorter term (6-week) period. The ERβ agonist was tested in the shorter term model in intact male rats treated with testosterone in combination with the ERα agonist, ERA-45, followed by administration of the ERβ agonist, ERB-26, during the last 2 weeks.

RESULTS

Treatment of rats with testosterone in combination with ERA-45 induced mild PIN lesions at 6 weeks and severe precancerous PIN lesions at 20 weeks. The ERβ agonist prevented the onset of PIN lesions at 6 weeks. Moreover, prostate epithelial cell apoptosis was increased and proliferation was decreased.

CONCLUSION

These findings confirm the opposing roles ERα and ERβ play in prostate carcinogenesis and suggest a therapeutic opportunity of ERβ for treating precancerous PIN lesions.

Seasonal variation in the gonadotropin-releasing hormone response to kisspeptin in sheep: possible kisspeptin regulation of the kisspeptin receptor

Kisspeptin signaling in the hypothalamus appears critical for the onset of puberty and driving the reproductive axis. In sheep, reproduction is seasonal, being activated by short days and inhibited by long days. During the non-breeding (anestrous) season, gonadotropin-releasing hormone (GnRH) and gonadotropin secretion is reduced, as is the expression of Kiss1 mRNA in the brain. Conversely, the luteinizing hormone response to kisspeptin during this time is greater. To determine whether the GnRH response to kisspeptin is increased during anestrus, we utilized hypophysial portal blood sampling. In anestrus ewes, the GnRH and LH responses to kisspeptin were greater compared to the breeding season (luteal phase). To ascertain whether this difference reflects a change in Kiss1r, we measured its expression on GnRH neurons using in situ hybridization. The level of Kiss1r was greater during the non-breeding season compared to the breeding season. To further examine the mechanism underlying this change in Kiss1r, we examined Kiss1r/GnRH expression in ovariectomized ewes (controlling for sex steroids) during the breeding and non-breeding seasons, and also ovariectomized non-breeding season ewes with or without estradiol replacement. In both experiments, Kiss1r expression on GnRH neurons was unchanged. Finally, we examined the effect of kisspeptin treatment on Kiss1r. Kiss1r expression on GnRH neurons was reduced by kisspeptin infusion. These studies indicate the kisspeptin response is indeed greater during the non-breeding season and this may be due in part to increased Kiss1r expression on GnRH neurons. We also show that kisspeptin may regulate the expression of its own receptor.

Roles for oestrogen receptor β in adult brain function

Oestradiol exerts a profound influence upon multiple brain circuits. For the most part, these effects are mediated by oestrogen receptor (ER)α. We review here the roles of ERβ, the other ER isoform, in mediating rodent oestradiol-regulated anxiety, aggressive and sexual behaviours, the control of gonadotrophin secretion, and adult neurogenesis. Evidence exists for: (i) ERβ located in the paraventricular nucleus underpinning the suppressive influence of oestradiol on the stress axis and anxiety-like behaviour; (ii) ERβ expressed in gonadotrophin-releasing hormone neurones contributing to oestrogen negative-feedback control of gonadotrophin secretion; (iii) ERβ controlling the offset of lordosis behaviour; (iv) ERβ suppressing aggressive behaviour in males; (v) ERβ modulating responses to social stimuli; and (vi) ERβ in controlling adult neurogenesis. This review highlights two major themes; first, ERβ and ERα are usually tightly inter-related in the oestradiol-dependent control of a particular brain function. For example, even though oestradiol feedback to control reproduction occurs principally through ERα-dependent mechanisms, modulatory roles for ERβ also exist. Second, the roles of ERα and ERβ within a particular neural network may be synergistic or antagonistic. Examples of the latter include the role of ERα to enhance, and ERβ to suppress, anxiety-like and aggressive behaviours. Splice variants such as ERβ2, acting as dominant negative receptors, are of further particular interest because their expression levels may reflect preceeding oestradiol exposure of relevance to oestradiol replacement therapy. Together, this review highlights the predominant modulatory, but nonetheless important, roles of ERβ in mediating the many effects of oestradiol upon adult brain function.

Sex steroids and the control of the Kiss1 system: developmental roles and major regulatory actions

Kisspeptins, encoded by the Kiss1 gene, and their canonical receptor, GPR54 (also termed Kiss1R), are unanimously recognised as essential regulators of puberty onset and gonadotrophin secretion. These key reproductive functions stem from the capacity of kisspeptins to stimulate gonadotrophin-releasing hormone (GnRH) secretion in the hypothalamus, where discrete populations of Kiss1 neurones have been identified. In rodents, two major groups of hypothalamic Kiss1 neurones exist: one present in the arcuate nucleus (ARC) and the other located in the anteroventral periventricular area (AVPV/RP3V). In recent years, numerous signals have been identified as putative modulators of the hypothalamic Kiss1 system. Among them, the prominent role of sex steroids as being important regulators of Kiss1 neurones has been documented in different species and developmental stages, such as early brain sex differentiation, puberty, adulthood and senescence. These regulatory actions are (mainly) conducted via oestrogen receptor (ER)α, which is expressed in almost all Kiss1 neurones, and likely involve both classical and nonclassical pathways. The regulatory effects of sex steroids are nucleus-specific. Thus, sex steroids inhibit the expression of Kiss1/kisspeptin at the ARC, as a mechanism to conduct their negative-feedback actions on gonadotrophin secretion. By contrast, oestrogens enhance Kiss1 expression at the AVPV/RP3V in rodents, suggesting the involvement of this population in the positive-feedback actions of oestradiol to generate the preovulatory surge of gonadotrophins. In addition, sex steroids have been shown to act post-transcriptionally, modulating GnRH/gonadotrophin responsiveness to kisspeptin. Finally, sex steroids also regulate the expression of co-transmitters of Kiss1 neurones, such as neurokinin B, whose mRNA content in the ARC fluctuates in parallel to that of Kiss1 in response to changes in the circulating levels of sex steroids, therefore suggesting the contribution of this neuropeptide in the feedback control of gonadotrophin secretion. In sum, compelling experimental evidence obtained in different mammalian (and non-mammalian) species, including primates, demonstrates that sex steroids are essential regulators of hypothalamic Kiss1 neurones, which in turn operate as conduits for their effects on GnRH neurones. The physiological relevance of such regulatory phenomena is thoroughly discussed.

The role of kisspeptin and RFamide-related peptide-3 neurones in the circadian-timed preovulatory luteinising hormone surge

Many aspects of female reproduction often require intricate timing, ranging from the temporal regulation of reproductive hormone secretion to the precise timing of sexual behaviour. In particular, in rodents and other species, ovulation is triggered by a surge in pituitary luteinising hormone (LH) secretion that is governed by a complex interaction between circadian signals arising in the hypothalamus and ovarian-derived oestradiol signals acting on multiple brain circuitries. These circadian and hormonal pathways converge to stimulate a precisely-timed surge in gonadotropin-releasing hormone (GnRH) release (i.e. positive-feedback), thereby triggering the preovulatory LH surge. Reflecting its control by afferent circadian signals, the preovulatory LH surge occurs at a specific time of day, typically late afternoon in nocturnal rodents. Although the specific mechanisms mediating the hormonal and circadian regulation of GnRH/LH release have remained poorly understood, recent findings now suggest that oestradiol and circadian signals govern specific reproductive neuropeptide circuits in the hypothalamus, including the newly-identified kisspeptin and RFamide-related peptide (RFRP)-3 neuronal populations. Neurones producing kisspeptin, the protein product of the Kiss1 gene, and RFRP-3 have been shown to provide excitatory and inhibitory input to GnRH neurones, respectively, and are also influenced by sex steroid and circadian signals. In the present review, we integrate classic and recent findings to form a new working model for the neuroendocrine regulation of the circadian-timed preovulatory LH surge in rodents. This model proposes kisspeptin and RFRP-3 neuronal populations as key nodal points for integrating and transducing circadian and hormonal signals to the reproductive axis, thereby governing the precisely-timed LH surge.

Milestones on Steroids and the Nervous System: 10 years of basic and translational research

During the last 10 years, the conference on 'Steroids and Nervous System' held in Torino (Italy) has been an important international point of discussion for scientists involved in this exciting and expanding research field. The present review aims to recapitulate the main topics that have been presented through the various meetings. Two broad areas have been explored: the impact of gonadal hormones on brain circuits and behaviour, as well as the mechanism of action of neuroactive steroids. Relationships among steroids, brain and behaviour, the sexual differentiation of the brain and the impact of gonadal hormones, the interactions of exogenous steroidal molecules (endocrine disrupters) with neural circuits and behaviour, and how gonadal steroids modulate the behaviour of gonadotrophin-releasing hormone neurones, have been the topics of several lectures and symposia during this series of meetings. At the same time, many contributions have been dedicated to the biosynthetic pathways, the physiopathological relevance of neurosteroids, the demonstration of the cellular localisation of different enzymes involved in neurosteroidogenesis, the mechanisms by which steroids may exert some of their effects, both the classical and nonclassical actions of different steroids, the role of neuroactive steroids on neurodegeneration, neuroprotection, and the response of the neural tissue to injury. In these 10 years, this field has significantly advanced and neuroactive steroids have emerged as new potential therapeutic tools to counteract neurodegenerative events.

Neonatal Bisphenol A exposure alters sexually dimorphic gene expression in the postnatal rat hypothalamus

Developmental exposure to Bisphenol A (BPA), a component of polycarbonate and epoxy resins, has been purported to adversely impact reproductive function in female rodents. Because neonatal life is a critical window for the sexual dimorphic organization of the hypothalamic-pituitary-gonadal (HPG) axis, interference with this process could underlie compromised adult reproductive physiology. The goal of the present study was to determine if neonatal BPA exposure interferes with sex specific gene expression of estrogen receptor alpha (ERα), ER beta (ERβ) and kisspeptin (Kiss1) in the anterior and mediobasal hypothalamus. Long Evans (LE) neonatal rats were exposed to vehicle, 10μg estradiol benzoate (EB), 50mg/kg BPA or 50μg/kg BPA by subcutaneous injection daily from postnatal day 0 (PND 0) to PND 2. Gene expression was assessed by in situ hybridization on PNDs 4 and 10. Within the anterior hypothalamus ERα expression was augmented by BPA in PND 4 females, then fell to male-typical levels by PND 10. ERβ expression was not altered by BPA on PND 4, but significantly decreased or eliminated in both sexes by PND 10. Kiss1 expression was diminished by BPA in the anterior hypothalamus, especially in females. There were no significant impacts of BPA in the mediobasal hypothalamus. Collectively, BPA effects did not mirror those of EB. The results show that neonatal hypothalamic ER and Kiss1 expression is sensitive to BPA exposure. This disruption may alter sexually dimorphic hypothalamic organization and underlie adult reproductive deficiencies. Additionally, the discordant effects of EB and BPA indicate that BPA likely disrupts hypothalamic organization by a mechanism other than simply acting as an estrogen mimic.

Differential effects of hypothalamic IGF-I on gonadotropin releasing hormone neuronal activation during steroid-induced LH surges in young and middle-aged female rats

Interactions between brain IGF-I receptors and estrogen receptors regulate female reproductive physiology and behavior. The present study investigated potential mechanisms by which IGF-I receptors in the neuroendocrine hypothalamus regulate GnRH neuronal activation and LH release in young and middle-aged female rats under estradiol (E2) positive feedback conditions. We infused vehicle, IGF-I, or JB-1, a selective antagonist of IGF-I receptors, into the third ventricle of ovariectomized female rats primed with E2 and progesterone or vehicle. In young females, blockade of IGF-I receptors attenuated the steroid hormone-induced LH surge, reduced the percent of GnRH neurons expressing c-fos on the day of the LH surge, and decreased the total number of neurons expressing c-fos in the preoptic area. Middle-aged females had fewer GnRH neurons expressing c-fos during the LH surge than young females, and the LH surge amplitude was attenuated. Infusion of an IGF-I dose previously shown to increase LH surge amplitude did not increase the percent of GnRH neurons expressing c-fos in middle-aged females. Brain IGF-I receptor blockade did not modify E2 induction of progestin receptor-immunoreactive neurons in the preoptic area, arcuate, or ventromedial hypothalamus of young rats. These findings indicate that brain IGF-I receptors are required for E2 activation of GnRH neurons in young rats and for robust GnRH release from axon terminals in middle-aged females. IGF-I likely exerts its effects by actions on E2-sensitive neurons that are upstream of GnRH neurons and terminals.

Neuroendocrine control by kisspeptins: role in metabolic regulation of fertility

The neurohormonal control of reproduction involves a hierarchical network of central and peripheral signals in the hypothalamic-pituitary-gonadal (HPG) axis. Development and function of this neuroendocrine system is the result of a lifelong delicate balance between endogenous regulators and environmental cues, including nutritional and metabolic factors. Kisspeptins are the peptide products of KISS1, which operate via the G-protein-coupled receptor GPR54 (also known as Kiss1R). These peptides have emerged as essential upstream regulators of neurons secreting gonadotropin-releasing hormone (GnRH), the major hypothalamic node for the stimulatory control of the HPG axis. They are potent elicitors of gonadotropin secretion in various species and physiological settings. Moreover, Kiss1 neurons in the hypothalamus participate in crucial features of reproductive maturation and function, such as brain-level sex differentiation, puberty onset and the neuroendocrine regulation of gonadotropin secretion and ovulation. Cotransmitters of Kiss1 neurons, such as neurokinin B, with roles in controlling the HPG axis have been identified by genetic, neuroanatomical and physiological studies. In addition, a putative role has been proposed for Kiss1 neurons in transmitting metabolic information to GnRH neurons, although the precise mechanisms are as yet unclear. In this Review, we present the major reproductive features of kisspeptins, especially their interplay with neurokinin B and potential roles in the metabolic control of puberty and fertility, and suggest new avenues for research.

International Union of Basic and Clinical Pharmacology. LXXVII. Kisspeptin receptor nomenclature, distribution, and function

Kisspeptins are members of the Arg-Phe amide family of peptides, which have been identified as endogenous ligands for a G-protein-coupled receptor encoded by a gene originally called GPR54 (also known as AXOR12 or hOT7T175). After this pairing, the gene has been renamed KISS1R. The International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification recommends that the official name for the receptor is the kisspeptin receptor to follow the convention of naming the receptor protein after the endogenous ligand. The endogenous ligand was initially called metastin, after its role as a metastasis suppressor, and is now referred to as kisspeptin-54 (KP-54), a C-terminally amidated 54-amino acid peptide cleaved from the 145-amino acid gene product. Shorter C-terminal cleavage fragments [KP-14, KP-13 and KP-10 (the smallest active fragment)] are also biologically active. Both receptor and peptide are widely expressed in human, rat, and mouse; the receptor sequence shares more than 80% homology in these species. Activation of the kisspeptin receptor by kisspeptin is via coupling to G(q/11) and the phospholipase C pathway, causing Ca(2+) mobilization. Mutations in the KISS1R gene result in hypogonadotropic hypogonadotropism, and targeted disruption of Kiss1r in mice reproduces this phenotype, which led to the discovery of the remarkable ability of the kisspeptin receptor to act as a molecular switch for puberty. In addition to regulating the reproductive axis, the kisspeptin receptor is also implicated in cancer, placentation, diabetes, and the cardiovascular system.

Kisspeptin regulates gonadotroph and somatotroph function in nonhuman primate pituitary via common and distinct signaling mechanisms

Kisspeptins (Kps) have emerged as key players in the control of reproductive-axis function, in which they operate as primary regulators of hypothalamic GnRH release. In addition, recent data indicate that Kps can also directly act on the pituitary to stimulate LH and GH release in primary pituitary cell culture prepared from rats, cows, and sheep. We present herein evidence that Kps (specifically Kp-10) can also stimulate LH and GH release in primary pituitary cell cultures prepared from female baboons (Papio anubis), a species that more closely models human physiology. The stimulatory effect of Kp-10 on LH and GH release was dose and time dependent and enhanced the hormonal responses to their major regulators (GnRH for LH; GHRH/ghrelin for GH) without affecting the release of other pituitary hormones (TSH, FSH, ACTH, prolactin). Use of pharmacological intracellular signaling blockers indicated Kp-10 signals through phospholipase C, protein kinase C, MAPK, and intracellular Ca(2+) mobilization, but not adenylyl cyclase, protein kinase A, extracellular Ca(2+) influx (through L-type channels), or nitric oxide synthase, to stimulate both LH and GH release. Interestingly, blockade of mammalian target of rapamycin or phosphoinositol 3-kinase activity fully abolished the stimulatory effect of Kp-10 on LH but not GH release. Of note, estradiol enhanced the relative LH response to Kp-10, alone or in combination with GnRH. In sum, our data are the first to provide evidence that, in a primate model, there is a functional Kp-signaling system within the pituitary, which is dynamically regulated and may contribute to the direct control of gonadotropic and somatotropic axes.

Circadian control of kisspeptin and a gated GnRH response mediate the preovulatory luteinizing hormone surge

In spontaneously ovulating rodents, the preovulatory LH surge is initiated on the day of proestrus by a timed, stimulatory signal originating from the circadian clock in the suprachiasmatic nucleus (SCN). The present studies explored whether kisspeptin is part of the essential neural circuit linking the SCN to the GnRH system to stimulate ovulation in Syrian hamsters (Mesocricetus auratus). Kisspeptin neurons exhibit an estrogen-dependent, daily pattern of cellular activity consistent with a role in the circadian control of the LH surge. The SCN targets kisspeptin neurons via vasopressinergic (AVP), but not vasoactive intestinal polypeptide-ergic, projections. Because AVP administration can only stimulate the LH surge during a restricted time of day, we examined the possibility that the response to AVP is gated at the level of kisspeptin and/or GnRH neurons. Kisspeptin and GnRH activation were assessed after the administration of AVP during the morning (when AVP is incapable of initiating the LH surge) and the afternoon (when AVP injections stimulate the LH surge). Kisspeptin, but not GnRH, cellular activity was up-regulated after morning injections of AVP, suggesting that time-dependent sensitivity to SCN signaling is gated within GnRH but not kisspeptin neurons. In support of this possibility, we found that the GnRH system exhibits pronounced daily changes in sensitivity to kisspeptin stimulation, with maximal sensitivity in the afternoon. Together these studies reveal a novel mechanism of ovulatory control with interactions among the circadian system, kisspeptin signaling, and a GnRH gating mechanism of control.

Interactions between kisspeptin and neurokinin B in the control of GnRH secretion in the female rat

Neurokinin B (NKB) and its cognate receptor neurokinin 3 (NK3R) play a critical role in reproduction. NKB and NK3R are coexpressed with dynorphin (Dyn) and kisspeptin (Kiss1) genes in neurons of the arcuate nucleus (Arc). However, the mechanisms of action of NKB as a cotransmitter with kisspeptin and dynorphin remain poorly understood. We explored the role of NKB in the control of LH secretion in the female rat as follows. 1) We examined the effect of an NKB agonist (senktide, 600 pmol, administered into the lateral cerebral ventricle) on luteinizing hormone (LH) secretion. In the presence of physiological levels of estradiol (E(2)), senktide induced a profound increase in serum levels of LH and a 10-fold increase in the number of Kiss1 neurons expressing c-fos in the Arc (P < 0.01 for both). 2) We mapped the distribution of NKB and NK3R mRNAs in the central forebrain and found that both are widely expressed, with intense expression in several hypothalamic nuclei that control reproduction, including the Arc. 3) We studied the effect of E(2) on the expression of NKB and NK3R mRNAs in the Arc and found that E(2) inhibits the expression of both genes (P < 0.01) and that the expression of NKB and NK3R reaches its nadir on the afternoon of proestrus (when circulating levels of E(2) are high). These observations suggest that NKB/NK3R signaling in Kiss1/NKB/Dyn-producing neurons in the Arc has a pivotal role in the control of gonadotropin-releasing hormone (GnRH)/LH secretion and its regulation by E(2)-dependent negative feedback in the rat.

The anorexigenic neuropeptide, nesfatin-1, is indispensable for normal puberty onset in the female rat

The hypothalamic peptide, nesfatin-1, derived from the precursor NEFA/nucleobindin 2 (NUCB2), was recently identified as anorexigenic signal, acting in a leptin-independent manner. Yet its participation in the regulation of other biological functions gated by body energy status remains unexplored. We show herein that NUCB2/nesfatin-1 is involved in the control of female puberty. NUCB2/nesfatin mRNA and protein were detected at the hypothalamus of pubertal female rats, with prominent signals at lateral hypothalamus (LHA), paraventricular (PVN), and supraoptic (SON) nuclei. Hypothalamic NUCB2 expression raised along pubertal transition, with detectable elevations of its mRNA levels at LHA, PVN, and SON, and threefold increase of its total protein content between late-infantile and peripubertal periods. Conditions of negative energy balance, such as 48 h fasting or sustained subnutrition, decreased hypothalamic NUCB2 mRNA and/or protein levels in pubertal females. At this age, central administration of nesfatin-1 induced modest but significant elevations of circulating gonadotropins, whose magnitude was notably augmented in conditions of food deprivation. Continuous intracerebroventricular infusion of antisense morpholino oligonucleotides (as-MONs) against NUCB2 along pubertal maturation, which markedly reduced hypothalamic NUCB2 protein content, delayed vaginal opening and decreased ovarian weights and serum luteinizing hormone (LH) levels. In contrast, in adult female rats, intracerebroventricular injection of nesfatin did not stimulate LH or follicle-stimulating hormone secretion; neither did central as-MON infusion alter preovulatory gonadotropin surges, despite suppression of hypothalamic NUCB2. In sum, our data are the first to disclose the indispensable role of NUCB2/nesfatin-1 in the central networks driving puberty onset, a function that may contribute to its functional coupling to energy homeostasis.