17-Beta-estradiol directly regulates the expression of adrenergic receptors and kisspeptin/GPR54 system in GT1-7 GnRH neurons

Epigenetic regulation of 5α reductase-1 underlies adaptive plasticity of reproductive function and pubertal timing

Background

Women facing increased energetic demands in childhood commonly have altered adult ovarian activity and shorter reproductive lifespan, possibly comprising a strategy to optimize reproductive success. Here, we sought to understand the mechanisms of early-life programming of reproductive function, by integrating analysis of reproductive tissues in an appropriate mouse model with methylation analysis of proxy tissue DNA in a well-characterized population of Bangladeshi migrants in the UK. Bangladeshi women whose childhood was in Bangladesh were found to have later pubertal onset and lower age-matched ovarian reserve than Bangladeshi women who grew-up in England. Subsequently, we aimed to explore the potential relevance to the altered reproductive phenotype of one of the genes that emerged from the screens.

Results

Of the genes associated with differential methylation in the Bangladeshi women whose childhood was in Bangladesh as compared to Bangladeshi women who grew up in the UK, 13 correlated with altered expression of the orthologous gene in the mouse model ovaries. These mice had delayed pubertal onset and a smaller ovarian reserve compared to controls. The most relevant of these genes for reproductive function appeared to be SRD5A1, which encodes the steroidogenic enzyme 5α reductase-1. SRD5A1 was more methylated at the same transcriptional enhancer in mice ovaries as in the women’s buccal DNA, and its expression was lower in the hypothalamus of the mice as well, suggesting a possible role in the central control of reproduction. The expression of Kiss1 and Gnrh was also lower in these mice compared to controls, and inhibition of 5α reductase-1 reduced Kiss1 and Gnrh mRNA levels and blocked GnRH release in GnRH neuronal cell cultures. Crucially, we show that inhibition of this enzyme in female mice in vivo delayed pubertal onset.

Conclusions

SRD5A1/5α reductase-1 responds epigenetically to the environment and its downregulation appears to alter the reproductive phenotype. These findings help to explain diversity in reproductive characteristics and how they are shaped by early-life environment and reveal novel pathways that might be targeted to mitigate health issues caused by life-history trade-offs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01219-6.

Kisspeptin receptor agonist has therapeutic potential for female reproductive disorders

BACKGROUNDKisspeptin is a key regulator of hypothalamic gonadotropin-releasing hormone (GnRH) neurons and is essential for reproductive health. A specific kisspeptin receptor (KISS1R) agonist could significantly expand the potential clinical utility of therapeutics targeting the kisspeptin pathway. Herein, we investigate the effects of a KISS1R agonist, MVT-602, in healthy women and in women with reproductive disorders.METHODSWe conducted in vivo and in vitro studies to characterize the action of MVT-602 in comparison with native kisspeptin-54 (KP54). We determined the pharmacokinetic and pharmacodynamic properties of MVT-602 (doses 0.01 and 0.03 nmol/kg) versus KP54 (9.6 nmol/kg) in the follicular phase of healthy women (n = 9), and in women with polycystic ovary syndrome (PCOS; n = 6) or hypothalamic amenorrhea (HA; n = 6). Further, we investigated their effects on KISS1R-mediated inositol monophosphate (IP1) and Ca2+ signaling in cell lines and on action potential firing of GnRH neurons in brain slices.RESULTSIn healthy women, the amplitude of luteinizing hormone (LH) rise was similar to that after KP54, but peaked later (21.4 vs. 4.7 hours; P = 0.0002), with correspondingly increased AUC of LH exposure (169.0 vs. 38.5 IU∙h/L; P = 0.0058). LH increases following MVT-602 were similar in PCOS and healthy women, but advanced in HA (P = 0.004). In keeping with the clinical data, MVT-602 induced more potent signaling of KISS1R-mediated IP1 accumulation and a longer duration of GnRH neuron firing than KP54 (115 vs. 55 minutes; P = 0.0012).CONCLUSIONTaken together, these clinical and mechanistic data identify MVT-602 as having considerable therapeutic potential for the treatment of female reproductive disorders.TRIAL REGISTRATIONInternational Standard Randomised Controlled Trial Number (ISRCTN) Registry, ISRCTN21681316.FUNDINGNational Institute for Health Research and NIH.

In silico analysis of kiss2, expression studies and protein-protein interaction with gonadotropin-releasing hormone 2 (GnRH2) and luteinizing hormone beta (LHβ) in Heteropneustes fossilis

Kisspeptins, encoded by the kiss genes, are neuropeptides that regulate the onset of puberty, maturation of gonads, and fertility in higher vertebrates including fishes. The gene ontology suggests that kisspeptin plays an important role not only in reproduction but also in cell signaling, immune response and metabolic processes, and to decipher protein-protein interactions, computational approach has been favored. The present investigation focuses on the detailed structural analysis and molecular docking of kiss2 gene using in silico tools. A putative kiss2 protein of 113 amino acids was encoded by an open reading frame of 342 bp kiss2 gene. The protein is of 13.12 kDa with isoelectric point of 9.45. The secondary structure of the protein indicates more than 50% random coils, followed by 34% of alpha helix and 13% extended strand. The protein was found to be extracellular and secretory in nature. Since, protein-protein interactions play a very crucial role in every cellular process and due to unavailability of crystal structure of our protein of interest in fishes computational approach has been employed. The 3D PDB modeling and the molecular docking of kiss2, Gonadotropin-releasing hormone 2 (GnRH2) and luteinizing hormone beta (LHβ) proteins in fishes have been demonstrated applying protein-docking approach. Molecular interactions of kiss2 protein were the highest with kisspeptin receptor 2 and lowest for the neuropeptide FF-amide peptide precursor protein. Expression of kiss2 transcripts, mainly in the brain and ovary of H. fossilis, supports its hypothalamic-pituitary-gonadal axis signaling and reproductive function. Further, changes in expression patterns of kiss2 mRNA during different developmental stages, indicate its potential role in embryonic development also. The present study conclusively reveals interaction of kiss2 with other neuropeptides. Prediction of binding structures and identification of key residues in protein-protein interaction illustrate direct interaction among these proteins, playing a cardinal role in neuroendocrine regulation of reproduction in catfish. Communicated by Ramaswamy H. Sarma.

Role of core circadian clock genes in hormone release and target tissue sensitivity in the reproductive axis

Precise timing in hormone release from the hypothalamus, the pituitary and ovary is critical for fertility. Hormonal release patterns of the reproductive axis are regulated by a feedback loop within the hypothalamic-pituitary-gonadal (HPG) axis. The timing and rhythmicity of hormone release and tissue sensitivity in the HPG axis is regulated by circadian clocks located in the hypothalamus (suprachiasmatic nucleus, kisspeptin and GnRH neurons), the pituitary (gonadotrophs), the ovary (theca and granulosa cells), the testis (Leydig cells), as well as the uterus (endometrium and myometrium). The circadian clocks integrate environmental and physiological signals to produce cell endogenous rhythms generated by a transcriptional-translational feedback loop of transcription factors that are collectively called the "molecular clock". This review specifically focuses on the contribution of molecular clock transcription factors in regulating hormone release patterns in the reproductive axis, with an emphasis on the female reproductive system. Specifically, we discuss the contributions of circadian rhythms in distinct neuronal populations of the female hypothalamus, the molecular clock in the pituitary and its overall impact on female and male fertility.

Neurotransmitter, neuropeptide and gut peptide profile in PCOS-pathways contributing to the pathophysiology, food intake and psychiatric manifestations of PCOS

Polycystic ovary syndrome (PCOS) is a major health problem with a heterogeneous hormone-imbalance and clinical presentation across the lifespan of women. Increased androgen production and abnormal gonadotropin-releasing hormone (GnRH) release and gonadotropin secretion, resulting in chronic anovulation are well-known features of the PCOS. The brain is both at the top of the neuroendocrine axis regulating ovarian function and a sensitive target of peripheral gonadal hormones and peptides. Current literature illustrates that neurotransmitters regulate various functions of the body, including reproduction, mood and body weight. Neurotransmitter alteration could be one of the reasons for disturbed GnRH release, consequently directing the ovarian dysfunction in PCOS, since there is plenty evidence for altered catecholamine metabolism and brain serotonin or opioid activity described in PCOS. Further, the dysregulated neurotransmitter and neuropeptide profile in PCOS could also be the reason for low self-esteem, anxiety, mood swings and depression or obesity, features closely associated with PCOS women. Can these altered central brain circuits, or the disrupted gut-brain axis be the tie that would both explain and link the pathogenesis of this disorder, the occurrence of depression, anxiety and other mood disorders as well as of obesity, insulin resistance and abnormal appetite in PCOS? This review intends to provide the reader with a comprehensive overview of what is known about the relatively understudied, but very complex role that neurotransmitters, neuropeptides and gut peptides play in PCOS. The answer to the above question may help the development of drugs to specifically target these central and peripheral circuits, thereby providing a valuable treatment for PCOS patients that present to the clinic with GnRH/LH hypersecretion, obesity or psychiatric manifestations.

Effects of N-carbamylglutamate and L-arginine on gonadotrophin-releasing hormone (GnRH) gene expression and secretion in GT1-7 cells

Recent studies have shown that N-carbamylglutamate (NCG) and arginine (ARG) supplementation improves reproductive performance in livestock. The objectives of the present study were to evaluate the effects of NCG and ARG on GT1-7 cell gonadotrophin-releasing hormone (GnRH) secretion, gene expression and cell proliferation. GT1-7 cells were treated in vitro with different concentrations of NCG (0-1.0mM) or ARG (0-4.0mM) in serum-free medium for 12 or 24h. For GnRH secretion and cell proliferation, GT1-7 cells were more sensitive to NCG than ARG. NCG treatment after 12h increased cell numbers and inhibited GnRH secretion in a dose-dependent manner (P<0.05), although there was no significant effect of NCG on these parameters after 24h culture. ARG treatment decreased GnRH secretion after 24h (P<0.05), whereas it had no effect after 12h. GT1-7 cells express GnRH, Kiss-1 metastasis-suppressor (Kiss1), G-protein coupled receptor 54 (GPR54), neuronal nitric oxide synthase (nNOS) and estrogen receptor α (ERα) genes. High concentrations of NCG (1.0mM) and ARG (4.0mM) inhibited (P<0.05) GnRH and nNOS mRNA abundance in GT1-7 cells. ARG treatment decreased Kiss1 and increased ERα mRNA abundance. Thus, high concentrations of NCG (1.0mM) and ARG (4.0mM) may act both directly and indirectly to regulate GnRH neuron function by downregulating genes related to GnRH synthesis and secretion to slow GnRH production while stimulating GT1-7 cell proliferation.

Label-free dynamic mass redistribution analysis of endogenous adrenergic receptor signaling in primary preadipocytes and differentiated adipocytes

INTRODUCTION

Adipose tissues release adipokines, which regulate energy intake and expenditure. G protein-coupled receptors (GPCRs) and associated signaling pathways in adipocytes are potentially important drug targets for conditions with disturbed energy metabolism.

METHODS

The aim of the current study was to compare signaling of endogenously expressed GPCRs between primary preadipocytes and differentiated adipocytes using a novel state-of-the-art unbiased method that measures dynamic mass redistribution (DMR) in real-time. Adrenergic agonists were chosen since they control adipocyte functions such as lipolysis and glycogenolysis.

RESULTS

Isoprenaline (ISO) and phenylephrine (PE) elicited concentration-dependent responses in preadipocytes and differentiated adipocytes. The effect of ISO was cholera toxin (CTX)-sensitive, indicating it is G_s-dependent. The effect could also be blocked by propranolol proving the signal is mediated through β-adrenergic receptors. The signaling resulting from PE stimulation was completely abolished by the G_q/11-selective inhibitor FR900359 and CTX in preadipocytes but surprisingly became FR900359-insensitive but remained CTX-sensitive in differentiated adipocytes. The use of prazosin and propranolol revealed that the PE-response in differentiated adipocytes had a β-adrenergic receptor component to it. In addition, we tested the bone-derived peptide osteocalcin, which did not result in DMR changes in preadipocytes or differentiated adipocytes.

DISCUSSION

In conclusion, this study for the first time demonstrates that DMR assays can be used to assess signaling in differentiated adipocytes. This platform can serve as a tool for future drug screening in primary adipocytes. Furthermore, this study illustrates that PE-induced effects on adipocytes vary by developmental stage and are not as selective as originally thought.

Region-specific changes in brain kisspeptin receptor expression during estrogen depletion and the estrous cycle

Kisspeptin acts as a potent neuropeptide regulator of reproduction through modulation of the hypothalamic-pituitary-gonadal axis. Previous studies revealed sex differences in brain expression patterns as well as regulation of expression by estrogen. Alternatively, sex differences and estrogen regulation of the kisspeptin receptor (encoded by Kiss1r) have not been examined at cellular resolution. In the current study, we examined whether Kiss1r mRNA expression also exhibits estrogen sensitivity and sex-dependent differences using in situ hybridization. We compared Kiss1r mRNA expression between ovariectomized (OVX) rats and estradiol (E2)-replenished OVX rats to examine estrogen sensitivity, and compared expression between gonadally intact male rats and female rats in diestrus or proestrus to examine sex differences. In OVX rats, E2 replenishment significantly reduced Kiss1r expression specifically in the hypothalamic arcuate nucleus (ARC). A difference in Kiss1r expression was also observed between diestrus and proestrus rats in the hypothalamic paraventricular nucleus (PVN), but not in the ARC. Thus, estrogen appears to have region- and context-specific effects on Kiss1r expression. However, immunostaining revealed minimal colocalization of estrogen receptor alpha (ERα) in Kiss1r-expressing neuronal populations of ARC and PVN, indicating indirect or ERα-independent regulation of Kiss1r expression. Surprisingly, unlike the kisspeptin ligand, no sexual dimorphisms were observed in either the brain distribution of Kiss1r expression or in the number of Kiss1r-expressing neurons within enriched brain nuclei. The current study reveals marked differences in regulation between kisspeptin and kisspeptin receptor, and provides an essential foundation for further study of kisspeptin signaling and function in reproduction.

GnRH dysregulation in polycystic ovarian syndrome (PCOS) is a manifestation of an altered neurotransmitter profile

BACKGROUND

GnRH is the master molecule of reproduction that is influenced by several intrinsic and extrinsic factors such as neurotransmitters and neuropeptides. Any alteration in these regulatory loops may result in reproductive-endocrine dysfunction such as the polycystic ovarian syndrome (PCOS). Although low dopaminergic tone has been associated with PCOS, the role of neurotransmitters in PCOS remains unknown. The present study was therefore aimed at understanding the status of GnRH regulatory neurotransmitters to decipher the neuroendocrine pathology in PCOS.

METHODS

PCOS was induced in rats by oral administration of letrozole (aromatase inhibitor). Following PCOS validation, animals were assessed for gonadotropin levels and their mRNA expression. Neurotrasnmitter status was evaluated by estimating their levels, their metabolism and their receptor expression in hypothalamus, pituitary, hippocampus and frontal cortex of PCOS rat model.

RESULTS

We demonstrate that GnRH and LH inhibitory neurotransmitters - serotonin, dopamine, GABA and acetylcholine - are reduced while glutamate, a major stimulator of GnRH and LH release, is increased in the PCOS condition. Concomitant changes were observed for neurotransmitter metabolising enzymes and their receptors as well.

CONCLUSION

Our results reveal that increased GnRH and LH pulsatility in PCOS condition likely result from the cumulative effect of altered GnRH stimulatory and inhibitory neurotransmitters in hypothalamic-pituitary centre. This, we hypothesise, is responsible for the depression and anxiety-like mood disorders commonly seen in PCOS women.

The kisspeptin receptor: A key G-protein-coupled receptor in the control of the reproductive axis

The kisspeptin receptor, Kiss1R, also known as Gpr54, is a G protein-coupled receptor (GPCR), deorphanized in 2001, when it was recognized as canonical receptor for the Kiss1-derived peptides, kisspeptins. In 2003, inactivating mutations of Kiss1R gene were first associated to lack of pubertal maturation and hypogonadotropic hypogonadism in humans and rodents. These seminal findings pointed out the previously unsuspected, essential role of Kiss1R and its ligands in control of reproductive maturation and function. This contention has been fully substantiated during the last decade by a wealth of clinical and experimental data, which has documented a fundamental function of the so-called Kiss1/Kiss1R system in the regulation of puberty onset, gonadotropin secretion and ovulation, as well as the metabolic and environmental modulation of fertility. In this review, we provide a succinct summary of some of the most salient facets of Kiss1R, as essential GPCR for the proper maturation and function of the reproductive axis.

Reconsidering the roles of endogenous estrogens and xenoestrogens: the membrane estradiol receptor G protein-coupled receptor 30 (GPR30) mediates the effects of various estrogens

Estrone (E1) and estriol (E3) are considered “weak” estrogens, which exert suppressive effects through estrogen receptors α and β. However, recent studies have demonstrated that E1 and E3, as well as estradiol (E2), suppress gonadotropin-releasing hormone-induced luteinizing hormone secretion from bovine gonadotrophs via G-protein-coupled receptor 30, which is expressed in various reproductive organs. Currently, there is a lack of fundamental knowledge regarding E1 and E3, including their blood levels. In addition, xenoestrogens may remain in the body over long time periods because of enterohepatic circulation. Therefore, it is time to reconsider the roles of endogenous estrogens and xenoestrogens for reproduction.

Lordosis facilitated by GPER-1 receptor activation involves GnRH-1, progestin and estrogen receptors in estrogen-primed rats

The present study assessed the participation of membrane G-protein coupled estrogen receptor 1 (GPER-1) and gonadotropin releasing hormone 1 (GnRH-1) receptor in the display of lordosis induced by intracerebroventricular (icv) administration of G1, a GPER-1 agonist, and by unesterified 17β-estradiol (free E₂). In addition, we assessed the participation of both estrogen and progestin receptors in the lordosis behavior induced by G1 in ovariectomized (OVX), E₂-benzoate (EB)-primed rats. In Experiment 1, icv injection of G1 induced lordosis behavior at 120 and 240min. In Experiment 2, icv injection of the GPER-1 antagonist G15 significantly reduced lordosis behavior induced by either G1 or free E₂. In addition, Antide, a GnRH-1 receptor antagonist, significantly depressed G1 facilitation of lordosis behavior in OVX, EB-primed rats. Similarly, icv injection of Antide blocked the stimulatory effect of E₂ on lordosis behavior. In Experiment 3, systemic injection of either tamoxifen or RU486 significantly reduced lordosis behavior induced by icv administration of G1 in OVX, EB-primed rats. The results suggest that GnRH release activates both estrogen and progestin receptors and that this activation is important in the chain of events leading to the display of lordosis behavior in response to activation of GPER-1 in estrogen-primed rats.

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.

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.

The non-steroidal mycoestrogen zeranol suppresses luteinizing hormone secretion from the anterior pituitary of cattle via the estradiol receptor GPR30 in a rapid, non-genomic manner

Picomolar concentrations of estradiol produce rapid suppression of GnRH-induced luteinizing hormone (LH) secretion from the anterior pituitary (AP) of cattle via G-protein-coupled receptor 30 (GPR30). Zeranol is a strong estrogenic metabolite derived from zearalenone, a non-steroidal mycoestrogen produced by Fusarium that induces reproductive disorders in domestic animals. The hypothesis was tested that zeranol suppresses GnRH-induced LH release from the AP of cattle via GPR30 in a rapid, non-genomic manner. The AP cells (n=15) were cultured for 3 days in steroid-free conditions and then treated them with estradiol (0.001-10nM) or zeranol (0.001-100nM) for 5min before GnRH stimulation. Pre-treatment with 0.001-0.1nM estradiol suppressed GnRH-stimulated LH secretion. Pre-treatment with zeranol at concentrations of 0.001nM (P<0.01), 0.01nM (P<0.01), 0.1nM (P<0.05), and 1nM (P<0.05), but not at concentrations of 10 and 100nM, also inhibited GnRH-stimulated LH secretion from AP cells. Pre-treatment for 5min with a GPR30-specific antagonist, G36, inhibited estradiol or zeranol suppression of LH secretion from cultured AP cells. Cyclic AMP measurements and quantitative PCR analyses revealed that pre-treatment with small amounts of estradiol (P<0.05) or zeranol (P<0.01) decreased cAMP, but not gene expressions of the LHα, LHβ, or FSHβ subunits in the AP cells. Hence, zeranol may suppress luteinizing hormone secretion from the AP of cattle via GPR30 in a rapid, non-genomic manner.

Kisspeptin antagonist prevents RF9-induced reproductive changes in female rats

The aim of this study was to determine the modulatory effects of peptide 234 (p234) (an antagonist of GPR54 receptors) on kisspeptin and RF9 (an RFamide-related peptide antagonist)-induced changes in reproductive functions and energy balance in female rats. Female Sprague-Dawley rats were weaned on postnatal day (pnd) 21. The animals were intracerebroventricularly cannulated under general anesthesia on pnd 23. Groups of female rats were injected with kisspeptin, RF9, p234, kisspeptin plus p234, or RF9 plus p234, daily. The experiments were ended on the day of first diestrus following pnd 60. Kisspeptin or RF9 alone advanced vaginal opening (VO), which was delayed by administration of kisspeptin antagonist alone. In the rats given kisspeptin plus p234 or RF9 plus p234, VO was not different from control rats. Kisspeptin and RF9 elicited significant elevations in circulating LH levels. Coadministrations of kisspeptin or RF9 with p234 decreased LH levels significantly. The use of p234 alone did not cause any significant change in LH secretion. Kisspeptin decreased both food intake and body weight while RF9 decreased only food intake without affecting body weight. The effects of kisspeptin on energy balance were also reversed by central administration of p234. In conclusion, kisspeptin antagonist, p234, modulates the effects of kisspeptin on reproductive functions and energy balance, whereas RF9 seems to exert only its effects on reproductive functions by means of GPR54 signaling in female rats.

A Multi-Oscillatory Circadian System Times Female Reproduction

Rhythms in female reproduction are critical to insure that timing of ovulation coincides with oocyte maturation and optimal sexual arousal. This fine tuning of female reproduction involves both the estradiol feedback as an indicator of oocyte maturation, and the master circadian clock of the suprachiasmatic nuclei (SCN) as an indicator of the time of the day. Herein, we are providing an overview of the state of knowledge regarding the differential inhibitory and stimulatory effects of estradiol at different stages of the reproductive axis, and the mechanisms through which the two main neurotransmitters of the SCN, arginine vasopressin, and vasoactive intestinal peptide, convey daily time cues to the reproductive axis. In addition, we will report the most recent findings on the putative functions of peripheral clocks located throughout the reproductive axis [kisspeptin (Kp) neurons, gonadotropin-releasing hormone neurons, gonadotropic cells, the ovary, and the uterus]. This review will point to the critical position of the Kp neurons of the anteroventral periventricular nucleus, which integrate both the stimulatory estradiol signal, and the daily arginine vasopressinergic signal, while displaying a circadian clock. Finally, given the critical role of the light/dark cycle in the synchronization of female reproduction, we will discuss the impact of circadian disruptions observed during shift-work conditions on female reproductive performance and fertility in both animal model and humans.

Direct regulation of gonadotrophin-releasing hormone (GnRH) transcription by RF-amide-related peptide-3 and kisspeptin in a novel GnRH-secreting cell line, mHypoA-GnRH/GFP

RF-amide-related peptide-3 [RFRP-3; also often referred to as the mammalian orthologue of the avian gonadotrophin-inhibitory hormone (GnIH)] and kisspeptin have emerged as potent modulators of neuroendocrine function via direct regulation of the reproductive axis in the hypothalamus and pituitary. There are few studies focusing on the direct regulatory effects of RFRP-3 and kisspeptin on gonadotrophin-releasing hormones (GnRH) neurones. We report their effect on GnRH mRNA expression and release in a novel GnRH neuronal cell model, mHypoA-GnRH/GFP, generated from adult-derived GnRH-GFP neurones. The neurones express receptors for both RFRP-3 and kisspeptin, Gpr147 and Gpr54, respectively. Incubation with 100 nm RFRP-3 results in attenuation of GnRH mRNA expression by approximately 60%. Conversely, incubation with 10 nm of Kiss-10 induced GnRH mRNA expression, whereas the combined effect was an overall repression of GnRH mRNA levels. With transcription inhibitors, the repression of GnRH mRNA levels was linked to a transcriptional mechanism but not mRNA stability. No significant changes in GnRH secretion were observed upon RFRP-3 exposure in these neurones. Our findings suggest that the suppressive signalling of RFRP-3 on GnRH transcription may dominate over kisspeptin induction in the mHypoA-GnRH/GFP GnRH neuronal cell model.

Disrupted kisspeptin signaling in GnRH neurons leads to hypogonadotrophic hypogonadism

Landmark studies have shown that mutations in kisspeptin and the kisspeptin receptor (Kiss1r) result in reproductive dysfunction in humans and genetically altered mouse models. However, because kisspeptin and its receptor are present in target cells of the central and peripheral reproductive axis, the precise location(s) for the pathogenic signal is unknown. The study described herein shows that the kisspeptin-Kiss1r signaling pathway in the GnRH neuron is singularly critical for both the onset of puberty as well as the attainment of normal reproductive function. In this study, we directly test the hypothesis that kisspeptin neurons regulate GnRH secretion through the activation of Kiss1r on the plasma membrane of GnRH neurons. A GnRH neuron-specific Kiss1r knockout mouse model (GKirKO) was generated, and reproductive development and phenotype were assessed. Both female and male GKirKO mice were infertile, having low serum LH and FSH levels. External abnormalities such as microphallus and decreased anogenital distance associated with failure of preputial gland separation were present in GKirKO males. A delay in pubertal onset and abnormal estrous cyclicity were observed in female GKirKO mice. Taken together, these data provide in vivo evidence that Kiss1r in GnRH neurons is critical for reproductive development and fertility.

An alternative transcription start site yields estrogen-unresponsive Kiss1 mRNA transcripts in the hypothalamus of prepubertal female rats

The importance of the Kiss1 gene in the control of reproductive development is well documented. However, much less is known about the transcriptional regulation of Kiss1 expression in the hypothalamus. Critical for these studies is an accurate identification of the site(s) where Kiss1 transcription is initiated. Employing 5'-RACE PCR, we detected a transcription start site (TSS1) used by the hypothalamus of rats, mice, nonhuman primates and humans to initiate Kiss1 transcription. In rodents, an exon 1 encoding 5'-untranslated sequences is followed by an alternatively spliced second exon, which encodes 5'-untranslated regions of two different lengths and contains the translation initiation codon (ATG). In nonhuman primates and humans, exon 2 is not alternatively spliced. Surprisingly, in rat mediobasal hypothalamus (MBH), but not preoptic area (POA), an additional TSS (TSS2) located upstream from TSS1 generates an exon 1 longer (377 bp) than the TSS1-derived exon 1 (98 bp). The content of TSS1-derived transcripts increased at puberty in the POA and MBH of female rats. It also increased in the MBH after ovariectomy, and this change was prevented by estrogen. In contrast, no such changes in TSS2-derived transcript abundance were detected. Promoter assays showed that the proximal TSS1 promoter is much more active than the putative TSS2 promoter, and that only the TSS1 promoter is regulated by estrogen. These differences appear to be related to the presence of a TATA box and binding sites for transcription factors activating transcription and interacting with estrogen receptor-α in the TSS1, but not TSS2, promoter.

GnRH neurons of young and aged female rhesus monkeys co-express GPER but are unaffected by long-term hormone replacement

Menopause is caused by changes in the function of the hypothalamic-pituitary-gonadal axis that controls reproduction. Hypophysiotropic gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus orchestrate the activity of this axis and are regulated by hormonal feedback loops. The mechanisms by which GnRH responds to the primary regulatory sex steroid hormone, estradiol (E2), are still poorly understood in the context of menopause. Our goal was to determine whether the G protein-coupled estrogen receptor (GPER) is co-expressed in adult primate GnRH neurons and whether this changes with aging and/or E2 treatment. We used immunofluorescence double-labeling to characterize the co-expression of GPER in GnRH perikarya and terminals in the hypothalamus. Young and aged rhesus macaques were ovariectomized and given long-term (~2-year) hormone treatments (E2, E2 + progesterone, or vehicle) selected to mimic currently prescribed hormone replacement therapies used for the alleviation of menopausal symptoms in women. We found that about half of GnRH perikarya co-expressed GPER, while only about 12% of GnRH processes and terminals in the median eminence (ME) were double-labeled. Additionally, many GPER-labeled processes were in direct contact with GnRH neurons, often wrapped around the perikarya and processes and in close proximity in the ME. These results extend prior work by showing robust co-localization of GPER in GnRH in a clinically relevant model, and they support the possibility that GPER-mediated E2 regulation of GnRH occurs both in the soma and terminals in nonhuman primates.

Targeting GPR30 with G-1: a new therapeutic target for castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) is an advanced-stage prostate cancer (PC) associated with high mortality. We reported that G-1, a selective agonist of G protein-coupled receptor 30 (GPR30), inhibited PC cell growth by inducing G2 cell cycle arrest and arrested PC-3 xenograft growth. However, the therapeutic actions of G-1 and their relationships with androgen in vivo are unclear. Using the LNCaP xenograft to model PC growth during the androgen-sensitive (AS) versus the castration-resistant (CR) phase, we found that G-1 inhibited growth of CR but not AS tumors with no observable toxicity to the host. Substantial necrosis (approximately 65%) accompanied by marked intratumoral infiltration of neutrophils was observed only in CR tumors. Global transcriptome profiling of human genes identified 99 differentially expressed genes with 'interplay between innate and adaptive immune responses' as the top pathway. Quantitative PCR confirmed upregulation of neutrophil-related chemokines and inflammation-mediated cytokines only in the G-1-treated CR tumors. Expression of murine neutrophil-related cytokines also was elevated in these tumors. GPR30 (GPER1) expression was significantly higher in CR tumors than in AS tumors. In cell-based experiments, androgen repressed GPR30 expression, a response reversible by anti-androgen or siRNA-induced androgen receptor silencing. Finally, in clinical specimens, 80% of CRPC metastases (n=123) expressed a high level of GPR30, whereas only 54% of the primary PCs (n=232) showed high GPR30 expression. Together, these results provide the first evidence, to our knowledge, that GPR30 is an androgen-repressed target and G-1 mediates the anti-tumor effect via neutrophil-infiltration-associated necrosis in CRPC. Additional studies are warranted to firmly establish GPR30 as a therapeutic target in CRPC.

Mutual interaction of kisspeptin, estrogen and bone morphogenetic protein-4 activity in GnRH regulation by GT1-7 cells

Reproduction is integrated by interaction of neural and hormonal signals converging on hypothalamic neurons for controlling gonadotropin-releasing hormone (GnRH). Kisspeptin, the peptide product of the kiss1 gene and the endogenous agonist for the GRP54 receptor, plays a key role in the regulation of GnRH secretion. In the present study, we investigated the interaction between kisspeptin, estrogen and BMPs in the regulation of GnRH production by using mouse hypothalamic GT1-7 cells. Treatment with kisspeptin increased GnRH mRNA expression and GnRH protein production in a concentration-dependent manner. The expression levels of kiss1 and GPR54 were not changed by kisspeptin stimulation. Kisspeptin induction of GnRH was suppressed by co-treatment with BMPs, with BMP-4 action being the most potent for suppressing the kisspeptin effect. The expression of kisspeptin receptor, GPR54, was suppressed by BMPs, and this effect was reversed in the presence of kisspeptin. It was also revealed that BMP-induced Smad1/5/8 phosphorylation and Id-1 expression were suppressed and inhibitory Smad6/7 was induced by kisspeptin. In addition, estrogen induced GPR54 expression, while kisspeptin increased the expression levels of ERα and ERβ, suggesting that the actions of estrogen and kisspeptin are mutually enhanced in GT1-7 cells. Moreover, kisspeptin stimulated MAPKs and AKT signaling, and ERK signaling was functionally involved in the kisspeptin-induced GnRH expression. BMP-4 was found to suppress kisspeptin-induced GnRH expression by reducing ERK signaling activity. Collectively, the results indicate that the axis of kisspeptin-induced GnRH production is bi-directionally controlled, being augmented by an interaction between ERα/β and GPR54 signaling and suppressed by BMP-4 action in GT1-7 neuron cells.

Arg-Phe-amide-related peptides influence gonadotropin-releasing hormone neurons

The hypothalamic Arg-Phe-amide-related peptides, gonadotropin-inhibitory hormone and orthologous mammalian peptides of Arg-Phe-amide, may be important regulators of the hypothalamus-pituitary-gonadal reproductive axis. These peptides may modulate the effects of kisspeptins because they are presently recognized as the most potent activators of the hypothalamus-pituitary-gonadal axis. However, their effects on gonadotropin-releasing hormone neurons have not been investigated. In the current study, the GT1-7 cell line-expressing gonadotropin-releasing hormone was used as a model to explore the effects of Arg-Pheamide-related peptides on kisspeptin activation. Intracellular calcium concentration was quantified using the calcium-sensitive dye, fura-2 acetoxymethyl ester. Gonadotropin-releasing hormone released into the medium was detected via enzyme-linked immunosorbent assay. Results showed that 100 nmol/L kisspeptin-10 significantly increased gonadotropin-releasing hormone levels (at 120 minutes of exposure) and intracellular calcium concentrations. Co-treatment of kisspeptin with 1 μmol/L gonadotropin-inhibitory hormone or 1 μmol/L Arg-Phe-amide-related peptide-1 significantly attenuated levels of kisspeptin-induced gonadotropin-releasing hormone but did not affect kisspeptin-induced elevations of intracellular calcium concentration. Overall, the results suggest that gonadotropin-inhibitory hormone and Arg-Phe-amide-related peptide-1 may have inhibitory effects on kisspeptin-activated gonadotropin-releasing hormone neurons independent of the calcium signaling pathway.

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.

Model systems for studying kisspeptin signalling: mice and cells

Kisspeptins are a family of overlapping neuropeptides, encoded by the Kiss1 gene, that are required for activation and maintenance of the mammalian reproductive axis. Kisspeptins act within the hypothalamus to stimulate release of gonadotrophic releasing hormone and activation of the pituitary-gonadal axis. Robust model systems are required to dissect the regulatory mechanisms that control Kiss1 neuronal activity and to examine the molecular consequences of kisspeptin signalling. While studies in normal animals have been important in this, transgenic mice with targeted mutations affecting the kisspeptin signalling pathway have played a significant role in extending our understanding of kisspeptin physiology. Knock-out mice recapitulate the reproductive defects associated with mutations in humans and provide an experimentally tractable model system to interrogate regulatory feedback mechanisms. In addition, transgenic mice with cell-specific expression of modulator proteins such as the CRE recombinase or fluorescent reporter proteins such as GFP allow more sophisticated analyses such as cell or gene ablation or electrophysiological profiling. At a less complex level, immortalized cell lines have been useful for studying the role of kisspeptin in cell migration and metastasis and examining the intracellular signalling events associated with kisspeptin signalling.

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.

Clocks on top: the role of the circadian clock in the hypothalamic and pituitary regulation of endocrine physiology

Recent strides in circadian biology over the last several decades have allowed researchers new insight into how molecular circadian clocks influence the broader physiology of mammals. Elucidation of transcriptional feedback loops at the heart of endogenous circadian clocks has allowed for a deeper analysis of how timed cellular programs exert effects on multiple endocrine axes. While the full understanding of endogenous clocks is currently incomplete, recent work has re-evaluated prior findings with a new understanding of the involvement of these cellular oscillators, and how they may play a role in constructing rhythmic hormone synthesis, secretion, reception, and metabolism. This review addresses current research into how multiple circadian clocks in the hypothalamus and pituitary receive photic information from oscillators within the hypothalamic suprachiasmatic nucleus (SCN), and how resultant hypophysiotropic and pituitary hormone release is then temporally gated to produce an optimal result at the cognate target tissue. Special emphasis is placed not only on neural communication among the SCN and other hypothalamic nuclei, but also how endogenous clocks within the endocrine hypothalamus and pituitary may modulate local hormone synthesis and secretion in response to SCN cues. Through evaluation of a larger body of research into the impact of circadian biology on endocrinology, we can develop a greater appreciation into the importance of timing in endocrine systems, and how understanding of these endogenous rhythms can aid in constructing appropriate therapeutic treatments for a variety of endocrinopathies.

Oestrogen induces rhythmic expression of the Kisspeptin-1 receptor GPR54 in hypothalamic gonadotrophin-releasing hormone-secreting GT1-7 cells

Oestrogen-stimulated preovulatory gonadotrophin surges are temporally regulated in a way that remains not fully understood. Mammalian ovulation requires surges of gonadotrophin-releasing hormone (GnRH), released from specialised neurones in the hypothalamus. Surge regulation is mediated by ovarian oestrogen (17 β-oestradiol; E(2) ) feedback-acting as a negative signal until the early afternoon of the pro-oestrous phase, at which point it stimulates robust increases in GnRH release. Multiple lines of evidence suggest a role for the circadian clock in surge generation, although the presence of endogenous oscillators in several neuronal populations throughout the mediobasal hypothalamus complicates an elucidation of the underlying mechanisms of circadian regulation. In the present study, we propose that endogenous oscillators within GnRH neurones are modulated by oestrogen to elicit GnRH surge secretion. One mechanism by which this may occur is through the up-regulation of receptors of known stimulators of GnRH, such as kisspeptin's cognate receptor, GPR54. Through analysis of mRNA and protein abundance patterns, we found that high levels of E(2) elicit circadian expression profiles of GPR54 in vitro, and that disruption of endogenous GnRH oscillators of the clock dampens this effect. Additionally, although kisspeptin administration to GT1-7 cells does not result in surge-level secretion, we observed increased GnRH secretion from GT1-7 cells treated with positive feedback levels of E(2) . These results in this in vitro neuronal model system suggest a possible mechanism whereby receptor expression levels, and thus GnRH sensitivity to kisspeptin, may change dramatically over the pro-oestrous day. In this way, elevated ovarian E(2) may increase kisspeptidergic tone at the same time as increasing GnRH neuronal sensitivity to this neuropeptide for maximal surge release.

Kisspeptin increases GnRH mRNA expression and secretion in GnRH secreting neuronal cell lines

Kisspeptins, and their G-protein coupled receptor 54 (GPR54), are key components in the regulation of gonadotropin-releasing hormone (GnRH) secretion in humans and other mammals. Several studies demonstrate that the central or systemic administration of kisspeptin increases GnRH and gonadotropin secretion in both prepubertal and adult animals; however, the cellular targets and intracellular mechanisms of action in the central reproductive axis are unclear. In this study, we documented the presence of GPR54 in two GnRH secreting neuronal cell lines (GT1-7 and GN11). Kisspeptin treatment increases GnRH secretion and GnRH mRNA levels in a dose and time dependent manner. 10(-9)M kisspeptin maximally stimulated GnRH secretion by 2-fold and GnRH mRNA levels up to 4-fold after 4h of treatment in both cell lines. Negative regulation by 17beta-estradiol of GnRH secretion and GnRH mRNA was antagonized by kisspeptin. Co-treatment with kisspeptin and 17beta-estradiol increased GnRH secretion by 2-fold and GnRH mRNA by 4-fold over estradiol alone in both cell lines. Intracellular signaling pathway studies showed that an ERK1/2 MAPK inhibitor (PD98059) and a PI3K inhibitor, LY29402, attenuated the effects of kisspeptin on GnRH mRNA modulation. Furthermore, Western blot analysis showed that phosphorylation of both MAPK and Akt substrates increased with kisspeptin treatment. This work demonstrates that the kisspeptin-GPR54 system plays a significant role stimulating GnRH secretion and positive regulation of GnRH mRNA levels in GnRH neurons in culture, and also, demonstrates the activation of MAPK and Akt signaling pathways by kisspeptin in GT1-7 and GN11 cell lines.

GPR30/GPER1: searching for a role in estrogen physiology

Estrogens are sex hormones that are central to health and disease in both genders. These hormones have long been recognized to act in complex ways, both through relatively slow genomic mechanisms and via fast non-genomic mechanisms. Several recent in vitro studies suggest that GPR30, or G protein-coupled estrogen receptor 1 (GPER1), is a functional membrane estrogen receptor involved in non-genomic estrogen signaling. However, this function is not universally accepted. Studies concerning the role of GPER1 in vivo are now beginning to appear but with divergent results. In this review we discuss current knowledge on the physiological role of GPER1 in the nervous system as well as in reproduction, metabolism, bone, and in the cardiovascular and immune systems.

Hypothalamic cell lines to investigate neuroendocrine control mechanisms

The hypothalamus is the control center for most physiological processes; yet has been difficult to study due to the inherent heterogeneity of this brain region. For this reason, researchers have turned towards cell models. Primary hypothalamic cultures are difficult to maintain, are heterogeneous neuronal and glial cell populations and often contain a minimal number of viable peptide-secreting neurons. In contrast, immortalized, clonal cell lines represent an unlimited, homogeneous population of neurons that can be manipulated using a number of elegant molecular techniques. Cell line studies and in vivo experimentation are complementary and together provide a powerful tool to drive scientific discovery. This review focuses on three key neuroendocrine systems: energy homeostasis, reproduction, and circadian rhythms; and the use of hypothalamic cell lines to dissect the complex pathways utilized by individual neurons in these systems.

Modulation of gonadotrophin-releasing hormone secretion by an endogenous circadian clock

The mechanisms mediating positive feedback effects of oestradiol on pre-ovulatory gonadotrophin releasing-hormone (GnRH) surge generation in female mammals, although well-explored, are still incompletely understood. In addition to binding to and signalling through classical nuclear receptor-mediated pathways in afferent hypothalamic neurones, recent evidence suggests that ovarian steroids may use membrane-bound receptors or nonclassical signalling pathways to directly influence cell function leading to the generation of GnRH surge secretion. We review recent investigations into the role of the endogenous molecular circadian clock on modulation of GnRH gene expression and neuropeptide secretion, and will explore potential molecular mechanisms by which ovarian steroids may directly induce secretory changes at the level of the GnRH neurone, examining closely whether circadian clock gene oscillations may be involved.

Kisspeptins and the control of gonadotropin secretion in male and female rodents

Kisspeptins, the products of KiSS-1 gene acting via G protein-coupled receptor 54 (GPR54), have recently emerged as fundamental gatekeepers of gonadal function by virtue of their ability to stimulate gonadotropin secretion. Indeed, since the original disclosure of the reproductive facet of the KiSS-1/GPR54 system, an ever-growing number of studies have substantiated the extraordinary potency of kisspeptins to elicit gonadotropin secretion in different mammalian species, under different physiologic and experimental conditions, and through different routes of administration. In this context, studies conducted in laboratory rodents have been enormously instrumental to characterize: (i) the primary mechanisms of action of kisspeptins in the control of gonadotropin secretion; (ii) the pharmacological consequences of acute vs. continuous activation of GPR54; (iii) the roles of specific populations of kisspeptin-producing neurons at the hypothalamus in mediating the feedback effects of sex steroids; (v) the function of kisspeptins in the generation of the pre-ovulatory surge of gonadotropins; and (iv) the influence of sex steroids on GnRH/gonadotropin responsiveness to kisspeptins. While some of those aspects of kisspeptin function will be covered elsewhere in this Special Issue, we summarize herein the most salient data, obtained in laboratory rodents, that have helped to define the physiologic roles and putative pharmacological implications of kisspeptins in the control of male and female gonadotropic axis.

Regulation of KiSS1 gene expression

Kisspeptins are the protein products encoded by KiSS1 gene, an important tumor metastatic suppressor and pivotal master hormone of puberty. Although KiSS1 gene is expressed in both central and peripheral tissues, the molecular mechanisms that determine the temporal and spatial expression of KiSS1 gene are not well understood. This review provides an update on the latest studies and ideas about the expression of KiSS1 gene as a puberty gatekeeper and a metastasis suppressor, with special emphasis on the molecular mechanisms for the transcriptional regulation of KiSS1 gene expression.

Daily changes in GT1-7 cell sensitivity to GnRH secretagogues that trigger ovulation

Circadian rhythms in behavior and physiology are orchestrated by a master biological clock located in the suprachiasmatic nucleus (SCN). Circadian oscillations are a cellular property, with 'clock' genes and their protein products forming transcription-translation feedback loops that maintain 24-hour rhythmicity. Although the expression of clock genes is thought to be ubiquitous, the function of local, extra-SCN timing mechanisms remains elusive. We hypothesized that extra-SCN clock genes control local temporal sensitivity to upstream modulatory signals, allowing system-specific processes to be carried out during individual, optimal times of day. To test this possibility, we examined changes in the sensitivity of immortalized GnRH neurons, GT1-7 cells, to timed stimulation by two key neuropeptides thought to trigger ovulation on the afternoon of proestrus, kisspeptin and vasoactive intestinal polypeptide (VIP). We noted a prominent daily rhythm of clock gene expression in this cell line. GT1-7 cells also exhibited daily changes in cellular peptide expression and GnRH secretion in response to kisspeptin and VIP stimulation. These responses occurred without changes in GnRH transcription. These findings are consistent with the notion that GnRH cells are capable of intrinsic circadian cycles that may be fundamental for coordinating daily changes in sensitivity to signals impacting the reproductive axis.

The distribution of kisspeptin and its receptor GPR54 in rat dorsal root ganglion and up-regulation of its expression after CFA injection

Kisspeptin/GPR54 system plays a crucial role in the control of puberty onset and reproductive function. In the present study, we gave the first report that kisspeptin and GPR54 were expressed in the small- to large-sized neurons, and co-localized with Bandeiraea simplicifolia isolectin B4 (IB4), calcitonin-gene-related peptide (CGRP) and neurofilament 200 (NF200) in the L4/5 dorsal root ganglion (DRG) of naïve rats, detected by the double immunofluorescent staining. Interestingly, a marked elevation in the levels of KiSS-1 and GPR54 mRNA as well as protein was observed in the spinal dorsal horn and DRG 4 and 14 days following intra-articular injection of complete Freund's adjuvant (CFA), indicating a possible involvement of the kisspeptin/GPR54 system in chronic inflammatory pain.

Modulation of estrogen receptors during development inhibits neurogenesis of precursors to GnRH-1 neurones: in vitro studies with explants of ovine olfactory placode

The aim of the present study was to explore the putative effects of agonists and antagonists of the estradiol receptor on the early phase of GnRH-1 neuron development. To address this question we used an in vitro model of GnRH-1 neurons using cultured olfactory placode from sheep embryos on day 26 of gestation. Previous studies on this model have shown that in vitro the development of GnRH-1 neurons mimics in vivo development up to the start of pulsatile GnRH-1 secretion, To address the effects of modulating the estrogen receptor, cultures were treated with the endogenous and synthetic ligands of estradiol receptors: 17beta-estradiol, 17alpha-estradiol and tamoxifen. Neurogenesis was measured by incorporation of [(3)H]-thymidine. Morphometric parameters were evaluated by image analysis. The main results are that antagonism of estradiol receptors induced an important decrease in neurogenesis but had little effect on morphometric parameters, suggesting that during this early phase of development, maternal estrogens are important to achieve correct development of the GnRH-1 neuronal network.

The kisspeptin/gonadotropin-releasing hormone pathway and molecular signaling of puberty in fish

The mechanisms underlying the initiation of puberty in fish are poorly understood, and whether the Kiss1 receptor (Kiss1r; previously designated G protein-coupled receptor 54; GPR54) and its ligands, kisspeptins, play a significant role, as has been established in mammals, is not yet known. We determined (via real-time PCR) temporal patterns of expression in the brain of kiss1r, gnrh2, and gnrh3 and a suite of related genes in the hypothalamo-pituitary-gonadal (HPG) axis and analyzed them against the timing of gonadal germ cell development in male and female fathead minnow (Pimephales promelas). Full- or partial-length cDNAs for kiss1r (736 bp), gnrh2 (698 bp), and gnrh3 (804 bp) cloned from fathead minnow were found to be expressed only in the brain, testis, and ovary of adult fish. Localization of kiss1r, gnrh2, and gnrh3 within the brain provided evidence for their physiological roles and a likely hypophysiotropic role for GnRH3 in this species (which, like other cyprinids, does not appear to express gnrh1). In both sexes, kiss1r expression in the brain increased at the onset of puberty and reached maximal expression in males when spermatagonia type B appeared in the testis and in females when cortical alveolus-stage oocytes first appeared in the ovary, the timings of which differed for the two sexes. However, kiss1r expression was considerably lower during more advanced stages of spermatogenesis and oogenesis. The expression of kiss1r closely aligned with that of the gnrh genes (gnrh3 in particular), suggesting the Kiss1r/kisspeptin system in fish has a similar role in puberty to that occurring in mammals, and this hypothesis was supported by the induction of gnrh3 (2.25-fold) and kiss1r (1.5-fold) in early-mid pubertal fish injected with mammalian kisspeptin-10 (2 nmol/g wet weight). An intriguing finding, and contrasting that in mammals, was an elevated expression of esr1, ar, and cyp19a2 (genes involved in sex steroid signaling) in the brain at the onset of puberty, and in females slightly in advance of the elevation in the expression of kiss1r.