Female reproductive maturation in the absence of kisspeptin/GPR54 signaling

The Emerging Therapeutic Potential of Kisspeptin and Neurokinin B

Kisspeptin (KP) and neurokinin B (NKB) are neuropeptides that govern the reproductive endocrine axis through regulating hypothalamic gonadotropin-releasing hormone (GnRH) neuronal activity and pulsatile GnRH secretion. Their critical role in reproductive health was first identified after inactivating variants in genes encoding for KP or NKB signaling were shown to result in congenital hypogonadotropic hypogonadism and a failure of pubertal development. Over the past 2 decades since their discovery, a wealth of evidence from both basic and translational research has laid the foundation for potential therapeutic applications. Beyond KP's function in the hypothalamus, it is also expressed in the placenta, liver, pancreas, adipose tissue, bone, and limbic regions, giving rise to several avenues of research for use in the diagnosis and treatment of pregnancy, metabolic, liver, bone, and behavioral disorders. The role played by NKB in stimulating the hypothalamic thermoregulatory center to mediate menopausal hot flashes has led to the development of medications that antagonize its action as a novel nonsteroidal therapeutic agent for this indication. Furthermore, the ability of NKB antagonism to partially suppress (but not abolish) the reproductive endocrine axis has supported its potential use for the treatment of various reproductive disorders including polycystic ovary syndrome, uterine fibroids, and endometriosis. This review will provide a comprehensive up-to-date overview of the preclinical and clinical data that have paved the way for the development of diagnostic and therapeutic applications of KP and NKB.

Arcuate Nucleus of the Hypothalamus: Anatomy, Physiology, and Diseases

The hypothalamus is part of the diencephalon and has several nuclei, one of which is the arcuate nucleus. The arcuate nucleus of hypothalamus (ARH) consists of neuroendocrine neurons and centrally-projecting neurons. The ARH is the center where the homeostasis of nutrition/metabolism and reproduction are maintained. As such, dysfunction of the ARH can lead to disorders of nutrition/metabolism and reproduction. Here, we review various types of neurons in the ARH and several genetic disorders caused by mutations in the ARH.

KNDy Neurons of the Hypothalamus and Their Role in GnRH Pulse Generation: an Update

There is considerable evidence that synchronized activity within a reciprocally connected population of cells in the arcuate nucleus (ARC) coexpressing kisspeptin, neurokinin B (NKB), and dynorphin (KNDy cells) is crucial for the generation of gonadotrophin-releasing hormone (GnRH) pulses in mammals. The initial "KNDy hypothesis" proposed that pulsatile GnRH secretion is elicited by episodic kisspeptin release from KNDy cells following synchronized activation and termination of the population by NKB and dynorphin, respectively. Since then, the role of KNDy cells as a critical component of the pulse generator has been further supported by studies at the single-cell level, demonstrating that the population is both necessary and sufficient for pulsatility. In addition, there have been considerable modifications and expansion of the original hypothesis, including work demonstrating the critical role of glutamate in synchronization of the KNDy cell network, functional interactions with other ARC subpopulations, and the existence of species differences in the role of dynorphin in pulse generation. Here we review these recent changes and discuss how the translation of these findings has led to the development of new therapies for disorders related to pulse generation. We also outline critical gaps in knowledge that are currently limiting the application of KNDy research in the clinic, particularly regarding the role of dynorphin in pulse generation in primates.

KNDy neurones and GnRH/LH pulse generation: Current understanding and future aspects

Uncovering the central mechanism underlying mammalian reproduction is warranted to develop new therapeutic approaches for reproductive disorders in humans and domestic animals. The present study focused on the role of arcuate kisspeptin neurones (also known as KNDy neurones) as an intrinsic gonadotropin-releasing hormone (GnRH) pulse generator, which plays a fundamental role in mammalian reproduction via the stimulation of pituitary gonadotropin synthesis and release and thereby in gametogenesis and steroidogenesis in the gonads of mammals. We also discuss the mechanism that inhibits pulsatile GnRH/gonadotropin release under a negative energy balance, considering that reproductive disorders often occur during malnutrition in humans and livestock.

Subacute high-refined carbohydrate diet leads to abnormal reproductive control of the hypothalamic-pituitary axis in female rats

We previously reported that female rats placed on a diet containing refined carbohydrates (HCD) resulted in obesity and reproductive abnormalities, such as high serum LH concentration and abnormal ovarian function. However, the impacts at the hypothalamic-pituitary (HP) function, specifically regarding pathways linked to reproductive axis modulation are unknown. In this study, we assessed whether subacute feeding with HCD results in abnormal reproductive control in the HP axis. Female rats were fed with HCD for 15 days and reproductive HP axis morphophysiology was assessed. HCD reduced hypothalamic mRNA expression (Kiss1, Lepr, and Amhr2) and increased pituitary LHβ+ cells. These changes likely contribute to the increase in serum LH concentration observed in HCD. Blunted estrogen negative feedback was observed in HCD, with increased kisspeptin protein expression in the arcuate nucleus of the hypothalamus (ARH), lower LHβ+ cells and LH concentration in ovariectomized (OVX)+HCD rats. Thus, these data suggest that HCD feeding led to female abnormal reproductive control of HP axis.

Kisspeptin neuron projections to oxytocin neurons are not necessary for parturition in the mouse

Oxytocin is synthesized by hypothalamic supraoptic nucleus (SON) and paraventricular nucleus (PVN) neurons and is released from the posterior pituitary gland to trigger uterine contractions during parturition. In rats, oxytocin neuron innervation by periventricular nucleus (PeN) kisspeptin neurons increases over pregnancy and intra-SON kisspeptin administration excites oxytocin neurons only in late pregnancy. To test the hypothesis that kisspeptin neurons excite oxytocin neurons to trigger uterine contractions during birth in C57/B6J mice, double-label immunohistochemistry for kisspeptin and oxytocin first confirmed that kisspeptin neurons project to the SON and PVN. Furthermore, kisspeptin fibers expressed synaptophysin and formed close appositions with oxytocin neurons in the mouse SON and PVN before and during pregnancy. Stereotaxic viral delivery of caspase-3 into the AVPV/PeN of Kiss-Cre mice before mating reduced kisspeptin expression in the AVPV, PeN, SON and PVN by > 90% but did not affect the duration of pregnancy or the timing of delivery of each pup during parturition. Therefore, it appears that AVPV/PeN kisspeptin neuron projections to oxytocin neurons are not necessary for parturition in the mouse.

Acid-Resistant BODIPY Amino Acids for Peptide-Based Fluorescence Imaging of GPR54 Receptors in Pancreatic Islets

The G protein-coupled kisspeptin receptor (GPR54 or KISS1R) is an important mediator in reproduction, metabolism and cancer biology; however, there are limited fluorescent probes or antibodies for direct imaging of these receptors in cells and intact tissues, which can help to interrogate their multiple biological roles. Herein, we describe the rational design and characterization of a new acid-resistant BODIPY-based amino acid (Trp-BODIPY PLUS), and its implementation for solid-phase synthesis of fluorescent bioactive peptides. Trp-BODIPY PLUS retains the binding capabilities of both short linear and cyclic peptides and displays notable turn-on fluorescence emission upon target binding for wash-free imaging. Finally, we employed Trp-BODIPY PLUS to prepare some of the first fluorogenic kisspeptin-based probes and visualized the expression and localization of GPR54 receptors in human cells and in whole mouse pancreatic islets by fluorescence imaging.

Acid-Resistant BODIPY Amino Acids for Peptide-Based Fluorescence Imaging of GPR54 Receptors in Pancreatic Islets

The G protein-coupled kisspeptin receptor (GPR54 or KISS1R) is an important mediator in reproduction, metabolism and cancer biology; however, there are limited fluorescent probes or antibodies for direct imaging of these receptors in cells and intact tissues, which can help to interrogate their multiple biological roles. Herein, we describe the rational design and characterization of a new acid-resistant BODIPY-based amino acid (Trp-BODIPY PLUS), and its implementation for solid-phase synthesis of fluorescent bioactive peptides. Trp-BODIPY PLUS retains the binding capabilities of both short linear and cyclic peptides and displays notable turn-on fluorescence emission upon target binding for wash-free imaging. Finally, we employed Trp-BODIPY PLUS to prepare some of the first fluorogenic kisspeptin-based probes and visualized the expression and localization of GPR54 receptors in human cells and in whole mouse pancreatic islets by fluorescence imaging.

Hypothalamic kisspeptin neurons as potential mediators of estradiol negative and positive feedback

Gonadal steroid feedback regulates the brain's patterned secretion of gonadotropin-releasing hormone (GnRH). Negative feedback, which occurs in males and during the majority of the female cycle, modulates the amplitude and frequency of GnRH pulses. Positive feedback occurs in females when high estradiol induces a surge pattern of GnRH release. These two forms of feedback and their corresponding patterns of GnRH secretion are thought to be mediated by kisspeptin-expressing neurons in two hypothalamic areas: the arcuate nucleus and the anteroventral periventricular area. In this review, we present evidence for this theory and remaining questions to be addressed.

Dissecting the KNDy hypothesis: KNDy neuron-derived kisspeptins are dispensable for puberty but essential for preserved female fertility and gonadotropin pulsatility

BACKGROUND

Kiss1 neurons in the hypothalamic arcuate-nucleus (ARC) play key roles in the control of GnRH pulsatility and fertility. A fraction of ARC Kiss1 neurons, termed KNDy, co-express neurokinin B (NKB; encoded by Tac2). Yet, NKB- and Kiss1-only neurons are also found in the ARC, while a second major Kiss1-neuronal population is present in the rostral hypothalamus. The specific contribution of different Kiss1 neuron sub-sets and kisspeptins originating from them to the control of reproduction and eventually other bodily functions remains to be fully determined.

METHODS

To tease apart the physiological roles of KNDy-born kisspeptins, conditional ablation of Kiss1 in Tac2-expressing cells was implemented in vivo. To this end, mice with Tac2 cell-specific Kiss1 KO (TaKKO) were generated and subjected to extensive reproductive and metabolic characterization.

RESULTS

TaKKO mice displayed reduced ARC kisspeptin content and Kiss1 expression, with greater suppression in females, which was detectable at infantile-pubertal age. In contrast, Tac2/NKB levels were fully preserved. Despite the drop of ARC Kiss1/kisspeptin, pubertal timing was normal in TaKKO mice of both sexes. However, young-adult TaKKO females displayed disturbed LH pulsatility and sex steroid levels, with suppressed basal LH and pre-ovulatory LH surges, early-onset subfertility and premature ovarian insufficiency. Conversely, testicular histology and fertility were grossly conserved in TaKKO males. Ablation of Kiss1 in Tac2-cells led also to sex-dependent alterations in body composition, glucose homeostasis, especially in males, and locomotor activity, specifically in females.

CONCLUSIONS

Our data document that KNDy-born kisspeptins are dispensable/compensable for puberty in both sexes, but required for maintenance of female gonadotropin pulsatility and fertility, as well as for adult metabolic homeostasis.

SIGNIFICANCE STATEMENT

Neurons in the hypothalamic arcuate nucleus (ARC) co-expressing kisspeptins and NKB, named KNDy, have been recently suggested to play a key role in pulsatile secretion of gonadotropins, and hence reproduction. However, the relative contribution of this Kiss1 neuronal-subset, vs. ARC Kiss1-only and NKB-only neurons, as well as other Kiss1 neuronal populations, has not been assessed in physiological settings. We report here findings in a novel mouse-model with elimination of KNDy-born kisspeptins, without altering other kisspeptin compartments. Our data highlights the heterogeneity of ARC Kiss1 populations and document that, while dispensable/compensable for puberty, KNDy-born kisspeptins are required for proper gonadotropin pulsatility and fertility, specifically in females, and adult metabolic homeostasis. Characterization of this functional diversity is especially relevant, considering the potential of kisspeptin-based therapies for management of human reproductive disorders.

Long-term effects of prenatal undernutrition on female rat hypothalamic KNDy neurons

The nutritional environment during development periods induces metabolic programming, leading to metabolic disorders and detrimental influences on human reproductive health. This study aimed to determine the long-term adverse effect of intrauterine malnutrition on the reproductive center kisspeptin-neurokinin B-dynorphin A (KNDy) neurons in the hypothalamic arcuate nucleus (ARC) of female offspring. Twelve pregnant rats were divided into ad-lib-fed (control, n = 6) and 50% undernutrition (UN, n = 6) groups. The UN group was restricted to 50% daily food intake of the control dams from gestation day 9 until term delivery. Differences between the two groups in terms of various maternal parameters, including body weight (BW), pregnancy duration, and litter size, as well as birth weight, puberty onset, estrous cyclicity, pulsatile luteinizing hormone (LH) secretion, and hypothalamic gene expression of offspring, were determined. Female offspring of UN dams exhibited low BW from birth to 3 weeks, whereas UN offspring showed signs of precocious puberty; hypothalamic Tac3 (a neurokinin B gene) expression was increased in prepubertal UN offspring, and the BW at the virginal opening was lower in UN offspring than that in the control group. Interestingly, the UN offspring showed significant decreases in the number of KNDy gene-expressing cells after 29 weeks of age, but the number of ARC kisspeptin-immunoreactive cells, pulsatile LH secretions, and estrous cyclicity were comparable between the groups. In conclusion, intrauterine undernutrition induced various changes in KNDy gene expression depending on the life stage. Thus, intrauterine undernutrition affected hypothalamic developmental programming in female rats.

Mammalian puberty: a fly perspective

Mammalian puberty and Drosophila metamorphosis, despite their evolutionary distance, exhibit similar design principles and conservation of molecular components. In this Viewpoint, we review recent advances in this area and the similarities between both processes in terms of the signaling pathways and neuroendocrine circuits involved. We argue that the detection and uptake of peripheral fat by Drosophila prothoracic endocrine cells induces endomembrane remodeling and ribosomal maturation, leading to the acquisition of high biosynthetic and secretory capacity. The absence of this fat-neuroendocrine interorgan communication leads to giant, obese, non-pupating larvae. Importantly, human leptin is capable of signaling the pupariation process in Drosophila, and its expression prevents obesity and triggers maturation in mutants that do not pupate. This implies that insect metamorphosis can be used to address issues related to the biology of leptin and puberty.

Hierarchical deployment of Tbx3 dictates the identity of hypothalamic KNDy neurons to control puberty onset

The neuroendocrine system consists of a heterogeneous collection of neuropeptidergic neurons in the brain, among which hypothalamic KNDy neurons represent an indispensable cell subtype controlling puberty onset. Although neural progenitors and neuronal precursors along the cell lineage hierarchy adopt a cascade diversification strategy to generate hypothalamic neuronal heterogeneity, the cellular logic operating within the lineage to specify a subtype of neuroendocrine neurons remains unclear. As human genetic studies have recently established a link between TBX3 mutations and delayed puberty onset, we systematically studied Tbx3-derived neuronal lineage and Tbx3-dependent neuronal specification and found that Tbx3 hierarchically established and maintained the identity of KNDy neurons for triggering puberty. Apart from the well-established lineage-dependent fate determination, we uncovered rules of interlineage interaction and intralineage retention operating through neuronal differentiation in the absence of Tbx3. Moreover, we revealed that human TBX3 mutations disturbed the phase separation of encoded proteins and impaired transcriptional regulation of key neuropeptides, providing a pathological mechanism underlying TBX3-associated puberty disorders.

Conditional Deletion of KOR (Oprk1) in Kisspeptin Cells Does Not Alter LH Pulses, Puberty, or Fertility in Mice

Classic pharmacological studies suggested that endogenous dynorphin-KOR signaling is important for reproductive neuroendocrine regulation. With the seminal discovery of an interconnected network of hypothalamic arcuate neurons co-expressing kisspeptin, neurokinin B, and dynorphin (KNDy neurons), the KNDy hypothesis was developed to explain how gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) pulses are generated. Key to this hypothesis is dynorphin released from KNDy neurons acting in a paracrine manner on other KNDy neurons via kappa opioid receptor (KOR) signaling to terminate neural "pulse" events. While in vitro evidence supports this aspect of the KNDy hypothesis, a direct in vivo test of the necessity of KOR signaling in kisspeptin neurons for proper LH secretion has been lacking. We therefore conditionally knocked out KOR selectively from kisspeptin neurons of male and female mice and tested numerous reproductive measures, including in vivo LH pulse secretion. Surprisingly, despite validating successful knockout of KOR in kisspeptin neurons, we found no significant effect of kisspeptin cell-specific deletion of KOR on any measure of puberty, LH pulse parameters, LH surges, follicle-stimulating hormone (FSH) levels, estrous cycles, or fertility. These outcomes suggest that the KNDy hypothesis, while sufficient normally, may not be the only neural mechanism for sculpting GnRH and LH pulses, supported by recent findings in humans and mice. Thus, besides normally acting via KOR in KNDy neurons, endogenous dynorphin and other opioids may, under some conditions, regulate LH and FSH secretion via KOR in non-kisspeptin cells or perhaps via non-KOR pathways. The current models for GnRH and LH pulse generation should be expanded to consider such alternate mechanisms.

Precocious puberty in narcolepsy type 1: Orexin loss and/or neuroinflammation, which is to blame?

Narcolepsy type 1 (NT1) is a rare neurological sleep disorder triggered by postnatal loss of the orexin/hypocretin neuropeptides. Overweight/obesity and precocious puberty are highly prevalent comorbidities of NT1, with a close temporal correlation with disease onset, suggesting a common origin. However, the underlying mechanisms remain unknown and merit further investigation. The main question we address in this review is whether the occurrence of precocious puberty in NT1 is due to the lack of orexin/hypocretin or rather to a wider hypothalamic dysfunction in the context of neuroinflammation, which is likely to accompany the disease given its autoimmune origins. Our analysis suggests that the suspected generalized neuroinflammation of the hypothalamus in NT1 would tend to delay puberty rather than hastening it. In contrast, that the brutal loss of orexin/hypocretin would favor an early reactivation of gonadotropin-releasing hormone (GnRH) secretion during the prepubertal period in vulnerable children, leading to early puberty onset. Orexin/hypocretin replacement could thus be envisaged as a potential treatment for precocious puberty in NT1. Additionally, we put forward an alternative hypothesis regarding the concomitant occurrence of sleepiness, weight gain and early puberty in NT1.

Socs3 ablation in kisspeptin cells partially prevents lipopolysaccharide-induced body weight loss

Many cytokines have been proposed to regulate reproduction due to their actions on hypothalamic kisspeptin cells, the main modulators of gonadotropin-releasing hormone (GnRH) neurons. Hormones such as leptin, prolactin and growth hormone are good examples of cytokines that lead to Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway activation, consequently exerting effects in kisspeptin neurons. Different studies have investigated how specific components of the JAK/STAT signaling pathway affect the functions of kisspeptin cells, but the role of the suppressor of cytokine signaling 3 (SOCS3) in mediating cytokine actions in kisspeptin cells remains unknown. Cre-Loxp technology was used in the present study to ablate Socs3 expression in kisspeptin cells (Kiss1/Socs3-KO). Then, male and female control and Kiss1/Socs3-KO mice were evaluated for sexual maturation, energy homeostasis features, and fertility. It was found that hypothalamic Kiss1 mRNA expression is significantly downregulated in Kiss1/Socs3-KO mice. Despite reduced hypothalamic Kiss1 mRNA content, these mice did not present any sexual maturation or fertility impairments. Additionally, body weight gain, leptin sensitivity and glucose homeostasis were similar to control mice. Interestingly, Kiss1/Socs3-KO mice were partially protected against lipopolysaccharide (LPS)-induced body weight loss. Our results suggest that Socs3 ablation in kisspeptin cells partially prevents the sickness behavior induced by LPS, suggesting that kisspeptin cells can modulate energy metabolism in mice in certain situations.

Female fertility does not require Bmal1 in suprachiasmatic nucleus neurons expressing arginine vasopressin, vasoactive intestinal peptide, or neuromedin-S

Disruptions to the circadian system alter reproductive capacity, particularly in females. Mice lacking the core circadian clock gene, Bmal1, are infertile and have evidence of neuroendocrine disruption including the absence of the preovulatory luteinizing hormone (LH) surge and enhanced responsiveness to exogenous kisspeptin. Here, we explore the role of Bmal1 in suprachiasmatic nucleus (SCN) neuron populations known to project to the neuroendocrine axis. We generated four mouse lines using Cre/Lox technology to create conditional deletion of Bmal1 in arginine vasopressin (Bmal1fl/fl:Avpcre ), vasoactive intestinal peptide (Bmal1fl/fl:Vipcre ), both (Bmal1fl/fl:Avpcre+Vipcre ), and neuromedin-s (Bmal1fl/fl:Nmscre ) neurons. We demonstrate that the loss of Bmal1 in these populations has substantial effects on home-cage circadian activity and temperature rhythms. Despite this, we found that female mice from these lines demonstrated normal estrus cycles, fecundity, kisspeptin responsiveness, and inducible LH surge. We found no evidence of reproductive disruption in constant darkness. Overall, our results indicate that while conditional Bmal1 knockout in AVP, VIP, or NMS neurons is sufficient to disrupted locomotor activity, this disruption is insufficient to recapitulate the neuroendocrine reproductive effects of the whole-body Bmal1 knockout.

Neuroendocrine control of gonadotropin-releasing hormone: Pulsatile and surge modes of secretion

The concept that different systems control episodic and surge secretion of gonadotropin-releasing hormone (GnRH) was well established by the time that GnRH was identified and formed the framework for studies of the physiological roles of GnRH, and later kisspeptin. Here, we focus on recent studies identifying the neural mechanisms underlying these two modes of secretion, with an emphasis on their core components. There is now compelling data that kisspeptin neurons in the arcuate nucleus that also contain neurokinin B (NKB) and dynorphin (i.e., KNDy cells) and their projections to GnRH dendrons constitute the GnRH pulse generator in mice and rats. There is also strong evidence for a similar role for KNDy neurons in sheep and goats, and weaker data in monkeys and humans. However, whether KNDy neurons act on GnRH dendrons and/or GnRH soma and dendrites that are found in the mediobasal hypothalamus (MBH) of these species remains unclear. The core components of the GnRH/luteinising hormone surge consist of an endocrine signal that initiates the process and a neural trigger that drives GnRH secretion during the surge. In all spontaneous ovulators, the core endocrine signal is a rise in estradiol secretion from the maturing follicle(s), with the site of estrogen positive feedback being the rostral periventricular kisspeptin neurons in rodents and neurons in the MBH of sheep and primates. There is considerable species variations in the neural trigger, with three major classes. First, in reflex ovulators, this trigger is initiated by coitus and carried to the hypothalamus by neural or vascular pathways. Second, in rodents, there is a time of day signal that originates in the suprachiasmatic nucleus and activates rostral periventricular kisspeptin neurons and GnRH soma and dendrites. Finally, in sheep nitric oxide-producing neurons in the ventromedial nucleus, KNDy neurons and rostral kisspeptin neurons all appear to participate in driving GnRH release during the surge.

Kisspeptins and the neuroendocrine control of reproduction: Recent progress and new frontiers in kisspeptin research

In late 2003, a major breakthrough in our understanding of the mechanisms that govern reproduction occurred with the identification of the reproductive roles of kisspeptins, encoded by the Kiss1 gene, and their receptor, Gpr54 (aka, Kiss1R). The discovery of this unsuspected reproductive facet attracted an extraordinary interest and boosted an intense research activity, in human and model species, that, in a relatively short period, established a series of basic concepts on the physiological roles of kisspeptins. Such fundamental knowledge, gathered in these early years of kisspeptin research, set the scene for the more recent in-depth dissection of the intimacies of the neuronal networks involving Kiss1 neurons, their precise mechanisms of regulation and the molecular underpinnings of the function of kisspeptins as pivotal regulators of all key aspects of reproductive function, from puberty onset to pulsatile gonadotropin secretion and the metabolic control of fertility. While no clear temporal boundaries between these two periods can be defined, in this review we will summarize the most prominent advances in kisspeptin research occurred in the last ten years, as a means to provide an up-dated view of the state of the art and potential paths of future progress in this dynamic, and ever growing domain of Neuroendocrinology.

Effects of Fuyou Formula on GnRH Secretion and Related Gene Expression in Treating Precocious Puberty

The Fuyou (Fy) formula is an in-hospital preparation consisting of traditional Chinese medicine (TCM) that has been used for treating precocious puberty (PP) for more than 20 years. In this study, we aimed to clarify the effect of the Fy formula and its major components on PP. To confirm the effect of the Fy formula on the release of hypothalamic gonadotropin-releasing hormone (GnRH), GT1-7 cells were treated with estrogen to build the model group and subsequently treated with the Fy formula and its major components to explore their effects on the secretion of GnRH. The level of GnRH in GT1-7 cells was determined using enzyme-linked immunosorbent assay. The results illustrated that, compared to the model group, the Fy formula inhibited the release of GnRH. In addition, the expression levels of proteins related to GnRH secretion, including GnRH, gonadotropin-releasing hormone receptor (GnRHR), Kiss-1 metastasis-suppressor (Kiss1), G-protein coupled receptor 54 (GPR54), estrogen receptor α (ERα), insulin-like growth factor-1 (IGF-1), and insulin-like growth factor-1 receptor (IGF-1R), were detected by real-time polymerase chain reaction (RT-qPCR). The results demonstrated that the Fy formula significantly reduced the level of GnRH secretion in the GT1-7 cell lines compared with the model group. Moreover, it significantly downregulated the expression of GnRH, GnRHR, Kiss1, GPR54, ERα, IGF-1, and IGF-1R. In summary, our results indicate that the Fy formula and its major components may inhibit the effects of estrogen, which alleviates PP through transcriptional regulation of target genes.

Genetic Basis of Sexual Maturation Heterosis: Insights From Ovary lncRNA and mRNA Repertoire in Chicken

Sexual maturation is fundamental to the reproduction and production performance, heterosis of which has been widely used in animal crossbreeding. However, the underlying mechanism have long remained elusive, despite its profound biological and agricultural significance. In the current study, the reciprocal crossing between White Leghorns and Beijing You chickens were performed to measure the sexual maturation heterosis, and the ovary lncRNAs and mRNAs of purebreds and crossbreeds were profiled to illustrate molecular mechanism of heterosis. Heterosis larger than 20% was found for pubic space and oviduct length, whereas age at first egg showed negative heterosis in both crossbreeds. We identified 1170 known lncRNAs and 1994 putative lncRNAs in chicken ovary using a stringent pipeline. Gene expression pattern showed that nonadditivity was predominant, and the proportion of nonadditive lncRNAs and genes was similar between two crossbreeds, ranging from 44.24% to 49.15%. A total of 200 lncRNAs and 682 genes were shared by two crossbreeds, respectively. GO and KEGG analysis showed that the common genes were significantly enriched in the cell cycle, animal organ development, gonad development, ECM-receptor interaction, calcium signaling pathway and GnRH signaling pathway. Weighted gene co-expression network analysis (WGCNA) identified that 7 out of 20 co-expressed lncRNA-mRNA modules significantly correlated with oviduct length and pubic space. Interestingly, genes harbored in seven modules were also enriched in the similar biological process and pathways, in which nonadditive lncRNAs, such as MSTRG.17017.1 and MSTRG.6475.20, were strongly associated with nonadditive genes, such as CACNA1C and TGFB1 to affect gonad development and GnRH signaling pathway, respectively. Moreover, the results of real-time quantitative PCR (RT-qPCR) correlated well with the transcriptome data. Integrated with positive heterosis of serum GnRH and melatonin content detected in crossbreeds, we speculated that nonadditive genes involved in the GnRH signaling pathway elevated the gonad development, leading to the sexual maturation heterosis. We characterized a systematic landscape of ovary lncRNAs and mRNAs related to sexual maturation heterosis in chicken. The quantitative exploration of hybrid transcriptome changes lays foundation for genetic improvement of sexual maturation traits and provides insights into endocrine control of sexual maturation.

Hypothalamic kisspeptin and kisspeptin receptors: Species variation in reproduction and reproductive behaviours

Kisspeptin, encoded by the KISS1 gene, was first discovered as a potential metastasis suppressor gene. The prepro-kisspeptin precursor is cleaved into shorter mature bioactive peptides of varying sizes that bind to the G protein-coupled receptor GPR54 (=KISS1R). Over the last two decades, multiple types of Kiss and KissR genes have been discovered in mammalian and non-mammalian vertebrate species, but they are remarkably absent in birds. Kiss neuronal populations are distributed mainly in the hypothalamus. The KissRs are widely distributed in the brain, including the hypothalamic and non-hypothalamic regions, such as the hippocampus, amygdala, and habenula. The role of KISS1-KISS1R in humans and Kiss1-Kiss1R in rodents is associated with puberty, gonadal maturation, and the reproductive axis. However, recent gene deletion studies in zebrafish and medaka have provided controversial results, suggesting that the reproductive role of kiss is dispensable. This review highlights the evolutionary history, localisation, and significance of Kiss-KissR in reproduction and reproductive behaviours in mammalian and non-mammalian vertebrates.

Distinct effects of growth hormone deficiency and disruption of hypothalamic kisspeptin system on reproduction of male mice

Growth hormone (GH) deficiency is a common cause of late sexual maturation and fertility issues. To determine whether GH-induced effects on reproduction are associated with alterations in hypothalamic kisspeptin system, we studied the male reproduction in two distinct GH deficiency mouse models. In the first model, mice present GH deficiency secondary to arcuate nucleus of the hypothalamus (ARH) lesions induced by posnatal monosodium glutamate (MSG) injections. MSG-induced ARH lesions led to significant reductions in hypothalamic Ghrh mRNA expression and consequently growth. Hypothalamic Kiss1 mRNA expression and Kiss1-expressing cells in the ARH were disrupted in the MSG-treated mice. In contrast, kisspeptin immunoreactivity remained preserved in the anteroventral periventricular and rostral periventricular nuclei (AVPV/PeN) of MSG-treated mice. Importantly, ARH lesions caused late sexual maturation and infertility in male mice. In our second mouse model, we studied animals profound GH deficiency due to a loss-of-function mutation in the Ghrhr gene (Ghrhr^lit/lit mice). Interestingly, although Ghrhr^lit/lit mice exhibited late puberty onset, hypothalamic Kiss1 mRNA expression and hypothalamic kisspeptin fiber density were normal in Ghrhr^lit/lit mice. Despite presenting dwarfism, the majority of Ghrhr^lit/lit male mice were fertile. These findings suggest that spontaneous GH deficiency during development does not compromise the kisspeptin system. Furthermore, ARH Kiss1-expressing neurons are required for fertility, while AVPV/PeN kisspeptin expression is sufficient to allow maturation of the hypothalamic-pituitary-gonadal axis in male mice.

Gonadotrophin-releasing hormone and kisspeptin: It takes two to tango

Kisspeptin (Kp), a family of peptides comprising products of the Kiss1 gene, was discovered 20 years ago; it is recognised as the major factor controlling the activity of the gonadotrophin-releasing hormone (GnRH) neurones and thus the activation of the reproductive axis in mammals. It has been widely documented that the effects of Kp on reproduction through its action on GnRH neurones are mediated by the GPR54 receptor. Kp controls the activation of the reproductive axis at puberty, maintains reproductive axis activity in adults and is involved in triggering ovulation in some species. Although there is ample evidence coming from both conditional knockout models and conditional-induced Kp neurone death implicating the Kp/GPR54 pathway in the control of reproduction, the mechanism(s) underlying this process may be more complex than a sole direct control of GnRH neuronal activity by Kp. In this review, we provide an overview of the recent advances made in elucidating the interplay between Kp- and GnRH- neuronal networks with respect to regulating the reproductive axis. We highlight the existence of a possible mutual regulation between GnRH and Kp neurones, as well as the implication of Kp-dependent volume transmission in this process. We also discuss the capacity of heterodimerisation between GPR54 and GnRH receptor (GnRH-R) and its consequences on signalling. Finally, we illustrate the role of mathematical modelling that accounts for the synergy between GnRH-R and GPR54 in explaining the role of these two receptors when defining GnRH neuronal activity and GnRH pulsatile release.

Kisspeptin signaling and nNOS neurons in the VMHvl modulate lordosis behavior but not mate preference in female mice

It was recently shown that kisspeptin neurons in the anteroventral periventricular area (AVPV) orchestrate female sexual behavior, including lordosis behavior and mate preference. A potential target of AVPV kisspeptin signaling could be neurons expressing the neuronal form of nitric oxide synthase (nNOS) in the ventrolateral part of the ventromedial hypothalamus (VMHvl). Therefore, in the present study, we further refined the role of the VHMvl in female sexual behavior. Adult female mice received a bilateral cannula aimed at the VMHvl. A single injection with kisspeptin (Kp-10) or SNAP/BAY, a nitric oxide donor, significantly increased lordosis, whereas the nNOS inhibitor l-NAME decreased it. None of these drugs affected mate preference. Interestingly, administration of GnRH into the VMHvl had no effect on lordosis or mate preference. To determine whether the stimulatory effect of Kp-10 on lordosis was specific to the VMHvl, an additional group of females received Kp-10 directly into the paraventricular nucleus (PVN). No effect was found on lordosis and mate preference. These results suggest that kisspeptin most likely modulates lordosis behavior through nNOS neurons in the VMHvl whereas mate preference is modulated by kisspeptin through a separate neuronal circuit not including the VMHvl.

The KiNG of reproduction: Kisspeptin/ nNOS interactions shaping hypothalamic GnRH release

Gonadotropin-releasing hormone (GnRH) is the master regulator of the hypothalamic-pituitary-gonadal (HPG) axis, and therefore of fertility and reproduction. The release pattern of GnRH by the hypothalamus includes both pulses and surges. However, despite a considerable body of evidence in support of a determinant role for kisspeptin, the mechanisms regulating a GnRH pulse and surge remain a topic of debate. In this review we challenge the view of kisspeptin as an absolute "monarch", and instead present the idea of a Kisspeptin-nNOS-GnRH or "KiNG" network that is responsible for generating the "GnRH pulse" and "GnRH surge". In particular, the neuromodulator nitric oxide (NO) has opposite effects to kisspeptin on GnRH secretion in many respects, acting as the Yin to kisspeptin's Yang and creating a dynamic system in which kisspeptin provides the "ON" signal, promoting GnRH release, while NO mediates the "OFF" signal, acting as a tonic brake on GnRH secretion. This interplay between an activator and an inhibitor, which is in turn fine-tuned by the gonadal steroid environment, thus leads to the generation of GnRH pulses and surges and is crucial for the proper development and function of the reproductive axis.

Direct evidence that KNDy neurons maintain gonadotropin pulses and folliculogenesis as the GnRH pulse generator

The gonadotropin-releasing hormone (GnRH) pulse is fundamental for mammalian reproduction: GnRH pulse regimens are needed as therapies for infertile women as continuous GnRH treatment paradoxically inhibits gonadotropin release. Circumstantial evidence suggests that the hypothalamic arcuate KNDy neurons expressing kisspeptin (encoded by Kiss1), neurokinin B (encoded by Tac3), and d ynorphin A serve as a GnRH pulse generator; however, no direct evidence is currently available. Here, we show that rescuing >20% KNDy neurons by transfecting Kiss1 inside arcuate Tac3 neurons, but not outside of these neurons, recovered folliculogenesis and luteinizing hormone (LH) pulses, an indicator of GnRH pulses, in female global Kiss1 knockout (KO) rats and that >90% conditional arcuate Kiss1 KO in newly generated Kiss1-floxed rats completely suppressed LH pulses. These results first provide direct evidence that KNDy neurons are the GnRH pulse generator, and at least 20% of KNDy neurons are sufficient to maintain folliculogenesis via generating GnRH/gonadotropin pulses.

The abnormal expression of kisspeptin regulates pro-inflammatory cytokines, cell viability and apoptosis of macrophages in hyperandrogenism induced by testosterone

BACKGROUND

Increasing evidences have proposed that kisspeptins may be involved in polycystic ovary syndrome (PCOS) including hyperandrogenism. This work aimed to investigate the effect of kisspeptin in hyperandrogenism induced by testosterone.

METHODS

The most suitable concentration of testosterone to induce hyperandrogenism was determined by detecting the mRNA changes of kisspeptin and macrophages pro-inflammatory cytokines. The role of kisspeptin in hyperandrogenism was investigated by RT-PCR of kisspeptin and pro-inflammatory cytokines, by CCK-8 of cell viability, by Annexin V-FITC/PI staining followed by flow cytometry of apoptosis, by ELISA of pro-inflammatory cytokines and by Western blot of kisspeptin and antiapoptotic Bcl-2 and proapoptotic Bax.

RESULTS

We found that testosterone elevated kisspeptin, pro-inflammatory cytokines expressions and nitrite release in excessive androgen stimulated macrophages and further inhibited the macrophages cell viability and increased apoptosis. Kisspeptin knockdown reversed the tendency caused by testosterone and decreased apoptosis in macrophages treated with testosterone. Moreover, mRNA and protein expression levels of Bcl-2 and Bax were assessed. We showed a reduction in Bcl-2 mRNA and protein expression levels and an overexpression of Bax mRNA and protein expression levels. Kiss1 silencing reversed Bcl-2 and Bax expressions.

CONCLUSION

Kisspeptin inactivation confers resistance in hyperandrogenism by inhibiting pro-inflammatory cytokines expressions and apoptosis. Our results may help to comprehend the role of kisspeptin in the mechanisms of hyperandrogenism.

Knockout of the Glucocorticoid Receptor Impairs Reproduction in Female Zebrafish

The pleiotropic effects of glucocorticoids in metabolic, developmental, immune and stress response processes have been extensively investigated; conversely, their roles in reproduction are still less documented. It is well known that stress or long-lasting therapies can cause a strong increase in these hormones, negatively affecting reproduction. Moreover, the need of glucocorticoid (GC) homeostatic levels is highlighted by the reduced fertility reported in the zebrafish glucocorticoid receptor mutant (nr3c1^ia30/ia30) line (hereafter named gr^−/−). Starting from such evidence, in this study, we have investigated the role of glucocorticoid receptor (Gr) in the reproduction of female zebrafish. Key signals orchestrating the reproductive process at the brain, liver, and ovarian levels were analyzed using a multidisciplinary approach. An impairment of the kiss-GnRH system was observed at the central level in (gr^−/−) mutants as compared to wild-type (wt) females while, in the liver, vitellogenin (vtg) mRNA transcription was not affected. Changes were instead observed in the ovary, particularly in maturing and fully grown follicles (classes III and IV), as documented by the mRNA levels of signals involved in oocyte maturation and ovulation. Follicles isolated from gr^−/− females displayed a decreased level of signals involved in the acquisition of competence and maturation, causing a reduction in ovulation with respect to wt females. Fourier transform infrared imaging (FTIRI) analysis of gr^−/− follicle cytoplasm showed major changes in macromolecule abundance and distribution with a clear alteration of oocyte composition. Finally, differences in the molecular structure of the zona radiata layer of gr^−/− follicles are likely to contribute to the reduced fertilization rate observed in mutants.

Neonatal exposure to genistein affects reproductive physiology and behavior in female and male Long-Evans rats

The present study was designed to examine the effects of neonatal genistein exposure on measures of reproductive physiology and behavior. Approximately 24 h after birth, female and male Long-Evans rat pups were injected daily with genistein (150 µg, subcutaneous; n = 29) or olive oil (n = 23) between postnatal days 1 and 5. After weaning, we examined all subjects daily until they reached puberty (i.e. vaginal opening in female rats and preputial separation in male rats). For all female subjects, we also examined vaginal cytology. After monitoring estrous cyclicity, the female subjects were given the opportunity to interact with a gonadally intact male or a sexually receptive female rat on the day of behavioral estrus to assess sexual motivation (i.e. partner-preference test with and without physical contact), which has never been evaluated before. For all male subjects, we assessed the development of copulatory behavior and sexual motivation (partner-preference test without physical contact). Consistent with previous findings, we found that neonatal exposure to genistein did not affect puberty onset in female or male rats. However, female rats exposed to genistein displayed significantly more irregular estrous cycles than controls. Neonatal genistein exposure also altered the development of male copulatory behavior, as indicated by an increase in mount frequency and intromission frequency and shorter interintromission intervals. We extended previous findings confirming that neither female nor male sexual motivation was affected by neonatal genistein. The results of the present study have important implications for the development of reproductive physiology and behavior in human neonates exposed to genistein in soy-based baby formula.

Tachykinin signaling in the control of puberty onset

The tachykinin family of peptides has emerged as a critical component of the central control of the reproductive axis. Mounting evidence suggests that neurokinin B (NKB) plays an essential role in sexual maturation and fertility by directly stimulating the release of kisspeptin, with the contribution of additional tachykinins (neurokinin A [NKA] and substance P [SP]) in the fine tuning of the activity of Kiss1 neurons. The expression of tachykinins increases in the hypothalamus before puberty and, therefore, they are considered as initiators of pubertal development by stimulating the awakening of Kiss1 neurons. This is supported by studies showing delayed or absent puberty onset in humans and mice devoid of tachykinin signaling, and the advancement of puberty onset in rodents subjected to chronic activation of tachykinin receptors. This review compiles the current knowledge on the role of tachykinins in the control of puberty onset.

Chronic exposure to low dose of bisphenol A causes follicular atresia by inhibiting kisspeptin neurons in anteroventral periventricular nucleus in female mice

Bisphenol-A (BPA) is an estrogenic chemical extensively used in industrial and household applications. The present study was conducted to investigate the effect of chronic exposure to BPA on the adult female neuroendocrine system. Herein, we found that expose of adult female mice to BPA (50 μg/kg) by oral gavage for 60 days (BPA mice) prolonged diestrus and decreased serum 17β-estradiol (E2) concentration by reducing the number of antral follicles and corpora luteum. In comparison with controls, the levels of serum luteinizing hormone (LH), follicle stimulating hormone (FSH), hypothalamic gonadotrophin releasing hormone (GnRH) and the expression of kisspeptin in anteroventral periventricular nucleus (AVPV) decreased in BPA mice, which could be reversed by injecting kisspeptin-10 (i.c.v.). Treatment with BPA or estrogen receptor α (ERα) antagonist MPP, but not ERβ antagonist PHTPP inhibited E2-induced AVPV-kisspeptin expression in ovariectomized mice. Use of ERα agonist PPT rather than ERβ agonist DPN enhanced AVPV-kisspepetin expression, which decreased after treatment with BPA. The amplitude of the proestrus LH surge decreased in mice exposed to BPA, but was recovered by administering kisspeptin-10. The present study provides in vivo evidence that chronic exposure to a low dose of BPA suppressed ERα-induced activation of AVPV-kisspeptin neurons, leading to prolonged diestrus and reduced ovulation in adult female mice.

Inducible Kiss1 knockdown in the hypothalamic arcuate nucleus suppressed pulsatile secretion of luteinizing hormone in male mice

Accumulating evidence suggests that kisspeptin-GPR54 signaling is indispensable for gonadotropin-releasing hormone (GnRH)/gonadotropin secretion and consequent reproductive functions in mammals. Conventional Kiss1 knockout (KO) mice and rats are reported to be infertile. To date, however, no study has investigated the effect of inducible central Kiss1 KO/knockdown on pulsatile gonadotropin release in male mammals. Here we report an in vivo analysis of inducible conditional Kiss1 knockdown male mice. The mice were generated by a bilateral injections of either adeno-associated virus (AAV) vectors driving Cre recombinase (AAV-Cre) or AAV vectors driving GFP (AAV-GFP, control) into the hypothalamic arcuate nucleus (ARC) of Kiss1-floxed male mice, in which exon 3 of the Kiss1 gene were floxed with loxP sites. Four weeks after the AAV-Cre injection, the mice showed a profound decrease in the both number of ARC Kiss1-expressing cells and the luteinizing hormone (LH) pulse frequency. Interestingly, pulsatile LH secretion was apparent 8 weeks after the AAV-Cre injection despite the suppression of ARC Kiss1 expression. The control Kiss1-floxed mice infected with AAV-GFP showed apparent LH pulses and Kiss1 expression in the ARC at both 4 and 8 weeks after the AAV-GFP injection. These results with an inducible conditional Kiss1 knockdown in the ARC of male mice suggest that ARC kisspeptin neurons are responsible for pulsatile LH secretion in male mice, and indicate the possibility of a compensatory mechanism that restores GnRH/LH pulse generation.

Effect of different extracts and fractions of Senecio biafrae (Oliv. &Hiern) J. Moore on in vivo and in vitro parameters of folliculogenesis in experimental animals

BACKGROUND

Senecio biafrae is a medicinal plant widely used in traditional medicine to cure female infertility. Some effects have been pharmacologically demonstrated on immature female rats but in vivo and in vitro investigations are still necessary for determining its mechanism of action. The aim of the present study was to evaluate the estrogenic and FSH-like effects of the plant extracts and fractions on some fertility parameters in immature female rats and on in vitro survival and growth of swine preantral follicles.

METHODS

21-23 days old female Wistar rats orally received extracts and fractions of S. biafrae at 0, 8 and 64 mg/kg doses over 20 days. The LH, FSH, estradiol and progesterone serum levels were evaluated as well as the ovarian cholesterol, uterus and ovaries masses and proteins. The numbers of follicles at different developmental stages were recorded in ovarian cortexes after histology. Slices of swine ovarian cortexes were cultured along 1 or 7 days in alpha-minimum essential medium (α-MEM) and fixed for morphological analysis of preantral follicles. The fresh control, cultured control (CIV control) and different Senecio biafrae-treated ovarian fragments were analyzed for preantral follicles development. Treatments that showed the best follicle growth in culture were submitted to AgNOR test. The aqueous and MeOH/CH₂Cl₂ extracts as well as the ethyl acetate and hexane fractions of S. biafrae were submitted to the HPLC for analysis of polyphenolic secondary metabolites.

RESULTS

Ovarian and uterine proteins were significantly high (p < 0.01) in animals treated with the two dosages of ethyl acetate and n-butanol fractions. The same result was recorded with uterine proteins in animals treated with the hexane fraction. The FSH level significantly dropped with all ethanolic extract doses and with the 64 mg/kg dosage of the methanol/methylene chloride (MeOH/CH₂Cl₂) extract while LH was reduced (p < 0.01) in almost all the treated groups. Estradiol level was significantly increased (p < 0.001) in the three groups receiving the extracts, but reduced (p < 0.001) in the three groups receiving the fractions of the plant. The progesterone level increased with almost all the treated groups. Primary and secondary follicles augmented (p < 0.01) in MeOH/CH₂Cl₂ extract and n-butanol fraction while tertiary follicles increased with the same extract and the ethyl acetate fraction (p < 0.05). Treatments with aqueous and ethanolic extracts as well as ethyl acetate fraction led to a significant increase (p < 0.05) in the number of morphologically normal follicles after 7 days of culture as compared to the CIV control. The number of AgNOR dots per follicle was significantly low (p < 0.05) in all cultured groups as compared to the fresh control, except the ethyl acetate 2.8 ng/ml dosage. The same observation was done with AgNOR dots per cell in the 2.8 ng/ml dosage aqueous extract-treated fragments. The phenolic compounds mainly encountered in the plant, independently of the extract or fraction are apigenin, eugenol and rutin.

CONCLUSION

Extracts and fractions of S. biafrae have an important FSH-like effect which induces follicular survival and growth.

Targeted Deletion of PTEN in Kisspeptin Cells Results in Brain Region- and Sex-Specific Effects on Kisspeptin Expression and Gonadotropin Release

Kisspeptin-expressing neurons in the anteroventral periventricular nucleus (AVPV) and the arcuate nucleus (ARC) of the hypothalamus relay hormonal and metabolic information to gonadotropin-releasing hormone neurons, which in turn regulate pituitary and gonadal function. Phosphatase and tensin homolog (PTEN) blocks phosphatidylinositol 3-kinase (PI3K), a signaling pathway utilized by peripheral factors to transmit their signals. However, whether PTEN signaling in kisspeptin neurons helps to integrate peripheral hormonal cues to regulate gonadotropin release is unknown. To address this question, we generated mice with a kisspeptin cell-specific deletion of Pten (Kiss-PTEN KO), and first assessed kisspeptin protein expression and gonadotropin release in these animals. Kiss-PTEN KO mice displayed a profound sex and region-specific kisspeptin neuron hyperthrophy. We detected both kisspeptin neuron hyperthrophy as well as increased kisspeptin fiber densities in the AVPV and ARC of Kiss-PTEN KO females and in the ARC of Kiss-PTEN KO males. Moreover, Kiss-PTEN KO mice showed a reduced gonadotropin release in response to gonadectomy. We also found a hyperactivation of mTOR, a downstream PI3K target and central regulator of cell metabolism, in the AVPV and ARC of Kiss-PTEN KO females but not males. Fasting, known to inhibit hypothalamic kisspeptin expression and luteinizing hormone levels, failed to induce these changes in Kiss-PTEN KO females. We conclude that PTEN signaling regulates kisspeptin protein synthesis in both sexes and that its role as a metabolic signaling molecule in kisspeptin neurons is sex-specific.

Circadian Clock, Time-Restricted Feeding and Reproduction

The goal of this review was to seek a better understanding of the function and differential expression of circadian clock genes during the reproductive process. Through a discussion of how the circadian clock is involved in these steps, the identification of new clinical targets for sleep disorder-related diseases, such as reproductive failure, will be elucidated. Here, we focus on recent research findings regarding circadian clock regulation within the reproductive system, shedding new light on circadian rhythm-related problems in women. Discussions on the roles that circadian clock plays in these reproductive processes will help identify new clinical targets for such sleep disorder-related diseases.

Differential Roles of Hypothalamic AVPV and Arcuate Kisspeptin Neurons in Estradiol Feedback Regulation of Female Reproduction

Mammalian reproductive function includes puberty onset and completion, reproductive cyclicity, steroidogenesis, gametogenesis, fertilization, pregnancy, and lactation; all are indispensable to perpetuate species. Reproductive cycles are critical for providing the hormonal milieu needed for follicular development and maturation of eggs, but cycles, in and of themselves, do not guarantee ovulation will occur. Here, we review the roles in female reproductive neuroendocrine function of two hypothalamic populations that produce the neuropeptide kisspeptin, demonstrating distinct roles in maintaining cycles and ovulation.

Should We Make More Bone or Not, As Told by Kisspeptin Neurons in the Arcuate Nucleus

Since its initial discovery in 2002, the neuropeptide Kisspeptin (Kiss1) has been anointed as the master regulator controlling the onset of puberty in males and females. Over the last several years, multiple groups found that Kiss1 signaling is mediated by the 7TM surface receptor GPCR54. Kiss1 mRNA is highly enriched in the basal medial and lateral subregions of the arcuate nucleus (ARC) in the medial basal hypothalamus. Thus, Kiss1^ARC neurons reside in a unique anatomical location ideal for sensing and responding to circulating steroid hormones as well as nutrients. Kiss1 expression is highly responsive to fluctuations of the gonadal hormone, estrogen, with nearly 90% of Kiss1^ARC neurons expressing the nuclear hormone estrogen receptor alpha (ERa). Here we review recent research that extends the function of Kiss1ARC neurons beyond the regulation of puberty and highlight their emerging, novel roles in controlling energy allocation, behavioral outputs, and sex-dependent bone remodeling in females. Indeed, some of these previously unknown functions for Kiss1 neurons are quite striking as exemplified by the remarkable increase in bone mass after manipulating estrogen signaling in Kiss1^ARC neurons. Taken together, we suggest that Kiss1^ARC neurons are highly sensitive to nutritional and hormonal cues that dictate energy utilization and reproduction.

Mechanism of pulsatile GnRH release in primates: Unresolved questions

The pulsatility of GnRH release is essential for reproductive function. The key events in reproductive function, such as puberty onset and ovulatory cycles, are regulated by the frequency and amplitude modulation of pulsatile GnRH release. Abnormal patterns of GnRH pulsatility are seen in association with disease states, such as polycystic ovarian syndrome and anorexia nervosa. Recent studies with physiological, track-tracing, optogenetic and electrophysiological recording experiments indicate that a group of kisspeptin neurons in the arcuate nucleus (ARC) of the hypothalamus are responsible for pulsatile GnRH release. Thus, the kisspeptin neuron in the ARC has been called the "GnRH pulse-generator." However, a few pieces of evidence do not quite fit into this concept. This article reviews some old works and discusses unresolved issues on the mechanism of GnRH pulse generation.

Origin and Evolution of the Neuroendocrine Control of Reproduction in Vertebrates, With Special Focus on Genome and Gene Duplications

In humans, as in the other mammals, the neuroendocrine control of reproduction is ensured by the brain-pituitary gonadotropic axis. Multiple internal and environmental cues are integrated via brain neuronal networks, ultimately leading to the modulation of the activity of gonadotropin-releasing hormone (GnRH) neurons. The decapeptide GnRH is released into the hypothalamic-hypophysial portal blood system and stimulates the production of pituitary glycoprotein hormones, the two gonadotropins luteinizing hormone and follicle-stimulating hormone. A novel actor, the neuropeptide kisspeptin, acting upstream of GnRH, has attracted increasing attention in recent years. Other neuropeptides, such as gonadotropin-inhibiting hormone/RF-amide related peptide, and other members of the RF-amide peptide superfamily, as well as various nonpeptidic neuromediators such as dopamine and serotonin also provide a large panel of stimulatory or inhibitory regulators. This paper addresses the origin and evolution of the vertebrate gonadotropic axis. Brain-pituitary neuroendocrine axes are typical of vertebrates, the pituitary gland, mediator and amplifier of brain control on peripheral organs, being a vertebrate innovation. The paper reviews, from molecular and functional perspectives, the evolution across vertebrate radiation of some key actors of the vertebrate neuroendocrine control of reproduction and traces back their origin along the vertebrate lineage and in other metazoa before the emergence of vertebrates. A focus is given on how gene duplications, resulting from either local events or from whole genome duplication events, and followed by paralogous gene loss or conservation, might have shaped the evolutionary scenarios of current families of key actors of the gonadotropic axis.

Circadian Function in Multiple Cell Types Is Necessary for Proper Timing of the Preovulatory LH Surge

The timing of the preovulatory surge of luteinizing hormone (LH), which occurs on the evening of proestrus in female mice, is determined by the circadian system. The identity of cells that control the phase of the LH surge is unclear: evidence supports a role of arginine vasopressin (AVP) cells of the suprachiasmatic nucleus (SCN), but it is not known whether vasopressinergic neurons are necessary or sufficient to account for circadian control of ovulation. Among other cell types, evidence also suggests important roles of circadian function of kisspeptin cells of the anteroventral periventricular nucleus (AvPV) and gonadotropin-releasing hormone (GnRH) neurons of the preoptic area (POA), whose discharge is immediately responsible for the discharge of LH from the anterior pituitary. The present studies used an ovariectomized, estradiol-treated preparation to determine critical cell types whose clock function is critical to the timing of LH secretion. As expected, the LH surge occurred at or shortly after ZT12 in control mice. In further confirmation of circadian control, the surge was advanced by 2 h in tau mutant animals. The timing of the surge was altered to varying degrees by conditional deletion of Bmal1 in AVP^Cre, Kiss^CreBAC, and GnRH^CreBAC mice. Excision of the mutant Cnsk1e (tau) allele in AVP neurons resulted in a reversion of the surge to the ZT12. Conditional deletion of Bmal1 in Kiss1 or GnRH neurons had no noticeable effect on locomotor rhythms, but targeting of AVP neurons produced variable effects on circadian period that did not always correspond to changes in the phase of LH secretion. The results indicate that circadian function in multiple cell types is necessary for proper timing of the LH surge.

Central growth hormone signaling is not required for the timing of puberty

Growth hormone (GH) is a key factor in the regulation of body growth, as well as a variety of other cellular and metabolic processes. Neurons expressing kisspeptin and leptin receptors (LepR) have been shown to modulate the hypothalamic-pituitary-gonadal (HPG) axis and are considered GH-responsive. The presence of functional GH receptors (GHR) in these neural populations suggests that GH may regulate the HPG axis via a central mechanism. However, there have been no studies evaluating whether or not GH-induced intracellular signaling in the brain plays a role in the timing of puberty or mediates the ovulatory cycle. Towards the goal of understanding the influence of GH on the central nervous system as a mediator of reproductive functions, GHR ablation was induced in kisspeptin and LepR expressing cells or in the entire brain. The results demonstrated that GH signaling in specific neural populations can potentially modulate the hypothalamic expression of genes related to the reproductive system or indirectly contribute to the progression of puberty. GH action in kisspeptin cells or in the entire brain was not required for sexual maturation. On the other hand, GHR ablation in LepR cells delayed puberty progression, reduced serum leptin levels, decreased body weight gain and compromised the ovulatory cycle in some individuals, while the lack of GH effects in the entire brain prompted shorter estrous cycles. These findings suggest that GH can modulate brain components of the HPG axis, although central GH signaling is not required for the timing of puberty.

The neurobiological mechanism underlying hypothalamic GnRH pulse generation: the role of kisspeptin neurons in the arcuate nucleus

This review recounts the origins and development of the concept of the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator. It starts in the late 1960s when striking rhythmic episodes of luteinizing hormone secretion, as reflected by circulating concentrations of this gonadotropin, were first observed in monkeys and ends in the present day. It is currently an exciting time witnessing the application, primarily to the mouse, of contemporary neurobiological approaches to delineate the mechanisms whereby Kiss1/NKB/Dyn (KNDy) neurons in the arcuate nucleus of the hypothalamus generate and time the pulsatile output of kisspeptin from their terminals in the median eminence that in turn dictates intermittent GnRH release and entry of this decapeptide into the primary plexus of the hypophysial portal circulation. The review concludes with an examination of questions that remain to be addressed.

The neurobiological mechanism underlying hypothalamic GnRH pulse generation: the role of kisspeptin neurons in the arcuate nucleus

This review recounts the origins and development of the concept of the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator. It starts in the late 1960s when striking rhythmic episodes of luteinizing hormone secretion, as reflected by circulating concentrations of this gonadotropin, were first observed in monkeys and ends in the present day. It is currently an exciting time witnessing the application, primarily to the mouse, of contemporary neurobiological approaches to delineate the mechanisms whereby Kiss1/NKB/Dyn (KNDy) neurons in the arcuate nucleus of the hypothalamus generate and time the pulsatile output of kisspeptin from their terminals in the median eminence that in turn dictates intermittent GnRH release and entry of this decapeptide into the primary plexus of the hypophysial portal circulation. The review concludes with an examination of questions that remain to be addressed.

Kisspeptin Neurons in the Arcuate Nucleus of the Hypothalamus Orchestrate Circadian Rhythms and Metabolism

Successful reproduction in female mammals is precisely timed and must be able to withstand the metabolic demand of pregnancy and lactation. We show that kisspeptin-expressing neurons in the arcuate hypothalamus (Kiss1^ARH) of female mice control the daily timing of food intake, along with the circadian regulation of locomotor activity, sleep, and core body temperature. Toxin-induced silencing of Kiss1^ARH neurons shifts wakefulness and food consumption to the light phase and induces weight gain. Toxin-silenced mice are less physically active and have attenuated temperature rhythms. Because the rhythm of the master clock in the suprachiasmatic nucleus (SCN) appears to be intact, we hypothesize that Kiss1^ARH neurons signal to neurons downstream of the master clock to modulate the output of the SCN. We conclude that, in addition to their well-established role in regulating fertility, Kiss1^ARH neurons are a critical component of the hypothalamic circadian oscillator network that times overt rhythms of physiology and behavior.

The Gonadotropin-Releasing Hormone Pulse Generator

The pulsatile release of GnRH and LH secretion is essential for fertility in all mammals. Pulses of LH occur approximately every hour in follicular-phase females and every 2 to 3 hours in luteal-phase females and males. Many studies over the last 50 years have sought to identify the nature and mechanism of the "GnRH pulse generator" responsible for pulsatile LH release. This review examines the characteristics of pulsatile hormone release and summarizes investigations that have led to our present understanding of the GnRH pulse generator. There is presently little compelling evidence for an intrinsic mechanism of pulse generation involving interactions between GnRH neuron cell bodies. Rather, data support the presence of an extrinsic pulse generator located within the arcuate nucleus, and attention has focused on the kisspeptin neurons and their projections to GnRH neuron dendrons concentrated around the median eminence. Sufficient evidence has been gathered in rodents to conclude that a subpopulation of arcuate kisspeptin neurons is, indeed, the GnRH pulse generator. Findings in other species are generally compatible with this view and suggest that arcuate/infundibular kisspeptin neurons represent the mammalian GnRH pulse generator. With hindsight, it is likely that past arcuate nucleus multiunit activity recordings have been from kisspeptin neurons. Despite advances in identifying the cells forming the pulse generator, almost nothing is known about their mechanisms of synchronicity and the afferent hormonal and transmitter modulation required to establish the normal patterns of LH pulsatility in mammals.

Estradiol Increases Glutamate and GABA Neurotransmission into GnRH Neurons via Retrograde NO-Signaling in Proestrous Mice during the Positive Estradiol Feedback Period

Surge release of gonadotropin-releasing hormone (GnRH) is essential in the activation of pituitary gonadal unit at proestrus afternoon preceded by the rise of serum 17β-estradiol (E2) level during positive feedback period. Here, we describe a mechanism of positive estradiol feedback regulation acting directly on GnRH-green fluorescent protein (GFP) neurons of mice. Whole-cell clamp and loose patch recordings revealed that a high physiological dose of estradiol (200 pM), significantly increased firing rate at proestrus afternoon. The mPSC frequency at proestrus afternoon also increased, whereas it decreased at metestrus afternoon and had no effect at proestrus morning. Inhibition of the estrogen receptor β (ERβ), intracellular blockade of the Src kinase and phosphatidylinositol 3 kinase (PI3K) and scavenge of nitric oxide (NO) inside GnRH neurons prevented the facilitatory estradiol effect indicating involvement of the ERβ/Src/PI3K/Akt/nNOS pathway in this fast, direct stimulatory effect. Immunohistochemistry localized soluble guanylate cyclase, the main NO receptor, in both glutamatergic and GABAergic terminals innervating GnRH neurons. Accordingly, estradiol facilitated neurotransmissions to GnRH neurons via both GABA_A-R and glutamate/AMPA/kainate-R. These results indicate that estradiol acts directly on GnRH neurons via the ERβ/Akt/nNOS pathway at proestrus afternoon generating NO that retrogradely accelerates GABA and glutamate release from the presynaptic terminals contacting GnRH neurons. The newly explored mechanism might contribute to the regulation of the GnRH surge, a fundamental prerequisite of the ovulation.

Di-(2-ethylhexyl) phthalate induces precocious puberty in adolescent female rats

OBJECTIVES

Nowadays, Di-(2-ethylhexyl) phthalate (DEHP) is widely used in different kinds of commercial products as a plasticizer. Previous studies have revealed that exposures to DEHP could be associated with precocious puberty in teenagers, but the exact mechanism is yet to be known.

MATERIALS AND METHODS

In this study, 48 prepubertal Wistar female rats were randomly apportioned into 4 groups and orally treated with 0, 250, 500, and 1000 mg/kg/d DEHP from postnatal day 21 up to 4 weeks. Subsequently, we examined the indicators related to the initiation of sexual development.

RESULTS

DEHP was able to shorten the vaginal opening time and prolong the estrous cycles of female rats. IGF-1 expression was significantly upregulated by 1000 mg/kg/d DEHP in the hypothalamus, and the hypothalamic, as well as serum levels of GH, were also upregulated by DEHP. It also caused decrements in serum levels of FSH, LH, and T and the increment in level of progesterone. Meanwhile, DEHP was able to exert its effect on the mRNA and protein expression levels of Kiss-1, GPR54, and GnRH in the hypothalamus in pubertal female rats.

CONCLUSION

These findings are revealing that DEHP exposure more likely causes imbalances of hypothalamus functioning in pubertal female rats and thus induces precautious puberty in these animals.

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.