Colocalization of kisspeptin and gonadotropin-releasing hormone in the ovine brain

Neuropeptides as regulators of the hypothalamus-pituitary-gonadal (HPG) axis activity and their putative roles in stress-induced fertility disorders

Neuropeptides being regulators of the hypothalamus-pituitary-adrenal (HPA) axis activity, also affect the function of the hypothalamus-pituitary-gonadal (HPG) axis by regulating gonadotrophin-releasing hormone (GnRH) secretion from hypothalamic neurons. Here, we review the available data on how neuropeptides affect HPG axis activity directly or indirectly via their influence on the HPA axis. The putative role of neuropeptides in stress-induced infertility, such as polycystic ovary syndrome, is also described. This review discusses both well-known neuropeptides (i.e., kisspeptin, Kp; oxytocin, OT; arginine-vasopressin, AVP) and more recently discovered peptides (i.e., relaxin-3, RLN-3; nesfatin-1, NEFA; phoenixin, PNX; spexin, SPX). For the first time, we present an up-to-date review of all published data regarding interactions between the aforementioned neuropeptide systems. The reviewed literature suggest new pathophysiological mechanisms leading to fertility disturbances that are induced by stress.

Hormonal and neuroendocrine control of reproductive function in teleost fish

Reproduction is one of the important physiological events for the maintenance of the species. Hormonal and neuroendocrine regulation of teleost requires multiple and complex interactions along the hypothalamic-pituitary-gonad (HPG) axis. Within this axis, gonadotropin-releasing hormone (GnRH) regulates the synthesis and release of gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). Steroidogenesis drives reproduction function in which the development and differentiation of gonads. In recent years, new neuropeptides have become the focus of reproductive physiology research as they are involved in the different regulatory mechanisms of these species' growth, metabolism, and reproduction. However, especially in fish, the role of these neuropeptides in the control of reproductive function is not well studied. The study of hormonal and neuroendocrine events that regulate reproduction is crucial for the development and success of aquaculture.

Distribution of GnRH and Kisspeptin Immunoreactivity in the Female Llama Hypothalamus

Llamas are induced non-reflex ovulators, which ovulate in response to the hormonal stimulus of the male protein beta-nerve growth factor (β-NGF) that is present in the seminal plasma; this response is dependent on the preovulatory gonadotrophin-releasing hormone (GnRH) release from the hypothalamus. GnRH neurones are vital for reproduction, as these provide the input that controls the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. However, in spontaneous ovulators, the activity of GnRH cells is regulated by kisspeptin neurones that relay the oestrogen signal arising from the periphery. Here, we investigated the organisation of GnRH and kisspeptin systems in the hypothalamus of receptive adult female llamas. We found that GnRH cells exhibiting different shapes were distributed throughout the ventral forebrain and some of these were located in proximity to blood vessels; sections of the mediobasal hypothalamus (MBH) displayed the highest number of cells. GnRH fibres were observed in both the organum vasculosum laminae terminalis (OVLT) and median eminence (ME). We also detected abundant kisspeptin fibres in the MBH and ME; kisspeptin cells were found in the arcuate nucleus (ARC), but not in rostral areas of the hypothalamus. Quantitative analysis of GnRH and kisspeptin fibres in the ME revealed a higher innervation density of kisspeptin than of GnRH fibres. The physiological significance of the anatomical findings reported here for the ovulatory mechanism in llamas is still to be determined.

Role of Kisspeptin in Regulation of Reproductive and Immune Reactions

The work is focused on physiological role of the hormone kisspeptin produced by neurons of the hypothalamus anterior zone, which is a key regulator of reproduction processes. Role of the hormone in transmission of information on metabolic activity and induction of the secretion of gonadotropin-releasing hormone (GnRH) by the hypothalamus that determines gestation processes involving fertilization, placentation, fetal development, and child birth is considered. The literature data on molecular mechanisms and effects of kisspeptin on reproductive system including puberty initiation are summarized and analyzed. In addition, attention is paid to hormone-mediated changes in the cardiovascular system in pregnant women. For the first time, the review examines the effect of kisspeptin on functional activity of immune system cells presenting molecular mechanisms of the hormone signal transduction on the level of lymphoid cells that lead to the immune tolerance induction. In conclusion, a conceptual model is presented that determines the role of kisspeptin as an integrator of reproductive and immune functions during pregnancy.

The kisspeptin system in domestic animals: what we know and what we still need to understand of its role in reproduction

The discovery of the kisspeptin (Kp) system stirred a burst of research in the field of reproductive neuroendocrinology. In the last 15 yr, the organization and activity of the system, including its neuroanatomical structure, its major physiological functions, and its main pharmacological properties, were outlined. To this endeavor, the use of genetic tools to delete and to restore Kp system functionality in a specific tissue was essential. At present, there is no question as to the key role of the Kp system in mammalian reproduction. However, easily applicable genetic manipulations are unavailable for domestic animals. Hence, many essential details on the physiological mechanisms underlying its action on domestic animals require further investigation. The potentially different effects of the various Kp isoforms, the precise anatomical localization of the Kp receptor, and the respective role played by the 2 main populations of Kp cells in different species are only few of the questions that remain unanswered and that will be illustrated in this review. Furthermore, the application of synthetic pharmacologic tools to manipulate the Kp system is still in its infancy but has produced some interesting results, suggesting the possibility of developing new methods to manage reproduction in domestic animals. In spite of a decade and a half of intense research effort, much work is still required to achieve a comprehensive understanding of the influence of the Kp system on reproduction. Furthermore, Kp system ramifications in other physiological functions are emerging and open new research perspectives.

Circuit-level analysis identifies target genes of sex steroids in ewe seasonal breeding

Thyroid hormone (TH) and estradiol (E2) direct seasonal switches in ovine reproductive physiology. In sheep, as in other mammals and birds, control of thyrotropin (TSH) production by the pars tuberalis (PT) links photoperiod responsiveness to seasonal breeding. PT-derived TSH governs opposite seasonal patterns of the TH deiodinases Dio2/Dio3 expression in tanycytes of the neighboring medio-basal hypothalamus (MBH), which explain the key role of TH. We recently used RNA-Seq to identify seasonal markers in the MBH and define the impact of TH. This impact was found to be quite limited, in terms of number of target genes, and very restricted with regards to neuroanatomical location, as TH specifically impacts genes expressed in tanycytes and hypothalamus, not in the PT. Here we address the impact of E2 on these seasonal markers, which are specifically expressed in either PT, tanycytes or hypothalamus. We also investigate if progesterone (P4) may be involved in timing the seasonal transition to anestrus. Our analysis provides circuit-level insights into the impact of sex steroids on the ewe seasonal breeding cycle. First, seasonal gene expression in the PT is independent of the sex steroid status. The fact that seasonal gene expression in the PT is also TH-independent strengthens the view that the PT is a circannual timer. Second, select tanycytic markers display some level of responsiveness to E2 and P4, which indicates another potential level of feedback control by sex steroids. Third, Kiss1 neurons of the arcuate nucleus are responsive to both TH and E2, which places them at the crossroads of photoperiodic transduction pathway and sex steroid feedback. This provides strong support to the concept that these Kiss1 neurons are pivotal to the long-recognized "seasonal switch in the ability of E2 to exert negative feedback", which drives seasonal breeding.

Expression of Kisspeptin and its receptor in the hypothalamus of cyclic and acyclic buffalo (Bubalus bubalis)

Kisspeptin (Kiss1), neurokinin-B (NKB) and dynorphin (Dyn) neurons regulate the surge and pulsatile centres of gonadotropin releasing hormone (GnRH) in the hypothalamus and are modulated by the ovarian steroids. Accordingly, we studied the temporospatial expression of Kiss1, its receptor and other genes that regulate GnRH in the preoptic area (POA) and arcuate (ARC) regions of hypothalamus at different phases of bubaline estrous cycle. Brain of buffalo (n = 32) was collected immediately after exsanguination and categorized into early luteal (EL), mid luteal (ML), follicular (FL) stages and acyclic (n = 8/group). Total RNA was extracted from the POA and ARC of each stage and real time PCR amplification of Kiss1, Kiss1r, NKB, NKB receptor (NKBR), Dyn, Dyn receptor (OPRK1), GnRH1, ERα, PR, LEPR and GHSR was done using GAPDH as endogenous control and acyclic stage as calibrator group. Further, immunolocalization of Kiss1 and Kiss1r was done on the hypothalamus. In the POA, significant up-regulation of Kiss1 and NKB with a concomitant down-regulation of Dyn transcripts was recorded at FL stage. There was, however, down-regulation of Kiss1 and Kiss1r during the EL perhaps due to the loss of estradiol as a consequence of ovulation. On the other hand, in the ARC, there was a significant up-regulation of Kiss1 and Dyn at FL and ML, while NKB transcript was consistently down-regulated at any stage of estrous cycle. In the POA, expression of ERα was not modulated; however, PR was down-regulated in the EL. In the ARC, the ERα expression was significantly up-regulated in the EL, whereas, PR was moderately expressed irrespective of the stage of estrous cycle. The immunolocalization study revealed the presence of Kiss1 and Kiss1r in the POA and ARC in the cyclic buffalo with relative abundance at FL. The transcriptional profile of the genes suggests that there is estrous cycle stage specific expression of Kiss1, Kiss1r and other GnRH regulating genes in the POA and ARC regions of hypothalamus in the buffalo. Up-regulation of Kiss1r in the POA during ML and ARC during EL indicates the involvement of kisspeptinergic system in the regulation of low LH pulse frequencies during the early and mid luteal phases in the cyclic buffalo.

The possible effects of anthropogenic acoustic pollution on marine mammals' reproduction: an emerging threat to animal extinction

For about 119 species of cetaceans and other aquatic animals, sound is the key source of learning about the environment, navigation, communication, foraging, and avoiding predators. However, in the recent era, the introduction of large quantities of anthropogenic noise into the ocean has significantly altered the ocean's acoustic environment. The anthropogenic noises travel very long distances, blanketing enormous areas. This can affect cetaceans, either by direct killing or compromising hearing, navigation, communication, predation, as well as normal behaviors. It has been suggested that acoustic pollution could possibly negatively affect cetacean reproduction, which is harmful for endangered and threatened species. However, it is still unknown how acoustic pollution can suppress cetacean reproduction. This is the first comprehensive review article, which focuses on the possible consequences affecting the reproduction of marine mammals resulting from acoustic pollution.

Hypothalamic epigenetics driving female puberty

Puberty involves a series of morphological, physiological and behavioural changes during the last part of the juvenile period that culminates in the attainment of fertility. The activation of the pituitary-gonadal axis by increased hypothalamic secretion of gonadotrophin-releasing hormone (GnRH) is an essential step in the process. The current hypothesis postulates that a loss of transsynaptic inhibition and a rise in excitatory inputs are responsible for the activation of GnRH release. Similarly, a shift in the balance in the expression of puberty activating and puberty inhibitory genes exists during the pubertal transition. In addition, recent evidence suggests that the epigenetic machinery controls this genetic balance, giving rise to the tantalising possibility that epigenetics serves as a relay of environmental signals known for many years to modulate pubertal development. Here, we review the contribution of epigenetics as a regulatory mechanism in the hypothalamic control of female puberty.

Kisspeptin-10 Induces β-Casein Synthesis via GPR54 and Its Downstream Signaling Pathways in Bovine Mammary Epithelial Cells

Kisspeptins (Kps) play a key role in the regulation of GnRH axis and as an anti-metastasis agent by binding with GPR54. Recently, we observed that the expression of GPR54 was higher in the lactating mammary tissues of dairy cows with high-quality milk (0.81 ± 0.13 kg/day of milk protein yield; 1.07 ± 0.18 kg/day of milk fat yield) than in those with low-quality milk (0.51 ± 0.14 kg/day of milk protein yield; 0.67 ± 0.22 kg/day of milk fat yield). We hypothesized that Kp-10 might regulate the milk protein, β-casein (CSN2) synthesis via GPR54 and its downstream signaling. First, we isolated the bovine mammary epithelial cells (bMECs) from lactating Holstein dairy cows, and treated them with different concentrations of Kp-10. Compared with the control cells, the synthesis of CSN2 is significantly increased at a concentration of 100 nM of Kp-10. In addition, the increased effect of CSN2 synthesis was blocked when the cells were pre-treated with the selective inhibitor of GPR54 Peptide-234 (P-234). Mechanistic study revealed that Kp-10 activated ERK1/2, AKT, mTOR and STAT5 in bMECs. Moreover, inhibiting ERK1/2, AKT, mTOR and STAT5 with U0126, MK2206, Rapamycin and AG490 could block the effects of Kp-10. Together, these results demonstrate that Kp-10 facilitates the synthesis of CSN2 via GPR54 and its downstream signaling pathways mTOR, ERK1/2, STAT5 and AKT.

Mapping of KNDy neurons and immunohistochemical analysis of the interaction between KNDy and substance P neural systems in goat

A population of neurons in the arcuate nucleus (ARC) coexpresses kisspeptin, neurokinin B (NKB), and dynorphin, and therefore they are referred to as KNDy neurons. It has been suggested that KNDy neurons participate in several brain functions, including the control of reproduction. The present study aimed to advance our understanding of the anatomy of the KNDy neural system. We first produced an antiserum against goat kisspeptin. After confirming its specificity, the antiserum was used to histochemically detect kisspeptin-positive signals. Using the colocalization of kisspeptin and NKB immunoreactivity as a marker for KNDy neurons, we mapped distributions of their cell somata and fibers in the whole brain (except the cerebellum) of ovariectomized (OVX) goats. KNDy neuronal somata were distributed throughout the ARC, and were particularly abundant in its caudal aspect. KNDy neuronal fibers projected into several areas within the septo-preoptic-hypothalamic continuum, such as the ARC, median eminence, medial preoptic nucleus, and bed nucleus of the stria terminalis. Kisspeptin immunoreactivity was not found outside of the continuum. We then addressed to the hypothesis that substance P (SP) is also involved in the KNDy neural system. Double-labeling immunohistochemistry for kisspeptin and SP revealed that KNDy neurons did not coexpress SP, but nearly all of the KNDy neuronal somata were surrounded by fibers containing SP in the OVX goats. The present results demonstrate anatomical evidence for a robust association between the KNDy and SP neural systems.

Effect of kisspeptin on in vitro maturation of sheep oocytes

Aim:

The aim of this study was to investigate the effect of kisspeptin (KP) on in vitro maturation (IVM) of sheep oocytes aspirated from the ovaries collected from slaughterhouse.

Materials and Methods:

Two different experiments were conducted to investigate the effect of KP (5, 10 and 15 µg/ml) alone (experiment 1) or in combination with follicle-stimulating hormone (FSH), luteinizing hormone (LH), and Estradiol (E₂) (experiment 2) on IVM of sheep oocytes. Tissue culture medium 199 supplemented with Gentamicin was used as control medium. Good quality oocytes were randomly allocated into different IVM media and cultured at 38.5°C in 5% CO₂ under humidified atmosphere for 24 h. The oocytes were evaluated for their cumulus cell expansion (CCE) and extrusion of the 1^st polar body (PB) at the end of maturation.

Results:

The proportion of oocytes showing CCE and extrusion of PB was highest when the oocytes were matured in the medium supplemented with 10 µg/ml of KP. In experiment 2, oocytes were matured in 12 different maturation media (G₁-G₁₂: G₁: Control, G₂: KP alone, G₃: FSH, G₄: FSH+KP, G₅: LH, G₆: LH+KP, G₇: E₂, G₈: E₂+KP, G₉: FSH+LH+E₂, G₁₀: FSH+LH+E₂+KP, G₁₁: FSH+LH+E2+fetal bovine serum (FBS), G₁₂: FSH+LH+E₂+FBS+KP). The proportion of oocytes showing cumulus expansion and PB extrusion was highest (98.33±1.05 and 89.17±2.38) when they were matured in FSH+LH+E₂+FBS+KP (G₁₂) and was significantly higher than other groups. The proportion of CCE and extrusion of PB was significantly increased when KP was supplemented to FSH and E₂, but no effect was observed with LH. The maturation rates were significantly increased when FSH, LH, and E₂ (G₉) containing media were additionally supplemented with KP (G₁₀).

Conclusion:

This study demonstrated that the addition of KP (10 µg/ml) to the FSH, LH, and E₂ supplemented media would enhance the sheep oocyte maturation in vitro.

Tumor Necrosis Factor-α Impairs Kisspeptin Signaling in Human Gonadotropin-Releasing Hormone Primary Neurons

CONTEXT

Inflammatory pathways may impair central regulatory networks involving gonadotropin-releasing hormone (GnRH) neuron activity. Studies in humans are limited by the lack of human GnRH neuron cell lines.

OBJECTIVE

To establish an in vitro model of human GnRH neurons and analyze the effects of proinflammatory cytokines.

DESIGN

The primary human fetal hypothalamic cells (hfHypo) were isolated from 12-week-old fetuses. Responsiveness to kisspeptin, the main GnRH neurons' physiological regulator, was evaluated for biological characterization. Tumor necrosis factor alpha (TNF-α) was used as a proinflammatory stimulus. Main Outcome Measures: Expression of specific GnRH neuron markers by quantitative reverse transcription-polymerase chain reaction, flow cytometry, and immunocytochemistry analyses; and GnRH-releasing ability and electrophysiological changes in response to kisspeptin.

RESULTS

The primary hfHypo showed a high percentage of GnRH-positive cells (80%), expressing a functional kisspeptin receptor (KISS1R) and able to release GnRH in response to kisspeptin. TNF-α exposure determined a specific inflammatory intracellular signaling and reduced GnRH secretion, KISS1R expression, and kisspeptin-induced depolarizing effect. Moreover, hfHypo possessed a primary cilium, whose assembly was inhibited by TNF-α.

CONCLUSION

The hfHypo cells represent a novel tool for investigations on human GnRH neuron biology. TNF-α directly affects GnRH neuron function by interfering with KISS1R expression and ciliogenesis, thereby impairing kisspeptin signaling.

Unaltered Hypothalamic Metabolic Gene Expression in Kiss1r Knockout Mice Despite Obesity and Reduced Energy Expenditure

Kisspeptin controls reproduction by stimulating gonadotrophin-releasing hormone neurones via its receptor Kiss1r. Kiss1r is also expressed other brain areas and in peripheral tissues, suggesting additional nonreproductive roles. We recently determined that Kiss1r knockout (KO) mice develop an obese and diabetic phenotype. In the present study, we investigated whether Kiss1r KOs develop this metabolic phenotype as a result of alterations in the expression of metabolic genes involved in the appetite regulating system of the hypothalamus, including neuropeptide Y (Npy) and pro-opiomelanocortin (Pomc), as well as leptin receptor (Lepr), ghrelin receptor (Ghsr), and melanocortin receptors 3 and 4 (Mc3r, Mc4r). Body weights, leptin levels and hypothalamic gene expression were measured in both gonad-intact and gonadectomised (GNX) mice at 8 and 20 weeks of age that had received either normal chow or a high-fat diet. We detected significant increases in Pomc expression in gonad-intact Kiss1r KO mice at 8 and 20 weeks, although there were no alterations in the other metabolic-related genes. However, the Pomc increases appeared to reflect genotype differences in circulating sex steroids, because GNX wild-type and Kiss1r KO mice exhibited similar Pomc levels, along with similar Npy levels. The altered Pomc gene expression in gonad-intact Kiss1r KO mice is consistent with previous reports of reduced food intake in these mice and may serve to increase the anorexigenic drive, perhaps compensating for the obese state. However, the surprising overall lack of changes in any of the hypothalamic metabolic genes in GNX KO mice suggests that the aetiology of obesity in the absence of kisspeptin signalling may reflect peripheral rather than central metabolic impairments.

Relationships between leptin, KiSS-1/GPR54 expression and TSH secretion from pituitary cells of pubertal ewes in vitro

Kisspeptin and leptin play a crucial role in the puberty of sheep as they initiate the activity of hypothalamic-pituitary-ovarian axis. Also hormones of thyrotropic axis are probably involved in this process. The aim of study was to analyze the impact of leptin on kisspeptin-10 secretion as well as kisspeptin-1 and G protein-coupled receptor (GPR54) mRNA expression in pituitary cells of pubertal ewes in vitro. The influence of kisspeptin on TSH secretion was also examined. Cells were cultured in McCoy's 5A medium without hormones; with 10(-10)-10(-5)M of leptin; with 10(-11)-10(-5)M of kisspeptin-10; with peptide 234 (10(-7)M, antagonist of GPR54) or 10(-11)-10(-5)M of kisspeptin-10 and peptide 234. Then, kisspeptin-10 and TSH secretion as well as KiSS-1 and GPR54 expression were analyzed. We found that leptin directly affected kisspeptin-10 secretion and kisspeptin-1/GPR54 expression in pituitary cells of pubertal ewes. Kisspeptin-10 did not change TSH secretion, except exerting a short-term influence after 2h.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

Reproduction and beyond, kisspeptin in ruminants

Kisspeptin (Kp) is synthesized in the arcuate nucleus and preoptic area of the hypothalamus and is a regulator of gonadotropin releasing hormone in the hypothalamus. In addition, Kp may regulate additional functions such as increased neuropeptide Y gene expression and reduced proopiomelanocortin (POMC) gene expression in sheep. Other studies have found a role for Kp to release growth hormone (GH), prolactin and luteinizing hormone (LH) from cattle, rat and monkey pituitary cells. Intravenous injection of Kp stimulated release LH, GH, prolactin and follicle stimulating hormone in some experiments in cattle and sheep, but other studies have failed to find an effect of peripheral injection of Kp on GH release. Recent studies indicate that Kp can stimulate GH release after intracerebroventricular injection in sheep at doses that do not release GH after intravenous injection. These studies suggest that Kp may have a role in regulation of both reproduction and metabolism in sheep. Since GH plays a role in luteal development, it is tempting to speculate that the ability of Kp to release GH and LH is related to normal control of reproduction.

Epigenetic regulation of female puberty

Substantial progress has been made in recent years toward deciphering the molecular and genetic underpinnings of the pubertal process. The availability of powerful new methods to interrogate the human genome has led to the identification of genes that are essential for puberty to occur. Evidence has also emerged suggesting that the initiation of puberty requires the coordinated activity of gene sets organized into functional networks. At a cellular level, it is currently thought that loss of transsynaptic inhibition, accompanied by an increase in excitatory inputs, results in the pubertal activation of GnRH release. This concept notwithstanding, a mechanism of epigenetic repression targeting genes required for the pubertal activation of GnRH neurons was recently identified as a core component of the molecular machinery underlying the central restraint of puberty. In this chapter we will discuss the potential contribution of various mechanisms of epigenetic regulation to the hypothalamic control of female puberty.

Effect of Peripheral Administration of Kisspeptin-10 on Dynamic LH Secretion in Prepubertal Ewes

The aim of the present study was to clarify the effect of kisspeptin-10 on LH secretion in prepubertal ewes. In experiment 1, prepubertal ewes fitted with indwelling jugular catheters were randomly assigned to receive 0, 0.5, 1 or 2 mg of kisspeptin-10 dissolved in saline, and serial blood samples were collected at 15-min intervals for 180 min to analyze the response curves of LH after injection. In experiment 2, prepubertal ewes fitted with indwelling jugular catheters were injected with 0 or 1 mg of kisspeptin-10 dissolved in saline and the injection was repeated 3 times at 1 h interval and serial blood samples were collected at 15-min intervals for 210 min to analyze the response curves of LH after injection. The results showed that single intravenous administration of 0.5, 1 and 2 mg of kisspeptin-10 all could significantly increased LH secretion in prepubertal ewes, and the effect of 1 and 2 mg of kisspeptin-10 on LH secretion was higher than that of 0.5 mg group. The results also showed that repeated intravenous administration of kisspeptin-10 could effectively increase LH secretion and repeated administration did not influence the effect of kisspeptin-10 on LH secretion in prepubertal ewe. In conclusion, the present study indicated that single or repeated intravenous administration of kisspeptin-10 could effectively increase LH secretion in prepubertal ewes.

The kisspeptin-GnRH pathway in human reproductive health and disease

BACKGROUND

The discovery of kisspeptin as key central regulator of GnRH secretion has led to a new level of understanding of the neuroendocrine regulation of human reproduction. The related discovery of the kisspeptin-neurokinin B-dynorphin (KNDy) pathway in the last decade has further strengthened our understanding of the modulation of GnRH secretion by endocrine, metabolic and environmental inputs. In this review, we summarize current understanding of the physiological roles of these novel neuropeptides, and discuss the clinical relevance of these discoveries and their potential translational applications.

METHODS

A systematic literature search was performed using PUBMED for all English language articles up to January 2014. In addition, the reference lists of all relevant original research articles and reviews were examined. This review focuses mainly on published human studies but also draws on relevant animal data.

RESULTS

Kisspeptin is a principal regulator of the secretion of gonadotrophins, and through this key role it is critical for the onset of puberty, the regulation of sex steroid-mediated feedback and the control of adult fertility. Although there is some sexual dimorphism, both neuroanatomically and functionally, these functions are apparent in both men and women. Kisspeptin acts upstream of GnRH and, following paracrine stimulatory and inhibitory inputs from neurokinin B and dynorphin (KNDy neuropeptides), signals directly to GnRH neurones to control pulsatile GnRH release. When administered to humans in different isoforms, routes and doses, kisspeptin robustly stimulates LH secretion and LH pulse frequency. Manipulation of the KNDy system is currently the focus of translational research with the possibility of future clinical application to regulate LH pulsatility, increasing gonadal sex steroid secretion in reproductive disorders characterized by decreased LH pulsatility, including hypothalamic amenorrhoea and hypogonadotropic hypogonadism. Conversely there may be scope to reduce the activity of the KNDy system to reduce LH secretion where hypersecretion of LH adds to the phenotype, such as in polycystic ovary syndrome.

CONCLUSIONS

Kisspeptin is a recently discovered neuromodulator that controls GnRH secretion mediating endocrine and metabolic inputs to the regulation of human reproduction. Manipulation of kisspeptin signalling has the potential for novel therapies in patients with pathologically low or high LH pulsatility.

Current and future applications of GnRH, kisspeptin and neurokinin B analogues

Reproductive hormones affect all stages of life from gamete production, fertilization, fetal development and parturition, neonatal development and puberty through to adulthood and senescence. The reproductive hormone cascade has, therefore, been the target for the development of numerous drugs that modulate its activity at many levels. As the central regulator of the cascade, gonadotropin-releasing hormone (GnRH) agonists and antagonists have found extensive applications in treating a wide range of hormone-dependent diseases, such as precocious puberty, prostate cancer, benign prostatic hyperplasia, endometriosis and uterine fibroids, as well as being an essential component of in vitro fertilization protocols. The neuroendocrine peptides that regulate GnRH neurons, kisspeptin and neurokinin B, have also been identified as therapeutic targets, and novel agonists and antagonists are being developed as modulators of the cascade upstream of GnRH. Here, we review the development and applications of analogues of the major neuroendocrine peptide regulators of the reproductive hormone cascade: GnRH, kisspeptin and neurokinin B.

Kisspeptin as a link between metabolism and reproduction: evidences from rodent and primate studies

Changes in metabolic status gate reproductive activity by still incompletely deciphered mechanisms. Many neuropeptides have been shown to be involved in restraining hypothalamic gonadotropin releasing hormone (GnRH) release under conditions of negative energy balance. Broadly, on the basis of their effect on feeding, these can be grouped as orexigenic and anorexigenic neuropeptides. Reciprocally correlated, in response to changes in systemic concentrations of metabolic hormones, the secretion of orexigenic neuropeptides increases while that of anorexigenic neuropeptides decreases during conditions of food restriction. Recently, kisspeptin signaling in hypothalamus has appeared as a pivotal regulator of the GnRH pulse generator. Kisspeptin apparently does not affect feeding, but in light of accumulating data, it has emerged as one of the major conduits in relaying body metabolic status information to GnRH neurons. The present review examines such data obtained from rodent and primate models, which suggest kisspeptin-Kiss1r signaling as a possible pathway providing a link between metabolism and reproduction.

Intratesticular action of kisspeptin in rhesus monkey (Macaca mulatta)

Kisspeptin-Kiss1R signalling in mammals has been implicated as an integral part of the reproductive cascade. Kisspeptinergic neurons upstream of GnRH neurons are involved in the activation of the hypothalamic GnRH pulse generator during pubertal onset. Thus, the major research focus has been on the central effects of kisspeptin. The demonstration of the presence of KissR expression in human testes suggests additional unknown actions of kisspeptin-KISS1R signalling at the distal component of the male reproductive axis. Here we explored the impact of kisspeptin at the testis in the adult male rhesus monkey. We employed the clamped monkey model to assess the intratesticular actions of kisspeptin. Plasma testosterone and LH levels were monitored in four adult male monkeys. The peripheral administration of human kisspeptin-10 (50 μg, iv bolus) caused a single LH pulse, which was followed by a robust increase in plasma testosterone levels sustained for at least 180 min. This response was abolished when kisspeptin was administered to GnRH receptor antagonist (acyline) pre-treated animals. However, kisspeptin administration significantly (P < 0.005) elevated hCG-stimulated testosterone levels in acyline pre-treated monkeys when compared with saline+ hCG treatment. These results revealed a novel peripheral facet of kisspeptin signalling.

Kisspeptin as a master player in the central control of reproduction in mammals: an overview of kisspeptin research in domestic animals

The hypothalamo-pituitary-gonadal (HPG) axis is the regulatory system for reproduction in mammals. Because secretion of gonadotropin-releasing hormone (GnRH) into the portal vessels is the final step at which the brain controls gonadal activities, the GnRH neuronal system had been thought to be central to the HPG axis. A newly discovered neural peptide, kisspeptin, has opened a new era in reproductive neuroendocrinology. As shown in a variety of mammals, kisspeptin is a potent endogenous secretagogue of GnRH, and the kisspeptin neuronal system governs both the pulsatile GnRH secretion that drives folliculogenesis, spermatogenesis and steroidogenesis, and the GnRH surge that triggers ovulation in females. The kisspeptin neuronal system is therefore considered a master player in the central control of mammalian reproduction, and kisspeptin and related substances could therefore be valuable for the development of novel strategies for the management of fertility in farm animals. To this end, the present review aimed to summarize the current research on kisspeptin signaling with a focus on domestic animals such as sheep, goats, cattle, pigs and horses.

Neurochemical characterization and sexual dimorphism of projections from the brain to abdominal and subcutaneous white adipose tissue in the rat

Retroperitoneal white adipose tissue (rWAT) and subcutaneous (inguinal) white adipose tissue (iWAT) are both innervated and regulated by sympathetic efferents, but the distribution and identity of the cells in the brain that regulate sympathetic outflow are poorly characterized. Our aim was to use two isogenic strains of a neurotropic virus (pseudorabies, Bartha) tagged with either green or red fluorescent reporters to identify cells in the brain that project to rWAT and/or iWAT. These viruses were injected into separate WAT depots in male and female Sprague Dawley rats. Retrogradely labeled neurons in the CNS were characterized by immunohistochemistry and PCR. For the latter, laser capture of individual virally labeled neurons was used. All virally labeled brain regions contained neurons projecting to either and both WAT depots. Neurons to abdominal fat were the most abundant in males, whereas females contained a greater proportion of neurons to subcutaneous via private lines and collateral branches. Retrogradely labeled neurons directed to WAT expressed estrogen receptor-α (ERα), and fewer neurons to subcutaneous WAT expressed ERα in males. Regardless of sex, projections from the arcuate nucleus were predominantly from pro-opiomelanocortin cells, with a notable lack of projections from agouti-related protein-expressing neurons. Within the lateral hypothalamus, neurons directed to rWAT and iWAT expressed orexin and melanin-concentrating hormone (MCH), but male rats had a predominance of MCH directed to iWAT. In conclusion, the neurochemical substrates that project through polysynaptic pathways to iWAT and rWAT are different in male and female rats, suggesting that metabolic regulation of rWAT and iWAT is sexually dimorphic.

Estrogenic regulation of Kiss1 mRNA variants in Hatano rats

Differences in reproductive endocrinology distinguish Hatano high-avoidance animals (HAA) from low-avoidance animals (LAA). Compared to HAA rats, female LAA rats secrete low levels of basal luteinizing hormone (LH) and a reduced LH surge. To investigate the underlying cause of the differences between the two strains, levels of the following mRNAs were measured in the hypothalamus of intact and ovariectomized (OVX) females treated with vehicle control or estradiol-17β (E2): gonadotropin-releasing hormone (Gnrh), newly isolated rat kisspeptin (Kiss)1 mRNA variant-1 (Kiss1V1) and variant-2 (Kiss1V2) and estrogen receptor (Er) α. In OVX-HAA rats, the levels of Gnrh mRNA in the preoptic area (POA) 30 h after E2 treatment were significantly higher than in OVX-LAA rats. For HAA rats, the levels of Kiss1V1 and Kiss1V2 mRNA in the anteroventral periventricular nucleus (AVPV) were significantly higher in the E2-treated group than in the vehicle-treated group. In the arcuate nucleus (Arc) of HAA rats, Kiss1V1 and Kiss1V2 expression was significantly lower in E2-treated females compared to vehicle-treated females. Kiss1V2 expression was significantly higher than Kiss1V1 expression in intact HAA rats. In E2-treated OVX-LAA rats, there were no changes in the expression levels of Gnrh, Kiss1V1 or Kiss1V2. In intact LAA rats, no differences were observed in the expression levels of Kiss1V1 or Kiss1V2 in the AVPV, but the expression levels of these mRNAs in the Arc were significantly lower in E2-treated OVX-LAA rats. Additionally, no strain differences were observed for Erα mRNA expression in either the AVPV or Arc. These results indicate that the failure of estrogenic regulation of GnRH neurons in the POA and of kisspeptin neurons in the AVPV of LAA rats causes low LH secretion and reduced reproductive function.

Kisspeptin and seasonality of reproduction

Wild and domesticated species display seasonality in reproductive function, controlled predominantly by photoperiod. Seasonal alterations in breeding status are caused by changes in the secretion of gonadotropin-releasing hormone (GnRH) that are mediated by upstream neuronal afferents that regulate the GnRH cells. In particular, kisspeptin appears to play a major role in seasonality of reproduction, transducing the feedback effect of gonadal steroids as well as having an independent (nonsteroid dependent) circannual rhythm. A substantial body of data on this issue has been obtained from studies in sheep and hamsters and this is reviewed here in detail. Kisspeptin function is upregulated during the breeding season in sheep, stimulating reproductive function, but contradictory data are found in Siberian and Syrian hamsters. The relative quiescence of kisspeptin cells in the nonbreeding season can be counteracted by administration of the peptide, leading to activation of reproductive function. Although there is a major role for melatonin in the transduction of photoperiod to the reproductive system, kisspeptin cells do not appear to express the melatonin receptor, so the means by which seasonality changes the level of kisspeptin activity remains unknown.

Negative fetal FSH/LH regulation in late pregnancy is associated with declined kisspeptin/KISS1R expression in the tuberal hypothalamus

OBJECTIVE

Kisspeptins were recently identified as hypothalamic neuropeptides that control GnRH release at pubertal onset and in adults via the activation of KISS-1 receptor (KISS1R). Here, we have tested whether the fetal activation of the gonadotropic axis is related to the hypothalamic expression of kisspeptins and KISS1R.

DESIGN AND METHODS

LH and FSH levels were measured in fetal blood from the 15th week of gestation (WG) to birth. Immunohistochemistry was performed on the hypothalamus and pituitary at different developmental stages.

RESULTS

Immunostaining for kisspeptins and KISS1R appeared for both proteins in the hypothalamus as early as 15 WG and subsequently increased until 30-31 WG. In the meantime, serum LH and FSH levels decreased from postmenopausal levels in females or adult levels in males to very low levels. At full term, kisspeptin and KISS1R staining was still observed in the paraventricular, supraoptic, and ventromedial hypothalamic nuclei but not in the arcuate nucleus or median eminence. Hypothalamic GnRH staining was observed at 15 WG and did not vary after the first trimester. In an arhinencephalic fetus of 23 WG, very few GnRH neurons were observed in the hypothalamus, but serum FSH and LH levels were postmenopausal.

CONCLUSION

Serum LH and FSH levels are independent from GnRH and kisspeptins at midgestation, and then GnRH progressively controls LH and FSH release. A shift from kisspeptin-independent to kisspeptin-dependent GnRH-induced LH and FSH release seems to occur after 30-31 WG. In addition to their function in adults, kisspeptins are also the master regulators of the gonadotropic axis activation in the fetus.

Hypothalamic galanin-like peptide rescues the onset of puberty in food-restricted weanling rats

Galanin-like peptide (GALP) is a known mediator of metabolism and reproduction; however, the role that GALP plays in the onset of puberty is unknown. First, we tested the hypothesis that central GALP administration could rescue puberty in food-restricted weanling rats. GALP treatment in food-restricted rats of both sexes rescued the timing of the onset of puberty to that seen in ad lib. fed controls. Second, we tested whether GALP translation knocked-down in ad lib. fed, prepubertal rats would alter the timing of puberty. Knock-down females, but not males, showed a significant (P < 0.01) delay in the onset of puberty compared to controls. Third, we sought evidence that the role of GALP in pubertal onset is mediated by the kisspeptin system. In situ hybridisation analyses showed a significant (P < 0.01) reduction in Kiss1 mRNA within the hypothalamic arcuate nucleus in food-restricted rats compared to ad lib. fed controls and this reduction was prevented with i.c.v. GALP administration. Furthermore, analyses of Fos-immunoreactivity (-IR) after i.c.v. GALP treatment did not elicit Fos-IR within any kisspeptin neurones, nor are GALP and kisspeptin peptides or mRNA colocalised. These data demonstrate that hypothalamic GALP infusion maintained the onset of puberty in food-restricted weanling rats, although probably not via direct innervation of kisspeptin neurones.

Disrupted organization of RFamide pathways in the hypothalamus is associated with advanced puberty in female rats neonatally exposed to bisphenol A

Hypothalamic neurons, which produce the kisspeptin family of peptide hormones (Kp), are critical for initiating puberty and maintaining estrous cyclicity by stimulating gonadotropin-releasing hormone (GnRH) release. Conversely, RFamide-related peptide-3 (RFRP3) neurons inhibit GnRH activity. It has previously been shown that neonatal exposure to bisphenol A (BPA) can alter the timing of female pubertal onset and induce irregular estrous cycles or premature anestrus. Here we tested the hypothesis that disrupted ontogeny of RFamide signaling pathways may be a mechanism underlying advanced puberty. To test this, we used a transgenic strain of Wistar rats whose GnRH neurons express enhanced green fluorescent protein. Pups were exposed by daily subcutaneous injection to vehicle, 17beta-estradiol (E2), 50 μg/kg BPA, or 50 mg/kg BPA, from Postnatal Day (PND) 0 through PND 3, and then cohorts were euthanized on PNDs 17, 21, 24, 28, and 33 (5-8 animals per age per exposure; males were collected on PNDs 21 and 33). Vaginal opening was advanced by E2 and 50 μg/kg BPA. On PND 28, females exposed to E2 and 50 μg/kg BPA had decreased RFRP-3 fiber density and contacts on GnRH neurons. RFRP3 perikarya were also decreased in females exposed to 50 μg/kg BPA. Data suggest that BPA-induced premature puberty results from decreased inhibition of GnRH neurons.

Co-localisation of kisspeptin with galanin or neurokinin B in afferents to mouse GnRH neurones

The gonadotrophin-releasing hormone (GnRH) secreting neurones, which form the final common pathway for the central regulation of reproduction, are directly targeted by kisspeptin (KP) via the G protein-coupled receptor, GPR54. In these multiple labelling studies, we used ovariectomised mice treated with 17β-oestradiol (OVX + E(2)) or vehicle (OVX + oil) to determine: (i) the ultrastructural characteristics of KP-immunoreactive (IR) afferents to GnRH neurones; (ii) their galanin or neurokinin B (NKB) content; and (iii) the co-expression of galanin or NKB with KP in the two major subpopulations of KP neurones located in the rostral periventricular area of the third ventricle (RP3V) and the arcuate nucleus (Arc). Electron microscopic investigation of the neuronal juxtapositions revealed axosomatic and axodendritic synapses; these showed symmetrical or asymmetrical characteristics, suggesting a phenotypic diversity of KP afferents. Heterogeneity of afferents was also demonstrated by differential co-expression of neuropeptides; in OVX + E(2) mice, KP afferents to GnRH neurones showed galanin-immunoreactivity with an incidence of 22.50 ± 2.41% and NKB-immunoreactivity with an incidence of 5.61 ± 2.57%. In OVX + oil animals, galanin-immunoreactivity in the KP afferents showed a major reduction, appearing in only 5.78 ± 1.57%. Analysis for co-localisation of galanin or NKB with KP was extended to the perikaryal level in animal models, which showed the highest KP incidence; these were OVX + E(2) females for the RP3V and OVX + oil females for the ARC. In the RP3V of colchicine-treated OVX + E(2) animals, 87.84 ± 2.65% of KP-IR neurones were galanin positive. In the Arc of the colchicine-treated OVX + oil animals, galanin immunoreactivity was detected in only 12.50 ± 1.92% of the KP expressing neurones. By contrast, the incidence of co-localisation with NKB in the Arc of those animals was 98.09 ± 1.30%. In situ hybridisation histochemistry of sections from OVX + E(2) animals identified galanin message in more than a third of the KP neurones in the RP3V (38.67 ± 11.57%) and in the Arc (42.50 ± 12.52%). These data suggest that GnRH neurones are innervated by chemically heterogeneous KP cell populations, with a small proportion deriving from the Arc group. The presence of galanin within KP axons innervating GnRH neurones and the oestrogen-dependent regulation of that presence add a new dimension to the roles played by galanin in the central regulation of reproduction.

Control of GnRH secretion: one step back

The reproductive system is controlled by gonadotropin releasing hormone (GnRH) secretion from the brain, which is finely modulated by a number of factors including gonadal sex steroids. GnRH cells do not express estrogen receptor α, but feedback is transmitted by neurons that are at least 'one step back' from the GnRH cells. Modulation by season, stress and nutrition are effected by neuronal pathways that converge on the GnRH cells. Kisspeptin and gonadotropin inhibitory hormone (GnIH) neurons are regulators of GnRH secretion, the former being a major conduit for transmission of sex steroid feedback. GnIH cells project to GnRH cells and may play a role in the seasonal changes in reproductive activity in sheep. GnIH also modulates the action of GnRH at the level of the pituitary gonadotrope. This review focuses on the role that kisspeptin and GnIH neurons play, as modulators that are 'one step back' from GnRH neurons.

Polymorphisms of KiSS-1 and GPR54 genes and their relationships with litter size in sheep

The KiSS-1 and GPR54 genes were studied as candidate genes for the prolificacy in sheep. Four pairs of primers were designed to detect single nucleotide polymorphisms of exon 1 of KiSS-1 gene and exon 1, exon 2 and partial exon 5 of GPR54 gene in high fecundity breeds (Small Tail Han and Hu sheep) and low fecundity breeds (Dorset, Texel and Corriedale sheep) by PCR-SSCP. Polymorphisms in exon 1 of KiSS-1 gene were detected in prolific Small Tail Han sheep (AA, AB and BB genotypes) and Hu sheep (AA and CC genotypes), no polymorphism was found in low fecundity sheep breeds (only AA genotype). Polymorphisms in exon 2 of GPR54 gene were detected in prolific Hu sheep (DD and EE genotypes) and no polymorphism was found in prolific Small Tail Han sheep and low fecundity sheep breeds (only DD genotype). No polymorphism was detected in exon 1 and partial exon 5 of GPR54 gene in five sheep breeds. The polymorphic genotypes were sequenced. While compared the BB genotype with the AA genotype, one nucleotide mutation (G1035A) was detected, which resulted in amino acid change, Val25Met. Five nucleotide mutations were detected from AA to CC genotype (C981T, C996T, T997C, C1034G, C1039T), and among them four caused amino acid changes, that is, Arg7Trp, Phe12Leu, Asn24Lys, Ala26Val. While compared the EE genotype with the DD genotype, two nucleotide mutations (T2360C, A2411C) were detected, which gave rise to amino acid changes, Met90Thr and Asp107Ala, respectively. Genotype frequencies of AA, BB and AB were 0.62, 0.05 and 0.33 in Small Tail Han sheep, respectively. The Small Tail Han sheep ewes with genotype BB or AB had 0.88 (P < 0.05) or 0.51 (P < 0.05) lambs more than those with genotype AA; the Small Tail Han sheep ewes with genotype BB had 0.37 (P > 0.05) lambs more than those with genotype AB. These results preliminarily indicated that the KiSS-1 gene may have some association with prolificacy in sheep.

The relationship between pulsatile GnRH secretion and cAMP production in immortalized GnRH neurons

In perifused immortalized GnRH neurons (GT1-7), simultaneous measurements of GnRH and cAMP revealed that the secretory profiles for both GnRH and cAMP are pulsatile. An analysis of GnRH and cAMP pulses in 16 independent experiments revealed that 25% of pulses coincide. Inversion of the peak and nadir levels was found in 33% and random relationship between GnRH and cAMP found in 42% of analyzed pulses. The random relation between GnRH and cAMP pulse resets to synchronous after an inverse relation between pulses occurred during the major GnRH release, indicating that GnRH acts as a switching mechanism to synchronize cAMP and GnRH release in perifused GT1-7 neurons. Activation of GnRH receptors with increasing agonist concentrations caused a biphasic change in cAMP levels. Low nanomolar concentrations increased cAMP production, but at high concentrations the initial increase was followed by a rapid decline to below the basal level. Blockade of the GnRH receptors by peptide and nonpeptide antagonists generated monotonic nonpulsatile increases in both GnRH and cAMP production. These findings indicate that cAMP positively regulates GnRH secretion but does not participate in the mechanism of pulsatile GnRH release.

Neonatal exposure to genistein adversely impacts the ontogeny of hypothalamic kisspeptin signaling pathways and ovarian development in the peripubertal female rat

Neonatal exposure to estrogenic endocrine disrupting compounds (EDCs) can advance pubertal onset and induce premature anestrous in female rats. It was recently discovered that hypothalamic kisspeptin (KISS) signaling pathways are sexually dimorphic and regulate both the timing of pubertal onset and estrous cyclicity. Thus we hypothesized that disrupted sex specific ontogeny of KISS signaling pathways might be a mechanism underlying these EDC effects. We first established the sex specific development of KISS gene expression, cell number and neural fiber density across peripuberty in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC), hypothesizing that the sexually dimorphic aspects of KISS signaling would be most vulnerable to EDCs. We next exposed female rats to the phytoestrogen genistein (GEN, 1 or 10 mg/kg bw), estradiol benzoate (EB, 10 μg), or vehicle from post natal day (P) 0-3 via subcutaneous (sc) injection. Animals were sacrificed on either P21, 24, 28, or 33 (n=5-14 per group at each age). Vaginal opening was significantly advanced by EB and the higher dose of GEN compared to control animals and was accompanied by lower numbers of KISS immunoreactive fibers in the AVPV and ARC. Ovarian morphology was also assessed in all age groups for the presence of multiple oocyte follicles (MOFs). The number of MOFs decreased over time in each group, and none were observed in control animals by P24. MOFs were still present, however, in the EB and 10 mg/kg GEN groups beyond P24 indicating a disruption in the timing of ovarian development.

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

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

Expression of fos and in vivo median eminence release of LHRH identifies an active role for preoptic area kisspeptin neurons in synchronized surges of LH and LHRH in the ewe

We tested the working hypothesis that Fos will identify the critical population of kisspeptin neurons that accompanies the LHRH surge using a synchronized follicular phase model in intact cycling ewes. The model generates an LH surge that starts within a defined 2-h window in a 20-d synchronized cycle. With a modified push-pull cannula in vivo LHRH release from the median eminence was sampled in luteal phase ewes, ewes undergoing an LH surge for 2-4 h, and postsurge animals whose LH surge peaked 10-12 h earlier. In vivo release of LHRH was lower in the luteal and follicular phases than in animals undergoing an LH surge (P < 0.01); it fell to presurge levels after the LH surge. Ewes killed 2-4 h after the surge started, expressed Fos in a large portion of preoptic area (POA) kisspeptin (53.90 ± 4.69%, P < 0.01) and LHRH neurons (48.20 ± 4.49%, P < 0.0001) compared with animals euthanized at any of the other times tested (under <5% of the cells activated). Little Fos activation (under 5%) was observed during any of the times sampled in arcuate (Arc) kisspeptin neurons. The relationship between the number of LHRH neurons and the POA kisspeptin neurons stimulated showed a striking positive correlation with r(2) = 0.68, P = 0.0003, reinforcing the evidence that POA kisspeptin neurons actively participate in the stimulation of LHRH surges.

Plasma levels of kisspeptins in postmenopausal Chinese women do not show substantial elevation

The menopause, defined as the permanent cessation of menstruation resulting from ovarian failure, is characterized by elevated levels of serum gonadotropins. Recent studies have demonstrated that the gonadotropin hypersecretion in postmenopausal women is secondary to increase of KiSS-1 mRNA from the hypothalamus neurons, which encoded kisspeptin peptides. The present study was designed to determine whether plasma kisspeptins levels are altered in postmenopausal women. Blood samples were taken from 145 postmenopausal women, 35 young women and 30 pregnant women control in the first trimester. The plasma concentration of kisspeptins, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and estradiol (E₂) was measured using immunoassay kits. Results indicated that plasma kisspeptins levels in postmenopausal women had higher than those in young women (5.25±0.36; 4.48±0.34 pmol/L), but no significant difference was found between the two groups (p=0.179). Plasma FSH and LH levels were significantly higher in postmenopausal women (124.67±12.78, 57.14±3.57 mIu/mL) than those in young women (9.23±2.78, 7.56±2.71 mIu/mL, p<0.001). However, Plasma kisspeptins levels were not significantly correlated to FSH and LH in postmenopausal women (r=-0.23, 0.324; p=0.927, 0.176, respectively), and also there was no any correlation between plasma kisspeptins and E₂ in postmenopausal women (r=-0.065; p=0.792). Collectively, there was no significant difference in plasma kisspeptins levels between postmenopausal and young women. Our result suggested that kisspeptins' role during menopause might mainly act in central rather than peripheral system and it could not be currently used as a clinical marker for menopause.