KiSS-1 and GPR54 genes are co-expressed in rat gonadotrophs and differentially regulated in vivo by oestradiol and gonadotrophin-releasing hormone

Recurrent spontaneous ovarian hyperstimulation in a young nonpregnant Chinese woman with Rathke cleft cyst and a KISS1R variant: A rare case report and literature review

Unexplained spontaneous ovarian hyperstimulation syndrome (sOHSS) in a nonpregnant young woman is rare, with fewer than five cases documented in the literature. Although four distinct causative types of sOHSS have been identified, some cases remain beyond the scope of our current understanding. A young Chinese woman with sOHSS presented on multiple occasions with sOHSS between the ages of 18.6 and 20.6 years, with acute abdominal discomfort, ascites, hemoconcentration, and pronounced ovarian enlargement coinciding with minor ovulatory anomalies. During the most recent episode, concern regarding a malignant ovarian neoplasm led to emergent unilateral salpingo-oophorectomy. Remarkably, her menstrual cycle normalized after surgery, with no subsequent recurrence of sOHSS. Subsequent diagnostic evaluations identified a Rathke cleft cyst (RCC) in the pituitary gland and a heterozygous mutation in the KISS1R gene. Neither of these findings corresponded with any of the four informally recognized causes of sOHSS, suggesting a hitherto unrecognized pathology. RCCs may cause OHSS by disrupting the endocrine system, while interactions between the kisspeptin system and estradiol may reach a critical threshold, culminating in sOHSS. This case provides important insights into sOHSS and will hopefully spearhead further research into pituitary anomalies and the intricacies of the kisspeptin system. Clinicians are urged to maintain a high level of vigilance for similar presentations and ensure timely and tailored therapeutic interventions.

Kisspeptin and neurokinin B: roles in reproductive health

Kisspeptin and neurokinin B (NKB) play a key role in several physiological processes including in puberty, adult reproductive function including the menstrual cycle, as well as mediating the symptoms of menopause. Infundibular kisspeptin neurons, which coexpress NKB, regulate the activity of gonadotropin-releasing hormone (GnRH) neurons and thus the physiological pulsatile secretion of GnRH from the hypothalamus. Outside of their hypothalamic reproductive roles, these peptides are implicated in several physiological functions including sexual behavior and attraction, placental function, and bone health. Over the last two decades, research findings have considerably enhanced our understanding of the physiological regulation of the hypothalamic-pituitary-gonadal (HPG) axis and identified potential therapeutic applications. For example, recognition of the role of kisspeptin as the natural inductor of ovulation has led to research investigating its use as a safer, more physiological trigger of oocyte maturation in in vitro fertilization (IVF) treatment. Moreover, the key role of NKB in the pathophysiology of menopausal hot flashes has led to the development of pharmacological antagonism of this pathway. Indeed, fezolinetant, a neurokinin 3 receptor antagonist, has recently received Food and Drug Administration (FDA) approval for clinical use to treat menopausal vasomotor symptoms. Here, we discuss the roles of kisspeptin and NKB in human physiology, including in the regulation of puberty, menstrual cyclicity, reproductive behavior, pregnancy, menopause, and bone homeostasis. We describe how perturbations of these key physiological processes can result in disease states and consider how kisspeptin and NKB could be exploited diagnostically as well as therapeutically to treat reproductive disorders.

Kisspeptin control of hypothalamus-pituitary-ovarian functions

The discovery of Kisspeptin (Kiss) has opened a new direction in research on neuroendocrine control of reproduction in vertebrates. Belonging to the RF amide family of peptides, Kiss and its cognate receptor Gpr54 (Kissr) have a long and complex evolutionary history. Multiple forms of Kiss and Kissr are identified in non-mammalian vertebrates, with the exception of birds, and monotreme mammals. However, only a single form of the ligand (KISS1/Kiss1) and receptor (KISS1R/Kiss1r) is retained in higher mammals. Kiss1 is distributed in the hypothalamus-pituitary-gonadal (HPG) axis and its primary function is to stimulate gonadotropin-releasing hormone (GnRH) secretion. Kiss1 neurons are distributed in the rostral periventricular area of the third ventricle (RP3V) and arcuate/infundibular nucleus (ARN/IFN). The ARN/IFN is considered the GnRH pulse generator controlled by steroid negative feedback, and the RP3V neurons is concerned with GnRH surge induced by steroid positive feedback in females. The Kiss1-Kiss1r signaling is important in all aspects of reproduction: puberty onset, maintenance of adult gonadal functions and reproductive aging, and hence assumes therapeutic potentials in the treatment of reproductive dysfunctions and induction of artificial reproduction. This chapter reviews involvement of Kiss1 in the control of the HPG axis functions in female mammals.

Investigation of subfertility in the female Nsmf knockout mouse

OBJECTIVE

To study if a pituitary or ovarian defect contributes to subfertility of the female Nsmf knockout (KO) mouse, an animal model of the hypogonadotropic hypogonadism gene NSMF.

DESIGN

Analysis of hypothalamic, pituitary and ovarian gene expression at baseline, serum gonadotropin levels before and after gonadotropin-releasing hormone (GnRH) stimulation, ovarian response and implantation after superovulation, gonadotropin effects after ovariectomy, and ovarian NSMF protein expression.

SETTING

University research laboratory.

PATIENTS

None; mice were used.

INTERVENTIONS

Gonadotropin-releasing hormone stimulation, superovulation, and ovariectomy in separate experiments.

MAIN OUTCOME MEASURES

Gene expression in the hypothalamus, pituitary, and ovary; ovarian response and implantation after superovulation; serum gonadotropins after GnRH stimulation and ovariectomy; Western blot to measure ovarian NSMF expression.

RESULTS

We found increased hypothalamic Kiss1, Gnrh1, and Jak2 mRNA expression in female Nsmf KO vs. wild type (WT) mice. However, pituitary gonadotropin, and GnRH receptor gene expression was not affected, and serum gonadotropin levels were normal. Gonadotropins increased after ovariectomy for both groups. Baseline Kiss1, Fshr, Prkaca, Prkar1a, and Gdf9 ovarian mRNA expression was increased and Cyp19a1 expression was decreased in Nsmf KO mice, while superovulated Nsmf KO mice had reduced ovarian Kiss1r, Prkar1a, and Fshr mRNA expression, 50% less oocytes, and normal implantation. Western blot demonstrated NSMF protein expression in the ovary of WT mice.

CONCLUSIONS

Altered hypothalamic and ovarian gene expression was demonstrated in female Nsmf KO mice. It is possible that increased hypothalamic Gnrh1 and Kiss1 mRNA expression could compensate for reduced NSMF enabling a normal pituitary gonadotropin response. Impaired superovulation response, altered ovarian gene expression, and decreased number of oocytes indicate ovarian dysfunction, but a uterine factor cannot be excluded. These findings provide an anatomic basis for future mechanistic studies of subfertility in female Nsmf KO mice.

Clinical characteristics of functioning gonadotroph adenoma in women presenting with ovarian hyperstimulation: Audit of UK pituitary centres

OBJECTIVE

Functioning gonadotroph adenomas (FGAs) are rare pituitary tumours stimulating ovarian function with potential life-threatening consequences in women. However, a lack of aggregated clinical experience of FGAs impairs management in affected women. The aim of this study is to present the clinical course of FGA-induced ovarian hyperstimulation syndrome (OHSS) cases as identified by some of the largest UK pituitary endocrine tertiary centres with a view to increasing awareness and improving diagnosis and management of women with FGA.

DESIGN

A retrospective observational study; audit of eight UK regional pituitary centres for cases of FGAs.

SETTING

Specialist neuroendocrine centres in the United Kingdom.

PATIENTS AND MEASUREMENTS

Women diagnosed with FGA-induced OHSS. Description of their clinical course.

RESULTS

Seven cases of FGA were identified in women, all causing OHSS. Mean age was 33.4 years at diagnosis. Abdominal pain, irregular periods, headache, and visual disturbances were reported at presentation by 100%, 71%, 57% and 43% of women, respectively. Three of seven women underwent ovarian surgery before FGA diagnosis. Six women underwent transsphenoidal surgery (TSS) with incomplete tumour resection in five of those, but all showed improvement or resolution in symptoms and biochemistry postoperatively.

CONCLUSION

FGA is a rare cause of spontaneous OHSS. TSS improves clinical and biochemical features of ovarian hyperstimulation in FGAs. Improved awareness of FGA will prevent inappropriate emergency ovarian surgery.

Impact of Ovariectomy on the Anterior Pituitary Gland in Female Rats

Ovariectomy (OVX) causes a depletion of circulating estradiol (E2) and influences hypothalamic kisspeptin neurons, which govern gonadotropin-releasing hormone (GnRH) release and ultimately gonadotropin secretion. In this study, we examined the changes induced by OVX on the anterior pituitary gland in female rats. OVX significantly increased the mRNA expression of gonadotropin α, luteinizing hormone (LH) β, and follicle-stimulating hormone (FSH) β subunits within the pituitary gland compared with control (sham-operated) rats, and this was completely suppressed by E2 supplementation. High-dose dihydrotestosterone supplementation also prevented the OVX-induced increase in the expression of the three gonadotropin subunits. GnRH receptor mRNA expression within the pituitary was significantly increased in OVX rats, and this increase was completely inhibited by E2 supplementation. The mRNA expression of the receptors for adenylate cyclase-activating polypeptide and kisspeptin was unchanged by OVX. Although the mRNA levels of inhibin α, βA, and βB subunits within the pituitary gland were not modulated by OVX, follistatin gene expression within the pituitary gland was increased by OVX, and this increase was completely inhibited by E2 supplementation after OVX. In experiments using a pituitary gonadotroph cell model (LβT2 cells), follistatin itself did not modulate the mRNA expression of gonadotropin LHβ and FSHβ subunits, and the GnRH-induced increase in the expression of these genes was slightly inhibited in the presence of follistatin. Our current observations suggest that OVX induces several characteristic changes in the pituitary gland of rats.

Serum kisspeptin levels mainly depend on ovarian expression of Kiss1 mRNA in female rats

The hypothalamic kisspeptin/KISS1 receptor system is essential for puberty onset and reproductive development. Although serum kisspeptin might be associated with puberty, its levels, according to developmental stage, and its origin still remain unclear. This study evaluated the changes in serum kisspeptin levels during puberty and the corresponding Kiss1 mRNA and protein expression in various organs of female rats to identify the source of serum kisspeptin. Tissues from several organs, including the ovaries and anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) in the hypothalamus, were obtained for assessing Kiss1 mRNA and protein expressions. Serum kisspeptin levels progressively increased with developmental stages until the peripubertal stage. The ovaries showed the highest Kiss1 expression among the organs examined. Next, we explored the changes in serum kisspeptin levels and hypothalamic Kiss1 expression in ovariectomized and estradiol-treated ovariectomized rats. Serum kisspeptin levels decreased regardless of estradiol treatment; Kiss1 expression was enhanced by ovariectomy and estradiol treatment in the ARC, while it was decreased by ovariectomy and enhanced by estradiol in the AVPV, suggesting that serum kisspeptin may be associated with pubertal development and mainly depended on ovarian Kiss1 expression. Thus, serum kisspeptin levels are associated with puberty and may serve as a downstream marker of ovarian reproductive function.

Kisspeptin Modulation of Reproductive Function

Kisspeptin is a peptide expressed mainly in the infundibular nucleus of the hypothalamus. Kisspeptin plays a crucial role in the regulation of reproductive functions. It is regarded as the most important factor responsible for the control of the hypothalamic–pituitary–gonadal axis, the onset of puberty, and the regulation of menstruation and fertility. Kisspeptin activity influences numerous processes such as steroidogenesis, follicular maturation, ovulation, and ovarian senescence. The identification of kisspeptin receptor mutations that cause hypogonadotropic hypogonadism has initiated studies on the role of kisspeptin in puberty. Pathologies affecting the neurons secreting kisspeptin play a major role in the development of PCOS, functional hypothalamic amenorrhea, and perimenopausal vasomotor symptoms. Kisspeptin analogs (both agonists and antagonists), therefore, may be beneficial as therapy in those afflicted with such pathologies. The aim of this review is to summarize the influence of kisspeptin in the physiology and pathology of the reproductive system in humans, as well as its potential use in therapy.

Functioning gonadotroph adenomas in premenopausal women: clinical and molecular characterization and review of the literature

PURPOSE

To summary the clinical features of premenopausal women with functioning gonadotroph adenomas (FGAs) and preliminarily explore their molecular characterization.

METHODS

12 premenopausal females with FGAs in our center were retrospectively analyzed. Previously reported cases were also summarized. The patients were clinically divided into FSH- or LH-predominant types according to their preoperative serum FSH/LH ratio. The expressions of related genes in the tumor tissues of female FGAs, non-functioning gonadotroph adenomas (NFGAs), and silent corticotropin adenomas were evaluated by RT-qPCR.

RESULTS

Of all the 12 patients with FGAs from our center, 11 (91.7%) were diagnosed as FSH-predominant type, and they all had menstrual disorders, including 9 with spontaneous ovarian hyperstimulation syndrome (sOHSS). Their hormonal profiles showed non-suppressed FSH (12.45 ± 7.34 IU/L) with hyperestrogenemia [median estradiol level 1353.0 pg/mL (636.0, 3535.0)]. The other patient (8.3%) with LH-predominant type mainly manifested with infertility and sustained elevated serum LH without FSH or estradiol increasing. 65 premenopausal FGAs patients were systematic reviewed. 60 patients (92.3%) were FSH-predominant type, including 86.7% presented with menstrual disorders, 16.7% reported infertility, and 98.2% (55/56) showed sOHSS. No sOHSS or hyperestrogenemia were found in the 5 patients (7.7%) with LH-predominant type. Pituitary imaging data revealed macroadenomas and microadenomas accounted for 89.2% and 10.8%, respectively. Of 63 patients (96.9%) who underwent pituitary adenoma resection, 77.8% had complete tumor resection and no recurrence at the last follow-up. The relative expressions of KISS1 mRNA were significantly higher in FGA group than in NFGA group (p = 0.018), and significantly positively correlated with the preoperative serum estradiol levels (p = 0.004).

CONCLUSIONS

Different clinical features were observed in premenopausal women with FGAs of FSH- or LH-predominant types. The elevated KISS1 expression in tumor tissues might involve in the secretion function of FGAs.

Lower FSH With Normal Fertility in Male Mice Lacking Gonadotroph Kisspeptin Receptor

The kisspeptin receptor, crucial for hypothalamic control of puberty and reproduction, is also present in the pituitary gland. Its role in the pituitary gland is not defined. Kisspeptin signaling via the Kiss1r could potentially regulate reproductive function at the level of pituitary gonadotrope. Using Cre/Lox technology, we deleted the Kiss1r gene in pituitary gonadotropes (PKiRKO). PKiRKO males have normal genital development (anogenital distance WT: 19.1 ± 0.4 vs. PKiRKO: 18.5 ± 0.4 mm), puberty onset, testes cell structure on gross histology, normal testes size, and fertility. PKiRKO males showed significantly decreased serum FSH levels compared to WT males (5.6 ± 1.9 vs. 10.2 ± 1.8 ng/ml) with comparable LH (1.1 ± 0.2 vs. 1.8 ± 0.4 ng/ml) and testosterone levels (351.8 ± 213.0 vs. 342.2 ± 183.0 ng/dl). PKiRKO females have normal puberty onset, cyclicity, LH and FSH levels and fertility. Overall, these findings indicate that absence of pituitary Kiss1r reduces FSH levels in male mice without affecting testis function. PKiRKO mice have normal reproductive function in both males and females.

Intraperitoneal kisspeptin-10 administration ameliorates sodium arsenite-induced reproductive toxicity in adult male mice

The current study investigated the protective ameliorative effect of intraperitoneally administered kisspeptin-10 (50 nmol/day) against reproductive toxicity in adult male mice challenged with 35 days of exposure to sodium arsenite in drinking water. Mice were divided into tap water control, sodium arsenite-alone (4 ppm and 10 ppm), kisspeptin-alone (intermittent and continuous) and combined (sodium arsenite +kisspeptin-10 intermittent and continuous) treatment groups. Results revealed protective effect of both intermittent and continuous kisspeptin doses on reproductive organs against sodium arsenite-induced toxicity. This was indicated by an increase (p < 0.001) in the activity of antioxidant enzymes and a decrease (p < 0.001) in the levels of oxidative stress biomarkers. Concomitant significant increase was noticeable in the relative organ weight (p < 0.01), and serum testosterone and seminal fructose (p < 0.001), and a significant improvement in sperm parameters was also observed. A significant downregulation of lactate dehydrogenase concentration demonstrated further the protective effect of kisspeptin against tissue damage. Histologically, both treatment regimens of kisspeptin combined with sodium arsenite exposure prevented massive germ cell loss and tissue damage, a condition prominent in sodium arsenite-alone-treated mice. The study demonstrates for the first time kisspeptin's potential to mitigate the biochemical and histotoxic effects of arsenic on male reproductive system.

Effect of anti-Müllerian hormone on the regulation of pituitary gonadotropin subunit expression: roles of kisspeptin and its receptors in gonadotroph LβT2 cells

Anti-Müllerian hormone (AMH) is primarily produced by ovarian granulosa cells and contributes to follicle development. AMH is also produced in other tissues, including the brain and pituitary; however, its roles in these tissues are not well understood. In this study, we examined the effect of AMH on pituitary gonadotrophs. We detected AMH and AMH receptor type 2 expression in LβT2 cells. In these cells, the expression of FSHβ- but not α- and LHβ-subunits increased significantly as the concentration of AMH increased. LβT2 cells expressed Kiss-1 and Kiss-1R. AMH stimulation resulted in decreases in both Kiss-1 and Kiss-1R. The siRNA-mediated knockdown of Kiss-1 in LβT2 cells did not alter the basal expression levels of α-, LHβ-, and FSHβ-subunits. In LβT2 cells overexpressing Kiss-1R, exogenous kisspeptin stimulation significantly increased the expression of all three gonadotropin subunits. However, kisspeptin-induced increases in these subunits were almost completely eliminated in the presence of AMH. In contrast, GnRH-induced increases in the three gonadotropin subunits were not modulated by AMH. Our observations suggested that AMH acts on pituitary gonadotrophs and induces FSHβ-subunit expression with concomitant decreases in Kiss-1 and Kiss-1R gene expression. Kisspeptin, but not GnRH-induced gonadotropin subunit expression, was inhibited by AMH, suggesting that it functions in association with the kisspeptin/Kiss-1R system in gonadotrophs.

Aging reduces kisspeptin receptor (GPR54) expression levels in the hypothalamus and extra-hypothalamic brain regions

Aging leads to the diminished pulsatile secretion of hypothalamic gonadotropin-releasing hormone (GnRH). Kisspeptin (Kp), the upstream regulator of the hypothalamic-pituitary-gonadal (HPG) axis, regulates GnRH synthesis and release through its cognate receptor, G-protein coupled receptor 54 (GPR54). In turn, GnRH regulates GPR54 expression. GnRH administration into the third ventricle has been shown to induce neurogenesis in different brain regions in old age. However, aging-associated changes in hypothalamic and extra-hypothalamic GPR54 expression were unclear. Therefore, the expression levels of GPR54 were evaluated in various brain regions of adult (age, 3-4 months) and old (age, 20-24 months) male Wistar rats in the present study. In the hypothalamus, mRNA and protein levels of Kp and GPR54 were identified to be significantly decreased in old age. Furthermore, GnRH1 expression in the hypothalamus was analyzed to observe the functional consequence of a reduced Kp-GPR54 system in the hypothalamus. It was found that hypothalamic GnRH1 levels were significantly decreased in old age. As GnRH regulates GPR54 levels, GPR54 was examined in extra-hypothalamic regions. GPR54 levels were found to be significantly decreased in the hippocampus and medulla and pons in old-age rats when compared to adult rats. Notably, GPR54 expression was observed in the frontal lobe, cortex, midbrain and cerebellum of adult and old-age rats; however, the difference between the two groups was not statistically significant. To the best of our knowledge, this is the first study that provides the quantitative distribution of GPR54 in different brain regions during aging. Thus, the reduced levels of Kp and its receptor, GPR54 in the hypothalamus could be cumulatively responsible for reduced levels of GnRH observed in old age.

Peripheral action of kisspeptin at reproductive tissues-role in ovarian function and embryo implantation and relevance to assisted reproductive technology in livestock: a review

Kisspeptin (KISS1) is encoded by the KISS1 gene and was initially found to be a repressor of metastasis. Natural mutations in the KISS1 receptor gene (KISS1R) were subsequently shown to be associated with idiopathic hypothalamic hypogonadism and impaired puberty. This led to interest in the role of KISS1 in reproduction. It was established that KISS1 had a fundamental role in the control of gonadotropin releasing hormone (GnRH) secretion. KISS1 neurons have receptors for leptin and estrogen receptor α (ERα), which places KISS1 at the gateway of metabolic (leptin) and gonadal (ERα) regulation of GnRH secretion. More recently, KISS1 has been shown to act at peripheral reproductive tissues. KISS1 and KISS1R genes are expressed in follicles (granulosa, theca, oocyte), trophoblast, and uterus. KISS1 and KISS1R proteins are found in the same tissues. KISS1 appears to have autocrine and paracrine actions in follicle and oocyte maturation, trophoblast development, and implantation and placentation. In some studies, KISS1 was beneficial to in vitro oocyte maturation and blastocyst development. The next phase of KISS1 research will explore potential benefits on embryo survival and pregnancy. This will likely involve longer-term KISS1 treatments during proestrus, early embryo development, trophoblast attachment, and implantation and pregnancy. A deeper understanding of the direct action of KISS1 at reproductive tissues could help to achieve the next step change in embryo survival and improvement in the efficiency of assisted reproductive technology.

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.

Effects of Kiss2 on the Expression of Gonadotropin Genes in the Pituitary of Nile Tilapia (Oreochromis niloticus)

Kisspeptin, expressed mainly in the hypothalamus, stimulates gonadotropin-releasing hormone neurons to facilitate reproduction. In some model animals, the kisspeptin is also expressed in the pituitary. Recently, a pathway has been suggested in which kisspeptin acts directly on the pituitary to secretion of gonadotropin in mammals. In the present study, pituitaries of the Nile tilapia (Oreochromis niloticus) were cultured at different concentrations of kisspeptin-10 (Kp-10, FNYNPLSLRF) for 3 hours to observe the effect of kisspeptin on the expression of follicle-stimulating hormone β subunit (fshβ) gene and luteinizing hormone β subunit (lhβ) gene. Pituitary tissues were cultured with 0.1 μM of Kp-10, luteinizing hormone releasing hormone (LHRH), or LHRH+Kp-10 for 3, 6, 12, and 24 hours to investigate changes in the expression of fshβ and lhβ mRNA. Pituitaries cultured with high concentration of Kp-10 more than 0.1 μM for 3 hours exhibited a significant increase of fshβ mRNA expression, but not lhβ mRNA. The expression of both fshβ and lhβ mRNA increased after 6 hours in 0.1 μM of Kp-10 medium in comparison with that in the control medium. Tissues cultured in the LHRH medium however exhibited increased expression of both genes not only at 6 but also 12 hours. There were no significant differences of fshβ and lhβ gene expression in tissues cultured with LHRH+KP-10 medium compared with the control. These results suggested that although kisspeptin plays an important role in fshβ and lhβ expression in the pituitary of Nile tilapia, its action is far more complicated than expected.

Role of kisspeptins in the control of the hypothalamic-pituitary-ovarian axis: old dogmas and new challenges

In humans and other mammals, a hallmark of female reproductive function is the capacity to episodically release fertilizable oocytes under the precise control of a cascade of hormonal regulators that interplay in a cyclic manner within the hypothalamic-pituitary-ovarian (HPO) axis. Although the basic elements of this neurohormonal system were disclosed several decades before, a major breakthrough in our understanding of how the HPO axis is controlled during the lifespan came in the first decade of the 21st century, when the reproductive dimension of kisspeptins was disclosed by seminal studies documenting that genetic inactivation of the kisspeptin pathway is linked to central hypogonadism and infertility. Kisspeptins are a family of peptides, encoded by the Kiss1 gene, that operate via the surface receptor, Gpr54 (also called Kiss1r), to regulate virtually all aspects of reproduction in both sexes. The primary site of action of kisspeptins is the hypothalamus, where Kiss1 neurons engage in the precise control of the pulsatile release of GnRH to modulate gonadotropin secretion and, thereby, ovarian function. Nonetheless, additional sites of action of kisspeptins within the HPO axis, including the pituitary and the ovary, have been proposed; yet, the physiologic relevance of such extrahypothalamic actions of kisspeptins is still a matter of debate. In this review, we summarize the current consensus knowledge and open questions on the sites of action, physiologic roles, and eventual therapeutic implications of kisspeptins in the control of the female reproductive axis.

Kisspeptin has an independent and direct effect on the pituitary gland in the mare

To more clearly understand the equine gonadotrope response to kisspeptin and gonadotropin releasing hormone (GnRH), peripheral LH and FSH were quantified in diestrous mares after treatment with either equine kisspeptide (eKp-10, 0.5 mg iv), GnRH (25 μg iv), or a combination thereof every 4 h for 3 days. The following observations were made: 1) a diminished LH and FSH response to eKp-10 and GnRH was observed by Day 3, but was not different by treatment, 2) a decrease in basal LH concentration was observed from Day 1 to Day 3 for the eKp-10, but not the GnRH treated mares, 3) there was no change in basal FSH with either treatment. Additionally, pre-treatment with GnRH antagonist (antide 1.0 mg iv) eliminated any measurable change in LH after eKp-10 (1.0 mg iv) treatment. Both GnRH and kisspeptin are Gα_q/11 coupled receptors, therefore quantifying the rise in intracellular calcium following treatment with cognate ligand allows simultaneous assessment of receptor activation. Direct stimulation of equine primary pituitary cells with GnRH and/or eKp-10 demonstrates three distinct populations of pituitary cells: one population responded to both eKp-10 and GnRH, a second, independent population, responded to only eKp-10, and a third population responded only to GnRH. These populations were confirmed using co-immunofluorescence of hemipituitaries from mares in diestrus. Although the rise in peripheral LH concentration elicited by eKp-10 is dependent on GnRH, this work suggests that kisspeptin also has a specific and direct effect on the equine gonadotrope, independent of GnRH.

Cloning, characterisation and expression profile of kisspeptin1 and the kisspeptin1 receptor in the hypothalamic–pituitary–ovarian axis of Chinese alligator Alligator sinensis during the reproductive cycle

Kisspeptin1 (Kiss1), a product of the Kiss1 gene, plays an important role in the regulation of reproduction in vertebrates by activating the Kiss1 receptor (Kiss1R) and its coexpression with gonadotrophin-releasing hormone (GnRH) in GnRH neurons. The purpose of this study was to clone the Kiss1 and Kiss1R genes found in the brain of Alligator sinensis and to explore their relationship with reproduction. The full-length cDNA of Kiss1 is 816bp, the open reading frame (ORF) is 417bp and the gene encodes a 138-amino acid precursor protein. The full-length cDNA of Kiss1R is 2348bp, the ORF is 1086bp and the gene encodes a 361-amino acid protein. Quantitative polymerase chain reaction showed that, except for Kiss1R expression in the hypothalamus, the expression of Kiss1 and Kiss1Rduring the reproductive period of A. sinensis was higher than that in the hypothalamus, pituitary gland and ovary during the hibernation period. The changes in GnRH2 mRNA in the hypothalamus were similar to those of GnRH1 and peaked during the reproductive period. This study confirms the existence of Kiss1 and Kiss1R in A. sinensis and the findings strongly suggest that Kiss1 and Kiss1R may participate in the regulation of GnRH secretion in the hypothalamus of alligators during the reproductive period. Furthermore, this is the first report of the full-length cDNA sequences of Kiss1 and Kiss1R in reptiles.

The hypothalamus-pituitary-gonad axis: Tales of mice and men

Reproduction is controlled by the hypothalamic-pituitary-gonadal (HPG) axis. Gonadotropin-releasing hormone (GnRH) neurons play a central role in this axis through production of GnRH, which binds to a membrane receptor on pituitary gonadotrophs and stimulates the biosynthesis and secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Multiple factors affect GnRH neuron migration, GnRH gene expression, GnRH pulse generator, GnRH secretion, GnRH receptor expression, and gonadotropin synthesis and release. Among them anosmin is involved in the guidance of the GnRH neuron migration, and a loss-of-function mutation in its gene leads to a failure of their migration from the olfactory placode to the hypothalamus, with consequent anosmic hypogonadotropic hypogonadism (Kallmann syndrome). There are also cases of hypogonadotropic hypogonadim with normal sense of smell, due to mutations of other genes. Another protein, kisspeptin plays a crucial role in the regulation of GnRH pulse generator and the pubertal development. GnRH is the main hypothalamic regulator of the release of gonadotropins. Finally, FSH and LH are the essential hormonal regulators of testicular functions, acting through their receptors in Sertoli and Leydig cells, respectively. The main features of the male HPG axis will be described in this review.

Interaction between kisspeptin and adenylate cyclase-activating polypeptide 1 on the expression of pituitary gonadotropin subunits: a study using mouse pituitary lbetaT2 cells

We examined direct effect of kisspeptin on pituitary gonadotrophs. Kisspeptin-10 (KP10) significantly increased the promoter activities of the gonadotropin subunits, common alpha-glycoprotein (Cga), luteinizing hormone beta (Lhb), and follicle-stimulatinghormone beta (Fshb) in LbetaT2 cells overexpressing kisspeptin receptor (Kiss1r). KP10 and gonadotropin-releasing hormone (GnRH) increased gonadotropin subunit levels to similar degrees and combined treatment with GnRH and KP10 did not potentiate their individual effects. Adenylate cyclase-activating polypeptide 1 (ADCYAP1) also stimulates all three gonadotropin subunits. When cells were stimulated with both KP10 and ADCYAP1, expression of gonadotropin subunits was further increased compared to KP10 or ADCYAP1 alone. KP10 and GnRH dramatically increased serum response element (Sre) promoter levels but only slightly increased cAMP response element (Cre) promoter levels. Combined stimulation with KP10 and GnRH further increased Sre promoter levels. In contrast, ADCYAP1 slightly increased Sre promoter expression but did not modify the effect of KP10. However, ADCYAP1 increased Cre promoter to greater levels than KP10 alone, and combined treatment with KP10 and ADCYAP1 further increased Cre promoter expression. KP10 increased the expression of ADCYAP1 type I receptor (Adcyap1r) and the basal activity of the Cga promoter was increased at a higher Adcyap1r transfection level. The KP10-induced fold increase in all three gonadotropin subunit promoters was not altered by transfection with a higher amount of Adcyap1r vector. Our findings using model cells show that distinct signaling activation by ADCYAP1 potentiates the action of KP10. We also found that KP10 increases Adcyap1r expression.

Stimulation of growth hormone by kisspeptin antagonists in ewes

Kisspeptin signalling is indispensable for fertility, stimulating gonadotropin-releasing hormone (GnRH) secretion and mediating gonadal steroid feedback on GnRH neurons. Moreover, kisspeptin neurons have been implicated in other non-reproductive neuroendocrine roles. Kisspeptin appears to also regulate growth hormone secretion but much of the data appear contradictory. We sought to clarify a potential role of kisspeptin in growth hormone (GH) regulation by examining the effect of kisspeptin antagonists on GH secretion in ewes under various physiological conditions. Our data show clear and robust increases in GH secretion following lateral ventricle or third ventricle infusion of kisspeptin antagonists p-234 and p-271 in either ovariectomized or anestrous ewes. Central infusion of kisspeptin-10 had no effect on GH secretion. To determine the level at which kisspeptin may influence GH secretion, we examined expression of the cognate kisspeptin receptor, GPR54, in pituitary cells and showed by immunocytochemistry that the majority of somatotropes express GPR54 while expression was largely negative in other pituitary cells. Overall, we have demonstrated that blocking kisspeptin signalling by antagonists stimulates GH secretion in ewes and that this is likely mediated by inhibiting endogenous kisspeptin activation of GPR54 expressed on somatotropes. The findings suggest that endogenous kisspeptin inhibits GH secretion through GPR54 expressed on somatotropes.

The Emerging Role(s) for Kisspeptin in Metabolism in Mammals

Kisspeptin was initially identified as a metastasis suppressor. Shortly after the initial discovery, a key physiologic role for kisspeptin emerged in the regulation of fertility, with kisspeptin acting as a neurotransmitter via the kisspeptin receptor, its cognate receptor, to regulate hypothalamic GnRH neurons, thereby affecting pituitary-gonadal function. Recent work has demonstrated a more expansive role for kisspeptin signaling in a variety of organ systems. Kisspeptin has been revealed as a significant player in regulating glucose homeostasis, feeding behavior, body composition as well as cardiac function. The direct impact of kisspeptin on peripheral metabolic tissues has only recently been recognized. Here, we review the emerging endocrine role of kisspeptin in regulating metabolic function. Controversies and current limitations in the field as well as areas of future studies toward kisspeptin's diverse array of functions will be highlighted.

Continuous Kisspeptin Restores Luteinizing Hormone Pulsatility Following Cessation by a Neurokinin B Antagonist in Female Sheep

Pulsatile secretion of the gonadotropin-releasing hormone (GnRH) drives pulsatile secretion of the luteinizing hormone (LH), with evidence that this depends on kisspeptin (Kiss) input to GnRH neurons. Kiss administration causes acute GnRH/LH secretion, and electrophysiological data suggest that Kiss neurons may act in a phasic manner to drive GnRH secretion, but there is not definitive evidence for this. The product of the Kiss-1 gene is proteolytically cleaved to smaller products, and the 10 amino acid C-terminal product (Kiss-10) displays full bioactivity. We have shown previously that continuous delivery of Kiss-10 to anestrous ewes can cause a surge in GnRH secretion and ovulation and increases LH pulse frequency in humans. Here, we tested the hypothesis that continuous Kiss-10 delivery can support pulsatile GnRH/LH secretion in the sheep. Neurokinin B (NKB) provides positive drive to Kiss neurons, so we therefore infused an NKB antagonist (ANT-08) intracerebroventricularly to induce cessation of pulsatile GnRH/LH secretion, with or without concomitant continuous Kiss-10 infusion. ANT-08 suppressed GnRH/LH pulsatility, which was immediately restored with continuous Kiss-10 infusion. These data support the notion that Kiss-10 action is downstream of NKB signaling and that continuous Kiss-10 stimulation of GnRH neurons is sufficient to support a pulsatile pattern of GnRH/LH secretion. This offers further support to the theory that GnRH pulse generation is intrinsic to GnRH neurons and that pulsatile GnRH release can be affected with continuous stimulation by Kiss-10.

The Role of Kisspeptin in Female Reproduction

CONTEXT

Kisspeptin (KISS1), a recently discovered neuropeptide that acts upstream of gonadotropin-releasing hormone (GnRH) neurons, is critical for maturation and function of the reproductive axis. This review aimed at providing comprehensive and up-to-date information on Kisspeptin and its role in female reproduction.

EVIDENCE ACQUISITION

A literature review was performed using PubMed for all English language articles published between 1999 and 2016.

RESULTS

The kisspeptin system (KISS1/G protein-coupled receptor-54,GPR54) has recently been addressed as an essential gatekeeper of puberty onset and gonadotropin secretion. Compelling evidence has documented that hypothalamic Kisspeptin mediates steroid feedback and metabolic cues at different developmental stages throughout lifespan. Furthermore, in pre/postnatally androgenized animal models, which exhibit many of the characteristics of Polycystic Ovarian Syndrome (PCOS), the hypothalamic expression of KISS1 and GnRH is abnormal, which might lead to multiple tissue abnormalities observed in this disorder.

CONCLUSIONS

Kisspeptin, a principal activator of GnRH neurons and the target of endocrine and metabolic cues, is a prerequisite for the onset of puberty and maintenance of normal reproductive function, as abnormal KISS1/GPR54 system has been reported in both animal models and patients with certain forms of infertility, e.g. Idiopathic Hypogonadotropic hypogonadism (IHH) and PCOS. The information suggests that kisspeptin or its receptor represents a potential therapeutic target in the treatment of patients with fertility disorders.

Mutual regulation by GnRH and kisspeptin of their receptor expression and its impact on the gene expression of gonadotropin subunits

Hypothalamic kisspeptin plays a pivotal role in the regulation of the hypothalamic-pituitary-gonadal axis by stimulating gonadotropin-releasing hormone (GnRH) release into the portal circulation, with the subsequent release of gonadotropins. Kisspeptin and its receptor, the kisspeptin 1 receptor (Kiss1R), are also expressed in the pituitary gland. This study demonstrates the interaction between GnRH and kisspeptin within the pituitary gonadotrophs by altering their individual receptor expression. Our results show that kisspeptin and Kiss1R are expressed in the mouse pituitary gonadotroph cell line LβT2. Endogenous Kiss1R did not respond to kisspeptin and failed to stimulate gonadotropin LHβ and FSHβ expression in LβT2 cells; however, kisspeptin increased both LHβ and FSHβ promoter activity in Kiss1R-overexpressing LβT2 cells. Stimulating the cells with GnRH significantly increased Kiss1R expression, whereas kisspeptin increased the expression of the GnRH receptor (GnRHR) in these cells. Elevating the Kiss1R concentration led to an increase in the basal activities of gonadotropin LHβ- and FSHβ-subunit promoters. In addition, the level of kisspeptin-induced LHβ promoter activity, but not that of FSHβ, was significantly increased when a large number of Kiss1R expression vectors was introduced into the cells. The level of induction of GnRH-induced gonadotropin promoter activities was not significantly changed by increasing Kiss1R expression. Increasing the amount of GnRHR by overexpressing cellular GnRHR did not potentiate basal gonadotropin promoter activities; however, kisspeptin- and GnRH-stimulated increases in gonadotropin promoter activities were significantly potentiated (except GnRH-induced LHβ promoters). The activities of serum response element-containing promoters were also modified in cells overexpressing Kiss1R or GnRHR. Our current observations demonstrate that GnRH and kisspeptin affect each other's function to stimulate gonadotropin subunit gene expression by reciprocally increasing the expression of their receptors.

Eel Kisspeptins: Identification, Functional Activity, and Inhibition on both Pituitary LH and GnRH Receptor Expression

The European eel (Anguilla anguilla) presents a blockade of sexual maturation at a prepubertal stage due to a deficient production of gonadotropins. We previously initiated, in the eel, the investigation of the kisspeptin system, one of the major gatekeepers of puberty in mammals, and we predicted the sequence of two Kiss genes. In the present study, we cloned and sequenced Kiss1 and Kiss2 cDNAs from the eel brain. The tissue distributions of Kiss1 and Kiss2 transcripts, as investigated by quantitative real-time PCR, showed that both genes are primarily expressed in the eel brain and pituitary. The two 10-residue long sequences characteristic of kisspeptin, eel Kp1(10) and Kp2(10), as well as two longer sequences, predicted as mature peptides, eel Kp1(15) and Kp2(12), were synthesized and functionally analyzed. Using rat Kiss1 receptor-transfected Chinese hamster ovary cells, we found that the four synthesized eel peptides were able to induce [Ca²⁺]_i responses, indicating their ability to bind mammalian KissR-1 and to activate second messenger pathways. In primary culture of eel pituitary cells, all four peptides were able to specifically and dose-dependently inhibit lhβ expression, without any effect on fshβ, confirming our previous data with heterologous kisspeptins. Furthermore, in this eel in vitro system, all four peptides inhibited the expression of the type 2 GnRH receptor (gnrh-r2). Our data revealed a dual inhibitory effect of homologous kisspeptins on both pituitary lhβ and gnrh-r2 expression in the European eel.

Role of the Kiss1/Kiss1r system in the regulation of pituitary cell function

Kisspeptin (Kiss1) is an amidated neurohormone that belongs to the RF-amide peptide family, which has a key role in the control of reproduction. Specifically, kisspeptin regulates reproductive events, including puberty and ovulation, primarily by activating the surface receptor Kiss1r (aka GPR54), at hypothalamic gonadotropin-releasing hormone (GnRH) neurons. More recently, it has been found that kisspeptin peptide is present in the hypophyseal portal circulation and that the Kiss1/Kiss1r system is expressed in pituitary cells, which suggest that kisspeptin could exert an endocrine, paracrine or even autocrine role at the pituitary gland level. Indeed, mounting evidence is pointing towards a direct role of kisspeptin in the control of not only gonadotropins but also other pituitary secretions such as growth hormone or prolactin. In this review, we summarize the most recent advances in the study of the role that the Kiss/Kiss1r system plays in the control of pituitary gland function, paying special attention to the direct role of this neuropeptide on pituitary cells and its interactions with other relevant regulators.

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.

Peptides: Basic determinants of reproductive functions

Mammalian reproduction is a costly process in terms of energy consumption. The critical information regarding metabolic status is signaled to the hypothalamus mainly through peripheral peptides from the adipose tissue and gastrointestinal tract. Changes in energy stores produce fluctuations in leptin, insulin, ghrelin and glucose signals that feedback mainly to the hypothalamus to regulate metabolism and fertility. In near future, possible effects of the nutritional status on GnRH regulation can be evaluated by measuring serum or tissue levels of leptin and ghrelin in patiens suffering from infertility. The fact that leptin and ghrelin are antagonistic in their effects on GnRH neurons, their respective agonistic and antagonistic roles make them ideal candidates to use instead of GnRH agonist and antagonist. Similarly, kisspeptin expressing neurons are likely to mediate the well-established link between energy balance and reproductive functions. Exogenous kisspeptin can be used for physiological ovarian hyperstimulation for in-vitro fertilization. Moreover, kisspeptin antagonist therapy can be used for the treatment of postmenapousal women, precocious puberty, PCOS, endometriosis and uterine fibroids. In this review, we will analyze the central mechanisms involved in the integration of metabolic information and their contribution to the control of the reproductive function. Particular attention will be paid to summarize the participation of leptin, kisspeptin, ghrelin, NPY, orexin, urocortin, VIP, insulin, galanin, galanin like peptide, oxytocin, agouti gene-related peptide, and POMC neurons in this process and their possible interactions to contribute to the metabolic control of reproduction.

Bisphenol-A and Female Infertility: A Possible Role of Gene-Environment Interactions

Background: Bisphenol-A (BPA) is widely used and ubiquitous in the environment. Animal studies indicate that BPA affects reproduction, however, the gene-environment interaction mechanism(s) involved in this association remains unclear. We performed a literature review to summarize the evidence on this topic. Methods: A comprehensive search was conducted in PubMed using as keywords BPA, gene, infertility and female reproduction. Full-text articles in both human and animals published in English prior to December 2014 were selected. Results: Evidence shows that BPA can interfere with endocrine function of hypothalamic-pituitary axis, such as by changing gonadotropin-releasing hormones (GnRH) secretion in hypothalamus and promoting pituitary proliferation. Such actions affect puberty, ovulation and may even result in infertility. Ovary, uterus and other reproductive organs are also targets of BPA. BPA exposure impairs the structure and functions of female reproductive system in different times of life cycle and may contribute to infertility. Both epidemiological and experimental evidences demonstrate that BPA affects reproduction-related gene expression and epigenetic modification that are closely associated with infertility. The detrimental effects on reproduction may be lifelong and transgenerational. Conclusions: Evidence on gene-environment interactions, especially from human studies, is still limited. Further research on this topic is warranted.

KISS1 receptor is preferentially expressed in clinically non-functioning pituitary tumors

OBJECTIVE

KISS1 is a metastasis suppressor gene involved in cancer biology. Given the high expression levels of KISS1 and KISS1R in the hypothalamus and the pituitary respectively, we hypothesized that this system could possibly affect tumor invasiveness and clinical behavior of pituitary tumors.

METHODS

Expression levels of KISS1 and KISS1R mRNA were evaluated by RT-PCR. Clinical information pertaining tumor characteristics was extracted from patients' charts.

RESULTS

Tumors from 39 patients (21 females, mean age 47.5 years) were examined. KISS1R was expressed in 26 (67%) of samples (94% of NFPA, 42% of GH-, 67% of ACTH-, and 25% of PRL-secreting adenomas) and was found more often in female patients (81 vs. 50% males, p < 0.05); and in NFPA (94 vs. 45.5% in secreting tumors; p = 0.003). Patients expressing KISS1R were older at presentation (50.5 ± 1.4 vs. 38.1 ± 1.3 years; p = 0.008). In the multivariate analysis, factors significantly associated with KISS1R expression included female gender (OR 13.8, 95 % CI 1.22-155.9; p = 0.03) and having a NFPA (OR 24.7, 95% CI 1.50-406.4; p = 0.02). Tumor size, invasiveness and age at presentation were not independently associated with KISS1R expression. Pituitary tumors and normal pituitary were negative for KISS1 mRNA expression.

CONCLUSIONS

The majority of human NFPA expressed KISS1R with lower rates of expression in other types of pituitary tumors. KISS1R expression did not impart a clinical beneficial tumor phenotype, as it was not associated with tumor size or invasiveness. Additional studies are required to elucidate the role of KISS1 receptor in pituitary gland physiology and pathology.

A Multi-Oscillatory Circadian System Times Female Reproduction

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

Kisspeptin induction of somatolactin-α release in goldfish pituitary cells: functional role of cAMP/PKA-, PLC/PKC-, and Ca(2+)/calmodulin-dependent cascades

Although the importance of kisspeptin in the pituitary is firmly established, the signaling mechanisms for the pituitary actions of kisspeptin are still largely unknown. Somatolactin (SL), a member of the growth hormone (GH)/prolactin (PRL) family, is a pituitary hormone with pleiotropic functions in fish, but its regulation by kisspeptin has not been examined. To investigate the functional role of kisspeptin in SL regulation, expression of two paralogues of goldfish Kiss1 receptors (Kiss1ra and Kiss1rb) were confirmed in immunoidentified SLα but not SLβ cells isolated by RT-PCR coupled with laser capture microdissection. In goldfish pituitary cells prepared from neurointermediate lobe (NIL), synthetic goldfish Kiss decapeptides (gKiss1-10 and gKiss2-10) could increase SLα release. Consistent with the lack of Kiss1r expression in SLβ cells, SLβ release was not altered by kisspeptin stimulation. In parallel experiments, goldfish gKiss1-10 could elevate cyclic adenosine monophosphate (cAMP) production, upregulate protein kinase A (PKA) and protein kinase C (PKC) activities, and trigger a rapid rise in intracellular Ca(2+) levels in goldfish NIL cells. Using a pharmacological approach, cAMP/PKA and phospholipase C (PLC)/PKC pathways and subsequent activation of Ca(2+)/calmodulin (CaM)-dependent cascades were shown to be involved in SLα release induced by gKiss1-10. Apparently, the Ca(2+)-dependent cascades were triggered by extracellular Ca(2+) entry via voltage-sensitive Ca(2+) channels and mobilization of inositol trisphosphate-sensitive intracellular Ca(2+) stores. Our results demonstrate that gKiss1-10 can act directly at the pituitary level to trigger SLα release via a complex network of post-receptor signaling mechanisms.

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.

Neuroanatomy of the human hypothalamic kisspeptin system

Hypothalamic kisspeptin (KP) neurons are key players in the neuronal network that regulates the onset of puberty and the pulsatile secretion of gonadotropin-releasing hormone (GnRH). In various mammalian species, the majority of KP-synthesizing neurons are concentrated in two distinct cell populations in the preoptic region and the arcuate nucleus (ARC). While studies of female rodents have provided evidence that preoptic KP neurons play a critical sex-specific role in positive estrogen feedback, KP neurons of the ARC have been implicated in negative sex steroid feedback and they have also been hypothesized to contribute to the pulse generator network which regulates episodic GnRH secretion in both females and males. Except for relatively few morphological studies available in monkeys and humans, our neuroanatomical knowledge of the hypothalamic KP systems is predominantly based on observations of laboratory species which are phylogenetically distant from the human. This review article discusses the currently available literature on the topographic distribution, network connectivity, neurochemistry, sexual dimorphism, and aging-dependent morphological plasticity of the human hypothalamic KP neuronal system.

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

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

Twice-daily subcutaneous injection of kisspeptin-54 does not abolish menstrual cyclicity in healthy female volunteers

BACKGROUND

Kisspeptin is a critical hypothalamic regulator of reproductive function. Chronic kisspeptin administration causes profound tachyphylaxis in male monkeys and in women with functional hypothalamic amenorrhea. The pharmacological effects of chronic kisspeptin exposure in healthy women with normal menstrual cycles have not been studied previously.

AIM

Our aim was to determine the effects of follicular-phase kisspeptin-54 treatment on menstrual cyclicity in healthy women.

METHODS

We performed a prospective, single-blinded, 1-way crossover study. Healthy women received twice-daily sc injections of kisspeptin (6.4 nmol/kg) or 0.9% saline during menstrual days 7-14 (n = 5 per treatment arm). Serial assessments of basal reproductive hormones, ultrasound parameters, LH pulsatility, and acute sensitivity to GnRH and kisspeptin-54 injection were performed.

RESULTS

Menstrual cyclicity persisted in all women after follicular-phase kisspeptin-54 treatment. Chronic exposure to kisspeptin-54 did not abolish acute stimulation of LH after injection of kisspeptin-54 or GnRH. In addition, kisspeptin-54 treatment was associated with a shorter mean length of the menstrual cycle (mean length of menstrual cycle was 28.6 ± 1.4 days with saline vs 26.8 ± 3.1 days with kisspeptin, P < .01), earlier onset of highest recorded serum LH (mean menstrual day of highest LH was 15.2 ± 1.3 with saline vs 13.0 ± 1.9 with kisspeptin, P < .05), and earlier onset of the luteal phase (mean menstrual day of progesterone increase was 18.0 ± 2.1 with saline vs 15.8 ± 0.9 with kisspeptin, P < .05).

CONCLUSION

Our data suggest that 1 week of exogenous kisspeptin-54 does not abolish menstrual cyclicity in healthy women. Further work is needed to determine whether kisspeptin could be used to treat certain anovulatory disorders.

Effects of full-length kisspeptin administration on follicular development in Japanese Black beef cows

Kisspeptin is a key molecule that stimulates gonadotropin secretion via release of gonadotropin-releasing hormone (GnRH). In the present study, our aim was to investigate whether kisspeptin has stimulatory effects on follicular development via GnRH/gonadotropin secretion in cows. Japanese Black beef cows were intravenously injected with full-length bovine kisspeptin [Kp-53 (0.2 or 2 nmol/kg)] or vehicle 5 days after they exhibited standing estrus (Day 0). In cows injected with Kp-53 at 2 nmol/kg, the follicular sizes of the first dominant follicles increased on Day 6 and thereafter. Ovulation of the first dominant follicle occurred in 1 out of 4 cows treated with Kp-53 at 2 nmol/kg. Injection of Kp-53 at 2 nmol/kg increased the concentration of plasma luteinizing hormone (LH) but not follicle-stimulating hormone, over a 4-h period following injection in all cows. The present study suggests that administration of full-length kisspeptin causes LH secretion, which is sustained for a few hours, and it is capable of stimulating follicular development and/or ovulation.

Kisspeptin regulates gonadotropin genes via immediate early gene induction in pituitary gonadotropes

Kisspeptin signaling through its receptor, Kiss1R, is crucial for many reproductive functions including puberty, sex steroid feedback, and overall fertility. Although the importance of Kiss1R in the brain is firmly established, its role in regulating reproduction at the level of the pituitary is not well understood. This study presents molecular analysis of the role of kisspeptin and Kiss1R signaling in the transcriptional regulation of the gonadotropin gene β-subunits, LHβ and FSHβ, using LβT2 gonadotrope cells and murine primary pituitary cells. We show that kisspeptin induces LHβ and FSHβ gene expression, and this induction is protein kinase C dependent and mediated by the immediate early genes, early growth response factor 1 and cFos, respectively. Additionally, kisspeptin induces transcription of the early growth response factor 1 and cFos promoters in LβT2 cells. Kisspeptin also increases gonadotropin gene expression in mouse primary pituitary cells in culture. Furthermore, we find that Kiss1r expression is enhanced in the pituitary of female mice during the estradiol-induced LH surge, a critical component of the reproductive cycle. Overall, our findings indicate that kisspeptin regulates gonadotropin gene expression through the activation of Kiss1R signaling through protein kinase C, inducing immediate early genes in vitro, and responds to physiologically relevant cues in vivo, suggesting that kisspeptin affects pituitary gene expression to regulate reproductive function.

Human ghrelin decreases pituitary response to GnRH in superovulated ewes

In addition to its metabolic role, ghrelin has been found to suppress luteinizing hormone secretion in many species acting mainly at the hypothalamic level. The objectives of the present study were to test the hypothesis that besides its effects on the hypothalamic level, ghrelin exerts a direct action on the pituitary. Twelve cycling ewes were synchronized, using progestagen intravaginal sponges and superovulated using eCG. At the time of sponge withdrawal, animals were allocated into two groups, ghrelin-treated (Gh) and control. Two days after the sponge removal, GnRH was given to synchronize ovulations. Simultaneously with GnRH treatment, animals of the Gh group received the first of four treatments of acylated human ghrelin at a dose of 6 μg/kg body weight iv; three additional treatments of ghrelin iv were given every 15 minutes thereafter. Control animals received saline iv. Blood samples were collected before challenge (-30 and 0 minutes) and at 30, 60, 75, 90, 105, 120, 135, 150, and 180 minutes after GnRH treatment, and were analyzed for LH, FSH, estradiol, progesterone, insulin, and insulin-like growth factor-I concentrations. Ghrelin treatment attenuated GnRH-induced a preovulatory surge of both gonadotrophins, with the effect being greater for LH. No difference was detected for insulin, estradiol, and progesterone concentrations, and insulin-like growth factor-I levels were increased in the Gh group. Our results imply that in sheep, ghrelin conducts specific regulatory effects on the GnRH/LH axis, and provide for the first time strong evidence that besides its central action, ghrelin might regulate gonadotrophin release acting at the pituitary level.

Distribution and seasonal variation in hypothalamic RF-amide peptides in a semi-desert rodent, the jerboa

The jerboa is a semi-desert rodent, in which reproductive activity depends on the seasons, being sexually active in the spring-summer. The present study aimed to determine whether the expression of two RF-amide peptides recently described to regulate gonadotrophin-releasing hormone neurone activity, kisspeptin (Kp) and RF-amide-related peptide (RFRP)-3, displays seasonal variation in jerboa. Kp and/or RFRP-3 immunoreactivity was investigated in the hypothalamus of jerboas captured in the field of the Middle Atlas mountain (Morocco), either in the spring or autumn. As in other rodents, the Kp-immunoreactive (-IR) neurones were found in the anteroventro-periventricular and arcuate nuclei. RFRP-3 neurones were noted within the dorso/ventromedial hypothalamus. A marked sexual dimorphism in the expression of Kp (but not RFRP-3) was observed. The number of Kp-IR neurones was nine-fold higher, and the density of Kp-IR fibres and terminal-like elements in the median eminence was two-fold higher in females than in males. Furthermore, a significant seasonal variation in peptide expression was obtained with an increase in both Kp- and RFRP-3-IR cell bodies in sexually active male jerboas captured in the spring compared to sexually inactive autumn animals. In the arcuate nucleus, the level of Kp-IR cells and fibres was significant higher during the sexually active period in the spring than during the autumnal sexual quiescence. Similarly, the number of RFRP-3-IR neurones in the ventro/dorsomedial hypothalamus was approximately three-fold higher in sexually active jerboa captured in the spring compared to sexually inactive autumn animals. Altogether, the present study reports the distribution of Kp and RFRP-3 neurones in the hypothalamus of a desert species and reveals a seasonal difference in their expression that correlates with sexual activity. These findings suggest that these two RF-amide peptides may act in concert to synchronise the gonadotrophic activity of jerboas with the seasons.

Kisspeptin receptor, GPR54, as a candidate for the regulation of testicular activity in the frog Rana esculenta

Kisspeptins, acting via GPR54, are new players in the control of reproductive axis. They have the ability to communicate with GnRH neurons sending environmental, metabolic, and gonadal signals, with the induction of GnRH and LH secretion as final effect. At present, the physiological significance of kisspeptin signaling in the gonad is poorly investigated. We cloned GPR54 receptor from the anuran amphibian Rana esculenta testis and investigated its expression in several tissues (brain, spinal cord, ovary, muscle, and kidney). In particular, the expression analysis was carried out in pituitary and testis during the annual sexual cycle. Pituitary and testicular GPR54 mRNA increased at the end of the winter stasis (February) and reached high levels during the breeding season (April). The analysis of GPR54 expression in testis was reinforced by in situ hybridization that revealed GPR54 presence in the interstitial compartment and in proliferating germ cells. Testicular GPR54 expression in February and in June was indicated to be estradiol dependent. Furthermore, in February, kisspeptin-10 (Kp-10) induced the testicular expression of both GPR54 and estrogen receptor alpha (ERalpha) in a dose-dependent manner. Conversely, in March, Kp-10 had a biphasic effect on the expression of ERalpha, being inhibitory at short (1 h) and stimulatory at longer (4 h) incubation time. In conclusion, our results demonstrate that frog testis expresses GPR54 in an estradiol-dependent manner and that Kp-10 modulates the testicular expression of ERalpha; thus, the kisspeptin/GPR54 system might be locally involved in the regulation of estrogen-dependent testicular functions such as germ cell proliferation and steroidogenesis.

Neuroanatomy of the kisspeptin signaling system in mammals: comparative and developmental aspects

Our understanding of kisspeptin and its actions depends, in part, on a detailed knowledge of the neuroanatomy of the kisspeptin signaling system in the brain. In this chapter, we will review our current knowledge of the distribution of kisspeptin cells, fibers, and receptors in the mammalian brain, including the development, phenotype, and projections of different kisspeptin subpopulations. A fairly consistent picture emerges from this analysis. There are two major groups of kisspeptin cell bodies: a large number in the arcuate nucleus (ARC) and a smaller collection in the rostral periventricular area of the third ventricle (RP3V) of rodents and preoptic area (POA) of non-rodents. Both sets of neurons project to GnRH cell bodies, which contain Kiss1r, and the ARC kisspeptin population also projects to GnRH axons in the median eminence. ARC kisspeptin neurons contain neurokinin B and dynorphin, while a variable percentage of those cells in the RP3V of rodents contain galanin and/or dopamine. Neurokinin B and dynorphin have been postulated to contribute to the control of GnRH pulses and sex steroid negative feedback, while the role of galanin and dopamine in rostral kisspeptin neurons is not entirely clear. Kisspeptin neurons, fibers, and Kiss1r are found in other areas, including widespread areas outside the hypothalamus, but their physiological role(s) in these regions remains to be determined.