Plasma kisspeptin is raised in patients with gestational trophoblastic neoplasia and falls during treatment

Potential biomarkers to predict return to fertility after discontinuation of female contraceptives-looking to the future

Nowadays there are multiple types of contraceptive methods, from reversible to permanent, for those choosing to delay pregnancy. Misconceptions about contraception and infertility are a key factor for discontinuation or the uptake of family planning methods. Regaining fertility (the ability to conceive) after contraceptive discontinuation is therefore pivotal. Technical studies to date have evaluated return to fertility by assessing pregnancy as an outcome, with variable results, or return to ovulation as a surrogate measure by assessing hormone levels (such as progesterone, LH, FSH) with or without transvaginal ultrasound. In general, relying on time to pregnancy as an indicator of return to fertility following contraceptive method discontinuation can be problematic due to variable factors independent of contraceptive effects on fertility, hormone clearance, and fertility recovery. Since the ability to conceive after contraceptive method discontinuation is a critical factor influencing product uptake, it is important to have robust biomarkers that easily and accurately predict the timing of fertility return following contraception and isolate that recovery from extrinsic and circumstantial factors. The main aim of this review is to summarize the current approaches, existing knowledge, and gaps in methods of evaluating return-to-fertility as well as to provide insights into the potential of new biomarkers to more accurately predict fertility restoration after contraceptive discontinuation. Biomarker candidates proposed in this document include those associated with folliculogenesis, cumulus cell expansion, follicular rupture and ovulation, and endometrial transport and receptivity which have been selected and scored on predefined criteria meant to evaluate their probable viability for advancement. The review also describes limitations, regulatory requirements, and a potential path to clinically testing these selected biomarkers. It is important to understand fertility restoration after contraceptive method discontinuation to provide users and health providers with accurate evidence-based information. Predictive biomarkers, if easy and low-cost, have the potential to enable robust evaluation of RTF, and provide potential users the information they desire when selecting a contraceptive method. This could lead to expanded uptake and continuation of modern contraception and inform the development of new contraceptive methods to widen user's family planning choices.

Novel therapeutic avenues for kisspeptin

Kisspeptin is a hypothalamic neuropeptide that acts via the hypothalamus to stimulate hypothalamic gonadotrophin-releasing hormone secretion and downstream gonadotrophin release. In health, kisspeptin induces normal puberty and modulates ovulation in healthy women. Hypothalamic kisspeptin expression is reduced in several functional reproductive disorders; thus, treating such conditions with kisspeptin is conceptually attractive. Recent studies have demonstrated that kisspeptin can induce a more physiological degree of oocyte maturation during in vitro fertilisation treatment that can reduce the risk of potentially life-threatening complications such as ovarian hyperstimulation syndrome seen with human chorionic gonadotrophin. Furthermore, chronic use of kisspeptin could potentially restore reproductive health in females with hypothalamic amenorrhoea, treat hyposexual drive disorder in otherwise healthy males and has potential indications in polycystic ovary syndrome, osteoporosis and metabolic dysfunction-associated fatty liver disease. Finally, kisspeptin analogues could potentially overcome some of the pharmacological challenges associated with the natural forms of kisspeptin such as short duration of action and development of tachyphylaxis.

Kisspeptin in the Prediction of Pregnancy Complications

Kisspeptin and its receptor are central to reproductive health acting as key regulators of the reproductive endocrine axis in humans. Kisspeptin is most widely recognised as a regulator of gonadotrophin releasing hormone (GnRH) neuronal function. However, recent evidence has demonstrated that kisspeptin and its receptor also play a fundamental role during pregnancy in the regulation of placentation. Kisspeptin is abundantly expressed in syncytiotrophoblasts, and its receptor in both cyto- and syncytio-trophoblasts. Circulating levels of kisspeptin rise dramatically during healthy pregnancy, which have been proposed as having potential as a biomarker of placental function. Indeed, alterations in kisspeptin levels are associated with an increased risk of adverse maternal and foetal complications. This review summarises data evaluating kisspeptin's role as a putative biomarker of pregnancy complications including miscarriage, ectopic pregnancy (EP), preterm birth (PTB), foetal growth restriction (FGR), hypertensive disorders of pregnancy (HDP), pre-eclampsia (PE), gestational diabetes mellitus (GDM), and gestational trophoblastic disease (GTD).

Targeting hepatic kisspeptin receptor ameliorates nonalcoholic fatty liver disease in a mouse model

Nonalcoholic fatty liver disease (NAFLD), the most common liver disease, has become a silent worldwide pandemic. The incidence of NAFLD correlates with the rise in obesity, type 2 diabetes, and metabolic syndrome. A hallmark featureof NAFLD is excessive hepatic fat accumulation or steatosis, due to dysregulated hepatic fat metabolism, which can progress to nonalcoholic steatohepatitis (NASH), fibrosis, and cirrhosis. Currently, there are no approved pharmacotherapies to treat this disease. Here, we have found that activation of the kisspeptin 1 receptor (KISS1R) signaling pathway has therapeutic effects in NAFLD. Using high-fat diet-fed mice, we demonstrated that a deletion of hepatic Kiss1r exacerbated hepatic steatosis. In contrast, enhanced stimulation of KISS1R protected against steatosis in wild-type C57BL/6J mice and decreased fibrosis using a diet-induced mouse model of NASH. Mechanistically, we found that hepatic KISS1R signaling activates the master energy regulator, AMPK, to thereby decrease lipogenesis and progression to NASH. In patients with NAFLD and in high-fat diet-fed mice, hepatic KISS1/KISS1R expression and plasma kisspeptin levels were elevated, suggesting a compensatory mechanism to reduce triglyceride synthesis. These findings establish KISS1R as a therapeutic target to treat NASH.

Sexual Dimorphism in Kisspeptin Signaling

Kisspeptin (KP) and kisspeptin receptor (KPR) are essential for the onset of puberty, development of gonads, and maintenance of gonadal function in both males and females. Hypothalamic KPs and KPR display a high degree of sexual dimorphism in expression and function. KPs act on KPR in gonadotropin releasing hormone (GnRH) neurons and induce distinct patterns of GnRH secretion in males and females. GnRH acts on the anterior pituitary to secrete gonadotropins, which are required for steroidogenesis and gametogenesis in testes and ovaries. Gonadal steroid hormones in turn regulate the KP neurons. Gonadal hormones inhibit the KP neurons within the arcuate nucleus and generate pulsatile GnRH mediated gonadotropin (GPN) secretion in both sexes. However, the numbers of KP neurons in the anteroventral periventricular nucleus and preoptic area are greater in females, which release a large amount of KPs in response to a high estrogen level and induce the preovulatory GPN surge. In addition to the hypothalamus, KPs and KPR are also expressed in various extrahypothalamic tissues including the liver, pancreas, fat, and gonads. There is a remarkable difference in circulating KP levels between males and females. An increased level of KPs in females can be linked to increased numbers of KP neurons in female hypothalamus and more KP production in the ovaries and adipose tissues. Although the sexually dimorphic features are well characterized for hypothalamic KPs, very little is known about the extrahypothalamic KPs. This review article summarizes current knowledge regarding the sexual dimorphism in hypothalamic as well as extrahypothalamic KP and KPR system in primates and rodents.

Metabolic actions of kisspeptin signaling: Effects on body weight, energy expenditure, and feeding

Kisspeptin (encoded by the Kiss1 gene) and its receptor, KISS1R (encoded by the Kiss1r gene), have well-established roles in stimulating reproduction via central actions on reproductive neural circuits, but recent evidence suggests that kisspeptin signaling also influences metabolism and energy balance. Indeed, both Kiss1 and Kiss1r are expressed in many metabolically-relevant peripheral tissues, including both white and brown adipose tissue, the liver, and the pancreas, suggesting possible actions on these tissues or involvement in their physiology. In addition, there may be central actions of kisspeptin signaling, or factors co-released from kisspeptin neurons, that modulate metabolic, feeding, or thermoregulatory processes. Accumulating data from animal models suggests that kisspeptin signaling regulates a wide variety of metabolic parameters, including body weight and energy expenditure, adiposity and adipose tissue function, food intake, glucose metabolism, respiratory rates, locomotor activity, and thermoregulation. Herein, the current evidence for the involvement of kisspeptin signaling in each of these physiological parameters is reviewed, gaps in knowledge identified, and future avenues of important research highlighted. Collectively, the discussed findings highlight emerging non-reproductive actions of kisspeptin signaling in metabolism and energy balance, in addition to previously documented roles in reproductive control, but also emphasize the need for more research to resolve current controversies and uncover underlying molecular and physiological mechanisms.

Performance of plasma kisspeptin as a biomarker for miscarriage improves with gestational age during the first trimester

OBJECTIVE

To compare the performance of kisspeptin and beta human chorionic gonadotropin (βhCG), both alone and in combination, as biomarkers for miscarriage throughout the first trimester.

DESIGN

Prospective, nested case-control study.

SETTING

Tertiary Centre, Queen Charlotte Hospital, London, United Kingdom.

PATIENT(S)

Adult women who had miscarriages (n = 95, 173 samples) and women with healthy pregnancies (n = 265, 557 samples).

INTERVENTION(S)

The participants underwent serial ultrasound scans and blood sampling for measurement of plasma kisspeptin and βhCG levels during the first trimester.

MAIN OUTCOME MEASURE(S)

The ability of plasma kisspeptin and βhCG levels to distinguish pregnancies complicated by miscarriage from healthy pregnancies unaffected by miscarriage.

RESULT(S)

Gestation-adjusted levels of circulating kisspeptin and βhCG were lower in samples from women with miscarriages than in women with healthy pregnancies by 79% and 70%, respectively. The area under the receiver-operating characteristic curve for identifying miscarriage during the first trimester was 0.874 (95% confidence interval [CI] 0.844-0.904) for kisspeptin, 0.859 (95% CI 0.820-0.899) for βhCG, and 0.916 (95% CI 0.886-0.946) for the sum of the two markers. The performance of kisspeptin in identifying miscarriage improved with increasing length of gestation, whereas that of βhCG worsened. A decision matrix incorporating kisspeptin, βhCG, and gestational age had 83% to 87% accuracy for the prediction of miscarriage.

CONCLUSION(S)

Plasma kisspeptin is a promising biomarker for miscarriage and provides additional value to βhCG alone, especially during later gestational weeks of the first trimester.

Pregnancy-induced changes in β-cell function: what are the key players?

Maternal metabolic adaptations during pregnancy ensure appropriate nutrient supply to the developing fetus. This is facilitated by reductions in maternal peripheral insulin sensitivity, which enables glucose to be available in the maternal circulation for transfer to the fetus for growth. To balance this process and avoid excessive hyperglycaemia and glucose intolerance in the mother during pregnancy, maternal pancreatic β-cells undergo remarkable changes in their function including increasing their proliferation and glucose-stimulated insulin secretion. In this review we examine how placental and maternal hormones work cooperatively to activate several signalling pathways, transcription factors and epigenetic regulators to drive adaptations in β-cell function during pregnancy. We also explore how adverse maternal environmental conditions, including malnutrition, obesity, circadian rhythm disruption and environmental pollutants, may impact the endocrine and molecular mechanisms controlling β-cell adaptations during pregnancy. The available data from human and experimental animal studies highlight the need to better understand how maternal β-cells integrate the various environmental, metabolic and endocrine cues and thereby determine appropriate β-cell adaptation during gestation. In doing so, these studies may identify targetable pathways that could be used to prevent not only the development of pregnancy complications like gestational diabetes that impact maternal and fetal wellbeing, but also more generally the pathogenesis of other metabolic conditions like type 2 diabetes.

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.

Potential roles for the kisspeptin/kisspeptin receptor system in implantation and placentation

BACKGROUND

Initially identified as suppressors of metastasis in various types of cancer, kisspeptins are a family of neuropeptides that are key regulators of the mammalian reproductive axis. Accumulating evidence has shown that kisspeptin is able to control both the pulsatile and surge GnRH release, playing fundamental roles in female reproduction, which include the secretion of gonadotropins, puberty onset, brain sex differentiation, ovulation and the metabolic regulation of fertility. Furthermore, recent studies have demonstrated the involvement of the kisspeptin system in the processes of implantation and placentation. This review summarizes the current knowledge of the pathophysiological role and utility of these local placental regulatory factors as potential biomarkers during the early human gestation.

OBJECTIVE AND RATIONALE

A successful pregnancy, from the initiation of embryo implantation to parturition, is a complex process that requires the orchestration of a series of events. This review aims to concisely summarize what is known about the role of the kisspeptin system in implantation, placentation, early human pregnancy and pregnancy-related disorders, and to develop strategies for predicting, diagnosing and treating these abnormalities.

SEARCH METHODS

Using the PubMed and Google Scholar databases, we performed comprehensive literature searches in the English language describing the advancement of kisspeptins and the kisspeptin receptor (KISS1R) in implantation, placentation and early pregnancy in humans, since its initial identification in 1996 and ending in July 2018.

OUTCOMES

Recent studies have shown the coordinated spatial and temporal expression patterns of kisspeptins and KISS1R during human pregnancy. The experimental data gathered recently suggest putative roles of kisspeptin signaling in the regulation of trophoblast invasion, embryo implantation, placentation and early pregnancy. Dysregulation of the kisspeptin system may negatively affect the processes of implantation as well as placentation. Clinical studies indicate that the circulating levels of kisspeptins or the expression levels of kisspeptin/KISS1R in the placental tissues may be used as potential diagnostic markers for women with miscarriage and gestational trophoblastic neoplasia.

WIDER IMPLICATIONS

Comprehensive research on the pathophysiological role of the kisspeptin/KISS1R system in implantation and placentation will provide a dynamic and powerful approach to understanding the processes of early pregnancy, with potential applications in observational and analytic screening as well as the diagnosis, prognosis and treatment of implantation failure and early pregnancy-related disorders.

UCN2: a new candidate influencing pancreatic β-cell adaptations in pregnancy

The corticotropin-releasing hormone (CRH) family of peptides, including urocortin (UCN) 1, 2 and 3, are established hypothalamic neuroendocrine peptides, regulating the physiological and behaviour responses to stress indirectly, via the hypothalamic-pituitary-adrenal (HPA) axis. More recently, these peptides have been implicated in diverse roles in peripheral organs through direct signalling, including in placental and pancreatic islet physiology. CRH has been shown to stimulate insulin release through activation of its cognate receptors, CRH receptor 1 (CRHR1) and 2. However, the physiological significance of this is unknown. We have previously reported that during mouse pregnancy, expression of CRH peptides increase in mouse placenta suggesting that these peptides may play a role in various biological functions associated with pregnancy, particularly the pancreatic islet adaptations that occur in the pregnant state to compensate for the physiological increase in maternal insulin resistance. In the current study, we show that mouse pregnancy is associated with increased circulating levels of UCN2 and that when we pharmacologically block endogenous CRHR signalling in pregnant mice, impairment of glucose tolerance is observed. This effect on glucose tolerance was comparable to that displayed with specific CRHR2 blockade and not with specific CRHR1 blockade. No effects on insulin sensitivity or the proliferative capacity of β-cells were detected. Thus, CRHR2 signalling appears to be involved in β-cell adaptive responses to pregnancy in the mouse, with endogenous placental UCN2 being the likely signal mediating this.

KISS1 in breast cancer progression and autophagy

Tumor suppressors are cellular proteins typically expressed in normal (non-cancer) cells that not only regulate such cellular functions as proliferation, migration and adhesion, but can also be secreted into extracellular space and serve as biomarkers for pathological conditions or tumor progression. KISS1, a precursor for several shorter peptides, known as metastin (Kisspeptin-54), Kisspeptin-14, Kisspeptin-13 and Kisspeptin-10, is one of those metastasis suppressor proteins, whose expression is commonly downregulated in the metastatic tumors of various origins. The commonly accepted role of KISS1 in metastatic tumor progression mechanism is the ability of this protein to suppress colonization of disseminated cancer cells in distant organs critical for the formation of the secondary tumor foci. Besides, recent evidence suggests involvement of KISS1 in the mechanisms of tumor angiogenesis, autophagy and apoptosis regulation, suggesting a possible role in both restricting and promoting cancer cell invasion. Here, we discuss the role of KISS1 in regulating metastases, the link between KISS1 expression and the autophagy-related biology of cancer cells and the perspectives of using KISS1 as a potential diagnostic marker for cancer progression as well as a new anti-cancer therapeutics.

Kisspeptin injection improved the semen characteristics and sperm rheotaxis in Ossimi ram

The aim of the present study was to investigate the effect of kisspeptin-10 (Kp10) injection on semen characteristics, testosterone (T) production and sperm rheotaxis using microfluidic devices in immature ram. Computer-assisted sperm analysis (CASA) with controlled flow velocity was used to explore the kinetic parameters of sperm and positive rheotaxis (PR %). PR % was defined as the number of PR sperms over the number of motile sperms. Healthy Ossimi rams were randomly divided into two groups; a saline-treated control group and Kp10-treated one (5 µg/kg body weight). Treatments were given by intramuscular injection once a week for 1 month. After 1 month, the semen was collected and evaluated weekly for 6 weeks, while the blood samples were collected every 2 weeks for the next 8 weeks. Semen properties were significantly affected by Kp10 injection (p < .01). The Kp10 increased the volume, sperm concentration and percentages of live sperm compared with those of control. Additionally, sperm trajectories and rheotaxis get improved by the injection of Kp10 with time. Furthermore, kisspeptin improved the secretion of testosterone levels throughout the period of study. In conclusion, injections of the Kp10 had a positive impact on semen characteristics as well as improved sperm rheotaxis of Ossimi rams in subtropics.

A role for placental kisspeptin in β cell adaptation to pregnancy

During pregnancy the maternal pancreatic islets of Langerhans undergo adaptive changes to compensate for gestational insulin resistance. Kisspeptin has been shown to stimulate insulin release, through its receptor, GPR54. The placenta releases high levels of kisspeptin into the maternal circulation, suggesting a role in modulating the islet adaptation to pregnancy. In the present study we show that pharmacological blockade of endogenous kisspeptin in pregnant mice resulted in impaired glucose homeostasis. This glucose intolerance was due to a reduced insulin response to glucose as opposed to any effect on insulin sensitivity. A β cell–specific GPR54-knockdown mouse line was found to exhibit glucose intolerance during pregnancy, with no phenotype observed outside of pregnancy. Furthermore, in pregnant women circulating kisspeptin levels significantly correlated with insulin responses to oral glucose challenge and were significantly lower in women with gestational diabetes (GDM) compared with those without GDM. Thus, kisspeptin represents a placental signal that plays a physiological role in the islet adaptation to pregnancy, maintaining maternal glucose homeostasis by acting through the β cell GPR54 receptor. Our data suggest reduced placental kisspeptin production, with consequent impaired kisspeptin-dependent β cell compensation, may be a factor in the development of GDM in humans.

Placental kisspeptin regulates islet adaptation to pregnancy that is necessary for preventing gestational diabetes in mice and humans.

Kisspeptin as a potential biomarker throughout pregnancy

Kisspeptins are a family of neuropeptides that are critical for the puberty initiation and female fertility. Plasma or serum kisspeptin is mainly derived from the placenta during pregnancy and plasma kisspeptin levels significantly increase across pregnancy. Plasma kisspeptin levels could be used as a potential biomarker for the detection of miscarriage, pre-eclampsia, gestational trophoblastic neoplasia (GTN), and fetal development. Kisspeptin may also be involved in the process of parturition by stimulating oxytocin secretion during term pregnancy. This review discussed the potential use of kisspeptin as a marker across pregnancy and highlighted the unresolved problems in this area. Tweetable abstract: Plasma kisspeptin levels could be used as a potential biomarker across pregnancy.

Deregulation of miR-324/KISS1/kisspeptin in early ectopic pregnancy: mechanistic findings with clinical and diagnostic implications

BACKGROUND

Ectopic pregnancy is a life-threatening condition for which novel screening tools that would enable early accurate diagnosis would improve clinical outcomes. Kisspeptins, encoded by KISS1, play an essential role in human reproduction, at least partially by regulating placental function and possibly embryo implantation. Kisspeptin levels are elevated massively in normal pregnancy and reportedly altered in various gestational pathologic diseases. Yet, the pathophysiologic role of KISS1/kisspeptin in ectopic pregnancy has not been investigated previously.

OBJECTIVE

The purpose of this study was to evaluate changes of KISS1/kisspeptin levels in ectopic pregnancy and their underlaying molecular mechanisms and to ascertain the diagnostic implications of these changes.

STUDY DESIGN

A total of 122 women with normal pregnancy who underwent voluntary termination of pregnancy and 84 patients who experienced tubal ectopic pregnancy were recruited. Measurements of plasma kisspeptins and KISS1 expression analyses in human embryonic/placental tissue were conducted in ectopic pregnancy and voluntary termination of pregnancy control subjects during the early gestational window (<12 weeks). Putative microRNA regulators of KISS1 were predicted in silico, followed by expression analyses of selected microRNAs and validation of repressive interactions in vitro. Circulating levels of these microRNAs were also assayed in ectopic pregnancy vs voluntary termination of pregnancy.

RESULTS

Circulating kisspeptins gradually increased during the first trimester of normal pregnancy but were reduced markedly in ectopic pregnancy. This profile correlated with the expression levels of KISS1 in human embryonic/placental tissue, which increased in voluntary termination of pregnancy but remained suppressed in ectopic pregnancy. Bioinformatic predictions and expression analyses identified miR-27b-3p and miR-324-3p as putative repressors of KISS1 in human embryonic/placental tissue at <12 weeks gestation, when expression of microRNAs was low in voluntary termination of pregnancy control subjects but significantly increased in ectopic pregnancy. Yet, a significant repressive interaction was documented only for miR-324-3p, occurring at the predicted 3'-UTR of KISS1. Interestingly, circulating levels of miR-324-3p, but not of miR-27b-3p, were suppressed distinctly in ectopic pregnancy, despite elevated tissue expression of the pre-microRNA. A decision-tree model that used kisspeptin and miR-324-3p levels was successful in discriminating ectopic pregnancy vs voluntary termination of pregnancy, with a receiver-operating characteristic area under the curve of 0.95±0.02 (95% confidence interval).

CONCLUSION

Our results document a significant down-regulation of KISS1/kisspeptins in early stages of ectopic pregnancy via, at least partially, a repressive interaction with miR-324-3p. Our data identify circulating kisspeptins and miR-324-3p as putative biomarkers for accurate screening of ectopic pregnancy at early gestational ages.

Predictive value of serum kisspeptin concentration at 14 and 21 days after frozen-thawed embryo transfer

RESEARCH QUESTION

Can serum kisspeptin levels 14 and 21 days after frozen-thawed embryo transfer predict the early pregnancy outcome of patients?

DESIGN

Prospective study, with 133 patients undergoing frozen-thawed embryo transfer. Patients were divided into non-pregnant group and pregnant group (including biochemical pregnancy, singleton pregnancy, miscarriage and twin groups).

RESULTS

Serum kisspeptin levels on day 21 were significantly higher than day 14 in singleton pregnancy, miscarriage and twin groups (all P < 0.0001), but not in the biochemical pregnancy group. Similarly, serum human chorionic gonadotrophin (HCG) levels were higher on day 21 compared with day 14 except for the biochemical pregnancy group. Compared with the twin group (296.9 pg/ml), the other four groups showed significantly higher serum kisspeptin levels on day 14 (non-pregnant 548.9, biochemical pregnancy 440.4, miscarriage 434.9, singleton pregnancy group 420.9 pg/ml, P < 0.01, P = 0.016, P = 0.034, P = 0.036, respectively). The miscarriage (762.2 pg/ml), singleton pregnancy (730.8 pg/ml) and twin groups (826.3 pg/ml) had significantly higher kisspeptin levels than the biochemical pregnancy group (397.3 pg/ml) on day 21 (P < 0.001, P < 0.01, P < 0.001, respectively). Serum kisspeptin levels on day 14 were negatively correlated with embryo implantation rate (P = 0.035, R² = -0.880). Serum kisspeptin levels on day 21 have a poor predictive value of miscarriage compared with serum HCG levels (area under the curve = 0.53 and 0.78, respectively).

CONCLUSIONS

Serum kisspeptin levels on day 14 are negatively correlated with embryo implantation rate. Serum kisspeptin levels on day 21 have a poor predictive value of miscarriage.

The roles of kisspeptin revisited: inside and outside the hypothalamus

Kisspeptin, encoded by KISS1/Kiss1 gene, is now considered a master regulator of reproductive functions in mammals owing to its involvement in the direct activation of gonadotropin-releasing hormone (GnRH) neurons after binding to its cognate receptor, GPR54. Ever since the discovery of kisspeptin, intensive studies on hypothalamic expression of KISS1/Kiss1 and on physiological roles of hypothalamic kisspeptin neurons have provided clues as to how the brain controls sexual maturation at the onset of puberty and subsequent reproductive performance in mammals. Additionally, emerging evidence indicates the potential involvement of extra-hypothalamic kisspeptin in reproductive functions. Here, we summarize data regarding kisspeptin inside and outside the hypothalamus and revisit the physiological roles of central and peripheral kisspeptins in the reproductive functions of mammals.

Comprehensive Review on Kisspeptin and Its Role in Reproductive Disorders

Kisspeptin has recently emerged as a key regulator of the mammalian reproductive axis. It is known that kisspeptin, acting centrally via the kisspeptin receptor, stimulates secretion of gonadotrophin releasing hormone (GnRH). Loss of kisspeptin signaling causes hypogonadotrophic hypogonadism in humans and other mammals. Kisspeptin interacts with other neuropeptides such as neurokinin B and dynorphin, to regulate GnRH pulse generation. In addition, a growing body of evidence suggests that kisspeptin signaling be regulated by nutritional status and stress. Kisspeptin may also represent a novel potential therapeutic target in the treatment of fertility disorders. Early human studies suggest that peripheral exogenous kisspeptin administration stimulates gonadotrophin release in healthy adults and in patients with certain forms of infertility. This review aims to concisely summarize what is known about kisspeptin as a regulator of reproductive function, and provide an update on recent advances within this field.

The effects of kisspeptin-10 on migration and proliferation of endothelial cell

BACKGROUND

Migration, expansion and survival of endothelial cells that are an important cellular component of blood vessels plays an important role in the induction of tumor growth. Kisspeptins (kp), peptides that bind to coupled-G protein receptor (GPR54), inhibit each step of metastatic cascade include invasion, migration and homing, angiogenesis, survival and proliferation. In this study we investigated effects of kisspeptin-10, the most potent member of kisspeptin family, on Migration and proliferation of endothelial cells that are necessary for angiogenesis and tumor metastasis.

MATERIALS AND METHODS

We compared migration of Human Umbilical Vein Endothelial Cells (HUVECs) were treated with 10-100 or 500 nM kp-10 for 24 hours and no treated cells using an in vitro trans membrane migration assay and HUVEC proliferation of treated endothelial cells with 10-100 or 500 nM kp-10 for 48 hours and no treated cells was measured by MTT Cell Proliferation Assay Kit. Analysis of data was performed using the Kruskal-Wallis test followed by the Mann-Whitney test.

RESULTS

Migration and proliferation of endothelial cells were increased at lower concentration of kp-10 specially at 100 nM while higher concentration reduced both migration and proliferation.

CONCLUSION

Our data showed that different concentrations of kp-10 have distinct effects on migration and proliferation of endothelial cells.

Kiss1 mutant placentas show normal structure and function in the mouse

Introduction

Kisspeptins, encoded by the Kiss1 gene, are a set of related neuropeptides that are required for activation of the mammalian reproductive axis at puberty and to maintain fertility. In addition, kisspeptin signaling via the G-protein coupled receptor GPR54 (KISS1R) has been suggested to regulate human placental formation and correlations have been found between altered kisspeptin levels in the maternal blood and the development of pre-eclampsia.

Methods

We have used Kiss1 and Gpr54 mutant mice to investigate the role of kisspeptin signaling in the structure and function of the mouse placenta.

Results

Expression of Kiss1 and Gpr54 was confirmed in the mouse placenta but no differences in birth weight were found in mice that had been supported by a mutant placenta during fetal development. Stereological measurements found no differences between Kiss1 mutant and wild-type placentas. Measurement of amino-acid and glucose transport across the Kiss1 mutant placentas at E15.5 days did not reveal any functional defects.

Discussion

These data indicate that mouse placentas can develop a normal structure and function without kisspeptin signaling and can support normal fetal development and growth.

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The structure and function of Kiss1 and Gpr54 mutant placentas was examined in transgenic mice.

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Kiss1 and Gpr54 mutant placentas are not associated with fetal loss during gestation or reduced pup weight at birth.

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Kiss1 mutant placentas show normal structural components.

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Kiss1 mutant placentas show normal transport of glucose and amino-acids.

Expression and function of kisspeptin during mouse decidualization

BACKGROUND

Plasma kisspeptin levels dramatically increased during the first trimester of human pregnancy, which is similar to pregnancy specific glycoprotein-human chorionic gonadotropin. However, its particular role in the implantation and decidualization has not been fully unraveled. Here, the study was conducted to investigate the expression and function of kisspeptin in mouse uterus during early pregnancy and decidualization.

METHODOLOGY/PRINCIPAL FINDINGS

Quantitative PCR results demonstrated that Kiss1 and GPR54 mRNA levels showed dynamic increase in the mouse uterus during early pregnancy and artificially induced decidualization in vivo. KISS-1 and GPR54 proteins were spatiotemporally expressed in decidualizing stromal cells in intact pregnant females, as well as in pseudopregnant mice undergoing artificially induced decidualization. In the ovariectomized mouse uterus, the expression of Kiss1 mRNA was upregulated after progesterone or/and estradiol treatment. Moreover, in a stromal cell culture model, the expression of Kiss1 and GPR54 mRNA gradually rise with the progression of stromal cell decidualization, whereas the attenuated expression of Kiss1 using small interfering RNA approaches significantly blocked the progression of stromal cell decidualization.

CONCLUSION

our results demonstrated that Kiss1/GPR54 system was involved in promoting uterine decidualization during early pregnancy in mice.

The Kiss-1/Kiss-1R complex as a negative regulator of cell motility and cancer metastasis (Review)

Metastasis is a complex multistep process that involves the impairment of cell-cell adhesion in the neoplastic epithelium, invasion into adjacent tissues and the dissemination of cancer cells through the lymphatic and haematogenous routes. The inhibition of the metastatic process at an early stage has become a hot topic in cancer research. The Kiss-1 gene, initially described as a suppressor of metastasis in malignant melanoma, encodes the Kiss-1 protein which can be processed to other peptides, e.g., Kisspeptin-10, Kisspeptin-13, Kisspeptin-14 and Kisspeptin-54. These peptides are endogenous ligands of the Kiss‑1 receptor (Kiss-1R), a G protein-coupled receptor (GPR) also known as hOT7T175, AXOR12 or GPR54. The Kiss-1 gene has been suggested as a suppressor of metastasis in a various types of cancer, including gastric cancer, oesophageal carcinoma, pancreatic, ovarian, bladder and prostate cancer, through the regulation of cellular migration and invasion. In the current review, we summarise the current understanding of the role of Kiss‑1 and Kiss‑1R in cancer and cancer metastasis.

Age-dependent elevations in plasma kisspeptin are observed in boys and girls when compared with adults

Background

Kisspeptin is a hypothalamic neuropeptide playing a physiological role in human reproduction. Genetic over-activation of kisspeptin causes precocious puberty in children. Concentrations of circulating kisspeptin are low in adults. The concentrations of plasma kisspeptin in boys and girls have not been studied previously.

Methods

Blood was obtained from 51 children and 63 adults. Plasma samples were analysed using radioimmunoassay. Children were aged 2–18 years, and attending hospital for a medically requested blood test unrelated to reproductive development. Data on pubertal status were not collected due to ethical reasons.

Results

Mean plasma kisspeptin was significantly higher in children when compared with adults (mean plasma kisspeptin in pmol/L: 12.3 ± 0.9, adults; 40.9 ± 3.3, children, P < 0.001 vs. adults). Overall mean concentrations of plasma kisspeptin were not significantly different between sexes (mean plasma kisspeptin in pmol/L: 39.5 ± 3.2, boys; 44.3 ± 6.3, girls, P = 0.48). In both sexes, concentrations of plasma kisspeptin increased with age to peak concentrations between 9 and 12 years of age, before decreasing beyond 12 years of age to adulthood. Plasma kisspeptin concentrations were highly significantly elevated in both girls and boys aged 9–12 when compared with adults (mean plasma kisspeptin in pmol/L: 59.5 ± 18.3, girls, P < 0.01 vs. adult women; 43.8 ± 6.2, boys, P < 0.001 vs. adult men).

Conclusions

We report that circulating kisspeptin is elevated in both boys and girls when compared with adults. Furthermore both boys and girls may have distinct, age-dependent concentrations of circulating kisspeptin. Further studies may determine if plasma kisspeptin could be used as a clinically useful biochemical marker of reproductive development in children.

Circulating kisspeptin and pituitary adenylate cyclase-activating polypeptide (PACAP) do not correlate with gonadotropin serum levels

Kisspeptins are known to be the principle regulators of the hypothalamic-pituitary gonadal (HPG) axis. In addition, the role of pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of pituitary gonadotropins has been elucidated. We measured plasma concentrations of kisspeptin and PACAP and determined whether the levels of these peptides varied in proportion to circulating gonadotropin levels. Plasma luteinizing hormone (LH) levels were higher in postmenopausal women and in patients with premature ovarian failure (POF) and lower in patients with idiopathic hypogonadotropic hypogonadism (IHH) compared with the LH level in normally menstruating women. Similarly, serum follicle-stimulating hormone levels were higher in postmenopausal women and in patients with POF but lower in pregnant women and patients with IHH compared with normally menstruating women. Plasma levels of kisspeptins were significantly higher in pregnant women compared with normally menstruating women. However, no significant differences were observed in postmenopausal women, patients with POF, and patients with IHH. On the other hand, plasma levels of PACAP were significantly lower in pregnant women, patients with POF, and in IHH patients when compared with normally menstruating women. No significant differences were observed in PACAP concentration between postmenopausal women and in normally menstruating women. Our observations suggest that the serum levels of kisspeptins and PACAP did not correlate with variations in serum gonadotropin levels.

LC-MS/MS quantification of a neuropeptide fragment kisspeptin-10 (NSC 741805) and characterization of its decomposition product and pharmacokinetics in rats

The kisspeptins are critical regulators of mammalian reproduction. Kisspeptin-10 ((45)YNWNSFGLRF-NH2(54), kisspeptin-112-121 or metastin 45-54, NSC 741805), an active fragment of kisspeptin, has been shown to be a potent stimulator of gonadotropin-releasing hormone and secretion of luteinizing hormone in both rodents and primates. This shorter peptide fragment may have clinical utility potential and it is important to characterize its pharmacokinetic property. Recently, the pharmacokinetics of both kisspeptin-54 and kisspeptin-10 were characterized in humans using a radioimmunoassay (RIA), which measures only the immunoreactive kisspeptin (kisspeptin-IR). In this study, a highly sensitive and specific LC-MS/MS assay was developed to quantify kisspeptin-10 levels in rat plasma. The lower limit of quantitation (LLOQ) was 0.5 ng/mL, the within-day and between-day coefficient of variations (CVs) ranged from 5.2 to 15.4% and 1.3 to 14.2%, and the accuracy values ranged from 98 to 114% and 99 to 105%, respectively. With this method, stability studies demonstrated that kisspeptin-10 degraded rapidly with decomposition half-lives of 6.8 min, 2.9 min and 1.7 min at 4 °C, 25 °C, and 37 °C, respectively. The principal decomposition product was characterized as the N-terminal tyrosine deleted kisspeptin-10 (46)NWDSFGLRF-NH2(54). Pharmacokinetic study in rats showed that low ng/mL kisspeptin-10 was detected in the first few minutes, and eliminated rapidly and became undetectable 30 min after intravenous (i.v.) bolus administration of 1.0 mg/kg kisspeptin-10.

Paradoxical effects of kisspeptin: it enhances oocyte in vitro maturation but has an adverse impact on hatched blastocysts during in vitro culture

Kisspeptin (Kp) is best known as a multifunctional peptide with roles in reproduction, the cardiovascular system and cancer. In the present study the expression of kisspeptin hierarchy elements (KISS1, GNRH1 and LHB) and their receptors (KISS1R, GNRHR and LHCGR, respectively) in porcine ovary and in cumulus-oocyte complexes (COCs) were investigated, as were its effects on the in vitro maturation (IVM) of oocytes and their subsequent ability to sustain preimplantation embryo competence after parthenogenetic electrical activation. Kp system elements were expressed and affected IVM of oocytes when maturation medium was supplemented with 10(-6)M Kp. Oocyte maturation, maternal gene expression (MOS, GDF9 and BMP15), blastocyst formation rate, blastocyst hatching and blastocyst total cell count were all significantly increased when oocytes were matured in medium containing Kp compared with the control group (without Kp). A Kp antagonist (p234) at 4×10(-6)M interfered with this hierarchy but did not influence the threshold effect of gonadotrophins on oocyte maturation. FSH was critical and permissive to Kp action on COCs by increasing the relative expression of KISS1R. In contrast, Kp significantly increased apoptosis, the expression of pro-apoptotic gene, BAK1, and suppressed trophoblast outgrowths from hatched blastocysts cultured on feeder cells. The present study provides the first functional evidence of the Kp hierarchy in porcine COCs and its role in enhancing oocyte maturation and subsequent developmental competence in an autocrine-paracrine manner. However, Kp supplementation may have a harmful impact on cultured hatched blastocysts reflecting systemic or local regulation during the critical early period of embryonic development.

Kisspeptins in human reproduction-future therapeutic potential

OBJECTIVE

Kisspeptins (Kps), were first found to regulate the hypothalamopituitary-gonadal axis (HPG) axis in 2003, when two groups-demonstrated that mutations of GPR54 causes idiopathic hypogonadotropic hypogonadism (IHH) characterized by delayed puberty. Objective of this review is to highlight both animal and human discoveries in KISS1/GPR54 system in last decade and extrapolate the therapeutic potential in humans from till date human studies.

DESIGN

A systematic review of international scientific literature by a search of PUBMED and the authors files was done for Kp in reproduction, metabolic control & signal transduction.

SETTING

None Patient(s): In human studies--normal subjects patients with HH, or HA.

MAIN OUTCOME MEASURES

Effects of Kp on puberty, brain sexual maturation, regulation of GnRH secretion, metabolic control of GnRH Neurons (N).

RESULTS

Kps/GPR54 are critical for brain sexual maturation, puberty and regulation of reproduction. Kps have been implicated in mediating signals to GnRH N--positive and negative feedback, metabolic input. Ability of Kp neurons to coordinate signals impinging on the HPG axis makes it one of most important regulators of reproductive axis since GnRH N's lack many receptors, with Kp neurons serving as upstream modulators.

CONCLUSIONS

Kps have proven as pivotal regulators of the reproduction, with the ability to integrate signals from both internal and external sources. Knowledge about signaling mechanisms involved in Kp stimulation of GnRH and with human studies has made it possible that therapeutically available Kp agonists/antagonists may be used for treatment of delayed puberty/HH, Hypothalamic amenorrhea and in prevention of spread of malignant ovarian/gonadal malignancies along with uses in some eating disorders.

KISS1 expression in human female adipose tissue

OBJECTIVE

The current focus of kisspeptin research is an exploration of its key role in the hypothalamic control of human and animal fertility. Notwithstanding the importance of these studies, strong evidence exists that the gene encoding human kisspeptin, KISS1, is present in several peripheral sites, including the placenta. We also provided evidence that kiss1 is also expressed and regulated in rodent adipose tissue. This study describes a pilot investigation into the possibility that human female adipose tissue might also express the KISS1 gene.

METHODS

Samples of fat were taken from women undergoing open abdominal surgery, for example, during caesarian section. Two small samples of fat were obtained, one from subcutaneous tissue (n = 35) and one from the omentum (n = 32). RNA was isolated from all fat samples and KISS1 mRNA was detected by realtime RT-PCR.

RESULTS

KISS1 gene expression was detected at varying levels in all samples of fat tissue but levels were significantly higher in subcutaneous fat. There was no significant correlation between KISS1 gene expression and body mass index (BMI) in subcutaneous fat (P = 0.43), but there was a significant positive correlation (P = 0.01) between KISS1 mRNA levels and BMI in omental adipose tissue.

CONCLUSION

We have shown for the first time that human female adipose tissue may be a source of kisspeptins. Further studies are required to establish whether kisspeptins of adipose tissue origin might be correlated with some aspects of infertility.

Altered placental expression of kisspeptin and its receptor in pre-eclampsia

Kisspeptin, originally identified as metastatin, important in preventing cancer metastasis, has more recently been shown to be important in pregnancy. Roles indicated for kisspeptin in pregnancy include regulating trophoblast invasion and migration during placentation. The pregnancy-specific disorder pre-eclampsia (PE) is now accepted to begin with inadequate trophoblast invasion and the current study therefore sets out to characterise placental expression of both kisspeptin (KISS1) and its receptor (KISS1R) throughout pregnancy and in PE. Placental tissue was obtained from women undergoing elective surgical termination of early pregnancy (n=10) and from women following Caesarean section at term in normal pregnancy (n=10) and with PE (n=10). Immunohistochemistry of paraffin embedded sections and western immunoblotting were performed to assess protein localisation and expression. Quantitative real-time PCR was carried out to evaluate mRNA expression of both KISS1 and KISS1R. Protein and mRNA expression was found to mirror each other with KISS1 expression found to be reduced in PE compared with that in normal term pregnancy. Interestingly, KISS1R expression at both the mRNA and protein levels was found to be increased in PE compared with that in normal term pregnancy. The current findings of increased KISS1R expression may represent a mechanism by which functional activity of KISS1 is higher in PE than in normal pregnancy. Higher levels of activity of KISS1R may be involved in inhibition of trophoblast invasion and angiogenesis, which are associated with PE.

Evaluation of kisspeptin levels in obese pregnancy as a biomarker for pre-eclampsia

OBJECTIVES

Circulating concentrations of the peptide kisspeptin have been proposed as a novel biomarker for early detection of pre-eclampsia. Our aims were to assess analytical and clinical performance characteristics of a commercial kisspeptin assay and to determine sensitivity and specificity of the test for pre-eclampsia.

DESIGN

Prospective, longitudinal study in a United Kingdom tertiary referral Antenatal Metabolic Clinic.

PATIENTS

Severely obese (body mass index, BMI > 40 kg/m(2), n = 194) and lean (BMI < 25 kg/m(2), n = 78) pregnant women.

MEASUREMENTS

A commercial kisspeptin ELISA (Phoenix Pharmaceuticals) was assessed for analytical sensitivity, specificity, precision, linearity, recovery and stability in maternal plasma samples at 16, 28 and 36 weeks gestation. Pre-eclampsia, defined using International Society for the Study of Hypertension in Pregnancy guidelines; blood pressure; delivery gestation; birthweight.

RESULTS

Kisspeptin concentrations were lower in early pregnancy in obese women (P < 0.001), and in women who later developed pre-eclampsia (P < 0.05), compared with women with uncomplicated pregnancies. For 16-week plasma kisspeptin in prediction of pre-eclampsia, area under the receiver-operator characteristic curve was 0.80 (P < 0.01), positive and negative likelihood ratios were 3.0 and 0.2, and test sensitivity and specificity were 85.7 and 71.4%, respectively. In regression analyses, kisspeptin (16 weeks) associated positively with delivery gestation (P < 0.05) and birthweight (P < 0.0001), and negatively with 28- and 36-week blood pressure (P < 0.0001).

CONCLUSIONS

Kisspeptin concentration in early pregnancy is a promising biomarker for pre-eclampsia and low birthweight but cannot be recommended, in isolation, for universal screening because of inadequate test sensitivity and specificity. Large-scale studies are required to assess its potential in a panel of biomarkers.

DNA polymorphisms of the KiSS1 3' untranslated region interfere with the folding of a G-rich sequence into G-quadruplex

KISS1R and its ligand, the kisspeptins, are key hypothalamic factors that regulate GnRH hypothalamic secretion and therefore the pubertal timing. During studies analysing KiSS1 as a candidate gene in pubertal onset disorders, two SNP and one nucleotide insertion were observed in a 23 nucleotides G-rich sequence located 65 nucleotides downstream of the stop codon. The polymorphisms formed four haplotypes. Biophysical experiments revealed the ability of this G-rich sequence to fold into G-quadruplex structures and demonstrated that the three DNA polymorphisms did not perturb the folding into G-quadruplex but affected G-quadruplex conformation. A functional luciferase reporter-based assay revealed functional differences between 3'UTR haplotypes. These data show that polymorphisms in a G-rich sequence of the 3'UTR of KISS1, able to fold into G-quadruplex structures, can modulate gene expression. They highlight the potential role of this G-quadruplex in the regulation of KISS1 expression and in the timing of pubertal onset.

Circulating kisspeptin levels exhibit sexual dimorphism in adults, are increased in obese prepubertal girls and do not suffer modifications in girls with idiopathic central precocious puberty

The system KISS1-KISS1R is one of the main regulators of the hypothalamic-pituitary-gonadal axis and constitutes a link between metabolism and reproduction through its interaction with leptin. The aim of this study was to clarify the possible utility of kisspeptin as a pubertal marker and/or the possible influence of nutritional status in kisspeptin levels. To this end, we have studied kisspeptin plasma levels throughout sexual development and in prepubertal obese girls and girls affected by idiopathic central precocious puberty (CPP). Plasma kisspeptin concentrations were analyzed by RIA. An increase in kisspeptin levels was observed in adult females compared to healthy prepubertal and pubertal girls (p<0.001) and to adult males (p<0.001). Additionally, kisspeptin was increased in prepubertal obese girls compared to healthy prepubertal girls (p<0.01) and girls with idiopathic CPP (p<0.05). As revealed by the regression analysis, in prepubertal healthy and obese girls and girls with idiopathic CCP, the parameters that influenced kisspeptin levels were BMI (R(2)=0.10, p<0.05) and leptin levels (R(2)=0.14, p<0.01). In conclusion, kisspeptin levels do not seem to be a good pubertal marker. The results obtained in prepubertal and idiopathic CCP girls point to a relationship between leptin, BMI and kisspeptin at least in this group, and suggest a possible role for adipose tissue in the modulation kisspeptin synthesis.

Plasma kisspeptin levels are elevated in cord blood and present sexual dimorphism in the adult population: relation with leptin, gonadotropins and anthropometrical data

Kisspeptin, the product of the hypothalamic KISS1 gene, is a main regulator of the hypothalamic-pituitary-gonadal axis and could be a link between metabolism and reproduction through its interaction with leptin. Kisspeptin could be involved in gonadotropin regulation and responsive to leptin levels from the first stages of life, exhibiting, as does leptin, sexual dimorphism. To test our hypothesis, we have analyzed plasma kisspeptin levels and their possible relationship with gonadotropins and leptin in a cohort composed of newborns (n = 86) and adults (n = 55). Plasma kisspeptin, gonadotropin and leptin levels were measured by RIA and multiplexed bead immunoassays, respectively. We have built a multivariate linear regression model (analyzing kisspeptin and LH separately as dependent variables) by stepwise analysis, incorporating the variables that had shown significant correlation in the univariate analysis. Cord blood samples exhibited high kisspeptin levels 127.01(113-141.02 pmol/l), but these were not sexually dimorphic. The adult population exhibited sexual dimorphism (3.72(2.95-4.49) vs. 1.77(1.23-2.31)pmol/l women vs. men, p<0.05). Leptin levels showed sexual dimorphism in cord blood samples and also in the adult population. Furthermore, there was a significant interaction between LH and kisspeptin levels and kisspeptin was negatively correlated with age. The high kisspeptin levels observed in cord blood, with no sexual dimorphism, suggest a placental source. The sexual dimorphism exhibited in adulthood supports the notion that there are different sources and/or differential kisspeptin regulation between men and women.

Bioanalytical determination of unstable endogenous small peptides: RFRP3 and its metabolites in rat blood

Background: Targeting the gonadotropin-releasing hormone pathway for the treatment of endometriosis leads to an interest in monitoring for endogenous modulators of this pathway (RFRP3 and kisspeptin) as baseline controls for treatment development. Results: Stabilization of RFRP3 was shown to be extremely difficult in a highly enzymatically active matrix, such as rat blood. Sample denaturing with solvent at collection was necessary due to enzyme inhibition being unsuccessful at stabilization leading to difficulties in sample processing. Monitoring multiple fragments formed in blood can aid in profiling these peptides once in-source conversion is controlled. Conclusion: generic high-sensitivity LC–MS/MS assay was developed for RFRP3 and the fragments formed from it in whole blood. Use of 2D chromatography circumvents concentration and retention issues related to small fragments with a normal flow setup, making a more open-access approach feasible.

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.

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.

Kisspeptin-10 inhibits angiogenesis in human placental vessels ex vivo and endothelial cells in vitro

Recent studies suggest that kisspeptin (a neuropeptide central to the regulation of gonadotrophin secretion) has diverse roles in human physiology, including a putative role in implantation and placental function. Kisspeptin and its receptor are present in human blood vessels, where they mediate vasoconstriction, and kisspeptin is known to inhibit tumor metastasis and trophoblast invasion, both processes involving angiogenesis. We hypothesized that kisspeptin contributes to the regulation of angiogenesis in the reproductive system. The presence of the kisspeptin receptor was confirmed in human placental blood vessels and human umbilical vein endothelial cells (HUVEC) using immunochemistry. The ability of kisspeptin-10 (KP-10) (a shorter biologically active processed peptide) to inhibit angiogenesis was tested in explanted human placental arteries and HUVEC using complementary ex vivo and in vitro assays. KP-10 inhibited new vessel sprouting from placental arteries embedded in Matrigel and tube-like structure formation by HUVEC, in a concentration-dependent manner. KP-10 had no effect on HUVEC viability or apoptosis but induced concentration-dependent inhibition of proliferation and migration. In conclusion, KP-10 has antiangiogenic effects and, given its high expression in the placenta, may contribute to the regulation of angiogenesis in this tissue.

Maturation of kisspeptinergic neurons coincides with puberty onset in male rats

Kisspeptins, derived from the Kiss1 gene play a central role in activation of the hypothalamo-pituitary gonadal (HPG) axis via stimulation of GnRH neurons. Both Kiss1 and Kiss1R (receptor) mRNA levels are found to be low in pre-pubertal rats, but whether an increase in kisspeptin and/or its receptor is the primary component in the initiation of puberty and where in the hypothalamus regulation of the kisspeptin/Kiss1R system occurs is unresolved. Using immunohistochemistry and in situ hybridization, we analyzed the level of Kiss1 mRNA and kisspeptin-immunoreactivity in the anteroventral periventricular nucleus (AVPV) and the arcuate nucleus of male rats along pubertal development. Neurons expressing Kiss1 mRNA were first detected at PND15, but increased significantly around puberty, and declined again in the adult rat. While virtually no immunoreactive cell bodies were detectable in the AVPV at any age, numerous kisspeptin-positive neurons in the arcuate nucleus were detected in the adult rat. Increasing doses of kisspeptin-54 given peripherally to male rats at PND15, 30, 45, and 60 evoked roughly similar effects, as revealed by the induction of c-Fos in the pituitary and secretion of LH and testosterone. These results show that both Kiss1 mRNA and the peptide increase in arcuate nucleus along pubertal maturation. Since kisspeptin signaling is potentially functional, even for peripheral activation, and well before the kisspeptin neuronal system is fully matured, our data support that the regulation of kisspeptin synthesis and release are key events in puberty onset in the male rat.

A role for kisspeptins in pregnancy: facts and speculations

Kisspeptin is a neuropeptide that was originally discovered in 1996 from a metastasis tumour suppressor gene,KISS1and was appropriately named metastin. More recently, the discovery of inactivating mutations in the receptor for kisspeptin, a G protein-coupled receptor, GPR54 (KISS1R), have been shown to result in a failure to progress through puberty in man. These findings have led to the kisspeptin/KISS1R system being described as an essential gatekeeper of reproductive function. Recent studies have suggested additional roles of kisspeptin, other than in the central control of the gonadotropic axis including placentation and pregnancy, energy homeostasis and cardiovascular function. Therefore, kisspeptin–KISS1R signalling potentially plays diverse roles in human physiology. Here, we review the literature regarding the role and physiological significance of kisspeptin in pregnancy and highlight some of the key questions that require addressing.

Kisspeptin stimulation of insulin secretion: mechanisms of action in mouse islets and rats

AIMS/HYPOTHESIS

Kisspeptin is a novel peptide identified as an endogenous ligand of the G-protein-coupled receptor 54 (GPR-54), which plays a crucial role in puberty and reproductive function. High levels of GPR-54 and kisspeptin have been reported in the pancreas and we have previously shown that kisspeptin potentiates glucose-induced insulin release from isolated islets, although the mechanisms underlying this effect were unclear.

METHODS

Insulin secretion from isolated mouse islets was measured to characterise the effects of kisspeptin. The effects of kisspeptin on both p42/44 mitogen-activated protein kinase (MAPK) phosphorylation and intracellular Ca(2+)([Ca(2+)](i)) in mouse islets were also investigated. Furthermore, kisspeptin was administered to rats in vivo and effects on plasma insulin levels measured.

RESULTS

In the current study, kisspeptin induced a concentration-dependent potentiation of glucose-induced (20 mmol/l) insulin secretion from mouse islets, with maximal effects at 1 micromol/l, but had no effect on insulin secretion at a substimulatory concentration of glucose (2 mmol/l). Activation of GPR-54 by kisspeptin also caused reversible increases in [Ca(2+)](i) in Fura-2 loaded dispersed islet cells. The kisspeptin-induced potentiation of glucose-induced insulin secretion was completely abolished by inhibitors of phospholipase C and p42/44 MAPK, but not by inhibitors of protein kinase C or p38 MAPK. Intravenous administration of kisspeptin into conscious, unrestrained rats caused an increase in circulating insulin levels, whilst central administration of kisspeptin had no effect, indicating a peripheral site of action.

CONCLUSIONS/INTERPRETATION

These observations suggest that neither typical protein kinase C isoforms nor p38 MAPK are involved in the potentiation of glucose-induced insulin release by kisspeptin, but intracellular signalling pathways involving phospholipase C, p42/44 MAPK and increased [Ca(2+)](i) are required for the stimulatory effects on insulin secretion. The observation that kisspeptin is also capable of stimulating insulin release in vivo supports the conclusion that kisspeptin is a regulator of beta cell function.

Kisspeptins and the control of gonadotropin secretion in humans

The kisspeptin hormones are a family of peptides encoded by the KiSS-1 gene, which bind to the G-protein coupled receptor-54 (GPR54). Interactions between kisspeptin and GPR54 are thought to play a critical role in reproduction. In agreement with animal data, kisspeptin-54 administration acutely stimulates the release of gonadotrophins in both male and female healthy subjects, with no observed adverse effects. Furthermore, its potency is comparable to those of other gonadotrophin secretagogues studied. The kisspeptin-GPR54 system thus offers a novel means of therapeutically manipulating the hypothalamo-pituitary-gonadal (HPG) axis in humans. This article aims to provide a focused review of the experimental data which inform us how kisspeptin influences the HPG axis in humans.

GPR54 and kisspeptins

The G-protein coupled receptor GPR54 has an essential role in the initiation and maintenance of mammalian fertility. Humans and mice with mutations in GPR54 have hypogonadotropic hypogonadism characterized by absence of sexual maturation and low levels of gonadotropic hormones (LH and FSH). The ligand for GPR54 is encoded by the KISS1 gene, which produces a 54-amino-acid peptide (metastin or kisspeptin-54) that can be cleaved into shorter peptides (kisspeptins 14, 13 and 10) with similar potencies. Kisspeptin administration stimulates gonadotropin release in several species by inducing GnRH secretion from hypothalamic GnRH neurons expressing GPR54. Kisspeptins are produced by neurons located in the AVPV and ARC regions of the hypothalamus. Expression of Kiss1 in these neurons is differentially regulated by sex steroids providing a mechanism by which testosterone or estrogen can regulate GnRH release. The AVPV region is sexually dimorphic with highest expression of kisspeptin in females. Positive feedback by estrogen on expression of Kiss1 in the AVPV region may be responsible for the pre-ovulatory LH surge during the estrus cycle. Central administration of kisspeptin to immature female rats can induce precocious activation of the gonadotropic axis, causing advanced vaginal opening, elevated uterus weight, increased serum levels of LH and estrogen and induce ovulation. Kisspeptins/GPR54 have also been implicated in regulating the estrus cycle of seasonal breeders and in the control of lactational amenorrhea. Expression of Gpr54 and Kiss1 have also been reported in several peripheral tissues including the pituitary, ovary, testes and the placenta raising the possibility that these genes may have additional functions in these tissues. Regulation of kisspeptin expression by peripheral factors such as leptin may be involved in coordinating metabolic status with the reproductive axis.