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

Kisspeptin a potential therapeutic target in treatment of both metabolic and reproductive dysfunction

Kisspeptins (KPs) are proteins that were first recognized to have antimetastatic action. Later, the critical role of this peptide in the regulation of reproduction was proved. In recent years, evidence has been accumulated supporting a role for KPs in regulating metabolic processes in a sexual dimorphic manner. It has been proposed that KPs regulate metabolism both indirectly via gonadal hormones and/or directly via the kisspeptin receptor in the brain, brown adipose tissue, and pancreas. The aim of the review is to provide both experimental and clinical evidence indicating that KPs are peptides linking metabolism and reproduction. We propose that KPs could be used as a potential target to treat both metabolic and reproductive abnormalities. Thus, we focus on the consequences of disruptions in KPs and their receptors in metabolic conditions such as diabetes, undernutrition, obesity, and reproductive disorders (hypogonadotropic hypogonadism and polycystic ovary syndrome). Data from both animal models and human subjects indicate that alterations in KPs in the case of metabolic imbalance lead also to disruptions in reproductive functions. Changes both in the hypothalamic and peripheral KP systems in animal models of the aforementioned disorders are discussed. Finally, an overview of current clinical studies involving KP in fertility and metabolism show fewer studies on metabolism (15%) and only one to date on both. Presented data indicate a dynamic and emerging field of KP studies as possible therapeutic targets in treatments of both reproductive and metabolic dysfunctions.

Cryptorchidism and puberty

Cryptorchidism is the condition in which one or both testes have not descended adequately into the scrotum. The congenital form of cryptorchidism is one of the most prevalent urogenital anomalies in male newborns. In the acquired form of cryptorchidism, the testis that was previously descended normally is no longer located in the scrotum. Cryptorchidism is associated with an increased risk of infertility and testicular germ cell tumors. However, data on pubertal progression are less well-established because of the limited number of studies. Here, we aim to review the currently available data on pubertal development in boys with a history of non-syndromic cryptorchidism-both congenital and acquired cryptorchidism. The review is focused on the timing of puberty, physical changes, testicular growth, and endocrine development during puberty. The available evidence demonstrated that the timing of the onset of puberty in boys with a history of congenital cryptorchidism does not differ from that of non-cryptorchid boys. Hypothalamic-pituitary-gonadal hormone measurements showed an impaired function or fewer Sertoli cells and/or germ cells among boys with a history of cryptorchidism, particularly with a history of bilateral cryptorchidism treated with orchiopexy. Leydig cell function is generally not affected in boys with a history of cryptorchidism. Data on pubertal development among boys with acquired cryptorchidism are lacking; therefore, more research is needed to investigate pubertal progression among such boys.

Current Insights in Prolactin Signaling and Ovulatory Function

Prolactin (PRL) is a pleiotropic hormone released from lactotrophic cells of the anterior pituitary gland that also originates from extrapituitary sources and plays an important role in regulating lactation in mammals, as well as other actions. Acting in an endocrine and paracrine/autocrine manner, PRL regulates the hypothalamic-pituitary-ovarian axis, thus influencing the maturation of ovarian follicles and ovulation. This review provides a detailed discussion of the current knowledge on the role of PRL in the context of ovulation and ovulatory disorders, particularly with regard to hyperprolactinemia, which is one of the most common causes of infertility in women. Much attention has been given to the PRL structure and the PRL receptor (PRLR), as well as the diverse functions of PRLR signaling under normal and pathological conditions. The hormonal regulation of the menstrual cycle in connection with folliculogenesis and ovulation, as well as the current classifications of ovulation disorders, are also described. Finally, the state of knowledge regarding the importance of TIDA (tuberoinfundibular dopamine), KNDγ (kisspeptin/neurokinin B/dynorphin), and GnRH (gonadotropin-releasing hormone) neurons in PRL- and kisspeptin (KP)-dependent regulation of the hypothalamic-pituitary-gonadal (HPG) axis in women is reviewed. Based on this review, a rationale for influencing PRL signaling pathways in therapeutic activities accompanying ovulation disorders is presented.

Kisspeptin regulates airway hyperresponsiveness and remodeling in a mouse model of asthma

Asthma is a multifactorial disease of origin characterized by airway hyperresponsiveness (AHR) and airway remodeling. Several pieces of evidence from other pathologies suggest that Kisspeptins (Kp) regulate cell proliferation, migration, and invasion, mechanisms that are highly relevant to asthma. Our recent in vitro studies show Kp-10 (active peptide of Kp), via its receptor, KISS1R, inhibits human airway smooth muscle cell proliferation. Here, we hypothesize a crucial role for Kp-10 in regulating AHR and airway remodeling in vivo. Utilizing C57BL/6J mice, we assessed the effect of chronic intranasal Kp-10 exposure on mixed allergen (MA)-induced mouse model of asthma. MA-challenged mice showed significant deterioration of lung function compared to those exposed to vehicle (DPBS); Kp-10 treatment significantly improved the MA-altered lung functions. Mice treated with Kp-10 alone did not show any notable changes in lung functions. MA-exposed mice showed a significant reduction in KISS1R expression as compared to vehicle alone. MA-challenged mice showed significant alterations in immune cell infiltration in the airways and remodeling changes. Proinflammatory cytokines were significantly increased upon MA exposure, an effect abrogated by Kp-10 treatment. Furthermore, biochemical and histological studies showed Kp-10 exposure significantly reduced MA-induced smooth muscle mass and soluble collagen in the lung. Overall, our findings highlight the effect of chronic Kp-10 exposure in regulating MA-induced AHR and remodeling. © 2023 The Pathological Society of Great Britain and Ireland.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

SIGNIFICANCE STATEMENT

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

Modelling KNDy neurons and gonadotropin-releasing hormone pulse generation

The pulsatile release of gonadotropin-releasing hormone (GnRH) and its frequency are crucial for healthy reproductive function. To understand what drives GnRH pulses, a combination of experimental and mathematical modelling approaches has been used. Early work focussed on the possibility that GnRH pulse generation is an intrinsic feature of GnRH neurons, with autocrine feedback generating pulsatility. However, there is now ample evidence suggesting that a network of upstream neurons secreting kisspeptin, neurokinin-B and dynorphin are the source of this GnRH pulse generator. The interplay of slow positive and negative feedback via neurokinin-B and dynorphin, respectively, allows the network to act as a relaxation oscillator, driving pulsatile secretion of kisspeptin, and consequently, of GnRH and LH. Here, we review the mathematical modelling approaches exploring both scenarios and suggest that with pulsatile GnRH secretion driven by the KNDy pulse generator, autocrine feedback still has the potential to modulate GnRH output.

Receptor deorphanization in an echinoderm reveals kisspeptin evolution and relationship with SALMFamide neuropeptides

BACKGROUND

Kisspeptins are neuropeptides that regulate reproductive maturation in mammals via G-protein-coupled receptor-mediated stimulation of gonadotropin-releasing hormone secretion from the hypothalamus. Phylogenetic analysis of kisspeptin-type receptors indicates that this neuropeptide signaling system originated in a common ancestor of the Bilateria, but little is known about kisspeptin signaling in invertebrates.

RESULTS

Contrasting with the occurrence of a single kisspeptin receptor in mammalian species, here, we report the discovery of an expanded family of eleven kisspeptin-type receptors in a deuterostome invertebrate - the starfish Asterias rubens (phylum Echinodermata). Furthermore, neuropeptides derived from four precursor proteins were identified as ligands for six of these receptors. One or more kisspeptin-like neuropeptides derived from two precursor proteins (ArKPP1, ArKPP2) act as ligands for four A. rubens kisspeptin-type receptors (ArKPR1,3,8,9). Furthermore, a family of neuropeptides that act as muscle relaxants in echinoderms (SALMFamides) are ligands for two A. rubens kisspeptin-type receptors (ArKPR6,7). The SALMFamide neuropeptide S1 (or ArS1.4) and a 'cocktail' of the seven neuropeptides derived from the S1 precursor protein (ArS1.1-ArS1.7) act as ligands for ArKPR7. The SALMFamide neuropeptide S2 (or ArS2.3) and a 'cocktail' of the eight neuropeptides derived from the S2 precursor protein (ArS2.1-ArS2.8) act as ligands for ArKPR6.

CONCLUSIONS

Our findings reveal a remarkable diversity of neuropeptides that act as ligands for kisspeptin-type receptors in starfish and provide important new insights into the evolution of kisspeptin signaling. Furthermore, the discovery of the hitherto unknown relationship of kisspeptins with SALMFamides, neuropeptides that were discovered in starfish prior to the identification of kisspeptins in mammals, presents a radical change in perspective for research on kisspeptin signaling.

Acute Effects of Kisspeptin Administration on Bone Metabolism in Healthy Men

CONTEXT

Osteoporosis results from disturbances in bone formation and resorption. Recent nonhuman data suggest that the reproductive hormone kisspeptin directly stimulates osteoblast differentiation in vitro and thus could have clinical therapeutic potential. However, the effects of kisspeptin on human bone metabolism are currently unknown.

OBJECTIVE

To assess the effects of kisspeptin on human bone metabolism in vitro and in vivo.

METHODS

In vitro study: of Mono- and cocultures of human osteoblasts and osteoclasts treated with kisspeptin. Clinical study: Randomized, placebo-controlled, double-blind, 2-way crossover clinical study in 26 men investigating the effects of acute kisspeptin administration (90 minutes) on human bone metabolism, with blood sampling every 30 minutes to +90 minutes. Cells for the in vitro study were from 12 male blood donors and 8 patients undergoing hip replacement surgery. Twenty-six healthy eugonadal men (age 26.8 ± 5.8 years) were included in the clinical study. The intervention was Kisspeptin (vs placebo) administration. The main outcome measures were changes in bone parameters and turnover markers.

RESULTS

Incubation with kisspeptin in vitro increased alkaline phosphatase levels in human bone marrow mesenchymal stem cells by 41.1% (P = .0022), and robustly inhibited osteoclastic resorptive activity by up to 53.4% (P < .0001), in a dose-dependent manner. Kisspeptin administration to healthy men increased osteoblast activity, as evidenced by a 20.3% maximal increase in total osteocalcin (P = .021) and 24.3% maximal increase in carboxylated osteocalcin levels (P = .014).

CONCLUSION

Collectively, these data provide the first human evidence that kisspeptin promotes osteogenic differentiation of osteoblast progenitors and inhibits bone resorption in vitro. Furthermore, kisspeptin acutely increases the bone formation marker osteocalcin but not resorption markers in healthy men, independent of downstream sex steroid levels. Kisspeptin could therefore have clinical therapeutic application in the treatment of osteoporosis.

Putative Role of the Kisspeptin/Kiss1R System in Promoting Hypothalamic GnRH Release, Pubertal Maturation, and Regulation of Ovulation Considering the Central Reproductive Axis

Kisspeptin is a class of neuropeptides that are the product of the Kiss1 gene. These neuropeptides play an important role in maintaining gonadotropin-releasing hormone (GnRH) levels and their release through hypothalamic neurons. Subsequently, they also play an important role in maintaining gonadotropin levels, as GnRH levels stimulate the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which allow induction of gametogenesis of pubertal maturation. The importance of the Kiss1 gene in reproduction became evident when natural mutations in this gene were discovered, which were associated with hypothalamic hypogonadism (HH) and delayed puberty. Kisspeptin and its KISS1R receptors are expressed in the mammalian ovary. The putative role of the Kisspeptin system in the ovary directly controls oocyte maturation, follicular development, and ovulation in an autocrine and paracrine fashion. These essential facts of kisspeptin and its receptor are necessary to maintain the central reproductive axis.

Distribution of kisspeptin system and its relation with gonadotropin-releasing hormone in the hypothalamus of the South American plains vizcacha, Lagostomus maximus

Kisspeptin (KISS), a key hormone involved in the regulation of the hypothalamic-pituitary-ovarian (HPO) axis, has been localized in the anteroventral periventricular (AVPV) nucleus and the neighboring rostral periventricular nucleus (PeVN), and in the arcuate (ARC) nucleus of the mammalian hypothalamus. In the ARC, the KISS neurons that co-express neurokinin B (NKB) and dynorphin A (Dyn) are named KNDy cells. The South American plains vizcacha is a rodent with peculiar reproductive traits. Around mid-pregnancy, vizcacha shows the reactivation of its HPO axis with the pulsatile release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH), an essential event for the success of gestation. Considering the role of KISS system in GnRH modulation, the aim of this work was to study their neuroanatomical distribution in adult vizcachas. AVPV showed sexual dimorphism with a significant smaller area in males (t-Test, p < 0.05), and KISS immunoreactivity was detected in somas and varicosities homogenously distributed in the AVPV with a concordant sex-related expression pattern. NKB and Dyn expression was also observed in cytoplasm of neurons scattered in the AVPV. Three subpopulations of neurons were detected in the AVPV: neurons expressing Dyn and NKB (DyNK cells), neurons expressing KISS and NKB (KiNK cells), and single NKB expressing neurons. Strikingly, KISS and Dyn were always expressed in different cells. In addition, in the ARC nucleus, KNDy cells were detected. On the other hand, KISS and GnRH expression was detected in different subpopulations of neurons, GnRH cells showed KISS receptor (KISSR or GPR-54) expression, and KISS immunoreactive afferent contacts were detected making close appositions onto somas and dendrites of GnRH cells. These results show similarities and differences between the KISS system in the hypothalamus of the vizcacha and other mammals, and constitute crucial observations about KISS and GnRH relation. Considering the peculiarity of HPO axis regulation in this species, the present work provides a neuroanatomical framework for the further elucidation of molecular mechanisms underlying GnRH expression and secretion.

The relation between obesity, kisspeptin, leptin, and male fertility

Over the past decades, obesity and infertility in men increased in parallel, and the association between both phenomena have been examined by several researchers. despite the fact that there is no agreement, obesity appears to affect the reproductive potential of men through various mechanisms, such as changes in the hypothalamic-pituitary-testicular (HPT) axis, spermatogenesis, sperm quality and/or alteration of sexual health. Leptin is a hormone produced by the adipose tissue, and its production elevates with increasing body fat. Many studies have supported the relationship between raised leptin production and reproductive function regulation. In fact, Leptin acts on the HPT axis in men at all levels. However, most obese men are insensitive to increased production of endogenous leptin and functional leptin resistance development. Recently, it has been recommended that Kisspeptin neurons mediate the leptin's effects on the reproductive system. Kisspeptin binding to its receptor on gonadotropin-releasing hormone (GnRH) neurons, activates the mammal's reproductive axis and stimulates GnRH release. Increasing infertility associated with obesity is probably mediated by the Kisspeptin-GnRH pathway. In this review, the link between obesity, kisspeptin, leptin, and male fertility will be discussed.

A dual kisspeptin-GnRH immunogen for reproductive immunosterilization

GnRH immunogens have been extensively employed in immunocontraception of animals. While they are effective, they are not 100% efficacious and of limited duration. GnRH secretion is dependent on upstream stimulation by kisspeptin. We therefore hypothesised that a dual immunogen combining GnRH and kisspeptin may be more efficacious through targeting two levels of the axis. We have previously shown GnRH immunogen elicits permanent sterilisation when sheep are vaccinated neonatally suggesting that the efficacy of GnRH immunisation may be dependent on the stage of reproductive development. We have now studied over 300 days the efficacy of immunisation with a dual immunogen comprising GnRH linked to kisspeptin via a hepatitis B T helper peptide sequence (GKT) administered to male and female rats prepubertally, pubertally and as adults. At all stages of development all immunised animals produced antibodies to GnRH, kisspeptin and GKT but differentially in titre with respect to sex and stage of development. In immunised adult, prepubertal and pubertal males testosterone and testes length was markedly reduced by 60 days and remained at low levels until day 150. Thereafter, testosterone recovered to pre immunisation levels and testes length increased to a maximum of about 40% of controls. 80% of males were infertile in three matings over 250 days. In prepubertal and pubertal female rats a single immunisation at day 0 reduced estradiol to low levels by day 60 which remained low until termination of the experiment on day 300. In matings of these females with fertile males on days 90, 120 and 250, 74% of prepubertal females were infertile and impressively, 100% (10/10) of pubertal females were infertile after a single immunisation on day 0. These findings set the scene for exploration of immunosterilisation of wild and domestic animals after a single immunisation.

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

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

Effects of total flavonoids from Eucommia ulmoides Oliv. leaves on polycystic ovary syndrome with insulin resistance model rats induced by letrozole combined with a high-fat diet

ETHNOPHARMACOLOGICAL RELEVANCE

Eucommia ulmoides Oliv. leaves are the dry leaves of Eucommia ulmoides Oliv. Modern studies have shown that Eucommia ulmoides Oliv. leaves and its extracts have many pharmacological effects, such as regulating hypothalamus pituitary ovary (HPO) axis function, estrogen like effects, correcting insulin resistance (IR), regulating lipids, and reducing weight, which are consistent with the clinical manifestations in polycystic ovary syndrome (PCOS) patients. PCOS patients often have HPO axis disorder, low estrogen, high androgen, high IR complication rate, and obesity. Previous preclinical studies have shown that total flavonoids from Eucommia ulmoides Oliv. leaves (TFEL) can improve the imbalance in sex hormone secretion in perimenopausal animal models by regulating the function of the HPO axis. Thus, it is important to understand if flavonoids are the active parts of Eucommia ulmoides Oliv. leaves that interfere with polycystic ovary syndrome with insulin resistance (PCOS-IR), and determine the regulatory role they play in sex hormones and IR?

AIM OF THE STUDY

Investigate the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway in the ovary and kisspeptin/insulin like growth factor/leptin receptor1/androgen receptor (Kiss1/IGF-1/LEPR/AR) in the HPO axis to determine the mechanism of TFEL intervention in a rat model of PCOS-IR model rats.

MATERIALS AND METHODS

A rat model of PCOS-IR was established using a high-fat diet (49 d) combined with letrozole (1 mg/kg·d, for 28 d). Then, metformin (300 mg/kg·d) and TFEL (220 mg/kg·d, 110 mg/kg·d, and 55 mg/kg·d) were administered continuously for 21 days. At the end of the experiment, samples were taken and the related indexes were measured.

RESULTS

TFEL reduced the body weight, Lee's index, ovarian index, ovarian area and ovarian volume, increased serum E2, SHBG levels and ISI, decreased serum levels of T, LEP, INS, and FBG (whole blood), and reduced the HOMA-IR in rats with PCOS-IR. TFEL downregulate Kiss1, IGF-1, and AR in the arcuate nucleus of hypothalamus, and upregulate Kiss1, downregulate IGF-1 and AR in the pituitary gland, and upregulate Kiss1, downregulate IGF-1, LEPR, and AR in the ovary of rats with PCOS-IR. TFEL could downregulate p-IRS-1Ser307, upregulate IRS-1, p-IRS-1Tyr895, PI3Kp85α, p-PI3Kp85α, AKT, p-AKT, and GLUT4 in the ovary, and ameliorated histopathological changes in the ovary and pancreas of rats with PCOS-IR.

CONCLUSION

TFEL can inhibit ovarian hyperplasia, regulate disorders of glucose and lipid metabolism and improve the secretion of sex hormones, by regulating the expression of PI3K/AKT signaling pathway-related proteins in the ovary and Kiss1/IGF-1/LEPR/AR in the HPO axis.

Kisspeptin receptor agonist has therapeutic potential for female reproductive disorders

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

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.

Regulation of breast cancer metastasis signaling by miRNAs

Despite the decline in death rate from breast cancer and recent advances in targeted therapies and combinations for the treatment of metastatic disease, metastatic breast cancer remains the second leading cause of cancer-associated death in U.S. women. The invasion-metastasis cascade involves a number of steps and multitudes of proteins and signaling molecules. The pathways include invasion, intravasation, circulation, extravasation, infiltration into a distant site to form a metastatic niche, and micrometastasis formation in a new environment. Each of these processes is regulated by changes in gene expression. Noncoding RNAs including microRNAs (miRNAs) are involved in breast cancer tumorigenesis, progression, and metastasis by post-transcriptional regulation of target gene expression. miRNAs can stimulate oncogenesis (oncomiRs), inhibit tumor growth (tumor suppressors or miRsupps), and regulate gene targets in metastasis (metastamiRs). The goal of this review is to summarize some of the key miRNAs that regulate genes and pathways involved in metastatic breast cancer with an emphasis on estrogen receptor α (ERα+) breast cancer. We reviewed the identity, regulation, human breast tumor expression, and reported prognostic significance of miRNAs that have been documented to directly target key genes in pathways, including epithelial-to-mesenchymal transition (EMT) contributing to the metastatic cascade. We critically evaluated the evidence for metastamiRs and their targets and miRNA regulation of metastasis suppressor genes in breast cancer progression and metastasis. It is clear that our understanding of miRNA regulation of targets in metastasis is incomplete.

Kisspeptin-8 Induces Anxiety-Like Behavior and Hypolocomotion by Activating the HPA Axis and Increasing GABA Release in the Nucleus Accumbens in Rats

Kisspeptins (Kp) are RF-amide neuropeptide regulators of the reproductive axis that also influence anxiety, locomotion, and metabolism. We aimed to investigate the effects of intracerebroventricular Kp-8 (an N-terminally truncated octapeptide) treatment in Wistar rats. Elevated plus maze (EPM), computerized open field (OF), and marble burying (MB) tests were performed for the assessment of behavior. Serum LH and corticosterone levels were determined to assess kisspeptin1 receptor (Kiss1r) activation and hypothalamic-pituitary-adrenal axis (HPA) stimulation, respectively. GABA release from the nucleus accumbens (NAc) and dopamine release from the ventral tegmental area (VTA) and NAc were measured via ex vivo superfusion. Kp-8 decreased open arm time and entries in EPM, and also raised corticosterone concentration, pointing to an anxiogenic effect. Moreover, the decrease in arm entries in EPM, the delayed increase in immobility accompanied by reduced ambulatory activity in OF, and the reduction in interactions with marbles show that Kp-8 suppressed exploratory and spontaneous locomotion. The increase in GABA release from the NAc might be in the background of hypolocomotion by inhibiting the VTA-NAc dopaminergic circuitry. As Kp-8 raised LH concentration, it could activate Kiss1r and stimulate the reproductive axis. As Kiss1r is associated with hyperlocomotion, it is more likely that neuropeptide FF receptor activation is involved in the suppression of locomotor activity.

Current Knowledge on the Multifactorial Regulation of Corpora Lutea Lifespan: The Rabbit Model

Simple Summary

Corpora lutea (CL) are temporary endocrine structures that secrete progesterone, which is essential for maintaining a healthy pregnancy. A variety of regulatory factors come into play in modulating the functional lifespan of CL, with luteotropic and luteolytic effects. Many aspects of luteal phase physiology have been clarified, yet many others have not yet been determined, including the molecular and/or cellular mechanisms that maintain the CL from the beginning of luteolysis during early CL development. This paper summarizes our current knowledge of the endocrine and cellular mechanisms involved in multifactorial CL lifespan regulation, using the pseudopregnant rabbit model.

Abstract

Our research group studied the biological regulatory mechanisms of the corpora lutea (CL), paying particular attention to the pseudopregnant rabbit model, which has the advantage that the relative luteal age following ovulation is induced by the gonadotrophin-releasing hormone (GnRH). CL are temporary endocrine structures that secrete progesterone, which is essential for maintaining a healthy pregnancy. It is now clear that, besides the classical regulatory mechanism exerted by prostaglandin E2 (luteotropic) and prostaglandin F2α (luteolytic), a considerable number of other effectors assist in the regulation of CL. The aim of this paper is to summarize our current knowledge of the multifactorial mechanisms regulating CL lifespan in rabbits. Given the essential role of CL in reproductive success, a deeper understanding of the regulatory mechanisms will provide us with valuable insights on various reproductive issues that hinder fertility in this and other mammalian species, allowing to overcome the challenges for new and more efficient breeding strategies.

Existence and functions of a kisspeptin neuropeptide signaling system in a non-chordate deuterostome species

The kisspeptin system is a central modulator of the hypothalamic-pituitary-gonadal axis in vertebrates. Its existence outside the vertebrate lineage remains largely unknown. Here, we report the identification and characterization of the kisspeptin system in the sea cucumber Apostichopus japonicus. The gene encoding the kisspeptin precursor generates two mature neuropeptides, AjKiss1a and AjKiss1b. The receptors for these neuropeptides, AjKissR1 and AjKissR2, are strongly activated by synthetic A. japonicus and vertebrate kisspeptins, triggering a rapid intracellular mobilization of Ca²⁺, followed by receptor internalization. AjKissR1 and AjKissR2 share similar intracellular signaling pathways via G_αq/PLC/PKC/MAPK cascade, when activated by C-terminal decapeptide. The A. japonicus kisspeptin system functions in multiple tissues that are closely related to seasonal reproduction and metabolism. Overall, our findings uncover for the first time the existence and function of the kisspeptin system in a non-chordate species and provide new evidence to support the ancient origin of intracellular signaling and physiological functions that are mediated by this molecular system.

Association of Polymorphisms in the Kisspeptin/GPR54 Pathway Genes With Risk of Early Puberty in Chinese Girls

CONTEXT AND OBJECTIVE

This case control study was designed to investigate the association between mutation of 10 single nucleotide polymorphism (SNP) loci (rs1132506, rs5780218, rs192636495, rs4889, rs184749, rs12985070, rs708910, rs932491, rs8074995, and rs2306877) in all 5 genes (KISS1, GPR54, PLCB1, PRKCA, and ITPR1) in the kisspeptin/GPR54 pathway and the risk of early puberty in Chinese Han girls.

DESIGN AND PARTICIPANTS

A total of 314 pairs of early puberty girls on their first visit to hospital and age-matched controls (± 3 months) were recruited. The genotypes of each SNP were determined and the effect of loci variation on early puberty was investigated.

RESULTS

rs5780218 was significantly associated with early puberty in additive, dominant, and recessive models of inheritance after adjusting for confounding factors (Pr < .05). After stratification, rs5780218 variation (odds ratio [OR], 1.650, 95% confidence interval [CI], 1.155-2.355 in additive models and OR, 2.116; 95% CI, 1.187-3.770 in recessive models) increased the risk of central precocious puberty (CPP); mutation in rs708910 (OR, 2.768; 95% CI, 1.305-5.872 in recessive model) had a positive association with the risk of CPP; and rs932491 variation was negatively associated with early and fast puberty (EFP) (OR, 0.309; 95% CI, 0.144-0.661 in additive models and OR, 0.317; 95% CI, 0.141-0.713 in dominant models).

CONCLUSIONS

Our study suggests that mutation in rs5780218 and rs708910 increases the risk of CPP. rs932491 variation may have a protective effect on the risk of EFP. Further studies in larger populations or with people from different regions are needed to verify our findings.

Role of the tumor microenvironment in regulating the anti-metastatic effect of KISS1

KISS1, a metastasis suppressor gene, has been shown to block metastasis without affecting primary tumor formation. Loss of KISS1 leads to invasion and metastasis in multiple cancers, which is the leading cause of cancer morbidity and mortality. The discovery of KISS1 has provided a ray of hope for early clinical diagnosis and for designing effective treatments targeting metastatic cancer. However, this goal requires greater holistic understanding of its mechanism of action. In this review, we go back into history and highlight some key developments, from the discovery of KISS1 to its role in regulating multiple physiological processes including cancer. We discuss key emerging roles for KISS1, specifically interactions with tissue microenvironment to promote dormancy and regulation of tumor cell metabolism, acknowledged as some of the key players in tumor progression and metastasis. We finally discuss strategies whereby KISS1 might be exploited clinically to treat metastasis.

Three Siblings with Idiopathic Hypogonadotropic Hypogonadism in a Nonconsanguineous Family: A Novel KISS1R/GPR54 Loss-of-Function Mutation

Idiopathic hypogonadotropic hypogonadism (IHH) is a rare disease caused by defects in the secretion of gonadotropin releasing hormone (GnRH) or the action of GnRH on the pituitary gonadotrophes. KISS1R is one of the genes which, when mutated, cause IHH and mutations of this gene are responsible for about 2-5% of patients with normosmic IHH (NIHH). In this report, we present three siblings with NIHH due to a compound heterozygous KISS1R mutation. Genetic studies were carried out in the 14 year old index case with IHH and three siblings, two of whom were prepubertal. Genomic DNA was extracted from peripheral leukocytes and KISS1R gene was sequenced by using standard polymerase chain reaction amplification procedures. In molecular analysis of the index case, a compound heterozygous mutation was determined in KISS1R gene c.969C>A (p.Y323X) (known pathogenic) and c.170T>C (p.L57P) (novel). Mutation c.170T>C (p.L57P) was inherited from the mother while c.969C>A (p.Y323X) was inherited from the father. The same genotype was also found in two of the three siblings. A compound heterozygous mutation of the KISS1 gene, including one novel mutation, was found to cause NIHH and also incomplete puberty in a non-consanguineous family.

Understanding the functions of kisspeptin and kisspeptin receptor (Kiss1R) from clinical case studies

It is widely acknowledged that kisspeptin and its receptor Kiss1R play central regulatory roles in the hypothalamus-pituitary-gonad (HPG) axis and reproduction. Mutations of KISS1 and KISS1R lead to disorders associated with pubertal development, such as central precocious puberty (CPP) and idiopathic hypogonadotropic hypogonadism (IHH). This review focuses on KISS1 and KISS1R mutations found in CPP and IHH and its purposes are twofold: Firstly, based on the mutations found in KISS1 and KISS1R, this review provides insights into the precise mechanism of kisspeptin and the kisspeptin/Kiss1R pathway in the reproductive axis and in puberty. Secondly, G protein-coupled receptors (GPCRs) are known to share highly conserved structural motifs; therefore, knowledge of mutations found at different structural domains of Kiss1R in the diseased state, and how they affect Kiss1R function can be used to decipher GPCR domain function.

Reproductive functions of Kisspeptin/KISS1R Systems in the Periphery

Kisspeptin and its G protein-coupled receptor KISS1R play key roles in mammalian reproduction due to their involvement in the onset of puberty and control of the hypothalamic-pituitary-gonadal axis. However, recent studies have indicated a potential role of extra-hypothalamic kisspeptin in reproductive function. Here, we summarize recent advances in our understanding of the physiological significance of kisspeptin/KISS1R in the peripheral reproductive system (including the ovary, testis, uterus, and placenta) and the potential role of kisspeptin/KISS1R in reproductive diseases. A comprehensive understanding of the expression, function, and potential molecular mechanisms of kisspeptin/KISS1R in the peripheral reproductive system will contribute to the diagnosis, treatment and prevention of reproductive diseases.

How Pulsatile Kisspeptin Stimulation and GnRH Autocrine Feedback Can Drive GnRH Secretion: A Modeling Investigation

Pulsatile secretion of GnRH from hypothalamic GnRH neurons tightly regulates the release of mammalian reproductive hormones. Although key factors such as electrical activity and stimulation by kisspeptin have been extensively studied, the underlying mechanisms that regulate GnRH release are still not fully understood. Previously developed mathematical models studied hormonal release and electrical properties of GnRH neurons separately, but they never integrated both components. Herein, we present a more complete biophysical model to investigate how electrical activity and hormonal release interact. The model consists of two components: an electrical submodel comprised of a modified Izhikevich formalism incorporating several key ionic currents to reproduce GnRH neuronal bursting behavior, and a hormonal submodel that incorporates pulsatile kisspeptin stimulation and a GnRH autocrine feedback mechanism. Using the model, we examine the electrical activity of GnRH neurons and how kisspeptin affects GnRH pulsatility. The model reproduces the noise-driven bursting behavior of GnRH neurons as well as the experimentally observed electrophysiological effects induced by GnRH and kisspeptin. Specifically, the model reveals that external application of GnRH causes a transient hyperpolarization followed by an increase in firing frequency, whereas administration of kisspeptin leads to long-lasting depolarization of the neuron. The model also shows that GnRH release follows a pulsatile profile similar to that observed experimentally and that kisspeptin and GnRH exhibit ∼7-1 locking in their pulsatility. These results suggest that external kisspeptin stimulation with a period of ∼8 minutes drives the autocrine mechanism beyond a threshold to generate pronounced GnRH pulses every hour.

Kisspeptin/kisspeptin receptor system in pseudopregnant rabbit corpora lutea: presence and function

Kisspeptin (KiSS) and its related receptors (KiSS1R) have a critical role in the reproduction of mammals. The KiSS/KiSS1R system is expressed in numerous reproductive organs including the ovary. Here, we studied the expression of the KiSS/KiSS1R system and its functional role in rabbit corpora lutea (CL) at days 4 (early-), 9 (mid-), and 13 (late-stage) of pseudopregnancy. In vitro progesterone, prostaglandin (PG) F2α (PGF2α) and E2 (PGE2) productions and prostaglandin-endoperoxide synthase 1 (PTGS1) and 2 (PTGS2) activities were evaluated. Immune reactivity (IR) for KiSS and KiSS1R were detected in luteal cells at nuclear and cytoplasmic level at all luteal stage for KiSS and only at early- and mid-stage for KiSS1R; IR decreased from early- to later stages of pseudopregnancy. The KiSS-10 augmented progesterone and PGE2 and diminished PGF2α secretions by early- and mid-CL; KiSS-10 reduced PTGS2 activity at early- and mid-stages, but did not affect PTGS1 at any luteal stages. The antagonist KiSS-234 counteracted all KiSS-10 effects. This study shows that the KiSS/KiSS1R system is expressed in CL of pseudopregnant rabbits and exerts a luteotropic action by down-regulating PTGS2, which decreases PGF2α and increases PGE2 and progesterone.

Germline and mosaic mutations causing pituitary tumours: genetic and molecular aspects

While 95% of pituitary adenomas arise sporadically without a known inheritable predisposing mutation, in about 5% of the cases they can arise in a familial setting, either isolated (familial isolated pituitary adenoma or FIPA) or as part of a syndrome. FIPA is caused, in 15-30% of all kindreds, by inactivating mutations in the AIP gene, encoding a co-chaperone with a vast array of interacting partners and causing most commonly growth hormone excess. While the mechanisms linking AIP with pituitary tumorigenesis have not been fully understood, they are likely to involve several pathways, including the cAMP-dependent protein kinase A pathway via defective G inhibitory protein signalling or altered interaction with phosphodiesterases. The cAMP pathway is also affected by other conditions predisposing to pituitary tumours, including X-linked acrogigantism caused by duplications of the GPR101 gene, encoding an orphan G stimulatory protein-coupled receptor. Activating mosaic mutations in the GNAS gene, coding for the Gα stimulatory protein, cause McCune-Albright syndrome, while inactivating mutations in the regulatory type 1α subunit of protein kinase A represent the most frequent genetic cause of Carney complex, a syndromic condition with multi-organ manifestations also involving the pituitary gland. In this review, we discuss the genetic and molecular aspects of isolated and syndromic familial pituitary adenomas due to germline or mosaic mutations, including those secondary to AIP and GPR101 mutations, multiple endocrine neoplasia type 1 and 4, Carney complex, McCune-Albright syndrome, DICER1 syndrome and mutations in the SDHx genes underlying the association of familial paragangliomas and phaeochromocytomas with pituitary adenomas.

Modulations of human resting brain connectivity by kisspeptin enhance sexual and emotional functions

BACKGROUND

Resting brain connectivity is a crucial component of human behavior demonstrated by disruptions in psychosexual and emotional disorders. Kisspeptin, a recently identified critical reproductive hormone, can alter activity in certain brain structures but its effects on resting brain connectivity and networks in humans remain elusive.

METHODS

We determined the effects of kisspeptin on resting brain connectivity (using functional neuroimaging) and behavior (using psychometric analyses) in healthy men, in a randomized double-blinded 2-way placebo-controlled study.

RESULTS

Kisspeptin's modulation of the default mode network (DMN) correlated with increased limbic activity in response to sexual stimuli (globus pallidus r = 0.500, P = 0.005; cingulate r = 0.475, P = 0.009). Furthermore, kisspeptin's DMN modulation was greater in men with less reward drive (r = -0.489, P = 0.008) and predicted reduced sexual aversion (r = -0.499, P = 0.006), providing key functional significance. Kisspeptin also enhanced key mood connections including between the amygdala-cingulate, hippocampus-cingulate, and hippocampus-globus pallidus (all P < 0.05). Consistent with this, kisspeptin's enhancement of hippocampus-globus pallidus connectivity predicted increased responses to negative stimuli in limbic structures (including the thalamus and cingulate [all P < 0.01]).

CONCLUSION

Taken together, our data demonstrate a previously unknown role for kisspeptin in the modulation of functional brain connectivity and networks, integrating these with reproductive hormones and behaviors. Our findings that kisspeptin modulates resting brain connectivity to enhance sexual and emotional processing and decrease sexual aversion, provide foundation for kisspeptin-based therapies for associated disorders of body and mind.

FUNDING

NIHR, MRC, and Wellcome Trust.

β-arrestins and biased signaling in gonadotropin receptors

Gonadotropin receptors include the follicle stimulating hormone receptor (FSHR) and the luteinizing hormone/choriogonadotropin receptor (LHCGR), both belong to the G protein-coupled receptor (GPCR) superfamily and are essential to reproduction. FSHR is activated by follicle stimulating hormone (FSH) while LHCGR is activated by either luteinizing hormone (LH) or choriogonadotropin (CG). Upon ligand binding, gonadotropin receptors undergo conformational changes that lead to the activation of the heterotrimeric G protein, resulting in the production of different second messengers. Gonadotropin receptors can also recruit and bind β-arrestins. This particular class of scaffold proteins were initially identified to mediate GPCRs desensitization and recycling, but it is now well established that β-arrestins can also initiate Gs-independent signaling by assembling signaling modules. Furthermore, new advances in structural biology and biophysical techniques have revealed novel activation mechanisms allowing β-arrestins and G proteins to control signaling in time and space. The ability of different ligands to preferentially elicit G- or β-arrestin-mediated signaling is known as functional selectivity or biased signaling. This new concept has switched the view of pharmacology efficacy from monodimensional to multidimensional. Biased signaling offers the possibility to separate therapeutic benefits of a drug from its adverse effects. The proof of concept that gonadotropin receptors can be subjected to biased signaling is now established. The challenge will now be the design of molecules that can specifically activate beneficial signaling pathway at gonadotropin receptors while reducing or abolishing those leading to side effects. Such strategy could for instance lead to improved treatments for infertility.