GPR54 regulates ERK1/2 activity and hypothalamic gene expression in a Gα(q/11) and β-arrestin-dependent manner

Brain RFamide Neuropeptides in Stress-Related Psychopathologies

The RFamide peptide family is a group of proteins that share a common C-terminal arginine-phenylalanine-amide motif. To date, the family comprises five groups in mammals: neuropeptide FF, LPXRFamides/RFamide-related peptides, prolactin releasing peptide, QRFP, and kisspeptins. Different RFamide peptides have their own cognate receptors and are produced by different cell populations, although they all can also bind to neuropeptide FF receptors with different affinities. RFamide peptides function in the brain as neuropeptides regulating key aspects of homeostasis such as energy balance, reproduction, and cardiovascular function. Furthermore, they are involved in the organization of the stress response including modulation of pain. Considering the interaction between stress and various parameters of homeostasis, the role of RFamide peptides may be critical in the development of stress-related neuropathologies. This review will therefore focus on the role of RFamide peptides as possible key hubs in stress and stress-related psychopathologies. The neurotransmitter coexpression profile of RFamide-producing cells is also discussed, highlighting its potential functional significance. The development of novel pharmaceutical agents for the treatment of stress-related disorders is an ongoing need. Thus, the importance of RFamide research is underlined by the emergence of peptidergic and G-protein coupled receptor-based therapeutic targets in the pharmaceutical industry.

Asprosin aggravates atherosclerosis via regulating the phenotype transformation of vascular smooth muscle cells

Phenotype transformation of vascular smooth muscle cells (VSMCs) plays an important role in the development of atherosclerosis. Asprosin is a newly discovered adipokine, which is critical in regulating metabolism. However, the relationship between asprosin and phenotype transformation of VSMCs in atherosclerosis remains unclear. The aim of this study is to investigate whether asprosin affects the progression of atherosclerosis by inducing phenotype transformation of VSMCs. We established an atherosclerosis model in ApoE-/- mice and administered asprosin recombinant protein and asprosin antibody to mice. Knocking down asprosin was also as an intervention. Interestingly, we found a correlation between asprosin levels and atherosclerosis. Asprosin promoted plaque formation and phenotype transformation of VSMCs. While, AspKD or asprosin antibody reduced the plaque lesion and suppressed vascular stiffness in ApoE-/- mice. Mechanistically, asprosin induced phenotype transformation of MOVAs by binding to GPR54, leading to Gαq/11 recruitment and activation of the PLC-PKC-ERK1/2-STAT3 signaling pathway. Si GPR54 or GPR54 antagonist partially inhibited the action of asprosin in MOVAs. Mutant GPR54-(267, 307) residue cancelled the binding of asprosin and GPR54. In summary, this study confirmed asprosin activated GPR54/Gαq/11-dependent ERK1/2-STAT3 signaling pathway, thereby promoting VSMCs phenotype transformation and aggravating atherosclerosis, thus providing a new target for the treatment of atherosclerosis.

Enhancement of progesterone biosynthesis via kisspeptin stimulation: Upregulation of steroidogenic transcripts and phosphorylated extracellular signal-regulated kinase (p-ERK1/2) expression in the buffalo luteal cells

The presence of Kisspeptin (Kp) and its receptors in the corpus luteum (CL) of buffalo has recently been demonstrated. In this study, we investigated the role of Kp in the modulation of progesterone (P4) synthesis in vitro. The primary culture of bubaline luteal cells (LCs) was treated with 10, 50, and 100 nM of Kp and Kp antagonist (KpA) alongside a vehicle control. The combined effect of Kp and KpA was assessed at 100 nM concentration. Intracellular response to Kp treatment in the LCs was assessed by examining transcript profiles (LHR, STAR, CYP11A1, HSD3B1, and ERK1/2) using quantitative polymerase chain reaction (qPCR). In addition, the immunolocalization of ERK1/2 and phosphorylated ERK1/2 (p-ERK1/2) in the LCs was studied using immunocytochemistry. Accumulation of P4 from the culture supernatant was determined using enzyme-linked immunosorbent assay (ELISA). The results indicated that LCs had a greater p-ERK1/2 expression in the Kp treatment groups. A significant increase in the P4 concentration was recorded at 50 nM and 100 nM Kp, while KpA did not affect the basal concentration of P4. However, the addition of KpA to the Kp-treated group at 100 nM concentration suppressed the Kp-induced P4 accumulation into a concentration similar to the control. There was significant upregulation of ERK1/2 and CYP11A1 expressions in the Kp-treated LCs at 100 nM (18.1 and 37fold, respectively, p < 0.01). However, the addition of KpA to Kp-treated LCs modulated ERK1/2, LHR, STAR, CYP11A1, and HSD3B1 at 100 nM concentration. It can be concluded that Kp at 100 nM stimulated P4 production, while the addition of KpA suppressed Kp-induced P4 production in the buffalo LCs culture. Furthermore, an increment in p-ERK1/2 expression in the LCs indicated activation of the Kp signaling pathway was associated with luteal steroidogenesis.

The Emerging Therapeutic Potential of Kisspeptin and Neurokinin B

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

Key aspects of modern GPCR drug discovery

G-protein-coupled receptors (GPCRs) are the largest and most versatile cell surface receptor family with a broad repertoire of ligands and functions. We've learned an enormous amount about discovering drugs of this receptor class since the first GPCR was cloned and expressed in 1986, such that it's now well-recognized that GPCRs are the most successful target class for approved drugs. Here we take the reader through a GPCR drug discovery journey from target to the clinic, highlighting the key learnings, best practices, challenges, trends and insights on discovering drugs that ultimately modulate GPCR function therapeutically in patients. The future of GPCR drug discovery is inspiring, with more desirable drug mechanisms and new technologies enabling the delivery of better and more successful drugs.

Effects of benzo[a]pyrene on the reproductive axis: Impairment of kisspeptin signaling in human gonadotropin-releasing hormone primary neurons

The neuroendocrine control of reproduction is strictly coordinated at the central level by the pulsatile release of gonadotropin-releasing hormone (GnRH) by the hypothalamic GnRH neurons. Alterations of the GnRH-network, especially during development, lead to long-term reproductive and systemic consequences, also causing infertility. Recent evidence shows that benzo[a]pyrene (BaP), a diffuse pollutant that can play a role as an endocrine disruptor, affects gonadal function and gamete maturation, whereas data demonstrating its impact at hypothalamic level are very scarce. This study investigated the effects of BaP (10 μM) in a primary cell culture isolated from the human fetal hypothalamus (hfHypo) and exhibiting a clear GnRH neuron phenotype. BaP significantly decreased gene and protein expression of both GnRH and kisspeptin receptor (KISS1R), the master regulator of GnRH neuron function. Moreover, BaP exposure increased phospho-ERK1/2 signaling, a well-known mechanism associated with KISS1R activation. Interestingly, BaP altered the electrophysiological membrane properties leading to a significant depolarizing effect and it also significantly increased GnRH release, with both effects being not affected by kisspeptin addition. In conclusion, our findings demonstrate that BaP may alter GnRH neuron phenotype and function, mainly interfering with KISS1R signaling and GnRH secretion and therefore with crucial mechanisms implicated in the central neuroendocrine control of reproduction.

The role of KiSS1 gene on the growth and migration of prostate cancer and the underlying molecular mechanisms

Metastatic prostate cancers have a high mortality rate. KiSS1 was originally identified as a metastasis suppressor gene in metastatic melanoma and breast cancer, but its role in prostate cancer has been contradictory. This study was therefore undertaken to investigate the effects of KiSS1 overexpression on the growth and migration of human metastatic prostate cancer cells. We first tested the effect of KiSS1 overexpression on the growth and migration of DU145 human metastatic prostate cancer cells in vitro. DU145 cells were infected with the culture medium of 293T cells, which produce lentivirus particles containing KiSS1. A 2.5-fold increase in proliferation of KiSS1-overexpressing cancer cells was observed, and these cells formed tumor spheroids about 3 times larger than the vector control group. qPCR and immunoblotting revealed the association between increased cell growth and regulation of the PI3K/Akt and cell cycle genes, and also that increases in β-catenin and CD133 contribute to tumor aggregation. KiSS1 overexpression resulted in upregulation of the β-arrestin1/2 and Raf-MEK-ERK-NF-κB pathways via KiSS1R. Moreover, the migration and invasion of KiSS1-overexpressing cells were determined to be faster than the control group, along with 1.6-fold increased metastatic colonization of the KiSS1-overexpressing cancer cells. These were associated to the regulation of EMT gene expressions, such as E-cadherin and N-cadherin, and the upregulation of MMP9. In a xenograft mouse model inoculated with DU145 cells infected GFP or KiSS1 via a lentiviral vector, KiSS1 statistically significantly increased the tumor growth, with upregulation of PCNA and Ki-67 in the tumor tissues. In addition, KiSS1 increased the angiogenic capacity by upregulating VEGF-A and CD31, both in vitro and in vivo. Taken together, our results indicate that KiSS1 not only induces prostate cancer proliferation, but also promotes metastasis by increasing the migration, invasion, and angiogenesis of malignant cells.

Lack of Oestrogen Receptor Expression in Breast Cancer Cells Does Not Correlate with Kisspeptin Signalling and Migration

Kisspeptin is an anti-metastatic mediator in many cancer types, acting through its receptor, KISS1R. However, controversy remains regarding its role in breast cancer since both pro- and anti-metastatic roles have been ascribed to it. In KISS1R overexpressing triple-negative breast cancer (TNBC) cells, stimulation has been associated with increased invasion and MMP-9 expression, leading to the suggestion that hormone receptor status determines the metastatic effects of kisspeptin. To assess the veracity of this claim, we compared endogenous KISS1R signalling and physiological output in the hormone receptor-negative MDA-MB-231 and BT-20 cell lines after KP-10 (shortest active kisspeptin peptide) stimulation. MDA-MB-231 cells are metastatic when implanted in mice while BT-20 are not and remain epithelial-like. We show that both cell lines express KISS1R mRNA and respond to KP-10 by elevating calcium mobilisation. However, KP-10 stimulation induced migration of MDA-MB-231, but not BT-20 cells, in a calcium-dependent manner. Moreover, only BT-20 cells responded to KP-10 by increasing ERK phosphorylation in a β-arrestin-dependent manner. Interestingly, both cell lines displayed different complements of β-arrestin 1 and 2 expression. Overall, our data shows that, in TNBC, it is not universally true that kisspeptin/KISS1R stimulate migration or pro-metastatic behaviour, as divergent responses were observed in the two TNBC lines tested. Whether this divergence is related to the observed differences in β-arrestin complements warrants further investigation and may enable further stratification of the ability of kisspeptin to influence breast tumour behaviour.

The Role of Kisspeptin in the Pathogenesis of Pregnancy Complications: A Narrative Review

Kisspeptins are the family of neuropeptide products of the KISS-1 gene that exert the biological action by binding with the G-protein coupled receptor 54 (GPR54), also known as the KISS-1 receptor. The kisspeptin level dramatically increases during pregnancy, and the placenta is supposed to be its primary source. The role of kisspeptin has already been widely studied in hypogonadotropic hypogonadism, fertility, puberty disorders, and insulin resistance-related conditions, including type 2 diabetes mellitus, polycystic ovary syndrome, and obesity. Gestational diabetes mellitus (GDM), preeclampsia (PE), preterm birth, fetal growth restriction (FGR), or spontaneous abortion affected 2 to 20% of pregnancies worldwide. Their occurrence is associated with numerous short and long-term consequences for mothers and newborns; hence, novel, non-invasive predictors of their development are intensively investigated. The study aims to present a comprehensive review emphasizing the role of kisspeptin in the most common pregnancy-related disorders and neonatal outcomes. The decreased level of kisspeptin is observed in women with GDM, FGR, and a high risk of spontaneous abortion. Nevertheless, there are still many inconsistencies in kisspeptin concentration in pregnancies with preterm birth or PE. Further research is needed to determine the usefulness of kisspeptin as an early marker of gestational and neonatal complications.

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.

The Role of Kisspeptin in the Control of the Hypothalamic-Pituitary-Gonadal Axis and Reproduction

The discovery of kisspeptin as a critical central regulatory factor of GnRH release has given people a novel understanding of the neuroendocrine regulation in human reproduction. Kisspeptin activates the signaling pathway by binding to its receptor kisspeptin receptor (KISS1R) to promote GnRH secretion, thereby regulating the hypothalamic-pituitary-gonadal axis (HPG) axis. Recent studies have shown that kisspeptin neurons located in arcuate nucleus (ARC) co-express neurokinin B (NKB) and dynorphin (Dyn). Such neurons are called KNDy neurons. KNDy neurons participate in the positive and negative feedback of estrogen to GnRH secretion. In addition, kisspeptin is a key factor in the initiation of puberty, and also regulates the processes of female follicle development, oocyte maturation, and ovulation through the HPG axis. In male reproduction, kisspeptin also plays an important role, getting involved in the regulation of Leydig cells, spermatogenesis, sperm functions and reproductive behaviors. Mutations in the KISS1 gene or disorders of the kisspeptin/KISS1R system may lead to clinical symptoms such as idiopathic hypogonadotropic hypogonadism (iHH), central precocious puberty (CPP) and female infertility. Understanding the influence of kisspeptin on the reproductive axis and related mechanisms will help the future application of kisspeptin in disease diagnosis and treatment. In this review, we critically appraise the role of kisspeptin in the HPG axis, including its signaling pathways, negative and positive feedback mechanisms, and its control on female and male reproduction.

Functional analysis of the emerging roles for the KISS1/KISS1R signaling pathway in cancer metastasis

Cancer metastasis, a process that primary tumor cells disseminate to secondary organs, is the most lethal and least effectively treated characteristic of human cancers. Kisspeptins are proteins encoded by the KISS1 gene that was originally described as a melanoma metastasis suppressor gene. Then, Kisspeptins were discovered as the natural ligands of the G-protein-coupled receptor 54 (GPR54) that is also called KISS1R. The KISS1/KISS1R signaling is essential to control GnRH secretion during puberty and to establish mammalian reproductive function through the hypothalamic-pituitary-gonadal (HPG) axis. Although KISS1 primarily plays a suppressive role in the metastasis progression in several cancer types, emerging evidence indicates that the physiological effect of KISS1/KISS1R in cancer metastasis is tissue context-dependent and still controversial. Here, we will discuss the epigenetic mechanism regulation of KISS1 gene expression, the context-dependent role of KISS1/KISS1R, pro-/anti-metastasis signaling pathways of KISS1/KISS1R, and the perspective anti-cancer therapeutics via targeting KISS1/KISS1R.

Uterine kisspeptin receptor critically regulates epithelial estrogen receptor α transcriptional activity at the time of embryo implantation in a mouse model

Embryo implantation failure is a major cause of infertility in women of reproductive age and a better understanding of uterine factors that regulate implantation is required for developing effective treatments for female infertility. This study investigated the role of the uterine kisspeptin receptor (KISS1R) in the molecular regulation of implantation in a mouse model. To conduct this study, a conditional uterine knockout (KO) of Kiss1r was created using the Pgr-Cre (progesterone receptor-CRE recombinase) driver. Reproductive profiling revealed that while KO females exhibited normal ovarian function and mated successfully to stud males, they exhibited significantly fewer implantation sites, reduced litter size and increased neonatal mortality demonstrating that uterine KISS1R is required for embryo implantation and a healthy pregnancy. Strikingly, in the uterus of Kiss1r KO mice on day 4 (D4) of pregnancy, the day of embryo implantation, KO females exhibited aberrantly elevated epithelial ERα (estrogen receptor α) transcriptional activity. This led to the temporal misexpression of several epithelial genes [Cftr (Cystic fibrosis transmembrane conductance regulator), Aqp5 (aquaporin 5), Aqp8 (aquaporin 8) and Cldn7 (claudin 7)] that mediate luminal fluid secretion and luminal opening. As a result, on D4 of pregnancy, the lumen remained open disrupting the final acquisition of endometrial receptivity and likely accounting for the reduction in implantation events. Our data clearly show that uterine KISS1R negatively regulates ERα signaling at the time of implantation, in part by inhibiting ERα overexpression and preventing detrimentally high ERα activity. To date, there are no reports on the regulation of ERα by KISS1R; therefore, this study has uncovered an important and powerful regulator of uterine ERα during early pregnancy.

Kisspeptin-54 attenuates oxidative stress and neuronal apoptosis in early brain injury after subarachnoid hemorrhage in rats via GPR54/ARRB2/AKT/GSK3β signaling pathway

Oxidative stress-induced neuron apoptosis plays a crucial role in the early brain injury (EBI) after subarachnoid hemorrhage (SAH). Kisspeptin has been reported as antioxidant to reduce oxidative stress-induced neuronal cell death through G protein-coupled receptor 54 (GPR54). The goal of this study was to determine the neuroprotection of the Kisspeptin/GRP54 signaling pathway against EBI after SAH. Two hundred and ninety-two Sprague Dawley male rats were used and SAH was induced by the endovascular perforation. Exogenous Kisspeptin 54 (KP54) was delivered intranasally. Small interfering ribonucleic acid (siRNA) for endogenous KISS1, a selective GPR54 antagonist kisspeptin 234, or β-arrestin 2 siRNA for ARRB2 (a functional adaptor of GPR54) were administered intracerebroventricularly. Post-SAH evaluations included neurobehavioral tests, SAH grade, Western blot, immunofluorescence, Fluoro-Jade C, TUNEL, and Nissl staining. The results showed that endogenous KISS1 knockdown aggravated but exogenous KP54 (1.0 nmol/kg) treatment attenuated neurological deficits, brain oxidative stress, and neuronal apoptosis at 24 h after SAH. The benefits of KP54 persisted to 28 days after SAH, which significantly improved cognitive function in SAH rats. The GPR54 blockade or the ARRB2 knockout offset the neuroprotective effects of KP54 in SAH rats. In conclusion, our results suggested that administration of KP54 attenuated oxidative stress, neuronal apoptosis and neurobehavioral impairments through GPR54/ARRB2/AKT/GSK3β signaling pathway after SAH in rat. Thus, KP54 may provide an effective treatment strategy for SAH patients.

Clinical Potential of Kisspeptin in Reproductive Health

Kisspeptins are a family of hypothalamic neuropeptides that are essential for the regulation of reproductive physiology. Their importance in reproductive health became apparent in 2003, when loss-of-function variants in the gene encoding the kisspeptin receptor were reported to result in isolated congenital hypogonadotropic hypogonadism (CHH). It has since been ascertained that hypothalamic kisspeptin neurons regulate gonadotropin-releasing hormone (GnRH) secretion to thus stimulate the remainder of the reproductive endocrine axis. In this review, we discuss genetic variants that affect kisspeptin receptor signaling, summarize data on KISS1R agonists, and posit possible clinical uses of native and synthetic kisspeptin receptor agonists for the investigation and treatment of reproductive disorders.

Gametogenic and steroidogenic action of kisspeptin-10 in the Asian catfish, Clarias batrachus: Putative underlying mechanistic cascade

Unlike mammals, two kisspeptins genes encoding, kiss1 and kiss2 are detected in fishes with highly varied and contradictory difference in their reproductive activities. The present study was undertaken to examine the direct action of kisspeptin-10 and its role in gonadal activities in the gonadally quiescent Asian catfish using native mammalian kisspeptin decapeptide (KP-10) involving in vivo and in vitro approaches. The in vivo KP-10 treatment caused precocious onset of gametogenesis and its rapid progression, as was evident from the appearance of advanced stages of ovarian follicles in ovary, and advanced germ cells (spermatocytes/ spermatids) in the testis of the treated Clarias batrachus in comparison to the control gonads. It also elevated the steroid levels in gonads of the catfish in vivo and in vitro conditions. Simultaneously, it increased the expressions of key steroidogenic enzymes like 3β-HSD, 17β-HSD, and StAR protein, responsible for transfer of cholesterol from outer to inner membrane of the mitochondria of steroidogenic cells. Concurrently, it augmented the activities of 3β-HSD and 17β-HSD in the ovarian explants. The expressions of MAPK component (pERK1/2 and ERK1/2) were also up-regulated by KP-10 in gonadal explants. Thus, the data suggest that kisspeptin-10 stimulates gametogenesis by enhancing gonadal steroid production. The study also describes the putative mechanistic cascade of steroidogenic actions of kisspeptin-10 in the catfish so much so in teleost fish. The study also suggests that, kisspeptin may act locally to regulate gonadal activities in an autocrine/paracine manner, independent of known extra-gonadal factors in the catfish.

Meta-Analysis of Heifer Traits Identified Reproductive Pathways in Bos indicus Cattle

Fertility traits measured early in life define the reproductive potential of heifers. Knowledge of genetics and biology can help devise genomic selection methods to improve heifer fertility. In this study, we used ~2400 Brahman cattle to perform GWAS and multi-trait meta-analysis to determine genomic regions associated with heifer fertility. Heifer traits measured were pregnancy at first mating opportunity (PREG1, a binary trait), first conception score (FCS, score 1 to 3) and rebreeding score (REB, score 1 to 3.5). The heritability estimates were 0.17 (0.03) for PREG1, 0.11 (0.05) for FCS and 0.28 (0.05) for REB. The three traits were highly genetically correlated (0.75-0.83) as expected. Meta-analysis was performed using SNP effects estimated for each of the three traits, adjusted for standard error. We identified 1359 significant SNPs (p-value < 9.9 × 10-6 at FDR < 0.0001) in the multi-trait meta-analysis. Genomic regions of 0.5 Mb around each significant SNP from the meta-analysis were annotated to create a list of 2560 positional candidate genes. The most significant SNP was in the vicinity of a genomic region on chromosome 8, encompassing the genes SLC44A1, FSD1L, FKTN, TAL2 and TMEM38B. The genomic region in humans that contains homologs of these genes is associated with age at puberty in girls. Top significant SNPs pointed to additional fertility-related genes, again within a 0.5 Mb region, including ESR2, ITPR1, GNG2, RGS9BP, ANKRD27, TDRD12, GRM1, MTHFD1, PTGDR and NTNG1. Functional pathway enrichment analysis resulted in many positional candidate genes relating to known fertility pathways, including GnRH signaling, estrogen signaling, progesterone mediated oocyte maturation, cAMP signaling, calcium signaling, glutamatergic signaling, focal adhesion, PI3K-AKT signaling and ovarian steroidogenesis pathway. The comparison of results from this study with previous transcriptomics and proteomics studies on puberty of the same cattle breed (Brahman) but in a different population identified 392 genes in common from which some genes-BRAF, GABRA2, GABR1B, GAD1, FSHR, CNGA3, PDE10A, SNAP25, ESR2, GRIA2, ORAI1, EGFR, CHRNA5, VDAC2, ACVR2B, ORAI3, CYP11A1, GRIN2A, ATP2B3, CAMK2A, PLA2G, CAMK2D and MAPK3-are also part of the above-mentioned pathways. The biological functions of the positional candidate genes and their annotation to known pathways allowed integrating the results into a bigger picture of molecular mechanisms related to puberty in the hypothalamus-pituitary-ovarian axis. A reasonable number of genes, common between previous puberty studies and this study on early reproductive traits, corroborates the proposed molecular mechanisms. This study identified the polymorphism associated with early reproductive traits, and candidate genes that provided a visualization of the proposed mechanisms, coordinating the hypothalamic, pituitary, and ovarian functions for reproductive performance in Brahman cattle.

The Traditional Chinese Medicine Fuyou Formula Alleviates Precocious Puberty by Inhibiting GPR54/GnRH in the Hypothalamus

The purpose of this study was to explore the effect of the traditional Chinese medicine Fuyou formula on precocious puberty (PP). The Fy formula may exert an effect in female rats with PP and GT-7 cells through the GPR54/GnRH signaling pathway. To confirm the effect of the Fy formula on PP through the GPR54/GnRH signaling pathway, we first treated GT1-7 cells with the Fy formula and observed changes in the expression of related genes and proteins and in GnRH secretion. Then, we randomly divided young female Sprague-Dawley rats into the control group, model group, leuprorelin group and the Fy formula group. A PP model was established by injection of danazol on postnatal day 5, and the Fy formula was administered on PND15. The time of vaginal opening, the wet weights of the ovary and uterus, serum hormone levels and the expression of hypothalamic-related genes were observed. We found that the Fy formula delayed vaginal opening, decreased the wet weights and coefficients of the ovary and uterus, decreased the levels of serum hormones (E2, follicle-stimulating hormone and luteinizing hormone) and the cellular GnRH level, and downregulated the gene expression of Kiss1, GPR54 and GnRH in the hypothalamus and the gene and protein expression of GPR54 and GnRH in GT1-7 cells. In conclusion, the Fy formula may alleviate PP via the GPR54/GnRH signaling pathway.

Hypothalamic reproductive neurons communicate through signal transduction to control reproduction

Gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus coordinate fertility and puberty. In order to achieve successful reproductive capacity, they receive signals from the periphery and from other hypothalamic neurons that coordinate energy homeostasis. Hormones, such as estradiol, insulin, leptin, and adiponectin, act directly or indirectly on GnRH and its associated reproductive neurons. Nutrients like glucose and fatty acids can also affect reproductive neurons to signal nutrient availability. Additionally, acute and chronic inflammation is reported to detrimentally affect GnRH and kisspeptin expression. All of these cues activate signal transduction pathways within neurons that lead to the changes in GnRH neuronal function. The signalling pathways can also be dysregulated by endocrine disrupting chemicals, which impair fertility by misappropriating common signalling pathways. The complex mechanisms controlling the levels of GnRH during the reproductive cycle rely on a carefully orchestrated set of signal transduction events to regulate the positive and negative feedback arms of the hypothalamic-pituitary-gonadal axis. If these signalling events are dysregulated, this will result is a downregulatory event leading to hypogonadal hypogonadism with decreased or absent fertility. Therefore, an understanding of the mechanisms involved in distinct neuronal signalling could provide an advantage to inform therapeutic interventions for infertility and reproductive disorders.

The wonderful and masterful G protein-coupled receptor (GPCR): A focus on signaling mechanisms and the neuroendocrine control of fertility

Human GnRH deficiency, both clinically and genetically, is a heterogeneous disorder comprising of congenital GnRH deficiency with anosmia (Kallmann syndrome), or with normal olfaction [normosmic idiopathic hypogonadotropic hypogonadism (IHH)], and adult-onset hypogonadotropic hypogonadism. Our understanding of the neural mechanisms underlying GnRH secretion and GnRH signaling continues to increase at a rapid rate and strikingly, the heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) continue to emerge as essential players in these processes. GPCRs were once viewed as binary on-off switches, where in the "on" state they are bound to their Gα protein, but now we understand that view is overly simplistic and does not adequately characterize GPCRs. Instead, GPCRs have emerged as masterful signaling molecules exploiting different physical conformational states of itself to elicit an array of downstream signaling events via their G proteins and the β-arrestins. The "one receptor-multiple signaling conformations" model is likely an evolved strategy that can be used to our advantage as researchers have shown that targeting specific receptor conformations via biased ligands is proving to be a powerful tool in the effective treatment of human diseases. Can biased ligands be used to selectively modulate signaling by GPCR regulators of the neuroendocrine axis in the treatment of IHH? As discussed in this review, the grand possibility exists. However, while we are still very far from developing these treatments, this exciting likelihood can happen through a much greater mechanistic understanding of how GPCRs signal within the cell.

Uterine Gpr83 mRNA is highly expressed during early pregnancy and GPR83 mediates the actions of PEN in endometrial and non-endometrial cells

OBJECTIVE

To characterize the expression and signaling of uterine GPR83 in vivo in the nonpregnant and pregnant mouse and in vitro in human endometrial and nonendometrial cells.

DESIGN

Controlled laboratory study.

SETTING

Not applicable.

PATIENTS

Not applicable.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Expression of uterine Gpr83 was determined by quantitative polymerase chain reaction throughout the estrous cycle and during early pregnancy in ovarian-stimulated and non-ovarian-stimulated mice and pregnant and pseudopregnant mice. Expression was also determined in ovariectomized mice after the administration of oil, E2, P4, or E2 + P4 and in stromal cells following 6 days of in vitro decidualization. GPR83 signaling was studied in human endometrial and embryonic kidney cell lines. Cells were treated by PEN, a GPR83 ligand, and PEN-induced extracellular signal-regulated kinase (ERK) phosphorylation was assayed under conditions that blocked Gα_q/11 and/or β-arrestin signaling.

RESULTS

Uterine Gpr83 is expressed throughout the estrous cycle and during early pregnancy; expression increases dramatically at the time of uterine receptivity, embryo implantation, and stromal cell decidualization. In the ovariectomized mouse, hormone add-back reveals that Gpr83 expression is highly responsive to the combined treatment of E2 and P4, and studies in the ovarian-stimulated mouse show that expression is also very sensitive to changes in E2 and P4 and is therefore tightly regulated by E2 and P4. At the implantation site, expression is elevated up to D6 of pregnancy and then declines rapidly on D7 and D8, suggesting that if there is any involvement in decidualization, it is likely associated with primary but not secondary stromal cell decidualization. This premise was supported by the observation that stromal cell decidualization in vitro progresses with a decline in Gpr83 expression. In ERα/PR-expressing endometrial Ishikawa cells, GPR83 mediates PEN signals in a Gα_q/11-dependent manner, and studies conducted in HEK 293 cells lacking β-arrestin revealed that GPR83 also signals via a β-arrestin-dependent manner. When signaling by either one or both pathways is downregulated, cells exhibit a major reduction in responsiveness to PEN treatment, demonstrating that signaling by both pathways is significant.

CONCLUSION

We hypothesize that PEN/GPR83 signaling regulates uterine receptivity, embryo implantation, and primary stromal cell decidualization by coupling to Gα_q/11- and β-arrestin-dependent pathways.

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.

G protein-coupled kisspeptin receptor induces metabolic reprograming and tumorigenesis in estrogen receptor-negative breast cancer

Triple-negative breast cancer (TNBC) is a highly metastatic and deadly disease. TNBC tumors lack estrogen receptor (ERα), progesterone receptor (PR), and HER2 (ErbB2) and exhibit increased glutamine metabolism, a requirement for tumor growth. The G protein-coupled kisspeptin receptor (KISS1R) is highly expressed in patient TNBC tumors and promotes malignant transformation of breast epithelial cells. This study found that TNBC patients displayed elevated plasma kisspeptin levels compared with healthy subjects. It also provides the first evidence that in addition to promoting tumor growth and metastasis in vivo, KISS1R-induced glutamine dependence of tumors. In addition, tracer-based metabolomics analyses revealed that KISS1R promoted glutaminolysis and nucleotide biosynthesis by increasing c-Myc and glutaminase levels, key regulators of glutamine metabolism. Overall, this study establishes KISS1R as a novel regulator of TNBC metabolism and metastasis, suggesting that targeting KISS1R could have therapeutic potential in the treatment of TNBC.

The Nuclear Translocation of Mitogen-Activated Protein Kinases: Molecular Mechanisms and Use as Novel Therapeutic Target

The mitogen-activated protein kinase (MAPK) cascades are central signaling pathways that play a central role in the regulation of most stimulated cellular processes including proliferation, differentiation, stress response and apoptosis. Currently 4 such cascades are known, each termed by its downstream MAPK components: the extracellular signal-regulated kinase 1/2 (ERK1/2), cJun-N-terminal kinase (JNK), p38 and ERK5. One of the hallmarks of these cascades is the stimulated nuclear translocation of their MAPK components using distinct mechanisms. ERK1/2 are shuttled into the nucleus by importin7, JNK and p38 by a dimer of importin3 with either importin9 or importin7, and ERK5 by importin-α/β. Dysregulation of these cascades often results in diseases, including cancer and inflammation, as well as developmental and neurological disorders. Much effort has been invested over the years in developing inhibitors to the MAPK cascades to combat these diseases. Although some inhibitors are already in clinical use or clinical trials, their effects are hampered by development of resistance or adverse side-effects. Recently, our group developed 2 myristoylated peptides: EPE peptide, which inhibits the interaction of ERK1/2 with importin7, and PERY peptide, which prevents JNK/p38 interaction with either importin7 or importin9. These peptides block the nuclear translocation of their corresponding kinases, resulting in prevention of several cancers, while the PERY peptide also inhibits inflammation-induced diseases. These peptides provide a proof of concept for the use of the nuclear translocation of MAPKs as therapeutic targets for cancer and/or inflammation.

The matrix protein Fibulin-3 promotes KISS1R induced triple negative breast cancer cell invasion

Breast cancer is a leading cause of cancer mortality. In particular, triple negative breast cancer (TNBC) comprise a heterogeneous group of basal-like tumors lacking estrogen receptor (ERα), progesterone receptor (PR) and HER2 (ErbB2). TNBC represents 15-20% of all breast cancers and occurs frequently in women under 50 years of age. Unfortunately, these patients lack targeted therapy, are typically high grade and metastatic at time of diagnosis. The mechanisms regulating metastasis remain poorly understood. We have previously shown that the kisspeptin receptor, KISS1R stimulates invasiveness of TNBC cells. In this report, we demonstrate that KISS1R signals via the secreted extracellular matrix protein, fibulin-3, to regulate TNBC invasion. We found that the fibulin-3 gene is amplified in TNBC primary tumors and that plasma fibulin-3 levels are elevated in TNBC patients compared to healthy subjects. In this study, we show that KISS1R activation increases fibulin-3 expression and secretion. We show that fibulin-3 regulates TNBC metastasis in a mouse experimental metastasis xenograft model and signals downstream of KISS1R to stimulate TNBC invasion, by activating matrix metalloproteinase 9 (MMP-9) and the MAPK pathway. These results identify fibulin-3 as a new downstream mediator of KISS1R signaling and as a potential biomarker for TNBC progression and metastasis, thus revealing KISS1R and fibulin-3 as novel drug targets in TNBC.

Controversial Role of Kisspeptins/KiSS-1R Signaling System in Tumor Development

KiSS-1 was first described as a metastasis suppressor gene in malignant melanoma. KiSS-1 encodes a 145 amino-acid residue peptide that is further processed, producing the 54 amino acid metastin and shorter peptides collectively named kisspeptins (KPs). KPs bind and activate KiSS-1R (GPR54). Although the KPs system has been extensively studied for its role in endocrinology of reproductive axis in mammals, its role in cancer is still controversial. Experimental evidences show that KP system exerts an anti-metastatic effect by the regulation of cellular migration and invasion in several cancer types. However, the role of KPs/KiSS-1R is very complex. Genomic studies suggest that KiSS-1/KiSS-1R expression might be different in the various stages of tumor development. Furthermore, overexpression of KiSS-1R has been reported to elicit drug resistance in triple negative breast cancer. In this review, we focused on multiple functions exerted by the KPs/KiSS-1R system in regulating tumor progression.

β-arrestin signalling and bias in hormone-responsive GPCRs

G protein-coupled receptors (GPCRs) play crucial roles in the ability of target organs to respond to hormonal cues. GPCRs' activation mechanisms have long been considered as a two-state process connecting the agonist-bound receptor to heterotrimeric G proteins. This view is now challenged as mounting evidence point to GPCRs being connected to large arrays of transduction mechanisms involving heterotrimeric G proteins as well as other players. Amongst the G protein-independent transduction mechanisms, those elicited by β-arrestins upon their recruitment to the active receptors are by far the best characterized and apply to most GPCRs. These concepts, in conjunction with remarkable advances made in the field of GPCR structural biology and biophysics, have supported the notion of ligand-selective signalling also known as pharmacological bias. Interestingly, recent reports have opened intriguing prospects to the way β-arrestins control GPCR-mediated signalling in space and time within the cells. In the present paper, we review the existing evidence linking endocrine-related GPCRs to β-arrestin recruitement, signalling, pathophysiological implications and selective activation by biased ligands and/or receptor modifications. Emerging concepts surrounding β-arrestin-mediated transduction are discussed in the light of the peculiarities of endocrine systems.

Continuous Kisspeptin Administration in Postmenopausal Women: Impact of Estradiol on Luteinizing Hormone Secretion

CONTEXT

Kisspeptin stimulates the reproductive endocrine cascade in both men and women. Circulating sex steroids are thought to modulate the ability of kisspeptin to stimulate gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) release.

OBJECTIVE

To probe the effects of sex steroids on kisspeptin-stimulated GnRH-induced LH pulses.

PARTICIPANTS

Eight healthy postmenopausal women.

INTERVENTION

Subjects underwent every-10-minute blood sampling to measure GnRH-induced LH secretion at baseline and in response to a continuous kisspeptin infusion (12.5 µg/kg/h) over 24 hours. A subset of the participants also received kisspeptin (0.313 µg/kg) and GnRH (75 ng/kg) intravenous boluses.

RESULTS

Postmenopausal women are resistant to the stimulatory effect of continuous kisspeptin on LH secretion. Postmenopausal women receiving estradiol replacement therapy are also resistant to kisspeptin initially, but they demonstrate a significant increase in LH pulse amplitude in direct proportion to the circulating estradiol concentration and duration of kisspeptin administration.

CONCLUSIONS

Kisspeptin administration has complex effects on GnRH, and by extension, on LH secretion. The ability of kisspeptin to affect LH secretion can be modulated by the ambient sex-steroid milieu in a time- and dose-dependent manner.

Kisspeptin/Kisspeptin Receptor System in the Ovary

Kisspeptins are a family of neuropeptides that are critical for initiating puberty and regulating ovulation in sexually mature females via the central control of the hypothalamic-pituitary-gonadal axis. Recent studies have shown that kisspeptin and its receptor kisspeptin receptor (KISS1R) are expressed in the mammalian ovary. Convincing evidence indicates that kisspeptins can activate a wide variety of signals via its binding to KISS1R. Experimental data gathered recently suggest a putative role of kisspeptin signaling in the direct control of ovarian function, including follicular development, oocyte maturation, steroidogenesis, and ovulation. Dysregulation or naturally occurring mutations of the kisspeptin/KISS1R system may negatively affect the ovarian function, leading to reproductive pathology or female infertility. A comprehensive understanding of the expression, actions, and underlying molecular mechanisms of this system in the human ovary is essential for novel approaches to therapeutic and diagnostic interventions in reproductive diseases and infertility.

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

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

GnRH Neuron-Specific Ablation of Gαq/11 Results in Only Partial Inactivation of the Neuroendocrine-Reproductive Axis in Both Male and Female Mice: In Vivo Evidence for Kiss1r-Coupled Gαq/11-Independent GnRH Secretion

The gonadotropin-releasing hormone (GnRH) is the master regulator of fertility and kisspeptin (KP) is a potent trigger of GnRH secretion from GnRH neurons. KP signals via KISS1R, a Gαq/11-coupled receptor, and mice bearing a global deletion of Kiss1r (Kiss1r(-/-)) or a GnRH neuron-specific deletion of Kiss1r (Kiss1r(d/d)) display hypogonadotropic hypogonadism and infertility. KISS1R also signals via β-arrestin, and in mice lacking β-arrestin-1 or -2, KP-triggered GnRH secretion is significantly diminished. Based on these findings, we hypothesized that ablation of Gαq/11 in GnRH neurons would diminish but not completely block KP-triggered GnRH secretion and that Gαq/11-independent GnRH secretion would be sufficient to maintain fertility. To test this, Gnaq (encodes Gαq) was selectively inactivated in the GnRH neurons of global Gna11 (encodes Gα11)-null mice by crossing Gnrh-Cre and Gnaq(fl/fl);Gna11(-/-) mice. Experimental Gnaq(fl/fl);Gna11(-/-);Gnrh-Cre (Gnaq(d/d)) and control Gnaq(fl/fl);Gna11(-/-) (Gnaq(fl/fl)) littermate mice were generated and subjected to reproductive profiling. This process revealed that testicular development and spermatogenesis, preputial separation, and anogenital distance in males and day of vaginal opening and of first estrus in females were significantly less affected in Gnaq(d/d) mice than in previously characterized Kiss1r(-/-) or Kiss1r(d/d) mice. Additionally, Gnaq(d/d) males were subfertile, and although Gnaq(d/d) females did not ovulate spontaneously, they responded efficiently to a single dose of gonadotropins. Finally, KP stimulation triggered a significant increase in gonadotropins and testosterone levels in Gnaq(d/d) mice. We therefore conclude that the milder reproductive phenotypes and maintained responsiveness to KP and gonadotropins reflect Gαq/11-independent GnRH secretion and activation of the neuroendocrine-reproductive axis in Gnaq(d/d) mice.

SIGNIFICANCE STATEMENT

The gonadotropin-releasing hormone (GnRH) is the master regulator of fertility. Over the last decade, several studies have established that the KISS1 receptor, KISS1R, is a potent trigger of GnRH secretion and inactivation of KISS1R on the GnRH neuron results in infertility. While KISS1R is best understood as a Gαq/11-coupled receptor, we previously demonstrated that it could couple to and signal via non-Gαq/11-coupled pathways. The present study confirms these findings and, more importantly, while it establishes Gαq/11-coupled signaling as a major conduit of GnRH secretion, it also uncovers a significant role for non-Gαq/11-coupled signaling in potentiating reproductive development and function. This study further suggests that by augmenting signaling via these pathways, GnRH secretion can be enhanced to treat some forms of infertility.

KiSS‑1‑mediated suppression of the invasive ability of human pancreatic carcinoma cells is not dependent on the level of KiSS‑1 receptor GPR54

The onset of local invasion and lymphatic metastasis in pancreatic cancer limits survival following surgical intervention and additional therapies. Reduced expression of KiSS‑1 in pancreatic cancer is associated with cancer metastasis. Previous studies have indicated that kisspeptin, the KiSS‑1 peptide, is able to bind to its receptor‑GPR54 (hOT7T175) and suppress the migration of PANC‑1 pancreatic cancer cells. Whether the metastatic suppression of KiSS‑1 is dependent on the levels of GPR54 in pancreatic cancer cell lines remains unclear. Human BxPC‑3 pancreatic carcinoma cells are highly differentiated without exhibiting metastasis, however PANC‑1 pancreatic carcinoma cells are poorly differentiated and exhibit local and lymph node metastasis. Compared with primary cultured trophoblasts, BxPc‑3 and PANC‑1 cells were observed to express low levels of KiSS‑1 mRNA and protein, measured using reverse transcription‑quantitative polymerase chain reaction and western blotting, respectively. However, greater mRNA and protein expression levels of GPR54 were observed in PANC‑1 cells compared with BxPc‑3 cells. An MTT assay was used to investigate the effect of KiSS‑1 on BxPc‑3 and PANC‑1 cell proliferation. There were no significant differences in proliferation following transfection with KiSS‑1 in BxPc‑3 and PANC‑1 cells compared with the controls (P>0.05). A Transwell assay with chambers coated with Matrigel was used to evaluate the in vitro invasive ability of BxPc‑3 and PANC‑1 cells, with the invasion index of BxPc‑3 and PANC‑1 cells significantly reduced following 48 h of KiSS‑1 overexpression (P<0.05). The mRNA and protein expression levels of KiSS‑1 were significantly increased in BxPc‑3 and PANC‑1 cells 48 h subsequent to transfection with KiSS‑1 (P<0.05), while GPR54 expression was not altered (P>0.05). KiSS‑1 is a metastasis suppressor gene of pancreatic cancer, and this suppression is not dependent on the expression levels of GPR54. Therefore, KiSS‑1 is potentially a novel target for gene therapy.

KISS1R signaling promotes invadopodia formation in human breast cancer cell via β-arrestin2/ERK

Kisspeptins (KPs), peptide products of the KISS1 gene are endogenous ligands for the kisspeptin receptor (KISS1R), a G protein-coupled receptor. In numerous cancers, KISS1R signaling plays anti-metastatic roles. However, we have previously shown that in breast cancer cells lacking the estrogen receptor (ERα), kisspeptin-10 stimulates cell migration and invasion by cross-talking with the epidermal growth factor receptor (EGFR), via a β-arrestin-2-dependent mechanism. To further define the mechanisms by which KISS1R stimulates invasion, we determined the effect of down-regulating KISS1R expression in triple negative breast cancer cells. We found that depletion of KISS1R reduced their mesenchymal phenotype and invasiveness. We show for the first time that KISS1R signaling induces invadopodia formation and activation of key invadopodia proteins, cortactin, cofilin and membrane type I matrix metalloproteases (MT1-MMP). Moreover, KISS1R stimulated invadopodia formation occurs via a new pathway involving a β-arrestin2 and ERK1/2-dependent mechanism, independent of Src. Taken together, our findings suggest that targeting the KISS1R signaling axis might be a promising strategy to inhibit invasiveness and metastasis.

The pregnant mouse uterus exhibits a functional kisspeptin/KISS1R signaling system on the day of embryo implantation

BACKGROUND

Expression of kisspeptin (protein) and Kiss1r (mRNA) was recently documented in the mouse uterus on D4 of pregnancy (the day of embryo implantation) suggesting that the uterine-based kisspeptin (KP)/kisspeptin receptor (KISS1R) signaling system regulates embryo implantation. Despite this important suggestion, it was never demonstrated that the uterus actually exhibits a functional KP/KISS1R signaling system on D4 of pregnancy. Thus, the goal of this study was to determine whether a functional KP/KISS1R signaling system exists in the mouse uterus on D4 of pregnancy.

FINDINGS

Since kisspeptin/KISS1R signaling triggers the phosphorylation of the mitogen-activated protein kinases p38 and ERK1/2, through immunohistochemical analyses, we determined whether exogenously administered kisspeptin could trigger p38 and ERK1/2 phosphorylation in the uterus on D4 of pregnancy. The results clearly demonstrated that kisspeptin could and that its effects were mediated via KISS1R. Additionally, the robust kisspeptin-triggered response was observed in the pregnant uterus only. Finally, it was demonstrated that on D4 of pregnancy the Kiss1 null uterus expresses functional KISS1R molecules capable of mediating the effects of kisspeptin.

CONCLUSIONS

These results lead us to conclude that on D4 of pregnancy, the mouse uterus expresses a functional KP/KISS1R signaling system strengthening the possibility that this signaling system regulates embryo implantation. These findings strengthen the rationale for determining whether such a functional system exists in the uterus of the human female and if so, what role it might play in human pregnancy.

Structure, Function, Pharmacology, and Therapeutic Potential of the G Protein, Gα/q,11

G protein coupled receptors (GPCRs) are one of the major classes of cell surface receptors and are associated with a group of G proteins consisting of three subunits termed alpha, beta, and gamma. G proteins are classified into four families according to their α subunit; Gα_i, Gα_s, Gα_12/13, and Gα_q. There are several downstream pathways of Gα_q of which the best known is upon activation via guanosine triphosphate (GTP), Gα_q activates phospholipase Cβ, hydrolyzing phosphatidylinositol 4,5-biphosphate into diacylglycerol and inositol triphosphate and activating protein kinase C and increasing calcium efflux from the endoplasmic reticulum. Although G proteins, in particular, the Gα_q/11 are central elements in GPCR signaling, their actual roles have not yet been thoroughly investigated. The lack of research of the role on Gα_q/11 in cell biology is partially due to the obscure nature of the available pharmacological agents. YM-254890 is the most useful Gα_q-selective inhibitor with antiplatelet, antithrombotic, and thrombolytic effects. YM-254890 inhibits Gα_q signaling pathways by preventing the exchange of guanosine diphosphate for GTP. UBO-QIC is a structurally similar compound to YM-254890, which can inhibit platelet aggregation and cause vasorelaxation in rats. Many agents are available for the study of signaling downstream of Gα_q/11. The role of G proteins could potentially represent a novel therapeutic target. This review will explore the range of pharmacological and molecular tools available for the study of the role of Gα_q/11 in GPCR signaling.

Quantifying GPCR internalization: a focus on the Kisspeptin receptor

GPCR internalization is a critical regulatory step in determining receptor activity. While internalization terminates G protein-coupled signaling, it might be required for G protein-independent signaling. A large number of clinical therapies are based on preventing or promoting GPCR internalization. Thus, for any given GPCR, it is important to characterize its internalization and understand the factors that regulate such internalization. Here we describe different experimental protocols to evaluate the internalization of any GPCR transiently expressed in HEK 293 cells. The protocols describe the use of immunofluorescence and imaging techniques as well as flow cytometry. The techniques described use the FLAG-tagged kisspeptin receptor (KISS1R) as an example but are equally applicable to any other GPCR.

KISS1R: Hallmarks of an Effective Regulator of the Neuroendocrine Axis

Kisspeptin (KP) is now well recognized as a potent stimulator of gonadotropin-releasing hormone (GnRH) secretion and thereby a major regulator of the neuroendocrine-reproductive axis. KP signals via KISS1R, a G protein-coupled receptor (GPCR) that activates the G proteins Gαq/11. Modulation of the interaction of KP with KISS1R is therefore a potential new therapeutic target for stimulating (in infertility) or inhibiting (in hormone-dependent diseases) the reproductive hormone cascade. Major efforts are underway to target KISS1R in the treatment of sex steroid hormone-dependent disorders and to stimulate endogenous hormonal responses along the neuroendocrine axis as part of in vitro fertilization protocols. The development of analogs modulating KISS1R signaling will be aided by an understanding of the intracellular pathways and dynamics of KISS1R signaling under normal and pathological conditions. This review focuses on KISS1R recruitment of intracellular signaling (Gαq/11- and β-arrestin-dependent) pathways that mediate GnRH secretion and the respective roles of rapid desensitization, internalization, and recycling of resensitized receptors in maintaining an active population of KISS1R at the cell surface to facilitate prolonged KP signaling. Additionally, this review summarizes and discusses the major findings of an array of studies examining the desensitization of KP signaling in man, domestic and laboratory animals. This discussion highlights the major effects of ligand efficacy and concentration and the physiological, developmental, and metabolic status of the organism on KP signaling. Finally, the potential for the utilization of KP and analogs in stimulating and inhibiting the reproductive hormone cascade as an alternative to targeting the downstream GnRH receptor is discussed.

KISS1R signals independently of Gαq/11 and triggers LH secretion via the β-arrestin pathway in the male mouse

Hypothalamic GnRH is the master regulator of the neuroendocrine reproductive axis, and its secretion is regulated by many factors. Among these is kisspeptin (Kp), a potent trigger of GnRH secretion. Kp signals via the Kp receptor (KISS1R), a Gαq/11-coupled 7-transmembrane-spanning receptor. Until this study, it was understood that KISS1R mediates GnRH secretion via the Gαq/11-coupled pathway in an ERK1/2-dependent manner. We recently demonstrated that KISS1R also signals independently of Gαq/11 via β-arrestin and that this pathway also mediates ERK1/2 activation. Because GnRH secretion is ERK1/2-dependent, we hypothesized that KISS1R regulates GnRH secretion via both the Gαq/11- and β-arrestin-coupled pathways. To test this hypothesis, we measured LH secretion, a surrogate marker of GnRH secretion, in mice lacking either β-arrestin-1 or β-arrestin-2. Results revealed that Kp-dependent LH secretion was significantly diminished relative to wild-type mice (P < .001), thus supporting that β-arrestin mediates Kp-induced GnRH secretion. Based on this, we hypothesized that Gαq/11-uncoupled KISS1R mutants, like L148S, will display Gαq/11-independent signaling. To test this hypothesis, L148S was expressed in HEK 293 cells. and results confirmed that, although strongly uncoupled from Gαq/11, L148S retained the ability to trigger significant Kp-dependent ERK1/2 phosphorylation (P < .05). Furthermore, using mouse embryonic fibroblasts lacking β-arrestin-1 and -2, we demonstrated that L148S-mediated ERK1/2 phosphorylation is β-arrestin-dependent. Overall, we conclude that KISS1R signals via Gαq/11 and β-arrestin to regulate GnRH secretion. This novel and important finding could explain why patients bearing some types of Gαq/11-uncoupled KISS1R mutants display partial gonadotropic deficiency and even a reversal of the condition, idiopathic hypogonadotropic hypogonadism.

LIM-homeodomain transcription factor Isl-1 mediates kisspeptin's effect on insulin secretion in mice

Kisspeptin and the G protein-coupled receptor 54 (GPR54) are highly abundant in the pancreas. In addition, circulating kisspeptin directly influences insulin secretion through GPR54. However, the mechanisms by which kisspeptin affects insulin release are unclear. The LIM-homeodomain transcription factor, Isl-1, is expressed in all pancreatic islet cells and is involved in regulating both islet development and insulin secretion. We therefore investigated potential interactions between kisspeptin and Isl-1. Our results demonstrate that Isl-1 and GPR54 are coexpressed in mouse pancreatic islet β-cells and NIT cells. Both in vitro and in vivo results demonstrate that kisspeptin-54 (KISS-54) inhibits Isl-1 expression and insulin secretion and both the in vivo and in vitro effects of KISS-54 on insulin gene expression and secretion are abolished when an Isl-1-inducible knockout model is used. Moreover, our results demonstrate that the direct action of KISS-54 on insulin secretion is mediated by Isl-1. Our results further show that KISS-54 influences Isl-1 expression and insulin secretion through the protein kinase C-ERK1/2 pathway. Conversely, insulin has a feedback loop via the Janus kinase-phosphatidylinositol 3-kinase pathway regulating kisspeptin expression and secretion. These findings are important in understanding mechanisms of insulin secretion and metabolism in diabetes.

Cellular mechanisms and integrative timing of neuroendocrine control of GnRH secretion by kisspeptin

The hypothalamus integrates endogenous and exogenous inputs to control the pituitary-gonadal axis. The ultimate hypothalamic influence on reproductive activity is mediated through timely secretion of GnRH in the portal blood, which modulates the release of gonadotropins from the pituitary. In this context neurons expressing the RF-amide neuropeptide kisspeptin present required features to fulfill the role of the long sought-after hypothalamic integrative centre governing the stimulation of GnRH neurons. Here we focus on the intracellular signaling pathways triggered by kisspeptin through its cognate receptor KISS1R and on the potential role of proteins interacting with this receptor. We then review evidence implicating both kisspeptin and RFRP3--another RF-amide neuropeptide--in the temporal orchestration of both the pre-ovulatory LH surge in female rodents and the organization of seasonal breeding in photoperiodic species.

Kisspeptin/KISS1R signaling potentiates extravillous trophoblast adhesion to type-I collagen in a PKC- and ERK1/2-dependent manner

During the first trimester of human pregnancy, cytotrophoblasts proliferate within the tips of the chorionic villi to form cell columns that anchor the placenta to the uterus. This migration coincides with a widespread change in the adhesion molecule repertoire of these trophoblasts. Kisspeptin and its receptor, KISS1R, are best known as potent triggers of gonadotropin-releasing hormone secretion. The kisspeptin/KISS1R signaling system is also highly expressed in the human placenta, where it was demonstrated to inhibit extra-villous trophoblast (EVT) migration and invasion in vitro. Here we show that kisspeptin, in a dose- and time-dependent manner, induces increased adhesion of human EVTs to type-I collagen, a major component of the human placenta. This increased adhesion was both rapid and transient, suggesting that it likely occurred through the activation of KISS1R secondary effectors such as PKC and ERK, which underwent rapid and transient kisspeptin-dependent activation in EVTs. We then showed that inhibition of both PKC and ERK1/2 attenuated the kisspeptin-dependent increase in EVT adhesion, suggesting that these molecules are key positive regulators of trophoblast adhesion. We therefore propose that kisspeptin/KISS1R signaling potentiates EVT adhesion to type-I collagen via "inside-out signaling." Furthermore, kisspeptin treatment increased mouse blastocyst adhesion to collagen I, suggesting that kisspeptin signaling is a key regulator of trophoblast function during implantation as well as early placentation.

Molecular evolution of kiss2 genes and peptides in vertebrates

The kiss1 peptide (kisspeptin), a product of the kiss1 gene, is one of the key neuropeptides regulating vertebrate reproduction. In 2009, we identified a paralogous gene of kiss1 in the brain of amphibians and named it kiss2. Currently, the presence of the kiss2 gene and the kiss2 peptide is still obscure in amniotes compared with that in other vertebrates. Therefore, we performed genome database analyses in primates and reptiles to investigate the molecular evolution of the kiss2 gene in vertebrates. Because the mature kiss2 peptide has been identified only in amphibians, we further performed immunoaffinity purification and mass spectrometry to identify the mature endogenous kiss2 peptide in the brains of salmon and turtle that possessed the kiss2 gene. Here we provide the first evidence for the presence of a kiss2-like gene in the genome database of primates including humans. Synthetic amidated human KISS2 peptide activated human GPR54 expressed in COS7 cells, but nonamidated KISS2 peptide was inactive. The endogenous amidated kiss2 peptide may not be produced in primates because of the lack of an amidation signal in the precursor polypeptide. The kiss2-like gene may be nonfunctional in crocodilians because of premature stop codons. We identified the mature amidated kiss2 peptide in turtles and fish and analyzed the localization of kiss2 peptide mRNA expression in fish. The present study suggests that the kiss2 gene may have mutated in primates and crocodilians and been lost in birds during the course of evolution. In contrast, the kiss2 gene and mature kiss2 peptide are present in turtles and fish.

Kisspeptin/KISS1R System in Breast Cancer

Kisspeptins (KP), peptide products of the kisspeptin-1 (KISS1) gene are the endogenous ligands for a G protein-coupled receptor (GPCR) - KP receptor (KISS1R). KISS1R couples to the Gα_q/11 signaling pathway. KISS1 is a metastasis suppressor gene and the KP/KISS1R signaling has anti-metastatic and tumor-suppressant effects in numerous human cancers. On the other hand, recent studies indicate that KP/KISS1R pathway plays detrimental roles in breast cancer. In this review, we summarize recent developments in the understanding of the mechanisms regulating KP/KISS1R signaling in breast cancer metastasis.

KISS1R induces invasiveness of estrogen receptor-negative human mammary epithelial and breast cancer cells

Kisspeptins (KPs), peptide products of the KISS1 metastasis-suppressor gene, are endogenous ligands for a G protein-coupled receptor (KISS1R). KISS1 acts as a metastasis suppressor in numerous human cancers. However, recent studies have demonstrated that an increase in KISS1 and KISS1R expression in patient breast tumors correlates with higher tumor grade and metastatic potential. We have shown that KP-10 stimulates invasion of estrogen receptor α (ERα)-negative MDA-MB-231 breast cancer cells via transactivation of the epidermal growth factor receptor (EGFR). Here, we report that either KP-10 treatment of ERα-negative nonmalignant mammary epithelial MCF10A cells or expression of KISS1R in MCF10A cells induced a mesenchymal phenotype and stimulated invasiveness. Similarly, exogenous expression of KISS1R in ERα-negative SKBR3 breast cancer cells was sufficient to trigger invasion and induced extravasation in vivo. In contrast, KP-10 failed to transactivate EGFR or stimulate invasiveness in the ERα-positive MCF7 and T47D breast cancer cells. This suggested that ERα negatively regulates KISS1R-dependent breast cancer cell migration, invasion, and EGFR transactivation. In support of this, we found that these KP-10-induced effects were ablated upon exogenous expression of ERα in the MDA-MB-231 cells, by down-regulating KISS1R expression. Lastly, we have identified IQGAP1, an actin cytoskeletal binding protein as a novel binding partner of KISS1R, and have shown that KISS1R regulates EGFR transactivation in breast cancer cells in an IQGAP1-dependent manner. Overall, our data strongly suggest that the ERα status of mammary cells dictates whether KISS1R may be a novel clinical target for treating breast cancer metastasis.

Two families with normosmic congenital hypogonadotropic hypogonadism and biallelic mutations in KISS1R (KISS1 receptor): clinical evaluation and molecular characterization of a novel mutation

Context

KISS1R mutations have been reported in few patients with normosmic congenital hypogonadotropic hypogonadism (nCHH) (OMIM #146110).

Objective

To describe in detail nCHH patients with biallelic KISS1R mutations belonging to 2 unrelated families, and to functionally characterize a novel KISS1R mutation.

Results

An original mutant, p.Tyr313His, was found in the homozygous state in 3 affected kindred (2 females and 1 male) from a consanguineous Portuguese family. This mutation, located in the seventh transmembrane domain, affects a highly conserved amino acid, perturbs the conformation of the transmembrane segment, and impairs MAP kinase signaling and intracellular calcium release. In the second family, a French Caucasian male patient with nCHH was found to carry two recurrent mutations in the compound heterozygous state (p.Leu102Pro/Stop399Arg). In this man, pulsatile GnRH (Gonadotropin Releasing Hormone) administration restored pulsatile LH (Luteinizing Hormone) secretion and testicular hormone secretion. Later, long-term combined gonadotropin therapy induced spermatogenesis, enabling 3 successive pregnancies that resulted in 2 miscarriages and the birth of a healthy boy.

Conclusion

We show that a novel loss-of-function mutation (p.Tyr313His) in the KISS1R gene can cause familial nCHH, revealing the crucial role of this amino acid in KISS1R function. The observed restoration of gonadotropin secretion by exogenous GnRH administration further supports, in humans, the hypothalamic origin of the gonadotropin deficiency in this genetic form of nCHH.

Molecular biology of the kisspeptin receptor: signaling, function, and mutations

Kisspeptin receptor (KISS1R) signaling is essential for the hallmark increase in pulsatile GnRH secretion characteristic of the onset of puberty in humans and experimental animals. Loss-of-function mutations in KISS1R are associated with idiopathic hypogonadotropic hypogonadism in humans. Also, mutations with confirmed association with idiopathic central precocious puberty were identified in kisspeptin and KISS1R. These observations underscore the role of KISS1R signaling for normal pubertal development. Moreover, investigation of the mechanisms underlying the gain-of-function mutation in KISS1R indicates that the duration of KISS1R signaling is critical for the role of this receptor in timing the onset of puberty in humans. These findings further endorse the need to uncover the mechanisms, as well as yet-unknown proteins, involved in each step of KISS1R signaling. This knowledge is expected to advance our understanding of normal and abnormal pubertal development, as well as to help uncover the role of KISS1R signaling in non-hypothalamic tissues such as the placenta. This chapter discusses recent advances in the investigation of KISS1R signaling and function, as well as potential pathophysiological implications of naturally occurring mutations in this receptor identified in humans with reproductive disorders.

Single-cell analyses reveal that KISS1R-expressing cells undergo sustained kisspeptin-induced signaling that is dependent upon an influx of extracellular Ca2+

The kisspeptin receptor (KISS1R) is a Gα(q/11)-coupled seven-transmembrane receptor activated by a group of peptides referred to as kisspeptins (Kps). The Kp/KISS1R signaling system is a powerful regulator of GnRH secretion, and inactivating mutations in this system are associated with hypogonadotropic hypogonadism. A recent study revealed that Kp triggers prolonged signaling; not from the inability of the receptor to undergo rapid desensitization, but instead from the maintenance of a dynamic and active pool of KISS1R at the cell surface. To investigate this further, we hypothesized that if a dynamic pool of receptor is maintained at the cell surface for a protracted period, chronic Kp-10 treatment would trigger the sustained activation of Gα(q/11) as evidenced through the prolonged activation of phospholipase C, protein kinase C, and prolonged mobilization of intracellular Ca(2+). Through single-cell analyses, we tested our hypothesis in human embryonic kidney (HEK) 293 cells and found that was indeed the case. We subsequently determined that prolonged KISS1R signaling was not a phenomenon specific to HEK 293 cells but is likely a conserved property of KISS1R-expressing cells because evidence of sustained KISS1R signaling was also observed in the GT1-7 GnRH neuronal and Chinese hamster ovary cell lines. While exploring the regulation of prolonged KISS1R signaling, we identified a critical role for extracellular Ca(2+). We found that although free intracellular Ca(2+), primarily derived from intracellular stores, was sufficient to trigger the acute activation of a major KISS1R secondary effector, protein kinase C, it was insufficient to sustain chronic KISS1R signaling; instead extracellular Ca(2+) was absolutely required for this.

Kisspeptins and Reproduction: Physiological Roles and Regulatory Mechanisms

Procreation is essential for survival of species. Not surprisingly, complex neuronal networks have evolved to mediate the diverse internal and external environmental inputs that regulate reproduction in vertebrates. Ultimately, these regulatory factors impinge, directly or indirectly, on a final common pathway, the neurons producing the gonadotropin-releasing hormone (GnRH), which stimulates pituitary gonadotropin secretion and thereby gonadal function. Compelling evidence, accumulated in the last few years, has revealed that kisspeptins, a family of neuropeptides encoded by the Kiss1 gene and produced mainly by neuronal clusters at discrete hypothalamic nuclei, are pivotal upstream regulators of GnRH neurons. As such, kisspeptins have emerged as important gatekeepers of key aspects of reproductive maturation and function, from sexual differentiation of the brain and puberty onset to adult regulation of gonadotropin secretion and the metabolic control of fertility. This review aims to provide a comprehensive account of the state-of-the-art in the field of kisspeptin physiology by covering in-depth the consensus knowledge on the major molecular features, biological effects, and mechanisms of action of kisspeptins in mammals and, to a lesser extent, in nonmammalian vertebrates. This review will also address unsolved and contentious issues to set the scene for future research challenges in the area. By doing so, we aim to endow the reader with a critical and updated view of the physiological roles and potential translational relevance of kisspeptins in the integral control of reproductive function.

G protein-coupled receptors involved in GnRH regulation: molecular insights from human disease

In the past two decades, an increasing body of evidence has demonstrated that several G protein-coupled receptor (GPCR)-ligand pairs are critical for normal human reproductive development and function. Patients harboring genetic insults in either the receptors or their cognate ligands have presented with reproductive disorders characterized by varying degrees of GnRH deficiency. These disorders include idiopathic hypogonadotropic hypogonadism (IHH) and Kallmann Syndrome (KS). Conversely, mutations in some of these ligand-receptor pairs have been associated with accelerated reproductive maturation, manifested as central precocious puberty (CPP). To date, a series of elegant studies have characterized four GPCRs that play important roles in the neuroendocrine control of human reproductive development and function: GnRHR, KISS1R, PROKR2 and NK3R. Furthermore, these studies provide insights into the mechanisms by which mutations in these receptors give rise to reproductive disease phenotypes. This report will review mutations identified in GPCRs involved in the neuroendocrine control of the human reproductive axis with the aims of elucidating structure-function relationships of these GPCRs and identifying correlations between these structure-function relationships and the genotypic-phenotypic characterization of the patients.