Hypertrophy and increased kisspeptin gene expression in the hypothalamic infundibular nucleus of postmenopausal women and ovariectomized monkeys

The Neuroendocrine Regulation of Reproductive Behavior and Emotional Control by Kisspeptin

Reproductive success and ultimately species survival at a population level is contingent on a plethora of neuroendocrine signals working in concert to regulate gonadal function and reproductive behavior. Among these, the neuropeptide kisspeptin (encoded by the KISS1/Kiss1 gene) has emerged as the master regulator of the hypothalamic-pituitary-gonadal axis. Besides the hypothalamus, both kisspeptin and its cognate receptor are extensively expressed throughout cortico-limbic brain structures in rodents and humans, which are regions traditionally implicated in behavioral and emotional responses. Thus, there exists a neuroanatomical framework through which kisspeptin can integrate reproductive behavior and emotional regulation with the reproductive axis. Accordingly, this sets the scene for recent findings derived from an assortment of species, including humans, unveiling kisspeptin as an important gatekeeper of reproductive behavior and emotional control. Herein, we summarize the major preclinical animal and human experimental evidence identifying kisspeptin as a key neuromodulator of reproductive behavior and emotional state. Such findings have laid the foundations for clinical applications of kisspeptin-based therapies for patients with related reproductive and psychosexual disorders.

Kisspeptin fiber and receptor distribution analysis suggests its potential role in central sensorial processing and behavioral state control

Kisspeptin (KP) signaling in the brain is defined by the anatomical distribution of KP-producing neurons, their fibers, receptors, and connectivity. Technological advances have prompted a re-evaluation of these chemoanatomical aspects, originally studied in the early years after the discovery of KP and its receptor Kiss1r. Previously, we characterized (Hernández et al. bioRxiv 2024) seven KP neuronal populations in the mouse brain at the mRNA level, including two novel populations, and examined their response to gonadectomy. In this study, we mapped KP fiber distribution in rats and mice using immunohistochemistry under intact as well as short- and long-term post-gonadectomy conditions. Kiss1r mRNA expression was examined via RNAscope, in relation to vesicular GABA transporter (Slc32a1) in whole mouse brain, and to KP and vesicular glutamate transporter 2 (Slc17a6), Kiss1, and Slc32a1 in hypothalamic RP3V and arcuate regions. We identified KP fibers in 118 brain regions, primarily in extra-hypothalamic areas associated with sensorial processing and behavioral state control. KP-immunoreactive fiber density and distribution were largely unchanged by gonadectomy. Kiss1r was expressed prominently in sensorial and state control regions such as the septal nuclei, the suprachiasmatic nucleus, locus coeruleus, hippocampal layers, thalamic nuclei, and cerebellar structures. Co-expression of Kiss1r and Kiss1 was observed in hypothalamic neurons, suggesting both autocrine and paracrine KP signaling mechanisms. These findings enhance our understanding of KP signaling beyond reproductive functions, particularly in sensorial processing and behavioral state regulation. This study opens new avenues for investigating KP's role in controlling complex physiological processes, including those unrelated to reproduction.

Effects of menopause on temperature regulation

Changes in thermoregulation, notably the emergence of hot flashes, occur during the menopause transition in association with reproductive hormonal changes. Hot flashes constitute the most characteristic symptom of menopause (prevalence of 50-80%), and have a substantial negative effect on quality of life. Here, we review the endocrine changes associated with menopause and the thermoregulatory system and its sensitivity to female sex hormones. We then review current knowledge on the underlying neural mechanisms of hot flashes and how the reproductive and thermoregulatory systems interact in females. We consider the kisspeptin-neurokinin B-dynorphin (KNDy) neuron complex, which becomes hyperactive when estradiol levels decrease. KNDy neurons project from the arcuate nucleus to thermoregulatory areas within the hypothalamic preoptic area, where heat loss mechanisms are triggered, including cutaneous vasodilation and sweating - characteristics of the hot flash. We describe the physiology and measurement of hot flashes and discuss the mixed research findings about thresholds for sweating in symptomatic individuals. We consider the unique situation of hot flashes that arise during sleep, and discuss the relationships between the environment, exercise, and body mass index with hot flashes. We also discuss the unique situation of surgical menopause (with oophorectomy) and cancer therapy, conditions that are associated with frequent, severe, hot flashes. We then provide an overview of treatments of hot flashes, including hormone therapy and targeted neurokinin B-antagonists, recently developed to target the neural mechanism of hot flashes. Finally, we highlight gaps in knowledge about menopausal thermoregulation and hot flashes and suggest future directions for research.

Kisspeptin and neurokinin B: roles in reproductive health

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

Effects of Integrated Extracts of Trigonella foenum-graecum and Asparagus racemosus on Hot Flash-like Symptoms in Ovariectomized Rats

Vasomotor symptoms, such as hot flashes (HFs), commonly affect women during menopause, leading to a reduced quality of life. The current study evaluates the combined effect of active components Asparagus racemosus (AR) and Trigonella foenum-graecum (TFG) in a single oral formulation (IAT) for alleviating menopausal symptoms in ovariectomized rats. Following bilateral ovariectomy, the animals were randomly assigned to nine groups: (1) Control, (2) Ovariectomy (OVX), (3) OVX+TA1 (TA: Combination of Trigonella and Asparagus; TFG 30 mg/kg + AR 30 mg/kg), (4) OVX+TA2 (TFG 30 mg/kg + AR 15 mg/kg), (5) OVX+TA3 (TFG 15 mg/kg + AR 30 mg/kg), (6) OVX+TA4 (TFG 40 mg/kg + AR 30 mg/kg), (7) OVX+TA5 (TFG 30 mg/kg + AR 40 mg/kg), (8) OVX+IAT1 (IAT: Integrated Asparagus and Trigonella; TFG+AR integrated extract, 30 mg/kg), and (9) OVX+IAT2 (TFG+AR integrated extract, 60 mg/kg). On the 8th day of treatment, tail and skin temperatures were recorded every 30 min for 24 h. Ovariectomized rats exhibited menopausal symptoms, such as hormonal imbalances and elevated skin temperature. Administration of AR, TFG, and IAT significantly decreased serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), and cortisol while increasing estradiol, progesterone, and dopamine (p < 0.0001), effectively alleviating hot flash-like symptoms. Additionally, they mitigated ovariectomy-induced oxidative stress by lowering malondialdehyde (MDA) levels and restoring antioxidant enzyme activity. Ovariectomized rats exhibited increased expression of a proto-oncogene (c-FOS), gonadotropin-releasing hormone (GnRH), Kisspeptin, Neurokinin B (NKB), and Transient receptor potential vanilloid 1 (TRPV1), along with reduced expressing brain-derived neurotrophic factor (BDNF) levels, which were reversed by treatment, especially with the IAT2 combination. The AR and TFG combination, particularly in IAT formulations, showed strong potential in alleviating menopausal symptoms in ovariectomized rats. These findings suggest that the combination of AR and TFG extracts could be a natural alternative for managing postmenopausal symptoms by restoring reproductive hormone levels, regulating lipid profiles, and enhancing antioxidant defense systems.

NK3 receptor antagonist alters the centrally controlled perception of menopausal flushing - a pilot study

OBJECTIVE

Kisspeptin/neurokinin/dynorphin (KNDy) signaling links reproductive and thermoregulatory systems, and improvements in menopausal flushing are reported with neurokinin 3 receptor (NK3R) antagonists. A rise in brainstem activity preceding a flush has been proposed as its functional origin, with subsequent activity in the insula and prefrontal cortices reflecting individual perception. Using functional magnetic resonance imaging (fMRI), this study investigated the central effect of the NK3R antagonist MLE4901 during a flush, particularly functional connectivity changes in the salience network.

METHOD

Five postmenopausal women with flushes completed a 1-week flush diary prior to baseline fMRI, during which hot flushes were triggered by heating. Diaries were continued during 7 days of treatment with the NK3R antagonist MLE4901, with repeat fMRI on day 7. Sternal monitors recorded objective flushing before each fMRI. Connectivity changes in the salience network post flush were assessed.

RESULTS

Treatment with MLE4901 reduced the subjective flush frequency (from median 6.9 to 1.1 per day; p = 0.02) without changes in objective flushes. Treatment decreased right anterior insula connectivity, which correlated significantly with decreased subjective flushing.

CONCLUSION

This pilot study demonstrates decreased connectivity in the salience network during NK3R antagonist treatment. This may indicate areas of interest for further targeted fMRI studies and mechanistic investigation of this novel treatment for flushing.

A New Hope for Woman with Vasomotor Symptoms: Neurokinin B Antagonists

KNDy (kisspeptine, neurokinin B, dynorphin) neurons, located in the hypothalamus, play a crucial role in the development of vasomotor symptoms (VSM) in menopausal women. Estrogen withdrawal during menopause leads to the hyperactivation of kisspeptin and neurokinin B (NKB) secretion, contributing to the onset of these symptoms. The identification of NKB/neurokinin B receptor (NK3R) signaling as a key mechanism in menopausal hot flashes has driven the development of NK3R antagonists. These antagonists restore the disrupted balance in KNDy neuron activity caused by estrogen deficiency, thereby reducing the frequency and severity of VMS. In 2023, the FDA approved fezolinetant, the first selective NK3R antagonist, for the treatment of moderate to severe VMS associated with menopause. Additionally, elinzanetant, a dual neurokinin-1 and neurokinin-3 receptor antagonist, has demonstrated promising results. The approval application for elinzanetant was supported by positive findings from the OASIS 1, 2, and 3 Phase III clinical studies. The dual antagonism of NK-1 and NK-3 receptors enhances its efficacy by alleviating menopause-related sleep disturbances and modulating peripheral vasodilatation. In this regard, elinzanetant represents a promising non-hormonal treatment that targets the underlying causes of VMS through NK-1 and NK-3 receptor pathways. The development of neurokinin B antagonist for VMS treatment exemplifies the impact of advanced pharmacological research on gynecological endocrinology.

Estrogen-Regulated Lateral Septal Kisspeptin Neurons Abundantly Project to GnRH Neurons and the Hypothalamic Supramammillary Nucleus

While hypothalamic kisspeptin (KP) neurons play well-established roles in the estrogen-dependent regulation of reproduction, little is known about extrahypothalamic KP-producing (KPLS) neurons of the lateral septum. As established previously, Kiss1 expression in this region is low and regulated by estrogen receptor- and GABAB receptor-dependent mechanisms. Our present experiments on Kiss1-Cre/ZsGreen knock-in mice revealed that transgene expression in the LS begins at Postnatal Day (P)33-36 in females and P40-45 in males and is stimulated by estrogen receptor signaling. Fluorescent cell numbers continue to increase in adulthood and are higher in females. Viral tracing uncovered that the bulk of KPLS fibers joins the medial forebrain bundle and terminates in the hypothalamic supramammillary nucleus. Smaller subsets innervate the medial amygdala or project to other limbic structures. One-quarter of gonadotropin-releasing hormone (GnRH)-immunoreactive perikarya in the preoptic area and their dendrites receive appositions from KPLS axons. OVX adult Kiss1-Cre/ZsGreen mice treated for 4 d with 17β-estradiol or vehicle were used for RNA sequencing studies of laser-microdissected KPLS neurons. The transcriptome included markers of GABAergic and neuropeptidergic (Penk, Cartpt, Vgf) cotransmission and 571 estrogen-regulated transcripts. Estrogen treatment upregulated the acetylcholine receptor transcript Chrm2 and, in slice electrophysiology experiments, caused enhanced muscarinic inhibition of KPLS neurons. Finally, we provided immunohistochemical evidence for homologous neurons in the postmortem human brain, suggesting that KPLS neurons may contribute to evolutionarily conserved regulatory mechanisms. Future studies will need to investigate the putative roles of KPLS neurons in the estrogen-dependent control of GnRH neurons and/or various hypothalamic/limbic functions.

Estradiol metabolism by gut microbiota in women's depression pathogenesis: inspiration from nature

The recurrence and treatment resistance of depression remain significant issues, primarily due to an inadequate understanding of its pathogenesis. Recent scientific evidence indicates that gut microbiota influence estradiol metabolism and are associated with the development of depression in nonpremenopausal women. Integrating existing studies on the regulation of estradiol metabolism by microorganisms in nature and the relevance of its degradation products to depression, recent scientific explorations have further elucidated the key mechanisms by which gut microbiota catabolize estradiol through specific metabolic pathways. These emerging scientific findings suggest that the unique metabolic effects of gut microbiota on estradiol may be one of the central drivers in the onset and course of depression in non-menopausal women.

Kisspeptin and its Current Clinical Status-A Systematic Review

BACKGROUND

Kisspeptin was initially known as metastin for its role in suppressing metastasis in melanoma and breast cancer. Later, based on its ability to stimulate GPR54, its importance in maintaining an intact hypothalamic-pituitary-ovarian axis was recognised, which is the basis for the widespread application of the drug in several conditions such as secondary amenorrhea, regulation of puberty onset, ovarian function, trophoblast invasion, fertility regulation, parturition, and lactation. This systematic study aims to evaluate the current status of kisspentin in clinical trials.

METHODS

The keywords 'kisspeptin' or 'metastin' were used in the clinicaltrials.gov website and Clinical Trial Registry of India (CTRI) to find eligible clinical trials or records carried out without time constraints until February 26, 2023.

RESULTS

A total of 33 records were identified through clinical trial databases. All records were screened, and four trials were rejected as they failed to meet the inclusion criteria. Finally, 29 (87.9%) reports of interventional clinical trials with kisspeptin were reviewed.

CONCLUSION

Kisspeptin can be viewed as a multipurpose drug with considerably fewer side effects due to its effects simulating normal physiological processes in our body.

Kisspeptin and Endometriosis-Is There a Link?

This article presents a narrative review that explores the potential link between kisspeptin-a key regulator of the hypothalamic-pituitary-gonadal axis-and the pathogenesis of endometriosis. Kisspeptin plays a significant role in regulating reproductive functions by modulating the release of gonadotropin-releasing hormone (GnRH), which in turn stimulates the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Recent studies suggest that kisspeptin may also impact peripheral reproductive tissues and influence inflammatory processes involved in the development of endometriosis. Altered kisspeptin signaling has been associated with the abnormal hormonal environment observed in endometriosis, which affects menstrual cycles and ovarian function. Research indicates that women with endometriosis exhibit altered levels of kisspeptin and its receptor, KISS1R, in both eutopic and ectopic endometrial tissues, suggesting a role in disease progression, particularly in tissue invasion and lesion formation. Kisspeptin's role in regulating matrix metalloproteinases (MMPs), enzymes essential for tissue remodeling, further supports its potential contribution to the pathophysiology of endometriosis. Moreover, kisspeptin-based therapeutic strategies are currently under investigation, with the aim of providing targeted treatments that reduce the side effects commonly associated with existing therapies. Despite promising findings, further research is needed to fully understand the mechanisms by which kisspeptin influences endometriosis.

Kisspeptin fiber and receptor distribution analysis suggests its potential role in central sensorial processing and behavioral state control

Background

Kisspeptin (KP) signaling in the brain is defined by the anatomical distribution of KP-producing neurons, their fibers, receptors, and connectivity. Technological advances have prompted a re-evaluation of these chemoanatomical aspects, originally studied in the early years after the discovery of KP and its receptor Kiss1r. We have previously characterized(1) seven KP neuronal populations in the mouse brain at the mRNA level, including two novel populations, and examined their short-term response to gonadectomy.

Methods

In this study, we mapped KP fiber distribution in rats and mice using immunohistochemistry under intact and short- and long-term post-gonadectomy conditions. Kiss1r mRNA expression was examined via RNAscope, in relation to vesicular GABA transporter ( Slc32a1 ) in whole mouse brain and to KP and vesicular glutamate transporter 2 ( Kiss1 and Slc17a6 ) in hypothalamic RP3V and arcuate regions.

Results

We identified KP fibers in 118 brain regions, primarily in extra-hypothalamic areas associated with sensorial processing and behavioral state control. KP-immunoreactive fiber density and distribution were largely unchanged by gonadectomy. Kiss1r was expressed prominently in sensorial and state control regions such as septal nuclei, the suprachiasmatic nucleus, locus coeruleus, hippocampal layers, thalamic nuclei, and cerebellar structures. Co-expression of Kiss1r and Kiss1 was observed in hypothalamic neurons, suggesting both autocrine and paracrine KP signaling mechanisms.

Conclusion

These findings enhance our understanding of KP signaling beyond reproductive functions, particularly in sensorial and behavioral state regulation. This study opens new avenues for investigating KP's role in controlling complex physiological processes, including those not related to reproduction.

Kisspeptin in functional hypothalamic amenorrhea: Pathophysiology and therapeutic potential

Functional hypothalamic amenorrhea (FHA) is one of the most common causes of secondary amenorrhea, resulting in anovulation and infertility, and is a low estrogen state that increases the risk of cardiovascular disease and impairs bone health. FHA is characterized by acquired suppression of physiological pulsatile gonadotropin-releasing hormone (GnRH) release by the hypothalamus in the absence of an identifiable structural cause, resulting in a functional hypogonadotropic hypogonadism. FHA results from either decreased energy intake and/or excessive exercise, leading to low energy availability and weight loss-often in combination with psychological stress on top of a background of genetic susceptibility. The hypothalamic neuropeptide kisspeptin is a key component of the GnRH pulse generator, tightly regulating pulsatile GnRH secretion and the downstream reproductive axis. Here, we review the physiological regulation of pulsatile GnRH secretion by hypothalamic kisspeptin neurons and how their activity is modulated by signals of energy status to affect reproductive function. We explore endocrine factors contributing to the suppression of GnRH pulsatility in the pathophysiology of FHA and how hypothalamic kisspeptin neurons likely represent a final common pathway through which these factors affect GnRH pulse generation. Finally, we discuss the therapeutic potential of kisspeptin as a novel treatment for women with FHA.

Interactions between kisspeptin and bone: Cellular mechanisms, clinical evidence, and future potential

The neuropeptide kisspeptin and its cognate receptor have been extensively studied in reproductive physiology, with diverse and well-established functions, including as an upstream regulator of pubertal onset, reproductive hormone secretion, and sexual behavior. Besides classical reproduction, both kisspeptin and its receptor are extensively expressed in bone-resorbing osteoclasts and bone-forming osteoblasts, which putatively permits direct bone effects. Accordingly, this sets the scene for recent compelling findings derived from in vitro experiments through to in vivo and clinical studies revealing prominent regulatory interactions for kisspeptin signaling in bone metabolism, as well as certain oncological aspects of bone metabolism. Herein, we comprehensively examine the experimental evidence obtained to date supporting the interaction between kisspeptin and bone. A comprehensive understanding of this emerging facet of kisspeptin biology is fundamental to exploiting the future therapeutic potential of kisspeptin-based medicines as a novel strategy for treating bone-related disorders.

Kisspeptin control of hypothalamus-pituitary-ovarian functions

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

Male animal sterilization: history, current practices, and potential methods for replacing castration

Sterilization and castration have been synonyms for thousands of years. Making an animal sterile meant to render them incapable of producing offspring. Castration or the physical removal of the testes was discovered to be the most simple but reliable method for managing reproduction and sexual behavior in the male. Today, there continues to be global utilization of castration in domestic animals. More than six hundred million pigs are castrated every year, and surgical removal of testes in dogs and cats is a routine practice in veterinary medicine. However, modern biological research has extended the meaning of sterilization to include methods that spare testis removal and involve a variety of options, from chemical castration and immunocastration to various methods of vasectomy. This review begins with the history of sterilization, showing a direct link between its practice in man and animals. Then, it traces the evolution of concepts for inducing sterility, where research has overlapped with basic studies of reproductive hormones and the discovery of testicular toxicants, some of which serve as sterilizing agents in rodent pests. Finally, the most recent efforts to use the immune system and gene editing to block hormonal stimulation of testis function are discussed. As we respond to the crisis of animal overpopulation and strive for better animal welfare, these novel methods provide optimism for replacing surgical castration in some species.

Spatial local expressions of kisspeptin in the uterus and uterine tubes and its relationship to the reproductive potential in goats

Kisspeptins are neuropeptides encoded by the Kiss1 gene that was discovered as a metastasis suppressor gene in melanoma and breast cancer. Kisspeptin has pivotal functions for gonadotropin-releasing hormone secretion and plays integrated roles in the hypothalamic-pituitary-gonadal axis. However, little is known about the peripheral expression of kisspeptin in ruminants, especially in the female reproductive tract. Here, the objectives of the current study were to investigate the spatial localization of kisspeptin and mRNA expression of Kiss1 and its receptor (Kiss1r) in the fallopian tubes (FT) and uterus of goats at varied reproductive activity (cyclic versus true anoestrous goats, n=6, each). Specimens of the uterus and FT were collected and fixed using paraformaldehyde to investigate the localizations of kisspeptin in the selected tissues by immunohistochemistry. Another set of samples was snape-frozen to identify the expressions of mRNAs encoding Kiss1 and Kiss1r using real-time PCR. Results revealed immunolocalizations of kisspeptin in the uterus and the FT. The staining of kisspeptin was found mainly in the mucosal epithelium of the uterus the FT, and the endometrial glands. Very intense staining of kisspeptin was found in the uterine and FT specimens in the true anoestrous goats compared to that in cyclic ones. The expression of mRNA encoding Kiss1 gene was significantly higher in the uterine specimen of cyclic goats (1.00±0.09) compared to that in the true anoestrous goats (0.62±0.08) (P ˂0.05), while the expression of mRNA encoding Kiss1r was significantly (P ˂0.001) higher in the uterine tissues of true anoestrous goats (1.78±0.17) compared to that in cyclic ones (1.00±0.11). In conclusion, immunohistochemical localization of kisspeptin and the expression of mRNA encoding Kiss1/Kiss1r revealed spatial changes in the uterus and FT of goats according to the reproductive potential of goats (cyclic versus true anoestrous goats). However, the definitive local role of kisspeptin in the uterus and FT need further investigation.

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.

Distribution of the kisspeptin system and its relation with gonadotropin-releasing hormone in the hypothalamus

Kisspeptin (KISS1), originally catalogued as metastin because of its capacity as a metastasis suppressor in human melanoma and breast cancer, is now recognized as the major puberty gatekeeper and gonadotropin-releasing hormone (GnRH) neuroendocrine system modulator. It is a member of the family of RFamide-related peptides that also includes the neuropeptide FF group, the gonadotropin-inhibitory hormone, the prolactin-releasing peptide, and the 26RFa peptides. The KISS1 precursor peptide is processed into a family of peptides known as kisspeptins. Its expression has been described in the hypothalamus as well as in the whole reproductive axis and several extra reproductive tissues of mammals as well as fish and amphibians, but not in birds. KISS1 plays an essential role as a regulator of the reproductive axis by inducing the synthesis and release of GnRH, acting through specific receptors. The study of the kisspeptin system and its relation with reproduction in wild and non-classical laboratory species is extremely useful to understand and become aware of the role of KISS1 in the wide variety of possible different reproductive strategies. In this chapter, KISS1 involvement in non-classical laboratory rodents, fishes, and birds is discussed.

Postmortem tissue biomarkers of menopausal transition

The menopausal transition (MT) is associated with an increased risk for many disorders including neurological and mental disorders. Brain imaging studies in living humans show changes in brain metabolism and structure that may contribute to the MT-associated brain disease risk. Although deficits in ovarian hormones have been implicated, cellular and molecular studies of the brain undergoing MT are currently lacking, mostly due to a difficulty in studying MT in postmortem human brain. To enable this research, we explored 39 candidate biomarkers for menopausal status in 42 pre-, peri-, and post-menopausal subjects across three postmortem tissues: blood, the hypothalamus, and pituitary gland. We identified thirteen significant and seven strongest menopausal biomarkers across the three tissues. Using these biomarkers, we generated multi-tissue and tissue-specific composite measures that allow the postmortem identification of the menopausal status across different age ranges, including the "perimenopausal", 45-55-year-old group. Our findings enable the study of cellular and molecular mechanisms underlying increased neuropsychiatric risk during the MT, opening the path for hormone status-informed, precision medicine approach in women's mental health.

Elinzanetant, a new combined neurokinin-1/-3 receptor antagonist for the treatment of postmenopausal vasomotor symptoms

INTRODUCTION

In many postmenopausal women, quality of life is decreased due to vasomotor symptoms. Efficient and well-tolerated non-hormonal treatment options are needed.

AREAS COVERED

The present review summarizes what is known about the etiology of postmenopausal vasomotor symptoms as a rationale for the mechanism of action of Elinzanetant, a new neurokinin (NK)-1/-3 receptor antagonist, as well as its efficacy and side effect profile.

EXPERT OPINION

Elinzanetant likely exerts an antagonistic effect on the NK-3 receptor in the preoptic thermoregulatory zone, but also an additional antagonistic effect on the NK-1 receptor possibly leading to a reduction in vasodilatation and heat-sensing neuro-activity. Elinzanetant's reported peak drug concentrations are reached within one hour and the terminal elimination half-life is approximately 15 hours. Two phase IIb clinical trials evaluated the safety profile and efficacy of several doses. There were no serious adverse events, which also included a lack of evidence of drug-related hepatotoxicity. Overall, Elinzanetant seems to be well-tolerated. In the SWITCH-1 study, the 120 mg/day and 160 mg/day regimen showed good efficacy for the treatment of vasomotor symptoms and led to significant improvements in quality of life. Thus, 120 mg oral Elinzanetant/day was used in phase III trials, whose results have not yet been published.

Metalloestrogens exposure and risk of gestational diabetes mellitus: Evidence emerging from the systematic review and meta-analysis

BACKGROUND

Metalloestrogens are metals and metalloid elements with estrogenic activity found everywhere. Their impact on human health is becoming more apparent as human activities increase.

OBJECTIVE

Our aim is to conduct a comprehensive systematic review and meta-analysis of observational studies exploring the correlation between metalloestrogens (specifically As, Sb, Cr, Cd, Cu, Se, Hg) and Gestational Diabetes Mellitus (GDM).

METHODS

PubMed, Web of Science, and Embase were searched to examine the link between metalloestrogens (As, Sb, Cr, Cd, Cu, Se, and Hg) and GDM until December 2023. Risk estimates were derived using random effects models. Subgroup analyses were conducted based on study countries, exposure sample, exposure assessment method, and detection methods. Sensitivity analyses and adjustments for publication bias were carried out to assess the strength of the findings.

RESULTS

Out of the 389 articles identified initially, 350 met our criteria and 33 were included in the meta-analysis, involving 141,175 subjects (9450 cases, 131,725 controls). Arsenic, antimony, and copper exposure exhibited a potential increase in GDM risk to some extent (As: OR = 1.28, 95 % CI [1.08, 1.52]; Sb: OR = 1.73, 95 % CI [1.13, 2.65]; Cu: OR = 1.29, 95 % CI [1.02, 1.63]), although there is a high degree of heterogeneity (As: Q = 52.93, p < 0.05, I2 = 64.1 %; Sb: Q = 31.40, p < 0.05, I2 = 80.9 %; Cu: Q = 21.14, p < 0.05, I2 = 71.6 %). Conversely, selenium, cadmium, chromium, and mercury exposure did not exhibit any association with the risk of GDM in our study.

DISCUSSION

Our research indicates that the existence of harmful metalloestrogens in the surroundings has a notable effect on the likelihood of GDM. Hence, we stress the significance of environmental elements in the development of GDM and the pressing need for relevant policies and measures.

The kisspeptin system in and beyond reproduction: exploring intricate pathways and potential links between endometriosis and polycystic ovary syndrome

Endometriosis and polycystic ovary syndrome (PCOS) are two common female reproductive disorders with a significant impact on the health and quality of life of women affected. A novel hypothesis by evolutionary biologists suggested that these two diseases are inversely related to one another, representing a pair of diametrical diseases in terms of opposite alterations in reproductive physiological processes but also contrasting phenotypic traits. However, to fully explain the phenotypic features observed in women with these conditions, we need to establish a potential nexus system between the reproductive system and general biological functions. The recent discovery of kisspeptin as pivotal mediator of internal and external inputs on the hypothalamic-pituitary-gonadal axis has led to a new understanding of the neuroendocrine upstream regulation of the human reproductive system. In this review, we summarize the current knowledge on the physiological roles of kisspeptin in human reproduction, as well as its involvement in complex biological functions such as metabolism, inflammation and pain sensitivity. Importantly, these functions are known to be dysregulated in both PCOS and endometriosis. Within the evolving scientific field of "kisspeptinology", we critically discuss the clinical relevance of these discoveries and their potential translational applications in endometriosis and PCOS. By exploring the possibilities of manipulating this complex signaling system, we aim to pave the way for novel targeted therapies in these reproductive diseases.

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.

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.

New advances in menopause symptom management

Vasomotor symptoms (VMS) are characteristic of menopause experienced by over 75% of postmenopausal women with significant health and socioeconomic implications. Although the average duration of symptoms is seven years, 10% of women experience symptoms for more than a decade. Although menopausal hormone therapy (MHT) remains an efficacious and cost-effective treatment, its use may not be suitable in all women, such as those at an increased risk of breast cancer or gynaecological malignancy. The neurokinin B (NKB) signaling pathway, together with its intricate connection to the median preoptic nucleus (MnPO), has been postulated to provide integrated reproductive and thermoregulatory responses, with a central role in mediating postmenopausal VMS. This review describes the physiological hypothalamo-pituitary-ovary (HPO) axis, and subsequently the neuroendocrine changes that occur with menopause using evidence derived from animal and human studies. Finally, data from the latest clinical trials using novel therapeutic agents that antagonise NKB signaling are reviewed.

Elinzanetant: a phase III therapy for postmenopausal patients with vasomotor symptoms

INTRODUCTION

Menopausal vasomotor symptoms (VMS) are experienced by most women and are often debilitating and can last for years. While hormone replacement therapy is effective, it carries risks that have impacted its wider use, and it can be contraindicated. There is a large unmet need for a safe, effective non-hormonal therapy.

AREAS COVERED

The importance of the neurokinin (NK) system in the hypothalamic regulation of the vasomotor center has become clear. NK antagonists, previously developed for other indications, have therefore been investigated for the treatment of VMS. Elinzanetant is a potent antagonist at both NK1 (endogenous ligand Substance P) and NK3 (neurokinin B) receptors, whereas other related drugs in development are selective NK3 antagonists. Elinzanetant has been investigated in 2 Phase II trials for menopausal VMS, demonstrating rapid onset and dose-dependant efficacy for the relief of VMS and improvement in quality of life for up to 12 weeks. Phase III trials are underway in women both with physiological menopause and after treatment for breast cancer.

EXPERT OPINION

Elinzanetant is a very promising non-hormonal approach to a highly prevalent symptom constellation, with rapid onset and high efficacy. Wider indications are being explored in current Phase III trials.

Neurokinin 1/3 receptor antagonists for menopausal women: A current systematic review and insights into the investigational non-hormonal therapy

BACKGROUND

Over 75% of menopausal women experience vasomotor symptoms (VMS), such as night sweats and hot flashes. Despite the prevalence of these symptoms, there is limited data on non-hormonal therapies to alleviate them.

METHODS

PubMed, Cochrane, Scopus, Ovid, Web of Science, and ClinicalTrials.Gov were searched for relevant studies. The search was performed using the following keywords, which were customized to suit the specific databases/registers: menopause, women, neurokinin 3, and/or Fezolinetant. The search was conducted until December 20, 2022. This systematic review was conducted in compliance with the PRISMA Statement 2020 guidelines.

RESULTS

A total of 326 records were found, with 10 studies (enrolling 1993 women) selected for inclusion. The women received 40-mg doses of NK1/3 receptor antagonists twice daily, with follow-ups at 1 to 3 weeks. Moderately strong evidence was found suggesting that NK1/3 receptor antagonists can help limit the frequency and severity of hot flashes in menopausal women.

CONCLUSION

While the results should be interpreted with caution until further clinical trials validate the efficacy and safety of NK1/3 receptor antagonists among menopausal women, these findings suggest that they are promising targets for future pharmacological and clinical studies in addressing vasomotor symptoms.

Optogenetics studies of kisspeptin neurons

Optical systems and genetic engineering technologies have made it possible to control neurons and unravel neuronal circuit behavior with high temporal and spatial resolution. The application of optogenetic strategies to understand the physiology of kisspeptin neuronal circuits has evolved in recent years among the neuroendocrine community. Kisspeptin neurons are fundamentally involved in controlling mammalian reproduction but also are implicated in numerous other physiological processes, including but not limited to feeding, energy expenditure, core body temperature and behavior. We conducted a review aiming to shed light on the novel findings obtained from in vitro and in vivo optogenetic studies interrogating kisspeptin neuronal circuits to date. Understanding the function of kisspeptin networks in the brain can greatly inform a wide range of clinical studies investigating infertility treatments, gender identity, metabolic disorders, hot flushes and psychosexual disorders.

Efficacy and safety of elinzanetant, a selective neurokinin-1,3 receptor antagonist for vasomotor symptoms: a dose-finding clinical trial (SWITCH-1)

OBJECTIVE

Neurokinin (NK)-3 and NK-1 receptors have been implicated in the etiology of vasomotor symptoms (VMS) and sleep disturbances associated with menopause. This phase 2b, adaptive, dose-range finding study aimed to assess the efficacy and safety of multiple doses of elinzanetant (NT-814), a selective NK-1,3 receptor antagonist, in women experiencing VMS associated with menopause, and investigate the impact of elinzanetant on sleep and quality of life.

METHODS

Postmenopausal women aged 40 to 65 years who experienced seven or more moderate-to-severe VMS per day were randomized to receive elinzanetant 40, 80, 120, or 160 mg or placebo once daily using an adaptive design algorithm. Coprimary endpoints were reduction in mean frequency and severity of moderate-to-severe VMS at weeks 4 and 12. Secondary endpoints included patient-reported assessments of sleep and quality of life.

RESULTS

Elinzanetant 120 mg and 160 mg achieved reductions in VMS frequency versus placebo from week 1 throughout 12 weeks of treatment. Least square mean reductions were statistically significant versus placebo at both primary endpoint time points for elinzanetant 120 mg (week 4: -3.93 [SE, 1.02], P < 0.001; week 12: -2.95 [1.15], P = 0.01) and at week 4 for elinzanetant 160 mg (-2.63 [1.03]; P = 0.01). Both doses also led to clinically meaningful improvements in measures of sleep and quality of life. All doses of elinzanetant were well tolerated.

CONCLUSIONS

Elinzanetant is an effective and well-tolerated nonhormone treatment option for postmenopausal women with VMS and associated sleep disturbance. Elinzanetant also improves quality of life in women with VMS.

Definition of the estrogen negative feedback pathway controlling the GnRH pulse generator in female mice

The mechanisms underlying the homeostatic estrogen negative feedback pathway central to mammalian fertility have remained unresolved. Direct measurement of gonadotropin-releasing hormone (GnRH) pulse generator activity in freely behaving mice with GCaMP photometry demonstrated striking estradiol-dependent plasticity in the frequency, duration, amplitude, and profile of pulse generator synchronization events. Mice with Cre-dependent deletion of ESR1 from all kisspeptin neurons exhibited pulse generator activity identical to that of ovariectomized wild-type mice. An in vivo CRISPR-Cas9 approach was used to knockdown ESR1 expression selectively in arcuate nucleus (ARN) kisspeptin neurons. Mice with >80% deletion of ESR1 in ARN kisspeptin neurons exhibited the ovariectomized pattern of GnRH pulse generator activity and high frequency LH pulses but with very low amplitude due to reduced responsiveness of the pituitary. Together, these studies demonstrate that estrogen utilizes ESR1 in ARN kisspeptin neurons to achieve estrogen negative feedback of the GnRH pulse generator in mice.

Prior aerobic physical training modulates neuropeptide expression and central thermoregulation after ovariectomy in the rat

This study compared the effects of aerobic physical training and estradiol (E2) replacement on central pathways involved with thermoregulation in ovariectomized rats. Rats were assigned to untrained ovariectomized treated with placebo (UN-OVX), untrained ovariectomized treated with E2 (E2-OVX), and trained ovariectomized (TR-OVX) groups. Tail skin temperature (TST), internal temperature (Tint), and basal oxygen consumption (VO₂) were recorded. Neuronal activity, brain expression of Kiss1, NKB and Prodyn, and central norepinephrine (NE) levels were measured. UN-OVX had the highest TST. Compared to UN-OVX rats, TR-OVX and E2-OVX had lower Fos expression in the paraventricular and arcuate (ARC) nuclei, and lower double labeling for Tyrosine Hydroxylase and Fos in the brainstem. Compared to UN-OVX, only TR-OVX group exhibited lower kisspeptin (Kiss1), neurokinin B (NKB), and prodynorphin expression in the ARC and higher central NE levels. Aerobic physical training before menopause may prevent the heat dissipation imbalance induced by reduction of E2, through central NE release, modulation of Kiss1, NKB and prodynorphin expression in neurons from ARC nucleus.

Targeting KNDy neurons to control GnRH pulses

Gonadotropin-releasing hormone (GnRH) is the final output of the central nervous system that drives fertility. A characteristic of GnRH secretion is its pulsatility, which is driven by a pulse generator. Each GnRH pulse triggers a luteinizing hormone (LH) pulse. However, the puzzle has been to reconcile the synchronicity of GnRH neurons with the scattered hypothalamic distribution of their cell bodies. A leap toward understanding GnRH pulses was the discovery of kisspeptin neurons near the distal processes of GnRH neurons, which secrete kisspeptins, potent excitatory neuropeptides on GnRH neurons, and equipped with dual, but opposite, self-modulatory neuropeptides, neurokinin B and dynorphin. Over the last decade, this cell-to-cell communication has been dissected in animal models. Today the 50-year quest for the basic mechanism of GnRH pulse generation may be over, but questions about its physiological tuning remain. Here is an overview of recent basic research that frames translational research.

Serum kisspeptin levels in deep-infiltrating, ovarian, and superficial endometriosis: A prospective observational study

The diagnosis of endometriosis may delay for many years due to non-deterministic symptoms and avoiding surgical interventions. Kisspeptins are hormones that interact with endometrial tissue to limit invasions during placentation and various cancers and are suggested to be also associated with endometriosis. This study evaluated if serum kisspeptin levels are associated with the invasion depth in endometriosis. Forty patients between 18 and 45 years of age and admitted to a tertiary-care Obstetrics and Gynecology Department between 2020 and 2021 with a diagnosis of endometriosis, and 40 patients without endometrioma were included in the study. Demographic, obstetric, clinical, and biochemical characteristics were evaluated in patients with superficial (SE) and deep infiltrating (DIE) endometriosis and healthy controls. Twenty patients (50%) had SE, 14 (35%) had DIE, and 22 (55%) had endometrioma in the patient group. Fertility rates were higher among controls, but similar between patients with SE and DIE. CA125 levels were significantly higher in the DIE group. SE and DIE groups had similar kisspeptin values, significantly higher than controls. CA125 and kisspeptin levels were not correlated in study groups. Serum kisspeptin levels were significantly different between endometriosis patients and healthy controls. However, kisspeptin levels were unable to differentiate endometriosis severity. Our results suggest that kisspeptins might play a role in the pathogenesis of endometriosis, which needs further assessment in more comprehensive studies.

Estradiol and progesterone-induced lordosis behavior is modulated by both the Kisspeptin receptor and melanin-concentrating hormone in estradiol benzoate-primed rats

Intracerebroventricular (ICV) administration of estradiol benzoate (E₂B) and progesterone (P) induces intense lordosis behavior in ovariectomized rats primed peripherally with E₂B. The present study tested the hypothesis that the Kisspeptin (Kiss) and melanin-concentrating hormone (MCH) pathways regulate female sexual behavior induced by these steroid hormones. In Experiment 1, we tested the relevance of the Kiss pathway by ICV infusion of its inhibitor, kiss-234, before administration of E₂B or P in estrogen-primed rats. Lordosis induced by E₂B alone or with the addition of P was reduced significantly at 30, 120, and 240 min. In Experiment 2, ICV infusion of MCH 30 min before E₂B or P significantly reduced lordosis in rats primed with E₂B alone. These data support the hypothesis that the Kiss and MCH pathways, which can release or modulate gonadotropin-releasing hormone (GnRH), are involved in E₂B- and P-induced lordosis.

Invited review: Translating kisspeptin and neurokinin B biology into new therapies for reproductive health

The reproductive neuropeptide kisspeptin has emerged as the master regulator of mammalian reproduction due to its key roles in the initiation of puberty and the control of fertility. Alongside the tachykinin neurokinin B and the endogenous opioid dynorphin, these peptides are central to the hormonal control of reproduction. Building on the expanding body of experimental animal models, interest has flourished with human studies revealing that kisspeptin administration stimulates physiological reproductive hormone secretion in both healthy men and women, as well as patients with common reproductive disorders. In addition, emerging therapeutic roles based on neurokinin B for the management of menopausal flushing, endometriosis and uterine fibroids are increasingly recognised. In this review, we focus on kisspeptin and neurokinin B and their potential application as novel clinical strategies for the management of reproductive disorders.

Norepinephrine modulation of heat dissipation in female rats lacking estrogen

Postmenopausal hot flushes are caused by lack of estradiol (E2) but their neuroendocrine basis is still poorly understood. Here, we investigated the interrelationship between norepinephrine and hypothalamic neurons, with emphasis on kisspeptin neurons in the arcuate nucleus (ARC), as a regulatory pathway in the vasomotor effects of E2. Ovariectomized (OVX) rats displayed increased tail skin temperature (TST), and this increase was prevented in OVX rats treated with E2 (OVX + E2). Expression of Fos in the hypothalamus and the number of ARC kisspeptin neurons coexpressing Fos were increased in OVX rats. Likewise, brainstem norepinephrine neurons of OVX rats displayed higher Fos immunoreactivity associated with the increase in TST. In the ARC, the density of dopamine-ß-hydroxylase (DBH)-immunoreactive (ir) fibers was not altered by E2 but, importantly, DBH-ir terminals were found in close apposition to kisspeptin cells, revealing norepinephrine inputs to ARC kisspeptin neurons. Intracerebroventricular injection of the α2-adrenergic agonist clonidine (CLO) was used to reduce central norepinephrine release, confirmed by the decreased 3-methoxy-4-hydroxyphenylglycol/norepinephrine ratio in the preoptic area and ARC. Accordingly, CLO treatment in OVX rats reduced ARC Kiss1 mRNA levels and TST to the values of OVX + E2 rats. Conversely, CLO stimulated Kiss1 expression in the anteroventral periventricular nucleus (AVPV) and increased luteinizing hormone secretion. These findings provide evidence that augmented heat dissipation in OVX rats involves the increase in central norepinephrine that modulates hypothalamic areas related to thermoregulation, including ARC kisspeptin neurons. This neuronal network is suppressed by E2 and its imbalance may be implicated in the vasomotor symptoms of postmenopausal hot flushes.

DNA hypermethylation of Kiss1r promoter and reduction of hepatic Kiss1r in female rats with type 2 diabetes

Kisspeptin, produced from the brain and peripheral tissues, may constitute an important link in metabolic regulation in response to external cues, such as diet. The kisspeptin system is well described in the brain. However, its function and regulation in the peripheral tissues, especially in relation to metabolic disease and sex differences, remain to be elucidated. As Kiss1 and Kiss1r, encoding for kisspeptin and kisspeptin receptors, respectively, are altered by overnutrition/fasting and regulated by DNA methylation during puberty and cancer, epigenetic mechanisms in metabolic disorders are highly probable. In the present study, we experimentally induced type 2 diabetes mellitus (DM2) in female Wistar rats using high-fat diet/streptozocin. We analysed expression and DNA methylation of Kiss1 and Kiss1r in the peripheral tissues, using quantitative-reverse-transcription PCR (qRT-PCR) and pyrosequencing. We discovered differential expression of Kiss1 and Kiss1r in peripheral organs in DM2 females, as compared with healthy controls, and the profile differed from patterns reported earlier in males. DM2 in females was linked to the increased Kiss1 mRNA in the liver and increased Kiss1r mRNA in the liver and adipose tissue. However, Kiss1r promoter was hypermethylated in the liver, suggesting gene silencing. Indeed, the increase in DNA methylation of Kiss1r promoter was accompanied by a reduction in Kiss1r protein, implying epigenetic or translational gene repression. Our results deliver novel evidence for tissue-specific differences in Kiss1 and Kiss1r expression in peripheral organs in DM2 females and suggest DNA methylation as a player in regulation of the hepatic kisspeptin system in DM2.

The roles of GnRH in the human central nervous system

It is widely known that GnRH plays a role in facilitating reproductive function via the HPG axis, and this was once believed to be its only function. However, over the last several decades important neuromodulatory roles of GnRH in multiple brain functions have been elucidated. Multiple GnRH isoforms and receptors have been detected outside the HPG-axis across different species. In this review, we focus on the human CNS where GnRH I and II isoforms and a functional GnRH I receptor have been isolated. We first describe the traditional understanding of GnRH within the hypothalamus and the pituitary and current clinical use of GnRH analogues. We then review the location and function of GnRH-producing neurons and receptors located outside the HPG axis. We next review the GnRH I and II neuron location and quantity and GnRH I receptor gene expression throughout the human brain, using the Allen Brain Map Atlas. This analysis demonstrates a wide expression of GnRH throughout the brain, including prominent expression in the basal forebrain and cerebellum. Lastly, we examine the potential role of GnRH in aging and inflammation and its therapeutic potential for neurodegenerative disease and spinal cord lesions.

The role of Kisspeptin signaling in Oocyte maturation

Kisspeptins (KPs) secreted from the hypothalamic KP neurons act on KP receptors (KPRs) in gonadotropin (GPN) releasing hormone (GnRH) neurons to produce GnRH. GnRH acts on pituitary gonadotrophs to induce secretion of GPNs, namely follicle stimulating hormone (FSH) and luteinizing hormone (LH), which are essential for ovarian follicle development, oocyte maturation and ovulation. Thus, hypothalamic KPs regulate oocyte maturation indirectly through GPNs. KPs and KPRs are also expressed in the ovarian follicles across species. Recent studies demonstrated that intraovarian KPs also act directly on the KPRs expressed in oocytes to promote oocyte maturation and ovulation. In this review article, we have summarized published reports on the role of hypothalamic and ovarian KP-signaling in oocyte maturation. Gonadal steroid hormones regulate KP secretion from hypothalamic KP neurons, which in turn induces GPN secretion from the hypothalamic-pituitary (HP) axis. On the other hand, GPNs secreted from the HP axis act on the granulosa cells (GCs) and upregulate the expression of ovarian KPs. While KPs are expressed predominantly in the GCs, the KPRs are in the oocytes. Expression of KPs in the ovaries increases with the progression of the estrous cycle and peaks during the preovulatory GPN surge. Intrafollicular KP levels in the ovaries rise with the advancement of developmental stages. Moreover, loss of KPRs in oocytes in mice leads to failure of oocyte maturation and ovulation similar to that of premature ovarian insufficiency (POI). These findings suggest that GC-derived KPs may act on the KPRs in oocytes during their preovulatory maturation. In addition to the intraovarian role of KP-signaling in oocyte maturation, in vivo, a direct role of KP has been identified during in vitro maturation of sheep, porcine, and rat oocytes. KP-stimulation of rat oocytes, in vitro, resulted in Ca2+ release and activation of the mitogen-activated protein kinase, extracellular signal-regulated kinase 1 and 2. In vitro treatment of rat or porcine oocytes with KPs upregulated messenger RNA levels of the factors that favor oocyte maturation. In clinical trials, human KP-54 has also been administered successfully to patients undergoing assisted reproductive technologies (ARTs) for increasing oocyte maturation. Exogenous KPs can induce GPN secretion from hypothalamus; however, the possibility of direct KP action on the oocytes cannot be excluded. Understanding the direct in vivo and in vitro roles of KP-signaling in oocyte maturation will help in developing novel KP-based ARTs.

Morphometric and Myelin Basic Protein Expression Changes in Arcuate Nucleus Kisspeptin Neurons Underlie Activation of Hypothalamic Pituitary Gonadal-axis in Monkeys (Macaca Mulatta) during the Breeding Season

INTRODUCTION

Kisspeptin is involved in the hypothalamic pituitary gonadal-axis' seasonal regulation in rodents and sheep. Studies of kisspeptin signaling in regulating the transition between breeding and nonbreeding seasons have focused on kisspeptin expression, myelin basic protein (MBP) expression around kisspeptin-ir cells, and quantifying the synaptic connections between kisspeptin and gonadotropin-releasing hormone (GnRH) neurons in various animal models; however, the role of kisspeptin in regulating the seasonal breeding of primates has not been explored yet.

OBJECTIVE

This study investigated changes in kisspeptin signaling during breeding and a non-breeding season in a non-human primate model, the rhesus monkey.

METHODS

Three adult male monkeys (n = 3) from the breeding season and two monkeys (n = 2) from the non-breeding season were used in this study. After measuring the testicular volume and collecting a single blood sample, all animals were humanely euthanized under controlled conditions, and their hypothalami were collected and processed. Two 20 µm thick hypothalamic sections (mediobasal hypothalamus) from each animal were processed for kisspeptin-MBP and kisspeptin-GnRH immunohistochemistry (IHC). One section from each animal was used as a primary antibody omitted control to check the nonspecific binding in each IHC.

RESULTS

Compared to the non-breeding season, plasma testosterone levels and testicular volumes were significantly higher in monkeys during the breeding season. Furthermore, compared to the non-breeding season, increased kisspeptin expression and a higher number of synaptic contacts between kisspeptin fibers and GnRH cell bodies were observed in the arcuate nucleus of the breeding season monkeys. In contrast, enlarged kisspeptin soma and higher MBP expression were observed in non-breeding monkeys.

CONCLUSION

Our results indicated enhanced kisspeptin signaling in primate hypothalamus during the breeding season. These findings support the idea that kisspeptin acts as a mediator for the seasonal regulation of the reproductive axis in higher primates.

Anxiety and Depression: What Do We Know of Neuropeptides?

In modern society, there has been a rising trend of depression and anxiety. This trend heavily impacts the population's mental health and thus contributes significantly to morbidity and, in the worst case, to suicides. Modern medicine, with many antidepressants and anxiolytics at hand, is still unable to achieve remission in many patients. The pathophysiology of depression and anxiety is still only marginally understood, which encouraged researchers to focus on neuropeptides, as they are a vast group of signaling molecules in the nervous system. Neuropeptides are involved in the regulation of many physiological functions. Some act as neuromodulators and are often co-released with neurotransmitters that allow for reciprocal communication between the brain and the body. Most studied in the past were the antidepressant and anxiolytic effects of oxytocin, vasopressin or neuropeptide Y and S, or Substance P. However, in recent years, more and more novel neuropeptides have been added to the list, with implications for the research and development of new targets, diagnostic elements, and even therapies to treat anxiety and depressive disorders. In this review, we take a close look at all currently studied neuropeptides, their related pathways, their roles in stress adaptation, and the etiology of anxiety and depression in humans and animal models. We will focus on the latest research and information regarding these associated neuropeptides and thus picture their potential uses in the future.

Transcriptome profiling of kisspeptin neurons from the mouse arcuate nucleus reveals new mechanisms in estrogenic control of fertility

Kisspeptin neurons in the mediobasal hypothalamus (MBH) are critical targets of ovarian estrogen feedback regulating mammalian fertility. To reveal molecular mechanisms underlying this signaling, we thoroughly characterized the estrogen-regulated transcriptome of kisspeptin cells from ovariectomized transgenic mice substituted with 17β-estradiol or vehicle. MBH kisspeptin neurons were harvested using laser-capture microdissection, pooled, and subjected to RNA sequencing. Estrogen treatment significantly (p.adj. < 0.05) up-regulated 1,190 and down-regulated 1,139 transcripts, including transcription factors, neuropeptides, ribosomal and mitochondrial proteins, ion channels, transporters, receptors, and regulatory RNAs. Reduced expression of the excitatory serotonin receptor-4 transcript (Htr4) diminished kisspeptin neuron responsiveness to serotonergic stimulation. Many estrogen-regulated transcripts have been implicated in puberty/fertility disorders. Patients (n = 337) with congenital hypogonadotropic hypogonadism (CHH) showed enrichment of rare variants in putative CHH-candidate genes (e.g., LRP1B, CACNA1G, FNDC3A). Comprehensive characterization of the estrogen-dependent kisspeptin neuron transcriptome sheds light on the molecular mechanisms of ovary-brain communication and informs genetic research on human fertility disorders.

Resistance training reduced luteinising hormone levels in postmenopausal women in a substudy of a randomised controlled clinical trial: A clue to how resistance training reduced vasomotor symptoms

Background

Vasomotor symptoms (VMS) are common around menopause. Menopausal hormone therapy is the most effective treatment for VMS. Physical exercise has been proposed as an alternative treatment since physically active women have previously been found to experience fewer VMS than inactive women. In our randomised controlled trial on resistance training to treat VMS, sympoms were reduced by 50% in the intervention group compared with the control group.

Objectives

To propose a mechanism to explain how resistance training reduced VMS and to assess if luteinizing hormone (LH) and follicle stimulating hormone (FSH) were affected in accordance with the proposed mechanism.

Trial design and methods

A substudy of a randomized controlled trial on 65 postmenopausal women with VMS and low physical activity who were randomised to 15 weeks of resistance training three times per week (n = 33) or to a control group (n = 32). To be regarded compliant to the intervention we predecided a mean of two training sessions per week. The daily number of VMS were registered before and during the 15 weeks. Blood samples were drawn for analysis of LH and FSH at baseline and after 15 weeks.

Results

LH decreased significantly in the compliant intervention group compared with the control group (-4.0±10.6 versus 2.9±9.0, p = 0.028 with Mann-Whitney U test). FSH also decreased in the compliant intervention group compared with the control group, however not enough to reach statistical significance (-3.5±16.3 versus 3.2±18.2, p = 0.063 with Mann-Whitney U test). As previously published the number of hot flushes decreased significantly more in the intervention group than in the control group but there was no association between change in LH or FSH and in number of VMS.

Conclusions

We propose that endogenous opiods such as β-endorphin or dynorphin produced during resistance training decreased VMS by stimulating KNDγ-neurons to release neurokinin B to the hypothalamic thermoregulatory centre. Through effects on KNDγ-neurons, β-endorphin could also inhibit GnRH and thereby decrease the production of LH and FSH. The significanty decreased LH in the compliant intervention group compared with the control group was in accordance with the proposed mechanism.

Advances in clinical applications of kisspeptin-GnRH pathway in female reproduction

BACKGROUND

Kisspeptin is the leading upstream regulator of pulsatile and surge Gonadotrophin-Releasing Hormone secretion (GnRH) in the hypothalamus, which acts as the key governor of the hypothalamic-pituitary-ovary axis.

MAIN TEXT

Exogenous kisspeptin or its receptor agonist can stimulate GnRH release and subsequent physiological gonadotropin secretion in humans. Based on the role of kisspeptin in the hypothalamus, a broad application of kisspeptin and its receptor agonist has been recently uncovered in humans, including central control of ovulation, oocyte maturation (particularly in women at a high risk of ovarian hyperstimulation syndrome), test for GnRH neuronal function, and gatekeepers of puberty onset. In addition, the kisspeptin analogs, such as TAK-448, showed promising agonistic activity in healthy women as well as in women with hypothalamic amenorrhoea or polycystic ovary syndrome.

CONCLUSION

More clinical trials should focus on the therapeutic effect of kisspeptin, its receptor agonist and antagonist in women with reproductive disorders, such as hypothalamic amenorrhoea, polycystic ovary syndrome, and endometriosis.

Highlights of neuroanatomical discoveries of the mammalian gonadotropin-releasing hormone system

The anatomy and morphology of gonadotropin-releasing hormone (GnRH) neurons makes them both a joy and a challenge to investigate. They are a highly unique population of neurons given their developmental migration into the brain from the olfactory placode, their relatively small number, their largely scattered distribution within the rostral forebrain, and, in some species, their highly varied individual anatomical characteristics. These unique features have posed technological hurdles to overcome and promoted fertile ground for the establishment and use of creative approaches. Historical and more contemporary discoveries defining GnRH neuron anatomy remain critical in shaping and challenging our views of GnRH neuron function in the regulation of reproductive function. We begin this review with a historical overview of anatomical discoveries and developing methodologies that have shaped our understanding of the reproductive axis. We then highlight significant discoveries across specific groups of mammalian species to address some of the important comparative aspects of GnRH neuroanatomy. Lastly, we touch on unresolved questions and opportunities for future neuroanatomical research on this fascinating and important population of neurons.

Review of human genetic and clinical studies directly relevant to GnRH signalling

GnRH is the pivotal hormone in controlling the hypothalamic-pituitary gonadal (HPG) axis in humans and other mammalian species. GnRH function is influenced by a multitude of known and still unknown environmental and genetic factors. Molecular genetic studies on human families with hypogonadotropic hypogonadism over the past two decades have been instrumental in delineating the kisspeptin and neurokinin B signalling, which integrally modulates GnRH release from the hypothalamus. The identification of kisspeptin and neurokinin B ligand-receptor gene pair mutations in patients with absent puberty have paved the way to a greater understanding of the central regulation of the HPG cascade. In this article, we aim to review the literature on the genetic and clinical aspects of GnRH and its receptor, as well as the two ligand-receptor sets directly pertinent to the function of GnRH hormone signalling, kisspeptin/ kisspeptin receptor and NKB/NK3R.