Kisspeptin signaling in the brain

Neuropeptides and receptors in the cephalochordate: A crucial model for understanding the origin and evolution of vertebrate neuropeptide systems

Genomes and transcriptomes from diverse organisms are providing a wealth of data to explore the evolution and origin of neuropeptides and their receptors in metazoans. While most neuropeptide-receptor systems have been extensively studied in vertebrates, there is still a considerable lack of understanding regarding their functions in invertebrates, an extraordinarily diverse group that account for the majority of animal species on Earth. Cephalochordates, commonly known as amphioxus or lancelets, serve as the evolutionary proxy of the chordate ancestor. Their key evolutionary position, bridging the invertebrate to vertebrate transition, has been explored to uncover the origin, evolution, and function of vertebrate neuropeptide systems. Amphioxus genomes exhibit a high degree of sequence and structural conservation with vertebrates, and sequence and functional homologues of several vertebrate neuropeptide families are present in cephalochordates. This review aims to provide a comprehensively overview of the recent findings on neuropeptides and their receptors in cephalochordates, highlighting their significance as a model for understanding the complex evolution of neuropeptide signaling in vertebrates.

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.

Characterization of Kiss/Kissr system and expression profiling through developmental stages indicate kiss1 to be the active isotype in Clarias magur

Kisspeptin (Kiss) and kisspeptin receptor (Kissr) system is a key regulator of GnRH expression in several vertebrates. The Indian catfish, Clarias magur, is popular in the Indian sub-continent, and a neo-type of the Asian catfish, C. batrachus. Catfish breeding is constrained as males do not release milt captivity with/without stimulation. Magur Kiss/Kissr system comprising of kiss1, kiss2, kissr1, and kissr2 genes was characterized for the first time. Full-length mRNA was sequenced using RACE PCR. Neighbor-joining tree of predicted proteins shows one clade of teleost orthologs. Magur whole genome (NCBI GenBank) has single copies of each gene, though yet unannotated/misannotated. Anomalies in the nomenclature of earlier sequences in GenBank were noted. Relative gene expression was profiled during various ontogenic stages, in six tissues including brain and gonads at maturity, and also in brains and gonads of premature and spent fish. Expression of gnrh1, gnrhr1, and gnrhr2 was estimated concomitantly. The kiss1 was the first to be twofold upregulated (P < 0.05) at 12 h post fertilization. Kiss/Kissr genes expressed primarily in the brain, ovary, and testis. Though kiss2 was 10 times higher than kiss1, only kiss1 showed significant modulation across stages and appears to be the active isotype that regulates GnRH in magur.

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.

Role of the kisspeptin-KISS1R axis in the pathogenesis of chronic kidney disease and uremic cardiomyopathy

The prevalence of chronic kidney disease (CKD) is increasing globally, especially in elderly patients. Uremic cardiomyopathy is a common cardiovascular complication of CKD, characterized by left ventricular hypertrophy (LVH), diastolic dysfunction, and fibrosis. Kisspeptins and their receptor, KISS1R, exert a pivotal influence on kidney pathophysiology and modulate age-related pathologies across various organ systems. KISS1R agonists, including kisspeptin-13 (KP-13), hold promise as novel therapeutic agents within age-related biological processes and kidney-related disorders. Our investigation aimed to elucidate the impact of KP-13 on the trajectory of CKD and uremic cardiomyopathy. Male Wistar rats (300-350 g) were randomized into four groups: (I) sham-operated, (II) 5/6 nephrectomy-induced CKD, (III) CKD subjected to a low dose of KP-13 (intraperitoneal 13 µg/day), and (IV) CKD treated with a higher KP-13 dose (intraperitoneal 26 µg/day). Treatments were administered daily from week 3 for 10 days. After 13 weeks, KP-13 increased systemic blood pressure, accentuating diastolic dysfunction's echocardiographic indicators and intensifying CKD-associated markers such as serum urea levels, glomerular hypertrophy, and tubular dilation. Notably, KP-13 did not exacerbate circulatory uremic toxin levels, renal inflammation, or fibrosis markers. In contrast, the higher KP-13 dose correlated with reduced posterior and anterior wall thickness, coupled with diminished cardiomyocyte cross-sectional areas and concurrent elevation of inflammatory (Il6, Tnf), fibrosis (Col1), and apoptosis markers (Bax/Bcl2) relative to the CKD group. In summary, KP-13's influence on CKD and uremic cardiomyopathy encompassed heightened blood pressure and potentially activated inflammatory and apoptotic pathways in the left ventricle.

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.

Causal association between mTOR-dependent circulating protein levels and central precocious puberty: a Mendelian randomization study

Background

The mechanistic target of rapamycin (mTOR) signaling pathway has a significant effect on central precocious puberty (CPP). However, the causality between mTOR-dependent circulating protein levels and CPP is still unclear. Our aim is to assess the effects of seven mTOR-dependent circulating protein levels on CPP using Mendelian randomization (MR).

Methods

Instrumental variables (IVs) for mTOR-dependent circulating protein levels were retrieved from the proteomics-GWAS INTERVAL study and eQTLGen. The summary-level genetic datasets for CPP outcome were obtained from the FinnGen Consortium. Inverse-variance weighted (IVW) was used as the primary method and the pleiotropy, heterogeneity and robustness of the analyses were detected as sensitivity analysis. Positive exposures in the discovery cohort would be revalidated in the validation cohort.

Results

This two-sample MR study revealed a causal association between eIF4G level in plasma and CPP in both discovery cohort (IVW: OR = 0.45, 95% CI = 0.22-0.91, p = 0.026) and validation cohort (IVW: OR = 0.45, 95% CI = 0.24-0.85, p = 0.014).

Conclusions

There was a causal association between eIF4G level in plasma and CPP. Whether eIF4G can be used for the prevention or treatment of CPP needs to be explored in further studies.

Epigenetics of inflammation in hypothalamus pituitary gonadal and neuroendocrine disorders

The hormone producing hypothalamus, pituitary and gonadal are arranged in hierarchy to form the hypothalamic-pituitary-gonadal axis (HPG axis). The axis is neuroendocrine in nature and releases hormones in response to the inputs from nervous systems. The axis maintains homeostasis and ensures smooth body functions, particularly those related to growth and reproduction. A deregulated HPG axis, such as observed under inflammation and other conditions, is therefore associated with several disorders such as polycystic ovary syndrome, functional hypothalamic amenorrhea etc. Several factors, both genetic as well as environmental, in addition to aging, obesity etc. affect HPG axis with resulting effects on puberty, sexual maturation and reproductive health. More research is now indicative of a role of epigenetics in mediating these HPG-affecting factors. Hypothalamus-secreted gonadotropin-releasing hormone is important for eventual release of sex hormones and it is subjected to several neuronal and epigenetic regulations. Gene promoter methylation as well as histone methylations and acetylations form the backbone of epigenetic regulation of HPG-axis, as the incoming reports suggest. Epigenetic events also mediate several feedback mechanisms within HPG axis and between HPG axis and the central nervous system. In addition, data is emerging for a role of non-coding RNAs, particularly the miRNAs, in regulation and normal functioning of HPG axis. Thus, the epigenetic interactions need better understanding to understand the functioning and regulation of HPG axis.

Lunar Age-Dependent Oscillations in Expression of the Genes for Kisspeptin, GnIH, and Their Receptors in the Grass Puffer during the Spawning Season

Grass puffer is a semilunar-synchronized spawner: spawning occurs on beaches only for several days of spring tide around new moon (lunar age 0) and full moon (lunar age 15) every 2 weeks from spring to early summer. To investigate the role of kisspeptin and gonadotropin-inhibitory hormone (GnIH) in the semilunar-synchronized spawning, lunar age-dependent expression of the genes encoding kisspeptin (kiss2), kisspeptin receptor (kissr2), GnIH (gnih), GnIH receptor (gnihr), gonadotropin-releasing hormone 1 (GnRH1) (gnrh1), and three gonadotropin (GTH) subunits (gpa, fshb, lhb) was examined in the male grass puffer, which was kept in an aquarium under natural light condition in a lunar month during the spawning period. In the brain, both kiss2 and kissr2 showed lunar variations with a peak at lunar age 10, while both gnih and gnihr showed semilunar variations with two peaks at lunar age 0 and 20. On the other hand, gnrh1 showed semilunar variation with two peaks at lunar age 0 and 15. In the pituitary, kiss2, kissr2, gnih, and gnihr showed similar variations to those shown in the brain. The fshb and lhb mRNA levels showed semilunar variations with two peaks at lunar age 0 and 15. The present study shows lunar and semilunar oscillations of kiss2/kissr2 and gnih/gnihr expressions, respectively, with their peaks around spring tide in the brain and pituitary along with the semilunar expressions of gnrh1 and the pituitary GTH subunit genes. These results suggest that the lunar age-dependent expressions of the kisspeptin, GnIH, and their receptor genes may be primarily important in the control of the precisely timed semilunar spawning of the grass puffer.

Effects of sub-chronic exposure to microcystin-LR on the endocrine system of male rats

Microcystins (MCs) can cause reproductive and developmental toxicity and disrupt endocrine homeostasis in mammals. In the present study, male, Sprague-Dawley (SD) rats were administrated 3 or 30 μg MC-LR/kg, body mass (bm) per day via intraperitoneal (i.p.) injections for 6 weeks. Effects of MC-LR on histology, hormone concentrations, gene transcriptional profiles and protein expressions along the hypothalamic-pituitary-adrenal (HPA), -gonad (HPG) and -thyroid (HPT) axes were assessed. Sub-chronic administration with MC-LR caused histological damage to hypothalamus, pituitary, adrenal, testes and thyroid and affected relative masses of pituitary, adrenal and testes. The HPA axis was activated and serum concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were significantly augmented. Along the HPG axis, serum concentrations of gonadotropin-releasing hormone (GnRH) and dihydrotestosterone (DHT) were diminished, while concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T) and estradiol (E2) were augmented. For the HPT axis, only concentrations of free tetra-iodothyronine (fT4) were significantly diminished, while concentrations of thyrotropin-releasing hormone (TRH), thyroid-stimulating hormone (TSH) or free tri-iodothyronine (fT3) were not significantly changed. Also, several genes and proteins related to synthesis of steroid hormones were significantly altered. Findings of the present study illustrate that MC-LR can cause endocrine-disrupting effects through the disruption of synthesis and secretion of hormones along the HPA, HPG and HPT axes and negative feedback regulation. Also, there could be crosstalk among HPA, HPG and HPT axes. These findings elucidate mechanisms of endocrine-disrupting effects of MCs.

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.

Impose of KNDy/GnRH neural circuit in PCOS, ageing, cancer and Alzheimer's disease: StAR actions in prevention of neuroendocrine dysfunction

The Kisspeptin1 (KISS1)/neurokinin B (NKB)/Dynorphin (Dyn) [KNDy] neurons in the hypothalamus regulate the reproduction stage in human beings and rodents. KNDy neurons co-expressed all KISS1, NKB, and Dyn peptides, and hence commonly regarded as KISS1 neurons. KNDy neurons contribute to the "GnRH pulse generator" and are implicated in the regulation of pulsatile GnRH release. The estradiol (E2)-estrogen receptor (ER) interactions over GnRH neurons in the hypothalamus cause nitric oxide (NO) discharge, in addition to presynaptic GABA and glutamate discharge from respective neurons. The released GABA and glutamate facilitate the activity of GnRH neurons via GABAA-R and AMPA/kainate-R. The KISS1 stimulates MAPK/ERK1/2 signaling and cause the release of Ca2+ from intracellular store, which contribute to neuroendocrine function, increase apoptosis and decrease cell proliferation and metastasis. The ageing in women deteriorates KISS1/KISS1R interaction in the hypothalamus which causes lower levels of GnRH. Because examining the human brain is so challenging, decades of clinical research have failed to find the causes of KNDy/GnRH dysfunction. The KISS1/KISS1R interactions in the brain have a neuroprotective effect against Alzheimer's disease (AD). These findings modulate the pathophysiological role of the KNDy/GnRH neural network in polycystic ovarian syndrome (PCOS) associated with ageing and, its protective role in cancer and AD. This review concludes with protecting effect of the steroid-derived acute regulatory enzyme (StAR) against neurotoxicity in the hippocampus, and hypothalamus, and these measures are fundamental for delaying ageing with PCOS. StAR could serve as novel diagnostic marker and therapeutic target for the most prevalent hormone-sensitive breast cancers (BCs).

Kisspeptin modulation of nonapeptide and cytochrome P450 aromatase mRNA expression in the brain and ovary of the catfish Heteropneustes fossilis: in vivo and in vitro studies

In Heteropneustes fossilis, kisspeptins (Kiss) and nonapeptides (NPs; vasotocin, Vt; isotocin, Itb; Val8-isotocin, Ita) stimulate the hypothalamus-pituitary-gonadal (HPG) axis, and estrogen feedback modulates the expression of these systems. In this study, functional interactions among these regulatory systems were demonstrated in the brain and ovary at the mRNA expression level. Human KISS1 (hKISS1) and H. fossilis Kiss2 (HfKiss2) produced biphasic effects on brain and ovarian vt, itb and ita expression at 24 h post injection: low and median doses produced inhibition, no change or mild stimulation, and the highest dose consistently stimulated the mRNA levels. The Kiss peptides produced an upregulation of NP mRNA expression at 24 h incubation of brain and ovarian slices by increasing the concentration of hKISS1 and HfKiss2. The kiss peptides stimulated brain cyp19a1b and ovary cyp19a1a expression, both in vivo and in vitro. Peptide234, a Kiss1 receptor antagonist, inhibited basal mRNA expression of the NPs, cyp19a1b and cyp19a1a, which was prevented by the Kiss peptides, both in vivo and in vitro. In all the experiments, HfKiss2 was more effective than hKISS1 in modulating mRNA expression. The results suggest that the NP and E2 systems are functional targets of Kiss peptides and interact with each other.

The methanolic extract of Hibiscus sabdariffa downregulates the relative expression of Kiss1 gene in the hypothalamus of Wistar rats: A preliminary report

Objective

Kiss1 gene expression in the rat hypothalamus was investigated following administration of methanolic extract of Hibiscus sabdariffa (MEHS) to provide mechanistic evidence for the reproductive effect of the MEHS as a potential regulator of Kiss1 gene (which directly controls the hypogonadal axis).

Materials and Methods

This experiment was done using fifteen (15) male rats with average weight of 148 g, randomly grouped into three (3) groups (A-C). Group A was the control group and received no treatment. Group B and C were orally administered with 200 mg/kg and 400 mg/kg of MEHS, respectively. The animals received the extract once a day for twenty-one (21) days. The hypothalamus was harvested on the last day of administration to investigate antioxidant levels, histopathology, and Kiss1 gene expression.

Results

The relative expression of Kiss1 gene in the group C was downregulated compared to the control group (p=0.023). No significant changes were seen in the antioxidant levels of the groups treated with MEHS when compared to the control. MEHS had no histopathological effects in the hypothalamus at both low (200 mg/kg) and high (400 mg/kg) doses.

Conclusion

High-dose MEHS lowers the expression of the Kiss1 gene in the hypothalamus. However, this effect could not be explained by the oxidative profile or histology of the hypothalamus.

The kisspeptin-1 receptor antagonist peptide-234 aggravates uremic cardiomyopathy in a rat model

Uremic cardiomyopathy is characterized by diastolic dysfunction, left ventricular hypertrophy (LVH), and fibrosis. Dysregulation of the kisspeptin receptor (KISS1R)-mediated pathways are associated with the development of fibrosis in cancerous diseases. Here, we investigated the effects of the KISS1R antagonist peptide-234 (P234) on the development of uremic cardiomyopathy. Male Wistar rats (300-350 g) were randomized into four groups: (i) Sham, (ii) chronic kidney disease (CKD) induced by 5/6 nephrectomy, (iii) CKD treated with a lower dose of P234 (ip. 13 µg/day), (iv) CKD treated with a higher dose of P234 (ip. 26 µg/day). Treatments were administered daily from week 3 for 10 days. At week 13, the P234 administration did not influence the creatinine clearance and urinary protein excretion. However, the higher dose of P234 led to reduced anterior and posterior wall thicknesses, more severe interstitial fibrosis, and overexpression of genes associated with left ventricular remodeling (Ctgf, Tgfb, Col3a1, Mmp9), stretch (Nppa), and apoptosis (Bax, Bcl2, Casp7) compared to the CKD group. In contrast, no significant differences were found in the expressions of apoptosis-associated proteins between the groups. Our results suggest that the higher dose of P234 hastens the development and pathophysiology of uremic cardiomyopathy by activating the fibrotic TGF-β-mediated pathways.

Continuous acceleration of neural activity of the GnRH pulse generator during chronic peripheral infusion of neurokinin 3 receptor agonist in goats

Secretion of pulsatile gonadotropin-releasing hormone (GnRH) is essential for reproduction. Kisspeptin neurons in the arcuate nucleus (ARC), which coexpress neurokinin B (NKB) and its receptor (NK3R), are believed to be components of the GnRH pulse generator that regulates pulsatile GnRH secretion. We examined the effects of peripheral infusion of senktide, an NK3R selective agonist, on GnRH pulse generator activity by monitoring multiple unit activity (MUA) in the goat ARC. Previous studies have shown that characteristic increases in MUA (MUA volleys) reflect GnRH pulse generator activity. Senktide was infused intravenously or intravaginally for 2 h while recording MUA. Both infusions significantly increased the MUA volley frequency compared with the control. These results demonstrate that peripherally administered senktide acts centrally to sustainably accelerate the neural activity of the GnRH pulse generator throughout the infusion period. This suggests the possibility of practical applications of NK3R agonists for improving reproductive activity in farm animals.

Low-Dose Estrogens as Neuroendocrine Modulators in Functional Hypothalamic Amenorrhea (FHA): The Putative Triggering of the Positive Feedback Mechanism(s)

Functional hypothalamic amenorrhea (FHA) is a non-organic reversible chronic endocrine disorder characterized by an impaired pulsatile secretion of the gonadotropin-releasing hormone (GnRH) from the hypothalamus. This impaired secretion, triggered by psychosocial and metabolic stressors, leads to an abnormal pituitary production of gonadotropins. As LH and FSH release is defective, the ovarian function is steadily reduced, inducing a systemic hypoestrogenic condition characterized by amenorrhea, vaginal atrophy, mood changes and increased risk of osteoporosis and cardiovascular disease. Diagnosis of FHA is made excluding other possible causes for secondary amenorrhea, and it is based upon the findings of low serum gonadotropins and estradiol (E2) with evidence of precipitating factors (excessive exercise, low weight, stress). Treatments of women with FHA include weight gain through an appropriate diet and physical activity reduction, psychological support, and integrative approach up to estrogen replacement therapy. If no spontaneous ovarian function is restored, assisted reproductive technologies may be used when pregnancy is desired. Because subjects with FHA are hypoestrogenic, the use of low-dose estrogens has been proposed as a putative treatment to positively modulate the spontaneous restart of gonadotropin secretion, counteracting the blockade of the reproductive axis triggered by stress acting through the neuroendocrine pathways at the basis of positive feedback of estrogens. The mechanism through which low-dose estrogens acts is still unknown, but kisspeptin-secreting neurons may be involved.

Effects of Kisspeptin on the reproductive function in the Dabry's sturgeon (Acipenser dabrynus)

Kisspeptin, a kind of neuropeptide, is involved in various physiological processes such as tumor metastasis inhibition and reproductive regulation due to its ability to interact with Kisspeptin receptor-Kissr. In teleost, Kisspeptin/Kissr system stimulates the hypothalamus-pituitary-gonadal axis (HPG axis), which is crucial for the reproductive regulation. Compared to one Kisspeptin protein Kiss1 was existed in mammals, two Kisspeptin were identified in sturgeon species, including Kiss1 and Kiss2, with specific receptors of Kissr1 and Kissr2, respectively. However, few reports described the effects of the two isoforms of Kisspeptin on the reproductive regulation in sturgeon. The core peptides of Kiss1 and Kiss2 (Kiss1-10 and Kiss2-10) of Dabry's sturgeon were successfully synthesized to explore the functional influence of Kisspeptin on the sturgeon HPG axis in the present study. The present findings suggested that intraperitoneal injection of Kiss1-10 and Kiss2-10 could significantly up-regulate the mRNA expression of Gnrh、Fsh and Lh in the hypothalamus and pituitary and the content of Lh protein in the serum. Assays of Kisspeptin-treated cells demonstrated that Kiss1-10 and Kiss2-10 can significantly promote the expression of Gnrh in hypothalamus cells and Lh and Fsh in pituitary cells of Dabry's sturgeon, indicating their direct-acting effect on pituitary cells and regulatory function on the reproductive development of sturgeon. This study described the reproductive function of the Kisspeptin in the Dabry's sturgeon for the first time, and provided supportive reference for the development of high-efficiency ripening technologies of artificially breeding sturgeon.

Review: Gestational and postnatal nutritional effects on the neuroendocrine control of puberty and subsequent reproductive performance in heifers

Pubertal attainment is an intricate biological process that involves maturation of the reproductive neuroendocrine axis and increased pulsatile release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone. Nutrition is a critical environmental factor controlling the timing of puberty attainment. Nutrient restriction during early postnatal development delays puberty, whereas increased feed intake and adiposity during this period hasten pubertal maturation by imprinting the hypothalamus. Moreover, the dam's nutrition during gestation can program the neuroendocrine system in the developing fetus and has the potential to advance or delay puberty in the offspring. Leptin, a hormone produced primarily by adipose cells, plays an important role in communicating energy status to the brain and regulating sexual maturation. Leptin's regulation of GnRH release is mediated by an upstream neuronal network since GnRH neurons do not contain the leptin receptor. Two groups of neurons located in the arcuate nucleus of the hypothalamus that express neuropeptide Y (NPY), an orexigenic peptide, and alpha melanocyte-stimulating hormone (αMSH), an anorexigenic peptide, are central elements of the neural circuitry that relay inhibitory (NPY) and excitatory (αMSH) inputs to GnRH neurons. Moreover, KNDy neurons, neurons in the arcuate nucleus that co-express kisspeptin, neurokinin B (NKB), and dynorphin, also play a role in the metabolic regulation of puberty. Our studies in beef heifers demonstrate that increased rates of BW gain during early postweaning (4-9 mo of age) result in reduced expression of NPY mRNA, increased expression of proopiomelanocortin and kisspeptin receptor mRNA, reduced NPY inhibitory inputs to GnRH neurons, and increased excitatory αMSH inputs to KNDy neurons. Finally, our most recent data demonstrate that nutrition of the cow during the last two trimesters of gestation can also induce transcriptional and structural changes in hypothalamic neurocircuitries in the heifer progeny that likely persist long-term after birth. Managerial approaches, such as supplementation of the dam during gestation (fetal programming), creep feeding, early weaning, and stair-step nutritional regimens have been developed to exploit brain plasticity and advance pubertal maturation in heifers.

Physiological and pathological roles of locally expressed kisspeptin and KISS1R in the endometrium

Kisspeptins, encoded by the KISS1 gene, are a family of polypeptides that bind the kisspeptin receptor (KISS1R) to perform biological functions. Produced mainly in the hypothalamus, these neuropeptides regulate the pulsatile secretion of GnRH and trigger the hypothalamus-pituitary-gonadal axis. Other peripheral organs also express kisspeptin, which inhibits metastasis. Kisspeptin and KISS1R are reportedly present in the endometrium and may play roles in limiting the migration and invasion of trophoblasts into the endometrium during pregnancy (decidua) to maintain endometrial homeostasis. A deficiency of kisspeptin and KISS1R in the endometrium can lead to pathological conditions such as endometriosis and endometrial carcinoma. Kisspeptin and KISS1R in the endometrium can also promote endometrial receptivity and decidualization. Overall, kisspeptin and KISS1R are important for maintaining the normal physiological functions of the endometrium. By summarizing the roles of kisspeptin and KISS1R in the endometrium, our review explores the regulatory roles in the peripheral reproductive system of this peptide family that plays broad and profound roles in many physiological processes.

Review: Recent Applications of Gene Editing in Fish Species and Aquatic Medicine

Gene editing and gene silencing techniques have the potential to revolutionize our knowledge of biology and diseases of fish and other aquatic animals. By using such techniques, it is feasible to change the phenotype and modify cells, tissues and organs of animals in order to cure abnormalities and dysfunctions in the organisms. Gene editing is currently experimental in wide fields of aquaculture, including growth, controlled reproduction, sterility and disease resistance. Zink finger nucleases, TALENs and CRISPR/Cas9 targeted cleavage of the DNA induce favorable changes to site-specific locations. Moreover, gene silencing can be used to inhibit the translation of RNA, namely, to regulate gene expression. This methodology is widely used by researchers to investigate genes involved in different disorders. It is a promising tool in biotechnology and in medicine for investigating gene function and diseases. The production of food fish has increased markedly, making fish and seafood globally more popular. Consequently, the incidence of associated problems and disease outbreaks has also increased. A greater investment in new technologies is therefore needed to overcome such problems in this industry. To put it concisely, the modification of genomic DNA and gene silencing can comprehensively influence aquatic animal medicine in the future. On the ethical side, these precise genetic modifications make it more complicated to recognize genetically modified organisms in nature and can cause several side effects through created mutations. The aim of this review is to summarize the current state of applications of gene modifications and genome editing in fish medicine.

Kisspeptin-10 Mitigates α-Synuclein-Mediated Mitochondrial Apoptosis in SH-SY5Y-Derived Neurons via a Kisspeptin Receptor-Independent Manner

The hypothalamic neurohormone kisspeptin-10 (KP-10) was inherently implicated in cholinergic pathologies when aberrant fluctuations of expression patterns and receptor densities were discerned in neurodegenerative micromilieus. That said, despite variable degrees of functional redundancy, KP-10, which is biologically governed by its cognate G-protein-coupled receptor, GPR54, attenuated the progressive demise of α-synuclein (α-syn)-rich cholinergic-like neurons. Under explicitly modeled environments, in silico algorithms further rationalized the surface complementarities between KP-10 and α-syn when KP-10 was unambiguously accommodated in the C-terminal binding pockets of α-syn. Indeed, the neuroprotective relevance of KP-10's binding mechanisms can be insinuated in the amelioration of α-syn-mediated neurotoxicity; yet it is obscure whether these extenuative circumstances are contingent upon prior GPR54 activation. Herein, choline acetyltransferase (ChAT)-positive SH-SY5Y neurons were engineered ad hoc to transiently overexpress human wild-type or E46K mutant α-syn while the mitigation of α-syn-induced neuronal death was ascertained via flow cytometric and immunocytochemical quantification. Recapitulating the specificity observed on cell viability, exogenously administered KP-10 (0.1 µM) substantially suppressed wild-type and E46K mutant α-syn-mediated apoptosis and mitochondrial depolarization in cholinergic differentiated neurons. In particular, co-administrations with a GPR54 antagonist, kisspeptin-234 (KP-234), failed to abrogate the robust neuroprotection elicited by KP-10, thereby signifying a GPR54 dispensable mechanism of action. Consistent with these observations, KP-10 treatment further diminished α-syn and ChAT immunoreactivity in neurons overexpressing wild-type and E46K mutant α-syn. Overall, these findings lend additional credence to the previous notion that KP-10's binding zone may harness efficacious moieties of neuroprotective intent.

Hypothalamic Kisspeptin Neurons: Integral Elements of the GnRH System

Highly sophisticated and synchronized interactions of various cells and hormonal signals are required to make organisms competent for reproduction. GnRH neurons act as a common pathway for multiple cues for the onset of puberty and attaining reproductive function. GnRH is not directly receptive to most of the signals required for the GnRH secretion during the various phases of the ovarian cycle. Kisspeptin neurons of the hypothalamus convey these signals required for the synchronized release of the GnRH. The steroid-sensitive anteroventral periventricular nucleus (AVPV) kisspeptin and arcuate nucleus (ARC) KNDy neurons convey steroid feedback during the reproductive cycle necessary for GnRH surge and pulse, respectively. AVPV region kisspeptin neurons also communicate with nNOS synthesizing neurons and suprachiasmatic nucleus (SCN) neurons to coordinate the process of the ovarian cycle. Neurokinin B (NKB) and dynorphin play roles in the GnRH pulse stimulation and inhibition, respectively. The loss of NKB and kisspeptin function results in the development of neuroendocrine disorders such as hypogonadotropic hypogonadism (HH) and infertility. Ca²⁺ signaling is essential for GnRH pulse generation, which is propagated through gap junctions between astrocytes-KNDy and KNDy-KNDy neurons. Impaired functioning of KNDy neurons could develop the characteristics associated with polycystic ovarian syndrome (PCOS) in rodents. Kisspeptin-increased synthesis led to excessive secretion of the LH associated with PCOS. This review provides the latest insights and understanding into the role of the KNDy and AVPV/POA kisspeptin neurons in GnRH secretion and PCOS.

The effect of estrogen and progesterone on melanin-concentrating hormone producing-neurons in brain areas related to reproductive behavior in lactating dams

The hypothalamus plays a role in reproductive cycle control, and it is a site of action of steroid hormones. Throughout the production of melanin-concentrating hormone (MCH), the hypothalamus shows adaptive changes during lactation. Therefore, in this work, we aimed to test the effects of estrogen and progesterone manipulation on MCH-immunoreactive (ir) neurons in hypothalamic brain areas related to reproductive behavior and on the MCH serum concentration. Our results show that the removal of steroid hormones by ovariectomy increases the number of MCH-ir neurons in the medial preoptic area (MPOA) and incerto-hypothalamic area (IHy) but not in the anterior part of the paraventricular nucleus of the hypothalamus (PVHa). The MCH in the serum levels also increases. In accordance, the injection of estradiol alone or estradiol and progesterone decreased the number of MCH-ir neurons in the MPOA and IHy, as well as its serum levels. The MPOA and IHy are the brain areas targeted by the steroid hormone inhibitory effect of the MCH system during lactation. This effect is also reflected in the MCH serum levels.

Does kisspeptin exert a local modulatory effect on bovine ovarian steroidogenesis?

Kisspeptin, a hypothalamic neuropeptide encoded by the KISS1 gene, has a pivotal role in promoting GnRH secretion in mammals. Kisspeptin and its receptor (KISS1R) are also expressed in certain peripheral tissues including gonads, suggesting intra-gonadal roles. Such actions at the level of the bovine ovary have not been explored previously. The current aims were to determine whether KISS1 and its receptor (KISS1R) are expressed in the bovine ovary and whether kisspeptin or a kisspeptin antagonist can modulate ovarian steroid production by cultured ovarian cells. Granulosa (GC) and theca interna (TC) were collected from antral follicles (3-18 mm) categorized into five class sizes. Early, mid and regressing corpora lutea (CL) were also collected for RT-qPCR analysis of KISS1 and KISS1R expression. Bovine TC and GC cultured under both non-luteinizing (serum-free) and luteinizing (serum-supplemented) conditions were treated for 4 days with kisspeptin-10 (10-10-10-6M) or kisspeptin antagonist (p234; 10-10-10-6M), alone and in combination with either FSH (GC), LH (TC) or forskolin (luteinized GC/TC). Steroid secretion (GC: oestradiol, progesterone; TC: androstenedione, progesterone; luteinized GC/TC: progesterone) was measured by ELISA and viable cell number determined by neutral red uptake assay. KISS1 and KISS1R transcripts were detected in TC, GC and CL with significant differences between follicle categories and CL stages. However, neither kisspeptin-10 nor kisspeptin antagonist affected steroid secretion or viable cell number in any of the four ovarian cell culture models. As such, the hypothesis that kisspeptin has a direct intra-ovarian role to modulate follicular or luteal steroidogenesis, or cell proliferation/survival, is not supported.

The role of kisspeptin in the pathogenesis of a polycystic ovary syndrome

Hypothalamic-pituitary gonadal (HPG) axis is responsible for the development and regulation of the female reproductive system. In polycystic ovary syndrome (PCOS), there is a disturbance in the HPG axis. Kisspeptin, a neuropeptide produced by the KISS1 gene, plays a vital role in the regulation of HPG axis by binding with its receptors KISS1R/GPR54, and stimulates gonadotropin secretion from the hypothalamus into pituitary to release luteinizing hormone (LH) and follicle stimulating hormone (FSH). Polymorphisms or mutations in the KISS1 gene can cause disturbance in the kisspeptin signaling pathway and is thought to disrupt HPG axis. Altered signaling of kisspeptin can cause abnormal secretion of GnRH pulse, which leads to increased LH/FSH ratio, thereby affecting androgen levels and ovulation. The increased levels of androgen worsen the symptoms of PCOS. In the present article, we review the molecular physiology and pathology of kisspeptin and how it is responsible for the development of PCOS. The goal of this review article is to provide an overview and metabolic profile of kisspeptin in PCOS patients and the expression of kisspeptin in PCOS animal models. In the present article, we also review the molecular physiology and pathology of kisspeptin and how it is responsible for the development of PCOS.

Overexpression of KiSS1 Induces the Proliferation of Hepatocarcinoma and Increases Metastatic Potential by Increasing Migratory Ability and Angiogenic Capacity

Liver cancer has a high prevalence, with majority of the cases presenting as hepatocellular carcinoma (HCC). The prognosis of metastatic HCC has hardly improved over the past decade, highlighting the necessity for liver cancer research. Studies have reported the ability of the KiSS1 gene to inhibit the growth or metastasis of liver cancer, but contradictory research results are also emerging. We, therefore, sought to investigate the effects of KiSS1 on growth and migration in human HCC cells. HepG2 human HCC cells were infected with lentivirus particles containing KiSS1. The overexpression of KiSS1 resulted in an increased proliferation rate of HCC cells. Quantitative polymerase chain reaction and immunoblotting revealed increased Akt activity, and downregulation of the G1/S phase cell cycle inhibitors. A significant increase in tumor spheroid formation with upregulation of β-catenin and CD133 was also observed. KiSS1 overexpression promoted the migratory, invasive ability, and metastatic capacity of the hepatocarcinoma cell line, and these effects were associated with changes in the expressions of epithelial mesenchymal transition (EMT)-related genes such as E-cadherin, N-cadherin, and slug. KiSS1 overexpression also resulted in dramatically increased tumor growth in the xenograft mouse model, and upregulation of proliferating cell nuclear antigen (PCNA) and Ki-67 in the HCC tumors. Furthermore, KiSS1 increased the angiogenic capacity by upregulation of the vascular endothelial growth factor A (VEGF-A) and CD31. Based on these observations, we infer that KiSS1 not only induces HCC proliferation, but also increases the metastatic potential by increasing the migratory ability and angiogenic capacity.

The role of testosterone, the androgen receptor, and hypothalamic-pituitary-gonadal axis in depression in ageing Men

Considerable research has shown that testosterone regulates many physiological systems, modulates clinical disorders, and contributes to health outcome. However, studies on the interaction of testosterone levels with depression and the antidepressant effect of testosterone replacement therapy in hypogonadal men with depression have been inconclusive. Current findings indicate that low circulating levels of total testosterone meeting stringent clinical criteria for hypogonadism and testosterone deficiency induced by androgen deprivation therapy are associated with increased risk for depression and current depressive symptoms. The benefits of testosterone replacement therapy in men with major depressive disorder and low testosterone levels in the clinically defined hypogonadal range remain uncertain and require further investigation. Important considerations going forward are that major depressive disorder is a heterogeneous phenotype with depressed individuals differing in inherited polygenic determinants, onset and clinical course, symptom complexes, and comorbidities that contribute to potential multifactorial differences in pathophysiology. Furthermore, polygenic mechanisms are likely to be critical to the biological heterogeneity that influences testosterone-depression interactions. A genetically informed precision medicine approach using genes regulating testosterone levels and androgen receptor sensitivity will likely be essential in gaining critical insight into the role of testosterone in depression.

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.

Sex-specific association between urinary kisspeptin and pubertal development

Kisspeptins play a crucial role during pubertal development, but little is known about how their peripheral concentrations relate to sexual maturation. This is partly due to the lack of non-invasive, quick, and reliable peripheral kisspeptin measures, which limit widespread testing. Here, we investigated the relationship between kisspeptin concentrations measured from midstream urine samples with 2-h retention periods and developmental markers (age, self-reported pubertal status, and saliva concentrations of testosterone and DHEA sulphate ) in 209 typically developing 9- to 15-year-old males and females. As a result of the study, we found marked sex differences. Kisspeptin concentrations were similar between sexes until around 12 years of age, but, thereafter, kisspeptin concentrations in females did not change significantly, whereas, in males, there was a clear positive correlation with developmental measures. Our results replicate previous findings regarding kisspeptin concentration changes across the pubertal transition obtained from blood samples, suggesting that measuring these peptides in urine has the potential for exploring kisspeptins' peripheral effects and their associations with pubertal status.

Deletion of Growth Hormone Secretagogue Receptor in Kisspeptin Neurons in Female Mice Blocks Diet-Induced Obesity

The gut peptide, ghrelin, mediates energy homeostasis and reproduction by acting through its receptor, growth hormone secretagogue receptor (GHSR), expressed in hypothalamic neurons in the arcuate (ARC). We have shown 17β-estradiol (E2) increases Ghsr expression in Kisspeptin/Neurokinin B/Dynorphin (KNDy) neurons, enhancing sensitivity to ghrelin. We hypothesized that E2-induced Ghsr expression augments KNDy sensitivity in a fasting state by elevating ghrelin to disrupt energy expenditure in females. We produced a Kiss1-GHSR knockout to determine the role of GHSR in ARC KNDy neurons. We found that changes in ARC gene expression with estradiol benzoate (EB) treatment were abrogated by the deletion of GHSR and ghrelin abolished these differences. We also observed changes in metabolism and fasting glucose levels. Additionally, knockouts were resistant to body weight gain on a high fat diet (HFD). Behaviorally, we found that knockouts on HFD exhibited reduced anxiety-like behavior. Furthermore, knockouts did not refeed to the same extent as controls after a 24 h fast. Finally, in response to cold stress, knockout females had elevated metabolic parameters compared to controls. These data indicate GHSR in Kiss1 neurons modulate ARC gene expression, metabolism, glucose homeostasis, behavior, and thermoregulation, illustrating a novel mechanism for E2 and ghrelin to control Kiss1 neurons.

Hyperinsulinemia induces early and dyssynchronous puberty in lean female mice

Girls with obesity are at increased risk of early puberty. Obesity is associated with insulin resistance and hyperinsulinemia. We hypothesized that insulin plays a physiological role in pubertal transition, and super-imposed hyperinsulinemia due to childhood obesity promotes early initiation of puberty in girls. To isolate the effect of hyperinsulinemia from adiposity, we compared pre-pubertal and pubertal states in hyperinsulinemic, lean muscle (M)-insulin-like growth factor 1 receptor (IGF-1R)-lysine (K)-arginine (R) (MKR) mice to normoinsulinemic WT, with puberty onset defined by vaginal opening (VO). Our results show MKR had greater insulin resistance and higher insulin levels (P < 0.05) than WT despite lower body weight (P < 0.0001) and similar IGF-1 levels (P = NS). Serum luteinizing hormone (LH) levels were higher in hyperinsulinemic MKR (P = 0.005), and insulin stimulation induced an increase in LH levels in WT. VO was earlier in hyperinsulinemic MKR vs WT (P < 0.0001). When compared on the day of VO, kisspeptin expression was higher in hyperinsulinemic MKR vs WT (P < 0.05), and gonadotropin-releasing hormone and insulin receptor isoform expression was similar (P = NS). Despite accelerated VO, MKR had delayed, disordered ovarian follicle and mammary gland development. In conclusion, we found that hyperinsulinemia alone without adiposity triggers earlier puberty. In our study, hyperinsulinemia also promoted dyssynchrony between pubertal initiation and progression, urging future studies in girls with obesity to assess alterations in transition to adulthood.

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.

Sexually dimorphic distribution of kiss1 and kiss2 in the brain of yellowtail clownfish, Amphiprion clarkii

Kisspeptin system was shown to be a key factor in mediating social stress and reproduction. Yellowtail clownfish, Amphiprion clarkii, is a hermaphrodite fish, whose sex determination and gonadal development are affected by the social status of individuals. The yellowtail clownfish is a fantastic animal model to explore sex determination, but the social status and precise distribution of kiss mRNAs in the brain of this species are unknown. Hererin, a novel in situ hybridization technique, RNAscope, was used to investigate the distribution of kiss1 and kiss2 expressions in the brain of yellowtail clownfish. The coronal planes of brain showed that the kiss1 signal was mainly present in dorsal habenular nucleus (NHd) and kiss2 mRNA was widely expressed in telencephalon, midbrain, and hypothalamus, especially in dorsal part of the nucleus of the lateral recess (NRLd). Additionally, kiss1 and kiss2 signals have sexually dimorphic distribution. The kiss1 mRNA was distributed in NHd, the telencephalon, and lateral part of the diffuse nucleus of the inferior lobe (NDLIl) of females but in NHd and NDLIl of males. kiss2 signals were stronger in females than that in males. The distribution of kiss1 and kiss2 neurons in NHd of habenula and NRLd of hypothalamus may suggest that kiss genes associate environmental signaling and reproductive function in yellowtail clownfish.

Expression and distribution of MTNR1A in the hypothalamus-pituitary-gonadal axis of Tibetan sheep during the estrous cycle

The melatonin 1A receptor (MTNR1A) is a membrane receptor distributed across the mammalian gonadal axis-associated membrane. Melatonin (MT) can specifically bind with MTNR1A on the cell membrane and regulates mammalian reproductive activities. However, the role of MTNR1A in regulating the reproductive physiological activities of sheep in the Tibetan Plateau remains unclear. In this study, the MT content in Tibetan sheep blood during the estrous cycle was detected by ELISA. The distribution of MTNR1A in the hypothalamus-pituitary-gonadal axis (HPGA) was analyzed by immunohistochemistry and immunofluorescence. Western blot and qRT-PCR were used to detect dynamic changes of MTNR1A mRNA and protein expression, and the protein distributions in the HPGA. The results showed that the average secretion level of MT in Tibetan sheep blood was highest occurred during diestrus and the lowest during proestrus. Additionally, the secretion of MT at night was significantly higher than during the day. The immunopositive products of MTNR1A were primarily distributed around the glial cells in the dorsal hypothalamic nucleus region, chromophobe cells, and eosinophilic cytoplasm in the pituitary gland, follicular granular layer, follicular adventitia, tubal mucosa, cilia, endometrium, interstices, and glands in the uterus. The expression trends of MTNR1A mRNA and proteins in the HPGA during the estrous cycle were the same. The relative expression levels of MTNR1A mRNA and proteins in the hypothalamus and ovaries were the highest during proestrus and the lowest during metestrus; the highest during diestrus in the pituitary and oviducts; the highest during metestrus in the uterus. Collectively, the differences in the secretion of MT in Tibetan sheep blood and the expression of MTNR1A in HPGA suggest that they may be affected by steroid hormone secretion during the estrous cycle of Tibetan sheep, which has a potential impact on the regulation of animal estrous cycle.

KISS1R and ANKRD31 Cooperate to Enhance Leydig Cell Gene Expression via the Cytoskeletal-Nucleoskeletal Pathway

Kisspeptins are involved in the regulation of hypothalamic-pituitary-gonadal axis, Leydig cell functions, and testosterone secretion, acting as endogenous ligands of the KISS1 receptor. ANKRD31 protein participates in male fertility, regulating meiotic progression, and epididymal sperm maturation. Here, we show that in Leydig cells, KISS1 receptor and ANKRD31 proteins physically interact; the formation of this protein complex is enhanced by Kisspeptin-10 that also modulates F-actin synthesis, favoring histone acetylation in chromatin and gene expression via the cytoskeletal–nucleoskeletal pathway. Kp/KISS1R system deregulation, expression impairment of cytoskeletal–nucleoskeletal mediators, Leydig gene targets, and the decreased testosterone secretion in Ankrd31^−/− testis strongly supported our hypothesis. Furthermore, cytochalasin D treatment subverted the gene expression induction dependent on Kisspeptin-10 action. In conclusion, the current work highlights a novel role for the Kisspeptin-10 in the induction of the cytoskeletal–nucleoskeletal route, downstream a physical interaction between KISS1 receptor and ANKRD31, with gene expression activation as final effect, in Leydig cells.

Sex-specific hypothalamic expression of kisspeptin, gonadotropin releasing hormone, and kisspeptin receptor in progressive demyelination model

Demyelinating diseases, such as multiple sclerosis, decrease the quality of life of patients and can affect reproduction. Assisted reproductive therapies are available, which although effective, aggravate motor symptoms. For this reason, it is important to determine how the control of the hypothalamus-pituitary-gonadal axis is affected in order to develop better strategies for these patients. One way to determine this is using animal models such as the taiep rat, which shows progressive demyelination of the central nervous system, and was used in the present study to characterize the expression of gonadotrophin-releasing hormone (GnRH), Kisspeptin, and kisspeptin receptor (Kiss1R) and luteinizing hormone (LH) secretion. The expression of kisspeptin, GnRH, and Kiss1R was determined at the hypothalamic level by immunofluorescence and serum LH levels were determined by ELISA. The expression of kisspeptin at the hypothalamic level showed sexual dimorphism, where there was an increase in males and a decrease in females during oestrus. There was no change in the expression of GnRH or kisspeptin receptor, regardless of sex. However, a decrease in serum LH concentration was observed in both sexes. The taiep rat showed changes in the expression of kisspeptin at the hypothalamic level. These changes are different from those reported in the literature with the use of animals with experimental allergic encephalomyelitis, this is because both animal models represent different degrees of progression of multiple sclerosis. Our results suggest that the effects on the hypothalamus-pituitary-gonadal axis depend on the differences between the demyelinating processes, their progression, and even individual factors, and it is thus important that fertility treatments are individualized to maximize therapeutic effects.

Anomalous Temperature Interdicts the Reproductive Activity in Fish: Neuroendocrine Mechanisms of Reproductive Function in Response to Water Temperature

Fish are poikilotherm and small changes in water temperature can greatly affect physiological processes including reproduction, which is regulated by complex neuroendocrine mechanisms that respond to climatic events. This review provides evidence that anomalous high and low temperature may directly affect reproduction in fish by suppressing the expression of genes in the reproductive neuroendocrine system. The grass puffer, Takifugu alboplumbeus, is an excellent animal model for studying the thermal regulation of reproduction, for they exhibit periodic spawning activities, which are synchronized with seasonal, lunar and daily cycles. In the grass puffer, the expression of the genes encoding gonadotropin-releasing hormone (GnRH) 1, kisspeptin, gonadotropin-inhibitory hormone (GnIH) and their receptors were markedly suppressed in the diencephalon of fish exposed to high temperature (28°C) when compared to normal temperature (21°C), followed by the decrease in the pituitary mRNA levels for follicle-stimulating hormone (FSH), luteinizing hormone (LH) and growth hormone (GH). On the other hand, the exposure to low temperature (14°C) also inhibited the expression of gnrh1, kiss2, gnih and their receptor genes in the brain and fshb, lhb, gh and prl in the pituitary. Taken together, it is plausible that anomalous high and low temperature may be a proximate driver of termination of reproduction by suppressing the activity of the reproductive GnRH/kisspeptin/GnIH system, possibly through direct action of temperature signals at transcription level.

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.

Sheep as a model for neuroendocrinology research

Animal models remain essential to understand the fundamental mechanisms of physiology and pathology. Particularly, the complex and dynamic nature of neuroendocrine cells of the hypothalamus make them difficult to study. The neuroendocrine systems of the hypothalamus are critical for survival and reproduction, and are highly conserved throughout vertebrate evolution. Their roles in controlling body metabolism, growth and body composition, stress, electrolyte balance, and reproduction, have been intensively studied, and have yielded groundbreaking discoveries. Many of these discoveries would not have been feasible without the use of the domestic sheep (Ovis aries). The sheep has been used for decades to study the neuroendocrine systems of the hypothalamus and has become a model for human neuroendocrinology. The aim of this chapter is to review some of the profound biomedical discoveries made possible by the use of sheep. The advantages and limitations of sheep as a neuroendocrine model will be discussed. While no animal model can perfectly recapitulate a human disease or condition, sheep are invaluable for enabling manipulations not possible in human subjects and isolating physiologic variables to garner insight into neuroendocrinology and associated pathologies.

The mechanism underlying the pubertal increase in pulsatile GnRH release in primates

In primates, the gonatotropin-releasing hormone (GnRH) neurosecretory system, consisting of GnRH, kisspeptin, and neurokinin B neurons, is active during the neonatal/early infantile period. During the late infantile period, however, activity of the GnRH neurosecretory system becomes minimal as a result of gonadal steroid independent central inhibition, and this suppressed GnRH neurosecretory state continues throughout the prepubertal period. At the initiation of puberty, the GnRH neurosecretory system becomes active again because of the decrease in central inhibition. During the progress of puberty, kisspeptin and neurokinin B signaling to GnRH neurons further increases, resulting in the release of gonadotropins and subsequent gonadal maturation, and hence puberty. This review further discusses potential substrates of central inhibition and subsequent pubertal modification of the GnRH neurosecretory system by the pubertal increase in steroid hormones, which ensures the regulation of adult reproductive function.

Kisspeptins and the neuroendocrine control of reproduction: Recent progress and new frontiers in kisspeptin research

In late 2003, a major breakthrough in our understanding of the mechanisms that govern reproduction occurred with the identification of the reproductive roles of kisspeptins, encoded by the Kiss1 gene, and their receptor, Gpr54 (aka, Kiss1R). The discovery of this unsuspected reproductive facet attracted an extraordinary interest and boosted an intense research activity, in human and model species, that, in a relatively short period, established a series of basic concepts on the physiological roles of kisspeptins. Such fundamental knowledge, gathered in these early years of kisspeptin research, set the scene for the more recent in-depth dissection of the intimacies of the neuronal networks involving Kiss1 neurons, their precise mechanisms of regulation and the molecular underpinnings of the function of kisspeptins as pivotal regulators of all key aspects of reproductive function, from puberty onset to pulsatile gonadotropin secretion and the metabolic control of fertility. While no clear temporal boundaries between these two periods can be defined, in this review we will summarize the most prominent advances in kisspeptin research occurred in the last ten years, as a means to provide an up-dated view of the state of the art and potential paths of future progress in this dynamic, and ever growing domain of Neuroendocrinology.

The Kisspeptin System in Male Reproduction

The kisspeptin system includes the cleavage products Kiss1 precursor and kisspeptin receptor (Kiss1R). It was originally discovered and studied in cancer metastasis, but the identification of KISS1/KISS1R gene mutations causing hypogonadotropic hypogonadism (HH) revealed unexpected effects in reproduction. Nowadays, the kisspeptin system is the main central gatekeeper of the reproductive axis at puberty and adulthood, but it also has a widespread functional role in the control of endocrine functions. At the periphery, Kiss1 and Kiss1R are expressed in the testes, but the need for kisspeptin signaling for spermatogenesis and sperm quality is still unclear and debated. This brief manuscript summarizes the main findings on kisspeptin and male reproduction; upcoming data on sperm maturation are also discussed.

Sexual Dimorphism in Kisspeptin Signaling

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

Differential Expression of Kisspeptin System and Kisspeptin Receptor Trafficking during Spermatozoa Transit in the Epididymis

The hypothalamus–pituitary–testis axis controls the production of spermatozoa, and the kisspeptin system, comprising Kiss1 and Kiss1 receptor (Kiss1R), is the main central gatekeeper. The activity of the kisspeptin system also occurs in testis and spermatozoa, but currently the need of peripheral kisspeptin to produce gametes is not fully understood. Hence, we characterized kisspeptin system in rat spermatozoa and epididymis caput and cauda and analyzed the possible presence of Kiss1 in the epididymal fluid. The presence of Kiss1 and Kiss1R in spermatozoa collected from epididymis caput and cauda was evaluated by Western blot; significant high Kiss1 levels in the caput (p < 0.001 vs. cauda) and constant levels of Kiss1R proteins were observed. Immunofluorescence analysis revealed that the localization of Kiss1R in sperm head shifts from the posterior region in the epididymis caput to perforatorium in the epididymis cauda. In spermatozoa-free epididymis, Western blot revealed higher expression of Kiss1 and Kiss1R in caput (p < 0.05 vs. cauda). Moreover, immunohistochemistry revealed that Kiss1 and Kiss1R proteins were mainly localized in the secretory epithelial cell types and in contractile myoid cells, respectively. Finally, both dot blot and Elisa revealed the presence of Kiss1 in the epididymal fluid collected from epididymis cauda and caput, indicating that rat epididymis and spermatozoa possess a complete kisspeptin system. In conclusion, we reported for the first time in rodents Kiss1R trafficking in spermatozoa during the epididymis transit and Kiss1 measure in the epididymal fluid, thus suggesting a possible role for the system in spermatozoa maturation and storage within the epididymis.