A simple model of estrous cycle negative and positive feedback regulation of GnRH secretion

Cascaded autocatalytic hairpin assembly molecular circuit for amplified fluorescent aptamer luteinising hormone assay

The quantitative detection of luteinising hormone (LH) is critical for the study of the physiological mechanism of reproductive function and the assessment of infertility and the clinical treatment of reproductive disorders. However, conventional approaches for LH detection are mostly based on an antibody recognition module with the limitations of sensitivity, simplicity and cost. The development of robust LH sensing methods is therefore highly demanded for facilitating the diagnosis of LH-related diseases. We establish a convenient, amplified and sensitive fluorescent aptamer LH assay based on new target-triggered and cascaded autocatalytic hairpin assembly (C-aCHA) circuit amplification means via initiator sequence replication. Target LH molecules bind the aptamers in the aptamer/initiator duplexes to release the initiator sequences, which trigger CHA formation of DNA three-way junctions (TWJs) and the unfolding of fluorescently quenched signal hairpins to show amplified fluorescence. The TWJs further activate another CHA cycle for the yield of more initiator sequences to form the C-aCHA circuit amplification cycles, which lead to the unfolding of many signal hairpins to exhibit substantially magnified fluorescence recovery for detecting LH down to 8.56 pM in the range from 10 pM to 50 nM. In addition, the monitoring of trace LH in diluted serums by this sensing approach has been also verified. Our LH assay clearly outperforms current existing antibody-based methods and the C-aCHA signal amplification strategy can be easily extended as a robust means for sensitively monitoring various biomolecular markers with simple replacement of the corresponding aptamers for diverse applications.

Brain Gene Regulatory Networks Coordinate Nest Construction in Birds

Nest building is a vital behavior exhibited during breeding in birds, and is possibly induced by environmental and social cues. Although such behavioral plasticity has been hypothesized to be controlled by adult neuronal plasticity, empirical evidence, especially at the neurogenomic level, remains limited. Here, we aim to uncover the gene regulatory networks that govern avian nest construction and examine whether they are associated with circuit rewiring. We designed an experiment to dissect this complex behavior into components in response to pair bonding and nest material acquisition by manipulating the presence of mates and nest materials in 30 pairs of zebra finches. Whole-transcriptome analysis of 300 samples from five brain regions linked to avian nesting behaviors revealed nesting-associated gene expression enriched with neural rewiring functions, including neurogenesis and neuron projection. The enriched expression was observed in the motor/sensorimotor and social behavior networks of female finches, and in the dopaminergic reward system of males. Female birds exhibited predominant neurotranscriptomic changes to initiate the nesting stage, while males showed major changes after entering this stage, underscoring sex-specific roles in nesting behavior. Notably, major neurotranscriptomic changes occurred during pair bonding, with minor changes during nest material acquisition, emphasizing social interactions in nest construction. We also revealed gene expression associated with reproductive behaviors and tactile sensing for nesting behavior. This study presents novel neurogenomic evidence supporting the hypothesis of adult neural plasticity underlying avian nest-construction behavior. By uncovering the genetic toolkits involved, we offer novel insights into the evolution of animals' innate ability to construct nests.

Genetic Variants in KNDy Pathway Lack Association with Premature Ovarian Insufficiency in Mexican Women: A Sequencing-Based Cohort Study

Previous studies have demonstrated the essential role of the Kisspeptin/Neurokinin B/Dynorphin A (KNDy) pathway in female reproductive biology by regulating the activity of the hypothalamic-pituitary-gonadal axis. Identified loss-of-function mutations in these genes are linked to various reproductive disorders. This study investigated genetic disorders linked to mutations in the KNDy genes related to premature ovarian insufficiency (POI). A cohort of 14 Mexican POI patients underwent genetic screening using PCR-SSCP and Sanger sequencing, assessing the genetic variations' impact on protein function thereafter using multiple in silico tools. The PCR excluded extensive deletions, insertions, and duplications, while SSCP detected five genetic variants. Variations occurred in the KISS1 (c.58G>A and c.242C>G), KISS1R (c.1091A>T), PDYN (c.600C>T), and OPRK1 (c.36G>T) genes, whereas no genetic anomalies were found in NK3/NK3R genes. Each single-nucleotide variant underwent genotyping using PCR-SSCP in 100 POI-free subjects. Their allelic frequencies paralleled the patient group. These observations indicate that allelic variations in the KNDy genes may not contribute to POI etiology. Hence, screening for mutations in KNDy genes should not be a part of the diagnostic protocol for POI.

Novel insights into minipuberty and GnRH: Implications on neurodevelopment, cognition, and COVID-19 therapeutics

In humans, the first 1000 days of life are pivotal for brain and organism development. Shortly after birth, gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus are activated, a phenomenon known as minipuberty. This phenomenon, observed in all mammals studied, influences the postnatal development of the hypothalamic-pituitary-gonadal (HPG) axis and reproductive function. This review will put into perspective the results of recent studies showing that the impact of minipuberty extends beyond reproductive function, influencing sensory and cognitive maturation. Studies in mice have revealed the role of nitric oxide (NO) in regulating minipuberty amplitude, with NO deficiency linked to cognitive and olfactory deficits. Additionally, findings indicate that cognitive and sensory defects in adulthood in a mouse model of Down syndrome are associated with an age-dependent decline of GnRH production, whose origin can be traced back to minipuberty, and point to the potential therapeutic role of pulsatile GnRH administration in cognitive disorders. Furthermore, this review delves into the repercussions of COVID-19 on GnRH production, emphasizing potential consequences for neurodevelopment and cognitive function in infected individuals. Notably, GnRH neurons appear susceptible to SARS-CoV-2 infection, raising concerns about potential long-term effects on brain development and function. In conclusion, the intricate interplay between GnRH neurons, GnRH release, and the activity of various extrahypothalamic brain circuits reveals an unexpected role for these neuroendocrine neurons in the development and maintenance of sensory and cognitive functions, supplementing their established function in reproduction. Therapeutic interventions targeting the HPG axis, such as inhaled NO therapy in infancy and pulsatile GnRH administration in adults, emerge as promising approaches for addressing neurodevelopmental cognitive disorders and pathological aging.

CIRBP Increases the synthesis and secretion of steroid hormones by in yak granulaso cells

As a regulatory protein that upregulates transcription in response to various stresses, cold-induced RNA-binding protein (CIRBP) is involved in a variety of physiological pathological processes in cells. However, little is known about the role of CIRBP in regulating autophagy and the synthesis and secretion of ovarian steroid hormones (estradiol E2 and progesterone P4). This study aimed to explore whether the synthetic secretion of ovarian steroid hormones is related to CIRBP-regulated autophagy. We detected the differential expression of CIRBP, LC3, E2 and P4 in YGCs cultured at mild low temperature (32 °C) for 6 and 12 h. CIRBP, LC3, E2 and P4 expression was increased in response to low temperature in YGCs. In order to illustrate that the changes in secretion of E2/P4 and autophagy might be caused by CIRBP induced by low temperature, we overexpressed CIRBP in YGCs cultured in vitro to detect its effects on autophagy and steroid hormone synthesis and secretion. We found that overexpression of CIRBP can induce autophagy of YGCs and enhance the synthesis and secretion of E2 and P4, suggesting that mild hypothermia may activate autophagy by inducing the expression of CIRBP and enhance the synthesis and secretion of E2 and P4. To further explore the relationship between CIRBP regulated autophagy and steroid hormone synthesis and secretion, we verified it by regulating autophagy. The results showed that Inhibition of autophagy significantly reversed CIRBP overexpression-enhanced autophagy and synthetic secretion of E2, P4 in YGCs, while activated autophagy showed similar results to overexpression of CIRBP. In conclusion, our data suggest that autophagy is involved in the synthesis and secretion of YGCs E2 and P4 and is associated with overexpression of CIRBP.

Long-term Recordings of Arcuate Nucleus Kisspeptin Neurons Across the Mouse Estrous Cycle

The arcuate nucleus kisspeptin (ARNKISS) neurons represent the GnRH pulse generator that likely drives pulsatile gonadotropin secretion in all mammals. Using an improved GCaMP fiber photometry system enabling long-term continuous recordings, we aimed to establish a definitive profile of ARNKISS neuronal activity across the murine estrous cycle. As noted previously, a substantial reduction in the frequency of ARNKISS neuron synchronization events (SEs) occurs on late proestrus and extends into estrus. The SE amplitude remains constant throughout the cycle. During metestrus, we unexpectedly detected many multipeak SEs where many SEs occurred rapidly, within 160 seconds of each other. By applying a machine learning-based, k-means clustering analysis, we were further able to detect substantial within-stage variability in the patterns of pulse generator activity. Estrous cycle-dependent changes in SE activity occurred around the time of lights on and off. We also find that a mild stressor such as vaginal lavage reduces ARNKISS neuron SE frequency for up to 3 hours. These observations provide a comprehensive account of ARNKISS neuron activity across the estrous cycle, highlight a new pattern of multipeak SE activity, and introduce a new k-means clustering approach for analyzing ARNKISS neuron population behavior.

Transcriptomic Analysis Reveals Differentially Expressed Circular RNAs Associated with Fecundity in the Sheep Hypothalamus with Different FecB Genotypes

Circular RNAs (circRNAs) are a specific type of noncoding RNA, and some have defined roles in cellular and biological processes. However, little is known about the role of circRNAs in follicular development in sheep with FecB (fecundity Booroola) mutations. Here, the expression profiles of circRNAs were investigated using RNA sequencing (RNA-seq) in the follicular phase (F) and the luteal phase (L) of FecB mutant homozygous (BB) and wild-type (WW) Small Tail Han sheep. A total of 38,979 circRNAs were identified, and 314, 343, 336, and 296 of them were differentially expressed (DE) between BB_F and BB_L, WW_F and WW_L, BB_F and WW_F, and BB_L and WW_L, respectively. The length, type, and chromosome distribution of the circRNAs and the expression characteristic between the circRNAs and their host genes in the sheep hypothalamus were ascertained. Enrichment analysis showed that the host genes of DE circRNAs in the follicular and luteal phases were annotated to MAPK, gap junctions, progesterone-mediated oocyte maturation, oocyte meiosis, and other hormone-related signaling pathways, and the different FecB genotypes were annotated to the gap junctions, circadian entrainment, MAPK, and other hormone-related signaling pathways. The competing endogenous RNA network prediction revealed that the 129 target miRNAs might be bound to 336 DE circRNAs. oar_circ_0000523 and oar_circ_0028984, which were specifically expressed during the follicular phase in the BB genotype sheep, probably acted as miRNA sponges involved in the regulation of LH synthesis and secretion. This study reveals the expression profiles and characterization of circRNAs at two phases of follicular development considering different FecB genotypes, thereby providing an improved understanding of the roles of circRNAs in the sheep hypothalamus and their involvement in follicular development and ovulation.

KNDy Neurons of the Hypothalamus and Their Role in GnRH Pulse Generation: an Update

There is considerable evidence that synchronized activity within a reciprocally connected population of cells in the arcuate nucleus (ARC) coexpressing kisspeptin, neurokinin B (NKB), and dynorphin (KNDy cells) is crucial for the generation of gonadotrophin-releasing hormone (GnRH) pulses in mammals. The initial "KNDy hypothesis" proposed that pulsatile GnRH secretion is elicited by episodic kisspeptin release from KNDy cells following synchronized activation and termination of the population by NKB and dynorphin, respectively. Since then, the role of KNDy cells as a critical component of the pulse generator has been further supported by studies at the single-cell level, demonstrating that the population is both necessary and sufficient for pulsatility. In addition, there have been considerable modifications and expansion of the original hypothesis, including work demonstrating the critical role of glutamate in synchronization of the KNDy cell network, functional interactions with other ARC subpopulations, and the existence of species differences in the role of dynorphin in pulse generation. Here we review these recent changes and discuss how the translation of these findings has led to the development of new therapies for disorders related to pulse generation. We also outline critical gaps in knowledge that are currently limiting the application of KNDy research in the clinic, particularly regarding the role of dynorphin in pulse generation in primates.

CRISPR-Cas9 knockdown of ESR1 in preoptic GABA-kisspeptin neurons suppresses the preovulatory surge and estrous cycles in female mice

Evidence suggests that estradiol-sensing preoptic area GABA neurons are involved in the preovulatory surge mechanism necessary for ovulation. In vivo CRISPR-Cas9 editing was used to achieve a 60-70% knockdown in estrogen receptor alpha (ESR1) expression by GABA neurons located within the regions of the rostral periventricular area of the third ventricle (RP3V) and medial preoptic nuclei (MPN) in adult female mice. Mice exhibited variable reproductive phenotypes with the only significant finding being mice with bilateral ESR1 deletion in RP3V GABA neurons having reduced cFos expression in gonadotropin-releasing hormone (GnRH) neurons at the time of the surge. One sub-population of RP3V GABA neurons expresses kisspeptin. Re-grouping ESR1-edited mice on the basis of their RP3V kisspeptin expression revealed a highly consistent phenotype; mice with a near-complete loss of kisspeptin immunoreactivity displayed constant estrus and failed to exhibit surge activation but retained pulsatile luteinizing hormone (LH) secretion. These observations demonstrate that ESR1-expressing GABA-kisspeptin neurons in the RP3V are essential for the murine preovulatory LH surge mechanism.

Deubiquitinase UCHL1 regulates estradiol synthesis by stabilizing voltage-dependent anion channel 2

Lack of estradiol production by granulosa cells blocks follicle development, causes failure of estrous initiation, and results in an inability to ovulate. The ubiquitin-proteasome system plays a critical role in maintaining protein homeostasis and stability of the estrous cycle, but knowledge of deubiquitination enzyme function in estradiol synthesis is limited. Here, we observe that the deubiquitinase ubiquitin C-terminal hydrolase 1 (UCHL1) is more significant in estrous sows and high litter-size sows than in nonestrous sows and low-yielding sows. Overexpression of UCHL1 promotes estradiol synthesis in granulosa cells, and interference with UCHL1 has the opposite effect. UCHL1 binds, deubiquitinates, and stabilizes voltage-dependent anion channel 2 (VDAC2), promoting the synthesis of the estradiol precursor pregnenolone. Cysteine 90 (C90) of UCHL1 is necessary for its deubiquitination activity, and Lys45 and Lys64 in VDAC2 are essential for its ubiquitination and degradation. In vivo, compared with WT and sh-NC-AAV groups, the estrus cycle of female mice is disturbed, estradiol level is decreased, and the number of antral follicles is decreased after the injection of sh-UCHL1-AAV into ovarian tissue. These findings suggest that UCHL1 promotes estradiol synthesis by stabilizing VDAC2 and identify UCHL1 as a candidate gene affecting reproductive performance.

The Role of RFRP Neurons in the Allostatic Control of Reproductive Function

Reproductive function is critical for species survival; however, it is energetically costly and physically demanding. Reproductive suppression is therefore a physiologically appropriate adaptation to certain ecological, environmental, and/or temporal conditions. This 'allostatic' suppression of fertility enables individuals to accommodate unfavorable reproductive circumstances and safeguard survival. The mechanisms underpinning this reproductive suppression are complex, yet culminate with the reduced secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus, which in turn suppresses gonadotropin release from the pituitary, thereby impairing gonadal function. The focus of this review will be on the role of RFamide-related peptide (RFRP) neurons in different examples of allostatic reproductive suppression. RFRP neurons release the RFRP-3 peptide, which negatively regulates GnRH neurons and thus appears to act as a 'brake' on the neuroendocrine reproductive axis. In a multitude of predictable (e.g., pre-puberty, reproductive senescence, and seasonal or lactational reproductive quiescence) and unpredictable (e.g., metabolic, immune and/or psychosocial stress) situations in which GnRH secretion is suppressed, the RFRP neurons have been suggested to act as modulators. This review examines evidence for and against these roles.

New Horizons: Gonadotropin-Releasing Hormone and Cognition

Pulsatile secretion of gonadotropin-releasing hormone (GnRH) is essential for activating and maintaining the function of the hypothalamic-pituitary-gonadal axis, which controls the onset of puberty and fertility. Two recent studies suggest that, in addition to controlling reproduction, the neurons in the brain that produce GnRH are also involved in the control of postnatal brain maturation, odor discrimination, and adult cognition. This review will summarize the development and establishment of the GnRH system, with particular attention to the importance of its first postnatal activation, a phenomenon known as minipuberty, for later reproductive and nonreproductive functions. In addition, we will discuss the beneficial effects of restoring physiological (ie, pulsatile) GnRH levels on olfactory and cognitive alterations in preclinical Down syndrome and Alzheimer disease models, as well as the potential risks associated with long-term continuous (ie, nonphysiological) GnRH administration in certain disorders. Finally, this review addresses the intriguing possibility that pulsatile GnRH therapy may hold therapeutic potential for the management of some neurodevelopmental cognitive disorders and pathological aging in elderly people.

Long-COVID cognitive impairments and reproductive hormone deficits in men may stem from GnRH neuronal death

BACKGROUND

We have recently demonstrated a causal link between loss of gonadotropin-releasing hormone (GnRH), the master molecule regulating reproduction, and cognitive deficits during pathological aging, including Down syndrome and Alzheimer's disease. Olfactory and cognitive alterations, which persist in some COVID-19 patients, and long-term hypotestosteronaemia in SARS-CoV-2-infected men are also reminiscent of the consequences of deficient GnRH, suggesting that GnRH system neuroinvasion could underlie certain post-COVID symptoms and thus lead to accelerated or exacerbated cognitive decline.

METHODS

We explored the hormonal profile of COVID-19 patients and targets of SARS-CoV-2 infection in post-mortem patient brains and human fetal tissue.

FINDINGS

We found that persistent hypotestosteronaemia in some men could indeed be of hypothalamic origin, favouring post-COVID cognitive or neurological symptoms, and that changes in testosterone levels and body weight over time were inversely correlated. Infection of olfactory sensory neurons and multifunctional hypothalamic glia called tanycytes highlighted at least two viable neuroinvasion routes. Furthermore, GnRH neurons themselves were dying in all patient brains studied, dramatically reducing GnRH expression. Human fetal olfactory and vomeronasal epithelia, from which GnRH neurons arise, and fetal GnRH neurons also appeared susceptible to infection.

INTERPRETATION

Putative GnRH neuron and tanycyte dysfunction following SARS-CoV-2 neuroinvasion could be responsible for serious reproductive, metabolic, and mental health consequences in long-COVID and lead to an increased risk of neurodevelopmental and neurodegenerative pathologies over time in all age groups.

FUNDING

European Research Council (ERC) grant agreements No 810331, No 725149, No 804236, the European Union Horizon 2020 research and innovation program No 847941, the Fondation pour la Recherche Médicale (FRM) and the Agence Nationale de la Recherche en Santé (ANRS) No ECTZ200878 Long Covid 2021 ANRS0167 SIGNAL, Agence Nationale de la recherche (ANR) grant agreements No ANR-19-CE16-0021-02, No ANR-11-LABEX-0009, No. ANR-10-LABEX-0046, No. ANR-16-IDEX-0004, Inserm Cross-Cutting Scientific Program HuDeCA, the CHU Lille Bonus H, the UK Medical Research Council (MRC) and National Institute of Health and care Research (NIHR).

A role for GnRH in olfaction and cognition: Implications for veterinary medicine

Pulsatile secretion of gonadotropin-releasing hormone (GnRH) is essential for the activation and maintenance of the function of the hypothalamic-pituitary-gonadal (HPG) axis, which controls the onset of puberty and fertility. Two provocative recent studies suggest that, in addition to control reproduction, the neurons in the brain that produce GnRH are also involved in the control postnatal brain maturation, odour discrimination and adult cognition. Long-acting GnRH antagonists and agonists are commonly used to control fertility and behaviour in veterinary medicine, primarily in males. This review puts into perspective the potential risks of these androgen deprivation therapies and immunization on olfactory and cognitive performances and well-aging in domestic animals, including pets. We will also discuss the results reporting beneficial effects of pharmacological interventions restoring physiological GnRH levels on olfactory and cognitive alterations in preclinical models of Alzheimer's disease, which shares many pathophysiological and behavioural hallmarks with canine cognitive dysfunction. These novel findings raise the intriguing possibility that pulsatile GnRH therapy holds therapeutic potential for the management of this behavioural syndrome affecting older dogs.

High Fat Diet Exaggerate Metabolic and Reproductive PCOS Features by Promoting Oxidative Stress: An Improved EV Model in Rats

Background and Objectives: Polycystic ovary syndrome (PCOS) is a frequent multifactorial endocrinopathy affecting women in the reproductive period, often associated with infertility and metabolic disorders. The use of animal models helps to better understand etiopathogenesis, enabling the examination of the effects of certain drugs in order to discover the best possible therapeutic approach. We tried to investigate the additional effect of estradiol-valerate (EV) and high-fat diet (HFD) in female rats to explore PCOS-related alterations with special focus on oxidative stress. Materials and Methods: Animals were divided into three groups: control group (CTRL, n = 6), estradiol-valerate group (EV, n = 6), and estradiol-valerate group on HFD (EV + HFD, n = 6). PCOS was induced by single subcutaneous injection of long-acting EV in a dose of 4 mg/per rat. We tried to improve the metabolic characteristics of the PCOS animal model by adding HFD, so the CTRL and EV group had a regular diet, while the EV + HFD group had HFD during the induction period of 60 days. Results: We observed alterations of anthropometric parameters and hormonal disturbances, along with estrus cycle impairment reassembly to obese-type PCOS phenotype. Moreover, glucose metabolism was impaired after addition of HFD to EV protocol, contrary to EV administered alone. Histological analysis confirmed more numerous cystic follicles after the combination of EV and HFD protocol. The alterations of oxidative stress markers could be related to and serve as the mechanistic base for development of PCOS-related endocrine, reproductive, and metabolic properties. Conclusions: The additive effect of EV and HFD was obvious in the majority of the parameters observed. Our study strongly demonstrated metabolic as well as reproductive properties of PCOS in rats.

Defining potential targets of prenatal androgen excess: Expression analysis of androgen receptor on hypothalamic neurons in the fetal female mouse brain

Polycystic ovary syndrome (PCOS) is a female endocrine disorder that is associated with prenatal exposure to excess androgens. In prenatally androgenized (PNA) mice that model PCOS, GABAergic neural transmission to and innervation of GnRH neurons is increased. Evidence suggests that elevated GABAergic innervation originates in the arcuate nucleus (ARC). We hypothesized that GABA-GnRH circuit abnormalities are a direct consequence of PNA, resulting from DHT binding to androgen receptor (AR) in the prenatal brain. However, whether prenatal ARC neurons express AR at the time of PNA treatment is presently unknown. We used RNAScope in situ hybridization to localize AR mRNA (Ar)-expressing cells in healthy gestational day (GD) 17.5 female mouse brains and to assess coexpression levels in specific neuronal phenotypes. Our study revealed that less than 10% of ARC GABA cells expressed Ar. In contrast, we found that ARC kisspeptin neurons, critical regulators of GnRH neurons, were highly colocalized with Ar. Approximately 75% of ARC Kiss1-expressing cells also expressed Ar at GD17.5, suggesting that ARC kisspeptin neurons are potential targets of PNA. Investigating other neuronal populations in the ARC we found that ~50% of pro-opiomelanocortin (Pomc) cells, 22% of tyrosine hydroxylase (Th) cells, 8% of agouti-related protein (Agrp) cells and 8% of somatostatin (Sst) cells express Ar. Lastly, RNAscope in coronal sections showed Ar expression in the medial preoptic area (mPOA), and the ventral part of the lateral septum (vLS). These Ar-expressing regions were highly GABAergic, and 22% of GABA cells in the mPOA and 25% of GABA cells in the vLS also expressed Ar. Our findings identify specific neuronal phenotypes in the ARC, mPOA, and vLS that are androgen sensitive in late gestation. PNA-induced functional changes in these neurons may be related to the development of impaired central mechanisms associated with PCOS-like features.

Dax1 modulates ERα-dependent hypothalamic estrogen sensing in female mice

Coupling the release of pituitary hormones to the developmental stage of the oocyte is essential for female fertility. It requires estrogen to restrain kisspeptin (KISS1)-neuron pulsatility in the arcuate hypothalamic nucleus, while also exerting a surge-like effect on KISS1-neuron activity in the AVPV hypothalamic nucleus. However, a mechanistic basis for this region-specific effect has remained elusive. Our genomic analysis in female mice demonstrate that some processes, such as restraint of KISS1-neuron activity in the arcuate nucleus, may be explained by region-specific estrogen receptor alpha (ERα) DNA binding at gene regulatory regions. Furthermore, we find that the Kiss1-locus is uniquely regulated in these hypothalamic nuclei, and that the nuclear receptor co-repressor NR0B1 (DAX1) restrains its transcription specifically in the arcuate nucleus. These studies provide mechanistic insight into how ERα may control the KISS1-neuron, and Kiss1 gene expression, to couple gonadotropin release to the developmental stage of the oocyte.

Expression of Locally Produced Adipokines and Their Receptors during Different Physiological and Reproductive Stages in the Bovine Corpus Luteum

This study aimed to determine the gene expression of different local novel adipokines, such as vaspin, adiponectin, visfatin, and resistin, and their known receptors, namely, heat shock 70 protein 5, adiponectin receptor 1, and adiponectin receptor 2, in the bovine corpus luteum (CL) during different phases of the estrous cycle (on days 1-2, 3-4, 5-7, 8-12, 13-18, >18) and pregnancy (at months 1-2, 3-4, 5-7, >7). The mRNA expression was measured by reverse transcription polymerase chain reaction (RT-qPCR). The mRNA expression levels were normalized to the geometric mean of all three constantly expressed reference genes (cyclophilin A, ubiquitin, ubiquitin C). Our findings suggest that adipokines are expressed and present in all investigated groups, and are specifically up- or downregulated during the estrus cycle and during pregnancy. Vaspin and adiponectin levels were upregulated in the middle and late cycle stages. Resistin was abundant during the CL regression stage and in the first months of pregnancy. The specific expression of adipokine receptors indicates their involvement in the local mechanisms that regulate CL function. Further investigations are required to elucidate the regulative mechanisms underlying the different local effects of adipokines on the ovarian physiology of cows.

Circadian and kisspeptin regulation of the preovulatory surge

Fertility in mammals is ultimately controlled by a small population of neurons - the gonadotropin-releasing hormone (GnRH) neurons - located in the ventral forebrain. GnRH neurons control gonadal function through the release of GnRH, which in turn stimulates the secretion of the anterior pituitary gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In spontaneous ovulators, ovarian follicle maturation eventually stimulates, via sex steroid feedback, the mid-cycle surge in GnRH and LH secretion that causes ovulation. The GnRH/LH surge is initiated in many species just before the onset of activity through processes controlled by the central circadian clock, ensuring that the neuroendocrine control of ovulation and sex behavior are coordinated. This review aims to give an overview of anatomical and functional studies that collectively reveal some of the mechanisms through which the central circadian clock regulates GnRH neurons and their afferent circuits to drive the preovulatory surge.

Neural control of female sexual behaviors

Reproduction is the biological process by which new individuals are produced by their parents. It is the fundamental feature of all known life and is required for the existence of all species. All mammals reproduce sexually, a process that involves the union of two reproductive cells, one from a male and one from a female. Sexual behaviors are a series of actions leading to reproduction. They are composed of appetitive, action, and refractory phases, each supported by dedicated developmentally-wired neural circuits to ensure high reproduction success. In rodents, successful reproduction can only occur during female ovulation. Thus, female sexual behavior is tightly coupled with ovarian activity, namely the estrous cycle. This is achieved through the close interaction between the female sexual behavior circuit and the hypothalamic-pituitary-gonadal (HPG) axis. In this review, we will summarize our current understanding, learned mainly in rodents, regarding the neural circuits underlying each phase of the female sexual behaviors and their interaction with the HPG axis, highlighting the gaps in our knowledge that require future investigation.

Mitochondrial function and E2 synthesis are impaired following alteration of CLOCK gene expression in porcine ovarian granulosa cells

Circadian locomotor output cycles kaput (CLOCK) is a critical component of the mammalian circadian clock system and regulates ovarian physiology. However, the functions and mechanisms of CLOCK in porcine granulosa cells (GCs) are poorly understood. The present study focused on CLOCK's effects on estradiol synthesis. Similarity analysis showed that CLOCK is highly conserved between pigs and other species. The phylogenetic tree analysis indicated that porcine CLOCK was most closely related to that in Arabian camels. CLOCK significantly reduced E₂ synthesis in GCs. CLOCK reduced the expression of steroidogenesis-related genes at the mRNA and protein levels, including CYP19A1, CYP11A1, and StAR. CYP17A1 levels were significantly downregulated. We demonstrated that CLOCK dramatically decreased ATP content, mitochondrial copy number, and mitochondrial membrane potential (MMP) and increased reactive oxygen species levels in GCs. We observed that mitochondria were severely damaged with fuzzy and fractured cristae and swollen matrix. These findings suggest that mitochondrial function and E₂ synthesis are impaired following the alteration of CLOCK gene expression in porcine ovarian GCs.

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.

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.

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.

Pattern of gonadotropin secretion along the estrous cycle of C57BL/6 female mice

The pattern of gonadotropin secretion along the estrous cycle was elegantly described in rats. Less information exists about the pattern of gonadotropin secretion in gonad-intact mice, particularly regarding the follicle-stimulating hormone (FSH). Using serial blood collections from the tail-tip of gonad-intact C57BL/6 mice on the first day of cornification (transition from diestrus to estrus; hereafter called proestrus), we observed that the luteinizing hormone (LH) and FSH surge cannot be consistently detected since only one out of eight females (12%) showed increased LH levels. In contrast, a high percentage of mice (15 out of 21 animals; 71%) exhibited LH and FSH surges on the proestrus when a single serum sample was collected. Mice that exhibited LH and FSH surges on the proestrus showed c-Fos expression in gonadotropin-releasing hormone- (GnRH; 83.4% of co-localization) and kisspeptin-expressing neurons (42.3% of co-localization) of the anteroventral periventricular nucleus (AVPV). Noteworthy, mice perfused on proestrus, but that failed to exhibit LH surge, showed a smaller, but significant expression of c-Fos in GnRH (32.7%) and AVPVKisspeptin (14.0%) neurons. Finally, 96 serial blood samples were collected hourly in eight regular cycling C57BL/6 females to describe the pattern of LH and FSH secretion along the estrous cycle. Small elevations in LH and FSH levels were detected at the time expected for the LH surge. In summary, the present study improves our understanding of the pattern of gonadotropin secretion and the activation of central components of the hypothalamic-pituitary-gonadal axis along the estrous cycle of C57BL/6 female mice.

Opioidergic pathways and kisspeptin in the regulation of female reproduction in mammals

Endogenous opioid peptides have attracted attention as critical neuropeptides in the central mechanism regulating female reproduction ever since the discovery that arcuate dynorphin neurons that coexpress kisspeptin and neurokinin B (NKB), which are also known as kisspeptin/neurokinin B/dynorphin (KNDy) neurons, play a role as a master regulator of pulsatile gonadotropin-releasing hormone (GnRH) release in mammals. In this study, we first focus on the role of dynorphin released by KNDy neurons in the GnRH pulse generation. Second, we provide a historical overview of studies on endogenous opioid peptides. Third, we discuss how endogenous opioid peptides modulate tonic GnRH/gonadotropin release in female mammals as a mediator of inhibitory internal and external cues, such as ovarian steroids, nutritional status, or stress, on reproduction. Then, we discuss the role of endogenous opioid peptides in GnRH surge generation in female mammals.

Neuroendocrine mechanisms underlying estrogen positive feedback and the LH surge

A fundamental principle in reproductive neuroendocrinology is sex steroid feedback: steroid hormones secreted by the gonads circulate back to the brain to regulate the neural circuits governing the reproductive neuroendocrine axis. These regulatory feedback loops ultimately act to modulate gonadotropin-releasing hormone (GnRH) secretion, thereby affecting gonadotropin secretion from the anterior pituitary. In females, rising estradiol (E₂) during the middle of the menstrual (or estrous) cycle paradoxically "switch" from being inhibitory on GnRH secretion ("negative feedback") to stimulating GnRH release ("positive feedback"), resulting in a surge in GnRH secretion and a downstream LH surge that triggers ovulation. While upstream neural afferents of GnRH neurons, including kisspeptin neurons in the rostral hypothalamus, are proposed as critical loci of E₂ feedback action, the underlying mechanisms governing the shift between E₂ negative and positive feedback are still poorly understood. Indeed, the precise cell targets, neural signaling factors and receptors, hormonal pathways, and molecular mechanisms by which ovarian-derived E₂ indirectly stimulates GnRH surge secretion remain incompletely known. In many species, there is also a circadian component to the LH surge, restricting its occurrence to specific times of day, but how the circadian clock interacts with endocrine signals to ultimately time LH surge generation also remains a major gap in knowledge. Here, we focus on classic and recent data from rodent models and discuss the consensus knowledge of the neural players, including kisspeptin, the suprachiasmatic nucleus, and glia, as well as endocrine players, including estradiol and progesterone, in the complex regulation and generation of E₂-induced LH surges in females.

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.

Kisspeptin neuron electrophysiology: Intrinsic properties, hormonal modulation, and regulation of homeostatic circuits

The obligatory role of kisspeptin (KISS1) and its receptor (KISS1R) in regulating the hypothalamic-pituitary-gonadal axis, puberty and fertility was uncovered in 2003. In the few years that followed, an impressive body of work undertaken in many species established that neurons producing kisspeptin orchestrate gonadotropin-releasing hormone (GnRH) neuron activity and subsequent GnRH and gonadotropin hormone secretory patterns, through kisspeptin-KISS1R signaling, and mediate many aspects of gonadal steroid hormone feedback regulation of GnRH neurons. Here, we review knowledge accrued over the past decade, mainly in genetically modified mouse models, of the electrophysiological properties of kisspeptin neurons and their regulation by hormonal feedback. We also discuss recent progress in our understanding of the role of these cells within neuronal circuits that control GnRH neuron activity and GnRH secretion, energy balance and, potentially, other homeostatic and reproductive functions.

GABA System Modifications During Periods of Hormonal Flux Across the Female Lifespan

The female lifespan is marked by periods of dramatic hormonal fluctuation. Changes in the ovarian hormones estradiol and progesterone, in addition to the progesterone metabolite allopregnanolone, are among the most significant and have been shown to have widespread effects on the brain. This review summarizes current understanding of alterations that occur within the GABA system during the major hormonal transition periods of puberty, the ovarian cycle, pregnancy and the postpartum period, as well as reproductive aging. The functional impacts of altered inhibitory activity during these times are also discussed. Lastly, avenues for future research are identified, which, if pursued, can broaden understanding of the GABA system in the female brain and potentially lead to better treatments for women experiencing changes in brain function at each of these hormonal transition periods.

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.

Pharmacological characterization of linzagolix, a novel, orally active, non-peptide antagonist of gonadotropin-releasing hormone receptors

Control of gonadotropin-releasing hormone (GnRH) signaling is an effective strategy for the treatment of sex hormone-dependent diseases. GnRH analogs have been widely used for treating these diseases; however, initial stimulation or complete suppression of GnRH signaling by GnRH analogs results in the occurrence of several distinct adverse effects. Accordingly, we aimed to discover small molecule GnRH antagonists with superior pharmacokinetic (PK) and pharmacodynamic profiles. Linzagolix is a potent, orally available, and selective GnRH antagonist. Herein, we reported the pharmacological characterization of linzagolix in vitro and in vivo. Linzagolix selectively binds to the GnRH receptor and inhibits GnRH-stimulated signaling, in a manner comparable to cetrorelix, a peptide GnRH antagonist. Since the inhibitory effect of the gonad axis is useful for the treatment of gynecological conditions such as endometriosis and uterine fibroids, we investigated the effect of orally administered linzagolix on the gonadal axis in ovariectomized and intact cynomolgus monkeys. In ovariectomized monkeys, linzagolix immediately suppressed the serum luteinizing hormone concentration at doses over 1 mg/kg, indicating dose-dependent inhibition that correlated with serum linzagolix concentrations. In intact female monkeys, repeated linzagolix administration suppressed hormone surges and ceased or prolonged menstrual cycles. Furthermore, all animals presenting arrested menstrual cycles following linzagolix treatment showed recovery of hormone secretion and regular menstrual cycles after administration periods ended. Our results demonstrated that linzagolix has potential as a novel agent for reproductive-aged women suffering from sex hormone-dependent diseases. This article is protected by copyright. All rights reserved.

Unusual suspects: Glial cells in fertility regulation and their suspected role in polycystic ovary syndrome

Gonadotropin-releasing-hormone (GnRH) neurons sitting within the hypothalamus control the production of gametes and sex steroids by the gonads, therefore ensuring survival of species. As orchestrators of reproductive function, GnRH neurons integrate information from external and internal cues. This occurs through an extensively studied neuronal network known as the "GnRH neuronal network." However, the brain is not simply composed of neurons. Evidence suggests a role for glial cells in controlling GnRH neuron activity, secretion and fertility outcomes, although numerous questions remain. Glial cells have historically been seen as support cells for neurons. This idea has been challenged by the discovery that some neurological diseases originate from glial dysfunction. The prevalence of infertility disorders is increasing worldwide, with one in four couples being affected; therefore, it remains essential to understand the mechanisms by which the brain controls fertility. The "GnRH glial network" could be a major player in infertility disorders and represent a potential therapeutic target. In polycystic ovary syndrome (PCOS), the most common infertility disorder of reproductive aged women worldwide, the brain is considered a prime suspect. Recent studies have demonstrated pathological neuronal wiring of the "GnRH neuronal network" in PCOS-like animal models. However, the role of the "GnRH glial network" remains to be elucidated. In this review, I aim to propose glial cells as unusual suspects in infertility disorders such as PCOS. In the first part, I state our current knowledge about the role of glia in the regulation of GnRH neurons and fertility. In the second part, based on our recent findings, I discuss how glial cells could be implicated in PCOS pathology.

Neuroendocrine control of gonadotropin-releasing hormone: Pulsatile and surge modes of secretion

The concept that different systems control episodic and surge secretion of gonadotropin-releasing hormone (GnRH) was well established by the time that GnRH was identified and formed the framework for studies of the physiological roles of GnRH, and later kisspeptin. Here, we focus on recent studies identifying the neural mechanisms underlying these two modes of secretion, with an emphasis on their core components. There is now compelling data that kisspeptin neurons in the arcuate nucleus that also contain neurokinin B (NKB) and dynorphin (i.e., KNDy cells) and their projections to GnRH dendrons constitute the GnRH pulse generator in mice and rats. There is also strong evidence for a similar role for KNDy neurons in sheep and goats, and weaker data in monkeys and humans. However, whether KNDy neurons act on GnRH dendrons and/or GnRH soma and dendrites that are found in the mediobasal hypothalamus (MBH) of these species remains unclear. The core components of the GnRH/luteinising hormone surge consist of an endocrine signal that initiates the process and a neural trigger that drives GnRH secretion during the surge. In all spontaneous ovulators, the core endocrine signal is a rise in estradiol secretion from the maturing follicle(s), with the site of estrogen positive feedback being the rostral periventricular kisspeptin neurons in rodents and neurons in the MBH of sheep and primates. There is considerable species variations in the neural trigger, with three major classes. First, in reflex ovulators, this trigger is initiated by coitus and carried to the hypothalamus by neural or vascular pathways. Second, in rodents, there is a time of day signal that originates in the suprachiasmatic nucleus and activates rostral periventricular kisspeptin neurons and GnRH soma and dendrites. Finally, in sheep nitric oxide-producing neurons in the ventromedial nucleus, KNDy neurons and rostral kisspeptin neurons all appear to participate in driving GnRH release during the surge.

Estradiol and Estrogen-like Alternative Therapies in Use: The Importance of the Selective and Non-Classical Actions

Estrogen is one of the most important female sex hormones, and is indispensable for reproduction. However, its role is much wider. Among others, due to its neuroprotective effects, estrogen protects the brain against dementia and complications of traumatic injury. Previously, it was used mainly as a therapeutic option for influencing the menstrual cycle and treating menopausal symptoms. Unfortunately, hormone replacement therapy might be associated with detrimental side effects, such as increased risk of stroke and breast cancer, raising concerns about its safety. Thus, tissue-selective and non-classical estrogen analogues have become the focus of interest. Here, we review the current knowledge about estrogen effects in a broader sense, and the possibility of using selective estrogen-receptor modulators (SERMs), selective estrogen-receptor downregulators (SERDs), phytoestrogens, and activators of non-genomic estrogen-like signaling (ANGELS) molecules as treatment.

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

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

Optogenetic stimulation of Kiss1ARC terminals in the AVPV induces surge-like luteinizing hormone secretion via glutamate release in mice

Kisspeptin neurons are mainly located in the arcuate (Kiss1^ARC, vis-à-vis the GnRH pulse generator) and anteroventral periventricular nucleus (Kiss1^AVPV, vis-à-vis the GnRH surge generator). Kiss1^ARC send fibre projections that connect with Kiss1^AVPV somata. However, studies focused on the role of Kiss1^ARC neurons in the LH surge are limited, and the role of Kiss1^ARC projections to AVPV (Kiss1^ARC→AVPV) in the preovulatory LH surge is still unknown. To investigate its function, this study used optogenetics to selectively stimulate Kiss1^ARC→AVPV and measured changes in circulating LH levels. Kiss1^ARC in Kiss-Cre-tdTomato mice were virally infected to express channelrhodopsin-2 proteins, and optical stimulation was applied selectively via a fibre optic cannula in the AVPV. Sustained 20 Hz optical stimulation of Kiss1^ARC→AVPV from 15:30 to 16:30 h on proestrus effectively induced an immediate increase in LH reaching peak surge-like levels of around 8 ng/ml within 10 min, followed by a gradual decline to baseline over about 40 min. Stimulation at 10 Hz resulted in a non-significant increase in LH levels and 5 Hz stimulation had no effect in proestrous animals. The 20 Hz stimulation induced significantly higher circulating LH levels on proestrus compared with diestrus or estrus, which suggested that the effect of terminal stimulation is modulated by the sex steroid milieu. Additionally, intra-AVPV infusion of glutamate antagonists, AP5+CNQX, completely blocked the increase on LH levels induced by Kiss1^ARC→AVPV terminal photostimulation in proestrous animals. These results demonstrate for the first time that optical stimulation of Kiss1^ARC→AVPV induces an LH surge-like secretion via glutamatergic mechanisms. In conclusion, Kiss1^ARC may participate in LH surge generation by glutamate release from terminal projections in the AVPV.

Heterogeneity in GnRH and kisspeptin neurons and their significance in vertebrate reproductive biology

Vertebrate reproduction is essentially controlled by the hypothalamus-pituitary-gonadal (HPG) axis, which is a central dogma of reproductive biology. Two major hypothalamic neuroendocrine cell groups containing gonadotropin-releasing hormone (GnRH) and kisspeptin are crucial for control of the HPG axis in vertebrates. GnRH and kisspeptin neurons exhibit high levels of heterogeneity including their cellular morphology, biochemistry, neurophysiology and functions. However, the molecular foundation underlying heterogeneities in GnRH and kisspeptin neurons remains unknown. More importantly, the biological and physiological significance of their heterogeneity in reproductive biology is poorly understood. In this review, we first describe the recent advances in the neuroendocrine functions of kisspeptin-GnRH pathways. We then view the recent emerging progress in the heterogeneity of GnRH and kisspeptin neurons using morphological and single-cell transcriptomic analyses. Finally, we discuss our views on the significance of functional heterogeneity of reproductive endocrine cells and their potential relevance to reproductive health.

The effect of fixed-time artificial insemination protocol initiated at different stages of the estrous cycle on follicle development and ovulation in gilts

Hormonal products have been developed for fixed-time artificial insemination (FTAI) to improve the efficiency of swine production. Here, we evaluated the effect of an FTAI protocol initiated during different phases of the estrous cycle on follicle development and ovulation in gilts. A total of 36 gilts were equally divided into three groups designated as the luteal (L), follicular (F), and post-ovulation (O) groups and fed with 20 mg of altrenogest for 18 days, followed by intramuscular injection of 1000 IU PMSG at 42 h after withdrawal of altrenogest, and 100 μg of GnRH after an 80-h interval. The L group had the highest number of follicles 4-6 mm in diameter, as well as corpora hemorrhagica. The mRNA expression of caspase-9 in the L group were significantly lower than those in the O and F groups (P < 0.05), while CYP11A1 and VEGF mRNA expression levels were significantly higher (P < 0.05). Moreover, FSHR mRNA levels were significantly higher in the O group than in the L, F, and control groups (P < 0.05). LHCGR and CYP19A1 mRNA levels were the highest in the F group (P < 0.05). Thus, the changes in the expression of genes associated with follicular development, maturation, and ovulation identified in this study indicated that initiation of the FTAI protocol during the luteal phase induced a better environment for follicle development and ovulation in gilts.

Profile of gene expression changes during estrodiol-17β-induced feminization in the Takifugu rubripes brain

Background

As the critical tissue of the central nervous system, the brain has been found to be involved in gonad development. Previous studies have suggested that gonadal fate may be affected by the brain. Identifying brain-specific molecular changes that occur during estrodiol-17β (E₂) -induced feminization is crucial to our understanding of the molecular control of sex differentiation by the brains of fish.

Results

In this study, the differential transcriptomic responses of the Takifugu rubripes larvae brain were compared after E₂ treatment for 55 days. Our results showed that 514 genes were differentially expressed between E₂-treated-XX (E-XX) and Control-XX (C-XX) T. rubripes, while 362 genes were differentially expressed between E₂-treated-XY (E-XY) and Control-XY (C-XY). For example, the expression of cyp19a1b, gnrh1 and pgr was significantly up-regulated, while st, sl, tshβ, prl and pit-1, which belong to the growth hormone/prolactin family, were significantly down-regulated after E₂ treatment, in both sexes. The arntl1, bhlbe, nr1d2, per1b, per3, cry1, cipc and ciart genes, which are involved in the circadian rhythm, were also found to be altered. Differentially expressed genes (DEGs), which were identified between E-XX and C-XX, were significantly enriched in neuroactive ligand-receptor interaction, arachidonic acid metabolism, cytokine-cytokine receptor interaction and the calcium signaling pathway. The DEGs that were identified between E-XY and C-XY were significantly enriched in tyrosine metabolism, phenylalanine metabolism, arachidonic acid metabolism and linoleic acid metabolism.

Conclusion

A number of genes and pathways were identified in the brain of E₂-treated T. rubripes larvae by RNA-seq. It provided the opportunity for further study on the possible involvement of networks in the brain-pituitary-gonadal axis in sex differentiation in T. rubripes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08158-0.

The dendron and episodic neuropeptide release

The unexpected observation that the long processes of gonadotrophin-releasing hormone (GnRH) neurons not only conducted action potentials, but also operated to integrate afferent information at their distal-most extent gave rise to the concept of a blended dendritic-axonal process termed the "dendron". The proximal dendrites of the GnRH neuron function in a conventional manner, receiving synaptic inputs and initiating action potentials that are critical for the surge mode of GnRH secretion. The distal dendrons are regulated by both classical synapses and volume transmission and likely operate using subthreshold electrotonic propagation into the nearby axon terminals in the median eminence. Evidence indicates that neural processing at the distal dendron is responsible for the pulsatile patterning of GnRH secretion. Although the dendron remains unique to the GnRH neuron, data show that it exists in both mice and rats and may be a common feature of mammalian species in which GnRH neuron cell bodies do not migrate into the basal hypothalamus. This review outlines the discovery and function of the dendron as a unique neuronal structure optimised to generate episodic neuronal output.

Estrogen Regulation of the Molecular Phenotype and Active Translatome of AVPV Kisspeptin Neurons

In females, ovarian estradiol (E2) exerts both negative and positive feedback regulation on the neural circuits governing reproductive hormone secretion, but the cellular and molecular mechanisms underlying this remain poorly understood. In rodents, estrogen receptor α-expressing kisspeptin neurons in the hypothalamic anteroventral periventricular region (AVPV) are prime candidates to mediate E2 positive feedback induction of preovulatory gonadotropin-releasing hormone and luteinizing hormone (LH) surges. E2 stimulates AVPV Kiss1 expression, but the full extent of estrogen effects in these neurons is unknown; whether E2 stimulates or inhibits other genes in AVPV Kiss1 cells has not been determined. Indeed, understanding of the function(s) of AVPV kisspeptin cells is limited, in part, by minimal knowledge of their overall molecular phenotype, as only a few genes are currently known to be co-expressed in AVPV Kiss1 cells. To provide a more detailed profiling of co-expressed genes in AVPV Kiss1 cells, including receptors and other signaling factors, and test how these genes respond to E2, we selectively isolated actively translated mRNAs from AVPV Kiss1 cells of female mice and performed RNA sequencing (RNA-seq). This identified >13 000 mRNAs co-expressed in AVPV Kiss1 cells, including multiple receptor and ligand transcripts positively or negatively regulated by E2. We also performed RNAscope to validate co-expression of several transcripts identified by RNA-seq, including Pdyn (prodynorphin), Penk (proenkephalin), Vgf (VGF), and Cartpt (CART), in female AVPV Kiss1 cells. Given the important role of AVPV kisspeptin cells in positive feedback, E2 effects on identified genes may relate to the LH surge mechanism and/or other physiological processes involving these cells.

Morphological assessment of GABA and glutamate inputs to GnRH neurons in intact female mice using expansion microscopy

The roles GABAergic and glutamatergic inputs in regulating the activity of the gonadotrophin-releasing hormone (GnRH) neurons at the time of the preovulatory surge remain unclear. We used expansion microscopy to compare the density of GABAergic and glutamatergic synapses on the GnRH neuron cell body and proximal dendrite in dioestrous and pro-oestrous female mice. An evaluation of all synapses immunoreactive for synaptophysin revealed that the highest density of inputs to rostral preoptic area GnRH neurons occurred within the first 45 µm of the primary dendrite (approximately 0.19 synapses µm-1 ) with relatively few synapses on the GnRH neuron soma or beyond 45 µm of the dendrite (0.05-0.08 synapses µm-1 ). Triple immunofluorescence labelling demonstrated a predominance of glutamatergic signalling with twice as many vesicular glutamate transporter 2 synapses detected compared to vesicular GABA transporter. Co-labelling with the GABAA receptor scaffold protein gephyrin and the glutamate receptor postsynaptic density marker Homer1 confirmed these observations, as well as the different spatial distribution of GABA and glutamate inputs along the dendrite. Quantitative assessments revealed no differences in synaptophysin, GABA or glutamate synapses at the proximal dendrite and soma of GnRH neurons between dioestrous and pro-oestrous mice. Taken together, these studies demonstrate that the GnRH neuron receives twice as many glutamatergic synapses compared to GABAergic synapses and that these inputs preferentially target the first 45 µm of the GnRH neuron proximal dendrite. These inputs appear to be structurally stable before the onset of pro-oestrous GnRH surge.

Randomized Controlled Trial of Neurokinin 3 Receptor Antagonist Fezolinetant for Treatment of Polycystic Ovary Syndrome

CONTEXT

Polycystic ovary syndrome (PCOS), a highly prevalent endocrine disorder characterized by hyperandrogenism, is the leading cause of anovulatory infertility.

OBJECTIVE

This proof-of-concept study evaluated clinical efficacy and safety of the neurokinin 3 (NK3) receptor antagonist fezolinetant in PCOS.

METHODS

This was a phase 2a, randomized, double-blind, placebo-controlled, multicenter study (EudraCT 2014-004409-34). The study was conducted at 5 European clinical centers. Women with PCOS participated in the study. Interventions included fezolinetant 60 or 180 mg/day or placebo for 12 weeks. The primary efficacy end point was change in total testosterone. Gonadotropins, ovarian hormones, safety and tolerability were also assessed.

RESULTS

Seventy-three women were randomly assigned, and 64 participants completed the study. Adjusted mean (SE) changes in total testosterone from baseline to week 12 for fezolinetant 180 and 60 mg/day were -0.80 (0.13) and -0.39 (0.12) nmol/L vs -0.05 (0.10) nmol/L with placebo (P < .001 and P < .05, respectively). Adjusted mean (SE) changes from baseline in luteinizing hormone (LH) for fezolinetant 180 and 60 mg/d were -10.17 (1.28) and -8.21 (1.18) vs -3.16 (1.04) IU/L with placebo (P < .001 and P = .002); corresponding changes in follicle-stimulating hormone (FSH) were -1.46 (0.32) and -0.92 (0.30) vs -0.57 (0.26) IU/L (P = .03 and P = .38), underpinning a dose-dependent decrease in the LH-to-FSH ratio vs placebo (P < .001). Circulating levels of progesterone and estradiol did not change significantly vs placebo (P > .10). Fezolinetant was well tolerated.

CONCLUSION

Fezolinetant had a sustained effect to suppress hyperandrogenism and reduce the LH-to-FSH ratio in women with PCOS.

Fezolinetant in the treatment of vasomotor symptoms associated with menopause

Introduction: Although international clinical practice guidelines recognize a continued role for menopausal hormone therapy (HT), particularly for symptomatic women <60 years of age or within 10 years of menopause, safety and tolerability concerns have discouraged HT use due to potential links with a perceived increased risk of hormone-dependent cancers, and an established risk of stroke and venous thromboembolism. There is therefore a need for safe, effective non-hormonal therapy for relief of menopausal vasomotor symptoms (VMS).Areas covered: This narrative review summarizes the dataset accrued for fezolinetant, a neurokinin-3 receptor (NK3R) antagonist in clinical development for menopause-associated VMS.Expert opinion: Altered signaling in neuroendocrine circuits at menopause leads to VMS wherein NK3R activity plays a key role to modulate the thermoregulatory center in a manner conducive to triggering the 'hot flash' response. Thus, a new generation of NK3R antagonists has entered clinical development to specifically target the mechanistic basis of VMS. Fezolinetant is the most advanced NK3R antagonist in terms of stage of clinical development. Results to date have demonstrated rapid and substantial reduction in VMS frequency and severity and associated improvements in health-related quality of life. NK3R antagonists offer a non-hormonal alternative to HT for the treatment of menopause-related VMS.

Endocrine disrupting chemicals (EDCs) and the neuroendocrine system: Beyond estrogen, androgen, and thyroid

Hundreds of anthropogenic chemicals occupy our bodies, a situation that threatens the health of present and future generations. This chapter focuses on endocrine disrupting compounds (EDCs), both naturally occurring and man-made, that affect the neuroendocrine system to adversely impact health, with an emphasis on reproductive and metabolic pathways. The neuroendocrine system is highly sexually dimorphic and essential for maintaining homeostasis and appropriately responding to the environment. Comprising both neural and endocrine components, the neuroendocrine system is hormone sensitive throughout life and touches every organ system in the body. The integrative nature of the neuroendocrine system means that EDCs can have multi-system effects. Additionally, because gonadal hormones are essential for the sex-specific organization of numerous neuroendocrine pathways, endocrine disruption of this programming can lead to permanent deficits. Included in this review is a brief history of the neuroendocrine disruption field and a thorough discussion of the most common and less well understood neuroendocrine disruption modes of action. Also provided are extensive examples of how EDCs are likely contributing to neuroendocrine disorders such as obesity, and evidence that they have the potential for multi-generational effects.

Whole Transcriptome Analysis: Implication to Estrous Cycle Regulation

Simple Summary

The databases of mRNA and non-coding-RNAs (miRNA, circRNA, lncRNA) in the ovary of Xinong Sannen goat were reported in this study. The differential expression of mRNA and non-coding RNAs were analyzed, and the comprehensive analysis of the four databases provided RNA networks that regulate estrous cycle, which is essential to improve reproduction.

Abstract

Estrous cycle is one of the placental mammal characteristics after sexual maturity, including estrus stage (ES) and diestrus stage (DS). Estrous cycle is important in female physiology and its disorder may lead to diseases, such as polycystic ovary syndrome, ovarian carcinoma, anxiety, and epilepsy. In the latest years, effects of non-coding RNAs and messenger RNA (mRNA) on estrous cycle have started to arouse much concern, however, a whole transcriptome analysis among non-coding RNAs and mRNA has not been reported. Here, we report a whole transcriptome analysis of goat ovary in estrus and diestrus periods. Estrus synchronization was conducted to induce the estrus phase and on day 32, the goats shifted into the diestrus stage. The ovary RNA of estrus and diestrus stages was respectively collected to perform RNA-sequencing. Then, the circular RNA (circRNA), microRNA (miRNA), long non-coding RNA (lncRNA), and mRNA databases of goat ovary were acquired, and the differential expressions between estrus and diestrus stages were screened to construct circRNA-miRNA-mRNA/lncRNA and lncRNA-miRNA/mRNA networks, thus providing potential pathways that are involved in the regulation of estrous cycle. Differentially expressed mRNAs, such as MMP9, TIMP1, 3BHSD, and PTGIS, and differentially expressed miRNAs that play key roles in the regulation of estrous cycle, such as miR-21-3p, miR-202-3p, and miR-223-3p, were extracted from the network. Our data provided the miRNA, circRNA, lncRNA, and mRNA databases of goat ovary and each differentially expressed profile between ES and DS. Networks among differentially expressed miRNAs, circRNAs, lncRNAs, and mRNAs were constructed to provide valuable resources for the study of estrous cycle and related diseases.

Daily and Estral Regulation of RFRP-3 Neurons in the Female Mice

Female reproductive success relies on proper integration of circadian- and ovarian- signals to the hypothalamic-pituitary-gonadal axis in order to synchronize the preovulatory LH surge at the end of the ovarian follicular stage with the onset of the main active period. In this study, we used a combination of neuroanatomical and electrophysiological approaches to assess whether the hypothalamic neurons expressing Arg-Phe amide-related peptide (RFRP-3), a gonadotropin inhibitory peptide, exhibit daily and estrous stage dependent variations in female mice. Furthermore, we investigated whether arginine vasopressin (AVP), a circadian peptide produced by the suprachiamatic nucleus regulates RFRP-3 neurons. The number of c-Fos–positive RFRP-3 immunoreactive neurons is significantly reduced at the day-to-night transition with no difference between diestrus and proestrus. Contrastingly, RFRP neuron firing rate is higher in proestrus as compared to diestrus, independently of the time of the day. AVP immunoreactive fibers contact RFRP neurons with the highest density observed during the late afternoon of diestrus and proestrus. Application of AVP increases RFRP neurons firing in the afternoon (ZT6-10) of diestrus, but not at the same time point of proestrus, indicating that AVP signaling on RFRP neurons may depend on circulating ovarian steroids. Together, these studies show that RFRP neurons integrate both daily and estrogenic signals, which downstream may help to properly time the preovulatory LH surge.

Transcriptomic Data Analyses Reveal That Sow Fertility-Related lincRNA NORFA Is Essential for the Normal States and Functions of Granulosa Cells

NORFA, the first lincRNA associated with sow fertility, has been shown to control granulosa cell (GC) functions and follicular atresia. However, the underlying mechanism is not fully understood. In this study, RNA-seq was performed and we noticed that inhibition of NORFA led to dramatic transcriptomic alterations in porcine GCs. A total of 1,272 differentially expressed transcripts were identified, including 1167 DEmRNAs and 105 DEmiRNAs. Furthermore, protein-protein interaction, gene-pathway function, and TF-miRNA-mRNA regulatory networks were established and yielded four regulatory modules with multiple hub genes, such as AR, ATG5, BAK1, CENPE, NR5A1, NFIX, WNT5B, ssc-miR-27b, and ssc-miR-126. Functional assessment showed that these hub DEGs were mainly enriched in TGF-β, PI3K-Akt, FoxO, Wnt, MAPK, and ubiquitin pathways that are essential for GC states (apoptosis and proliferation) and functions (hormone secretion). In vitro, we also found that knockdown of NORFA in porcine GCs significantly induced cell apoptosis, impaired cell viability, and suppressed 17β-estradiol (E2) synthesis. Notably, four candidate genes for sow reproductive traits (INHBA, NCOA1, TGFβ-1, and TGFBR2) were also identified as potential targets of NORFA. These findings present a panoramic view of the transcriptome in NORFA-reduced GCs, highlighting that NORFA, a candidate lincRNA for sow fertility, is crucial for the normal states and functions of GCs.

Neurobiology of puberty and its disorders

Puberty, which in humans is considered to include both gonadarche and adrenarche, is the period of becoming capable of reproducing sexually and is recognized by maturation of the gonads and development of secondary sex characteristics. Gonadarche referring to growth and maturation of the gonads is fundamental to puberty since it encompasses increased gonadal steroid secretion and initiation of gametogenesis resulting from enhanced pituitary gonadotropin secretion, triggered in turn by robust pulsatile GnRH release from the hypothalamus. This chapter reviews the development of GnRH pulsatility from before birth until the onset of puberty. In humans, GnRH pulse generation is restrained during childhood and juvenile development. This prepubertal hiatus in hypothalamic activity is considered to result from a neurobiological brake imposed upon the GnRH pulse generator resident in the infundibular nucleus. Reactivation of the GnRH pulse generator initiates pubertal development. Current understanding of the genetics and physiology of the brake will be discussed, as will hypotheses proposed to account for timing the resurgence in pulsatile GnRH and initiation of puberty. The chapter ends with a discussion of disorders associated with precocious or delayed puberty with a focus on those with etiologies attributed to aberrant GnRH neuron anatomy or function. A pediatric approach to patients with pubertal disorders is provided and contemporary treatments for both precocious and delayed puberty outlined.