Gonadotropin-releasing Hormone Pulse Frequency Research Articles

SAT375 Impact of Flutamide on Wake vs. Sleep LH Pulse Frequency in PCOS: An Interim Analysis

Abstract Disclosure: C.K. Matingou: None. S. Kim: None. M. Gilrain: None. C.M. Burt Solorzano: None. C.R. McCartney: None. Polycystic ovary syndrome (PCOS) is characterized by hyperandrogenism and ovulatory dysfunction. PCOS is also associated with luteinizing hormone (LH) excess, in part related to persistently high gonadotropin-releasing hormone (GnRH) pulse frequency. Furthermore, late pubertal girls with obesity and hyperandrogenemia did not exhibit sleep-associated decreases in LH (GnRH) pulse frequency when studied during the follicular phase, in contrast to non-hyperandrogenemic controls with or without obesity (JCEM 2014;99:2887-96). We therefore aimed to test two hypotheses: (1) sleep-associated reductions in LH pulse frequency are less pronounced in adult PCOS compared to late-follicular controls; and (2) sleep-associated reductions in LH pulse frequency are normalized in PCOS with 4 weeks of flutamide (androgen-receptor antagonist) pretreatment. To date, we have studied 5 women with PCOS (median age 30 y, BMI 42.6 kg/m2) and 5 ovulatory controls (median age 22 y, BMI 23.2 kg/m2). Subjects underwent two separate 16-hour frequent-blood-sampling studies to characterize pulsatile LH secretion, once after flutamide pretreatment (250 mg BID x 4 weeks) and once after placebo (PBO) pretreatment (BID for 4 weeks). In each study, 1500-2300 h and 2300-0700 h were designated the wake and sleep periods, respectively. The order of flutamide and PBO administration was randomized, and treatment allocation was switched after the first admission per a cross-over design. Controls were studied on cycle days 7-10, while those with PCOS were studied no earlier than cycle day 7. Serum progesterone concentrations were < 1.5 ng/dl for all admissions. With PBO pretreatment, participants with PCOS and controls exhibited the following: wake LH pulse frequency 1.19 (1.08-1.33) (median [interquartile range]) and 1.22 (0.97-1.27) pulses/h, respectively; sleep LH pulse frequency 0.93 (0.78-1.28) and 0.83 (0.78-0.99) pulses/h, respectively; and wake-to-sleep change in LH pulse frequency of -19.4 (-21.9 to +2.9) and -15.5 (-31.8 to -12.0) percent, respectively. For participants with PCOS, pretreatment with flutamide was associated with the following changes compared to PBO: wake LH pulse frequency +0.01 (-0.06 to +0.03) pulses/h; sleep LH pulse frequency +0.06 (+0.01 to +0.07) pulses/h; and wake-to-sleep LH pulse frequency change +5 (+7 to -12) percent. None of these differences were statistically significant by conservative nonparametric testing. We conclude that this interim analysis does not offer any indication that wake- and sleep-associated LH pulse frequencies are different between PCOS and late-follicular controls, nor does it suggest clear differences in wake-to-sleep changes in late-follicular LH pulse frequency between groups. Furthermore, this analysis does not seem to offer any indication that flutamide alone alters wake- and/or sleep-associated LH pulse frequencies in PCOS. Presentation Date: Saturday, June 17, 2023

P-691 Does serum Kisspeptin levels discriminate between fertile and infertile women with polycystic ovary syndrome?

Abstract Study question Does serum Kisspeptin (KP) levels discriminate between fertile and infertile women with polycystic ovary syndrome (PCOS)? Summary answer Serum KP levels can be used as a potential discriminatory biomarker for infertility in women with PCOS. What is known already PCOS is the most common cause of anovulatory infertility and not fully elucidated pathology. A persistent rapid gonadotropin-releasing hormone (GnRH) pulse frequency in patients with PCOS exist throughout ovulatory cycle. KP is a neuropeptide that increases GnRH pulsatile release during ovulation. Therefore, KP may have a key role as a central regulator of fertility in PCOS patients. Although, recent studies showed that the KP concentration is higher in PCOS patients, the evidence is limited as to whether serum KP levels determine infertility in PCOS. Study design, size, duration This was a single center prospective cohort study conducted at Goztepe Prof. Dr. Suleyman Yalcin City Hospital Affiliated to Istanbul Medeniyet University, Istanbul, Turkey between January 2023 to February 2023. Our study enrolled 30 fertile and 30 infertile women with PCOS, who were aged between 18 and 45 years. PCOS was defined according to the criteria of the Rotterdam ESHRE- ASRM sponsored consensus group (2004). Participants/materials, setting, methods Venous blood samples from the participants were obtained after fasting and between 8 a.m. and 10 a.m. on days 2-5 of the menstrual cycle. Samples were thawed, and a human KISS1 (Kisspeptin 1) ELISA kit (Elabscience, USA,lot no:E-EL-H5618) was applied to measure KP serum concentrations. Patient characteristics and KP concentrations were compared among the two groups. Statistical analysis was performed by Mann-Whitney, Spearman correlations, and linear regression analysis. A p-value <0.05 was considered significant. Main results and the role of chance The mean age of the patients was 27.57±5.39 years in the fertile PCOS group and 26.80± 4.85 years in the infertile PCOS group (p = 0.63). There was no significant difference among the groups in terms of body mass index (BMI), duration of infertility, serum FSH, LH, LH-to-FSH ratio, E2, antimullerian hormone (AMH), TSH, prolactin, 17OHP, total testosterone, SHBG, HbA1c, HOMA-IR, neutrophil–lymphocyte ratio levels and antral follicle count (AFC). DHEA-S was significantly higher in the infertile PCOS group (306.73±94.869 mcg/ dL), compared to the fertile PCOS group (258.08±84.29 mcg/ dL, p = 0.037). The mean KP level was significantly higher in the infertile PCOS group (444.80±136.61 ng/ mL), compared to the fertile PCOS group (333.02±131.10 ng/ mL, p = 0.001). The KP level was positively correlated with AFC, AMH, and total testosterone levels (R = 0.495, R = 0.548, R = 0.362, p < 0.05, respectively) in the infertile PCOS group. Furthermore, ROC analysis showed that the optimal cut-point value was found to be 285.59. When this cut-off value of serum KP levels was taken, the sensitivity was 0.96 and the specificity was 0.50. Linear regression analysis revealed that AMH was positively associated with KP levels (p = 0.022). Limitations, reasons for caution Due to the limited number of women with available samples, we were not able to analyze KP serum levels according to specific PCOS phenotypes Wider implications of the findings Serum KP levels are higher in infertile women with PCOS compared to fertile women with PCOS. Infertility caused by PCOS can be predicted by serum KP levels. In the future identification, KP in PCOS may be applied to develop potential therapeutic agents. Trial registration number Not applicable

Clomiphene citrate therapy for testosterone deficiency: a proposed clinical care pathway.

Several testosterone (T) therapy options are currently available, including oral, intranasal, transdermal (gel, patches), intramuscular, and subcutaneous agents. The practice guidelines of some professional societies, including the American Urological Association and the European Association of Urology but not all international societies,1,2 suggest treating with aromatase inhibitors or selective estrogen receptor modulators for men with infertility. However, selective estrogen receptor modulators (ie, clomiphene citrate [CC]) may be a reasonable alternative for men experiencing low T with infertility or a wish to maintain their fertility.3 In clinical practice, CC—a nonsteroidal triphenylethylene derivative distantly related to diethylstilbestrol and a selective estrogen receptor modulator—is also used as an effective treatment for men with low T to improve T levels and T deficiency symptoms. CC is an oral agent that acts centrally. CC is a mixture of enclomiphene (62%), which is a trans isomer with pure antiestrogen effect, and zuclomiphene (38%), which is a cis isomer that has a mixed action with a predominant estrogen receptor agonistic property. It selectively binds to estrogen receptors primarily in the hypothalamus to produce a partial estrogen agonist effect resulting in an estrogenic negative feedback inhibition, thus increasing the hypothalamic gonadotropin-releasing hormone pulse frequency and, as a result, elevating luteinizing hormone (LH) secretion to stimulate the gonads to increase sexual hormones—for men, the Leydig cells to raise T levels.4 In vitro data have also suggested that CC has a pituitary site of action where it causes an increase in the gonadotropin response to gonadotropin-releasing hormone.5

The enigma of the gonadotropin-releasing hormone pulse frequency governing individual secretion of luteinizing hormone and follicle-stimulating hormone

Luteinizing hormone and follicle-stimulating hormone are the two gonadotropic pituitary hormones stimulated by one hypothalamic gonadotropin-releasing hormone (GnRH) in a pulsatile way. Under several experimental conditions, it appears that a low pulse frequency promotes follicle-stimulating hormone secretion, pointing to an elegant mechanism by which, under governance of one stimulating hormone, the responses of two separate hormones can be individualized. Several experimental and fundamental studies have indicated the underlying mechanisms at the level of gene expression and post receptor events. In this article, an additional explanation is hypothetically put forward on the basis of dynamic and kinetic differences between both hormones in response to GnRH, with a key role of their difference in serum half-life combined with some GnRH-related desensitization features. Although experimentally demonstrated, under clinical conditions its effect remains obscure, likely because of overwhelming hormonal gonadal feedback.

Hypothalamic kisspeptin neurons as potential mediators of estradiol negative and positive feedback

Gonadal steroid feedback regulates the brain’s patterned secretion of gonadotropin-releasing hormone (GnRH). Negative feedback, which occurs in males and during the majority of the female cycle, modulates the amplitude and frequency of GnRH pulses. Positive feedback occurs in females when high estradiol induces a surge pattern of GnRH release. These two forms of feedback and their corresponding patterns of GnRH secretion are thought to be mediated by kisspeptin-expressing neurons in two hypothalamic areas: the arcuate nucleus and the anteroventral periventricular area. In this review, we present evidence for this theory and remaining questions to be addressed.

Neuroendocrine Determinants of Polycystic Ovary Syndrome.

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women and a major cause of anovulatory infertility. A diagnosis of PCOS is established based the presence of two out of three clinical symptoms, which are criteria accepted by the ESHRE/ASRM (European Society of Human Reproduction and Embryology/American Society for Reproductive Medicine). Gonadotropin-releasing hormone (GnRH) is responsible for the release of luteinizing hormone, and follicle stimulating hormone from the pituitary and contributes a leading role in controlling reproductive function in humans. The goal of this review is to present the current knowledge on neuroendocrine determinations of PCOS. The role of such neurohormones as GnRH, and neuropeptides kisspeptin, neurokinin B, phoenixin-14, and galanin is discussed in this aspect. Additionally, different neurotransmitters (gamma-aminobutyric acid (GABA), glutamate, serotonin, dopamine, and acetylcholine) can also be involved in neuroendocrine etiopathogenesis of PCOS. Studies have shown a persistent rapid GnRH pulse frequency in women with PCOS present during the whole ovulatory cycle. Other studies have proved that patients with PCOS are characterized by higher serum kisspeptin levels. The observations of elevated serum kisspeptin levels in PCOS correspond with the hypothesis that overactivity in the kisspeptin system is responsible for hypothalamic-pituitary-gonadal axis overactivity. In turn, this causes menstrual disorders, hyperandrogenemia and hyperandrogenism. Moreover, abnormal regulation of Neurokinin B (NKB) is also suspected of contributing to PCOS development, while NKB antagonists are used in the treatment of PCOS leading to reduction in Luteinizing hormone (LH) concentration and total testosterone concentration. GnRH secretion is regulated not only by kisspeptin and neurokinin B, but also by other neurohormones, such as phoenixin-14, galanin, and Glucagon-like peptide-1 (GLP-1), that have favorable effects in counteracting the progress of PCOS. A similar process is associated with the neurotransmitters such as GABA, glutamate, serotonin, dopamine, and acetylcholine, as well as the opioid system, which may interfere with secretion of GnRH, and therefore, influence the development and severity of symptoms in PCOS patients. Additional studies are required to explain entire, real mechanisms responsible for PCOS neuroendocrine background.

Deletion of Gαq/11 or Gαs Proteins in Gonadotropes Differentially Affects Gonadotropin Production and Secretion in Mice.

Gonadotropin-releasing hormone (GnRH) regulates gonadal function via its stimulatory effects on gonadotropin production by pituitary gonadotrope cells. GnRH is released from the hypothalamus in pulses and GnRH pulse frequency differentially regulates follicle-stimulating hormone (FSH) and luteinizing hormone (LH) synthesis and secretion. The GnRH receptor (GnRHR) is a G protein-coupled receptor that canonically activates Gα q/11-dependent signaling on ligand binding. However, the receptor can also couple to Gα s and in vitro data suggest that toggling between different G proteins may contribute to GnRH pulse frequency decoding. For example, as we show here, knockdown of Gα s impairs GnRH-stimulated FSH synthesis at low- but not high-pulse frequency in a model gonadotrope-derived cell line. We next used a Cre-lox conditional knockout approach to interrogate the relative roles of Gα q/11 and Gα s proteins in gonadotrope function in mice. Gonadotrope-specific Gα q/11 knockouts exhibit hypogonadotropic hypogonadism and infertility, akin to the phenotypes seen in GnRH- or GnRHR-deficient mice. In contrast, under standard conditions, gonadotrope-specific Gα s knockouts produce gonadotropins at normal levels and are fertile. However, the LH surge amplitude is blunted in Gα s knockout females and postgonadectomy increases in FSH and LH are reduced both in males and females. These data suggest that GnRH may signal principally via Gα q/11 to stimulate gonadotropin production, but that Gα s plays important roles in gonadotrope function in vivo when GnRH secretion is enhanced.

GnRH pulse frequency and irregularity play a role in male aging.

Gonadotropin-releasing hormone (GnRH) has a role in hypothalamic control of aging, but the underlying patterns and relationship with downstream reproductive hormones are still unclear. Here we report that hypothalamic GnRH pulse frequency and irregularity increase before GnRH pulse amplitude slowly decreases during aging. GnRH is inhibited by nuclear factor (NF)-κB, and GnRH pulses were controlled by oscillations in the transcriptional activity of NF-κB. Exposure to testosterone under pro-inflammatory conditions stimulated both NF-κB oscillations and GnRH pulses. While castration of middle-aged mice induced short-term anti-aging effects, preventing elevation of luteinizing hormone (LH) levels after castration led to long-term anti-aging effects and lifespan extension, indicating that high-frequency GnRH pulses and high-magnitude LH levels coordinately mediate aging. Reprogramming the endogenous GnRH pulses of middle-aged male mice via an optogenetic approach revealed that increasing GnRH pulses frequency causes LH excess and aging acceleration, while lowering the frequency of and stabilizing GnRH pulses can slow down aging. In conclusion, GnRH pulses are important for aging in male mice.

A Clinician’s Guide to Functional Hypothalamic Amenorrhea

Patients and clinicians alike want to know if stress causes infertility. Stress could impair with reproductive function by a variety of mechanisms, including compromise of ovarian function, spermatogenesis, fertilization, endometrial development, implantation, and placentation. Herein we focus on the pathogenesis and treatment of stress-induced anovulation, which is often termed functional hypothalamic amenorrhea (FHA), with the objective of summarizing the actual knowledge as a clinical guide. FHA is a reversible form of anovulation due to slowing of gonadotropin-releasing hormone pulse frequency that results in insufficient pituitary secretion of gonadotropins to support full folliculogenesis. Importantly, FHA heralds a constellation of neuroendocrine alterations with health concomitants. The activity of the hypothalamic-pituitary-adrenal axis is increased in women with FHA and this observation supports the notion that stress is the cause. The extent of reproductive suppression relates to individual endocrinological and physiological sensitivity to stressors, both metabolic and psychogenic, and chronicity.

Clinical Implications of Polycystic Ovary Syndrome in Adolescents

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy, affecting as many as 5% to 20% of women of reproductive age, depending on the diagnostic criteria applied. Features of PCOS include physiologic anovulation, hyperandrogenism, elevated luteinizing hormone, and increased gonadotropin-releasing hormone pulse frequency, which often manifest physically as acne and hirsutism. The clinical presentation of PCOS often mimics normal pubertal physiologic development, which may delay diagnosis and treatment of the condition in adolescent girls. A diagnosis of PCOS has life-long implications and is associated with increased risk for infertility, obesity, Type 2 diabetes, endometrial hyperplasia, uterine carcinoma, metabolic disorder, and cardiovascular disease. In this article, we provide an overview of clinical presentation, diagnostic criteria, health consequences, and current evidence-based clinical guidelines for the appropriate diagnosis and management of PCOS in adolescents.

Multiple failures in the lutenising hormone surge generating system in GABAB1KO female mice.

Female mice lacking GABAB receptors, GABAB1KO, show disrupted oestrous cycles, reduced pregnancies and increased hypothalamic Gnrh1 mRNA expression, whereas anteroventral periventricular/periventricular preoptic nucleus (AVPV/PeN) Kiss1 mRNA was not affected. In the present study, we characterise the important components of the gonadotrophic preovulatory surge, aiming to unravel the origin of this reproductive impairment. In GABAB1KO and wild-type (WT) females, we determined: (i) hypothalamic oestrogen receptor (ER)α and β and aromatase mRNA and protein expression; (ii) ovulation index and oestrus serum follicle-stimulating hormone (FSH) and pituitary Gnrh1r expression; (iii) in ovariectomised-oestradiol valerate-treated mice, we evaluated ex vivo hypothalamic gonadotrophin-releasing hormone (GnRH) pulsatility in the presence/absence of kisspeptin (Kiss-10, constant or pulsatile) and oestradiol (constant); and (iv) in ovariectomised-oestradiol silastic capsule-treated mice (proestrous-like environment), we evaluated morning and evening kisspeptin neurone activation (c-Fos+) and serum luteinising homrone (LH). In the medial basal hypothalamus of oestrus GABAB1KOs, aromatase and ERα mRNA and protein were increased, whereas ERβ was decreased. In GABAB1KOs, the ovulation index was decreased together with decreased first oestrus serum FSH and increased pituitary Gnrh1r mRNA. Under constant Kiss-10 stimulation, hypothalamic GnRH pulse frequency did not vary, although GnRH mass/pulse was increased in GABAB1KOs. In WTs, pulsatile Kiss-10 together with constant oestradiol significantly increased GnRH pulsatility, whereas, in GABAB1KOs, oestradiol alone increased GnRH pulsatility and this was reversed by pulsatile Kiss-10 addition. In GABAB1KOs AVPV/PeN kisspeptin neurones were similarly activated (c-Fos+) in the morning and evening, whereas WTs showed the expected, marked evening stimulation. LH correlated with activated kisspeptin cells in WT mice, whereas GABAB1KO mice showed high, similar LH levels both in the morning and evening. Taken together, all of these alterations point to impairment in the trigger of the preovulatory GnRH surge that entails the reproductive alterations described.

Regulation of GnRH pulsatility in ewes.

Early work in ewes provided a wealth of information on the physiological regulation of pulsatile gonadotropin-releasing hormone (GnRH) secretion by internal and external inputs. Identification of the neural systems involved, however, was limited by the lack of information on neural mechanisms underlying generation of GnRH pulses. Over the last decade, considerable evidence supported the hypothesis that a group of neurons in the arcuate nucleus that contain kisspeptin, neurokinin B and dynorphin (KNDy neurons) are responsible for synchronizing secretion of GnRH during each pulse in ewes. In this review, we describe our current understanding of the neural systems mediating the actions of ovarian steroids and three external inputs on GnRH pulsatility in light of the hypothesis that KNDy neurons play a key role in GnRH pulse generation. In breeding season adults, estradiol (E2) and progesterone decrease GnRH pulse amplitude and frequency, respectively, by actions on KNDy neurons, with E2 decreasing kisspeptin and progesterone increasing dynorphin release onto GnRH neurons. In pre-pubertal lambs, E2 inhibits GnRH pulse frequency by decreasing kisspeptin and increasing dynorphin release, actions that wane as the lamb matures to allow increased pulsatile GnRH secretion at puberty. Less is known about mediators of undernutrition and stress, although some evidence implicates kisspeptin and dynorphin, respectively, in the inhibition of GnRH pulse frequency by these factors. During the anoestrus, inhibitory photoperiod acting via melatonin activates A15 dopaminergic neurons that innervate KNDy neurons; E2 increases dopamine release from these neurons to inhibit KNDy neurons and suppress the frequency of kisspeptin and GnRH release.

The Role of Kiss1 Neurons As Integrators of Endocrine, Metabolic, and Environmental Factors in the Hypothalamic-Pituitary-Gonadal Axis.

Kisspeptin–GPR54 signaling in the hypothalamus is required for reproduction and fertility in mammals. Kiss1 neurons are key regulators of gonadotropin-releasing hormone (GnRH) release and modulation of the hypothalamic–pituitary–gonadal (HPG) axis. Arcuate Kiss1 neurons project to GnRH nerve terminals in the median eminence, orchestrating the pulsatile secretion of luteinizing hormone (LH) through the intricate interaction between GnRH pulse frequency and the pituitary gonadotrophs. Arcuate Kiss1 neurons, also known as KNDy neurons in rodents and ruminants because of their co-expression of neurokinin B and dynorphin represent an ideal hub to receive afferent inputs from other brain regions in response to physiological and environmental changes, which can regulate the HPG axis. This review will focus on studies performed primarily in rodent and ruminant species to explore potential afferent inputs to Kiss1 neurons with emphasis on the arcuate region but also considering the rostral periventricular region of the third ventricle (RP3V). Specifically, we will discuss how these inputs can be modulated by hormonal, metabolic, and environmental factors to control gonadotropin secretion and fertility. We also summarize the methods and techniques that can be used to study functional inputs into Kiss1 neurons.

Roles of Hypothalamic-Pituitary-Adrenal Axis and Hypothalamus-Pituitary-Ovary Axis in the Abnormal Endocrine Functions in Patients with Polycystic Ovary Syndrome.

Polycystic ovary syndrome(PCOS) is a common reproductive endocrine disease in women of childbearing age. While it can be affected by a variety of factors,its pathophysiology remains unclear. Its clinical features mainly include anovulation,hyperandrogenism,and hyperinsulinemia,which are closely related with abnormal neuroendocrine system. Hypothalamic-pituitary-gonadal axis(HPG) plays a crucial regulatory role in various life activities in mammals. In particular,hypothalamic-pituitary-adrenal(HPA) axis and hypothalamus-pituitary-ovary(HPO) axis can be abnormal in PCOS patients. The corresponding abnormalities include abnormal gonadotropin releasing hormone pulse frequency,increased luteinizing hormone/follicle-stimulating hormone ratio,and excessive excretion of adrenal and ovarian androgens. Meanwhile,insulin and leptin also play key roles in endocrine dysfunction in PCOS patients. This article systematically reviews the role of HPA axis and HPO axis in the neuroendocrine dysfunction in PCOS patients.

Pyrethroid Insecticide Cypermethrin Accelerates Pubertal Onset in Male Mice via Disrupting Hypothalamic-Pituitary-Gonadal Axis.

Pyrethroids, a class of insecticides that are widely used worldwide, have been identified as endocrine-disrupting chemicals (EDCs). Our recent epidemiological study reported on an association of increased pyrethroids exposure with elevated gonadotropins levels and earlier pubertal development in Chinese boys. In this study, we further investigated the effects of cypermethrin (CP), one of the most ubiquitous pyrethroid insecticides, on hypothalamic-pituitary-gonadal (HPG) axis and pubertal onset in male animal models. Early postnatal exposure to CP at environmentally relevant doses (0.5, 5, and 50 μg/kg CP) significantly accelerated the age of puberty onset in male mice. Administration of CP induced a dose-dependent increase in serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone in male mice. CP did not affect gonadotropin-releasing hormone (GnRH) gene expression in the hypothalamus, but CP at higher concentrations stimulated GnRH pulse frequency. CP could induce the secretion of LH and FSH, as well as the expression of gonadotropin subunit genes [chorionic gonadotropin α (CGα), LHβ, and FSHβ] in pituitary gonadotropes. CP stimulated testosterone production and the expression of steroidogenesis-related genes [steroidogenic acute regulatory (StAR) and Cytochrome p 450, family 11, subfamily A, polypeptide 1 (CYP11A1)] in testicular Leydig cells. The interference with hypothalamic sodium channels as well as calcium channels in pituitary gonadotropes and testicular Leydig cells was responsible for CP-induced HPG axis maturation. Our findings established in animal models provide further evidence for the biological plausibility of pyrethroid exposure as a potentially environmental contributor to earlier puberty in males.

Modeling and high-throughput experimental data uncover the mechanisms underlying Fshb gene sensitivity to gonadotropin-releasing hormone pulse frequency

Neuroendocrine control of reproduction by brain-secreted pulses of gonadotropin-releasing hormone (GnRH) represents a longstanding puzzle about extracellular signal decoding mechanisms. GnRH regulates the pituitary gonadotropin's follicle-stimulating hormone (FSH) and luteinizing hormone (LH), both of which are heterodimers specified by unique β subunits (FSHβ/LHβ). Contrary to Lhb, Fshb gene induction has a preference for low-frequency GnRH pulses. To clarify the underlying regulatory mechanisms, we developed three biologically anchored mathematical models: 1) parallel activation of Fshb inhibitory factors (e.g. inhibin α and VGF nerve growth factor-inducible), 2) activation of a signaling component with a refractory period (e.g. G protein), and 3) inactivation of a factor needed for Fshb induction (e.g. growth differentiation factor 9). Simulations with all three models recapitulated the Fshb expression levels obtained in pituitary gonadotrope cells perifused with varying GnRH pulse frequencies. Notably, simulations altering average concentration, pulse duration, and pulse frequency revealed that the apparent frequency-dependent pattern of Fshb expression in model 1 actually resulted from variations in average GnRH concentration. In contrast, models 2 and 3 showed "true" pulse frequency sensing. To resolve which components of this GnRH signal induce Fshb, we developed a high-throughput parallel experimental system. We analyzed over 4,000 samples in experiments with varying near-physiological GnRH concentrations and pulse patterns. Whereas Egr1 and Fos genes responded only to variations in average GnRH concentration, Fshb levels were sensitive to both average concentration and true pulse frequency. These results provide a foundation for understanding the role of multiple regulatory factors in modulating Fshb gene activity.

Characterization of Gonadotrope Secretoproteome Identifies Neurosecretory Protein VGF-derived Peptide Suppression of Follicle-stimulating Hormone Gene Expression

Reproductive function is controlled by the pulsatile release of hypothalamic gonadotropin-releasing hormone (GnRH), which regulates the expression of the gonadotropins luteinizing hormone and FSH in pituitary gonadotropes. Paradoxically, Fshb gene expression is maximally induced at lower frequency GnRH pulses, which provide a very low average concentration of GnRH stimulation. We studied the role of secreted factors in modulating gonadotropin gene expression. Inhibition of secretion specifically disrupted gonadotropin subunit gene regulation but left early gene induction intact. We characterized the gonadotrope secretoproteome and global mRNA expression at baseline and after Gαs knockdown, which has been found to increase Fshb gene expression (1). We identified 1077 secreted proteins or peptides, 19 of which showed mRNA regulation by GnRH or/and Gαs knockdown. Among several novel secreted factors implicated in Fshb gene regulation, we focused on the neurosecretory protein VGF. Vgf mRNA, whose gene has been implicated in fertility (2), exhibited high induction by GnRH and depended on Gαs. In contrast with Fshb induction, Vgf induction occurred preferentially at high GnRH pulse frequency. We hypothesized that a VGF-derived peptide might regulate Fshb gene induction. siRNA knockdown or extracellular immunoneutralization of VGF augmented Fshb mRNA induction by GnRH. GnRH stimulated the secretion of the VGF-derived peptide NERP1. NERP1 caused a concentration-dependent decrease in Fshb gene induction. These findings implicate a VGF-derived peptide in selective regulation of the Fshb gene. Our results support the concept that signaling specificity from the cell membrane GnRH receptor to the nuclear Fshb gene involves integration of intracellular signaling and exosignaling regulatory motifs.

Growth Differentiation Factor 9 (GDF9) Forms an Incoherent Feed-forward Loop Modulating Follicle-stimulating Hormone β-Subunit (FSHβ) Gene Expression

Gonadotropin-releasing hormone (GnRH) is secreted in brief pulses from the hypothalamus and regulates follicle-stimulating hormone β-subunit (FSHβ) gene expression in pituitary gonadotropes in a frequency-sensitive manner. The mechanisms underlying its preferential and paradoxical induction of FSHβ by low frequency GnRH pulses are incompletely understood. Here, we identify growth differentiation factor 9 (GDF9) as a GnRH-suppressed autocrine inducer of FSHβ gene expression. GDF9 gene transcription and expression were preferentially decreased by high frequency GnRH pulses. GnRH regulation of GDF9 was concentration-dependent and involved ERK and PKA. GDF9 knockdown or immunoneutralization reduced FSHβ mRNA expression. Conversely, exogenous GDF9 induced FSHβ expression in immortalized gonadotropes and in mouse primary pituitary cells. GDF9 exposure increased FSH secretion in rat primary pituitary cells. GDF9 induced Smad2/3 phosphorylation, which was impeded by ALK5 knockdown and by activin receptor-like kinase (ALK) receptor inhibitor SB-505124, which also suppressed FSHβ expression. Smad2/3 knockdown indicated that FSHβ induction by GDF9 involved Smad2 and Smad3. FSHβ mRNA induction by GDF9 and GnRH was synergistic. We hypothesized that GDF9 contributes to a regulatory loop that tunes the GnRH frequency-response characteristics of the FSHβ gene. To test this, we determined the effects of GDF9 knockdown on FSHβ induction at different GnRH pulse frequencies using a parallel perifusion system. Reduction of GDF9 shifted the characteristic pattern of GnRH pulse frequency sensitivity. These results identify GDF9 as contributing to an incoherent feed-forward loop, comprising both intracellular and secreted components, that regulates FSHβ expression in response to activation of cell surface GnRH receptors.

Pulsatile Hormonal Signaling to Extracellular Signal-regulated Kinase: EXPLORING SYSTEM SENSITIVITY TO GONADOTROPIN-RELEASING HORMONE PULSE FREQUENCY AND WIDTH

Gonadotropin-releasing hormone (GnRH) is secreted in brief pulses that stimulate synthesis and secretion of pituitary gonadotropin hormones and thereby mediate control of reproduction. It acts via G-protein-coupled receptors to stimulate effectors, including ERK. Information could be encoded in GnRH pulse frequency, width, amplitude, or other features of pulse shape, but the relative importance of these features is unknown. Here we examine this using automated fluorescence microscopy and mathematical modeling, focusing on ERK signaling. The simplest scenario is one in which the system is linear, and response dynamics are relatively fast (compared with the signal dynamics). In this case integrated system output (ERK activation or ERK-driven transcription) will be roughly proportional to integrated input, but we find that this is not the case. Notably, we find that relatively slow response kinetics lead to ERK activity beyond the GnRH pulse, and this reduces sensitivity to pulse width. More generally, we show that the slowing of response kinetics through the signaling cascade creates a system that is robust to pulse width. We, therefore, show how various levels of response kinetics synergize to dictate system sensitivity to different features of pulsatile hormone input. We reveal the mathematical and biochemical basis of a dynamic GnRH signaling system that is robust to changes in pulse amplitude and width but is sensitive to changes in receptor occupancy and frequency, precisely the features that are tightly regulated and exploited to exert physiological control in vivo.

Early Neuroendocrine Disruption in Hypothalamus and Hippocampus: Developmental Effects Including Female Sexual Maturation and Implications for Endocrine Disrupting Chemical Screening

The timing of puberty has been mainly studied in females for several reasons, including the possible evaluation of a precise timer (i.e. menarcheal age) and concerns with respect to the high prevalence of precocity in females as opposed to males. Human evidence of altered female pubertal timing after exposure to endocrine disrupting chemicals (EDCs) is equivocal. Among the limiting factors, most studies evaluate exposure to single EDCs at the time of puberty and hardly assess the impact of lifelong exposure to mixtures of EDCs. Some rodent and ovine studies indicate a possible role of foetal and neonatal exposure to EDCs, in accordance with the concept of an early origin of health and disease. Such effects possibly involve neuroendocrine mechanisms because the hypothalamus is a site where homeostasis of reproduction, as well as control of energy balance, is programmed and regulated. In our previous studies, pulsatile gonadotrophin-releasing hormone (GnRH) secretion control via oestrogen, glutamate and aryl hydrocarbon receptors was shown to be involved in the mechanism of sexual precocity after early postnatal exposure to the insecticide dichlorodiphenyltrichloroethane. Very recently, we have shown that neonatal exposure to the potent synthetic oestrogen diethylstilbestrol (DES) is followed by early or delayed puberty depending on the dose, with consistent changes in developmental increase of GnRH pulse frequency. Moreover, DES results in reduced leptin stimulation of GnRH secretion in vitro, an effect that is additive with prenatal food restriction. Thus, using puberty as an endpoint of the effects of EDC, it appears necessary to consider pre- and perinatal exposure to low doses and to pay attention to the other conditions of prenatal life, such as energy availability, keeping in mind the possibility that puberty could not only be advanced, but also delayed through neuroendocrine mechanisms.