Estrogen regulates KiSS1 gene expression through estrogen receptor alpha and SP protein complexes

The role of LH in follicle development: from physiology to new clinical implications

The process of follicle development is closely regulated by two pituitary gonadotropins: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Traditionally, folliculogenesis is considered to be divided into a gonadotropin-independent phase and a gonadotropin-dependent phase. Despite this, recent evidence has demonstrated that functional LH receptors are expressed even in smaller follicles during the phase considered to be gonadotropin independent. Luteinizing hormone promotes androgen synthesis within ovarian follicles and seems to significantly contribute to accelerate and enhance the transition from the primordial to the antral stage of folliculogenesis. Thus, LH could play a fundamental role in determining the number of recruitable antral follicles, with a direct impact on the cyclic recruitment of follicles and reproductive potential. Common clinical conditions of pituitary suppression such as hypogonadotropic hypogonadism, other than pregnancy and combined oral contraceptive use, have been considered to analyze the effect of lower serum LH levels on the functional ovarian reserve. This review outlines recent findings on the mechanisms of human follicle development, based on human and animal models, with a direct focus on possible new clinical applications.

The Hypothalamus and Pituitary Gland Regulate Reproduction and Are Involved in the Development of Polycystic Ovary Syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is a complex condition with unclear mechanisms, posing a challenge for prevention and treatment of PCOS. The role of the hypothalamus and pituitary gland in regulating female reproduction is critical. Abnormalities in the hypothalamus and pituitary can impair reproductive function. It is important to study hypothalamic and pituitary changes in patients with PCOS.

SUMMARY

This article reviews articles on the hypothalamus and PCOS with the goal of summarizing what abnormalities of the hypothalamic-pituitary-ovarian axis are present in patients with PCOS and to clarify the pathogenesis of PCOS. We find that the mechanisms by which the hypothalamus and pituitary regulate reproduction in girls are complex and are associated with altered sex hormone levels, obesity, and insulin resistance. Different animal models of PCOS are characterized by different alterations in the hypothalamus and pituitary and respond differently to different treatments, which correspond to the complex pathogenesis of patients with PCOS.

KEY MESSAGES

Arcuate nucleus (ARC) is associated with luteinizing hormone (LH) surges. Suprachiasmatic nucleus, ARC, and RP3V are associated with LH surges. Animal models of PCOS have different characteristics.

Cellular and molecular mechanisms of action of ovarian steroid hormones II: Regulation of sexual behavior in female rodents

Female sexual behaviors in rodents (lordosis and appetitive or "proceptive" behaviors) are induced through a genomic mechanism by the sequential actions of estradiol (E2) and progesterone (P), or E2 and testosterone (T) at their respective receptors. However, non-steroidal agents, such as gonadotropin-releasing hormone (GnRH), Prostaglandin E2 (PGE2), noradrenaline, dopamine, oxytocin, α-melanocyte stimulating hormone, nitric oxide, leptin, apelin, and others, facilitate different aspects of female sexual behavior through their cellular and intracellular effects at the membrane and genomic levels in ovariectomized rats primed with E2. These neurotransmitters often act as intermediaries of E2 and P (or T). The classical model of steroid hormone action through intracellular receptor binding has been complemented by an alternative scenario wherein the steroid functions as a transcription factor after binding the receptor protein to DNA. Another possible mechanism occurs through the activation of second messenger systems (cyclic AMP, cyclic GMP, calcium), which subsequently initiate phosphorylation events via diverse kinase systems (protein kinases A, G, or C). These kinases target the progesterone receptor (PR) or associated effector proteins that connect the PR to the trans-activation machinery. This may also happen to the androgen receptor (AR). In addition, other cellular mechanisms could be involved since the chemical structure of these non-steroidal agents causes a change in their lipophobicity that prevents them from penetrating the cell and exerting direct transcriptional effects; however, they can exert effects on different components of the cell membrane activating a cross-talk between the cell membrane and the regulation of the transcriptional mechanisms.

Kisspeptin regulates airway hyperresponsiveness and remodeling in a mouse model of asthma

Asthma is a multifactorial disease of origin characterized by airway hyperresponsiveness (AHR) and airway remodeling. Several pieces of evidence from other pathologies suggest that Kisspeptins (Kp) regulate cell proliferation, migration, and invasion, mechanisms that are highly relevant to asthma. Our recent in vitro studies show Kp-10 (active peptide of Kp), via its receptor, KISS1R, inhibits human airway smooth muscle cell proliferation. Here, we hypothesize a crucial role for Kp-10 in regulating AHR and airway remodeling in vivo. Utilizing C57BL/6J mice, we assessed the effect of chronic intranasal Kp-10 exposure on mixed allergen (MA)-induced mouse model of asthma. MA-challenged mice showed significant deterioration of lung function compared to those exposed to vehicle (DPBS); Kp-10 treatment significantly improved the MA-altered lung functions. Mice treated with Kp-10 alone did not show any notable changes in lung functions. MA-exposed mice showed a significant reduction in KISS1R expression as compared to vehicle alone. MA-challenged mice showed significant alterations in immune cell infiltration in the airways and remodeling changes. Proinflammatory cytokines were significantly increased upon MA exposure, an effect abrogated by Kp-10 treatment. Furthermore, biochemical and histological studies showed Kp-10 exposure significantly reduced MA-induced smooth muscle mass and soluble collagen in the lung. Overall, our findings highlight the effect of chronic Kp-10 exposure in regulating MA-induced AHR and remodeling. © 2023 The Pathological Society of Great Britain and Ireland.

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

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

Estrogen Receptor α Inactivation in 2 Sisters: Different Phenotypic Severities for the Same Pathogenic Variant

CONTEXT

Estrogens play an essential role in reproduction. Their action is mediated by nuclear α and β receptors (ER) and by membrane receptors. Only 3 females and 2 males, from 3 families, with a loss of ERα function have been reported to date.

OBJECTIVE

We describe here a new family, in which 2 sisters display endocrine and ovarian defects of different severities despite carrying the same homozygous rare variant of ESR1.

METHODS

A 36-year-old woman from a consanguineous Jordanian family presented with primary amenorrhea and no breast development, with high plasma levels of 17β-estradiol (E2), follicle-stimulating hormone and luteinizing hormone, and enlarged multifollicular ovaries, strongly suggesting estrogen resistance. Her 18-year-old sister did not enter puberty and had moderately high levels of E2, high plasma gonadotropin levels, and normal ovaries.

RESULTS

Genetic analysis identified a homozygous variant of ESR1 leading to the replacement of a highly conserved glutamic acid with a valine (ERα-E385V). The transient expression of ERα-E385V in HEK293A and MDA-MB231 cells revealed highly impaired ERE-dependent transcriptional activation by E2. The analysis of the KISS1 promoter activity revealed that the E385V substitution induced a ligand independent activation of ERα. Immunofluorescence analysis showed that less ERα-E385V than ERα-WT was translocated into the nucleus in the presence of E2.

CONCLUSION

These 2 new cases are remarkable given the difference in the severity of their ovarian and hormonal phenotypes. This phenotypic discrepancy may be due to a mechanism partially compensating for the ERα loss of function.

Chlorobisphenol A activated kisspeptin/GPR54-GnRH neuroendocrine signals through ERα and GPER pathway in neuronal GT1-7 cells

Chlorobisphenol A (Cl_xBPA) is a kind of novel estrogenic compounds. The present study aims to investigate the effects of three Cl_xBPA compounds on the kisspeptin/G protein-coupled receptor 54 (GPR54, also named KissR1)-gonadotropin-releasing hormone (GnRH) (KGG) system in neuronal GT1-7 cells with mechanistic insights by estrogen receptor signaling pathways. The study demonstrated that low-concentration Cl_xBPA induced the cell proliferation, promoted GnRH secretion, upregulated the expression of KGG neuroendocrine signal-related proteins (KissR1, GnRH1 and kisspeptin) and genes including Kiss1, GnRH1, KissR1, luteinizing hormone receptor (Lhr) and follicle-stimulating hormone receptor (Fshr) in GT1-7 cells. Additionally, Cl_xBPA activated nuclear estrogen receptor alpha (ERα) and member estrogen receptor G protein-coupled estrogen receptor (GPER)-regulated phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) and extracellular signal-regulated kinase (Erk1/2) signaling pathways. Pretreatment of GT1-7 cells with GPER inhibitor G15 and ERα inhibitor ICI reduced the expression of KissR1, GnRH1 and kisspeptin proteins, attenuated mRNA levels of Kiss1, GnRH1, KissR1, Fshr and Lhr genes, and decreased Cl_xBPA-induced GT1-7 cell proliferation. The results suggested that Cl_xBPA activated the KGG neuroendocrine signals and induced the proliferation of GT1-7 cells via ERα and GPER signaling pathways. This study provides a new perspective to explore the neuroendocrine toxicity mechanism of Cl_xBPA. CAPSULE: Cl_xBPA activated KGG neuroendocrine signaling pathway via ERα and GPER and induced the proliferation of GT1-7 cells.

Kisspeptin neurons as an integration center of reproductive regulation: Observation of reproductive function based on a new concept of reproductive regulatory nervous system

Background

Regulation of the reproductive system has been explained by the actions and feedback of gonadotropin releasing hormone‐luteinizing hormone/follicle stimulating hormone (GnRH‐LH/FSH) ‐sex steroids; however, the discovery of kisspeptin neurons and a kisspeptin‐GnRH‐LH/FSH axis has prompted this regulation to be reviewed.

Methods

We investigated changes in kisspeptin neurons and associated changes in the hypothalamic‐pituitary‐gonadal (HPG) axis under various situations and experimental conditions using histochemical methods.

Main findings (Results)

Kisspeptin neurons play an important role in receiving and integrating information from internal and external environmental factors and communicating it to the conventional HPG axis.

Conclusion

The recently described Kisspeptin‐GnRH‐LH/FSH‐gonad system regulates reproductive function via mechanisms that until recently were not completely understood.

Hypothalamic reproductive neurons communicate through signal transduction to control reproduction

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

The chemical environmental pollutants BPA and BPS induce alterations of the proteomic profile of different phenotypes of human breast cancer cells: A proposed interactome

Breast cancer is one of the most common malignancies and the second leading cause of death in women. Despite efforts for its early detection, its worldwide incidence continues to increase. Thus, identification of risk factors for its development and new targets for its therapy are of vital importance. Environmental pollutants derived from human activity have been associated with predisposition to the development of cancer. Bisphenol A (BPA) is an endocrine disruptor compound (EDC) widely used in the manufacture of polycarbonates, and it has affinity for the estrogen receptor (ER). Scientific evidence has proposed an association between increased incidence of breast cancer and BPA exposure at lower doses. Among worldwide concerns with BPA exposure, different industries proceeded to replace BPA with analogs such as bisphenol S (BPS), which is now employed in products labelled as BPA-free. Nevertheless, recent studies exhibit that its exposure results in altered mammary gland development and morphogenesis; and promotes breast cancer cell proliferation. Of note, most of the effects of both BPA and BPS have been performed in estrogen-dependent breast cancer models. However, gaps in knowledge still exist on the roles and mechanisms that both compounds, specifically BPS, may play in cancer initiation and development in hormone-dependent and other types of breast cancer. Thus, the aim of the present study was to deepen the understanding of biological targets modulated by these ubiquitous pollutants in different breast cancer cell lines, representing two scenarios of this pathology: hormone-dependent and hormone-independent breast cancer. Results point out that both compounds induced proliferation in ER positive cells, not showing this effect in the ER-negative breast cancer cells. Different targets modified at the proteomic level in both breast cancer scenarios were also identified. Stem cell markers (eg. CD44) and invasion proteins (eg. MMP-14) were importantly increased by BPA and BPS in ER-positive breast cancer cells. In contrast, growth factors and associated receptors such as EGFR and TGF-β were induced by BPS in the ER-negative breast cancer cells; both pollutants induced an increase of vascular endothelial growth factor (VEGF) protein secretion. This finding suggests that the use of BPS must be considered with more caution than BPA, since it can act independently of the presence of the hormonal receptor. These findings show new evidence that BPA and BPS exposure can contribute to breast cancer development and progression. Our results suggest that both BPA and BPS must be considered equally as outstanding risk factors for this pathology.

MiR-199-3p modulates the onset of puberty in rodents probably by regulating the expression of Kiss1 via the p38 MAPK pathway

The Kiss1 gene plays an indispensable role in modulating the onset of puberty and fertility in mammals. Although an increasing number of genetic and environmental factors that influence reproduction through Kiss1 have been identified, the function of microRNAs, a class of posttranscriptional regulators, in regulating Kiss1 expression remains poorly understood. This study aimed at investigating the mechanism by which Kiss1 expression is regulated by microRNAs. A simplified miRNome screen by a dual-fluorescence reporter system based on Kiss1 was performed to identify microRNAs that affect the expression of Kiss1. The expression patterns of the identified microRNAs during the period of murine sexual development were investigated, and only miR-199-3p was studied further. Aided by bioinformatics algorithms, miR-199-3p was demonstrated to be a repressor of Kiss1 expression, as it blocked the expression of Kiss1 through the p38 MAPK pathway by simultaneously inhibiting several targets in both GT1-7 cells and primary hypothalamic neurons. Both the inhibition of the p38 MAPK pathway by the intracerebroventricular administration of chemical agents in rats and the ectopic expression of miR-199-3p by lentivirus injection in the hypothalamus in mice delayed puberty onset and gonad development. Our results presented a novel regulatory mechanism of puberty onset which the sustained downregulation of miR-199-3p might gradually release the inhibition of the p38 MAPK/Fos/CREB/Kiss1 pathway during puberty development.

Evolution of the regulatory mechanisms for the hypothalamic-pituitary-gonadal axis in vertebrates-hypothesis from a comparative view

Reproduction is regulated by the hypothalamic-pituitary-gonadal (HPG) axis in vertebrates. In addition to wealth of knowledge in mammals, recent studies in non-mammalian species, especially teleosts, have provided evidence that some of the components in the HPG axis are conserved in bony vertebrates. On the other hand, from the comparisons of the recent accumulating knowledge between mammals and teleosts, unique characteristics of the regulatory system in each group have been unveiled. A hypophysiotropic neurotransmitter/hormone, gonadotropin releasing hormone (GnRH), pituitary gonadotropins, follicle stimulating hormone (FSH), and luteinizing hormone (LH) were proven to be common important elements of the HPG axis in teleosts and mammals, although the roles of each vary. Conversely, there are some modulators of GnRH or gonadotropins that are not common to all vertebrates. In this review, I will introduce the mechanism for HPG axis regulation in mammals and teleosts, and describe their evolution from a hypothetical common ancestor.

Effects of N-carbamylglutamate and L-arginine on gonadotrophin-releasing hormone (GnRH) gene expression and secretion in GT1-7 cells

Recent studies have shown that N-carbamylglutamate (NCG) and arginine (ARG) supplementation improves reproductive performance in livestock. The objectives of the present study were to evaluate the effects of NCG and ARG on GT1-7 cell gonadotrophin-releasing hormone (GnRH) secretion, gene expression and cell proliferation. GT1-7 cells were treated in vitro with different concentrations of NCG (0-1.0mM) or ARG (0-4.0mM) in serum-free medium for 12 or 24h. For GnRH secretion and cell proliferation, GT1-7 cells were more sensitive to NCG than ARG. NCG treatment after 12h increased cell numbers and inhibited GnRH secretion in a dose-dependent manner (P<0.05), although there was no significant effect of NCG on these parameters after 24h culture. ARG treatment decreased GnRH secretion after 24h (P<0.05), whereas it had no effect after 12h. GT1-7 cells express GnRH, Kiss-1 metastasis-suppressor (Kiss1), G-protein coupled receptor 54 (GPR54), neuronal nitric oxide synthase (nNOS) and estrogen receptor α (ERα) genes. High concentrations of NCG (1.0mM) and ARG (4.0mM) inhibited (P<0.05) GnRH and nNOS mRNA abundance in GT1-7 cells. ARG treatment decreased Kiss1 and increased ERα mRNA abundance. Thus, high concentrations of NCG (1.0mM) and ARG (4.0mM) may act both directly and indirectly to regulate GnRH neuron function by downregulating genes related to GnRH synthesis and secretion to slow GnRH production while stimulating GT1-7 cell proliferation.

Animal models of polycystic ovary syndrome: A review of hormone-induced rodent models focused on hypothalamus-pituitary-ovary axis and neuropeptides

BACKGROUND

Polycystic ovary syndrome (PCOS) is a common endocrine disorder among women of reproductive age and a major cause of infertility; however, the pathophysiology of this syndrome is not fully understood. This can be addressed using appropriate animal models of PCOS. In this review, we describe rodent models of hormone-induced PCOS that focus on the perturbation of the hypothalamic-pituitary-ovary (HPO) axis and abnormalities in neuropeptide levels.

METHODS

Comparison of rodent models of hormone-induced PCOS.

MAIN FINDINGS

The main method used to generate rodent models of PCOS was subcutaneous injection or implantation of androgens, estrogens, antiprogestin, or aromatase inhibitor. Androgens were administered to animals pre- or postnatally. Alterations in the levels of kisspeptin and related molecules have been reported in these models.

CONCLUSION

The most appropriate model for the research objective and hypothesis should be established. Dysregulation of the HPO axis followed by elevated serum luteinizing hormone levels, hyperandrogenism, and metabolic disturbance contribute to the complex etiology of PCOS. These phenotypes of the human disease are recapitulated in hormone-induced PCOS models. Thus, evidence from animal models can help to clarify the pathophysiology of PCOS.

The 17β-estradiol induced upregulation of the adhesion G-protein coupled receptor (ADGRG7) is modulated by ESRα and SP1 complex

The physiological role and the regulation of ADGRG7 are not yet elucidated. The functional involvement of this receptor was linked with different physiological process such as reduced body weight, gastrointestinal function and recently, a gene variant in ADGRG7 was observed in patients with adolescent idiopathic scoliosis. Here, we identify the ADGRG7 as an estrogen-responsive gene under the regulation of estrogen receptor ERα in scoliotic osteoblasts and other cells lines. We found that ADGRG7 expression was upregulated in response to estrogen (E2) in adolescent idiopathic scoliosis (AIS) cells. ADGRG7 promoter studies indicate the presence of an ERα response half site in close vicinity of a specificity protein 1 (SP1) binding site. Mutation of the SP1 site completely abrogated the response to E2, indicating its essential requirement. ChIP confirmed the binding of SP1 and ERα to the ADGRG7 promoter. Our results identify the ADGRG7 gene as an estrogen-responsive gene under the control of ERα and SP1 tethered actions, suggesting a possible role of estrogens in the regulation of ADGRG7 This article has an associated First Person interview with the first author of the paper.

ESR2 Is Essential for Gonadotropin-Induced Kiss1 Expression in Granulosa Cells

Hypothalamic expression of Kiss1 plays an essential role in the onset of puberty, gonadal development, and ovulation. Estrogens regulate the expression of Kiss1 in the hypothalamus through estrogen receptor-α. Kiss1 is also expressed in the ovary, where its expression correlates with the onset of puberty and progression of the estrous cycle. To date, estrogen regulation of Kiss1 expression in the ovary has not been investigated. We recently observed that gonadotropin-induced Kiss1 expression was absent in Esr2-null rat ovaries even though Esr1 was present. Wild-type granulosa cells abundantly expressed Kiss1 and oocytes expressed the Kiss1 receptor. We characterized estrogen receptor-β (ESR2) regulation of Kiss1 expression in granulosa cells by identifying granulosa cell-specific transcript variants and potential regulatory regions. The Kiss1 promoter, an upstream enhancer, and a downstream enhancer all possessed conserved estrogen response elements (EREs) and showed active histone marks in gonadotropin-stimulated granulosa cells. The transcriptionally active Kiss1 promoter, as well as the enhancers, also revealed enrichment for ESR2 binding. Furthermore, activity of a Kiss1 promoter construct was induced after overexpression of ESR2 and was blocked upon mutation of an ERE within the promoter. Finally, pregnant mare serum gonadotropin and human chorionic gonadotropin administration induced phosphorylation of ESR2 and upregulated the AP-1 proteins FOSL2 and JUNB in granulosa cells. Activated MAPK ERK2 was associated with the ESR2 phosphorylation in granulosa cells, and AP-1 factors could synergistically activate the Kiss1 promoter activity. These gonadotropin-induced changes paralleled Kiss1 expression in granulosa cells. We conclude that gonadotropin-stimulated Kiss1 expression in granulosa cells is dependent on both the activation of ESR2 and the upregulation of AP-1.

A dual fluorescence reporter system for high throughput screening of effectors of Kiss1 gene expression

Kisspeptin is a multifunctional peptide encoded by the Kiss1 gene that plays critical roles in mammalian puberty onset modulation and fertility maintenance in the hypothalamus. Understanding how Kiss1 expression is regulated is essential for elucidating the molecular mechanisms responsible for these reproductive events. In this study, we constructed an in vitro dual fluorescence reporter system to facilitate high throughput screening of effectors influencing the expression of Kiss1. In GT1‐7 cells, an enhanced GFP gene was placed under the control of the Kiss1 gene regulatory elements and translated together with this gene. A tdTomato gene cassette was simultaneously introduced into the same cell for normalization of the fluorescence signal. After treatment with different effectors, the cells were analyzed by flow cytometry. We first tested the efficacy of the system using canonical regulators and then carried out high throughput functional screening to identify chemical compounds that can regulate Kiss1 gene expression. Of 22 tested compounds from natural sources, 13 significantly affected Kiss1 expression. Verification by western blot and quantitative reverse transcription PCR (qRT‐PCR) assays and structural analysis identified two chalcone compounds as possible regulators of Kiss1 gene expression. This system may be suitable for gene functional analysis, drug screening and pharmaceutical studies.

Gamma-aminobutyric acidA receptor agonist, muscimol, increases KiSS-1 gene expression in hypothalamic cell models

Purpose

Accumulating evidence indicates that hypothalamic kisspeptin plays a pivotal role in the regulation of the hypothalamic-pituitary-gonadal (HPG) axis. In this study, the direct action of the gamma-aminobutyric acid (GABA)_A receptor agonist on kisspeptin-expressing neuronal cells was examined.

Methods

A hypothalamic cell model of rat hypothalamic cell line R8 (rHypoE8) cells and primary cultures of neuronal cells from fetal rat brains were stimulated with a potent and selective GABA_A receptor agonist, muscimol, to determine the expression of the KiSS-1 gene.

Results

Stimulation of the rHypoE8 cells with muscimol significantly increased the level of KiSS-1 messenger (m)RNA expression. The ability of muscimol to increase the level of KiSS-1 mRNA also was observed in the primary cultures of the neuronal cells from the fetal rat brains. The muscimol-induced increase in KiSS-1 mRNA expression was completely inhibited in the presence of the GABA_A receptor antagonist. Although muscimol increased the expression of KiSS-1, the natural compound, GABA, failed to induce the expression of KiSS-1 in the rHypoE8 cells. Muscimol did not modulate gonadotropin-releasing hormone expression in either the rHypoE8 cells or the primary cultures of the fetal rat brains.

Conclusions

This study's observations suggest that the activation of the GABA_A receptor modulates the HPG axis by increasing kisspeptin expression in the hypothalamic neurons.

Elevation of GPRC5A expression in colorectal cancer promotes tumor progression through VNN-1 induced oxidative stress

The clearance of oxidative stress compounds is critical for the protection of the organism from malignancy, but how this key physiological process is regulated is not fully understood. Here, we found that the expression of GPRC5A, a well-characterized tumor suppressor in lung cancer, was elevated in colorectal cancer tissues in patients. In both cancer cell lines and a colitis-associated cancer model in mice, we found that GPRC5A deficiency reduced cell proliferation and increased cell apoptosis as well as inhibited tumorigenesis in vivo. Through RNA-Seq transcriptome analysis, we identified oxidative stress associated pathways were dysregulated. Moreover, in GPRC5A deficient cells and mouse tissues, the oxidative agents were reduced partially due to increased glutathione (GSH) level. Mechanistically, GPRC5A regulates NF-κB mediated Vanin-1 expression which is the predominant enzyme for cysteamine generation. Administration of cystamine (the disulfide form of cysteamine) in GPRC5A deficient cell lines inhibited γ-GCS activity, leading to reduction of GSH level and increase of cell growth. Taken together, our studies suggest that GPRC5a is a potential biomarker for colon cancer and promotes tumorigenesis through stimulation of Vanin-1 expression and oxidative stress in colitis associated cancer. This study revealed an unexpected oncogenic role of GPRC5A in colorectal cancer suggesting there are complicated functional and molecular mechanism differences of this gene in distinct tissues.

Evaluation of Immortalized AVPV- and Arcuate-Specific Neuronal Kisspeptin Cell Lines to Elucidate Potential Mechanisms of Estrogen Responsiveness and Temporal Gene Expression in Females

In females, ovarian estradiol modulates kisspeptin (Kiss-1) synthesis to act as an obligatory regulator of downstream gonadotropin release in vivo, via stimulation of GnRH neurons. Changes in the ovarian condition are relayed to the neuroendocrine hypothalamus via two sexually dimorphic Kiss-1 populations, located in the anteroventral periventricular (AVPV) and arcuate nuclei, conveying estradiol-positive and -negative feedback, respectively. To elucidate how differential responsiveness to estradiol is mediated in these populations, we generated two kisspeptin-secreting cell lines from an adult kiss1-green fluorescent protein (GFP) female mouse. These lines recapitulate in vivo responsiveness to estradiol, with KTaV-3 (AVPV) cells demonstrating significantly increased kiss1 expression under high physiological estradiol exposure, whereas KTaR-1 (arcuate) cells exhibit kiss1 suppression after lower estradiol exposure. Baseline expression of estrogen receptor-α (esr1) differs significantly between KTaV-3 and KTaR-1 cells, with KTaR-1 cells demonstrating higher basal expression of esr1. Estradiol stimulation of kiss1 expression in KTaV-3 cells is modulated in a dose-dependent manner up to 25.0 pM, with less responsiveness observed at higher doses (>50.0 pM). In contrast, KTaR-1 kiss1 attenuates at lower estradiol doses (2.0-5.0 pM), returning to baseline levels at 25.0 pM and greater. Furthermore, the expression of the core clock genes bmal1 and per2 show normal rhythms in KTaV-3 cells, regardless of estradiol treatment. Conversely, KTaR-1 antiphasic transcription of bmal1 and per2 is phase delayed by low estradiol treatment. Strikingly, estradiol induces circadian rhythms of kiss1 expression only in KTaV-3 cells. Further exploration into estradiol responsiveness will reveal mechanisms responsible for the differential expression pattern demonstrated in vivo between these cell types.

Subcutaneous infusion of kisspeptin-54 stimulates gonadotrophin release in women and the response correlates with basal oestradiol levels

BACKGROUND AND OBJECTIVE

Kisspeptin stimulates hypothalamic GnRH secretion resulting in gonadotrophin release and has potential as a future therapeutic. Chronic subcutaneous infusion of kisspeptin via a pump (similar to an insulin pump) may provide an alternative route of administration in the future. We investigated for the first time in humans, the gonadotrophin response to subcutaneous (SC) infusions of kisspeptin-54 in healthy women. Women are markedly more responsive to exogenous kisspeptin in the late follicular phase preovulation when oestradiol levels are naturally high. Therefore, we further investigated whether there was a correlation between baseline oestradiol levels and LH response to kisspeptin.

DESIGN AND PATIENTS

A prospective, single-blinded placebo-controlled study. Healthy women (n = 4) received an 8-h SC infusion of kisspeptin-54 0·1, 0·3 or 1·0 nmol/kg/h or saline in the early follicular phase of 4 separate menstrual cycles. Gonadotrophins and oestradiol were measured every 10 min during the infusions.

RESULTS

SC infusion of kisspeptin-54 increased LH and FSH. The LH response to SC infusion of kisspeptin-54 (0·3 and 1·0 nmol/kg/h) positively correlated with baseline oestradiol levels (P < 0·001). Further statistical analyses showed that in the 1·0 nmol/kg/h group, a 100pmol/l rise in baseline oestradiol was associated with a 1·0 IU/l increase in LH.

CONCLUSIONS

Kisspeptin administered via a SC infusion could be a viable future therapeutic route of administration for patients with infertility. Baseline oestradiol levels may be an important determinant of the gonadotrophin response to kisspeptin treatment in women and should be taken into consideration when evaluating gonadotrophin response.

Identification of hypothalamic arcuate nucleus-specific enhancer region of Kiss1 gene in mice

Pulsatile secretion of GnRH plays a pivotal role in follicular development via stimulating tonic gonadotropin secretion in mammals. Kisspeptin neurons, located in the arcuate nucleus (ARC), are considered to be an intrinsic source of the GnRH pulse generator. The present study aimed to determine ARC-specific enhancer(s) of the Kiss1 gene by an in vivo reporter assay. Three green fluorescent protein (GFP) reporter constructs (long, medium length, and short) were generated by insertion of GFP cDNA at the Kiss1 locus. Transgenic female mice bearing the long and medium-length constructs showed apparent GFP signals in kisspeptin-immunoreactive cells in both the ARC and anteroventral periventricular nucleus, in which another population of kisspeptin neurons are located. On the other hand, transgenic mice bearing 5'-truncated short construct showed few GFP signals in the ARC kisspeptin-immunoreactive cells, whereas they showed colocalization of GFP- and kisspeptin-immunoreactivities in the anteroventral periventricular nucleus. In addition, chromatin immunoprecipitation and chromosome conformation capture assays revealed recruitment of unoccupied estrogen receptor-α in the 5'-upstream region and intricate chromatin loop formation between the 5'-upstream and promoter regions of Kiss1 locus in the ARC. Taken together, the present results indicate that 5'-upstream region of Kiss1 locus plays a critical role in Kiss1 gene expression in an ARC-specific manner and that the recruitment of estrogen receptor-α and formation of a chromatin loop between the Kiss1 promoter and the 5' enhancer region may be required for the induction of ARC-specific Kiss1 gene expression. These results suggest that the 5'-upstream region of Kiss1 locus functions as an enhancer for ARC Kiss1 gene expression in mice.

Pubertal development and regulation

Puberty marks the end of childhood and is a period when individuals undergo physiological and psychological changes to achieve sexual maturation and fertility. The hypothalamic-pituitary-gonadal axis controls puberty and reproduction and is tightly regulated by a complex network of excitatory and inhibitory factors. This axis is active in the embryonic and early postnatal stages of life and is subsequently restrained during childhood, and its reactivation culminates in puberty initiation. The mechanisms underlying this reactivation are not completely known. The age of puberty onset varies between individuals and the timing of puberty initiation is associated with several health outcomes in adult life. In this Series paper, we discuss pubertal markers, epidemiological trends of puberty initiation over time, and the mechanisms whereby genetic, metabolic, and other factors control secretion of gonadotropin-releasing hormone to determine initiation of puberty.

Gonadotropin and kisspeptin gene expression, but not GnRH, are impaired in cFOS deficient mice

cFOS is a pleiotropic transcription factor, which binds to the AP1 site in the promoter of target genes. In the pituitary gonadotropes, cFOS mediates induction of FSHβ and GnRH receptor genes. Herein, we analyzed reproductive function in the cFOS-deficient mice to determine its role in vivo. In the pituitary cFOS is necessary for gonadotropin subunit expression, while TSHβ is unaffected. Additionally, cFOS null animals have the same sex-steroid levels, although gametogenesis is impeded. In the brain, cFOS is not necessary for GnRH neuronal migration, axon targeting, cell number, or mRNA levels. Conversely, cFOS nulls, particularly females, have decreased Kiss1 neuron numbers and lower Kiss1 mRNA levels. Collectively, our novel findings suggest that cFOS plays a cell-specific role at multiple levels of the hypothalamic-pituitary-gonadal axis, affecting gonadotropes but not thyrotropes in the pituitary, and kisspeptin neurons but not GnRH neurons in the hypothalamus, thereby contributing to the overall control of reproduction.

Sp1 and the 'hallmarks of cancer'

For many years, transcription factor Sp1 was viewed as a basal transcription factor and relegated to a role in the regulation of so-called housekeeping genes. Identification of Sp1's role in recruiting the general transcription machinery in the absence of a TATA box increased its importance in gene regulation, particularly in light of recent estimates that the majority of mammalian genes lack a TATA box. In this review, we briefly consider the history of Sp1, the founding member of the Sp family of transcription factors. We review the evidence suggesting that Sp1 is highly regulated by post-translational modifications that positively and negatively affect the activity of Sp1 on a wide array of genes. Sp1 is over-expressed in many cancers and is associated with poor prognosis. Targeting Sp1 in cancer treatment has been suggested; however, our review of the literature on the role of Sp1 in the regulation of genes that contribute to the 'hallmarks of cancer' illustrates the extreme complexity of Sp1 functions. Sp1 both activates and suppresses the expression of a number of essential oncogenes and tumor suppressors, as well as genes involved in essential cellular functions, including proliferation, differentiation, the DNA damage response, apoptosis, senescence and angiogenesis. Sp1 is also implicated in inflammation and genomic instability, as well as epigenetic silencing. Given the apparently opposing effects of Sp1, a more complete understanding of the function of Sp1 in cancer is required to validate its potential as a therapeutic target.

Up-regulation of type II collagen gene by 17β-estradiol in articular chondrocytes involves Sp1/3, Sox-9, and estrogen receptor α

The existence of a link between estrogen deprivation and osteoarthritis (OA) in postmenopausal women suggests that 17β-estradiol (17β-E2) may be a modulator of cartilage homeostasis. Here, we demonstrate that 17β-E2 stimulates, via its receptor human estrogen receptor α 66 (hERα66), type II collagen expression in differentiated and dedifferentiated (reflecting the OA phenotype) articular chondrocytes. Transactivation of type II collagen gene (COL2A1) by ligand-independent transactivation domain (AF-1) of hERα66 was mediated by "GC" binding sites of the -266/-63-bp promoter, through physical interactions between ERα, Sp1/Sp3, Sox9, and p300, as demonstrated in chromatin immunoprecipitation (ChIP) and Re-Chromatin Immuno-Precipitation (Re-ChIP) assays in primary and dedifferentiated cells. 17β-E2 and hERα66 increased the DNA-binding activities of Sp1/Sp3 and Sox-9 to both COL2A1 promoter and enhancer regions. Besides, Sp1, Sp3, and Sox-9 small interfering RNAs (siRNAs) prevented hERα66-induced transactivation of COL2A1, suggesting that these factors and their respective cis-regions are required for hERα66-mediated COL2A1 up-regulation. Our results highlight the genomic pathway by which 17β-E2 and hERα66 modulate Sp1/Sp3 heteromer binding activity and simultaneously participate in the recruitment of the essential factors Sox-9 and p300 involved respectively in the chondrocyte-differentiated status and COL2A1 transcriptional activation. These novel findings could therefore be attractive for tissue engineering of cartilage in OA, by the fact that 17β-E2 could promote chondrocyte redifferentiation.

KEY MESSAGES

17β-E2 up-regulates type II collagen gene expression in articular chondrocytes. An ERα66/Sp1/Sp3/Sox-9/p300 protein complex mediates this stimulatory effect. This heteromeric complex interacts and binds to Col2a1 promoter and enhancer in vivo. Our findings highlight a new regulatory mechanism for 17β-E2 action in chondrocytes. 17β-E2 might be an attractive candidate for cartilage engineering applications.

An alternative transcription start site yields estrogen-unresponsive Kiss1 mRNA transcripts in the hypothalamus of prepubertal female rats

The importance of the Kiss1 gene in the control of reproductive development is well documented. However, much less is known about the transcriptional regulation of Kiss1 expression in the hypothalamus. Critical for these studies is an accurate identification of the site(s) where Kiss1 transcription is initiated. Employing 5'-RACE PCR, we detected a transcription start site (TSS1) used by the hypothalamus of rats, mice, nonhuman primates and humans to initiate Kiss1 transcription. In rodents, an exon 1 encoding 5'-untranslated sequences is followed by an alternatively spliced second exon, which encodes 5'-untranslated regions of two different lengths and contains the translation initiation codon (ATG). In nonhuman primates and humans, exon 2 is not alternatively spliced. Surprisingly, in rat mediobasal hypothalamus (MBH), but not preoptic area (POA), an additional TSS (TSS2) located upstream from TSS1 generates an exon 1 longer (377 bp) than the TSS1-derived exon 1 (98 bp). The content of TSS1-derived transcripts increased at puberty in the POA and MBH of female rats. It also increased in the MBH after ovariectomy, and this change was prevented by estrogen. In contrast, no such changes in TSS2-derived transcript abundance were detected. Promoter assays showed that the proximal TSS1 promoter is much more active than the putative TSS2 promoter, and that only the TSS1 promoter is regulated by estrogen. These differences appear to be related to the presence of a TATA box and binding sites for transcription factors activating transcription and interacting with estrogen receptor-α in the TSS1, but not TSS2, promoter.

The Kiss-1/Kiss-1R complex as a negative regulator of cell motility and cancer metastasis (Review)

Metastasis is a complex multistep process that involves the impairment of cell-cell adhesion in the neoplastic epithelium, invasion into adjacent tissues and the dissemination of cancer cells through the lymphatic and haematogenous routes. The inhibition of the metastatic process at an early stage has become a hot topic in cancer research. The Kiss-1 gene, initially described as a suppressor of metastasis in malignant melanoma, encodes the Kiss-1 protein which can be processed to other peptides, e.g., Kisspeptin-10, Kisspeptin-13, Kisspeptin-14 and Kisspeptin-54. These peptides are endogenous ligands of the Kiss‑1 receptor (Kiss-1R), a G protein-coupled receptor (GPR) also known as hOT7T175, AXOR12 or GPR54. The Kiss-1 gene has been suggested as a suppressor of metastasis in a various types of cancer, including gastric cancer, oesophageal carcinoma, pancreatic, ovarian, bladder and prostate cancer, through the regulation of cellular migration and invasion. In the current review, we summarise the current understanding of the role of Kiss‑1 and Kiss‑1R in cancer and cancer metastasis.

Regulation of the two kiss promoters in goldfish (Carassius auratus) by estrogen via different ERα pathways

Kisspeptin stimulates the synthesis and release of gonadotropin via controlling the secretion of gonadotropin releasing hormone in vertebrates. It also mediates the positive or negative feedback regulation of sex steroids on the hypothalamus-gonadotropic axis. In contrast to mammals, two paralogous genes of kisspeptin (kiss1 and kiss2) have been identified in several teleosts, implying the multiplicity of their physiological functions. In the present study, we cloned the promoters of kiss1 and kiss2 genes in goldfish (Carassius auratus), and identified the presence of putative binding sites for estrogen receptors, glucocorticoid receptors, Sp1, AP1, C/EBP and Oct-1. We further demonstrated that the goldfish Kiss neurons co-express the estrogen receptors, with era1 and erb1 in the habenula Kiss1 neurons and era1, era2 and erb1 in the preoptic and hypothalamic Kiss2 neurons. Using transient transfection in HEK293T cells of the two goldfish kiss gene promoters cloned upstream of a luciferase reporter, estrogen (E2, 17β-estradiol) treatment was shown to enhance the promoter activities of the two goldfish kiss genes in the presence of ERα. Deletion analysis of kiss1 promoter indicated that the E2-induced promoter activity was located between position -633 and -317 where no half ERE motifs were found. Point mutation studies on the kiss2 promoter indicated that the E2-stimulated promoter activity was mediated by a half ERE site located at position -57. Results of the present study provide evidence that E2 is capable of exerting positive feedback regulation on the expression of kiss1 and kiss2 in goldfish via ERE-independent or ERE-dependent ERα pathway, respectively.

Mineralocorticoid receptor interaction with SP1 generates a new response element for pathophysiologically relevant gene expression

The mineralocorticoid receptor (MR) is a ligand-induced transcription factor belonging to the steroid receptor family and involved in water-electrolyte homeostasis, blood pressure regulation, inflammation and fibrosis in the renocardiovascular system. The MR shares a common hormone-response-element with the glucocorticoid receptor but nevertheless elicits MR-specific effects including enhanced epidermal growth factor receptor (EGFR) expression via unknown mechanisms. The EGFR is a receptor tyrosine kinase that leads to activation of MAP kinases, but that can also function as a signal transducer for other signaling pathways. In the present study, we mechanistically investigate the interaction between a newly discovered MR- but not glucocorticoid receptor- responsive-element (=MRE1) of the EGFR promoter, specificity protein 1 (SP1) and MR to gain general insights into MR-specificity. Biological relevance of the interaction for EGFR expression and consequently for different signaling pathways in general is demonstrated in human, rat and murine vascular smooth muscle cells and cells of EGFR knockout mice. A genome-wide promoter search for identical binding regions followed by quantitative PCR validation suggests that the identified MR-SP1-MRE1 interaction might be applicable to other genes. Overall, a novel principle of MR-specific gene expression is explored that applies to the pathophysiologically relevant expression of the EGFR and potentially also to other genes.

Circulating kisspeptin and pituitary adenylate cyclase-activating polypeptide (PACAP) do not correlate with gonadotropin serum levels

Kisspeptins are known to be the principle regulators of the hypothalamic-pituitary gonadal (HPG) axis. In addition, the role of pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of pituitary gonadotropins has been elucidated. We measured plasma concentrations of kisspeptin and PACAP and determined whether the levels of these peptides varied in proportion to circulating gonadotropin levels. Plasma luteinizing hormone (LH) levels were higher in postmenopausal women and in patients with premature ovarian failure (POF) and lower in patients with idiopathic hypogonadotropic hypogonadism (IHH) compared with the LH level in normally menstruating women. Similarly, serum follicle-stimulating hormone levels were higher in postmenopausal women and in patients with POF but lower in pregnant women and patients with IHH compared with normally menstruating women. Plasma levels of kisspeptins were significantly higher in pregnant women compared with normally menstruating women. However, no significant differences were observed in postmenopausal women, patients with POF, and patients with IHH. On the other hand, plasma levels of PACAP were significantly lower in pregnant women, patients with POF, and in IHH patients when compared with normally menstruating women. No significant differences were observed in PACAP concentration between postmenopausal women and in normally menstruating women. Our observations suggest that the serum levels of kisspeptins and PACAP did not correlate with variations in serum gonadotropin levels.

Comparative aspects of kisspeptin gene regulation

Kisspeptin plays an important role in the onset of puberty through stimulation of gonadotropin-releasing hormone (GnRH), a master molecule of reproduction. Furthermore, the existence of multiple kisspeptins is evident in most vertebrate species. Therefore, elucidating the regulatory mechanisms of the kisspeptin genes is important to understand the functions of multiple kisspeptin forms in the brain. This review focuses on the comparative aspects of kisspeptin gene regulation with an emphasis on the role of environmental signals including gonadal steroids, photoperiods and metabolic signals. These environmental signals differently regulate the kisspeptin genes distinctively in each species. In addition, photoperiodic regulation of the kisspeptin genes alters during sexual maturational, suggesting interactions between the gonadal hormone pathway and the photoperiod pathway. Further studies of the regulatory mechanisms of kisspeptin genes especially in teleosts which possess multiple kisspeptin/kisspeptin receptor systems will help to understand the precise role of multiple kisspeptin forms in different species.

Model systems for studying kisspeptin signalling: mice and cells

Kisspeptins are a family of overlapping neuropeptides, encoded by the Kiss1 gene, that are required for activation and maintenance of the mammalian reproductive axis. Kisspeptins act within the hypothalamus to stimulate release of gonadotrophic releasing hormone and activation of the pituitary-gonadal axis. Robust model systems are required to dissect the regulatory mechanisms that control Kiss1 neuronal activity and to examine the molecular consequences of kisspeptin signalling. While studies in normal animals have been important in this, transgenic mice with targeted mutations affecting the kisspeptin signalling pathway have played a significant role in extending our understanding of kisspeptin physiology. Knock-out mice recapitulate the reproductive defects associated with mutations in humans and provide an experimentally tractable model system to interrogate regulatory feedback mechanisms. In addition, transgenic mice with cell-specific expression of modulator proteins such as the CRE recombinase or fluorescent reporter proteins such as GFP allow more sophisticated analyses such as cell or gene ablation or electrophysiological profiling. At a less complex level, immortalized cell lines have been useful for studying the role of kisspeptin in cell migration and metastasis and examining the intracellular signalling events associated with kisspeptin signalling.

Structure, synthesis, and phylogeny of kisspeptin and its receptor

The kisspeptin system is considered to be essential for successful mammalian reproduction. In addition to the Kiss1 peptide, Kiss2, the product of kiss2 (the kiss1 paralogue), has also been shown to activate kisspeptin receptor signaling pathways in nonmammalian species. Furthermore, in nonmammalian species, there are two subtypes of receptors, Gpr54-1 (known as GPR54 or Kiss1R in mammals) and Gpr54-2. Although complete understanding of the two kisspeptin-two kisspeptin receptor systems in vertebrates is not so simple, a careful examination of the phylogeny of their genes may provide insights into the functional generality and differences among the kisspeptin systems in different animal phyla. In this chapter, we first discuss the structure of kisspeptin ligands, Kiss1 and Kiss2, and their characteristics as physiologically active peptides. Then, we discuss the evolutionary traits of kiss1 and kiss2 genes and their receptor genes, gpr54-1 and gpr54-2. It appears that each animal species has selected either kiss1 or kiss2 rather randomly, leading us to propose that some of the important characteristics of kisspeptin neurons, such as steroid sensitivity and the anatomical relationship with the hypophysiotropic GnRH1 neurons, may be the keys to understanding the general functions of different kisspeptin neuronal populations throughout vertebrates. Species differences in kiss1/kiss2 may also provide insights into the evolutionary mechanisms of paralogous gene-expressing neuronal systems. Finally, because kisspeptins belong to one of the members of the RFamide peptide families, we discuss the functional divergence of kisspeptins from the other RFamide peptides, which may be explained from phylogenetic viewpoints.

Sex steroid regulation of kisspeptin circuits

Kisspeptin cells appear to be the "missing link," bridging the divide between levels of gonadal steroids and feedback control of gonadotropin-releasing hormone (GnRH) secretion. Kisspeptin neurons are important in the generation of both sex steroid negative and estrogen positive feedback signals to GnRH neurons, the former being involved in the tonic regulation of GnRH secretion in males and females and the latter governing the preovulatory GnRH/luteinizing hormone (LH) surge in females. In rodents, kisspeptin-producing cells populate the anteroventral periventricular nucleus (AVPV) and the arcuate nucleus (ARC), and estrogen regulation of kisspeptin has been extensively studied in these regions. Kisspeptin cells in the ARC appear to receive and forward signals applicable to negative feedback regulation of GnRH. In the female rodent AVPV, kisspeptin cells are important for positive feedback regulation of GnRH and the preovulatory LH surge. In sheep and primates, a rostral population of kisspeptin cells is located in the dorsolateral preoptic area (POA) as well as the ARC. Initial studies showed kisspeptin cells in the latter were involved in both the positive and negative feedback regulation of GnRH. Interestingly, further studies now suggest that kisspeptin cells in the ovine POA may also play an important role in generating estrogen positive feedback. This chapter discusses the current consensus knowledge regarding the interaction between sex steroids and kisspeptin neurons in mammals.

Mitochondria-localized glutamic acid-rich protein (MGARP) gene transcription is regulated by Sp1

Background

Mitochondria-localized glutamic acid-rich protein (MGARP) is a novel mitochondrial transmembrane protein expressed mainly in steroidogenic tissues and in the visual system. Previous studies showed that MGARP functions in hormone biosynthesis and its expression is modulated by the HPG axis.

Methodology/Principal Findings

By bioinformatics, we identified two characteristic GC-rich motifs that are located proximal to the transcription start site (TSS) of MGARP, and each contains two Specificity protein 1 (Sp1) binding elements. We then determined that the −3 kb proximal MGARP promoter is activated in a Sp1-dependent manner using reporter assays and knockdown of Sp1 led to decreased expression of endogenous MGARP messages. We also demonstrated that one of the two GC-rich motifs, GC-Box1, harbors prominent promoter activity mediated by Sp1, and that it requires both GC boxes for full transcriptional activation. These findings suggest a dominant role for these GC boxes and Sp1 in activating the MGARP promoter through a synergistic mechanism. Consistently, the results of an Electrophoretic Mobility Gel Shift Assay (EMSA) and Chromatin Immunoprecipitation (ChIP) confirmed that Sp1 specifically interacts with the GC-rich region. We further found that estrogen receptor α (ERα), a known Sp1 co-activator, could potentiate GC-boxes containing MGARP promoter activity and this effect is mediated by Sp1. Knockdown of Sp1 significantly diminished the MGARP promoter transactivation and the expression of endogenous MGARP mediated by both Sp1 and ERα.

Conclusions/Significance

The present study identified a proximal core sequence in the MGARP promoter that is composed of two enriched Sp1 binding motifs and established Sp1 as one major MGARP transactivator whose functions are synergistic with ERα, providing a novel understanding of the mechanisms of MGARP gene transcriptional regulation.

Adiponectin inhibits KISS1 gene transcription through AMPK and specificity protein-1 in the hypothalamic GT1-7 neurons

Adiponectin secreted from adipose tissues plays a role in the regulation of energy homeostasis, food intake, and reproduction in the hypothalamus. We have previously demonstrated that adiponectin significantly inhibited GNRH secretion from GT1-7 hypothalamic GNRH neuron cells. In this study, we further investigated the effect of adiponectin on hypothalamic KISS1 gene transcription, which is the upstream signal of GNRH. We found that globular adiponectin (gAd) or AICAR, an artificial AMPK activator, decreased KISS1 mRNA transcription and promoter activity. Conversely, inhibition of AMPK by Compound C or AMPKα1-SiRNA augmented KISS1 mRNA transcription and promoter activity. Additionally, gAd and AICAR decreased the translocation of specificity protein-1 (SP1) from cytoplasm to nucleus; however, Compound C and AMPKα1-siRNA played an inverse role. Our experiments in vivo demonstrated that the expression of Kiss1 mRNA was stimulated twofold in the Compound C-treated rats and decreased about 60-70% in gAd- or AICAR-treated rats compared with control group. The numbers of kisspeptin immunopositive neurons in the arcuate nucleus region of Sprague Dawley rats mimicked the same trend seen in Kiss1 mRNA levels in animal groups with different treatments. In conclusion, our results provide the first evidence that adiponectin reduces Kiss1 gene transcription in GT1-7 cells through activation of AMPK and subsequently decreased translocation of SP1.

Epigenetic regulation of Kiss1 gene expression mediating estrogen-positive feedback action in the mouse brain

This study aims to determine the epigenetic mechanism regulating Kiss1 gene expression in the anteroventral periventricular nucleus (AVPV) to understand the mechanism underlying estrogen-positive feedback action on gonadotropin-releasing hormone/gonadotropin surge. We investigated estrogen regulation of the epigenetic status of the mouse AVPV Kiss1 gene locus in comparison with the arcuate nucleus (ARC), in which Kiss1 expression is down-regulated by estrogen. Histone of AVPV Kiss1 promoter region was highly acetylated, and estrogen receptor α was highly recruited at the region by estrogen. In contrast, the histone of ARC Kiss1 promoter region was deacetylated by estrogen. Inhibition of histone deacetylation up-regulated in vitro Kiss1 expression in a hypothalamic non-Kiss1-expressing cell line. Gene conformation analysis indicated that estrogen induced formation of a chromatin loop between Kiss1 promoter and the 3' intergenic region, suggesting that the intergenic region serves to enhance estrogen-dependent Kiss1 expression in the AVPV. This notion was proved, because transgenic reporter mice with a complete Kiss1 locus sequence showed kisspeptin neuron-specific GFP expression in both the AVPV and ARC, but the deletion of the 3' region resulted in greatly reduced GFP expression only in the AVPV. Taken together, these results demonstrate that estrogen induces recruitment of estrogen receptor α and histone acetylation in the Kiss1 promoter region of the AVPV and consequently enhances chromatin loop formation of Kiss1 promoter and Kiss1 gene enhancer, resulting in an increase in AVPV-specific Kiss1 gene expression. These results indicate that epigenetic regulation of the Kiss1 gene is involved in estrogen-positive feedback to generate the gonadotropin-releasing hormone/gonadotropin surge.

Melatonin-dependent timing of seasonal reproduction by the pars tuberalis: pivotal roles for long daylengths and thyroid hormones

Most mammals living at temperate latitudes exhibit marked seasonal variations in reproduction. In long-lived species, it is assumed that timely physiological alternations between a breeding season and a period of sexual rest depend upon the ability of day length (photoperiod) to synchronise an endogenous timing mechanism called the circannual clock. The sheep has been extensively used to characterise the time-measurement mechanisms of seasonal reproduction. Melatonin, secreted only during the night, acts as the endocrine transducer of the photoperiodic message. The present review is concerned with the endocrine mechanisms of seasonal reproduction in sheep and the evidence that long day length and thyroid hormones are mandatory to their proper timing. Recent evidence for a circadian-based molecular mechanism within the pars tuberalis of the pituitary, which ties the short duration melatonin signal reflecting long day length to the hypothalamic increase of triiodothyronine (T3) through a thyroid-stimulating hormone/deiodinase2 paracrine mechanism is presented and evaluated in this context. A parallel is also drawn with the golden hamster, a long-day breeder, aiming to demonstrate that features of seasonality appear to be phylogenetically conserved. Finally, potential mechanisms of T3 action within the hypothalamus/median eminence in relationship to seasonal timing are examined.

The genes associated with gonadotropin-releasing hormone-dependent precocious puberty

Human puberty is a complex, coordinated biological process with multiple levels of regulations. The timing of puberty varies greatly in children and is influenced by both environmental and genetic factors. The key genes of pubertal onset, KISS1, GPR54, GNRH1 and GNRHR, may be major causal factors underlying gonadotropin-releasing hormone-dependent precocious puberty (GDPP). Two gain-of-function mutations in KISS1 and GPR54 have been identified recently as genetic causes of GDPP. GNRH1 and GNRHR are also gene candidates for GDPP; however no mutations have been identified in these genes. Presently potential genetic causes like LIN28B continues to appear; many areas of research await exploration in this context. In this review, I focus primarily on the genetic causes of GDPP.

KiSS1/GPR54 and estrogen-related gene expression profiles in primary breast cancer

The estrogen receptor α (ERα)-mediated pathway plays a critical role in breast cancer development and progression. KiSS1 was previously described as a metastasis suppressor gene in certain carcinomas. However, the role of KiSS1/GPR54 in breast cancer remains controversial. Whether the function of the KiSS1/GPR54 system depends on estrogen signaling in the breast cancer cell remains to be determined. This study aimed to determine the expression profiles of the KiSS1/GPR54, ERα, ERβ, aromatase and cyclin D1 genes in human breast cancer tissues, and to identify a possible link between the expression levels of the studied genes and the selected clinical and pathological features. The study subjects comprised 59 females treated surgically for primary breast cancer. Total RNA was extracted from frozen breast cancer tissues, and expression levels were examined to determine any correlations. We observed strong positive correlations between the expression levels of the studied genes. The expression of ERα correlated positively with progesterone receptors (PRs), and in these tumors we also observed positive correlations between KiSS1, GPR54 and cyclin D1 mRNAs and the ERα protein. ER-positive breast tumors exhibited higher KiSS1 and GPR54 levels than the ER-negative tumors. The expression levels of the ERα and GPR54 transcripts were higher in the moderately differentiated tumors (G2) compared to the poorly differentiated high-grade (G3) cancers. We also found that HER-2/neu status in breast cancer is negatively associated with GPR54 mRNA expression. Decreasing GPR54 mRNA expression levels in HER-2/neu (+) tumors may be associated with the deregulation of the classical estrogen-mediated signaling pathway in breast tumors, and therefore, with promotion of tumor invasiveness. Our findings indicate that genes involved in the KiSS1/GPR54 system, as well as in the estrogen signaling pathway, may be utilizable molecular factors in pathogenesis studies of breast cancer.

Evolutionary Insights into the Steroid Sensitive kiss1 and kiss2 Neurons in the Vertebrate Brain

Kisspeptin was originally found as a peptide product of Kiss1 gene and is now supposed to be an essential central regulator of reproduction in mammals. However, there is now a growing body of evidence to suggest that kiss2, the paralogous gene for kiss1, evolved in parallel during vertebrate lineage, and the kiss2 product also activates the GPR54 (kisspeptin receptor) signaling pathways. Therefore, it is now widely accepted that both kiss1 and kiss2 are the kisspeptin genes. Interestingly, either kiss1 or kiss2 or both have been lost during evolution in many vertebrate species, and the functional significance of kiss1 or kiss2 for the central regulation of reproduction is suggested to vary according to the species. Here, we argue that the steroid sensitivity of the kiss1 or kiss2 neurons has been well conserved during evolution among tetrapods and teleosts, and thus it may be the key to understanding the functional homologies of certain populations of kisspeptin (kiss1 or kiss2) neurons among different species of vertebrates. In the present review, we will first introduce recent advances in the study of steroid sensitive kiss1 and kiss2 systems in vertebrates and effects of peptide administrations in vivo. By comparing the similarities and differences between kiss1 and kiss2 of neuronal localization and sensitivity to gonadal steroids in various tetrapods and teleosts, we discuss the evolution of kisspeptin neuronal systems after gene duplication of ancestral kisspeptin genes to give rise to kiss1 and kiss2.

Sex steroids and the control of the Kiss1 system: developmental roles and major regulatory actions

Kisspeptins, encoded by the Kiss1 gene, and their canonical receptor, GPR54 (also termed Kiss1R), are unanimously recognised as essential regulators of puberty onset and gonadotrophin secretion. These key reproductive functions stem from the capacity of kisspeptins to stimulate gonadotrophin-releasing hormone (GnRH) secretion in the hypothalamus, where discrete populations of Kiss1 neurones have been identified. In rodents, two major groups of hypothalamic Kiss1 neurones exist: one present in the arcuate nucleus (ARC) and the other located in the anteroventral periventricular area (AVPV/RP3V). In recent years, numerous signals have been identified as putative modulators of the hypothalamic Kiss1 system. Among them, the prominent role of sex steroids as being important regulators of Kiss1 neurones has been documented in different species and developmental stages, such as early brain sex differentiation, puberty, adulthood and senescence. These regulatory actions are (mainly) conducted via oestrogen receptor (ER)α, which is expressed in almost all Kiss1 neurones, and likely involve both classical and nonclassical pathways. The regulatory effects of sex steroids are nucleus-specific. Thus, sex steroids inhibit the expression of Kiss1/kisspeptin at the ARC, as a mechanism to conduct their negative-feedback actions on gonadotrophin secretion. By contrast, oestrogens enhance Kiss1 expression at the AVPV/RP3V in rodents, suggesting the involvement of this population in the positive-feedback actions of oestradiol to generate the preovulatory surge of gonadotrophins. In addition, sex steroids have been shown to act post-transcriptionally, modulating GnRH/gonadotrophin responsiveness to kisspeptin. Finally, sex steroids also regulate the expression of co-transmitters of Kiss1 neurones, such as neurokinin B, whose mRNA content in the ARC fluctuates in parallel to that of Kiss1 in response to changes in the circulating levels of sex steroids, therefore suggesting the contribution of this neuropeptide in the feedback control of gonadotrophin secretion. In sum, compelling experimental evidence obtained in different mammalian (and non-mammalian) species, including primates, demonstrates that sex steroids are essential regulators of hypothalamic Kiss1 neurones, which in turn operate as conduits for their effects on GnRH neurones. The physiological relevance of such regulatory phenomena is thoroughly discussed.

Circadian transcriptional factor DBP regulates expression of Kiss1 in the anteroventral periventricular nucleus

The expression of Kiss1 in the anteroventral periventricular nucleus (AVPV) and its product, metastin/kisspeptin, show a circadian pattern with a peak in the evening, which shows a strong phase relationship with the time of the gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) surge in rodents. Here we report that a circadian transcriptional factor, albumin D-site binding protein (Dbp), was able to trigger mKiss1 transcription via the D-box, and this effect was combined with those of estrogen receptor α (ERα) and its ligand, estrogen. A histological study demonstrated that some cells in the AVPV co-expressed Dbp with ERα in adult female rats. Expression of ERα was not rhythmic in the AVPV, however, mRNA of Dbp in the AVPV accumulated with a robust diurnal rhythm in proestrus, but not on the first day of diestrus. Thus, these results suggest that Dbp and estrogen regulate the expression of Kiss1 in the AVPV, thereby mediating the GnRH/LH surge.

The role of kisspeptin signaling in reproduction

Kisspeptins are a group of peptides that stimulate GnRH release and are required for puberty and maintenance of normal reproductive function. This review focuses on our understanding of the way in which kisspeptin signaling regulates mammalian fertility and how they act as central integrators of different hormonal and physiological signals.

Plasma levels of kisspeptins in postmenopausal Chinese women do not show substantial elevation

The menopause, defined as the permanent cessation of menstruation resulting from ovarian failure, is characterized by elevated levels of serum gonadotropins. Recent studies have demonstrated that the gonadotropin hypersecretion in postmenopausal women is secondary to increase of KiSS-1 mRNA from the hypothalamus neurons, which encoded kisspeptin peptides. The present study was designed to determine whether plasma kisspeptins levels are altered in postmenopausal women. Blood samples were taken from 145 postmenopausal women, 35 young women and 30 pregnant women control in the first trimester. The plasma concentration of kisspeptins, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and estradiol (E₂) was measured using immunoassay kits. Results indicated that plasma kisspeptins levels in postmenopausal women had higher than those in young women (5.25±0.36; 4.48±0.34 pmol/L), but no significant difference was found between the two groups (p=0.179). Plasma FSH and LH levels were significantly higher in postmenopausal women (124.67±12.78, 57.14±3.57 mIu/mL) than those in young women (9.23±2.78, 7.56±2.71 mIu/mL, p<0.001). However, Plasma kisspeptins levels were not significantly correlated to FSH and LH in postmenopausal women (r=-0.23, 0.324; p=0.927, 0.176, respectively), and also there was no any correlation between plasma kisspeptins and E₂ in postmenopausal women (r=-0.065; p=0.792). Collectively, there was no significant difference in plasma kisspeptins levels between postmenopausal and young women. Our result suggested that kisspeptins' role during menopause might mainly act in central rather than peripheral system and it could not be currently used as a clinical marker for menopause.