Stimulation of luteinizing hormone-releasing hormone (LHRH) gene expression in GT1-7 cells by its metabolite, LHRH-(1-5)

The Genetic Pathophysiology and Clinical Management of the TADopathy, X-Linked Acrogigantism

Pituitary gigantism is a rare manifestation of chronic growth hormone (GH) excess that begins before closure of the growth plates. Nearly half of patients with pituitary gigantism have an identifiable genetic cause. X-linked acrogigantism (X-LAG; 10% of pituitary gigantism) typically begins during infancy and can lead to the tallest individuals described. In the 10 years since its discovery, about 40 patients have been identified. Patients with X-LAG usually develop mixed GH and prolactin macroadenomas with occasional hyperplasia that secrete copious amounts of GH, and frequently prolactin. Circulating GH-releasing hormone is also elevated in a proportion of patients. X-LAG is caused by constitutive or sporadic mosaic duplications at chromosome Xq26.3 that disrupt the normal chromatin architecture of a topologically associating domain (TAD) around the orphan G-protein-coupled receptor, GPR101. This leads to the formation of a neo-TAD in which GPR101 overexpression is driven by ectopic enhancers ("TADopathy"). X-LAG has been seen in 3 families due to transmission of the duplication from affected mothers to sons. GPR101 is a constitutively active receptor with an unknown natural ligand that signals via multiple G proteins and protein kinases A and C to promote GH/prolactin hypersecretion. Treatment of X-LAG is challenging due to the young patient population and resistance to somatostatin analogs; the GH receptor antagonist pegvisomant is often an effective option. GH, insulin-like growth factor 1, and prolactin hypersecretion and physical overgrowth can be controlled before definitive adult gigantism occurs, often at the cost of permanent hypopituitarism.

Current state of phoenixin-the implications of the pleiotropic peptide in stress and its potential as a therapeutic target

Phoenixin is a pleiotropic peptide, whose known functions have broadened significantly over the last decade. Initially first described as a reproductive peptide in 2013, phoenixin is now recognized as being implicated in hypertension, neuroinflammation, pruritus, food intake, anxiety as well as stress. Due to its wide field of involvement, an interaction with physiological as well as psychological control loops has been speculated. It has shown to be both able to actively reduce anxiety as well as being influenced by external stressors. Initial rodent models have shown that central administration of phoenixin alters the behavior of the subjects when confronted with stress-inducing situations, proposing an interaction with the perception and processing of stress and anxiety. Although the research on phoenixin is still in its infancy, there are several promising insights into its functionality, which might prove to be of value in the pharmacological treatment of several psychiatric and psychosomatic illnesses such as anorexia nervosa, post-traumatic stress disorder as well as the increasingly prevalent stress-related illnesses of burnout and depression. In this review, we aim to provide an overview of the current state of knowledge of phoenixin, its interactions with physiological processes as well as focus on the recent developments in stress response and the possible novel treatment options this might entail.

The role of GnRH metabolite, GnRH-(1-5), in endometrial cancer

From the time of its discovery and isolation in the mammalian hypothalamus, the decapeptide, gonadotropin-releasing hormone (GnRH), has also been found to be expressed in non-hypothalamic tissues and can elicit a diverse array of functions both in the brain and periphery. In cancer, past studies have targeted the gonadotropin-releasing hormone receptors (GnRHR) as a way to treat reproductive cancers due to its anti-tumorigenic effects. On the contrary, its metabolite, GnRH-(1-5), behaves divergently from its parental peptide through putative orphan G-protein coupled receptor (oGPCR), GPR101. In this review, we will focus on the potential roles of GnRH-(1-5) in the periphery with an emphasis on its effects on endometrial cancer progression.

Gonadotropin-Releasing Hormone and GnRH Receptor: Structure, Function and Drug Development

BACKGROUND

Gonadotropin-Releasing Hormone (GnRH) is a key element in sexual maturation and regulation of the reproductive cycle in the human organism. GnRH interacts with the pituitary cells through the activation of the Gonadotropin Releasing Hormone Receptors (GnRHR). Any impairments/dysfunctions of the GnRH-GnRHR complex lead to the development of various cancer types and disorders. Furthermore, the identification of GnRHR as a potential drug target has led to the development of agonist and antagonist molecules implemented in various treatment protocols. The development of these drugs was based on the information derived from the functional studies of GnRH and GnRHR.

OBJECTIVE

This review aims at shedding light on the versatile function of GnRH and GnRH receptor and offers an apprehensive summary regarding the development of different agonists, antagonists and non-peptide GnRH analogues.

CONCLUSION

The information derived from these studies can enhance our understanding of the GnRH-GnRHR versatile nature and offer valuable insight into the design of new more potent molecules.

Regulation of Gpr173 expression, a putative phoenixin receptor, by saturated fatty acid palmitate and endocrine-disrupting chemical bisphenol A through a p38-mediated mechanism in immortalized hypothalamic neurons

GPR173 is a highly conserved G protein coupled receptor associated with the hypothalamic-pituitary-gonadal reproductive axis. It is expressed in the brain and ovaries, however considerable knowledge about its function remains unknown. One putative ligand for this receptor is phoenixin (PNX), a newly identified reproductive peptide involved in hypothalamic coordination of the estrous cycle. In order to characterize GPR173, it is vital to determine how Gpr173 is regulated in the hypothalamus. Since the hypothalamus senses compounds from the blood, such as nutrients and chemicals, we examined the effect of palmitate, a saturated fatty acid, and bisphenol A (BPA), an endocrine disrupting chemical, on Gpr173 gene expression. Immortalized hypothalamic neurons were treated with palmitate or BPA for 2-24 h and Gpr173 mRNA levels were assessed with RT-qPCR. Palmitate and BPA both reduced Gpr173 mRNA levels, in part through the mitogen-activated protein kinase (MAPK), p38. Pre-treatment with palmitate for 24 h blocked the PNX-induction of phosphorylated cAMP response element-binding protein (CREB) levels. In conclusion, nutrition levels and environmental chemicals may influence reproductive function through modulation of Gpr173 expression, which may prove to be a future therapeutic target in reproductive health.

Antisense techniques provide robust decrease in GnRH receptor expression with minimal cytotoxicity in GT1-7 cells

The episodic pattern of gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus is driven by an integrated network of cells termed the GnRH pulse generator. Cultured and immortalized GnRH neurons also produce a pulsatile pattern of GnRH secretions when grown in the absence of other cell types, suggesting the presence of an intrinsic oscillator mediating GnRH secretion. The mechanisms underlying such pulsatility comprise one of the most tantalizing problems in contemporary neuroendocrinology. In order to study the mechanism by which GnRH is produced in a pulsatile fashion, the autocrine effect of GnRH on GnRH-producing neurons must be eliminated. This may be performed by downregulating the expression of the GnRH receptor. Treatment with three 21-mer exogenous phosphorothioates and transient transfections with an inducible plasmid containing an antisense construct to the GnRH receptor gene decreased GnRH receptor expression further. This resulted in less cytotoxicity compared to inhibition of RNA or protein synthesis with actinomycin D, α-amanitin, puromycin, and cycloheximide. This study shows methods and optimized conditions established for the generation of a stable GT1-7 cell line containing an inducible construct allowing the downregulation of GnRH receptor expression.

ABBREVIATIONS

ANOVA: analysis of the variance; DMEM: Dulbecco's modified Eagle's medium; GnRH: gonadotropin-releasing hormone; RXR: retinoid X receptor.

GnRH-(1-5) Inhibits TGF-β Signaling to Regulate the Migration of Immortalized Gonadotropin-Releasing Hormone Neurons

Gonadotropin-releasing hormone (GnRH) neurons originate outside the central nervous system (CNS) in the nasal placode where their migration to the basal forebrain is dependent on the integration of multiple signaling cues during development. The proper migration and establishment of the GnRH neuronal population within the CNS are critical for normal pubertal onset and reproductive function. The endopeptidase EP24.15 is expressed along the migratory path of GnRH neurons and cleaves the full-length GnRH to generate the metabolite GnRH-(1-5). Using the GN11 cell model, which is considered a pre-migratory GnRH neuronal cell line, we demonstrated that GnRH-(1-5) inhibits cellular migration in a wound closure assay by binding the orphan G protein-coupled receptor 173 (GPR173). In our current experiments, we sought to utilize an in vitro migration assay that better reflects the external environment that migrating GnRH neurons are exposed to during development. Therefore, we used a transwell assay where the inserts were coated with or without a matrigel, a gelatinous mixture containing extracellular matrix (ECM) proteins, to mimic the extracellular environment. Interestingly, GnRH-(1-5) inhibited the ability of GN11 cells to migrate only through ECM mimetic and was dependent on GPR173. Furthermore, we found that GN11 cells secrete TGF-β1, 2, and 3 but only TGF-β1 release and signaling were inhibited by GnRH-(1-5). To identify potential mechanisms involved in the proteolytic activation of TGF-β, we measured a panel of genes implicated in ECM remodeling. We found that GnRH-(1-5) consistently increased tissue inhibitors of metalloproteinase 1 expression, which is an inhibitor of proteinase activity, leading to a decrease in bioactive TGF-β and subsequent signaling. These results suggest that GnRH-(1-5) activating GPR173 may modulate the response of migrating GnRH neurons to external cues present in the ECM environment via an autocrine-dependent mechanism involving TGF-β.

Regulation of Gonadotropin-Releasing Hormone-(1-5) Signaling Genes by Estradiol Is Age Dependent

Gonadotropin-releasing hormone (GnRH) is a key regulatory molecule of the hypothalamus-pituitary (PIT)-gonadal (HPG) axis that ultimately leads to the downstream release of estradiol (E2) and progesterone (P). These gonadal steroids feed back to the hypothalamus and PIT to regulate reproductive function and behavior. While GnRH is thought to be the master regulator of reproduction, its metabolic product GnRH-(1-5) is also biologically active. Thimet oligopeptidase 1 (also known as EP24.15) cleaves GnRH to form GnRH-(1-5). GnRH-(1-5) is involved in regulation of the HPG axis, exerting its actions through a pair of orphan G protein-coupled receptors, GPR101 and GPR173. The physiological importance of GnRH-(1-5) signaling has been studied in several contexts, but its potential role during reproductive senescence is poorly understood. We used an ovariectomized (OVX) rat model of reproductive senescence to assess whether and how GnRH-(1-5) signaling genes in hypothalamic subnuclei change in response to aging and/or different estradiol replacement regimens designed to model clinical hormone replacement in women. We found that Gpr101 and Gpr173 mRNA expression was increased with age in the arcuate nucleus, while expression of Gpr173 and EP24.15 increased with age in the medial preoptic area. Treatment with E2 in younger OVX animals increased expression of Gpr101, Gpr173, and EP24.15. However, older animals treated with E2 showed decreased expression of these GnRH-(1-5) signaling genes, displaying an age-related decline in responsiveness to E2. To our knowledge, this is the first study to systematically assess the effects of age and different clinically relevant regimens of E2 replacement on GnRH-(1-5) signaling genes.

Genome-wide association for the outcome of fixed-time artificial insemination of Brahman heifers in northern Australia

Fixed-time AI (FTAI) is a powerful tool for genetic improvement of extensively managed beef cattle. A genomewide association study (GWAS) was conducted to investigate genes and genetic markers associated with the outcome (pregnant or not pregnant) of FTAI in 614 commercial Brahman heifers genotyped for 18,895 SNP and imputed to 51,588 SNP. The likelihood of Brahman heifers becoming pregnant after hormonal treatment to synchronize ovulation followed by FTAI was influenced by the content of their genomes, as determined by a principal component analysis. The principal component analysis involved comparisons between the studied heifers and populations of known and ancestry. The heritability of FTAI outcome was = 0.18, which is higher than for most other reproductive outcome traits. The number of SNP associated with FTAI outcome was 101 ( < 0.001, false discovery rate = 0.53). Compared with all SNP tested, associated SNP had a tendency for highly divergent allelic frequencies between and . Associated SNP were located in nearly all chromosomes, a result that shows a complex genetic architecture that is typical of highly complex traits with low heritability. Considering this and previous GWAS that examined Brahman heifer puberty and postpartum anestrus interval, 3 genomic regions emerge as important for overall Brahman heifer fertility, which mapped to chromosomes 1, 7, and 9. Further analyses, including improved genome annotation, are required to elucidate the link between these regions and heifer fertility. Additional studies are needed to confirm SNP and gene associations reported herein and further elucidate the genetics of FTAI outcome. Future GWAS should target other Braham populations and additional cattle breeds with FTAI records, including breeds with higher ancestry.

Peripheral and Central Mechanisms Involved in the Hormonal Control of Male and Female Reproduction

Reproduction involves the integration of hormonal signals acting across multiple systems to generate a synchronised physiological output. A critical component of reproduction is the luteinising hormone (LH) surge, which is mediated by oestradiol (E2 ) and neuroprogesterone interacting to stimulate kisspeptin release in the rostral periventricular nucleus of the third ventricle in rats. Recent evidence indicates the involvement of both classical and membrane E2 and progesterone signalling in this pathway. A metabolite of gonadotrophin-releasing hormone (GnRH), GnRH-(1-5), has been shown to stimulate GnRH expression and secretion, and has a role in the regulation of lordosis. Additionally, gonadotrophin release-inhibitory hormone (GnIH) projects to and influences the activity of GnRH neurones in birds. Stress-induced changes in GnIH have been shown to alter breeding behaviour in birds, demonstrating another mechanism for the molecular control of reproduction. Peripherally, paracrine and autocrine actions within the gonad have been suggested as therapeutic targets for infertility in both males and females. Dysfunction of testicular prostaglandin synthesis is a possible cause of idiopathic male infertility. Indeed, local production of melatonin and corticotrophin-releasing hormone could influence spermatogenesis via immune pathways in the gonad. In females, vascular endothelial growth factor A has been implicated in an angiogenic process that mediates development of the corpus luteum and thus fertility via the Notch signalling pathway. Age-induced decreases in fertility involve ovarian kisspeptin and its regulation of ovarian sympathetic innervation. Finally, morphological changes in the arcuate nucleus of the hypothalamus influence female sexual receptivity in rats. The processes mediating these morphological changes have been shown to involve the rapid effects of E2 controlling synaptogenesis in this hypothalamic nucleus. In summary, this review highlights new research in these areas, focusing on recent findings concerning the molecular mechanisms involved in the central and peripheral hormonal control of reproduction.

Phoenixin Activates Immortalized GnRH and Kisspeptin Neurons Through the Novel Receptor GPR173

Reproductive function is coordinated by kisspeptin (Kiss) and GnRH neurons. Phoenixin-20 amide (PNX) is a recently described peptide found to increase GnRH-stimulated LH secretion in the pituitary. However, the effects of PNX in the hypothalamus, the putative signaling pathways, and PNX receptor have yet to be identified. The mHypoA-GnRH/GFP and mHypoA-Kiss/GFP-3 cell lines represent populations of GnRH and Kiss neurons, respectively. PNX increased GnRH and GnRH receptor (GnRH-R) mRNA expression, as well as GnRH secretion, in the mHypoA-GnRH/GFP cell model. In the mHypoA-Kiss/GFP-3 cell line, PNX increased Kiss1 mRNA expression. CCAAT/enhancer-binding protein (C/EBP)-β, octamer transcription factor-1 (Oct-1), and cAMP response element binding protein (CREB) binding sites are localized to the 5' flanking regions of the GnRH, GnRH-R, and Kiss1 genes. PNX decreased C/EBP-β mRNA expression in both cell models and increased Oct-1 mRNA expression in the mHypoA-GnRH/GFP neurons. PNX increased CREB phosphorylation in both cell models and phospho-ERK1/2 in the mHypoA-GnRH/GFP cell model, whereas inhibiting the cAMP/protein kinase A pathway prevented PNX induction of GnRH and Kiss1 mRNA expression. Importantly, we determined that the G protein-coupled receptor, GPR173, was strongly expressed in both GnRH and kisspeptin cell models and small interfering RNA knockdown of GPR173 prevented the PNX-mediated up-regulation of GnRH, GnRH-R, and Kiss1 mRNA expression and the down-regulation of C/EBP-β mRNA expression. PNX also increased GPR173 mRNA expression in the mHypoA-GnRH/GFP cells. Taken together, these studies are the first to implicate that PNX acts through GPR173 to activate the cAMP/protein kinase A pathway through CREB, and potentially C/EBP-β and/or Oct-1 to increase GnRH, GnRH-R, and Kiss1 gene expression, ultimately having a stimulatory effect on reproductive function.

GnRH-(1-5) activates matrix metallopeptidase-9 to release epidermal growth factor and promote cellular invasion

In the extracellular space, the gonadotropin-releasing hormone (GnRH) is metabolized by the zinc metalloendopeptidase EC3.4.24.15 (EP24.15) to form the pentapeptide, GnRH-(1-5). GnRH-(1-5) diverges in function and mechanism of action from GnRH in the brain and periphery. GnRH-(1-5) acts on the orphan G protein-coupled receptor 101 (GPR101) to sequentially stimulate epidermal growth factor (EGF) release, phosphorylate the EGF receptor (EGFR), and facilitate cellular migration. These GnRH-(1-5) actions are dependent on matrix metallopeptidase (MMP) activity. Here, we demonstrated that these GnRH-(1-5) effects are dependent on increased MMP-9 enzymatic activity in the Ishikawa and ECC-1 cell lines. Furthermore, the effects of GnRH-(1-5) mediated by GPR101 and the subsequent increase in MMP-9 enzymatic activity lead to an increase in cellular invasion. These results suggest that GnRH-(1-5) and GPR101 regulation of MMP-9 may have physiological relevance in the metastatic potential of endometrial cancer cells.

Autoshortloop feedback regulation of pulsatile gonadotropin-releasing hormone (GnRH) secretion by its metabolite, GnRH-(1-5)

Given the central role of the decapeptide gonadotropin-releasing hormone (GnRH) in reproductive function, our long-term objective is to delineate the underlying mechanism regulating these reproductive processes. The outcome of GnRH secretion is in part dependent on the proteolytic metabolism of this decapeptide. In contrast to the belief that the metabolism of GnRH serves only as a degradative process that removes excess GnRH, we have shown that a metabolite of the decapeptide, GnRH-(1-5), can directly regulate GnRH gene expression and reproductive behavior. To further characterize the effect of GnRH-(1-5) on GnRH neuronal function, we determined whether GnRH-(1-5) can directly regulate GnRH secretion and pulsatility using an in vitro perifusion system. We compared the effect of GnRH-(1-5) on GnRH secretion in the immortalized GnRH neuron (GT1-7 cell line), whole rat hypothalamic explant, and enzymatically dispersed rat hypothalamic cells. Tissue preparations were perifused continuously for 9 h during which a 3-h challenge with GnRH-(1-5) was administered (4-6 h). The results show that treatment with GnRH-(1-5) increased (p < 0.05) the mean GnRH secretion and the amplitude of the pulses but not the pulse frequency. The present study supports the notion that GnRH-(1-5) is functionally capable of regulating the reproductive neuroendocrine system.

β-Arrestin 2 is a mediator of GnRH-(1-5) signaling in immortalized GnRH neurons

We have previously demonstrated that the cleavage product of the full-length GnRH, GnRH-(1-5), is biologically active, binds G protein-coupled receptor 173 (GPR173), and inhibits the migration of cells in the immortalized GnRH-secreting GN11 cell. In this study, we attempted to characterize the GnRH-(1-5) intracellular signaling mechanism. To determine whether the signaling pathway mediating GnRH-(1-5) regulation of migration involves a G protein-dependent mechanism, cells were treated with a generic G protein antagonist in the presence and absence of GnRH-(1-5), and a wound-healing assay was conducted to measure migration. G Protein antagonist 2 treatment abolished the GnRH-(1-5) inhibition of migration, indicating that the mechanism of GnRH-(1-5) is G protein coupled. To identify the potential Gα-subunit recruited by GnRH-(1-5) binding GPR173, we measured the second messengers cAMP and inositol triphosphate levels. GnRH-(1-5) treatment did not alter cAMP levels relative to cells treated with vehicle or forskolin, suggesting that GnRH-(1-5) does not couple to the Gαs or Gαi subunits. Similarly, inositol triphosphate levels remained unchanged with GnRH-(1-5) treatment, indicating a mechanism not mediated by the Gαq/11 subunit. Therefore, we also examined whether GnRH-(1-5) activating GPR173 deviated from the canonical G protein-coupled receptor signaling pathway by coupling to β-arrestin 1/2 to regulate migration. Our coimmunoprecipitation studies indicate that GnRH-(1-5) induces the rapid interaction between GPR173 and β-arrestin 2 in GN11 cells. Furthermore, we demonstrate that this association recruits phosphatase and tensin homolog to mediate the downstream action of GnRH-(1-5). These findings suggest that the GnRH-(1-5) mechanism deviates from the canonical G protein-coupled receptor pathway to regulate cell migration in immortalized GnRH neurons.

The metabolite GnRH-(1-5) inhibits the migration of immortalized GnRH neurons

The decapeptide GnRH is an important regulator of reproductive behavior and function. In the extracellular matrix, GnRH is metabolized by the endopeptidase EC3.4.24.15 (EP24.15) to generate the pentapeptide GnRH-(1-5). In addition to its expression in the adult hypothalamus, EP24.15 is expressed along the migratory path of GnRH-expressing neurons during development. Although we have previously demonstrated a role for EP24.15 in the generation of the biologically active pentapeptide GnRH-(1-5) in regulating GnRH expression and mediating sexual behavior during adulthood in rodents, the modulatory role of GnRH-(1-5) in the migration of GnRH neurons during development remains unknown. To address this information gap, we examined the effect of GnRH-(1-5) on the cellular migration of a premigratory GnRH-secreting neuronal cell line, the GN11 cell, using a wound-healing assay. Dose- and time-response studies demonstrated that GnRH-(1-5) significantly delayed wound closure. We then sought to identify the mechanism by which GnRH-(1-5) inhibits migration. Because the cognate GnRH receptor is a G protein-coupled receptor, we examined whether GnRH-(1-5) regulates migration by also activating a G protein-coupled receptor. Using a high-throughput β-arrestin recruitment assay, we identified an orphan G protein-coupled receptor (GPR173) that was specifically activated by GnRH-(1-5). Interestingly, small interfering RNA to GPR173 reversed the GnRH-(1-5)-mediated inhibition on migration of GN11 neurons. Furthermore, we also demonstrate that the GnRH-(1-5)-activated GPR173-dependent signal transduction pathway involves the activation of the signal transducer and activator of transcription 3 in GnRH migration. These findings indicate a potential regulatory role for GnRH-(1-5) in GnRH neuronal migration during development.

The Novel Actions of the Metabolite GnRH-(1-5) are Mediated by a G Protein-Coupled Receptor

The gonadotropin-releasing hormone (GnRH) was originally isolated from the mammalian hypothalamus for its role as the primary regulator of reproductive function. Since its discovery, GnRH has also been shown to be located in non-hypothalamic tissues and is known to have diverse functions. Although the regulation of GnRH synthesis and release has been extensively studied, there is additional evidence to suggest that the processing of GnRH to the metabolite GnRH-(1-5) represents another layer of regulation. The focus of this review will be on the current evidence for the action of the pentapeptide metabolite GnRH-(1-5) in regulating cellular migration. We discuss the potential role of GnRH-(1-5) in regulating GnRH neuronal migration during development. Furthermore, we demonstrate these actions are mediated by the activation of a G protein-coupled receptor. Our findings suggest that GnRH-(1-5) may play a developmental function in addition to regulating developing cells.

GnRH-(1-5) transactivates EGFR in Ishikawa human endometrial cells via an orphan G protein-coupled receptor

The decapeptide GnRH is known for its central role in the regulation of the hypothalamo-pituitary-gonadal axis. In addition, it is also known to have local effects within peripheral tissues. The zinc metalloendopeptidase, EC 3.4.24.15 (EP24.15), can cleave GnRH at the Tyr(5)-Gly(6) bond to form the pentapeptide, GnRH-(1-5). The central and peripheral effect of GnRH-(1-5) is different from its parent peptide, GnRH. In the current study, we examined the effect of GnRH-(1-5) on epidermal growth factor receptor (EGFR) phosphorylation and cellular migration. Using the Ishikawa cell line as a model of endometrial cancer, we demonstrate that GnRH-(1-5) stimulates epidermal growth factor release, increases the phosphorylation of EGFR (P < .05) at three tyrosine sites (992, 1045, 1068), and promotes cellular migration. In addition, we also demonstrate that these actions of GnRH-(1-5) are mediated by the orphan G protein-coupled receptor 101 (GPR101). Down-regulation of GPR101 expression blocked the GnRH-(1-5)-mediated release of epidermal growth factor and the subsequent phosphorylation of EGFR and cellular migration. These results suggest that GPR101 is a critical requirement for GnRH-(1-5) transactivation of EGFR in Ishikawa cells.

Hormonal regulation of female reproduction

Reproduction is an event that requires the coordination of peripheral organs with the nervous system to ensure that the internal and external environments are optimal for successful procreation of the species. This is accomplished by the hypothalamic-pituitary-gonadal axis that coordinates reproductive behavior with ovulation. The primary signal from the central nervous system is gonadotropin-releasing hormone (GnRH), which modulates the activity of anterior pituitary gonadotropes regulating follicle stimulating hormone (FSH) and luteinizing hormone (LH) release. As ovarian follicles develop they release estradiol, which negatively regulates further release of GnRH and FSH. As estradiol concentrations peak they trigger the surge release of GnRH, which leads to LH release inducing ovulation. Release of GnRH within the central nervous system helps modulate reproductive behaviors providing a node at which control of reproduction is regulated. To address these issues, this review focuses on several critical questions. How is the HPG axis regulated in species with different reproductive strategies? What internal and external conditions modulate the synthesis and release of GnRH? How does GnRH modulate reproductive behavior within the hypothalamus? How does disease shift the activity of the HPG axis?

Is the metalloendopeptidase EC 3.4.24.15 (EP24.15), the enzyme that cleaves luteinizing hormone-releasing hormone (LHRH), an activating enzyme?

LHRH (GNRH) was first isolated in the mammalian hypothalamus and shown to be the primary regulator of the reproductive neuroendocrine axis comprising of the hypothalamus, pituitary and gonads. LHRH acts centrally through its initiation of pituitary gonadotrophin release. Since its discovery, this form of LHRH (LHRH-I) has been shown to be one of over 20 structural variants with a variety of roles in both the brain and peripheral tissues. LHRH-I is processed by a zinc metalloendopeptidase EC 3.4.24.15 (EP24.15) that cleaves the hormone at the fifth and sixth bond of the decapeptide (Tyr5-Gly6) to form LHRH-(1–5). We have previously reported that the auto-regulation of LHRH-I (GNRH1) gene expression and secretion can also be mediated by itself and its processed peptide, LHRH-(1–5), centrally and in peripheral tissues. In this review, we present the evidence that EP24.15 is the main enzyme of LHRH metabolism. Following this, we look at the metabolism of other neuropeptides where an active peptide fragments is formed during degradation and use this as a platform to postulate that EP24.15 may also produce an active peptide fragment in the process of breaking down LHRH. We close this review by the role EP24.15 may have in regulation of the complex LHRH system.

A biological role for the gonadotrophin-releasing hormone (GnRH) metabolite, GnRH-(1-5)

Gonadotrophin-releasing hormone (GnRH) was first isolated in the mammal and shown to be the primary regulator of the reproductive system through its initiation of pituitary gonadotrophin release. Subsequent to its discovery, this form of GnRH has been shown to be one of many structural variants found in the brain and peripheral tissues. Accordingly, the original form first discovered and cloned in the mammal is commonly referred to as GnRH-I. In addition to the complex regulation of GnRH-I synthesis, release and function, further evidence suggests that the processing of GnRH-I produces yet another layer of complexity in its activity. GnRH-I is processed by a zinc metalloendopeptidase EC 3.4.24.15 (EP24.15), which cleaves the hormone at the covalent bond between the fifth and sixth residue of the decapeptide (Tyr(5)-Gly(6)) to form GnRH-(1-5). It was previously thought that the cleavage of GnRH-I by EP24.15 represents the initiation of its degradation. Here, we review the evidence for the involvement of GnRH-(1-5), the metabolite of GnRH-I, in the regulation of GnRH-I synthesis, secretion and facilitation of reproductive behaviour.

Luteinizing Hormone-Releasing Hormone I (LHRH-I) and Its Metabolite in Peripheral Tissues

Luteinizing hormone-releasing hormone (LHRH) was first isolated in the mammalian hypothalamus and shown to be the primary regulator of the reproductive system through its initiation of pituitary gonadotropin release. Since its discovery, this form of LHRH (LHRH-I) has been shown to be one of many structural variants with a variety of roles in both the brain and peripheral tissues. Enormous interest has been focused on LHRH-I and LHRH-II and their cognate receptors as targets for designing therapies to treat cancers of the reproductive system. LHRH-I is processed by a zinc metalloendopeptidase EC 3.4.24.15 (EP24.15) that cleaves the hormone at the fifth and sixth bond of the decapeptide (Tyr5-Gly6) to form LHRH-( 1 – 5 ). We have previously reported that the autoregulation of LHRH gene expression can also be mediated by its processed peptide, LHRH-( 1 – 5 ). Furthermore, LHRH-( 1 – 5 ) has also been shown to be involved in cell proliferation. This review will focus on the possible roles of LHRH and its processed peptide, LHRH-( 1 – 5 ), in non-hypothalamic tissues.

LHRH-(1-5): a bioactive peptide regulating reproduction

Luteinizing hormone-releasing hormone-I (LHRH-I) was isolated from the mammalian hypothalamus and shown to be the primary regulator of reproduction through its initiation of pituitary gonadotropin release. Subsequently, it has also been shown to have non-pituitary actions. Although the regulation of LHRH-I synthesis and release has been extensively studied, there is additional evidence to suggest that processing of the peptide represents another layer of regulation. The focus of this review will be on evidence for the action of LHRH-(1-5), the pentapeptide metabolite of LHRH-I, in regulating LHRH-I synthesis, secretion and reproductive behavior. The involvement of LHRH-(1-5) in the control of aspects of reproduction might represent yet another level of regulatory complexity through neuropeptide processing.

A processed metabolite of luteinizing hormone-releasing hormone has proliferative effects in endometrial cells

OBJECTIVE

The purpose of this study is to determine the possible role of the processed peptide of LHRH, LHRH-(1-5), in regulating growth of endometrial cancer cells.

STUDY DESIGN

An endometrial cancer cell line, the Ishikawa cell line, was cultured under standard conditions and treated in a dose-dependent manner with 1 of 2 hormones, LHRH and LHRH-(1-5) to determine the ability of these peptides to regulate cellular growth. A tetrazolium-based assay was used to determine the effect these peptides have on cell proliferation. Furthermore, enzyme-linked immunosorbent assay (ELISA)-based assays were used to determine the expression of caspase-3/7 and pERK-1/2. Statistical analyses were conducted using an analysis of variance followed by Fisher LSD as the post-hoc test.

RESULTS

The results show that LHRH is anti-proliferative whereas LHRH-(1-5) is proliferative on the cells. Furthermore, LHRH-(1-5) decreased caspase-3/7 and pERK1/2 expression.

CONCLUSION

This is the first time LHRH-(1-5) is shown to have proliferative effects on cells.

The protein kinase C pathway acts through multiple transcription factors to repress gonadotropin-releasing hormone gene expression in hypothalamic GT1-7 neuronal cells

The GnRH gene uses two well-defined regions to target expression to a small population of hypothalamic GnRH neurons: a 173-bp proximal promoter and a 300-bp enhancer localized at approximately -1800 to -1500 bp from the start site. Interaction of multiple factors with the GnRH enhancer and promoter is required to confer neuron-specific expression in vivo and in cells in culture. In addition, the expression of the GnRH gene is regulated by numerous neurotransmitters and hormones. Several of these effectors act through membrane receptors to trigger the protein kinase C pathway, and 12-O-tetradecanoyl phorbol-13-acetate (TPA), a modulator of this pathway, has been shown to suppress GnRH gene expression through the promoter. We find that TPA suppresses expression through the GnRH enhancer as well as the promoter. In the enhancer, an Oct-1 binding site, a Pbx/Prep binding site, Msx/Dlx binding sites, and a previously unidentified protein-binding element at -1793, all contribute to TPA suppression. TPA treatment leads to decreased binding of Oct-1 and Pbx1a/Prep to their sites. However, a complex formed by GT1-7 nuclear extracts on the -1793 site is not affected by TPA treatment. It is known that cooperative interaction among multiple factors is necessary for GnRH gene expression; thus, one mechanism by which TPA suppresses GnRH gene expression is to disengage some of these factors from their cis-regulatory elements.

Mutations remote from the human gonadotropin-releasing hormone (GnRH) receptor-binding sites specifically increase binding affinity for GnRH II but not GnRH I: evidence for ligand-selective, receptor-active conformations

The human gonadotropin-releasing hormone (GnRH) receptor is evolutionarily configured for high affinity binding of GnRH I ([Tyr(5),Leu(7),Arg(8)]GnRH) but at lower affinity for GnRH II ([His(5),Trp(7),Tyr(8)]GnRH). GnRH I is more potent in the activation of the G(q/11) protein in the gonadotrope; however, GnRH II is more potent in the stimulation of apoptosis and antiproliferative effects through activating G(i) protein-mediated signaling, implying that GnRH I and II selectively stabilize different receptor-active conformations that preferentially couple to different signaling pathways. Receptor activation involves ligand induction or conformational selection, but the molecular basis of the communication between ligand-binding sites and receptor allosteric sites remains unclear. We have sought conformational coupling between receptor-ligand intermolecular interactions and intramolecular interaction networks in the human GnRH receptor by mutating remote residues that induce differential ligand binding affinity shifts for GnRH I and II. We have demonstrated that certain Ala mutations in the intracellular segments of transmembrane domains 3 (Met(132)), 5 (Met(227)), 6 (Phe(272) and Phe(276)), and 7 (Ile(322) and Tyr(323)) of the human GnRH receptor allosterically increased ligand binding affinity for GnRH II but had little effect on GnRH I binding affinity. We examined the role of the three amino acids that differ in these two ligands, and we found that Tyr(8) in GnRH II plays a dominant role for the increased affinity of the receptor mutants for GnRH II. We propose that creation of a high affinity binding site for GnRH II accompanies receptor conformational changes, i.e."induced fit" or "conformational selection," mainly determined by the intermolecular interactions between Tyr(8) and the receptor contact residues, which can be facilitated by disruption of particular sets of receptor-stabilizing intramolecular interactions. The findings suggest that GnRH I and II binding may selectively stabilize different receptor-active conformations and therefore different ligand-induced selective signaling described previously for these ligands.