Mechanisms underlying the tissue-specific and regulated activity of the Gnrhr promoter in mammals

Inter-Individual Variation in DNA Methylation Patterns across Two Tissues and Leukocytes in Mature Brahman Cattle

Quantifying the natural inter-individual variation in DNA methylation patterns is important for identifying its contribution to phenotypic variation, but also for understanding how the environment affects variability, and for incorporation into statistical analyses. The inter-individual variation in DNA methylation patterns in female cattle and the effect that a prenatal stressor has on such variability have yet to be quantified. Thus, the objective of this study was to utilize methylation data from mature Brahman females to quantify the inter-individual variation in DNA methylation. Pregnant Brahman cows were transported for 2 h durations at days 60 ± 5; 80 ± 5; 100 ± 5; 120 ± 5; and 140 ± 5 of gestation. A non-transport group was maintained as a control. Leukocytes, amygdala, and anterior pituitary glands were harvested from eight cows born from the non-transport group (Control) and six from the transport group (PNS) at 5 years of age. The DNA harvested from the anterior pituitary contained the greatest variability in DNA methylation of cytosine-phosphate-guanine (mCpG) sites from both the PNS and Control groups, and the amygdala had the least. Numerous variable mCpG sites were associated with retrotransposable elements and highly repetitive regions of the genome. Some of the genomic features that had high variation in DNA methylation are involved in immune responses, signaling, responses to stimuli, and metabolic processes. The small overlap of highly variable CpG sites and features between tissues and leukocytes supports the role of variable DNA methylation in regulating tissue-specific gene expression. Many of the CpG sites that exhibited high variability in DNA methylation were common between the PNS and Control groups within a tissue, but there was little overlap in genomic features with high variability. The interaction between the prenatal environment and the genome could be responsible for the differences in location of the variable DNA methylation.

Molecular basis for the evolved instability of a human G-protein coupled receptor

Membrane proteins are prone to misfolding and degradation. This is particularly true for mammalian forms of the gonadotropin-releasing hormone receptor (GnRHR). Although they function at the plasma membrane, mammalian GnRHRs accumulate within the secretory pathway. Their apparent instability is believed to have evolved through selection for attenuated GnRHR activity. Nevertheless, the molecular basis of this adaptation remains unclear. We show that adaptation coincides with a C-terminal truncation that compromises the translocon-mediated membrane integration of its seventh transmembrane domain (TM7). We also identify a series of polar residues in mammalian GnRHRs that compromise the membrane integration of TM2 and TM6. Reverting a lipid-exposed polar residue in TM6 to an ancestral hydrophobic residue restores expression with no impact on function. Evolutionary trends suggest variations in the polarity of this residue track with reproductive phenotypes. Our findings suggest that the marginal energetics of cotranslational folding can be exploited to tune membrane protein fitness.

Integral membrane proteins are prone to misfolding, especially mammalian gonadotropin-releasing hormone receptors (GnRHRs). Chamness et al. show that the evolved instability of mammalian GnRHRs stems from adaptive modifications that disrupt translocon-mediated membrane integration, suggesting that membrane protein misfolding can be exploited to tune fitness.

The Effects of Zearalenone on the Localization and Expression of Reproductive Hormones in the Ovaries of Weaned Gilts

This study aims to investigate the effects of zearalenone (ZEA) on the localizations and expressions of follicle stimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR), gonadotropin releasing hormone (GnRH) and gonadotropin releasing hormone receptor (GnRHR) in the ovaries of weaned gilts. Twenty 42-day-old weaned gilts were randomly allocated into two groups, and treated with a control diet and a ZEA-contaminated diet (ZEA 1.04 mg/kg), respectively. After 7-day adjustment, gilts were fed individually for 35 days and euthanized for blood and ovarian samples collection before morning feeding on the 36th day. Serum hormones of E₂, PRG, FSH, LH and GnRH were determined using radioimmunoassay kits. The ovaries were collected for relative mRNA and protein expression, and immunohistochemical analysis of FSHR, LHR, GnRH and GnRHR. The results revealed that ZEA exposure significantly increased the final vulva area (p < 0.05), significantly elevated the serum concentrations of estradiol, follicle stimulating hormone and GnRH (p < 0.05), and markedly up-regulated the mRNA and protein expressions of FSHR, LHR, GnRH and GnRHR (p < 0.05). Besides, the results of immunohistochemistry showed that the immunoreactive substances of ovarian FSHR, LHR, GnRH and GnRHR in the gilts fed the ZEA-contaminated diet were stronger than the gilts fed the control diet. Our findings indicated that dietary ZEA (1.04 mg/kg) could cause follicular proliferation by interfering with the localization and expression of FSHR, LHR, GnRH and GnRHR, and then affect the follicular development of weaned gilts.

Enhancing Gonadotrope Gene Expression Through Regulatory lncRNAs

The world of long non-coding RNAs (lncRNAs) has opened up massive new prospects in understanding the regulation of gene expression. Not only are there seemingly almost infinite numbers of lncRNAs in the mammalian cell, but they have highly diverse mechanisms of action. In the nucleus, some are chromatin-associated, transcribed from transcriptional enhancers (eRNAs) and/or direct changes in the epigenetic landscape with profound effects on gene expression. The pituitary gonadotrope is responsible for activation of reproduction through production and secretion of appropriate levels of the gonadotropic hormones. As such, it exemplifies a cell whose function is defined through changes in developmental and temporal patterns of gene expression, including those that are hormonally induced. Roles for diverse distal regulatory elements and eRNAs in gonadotrope biology have only just begun to emerge. Here, we will present an overview of the different kinds of lncRNAs that alter gene expression, and what is known about their roles in regulating some of the key gonadotrope genes. We will also review various screens that have detected differentially expressed pituitary lncRNAs associated with changes in reproductive state and those whose expression is found to play a role in gonadotrope-derived nonfunctioning pituitary adenomas. We hope to shed light on this exciting new field, emphasize the open questions, and encourage research to illuminate the roles of lncRNAs in various endocrine systems.

Androgen receptor positively regulates gonadotropin-releasing hormone receptor in pituitary gonadotropes

Within pituitary gonadotropes, the gonadotropin-releasing hormone receptor (GnRHR) receives hypothalamic input from GnRH neurons that is critical for reproduction. Previous studies have suggested that androgens may regulate GnRHR, although the mechanisms remain unknown. In this study, we demonstrated that androgens positively regulate Gnrhr mRNA in mice. We then investigated the effects of androgens and androgen receptor (AR) on Gnrhr promoter activity in immortalized mouse LβT2 cells, which represent mature gonadotropes. We found that AR positively regulates the Gnrhr proximal promoter, and that this effect requires a hormone response element (HRE) half site at -159/-153 relative to the transcription start site. We also identified nonconsensus, full-length HREs at -499/-484 and -159/-144, which are both positively regulated by androgens on a heterologous promoter. Furthermore, AR associates with the Gnrhr promoter in ChIP. Altogether, we report that GnRHR is positively regulated by androgens through recruitment of AR to the Gnrhr proximal promoter.

Post-Transcriptional Regulation of Gnrhr: A Checkpoint for Metabolic Control of Female Reproduction

The proper expression of gonadotropin-releasing hormone receptors (GnRHRs) by pituitary gonadotropes is critical for maintaining maximum reproductive capacity. GnRH receptor expression must be tightly regulated in order to maintain the normal pattern of expression through the estrous cycle in rodents, which is believed to be important for interpreting the finely tuned pulses of GnRH from the hypothalamus. Much work has shown that Gnrhr expression is heavily regulated at the level of transcription. However, researchers have also discovered that Gnrhr is regulated post-transcriptionally. This review will discuss how RNA-binding proteins and microRNAs may play critical roles in the regulation of GnRHR expression. We will also discuss how these post-transcriptional regulators may themselves be affected by metabolic cues, specifically with regards to the adipokine leptin. All together, we present evidence that Gnrhr is regulated post-transcriptionally, and that this concept must be further explored in order to fully understand the complex nature of this receptor.

HSP70 inhibits pig pituitary gonadotrophin synthesis and secretion by regulating the corticotropin-releasing hormone signaling pathway and targeting SMAD3

High levels or long periods of stress have been shown to negatively impact cell homeostasis, including with respect to abnormalities in domestic animal reproduction, which are typically activated through the hypothalamus-pituitary-adrenal axis, in which corticotropin-releasing hormone (CRH) and heat shock protein 70 (HSP70) are involved. In addition, CRH has been reported to inhibit pituitary gonadotrophin synthesis, and HSP70 is expressed in the pituitary gland. The aim of this study was to determine whether HSP70 was involved in regulating gonadotrophin synthesis and secretion by mediating the CRH pathway in the porcine pituitary gland. Our results showed that HSP70 was highly expressed in the porcine pituitary gland, with over 90% of gonadotrophic cells testing HSP70 positive. The results of functional studies demonstrated that the HSP70 inducer decreased FSH and LH levels in cultured porcine primary pituitary cells, whereas an HSP70 inhibitor blocked the negative effect of CRH on gonadotrophin synthesis and secretion. Furthermore, our results demonstrated that HSP70 inhibited gonadotrophin synthesis and secretion by blocking GnRH-induced SMAD3 phosphorylation, which acts as the targeting molecule of HSP70, while CRH upregulated HSP70 expression through the PKC and ERK pathways. Collectively, these data demonstrate that HSP70 inhibits pituitary gonadotrophin synthesis and secretion by regulating the CRH signaling pathway and inhibiting SMAD3 phosphorylation, which are important for our understanding the mechanisms of the stress affects domestic animal reproductive functions.

Sex- and Age-Specific Impact of ERK Loss Within the Pituitary Gonadotrope in Mice

Extracellular signal-regulated kinase (ERK) signaling regulates hormone action in the reproductive axis, but specific mechanisms have yet to be completely elucidated. In the current study, ERK1 null and ERK2 floxed mice were combined with a gonadotropin-releasing hormone receptor (GnRHR)-internal ribosomal entry site-Cre (GRIC) driver. Female ERK double-knockout (ERKdko) animals were hypogonadotropic, resulting in anovulation and complete infertility. Transcript levels of four gonadotrope-specific genes (GnRHR and the three gonadotropin subunits) were reduced in pituitaries at estrus in ERKdko females, and the postcastration response to endogenous GnRH hyperstimulation was blunted. As females aged, they exhibited abnormal ovarian histology, as well as increased body weight. ERKdko males were initially less affected, showing moderate subfertility, up to 6 months of age. Male ERKdko mice also displayed a blunted response to endogenous GnRH following castration. By 12 months of age, ERKdko males had reduced testicular weights and sperm production. By 18 months of age, the ERKdko males displayed reduced testis and seminal vesicle weights, marked seminiferous tubule degeneration, and a 77% reduction in sperm production relative to controls. As the GRIC is also active in the male germ line, we examined the specific role of ERK loss in the testes using the stimulated by retinoic acid 8 (Stra8)-Cre driver. Whereas ERK loss in GRIC and Stra8 males resulted in comparable losses in sperm production, seminiferous tubule histological degeneration was only observed in the GRIC-ERKdko animals. Our data suggest that loss of ERK signaling and hypogonadotropism within the reproductive axis impacts fertility and gonadal aging.

A physiologically based pharmacokinetic (PBPK) parent-metabolite model of the chemotherapeutic zoptarelin doxorubicin-integration of in vitro results, Phase I and Phase II data and model application for drug-drug interaction potential analysis

PURPOSE

Zoptarelin doxorubicin is a fusion molecule of the chemotherapeutic doxorubicin and a luteinizing hormone-releasing hormone receptor (LHRHR) agonist, designed for drug targeting to LHRHR positive tumors. The aim of this study was to establish a physiologically based pharmacokinetic (PBPK) parent-metabolite model of zoptarelin doxorubicin and to apply it for drug-drug interaction (DDI) potential analysis.

METHODS

The PBPK model was built in a two-step procedure. First, a model for doxorubicin was developed, using clinical data of a doxorubicin study arm. Second, a parent-metabolite model for zoptarelin doxorubicin was built, using clinical data of three different zoptarelin doxorubicin studies with a dosing range of 10-267 mg/m², integrating the established doxorubicin model. DDI parameters determined in vitro were implemented to predict the impact of zoptarelin doxorubicin on possible victim drugs.

RESULTS

In vitro, zoptarelin doxorubicin inhibits the drug transporters organic anion-transporting polypeptide 1B3 (OATP1B3) and organic cation transporter 2 (OCT2). The model was applied to evaluate the in vivo inhibition of these transporters in a generic manner, predicting worst-case scenario decreases of 0.5% for OATP1B3 and of 2.5% for OCT2 transport rates. Specific DDI simulations using PBPK models of simvastatin (OATP1B3 substrate) and metformin (OCT2 substrate) predict no significant changes of the plasma concentrations of these two victim drugs during co-administration.

CONCLUSIONS

The first whole-body PBPK model of zoptarelin doxorubicin and its active metabolite doxorubicin has been successfully established. Zoptarelin doxorubicin shows no potential for DDIs via OATP1B3 and OCT2.

Intrinsic and Regulated Gonadotropin-Releasing Hormone Receptor Gene Transcription in Mammalian Pituitary Gonadotrophs

The hypothalamic decapeptide gonadotropin-releasing hormone (GnRH), acting via its receptors (GnRHRs) expressed in pituitary gonadotrophs, represents a critical molecule in control of reproductive functions in all vertebrate species. GnRH-activated receptors regulate synthesis of gonadotropins in a frequency-dependent manner. The number of GnRHRs on the plasma membrane determines the responsiveness of gonadotrophs to GnRH and varies in relation to age, sex, and physiological status. This is achieved by a complex control that operates at transcriptional, translational, and posttranslational levels. This review aims to overview the mechanisms of GnRHR gene (Gnrhr) transcription in mammalian gonadotrophs. In general, Gnrhr exhibits basal and regulated transcription activities. Basal Gnrhr transcription appears to be an intrinsic property of native and immortalized gonadotrophs that secures the presence of a sufficient number GnRHRs to preserve their functionality independently of the status of regulated transcription. On the other hand, regulated transcription modulates GnRHR expression during development, reproductive cycle, and aging. GnRH is crucial for regulated Gnrhr transcription in native gonadotrophs but is ineffective in immortalized gonadotrophs. In rat and mouse, both basal and GnRH-induced Gnrhr transcription rely primarily on the protein kinase C signaling pathway, with subsequent activation of mitogen-activated protein kinases. Continuous GnRH application, after a transient stimulation, shuts off regulated but not basal transcription, suggesting that different branches of this signaling pathway control transcription. Pituitary adenylate cyclase-activating polypeptide, but not activins, contributes to the regulated transcription utilizing the protein kinase A signaling pathway, whereas a mechanisms by which steroid hormones modulate Gnrhr transcription has not been well characterized.

The relationship between basal and regulated Gnrhr expression in rodent pituitary gonadotrophs

Hypothalamic GnRH together with gonadal steroids and activins/inhibin regulate its receptor gene (Gnrhr) expression in vivo, which leads to crucial changes in GnRHR numbers on the plasma membrane. This is accompanied by alterations in the gonadotroph sensitivity and responsiveness during physiologically relevant situations. Here we investigated basal and GnRH-regulated Gnrhr expression in rodent pituitary gonadotrophs in vitro. In pituitary cells from adult animals cultured in the absence of GnRH and steroid hormones, the Gnrhr expression was progressively reduced but not completely abolished. The basal Gnrhr expression was also operative in LβT2 immortalized gonadotrophs never exposed to GnRH. In both cell types, basal transcription was sufficient for the expression of functional GnRHRs. Continuous application of GnRH transiently elevated the Gnrhr expression in cultured pituitary cells followed by a sustained fall without affecting basal transcription. Both basal and regulated Gnrhr transcriptions were dependent on the protein kinase C signaling pathway. The GnRH-regulated Gnrhr expression was not operative in embryonal pituitary and LβT2 cells and was established neonatally, the sex-specific response patterns were formed at the juvenile-peripubertal stage and there was a strong correlation between basal and regulated gene expression during development. Thus, the age-dependent basal and regulated Gnrhr transcription could account for the initial blockade and subsequent activation of the reproductive system during development.

Gonadotropin-releasing hormone stimulates biliary proliferation by paracrine/autocrine mechanisms

During cholestatic liver disease, there is dysregulation in the balance between biliary growth and loss in bile duct-ligated (BDL) rats modulated by neuroendocrine peptides via autocrine/paracrine pathways. Gonadotropin-releasing hormone (GnRH) is a trophic peptide hormone that modulates reproductive function and proliferation in many cell types. We evaluated the autocrine role of GnRH in the regulation of cholangiocyte proliferation. The expression of GnRH receptors was assessed in a normal mouse cholangiocyte cell line (NMC), sham, and BDL rats. The effect of GnRH administration was evaluated in normal rats and in NMC. GnRH-induced biliary proliferation was evaluated by changes in intrahepatic bile duct mass and the expression of proliferation and function markers. The expression and secretion of GnRH in NMC and isolated cholangiocytes was assessed. GnRH receptor subtypes GnRHR1 and GnRHR2 were expressed in cholangiocytes. Treatment with GnRH increased intrahepatic bile duct mass as well as proliferation and function markers in cholangiocytes. Transient knockdown and pharmacologic inhibition of GnRHR1 in NMC decreased proliferation. BDL cholangiocytes had increased expression of GnRH compared with normal rats, accompanied by increased GnRH secretion. In vivo and in vitro knockdown of GnRH decreased intrahepatic bile duct mass/cholangiocyte proliferation and fibrosis. GnRH secreted by cholangiocytes promotes biliary proliferation via an autocrine pathway. Disruption of GnRH/GnRHR signaling may be important for the management of cholestatic liver diseases.

Intracellular mechanisms involved in copper-gonadotropin-releasing hormone (Cu-GnRH) complex-induced cAMP/PKA signaling in female rat anterior pituitary cells in vitro

The copper-gonadotropin-releasing hormone molecule (Cu-GnRH) is a GnRH analog, which preserves its amino acid sequence, but which contains a Cu(2+) ion stably bound to the nitrogen atoms including that of the imidazole ring of Histidine(2). A previous report indicated that Cu-GnRH was able to activate cAMP/PKA signaling in anterior pituitary cells in vitro, but raised the question of which intracellular mechanism(s) mediated the Cu-GnRH-induced cAMP synthesis in gonadotropes. To investigate this mechanism, in the present study, female rat anterior pituitary cells in vitro were pretreated with 0.1 μM antide, a GnRH antagonist; 0.1 μM cetrorelix, a GnRH receptor antagonist; 0.1 μM PACAP6-38, a PAC-1 receptor antagonist; 2 μM GF109203X, a protein kinase C inhibitor; 50 mM PMA, a protein kinase C activator; the protein kinase A inhibitors H89 (30 μM) and KT5720 (60 nM); factors affecting intracellular calcium activity: 2.5 mM EGTA; 2 μM thapsigargin; 5 μM A23187, a Ca(2+) ionophore; or 10 μg/ml cycloheximide, a protein synthesis inhibitor. After one of the above pretreatments, cells were incubated in the presence of 0.1 μM Cu-GnRH for 0.5, 1, and 3 h. Radioimmunoassay analysis of cAMP confirmed the functional link between Cu-GnRH stimulation and cAMP/PKA signal transduction in rat anterior pituitary cells, demonstrating increased intracellular cAMP, which was reduced in the presence of specific PKA inhibitors. The stimulatory effect of Cu-GnRH on cAMP production was partly dependent on GnRH receptor activation. In addition, an indirect and Ca(2+)-dependent mechanism might be involved in intracellular adenylate cyclase stimulation. Neither activation of protein kinase C nor new protein synthesis was involved in the Cu-GnRH-induced increase of cAMP in the rat anterior pituitary primary cultures. Presented data indicate that conformational changes of GnRH molecule resulting from cooper ion coordination affect specific pharmacological properties of Cu-GnRH molecule including specific pattern of intracellular activity induced by complex in anterior pituitary cells in vitro.

Inside and outside the pituitary: comparative analysis of Gnrhr expression provides insight into the mechanisms underlying the evolution of gene expression

DNA cis-acting elements involved in gene regulation may actively contribute to adaptation processes because they are submitted to lower evolutionary constraints than coding DNA. In this regard, comparisons of the mechanisms underlying basal and regulated Gnrhr expression have revealed some features that promote stable and consistent Gnrhr expression in pituitary gonadotroph cells in different species. The presence of two divergent SF1 (NR5A1) response elements in all analysed mammalian Gnrhr promoters probably comprises one of the features that ensures reliable expression in the pituitary. By contrast, in other tissues, such as the hippocampus and testis, our analyses revealed dissimilar levels of Gnrhr expression among species. Indeed, Gnrhr was consistently expressed after birth in the rat but not the mouse hippocampus. Similar discrepancies were observed in foetal and adult testes. The ability of the rat promoter to drive reporter gene expression in the hippocampus and testis of transgenic mice just as it naturally directs the expression of the endogenous Gnrhr in rats strongly suggests that regulatory DNA sequences contained species-specific instructions prevailing over other controls. The major conclusion emerging from these studies is that Gnrhr promoter sequences are mainly responsible for directing transcriptional programmes and play a predominant role over the species-specific cell environment.

Molecular regulation of hypothalamus-pituitary-gonads axis in males

The hypothalamic-pituitary-gonadal axis (HPG) plays vital roles in reproduction and steroid hormone production in both sexes. The focus of this review is upon gene structures, receptor structures and the signaling pathways of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The hormones' functions in reproduction as well as consequences resulting from mutations are also summarized. Specific characteristics of hormones such as the pulsatile secretions of GnRH are also covered. The different regulators of the HPG axis are introduced including kisspeptin, activin, inhibin, follistatin, androgens and estrogen. This review includes not only their basic information, but also their unique function in the HPG axis. Here we view the HPG axis as a whole, so relations between ligands and receptors are well described crossing different levels of the HPG axis. Hormone interactions and transformations are also considered. The major information of this article is depicted in three figures summarizing the current discoveries on the HPG axis. This article systematically introduces the basic knowledge of the HPG axis and provides information of the current advances relating to reproductive hormones.