Mitogen- and stress-activated protein kinase 1 is required for gonadotropin-releasing hormone-mediated activation of gonadotropin α-subunit expression

Stimulus-Induced Activation of the Glycoprotein Hormone α-Subunit Promoter in Human Placental Choriocarcinoma Cells: Major Role of a tandem cAMP Response Element

The glycoprotein hormones LH, FSH, TSH and chorionic gonadotropin consist of a common α-subunit and a hormone-specific β-subunit. The α-subunit is expressed in the pituitary and the placental cells, and its expression is regulated by extracellular signal molecules. Much is known about the regulation of the α-subunit gene in the pituitary, but few studies have addressed the regulation of this gene in trophoblasts. The aim of this study was to characterize the molecular mechanism of stimulus-induced α-subunit gene transcription in JEG-3 cells, a cellular model for human trophoblasts, using chromatin-embedded reporter genes under the control of the α-subunit promoter. The results show that increasing the concentration of the second messengers cAMP or Ca2+, or expressing the catalytic subunit of cAMP-dependent protein kinase in the nucleus activated the α-subunit promoter. Similarly, the stimulation of p38 protein kinase activated the α-subunit promoter, linking α-subunit expression to stress response. The stimulation of a Gαq-coupled designer receptor activated the α-subunit promoter, involving the transcription factor CREB, linking α-subunit expression to hormonal stimulation and an increase in intracellular Ca2+. Deletion mutagenesis underscores the importance of a tandem cAMP response element within the glycoprotein hormone α-subunit promoter, which acts as a point of convergence for a multiple signaling pathway.

Epigenetic repression of gonadotropin gene expression via a GnRH-mediated DNA delivery system

The reproductive axis is activated by gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gonadotropes to secrete hormones that drive gonadal function and steroidogenesis. Thus repression of this axis, which is conserved across mammals and sexes, can reduce steroid levels and/or prevent reproduction. Steroid-dependent pathologies, including various cancers, are commonly treated with GnRH super-analogs which have long-term side-effects, while humane solutions for controlling reproduction in domestic and wild animal populations are lacking. GnRH-conjugated toxins are undergoing clinical trials for GnRHR-expressing cancer cells, and have been examined for gonadotrope ablation in animals, but showed low and/or transient effects and administration of toxins has many potential complications. Here we exploit GnRH targeting to gonadotropes to deliver DNA encoding an effector that induces gonadotropin gene repressive epigenetic modifications which are perpetuated over time. Several layers of specificity are endowed through targeting to GnRHR-expressing cells and due to local cleavage of the peptide packaging the DNA; the DNA-encoded effector is expressed and directed to the target genes by the DNA binding domain of a highly specific transcription factor. This design has multiple advantages over existing methods of shutting down the reproductive axis, and its modular design should allow adaptation for broad applications.

Epigenetic regulation of 5α reductase-1 underlies adaptive plasticity of reproductive function and pubertal timing

Background

Women facing increased energetic demands in childhood commonly have altered adult ovarian activity and shorter reproductive lifespan, possibly comprising a strategy to optimize reproductive success. Here, we sought to understand the mechanisms of early-life programming of reproductive function, by integrating analysis of reproductive tissues in an appropriate mouse model with methylation analysis of proxy tissue DNA in a well-characterized population of Bangladeshi migrants in the UK. Bangladeshi women whose childhood was in Bangladesh were found to have later pubertal onset and lower age-matched ovarian reserve than Bangladeshi women who grew-up in England. Subsequently, we aimed to explore the potential relevance to the altered reproductive phenotype of one of the genes that emerged from the screens.

Results

Of the genes associated with differential methylation in the Bangladeshi women whose childhood was in Bangladesh as compared to Bangladeshi women who grew up in the UK, 13 correlated with altered expression of the orthologous gene in the mouse model ovaries. These mice had delayed pubertal onset and a smaller ovarian reserve compared to controls. The most relevant of these genes for reproductive function appeared to be SRD5A1, which encodes the steroidogenic enzyme 5α reductase-1. SRD5A1 was more methylated at the same transcriptional enhancer in mice ovaries as in the women’s buccal DNA, and its expression was lower in the hypothalamus of the mice as well, suggesting a possible role in the central control of reproduction. The expression of Kiss1 and Gnrh was also lower in these mice compared to controls, and inhibition of 5α reductase-1 reduced Kiss1 and Gnrh mRNA levels and blocked GnRH release in GnRH neuronal cell cultures. Crucially, we show that inhibition of this enzyme in female mice in vivo delayed pubertal onset.

Conclusions

SRD5A1/5α reductase-1 responds epigenetically to the environment and its downregulation appears to alter the reproductive phenotype. These findings help to explain diversity in reproductive characteristics and how they are shaped by early-life environment and reveal novel pathways that might be targeted to mitigate health issues caused by life-history trade-offs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01219-6.

Genetic, epigenetic and enviromental influencing factors on the regulation of precocious and delayed puberty

The pubertal development onset is controlled by a network of genes that regulate the gonadotropin releasing hormone (GnRH) pulsatile release and the subsequent increase of the circulating levels of pituitary gonadotropins that activate the gonadal function. Although the transition from pre-pubertal condition to puberty occurs physiologically in a delimited age-range, the inception of pubertal development can be anticipated or delayed due to genetic and epigenetic changes or environmental conditions. Most of the genetic and epigenetic alterations concern genes which encode for kisspeptin, GnRH, LH, FSH and their receptor, which represent crucial factors of the hypothalamic-pituitary-gonadal (HPG) axis. Recent data indicate a central role of the epigenome in the regulation of genes in the hypothalamus and pituitary that could mediate the flexibility of pubertal timing. Identification of epigenetically regulated genes, such as Makorin ring finger 3 (MKRN3) and Delta-like 1 homologue (DLK1), respectively responsible for the repression and the activation of pubertal development, provides additional evidence of how epigenetic variations affect pubertal timing. This review aims to investigate genetic, epigenetic, and environmental factors responsible for the regulation of precocious and delayed puberty.

Proliferating primary pituitary cells as a model for studying regulation of gonadotrope chromatin and gene expression

The chromatin organization of the gonadotropin gene promoters in the pituitary gonadotropes plays a major role in determining how these gene are activated, but is difficult to study because of the low numbers of these cells in the pituitary gland. Here, we set out to create a cell model to study gonadotropin chromatin, and found that by optimizing cell culture conditions, we can maintain stable proliferating cultures of primary non-transformed gonadotrope cells over weeks to months. Although expression of the gonadotropin genes drops very low, these cells are enriched in gonadotrope markers and respond to GnRH. Furthermore, >85% of the cells contained Lhb and/or Fshb mature transcripts; though these were virtually restricted to the nuclei. The gonadotropes were harvested initially due to expression of dTOMATO, following activation of Cre recombinase by the Gnrhr promoter. Over 6 mo in culture, a similar proportion of the recombined DNA was maintained (i.e. cells derived from the original gonadotropes or having acquired Gnrhr-promoter activity), together with cells of a distinct origin. The cells are enriched with markers of proliferating pituitary and stem cells, including Sox2, suggesting that multipotent precursor cells might have proliferated and differentiated into gonadotrope-like cells. These cell cultures offer a new and versatile methodology for research in gonadotrope differentiation and function, and can provide enough primary cells for chromatin immunoprecipitation and epigenetic analysis, while our initial studies also indicate a possible regulatory mechanism that might be involved in the nuclear export of gonadotropin gene mRNAs.

Advances in the Regulation of Mammalian Follicle-Stimulating Hormone Secretion

Simple Summary

The reproduction of mammals is regulated by the hypothalamic-pituitary-gonadal axis. Follicle stimulating hormone, as one of the gonadotropins secreted by the pituitary gland, plays an immeasurable role. This article mainly reviews the molecular basis and classical signaling pathways that regulate the synthesis and secretion of follicle stimulating hormone, and summarizes its internal molecular mechanism, which provides a certain theoretical basis for the research of mammalian reproduction regulation and the application of follicle stimulating hormone in production practice.

Abstract

Mammalian reproduction is mainly driven and regulated by the hypothalamic-pituitary-gonadal (HPG) axis. Follicle-stimulating hormone (FSH), which is synthesized and secreted by the anterior pituitary gland, is a key regulator that ultimately affects animal fertility. As a dimeric glycoprotein hormone, the biological specificity of FSH is mainly determined by the β subunit. As research techniques are being continuously innovated, studies are exploring the underlying molecular mechanism regulating the secretion of mammalian FSH. This article will review the current knowledge on the molecular mechanisms and signaling pathways systematically regulating FSH synthesis and will present the latest hypothesis about the nuclear cross-talk among the various endocrine-induced pathways for transcriptional regulation of the FSH β subunit. This article will provide novel ideas and potential targets for the improved use of FSH in livestock breeding and therapeutic development.

The role of the hypothalamus and pituitary epigenomes in central activation of the reproductive axis at puberty

Puberty is programmed through a multifactorial gene network which works to activate the pulsatile secretion of the gonadotropin releasing hormone (GnRH), and subsequently elevate circulating levels of the pituitary gonadotropins that stimulate gonadal activity. Although this developmental transition normally occurs at a limited age-range in individuals of the same genetic background and environment, pubertal onset can occur prematurely or be delayed following changes in ambient conditions, or due to genetic variations or mutations, many of which have remained elusive due to their location in distal regulatory elements. Growing evidence is pointing to a pivotal role for the epigenome in regulating key genes in the reproductive hypothalamus and pituitary at this time, which might mediate some of the plasticity of pubertal timing. This review will address epigenetic mechanisms which have been demonstrated in the KNDy neurons that increase the output of pulsatile GnRH, and those involved in activation of the GnRH gene and its receptor, and describes how GnRH utilizes epigenetic mechanisms to stimulate transcription of the pituitary gonadotropin genes in the context of the chromatin landscape.

Unravelling the role of epigenetics in reproductive adaptations to early-life environment

Reproductive function adjusts in response to environmental conditions in order to optimize success. In humans, this plasticity includes age of pubertal onset, hormone levels and age at menopause. These reproductive characteristics vary across populations with distinct lifestyles and following specific childhood events, and point to a role for the early-life environment in shaping adult reproductive trajectories. Epigenetic mechanisms respond to external signals, exert long-term effects on gene expression and have been shown in animal and cellular studies to regulate normal reproductive function, strongly implicating their role in these adaptations. Moreover, human cohort data have revealed differential DNA methylation signatures in proxy tissues that are associated with reproductive phenotypic variation, although the cause-effect relationships are difficult to discern, calling for additional complementary approaches to establish functionality. In this Review, we summarize how adult reproductive function can be shaped by childhood events. We discuss why the influence of the childhood environment on adult reproductive function is an important consideration in understanding how reproduction is regulated and necessitates consideration by clinicians treating women with diverse life histories. The resolution of the molecular mechanisms responsible for human reproductive plasticity could also lead to new approaches for intervention by targeting these epigenetic modifications.

AMP-activated protein kinase activation reduces the transcriptional activity of the murine luteinizing hormone β-subunit gene

Malnutrition is one of the factors that induces reproductive disorders. However, the underlying biological processes are unclear. AMP-activated protein kinase (AMPK) is an enzyme that plays crucial role as a cellular energy sensor. In the present study, we examined the effects of AMPK activation on the transcription of the murine gonadotropin subunit genes Cga, Lhb, and Fshb, and the gonadotropin-releasing hormone receptor Gnrh-r. Real-time PCR and transcription assay using LβT2 cells demonstrated that 5-amino-imidazole carboxamide riboside (AICAR), a cell-permeable AMP analog, repressed the expression of Lhb. Next, we examined deletion mutants of the upstream region of Lhb and found that the upstream regulatory region of Lhb (-2527 to -2198 b) was responsible for the repression by AICAR. Furthermore, putative transcription factors (SP1, STAT5a, and TEF) that might mediate transcriptional control of the Lhb repression induced by AICAR were identified. In addition, it was confirmed that both AICAR and a competitive inhibitor of glucose metabolism, 2-deoxy-D-glucose, induced AMPK phosphorylation in LβT2 cells. Therefore, the upstream region of Lhb is one of the target sites for glucoprivation inducing AMPK activation. In addition, AMPK plays a role in repressing Lhb expression through the distal -2527 to -2198 b region.

Investigating the toxicities of different functionalized polystyrene nanoplastics on Daphnia magna

Nanoplastics (NPs) spread widely with water and air current, and they can accumulate in aquatic organisms, even penetrating biofilms, which may cause persistent toxicity and potential hazards. This current study aimed to reveal the toxicological mechanism of different functionalized polystyrene (PS) NPs on Daphnia magna (D. magna) by investigating toxicity endpoints in individual level and biochemical level. In this study, acute toxicity, behavioral parameters and biomarker responses of D. magna was measured in the exposure of different functionalized PS NPs (plain PS, PS-p-NH₂, PS-n-NH₂ and PS-COOH). The results indicated that when exposed to the plain PS, ROS induction would activate MAPKs, thereby causing lethality and adverse behavior effects on D. magna; while the functionalized PS NPs were less toxic than the plain PS, especially for PS-p-NH₂ which was severely flocculated after exposure, thus showing no immobilization at the investigated concentrations. Also, the antioxidant system was mainly stimulated due to the direct interaction with the cell surface receptor, which was different from the plain PS. Consequently, this work suggests significant effects of functional groups on NPs for environmental toxicity studies, and provides a better understanding of the toxicological mechanism on the toxicity of PS NPs toward D. magna.

The role of mitogen-activated protein kinase-extracellular receptor kinase pathway in female fertility outcomes: a focus on pituitary gonadotropins regulation

Mammalian reproduction systems are largely regulated by the secretion of two gonadotropins, that is, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The main action of LH and FSH on the ovary is to stimulate secretion of estradiol and progesterone, which play an important role in the ovarian function and reproductive cycle control. FSH and LH secretions are strictly controlled by the gonadotropin-releasing hormone (GnRH), which is secreted from the hypothalamus into the pituitary vascular system. Maintaining normal secretion of LH and FSH is dependent on pulsatile secretion of GnRH. Extracellular signal-regulated kinase (ERK) proteins, as the main components of mitogen-activated protein kinase (MAPK) signaling pathways, are involved in the primary regulation of GnRH-stimulated transcription of the gonadotropins' α subunit in the pituitary cells. However, GnRH-stimulated expression of the β subunit has not yet been reported. Furthermore, GnRH-mediated stimulation of ERK1 and ERK2 leads to several important events such as cell proliferation and differentiation. In this review, we briefly introduce the relationship between ERK signaling and gonadotropin secretion, and its importance in female infertility.

Molecular regulation of follicle-stimulating hormone synthesis, secretion and action

Follicle-stimulating hormone (FSH) plays fundamental roles in male and female fertility. FSH is a heterodimeric glycoprotein expressed by gonadotrophs in the anterior pituitary. The hormone-specific FSHβ-subunit is non-covalently associated with the common α-subunit that is also present in the luteinizing hormone (LH), another gonadotrophic hormone secreted by gonadotrophs and thyroid-stimulating hormone (TSH) secreted by thyrotrophs. Several decades of research led to the purification, structural characterization and physiological regulation of FSH in a variety of species including humans. With the advent of molecular tools, availability of immortalized gonadotroph cell lines and genetically modified mouse models, our knowledge on molecular mechanisms of FSH regulation has tremendously expanded. Several key players that regulate FSH synthesis, sorting, secretion and action in gonads and extragonadal tissues have been identified in a physiological setting. Novel post-transcriptional and post-translational regulatory mechanisms have also been identified that provide additional layers of regulation mediating FSH homeostasis. Recombinant human FSH analogs hold promise for a variety of clinical applications, whereas blocking antibodies against FSH may prove efficacious for preventing age-dependent bone loss and adiposity. It is anticipated that several exciting new discoveries uncovering all aspects of FSH biology will soon be forthcoming.

Multifaceted Targeting of the Chromatin Mediates Gonadotropin-Releasing Hormone Effects on Gene Expression in the Gonadotrope

Gonadotropin-releasing hormone (GnRH) stimulates the expression of multiple genes in the pituitary gonadotropes, most notably to induce synthesis of the gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH), but also to ensure the appropriate functioning of these cells at the center of the mammalian reproductive endocrine axis. Aside from the activation of gene-specific transcription factors, GnRH stimulates through its membrane-bound receptor, alterations in the chromatin that facilitate transcription of its target genes. These include changes in the histone and DNA modifications, nucleosome positioning, and chromatin packaging at the regulatory regions of each gene. The requirements for each of these events vary according to the DNA sequence which determines the basal chromatin packaging at the regulatory regions. Despite considerable progress in this field in recent years, we are only beginning to understand some of the complexities involved in the role and regulation of this chromatin structure, including new modifications, extensive cross talk, histone variants, and the actions of distal enhancers and non-coding RNAs. This short review aims to integrate the latest findings on GnRH-induced alterations in the chromatin of its target genes, which indicate multiple and diverse actions. Understanding these processes is illuminating not only in the context of the activation of these hormones during the reproductive life span but may also reveal how aberrant epigenetic regulation of these genes leads to sub-fertility.