Effect of interleukin-1beta on gonadotropin-releasing hormone (GnRH) and GnRH receptor gene expression in castrated male rats

Immune signaling as a node of interaction between systems that sex-specifically develop during puberty and adolescence

Adolescence is pivotal for neural and behavioral development across species. During this period, maturation occurs in several biological systems, the most well-recognized being activation of the hypothalamic-pituitary-gonadal axis marking pubertal onset. Increasing comparative studies of sex differences have enriched our understanding of systems integration during neurodevelopment. In recent years, immune signaling has emerged as a key node of interaction between a variety of biological signaling processes. Herein, we review the age- and sex-specific changes that occur in neural, hypothalamic-pituitary, and microbiome systems during adolescence. We then describe how immune signaling interacts with these systems, and review recent preclinical evidence indicating that immune signaling may play a central role in integrating changes in their typical and atypical development during adolescence. Finally, we discuss the translational relevance of these preclinical studies to human health and wellness.

Skin exposure to UVB light induces a skin-brain-gonad axis and sexual behavior

Ultraviolet (UV) light affects endocrinological and behavioral aspects of sexuality via an unknown mechanism. Here we discover that ultraviolet B (UVB) exposure enhances the levels of sex-steroid hormones and sexual behavior, which are mediated by the skin. In female mice, UVB exposure increases hypothalamus-pituitary-gonadal axis hormone levels, resulting in larger ovaries; extends estrus days; and increases anti-Mullerian hormone (AMH) expression. UVB exposure also enhances the sexual responsiveness and attractiveness of females and male-female interactions. Conditional knockout of p53 specifically in skin keratinocytes abolishes the effects of UVB. Thus, UVB triggers a skin-brain-gonadal axis through skin p53 activation. In humans, solar exposure enhances romantic passion in both genders and aggressiveness in men, as seen in analysis of individual questionaries, and positively correlates with testosterone level. Our findings suggest opportunities for treatment of sex-steroid-related dysfunctions.

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UVB exposure increases circulating sex-steroid levels in mice and humans

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UVB exposure enhances female attractiveness and receptiveness toward males

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UVB exposure increases females’ estrus phase, HPG axis hormones, and follicle growth

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Skin p53 regulates UVB-induced sexual behavior and ovarian physiological changes

Laboratory predictors of pregnancy in vitro fertilization

Identification of factors determining both of favorable and unfavorable outcome of IVF will increase the effectiveness of this method and optimize infertility treatment. The aim of the research is to analyze the correlation between serum IL-1α concentration, its gene rs1800587 (C/T) genotype carrier and thyroid-stimulating hormone (TSH), thyroid hormones (triiodothyronine (T3) and tetraiodothyronine (T4)), and evaluate the prognostic significance of their combinations in women with tube-peritoneal infertility under the IVF program. 120 patients with tube-peritoneal infertility who applied for an IVF program were examined. Depending on the outcome of the procedure, 2 groups of patients were allocated: 1 group - 40 women who had a pregnancy after IVF, 2 group - 80 patients who did not have a pregnancy. The content of IL-1α, TSH, T3, T4 was determined in blood by ELISA. Genotyping was performed on the rs1800587 (C/T) polymorphic marker of the IL-1α gene. TSH, T3, T4 were within the norm for both groups. In our study, women with a TSH concentration of 0.23 to 1.7 nmol/L had a chance of a favorable IVF outcome 1.4 times higher than with other TSH levels (p = 0.042901); with a T3 level of 1.0 to 1.8 nmol/L had a chance of becoming pregnant 5.7 times higher than with other levels of T3 (p = 0.00002). For T4 concentration, the confidence test was not achieved (p = 0.068505). The individual indicators of IL-1α, TSH, T3 and carrier of the genotype of the gene IL-1α at the preconceptive stage have lower diagnostic value than their combined combination. Three combinations have maximum predictive value: a combination of the T/T genotype of the IL-1α gene and the TSH level of 0.23 to 1.7 nmol/l - OR = 8.1 (p = 0.000048); combination of IL-1α of 28.7 to 85.1 pg/ml, T/T gene genotype IL-1α and TSH level of 0.23 to 1.7 nmol/l - OR = 8.1 (p = 0.000048); combination of IL-1α of 28.7 to 85.1 pg/ml, T/T gene genotype IL-1α, TSH level of 0.23 to 1.7 nmol/l and T3 level of 1.0 to 1.8 nmol/l - OR = 8.1 (p = 0.000146). Thus, proposed new prognostic markers of IVF program effectiveness.

Anandamide Influences Interleukin-1β Synthesis and IL-1 System Gene Expressions in the Ovine Hypothalamus during Endo-Toxin-Induced Inflammation

Simple Summary

Pro-inflammatory cytokines are considered to be one of the most important mediators affecting the function of central nervous system during an immune/inflammatory challenge. It was found that in acting on different hypothalamic nuclei, pro-inflammatory cytokines influence the centrally regulated processes including reproduction. Recently, it has been shown that the endocannabinoid system and endogenous cannabinoids may attenuate the inflammatory response. Therefore, in our study we examined the influence of anandamide, one of the earliest known endocannabinoids, on the synthesis of interleukin (IL)-1β and IL-1 system gene expressions in the hypothalamic structures involved in gonadotropin-releasing hormone (GnRH)-ergic activity, and thus the central control of reproduction, during immune stress induced by endotoxin injection. It was found that anandamide inhibited lipopolysaccharide (LPS)-stimulated synthesis of IL-1β in the hypothalamus, likely affecting posttranscriptional levels of this cytokine synthesis. Anti-inflammatory effect of anandamide at the level of central nervous system might also result from its stimulating action on IL-1 antagonist and IL-1 type II receptor gene expression. This study suggests the potential of endocannabinoids and/or their metabolites in the inhibition of inflammatory process at the level of the central nervous system, as well as their usefulness in the therapy of inflammation-induced neuroendocrine disorders, but further detailed research is required to investigate this issue.

Abstract

This study evaluated the effect of anandamide (AEA) on interleukin (IL)-1β synthesis and gene expression of IL-1β, its type I (IL-1R1) and II (IL-1R2) receptors, and IL-1 receptor antagonist (IL-1RN) in the hypothalamic structures, involved in the central control of reproduction, during inflammation. Animals were intravenously (i.v.) injected with bacterial endotoxin-lipopolysaccharide (LPS) (400 ng/kg) or saline, and two hours after LPS administration., a third group received i.v. injection of AEA (10 μg/kg). Ewes were euthanized one hour later. AEA injection (p < 0.05) suppressed LPS-induced expression of IL-1β protein in the hypothalamus. The gene expression of IL-1β, IL-1RN, and IL-1R2 in the hypothalamic structures was higher (p < 0.05) in animals treated with both LPS and AEA in comparison to other experimental groups. AEA administration did not influence LPS-stimulated IL-1R1 gene expression. Our study shows that AEA suppressed IL-1β synthesis in the hypothalamus, likely affecting posttranscriptional levels of this cytokine synthesis. However, anti-inflammatory effect of AEA might also result from its stimulating action on IL-1RN and IL-1R2 gene expression. These results indicate the potential of endocannabinoids and/or their metabolites in the inhibition of inflammatory process at the level of central nervous system, and therefore their usefulness in the therapy of inflammation-induced neuroendocrine disorders.

Estradiol-induced senescence of hypothalamic astrocytes contributes to aging-related reproductive function declines in female mice

Hypothalamic astrocytes are important contributors that activate gonadotropin-releasing hormone (GnRH) neurons and promote GnRH/LH (luteinizing hormone) surge. However, the potential roles and mechanisms of astrocytes during the early reproductive decline remain obscure. The current study reported that, in intact middle-aged female mice, astrocytes within the hypothalamic RP3V accumulated senescence-related markers with increasing age. It employed an ovariectomized animal model and a cell model receiving estrogen intervention to confirm the estrogen-induced senescence of hypothalamic astrocytes. It found that estrogen metabolites may be an important factor for the estrogen-induced astrocyte senescence. In vitro molecular analysis revealed that ovarian estradiol activated PKA and up-regulated CYPs expression, metabolizing estradiol into 2-OHE₂ and 4-OHE₂. Of note, in middle-aged mice, the progesterone synthesis and the ability to promote GnRH release were significantly reduced. Besides, the expression of growth factors decreased and the mRNA levels of proinflammatory cytokines significantly increased in the aging astrocytes. The findings confirm that ovarian estradiol induces the senescence of hypothalamic astrocytes and that the senescent astrocytes compromise the regulation of progesterone synthesis and GnRH secretion, which may contribute to the aging-related declines in female reproductive function.

Effect of Inflammation on Female Gonadotropin-Releasing Hormone (GnRH) Neurons: Mechanisms and Consequences

: Inflammation has a well-known suppressive effect on fertility. The function of gonadotropin-releasing hormone (GnRH) neurons, the central regulator of fertility is substantially altered during inflammation in females. In our review we discuss the latest results on how the function of GnRH neurons is modified by inflammation in females. We first address the various effects of inflammation on GnRH neurons and their functional consequences. Second, we survey the possible mechanisms underlying the inflammation-induced actions on GnRH neurons. The role of several factors will be discerned in transmitting inflammatory signals to the GnRH neurons: cytokines, kisspeptin, RFamide-related peptides, estradiol and the anti-inflammatory cholinergic pathway. Since aging and obesity are both characterized by reproductive decline our review also focuses on the mechanisms and pathophysiological consequences of the impact of inflammation on GnRH neurons in aging and obesity.

Effect of Central Injection of Neostigmine on the Bacterial Endotoxin Induced Suppression of GnRH/LH Secretion in Ewes during the Follicular Phase of the Estrous Cycle

Induced by a bacterial infection, an immune/inflammatory challenge is a potent negative regulator of the reproduction process in females. The reduction of the synthesis of pro-inflammatory cytokine is considered as an effective strategy in the treatment of inflammatory induced neuroendocrine disorders. Therefore, the effect of direct administration of acetylcholinesterase inhibitor—neostigmine—into the third ventricle of the brain on the gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretions under basal and immune stress conditions was evaluated in this study. In the study, 24 adult, 2-years-old Blackhead ewes during the follicular phase of their estrous cycle were used. Immune stress was induced by the intravenous injection of LPS Escherichia coli in a dose of 400 ng/kg. Animals received an intracerebroventricular injection of neostigmine (1 mg/animal) 0.5 h before LPS/saline treatment. It was shown that central administration of neostigmine might prevent the inflammatory-dependent decrease of GnRH/LH secretion in ewes and it had a stimulatory effect on LH release. This central action of neostigmine is connected with its inhibitory action on local pro-inflammatory cytokines, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)α synthesis in the hypothalamus, which indicates the importance of this mediator in the inhibition of GnRH secretion during acute inflammation.

Effect of CD14/TLR4 antagonist on GnRH/LH secretion in ewe during central inflammation induced by intracerebroventricular administration of LPS

BACKGROUND

Immune stress induced by lipopolysaccharide (LPS) influences the gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) secretion. Presence of LPS interacting Toll-like receptor (TLR) 4 in the hypothalamus may enable the direct action of LPS on the GnRH/LH secretion. So, the aim of the study was to investigate the influence of intracerebroventricular (icv) injection of TLR4 antagonist on GnRH/LH secretion in anestrous ewes during LPS-induced central inflammation. Animals were divided into three groups icv-treated with: Ringer-Locke solution, LPS and TLR4 antagonist followed by LPS.

RESULTS

It was demonstrated that TLR4 antagonist reduced LPS-dependent suppression of GnRH gene expression in the preoptic area and in the medial basal hypothalamus, and suppression of receptor for GnRH gene expression in the anterior pituitary gland. It was also shown that TLR4 antagonist reduced suppression of LH release caused by icv injection of LPS. Central administration of LPS stimulated TLR4 gene expression in the medial basal hypothalamus.

CONCLUSIONS

It was indicated that blockade of TLR4 prevents the inhibitory effect of centrally acting LPS on the GnRH/LH secretion. This suggests that some negative effects of bacterial infection on the hypothalamic-pituitary-gonadal axis activity at the hypothalamic level may be caused by central action of LPS acting through TLR4.

Effects of puerarin on estrogen-regulated gene expression in gonadotropin-releasing hormone pulse generator of ovariectomized rats

Effects of puerarin on the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator function is investigated, for the first time, in ovariectomized rats at the level of mRNA expression of estrogen-responsive genes, e.g., estrogen receptor (ER), GnRH and its receptor (GnRHR). Rats were treated orally for 90 days either with a soy-free diet containing two different doses of puerarin (low dose of 600 mg/kg and high dose of 3000 mg/kg) or estradiol benzoate (E2B) at either low dose (4.3 mg/kg) or high dose (17.3 mg/kg). Levels of mRNA expression in the medial preoptic area/anterior hypothalamus (MPOA/AH), mediobasal hypothalamus/median eminence (MBH/ME) and adenohypophysis were measured by quantitative TaqMan® real-time RT-PCR. Plasma levels of luteinizing hormone (LH) and prolactin (PRL) were measured by radioimmunoassay. In the MPOA/AH, both puerarin and E2B decreased ERα mRNA levels without any significant changes in ERβ and GnRH mRNA levels. Both puerarin and E2B did not significantly alter the expression levels of ERα, ERβ and GnRHR in the MBH/ME. E2B exerted significant effects on the down-regulation of adenohypophyseal GnRHR mRNA transcripts and serum LH levels. Puerarin did not cause significant changes in pituitary GnRHR mRNA transcripts and serum LH and PRL levels. This is the first study to demonstrate that in ovariectomized rat models of ovarian hormone deprivation, puerarin acted as a weak estrogen-active compound in the hypothalamic GnRH pulse generator through the downregulation of MPOA/AH ERα mRNA expression.

Involvement of prolactin in the meloxicam-dependent inflammatory response of the gonadotropic axis to prolonged lipopolysaccharide treatment in anoestrous ewes

An immune challenge can affect the reproductive process in females. Peripheral administration of bacterial endotoxin (lipopolysaccharide; LPS) decreases LH secretion and disrupts ovarian cyclicity. The aim of the present study was to determine the effects of a cyclo-oxygenase (COX)-2 inhibitor (meloxicam) on gonadotropin-releasing hormone (GnRH) and LH secretion in anoestrous ewes during systemic inflammation induced by LPS. LPS (400ngkg^-1 per day) suppressed LH release. In three individuals, meloxicam (500μgkg^-1, i.v.) abolished LPS-induced LH suppression. In another three ewes LH was ineffective. Similar changes were observed in hypothalamic GnRH expression. The effect of meloxicam depended on the circulating level of prolactin: meloxicam abolished inflammatory-dependent suppression of GnRH and LH secretion when plasma prolactin levels were similar to those in untreated animals, but was ineffective in those with elevated levels of prolactin. We conclude that COX-2 inhibitors minimise the negative effect of inflammation on the reproductive system but that this effect may be antagonised by prolactin.

Endotoxin-Induced Inflammation Suppresses the Effect of Melatonin on the Release of LH from the Ovine Pars Tuberalis Explants-Ex Vivo Study

The secretion of the hormone melatonin reliably reflects environmental light conditions. Among numerous actions, in seasonal breeders, melatonin may regulate the secretion of the gonadotropins acting via its corresponding receptors occurring in the Pars Tuberalis (PT). However, it was previously found that the secretory activity of the pituitary may be dependent on the immune status of the animal. Therefore, this study was designed to determine the role of melatonin in the modulation of luteinizing hormone (LH) secretion from the PT explants collected from saline- and endotoxin-treated ewes in the follicular phase of the oestrous cycle. Twelve Blackhead ewes were sacrificed 3 h after injection with lipopolysaccharide (LPS; 400 ng/kg) or saline, and the PTs were collected. Each PT was cut into 4 explants, which were then divided into 4 groups: I, incubated with 'pure' medium 199; II, treated with gonadotropin-releasing hormone (GnRH) (100 pg/mL); III, treated with melatonin (10 nmol/mL); and IV, incubated with GnRH and melatonin. Melatonin reduced (p < 0.05) GnRH-induced secretion of LH only in the PT from saline-treated ewes. Explants collected from LPS-treated ewes were characterized by lower (p < 0.05) GnRH-dependent response in LH release. It was also found that inflammation reduced the gene expression of the GnRH receptor and the MT1 melatonin receptors in the PT. Therefore, it was shown that inflammation affects the melatonin action on LH secretion from the PT, which may be one of the mechanisms via which immune/inflammatory challenges disturb reproduction processes in animals.

Peripheral Inhibitor of AChE, Neostigmine, Prevents the Inflammatory Dependent Suppression of GnRH/LH Secretion during the Follicular Phase of the Estrous Cycle

The study was designed to test the hypothesis that the inhibition of acetylcholinesterase (AChE) activity at the periphery by Neostigmine (0.5 mg/animal) will be sufficient to prevent inflammatory dependent suppression of the gonadotropin-releasing hormone (GnRH)/luteinising hormone (LH) secretion in ewes in the follicular phase of the estrous cycle, and this effect will be comparable with the systemic AChE inhibitor, Donepezil (2.5 mg/animal). An immune/inflammatory challenge was induced by peripheral administration of lipopolysaccharide (LPS; 400 ng/kg). Peripheral treatment with Donepezil and Neostigmine prevented the LPS-induced decrease (P < 0.05) in LHβ gene expression in the anterior pituitary gland (AP) and in LH release. Moreover, Donepezil completely abolished (P < 0.05) the suppressory effect of inflammation on GnRH synthesis in the preoptic area, when pretreatment with Neostigmine reduced (P < 0.05) the decrease in GnRH content in this hypothalamic structure. Moreover, administration of both AChE inhibitors diminished (P < 0.05) the inhibitory effect of LPS treatment on the expression of GnRH receptor in the AP. Our study shows that inflammatory dependent changes in the GnRH/LH secretion may be eliminated or reduced by AChE inhibitors suppressing inflammatory reaction only at the periphery such as Neostigmine, without the need for interfering in the central nervous system.

Effect of short-term and prolonged stress on the biosynthesis of gonadotropin-releasing hormone (GnRH) and GnRH receptor (GnRHR) in the hypothalamus and GnRHR in the pituitary of ewes during various physiological states

Using an ELISA assay, the levels of GnRH and GnRHR were analysed in the preoptic area (POA), anterior (AH) and ventromedial hypothalamus (VM), stalk/median eminence (SME); and GnRHR in the anterior pituitary gland (AP) of non-breeding and breeding sheep subjected to short-term or prolonged stress. The ELISA study was supplemented with an analysis of plasma LH concentration. Short-term footshock stimulation significantly increased GnRH levels in hypothalamus in both seasons. Prolonged stress elevated or decreased GnRH concentrations in the POA and the VM, respectively during anoestrus, and lowered GnRH amount in the POA-hypothalamus of follicular-phase sheep. An up-regulation of GnRHR levels was noted in both, anoestrous and follicular-phase animals. In the non-breeding period, a prolonged stress procedure increased GnRHR biosynthesis in the VM and decreased it in the SME and AP, while in the breeding time the quantities of GnRHR were significantly lower in the whole hypothalamus. In follicular-phase ewes the fluctuations of GnRH and GnRHR levels under short-term and prolonged stress were reflected in the changes of LH secretion, suggesting the existence of a direct relationship between GnRH and GnRH-R biosynthesis and GnRH/LH release in this period. The study showed that stress was capable of modulating the biosynthesis of GnRH and GnRHR; the pattern of changes was dependent upon the animal's physiological state and on the time course of stressor application. The obtained results indicate that the disturbances of gonadotropin secretion under stress conditions in sheep may be due to a dysfunction of GnRH and GnRHR biosynthetic pathways.

Lack of anti-androgenic effects of equol on reproductive neuroendocrine function in the adult male rat

Equol (EQ), a metabolite of the soy isoflavone daidzein, has well known estrogenic properties. Data from animal studies suggested that EQ may act also as an anti-androgen. However, data regarding how EQ may affect brain functions like the regulation of neuroendocrine activity and reproductive outcomes in adult male rats are still lacking. We therefore investigated the effects of EQ on sex-steroid regulated gene expression in the brain [medial preoptic area/anterior hypothalamus (MPOA/AH) and medial basal hypothalamus/median eminence (MBH/ME)], pituitary, and prostate as a reference androgen-dependent organ. Furthermore reproductive outcomes were evaluated. The anti-androgen flutamide (FLUT) served as reference compound. Male rats (n=12 per group) were treated by gavage for 5 days with either EQ (100 or 250 mg/kgBW/day), or FLUT 100 mg/kgBW/day. All vehicle- and EQ-treated males showed successful reproductive outcomes, whereas FLUT-exposed males had severe reproductive impairments resulted in infertility. FLUT decreased relative weights of prostate, seminal vesicles and epididymides, and increased serum levels of luteinizing hormone, follicle-stimulating hormone, testosterone and 5α-dihydrotestosterone without altering prolactin levels, whereas EQ exerted opposite effects. Both EQ and FLUT decreased gonadotropin releasing hormone (GnRH) expression in the MPOA/AH. Only FLUT upregulated levels of GnRH receptor expression both in the MBH/ME and pituitary. While EQ downregulated the hypothalamic ERα and ERβ expressions, but FLUT did not. In the prostate, only FLUT upregulated both ERα and AR mRNA expression levels. Taken together, our findings are the first data that EQ did not induce anti-androgenic effects on brain, prostate and male reproductive parameters, however, estrogenic neuroendocrine and reproductive effects of EQ were observed.

LPS-induced inflammation potentiates the IL-1β-mediated reduction of LH secretion from the anterior pituitary explants

Acting at the level of the brain, interleukin- (IL-)1 β is considered to be one of the most potent downregulators of reproduction processes during immune/inflammatory challenge. IL-1 β suppresses gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus resulting in the inhibition of the luteinizing hormone (LH) release from the anterior pituitary (AP). However, the presence of IL-1 β receptors in the AP suggests the possible direct action of this cytokine on LH secretion. The study was designed to determine the effect of IL-1 β on the LH secretion from the AP explants collected from saline and LPS-treated ewes in the follicular phase. It was found that IL-1 β suppressed (P ≤ 0.01) GnRH-stimulated LH release and LH β gene expression in AP explants in both groups. However, IL-1 β action was more potent in the explants collected from LPS-treated animals. Pituitaries from LPS-treated animals were characterized by increased (P ≤ 0.01) IL-1 type I receptor and decreased (P ≤ 0.01) GnRH receptor gene expression level compared to the saline-treated group. IL-1 β also affected the GnRH-R gene expression in explants collected from LPS-treated animals. Our results show that direct action of IL-1 β on the pituitary gonadotropes could be one of the reasons of the reproductive processes disorders accompanying an inflammatory state.

Interleukin-1 beta simultaneously affects the stress and reproductive axes by modulating norepinephrine levels in different brain areas

AIMS

Interleukin-1β (IL-1β) is a cytokine that is known to activate the stress axis and suppress the reproductive axis. Different brain areas are involved in the regulation of these two axes. However, they are both under the stimulatory control of the catecholamine, norepinephrine (NE). Here, we hypothesized that IL-1β differentially affects these two axes by modulating NE levels in specific brain regions.

MAIN METHODS

Female Sprague-Dawley rats in proestrus were injected intraperitoneally with either PBS-1.0% BSA (control) or 5μg of IL-1β at 1pm. Groups of rats were sacrificed at 1, 3, and 5pm and their brains were collected. Brain areas associated with reproduction as well as areas associated with stress axis activity were isolated and analyzed for NE concentrations using HPLC-EC. Trunk blood was analyzed for IL-1β, corticosterone and luteinizing hormone levels.

KEY FINDINGS

As a general trend, treatment with IL-1β significantly decreased NE levels (p<0.05) in the areas controlling reproductive functions when compared to the control group. In contrast, NE levels increased significantly (p<0.05) in the stress associated areas. LH levels were markedly decreased with IL-1β treatment while corticosterone levels increased dramatically.

SIGNIFICANCE

The ability of IL-1β to produce differential effects on the stress and reproductive axis could be explained by modulation of NE levels in specific brain areas that are associated with these functions. This differential regulation of NE may be an adaptive phenomenon in response to a systemic immune challenge.

Signaling of cytokines is important in regulation of GnRH neurons

Cytokines encompass a broad class of peptides that mediate signals in a broad range of physiological situations including inflammation, infection, and obesity. The cytokine receptor-associated tyrosine kinase, Jak2, is one of the most important proteins mediating cytokine signaling pathway activation. Recently, our group has demonstrated that Jak2 signaling in the gonadotropin-releasing hormone (GnRH) neuron plays a critical role in fertility in males and females, implicating cytokine activation of the neuron in GnRH neuronal development and function. To date, the specific cytokine(s) essential for activating Jak2 during neuroendocrine development are not known. In this article, we review the evidence for the role of several class 1 cytokines in regulating GnRH neuronal development, GnRH secretion, and GnRH expression.

Neuroendocrine regulation of GnRH release and expression of GnRH and GnRH receptor genes in the hypothalamus-pituitary unit in different physiological states

This review is focused on the relationship between neuroendocrine regulation of GnRH/LH secretion and the expression of GnRH and GnRH receptor (GnRHR) genes in the hypothalamic-pituitary unit during different physiological states of animals and under stress. Moreover, the involvement of hypothalamic GABA-ergic, Beta-endorphinergic, CRH-ergic, noradrenergic, dopaminergic and GnRH-ergic systems in the regulation of expression of the GnRH and GnRHR genes as well as secretion of GnRH/LH is analyzed. It appears that the neural mechanisms controlling GnRH gene expression in different physiological states may be distinct from those regulating GnRH/LH release. The hypothalamic GnRHR gene is probably located in different neural systems and may act in a specific way on GnRH gene expression and GnRH release.

Profound effects of burn and ethanol on proinflammatory cytokines of the reproductive axis in the male mouse

Thermal injury is often associated with previous ethanol exposure, and close to 50% of patients admitted to a burn unit have a potentially high blood ethanol level. Cellular mechanisms by which ethanol and/or burn affect the hypothalamic-pituitary-gonadal (HPG) axis are not entirely understood. However, it is known that the proinflammatory cytokines, tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 influence negatively on the endocrine functions of the HPG. We report a time course study (6, 12, 24, and 48 hours) of the effects of ethanol, burn, or the combination of burn/ethanol on proinflammatory cytokines of the hypothalamus, pituitary and testes of male C57Bl/6 mice. We found that there were highly significant increases in each of these cytokines caused by ethanol, burn, and burn/ethanol compared with sham/vehicle (P < .001). This was true in hypothalamus, pituitary, and testes. Because these cytokines generally reduce reproductive function, it may be that proinflammatory cytokines of HPG axis mediate the deleterious effects of burn and/or ethanol on mammalian reproduction.

Effects of a 5-day treatment with vinclozolin on the hypothalamo-pituitary-gonadal axis in male rats

Vinclozolin (VZ), a potent antiandrogenic fungicide, is known to interfere with male reproductive function. Little data are currently available regarding possible impacts of VZ on brain function, particularly neuroendocrine activity and regulation of the hypothalamo-pituitary-gonadal (HPG) axis. Therefore, we examined the effects of VZ on gene expression in the brain (MBH/ME, MPOA/AH, striatum, hippocampus), pituitary, prostate, seminal vesicles, and epididymis of 4-month-old male rats treated daily by gavage for 5 days with VZ (150 mg/kg body weight/day). Alterations in levels of serum hormones and gene expression were determined by RIA and qRT-PCR, respectively. Our results revealed that (i) VZ decreases epididymis weights, increases serum levels of LH and T, and decreases serum TSH and total T(4) levels; (ii) VZ affects the hypothalamic expression of both estrogen receptor (ERs) subtypes, ERalpha and ERbeta; (iii) in the extrahypothalamic brain areas, VZ alters expression of ERs and androgen receptor (AR); (iv) in the pituitary, VZ up-regulates expression of the GnRH receptor, LHbeta, alpha-subunit, and TERP-1/-2; (v) in the ventral prostate, VZ increases and decreases levels of AR and ERbeta mRNA, respectively; (vi) in the seminal vesicles, VZ increases levels of AR and ERalpha mRNA expressions; (vii) in the epididymis, VZ up-regulates AR and ERbeta mRNA expression. These results indicate that in vivo VZ is not a 'pure' antiandrogen, since it exerts mixed AR antagonistic/ERs agonistic actions observed at the levels of mRNA expression of selected androgen- and estrogen-regulated genes in the CNS, pituitary, and male accessory sex organs.

Interleukin 1-beta injected into the testis acutely stimulates and later attenuates testicular steroidogenesis of the immature rat

The effect of intratesticular administration of interleukin-1beta (IL-1beta) on steroidogenesis was studied in immature and adult rats. In 21-d-old animals local bilateral injection or unilateral administration of 0.1 microg/testis of IL-1beta to hemicastrates resulted in a significant increase in basal testosterone secretion in vitro and serum testosterone concentration one day posttreatment. Six days after treatment the cytokine induced opposite effect in animals with two testes in situ, i.e., it suppressed steroidogenesis. When IL-1beta was combined with hemi-castration, IL-1beta failed to alter the parameters studied. In adult animals subjected to bilateral treatment or to unilateral injection followed by hemicastration, IL-1beta in doses of 1.5 microg/testis or 15 microg/testis did not influence steroidogenesis and serum testosterone concentration. No change in serum LH and FSH concentration could be observed in any experimental group. The data suggest that the proinflammatory cytokine IL-1beta exerts a local action on testicular steroidogenesis, and the effect is age-dependent.

Regulation of expression of mammalian gonadotrophin-releasing hormone receptor genes

Gonadotrophin-releasing hormone (GnRH), acting via its cognate GnRH receptor (GnRHR), is the primary regulator of mammalian reproductive function, and hence GnRH analogues are extensively used in the treatment of hormone-dependent diseases, as well as for assisted reproductive techniques. In addition to its established endocrine role in gonadotrophin regulation in the pituitary, evidence is rapidly accumulating to support the expression and functional roles for two forms of GnRHR (GnRHR I and GnRHR II) in multiple and diverse extra-pituitary mammalian tissues and cells. These findings, together with findings indicating that mutations of the GnRHR are linked to the disease hypogonadotrophic hypogonadism and that GnRHRs play a direct role in neuronal migration and reproductive cancers, have presented new therapeutic targets and intensified research into the structure, function and mechanisms of regulation of expression of GnRHR genes. The present review focuses on the current knowledge on tissue-specific and hormonal regulation of transcription of mammalian GnRH receptor genes. Emerging insights, such as the discovery of diverse regulatory mechanisms in pituitary and extra-pituitary cell types, nonclassical mechanisms of steroid regulation, the use of composite elements for cell-specific expression, the increasing profile of hormones involved in regulation, the complexity of kinase pathways that target the GnRHR I gene, as well as species-differences, are highlighted. Although further research is necessary to understand the mechanisms of regulation of expression of GnRHR I and GnRHR II genes, the GnRHR is emerging as a potential target gene for facilitating cross-talk between neuroendocrine, immune and stress-response systems in multiple tissues via autocrine, paracrine and endocrine signalling.

Hypothalamic interleukin-1 beta and tumor necrosis factor-alpha, but not interleukin-6, mediate the endotoxin-induced suppression of the reproductive axis in rats

It is well established that endotoxemia disrupts reproductive capability, and several proinflammatory cytokines, especially IL-1 beta, IL-6, and TNF-alpha in the brain, have been implicated in this endocrine aberration. However, no previous study has directly compared the effects of the three major proinflammatory cytokines (IL-1 beta, IL-6, and TNF-alpha) on the in vivo release of hypothalamic GnRH, a secretagogue of LH from the pituitary. Therefore, in this study, we addressed this issue with two complementary approaches involving push-pull perfusion in freely moving ovariectomized female rats. First, we examined the effects of systemic lipopolysaccharide (LPS) treatment on the release of plasma LH, and of GnRH, IL-1 beta, IL-6, and TNF-alpha in the hypothalamic medial preoptic area (MPOA), where the majority of GnRH neuronal perikarya are located. LPS inhibited the secretion of both LH and GnRH and concomitantly stimulated the release of all three cytokines. We next tested the effects of direct MPOA perfusion with the respective cytokines (at three different concentrations each) on the GnRH and LH secretion. IL-1 beta and TNF-alpha, at the concentrations that were observed in the MPOA after the LPS injection, were equipotent in inhibiting the GnRH-LH system, whereas IL-6 was ineffective (even at a supraphysiological concentration). These results strongly suggest that IL-1 beta and TNF-alpha may represent the major proinflammatory cytokines mediating the LPS-induced suppression of GnRH and LH release, whereas the role of IL-6 seems to be insignificant.

Excision of the first intron from the gonadotropin-releasing hormone (GnRH) transcript serves as a key regulatory step for GnRH biosynthesis

The mammalian gonadotropin-releasing hormone (GnRH) gene consists of four short exons (denoted as 1, 2, 3, and 4) and three intervening introns (A, B, and C). Recently, we demonstrated that excision of the first intron (intron A) from the GnRH transcript is regulated in a tissue- and developmental stage-specific fashion and is severely attenuated in hypogonadal (hpg) mouse because of its lack of exonic splicing enhancers (ESE) 3 and 4. In the present study, we examined the influence of intron A on translational efficiency, thereby establishing a post-transcriptional control over GnRH biosynthesis. First, we verified that an intron A-retained GnRH transcript is a splicing variant but not a splicing intermediate. Intron A-retained transcripts can be transported to the cytoplasm in contrast to intron B-containing transcripts, which are restricted to the nucleus. This result implicates the intron A-retained GnRH transcript as a splicing variant; it has a long 5'-untranslated region, as the GnRH prohormone open reading frame (ORF) begins on exon 2. We investigated whether an intron A-retained GnRH transcript can properly initiate translation at the appropriate start codon and found that intron A completely blocks the translation initiation of its downstream reporter ORF both in vivo and in vitro. The inhibition of translation initiation appears to be due to the presence of a tandem repeat of ATG sequences within intron A. Constructs bearing mutations of ATGs to AAGs restored translation initiation at the downstream start codon; the extent of this restoration correlated with the number of mutated ATGs. Besides the failure in the translation initiation of GnRH-coding region in the intron A-containing variant, the present study also suggests that the interference between mature GnRH mRNA and intron A-retained splicing variant could occur to lower the efficiency of GnRH biosynthesis in the GT1-1-immortalized GnRH-producing cell line. Therefore, our results indicate that the precise and efficient excision of intron A and the joining of adjacent exons may be a critical regulatory step for the post-transcriptional regulation of GnRH biosynthesis.

Cell differentiation of gonadotropin-releasing hormone neurons and alternative RNA splicing of the gonadotropin-releasing hormone transcript

Two different, yet related issues regarding gonadotropin-releasing hormone (GnRH), i.e. the development and differentiation of hypothalamic GnRH neurons and the alternative RNA splicing of GnRH gene transcripts, are addressed in the present review. Using the immortalized GnRH-producing GT1 cell line, we found that activation of protein kinase C (PKC) with 12-O-tetradecanoylphorbol-13-acetate induces morphological and functional differentiation of these neurons. Specific isoforms of PKC are involved in neurite growth, cell migration and synaptic contacts and involve different signaling pathways. Using an in vitro splicing assay with HeLa nuclear extract, we found that excision of the first intron of the GnRH primary transcript is attenuated in non-GnRH-producing cells, but not in GnRH-producing cells such as GT1. This attenuation was relieved by exonic splicing enhancers located in the GnRH exons 3 and 4. Interestingly, addition of nuclear extract derived from GT1 cells further increased the excision rate of intron A, indicating that GnRH neurons contain TRANS-acting splicing factors. Extensive biochemical analysis indicates that Tra2alpha, a serine/arginine-rich RNA-binding protein, and other cofactors are likely involved in mediating neuron-specific excision of intron A from the GnRH primary transcript. An understanding of the GnRH neuron-specific splicing machinery provides critical insight into the molecular mechanism of GnRH gene regulation and consequently of mammalian reproductive development.

Altered gonadal steroidogenesis in critical illness: is treatment with anabolic steroids indicated?

The physiology of the reproductive system changes dramatically with the onset of major illness. The serum testosterone concentrations fall to pre-pubertal levels secondary to a decreased secretion of gonadotropins and a decreased Leydig cell response to luteinizing hormone. At the same time, the serum oestrogen concentration rises as the result of an increased rate of peripheral aromatization. The clinical consequences of these marked changes are not yet well understood. One line of evidence argues for the administration of anabolic steroids (derivatives of testosterone) to critically ill patients to improve their catabolic state. Another line of evidence in animal models suggests that testosterone may suppress the immune system and myocardial function in critical illness. No clinical trials of oestrogen administration to critically ill patients have been reported, although two animal studies suggest that oestrogen may have a positive effect on survival. This chapter reviews changes in the physiology of the reproductive system in major illness as well as current evidence regarding the clinical effects of androgens and oestrogens in critical illness and their potential therapeutic roles.