Effects of leptin on secretion of LH and FSH from primary cultured female rat pituitary cells

Comprehensive expression analysis of hormone-like substances in the subcutaneous adipose tissue of the common bottlenose dolphin Tursiops truncatus

Marine mammals possess a specific subcutaneous fat layer called blubber that not only insulates and stores energy but also secretes bioactive substances. However, our understanding of its role as a secretory organ in cetaceans is incomplete. To exhaustively explore the hormone-like substances produced in dolphin subcutaneous adipose tissue, we performed seasonal blubber biopsies from captive female common bottlenose dolphins (Tursiops truncatus; N = 8, n = 32) and analyzed gene expression via transcriptomics. Analysis of 186 hormone-like substances revealed the expression of 58 substances involved in regulating energy metabolism, tissue growth/differentiation, vascular regulation, immunity, and ion/mineral homeostasis. Adiponectin was the most abundantly expressed gene, followed by angiopoietin protein like 4 and insulin-like growth factor 2. To investigate the endocrine/secretory responses of subcutaneous adipose tissue to the surrounding temperature, we subsequently compared the mean expression levels of the genes during the colder and warmer seasons. In the colder season, molecules associated with appetite suppression, vasodilation, and tissue proliferation were relatively highly expressed. In contrast, warmer seasons enhanced the expression of substances involved in tissue remodeling, immunity, metabolism, and vasoconstriction. These findings suggest that dolphin blubber may function as an active secretory organ involved in the regulation of metabolism, appetite, and tissue reorganization in response to changes in the surrounding environment, providing a basis for elucidating the function of hormone-like substances in group-specific evolved subcutaneous adipose tissue.

High-Grade Serous Ovarian Cancer-A Risk Factor Puzzle and Screening Fugitive

High-grade serous ovarian cancer (HGSOC) is the most lethal tumor of the female genital tract. Despite extensive studies and the identification of some precursor lesions like serous tubal intraepithelial cancer (STIC) or the deviated mutational status of the patients (BRCA germinal mutation), the pathophysiology of HGSOC and the existence of particular risk factors is still a puzzle. Moreover, a lack of screening programs results in delayed diagnosis, which is accompanied by a secondary chemo-resistance of the tumor and usually results in a high recurrence rate after the primary therapy. Therefore, there is an urgent need to identify the substantial risk factors for both predisposed and low-risk populations of women, as well as to create an economically and clinically justified screening program. This paper reviews the classic and novel risk factors for HGSOC and methods of diagnosis and prediction, including serum biomarkers, the liquid biopsy of circulating tumor cells or circulating tumor DNA, epigenetic markers, exosomes, and genomic and proteomic biomarkers. The novel future complex approach to ovarian cancer diagnosis should be devised based on these findings, and the general outcome of such an approach is proposed and discussed in the paper.

Sequence identification and expression characterization of leptin in the spotted scat, Scatophagus argus

Scatophagus argus is an important marine culture fish in South and South-East Asia, including Southeast coastal areas of China. Artificial propagation technology for S. argus is not optimum; thus further studies on its reproduction biology are required. Although previous studies have shown that leptin (Lep) can regulate fish reproduction, the role of lep genes in S. argus is unknown. Herein, in silico analysis showed that S. argus has two lep genes (lepa and lepb). Protein 3D-structure prediction showed that Lepa has four α-helices (similar to mammals), while Lepb only has three. Tissue distribution analysis showed that lepa is highly expressed in the liver, whereas lepb was not detected in any tissue. Notably, lepr was expressed in all tissues. Lepa mRNA expression levels in the liver and serum Lep, estradiol (E2) and vitellogenin (Vtg) levels of female fish were significantly higher in ovaries at stage IV than in ovaries at stage II. Serum E2 levels were significantly positively correlated with Vtg levels in female fish at different development stages, while serum E2 was not correlated with Lep levels. Consistently, in vitro incubation of the liver with E2 significantly up-regulated vtga, while it did not affect lepa expression. Recombinant Lep (10 nM) significantly up-regulated chicken gonadotropin-releasing hormone (cGnRH/GnRH-II) in the hypothalamus and GnRH receptor (GnRHR) and luteinizing hormone beta (Lhb) in the pituitary. These results suggest that lepa regulates female reproduction in S. argus.

The ontogenies of endometrial and myometrial leptin and adiponectin receptors in pregnant rats: Their putative impact on uterine contractility

AIMS

Limited data are available about the functions and expressions of leptin and adiponectin receptors (LEPR, AdipoRs) in the uterus. Our aim was to investigate the effects of leptin and adiponectin on the contractions of intact and denuded nonpregnant and pregnant uteri, as well as the changes in mRNA and protein expressions of LEPR and AdipoRs during the gestational period.

MAIN METHODS

Contractions of nonpregnant and 5-, 15-, 18-, 20- or 22-day pregnant uterine rings were measured in an isolated organ bath system. The tissue contractions were stimulated with KCl and modified by cumulative concentrations of leptin or adiponectin. The mRNAs, protein expressions and localizations of LEPR and AdipoRs were determined by RT-PCR, Western blot and immunohistochemistry, respectively.

KEY FINDINGS

Both adipokines relaxed the nonpregnant intact uterus more effectively than the denuded myometrium. Leptin inhibited the contractions of endometrium-denuded uteri throughout pregnancy, while its action was weakened on intact uteri towards term. The changes in LEPR receptor densities were independent of the relaxing effect. Adiponectin inhibited contractions, but this effect ceased on pregnancy day 22, while a gradual decrease was detected towards term on denuded myometria. These modifications were in harmony with changes in the expressions of AdipoRs.

SIGNIFICANCE

Both leptin and adiponectin play a role in the relaxation of the pregnant uterus, but their efficacy significantly decreases towards the end of gestation. Their endometrial receptors may have a fine-tuning role in uterine contractions, predicting the importance of these adipokines in uterine contractions under altered adipokine level conditions.

Nonobese Male Patients with Alzheimer's Disease Are Vulnerable to Decrease in Plasma Leptin

BACKGROUND

Metabolic dysfunction links to cognitive deficits in Alzheimer's disease (AD). Leptin is an anti-obesity hormone that modulates energy homeostasis and memory function. Although leptin deregulation is implicated in mouse models of AD-like brain pathology, clinical studies have shown inconsistent results regarding an association of leptin with the development of this neurodegenerative disorder.

OBJECTIVE

We investigated the changes of plasma leptin and the correlation of sex-stratified circulating leptin with cognitive performance, AD-related biological markers, and metabolic status in patients with AD and cognitively unimpaired (CU) counterparts.

METHODS

We used nonobese AD patients and CU controls in a University of Kansas Medical Center (KUMC) cohort. Plasma leptin levels, circulating AD-related molecules and metabolic profiles were examined and analyzed.

RESULTS

In contrast to unchanged circulating leptin in females, male patients exhibited decreased plasma leptin levels compared with male CU counterparts. Moreover, plasma leptin showed no correlation with cognitive performance and AD blood biomarkers in patients with either sex. Of note, females but not males demonstrated an association of plasma leptin with body mass index, high density lipoprotein-cholesterol and its ratio with total cholesterol and triglycerides.

CONCLUSION

Our findings suggest that leptin deficiency is associated with nonobese male AD patients, supporting systemic dysmetabolism in the development of this neurodegenerative disorder in certain populations. Although plasma leptin may have limited capacity to reflect disease severity or progression, future mechanistic studies on the regulation of leptin in nonobese patients with AD would deepen our understanding of the sex-related disparity of AD etiopathogenesis.

Leptin Is an Important Endocrine Player That Directly Activates Gonadotropic Cells in Teleost Fish, Chub Mackerel

Leptin, secreted by adipocytes, directly influences the onset of puberty in mammals. Our previous study showed that leptin stimulation could promote the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from pituitary cells in primary culture and ovarian development in chub mackerel. This study aimed to elucidate the detailed mechanism of leptin-induced effects on gonadotropin hormone-producing cells. We produced recombinant leptin using silkworm pupae and investigated the effects of leptin on FSH and LH secretion and gene expression in the primary culture of pituitary cells from chub mackerel. The presence or absence of co-expression of lepr mRNA, FSH and LH b-subunit mRNA in gonadotropic cells was examined by double-labeled in situ hybridization. The addition of leptin significantly increased the secretion and gene expression of FSH and LH from male and female pituitary cells in primary culture. In contrast, gonadotropin-releasing hormone 1 affected neither FSH secretion in cells from females nor fshb and lhb expression in cells from males and females. The expression of lepr was observed in FSH- and LH-producing cells of both males and females. The results indicate that leptin directly regulates gonadotropin synthesis and secretion and plays an important role in the induction of puberty in teleost fish.

Trajectory of leptin and leptin receptor in vertebrates: Structure, function and their regulation

The present review provides a comparative insight into structure, function and control of leptin system in fishes, herptiles, birds and mammals. In general, leptin acts as an anorexigenic hormone since its administration results in decrease of food intake in vertebrates. Nonetheless, functional paradox arises in fishes from contradictory observations on level of leptin during fasting and re-feeding. In addition, leptin is shown to modulate metabolic functions in fishes, reptiles, birds and mammals. Leptin also regulates reproductive and immune functions though more studies are warranted in non-mammalian vertebrates. The expression of leptin and its receptor is influenced by numerous factors including sex steroids, stress and stress-induced catecholamines and glucocorticoids though their effect in non-mammalian vertebrates is hard to be generalized due to limited studies.

The Importance of Leptin to Reproduction

A healthy nutritional state is required for all aspects of reproduction and is signaled by the adipokine leptin. Leptin acts in a relatively narrow concentration range: too much or too little will compromise fertility. The leptin signal timing is important to prepubertal development in both sexes. In the brain, leptin acts on ventral premammillary neurons which signal kisspeptin (Kiss1) neurons to stimulate gonadotropin releasing hormone (GnRH) neurons. Suppression of Kiss1 neurons occurs when agouti-related peptide neurons are activated by reduced leptin, because leptin normally suppresses these orexigenic neurons. In the pituitary, leptin stimulates production of GnRH receptors (GnRHRs) and follicle-stimulating hormone at midcycle, by activating pathways that derepress actions of the messenger ribonucleic acid translational regulatory protein Musashi. In females, rising estrogen stimulates a rise in serum leptin, which peaks at midcycle, synchronizing with nocturnal luteinizing hormone pulses. The normal range of serum leptin levels (10-20 ng/mL) along with gonadotropins and growth factors promote ovarian granulosa and theca cell functions and oocyte maturation. In males, the prepubertal rise in leptin promotes testicular development. However, a decline in leptin levels in prepubertal boys reflects inhibition of leptin secretion by rising androgens. In adult males, leptin levels are 10% to 50% of those in females, and high leptin inhibits testicular function. The obesity epidemic has elucidated leptin resistance pathways, with too much leptin in either sex leading to infertility. Under conditions of balanced nutrition, however, the secretion of leptin is timed and regulated within a narrow level range that optimizes its trophic effects.

In vitro action of leptin on gonadotropin secretion in pre-pubertal male chub mackerel

Leptin directly influences gonadotropin (GTH) secretion from female pituitary cells in vitro and is a key signal at the onset of puberty in female chub mackerel (Scomber japonicus). Here, we investigated whether leptin also influences GTH secretion in male chub mackerel. The addition of 1 nM homologous recombinant leptin to pre-pubertal male pituitary cells stimulated follicle-stimulating hormone secretion after 1 and 2 h of culture. Therefore, leptin signaling could also directly facilitate GTH secretion in male chub mackerel.

FSH/AMH Ratio and Adipocyte Size are Linked to Ovarian Dysfunction

While the relationship between obesity and reproductive dysfunction is well known, the physiological mechanism behind obesity-related infertility remains unclear. Previous work suggests that follicle development prior to ovulation is disrupted in obese individuals. Follicle-stimulating hormone (FSH) and anti-Mullerian hormone (AMH) are two key regulators of follicle development, and the poorest reproductive outcomes have been recorded when these hormones are imbalanced. In order to understand how obesity impacts the reproductive axis, the present study induces reproductive dysfunction in female rats using a high-fat, high-sugar diet (HFHS). Results: In our study, several animals on the HFHS diet displayed abnormal estrous cycles. The HFHS diet also resulted in an increased prevalence of ovarian cysts and decreased formation of corpora lutea. Across all groups, the FSH/AMH ratio displayed a strong negative correlation with pre-antral, antral, and total follicle counts. Moreover, rats on the HFHS diet displayed larger adipocytes and produced higher levels of leptin than controls. When combined with average adipocyte size in multiple regression, the FSH/AMH ratio was strongly associated with cyst formation in the ovary. Conclusions: These findings provide strong evidence for the potential relevance of a combined FSH/AMH ratio as a marker of ovarian health and follicular status. Therefore, this ratio reflects a complex interaction between the reproductive and metabolic systems.

Leptin stimulates gonadotropin release and ovarian development in marine teleost chub mackerel

Leptin transmits information about energy stored in the periphery to the reproductive axis and is an essential signal for puberty initiation in mammals; however, to date, few studies have focused on the direct effects of leptin stimulation on reproductive factors in fish. This study demonstrated the effect of leptin stimulation on important reproductive factors and ovarian development in the marine teleost chub mackerel (Scomber japonicus). We prepared recombinant leptin and conducted functional analyses through in vitro bioassays using primary pituitary cells, long-term leptin treatment administered to pre-pubertal females, and intracerebroventricular (ICV) administration. The results showed that leptin stimulation strongly induced gonadotropin (follicle-stimulating hormone: FSH and luteinizing hormone: LH) secretion from pituitary cells collected from pre-pubertal females, and that long-term leptin treatment significantly promoted ovarian development and triggered pubertal onset. Furthermore, ICV administration of leptin did not affect kisspeptin gene expression but significantly upregulated gonadotropin-releasing hormone 1 (gnrh1), fshb and lhb gene expression in sexually immature females. These results strongly suggest leptin as an important signal for reproductive-axis activation in chub mackerel.

Undernutrition and hyperandrogenism during pregnancy: Role in programming of cardiovascular disease and infertility

Maternal nutritional status programs the development of several systems in female offspring, with effects that depend on the severity, duration, and window of development when the nutritional perturbation is imposed. On the basis of the developmental origins of health and disease concept, we hypothesize that gestational low caloric intake may induce maternal subclinical hyperandrogenism during early pregnancy and compromise cardiovascular health and fertility in the female offspring. To examine this possibility, a literature search for human and animal studies was conducted using two electronic databases, PubMed and Cochrane until April 2019 to address the following questions: (a) Do androgens have a developmental role in cardiovascular and ovarian development? (b) Is excess maternal testosterone linked to cardiovascular disease and infertility? and (c) Could early pregnancy undernutrition enhance maternal androgen production and compromise health and fertility in female offspring? The observations reviewed, establish a potential causative link between maternal undernutrition and subclinical hyperandrogenism with hypertension and reduced ovarian reserve in the progeny. Further studies in appropriate models are needed to better understand whether low energy intake and subclinical maternal hyperandrogenism during early pregnancy can negatively affect the health of the female offspring.

Diet, menopause and the risk of ovarian, endometrial and breast cancer

Menopause, the permanent cessation of the menstrual cycle, marks the end of a woman's reproductive lifespan. In addition to changes in sex hormone levels associated with menopause, its timing is another predictor of future health outcomes such as duration of the presence of vasomotor symptoms (VMS) and the risk of hormone-related cancers. With ageing of the population, it is estimated that worldwide 1·2 billion women will be menopausal by the year 2030. Previously the effects of reproductive factors (e.g. parity, age at menarche, pregnancy) and socio-demographic factors on intermediate and long-term health outcomes of menopause have been widely documented. However, little is known about whether diet could have an impact on these. Therefore, we review current evidence on the associations of diet with menopause, presence of VMS and the risk of hormone-related cancers such as ovarian, endometrial and breast cancer. Dietary factors could influence the lifespan of the ovaries and sex-hormones levels, hence the timing of natural menopause. Few studies reported an association between diet, in particular soya consumption, and a reduced risk of VMS. Sustained oestrogen exposure has been associated with a higher risk of hormone-related cancers and thus high-fat and meat diets have been linked with an increased risk of these cancers. However, to better understand the mechanistic pathways involved and to make stronger conclusions for these relationships, further studies investigating the associations of dietary intakes and dietary patterns with menopause, presence of VMS and the risk of hormone-related cancers are required.

Visfatin and resistin in gonadotroph cells: expression, regulation of LH secretion and signalling pathways

Visfatin and resistin appear to interfere with reproduction in the gonads, but their potential action at the hypothalamic-pituitary level is not yet known. The aim of the present study was to investigate the mRNA and protein expression of these adipokines in murine gonadotroph cells and to analyse the effects of different concentrations of recombinant mouse visfatin and resistin (0.01, 0.1, 1 and 10ngmL^-1) on LH secretion and signalling pathways in LβT2 cells and/or in primary female mouse pituitary cells. Both visfatin and resistin mRNA and protein were found in vivo in gonadotroph cells. In contrast with resistin, the primary tissue source of visfatin in the mouse was the skeletal muscle, and not adipose tissue. Visfatin and resistin both decreased LH secretion from LβT2 cells after 24h exposure of cells (P<0.03). These results were confirmed for resistin in primary cell culture (P<0.05). Both visfatin (1ngmL^-1) and resistin (1ngmL^-1) increased AMP-activated protein kinase α phosphorylation in LβT2 cells after 5 or 10min treatment, up to 60min (P<0.04). Extracellular signal-regulated kinase 1/2 phosphorylation was transiently increased only after 5min resistin (1ngmL^-1) treatment (P<0.01). In conclusion, visfatin and resistin are expressed in gonadotroph cells and they may affect mouse female fertility by regulating LH secretion at the level of the pituitary.

Leptin Regulation of Gonadotrope Gonadotropin-Releasing Hormone Receptors As a Metabolic Checkpoint and Gateway to Reproductive Competence

The adipokine leptin signals the body's nutritional status to the brain, and particularly, the hypothalamus. However, leptin receptors (LEPRs) can be found all throughout the body and brain, including the pituitary. It is known that leptin is permissive for reproduction, and mice that cannot produce leptin (Lep/Lep) are infertile. Many studies have pinpointed leptin's regulation of reproduction to the hypothalamus. However, LEPRs exist at all levels of the hypothalamic-pituitary-gonadal axis. We have previously shown that deleting the signaling portion of the LEPR specifically in gonadotropes impairs fertility in female mice. Our recent studies have targeted this regulation to the control of gonadotropin releasing hormone receptor (GnRHR) expression. The hypotheses presented here are twofold: (1) cyclic regulation of pituitary GnRHR levels sets up a target metabolic checkpoint for control of the reproductive axis and (2) multiple checkpoints are required for the metabolic signaling that regulates the reproductive axis. Here, we emphasize and explore the relationship between the hypothalamus and the pituitary with regard to the regulation of GnRHR. The original data we present strengthen these hypotheses and build on our previous studies. We show that we can cause infertility in 70% of female mice by deleting all isoforms of LEPR specifically in gonadotropes. Our findings implicate activin subunit (InhBa) mRNA as a potential leptin target in gonadotropes. We further show gonadotrope-specific upregulation of GnRHR protein (but not mRNA levels) following leptin stimulation. In order to try and understand this post-transcriptional regulation, we tested candidate miRNAs (identified with in silico analysis) that may be binding the Gnrhr mRNA. We show significant upregulation of one of these miRNAs in our gonadotrope-Lepr-null females. The evidence provided here, combined with our previous work, lay the foundation for metabolically regulated post-transcriptional control of the gonadotrope. We discuss possible mechanisms, including miRNA regulation and the involvement of the RNA binding protein, Musashi. We also demonstrate how this regulation may be vital for the dynamic remodeling of gonadotropes in the cycling female. Finally, we propose that the leptin receptivity of both the hypothalamus and the pituitary are vital for the body's ability to delay or slow reproduction during periods of low nutrition.

Effects of 17β-estradiol on leptin signaling in anterior pituitary of ovariectomized rats

Leptin is secreted predominantly by adipocytes and exerts its role mainly by interaction with the long form of leptin receptor (LEPR_V2). It has been identified that LEPR_V2 is widely distributed in various tissues, including the anterior pituitary. Cross-talk between leptin and estrogens has been indentified. Estrogen is known to modulate the tissue-specific expression of LEPR_V2 and leptin in ovariectomized (OVX) rats, a model of postmenopausal condition. Our previous data showed that 17β-estradiol (E₂) up-regulated the expression of LEPR_V2 protein and mRNA in rat dorsal root ganglion (DRG) in an estrogen receptor alpha (ERα)-dependent manner. But it is still unclear whether estrogen can regulate leptin signalling in the pituitary of OVX rats. In the present study, we found that ovariectomy decreased the expressions of LEPR_V2. Administration of E₂ increased the expressions of LEPR_V2 in a dose-dependent manner. In addition, E₂ improved LEPR_V2, STAT3, and SOCS3 protein levels in OVX rats. The effects of exogenous E₂ were attenuated by ICI 182,780, a specific estrogen receptors antagonist. However, E₂ did not change the Lepr_v1, a type of short form of leptin receptor (LEPR), or leptin mRNA levels. Thus, E₂ plays a crucial role in regulating pituitary sensitivity to leptin in OVX rats. Our findings implied that exogenous E₂ had potential roles in modification of the function of pituitary in postmenopausal women.

Regulation of Leptin mRNA and Protein Expression in Pituitary Somatotropes

Leptin, the ob protein, regulates food intake and satiety and can be found in the anterior pituitary. Leptin antigens and mRNA were studied in the anterior pituitary (AP) cells of male and female rats to learn more about its regulation. Leptin antigens were found in over 40% of cells in diestrous or proestrous female rats and in male rats. Lower percentages of AP cells were seen in the estrous population (21 ± 7%). During peak expression of antigens, co-expression of leptin and growth hormone (GH) was found in 27 ± 4% of AP cells. Affinity cytochemistry studies detected 24 ± 3% of AP cells with leptin proteins and growth hormone releasing hormone (GHRH) receptors. These data suggested that somatotropes were a significant source of leptin. To test regulatory factors, estrous and diestrous AP populations were treated with estrogen (100 pM) and/or GHRH (2 nM) to learn if either would increase leptin expression in GH cells. To rule out the possibility that the immunoreactive leptin was bound to receptors in somatotropes, leptin mRNA was also detected by non-radioactive in situ hybridization in this group of cells. In estrous female rats, 39 ± 0.9% of AP cells expressed leptin mRNA, indicating that the potential for leptin production was greater than predicted from the immunolabeling. Estrogen and GHRH together (but not alone) increased percentages of cells with leptin protein (41 ± 9%) or mRNA (57 ± 5%). Estrogen and GHRH also increased the percentages of AP cells that co-express leptin mRNA and GH antigens from 20 ± 2% of AP cells to 37 ± 5%. Although the significance of leptin in GH cells is not understood, it is clearly increased after stimulation with GHRH and estrogen. Because GH cells also have leptin receptors, this AP leptin may be an autocrine or paracrine regulator of pituitary cell function.

Diet-Induced Obesity and Ghrelin Effects on Pituitary Gonadotrophs: Immunohistomorphometric Study in Male Rats

Objective

The close relationship between energy metabolism, nutritional state, and reproductive physiology suggests that nutritional and metabolic disorders can disrupt normal reproductive function and fertility. Considering the importance of leptin and ghrelin effects in regulation of the hypothalamic-pituitary-gonadal axis, the objective of this study was to investigate the influence of obesity and centrally applied ghrelin on immunohistochemical appearance and quantitative morphology of the pituitary follicle-stimulating hormone (FSH) and luteinizing hormone (LH) producing cells in adult male rats.

Materials and Methods

In this experimental study, animals were given two differ- ent diets: normal-fat (NF) and high-fat (HF), for 4 weeks, corresponding to normal and positive energy balance (n=2×14), respectively. Each group was subsequently divided into two subgroups (n=7) receiving intracerebroventricular (ICV) injections of either ghrelin [G, 1 µg/5 µL phosphate buffered saline (PBS)] or vehicle (5 µL PBS, control group) every 24 hours for five consecutive days.

Results

Morphometric analyses showed that in HF control group, the percentage of FSH cells per unit volume of total pituitary gland tissue (in μm³), i.e. volume density (Vvc), was increased (P<0.05) by 9.1% in comparison with the NF controls. After ICV treatment with ghrelin, volume (Vc) and volume density (Vvc) of FSH cells in ghrelin+NF (GNF) and ghrelin+HF (GHF) groups remained unchanged in comparison with NF and HF controls. Volume of LH cells in HF control group was increased by 17% (P<0.05), but their Vvc was decreased by 8.3% (P<0.05) in comparison with NF controls. In GNF group, the volume of LH cells increased by 7% (P<0.05), in comparison with the NF controls, but in GHF group, the same parameter remained unchanged when compared with HF controls. The central application of ghrelin de- creased the Vvc of LH cells only in GNF group by 38.9% (P<0.05) in comparison with the NF control animals.

Conclusion

The present study has shown that obesity and repetitive ICV administra- tion of low doses of ghrelin, in NF and HF rats, modulated the immunohistomorphometric features of gonadotrophs, indicating the importance of obesity and ghrelin in regulation of the reproductive function.

Two leptin genes and a leptin receptor gene of female chub mackerel (Scomber japonicus): Molecular cloning, tissue distribution and expression in different obesity indices and pubertal stages

Leptin is a hormone produced by fat cells that regulates the amount of fat stored in the body and conveys nutritional status to the reproductive axis in mammals. In the present study we identified two subtypes of leptin genes (lepa and lepb) and a leptin receptor gene (lepr) from chub mackerel (Scomber japonicus) and there gene expression under different feeding conditions (control and high-feed) and pubertal development stages was analyzed using quantitative real-time PCR. The protein lengths of LepA, LepB and LepR were 161 amino acids (aa), 163 aa and 1149 aa, respectively and both leptin subtypes shared only 15% similarity in aa sequences. In pubertal females, lepa was expressed in the brain, pituitary gland, liver, adipose tissue and ovary; however, in adult (gonadal maturation after the second in the life) females, lepa was expressed only in the liver. lepb was expressed primarily in the brain of all fish tested and was expressed strongly in the adipose tissue of adults. lepr was characterized by expression in the pituitary. The high-feed group showed a high conditioning factor level; unexpectedly, hepatic lepa and brain lepr were significantly more weakly expressed compared with the control-feed group. Furthermore, the expression levels of lepa, lepb and lepr genes showed no significant differences between pre-pubertal and post-pubertal fish. On the other hand, pituitary fshβ and lhβ showed no significant differences between different feeding groups of pre-pubertal fish. In contrast, fshβ and lhβ expressed abundantly in the post-pubertal fish of control feed group. Based on these results, whether leptin plays an important role in the nutritional status and pubertal onset of chub mackerel remains unknown.

Selective deletion of leptin receptors in gonadotropes reveals activin and GnRH-binding sites as leptin targets in support of fertility

The adipokine, leptin (LEP), is a hormonal gateway, signaling energy stores to appetite-regulatory neurons, permitting reproduction when stores are sufficient. Dual-labeling for LEP receptors (LEPRs) and gonadotropins or GH revealed a 2-fold increase in LEPR during proestrus, some of which was seen in LH gonadotropes. We therefore investigated LEPR functions in gonadotropes with Cre-LoxP technology, deleting the signaling domain of the LEPR (Lepr-exon 17) with Cre-recombinase driven by the rat LH-β promoter (Lhβ-cre). Selectivity of the deletion was validated by organ genotyping and lack of LEPR and responses to LEP by mutant gonadotropes. The mutation had no impact on growth, body weight, the timing of puberty, or pregnancy. Mutant females took 36% longer to produce their first litter and had 50% fewer pups/litter. When the broad impact of the loss of gonadotrope LEPR on all pituitary hormones was studied, mutant diestrous females had reduced serum levels of LH (40%), FSH (70%), and GH (54%) and mRNA levels of Fshβ (59%) and inhibin/activin β A and β B (25%). Mutant males had reduced serum levels of GH (74%), TSH (31%), and prolactin (69%) and mRNA levels of Gh (31%), Ghrhr (30%), Fshβ (22%), and glycoprotein α-subunit (Cga) (22%). Serum levels of LEP and ACTH and mRNA levels of Gnrhr were unchanged. However, binding to GnRH receptors was reduced in LEPR-null LH or FSH gonadotropes by 82% or 89%, respectively, in females (P < .0001) and 27% or 53%, respectively, in males (P < .03). This correlated with reductions in GnRH receptor protein immunolabeling, suggesting that LEP's actions may be posttranscriptional. Collectively, these studies highlight the importance of LEP to gonadotropes with GnRH-binding sites and activin as potential targets. LEP may modulate population growth, adjusting the number of offspring to the availability of food supplies.

Nutritional signals and reproduction

There is extensive evidence that nutrition influences reproductive function in various mammalian species (agricultural animals, rodents and human). However, the mechanisms underlying the relationship between nutrition, energy metabolism and reproductive function are poorly understood. This review considers nutrient sensors as a molecular link between food molecules and consequences for female and male fertility. It focuses on the roles and the molecular mechanisms of some of the relevant hormones, such as insulin and adipokines, and of energy substrates (glucose, fatty acids and amino acids), in the gonadotropic axis (central nervous system and gonads). A greater understanding of the interactions between nutrition and fertility is required for both better management of the physiological processes and the development of new molecules to prevent or cure metabolic diseases and their consequences for fertility.

Forkhead box O1 is a repressor of basal and GnRH-induced Fshb transcription in gonadotropes

Synthesis of the gonadotropin β-subunits is tightly controlled by a complex network of hormonal signaling pathways that may be modulated by metabolic cues. Recently, we reported that insulin regulates FOXO1 phosphorylation and cellular localization in pituitary gonadotropes and that FOXO1 overexpression inhibits Lhb transcription. In the current study, we investigated whether FOXO1 modulates Fshb synthesis. Here, we demonstrate that FOXO1 represses basal and GnRH-induced Fshb transcription in LβT2 cells. In addition, we show that PI3K inhibition, which increases FOXO1 nuclear localization, results in decreased Fshb mRNA levels in murine primary pituitary cells. FOXO1 also decreases transcription from the human FSHB promoter, suggesting that FOXO1 regulation of FSHB transcription may be conserved between rodents and humans. Although the FOXO1 DNA-binding domain is necessary for suppression of Fshb, we do not observe direct binding of FOXO1 to the Fshb promoter, suggesting that FOXO1 exerts its effect through protein-protein interactions with transcription factors required for Fshb synthesis. FOXO1 suppression of basal Fshb transcription may involve PITX1 because PITX1 interacts with FOXO1, FOXO1 repression maps to the proximal Fshb promoter containing a PITX1-binding site, PITX1 induction of Fshb or a PITX1 binding element in CV-1 cells is decreased by FOXO1, and FOXO1 suppresses Pitx1 mRNA and protein levels. GnRH induction of an Fshb promoter containing a deletion at -50/-41 or -30/-21 is not repressed by FOXO1, suggesting that these two regions may be involved in FOXO1 suppression of GnRH-induced Fshb synthesis. In summary, our data demonstrate that FOXO1 can negatively regulate Fshb transcription and suggest that FOXO1 may relay metabolic hormonal signals to modulate gonadotropin production.

Adipokines in reproductive function: a link between obesity and polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy associated with infertility and metabolic disorder in women of reproductive age. Dysfunction of adipose tissue has been implicated in the pathophysiology of PCOS. Increasing evidence shows that the dysregulated expression of adipokines, the secreted products of adipose tissue, plays an important role in the pathology of PCOS. Here, we review the role of several identified adipokines that may act as a link between obesity and PCOS. PCOS also reciprocally influences the profile of adipokines. Insight into the underlying mechanisms will help better understand the pathology of PCOS and identify new therapeutic targets of this syndrome.

Differentially expressed miRNAs after GnRH treatment and their potential roles in FSH regulation in porcine anterior pituitary cell

Hypothalamic gonadotropin-releasing hormone (GnRH) is a major regulator of follicle-stimulating hormone (FSH) secretion in gonadotrope cell in the anterior pituitary gland. microRNAs (miRNAs) are small RNA molecules that control gene expression by imperfect binding to the 3′-untranslated region (3′-UTR) of mRNA at the post-transcriptional level. It has been proven that miRNAs play an important role in hormone response and/or regulation. However, little is known about miRNAs in the regulation of FSH secretion. In this study, primary anterior pituitary cells were treated with 100 nM GnRH. The supernatant of pituitary cell was collected for FSH determination by enzyme-linked immunosorbent assay (ELISA) at 3 hours and 6 hours post GnRH treatment respectively. Results revealed that GnRH significantly promoted FSH secretion at 3 h and 6 h post-treatment by 1.40-fold and 1.80-fold, respectively. FSHβ mRNA at 6 h post GnRH treatment significantly increased by 1.60-fold. At 6 hours, cells were collected for miRNA expression profile analysis using MiRCURY LNA Array and quantitative PCR (qPCR). Consequently, 21 up-regulated and 10 down-regulated miRNAs were identified, and qPCR verification of 10 randomly selected miRNAs showed a strong correlation with microarray results. Chromosome location analysis indicated that 8 miRNAs were mapped to chromosome 12 and 4 miRNAs to chromosome X. Target and pathway analysis showed that some miRNAs may be associated with GnRH regulation pathways. In addition, In-depth analysis indicated that 10 up-regulated and 3 down-regulated miRNAs probably target FSHβ mRNA 3′-UTR directly, including miR-361-3p, a highly conserved X-linked miRNA. Most importantly, functional experimental results showed that miR-361-3p was involved in FSH secretion regulation, and up-regulated miR-361-3p expression inhibited FSH secretion, while down-regulated miR-361-3p expression promoted FSH secretion in pig pituitary cell model. These differentially expressed miRNAs resolved in this study provide the first guide for post-transcriptional regulation of pituitary gonadotrope FSH secretion in pig, as well as in other mammals.

Monosodium glutamate versus diet induced obesity in pregnant rats and their offspring

BACKGROUND

We aim at determining the role of monosodium glutamate (MSG) compared with high caloric chow(HCC) in development of obesity in pregnant rats and their offspring.

METHODS

Ninety pregnant rats were divided into 3 groups, control, MSG and HCC fed. We determined energy intake, body weight (BW), abdominal fat, fat to body weight ratio, serum glucose, insulin, leptin, lipid profile, ob and leptin receptor-b gene expressions in pregnant rats and ob and leptin receptor-b gene expressions, serum insulin,glucose, leptin, triacylglycerides (TAG), total lipids (TL) and BW in offspring.

RESULTS

Although daily energy intake and BW of MSG treated rats were lower than those of HCC fed rats, their abdominal fat and fat body weight ratio were higher. MSG or HCC increased Ob gene expression, leptin, insulin,LDL, cholesterol, total lipids (TL), glucose and decreased leptin receptor-b gene expression. In offspring of MSG treated rats, BW, serum glucose, insulin, leptin, TAG, TL and Ob gene expression increased and leptin receptor-b gene expression decreased whereas in offspring of HCC fed rats, serum insulin, leptin, Ob and leptin receptor-b gene expression increased but serum glucose, TAG, TL or BW did not change.

CONCLUSION

We conclude that in pregnant rats, MSG, in spite of mild hypophagia, caused severe increase in fat body weight ratio, via leptin resistance, whereas, HCC increased BW and fat body weight ratio, due to hyperphagia with consequent leptin resistance. Moreover, maternal obesity in pregnancy, caused by MSG, has greater impact on offspring metabolism and BW than that induced by HCC.

Transition of leptin receptor expression during pubertal development in female rat pituitary

Leptin is thought to play important roles in pubertal development and reproductive function in the female. Leptin receptor is expressed in various tissues including the pituitary and hypothalamus. We investigated the transition of leptin receptor (Ob-R) expression in female rat pituitary during pubertal development. Real-time RT-PCR was performed for long-form leptin receptor (Ob-Rb) and short-form leptin receptor (Ob-Ra) in the pituitary and cerebrum of the rats aged 4 (juvenile), 6 (pubertal), and 8 weeks (adult). Double immunohistochemical colocalization of Ob-R and luteinizing hormone (LH) was performed in pituitaries from 4-week-old female rats. Serum leptin concentrations of 4-, 6-, and 8-week-old rats were measured by radioimmunoassay. In the pituitary, expression of Ob-Rb mRNA in 4-week-old rats (1.00 +/- 0.16) was significantly higher than in 8-week-old rats (0.61 +/- 0.07, p<0.05), although expression of Ob-Ra mRNA did not differ among 4-, 6-, and 8-week-old rats. In cerebrum, Ob-Ra and Ob-Rb mRNA expressions did not differ significantly among 4-, 6-, and 8-week-old rats. Intense staining of Ob-R and colocalization of Ob-R and LH were seen in 4-week-old rat pituitary. On the other hand, serum concentrations of leptin in 6- and 8-week-old rats were significantly higher than those in 4-week-old rats (p<0.05, p<0.01, respectively). In conclusion, since the pituitary gonadotroph is a potential target of leptin, the juvenile rat pituitary might prepare for a subsequent increase of serum leptin concentration by expressing Ob-Rb.

Metabolic syndrome and reproduction: I. testicular function

In recent years there is increasing evidence of an interaction between metabolic syndrome and testicular function. Metabolic syndrome, in particular obesity, affects testicular function by reducing total testosterone and sex hormone-binding globulin levels, as well as having a detrimental effect on spermatogenesis. On the other hand, hypogonadism further increases insulin resistance, which is the main pathophysiological feature of metabolic syndrome. There are implications that testosterone replacement can improve not only testicular function, but also parameters of the metabolic syndrome. Although the exact pathophysiological mechanisms remain unclear, leptin, resistin and ghrelin appear to play crucial roles in the interaction between metabolic syndrome and testicular function. All of this evidence supports the notion that the metabolic syndrome is a complex clinical entity characterized by pathophysiological mechanisms that affect the endocrine system as a whole; for these reasons it has been proposed to rename it 'metabolic-neuroendocrine syndrome'.

Fasting and glucose effects on pituitary leptin expression: is leptin a local signal for nutrient status?

Leptin, a potent anorexigenic hormone, is found in the anterior pituitary (AP). The aim of this study was to determine whether and how pituitary leptin-bearing cells are regulated by nutritional status. Male rats showed 64% reductions in pituitary leptin mRNA 24 hr after fasting, accompanied by significant (30-50%) reductions in growth hormone (GH), prolactin, and luteinizing hormone (LH), and 70-80% reductions in target cells for gonadotropin-releasing hormone or growth hormone-releasing hormone. There was a 2-fold increase in corticotropes. Subsets (22%) of pituitary cells coexpressed leptin and GH, and <5% coexpressed leptin and LH, prolactin, thyroid-stimulating hormone, or adrenocorticotropic hormone. Fasting resulted in significant (55-75%) losses in cells with leptin proteins or mRNA, and GH or LH. To determine whether restoration of serum glucose could rescue leptin, LH, and GH, additional fasted rats were given 10% glucose water for 24 hr. Restoring serum glucose in fasted rats resulted in pituitary cell populations with normal levels of leptin and GH and LH cells. Similarly, LH and GH cells were restored in vitro after populations from fasted rats were treated for as little as 1 hr in 10-100 pg/ml leptin. These correlative changes in pituitary leptin, LH, and GH, coupled with leptin's rapid restoration of GH and LH in vitro, suggest that pituitary leptin may signal nutritional changes. Collectively, the findings suggest that pituitary leptin expression could be coupled to glucose sensors like glucokinase to facilitate rapid responses by the neuroendocrine system to nutritional cues.

Adipokines: implications for female fertility and obesity

Obesity is associated with a diverse set of metabolic disorders, and has reproductive consequences that are complex and not well understood. The adipose tissue-produced leptin has dominated the literature with regards to female fertility complications, but it is pertinent to explore the likely role of other adipokines--adiponectin and resistin--as our understanding of their biological functions emerge. Leptin influences the developing embryo, the functioning of the ovary and the endometrium, interacts with the release and activity of gonadotrophins and the hormones that control their synthesis. In this review such biological actions and potential roles of the adipokines leptin, adiponectin and resistin are explored in relation to female fertility and the complexity of the obese metabolic state.

Effects of leptin on gonadotropin-releasing hormone release from hypothalamic–infundibular explants and gonadotropin release from adenohypophyseal primary cell cultures: further evidence that fully nourished cattle are resistant to leptin

In rodents and pigs, leptin stimulates the release of gonadotropin-releasing hormone (GnRH) from hypothalamus, gonadotropins from adenohypophyseal (AP) explants and cells, and luteinizing hormone (LH) from full-fed animals. In the current studies, we investigated whether leptin could stimulate the release of GnRH from bovine hypothalamic-infundibular (HYP) explants and gonadotropins from bovine adenohypophyseal cells. In Experiment 1A, HYP explants collected from 17 bulls and seven steers were incubated with Krebs-Ringer bicarbonate buffer (KRB) containing 0, 10, 100, or 1000 ng/ml recombinant ovine leptin (oleptin) for 30 min after a 3-h period of equilibration. None of the doses of leptin affected (P > 0.05) GnRH release into the media. In Experiment 1B, HYP explants collected from six steers were incubated with KRB containing 0 or 1000 ng/ml oleptin for two consecutive 30-min periods and challenged with 60 mM K(+) afterwards. Leptin did not affect (P > 0.05) basal or K(+)-stimulated release of GnRH. In Experiment 2, adenohypophyses from steers were collected at slaughter and cells dispersed and cultured for 4 days. On day 5, cells were treated with media alone (control) or media containing 10(-11), 10(-10), 10(-9), and 10(-8)M oleptin. Three independent replications were performed. None of the doses of leptin stimulated (P > 0.05) the release of LH. Although leptin at 10(-11), 10(-10), and 10(-9)M increased (P < 0.03) slightly the release of FSH compared to control-treated cells in one replicate, this effect was not confirmed in the other two replicates. Results support the hypothesis that leptin has limited effects on the release of GnRH and gonadotropins in full-fed cattle and reiterate important species differences in responsiveness to leptin.

Role of leptin in modulating the hypothalamic-pituitary axis and luteinizing hormone secretion in the prepuberal gilt

Three experiments (EXP) were conducted to test the hypothesis that leptin modulates LH, GnRH, and neuropeptide Y (NPY) secretion. In EXP I, prepuberal gilts received intracerebroventricular (i.c.v.) leptin injections and blood samples were collected. In EXP II, anterior pituitary cells from prepuberal gilts in primary culture were challenged with 10(-14), 10(-13), 10(-12), 10(-11), 10(-10), 10(-9), 10(-8), 10(-7), or 10(-6) M leptin individually or in combinations with 10(-10), 10(-9), and 10(-8) M GnRH. In EXP III, hypothalamic-preoptic area (HYP-POA) explants were placed in perfusion system and exposed to 0 (n=5), 10(-12) M (n=4), 10(-10) M (n=4), 10(-8) M (n=4), or 10(-6) M (n=5) human recombinant leptin (LEP) for 30 min. In EXP I, serum LH concentrations were unaffected by leptin treatment. In EXP II, all doses of leptin increased LH secretion except for 10(-12) and 10(-7) M. Only 10(-7), or 10(-13) M leptin in combination with 10(-8) or 10(-9) M GnRH, respectively, suppressed LH secretion. In EXP III, prior to leptin, media GnRH concentrations were similar across treatments. Media GnRH concentrations increased after 10(-12), 10(-10), and 10(-8) M leptin compared to control. Leptin treatment failed to influence NPY secretion across treatments. These results indicate that components of the neuroendocrine axis that regulate GnRH and LH secretion are functional and leptin sensitive before the onset of puberty. Other neural peptides in addition to NPY may mediate the acute effects of leptin on the GnRH-LH system and lastly, the inability of i.c.v. leptin treatment to increase LH secretion may in part be related to stage of sexual maturation and associated change in negative feedback action of estradiol on LH secretion.

Effects of leptin on intracellular calcium concentrations in isolated porcine somatotropes

Leptin, the product of the obese gene, is a protein that is secreted primarily from adipocytes. Leptin can influence the function of the pituitary gland through its action on the hypothalamus, but it can also directly act at the level of the pituitary gland. The ability of leptin to induce an increase in intracellular Ca2+ concentration ([Ca2+]i) in somatotropes was examined in dispersed porcine pituitary cells using a calcium imaging system. Somatotropes were functionally identified by the application of human growth hormone releasing hormone. Leptin increased [Ca2+]i in porcine somatotropes in a dose-dependent manner. The application of 100 nM leptin for 3 min did not have a significant effect on [Ca2+]i, while a 3-min application of 1 microM leptin increased [Ca2+]i in about 50% of the somatotropes (p < 0.01). The application of a second leptin challenge (1 microM) evoked a response in only 18% of the observed somatotropes. The stimulatory effect of leptin was abolished in low calcium saline and blocked by nifedipine, an L-calcium channel blocker, suggesting an involvement of calcium channels. Pretreatment of the cultures with AG 490, a specific Janus kinase inhibitor, and with SB 203580, a mitogen-activated protein kinase (MAP kinase) inhibitor, abolished the increase in [Ca2+]i evoked by leptin. In the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, the magnitude of the increase in [Ca2+]i evoked by 1 microM leptin was not significantly changed. However, in the presence of L-NAME only 24% of the somatotropes responded to leptin, while in parallel control cultures 70% of the somatotropes responded to leptin. These results imply an involvement of Janus kinase/signal transducer and activator or transcription, MAP kinase and NOS-signaling pathways in the stimulatory effect of leptin on porcine somatotropes.

Effects of perinatal maternal food restriction on pituitary-gonadal axis and plasma leptin level in rat pup at birth and weaning and on timing of puberty

The effects of maternal 50% food restriction (FR) during the last week of gestation and/or lactation on pituitary-gonadal axis (at birth and weaning), on circulating levels of leptin (at weaning), and on the onset of puberty have been determined in rats at birth and at weaning. Maternal FR during pregnancy has no effect at term on the litter size, on the basal level of testosterone in male pups, and on the drastic surge of circulating testosterone that occurs 2 h after birth. At weaning, similar retardation of body growth is observed in male and female pups from mothers exposed to FR. This undernutrition induces the most drastic effects when it is performed during both gestation and lactation or during lactation alone. Drastic retardation of testicle growth with reduction of cross-sectional area and intratubular lumen of the seminiferous tubules is observed in male pups from mothers exposed to undernutrition during both gestation and lactation or during lactation alone. Maternal FR during the perinatal period reduces circulating levels of FSH in male pups without affecting LH and testosterone concentrations. Maternal FR does not affect circulating levels of LH, estradiol, and progesterone in female pups. Female pups from mothers exposed to FR during both gestation and lactation show a significant increase of plasma FSH as well as a drastic retardation of ovarian growth. The follicular population was also altered. The number of antral follicles of small size (vesicular follicles) was increased, although the number of antral follicles of large size (graafian follicles) was reduced. Maternal FR occurring during both late gestation and lactation (male and female pups), during lactation alone (male and female pups), or during late gestation (female pups) induces a drastic reduction of plasma leptin and fat mass in pups at weaning. The onset of puberty is delayed in pups of both sexes from mothers exposed to FR during lactation and during both gestation and lactation. In conclusion, these data demonstrate that a perinatal growth retardation induced by maternal FR has long-term consequences on both size and histology of the genitals, on plasma gonadotropins and leptin levels, on fat stores at weaning, and on the onset of puberty.