AMP-activated protein kinase is a key intermediary in GnRH-stimulated LHβ gene transcription

Fasting-mimicking diet cycles reduce neuroinflammation to attenuate cognitive decline in Alzheimer's models

The effects of fasting-mimicking diet (FMD) cycles in reducing many aging and disease risk factors indicate it could affect Alzheimer's disease (AD). Here, we show that FMD cycles reduce cognitive decline and AD pathology in E4FAD and 3xTg AD mouse models, with effects superior to those caused by protein restriction cycles. In 3xTg mice, long-term FMD cycles reduce hippocampal Aβ load and hyperphosphorylated tau, enhance genesis of neural stem cells, decrease microglia number, and reduce expression of neuroinflammatory genes, including superoxide-generating NADPH oxidase (Nox2). 3xTg mice lacking Nox2 or mice treated with the NADPH oxidase inhibitor apocynin also display improved cognition and reduced microglia activation compared with controls. Clinical data indicate that FMD cycles are feasible and generally safe in a small group of AD patients. These results indicate that FMD cycles delay cognitive decline in AD models in part by reducing neuroinflammation and/or superoxide production in the brain.

Vitamin B3 (niacin), B6, C, and iron intake are associated with the free androgen index, especially in normoandrogenic polycystic ovary syndrome

Objective

Nutritional intake is one of the most common environmental risk factors of polycystic ovary syndrome (PCOS) because it is associated with obesity and insulin resistance. This study aims to determine the relationship between micronutrient intake and androgen levels associated with PCOS.

Material and Methods

This cross-sectional study was performed on 79 PCOS patients, consisted of 50 normoandrogenic (NA) and 29 hyperandrogenic (HA) patients and 66 healthy controls. Dietary intake assessment was performed using a modified 38-item semi-quantitative food frequency questionnaire. Bivariate, correlation, and multivariate analyses were performed to determine the association between study variables, and p-value less than 0.05 was considered as statistically significant difference.

Results

The baseline characteristics in all groups were similar, except for body mass index and hormonal profile, compared to those in the other groups, found to be higher in the hyperandrogenic PCOS group. There was found a significantly negative correlation between the free androgen index and intake of vitamin B1, vitamin B2, niacin, vitamin B6, calcium, and iron in the normoandrogenic PCOS group, while we did not observe it in the hyperandrogenic PCOS group. Multivariate linear regression analysis reveals that the intake of vitamin B6, vitamin C, niacin, and iron had a significant effect on the free androgen index.

Conclusion

There is an effect of micronutrient intake on androgen levels in women with PCOS. The association was more significant in the normoandrogenic PCOS than in the hyperandrogenic PCOS. These findings reveal an association between micronutrients and androgens and PCOS at a systemic level.

Roles of AMP-Activated Protein Kinase (AMPK) in Mammalian Reproduction

Reproduction is an energy demanding function and only take place in case of sufficient available energy status in mammals. Metabolic diseases such as anorexia nervosa are clinically associated with reduced fertility. AMP-activated protein kinase (AMPK), as a major regulator of cellular energy homeostasis, is activated in limited energy reserves to ensure the orderly progress of various physiological activities. In recent years, mounting evidence shows that AMPK is involved in the regulation of reproductive function through multiple mechanisms. AMPK is likely to be a metabolic sensor integrating central and peripheral signals. In this review, we aim to explore the preclinical studies published in the last decade that investigate the role of AMP-activated protein kinase in the reproductive field, and its role as a target for drug therapy of reproductive system-related diseases. We also emphasized the emerging roles of AMPK in transcriptional regulation of reproduction processes and metabolisms, which are tightly related to the energy state and fertility of an organism.

Chronic effects of maternal tobacco-smoke exposure and/or α-lipoic acid treatment on reproductive parameters in female rat offspring

Prenatal tobacco-smoke exposure negatively affects the reproductive functions of female offspring and oxidative stress plays a major role at this point. Alpha-lipoic acid (ALA), well known as a biological antioxidant, has been used as a nutritional supplement and as a therapeutic agent in the treatment of certain complications during pregnancy. We aimed to investigate the effects of maternal tobacco-smoke exposure and/or ALA administration on puberty onset, sexual behavior, gonadotrophin levels, apoptosis-related genes, apoptotic cell numbers and oxidative stress markers in the adult female rat offspring. Sprague-Dawley rats were divided into four groups; control, tobacco smoke (TS), TS+ALA and ALA groups. Animals were exposed to TS and/or ALA for 8 weeks before pregnancy and throughout pregnancy. All treatments ended with birth and later newborn female rats were selected for each experimental group. The experiment ended at postnatal day 74-77. Maternal tobacco smoke advanced the onset of puberty in the female offspring of the TS group (p < 0.05). In all treatment groups; the mean number of anogenital investigations and lordosis quality scores showed a decline, serum luteinizing hormone levels significantly increased (p < 0.05) and several histopathological changes in ovaries were observed compared to the control group. In addition, an increase in apoptotic marker levels and apoptotic cell numbers was detected in the ovaries of all treatment groups. Decreased TAS and increased TOS levels were detected in all treatment groups compared to control. These findings suggested that maternal tobacco smoke and/or ALA administration may be leading to the impaired reproductive health of female offspring. Abbreviations: ALA: alpha-lipoic acid; LH: luteinizing hormone; FSH: follicle-stimulating hormone; TAS: total antioxidant status; TOS: total oxidant status; Apaf1: apoptotic protease-activating factor 1; Casp3: caspase 3; Casp9: caspase 9; CF: cyst follicles; 4-HNE: 4-Hidroxynonenal; 8-OHdG: 8-hydroxydeoxyguanosine; TUNEL: terminal deoxynucleotidyl transferase-mediated deoxyuridine-biotin nick end labeling; ROS: reactive oxygen species; GnRHR: gonadotropin-releasing hormone receptor; HPG: hypothalamic-pituitary-gonadal; AMPK: AMP-activated protein kinase; ELISA: enzyme-linked immunosorbent assay; cDNA: complementary DNA; qPCR: quantitative real-time PCR; FC: follicular cysts; PF: primary follicle; SF: secondary follicle; GF: graafian follicle; CL: corpus luteum; DF: degenerated follicle; AF: atretic follicle.

GLUT1-mediated glycolysis supports GnRH-induced secretion of luteinizing hormone from female gonadotropes

The mechanisms mediating suppression of reproduction in response to decreased nutrient availability remain undefined, with studies suggesting regulation occurs within the hypothalamus, pituitary, or gonads. By manipulating glucose utilization and GLUT1 expression in a pituitary gonadotrope cell model and in primary gonadotropes, we show GLUT1-dependent stimulation of glycolysis, but not mitochondrial respiration, by the reproductive neuropeptide GnRH. GnRH stimulation increases gonadotrope GLUT1 expression and translocation to the extracellular membrane. Maximal secretion of the gonadotropin Luteinizing Hormone is supported by GLUT1 expression and activity, and GnRH-induced glycolysis is recapitulated in primary gonadotropes. GLUT1 expression increases in vivo during the GnRH-induced ovulatory LH surge and correlates with GnRHR. We conclude that the gonadotropes of the anterior pituitary sense glucose availability and integrate this status with input from the hypothalamus via GnRH receptor signaling to regulate reproductive hormone synthesis and secretion.

Metabolic regulation of kisspeptin - the link between energy balance and reproduction

Hypothalamic kisspeptin neurons serve as the nodal regulatory centre of reproductive function. These neurons are subjected to a plethora of regulatory factors that ultimately affect the release of kisspeptin, which modulates gonadotropin-releasing hormone (GnRH) release from GnRH neurons to control the reproductive axis. The presence of sufficient energy reserves is critical to achieve successful reproduction. Consequently, metabolic factors impose a very tight control over kisspeptin synthesis and release. This Review offers a synoptic overview of the different steps in which kisspeptin neurons are subjected to metabolic regulation, from early developmental stages to adulthood. We cover an ample array of known mechanisms that underlie the metabolic regulation of KISS1 expression and kisspeptin release. Furthermore, the novel role of kisspeptin neurons as active players within the neuronal circuits that govern energy balance is discussed, offering evidence of a bidirectional role of these neurons as a nexus between metabolism and reproduction.

Expression of chemerin receptors CMKLR1, GPR1 and CCRL2 in the porcine pituitary during the oestrous cycle and early pregnancy and the effect of chemerin on MAPK/Erk1/2, Akt and AMPK signalling pathways

Studies on adipokines, substances that are produced in adipose tissue, indicate that they influence both metabolism and reproduction. Chemerin is a novel addition to the adipokine family. It is believed that chemerin receptors are expressed in different structures of the hypothalamic-pituitary-gonadal (HPG) axis, which are crucial for endocrine control of reproductive functions, including the pituitary. The aim of this study was to investigate the expression of chemerin receptors (CMKLR1, GPR1, CCRL2) genes and proteins in the porcine pituitary. The effect of chemerin on MAPK/Erk1/2, Akt and AMPK signalling pathways was also investigated. The anterior (AP) and posterior (PP) lobes of the pituitary were examined on days 2 to 3, 10 to 12, 14 to 16, and 17 to 19 of the oestrous cycle and on days 10 to 11, 12 to 13, 15 to 16, and 27 to 28 of pregnancy. This is the first study to demonstrate that CMKLR1, GPR1 and CCRL2 are expressed in the porcine AP and PP, which implies that this gland is sensitive to chemerin action. The expression of the studied chemerin receptors fluctuated during different phases of the cycle and early gestation, which could be related to changes in the endocrine status of female pigs. The study also revealed that CMKLR1 and CCRL2 proteins were present in gonadotrophs and thyrotrophs, whereas CCRL2 was also present in somatotrophs, during the cycle and early pregnancy. We observed that chemerin affected MAPK/Erk1/2, Akt and AMPK signalling pathways in the porcine AP. These results suggest that chemerin may participate in the regulation of reproductive functions at the level of the pituitary.

Expression of genes that regulate follicle development and maturation during ovarian stimulation in poor responders

RESEARCH QUESTION

Sex hormone-binding globulin (SHBG), androgen receptor (AR), LH beta polypeptide (LHB), progesterone receptor membrane component 1 (PGRMC1) and progesterone receptor membrane component 2 (PGRMC2) regulate follicle development and maturation. Their mRNA expression was assessed in peripheral blood mononuclear cells (PBMC) of normal and poor responders, during ovarian stimulation.

DESIGN

Fifty-two normal responders and 15 poor responders according to the Bologna criteria were enrolled for IVF and intracytoplasmic sperm injection and stimulated with 200 IU of follitrophin alpha and gonadotrophin-releasing hormone antagonist. HCG was administered for final oocyte maturation. On days 1, 6 and 10 of stimulation, blood samples were obtained, serum hormone levels were measured, RNA was extracted from PBMC and real-time polymerase chain reaction was carried out to identify the mRNA levels. Relative mRNA expression of each gene was calculated by the comparative 2^-DDCt method.

RESULTS

Differences between mRNA levels of each gene on the same time point between the two groups were not significant. PGRMC1 and PGRMC2 mRNA levels were downregulated, adjusted for ovarian response and age. Positive correlations between PGRMC1 and AR (standardized beta = 0.890, P < 0.001) from day 1 to 6 and PGRMC1 and LHB (standardized beta = 0.806, P < 0.001) from day 1 to 10 were found in poor responders. PGRMC1 and PGRMC2 were positively correlated on days 6 and 10 in normal responders.

CONCLUSIONS

PGRMC1 and PGRMC2 mRNA are significantly decreased during ovarian stimulation, with some potential differences between normal and poor responders.

Insulin-induced hypoglycaemia suppresses pulsatile luteinising hormone secretion and arcuate Kiss1 cell activation in female mice

Stress suppresses pulsatile luteinising hormone (LH) secretion in a variety of species, although the mechanism underlying this inhibition of reproductive function remains unclear. Metabolic stress, particularly hypoglycaemia, is a clinically-relevant stress type that is modelled with bolus insulin injection (insulin-induced hypoglycaemia). The present study utilised ovariectomised C57BL/6 mice to test the hypothesis that acute hypoglycaemia suppresses pulsatile LH secretion via central mechanisms. Pulsatile LH secretion was measured in 90-minute sampling periods immediately prior to and following i.p. injection of saline or insulin. The secretion of LH was not altered over time in fed animals or acutely fasted (5 hours) animals following an i.p. saline injection. By contrast, insulin elicited a robust suppression of pulsatile LH secretion in fasted animals, preventing LH pulses in five of six mice. To identify the neuroendocrine site of impairment, a kisspeptin challenge was performed in saline or insulin pre-treated animals in a cross-over design. LH secretion in response to exogenous kisspeptin was not different between animals pre-treated with saline or insulin, indicating normal gonadotrophin-releasing hormone cell and pituitary responses during acute hypoglycaemia. Based on this finding, the effect of insulin-induced hypoglycaemia on arcuate kisspeptin (Kiss1) cell function was determined using c-Fos as a marker of neuronal activation. Insulin caused a significant suppression in the percentage of Kiss1 cells in the arcuate nucleus that contained c-Fos compared to saline-injected controls. Taken together, these data support the hypothesis that insulin-induced hypoglycaemia suppresses pulsatile LH secretion in the female mouse via predominantly central mechanisms, which culminates in the suppression of the arcuate Kiss1 population.

Modulation of hepatic inflammation and energy-sensing pathways in the rat liver by high-fructose diet and chronic stress

PURPOSE

High-fructose consumption and chronic stress are both associated with metabolic inflammation and insulin resistance. Recently, disturbed activity of energy sensor AMP-activated protein kinase (AMPK) was recognized as mediator between nutrient-induced stress and inflammation. Thus, we analyzed the effects of high-fructose diet, alone or in combination with chronic stress, on glucose homeostasis, inflammation and expression of energy sensing proteins in the rat liver.

METHODS

In male Wistar rats exposed to 9-week 20% fructose diet and/or 4-week chronic unpredictable stress we measured plasma and hepatic corticosterone level, indicators of glucose homeostasis and lipid metabolism, hepatic inflammation (pro- and anti-inflammatory cytokine levels, Toll-like receptor 4, NLRP3, activation of NFκB, JNK and ERK pathways) and levels of energy-sensing proteins AMPK, SIRT1 and peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α).

RESULTS

High-fructose diet led to glucose intolerance, activation of NFκB and JNK pathways and increased intrahepatic IL-1β, TNFα and inhibitory phosphorylation of insulin receptor substrate 1 on Ser³⁰⁷. It also decreased phospho-AMPK/AMPK ratio and increased SIRT1 expression. Stress alone increased plasma and hepatic corticosterone but did not influence glucose tolerance, nor hepatic inflammatory or energy-sensing proteins. After the combined treatment, hepatic corticosterone was increased, glucose tolerance remained preserved, while hepatic inflammation was partially prevented despite decreased AMPK activity.

CONCLUSION

High-fructose diet resulted in glucose intolerance, hepatic inflammation, decreased AMPK activity and reduced insulin sensitivity. Chronic stress alone did not exert such effects, but when applied together with high-fructose diet it could partially prevent fructose-induced inflammation, presumably due to increased hepatic glucocorticoids.

α-Lipoic acid potentially targets AMP-activated protein kinase and energy production in the fetal brain to ameliorate dioxin-produced attenuation in fetal steroidogenesis

Our previous studies demonstrated that treating pregnant rats with dioxins, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), targets the pituitary expression of luteinizing hormone (LH) to attenuate testicular steroidogenesis in fetuses, resulting in the imprinting of sexual immaturity of the offspring after reaching maturity. Furthermore, we found that although TCDD disturbs the tricarboxylic acid (TCA) cycle in the fetal hypothalamus, maternal co-treatment with α-lipoic acid (α-LA), a cofactor of the TCA cycle, restores a TCDD-produced reduction in the LH-evoked steroidogenesis as well as the TCA cycle activity in fetuses. However, the mechanism underlying the beneficial effect of α-LA remains to be fully elucidated. To address this issue, we compared the effect of α-LA with that of thiamine, another cofactor of the TCA cycle. As with α-LA, supplying thiamine to dams exposed to TCDD alleviates the reduced level of not only hypothalamic ATP but also pituitary LH and testicular steroidogenic protein in fetuses. However, thiamine had a much weaker effect than α-LA. In agreement with ATP attenuation, TCDD activated AMP-activated protein kinase (AMPK), a negative regulator of LH production, whereas the supplementation of α-LA allowed recovery from this defect. Furthermore, α-LA restored the TCDD-produced reduction in the pituitary expression of the receptor for gonadotropin-releasing hormone (GnRH), an upstream regulator of LH synthesis. These results suggest that α-LA rescues TCDD-produced attenuation during fetal steroidogenesis due not only to facilitation of energy production through the TCA cycle but also through suppression of AMPK activation, and the pituitary GnRH receptor may serve as a mediator of these effects.

Fasting regulates EGR1 and protects from glucose- and dexamethasone-dependent sensitization to chemotherapy

Fasting reduces glucose levels and protects mice against chemotoxicity, yet drugs that promote hyperglycemia are widely used in cancer treatment. Here, we show that dexamethasone (Dexa) and rapamycin (Rapa), commonly administered to cancer patients, elevate glucose and sensitize cardiomyocytes and mice to the cancer drug doxorubicin (DXR). Such toxicity can be reversed by reducing circulating glucose levels by fasting or insulin. Furthermore, glucose injections alone reversed the fasting-dependent protection against DXR in mice, indicating that elevated glucose mediates, at least in part, the sensitizing effects of rapamycin and dexamethasone. In yeast, glucose activates protein kinase A (PKA) to accelerate aging by inhibiting transcription factors Msn2/4. Here, we show that fasting or glucose restriction (GR) regulate PKA and AMP-activated protein kinase (AMPK) to protect against DXR in part by activating the mammalian Msn2/4 ortholog early growth response protein 1 (EGR1). Increased expression of the EGR1-regulated cardioprotective peptides atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in heart tissue may also contribute to DXR resistance. Our findings suggest the existence of a glucose-PKA pathway that inactivates conserved zinc finger stress-resistance transcription factors to sensitize cells to toxins conserved from yeast to mammals. Our findings also describe a toxic role for drugs widely used in cancer treatment that promote hyperglycemia and identify dietary interventions that reverse these effects.

Oocyte activation and latent HIV-1 reactivation: AMPK as a common mechanism of action linking the beginnings of life and the potential eradication of HIV-1

In all mammalian species studied to date, the initiation of oocyte activation is orchestrated through alterations in intracellular calcium (Ca(2+)) signaling. Upon sperm binding to the oocyte plasma membrane, a sperm-associated phospholipase C (PLC) isoform, PLC zeta (PLCζ), is released into the oocyte cytoplasm. PLCζ hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to produce diacylglycerol (DAG), which activates protein kinase C (PKC), and inositol 1,4,5-trisphosphate (IP3), which induces the release of Ca(2+) from endoplasmic reticulum (ER) Ca(2+) stores. Subsequent Ca(2+) oscillations are generated that drive oocyte activation to completion. Ca(2+) ionophores such as ionomycin have been successfully used to induce artificial human oocyte activation, facilitating fertilization during intra-cytoplasmic sperm injection (ICSI) procedures. Early studies have also demonstrated that the PKC activator phorbol 12-myristate 13-acetate (PMA) acts synergistically with Ca(2+) ionophores to induce parthenogenetic activation of mouse oocytes. Interestingly, the Ca(2+)-induced signaling cascade characterizing sperm or chemically-induced oocyte activation, i.e. the "shock and live" approach, bears a striking resemblance to the reactivation of latently infected HIV-1 viral reservoirs via the so called "shock and kill" approach, a method currently being pursued to eradicate HIV-1 from infected individuals. PMA and ionomycin combined, used as positive controls in HIV-1 latency reversal studies, have been shown to be extremely efficient in reactivating latent HIV-1 in CD4(+) memory T cells by inducing T cell activation. Similar to oocyte activation, T cell activation by PMA and ionomycin induces an increase in intracellular Ca(2+) concentrations and activation of DAG, PKC, and downstream Ca(2+)-dependent signaling pathways necessary for proviral transcription. Interestingly, AMPK, a master regulator of cell metabolism that is activated thorough the induction of cellular stress (e.g. increase in Ca(2+) concentration, reactive oxygen species generation, increase in AMP/ATP ratio) is essential for oocyte maturation, T cell activation, and mitochondrial function. In addition to the AMPK kinase LKB1, CaMKK2, a Ca(2+)/calmodulin-dependent kinase that also activates AMPK, is present in and activated on T cell activation and is also present in mouse oocytes and persists until the zygote and two-cell stages. It is our hypothesis that AMPK activation represents a central node linking T cell activation-induced latent HIV-1 reactivation and both physiological and artificial oocyte activation. We further propose the novel observation that various compounds that have been shown to reactivate latent HIV-1 (e.g. PMA, ionomycin, metformin, bryostatin, resveratrol, etc.) or activate oocytes (PMA, ionomycin, ethanol, puromycin, etc.) either alone or in combination likely do so via stress-induced activation of AMPK.

AMP-activated protein kinase (AMPK) activity negatively regulates chondrogenic differentiation

Chondrocytes are derived from mesenchymal stem cells, and play an important role in cartilage formation. Sex determining region Y box (Sox) family transcription factors are essential for chondrogenic differentiation, whereas the intracellular signal pathways of Sox activation have not been clearly elucidated. AMP-activated protein kinase (AMPK) is a serine-threonine kinase generally regarded as a key regulator of cellular energy homeostasis. It is known that the catalytic alpha subunit of AMPK is activated by upstream AMPK kinases (AMPKKs) including liver kinase B1 (LKB1). We have previously reported that AMPK is a negative regulator of osteoblastic differentiation. Here, we have explored the role of AMPK in chondrogenic differentiation using in vitro culture models. The phosphorylation level of the catalytic AMPK alpha subunit significantly decreased during chondrogenic differentiation of primary chondrocyte precursors as well as ATDC-5, a well-characterized chondrogenic cell line. Treatment with metformin, an activator of AMPK, significantly reduced cartilage matrix formation and inhibited gene expression of sox6, sox9, col2a1 and aggrecan core protein (acp). Thus, chondrocyte differentiation is functionally associated with decreased AMPK activity.

FOXO1 is regulated by insulin and IGF1 in pituitary gonadotropes

The FOXO1 transcription factor is important for multiple aspects of reproductive function. We previously reported that FOXO1 functions as a repressor of gonadotropin hormone synthesis, but how FOXO1 is regulated in pituitary gonadotropes is unknown. The growth factors, insulin and insulin-like growth factor I (IGF1), function as key regulators of cell proliferation, metabolism and apoptosis in multiple cell types through the PI3K/AKT signaling pathway. In this study, we found that insulin and IGF1 signaling in gonadotropes induced FOXO1 phosphorylation through the PI3K/AKT pathway in immortalized and primary cells, resulting in FOXO1 relocation from the nucleus to the cytoplasm. Furthermore, insulin administration in vivo induced phosphorylation of FOXO1 and AKT in the pituitary. Thus, insulin and IGF1 act as negative regulators of FOXO1 activity and may serve to fine-tune gonadotropin expression.

A new role for wilms tumor protein 1: differential activities of + KTS and -KTS variants to regulate LHβ transcription

Luteinizing hormone (LH) is synthesized and secreted throughout the reproductive cycle from gonadotrope cells in the anterior pituitary, and is required for steroidogenesis and ovulation. LH contains an α-subunit common with FSH, and a unique LHβ subunit that defines biological activity. Basal LHβ transcription is low and stimulated by hypothalamic GnRH, which induces synthesis of early growth response protein-1 (Egr1), and stimulates binding of transcription factors Egr1 and steroidogenic factor-1 (SF1) on the promoter. WT1 (Wilms tumor protein1) is a zinc finger transcription factor with an essential role in urogenital system development, and which regulates several reproductive genes via interactions with SF1 or binding to GC-rich elements such as Egr1 binding sites. We investigated a potential role for WT1 in LHβ transcription in clonal mouse gonadotrope LβT2 cells. WT1 was present in LβT2 and mouse pituitary cells, and protein bound to the endogenous LHβ promoter. Interestingly, mRNAs for WT1(+KTS), which contains a three amino-acid insertion between the 3rd and 4th zinc fingers, and the WT1 (-KTS) variant were both expressed at significant levels. WT1 mRNAs and protein were decreased approximately 50% by GnRH treatment, under conditions where Egr1 mRNA and protein, and LHβ transcription, were stimulated. Decreasing expression of mRNA for WT1 (-KTS) decreased stimulation of LHβ and Egr1 by GnRH, whereas decreasing both WT1 (-KTS) and (+KTS) increased endogenous LHβ transcription, and prevented LHβ but not Egr1 stimulation by GnRH, suggesting differing biological activities for the WT1 isoforms. Overexpression of WT1 showed that WT1(-KTS) enhanced LHβ promoter GnRH stimulation 2-to-3-fold and required the 3'Egr1 site, but WT1(+KTS) repressed both basal and GnRH-stimulated LHβ promoter activity by approximately 70%. Our data suggest that WT1 can modulate LHβ transcription, with differential roles for the two WT1 variants; WT1 (-KTS) enhances and WT1 (+KTS) suppresses transcription.

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.

Molecular mechanisms of gonadotropin-releasing hormone signaling: integrating cyclic nucleotides into the network

Gonadotropin-releasing hormone (GnRH) is the primary regulator of mammalian reproductive function in both males and females. It acts via G-protein coupled receptors on gonadotropes to stimulate synthesis and secretion of the gonadotropin hormones luteinizing hormone and follicle-stimulating hormone. These receptors couple primarily via G-proteins of the Gq/ll family, driving activation of phospholipases C and mediating GnRH effects on gonadotropin synthesis and secretion. There is also good evidence that GnRH causes activation of other heterotrimeric G-proteins (Gs and Gi) with consequent effects on cyclic AMP production, as well as for effects on the soluble and particulate guanylyl cyclases that generate cGMP. Here we provide an overview of these pathways. We emphasize mechanisms underpinning pulsatile hormone signaling and the possible interplay of GnRH and autocrine or paracrine regulatory mechanisms in control of cyclic nucleotide signaling.