Leptin action in pubertal development: recent advances and unanswered questions

Alternate-day fasting delays pubertal development in normal-weight mice but prevents high-fat diet-induced obesity and precocious puberty

BACKGROUND/OBJECTIVES

Childhood obesity, particularly in girls, is linked to early puberty onset, heightening risks for adult-onset diseases. Addressing childhood obesity and precocious puberty is vital to mitigate societal burdens. Despite existing costly and invasive medical interventions, introducing lifestyle-based alternatives is essential. Our study investigates alternate-day fasting's (ADF) impact on pubertal development in normal-weight and high-fat diet (HFD)-induced obese female mice.

METHODS

Four groups of female mice were utilized, with dams initially fed control chow during and before pregnancy. Post-parturition, two groups continued on control chow, while two switched to an HFD. Offspring diets mirrored maternal exposure. One control and one HFD group were subjected to ADF. Morphometry and hormone analyses at various time points were performed.

RESULTS

Our findings demonstrate that ADF in normal-weight mice led to reduced body length, weight, uterine, and ovarian weights, accompanied by delayed puberty and lower levels of sex hormones and growth hormone (GH). Remarkably, GH treatment effectively prevented ADF-induced growth reduction but did not prevent delayed puberty. Conversely, an HFD increased body length, induced obesity and precocious puberty, and altered sex hormones and leptin levels, which were counteracted by ADF regimen. Our data indicate ADF's potential in managing childhood obesity and precocious puberty.

CONCLUSIONS

ADF reduced GH and sex hormone levels, contributing to reduced growth and delayed puberty, respectively. Therefore, parents of normal-weight children should be cautious about prolonged overnight fasting. ADF prevented HFD-induced obesity and precocious puberty, offering an alternative to medical approaches; nevertheless, further studies are needed for translation into clinical practice.

Association of diabetes mellitus with risk of reproductive impairment in females: A comprehensive review

Reproductive impairment is the most prevalent yet most ignored complication of diabetes mellitus. In diabetes, the problem associated with reproductive health is comprehensive in both males and females. Diabetic females have problems like delayed menarche, irregular menstrual cycle, subfertility, complications in pregnancy and early menopause. This may decrease reproductive age in diabetic females as the menarche is delayed and menopause is early in them. Like diabetic males, diabetic females also have the negative effect of oxidative stress on the reproductive system. This may lead to dysfunction of the ovary. It affects the physiological cycle like the ovary's maturation, embryo development and pregnancy. These complications also affect the offspring, and they may also become diabetic. This review aims to concentrate on the effect of diabetes on the reproductive system of females and the impairment caused by it. We will also discuss in detail the role of the hypothalamus-pituitary ovary axis, diabetes impact on different reproductive phases of females, and the sexual disorders that occur in them.

Changes in the Bile Acid Pool and Timing of Female Puberty: Potential Novel Role of Hypothalamic TGR5

CONTEXT

The regulation of pubertal timing and reproductive axis maturation is influenced by a myriad of physiologic and environmental inputs yet remains incompletely understood.

OBJECTIVE

To contrast differences in bile acid isoform profiles across defined stages of reproductive maturity in humans and a rat model of puberty and to characterize the role of bile acid signaling via hypothalamic expression of bile acid receptor populations in the rodent model.

METHODS

Secondary analysis and pilot studies of clinical cohorts, rodent models, ex vivo analyses of rodent hypothalamic tissues. Bile acid concentrations is the main outcome measure.

RESULTS

Lower circulatory conjugated:deconjugated bile acid concentrations and higher total secondary bile acids were observed in postmenarcheal vs pre-/early pubertal adolescents, with similar shifts observed in infantile (postnatal day [PN]14) vs early juvenile (PN21) rats alongside increased tgr5 receptor mRNA expression within the mediobasal hypothalamus of female rats. 16S rRNA gene sequencing of the rodent gut microbiome across postnatal life revealed changes in the gut microbial composition predicted to have bile salt hydrolase activity, which was observed in parallel with the increased deconjugated and increased concentrations of secondary bile acids. We show that TGR5-stimulated GnRH release from hypothalamic explants is mediated through kisspeptin receptors and that early overexpression of human-TGR5 within the arcuate nucleus accelerates pubertal onset in female rats.

CONCLUSION

Bile acid isoform shifts along stages of reproductive maturation are conserved across rodents and humans, with preclinical models providing mechanistic insight for the neuroendocrine-hepatic-gut microbiome axis as a potential moderator of pubertal timing in females.

Effect of TSH on aromatase expression of ovarian granulosa cells in obese mice

PURPOSE

Aromatase plays an important role in ovarian development, the normal progress of the menstrual cycle, and fertility status. Elevated aromatase activity is linked to obesity. There is a bidirectional relationship between obesity and thyroid function. Few studies have investigated the relationship between TSH and ovarian aromatase in obesity. Our aim was to investigate the effect of TSH on aromatase expression of ovarian granulosa cells in obese mice.

METHODS

Female mice pups were divided into an obesity group and a control group. Obese parameters and the time of pubertal onset were recorded. At the age of 5 weeks, blood and tissues were obtained. Serum aromatase and hormone concentrations were measured using ELISA. The granulosa cells were isolated and exposed to variable concentrations (0 μM, 1 μM, 10 μM, 100 μM) of TSH. The expression of CYP19A1 mRNA and protein were assessed via RT-qPCR and western blot.

RESULTS

In female mice, body weight, Lee's obesity index, and serum levels of E2, aromatase, and TSH were significantly higher in the obesity group compared to the control group, whereas the time of pubertal onset and serum T3 and T4 concentrations were significantly lower (all P < 0.001). In granulosa cells, the expression of CYP19A1 mRNA in the obesity group was lower than that in the control group at 1 μM and 100 μM concentrations of TSH (both P < 0.001). The expression of CYP19A1 protein in the obesity group was higher than that in the control group after TSH stimulation (P = 0.014, P < 0.001, and P = 0.004, respectively). With the increase of TSH concentrations, the expression of CYP19A1 mRNA and protein in the two groups significantly increased (all P < 0.001).

CONCLUSION

Early puberty and elevated serum aromatase and TSH levels were found in obese female mice. In the granulosa cells of obese mice, TSH directly regulates aromatase expression in a dose-dependent manner.

Beyond the Metabolic Syndrome: Non-Obvious Complications of Obesity in Children

Obesity is currently one of the most significant public health challenges worldwide due to the continuous increase in obesity rates among children, especially younger children. Complications related to obesity, including serious ones, are increasingly being diagnosed in younger children. A search was performed from January 2023 to September 2023 using the PubMed, Cochrane Library, Science Direct, MEDLINE, and EBSCO databases. The focus was on English-language meta-analyses, systematic reviews, randomized clinical trials, and observational studies worldwide. Four main topics were defined as follows: disorders of glucose metabolism; liver disease associated with childhood obesity; the relationship between respiratory disorders and obesity in children; and the effects of obesity on the hypothalamic-pituitary-gonadal axis and puberty. Understanding potential complications and their underlying mechanisms can expedite the diagnostic process and enhance the effectiveness of treatment. We aspire that this study will bring insight into the often-overlooked complications associated with obesity.

The effects of weight loss-related amenorrhea on women's health and the therapeutic approaches: a narrative review

Background and Objective

Weight loss-related amenorrhea is defined as the reversible functional inhibition of the hypothalamic-pituitary-ovarian (HPO) axis associated with weight loss or low body weight, which occurs mostly in adolescents and women of reproductive age. The specific pathological mechanisms of this disease have not yet been elucidated, and the optimal evidence-based guidelines for its clinical assessment and management are limited. This review summarizes its adverse effects on female health, and the individualized, emerging, and multidisciplinary therapeutic approaches used to treat it.

Methods

We searched the PubMed, Web of Science, and China National Knowledge Infrastructure (CNKI) databases for Chinese and English literature on functional hypothalamic amenorrhea (FHA), and retrieved original articles (on basic and clinical research) and reviews published up to December 2022.

Key Content and Findings

We reviewed the findings on the unfavorable effects of weight loss-related amenorrhea with a focus on reproduction, the skeletal and cardiovascular system, other endocrine effects, and mental health. Lifestyle changes and hormonal replacement have been shown to alleviate the underlying causes and lead to the recovery of menstruation. However, the efficacy of treatments is affected by many factors, such as psychological stress and heterogeneity.

Conclusions

Weight loss-related amenorrhea, which is an important type of FHA, is manifested by anovulation and hypoestrogenism, and has both short- and long-term adverse effects on women's overall health. It is difficult to alleviate its underlying causes. Individualized treatments need to be optimized and emerging or multidisciplinary therapeutic approaches need to be explored that aim to recover normal menstruation and ovulation, eliminate the undesirable effects of prolonged hypoestrogenism and alleviate psychological disorders.

The Interaction of Obesity and Reproductive Function in Adolescents

Obesity is increasing worldwide, including in pediatrics. Adequate nutrition is required for initiation of menses, and there is a clear secular trend toward earlier pubertal onset and menarche in females in countries around the globe. Similar findings of earlier pubertal start are suggested in males. However, as individuals and populations have crossed into over-nutritional states including overweight and obesity, the effect of excess weight on disrupting reproductive function has become apparent. Hypothalamic hypogonadism and polycystic ovary syndrome are two conditions where reproductive function appears to directly relate to excess weight. Clinical findings in individuals with certain polygenic and monogenic obesity syndromes, which also have reproductive disruptions, have helped elucidate neurologic pathways that are common to both. Clinical endocrinopathies such as hypothyroidism or panhypopituitarism also aide in the understanding of the role of the endocrine system in weight gain. Understanding the intersection of obesity and reproductive function may lead to future therapies which can treat both conditions.

Insulin signaling couples growth and early maturation to cholesterol intake in Drosophila

Nutrition is one of the most important influences on growth and the timing of maturational transitions including mammalian puberty and insect metamorphosis. Childhood obesity is associated with precocious puberty, but the assessment mechanism that links body fat to early maturation is unknown. During development, the intake of nutrients promotes signaling through insulin-like systems that govern the growth of cells and tissues and also regulates the timely production of the steroid hormones that initiate the juvenile-adult transition. We show here that the dietary lipid cholesterol, which is required as a component of cell membranes and as a substrate for steroid biosynthesis, also governs body growth and maturation in Drosophila via promoting the expression and release of insulin-like peptides. This nutritional input acts via the nutrient sensor TOR, which is regulated by the Niemann-Pick-type-C 1 (Npc1) cholesterol transporter, in the glia of the blood-brain barrier and cells of the adipose tissue to remotely drive systemic insulin signaling and body growth. Furthermore, increasing intracellular cholesterol levels in the steroid-producing prothoracic gland strongly promotes endoreduplication, leading to an accelerated attainment of a nutritional checkpoint that normally ensures that animals do not initiate maturation prematurely. These findings, therefore, show that a Npc1-TOR signaling system couples the sensing of the lipid cholesterol with cellular and systemic growth control and maturational timing, which may help explain both the link between cholesterol and cancer as well as the connection between body fat (obesity) and early puberty.

Leptin enhances social motivation and reverses chronic unpredictable stress-induced social anhedonia during adolescence

Social anhedonia, a loss of interest and pleasure in social interactions, is a common symptom of major depression as well as other psychiatric disorders. Depression can occur at any age, but typically emerges in adolescence or early adulthood, which represents a sensitive period for social interaction that is vulnerable to stress. In this study, we evaluated social interaction reward using a conditioned place preference (CPP) paradigm in adolescent male and female mice. Adolescent mice of both sexes exhibited a preference for the social interaction-associated context. Chronic unpredictable stress (CUS) impaired the development of CPP for social interaction, mimicking social anhedonia in depressed adolescents. Conversely, administration of leptin, an adipocyte-derived hormone, enhanced social interaction-induced CPP in non-stressed control mice and reversed social anhedonia in CUS mice. By dissecting the motivational processes of social CPP into social approach and isolation avoidance components, we demonstrated that leptin treatment increased isolation aversion without overt social reward effect. Further mechanistic exploration revealed that leptin stimulated oxytocin gene transcription in the paraventricular nucleus of the hypothalamus, while oxytocin receptor blockade abolished the leptin-induced enhancement of socially-induced CPP. These results establish that chronic unpredictable stress can be used to study social anhedonia in adolescent mice and provide evidence that leptin modulates social motivation possibly via increasing oxytocin synthesis and oxytocin receptor activation.

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.

Pubertal timing in boys and girls born to mothers with gestational diabetes mellitus: a systematic review

CONTEXT

The incidence of gestational diabetes mellitus (GDM) has been on the rise, driven by maternal obesity. In parallel, pubertal tempo has increased in the general population, driven by childhood obesity.

OBJECTIVE

To evaluate the available evidence on pubertal timing of boys and girls born to mothers with GDM.

DATA SOURCES

We searched MEDLINE, EMBASE, CINAHL Plus, Cochrane library and grey literature for observational studies up to October 2019.

STUDY SELECTION AND EXTRACTION

Two reviewers independently selected studies, collected data and appraised the studies for risk of bias. Results were tabulated and narratively described as reported in the primary studies.

RESULTS

Seven articles (six for girls and four for boys) were included. Study quality score was mostly moderate (ranging from 4 to 10 out of 11). In girls born to mothers with GDM, estimates suggest earlier timing of pubarche, thelarche and menarche although for each of these outcomes only one study each showed a statistically significant association. In boys, there was some association between maternal GDM and earlier pubarche, but inconsistency in the direction of shift of age at onset of genital and testicular development and first ejaculation. Only a single study analysed growth patterns in children of mothers with GDM, describing a 3-month advancement in the age of attainment of peak height velocity and a slight increase in pubertal tempo.

CONCLUSIONS

Pubertal timing may be influenced by the presence of maternal GDM, though current evidence is sparse and of limited quality. Prospective cohort studies should be conducted, ideally coupled with objective biochemical tests.

The LEPR Gene Is Associated with Reproductive Seasonality Traits in Rasa Aragonesa Sheep

The aim of this study was to characterize and identify causative polymorphisms in the leptin receptor (LEPR) gene responsible for the seasonal variation of reproductive traits in sheep. Three reproductive seasonality traits were studied: the total days of anoestrous (TDA), the progesterone cycling months (P4CM) and the oestrous cycling months (OCM). In total, 18 SNPs were detected in 33 ewes with extreme values for TDA and OCM. Six SNPs were non-synonymous substitutions and two of them were predicted in silico as deleterious: rs596133197 and rs403578195. These polymorphisms were then validated in 239 ewes. The SNP rs403578195, located in exon 8 and leading to a change of alanine to glycine (Ala284Gly) in the extracellular domain of the protein, was associated with the OCM trait, being the G allele associated with a decrease of 12 percent of the OCM trait. Haplotype analyses also suggested the involvement of other non-synonymous SNP located in exon 20 (rs405459906). This SNP also produces an amino acid change (Lys1069Glu) in the intracellular domain of the protein and segregates independently of rs403578195. These results confirm for the first time the role of the LEPR gene in sheep reproductive seasonality.

Adipokines expression profiles in both plasma and peri renal adipose tissue in Large White and Meishan sows: A possible involvement in the fattening and the onset of puberty

In pig, backfat deposition is strongly related to the growth and reproductive performance. However, the molecular regulatory mechanisms of adipose tissue are not clearly understood. Adipose tissue is now recognized as an important endocrine organ that secretes a variety of factors including adipokines. However, the regulation of expression pattern of these adipokines in both plasma and visceral white adipose tissue (WAT) in lean and fat pig is unclear. In the present study, we used two representative porcine breeds (Large White, LW; Meishan, MS) with contrasting backfat thickness and sexual maturity age. Using specific ELISA assays, we determined the plasma profile of eight adipokines, leptin, adiponectin, visfatin, apelin, chemerin, resistin, omentin and vaspin in LW and MS sows. By RT-qPCR and western-blot we also investigated the mRNA and protein levels of these adipokines and their cognate receptors (LEPR, ADIPOR1, ADIPOR2, CMKLR1, CCRL2, GPR1, APLNR, TLR4, ROR1, CAP1 and HSPA5) in the peri renal WAT, respectively. At both plasma and peri renal WAT level, we found that the amounts of leptin, chemerin, resistin and vaspin were higher whereas those of adiponectin and omentin were lower in MS than LW sows. Plasma and adipose tissue visfatin and apelin levels were not different between the two breeds. Moreover, we noted that the variations of peri renal WAT adipokines observed between MS and LW were similar at the protein and mRNA level except for chemerin and apelin suggesting post-transcriptional modifications for these two adipokines. Finally, among the eight adipokines studied, we showed that only the plasma concentrations of leptin and chemerin were positively and those of adiponectin, negatively associated with the thickness of fat and opposite correlation was found for the onset of puberty in both LW and MS animals. Taken together, these results support a potential involvement of adipokines in WAT regulation and its link with the onset of the puberty in sows.

Reproductive health in women with type 2 diabetes mellitus

As type 2 diabetes mellitus (T2DM) reaches epidemic proportions in the developed world and the age at diagnosis decreases, more women of reproductive age are being affected. In this article, we provide a synoptic view on potential mechanisms and relevant factors underlying menstrual cycle disorders and fertility issues in women with T2DM. The article discusses the function of the hypothalamic-pituitary-ovarian (HPO) axis, the central role of the hypothalamus in the homeostasis of this system, the central modulators of the axis, and the peripheral metabolic signals involved in neuroendocrine control of reproduction. The available literature on the relationship between T2DM and the female reproductive lifespan, menstrual cycle disorders, fertility issues, and gestational health in women with T2DM are also discussed. The data so far indicate that there is a "U-shaped" relationship between menarche, menopause, and T2DM, both early and late menarche/menopause being risk factors for T2DM. Hyperglycemia and its consequences may be responsible for the effects of T2DM on reproductive health in women, but the exact mechanisms are not as yet fully understood; thus, more studies are needed in order to identify factors causing disruption of the HPO axis.

Prenatal exposure to antibiotics and timing of puberty in sons and daughters: A population-based cohort study

OBJECTIVE

To investigate if prenatal exposure to antibiotics is associated with earlier timing of pubertal development in sons and daughters.

STUDY DESIGN

This population-based cohort study is based upon the Puberty Cohort and includes a sample of 15,638 children born 2000-2003 in Denmark. Information on maternal use of antibiotics was collected around gestational week 30 and 6 months postpartum. The children were followed-up half-yearly from 11 years of age and throughout sexual maturation providing information on Tanner stages, acne and axillary hair, in addition to voice break and first ejaculation in sons and menarche in daughters. Due to the half-yearly collection of data on pubertal timing, the data was censored and therefore analysed using a multivariable censored time-to-event regression model. We examined both prenatal exposure to antibiotics at any time in pregnancy and trimester-specific prenatal exposure to antibiotics and pubertal timing, adjusting for maternal baseline socioeconomic and lifestyle characteristics. Mean age differences for the pubertal milestones between exposure groups were estimated. A combined estimate for overall pubertal timing was calculated based on combining all pubertal milestones into one model for sons and daughters, using Huber-White robust variance estimation which handles the risk of type 1 errors due to multiple testing of correlated outcomes. An active comparator approach with restriction to women reporting to have a urinary tract infection (cystitis) treated with either penicillin or sulfonamides was employed in a sub-analysis.

RESULTS

The prevalence of any maternal use of antibiotics in pregnancy was 21.1 %. There was no association between prenatal exposure to antibiotics and timing of pubertal development for the individual milestones. The adjusted combined estimate for pubertal timing in sons prenatally exposed to antibiotics at any point in pregnancy was -0.4 (95 % confidence interval (CI): -1.2; 0.4) months compared to unexposed sons. The adjusted combined estimate for pubertal timing in daughters prenatally exposed to antibiotics at any point in pregnancy was -0.1 (95 % CI: -0.9; 0.7) months compared to unexposed daughters. Both the trimester-specific analyses and the active comparator analysis revealed similar results.

CONCLUSION

Prenatal exposure to antibiotics was not associated with pubertal timing.

Determinants of Circulating Soluble Leptin Receptor and Free Leptin Index in Indonesian Pre-Pubertal Obese Male Children: A Preliminary Cross-Sectional Study

PURPOSE

This study aimed to investigate the clinical and metabolic determinants of circulating soluble leptin receptor (CSLR) and free leptin index (FLI) in pre-pubertal obese male children.

METHODS

We conducted a preliminary cross-sectional study at three tertiary hospitals and one public primary school. Eighty obese male children without growth and developmental abnormalities aged 5-9 years were recruited. In these children, obesity was solely caused by excessive food intake, and not by acute illness, medications, endocrine abnormalities, or any syndrome. Body mass index (BMI), body fat mass, carbohydrate intake, fat intake, high density lipoprotein cholesterol level, low density lipoprotein cholesterol level, triglyceride level, and Homeostatic Model Assessment for Insulin Resistance are the potential determinants for leptin regulation, which is represented by CSLR level and FLI.

RESULTS

Carbohydrate was the main source of energy. BMI and body fat mass had negative weak correlation with CSLR and positive weak correlation with FLI. Furthermore, carbohydrate intake was found to be independently associated with CSLR based on the results of the multiple linear regression analysis. Following an increase in carbohydrate intake, CSLR level decreased progressively without any negative peak.

CONCLUSION

Leptin regulation in prepubertal obese male children is associated with body composition and dietary intake. Carbohydrate intake is useful for predicting CSLR. Lipid profiles and insulin resistance are not related to both CSLR and FLI. Treatment and prevention of leptin resistance in obese children should focus on reducing BMI, fat mass, and carbohydrate intake.

Leptin actions through the nitrergic system to modulate the hypothalamic expression of the kiss1 mRNA in the female rat

Gonadotrophin-releasing hormone (GnRH) is the main controller of the reproductive axis and stimulates the synthesis and secretion of gonadotrophins. Estrogen is the main peripheral factor controlling GnRH secretion, and this action is mainly mediated by the transsynaptic pathway through nitric oxide, kisspeptin, leptin, among other factors. Kisspeptin is the most potent factor known to induce GnRH release. Nitric oxide and leptin also promote GnRH release; however, neurons expressing GnRH do not express the leptin receptor (OB-R). Leptin seems to modulate the expression of genes and proteins involved in the kisspeptin system. However, few kisspeptin-synthesizing cells in the arcuate nucleus (ARC) and few cells, if any, in the preoptic area (POA) express OB-R; this indicates an indirect mechanism of leptin action on kisspeptin. Nitric oxide is an important intermediate in the actions of leptin in the central nervous system. Thus, this work aimed to verify the numbers of nNOS cells were activated by leptin in different hypothalamic areas; the modulatory effects of the nitrergic system on the kisspeptin system; and the indirect regulatory effect of leptin on the kisspeptin system via nitric oxide. Ovariectomized rats were treated with estrogen or a vehicle and received an intracerebroventricular (i.c.v.) injection of a nitric oxide donor, leptin or neuronal nitric oxide synthase (nNOS) enzyme inhibitor. Thirty minutes after the injection, the animals were decapitated. Leptin acts directly on nitrergic neurons in different hypothalamic regions, and the effects on the ventral premammillary nucleus (PMV) and ventral dorsomedial hypothalamus (vDMH) are enhanced. The use of a nitric oxide donor or the administration of leptin stimulates the expression of the kisspeptin mRNA in the ARC of animals with or without estrogenic action; however, these changes are not observed in the POA. In addition, the action of leptin on the expression of the kisspeptin mRNA in the ARC is blocked by a nitric oxide synthesis inhibitor. We concluded that the effects of leptin on the central nervous system are at least partially mediated by the nitrergic system. Also, nitric oxide acts on the kisspeptin system by modulating the expression of the kisspeptin mRNA, and leptin at least partially modulates the kisspeptin system through the nitrergic system, particularly in the ARC.

Obesity, Neuroinflammation, and Reproductive Function

The increasing occurrence of obesity has become a significant public health concern. Individuals with obesity have higher prevalence of heart disease, stroke, osteoarthritis, diabetes, and reproductive disorders. Reproductive problems include menstrual irregularities, pregnancy complications, and infertility due to anovulation, in women, and lower testosterone and diminished sperm count, in men. In particular, women with obesity have reduced levels of both gonadotropin hormones, and, in obese men, lower testosterone is accompanied by diminished LH. Taken together, these findings indicate central dysregulation of the hypothalamic-pituitary-gonadal axis, specifically at the level of the GnRH neuron function, which is the final brain output for the regulation of reproduction. Obesity is a state of hyperinsulinemia, hyperlipidemia, hyperleptinemia, and chronic inflammation. Herein, we review recent advances in our understanding of how these metabolic and immune changes affect hypothalamic function and regulation of GnRH neurons. In the latter part, we focus on neuroinflammation as a major consequence of obesity and discuss findings that reveal that GnRH neurons are uniquely positioned to respond to inflammatory changes.

Emerging Genetic and Epigenetic Mechanisms Underlying Pubertal Maturation in Adolescence

The adolescent transition begins with the onset of puberty which, upstream in the brain, is initiated by the gonadotropin-releasing hormone (GnRH) pulse generator that activates the release of peripheral sex hormones. Substantial research in human and animal models has revealed a myriad of cellular networks and heritable genes that control the GnRH pulse generator allowing the individual to begin the process of reproductive competence and sexual maturation. Here, we review the latest knowledge in neuroendocrine pubertal research with emphasis on genetic and epigenetic mechanisms underlying the pubertal transition.

Effect of Commercially Available Sugar-Sweetened Beverages on Subjective Appetite and Short-Term Food Intake in Boys

It is unclear whether sugar sweetened beverages bypass regulatory controls of food intake (FI) in boys. The objective of the present study was to determine the effects of isovolumetric preloads (350 mL) of a fruit-flavoured drink (154 kcal), cola (158 kcal), 1% M.F. chocolate milk (224 kcal), and water (0 kcal) on subjective appetite and FI in boys aged 9–14 years. On four separate mornings, boys consumed one of the preloads in a random order; subjective appetite was measured at 15 min intervals, and FI was measured via an ad libitum pizza lunch at 60 min post-beverage consumption. In the 32 boys (age: 11.8 ± 0.3 years), FI was reduced (p < 0.001) after cola (940 ± 46 kcal) and chocolate milk (878 ± 41 kcal) compared with the water control (1048 ± 35 kcal) and after chocolate milk compared to the fruit drink (1005 ± 44 kcal). Cumulative FI after the fruit drink was greater than the water control (1159 ± 44 vs. 1048 ± 35 kcal; p = 0.03). Average appetite was not affected by the treatment, but the cola treatment resulted in greater fullness (p = 0.04) and lower prospective food consumption (p = 0.004) compared with the fruit drink. In conclusion, chocolate milk and cola suppressed next-meal FI at 60 min, while fruit drink increased cumulative FI (beverage + next meal) over 60 min in boys. Results from this study suggest that beverage composition is an important determinant of FI suppression in boys.

Neuroanatomical Framework of the Metabolic Control of Reproduction

A minimum amount of energy is required for basic physiological processes, such as protein biosynthesis, thermoregulation, locomotion, cardiovascular function, and digestion. However, for reproductive function and survival of the species, extra energy stores are necessary. Production of sex hormones and gametes, pubertal development, pregnancy, lactation, and parental care all require energy reserves. Thus the physiological systems that control energy homeostasis and reproductive function coevolved in mammals to support both individual health and species subsistence. In this review, we aim to gather scientific knowledge produced by laboratories around the world on the role of the brain in integrating metabolism and reproduction. We describe essential neuronal networks, highlighting key nodes and potential downstream targets. Novel animal models and genetic tools have produced substantial advances, but critical gaps remain. In times of soaring worldwide obesity and metabolic dysfunction, understanding the mechanisms by which metabolic stress alters reproductive physiology has become crucial for human health.

Leptin and adiposity as mediators on the association between early puberty and several biomarkers in European adolescents: the HELENA Study

Background Adolescents having early puberty (EP) are more likely to have obesity and increased cardiometabolic and inflammatory markers and atherosclerosis risk. We aimed to assess the indirect and mediated effects of leptin and adiposity on the relation between EP and cardiometabolic and inflammatory markers in European adolescents. Methods A sample of 511 adolescents with EP (12.5-17.5 years) from the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) cross-sectional study was studied. To assess whether leptin levels and adiposity mediate the relation between EP and several biomarkers, linear regression models for mediation analyses were performed. Results EP was positively associated with the atherogenic index (Ath-I) (β=0.174; 95%CI 0.029-0.265) and negatively associated with the C-reactive protein (CRP) (β=-0.284; 95%CI -0.542 to -0.028) in girls. These associations were fully mediated by leptin levels (9.5%) and adiposity (44%), respectively. Moreover, EP has indirect effects on the apolipoprotein A-1 (ApoA-1) levels through adiposity in girls (for body mass index [BMI], β=0.014; 95%CI 0.005-0.028, and for waist circumference [WC], β=0.011; 95%CI 0.003-0.024), and on ApoA-1 (β=0.012; 95%CI 0.004-0.025), apolipoprotein B (ApoB) (β=-0.004; 95%CI -0.011 to -0.0004) and CRP (β=-0.265; 95%CI -0.819 to -0.047) through abdominal fat in boys. Conclusions Leptin levels and adiposity seem to play an important indirect and mediation role in the association between EP and cardiometabolic and inflammatory markers in adolescents. Weight control should be recommended in order to control the impaired cardiometabolic and inflammatory status arising in early pubertal adolescents.

Genes underlying delayed puberty

The genetic control of pubertal timing has been a field of active investigation for the last decade, but remains a fascinating and mysterious conundrum. Self-limited delayed puberty (DP), also known as constitutional delay of growth and puberty, represents the extreme end of normal pubertal timing, and is the commonest cause of DP in both boys and girls. Familial self-limited DP has a clear genetic basis. It is a highly heritable condition, which often segregates in an autosomal dominant pattern (with or without complete penetrance) in the majority of families. However, the underlying neuroendocrine pathophysiology and genetic regulation has been largely unknown. Very recently novel gene discoveries from next generation sequencing studies have provided insights into the genetic mutations that lead to familial DP. Further understanding has come from sequencing genes known to cause GnRH deficiency, next generation sequencing studies in patients with early puberty, and from large-scale genome wide association studies in the general population. Results of these studies suggest that the genetic basis of DP is likely to be highly heterogeneous. Abnormalities of GnRH neuronal development, function, and its downstream pathways, metabolic and energy homeostatic derangements, and transcriptional regulation of the hypothalamic-pituitary-gonadal axis may all lead to DP. This variety of different pathogenic mechanisms affecting the release of the puberty 'brake' may take place in several age windows between fetal life and puberty.

Sex-Biased Physiological Roles of NPFF1R, the Canonical Receptor of RFRP-3, in Food Intake and Metabolic Homeostasis Revealed by its Congenital Ablation in mice

BACKGROUND

RF-amide-related peptide-3 (RFRP-3), the mammalian ortholog of gonadotropin-inhibiting hormone, operates as inhibitory signal for the reproductive axis. Recently, RFRP-3 has been also suggested to stimulate feeding, and therefore might contribute to the control of body weight and its alterations. Yet, characterization of the metabolic actions of RFRP-3 has been so far superficial and mostly pharmacological. Here, we aim to investigate the physiological roles of RFRP-3 signaling in the control of feeding and metabolic homeostasis using a novel mouse model of genetic ablation of its canonical receptor, NPFF1R.

METHODS

Food intake, body weight gain and composition, and key metabolic parameters, including glucose tolerance and insulin sensitivity, were monitored in mice with constitutive inactivation of NPFF1R.

RESULTS

Congenital elimination of NPFF1R in male mice resulted in changes in feeding patterns, with a decrease in spontaneous food intake and altered responses to leptin and ghrelin: leptin-induced feeding suppression was exaggerated in NPFF1R null mice, whereas orexigenic responses to ghrelin were partially blunted. Concordant with this pro-anorectic phenotype, hypothalamic expression of Pomc was increased in NPFF1R null mice. In contrast, spontaneous feeding and neuropeptide expression remained unaltered in NPFF1R KO female mice. Despite propensity for reduced feeding, ablation of NPFF1R signaling in male mice did not cause overt alterations in body weight (BW) gain or composition, neither it affected BW responses to high fat diet (HFD), total energy expenditure or RQ ratios. Yet, NPFF1R KO males showed a decrease in locomotor activity. Conversely, NPFF1R null female mice tended to be heavier and displayed exaggerated BW increases in response to obesogenic insults, such as HFD or ovariectomy. These were associated to increased fat mass, decreased total energy expenditure in HFD, and unaltered RQ ratios or spontaneous locomotor activity. Finally, lack of NPFF1R signaling worsened the metabolic impact of HFD on glycemic homeostasis in males, as revealed by impaired glucose tolerance and insulin sensitivity, while female mice remained unaffected.

CONCLUSION

Our data support a discernible orexigenic role of NPFF1R signaling selectively in males, which might modulate the effects of leptin and ghrelin on food intake. In addition, our study is the first to disclose the sex-biased, deleterious impact of the lack of NPFF1R signaling on body weight and fat composition, energy expenditure, locomotor activity and glucose balance, which exaggerates some of the metabolic consequences of concurrent obesogenic insults, such as HFD, in a sexually dimorphic manner.

SUMMARY OF TRANSLATIONAL RELEVANCE

Our data are the first to document the nature and magnitude of the regulatory actions of RFRP-3/NPFF1R signaling in the control of feeding and metabolic homeostasis in a physiological setting. Our results not only suggest an orexigenic action of endogenous RFRP-3, specifically in males, but reveal also the detrimental impact of ablation of NPFF1R signaling on body composition, energy expenditure, locomotor activity or glucose balance, especially when concurrent with other obesogenic insults, as HFD, thereby providing the first evidence for additional metabolic effects of RFRP-3, other that the mere control of feeding. Interestingly, alterations of such key metabolic parameters occurred in a sex-biased manner, with males being more sensitive to deregulation of locomotor activity and glycemic control, while females displayed clearer obesogenic responses and deregulated energy expenditure. While our study cannot discard the possibility of RFRP-3 actions via alternative pathways, such as NPFF2R, our data pave the way for future analyses addressing the eventual contribution of altered RFRP-3/NPFF1R signaling in the development of metabolic alterations (including obesity and its comorbidities), especially in conditions associated to reproductive dysfunction.

Functional and Phenotypic Characteristics of Human Leptin Receptor Mutations

Several case series of extreme early-onset obesity due to mutations in the human leptin receptor (LEPR) gene have been reported. In this review we summarize published functional and phenotypic data on mutations in the human LEPR gene causing severe early-onset obesity. Additionally, we included data on six new cases from our obesity center. Literature research was performed using PubMed and OMIM. Functional relevance of mutations was estimated based on reported functional analysis, mutation size, and location, as well as phenotypic characteristics of affected patients. We identified 57 cases with 38 distinct LEPR mutations. We found severe early-onset obesity, hyperphagia, and hypogonadotropic hypogonadism as cardinal features of a complete loss of LEPR function. Other features, for example, metabolic disorders and recurring infections, were variable in manifestation. Obesity degree or other manifestations did not aggregate by genotype. Few patients underwent bariatric surgery with variable success. Most mutations occurred in the fibronectin III and cytokine receptor homology II domains, whereas none was found in cytoplasmic domain. In silico data were available for 25 mutations and in vitro data were available for four mutations, revealing residual activity in one case. By assessing provided information on the clinical phenotype, functional analysis, and character of the 38 mutations, we assume residual LEPR activity for five additional mutations. Functional in vitro analysis is necessary to confirm this assumption.

The obesogen tributyltin induces features of polycystic ovary syndrome (PCOS): a review

Polycystic ovary syndrome (PCOS) is a heterogeneous syndrome characterized by abnormal reproductive cycles, irregular ovulation, and hyperandrogenism. This complex disorder has its origins both within and outside the hypothalamic-pituitary-ovarian axis. Cardio-metabolic factors, such as obesity and insulin resistance, contribute to the manifestation of the PCOS phenotype. Polycystic ovary syndrome is one of the most common endocrine disorders among women of reproductive age. Growing evidence suggested an association between reproductive and metabolic features of PCOS and exposure to endocrine-disrupting chemicals (EDC), such as bisphenol A. Further, the environmental obesogen tributyltin (TBT) was shown to induce reproductive, metabolic and cardiovascular abnormalities resembling those found in women and animal models of PCOS. However, the causal link between TBT exposure and PCOS development remains unclear. The objective of this review was to summarize the most recent research findings on the potential association between TBT exposure and development of PCOS-like features in animal models and humans.

The War on the Placenta: The Differing Battles of High-Fat Diet and Obesity

Commentary on Mahany et al., “Obesity and High-Fat Diet Induce Distinct Changes in Placental Gene Expression and Pregnancy Outcome.”

Disentangling puberty: novel neuroendocrine pathways and mechanisms for the control of mammalian puberty

BACKGROUND

Puberty is a complex developmental event, controlled by sophisticated regulatory networks that integrate peripheral and internal cues and impinge at the brain centers driving the reproductive axis. The tempo of puberty is genetically determined but is also sensitive to numerous modifiers, from metabolic and sex steroid signals to environmental factors. Recent epidemiological evidence suggests that the onset of puberty is advancing in humans, through as yet unknown mechanisms. In fact, while much knowledge has been gleaned recently on the mechanisms responsible for the control of mammalian puberty, fundamental questions regarding the intimate molecular and neuroendocrine pathways responsible for the precise timing of puberty and its deviations remain unsolved.

OBJECTIVE AND RATIONALE

By combining data from suitable model species and humans, we aim to provide a comprehensive summary of our current understanding of the neuroendocrine mechanisms governing puberty, with particular focus on its central regulatory pathways, underlying molecular basis and mechanisms for metabolic control.

SEARCH METHODS

A comprehensive MEDLINE search of articles published mostly from 2003 to 2017 has been carried out. Data from cellular and animal models (including our own results) as well as clinical studies focusing on the pathophysiology of puberty in mammals were considered and cross-referenced with terms related with central neuroendocrine mechanisms, metabolic control and epigenetic/miRNA regulation.

OUTCOMES

Studies conducted during the last decade have revealed the essential role of novel central neuroendocrine pathways in the control of puberty, with a prominent role of kisspeptins in the precise regulation of the pubertal activation of GnRH neurosecretory activity. In addition, different transmitters, including neurokinin-B (NKB) and, possibly, melanocortins, have been shown to interplay with kisspeptins in tuning puberty onset. Alike, recent studies have documented the role of epigenetic mechanisms, involving mainly modulation of repressors that target kisspeptins and NKB pathways, as well as microRNAs and the related binding protein, Lin28B, in the central control of puberty. These novel pathways provide the molecular and neuroendocrine basis for the modulation of puberty by different endogenous and environmental cues, including nutritional and metabolic factors, such as leptin, ghrelin and insulin, which are known to play an important role in pubertal timing.

WIDER IMPLICATIONS

Despite recent advancements, our understanding of the basis of mammalian puberty remains incomplete. Complete elucidation of the novel neuropeptidergic and molecular mechanisms summarized in this review will not only expand our knowledge of the intimate mechanisms responsible for puberty onset in humans, but might also provide new tools and targets for better prevention and management of pubertal deviations in the clinical setting.

Why monkeys do not get multiple sclerosis (spontaneously): An evolutionary approach

The goal of this review is to apply an evolutionary lens to understanding the origins of multiple sclerosis (MS), integrating three broad observations. First, only humans are known to develop MS spontaneously. Second, humans have evolved large brains, with characteristically large amounts of metabolically costly myelin. This myelin is generated over long periods of neurologic development—and peak MS onset coincides with the end of myelination. Third, over the past century there has been a disproportionate increase in the rate of MS in young women of childbearing age, paralleling increasing westernization and urbanization, indicating sexually specific susceptibility in response to changing exposures. From these three observations about MS, a life history approach leads us to hypothesize that MS arises in humans from disruption of the normal homeostatic mechanisms of myelin production and maintenance, during our uniquely long myelination period. This review will highlight under-explored areas of homeostasis in brain development, that are likely to shed new light on the origins of MS and to raise further questions about the interactions between our ancestral genes and modern environments.

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.

Connecting metabolism and gonadal function: Novel central neuropeptide pathways involved in the metabolic control of puberty and fertility

Albeit essential for perpetuation of species, reproduction is an energy-demanding function that can be adjusted to body metabolic status. Reproductive maturation and function can be suppressed in conditions of energy deficit, but can be altered also in situations of persistent energy excess, e.g., morbid obesity. This metabolic-reproductive integration, of considerable pathophysiological relevance to explain different forms of perturbed puberty and sub/infertility, is implemented by the concerted action of numerous central and peripheral regulators, which impinge at different levels of the hypothalamic-pituitary-gonadal (HPG) axis, permitting a tight fit between nutritional/energy status and gonadal function. We summarize here the major physiological mechanisms whereby nutritional and metabolic cues modulate the maturation and function of the HPG axis. We will focus on recent progress on the major central neuropeptide pathways, including kisspeptins, neurokinin B and the products of POMC and NPY neurons, which convey metabolic information to GnRH neurons, as major hierarchical hub of our reproductive brain.

Micronutrient status in middle childhood and age at menarche: results from the Bogotá School Children Cohort

Childhood intake of animal foods is associated with age at first menstrual period (menarche). It is unknown whether the micronutrients present in these foods could explain this association. Our objective was to investigate the associations of micronutrient status biomarkers in middle childhood with age at menarche. We quantified circulating Hb, ferritin, mean corpuscular volume, Zn, vitamin B12, erythrocyte folate and retinol in 1464 pre-menarcheal girls aged 5–12 years in Bogotá, Colombia, and followed them for a median 5·7 years for the occurrence and date of menarche. We estimated median age at menarche and hazard ratios (HR) with 95 % CI by levels of each biomarker with use of Kaplan–Meier survival probabilities and Cox regression, respectively. Median age at menarche was 12·4 years. Middle childhood Hb was inversely related to age at menarche whereas plasma ferritin was positively associated with this outcome in a linear manner. HR of menarche for every 1sdof Hb (11 g/l) and ferritin (23·2 µg/l) were 1·11 (95 % CI 1·04, 1·18;P=0·001) and 0·94 (95 % CI 0·88, 0·99;P=0·02), respectively, after adjustment for baseline age, C-reactive protein concentration, maternal age at menarche and parity and socioeconomic status. The association with ferritin was stronger in girls aged 9–10 years at baseline. Additional adjustment for baseline height- and BMI-for-age did not change the results. We conclude that higher Fe status in middle childhood is related to later age at menarche whereas Hb concentrations are inversely associated with age at onset of menses.

Effect of Weight Loss on Puberty Onset in Overweight Children

OBJECTIVE

To assess the impact of weight changes on the onset of puberty in overweight children.

STUDY DESIGN

We evaluated the timing of puberty onset in 160 prepubertal overweight children (aged 11.2 ± 1.0 years) depending on the changes of their weight status in a 1-year lifestyle intervention. We determined body mass index (BMI), pubertal stage, luteinizing hormone (LH), follicle-stimulating hormone, insulin-like growth factor (IGF)-1, insulin-like growth factor binding protein-3, insulin resistance index homeostatic model assessment, and serum gonadotropins at baseline and 1 year later.

RESULTS

Puberty onset during the 1-year follow-up was significantly (P = .014) more frequent in girls without BMI-SDS reduction (75.0%) compared with girls with BMI-SDS reduction (45.7%). The start of puberty was significantly (P = .024) more frequent in boys with BMI-SDS reduction (76.9%) compared with boys without BMI-SDS reduction (53.6%). In logistic regression analyses adjusted for baseline age and BMI-SDS, BMI-SDS reduction was associated with a decreased likelihood for puberty onset in girls (OR 0.24; 95% CI 0.07-0.85) and an increased likelihood in boys (OR 3.77; 95% CI 1.34-10.52). Central onset of puberty was confirmed by an increase of LH concentration and LH/follicle-stimulating hormone ratio in both boys and girls. Homeostatic model assessment, IGF-1, and IGF-1/insulin-like growth factor binding protein-3 ratio as marker for free IGF-1 at baseline or their changes were not associated with the onset of puberty.

CONCLUSIONS

BMI-SDS reduction in overweight children was associated with earlier gonadotropin-dependent onset of puberty in boys and later onset of puberty in girls, suggesting earlier puberty in obese girls and later puberty in obese boys. We found no evidence that insulin resistance or IGF-1 have an impact on the start of puberty in obese children.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00435734.

Clinical Exome Sequencing Reveals MKRN3 Pathogenic Variants in Familial and Nonfamilial Idiopathic Central Precocious Puberty

BACKGROUND/AIMS

Idiopathic central precocious puberty (ICPP) is the premature activation of the hypothalamic-pituitary-gonadal axis in the absence of organic disease. Up to now, just gain-of-function mutations of KISS1/KISS1R and loss-of-function mutations of the maternally imprinted gene MKRN3 are the known genetic causes of ICPP. Our intention is to evaluate variants present in genes related to the pubertal onset pathway that could act as disease-causing or predisposing variants.

METHODS

We studied the clinical exome of 20 patients diagnosed with ICPP using the Illumina platform. The bioinformatics analysis was performed using 2 different programs, and the variants were filtered according to a list of genes related to the gonadotropin-releasing hormone pathway.

RESULTS

In a "sporadic case," we found a missense variant in MKRN3 NM_005664.3: c.203G>A, causing the protein change NP_005655.1:p.Arg68His, predicted as pathogenic by 2 informatics tools. The proband carrying this variant was diagnosed with ICPP at 7.75 years of age. We did not find any pathogenic variants in KISS1, KISS1R, LIN28, GNRH, GNRHR, TACR3, and TAC3.

CONCLUSION

MKRN3 is the most frequent genetic cause of familial ICPP, so it is wise to screen for MKRN3 mutations in all patients with familial ICPP and in patients with an unclear paternal pubertal history.

From Placenta to Polycystic Ovarian Syndrome: The Role of Adipokines

Adipokines are cytokines produced mainly by adipose tissue, besides many other tissues such as placenta, ovaries, peripheral-blood mononuclear cells, liver, muscle, kidney, heart, and bone marrow. Adipokines play a significant role in the metabolic syndrome and in cardiovascular diseases, have implications in regulating insulin sensitivity and inflammation, and have significant effects on growth and reproductive function. The objective of this review was to analyze the functions known today of adiponectin, leptin, resistin, and visfatin from placenta throughout childhood and adolescence. It is well known now that their serum concentrations during pregnancy and lactation have long-term effects beyond the fetus and newborn. With regard to puberty, adipokines are involved in the regulation of the relationship between nutritional status and normal physiology or disorders of puberty and altered gonadal function, as, for example, premature pubarche and polycystic ovarian syndrome (PCOS). Cytokines are involved in the maturation of oocytes and in the regular progression of puberty and pregnancy.

Defining a novel leptin-melanocortin-kisspeptin pathway involved in the metabolic control of puberty

Objective

Puberty is a key developmental phenomenon highly sensitive to metabolic modulation. Worrying trends of changes in the timing of puberty have been reported in humans. These might be linked to the escalating prevalence of childhood obesity and could have deleterious impacts on later (cardio-metabolic) health, but their underlying mechanisms remain unsolved. The neuropeptide α-MSH, made by POMC neurons, plays a key role in energy homeostasis by mediating the actions of leptin and likely participates in the control of reproduction. However, its role in the metabolic regulation of puberty and interplay with kisspeptin, an essential puberty-regulating neuropeptide encoded by Kiss1, remain largely unknown. We aim here to unveil the potential contribution of central α-MSH signaling in the metabolic control of puberty by addressing its role in mediating the pubertal effects of leptin and its potential interaction with kisspeptin.

Methods

Using wild type and genetically modified rodent models, we implemented pharmacological studies, expression analyses, electrophysiological recordings, and virogenetic approaches involving DREADD technology to selectively inhibit Kiss1 neurons, in order to interrogate the physiological role of a putative leptin→α-MSH→kisspeptin pathway in the metabolic control of puberty.

Results

Stimulation of central α-MSH signaling robustly activated the reproductive axis in pubertal rats, whereas chronic inhibition of melanocortin receptors MC3/4R, delayed puberty, and prevented the permissive effect of leptin on puberty onset. Central blockade of MC3/4R or genetic elimination of kisspeptin receptors from POMC neurons did not affect kisspeptin effects. Conversely, congenital ablation of kisspeptin receptors or inducible, DREADD-mediated inhibition of arcuate nucleus (ARC) Kiss1 neurons resulted in markedly attenuated gonadotropic responses to MC3/4R activation. Furthermore, close appositions were observed between POMC fibers and ARC Kiss1 neurons while blockade of α-MSH signaling suppressed Kiss1 expression in the ARC of pubertal rats.

Conclusions

Our physiological, virogenetic, and functional genomic studies document a novel α-MSH→kisspeptin→GnRH neuronal signaling pathway involved in transmitting the permissive effects of leptin on pubertal maturation, which is relevant for the metabolic (and, eventually, pharmacological) regulation of puberty onset.

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Puberty is highly sensitive to metabolic modulation and disturbed by child obesity.

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Altered puberty is linked to adverse metabolic health outcomes via unclear mechanisms.

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The POMC product, α-MSH, transmit leptin-mediated metabolic regulation of puberty.

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A novel α-MSH→kisspeptin→GnRH signaling pathway is involved in the control of puberty

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This pathway is important for the metabolic (and pharmacologic) control of puberty.

Control of the onset of puberty

PURPOSE OF REVIEW

The mechanism of puberty initiation remains an enigma, despite extensive research in the field. Pulsatile pituitary gonadotropin secretion under the guidance of hypothalamic gonadotropin-releasing hormone (GnRH) constitutes a sine qua non for pubertal onset. In turn, the secretion of GnRH in the human hypothalamus is regulated by kisspeptin and its receptor as well as by permissive or opposing signals mediated by neurokinin B and dynorphin acting on their respective receptors. These three supra-GnRH regulators compose the Kisspeptin, Neurokinin B and Dynorhin neurons (KNDy) system, a key player in pubertal onset and progression.

RECENT FINDINGS

The recent discovery that makorin ring finger protein 3 is also involved in puberty initiation provided further insights into the regulation of the KNDy pathway. In fact, the inhibitory (γ-amino butyric acid, neuropeptide Y, and RFamide-related peptide-3) and stimulatory signals (glutamate) acting upstream of KNDy called into question the role of makorin ring finger protein 3 as the gatekeeper of puberty. Meanwhile, the findings that 'neuroestradiol' produced locally and endocrine disruptors from the environment may influence GnRH secretion is intriguing. Finally, epigenetic mechanisms have been implicated in pubertal onset through recently discovered mechanisms.

SUMMARY

The exact molecular machinery underlying puberty initiation in humans is under intensive investigation. In this review, we summarize research evidence in the field, while emphasizing the areas of uncertainty and underlining the impact of current information on the evolving theory regarding this fascinating phenomenon.

Metabolic control of female puberty: potential therapeutic targets

INTRODUCTION

The onset of puberty in females is highly sensitive to the nutritional status and the amount of energy reserves of the organism. This metabolic information is sensed and transmitted to hypothalamic GnRH neurons, considered to be ultimately responsible for triggering puberty through the coordinated action of different peripheral hormones, central neurotransmitters, and molecular mediators.

AREAS COVERED

This article will review and discuss (i) the relevant actions of the adipose hormone leptin, as a stimulatory/permissive signal, and the gut hormone ghrelin, as an inhibitory factor, in the metabolic control of female puberty; (ii) the crucial role of the hypothalamic kisspeptin neurons, recently emerged as essential gatekeepers of puberty, in transmitting this metabolic information to GnRH neurons; and (iii) the potential involvement of key cellular energy sensors, such as mTOR, as molecular mediators in this setting.

EXPERT OPINION

The thorough characterization of the physiological roles of the above elements in the metabolic control of female puberty, along with the discovery of novel factors, pathways, and mechanisms involved, will promote our understanding of the complex networks connecting metabolism and puberty and, ultimately, will aid in the design of target-specific treatments for female pubertal disorders linked to conditions of metabolic stress.

Dietary-Induced Chronic Hypothyroidism Negatively Affects Rat Follicular Development and Ovulation Rate and Is Associated with Oxidative Stress

The long-term effects of chronic hypothyroidism on ovarian follicular development in adulthood are not well known. Using a rat model of chronic diet-induced hypothyroidism initiated in the fetal period, we investigated the effects of prolonged reduced plasma thyroid hormone concentrations on the ovarian follicular reserve and ovulation rate in prepubertal (12-day-old) and adult (64-day-old and 120-day-old) rats. Besides, antioxidant gene expression, mitochondrial density and the occurrence of oxidative stress were analyzed. Our results show that continuous hypothyroidism results in lower preantral and antral follicle numbers in adulthood, accompanied by a higher percentage of atretic follicles, when compared to euthyroid age-matched controls. Not surprisingly, ovulation rate was lower in the hypothyroid rats. At the age of 120 days, the mRNA and protein content of superoxide dismutase 1 (SOD1) were significantly increased while catalase (CAT) mRNA and protein content was significantly decreased, suggesting a disturbed antioxidant defense capacity of ovarian cells in the hypothyroid animals. This was supported by a significant reduction in the expression of peroxiredoxin 3 ( ITALIC! Prdx3), thioredoxin reductase 1 ( ITALIC! Txnrd1), and uncoupling protein 2 ( ITALIC! Ucp2) and a downward trend in glutathione peroxidase 3 ( ITALIC! Gpx3) and glutathione S-transferase mu 2 ( ITALIC! Gstm2) expression. These changes in gene expression were likely responsible for the increased immunostaining of the oxidative stress marker 4-hydroxynonenal. Together these results suggest that chronic hypothyroidism initiated in the fetal/neonatal period results in a decreased ovulation rate associated with a disturbance of the antioxidant defense system in the ovary.

Altered Gene Expression Profiles of the Hypothalamic Arcuate Nucleus of Male Mice Suggest Profound Developmental Changes in Peptidergic Signaling

Neuropeptides of the hypothalamic arcuate nucleus (ARC) regulate important homeostatic and endocrine functions and also play critical roles in pubertal development. The altered peptidergic and aminoacidergic neurotransmission accompanying pubertal maturation of the ARC is not fully understood. Here we studied the developmental shift in the gene expression profile of the ARC of male mice. RNA samples for quantitative RT-PCR studies were isolated from the ARC of 14-day-old infantile and 60-day-old adult male mice with laser capture microdissection. The expression of 18 neuropeptide, 15 neuropeptide receptor, 4 sex steroid receptor and 6 classic neurotransmitter marker mRNAs was compared between the two time points. The adult animals showed increased mRNA levels encoding cocaine- and amphetamine-regulated transcripts, galanin-like peptide, dynorphin, kisspeptin, proopiomelanocortin, proenkephalin and galanin and a reduced expression of mRNAs for pituitary adenylate cyclase-activating peptide, calcitonin gene-related peptide, neuropeptide Y, substance P, agouti-related protein, neurotensin and growth hormone-releasing hormone. From the neuropeptide receptors tested, melanocortin receptor-4 showed the most striking increase (5-fold). Melanocortin receptor-3 and the Y1 and Y5 neuropeptide Y receptors increased 1.5- to 1.8-fold, whereas δ-opioid receptor and neurotensin receptor-1 transcripts were reduced by 27 and 21%, respectively. Androgen receptor, progesterone receptor and α-estrogen receptor transcripts increased by 54-72%. The mRNAs of glutamic acid decarboxylases-65 and -67, vesicular GABA transporter and choline acetyltransferase remained unchanged. Tyrosine hydroxylase mRNA increased by 44%, whereas type-2 vesicular glutamate transporter mRNA decreased by 43% by adulthood. Many of the developmental changes we revealed in this study suggest a reduced inhibitory and/or enhanced excitatory neuropeptidergic drive on fertility in adult animals.

Body weight and reproductive parameters in fast and weak growing Awassi ram lambs during different age stages

This study was carried out on 30 Syrian Awassi ram lambs around 3 months of age. Lambs were divided equally in 2 groups as fast growing (FG) and weak growing (WG) lambs to identify body weight and reproductive parameters in each group during different age stages. Blood samples were collected to determine testosterone and leptin concentrations using radioimmunoassay. At puberty, average body weight and age of FG and WG lambs was 52.4 and 43.1 kg, and 225.9 and 248.0 days, respectively, with a significant (P < 0.05) difference between them in both parameters. Testosterone concentration was very low at 3 months of age (below 1.0 nmol L(-1)) and increased with advancing age with a sharp increase occurring at 7 months of age and at puberty, averages were 12.58 and 11.86 nmol L(-1) for FG and WG groups, respectively, with no significant (P > 0.05) differences. At puberty, average leptin concentration was 3.16 and 2.98 ng mL(-1) for FG and WG groups, respectively, with no significant (P > 0.05) difference.

Grow first, gain fat in the meantime. Longitudinal study of anthropometric changes around menarche

There is a long dispute among anthropologist over which factor is more important – skeletal maturation or energy accumulation – for menarche occurrence. Here we report results of longitudinal study conducted on the sample of 178 girls followed for the period from 2 years before to 2 years after the age of menarche. Each year during this period anthropometric measures of waist and hip circumference, pelvis breadth, subscapular, triceps and abdominal skinfold thickness were taken to document girls’ physical development. We found that changes in hip circumference and pelvis breadth were the most closely associated with menarche appearance. We also found that changes in anthropometric measures of lower body part preceded changes in anthropometric measures of upper body part and tended to peak one year before menarche occurrence while changes in upper body part tended to peak one year after menarche occurrence. These results suggest that both skeletal maturation and energy accumulation in the form of fat are equally important for menarche to occur. Furthermore, we are proposing a new indicator describing allometric changes of pelvis around menarche: hip circumference to pelvis breadth ratio (HCPBR).

Physiology of leptin: energy homeostasis, neuroendocrine function and metabolism

Leptin is secreted by adipose tissue and regulates energy homeostasis, neuroendocrine function, metabolism, immune function and other systems through its effects on the central nervous system and peripheral tissues. Leptin administration has been shown to restore metabolic and neuroendocrine abnormalities in individuals with leptin-deficient states, including hypothalamic amenorrhea and lipoatrophy. In contrast, obese individuals are resistant to leptin. Recombinant leptin is beneficial in patients with congenital leptin deficiency or generalized lipodystrophy. However, further research on molecular mediators of leptin resistance is needed for the development of targeted leptin sensitizing therapies for obesity and related metabolic diseases.

Epigenetic regulation of female puberty

Substantial progress has been made in recent years toward deciphering the molecular and genetic underpinnings of the pubertal process. The availability of powerful new methods to interrogate the human genome has led to the identification of genes that are essential for puberty to occur. Evidence has also emerged suggesting that the initiation of puberty requires the coordinated activity of gene sets organized into functional networks. At a cellular level, it is currently thought that loss of transsynaptic inhibition, accompanied by an increase in excitatory inputs, results in the pubertal activation of GnRH release. This concept notwithstanding, a mechanism of epigenetic repression targeting genes required for the pubertal activation of GnRH neurons was recently identified as a core component of the molecular machinery underlying the central restraint of puberty. In this chapter we will discuss the potential contribution of various mechanisms of epigenetic regulation to the hypothalamic control of female puberty.

Roles of leptin in reproduction, pregnancy and polycystic ovary syndrome: consensus knowledge and recent developments

As an essential function for perpetuation of species, reproduction, including puberty onset, is sensitive to the size of body energy stores and the metabolic state of the organism. Accordingly, impaired energy homeostasis, ranging from extreme leanness, such as in anorexia or cachexia, to morbid obesity has an impact on the timing of puberty and is often associated to fertility problems. The neuroendocrine basis for such phenomenon is the close connection between numerous metabolic hormones and nutritional cues with the various elements of the so-called hypothalamic-pituitary-gonadal (HPG) axis. Yet, despite previous fragmentary knowledge, it was only the discovery of the adipose-hormone, leptin, in 1994 what revolutionized our understanding on how metabolic and reproductive systems closely interplay and allowed the definition of the neurohormonal causes of perturbations of puberty and fertility in conditions of impaired body energy homeostasis. In this article, we aim to provide a synoptic view of the mechanisms whereby leptin engages in the regulation of different elements of the HPG axis, with special attention to its effects and mechanisms of action on the different elements of the reproductive brain and its proven direct effects in the gonads. In addition, we will summarize the state-of-the-art regarding the putative roles of leptin during gestation, including its potential function as placental hormone. Finally, comments will be made on the eventual leptin alterations in reproductive disorders, with special attention to the polycystic ovary syndrome (PCOS), a disease in which reproductive, metabolic and neuroendocrine alterations are commonly observed. All in all, we intend to provide an updated account of our knowledge on the physiological roles of leptin in the metabolic regulation of the reproductive axis and its eventual pathophysiological implications in prevalent reproductive disorders, such as PCOS.

Precocious pubertal development: a challenge for pediatric endocrinologists

Precocious puberty is one of the most common conditions encountered in the pediatric endocrinology clinic and can be defined as the appearance of secondary sexual characteristics in girls under 8 years and boys under 9 years of age. The timing of pubertal onset has received increasing attention because of a reported gradual decline in age at menarche in most populations. Proposed mechanisms for these changes include: an improvement in socioeconomic conditions with consequent increased nutritional status and a rise in a number of environmental pollutants. The challenges for pediatric endocrinologists are increasing: what are the mechanisms of precocious puberty in modern society? Should our diagnostic criteria be changed? When to treat? What are the consequences of treatment? Little is known of the short and long term consequences of GnRH-analog treatment, especially in terms of psychological consequences for children and their families.

Segregated responses of mammary gland development and vaginal opening to prepubertal genistein exposure in Bscl2(-/-) female mice with lipodystrophy

Berardinelli-Seip congenital lipodystrophy 2-deficient (Bscl2(-/-)) mice recapitulate human BSCL2 disease with lipodystrophy. Bscl2-encoded seipin is detected in adipocytes and epithelium of mammary gland. Postnatal mammary gland growth spurt and vaginal opening signify pubertal onset in female mice. Bscl2(-/-) females have longer and dilated mammary gland ducts at 5-week old and delayed vaginal opening. Prepubertal exposure to 500ppm genistein diet increases mammary gland area and accelerates vaginal opening in both control and Bscl2(-/-) females. However, genistein treatment increases ductal length in control but not Bscl2(-/-) females. Neither prepubertal genistein treatment nor Bscl2-deficiency affects phospho-estrogen receptor α or progesterone receptor expression patterns in 5-week old mammary gland. Interestingly, Bscl2-deficiency specifically reduces estrogen receptor β expression in mammary gland ductal epithelium. In summary, Bscl2(-/-) females have accelerated postnatal mammary ductal development but delayed vaginal opening; they display segregated responses in mammary gland development and vaginal opening to prepubertal genistein treatment.