SIRT1 mediates obesity- and nutrient-dependent perturbation of pubertal timing by epigenetically controlling Kiss1 expression

Hypothalamic SIRT1-mediated regulation of the hormonal trigger of ovulation and its repression in energy deficit

Female reproduction is highly sensitive to body energy stores; persistent energy deficit, as seen in anorexia or strenuous exercise, is known to suppress ovulation via ill-defined mechanisms. We report herein that hypothalamic SIRT1, a key component of the epigenetic machinery that links nutritional status and puberty onset via modulation of Kiss1, plays a critical role in the control of the preovulatory surge of gonadotropins, i.e., the hormonal trigger of ovulation, and its repression by conditions of energy deficit. Kiss1 neurons in the preoptic area, with proven roles in the control of ovulation, express Sirt1 mRNA. Reciprocal changes in hypothalamic SIRT1 content and Kiss1 expression were observed during the pre-ovulatory phase in adult female rats. Central activation of SIRT1 reduced Kiss1 expression in the rostral hypothalamus, and attenuated the preovulatory surge, while blockade of central SIRT1 augmented it. Conditions of energy deficit enhanced hypothalamic SIRT1 activity and caused suppression of the pre-ovulatory surge and ovulation, which could be rescued by central SIRT1 inhibition. In turn, virogenetic induction of SIRT1 in rostral hypothalamic Kiss1 neurons in adult female mice disrupted ovarian cyclicity and suppressed reproductive indices, despite preserved body weight. Our data document the prominent function of hypothalamic SIRT1 as a key modulator of Kiss1 neurons and the hormonal surge driving ovulation in adulthood, with a major role in its inhibition during conditions of energy insufficiency.

Insights into pubertal development: a narrative review on the role of epigenetics

PURPOSE

Puberty is a key phase of growth and development, characterized by psychophysical transformations. It is driven by a combination of genetic, hormonal, and environmental variables. Epigenetic mechanisms, including histone post-translational modifications and chromatin remodeling, microRNAs, and DNA methylation, play important roles in orchestrating the developmental processes. We describe environmental factors that may interact with genetics, and factors influencing puberty onset, focusing in particular on epigenetic mechanisms that can help understand the timing and variations that lead to precocious or delayed puberty.

METHODS

We conducted a narrative review of associations between puberty and epigenetic mechanisms through a comprehensive search of PubMed, Scopus, and Web of Science databases.

RESULTS

The chromatin landscape of genes as KISS1 has revealed dynamic changes in histone modifications as puberty approaches, influencing the stimulation or inhibition of gene expression critical for reproductive maturation. MiRNAs regulate gene expression, whereas DNA methylation affects activation or repression of gene transcription of genes involved in pubertal timing. Moreover, studies in animal models have provided insights into the role of DNA methylation and miRNAs in brain sexual differentiation, highlighting the active involvement of epigenetic mechanisms in shaping sexually dimorphic brain structures.

CONCLUSION

This review highlights the importance of understanding the complex interplay between epigenetic regulation and pubertal development, which can lead to new therapeutic options and shed light on the fundamental processes driving reproductive maturation.

A tale of two endothelins: the rise and fall of the corpus luteum

Endothelins are small 21 amino acid peptides that interact with G-protein-coupled receptors. They are highly conserved across species and play important roles in vascular biology as well as in disease development and progression. Endothelins, mainly endothelin-1 and endothelin-2, are intricately involved in ovarian function and metabolism. These two peptides differ only in two amino acids but are encoded by different genes, which suggests an independent regulation and a cell-specific mode of expression. This review aims to comprehensively discuss the distinct regulation and roles of endothelin-1 and endothelin-2 regarding corpus luteum function throughout its life span.

The Estrogen-Autophagy Axis: Insights into Cytoprotection and Therapeutic Potential in Cancer and Infection

Macroautophagy, commonly referred to as autophagy, is an essential cytoprotective mechanism that plays a significant role in cellular homeostasis. It has emerged as a promising target for drug development aimed at treating various cancers and infectious diseases. However, the scientific community has yet to reach a consensus on the most effective approach to manipulating autophagy, with ongoing debates about whether its inhibition or stimulation is preferable for managing these complex conditions. One critical factor contributing to the variability in treatment responses for both cancers and infectious diseases is estrogen, a hormone known for its diverse biological effects. Given the strong correlations observed between estrogen signaling and autophagy, this review seeks to summarize the intricate molecular mechanisms that underlie the dual cytoprotective effects of estrogen signaling in conjunction with autophagy. We highlight recent findings from studies that involve various ligands, disease contexts, and cell types, including immune cells. Furthermore, we discuss several factors that regulate autophagy in the context of estrogen's influence. Ultimately, we propose a hypothetical model to elucidate the regulatory effects of the estrogen-autophagy axis on cell fate. Understanding these interactions is crucial for advancing our knowledge of related diseases and facilitating the development of innovative treatment strategies.

The Role of DLK1 Deficiency in Central Precocious Puberty and Association with Metabolic Dysregulation

INTRODUCTION

Precocious puberty is defined as the appearance of secondary sexual characteristics before the age of 8 years in girls and 9 years in boys. Central precocious puberty (CPP) is a rare condition that is diagnosed when premature activation of the hypothalamic-pituitary-gonadal axis is detected, in association with precocious breast development or testicular growth. Idiopathic CPP is historically considered to be the most common form, but in recent years defects in a small but growing number of genes regulating the timing of puberty have been identified in an increasing proportion of cases of CPP. Delta-like non-canonical Notch ligand 1 (DLK1) is understood to be one of the key genes involved in the etiology of CPP, although its mechanistic role is not yet fully understood.

CASE PRESENTATION

We identified a novel de novo variant of DLK1 (c.835C>T; p.Gln279*) in an 8-year-old girl of Bangladeshi origin. She presented with an advanced Tanner staging of B4P4A2, significantly advanced bone age (BA, 13 years), a near-adult proportioned uterus, with a history of menarche at the age of 7.4 years. Diagnosis was confirmed by raised basal luteinizing hormone concentration. She was found to have truncal obesity associated with abnormal fasting insulin levels and mildly elevated cholesterol levels. These findings are consistent with previous literature describing an association between patients with DLK1 deficiency and an impaired metabolic profile. The patient was treated for 2 years with GnRH agonists with ongoing biochemical follow-up into adolescence.

CONCLUSION

This case illustrates the susceptibility to metabolic derangement for patients with mutations in DLK1 and the need for ongoing monitoring after puberty. Our summary of previously identified DLK1 variants and their metabolic consequences demonstrates the frequency of obesity, lipid abnormalities, and insulin dysregulation in this patient cohort in childhood and beyond. This knowledge can guide future clinical practice for patients with CPP patients due to DLK1 deficiency.

The Metabolic Programming of Pubertal Onset

BACKGROUND

There is increasing evidence that maternal factors such as nutritional status (both under and over-nutrition) and diabetes, alongside prenatal exposure to endocrine disrupting chemicals (EDCs), are associated with early pubertal onset in offspring. Such children are also at increased risk of the metabolic syndrome during adolescence and young adulthood.

AIM

This literature review focuses on the role of the prenatal environment in programming pubertal onset, and the impact of prenatal metabolic stressors on the declining average age of puberty.

METHOD

A review of all relevant literature was conducted in PubMed by the authors.

OUTCOME

The mechanism for this appears to be mediated through metabolic signals, such as leptin and insulin, on the kisspeptin-neuronal nitric oxide-gonadotropin releasing hormone (KiNG) axis. Exposed children have an elevated risk of childhood obesity and display a phenotype of hyperinsunlinaemia and hyperleptinaemia. These metabolic changes permit an earlier attainment of the nutritional "threshold" for puberty. Unfortunately, this cycle may be amplified across subsequent generations, however early intervention may help "rescue" progression of this programming.

Emerging roles of lipid and metabolic sensing in the neuroendocrine control of body weight and reproduction

The hypothalamus lies at the intersection of brain and hormonal mechanisms governing essential bodily functions, including metabolic/body weight homeostasis and reproduction. While metabolism and fertility are precisely regulated by independent neuroendocrine axes, these are tightly connected, as reflection of the bidirectional interplay between the energy status of the organisms and their capacity to reproduce; a connection with important pathophysiological implications in disorders affecting these two crucial systems. Beyond the well-characterized roles of key hormones (e.g., leptin, insulin, ghrelin) and neuropeptides (e.g., melanocortins, kisspeptins) in the integral control of metabolism and reproduction, mounting evidence has pointed out a relevant function of cell energy sensors and lipid sensing mechanisms in the hypothalamic control of metabolism, with prominent roles also for metabolic sensors, such as mTOR, AMPK and SIRT1, in the nutritional regulation of key aspects of reproduction, such as pubertal maturation. We provide herein a synoptic overview of these novel regulatory pathways, with a particular focus on their putative function in the metabolic control of puberty, and delineate new avenues for further exploration of the intricate mechanisms whereby metabolism and reproduction are tightly connected.

Gene-environment interaction in functional hypothalamic amenorrhea

Functional hypothalamic amenorrhea (FHA) is a common cause of amenorrhea and chronic anovulation in adolescent girls and young women, diagnosed after excluding other organic causes. It is commonly associated with calorie restriction, excessive physical exercise, and psychosocial stress. These stressors alter the pulsatile secretion of gonadotropin-releasing hormone, leading to a chronic condition of hypoestrogenism and significant health consequences. Recent evidence has highlighted a genetic predisposition to FHA that could explain interindividual variability in stress response. Indeed, not all women experience FHA in response to stress. Rare variants in genes associated with idiopathic hypogonadotropic hypogonadism have been identified in women with FHA, suggesting that these mutations may contribute to an increased susceptibility of women to the trigger of stress exposure. FHA appears today as a complex disease resulting from the combination of genetic predisposition, environmental factors, and epigenetic changes. Furthermore, the genetic background of FHA allows for the hypothesis of a male counterpart. Despite the paucity of data, preliminary findings indicate that an equivalent condition of FHA exists in men, warranting further investigation. This narrative review aims to summarize the recent genetic evidence contributing to the pathophysiology of FHA and to raise awareness on a possible male counterpart.

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.

Methylome analysis in girls with idiopathic central precocious puberty

BACKGROUND

Genetic and environmental factors are implicated in many developmental processes. Recent evidence, however, has suggested that epigenetic changes may also influence the onset of puberty or the susceptibility to a wide range of diseases later in life. The present study aims to investigate changes in genomic DNA methylation profiles associated with pubertal onset analyzing human peripheral blood leukocytes from three different groups of subjects: 19 girls with central precocious puberty (CPP), 14 healthy prepubertal girls matched by age and 13 healthy pubertal girls matched by pubertal stage. For this purpose, the comparisons were performed between pre- and pubertal controls to identify changes in normal pubertal transition and CPP versus pre- and pubertal controls.

RESULTS

Analysis of methylation changes associated with normal pubertal transition identified 1006 differentially methylated CpG sites, 86% of them were found to be hypermethylated in prepubertal controls. Some of these CpG sites reside in genes associated with the age of menarche or transcription factors involved in the process of pubertal development. Analysis of methylome profiles in CPP patients showed 65% and 55% hypomethylated CpG sites compared with prepubertal and pubertal controls, respectively. In addition, interestingly, our results revealed the presence of 43 differentially methylated genes coding for zinc finger (ZNF) proteins. Gene ontology and IPA analysis performed in the three groups studied revealed significant enrichment of them in some pathways related to neuronal communication (semaphorin and gustation pathways), estrogens action, some cancers (particularly breast and ovarian) or metabolism (particularly sirtuin).

CONCLUSIONS

The different methylation profiles of girls with normal and precocious puberty indicate that regulation of the pubertal process in humans is associated with specific epigenetic changes. Differentially methylated genes include ZNF genes that may play a role in developmental control. In addition, our data highlight changes in the methylation status of genes involved in signaling pathways that determine the migration and function of GnRH neurons and the onset of metabolic and neoplastic diseases that may be associated with CPP in later life.

Kisspeptin signaling in astrocytes modulates the reproductive axis

Reproduction is safeguarded by multiple, often cooperative, regulatory networks. Kisspeptin signaling, via KISS1R, plays a fundamental role in reproductive control, primarily by regulation of hypothalamic GnRH neurons. We disclose herein a pathway for direct kisspeptin actions in astrocytes that contributes to central reproductive modulation. Protein-protein interaction and ontology analyses of hypothalamic proteomic profiles after kisspeptin stimulation revealed that glial/astrocyte markers are regulated by kisspeptin in mice. This glial-kisspeptin pathway was validated by the demonstrated expression of Kiss1r in mouse astrocytes in vivo and astrocyte cultures from humans, rats, and mice, where kisspeptin activated canonical intracellular signaling-pathways. Cellular coexpression of Kiss1r with the astrocyte markers GFAP and S100-β occurred in different brain regions, with higher percentage in Kiss1- and GnRH-enriched areas. Conditional ablation of Kiss1r in GFAP-positive cells in the G-KiR-KO mouse altered gene expression of key factors in PGE2 synthesis in astrocytes and perturbed astrocyte-GnRH neuronal appositions, as well as LH responses to kisspeptin and LH pulsatility, as surrogate marker of GnRH secretion. G-KiR-KO mice also displayed changes in reproductive responses to metabolic stress induced by high-fat diet, affecting female pubertal onset, estrous cyclicity, and LH-secretory profiles. Our data unveil a nonneuronal pathway for kisspeptin actions in astrocytes, which cooperates in fine-tuning the reproductive axis and its responses to metabolic stress.

Epigenetic programming for obesity and noncommunicable disease: From womb to tomb

Several epidemiological, clinical and experimental studies in recent decades have shown the relationship between exposure to stressors during development and health outcomes later in life. The characterization of these susceptible phases, such as preconception, gestation, lactation and adolescence, and the understanding of factors that influence the risk of an adult individual for developing obesity, metabolic and cardiovascular diseases, is the focus of the DOHaD (Developmental Origins of Health and Disease) research line. In this sense, advancements in molecular biology techniques have contributed significantly to the understanding of the mechanisms underlying the observed phenotypes, their morphological and physiological alterations, having as a main driving factor the epigenetic modifications and their consequent modulation of gene expression. The present narrative review aimed to characterize the different susceptible phases of development and associated epigenetic modifications, and their implication in the development of non-communicable diseases. Additionally, we provide useful insights into interventions during development to counteract or prevent long-term programming for disease susceptibility.

Sirtuin 1 serum concentration in healthy children - dependence on sex, age, stage of puberty, body weight and diet

Introduction

Sirtuin 1 (SIRT1) is known to be involved in sensing cellular energy levels and regulating energy metabolism. This study aimed to evaluate fasting serum SIRT1 levels in healthy children, and to analyse the influence of age, sex, puberty, body weight, height, and diet on its concentration.

Methods

47 healthy children aged 4-14 with weight and height within normal range and no chronic disease were included into the study. Fasting serum SIRT1 concentrations were estimated by Enzyme Linked Immunosorbent Assay (ELISA).

Results

Results showed that serum SIRT1 concentrations in healthy children did not differ with respect to sex, age, height, weight and puberty. Whereas, it appeared that a higher frequency of fruits, vegetables and dairy products consumption was associated with an increase in serum SIRT1 levels.

Discussion

Studying SIRT1 in the context of children's health may have implications for a broader understanding of growth processes, pubertal development, metabolic disorders and nutrition.

Metabolic control of puberty: 60 years in the footsteps of Kennedy and Mitra's seminal work

An individual's nutritional status has a powerful effect on sexual maturation. Puberty onset is delayed in response to chronic energy insufficiency and is advanced under energy abundance. The consequences of altered pubertal timing for human health are profound. Late puberty increases the chances of cardiometabolic, musculoskeletal and neurocognitive disorders, whereas early puberty is associated with increased risks of adult obesity, type 2 diabetes mellitus, cardiovascular diseases and various cancers, such as breast, endometrial and prostate cancer. Kennedy and Mitra's trailblazing studies, published in 1963 and using experimental models, were the first to demonstrate that nutrition is a key factor in puberty onset. Building on this work, the field has advanced substantially in the past decade, which is largely due to the impressive development of molecular tools for experimentation and population genetics. In this Review, we discuss the latest advances in basic and translational sciences underlying the nutritional and metabolic control of pubertal development, with a focus on perspectives and future directions.

Epigenetic mechanisms underlying sex differences in the brain and behavior

Sex differences are found across brain regions, behaviors, and brain diseases. Sexual differentiation of the brain is initiated prenatally but it continues throughout life, as a result of the interaction of three major factors: gonadal hormones, sex chromosomes, and the environment. These factors are thought to act, in part, via epigenetic mechanisms which control chromatin and transcriptional states in brain cells. In this review, we discuss evidence that epigenetic mechanisms underlie sex-specific neurobehavioral changes during critical organizational periods, across the estrous cycle, and in response to diverse environments throughout life. We further identify future directions for the field that will provide novel mechanistic insights into brain sex differences, inform brain disease treatments and women's brain health in particular, and apply to people across genders.

Transcriptomic signatures associated with underlying rapid changes in the early phase brain of bi-directional sex change in Trimma okinawae

Teleost fish exhibit remarkable sexual plasticity and divergent developmental systems, including sequential hermaphroditism. One of the more fascinating models of sexual plasticity is socially controlled sex change, which is often observed in coral reef fish. The Okinawa rubble goby, Trimma okinawae, is a bi-directional sex-changing fish. It can rapidly change sex in either direction based on social circumstances. Although behavioural and neuroendocrine sex change occurs immediately and is believed to trigger gonadal changes, the underlying mechanisms remain poorly understood. In this study, we conducted a de novo transcriptome analysis of the T. okinawae brain and identified genes that are differentially expressed between the sexes and genes that were immediately controlled by social stimulation implicating sex change. Several genes showed concordant expression shifts regardless of the sex change direction and were associated with histone modification in nerve cells. These genes are known to function in the neuroendocrine control of reproduction in nerve cells. Overall, we identified genes associated with the initiation of sex change, which provides insight into the regulation of sex change and sexual plasticity.

Maternal cafeteria diet influences kisspeptin (Kiss1), kisspeptin receptor(Gpr54), and sirtuin (Sirt1) genes, hormonal and metabolic profiles, and reproductive functions in rat offspring in a sex-specific manner†

Kisspeptin (KP, encoded by Kiss1, binding to the Gpr54 receptor) is a neuropeptide conveying information on the metabolic status to the hypothalamic-pituitary-gonadal axis. KP acts together with dynorphin A (encoded by Pdyn) and neurokinin B (encoded by Tac2) to regulate reproduction. KP is crucial for the onset of puberty and is under the control of sirtuin (encoded by Sirt1). We hypothesize that the maternal cafeteria (CAF) diet has adverse effects on the offspring's hormonal, metabolic, and reproductive functions due to sex-specific alterations in the expression of Kiss1, Gpr54, Pdyn, Tac2, and Sirt1 in the hypothalamus, and Kiss1, Gpr54, and Sirt1 in the liver. Rats were fed a CAF diet before pregnancy, during pregnancy, and during lactation. The vaginal opening was monitored. Offspring were sacrificed in three age points: PND 30, PND 35, and PND 60 (females) and PND 40, PND 45, and PND 60 (males). Their metabolic and hormonal status was assessed. mRNA for Kiss1, Gpr54, Pdyn, Tac2, and Sirt1 were measured by real-time PCR in the hypothalamus and/or livers. We found that CAF offspring had lower weight and altered body composition; increased cholesterol and triglyceride levels, sex-specific changes in glucose and insulin levels; sex-dependent changes in Sirt1/Kiss1 mRNA ratio in the hypothalamus; sex-specific alterations in Kiss1 and Sirt1 mRNA in the liver with more diversity in males; and a delayed puberty onset in females. We concluded that the mother's CAF diet leads to sex-specific alterations in metabolic and reproductive outcomes via Kiss1/Gpr54 and Sirt1 systems in offspring.

Central and peripheral mechanisms involved in the control of GnRH neuronal function by metabolic factors

Gonadotropin-releasing hormone (GnRH) neurons are the final output pathway for the brain control of reproduction. The activity of this neuronal population, mainly located at the preoptic area of the hypothalamus, is controlled by a plethora of metabolic signals. However, it has been documented that most of these signal impact on GnRH neurons through indirect neuronal circuits, Kiss1, proopiomelanocortin, and neuropeptide Y/agouti-related peptide neurons being some of the most prominent mediators. In this context, compelling evidence has been gathered in recent years on the role of a large range of neuropeptides and energy sensors in the regulation of GnRH neuronal activity through both direct and indirect mechanisms. The present review summarizes some of the most prominent recent advances in our understanding of the peripheral factors and central mechanisms involved in the metabolic control of GnRH neurons.

The Congenital and Acquired Mechanisms Implicated in the Etiology of Central Precocious Puberty

The etiology of central precocious puberty (CPP) is multiple and heterogeneous, including congenital and acquired causes that can be associated with structural or functional brain alterations. All causes of CPP culminate in the premature pulsatile secretion of hypothalamic GnRH and, consequently, in the premature reactivation of hypothalamic-pituitary-gonadal axis. The activation of excitatory factors or suppression of inhibitory factors during childhood represent the 2 major mechanisms of CPP, revealing a delicate balance of these opposing neuronal pathways. Hypothalamic hamartoma (HH) is the most well-known congenital cause of CPP with central nervous system abnormalities. Several mechanisms by which hamartoma causes CPP have been proposed, including an anatomical connection to the anterior hypothalamus, autonomous neuroendocrine activity in GnRH neurons, trophic factors secreted by HH, and mechanical pressure applied to the hypothalamus. The importance of genetic and/or epigenetic factors in the underlying mechanisms of CPP has grown significantly in the last decade, as demonstrated by the evidence of genetic abnormalities in hypothalamic structural lesions (eg, hamartomas, gliomas), syndromic disorders associated with CPP (Temple, Prader-Willi, Silver-Russell, and Rett syndromes), and isolated CPP from monogenic defects (MKRN3 and DLK1 loss-of-function mutations). Genetic and epigenetic discoveries involving the etiology of CPP have had influence on the diagnosis and familial counseling providing bases for potential prevention of premature sexual development and new treatment targets in the future. Global preventive actions inducing healthy lifestyle habits and less exposure to endocrine-disrupting chemicals during the lifespan are desirable because they are potentially associated with CPP.

Molecular basis of normal and pathological puberty: from basic mechanisms to clinical implications

Puberty is a major maturational event; its mechanisms and timing are driven by genetic determinants, but also controlled by endogenous and environmental cues. Substantial progress towards elucidation of the neuroendocrine networks governing puberty has taken place. However, key aspects of the mechanisms responsible for the precise timing of puberty and its alterations have only recently begun to be deciphered, propelled by epidemiological data suggesting that pubertal timing is changing in humans, via mechanisms that are not yet understood. By integrating basic and clinical data, we provide a comprehensive overview of current advances on the physiological basis of puberty, with a particular focus on the roles of kisspeptins and other central transmitters, the underlying molecular and endocrine mechanisms, and the pathways involved in pubertal modulation by nutritional and metabolic cues. Additionally, we have summarised molecular features of precocious and delayed puberty in both sexes, as revealed by clinical and genetic studies. This Review is a synoptic up-to-date view of how puberty is controlled and of the pathogenesis of major pubertal alterations, from both a clinical and translational perspective. We also highlight unsolved challenges that will seemingly concentrate future research efforts in this active domain of endocrinology.

Serum metabolomic analysis reveals key metabolites in drug treatment of central precocious puberty in female children

Precocious puberty (PP) is a common condition among children. According to the pathogenesis and clinical manifestations, PP can be divided into central precocious puberty (CPP, gonadotropin dependent), peripheral precocious puberty (PPP, gonadotropin independent), and incomplete precocious puberty (IPP). Identification of the variations in key metabolites involved in CPP and their underlying biological mechanisms has increased the understanding of the pathological processes of this condition. However, little is known about the role of metabolite variations in the drug treatment of CPP. Moreover, it remains unclear whether the understanding of the crucial metabolites and pathways can help predict disease progression after pharmacological therapy of CPP. In this study, systematic metabolomic analysis was used to examine three groups, namely, healthy control (group N, 30 healthy female children), CPP (group S, 31 female children with CPP), and treatment (group R, 29 female children) groups. A total of 14 pathways (the top two pathways were aminoacyl-tRNA biosynthesis and phenylalanine, tyrosine, and tryptophan biosynthesis) were significantly enriched in children with CPP. In addition, two short peptides (His-Arg-Lys-Glu and Lys-Met-His) were found to play a significant role in CPP. Various metabolites associated with different pathways including amino acids, PE [19:1(9Z)0:0], tumonoic acid I, palmitic amide, and linoleic acid-biotin were investigated in the serum of children in all groups. A total of 45 metabolites were found to interact with a chemical drug [a gonadotropin-releasing hormone (GnRH) analog] and a traditional Chinese medicinal formula (DBYW). This study helps to understand metabolic variations in CPP after drug therapy, and further investigation may help develop individualized treatment approaches for CPP in clinical practice.

Mammalian puberty: a fly perspective

Mammalian puberty and Drosophila metamorphosis, despite their evolutionary distance, exhibit similar design principles and conservation of molecular components. In this Viewpoint, we review recent advances in this area and the similarities between both processes in terms of the signaling pathways and neuroendocrine circuits involved. We argue that the detection and uptake of peripheral fat by Drosophila prothoracic endocrine cells induces endomembrane remodeling and ribosomal maturation, leading to the acquisition of high biosynthetic and secretory capacity. The absence of this fat-neuroendocrine interorgan communication leads to giant, obese, non-pupating larvae. Importantly, human leptin is capable of signaling the pupariation process in Drosophila, and its expression prevents obesity and triggers maturation in mutants that do not pupate. This implies that insect metamorphosis can be used to address issues related to the biology of leptin and puberty.

Modulation of sirtuins during monolayer chondrocyte culture influences cartilage regeneration upon transfer to a 3D culture environment

This study examined the role of sirtuins in the regenerative potential of articular chondrocytes. Sirtuins (SIRT1-7) play a key role in regulating cartilage homeostasis. By inhibiting pro-inflammatory pathways responsible for cartilage degradation and promoting the expression of key matrix components, sirtuins have the potential to drive a favourable balance between anabolic and catabolic processes critical to regenerative medicine. When subjected to osmolarity and glucose concentrations representative of the in vivo niche, freshly isolated bovine chondrocytes exhibited increases in SIRT1 but not SIRT3 gene expression. Replicating methods adopted for the in vitro monolayer expansion of chondrocytes for cartilage regenerative therapies, we found that SIRT1 gene expression declined during expansion. Manipulation of sirtuin activity during in vitro expansion by supplementation with the SIRT1-specific activator SRT1720, nicotinamide mononucleotide, or the pan-sirtuin inhibitor nicotinamide, significantly influenced cartilage regeneration in subsequent 3D culture. Tissue mass, cellularity and extracellular matrix content were reduced in response to sirtuin inhibition during expansion, whilst sirtuin activation enhanced these measures of cartilage tissue regeneration. Modulation of sirtuin activity during monolayer expansion influenced H3K27me3, a heterochromatin mark with an important role in development and differentiation. Unexpectedly, treatment of primary chondrocytes with sirtuin activators in 3D culture reduced their matrix synthesis. Thus, modulating sirtuin activity during the in vitro monolayer expansion phase may represent a distinct opportunity to enhance the outcome of cartilage regenerative medicine techniques.

Childhood obesity and central precocious puberty

Childhood obesity is a major public health problem worldwide, and the relationship between obesity and central precocious puberty has long been confirmed, however, the mechanisms underlying this association remain elusive. This review provides an overview of the recent progress regarding how childhood obesity impacts on hypothalamic-pituitary-gonadal axis and pubertal onset, focusing on adipokines (leptin and ghrelin), hormone (insulin), and lipid (ceramide), as well as critical signaling pathways (AMPK/SIRT, mTOR) that integrate the peripheral metabolism and central circuits. Notably, prevention of obesity and CPP is beneficial for the adult life of the children, thus we further summarize the potential strategies in treating and preventing childhood obesity and CPP. The updated understanding of metabolic stress and pediatric endocrine disease will arise the attention of society, and also contribute to preventing more serious comorbidities in the later period of life in children.

Grim-19 plays a key role in mitochondrial steroidogenic acute regulatory protein stability and ligand-binding properties in Leydig cells

Grim-19 (gene associated with retinoid-IFN-induced mortality 19), the essential component of complex I of mitochondrial respiratory chain, functions as a noncanonical tumor suppressor by controlling apoptosis and energy metabolism. However, additional biological actions of Grim-19 have been recently suggested in male reproduction. We investigated here the expression and functional role of Grim-19 in murine testis. Testicular Grim-19 expression was detected from mouse puberty and increased progressively thereafter, and GRIM-19 protein was observed to be expressed exclusively in interstitial Leydig cells (LCs), with a prominent mitochondrial localization. In vivo lentiviral vector-mediated knockdown of Grim-19 resulted in a significant decrease in testosterone production and triggered aberrant oxidative stress in testis, thus impairing male fertility by inducing germ cell apoptosis and oligozoospermia. The control of testicular steroidogenesis by GRIM-19 was validated using the in vivo knockdown model with isolated primary LCs and in vitro experiments with MA-10 mouse Leydig tumor cells. Mechanistically, we suggest that the negative regulation exerted by GRIM-19 deficiency-induced oxidative stress on steroidogenesis may be the result of two phenomena: a direct effect through inhibition of phosphorylation of steroidogenic acute regulatory protein (StAR) and subsequent impediment to StAR localization in mitochondria and an indirect pathway that is to facilitate the inhibiting role exerted by the extracellular matrix on the steroidogenic capacity of LCs via promotion of integrin activation. Altogether, our observations suggest that Grim-19 plays a potent role in testicular steroidogenesis and that its alterations may contribute to testosterone deficiency-related disorders linked to metabolic stress and male infertility.

Conditional Deletion of KOR (Oprk1) in Kisspeptin Cells Does Not Alter LH Pulses, Puberty, or Fertility in Mice

Classic pharmacological studies suggested that endogenous dynorphin-KOR signaling is important for reproductive neuroendocrine regulation. With the seminal discovery of an interconnected network of hypothalamic arcuate neurons co-expressing kisspeptin, neurokinin B, and dynorphin (KNDy neurons), the KNDy hypothesis was developed to explain how gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) pulses are generated. Key to this hypothesis is dynorphin released from KNDy neurons acting in a paracrine manner on other KNDy neurons via kappa opioid receptor (KOR) signaling to terminate neural "pulse" events. While in vitro evidence supports this aspect of the KNDy hypothesis, a direct in vivo test of the necessity of KOR signaling in kisspeptin neurons for proper LH secretion has been lacking. We therefore conditionally knocked out KOR selectively from kisspeptin neurons of male and female mice and tested numerous reproductive measures, including in vivo LH pulse secretion. Surprisingly, despite validating successful knockout of KOR in kisspeptin neurons, we found no significant effect of kisspeptin cell-specific deletion of KOR on any measure of puberty, LH pulse parameters, LH surges, follicle-stimulating hormone (FSH) levels, estrous cycles, or fertility. These outcomes suggest that the KNDy hypothesis, while sufficient normally, may not be the only neural mechanism for sculpting GnRH and LH pulses, supported by recent findings in humans and mice. Thus, besides normally acting via KOR in KNDy neurons, endogenous dynorphin and other opioids may, under some conditions, regulate LH and FSH secretion via KOR in non-kisspeptin cells or perhaps via non-KOR pathways. The current models for GnRH and LH pulse generation should be expanded to consider such alternate mechanisms.

Genetics of pubertal delay

The timing of pubertal development is strongly influenced by the genetic background, and clinical presentations of delayed puberty are often found within families with clear patterns of inheritance. The discovery of the underlying genetic regulators of such conditions, in recent years through next generation sequencing, has advanced the understanding of the pathogenesis of disorders of pubertal timing and the potential for genetic testing to assist diagnosis for patients with these conditions. This review covers the significant advances in the understanding of the biological mechanisms of delayed puberty that have occurred in the last two decades.

DNA hypermethylation of Kiss1r promoter and reduction of hepatic Kiss1r in female rats with type 2 diabetes

Kisspeptin, produced from the brain and peripheral tissues, may constitute an important link in metabolic regulation in response to external cues, such as diet. The kisspeptin system is well described in the brain. However, its function and regulation in the peripheral tissues, especially in relation to metabolic disease and sex differences, remain to be elucidated. As Kiss1 and Kiss1r, encoding for kisspeptin and kisspeptin receptors, respectively, are altered by overnutrition/fasting and regulated by DNA methylation during puberty and cancer, epigenetic mechanisms in metabolic disorders are highly probable. In the present study, we experimentally induced type 2 diabetes mellitus (DM2) in female Wistar rats using high-fat diet/streptozocin. We analysed expression and DNA methylation of Kiss1 and Kiss1r in the peripheral tissues, using quantitative-reverse-transcription PCR (qRT-PCR) and pyrosequencing. We discovered differential expression of Kiss1 and Kiss1r in peripheral organs in DM2 females, as compared with healthy controls, and the profile differed from patterns reported earlier in males. DM2 in females was linked to the increased Kiss1 mRNA in the liver and increased Kiss1r mRNA in the liver and adipose tissue. However, Kiss1r promoter was hypermethylated in the liver, suggesting gene silencing. Indeed, the increase in DNA methylation of Kiss1r promoter was accompanied by a reduction in Kiss1r protein, implying epigenetic or translational gene repression. Our results deliver novel evidence for tissue-specific differences in Kiss1 and Kiss1r expression in peripheral organs in DM2 females and suggest DNA methylation as a player in regulation of the hepatic kisspeptin system in DM2.

Dicer ablation in Kiss1 neurons impairs puberty and fertility preferentially in female mice

Kiss1 neurons, producing kisspeptins, are essential for puberty and fertility, but their molecular regulatory mechanisms remain unfolded. Here, we report that congenital ablation of the microRNA-synthesizing enzyme, Dicer, in Kiss1 cells, causes late-onset hypogonadotropic hypogonadism in both sexes, but is compatible with pubertal initiation and preserved Kiss1 neuronal populations at the infantile/juvenile period. Yet, failure to complete puberty and attain fertility is observed only in females. Kiss1-specific ablation of Dicer evokes disparate changes of Kiss1-cell numbers and Kiss1/kisspeptin expression between hypothalamic subpopulations during the pubertal-transition, with a predominant decline in arcuate-nucleus Kiss1 levels, linked to enhanced expression of its repressors, Mkrn3, Cbx7 and Eap1. Our data unveil that miRNA-biosynthesis in Kiss1 neurons is essential for pubertal completion and fertility, especially in females, but dispensable for initial reproductive maturation and neuronal survival in both sexes. Our results disclose a predominant miRNA-mediated inhibitory program of repressive signals that is key for precise regulation of Kiss1 expression and, thereby, reproductive function.

Developmental sex differences in the peri-pubertal pattern of hypothalamic reproductive gene expression, including Kiss1 and Tac2, may contribute to sex differences in puberty onset

The mechanisms regulating puberty still remain elusive, as do the underlying causes for sex differences in puberty onset (girls before boys) and pubertal disorders. Neuroendocrine puberty onset is signified by increased pulsatile GnRH secretion, yet how and when various upstream reproductive neural circuits change developmentally to govern this process is poorly understood. We previously reported day-by-day peri-pubertal increases (Kiss1, Tac2) or decreases (Rfrp) in hypothalamic gene expression of female mice, with several brain mRNA changes preceding external pubertal markers. However, similar pubertal measures in males were not previously reported. Here, to identify possible neural sex differences underlying sex differences in puberty onset, we analyzed peri-pubertal males and directly compared them with female littermates. Kiss1 expression in male mice increased over the peri-pubertal period in both the AVPV and ARC nuclei but with lower levels than in females at several ages. Likewise, Tac2 expression in the male ARC increased between juvenile and older peri-pubertal stages but with levels lower than females at most ages. By contrast, both DMN Rfrp expressionand Rfrp neuronal activation strongly decreased in males between juvenile and peri-pubertal stages, but with similar levels as females. Neither ARC KNDy neuronal activation nor Kiss1r expression in GnRH neurons differed between males and females or changed with age. These findings delineate several peri-pubertal changes in neural populations in developing males, with notable sex differences in kisspeptin and NKB neuron developmental patterns. Whether these peri-pubertal hypothalamic sex differences underlie sex differences in puberty onset deserves future investigation.

Advances in clinical applications of kisspeptin-GnRH pathway in female reproduction

BACKGROUND

Kisspeptin is the leading upstream regulator of pulsatile and surge Gonadotrophin-Releasing Hormone secretion (GnRH) in the hypothalamus, which acts as the key governor of the hypothalamic-pituitary-ovary axis.

MAIN TEXT

Exogenous kisspeptin or its receptor agonist can stimulate GnRH release and subsequent physiological gonadotropin secretion in humans. Based on the role of kisspeptin in the hypothalamus, a broad application of kisspeptin and its receptor agonist has been recently uncovered in humans, including central control of ovulation, oocyte maturation (particularly in women at a high risk of ovarian hyperstimulation syndrome), test for GnRH neuronal function, and gatekeepers of puberty onset. In addition, the kisspeptin analogs, such as TAK-448, showed promising agonistic activity in healthy women as well as in women with hypothalamic amenorrhoea or polycystic ovary syndrome.

CONCLUSION

More clinical trials should focus on the therapeutic effect of kisspeptin, its receptor agonist and antagonist in women with reproductive disorders, such as hypothalamic amenorrhoea, polycystic ovary syndrome, and endometriosis.

An Approach to the Patient With Delayed Puberty

Pediatric endocrinologists often evaluate and treat youth with delayed puberty. Stereotypically, these patients are 14-year-old young men who present due to lack of pubertal development. Concerns about stature are often present, arising from gradual shifts to lower height percentiles on the population-based, cross-sectional curves. Fathers and/or mothers may have also experienced later than average pubertal onset. In this review, we will discuss a practical clinical approach to the evaluation and management of youth with delayed puberty, including the differential diagnosis and key aspects of evaluation and management informed by recent review of the existing literature. We will also discuss scenarios that pose additional clinical challenges, including: (1) the young woman whose case poses questions regarding how presentation and approach differs for females vs males; (2) the 14-year-old female or 16-year-old young man who highlight the need to reconsider the most likely diagnoses, including whether idiopathic delayed puberty can still be considered constitutional delay of growth and puberty at such late ages; and finally (3) the 12- to 13-year-old whose presentation raises questions about whether age cutoffs for the diagnosis and treatment of delayed puberty should be adjusted downward to coincide with the earlier onset of puberty in the general population.

Early programming of reproductive health and fertility: novel neuroendocrine mechanisms and implications in reproductive medicine

BACKGROUND

According to the Developmental Origins of Health and Disease (DOHaD) hypothesis, environmental changes taking place during early maturational periods may alter normal development and predispose to the occurrence of diverse pathologies later in life. Indeed, adverse conditions during these critical developmental windows of high plasticity have been reported to alter the offspring developmental trajectory, causing permanent functional and structural perturbations that in the long term may enhance disease susceptibility. However, while solid evidence has documented that fluctuations in environmental factors, ranging from nutrient availability to chemicals, in early developmental stages (including the peri-conceptional period) have discernible programming effects that increase vulnerability to develop metabolic perturbations, the impact and eventual mechanisms involved, of such developmental alterations on the reproductive phenotype of offspring have received less attention.

OBJECTIVE AND RATIONALE

This review will summarize recent advances in basic and clinical research that support the concept of DOHaD in the context of the impact of nutritional and hormonal perturbations, occurring during the periconceptional, fetal and early postnatal stages, on different aspects of reproductive function in both sexes. Special emphasis will be given to the effects of early nutritional stress on the timing of puberty and adult gonadotropic function, and to address the underlying neuroendocrine pathways, with particular attention to involvement of the Kiss1 system in these reproductive perturbations. The implications of such phenomena in terms of reproductive medicine will also be considered.

SEARCH METHODS

A comprehensive MEDLINE search, using PubMed as main interface, of research articles and reviews, published mainly between 2006 and 2021, has been carried out. Search was implemented using multiple terms, focusing on clinical and preclinical data from DOHaD studies, addressing periconceptional, gestational and perinatal programming of reproduction. Selected studies addressing early programming of metabolic function have also been considered, when relevant.

OUTCOMES

A solid body of evidence, from clinical and preclinical studies, has documented the impact of nutritional and hormonal fluctuations during the periconceptional, prenatal and early postnatal periods on pubertal maturation, as well as adult gonadotropic function and fertility. Furthermore, exposure to environmental chemicals, such as bisphenol A, and maternal stress has been shown to negatively influence pubertal development and gonadotropic function in adulthood. The underlying neuroendocrine pathways and mechanisms involved have been also addressed, mainly by preclinical studies, which have identified an, as yet incomplete, array of molecular and neurohormonal effectors. These include, prominently, epigenetic regulatory mechanisms and the hypothalamic Kiss1 system, which likely contribute to the generation of reproductive alterations in conditions of early nutritional and/or metabolic stress. In addition to the Kiss1 system, other major hypothalamic regulators of GnRH neurosecretion, such as γ-aminobutyric acid and glutamate, may be targets of developmental programming.

WIDER IMPLICATIONS

This review addresses an underdeveloped area of reproductive biology and medicine that may help to improve our understanding of human reproductive disorders and stresses the importance, and eventual pathogenic impact, of early determinants of puberty, adult reproductive function and fertility.

Kisspeptins and the neuroendocrine control of reproduction: Recent progress and new frontiers in kisspeptin research

In late 2003, a major breakthrough in our understanding of the mechanisms that govern reproduction occurred with the identification of the reproductive roles of kisspeptins, encoded by the Kiss1 gene, and their receptor, Gpr54 (aka, Kiss1R). The discovery of this unsuspected reproductive facet attracted an extraordinary interest and boosted an intense research activity, in human and model species, that, in a relatively short period, established a series of basic concepts on the physiological roles of kisspeptins. Such fundamental knowledge, gathered in these early years of kisspeptin research, set the scene for the more recent in-depth dissection of the intimacies of the neuronal networks involving Kiss1 neurons, their precise mechanisms of regulation and the molecular underpinnings of the function of kisspeptins as pivotal regulators of all key aspects of reproductive function, from puberty onset to pulsatile gonadotropin secretion and the metabolic control of fertility. While no clear temporal boundaries between these two periods can be defined, in this review we will summarize the most prominent advances in kisspeptin research occurred in the last ten years, as a means to provide an up-dated view of the state of the art and potential paths of future progress in this dynamic, and ever growing domain of Neuroendocrinology.

Connecting nutritional deprivation and pubertal inhibition via GRK2-mediated repression of kisspeptin actions in GnRH neurons

BACKGROUND

Perturbations in the timing of puberty, with potential adverse consequences in later health, are increasingly common. The underlying neurohormonal mechanisms are unfolded, but nutritional alterations are key contributors. Efforts to unveil the basis of normal puberty and its metabolic control have focused on mechanisms controlling expression of Kiss1, the gene encoding the puberty-activating neuropeptide, kisspeptin. However, other regulatory phenomena remain ill-defined. Here, we address the putative role of the G protein-coupled-receptor kinase-2, GRK2, in GnRH neurons, as modulator of pubertal timing via repression of the actions of kisspeptin, in normal maturation and conditions of nutritional deficiency.

METHODS

Hypothalamic RNA and protein expression analyses were conducted in maturing female rats. Pharmacological studies involved central administration of GRK2 inhibitor, βARK1-I, and assessment of gonadotropin responses to kisspeptin or phenotypic and hormonal markers of puberty, under normal nutrition or early subnutrition in female rats. In addition, a mouse line with selective ablation of GRK2 in GnRH neurons, aka G-GRKO, was generated, in which hormonal responses to kisspeptin and puberty onset were monitored, in normal conditions and after nutritional deprivation.

RESULTS

Hypothalamic GRK2 expression increased along postnatal maturation in female rats, especially in the preoptic area, where most GnRH neurons reside, but decreased during the juvenile-to-pubertal transition. Blockade of GRK2 activity enhanced Ca+2 responses to kisspeptin in vitro, while central inhibition of GRK2 in vivo augmented gonadotropin responses to kisspeptin and advanced puberty onset. Postnatal undernutrition increased hypothalamic GRK2 expression and delayed puberty onset, the latter being partially reversed by central GRK2 inhibition. Conditional ablation of GRK2 in GnRH neurons enhanced gonadotropin responses to kisspeptin, accelerated puberty onset, and increased LH pulse frequency, while partially prevented the negative impact of subnutrition on pubertal timing and LH pulsatility in mice.

CONCLUSIONS

Our data disclose a novel pathway whereby GRK2 negatively regulates kisspeptin actions in GnRH neurons, as major regulatory mechanism for tuning pubertal timing in nutritionally-compromised conditions.

The Kisspeptin System in Male Reproduction

The kisspeptin system includes the cleavage products Kiss1 precursor and kisspeptin receptor (Kiss1R). It was originally discovered and studied in cancer metastasis, but the identification of KISS1/KISS1R gene mutations causing hypogonadotropic hypogonadism (HH) revealed unexpected effects in reproduction. Nowadays, the kisspeptin system is the main central gatekeeper of the reproductive axis at puberty and adulthood, but it also has a widespread functional role in the control of endocrine functions. At the periphery, Kiss1 and Kiss1R are expressed in the testes, but the need for kisspeptin signaling for spermatogenesis and sperm quality is still unclear and debated. This brief manuscript summarizes the main findings on kisspeptin and male reproduction; upcoming data on sperm maturation are also discussed.

SIRT1: A Key Player in Male Reproduction

Reproduction is the way to immortality for an individual, and it is essential to the continuation of the species. Sirtuins are involved in cellular homeostasis, energy metabolism, apoptosis, age-related problems, and sexual reproduction. Sirtuin 1 (SIRT1) belongs to the sirtuin family of deacetylases, and it is a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase. It removes the acetyl group from a variety of substrates. SIRT1 regulates endocrine/metabolic, reproductive, and placental development by deacetylating histone, different transcription factors, and signal transduction molecules in a variety of cellular processes. It also plays a very important role in the synthesis and secretion of sex hormones via regulating the hypothalamus-pituitary-gonadal (HPG) axis. Moreover, SIRT1 participates in several key stages of spermatogenesis and sperm maturation. The current review will give a thorough overview of SIRT1's functions in male reproductive processes, thus paving the way for more research on restorative techniques and their uses in reproductive medicine.

Combinational exposure to Bisphenol A and a high-fat diet causes trans-generational Malfunction of the female reproductive system in mice

Bisphenol A (BPA) is a common endocrine disruptor and a high-fat diet (HFD) also affects fertility. However, little is known about the long-term consequences of simultaneous exposure to BPA and a HFD on reproductive health. Herein, we assessed the effects of maternal exposure to BPA in combination with a HFD on reproductive function in subsequent generations of female mice and evaluated its effects on the hypothalamic-pituitary-gonadal axis. We found that the combination of maternal exposure to BPA and a HFD led to increased urine BPA levels, precocious puberty, altered estrous cyclicity, decreased follicle numbers, and altered hypothalamic Kiss1 methylation status in F1 and F2 mice. Therefore, we demonstrated that maternal exposure to BPA in combination with a HFD exerts a trans-generational effect on female reproduction.

Precocious sexual maturation: Unravelling the mechanisms of pubertal onset through clinical observations

Puberty is a crucial biological process normally occurring at a specific time during the lifespan, during which sexual and somatic maturation are completed, and reproductive capacity is reached. Pubertal timing is not only determined by genetics, but also by endogenous and environmental cues, including nutritional and metabolic signals. During the last decade, we have learned much regarding the essential roles of kisspeptins and the neuropeptide pathways that converge on these neurones to modulate kisspeptin signalling, as well as neurokinin B and dynorphin, the co-transmitters of Kiss1 neurones in the arcuate nucleus, and the effects of melanocortins on puberty. Indeed, melanocortins are involved in transmitting the regulatory actions of metabolic cues on pubertal maturation. Intracellular metabolic sensors, such as the AMP-activated protein kinase and the fuel-sensing deacetylase SIRT1, have been shown to contribute to puberty. Further understanding of these signals and regulatory circuits will help uncover the intimacies of the central control of puberty, as well as how alterations in metabolic status, ranging from undernutrition to obesity, affect the pubertal process. Precocious puberty is rare and has a clear female predominance. Central precocious puberty (CPP) is diagnosed when premature activation of the hypothalamic-pituitary axis occurs. Its causes are heterogeneous, with alterations of the central nervous system being of special interest, and with environmental factors also playing a role in some cases. During the last decade, several mutations in different genes (including KISS1, KISS1R, MKRN3 and DLK1) that cause CPP have been discovered. Loss-of-function mutations in MKRN3 are the most common monogenic cause of CPP known to date. Here, we review and update what is known regarding the genotype-phenotype relationship in patients with CPP.

A Putative Adverse Outcome Pathway Network for Disrupted Female Pubertal Onset to Improve Testing and Regulation of Endocrine Disrupting Chemicals

The average age for pubertal onset in girls has declined over recent decades. Epidemiological studies in humans and experimental studies in animals suggest a causal role for endocrine disrupting chemicals (EDCs) that are present in our environment. Of concern, current testing and screening regimens are inadequate in identifying EDCs that may affect pubertal maturation, not least because they do not consider early-life exposure. Also, the causal relationship between EDC exposure and pubertal timing is still a matter of debate. To address this issue, we have used current knowledge to elaborate a network of putative adverse outcome pathways (pAOPs) to identify how chemicals can affect pubertal onset. By using the AOP framework, we highlight current gaps in mechanistic understanding that need to be addressed and simultaneously point towards events causative of pubertal disturbance that could be exploited for alternative test methods. We propose 6 pAOPs that could explain the disruption of pubertal timing by interfering with the central hypothalamic trigger of puberty, GnRH neurons, and by so doing highlight specific modes of action that could be targeted for alternative test method development.

Methylation status of hypothalamic Mkrn3 promoter across puberty

Makorin RING finger protein 3 (MKRN3) is an important factor located on chromosome 15 in the imprinting region associated with Prader-Willi syndrome. Imprinted MKRN3 is expressed in hypothalamic regions essential for the onset of puberty and mutations in the gene have been found in patients with central precocious puberty. The pubertal process is largely controlled by epigenetic mechanisms that include, among other things, DNA methylation at CpG dinucleotides of puberty-related genes. In the present study, we investigated the methylation status of the Mkrn3 promoter in the hypothalamus of the female mouse before, during and after puberty. Initially, we mapped the 32 CpG dinucleotides in the promoter, the 5'UTR and the first 50 nucleotides of the coding region of the Mkrn3 gene. Moreover, we identified a short CpG island region (CpG islet) located within the promoter. Methylation analysis using bisulfite sequencing revealed that CpG dinucleotides were methylated regardless of developmental stage, with the lowest levels of methylation being found within the CpG islet region. In addition, the CpG islet region showed significantly lower methylation levels at the pre-pubertal stage when compared with the pubertal or post-pubertal stage. Finally, in silico analysis of transcription factor binding sites on the Mkrn3 CpG islet identified the recruitment of 29 transcriptional regulators of which 14 were transcriptional repressors. Our findings demonstrate the characterization and differential methylation of the CpG dinucleotides located in the Mkrn3 promoter that could influence the transcriptional activity in pre-pubertal compared to pubertal or post-pubertal period. Further studies are needed to clarify the possible mechanisms and effects of differential methylation of the Mkrn3 promoter.

Gene Polymorphisms Associated with Central Precocious Puberty and Hormone Levels in Chinese Girls

Central precocious puberty (CPP) is associated with adverse health outcomes in females; however, CPP pathogenesis remains unclear. In this study, we investigated the association of 20 single nucleotide polymorphisms (SNPs) in eight genes with CPP risk and hormone levels. A case-control study on 247 and 243 girls with and without CPP, respectively, was conducted at Kunming Children's Hospital, China, from September 2019 to August 2020. The genotype of the SNPs and their haplotypes were identified. Additionally, the effects of the polymorphisms on hormone levels were investigated. Three variants (rs10159082, rs7538038, and rs5780218) in KISS1 and two variants (rs7895833 and rs3758391) in SIRT1 were related to an increased CPP risk (odds ratio (OR) = 1.524, 1.507, 1.409, 1.348, and 1.737; 95% confidence interval (CI) = 1.176-1.974, 1.152-1.970, 1.089-1.824, 1.023-1.777, and 1.242-2.430, respectively). Rs3740051in SIRT1 and rs1544410 in VDR reduced CPP risk (OR = 0.689, 0.464; 95% CI, 0.511-0.928, 0.232-0.925, respectively). Rs1544410, rs7975232, and rs731236 in VDR were negatively correlated with peak follicle-stimulating hormone (FSH; β = -2.181; P=0.045), basal FSH (β = -0.391; P=0.010), and insulin-like growth factor (β = -50.360; P=0.041) levels, respectively. KISS1, SIRT1, and VDR variants were associated with CPP susceptibility, and VDR SNPs influenced hormonal levels in Chinese females with CPP. In particular, VDR polymorphism rs1544410 was associated with both CPP risk and GnRH-stimulated peak FSH levels. Further functional research and large-scale genetic studies of these loci and genes are required to confirm our findings.

Anxiety and Cognition in Cre- Collagen Type II Sirt1 K/O Male Mice

Introduction

Using transgenic collagen type II-specific Sirt1 knockout (CKO) mice we studied the role of Sirt1 in nutritional induced catch up growth (CUG) and we found that these mice have a less organized growth plate and reduced efficiency of CUG. In addition, we noted that they weigh more than control (CTL) mice. Studying the reason for the increased weigh, we found differences in activity and brain function.

Methods

Several tests for behavior and activity were used: open field; elevated plus maze, Morris water maze, and home cage running wheels. The level of Glu- osteocalcin, known to connect bone and brain function, was measured by Elisa; brain Sirt1 was analyzed by western blot.

Results

We found that CKO mice had increased anxiety, with less spatial memory, learning capabilities and reduced activity in their home cages. No significant differences were found between CKO and CTL mice in Glu- osteocalcin levels; nor in the level of brain SIRT1.

Discussion/Conclusion

Using transgenic collagen type II-specific Sirt1 knockout (CKO) mice we found a close connection between linear growth and brain function. Using a collagen type II derived system we affected a central regulatory mechanism leading to hypo activity, increased anxiety, and slower learning, without affecting circadian period. As children with idiopathic short stature are more likely to have lower IQ, with substantial deficits in working memory than healthy controls, the results of the current study suggest that SIRT1 may be the underlying factor connecting growth and brain function.

Functional analysis of the emerging roles for the KISS1/KISS1R signaling pathway in cancer metastasis

Cancer metastasis, a process that primary tumor cells disseminate to secondary organs, is the most lethal and least effectively treated characteristic of human cancers. Kisspeptins are proteins encoded by the KISS1 gene that was originally described as a melanoma metastasis suppressor gene. Then, Kisspeptins were discovered as the natural ligands of the G-protein-coupled receptor 54 (GPR54) that is also called KISS1R. The KISS1/KISS1R signaling is essential to control GnRH secretion during puberty and to establish mammalian reproductive function through the hypothalamic-pituitary-gonadal (HPG) axis. Although KISS1 primarily plays a suppressive role in the metastasis progression in several cancer types, emerging evidence indicates that the physiological effect of KISS1/KISS1R in cancer metastasis is tissue context-dependent and still controversial. Here, we will discuss the epigenetic mechanism regulation of KISS1 gene expression, the context-dependent role of KISS1/KISS1R, pro-/anti-metastasis signaling pathways of KISS1/KISS1R, and the perspective anti-cancer therapeutics via targeting KISS1/KISS1R.

Emerging Roles of Epigenetics in the Control of Reproductive Function: Focus on Central Neuroendocrine Mechanisms

Reproduction is an essential function for perpetuation of the species. As such, it is controlled by sophisticated regulatory mechanisms that allow a perfect match between environmental conditions and internal cues to ensure adequate pubertal maturation and achievement of reproductive capacity. Besides classical genetic regulatory events, mounting evidence has documented that different epigenetic mechanisms operate at different levels of the reproductive axis to finely tune the development and function of this complex neuroendocrine system along the lifespan. In this mini-review, we summarize recent evidence on the role of epigenetics in the control of reproduction, with special focus on the modulation of the central components of this axis. Particular attention will be paid to the epigenetic control of puberty and Kiss1 neurons because major developments have taken place in this domain recently. In addition, the putative role of central epigenetic mechanisms in mediating the influence of nutritional and environmental cues on reproductive function will be discussed.

Genetic and Epigenetic Control of Puberty

Puberty is a complex transitional phase in which reproductive capacity is achieved. There is a very wide variation in the age range of the onset of puberty, which follows a familial, ethnic, and sex pattern. The hypothalamic-pituitary-gonadal axis and several genetic, environmental, and nutritional factors play an important role in the onset of and throughout puberty. Recently, there has been significant progress in identifying factors that affect normal pubertal timing. Different studies have identified single nucleotide polymorphisms (SNPs) that affect pubertal timing in both sexes and across ethnic groups. Single genes are implicated in both precocious and delayed puberty, and epigenetic mechanisms have been suggested to affect the development and function of the GnRH neuronal network and responsiveness of end organs. All these factors can influence normal puberty timing, precocious puberty, and delayed puberty. The objective of this review is to describe recent findings related to the genetic and epigenetic control of puberty and highlight the need to deepen the knowledge of the regulatory mechanisms of this process in the normal and abnormal context.