Exogenous Melatonin Regulates Puberty and the Hypothalamic GnRH-GnIH System in Female Mice

Melatonin secretion across puberty: A systematic review and meta-analysis

BACKGROUND

Melatonin levels decrease with aging and substantially during puberty. Studies have presented distinct melatonin levels in patients with disorders related to their pubertal development compared to healthy controls. The discrepancy suggests that a decrease in melatonin concentrations seen during adolescence might be related to the physical, hormonal, and/or neuronal alterations that occur during the pubertal period. The aim of this review was to analyze the literature reporting melatonin levels in healthy children and adolescents during puberty, and to look for a potential relationship.

METHODS

The Medline and Embase databases were searched on November 28th 2024, including all articles published from 1974 to 2024. Moreover, in the studies eligible for full-text review, a "snowball" search based by backwards referencing was carried out to identify additional studies. This means going through the references of the eligible studies, to find potential other articles relevant for our review and met our inclusion criteria. Lastly, a meta-analysis on serum melatonin concentrations with increasing age and Tanner status was performed.

RESULTS

21 studies were included. 12 studies found a decrease, 5 found no difference and 3 reported an increase in melatonin levels during pubertal advancement. One study could not report secretory alterations but was eligible for inclusion in the meta-analysis. This analysis revealed that Tanner stages were significantly associated with decreasing average as well as peak concentrations of melatonin.

CONCLUSION

The simultaneous occurrence of pubertal progression and chronological aging complicates potential reasons to the decrease observed. However, possible explanations could be related to sex hormones, physical properties of puberty or light exposure. To justify these explanations research in controlled conditions along with biochemical and clinical assessment of pubertal status is needed.

Melatonin Alleviates Circadian Rhythm Disruption-Induced Enhanced Luteinizing Hormone Pulse Frequency and Ovarian Dysfunction

Circadian rhythm disruption (CRD), stemming from sleep disorders and/or shift work, is a risk factor for reproductive dysfunction. CRD has been reported to disturb nocturnal melatonin signaling, which plays a crucial role in female reproduction as a circadian regulator and an antioxidant. The hypothalamic-pituitary-ovarian (HPO) axis regulates female reproduction, with luteinizing hormone (LH) pulse pattern playing a pivotal role in folliculogenesis and steroidogenesis. However, the effect of CRD on the HPO axis and the involvement of melatonin remains unclear. Female CBA/CaJ mice underwent CRD modeling, which involves alternating between standard light conditions and an 8-h advance schedule every 3 days for 8 weeks, whereas control mice were maintained under a standard 12:12-h light/dark (LD) cycle. Subsequent measurements of diurnal melatonin levels, LH pulse patterns assessments via serial tail-tip blood sampling and evaluations of ovarian function were conducted. CRD altered the circadian rhythms of wheel-running activity and melatonin secretion in mice and led to an augmented LH pulse pattern, evidenced by increased LH pulse frequency, mean LH levels, and pituitary LH beta-subunit (LHβ) expression, irregular estrous cycles, abnormal luteal function, altered endocrine function, and ovarian oxidative stress. Melatonin treatment (10 mg/kg/day for 4 weeks) significantly improved the HPO axis disorder in CRD mice, decreasing the enhanced LH pulse frequency and pituitary LHβ expression. These findings were further validated using an in vitro LβT2 cell perfusion model. Furthermore, melatonin restored ovarian function and scavenged reactive oxygen species, thereby preventing apoptosis and preserving ovarian function. This study offers new insights into the impact of CRD on the HPO axis and emphasizes the potential of melatonin supplementation in mitigating its effects on female reproduction.

Melatonin treatment during the breeding season increases testosterone in male green anole lizards (Anolis carolinensis)

Melatonin is a natural hormone that regulates seasonal behaviors in vertebrates by binding to its receptors (MT1 and MT2). Specifically, high levels of melatonin are associated with short photoperiods, often coinciding with the non-breeding season, meaning that melatonin may inhibit seasonal reproduction. Green anole lizards (Anolis carolinensis), have large, active gonads, increased levels of testosterone and estradiol, and increased reproductive behaviors during the breeding season. Previous studies have examined the role of melatonin in seasonal reproduction in this species, but it is unclear how melatonin receptors change seasonally or if melatonin treatment during the early breeding season influences reproduction. In Experiment 1, we measured MT1 and MT2 mRNA expression in the brains and gonads of unmanipulated anoles between breeding and non-breeding seasons. MT1 mRNA expression was significantly higher in the male brain during the breeding season compared to the non-breeding season, and MT1 mRNA levels were generally higher compared to MT2. This suggests that melatonin may regulate seasonal reproduction through MT1 in the brain, and higher levels during the breeding season may compensate for low seasonal levels of melatonin. In Experiment 2, anoles were treated with melatonin or a blank control for 10 weeks during the breeding season. In males, melatonin treatment increased testosterone levels. This suggests that rather than inhibiting reproduction, continuous high doses of melatonin may increase reproductive hormones during the breeding season. Our findings support the role of melatonin in modulating seasonal reproduction, but the exact mechanisms behind melatonin's stimulatory effect is unclear.

Association of screen exposure/sedentary behavior and precocious puberty/early puberty

Background

In recent years, with the development of society, children's daily exposure to screen time has gradually increased. Screen exposure and sedentary behavior have brought a host of harms to children's lives. The aim of this study was to explore the effects of screen exposure and sedentary behavior on precocious puberty and early development.

Methods

This is a cross-sectional study in the school-based population. A total of 3,560 children were recruited from Qufu City, Shandong province using multistage stratified cluster random sampling. All study subjects had a physical examination by professional pediatricians in October 2019, and were investigated with health questionnaires. Precocious puberty is defined as development of secondary sexual signs in boys before 9 years or in girls before 8 years. Screen time was calculated as the average of screen time on weekdays and weekend days, and sedentary time was calculated as the average of sedentary time on weekdays and weekend days. After adjusting for potential confounders, logistic regression was used to examine the association between screen exposure and sedentary behavior and early puberty and precocious puberty.

Results

Sedentary time was a risk factor for precocious puberty and early development (OR = 1.428, 95% CI = 1.087-1.876) in girls without adjustment. No significant association was found between screen exposure and early puberty and early development both in girls and boys.

Conclusions

Excessive sedentary behavior was associated with an increased risk of early puberty, especially in girls, while there was no significant association between screen exposure and early puberty and early development. In addition, further longitudinal investigations are needed to determine the causal relationship between screen exposure, sedentary behavior and precocious puberty.

Overlapping action of melatonin and female reproductive hormones-Understand the impact in pregnancy and menopause

Melatonin is an indolamine secreted to circulation by the pineal gland according to a circadian rhythm. Melatonin levels are higher during nighttime, and the principal function of this hormone is to organize the temporal night and day distribution of physiological adaptive processes. Besides hormonal pineal production, melatonin is synthesized in various organs and tissues like the ovaries or the placenta for local utilization. In addition to its function as a circadian messenger, melatonin is also associated with many physiological functions. For example, melatonin has antioxidant properties and is involved in the regulation of energy and bone metabolism, and reproduction. Melatonin impacts several stages of reproduction and the action across the hypothalamus-pituitary-gonadal axis is well described. However, it is not well understood how those actions impact the female reproductive hormones secretion nor the consequent physiological outcomes. Thus, the first part of this chapter describes the regulation of female reproductive hormone synthesis by melatonin. Moreover, melatonin and female reproductive hormones have coincident physiological functions. Life stages like pregnancy or menopause are characterized by alterations in the reproductive hormones secretion that may be associated with certain physiological stages. Therefore, the second part discusses whether melatonin fluctuations could have an overlapping role with reproductive hormones in contributing to clinical outcomes associated with pregnancy and menopause.

Melatonin, modulation of hypothalamic activity, and reproduction

Light is the most reliable environmental cue allowing animals to breed successfully when conditions are optimal. In seasonal breeders, photoperiod (length of daylight) information is sensed by the eyes and transmitted to the suprachiasmatic nucleus, the master clock region located in the hypothalamus. This structure has a 24-h firing rhythm involving a cycle of clock protein synthesis and degradation, and provides the timing to synchronize the synthesis and release of melatonin, the chemical signal that transduces the photoperiod information. The enzyme arylalkylamine N-acetyltransferase, responsible for melatonin synthesis in the pineal gland, is modulated by environmental light. Melatonin is secreted during the dark hours of the night to blood circulation and cerebrospinal fluid conveying photoperiod information to other tissues. Melatonin exerts its action by binding to specific membrane receptors MT1 and MT2, and can modulate several pathways including neurotransmitters, and hormones like kisspeptin, the gonadotropin-inhibitory hormone, and thyroid hormones, all of them impacting on gonadotropin-releasing hormone (GnRH) secretion. Then, GnRH will modulate in turn the reproductive axis. In conclusion, acting as a transducer of photoperiod information, this hormone exerts precisely timed activation of different pathways that modulate seasonal breeding ensuring optimal conditions for reproduction.

Therapeutic effects of melatonin in female mice with central precocious puberty by regulating the hypothalamic Kiss-1/Kiss1R system

In recent years, central precocious puberty (CPP) in children is becoming more common, which seriously affects their physical and psychological health and requires finding a safe and effective treatment method. The aim of this study was to investigate the therapeutic effect of melatonin on CPP. A CPP model was established by subcutaneous injection of 300 micrograms of danazol into 5-day-old female mice, followed by treatment with melatonin and leuprolide. The vaginal opening was checked daily. Mice were weighed, gonads were weighed, gonadal index was calculated, and gonadal development was observed by hematoxylin and eosin (HE) staining. Serum follicle stimulating hormone (FSH), luteinizing hormone (LH) and estradiol (E2) levels were measured by ELISA. By using RT-PCR and Western blotting, the mRNA and protein expression of the hypothalamus Kiss-1, Kiss-1 receptor (Kiss1R), gonadotropin-releasing hormone (GnRH), and pituitary GnRH receptor (GnRHR) were identified. The results showed that melatonin delayed vaginal opening time and reduced body weight, gonadal weight and indices in female CPP mice. Melatonin treatment prevents uterine wall thickening and ovarian luteinization in female CPP mice. Melatonin treatment reduces serum concentrations of FSH, LH, and E2 in female CPP mice. Melatonin suppressed the expressions of Kiss-1, Kiss1R and GnRH in the hypothalamus, and the expression of GnRHR in the pituitary of the female CPP mice. Our results suggest that melatonin can inhibit the hypothalamic-pituitary-gonadal (HPG) axis by down-regulating the Kiss-1/Kiss1R system, thereby treating CPP in female mice.

Pineal cysts may promote pubertal development in girls with central precocious puberty: a single-center study from China

Introduction

Pineal cysts have long been considered a benign intracranial variation. However, in our clinical practice, it has been observed that some children with central precocious puberty (CPP) who have pineal cysts experience rapid progression in adolescent development. In recent years, there has been a significant increase in the prevalence of CPP in girls, leading to more diagnoses of CPP among children with pineal cysts. Despite this, there is no consensus regarding whether pineal cysts contribute to CPP as one of its organic factors. This study aimed to analyze the clinical characteristics of pineal cysts in children with CPP and explore the potential effects of pineal cysts on puberty development.

Methods

This single-center study retrospectively analyzed clinical data from girls aged 3 to 10 years who underwent head/pituitary magnetic resonance imaging at the Children's Hospital Affiliated to Zhengzhou University between 2019 and 2022. The study categorized the detection rates of pineal cysts based on systematic disease classification and compared the rates of cyst detection between girls diagnosed with CPP and those without CPP. Subsequently, CPP-diagnosed girls with pineal cysts were examined. Among CPP-diagnosed girls meeting the study's criteria, those with pineal cysts formed the 'cyst group,' while those without cysts were matched in a 1:1 ratio based on age and body mass index to form the 'non-cyst group.' Comparative analyses were conducted to assess the clinical characteristics between these two groups. CPP-diagnosed girls with cysts were further subdivided into three groups according to cyst size (≤5 mm, 5.1-9.9 mm, and ≥10 mm) to investigate potential differences in clinical characteristics among these subgroups. The study involved an analysis of clinical data from girls diagnosed with CPP and included imaging follow-ups to explore the progression of pineal cysts over time.

Results

Among the 23,245 girls who underwent head/pituitary magnetic resonance imaging scans, the detection rate of pineal cysts was 3.6% (837/23,245), with most cases being associated with endocrine diseases. The detection rate of pineal cysts in CPP patients was 6.4% (262/4099), which was significantly higher than the 3.0% (575/19,146) in patients without CPP. In comparison to the non-cyst group, the cyst group exhibited statistically significant increases in estradiol levels, peak luteinizing hormone (LH) levels, peak LH/follicle-stimulating hormone (FSH) ratios, uterine body length, and cervix length (P < 0.001). As cyst size increased, there were significant rises in LH peak, peak LH/FSH ratio, uterine body length, and cervical length (P < 0.01). Estradiol levels and left ovarian volume also showed an increasing trend (P < 0.05). Among girls who underwent follow-up imaging, 26.3% (5/19) exhibited an increase in cyst size.

Conclusion

Pineal cysts are relatively common in children with CPP. They may affect the pubertal development process, with larger cysts correlating to faster pubertal development. Therefore, the authors hypothesize that pineal cysts may trigger CPP in some cases, especially when the cysts are larger than 5 mm in size, as indicated by our data.

Analysis of the Imprinting Status and Expression of the MAGEL2 Gene During Initiation at Puberty in the Dolang Sheep

Genomic imprinting refers to the expression of parent-specific genes in diploid mammalian cells. MAGEL2 gene is a maternally imprinted gene that has been identified in mice and humans and is associated with the onset of puberty. The purpose of this study was to investigate its imprinting status and its relationship with the onset of puberty in Dolang sheep. The sequence of 3734 bp cDNA of MAGEL2 in Dolang sheep was obtained by cloning and sequencing, encoding 1173 amino acids. The results of the nucleotide and amino acid similarity analysis showed that it was highly conserved among different mammalian species. The MAGEL2 gene was expressed monoallelically in the tissues of adult and neonatal umbilical cords, and the expressed allele was paternally inherited. Real Time quantitative PCR (RT-qPCR) results showed that the MAGEL2 gene was highly expressed in the hypothalamus and pituitary gland, increased significantly from prepuberty to puberty, and decreased significantly after puberty. This study suggests that MAGEL2 is a paternally expressed and maternally imprinted gene in Dolang sheep, which may be involved in the initiation of puberty in Dolang sheep. This study provides a theoretical basis for further research on the mechanism of the imprinted gene MAGEL2 regulating the onset of puberty in sheep, and provides a new idea for the future research on the mechanism of onset of puberty in sheep.