Ovarian expression of melatonin Mel(1a) receptor mRNA during mouse development

Exploring melatonin's multifaceted role in female reproductive health: From follicular development to lactation and its therapeutic potential in obstetric syndromes

BACKGROUND

Melatonin is mainly secreted by the pineal gland during darkness and regulates biological rhythms through its receptors in the suprachiasmatic nucleus of the hypothalamus. In addition, it also plays a role in the reproductive system by affecting the function of the hypothalamic-pituitary-gonadal axis, and by acting as a free radical scavenger thus contributing to the maintenance of the optimal physiological state of the gonads. Besides, melatonin can freely cross the placenta to influence fetal development. However, there is still a lack of overall understanding of the role of melatonin in the reproductive cycle of female mammals.

AIM OF REVIEW

Here we focus the role of melatonin in female reproduction from follicular development to delivery as well as the relationship between melatonin and lactation. We further summarize the potential role of melatonin in the treatment of preeclampsia, polycystic ovary syndrome, endometriosis, and ovarian aging.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Understanding the physiological role of melatonin in female reproductive processes will contribute to the advancement of human fertility and reproductive medicine research.

Chemotherapy and female fertility

Chemotherapy to treat cancer is usually responsible for early ovarian follicle depletion. Ovarian damage induced by cancer treatments frequently results in infertility in surviving patients of childbearing age. Several fertility preservation techniques have been developed. Nowadays, oocyte or embryo cryopreservation with or without ovarian stimulation and cryopreservation of the ovarian cortex are the most commonly used. However, these methods may be difficult to implement in some situations, and subsequent use of the cryopreserved germ cells remains uncertain, with no guarantee of pregnancy. Improved knowledge of the molecular mechanisms and signaling pathways involved in chemotherapy-induced ovarian damage is therefore necessary, to develop new strategies for fertility preservation. The effects of various chemotherapies have been studied in animal models or in vitro on ovarian cultures, suggesting various mechanisms of gonadotoxicity. Today the challenge is to develop molecules and techniques to limit the negative impact of chemotherapy on the ovaries, using experimental models, especially in animals. In this review, the various theories concerning ovarian damage induced by chemotherapy will be reviewed and emerging approaches for ovarian protection will be explained.

Effects of melatonin on development and hormone secretion of sheep theca cells in vitro

Theca cells (TCs) play a unique role in the structure and function of the ovary. They are not only the structural basis of the follicle but also the androgen-secreting cells in female mammals, which can affect the normal development and atresia of the follicle. The results showed that melatonin receptor (MTR) MT1 and MT2 were expressed on sheep TCs. In the present study, the effects of different concentrations of MT at 0, 10^-10, 10^-8, 10^-6 and 10^-4 M/L on sheep TCs with regards to the antioxidant levels, proliferation, apoptosis and steroid hormone secretion were investigated. The results showed that in sheep TCs, all concentrations of MT significantly decreased reactive oxygen species (ROS) concentration and BAX expression; increased Cat, Sod1, and BCL-2 expression. The proliferation viability of TCs was significantly inhibited in all groups except for 10^-10 M/L MT, and the expression of cyclin D1 and CDK4 was significantly reduced. MT significantly increased StAR expression and progesterone secretion in TCs, but there was no significant effect on androgen secretion and CYP11A1, CYP17A1 and 3β-HSD expression in all groups. MT-induced progesterone secretion was completely inhibited by Luzindole (a nonspecific MT1 and MT2 inhibitor) and partially inhibited by 4p-PDOT (specific MT2 inhibitor). MT-induced progesterone secretion can be inhibited by LY294002 (PI3K/AKT pathway inhibitor). This study indicated that MT inhibits apoptosis and proliferation of in vitro cultured sheep TCs, which has implications for slowing ovarian atresia and aging. MT activates the PI3K/Akt pathway to mediate the synthesis and secretion of progesterone by TCs. This study provides a basis for further exploration of the role of TCs on follicle development and ovarian steroid hormone secretion.

Immunolocalization of melatonin receptors in bovine ovarian follicles and in vitro effects of melatonin on growth, viability and gene expression in secondary follicles

This study aims to investigate the (1) expression of melatonin receptors types 1A/B (MTNR1A/B) in bovine ovaries and (2) the in vitro effects of melatonin on secondary follicle development, antrum formation, viability, and expression of messenger ribonucleic acid (mRNA) for superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase-1 (GPX1) and peroxiredoxin 6 (PRDX6). The expression of MTNR1A/B in bovine ovarian follicles was demonstrated by immunohistochemistry. To choose the most effective concentration of melatonin on follicular growth and viability, isolated secondary follicles were cultured individually at 38.5°C, with 5% CO₂ in air, for 18 d in TCM-199⁺ alone or supplemented with 10^-11, 10^-9, 10^-7 or 10^-5 M melatonin. Then, melatonin receptor antagonist, luzindole, was tested to further evaluate the mechanisms of actions of melatonin, that is, the follicles were cultured in control medium alone or supplemented with 10^-7 M melatonin, 10 µM luzindole and both 10^-7 M melatonin and 10 µM luzindole. Follicular growth, morphology and antrum formation were evaluated at days 6, 12 and 18. At the end of culture, viability of secondary follicles was analyzed by calcein-AM and ethidium homodimer-1, and the relative levels of mRNA for SOD, CAT, GPX1 and PRDX6 were evaluated by real time polymerase chain reaction. Immunohistochemistry results showed expression of MTNR1A/B in oocyte and granulosa cells of primordial, primary, secondary and antral follicles. Secondary follicles cultured in medium supplemented with melatonin at different concentrations had well preserved follicles after 18 d of culture. Furthermore, follicles cultured in presence of 10^-7 M melatonin presented significantly higher diameters than those cultured in other treatments. The presence of melatonin receptor antagonist, luzindole, blocked the effects of melatonin on follicular growth and viability. In addition, follicles cultured in medium containing only melatonin had significantly higher rates of antrum formation. Follicles cultured in medium containing only melatonin had higher relative levels of mRNA for CAT, SOD and PRDX-6 than those cultured with both melatonin and luzindole. Follicles cultured with luzindole only or both melatonin and luzindole had lower relative levels of mRNA for PRDX6 and GPX1 than those cultured control medium. In conclusion, melatonin promotes growth of bovine secondary follicles through its membrane-coupled receptors, while luzindole blocks the effects of melatonin on follicle growth and reduces the expression of antioxidant enzymes in cultured follicles.

Therapeutic Effect of Melatonin in Premature Ovarian Insufficiency: Hippo Pathway Is Involved

Objective

Premature ovarian insufficiency (POI) is a female reproductive disorder of unknown etiology with no definite pathogenesis. Melatonin (MT) is an endogenous hormone synthesized mainly by pineal cells and has strong endogenous effects in regulating ovarian function. To systematically explore the pharmacological mechanism of MT on POI therapy, a literature review approach was conducted at the signaling pathways level.

Methods

Relevant literatures were searched and downloaded from databases, including PubMed and China National Knowledge Infrastructure, using the keywords “premature ovarian insufficiency,” “Hippo signaling pathways,” and “melatonin.” The search criteria were from 2010 to 2022. Text mining was also performed.

Results

MT is involved in the regulation of Hippo signaling pathway in a variety of modes and has been correlated with ovarian function.

Conclusions

The purpose of this review is to summarize the research progress of Hippo signaling pathways and significance of MT in POI, the potential crosstalk between MT and Hippo signaling pathways, and the prospective therapy.

The Effect of Melatonin on OCT4 Expression and Granulosa Cell Growth in Female Mice

Melatonin is mainly secreted by the pineal gland as a neurotransmitter. Moreover, melatonin is also produced by the ovary and plays important roles in female reproduction. However, it is unclear whether melatonin has any effect on the transition from the preantral follicle to the early antral follicle. Octamer-binding transcription factor 4 (OCT4) is important to granulosa cells development, which is regulated by gonadotropin. And these regulations are mediated by the GSK3β/β-catenin pathway via the activated PI3K/Akt signaling. The aim of the present study was to determine the effects and the possible mechanisms of melatonin on ovarian cells development. The results showed that melatonin inhibited granulosa cells development, which was accompanied by the downregulation of OCT4 expression. Meanwhile, melatonin also decreased the expression of p-GSK3β (glycogen synthase kinase 3 beta), p-Akt, β-catenin, and its translocation to the nucleus in granulosa cells. Moreover, melatonin attenuated the effects of FSH in vitro and eCG in vivo on these regulations. In conclusion, this study shows that melatonin inhibits ovarian cell development by downregulating the OCT4 expression level, which is possibly mediated by inhibiting the PI3K/Akt and GSK3β/β-catenin pathway. Melatonin attenuates the effects of gonadotropin on ovarian granulosa cells as a negative regulator.

Adipose-Derived Mesenchymal Stem Cells: A Promising Tool in the Treatment of pre mature ovarian failure

Despite being rare, primary ovarian insufficiency (POI) is a significant cause of infertility and deficiency of ovarian hormone in women. Several health risks are also associated with POI, which include dry eye syndrome, reduced density of bones and enhanced fracture risks, troublesome menopausal symptoms, early development of cardiovascular disease, and psychological effects such as declined cognition, reduced perceived psychological support, anxiety, and depression. Replacing premenopausal levels of ovarian sex steroids through proper hormone replacement therapy could improve the quality of life for POI women and ameliorate related health risks. Herein, POI and its complications, in addition to hormone replacement therapies, which are safe and effective, are discussed. It is proposed that the use of HRT) Hormone replacement therapy (formulations which mimic normal production of ovarian hormones could reduce POI-associated morbidity rates if they are continued by the age 50, which is approximately the natural age of menopause. Particular populations of POI women are also addressed, which include those with enhanced risk of ovarian or breast cancer, those with Turner syndrome, those approaching natural menopause, and those who are breastfeeding. It is generally predicted that stem cell-based therapies would be both safe and effective. In fact, several types of cells have been described as safe, though their effectiveness and therapeutic application are yet to be defined. Several factors exist which could affect the results of treatment, such as cell handling, ex-vivo preparation strategies, variations in tissue of origin, potency, and immunocompatibility. Accordingly, cell types potentially effective in regenerative medicine could be recognized. Notably, products of MSCs from various sources of tissues show different levels of regenerative capabilities. The ultimate focus of the review is on adipose tissue-derive MCSs (ADMSCs), which possess exceptional features such as general availability, great ability to proliferate and differentiate, immunomodulatory capabilities, and low immunogenicity.

Continuous gibberellin A3 exposure from weaning to sexual maturity induces ovarian granulosa cell apoptosis by activating Fas-mediated death receptor signaling pathways and changing methylation patterns on caspase-3 gene promoters

Information on the effects of gibberellic acid (gibberellin A3, GA3) on ovarian follicle development is limited. In our present study, 21-day-old female Wistar rats were exposed to GA3 by gavage (25, 50, and 100 mg/kg body weight, once per day) for eight weeks to evaluate the influence of GA3 on ovarian follicle development. After treatment, significant (P < 0.05) increases (to 40.17 % and 44.5 %, respectively) in atretic follicle proportions and significant decreases (to 19.49 % and 17.86 %, respectively) in corpus luteum proportions were observed in the 50 and 100 mg/kg treatment groups compared to the control group. Significant (P < 0.05) increases (to 31.3 % and 42.0 %, respectively) in follicle apoptosis were observed in the 50 and 100 mg/kg treatment groups by transmission electron microscopy and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays. Significantly increased expression of caspase-3, caspase-8, caspase-9 and Fas was observed by real-time PCR and Western blotting. Bisulfite sequencing PCR (BSP) revealed obviously decreased total methylation percentages of the caspase-3 promoter region in the two treatment groups. Real-time quantitative PCR also showed significantly decreased mRNA expression of DNA methyltransferase (Dnmt) 3a and Dnmt3b. Further in vitro studies showed that a DNA methylation inhibitor could enhance the GA3-induced increase in the mRNA expression of caspase-3. Overall, our present study indicates that GA3 administration from weaning until sexual maturity can affect ovarian follicle development by inducing apoptosis and suggests that signaling through the Fas-mediated apoptotic pathway may be an important underlying mechanism of this apoptosis. In addition, GA3-induced aberrant DNA methylation patterns might be partly responsible for upregulation of caspase-3 gene expression.

Fetal liver mesenchymal stem cells restore ovarian function in premature ovarian insufficiency by targeting MT1

Background

With the development of regenerative medicine and tissue engineering technology, almost all stem cell therapy is efficacious for the treatment of premature ovarian failure (POF) or premature ovarian insufficiency (POI) animal models, whereas little stem cell therapy has been practiced in clinical settings. The underlying molecular mechanism and safety of stem cell treatment in POI are not fully understood. In this study, we explored whether fetal mesenchymal stem cells (fMSCs) from the liver restore ovarian function and whether melatonin membrane receptor 1 (MT1) acts as a regulator for treating POI disease.

Methods

We designed an in vivo model (chemotherapy-induced ovary damage) and an in vitro model (human ovarian granulosa cells (hGCs)) to understand the efficacy and molecular cues of fMSC treatment of POI. Follicle development was observed by H&E staining. The concentration of sex hormones in serum (E2, AMH, and FSH) and the concentration of oxidative and antioxidative metabolites and the enzymes MDA, SOD, CAT, LDH, GR, and GPx were measured by ELISA. Flow cytometry (FACS) was employed to detect the percentages of ROS and proliferation rates. mRNA and protein expression of antiapoptotic genes (SURVIVIN and BCL2), apoptotic genes (CASPASE-3 and CASPASE-9), and MT1 and its downstream genes (JNK1, PCNA, AMPK) were tested by qPCR and western blotting. MT1 siRNA and related antagonists were used to assess the mechanism.

Results

fMSC treatment prevented cyclophosphamide (CTX)-induced follicle loss and recovered sex hormone levels. Additionally, fMSCs significantly decreased oxidative damage, increased oxidative protection, improved antiapoptotic effects, and inhibited apoptotic genes in vivo and in vitro. Furthermore, fMSCs also upregulated MT1, JNK1, PCNA, and AMPK at the mRNA and protein levels. With MT1 knockdown or antagonist treatment in normal hGCs, the protein expression of JNK1, PCNA, and AMPK and the percentage of proliferation were impaired.

Conclusions

fMSCs might play a crucial role in mediating follicular development in the POI mouse model and stimulating the activity of POI hGCs by targeting MT1.

The Impact of Chemotherapy on the Ovaries: Molecular Aspects and the Prevention of Ovarian Damage

Cancer treatment, such as chemotherapy, induces early ovarian follicular depletion and subsequent infertility. In order to protect gametes from the gonadotoxic effects of chemotherapy, several fertility preservation techniques—such as oocyte or embryo cryopreservation with or without ovarian stimulation, or cryopreservation of the ovarian cortex—should be considered. However, these methods may be difficult to perform, and the future use of cryopreserved germ cells remains uncertain. Therefore, improving the methods currently available and developing new strategies to preserve fertility represent major challenges in the area of oncofertility. Animal and ovarian culture models have been used to decipher the effects of different cytotoxic agents on ovarian function and several theories regarding chemotherapy gonadotoxicity have been raised. For example, cytotoxic agents might (i) have a direct detrimental effect on the DNA of primordial follicles constituting the ovarian reserve and induce apoptosis; (ii) induce a massive growth of dormant follicles, which are then destroyed; or (ii) induce vascular ovarian damage. Thanks to improvements in the understanding of the mechanisms involved, a large number of studies have been carried out to develop molecules limiting the negative impact of chemotherapy on the ovaries.

Protective effects of melatonin against nicotine-induced disorder of mouse early folliculogenesis

In this paper, we show that neonatal mice injected for five consecutive days with nicotine display impaired germ cell cyst breakdown and primordial follicle assembly resulting in decreased ovarian reserve lasting until sex maturation age. The effects of nicotine on the pups ovaries were associated with decreased expression of oocyte specific genes such as Nobox, Lhx8, Figlα and Sohlh2. Moreover, the ovaries of pups injected with nicotine showed increased level of cell oxidative stress and autophagic markers (upregulation of AMPKα-1, increased ratio LC3-II/LC3-I, downregulation of AKT and mTOR). Noteworthy, all these effects were counteracted by the administration of the hormone melatonin in 1 μM. In vitro culture of 0 dpp ovaries for 5 days in the presence of 10 μM nicotine reproduced its effect on germ cell cyst breakdown and primordial follicle assembly, furthermore it also revealing about 20% reduction of somatic cells proliferation, and these effects was prevented when melatonin was added to the medium. Taken together these results show that nicotine exposure can adversely affect the establishment of the ovarian reserve in the mouse likely by locally inducing cellular stress altering the primordial follicle assembly and that melatonin, however, is able to counteract such effects.

Melatonin protects against cisplatin-induced ovarian damage in mice via the MT1 receptor and antioxidant activity

This study evaluated the receptor- and/or antioxidant stress-mediated mechanisms by which melatonin prevents the ovarian toxicity of cisplatin treatment. The expression of the MT1 receptor in mouse ovaries was investigated by immunohistochemistry. Pretreatment with melatonin (5, 10, or 20 mg/kg body weight, i.p.) before cisplatin (5 mg/kg body weight, i.p.) was administered to mice once daily for 3 days (phase I). The pharmacological modulation via melatonin type 1 and/or 2 receptors was analyzed by administration of receptor antagonists (luzindole: nonselective MT1/MT2 antagonist; 5 mg/kg body weight or 4-phenyl-2-propionamidotetralin: selective MT2 antagonist; 4 mg/kg body weight) once daily for 3 days, 15 min before the treatment with melatonin and cisplatin (phase II). Thereafter, the ovaries were harvested and used for histological (morphology and activation), immunohistochemical (PCNA, activated caspase-3 and bcl-2 expression), terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, and fluorescence (reactive oxygen species [ROS], glutathione [GSH], and active mitochondria levels) analyses. The expression of the MT1 protein in mouse ovaries was documented. Pretreatment with 20 mg/kg melatonin before cisplatin administration preserved the normal follicular morphology and cell proliferation rate, reduced apoptosis, ROS production, mitochondrial damage and increased GSH expression, as compared to the cisplatin treatment alone. Additionally, administration of the nonselective MT1/MT2 receptor antagonist inhibited the melatonin ovarian protection from the cytotoxic effects of cisplatin. However, administration of a selective MT2 antagonist did not modify the protective effects observed at 20 mg/kg melatonin. In conclusion, pretreatment with 20 mg/kg melatonin effectively protected the ovaries against cisplatin-induced damage. Moreover, the MT1 receptor and melatonin antioxidant effects mediated this cytoprotective activity.

Research progress on the role of melatonin and its receptors in animal reproduction: A comprehensive review

Melatonin and its receptors play a crucial role in the regulation of the animal reproductive process, primarily in follicular development. However, the role that melatonin performs in regulating hormones related with reproduction remains unclear. Melatonin and its receptors are present both in female and male animals' organs, such as ovaries, heart, brain and liver. Melatonin regulates ovarian actions and is a key mediator of reproductive actions. Melatonin has numerous effects on animal reproduction, such as protection of gametes and embryos, response to clock genes, immune-neuroendocrine, reconciliation of seasonal variations in immune function, and silence or blockage of genes. The growth ratio of reproductive illnesses in animals has raised a remarkable concern for the government, animal caretakers and farm managers. In order to resolve this challenging issue, it is very necessary to conduct state-of-the-art research on melatonin and its receptors because melatonin has considerable physiognomies. This review article presents a current contemporary research conducted by numerous researchers from the entire world on the role of melatonin and its receptors in animal reproduction, from the year 1985 to the year 2017. Furthermore, this review shows scientific research challenges related to melatonin receptors and their explanations based on the findings of 172 numerous research articles, and also represents significant proficiencies of melatonin in order to show enthusiastic study direction for animal reproduction researchers.

Melatonin reduces oxidative damage in mouse granulosa cells via restraining JNK-dependent autophagy

Oxidative stress-induced granulosa cell (GCs) injury is believed to be a common trigger for follicular atresia. Emerging evidence indicates that excessive autophagy occurs in mammalian cells with oxidative damage. N-acetyl-5-methoxytrypamine (melatonin) has been shown to prevent GCs from oxidative injury, although the exact mechanism remains to be elucidated. Here, we first demonstrated that the suppression of autophagy through the JNK/BCL-2/BECN1 signaling is engaged in melatonin-mediated GCs protection against oxidative damage. Melatonin inhibited the loss of GCs viability, formation of GFP-MAP1LC3B puncta, accumulation of MAP1LC3B-II blots, degradation of SQSTM1 and the expression of BECN1, which was correlated with impaired activation of JNK during oxidative stress. On the other hand, blocking of autophagy and/or JNK also reduced the level of H2O2-induced GCs death, but failed to further restore GCs viability in the presence of melatonin. Particularly, the suppression of autophagy provided no additional protective effects when GCs were pretreated with JNK inhibitor and/or melatonin. Importantly, we found that the enhanced interaction between BCL-2 and BECN1 might be a responsive mechanism for autophagy suppression via the melatonin/JNK pathway. Moreover, blocking the downstream antioxidant system of melatonin using specific inhibitors further confirmed a direct role of melatonin/JNK/autophagy axis in preserving GCs survival without scavenging reactive oxygen species (ROS). Taken together, our findings uncover a novel function of melatonin in preventing GCs from oxidative damage by targeting JNK-mediated autophagy, which might contribute to develop therapeutic strategies for patients with ovulation failure-related disorders.

Effect of melatonin on bovine theca cells in vitro

Melatonin affects granulosa cell function in several species but its function in theca cells is less clear, particularly in monotocous animals. Thus, the objectives of this study were to determine the effects of melatonin on theca cell steroidogenesis, gene expression and cell proliferation in a monotocous species, namely cattle. Ovaries were collected from a local bovine abattoir, from which theca cells were isolated from large (8–22 mm) follicles and treated with various hormones in serum-free medium for 24 h or 48 h. Melatonin caused a dose-dependent inhibition (P < 0.05) of LH+insulin-like growth factor 1 (IGF1)-induced androstenedione and progesterone production. Also, melatonin inhibited (P < 0.05) LH+IGF1-induced expression of steroidogenic acute regulatory protein (StAR) mRNA (via real-time polymerase chain reaction) in theca cells, but it had no effect (P > 0.10) on cytochrome P450 11A1 (CYP11A1) and cytochrome P450 17A1 (CYP17A1) mRNA abundance. In LH+IGF1-treated theca cells, melatonin decreased caspase 3 (CASP3) mRNA to levels similar to those observed in LH-treated theca cells. In contrast, melatonin increased (P < 0.05) the number of bovine theca cells in both LH- and LH+IGF1-treated cultures. In conclusion, melatonin may act as an endocrine regulator of ovarian function in cattle by stimulating theca cell proliferation and inhibiting differentiation via inhibition of hormone-induced steroidogenesis.

Knockdown of melatonin receptor 1 and induction of follicle-stimulating hormone on the regulation of mouse granulosa cell function

Melatonin receptor 1 (MT1) performs a critical role in the regulation of the animal reproductive system, particularly in follicular growth, and has a considerable effect on reproductive performance. However, the role that MT1 plays in regulating hormones associated with reproduction remains unclear. This study was designed to examine the physiological role of constitutive MT1 silencing and follicle stimulating hormone (FSH) treatment in reproduction, making use of mouse granulosa cells (mGCs) as a model. To understand the constitutive role of MT1 in ovarian physiology, the RNAi-Ready pSIREN-RETROQ-ZsGreen Vector mediated recombinant pshRNA was used to silence MT1 gene expression. Furthermore, we observed that the expression of MT1 was successfully inhibited both at the protein and mRNA levels (P<0.001). We demonstrated that RNAi-B-mediated MT1 down-regulation significantly promoted apoptosis (P<0.001), inhibited proliferation, and regulated the cell cycle at the S-phase; conversely, FSH treatment partially aided the apoptotic effect and improved proliferation but showed a significant effect at the S-phase of the cell cycle. Transitory knockdown of MT1 proved essential in the function of mGCs, as it significantly decreased cyclic adenosine monophospahte (cAMP) level and increased cell apoptosis. Following knockdown of MT1, the expression of Bax was significantly up-regulated (P<0.001), but Bcl-2 was slightly down-regulated, both at the transcriptional and at translational levels. Moreover, the silencing of MT1 and its constitutive effect on FSH significantly promoted an increase in estradiol (P<0.001) and slightly decreased the concentration of progesterone. Together, our data indicates that MT1 suppression leads to interference in the normal physiological function of the ovary by enhancing follicular apoptosis, inhibiting proliferation, and influencing hormonal signaling, whereas constitutive FSH treatment counteracted the negative down-regulatory effects of MT1 on mGCs.

Melatonin influences the sonic hedgehog signaling pathway in porcine cumulus oocyte complexes

Melatonin, which is synthesized in the pineal gland and peripheral reproductive organs, has antioxidant properties and regulates physiological processes. It is well known that melatonin affects in vitro maturation (IVM) of oocytes and embryonic development in many species. However, beneficial effects of melatonin on IVM have been explained mainly by indirect antioxidant effects and little information is available on the underlying mechanism by which melatonin directly acts on porcine cumulus oocyte complexes (COCs). Sonic hedgehog (Shh) signaling is important for follicle development, oocyte maturation, and embryo development, and there may be a relationship between melatonin and Shh signaling. To examine this, we designed three groups: (i) control, (ii) melatonin (10^-9  mol/L), and (iii) melatonin with cyclopamine (2 μmol/L; Shh signaling inhibitor). The aim of this study was to investigate the effects of these agents on cumulus expansion, oocyte maturation, embryo development after parthenogenetic activation (PA), gene expression in cumulus cells, oocytes and blastocysts, and protein expression in COCs. Melatonin significantly increased the proportion of COCs exhibiting complete cumulus expansion (degree 4), PA blastocyst formation rates, and total cell numbers, which were inhibited by addition of cyclopamine. Simultaneously, the expression of cumulus expansion-related genes (Ptgs1, Ptgs2, and Has2) and Shh signaling-related genes (Shh, Pthc1, Smo, and Gli1) and proteins (Ptch1, Smo, and Gli1) in cumulus cells was upregulated in the melatonin-treated group, and these effects were also inhibited by cyclopamine. In conclusion, our results suggest that Shh signaling mediates effects of melatonin to improve porcine cumulus expansion and subsequent embryo development.

Melatonin and Fertoprotective Adjuvants: Prevention against Premature Ovarian Failure during Chemotherapy

Premature ovarian failure is one of the side effects of chemotherapy in pre-menopausal cancer patients. Preservation of fertility has become increasingly important in improving the quality of life of completely recovered cancer patients. Among the possible strategies for preserving fertility such as ovarian tissue cryopreservation, co-treatment with a pharmacological adjuvant is highly effective and poses less of a burden on the human body. Melatonin is generally produced in various tissues and acts as a universally acting antioxidant in cells. Melatonin is now more widely used in various biological processes including treating insomnia and an adjuvant during chemotherapy. In this review, we summarize the information indicating that melatonin may be useful for reducing and preventing premature ovarian failure in chemotherapy-treated female patients. We also mention that many adjuvants other than melatonin are developed and used to inhibit chemotherapy-induced infertility. This information will give us novel insights on the clinical use of melatonin and other agents as fertoprotective adjuvants for female cancer patients.

Melatonin and its receptor MT1 are involved in the downstream reaction to luteinizing hormone and participate in the regulation of luteinization in different species

The functions of melatonin in preovulatory fluid remain elusive. In the current study, we observed that the extremely high level of expression of MT1 in mice granulosa cells was rapidly induced by hCG (equivalent LH) within 2 hours and this was referred as MT1 surge. In cumulus cells, serotonin N-acetyltransferase (SNAT) was also upregulated by hCG and led to elevated melatonin levels in ovarian follicle fluid. Melatonin application before MT1 surge significantly promoted embryo implantation, and this was probably attributed to a rise in progesterone levels in the serum. The mechanistic studies indicated that melatonin/MT1 (MLT/MT1) signaling remarkably improved the expression of corpus luteum marker genes, that is, Akr1c18 and Cyp11a1. High-throughput sequencing results suggested that extracellular matrix (ECM) receptor interaction, focal adhesion, and activation of PI3K/Akt pathway which are involved in granulosa cell luteinization might mediate the actions of MLT/MT1 signal. In addition, this effect on luteinization was compared in different species. It was verified that high melatonin levels exist in serum at estrum of cows and help to improve the first estrus fecundation rate. These results suggested that both melatonin and MT1 are involved in the downstream reaction of hCG (LH) and they play important roles in luteinization. These findings provide the novel information on the physiology of melatonin in animal reproduction.

Melatonin-related genes expressed in the mouse uterus during early gestation promote embryo implantation

Melatonin, a superior antioxidant, is an important molecule which regulates female reproduction due to its receptor-mediated and receptor-independent antioxidant actions. In this study, we investigated the effect of melatonin on early gestation in a mouse model. During early gestation, the expression of the melatonin's rate-limiting enzyme, AANAT, gradually increased - in the uterus while the MT2 melatonin receptor was only expressed at day 2 of gestation and no MT1 was detected. Based on these findings, we conducted a melatonin injection experiment which demonstrated that 15 mg/kg melatonin significantly improved the number of implantation sites and the litter size. Also, the blastocyst and uterus were collected to identify the local action of melatonin. In the melatonin-treated mice, the endometrium was thicker than in the control mice; melatonin also caused an increase in density of uterine glands, and the uterine gland index (UGI) was significantly elevated over that of the control. Serum steroid hormone measurements revealed that at day 6 of gestation (postimplantation), melatonin significantly downregulated the E2 level, with no obvious effects on progesterone. Gene expression assay revealed that melatonin significantly upregulated expression of HB-EGF, a crucial gene involved in implantation as well as its receptor ErbB1 in the blastocyst. In addition, PRA, an important gene which influences the decidual response and luminal cell differentiation, p53, which regulates uterine through leukaemia inhibitory factor (LIF), were both increased after melatonin treatment. These data suggest that melatonin and its MT2 receptor influence early gestation. Exogenous melatonin treatment can improve mouse embryo implantation and litter size, which may have important applications in human reproductive health and animal husbandry.

Melatonin inhibits GnRH-1, GnRH-3 and GnRH receptor expression in the brain of the European Sea Bass, Dicentrarchus labrax

Several evidences supported the existence of melatonin effects on reproductive system in fish. In order to investigate whether melatonin is involved in the modulation of GnRH systems in the European sea bass, we have injected melatonin (0.5 μg/g body mass) in male specimens. The brain mRNA transcript levels of the three GnRH forms and the five GnRH receptors present in this species were determined by real time quantitative PCR. Our findings revealed day–night variations in the brain expression of GnRH-1, GnRH-3 and several GnRH receptors (dlGnRHR-II-1c, -2a), which exhibited higher transcript levels at mid-light compared to mid-dark phase of the photocycle. Moreover, an inhibitory effect of melatonin on the nocturnal expression of GnRH-1, GnRH-3, and GnRH receptors subtypes 1c, 2a and 2b was also demonstrated. Interestingly, the inhibitory effect of melatonin affected the expression of hypophysiotrophic GnRH forms and GnRH receptors that exhibit day–night fluctuations, suggesting that exogenous melatonin reinforce physiological mechanisms already established. These interactions between melatoninergic and GnRH systems could be mediating photoperiod effects on reproductive and other rhythmic physiological events in the European sea bass.

Melatonin effects on Fundulus heteroclitus reproduction

This study aimed to investigate the effects of two different doses (100 nM (M1) and 1 µM (M2)) of exogenous melatonin on the reproductive capacity of Fundulus heteroclitus. Eight days of melatonin exposure significantly increased the fecundity and embryo survival of F. heteroclitus only in the M2 group compared with the control; the hatching rate was unaffected. Moreover, increases in the local expression of the melatonin receptor (mtnr) gene during follicle maturation were found; however, there were no differences between the experimental groups. Furthermore, in vitro melatonin-treated follicles showed a significantly higher germinal vesicle break down percentage compared with the control, while SDS–PAGE showed no difference in the electrophoretic pattern of the major yolk proteins. Nevertheless, densitometry revealed a greater intensity of the 118-, 95- and 40-kDa components in groups treated with melatonin. Finally, Fourier transform infrared microspectroscopy was applied to classify the different stages of oocyte development (Stages I–II, III and IV) on the basis of their macromolecular composition. The effects induced by melatonin on oogenesis were investigated by comparing vibrational spectra of females exposed to melatonin with those of controls. Changes to the Amide I band, corresponding to an increase in β-structure, were found in oocytes of females exposed to the highest melatonin dose. These results highlight the positive role of melatonin, which is able to enhance the reproductive capacity of F. heteroclitus. Further studies are in progress to better explain the molecular mechanisms by which melatonin treatment affects reproduction in this marine species.

Follicular dynamic and immunoreactions of the vitrified ovarian graft after host treatment with variable regimens of melatonin

PROBLEM

This study investigates dose-dependent effects of melatonin on ovarian graft.

METHOD OF STUDY

Vitrified-thawed whole ovaries of newborn mice were grafted into ovariectomized mature ones. Melatonin (20, 50, 100, and 200 mg/kg/day) was administrated to separate groups of host mice for 32 days. IgM and IgG antibodies, Th1 and Th2 cytokines, and melatonin in recipient's blood were measured. Subsequent survival of the grafted ovaries was scored. An assessment of follicular morphology was performed using TUNEL assay and hematoxylin-eosin staining.

RESULTS

The administration of melatonin did not disturb the circadian rhythm of melatonin concentration. The ovarian graft lifespan was prolonged at 200 mg/kg/day melatonin (P < 0.001). However, in doses of higher than 20 mg/kg/day melatonin, the proportion of healthy follicles and ovary size decreased. Th1 cytokines levels were reduced dose dependently. However, the effect of melatonin on Th2 cytokines was not pronounced. IgM and IgG2a decreased in recipients receiving 200 mg/kg/day melatonin in comparison with non-treated group (P < 0.001), while this variables were significantly increased at the dose of 50 mg/kg/day (P < 0.001).

CONCLUSION

Melatonin at 200 mg/kg/day has an immunosuppresent effect and produce prolongation of graft survival. However, the associated reduction in healthy follicles suggests that melatonin in doses of higher than 20 mg/kg/day has no preventative ischemic action.

Melatonin's stimulatory effect on adult hippocampal neurogenesis in mice persists after ovariectomy

In this study, we examined whether melatonin treatment would increase new cell formation in the hippocampus in ovariectomized (OVX) mice. Chronic exogenous melatonin administration increased bromodeoxyuridine (BrdU) (OVX-sham 72 ± 3.2 versus OVX-mel 122 ± 12.0; P < 0.05) and doublecortin (DCX) (OVX-sham 88 ± 3.1 versus OVX-mel 176 ± 9.9; P < 0.05) immunoreactive cells in the hippocampus of ovariectomized mice. This neuronal development was correlated with synaptic plasticity, identified using the Golgi impregnation method to quantify dendritic spines in mouse dentate gyrus (DG). Finally, the antidepressant-like state of the animals was evaluated by the tail suspension test. The results indicate that melatonin acts on birth, survival, and differentiation of new neurons in the hippocampus, stimulates maturation of spines, and exerts an antidepressant-like action under estrogen-deprived conditions, in both a strain- and gender-independent manner, suggesting that this indoleamine may be useful in improving brain functions.

Exogenous melatonin positively influences follicular dynamics, oocyte developmental competence and blastocyst output in a goat model

The role of melatonin in modulating mammalian reproduction is of particular interest; however, its effects on ovarian follicles and their oocytes still remain to be characterized. This study determined the influence of melatonin treatment on follicular growth patterns and on in vitro oocyte developmental competence. In a first experiment, the effects of melatonin supplementation on follicular dynamics were evaluated using daily transrectal ultrasonographies for 21 days, in 7 multiparous Sarda goats receiving a subcutaneous implant of 18 mg of melatonin and in 5 control untreated does. Melatonin caused more follicular waves (5.2 +/- 0.2 versus 4 +/- 0.3; P < 0.05) as the waves were shortened at around 2 days when compared with the non-melatonin treated control goats (P < 0.001). Oocyte developmental competence was evaluated in a second experiment by applying procedures for in vitro embryo production. There were no significant differences in the total number of oocytes obtained from 6 control (n = 192) and 7 melatonin-treated (n = 265) goats given follicle stimulating hormone to induce follicular development. Differences in oocyte developmental competence between the two groups became evident after in vitro fertilization and culture; melatonin increased the rate of cleaved oocytes in comparison with control animals (82.5 versus 63.4%; P < 0.001), advanced timing of embryo development and enhanced blastocyst output (31.5 versus 16.3%; P < 0.01). However, blastocyst quality, as evaluated by cryotolerance and gene expression analysis, was not found to be different between the groups. In conclusion, in vivo melatonin treatment is beneficial for increasing ovarian follicle turnover and improving oocyte developmental competence and kinetics of the blastocyst.

Melatonin activates brain dopaminergic systems in the eel with an inhibitory impact on reproductive function

In the eel, a deficit in gonadotrophin-releasing hormone (GnRH) and a strong dopaminergic (DA) inhibition are responsible for the blockade of gonad development if silver eels are prevented from their reproductive migration. Environmental factors that eels encounter during their oceanic reproductive migration are thought to play an important role in the stimulation of eel pubertal development. We investigated the potential role of melatonin, a known mediator of the effects of external factors on reproductive function in vertebrates. We demonstrated that a long-term melatonin treatment increased brain tyrosine hydroxylase (TH, the rate limiting enzyme of DA synthesis) mRNA expression in a region-dependent way. Melatonin stimulated the dopaminergic system of the preoptic area, which is involved in the inhibitory control of gonadotrophin [luteinising hormone (LH) and follicle-stimulating hormone (FSH)] synthesis and release. Moreover, we showed that the increased TH expression appeared to be consistent with melatonin binding site distribution as shown by 2[(125)I]-melatonin labelling studies. On the other hand, melatonin had no effects on the two eel native forms of GnRH (mGnRH and cGnRH-II) mRNA expression. Concerning the pituitary-gonad axis, we showed that melatonin treatment decreased both gonadotrophin beta-subunit (LHbeta, FSHbeta) mRNA expression and reduced sexual steroid (11-ketotestosterone, oestradiol) plasma levels. This indicates that melatonin treatment had a negative effect on eel reproductive function. To our knowledge, the results of the present study provide the first evidence that melatonin enhances TH expression in specific brain regions in a non-mammalian species. By this mechanism melatonin could represent one pathway by which environmental factors could modulate reproductive function in the eel.

Molecular biology of gonadotropin-releasing hormone (GnRH)-I, GnRH-II, and their receptors in humans

In human beings, two forms of GnRH, termed GnRH-I and GnRH-II, encoded by separate genes have been identified. Although these hormones share comparable cDNA and genomic structures, their tissue distribution and regulation of gene expression are significantly dissimilar. The actions of GnRH are mediated by the GnRH receptor, which belongs to a member of the rhodopsin-like G protein-coupled receptor superfamily. However, to date, only one conventional GnRH receptor subtype (type I GnRH receptor) uniquely lacking a carboxyl-terminal tail has been found in the human body. Studies on the transcriptional regulation of the human GnRH receptor gene have indicated that tissue-specific gene expression is mediated by differential promoter usage in various cell types. Functionally, there is growing evidence showing that both GnRH-I and GnRH-II are potentially important autocrine and/or paracrine regulators in some extrapituitary compartments. Recent cloning of a second GnRH receptor subtype (type II GnRH receptor) in nonhuman primates revealed that it is structurally and functionally distinct from the mammalian type I receptor. However, the human type II receptor gene homolog carries a frameshift and a premature stop codon, suggesting that a full-length type II receptor does not exist in humans.

Melatonin receptors and their regulation: biochemical and structural mechanisms

There is growing evidence demonstrating the complexity of melatonin's role in modulating a diverse number of physiological processes. This complexity could be attributed to the fact that melatonin receptors belong to two distinct classes of proteins, that is, the G-protein coupled receptor superfamily (MT(1), MT(2)) and the quinone reductase enzyme family (MT(3)) which makes them unique at the molecular level. Also, within the G-protein coupled receptor family of proteins, the MT(1) and MT(2) receptors can couple to multiple and distinct signal transduction cascades whose activation can lead to unique cellular responses. Also, throughout the 24-hour cycle, the receptors' sensitivity to specific cues fluctuates and this sensitivity can be modulated in a homologous fashion, that is, by melatonin itself, and in a heterologous manner, that is, by other cues including the photoperiod or estrogen. This sensitivity of response may reflect changes in melatonin receptor density that also occurs throughout the 24-hour light/dark cycle but out of phase with circulating melatonin levels. The mechanisms that underlie the changes in melatonin receptor density and function are still not well-understood, but data is beginning to show that transcriptional events and G-protein uncoupling may be involved. Even though this area of research is still in its infancy, great strides are being made everyday in elucidating the mechanisms that underlie melatonin receptor function and regulation. The focus of this review is to highlight some of these discoveries in an attempt to reveal the uniqueness of the melatonin receptor family while at the same time provide thought-provoking ideas to further advance this area of research. Thus, a brief overview of each of the mammalian melatonin receptor subtypes and the signal transduction cascades to which they couple will be discussed with a greater emphasis placed on the mechanisms underlying their regulation and the domains within the receptors essential for proper signaling.