Melatonin affects steroidogenesis and delayed ovulation during winter in vespertilionid bat, Scotophilus heathi

Orchestrated feedback regulation between melatonin and sex hormones involving GPER1-PKA-CREB signaling in the placenta

Maintaining placental endocrine homeostasis is crucial for a successful pregnancy. Pre-eclampsia (PE), a gestational complication, is a leading cause of maternal and perinatal morbidity and mortality. Aberrant elevation of testosterone (T0 ) synthesis, reduced estradiol (E2 ), and melatonin productions have been identified in preeclamptic placentas. However, the precise contribution of disrupted homeostasis among these hormones to the occurrence of PE remains unknown. In this study, we established a strong correlation between suppressed melatonin production and decreased E2 as well as elevated T0 synthesis in PE placentas. Administration of the T0 analog testosterone propionate (TP; 2 mg/kg/day) to pregnant mice from E7.5 onwards resulted in PE-like symptoms, along with elevated T0 production and reduced E2 and melatonin production. Notably, supplementation with melatonin (10 mg/kg/day) in TP-treated mice had detrimental effects on fetal and placental development and compromised hormone synthesis. Importantly, E2 , but not T0 , actively enhanced melatonin synthetase AANAT expression and melatonin production in primary human trophoblast (PHT) cells through GPER1-PKA-CREB signaling pathway. On the other hand, melatonin suppressed the level of estrogen synthetase aromatase while promoting the expressions of androgen synthetic enzymes including 17β-HSD3 and 3β-HSD1 in PHT cells. These findings reveal an orchestrated feedback mechanism that maintains homeostasis of placental sex hormones and melatonin. It is implied that abnormal elevation of T0 synthesis likely serves as the primary cause of placental endocrine disturbances associated with PE. The suppression of melatonin may represent an adaptive strategy to correct the imbalance in sex hormone levels within preeclamptic placentas. The findings of this study offer novel evidence that identifies potential targets for the development of innovative therapeutic strategies for PE.

Effects of melatonin on a d-galactose-induced male reproductive aging mouse model

Understanding the aging mechanism of the male reproductive system and developing anti-aging interventions are essential for preventing age-related male infertility. The pineal hormone melatonin has been effectively used as an antioxidant and anti-apoptotic molecule in various cells and tissues. However, the effects of melatonin on d-galactose (D-gal)-induced aging have not been studied with regards to testicular function. Thus, we investigated whether melatonin suppresses the dysfunction of male reproductive function induced by D-gal treatment. The mice were divided into the following four groups receiving treatments for six weeks: phosphate-buffered saline (PBS) group, d-galactose (200 mg/kg) group, melatonin (20 mg/kg) group, and d-galactose (200 mg/kg)+ melatonin (20 mg/kg) group. At six weeks of treatments, sperm parameters, body and testes weight, gene and protein expression of germ cell and spermatozoa marker were analyzed. Our results showed that melatonin suppressed the decrease in body weight, sperm vitality, motility, and gene expression levels of spermatozoa markers such as Protamine 1, PGK2, Camk4, TP1, and Crem in the testis of D-gal-induced aging models. However, the gene expression levels of the pre-meiotic and meiotic markers in the testes did not change in the D-gal-injected model. The injection of D-gal impaired the decreased expression of steroidogenic enzyme genes, such as HSD3b1, Cyp17a1, and Cyp11a1, but melatonin inhibited the decrease in the expression of these genes. In addition, protein levels of spermatozoa and germ cell markers were evaluated by immunostaining and immunoblotting. Consistent with the qPCR results, PGK2 protein levels were decreased by d-galactose treatment. A decrease in PGK2 protein levels by D-gal was inhibited by melatonin treatment. In conclusion, melatonin administration improves testicular function with age.

Effect of Acute Melatonin Injection on Metabolomic and Testicular Artery Hemodynamic Changes and Circulating Hormones in Shiba Goats under Sub-Tropical Environmental Conditions

The beneficial effects of melatonin were investigated to mitigate various detrimental effects and toxicity on reproductive performance. The present study aimed, for the first time, to explore the effect of intravenous melatonin injection on testicular artery hemodynamics (TH) and metabolomic changes, reproductive hormones in heat-stressed bucks. Ten bucks were randomly split into two groups (five each): (1) the melatonin group, treated with a single intravenous dose of melatonin solution containing 10 mg melatonin each, and (2) the control group, which was treated with 10 mL of the vehicle without melatonin. Changes in the TH at the level of the supra testicular artery (STA) were assessed by triplex ultrasonography just before (0 h) and at 0.5, 2, 7, 24, and 168 h after melatonin or vehicle administration. Doppler velocity parameters of peak systolic velocity (PSV; cm/s), end-diastolic velocity (EDV; cm/s), and time average maximum velocity (TAMAX; cm/s) were measured. Doppler indices (resistive index; RI and pulsatility index; PI), systole/diastole (S/D) ratio and total arterial blood flow volume (TABFV; ml/minute) were measured. Peripheral concentrations of FSH, LH, inhibin, melatonin, testosterone (T), estradiol (E2), and cortisol were measured just before injection (0 h) and at 0.5, 2, 7, and 24 h and daily up to day 7 post administration in both groups. Results revealed reductions in the RI values and increases in the TABFV in the melatonin group compared to the control one, especially 2 h after administration. Significant increases in concentrations of FSH, T, E2, and melatonin and decreases in cortisol and inhibin in the melatonin group compared to the control one. Plasma metabolomic analysis at 2 h indicated the up-regulation of L-glutamine, L-arginine, sorbitol, D-glucose, ascorbic acid, and ornithine and the down-regulation of D-xylose, D-arabitol, ribitol, and oleic acid in the melatonin versus the control group. In conclusion, acute administration of melatonin (10 mg IV) enhanced testicular artery blood flow and plasma reproductive hormones in the Shiba goat under heat-stress circumstances.

A systematic review on the role of melatonin and its mechanisms on diabetes-related reproductive impairment in non-clinical studies

BACKGROUND

Diabetes-induced reproductive complications can lead to subfertility and infertility, raising the need to protect reproductive organs. There are limited medications used to improve reproductive health in diabetic patients. Melatonin, mainly produced by the pineal gland, may improve diabetes-associated reproductive complications through various mechanisms and may be a preferred candidate to protect the reproductive system. The present review aims to elucidate the underlying mechanisms of melatonin's effect on the reproductive system adversely affected by diabetes mellitus (DM).

METHODS

A comprehensive systematic literature electronic search was done using the PRISMA guidelines. Web of Science, PubMed, Embase, and Scopus were searched for publications up to June 2022. Search terms were selected based on the study purpose and were explored in titles and abstracts. After screening, out of a total of 169 articles, 14 pertinent articles were included based on our inclusion and exclusion criteria.

RESULTS

The results of studies using rats and mice suggest that DM adversely affects reproductive tissues, including testes and epididymis, prostate, corpus cavernosum, and ovary leading to alterations in histological and biochemical parameters compared to the normal groups. Treatment with melatonin improves oxidative stress, blocks apoptosis induced by endoplasmic reticulum stress and caspase activation, reduces pro-inflammation cytokines, and enhances steroidogenesis.

CONCLUSION

Melatonin exerted a protective action on the impaired reproductive system in in-vivo and in-vitro models of DM. The topic has to be followed up in human pregnancy cases that will need more time to be collected and approved.

Melatonin Regulates the Synthesis of Steroid Hormones on Male Reproduction: A Review

Melatonin is a ubiquitous molecule and exhibits different effects in long-day and short-day breeding animals. Testosterone, the main resource of androgens in the testis, is produced by Leydig cells but regulated mainly by cytokine secreted by Sertoli cells. Melatonin acts as a local modulator of the endocrine activity in Leydig cells. In Sertoli cells, melatonin influences cellular proliferation and energy metabolism and, consequently, can regulate steroidogenesis. These suggest melatonin as a key player in the regulation of steroidogenesis. However, the melatonin-induced regulation of steroid hormones may differ among species, and the literature data indicate that melatonin has important effects on steroidogenesis and male reproduction.

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.

Melatonin up-regulates the expression of the GATA-4 transcription factor and increases testosterone secretion from Leydig cells through RORα signaling in an in vitro goat spermatogonial stem cell differentiation culture system

Because androgen function is regulated by its receptors, androgen-androgen receptor signaling is crucial for regulating spermatogenesis. Androgen is mainly testosterone secreted by testis. Based on the results of early studies in goats, the administration of melatonin over an extended period of time increases steroid production, but the underlying mechanism remains unclear. Here, we report the expression of the melatonin membrane receptors MT1 and MT2 and the retinoic acid receptor-related orphan receptor-alpha (RORα) in the goat testis. An in vitro differentiation system using spermatogonial stem cells (SSCs) cultured in the presence of testicular somatic cells was able to support the formation of sperm-like cells with a single flagellum. The addition of 10^-7 M melatonin to the in vitro culture system increased RORα expression and considerably improved the efficiency of haploid cell differentiation, and the addition of the RORα agonist CGP52608 significantly increased the testosterone concentration and expression of GATA binding factor 4 (GATA-4). Furthermore, inhibitors of melatonin membrane receptors and a RORα antagonist (T0901317) also led to a considerable reduction in the efficiency of haploid spermatid formation, which was coupled with the suppression of GATA-4 expression. Based on these results, RORα may play a crucial role in enhancing melatonin-regulated GATA-4 transcription and steroid hormone synthesis in the goat spermatogonial stem cell differentiation culture system.