Melatonin Receptor Expression Research Articles

Adrenal MT1 melatonin receptor expression is linked with seasonal variation in social behavior in male Siberian hamsters

Many animals exhibit pronounced changes in physiology and behavior on a seasonal basis, and these adaptations have evolved to promote survival and reproductive success. While the neuroendocrine pathways mediating seasonal reproduction are well-studied, far less is known about the mechanisms underlying seasonal changes in social behavior, particularly outside of the context of the breeding season. Our previous work suggests that seasonal changes in melatonin secretion are important in regulating aggression in Siberian hamsters (Phodopus sungorus); it is unclear, however, how melatonin acts via its receptors to modulate seasonal variation in social behavior. In this study, we infused a MT1 melatonin receptor-expressing (MT1) or control (CON) lentivirus into the adrenal glands of male Siberian hamsters. We then housed hamsters in long-day (LD) or short-day (SD) photoperiods, administered timed melatonin or control injections, and quantified aggressive and non-aggressive social behaviors (e.g., investigation, self-grooming) following 10 weeks of treatment. LD hamsters infused with the MT1 lentivirus had significantly higher adrenal mt1 expression than LD CON hamsters, as determined via quantitative PCR. While melatonin administration was necessary to induce SD-like reductions in body and relative reproductive mass, only LD hamsters infused with the MT1 lentivirus displayed SD-like changes in social behavior, including increased aggression and decreased investigation and grooming. In addition, SD CON and LD hamsters infused with the MT1 lentivirus exhibited similar relationships between adrenal mt1 expression and aggressive behavior. Together, our findings suggest a role for adrenal MT1 receptor signaling in regulating behavior, but not energetics or reproduction in seasonally breeding species.

Differential expression and interaction of melatonin and thyroid hormone receptors with estrogen receptor α improve ovarian functions in letrozole-induced rat polycystic ovary syndrome

AimsThe objective of the present study was to investigate the effect of melatonin and L-thyroxine (T4) on the expression of various receptors, and some metabolic, reproductive, and gonadotropic hormones in letrozole-induced polycystic ovary syndrome (PCOS) in rats. Material and methodsAssessment of gravimetric, hormonal profile and thyroid histology and relative expression of melatonin receptors (MT1, MT2) and estrogen receptor α (Erα) in thyroid and ovary, and type II iodothyronine deiodinase (Dio2) and thyroid hormone receptor α (TRα) in the ovary were performed using standard protocols. Key findingsA significant increase in thyroid follicles numbers was noted in the hyperthyroid rat. T4 treatment to PCOS showed the expected increment in the circulating level of triiodothyronine (T3) and T4. Melatonin and T4 treatment of PCOS rats resulted in a significant decrease in the circulating level of T3 and T4. Hyperthyroid rats showed a decrement in plasma melatonin levels. However, T4 treatment to PCOS rats showed increased circulating melatonin levels, and a decrease in the circulating level of gonadotropins (LH and FSH), and testosterone. Melatonin treatment to PCOS-hyperthyroid rats resulted in the normal expression of ovarian and thyroid MT1 and ERα, receptors, which had been altered in PCOS and hyperthyroid rats, without any significant change in the MT2 receptor. SignificanceThe present findings suggest a fine interplay and cross-talk via melatonin and its two receptors with ERα, TRα, and Dio2in thyroid and ovarian tissue during PCOS and hyperthyroidism pathogenicity.

Coadministration of Melatonin and Insulin Improves Diabetes-Induced Impairment of Rat Kidney Function

Introduction: The present study was designed to evaluate the therapeutic efficacy of melatonin and insulin coadministration in diabetes-induced renal injury in rats. Research Design and Methods: Diabetes was achieved by giving streptozotocin (15 mg/kg) for 6 consecutive days. The diabetic condition was confirmed by assessing the blood glucose level; animals having blood glucose levels above 250 mg were considered as diabetic. Following the confirmation, animals were randomly divided into different experimental groups, viz group I served as the control (CON), group II diabetic (D), group III D+melatonin (MEL), group IV D+insulin (INS), group V D+MEL+INS, group VI D+glibenclamide (GB), group VII CON+MEL, group VIII CON+INS, and group IX CON+GB. Following the completion of the experimental period, animals were sacrificed, blood was collected via a retro-orbital puncture, and kidneys were harvested. Diabetic rats exhibited a significant increment in blood glucose and biochemical indexes of renal injury (tubular disruption, swollen glomeruli with loss of glomerular spaces, and distortion of the endothelial lining) including augmented levels of serum creatinine, urea, uric acid, Na+, and K+, and inhibition/suppression of the activity of glutathione (GSH) peroxidase, GSH reductase, glucose-6-phosphate dehydrogenase, and GSH-S-transferase in the renal cortex. Results: By examining thiobarbiturate reactive substances, reduced GSH, superoxide dismutase activity, and catalase activity in the renal cortex of control and diabetic rats, it was documented that treatment with melatonin or insulin alone or in combination showed a significant ad integrum recovery of GSH-dependent antioxidative enzymatic activities. Melatonin and insulin coadministration caused greater reductions in circulating tumor necrosis factor-α, tumor growth factor-β1, interleukin (IL)-1β, and IL-6 levels in diabetic rats, whereas IL-10 levels increased, as compared to each treatment alone. Diabetic rats showed a significant increase in the expression of both MT1 and MT2 melatonin receptor genes. Melatonin or insulin treatment alone or in combination resulted in significant restoration of the relative expression of both melatonin receptors in the renal cortex. Conclusion: The coadministration of exogenous melatonin and insulin abolished many of the deleterious effects of type 1 diabetes on rat renal function.

Melatonin - A Cutaneous Perspective

Melatonin (MLT) is an endogenous hormone secreted from the pineal gland, located deep in the brain in the epithalamus associated with numerous biological activities. The primary function of melatonin is to regulate sleep-wake cycles. However, research over the last few years has enlightened a range of functions associated with this molecule, including anti-inflammatory, direct and indirect antioxidant activity, regenerative tissue benefits, and preservation of mitochondrial function. Melatonin’s anti-inflammatory and antioxidant support, coupled with its mitochondrial modulation, makes it a vital molecule to use for skin health homeostasis. The cutaneous melatoninergic system’s widespread expression and pleiotropic activity provides for a high level of cell-specific selectivity. Several skin cells, including normal and malignant keratinocytes, melanocytes, fibroblasts and hair follicles, express melatonin receptors. Melatonin also has receptor-independent effects that protect against oxidative stress and can reduce ultraviolet radiation-induced damage. Several functions of melatonin in the skin have been experimentally implicated such as hair growth cycling, fur pigmentation, melanoma control, suppression of ultraviolet-induced damage to the skin cell. Melatonin may play a role in treating several dermatoses e.g., atopic eczema, psoriasis, melasma, ulcer healing, and malignant melanoma. There is a plethora of functional melatonin properties, which still await to be fully appreciated by dermatologists. The current review emphasizes few of the established uses and few emerging potentialities that render melatonin a promising candidate for managing several diseases.

Features of the expression of melatonin MT1 receptors in the general cover of rats caused by light deprivation

Background. It has now been established that any change in the synchronized work of the circadian clock leads to a disruption of the body's regulatory systems, which consists in the development of metabolic disorders and tissue damage. Objective: to study the dynamics of the expression of the MT1 melatonin receptor in the skin of white male rats under light deprivation. Methods. In this work, using immunohistochemistry, the features of the expression of receptors for melatonin (MT1) were studied. The experiments were performed on outbred male rats weighing 170-220 g, which were divided into 2 groups; intact - animals kept under standard fixed lighting conditions (12 h light / 12 h dark); Group 2 - animals with simulated light deprivation in conditions of round-the-clock darkness (24 hours of darkness). Results. A strong circadian dependence of the expression of MT1 melatonin receptors in the general integument was established. In the cells of the epidermis and sebaceous glands, by the 14th day, MT1 expression significantly decreased, which then sharply increased by the 21st day. In the keratinocytes of the epidermis, a wavelike character of changes in indicators is noted throughout the study: an increase (7th day) - a decrease (14th day) - a sharp increase (21st day). Conclusion. Initially, light deprivation leads to a decrease in the number of immunopositive cells, and then their level increases compensatory, which is one of the manifestations of the body's adaptation mechanisms to chronodestruction.

Sudden infant death syndrome: Melatonin, serotonin, and CD34 factor as possible diagnostic markers and prophylactic targets.

Sudden infant death syndrome (SIDS) is one of the primary causes of death of infants in the first year of life. According to the WHO’s data, the global infant mortality rate is 0.64–2 per 1,000 live-born children. Molecular and cellular aspects of SIDS development have not been identified so far. The purpose of this paper is to verify and analyze the expression of melatonin 1 and 2 receptors, serotonin (as a melatonin precursor), and CD34 molecules (as hematopoietic and endothelial markers of cardiovascular damage) in the medulla, heart, and aorta in infants who died from SIDS. An immunohistochemical method was used to investigate samples of medulla, heart, and aorta tissues of infants 3 to 9 months of age who died from SIDS. The control group included children who died from accidents. It has been shown that the expression of melatonin receptors as well as serotonin and CD34 angiogenesis markers in tissues of the medulla, heart, and aorta of infants who died from SIDS is statistically lower as compared with their expression in the same tissues in children who died from accidents. The obtained data help to clarify in detail the role of melatonin and such signaling molecules as serotonin and CD34 in SIDS pathogenesis, which can open new prospects for devising novel methods for predictive diagnosis of development and targeted prophylaxis of SIDS.

Effects of melatonin receptor expression on prognosis and survival in oral squamous cell carcinoma patients

Melatonin receptors can inhibit breast and prostate cancers; however, little is known regarding their effects on oral squamous cell carcinoma. In this study, we collected specimens from 81 patients with oral squamous cell carcinoma and analysed clinicopathological data retrospectively. In addition, the expression of the melatonin receptor was analysed immunohistochemically. Survival rates were calculated using the Kaplan–Meier method and log-rank test. Multivariate analysis was performed based on the Cox proportional-hazards model. Further, an in vitro study was performed using YD15 cells. The cells were transfected with siRNA targeting melatonin receptor 1A and 1B for evaluating the malignancy of melatonin receptors by western blotting, trypan blue-exclusion, colony-forming, wound-healing, and invasion assays. Survival decreased as melatonin receptor expression and clinical and pathological tumour–node–metastasis stages increased. A Cox proportional-hazard model showed that melatonin receptor 1A may serve as a significant predictor of the survival rate of patients with oral squamous cell carcinoma [hazard ratio = 1.423, 95% confidence interval (CI) = 1.019–1.988, p = 0.038]. Melatonin receptor 1A and 1B knockdown significantly suppressed proliferation, migration ability, and invasion ability of YD15 cells in vitro. Our findings reveal that inhibiting melatonin receptor expression may suppress oral squamous cell carcinoma development.

Melatonin receptor 2 mediated spinal dorsal horn astrocytes IL-17 inhibition contributes to electroacupuncture analgesia in neuropathic pain rats

To investigate the effect of electroacupuncture (EA) on pain behaviors and expression of spinal dorsal horn melatonin receptor 2 (MT2) and interleukin-17 (IL-17) in neuropathic pain rats, so as to explore its mechanism underlying pain relief. The present study includes 3 parts. In the first part, eighteen male SD rats were randomly divided into 3 groups: sham operation, model and EA groups, with 6 rats in each group. The neuropathic pain model was established by chronic constriction injury (CCI) of the right sciatic nerve. On the 7th day following modeling, EA was applied to the right "Zusanli" (ST36) and "Sanyinjiao" (SP6) (1 mA,2 Hz/100 Hz) for 30 min. The mechanical pain threshold(MWT) and thermal pain thre-shold(TPT) of the affected limb were detected before modeling, 7 days following modeling and 60 min after EA. The expression of MT2 in spinal dorsal horn was detected by Western blot. The contents of melatonin （Mel） and IL-17 in the spinal dorsal horn were determined by ELISA. The expression of glial fibrillary acidic protein (GFAP) in the spinal dorsal horn was determined by Western blot and immunohistochemistry. In the second part, 30 rats were divided into 5 groups: sham operation, model, EA, MT2 antagonist (4-P-PDOT), and dimethyl sulfoxide (DMSO) groups, with 6 rats in each group. Rats of the 4-P-PDOT and DMSO groups were intrathecal injection with 10 μL MT2 antagonist 4-P-PDOT (100 μg) and equivalent DMSO 30 min before EA. The MWT and TPT of affected limb were detected. The GFAP expression and IL-17 content in the spinal dorsal horn was detected by Western blot， immunohistochemistry and ELISA, respectively. In the third part, 30 rats were randomly divided into 5 groups: sham operation, model, EA, recombinant IL-17, and normal saline groups, with 6 rats in each group. The recombinant IL-17 protein (100 ng, 10 μL) and the same amount of 0.9% sodium chloride solution were intrathecal injection into the rats of the recombinant IL-17 group and the normal saline group 30 min before the EA. The MWT and TPT of affected limb were measured. On the 7th day after modeling, the MWT of rats in the model group and the EA group were significantly higher, while TPT were lower than those before the modeling (P<0.05). At 60 min after EA, compared with the model group, the MWT and TPT of the EA group reversed significantly (P<0.05). The levels of GFAP and IL-17 were significantly increased, while the levels of Mel and MT2 were significantly decreased in the model group than in the sham operation group (P<0.05), and those were considerably reversed in the EA group than in the model group (P<0.05). Compared with the EA and DMSO groups, the MWT in the 4-P-PDOT group were significantly increased, while TPT were decreased (P<0.05), and the contents of GFAP and IL-17 were significantly increased (P<0.05). Compared to the EA and normal saline groups, MWT of the rats in the recombinant IL-17 group were significantly increased, while TPT decreased (P<0.05). EA of ST36 and SP6 can alleviate neuropathic pain in CCI rats, which is closely related to its effect in inhibiting the release of IL-17 from astrocytes mediated by MT2.

Effect of exogenous melatonin and flaxseed oil on the expression state of MT1 receptors in rat skin under light deprivation

Most of the skin cells have their own autonomous functional circadian system, which is able to control physiological and biochemical processes in the general integument. A special role in these processes is assigned to the “clock” hormone of the pineal gland, melatonin, which acts on target cells through specific receptors (MT1, MT2, MT3 and RORα). Any disturbance of circadian rhythms can lead to rearrangements (disturbances) in the receptor apparatus of the cells of the general cover, which require a certain correction. Consequently, there is a need to search for effective and reliable drugs that will prevent the negative consequences caused by chronodestruction. In the present work, we studied the effectiveness of the effect of exogenous melatonin and flaxseed oil on the expression of MT1 receptors in the general coat of rats under light deprivation. An experimental study was carried out on 130 white outbred male rats (170-220 g), which were randomly divided into 5 groups: intact, light deprivation animals, light deprivation animals, which were injected intragastrically with flaxseed oil and melatonin. On days 7, 14 and 21, histological material was taken (fragments of the skin of the interscapular region of the back). For immunohistochemical studies, serial sections were stained using MTNR1A polyclonal antibodies. For morphometric data analysis, the Image Scope Color and ImageJ computer programs were used. All statistical data processing was performed using the Statistica 10.0 software. Differences were considered significant at a significance level of less than 0.01 (p &lt;0.01). In the course of the experiment, it was found that light deprivation contributes to a change in the activity of expression of the MT1 melatonin receptors in the epidermis, sebaceous glands and hair follicles. Studies have shown that the administration of flaxseed oil, melatonin, and their combination to rats with desynchronosis is accompanied by the leveling of the adverse effect of desynchronosis on the studied parameters of MT1 receptors. The most pronounced corrective effect on the expression of MT1 receptors is observed with the introduction of exogenous melatonin on the 21st day of the experiment.

Melatonin Alleviates Acute Gouty Inflammation In Vivo and In Vitro.

The aim of this study was to identify the effects of melatonin on acute gouty inflammation and to investigate the underlying mechanisms. We found significantly lower serum melatonin levels in gout patients in the acute phase than in those in the remission phase or in normal individuals. The mRNA expression of melatonin receptor 2 (MT2) was also lower in gout patients than in normal individuals. To verify the in-vivo role of melatonin, a gouty arthritis model was established by intraarticular injection of monosodium urate (MSU, 1 mg) crystals into the paws of C57BL/6 mice. Joint inflammation in the mouse model was evaluated by measuring the thickness of the right paw/left paw, and the inflammation index was determined by examining infiltrating neutrophils with haematoxylin and eosin (H&E) staining. Melatonin was found to reduce both paw thickness and the inflammation index in the mouse model, and melatonin also reduced the mRNA levels of interleukin-1 beta (IL-1β), IL-6 and NLR family pyrin domain containing 3 (NLRP3) inflammasome. To mimic gouty inflammation in vitro, mouse peritoneal macrophages were stimulated with lipopolysaccharides (LPS) plus MSU. Melatonin was revealed to reduce IL-1β secretion by stimulated macrophages. The mRNA expression levels of IL-1β and IL-6 were also inhibited by melatonin. Western blot analysis showed that the expression of NLRP3, caspase-1 and pro-IL-1β was also inhibited by melatonin. In conclusion, our study demonstrated that melatonin alleviated gouty inflammation in vivo and in vitro, and the underlying mechanism may involve inhibiting the assembly of the NLRP3 inflammasome.

Melatonin protects inner retinal neurons of newborn mice after hypoxia-ischemia.

Retinopathy of prematurity is a vision-threatening disease associated with retinal hypoxia-ischemia, leading to the death of retinal neurons and chronic neuronal degeneration. During this study, we used the oxygen-induced retinopathy mice model to mimic retinal hypoxia-ischemia phenotypes to investigate further the neuroprotective effect of melatonin on neonatal retinal neurons. Melatonin helped maintain relatively normal inner retinal architecture and thickness and preserve inner retinal neuron populations in avascular areas by rescuing retinal ganglion and bipolar cells, and horizontal and amacrine neurons, from apoptosis. Meanwhile, melatonin recovered visual dysfunction, as reflected by the improved amplitudes and implicit times of a-wave, b-wave, and oscillatory potentials. Additionally, elevated cleaved caspase-3 and Bax protein levels and reduced Bcl-2 protein levels in response to hypoxia-ischemia were diminished after melatonin treatment. Moreover, melatonin increased BDNF and downstream phospho-TrkB/Akt/ERK/CREB levels. ANA-12, a TrkB receptor antagonist, antagonized these melatonin actions and reduced melatonin-induced neuroprotection. Furthermore, melatonin rescued the reduction in melatonin receptor expression. This study suggests that melatonin exerted anti-apoptotic and neuroprotective effects in inner retinal neurons after hypoxia-ischemia, at least partly due to modulation of the BDNF-TrkB pathway.

Melatonin mitigates the adverse effect of hypoxia during myocardial differentiation in mouse embryonic stem cells.

BackgroundHypoxia causes oxidative stress and affects cardiovascular function and the programming of cardiovascular disease. Melatonin promotes antioxidant enzymes such as superoxide dismutase, glutathione reductase, glutathione peroxidase, and catalase.ObjectivesThis study aims to investigate the correlation between melatonin and hypoxia induction in cardiomyocytes differentiation.MethodsMouse embryonic stem cells (mESCs) were induced to myocardial differentiation. To demonstrate the influence of melatonin under hypoxia, mESC was pretreated with melatonin and then cultured in hypoxic condition. The cardiac beating ratio of the mESC-derived cardiomyocytes, mRNA and protein expression levels were investigated.ResultsUnder hypoxic condition, the mRNA expression of cardiac-lineage markers (Brachyury, Tbx20, and cTn1) and melatonin receptor (Mtnr1a) was reduced. The mRNA expression of cTn1 and the beating ratio of mESCs increased when melatonin was treated simultaneously with hypoxia, compared to when only exposed to hypoxia. Hypoxia-inducible factor (HIF)-1α protein decreased with melatonin treatment under hypoxia, and Mtnr1a mRNA expression increased. When the cells were exposed to hypoxia with melatonin treatment, the protein expressions of phospho-extracellular signal-related kinase (p-ERK) and Bcl-2-associated X proteins (Bax) decreased, however, the levels of phospho-protein kinase B (p-Akt), phosphatidylinositol 3-kinase (PI3K), B-cell lymphoma 2 (Bcl-2) proteins, and antioxidant enzymes including Cu/Zn-SOD, Mn-SOD, and catalase were increased. Competitive melatonin receptor antagonist luzindole blocked the melatonin-induced effects.ConclusionsThis study demonstrates that hypoxia inhibits cardiomyocytes differentiation and melatonin partially mitigates the adverse effect of hypoxia in myocardial differentiation by regulating apoptosis and oxidative stress through the p-AKT and PI3K pathway.

Retinal and extra-retinal photoreceptor responses and reproductive performance of Japanese quail (Coturnix coturnix japonica) following exposure to different photoperiodic regime

Japanese quail is a truly photoperiodic avian species. In general long days are gonado-stimulatory and short days are gonado-inhibitory for this poultry bird. To investigate the correlation of retinal and extra-retinal photoreceptors with different photoperiodic conditions quail were divided into 2 groups and kept under long day (16L: 8D) and short day (8L: 16D) condition separately to develop photosensitivity and scotosensitivity respectively. Transfer of long day quail to intermediate day-length (13.5L: 10.5D) developed photorefractoriness (relative) and prolonged exposure to short photoperiodic conditions led the birds to develop scotorefractoriness. Increased expression of mRNA and immunosignaling of photoreceptors rhodopsin, transducin in eye and hypothalamus while decreased mRNA expression of melatonin receptors (Mel1b, Mel1c) were noted in the eyes of photosensitive (PS) and scotorefractory (SR) quail compared to photorefractory (PR) and scotosensitive (SS) birds respectively. Decreased expression of hypothalamic GnIH and melatonin receptors mRNA was observed in PS and SR birds compared to PR and SS birds respectively. Modulation of retinal and extra retinal photoreceptors leads to increased spermatogenesis as well as mRNA expression of steroidogenic genes and androgen receptor in the testis of sexually active PS and SR quail. These results led us to conclude that gonadal stimulation in PS as well as SR quail is outcome of activated retinal and extra retinal photoreceptors which lowered melatonin receptors and GnIH expression. Contrarily testicular inhibition in PR and SS is the outcome of decreased photoperception. It is suggested that decreased photoperception in SS quail increases after prolong exposure of the short day (in SR) leading to increased activity of HPG axis.

Melatonin exerts immunoregulatory effects by balancing peripheral effector and regulatory T helper cells in myasthenia gravis

Myasthenia gravis (MG) is a prototypic organ-specific autoimmune disorder that, in most cases, is mainly mediated by antibodies against the acetylcholine receptor. Evidence implicates CD4+ T helper (Th) cells in the development of MG, whereas regulatory T cells (Tregs) are associated with disease resolution. Melatonin has important immunoregulatory effects in many T cell-mediated autoimmune diseases. However, there are few studies on the role of melatonin in MG. In the present study, we investigated serum melatonin levels and melatonin receptor expression in MG patients and healthy controls (HCs). We also evaluated the impact of melatonin administration on peripheral CD4+ Th cells and related cytokine production. Serum melatonin levels were lower in MG patients than in HCs, and MT1 expression was lower in PBMCs from MG patients than in those from HCs. Administration of melatonin significantly decreased Th1 and Th17 cell responses and proinflammatory cytokine production. Further investigation in vitro revealed that melatonin administration increased FoxP3 and IL-10 expression in CD4+ T cells from MG patients and enhanced the suppressive function of Tregs. These findings indicate that melatonin exerts immunoregulatory activity in MG by balancing effector and regulatory Th cell populations as well as by suppressing proinflammatory cytokine production.

Melatonin ameliorates Bisphenol S induced testicular damages by modulating Nrf-2/HO-1 and SIRT-1/FOXO-1 expressions.

BPS has detrimental effects on human reproductive health and emerged as an environmental contaminant for global health concern. This study deals with the adverse impact of BPS exposure on testicular oxidative stress, inflammation and apoptosis in adult male golden hamster, Mesocricetus auratus and its amelioration by melatonin. BPS (75 mg/kg BW/day) exposure caused testicular impairment as evident by histological degenerative changes, declined sperm quality (viability and motility), serum levels of testosterone and melatonin with a concomitant decrease in testicular androgen receptor (AR) and melatonin receptor (MT1) expression. The BPS exposure caused marked increase in testicular oxidative load, inflammation (NF-kB/COX-2) and apoptosis (caspase-3). Melatonin (10 mg/kg BW/alternate day) pretreatment to BPS exposed hamsters resumed normal testicular histoarchitecture, sperm quality and decreased testicular oxidative load as evident by enhanced antioxidant enzymes (SOD and catalase) activities and decreased lipid peroxidation (LPO) level. Further, melatonin also stimulated the testicular antioxidant proteins Nrf-2/HO-1, SIRT-1/FOXO-1 and reduced inflammatory proteins NF-kB/COX-2 expression to counteract BPS induced testicular damages. Melatonin administration to the BPS treated hamsters resulted in increased testicular cell proliferation (PCNA), survival (Bcl-2), gap junction (connexin-43) and decreased apoptosis (caspase-3). In conclusion, our study documented the detrimental effects of BPS on testes that compromises male fertility. Further, melatonin was found as a potent molecule that rescued the BPS induced testicular damages in male golden hamster Mesocricetus auratus.

Pinealectomy increases thermogenesis and decreases lipogenesis.

The present study was designed to determine the effects of pineal gland-derived melatonin on obesity by employing a rat pinealectomy (Pnx) model. After 10 weeks of a high-fat diet, rats received sham or Pnx surgery followed by a normal chow diet for 10 weeks. Reverse transcription-quantitative PCR, western blotting analysis, immunohistochemistry and ELISA were used to determine the effects of Pnx. Pnx decreased the expression of melatonin receptor (MTNR)1A and MTNR1B, in brown adipose tissues (BAT) and white adipose tissues (WAT). Pnx rats showed increased insulin sensitivity compared with those that received sham surgery. Leptin levels were significantly decreased in the serum of the Pnx group. In addition, Pnx stimulated thermogenic genes in BAT and attenuated lipogenic genes in both WAT and the liver. Histological analyses revealed a marked decrease in the size of lipid droplets and increased expression of uncoupling protein 1 in BAT. In the liver of the Pnx group, the size and number of lipid droplets had also decreased. In conclusion, the results presented in the current study suggested that Pnx increases thermogenesis in BAT and decreases lipogenesis in WAT and the liver.

Expression of melatonin receptors in the gastroesophageal reflux disease associated with obstructive sleep apnea/hypopnea syndrome

The aim of the present research was to assess the expression of melatonin receptors (MTNR1B) in the esophageal mucosa in the gastroesophageal reflux disease associated with obstructive sleep apnea/hypopnea syndrome and to study the relationship between the detected changes and the sleep apnea severity. 84 patients aged 30–60 years, including those with gastroesophageal reflux disease (group 1, n = 25), those with gastroesophageal reflux disease associated with sleep apnea/hypopnea (group 2, n = 23), those with obstructive sleep apnoe/ hypopnoe syndrome (group 3, n = 18), and almost healthy people (group 4, n = 18), were studied. Diagnoses were based on endoscopic imaging and respiratory monitoring. The MTNR1B expression in the esophageal mucosa was determined by the immunohistochemical method using specific antibodies. The MTNR1 B expression was evaluated quantitatively using the computer program Aperio ImageScope _v9.1.19.1567. The obtained material was analyzed statistically using the software Statistica 10.0. The group 2 patients were shown to have a higher MTNR1B expression compared to the group 1 patients (0.122 [0.064; 0.266] versus 0.620 [0.332; 0.983]; p = 0.00001) and the group 3 patients (0.620 [0.332; 0.983] versus 0.232 [0.120; 0.418]; р = 0.0098). The MTNR1 B expression increased with growing sleep apnea severity: it is 0.295 [0.198; 0.403] in patients with mild apnea versus 0.941 [0.345; 0.992] in patients with moderate and severe apnea (p = 0.0021). A direct correlation between the MTNR1B expression and the sleep apnea severity degree (r = 0.50; р = 0.0016) was revealed. Patients with gastroesophageal reflux disease combined with sleep apnea revealed an increase in the MTNR1 B expression associated with the apnea severity. The revealed features of the MTNR1 B expression secondary to esophageal mucosal damage indicate the MTNR1 B inactivation secondary to accompanying apnea of hypoxia.

Melatonin promotes Schwann cell dedifferentiation and proliferation through the Ras/Raf/ERK and MAPK pathways, and glial cell‑derived neurotrophic factor expression

Upon peripheral nerve injury (PNI), continuous proliferation of Schwann cells is critical for axon regeneration and tubular reconstruction for nerve regeneration. Melatonin is a hormone that is able to induce proliferation in various cell types. In the present study, the effects of melatonin on promoting Schwann cell proliferation and the molecular mechanism involved were investigated. The present results showed that melatonin enhanced the melatonin receptors (MT1 and MT2) expression in Schwann cells. Melatonin induced Schwann cell dedifferentiation into progenitor-like Schwann cells, as observed by immunofluorescence staining, which showed Sox2 marker expression. In addition, melatonin enhanced Schwann cell proliferation, mediated by the upregulation of glial cell-derived neurotropic factor (GNDF) and protein kinase C (PKC). Furthermore, the Ras/Raf/ERK and MAPK signaling pathways were also involved in Schwann cell dedifferentiation and proliferation. In conclusion, melatonin induced Schwann cell dedifferentiation and proliferation via the Ras/Raf/ERK, MAPK and GDNF/PKC pathways. The present results suggested that melatonin could be used to enhance the recovery of PNI.

Melatonin suppresses both osteoblast and osteoclast differentiation through repression of epidermal Erk signaling in the zebrafish scale

Melatonin has been implicated in the regulation of bone metabolism; however, the molecular mechanisms underlying its involvement in fracture healing are still obscure. We previously developed an in vivo fracture healing model using the scale of a double-transgenic zebrafish, trap:GFP; osterix:mCherry, which labels osteoclasts and osteoblasts with GFP and mCherry, respectively. Here we show using this model that melatonin inhibits both osteoblast and osteoclast differentiation under fracture stress through the repression of Erk signaling in epidermal cells of the scale. Melatonin treatment resulted in reduced numbers of both osteoblasts and osteoclasts in the fractured scale. Immunochemistry analysis revealed that Erk signals in epidermal cells, which express melatonin receptors, were greatly enhanced in response to fracture stress, but this enhancement was blocked by melatonin treatment. Moreover, inhibition of Erk signaling phenocopied the effects of melatonin treatment in the fractured scale. Collectively, these data suggest that the activation of epidermal Erk signaling is required for both osteoblast and osteoclast differentiation in the early stage of fracture healing, and melatonin suppresses epidermal Erk signaling, leading to impaired fracture healing.

Expression of Melatonin Receptor 1 in Rat Mesenteric Artery and Perivascular Adipose Tissue and Vasoactive Action of Melatonin

Melatonin is released by the pineal gland and can modulate cardiovascular system function via the G protein-coupled melatonin receptors MT1 and MT2. Most vessels are surrounded by perivascular adipose tissue (PVAT), which affects their contractility. The aim of our study was to evaluate mRNA and protein expression of MT1 and MT2 in the mesenteric artery (MA) and associated PVAT of male rats by RT-PCR and Western blot. Receptor localization was further studied by immunofluorescence microscopy. Effects of melatonin on neurogenic contractions were explored in isolated superior MA ex vivo by measurement of isometric contractile tension. MT1, but not MT2, was present in MA, and MT1 was localized mainly in vascular smooth muscle. Moreover, we proved the presence of MT1, but not MT2 receptors, in MA-associated PVAT. In isolated superior MA with intact PVAT, neuro-adrenergic contractile responses were significantly smaller when compared to arteries with removed PVAT. Pre-treatment with melatonin of PVAT-stripped arterial rings enhanced neurogenic contractions, while the potentiating effect of melatonin was not detected in preparations with preserved PVAT. We hypothesize that melatonin can stimulate the release of PVAT-derived relaxing factor(s) via MT1, which can override the direct pro-contractile effect of melatonin on vascular smooth muscle. Our results suggest that melatonin is involved in the control of vascular tone in a complex way, which is vessel specific and can reflect a sum of action on different layers of the vessel wall and surrounding PVAT.