RESUMO
The placenta, as a "transit station" between mother and fetus, has functions delivering nutrients, excreting metabolic wastes and secreting hormones. A healthy placenta is essential for fetal growth and development while the melatonergic system seems to play a critical physiological role in this organ since melatonin, its synthetic enzymes and receptors are present in the placenta. In current study, Mtnr1a and Mtnr1b knockout mice were constructed to explore the potential roles of melatonergic system played on the placental function and intrauterine growth retardation (IUGR). The result showed that Mtnr1a knockout had little effect on placental function while Mtnr1b knockout reduced placental efficiency and increased IUGR. Considering the extremely high incidence of IURG in sows, the pregnant sows were treated with melatonin. This treatment reduced the incidence of IUGR. All the evidence suggests that the intact melatonergic system in placenta is required for its function. Mechanistical studies uncovered that Mtnr1b knockout increased placental oxidative stress and apoptosis but reduced the angiogenesis. The RNA sequencing combined with histochemistry study identified the reduced angiogenesis and placental vascular density in Mtnr1b knockout mice. These alterations were mediated by the disrupted STAT3/VEGFR2/PI3K/AKT pathway, i.e., Mtnr1b knockout reduced the phosphorylation of STAT3 which is the promotor of VEGFR2. The downregulated VEGFR2 and its downstream elements of PI3K and AKT expressions, then, jeopardizes the angiogenesis and placental development.
Assuntos
Retardo do Crescimento Fetal , Melatonina , Camundongos Knockout , Neovascularização Fisiológica , Placenta , Receptor MT2 de Melatonina , Transdução de Sinais , Fator A de Crescimento do Endotélio Vascular , Receptor 2 de Fatores de Crescimento do Endotélio Vascular , Animais , Feminino , Gravidez , Placenta/metabolismo , Placenta/irrigação sanguínea , Retardo do Crescimento Fetal/genética , Retardo do Crescimento Fetal/metabolismo , Fator A de Crescimento do Endotélio Vascular/metabolismo , Fator A de Crescimento do Endotélio Vascular/genética , Neovascularização Fisiológica/efeitos dos fármacos , Neovascularização Fisiológica/genética , Receptor 2 de Fatores de Crescimento do Endotélio Vascular/metabolismo , Receptor 2 de Fatores de Crescimento do Endotélio Vascular/genética , Melatonina/farmacologia , Receptor MT2 de Melatonina/genética , Receptor MT2 de Melatonina/metabolismo , Camundongos , Receptor MT1 de Melatonina/genética , Receptor MT1 de Melatonina/metabolismo , Fator de Transcrição STAT3/metabolismo , Fator de Transcrição STAT3/genética , Apoptose , Camundongos Endogâmicos C57BL , Estresse Oxidativo , Suínos , AngiogêneseRESUMO
Objective: The mechanisms of intervertebral disc degeneration (IVDD) in low back pain (LBP) patients are multiples. In this study, we attempt to investigate whether melatonergic system plays a potential role in IVDD patients with LBP by analyzing their clinical specimens. The fucus will be given to the correlation between the melatonin receptor expression and intervertebral disc tissue apoptosis. Methods: In this clinical study, 107 lumbar intervertebral disc nucleus pulposus (NP) specimens from patients with LBP were collected with patients' consents. The disc height (DH) discrepancy ratio, range of motion and sagittal parameters of the pathological plane were measured and Pfirrmann grade was used to classified the grades of IVDD level. Discs at grades 1-3 were served as normal control and grades 4-5 were considered as IVDD. The expression levels of melatonin receptor 1A (MT1) and 1B (MT2) were measured by immunohistochemistry. The apoptosis of NP was assessed using TUNEL staining. Their potential associations among MT1/2, DH, apoptosis, sagittal parameters with IVDD and LBP were evaluated with statistical analysis. Results: The incidence of IVDD was positively associated with age and negatively related to VAS scores for LBP (p < 0.001). Patients with higher degree of IVDD also have higher DH discrepancy ratio (p < 0.001), higher prevalence of lumbar instability (p = 0.003) and higher cell apoptosis compared to the control. Nevertheless, no statistically significant correlation was identified between Pfirrmann grade and lumbar sagittal parameters. MT1 and MT2 both were highly expressed in the NP tissues. Importantly, MT1 expression but not MT2 was significantly increased in the intervertebral disc tissue of patients with IVDD and its level correlated well with cell apoptosis level and the severity of IVDD as well as lower VAS scores for LBP. Conclusion: The highly elevated MT1 expression was found in NP tissues of patients with IVDD and LBP compared to the control. This phenomenon probably reflects the compensating response of the body to the pathological alteration of the IVDD and LBP. Therefore, these findings provide the novel information to use selective agonists of MT1 to target IVDD and LBP clinically.
Assuntos
Apoptose , Degeneração do Disco Intervertebral , Dor Lombar , Humanos , Degeneração do Disco Intervertebral/metabolismo , Degeneração do Disco Intervertebral/patologia , Dor Lombar/patologia , Dor Lombar/metabolismo , Masculino , Feminino , Pessoa de Meia-Idade , Adulto , Núcleo Pulposo/metabolismo , Núcleo Pulposo/patologia , Vértebras Lombares/patologia , Receptor MT1 de Melatonina/metabolismo , Receptor MT2 de Melatonina/metabolismo , Idoso , Disco Intervertebral/patologia , Disco Intervertebral/metabolismoRESUMO
Context The Rsa I polymorphism of the melatonin receptor MTNR1A gene affects seasonal reproduction in sheep, but its effect on ram spermatozoa and their response to melatonin is unknown. Aims This study aims to evaluate whether Rsa I polymorphism of the MTNR1A gene influences the response of ram spermatozoa to in vitro added melatonin. Methods Spermatozoa from rams carrying different Rsa I allelic variants were incubated with melatonin in a TALP medium or a capacitation-triggering medium during the reproductive and non-reproductive seasons. After incubation, sperm motility, membrane integrity, mitochondria activity, oxidative damage, apoptotic markers and capacitation status were assessed. Key results In the reproductive season, the T/T genotype was related to some adverse effects of melatonin when spermatozoa were incubated in TALP medium, whereas the C/C genotype was linked with adverse effects when the hormone was added in a capacitation-triggering medium. The decapacitating effect of melatonin on spermatozoa was also different depending on genotype. Conclusions The melatonin effect on spermatozoa from rams carrying different Rsa I genotypes differed depending on the season and the medium. Implications The knowledge of the Rsa I allelic variant of the MTNR1A gene of rams could be helpful when carrying out in vitro reproductive techniques in the ovine species.
Assuntos
Melatonina , Estações do Ano , Motilidade dos Espermatozoides , Espermatozoides , Melatonina/farmacologia , Animais , Masculino , Espermatozoides/efeitos dos fármacos , Ovinos , Motilidade dos Espermatozoides/efeitos dos fármacos , Motilidade dos Espermatozoides/genética , Receptor MT1 de Melatonina/genética , Receptor MT1 de Melatonina/metabolismo , Polimorfismo Genético , Alelos , Capacitação Espermática/efeitos dos fármacos , Capacitação Espermática/genética , GenótipoRESUMO
Psychological stress affects the neuroendocrine regulation, which modulates mental status and behaviors. Melatonin, a hormone synthesized primarily by the pineal gland, regulates many brain functions, including circadian rhythms, pain, sleep, and mood. Selective pharmacological melatonin agonist ramelteon has been clinically used to treat mood and sleep disorders. Posttraumatic stress disorder (PTSD) is a psychiatric condition associated with severe trauma; it is generally triggered by traumatic events, which lead to severe anxiety and uncontrollable trauma recall. We recently reported that repeated social defeat stress (RSDS) may induce robust anxiety-like behaviors and social avoidance in mice. In the present study, we investigated whether melatonin receptor activation by melatonin and ramelteon regulates RSDS-induced behavioral changes. Melatonin treatment improved social avoidance and anxiety-like behaviors in RSDS mice. Moreover, treatment of the non-selective MT1/MT2 receptor agonist, ramelteon, markedly ameliorated RSDS-induced social avoidance and anxiety-like behaviors. Moreover, activating melatonin receptors also balanced the expression of monoamine oxidases, glucocorticoid receptors, and endogenous antioxidants in the hippocampus. Taken together, our findings indicate that the activation of both melatonin and ramelteon regulates RSDS-induced anxiety-like behaviors and PTSD symptoms. The current study also showed that the regulatory effects of neuroendocrine mechanisms and cognitive behaviors on melatonin receptor activation in repeated social defeat stress.
Assuntos
Ansiedade , Indenos , Melatonina , Derrota Social , Estresse Psicológico , Animais , Indenos/farmacologia , Camundongos , Masculino , Estresse Psicológico/metabolismo , Estresse Psicológico/tratamento farmacológico , Melatonina/farmacologia , Ansiedade/tratamento farmacológico , Ansiedade/psicologia , Comportamento Animal/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Receptores de Glucocorticoides/metabolismo , Receptores de Glucocorticoides/agonistas , Receptor MT1 de Melatonina/agonistas , Receptor MT1 de Melatonina/metabolismo , Receptor MT2 de Melatonina/agonistas , Receptor MT2 de Melatonina/metabolismo , Camundongos Endogâmicos C57BL , Monoaminoxidase/metabolismo , Receptores de Melatonina/agonistas , Receptores de Melatonina/metabolismo , Transtornos de Estresse Pós-Traumáticos/tratamento farmacológico , Transtornos de Estresse Pós-Traumáticos/psicologia , Transtornos de Estresse Pós-Traumáticos/metabolismoRESUMO
Our previous research has shown that melatonin (MLT) can reduce cryopreserved ovarian damage in mice. Yet, the molecular mechanism of MLT protection is still unclear. Some studies have shown that melatonin receptor 1 (MT1) is very important for animal reproductive system. To evaluate whether MLT exerts its protective effect on cryopreserved mice ovarian tissue via MT1, we added antagonist of MT1/MT2 (Luzindor) or antagonist of MT2 (4P-PDOT) to the freezing solution, followed by cryopreservation and thawing of ovarian tissue. The levels of total superoxide dismutase (T-SOD), catalase (CAT), nitric oxide (NO) and malondialdehyde (MDA) were detected. Besides, by using RT-PCR and Western blotting, the expression of Bcl-2, Bax and Nrf2/HO-1 signalling pathway-related proteins was detected. These findings demonstrated that compared with the melatonin group, the addition of Luzindor increased apoptosis, NO and MDA activities, decreased CAT and T-SOD activities and inhibited Nrf2/HO-1 signalling pathway. In conclusion, melatonin can play a protective role in cryopreserved ovarian tissue of mice through MT1 receptor.
Assuntos
Criopreservação , Melatonina , Fator 2 Relacionado a NF-E2 , Ovário , Estresse Oxidativo , Receptor MT1 de Melatonina , Transdução de Sinais , Animais , Feminino , Melatonina/farmacologia , Estresse Oxidativo/efeitos dos fármacos , Ovário/efeitos dos fármacos , Receptor MT1 de Melatonina/metabolismo , Receptor MT1 de Melatonina/genética , Transdução de Sinais/efeitos dos fármacos , Fator 2 Relacionado a NF-E2/metabolismo , Fator 2 Relacionado a NF-E2/genética , Camundongos , Criopreservação/veterinária , Triptaminas/farmacologia , Apoptose/efeitos dos fármacos , Heme Oxigenase (Desciclizante)/metabolismo , Heme Oxigenase (Desciclizante)/genética , Óxido Nítrico/metabolismo , Malondialdeído/metabolismo , Proteínas de Membrana , Heme Oxigenase-1RESUMO
Melatonin, a hormone synthesized in various tissues, plays a crucial role in modulating sperm characteristics, yet its protective function on boar sperm remains poorly understood. This study aimed to investigate the expression and localization of melatonin-related proteins (AANAT, ASMT, MT1, MT2, and NQO2) in pig tissues, assess the impact of melatonin on pig sperm motility parameters and quality, and elucidate the underlying molecular mechanisms. Our results revealed widespread expression of AANAT, ASMT, MT1, MT2, and NQO2 proteins in pig tissues, particularly in the testis. Specific localization patterns were observed in Leydig cells, reproductive epithelium, and columnar epithelium cells in the testis and cauda epididymis. Additionally, melatonin membrane receptors MT1 and MT2 were detected in boar sperm. Melatonin treatment significantly enhanced boar sperm motility parameters and quality, particularly with 10 nM melatonin treatment. Inhibition of the MT1 receptor, but not the MT2 receptor, resulted in decreased sperm motility, highlighting the pivotal role of the MT1 receptor in mediating melatonin's effects on boar sperm. Metabolomic analysis revealed significant alterations in sperm metabolites following melatonin supplementation, particularly in amino acid metabolism. Overall, our findings provide comprehensive insights into melatonin's mechanisms in improving boar sperm quality, suggesting its potential as a therapeutic agent for enhancing male fertility.
Assuntos
Melatonina , Receptor MT1 de Melatonina , Motilidade dos Espermatozoides , Animais , Melatonina/farmacologia , Masculino , Motilidade dos Espermatozoides/efeitos dos fármacos , Receptor MT1 de Melatonina/metabolismo , Suínos/fisiologia , Espermatozoides/efeitos dos fármacos , Espermatozoides/fisiologia , Fenômenos Biomecânicos , Análise do Sêmen/veterináriaRESUMO
Melatonin receptors MT1 and MT2 are G protein-coupled receptors that mediate the effects of melatonin, a hormone involved in circadian rhythms and other physiological functions. Understanding the molecular interactions between these receptors and their ligands is crucial for developing novel therapeutic agents. In this study, we used molecular docking, molecular dynamics simulations, and quantum mechanics calculation to investigate the binding modes and affinities of three ligands: melatonin (MLT), ramelteon (RMT), and 2-phenylmelatonin (2-PMT) with both receptors. Based on the results, we identified key amino acids that contributed to the receptor-ligand interactions, such as Gln181/194, Phe179/192, and Asn162/175, which are conserved in both receptors. Additionally, we described new meaningful interactions with Gly108/Gly121, Val111/Val124, and Val191/Val204. Our results provide insights into receptor-ligand recognition's structural and energetic determinants and suggest potential strategies for designing more optimized molecules. This study enhances our understanding of receptor-ligand interactions and offers implications for future drug development.
Assuntos
Melatonina , Simulação de Acoplamento Molecular , Simulação de Dinâmica Molecular , Ligação Proteica , Receptor MT1 de Melatonina , Receptor MT2 de Melatonina , Melatonina/metabolismo , Melatonina/química , Receptor MT2 de Melatonina/metabolismo , Receptor MT2 de Melatonina/química , Receptor MT1 de Melatonina/metabolismo , Receptor MT1 de Melatonina/química , Humanos , Ligantes , Teoria Quântica , Sítios de Ligação , Indenos/química , Indenos/metabolismoRESUMO
OBJECTIVE: To investigate the effects of excessive light exposure during gestation on intrauterine development and early growth of neonates in rats. METHODS: Pregnant rats were randomly allocated to three groups: the constant light exposure group, non-light exposure group and control group. Blood samples were collected from the tail vein to analyze melatonin and cortisol levels. Weight, daily food and water consumption were recorded. Uterine weight, placental weight and placental diameter were measured on gestational day 19. Natural birth and neonate growth were also monitored. The expression of NR1D1(nuclear receptor subfamily 1 group D member 1) in offspring's SCN (suprachiasmatic nuclei), liver and adipose tissue was measured. Expression of NR1D1, MT1(melatonin 1â¯A receptor) and 11ß-HSD2 (placental 11ß-hydroxysteroid dehydrogenase type 2) in placenta was also measured. Finally, the expression of MT1 and 11ß-HSD2 in NR1D1 siRNA transfected JEG-3 cells was evaluated. RESULTS: There were no significant differences in maternal weight gain, pregnancy duration, uterine weight, placental body weight, placental diameter, fetal number among three groups. There were no significant differences in weights or lengths of offspring at birth. Compared to other two groups, constant light exposure group showed significantly more rapid growth of offspring in 21st day post-birth. The expression of NR1D1 in SCN, liver and adipose tissues of offspring was not significantly different among three groups. The maternal serum melatonin and cortisol levels of the constant light exposure group were lower and higher than other two groups, respectively. The expressions of NR1D1, MT1 and 11ß-HSD2 were all decreased in placenta of the constant light exposure group. The expression of MT1 and 11ß-HSD2 in JEG-3 cells were decreased after NR1D1 siRNA transfection. CONCLUSION: Excessive light exposure during pregnancy results in elevated cortisol and reduced melatonin exposure to fetuses in uterus, potentially contributing to an accelerated early growth of offspring in rats.
Assuntos
Luz , Melatonina , Placenta , Animais , Feminino , Gravidez , Ratos , Placenta/efeitos da radiação , 11-beta-Hidroxiesteroide Desidrogenase Tipo 2 , Desenvolvimento Fetal/efeitos da radiação , Ratos Sprague-Dawley , Hidrocortisona/sangue , Membro 1 do Grupo D da Subfamília 1 de Receptores Nucleares/metabolismo , Efeitos Tardios da Exposição Pré-Natal , Receptor MT1 de Melatonina/metabolismo , Animais Recém-Nascidos , Exposição Materna , MasculinoRESUMO
Goat bucks are seasonal breeders that show variation in sperm quality, endogenous melatonin (MLT), and presumably in the expression of MLT receptors on the sperm throughout the year, which may modify sperm freezability. The aim of this study was to determine whether sperm freezability is associated with (i) endogenous melatonin levels in seminal plasma and (ii) the expression of sperm plasma membrane melatonin receptors (MT1, MT2). To evaluate this, spermatozoa from seven Saanen goat bucks were cryopreserved throughout the year in Mexico using a standard freezing protocol. Seminal plasma MLT concentrations were determined by ELISA and the expression and localization of MT1 and MT2 were detected by immunocytochemistry and confirmed by western blotting. The recovery rate of progressive motility after thawing was higher in spring than autumn and winter; in contrast, the F pattern (CTC assay) was higher in winter than in the other seasons. A proportional increase in the AR pattern (CTC assay) was smaller in winter than in the other seasons and the proportion of sperm showing high plasma membrane fluidity was higher in spring than in summer and autumn. The seminal plasma MLT concentrations showed no significant interseasonal differences. The MT1 receptor was immunolocalised at the apical region of the sperm head, while MT2 was mainly localised in the neck. The relative expression of MLT receptors showed significant differences between summer and winter for all bands, except at 75 kDa of MT2. In conclusion, there was an association between the relative expression of MT1 and MT2 receptors throughout the year and sperm freezability in goat bucks in México. Post-thaw sperm quality is enhanced in semen samples collected during breeding season.
Assuntos
Criopreservação , Cabras , Melatonina , Estações do Ano , Preservação do Sêmen , Sêmen , Espermatozoides , Animais , Masculino , Melatonina/metabolismo , Melatonina/sangue , Cabras/fisiologia , Cabras/metabolismo , Sêmen/química , Sêmen/metabolismo , Espermatozoides/metabolismo , Espermatozoides/fisiologia , Preservação do Sêmen/veterinária , Criopreservação/veterinária , Receptor MT1 de Melatonina/metabolismo , Receptor MT1 de Melatonina/genética , Receptor MT2 de Melatonina/metabolismo , Receptor MT2 de Melatonina/genética , Análise do Sêmen/veterinária , Receptores de Melatonina/metabolismoRESUMO
Context Several polymorphisms in the melatonin receptor 1A gene (MTNR1A ) have been related to reproductive performance in ovine. Aims To investigate the effect of the Rsa I and Mnl I polymorphisms on ram seminal quality. Methods Eighteen Rasa Aragonesa rams were genotyped for the Rsa I (C/C, C/T, T/T) and Mnl I (G/G, G/A, A/A) allelic variants of the MTNR1A gene. Individual ejaculates were analysed once a month throughout the whole year. Sperm motility, morphology, membrane integrity, levels of reactive oxygen species (ROS), phosphatidylserine (PS) inversion, DNA fragmentation and capacitation status were assessed. The effect of the season and polymorphisms on seminal quality was evaluated by mixed ANOVA. Key results Both polymorphisms had an effect on membrane integrity and viable spermatozoa with low levels of ROS and without PS translocation, and Rsa I also on motile and DNA-intact spermatozoa. An interaction between both polymorphisms was found, pointing to a negative effect on seminal quality of carrying the T or A allele in homozygosity. Differences were higher in the reproductive than in the non-reproductive season. Conclusions Mutations substituting C by T and G by A at Rsa I and Mnl I polymorphic sites, respectively, in the MTNR1A gene in rams could decrease the seminal quality. Implications Genotyping of rams based on melatonin receptor 1A could be a powerful tool in sire selection.
Assuntos
Receptor MT1 de Melatonina , Motilidade dos Espermatozoides , Espermatozoides , Masculino , Animais , Receptor MT1 de Melatonina/genética , Receptor MT1 de Melatonina/metabolismo , Espermatozoides/metabolismo , Motilidade dos Espermatozoides/genética , Ovinos/genética , Genótipo , Análise do Sêmen/veterinária , Polimorfismo Genético , Espécies Reativas de Oxigênio/metabolismo , Fragmentação do DNA , Polimorfismo de Nucleotídeo ÚnicoRESUMO
Sleep disorders affect millions of people around the world and have a high comorbidity with psychiatric disorders. While current hypnotics mostly increase non-rapid eye movement sleep (NREMS), drugs acting selectively on enhancing rapid eye movement sleep (REMS) are lacking. This polysomnographic study in male rats showed that the first-in-class selective melatonin MT1 receptor partial agonist UCM871 increases the duration of REMS without affecting that of NREMS. The REMS-promoting effects of UCM871 occurred by inhibiting, in a dose-response manner, the firing activity of the locus ceruleus (LC) norepinephrine (NE) neurons, which express MT1 receptors. The increase of REMS duration and the inhibition of LC-NE neuronal activity by UCM871 were abolished by MT1 pharmacological antagonism and by an adeno-associated viral (AAV) vector, which selectively knocked down MT1 receptors in the LC-NE neurons. In conclusion, MT1 receptor agonism inhibits LC-NE neurons and triggers REMS, thus representing a novel mechanism and target for REMS disorders and/or psychiatric disorders associated with REMS impairments.
Assuntos
Locus Cerúleo , Ratos Sprague-Dawley , Receptor MT1 de Melatonina , Sono REM , Animais , Masculino , Locus Cerúleo/efeitos dos fármacos , Locus Cerúleo/metabolismo , Locus Cerúleo/fisiologia , Ratos , Receptor MT1 de Melatonina/agonistas , Receptor MT1 de Melatonina/metabolismo , Sono REM/fisiologia , Sono REM/efeitos dos fármacos , Norepinefrina/metabolismo , Neurônios Adrenérgicos/efeitos dos fármacos , Neurônios Adrenérgicos/metabolismo , Neurônios Adrenérgicos/fisiologia , Neurônios/metabolismo , Neurônios/efeitos dos fármacos , Neurônios/fisiologiaRESUMO
Identifying the target cells of a hormone is a key step in understanding its function. Once the molecular nature of the receptors for a hormone has been established, researchers can use several techniques to detect these receptors. Here I will review the different tools used over the years to localize melatonin receptors and the problems associated with each of these techniques. The radioligand 2-[125I] iodomelatonin was the first tool to allow localization of melatonin receptors on tissue sections. Once the MT1 and MT2 receptors were cloned, in situ hybridization could be used to detect the messenger RNA for these receptors. The deduced amino acid sequences for MT1 and MT2 receptors allowed the production of peptide immunogens to generate antibodies against the MT1 and MT2 receptors. Finally, transgenic reporters driven by the promoter elements of the MT1 and MT2 genes have been used to map the expression of MT1 and MT2 in the brain and the retina. Several issues have complicated the localization of melatonin receptors and the characterization of melatonin target cells over the last three decades. Melatonin receptors are expressed at low levels, leading to sensitivity issues for their detection. The second problem are specificity issues with antibodies directed against the MT1 and MT2 melatonin receptors. These receptors are G protein-coupled receptors and many antibodies directed against such receptors have been shown to present similar problems concerning their specificity. Despite these specificity problems which start to be seriously addressed by recent studies, antibodies will be important tools in the future to identify and phenotype melatonin target cells. However, we will have to be more stringent than previously when establishing their specificity. The results obtained by these antibodies will have to be confronted and be coherent with results obtained by other techniques.
Assuntos
Encéfalo , Receptor MT1 de Melatonina , Receptor MT2 de Melatonina , Sequência de Aminoácidos , Encéfalo/metabolismo , Melatonina/metabolismo , Receptor MT1 de Melatonina/genética , Receptor MT1 de Melatonina/metabolismo , Receptor MT2 de Melatonina/genética , Receptor MT2 de Melatonina/metabolismoRESUMO
Melatonin is an important player in the regulation of many physiological functions within the body and in the retina. Melatonin synthesis in the retina primarily occurs during the night and its levels are low during the day. Retinal melatonin is primarily synthesized by the photoreceptors, but whether the synthesis occurs in the rods and/or cones is still unclear. Melatonin exerts its influence by binding to G protein-coupled receptors named melatonin receptor type 1 (MT1) and type 2 (MT2). MT1 and MT2 receptors activate a wide variety of signaling pathways and both receptors are present in the vertebrate photoreceptors where they may form MT1/MT2 heteromers (MT1/2h). Studies in rodents have shown that melatonin signaling plays an important role in the regulation of retinal dopamine levels, rod/cone coupling as well as the photopic and scotopic electroretinogram. In addition, melatonin may play an important role in protecting photoreceptors from oxidative stress and can protect photoreceptors from apoptosis. Critically, melatonin signaling is involved in the modulation of photoreceptor viability during aging and other studies have implicated melatonin in the pathogenesis of age-related macular degeneration. Hence melatonin may represent a useful tool in the fight to protect photoreceptors-and other retinal cells-against degeneration due to aging or diseases.
Assuntos
Melatonina , Animais , Melatonina/metabolismo , Neuroproteção , Retina/metabolismo , Receptores de Melatonina/metabolismo , Células Fotorreceptoras Retinianas Cones/metabolismo , Receptor MT1 de Melatonina/metabolismo , Receptor MT2 de Melatonina/metabolismo , Mamíferos/metabolismoRESUMO
Melatonin (5-methoxy-N-acetyltryptamine) binds with high affinity and specificity to membrane receptors. Several receptor subtypes exist in different species, of which the mammalian MT1 and MT2 receptors are the best-characterized. They are members of the G protein-coupled receptor superfamily, preferentially coupling to Gi/o proteins but also to other G proteins in a cell-context-depending manner. In this review, experts on melatonin receptors will summarize the current state of the field. We briefly report on the discovery and classification of melatonin receptors, then focus on the molecular structure of human MT1 and MT2 receptors and highlight the importance of molecular simulations to identify new ligands and to understand the structural dynamics of these receptors. We then describe the state-of-the-art of the intracellular signaling pathways activated by melatonin receptors and their complexes. Brief statements on the molecular toolbox available for melatonin receptor studies and future perspectives will round-up this review.
Assuntos
Melatonina , Receptor MT1 de Melatonina , Animais , Humanos , Receptores de Melatonina , Receptor MT1 de Melatonina/metabolismo , Receptor MT2 de Melatonina/metabolismo , Melatonina/metabolismo , Transdução de Sinais , Receptores Acoplados a Proteínas G , Mamíferos/metabolismoRESUMO
The labeled ligand commonly employed in competition binding studies for melatonin receptor ligands, 2-[125I]iodomelatonin, showed slow dissociation with different half-lives at the two receptor subtypes. This may affect the operational measures of affinity constants, which at short incubation times could not be obtained in equilibrium conditions, and structure-activity relationships, as the Ki values of tested ligands could depend on either interaction at the binding site or the dissociation path. To address these issues, the kinetic and saturation binding parameters of 2-[125I]iodomelatonin as well as the competition constants for a series of representative ligands were measured at a short (2 h) and a long (20 h) incubation time. Concurrently, we simulated by molecular modeling the dissociation path of 2-iodomelatonin from MT1 and MT2 receptors and investigated the role of interactions at the binding site on the stereoselectivity observed for the enantiomers of the subtype-selective ligand UCM1014. We found that equilibrium conditions for 2-[125I]iodomelatonin binding can be reached only with long incubation times, particularly for the MT2 receptor subtype, for which a time of 20 h approximates this condition. On the other hand, measured Ki values for a set of ligands including agonists, antagonists, nonselective, and subtype-selective compounds were not significantly affected by the length of incubation, suggesting that structure-activity relationships based on data collected at shorter time reflect different interactions at the binding site. Molecular modeling simulations evidenced that the slower dissociation of 2-iodomelatonin from the MT2 receptor can be related to the restricted mobility of a gatekeeper tyrosine along a lipophilic path from the binding site to the membrane bilayer. The enantiomers of the potent, MT2-selective agonist UCM1014 were separately synthesized and tested. Molecular dynamics simulations of the receptor-ligand complexes provided an explanation for their stereoselectivity as due to the preference shown by the eutomer at the binding site for the most abundant axial conformation adopted by the ligand in solution. These results suggest that, despite the slow-binding kinetics occurring for the labeled ligand, affinity measures at shorter incubation times give robust results consistent with known structure-activity relationships and with interactions taken at the receptor binding site.
Assuntos
Melatonina , Quinolinas , Ligantes , Receptores de Melatonina , Melatonina/metabolismo , Amidas , Receptor MT2 de Melatonina/metabolismo , Receptor MT1 de Melatonina/metabolismoRESUMO
The search for melatonin receptor agonists formed the main part of melatonin medicinal chemistry programs for the last three decades. In this short review, we summarize the two main aspects of these programs: the development of all the necessary tools to characterize the newly synthesized ligands at the two melatonin receptors MT1 and MT2, and the medicinal chemist's approaches to find chemically diverse ligands at these receptors. Both strategies are described. It turns out that the main source of tools were industrial laboratories, while the medicinal chemistry was mainly carried out in academia. Such complete accounts are interesting, as they delineate the spirits in which the teams were working demonstrating their strength and innovative character. Most of the programs were focused on nonselective agonists and few of them reached the market. In contrast, discovery of MT1-selective agonists and melatonergic antagonists with proven in vivo activity and MT1 or MT2-selectivity is still in its infancy, despite the considerable interest that subtype selective compounds may bring in the domain, as the physiological respective roles of the two subtypes of melatonin receptors, is still poorly understood. Poly-pharmacology applications and multitarget ligands have also been considered.
Assuntos
Receptor MT2 de Melatonina , Ligantes , Humanos , Animais , Receptor MT2 de Melatonina/metabolismo , Receptor MT2 de Melatonina/agonistas , Receptor MT1 de Melatonina/metabolismo , Receptor MT1 de Melatonina/agonistas , Receptor MT1 de Melatonina/antagonistas & inibidores , Receptores de Melatonina/metabolismo , Receptores de Melatonina/agonistas , Melatonina/metabolismo , História do Século XXRESUMO
Melatonin is a neuroendocrine hormone that regulates the circadian rhythm and many other physiological processes. Its functions are primarily exerted through two subtypes of human melatonin receptors, termed melatonin type-1 (MT1) and type-2 (MT2) receptors. Both MT1 and MT2 receptors are generally classified as Gi-coupled receptors owing to their well-recognized ability to inhibit cAMP accumulation in cells. However, it remains an enigma as to why melatonin stimulates cAMP production in a number of cell types that express the MT1 receptor. To address if MT1 can dually couple to Gs and Gi proteins, we employed a highly sensitive luminescent biosensor (GloSensorTM) to monitor the real-time changes in the intracellular cAMP level in intact live HEK293 cells that express MT1 and/or MT2. Our results demonstrate that the activation of MT1, but not MT2, leads to a robust enhancement on the forskolin-stimulated cAMP formation. In contrast, the activation of either MT1 or MT2 inhibited cAMP synthesis driven by the activation of the Gs-coupled ß2-adrenergic receptor, which is consistent with a typical Gi-mediated response. The co-expression of MT1 with Gs enabled melatonin itself to stimulate cAMP production, indicating a productive coupling between MT1 and Gs. The possible existence of a MT1-Gs complex was supported through molecular modeling as the predicted complex exhibited structural and thermodynamic characteristics that are comparable to that of MT1-Gi. Taken together, our data reveal that MT1, but not MT2, can dually couple to Gs and Gi proteins, thereby enabling the bi-directional regulation of adenylyl cyclase to differentially modulate cAMP levels in cells that express different complements of MT1, MT2, and G proteins.
Assuntos
Melatonina , Humanos , Receptores de Melatonina/metabolismo , Melatonina/farmacologia , Células HEK293 , Receptor MT1 de Melatonina/metabolismo , Receptor MT2 de Melatonina/metabolismo , Proteínas de Ligação ao GTP/metabolismoRESUMO
Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic (DA) neurons and aggregation of α-synuclein (α-syn). Ferroptosis, a form of cell death induced by iron accumulation and lipid peroxidation, is involved in the pathogenesis of PD. It is unknown whether melatonin receptor 1 (MT1) modulates α-syn and ferroptosis in PD. Here, we used α-syn preformed fibrils (PFFs) to induce PD models in vivo and in vitro. In PD mice, α-syn aggregation led to increased iron deposition and ferroptosis. MT1 knockout exacerbated these changes and resulted in more DA neuronal loss and severe motor impairment. MT1 knockout also suppressed the Sirt1/Nrf2/Ho1/Gpx4 pathway, reducing resistance to ferroptosis, and inhibited expression of ferritin Fth1, leading to more release of ferrous ions. In vitro experiments confirmed these findings. Knockdown of MT1 enhanced α-syn PFF-induced intracellular α-syn aggregation and suppressed expression of the Sirt1/Nrf2/Ho1/Gpx4 pathway and Fth1 protein, thereby aggravating ferroptosis. Conversely, overexpression of MT1 reversed these effects. Our findings reveal a novel mechanism by which MT1 activation prevents α-syn-induced ferroptosis in PD, highlighting the neuroprotective role of MT1 in PD.
Assuntos
Ferroptose , Melatonina , Doença de Parkinson , Camundongos , Animais , Doença de Parkinson/metabolismo , Doença de Parkinson/patologia , alfa-Sinucleína/metabolismo , alfa-Sinucleína/farmacologia , Fator 2 Relacionado a NF-E2/metabolismo , Melatonina/farmacologia , Receptor MT1 de Melatonina/metabolismo , Sirtuína 1/metabolismo , Neurônios Dopaminérgicos , Ferro/metabolismoRESUMO
Melatonin has antiproliferative, antiangiogenic, apoptotic, and immunomodulatory properties in ovarian cancer. Considering those, we evaluated the relationship between melatonin 1 (MT1) and melatonin 2 receptor (MT2) expression in tumor tissues of patients with epithelial ovarian cancer, disease-free survival (DFS), and overall survival (OS). Patients who received primary surgical treatment for epithelial ovarian cancer in our clinic between 2000 and 2019 were retrospectively scanned through patient files, electronic databases, and telephone calls. One hundred forty-two eligible patients were included in the study, their tumoral tissues were examined to determine MT1 and MT2 expression by immunohistochemical methods. The percentage of receptor-positive cells and intensity of staining were determined. MT1 receptor expression ( P = 0.002 for DFS and P = 0.002 for OS) showed a significant effect on DFS and OS. MT2 expression had no effect on survival ( P = 0.593 for DFS and P = 0.209 for OS). The results showed that the higher the MT1 receptor expression, the longer the DFS and OS. It is suggested that melatonin should be considered as adjuvant therapy for ovarian cancer patients in addition to standard treatment, and clinical progress should be observed.
Assuntos
Melatonina , Neoplasias Ovarianas , Humanos , Feminino , Melatonina/metabolismo , Receptor MT1 de Melatonina/metabolismo , Carcinoma Epitelial do Ovário , Receptor MT2 de Melatonina/metabolismo , Estudos RetrospectivosRESUMO
Stroke is the leading cause of death and disability worldwide. Novel and effective therapies for ischemic stroke are urgently needed. Here, we report that melatonin receptor 1A (MT1) agonist ramelteon is a neuroprotective drug candidate as demonstrated by comprehensive experimental models of ischemic stroke, including a middle cerebral artery occlusion (MCAO) mouse model of cerebral ischemia in vivo, organotypic hippocampal slice cultures ex vivo, and cultured neurons in vitro; the neuroprotective effects of ramelteon are diminished in MT1-knockout (KO) mice and MT1-KO cultured neurons. For the first time, we report that the MT1 receptor is significantly depleted in the brain of MCAO mice, and ramelteon treatment significantly recovers the brain MT1 losses in MCAO mice, which is further explained by the Connectivity Map L1000 bioinformatic analysis that shows gene-expression signatures of MCAO mice are negatively connected to melatonin receptor agonist like Ramelteon. We demonstrate that ramelteon improves the cerebral blood flow signals in ischemic stroke that is potentially mediated, at least, partly by mechanisms of activating endothelial nitric oxide synthase. Our results also show that the neuroprotection of ramelteon counteracts reactive oxygen species-induced oxidative stress and activates the nuclear factor erythroid 2-related factor 2/heme oxygenase-1 pathway. Ramelteon inhibits the mitochondrial and autophagic death pathways in MCAO mice and cultured neurons, consistent with gene set enrichment analysis from a bioinformatics perspective angle. Our data suggest that Ramelteon is a potential neuroprotective drug candidate, and MT1 is the neuroprotective target for ischemic stroke, which provides new insights into stroke therapy. MT1-KO mice and cultured neurons may provide animal and cellular models of accelerated ischemic damage and neuronal cell death.