Thirty-seven years of MT1 and MT2 melatonin receptor localization in the brain: Past and future challenges

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.

MTNR1B genotype and effects of carbohydrate quantity and dietary glycaemic index on glycaemic response to an oral glucose load: the OmniCarb trial

AIMS/HYPOTHESIS

A type 2 diabetes-risk-increasing variant, MTNR1B (melatonin receptor 1B) rs10830963, regulates the circadian function and may influence the variability in metabolic responses to dietary carbohydrates. We investigated whether the effects of carbohydrate quantity and dietary glycaemic index (GI) on glycaemic response during OGTTs varied by the risk G allele of MTNR1B-rs10830963.

METHODS

This study included participants (n=150) of a randomised crossover-controlled feeding trial of four diets with high/low GI levels and high/low carbohydrate content for 5 weeks. The MTNR1B-rs10830963 (C/G) variant was genotyped. Glucose response during 2 h OGTT was measured at baseline and the end of each diet intervention.

RESULTS

Among the four study diets, carrying the risk G allele (CG/GG vs CC genotype) of MTNR1B-rs10830963 was associated with the largest AUC of glucose during 2 h OGTT after consuming a high-carbohydrate/high-GI diet (β 134.32 [SE 45.69] mmol/l × min; p=0.004). The risk G-allele carriers showed greater increment of glucose during 0-60 min (β 1.26 [0.47] mmol/l; p=0.008) or 0-90 min (β 1.10 [0.50] mmol/l; p=0.028) after the high-carbohydrate/high-GI diet intervention, but not after consuming the other three diets. At high carbohydrate content, reducing GI levels decreased 60 min post-OGTT glucose (mean -0.67 [95% CI: -1.18, -0.17] mmol/l) and the increment of glucose during 0-60 min (mean -1.00 [95% CI: -1.67, -0.33] mmol/l) and 0-90 min, particularly in the risk G-allele carriers (pinteraction <0.05 for all).

CONCLUSIONS/INTERPRETATION

Our study shows that carrying the risk G allele of MTNR1B-rs10830963 is associated with greater glycaemic responses after consuming a diet with high carbohydrates and high GI levels. Reducing GI in a high-carbohydrate diet may decrease post-OGTT glucose concentrations among the risk G-allele carriers.

MTNR1B gene variations and high pre-pregnancy BMI increase gestational diabetes mellitus risk in Chinese women

AIM

To investigate the association of melatonin receptor 1B (MTNR1B) gene variations and pre-pregnancy body mass index (BMI) with gestational diabetes mellitus (GDM).

MATERIALS AND METHOD

In this study, 1566 Chinese Han pregnant women were enrolled and multiple genetic models were used to evaluate the association between MTNR1B gene polymorphisms and the risk of GDM. The clinical value of pre-pregnancy BMI in predicting GDM was analyzed and evaluated using receiver operating characteristic (ROC) curves. Several methods of analysis were used to examine the impact of gene-gene and gene-BMI interactions on the incidence of GDM influence.

RESULTS

For the MTNR1B gene, rs1387153 (C > T), rs10830962 (C > G), rs4753426 (T > C), and rs10830963 (C > G) are all risk mutations associated with the susceptibility of GDM. The ROC curve analysis indicated that the BMI demonstrated an area under the curve (AUC) of 0.595. Alongside, the sensitivity and specificity stood at 0.676 and 0.474 respectively. The maximum Joden index was found to be 0.150, with a corresponding critical BMI value of 20.5691 kg/m2. Interaction analysis revealed that gene-gene and gene-BMI interactions had no significant effect on GDM occurrence.

CONCLUSION

MTNR1B genetic variations confers the risk to GDM in Chinese women. Furthermore, the high pre-pregnancy BMI (≥20.5691 kg/m2) significantly increases the risk of GDM in Chinese women.

Melatonin Alleviates Lipopolysaccharide-Induced Abnormal Pregnancy through MTNR1B Regulation of m6A

Pregnancy is a highly intricate and delicate process, where inflammation during early stages may lead to pregnancy loss or defective implantation. Melatonin, primarily produced by the pineal gland, exerts several pharmacological effects. N6-methyladenosine (m6A) is the most prevalent mRNA modification in eukaryotes. This study aimed to investigate the association between melatonin and m6A during pregnancy and elucidate the underlying protective mechanism of melatonin. Melatonin was found to alleviate lipopolysaccharide (LPS)-induced reductions in the number of implantation sites. Additionally, it mitigated the activation of inflammation, autophagy, and apoptosis pathways, thereby protecting the pregnancy process in mice. The study also revealed that melatonin regulates uterine m6A methylation levels and counteracts abnormal changes in m6A modification of various genes following LPS stimulation. Furthermore, melatonin was shown to regulate m6A methylation through melatonin receptor 1B (MTNR1B) and subsequently modulate inflammation, autophagy, and apoptosis through m6A. In conclusion, our study demonstrates that melatonin protects pregnancy by influencing inflammation, autophagy, and apoptosis pathways in an m6A-dependent manner via MTNR1B. These findings provide valuable insights into the mechanisms underlying melatonin's protective effects during pregnancy and may have implications for potential therapeutic strategies in managing pregnancy-related complications.

MTNR 1B (rs10830963) Gene Polymorphism, but not MTNR 1A (rs2119882), Associated with Type 2 Diabetes Mellitus Risk in Saudi Arabia

BACKGROUND

Disrupted circadian rhythm has been linked to the pathogenesis of type 2 diabetes mellitus (T2DM). Single nucleotide polymorphisms (SNPs) in melatonin receptors (MTNR), MTNR 1A rs2119882 (T>C) and MTNR 1B rs10830963 (C>G) may interfere with the normal function of melatonin and increase the risk of T2DM. This study investigated the prevalence of MTNR 1A rs2119882 (T>C) and MTNR 1B rs10830963 (C>G) SNPs and tested their association with T2DM in Saudi Arabian population.

METHODS

A total of 459 Saudi Arabian participants from Jazan Province, Saudi Arabia, were selected and included 227 T2DM patients and 232 control subjects. DNA was extracted from all participants and genotyped for rs2119882 and rs10830963 SNPs using TaqMan technology. Genotype frequencies were determined for both SNPs, and logistic regression was fitted to test the association with T2DM.

RESULTS

No association was found between MTNR 1A rs2119882 (T>C) SNP and T2DM (odds ratio (OR) = 0.69; 95% confidence interval (CI) = 0.44 - 1.08; p-value = 0.111). However, the MTNR 1B rs10830963 (C>G) SNP was significantly associated with T2DM (OR = 1.73; 95% CI = 1.18 - 2.55; p-value = 0.0065). Co-inheritance of the MTNR 1B rs10830963 G allele and MTNR 1A rs2119882 T allele further increased the risk of T2DM (OR = 2.80; 95% CI = 1.71 - 4.57; p-value < 0.0001).

CONCLUSIONS

The minor G allele of the MTNR 1B rs10830963 SNP was significantly associated with T2DM in our population. This association further intensified with the presence of the T allele in MTNR 1A rs2119882 locus. This study sheds light on the importance of melatonin receptor polymorphisms as genetic candidates for the development of T2DM in Saudi Arabia.

Melatonin MT1 receptors as a target for the psychopharmacology of bipolar disorder: A translational study

The treatment of bipolar disorder (BD) still remains a challenge. Melatonin (MLT), acting through its two receptors MT1 and MT2, plays a key role in regulating circadian rhythms which are dysfunctional in BD. Using a translational approach, we examined the implication and potential of MT1 receptors in the pathophysiology and psychopharmacology of BD. We employed a murine model of the manic phase of BD (Clock mutant (ClockΔ19) mice) to study the activation of MT1 receptors by UCM871, a selective partial agonist, in behavioral pharmacology tests and in-vivo electrophysiology. We then performed a high-resolution Nuclear Magnetic Resonance study on isolated membranes to characterize the molecular mechanism of interaction of UCM871. Finally, in a cohort of BD patients, we investigated the link between clinical measures of BD and genetic variants located in the MT1 receptor and CLOCK genes. We demonstrated that: 1) UCM871 can revert behavioral and electrophysiological abnormalities of ClockΔ19 mice; 2) UCM871 promotes the activation state of MT1 receptors; 3) there is a significant association between the number of severe manic episodes and MLT levels, depending on the genetic configuration of the MT1 rs2165666 variant. Overall, this work lends support to the potentiality of MT1 receptors as target for the treatment of BD.

MTNR1B rs1387153 Polymorphism and Risk of Gestational Diabetes Mellitus: Meta-Analysis and Trial Sequential Analysis

BACKGROUND

Published data on the association between the MTNR1B rs1387153 polymorphism and gestational diabetes mellitus (GDM) risk are controversial.

OBJECTIVE

A meta-analysis was performed to assess whether the polymorphism of MTNR1B rs1387153 is associated with GDM risk.

METHOD

Medline, Embase, China National Knowledge Infrastructure, and Chinese Biomedicine Databases were searched to identify eligible studies. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) for MTNR1B rs1387153 polymorphism and GDM were appropriately derived from fixed-effects or random effects models.

RESULTS

A total of 8 studies were enrolled in this meta-analysis. The pooled analyses revealed that MTNR1B rs1387153 polymorphism significantly increased the risk of GDM in all models (allele contrast (C vs. T): OR, 0.78; 95% CI, 0.73-0.83; homozygote (CC vs. TT): OR, 0.61; 95% CI, 0.53-0.69; heterozygote (CT vs. TT): OR, 0.78; 95% CI, 0.69-0.89; dominant model (CC + CT vs. TT): OR, 0.71; 95% CI, 0.63-0.80; recessive model (CC vs. CT + TT): OR, 0.73; 95% CI, 0.67-0.81). Further subgroup analyses by ethnicity of participants yielded similar positive results.

CONCLUSIONS

Present meta-analysis reveals that MTNR1B rs1387153 variant may serve as genetic biomarkers of GDM.

Relationship Between Genetic Variant Of OXTR (Rs53576) And MTNR1B (Rs1387153) And Symptoms Of Psychological Stress In Females With Gestational Diabetes Mellitus

Objective

To assess the association of oxytocin receptor (rs53576) and melatonin hormone receptor 1B (rs1387153) gene single nucleotide polymorphisms with psychological symptoms in women with gestational diabetes mellitus.

METHODS

The case-control study was conducted from May 1 to June 1, 2022, at the Department of Physiology, University of Karachi, in collaboration with the Department of Biological and Biomedical Sciences, Aga Khan University, Karachi, and the Department of Obstetrics and Gynaecology, Jinnah Postgraduate Medical Centre, Karachi. Fifty gestational diabetic pregnant women and ninety healthy pregnant women were recruited. Sanger sequencing was performed to assess the genotypic frequency and polymorphic variation of all subjects. Perceived stress scale and diabetes-related distress scale were used to assess the stress levels. Data was analysed using SPSS 23.

RESULTS

Of the 140 subjects, 90 (64.3%) were controls with mean age 24.96±4.35 years, and 50 (35.7%) were cases with mean age 28.78±5.25 (p<0.05). Mean body weight and mean gestational age were not significantly different between the groups (p>0.05). Melatonin hormone receptor 1B rs1387153 frequency was significantly different between the groups (p<0.05). Among the cases, a significant mean difference for regimen distress scores between AA and GG was observed for oxytocin receptor rs53576 (p=0.04). A significant mean difference in sum of PSS, diabetes-related stress, total diabetes- related stress and emotional distress was noted between CC and TT genotypes for melatonin hormone receptor 1B rs1387153 (p=0.001).

Conclusion

MTNR1B rs1387153 genotypes were associated with perceived stress, diabetes-related stress, diabetic distress, and emotional burden, while OXTR rs53576 genotypes were associated with regimen distress in GDM women.

Astrocyte-Ablation of Mtnr1b Increases Anxiety-Like Behavior in Adult Male Mice

BACKGROUND

Astrocytes are essential for synaptic transmission, and their dysfunction can result in neuropsychiatric disorders such as anxiety and depression. Many studies have shown that global knockout of Melatonin receptor 2 (Mtnr1b) is associated with the development of various mental disorders.

AIM

This study aimed to investigate the effects of astrocyte ablation of Mtnr1b on cognitive function and anxiety-like behavior in mice, as well as the potential biological mechanisms.

METHODS

A conditional Cre-loxP system allowing deletion of Mtnr1b from astrocytes was developed to investigate the specific role Mtnr1b. Control and Mtnr1b cKO𝐺𝑓𝑎𝑝 mice were selected for cognitive function behavioral testing (Morris water maze test, novel object recognition test) and emotion-related behavioral testing (open field, elevated plus maze). After testing, brain tissue was collected and examined by immunofluorescence for the expression of neuronal nuclei (NeuN), glutamate decarboxylase 67 (GAD67), and vesicular glutamate transporter 1 (vGluT1). RNA-seq was performed on hippocampal tissue from control and Mtnr1b cKO𝐺𝑓𝑎𝑝 mice to identify differentially expressed genes. Additional confirmation of differential gene expression was performed using real-time quantitative polymerase chain reaction (qRT-PCR).

RESULTS

Mtnr1b cKO𝐺𝑓𝑎𝑝 mice were not significantly different from control mice in the Morris water maze and novel object recognition tests. Results from the open field and elevated plus maze tests showed that Mtnr1b cKO𝐺𝑓𝑎𝑝 mice exhibited significantly more anxiety-like behavior than did controls. Immunofluorescence revealed that the number of mature neurons did not differ significantly between Mtnr1b cKO𝐺𝑓𝑎𝑝 mice and controls. The expression of GAD67 in the hippocampal CA1 and CA3 areas of Mtnr1b cKO𝐺𝑓𝑎𝑝 mice was significantly lower than in the control group, but no significant difference was detected for vGluT1 expression. RNA-seq and qRT-PCR results showed that Mtnr1b knockout in astrocytes led to a decrease in the levels of gamma-aminobutyric acid sub-type A (GABAA) receptors and Kir2.2.

CONCLUSIONS

The astrocyte-specific knockout in Mtnr1b cKO𝐺𝑓𝑎𝑝 mice results in anxiety-like behavior, which is caused by down-regulation of gamma-aminobutyric acid-ergic (GABAergic) synaptic function.

Myocardial Infarction Susceptibility and the MTNR1B Polymorphisms

Melatonin is a circadian hormone with antioxidant properties that protects against myocardial ischemia-reperfusion injury. Genetic variations of the melatonin receptor 1B gene (MTNR1B) play an important role in the development of type 2 diabetes, a risk factor for cardiovascular diseases. Accordingly, MTNR1B polymorphisms are crucial in numerous disorders of the cardiovascular system. Therefore, the aim of the present study was to investigate a possible association of MTNR1B polymorphisms with chronotype and susceptibility to myocardial infarction. The present case-control study included 199 patients with myocardial infarction (MI) (57% men) and 198 control participants (52% men) without previous cardiovascular diseases who underwent genotyping for the MTNR1B polymorphisms rs10830963, rs1387153, and rs4753426 from peripheral blood samples. Chronotype was determined using the Morningness-Eveningness Questionnaire (MEQ). As estimated by the chi-square test, no significant association was found in the distribution of alleles and genotypes between myocardial infarction patients and controls. In addition, there was no association between MTNR1B polymorphisms and chronotype in MI patients. As some previous studies have shown, the present negative results do not exclude the role of the MTNR1B polymorphisms studied in the development of myocardial infarction. Rather, they may indicate that MTNR1B polymorphisms are a minor risk factor for myocardial infarction.

Molecular Mechanisms of the Melatonin Receptor Pathway Linking Circadian Rhythm to Type 2 Diabetes Mellitus

Night-shift work and sleep disorders are associated with type 2 diabetes (T2DM), and circadian rhythm disruption is intrinsically involved. Studies have identified several signaling pathways that separately link two melatonin receptors (MT1 and MT2) to insulin secretion and T2DM occurrence, but a comprehensive explanation of the molecular mechanism to elucidate the association between these receptors to T2DM, reasonably and precisely, has been lacking. This review thoroughly explicates the signaling system, which consists of four important pathways, linking melatonin receptors MT1 or MT2 to insulin secretion. Then, the association of the circadian rhythm with MTNR1B transcription is extensively expounded. Finally, a concrete molecular and evolutionary mechanism underlying the macroscopic association between the circadian rhythm and T2DM is established. This review provides new insights into the pathology, treatment, and prevention of T2DM.

MTNR1A and MTNR1B Gene Variants of the Melatonin Receptor and Arterial Stiffness in Persons without Arterial Hypertension

A comparative analysis of vascular stiffness indices and the results of blood test was carried out in 85 healthy donors aged 19-64 years, carriers of polymorphic variants of type 1 and type 2 melatonin receptor genes. The associations of polymorphic markers of type 1 MTNR1A (rs34532313) and type 2 MTNR1B (rs10830963) melatonin receptor genes with parameters of vascular stiffness and blood parameters in healthy patients were studied. Genotyping was performed using allele-specific PCR. In all patients, 24-h BP monitoring with assessment of arterial stiffness was performed. Allele C homozygotes of MTNR1A differed significantly from carriers of the major T allele by elevated triglyceride, LDL, and fibrinogen levels. The major allele C of the rs10830963 polymorphic variant of the MTNR1B gene is associated with elevated LDL and triglycerides, as well as with individual differences in the elastic properties of the vascular wall in the examined subjects.

No association between a common type 2 diabetes risk gene variant in the melatonin receptor gene (MTNR1B) and mortality among type 2 diabetes patients

The minor G risk allele in the common melatonin receptor gene (MTNR1B, rs10830963) has been associated with an increased risk of myocardial infarction among patients with type 2 diabetes (T2D). Furthermore, activating the melatonin receptor 1B through melatonin has been shown to promote cell proliferation, which could be hypothesized to increase cancer risk. Cardiovascular disease (CVD) and cancer are common causes of death among patients with T2D. Using data from 14 736  patients with T2D who participated in the UK Biobank investigation, we hypothesized an additive effect of the G risk allele on all-cause mortality, CVD mortality, and cancer mortality. As shown by Cox regression adjusted for confounders such as age, glucose-lowering medication, and socioeconomic status, no significant trend between the number of G risk alleles and mortality outcomes was found during the follow-up period of 11.1 years. Our negative findings do not speak against the role of this gene variant in the development of T2D, as repeatedly shown by previous large-scale studies. Instead, they may suggest that rs10830963 is less relevant for mortality risk in patients with T2D.

Beta-Galactosidase as a Transgenic Reporter for the Mapping and Phenotyping of MT1 and MT2 Melatonin Receptor-Expressing Cells

Genetic technology allows inserting transgenic reporters such as beta-galactosidase (LacZ) into the loci of the Mtnr1a (MT₁) and Mtnr1b (MT₂) receptor genes to track MT₁ and MT₂ melatonin receptor expression. Given the limited sensitivity of nonradioactive in situ hybridization and the problematic specificity of existing melatonin receptor antibodies for immunohistochemistry, this new technology is a key tool to study the localization and the phenotypes of cells expressing melatonin receptors. Here we describe two protocols to detect transgenic LacZ expression driven by the MT₁ or MT₂ promoters either by the enzymatic activity of the transgenic LacZ enzyme or by using specific antibodies against LacZ with immunohistochemistry. This approach has already yielded a detailed mapping of both MT₁ and MT₂ expression in the mouse brain and retina. Furthermore, we also phenotyped some of the most important types of cells expressing these two melatonin receptors.

The rs10830963 Polymorphism of the MTNR1B Gene: Association With Abnormal Glucose, Insulin and C-peptide Kinetics

BACKGROUND

The MTNR1B gene encodes a receptor for melatonin, a hormone regulating biorhythms. Disruptions in biorhythms contribute to the development of type 2 diabetes mellitus (T2DM). Genetic studies suggest that variability in the MTNR1B gene affects T2DM development. Our aim was to compare the distribution of the genetic variant rs10830963 between persons differing in glucose tolerance in a sample of the Czech population (N=1206). We also evaluated possible associations of the polymorphism with insulin sensitivity, beta cell function, with the shape of glucose, insulin and C-peptide trajectories measured 7 times during a 3-hour oral glucose tolerance test (OGTT) and with glucagon response. In a subgroup of 268 volunteers we also evaluated sleep patterns and biorhythm.

RESULTS

13 persons were diagnosed with T2DM, 119 had impaired fasting blood glucose (IFG) and/or impaired glucose tolerance (IGT). 1074 participants showed normal results and formed a control group. A higher frequency of minor allele G was found in the IFG/IGT group in comparison with controls. The GG constellation was present in 23% of diabetics, in 17% of IFG/IGT probands and in 11% of controls. Compared to CC and CG genotypes, GG homozygotes showed higher stimulated glycemia levels during the OGTT. Homozygous as well as heterozygous carriers of the G allele showed lower very early phase of insulin and C-peptide secretion with unchanged insulin sensitivity. These differences remained significant after excluding diabetics and the IFG/IGT group from the analysis. No associations of the genotype with the shape of OGTT-based trajectories, with glucagon or with chronobiological patterns were observed. However, the shape of the trajectories differed significantly between men and women.

CONCLUSION

In a representative sample of the Czech population, the G allele of the rs10830963 polymorphism is associated with impaired early phase of beta cell function, and this is evident even in healthy individuals.

MTNR1B polymorphisms with CDKN2A and MGMT methylation status are associated with poor prognosis of colorectal cancer in Taiwan

BACKGROUND

Identifying novel colorectal cancer (CRC) prognostic biomarkers is crucial to helping clinicians make appropriate therapy decisions. Melatonin plays a major role in managing the circadian rhythm and exerts oncostatic effects on different kinds of tumours.

AIM

To explore the relationship between MTNR1B single-nucleotide polymorphism (SNPs) combined with gene hypermethylation and CRC prognosis.

METHODS

A total of 94 CRC tumour tissues were investigated. Genotyping for the four MTNR1B SNPs (rs1387153, rs2166706, rs10830963, and rs1447352) was performed using multiplex polymerase chain reaction. The relationships between the MTNR1B SNPs and CRC 5-year overall survival (OS) was assessed by calculating hazard ratios with 95%CIs.

RESULTS

All SNPs (rs1387153, rs2166706, rs10830963, and rs1447352) were correlated with decreased 5-year OS. In stratified analysis, rs1387153, rs10830963, and rs1447352 risk genotype combined with CDKN2A and MGMT methylation status were associated with 5-year OS. A strong cumulative effect of the four polymorphisms on CRC prognosis was observed. Four haplotypes of MTNR1B SNPs were also associated with the 5-year OS. MTNR1B SNPs combined with CDKN2A and MGMT gene methylation status could be used to predict shorter CRC survival.

CONCLUSION

The novel genetic biomarkers combined with epigenetic biomarkers may be predictive tool for CRC prognosis and thus could be used to individualise treatment for patients with CRC.

MT1 and MT2 melatonin receptors play opposite roles in brain cancer progression

Primary brain tumors remain among the deadliest of all cancers. Glioma grade IV (glioblastoma), the most common and malignant type of brain cancer, is associated with a 5-year survival rate of < 5%. Melatonin has been widely reported as an anticancer molecule, and we have recently demonstrated that the ability of gliomas to synthesize and accumulate this indolamine in the surrounding microenvironment negatively correlates with tumor malignancy. However, our understanding of the specific effects mediated through the activation of melatonin membrane receptors remains limited. Thus, here we investigated the specific roles of MT1 and MT2 in gliomas and medulloblastomas. Using the MT2 antagonist DH97, we showed that MT1 activation has a negative impact on the proliferation of human glioma and medulloblastoma cell lines, while MT2 activation has an opposite effect. Accordingly, gliomas have a decreased mRNA expression of MT1 (also known as MTNR1A) and an increased mRNA expression of MT2 (also known as MTNR1B) compared to the normal brain cortex. The MT1/MT2 expression ratio negatively correlates with the expression of cell cycle-related genes and is a positive prognostic factor in gliomas. Notably, we showed that functional selective drugs that simultaneously activate MT1 and inhibit MT2 exert robust anti-tumor effects in vitro and in vivo, downregulating the expression of cell cycle and energy metabolism genes in glioma stem-like cells. Overall, we provided the first evidence regarding the differential roles of MT1 and MT2 in brain tumor progression, highlighting their relevance as druggable targets. KEY MESSAGES: • MT1 impairs while MT2 promotes the proliferation of glioma and medulloblastoma cell lines. • Gliomas have a decreased expression of MT1 and an increased expression of MT2 compared to normal brain cortex. • Tumors with a high MT1/MT2 expression ratio have significantly better survival rates. • Functional selective drugs that simultaneously activate MT1 and inhibit MT2 downregulate the expression of cell cycle and energy metabolism genes in glioma stem-like cells and exert robust anti-tumor effects in vivo.

Association of Common Genetic Risk Variants With Gestational Diabetes Mellitus and Their Role in GDM Prediction

OBJECTIVE

We aimed to explore the associations between common genetic risk variants with gestational diabetes mellitus (GDM) risk in Russian women and to assess their utility in the identification of GDM cases.

METHODS

We conducted a case-control study including 1,142 pregnant women (688 GDM cases and 454 controls) enrolled at Almazov National Medical Research Centre. The International Association of Diabetes and Pregnancy Study Groups criteria were used to diagnose GDM. A total of 11 single- nucleotide polymorphisms (SNPs), including those in HKDC1 (rs10762264), GCK (rs1799884), MTNR1B (rs10830963 and rs1387153), TCF7L2 (rs7903146 and rs12255372), KCNJ11 (rs5219), IGF2BP2 (rs4402960), IRS1 (rs1801278), FTO (rs9939609), and CDKAL1 (rs7754840) were genotyped using Taqman assays. A logistic regression model was used to calculate odds ratios (ORs) and their confidence intervals (CIs). A simple-count genetic risk score (GRS) was calculated using 6 SNPs. The area under the receiver operating characteristic curve (c-statistic) was calculated for the logistic regression model predicting the risk of GDM using clinical covariates, SNPs that had shown a significant association with GDM in our study, GRS, and their combinations.

RESULTS

Two variants in MTNR1B (rs1387153 and rs10830963) demonstrated a significant association with an increased risk of GDM. The association remained significant after adjustment for age, pre-gestational BMI, arterial hypertension, GDM in history, impaired glucose tolerance, polycystic ovary syndrome, family history of diabetes, and parity (P = 0.001 and P < 0.001, respectively). After being conditioned by each other, the effect of rs1387153 on GDM predisposition weakened while the effect of rs10830963 remained significant (P = 0.004). The risk of GDM was predicted by clinical variables (c-statistic 0.712, 95 % CI: 0.675 - 0.749), and the accuracy of prediction was modestly improved by adding GRS to the model (0.719, 95 % CI 0.682 - 0.755), and more by adding only rs10830963 (0.729, 95 % CI 0.693 - 0.764).

CONCLUSION

Among 11 SNPs associated with T2D and/or GDM in other populations, we confirmed significant association with GDM for two variants in MTNR1B in Russian women. However, these variants showed limited value in the identification of GDM cases.

Chronological Age Interacts with the Circadian Melatonin Receptor 1B Gene Variation, Determining Fasting Glucose Concentrations in Mediterranean Populations. Additional Analyses on Type-2 Diabetes Risk

Gene-age interactions have not been systematically investigated on metabolic phenotypes and this modulation will be key for a better understanding of the temporal regulation in nutrigenomics. Taking into account that aging is typically associated with both impairment of the circadian system and a decrease in melatonin secretion, we focused on the melatonin receptor 1B (MTNR1B)-rs10830963 C>G variant that has been associated with fasting glucose concentrations, gestational diabetes, and type-2 diabetes. Therefore, our main aim was to investigate whether the association between the MTNR1B-rs10830963 polymorphism and fasting glucose is age dependent. Our secondary aims were to analyze the polymorphism association with type-2 diabetes and explore the gene-pregnancies interactions on the later type-2 diabetes risk. Three Mediterranean cohorts (n = 2823) were analyzed. First, a cross-sectional study in the discovery cohort consisting of 1378 participants (aged 18 to 80 years; mean age 41 years) from the general population was carried out. To validate and extend the results, two replication cohorts consisting of elderly individuals were studied. In the discovery cohort, we observed a strong gene-age interaction (p = 0.001), determining fasting glucose in such a way that the increasing effect of the risk G-allele was much greater in young (p = 5.9 × 10^-10) than in elderly participants (p = 0.805). Consistently, the association of the MTNR1B-rs10830963 polymorphism with fasting glucose concentrations in the two replication cohorts (mean age over 65 years) did not reach statistical significance (p > 0.05 for both). However, in the elderly cohorts, significant associations between the polymorphism and type-2 diabetes at baseline were found. Moreover, in one of the cohorts, we obtained a statistically significant interaction between the MTNR1B polymorphism and the number of pregnancies, retrospectively assessed, on the type-2 diabetes risk. In conclusion, the association of the MTNR1B-rs10830963 polymorphism with fasting glucose is age-dependent, having a greater effect in younger people. However, in elderly subjects, associations of the polymorphism with type-2 diabetes were observed and our exploratory analysis suggested a modulatory effect of the number of past pregnancies on the future type-2 diabetes genetic risk.

A circadian rhythm-related MTNR1B genetic variant (rs10830963) modulate body weight change and insulin resistance after 9 months of a high protein/low carbohydrate vs a standard hypocaloric diet

BACKGROUND & AIMS

The risk allele (G) of rs10830963 in the melatonin receptor 1 B (MTNR1B) gene presents an association with biochemical parameters and obesity. We study the effect of this SNP on insulin resistance and weight loss secondary to two hypocaloric diets.

METHODS

270 obese subjects were randomly allocated during 9 months (Diet HP: a high protein/low carbohydrate vs. Diet S: a standard severe hypocaloric diets). Anthropometric parameters, fasting blood glucose, C-reactive protein (CRP), insulin concentration, insulin resistance (HOMA-IR), lipid profile and adipocytokines levels were measured. Genotype of MTNR1B gene polymorphism (rs10830963) was evaluated.

RESULTS

All adiposity parameters, systolic blood pressure and leptin levels decreased in all subjects after both diets. This improvement of adiposity parameters was higher in non-G allele carriers than G allele carriers. After weight loss with Diet HP, (CC vs. CG + GG at 9 months); total cholesterol (delta: -9.9 ± 2.4 mg/dl vs. -4.8 ± 2.2 mg/dl:p < 0.05), LDL-cholesterol (delta: -8.3 ± 1.9 mg/dl vs. -5.1 ± 2.2 mg/dl: p < 0.05), insulin (delta: -4.7 ± 0.8 UI/L vs. -0.9 ± 1.0 UI/L: p < 0.05), triglycerides (delta: -17.7 ± 3.9 mg/dl vs. -6.1 ± 2.8 mg/dl: p < 0.05) and HOMA IR (delta: -0.8 ± 0.2 units vs. -0.2 ± 0.1 units: p < 0.05) improved only in no G allele carriers. After weight loss with Diet S in non G allele carriers, insulin levels (delta (CC vs. CG + GG): -3.4 ± 0.6 UI/L vs. -1.2 ± 0.4 UI/L: p < 0.05), triglycerides (delta: -29.2 ± 3.4 mg/dl vs. -8.2 ± 3.8 mg/dl: p < 0.05), HOMA-IR (delta (CC vs. CG + GG): -1.1 ± 0.2 units vs. -0.1 ± 0.1 units: p < 0.05), total cholesterol (delta: -15.9 ± 7.4 mg/dl vs. -5.8 ± 2.9 mg/dl:ns) and LDL-cholesterol (delta: -13.7 ± 5.9 mg/dl vs. -6.0 ± 2.9 mg/dl: ns) decreased, too.

CONCLUSIONS

our study detected a relationship of rs10830963 variant of MTNR1B gene with adiposity changes, cholesterol changes and insulin resistance modification induced by two different hypocaloric during 9 months.

Maternal MTNR1B genotype, maternal gestational weight gain, and childhood obesity

BACKGROUND

Maternal metabolic abnormalities have been related to offspring obesity especially during childhood.

OBJECTIVES

We analyzed whether the gestational diabetes mellitus (GDM)-associated melatonin receptor 1B (MTNR1B) genotype of mothers modified the relation between maternal gestational weight gain and childhood obesity.

METHODS

A total of 1114 Chinese mother-child pairs (mothers with or without prior GDM) were included. Mothers' MTNR1B rs10830962 genotype and gestational weight gain were assessed. Indicators of childhood obesity included BMI-for-age z-score, weight-for-age z-score, waist circumference, and body fat. Childhood overweight and obesity were also analyzed.

RESULTS

We found that the maternal MTNR1B genotype significantly interacted with gestational weight gain on indicators of offspring's obesity (all P for interaction < 0.05). After multivariable adjustment, BMI-for-age z-scores associated with 1-kg gestational weight gain were 0.009 (SE 0.018), 0.026 (SE 0.010), and 0.061 (SE 0.010) in children with the maternal MTNR1B genotype CC, CG, and GG, respectively (P-interaction = 0.012). Similar interactions were observed for weight-for-age z-score, waist circumference, and body fat (P-interaction = 0.001, 0.003, and 0.012, respectively). The associations remained consistently significant in women with and without GDM. We also found significant interactions between the maternal MTNR1B genotype and gestational weight gain on the offspring's childhood overweight and obesity (P-interaction = 0.005 and 0.026, respectively).

CONCLUSIONS

The maternal MTNR1B genotype might interact with gestational weight gain on offspring's obesity risk during childhood.

Assessment of MTNR1B Type 2 Diabetes Genetic Risk Modification by Shift Work and Morningness-Eveningness Preference in the UK Biobank

Night shift work, behavioral rhythms, and the common MTNR1B risk single nucleotide polymorphism (SNP), rs10830963, associate with type 2 diabetes; however, whether they exert joint effects to exacerbate type 2 diabetes risk is unknown. Among employed participants of European ancestry in the UK Biobank (N = 189,488), we aimed to test the cross-sectional independent associations and joint interaction effects of these risk factors on odds of type 2 diabetes (n = 5,042 cases) and HbA_1c levels (n = 175,156). Current shift work, definite morning or evening preference, and MTNR1B rs10830963 risk allele associated with type 2 diabetes and HbA_1c levels. The effect of rs10830963 was not modified by shift work schedules. While marginal evidence of interaction between self-reported morningness-eveningness preference and rs10830963 on risk of type 2 diabetes was seen, this interaction did not persist when analysis was expanded to include all participants regardless of employment status and when accelerometer-derived sleep midpoint was used as an objective measure of morningness-eveningness preference. Our findings suggest that MTNR1B risk allele carriers who carry out shift work or have more extreme morningness-eveningness preference may not have enhanced risk of type 2 diabetes.

Genetic susceptibility, lifestyle intervention and glycemic changes among women with prior gestational diabetes

AIMS

Women with prior gestational diabetes mellitus (GDM) or high genetic susceptibility are prone to development of type 2 diabetes. We examined whether a lifestyle intervention modified the genetic effect on changes in glycemic markers among women with prior GDM.

RESEARCH DESIGN AND METHODS

This study included 560 women with prior GDM from a randomized controlled trial, the Tianjin Gestational Diabetes Mellitus Prevention Program, who were assigned into an intervention arm (improved physical activity and healthy dietary intakes) or a control arm. We assessed associations of GDM related genetic variants in/near the CDKAL1 (rs7754840) and MTNR1B (rs10830962) genes with changes in fasting levels of glucose and insulin, β-cell function (HOMA-B) and insulin resistance (HOMA-IR) at 1 year and 2 years after the baseline.

RESULTS

We found significant interactions between CDKAL1 variant rs7754840 and lifestyle intervention on changes in fasting insulin and HOMA-IR at 1 year (P for interactions = 0.008 and 0.006, respectively). The GDM-increasing C allele was associated with a 0.07-unit greater increase in fasting insulin (P = 0.048) and HOMA-IR (P = 0.045) in the control group, while opposite-directional associations were observed in the intervention group; women with the C allele seemed to decrease more in these glycemic markers than the non-C-carriers (both P ≤ 0.06). The interactions between the CDKAL1 genetic variant and lifestyle intervention on changes in fasting insulin (P = 0.035) and HOMA-IR (P = 0.024) remained significant over the 2-year period, even though the effects of lifestyle intervention were attenuated at 2-year. The MTNR1B variant rs10830962 did not show interaction with lifestyle intervention on changes in the glycemic markers.

CONCLUSIONS

Healthy lifestyle intervention may be beneficial for women with the GDM predisposing CDKAL1 genetic variant in improvement of insulin resistance.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov NCT01554358. URL OF REGISTRATION: https://clinicaltrials.gov/ct2/show/NCT01554358.

Activation of melatonin receptor 2 but not melatonin receptor 1 mediates melatonin-conferred cardioprotection against myocardial ischemia/reperfusion injury

Accumulated pieces of evidence have proved the beneficial effects of melatonin on myocardial ischemia/reperfusion (MI/R) injury, and these effects were largely dependent on melatonin membrane receptor activation. In humans and other mammals, there are two types of melatonin receptors, including the melatonin receptor 1 (MT1, melatonin receptor 1a or MTNR1A) and melatonin receptor 1 (MT2, melatonin receptor 1b or MTNR1B) receptor subtypes. However, which receptor mediates melatonin-conferred cardioprotection remains unclear. In this study, we employed both loss-of-function and gain-of-function approaches to reveal the answer. Mice (wild-type; MT1 or MT2 silencing by in vivo minicircle vector; and those overexpressing MT1 or MT2 by in vivo AAV9 vector) were exposed to MI/R injury. Both MT1 and MT2 were present in wild-type myocardium. MT2, but not MT1, was essentially upregulated after MI/R Melatonin administration significantly reduced myocardial injury and improved cardiac function after MI/R Mechanistically, melatonin treatment suppressed MI/R-initiated myocardial oxidative stress and nitrative stress, alleviated endoplasmic reticulum stress and mitochondrial injury, and inhibited myocardial apoptosis. These beneficial actions of melatonin were absent in MT2-silenced heart, but not the MT1 subtype. Furthermore, AAV9-mediated cardiomyocyte-specific overexpression of MT2, but not MT1, mitigated MI/R injury and improved cardiac dysfunction, which was accompanied by significant amelioration of oxidative stress, endoplasmic reticulum stress, and mitochondrial dysfunction. Mechanistically, MT2 protected primary cardiomyocytes against hypoxia/reoxygenation injury via MT2/Notch1/Hes1/RORα signaling. Our study presents the first direct evidence that the MT2 subtype, but not MT1, is a novel endogenous cardiac protective receptor against MI/R injury. Medications specifically targeting MT2 may hold promise in fighting ischemic heart disease.

MT1 and MT2 melatonin receptors are expressed in nonoverlapping neuronal populations

Melatonin (MLT) exerts its physiological effects principally through two high-affinity membrane receptors MT1 and MT2. Understanding the exact mechanism of MLT action necessitates the use of highly selective agonists/antagonists to stimulate/inhibit a given MLT receptor. The respective distribution of MT1 and MT2 within the CNS and elsewhere is controversial, and here we used a "knock-in" strategy replacing MT1 or MT2 coding sequences with a LacZ reporter. The data show striking differences in the distribution of MT1 and MT2 receptors in the mouse brain: whereas the MT1 subtype was expressed in very few structures (notably including the suprachiasmatic nucleus and pars tuberalis), MT2 subtype receptors were identified within numerous brain regions including the olfactory bulb, forebrain, hippocampus, amygdala and superior colliculus. Co-expression of the two subtypes was observed in very few structures, and even within these areas they were rarely present in the same individual cell. In conclusion, the expression and distribution of MT2 receptors are much more widespread than previously thought, and there is virtually no correspondence between MT1 and MT2 cellular expression. The precise phenotyping of cells/neurons containing MT1 or MT2 receptor subtypes opens new perspectives for the characterization of links between MLT brain targets, MLT actions and specific MLT receptor subtypes.

A Standardized Extract of Asparagus officinalis Stem (ETAS®) Ameliorates Cognitive Impairment, Inhibits Amyloid β Deposition via BACE-1 and Normalizes Circadian Rhythm Signaling via MT1 and MT2

The prevalence of cognitive impairments and circadian disturbances increases in the elderly and Alzheimer’s disease (AD) patients. This study investigated the effects of a standardized extract of Asparagus officinalis stem, ETAS^® on cognitive impairments and circadian rhythm status in senescence-accelerated mice prone 8 (SAMP8). ETAS^® consists of two major bioactive constituents: 5-hydroxymethyl-2-furfural (HMF), an abundant constituent, and (S)-asfural, a novel constituent, which is a derivative of HMF. Three-month-old SAMP8 male mice were divided into a control, 200 and 1000 mg/kg BW ETAS^® groups, while senescence-accelerated resistant mice (SAMR1) were used as the normal control. After 12-week feeding, ETAS^® significantly enhanced cognitive performance by an active avoidance test, inhibited the expressions of amyloid-beta precursor protein (APP) and BACE-1 and lowered the accumulation of amyloid β (Aβ) in the brain. ETAS^® also significantly increased neuron number in the suprachiasmatic nucleus (SCN) and normalized the expressions of the melatonin receptor 1 (MT1) and melatonin receptor 2 (MT2). In conclusion, ETAS^® enhances the cognitive ability, inhibits Aβ deposition and normalizes circadian rhythm signaling, suggesting it is beneficial for preventing cognitive impairments and circadian rhythm disturbances in aging.

Role of metabolic syndrome and its components as mediators of the genetic effect on type 2 diabetes: A family-based study in China

BACKGROUND

Metabolic syndrome (MetS) share a genetic basis with type 2 diabetes (T2D). However, whether MetS and its components mediate genetic susceptibility to T2D is not completely understood.

METHODS

We assessed the effects of MetS and its components on associations T2D and 18 genome-wide association studies-identified variants using a two-stage strategy based on parametric models involving 7110 Chinese participants (2436 were T2D patients) across 2885 families. Multilevel logistic regression was used to account for the intrafamilial correlation.

RESULTS

Metabolic syndrome significantly mediated the effect of a melatonin receptor 1B (MTNR1B) polymorphism on T2D risk (OR of average causal mediation effect [OR_ACME ] 1.004; 95% confidence interval [CI] 1.001-1.008; P = 0.018). In addition, low high-density lipoprotein cholesterol (HDL-C) levels mediated the genetic effects of MTNR1B (OR_ACME 1.012; 95% CI 1.007-1.015; P < 0.001), solute carrier family 30 member 8 (SLC30A8; OR_ACME 1.001; 95% CI 1.000-1.007; P < 0.040), B-cell lymphoma/leukemia 11A (BCL11A; OR_ACME 1.009; 95% CI 1.007-1.016; P < 0.001), prospero homeobox 1 (PROX1; OR_ACME 1.005; 95% CI 1.003-1.011; P < 0.001) and a disintegrin and metallopeptidase with thrombospondin type 1 motif 9 (ADAMTS9; OR_ACME 1.006; 95% CI 1.001-1.009; P = 0.022), whereas increased fasting blood glucose (FBG) significantly mediated the genetic effect of BCL11A (OR_ACME 1.017; 95% CI 1.003-1.021; P = 0.012).

CONCLUSIONS

This study provides evidence that MetS and two of its components (HDL-C, FBG) may be involved in mediating the genetic predisposition to T2D, which emphasize the importance of maintaining normal HDL-C and FBG levels.

Higher melatonin in the follicle fluid and MT2 expression in the granulosa cells contribute to the OHSS occurrence

BACKGROUND

Ovarian hyperstimulation syndrome (OHSS) is a common and severe complication for patients undergoing IVF/ICSI-ET. Melatonin widely participates in the regulation of female reproductive endocrine activity. However, whether melatonin participates in the progression of OHSS is largely unknown. This study aims to identify the predictive value of follicular fluid (FF) melatonin for OHSS establishment and the underlying mechanism.

METHODS

All participants of this case-control study were enrolled at the Reproductive Medicine Center located in the First Affiliated Hospital of Zhengzhou University in China from January to October in 2017. Quantitative real-time PCR and western blot were used to examine the mRNA and protein levels. Primary granulosa cells were extracted and cultured for in vitro studies. Melatonin concentration was measured by ELISA. Logistic analysis and receiver-operating characteristic (ROC) curves were used to evaluate the predicting value of melatonin on OHSS occurrence.

MAIN OUTCOME MEASURES

The expression level of melatonin receptor 2 (MT2), P450 aromatase cytochrome (aromatase), vascular endothelial growth factor (VEGF), and inducible nitric oxide synthase (iNOS) mRNA in human primary granulosa cells. The concentration of melatonin in FF. The predicting value of melatonin on OHSS and the cut-off value of the prediction.

RESULTS

FF melatonin concentrations were significantly higher in patients with OHSS compared to non-OHSS group (35.94 ± 10.18 ng/mL vs 23.93 ± 10.94 ng/mL, p<0.001). The expression of MT2 mRNA (p = 0.0459) and protein in granulosa cells was also significantly higher in the OHSS group. When using a cut-off level of 27.52 ng/ml, the sensitivity and specificity of FF melatonin to predict OHSS was 84.6 and 74.0%, respectively (p < 0.0001). We also found that melatonin could up-regulates aromatase mRNA, VEGF mRNA expression and down-regulates iNOS mRNA expression in the granulosa cells.

CONCLUSION

OHSS patients have higher melatonin in the FF as well as higher MT2 expression in the granulosa cells. The melatonin in FF might be used as an effective predictor for the occurrence of OHSS.

Antidepressant potential of Uncaria rhynchophylla and its active flavanol, catechin, targeting melatonin receptors

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicines (TCMs) are fascinating sources for natural drug candidates. Uncaria rhynchophylla (Gouteng) is a famous TCM used for alleviating central nervous system (CNS) disorders, while its antidepressant constituents are still disputed.

AIM OF THE STUDY

The present study was designed to assess the antidepressant property of U. rhynchophylla and characterize the active constituents targeting melatonin receptors which are closely related to CNS diseases.

MATERIALS AND METHODS

The total extract and each fraction of U. rhynchophylla were extensively assessed for their agonistic activity on melatonin receptors in vitro. The following bioassay-guided fractionation yielded the active constituents, whose activity was confirmed by dose-dependent bioassay and antagonistic experiment on HEK293 cells. Their antidepressant effects were evaluated on forced swimming test (FST), tail suspension test (TST) and open-field test (OFT) mice models in vivo. Their metabolic profiles in mice plasma were analyzed by LCMS-IT-TOF.

RESULTS

The stems and hooks of U. rhynchophylla were revealed with agonistic activity on melatonin receptors (MT₁ and MT₂). Under the guidance of bioassay, two flavanols, catechin and epicatechin were obtained and showed obviously activity agitating MT₁ (EC₅₀ = 25.8 and 156.1 μM) and MT₂ (EC₅₀ = 47.3 and 208.8 μM) receptors. The agonistic activity of catechin on melatonin receptors can be antagonized by luzindole at the concentrations of 1.57-100 μM. Catechin could significantly reduce the immobility time in both FST and TST mice models at doses of 80 and 40 mg/kg, without obvious effect on locomotor activity in OFT mice model. Five phase II (M1-M5) and one phase I (M6) metabolites of catechin were detected in mice plasma after intragastric (i.g.) administration.

CONCLUSION

Catechin is a potent antidepressant candidate from U. rhynchophylla by targeting melatonin receptors. The main metabolic pathways of catechin in mice plasma are glucuronidation (M3) and methylated glucuronidation (M4 and M5). This study provides valuable information for understanding the antidepressant potency of Gouteng and its active constituents.

Melatonin receptor activation provides cerebral protection after traumatic brain injury by mitigating oxidative stress and inflammation via the Nrf2 signaling pathway

Traumatic brain injury (TBI) is a principal cause of death and disability worldwide. Melatonin, a hormone made by the pineal gland, is known to have anti-inflammatory and antioxidant properties. In this study, using a weight-drop model of TBI, we investigated the protective effects of ramelteon, a melatonin MT1/MT2 receptor agonist, and its underlying mechanisms of action. Administration of ramelteon (10 mg/kg) daily at 10:00 a.m. alleviated TBI-induced early brain damage on day 3 and long-term neurobehavioral deficits on day 28 in C57BL/6 mice. Ramelteon also increased the protein levels of interleukin (IL)-10, IL-4, superoxide dismutase (SOD), glutathione, and glutathione peroxidase and reduced the protein levels of IL-1β, tumor necrosis factor, and malondialdehyde in brain tissue and serum on days 1, 3, and 7 post-TBI. Similarly, ramelteon attenuated microglial and astrocyte activation in the perilesional cortex on day 3. Furthermore, ramelteon decreased Keap 1 expression, promoted nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear accumulation, and increased levels of downstream proteins, including SOD-1, heme oxygenase-1, and NQO1 on day 3 post-TBI. However, in Nrf2 knockout mice with TBI, ramelteon did not decrease the lesion volume, neuronal degeneration, or myelin loss on day 3; nor did it mitigate depression-like behavior or most motor behavior deficits on day 28. Thus, timed ramelteon treatment appears to prevent inflammation and oxidative stress via the Nrf2-antioxidant response element pathway and might represent a potential chronotherapeutic strategy for treating TBI.

Melatonin in type 2 diabetes mellitus and obesity

Despite considerable advances in the past few years, obesity and type 2 diabetes mellitus (T2DM) remain two major challenges for public health systems globally. In the past 9 years, genome-wide association studies (GWAS) have established a major role for genetic variation within the MTNR1B locus in regulating fasting plasma levels of glucose and in affecting the risk of T2DM. This discovery generated a major interest in the melatonergic system, in particular the melatonin MT₂ receptor (which is encoded by MTNR1B). In this Review, we discuss the effect of melatonin and its receptors on glucose homeostasis, obesity and T2DM. Preclinical and clinical post-GWAS evidence of frequent and rare variants of the MTNR1B locus confirmed its importance in regulating glucose homeostasis and T2DM risk with minor effects on obesity. However, these studies did not solve the question of whether melatonin is beneficial or detrimental, an issue that will be discussed in the context of the peculiarities of the melatonergic system. Melatonin receptors might have therapeutic potential as they belong to the highly druggable G protein-coupled receptor superfamily. Clarifying the precise role of melatonin and its receptors on glucose homeostasis is urgent, as melatonin is widely used for other indications, either as a prescribed medication or as a supplement without medical prescription, in many countries in Europe and in the USA.

Melatonin Receptor 1β Gene Polymorphism rs10830963, Serum Melatonin, TNF-α, IL-6, IL-1β, in Egyptian Patients with Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease affecting all organ systems due to alterations of both innate and adaptive immune systems. Given the importance of several factors that may be incriminated in deregulation of immune system in SLE, we aimed to study MTNR1β gene polymorphisms rs10830963 C/G, serum levels of melatonin and pro-inflammatory cytokines; TNF-α, IL-6, and IL-1β in SLE patients and the correlation of these parameters to SLE disease activity and damage index at time of study. Subjects were subdivided into 2 groups: group I: 40 SLE patients attending Alexandria main university hospital and outpatient clinic, and group II: 40 control cases of apparently healthy individuals matched for age and sex. For all cases, MTNR1β gene polymorphism rs10830963 was analyzed by quantitative RT-PCR, serum levels of melatonin, TNF-α, IL-6 and IL-1β were detected by ELISA. Activity index (SLEDAI) and damage index (SLEDDI) were assessed in SLE patients. MTNR1β gene polymorphism rs10830963 genotype in SLE patients showed that 50% had GG, 35% CG and 15% CC. The control group had significantly lower ratios, 5% had GG, 15% CG and 80% CC (P < 0.001). Serum melatonin level was decreased in SLE patients (P < 0.001). Serum levels of TNF-α, IL-6, and IL-1β were increased in SLE patients compared to controls (P < 0.001, P < 0.001, P < 0.001 respectively). There was no correlation between serum melatonin level, TNF-α, IL-6, and IL-1β with SLEDAI or SLEDDI. In conclusion, MTNR1β gene polymorphism rs10830963 G allele may contribute in SLE pathogenesis. Inflammatory cytokines; TNF-α, IL-6, IL-1β may have role in SLE disease manifestations. Targeting immunoregulators as melatonin and proinflammatory cytokines in SLE treatment strategy can be a promising way to SLE cure.

Does the melatonin receptor 1B gene polymorphism have a role in postoperative delirium?

INTRODUCTION

Patients undergoing cardiac surgery are at high risk for postoperative delirium, which is associated with longer hospital and intensive care lengths of stays, increased morbidity and mortality. Because sleep disturbances are common in delirium, melatonin has been an area of interest in the treatment of delirium. The rs10830963 single nucleotide polymorphism of the melatonin receptor 1B gene can cause pathological dysfunction of this receptor and is associated with delayed morning offset of melatonin. We hypothesized patients undergoing aortic cardiac surgery who have the risk genotype of a melatonin receptor 1B polymorphism would have a higher incidence of postoperative delirium.

METHODS

Ninety-eight patients undergoing aortic root or valve surgery underwent analysis for melatonin receptor 1B single nucleotide polymorphism, rs10830963. Using a validated method, CHART-DEL, all charts were retrospectively reviewed and scored for the presence of delirium while blinded to the results of the melatonin receptor 1B gene polymorphism.

RESULTS

Genotyping for melatonin receptor 1B polymorphism was acceptable in 76 subjects of European descent of which 18 (23.7%) had delirium. Four of seven subjects with the risk genotype had delirium versus only 20.3% of subjects without the risk genotype. This carried an odds ratio of 5.2 (1.0, 26.1), p = 0.050.

CONCLUSION

This observation suggests a role of the risk genotype of a melatonin receptor 1B polymorphism in the development of postoperative delirium. These hypotheses generating results warrant further prospective studies in a larger cohort group with delirium, circadian rhythm and melatonin assessments.

Toward the precision breast cancer survival prediction utilizing combined whole genome-wide expression and somatic mutation analysis

BACKGROUND

Breast cancer is the most common type of invasive cancer in woman. It accounts for approximately 18% of all cancer deaths worldwide. It is well known that somatic mutation plays an essential role in cancer development. Hence, we propose that a prognostic prediction model that integrates somatic mutations with gene expression can improve survival prediction for cancer patients and also be able to reveal the genetic mutations associated with survival.

METHOD

Differential expression analysis was used to identify breast cancer related genes. Genetic algorithm (GA) and univariate Cox regression analysis were applied to filter out survival related genes. DAVID was used for enrichment analysis on somatic mutated gene set. The performance of survival predictors were assessed by Cox regression model and concordance index(C-index).

RESULTS

We investigated the genome-wide gene expression profile and somatic mutations of 1091 breast invasive carcinoma cases from The Cancer Genome Atlas (TCGA). We identified 118 genes with high hazard ratios as breast cancer survival risk gene candidates (log rank p <  0.0001 and c-index = 0.636). Multiple breast cancer survival related genes were found in this gene set, including FOXR2, FOXD1, MTNR1B and SDC1. Further genetic algorithm (GA) revealed an optimal gene set consisted of 88 genes with higher c-index (log rank p <  0.0001 and c-index = 0.656). We validated this gene set on an independent breast cancer data set and achieved a similar performance (log rank p <  0.0001 and c-index = 0.614). Moreover, we revealed 25 functional annotations, 15 gene ontology terms and 14 pathways that were significantly enriched in the genes that showed distinct mutation patterns in the different survival risk groups. These functional gene sets were used as new features for the survival prediction model. In particular, our results suggested that the Fanconi anemia pathway had an important role in breast cancer prognosis.

CONCLUSIONS

Our study indicated that the expression levels of the gene signatures remain the effective indicators for breast cancer survival prediction. Combining the gene expression information with other types of features derived from somatic mutations can further improve the performance of survival prediction. The pathways that were associated with survival risk suggested by our study can be further investigated for improving cancer patient survival.

Genome-wide interaction with the insulin secretion locus MTNR1B reveals CMIP as a novel type 2 diabetes susceptibility gene in African Americans

Although type 2 diabetes (T2D) results from metabolic defects in insulin secretion and insulin sensitivity, most of the genetic risk loci identified to date relates to insulin secretion. We reported that T2D loci influencing insulin sensitivity may be identified through interactions with insulin secretion loci, thereby leading to T2D. Here, we hypothesize that joint testing of variant main effects and interaction effects with an insulin secretion locus increases power to identify genetic interactions leading to T2D. We tested this hypothesis with an intronic MTNR1B SNP, rs10830963, which is associated with acute insulin response to glucose, a dynamic measure of insulin secretion. rs10830963 was tested for interaction and joint (main + interaction) effects with genome-wide data in African Americans (2,452 cases and 3,772 controls) from five cohorts. Genome-wide genotype data (Affymetrix Human Genome 6.0 array) was imputed to a 1000 Genomes Project reference panel. T2D risk was modeled using logistic regression with rs10830963 dosage, age, sex, and principal component as predictors. Joint effects were captured using the Kraft two degrees of freedom test. Genome-wide significant (P < 5 × 10-8 ) interaction with MTNR1B and joint effects were detected for CMIP intronic SNP rs17197883 (Pinteraction  = 1.43 × 10-8 ; Pjoint  = 4.70 × 10-8 ). CMIP variants have been nominally associated with T2D, fasting glucose, and adiponectin in individuals of East Asian ancestry, with high-density lipoprotein, and with waist-to-hip ratio adjusted for body mass index in Europeans. These data support the hypothesis that additional genetic factors contributing to T2D risk, including insulin sensitivity loci, can be identified through interactions with insulin secretion loci.

Hamster Melatonin Receptors: Cloning and Binding Characterization of MT₁ and Attempt to Clone MT₂

For many years, it was of interest to identify the sequences encoding the two melatonin receptors (MT₁ and MT₂) from various species. After publishing the basic molecular characterization of the human, rat, mouse, sheep, and platypus MT₁, MT₂, or Mel1c receptors, we began cloning the genes from other animals, such as birds, bats, and vipers. The goal was to advance the receptor crystallization, which could greatly contribute the understanding of the sequence/stability relationship. European hamster MT₁ receptor was cloned for the first time from this gender, was expressed in stable form in cells, and its binding characterized with a sample of 19 melatonin ligands. Siberian hamster (Phodopus sungorus) expresses a non-functional MT₂. We observed that unlike this hamster, the European hamster (Cricetus cricetus) does not have a stop codon in the MT₂ sequence. Thus, we undertook the tedious task of cloning the MT₂ receptor. We partially succeeded, sequencing the complete exon 2 and a fragment of exon 1 (from putative amino acids 12 to 38 and 77 to 323), after several years of efforts. In order to show that the protein parts we cloned were capable to sustain some binding capacities, we designed a chimeric MT₂ receptor using a consensus sequence to replace the unknown amino acids, based on other small rodent MT₂ sequences. This chimeric construct could bind melatonin in the nanomolar range. This work is meant to be the basis for attempts from other laboratories of the community to determine the complete natural sequence of the European hamster MT₂ receptor. The present work is the first to show that, among the hamsters, if the Siberian is a natural knockout for MT₂, the European one is not.

Impact of KCNQ1, CDKN2A/2B, CDKAL1, HHEX, MTNR1B, SLC30A8, TCF7L2, and UBE2E2 on risk of developing type 2 diabetes in Thai population

BACKGROUND

Several type 2 diabetes (T2D) susceptibility loci identified via genome-wide association studies were found to be replicated among various populations. However, the influence of these loci on T2D in Thai population is unknown. The aim of this study was to investigate the influence of eight single nucleotide polymorphisms (SNPs) reported in GWA studies on T2D and related quantitative traits in Thai population.

METHODS

Eight SNPs in or near the KCNQ1, CDKN2A/2B, SLC30A8, HHEX, CDKAL1, TCF7L2, MTNR1B, and UBE2E2 genes were genotyped. A case-control association study comprising 500 Thai patients with T2D and 500 ethnically-matched control subjects was conducted. Associations between SNPs and T2D were examined by logistic regression analysis. The impact of these SNPs on quantitative traits was examined by linear regression among case and control subjects.

RESULTS

Five SNPs in KCNQ1 (rs2237892), CDK2A/2B (rs108116610, SLC30A8 (rs13266634), TCF7L2 (rs7903146) and MTNR1B (rs1387153) were found to be marginally associated with risk of developing T2D, with odds ratios ranging from 1.43 to 2.02 (p = 0.047 to 3.0 × 10-4) with adjustments for age, sex, and body mass index. Interestingly, SNP rs13266634 of SLC30A8 gene reached statistical significance after correcting for multiple testing (p = 0.0003) (p < 0.006 after Bonferroni correction). However, no significant association was detected between HHEX (rs1111875), CDKAL1 (rs7756992), or UBE2E2 (rs7612463) and T2D. We also observed association between rs10811661 and both waist circumference and waist-hip ratio (p = 0.007 and p = 0.023, respectively). In addition, rs13266634 in SLC30A8 was associated with glycated hemoglobin (p = 0.018), and rs7903146 in TCF7L2 was associated with high-density lipoprotein cholesterol level (p = 0.023).

CONCLUSION

Of the eight genes included in our analysis, significant association was observed between KCNQ1, CDKN2A/2B, SLC30A8, TCF7L2, and MTNR1B loci and T2D in our Thai study population. Of these, CDKN2A/2B, SLC30A8, and TCF7L2 genes were also significantly associated with anthropometric, glycemic and lipid characteristics. Larger cohort studies and meta-analyses are needed to further confirm the effect of these variants in Thai population.

The Circadian Rhythm-Related MTNR1B Genotype, Gestational Weight Gain, and Postpartum Glycemic Changes

Context

Disturbed circadian rhythms and sleep quality during pregnancy have been related to gestational weight gain and gestational diabetes mellitus (GDM), which affect postpartum glucose metabolism and future risk of type 2 diabetes.

Objective

We assessed whether the circadian rhythm-related melatonin receptor 1B (MTNR1B) genotype was associated with 1 to 5 years of postpartum glycemic changes among women with a history of GDM and whether gestational weight gain modified such associations.

Design, Settings, and Participants

The established circadian rhythm-associated MTNR1B genetic variant (rs10830963) was genotyped in 1025 Chinese women with a history of GDM. Body weight and glycemic traits, during and after pregnancy, were longitudinally collected.

Main Outcome Measures

The main outcome measure was postpartum glycemic changes.

Results

We found that women carrying different MTNR1B genotypes showed distinct postpartum changes in 2-hour oral glucose tolerance test: 0.36, 0.20, and -0.19 mM per additional copy of the shorter sleep duration-related G allele in women with inadequate, adequate, and excessive gestational weight gain, respectively (for interaction, P = 0.028). The corresponding changes in fasting glucose were 0.14, 0.13, and 0.01 mM, although the modification effect of gestational weight gain on the genetic association was marginally significant (for interaction, P = 0.067).

Conclusions

Our findings suggest that gestational weight gain may modify the circadian rhythm-related MTNR1B genetic variant on long-term glycemic changes, highlighting the significance of gestational weight management in diabetes prevention among women with GDM.

Food-induced reinforcement is abrogated by the genetic deletion of the MT1 or MT2 melatonin receptor in C3H/HeN mice

Palatable food is known for its ability to enhance reinforcing responses. Studies have suggested a circadian variation in both drug and natural reinforcement, with each following its own time course. The goal of this study was to determine the role of the MT1 and MT2 melatonin receptors in palatable snack food-induced reinforcement, as measured by the conditioned place preference (CPP) paradigm during the light and dark phases. C3H/HeN wild-type mice were trained for snack food-induced CPP at either ZT 6 - 8 (ZT: Zeitgeber time; ZT 0 = lights on), when endogenous melatonin levels are low, or ZT 19 - 21, when melatonin levels are high. These time points also correspond to the high and low points for expression of the circadian gene Period1, respectively. The amount of snack food (chow, Cheetos®, Froot Loops® and Oreos®) consumed was of similar magnitude at both times, however only C3H/HeN mice conditioned to snack food at ZT 6 - 8 developed a place preference. C3H/HeN mice with a genetic deletion of either the MT1 (MT1KO) or MT2 (MT2KO) receptor tested at ZT 6 - 8 did not develop a place preference for snack food. Although the MT2KO mice showed a similar amount of snack food consumed when compared to wild-type mice, the MT1KO mice consumed significantly less than either genotype. We conclude that in our mouse model snack food-induced CPP is dependent on time of day and the presence of the MT1 or MT2 receptors, suggesting a role for melatonin and its receptors in snack food-induced reinforcement.

Characterization of the Mel1c melatoninergic receptor in platypus (Ornithorhynchus anatinus)

Melatonin is a neurohormone produced in both animals and plants. It binds at least three G-protein-coupled receptors: MT1 and MT2, and Mel1cGPR. Mammalian GPR50 evolved from the reptilian/avian Mel1c and lost its capacity to bind melatonin in all the therian mammal species that have been tested. In order to determine if binding is lost in the oldest surviving mammalian lineage of monotremes we investigated whether the melatonin receptor has the ability to bind melatonin in the platypus (Ornithorhynchus anatinus), and evaluated its pharmacological profile. Sequence and phylogenetic analysis showed that platypus has in fact retained the ancestral Mel1c and has the capacity to bind melatonin similar to other mammalian melatonin receptors (MT1 and MT2), with an affinity in the 1 nM range. We also investigated the binding of a set of melatoninergic ligands used previously to characterize the molecular pharmacology of the melatonin receptors from sheep, rats, mice, and humans and found that the general profiles of these compounds make Mel1c resemble human MT1 more than MT2. This work shows that the loss of GPR50 binding evolved after the divergence of monotremes less than 190MYA in therian mammals.

Disentangling the Role of Melatonin and its Receptor MTNR1B in Type 2 Diabetes: Still a Long Way to Go?

PURPOSE OF REVIEW

Type 2 diabetes (T2D) is a complex genetic metabolic disorder. T2D heritability has been estimated around 40-70%. In the last decade, exponential progress has been made in identifying T2D genetic determinants, through genome-wide association studies (GWAS). Among single-nucleotide polymorphisms mostly associated with T2D risk, rs10830963 is located in the MTNR1B gene, encoding one of the two receptors of melatonin, a neurohormone involved in circadian rhythms. Subsequent studies aiming to disentangle the role of MTNR1B in T2D pathophysiology led to controversies. In this review, we will tackle them and will try to give some directions to get a better view of MTNR1B contribution to T2D pathophysiology.

RECENT FINDINGS

Recent studies either based on genetic/genomic analyses, clinical/epidemiology data, functional analyses at rs10830963 locus, insulin secretion assays in response to melatonin (involving or not MTNR1B) or animal model analyses have led to strong controversies at each level of interpretation. We discuss possible caveats in these studies and present ways to go beyond these issues, towards a better understanding of T2D molecular mechanisms, keeping in mind that melatonin is a versatile hormone and regulates many functions via its primary role in the body clock.

Melatonin mediates vasodilation through both direct and indirect activation of BKCa channels

Melatonin, synthesized primarily by the pineal gland, is a neuroendocrine hormone with high membrane permeability. The vascular effects of melatonin, including vasoconstriction and vasodilation, have been demonstrated in numerous studies. However, the mechanisms underlying these effects are not fully understood. Large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels are expressed broadly on smooth muscle cells and play an important role in vascular tone regulation. This study explored the mechanisms of myocyte BK_Ca channels and endothelial factors underlying the action of melatonin on the mesenteric arteries (MAs). Vascular contractility and patch-clamp studies were performed on myocytes of MAs from Wistar rats. Melatonin induced significant vasodilation on MAs. In the presence of N^ω-nitro-l-arginine methyl ester (l-NAME), a potent endothelial oxide synthase (eNOS) inhibitor, melatonin elicited concentration-dependent relaxation, with lowered pIC₅₀ The effect of melatonin was significantly attenuated in the presence of BK_Ca channel blocker iberiotoxin or MT1/MT2 receptor antagonist luzindole in both (+) l-NAME and (-) l-NAME groups. In the (+) l-NAME group, iberiotoxin caused a parallel rightward shift of the melatonin concentration-relaxation curve, with pIC₅₀ lower than that of luzindole. Both inside-out and cell-attached patch-clamp recordings showed that melatonin significantly increased the open probability, mean open time and voltage sensitivity of BK_Ca channels. In a cell-attached patch-clamp configuration, the melatonin-induced enhancement of BK_Ca channel activity was significantly suppressed by luzindole. These findings indicate that in addition to the activation of eNOS, melatonin-induced vasorelaxation of MAs is partially attributable to its direct (passing through the cell membrane) and indirect (via MT1/MT2 receptors) activation of the BK_Ca channels on mesenteric arterial myocytes.

Regulation of bone mass through pineal-derived melatonin-MT2 receptor pathway

Tryptophan, an essential amino acid through a series of enzymatic reactions gives rise to various metabolites, viz. serotonin and melatonin, that regulate distinct biological functions. We show here that tryptophan metabolism in the pineal gland favors bone mass accrual through production of melatonin, a pineal-derived neurohormone. Pineal gland-specific deletion of Tph1, the enzyme that catalyzes the first step in the melatonin biosynthesis lead to a decrease in melatonin levels and a low bone mass due to an isolated decrease in bone formation while bone resorption parameters remained unaffected. Skeletal analysis of the mice deficient in MT1 or MT2 melatonin receptors showed a low bone mass in MT2-/- mice while MT1-/- mice had a normal bone mass compared to the WT mice. This low bone mass in the MT2-/- mice was due to an isolated decrease in osteoblast numbers and bone formation. In vitro assays of the osteoblast cultures derived from the MT1-/- and MT2-/- mice showed a cell intrinsic defect in the proliferation, differentiation and mineralization abilities of MT2-/- osteoblasts compared to WT counterparts, and the mutant cells did not respond to melatonin addition. Finally, we demonstrate that daily oral administration of melatonin can increase bone accrual during growth and can cure ovariectomy-induced structural and functional degeneration of bone by specifically increasing bone formation. By identifying pineal-derived melatonin as a regulator of bone mass through MT2 receptors, this study expands the role played by tryptophan derivatives in the regulation of bone mass and underscores its therapeutic relevance in postmenopausal osteoporosis.

MTNR1A and MTNR1B gene polymorphisms in women with gestational diabetes

Gestational diabetes mellitus (GDM) is glucose intolerance detected during pregnancy. The MTNR1B gene is the genetic locus associated with type 2 diabetes, that may affect insulin secretion and pancreatic glucose sensing. In this study, we examined the association between MTNR1A (rs2119882) and MTNR1B (rs10830963, rs4753426) gene polymorphisms and the risk of GDM. According to the results of their oral glucose tolerance test (OGTT), the women were divided into two groups: 204 pregnant women with GDM and 207 pregnant women with normal glucose tolerance (NGT). There were no statistically significant differences in the distribution of MTNR1A rs2119882 and MTNR1B rs4753426 genotypes and alleles between women with GDM and healthy pregnant women. With regard to the MTNR1B rs10830963 polymorphism, we observed a statistically significant prevalence of GG and CG genotypes and the G allele among pregnant women with GDM (GG + CG vs CC, OR 1.50, 95% CI 1.02-2.22, p = 0.04; G vs C, OR 1.43, 95% CI 1.07-1.90, p = 0.016). In a multivariate logistic regression analysis, a higher number of MTNR1B rs10830963 G alleles was an independent significant predictor of a higher risk of GDM. The results of our study indicate that MTNR1B rs10830963 polymorphism is associated with GDM susceptibility, and women with a higher number of G alleles have an increased risk of GDM development.

The case for too little melatonin signalling in increased diabetes risk

Genome-wide association studies have detected an association between type 2 diabetes risk and a non-coding SNP located in MTNR1B, the gene encoding melatonin receptor 2 (MT2). Melatonin regulates circadian rhythms and sleep and associates with metabolic disorders. However, the mechanisms underlying these actions are still unclear. Functional genomic, animal and clinical studies have not reached the same conclusions: while some studies have reported that decreased melatonin signalling increases type 2 diabetes risk, others have found the opposite. In this commentary, we have tried to provide an explanation for these contradictions and we suggest how the community may progress to reach a unified picture of the effect of melatonin and its signalling on type 2 diabetes.

Late dinner impairs glucose tolerance in MTNR1B risk allele carriers: A randomized, cross-over study

BACKGROUND & AIMS

Late-night dinner eating is associated with increased risk for type-2 diabetes. The underlying mechanism is unclear. One explanatory hypothesis is that the concurrence of elevated circulating melatonin and high glucose concentrations (characterizing late eating) leads to impaired glucose tolerance. However, to date no study has tested the influence of physiological melatonin concentrations on glucose-tolerance. The discovery of melatonin receptor MTNR1B as a diabetes risk gene provides evidence for a role of physiological levels of melatonin in glucose control. The aim of our study was to test the hypothesis that elevated endogenous melatonin concentrations worsen glucose control when eating late. Registered under ClinicalTrials.gov Identifier no. NCT03003936.

METHODS

We performed a randomized, cross-over trial to compare glucose tolerance in the presence (late dinner) or absence (early dinner) of elevated physiological melatonin concentrations and we compared the results between homozygous carriers and non-carriers of the MTNR1B risk allele.

RESULTS

The concurrence of meal timing with elevated endogenous melatonin concentrations resulted in impaired glucose tolerance. This effect was stronger in MTNR1B risk-carriers than in non-carriers. Furthermore, eating late significantly impaired glucose tolerance only in risk-carriers and not in the non-risk carriers.

CONCLUSIONS

The interaction of dinner timing with MTNR1B supports a causal role of endogenous melatonin in the impairment of glucose tolerance. These results suggest that moving the dinner to an earlier time may result in better glucose tolerance specially in MTNR1B carriers.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT03003936.

Melatonin MT₁ and MT₂ Receptors in the Ram Reproductive Tract

Some melatonin functions in mammals are exerted through MT₁ and MT₂ receptors. However, there are no reports of their presence in the reproductive tract of the ram, a seasonal species. Thus, we have investigated their existence in the ram testis, epididymis, accessory glands and ductus deferens. Real-time polymerase chain reaction (qPCR) revealed higher levels of m-RNA for both receptors in the testis, ampulla, seminal vesicles, and vas deferens, than in the other organs of the reproductive tract (p < 0.05). Western blot analyses showed protein bands compatible with the MT₁ in the testis and cauda epididymis, and for the MT₂ in the cauda epididymis and deferent duct. Immunohistochemistry analyses revealed the presence of MT₁ receptors in spermatogonias, spermatocytes, and spermatids, and MT₂ receptors in the newly-formed spermatozoa in the testis, whereas both receptors were located in the epithelial cells of the ampulla, seminal vesicles, and ductus deferens. Indirect immunofluorescence showed significant differences in the immunolocation of both receptors in spermatozoa during their transit in the epididymis. In conclusion, it was demonstrated that melatonin receptors are present in the ram reproductive tract. These results open the way for new studies on the molecular mechanism of melatonin and the biological significance of its receptors.

The Role of the Melatoninergic System in Light-Entrained Behavior of Mice

The role of endogenous melatonin for the control of the circadian system under entrained conditions and for the determination of the chronotype is still poorly understood. Mice with deletions in the melatoninergic system (melatonin deficiency or the lack of melatonin receptors, respectively) do not display any obvious defects in either their spontaneous (circadian) or entrained (diurnal) rhythmic behavior. However, there are effects that can be detected by analyzing the periodicity of the locomotor behaviors in some detail. We found that melatonin-deficient mice (C57Bl), as well as melatonin-proficient C3H mice that lack the melatonin receptors (MT) 1 and 2 (C3H MT1,2 KO), reproduce their diurnal locomotor rhythms with significantly less accuracy than mice with an intact melatoninergic system. However, their respective chronotypes remained unaltered. These results show that one function of the endogenous melatoninergic system might be to stabilize internal rhythms under conditions of a steady entrainment, while it has no effects on the chronotype.