Gene structures, biochemical characterization and distribution of rat melatonin receptors

Therapeutic effects of melatonin in female mice with central precocious puberty by regulating the hypothalamic Kiss-1/Kiss1R system

In recent years, central precocious puberty (CPP) in children is becoming more common, which seriously affects their physical and psychological health and requires finding a safe and effective treatment method. The aim of this study was to investigate the therapeutic effect of melatonin on CPP. A CPP model was established by subcutaneous injection of 300 micrograms of danazol into 5-day-old female mice, followed by treatment with melatonin and leuprolide. The vaginal opening was checked daily. Mice were weighed, gonads were weighed, gonadal index was calculated, and gonadal development was observed by hematoxylin and eosin (HE) staining. Serum follicle stimulating hormone (FSH), luteinizing hormone (LH) and estradiol (E2) levels were measured by ELISA. By using RT-PCR and Western blotting, the mRNA and protein expression of the hypothalamus Kiss-1, Kiss-1 receptor (Kiss1R), gonadotropin-releasing hormone (GnRH), and pituitary GnRH receptor (GnRHR) were identified. The results showed that melatonin delayed vaginal opening time and reduced body weight, gonadal weight and indices in female CPP mice. Melatonin treatment prevents uterine wall thickening and ovarian luteinization in female CPP mice. Melatonin treatment reduces serum concentrations of FSH, LH, and E2 in female CPP mice. Melatonin suppressed the expressions of Kiss-1, Kiss1R and GnRH in the hypothalamus, and the expression of GnRHR in the pituitary of the female CPP mice. Our results suggest that melatonin can inhibit the hypothalamic-pituitary-gonadal (HPG) axis by down-regulating the Kiss-1/Kiss1R system, thereby treating CPP in female mice.

Ramelteon administration enhances novel object recognition and spatial working memory in mice

Ramelteon is used to ameliorate sleep disorders that negatively affect memory performance; however, it remains unknown whether ramelteon strengthens neutral memories, which do not involve reward or punishment. To address this, we monitored behavior of mice treated with vehicle/ramelteon while they performed a novel object recognition task and a spontaneous alternation task. Object memory performance in the novel object recognition task was improved only if ramelteon was injected before training, suggesting that ramelteon specifically enhances the acquisition of object recognition memory. Ramelteon also enhanced spatial working memory in the spontaneous alternation task. Altogether, acute ramelteon treatment enhances memory in quasi-natural contexts.

Blast Exposure Dysregulates Nighttime Melatonin Synthesis and Signaling in the Pineal Gland: A Potential Mechanism of Blast-Induced Sleep Disruptions

Blast-induced traumatic brain injury (bTBI) frequently results in sleep-wake disturbances. However, limited studies have investigated the molecular signaling mechanisms underlying these sleep disturbances, and potentially efficacious therapies are lacking. We investigated the levels of melatonin and genes involved in melatonin synthesis pathway in the pineal glands of Sprague Dawley rats exposed to single and tightly coupled repeated blasts during the night and daytime. Rats were exposed to single and tightly coupled repeated blasts using an advanced blast simulator. The plasma, cerebrospinal fluid (CSF), and pineal gland were collected at 6 h, 24 h, or 1 month postblast at two different time points: one during the day (1000 h) and one at night (2200 h). Differential expressions of genes involved in pineal melatonin synthesis were quantified using quantitative real-time polymerase chain reaction (qRT-PCR). Plasma and CSF melatonin levels were assessed using a commercial melatonin ELISA kit. The plasma and CSF melatonin levels showed statistically significant decreases at 6 h and 24 h in the blast-exposed rats euthanized in the night (in dim light), with no significant alterations noted in rats euthanized in the morning (daylight) at all three-time points. Blast-exposed rats showed statistically significant decreases in Tph1, Aanat, Asmt, and Mtnr1b mRNA levels, along with increased Tph2 mRNA, in the pineal gland samples collected at night at 6 h and 24 h. No significant changes in the mRNA levels of these genes were noted at 1 month. These findings imply that the melatonin circadian rhythm is disrupted following blast exposure, which may be a factor in the sleep disturbances that blast victims frequently experience.

Olfaction and Melatonin: The Use of the Olfactory Discrimination Test

In order to investigate the role of melatonin in olfactory function, we present the olfactory discrimination test as a simple and low-cost behavioral assessment. The test consists in evaluating the time that each rat spent in two compartments: one has a familiar odor (sawdust with the smell from the animal) and the other one with an unfamiliar odor (clean sawdust). Animals with the normal olfactory functions will discriminate between these two odors and will spend more time in the familiar compartment. We used the olfactory discrimination test to evaluate the role of melatonin receptors expressed in the olfactory bulb of rats. In a previous study, our results have successfully detected an olfactory modulation, by mean of the olfactory discrimination test, promoted by the infusion of melatonin receptor ligands into the olfactory bulb of rats.

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

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

First evidence of the protective role of melatonin in counteracting cadmium toxicity in the rat ovary via the mTOR pathway

Herein, the first evidence of the ability of melatonin (MLT) to counteract cadmium (Cd) toxic effects on the rat ovary is reported. Cd treatment, enhancing oxidative stress, provoked clear morphological, histological and biomolecular alterations, i.e. in the estrous cycle duration, in the ovarian and serum E2 concentration other than in the steroidogenic and folliculogenic genes expression. Results demonstrated that the use of MLT, in combination with Cd, avoided the changes, strongly suggesting that it is an efficient antioxidant for preventing oxidative stress in the rat ovary. Moreover, to explore the underlying mechanism involved, at molecular level, in the effects of Cd-MLT interaction, the study focused on the mTOR and ERK1/2 pathways. Interestingly, data showed that Cd influenced the phosphorylation status of mTOR, of its downstream effectors and of ERK1/2, inducing autophagy and apoptosis, while cotreatment with MLT nullified these changes. This work highlights the beneficial role exerted by MLT in preventing Cd-induced toxicity in the rat ovary, encouraging further studies to confirm its action on human ovarian health with the aim to use this indolamine to ameliorate oocyte quality in women with fertility disorders.

MT2 melatonin receptors expressed in the olfactory bulb modulate depressive-like behavior and olfaction in the 6-OHDA model of Parkinson's disease

Melatonin MT1 and MT2 receptors are expressed in the glomerular layer of the olfactory bulb (OB); however, the role of these receptors has not been evaluated until now. Considering the association of the OB with olfactory and depressive disorders in Parkinson's disease (PD), we sought to investigate the involvement of melatonin receptors in these non-motor disturbances in an intranigral 6-hydroxydopamine (6-OHDA)-lesioned rat model of PD. We demonstrate the presence of functional melatonin receptors in dopaminergic neurons of the glomerular layer. Local administration of melatonin (MLT, 1 μg/μl), luzindole (LUZ, 5 μg/μl) or the MT2-selective receptor drug 4-P-PDOT (5 μg/μl) reversed the depressive-like behavior elicited by 6-OHDA. Sequential administration of 4-P-PDOT and MLT (5 μg/μl, 1 μg/μl) promoted additive antidepressant-like effects. In the evaluation of olfactory discrimination, LUZ induced an olfactory impairment when associated with the nigral lesion-induced impairment. Thus, our results suggest that melatonin MT2 receptors expressed in the glomerular layer are involved in depressive-like behaviors and in olfactory function associated with PD.

Maternal pineal melatonin in gestation and lactation physiology, and in fetal development and programming

Pregnancy and lactation are reproductive processes that rely on physiological adaptations that should be timely and adequately triggered to guarantee both maternal and fetal health. Pineal melatonin is a hormone that presents daily and seasonal variations that synchronizes the organism's physiology to the different demands across time through its specific mechanisms and ways of action. The reproductive system is a notable target for melatonin as it actively participates on reproductive physiology and regulates the hypothalamus-pituitary-gonads axis, influencing gonadotropins and sexual hormones synthesis and release. For its antioxidant properties, melatonin is also vital for the oocytes and spermatozoa quality and viability, and for blastocyst development. Maternal pineal melatonin blood levels increase during pregnancy and triggers the maternal physiological alterations in energy metabolism both during pregnancy and lactation to cope with the energy demands of both periods and to promote adequate mammary gland development. Moreover, maternal melatonin freely crosses the placenta and is the only source of this hormone to the fetus. It importantly times the conceptus physiology and influences its development and programing of several functions that depend on neural and brain development, ultimately priming adult behavior and energy and glucose metabolism. The present review aims to explain the above listed melatonin functions, including the potential alterations observed in the progeny gestated under maternal chronodisruption and/or hypomelatoninemia.

Accurate assessment of estrogen receptor profiles in non-functioning pituitary adenomas using RT-digital PCR and immunohistochemistry

BACKGROUND

Non-functioning pituitary adenomas (NFPAs) are common pituitary tumors, and surgery is generally the only treatment option. Few attempts have been made to explore target molecules for the development of NFPA pharmacological treatments.

METHOD

We quantitatively assessed the expression profiles of estrogen receptor (ER) transcripts and proteins in NFPA samples, using reverse transcription-digital polymerase chain reaction (RT-dPCR) and immunohistochemistry, and further investigated the correlations between the expression levels of ER and those of downstream responsive genes. All patients had undergone surgery at the same high-volume hospital. A total of 20 patients with NFPAs were included. All patients were new-onset, and none were diagnosed with intratumoral hemorrhages or cysts.

RESULTS

NFPA samples exhibited a bimodal ESR1 expression pattern and were categorized into significantly different high- and low-ESR1 expression level groups (P < 0.05). In contrast, expression levels of ESR1 variants and ESR2 could barely be detected. Similar results were obtained through the immunohistochemical staining of NFPAs, using well-validated antibodies against ERs. The expression levels of ESR1 positively correlated with those of GREB1, an estrogen-responsive gene [correlation coefficient (r) = 0.623, P = 0.003].

CONCLUSIONS

ESR1 expression levels in NFPAs exhibited a bimodal pattern and were positively correlated with GREB1 expression levels. The accurate assessment of ER expression levels may further advance future NFPA-related research.

Melatonin inhibits apoptosis and oxidative tissue damage in cisplatin-induced pulmonary toxicity in rats

Introduction

Cisplatin is one of the most frequently used chemotherapeutics, which is known to cause both tumor and normal lung tissue damage through the generation of free radicals and cells apoptosis/necrosis. Melatonin is a neurohormone that regulates numerous physiological processes in the body both through receptor pathways and by maintaining tissue redox homeostasis.

Material and methods

The extent of rat lung damage induced by cisplatin and the effects of melatonin on this process was determined based on the pathohistological changes and biochemical disturbances in tissue lipid peroxidation, protein carbonyl modification and in the activity of xanthine oxidase (XO), caspase-3 and DNases.

Results

Histopathological analysis of rat lung tissue obtained from animals that received cisplatin found them to be edematous, with significant deterioration of alveolar epithelium. These morphological changes are accompanied by a significant increase in all studied oxidative stress-related parameters, as well as with the activity of apoptosis-related enzymes. A five-day treatment with melatonin completely prevented a cisplatin-induced increase in oxidative stress-related parameters and in the activity of XO, caspase-3 and alkaline DNase. Also, the histopathological changes observed during microscopic analysis were much less pronounced than in the group that received cisplatin only.

Conclusions

These results can potentially be connected with the ability of melatonin to inhibit the activity of XO, caspase-3 and alkaline DNase and/or its ability to scavenge free radicals, thus preventing lung damage induced by cisplatin.

Melatonin and its anti-glioma functions: a comprehensive review

Melatonin (N-acetyl-5-methoxytryptamine) is a naturally synthesized hormone secreted from the pineal gland in a variety of animals and is primarily involved in the regulation of the circadian rhythm, which is the natural cycle controlling sleep in organisms. Melatonin acts on specific receptors and has an important role in overall energy metabolism. This review encompasses several aspects of melatonin activity, such as synthesis, source, structure, distribution, function, signaling and its role in normal physiology. The review highlights the cellular signaling and messenger systems involved in melatonin's action on the body and their wider implications, the distribution and diverse action of different melatonin receptors in specific areas of the brain, and the pharmacological agonists and antagonists that have specific action on these melatonin receptors. This review also incorporates the antitumor effects of melatonin in considerable detail, emphasizing on melatonin's role as an adjuvant therapeutic agent in glioma treatment. We conclude that the diminishing levels of melatonin have significant debilitating effects on normal physiology and can also be associated with malignant conditions such as glioma. Based on the review of the available evidence, our study provides a broad platform for a better understanding of the specific roles of melatonin and serves as a starting point for further investigation into the therapeutic effect of melatonin in glioma as an adjuvant therapeutic agent.

Melatonin ameliorates SGLT2 inhibitor-induced diabetic ketoacidosis by inhibiting lipolysis and hepatic ketogenesis in type 2 diabetic mice

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) are effective hypoglycemic agents that can induce glycosuria. However, there are increasing concerns that they might induce diabetic ketoacidosis. This study investigated the effect of melatonin on SGTL2i-induced ketoacidosis in insulin-deficient type 2 diabetic (T2D) mice. The SGLT2i dapagliflozin reduced blood glucose level and plasma insulin concentrations in T2D mice, but induced increases in the concentrations of plasma β-hydroxybutyrate, acetoacetate, and free fatty acid and a decrease in the concentration of plasma bicarbonate, resulting in ketoacidosis. Melatonin inhibited dapagliflozin-induced ketoacidosis without inducing any change in blood glucose level or plasma insulin concentration. In white adipose tissue, melatonin inhibited lipolysis and downregulated phosphorylation of PKA, HSL, and perilipin-1. In liver tissue, melatonin suppressed cellular cyclic AMP levels and downregulated phosphorylation of PKA, AMPK, and acetyl-CoA carboxylase (ACC). In addition, melatonin increased hepatic ACC activity, but decreased hepatic CPT1a activity and acetyl-CoA content. These effects of melatonin on lipolysis and hepatic ketogenesis were blocked by pretreatment with melatonin receptor antagonist or PKA activator. Collectively, these results suggest that melatonin can ameliorate SGLT2i-induced ketoacidosis by inhibiting lipolysis and hepatic ketogenesis though cyclic AMP/PKA signaling pathways in T2D mice. Thus, melatonin treatment may offer protection against SGLT2i-induced ketoacidosis.

Effects of Melatonin on Anterior Pituitary Plasticity: A Comparison Between Mammals and Teleosts

Melatonin is a key hormone involved in the photoperiodic signaling pathway. In both teleosts and mammals, melatonin produced in the pineal gland at night is released into the blood and cerebrospinal fluid, providing rhythmic information to the whole organism. Melatonin acts via specific receptors, allowing the synchronization of daily and annual physiological rhythms to environmental conditions. The pituitary gland, which produces several hormones involved in a variety of physiological processes such as growth, metabolism, stress and reproduction, is an important target of melatonin. Melatonin modulates pituitary cellular activities, adjusting the synthesis and release of the different pituitary hormones to the functional demands, which changes during the day, seasons and life stages. It is, however, not always clear whether melatonin acts directly or indirectly on the pituitary. Indeed, melatonin also acts both upstream, on brain centers that control the pituitary hormone production and release, as well as downstream, on the tissues targeted by the pituitary hormones, which provide positive and negative feedback to the pituitary gland. In this review, we describe the known pathways through which melatonin modulates anterior pituitary hormonal production, distinguishing indirect effects mediated by brain centers from direct effects on the anterior pituitary. We also highlight similarities and differences between teleosts and mammals, drawing attention to knowledge gaps, and suggesting aims for future research.

Pretraining hippocampal stimulation of melatonin type 2 receptors can improve memory acquisition in rats

BACKGROUND

Learning and memory are among the most important cognitive functions of the brain. Melatonin receptor type 2 (MT2R) is located in the hippocampus and participates in learning and memory processes. In the present study, we examined the role of hippocampal MT2R activation in the acquisition, consolidation, and retrieval of learning and memory in novel object recognition (NOR) and passive avoidance (PA) tasks.

METHODS

IIK7 (0.03, 0.3, and 3 μg/μl/side), as a selective MT2R agonist, or vehicle was injected bilaterally into the dentate gyrus (DG) region of the hippocampus in rats five minutes before training, immediately after training, and five minutes before the retrieval-behavioral tasks, respectively. The discrimination index (DI) was measured in the NOR task, while step-through latency in acquisition (STLa), number of trials to acquisition (NOT), step-through latency in the retention trial (STLr), and time spent in the dark compartment (TDC) were determined in the PA task.

RESULTS

The pretraining intrahippocampal injection of IIK7 at all doses significantly improved acquisition in the PA task. On the other hand, the posttraining intrahippocampal administration of IIK7 had no significant effects on consolidation. The preretrieval intrahippocampal injection of IIK7 at different doses attenuated the retrieval of memory. However, the NOR data showed that the intrahippocampal injection of IIK7 at different doses had no significant effects on the acquisition, consolidation, or retrieval in this task.

DISCUSSION

Based on the findings, stimulation of MT2R could improve acquisition, whereas it had no effects on consolidation. It could impair retrieval in the PA task, while it had no effects on object recognition in rats.

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

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

Altered MT1 and MT2 melatonin receptors expression in the hippocampus of pilocarpine-induced epileptic rats

Clinical and experimental findings show that melatonin may be used as an adjuvant to the treatment of epilepsy-related complications by alleviates sleep disturbances, circadian alterations and attenuates seizures alone or in combination with AEDs. In addition, it has been observed that there is a circadian component on seizures, which cause changes in circadian system and in melatonin production. Nevertheless, the dynamic changes of the melatoninergic system, especially with regard to its membrane receptors (MT₁ and MT₂) in the natural course of TLE remain largely unknown. The aim of this study was to evaluate the 24-hour profile of MT₁ and MT₂ mRNA and protein expression in the hippocampus of rats submitted to the pilocarpine-induced epilepsy model analyzing the influence of the circadian rhythm in the expression pattern during the acute, silent, and chronic phases. Melatonin receptor MT₁ and MT₂ mRNA expression levels were increased in the hippocampus of rats few hours after SE, with MT₁ returning to normal levels and MT₂ reducing during the silent phase. During the chronic phase, mRNA expression levels of both receptors return to levels close to control, however, presenting a different daily profile, showing that there is a circadian change during the chronic phase. Also, during the acute and silent phase it was possible to verify MT₁ label only in CA2 hippocampal region with an increased expression only in the dark period of the acute phase. The MT₂ receptor was present in all hippocampal regions, however, it was reduced in the acute phase and it was found in astrocytes. In chronic animals, there is a reduction in the presence of both receptors especially in regions where there is a typical damage derived from epilepsy. Therefore, we conclude that SE induced by pilocarpine is able to change melatonin receptor MT₁ and MT₂ protein and mRNA expression levels in the hippocampus of rats few hours after SE as well as in silent and chronic phases.

Melatonin regulates catecholamine biosynthesis by modulating bone morphogenetic protein and glucocorticoid actions

Melatonin is functionally involved in the control of circadian rhythm and hormonal secretion. In the present study, we investigated the roles of melatonin in the interaction of catecholamine synthesis with adrenocortical steroids by focusing on bone morphogenetic protein (BMP)-4 expressed in the adrenal medulla using rat pheochromocytoma PC12 cells. Melatonin treatment significantly reduced the mRNA expression of catecholamine synthases, including the rate-limiting enzyme tyrosine hydroxylase (Th), 3,4-dihydroxyphenylalanine decarboxylase and dopamine-β-hydroxylase expressed in PC12 cells. In accordance with changes in the expression levels of enzymes, dopamine production and cAMP synthesis determined in the culture medium and cell lysate were also suppressed by melatonin. The MT1 receptor, but not the MT2 receptor, was expressed in PC12 cells, and luzindole treatment reversed the inhibitory effect of melatonin on Th expression, suggesting that MT1 is a functional receptor for the control of catecholamine synthesis. Interestingly, melatonin enhanced the inhibitory effect of BMP-4 on Th mRNA expression in PC12 cells. Melatonin treatment accelerated BMP-4-induced phosphorylation of SMAD1/5/8 and transcription of the BMP target gene Id1. Of note, melatonin significantly upregulated Alk2 and Bmpr2 mRNA levels but suppressed inhibitory Smad6/7 expression, leading to the enhancement of SMAD1/5/8 signaling in PC12 cells, while BMP-4 did not affect Mt1 expression. Regarding the interaction with adrenocortical steroids, melatonin preferentially enhanced glucocorticoid-induced Th mRNA through upregulation of the glucocorticoid receptor and downregulation of Bmp4 expression, whereas melatonin repressed Th mRNA expression induced by aldosterone or androgen without affecting expression levels of the receptors for mineralocorticoid and androgen. Collectively, the results indicate that melatonin plays a modulatory role in catecholamine synthesis by cooperating with BMP-4 and glucocorticoid in the adrenal medulla.

Circadian Rhythm Regulates Development of Enamel in Mouse Mandibular First Molar

Rhythmic incremental growth lines and the presence of melatonin receptors were discovered in tooth enamel, suggesting possible role of circadian rhythm. We therefore hypothesized that circadian rhythm may regulate enamel formation through melatonin receptors. To test this hypothesis, we examined expression of melatonin receptors (MTs) and amelogenin (AMELX), a maker of enamel formation, during tooth germ development in mouse. Using qRT-PCR and immunocytochemistry, we found that mRNA and protein levels of both MTs and AMELX in normal mandibular first molar tooth germs increased gradually after birth, peaked at 3 or 4 day postnatal, and then decreased. Expression of MTs and AMELX by immunocytochemistry was significantly delayed in neonatal mice raised in all-dark or all-light environment as well as the enamel development. Furthermore, development of tooth enamel was also delayed showing significant immature histology in those animals, especially for newborn mice raised in all daylight condition. Interestingly, disruption in circadian rhythm in pregnant mice also resulted in delayed enamel development in their babies. Treatment with melatonin receptor antagonist 4P-PDOT in pregnant mice caused underexpression of MTs and AMELX associated with long-lasting deficiency in baby enamel tissue. Electromicroscopic evidence demonstrated increased necrosis and poor enamel mineralization in ameloblasts. The above results suggest that circadian rhythm is important for normal enamel development at both pre- and postnatal stages. Melatonin receptors were partly responsible for the regulation.

Endocrine and cardiovascular rhythms differentially adapt to chronic phase-delay shifts in rats

Disturbances in regular circadian oscillations can have negative effects on cardiovascular function, but epidemiological data are inconclusive and new data from animal experiments elucidating critical biological mechanisms are needed. To evaluate the consequences of chronic phase shifts of the light/dark (LD) cycle on hormonal and cardiovascular rhythms, two experiments were performed. In Experiment 1, male rats were exposed to either a regular 12:12 LD cycle (CONT) or rotating 8-h phase-delay shifts of LD every second day (SHIFT) for 10 weeks. During this period, blood pressure (BP) was monitored weekly, and daily rhythms of melatonin, corticosterone, leptin and testosterone were evaluated at the end of the experiment. In Experiment 2, female rats were exposed to the identical shifted LD schedule for 12 weeks, and daily rhythms of BP, heart rate (HR) and locomotor activity were recorded using telemetry. Preserved melatonin rhythms were found in the pineal gland, plasma, heart and kidney of SHIFT rats with damped amplitude in the plasma and heart, suggesting that the central oscillator can adapt to chronic phase-delay shifts. In contrast, daily rhythms of corticosterone, testosterone and leptin were eliminated in SHIFT rats. Exposure to phase shifts did not lead to increased body weight and elevated BP. However, a shifted LD schedule substantially decreased the amplitude and suppressed the circadian power of the daily rhythms of BP and HR, implying weakened circadian control of physiological and behavioural processes. The results demonstrate that endocrine and cardiovascular rhythms can differentially adapt to chronic phase-delay shifts, promoting internal desynchronization between central and peripheral oscillators, which in combination with other negative environmental stimuli may result in negative health effects.

Human C-terminally truncated ERα variants resulting from the use of alternative exons in the ligand-binding domain

The nuclear receptor genes contain alternative internal and terminal exons, with alternative exon incorporation yielding mRNA variants that encode various receptor types, including some with C-terminal truncation that exhibit constitutive activation or dominant-negative transcriptional transactivation. However, C-terminally truncated estrogen receptor α (ERα) variants with alternative sequences have rarely been reported in humans. Therefore, we assessed human ERα genomic organization and alternative splicing profiles, and identified both alternative exons and C-terminally truncated ERα variants. These naturally occurring C-terminally truncated ERα proteins were localized in the nuclei of transfected cells. In addition, ERαi45c and ERαΔ5 variants exhibited constitutive transactivation of an estrogen responsive element-driven promoter in transfected cells. We manufactured expression vectors encoding artificially truncated ERα constructs and evaluated their transactivation abilities to establish mechanisms determining the constitutive activity and dominant-negative properties of truncated variants. Lack of the region encoded in exon 8 eliminated basal and ligand-induced transcriptional transactivation. The C-terminally truncated ERα variants/constructs containing the helices 5 in their ligand-binding domains did not exhibit constitutive transactivation. Furthermore, we demonstrated that truncation from C-termini to helices 5 in the variant ligand-binding domains was required for constitutive activation and found that the remnant regions of the ligand-binding domains and variant-specific sequences influenced transcriptional transactivation efficiency. In conclusion, we elucidated the structural and functional features of novel C-terminally truncated ERα variants and revealed the mechanisms underlying constitutive transactivation by C-terminally truncated nuclear receptor variants.

Chronic low-dose melatonin treatment maintains nigrostriatal integrity in an intrastriatal rotenone model of Parkinson's disease

Parkinson's disease is a major neurodegenerative disorder which primarily involves the loss of dopaminergic neurons in the substantia nigra and related projections in the striatum. The pesticide/neurotoxin, rotenone, has been shown to cause systemic inhibition of mitochondrial complex I activity in nigral dopaminergic neurons, with consequent degeneration of the nigrostriatal pathway, as observed in Parkinson's disease. A novel intrastriatal rotenone model of Parkinson's disease was used to examine the neuroprotective effects of chronic low-dose treatment with the antioxidant indoleamine, melatonin, which can upregulate neurotrophic factors and other protective proteins in the brain. Sham or lesioned rats were treated with either vehicle (0.04% ethanol in drinking water) or melatonin at a dose of 4 µg/mL in drinking water. The right striatum was lesioned by stereotactic injection of rotenone at three sites (4 μg/site) along its rostrocaudal axis. Apomorphine administration to lesioned animals resulted in a significant (p<0.001) increase in ipsilateral rotations, which was suppressed by melatonin. Nine weeks post-surgery, animals were sacrificed by transcardial perfusion. Subsequent immunohistochemical examination revealed a decrease in tyrosine hydroxylase immunoreactivity within the striatum and substantia nigra of rotenone-lesioned animals. Melatonin treatment attenuated the decrease in tyrosine hydroxylase in the striatum and abolished it in the substantia nigra. Stereological cell counts indicated a significant (p<0.05) decrease in dopamine neurons in the substantia nigra of rotenone-lesioned animals, which was confirmed by Nissl staining. Importantly, chronic melatonin treatment blocked the loss of dopamine neurons in rotenone-lesioned animals. These findings strongly support the therapeutic potential of long-term and low-dose melatonin treatment in Parkinson's disease.

Melatonin Upregulates the Activity of AMPK and Attenuates Lipid Accumulation in Alcohol-induced Rats

AIMS

Melatonin is supposed to be an effective hepatoprotective agent. The effects and mechanisms of melatonin on alcoholic fatty liver (AFL) have not been well explored. The aim of this study was to investigate the preventive and therapeutic effects of melatonin on alcohol-induced fatty liver rats.

METHODS

The AFL rats were induced by intragastric infusion of alcohol plus a high-fat diet for 6 weeks, and melatonin (10, 20, 40 mg/kg) was administered by gastric perfusion. We also established fatty acid overload cell model in HepG2 cells to investigate the effect of melatonin on AMP-activated protein kinase (AMPK) activity.

RESULTS

The results showed that melatonin (20 and 40 mg/kg) administration significantly reduced alcohol-induced hepatic steatosis with lowering activities of serum alanine aminotransferase, aspartate aminotransferase and levels of serum and hepatic triglyceride. The activity of superoxide dismutase was increased and the content of malondialdehyde was decreased in liver homogenates of rats treated with melatonin. Melatonin increased the phosphorylation of AMPK in the liver tissues of alcohol-induced rats as well. Additionally, in vitro studies showed that melatonin increased the expression of melatonin1A receptor (MT1R), whereas luzindole, a receptor antagonist of melatonin, had no effect on its expression. In addition, melatonin reduced the levels of adenosine 3',5'-cyclic monophosphate (cAMP) and increased the phosphorylation of AMPK, and melatonin treatment could markedly reverse these effects.

CONCLUSION

In conclusion, melatonin could protect against liver injury caused by alcohol gastric perfusion. The effect may be related to alleviating lipid peroxidation and upregulating the activity of AMPK mediated by MT1R signaling pathway.

Melatonin: a "Higgs boson" in human reproduction

As the Higgs boson could be a key to unlocking mysteries regarding our Universe, melatonin, a somewhat mysterious substance secreted by the pineal gland primarily at night, might be a crucial factor in regulating numerous processes in human reproduction. Melatonin is a powerful antioxidant which has an essential role in controlling several physiological reactions, as well as biological rhythms throughout human reproductive life. Melatonin, which is referred to as a hormone, but also as an autocoid, a chronobiotic, a hypnotic, an immunomodulator and a biological modifier, plays a crucial part in establishing homeostatic, neurohumoral balance and circadian rhythm in the body through synergic actions with other hormones and neuropeptides. This paper aims to analyze the effects of melatonin on the reproductive function, as well as to shed light on immunological and oncostatic properties of one of the most powerful hormones.

Impact of melatonin receptor deletion on intracellular signaling in spleen cells of mice after polymicrobial sepsis

OBJECTIVE

Melatonin is known to influence immune functions and to ameliorate outcome after septic challenge but it is unknown whether this is mediated by melatonin receptor activation. This study aimed to elucidate molecular differences in spleen and ex vivo splenocytes of wild-type (WT) and melatonin receptor double knockout mice (KO) after polymicrobial sepsis.

SUBJECTS AND METHODS

C3H/HeN wild-type and MT1-/-/MT2-/- mice underwent sham operation or cecum ligation and incision (CLI) and remained anesthetized for 1 h. Splenocytes were isolated and treated in culture with physiological melatonin concentrations (1 nM).

RESULTS

Plasma TNFα levels were consistently high after 1 h of CLI. Basal circulating leukocyte numbers were slightly higher in KO animals. We detected transcriptional differences in splenocytes of the knockout strain concerning proinflammatory mediators. Expression levels of IL-1β, IL-2, CXCR2, L-Selectin, TNFα, CXCL2 and ICAM-1 were strongly increased in splenocytes of KO mice. Splenocytes of KO mice displayed reduced ERK and p38 as well as increased JNK phosphorylation. None of the analyzed factors were influenced by melatonin in the culture medium.

CONCLUSIONS

The results of this study indicate an increased proinflammatory status of mice deficient in both membrane-bound melatonin receptors reflected by altered activation of MAPK cascades and transcriptional activation of proinflammatory mediators.

Melatonin in the mammalian olfactory bulb

Melatonin is a neurohormone associated with circadian rhythms. A diurnal rhythm in olfactory sensitivity has been previously reported and melatonin receptor mRNAs have been observed in the olfactory bulb, but the effects of melatonin in the olfactory bulb have not been explored. First, we corroborated data from a previous study that identified melatonin receptor messenger RNAs in the olfactory bulb. We then investigated whether melatonin treatment would affect cells in the olfactory bulbs of rats. Using a combination of polymerase chain reaction (PCR), quantitative PCR (qPCR), cell culture, and electrophysiology, we discovered that melatonin receptors and melatonin synthesis enzymes were present in the olfactory bulb and we observed changes in connexin43 protein, GluR1 mRNA, GluR2 mRNA, Per1 mRNA, Cry2 mRNA, and K(+) currents in response to 2-iodomelatonin. Via qPCR, we observed that messenger RNAs encoding melatonin receptors and melatonin biosynthesis enzymes fluctuated in the olfactory bulb across 24h. Together, these data show that melatonin receptors are present in the olfactory bulb and likely affect olfactory function. Additionally, these data suggest that melatonin may be locally synthesized in the olfactory bulb.

Melatonin receptor subtypes Mel1a and Mel1c but not Mel1b are associated with monochromatic light-induced B-lymphocyte proliferation in broilers

This study determined the effects of melatonin (MEL) and its receptors on monochromatic light-induced bursal B-lymphocyte proliferation in broiler chickens. In vivo, green light (GL) enhanced the proliferation of B lymphocytes in bursas by 16.49% to 30.83% and the expression of MEL receptor subtypes 1a (Mel1a), Mel1b, and Mel1c receptors in bursas by 6.91% to 366.98% than other light colors. However, pinealectomy reduced these parameters and eliminated the differences between GL and other light groups. In vitro, the MEL-induced bursal B-lymphocyte proliferation was most suppressed by prazosin (P = 0.001, selective Mel1c antagonist), followed by luzindole (P = 0.022, nonselective Mel1a/Mel1b antagonist), but not by 4-phenyl-2-propionamideotetralin (P = 0.144, selective Mel1b antagonist). Similarly, dibutyryl-cyclic adenosine monophosphate (cAMP; analog of cAMP; P = 0.017) but not 8-(4-chloro-phenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate (P = 0.736; activator of exchange protein directly activated by cAMP) significantly inhibited bursal B-lymphocyte proliferation. These results suggest that MEL mediates GL-induced bursal B-lymphocyte proliferation through Mel1c and Mel1a receptors but not Mel1b receptors by activating the cAMP/protein kinase A pathway.

Melatonin attenuates isoflurane-induced acute memory impairments in aged rats

Melatonin is an endogenous hormone with neuroprotective effects. Melatonin levels in elderly patients are reduced after surgeries that require anaesthesia. Whether reduced melatonin levels are important for postoperative cognitive dysfunction (POCD) remains unclear. Here, we investigated the effects of melatonin on cognitive dysfunctions induced by isoflurane and mechanisms underlying these effects. Seventy-two 20-month-old Sprague-Dawley rats were randomly divided into six groups (n = 12). These groups included M1 and M10 groups that received intraperitoneal melatonin at 1 mg/kg or 10 mg/kg, respectively, and an ISO group that received 4 hr of inhaled 2% isoflurane. They also included M1+ISO and M10+ISO groups that received 1 mg/kg or 10 mg/kg of melatonin plus 4 hr of inhaled 2% isoflurane, respectively, and a control group that received an equal volume of saline. Injections were administered daily for 14 consecutive days. Memory was assessed in the Morris water maze. Plasma and hippocampi were harvested to determine melatonin concentrations and MT1/MT2 receptor expression. Rats treated only with isoflurane showed significantly longer latencies in Morris water maze test trials compared with the control group, with shorter time in the probe trial (p < 0.05). Although plasma melatonin levels and MT2 expression in the hippocampus were significantly decreased, MT1 expression was higher in the isoflurane group than in the control group (p < 0.001). However, these parameters did not significantly vary in animals administered melatonin compared with controls. Isoflurane may induce cognitive dysfunction by influencing melatonin and MT1/MT2 levels. Melatonin can improve cognitive dysfunction by normalizing plasma melatonin and its receptor levels.

Peripheral reproductive organ health and melatonin: ready for prime time

Melatonin has a wide variety of beneficial actions at the level of the gonads and their adnexa. Some actions are mediated via its classic membrane melatonin receptors while others seem to be receptor-independent. This review summarizes many of the published reports which confirm that melatonin, which is produced in the ovary, aids in advancing follicular maturation and preserving the integrity of the ovum prior to and at the time of ovulation. Likewise, when ova are collected for in vitro fertilization-embryo transfer, treating them with melatonin improves implantation and pregnancy rates. Melatonin synthesis as well as its receptors have also been identified in the placenta. In this organ, melatonin seems to be of particular importance for the maintenance of the optimal turnover of cells in the villous trophoblast via its ability to regulate apoptosis. For male gametes, melatonin has also proven useful in protecting them from oxidative damage and preserving their viability. Incubation of ejaculated animal sperm improves their motility and prolongs their viability. For human sperm as well, melatonin is also a valuable agent for protecting them from free radical damage. In general, the direct actions of melatonin on the gonads and adnexa of mammals indicate it is an important agent for maintaining optimal reproductive physiology.

Identification and immunolocalisation of melatonin MT(1) and MT(2) receptors in Rasa Aragonesa ram spermatozoa

The reproductive seasonality of sheep suggests that melatonin receptors may be present in ram spermatozoa. The present study confirms the presence of melatonin MT(1) and MT(2) receptors. The MT(1) receptor was detected using immunocytochemistry, with four sperm subpopulations identified based on the following labelling patterns: (1) one small subpopulation with labelling over the entire head and tail; (2) one of two main subpopulations that exhibited reactivity at the equatorial, post-acrosomal, neck and tail regions; (3) another main subpopulation with equatorial and tail labelling only; and (4) a subpopulation in which staining was detected only in the tail. Immunocytochemistry revealed the presence of the melatonin MT(2) receptor, with intense staining on the acrosome, post-acrosomal region and neck and tail regions of all cells, but not in the equatorial region. Western blot identification of ram protein extracts revealed a 39-kDa band compatible with both MT(1) and MT(2) receptors, a 75-kDa band compatible with MT(1)/MT(2) heterodimerisation, a 32-kDa band compatible with MT(1) receptor activation and a double band of 45-55 kDa that is compatible with MT(2) receptor homodimerisation or heterodimerisation with other G-proteins. In conclusion, we provide evidence of the presence of MT(1) and MT(2) receptors in ram spermatozoa, although the biochemical pathway triggered by these receptors and their function in terms of fertility remains to be elucidated.

Valproic acid up-regulates melatonin MT1 and MT2 receptors and neurotrophic factors CDNF and MANF in the rat brain

We have reported that clinically relevant concentrations of valproic acid (VPA) up-regulate the G-protein-coupled melatonin MT1 receptor in rat C6 glioma cells. To determine whether this effect occurs in vivo, the effects of chronic VPA treatment on the expression of both melatonin receptor subtypes, MT1 and MT2, were examined in the rat brain. Reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR analyses revealed significant increases in MT1 and MT2 mRNA expression in the hippocampus, following VPA (4 mg/ml drinking water) treatment for 17 d. Increases in the mRNA and protein expression of the novel neurotrophic factors, conserved dopamine neurotrophic factor and mesencephalic astrocyte-derived neurotrophic factor, were detected in the hippocampus and/or striatum. In addition, significant changes in persephin, glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor mRNA expression were observed. The robust multi-fold induction of MT1 and MT2 receptors in the hippocampus suggests a role for the melatonergic system in the psychotropic effects of VPA.

Thyroid transcription factor 1, a homeodomain containing transcription factor, contributes to regulating periodic oscillations in GnRH gene expression

Thyroid transcription factor 1 (TTF1), a member of the Nkx family of transcription factors required for basal forebrain morphogenesis, functions in the postnatal hypothalamus as a transcriptional regulator of genes encoding neuromodulators and hypophysiotrophic peptides. One of these peptides is gonadotrophin-releasing hormone (GnRH). In the present study, we show that Ttf1 mRNA abundance varies in a diurnal and melatonin-dependent fashion in the preoptic area of the rat, with maximal Ttf1 expression attained during the dark phase of the light/dark cycle, preceding the nocturnal peak in GnRH mRNA content. GnRH promoter activity oscillates in a circadian manner in GT1-7 cells, and this pattern is enhanced by TTF1 and blunted by small interfering RNA-mediated Ttf1 gene silencing. TTF1 transactivates GnRH transcription by binding to two sites in the GnRH promoter. Rat GnRH neurones in situ contain key proteins components of the positive (BMAL1, CLOCK) and negative (PER1) limbs of the circadian oscillator, and these proteins repress Ttf1 promoter activity in vitro. By contrast, Ttf1 transcription is activated by CRY1, a clock component required for circadian rhythmicity. In turn, TTF1 represses transcription of Rev-erbα, a heme receptor that controls circadian transcription within the positive limb of the circadian oscillator. These findings suggest that TTF1 is a component of the molecular machinery controlling circadian oscillations in GnRH gene transcription.

Melatonin modulation of intracellular signaling pathways in hepatocarcinoma HepG2 cell line: role of the MT1 receptor

Melatonin reduces proliferation in many different cancer cell lines. However, studies on the oncostatic effects of melatonin in hepatocarcinoma are limited. We have previously demonstrated that melatonin administration induces cycle arrest, apoptosis, and changes in the expression of its specific receptors in HepG2 human hepatocarcinoma cells. In this study, we used the receptor antagonist luzindole to assess the contribution of MT1 melatonin membrane receptor to melatonin effects on cell viability, mitogen-activated protein kinase (MAPKs) activation, and cAMP levels. Additionally, effects of MT1 inhibition on mRNA levels of cytosolic quinone reductase type-2 (NQO2) receptor and nuclear retinoic acid-related orphan receptor alpha (RORα) were tested. Melatonin, at 1000 and 2500 μm, significantly reduced cell viability. Pre-incubation with luzindole partially inhibited the effects of melatonin on cell viability. Melatonin at 2500 μm significantly reduced cAMP levels, and this effect was partially blocked by luzindole. Both melatonin concentrations increased the expression of phosphorylated p38, ERK, and JNK. ERK activation was completely abolished in the presence of luzindole. NQO2 but not RORα mRNA level significantly increased in luzindole-treated cells. Results obtained provide evidence that the melatonin effects on cell viability and proliferation in HepG2 cells are partially mediated through the MT1 membrane receptor, which seems to be related also with melatonin modulation of cAMP and ERK activation. This study also highlights a possible interplay between MT1 and NQO2 melatonin receptors in liver cancer cells.

Hepatoprotective actions of melatonin: Possible mediation by melatonin receptors

Melatonin, the hormone of darkness and messenger of the photoperiod, is also well known to exhibit strong direct and indirect antioxidant properties. Melatonin has previously been demonstrated to be a powerful organ protective substance in numerous models of injury; these beneficial effects have been attributed to the hormone’s intense radical scavenging capacity. The present report reviews the hepatoprotective potential of the pineal hormone in various models of oxidative stress in vivo, and summarizes the extensive literature showing that melatonin may be a suitable experimental substance to reduce liver damage after sepsis, hemorrhagic shock, ischemia/reperfusion, and in numerous models of toxic liver injury. Melatonin’s influence on hepatic antioxidant enzymes and other potentially relevant pathways, such as nitric oxide signaling, hepatic cytokine and heat shock protein expression, are evaluated. Based on recent literature demonstrating the functional relevance of melatonin receptor activation for hepatic organ protection, this article finally suggests that melatonin receptors could mediate the hepatoprotective actions of melatonin therapy.

International Union of Basic and Clinical Pharmacology. LXXV. Nomenclature, classification, and pharmacology of G protein-coupled melatonin receptors

The hormone melatonin (5-methoxy-N-acetyltryptamine) is synthesized primarily in the pineal gland and retina, and in several peripheral tissues and organs. In the circulation, the concentration of melatonin follows a circadian rhythm, with high levels at night providing timing cues to target tissues endowed with melatonin receptors. Melatonin receptors receive and translate melatonin's message to influence daily and seasonal rhythms of physiology and behavior. The melatonin message is translated through activation of two G protein-coupled receptors, MT(1) and MT(2), that are potential therapeutic targets in disorders ranging from insomnia and circadian sleep disorders to depression, cardiovascular diseases, and cancer. This review summarizes the steps taken since melatonin's discovery by Aaron Lerner in 1958 to functionally characterize, clone, and localize receptors in mammalian tissues. The pharmacological and molecular properties of the receptors are described as well as current efforts to discover and develop ligands for treatment of a number of illnesses, including sleep disorders, depression, and cancer.

Alternative promoter usage and alternative splicing of the rat estrogen receptor alpha gene generate numerous mRNA variants with distinct 5'-ends

The 5'-untranslated region (UTR) of the estrogen receptor alpha (ERalpha) gene plays an important role in determining tissue-specific expression. To elucidate the regulatory mechanisms of rat ERalpha gene expression, the genomic organization must be investigated. We therefore analyzed the structure of the rat ERalpha mRNA 5'-UTR using rapid amplification of 5'-cDNA ends (5'-RACE) and RT-PCR. The analysis showed the presence of multiple variants containing unique 5'-UTRs. We mapped the cDNA sequences on the rat genome, and newly identified one leader exon (exon 0U) and ten untranslated internal exons (exons I1-10). Both splicing from four different leader exons (exons 0S, 0N, 0U, and 0/B) onto exon 1 and alternative splicing in combination with eleven internal exons (exons I1-10, and 0T) produce multiple transcripts. RT-PCR analysis revealed that each variant had preferred expression sites, suggesting that promoter usage and splicing are regulated in tissue-specific manners. Moreover, we determined a splicing event to yield Deltaexon 1 variants (0S-2-3-4-5-6-7-8), which are translated into rat 46 kDa ERalpha proteins. Our results indicate that the rat ERalpha gene is more complex than previously thought in terms of genomic organization and that both alternative promoter usage and alternative splicing contribute to the remarkable diversity of ERalpha mRNAs.

Genetic variant in HK1 is associated with a proanemic state and A1C but not other glycemic control-related traits

OBJECTIVE

A1C is widely considered the gold standard for monitoring effective blood glucose levels. Recently, a genome-wide association study reported an association between A1C and rs7072268 within HK1 (encoding hexokinase 1), which catalyzes the first step of glycolysis. HK1 deficiency in erythrocytes (red blood cells [RBCs]) causes severe nonspherocytic hemolytic anemia in both humans and mice.

RESEARCH DESIGN AND METHODS

The contribution of rs7072268 to A1C and the RBC-related traits was assessed in 6,953 nondiabetic European participants. We additionally analyzed the association with hematologic traits in 5,229 nondiabetic European individuals (in whom A1C was not measured) and 1,924 diabetic patients. Glucose control-related markers other than A1C were analyzed in 18,694 nondiabetic European individuals. A type 2 diabetes case-control study included 7,447 French diabetic patients.

RESULTS

Our study confirms a strong association between the rs7072268-T allele and increased A1C (beta = 0.029%; P = 2.22 x 10(-7)). Surprisingly, despite adequate study power, rs7072268 showed no association with any other markers of glucose control (fasting- and 2-h post-OGTT-related parameters, n = 18,694). In contrast, rs7072268-T allele decreases hemoglobin levels (n = 13,416; beta = -0.054 g/dl; P = 3.74 x 10(-6)) and hematocrit (n = 11,492; beta = -0.13%; P = 2.26 x 10(-4)), suggesting a proanemic effect. The T allele also increases risk for anemia (836 cases; odds ratio 1.13; P = 0.018).

CONCLUSIONS

HK1 variation, although strongly associated with A1C, does not seem to be involved in blood glucose control. Since HK1 rs7072268 is associated with reduced hemoglobin levels and favors anemia, we propose that HK1 may influence A1C levels through its anemic effect or its effect on glucose metabolism in RBCs. These findings may have implications for type 2 diabetes diagnosis and clinical management because anemia is a frequent complication of the diabetes state.