Resequencing and association analysis of arylalkylamine N-acetyltransferase (AANAT) gene and its contribution to major depression susceptibility

Fetal malnutrition is associated with impairment of endogenous melatonin synthesis in pineal via hypermethylation of promoters of protein kinase C alpha and cAMP response element-binding

This study investigated whether and how fetal malnutrition would influence endogenous melatonin synthesis, and whether such effect of fetal malnutrition would transmit to the next generation. We enrolled 2466 participants and 1313 of their offspring. The urine 6-hydroxymelatonin sulfate and serum melatonin rhythm were measured. Methylation microarray detection and bioinformatics analysis were performed to identify hub methylated sites. Additionally, rat experiment was performed to elucidate mechanisms. The participants with fetal malnutrition had lower 6-hydroxymelatonin sulfate (16.59 ± 10.12 μg/24 hours vs 24.29 ± 11.99 μg/24 hours, P < .001) and arear under curve of melatonin rhythm (67.11 ± 8.16 pg/mL vs 77.11 ± 8.04 pg/mL, P < .001). We identified 961 differentially methylated sites, in which the hub methylated sites were locating on protein kinase C alpha (PRKCA) and cAMP response element-binding protein (CREB1) promoters, mediating the association of fetal malnutrition with impaired melatonin secretion. However, such effects were not observed in the offspring (all P > .05). Impaired histomorphology of pineal, decreased melatonin in serum, pineal, and pinealocyte were also found in the in vivo and in vitro experiments (P < .05 for the differences of the indicators). Hypermethylation of 10 CpG sites on the PRKCA promoter and 8 CpG sites on the CREB1 promoter were identified (all P < .05), which down-regulated PRKCA and CREB1 expressions, leading to decreased expression of AANAT, and then resulting in the impaired melatonin synthesis. Collectively, fetal malnutrition can impair melatonin synthesis through hypermethylation of PRKCA and CREB1 promoters, and such effects cannot be transmitted to the next generation.

[Association of polymorphic variants of DDC (AADC), AANAT and ASMT genes encoding enzymes for melatonin synthesis with the higher risk of neuropsychiatric disorders]

Melatonin is the most well-known regulator of the circadian rhythms of all living organisms and the main substrate synthesized at night. There are 4 stages in the synthesis of melatonin. This review focuses on the 2nd, 3rd, and 4th stages. The review is aimed at analyzing publications on molecular genetic association studies on the role of single nucleotide polymorphisms (SNPs) of the DDC (AADC), AANAT and ASMT genes encoding melatonin synthesis enzymes in the pathogenesis of socially significant neuropsychiatric disorders in humans. The authors analyzed the available full-text articles from several databases, as well as materials from electronic resources. Search depth was 15 years. The analysis of these studies over the past decade show the association of some SNPs of the studied genes with the risk of neuropsychiatric disorders such as delayed sleep phase disorder, attention deficit hyperactivity disorder, autism spectrum disorder, migraine, Parkinson's disease, depression, anxiety, bipolar-affective disorder, schizophrenia.

Melatonin's neuroprotective role in mitochondria and its potential as a biomarker in aging, cognition and psychiatric disorders

Melatonin is an ancient molecule that is evident in high concentrations in various tissues throughout the body. It can be separated into two pools; one of which is synthesized by the pineal and can be found in blood, and the second by various tissues and is present in these tissues. Pineal melatonin levels display a circadian rhythm while tissue melatonin does not. For decades now, melatonin has been implicated in promoting and maintaining sleep. More recently, evidence indicates that it also plays an important role in neuroprotection. The beginning of our review will summarize this literature. As an amphiphilic, pleiotropic indoleamine, melatonin has both direct actions and receptor-mediated effects. For example, melatonin has established effects as an antioxidant and free radical scavenger both in vitro and in animal models. This is also evident in melatonin's prominent role in mitochondria, which is reviewed in the next section. Melatonin is synthesized in, taken up by, and concentrated in mitochondria, the powerhouse of the cell. Mitochondria are also the major source of reactive oxygen species as a byproduct of mitochondrial oxidative metabolism. The final section of our review summarizes melatonin's potential role in aging and psychiatric disorders. Pineal and tissue melatonin levels both decline with age. Pineal melatonin declines in individuals suffering from psychiatric disorders. Melatonin's ability to act as a neuroprotectant opens new avenues of exploration for the molecule as it may be a potential treatment for cases with neurodegenerative disease.

Association between the Arylalkylamine N-Acetyltransferase (AANAT) Gene and Seasonality in Patients with Bipolar Disorder

OBJECTIVE

Bipolar disorder (BD) is complex genetic disorder. Therefore, approaches using clinical phenotypes such as biological rhythm disruption could be an alternative. In this study, we explored the relationship between melatonin pathway genes with circadian and seasonal rhythms of BD.

METHODS

We recruited clinically stable patients with BD (n=324). We measured the seasonal variation of mood and behavior (seasonality), and circadian preference, on a lifetime basis. We analyzed 34 variants in four genes (MTNR1a, MTNR1b, AANAT, ASMT) involved in the melatonin pathway.

RESULTS

Four variants were nominally associated with seasonality and circadian preference. After multiple test corrections, the rs116879618 in AANAT remained significantly associated with seasonality (corrected p=0.0151). When analyzing additional variants of AANAT through imputation, the rs117849139, rs77121614 and rs28936679 (corrected p=0.0086, 0.0154, and 0.0092) also showed a significant association with seasonality.

CONCLUSION

This is the first study reporting the relationship between variants of AANAT and seasonality in patients with BD. Since AANAT controls the level of melatonin production in accordance with light and darkness, this study suggests that melatonin may be involved in the pathogenesis of BD, which frequently shows a seasonality of behaviors and symptom manifestations.

Molecular Regulation of the Melatonin Biosynthesis Pathway in Unipolar and Bipolar Depression

Melatonin is a neurohormone that maintains the circadian rhythms of the body. By regulating the secretion of other hormones and neurotransmitters, it acts as a pleiotropic modulator that affects, for example, reproductive, immune, cardiovascular, sleep, and wake systems and mood. Thus, synthetic melatonin has become an essential component in the treatment of depressive disorders. Although we know the pathway of melatonin action in the brain, we lack comprehensive cross-sectional studies on the periphery of depressed patients. This study aimed to comprehensively analyze the differences between healthy control subjects (n = 84) and unipolar and bipolar depression patients (n = 94), including an analysis of the melatonin pathway at the level of the genes and serum biomarkers. An innovative approach is a pilot study based on gene expression profiling carried out on clinical and cell culture models using agomelatine and melatonin. We confirmed the melatonin biosynthesis pathway's molecular regulation dysfunctions, with a specific pattern for unipolar and bipolar depression, at the AANAT gene, its polymorphisms (rs8150 and rs3760138), and examined the serum biomarkers (serotonin, AANAT, ASMT, and melatonin). The biological pathway analysis uncovered pathways and genes that were uniquely altered after agomelatine treatment in a clinical model and melatonin treatment in a cell culture model. In both models, we confirmed the immunomodulatory effect of melatonin agents in depression.

Identification of the Antidepressant Function of the Edible Mushroom Pleurotus eryngii

Pleurotus eryngii produces various functional molecules that mediate physiological functions in humans. Recently, we observed that P. eryngii produces molecules that have antidepressant functions. An ethanol extract of the fruiting body of P. eryngii was obtained, and the extract was purified by XAD-16 resin using an open column system. The ethanol eluate was separated by HPLC, and the fraction with an antidepressant function was identified. Using LC-MS, the molecular structure of the HPLC fraction with antidepressant function was identified as that of tryptamine, a functional molecule that is a tryptophan derivative. The antidepressant effect was identified from the ethanol extract, XAD-16 column eluate, and HPLC fraction by a serotonin receptor binding assay and a cell-based binding assay. Furthermore, a forced swimming test (FST) showed that the mice treated with purified fractions of P. eryngii exhibited decreased immobility time compared with nontreated mice. From these results, we suggest that the extract of P. eryngii has an antidepressant function and that it may be employed as an antidepressant health supplement.

Poor sleep quality associates with self-reported psychiatric and cardiometabolic symptoms independently of sleep timing patterns in a large sample of rural and urban workers

Poor sleep associates with mental and cardiometabolic pathological outcomes. The participation of sleep timing features in the pathways by which this relationship occurs is not clear. This study aims to evaluate the interrelationship between sleep quality and self-reported psychiatric/cardiometabolic symptoms, considering mediation and moderation effects of sleep timing patterns, and urban versus rural work environment, respectively; and to verify the association between sleep quality and polymorphisms of AANAT, RORA and TIMELESS genes. An epidemiological survey was performed in a rural area in southern Brazil. Eight-hundred and twenty-nine subjects were evaluated for sleep quality using the Pittsburgh Sleep Quality Index, and sleep timing patterns using the Munich Chronotype Questionnaire. Work characteristics and psychiatric/cardiometabolic symptoms were assessed using a structured self-report questionnaire. Three polymorphisms of AANAT, RORA and TIMELESS (rs3760138, rs782931 and rs774045, respectively) were genotyped in blood samples. We found statistically significant associations of poor sleep quality with self-reported psychiatric symptoms (B = 0.382; 95% CI 0.289-0.476; adjusted p-value <.001), and with self-reported cardiometabolic symptoms (B = 0.079; 95% CI 0.013-0.151; adjusted p-value = .048). The genetic analysis showed that RORA GA/AA genotype was associated to poor sleep quality (B = 0.146, 95% CI 0.054-0.239; adjusted p-value = .004). No moderated mediation effects were observed in the conditional analysis. TIMELESS polymorphism was not included in the analysis due to the low frequency of risk genotypes. These results yield new insights regarding the interrelationship between sleep characteristics and psychiatric/cardiometabolic self-reported symptoms, taking into account genes related to the biological clocks and melatonin pathways.

Association of Melatonin Pathway Gene's Single-Nucleotide Polymorphisms with Systemic Lupus Erythematosus in a Chinese Population

Objectives

This study was to investigate the association of melatonin (MTN) pathway gene's single-nucleotide polymorphisms (SNPs) with susceptibility to systemic lupus erythematosus (SLE).

Methods

We recruited 495 SLE patients and 493 healthy controls, 11 tag SNPs in MTN receptor 1a (MTNR1a), MTNR1b, and arylalkylamine N-acetyltransferase (AANAT) genes were genotyped and analyzed. Serum MTN concentration was determined by enzyme-linked immunosorbent assay (ELISA) kits.

Results

Two SNPs of AANAT gene (rs8150 and rs3760138) associated with the risk of SLE; CC carriers of rs8150 had a lower risk as compared to GG (OR = 0.537, 95% CI: 0.361, 0.799), whereas GG carrier in rs3760138 had an increased risk (OR = 1.823, 95% CI: 1.154, 2.880) compared to TT. However, we did not find any genetic association between the other nine SNPs with SLE risk. Case-only analysis showed associations of rs2165667 and rs1562444 with arthritis, rs10830962 with malar rash, rs3760138 with immunological abnormality, and rs8150 with hematological abnormality. Furthermore, a significant difference between plasma MTN levels with different genotypes of rs1562444 was observed. Haplotype analyses revealed that haplotype of CCTAT, CTAGT, and GGG was significantly associated with the increased risk in SLE susceptibility, but TCTAT and CTG appeared to be a protective haplotype.

Conclusions

The present study supported the genetic association of MTN pathway genes with SLE susceptibility and specific clinical manifestations, suggesting the potential role of MTN pathway genes in the pathogenesis and development of SLE.

Pathophysiology of Depression: Molecular Regulation of Melatonin Homeostasis - Current Status

Circadian rhythm alterations resulting in disturbed sleep and disturbed melatonin secretion are flagship features of depression. Melatonin, known as a hormone of darkness, is secreted by the pineal gland located near to the center of the brain between the two hemispheres. Melatonin has an antidepressant effect by maintaining the body's circadian rhythm, by regulating the pattern of expression of the clock genes in the suprachiasmatic nucleus (SCN) and modifying the key genes of serotoninergic neurotransmission that are linked with a depressive mood. Melatonin is produced via the metabolism of serotonin in two steps which are catalyzed by serotonin N-acetyltransferase (SNAT) and acetylserotonin-O-methyltransferase (ASMT). Serotonin, SNAT, and ASMT are key melatonin level regulation factors. Melatonin acts mainly on the MT1 and MT2 receptors, which are present in the SCN, to regulate physiological and neuroendocrine functions including circadian entrainment, referred to as a chronobiotic effect. Although melatonin has been known about and refereed to for almost 50 years, the relationship between melatonin and depression is still not clear. In this review, we summarize current knowledge about the genetic and epigenetic regulation of enzymes involved in melatonin synthesis and metabolism as potential features of depression pathophysiology and treatment. Confirmation that melatonin metabolism in peripheral blood partially reflects a disorder in the brain could be a breakthrough in the standardization of measurements of melatonin level for the development of treatment standards, finding new therapeutic targets, and elaborating simple noninvasive clinical tests.

Dendritic cell nuclear protein-1 regulates melatonin biosynthesis by binding to BMAL1 and inhibiting the transcription of N-acetyltransferase in C6 cells

Dendritic cell nuclear protein-1 (DCNP1) is a protein associated with major depression. In the brains of depression patients, DCNP1 is up-regulated. However, how DCNP1 participates in the pathogenesis of major depression remains unknown. In this study, we first transfected HEK293 cells with EGFP-DCNP1 and demonstrated that the full-length DCNP1 protein was localized in the nucleus, and RRK (the residues 117-119) composed its nuclear localization signal (NLS). An RRK-deletion form of DCNP1 (DCNP1ΔRRK) and truncated form (DCNP11-116), each lacking the RRK residues, did not show the specific nuclear localization like full-length DCNP1 in the cells. A rat glioma cell line C6 can synthesize melatonin, a hormone that plays important roles in both sleep and depression. We then revealed that transfection of C6 cells with full-length DCNP1 but not DCNP1ΔRRK or DCNP11-116 significantly decreased the levels of melatonin. Furthermore, overexpression of full-length DCNP1, but not DCNP1ΔRRK or DCNP11-116, in C6 cells significantly decreased both the mRNA and protein levels of N-acetyltransferase (NAT), a key enzyme in melatonin synthesis. Full-length DCNP1 but not DCNP1ΔRRK or DCNP11-116 was detected to interact with the Nat promoter and inhibited its activity through its E-box motif. Furthermore, full-length DCNP1 but not the mutants interacted with and repressed the transcriptional activity of BMAL1, a transcription factor that transactivates Nat through the E-box motif. In conclusion, we have shown that RRK (the residues 117-119) are the NLS responsible for DCNP1 nuclear localization. Nuclear DCNP1 represses NAT expression and melatonin biosynthesis by interacting with BMAL1 and repressing its transcriptional activity. Our study reveals a connection between the major depression candidate protein DCNP1, circadian system and melatonin biosynthesis, which may contribute to the pathogenesis of depression.

A Comparison of Gene Expression Profiles between Glucocorticoid Responder and Non-Responder Bovine Trabecular Meshwork Cells Using RNA Sequencing

The most common ocular side effect of glucocorticoid (GC) therapy is GC-induced ocular hypertension (OHT) and GC-induced glaucoma (GIG). GC-induced OHT occurs in about 40% of the general population, while the other 60% are resistant. This study aims to determine the genes and pathways involved in differential GC responsiveness in the trabecular meshwork (TM). Using paired bovine eyes, one eye was perfusion-cultured with 100nM dexamethasone (DEX), while the fellow eye was used to establish a bovine TM (BTM) cell strain. Based on maximum IOP change in the perfused eye, the BTM cell strain was identified as a DEX-responder or non-responder strain. Three responder and three non-responder BTM cell strains were cultured, treated with 0.1% ethanol or 100nM DEX for 7 days. RNA and proteins were extracted for RNA sequencing (RNAseq), qPCR, and Western immunoblotting (WB), respectively. Data were analyzed using the human and bovine genome databases as well as Tophat2 software. Genes were grouped and compared using Student’s t-test. We found that DEX induced fibronectin expression in responder BTM cells but not in non-responder cells using WB. RNAseq showed between 93 and 606 differentially expressed genes in different expression groups between responder and non-responder BTM cells. The data generated by RNAseq were validated using qPCR. Pathway analyses showed 35 pathways associated with differentially expressed genes. These genes and pathways may play important roles in GC-induced OHT and will help us to better understand differential ocular responsiveness to GCs.

Associations of PER3 and RORA Circadian Gene Polymorphisms and Depressive Symptoms in Older Adults

BACKGROUND

Depressive symptoms are common in older adults and associated with poor outcomes. Although circadian genes have been implicated in depression, the relationship between circadian genes and depressive symptoms in older adults is unclear.

METHODS

A cross-sectional genetic association study of 529 single nucleotide polymorphisms (SNPs) representing 30 candidate circadian genes was performed in two population-based cohorts: the Osteoporotic Fractures in Men Study (MrOS; N=270, age: 76.58±5.61 years) and the Study of Osteoporotic Fractures (SOF) in women (N=1740, 84.05±3.53 years) and a meta-analysis was performed. Depressive symptoms were assessed with the Geriatric Depression Scale categorizing participants as having none-few symptoms (0-2), some depressive symptoms (>2 to <6), or many depressive symptoms (≥6).

RESULTS

We found associations meeting multiple testing criteria for significance between the PER3 intronic SNP rs12137927 and decreased odds of reporting "some depressive symptoms" in the SOF sample (odds ratio [OR]: 0.61, 95% confidence interval [CI]: 0.48-0.78, df=1, Wald χ2=-4.04, p=0.000054) and the meta-analysis (OR: 0.61, CI: 0.48-0.78, z=-4.04, p=0.000054) and between the PER3 intronic SNPs rs228644 (OR: 0.74, CI: 0.63-0.86, z=3.82, p=0.00013) and rs228682 (OR: 0.74, CI: 0.86-0.63, z=3.81, p=0.00014) and decreased odds of reporting "some depressive symptoms" in the meta-analysis compared to endorsing none-few depressive symptoms. The RORA intronic SNP rs11632098 was associated with greater odds of reporting "many depressive symptoms" (OR: 2.16, CI: 1.45-3.23, df=1, Wald χ2=3.76, p=0.000168) in the men. In the meta-analysis the association was attenuated and nominally significant (OR: 1.63, CI: 1.24-2.16, z=3.45, p=0.00056).

CONCLUSION

PER3 and RORA may play important roles in the development of depressive symptoms in older adults.

Neuronal DNA Methylation Profiling of Blast-Related Traumatic Brain Injury

Long-term molecular changes in the brain resulting from blast exposure may be mediated by epigenetic changes, such as deoxyribonucleic acid (DNA) methylation, that regulate gene expression. Aberrant regulation of gene expression is associated with behavioral abnormalities, where DNA methylation bridges environmental signals to sustained changes in gene expression. We assessed DNA methylation changes in the brains of rats exposed to three 74.5 kPa blast overpressure events, conditions that have been associated with long-term anxiogenic manifestations weeks or months following the initial exposures. Rat frontal cortex eight months post-exposure was used for cell sorting of whole brain tissue into neurons and glia. We interrogated DNA methylation profiles in these cells using Expanded Reduced Representation Bisulfite Sequencing. We obtained data for millions of cytosines, showing distinct methylation profiles for neurons and glia and an increase in global methylation in neuronal versus glial cells (p<10(-7)). We detected DNA methylation perturbations in blast overpressure-exposed animals, compared with sham blast controls, within 458 and 379 genes in neurons and glia, respectively. Differentially methylated neuronal genes showed enrichment in cell death and survival and nervous system development and function, including genes involved in transforming growth factor β and nitric oxide signaling. Functional validation via gene expression analysis of 30 differentially methylated neuronal and glial genes showed a 1.2 fold change in gene expression of the serotonin N-acetyltransferase gene (Aanat) in blast animals (p<0.05). These data provide the first genome-based evidence for changes in DNA methylation induced in response to multiple blast overpressure exposures. In particular, increased methylation and decreased gene expression were observed in the Aanat gene, which is involved in converting serotonin to the circadian hormone melatonin and is implicated in sleep disturbance and depression associated with traumatic brain injury.

Photoperiodic and circadian bifurcation theories of depression and mania

Seasonal effects on mood have been observed throughout much of human history.  Seasonal changes in animals and plants are largely mediated through the changing photoperiod (i.e., the photophase or duration of daylight).  We review that in mammals, daylight specifically regulates SCN (suprachiasmatic nucleus) circadian organization and its control of melatonin secretion.  The timing of melatonin secretion interacts with gene transcription in the pituitary pars tuberalis to modulate production of TSH (thyrotropin), hypothalamic T3 (triiodothyronine), and tuberalin peptides which modulate pituitary production of regulatory gonadotropins and other hormones.  Pituitary hormones largely mediate seasonal physiologic and behavioral variations.  As a result of long winter nights or inadequate illumination, we propose that delayed morning offset of nocturnal melatonin secretion, suppressing pars tuberalis function, could be the main cause for winter depression and even cause depressions at other times of year.  Irregularities of circadian sleep timing and thyroid homeostasis contribute to depression.  Bright light and sleep restriction are antidepressant and conversely, sometimes trigger mania.  We propose that internal desynchronization or bifurcation of SCN circadian rhythms may underlie rapid-cycling manic-depressive disorders and perhaps most mania.  Much further research will be needed to add substance to these theories.

Cry1 and Tef gene polymorphisms are associated with major depressive disorder in the Chinese population

INTRODUCTION

Accumulating evidences indicate that circadian abnormalities lead to sleep disorder, neurodegenerative diseases and depression. We have reported that the polymorphisms of a clock-related gene, Tef, contributed to the risk of sleep disturbances and depression in the Parkinson disease. The objective of the present study was to examine whether the three clock genes we previously studied are associated with major depressive disorder (MDD) in the Chinese population.

METHODS

105 Subjects with MDD and 485 control subjects participated in this case-control study. Demographics, Mini-mental Status Examination (MMSE), and the Hamilton rating scale for depression (HAMD) were obtained in all subjects. Genotypes of single nucleotide polymorphisms (SNPs) of Cry1 rs2287161, Cry2 rs10838524 and Tef rs738499 were screened by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

MDD cases had a significantly higher frequency carrying the C allele and CC genotype in Cry1 rs2287161 and the T allele and TT genotype in Tef rs738499 than controls.

LIMITATIONS

The sample size of MDD group was relatively small.

CONCLUSIONS

The polymorphisms of Cry1 rs2287161 and Tef rs738499 are associated to MDD.

FMR1, circadian genes and depression: suggestive associations or false discovery?

Background

There are several indications that malfunctions of the circadian clock contribute to depression. To search for particular circadian gene polymorphisms associated with depression, diverse polymorphisms were genotyped in two samples covering a range of depressed volunteers and participants with normal mood.

Methods

Depression mood self-ratings and DNA were collected independently from a sample of patients presenting to a sleep disorders center (1086 of European origin) and from a separate sample consisting of 399 participants claiming delayed sleep phase symptoms and 406 partly-matched controls. A custom Illumina Golden Gate array of 768 selected single nucleotide polymorphisms (SNPs) was assayed in both samples, supplemented by additional SNPlex and Taqman assays, including assay of 41 ancestry-associated markers (AIMs) to control stratification.

Results

In the Sleep Clinic sample, these assays yielded Bonferroni-significant association with depressed mood in three linked SNPs of the gene FMR1: rs25702 (nominal P=1.77E-05), rs25714 (P=1.83E-05), and rs28900 (P=5.24E-05). This FMR1 association was supported by 8 SNPs with nominal significance and a nominally-significant gene-wise set test. There was no association of depressed mood with FMR1 in the delayed sleep phase case–control sample or in downloaded GWAS data from the GenRED 2 sample contrasting an early-onset recurrent depression sample with controls. No replication was located in other GWAS studies of depression. Our data did weakly replicate a previously-reported association of depression with PPARGC1B rs7732671 (P=0.0235). Suggestive associations not meeting strict criteria for multiple testing and replication were found with GSK3B, NPAS2, RORA, PER3, CRY1, MTNR1A and NR1D1. Notably, 16 SNPs nominally associated with depressed mood (14 in GSK3B) were also nominally associated with delayed sleep phase syndrome (P=3E10^-6).

Conclusions

Considering the inconsistencies between samples and the likelihood that the significant three FMR1 SNPs might be linked to complex polymorphisms more functionally related to depression, large gene resequencing studies may be needed to clarify the import for depression of these circadian genes.

Chronobiology of Melatonin beyond the Feedback to the Suprachiasmatic Nucleus-Consequences to Melatonin Dysfunction

The mammalian circadian system is composed of numerous oscillators, which gradually differ with regard to their dependence on the pacemaker, the suprachiasmatic nucleus (SCN). Actions of melatonin on extra-SCN oscillators represent an emerging field. Melatonin receptors are widely expressed in numerous peripheral and central nervous tissues. Therefore, the circadian rhythm of circulating, pineal-derived melatonin can have profound consequences for the temporal organization of almost all organs, without necessarily involving the melatonin feedback to the suprachiasmatic nucleus. Experiments with melatonin-deficient mouse strains, pinealectomized animals and melatonin receptor knockouts, as well as phase-shifting experiments with explants, reveal a chronobiological role of melatonin in various tissues. In addition to directly steering melatonin-regulated gene expression, the pineal hormone is required for the rhythmic expression of circadian oscillator genes in peripheral organs and to enhance the coupling of parallel oscillators within the same tissue. It exerts additional effects by modulating the secretion of other hormones. The importance of melatonin for numerous organs is underlined by the association of various diseases with gene polymorphisms concerning melatonin receptors and the melatonin biosynthetic pathway. The possibilities and limits of melatonergic treatment are discussed with regard to reductions of melatonin during aging and in various diseases.

Polymorphisms in melatonin synthesis pathways: possible influences on depression

Background

It has been reported that rs4446909, a single nucleotide polymorphism (SNP) in the promoter of acetylserotonin methyltransferase (ASMT), influences the expression of the ASMT enzyme. The common G allele is associated with lower ASMT activity, and therefore, diminishes conversion of N-acetylserotonin to melatonin. The G allele was associated with recurrent depressive disorder in a Polish group. ASMT might also affect bipolar relapse, given evidence that N-acetylserotonin might stimulate TRKB receptors, and TRKB may influence mood relapse in bipolar disorder. Additionally, arylalkylamine N-acetyltransferase (AANAT) polymorphisms have been reported associated with depression, perhaps through their influence upon N-acetylserotonin or melatonin synthesis.

Results

To replicate and further explore these ideas, rs4446909 was genotyped in four research groups, as part of a panel of 610 SNPs surveyed by an Illumina Golden Gate assay. In 768 cases with delayed sleep phase disorder or matched controls, rs4446909 was indeed associated with the depressive symptoms on a self-report scale (P = 0.01, R² = 0.007). However, there was no significant association of rs4446909 with self-reported depression in a sleep clinic patient group or with two groups of elderly men and women from multicenter studies, nor was the response to lithium treatment associated with rs4446909 in bipolar patients. No associations of two AANAT SNPs with depression were found.

Conclusions

The evidence did not support a strong influence of rs4446909 upon mood, but the partial replication may be consistent with a modest effect. It is possible that larger or younger subject groups with improved phenotype ascertainment might demonstrate more persuasive replication.