Interaction between Methylation and CpG Single-Nucleotide Polymorphisms in the HTR2A Gene: Association Analysis with Suicide Attempt in Schizophrenia

Mood disorders and 5-HTR2A genetic variants - the moderator effect of inflammation on expression of affective polarity phenotype

BACKGROUND

Although repeatedly confirmed, the molecular nature of gene-environment (GxE) interactions has rarely been investigated in the clinical context of mood disorders. This study assesses the relationship between HTR2A genetic variants and the modulatory effect of inflammation in a collective cohort of patients with major depressive disorder (MDD) and bipolar disorder (BD), as a unified group with two distinct phenotypes.

METHODS

The study included 138 patients with acute mood episodes (BD = 83; MDD = 55). HTR2A rs6313 and rs6314 genotyping was performed while measuring platelet-derived indicators of inflammation (platelet count (PLT), mean platelet volume (MPV), plateletcrit, and platelet distribution width) and the MPV/PLT ratio.

RESULTS

The HTR2A rs6313 variant is a significant predictor of the polarity phenotype in mood disorders, with the MPV/PLT ratio moderating this relationship, but only under low-inflammatory conditions. In more pronounced inflammatory states, genetic influences lose their predictive role.

CONCLUSIONS

To our knowledge, this is the first study to investigate the complex interplay between platelet-derived indicators of inflammation and HTR2A variants in the context of mood disorders. Without pro-inflammatory conditions, mood disorders seem to be more genetically determined. Under pro-inflammatory conditions, phenotypic presentation is less dependent on genetic factors. GxE interactions in mood disorders are multifaceted, context-dependent and relevant for assessing their clinical presentation and course.

MicroRNA schizophrenia: Etiology, biomarkers and therapeutic targets

The three sets of symptoms associated with schizophrenia-positive, negative, and cognitive-are burdensome and have serious effects on public health, which affects up to 1% of the population. It is now commonly believed that in addition to the traditional dopaminergic mesolimbic pathway, the etiology of schizophrenia also includes neuronal networks, such as glutamate, GABA, serotonin, BDNF, oxidative stress, inflammation and the immune system. Small noncoding RNA molecules called microRNAs (miRNAs) have come to light as possible participants in the pathophysiology of schizophrenia in recent years by having an impact on these systems. These small RNAs regulate the stability and translation of hundreds of target transcripts, which has an impact on the entire gene network. There may be improved approaches to treat and diagnose schizophrenia if it is understood how these changes in miRNAs alter the critical related signaling pathways that drive the development and progression of the illness.

Epigenetic marks in suicide: a review

Suicide is a complex phenomenon and a global public health problem that involves several biological factors that could contribute to the pathophysiology of suicide. There is evidence that epigenetic factors influence some psychiatric disorders, suggesting a predisposition to suicide or suicidal behavior. Here, we review studies of molecular mechanisms of suicide in an epigenetic perspective in the postmortem brain of suicide completers and peripheral blood cells of suicide attempters. Besides, we include studies of gene-specific DNA methylation, epigenome-wide association, histone modification, and interfering RNAs as epigenetic factors. This review provides an overview of the epigenetic mechanisms described in different biological systems related to suicide, contributing to an understanding of the genetic regulation in suicide. We conclude that epigenetic marks are potential biomarkers in suicide, and they could become attractive therapeutic targets due to their reversibility and importance in regulating gene expression.

Gene-Based Association Analysis Suggests Association of HTR2A With Antidepressant Treatment Response in Depressed Patients

The serotonin [5-hydroxytryptamine (5-HT)] system has been implicated in the pathogenesis of major depressive disorder (MDD). Among the 5-HT receptor subtypes, 5-HT2 is one of the major pharmacological therapeutic targets for MDD. There have been inconsistent findings in previous pharmacogenetic studies investigating the antidepressant therapeutic response using one or several 5-HT2A (HTR2A) genetic polymorphisms. By using gene-based association analysis, we hope to identify genetic variants of HTR2A which are related to MDD susceptibility and its antidepressant therapeutic response. 288 HTR2A single nucleotide polymorphisms in MDD susceptibility have been investigated through a case–control (455 MDD patients and 2, 998 healthy controls) study, as well as in antidepressant efficacy (n = 455) in our current research. The 21-item Hamilton Rating Scale for Depression was used to evaluate measures of antidepressant therapeutic efficacy. From two MDD groups in the antidepressant therapeutic response, by using gene-based analyses, we have identified 14 polymorphisms as suggestive markers for therapeutic response (13 for remission and 1 for response) in both meta- and mega-analyses. All of these HTR2A reported polymorphisms did not reach statistical significance in the case–control association study. This current investigation supported the link between HTR2A variants and antidepressant therapeutic response in MDD but not with MDD susceptibility.

Association between temperament related traits and single nucleotide polymorphisms in the serotonin and oxytocin systems in Merino sheep

Animal temperament is defined as the consistent behavioral and physiological differences that are seen between individuals in response to the same stressor. Neurotransmitter systems, like serotonin and oxytocin in the central nervous system, underlie variation in behavioral traits in humans and other animals. Variations like single nucleotide polymorphisms (SNPs) in the genes for tryptophan 5-hydroxylase (TPH2), the serotonin transporter (SLC6A4), the serotonin receptor (HTR2A), and the oxytocin receptor (OXTR) are associated with behavioral phenotype in humans. Thus, the objective of this study was to identify SNPs in those genes and to test if those variations are associated with the temperament in Merino sheep. Using ewes from the University of Western Australia temperament flock, which has been selected on emotional reactivity for more than 20 generations, eight SNPs (rs107856757, rs107856818, rs107856856 and rs107857156 in TPH2, rs20917091 in SLC6A4, rs17196799 and rs17193181 in HTR2A, and rs17664565 in OXTR) were found to be distributed differently between calm and nervous sheep. These eight SNPs were then genotyped in 260 sheep from a flock that has never been selected on emotional reactivity, followed by the estimation of the behavioral traits of those 260 sheep using an arena test and an isolation box test. We found that several SNPs in TPH2 (rs107856757, rs107856818, rs107856856 and rs107857156) were in strong linkage disequilibrium, and all were associated with behavioral phenotype in the nonselected sheep. Similarly, rs17196799 in HTR2A was also associated with the behavioral phenotype.

Epigenetic marks and their relationship with BDNF in the brain of suicide victims

Background

Suicide is a common phenomenon affecting people of all ages. There is a strong relationship between suicidal ideation and depressive disorders. Increasing number of studies suggest that epigenetic modifications in certain brain areas are the main mechanism through which environmental and genetic factors interact with each other contributing to the development of mental disorders. To verify this hypothesis, some epigenetic marks: H3K9/14ac, HDAC2/3, H3K27me2 and Sin3a, as well as p-S421-MeCP2/MeCP2 were examined. On the other hand, BDNF protein level were studied.

Materials and methods

Western blot analysis were performed in the frontal cortex (FCx) and hippocampus (HP) of suicide victims (n = 14) and non-suicidal controls (n = 8). The differences between groups and correlations between selected proteins were evaluated using Mann-Whitney U-test and Spearman’s rank correlation.

Results

Statistically significant decrease in H3K9/14ac (FCx:↓~23%;HP:↓~33%) combined with increase in HDAC3 (FCx:↑~103%;HP:↑~85% in HP) protein levels in suicides compared to the controls was shown. These alterations were accompanied by an increase in H3K27me2 (FCx:↑45%;HP:↑~59%) and Sin3a (HP:↑50%) levels and decrease in p-S421-MeCP2/MeCP2 protein ratio (HP:↓~55%;FCx:↓~27%). Moreover, reduced BDNF protein level (FCx:↓~43%;HP:↓~28%) in suicides was observed. On the other hand, some significant correlations (e.g. between H3K9/14ac and HDAC2 or between BDNF and p-S421-MeCP2/MeCP2) were demonstrated.

Conclusions

Our findings confirm the role of epigenetic component and BDNF protein in suicidal behavior. Lowered BDNF protein level in suicides is probably due to decrease in histone acetylation and increased level of factors related with deacetylation and methylation processes, including MeCP2 factor, which may operate bidirectionally (an activator or inhibitor of transcription).

Genome-wide methylation association with current suicidal ideation in schizophrenia

In this study, we investigate the epigenetic mechanisms associated with current suicidal ideation. Gene expression changes have been found in post-mortem brain of suicide victims. However, it is not clear how in-vivo gene expression change confers risk for suicide. DNA methylation is a form of epigenetic modification that regulates gene expression. Our primary aim is to investigate genome-wide methylation in conferring risk for current suicidal ideation (SI) in schizophrenia. The presence of current SI and genome-wide methylation patterns were assessed in 107 patients with schizophrenia. DNA methylation has been measured in white blood cells as a possible peripheral biomarker of SI. SI was the primary outcome variable in a model including methylation status of white blood cells using the Illumina 450 array. We have tested the association with genome-wide methylation levels in 19 subjects with current SI and 88 subjects without current SI and we found that higher methylation level in the CpG cg06121808 located in the gene SLC20A1 on chromosome 2 was associated with current SI (p = 0.000003; beta difference = 0.06). Furthermore, the distal promoter analysis showed that the gene SMPD2 was hypermethylated in suicide ideators (p = 0.0001; beta difference = 0.02). Thus, molecular biomarkers could advance our understanding of the molecular mechanisms of stress-related SI. Furthermore, the methylation sites that we have identified should be replicated in other suicide related phenotypes to generate robust biomarkers with high translational value for proof of concept interventions aiming at reducing SI.

Suicide epigenetics, a review of recent progress

BACKGROUND

Suicide results in over 800,000 deaths every year, making it a major public health concern worldwide. It is highly complex, with genetic and environmental influences. Epigenetic mechanisms, including DNA methylation, miRNA, and histone modifications, could explain the complex interplay of environmental risk factors with genetic risk factors in the emergence of suicidal behavior.

METHODS

Here, we review the literature on suicide epigenetics over the past 10 years.

RESULTS

There has been significant progress in the field of suicide epigenetics, with emerging findings in the brain-derived neurotrophic factor and hypothalamic-pituitary-adrenal axis genes.

LIMITATIONS

Studying patient subgroups is needed in order to extract more comparable and reproducible epigenetic findings in suicide.

CONCLUSIONS

It is crucial to consider suicidal patients or suicide victims' distal and proximal past history e.g., early-life adversity and psychiatric disorder in epigenetic studies of suicidality.

Genetic variability of serotonin pathway associated with schizophrenia onset, progression, and treatment

Schizophrenia (SZ) onset and treatment outcome have important genetic components, however individual genes do not have strong effects on SZ phenotype. Therefore, it is important to use the pathway-based approach and study metabolic and signaling pathways, such as dopaminergic and serotonergic. Serotonin pathway has an important role in brain signaling, nevertheless, its role in SZ is not as thoroughly examined as that of dopamine pathway. In this study, we reviewed serotonin pathway genes and genetic variations associated with SZ, including variations at DNA, RNA, and epigenetic level. We obtained 30 serotonin pathway genes from Kyoto encyclopedia of genes and genomes and used these genes for the literature review. We extracted 20 protein coding serotonin pathway genes with genetic variations associated with SZ onset, development, and treatment from 31 research papers. Genes associated with SZ are present on all levels of serotonin pathway: serotonin synthesis, transport, receptor binding, intracellular signaling, and reuptake; however, regulatory genes are poorly researched. We summarized common challenges of genetic association studies and presented some solutions. The analysis of reported serotonin pathway-SZ associations revealed lack of information about certain serotonin pathway genes potentially associated with SZ. Furthermore, it is becoming clear that interactions among serotonin pathway genes and their regulators may bring further knowledge about their involvement in SZ.

The Role of Epigenetic Dysregulation in Suicidal Behaviors

Suicidal behaviors have been associated with both heritable genetic variables and environmental risk factors. Epigenetic processes, such as DNA methylation, have important roles in mediating the effects of the environment on behavior. Dysregulation of these processes has been observed in many psychiatric disorders, and evidence suggests that they may also be involved in suicidal behaviors. Herein, we have summarized candidate gene and epigenome-wide studies which have investigated DNA methylation in relation to suicidal behaviors, as well as discussed some of the limitations of the field to date.

Genome-wide significant regions in 43 Utah high-risk families implicate multiple genes involved in risk for completed suicide

Suicide is the 10th leading cause of death in the United States. Although environment has undeniable impact, evidence suggests that genetic factors play a significant role in completed suicide. We linked a resource of ~ 4500 DNA samples from completed suicides obtained from the Utah Medical Examiner to genealogical records and medical records data available on over eight million individuals. This linking has resulted in the identification of high-risk extended families (7-9 generations) with significant familial risk of completed suicide. Familial aggregation across distant relatives minimizes effects of shared environment, provides more genetically homogeneous risk groups, and magnifies genetic risks through familial repetition. We analyzed Illumina PsychArray genotypes from suicide cases in 43 high-risk families, identifying 30 distinct shared genomic segments with genome-wide evidence (p = 2.02E-07-1.30E-18) of segregation with completed suicide. The 207 genes implicated by the shared regions provide a focused set of genes for further study; 18 have been previously associated with suicide risk. Although PsychArray variants do not represent exhaustive variation within the 207 genes, we investigated these for specific segregation within the high-risk families, and for association of variants with predicted functional impact in ~ 1300 additional Utah suicides unrelated to the discovery families. None of the limited PsychArray variants explained the high-risk family segregation; sequencing of these regions will be needed to discover segregating risk variants, which may be rarer or regulatory. However, additional association tests yielded four significant PsychArray variants (SP110, rs181058279; AGBL2, rs76215382; SUCLA2, rs121908538; APH1B, rs745918508), raising the likelihood that these genes confer risk of completed suicide.

GRIN2B promoter methylation deficits in early-onset schizophrenia and its association with cognitive function

Aim: We investigated GRIN1 and GRIN2B promoter methylation in first-episode schizophrenia patients compared with siblings and controls, testing for correlations between DNA methylation, cognitive performance and clinical variables. Materials & methods: Blood-derived DNA from all groups underwent bisulfite conversion and pyrosequencing to determine methylation at CpG sites within the GRIN1 and GRIN2B promoters and results were compared with the measure of global methylation LINE-1.Results: We found hypomethylation among all CpGs analyzed within GRIN2B promoter in patients and greater LINE-1 methylation in patients and siblings. CpG4 was correlated to a measure of intellectual function. Conclusion: Changes in GRIN2B promoter methylation may represent an environmental influence contributing to glutamatergic dysfunction in psychosis and relate to lower cognitive performance in subjects with first-episode schizophrenia.

Childhood Adversity Moderates the Effects of HTR2A Epigenetic Regulatory Polymorphisms on Rumination

The serotonin system has been suggested to moderate the association between childhood maltreatment and rumination, with the latter in its turn reported to be a mediator in the depressogenic effect of childhood maltreatment. Therefore, we investigated whether the associations of two epigenetic regulatory polymorphisms in the HTR2A serotonin receptor gene with Ruminative Responses Scale rumination and its two subtypes, brooding and reflection, are moderated by childhood adversity (derived from the Childhood Trauma Questionnaire) among 1,501 European white adults. We tested post hoc whether the significant associations are due to depression. We also tested the replicability of the significant results within the two subsamples of Budapest and Manchester. We revealed two significant models: both the association of methylation site rs6311 with rumination and that of miRNA binding site rs3125 (supposed to bind miR-1270, miR-1304, miR-202, miR-539 and miR-620) with brooding were a function of childhood adversity, and both interaction findings were significantly present both in the never-depressed and in the ever-depressed group. Moreover, the association of rs3125 with brooding could be replicated across the separate subsamples, and remained significant even when controlling for lifetime depression and the Brief Symptom Inventory depression score. These findings indicate the crucial importance of involving stress factors when considering endophenotypes and suggest that brooding is a more promising endophenotype than a broader measure of rumination. Transdiagnostic relevance of the brooding endophenotype and the potential of targeting epigenetic regulatory polymorphisms of HTR2A in primary and secondary prevention of depression and possibly of other disorders are also discussed.

Gene-methylation epistatic analyses via the W-test identifies enriched signals of neuronal genes in patients undergoing lipid-control treatment

An increasing number of studies are focused on the epigenetic regulation of DNA to affect gene expression without modifications to the DNA sequence. Methylation plays an important role in shaping disease traits; however, previous studies were mainly experiment, based, resulting in few reports that measured gene-methylation interaction effects via statistical means. In this study, we applied the data set adaptive W-test to measure gene-methylation interactions. Performance was evaluated by the ability to detect a given set of causal markers in the data set obtained from the GAW20. Results from simulation data analyses showed that the W-test was able to detect most markers. The method was also applied to chromosome 11 of the experimental data set and identified clusters of genes with neuronal and retinal functions, including MPPED2I, GUCY2E, NAV2, and ZBTB16. Genes from the TRIM family were also identified; these genes are potentially related to the regulation of triglyceride levels. Our results suggest that the W-test could be an efficient and effective method to detect gene-methylation interactions. Furthermore, the identified genes suggest an interesting relationship between lipid levels and the etiology of neurological disorders.

Association between serotonin 2A receptor genetic variations, stressful life events and suicide

AIM

Life events are series of events that disrupt a person's psychological equilibrium and may enhance the development of a disorder such as suicide. Several studies have assessed a relationship between 5-hydroxytryptamine (serotonin) 2A receptor (5-HTR2A) gene polymorphisms with an increased risk of suicide. However, there has been no study about the association between three 5-HTR2A gene polymorphisms, A1438G (rs6311), T102C (rs6313) and C1354T (rs6314), suicide, stressful life, and loss events in a same time.

METHODS

Relatives of 191 suicide victims were interviewed using a semi-structured questionnaire designed according to Iranian culture. Venous blood was taken from all subjects for DNA isolation. 5-HTR2A polymorphisms in a total of 191 suicide victims and 218 healthy controls were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Chi-squared and Fisher's exact tests were used to compare genotype and allele frequencies between suicide and control groups. Correction for multiple comparisons was calculated using Bonferroni correction.

RESULTS

There was a significant association between the 102 C/C genotype of 5-HTR2A gene and suicide (к² = 8.700, P = 0.012). Furthermore, we found that suicide victims with a 102 C/C genotype had a significantly higher number of stressful life and loss events (P < 0.05). Genotype and allele distributions of A1438G (rs6311) and C1354T (rs6314) polymorphisms of 5-HTR2A gene showed no differences between suicide victims and control participants and there was no association between genotype distribution and higher number of stressful life and loss events (P > 0.05).

CONCLUSION

Our results suggest that C102T (rs6313) polymorphism of 5-HTR2A gene may be involved in the susceptibility to suicide, higher number of stressful life and loss events, but A1438G (rs6311) and C1354T (rs6314) polymorphisms of 5-HTR2A gene were not associated with suicide, higher number of stressful life and loss events.

Multiple tissue methylation analysis of HTR2A exon I in suicidal behavior

OBJECTIVE

The main aim of the current study was to investigate epigenetic alterations in serotonin 2A receptor (HTR2A) exon I CpG sites as possible risk factors for suicidal behavior. We also aimed to analyze the epigenetic alterations in two different tissues as epigenetic mechanisms are tissue specific. These epigenetic changes may lead to a better prediction of suicidal behavior.

METHODS

Direct CpG methylation analysis was carried out on genomic DNA from the saliva of 20 schizophrenia suicide attempters and 27 non-attempters, and from post-mortem brain tissues of nine suicide victims and 11 controls. We used bisulfite pyrosequencing to assess the contributions of six CpG sites including the rs6313 (C102T) site in the first exon of HTR2A in suicide attempters and suicide victims.

RESULTS

DNA methylation analysis did not find a significant difference in CpG methylation between suicide attempters and non-attempters (P=0.759) or between suicide victims and controls (P=0.189). We found a strong positive correlation between CpG methylation levels in blood and saliva (r=0.547, P<0.001).

DISCUSSION

DNA methylation analysis confirmed that the overall methylation level of HTR2A exon I was around 80% for DNA extracted from saliva and almost 30% in the frontal cortex DNA. The results of this investigation do not support the evidence that methylation analysis of the HTR2A may be useful for investigating the epigenetic factors involved in suicidal behavior.

Understanding epigenetic architecture of suicide neurobiology: A critical perspective

Current understanding of environmental cross-talk with genetic makeup is found to be mediated through an epigenetic interface which is associated with prominent reversible and heritable changes at gene expression level. Recent emergence of epigenetic modulation in shaping the genetic information has become a key regulatory factor in answering the underlying complexities associated with several mental disorders. A comprehensive understanding of the pertinent changes in the epigenetic makeup of suicide phenotype exhibits a characteristic signature with the possibility of using it as a biomarker to help predict the risk factors associated with suicide. Within the scope of this current review, the most sought after epigenetic changes of DNA methylation and histone modification are thoroughly scrutinized to understand their close functional association with the broad spectrum of suicide phenotype.