Epigenetic alterations of the dopaminergic system in major psychiatric disorders

Epigenetic Basis of Psychiatric Disorders: A Narrative Review

BACKGROUND

Psychiatric disorders are complex, multifactorial illnesses with a demonstrated biological component in their etiopathogenesis. Epigenetic modifications, through the modulation of DNA methylation, histone modifications and RNA interference, tune tissue-specific gene expression patterns and play a relevant role in the etiology of psychiatric illnesses.

OBJECTIVE

This review aims to discuss the epigenetic mechanisms involved in psychiatric disorders, their modulation by environmental factors and their interactions with genetic variants, in order to provide a comprehensive picture of their mutual crosstalk.

METHODS

In accordance with the PRISMA guidelines, systematic searches of Medline, EMBASE, PsycINFO, Web of Science, Scopus, and the Cochrane Library were conducted.

RESULTS

Exposure to environmental factors, such as poor socio-economic status, obstetric complications, migration, and early life stressors, may lead to stable changes in gene expression and neural circuit function, playing a role in the risk of psychiatric diseases. The most replicated genes involved by studies using different techniques are discussed. Increasing evidence indicates that these sustained abnormalities are maintained by epigenetic modifications in specific brain regions and they interact with genetic variants in determining the risk of psychiatric disorders.

CONCLUSION

An increasing amount of evidence suggests that epigenetics plays a pivotal role in the etiopathogenesis of psychiatric disorders. New therapeutic approaches may work by reversing detrimental epigenetic changes that occurred during the lifespan.

Influence of DAT1 Promotor Methylation on Sports Performance

In the mammalian genome, DNA methylation is an epigenetic mechanism involving the transfer of a methyl group onto the C5 position of the cytosine to form 5-methylcytosine. DNA methylation regulates gene expression by recruiting proteins involved in gene repression or by inhibiting the binding of transcription factors (TFs) to DNA. As there are still many questions concerning the role of methylation in creating personality, we concentrated on searching for such associations. The research group was 100 sports male subjects (mean age = 22.88, SD = 6.35), whereas the control group included 239 healthy male volunteers matched for age (mean age = 21.69, SD = 3.39), both of European origin. The methods used in our research were as follows: DNA isolation, methylation-specific PCR, sequencing chromatophores, all conducted according to the manufacturer’s procedure. To evaluate personality traits, the NEO Five-Factor Personality Inventory (NEO-FFI) and STAI Inventory were used. We observed the existence of a statistically significant correlation for all the aspects of personality covered and CpG islands’ methylation. Nonetheless, we think that the tested group and the number of tested promotor islands in the DAT1 gene are still too small to make explicit conclusions, so it needs further profound analysis.

Dopamine transporter (DAT1) gene in combat veterans with PTSD: A case-control study

The dopamine transporter (DAT1) gene has been postulated to be involved in PTSD; however, existing studies have shown inconsistencies when examining genotypic and allelic associations. The primary objective of this study was to examine whether DAT1-40bp-VNTR (DAT1) 9R polymorphism might increase the risk of PTSD development in combat veterans, utilizing a case-control gene association study with both control and PTSD cases having previous exposure to combat traumas. Participants with PTSD (N = 365) and combat-exposed controls without PTSD (N = 298) were included in analysis. After controlling for race, sex and age, when dichotomized, absence of DAT1 10R/10R genotypes was associated with PTSD diagnosis compared to no PTSD diagnosis; these results were not statistically significant when trichotomized 10R/10R, 10R/X, 9R/9R. Similarly, odds ratio for absence of 10R/10R genotype showed a statistically significant increase in the risk of developing PTSD. DAT1 genotype was also associated with statistically significant mean total CAPS scores, both when dichotomized and trichotomized. In conclusion, our results indicate that the absence of 10R/10R is associated with an increased risk of PTSD and higher CAPS total scores.

Epigenetic Modifications in Schizophrenia and Related Disorders: Molecular Scars of Environmental Exposures and Source of Phenotypic Variability

Epigenetic modifications are increasingly recognized to play a role in the etiology and pathophysiology of schizophrenia and other psychiatric disorders with developmental origins. Here, we summarize clinical and preclinical findings of epigenetic alterations in schizophrenia and relevant disease models and discuss their putative origin. Recent findings suggest that certain schizophrenia risk loci can influence stochastic variation in gene expression through epigenetic processes, highlighting the intricate interaction between genetic and epigenetic control of neurodevelopmental trajectories. In addition, a substantial portion of epigenetic alterations in schizophrenia and related disorders may be acquired through environmental factors and may be manifested as molecular "scars." Some of these scars can influence brain functions throughout the entire lifespan and may even be transmitted across generations via epigenetic germline inheritance. Epigenetic modifications, whether caused by genetic or environmental factors, are plausible molecular sources of phenotypic heterogeneity and offer a target for therapeutic interventions. The further elucidation of epigenetic modifications thus may increase our knowledge regarding schizophrenia's heterogeneous etiology and pathophysiology and, in the long term, may advance personalized treatments through the use of biomarker-guided epigenetic interventions.

Dopamine transporter availability in alcohol and opioid dependent subjects - a 99mTc-TRODAT-1SPECT imaging and genetic association study

Drug dependence associated with increased dopamine neurotransmission and neuroplastic changes is influenced by Dopamine transporters (DAT) which are modulated by genetic and epigenetic factors. This study assesses DAT availability in relation to the 40bp DAT1 VNTR (genetic) and DAT1 promoter methylation (epigenetic) changes in patients with alcohol dependence (AD) and opioid dependence (OD). A total of 60 subjects (n=20 each of AD, OD and controls) were recruited. SPECT/CT imaging using ^99mTc-TRODAT-1 was performed for measuring striatal DAT availability and DNA screened to check DAT1promoter methylation and 40bp VNTR polymorphism. SPECT/CT imaging revealed significant decrease in DAT availability in the striatum and putamen and significant increase in DAT1 promoter methylation in AD compared to control and OD. The 40bp VNTR distribution was similar in all three groups with 10repeat and 9repeat alleles being the most common. The AD individuals with DAT1promoter methylation showed significantly lower TRODAT-1 uptake compared to the ones with no methylation. AD individuals homozygous for the 10repeat VNTR also showed reduced DAT availability. This is the first imaging study using ^99mTc-TRODAT-1 from India documenting significantly reduced striatal DAT availability, increased DAT methylation and frequency of 10repeat individuals associated with decreased DAT availability in AD.

Duplicated dnmt3aa and dnmt3ab DNA Methyltransferase Genes Play Essential and Non-Overlapped Functions on Modulating Behavioral Control in Zebrafish

DNA methylation plays several roles in regulating neuronal proliferation, differentiation, and physiological functions. The major de novo methyltransferase, DNMT3, controls the DNA methylation pattern in neurons according to environmental stimulations and behavioral regulations. Previous studies demonstrated that knockout of Dnmt3 induced mouse anxiety; however, controversial results showed that activation of Dnmt3 causes anxiolytic behavior. Thus, an alternative animal model to clarify Dnmt3 on modulating behavior is crucial. Therefore, we aimed to establish a zebrafish (Danio rerio) model to clarify the function of dnmt3 on fish behavior by behavioral endpoint analyses. We evaluated the behaviors of the wild type, dnmt3aa, and dnmt3ab knockout (KO) fish by the novel tank, mirror biting, predator avoidance, social interaction, shoaling, circadian rhythm locomotor activity, color preference, and short-term memory tests. The results indicated that the dnmt3aa KO fish possessed abnormal exploratory behaviors and less fear response to the predator. On the other hand, dnmt3ab KO fish displayed less aggression, fear response to the predator, and interests to interact with their conspecifics, loosen shoaling formation, and dysregulated color preference index ranking. Furthermore, both knockout fishes showed higher locomotion activity during the night cycle, which is a sign of anxiety. However, changes in some neurotransmitter levels were observed in the mutant fishes. Lastly, whole-genome DNA methylation sequencing demonstrates a potential network of Dnmt3a proteins that is responsive to behavioral alterations. To sum up, the results suggested that the dnmt3aa KO or dnmt3ab KO fish display anxiety symptoms, which supported the idea that Dnmt3 modulates the function involved in emotional control, social interaction, and cognition.

The effect of cryopreservation on DNA methylation patterns of the chromosome 15q11-q13 region in human spermatozoa

Human sperm cryopreservation is a common technique which is used in assisted reproductive technologies. Despite the existence of evidence supporting the production of ROS and DNA fragmentation during sperm cryopreservation, there is little and equivocal information about the cryopreservation effects on methylation of imprinted genes and imprinting control regions. In this study, we have investigated the effects of cryopreservation on DNA methylation in promoter regions of SNURF-SNRPN and UBE3A imprinted genes, PWS-ICR and AS-ICR in the chromosome 15q11-q13 region. Semen samples from 10 healthy normozoospermic men were collected and each sample was divided into four equal aliquots: fresh, cryoprotectant, cryopreservation, and H₂O₂. We measured the ROS levels and DNA fragmentation using DCFH-DA and TUNEL assay respectively by flow cytometry. DNA methylation in promoter regions of SNURF-SNRPN and UBE3A imprinted genes, PWS-ICR and AS-ICR in the chromosome 15q11-q13 region were evaluated by quantitative methylation-specific PCR technique. Intracellular levels of ROS and percentage of TUNEL-positive spermatozoa significantly increased in cryopreservation group compared to fresh group. Exposure to cryoprotectant had no significant effect on ROS levels and DNA fragmentation. Neither cryopreservation nor exposure to cryoprotectant significantly affected DNA methylation of the selected gene regions. However, DNA fragmentation had positive correlation with DNA methylation of AS-ICR. In conclusion, based on our study, clinical use of sperm cryopreservation for fertility treatments appear to be safe in regard to DNA methylation in the chromosome 15q11-q13 region.

Antipsychotic Medications and DNA Methylation in Schizophrenia and Bipolar Disorder: A Systematic Review

The pharmacoepigenetics of antipsychotic treatment in severe mental illness is a growing area of research that aims to understand the interface between antipsychotic treatment and genetic regulation. Pharmacoepigenetics may some day assist in identifying treatment response mechanisms or become one of the components in the implementation of precision medicine. To understand the current evidence regarding the effects of antipsychotics on DNA methylation a systematic review with qualitative synthesis was performed through Pubmed, Embase and Psychinfo from earliest data to June 2019. Studies were included if they analyzed DNA methylation in an antipsychotic-treated population of patients with schizophrenia or bipolar disorder. Data extraction occurred via a standardized format and study quality was assessed. Twenty-nine studies were identified for inclusion. Study design, antipsychotic type, sample source, and methods of DNA methylation measurement varied across all studies. Eighteen studies analyzed methylation in patients with schizophrenia, four studies in patients with bipolar disorder, and seven studies in a combined sample of schizophrenia and bipolar disorder. Twenty-two studies used observational samples whereas the remainder used prospectively treated samples. Six studies assessed global methylation, five assessed epigenome-wide, and 15 performed a candidate epigenetic study. Two studies analyzed both global and gene-specific methylation, whereas one study performed a simultaneous epigenome-wide and gene-specific study. Only three genes were analyzed in more than one gene-specific study and the findings were discordant. The state of the pharmacoepigenetic literature on antipsychotic use is still in its early stages and uniform reporting of methylation site information is needed. Future work should concentrate on using prospective sampling with appropriate control groups and begin to replicate many of the novel associations that have been reported.

Aberrant transcriptomes and DNA methylomes define pathways that drive pathogenesis and loss of brain laterality/asymmetry in schizophrenia and bipolar disorder

Although the loss of brain laterality is one of the most consistent modalities in schizophrenia (SCZ) and bipolar disorder (BD), its molecular basis remains elusive. Our limited previous studies indicated that epigenetic modifications are key to the asymmetric transcriptomes of brain hemispheres. We used whole-genome expression microarrays to profile postmortem brain samples from subjects with SCZ, psychotic BD [BD[+]] or non-psychotic BD [BD(-)], or matched controls (10/group) and performed whole-genome DNA methylation (DNAM) profiling of the same samples (3-4/group) to identify pathways associated with SCZ or BD[+] and genes/sites susceptible to epigenetic regulation. qRT-PCR and quantitative DNAM analysis were employed to validate findings in larger sample sets (35/group). Gene Set Enrichment Analysis (GSEA) demonstrated that BMP signaling and astrocyte and cerebral cortex development are significantly (FDR q < 0.25) coordinately upregulated in both SCZ and BD[+], and glutamate signaling and TGFβ signaling are significantly coordinately upregulated in SCZ. GSEA also indicated that collagens are downregulated in right versus left brain of controls, but not in SCZ or BD[+] patients. Ingenuity Pathway Analysis predicted that TGFB2 is an upstream regulator of these genes (p = .0012). While lateralized expression of TGFB2 in controls (p = .017) is associated with a corresponding change in DNAM (p ≤ .023), lateralized expression and DNAM of TGFB2 are absent in SCZ or BD. Loss of brain laterality in SCZ and BD corresponds to aberrant epigenetic regulation of TGFB2 and changes in TGFβ signaling, indicating potential avenues for disease prevention/treatment.

Histone deacetylase inhibitors reverse age-related increases in side effects of haloperidol in mice

BACKGROUND

Older patients can be especially susceptible to antipsychotic-induced side effects, and the pharmacodynamic mechanism underlying this phenomenon remains unclear. We hypothesized that age-related epigenetic alterations lead to decreased expression and functionality of the dopamine D2 receptor (D2R), contributing to this susceptibility.

METHODS

In this study, we treated young (2-3 months old) and aged (22-24 months old) C57BL/6 mice with the D2R antagonist haloperidol (HAL) once a day for 14 days to evaluate HAL-induced motor side effects. In addition, we pretreated separate groups of young and aged mice with histone deacetylase (HDAC) inhibitors valproic acid (VPA) or entinostat (MS-275) and then administered HAL.

RESULTS

Our results show that the motor side effects of HAL are exaggerated in aged mice as compared to young mice and that HDAC inhibitors are able to reverse the severity of these deficits. HAL-induced motor deficits in aged mice are associated with an age- and drug-dependent decrease in striatal D2R protein levels and functionality. Further, histone acetylation was reduced while histone tri-methylation was increased at specific lysine residues of H3 and H4 within the Drd2 promoter in the striatum of aged mice. HDAC inhibitors, particularly VPA, restored striatal D2R protein levels and functionality and reversed age- and drug-related histone modifications at the Drd2 promoter.

CONCLUSIONS

These results suggest that epigenetic changes at the striatal Drd2 promoter drive age-related increases in antipsychotic side effect susceptibility, and HDAC inhibitors may be an effective adjunct treatment strategy to reduce side effects in aged populations.

Understanding the epigenetic basis of sex differences in depression

Epigenetics refers to potentially heritable processes that can mediate both lasting and transient changes in gene expression in the absence of genome sequence alterations. The field of epigenetics has introduced a novel understanding of the mechanisms through which the environment can shape an individual and potentially its offspring. This Mini-Review examines the current literature exploring the role of epigenetics in the development of mood disorders such as depression. Depression is twofold more common in females, yet the majority of preclinical research has been conducted exclusively in male subjects. Here we discuss what is known about sex differences in epigenetic regulation and function and how this may contribute to the etiology and onset of mood disorders. © 2016 Wiley Periodicals, Inc.

Methamphetamine-induced psychosis is associated with DNA hypomethylation and increased expression of AKT1 and key dopaminergic genes

Methamphetamine, one of the most frequently used illicit drugs worldwide, can induce psychosis in a large fraction of abusers and it is becoming a major problem for the health care institutions. There is some evidence that genetic and epigenetic factors may play roles in methamphetamine psychosis. In this study, we examined methamphetamine-induced epigenetic and expression changes of several key genes involved in psychosis. RNA and DNA extracted from the saliva samples of patients with methamphetamine dependency with and without psychosis as well as control subjects (each group 25) were analyzed for expression and promoter DNA methylation status of DRD1, DRD2, DRD3, DRD4, MB-COMT, GAD1, and AKT1 using qRT-PCR and q-MSP, respectively. We found statistically significant DNA hypomethylation of the promoter regions of DRD3 (P = 0.032), DRD4 (P = 0.05), MB-COMT (P = 0.009), and AKT1 (P = 0.0008) associated with increased expression of the corresponding genes in patients with methamphetamine psychosis (P = 0.022, P = 0.034, P = 0.035, P = 0.038, respectively), and to a lesser degree in some of the candidate genes in non-psychotic patients versus the control subjects. In general, methamphetamine dependency is associated with reduced DNA methylation and corresponding increase in expression of several key genes involved in the pathogenesis of psychotic disorders. While these epigenetic changes can be useful diagnostic biomarkers for psychosis in methamphetamine abusers, it is also consistent with the use of methyl rich diet for prevention or suppression of psychosis in these patients. However, this needs to be confirmed in future studies. © 2016 Wiley Periodicals, Inc.

Dissecting bipolar disorder complexity through epigenomic approach

In recent years, numerous studies of gene regulation mechanisms have emerged in neuroscience. Epigenetic modifications, described as heritable but reversible changes, include DNA methylation, DNA hydroxymethylation, histone modifications and noncoding RNAs. The pathogenesis of psychiatric disorders, such as bipolar disorder, may be ascribed to a complex gene-environment interaction (G × E) model, linking the genome, environmental factors and epigenetic marks. Both the high complexity and the high heritability of bipolar disorder make it a compelling candidate for neurobiological analyses beyond DNA sequencing. Questions that are being raised in this review are the precise phenotype of the disorder in question, and also the trait versus state debate and how these concepts are being implemented in a variety of study designs.

Decreased DNA Methylation in the Shati/Nat8l Promoter in Both Patients with Schizophrenia and a Methamphetamine-Induced Murine Model of Schizophrenia-Like Phenotype

The number of patients with schizophrenia has increased over the past decade. Previously, many studies have been performed to establish its diagnostic criteria, prophylactic methods, and effective therapies. In this study, we analyzed whether the ratios of DNA methylation in CpG islands of the Shati/Nat8l is decreased in model mice of schizophrenia-like phenotype using genomic DNA collected from brain regions and peripheral blood, since the mouse model of schizophrenia-like phenotype, mice treated repeatedly with methamphetamine showed increase of Shati/Nat8l mRNA expression in our previous experiment. The ratios of Shati/Nat8l CpG island methylation were significantly decreased in both the nucleus accumbens and the peripheral blood of model mice compared with those of control mice. We also investigated Shati/Nat8l methylation in the blood of patients with schizophrenia. We found that Shati/Nat8l CpG island methylation ratios were lower in the patients with schizophrenia than in the healthy controls, which is consistent with our findings in the mice model. To our knowledge, this is the first study to show similar alterations in methylation status of a particular genomic DNA site in both the brain and peripheral blood of mice. Furthermore, the same phenomenon was observed in corresponding human genomic sequences of the DNA extracted from the peripheral blood of patients with schizophrenia. Based on our findings, DNA methylation profiles of the CpG island of Shati/Nat8l might be a diagnostic biomarker of schizophrenia.

Validation of differential GDAP1 DNA methylation in alcohol dependence and its potential function as a biomarker for disease severity and therapy outcome

Alcohol dependence is a severe disorder contributing substantially to the global burden of disease. Despite the detrimental consequences of chronic alcohol abuse and dependence, effective prevention strategies as well as treatment options are largely missing to date. Accumulating evidence suggests that gene-environment interactions, including epigenetic mechanisms, play a role in the etiology of alcohol dependence. A recent epigenome-wide study reported widespread alterations of DNA methylation patterns in alcohol dependent patients compared to control individuals. In the present study, we validate and replicate one of the top findings from this previous investigation in an independent cohort: the hypomethylation of GDAP1 in patients. To our knowledge, this is the first independent replication of an epigenome-wide finding in alcohol dependence. Furthermore, the AUDIT as well as the GSI score were negatively associated with GDAP1 methylation and we found a trend toward a negative association between GDAP1 methylation and the years of alcohol dependency, pointing toward a potential role of GDAP1 hypomethylation as biomarker for disease severity. In addition, we show that the hypomethylation of GDAP1 in patients reverses during a short-term alcohol treatment program, suggesting that GDAP1 DNA methylation could also serve as a potential biomarker for treatment outcome. Our data add to the growing body of knowledge on epigenetic effects in alcohol dependence and support GDAP1 as a novel candidate gene implicated in this disorder. As the role of GDAP1 in alcohol dependence is unknown, this novel candidate gene should be followed up in future studies.

Dopamine-prolactin pathway potentially contributes to the schizophrenia and type 2 diabetes comorbidity

Schizophrenia (SCZ) and type 2 diabetes (T2D) are clinically associated, and common knowledge attributes this association to side effects of antipsychotic treatment. However, even drug-naive patients with SCZ are at increased risk for T2D. Dopamine dysfunction has a central role in SCZ. It is well-known that dopamine constitutively inhibits prolactin (PRL) secretion via the dopamine receptor 2 (DR2D). If dopamine is increased or if dopamine receptors hyperfunction, PRL may be reduced. During the first SCZ episode, low PRL levels are associated with worse symptoms. PRL is essential in human and social bonding, as well as it is implicated in glucose homeostasis. Dopamine dysfunction, beyond contributing to SCZ symptoms, may lead to altered appetite and T2D. To our knowledge, there are no studies of the genetics of the SCZ-T2D comorbidity focusing jointly on the dopamine and PRL pathway in the attempt to capture molecular heterogeneity correlated to possible disease manifestation heterogeneity. In this dopamine-PRL pathway-focused-hypothesis-driven review on the association of SCZ with T2D, we report a specific revision of what it is known about PRL and dopamine in relation to what we theorize is one of the missing links between the two disorders. We suggest that new studies are necessary to establish the genetic role of PRL and dopamine pathway in SCZ-T2D comorbidity.

Antipsychotic drugs attenuate aberrant DNA methylation of DTNBP1 (dysbindin) promoter in saliva and post-mortem brain of patients with schizophrenia and Psychotic bipolar disorder

Due to the lack of genetic association between individual genes and schizophrenia (SCZ) pathogenesis, the current consensus is to consider both genetic and epigenetic alterations. Here, we report the examination of DNA methylation status of DTNBP1 promoter region, one of the most credible candidate genes affected in SCZ, assayed in saliva and post-mortem brain samples. The Illumina DNA methylation profiling and bisulfite sequencing of representative samples were used to identify methylation status of the DTNBP1 promoter region. Quantitative methylation specific PCR (qMSP) was employed to assess methylation of DTNBP1 promoter CpGs flanking a SP1 binding site in the saliva of SCZ patients, their first-degree relatives and control subjects (30, 15, and 30/group, respectively) as well as in post-mortem brains of patients with SCZ and bipolar disorder (BD) versus controls (35/group). qRT-PCR was used to assess DTNBP1 expression. We found DNA hypermethylation of DTNBP1 promoter in the saliva of SCZ patients (∼12.5%, P = 0.036), particularly in drug-naïve patients (∼20%, P = 0.011), and a trend toward hypermethylation in their first-degree relatives (P = 0.085) versus controls. Analysis of post-mortem brain samples revealed an inverse correlation between DTNBP1 methylation and expression, and normalization of this epigenetic change by classic antipsychotic drugs. Additionally, BD patients with psychotic depression exhibited higher degree of methylation versus other BD patients (∼80%, P = 0.025). DTNBP1 promoter DNA methylation may become a key element in a panel of biomarkers for diagnosis, prevention, or therapy in SCZ and at risk individuals pending confirmatory studies with larger sample sizes to attain a higher degree of significance.

Insights into the origin of DNA methylation differences between monozygotic twins discordant for schizophrenia

Background

DNA methylation differences between monozygotic twins discordant for schizophrenia have been previously reported. However, the origin of methylation differences between monozygotic twins discordant for schizophrenia is not clear. The findings here argue that all DNA methylation differences may not necessarily represent the cause of the disease; rather some may result from the effect of antipsychotics.

Methods

Methylation differences in rat brain regions and also in two pairs of unrelated monozygotic twins discordant for schizophrenia have been studied using genome-wide DNA methylation arrays at Arraystar Inc. (Rockville, Maryland, USA). The identified gene promoters showing significant alterations to DNA methylation were then further characterized using ingenuity pathway analysis (Ingenuity System Inc, CA, USA).

Results

Pathway analysis of the most significant gene promoter hyper/hypomethylation revealed a significant enrichment of DNA methylation changes in biological networks and pathways directly relevant to neural development and psychiatric disorders. These included HIPPO signaling (p = 3.93E-03) and MAPK signaling (p = 4.27E-03) pathways involving hypermethylated genes in schizophrenia-affected patients as compared to their unaffected co-twins. Also, a number of significant pathways and networks involving genes with hypomethylated gene promoters have been identified. These included CREB signaling in neurons (p = 1.53E-02), Dopamine-DARPP32 feedback in cAMP signaling (p = 7.43E-03) and Ephrin receptors (p = 1.13E-02). Further, there was significant enrichment for pathways involved in nervous system development and function (p = 1.71E-03-4.28E-02).

Conclusion

The findings highlight the significance of antipsychotic drugs on DNA methylation in schizophrenia patients. The unique pathways affected by DNA methylation in the two pairs of monozygotic twins suggest that patient-specific pathways are responsible for the disease; suggesting that patient-specific treatment strategies may be necessary in treating the disorder. The study reflects the need for developing personalized medicine approaches that take into consideration epigenetic variations between patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40303-015-0013-5) contains supplementary material, which is available to authorized users.

Downregulation of GABAA receptor protein subunits α6, β2, δ, ε, γ2, θ, and ρ2 in superior frontal cortex of subjects with autism

We measured protein and mRNA levels for nine gamma-aminobutyric acid A (GABAA) receptor subunits in three brain regions (cerebellum, superior frontal cortex, and parietal cortex) in subjects with autism versus matched controls. We observed changes in mRNA for a number of GABAA and GABAB subunits and overall reduced protein expression for GABAA receptor alpha 6 (GABRα6), GABAA receptor beta 2 (GABRβ2), GABAA receptor delta (GABRδ), GABAA receptor epsilon (GABRε), GABAA receptor gamma 2 (GABRγ2), GABAA receptor theta (GABRθ), and GABAA receptor rho 2 (GABRρ2) in superior frontal cortex from subjects with autism. Our data demonstrate systematic changes in GABAA&B subunit expression in brains of subjects with autism, which may help explain the presence of cognitive abnormalities in subjects with autism.

The influence of genetic variants on striatal dopamine transporter and D2 receptor binding after TBI

Dopamine (DA) neurotransmission influences cognition and recovery after traumatic brain injury (TBI). We explored whether functional genetic variants affecting the DA transporter (DAT) and D2 receptor (DRD2) impacted in vivo dopaminergic binding with positron emission tomography (PET) using [(11)C]βCFT and [(11)C]raclopride. We examined subjects with moderate/severe TBI (N=12) ∼1 year post injury and similarly matched healthy controls (N=13). The variable number of tandem repeat polymorphism within the DAT gene and the TaqI restriction fragment length polymorphism near the DRD2 gene were assessed. TBI subjects had age-adjusted DAT-binding reductions in the caudate, putamen, and ventral striatum, and modestly increased D2 binding in ventral striatum versus controls. Despite small sample sizes, multivariate analysis showed lower caudate and putamen DAT binding among DAT 9-allele carriers and DRD2 A2/A2 homozygotes with TBI versus controls with the same genotype. Among TBI subjects, 9-allele carriers had lower caudate and putamen binding than 10/10 homozygotes. This PET study suggests a hypodopaminergic environment and altered DRD2 autoreceptor DAT interactions that may influence DA transmission after TBI. Future work will relate these findings to cognitive performance; future studies are required to determine how DRD2/DAT1 genotype and DA-ligand binding are associated with neurostimulant response and TBI recovery.

The 22q11.2 deletion syndrome as a window into complex neuropsychiatric disorders over the lifespan

Evidence is rapidly accumulating that rare, recurrent copy number variants represent large effect risk factors for neuropsychiatric disorders. 22q11.2 deletion syndrome (22q11DS) (velocardiofacial syndrome or DiGeorge syndrome) is the most common known contiguous gene deletion syndrome and is associated with diverse neuropsychiatric disorders across the life span. One of the most intriguing aspects of the syndrome is the variability in clinical and cognitive presentation: children with 22q11DS have high prevalence of autism spectrum, attention deficit, and anxiety disorders, as well as psychotic-like features, and up to 30% of adolescents and adults develop schizophrenia-like psychosis. Recently, cases of early-onset Parkinson's disease in adults have been reported, collectively suggesting a role for disrupted dopaminergic neurotransmission in the observed neuropsychiatric phenotypes. There is also some evidence that 22q11DS-associated autism spectrum disorder and schizophrenia represent two unrelated phenotypic manifestations, consistent with a neuropsychiatric pleiotropy model. This genetic lesion thus provides a unique model for the discovery of specific genomic risk and (potentially) protective factors for neuropsychiatric disease. Here, we provide an overview of neuropsychiatric findings to date, which highlight the value of this syndrome in mapping the developmental trajectory of dimensional phenotypes that traverse multiple diagnostic categories. Potential sources of genetic variability that may contribute to the disorder's heterogeneous presentation are reviewed. Because of its known genetic etiology, animal models can readily be developed that recapitulate specific aspects of the syndrome. Future research directions involve translational models and potential for drug screenable targets in the context of this human model system.

DNA hypermethylation of serotonin transporter gene promoter in drug naïve patients with schizophrenia

INTRODUCTION

Dysfunctional serotonin signaling has been linked to the pathogenesis of autism, obsessive compulsive disorder, mood disorders and schizophrenia. While the hypo-activity of serotonin signaling is involved in the pathogenesis of depression, anxiety and obsessive compulsive disorder; LSD, an agonist of serotonin type 2 receptor (5-HTR2A) induces psychosis. Therefore, anxiety and depressive disorders are treated by SSRIs which inhibit serotonin transporter (5-HTT) while psychotic disorders are controlled by drugs that block serotonin and/or dopamine receptors. Since genetic polymorphisms and epigenetic dysregulation of 5-HTT are involved in the pathogenesis of mental diseases, we analyzed DNA methylation of 5-HTT promoter in post-mortem brains and saliva samples of patients with schizophrenia (SCZ) and bipolar disorder (BD) to evaluate its potential application as a diagnostic and/or therapeutic biomarker in SCZ and BD.

METHODS

Whole genome DNA methylation profiling was performed for a total of 24 samples (including two saliva samples) using the Illumina 27K (for 12 samples) and 450K DNA methylation array platform (for another 12 samples), followed by bisulfite sequencing to identify candidate CpGs for further analysis. Quantitative methylation specific PCR (qMSP) was used to assess the degree of CpG methylation of 5-HTT promoter in 105 post-mortem brains (35 controls, 35 SCZ and 35 BD) and 100 saliva samples (30 controls, 30 SCZ, 20 BD and 20 first degree relatives of SCZ or BD). The U133 2.0 Plus Human Transcriptome array for a total of 30 post-mortem brain samples (each group 10) followed by quantitative real-time PCR was used to study 5-HTT expression in 105 post-mortem brain samples.

RESULTS

The qMSP analysis for 5-HTT promoter region showed DNA hypermethylation in post-mortem brain samples of SCZ patients (~30%), particularly in drug free patients (~60%, p=0.04). Similarly, there was a trend for DNA hypermethylation in antipsychotic free BD patients (~50%, p=0.066). qMSP analysis of DNA extracted from the saliva samples also exhibited hypermethylation of 5-HTT promoter in patients with SCZ (~30%, p=0.039), which was more significant in drug naïve SCZ patients (>50%, p=0.0025). However, the difference was not significant between the controls and unaffected first degree relatives of patients with SCZ (p=0.37) and versus patients using antipsychotic drugs (p=0.2). The whole genome transcriptome analysis of post-mortem brain samples showed reduced expression of 5-HTT in SCZ compared to the control subjects (~50%, p=0.008), confirmed by quantitative real-time PCR analysis (~40%, p=0.035) which was more significant in drug free SCZ patients (~70%, p=0.022).

CONCLUSION

A correlation between reduction in 5-HTT expression and DNA hypermethylation of the 5-HTT promoter in drug naïve SCZ patients suggests that an epigenetically defined hypo-activity of 5-HTT may be linked to SCZ pathogenesis. Furthermore, this epigenetic mark in DNA extracted from saliva can be considered as one of the key determinants in a panel of diagnostic and/or therapeutic biomarkers for SCZ.

Aberrant methylation of gene associated CpG sites occurs in borderline personality disorder

Borderline personality disorder (BPD) is a complex psychiatric disease with an increased impact in the last years. While the diagnosis and therapy are well established, little is known on the pathogenesis of borderline personality disorder. Previously, a significant increase in DNA methylation of relevant neuropsychiatric genes in BPD patients has been reported. In our study we performed genome wide methylation analysis and revealed specific CpG sites that exhibited increased methylation in 24 female BPD patients compared to 11 female healthy controls. Bead chip technology and quantitative bisulfite pyrosequencing showed a significantly increased methylation at CpG sites of APBA2 (1.1 fold) and APBA3 (1.1 fold), KCNQ1 (1.5 fold), MCF2 (1.1 fold) and NINJ2 (1.2 fold) in BPD patients. For the CpG sites of GATA4 and HLCS an increase in DNA methylation was observed, but was only significant in the bead chip assay. Moreover genome wide methylation levels of blood samples of BPD patients and control samples are similar. In summary, our results show a significant 1.26 fold average increase in methylation at the analyzed gene associated CpG sites in the blood of BPD patients compared to controls samples (p<0.001). This data may provide new insights into epigenetic mechanisms underlying the pathogenesis of BPD.

The epigenetic effect of nicotine on dopamine D1 receptor expression in rat prefrontal cortex

Nicotine is a highly addictive drug and exerts its effect partially through causing dopamine release, thereby increasing intrasynaptic dopamine levels in the brain reward systems. Dopaine D1 receptor (DRD1) mRNAs and receptors are localized in reward-related brain regions, which receive cholinergic input. The aim of this study is to evaluate whether nicotine administration affects the expression of DRD1s, and if so, whether epigenetic mechanisms, such as histone acetylation, are involved. Twenty Male Sprague Dawley rats received nicotine (0.4 mg/kg/day, s.c.) or saline injections for 15 days. After nicotine/saline treatment, rats were perfused with saline; prefrontal cortex (PFC), corpus striatum (STR), and ventral tegmental area (VTA) were dissected. Homogenates were divided into two parts for total RNA isolation and histone H4 acetylation studies. DRD1 mRNA expression was significantly higher in the PFC of the nicotine-treated group compared with controls; similar trends were observed in the VTA and STR. To study epigenetic regulation, the 2kb upstream region of the DRD1 gene promoter was investigated for histone H4 acetylation in PFC samples. After chromatin immunoprecipitation with anti-acetyl histone H4 antibody, we found an increase in histone acetylation by two different primer pairs which amplified the -1365 to -1202 (P < 0.005) and -170 to +12 (P < 0.05) upstream regions of the DRD1 promoter. Our results suggest that intermittent subcutaneous nicotine administration increases the expression of DRD1 mRNA in the PFC of rats, and this increase may be due to changes in histone H4 acetylation of the 2kb promoter of the DRD1 gene.

Combining redox-proteomics and epigenomics to explain the involvement of oxidative stress in psychiatric disorders

Psychiatric disorders affect approximately 10% of adults in North-America. The complex nature of these illnesses makes the search for their pathophysiology a challenge. However, studies have consistently shown that mitochondrial dysfunction and oxidative stress are common features across major psychiatric disorders, including bipolar disorder and schizophrenia. Nevertheless, little is known about specific targets of oxidation in the brain. The search for redox sensors (protein targets for oxidation) will offer information about which pathways are regulated by oxidation in psychiatric disorders. Additionally, DNA is also a target for oxidative damage and recently, studies have suggested that oxidation of cytosine and guanosine can serve as an epigenetic modulator by decreasing or preventing further DNA methylation. Therefore, this review aims to discuss how we can use redox-proteomics and epigenomics to help explain the role of oxidative damage in major psychiatric disorders, which may ultimately lead to the identification of targets for development of new medications.

Cerebrospinal fluid metabolome in mood disorders-remission state has a unique metabolic profile

Targeted metabolomics provides an approach to quantify metabolites involved in specific molecular pathways. We applied an electrochemistry-based, targeted metabolomics platform to define changes in tryptophan, tyrosine, purine and related pathways in the depressed and remitted phases of major depressive disorder (MDD). Biochemical profiles in the cerebrospinal fluid of unmedicated depressed (n = 14; dMDD) or remitted MDD subjects (n = 14; rMDD) were compared against those in healthy controls (n = 18; HC). The rMDD group showed differences in tryptophan and tyrosine metabolism relative to the other groups. The rMDD group also had higher methionine levels and larger methionine-to-glutathione ratios than the other groups, implicating methylation and oxidative stress pathways. The dMDD sample showed nonsignificant differences in the same direction in several of the metabolic branches assessed. The reductions in metabolites associated with tryptophan and tyrosine pathways in rMDD may relate to the vulnerability this population shows for developing depressive symptoms under tryptophan or catecholamine depletion.

Affect-modulated startle: interactive influence of catechol-O-methyltransferase Val158Met genotype and childhood trauma

The etiology of emotion-related disorders such as anxiety or affective disorders is considered to be complex with an interaction of biological and environmental factors. Particular evidence has accumulated for alterations in the dopaminergic and noradrenergic system--partly conferred by catechol-O-methyltransferase (COMT) gene variation--for the adenosinergic system as well as for early life trauma to constitute risk factors for those conditions. Applying a multi-level approach, in a sample of 95 healthy adults, we investigated effects of the functional COMT Val158Met polymorphism, caffeine as an adenosine A2A receptor antagonist (300 mg in a placebo-controlled intervention design) and childhood maltreatment (CTQ) as well as their interaction on the affect-modulated startle response as a neurobiologically founded defensive reflex potentially related to fear- and distress-related disorders. COMT val/val genotype significantly increased startle magnitude in response to unpleasant stimuli, while met/met homozygotes showed a blunted startle response to aversive pictures. Furthermore, significant gene-environment interaction of COMT Val158Met genotype with CTQ was discerned with more maltreatment being associated with higher startle potentiation in val/val subjects but not in met carriers. No main effect of or interaction effects with caffeine were observed. Results indicate a main as well as a GxE effect of the COMT Val158Met variant and childhood maltreatment on the affect-modulated startle reflex, supporting a complex pathogenetic model of the affect-modulated startle reflex as a basic neurobiological defensive reflex potentially related to anxiety and affective disorders.

Tanshinones inhibit the growth of breast cancer cells through epigenetic modification of Aurora A expression and function

The objectives of this study were to evaluate the effects of tanshinones from a Chinese herb Salvia Miltiorrhiza on the growth of breast cancer cells, and to elucidate cellular and molecular mechanisms of action. Tanshinones showed the dose-dependent effect on the growth inhibition of breast cancer cells in vitro, with tanshinone I (T1) the most potent agent. T1 was also the only tanshinone to have potent activity in inhibiting the growth of the triple-negative breast cancer cell line MDA-MB231. T1 caused cell cycle arrests of both estrogen-dependent and estrogen-independent cell lines associated with alterations of cyclinD, CDK4 and cyclinB, and induced breast cancer cell apoptosis associated with upregulation of c-PARP and downregulation of survivin and Aurora A. Among these associated biomarkers, Aurora A showed the most consistent pattern with the anti-growth activity of tanshinones. Overexpression of Aurora A was also verified in breast tumors. The gene function assay showed that knockdown of Aurora A by siRNA dramatically reduced the growth-inhibition and apoptosis-induction activities of T1, suggesting Aurora A as an important functional target of T1 action. On the other hand, tanshinones had much less adverse effects on normal mammary epithelial cells. Epigenetic mechanism studies showed that overexpression of Aurora A gene in breast cancer cells was not regulated by gene promoter DNA methylation, but by histone acetylation. T1 treatment significantly reduced acetylation levels of histone H3 associated with Aurora A gene. Our results supported the potent activity of T1 in inhibiting the growth of breast cancer cells in vitro in part by downregulation of Aurora A gene function. Our previous studies also demonstrated that T1 had potent anti-angiogenesis activity and minimal side effects in vivo. Altogether, this study warrants further investigation to develop T1 as an effective and safe agent for the therapy and prevention of breast cancer.

Smoking, but not malnutrition, influences promoter-specific DNA methylation of the proopiomelanocortin gene in patients with and without anorexia nervosa

OBJECTIVE

Our pilot study evaluates the impact of environmental factors, such as nutrition and smoking status, on epigenetic patterns in a disease-associated gene.

METHOD

We measured the effects of malnutrition and cigarette smoking on proopiomelanocortin (POMC) promoter-specific DNA methylation in female patients with and without anorexia nervosa (AN). POMC and its derived peptides (alpha melanocyte stimulating hormone and adrenocorticotropic hormone) are implicated in stress and feeding response. Promoter-specific DNA methylation of the POMC gene was determined in peripheral blood mononuclear cells of 54 healthy female control subjects, 40 underweight patients with AN, and 21 weight-restored patients with AN using bisulfite sequencing. Malnutrition was characterized by plasma leptin.

RESULTS

POMC promoter-specific DNA methylation was not affected by diagnosis or nutritional status but significantly negatively associated with cigarette smoking.

CONCLUSIONS

Although malnutrition may be expected to reduce DNA methylation through its effects on one-carbon metabolism, our negative results are in line with several in vitro and clinical studies that did not show a direct relation between gene-specific DNA methylation and folate levels. In contrast, smoking has been repeatedly reported to alter DNA methylation of specific genes and should be controlled for in future epigenetic studies.

DNA hypomethylation of MB-COMT promoter in the DNA derived from saliva in schizophrenia and bipolar disorder

The failure in the discovery of etiology of psychiatric diseases, despite extensive genetic studies, has directed the attention of neuroscientists to the contribution of epigenetic modulations, which play important roles in fine-tuning of gene expression in response to environmental factors. Previously, we analyzed 115 human post-mortem brain samples from the frontal lobe and reported DNA hypo methylation of the membrane-bound catechol-O-methyltransferase (MB-COMT) gene promoter, associated with an increased gene expression, as a risk factor for schizophrenia (SCZ) and bipolar disorder (BD). Since most epigenetic modifications are tissue specific and the availability of brain tissue to identify epigenetic aberrations in living subjects is limited, detection of epigenetic abnormalities in other tissues that represent the brain epigenetic marks is one of the critical steps to develop diagnostic and therapeutic biomarkers for mental diseases. Here, hypothesizing that; those factors that lead to the brain MB-COMT promoter DNA hypo-methylation may also cause concurrent epigenetic aberrations in peripheral tissues, we analyzed MB-COMT promoter methylation in DNA derived from the saliva in SCZ, BD and their first-degree relatives (20 cases each) as well as 25 control subjects. Using bisulfite DNA sequencing and quantitative methylation specific PCR (qMSP), we found that similar to the brain, MB-COMT promoter was hypo-methylated (∼50%) in DNA derived from the saliva in SCZ and BD compared to the control subjects (p = 0.02 and 0.037, respectively). These studies suggest that DNA methylation analysis of MB-COMT promoter in saliva can potentially be used as an available epigenetic biomarker for disease state in SCZ and BD.

Epigenetic dysregulation of HTR2A in the brain of patients with schizophrenia and bipolar disorder

INTRODUCTION

HTR2A gene has been the subject of numerous studies in psychiatric genetics because LSD, which resembles serotonin causes psychosis and atypical antipsychotic drugs target the HTR2A receptor. However, evidence for the role of HTR2A polymorphism(s) in schizophrenia (SCZ) and bipolar disorder (BD) has been elusive. We hypothesized that epigenetic dysregulation of HTR2A may be involved in psycho-pathogenesis and analyzed promoter DNA methylome and expression of HTR2A in SCZ, BD and control subjects.

METHOD

DNA derived from post-mortem brains of patients with SCZ and BD and matched control subjects (each 35) were obtained from the Stanley Medical Research Institute. While bisulfite DNA sequencing was used to screen and quantify cytosine methylation in the HTR2A promoter, corresponding gene expression was analyzed by qRT-PCR.

RESULTS

We found strong evidence for epigenetic fine-tuning of HTR2A expression. In general, the expression of HTR2A in individuals carrying the C allele of T102C (or G allele of -1438A/G polymorphism) was higher than TT genotype. Interestingly, promoter DNA of HTR2A was hypermethylated at and around the -1438A/G polymorphic site, but was hypomethylated at and around T102C polymorphic site in SCZ and BD compared to the controls. Furthermore, epigenetic down-regulation of HTR2A was associated with early age of disease onset in SCZ and BD.

CONCLUSION

Epigenetic dysregulation of HTR2A may contribute to SCZ, BD and earlier age of disease onset. Further research is required to delineate the dysregulation of other components of serotoninergic pathway to design new therapeutics based on the downstream effects of serotonin.

Promoter specific DNA methylation and gene expression of POMC in acutely underweight and recovered patients with anorexia nervosa

Proopiomelanocortin (POMC) and its derived peptides, in particular alpha-MSH, have been shown to play a crucial role in the regulation of hunger, satiety and energy homeostasis. Studies in patients with anorexia nervosa (AN) suggest an abnormal expression of appetite-regulating hormones. Hormone expression levels may be modulated by epigenetic mechanisms, which were recently shown to be implicated in the pathophysiology of eating disorders. We hypothesised that POMC promoter specific DNA methylation and gene expression will be affected by malnutrition and therefore differ in AN patients at distinct stages of the disorder. Promoter specific DNA methylation of the POMC gene and expression of POMC mRNA variants were determined in peripheral blood mononuclear cells (PBMC) of 30 healthy control women (HCW), 31 underweight (acAN) and 30 weight-recovered patients with AN (recAN). Malnutrition was characterized by plasma leptin. Expression of the functionally relevant long POMC mRNA transcript was significantly correlated with leptin levels and higher in acAN compared to recAN and HCW. Expression of the truncated form and mean promoter DNA methylation was similar in all three subgroups. Methylation of single CpG residues in the E2F binding site was inversely related to POMC expression. Our preliminary data on pattern of POMC regulation suggests an association with the underweight state rather than with persisting trait markers of AN. In contrast to POMC expression in the central nervous system, peripheral POMC mRNA expression decreased with malnutrition and hypoleptinemia. This may represent a counterregulatory mechanism as part of the crosstalk between the immune and neuroendocrine systems.

Proteomic investigation of epigenetics in neuropsychiatric disorders: a missing link between genetics and behavior?

Neuropsychiatric disorders affect a large segment of the human population and result in large costs to society. The majority of such disorders have unknown underlying causes. Recent evidence suggests an important role for epigenetic regulation in the emergence of neuropsychiatric disease. Epigenetics may provide a link between genetic and environmental factors and behavior. Epigenetic signaling involves changes on the structure of chromatin; such changes are often triggered and maintained by the post-translational modification of chromatin proteins and/or DNA. Recent proteomic technologies have enabled the study of epigenetic mechanisms in a high-throughput manner. This review will provide an overview of the major epigenetic pathways and modern techniques for their study, before focusing on experimental evidence supporting a strong role for epigenetics in selected psychiatric disorders such as depression, schizophrenia, and drug addiction. These results highlight a great need for the inclusion of the proteomic characterization of epigenetic mechanisms in the study of gene/disease associations in psychiatric disorders.

How the epigenome contributes to the development of psychiatric disorders

Epigenetics commonly refers to the developmental process by which cellular traits are established and inherited without a change in DNA sequence. These mechanisms of cellular memory also orchestrate gene expression in the adult brain and recent evidence suggests that the "epigenome" represents a critical interface between environmental signals, activation, repression and maintenance of genomic responses, and persistent behavior. We here review the current state of knowledge regarding the contribution of the epigenome toward the development of psychiatric disorders.

Methylated spirits: epigenetic hypotheses of psychiatric disorders

Our spirits may be regulated by the methylation of our genes. Methylation, acetylation, and other biochemical processes are the molecular switches for turning genes on and off. There is evidence now that certain behaviors, feelings, and psychiatric symptoms may be modified by turning various genes on or off. If classical genetics is the sequence of DNA that is inherited, then epigenetics is a parallel process determining whether a given gene (ie, a sequence of DNA coding for transcription) is expressed into its RNA or is silenced. Epigenetics is now entering psychiatry with the hypothesis that normal genes as well as risk genes can both contribute to a mental disorder. That is, it has long been hypothesized that when “abnormal” genes with an altered sequence of DNA are inherited as risk genes for a mental illness, these risk genes will make an abnormal gene product in neurons, contributing to inefficient information processing in various brain circuits and creating risk for developing a symptom of a mental illness. Now comes the role of epigenetic actions in mental illnesses.

The molecular pathology of schizophrenia--focus on histone and DNA modifications

Dysfunction of cerebral cortex and other brain regions in schizophrenia is often accompanied by dysregulated expression of numerous genes. However, the underlying genetic risk architecture remains unclear for a large majority of cases. Therefore, the study of epigenetic regulators of gene expression, including covalent modifications of DNA and nucleosome core histones, offers an attractive alternative to further explore the molecular pathology of schizophrenia beyond the level of RNA quantification. Several studies reported alterations in DNA cytosine methylation and histone methylation at specific genes and promoters in postmortem brain of subjects with schizophrenia, often in conjunction with changes in levels of the corresponding RNAs. While evidence for such "epigenetic dysregulation" is increasing, many of the reported alterations await independent replication. Interestingly, studies across the lifespan indicate that DNA and histone methylation markings are developmentally regulated in human cerebral cortex, suggesting that at least some of the epigenetic changes in the brain of adult subjects with schizophrenia reflect disordered neurodevelopment.

Epigenetic mechanisms in schizophrenia

Epidemiological research suggests that both an individual's genes and the environment underlie the pathophysiology of schizophrenia. Molecular mechanisms mediating the interplay between genes and the environment are likely to have a significant role in the onset of the disorder. Recent work indicates that epigenetic mechanisms, or the chemical markings of the DNA and the surrounding histone proteins, remain labile through the lifespan and can be altered by environmental factors. Thus, epigenetic mechanisms are an attractive molecular hypothesis for environmental contributions to schizophrenia. In this review, we first present an overview of schizophrenia and discuss the role of nature versus nurture in its pathology, where 'nature' is considered to be inherited or genetic vulnerability to schizophrenia, and 'nurture' is proposed to exert its effects through epigenetic mechanisms. Second, we define DNA methylation and discuss the evidence for its role in schizophrenia. Third, we define posttranslational histone modifications and discuss their place in schizophrenia. This research is likely to lead to the development of epigenetic therapy, which holds the promise of alleviating cognitive deficits associated with schizophrenia.

Early life exposure to a high fat diet promotes long-term changes in dietary preferences and central reward signaling

Overweight and obesity in the United States continues to grow at epidemic rates in large part due to the overconsumption of calorically-dense palatable foods. Identification of factors influencing long-term macronutrient preferences may elucidate points of prevention and behavioral modification. In our current study, we examined the adult macronutrient preferences of mice acutely exposed to a high fat diet during the third postnatal week. We hypothesized that the consumption of a high fat diet during early life would alter the programming of central pathways important in adult dietary preferences. As adults, the early-exposed mice displayed a significant preference for a diet high in fat compared to controls. This effect was not due to diet familiarity as mice exposed to a novel high carbohydrate diet during this same early period failed to show differences in macronutrient preferences as adults. The increased intake of high fat diet in early exposed mice was specific to dietary preferences as no changes were detected for total caloric intake or caloric efficiency. Mechanistically, mice exposed to a high fat diet during early life exhibited significant alterations in biochemical markers of dopamine signaling in the nucleus accumbens, including changes in levels of phospho-dopamine and cyclic AMP-regulated phosphoprotein, molecular weight 32 kDa (DARPP-32) threonine-75, DeltaFosB, and cyclin-dependent kinase 5. These results support our hypothesis that even brief early life exposure to calorically-dense palatable diets alters long-term programming of central mechanisms important in dietary preferences and reward. These changes may underlie the passive overconsumption of high fat foods contributing to the increasing body mass in the western world.

(Epi)genomics and neurodevelopment in schizophrenia: monozygotic twins discordant for schizophrenia augment the search for disease-related (epi)genomic alterations

Unlike stunning breakthroughs in the identification of genes for Mendelian disorders during the last three decades, gene identification in most complex disorders has been full of twists and turns and little progress. Doing more of the same will not guarantee success. The lessons learned argue for a need to reconsider genetic models that are appropriate for the disorder in question along with an interdisciplinary, systematic approach using genomic methods that have now become possible. We will use schizophrenia as an example to review the genetic progress to date that has been disappointing. We will argue that the causation of this complex disease may involve heterogeneous genomic changes of major effect. We will provide three approaches, retroviral transpositions, methylation, and copy number variations, to test this hypothesis. We will present arguments to suggest that such experiments will be most effective if undertaken on monozygotic twins. It will include our experience with associated experiments on the monozygotic twins discordant for schizophrenia. The results support that (epi)genomic changes of major effect, rather than accumulation of mutations of small effect, underlie the causation of this complex disease. More important, this experimental strategy will be an effective strategy for studies on other complex (behavioural) disorders as well.

Prospects for epigenetic epidemiology

Epigenetic modification can mediate environmental influences on gene expression and can modulate the disease risk associated with genetic variation. Epigenetic analysis therefore holds substantial promise for identifying mechanisms through which genetic and environmental factors jointly contribute to disease risk. The spatial and temporal variance in epigenetic profile is of particular relevance for developmental epidemiology and the study of aging, including the variable age at onset for many common diseases. This review serves as a general introduction to the topic by describing epigenetic mechanisms, with a focus on DNA methylation; genetic and environmental factors that influence DNA methylation; epigenetic influences on development, aging, and disease; and current methodology for measuring epigenetic profile. Methodological considerations for epidemiologic studies that seek to include epigenetic analysis are also discussed.

Pharmacogenomic Biomarkers in Neuropsychiatry: The Path to Personalized Medicine in Mental Disorders

Neuropsychiatric disorders and dementia represent a major cause of disability and high cost in developed societies. Most disorders of the central nervous system (CNS) share some common features, such as a genomic background in which hundreds of genes might be involved, genome-environment interactions, complex pathogenic pathways, poor therapeutic outcomes, and chronic disability.

Recent advances in genomic medicine can contribute to accelerate our understanding on the pathogenesis of CNS disorders, improve diagnostic accuracy with the introduction of novel biomarkers, and personalize therapeutics with the incorporation of pharmacogenetic and pharmacogenomic procedures to drug development and clinical practice.

The pharmacological treatment of CNS disorders, in general, accounts for 10–20% of direct costs, and less than 30–40% of the patients are moderate responders to conventional drugs, some of which may cause important adverse drugs reactions (ADRs). Pharmacogenetic and pharmacogenomic factors may account for 60–90% of drug variability in drug disposition and pharmacodynamics. Approximately 60–80% of CNS drugs are metabolized via enzymes of the CYP gene superfamily; 18% of neuroleptics are major substrates of CYP1A2 enzymes, 40% of CYP2D6, and 23% of CYP3A4; 24% of antidepressants are major substrates of CYP1A2 enzymes, 5% of CYP2B6, 38% of CYP2C19, 85% of CYP2D6, and 38% of CYP3A4; 7% of benzodiazepines are major substrates of CYP2C19 enzymes, 20% of CYP2D6, and 95% of

CYP3A4. About 10–20% of Caucasians are carriers of defective CYP2D6 polymorphic variants that alter the metabolism of many psychotropic agents. Other 100 genes participate in the efficacy and safety of psychotropic drugs. The incorporation of pharmacogenetic/ pharmacogenomic protocols to CNS research and clinical practice can foster therapeutics optimization by helping to develop cost-effective pharmaceuticals and improving drug efficacy and safety. To achieve this goal several measures have to be taken, including: (a) educate physicians and the public on the use of genetic/ genomic screening in the daily clinical practice; (b) standardize genetic testing for major categories of drugs; (c) validate pharmacogenetic and pharmacogenomic procedures according to drug category and pathology; (d) regulate ethical, social, and economic issues; and (e) incorporate pharmacogenetic and pharmacogenomic procedures to both drugs in development and drugs in the market to optimize therapeutics.

Pathways-based analyses of whole-genome association study data in bipolar disorder reveal genes mediating ion channel activity and synaptic neurotransmission

Despite known heritability, the complex genetic architecture of bipolar disorder (likely including trait, locus and allelic heterogeneity, as well as genetic interactions) has confounded genetic discovery for many years. Even modern day whole genome association studies (WGAS) using over half a million common SNPs have implicated only a handful of genes at the genomewide level. Temporally coincident with this series of WGAS, a host of pathways-based analyses (PBAs) have emerged as novel computational approaches in the examination of large-scale datasets, but thus far rarely have been applied to WGAS data in psychiatric disorders. Here, we report a series of PBAs conducted using exploratory visual analysis, an analytic and visualization software tool for examining genomic data, to examine results from the National Institutes of Mental Health and Wellcome-Trust Case Control Consortium WGAS in bipolar disorder. Consistent with a host of prior linkage findings, some candidate gene association studies, and recent WGAS, our strongest findings suggest involvement of ion channel structural and regulatory genes, including voltage-gated ion channels and the broader ion channel group that comprises both voltage- and ligand-gated channels. Moreover, we found only modest overlap in the particular genes driving the significance of these gene sets across the analyses. This observation strongly suggests that variation in ion channel genes, as a class of genes, may contribute to the susceptibility of bipolar disorder and that heterogeneity may figure prominently in the genetic architecture of this susceptibility.