The human reelin gene: Transcription factors (+), repressors (−) and the methylation switch (+/−) in schizophrenia

DNA methylation levels of RELN promoter region in ultra-high risk, first episode and chronic schizophrenia cohorts of schizophrenia

The essential role of the Reelin gene (RELN) during brain development makes it a prominent candidate in human epigenetic studies of Schizophrenia. Previous literature has reported differing levels of DNA methylation (DNAm) in patients with psychosis. Therefore, this study aimed to (1) examine and compare RELN DNAm levels in subjects at different stages of psychosis cross-sectionally, (2) analyse the effect of antipsychotics (AP) on DNAm, and (3) evaluate the effectiveness and applicability of RELN promoter DNAm as a possible biological-based marker for symptom severity in psychosis.. The study cohort consisted of 56 healthy controls, 87 ultra-high risk (UHR) individuals, 26 first-episode (FE) psychosis individuals and 30 chronic schizophrenia (CS) individuals. The Positive and Negative Syndrome Scale (PANSS) was used to assess Schizophrenia severity. After pyrosequencing selected CpG sites of peripheral blood, the Average mean DNAm levels were compared amongst the 4 subgroups. Our results showed differing levels of DNAm, with UHR having the lowest (7.72 ± 0.19) while the CS had the highest levels (HC: 8.78 ± 0.35; FE: 7.75 ± 0.37; CS: 8.82 ± 0.48). Significantly higher Average mean DNAm levels were found in CS subjects on AP (9.12 ± 0.61) compared to UHR without medication (UHR(-)) (7.39 ± 0.18). A significant association was also observed between the Average mean DNAm of FE and PANSS Negative symptom factor (R² = 0.237, ß = -0.401, *p = 0.033). In conclusion, our findings suggested different levels of DNAm for subjects at different stages of psychosis. Those subjects that took AP have different DNAm levels. There were significant associations between FE DNAm and Negative PANSS scores. With more future experiments and on larger cohorts, there may be potential use of DNAm of the RELN gene as one of the genes for the biological-based marker for symptom severity in psychosis.

L1 Retrotransposons: A Potential Endogenous Regulator for Schizophrenia

The long interspersed nuclear elements 1 (LINE-1/L1s) are the only active autonomous retrotransposons found in humans which can integrate anywhere in the human genome. They can expand the genome and thus bring good or bad effects to the host cells which really depends on their integration site and associated polymorphism. LINE-1 retrotransposition has been found participating in various neurological disorders such as autism spectrum disorder, Alzheimer’s disease, major depression disorder, post-traumatic stress disorder and schizophrenia. Despite the recent progress, the roles and pathological mechanism of LINE-1 retrotransposition in schizophrenia and its heritable risks, particularly, contribution to “missing heritability” are yet to be determined. Therefore, this review focuses on the potentially etiological roles of L1s in the development of schizophrenia, possible therapeutic choices and unaddressed questions in order to shed lights on the future research.

The Role of MeCP2 in Regulating Synaptic Plasticity in the Context of Stress and Depression

Methyl-CpG-binding protein 2 (MeCP2) is a transcriptional regulator that is highly abundant in the brain. It binds to methylated genomic DNA to regulate a range of physiological functions implicated in neuronal development and adult synaptic plasticity. MeCP2 has mainly been studied for its role in neurodevelopmental disorders, but alterations in MeCP2 are also present in stress-related disorders such as major depression. Impairments in both stress regulation and synaptic plasticity are associated with depression, but the specific mechanisms underlying these changes have not been identified. Here, we review the interplay between stress, synaptic plasticity, and MeCP2. We focus our attention on the transcriptional regulation of important neuronal plasticity genes such as BDNF and reelin (RELN). Moreover, we provide evidence from recent studies showing a link between chronic stress-induced depressive symptoms and dysregulation of MeCP2 expression, underscoring the role of this protein in stress-related pathology. We conclude that MeCP2 is a promising target for the development of novel, more efficacious therapeutics for the treatment of stress-related disorders such as depression.

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.

DNA Methylation and Schizophrenia: Current Literature and Future Perspective

Schizophrenia is a neuropsychiatric disorder characterized by dissociation of thoughts, idea, identity, and emotions. It has no central pathophysiological mechanism and precise diagnostic markers. Despite its high heritability, there are also environmental factors implicated in the development of schizophrenia. Epigenetic factors are thought to mediate the effects of environmental factors in the development of the disorder. Epigenetic modifications like DNA methylation are a risk factor for schizophrenia. Targeted gene approach studies attempted to find candidate gene methylation, but the results are contradictory. Genome-wide methylation studies are insufficient in literature and the available data do not cover different populations like the African populations. The current genome-wide studies have limitations related to the sample and methods used. Studies are required to control for these limitations. Integration of DNA methylation, gene expression, and their effects are important in the understanding of the development of schizophrenia and search for biomarkers. There are currently no precise and functional biomarkers for the disorder. Several epigenetic markers have been reported to be common in functional and peripheral tissue. This makes the peripheral tissue epigenetic changes a surrogate of functional tissue, suggesting common epigenetic alteration can be used as biomarkers of schizophrenia in peripheral tissue.

Reelin Supplementation Into the Hippocampus Rescues Abnormal Behavior in a Mouse Model of Neurodevelopmental Disorders

In the majority of schizophrenia patients, chronic atypical antipsychotic administration produces a significant reduction in or even complete remission of psychotic symptoms such as hallucinations and delusions. However, these drugs are not effective in improving cognitive and emotional deficits in patients with schizophrenia. Atypical antipsychotic drugs have a high affinity for the dopamine D₂ receptor, and a modest affinity for the serotonin 5-HT_2A receptor. The cognitive and emotional deficits in schizophrenia are thought to involve neural networks beyond the classical dopaminergic mesolimbic pathway, however, including serotonergic systems. For example, mutations in the RELN gene, which encodes Reelin, an extracellular matrix protein involved in neural development and synaptic plasticity, are associated with neurodevelopmental disorders such as schizophrenia and autism spectrum disorder. Furthermore, hippocampal Reelin levels are down-regulated in the brains of both schizophrenic patients and in rodent models of schizophrenia. In the present study, we investigated the effect of Reelin microinjection into the mouse hippocampus on behavioral phenotypes to evaluate the role of Reelin in neurodevelopmental disorders and to test a therapeutic approach that extends beyond classical monoamine targets. To model the cognitive and emotional deficits, as well as histological decreases in Reelin-positive cell numbers and hippocampal synaptoporin distribution, a synaptic vesicle protein, offspring that were prenatally exposed to maternal immune activation were used. Microinjections of recombinant Reelin protein into the hippocampus rescued impairments in object memory and anxiety-like behavior and recruited synaptoporin in the hippocampus in offspring exposed to antenatal inflammation. These results suggest that Reelin supplementation has the potential to treat cognitive and emotional impairments, as well as synaptic disturbances, in patients with neurodevelopmental disorders such as schizophrenia.

Plasticity of DNA methylation, functional brain connectivity and efficiency in cognitive remediation for schizophrenia

Cognitive remediation (CR) is predicated on principles of neuroplasticity, but the actual molecular and neurocircuitry changes underlying cognitive change in individuals with impaired neuroplastic processes is poorly understood. The present study examined epigenetic-neurocircuitry-behavioral outcome measures in schizophrenia, before and after participating in a CR program that targeted higher-order cognitive functions. Outcome measures included DNA methylation of genes central to synaptic plasticity (CpG sites of Reelin promoter and BDNF promoter) from buccal swabs, resting-state functional brain connectivity and topological network efficiency, and global scores of a cognitive battery from 35 inpatients in a rehabilitative ward (18 CR, 17 non-CR) with similar premorbid IQ to 15 healthy controls. Baseline group differences between healthy controls and schizophrenia, group-by-time effects of CR in schizophrenia, and associations between the outcome measures were tested. Baseline functional connectivity abnormalities within the frontal, fronto-temporal and fronto-parietal regions, and trending decreases in global efficiency, but not DNA methylation, were found in schizophrenia; the frontal and fronto-temporal connectivity, and global efficiency correlated with global cognitive performance across all individuals. Notably, CR resulted in differential changes in Reelin promoter CpG methylation levels, altered within-frontal and fronto-temporal functional connectivity, increasing global efficiency and improving cognitive performance in schizophrenia, when compared to non-CR. In the CR inpatients, positive associations between the micro to macro measures: Reelin methylation changes, higher global efficiency and improving global cognitive performance were found. Present findings provide a neurobiological insight into potential CR-led epigenetics-neurocircuitry modifications driving cognitive plasticity.

Specificity proteins 1 and 4 in peripheral blood mononuclear cells in postmenopausal women with schizophrenia: a 24-week double-blind, randomized, parallel, placebo-controlled trial

Accumulating evidence suggests that Specificity Protein 1 (SP1) and 4 (SP4) transcription factors are involved in the pathophysiology of schizophrenia. The therapeutic use of selective oestrogen modulators such as raloxifene added to antipsychotic drugs in the treatment of postmenopausal women with schizophrenia has been investigated in a few clinical trials, which reported an improvement in negative, positive, and general psychopathological symptoms. We aimed to investigate the possible association between peripheral SP protein levels and symptom improvement in postmenopausal women with schizophrenia treated with adjuvant raloxifene. In a subgroup of 14 postmenopausal women with schizophrenia from a 24-week, randomized, parallel, double-blind, placebo-controlled clinical trial (NCT015736370), we investigated changes in SP1 and SP4 protein levels in peripheral blood mononuclear cells. Participants were randomized to either 60 mg/day adjunctive raloxifene or placebo. Psychopathological symptoms were assessed at baseline and at week 24 with the Positive and Negative Syndrome Scale (PANSS). The expression of SP proteins was evaluated by immunoblot, and changes in PANSS scores and protein levels were compared at baseline and after 24 weeks of treatment. An improvement in symptoms was observed in the intervention group, but not in placebo group. Post-treatment protein levels of SP4, but not SP1, correlated with improvements in general and total PANSS subscales in the raloxifene intervention group. A reduction in SP4 levels was found after raloxifene treatment. These results suggest that SP4 may be involved in raloxifene symptom improvement in postmenopausal women and could be a potential candidate for future studies investigating blood-based biomarkers for raloxifene effectiveness.

Prenatal and early life diesel exhaust exposure disrupts cortical lamina organization: Evidence for a reelin-related pathogenic pathway induced by interleukin-6

Several epidemiological studies have shown associations between developmental exposure to traffic-related air pollution and increased risk for autism spectrum disorders (ASD), a spectrum of neurodevelopmental disorders with increasing prevalence rate in the United States. Though animal studies have provided support for these associations, little is known regarding possible underlying mechanisms. In a previous study we found that exposure of C57BL/6J mice of both sexes to environmentally relevant levels (250-300 µg/m³) of diesel exhaust (DE) from embryonic day 0 to postnatal day 21 (E0 to PND21) caused significant changes in all three characteristic behavioral domains of ASD in the offspring. In the present study we investigated a potential mechanistic pathway that may be of relevance for ASD-like changes associated with developmental DE exposure. Using the same DE exposure protocol (250-300 µg/m³ DE from E0 to PND21) several molecular markers were examined in the brains of male and female mice at PND3, 21, and 60. Exposure to DE as above increased levels of interleukin-6 (IL-6) in placenta and in neonatal brain. The JAK2/STAT3 pathway, a target for IL-6, was activated by STAT3 phosphorylation, and the expression of DNA methyltransferase 1 (DNMT1), a STAT3 target gene, was increased in DE-exposed neonatal brain. DNMT1 has been reported to down-regulate expression of reelin (RELN), an extracellular matrix glycoprotein important in regulating the processes of neuronal migration. RELN is considered an important modulator for ASD, since there are several polymorphisms in this gene linked to the disease, and since lower levels of RELN have been reported in brains of ASD patients. We observed decreased RELN expression in brains of the DE-exposed mice at PND3. Since disorganized patches in the prefrontal cortex have been reported in ASD patients and disrupted cortical organization has been found in RELN-deficient mice, we also assessed cortical organization, by labeling cells expressing the lamina-specific-markers RELN and calretinin. In DE-exposed mice we found increased cell density in deeper cortex (lamina layers VI-IV) for cells expressing either RELN or calretinin. These findings demonstrate that developmental DE exposure is associated with subtle disorganization of the cerebral cortex at PND60, and suggest a pathway involving IL-6, STAT3, and DNMT1 leading to downregulation of RELN expression that could be contributing to this long-lasting disruption in cortical laminar organization.

Over-expression of TGF-β1 gene in medication free Schizophrenia

BACKGROUND AND PURPOSE

Immunological pathways play a crucial role in developing and precipitating neuropsychiatric disorders. Although the exact pathogenesis of schizophrenia is unknown, the possible role of genetic and biomarker involvement of the immune system is gaining attention. Here we quantified the mRNA expression of cytokines as a key role player of the immune system from the peripheral blood mononuclear cells of patients with schizophrenia and healthy controls to identify the differentially expressed genes.

METHODS

Sixteen medication-free schizophrenia patients and 16 healthy subjects were enrolled in the current study. To investigate the desired expression level of mRNAs including TGF-β1, IL-1β, IL-23, TNF-α, NF-κB, and BDNF, quantitative real-time PCR was performed using specific oligonucleotide primers and the Applied Bio systems StepOne™ real time PCR system. DNA methylation was also analyzed through methylation-specific polymerase chain reaction (MSP).

RESULTS

TGF-β1 was significantly up-regulated in peripheral blood mononuclear cells of patients vs. healthy individuals (P value = 0.03). In addition, we found a significant correlation between the positive symptom scale and TGF-β1 gene overexpression (r = 0.536, P = 0.039). However, we did not observe any statistically significant differences for the methylation status of CpG Islands 1 and 2 between the patients and normal group. No statistical significance was found either for gene expression of IL-1β (P = 0.32), IL-23 (P = 0.12), TNF-α (P = 0.87), NF-κB (P = 0.07), and BDNF (P = 0.33).

CONCLUSIONS

Although the number of medication-free schizophrenia patients is extremely limited, our data highlighted the potential role of TGF-β1 as a regulatory cytokine in complex inflammatory mechanism involved in medication-free schizophrenia. In addition, we observed that increased level of TGF-β1 mRNA in this disease might not be under methylation as an epigenetic control element at the genomic level.

Parvalbumin promoter hypermethylation in postmortem brain in schizophrenia

Deficits of brain parvalbumin (PV) are a consistent finding in schizophrenia and models of psychosis. We investigated whether this is associated with abnormal PV gene (PVALB) methylation in the brain in schizophrenia. Bisulfite pyrosequencing was used to determine cytosine (CpG) methylation in a PVALB promoter sequence. Greater PVALB methylation was found in schizophrenia hippocampus, while no differences were observed in prefrontal cortex. LINE-1 methylation, a measure of global methylation, was also elevated in both regions in schizophrenia, although the PVALB change was independent of this effect. These results provide the first evidence that PVALB promoter methylation is abnormal in schizophrenia and suggest that this epigenetic finding may relate to the reduction of PV expression seen in the disease.

DNA Methylation and Psychiatric Disorders

DNA methylation has been an important area of research in the study of molecular mechanism to psychiatric disorders. Recent evidence has suggested that abnormalities in global methylation, methylation of genes, and pathways could play a role in the etiology of many forms of mental illness. In this article, we review the mechanisms of DNA methylation, including the genetic and environmental factors affecting methylation changes. We report and discuss major findings regarding DNA methylation in psychiatric patients, both within the context of global methylation studies and gene-specific methylation studies. Finally, we discuss issues surrounding data quality improvement, the limitations of current methylation analysis methods, and the possibility of using DNA methylation-based treatment for psychiatric disorders in the future.

Potential for diagnosis versus therapy monitoring of attention deficit hyperactivity disorder: a new epigenetic biomarker interacting with both genotype and auto-immunity

In view of the need for easily accessible biomarkers, we evaluated in ADHD children the epigenetic status of the 5'-untranslated region (UTR) in the SLC6A3 gene, coding for human dopamine transporter (DAT). We analysed buccal swabs and sera from 30 children who met DSM-IV-TR criteria for ADHD, assigned to treatment according to severity. Methylation levels at six-selected CpG sites (among which, a CGGCGGCGG and a CGCG motif), alone or in combination with serum titers in auto-antibodies against dopamine transporter (DAT aAbs), were analysed for correlation with CGAS scores (by clinicians) and Conners' scales (by parents), collected at recruitment and after 6 weeks. In addition, we characterized the DAT genotype, i.e., the variable number tandem repeat (VNTR) polymorphisms at the 3'-UTR of the gene. DAT methylation levels were greatly reduced in ADHD patients compared to control, healthy children. Within patients carrying at least one DAT 9 allele (DAT 9/x), methylation at positions CpG2 and/or CpG6 correlated with recovery, as evident from delta-CGAS scores as well as delta Conners' scales ('inattentive' and 'hyperactive' subscales). Moreover, hypermethylation at CpG1 position denoted severity, specifically for those patients carrying a DAT 10/10 genotype. Intriguingly, high serum DAT-aAbs titers appeared to corroborate indications from high CpG1 versus high CpG2/CpG6 levels, likewise denoting severity versus recovery in DAT 10/10 versus 9/x patients, respectively. These profiles suggest that DAT 5'UTR epigenetics plus serum aAbs can serve as suitable biomarkers, to confirm ADHD diagnosis and/or to predict the efficacy of treatment.

Global Transcriptome Analysis of Primary Cerebrocortical Cells: Identification of Genes Regulated by Triiodothyronine in Specific Cell Types

Thyroid hormones, thyroxine, and triiodothyronine (T3) are crucial for cerebral cortex development acting through regulation of gene expression. To define the transcriptional program under T3 regulation, we have performed RNA-Seq of T3-treated and untreated primary mouse cerebrocortical cells. The expression of 1145 genes or 7.7% of expressed genes was changed upon T3 addition, of which 371 responded to T3 in the presence of cycloheximide indicating direct transcriptional regulation. The results were compared with available transcriptomic datasets of defined cellular types. In this way, we could identify targets of T3 within genes enriched in astrocytes and neurons, in specific layers including the subplate, and in specific neurons such as prepronociceptin, cholecystokinin, or cortistatin neurons. The subplate and the prepronociceptin neurons appear as potentially major targets of T3 action. T3 upregulates mostly genes related to cell membrane events, such as G-protein signaling, neurotransmission, and ion transport and downregulates genes involved in nuclear events associated with the M phase of cell cycle, such as chromosome organization and segregation. Remarkably, the transcriptomic changes induced by T3 sustain the transition from fetal to adult patterns of gene expression. The results allow defining in molecular terms the elusive role of thyroid hormones on neocortical development.

Astrocyte-induced Reelin expression drives proliferation of Her2+ breast cancer metastases

Breast cancer metastasis to the brain develops after a clinical latency of years to even decades, suggesting that colonization of the brain is the most challenging step of the metastatic cascade. However, the underlying mechanisms used by breast cancer cells to successfully colonize the brain's microenvironment remain elusive. Reelin is an archetypal extracellular glycoprotein that regulates migration, proliferation, and lamination of neurons. It is epigenetically silenced in various cancers, and its expression in multiple myelomas is linked to poor patient survival. We found that Reelin expression was low in primary breast cancer tissue. However, its expression was significantly higher in Her2⁺ breast cancers metastasizing to the brain. In particular, Reelin was highly expressed in the tumor periphery adjacent to surrounding astrocytes. This augmented Reelin expression was seen in Her2⁺ metastases, but not in triple negative (TN) primary tumors or in TN breast to brain metastasis cells co-cultured with astrocytes. Furthermore, the elevated expression was sustained in Her2⁺ cells grown in the presence of the DNA methyltransferase inhibitor 5-azacytidine, indicating epigenetic regulation of Reelin expression. The relative growth and rate of spheroids formation derived from Her2⁺ primary and BBM cells co-cultured with astrocytes were higher than those of TN primary and BBM cells, and knockdown of both Reelin and Her2 suppressed the astrocyte-induced growth and spheroid forming ability of Her2⁺ cells. Collectively, our results indicate that within the neural niche, astrocytes epigenetically regulate Reelin expression and its interaction with Her2 leading to increased proliferation and survival fitness.

Down-regulation of serotonin and dopamine transporter genes in individual rats expressing a gambling-prone profile: A possible role for epigenetic mechanisms

Gambling Disorder (GD) is characterized by excessive gambling despite adverse consequences on individual functioning. In spite of some positive findings, it is difficult to draw any conclusion on the genetics of GD. Indeed, beyond DNA sequence variation, other regulatory mechanisms (like those that engage epigenetics) may explain gene alterations in this addictive disease. Wistar male rats underwent an operant task for the evaluation of individual propensity to gamble. Few rats, after having learnt to prefer nose-poking for a large over a small food reward, were sacrificed to obtain a baseline profile of gene expression at both central and peripheral levels. In the remaining rats, probability of occurrence of large-reward delivery decreased progressively to very low levels. Thus, rats were faced with temptation to "gamble", i.e. to nose-poke for a binge reward, whose delivery was omitted the majority of times. After 3weeks of testing, rats showing a clear-cut profile of either gambling proneness or aversion were selected and sacrificed after the last session. A selective down-regulation of i) serotonin transporter in prefrontal cortex, ii) tyrosine hydroxylase in ventral striatum, iii) dopamine transporter in lymphocytes was evidenced in "gambler" vs "non-gambler" rats. The exposure to such operant task (compared to home-cage alone) modulated ventrostriatal but not prefrontal genes. A consistent increase of DNA methylation, in one specific CpG site at serotonin transporter gene, was evident in prefrontal cortex of "gambler" rats. Elucidation of epigenetic changes occurring during GD progression may pave the way to the development of new therapeutic strategies through specific modulation of epigenetic factors.

Reelin-Dab1 signaling system in human colorectal cancer

Reelin is an extracellular matrix protein that plays a critical role in neuronal migration. Here we show that the mucosa of human colon expresses reelin, its receptors ApoER2 and VLDLR, and its effector protein Dab1. Immunohistochemical analyses reveal that reelin expression is restricted to pericryptal myofibroblasts; Dab1 is detected at myofibroblasts, the apical domain of surface epithelial and crypt cells, and a strong linear staining is observed at the basement membrane; VLDLR and ApoER2 are in the cytoplasm of surface epithelium and myofibroblasts, and VLDLR is also detected in the cytoplasm of the crypt cells. Human colorectal cancer downregulates reelin without change in vimentin or N-cadherin mRNA levels. Decreased Reelin mRNA expression is accompanied by decreased HIC1 mRNA levels, increased mRNA levels of ApoER2 and DNMT1, increased reelin hypermethylation and no change in either Cask or TGF-β1 mRNAs, suggesting that reelin repression results from a DNMT1-mediated hypermethylation of the reelin gene promoter. Decreased HIC1 expression may repress reelin transcription via increasing ApoER2 transcription. We conclude that the mucosa of human colon expresses the reelin-Dab1 signaling system and that reelin is repressed in colorectal cancer before epithelial-mesenchymal transition has occurred. The significant down-regulation of reelin expression makes this gene a promising biomarker for colorectal cancers. © 2016 Wiley Periodicals, Inc.

Specificity proteins 1 and 4, hippocampal volume and first-episode psychosis

We assessed specificity protein 1 (SP1) and 4 (SP4) transcription factor levels in peripheral blood mononuclear cells and conducted a voxel-based morphometry analysis on brain structural magnetic resonance images from 11 patients with first-episode psychosis and 14 healthy controls. We found lower SP1 and SP4 levels in patients, which correlated positively with right hippocampal volume. These results extend previous evidence showing that such transcription factors may constitute a molecular pathway to the development of psychosis.

Epigenetic regulation of reelin expression in multiple myeloma

Reelin (RELN) is a secreted extracellular matrix glycoprotein associated with the positioning and migration of neuronal cells and a few types of non-neuronal cells. We have previously reported RELN expression in multiple myeloma cells. High RELN expression was associated with poor prognosis and enhanced myeloma cell adhesion and survival. To examine the epigenetic regulation of RELN expression, its promoter methylation status in myeloma-derived cell lines and primary tumour cells from myeloma patients were analysed. RELN expression was moderate in CD19⁺ B cells and was upregulated in CD138⁺ plasma cells. A further upregulated RELN transcription was found in multiple myeloma cells. High expressions of RELN in myeloma cell lines as well as in patients were associated with hypomethylation in RELN promoter region. Demethylation increased RELN transcription in vitro. Together, we established that the methylation status of the promoter proximal cytosine-phospho-guanine dinucleotides determines the expression of RELN in myeloma cells. Copyright © 2016 John Wiley & Sons, Ltd.

Structural Insights into Reelin Function: Present and Future

Reelin is a neuronal glycoprotein secreted by the Cajal-Retzius cells in marginal regions of the cerebral cortex and the hippocampus where it plays important roles in the control of neuronal migration and the formation of cellular layers during brain development. This 3461 residue-long protein is composed of a signal peptide, an F-spondin-like domain, eight Reelin repeats (RR1-8), and a positively charged sequence at the C-terminus. Biochemical data indicate that the central region of Reelin binds to the low-density lipoprotein receptors apolipoprotein E receptor 2 (ApoER2) and the very-low-density lipoprotein receptor (VLDLR), leading to the phosphorylation of the intracellular adaptor protein Dab1. After secretion, Reelin is rapidly degraded in three major fragments, but the functional significance of this degradation is poorly understood. Probably due to its large mass and the complexity of its architecture, the high-resolution, three-dimensional structure of Reelin has never been determined. However, the crystal structures of some of the RRs have been solved, providing important insights into their fold and the interaction with the ApoER2 receptor. This review discusses the current findings on the structure of Reelin and its binding to the ApoER2 and VLDLR receptors, and we discuss some areas where proteomics and structural biology can help understanding Reelin function in brain development and human health.

RAS signalling through PI3-Kinase controls cell migration via modulation of Reelin expression

RAS signalling through phosphoinositide 3-kinase (PI3-Kinase) has been shown to have an essential role in tumour initiation and maintenance. RAS also regulates cell motility and tumour invasiveness, but the role of direct RAS binding to PI3-Kinase in this remains uncertain. Here, we provide evidence that disruption of RAS interaction with PI3-Kinase p110α decreases cell motility and prevents activation of Rac GTPase. Analysis of gene expression in cells lacking RAS interaction with p110α reveals increased levels of the extracellular matrix glycoprotein Reelin and activation of its downstream pathway resulting in upregulation of E-cadherin expression. Induction of the Reelin/E-cadherin axis is also observed in Kras mutant lung tumours that are regressing due to blockade of RAS interaction with PI3-Kinase. Furthermore, loss of Reelin correlates with decreased survival of lung and breast cancer patients. Reelin thus plays a role in restraining RAS and PI3-kinase promotion of cell motility and potentially tumour metastasis.

Epigenetic RELN Dysfunction in Schizophrenia and Related Neuropsychiatric Disorders

REELIN (RELN) is a large (420 kDa) glycoprotein that in adulthood is mostly synthesized in GABAergic neurons of corticolimbic structures. Upon secretion in the extracellular matrix (ECM), RELN binds to VLDL, APOE2, and α3β2 Integrin receptors located on dendritic shafts and spines of postsynaptic pyramidal neurons. Reduced levels of RELN expression in the adult brain induce cognitive impairment and dendritic spine density deficits. RELN supplementation recovers these deficits suggesting a trophic action for RELN in synaptic plasticity. We and others have shown that altered RELN expression in schizophrenia (SZ) and bipolar (BP) disorder patients is difficult to reconcile with classical Mendelian genetic disorders and it is instead plausible to associate these disorders with altered epigenetic homeostasis. Support for the contribution of altered epigenetic mechanisms in the down-regulation of RELN expression in corticolimbic structures of psychotic patients includes the concomitant increase of DNA-methyltransferases and the increased levels of the methyl donor S-adenosylmethionine (SAM). It is hypothesized that these conditions lead to RELN promoter hypermethylation and a reduction in RELN protein amounts in psychotic patients. The decreased synthesis and release of RELN from GABAergic corticolimbic neurons could serve as a model to elucidate the epigenetic pathophysiological mechanisms acting at pyramidal neuron dendrites that regulate synaptic plasticity and cognition in psychotic and non-psychotic subjects.

Schizophrenia and reelin: a model based on prenatal stress to study epigenetics, brain development and behavior

Schizophrenia is a severe psychiatric disorder that results in a significant disability for the patient. The disorder is characterized by impairment of the adaptive orchestration of actions, a cognitive function that is mainly dependent on the prefrontal cortex. This behavioral deficit, together with cellular and neurophysiological alterations in the prefrontal cortex, as well as reduced density of GABAergic cells and aberrant oscillatory activity, all indicate structural and functional deficits of the prefrontal cortex in schizophrenia. Among the several risk factors for the development of schizophrenia, stress during the prenatal period has been identified as crucial. Thus, it is proposed that prenatal stress induces neurodevelopmental alterations in the prefrontal cortex that are expressed as cognitive impairment observed in schizophrenia. However, the precise mechanisms that link prenatal stress with the impairment of prefrontal cortex function is largely unknown. Reelin is an extracellular matrix protein involved in the development of cortical neural connectivity at embryonic stages, and in synaptic plasticity at postnatal stages. Interestingly, down-regulation of reelin expression has been associated with epigenetic changes in the reelin gene of the prefrontal cortex of schizophrenic patients. We recently showed that, similar to schizophrenic patients, prenatal stress induces down-expression of reelin associated with the methylation of its promoter in the rodent prefrontal cortex. These alterations were paralleled with altered prefrontal cortex functional connectivity and impairment in prefrontal cortex-dependent behavioral tasks. Therefore, considering molecular, cellular, physiological and behavioral evidence, we propose a unifying framework that links prenatal stress and prefrontal malfunction through epigenetic alterations of the reelin gene.

Ezh2 is involved in radial neuronal migration through regulating Reelin expression in cerebral cortex

Radial migration of pyramidal neurons is an important event during the development of cerebral cortex. Neurons experience series of morphological and directional transitions to get to their final laminar positions. Here we report that the histone methyltransferase enhancer of zest homolog 2 (Ezh2) is involved in the regulation of cortical radial migration. We show that Ezh2 knockdown leads to disturbed neuronal orientation, which results in the impairment of radial migration. Further results reveal that this migration deficiency may be due to the derepression of Reelin transcription in the migrating neurons. Our study provides evidence that epigenetic regulation of Reelin by Ezh2 maintains appropriate Reelin expression pattern to fulfill proper orientation of migrating neurons.

Increased Blood-Reelin-Levels in First Episode Schizophrenia

Background

Reelin is an extracellular glycoprotein involved in several functions of brain development, synaptogenesis and dendritic proliferation. Numerous studies found perturbation in the reelin system and altered serum reelin levels in neuropsychiatric patients using the western blot procedure. In the international literature, this is the first study that made use of an enzyme-linked immunosorbent assay to analyze serum reelin protein concentration quantitatively.

Rationale

In order to study possible alterations in reelin blood levels in schizophrenia, we analyzed this signal in schizophrenic patients with a first episode hallucinatory and paranoid syndrome and control subjects in a pilot study design.

Results

We found increased blood reelin protein concentration in schizophrenic patients compared to healthy controls.

Discussion

Our findings point to a relevant role of reelin metabolism in the pathogenesis of schizophrenia.Reelin could be a biomarker for the course of disease or psychopharmacological treatment.

Conclusion

We conclude that the reelin protein blood concentration might be a relevant signal with respect to the pathophysiology of schizophrenia.

Consequences of dietary methyl donor supplements: Is more always better?

Epigenetic mechanisms are now recognized to play roles in disease etiology. Several diseases increasing in frequency are associated with altered DNA methylation. DNA methylation is accomplished through metabolism of methyl donors such as folate, vitamin B12, methionine, betaine (trimethylglycine), and choline. Increased intake of these compounds correlates with decreased neural tube defects, although this mechanism is not well understood. Consumption of these methyl donor pathway components has increased in recent years due to fortification of grains and high supplemental levels of these compounds (e.g. vitamins, energy drinks). Additionally, people with mutations in one of the enzymes that assists in the methyl donor pathway (5-MTHFR) are directed to consume higher amounts of methyl donors to compensate. Recent evidence suggests that high levels of methyl donor intake may also have detrimental effects. Individualized medicine may be necessary to determine the appropriate amounts of methyl donors to be consumed, particularly in women of child bearing age.

Prenatal stress down-regulates Reelin expression by methylation of its promoter and induces adult behavioral impairments in rats

Prenatal stress causes predisposition to cognitive and emotional disturbances and is a risk factor towards the development of neuropsychiatric conditions like depression, bipolar disorders and schizophrenia. The extracellular protein Reelin, expressed by Cajal-Retzius cells during cortical development, plays critical roles on cortical lamination and synaptic maturation, and its deregulation has been associated with maladaptive conditions. In the present study, we address the effect of prenatal restraint stress (PNS) upon Reelin expression and signaling in pregnant rats during the last 10 days of pregnancy. Animals from one group, including control and PNS exposed fetuses, were sacrificed and analyzed using immunohistochemical, biochemical, cell biology and molecular biology approaches. We scored changes in the expression of Reelin, its signaling pathway and in the methylation of its promoter. A second group included control and PNS exposed animals maintained until young adulthood for behavioral studies. Using the optical dissector, we show decreased numbers of Reelin-positive neurons in cortical layer I of PNS exposed animals. In addition, neurons from PNS exposed animals display decreased Reelin expression that is paralleled by changes in components of the Reelin-signaling cascade, both in vivo and in vitro. Furthermore, PNS induced changes in the DNA methylation levels of the Reelin promoter in culture and in histological samples. PNS adult rats display excessive spontaneous locomotor activity, high anxiety levels and problems of learning and memory consolidation. No significant visuo-spatial memory impairment was detected on the Morris water maze. These results highlight the effects of prenatal stress on the Cajal-Retzius neuronal population, and the persistence of behavioral consequences using this treatment in adults, thereby supporting a relevant role of PNS in the genesis of neuropsychiatric diseases. We also propose an in vitro model that can yield new insights on the molecular mechanisms behind the effects of prenatal stress.

Neurodevelopment, GABA system dysfunction, and schizophrenia

The origins of schizophrenia have eluded clinicians and researchers since Kraepelin and Bleuler began documenting their findings. However, large clinical research efforts in recent decades have identified numerous genetic and environmental risk factors for schizophrenia. The combined data strongly support the neurodevelopmental hypothesis of schizophrenia and underscore the importance of the common converging effects of diverse insults. In this review, we discuss the evidence that genetic and environmental risk factors that predispose to schizophrenia disrupt the development and normal functioning of the GABAergic system.

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.

DNA methylation and its implications and accessibility for neuropsychiatric therapeutics

In this review, we discuss the potential pharmacological targeting of a set of powerful epigenetic mechanisms: DNA methylation control systems in the central nervous system (CNS). Specifically, we focus on the possible use of these targets for novel future treatments for learning and memory disorders. We first describe several unique pharmacological attributes of epigenetic mechanisms, especially DNA cytosine methylation, as potential drug targets. We then present an overview of the existing literature regarding DNA methylation control pathways and enzymes in the nervous system, particularly as related to synaptic function, plasticity, learning and memory. Lastly, we speculate upon potential categories of CNS cognitive disorders that might be amenable to methylomic targeting.

Reelin in the Years: Controlling Neuronal Migration and Maturation in the Mammalian Brain

The extracellular protein Reelin was initially identified as an essential factor in the control of neuronal migration and layer formation in the developing mammalian brain. In the years following its discovery, however, it became clear that Reelin is a multifunctional protein that controls not only the positioning of neurons in the developing brain, but also their growth, maturation, and synaptic activity in the adult brain. In this review, we will highlight the major discoveries of the biological activities of Reelin and the underlying molecular mechanisms that affect the development and function of the mammalian brain, from embryonic ages to adulthood.

Reelin signaling in development, maintenance, and plasticity of neural networks

The developing brain is formed through an orchestrated pattern of neuronal migration, leading to the formation of heterogeneous functional regions in the adult. Several proteins and pathways have been identified as mediators of developmental neuronal migration and cell positioning. However, these pathways do not cease to be functionally relevant after the embryonic and early postnatal period; instead, they switch from guiding cells, to guiding synapses. The outcome of synaptic guidance determines the strength and plasticity of neuronal networks by creating a scalable functional architecture that is sculpted by cues from the internal and external environment. Reelin is a multifunctional signal that coordinates cortical and subcortical morphogenesis during development and regulates structural plasticity in adulthood and aging. Gain or loss of function in reelin or its receptors has the potential to influence synaptic strength and patterns of connectivity, with consequences for memory and cognition. The current review highlights similarities in the signaling cascades that modulate neuronal positioning during development, and synaptic plasticity in the adult, with a focus on reelin, a glycoprotein that is increasingly recognized for its dual role in the formation and maintenance of neural circuits.

Personalized medicine in psychiatry: problems and promises

The central theme of personalized medicine is the premise that an individual's unique physiologic characteristics play a significant role in both disease vulnerability and in response to specific therapies. The major goals of personalized medicine are therefore to predict an individual's susceptibility to developing an illness, achieve accurate diagnosis, and optimize the most efficient and favorable response to treatment. The goal of achieving personalized medicine in psychiatry is a laudable one, because its attainment should be associated with a marked reduction in morbidity and mortality. In this review, we summarize an illustrative selection of studies that are laying the foundation towards personalizing medicine in major depressive disorder, bipolar disorder, and schizophrenia. In addition, we present emerging applications that are likely to advance personalized medicine in psychiatry, with an emphasis on novel biomarkers and neuroimaging.

The involvement of Reelin in neurodevelopmental disorders

Reelin is a glycoprotein that serves important roles both during development (regulation of neuronal migration and brain lamination) and in adulthood (maintenance of synaptic function). A number of neuropsychiatric disorders including autism, schizophrenia, bipolar disorder, major depression, Alzheimer's disease and lissencephaly share a common feature of abnormal Reelin expression in the brain. Altered Reelin expression has been hypothesized to impair neuronal connectivity and synaptic plasticity, leading ultimately to the cognitive deficits present in these disorders. The mechanisms for abnormal Reelin expression in some of these disorders are currently unknown although possible explanations include early developmental insults, mutations, hypermethylation of the promoter for the Reelin gene (RELN), miRNA silencing of Reelin mRNA, FMRP underexpression and Reelin processing abnormalities. Increasing Reelin expression through pharmacological therapies may help ameliorate symptoms resulting from Reelin deficits. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Reelin supplementation recovers sensorimotor gating, synaptic plasticity and associative learning deficits in the heterozygous reeler mouse

The lipoprotein receptor ligand Reelin is important for the processes of normal synaptic plasticity, dendritic morphogenesis, and learning and memory. Heterozygous reeler mice (HRM) show many neuroanatomical, biochemical, and behavioral features that are associated with schizophrenia. HRM show subtle morphological defects including reductions in dendritic spine density, altered synaptic plasticity and behavioral deficits in associative learning and memory and pre-pulse inhibition. The present studies test the hypothesis that in vivo elevation of Reelin levels can rescue synaptic and behavioral phenotypes associated with HRM. We demonstrate that a single in vivo injection of Reelin increases GAD67 expression and alters dendritic spine morphology. In parallel we observed enhancement of hippocampal synaptic function and associative learning and memory. Reelin supplementation also increases pre-pulse inhibition. These results suggest that characteristics of HRM, similar to those observed in schizophrenia, are sensitive to Reelin levels and can be modified with Reelin supplementation in male and female adults.

Decreased cortical muscarinic M1 receptors in schizophrenia are associated with changes in gene promoter methylation, mRNA and gene targeting microRNA

Many studies have shown decreased cortical muscarinic M1 receptors (CHRM1) in schizophrenia (Sz), with one study showing Sz can be separated into two populations based on a marked loss of CHRM1 (-75%) in -25% of people (Def-Sz) with the disorder. To better understand the mechanism contributing to the loss of CHRM1 in Def-Sz, we measured specific markers of gene expression in the cortex of people with Sz as a whole, people differentiated into Def-Sz and people with Sz that do not have a deficit in cortical CHRM1 (Non-Def-Sz) and health controls. We now report that cortical CHRM1 gene promoter methylation and CHRM1 mRNA are decrease in Sz, Def-Sz and Non-Def-Sz but levels of the micro RNA (miR)-107, a CHRM1 targeting miR, are increased only in Def-Sz. We also report in vitro data strongly supporting the notion that miR-107 levels regulate CHRM1 expression. These data suggest there is a reversal of the expected inverse relationship between gene promoter methylation and CHRM1 mRNA in people with Sz and that a breakdown in gene promoter methylation control of CHRM1 expression is contributing to the global pathophysiology of the syndrome. In addition, our data argues that increased levels of at least one miR, miR-107, is contributing to the marked loss of cortical CHRM1 in Def-Sz and this may be a differentiating pathophysiology. These latter data continue to support the hypothesis that microRNAs (miRNA) have a role in the underlying neurobiology of Sz but argue they are differentially affected in subsets of people within that syndrome.

The dynamics of DNA methylation in schizophrenia and related psychiatric disorders

Major psychiatric disorders such as schizophrenia (SZ) and bipolar disorder (BP) with psychosis (BP+) express a complex symptomatology characterized by positive symptoms, negative symptoms, and cognitive impairment. Postmortem studies of human SZ and BP+ brains show considerable alterations in the transcriptome of a variety of cortical structures, including multiple mRNAs that are downregulated in both inhibitory GABAergic and excitatory pyramidal neurons compared with non-psychiatric subjects (NPS). Several reports show increased expression of DNA methyltransferases in telencephalic GABAergic neurons. Accumulating evidence suggests a critical role for altered DNA methylation processes in the pathogenesis of SZ and related psychiatric disorders. The establishment and maintenance of CpG site methylation is essential during central nervous system differentiation and this methylation has been implicated in synaptic plasticity, learning, and memory. Atypical hypermethylation of candidate gene promoters expressed in GABAergic neurons is associated with transcriptional downregulation of the corresponding mRNAs, including glutamic acid decarboxylase 67 (GAD67) and reelin (RELN). Recent reports indicate that the methylation status of promoter proximal CpG dinucleotides is in a dynamic balance between DNA methylation and DNA hydroxymethylation. Hydroxymethylation and subsequent DNA demethylation is more complex and involves additional proteins downstream of 5-hydroxymethylcytosine, including members of the base excision repair (BER) pathway. Recent advances in our understanding of altered CpG methylation, hydroxymethylation, and active DNA demethylation provide a framework for the identification of new targets, which may be exploited for the pharmacological intervention of the psychosis associated with SZ and possibly BP+.

An epigenetic framework for neurodevelopmental disorders: from pathogenesis to potential therapy

Neurodevelopmental disorders (NDDs) are characterized by aberrant and delayed early-life development of the brain, leading to deficits in language, cognition, motor behaviour and other functional domains, often accompanied by somatic symptoms. Environmental factors like perinatal infection, malnutrition and trauma can increase the risk of the heterogeneous, multifactorial and polygenic disorders, autism and schizophrenia. Conversely, discrete genetic anomalies are involved in Down, Rett and Fragile X syndromes, tuberous sclerosis and neurofibromatosis, the less familiar Phelan-McDermid, Sotos, Kleefstra, Coffin-Lowry and "ATRX" syndromes, and the disorders of imprinting, Angelman and Prader-Willi syndromes. NDDs have been termed "synaptopathies" in reference to structural and functional disturbance of synaptic plasticity, several involve abnormal Ras-Kinase signalling ("rasopathies"), and many are characterized by disrupted cerebral connectivity and an imbalance between excitatory and inhibitory transmission. However, at a different level of integration, NDDs are accompanied by aberrant "epigenetic" regulation of processes critical for normal and orderly development of the brain. Epigenetics refers to potentially-heritable (by mitosis and/or meiosis) mechanisms controlling gene expression without changes in DNA sequence. In certain NDDs, prototypical epigenetic processes of DNA methylation and covalent histone marking are impacted. Conversely, others involve anomalies in chromatin-modelling, mRNA splicing/editing, mRNA translation, ribosome biogenesis and/or the regulatory actions of small nucleolar RNAs and micro-RNAs. Since epigenetic mechanisms are modifiable, this raises the hope of novel therapy, though questions remain concerning efficacy and safety. The above issues are critically surveyed in this review, which advocates a broad-based epigenetic framework for understanding and ultimately treating a diverse assemblage of NDDs ("epigenopathies") lying at the interface of genetic, developmental and environmental processes. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

DNA methyltransferases1 (DNMT1) and 3a (DNMT3a) colocalize with GAD67-positive neurons in the GAD67-GFP mouse brain

DNA methylation is an epigenetic regulatory mechanism commonly associated with transcriptional silencing. DNA methyltransferases (DNMTs) are a family of related proteins that both catalyze the de novo formation of 5-methylcytosine and maintain these methylation marks in cell-specific patterns in virtually all mitotic cells of the body. In the adult brain, methylation occurs in progenitor cells of the neurogenic zones and in postmitotic neurons. Of the DNMTs, DNMT1 and DNMT3a are most highly expressed in postmitotic neurons. While it has been commonly thought all postmitotic neurons and glia express DNMTs at comparable levels, the coexpression of selected DNMTs with markers of distinct neurotransmitter phenotypes has not been previously examined in detail in the mouse. To this end, we analyzed the expression of DNMT1 and DNMT3a along with GAD67 in the brains of the glutamic acid decarboxylase67-enhanced green fluorescent protein (GAD67-GFP) knockin mice. After first confirming that GFP-immunopositive neurons were also GAD67-positive, we showed that in the motor cortex, piriform cortex, striatum, CA1 region of the hippocampus, dentate gyrus, and basolateral amygdala (BLA), GFP immunofluorescence coincided with the signal corresponding to DNMT1 and DNMT3a. A detailed examination of cortical neurons, showed that ≈30% of NeuN-immunopositive neurons were also DNMT1-positive. These data do not exclude the expression of DNMT1 or DNMT3a in glutamatergic neurons and glia. However, they suggest that their expression is low compared with the levels present in GABAergic neurons.

Prenatal nutrition, epigenetics and schizophrenia risk: can we test causal effects?

We posit that maternal prenatal nutrition can influence offspring schizophrenia risk via epigenetic effects. In this article, we consider evidence that prenatal nutrition is linked to epigenetic outcomes in offspring and schizophrenia in offspring, and that schizophrenia is associated with epigenetic changes. We focus upon one-carbon metabolism as a mediator of the pathway between perturbed prenatal nutrition and the subsequent risk of schizophrenia. Although post-mortem human studies demonstrate DNA methylation changes in brains of people with schizophrenia, such studies cannot establish causality. We suggest a testable hypothesis that utilizes a novel two-step Mendelian randomization approach, to test the component parts of the proposed causal pathway leading from prenatal nutritional exposure to schizophrenia. Applied here to a specific example, such an approach is applicable for wider use to strengthen causal inference of the mediating role of epigenetic factors linking exposures to health outcomes in population-based studies.

Epigenetic modifications of GABAergic interneurons are associated with the schizophrenia-like phenotype induced by prenatal stress in mice

Human studies suggest that a variety of prenatal stressors are related to high risk for cognitive and behavioral abnormalities associated with psychiatric illness (Markham and Koenig, 2011). Recently, a downregulation in the expression of GABAergic genes (i.e., glutamic acid decarboxylase 67 and reelin) associated with DNA methyltransferase (DNMT) overexpression in GABAergic neurons has been regarded as a characteristic phenotypic component of the neuropathology of psychotic disorders (Guidotti et al., 2011). Here, we characterized mice exposed to prenatal restraint stress (PRS) in order to study neurochemical and behavioral abnormalities related to development of schizophrenia in the adult. Offspring born from non-stressed mothers (control mice) showed high levels of DNMT1 and 3a mRNA expression in the frontal cortex at birth, but these levels progressively decreased at post-natal days (PND) 7, 14, and 60. Offspring born from stressed mothers (PRS mice) showed increased levels of DNMTs compared to controls at all time-points studied including at birth and at PND 60. Using GAD67-GFP transgenic mice, we established that, in both control and PRS mice, high levels of DNMT1 and 3a were preferentially expressed in GABAergic neurons of frontal cortex and hippocampus. Importantly, the overexpression of DNMT in GABAergic neurons was associated with a decrease in reelin and GAD67 expression in PRS mice in early and adult life. PRS mice also showed an increased binding of DNMT1 and MeCP2, and an increase in 5-methylcytosine and 5-hydroxymethylcytosine in specific CpG-rich regions of the reelin and GAD67 promoters. Thus, the epigenetic changes in PRS mice are similar to changes observed in the post-mortem brains of psychiatric patients. Behaviorally, adult PRS mice showed hyperactivity and deficits in social interaction, prepulse inhibition, and fear conditioning that were corrected by administration of valproic acid (a histone deacetylase inhibitor) or clozapine (an atypical antipsychotic with DNA-demethylation activity). Taken together, these data show that prenatal stress in mice induces abnormalities in the DNA methylation network and in behaviors indicative of a schizophrenia-like phenotype. Thus, PRS mice may be a valid model for the investigation of new drugs for schizophrenia treatment targeting DNA methylation. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Epigenetic mechanisms in experience-driven memory formation and behavior

Epigenetic mechanisms have long been associated with the regulation of gene-expression changes accompanying normal neuronal development and cellular differentiation; however, until recently these mechanisms were believed to be statically quiet in the adult brain. Behavioral neuroscientists have now begun to investigate these epigenetic mechanisms as potential regulators of gene-transcription changes in the CNS subserving synaptic plasticity and long-term memory (LTM) formation. Experimental evidence from learning and memory animal models has demonstrated that active chromatin remodeling occurs in terminally differentiated postmitotic neurons, suggesting that these molecular processes are indeed intimately involved in several stages of LTM formation, including consolidation, reconsolidation and extinction. Such chromatin modifications include the phosphorylation, acetylation and methylation of histone proteins and the methylation of associated DNA to subsequently affect transcriptional gene readout triggered by learning. The present article examines how such learning-induced epigenetic changes contribute to LTM formation and influence behavior. In particular, this article is a survey of the specific epigenetic mechanisms that have been demonstrated to regulate gene expression for both transcription factors and growth factors in the CNS, which are critical for LTM formation and storage, as well as how aberrant epigenetic processing can contribute to psychological states such as schizophrenia and drug addiction. Together, the findings highlighted in this article support a novel role for epigenetic mechanisms in the adult CNS serving as potential key molecular regulators of gene-transcription changes necessary for LTM formation and adult behavior.

Epigenetics of psychoactive drugs

Objectives

Epigenetics refers to the heritable, but reversible regulation of various biological functions. Changes in DNA methylation and chromatin structure derived from histone modifications are involved in the brain development, pathogenesis and pharmacotherapy of brain disorders.

Key findings

Evidence suggests that epigenetic modulations play key roles in psychiatric diseases such as schizophrenia and bipolar disorder. The analysis of epigenetic aberrations in the mechanisms of psychoactive drugs helps to determine dysfunctional genes and pathways in the brain, to predict side effects of drugs on human genome and identify new pharmaceutical targets for treatment of psychiatric diseases.

Summary

Although numerous studies have concentrated on epigenetics of psychosis, the epigenetic studies of antipsychotics are limited. Here we present epigenetic mechanisms of various psychoactive drugs and review the current literature on psychiatric epigenomics. Furthermore, we discuss various epigenetic modulations in the pharmacology and toxicology of typical and atypical antipsychotics, methionine, lithium and valproic acid.