Valproate and amitriptyline exert common and divergent influences on global and gene promoter-specific chromatin modifications in rat primary astrocytes

DNA methylation of serotonin genes as predictive biomarkers of antidepressant treatment response

Selective serotonin reuptake inhibitors (SSRI) are frequently ineffective in treating depressive episodes and biomarkers are needed to optimize antidepressant treatment outcomes. DNA methylation levels of serotonin transporter (SLC6A4) and tryptophan hydroxylase 2 genes (TPH2) have been suggested to predict antidepressant clinical outcomes but their applicability remains uncertain. In this study, we: 1) evaluated SLC6A4/TPH2 methylation biomarker potential for predicting clinical outcomes after escitalopram treatment; 2) evaluated whether changes in SLC6A4/TPH2 methylation are informative of treatment mechanisms. We used a cohort of 90 unmedicated patients with major depressive disorder that were part of a 12-week open-label longitudinal trial and compared our observations with previous findings. Depressive symptoms were measured at baseline and after 8 and 12 weeks of treatment using the Hamilton Depression Rating Scale (HAMD6/17). We found an association between baseline TPH2 methylation and both clinical response (β:3.43; p = 0.01; 95 % CI:[0.80; 6.06]) and change in depressive symptoms after 8 weeks (β:-45.44; p = 0.01; 95 %CI:[- -78.58; -12.30]). However, we found no evidence for predictive value of any gene (TPH2 AUC: 0.74 95 % CI:[0.42;0.79]; SLC6A4: AUC: 0.61; 95 % CI: [0.48-0.78]). Methylation levels changed at the trend level for CpG sites of SLC6A4 and TPH2 over the course of 12 weeks of treatment. In addition, similar to previous observations, we found a trend for an association between methylation of SLC6A4 CpG2 (chr17:30,236,083) and HAMD17 change after 12 weeks. Our findings suggest that although TPH2 and SLC6A4 methylation may be informative of antidepressant treatment outcome, they are unlikely to prove useful as clinical predictor tools.

Epigenetic studies in insects and the valproic acid perspective

Abstract Valproic acid in association with sodium valproate (VPA) is an important anticonvulsant drug used for decades to treat neurological disorders. VPA also acts as an epigenetic modulator by inhibiting histone deacetylases, permitting histone acetylation, affecting the DNA and histone methylation status and gene expression, and inducing chromatin remodeling. Insects represent an important animal model for studies in several areas of science. Their high phenotypic plasticity makes them alternative models for epigenetic studies. This brief review emphasizes recent reports on insect epigenetics and the contribution of studies on the VPA action in insects, including effects on epigenetic markers, extending the pharmacological understanding of the potential of this drug, and demonstrating the usefulness of insects as an alternative animal model to drug studies.

Epigenetic regulation of neurotransmitter signaling in neurological disorders

Neurotransmission signaling is a highly conserved system attributed to various regulatory events. The excitatory and inhibitory neurotransmitter systems have been extensively studied, and their role in neuronal cell proliferation, synaptogenesis and dendrite formation in the adult brain is well established. Recent research has shown that epigenetic regulation plays a crucial role in mediating the expression of key genes associated with neurotransmitter pathways, including neurotransmitter receptor and transporter genes. The dysregulation of these genes has been linked to a range of neurological disorders such as attention-deficit/hyperactivity disorder, Parkinson's disease and schizophrenia. This article focuses on epigenetic regulatory mechanisms that control the expression of genes associated with four major chemical carriers in the brain: dopamine (DA), Gamma-aminobutyric acid (GABA), glutamate and serotonin. Additionally, we explore how aberrant epigenetic regulation of these genes can contribute to the pathogenesis of relevant neurological disorders. By targeting the epigenetic mechanisms that control neurotransmitter gene expression, there is a promising opportunity to advance the development of more effective treatments for neurological disorders with the potential to significantly improve the quality of life of individuals impacted by these conditions.

Influence of antidepressant treatment on SLC6A4 methylation in Korean patients with major depression

Genetic variation of the serotonin transporter gene (SLC6A4) has been suggested as potential mediator for antidepressant response in patients with depression. This study aimed to determine whether DNA methylation in SLC6A4 changes after antidepressant treatment and whether it affects treatment response in patients with depression. Overall, 221 Korean patients with depression completed 6 weeks of selective serotonin reuptake inhibitor (SSRI) monotherapy. DNA was extracted from venous blood pre- and post-treatment, and DNA methylation was analyzed using polymerase chain reaction. We used Wilcoxon's signed-rank test to verify the difference in methylation after treatment. Treatment response was assessed using the 17-item Hamilton Depression Rating Scale, and mRNA levels were quantified. After adjusting for relevant covariates, DNA methylation was significantly altered in specific CpG sites in SLC6A4 (p < .001 in CpG3, CpG4, and CpG5) following 6 weeks of treatment. Methylation change's magnitude (ΔDNA methylation) after drug treatment was not associated with treatment response or mRNA level change. SSRI antidepressants can influence SLC6A4 methylation in patients with depression. However, ΔDNA methylation at CpG3, CpG4, and CpG5 in SLC6A4 was not associated with treatment response. Future studies should investigate the integrative effect of other genetic variants and CpG methylation on gene transcription and antidepressant treatment response.

Sodium Valproate Modulates the Methylation Status of Lysine Residues 4, 9 and 27 in Histone H3 of HeLa Cells

BACKGROUND

Valproic acid/sodium valproate (VPA), a well-known anti-epileptic agent, inhibits histone deacetylases, induces histone hyperacetylation, promotes DNA demethylation, and affects the histone methylation status in some cell models. Histone methylation profiles have been described as potential markers for cervical cancer prognosis. However, histone methylation markers that can be studied in a cervical cancer cell line, like HeLa cells, have not been investigated following treatment with VPA.

METHODS

In this study, the effect of 0.5 mM and 2.0 mM VPA for 24 h on H3K4me2/me3, H3K9me/me2 and H3K27me/me3 signals as well as on KMT2D, EZH2, and KDM3A gene expression was investigated using confocal microscopy, Western blotting, and RT-PCR. Histone methylation changes were also investigated by Fourier-transform infrared spectroscopy (FTIR).

RESULTS

We found that VPA induces increased levels of H3K4me2/me3 and H3K9me, which are indicative of chromatin activation. Particularly, H3K4me2 markers appeared intensified close to the nuclear periphery, which may suggest their implication in increased transcriptional memory. The abundance of H3K4me2/me3 in the presence of VPA was associated with increased methyltransferase KMT2D gene expression. VPA induced hypomethylation of H3K9me2, which is associated with gene silencing, and concomitant with the demethylase KDM3A, it increased gene expression. Although VPA induces increased H3K27me/me3 levels, it is suggested that the role of the methyltransferase EZH2 in this context could be affected by interactions with this drug.

CONCLUSION

Histone FTIR spectra were not affected by VPA under present experimental conditions. Whether our epigenetic results are consistent with VPA affecting the aggressive tumorous state of HeLa cells, further investigation is required.

Genomics in Treatment Development

The Human Genome Project mapped the 3 billion base pairs in the human genome, which ushered in a new generation of genomically focused treatment development. While this has been very successful in other areas, neuroscience has been largely devoid of such developments. This is in large part because there are very few neurological or mental health conditions that are related to single-gene variants. While developments in pharmacogenomics have been somewhat successful, the use of genetic information in practice has to do with drug metabolism and adverse reactions. Studies of drug metabolism related to genetic variations are an important part of drug development. However, outside of cancer biology, the actual translation of genomic information into novel therapies has been limited. Epigenetics, which relates in part to the effects of the environment on DNA, is a promising newer area of relevance to CNS disorders. The environment can induce chemical modifications of DNA (e.g., cytosine methylation), which can be induced by the environment and may represent either shorter- or longer-term changes. Given the importance of environmental influences on CNS disorders, epigenetics may identify important treatment targets in the future.

Regulation of glutamate transport and neuroinflammation in a term newborn rat model of hypoxic–ischaemic brain injury

In the newborn brain, moderate-severe hypoxia–ischaemia induces glutamate excitotoxicity and inflammation, possibly via dysregulation of candidate astrocytic glutamate transporter ( Glt1) and pro-inflammatory cytokines (e.g. Tnfα, Il1β, Il6). Epigenetic mechanisms may mediate dysregulation. Hypotheses: (1) hypoxia–ischaemia dysregulates mRNA expression of these candidate genes; (2) expression changes in Glt1 are mediated by DNA methylation changes; and (3) methylation values in brain and blood are correlated. Seven-day-old rat pups ( n = 42) were assigned to nine groups based on treatment (for each timepoint: naïve ( n = 3), sham ( n = 3), hypoxia–ischaemia ( n = 8) and timepoint for tissue collection (6, 12 and 24 h post-hypoxia). Moderate hypoxic–ischemic brain injury was induced via ligation of the left common carotid artery followed by 100 min hypoxia (8% O2, 36°C). mRNA was quantified in cortex and hippocampus for the candidate genes, myelin ( Mbp), astrocytic ( Gfap) and neuronal ( Map2) markers (qPCR). DNA methylation was measured for Glt1 in cortex and blood (bisulphite pyrosequencing). Hypoxia–ischaemia induced pro-inflammatory cytokine upregulation in both brain regions at 6 h. This was accompanied by gene expression changes potentially indicating onset of astrogliosis and myelin injury. There were no significant changes in expression or promoter DNA methylation of Glt1. This pilot study supports accumulating evidence that hypoxia–ischaemia causes neuroinflammation in the newborn brain and prioritises further expression and DNA methylation analyses focusing on this pathway. Epigenetic blood biomarkers may facilitate identification of high-risk newborns at birth, maximising chances of neuroprotective interventions.

Tricyclic antidepressants target FKBP51 SUMOylation to restore glucocorticoid receptor activity

FKBP51 is an important inhibitor of the glucocorticoid receptor (GR) signaling. High FKBP51 levels are associated to stress-related disorders, which are linked to GR resistance. SUMO conjugation to FKBP51 is necessary for FKBP51's inhibitory action on GR. The GR/FKBP51 pathway is target of antidepressant action. Thus we investigated if these drugs could inhibit FKBP51 SUMOylation and therefore restore GR activity. Screening cells using Ni²⁺ affinity and in vitro SUMOylation assays revealed that tricyclic antidepressants- particularly clomipramine- inhibited FKBP51 SUMOylation. Our data show that clomipramine binds to FKBP51 inhibiting its interaction with PIAS4 and therefore hindering its SUMOylation. The inhibition of FKBP51 SUMOylation decreased its binding to Hsp90 and GR facilitating FKBP52 recruitment, and enhancing GR activity. Reduction of PIAS4 expression in rat primary astrocytes impaired FKBP51 interaction with GR, while clomipramine could no longer exert its inhibitory action. This mechanism was verified in vivo in mice treated with clomipramine. These results describe the action of antidepressants as repressors of FKBP51 SUMOylation as a molecular switch for restoring GR sensitivity, thereby providing new potential routes of antidepressant intervention.

A history of childhood maltreatment is associated with altered DNA methylation levels of DNA methyltransferase 1 in maternal but not neonatal mononuclear immune cells

Childhood maltreatment (CM) is associated with alterations in DNA methylation (DNAm) especially in stress response genes. Due to the higher risk of overall health complications of individuals with a parental history of CM, intergenerational transmission of CM-associated DNAm changes has been investigated but remains unclear. In this study, we investigated if different severities of CM have any influence on the DNAm of DNA methyltransferase 1 (DNMT1), an important enzyme of the DNAm machinery, in immune and buccal cells of mother-newborn dyads. DNAm was assessed by mass spectrometry using immune cell DNA from mothers (N = 117) and their newborns (N = 113), and buccal cell DNA of mother-newborn dyads (N = 68 each). Mothers with a history of CM had lower mean methylation of DNMT1 in immune cells compared to the mothers without a CM history. CM status only influenced maternal DNMT1 gene expression when at least moderate CM was reported. Buccal cell DNAm was not associated with CM status. Maternal history of CM was not linked to any alterations in DNMT1 mean DNAm in any of the cell types studied in newborns. We conclude that the CM-associated alterations in DNMT1 DNAm might point to allostatic load and can be physiologically relevant, especially in individuals with more severe CM experiences, resulting in an activated DNA methylation machinery that might influence stress response genes. Our lack of significant findings in buccal cells shows the tissue-specific effects of CM on DNAm. In our sample with low to moderate maternal CM history, there was no intergenerational transmission of DNMT1 DNAm in newborns.

Epigenetics and postsurgical pain: A scoping review

OBJECTIVE

Multiple factors are involved in the physiology and variability of postsurgical pain, a great part of which can be explained by genetic and environmental factors and their interaction. Epigenetics refers to the mechanism by which the environment alters the stability and expression of genes. We conducted a scoping review to examine the available evidence in both animal models and clinical studies on epigenetic mechanisms involved in regulation of postsurgical and chronic postsurgical pain.

METHODS

The Arksey & ÓMalley framework and the PRISMA-ScR (Preferred Reporting Items for Systematic Review and Meta-Analysis, scoping reviews extension) guidelines were used. The PubMed, Web of Science and Google Scholar databases were searched, and the original articles cited in reviews located through the search were also reviewed. English-language articles without time limits were retrieved. Articles were selected if the abstract addressed information on the epigenetic or epigenomic mechanisms, histone, or DNA methylation and microribonucleic acids involved in postsurgical and chronic postsurgical pain in animal models and clinical studies.

RESULTS

The initial search provided 174 articles, and 81 were used. The available studies to date, mostly in animal models, have shown that epigenetics contributes to regulation of gene expression in the pathways involved in postsurgical pain and in maintaining long-term pain.

CONCLUSION

Research on possible epigenetic mechanisms involved in postsurgical pain and chronic postsurgical pain in humans is scarce. In view of the evidence available in animal models, there is a need to evaluate epigenetic pain mechanisms in the context of human and clinical studies.

Epigenetic biomarkers as tools for chemical hazard assessment: Gene expression profiling using the model Danio rerio

Recent reports raise the concern that exposure to several environmental chemicals may induce persistent changes that go beyond the exposed organisms, being transferred to subsequent generations even in the absence of the original chemical insult. These changes in subsequent non-exposed generations have been related to epigenetic changes. Although highly relevant for hazard and risk assessment, biomarkers of epigenetic modifications that can be associated with adversity, are still not integrated into hazard assessment frameworks. Here, in order to validate new biomarkers of epigenetic modifications in a popular animal model, zebrafish embryos were exposed to different concentrations of Bisphenol A (0.01, 0.1, 1 and 10 mg/L) and Valproic Acid (0.8, 4, 20 and 100 mg/L), two chemicals reported to alter the modulation of the epigenome. Morphological abnormalities and epigenetic changes were assessed at 80 hours-post fertilization, including DNA global methylation and gene expression of both DNA and histone epigenetic modifications. Gene expression changes were detected at concentrations below those inducing morphological abnormalities. These results further support the importance of combining epigenetic biomarkers with apical endpoints to improve guidelines for chemical testing and hazard assessment, and favour the integration of new biomarkers of epigenetic modifications into the standardized OECD test guideline 236 with zebrafish embryos.

Differential and paradoxical roles of new-generation antidepressants in primary astrocytic inflammation

Background

Selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) are commonly used new-generation drugs for depression. Depressive symptoms are thought to be closely related to neuroinflammation. In this study, we used up-to-date protocols of culture and stimulation and aimed to understand how astrocytes respond to the antidepressants.

Methods

Primary astrocytes were isolated and cultured using neurobasal-based serum-free medium. The cells were treated with a cytokine mixture comprising complement component 1q, tumor necrosis factor α, and interleukin 1α with or without pretreatments of antidepressants. Cell viability, phenotypes, inflammatory responses, and the underlying mechanisms were analyzed.

Results

All the SSRIs, including paroxetine, fluoxetine, sertraline, citalopram, and fluvoxamine, show a visible cytotoxicity within the range of applied doses, and a paradoxical effect on astrocytic inflammatory responses as manifested by the promotion of inducible nitric oxide synthase (iNOS) and/or nitric oxide (NO) and the inhibition of interleukin 6 (IL-6) and/or interleukin 1β (IL-1β). The SNRI venlafaxine was the least toxic to astrocytes and inhibited the production of IL-6 and IL-1β but with no impact on iNOS and NO. All the drugs had no regulation on the polarization of astrocytic A1 and A2 types. Mechanisms associated with the antidepressants in astrocytic inflammation route via inhibition of JNK1 activation and STAT3 basal activity.

Conclusions

The study demonstrated that the antidepressants possess differential cytotoxicity to astrocytes and function differently, also paradoxically for the SSRIs, to astrocytic inflammation. Our results provide novel pieces into understanding the differential efficacy and tolerability of the antidepressants in treating patients in the context of astrocytes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02097-z.

Epigenetic Neuropharmacology: Drugs Affecting the Epigenome in the Brain

This review explores how different classes of drugs, including those with therapeutic and abuse potential, alter brain functions and behavior via the epigenome. Epigenetics, in its simplest interpretation, is the study of the regulation of a genes' transcriptional potential. The epigenome is established during development but is malleable throughout life by a wide variety of drugs, with both clinical utility and abuse potential. An epigenetic effect can be central to the drug's therapeutic or abuse potential, or it can be independent from the main effect but nevertheless produce beneficial or adverse side effects. Here, I discuss the various epigenetic effects of main pharmacological drug classes, including antidepressants, antiepileptics, and drugs of abuse.

Neurobiology, Functions, and Relevance of Excitatory Amino Acid Transporters (EAATs) to Treatment of Refractory Epilepsy

Epilepsy is one of the most prevalent and devastating neurological disorders characterized by episodes of unusual sensations, loss of awareness, and reoccurring seizures. The frequency and intensity of epileptic fits can vary to a great degree, with almost a third of all cases resistant to available therapies. At present, there is a major unmet need for effective and specific therapeutic intervention. Impairments of the exquisite balance between excitatory and inhibitory synaptic processes in the brain are considered key in the onset and pathophysiology of the disease. As the primary excitatory neurotransmitter in the central nervous system, glutamate has been implicated in the process, with the glutamatergic system holding center stage in the pathobiology as well as in developing disease-modifying therapies. Emerging data pinpoint impairments of glutamate clearance as one of the key causative factors in drug-resistant disease forms. Reinstatement of glutamate homeostasis using pharmacological and genetic modulation of glutamate clearance is therefore considered to be of major translational relevance. In this article, we review the neurobiological and clinical evidence suggesting complex aberrations in the activity and functions of excitatory amino acid transporters (EAATs) in epilepsy, with knock-on effects on glutamate homeostasis as a leading cause for the development of refractory forms. We consider the emerging data on pharmacological and genetic manipulations of EAATs, with reference to seizures and glutamate dyshomeostasis, and review their fundamental and translational relevance. We discuss the most recent advances in the EAATs research in human and animal models, along with numerous questions that remain open for debate and critical appraisal. Contrary to the widely held view on EAATs as a promising therapeutic target for management of refractory epilepsy as well as other neurological and psychiatric conditions related to glutamatergic hyperactivity and glutamate-induced cytotoxicity, we stress that the true relevance of EAAT2 as a target for medical intervention remains to be fully appreciated and verified. Despite decades of research, the emerging properties and functional characteristics of glutamate transporters and their relationship with neurophysiological and behavioral correlates of epilepsy challenge the current perception of this disease and fit unambiguously in neither EAATs functional deficit nor in reversal models. We stress the pressing need for new approaches and models for research and restoration of the physiological activity of glutamate transporters and synaptic transmission to achieve much needed therapeutic effects. The complex mechanism of EAATs regulation by multiple factors, including changes in the electrochemical environment and ionic gradients related to epileptic hyperactivity, impose major therapeutic challenges. As a final note, we consider the evolving views and present a cautious perspective on the key areas of future progress in the field towards better management and treatment of refractory disease forms.

Astrocytic histone deacetylase 2 facilitates delayed depression and memory impairment after subarachnoid hemorrhage by negatively regulating glutamate transporter-1

Background

Delayed cognitive impairment (DCI) after subarachnoid hemorrhage (SAH) is one of the most common sequelae in patients. This study aimed to investigate the characteristics of the course and glutamatergic pathogenesis of DCI after SAH in mice.

Methods

A SAH mouse model of internal carotid puncture was used. Depressive and cognitive behaviors were detected by forced swimming and sucrose preference tests and Morris water maze test, respectively. Microdialysis and high-performance liquid chromatography (HPLC) were used to detect the interstitial glutamate. The expressions of histone deacetylases (HDACs), glutamate transporters, and glutamate receptors were examined. Primary astrocytes magnetically sorted from adult mice were cultured for glutamate uptake assay and protein and mRNA detection. Selective HDAC2 inhibitor and glutamate transporter-1 (GLT-1) inhibitor administered via were intraperitoneal injection to evaluate their effects on DCI in SAH mice.

Results

Depression and memory impairment lasted for more than 12 weeks and peaked at 8 weeks after SAH. Interstitial glutamate accumulation in the hippocampus and impaired glutamate uptake in astrocytes of the SAH mice were found during DCI, which could be explained by there being a significant decrease in GLT-1 expression but not in glutamate and aspartate transporter (GLAST) in hippocampal astrocytes. Meanwhile, the phosphorylation level of excitatory glutamate receptors (GluN2B and GluA1) in the hippocampus was significantly reduced, although there was no significant change in the expression of the receptors. Importantly, the expression of HDAC2 increased most significantly in astrocytes after SAH compared with that of other subtypes of HDACs. Inhibition of HDAC2 markedly rescued the decrease in GLT-1 expression after SAH through transcriptional regulation. Behavioral results showed that a selective HDAC2 inhibitor effectively improved DCI in SAH mice, but this effect could be weakened by GLT-1 inhibition.

Conclusions

In summary, our study suggests that the dysfunction of GLT-1-mediated glutamate uptake in astrocytes may be a key pathological mechanism of DCI after SAH, and that a specific inhibitor of HDAC2 may exert a potential therapy.

The Effect of Chronic Mild Stress and Venlafaxine on the Expression and Methylation Levels of Genes Involved in the Tryptophan Catabolites Pathway in the Blood and Brain Structures of Rats

A growing body of evidence suggests that depression may be associated with impairment of the tryptophan catabolites (TRYCATs) pathway. The present study investigated the effects of the chronic administration of venlafaxine on the expression and methylation status of Katl, Tph1/2, Ido1, Kmo and Kynu in the brain and blood of rats exposed to the CMS model of depression. The rats were subjected to the CMS procedure for 2 or 7 weeks and administered venlafaxine (10 mg/kg/day, IP) for 5 weeks. mRNA and protein expression and the methylation status of gene promoters in PBMCs and six brain structures were evaluated and analysed using the TaqMan Gene Expression Assay and Western blotting, and methylation-sensitive high-resolution melting (MS-HRM), respectively. We found that the CMS procedure increased KatI expression in the midbrain and KatII expression in the midbrain and the amygdala, while venlafaxine administration decreased KatII expression in the hypothalamus and the cerebral cortex. The methylation status of the Tph1 and Kmo promoters in peripheral blood mononuclear cells (PBMCs) was significantly increased in the stressed group after antidepressant therapy. The protein levels of Tph1 and Ido1 were decreased following venlafaxine administration. Our results confirmed that CMS and venlafaxine modulate the expression levels and methylation status of genes involved in the TRYCATs pathway.

Dissecting the Epigenetic Changes Induced by Non-Antipsychotic Mood Stabilizers on Schizophrenia and Affective Disorders: A Systematic Review

BACKGROUND

Epimutations secondary to gene-environment interactions have a key role in the pathophysiology of major psychiatric disorders. In vivo and in vitro evidence suggest that mood stabilizers can potentially reverse epigenetic deregulations found in patients with schizophrenia or mood disorders through mechanisms that are not yet fully understood. However, their activity on epigenetic processes has made them a research target for therapeutic approaches.

METHODS

We conducted a comprehensive literature search of PubMed and EMBASE for studies investigating the specific epigenetic changes induced by non-antipsychotic mood stabilizers (valproate, lithium, lamotrigine, and carbamazepine) in animal models, human cell lines, or patients with schizophrenia, bipolar disorder, or major depressive disorder. Each paper was reviewed for the nature of research, the species and tissue examined, sample size, mood stabilizer, targeted gene, epigenetic changes found, and associated psychiatric disorder. Every article was appraised for quality using a modified published process and those who met a quality score of moderate or high were included.

RESULTS

A total of 2,429 records were identified; 1,956 records remained after duplicates were removed and were screened via title, abstract and keywords; 129 records were selected for full-text screening and a remaining of 38 articles were included in the qualitative synthesis. Valproate and lithium were found to induce broader epigenetic changes through different mechanisms, mainly DNA demethylation and histones acetylation. There was less literature and hence smaller effects attributable to lamotrigine and carbamazepine could be associated overall with the small number of studies on these agents. Findings were congruent across sample types.

CONCLUSIONS

An advanced understanding of the specific epigenetic changes induced by classic mood stabilizers in patients with major psychiatric disorders will facilitate personalized interventions. Further related drug discovery should target the induction of selective chromatin remodeling and gene-specific expression effects.

Epigenetic Regulation of Excitatory Amino Acid Transporter 2 in Neurological Disorders

Excitatory amino acid transporter 2 (EAAT2) is the predominant astrocyte glutamate transporter involved in the reuptake of the majority of the synaptic glutamate in the mammalian central nervous system (CNS). Gene expression can be altered without changing DNA sequences through epigenetic mechanisms. Mechanisms of epigenetic regulation, include DNA methylation, post-translational modifications of histones, chromatin remodeling, and small non-coding RNAs. This review is focused on neurological disorders, such as glioblastoma multiforme (GBM), Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), Parkinson’s disease (PD), bipolar disorder (BD), and neuroHIV where there is evidence that epigenetics plays a role in the reduction of EAAT2 expression. The emerging field of pharmaco-epigenetics provides a novel avenue for epigenetics-based drug therapy. This review highlights findings on the role of epigenetics in the regulation of EAAT2 in different neurological disorders and discusses the current pharmacological approaches used and the potential use of novel therapeutic approaches to induce EAAT2 expression in neurological disorders using CRISPR/Cas9 technology.

Glutamate transport system as a key constituent of glutamosome: Molecular pathology and pharmacological modulation in chronic pain

Neural uptake of glutamate is executed by the structurally related members of the SLC1A family of solute transporters: GLAST/EAAT1, GLT-1/EAAT2, EAAC1/EAAT3, EAAT4, ASCT2. These plasma membrane proteins ensure supply of glutamate, aspartate and some neutral amino acids, including glutamine and cysteine, for synthetic, energetic and signaling purposes, whereas effective removal of glutamate from the synaptic cleft shapes excitatory neurotransmission and prevents glutamate toxicity. Glutamate transporters (GluTs) possess also receptor-like properties and can directly initiate signal transduction. GluTs are physically linked to other glutamate signaling-, transporting- and metabolizing molecules (e.g., glutamine transporters SNAT3 and ASCT2, glutamine synthetase, NMDA receptor, synaptic vesicles), as well as cellular machineries fueling the transmembrane transport of glutamate (e.g., ion gradient-generating Na/K-ATPase, glycolytic enzymes, mitochondrial membrane- and matrix proteins, glucose transporters). We designate this supramolecular functional assembly as 'glutamosome'. GluTs play important roles in the molecular pathology of chronic pain, due to the predominantly glutamatergic nature of nociceptive signaling in the spinal cord. Down-regulation of GluTs often precedes or occurs simultaneously with development of pain hypersensitivity. Pharmacological inhibition or gene knock-down of spinal GluTs can induce/aggravate pain, whereas enhancing expression of GluTs by viral gene transfer can mitigate chronic pain. Thus, functional up-regulation of GluTs is turning into a prospective pharmacotherapeutic approach for the management of chronic pain. A number of novel positive pharmacological regulators of GluTs, incl. pyridazine derivatives and β-lactams, have recently been introduced. However, design and development of new analgesics based on this principle will require more precise knowledge of molecular mechanisms underlying physiological or aberrant functioning of the glutamate transport system in nociceptive circuits. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

Moving pharmacoepigenetics tools for depression toward clinical use

BACKGROUND

Major depressive disorder (MDD) is a leading cause of disability worldwide, and over half of patients do not achieve symptom remission following an initial antidepressant course. Despite evidence implicating a strong genetic basis for the pathophysiology of MDD, there are no adequately validated biomarkers of treatment response routinely used in clinical practice. Pharmacoepigenetics is an emerging field that has the potential to combine both genetic and environmental information into treatment selection and further the goal of precision psychiatry. However, this field is in its infancy compared to the more established pharmacogenetics approaches.

METHODS

We prepared a narrative review using literature searches of studies in English pertaining to pharmacoepigenetics and treatment of depressive disorders conducted in PubMed, Google Scholar, PsychINFO, and Ovid Medicine from inception through January 2019. We reviewed studies of DNA methylation and histone modifications in both humans and animal models of depression.

RESULTS

Emerging evidence from human and animal work suggests a key role for epigenetic marks, including DNA methylation and histone modifications, in the prediction of antidepressant response. The challenges of heterogeneity of patient characteristics and loci studied as well as lack of replication that have impacted the field of pharmacogenetics also pose challenges to the development of pharmacoepigenetic tools. Additionally, given the tissue specific nature of epigenetic marks as well as their susceptibility to change in response to environmental factors and aging, pharmacoepigenetic tools face additional challenges to their development.

LIMITATIONS

This is a narrative and not systematic review of the literature on the pharmacoepigenetics of antidepressant response. We highlight key studies pertaining to pharmacoepigenetics and treatment of depressive disorders in humans and depressive-like behaviors in animal models, regardless of sample size or methodology. While we discuss DNA methylation and histone modifications, we do not cover microRNAs, which have been reviewed elsewhere recently.

CONCLUSIONS

Utilization of genome-wide approaches and reproducible epigenetic assays, careful selection of the tissue assessed, and integration of genetic and clinical information into pharmacoepigenetic tools will improve the likelihood of developing clinically useful tests.

DNA Methylation as a Biomarker of Treatment Response Variability in Serious Mental Illnesses: A Systematic Review Focused on Bipolar Disorder, Schizophrenia, and Major Depressive Disorder

So far, genetic studies of treatment response in schizophrenia, bipolar disorder, and major depression have returned results with limited clinical utility. A gene × environment interplay has been proposed as a factor influencing not only pathophysiology but also the treatment response. Therefore, epigenetics has emerged as a major field of research to study the treatment of these three disorders. Among the epigenetic marks that can modify gene expression, DNA methylation is the best studied. We performed a systematic search (PubMed) following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA guidelines for preclinical and clinical studies focused on genome-wide and gene-specific DNA methylation in the context of schizophrenia, bipolar disorders, and major depressive disorder. Out of the 112 studies initially identified, we selected 31 studies among them, with an emphasis on responses to the gold standard treatments in each disorder. Modulations of DNA methylation levels at specific CpG sites have been documented for all classes of treatments (antipsychotics, mood stabilizers, and antidepressants). The heterogeneity of the models and methodologies used complicate the interpretation of results. Although few studies in each disorder have assessed the potential of DNA methylation as biomarkers of treatment response, data support this hypothesis for antipsychotics, mood stabilizers and antidepressants.

Neuroactive steroids, neurosteroidogenesis and sex

The nervous system is a target and a source of steroids. Neuroactive steroids are steroids that target neurons and glial cells. They include hormonal steroids originated in the peripheral glands, steroids locally synthesized by the neurons and glial cells (neurosteroids) and synthetic steroids, some of them used in clinical practice. Here we review the mechanisms of synthesis, metabolism and action of neuroactive steroids, including the role of epigenetic modifications and the mitochondria in their sex specific actions. We examine sex differences in neuroactive steroid levels under physiological conditions and their role in the establishment of sex dimorphic structures in the nervous system and sex differences in its function. In addition, particular attention is paid to neuroactive steroids under pathological conditions, analyzing how pathology alters their levels and their role as neuroprotective factors, considering the influence of sex in both cases.

FKBP5 DNA methylation does not mediate the association between childhood maltreatment and depression symptom severity in the Detroit Neighborhood Health Study

Exposure to childhood maltreatment increases the risk of developing mental illness later in life. Childhood maltreatment and depression have both been associated with dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis-a key regulator of the body's stress response. Additionally, HPA axis dysregulation has been implicated in the etiology of a range of mental illnesses. A substantial body of work has shown history of childhood maltreatment alters DNA methylation levels within key HPA axis genes. We therefore investigated whether one of these key genes, FKBP5 mediates the relationship between childhood maltreatment and depression, and assessed FKBP5 DNA methylation and gene expression within 112 adults from the Detroit Neighborhood Health Study (DNHS). DNA methylation was assessed in 4 regions, including the upstream promoter, downstream promoter, and two glucocorticoid response elements (GREs) via pyrosequencing using whole blood derived DNA; Taqman assays measured relative RNA expression from leukocytes. Mediation analyses were conducted using sequential linear regression. Childhood maltreatment was significantly associated with depression symptom severity (FDR < 0.006), but was not a significant predictor of DNA methylation in any of the four loci examined. FKBP5 showed elevated expression levels in participants with vs. without a history of depression (p < 0.001); no significant difference in gene expression levels was observed in relation to childhood maltreatment (p > 0.05). Our results suggest DNA methylation does not mediate the childhood maltreatment-depression association in the DNHS.

Chronic Treatment with Fluoxetine Induces Sex-Dependent Analgesic Effects and Modulates HDAC2 and mGlu2 Expression in Female Mice

Gender and sex differences in pain recognition and drug responses have been reported in clinical trials and experimental models of pain. Among antidepressants, contradictory results have been observed in patients treated with selective serotonin reuptake inhibitors (SSRIs). This study evaluated sex differences in response to the SSRI fluoxetine after chronic administration in the mouse formalin test. Adult male and female CD1 mice were intraperitoneally injected with fluoxetine (10 mg/kg) for 21 days and subjected to pain assessment. Fluoxetine treatment reduced the second phase of the formalin test only in female mice without producing behavioral changes in males. We also observed that fluoxetine was able to specifically increase the expression of metabotropic glutamate receptor type-2 (mGlu2) in females. Also a reduced expression of the epigenetic modifying enzyme, histone deacetylase 2 (HDAC2), in dorsal root ganglia (DRG) and dorsal horn (DH) together with an increase histone 3 acetylation (H3) level was observed in females but not in males. With this study we provide evidence that fluoxetine induces sex specific changes in HDAC2 and mGlu2 expression in the DH of the spinal cord and in DRGs and suggests a molecular explanation for the analgesic effects in female mice.

Caregiver maltreatment causes altered neuronal DNA methylation in female rodents

Negative experiences with a caregiver during infancy can result in long-term changes in brain function and behavior, but underlying mechanisms are not well understood. It is our central hypothesis that brain and behavior changes are conferred by early childhood adversity through epigenetic changes involving DNA methylation. Using a rodent model of early-life caregiver maltreatment (involving exposure to an adverse caregiving environment for postnatal days 1-7), we have previously demonstrated abnormal methylation of DNA associated with the brain-derived neurotrophic factor (Bdnf) gene in the medial prefrontal cortex (mPFC) of adult rats. The aim of the current study was to characterize Bdnf DNA methylation in specific cell populations within the mPFC. In the prefrontal cortex, there is approximately twice as many neurons as glia, and studies have recently shown differential and distinctive DNA methylation patterns in neurons versus nonneurons. Here, we extracted nuclei from the mPFC of adult animals that had experienced maltreatment and used fluorescence-activated cell sorting to isolate cell types before performing bisulfite sequencing to estimate methylation of cytosine-guanine sites. Our data indicate that early-life stress induced methylation of DNA associated with Bdnf IV in a cell-type and sex-specific manner. Specifically, females that experienced early-life maltreatment exhibited greater neuronal cytosine-guanine methylation compared to controls, while no changes were detected in Bdnf methylation in males regardless of cell type. These changes localize the specificity of our previous findings to mPFC neurons and highlight the capacity of maltreatment to cause methylation changes that are likely to have functional consequences for neuronal function.

Valproate increases dopamine transporter expression through histone acetylation and enhanced promoter binding of Nurr1

The dopamine transporter (DAT) is the key regulator of dopaminergic transmission and is a target of several xenobiotics, including pesticides and pharmacological agents. Previously, we identified a prominent role for histone deacetylases in the regulation of DAT expression. Here, we utilized a rat dopaminergic cell line (N27) to probe the responsiveness of DAT mRNA expression to inhibitors of histone acetylation. Inhibition of histone deacetylases (HDACs) by valproate, butyrate and Trichostatin A led to a 3-10-fold increase in DAT mRNA expression, a 50% increase in protein levels, which were accompanied by increased H3 acetylation levels. To confirm the mechanism of valproate-mediated increase in DAT mRNA, chromatin immunoprecipitation (ChIP) assays were used and demonstrated a significant increase in enrichment of acetylation of histone 3 on lysines 9 and 14 (H3K9/K14ac) in the DAT promoter. Expression of Nurr1 and Pitx3, key regulators of DAT expression, were increased following valproate treatment and Nurr1 binding was enriched in the DAT promoter. Together, these results indicate that histone acetylation and subsequent enhancement of transcription factor binding are plausible mechanisms for DAT regulation by valproate and, perhaps, by other xenobiotics.

Glutamate Transport: A New Bench to Bedside Mechanism for Treating Drug Abuse

Drug addiction has often been described as a "hijacking" of the brain circuits involved in learning and memory. Glutamate is the principal excitatory neurotransmitter in the brain, and its contribution to synaptic plasticity and learning processes is well established in animal models. Likewise, over the past 20 years the addiction field has ascribed a critical role for glutamatergic transmission in the development of addiction. Chronic drug use produces enduring neuroadaptations in corticostriatal projections that are believed to contribute to a maladaptive deficit in inhibitory control over behavior. Much of this research focuses on the role played by ionotropic glutamate receptors directly involved in long-term potentiation and depression or metabotropic receptors indirectly modulating synaptic plasticity. Importantly, the balance between glutamate release and clearance tightly regulates the patterned activation of these glutamate receptors, emphasizing an important role for glutamate transporters in maintaining extracellular glutamate levels. Five excitatory amino acid transporters participate in active glutamate reuptake. Recent evidence suggests that these glutamate transporters can be modulated by chronic drug use at a variety of levels. In this review, we synopsize the evidence and mechanisms associated with drug-induced dysregulation of glutamate transport. We then summarize the preclinical and clinical data suggesting that glutamate transporters offer an effective target for the treatment of drug addiction. In particular, we focus on the role that altered glutamate transporters have in causing drug cues and contexts to develop an intrusive quality that guides maladaptive drug seeking behaviors.

Drugging the pain epigenome

More than 20% of adults worldwide experience different types of chronic pain, which are frequently associated with several comorbidities and a decrease in quality of life. Several approved painkillers are available, but current analgesics are often hampered by insufficient efficacy and/or severe adverse effects. Consequently, novel strategies for safe, highly efficacious treatments are highly desirable, particularly for chronic pain. Epigenetic mechanisms such as DNA methylation, histone modifications and microRNAs (miRNAs) strongly affect the regulation of gene expression, potentially for long periods over years or even generations, and have been associated with pathophysiological pain. Several studies, mostly in animals, revealed that inhibitors of DNA methylation, activators and inhibitors of histone modification and modulators of miRNAs reverse a number of pathological changes in the pain epigenome, which are associated with altered expression of pain-relevant genes. This epigenetic modulation might then reduce the nociceptive response and provide novel therapeutic options for analgesic therapy of chronic pain states. However, a number of challenges, such as nonspecific effects and poor delivery to target cells and tissues, hinder the rapid development of such analgesics. In this Review, we critically summarize data on epigenetics and pain, focusing on challenges in clinical development as well as possible new approaches to the drug modulation of the pain epigenome.

Pre-treatment with amitriptyline causes epigenetic up-regulation of neuroprotection-associated genes and has anti-apoptotic effects in mouse neuronal cells

Antidepressants, such as imipramine and fluoxetine, are known to alter gene expression patterns by inducing changes in the epigenetic status of neuronal cells. There is also some evidence for the anti-apoptotic effect of various groups of antidepressants; however, this effect is complicated and cell-type dependent. Antidepressants of the tricyclic group, in particular amitriptyline, have been suggested to be beneficial in the treatment of neurodegenerative disorders. We examined whether amitriptyline exerts an anti-apoptotic effect via epigenetic mechanisms. Using DNA microarray, we analyzed global gene expression in mouse primary cultured neocortical neurons after treatment with amitriptyline and imipramine. The neuroprotection-associated genes, activating transcription factor 3 (Atf3) and heme oxygenase 1 (Hmox1), were up-regulated at both mRNA and protein levels by treatment with amitriptyline. Quantitative chromatin immunoprecipitation assay revealed that amitriptyline increased enrichments of trimethylation of histone H3 lysine 4 in the promoter regions of Atf3 and Hmox1 and acetylation of histone H3 lysine 9 in the promoter regions of Atf3, which indicate an active epigenetic status. Amitriptyline pre-treatment attenuated 1-methyl-4-phenylpyridinium ion (MPP⁺)- or amyloid β peptide 1-42 (Aβ_1-42)-induced neuronal cell death and inhibited the activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2). We found that Atf3 and Hmox1 were also up-regulated after Aβ_1-42 treatment, and were further increased when pre-treated with amitriptyline. Interestingly, the highest up-regulation of Atf3 and Hmox1, at least at mRNA level, was observed after co-treatment with Aβ_1-42 and amitriptyline, together with the loss of the neuroprotective effect. These findings suggest preconditioning and neuroprotective effects of amitriptyline; however, further investigations are needed for clarifying the contribution of epigenetic up-regulation of Atf3 and Hmox1 genes.

DNA Methylation Changes in Valproic Acid-Treated HeLa Cells as Assessed by Image Analysis, Immunofluorescence and Vibrational Microspectroscopy

Valproic acid (VPA), a well-known histone deacetylase inhibitor, has been reported to affect the DNA methylation status in addition to inducing histone hyperacetylation in several cell types. In HeLa cells, VPA promotes histone acetylation and chromatin remodeling. However, DNA demethylation was not checked in this cell model for standing effects longer than those provided by histone acetylation, which is a rapid and transient phenomenon. Demonstration of VPA-induced DNA demethylation in HeLa cells would contribute to understanding the effect of VPA on an aggressive tumor cell line. In the present work, DNA demethylation in VPA-treated HeLa cells was assessed by image analysis of chromatin texture, the abundance of 5-methylcytosine (5mC) immunofluorescence signals and Fourier transform-infrared (FT-IR) microspectroscopy centered on spectral regions related to the vibration of–CH₃ groups. Image analysis indicated that increased chromatin unpacking promoted by a 4-h-treatment with 1.0 mM VPA persisted for 24 h in the absence of the drug, suggesting the occurrence of DNA demethylation that was confirmed by decreased 5mC immunofluorescence signals. FT-IR spectra of DNA samples from 1 mM or 20 mM VPA-treated cells subjected to a peak fitting analysis of the spectral window for–CH₃ stretching vibrations showed decreased vibrations and energy of these groups as a function of the decreased abundance of 5mC induced by increased VPA concentrations. Only the 20 mM-VPA treatment caused an increase in the ratio of -CH₃ bending vibrations evaluated at 1375 cm^-1 in relation to in-plane vibrations of overall cytosines evaluated at 1492 cm^-1. CH₃ stretching vibrations showed to be more sensitive than–CH₃ bending vibrations, as detected with FT-IR microspectroscopy, for studies aiming to associate vibrational spectroscopy and changes in DNA 5mC abundance.

Manganese Control of Glutamate Transporters' Gene Expression

Manganese (Mn) is an essential trace element, serving as a cofactor for several enzymes involved in various cellular and biochemical reactions in human body. However, chronic overexposure to Mn from occupational or environmental sources induces a neurological disorder, characterized by psychiatric, cognitive, and motor abnormalities, referred to as manganism. Mn-induced neurotoxicity is known to target astrocytes since these cells preferentially accumulate Mn. Astrocytes are the most abundant non-neuronal glial cells in the brain, and they play a critical role in maintaining the optimal glutamate levels to prevent excitotoxic death. The fine regulation of glutamate in the brain is accomplished by two major glutamate transporters - glutamate transporter-1 (GLT-1) and glutamate aspartate transporter (GLAST) that are predominantly expressed in astrocytes. Excitotoxic neuronal injury has been demonstrated as a critical mechanism involved in Mn neurotoxicity and implicated in the pathological signs of multiple neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Recent evidences also establish that Mn directly deregulates the expression and function of both astrocytic glutamate transporters by decreasing mRNA and protein levels of GLT-1 and GLAST. Herein, we will review the mechanisms of Mn-induced gene regulation of glutamate transporters at the transcriptional level and their role in Mn toxicity.

Glutamate Transport System as a Novel Therapeutic Target in Chronic Pain: Molecular Mechanisms and Pharmacology

The vast majority of peripheral neurons sensing noxious stimuli and conducting pain signals to the dorsal horn of the spinal cord utilize glutamate as a chemical transmitter of excitation. High-affinity glutamate transporter subtypes GLAST/EAAT1, GLT1/EAAT2, EAAC1/EAAT3, and EAAT4, differentially expressed on sensory neurons, postsynaptic spinal interneurons, and neighboring glia, ensure fine modulation of glutamate neurotransmission in the spinal cord. The glutamate transport system seems to play important roles in molecular mechanisms underlying chronic pain and analgesia. Downregulation of glutamate transporters (GluTs) often precedes or occurs simultaneously with development of hypersensitivity to thermal or tactile stimuli in various models of chronic pain. Moreover, antisense knockdown or pharmacological inhibition of these membrane proteins can induce or aggravate pain. In contrast, upregulation of GluTs by positive pharmacological modulators or by viral gene transfer to the spinal cord can reverse the development of such pathological hypersensitivity. Furthermore, some multi-target drugs displaying analgesic properties (e.g., tricyclic antidepressant amitriptyline, riluzole, anticonvulsant valproate, tetracycline antibiotic minocycline, β-lactam antibiotic ceftriaxone and its structural analog devoid of antibacterial activity, clavulanic acid) can significantly increase the spinal glutamate uptake. Thus, mounting evidence points at GluTs as prospective therapeutic target for chronic pain treatment. However, design and development of new analgesics based on the modulation of glutamate uptake will require more precise knowledge of molecular mechanisms underlying physiological or aberrant functioning of this transport system in the spinal cord.

Glucocorticoid receptor DNA methylation, childhood maltreatment and major depression

INTRODUCTION

Altered DNA methylation (DNAm) levels of hypothalamic-pituitary-adrenal (HPA) axis genes has been associated with exposure to childhood maltreatment (CM) and depression; however, it is unknown whether CM and depression have joint and potentially interacting effects on the glucocorticoid receptor (NR3C1) DNAm. We investigated the impact of CM and lifetime major depressive disorder (MDD) on NR3C1 DNAm and gene expression (GE) in 147 adult participants from the Detroit Neighborhood Health Study.

METHODS

NR3C1 promoter region DNAm was assessed via pyrosequencing using whole blood-derived DNA. Quantitative RT-PCR assays measured GE from leukocyte-derived RNA. Linear regression models were used to examine the relationship among CM, MDD, and DNAm.

RESULTS

Both CM and MDD were significant predictors of NR3C1 DNAm: CM was associated with an increase in DNAm in an EGR1 transcription factor binding site (TFBS), whereas MDD was associated with a decrease in DNAm downstream of the TFBS. No significant CM-MDD interactions were observed. CM alone was associated with significantly lower NR3C1 GE.

LIMITATIONS

Our report of CM is a retrospective self-report of abuse, which may introduce recall bias. DNAm was measured in whole blood and may not reflect brain-derived DNAm levels.

CONCLUSIONS

CM and MDD are both associated with altered DNAm levels in the NR3C1 promoter region, however the location and direction of effects differ between the two exposures, and the functional effects, as measured by GE, appear to be limited to CM exposure alone. CM exposure may be biologically embedded in this key HPA axis gene.

Epigenetic Mechanisms in Psychiatric Diseases and Epigenetic Therapy

Preclinical Research Epigenetic mechanisms refer covalent modification of DNA and histone proteins that control transcriptional regulation of gene expression. Epigenetic regulation is involved in the development of the nervous system and plays an important role in the pathophysiology of psychiatric disorders, including depression, bipolar disorder, and schizophrenia. Epigenetic drugs, including histone deacetylation and DNA methylation inhibitors have received increased attention for the management of psychiatric diseases. The purpose of this review is to discuss the potential of epigenetic drugs to treat these disorders and to clarify the mechanisms by which they regulate the dysfunctional genes in the brain. Drug Dev Res 77 : 407-413, 2016. © 2016 Wiley Periodicals, Inc.

Epigenetic Modifications of Major Depressive Disorder

Major depressive disorder (MDD) is a chronic disease whose neurological basis and pathophysiology remain poorly understood. Initially, it was proposed that genetic variations were responsible for the development of this disease. Nevertheless, several studies within the last decade have provided evidence suggesting that environmental factors play an important role in MDD pathophysiology. Alterations in epigenetics mechanism, such as DNA methylation, histone modification and microRNA expression could favor MDD advance in response to stressful experiences and environmental factors. The aim of this review is to describe genetic alterations, and particularly altered epigenetic mechanisms, that could be determinants for MDD progress, and how these alterations may arise as useful screening, diagnosis and treatment monitoring biomarkers of depressive disorders.

The role of DNA methylation in the pathophysiology and treatment of bipolar disorder

Bipolar disorder (BD) is a multifactorial illness thought to result from an interaction between genetic susceptibility and environmental stimuli. Epigenetic mechanisms, including DNA methylation, can modulate gene expression in response to the environment, and therefore might account for part of the heritability reported for BD. This paper aims to review evidence of the potential role of DNA methylation in the pathophysiology and treatment of BD. In summary, several studies suggest that alterations in DNA methylation may play an important role in the dysregulation of gene expression in BD, and some actually suggest their potential use as biomarkers to improve diagnosis, prognosis, and assessment of response to treatment. This is also supported by reports of alterations in the levels of DNA methyltransferases in patients and in the mechanism of action of classical mood stabilizers. In this sense, targeting specific alterations in DNA methylation represents exciting new treatment possibilities for BD, and the 'plastic' characteristic of DNA methylation accounts for a promising possibility of restoring environment-induced modifications in patients.

Beware of your Cre-Ation: lacZ expression impairs neuronal integrity and hippocampus-dependent memory

Expression of the lacZ-sequence is a widely used reporter-tool to assess the transgenic and/or transfection efficacy of a target gene in mice. Once activated, lacZ is permanently expressed. However, protein accumulation is one of the hallmarks of neurodegenerative diseases. Furthermore, the protein product of the bacterial lacZ gene is ß-galactosidase, an analog to the mammalian senescence-associated ß-galactosidase, a molecular marker for aging. Therefore we studied the behavioral, structural and molecular consequences of lacZ expression in distinct neuronal sub-populations. lacZ expression in cortical glutamatergic neurons resulted in severe impairments in hippocampus-dependent memory accompanied by marked structural alterations throughout the CNS. In contrast, GFP expression or the expression of the ChR2/YFP fusion product in the same cell populations did not result in either cognitive or structural deficits. GABAergic lacZ expression caused significantly decreased hyper-arousal and mild cognitive deficits. Attenuated structural and behavioral consequences of lacZ expression could also be induced in adulthood, and lacZ transfection in neuronal cell cultures significantly decreased their viability. Our findings provide a strong caveat against the use of lacZ reporter mice for phenotyping studies and point to a particular sensitivity of the hippocampus formation to detrimental consequences of lacZ expression. © 2016 Wiley Periodicals, Inc.

Targeting astrocytes in bipolar disorder

Astrocytes are homeostatic cells of the central nervous system, which are critical for development and maintenance of synaptic transmission and hence of synaptically connected neuronal ensembles. Astrocytic densities are reduced in bipolar disorder, and therefore deficient astroglial function may contribute to overall disbalance in neurotransmission and to pathological evolution. Classical anti-bipolar drugs (lithium salts, valproic acid and carbamazepine) affect expression of astroglial genes and modify astroglial signalling and homeostatic cascades. Many effects of both antidepressant and anti-bipolar drugs are exerted through regulation of glutamate homeostasis and glutamatergic transmission, through K(+) buffering, through regulation of calcium-dependent phospholipase A2 (that controls metabolism of arachidonic acid) or through Ca(2+) homeostatic and signalling pathways. Sometimes anti-depressant and anti-bipolar drugs exert opposite effects, and some effects on gene expression in drug treated animals are opposite in neurones vs. astrocytes. Changes in the intracellular pH induced by anti-bipolar drugs affect uptake of myo-inositol and thereby signalling via inositoltrisphosphate (InsP3), this being in accord with one of the main theories of mechanism of action for these drugs.

FKBP51 inhibits GSK3β and augments the effects of distinct psychotropic medications

Psychotropic medications target glycogen synthase kinase 3β (GSK3β), but the functional integration with other factors relevant for drug efficacy is poorly understood. We discovered that the suggested psychiatric risk factor FK506 binding protein 51 (FKBP51) increases phosphorylation of GSK3β at serine 9 (pGSK3β(S9)). FKBP51 associates with GSK3β mainly through its FK1 domain; furthermore, it also changes GSK3β's heterocomplex assembly by associating with the phosphatase PP2A and the kinase cyclin-dependent kinase 5. FKBP51 acts through GSK3β on the downstream targets Tau, β-catenin and T-cell factor/lymphoid enhancing factor (TCF/LEF). Lithium and the antidepressant (AD) paroxetine (PAR) functionally synergize with FKBP51, as revealed by reporter gene and protein association analyses. Deletion of FKBP51 blunted the PAR- or lithium-induced increase in pGSK3β(S9) in cells and mice and attenuated the behavioral effects of lithium treatment. Clinical improvement in depressive patients was predicted by baseline GSK3β pathway activity and by pGSK3β(S9) reactivity to ex vivo treatment of peripheral blood mononuclear lymphocytes with lithium or PAR. In sum, FKBP51-directed GSK3β activity contributes to the action of psychotropic medications. Components of the FKBP51-GSK3β pathway may be useful as biomarkers predicting AD response and as targets for the development of novel ADs.

DNA methylation signatures of mood stabilizers and antipsychotics in bipolar disorder

Aim: In view of the potential effects of psychiatric drugs on DNA methylation, we investigated whether medication use in bipolar disorder is associated with DNA methylation signatures. Experimental procedures: Blood-based DNA methylation patterns of six frequently used psychotropic drugs (lithium, quetiapine, olanzapine, lamotrigine, carbamazepine, and valproic acid) were examined in 172 bipolar disorder patients. After adjustment for cell type composition, we investigated gene networks, principal components, hypothesis-driven genes and epigenome-wide individual loci. Results: Valproic acid and quetiapine were significantly associated with altered methylation signatures after adjustment for drug-related changes on celltype composition. Conclusion: Psychiatric drugs influence DNA methylation patterns over and above cell type composition in bipolar disorder. Drug-related changes in DNA methylation are therefore not only an important confounder in psychiatric epigenetics but may also inform on the biological mechanisms underlying drug efficacy.

Valproic acid stimulates proliferation of glial precursors during cortical gliogenesis in developing rat

Valproic acid (VPA) is a neurotherapeutic drug prescribed for seizures, bipolar disorder, and migraine, including women of reproductive age. VPA is a well-known teratogen that produces congenital malformations in many organs including the nervous system, as well as later neurodevelopmental disorders, including mental retardation and autism. In developing brain, few studies have examined VPA effects on glial cells, particularly astrocytes. To investigate effects on primary glial precursors, we developed new cell culture and in vivo models using frontal cerebral cortex of postnatal day (P2) rat. In vitro, VPA exposure elicited dose-dependent, biphasic effects on DNA synthesis and proliferation. In vivo VPA (300 mg/kg) exposure from P2 to P4 increased both DNA synthesis and cell proliferation, affecting primarily astrocyte precursors, as >75% of mitotic cells expressed brain lipid-binding protein. Significantly, the consequence of early VPA exposure was increased astrocytes, as both S100-β+ cells and glial fibrillary acidic protein were increased in adolescent brain. Molecularly, VPA served as an HDAC inhibitor in vitro and in vivo as enhanced proliferation was accompanied by increased histone acetylation, whereas it elicited changes in culture in cell-cycle regulators, including cyclin D1 and E, and cyclin-dependent kinase (CDK) inhibitors, p21 and p27. Collectively, these data suggest clinically relevant VPA exposures stimulate glial precursor proliferation, though at higher doses can elicit inhibition through differential regulation of CDK inhibitors. Because changes in glial cell functions are proposed as mechanisms contributing to neuropsychiatric disorders, these observations suggest that VPA teratogenic actions may be mediated through changes in astrocyte generation during development. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 780-798, 2016.

Glutamate transporter EAAT2: regulation, function, and potential as a therapeutic target for neurological and psychiatric disease

Glutamate is the predominant excitatory neurotransmitter in the central nervous system. Excitatory amino acid transporter 2 (EAAT2) is primarily responsible for clearance of extracellular glutamate to prevent neuronal excitotoxicity and hyperexcitability. EAAT2 plays a critical role in regulation of synaptic activity and plasticity. In addition, EAAT2 has been implicated in the pathogenesis of many central nervous system disorders. In this review, we summarize current understanding of EAAT2, including structure, pharmacology, physiology, and functions, as well as disease relevancy, such as in stroke, Parkinson's disease, epilepsy, amyotrophic lateral sclerosis, Alzheimer's disease, major depressive disorder, and addiction. A large number of studies have demonstrated that up-regulation of EAAT2 protein provides significant beneficial effects in many disease models suggesting EAAT2 activation is a promising therapeutic approach. Several EAAT2 activators have been identified. Further understanding of EAAT2 regulatory mechanisms could improve development of drug-like compounds that spatiotemporally regulate EAAT2.

Epigenetic alterations in depression and antidepressant treatment

Epigenetic modifications control chromatin structure and function, and thus mediate changes in gene expression, ultimately influencing protein levels. Recent research indicates that environmental events can induce epigenetic changes and, by this, contribute to long-term changes in neural circuits and endocrine systems associated with altered risk for stress-related psychiatric disorders such as major depression. In this review, we describe recent approaches investigating epigenetic modifications associated with altered risk for major depression or response to antidepressant drugs, both on the candidate gene levels as well as the genome-wide level. In this review we focus on DNA methylation, as this is the most investigated epigenetic change in depression research.

Reduction of epileptiform activity by valproic acid in a mouse model of Alzheimer's disease is not long-lasting after treatment discontinuation

Patients with Alzheimer's disease are at increased risk for unprovoked seizures and epilepsy compared with age-matched controls. Experimental evidence suggests that neuronal hyperexcitability and epilepsy can be triggered by amyloid-β (Aβ), the main component of amyloid plaques. Previous studies demonstrated that the administration of an anticonvulsant and histone deacetylase inhibitor, valproic acid, leads to a long-lasting reduction in Aβ levels. Here we used an APdE9 mouse model of Alzheimer's disease with overproduction of Aβ to assess whether treatment with valproic acid initiated immediately after epilepsy onset modifies the occurrence of epileptiform activity. We also analyzed whether the effect is long-lasting and associated with antiamyloidogenesis and histone-modifications. Male APdE9 mice (15 week old) received daily intraperitoneal injections of 30mg/kg valproic acid for 1 week. After a 3-week wash-out, the same animals received injections of a higher dose of valproic acid (300mg/kg) daily for 1 week. Long-term video-electroencephalography monitoring was performed prior to, during, and after the treatments. Aβ and total histone H3 and H4 acetylation levels were measured at 1 month after the final valproic acid treatment. While 30mg/kg valproic acid reduced spontaneous seizures in APdE9 mice (p<0.05, chi-square), epileptiform discharges were not reduced. Administration of 300mg/kg valproic acid, however, reduced epileptiform discharges in APdE9 mice for at least 1 week after treatment discontinuation (p<0.05, Wilcoxon test), but there was no consistent long-term effects on epileptiform activity after treatment withdrawal. Further, we found no long-lasting effect on Aβ levels (p>0.05, Mann-Whitney test), only a meager increase in global acetylation of histone H3 (p<0.05), and no effects on H4 acetylation (p>0.05). In conclusion, valproic acid treatment of APdE9 mice at the stage when amyloid plaques are beginning to develop and epileptiform activity is detected reduced the amount of epileptiform activity, but the effect disappeared after treatment discontinuation.