Dopamine D2-like antagonists induce chromatin remodeling in striatal neurons through cyclic AMP-protein kinase A and NMDA receptor signaling

Beyond PDE4 inhibition: A comprehensive review on downstream cAMP signaling in the central nervous system

Cyclic adenosine monophosphate (cAMP) is a key second messenger that regulates signal transduction pathways pivotal for numerous biological functions. Intracellular cAMP levels are spatiotemporally regulated by their hydrolyzing enzymes called phosphodiesterases (PDEs). It has been shown that increased cAMP levels in the central nervous system (CNS) promote neuroplasticity, neurotransmission, neuronal survival, and myelination while suppressing neuroinflammation. Thus, elevating cAMP levels through PDE inhibition provides a therapeutic approach for multiple CNS disorders, including multiple sclerosis, stroke, spinal cord injury, amyotrophic lateral sclerosis, traumatic brain injury, and Alzheimer's disease. In particular, inhibition of the cAMP-specific PDE4 subfamily is widely studied because of its high expression in the CNS. So far, the clinical translation of full PDE4 inhibitors has been hampered because of dose-limiting side effects. Hence, focusing on signaling cascades downstream activated upon PDE4 inhibition presents a promising strategy, offering novel and pharmacologically safe targets for treating CNS disorders. Yet, the underlying downstream signaling pathways activated upon PDE(4) inhibition remain partially elusive. This review provides a comprehensive overview of the existing knowledge regarding downstream mediators of cAMP signaling induced by PDE4 inhibition or cAMP stimulators. Furthermore, we highlight existing gaps and future perspectives that may incentivize additional downstream research concerning PDE(4) inhibition, thereby providing novel therapeutic approaches for CNS disorders.

Permissive epigenetic regulatory mechanisms at the histone level are enhanced in postmortem dorsolateral prefrontal cortex of individuals with schizophrenia

BACKGROUND

Susceptibility to schizophrenia is determined by interactions between genes and environment, possibly via epigenetic mechanisms. Schizophrenia has been associated with a restrictive epigenome, and histone deacetylase (HDAC) inhibitors have been postulated as coadjuvant agents to potentiate the efficacy of current antipsychotic drugs. We aimed to evaluate global histone posttranslational modifications (HPTMs) and HDAC expression and activity in the dorsolateral prefrontal cortex (DLPFC) of individuals with schizophrenia.

METHODS

We used postmortem DLPFC samples of individuals with schizophrenia and controls matched for sex, age, and postmortem interval. Schizophrenia samples were classified into antipsychotic-treated or antipsychotic-free subgroups according to blood toxicology. Expression of HPTMs and HDAC was quantified by Western blot. HDAC activity was measured with a fluorometric assay.

RESULTS

H3K9ac, H3K27ac, and H3K4me3 were globally enhanced in the DLPFC of individuals with schizophrenia (+24%-42%, p < 0.05). HDAC activity (-17%, p < 0.01) and HDAC4 protein expression (-20%, p < 0.05) were downregulated in individuals with schizophrenia. Analyses of antipsychotic-free and antipsychotic-treated subgroups revealed enhanced H3K4me3 and H3K27ac (+24%-49%, p < 0.05) and reduced HDAC activity in the antipsychotic-treated, but not in the antipsychotic-free subgroup.

LIMITATIONS

Special care was taken to control the effect of confounding factors: age, sex, postmortem interval, and storage time. However, replication studies in bigger cohorts might strengthen the association between permissive HPTMs and schizophrenia.

CONCLUSION

We found global HPTM alterations consistent with an aberrantly permissive epigenome in schizophrenia. Further studies to elucidate the significance of enhanced permissive HPTMs in schizophrenia and its association with the mechanism of action of antipsychotic drugs are encouraged.

Drug addiction and treatment: An epigenetic perspective

Drug addiction is a complex disease affected by numerous genetic and environmental factors. Brain regions in reward pathway, neuronal adaptations, genetic and epigenetic interactions causing transcriptional enhancement or repression of multiple genes induce different addiction phenotypes for varying duration. Addictive drug use causes epigenetic alterations and similarly epigenetic changes induced by environment can promote addiction. Epigenetic mechanisms include DNA methylation and post-translational modifications like methylation, acetylation, phosphorylation, ubiquitylation, sumoylation, dopaminylation and crotonylation of histones, and ADP-ribosylation. Non-coding RNAs also induce epigenetic changes. This review discusses these above areas and stresses the need for exploring epidrugs as a treatment alternative and adjunct, considering the limited success of current addiction treatment strategies. Epigenome editing complexes have lately been effective in eukaryotic systems. Targeted DNA cleavage techniques such as CRISPR-Cas9 system, CRISPR-dCas9 complexes, transcription activator-like effector nucleases (TALENs) and zinc-finger nucleases (ZFNs) have been exploited as targeted DNA recognition or anchoring platforms, fused with epigenetic writer or eraser proteins and delivered by transfection or transduction methods. Efficacy of epidrugs is seen in various neuropsychiatric conditions and initial results in addiction treatment involving model organisms are remarkable. Epidrugs present a promising alternative treatment for addiction.

Rho kinase inhibitors ameliorate cognitive impairment in a male mouse model of methamphetamine-induced schizophrenia

Schizophrenia (SCZ) is a severe psychiatric disorder characterized by positive symptoms, negative symptoms, and cognitive deficits. Current antipsychotic treatment in SCZ improves positive symptoms but has major side effects and little impact on negative symptoms and cognitive impairment. The pathoetiology of SCZ remains unclear, but is known to involve small GTPase signaling. Rho kinase, an effector of small GTPase Rho, is highly expressed in the brain and plays a major role in neurite elongation and neuronal architecture. This study used a touchscreen-based visual discrimination (VD) task to investigate the effects of Rho kinase inhibitors on cognitive impairment in a methamphetamine (METH)-treated male mouse model of SCZ. Systemic injection of the Rho kinase inhibitor fasudil dose-dependently ameliorated METH-induced VD impairment. Fasudil also significantly suppressed the increase in the number of c-Fos-positive cells in the infralimbic medial prefrontal cortex (infralimbic mPFC) and dorsomedial striatum (DMS) following METH treatment. Bilateral microinjections of Y-27632, another Rho kinase inhibitor, into the infralimbic mPFC or DMS significantly ameliorated METH-induced VD impairment. Two proteins downstream of Rho kinase, myosin phosphatase-targeting subunit 1 (MYPT1; Thr696) and myosin light chain kinase 2 (MLC2; Thr18/Ser19), exhibited increased phosphorylation in the infralimbic mPFC and DMS, respectively, after METH treatment, and fasudil inhibited these increases. Oral administration of haloperidol and fasudil ameliorated METH-induced VD impairment, while clozapine had little effect. Oral administration of haloperidol and clozapine suppressed METH-induced hyperactivity, but fasudil had no effect. These results suggest that METH activates Rho kinase in the infralimbic mPFC and DMS, which leads to cognitive impairment in male mice. Rho kinase inhibitors ameliorate METH-induced cognitive impairment, perhaps via the cortico-striatal circuit.

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.

Haloperidol-Induced Immediate Early Genes in Striatopallidal Neurons Requires the Converging Action of cAMP/PKA/DARPP-32 and mTOR Pathways

Antipsychotics share the common pharmacological feature of antagonizing the dopamine 2 receptor (D2R), which is abundant in the striatum and involved in both the therapeutic and side effects of this drug’s class. The pharmacological blockade of striatal D2R, by disinhibiting the D2R-containing medium-sized spiny neurons (MSNs), leads to a plethora of molecular, cellular and behavioral adaptations, which are central in the action of antipsychotics. Here, we focused on the cell type-specific (D2R-MSNs) regulation of some striatal immediate early genes (IEGs), such as cFos, Arc and Zif268. Taking advantage of transgenic mouse models, pharmacological approaches and immunofluorescence analyses, we found that haloperidol-induced IEGs in the striatum required the synergistic activation of A2a (adenosine) and NMDA (glutamate) receptors. At the intracellular signaling level, we found that the PKA/DARPP-32 and mTOR pathways synergistically cooperate to control the induction of IEGs by haloperidol. By confirming and further expanding previous observations, our results provide novel insights into the regulatory mechanisms underlying the molecular/cellular action of antipsychotics in the striatum.

Tackling the Behavior of Cancer Cells: Molecular Bases for Repurposing Antipsychotic Drugs in the Treatment of Glioblastoma

Glioblastoma (GBM) is associated with a very dismal prognosis, and current therapeutic options still retain an overall unsatisfactorily efficacy in clinical practice. Therefore, novel therapeutic approaches and effective medications are highly needed. Since the development of new drugs is an extremely long, complex and expensive process, researchers and clinicians are increasingly considering drug repositioning/repurposing as a valid alternative to the standard research process. Drug repurposing is also under active investigation in GBM therapy, since a wide range of noncancer and cancer therapeutics have been proposed or investigated in clinical trials. Among these, a remarkable role is played by the antipsychotic drugs, thanks to some still partially unexplored, interesting features of these agents. Indeed, antipsychotic drugs have been described to interfere at variable incisiveness with most hallmarks of cancer. In this review, we analyze the effects of antipsychotics in oncology and how these drugs can interfere with the hallmarks of cancer in GBM. Overall, according to available evidence, mostly at the preclinical level, it is possible to speculate that repurposing of antipsychotics in GBM therapy might contribute to providing potentially effective and inexpensive therapies for patients with this disease.

HTR1A, HTR1B, HTR2A, HTR2C and HTR6 Gene Polymorphisms and Extrapyramidal Side Effects in Haloperidol-Treated Patients with Schizophrenia

Schizophrenia is a serious, chronic psychiatric disorder requiring lifelong treatment. Extrapyramidal side effects (EPS) are common adverse reactions to antipsychotic medications. In addition to the dopaminergic system, serotonergic mechanisms, including serotonin (5-HT) receptors, might be involved in EPS development. This study aimed to examine molecular associations of HTR1A, HTR1B, HTR2A, HTR2C and HTR6 gene polymorphisms with acute EPS in 229 male schizophrenia patients, following two weeks of haloperidol monotherapy. The Simpson-Angus Rating Scale for Extrapyramidal Side Effects (SAS), Barnes Akathisia Rating Scale (BARS) and Extrapyramidal Symptom Rating Scale (ESRS) were used to evaluate EPS severity. Genotyping was performed using real-time PCR, following extraction of blood DNA. Significant acute EPS appeared in 48.03% of schizophrenia patients. For the rs13212041 HTR1B gene polymorphism, affecting microRNA regulation of HTR1B gene expression, a higher frequency of TT carriers was found among haloperidol-treated patients with akathisia when compared to the group without akathisia symptoms. In comparison to C-allele carriers, patients carrying the TT genotype had higher akathisia severity, as determined by the SAS, BARS and ESRS scales. These molecular findings suggest potential involvement of 5-HT_1B receptors in akathisia development following haloperidol treatment, as well as possible epigenetic mechanisms of serotonergic modulation associated with antipsychotic-induced EPS.

NMDA receptor hypofunction for schizophrenia revisited: Perspectives from epigenetic mechanisms

Schizophrenia (SZ) is a neurodevelopmental disorder with cognitive deficits manifesting during early stages of the disease. Evidence suggests that genetic factors in combination with environmental insults lead to complex changes to glutamatergic, GABAergic, and dopaminergic systems. In particular, the N-methyl-d-aspartate receptor (NMDAR), a major glutamate receptor subtype, is implicated in both the disease progression and symptoms of SZ. NMDARs are critical for synaptic plasticity and cortical maturation, as well as learning and memory processes. In fact, any deviation from normal NMDAR expression and function can have devastating consequences. Surprisingly, there is little evidence from human patients that direct mutations of NMDAR genes contribute to SZ. One intriguing hypothesis is that epigenetic changes, which could result from early insults, alter protein expression and contribute to the NMDAR hypofunction found in SZ. Epigenetics is referred to as modifications that alter gene transcription without changing the DNA sequence itself. In this review, we first discuss how epigenetic changes to NMDAR genes could contribute to NMDAR hypofunction. We then explore how NMDAR hypofunction may contribute to epigenetic changes in other proteins or genes that lead to synaptic dysfunction and symptoms in SZ. We argue that NMDAR hypofunction occurs in early stage of the disease, and it may consequentially initiate GABA and dopamine deficits. Therefore, targeting NMDAR dysfunction during the early stages would be a promising avenue for prevention and therapeutic intervention of cognitive and social deficits that remain untreatable. Finally, we discuss potential questions regarding the epigenetic of SZ and future directions for research.

Putative COVID- 19 Induction of Reward Deficiency Syndrome (RDS) and Associated Behavioral Addictions with Potential Concomitant Dopamine Depletion: Is COVID-19 Social Distancing a Double Edged Sword?

The overwhelming fatalities of the global COVID-19 Pandemic will have daunting epigenetic sequala that can translate into an array of mental health issues, including panic, phobia, health anxiety, sleep disturbances to dissociative like symptoms including suicide. Method: We searched PUBMED for articles listed using the search terms "COVID 19 Pandemic", COVID19 and genes," "stress and COVID 19", Stress and Social distancing: Results: Long-term social distancing may be neurologically harmful, the consequence of epigenetic insults to the gene encoding the primary receptor for SARS-CoV2, and COVID 19. The gene is Angiotensin I Converting-Enzyme 2 (ACE2). According to the multi-experiment matrix (MEM), the gene exhibiting the most statistically significant co-expression link to ACE2 is Dopa Decarboxylase (DDC). DDC is a crucial enzyme that participates in the synthesis of both dopamine and serotonin. SARS-CoV2-induced downregulation of ACE2 expression might reduce dopamine and serotonin synthesis, causing hypodopaminergia. Discussion: Indeed, added to the known reduced dopamine function during periods of stress, including social distancing the consequence being both genetic and epigenetic vulnerability to all Reward Deficiency Syndrome (RDS) addictive behaviors. Stress seen in PTSD can generate downstream alterations in immune functions by reducing methylation levels of immune-related genes. Conclusion: Mitigation of these effects by identifying subjects at risk and promoting dopaminergic homeostasis to help regulate stress-relative hypodopaminergia, attenuate fears, and prevent subsequent unwanted drug and non-drug RDS type addictive behaviors seems prudent.

Gnal haploinsufficiency causes genomic instability and increased sensitivity to haloperidol

GNAL encodes guanine nucleotide-binding protein subunit Gα(olf) which plays a key role in striatal medium spiny neuron (MSN)-dopamine signaling. GNAL loss-of-function mutations are causally-associated with isolated dystonia, a movement disorder characterized by involuntary muscle contractions leading to abnormal postures. Dopamine D2 receptor (D2R) blockers such as haloperidol are mainstays in the treatment of psychosis but may contribute to the development of secondary acute and tardive dystonia. Administration of haloperidol promotes cAMP-dependent signaling in D2R-expressing indirect pathway MSNs. At present, little is known about the cellular relationships among isolated, acute, and tardive dystonia. Herein, we report the effects of acute D2R blockade on motor behavior, DNA repair, cAMP-mediated histone H3 phosphorylation (Ser10), and cell death in Gnal^+/- mice and their isogenic Gnal^+/+ littermates. In comparison to Gnal^+/+ littermates, Gnal^+/- mice exhibited increased catalepsy responses, persistent DNA breaks, decreased cAMP-dependent histone H3 phosphorylation (Ser10), and increased cell death in response to haloperidol. In striatum, aged Gnal^+/- mice exhibited increased global DNA methylation, increased euchromatin, and dendritic structural abnormalities. Our results provide evidence that Gα(olf) deficiency intensifies the effects of D2R antagonism and suggests that loss-of-function variants in GNAL may increase risk for movement disorders associated with D2R blockers. We hypothesize that the effects of Gα(olf) dysfunction and/or long-term D2R antagonism may lead to epigenetic silencing, transcriptional dysregulation, and, ultimately, cellular senescence and/or apoptosis in human brain.

Dopamine signaling in the striatum

The striatum integrates dopamine-mediated reward signals to generate appropriate behavior in response to glutamate-mediated sensory cues. Such associative learning relies on enduring neural plasticity in striatal GABAergic spiny projection neurons which, when altered, can lead to the development of a wide variety of pathological states. Considerable progress has been made in our understanding of the intracellular signaling mechanisms in dopamine-related behaviors and pathologies. Through the prism of the regulation of histone H3 and ribosomal protein S6 phosphorylation, we review how dopamine-mediated signaling events regulate gene transcription and mRNA translation. Particularly, we focus on the intracellular cascades controlling these phosphorylations downstream of the modulation of dopamine receptors by psychostimulants, antipsychotics and l-DOPA. Finally, we highlight the importance to precisely determine in which neuronal populations these signaling events occur in order to understand how they participate in remodeling neural circuits and altering dopamine-related behaviors.

Risperidone effects on heterochromatin: the role of kinase signaling

Epigenetic effects of anti-psychotic medications are poorly understood. We have appropriated a model whereby heterochromatin is established through 24- or 48-h lipopolysaccharide (LPS) treatment, and tested the epigenetic effects of risperidone along the adenylyl cyclase/protein kinase A (AC/PKA) pathway in human liposarcoma cells that express the LPS-sensitive Toll-like receptor (TLR)-4. Human SW872 cells were cultured with LPS and mRNA expression levels and epigenetic modifications of dimethylated lysine 9 of histone 2 (H3K9me2), geterochromatin protein 1γ (HP1γ) and phospho-H3S10 at promoters of interleukin (IL)-6, tumor necrosis factor (TNF)-α and IL1β were measured. Pharmacological manipulation of the AC/PKA pathway was achieved through treatment with a PKA inhibitor (H89), mitogen- and stress-activated kinase 1 (MSK1) inhibitor (SB-747651A) or forskolin. Twenty-four and 48-h LPS treatment establishes heterochromatin at selected promoters, corresponding to decreased mRNA expression. Concurrent risperidone treatment with LPS treatment can both 'block' and 'reverse' heterochromatin formation. Forskolin treatment resulted in a similar disassembling effect on heterochromatin. Conversely, inhibition of PKA by H89 or MSK1 both blocked 'normalizing' effects of risperidone on LPS-induced heterochromatin. Our results demonstrate that risperidone can disassemble heterochromatin, exerting this effect along the G-protein/AC/PKA pathway. This approach can also be utilized to investigate functional outcomes of single or combined pharmacological treatments on chromatin assemblies in human cells.

Brain changes in a maternal immune activation model of neurodevelopmental brain disorders

The developing brain is sensitive to a variety of insults. Epidemiological studies have identified prenatal exposure to infection as a risk factor for a range of neurological disorders, including autism spectrum disorder and schizophrenia. Animal models corroborate this association and have been used to probe the contribution of gene-environment interactions to the etiology of neurodevelopmental disorders. Here we review the behavior and brain phenotypes that have been characterized in MIA offspring, including the studies that have looked at the interaction between maternal immune activation and genetic risk factors for autism spectrum disorder or schizophrenia. These phenotypes include behaviors relevant to autism, schizophrenia, and other neurological disorders, alterations in brain anatomy, and structural and functional neuronal impairments. The link between maternal infection and these phenotypic changes is not fully understood, but there is increasing evidence that maternal immune activation induces prolonged immune alterations in the offspring's brain which could underlie epigenetic alterations which in turn may mediate the behavior and brain changes. These concepts will be discussed followed by a summary of the pharmacological interventions that have been tested in the maternal immune activation model.

Potential role for histone deacetylation in chronic diazepam-induced downregulation of α1-GABAA receptor subunit expression

Corroborating evidence indicate that the downregulation of GABAA receptor subunit expression may underlie tolerance to the anticonvulsant and anxiolytic actions of benzodiazepine (BZ) ligands that act as full allosteric modulators (FAMs) of GABA actions at a variety of GABAA receptor subtypes. We and others have shown that 10-14 days treatment with increasing doses of diazepam (a FAM) resulted in anticonvulsant tolerance and decreased the expression of the α1 GABAA receptor subunit mRNA and protein in frontal cortex. In addition, we have also shown that long-term treatment with imidazenil, a partial allosteric modulator of GABA action at selective GABAA receptor subtypes, fail to change the expression of the α1 subunit mRNA or induce tolerance to its anticonvulsant or anxiolytic action. However, little is known regarding the potential role of epigenetic mechanisms on long-term BZ-induced downregulation of GABAA receptor subunit. Therefore, we examined the role of histone acetylation and DNA methylation mechanisms on long-term diazepam-induced downregulation of the α1 subunit mRNA expression in rat frontal cortex. We found that 10 days treatment with increasing doses of diazepam but not imidazenil decreased the expression of the α1 GABAA receptor subunit mRNA and promoter acetylation in frontal cortex. In addition, we also found that 10 days treatment with diazepam but not imidazenil increased the expression of histone deacetylase (HDAC) 1 and 2 in frontal cortex. Thus, the increased expression of HDAC1 and HDAC2 (class 1 HDACs) and consequently increased histone deacetylation mechanism of this class 1 HDACs, may underlie long-term diazepam-induced decreased expression of the α1 GABAA receptor subunit mRNA in frontal cortex.

Proteomic study revealed antipsychotics-induced nuclear protein regulations in B35 cells are similar to the regulations in C6 cells and rat cortex

BACKGROUND

Based on accumulating evidence, the regulation of protein expression by antipsychotic drugs (APDs) might be closely related to the control of psychotic symptoms when these drugs are used to treat mental disorders. The low quantity of nuclear proteins in the cell hinders their detection because signal for rare proteins are masked in most proteomic detection systems.

METHODS

Nuclear proteins fractionated from APD-treated B35 cells were labeled with iTRAQ and detected by LC/MS/MS to investigate APD-induced alterations in nuclear protein expression. Western blot, immunofluorescent cell staining, and immunohistochemical staining were applied to validate the findings.

RESULTS

The expression of ADP/ATP translocase 2, heat shock cognate 71 kDa protein, histone H1.2, histone H3.3, histone H4, non-POU domain-containing octamer-binding protein, nucleolin, nucleophosmin, prelamin-A/C, plectin-1, vimentin, and 40S ribosomal protein S3a was regulated by APDs in B35 cells, according to our proteomic data. According to the results of the gene ontology analysis, all these proteins played important roles in biological processes or in molecular functions in cells. Western blot results showing APD-induced alterations in nuclear protein expression in B35 cells were consistent with the LC/MS/MS results. Heat shock cognate 71 kDa protein and vimentin expression in C6 cells were not affected by the three APDs. As shown in the immunofluorescent cell staining, all the three APDs altered protein expression to similar extents. We also examined whether the expression of these proteins was affected by APDs in the prefrontal cortex of rats administered sub-chronic and chronic APD treatments by western blotting and immunohistochemical staining.

CONCLUSIONS

The findings of the proteomic analysis of APD-treated B35 cells were recapitulated in the APD-treated rat cortex. The expression of some proteins was altered by APDs in rat prefrontal cortex in a time-dependent manner.

Haloperidol induces pharmacoepigenetic response by modulating miRNA expression, global DNA methylation and expression profiles of methylation maintenance genes and genes involved in neurotransmission in neuronal cells

Introduction

Haloperidol has been extensively used in various psychiatric conditions. It has also been reported to induce severe side effects. We aimed to evaluate whether haloperidol can influence host methylome, and if so what are the possible mechanisms for it in neuronal cells. Impact on host methylome and miRNAs can have wide spread alterations in gene expression, which might possibly help in understanding how haloperidol may impact treatment response or induce side effects.

Methods

SK-N-SH, a neuroblasoma cell line was treated with haloperidol at 10μm concentration for 24 hours and global DNA methylation was evaluated. Methylation at global level is maintained by methylation maintenance machinery and certain miRNAs. Therefore, the expression of methylation maintenance genes and their putative miRNA expression profiles were assessed. These global methylation alterations could result in gene expression changes. Therefore genes expressions for neurotransmitter receptors, regulators, ion channels and transporters were determined. Subsequently, we were also keen to identify a strong candidate miRNA based on biological and in-silico approach which can reflect on the pharmacoepigenetic trait of haloperidol and can also target the altered neuroscience panel of genes used in the study.

Results

Haloperidol induced increase in global DNA methylation which was found to be associated with corresponding increase in expression of various epigenetic modifiers that include DNMT1, DNMT3A, DNMT3B and MBD2. The expression of miR-29b that is known to putatively regulate the global methylation by modulating the expression of epigenetic modifiers was observed to be down regulated by haloperidol. In addition to miR-29b, miR-22 was also found to be downregulated by haloperidol treatment. Both these miRNA are known to putatively target several genes associated with various epigenetic modifiers, pharmacogenes and neurotransmission. Interestingly some of these putative target genes involved in neurotransmission were observed to be upregulated while CHRM2 gene expression was down regulated.

Conclusions

Haloperidol can influence methylation traits thereby inducing a pharmacoepigenomic response, which seems to be regulated by DNMTs and their putative miRNA expression. Increased methylation seems to influence CHRM2 gene expression while microRNA could influence neurotransmission, pharmacogene expression and methylation events. Altered expression of various therapeutically relevant genes and miRNA expression, could account for their role in therapeutic response or side effects.

The epigenomics of schizophrenia, in the mouse

Large-scale consortia including the Psychiatric Genomics Consortium, the Common Minds Consortium, BrainSeq and PsychENCODE, and many other studies taken together provide increasingly detailed insights into the genetic and epigenetic risk architectures of schizophrenia (SCZ) and offer vast amounts of molecular information, but with largely unexplored therapeutic potential. Here we discuss how epigenomic studies in human brain could guide animal work to test the impact of disease-associated alterations in chromatin structure and function on cognition and behavior. For example, transcription factors such as MYOCYTE-SPECIFIC ENHANCER FACTOR 2C (MEF2C), or multiple regulators of the open chromatin mark, methyl-histone H3-lysine 4, are associated with the genetic risk architectures of common psychiatric disease and alterations in chromatin structure and function in diseased brain tissue. Importantly, these molecules also affect cognition and behavior in genetically engineered mice, including virus-mediated expression changes in prefrontal cortex (PFC) and other key nodes in the circuitry underlying psychosis. Therefore, preclinical and small laboratory animal work could target genomic sequences affected by chromatin alterations in SCZ. To this end, in vivo editing of enhancer and other regulatory non-coding DNA by RNA-guided nucleases including CRISPR-Cas, and designer transcription factors, could be expected to deliver pipelines for novel therapeutic approaches aimed at improving cognitive dysfunction and other core symptoms of SCZ.

Consensus paper of the WFSBP Task Force on Biological Markers: Criteria for biomarkers and endophenotypes of schizophrenia, part III: Molecular mechanisms

OBJECTIVES

Despite progress in identifying molecular pathophysiological processes in schizophrenia, valid biomarkers are lacking for both the disease and treatment response.

METHODS

This comprehensive review summarises recent efforts to identify molecular mechanisms on the level of protein and gene expression and epigenetics, including DNA methylation, histone modifications and micro RNA expression. Furthermore, it summarises recent findings of alterations in lipid mediators and highlights inflammatory processes. The potential that this research will identify biomarkers of schizophrenia is discussed.

RESULTS

Recent studies have not identified clear biomarkers for schizophrenia. Although several molecular pathways have emerged as potential candidates for future research, a complete understanding of these metabolic pathways is required to reveal better treatment modalities for this disabling condition.

CONCLUSIONS

Large longitudinal cohort studies are essential that pair a thorough phenotypic and clinical evaluation for example with gene expression and proteome analysis in blood at multiple time points. This approach might identify biomarkers that allow patients to be stratified according to treatment response and ideally also allow treatment response to be predicted. Improved knowledge of molecular pathways and epigenetic mechanisms, including their potential association with environmental influences, will facilitate the discovery of biomarkers that could ultimately be effective tools in clinical practice.

Understanding epigenetics of schizophrenia in the backdrop of its antipsychotic drug therapy

The diatheses of gene and environment interaction in schizophrenia (SCZ) are becoming increasingly evident. Genetic and epigenetic backgrounds are being considered in stratifying and addressing phenotypic variation and drug response in SCZ. But how much of these epigenetic alterations are the primary contributing factor, toward disease pathogenesis and drug response, needs further clarity. Evidence indicates that antipsychotic drugs can also alter the epigenetic homeostasis thereby inducing pharmacoepigenomic effects. We re-examine the context of epigenetics in disease pathogenesis and antipsychotic drug therapy in SCZ to understand how much of these observations act as real indicators of the disease or therapeutic response. We propose that epigenetic viewpoint in SCZ needs to be critically examined under the genetic, epigenetic and pharmacoepigenetic background.

Histone Posttranslational Modifications in Schizophrenia

Schizophrenia is a complex neuropsychiatric disorder with high heritability; however, family and twin studies have indicated that environmental factors also play important roles in the etiology of disease. Environmental triggers exert their influence on behavior via epigenetic mechanisms. Epigenetic modifications, such as histone acetylation and methylation, as well as DNA methylation, can induce lasting changes in gene expression and have therefore been implicated in promoting the behavioral and neuronal behaviors that characterize this disorder. Importantly, because epigenetic processes are potentially reversible, they might serve as targets in the design of novel therapies in psychiatry. This chapter will review the current information regarding histone modifications in schizophrenia and the potential therapeutic relevance of such marks.

Dexmedetomidine increases acetylation level of histone through ERK1/2 pathway in dopamine neuron

Dexmedetomidine is a highly selective α2-adrenoceptor agonist with sedation, anesthetic sparing, analgesia, sympatholytic, and neuroprotective properties. This study evaluated neuroprotective effects of dexmedetomidine on dopamine neurons correlated to histone acetylation via extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) pathway. Animals were randomly assigned to four groups and treatments were given as onetime doses: dimethyl sulfoxide (DMSO; n = 6), dexmedetomidine 1 mg/kg ( n = 6), 10 mg/kg ( n = 6), and 100 mg/kg ( n = 6). Acetylation histone protein levels and ERK protein levels in rats dopamine neuron from striatum were determined by Western blotting after various doses of dexmedetomidine (1, 10, and 100 mg/kg) treatments. The messenger RNA expression related to signal transduction coupled to 5-hydroxytryptamine receptor (5-HTR) in striatum was assessed by quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Dexmedetomidine administration increased expression of ERK1/2 phosphorylation and histones H3 acetylation. PD098059, an inhibitor of pERK1/2, almost completely blocked dexmedetomidine-induced histones H3 acetylation. In addition, bioinformatics analysis in combination with qRT-PCR demonstrated that dexmedetomidine could regulate the genes that are related to signal transduction coupled to 5-HTR via α2-adrenoceptor. Our results define dexmedetomidine as a modulator of histones H3 acetylation via ERK1/2 signaling pathway in dopamine neuron from striatum, which may provide clues for the mechanism underlying the neuroprotective effects of dexmedetomidine.

A Role for Mitogen- and Stress-Activated Kinase 1 in L-DOPA-Induced Dyskinesia and ∆FosB Expression

BACKGROUND

Abnormal regulation of extracellular signal-regulated kinases 1 and 2 has been implicated in 3,4-dihydroxy-l-phenylalanine (L-DOPA)-induced dyskinesia (LID), a motor complication affecting Parkinson's disease patients subjected to standard pharmacotherapy. We examined the involvement of mitogen- and stress-activated kinase 1 (MSK1), a downstream target of extracellular signal-regulated kinases 1 and 2, and an important regulator of transcription in LID.

METHODS

6-Hydroxydopamine was used to produce a model of Parkinson's disease in MSK1 knockout mice and in ∆FosB- or ∆cJun-overexpressing transgenic mice, which were assessed for LID following long-term L-DOPA administration. Biochemical processes were evaluated by Western blotting or immunofluorescence. Histone H3 phosphorylation was analyzed by chromatin immunoprecipitation followed by promotor-specific quantitative polymerase chain reaction.

RESULTS

Genetic inactivation of MSK1 attenuated LID and reduced the phosphorylation of histone H3 at Ser10 in the striatum. Chromatin immunoprecipitation analysis showed that this reduction occurred at the level of the fosB gene promoter. In line with this observation, the accumulation of ∆FosB produced by chronic L-DOPA was reduced in MSK1 knockout. Moreover, inducible overexpression of ∆FosB in striatonigral medium spiny neurons exacerbated dyskinetic behavior, whereas overexpression of ∆cJun, which reduces ∆FosB-dependent transcriptional activation, counteracted LID.

CONCLUSIONS

Results indicate that abnormal regulation of MSK1 contributes to the development of LID and to the concomitant increase in striatal ∆FosB, which may occur via increased histone H3 phosphorylation at the fosB promoter. Results also show that accumulation of ∆FosB in striatonigral neurons is causally related to the development of dyskinesia.

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.

The Ticking of the Epigenetic Clock: Antipsychotic Drugs in Old Age

BACKGROUND

Exposed to antipsychotic drugs (APDs), older individuals with dementing illness are at risk of cerebrovascular adverse effects (CVAE), including sudden death. Transient microvascular dysfunctions are known to occur in younger persons exposed to APDs; however, they seldom progress to CVAE, suggesting that APDs alone are insufficient for engendering this untoward effect. It is, therefore, believed that a preexistent microvascular damage is necessary for CVAE to take place, but the exact nature of this lesion remains unclear. CNS small vessel disease (SVD) is a well-known age-related risk factor for strokes, dementia, and sudden death, which may constitute the initial CVAE-predisposing pathology. Therefore, we propose the two strikes CVAE paradigm, in which SVD represents the first strike, while exposure to APDs, the second. In this model, both strikes must be present for CVAE to take place, and the neuroimaging load of white matter hyperintensities may be directly proportional with the CVAE risk. To investigate this hypothesis at the molecular level, we focused on a seemingly unrelated phenomenon: both APDs and SVD were found protective against a similar repertoire of cancers and their spread to the brain (1-4). Since microRNA-29 has shown efficacy against the same malignancies and has been associated with small vessels pathology, we narrowed our search down to this miR, hypothesizing that the APDs mechanism of action includes miR-29 upregulation, which in turn facilitates the development of SVD.

AIM

To assess whether miR-29 can be utilized as a peripheral blood biomarker for SVD and CVAE risk.

METHOD

We conducted a search of experimentally verified miR-29 target genes utilizing the public domain tools miRanda, RNA22 and Weizemann Institute of Science miRNA Analysis. We identified in total 67 experimentally verified target genes for miR-29 family, 18 of which correlate with microvascular integrity and may be relevant for CVAE.

CONCLUSION

Upregulated microRNA-29 silences the expression of 18 genes connected with capillary stability, engendering a major vulnerability for SVD (first strike) which in turn increases the risk for CVAE after exposure to APDs (second strike).

Repetitive transcranial magnetic stimulation induces long-lasting changes in protein expression and histone acetylation

The use of non-invasive brain stimulation like repetitive transcranial magnetic stimulation (rTMS) is an increasingly popular set of methods with promising results for the treatment of neurological and psychiatric disorders. Despite great enthusiasm, the impact of non-invasive brain stimulation on its neuronal substrates remains largely unknown. Here we show that rTMS applied over the frontal cortex of awaken mice induces dopamine D₂ receptor dependent persistent changes of CDK5 and PSD-95 protein levels specifically within the stimulated brain area. Importantly, these modifications were associated with changes of histone acetylation at the promoter of these genes and prevented by administration of the histone deacetylase inhibitor MS-275. These findings show that, like several other psychoactive treatments, repeated rTMS sessions can exert long-lasting effects on neuronal substrates. This underscores the need of understanding these effects in the development of future clinical applications as well as in the establishment of improved guidelines to use rTMS in non-medical settings.

Epigenetic signaling in schizophrenia

Histone modifications and DNA methylation represent central dynamic and reversible processes that regulate gene expression and contribute to cellular phenotypes. These epigenetic marks have been shown to play fundamental roles in a diverse set of signaling and behavioral outcomes. Psychiatric disorders such as schizophrenia and depression are complex and heterogeneous diseases with multiple and independent factors that may contribute to their pathophysiology, making challenging to find a link between specific elements and the underlying mechanisms responsible for the disorder and its treatment. Growing evidences suggest that epigenetic modifications in certain brain regions and neural circuits represent a key mechanism through which environmental factors interact with individual's genetic constitution to affect risk of psychiatric conditions throughout life. This review focuses on recent advances that directly implicate epigenetic modifications in schizophrenia and antipsychotic drug action.

Histone-mediated epigenetics in addiction

Many of the brain regions, neurotransmitter systems, and behavioral changes that occur after occasional drug use in healthy subjects and after chronic drug abuse in addicted patients are well characterized. An emerging literature suggests that epigenetic processes, those processes that regulate the accessibility of DNA to regulatory proteins within the nucleus, are keys to how addiction develops and how it may be treated. Investigations of the regulation of chromatin, the organizational system of DNA, by histone modification are leading to a new understanding of the cellular and behavioral alterations that occur after drug use. We will describe how, when, and where histone tails are modified and how some of the most recognized histone regulation patterns are involved in the cycle of addiction, including initial and chronic drug intake, withdrawal, abstinence, and relapse. Finally, we consider how an approach that targets histone modifications may promote successful treatment.

Epigenetic mechanisms in schizophrenia

Schizophrenia is a major psychiatric disorder that lacks a unifying neuropathology, while currently available pharmacological treatments provide only limited benefits to many patients. This review will discuss how the field of neuroepigenetics could contribute to advancements of the existing knowledge on the neurobiology and treatment of psychosis. Genome-scale mapping of DMA methylation, histone modifications and variants, and chromosomal loopings for promoter-enhancer interactions and other epigenetic determinants of genome organization and function are likely to provide important clues about mechanisms contributing to dysregulated expression of synaptic and metabolic genes in schizophrenia brain, including the potential links to the underlying genetic risk architecture and environmental exposures. In addition, studies in animal models are providing a rapidly increasing list of chromatin-regulatory mechanisms with significant effects on cognition and complex behaviors, thereby pointing to the therapeutic potential of epigenetic drug targets in the nervous system.

A Comprehensive View of the Neurotoxicity Mechanisms of Cocaine and Ethanol

Substance use disorder is an emerging problem concerning to human health, causing severe side effects, including neurotoxicity. The use of illegal drugs and the misuse of prescription or over-the-counter drugs are growing in this century, being one of the major public health problems. Ethanol and cocaine are one of the most frequently used drugs and, according to the National Institute on Drug Abuse, their concurrent consumption is one of the major causes for emergency hospital room visits. These molecules act in the brain through different mechanisms, altering the nervous system function. Researchers have focused the attention not just in the mechanism of action of these drugs, but also in the mechanism by which they damage the nervous tissue (neurotoxicity). Therefore, the goal of the present review is to provide a global perspective about the mechanisms of the neurotoxicity of cocaine and ethanol.

Cocaine activates Rac1 to control structural and behavioral plasticity in caudate putamen

Repeated exposure to cocaine was previously found to cause sensitized behavioral responses and structural remodeling on medium spiny neurons of the nucleus accumbens (NAc) and caudate putamen (CPu). Rac1 has emerged as a key integrator of environmental cues that regulates dendritic cytoskeletons. In this study, we investigated the role of Rac1 in cocaine-induced dendritic and behavioral plasticity in the CPu. We found that Rac1 activation was reduced in the NAc but increased in the CPu following repeated cocaine treatment. Inhibition of Rac1 activity by a Rac1-specific inhibitor NSC23766, overexpression of a dominant negative mutant of Rac1 (T17N-Rac1) or local knockout of Rac1 attenuated the cocaine-induced increase in dendrites and spine density in the CPu, whereas overexpression of a constitutively active Rac1 exert the opposite effect. Moreover, NSC23766 reversed the increased number of asymmetric spine synapses in the CPu following chronic cocaine exposure. Downregulation of Rac1 activity likewise attenuates behavioral reward responses to cocaine exposure, with activation of Rac1 producing the opposite effect. Thus, Rac1 signaling is differentially regulated in the NAc and CPu after repeated cocaine treatment, and induction of Rac1 activation in the CPu is important for cocaine exposure-induced dendritic remodeling and behavioral plasticity.

Immunostaining analysis of tissue cultured cells and tissue sections using phospho-Histone H3 (Serine 10) antibody

Post-translational modifications of histones play an important role in regulation of gene expression through condensation and decondensation of chromatin structure. These modifications include acetylation, methylation, phosphorylation and ubiquitination. Phosphorylation on histones is associated with cellular responses such as DNA damage, transcription, chromatin compaction and mitosis or meiosis. One of the most extensively studied modifications of histones is the Serine 10 phosphorylation on histone H3 N-terminal tail. This specific phosphorylation on Histone H3 has been associated with condensation and transcriptional inactivation of mitotic chromosomes, but recent studies have suggested a role for this specific phosphorylation in chromatin relaxation and activation of transcription in interphase cells. Co-immunostaining analysis of cells using antibodies specific to serine 10P-Histone H3 together with those to cell cycle specific markers will allow us to determine the nature of phosphorylation in a cell cycle-specific manner. In a complex system, such as tissue specimens, analysis using P-Histone H3 and a cell type specific antibody will allow identification of specific cells that are affected by this histone modification. This is of particular interest in the field of cancer biology or neurobiology where identification or quantification of the transcriptionally active or mitotic cells will enable one to evaluate the progression of the disease development. The protocol described here provides details on how co-immunostaining and analysis can be performed in tissue cultured cells or tissue sections.

Epigenetic mechanisms of memory formation and reconsolidation

Memory consolidation involves transcriptional control of genes in neurons to stabilize a newly formed memory. Following retrieval, a once consolidated memory destabilizes and again requires gene transcription changes in order to restabilize, a process referred to as reconsolidation. Understanding the molecular mechanisms of gene transcription during the consolidation and reconsolidation processes could provide crucial insights into normal memory formation and memory dysfunction associated with psychiatric disorders. In the past decade, modifications of epigenetic markers such as DNA methylation and posttranslational modifications of histone proteins have emerged as critical transcriptional regulators of gene expression during initial memory formation and after retrieval. In light of the rapidly growing literature in this exciting area of research, we here examine the most recent and latest evidence demonstrating how memory acquisition and retrieval trigger epigenetic changes during the consolidation and reconsolidation phases to impact behavior. In particular we focus on the reconsolidation process, where we discuss the already identified epigenetic regulators of gene transcription during memory reconsolidation, while exploring other potential epigenetic modifications that may also be involved, and expand on how these epigenetic modifications may be precisely and temporally controlled by important signaling cascades critical to the reconsolidation process. Finally, we explore the possibility that epigenetic mechanisms may serve to regulate a system or circuit level reconsolidation process and may be involved in retrieval-dependent memory updating. Hence, we propose that epigenetic mechanisms coordinate changes in neuronal gene transcription, not only during the initial memory consolidation phase, but are triggered by retrieval to regulate molecular and cellular processes during memory reconsolidation.

Genomics and epigenomics in novel schizophrenia drug discovery: translating animal models to clinical research and back

INTRODUCTION

Schizophrenia is a major psychiatric disorder that afflicts about 1% of the world's population, falling into the top 10 medical disorders causing disability. Existing therapeutic strategies have had limited success; they have poor effects on core cognitive impairment and long-term disability. They are also burdened by relevant side effects. Although new antipsychotic medications have been launched in the past decades, there has been a general lack of significant innovation over the past 60 years. This lack of significant progress in the pharmacotherapy of schizophrenia is a reflection of the complexity and heterogeneity of its etiopathogenetic mechanisms.

AREAS COVERED

In this article, the authors briefly review genetic models of schizophrenia, focusing on examples of how new therapeutic strategies have been developed from them. They report on the evidence of epigenetic alterations in schizophrenia and their relevance to pharmacological studies. Further, they describe the implications of epigenetic mechanisms in the etiopathogenesis of the disease and the effects of current antipsychotic drugs on epigenetic processes. Finally, they provide their perspective of using epigenetic drugs for treating schizophrenia.

EXPERT OPINION

Current genetic and epigenetic studies are finally shedding light on the biomolecular mechanisms linked to the core pathogenetic alterations in schizophrenia, rather than just their symptoms. These advancements in the understanding of the physiopathology of schizophrenia provide exciting new perspectives for treatments. Indeed, the possibility of looking directly at the biomolecular level allows us to bypass the age-old issues of animal studies pertaining to their questionable validity as behavioral models.

Repeated treatment with electroconvulsive seizures induces HDAC2 expression and down-regulation of NMDA receptor-related genes through histone deacetylation in the rat frontal cortex

The enzymatic activity of histone deacetylases (HDACs) leads to a histone deacetylation-mediated condensed chromatic structure, resulting in transcriptional repression, which has been implicated in the modifications of neural circuits and behaviors. Repeated treatment with electroconvulsive seizure (ECS) induces changes in histone acetylation, expression of various genes, and intrabrain cellular changes, including neurogenesis. In this study, we examined the effects of repeated ECS on the expression of class I HDACs and related changes in histone modifications and gene expression in the rat frontal cortex. Ten days of repeated ECS treatments (E10X) up-regulated HDAC2 expression at the mRNA and protein levels in the rat frontal cortex compared with sham-treated controls; this was evident in the nuclei of neuronal cells in the prefrontal, cingulate, orbital, and insular cortices. Among the known HDAC2 target genes, mRNA expression of N-methyl-d-aspartate (NMDA) receptor signaling-related genes, including early growth response-1 (Egr1), c-Fos, glutamate receptor, ionotropic, N-methyl d-aspartate 2A (Nr2a), Nr2b, neuritin1 (Nrn1), and calcium/calmodulin-dependent protein kinase II alpha (Camk2α), were decreased, and the histone acetylation of H3 and/or H4 proteins was also reduced by E10X. Chromatin immunoprecipitation analysis revealed that HDAC2 occupancy in the promoters of down-regulated genes was increased significantly. Moreover, administration of sodium butyrate, a HDAC inhibitor, during the course of E10X ameliorated the ECS-induced down-regulation of genes in the rat frontal cortex. These findings suggest that induction of HDAC2 by repeated ECS treatment could play an important role in the down-regulation of NMDA receptor signaling-related genes in the rat frontal cortex through histone modification.

Whole genome methylation analyses of schizophrenia patients before and after treatment

The aetiology of schizophrenia is still unknown but it involves both heritable and non-heritable factors. DNA methylation is an inheritable epigenetic modification that stably alters gene expression. It takes part in the regulation of neurodevelopment and may be a contributing factor to the pathogenesis of brain diseases. It was found that many of the antipsychotic drugs may lead to epigenetic modifications. We have performed 42 high-resolution genome-wide methylation array analyses to determine the methylation status of 27,627 CpG islands. Differentially methylated regions were studied with samples from 20 Bulgarian individuals divided in four groups according to their gender (12 males/8 females) and their treatment response (6 in complete/14 in incomplete remission). They were compared to two age and sex matched control pools (110 females in female pool/110 males in male pool) before and after treatment. We found significant differences in the methylation profiles between male schizophrenia patients with complete remission and control male pool before treatment (C16orf70, CST3, DDRGK1, FA2H, FLJ30058, MFSD2B, RFX4, UBE2J1, ZNF311) and male schizophrenia patients with complete remission and control male pool after treatment (AP1S3, C16orf59, KCNK15, LOC146336, MGC16384, XRN2) that potentially could be used as target genes for new therapeutic strategies as well as markers for good treatment response. Our data revealed major differences in methylation profiles between male schizophrenia patients in complete remission before and after treatment and healthy controls which supports the hypothesis that antipsychotic drugs may play a role in epigenetic modifications.

Potential molecular and cellular mechanism of psychotropic drugs

Psychiatric disorders are among the most debilitating of all medical illnesses. Whilst there are drugs that can be used to treat these disorders, they give sub-optimal recovery in many people and a significant number of individuals do not respond to any treatments and remain treatment resistant. Surprisingly, the mechanism by which psychotropic drugs cause their therapeutic benefits remain unknown but likely involves the underlying molecular pathways affected by the drugs. Hence, in this review, we have focused on recent findings on the molecular mechanism affected by antipsychotic, mood stabilizing and antidepressant drugs at the levels of epigenetics, intracellular signalling cascades and microRNAs. We posit that understanding these important interactions will result in a better understanding of how these drugs act which in turn may aid in considering how to develop drugs with better efficacy or increased therapeutic reach.

Genetic Addiction Risk Score (GARS): molecular neurogenetic evidence for predisposition to Reward Deficiency Syndrome (RDS)

We have published extensively on the neurogenetics of brain reward systems with reference to the genes related to dopaminergic function in particular. In 1996, we coined “Reward Deficiency Syndrome” (RDS), to portray behaviors found to have gene-based association with hypodopaminergic function. RDS as a useful concept has been embraced in many subsequent studies, to increase our understanding of Substance Use Disorder (SUD), addictions, and other obsessive, compulsive, and impulsive behaviors. Interestingly, albeit others, in one published study, we were able to describe lifetime RDS behaviors in a recovering addict (17 years sober) blindly by assessing resultant Genetic Addiction Risk Score (GARS™) data only. We hypothesize that genetic testing at an early age may be an effective preventive strategy to reduce or eliminate pathological substance and behavioral seeking activity. Here, we consider a select number of genes, their polymorphisms, and associated risks for RDS whereby, utilizing GWAS, there is evidence for convergence to reward candidate genes. The evidence presented serves as a plausible brain-print providing relevant genetic information that will reinforce targeted therapies, to improve recovery and prevent relapse on an individualized basis. The primary driver of RDS is a hypodopaminergic trait (genes) as well as epigenetic states (methylation and deacetylation on chromatin structure). We now have entered a new era in addiction medicine that embraces the neuroscience of addiction and RDS as a pathological condition in brain reward circuitry that calls for appropriate evidence-based therapy and early genetic diagnosis and that requires further intensive investigation.

The role of epigenetic regulation in learning and memory

The formation of long-term memory involves a series of molecular and cellular changes, including gene transcription, protein synthesis and synaptic plasticity dynamics. Some of these changes arise during learning and are subsequently retained throughout life. 'Epigenetic' regulation, which involves DNA methylation and histone modifications, plays a critical role in retaining long-term changes in post-mitotic cells. Accumulating evidence suggests that the epigenetic machinery might regulate the formation and stabilization of long-term memory in two ways: a 'gating' role of the chromatin state to regulate activity-triggered gene expression; and a 'stabilizing' role of the chromatin state to maintain molecular and cellular changes induced by the memory-related event. The neuronal activation regulates the dynamics of the chromatin status under precise timing, with subsequent alterations in the gene expression profile. This review summarizes the existing literature, focusing on the involvement of epigenetic regulation in learning and memory. We propose that the identification of different epigenetic regulators and signaling pathways involved in memory-related epigenetic regulations will provide mechanistic insights into the formation of long-term memory.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Role of ERK signaling in activity-dependent modifications of histone proteins

It is well-established that neuronal intracellular signaling governed by the extracellular signal-regulated kinase (ERK/MAPK) plays a crucial role in long-term adaptive changes that occur during cognitive processes. ERK is a downstream component of a conserved signaling module that is activated by the serine/threonine kinase, Raf, which activates the MAPK/ERK kinase (MEK)1/2 protein kinases, which, in turn, activate ERK1/2. This signaling pathway has been reported to be activated in numerous physiological conditions due to a variety of stimuli, ranging from the activation of ionotropic glutamatergic receptors to metabotropic dopaminergic receptors and neurotrophin receptors. Interestingly, activated ERK can have early and late downstream effects at both the nuclear and synaptic levels. Locally, ERK signaling results in transient changes in the efficacy of synaptic transmission by modifying both pre- and post-synaptic targets. Once translocated into the nucleus, ERK signaling may control transcription by targeting several different regulators of gene expression such as transcription factors and histone proteins. ERK function is considered fundamental in processes such as long-term memory storage and drug addiction, by means of its role in activity-dependent epigenetic modifications that occur in the brain. In this review, we summarize the current understanding of ERK action in the neuroepigenetic processes underlying physiological responses, cognitive processes and drug addiction.

Epigenetics of schizophrenia: an open and shut case

During the last decade and a half, there has been an explosion of data regarding epigenetic changes in schizophrenia. Most initial studies have suggested that schizophrenia is characterized by an overly restrictive chromatin state based on increases in transcription silencing histone modifications and DNA methylation at schizophrenia candidate gene promoters and increases in the expression of enzymes that catalyze their formation. However, recent studies indicate that the pathology is more complex. This complexity may greatly impact pharmacological approaches directed at targeting epigenetic abnormalities in schizophrenia. The current review explores epigenetic studies of schizophrenia and what this can tell us about the underlying pathophysiology. We hypothesize based on recent studies that it is also plausible that drugs that further restrict chromatin may be efficacious.

Horizons of psychiatric genetics and epigenetics: where are we and where are we heading?

Today multinational studies using genome-wide association scan (GWAS) for >1000,000 polymorphisms on >100,000 cases with major psychiatric diseases versus controls, combined with next-generation sequencing have found ~100 genetic polymorphisms associated with schizophrenia (SCZ), bipolar disorder (BD), autism, attention deficit and hyperactivity disorder (ADHD), etc. However, the effect size of each genetic mutation has been generally low (<1%), and altogether could portray a tiny fraction of these mental diseases. Furthermore, none of these polymorphisms was specific to disease phenotypes indicating that they are simply genetic risk factors rather than causal mutations. The lack of identification of the major gene(s) in huge genetic studies increased the tendency for reexamining the roles of environmental factors in psychiatric and other complex diseases. However, this time at cellular/molecular levels mediated by epigenetic mechanisms that are heritable, but reversible while interacting with the environment. Now, gene-specific or whole-genome epigenetic analyses have introduced hundreds of aberrant epigenetic marks in the blood or brain of individuals with psychiatric diseases that include aberrations in DNA methylation, histone modifications and microRNA expression. Interestingly, most of the current psychiatric drugs such as valproate, lithium, antidepressants, antipsychotics and even electroconvulsive therapy (ECT) modulate epigenetic codes. The existing data indicate that, the impacts of environment/nurture, including the uterine milieu and early-life events might be more significant than genetic/nature in most psychiatric diseases. The lack of significant results in large-scale genetic studies led to revise the bolded roles of genetics and now we are at the turning point of genomics for reconsidering environmental factors that through epigenetic mechanisms may impact the brain development/functions causing disease phenotypes.

The future of neuroepigenetics in the human brain

Complex mechanisms shape the genome of brain cells into transcriptional units, clusters of condensed chromatin, and many other features that distinguish between various cell types and developmental stages sharing the same genetic material. Only a few years ago, the field's focus was almost entirely on a single mark, CpG methylation; the emerging complexity of neuronal and glial epigenomes now includes multiple types of DNA cytosine methylation, more than 100 residue-specific posttranslational histone modifications and histone variants, all of which superimposed by a dynamic and highly regulated three-dimensional organization of the chromosomal material inside the cell nucleus. Here, we provide an update on the most innovative approaches in neuroepigenetics and their potential contributions to approach cognitive functions and disorders unique to human. We propose that comprehensive, cell type-specific mappings of DNA and histone modifications, chromatin-associated RNAs, and chromosomal "loopings" and other determinants of three-dimensional genome organization will critically advance insight into the pathophysiology of the disease. For example, superimposing the epigenetic landscapes of neuronal and glial genomes onto genetic maps for complex disorders, ranging from Alzheimer's disease to schizophrenia, could provide important clues about neurological function for some of the risk-associated noncoding sequences in the human genome.