HDAC2 regulates atypical antipsychotic responses through the modulation of mGlu2 promoter activity

Erasing "bad memories": reversing aberrant synaptic plasticity as therapy for neurological and psychiatric disorders

Dopamine modulates corticostriatal plasticity in both the direct and indirect pathways of the cortico-striato-thalamo-cortical (CSTC) loops. These gradual changes in corticostriatal synaptic strengths produce long-lasting changes in behavioral responses. Under normal conditions, these mechanisms enable the selection of the most appropriate responses while inhibiting others. However, under dysregulated dopamine conditions, including a lack of dopamine release or dopamine signaling, these mechanisms could lead to the selection of maladaptive responses and/or the inhibition of appropriate responses in an experience-dependent and task-specific manner. In this review, we propose that preventing or reversing such maladaptive synaptic strengths and erasing such aberrant "memories" could be a disease-modifying therapeutic strategy for many neurological and psychiatric disorders. We review evidence from Parkinson's disease, drug-induced parkinsonism, L-DOPA-induced dyskinesia, obsessive-compulsive disorder, substance use disorders, and depression as well as research findings on animal disease models. Altogether, these studies allude to an emerging theme in translational neuroscience and promising new directions for therapy development. Specifically, we propose that combining pharmacotherapy with behavioral therapy or with deep brain stimulation (DBS) could potentially cause desired changes in specific neural circuits. If successful, one important advantage of correcting aberrant synaptic plasticity is long-lasting therapeutic effects even after treatment has ended. We will also discuss the potential molecular targets for these therapeutic approaches, including the cAMP pathway, proteins involved in synaptic plasticity as well as pathways involved in new protein synthesis. We place special emphasis on RNA binding proteins and epitranscriptomic mechanisms, as they represent a new frontier with the distinct advantage of rapidly and simultaneously altering the synthesis of many proteins locally.

Epigenetics factors in schizophrenia: future directions for etiologic and therapeutic study approaches

Schizophrenia is a complex, heterogeneous, and highly disabling severe mental disorder whose pathogenesis has not yet been fully elucidated. Epigenetics, as a bridge between genetic and environmental factors, plays an important role in the pathophysiology of schizophrenia. Over the past decade, epigenetic-wide association studies have rapidly become an important branch of psychiatric research, especially in deciphering the molecular mechanisms of schizophrenia. This review systematically analyzes recent advances in epigenome-wide association studies (EWAS) of schizophrenia, focusing on technological developments. We synthesize findings from large-scale EWAS alongside emerging evidence on DNA methylation patterns, histone modifications, and regulatory networks, emphasizing their roles in disease mechanisms and treatment responses. In addition, this review provides a prospective outlook, evaluating the impact that technological developments may have on future studies of schizophrenia. With the continuous advancement of high-throughput sequencing technology and the increasing maturity of big data analysis methods, epigenetics is expected to have a significant impact on the early diagnosis, prognosis assessment and even personalized treatment of schizophrenia.

IUPHAR review - Novel therapeutic targets for schizophrenia treatment: A translational perspective

Schizophrenia is a severe and debilitating psychiatric disorder that profoundly impacts cognitive, emotional, and social functioning. Despite its devastating personal and societal toll, current treatments often provide only partial relief, underscoring the urgent need for innovative therapeutic strategies. This review explores emerging approaches that target the complex neurobiological underpinnings of schizophrenia, moving beyond traditional dopamine-centric models. Among these, some novel drugs still employ multimodal mechanisms, simultaneously targeting dopaminergic and serotonergic systems to enhance efficacy and tolerability. Given the well-documented excitatory/inhibitory imbalance in schizophrenia, significant efforts have been directed toward addressing NMDA receptor hypofunctionality. However, strategies targeting this pathway have yet to demonstrate consistent clinical efficacy. In contrast, therapies targeting the cholinergic system have shown greater promise. For instance, the xanomeline-trospium combination, which modulates muscarinic receptors, has recently gained approval, and other molecules with similar mechanisms are currently under development. Beyond these approaches, novel strategies are being explored to target innovative pathways, including neuroplasticity, neuroinflammation, and mitochondrial dysfunction. These efforts are often designed as part of a combinatorial strategy to enhance the efficacy of currently available antipsychotic drugs. Despite significant progress, challenges remain in translating experimental discoveries into effective clinical applications. Future research should prioritize biomarker-driven approaches and precision medicine to optimize individualized treatment outcomes. By integrating these emerging therapeutic targets, schizophrenia treatment may evolve toward a more comprehensive and personalized approach, addressing the disorder's full spectrum of symptoms and improving patient quality of life.

Dusting off old blueprints: Is it time to reconsider metabotropic glutamate receptor 2 for therapeutic drug development?

The metabotropic glutamate receptor 2 (mGlu2) is a heavily studied therapeutic target in neuropsychiatry for which we anticipate a renewed interest in the near future. We review the rationale and the outcome of clinical trials with mGlu2/3 receptor agonists in schizophrenia, a field of intense research since a seminal publication by Patel and colleagues (2007). We summarize evidence about selective, potent and safe agents with quantifiable CNS penetration that can be used to test hypotheses of mGlu2 receptors involvement in neuropsychiatric diseases. We summarize lessons learned from previous programs that should be considered to maximize the probability of success when targeting orthosteric and allosteric enhancement of mGlu2 receptor function in schizophrenia and beyond. First, we propose expanding our focus beyond presynaptic mGlu2 receptor stimulation in schizophrenia to novel hypotheses and that the choice of a therapeutic indication no longer be dictated by commercial opportunity but following science as a driver. Second, evidence on internal validity of preclinical studies supporting efficacy claims in the mGlu2 field is very limited. This gap will need to be closed when reviewing the rationale to re-initiate efforts in this field. Third, the pomaglumetad program was halted due to insufficient clinical efficacy, partly because of the inability to identify a treatment responder population. In preclinical studies, effects of mGlu2/3 receptor stimulation also seemed to vary significantly between laboratories. Definition of the responsive subject population and development of response-predicting biomarkers is therefore one of the main avenues of further research in the mGlu2 field.

DNA methylation and histone modifications associated with antipsychotic treatment: a systematic review

Antipsychotic medications are essential when treating schizophrenia spectrum and other psychotic disorders, but the efficacy and tolerability of these medications vary from person to person. This interindividual variation is likely mediated, at least in part, by epigenomic processes that have yet to be fully elucidated. Herein, we systematically identified and evaluated 65 studies that examine the influence of antipsychotic drugs on epigenomic changes, including global methylation (9 studies), genome-wide methylation (22 studies), candidate gene methylation (16 studies), and histone modification (18 studies). Our evaluation revealed that haloperidol was consistently associated with increased global hypermethylation, which corroborates with genome-wide analyses, mostly performed by methylation arrays. In contrast, clozapine seems to promote hypomethylation across the epigenome. Candidate-gene methylation studies reveal varying effects post-antipsychotic therapy. Some genes like Glra1 and Drd2 are frequently found to undergo hypermethylation, whereas other genes such as SLC6A4, DUSP6, and DTNBP1 are more likely to exhibit hypomethylation in promoter regions. In examining histone modifications, the literature suggests that clozapine changes histone methylation patterns in the prefrontal cortex, particularly elevating H3K4me3 at the Gad1 gene and affecting the transcription of genes like mGlu2 by modifying histone acetylation and interacting with HDAC2 enzymes. Risperidone and quetiapine, however, exhibit distinct impacts on histone marks across different brain regions and cell types, with risperidone reducing H3K27ac in the striatum and quetiapine modifying global H3K9me2 levels in the prefrontal cortex, suggesting antipsychotics demonstrate selective influence on histone modifications, which demonstrates a complex and targeted mode of action. While this review summarizes current knowledge, the intricate dynamics between antipsychotics and epigenetics clearly warrant more exhaustive exploration with the potential to redefine our understanding and treatment of psychiatric conditions. By deciphering the epigenetic changes associated with drug treatment and therapeutic outcomes, we can move closer to personalized medicine in psychiatry.

Upregulation of the neuropeptide receptor calcitonin receptor-like in the spinal cord via MLL2 in a mouse model of paclitaxel-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a prevalent and severe side effect affecting cancer patients undergoing paclitaxel treatment. Growing evidence underscores the pivotal role of calcitonin-related peptide (CGRP) in the development of CIPN. Repeated administration of paclitaxel induces alterations in CGRP release from sensory neurons within the dorsal root ganglia (DRG). The density of the CGRP receptor is most prominent in the dorsal horn of the spinal cord, where it overlaps with the distribution of CGRP. However, the impact of chemotherapy treatment on expression of the CGRP receptor in the spinal cord remains unclear, as well as the potential therapeutic benefits of a CGRP receptor antagonist in an animal model of CIPN. Using a mouse model of paclitaxel-induced mechanical hypersensitivity, we show upregulation of Calcitonin receptor-like receptor (Calcrl) mRNA expression in the spinal cord, an event that occurred in association with upregulation of the H3K4 methyltransferase MLL2. This effect of repeated paclitaxel administration was also linked to an increase in the recruitment of MLL2, thereby enhancing levels of the active mark H3K4me2 at the Calcrl promoter. Furthermore, administration of the CGRP receptor antagonist BIBN4096 mitigated mechanical and cold hypersensitivity in paclitaxel-treated mice. Together, these observations suggest the CGRP receptor in the spinal cord as a potential target for reducing paclitaxel-induced neuropathic pain in animal models.

Epigenetic Control in Schizophrenia

Schizophrenia is a severe and complex psychiatric condition ranking among the top 15 leading causes of disability worldwide. Despite the well-established heritability component, a complex interplay between genetic and environmental risk factors plays a key role in the development of schizophrenia and psychotic disorders in general. This chapter covers all the clinical evidence showing how the analysis of the epigenetic modulation in schizophrenia might be relevant to understand the pathogenesis of schizophrenia as well as potentially useful to develop new pharmacotherapies.

Epigenetic aging in major depressive disorder: Clocks, mechanisms and therapeutic perspectives

Depression, a chronic mental disorder characterized by persistent sadness, loss of interest, and difficulty in daily tasks, impacts millions globally with varying treatment options. Antidepressants, despite their long half-life and minimal effectiveness, leave half of patients undertreated, highlighting the need for new therapies to enhance well-being. Epigenetics, which studies genetic changes in gene expression or cellular phenotype without altering the underlying Deoxyribonucleic Acid (DNA) sequence, is explored in this article. This article delves into the intricate relationship between epigenetic mechanisms and depression, shedding light on how environmental stressors, early-life adversity, and genetic predispositions shape gene expression patterns associated with depression. We have also discussed Histone Deacetylase (HDAC) inhibitors, which enhance cognitive function and mood regulation in depression. Non-coding RNAs, (ncRNAs) such as Long Non-Coding RNAs (lncRNAs) and micro RNA (miRNAs), are highlighted as potential biomarkers for detecting and monitoring major depressive disorder (MDD). This article also emphasizes the reversible nature of epigenetic modifications and their influence on neuronal growth processes, underscoring the dynamic interplay between genetics, environment, and epigenetics in depression development. It explores the therapeutic potential of targeting epigenetic pathways in treating clinical depression. Additionally, it examines clinical findings related to epigenetic clocks and their role in studying depression and biological aging.

Epigenetic modulators provide a path to understanding disease and therapeutic opportunity

The discovery of epigenetic modulators (writers, erasers, readers, and remodelers) has shed light on previously underappreciated biological mechanisms that promote diseases. With these insights, novel biomarkers and innovative combination therapies can be used to address challenging and difficult to treat disease states. This review highlights key mechanisms that epigenetic writers, erasers, readers, and remodelers control, as well as their connection with disease states and recent advances in associated epigenetic therapies.

Translation-independent association of mRNAs encoding protomers of the 5-HT 2A -mGlu2 receptor complex in living cells

The serotonin 2A receptor (5-HT 2A R) and the metabotropic glutamate 2 receptor (mGluR2) form heteromeric G protein-coupled receptor (GPCR) complexes through a direct physical interaction. Co-translational association of mRNAs encoding subunits of heteromeric ion channels has been reported, but whether complex assembly of GPCRs occurs during translation remains unknown. Our in vitro data reveal evidence of co-translational modulation in 5-HT 2A R and mGluR2 mRNAs following siRNA-mediated knockdown. Interestingly, immunoprecipitation of either 5-HT 2A R or mGluR2, using an antibody targeting epitope tags at their N-terminus, results in detection of both transcripts associated with ribonucleoprotein complexes containing RPS24. Additionally, we demonstrate that the mRNA transcripts of 5-HT 2A R and mGluR2 associate autonomously of their respective encoded proteins. Validation of this translation-independent association is extended ex vivo using mouse frontal cortex samples. Together, these findings provide mechanistic insights into the co-translational assembly of GPCR heteromeric complexes, unraveling regulatory processes governing protein-protein interactions and complex formation.

G protein-specific mechanisms in the serotonin 5-HT2A receptor regulate psychosis-related effects and memory deficits

G protein-coupled receptors (GPCRs) are sophisticated signaling machines able to simultaneously elicit multiple intracellular signaling pathways upon activation. Complete (in)activation of all pathways can be counterproductive for specific therapeutic applications. This is the case for the serotonin 2 A receptor (5-HT2AR), a prominent target for the treatment of schizophrenia. In this study, we elucidate the complex 5-HT2AR coupling signature in response to different signaling probes, and its physiological consequences by combining computational modeling, in vitro and in vivo experiments with human postmortem brain studies. We show how chemical modification of the endogenous agonist serotonin dramatically impacts the G protein coupling profile of the 5-HT2AR and the associated behavioral responses. Importantly, among these responses, we demonstrate that memory deficits are regulated by Gαq protein activation, whereas psychosis-related behavior is modulated through Gαi1 stimulation. These findings emphasize the complexity of GPCR pharmacology and physiology and open the path to designing improved therapeutics for the treatment of stchizophrenia.

Epigenetic drugs and psychedelics as emerging therapies for alcohol use disorder: insights from preclinical studies

Alcohol use disorder (AUD) is a public health issue that affects millions of people worldwide leading to physical, mental and socio-economic consequences. While current treatments for AUD have provided relief to individuals, their effectiveness on the long term is often limited, leaving a number of affected individuals without sustainable solutions. In this review, we aim to explore two emerging approaches for AUD: psychedelics and epigenetic drugs (i.e., epidrugs). By examining preclinical studies, different animal species and procedures, we delve into the potential benefits of each of these treatments in terms of addictive behaviors (alcohol drinking and seeking, motivation to drink alcohol and prevention of relapse). Because psychedelics and epidrugs may share common and complementary mechanisms of action, there is an exciting opportunity for exploring synergies between these approaches and their parallel effectiveness in treating AUD and the diverse associated psychiatric conditions.

Antipsychotic-induced epigenomic reorganization in frontal cortex of individuals with schizophrenia

Genome-wide association studies have revealed >270 loci associated with schizophrenia risk, yet these genetic factors do not seem to be sufficient to fully explain the molecular determinants behind this psychiatric condition. Epigenetic marks such as post-translational histone modifications remain largely plastic during development and adulthood, allowing a dynamic impact of environmental factors, including antipsychotic medications, on access to genes and regulatory elements. However, few studies so far have profiled cell-specific genome-wide histone modifications in postmortem brain samples from schizophrenia subjects, or the effect of antipsychotic treatment on such epigenetic marks. Here, we conducted ChIP-seq analyses focusing on histone marks indicative of active enhancers (H3K27ac) and active promoters (H3K4me3), alongside RNA-seq, using frontal cortex samples from antipsychotic-free (AF) and antipsychotic-treated (AT) individuals with schizophrenia, as well as individually matched controls (n=58). Schizophrenia subjects exhibited thousands of neuronal and non-neuronal epigenetic differences at regions that included several susceptibility genetic loci, such as NRG1, DISC1, and DRD3. By analyzing the AF and AT cohorts separately, we identified schizophrenia-associated alterations in specific transcription factors, their regulatees, and epigenomic and transcriptomic features that were reversed by antipsychotic treatment; as well as those that represented a consequence of antipsychotic medication rather than a hallmark of schizophrenia in postmortem human brain samples. Notably, we also found that the effect of age on epigenomic landscapes was more pronounced in frontal cortex of AT-schizophrenics, as compared to AF-schizophrenics and controls. Together, these data provide important evidence of epigenetic alterations in the frontal cortex of individuals with schizophrenia, and remark for the first time on the impact of age and antipsychotic treatment on chromatin organization.

Effect of antipsychotic drugs on group II metabotropic glutamate receptor expression and epigenetic control in postmortem brains of schizophrenia subjects

Antipsychotic-induced low availability of group II metabotropic glutamate receptors (including mGlu2R and mGlu3R) in brains of schizophrenia patients may explain the limited efficacy of mGlu2/3R ligands in clinical trials. Studies evaluating mGlu2/3R levels in well-designed, large postmortem brain cohorts are needed to address this issue. Postmortem samples from the dorsolateral prefrontal cortex of 96 schizophrenia subjects and matched controls were collected. Toxicological analyses identified cases who were (AP+) or were not (AP-) receiving antipsychotic treatment near the time of death. Protein and mRNA levels of mGlu2R and mGlu3R, as well as GRM2 and GRM3 promoter-attached histone posttranslational modifications, were quantified. Experimental animal models were used to compare with data obtained in human tissues. Compared to matched controls, schizophrenia cortical samples had lower mGlu2R protein amounts, regardless of antipsychotic medication. Downregulation of mGlu3R was observed in AP- schizophrenia subjects only. Greater predicted occupancy values of dopamine D2 and serotonin 5HT2A receptors correlated with higher density of mGlu3R, but not mGlu2R. Clozapine treatment and maternal immune activation in rodents mimicked the mGlu2R, but not mGlu3R regulation observed in schizophrenia brains. mGlu2R and mGlu3R mRNA levels, and the epigenetic control mechanisms did not parallel the alterations at the protein level, and in some groups correlated inversely. Insufficient cortical availability of mGlu2R and mGlu3R may be associated with schizophrenia. Antipsychotic treatment may normalize mGlu3R, but not mGlu2R protein levels. A model in which epigenetic feedback mechanisms controlling mGlu3R expression are activated to counterbalance mGluR loss of function is described.

Epigenetic Regulation in Schizophrenia: Focus on Methylation and Histone Modifications in Human Studies

Despite extensive research over the last few decades, the etiology of schizophrenia (SZ) remains unclear. SZ is a pathological disorder that is highly debilitating and deeply affects the lifestyle and minds of those affected. Several factors (one or in combination) have been reported as contributors to SZ pathogenesis, including neurodevelopmental, environmental, genetic and epigenetic factors. Deoxyribonucleic acid (DNA) methylation and post-translational modification (PTM) of histone proteins are potentially contributing epigenetic processes involved in transcriptional activity, chromatin folding, cell division and apoptotic processes, and DNA damage and repair. After establishing a summary of epigenetic processes in the context of schizophrenia, this review aims to highlight the current understanding of the role of DNA methylation and histone PTMs in this disorder and their potential roles in schizophrenia pathophysiology and pathogenesis.

The neuropsychopharmacology of acetyl-L-carnitine (LAC): basic, translational and therapeutic implications

Mitochondrial metabolism can contribute to nuclear histone acetylation among other epigenetic mechanisms. A central aspect of this signaling pathway is acetyl-L-carnitine (LAC), a pivotal mitochondrial metabolite best known for its role in fatty acid oxidation. Work from our and other groups suggested LAC as a novel epigenetic modulator of brain plasticity and a therapeutic target for clinical phenotypes of depression linked to childhood trauma. Aberrant mitochondrial metabolism of LAC has also been implicated in the pathophysiology of Alzheimer's disease. Furthermore, mitochondrial dysfunction is linked to other processes implicated in the pathophysiology of both major depressive disorders and Alzheimer's disease, such as oxidative stress, inflammation, and insulin resistance. In addition to the rapid epigenetic modulation of glutamatergic function, preclinical studies showed that boosting mitochondrial metabolism of LAC protects against oxidative stress, rapidly ameliorates insulin resistance, and reduces neuroinflammation by decreasing proinflammatory pathways such as NFkB in hippocampal and cortical neurons. These basic and translational neuroscience findings point to this mitochondrial signaling pathway as a potential target to identify novel mechanisms of brain plasticity and potential unique targets for therapeutic intervention targeted to specific clinical phenotypes.

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.

A comprehensive update on genetic inheritance, epigenetic factors, associated pathology, and recent therapeutic intervention by gene therapy in schizophrenia

Schizophrenia is a severe psychological disorder in which reality is interpreted abnormally by the patient. The symptoms of the disease include delusions and hallucinations, associated with extremely disordered behavior and thinking, which may affect the daily lives of the patients. Advancements in technology have led to understanding the dynamics of the disease and the identification of the underlying causes. Multiple investigations prove that it is regulated genetically, and epigenetically, and is affected by environmental factors. The molecular and neural pathways linked to the regulation of schizophrenia have been extensively studied. Over 180 Schizophrenic risk loci have now been recognized due to several genome-wide association studies (GWAS). It has been observed that multiple transcription factors (TF) binding-disrupting single nucleotide polymorphisms (SNPs) have been related to gene expression responsible for the disease in cerebral complexes. Copy number variation, SNP defects, and epigenetic changes in chromosomes may cause overexpression or underexpression of certain genes responsible for the disease. Nowadays, gene therapy is being implemented for its treatment as several of these genetic defects have been identified. Scientists are trying to use viral vectors, miRNA, siRNA, and CRISPR technology. In addition, nanotechnology is also being applied to target such genes. The primary aim of such targeting was to either delete or silence such hyperactive genes or induce certain genes that inhibit the expression of these genes. There are challenges in delivering the gene/DNA to the site of action in the brain, and scientists are working to resolve the same. The present article describes the basics regarding the disease, its causes and factors responsible, and the gene therapy solutions available to treat this disease.

Mechanisms and molecular targets surrounding the potential therapeutic effects of psychedelics

Psychedelics, also known as classical hallucinogens, have been investigated for decades due to their potential therapeutic effects in the treatment of neuropsychiatric and substance use disorders. The results from clinical trials have shown promise for the use of psychedelics to alleviate symptoms of depression and anxiety, as well as to promote substantial decreases in the use of nicotine and alcohol. While these studies provide compelling evidence for the powerful subjective experience and prolonged therapeutic adaptations, the underlying molecular reasons for these robust and clinically meaningful improvements are still poorly understood. Preclinical studies assessing the targets and circuitry of the post-acute effects of classical psychedelics are ongoing. Current literature is split between a serotonin 5-HT2A receptor (5-HT2AR)-dependent or -independent signaling pathway, as researchers are attempting to harness the mechanisms behind the sustained post-acute therapeutically relevant effects. A combination of molecular, behavioral, and genetic techniques in neuropharmacology has begun to show promise for elucidating these mechanisms. As the field progresses, increasing evidence points towards the importance of the subjective experience induced by psychedelic-assisted therapy, but without further cross validation between clinical and preclinical research, the why behind the experience and its translational validity may be lost.

Epigenetic regulation of metabotropic glutamate 2/3 receptors: Potential role for ultra-resistant schizophrenia?

Schizophrenia is a severe and debilitating psychiatric disorder characterized by early cognitive deficits, emotional and behavioral abnormalities resulted by a dysfunctional gene x environment interaction. Genetic and epigenetic abnormalities in cortical parvalbumin-positive GABAergic interneurons lead to alterations in glutamate-mediated excitatory neurotransmission, synaptic plasticity, and neuronal development. Epigenetic alterations during pregnancy or early phases of postnatal life are associated with schizophrenia vulnerability as well as inflammatory processes which are at the basis of brain pathology. An epigenetic animal model of schizophrenia showed specific changes in promoter DNA methylation activity of genes related to schizophrenia such as reelin, BDNF and GAD67, and altered expression and function of mGlu2/3 receptors in the frontal cortex. Although antipsychotic medications represent the main treatment for schizophrenia and generally show an optimal efficacy profile for positive symptoms and relatively poor efficacy for negative or cognitive symptoms, a considerable percentage of individuals show poor response, do not achieve a complete remission, and approximately 30 % of patients show treatment-resistance. Here, we explore the potential role of epigenetic abnormalities linked to metabotropic glutamate 2/3 receptors changes in expression and function as key molecular factors underlying the difference in response to antipsychotics.

The crosstalk between 5-HT2AR and mGluR2 in schizophrenia

Schizophrenia is a severe brain disorder that usually produces a lifetime of disability. First generation or typical antipsychotics such as haloperidol and second generation or atypical antipsychotics such as clozapine and risperidone remain the current standard for schizophrenia treatment. In some patients with schizophrenia, antipsychotics produce complete remission of positive symptoms, such as hallucinations and delusions. However, antipsychotic drugs are ineffective against cognitive deficits and indeed treated schizophrenia patients have small improvements or even deterioration in several cognitive domains. This underlines the need for novel and more efficient therapeutic targets for schizophrenia treatment. Serotonin and glutamate have been identified as key parts of two neurotransmitter systems involved in fundamental brain processes. Serotonin (or 5-hydroxytryptamine) 5-HT2A receptor (5-HT2AR) and metabotropic glutamate 2 receptor (mGluR2) are G protein-coupled receptors (GPCRs) that interact at epigenetic and functional levels. These two receptors can form GPCR heteromeric complexes through which their pharmacology, function and trafficking becomes affected. Here we review past and current research on the 5-HT2AR-mGluR2 heterocomplex and its potential implication in schizophrenia and antipsychotic drug action. This article is part of the Special Issue on "The receptor-receptor interaction as a new target for therapy".

Epidrugs in the Therapy of Central Nervous System Disorders: A Way to Drive on?

The polygenic nature of neurological and psychiatric syndromes and the significant impact of environmental factors on the underlying developmental, homeostatic, and neuroplastic mechanisms suggest that an efficient therapy for these disorders should be a complex one. Pharmacological interventions with drugs selectively influencing the epigenetic landscape (epidrugs) allow one to hit multiple targets, therefore, assumably addressing a wide spectrum of genetic and environmental mechanisms of central nervous system (CNS) disorders. The aim of this review is to understand what fundamental pathological mechanisms would be optimal to target with epidrugs in the treatment of neurological or psychiatric complications. To date, the use of histone deacetylases and DNA methyltransferase inhibitors (HDACis and DNMTis) in the clinic is focused on the treatment of neoplasms (mainly of a glial origin) and is based on the cytostatic and cytotoxic actions of these compounds. Preclinical data show that besides this activity, inhibitors of histone deacetylases, DNA methyltransferases, bromodomains, and ten-eleven translocation (TET) proteins impact the expression of neuroimmune inflammation mediators (cytokines and pro-apoptotic factors), neurotrophins (brain-derived neurotropic factor (BDNF) and nerve growth factor (NGF)), ion channels, ionotropic receptors, as well as pathoproteins (β-amyloid, tau protein, and α-synuclein). Based on this profile of activities, epidrugs may be favorable as a treatment for neurodegenerative diseases. For the treatment of neurodevelopmental disorders, drug addiction, as well as anxiety disorders, depression, schizophrenia, and epilepsy, contemporary epidrugs still require further development concerning a tuning of pharmacological effects, reduction in toxicity, and development of efficient treatment protocols. A promising strategy to further clarify the potential targets of epidrugs as therapeutic means to cure neurological and psychiatric syndromes is the profiling of the epigenetic mechanisms, which have evolved upon actions of complex physiological lifestyle factors, such as diet and physical exercise, and which are effective in the management of neurodegenerative diseases and dementia.

Psychedelic Targeting of Metabotropic Glutamate Receptor 2 and Its Implications for the Treatment of Alcoholism

Alcohol abuse is a leading risk factor for the public health burden worldwide. Approved pharmacotherapies have demonstrated limited effectiveness over the last few decades in treating alcohol use disorders (AUD). New therapeutic approaches are therefore urgently needed. Historical and recent clinical trials using psychedelics in conjunction with psychotherapy demonstrated encouraging results in reducing heavy drinking in AUD patients, with psilocybin being the most promising candidate. While psychedelics are known to induce changes in gene expression and neuroplasticity, we still lack crucial information about how this specifically counteracts the alterations that occur in neuronal circuits throughout the course of addiction. This review synthesizes well-established knowledge from addiction research about pathophysiological mechanisms related to the metabotropic glutamate receptor 2 (mGlu2), with findings and theories on how mGlu2 connects to the major signaling pathways induced by psychedelics via serotonin 2A receptors (2AR). We provide literature evidence that mGlu2 and 2AR are able to regulate each other's downstream signaling pathways, either through monovalent crosstalk or through the formation of a 2AR-mGlu2 heteromer, and highlight epigenetic mechanisms by which 2ARs can modulate mGlu2 expression. Lastly, we discuss how these pathways might be targeted therapeutically to restore mGlu2 function in AUD patients, thereby reducing the propensity to relapse.

Bromodomain and Extra-Terminal Proteins in Brain Physiology and Pathology: BET-ing on Epigenetic Regulation

BET proteins function as histone code readers of acetylated lysins that determine the positive regulation in transcription of genes involved in cell cycle progression, differentiation, inflammation, and many other pathways. In recent years, thanks to the development of BET inhibitors, interest in this protein family has risen for its relevance in brain development and function. For example, experimental evidence has shown that BET modulation affects neuronal activity and the expression of genes involved in learning and memory. In addition, BET inhibition strongly suppresses molecular pathways related to neuroinflammation. These observations suggest that BET modulation may play a critical role in the onset and during the development of diverse neurodegenerative and neuropsychiatric disorders, such as Alzheimer’s disease, fragile X syndrome, and Rett syndrome. In this review article, we summarize the most recent evidence regarding the involvement of BET proteins in brain physiology and pathology, as well as their pharmacological potential as targets for therapeutic purposes.

Epigenetic Targets in Schizophrenia Development and Therapy

Schizophrenia is regarded as a neurodevelopmental disorder with its course progressing throughout life. However, the aetiology and development of schizophrenia are still under investigation. Several data suggest that the dysfunction of epigenetic mechanisms is known to be involved in the pathomechanism of this mental disorder. The present article revised the epigenetic background of schizophrenia based on the data available in online databases (PubMed, Scopus). This paper focused on the role of epigenetic regulation, such as DNA methylation, histone modifications, and interference of non-coding RNAs, in schizophrenia development. The article also reviewed the available data related to epigenetic regulation that may modify the severity of the disease as a possible target for schizophrenia pharmacotherapy. Moreover, the effects of antipsychotics on epigenetic malfunction in schizophrenia are discussed based on preclinical and clinical results. The obtainable data suggest alterations of epigenetic regulation in schizophrenia. Moreover, they also showed the important role of epigenetic modifications in antipsychotic action. There is a need for more data to establish the role of epigenetic mechanisms in schizophrenia therapy. It would be of special interest to find and develop new targets for schizophrenia therapy because patients with schizophrenia could show little or no response to current pharmacotherapy and have treatment-resistant schizophrenia.

Small molecule modulators of chromatin remodeling: from neurodevelopment to neurodegeneration

The dynamic changes in chromatin conformation alter the organization and structure of the genome and further regulate gene transcription. Basically, the chromatin structure is controlled by reversible, enzyme-catalyzed covalent modifications to chromatin components and by noncovalent ATP-dependent modifications via chromatin remodeling complexes, including switch/sucrose nonfermentable (SWI/SNF), inositol-requiring 80 (INO80), imitation switch (ISWI) and chromodomain-helicase DNA-binding protein (CHD) complexes. Recent studies have shown that chromatin remodeling is essential in different stages of postnatal and adult neurogenesis. Chromatin deregulation, which leads to defects in epigenetic gene regulation and further pathological gene expression programs, often causes a wide range of pathologies. This review first gives an overview of the regulatory mechanisms of chromatin remodeling. We then focus mainly on discussing the physiological functions of chromatin remodeling, particularly histone and DNA modifications and the four classes of ATP-dependent chromatin-remodeling enzymes, in the central and peripheral nervous systems under healthy and pathological conditions, that is, in neurodegenerative disorders. Finally, we provide an update on the development of potent and selective small molecule modulators targeting various chromatin-modifying proteins commonly associated with neurodegenerative diseases and their potential clinical applications.

Are the epigenetic changes predictive of therapeutic efficacy for psychiatric disorders? A translational approach towards novel drug targets

The etiopathogenesis of mental disorders is not fully understood and accumulating evidence support that clinical symptomatology cannot be assigned to a single gene mutation, but it involves several genetic factors. More specifically, a tight association between genes and environmental risk factors, which could be mediated by epigenetic mechanisms, may play a role in the development of mental disorders. Several data suggest that epigenetic modifications such as DNA methylation, post-translational histone modification and interference of microRNA (miRNA) or long non-coding RNA (lncRNA) may modify the severity of the disease and the outcome of the therapy. Indeed, the study of these mechanisms may help to identify patients particularly vulnerable to mental disorders and may have potential utility as biomarkers to facilitate diagnosis and treatment of psychiatric disorders. This article summarizes the most relevant preclinical and human data showing how epigenetic modifications can be central to the therapeutic efficacy of antidepressant and/or antipsychotic agents, as possible predictor of drugs response.

Role of interaction of mGlu2 and 5-HT2A receptors in antipsychotic effects

The serotonergic and glutamatergic neurotransmitter systems have been implicated in the pathophysiology of schizophrenia, and increasing evidence shows that they interact functionally. Of note, the G_q/11-coupled serotonin 5-HT_2A (5-HT_2A) and the G_i/o-coupled metabotropic glutamate type 2 (mGlu2) receptors have been demonstrated to assemble into a functional heteromeric complex that modulates the function of each individual receptor. For conformation of the heteromeric complex, corresponding transmembrane-4 segment of 5-HT_2A and mGlu2 are required. The 5-HT_2A/mGlu2 heteromeric complex is necessary for the activation of G_q/11 proteins and for the subsequent increase in the levels of the intracellular messenger Ca²⁺. Furthermore, signaling via the heteromeric complex is dysregulated in the post-mortem brains of patients with schizophrenia, and could be linked to altered cortical function. From a behavioral perspective, this complex contributes to the hallucinatory and antipsychotic behaviors associated with 5-HT_2A and mGlu2/3 agonists, respectively. Synaptic and epigenetic mechanisms have also been found to be significantly associated with the mGlu2/5-HT_2A heteromeric complex. This review summarizes the role of crosstalk between mGlu2 and 5-HT_2A in the mechanism of antipsychotic effects and introduces recent key advancements on this topic.

The role of Gadd45b in neurologic and neuropsychiatric disorders: An overview

Growth arrest and DNA damage-inducible beta (Gadd45b) is directly intertwined with stress-induced DNA repair, cell cycle arrest, survival, and apoptosis. Previous research on Gadd45b has focused chiefly on non-neuronal cells. Gadd45b is extensively expressed in the nervous system and plays a critical role in epigenetic DNA demethylation, neuroplasticity, and neuroprotection, according to accumulating evidence. This article provided an overview of the preclinical and clinical effects of Gadd45b, as well as its hypothesized mechanisms of action, focusing on major psychosis, depression, autism, stroke, seizure, dementia, Parkinson’s disease, and autoimmune diseases of the nervous system.

Presynaptic 5-HT2A-mGlu2/3 Receptor–Receptor Crosstalk in the Prefrontal Cortex: Metamodulation of Glutamate Exocytosis

The glutamatergic nerve endings of a rat prefrontal cortex (PFc) possess presynaptic 5-HT_2A heteroreceptors and mGlu2/3 autoreceptors, whose activation inhibits glutamate exocytosis, and is measured as 15 mM KCl-evoked [³H]D-aspartate ([³H]D-asp) release (which mimics glutamate exocytosis). The concomitant activation of the two receptors nulls their inhibitory activities, whereas blockade of the 5-HT_2A heteroreceptors with MDL11,939 (1 μM) strengthens the inhibitory effect elicited by the mGlu2/3 receptor agonist LY329268 (1 μM). 5-HT_2A receptor antagonists (MDL11,939; ketanserin; trazodone) amplify the impact of low (3 nM) LY379268. Clozapine (0.1–10 μM) mimics the 5-HT_2A agonist (±) DOI and inhibits the KCl-evoked [³H]D-asp overflow in a MDL11,939-dependent fashion, but does not modify the (±) DOI-induced effect. mGlu2 and 5-HT_2A proteins do not co-immunoprecipitate from synaptosomal lysates, nor does the incubation of PFc synaptosomes with MDL11,939 (1 μM) or clozapine (10 µM) modify the insertion of mGlu2 subunits in synaptosomal plasma membranes. In conclusion, 5-HT_2A and mGlu2/3 receptors colocalize, but do not physically associate, in PFc glutamatergic terminals, where they functionally interact in an antagonist-like fashion to control glutamate exocytosis. The mGlu2/3-5-HT_2A metamodulation could be relevant to therapy for central neuropsychiatric disorders, including schizophrenia, but also unveil cellular events accounting for their development, which also influence the responsiveness to drugs regimens.

Glucocorticoid receptor dysregulation underlies 5-HT2AR-dependent synaptic and behavioral deficits in a mouse neurodevelopmental disorder model

Prenatal environmental insults increase the risk of neurodevelopmental psychiatric conditions in the offspring. Structural modifications of dendritic spines are central to brain development and plasticity. Using maternal immune activation (MIA) as a rodent model of prenatal environmental insult, previous results have reported dendritic structural deficits in the frontal cortex. However, very little is known about the molecular mechanism underlying MIA-induced synaptic structural alterations in the offspring. Using prenatal (E12.5) injection with poly-(I:C) as a mouse MIA model, we show here that upregulation of the serotonin 5-HT_2A receptor (5-HT_2AR) is at least in part responsible for some of the effects of prenatal insults on frontal cortex dendritic spine structure and sensorimotor gating processes. Mechanistically, we report that this upregulation of frontal cortex 5-HT_2AR expression is associated with MIA-induced reduction of nuclear translocation of the glucocorticoid receptor (GR) and, consequently, a decrease in the enrichment of GR at the 5-HT_2AR promoter. The translational significance of these preclinical findings is supported by data in postmortem human brain samples suggesting dysregulation of GR translocation in frontal cortex of schizophrenia subjects. We also found that repeated corticosterone administration augmented frontal cortex 5-HT_2AR expression and reduced GR binding to the 5-HT_2AR promoter. However, virally (AAV)-mediated augmentation of GR function reduced frontal cortex 5-HT_2AR expression and improved sensorimotor gating processes via 5-HT_2AR. Together, these data support a negative regulatory relationship between GR signaling and 5-HT_2AR expression in the mouse frontal cortex that may carry implications for the pathophysiology underlying 5-HT_2AR dysregulation in neurodevelopmental psychiatric disorders.

Dengue and Psychiatry: Manifestations, Mechanisms, and Management Options

Dengue is an arboviral infection endemic in tropical countries. Neurological sequelae to dengue infection are not uncommon, and psychiatric manifestations are increasingly reported. This narrative review aims to present the varied manifestations, postulated mechanisms, and the available treatment options for psychiatric morbidity associated with dengue. The evidence available from eight observational studies is summarized in this review. Depression and anxiety are noted to be prevalent during both the acute and convalescent stages of the infection. The presence of encephalopathy and other neurological conditions is not a prerequisite for developing psychiatric disorders. However, treatment options to manage such psychiatric manifestations were not specified in the observational studies. Anecdotal evidence from case reports is outlined. Special attention is paid to the role of epigenetic modifications following dengue infections and the role of histone deacetylase inhibitors in the management. DNA methylation inhibitors such as valproic acid play a significant role in reversing stress-, viral-, or drug-induced epigenetic modifications.

Time course of epigenetic modulation in response to concurrent exercise training in patients with schizophrenia

This study aimed to investigate the short and long-term effects of concurrent exercise training on anthropometric variables, HDCA2 activity and cortisol levels of individuals with schizophrenia (SZ). Therefore, 10 patients were submitted to the program (endurance and strength exercises in the same session, 60 min of duration, three times a week) and blood samples were collected before, 30 days and 180 days after the intervention started. Exercise training reduced the body mass index and body mass after 180 days of the intervention. A significant decrease on HDAC2 activity was found 180 days after intervention compared to before the intervention. The cortisol levels remained unchanged in any evaluated time-points. The concurrent exercise training was able to modulate HDAC2 activity in mononuclear cells and improve anthropometric variables in a time-dependent manner in patients with SZ.

Sex-specific effects of psychedelics on prepulse inhibition of startle in 129S6/SvEv mice

BACKGROUND

Prepulse inhibition (PPI) of startle is a sensorimotor gating phenomenon perturbed in a variety of neuropsychiatric conditions. Psychedelics disrupt PPI in rats and humans, but their effects and involvement of the serotonin 5-HT_2A receptor (5-HT_2AR) in mice remain unexplored.

METHODS

We tested the effect of the psychedelic 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (0.5 mg/kg, i.p.) on startle amplitude and %PPI in response to acoustic stimuli under up to four different experimental conditions that included changes in background and stimulus intensity, prepulse and pulse duration, and interstimulus interval in male and female 129S6/SvEv mice. We also evaluated the effect of the 5-HT_2AR antagonist M100,907 (1 mg/kg, i.p.) on DOI-induced startle amplitude and %PPI, as well as the effect of the psychedelic LSD (0.24 mg/kg, i.p.) and the dopamine agonists apomorphine (5 mg/kg, s.c.) and SKF-82,958 (0.5 mg/kg, i.p.) in male 129S6/SvEv mice.

RESULTS

DOI altered startle amplitude with either pulse alone or prepulse + pulse presentations in all PPI conditions, and increased %PPI in three out of four PPI conditions in male mice - an effect that was prevented by M100,907. In female mice, DOI increased %PPI without affecting startle amplitude. %PPI was positively correlated with startle amplitude in males while being negatively correlated in female mice. In male mice, LSD also increased %PPI, although it did not affect startle amplitude, whereas apomorphine and SKF-82,958 induced decreases in %PPI.

CONCLUSION

Our findings highlight a distinct effect of the psychedelic DOI on PPI in 129S6/SvEv mice, suggesting 5-HT_2AR-dependent PPI improvement in a paradigm-dependent and sex-dependent manner.

The lysine deacetylase activity of histone deacetylases 1 and 2 is required to safeguard zygotic genome activation in mice and cattle

The genome is transcriptionally inert at fertilization and must be activated through a remarkable developmental process called zygotic genome activation (ZGA). Epigenetic reprogramming contributes significantly to the dynamic gene expression during ZGA; however, the mechanism has yet to be resolved. Here, we find histone deacetylases 1 and 2 (HDAC1/2) can regulate ZGA through lysine deacetylase activity. Notably, in mouse embryos, overexpression of a HDAC1/2 dominant-negative mutant leads to developmental arrest at the two-cell stage. RNA-seq reveals that 64% of downregulated genes are ZGA genes and 49% of upregulated genes are developmental genes. Inhibition of the deacetylase activity of HDAC1/2 causes a failure of histone deacetylation at multiple sites, including H4K5, H4K16, H3K14, H3K18 and H3K27. ChIP-seq analysis exhibits an increase and decrease of H3K27ac enrichment at promoters of up- and downregulated genes, respectively. Moreover, HDAC1 mutants prohibit the removal of H3K4me3 by impeding expression of Kdm5 genes. Importantly, the developmental block can be greatly rescued by Kdm5b injection and by partially correcting the expression of the majority of dysregulated genes. Similar functional significance of HDAC1/2 is conserved in bovine embryos. Overall, we propose that HDAC1/2 are indispensable for ZGA by creating correct transcriptional repressive and active states in mouse and bovine embryos.

Gadd45 in Neuronal Development, Function, and Injury

The growth arrest and DNA damage-inducible (Gadd) 45 proteins have been associated with numerous cellular mechanisms including cell cycle control, DNA damage sensation and repair, genotoxic stress, neoplasia, and molecular epigenetics. The genes were originally identified in in vitro screens of irradiation- and interleukin-induced transcription and have since been implicated in a host of normal and aberrant central nervous system processes. These include early and postnatal development, injury, cancer, memory, aging, and neurodegenerative and psychiatric disease states. The proteins act through a variety of molecular signaling cascades including the MAPK cascade, cell cycle control mechanisms, histone regulation, and epigenetic DNA demethylation. In this review, we provide a comprehensive discussion of the literature implicating each of the three members of the Gadd45 family in these processes.

Histone Acetylation and Methylation Underlie Oligodendroglial and Myelin Susceptibility in Schizophrenia

Schizophrenia is a complex neuropsychiatric disorder affected by both genetic and epigenetic factors. Except for neuronal dysfunction, oligodendroglial abnormalities also contribute to the disease pathogenesis, characterized by a robust dysregulation of oligodendrocyte and myelin related genes. Accumulating evidence shows that histone modifications play important roles in transcriptional regulation of the genes crucial for oligodendrocyte differentiation and myelination. Specifically, the histone acetylation and methylation were two well-recognized histone modification abnormalities in the schizophrenic brains. In this mini-review, we will describe the dynamic changes of histone acetylation and methylation in schizophrenia, which may coordinate and induce deleterious epigenetic memory in oligodendroglial cells, and further lead to oligodendrocyte and myelin deficits. Precise modulation of histone modification status in oligodendroglial cells needs to secure the balance of epigenetic marks, which may revise the therapeutic strategy for the white matter etiology of neuropsychiatric disorders.

Sex-specific role for serotonin 5-HT2A receptor in modulation of opioid-induced antinociception and reward in mice

Opioids are among the most effective analgesics and the mainstay of pain management. However, concerns about safety and abuse liability have challenged their widespread use by the medical community. Opioid-sparing therapies include drugs that in combination with opioids have the ability to enhance analgesia while decreasing opioid requirement as well as their side effects. Sex differences in antinociceptive responses to opioids have received increasing attention in recent years. However, the molecular mechanisms underlying sex differences related to opioid-sparing adjuncts remain largely unexplored. Using warm water tail-withdrawal as a mouse model of acute thermal nociception, our data suggest that adjunctive administration of the serotonin 5-HT_2A receptor (5-HT_2AR) antagonist volinanserin dose-dependently enhanced potency of the opioid analgesic oxycodone in male, but not female, mice. This antinociceptive-like response induced by oxycodone was also augmented in 5-HT_2AR knockout (5-HT_2AR^-/-) male, but not female mice; an effect that was reversed by Cre-loxP-mediated selective expression of 5-HT_2AR in dorsal root ganglion (DRG) neurons of 5-HT_2AR^-/- littermates. Pharmacological inhibition with volinanserin or genetic deletion in 5-HT_2AR^-/- animals potentiated the ability of oxycodone to reduce DRG excitability in male mice. Adjunctive volinanserin did not affect oxycodone-induced conditioned place preference (CPP), whereas it reduced oxycodone-induced locomotor sensitization in male and female mice. Together, these results suggest that adjunctive volinanserin augments opioid-induced antinociception, but not abuse-related behavior, through a sex-specific signaling crosstalk mechanism that requires 5-HT_2AR expression in mouse DRG neurons. Ultimately, our results may pave the way for the clinical evaluation of volinanserin as a potential sex-specific opioid adjuvant.

Integrative omics of schizophrenia: from genetic determinants to clinical classification and risk prediction

Schizophrenia (SCZ) is a debilitating neuropsychiatric disorder with high heritability and complex inheritance. In the past decade, successful identification of numerous susceptibility loci has provided useful insights into the molecular etiology of SCZ. However, applications of these findings to clinical classification and diagnosis, risk prediction, or intervention for SCZ have been limited, and elucidating the underlying genomic and molecular mechanisms of SCZ is still challenging. More recently, multiple Omics technologies - genomics, transcriptomics, epigenomics, proteomics, metabolomics, connectomics, and gut microbiomics - have all been applied to examine different aspects of SCZ pathogenesis. Integration of multi-Omics data has thus emerged as an approach to provide a more comprehensive view of biological complexity, which is vital to enable translation into assessments and interventions of clinical benefit to individuals with SCZ. In this review, we provide a broad survey of the single-omics studies of SCZ, summarize the advantages and challenges of different Omics technologies, and then focus on studies in which multiple omics data are integrated to unravel the complex pathophysiology of SCZ. We believe that integration of multi-Omics technologies would provide a roadmap to create a more comprehensive picture of interactions involved in the complex pathogenesis of SCZ, constitute a rich resource for elucidating the potential molecular mechanisms of the illness, and eventually improve clinical assessments and interventions of SCZ to address clinical translational questions from bench to bedside.

Differential brain ADRA2A and ADRA2C gene expression and epigenetic regulation in schizophrenia. Effect of antipsychotic drug treatment

Postsynaptic α_2A-adrenoceptor density is enhanced in the dorsolateral prefrontal cortex (DLPFC) of antipsychotic-treated schizophrenia subjects. This alteration might be due to transcriptional activation, and could be regulated by epigenetic mechanisms such as histone posttranslational modifications (PTMs). The aim of this study was to evaluate ADRA2A and ADRA2C gene expression (codifying for α₂-adrenoceptor subtypes), and permissive and repressive histone PTMs at gene promoter regions in the DLPFC of subjects with schizophrenia and matched controls (n = 24 pairs). We studied the effect of antipsychotic (AP) treatment in AP-free (n = 12) and AP-treated (n = 12) subgroups of schizophrenia subjects and in rats acutely and chronically treated with typical and atypical antipsychotics. ADRA2A mRNA expression was selectively upregulated in AP-treated schizophrenia subjects (+93%) whereas ADRA2C mRNA expression was upregulated in all schizophrenia subjects (+53%) regardless of antipsychotic treatment. Acute and chronic clozapine treatment in rats did not alter brain cortex Adra2a mRNA expression but increased Adra2c mRNA expression. Both ADRA2A and ADRA2C promoter regions showed epigenetic modification by histone methylation and acetylation in human DLPFC. The upregulation of ADRA2A expression in AP-treated schizophrenia subjects might be related to observed bivalent chromatin at ADRA2A promoter region in schizophrenia (depicted by increased permissive H3K4me3 and repressive H3K27me3) and could be triggered by the enhanced H4K16ac at ADRA2A promoter. In conclusion, epigenetic predisposition differentially modulated ADRA2A and ADRA2C mRNA expression in DLPFC of schizophrenia subjects.

Dose Effects of Histone Deacetylase Inhibitor Tacedinaline (CI-994) on Antipsychotic Haloperidol-Induced Motor and Memory Side Effects in Aged Mice

Background: Elderly patients treated with antipsychotic drugs often experience increased severity and frequency of side effects, yet the mechanisms are not well understood. Studies from our group indicate age-related histone modifications at drug targeted receptor gene promoters may contribute to the increased side effects, and histone deacetylase (HDAC) inhibitors entinostat (MS-275) and valproic acid (VPA) could reverse typical antipsychotic haloperidol (HAL) induced motor-side effects. However, whether such effects could be dose dependent and whether HDAC inhibitors could improve memory function in aged mice is unknown. Methods: We co-treated selective class 1 HDAC inhibitor tacedinaline (CI-994) at different doses (10, 20, and 30 mg/kg) with HAL (0.05 mg/kg) in young (3 months) and aged (21 months) mice for 14 consecutive days, then motor and memory behavioral tests were conducted, followed by biochemical measurements. Results: CI-994 at doses of 10 and 20 mg/kg could decrease HAL-induced cataleptic episodes but only 20 mg/kg was sufficient to improve motor coordination in aged mice. Additionally, CI-994 at 10 and 20 mg/kg mitigate HAL-induced memory impairment in aged mice. Biochemical analyses showed increased acetylation of histone marks H3K27ac and H3K18ac at the dopamine 2 receptor (D2R) gene (Drd2) promoter and increased expression of the Drd2 mRNA and D2R protein in the striatum of aged mice after administration of CI-994 at 20 mg/kg. Conclusions: Our results suggest CI-994 can reduce HAL-induced motor and memory side effects in aged mice. These effects may act through an increase of acetylation at the Drd2 promoter, thereby restoring D2R expression and improving antipsychotic drug action.

Prolonged epigenomic and synaptic plasticity alterations following single exposure to a psychedelic in mice

Clinical evidence suggests that rapid and sustained antidepressant action can be attained with a single exposure to psychedelics. However, the biological substrates and key mediators of psychedelics' enduring action remain unknown. Here, we show that a single administration of the psychedelic DOI produces fast-acting effects on frontal cortex dendritic spine structure and acceleration of fear extinction via the 5-HT2A receptor. Additionally, a single dose of DOI leads to changes in chromatin organization, particularly at enhancer regions of genes involved in synaptic assembly that stretch for days after the psychedelic exposure. These DOI-induced alterations in the neuronal epigenome overlap with genetic loci associated with schizophrenia, depression, and attention deficit hyperactivity disorder. Together, these data support that epigenomic-driven changes in synaptic plasticity sustain psychedelics' long-lasting antidepressant action but also warn about potential substrate overlap with genetic risks for certain psychiatric conditions.

Histone deacetylase in neuropathology

Neuroepigenetics, a new branch of epigenetics, plays an important role in the regulation of gene expression. Neuroepigenetics is associated with holistic neuronal function and helps in formation and maintenance of memory and learning processes. This includes neurodevelopment and neurodegenerative defects in which histone modification enzymes appear to play a crucial role. These modifications, carried out by acetyltransferases and deacetylases, regulate biologic and cellular processes such as apoptosis and autophagy, inflammatory response, mitochondrial dysfunction, cell-cycle progression and oxidative stress. Alterations in acetylation status of histone as well as non-histone substrates lead to transcriptional deregulation. Histone deacetylase decreases acetylation status and causes transcriptional repression of regulatory genes involved in neural plasticity, synaptogenesis, synaptic and neural plasticity, cognition and memory, and neural differentiation. Transcriptional deactivation in the brain results in development of neurodevelopmental and neurodegenerative disorders. Mounting evidence implicates histone deacetylase inhibitors as potential therapeutic targets to combat neurologic disorders. Recent studies have targeted naturally-occurring biomolecules and micro-RNAs to improve cognitive defects and memory. Multi-target drug ligands targeting HDAC have been developed and used in cell-culture and animal-models of neurologic disorders to ameliorate synaptic and cognitive dysfunction. Herein, we focus on the implications of histone deacetylase enzymes in neuropathology, their regulation of brain function and plausible involvement in the pathogenesis of neurologic defects.

Valproate reverses mania-like behaviors in mice via preferential targeting of HDAC2

Valproate (VPA) has been used in the treatment of bipolar disorder since the 1990s. However, the therapeutic targets of VPA have remained elusive. Here we employ a preclinical model to identify the therapeutic targets of VPA. We find compounds that inhibit histone deacetylase proteins (HDACs) are effective in normalizing manic-like behavior, and that class I HDACs (e.g., HDAC1 and HDAC2) are most important in this response. Using an RNAi approach, we find that HDAC2, but not HDAC1, inhibition in the ventral tegmental area (VTA) is sufficient to normalize behavior. Furthermore, HDAC2 overexpression in the VTA prevents the actions of VPA. We used RNA sequencing in both mice and human induced pluripotent stem cells (iPSCs) derived from bipolar patients to further identify important molecular targets. Together, these studies identify HDAC2 and downstream targets for the development of novel therapeutics for bipolar mania.

The G Protein-Coupled Glutamate Receptors as Novel Molecular Targets in Schizophrenia Treatment-A Narrative Review

Schizophrenia is a severe neuropsychiatric disease with an unknown etiology. The research into the neurobiology of this disease led to several models aimed at explaining the link between perturbations in brain function and the manifestation of psychotic symptoms. The glutamatergic hypothesis postulates that disrupted glutamate neurotransmission may mediate cognitive and psychosocial impairments by affecting the connections between the cortex and the thalamus. In this regard, the greatest attention has been given to ionotropic NMDA receptor hypofunction. However, converging data indicates metabotropic glutamate receptors as crucial for cognitive and psychomotor function. The distribution of these receptors in the brain regions related to schizophrenia and their regulatory role in glutamate release make them promising molecular targets for novel antipsychotics. This article reviews the progress in the research on the role of metabotropic glutamate receptors in schizophrenia etiopathology.

Effect of 5-HT2A receptor antagonism on levels of D2/3 receptor occupancy and adverse behavioral side-effects induced by haloperidol: a SPECT imaging study in the rat

Several studies suggested that 5-HT_2A receptor (5-HT_2AR) blockade may provide a more favorable efficacy and side-effect profile to antipsychotic treatment. We hypothesized that a combined haloperidol (a D_2/3 receptor (D_2/3R) antagonist) and MDL-100,907 (a 5-HT_2AR antagonist) treatment would reverse the side effects and the neurochemical alterations induced by haloperidol alone and would potentialize its efficacy. We thus chronically treated male Mdr1a knock-out rats with several doses of haloperidol alone or in combination with a saturating dose of a MDL-100,907. Receptor occupancy at clinically relevant levels was validated with a dual-radiotracer in-vivo SPECT imaging of D_2/3R and 5-HT_2AR occupancy. Experimental tests of efficacy (dizocilpine-disrupted prepulse inhibition (PPI) of the startle reflex) and side effects (catalepsy, vacuous chewing movements) were performed. Finally, a second dual-radiotracer in-vivo SPECT scan assessed the neurochemical changes induced by the chronic treatments. Chronic haloperidol failed to reverse PPI disruption induced by dizocilpine, whilst administration of MDL-100,907 along with haloperidol was associated with a reversal of the effect of dizocilpine. Haloperidol at 0.5 mg/kg/day and at 1 mg/kg/day induced catalepsy that was significantly alleviated (by ~50%) by co-treatment with MDL-100,907 but only at 0.5 mg/kg/day dose of haloperidol. Chronic haloperidol treatment, event at doses as low as 0.1 mg/kg/day induced a significant upregulation of the D_2/3R in the striatum (by over 40% in the nucleus accumbens and over 20% in the caudate-putamen nuclei), that was not reversed by MDL-100,907. Finally, an upregulation of 5-HT_2AR after chronic haloperidol treatment at a moderate dose only (0.25 mg/kg/day) was demonstrated in frontal cortical regions and the ventral tegmental area. Overall, a partial contribution of a 5-HT_2AR antagonism to the efficacy and side-effect profile of antipsychotic agents is suggested.

Targeting Corticotroph HDAC and PI3-Kinase in Cushing Disease

CONTEXT

Cushing disease (CD) is a life-threatening disorder. Therapeutic goals include symptom relief, biochemical control, and tumor growth inhibition. Current medical therapies for CD by and large exert no action on tumor growth.

OBJECTIVE

To identify drugs that inhibit corticotroph tumor adrenocorticotropic hormone (ACTH) secretion and growth.

DESIGN

High throughput screen employing a novel "gain of signal" ACTH AlphaLISA assay.

SETTING

Academic medical center.

PATIENTS

Corticotroph tumor tissues from patients with CD.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Potent inhibitors of corticotroph tumor ACTH secretion and growth.

RESULTS

From a kinase inhibitor library, we identified the dual PI3K/HDAC inhibitor CUDC-907 as a potent inhibitor of murine and human corticotroph tumor ACTH secretion (median effective concentration 1-5 nM), and cell proliferation (median inhibitory concentration 5 nM). In an in vivo murine corticotroph tumor xenograft model, orally administered CUDC-907 (300 mg/kg) reduced corticotroph tumor volume (TV [cm3], control 0.17 ± 0.05 vs CUDC-907 0.07 ± 0.02, P < .05) by 65% and suppressed plasma ACTH (ACTH [pg/mL] control 206 ± 27 vs CUDC-907 47 ± 7, P < .05) and corticosterone (corticosterone [ng/mL] control 180 ± 87 vs CUDC-907 27 ± 5, P < .05) levels by 77% and 85% respectively compared with controls. We also demonstrated that CUDC-907 acts through HDAC1/2 inhibition at the proopiomelanocortin transcriptional level combined with its PI3K-mediated inhibition of corticotroph cell viability to reduce ACTH secretion.

CONCLUSIONS

Given its potent efficacy in in vitro and in vivo models of CD, combined with proven safety and tolerance in clinical trials, we propose CUDC-907 may be a promising therapy for CD.

International Union of Basic and Clinical Pharmacology. CXI. Pharmacology, Signaling, and Physiology of Metabotropic Glutamate Receptors

Metabotropic glutamate (mGlu) receptors respond to glutamate, the major excitatory neurotransmitter in the mammalian brain, mediating a modulatory role that is critical for higher-order brain functions such as learning and memory. Since the first mGlu receptor was cloned in 1992, eight subtypes have been identified along with many isoforms and splice variants. The mGlu receptors are transmembrane-spanning proteins belonging to the class C G protein-coupled receptor family and represent attractive targets for a multitude of central nervous system disorders. Concerted drug discovery efforts over the past three decades have yielded a wealth of pharmacological tools including subtype-selective agents that competitively block or mimic the actions of glutamate or act allosterically via distinct sites to enhance or inhibit receptor activity. Herein, we review the physiologic and pathophysiological roles for individual mGlu receptor subtypes including the pleiotropic nature of intracellular signal transduction arising from each. We provide a comprehensive analysis of the in vitro and in vivo pharmacological properties of prototypical and commercially available orthosteric agonists and antagonists as well as allosteric modulators, including ligands that have entered clinical trials. Finally, we highlight emerging areas of research that hold promise to facilitate rational design of highly selective mGlu receptor-targeting therapeutics in the future. SIGNIFICANCE STATEMENT: The metabotropic glutamate receptors are attractive therapeutic targets for a range of psychiatric and neurological disorders. Over the past three decades, intense discovery efforts have yielded diverse pharmacological tools acting either competitively or allosterically, which have enabled dissection of fundamental biological process modulated by metabotropic glutamate receptors and established proof of concept for many therapeutic indications. We review metabotropic glutamate receptor molecular pharmacology and highlight emerging areas that are offering new avenues to selectively modulate neurotransmission.

Interclass GPCR heteromerization affects localization and trafficking

Membrane trafficking processes regulate G protein-coupled receptor (GPCR) activity. Although class A GPCRs are capable of activating G proteins in a monomeric form, they can also potentially assemble into functional GPCR heteromers. Here, we showed that the class A serotonin 5-HT2A receptors (5-HT2ARs) affected the localization and trafficking of class C metabotropic glutamate receptor 2 (mGluR2) through a mechanism that required their assembly as heteromers in mammalian cells. In the absence of agonists, 5-HT2AR was primarily localized within intracellular compartments, and coexpression of 5-HT2AR with mGluR2 increased the intracellular distribution of the otherwise plasma membrane-localized mGluR2. Agonists for either 5-HT2AR or mGluR2 differentially affected trafficking through Rab5-positive endosomes in cells expressing each component of the 5-HT2AR-mGluR2 heterocomplex alone, or together. In addition, overnight pharmacological 5-HT2AR blockade with clozapine, but not with M100907, decreased mGluR2 density through a mechanism that involved heteromerization between 5-HT2AR and mGluR2. Using TAT-tagged peptides and chimeric constructs that are unable to form the interclass 5-HT2AR-mGluR2 complex, we demonstrated that heteromerization was necessary for the 5-HT2AR-dependent effects on mGluR2 subcellular distribution. The expression of 5-HT2AR also augmented intracellular localization of mGluR2 in mouse frontal cortex pyramidal neurons. Together, our data suggest that GPCR heteromerization may itself represent a mechanism of receptor trafficking and sorting.

BET bromodomains as novel epigenetic targets for brain health and disease

Epigenetic pharmacotherapy for CNS-related diseases is a burgeoning area of research. In particular, members of the bromodomain and extra-terminal domain (BET) family of proteins have emerged as intriguing therapeutic targets due to their putative involvement in an array of brain diseases. With their ability to bind to acetylated histones and act as a scaffold for chromatin modifying complexes, BET proteins were originally thought of as passive epigenetic 'reader' proteins. However, new research depicts a more complex reality where BET proteins act as key nodes in lineage-specific and signal-dependent transcriptional mechanisms to influence disease-relevant functions. Amid a recent wave of drug development efforts from basic scientists and pharmaceutical companies, BET inhibitors are currently being studied in several CNS-related disease models, but safety and tolerability remain a concern. Here we review the progress in understanding the neurobiological mechanisms of BET proteins and the therapeutic potential of targeting BET proteins for brain health and disease.