Histone modifications around individual BDNF gene promoters in prefrontal cortex are associated with extinction of conditioned fear

Neurobiology and Treatment of Posttraumatic Stress Disorder

The recent worldwide surge of warfare and hostilities exposes increasingly large numbers of individuals to traumatic events, placing them at risk of developing posttraumatic stress disorder (PTSD) and challenging both clinicians and service delivery systems. This overview summarizes and updates the core knowledge of the genetic, molecular, and neural circuit features of the neurobiology of PTSD and advances in evidence-based psychotherapy, pharmacotherapy, neuromodulation, and digital treatments. While the complexity of the neurobiology and the biological and clinical heterogeneity of PTSD have challenged clinicians and researchers, there is an emerging consensus concerning the underlying mechanisms and approaches to diagnosis, treatment, and prevention of PTSD. This update addresses PTSD diagnosis, prevalence, course, risk factors, neurobiological mechanisms, current standard of care, and innovations in next-generation treatment and prevention strategies. It provides a comprehensive summary and concludes with areas of research for integrating advances in the neurobiology of the disorder with novel treatment and prevention targets.

Involvement of dysregulated hippocampal histone H3K9 methylation at the promoter of the BDNF gene in impaired memory extinction

RATIONALE

Since the precise mechanisms of posttraumatic stress disorder (PTSD) remain unknown, effective treatment interventions have not yet been established. Impaired extinction of fear memory (EFM) is one of the core symptoms of PTSD and is associated with stress-induced epigenetic change in gene expression.

OBJECTIVES

In this study, we examined whether the involvement of histone H3 lysine 9 dimethylation (H3K9me2) in EFM is mediated through brain-derived neurotrophic factor (BDNF) expression in the hippocampus, and whether BIX01294, a selective G9a and GLP histone methyltransferase inhibitor, could be treatment for impaired EFM in an animal model of PTSD.

METHODS

The single prolonged stress (SPS) paradigm was used to model PTSD. We measured BDNF mRNA levels by RT-PCR, and H3K9me2 levels in the BDNF gene promoters by chromatin immunoprecipitation-qPCR. After undergoing contextual fear conditioning and hippocampal injection of BIX01294, male rats were subjected to extinction training and extinction testing and their freezing times and BDNF mRNA levels were measured.

RESULTS

Compared to sham rats, SPS rats showed decreased BDNF mRNA levels 2 h after extinction training, no significant changes in levels of global H3K9me2 prior to extinction training, and increased levels of H3K9me2 in BDNF gene promoter IV, but not in BDNF gene promoter I. Administration of BIX01294 ameliorated the decrease in BDNF mRNA levels 2 h after extinction training and subsequently alleviated impaired EFM in extinction tests in SPS rats.

CONCLUSION

We conclude that reduced hippocampal levels of BDNF mRNA due to increase in H3K9me2 levels may play a role in PTSD-associated EFM impairment, and BIX01294 could be a PTSD treatment option.

Ketamine's Amelioration of Fear Extinction in Adolescent Male Mice Is Associated with the Activation of the Hippocampal Akt-mTOR-GluA1 Pathway

Fear-related disorders, including post-traumatic stress disorder (PTSD), and anxiety disorders are pervasive psychiatric conditions marked by persistent fear, stemming from its dysregulated acquisition and extinction. The primary treatment for these disorders, exposure therapy (ET), relies heavily on fear extinction (FE) principles. Adolescence, a vulnerable period for developing psychiatric disorders, is characterized by neurobiological changes in the fear circuitry, leading to impaired FE and increased susceptibility to relapse following ET. Ketamine, known for relieving anxiety and reducing PTSD symptoms, influences fear-related learning processes and synaptic plasticity across the fear circuitry. Our study aimed to investigate the effects of ketamine (10 mg/kg) on FE in adolescent male C57 BL/6 mice at the behavioral and molecular levels. We analyzed the protein and gene expression of synaptic plasticity markers in the hippocampus (HPC) and prefrontal cortex (PFC) and sought to identify neural correlates associated with ketamine's effects on adolescent extinction learning. Ketamine ameliorated FE in the adolescent males, likely affecting the consolidation and/or recall of extinction memory. Ketamine also increased the Akt and mTOR activity and the GluA1 and GluN2A levels in the HPC and upregulated BDNF exon IV mRNA expression in the HPC and PFC of the fear-extinguished mice. Furthermore, ketamine increased the c-Fos expression in specific brain regions, including the ventral HPC (vHPC) and the left infralimbic ventromedial PFC (IL vmPFC). Providing a comprehensive exploration of ketamine's mechanisms in adolescent FE, our study suggests that ketamine's effects on FE in adolescent males are associated with the activation of hippocampal Akt-mTOR-GluA1 signaling, with the vHPC and the left IL vmPFC as the proposed neural correlates.

Virtual realities, real recoveries: exploring the efficacy of 3MDR therapy for treatment-resistant PTSD

Exposure-based therapies have shown promise in treating post-traumatic stress disorder (PTSD), but challenges exist in maintaining patient engagement and finding appropriate stimuli for graded exposure. Virtual reality (VR) technology has been used to enhance exposure therapy, but current software lacks customization and some patients remain treatment-resistant. A novel approach called multimodular motion-assisted memory desensitization and reconsolidation (3MDR) has the potential to solve some of the current limitations of VR-assisted exposure therapy. This study examines the efficacy of 3MDR treatment for individuals with treatment-resistant PTSD through a systematic review of relevant literature and clinical studies. Preliminary findings indicate promise for 3MDR in reducing PTSD symptoms, including emotional regulation and moral injury. However, further research with larger samples and controlled studies is needed to understand underlying mechanisms and validate these results. Moreover, this study highlights the importance of health-economic evaluations to assess costs and resource utilization associated with implementing 3MDR treatment in clinical services.

DNA G-Quadruplex Is a Transcriptional Control Device That Regulates Memory

The conformational state of DNA fine-tunes the transcriptional rate and abundance of RNA. Here, we report that G-quadruplex DNA (G4-DNA) accumulates in neurons, in an experience-dependent manner, and that this is required for the transient silencing and activation of genes that are critically involved in learning and memory in male C57/BL6 mice. In addition, site-specific resolution of G4-DNA by dCas9-mediated deposition of the helicase DHX36 impairs fear extinction memory. Dynamic DNA structure states therefore represent a key molecular mechanism underlying memory consolidation.One-Sentence Summary: G4-DNA is a molecular switch that enables the temporal regulation of the gene expression underlying the formation of fear extinction memory.

Unlocking the epigenetic symphony: histone acetylation's impact on neurobehavioral change in neurodegenerative disorders

Recent genomics and epigenetic advances have empowered the exploration of DNA/RNA methylation and histone modifications crucial for gene expression in response to stress, aging and disease. Interest in understanding neuronal plasticity's epigenetic mechanisms, influencing brain rewiring amid development, aging and neurodegenerative disorders, continues to grow. Histone acetylation dysregulation, a commonality in diverse brain disorders, has become a therapeutic focus. Histone acetyltransferases and histone deacetylases have emerged as promising targets for neurodegenerative disorder treatment. This review delves into histone acetylation regulation, potential therapies and future perspectives for disorders like Alzheimer's, Parkinson's and Huntington's. Exploring genetic-environmental interplay through models and studies reveals molecular changes, behavioral insights and early intervention possibilities targeting the epigenome in at-risk individuals.

Epigenetics of Fear, Anxiety and Stress - Focus on Histone Modifications

Fear-, anxiety- and stress-related disorders are among the most frequent mental disorders. Given substantial rates of insufficient treatment response and often a chronic course, a better understanding of the pathomechanisms of fear-, anxiety- and stress-related disorders is urgently warranted. Epigenetic mechanisms such as histone modifications - positioned at the interface between the biological and the environmental level in the complex pathogenesis of mental disorders - might be highly informative in this context. The current state of knowledge on histone modifications, chromatin-related pharmacology and animal models modified for genes involved in the histone-related epigenetic machinery will be reviewed with respect to fear-, anxiety- and stress-related states. Relevant studies, published until 30th June 2022, were identified using a multi-step systematic literature search of the Pub- Med and Web of Science databases. Animal studies point towards histone modifications (e.g., H3K4me3, H3K9me1/2/3, H3K27me2/3, H3K9ac, H3K14ac and H4K5ac) to be dynamically and mostly brain region-, task- and time-dependently altered on a genome-wide level or gene-specifically (e.g., Bdnf) in models of fear conditioning, retrieval and extinction, acute and (sub-)chronic stress. Singular and underpowered studies on histone modifications in human fear-, anxiety- or stress-related phenotypes are currently restricted to the phenotype of PTSD. Provided consistent validation in human phenotypes, epigenetic biomarkers might ultimately inform indicated preventive interventions as well as personalized treatment approaches, and could inspire future innovative pharmacological treatment options targeting the epigenetic machinery improving treatment response in fear-, anxiety- and stressrelated disorders.

Monoamine Oxidase: A Potential Link in Papez Circuit to Generalized Anxiety Disorders

Anxiety is a common mental illness that affects a large number of people around the world, and its treatment is often based on the use of pharmacological substances such as benzodiazepines, serotonin, and 5-hydroxytyrosine (MAO) neurotransmitters. MAO neurotransmitters levels are deciding factors in the biological effects. This review summarizes the current understanding of the MAO system and its role in the modulation of anxiety-related brain circuits and behavior. The MAO-A polymorphisms have been implicated in the susceptibility to generalized anxiety disorder (GAD) in several investigations. The 5-HT system is involved in a wide range of physiological and behavioral processes, involving anxiety, aggressiveness, stress reactions, and other elements of emotional intensity. Among these, 5-HT, NA, and DA are the traditional 5-HT neurons that govern a range of biological activities, including sleep, alertness, eating, thermoregulation, pains, emotion, and memory, as anticipated considering their broad projection distribution in distinct brain locations. The DNMTs (DNA methyltransferase) protein family, which increasingly leads a prominent role in epigenetics, is connected with lower transcriptional activity and activates DNA methylation. In this paper, we provide an overview of the current state of the art in the elucidation of the brain's complex functions in the regulation of anxiety.

Histone deacetylase inhibitor RG2833 has therapeutic potential for Alzheimer's disease in females

Nearly two-thirds of patients with Alzheimer's are women. Identifying therapeutics specific for women is critical to lowering their elevated risk for developing this major cause of adult dementia. Moreover, targeting epigenetic processes that regulate multiple cellular pathways is advantageous given Alzheimer's multifactorial nature. Histone acetylation is an epigenetic process heavily involved in memory consolidation. Its disruption is linked to Alzheimer's. Through our computational studies, we predicted that the investigational drug RG2833 (N-[6-(2-aminoanilino)-6-oxohexyl]-4-methylbenzamide) has repurposing potential for Alzheimer's. RG2833 is a histone deacetylase HDAC1/3 inhibitor that is orally bioavailable and permeates the blood-brain-barrier. We investigated the RG2833 therapeutic potential in TgF344-AD rats, which are a model of Alzheimer's that exhibits age-dependent progression, thus mimicking this aspect of Alzheimer's patients that is difficult to establish in animal models. We investigated the RG2833 effects on cognitive performance, gene expression, and AD-like pathology in 11-month TgF344-AD female and male rats. A total of 89 rats were used: wild type n = 45 (17 females, 28 males), and TgF344-AD n = 44 (24 females, 20 males)] across multiple cohorts. No obvious toxicity was detected in the TgF344-AD rats up to 6 months of RG2833-treatment starting at 5 months of age administering the drug in rodent chow at ∼30mg/kg of body weight. We started treatment early in the course of pathology when therapeutic intervention is predicted to be more effective than in later stages of the disease. The drug-treatment significantly mitigated hippocampal-dependent spatial memory deficits in 11-month TgF344-AD females but not in males, compared to wild type littermates. This female sex-specific drug effect has not been previously reported. RG2833-treatment failed to ameliorate amyloid beta accumulation and microgliosis in female and male TgF344-AD rats. However, RNAseq analysis of hippocampal tissue from TgF344-AD rats showed that drug-treatment in females upregulated the expression of immediate early genes, such as Arc, Egr1 and c-Fos, and other genes involved in synaptic plasticity and memory consolidation. Remarkably, out of 17,168 genes analyzed for each sex, no significant changes in gene expression were detected in males at P < 0.05, false discovery rate < 0.05, and fold-change ≥ 1.5. Our data suggest that histone modifying therapeutics such as RG2833 improve cognitive behavior by modulating the expression of immediate early, neuroprotective and synaptic plasticity genes. Our preclinical study supports that RG2833 has therapeutic potential specifically for female Alzheimer's patients. RG2833 evaluations using other AD-related models is necessary to confirm our findings.

The role of epigenetics in anxiety disorders

Anxiety disorders (ADs) are extremely common psychiatric conditions that frequently co-occur with other physical and mental disorders. The pathophysiology of ADs is multifaceted and involves intricate connections among biological elements, environmental stimuli, and psychological mechanisms. Recent discoveries have highlighted the significance of epigenetics in bridging the gap between multiple risk factors that contribute to ADs and expanding our understanding of the pathomechanisms underlying ADs. Epigenetics is the study of how changes in the environment and behavior can have an impact on gene function. Indeed, researchers have found that epigenetic mechanisms can affect how genes are activated or inactivated, as well as whether they are expressed. Such mechanisms may also affect how ADs form and are protected. That is, the bulk of pharmacological trials evaluating epigenetic treatments for the treatment of ADs have used histone deacetylase inhibitors (HDACi), yielding promising outcomes in both preclinical and clinical studies. This review will provide an outline of how epigenetic pathways can be used to treat ADs or lessen their risk. It will also present the findings from preclinical and clinical trials that are currently available on the use of epigenetic drugs to treat ADs.

Predator-prey systems as models for integrative research in biology: the value of a non-consumptive effects framework

Predator-prey interactions are a cornerstone of many ecological and evolutionary processes that influence various levels of biological organization, from individuals to ecosystems. Predators play a crucial role in shaping ecosystems through the consumption of prey species and non-consumptive effects. Non-consumptive effects (NCEs) can induce changes in prey behavior, including altered foraging strategies, habitat selection, life history and anti-predator responses. These defensive strategies have physiological consequences for prey, affecting their growth, reproduction and immune function to name a few. Numerous experimental studies have incorporated NCEs in investigating predator-prey dynamics in the past decade. Interestingly, predator-prey systems can also be used as experimental models to answer physiology, cognition and adaptability questions. In this Commentary, I highlight research that uses NCEs in predator-prey systems to provide novel insights into cognition, adaptation, epigenetic inheritance and aging. I discuss the evolution of instinct, anxiety and other cognitive disorders, the shaping of brain connectomes, stress-induced aging and the development of behavioral coping styles. I outline how studies can integrate the investigation of NCEs with advanced behavioral, genomic and neurological tools to provide novel insights into physiological and cognitive health.

A Randomized, Double-Blind, Placebo-Controlled Study of an Anthocyanin-Rich Functional Ingredient on Cognitive Function and Eye Dryness in Late Adulthood Volunteers: Roles of Epigenetic and Gut Microbiome Modulations

Due to the rising demand for supplements targeting cognitive enhancement and dry eye together with the health benefits of anthocyanins, we have developed a functional soup containing an anthocyanin-rich functional ingredient, or "Anthaplex," and assessed the effects on cognitive function and eye dryness together with the possible mechanisms. A total of 69 male and female health volunteers were randomized and divided into placebo, D2, and D4 groups. All subjects consumed 120 mL of placebo or functional soup containing "Anthaplex" either at 2 or 4 g per serving per day within 5 min in the morning for eight weeks. The cognitive function, working memory, dry eye, AChE, MAO, MAO-A, MAO-B, and GABA-T activities, BDNF, HAC, HDAC, and DNMT activities, pH, and amount of lactic acid-producing bacteria, particularly Lactobacillus and Bifidobacterium spp. in feces, were determined before intervention and after eight weeks of consumption. Subjects who consumed the "Anthaplex" soup had improved cognitive function, working memory, eye dryness, histone acetylation, ACh E suppression, and BDNF with increased Bifidobacterium spp. but decreased pH in feces. These data suggest that "Anthaplex" improves cognitive function and eye dryness via the modulations of the histone acetylation process, gut microbiome, and cholinergic function.

Update on neurobiological mechanisms of fear: illuminating the direction of mechanism exploration and treatment development of trauma and fear-related disorders

Fear refers to an adaptive response in the face of danger, and the formed fear memory acts as a warning when the individual faces a dangerous situation again, which is of great significance to the survival of humans and animals. Excessive fear response caused by abnormal fear memory can lead to neuropsychiatric disorders. Fear memory has been studied for a long time, which is of a certain guiding effect on the treatment of fear-related disorders. With continuous technological innovations, the study of fear has gradually shifted from the level of brain regions to deeper neural (micro) circuits between brain regions and even within single brain regions, as well as molecular mechanisms. This article briefly outlines the basic knowledge of fear memory and reviews the neurobiological mechanisms of fear extinction and relapse, which aims to provide new insights for future basic research on fear emotions and new ideas for treating trauma and fear-related disorders.

On the origin and nature of nongenetic information in eumetazoans

Nongenetic information implies all the forms of biological information not related to genes and DNA in general. Despite the deep scientific relevance of the concept, we currently lack reliable knowledge about its carriers and origins; hence, we still do not understand its true nature. Given that genes are the targets of nongenetic information, it appears that a parsimonious approach to find the ultimate source of that information is to trace back the sequential steps of the causal chain upstream of the target genes up to the ultimate link as the source of the nongenetic information. From this perspective, I examine seven nongenetically determined phenomena: placement of locus-specific epigenetic marks on DNA and histones, changes in snRNA expression patterns, neural induction of gene expression, site-specific alternative gene splicing, predator-induced morphological changes, and cultural inheritance. Based on the available evidence, I propose a general model of the common neural origin of all these forms of nongenetic information in eumetazoans.

Face your fears: attenuating remote fear memories by reconsolidation-updating

Traumatic events generate some of the most enduring memories, yet little is known about how long-lasting fear memories can be attenuated. In this review, we collect the surprisingly sparse evidence on remote fear memory attenuation from both animal and human research. What is becoming apparent is twofold: although remote fear memories are more resistant to change compared with recent ones, they can nevertheless be attenuated when interventions are targeted toward the period of memory malleability instigated by memory recall, the reconsolidation window. We describe the physiological mechanisms underlying remote reconsolidation-updating approaches and highlight how they can be enhanced through interventions promoting synaptic plasticity. By capitalizing on an intrinsically relevant phase of memory, reconsolidation-updating harbors the potential to permanently alter remote fear memories.

Hearing Vocalizations during First Social Experience with Pups Increase Bdnf Transcription in Mouse Auditory Cortex

While infant cues are often assumed to innately motivate maternal response, recent research highlights how the neural coding of infant cues is altered through maternal care. Infant vocalizations are important social signals for caregivers, and evidence from mice suggests that experience caring for mouse pups induces inhibitory plasticity in the auditory cortex (AC), though the molecular mediators for such AC plasticity during the initial pup experience are not well delineated. Here, we used the maternal mouse communication model to explore whether transcription in AC of a specific, inhibition-linked, memory-associated gene, brain-derived neurotrophic factor (Bdnf) changes due to the very first pup caring experience hearing vocalizations, while controlling for the systemic influence of the hormone estrogen. Ovariectomized and estradiol or blank-implanted virgin female mice hearing pup calls with pups present had significantly higher AC exon IV Bdnf mRNA compared to females without pups present, suggesting that the social context of vocalizations induces immediate molecular changes at the site of auditory cortical processing. E2 influenced the rate of maternal behavior but did not significantly affect Bdnf mRNA transcription in the AC. To our knowledge, this is the first time Bdnf has been associated with processing social vocalizations in the AC, and our results suggest that it is a potential molecular component responsible for enhancing future recognition of infant cues by contributing to AC plasticity.

Gut-Brain cross talk: The pathogenesis of neurodevelopmental impairment in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating condition of multi-factorial origin that affects the intestine of premature infants and results in high morbidity and mortality. Infants that survive contend with several long-term sequelae including neurodevelopmental impairment (NDI)-which encompasses cognitive and psychosocial deficits as well as motor, vision, and hearing impairment. Alterations in the gut-brain axis (GBA) homeostasis have been implicated in the pathogenesis of NEC and the development of NDI. The crosstalk along the GBA suggests that microbial dysbiosis and subsequent bowel injury can initiate systemic inflammation which is followed by pathogenic signaling cascades with multiple pathways that ultimately lead to the brain. These signals reach the brain and activate an inflammatory cascade in the brain resulting in white matter injury, impaired myelination, delayed head growth, and eventual downstream NDI. The purpose of this review is to summarize the NDI seen in NEC, discuss what is known about the GBA, explore the relationship between the GBA and perinatal brain injury in the setting of NEC, and finally, highlight the existing research into possible therapies to help prevent these deleterious outcomes.

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.

L-Serine Influences Epigenetic Modifications to Improve Cognition and Behaviors in Growth Hormone-Releasing Hormone Knockout Mice

Neurodegenerative diseases feature changes in cognition, and anxiety-like and autism-like behaviors, which are associated with epigenetic alterations such as DNA methylation and histone modifications. The amino acid L-serine has been shown to have beneficial effects on neurological symptoms. Here, we found that growth hormone-releasing hormone knockout (GHRH-KO) mice, a GH-deficiency mouse model characterized by extended lifespan and enhanced insulin sensitivity, showed a lower anxiety symptom and impairment of short-term object recognition memory and autism-like behaviors. Interestingly, L-serine administration exerted anxiolytic effects in mice and ameliorated the behavioral deficits in GHRH-KO. L-serine treatment upregulated histone epigenetic markers of H3K4me, H3K9ac, H3K14ac and H3K18ac in the hippocampus and H3K4me in the cerebral cortex in both GHRH-KO mice and wild type controls. L-serine-modulated epigenetic marker changes, in turn, were found to regulate mRNA expression of BDNF, grm3, foxp1, shank3, auts2 and marcksl1, which are involved in anxiety-, cognitive- and autism-like behaviors. Our study provides a novel insight into the beneficial effects of L-serine intervention on neuropsychological impairments.

Association of DNA methylation with energy and fear-related behaviors in canines

Introduction

Behavioral traits are influenced by gene by environment interactions. To study the genetic and epigenetic components of behavior, we analyzed whether dog behavioral traits could be predicted by their DNA methylation and genotypes.

Methods

We conducted an analysis on dog behaviors such as sociability, trainability and energy as measured by Canine Behavioral and Research Assessment Questionnaire (C-BARQ) behavioral surveys paired with buccal swabs from 46 dogs. Previously we used targeted bisulfite sequencing to analyze DNA methylation and collected genotype data from over 1,500 single nucleotide polymorphisms (SNPs). Owner-reported C-BARQ responses were used to quantify 14 behavioral trait values.

Results

Using Partial Least Squares (PLS) Regression analysis we found behavioral traits such as energy, attachment/attention-seeking, non-social fear, and stranger-directed fear to be significantly associated with DNA methylation across 3,059 loci. After we adjusted for age as a confounding variable, energy and stranger-directed fear remained significantly associated with methylation. We found that most behavioral traits were not predictable by our limited set of SNPs.

Discussion

By identifying individual genes whose methylation is significantly associated with behavioral traits, we generate hypotheses about possible mechanisms involved in behavioral regulation. Overall, our study extends previous work in behavioral epigenetics, shows that canine behaviors are predictable by DNA methylation, and serves as a proof of concept for future studies in behavioral epigenetics.

Epigenetic histone acetylation modulating prenatal Poly I:C induced neuroinflammation in the prefrontal cortex of rats: a study in a maternal immune activation model

Introduction: Neuroinflammation in the central nervous system, particularly the prefrontal cortex (PFC), plays a role in the pathogenesis of schizophrenia, which has been found to be associated with maternal immune activation (MIA). Recent evidence suggests that epigenetic regulation involves in the MIA-induced neurodevelopmental disturbance. However, it is not well-understood how epigenetic modulation is involved in the neuroinflammation and pathogenesis of schizophrenia.

Methods: This study explored the modulation of histone acetylation in both neuroinflammation and neurotransmission using an MIA rat model induced by prenatal polyriboinosinic-polyribocytidylic acid (Poly I:C) exposure, specifically examining those genes that were previously observed to be impacted by the exposure, including a subunit of nuclear factor kappa-B (Rela), Nod-Like-Receptor family Pyrin domain containing 3 (Nlrp3), NMDA receptor subunit 2A (Grin2a), 5-HT2A (Htr2a), and GABAA subunit β3 (Gabrb3).

Results: Our results revealed global changes of histone acetylation on H3 (H3ace) and H4 (H4ace) in the PFC of offspring rats with prenatal Poly I:C exposure. In addition, it revealed enhancement of both H3ace and H4ace binding on the promoter region of Rela, as well as positive correlations between Rela and genes encoding histone acetyltransferases (HATs) including CREB-binding protein (CBP) and E1A-associated protein p300 (EP300). Although there was no change in H3ace or H4ace enrichment on the promoter region of Nlrp3, a significant enhancement of histone deacetylase 6 (HDAC6) binding on the promoter region of Nlrp3 and a positive correlation between Nlrp3 and Hdac6 were also observed. However, prenatal Poly I:C treatment did not lead to any specific changes of H3ace and H4ace on the promoter region of the target genes encoding neurotransmitter receptors in this study.

Discussion: These findings demonstrated that epigenetic modulation contributes to NF-κB/NLRP3 mediated neuroinflammation induced by prenatal Poly I:C exposure via enhancement of histone acetylation of H3ace and H4ace on Rela and HDAC6-mediated NLRP3 transcriptional activation. This may further lead to deficits in neurotransmissions and schizophrenia-like behaviors observed in offspring.

A narrative review of the epigenetics of post-traumatic stress disorder and post-traumatic stress disorder treatment

Epigenetic research in post-traumatic stress disorder (PTSD) is essential, given that environmental stressors and fear play such a crucial role in its development. As such, it may provide a framework for understanding individual differences in the prevalence of the disorder and in treatment response. This paper reviews the epigenetic markers associated with PTSD and its treatment, including candidate genes and epigenome-wide studies. Because the etiopathogenesis of PTSD rests heavily on learning and memory, we also draw upon animal neuroepigenetic research on the acquisition, update and erasure of fear memory, focusing on the mechanisms associated with memory reconsolidation. Reconsolidation blockade (or impairment) treatment in PTSD has been studied in clinical trials and, from a neurological perspective, may hold promise for identifying epigenetic markers of successful therapy. We conclude this paper by discussing several key considerations and challenges in epigenetic research on PTSD in humans.

Intra-mPFC injection of sodium butyrate promotes BDNF expression and ameliorates extinction recall impairment in an experimental paradigm of post-traumatic stress disorder

Objectives

Therapeutic strategies that facilitate extinction are promising in the treatment of post-traumatic stress disorder (PTSD). Brain-derived neurotrophic factor (BDNF) has a crucial role in neural plasticity, a process needed for the retention of fear extinction. In this study, we investigated the effects of local administration of a histone deacetylase (HDAC) inhibitor, sodium butyrate (NaBu), on BDNF transcription and behavioral markers of extinction in the single prolonged stress (SPS) model of PTSD.

Materials and Methods

NaBu was infused into the infralimbic (IL) subregion of the medial prefrontal cortex (mPFC) of male rats. The freezing response was recorded as the criterion to assess fear strength on the day of extinction as well as 24 hr later in the retention test. Other behavioral tests were also measured to evaluate the anxiety level, locomotor activity, and working memory on the retention day. HDAC activity and BDNF mRNA expression were evaluated after the behavioral experiments.

Results

NaBu facilitated the recall of fear extinction in SPS rats (P<0.0001). SPS rats had higher HDAC activity (P<0.0001) and lower BDNF expression (P<0.05) than non-SPS animals. Also, anxiety was higher in the SPS group (P<0.0001), but locomotor activity (P=0.61) and working memory (P=0.36) were not different between SPS and Non-SPS groups.

Conclusion

Our findings provide evidence that the mechanism of action of NaBu in the improvement of extinction recall is mediated, in part, by enhancing histone acetylation and reviving BDNF expression in IL.

Epigenetic mechanisms regulate cue memory underlying discriminative behavior

The burgeoning field of neuroepigenetics has introduced chromatin modification as an important interface between experience and brain function. For example, epigenetic mechanisms like histone acetylation and DNA methylation operate throughout a lifetime to powerfully regulate gene expression in the brain that is required for experiences to be transformed into long-term memories. This review highlights emerging evidence from sensory models of memory that converge on the premise that epigenetic regulation of activity-dependent transcription in the sensory brain facilitates highly precise memory recall. Chromatin modifications may be key for neurophysiological responses to transient sensory cue features experienced in the "here and now" to be recapitulated over the long term. We conclude that the function of epigenetic control of sensory system neuroplasticity is to regulate the amount and type of sensory information retained in long-term memories by regulating neural representations of behaviorally relevant cues that guide behavior. This is of broad importance in the neuroscience field because there are few circumstances in which behavioral acts are devoid of an initiating sensory experience.

Epigenetics of Autism Spectrum Disorder: Histone Deacetylases

The etiology of autism spectrum disorder (ASD) remains unknown, but gene-environment interactions, mediated through epigenetic mechanisms, are thought to be a key contributing factor. Prenatal environmental factors have been shown to be associated with both increased risk of ASD and altered histone deacetylases (HDACs) or acetylation levels. The relationship between epigenetic changes and gene expression in ASD suggests that alterations in histone acetylation, which lead to changes in gene transcription, may play a key role in ASD. Alterations in the acetylome have been demonstrated for several genes in ASD, including genes involved in synaptic function, neuronal excitability, and immune responses, which are mechanisms previously implicated in ASD. We review preclinical and clinical studies that investigated HDACs and autism-associated behaviors and discuss risk genes for ASD that code for proteins associated with HDACs. HDACs are also implicated in neurodevelopmental disorders with a known genetic etiology, such as 15q11-q13 duplication and Phelan-McDermid syndrome, which share clinical features and diagnostic comorbidities (e.g., epilepsy, anxiety, and intellectual disability) with ASD. Furthermore, we highlight factors that affect the behavioral phenotype of acetylome changes, including sensitive developmental periods and brain region specificity in the context of epigenetic programming.

ADRAM is an experience-dependent long noncoding RNA that drives fear extinction through a direct interaction with the chaperone protein 14-3-3

Here, we used RNA capture-seq to identify a large population of lncRNAs that are expressed in the infralimbic prefrontal cortex of adult male mice in response to fear-related learning. Combining these data with cell-type-specific ATAC-seq on neurons that had been selectively activated by fear extinction learning, we find inducible 434 lncRNAs that are derived from enhancer regions in the vicinity of protein-coding genes. In particular, we discover an experience-induced lncRNA we call ADRAM (activity-dependent lncRNA associated with memory) that acts as both a scaffold and a combinatorial guide to recruit the brain-enriched chaperone protein 14-3-3 to the promoter of the memory-associated immediate-early gene Nr4a2 and is required fear extinction memory. This study expands the lexicon of experience-dependent lncRNA activity in the brain and highlights enhancer-derived RNAs (eRNAs) as key players in the epigenomic regulation of gene expression associated with the formation of fear extinction memory.

Wei et al. use targeted RNA capture sequencing to examine experience-dependent long noncoding RNA activity in the infralimbic prefrontal cortex of adult mice. They discover a gene, which they call ADRAM, that is directly involved in the epigenomic regulation of gene expression underlying memory formation.

Sex-dependent effects of chronic exercise on cognitive flexibility but not hippocampal Bdnf in aging mice

Cognitive impairments associated with advanced age involve alterations in the hippocampus that changes with experience throughout life. The hippocampus is critical for cognitive flexibility involved with extinction and reinstatement of conditioned fear. It is widely accepted that regular exercise can be beneficial for hippocampal function. Therefore, we asked whether chronic voluntary exercise in middle-aged mice can improve extinction and/or reinstatement of conditioned fear compared with standard-housing. Eight-month-old male and female C57Bl/6J mice had access to a running wheel or remained in standard-housing until 11 months of age. Alongside control standard-housed young adult (3-month-old) mice, they received tone-footshock pairings, which were subsequently extinguished with tone-alone presentations the next day. Half of the mice then received a reminder in the form of a single footshock. Male and female 11-month-old mice housed in standard conditions exhibited impaired reinstatement compared with young adult mice. However, for males that had access to a running wheel from 8 months of age, the reminder treatment rescued reinstatement ability. This was not observed in females. Additionally, exercise during middle age in both sexes increased expression of brain-derived neurotrophic factor (Bdnf) mRNA in the hippocampus, specifically exon 4 mRNA. These results show that, at least for males, physical exercise is beneficial for reducing age-related decline in cognitive abilities. Despite not affecting reinstatement, exercise also increased Bdnf gene expression in the female hippocampus, which could potentially benefit other forms of hippocampus-dependent cognition.

Prefrontal cortex, amygdala, and threat processing: implications for PTSD

Posttraumatic stress disorder can be viewed as a disorder of fear dysregulation. An abundance of research suggests that the prefrontal cortex is central to fear processing-that is, how fears are acquired and strategies to regulate or diminish fear responses. The current review covers foundational research on threat or fear acquisition and extinction in nonhuman animals, healthy humans, and patients with posttraumatic stress disorder, through the lens of the involvement of the prefrontal cortex in these processes. Research harnessing advances in technology to further probe the role of the prefrontal cortex in these processes, such as the use of optogenetics in rodents and brain stimulation in humans, will be highlighted, as well other fear regulation approaches that are relevant to the treatment of posttraumatic stress disorder and involve the prefrontal cortex, namely cognitive regulation and avoidance/active coping. Despite the large body of translational research, many questions remain unanswered and posttraumatic stress disorder remains difficult to treat. We conclude by outlining future research directions related to the role of the prefrontal cortex in fear processing and implications for the treatment of posttraumatic stress disorder.

Oxytocin in dorsal hippocampus facilitates auditory fear memory extinction in rats

Fear extinction is impaired in some psychiatric disorders. Any treatment that facilitates the extinction of fear is a way to advance the treatment of related psychiatric disorders. Recent studies have highlighted the role of oxytocin (OT) in fear extinction, but the endogenous release of OT during fear extinction in the dorsal hippocampal (dHPC) is not clear. We investigated the release of OT during fear extinction and the role of the HPC - medial prefrontal cortex (mPFC) circuit and BDNF in the effects of exogenous OT on auditory fear conditioning in male rats. We found that the release of endogenous OT in the dHPC is significantly increased during the fear extinction process as measured by the microdialysis method. Increased freezing response in the OT-treated rats compared to saline-treated rats showed that exogenous OT in the dHPC enhanced the fear extinction. Injection of BDNF antagonist (ANA-12) into the infralimbic (IL) blocked the effect of exogenous OT on the dHPC. Following OT injection, BDNF levels increased in the dHPC, ventral HPC, and IL cortex; but decreased in the prelimbic cortex (PL). Finally, OT microinjected into the dHPC significantly increased neural activity of pyramidal neurons of the CA1-vHPC and IL but decreased the neural activity in the PL cortex. Our findings strongly support that the dHPC endogenous OT plays a crucial role in enhancing fear extinction. It seems that the activation of the HPC-mPFC pathway, and consequently, the release of BDNF in the IL cortex mediates the enhancing effects of OT on fear extinction.

Aspirin ameliorates the cognition impairment in mice following benzo[a]pyrene treatment via down-regulating BDNF IV methylation

Benzo[a]pyrene (B[a]P) is neurotoxic, however, the mechanisms remain unclear and there is no effective prevention. Available evidence suggests a role of DNA methylation in B[a]P-induced neurotoxicity. This study investigated the brain-derived neurotrophic factor (BDNF) IV methylation in the development of and aspirin intervention against B[a]P's neurotoxicity in mice and HT22 cells. Mice were intraperitoneally treated with solvent or B[a]P (0.5, 2, and 10 mg/kg b.w.) for 60 days. An intervention group was treated simultaneously with B[a]P (10 mg/kg, i.p.) and aspirin (10 mg/kg, daily water-drinking). The treated mice showed a dose-dependent cognitive and behavioral impairment, and cerebral cell apoptosis, which were alleviated by aspirin co-treatment. Following B[a]P treatment, DNA methyltransferase (DNMTs) and BDNF IV hypermethylation were increased in the cerebral cortex of mice compared to controls, while significant decreases were found in BDNF IV and BDNF mRNA, and BDNF protein levels. Aspirin co-treatment rescued DNMTs activation and BDNF IV hypermethylation, and mitigated the recession in BDNF mRNA and protein induced by B[a]P treatment. Similar results were shown in HT22 cells. These findings reveal a critical role of BDNF IV methylation in the neurotoxicity of B[a]P, and demonstrate a promising prevention of aspirin against B[a]P-induced cognitive impairment via inhibiting BDNF IV hypermethylation.

A Review on Epigenetic Inheritance of Experiences in Humans

If genetics defines the inheritance of DNA, epigenetics aims to regulate and make it adaptable. Epigenetic alterations include DNA methylation, chromatin remodelling, post-translational modifications of histone proteins and activity of non-coding RNAs. Several studies, especially in animal models, have reported transgenerational inheritance of epigenetic marks. However, evidence of transgenerational inheritance in humans via germline in the absence of any direct exposure to the driving external stimulus remains controversial. Most of the epimutations exist in relation with genetic variants. The present review looks at intergenerational and transgenerational inheritance in humans, (both father and mother) in response to diet, exposure to chemicals, stress, exercise, and disease status. If not transgenerational, at least intergenerational human studies could help to understand early processes of inheritance. In humans, female and male germline development follow separate paths of epigenetic events and both oocyte and sperm possess their own unique epigenomes. While DNA methylation alterations are reset during epigenetic reprogramming, non-coding RNAs via human sperm provide evidence of being reliable carriers for transgenerational inheritance. Human studies reveal that one mechanism of epigenetic inheritance cannot be applied to the complete human genome. Multiple factors including time, type, and tissue of exposure determine if the modified epigenetic mark could be transmissible and till which generation. Population-specific differences should also be taken into consideration while associating inheritance to an environmental exposure. A longitudinal study targeting one environmental factor, but different population groups should be conducted at a specific geographical location to pinpoint heritable epigenetic changes.

Epigenetic Mechanisms in Memory and Cognitive Decline Associated with Aging and Alzheimer's Disease

Epigenetic mechanisms, which include DNA methylation, a variety of post-translational modifications of histone proteins (acetylation, phosphorylation, methylation, ubiquitination, sumoylation, serotonylation, dopaminylation), chromatin remodeling enzymes, and long non-coding RNAs, are robust regulators of activity-dependent changes in gene transcription. In the brain, many of these epigenetic modifications have been widely implicated in synaptic plasticity and memory formation. Dysregulation of epigenetic mechanisms has been reported in the aged brain and is associated with or contributes to memory decline across the lifespan. Furthermore, alterations in the epigenome have been reported in neurodegenerative disorders, including Alzheimer’s disease. Here, we review the diverse types of epigenetic modifications and their role in activity- and learning-dependent synaptic plasticity. We then discuss how these mechanisms become dysregulated across the lifespan and contribute to memory loss with age and in Alzheimer’s disease. Collectively, the evidence reviewed here strongly supports a role for diverse epigenetic mechanisms in memory formation, aging, and neurodegeneration in the brain.

Gadd45α is involved in regulating activity-dependent and exon-specific BDNF expression in postmitotic cortical neurons

OBJECTIVE

This study aimed to explore the epigenetic regulation of activity-dependent and exon-specific brain-derived neurotrophic factor (BDNF) expression under KCl depolarization in primary cortical neurons.

METHODS

We investigated BDNF exon I, exon IV and the growth arrest and DNA damage-inducible protein 45 alpha (Gadd45α) transcription levels under KCl-induced neuronal activation in postmitotic neurons. Gadd45α occupancy at BDNF I and IV promoter was measured by chromatin immunoprecipitation (ChIP) followed by quantitative PCR; DNA methylation level was checked by methylated DNA immunoprecipitation (MeDIP) followed by qPCR. In addition, lentiviral shRNA targeting Gadd45α was used to knockdown Gadd45α expression.

RESULTS

BDNF exon I and IV mRNA expressions were both highly induced by KCl depolarization. However, ChIP analysis demonstrated a significantly increased Gadd45α occupancy only at the BDNF P1 promotor, but not P4, which is associated with reducing DNA methylation within BDNF P1 promoter. Furthermore, after the lentiviral-mediated knockdown of Gadd45α, the increased Gadd45α occupancy at the BDNF P1 was inhibited, which was accompanying the complete blocking of the demethylation effect at P1. Nonetheless, the induction of BDNF exon I mRNA by KCl was only partially prevented by Gadd45α shRNA, indicting other mechanisms involved in regulating BDNF exon I expression.

CONCLUSIONS

DNA demethylation mediated by Gadd45α protein involves promoting the regulation of activity-dependent BDNF exon I expression in neurons.

Transcriptomic signature of extinction learning in the brain of the fire-bellied toad, Bombina orientalis

Insight into the molecular and cellular mechanisms of learning and memory from a diverse array of taxa contributes to our understanding of the evolution of these processes. The fire-bellied toad, Bombina orientalis, is a basal anuran amphibian model species who could help us describe shared and divergent characteristics of learning and memory mechanisms between amphibians and other vertebrates, and hence answer questions about the evolution of learning. Utilizing next generation sequencing techniques, we profiled gene expression patterns associated with the extinction of prey-catching conditioning in the brain of the fire-bellied toad. For this purpose, gene expression was at first compared between toads sacrificed after acquisition and extinction of the conditioned response. A second comparison was done between toads submitted to extinction following either short or long acquisition training, which results in toads displaying response extinction or resistance to extinction, respectively. We analyzed brain tissue transcription profiles common to both acquisition and extinction learning, or unique to extinction learning and resistance to extinction, and found significant overlap in gene expression related to molecular pathways involving neuronal plasticity (e.g. structural modification, transcription). However, extinction learning induced a unique GABAergic transcriptomic signal, which may be responsible for suppression of the original response memory. Further, when comparing extinction learning in short- and long-trained groups, short training engaged many pathways related to neuronal plasticity, as expected, but long training engaged molecular pathways related to the suppression of learning through epigenetic mediated transcriptional suppression and inhibitory neurotransmission. Overall, gene expression patterns associated with extinction learning in the fire-bellied toad were similar to those found in mammals submitted to extinction, although some divergent profiles highlighted potential differences in the mechanisms of learning and memory among tetrapods.

BDNF genotype Val66Met interacts with acute plasma BDNF levels to predict fear extinction and recall

Brain-derived neurotropic factor (BDNF) is a potent regulator of memory processes and is believed to influence the consolidation of fear extinction memories. No previous human study has tested the effect of unstimulated BDNF on fear extinction recall, and no study has tested the association between plasma BDNF levels and psychophysiological responding during an extinction paradigm. We tested the association between fear responses during a 2-day differential conditioning, extinction and extinction recall paradigm and Val66Met genotype in a group of healthy participants (N = 191). There were no group differences during habituation or acquisition. Met allele carriers compared to Val homozygotes displayed higher responses to the CS + compared to the CS- during extinction learning and had higher responding to both the CS+ and CS- during extinction recall. Plasma levels of BDNF protein that were collected in a sub-sample of the group (n = 56) moderated the effect of Met allele presence, such that lower BDNF level was associated with higher skin conductance response in the Met but not Val group to the CS+ during extinction learning and to both the CS+ and CS- during extinction recall. The current results extend previous observations of a Val66Met effect during fear extinction learning to extinction recall and show for the first time that these effects are moderated by plasma BDNF level.

Rubinstein-Taybi Syndrome: A Model of Epigenetic Disorder

The Rubinstein-Taybi syndrome (RSTS) is a rare congenital developmental disorder characterized by a typical facial dysmorphism, distal limb abnormalities, intellectual disability, and many additional phenotypical features. It occurs at between 1/100,000 and 1/125,000 births. Two genes are currently known to cause RSTS, CREBBP and EP300, mutated in around 55% and 8% of clinically diagnosed cases, respectively. To date, 500 pathogenic variants have been reported for the CREBBP gene and 118 for EP300. These two genes encode paralogs acting as lysine acetyltransferase involved in transcriptional regulation and chromatin remodeling with a key role in neuronal plasticity and cognition. Because of the clinical heterogeneity of this syndrome ranging from the typical clinical diagnosis to features overlapping with other Mendelian disorders of the epigenetic machinery, phenotype/genotype correlations remain difficult to establish. In this context, the deciphering of the patho-physiological process underlying these diseases and the definition of a specific episignature will likely improve the diagnostic efficiency but also open novel therapeutic perspectives. This review summarizes the current clinical and molecular knowledge and highlights the epigenetic regulation of RSTS as a model of chromatinopathy.

The Contribution of Epigenetic Inheritance Processes on Age-Related Cognitive Decline and Alzheimer's Disease

During the last years, epigenetic processes have emerged as important factors for many neurodegenerative diseases, such as Alzheimer’s disease (AD). These complex diseases seem to have a heritable component; however, genome-wide association studies failed to identify the genetic loci involved in the etiology. So, how can these changes be transmitted from one generation to the next? Answering this question would allow us to understand how the environment can affect human populations for multiple generations and explain the high prevalence of neurodegenerative diseases, such as AD. This review pays particular attention to the relationship among epigenetics, cognition, and neurodegeneration across generations, deepening the understanding of the relevance of heritability in neurodegenerative diseases. We highlight some recent examples of EI induced by experiences, focusing on their contribution of processes in learning and memory to point out new targets for therapeutic interventions. Here, we first describe the prominent role of epigenetic factors in memory processing. Then, we briefly discuss aspects of EI. Additionally, we summarize evidence of how epigenetic marks inherited by experience and/or environmental stimuli contribute to cognitive status offspring since better knowledge of EI can provide clues in the appearance and development of age-related cognitive decline and AD.

Ubiquitination of Histone H2B by Proteasome Subunit RPT6 Controls Histone Methylation Chromatin Dynamics During Memory Formation

BACKGROUND

Posttranslational histone modifications play a critical role in the regulation of gene transcription underlying synaptic plasticity and memory formation. One such epigenetic change is histone ubiquitination, a process that is mediated by the ubiquitin-proteasome system in a manner similar to that by which proteins are normally targeted for degradation. However, histone ubiquitination mechanisms are poorly understood in the brain and in learning. In this article, we describe a new role for the ubiquitin-proteasome system in histone crosstalk, showing that learning-induced monoubiquitination of histone H2B (H2Bubi) is required for increases in the transcriptionally active H3 lysine 4 trimethylation (H3K4me3) mark at learning-related genes in the hippocampus.

METHODS

Using a series of molecular, biochemical, electrophysiological, and behavioral experiments, we interrogated the effects of short interfering RNA-mediated knockdown and CRISPR (clustered regularly interspaced short palindromic repeats)-mediated upregulation of ubiquitin ligases, deubiquitinating enzymes and histone methyltransferases in the rat dorsal hippocampus during memory consolidation.

RESULTS

We show that H2Bubi recruits H3K4me3 through a process that is dependent on the 19S proteasome subunit RPT6 and that a loss of H2Bubi in the hippocampus prevents learning-induced increases in H3K4me3, gene transcription, synaptic plasticity, and memory formation. Furthermore, we show that CRISPR-dCas9-mediated increases in H2Bubi promote H3K4me3 and memory formation under weak training conditions and that promoting histone methylation does not rescue memory impairments resulting from loss of H2Bubi.

CONCLUSIONS

These results suggest that H2B ubiquitination regulates histone crosstalk in learning by way of nonproteolytic proteasome function, demonstrating a novel mechanism by which histone modifications are coordinated in response to learning.

Dysregulation of miR-15a-5p, miR-497a-5p and miR-511-5p Is Associated with Modulation of BDNF and FKBP5 in Brain Areas of PTSD-Related Susceptible and Resilient Mice

Post-traumatic stress disorder (PTSD) is a neuropsychiatric disorder occurring in susceptible individuals following a traumatic event. Understanding the mechanisms subserving trauma susceptibility/resilience is essential to develop new effective treatments. Increasing evidence suggests that non-coding RNAs, such as microRNAs (miRNAs), may play a prominent role in mediating trauma susceptibility/resilience. In this study, we evaluated the transcriptional expression of two key PTSD-related genes (FKBP5 and BDNF) and the relative targeting miRNAs (miR-15a-5p, miR-497a-5p, miR-511-5p, let-7d-5p) in brain areas of PTSD-related susceptible and resilient mice identified through our recently developed mouse model of PTSD (arousal-based individual screening (AIS) model). We observed lower transcript levels of miR-15a-5p, miR-497a-5p, and miR-511a-5p in the hippocampus and hypothalamus of susceptible mice compared to resilient mice, suggesting that the expression of these miRNAs could discriminate the two different phenotypes of stress-exposed mice. These miRNA variations could contribute, individually or synergically, to the inversely correlated transcript levels of FKBP5 and BDNF. Conversely, in the medial prefrontal cortex, downregulation of miR-15a-5p, miR-511-5p, and let-7d-5p was observed both in susceptible and resilient mice, and not accompanied by changes in their mRNA targets. Furthermore, miRNA expression in the different brain areas correlated to stress-induced behavioral scores (arousal score, avoidance-like score, social memory score and PTSD-like score), suggesting a linear connection between miRNA-based epigenetic modulation and stress-induced phenotypes. Pathway analysis of a miRNA network showed a statistically significant enrichment of molecular processes related to PTSD and stress. In conclusion, our results indicate that PTSD susceptibility/resilience might be shaped by brain-area-dependent modulation of miRNAs targeting FKBP5, BDNF, and other stress-related genes.

Epigenetic modification of BDNF mediates neuropathic pain via miR-30a-3p/EP300 axis in CCI rats

Recent investigation of microRNAs on chronic pain has developed a breakthrough in neuropathic pain management. In the present study, decreased expression of miR-30a-3p was reported using qRT-PCR analysis and loss of miR-30a-3p promoted neuropathic pain progression in sciatic nerve chronic constrictive injury rats through determining the pain threshold. We predicted miR-30a-3p could target E-cadherin transcriptional activator (EP300) via bioinformatics analysis. Meanwhile, we found that brain-derived neurotrophic factor (BDNF) is involved in neuropathic pain. Here, we exhibited that EP300 epigenetically up-regulated BDNF via enhancing acetylated histone H3 and H4 on the promoter. For another, miR-30a-3p was able to modify the level of BDNF and acetylated histone H3 and H4. Loss of miR-30a-3p enhanced EP300 and BDNF colocalization in CCI rats. Subsequently, it was shown that increased EP300 induced neuropathic pain by an enhancement of neuronal BDNF level in vivo. To sum up, it was revealed that epigenetic modification of BDNF promoted neuropathic pain via EP300 induced by miR-30a-3p in CCI rats.

Sensory cortical and subcortical auditory neurophysiological changes predict cue-specific extinction behavior enabled by the pharmacological inhibition of an epigenetic regulator during memory formation

Extinction learning and memory have been broadly investigated at both behavioral and neural levels, but sensory system contributions to extinction processes have been less explored. Using a sound-reward extinction paradigm in male rats, we reveal both cortical and subcortical forms of plasticity associated with the cue-specificity of behavioral extinction memory. In the auditory cortex, frequency tuning narrowed by up to two-thirds of an octave around the remembered extinguished sound cue. Subcortical signals revealed in the auditory brainstem response (ABR) in the same animals developed smaller amplitudes of some (but not all) ABR peaks evoked by the extinguished sound frequency. Interestingly, treatment with an inhibitor of histone deacetylase 3 (HDAC3-i) facilitated both auditory cortical tuning bandwidth changes and changes in subcortical peak amplitude evoked only by the extinguished sound frequency. These neurophysiological changes were correlated to each other, and to the highly precise extinction behavior enabled by HDAC3-i (compared to vehicle controls). Thus, we show for the first time that HDAC3 regulates the specificity of sensory features consolidated in extinction memory. Further, the sensory cortical changes in tuning bandwidth recapitulate known effects of blocking HDAC3 to enhance cue specificity in other behavioral tasks. Therefore, the findings demonstrate how some forms of sensory neuroplasticity may encode specific sensory features of learning experiences in order to enable cue-specific behaviors.

Sodium butyrate as a selective cognitive enhancer for weak or impaired memory

Several recent studies showed that memory can be modulated by manipulating chromatin modifications using histone deacetylase (HDAC) inhibitors during memory formation, consolidation, and reconsolidation. We used a context fear conditioning paradigm with minimal non-painful current as a reinforcement, what elicited alertness to the context and freezing during tests in rats. Such paradigm resulted in a relatively weak memory in significant part of the rats. Here, we demonstrate that intraperitoneal administration of the HDAC inhibitor sodium butyrate immediately following memory reactivation, produced memory enhancement in rats with weak memory, however, not in rats with strong memory. Additionally, we investigated the ability of the HDAC inhibitor sodium butyrate to restore the contextual memory impaired due to the blockade of protein synthesis during memory reactivation. The results obtained evidence that the HDAC inhibitor sodium butyrate reinstated the impaired contextual memory. This enhancement effect is consistent with other studies demonstrating a role for HDAC inhibitors in the facilitation of contextual fear.

Class I HDAC inhibition improves object recognition memory consolidation through BDNF/TrkB pathway in a time-dependent manner

There is increasing evidence showing that HDACs regulates BDNF (brain-derived neurotrophic factor) expression through its interaction with the Bdnf gene promoter, a key regulator to consolidate memory. Although the nuclear mechanisms regulated by HDACs that control BDNF expression have been partially described recently, the temporal events for memory consolidation remain unknown. Hence, in this work, we studied the temporal pattern for the activation of the BDNF/TrkB pathway through class I HDAC inhibition to enhance object recognition memory (ORM) consolidation. To this end, we inhibited class I HDAC into the insular cortex (IC) and a weak ORM protocol was used to assess temporal expression and function of the BDNF/TrkB pathway in the IC. We found that cortical class I HDAC inhibition enhanced long-term ORM, coincident with a clear peak of BDNF expression at 4 h after acquisition. Furthermore, the tyrosine kinase B (TrkB) receptor blockade at 4 h, but not at 8 h, impaired the consolidation of ORM. These results suggest that histone acetylation regulates the temporal expression of BDNF in cortical circuits potentiating the long-term recognition memory.

Optogenetic Stimulation of Prelimbic Pyramidal Neurons Maintains Fear Memories and Modulates Amygdala Pyramidal Neuron Transcriptome

Fear extinction requires coordinated neural activity within the amygdala and medial prefrontal cortex (mPFC). Any behavior has a transcriptomic signature that is modified by environmental experiences, and specific genes are involved in functional plasticity and synaptic wiring during fear extinction. Here, we investigated the effects of optogenetic manipulations of prelimbic (PrL) pyramidal neurons and amygdala gene expression to analyze the specific transcriptional pathways associated to adaptive and maladaptive fear extinction. To this aim, transgenic mice were (or not) fear-conditioned and during the extinction phase they received optogenetic (or sham) stimulations over photo-activable PrL pyramidal neurons. At the end of behavioral testing, electrophysiological (neural cellular excitability and Excitatory Post-Synaptic Currents) and morphological (spinogenesis) correlates were evaluated in the PrL pyramidal neurons. Furthermore, transcriptomic cell-specific RNA-analyses (differential gene expression profiling and functional enrichment analyses) were performed in amygdala pyramidal neurons. Our results show that the optogenetic activation of PrL pyramidal neurons in fear-conditioned mice induces fear extinction deficits, reflected in an increase of cellular excitability, excitatory neurotransmission, and spinogenesis of PrL pyramidal neurons, and associated to strong modifications of the transcriptome of amygdala pyramidal neurons. Understanding the electrophysiological, morphological, and transcriptomic architecture of fear extinction may facilitate the comprehension of fear-related disorders.

Brd4 participates in epigenetic regulation of the extinction of remote auditory fear memory

BACKGROUND

Inaccurate fear memories can be maladaptive and potentially portrait a core symptomatic dimension of fear adaptive disorders such as post-traumatic stress disorder (PTSD), which is generally characterized by an intense and enduring memory for the traumatic events. Evidence exists in support of epigenetic regulation of fear behavior. Brd4, a member of the bromodomain and extra-terminal domain (BET) protein family, serves as a chromatin "reader" by binding to histones in acetylated lysine residues, and hence promotes transcriptional activities. However, less is known whether Brd4 participates in modulating cognitive activities especially memory formation and extinction. Here we provide evidence for a role of Brd4 in modulation of auditory fear memory. Auditory fear conditioning resulted in a biphasic Brd4 activation in the anterior cingulate cortex (ACC) and hippocampus of adult mice. Thus, Brd4 phosphorylation occurred 6 h and 3-14 days, respectively, after auditory fear conditioning. Systemic inhibition of Brd4 with a BET inhibitor, JQ1, impaired the extinction of remote (i.e., 14 days after conditioning) fear memory. Further, conditional Brd4 knockout in excitatory neurons of the forebrain impaired remote fear extinction as observed in the JQ1-treated mice. Herein, we identified that Brd4 is essential for extinction of remote fear in rodents. These results thus indicate that Brd4 potentially plays a role in the pathogenesis of PTSD.

Effects of repeated anodal transcranial direct current stimulation on auditory fear extinction in C57BL/6J mice

BACKGROUND

Trauma-based psychotherapy is a first line treatment for post-traumatic stress disorder (PTSD) but not all patients achieve long-term remission. Transcranial direct current stimulation (tDCS) received considerable attention as a neuromodulation method that may improve trauma-based psychotherapy.

OBJECTIVE

We explored the effects of repeated anodal tDCS over the prefrontal cortex (PFC) on fear extinction in mice as a preclinical model for trauma-based psychotherapy.

METHODS

We performed auditory fear conditioning with moderate or high shock intensity on C57BL6/J mice. Next, mice received anodal tDCS (0.2 mA, 20 min) or sham stimulation over the PFC twice daily for five consecutive days. Extinction training was performed by repeatedly exposing mice to the auditory cue the day after the last stimulation session. Early and late retention of extinction were evaluated one day and three weeks after extinction training respectively.

RESULTS

We observed no significant effect of tDCS on the acquisition or retention of fear extinction in mice subjected to fear conditioning with moderate intensity. However, when the intensity of fear conditioning was high, tDCS significantly lowered freezing during the acquisition of extinction, regardless of the extinction protocol. Moreover, when tDCS was combined with a strong extinction protocol, we also observed a significant improvement of early extinction recall. Finally, we found that tDCS reduced generalized fear induced by contextual cues when the intensity of conditioning is high and extinction training limited.

CONCLUSIONS

Our data provide a rationale to further explore anodal tDCS over the PFC as potential support for trauma-based psychotherapy for PTSD.

Effects of exercise and pharmacological inhibition of histone deacetylases (HDACs) on epigenetic regulations and gene expressions crucial for neuronal plasticity in the motor cortex

The objective of this study was to examine the effect of epigenetic treatment using an histone deacetylases (HDAC) inhibitor in addition to aerobic exercise on the epigenetic markers and neurotrophic gene expressions in the motor cortex, to find a more enriched brain pre-conditioning for motor learning in neurorehabilitation. ICR mice were divided into four groups based on two factors: HDAC inhibition and exercise. Intraperitoneal administration of an HDAC inhibitor (1.2 g/kg sodium butyrate, NaB) and treadmill exercise (approximately at 10 m/min for 60 min) were conducted five days a week for four weeks. NaB administration inhibited total HDAC activity and enhanced acetylation level of histones specifically in histone H4, accompanying the increase of transcription levels of immediate-early genes (IEGs) (c-fos and Arc) and neurotrophins (BDNF and NT-4) crucial for neuroplasticity in the motor cortex. However, exercise enhanced HDAC activity and acetylation level of histone H4 and H3 without the modification of transcription levels. In addition, there were no synergic effects between HDAC inhibition and the exercise regime on the gene expressions. This study showed that HDAC inhibition could present more enriched condition for neuroplasticity to the motor cortex. However, exercise-induced neurotrophic gene expressions could depend on exercise regimen based on the intensity, the term etc. Therefore, this study has a novelty suggesting that pharmacological HDAC inhibition could be an alternative potent approach to present a neuronal platform with enriched neuroplasticity for motor learning and motor recovery, however, an appropriate exercise regimen is expected in this approach.

Repeated stress exposure in mid-adolescence attenuates behavioral, noradrenergic, and epigenetic effects of trauma-like stress in early adult male rats

Stress in adolescence can regulate vulnerability to traumatic stress in adulthood through region-specific epigenetic activity and catecholamine levels. We hypothesized that stress in adolescence would increase adult trauma vulnerability by impairing extinction-retention, a deficit in PTSD, by (1) altering class IIa histone deacetylases (HDACs), which integrate effects of stress on gene expression, and (2) enhancing norepinephrine in brain regions regulating cognitive effects of trauma. We investigated the effects of adolescent-stress on adult vulnerability to severe stress using the single-prolonged stress (SPS) model in male rats. Rats were exposed to either (1) adolescent-stress (33-35 postnatal days) then SPS (58-60 postnatal days; n = 14), or (2) no adolescent-stress and SPS (58-60 postnatal days; n = 14), or (3) unstressed conditions (n = 8). We then measured extinction-retention, norepinephrine, HDAC4, and HDAC5. As expected, SPS exposure induced an extinction-retention deficit. Adolescent-stress prior to SPS eliminated this deficit, suggesting adolescent-stress conferred resiliency to adult severe stress. Adolescent-stress also conferred region-specific resilience to norepinephrine changes. HDAC4 and HDAC5 were down-regulated following SPS, and these changes were also modulated by adolescent-stress. Regulation of HDAC levels was consistent with the pattern of cognitive effects of SPS; only animals exposed to SPS without adolescent-stress exhibited reduced HDAC4 and HDAC5 in the prelimbic cortex, hippocampus, and striatum. Thus, HDAC regulation caused by severe stress in adulthood interacts with stress history such that seemingly conflicting reports describing effects of adolescent stress on adult PTSD vulnerability may stem in part from dynamic HDAC changes following trauma that are shaped by adolescent stress history.

Neurobiology of BDNF in fear memory, sensitivity to stress, and stress-related disorders

Brain-derived neurotrophic factor (BDNF) is widely accepted for its involvement in resilience and antidepressant drug action, is a common genetic locus of risk for mental illnesses, and remains one of the most prominently studied molecules within psychiatry. Stress, which arguably remains the "lowest common denominator" risk factor for several mental illnesses, targets BDNF in disease-implicated brain regions and circuits. Altered stress-related responses have also been observed in animal models of BDNF deficiency in vivo, and BDNF is a common downstream intermediary for environmental factors that potentiate anxiety- and depressive-like behavior. However, BDNF's broad functionality has manifested a heterogeneous literature; likely reflecting that BDNF plays a hitherto under-recognized multifactorial role as both a regulator and target of stress hormone signaling within the brain. The role of BDNF in vulnerability to stress and stress-related disorders, such as posttraumatic stress disorder (PTSD), is a prominent example where inconsistent effects have emerged across numerous models, labs, and disciplines. In the current review we provide a contemporary update on the neurobiology of BDNF including new data from the behavioral neuroscience and neuropsychiatry literature on fear memory consolidation and extinction, stress, and PTSD. First we present an overview of recent advances in knowledge on the role of BDNF within the fear circuitry, as well as address mounting evidence whereby stress hormones interact with endogenous BDNF-TrkB signaling to alter brain homeostasis. Glucocorticoid signaling also acutely recruits BDNF to enhance the expression of fear memory. We then include observations that the functional common BDNF Val66Met polymorphism modulates stress susceptibility as well as stress-related and stress-inducible neuropsychiatric endophenotypes in both man and mouse. We conclude by proposing a BDNF stress-sensitivity hypothesis, which posits that disruption of endogenous BDNF activity by common factors (such as the BDNF Val66Met variant) potentiates sensitivity to stress and, by extension, vulnerability to stress-inducible illnesses. Thus, BDNF may induce plasticity to deleteriously promote the encoding of fear and trauma but, conversely, also enable adaptive plasticity during extinction learning to suppress PTSD-like fear responses. Ergo regulators of BDNF availability, such as the Val66Met polymorphism, may orchestrate sensitivity to stress, trauma, and risk of stress-induced disorders such as PTSD. Given an increasing interest in personalized psychiatry and clinically complex cases, this model provides a framework from which to experimentally disentangle the causal actions of BDNF in stress responses, which likely interact to potentiate, produce, and impair treatment of, stress-related psychiatric disorders.

Molecularly Defined Hippocampal Inputs Regulate Population Dynamics in the Prelimbic Cortex to Suppress Context Fear Memory Retrieval

BACKGROUND

Context fear memory dysregulation is a hallmark symptom of several neuropsychiatric disorders, including generalized anxiety disorder and posttraumatic stress disorder. The hippocampus (HC) and prelimbic (PrL) subregion of the medial prefrontal cortex have been linked with context fear memory retrieval in rodents, but the mechanisms by which HC-PrL circuitry regulates this process remain poorly understood.

METHODS

Spatial and genetic targeting of HC-PrL circuitry was used for RNA sequencing (n = 31), chemogenetic stimulation (n = 44), in vivo calcium imaging (n = 20), ex vivo electrophysiology (n = 8), and molecular regulation of plasticity cascades during fear behavior (context fear retrieval) (n = 16).

RESULTS

We showed that ventral HC (vHC) neurons with projections to the PrL cortex (vHC-PrL projectors) are a transcriptomically distinct subpopulation compared with adjacent nonprojecting neurons, and we showed complementary enrichment for diverse neuronal processes and central nervous system-related clinical gene sets. We further showed that stimulation of this population of vHC-PrL projectors suppresses context fear memory retrieval and impairs the ability of PrL neurons to dynamically distinguish between distinct phases of fear learning. Using transgenic and circuit-specific molecular targeting approaches, we demonstrated that unique patterns of activity-dependent gene transcription associated with brain-derived neurotrophic factor signaling within vHC-PrL projectors causally regulated activity in excitatory and inhibitory PrL neurons during context fear memory retrieval.

CONCLUSIONS

Together, our data show that activity-dependent brain-derived neurotrophic factor release from molecularly distinct vHC-PrL projection neurons modulates postsynaptic signaling in both inhibitory and excitatory PrL neurons, modifying activity in discrete populations of PrL neurons to suppress freezing during context fear memory retrieval.