Neuroepigenetics of Post-Traumatic Stress Disorder

Study on the Role of Dnmt3a Expression in the Dentate Gyrus of the Hippocampus in Reward Memory

Objective

Emotional memory has been associated with many psychiatric diseases. Understanding emotional memory could be beneficial in comprehending and discovering new therapies for diseases related to emotional memory, such as depression and post-traumatic stress disorder (PTSD). Our previous study revealed that Dnmt3a expression in the dentate gyrus (DG) contributes to fear memory. However, is there a correlation between Dnmt3a expression in the DG and reward memory? This study aims to explore the relationship between Dnmt3a expression and reward memory.

Methods

We induced fear memory (Fear group) or reward memory (Reward group) using fear conditioning and social interaction in females, respectively. We then measured the expression levels of Dnmt3a and c-fos after the retrieval of different types of memory. Additionally, we used a recombinant Adeno-Associated Virus (rAAV) to overexpress Dnmt3a in the DG and conducted conditioned place preference (CPP) tests to assess changes in reward memory.

Results

We observed a significant increase in Dnmt3a and c-fos expression in the Fear group compared with the Reward group. Overexpression of Dnmt3a in the DG led to an increase in time spent in the white box during CPP tests.

Conclusion

Dnmt3a expression levels varied after the retrieval of fear or reward memory, and overexpression of Dnmt3a in the DG enhanced reward memory. These findings suggest that Dnmt3a expression in the DG plays a role in reward memory.

MDMA-assisted psychotherapy for PTSD: Growing evidence for memory effects mediating treatment efficacy

The application of MDMA in conjunction with psychotherapy has in recent years seen a resurgence of clinical, scientific, and public interest in the treatment of posttraumatic stress disorder (PTSD). Clinical trials have shown promising safety and efficacy, but the mechanisms underlying this treatment form remain largely unestablished. This article explores recent preclinical and clinical evidence suggesting that the treatment's efficacy may be influenced by the mnemonic effects of MDMA. We review data on the effects of MDMA on fear extinction and fear reconsolidation and the utility of these processes for PTSD treatment. We corroborate our findings by incorporating research from cognitive psychology and psychopharmacology and offer recommendations for future research.

MicroRNA expression profiles of stress susceptibility and resilience in the prelimbic and infralimbic cortex of rats after single prolonged stress

The experience of traumatic stress can engender lasting memories associated with the trauma, often resulting in post-traumatic stress disorder (PTSD). However, only a minority of individuals develop PTSD symptoms upon exposure. The neurobiological mechanisms underlying the pathology of PTSD are poorly understood. Utilizing a rat model of PTSD, the Single Prolonged Stress (SPS) paradigm, we were able to differentiate between resilient and susceptible individuals. Fourteen days after the SPS exposure, we conducted the behavioral analyses using Elevated Plus Maze (EPM) and Open Field (OF) tests to identify male rats as trauma resilient or susceptible. We focused on the microRNA (miRNA) profiles of the infralimbic (IL) and prelimbic (PL) cortical regions, known to be crucial in regulating the stress response. Our investigation of stressed rats exposed to the SPS procedure yielded divergent response, and differential expression microRNAs (DEmiRs) analysis indicated significant differences in the IL and PL transcriptional response. In the IL cortex, the GO analysis revealed enriched GO terms in the resilient versus control comparison, specifically related to mitogen-activated protein kinase and MAP kinase signaling pathways for their molecular functions as well as cytosol and nucleoplasm for the biological process. In the susceptible versus resilient comparison, the changes in molecular functions were only manifested in the functions of regulation of transcription involved in the G1/S transition of the mitotic cell cycle and skeletal muscle satellite cell activation. However, no enriched GO terms were found in the susceptible versus control comparison. In the PL cortex, results indicated that the DEmiRs were enriched exclusively in the cellular component level of the endoplasmic reticulum lumen in the comparison between resilient and control rats. Overall, our study utilized an animal model of PTSD to investigate the potential correlation between stress-induced behavioral dysfunction and variations in miRNA expression. The aforementioned discoveries have the potential to pave the way for novel therapeutic approaches for PTSD, which could involve the targeted regulation of transcriptome expression.

On making (and turning adaptive to) maladaptive aversive memories in laboratory rodents

Fear conditioning and avoidance tasks usually elicit adaptive aversive memories. Traumatic memories are more intense, generalized, inflexible, and resistant to attenuation via extinction- and reconsolidation-based strategies. Inducing and assessing these dysfunctional, maladaptive features in the laboratory are crucial to interrogating posttraumatic stress disorder's neurobiology and exploring innovative treatments. Here we analyze over 350 studies addressing this question in adult rats and mice. There is a growing interest in modeling several qualitative and quantitative memory changes by exposing already stressed animals to freezing- and avoidance-related tests or using a relatively high aversive training magnitude. Other options combine aversive/fearful tasks with post-acquisition or post-retrieval administration of one or more drugs provoking neurochemical or epigenetic alterations reported in the trauma aftermath. It is potentially instructive to integrate these procedures and incorporate the measurement of autonomic and endocrine parameters. Factors to consider when defining the organismic and procedural variables, partially neglected aspects (sex-dependent differences and recent vs. remote data comparison) and suggestions for future research (identifying reliable individual risk and treatment-response predictors) are discussed.

Epigenetic Effects of Social Stress and Epigenetic Inheritance

Social events that cause stress can cause epigenetic changes on living things. The study of the effects of social events experienced by an individual on epigenetic marks on the genome has created the field of social epigenetics. Social epigenetics examines the effects of psychosocial stress factors such as poverty, war trauma and childhood abuse on epigenetic mechanisms. Epigenetic mechanisms alter chemical markers in the genome structure without changing the DNA sequence. Among these mechanisms, DNA methylation in particular may have different phenotypic effects in response to stressors that may occur in the psychosocial environment. Post-traumatic stress disorder is one of the most significant proofs of the effects of epigenetic expressions altered due to traumatic events on the phenotype. The field of epigenetic inheritance has shown that epigenetic changes triggered by environmental influences can, in some cases, be transmitted through generations. This field provides a better understanding of the basis of many psychological disorders. This review provides an overview of social epigenetics, PTSD, and epigenetic inheritance.

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.

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.

Clinical Manifestations of Body Memories: The Impact of Past Bodily Experiences on Mental Health

Bodily experiences such as the feeling of touch, pain or inner signals of the body are deeply emotional and activate brain networks that mediate their perception and higher-order processing. While the ad hoc perception of bodily signals and their influence on behavior is empirically well studied, there is a knowledge gap on how we store and retrieve bodily experiences that we perceived in the past, and how this influences our everyday life. Here, we explore the hypothesis that negative body memories, that is, negative bodily experiences of the past that are stored in memory and influence behavior, contribute to the development of somatic manifestations of mental health problems including somatic symptoms, traumatic re-experiences or dissociative symptoms. By combining knowledge from the areas of cognitive neuroscience and clinical neuroscience with insights from psychotherapy, we identify Clinical Body Memory (CBM) mechanisms that specify how mental health problems could be driven by corporeal experiences stored in memory. The major argument is that the investigation of the neuronal mechanisms that underlie the storage and retrieval of body memories provides us with empirical access to reduce the negative impact of body memories on mental health.

Posttraumatic Stress Disorder Brain Transcriptomics: Convergent Genomic Signatures Across Biological Sex

While a definitive understanding of the molecular pathology of posttraumatic stress disorder (PTSD) is far from a current reality, it has become increasingly clear that many of the molecular effects of PTSD are sex specific. Women are twice as likely as men to develop PTSD after a traumatic event, and neurobiological evidence suggests that there are structural differences between the brains of males versus females with PTSD. Recent advances in genomic technologies have begun to shed light on the sex-specific molecular determinants of PTSD, which seem to be governed predominantly by dysfunction of GABAergic (gamma-aminobutyric acidergic) signaling and immune function. We review the current state of the field of PTSD genomics focusing on the effect of sex. We provide an overview of difference in heritability of PTSD based on sex, how difference in gene regulation based on sex impacts the PTSD brain, and what is known about genomic regulation that is dysregulated in specific cell types in PTSD.

Epigenetic Approach to PTSD: In the Aspects of Rat Models

Posttraumatic stress disorder (PTSD) is a stress-related mental disorder and develops after exposure to life-threatening traumatic experiences. The risk factors of PTSD included genetic factors; alterations in hypothalamic–pituitary–adrenal (HPA) axis; neurotrophic, serotonergic, dopaminergic, and catecholaminergic systems; and a variety of environmental factors, such as war, accident, natural disaster, pandemic, physical, or sexual abuse, that cause stress or trauma in individuals. To be able to understand the molecular background of PTSD, rodent animal models are widely used by researchers. When looking for a solution for PTSD, it is important to consider preexisting genetic risk factors and physiological, molecular, and biochemical processes caused by trauma that may cause susceptibility to this disorder. In studies, it is reported that epigenetic mechanisms play important roles in the biological response affected by environmental factors, as well as the task of programming cell identity. In this article, we provided an overview of the role of epigenetic modifications in understanding the biology of PTSD. We also summarized the data from animal studies and their importance during the investigation of PTSD. This study shed light on the epigenetic background of stress and PTSD.

Gender Beneath the Skull: Agency, Trauma and Persisting Stereotypes in Neuroepigenetics

Epigenetics stands in a complex relationship to issues of sex and gender. As a scientific field, it has been heavily criticized for disproportionately targeting the maternal body and reproducing deterministic views of biological sex (Kenney and Müller, 2017; Lappé, 2018; Richardson et al., 2014). And yet, it also represents the culmination of a long tradition of engaging with developmental biology as a feminist cause, because of the dispersal of the supposed 'master code' of DNA among wider cellular, organismic and ecological contexts (Keller, 1988). In this paper, we explore a number of tensions at the intersection of sex, gender and trauma that are playing out in the emerging area of neuroepigenetics - a relatively new subfield of epigenetics specifically interested in environment-brain relations through epigenetic modifications in neurons. Using qualitative interviews with leading scientists, we explore how trauma is conceptualized in neuroepigenetics, paying attention to its gendered dimensions. We address a number of concerns raised by feminist STS researchers in regard to epigenetics, and illustrate why we believe close engagement with neuroepigenetic claims, and neuroepigenetic researchers themselves, is a crucial step for social scientists interested in questions of embodiment and trauma. We argue this for three reasons: (1) Neuroepigenetic studies are recognizing the agential capacities of biological materials such as genes, neurotransmitters and methyl groups, and how they influence memory formation; (2) Neuroepigenetic conceptions of trauma are yet to be robustly coupled with social and anthropological theories of violence (Eliot, 2021; Nelson, 2021; Walby, 2013); (3) In spite of the gendered assumptions we find in neuroepigenetics, there are fruitful spaces - through collaboration - to be conceptualizing gender beyond culture-biology and nature-nurture binaries (Lock and Nguyen, 2010). To borrow Gravlee's (2009: 51) phrase, we find reason for social scientists to consider how gender is not only constructed, but how it may "become biology" via epigenetic and other biological pathways. Ultimately, we argue that a robust epigenetic methodology is one which values the integrity of expertise outside its own field, and can have an open, not empty mind to cross-disciplinary dialogue.

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.

PTSD is associated with increased DNA methylation across regions of HLA-DPB1 and SPATC1L

Posttraumatic stress disorder (PTSD) is characterized by intrusive thoughts, avoidance, negative alterations in cognitions and mood, and arousal symptoms that adversely affect mental and physical health. Recent evidence links changes in DNA methylation of CpG cites to PTSD. Since clusters of proximal CpGs share similar methylation signatures, identification of PTSD-associated differentially methylated regions (DMRs) may elucidate the pathways defining differential risk and resilience of PTSD. Here we aimed to identify epigenetic differences associated with PTSD. DNA methylation data profiled from blood samples using the MethylationEPIC BeadChip were used to perform a DMR analysis in 187 PTSD cases and 367 trauma-exposed controls from the Grady Trauma Project (GTP). DMRs were assessed with R package bumphunter. We identified two regions that associate with PTSD after multiple test correction. These regions were in the gene body of HLA-DPB1 and in the promoter of SPATC1L. The DMR in HLA-DPB1 was associated with PTSD in an independent cohort. Both DMRs included CpGs whose methylation associated with nearby sequence variation (meQTL) and that associated with expression of their respective genes (eQTM). This study supports an emerging literature linking PTSD risk to genetic and epigenetic variation in the HLA region.

Epigenome-wide meta-analysis of PTSD across 10 military and civilian cohorts identifies methylation changes in AHRR

Epigenetic differences may help to distinguish between PTSD cases and trauma-exposed controls. Here, we describe the results of the largest DNA methylation meta-analysis of PTSD to date. Ten cohorts, military and civilian, contribute blood-derived DNA methylation data from 1,896 PTSD cases and trauma-exposed controls. Four CpG sites within the aryl-hydrocarbon receptor repressor (AHRR) associate with PTSD after adjustment for multiple comparisons, with lower DNA methylation in PTSD cases relative to controls. Although AHRR methylation is known to associate with smoking, the AHRR association with PTSD is most pronounced in non-smokers, suggesting the result was independent of smoking status. Evaluation of metabolomics data reveals that AHRR methylation associated with kynurenine levels, which are lower among subjects with PTSD. This study supports epigenetic differences in those with PTSD and suggests a role for decreased kynurenine as a contributor to immune dysregulation in PTSD.

Neuroepigenetics of Mental Illness: The Inside Outs of the Outside Within

Epigenetics refers to environmentally sensitive modifications to DNA and chromatin that regulate gene transcription without altering the genetic sequence itself. Because of the brain's central role in a person's adaptation to dynamic changes in the environment, the field of epigenetic research is particularly pertinent for the neurosciences and mental health and illness. "Neuroepigenetics" refers to the field of epigenetics, as applied to research of the nervous system and related functional abilities. The onset and course of mental disorders revolve around person-environment interactions, i.e., the interplay between environmental factors with people (and their brain) throughout life and on the background of an individual's inherited genomic make-up. With respect to the nervous system and its functional abilities, neuroepigenetic research aims to turn the inside outs by explicating the epigenetic profiles that regulate gene expression within cells while epigenetic profiles themselves may reflect the imprints of external factors (the outside of the organism). Neuroepigenetic research is of prime importance for elucidating the molecular underpinnings of gene-environment interplay in relation to functional abilities of the brain and mental health throughout life, and thus for identifying the mechanisms underlying onset and course of mental disorders. However, neuroepigenetic research is still in its infancy and many conceptual and methodological challenges are apparent. In addition, there are considerable complexities and major challenges in conceptualizing the nature and diagnosis of mental disorders, and these need to be taken into account in studying neuroepigenetics of mental disorders. The current manuscript provides an overview and conceptual framework for neuroepigenetic research in mental disorders.