Dynamic DNA methylation programs persistent adverse effects of early-life stress

A Comprehensive Overview of Stress, Resilience, and Neuroplasticity Mechanisms

Stress is a core concept in the mental health field that expands upon the seminal definition of stress as an acute response to the disruption of homeostasis. Stress is a complex process that involves both environmental challenges and the triggering of internal responses and impacts physiological, psychological, and behavioral systems. The capacity of the human brain to cope with stress is particularly crucial in early life, when neurodevelopment is highly plastic. Early-life stress (ELS), defined as exposure to severe chronic stress during sensitive periods of development, has been shown to cause lasting changes in brain structure and function. However, not all individuals exposed to ELS develop pathological outcomes, suggesting the presence of resilience mechanisms: adaptive processes that allow an individual to cope with adverse situations while maintaining psychological and neurobiological health. The aim of this review was to synthesize recent advances in the understanding of the neuroplasticity mechanisms underlying resilience to ELS. We discussed the neurobiological pathways implicated in stress response and adaptation, including the roles of neurogenesis, synaptic plasticity, and neural circuit remodeling. By focusing on the interplay between stress-induced neuroplastic changes and resilience mechanisms, we aimed to provide insights into potential therapeutic targets for stress-related psychopathology.

Prenatal maternal life adversity impacts on learning and memory in offspring: implication to transgenerational epigenetic inheritance

Maternal stress exposure during pregnancy is known to affect offspring behavior, including learning and memory. We hypothesized that maternal stress-induced changes transmit this effect through maternal line mediated transgenerational epigenetic inheritance. To test our hypothesis, pregnant rats (F0) were undisturbed (Control, Ctrl)/exposed to social stress during gestational days (GD) 16-18 (PMS)/exposed to social stress and treated with oxytocin during GD-16 to 18 (PMS+OXT). Subsequently, F1 female offspring from Ctrl, PMS, and PMS+OXT were mated with Ctrl F1 males to examine maternal line mediated transgenerational impacts. Female animals (F1 and F2) were subjected to behavioral test and the levels of global H3K4me2/H3K4me3 methylation, methylation in the CRH promoter, expression of Crh, Crh receptors (Crhr1, Crhr2), and BDNF were determined. It was found that prenatal maternal stress (PMS) reduced reference and working memory in F1 and F2 offspring, increased global and specific H3K4me2, H3K4me3 methylation in the CRH promoter, expression of Crh, Crh receptors, and corticosterone (CORT), and down-regulated the expression of pro-and mature BDNF by differentially regulating Bdnf transcripts III, IV and VI in the amygdala. Oxytocin exposure reduced PMS-induced global and specific H3K4me2/3 changes, which repressed the expression of Crh, Crh receptors, reduced CORT levels, up-regulated the expression of pro-BDNF and mature BDNF, and improved memory in F1 and F2 offspring. Collectively, our study revealed that PMS reduced reference and working memory performance in F1 and F2 offspring through maternal line transgenerational inheritance of H3K4me2, H3K4me3 methylation, and associated mechanisms that regulate BDNF expression and synaptic plasticity.

Sex-specific and developmental effects of early life adversity on stress reactivity are rescued by postnatal knockdown of 5-HT1A autoreceptors

Early Life Adversity (ELA) predisposes to stress hypersensitivity in adulthood, but neurobiological mechanisms that protect from the enduring effects of ELA are poorly understood. Serotonin 1A (5HT1A) autoreceptors in the raphé nuclei regulate adult stress vulnerability, but whether 5HT1A could be targeted to prevent ELA effects on susceptibility to future stressors is unknown. Here, we exposed mice with postnatal knockdown of 5HT1A autoreceptors to the limited bedding and nesting model of ELA from postnatal day (P)3-10 and tested behavioral, neuroendocrine, neurogenic, and neuroinflammatory responses to an acute swim stress in male and female mice in adolescence (P35) and in adulthood (P56). In females, ELA decreased raphé 5HT neuron activity in adulthood and increased passive coping with the acute swim stress, corticosterone levels, neuronal activity, and corticotropin-releasing factor (CRF) levels in the paraventricular nucleus (PVN) of the hypothalamus. ELA also reduced neurogenesis in the ventral dentate gyrus (vDG) of the hippocampus, an important mediator of individual differences in stress susceptibility, and increased microglia activation in the PVN and vDG. These effects of ELA were specific to females and manifested predominantly in adulthood, but not earlier on in adolescence. Postnatal knockdown of 5HT1A autoreceptors prevented these effects of ELA on 5HT neuron activity, stress reactivity, neurogenesis, and neuroinflammation in adult female mice. Our findings demonstrate that ELA induces long-lasting and sex-specific impairments in the serotonin system, stress reactivity, and vDG function, and identify 5HT1A autoreceptors as potential targets to prevent these enduring effects of ELA.

Weaning impact: Evaluating growth, behavior, and production performance in Sahiwal cows and their calves

Initial periods of life, beginning before birth and lasting until weaning are characterised by the greatest neural plasticity. Early postnatal stress causes lasting changes in a variety of behaviours as well as stress reactivity. Cow-calf contact for an extended period is believed to improve the social skills of calves and has also been linked to improved productivity of mothers. This research was carried out to investigate the impact of weaning stress on the growth, behaviour and performance of Sahiwal cows and their calves. For this, 32 healthy cows and their calves were selected from the Sahiwal herd of the Livestock Research Centre, ICAR-National Dairy Research Institute. They were grouped equally into two groups of 16 cow-calf pairs, which became the treatment groups (i.e., 'Fenceline' contact and 'Separated' groups). Calves in the fenceline contact group were allowed to suckle during the morning and evening milking and were housed together with fenceline separation. In the separated group, calves were separated from their mothers immediately after birth and fed colostrum and milk with a bottle throughout the experiment. Each calf was monitored for its growth and behavioural responses while cows were monitored for their production performance and behaviour. The results showed that growth and behaviour responses were better for fenceline calves compared to separated calves and also production performance and behaviour of Sahiwal cows provided with fenceline contact were better when compared to separated cows. From this study, it was concluded that fenceline cow-calf contact improved growth, behavioural response of calves; and production performance and behaviour of cows compared to separated cows and calves.

Remodeling the Epigenome Through Meditation: Effects on Brain, Body, and Well-being

Epigenetic mechanisms are key processes that constantly reshape genome activity carrying out physiological responses to environmental stimuli. Such mechanisms regulate gene activity without modifying the DNA sequence, providing real-time adaptation to changing environmental conditions. Both favorable and unfavorable lifestyles have been shown to influence body and brain by means of epigenetics, leaving marks on the genome that can either be rapidly reversed or persist in time and even be transmitted trans-generationally. Among virtuous habits, meditation seemingly represents a valuable way of activating inner resources to cope with adverse experiences. While unhealthy habits, stress, and traumatic early-life events may favor the onset of diseases linked to inflammation, neuroinflammation, and neuroendocrine dysregulation, the practice of mindfulness-based techniques was associated with the alleviation of many of the above symptoms, underlying the importance of lifestyles for health and well-being. Meditation influences brain and body systemwide, eliciting structural/morphological changes as well as modulating the levels of circulating factors and the expression of genes linked to the HPA axis and the immune and neuroimmune systems. The current chapter intends to give an overview of pioneering research showing how meditation can promote health through epigenetics, by reshaping the profiles of the three main epigenetic markers, namely DNA methylation, histone modifications, and non-coding RNAs.

Differential methylation of OPRK1 in borderline personality disorder is associated with childhood trauma

According to a growing body of neurobiological evidence, the core symptoms of borderline personality disorder (BPD) may be linked to an opioidergic imbalance between the hedonic and stimulatory activity of mu opioid receptors (MOR) and the reward system inhibiting effects of kappa opioid receptors (KOR). Childhood trauma (CT), which is etiologically relevant to BPD, is also likely to lead to epigenetic and neurobiological adaptations by extensive activation of the stress and endogenous opioid systems. In this study, we investigated the methylation differences in the promoter of the KOR gene (OPRK1) in subjects with BPD (N = 47) and healthy controls (N = 48). Comparing the average methylation rates of regulatorily relevant subregions (specified regions CGI-1, CGI-2, EH1), we found no differences between BPD and HC. Analyzing individual CG nucleotides (N = 175), we found eight differentially methylated CG sites, all of which were less methylated in BPD, with five showing highly interrelated methylation rates. This differentially methylated region (DMR) was found on the falling slope (5') of the promoter methylation gap, whose effect is enhanced by the DMR hypomethylation in BPD. A dimensional assessment of the correlation between disease severity and DMR methylation rate revealed DMR hypomethylation to be negatively associated with BPD symptom severity (measured by BSL-23). Finally, analyzing the influence of CT on DMR methylation, we found DMR hypomethylation to correlate with physical and emotional neglect in childhood (quantified by CTQ). Thus, the newly identified DMR may be a biomarker of the risks caused by CT, which likely epigenetically contribute to the development of BPD.

Intimate partner violence during pregnancy: To screen or not to screen?

Intimate partner violence (IPV) during pregnancy emerges as a compelling and urgent concern within the domain of public health, casting a long shadow over a substantial cohort of women. Its pernicious consequences extend beyond the individual, enveloping the well-being of both the mother and the fetus, giving rise to an elevated risk of preterm birth, low birth weight, fetal harm, and maternal psychological distress, including depression, anxiety, post-traumatic stress disorder, and, tragically, maternal mortality. Despite the prevalence of IPV being comparable to other conditions like gestational diabetes and preeclampsia, a universal screening protocol for IPV remains absent globally. We reviewed the clinical guidelines and practices concerning IPV screening, painstakingly scrutinizing their contextual nuances across diverse nations. Our study unveils multifaceted challenges of implementing universal screening. These hurdles encompass impediments to victim awareness and disclosure, limitations in healthcare providers' knowledge and training, and the formidable structural barriers entrenched within healthcare systems. Concurrently, we delve into the potential biomarkers intricately entwined with IPV. These promising markers encompass inflammatory indicators, epigenetic and genetic influences, and a diverse array of chemical compounds and proteins. Lastly, we discussed various criteria for universal screening including (1) valid and reliable screening tool; (2) target population as pregnant women; (3) scientific evidence of screening programme; and (4) integration of education, testing, clinical services, and programme management to minimise the challenges, which are paramount. With the advancement of digital technology and various biomarkers identification, screening and detecting IPV in clinical settings can be conducted systemically. A systems-level interventions with academia-community-indutrial partnerships can help connect pregnant women to desire support services to avoid adverse maternal and child health outcomes.

The Alpha-Synuclein Gene (SNCA) is a Genomic Target of Methyl-CpG Binding Protein 2 (MeCP2)-Implications for Parkinson's Disease and Rett Syndrome

Mounting evidence suggests a prominent role for alpha-synuclein (a-syn) in neuronal cell function. Alterations in the levels of cellular a-syn have been hypothesized to play a critical role in the development of Parkinson's disease (PD); however, mechanisms that control expression of the gene for a-syn (SNCA) in cis and trans as well as turnover of a-syn are not well understood. We analyzed whether methyl-CpG binding protein 2 (MeCP2), a protein that specifically binds methylated DNA, thus regulating transcription, binds at predicted binding sites in intron 1 of the SNCA gene and regulates a-syn protein expression. Chromatin immunoprecipitation (ChIP) and electrophoretic mobility-shift assays (EMSA) were used to confirm binding of MeCP2 to regulatory regions of SNCA. Site-specific methylation and introduction of localized mutations by CRISPR/Cas9 were used to investigate the binding properties of MeCP2 in human SK-N-SH neuroblastoma cells. The significance of MeCP2 for SNCA regulation was further investigated by overexpressing MeCP2 and mutated variants of MeCP2 in MeCP2 knockout cells. We found that methylation-dependent binding of MeCP2 at a restricted region of intron 1 of SNCA had a significant impact on the production of a-syn. A single nucleotide substitution near to CpG1 strongly increased the binding of MeCP2 to intron 1 of SNCA and decreased a-syn protein expression by 60%. In contrast, deletion of a single nucleotide closed to CpG2 led to reduced binding of MeCP2 and significantly increased a-syn levels. In accordance, knockout of MeCP2 in SK-N-SH cells resulted in a significant increase in a-syn production, demonstrating that SNCA is a genomic target for MeCP2 regulation. In addition, the expression of two mutated MeCP2 variants found in Rett syndrome (RTT) showed a loss of their ability to reduce a-syn expression. This study demonstrates that methylation of CpGs and binding of MeCP2 to intron 1 of the SNCA gene plays an important role in the control of a-syn expression. In addition, the changes in SNCA regulation found by expression of MeCP2 variants carrying mutations found in RTT patients may be of importance for the elucidation of a new molecular pathway in RTT, a rare neurological disorder caused by mutations in MECP2.

Cost-effective solutions for high-throughput enzymatic DNA methylation sequencing

Characterizing DNA methylation patterns is important for addressing key questions in evolutionary biology, geroscience, and medical genomics. While costs are decreasing, whole-genome DNA methylation profiling remains prohibitively expensive for most population-scale studies, creating a need for cost-effective, reduced representation approaches (i.e., assays that rely on microarrays, enzyme digests, or sequence capture to target a subset of the genome). Most common whole genome and reduced representation techniques rely on bisulfite conversion, which can damage DNA resulting in DNA loss and sequencing biases. Enzymatic methyl sequencing (EM-seq) was recently proposed to overcome these issues, but thorough benchmarking of EM-seq combined with cost-effective, reduced representation strategies has not yet been performed. To do so, we optimized Targeted Methylation Sequencing protocol (TMS)-which profiles ∼4 million CpG sites-for miniaturization, flexibility, and multispecies use at a cost of ∼$80. First, we tested modifications to increase throughput and reduce cost, including increasing multiplexing, decreasing DNA input, and using enzymatic rather than mechanical fragmentation to prepare DNA. Second, we compared our optimized TMS protocol to commonly used techniques, specifically the Infinium MethylationEPIC BeadChip (n=55 paired samples) and whole genome bisulfite sequencing (n=6 paired samples). In both cases, we found strong agreement between technologies (R² = 0.97 and 0.99, respectively). Third, we tested the optimized TMS protocol in three non-human primate species (rhesus macaques, geladas, and capuchins). We captured a high percentage (mean=77.1%) of targeted CpG sites and produced methylation level estimates that agreed with those generated from reduced representation bisulfite sequencing (R² = 0.98). Finally, we applied our protocol to profile age-associated DNA methylation variation in two subsistence-level populations-the Tsimane of lowland Bolivia and the Orang Asli of Peninsular Malaysia-and found age-methylation patterns that were strikingly similar to those reported in high income cohorts, despite known differences in age-health relationships between lifestyle contexts. Altogether, our optimized TMS protocol will enable cost-effective, population-scale studies of genome-wide DNA methylation levels across human and non-human primate species.

Sex-specific and Developmental Effects of Early Life Adversity on Stress Reactivity are Rescued by Postnatal Knockdown of 5-HT 1A Autoreceptors

Early Life Adversity (ELA) predisposes to stress hypersensitivity in adulthood, but neurobiological mechanisms that protect from the enduring effects of ELA are poorly understood. Serotonin 1A (5HT 1A ) autoreceptors in the raphé nuclei regulate adult stress vulnerability, but whether 5HT 1A could be targeted to prevent ELA effects on susceptibility to future stressors is unknown. Here, we exposed mice with postnatal knockdown of 5HT 1A autoreceptors to the limited bedding and nesting model of ELA from postnatal day (P)3-10 and tested behavioral, neuroendocrine, neurogenic, and neuroinflammatory responses to an acute swim stress in male and female mice in adolescence (P35) and in adulthood (P56). In females, ELA decreased raphé 5HT neuron activity in adulthood and increased passive coping with the acute swim stress, corticosterone levels, neuronal activity, and corticotropin-releasing factor (CRF) levels in the paraventricular nucleus (PVN) of the hypothalamus. ELA also reduced neurogenesis in the ventral dentate gyrus (vDG) of the hippocampus, an important mediator of individual differences in stress susceptibility, and increased microglia activation in the PVN and vDG. These effects of ELA were specific to females and manifested predominantly in adulthood, but not earlier on in adolescence. Postnatal knockdown of 5HT 1A autoreceptors prevented these effects of ELA on 5HT neuron activity, stress reactivity, neurogenesis, and neuroinflammation in adult female mice. Our findings demonstrate that ELA induces long-lasting and sex-specific impairments in the serotonin system, stress reactivity, and vDG function, and identify 5HT 1A autoreceptors as potential targets to prevent these enduring effects of ELA.

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

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

Epigenetic mechanisms of rapid-acting antidepressants

BACKGROUND

Rapid-acting antidepressants (RAADs), including dissociative anesthetics, psychedelics, and empathogens, elicit rapid and sustained therapeutic improvements in psychiatric disorders by purportedly modulating neuroplasticity, neurotransmission, and immunity. These outcomes may be mediated by, or result in, an acute and/or sustained entrainment of epigenetic processes, which remodel chromatin structure and alter DNA accessibility to regulate gene expression.

METHODS

In this perspective, we present an overview of the known mechanisms, knowledge gaps, and future directions surrounding the epigenetic effects of RAADs, with a focus on the regulation of stress-responsive DNA and brain regions, and on the comparison with conventional antidepressants.

MAIN BODY

Preliminary correlative evidence indicates that administration of RAADs is accompanied by epigenetic effects which are similar to those elicited by conventional antidepressants. These include changes in DNA methylation, post-translational modifications of histones, and differential regulation of non-coding RNAs in stress-responsive chromatin areas involved in neurotrophism, neurotransmission, and immunomodulation, in stress-responsive brain regions. Whether these epigenetic changes causally contribute to the therapeutic effects of RAADs, are a consequence thereof, or are unrelated, remains unknown. Moreover, the potential cell type-specificity and mechanisms involved are yet to be fully elucidated. Candidate mechanisms include neuronal activity- and serotonin and Tropomyosine Receptor Kinase B (TRKB) signaling-mediated epigenetic changes, and direct interaction with DNA, histones, or chromatin remodeling complexes.

CONCLUSION

Correlative evidence suggests that epigenetic changes induced by RAADs accompany therapeutic and side effects, although causation, mechanisms, and cell type-specificity remain largely unknown. Addressing these research gaps may lead to the development of novel neuroepigenetics-based precision therapeutics.

Reconsidering the nature of threat in infancy: Integrating animal and human studies on neurobiological effects of infant stress

Early life stress has been associated with elevated risk for later psychopathology. One mechanism that may contribute to such long-term risk is alterations in amygdala development, a brain region critical to stress responsivity. Yet effects of stress on the amygdala during human infancy, a period of particularly rapid brain development, remain largely unstudied. In order to model how early stressors may affect infant amygdala development, several discrepancies across the existing literatures on early life stress among rodents and early threat versus deprivation among older human children and adults need to be reconciled. We briefly review the key findings of each of these literatures. We then consider them in light of emerging findings from studies of human infants regarding relations among maternal caregiving, infant cortisol response, and infant amygdala volume. Finally, we advance a developmental salience model of how early threat may impact the rapidly developing infant brain, a model with the potential to integrate across these divergent literatures. Future work to assess the value of this model is also proposed.

Shaking Up Our Approach: The Need for Characterization and Optimization of Pre-clinical Models of Infant Abusive Head Trauma

Traumatic brain injuries (TBIs) are a large societal and individual burden. In the first year of life, the vast majority of these injuries are the result of inflicted abusive events by a trusted caregiver. Abusive head trauma (AHT) in infants, formerly known as shaken baby syndrome, is the leading cause of inflicted mortality and morbidity in this population. In this review we address clinical diagnosis, symptoms, prognosis, and neuropathology of AHT, emphasizing the burden of repetitive AHT. Next, we consider existing animal models of AHT, and we evaluate key features of an ideal model, highlighting important developmental milestones in children most vulnerable to AHT. We draw on insights from other injury models, such as repetitive, mild TBIs (RmTBIs), post-traumatic epilepsy (PTE), hypoxic-ischemic injuries, and maternal neglect, to speculate on key knowledge gaps and underline important new opportunities in pre-clinical AHT research. Finally, potential treatment options to facilitate healthy development in children following an AHT are considered. Together, this review aims to drive the field toward optimized, well-characterized animal models of AHT, which will allow for greater insight into the underlying neuropathological and neurobehavioral consequences of AHT.

Socioeconomic Status, Lifestyle, and DNA Methylation Age Among Racially and Ethnically Diverse Adults: NIMHD Social Epigenomics Program

Importance

Variation in DNA methylation at specific loci estimates biological age, which is associated with morbidity, mortality, and social experiences. Aging estimates known as epigenetic clocks, including the Dunedin Pace of Aging Calculated From the Epigenome (DunedinPACE), were trained on data predominately from individuals of European ancestry; however, limited research has explored DunedinPACE in underrepresented populations experiencing health disparities.

Objective

To investigate associations of neighborhood and individual sociobehavioral factors with biological aging in a racially and ethnically diverse population.

Design, Setting, and Participants

This cohort study, part of the Multiethnic Cohort study conducted from May 1993 to September 1996 to examine racial and ethnic disparities in chronic diseases, integrated biospecimen and self-reported data collected between April 2004 and November 2005 from healthy Hawaii residents aged 45 to 76 years. These participants self-identified as of Japanese American, Native Hawaiian, or White racial and ethnic background. Data were analyzed from January 2022 to May 2024.

Main Outcomes and Measures

DNA methylation data were generated from monocytes enriched from cryopreserved lymphocytes and used to derive DunedinPACE scores from November 2017 to June 2021. Neighborhood social economic status (NSES) was estimated from 1990 US Census Bureau data to include factors such as educational level, occupation, and income. Individual-level factors analyzed included educational level, body mass index (BMI), physical activity (PA), and diet quality measured by the Healthy Eating Index (HEI). Linear regression analysis of DunedinPACE scores was used to examine their associations with NSES and sociobehavioral variables.

Results

A total of 376 participants were included (113 [30.1%] Japanese American, 144 [38.3%] Native Hawaiian, and 119 [31.6%] White; 189 [50.3%] were female). Mean (SE) age was 57.81 (0.38) years. Overall, mean (SE) DunedinPACE scores were significantly higher among females than among males (1.28 [0.01] vs 1.25 [0.01]; P = .005); correlated negatively with NSES (R = -0.09; P = .08), HEI (R = -0.11; P = .03), and educational attainment (R = -0.15; P = .003) and positively with BMI (R = 0.31; P < .001); and varied by race and ethnicity. Native Hawaiian participants exhibited a higher mean (SE) DunedinPACE score (1.31 [0.01]) compared with Japanese American (1.25 [0.01]; P < .001) or White (1.22 [0.01]; P < .001) participants. Controlling for age, sex, HEI, BMI, and NSES, linear regression analyses revealed a negative association between educational level and DunedinPACE score among Japanese American (β, -0.005 [95% CI, -0.013 to 0.002]; P = .03) and Native Hawaiian (β, -0.003 [95% CI, -0.011 to 0.005]; P = .08) participants, yet this association was positive among White participants (β, 0.007; 95% CI, -0.001 to 0.015; P = .09). Moderate to vigorous PA was associated with lower DunedinPACE scores only among Native Hawaiian participants (β, -0.006; 95% CI, -0.011 to -0.001; P = .005), independent of NSES.

Conclusions and Relevance

In this study of a racially and ethnically diverse sample of 376 adults, low NSES was associated with a higher rate of biological aging measured by DunedinPACE score, yet individual-level factors such as educational level and physical activity affected this association, which varied by race and ethnicity. These findings support sociobehavioral interventions in addressing health inequities.

Metabolic memory: mechanisms and diseases

Metabolic diseases and their complications impose health and economic burdens worldwide. Evidence from past experimental studies and clinical trials suggests our body may have the ability to remember the past metabolic environment, such as hyperglycemia or hyperlipidemia, thus leading to chronic inflammatory disorders and other diseases even after the elimination of these metabolic environments. The long-term effects of that aberrant metabolism on the body have been summarized as metabolic memory and are found to assume a crucial role in states of health and disease. Multiple molecular mechanisms collectively participate in metabolic memory management, resulting in different cellular alterations as well as tissue and organ dysfunctions, culminating in disease progression and even affecting offspring. The elucidation and expansion of the concept of metabolic memory provides more comprehensive insight into pathogenic mechanisms underlying metabolic diseases and complications and promises to be a new target in disease detection and management. Here, we retrace the history of relevant research on metabolic memory and summarize its salient characteristics. We provide a detailed discussion of the mechanisms by which metabolic memory may be involved in disease development at molecular, cellular, and organ levels, with emphasis on the impact of epigenetic modulations. Finally, we present some of the pivotal findings arguing in favor of targeting metabolic memory to develop therapeutic strategies for metabolic diseases and provide the latest reflections on the consequences of metabolic memory as well as their implications for human health and diseases.

Abnormal DNA methylation within HPA-axis genes years after paediatric critical illness

BACKGROUND

Critically ill children suffer from impaired physical/neurocognitive development 2 years later. Glucocorticoid treatment alters DNA methylation within the hypothalamus-pituitary-adrenal (HPA) axis which may impair normal brain development, cognition and behaviour. We tested the hypothesis that paediatric-intensive-care-unit (PICU) patients, sex- and age-dependently, show long-term abnormal DNA methylation within the HPA-axis layers, possibly aggravated by glucocorticoid treatment in the PICU, which may contribute to the long-term developmental impairments.

RESULTS

In a pre-planned secondary analysis of the multicentre PEPaNIC-RCT and its 2-year follow-up, we identified differentially methylated positions and differentially methylated regions within HPA-axis genes in buccal mucosa DNA from 818 former PICU patients 2 years after PICU admission (n = 608 no glucocorticoid treatment; n = 210 glucocorticoid treatment) versus 392 healthy children and assessed interaction with sex and age, role of glucocorticoid treatment in the PICU and associations with long-term developmental impairments. Adjusting for technical variation and baseline risk factors and correcting for multiple testing (false discovery rate < 0.05), former PICU patients showed abnormal DNA methylation of 26 CpG sites (within CRHR1, POMC, MC2R, NR3C1, FKBP5, HSD11B1, SRD5A1, AKR1D1, DUSP1, TSC22D3 and TNF) and three DNA regions (within AVP, TSC22D3 and TNF) that were mostly hypomethylated. These abnormalities were sex-independent and only partially age-dependent. Abnormal methylation of three CpG sites within FKBP5 and one CpG site within SRD5A1 and AKR1D1 was partly attributable to glucocorticoid treatment during PICU stay. Finally, abnormal methylation within FKBP5 and AKR1D1 was most robustly associated with long-term impaired development.

CONCLUSIONS

Two years after critical illness in children, abnormal methylation within HPA-axis genes was present, predominantly within FKBP5 and AKR1D1, partly attributable to glucocorticoid treatment in the PICU, and explaining part of the long-term developmental impairments. These data call for caution regarding liberal glucocorticoid use in the PICU.

Epigenetics of prenatal stress in humans: the current research landscape

Fetal exposure to prenatal stress can have significant consequences on short- and long-term health. Epigenetic mechanisms, especially DNA methylation (DNAm), are a possible process how these adverse environmental events could be biologically embedded. We evaluated candidate gene as well as epigenome-wide association studies associating prenatal stress and DNAm changes in peripheral tissues; however, most of these findings lack robust replication. Prenatal stress-associated epigenetic changes have also been linked to child health including internalizing problems, neurobehavioral outcomes and stress reactivity. Future studies should focus on refined measurement and definition of prenatal stress and its timing, ideally also incorporating genomic as well as longitudinal information. This will provide further opportunities to enhance our understanding of the biological embedding of prenatal stress exposure.

The epigenome under pressure: On regulatory adaptation to chronic stress in the brain

Chronic stress (CS) can have long-lasting consequences on behavior and cognition, that are associated with stable changes in gene expression in the brain. Recent work has examined the role of the epigenome in the effects of CS on the brain. This review summarizes experimental evidence in rodents showing that CS can alter the epigenome and the expression of epigenetic modifiers in brain cells, and critically assesses their functional effect on genome function. It discusses the influence of the developmental time of stress exposure on the type of epigenetic changes, and proposes new lines of research that can help clarify these changes and their causal involvement in the impact of CS.

Early life stress modulates the genetic influence on brain structure and cognitive function in children

The enduring influence of early life stress (ELS) on brain and cognitive development has been widely acknowledged, yet the precise mechanisms underlying this association remain elusive. We hypothesize that ELS might disrupt the genome-wide influence on brain morphology and connectivity development, consequently exerting a detrimental impact on children's cognitive ability. We analyzed the multimodal data of DNA genotypes, brain imaging (structural and diffusion MRI), and neurocognitive battery (NIH Toolbox) of 4276 children (ages 9-10 years, European ancestry) from the Adolescent Brain Cognitive Development (ABCD) study. The genome-wide influence on cognitive function was estimated using the polygenic score (GPS). By using brain morphometry and tractography, we identified the brain correlates of the cognition GPSs. Statistical analyses revealed relationships for the gene-brain-cognition pathway. The brain structural variance significantly mediated the genetic influence on cognition (indirect effect = 0.016, PFDR < 0.001). Of note, this gene-brain relationship was significantly modulated by abuse, resulting in diminished cognitive capacity (Index of Moderated Mediation = -0.007; 95 % CI = -0.012 ∼ -0.002). Our results support a novel gene-brain-cognition model likely elucidating the long-lasting negative impact of ELS on children's cognitive development.

Epigenetic Modulations by Microbiome in Breast Cancer

Recent studies have identified a critical role of the diverse and dynamic microbiome in modulating various aspects of host physiology and intrinsic processes. However, the altered microbiome has also become a hallmark of cancer, which could influence the tumor microenvironment. Aberrations in epigenetic regulation of tumor suppressors, apoptotic genes, and oncogenes can accentuate breast cancer onset and progression. Interestingly, recent studies have established that the microbiota modulates the epigenetic mechanisms at global and gene-specific levels. While the mechanistic basis is unclear, the cross-talk between the microbiome and epigenetics influences breast cancer trajectory. Here, we review different epigenetic mechanisms of mammalian gene expression and summarize the host-associated microbiota distributed across the human body and their influence on cancer and other disease-related genes. Understanding this complex relationship between epigenetics and the microbiome holds promise for new insights into effective therapeutic strategies for breast cancer patients.

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.

Therapeutic and Preventive Interventions in Adolescents with Borderline Personality Disorder: Recent Findings, Current Challenges, and Future Directions

BACKGROUND

Borderline personality disorder (BPD) has long suffered from overshadowing in adolescents and hopelessness from the psychiatrists themselves. Comprehensive guidelines for this age group are lacking.

AIMS

This narrative review aims to describe current recommendations for BPD and recent empirical evidence on effective treatments (both pharmacological and non-pharmacological) and preventive approaches. Innovative approaches, based on recent and original research on BPD adolescents, are also discussed.

RESULTS

Very low-certainty evidence has supported that medication has a positive effect on core BPD symptoms in adolescents. Medication prescribed for suicidal crises or associated disorders should be included in a global therapeutic plan, including efficacy reassessment, treatment duration, and a security plan. The overall benefit of structured psychotherapy for adolescents with BPD (cognitive behavioral therapy, mentalization-based therapy, dialectic behavioral therapy, and group therapy) is more important for self-harm behaviors than other BPD symptoms. Their specific efficacy, although difficult to distinguish from the overall non-specific effect of integrative care.

CONCLUSIONS

structured care of young BPD individuals should be based on the following principles: (1) setting the frame of care, including recognition of the diagnosis, and sharing information with patients and families about symptoms, prognosis, and putative psychological mechanisms involved; and (2) promoting comprehensive approaches, including both specific and non specific therapy, ecological interventions, community care, and preventive interventions in at-risk groups.

The role of stress in the biological embedding of experience

Exposure to early adversity is one of the most important and pervasive risk factors for the development of nearly all major mental disorders across the lifespan. In the search for the mediating mechanisms and processes that underlie long-term stability of these effects, changes to stress-associated hormonal and cellular signalling have emerged as prime candidates. This review summarises evidence showing that experience of early adversity in the form of childhood abuse or neglect and exposure to severe institutional deprivation influences multiple interconnected bio-behavioural, physiological and cellular processes. This paper focusses on dysregulations of hormonal stress regulation, altered DNA methylation pattern, changes to transcriptomic profiles in the context of stress-immune interplay, and mitochondrial biology. Consistent findings that have emerged include a relative cortisol hypoactivity and hyporeactivity in response to challenge, increased activity of pro-inflammatory genes, and altered mitochondrial function. The majority of investigations have focussed on single outcomes, but there is a clear rationale of conceiving the implicated physiological processes as interconnected parts of a wider stress-associated regulatory network, which in turn is connected to behaviour and mental disorders. This calls for integrated and longitudinal investigations to come to a more comprehensive understanding of the role of stress in the biological embedding of experience. The review concludes with considerations of how stress research can contribute to translational efforts through characterising subtypes of mental disorders which arise as a function of early adversity, and have distinct features of behavioral and biological stress processing.

Accurate age prediction from blood using a small set of DNA methylation sites and a cohort-based machine learning algorithm

Chronological age prediction from DNA methylation sheds light on human aging, health, and lifespan. Current clocks are mostly based on linear models and rely upon hundreds of sites across the genome. Here, we present GP-age, an epigenetic non-linear cohort-based clock for blood, based upon 11,910 methylomes. Using 30 CpG sites alone, GP-age outperforms state-of-the-art models, with a median accuracy of ∼2 years on held-out blood samples, for both array and sequencing-based data. We show that aging-related changes occur at multiple neighboring CpGs, with implications for using fragment-level analysis of sequencing data in aging research. By training three independent clocks, we show enrichment of donors with consistent deviation between predicted and actual age, suggesting individual rates of biological aging. Overall, we provide a compact yet accurate alternative to array-based clocks for blood, with applications in longitudinal aging research, forensic profiling, and monitoring epigenetic processes in transplantation medicine and cancer.

Epigenetic modification of the hypothalamic-pituitary-adrenal (HPA) axis during development in the house sparrow (Passer domesticus)

Epigenetic modifications such as DNA methylation are important mechanisms for mediating developmental plasticity, where ontogenetic processes and their phenotypic outcomes are shaped by early environments. In particular, changes in DNA methylation of genes within the hypothalamic-pituitary-adrenal (HPA) axis can impact offspring growth and development. This relationship has been well documented in mammals but is less understood in other taxa. Here, we use target-enriched enzymatic methyl sequencing (TEEM-seq) to assess how DNA methylation in a suite of 25 genes changes over development, how these modifications relate to the early environment, and how they predict differential growth trajectories in the house sparrow (Passer domesticus). We found that DNA methylation changes dynamically over the postnatal developmental period: genes with initially low DNA methylation tended to decline in methylation over development, whereas genes with initially high DNA methylation tended to increase in methylation. However, sex-specific differentially methylated regions (DMRs) were maintained across the developmental period. We also found significant differences in post-hatching DNA methylation in relation to hatch date, with higher levels of DNA methylation in nestlings hatched earlier in the season. Although these differences were largely absent by the end of development, a number of DMRs in HPA-related genes (CRH, MC2R, NR3C1, NR3C2, POMC)-and to a lesser degree HPG-related genes (GNRHR2)-predicted nestling growth trajectories over development. These findings provide insight into the mechanisms by which the early environment shapes DNA methylation in the HPA axis, and how these changes subsequently influence growth and potentially mediate developmental plasticity.

Interaction of the pre- and postnatal environment in the maternal immune activation model

Adverse influences during pregnancy are associated with a range of unfavorable outcomes for the developing offspring. Maternal psychosocial stress, exposure to infections and nutritional imbalances are known risk factors for neurodevelopmental derangements and according psychiatric and neurological manifestations later in offspring life. In this context, the maternal immune activation (MIA) model has been extensively used in preclinical research to study how stimulation of the maternal immune system during gestation derails the tightly coordinated sequence of fetal neurodevelopment. The ensuing consequence of MIA for offspring brain structure and function are majorly manifested in behavioral and cognitive abnormalities, phenotypically presenting during the periods of adolescence and adulthood. These observations have been interpreted within the framework of the "double-hit-hypothesis" suggesting that an elevated risk for neurodevelopmental disorders results from an individual being subjected to two adverse environmental influences at distinct periods of life, jointly leading to the emergence of pathology. The early postnatal period, during which the caregiving parent is the major determinant of the newborn´s environment, constitutes a window of vulnerability to external stimuli. Considering that MIA not only affects the developing fetus, but also impinges on the mother´s brain, which is in a state of heightened malleability during pregnancy, the impact of MIA on maternal brain function and behavior postpartum may importantly contribute to the detrimental consequences for her progeny. Here we review current information on the interaction between the prenatal and postnatal maternal environments in the modulation of offspring development and their relevance for the pathophysiology of the MIA model.

Repetitive Transcranial Magnetic Stimulation Reduces Depressive-like Behaviors, Modifies Dendritic Plasticity, and Generates Global Epigenetic Changes in the Frontal Cortex and Hippocampus in a Rodent Model of Chronic Stress

Depression is the most common affective disorder worldwide, accounting for 4.4% of the global population, a figure that could increase in the coming decades. In depression, there exists a reduction in the availability of dendritic spines in the frontal cortex (FC) and hippocampus (Hp). In addition, histone modification and DNA methylation are also dysregulated epigenetic mechanisms in depression. Repetitive transcranial magnetic stimulation (rTMS) is a technique that is used to treat depression. However, the epigenetic mechanisms of its therapeutic effect are still not known. Therefore, in this study, we evaluated the antidepressant effect of 5 Hz rTMS and examined its effect on dendritic remodeling, immunoreactivity of synapse proteins, histone modification, and DNA methylation in the FC and Hp in a model of chronic mild stress. Our data indicated that stress generated depressive-like behaviors and that rTMS reverses this effect, romotes the formation of dendritic spines, and favors the presynaptic connection in the FC and DG (dentate gyrus), in addition to increasing histone H3 trimethylation and DNA methylation. These results suggest that the antidepressant effect of rTMS is associated with dendritic remodeling, which is probably regulated by epigenetic mechanisms. These data are a first approximation of the impact of rTMS at the epigenetic level in the context of depression. Therefore, it is necessary to analyze in future studies as to which genes are regulated by these mechanisms, and how they are associated with the neuroplastic modifications promoted by rTMS.

The impact of antidepressants on human neurodevelopment: Brain organoids as experimental tools

The use of antidepressants during pregnancy benefits the mother's well-being, but the effects of such substances on neurodevelopment remain poorly understood. Moreover, the consequences of early exposure to antidepressants may not be immediately apparent at birth. In utero exposure to selective serotonin reuptake inhibitors (SSRIs) has been related to developmental abnormalities, including a reduced white matter volume. Several reports have observed an increased incidence of autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) after prenatal exposure to SSRIs such as sertraline, the most widely prescribed SSRI. The advent of human-induced pluripotent stem cell (hiPSC) methods and assays now offers appropriate tools to test the consequences of such compounds for neurodevelopment in vitro. In particular, hiPSCs can be used to generate cerebral organoids - self-organized structures that recapitulate the morphology and complex physiology of the developing human brain, overcoming the limitations found in 2D cell culture and experimental animal models for testing drug efficacy and side effects. For example, single-cell RNA sequencing (scRNA-seq) and electrophysiological measurements on organoids can be used to evaluate the impact of antidepressants on the transcriptome and neuronal activity signatures in developing neurons. While the analysis of large-scale transcriptomic data depends on dimensionality reduction methods, electrophysiological recordings rely on temporal data series to discriminate statistical characteristics of neuronal activity, allowing for the rigorous analysis of the effects of antidepressants and other molecules that affect the developing nervous system, especially when applied in combination with relevant human cellular models such as brain organoids.

Methyl-CpG binding protein 2 expression is associated with symptom severity in patients with PTSD in a sex-dependent manner

Traumatic events may lead to post-traumatic stress disorder (PTSD), with higher prevalence in women. Adverse childhood experiences (ACE) increase PTSD risk in adulthood. Epigenetic mechanisms play important roles in PTSD pathogenesis and a mutation in the methyl-CpG binding protein 2 (MECP2) in mice provide susceptibility to PTSD-like alterations, with sex-dependent biological signatures. The present study examined whether the increased risk of PTSD associated with ACE exposure is accompanied by reduced MECP2 blood levels in humans, with an influence of sex. MECP2 mRNA levels were analyzed in the blood of 132 subjects (58 women). Participants were interviewed to assess PTSD symptomatology, and asked to retrospectively report ACE. Among trauma-exposed women, MECP2 downregulation was associated with the intensification of PTSD symptoms linked to ACE exposure. MECP2 expression emerges as a potential contributor to post-trauma pathophysiology fostering novel studies on the molecular mechanisms underlying its potential sex-dependent role in PTSD onset and progression.

Current Understanding of the Roles of Gut-Brain Axis in the Cognitive Deficits Caused by Perinatal Stress Exposure

The term 'perinatal environment' refers to the period surrounding birth, which plays a crucial role in brain development. It has been suggested that dynamic communication between the neuro-immune system and gut microbiota is essential in maintaining adequate brain function. This interaction depends on the mother's status during pregnancy and/or the newborn environment. Here, we show experimental and clinical evidence that indicates that the perinatal period is a critical window in which stress-induced immune activation and altered microbiota compositions produce lasting behavioral consequences, although a clear causative relationship has not yet been established. In addition, we discuss potential early treatments for preventing the deleterious effect of perinatal stress exposure. In this sense, early environmental enrichment exposure (including exercise) and melatonin use in the perinatal period could be valuable in improving the negative consequences of early adversities. The evidence presented in this review encourages the realization of studies investigating the beneficial role of melatonin administration and environmental enrichment exposure in mitigating cognitive alteration in offspring under perinatal stress exposure. On the other hand, direct evidence of microbiota restoration as the main mechanism behind the beneficial effects of this treatment has not been fully demonstrated and should be explored in future studies.

The impact of environmental factors during maternal separation on the behaviors of adolescent C57BL/6 mice

Neonatal maternal separation is a widely used method to construct an early-life stress model in rodents. In this method, pups are separated from their mothers for several hours every day during the first 2 weeks of life, which results in adverse early-life events. It is a known fact that maternal separation can exert a significant impact on the behavior and psychological health, such as anxiety and depression, in adolescent offspring. However, environmental conditions during maternal separation can differ such as the presence of other animals or by placing pups in a different dam. To investigate the differential effects of various conditions of maternal separation on the behavior of adolescent mice, we created the following groups: (1) iMS group: pups were moved to an isolated room with no other adult mice in a nearby cage, (2) eDam group: the pups randomly exchanged their dams, (3) OF group: pups were shifted to another cage with the bedding material containing maternal odor (olfactory stimulation), and (4) MS group: pups were shifted to another vivarium. From postnatal day (PND) 2-20 (i.e., 19 consecutive days), pups were separated from the dam daily for 4 h and exposed to various environments (MS, iMS, eDam, and OF) or were left undisturbed [control (CON) group]. A series of behavioral assessments were conducted to evaluate locomotion, anxiety, recognition, learning, and memory in adolescent offspring. The results showed that neonatal maternal separation led to impaired recognition memory, motor coordination, and motor skill learning across all groups. However, the iMS group exhibited anxiety-like behavior in the elevated plus maze test and enhanced the extinction of fear memory in the auditory fear conditioning test. The OF and eDam groups displayed partially recovered short-term working memory in the Y-maze test but exhibited opposite exploratory behaviors. The OF group spent more time in the center, while the eDam group spent less time. These findings demonstrated that exposure to different environmental conditions during maternal separation causes behavioral alterations in adolescent offspring, providing a potential explanation for the variation in behavioral phenotypes observed in the early-life stress models.

Connecting dots in disorders of gut-brain interaction: the interplay of stress and sex hormones in shaping visceral pain

Visceral pain and stress are tightly intertwined bodily and emotional phenomena, which enable a flexible adaptation to environmental challenges by activating a response repertoire to restore homeostasis along the gut-brain axis. However, visceral pain and stress can persist widely independent of the initial cause, acquiring independent disease values and posing major health burdens as predominant features in disorders of gut-brain interaction (DGBI). Epidemiological data consistently documents an increased prevalence for women to suffer from chronic visceral pain, possibly shaped by sex hormones and modulated by stress and its biological and psychosocial correlates. Yet, mechanisms underlying the complex interactions between altered visceroception, stress and sex remain widely elusive, especially in clinical populations with DGBI. We herein selectively review mechanisms of interactions between stress and sex in the complex pathophysiology of DGBI. A particular emphasis is laid on visceral pain, in which stress constitutes a major risk factor as well as mediator, and sex-related differences are particularly pronounced. Building on the neurobiology of stress and mechanisms of gut-brain interactions, we highlight putative target mechanisms via which visceral pain and stress may converge with sex effects into a triad. Accommodating a global demographic shift, we propose a lifespan perspective in future research, which may enable a more fine-tuned evaluation of this complex interplay exerting distinct challenges during vulnerable developmental phases. This viewpoint may advance our understanding of pathophysiological processes and can ultimately inspire novel tailored prevention strategies and therapeutic approaches in the treatment of chronic visceral pain and DGBI across the lifespan.

The Epigenetics of Animal Personality

Animal personality, consistent individual differences in behaviour, is an important concept for understanding how individuals vary in how they cope with environmental challenges. In order to understand the evolutionary significance of animal personality, it is crucial to understand the underlying regulatory mechanisms. Epigenetic marks such as DNA methylation are hypothesised to play a major role in explaining variation in phenotypic changes in response to environmental alterations. Several characteristics of DNA methylation also align well with the concept of animal personality. In this review paper, we summarise the current literature on the role that molecular epigenetic mechanisms may have in explaining personality variation. We elaborate on the potential for epigenetic mechanisms to explain behavioural variation, behavioural development and temporal consistency in behaviour. We then suggest future routes for this emerging field and point to potential pitfalls that may be encountered. We conclude that a more inclusive approach is needed for studying the epigenetics of animal personality and that epigenetic mechanisms cannot be studied without considering the genetic background.

Genome-Environment Interactions and Psychiatric Disorders

Environmental factors are known to interact with the genome by altering epigenetic mechanisms regulating gene expression and contributing to the pathogenesis of psychiatric disorders. This article is a narrative review of how the major environmental factors contribute to the pathogenesis of common psychiatric disorders such as schizophrenia, bipolar disorder, major depressive disorder, and anxiety disorder this way. The cited articles were published between 1 January 2000 and 31 December 2022 and were obtained from PubMed and Google Scholar. The search terms used were as follows: gene or genetic; genome; environment; mental or psychiatric disorder; epigenetic; and interaction. The following environmental factors were found to act epigenetically on the genome to influence the pathogenesis of psychiatric disorders: social determinants of mental health, maternal prenatal psychological stress, poverty, migration, urban dwelling, pregnancy and birth complications, alcohol and substance abuse, microbiota, and prenatal and postnatal infections. The article also discusses the ways by which factors such as drugs, psychotherapy, electroconvulsive therapy, and physical exercise act epigenetically to alleviate the symptoms of psychiatric disorders in affected patients. These data will be useful information for clinical psychiatrists and those researching the pathogenesis and treatment of psychiatric disorders.

Activation of D1R signaling in the medial prefrontal cortex rescues maternal separation-induced behavioral deficits through restoration of excitatory neurotransmission

Lack of maternal care and attention during infancy and childhood increases the likelihood of developing a range of neuropsychiatric disorders, such as social deficits, working memory impairment, and anxiety-like behaviors, in adulthood. However, the neuroregulatory signaling through which early-life stress causes behavioral and cognitive abnormalities in the offspring is largely unexplored. Here, we show that in mice, unpredictable maternal separation (MS) during the early postnatal period impairs neuronal development in the medial prefrontal cortex (mPFC) and results in long-lasting behavioral changes. Additionally, MS disrupts excitatory neurotransmission and inhibits the neuronal activity of pyramidal neurons in the mPFC. Differentially expressed gene (DEG) analysis of RNA sequencing (RNA-seq) data of mPFC showed that dopamine D1 receptor (D1R) was significantly downregulated in MS animals. Finally, we show that pharmacological activation of D1R signaling specifically in the mPFC improves neuronal excitability and rescues behavioral and cognitive dysfunction of MS mice, whereas pharmacologically inhibiting of D1R in the mPFC mimics MS-induced behavioral abnormalities in control mice. Together, our results identify D1R signaling in the mPFC, at least in part, as a potential therapeutic target for the behavioral and cognitive abnormalities caused by deprivation of maternal care in early life.

Basic Concepts and Hormonal Regulators of the Stress System

BACKGROUND

Human organisms have to cope with a large number of external or internal stressful stimuli that threaten - or are perceived as threatening - their internal dynamic balance or homeostasis. To face these disturbing forces, or stressors, organisms have developed a complex neuroendocrine system, the stress system, which consists of the hypothalamic-pituitary-adrenal axis and the locus caeruleus/norepinephrine-autonomic nervous system.

SUMMARY

Upon exposure to stressors beyond a certain threshold, the activation of the stress system leads to a series of physiological and behavioral adaptations that help achieve homeostasis and increase the chances of survival. When, however, the stress response to stressors is inadequate, excessive, or prolonged, the resultant maladaptation may lead to the development of several stress-related pathologic conditions. Adverse environmental events, especially during critical periods of life, such as prenatal life, childhood, and puberty/adolescence, in combination with the underlying genetic background, may leave deep, long-term epigenetic imprints in the human expressed genome.

KEY MESSAGES

In this review, we describe the components of the stress system and its functional interactions with other homeostatic systems of the organism; we present the hormonal regulators of the stress response, and we discuss the development of stress-related pathologies.

On the road to resilience: Epigenetic effects of meditation

Many environmental and lifestyle related factors may influence the physiology of the brain and body by acting on fundamental molecular pathways, such as the hypothalamus-pituitary-adrenal axis (HPA) and the immune system. For example, stressful conditions created by adverse early-life events, unhealthy habits and low socio-economic status may favor the onset of diseases linked to neuroendocrine dysregulation, inflammation and neuroinflammation. Beside pharmacological treatments used in clinical settings, much attention has been given to complementary treatments such as mind-body techniques involving meditation that rely on the activation of inner resources to regain health. At the molecular level, the effects of both stress and meditation are elicited epigenetically through a set of mechanisms that regulate gene expression as well as the circulating neuroendocrine and immune effectors. Epigenetic mechanisms constantly reshape genome activities in response to external stimuli, representing a molecular interface between organism and environment. In the present work, we aimed to review the current knowledge on the correlation between epigenetics, gene expression, stress and its possible antidote, meditation. After introducing the relationship between brain, physiology, and epigenetics, we will proceed to describe three basic epigenetic mechanisms: chromatin covalent modifications, DNA methylation and non-coding RNAs. Subsequently, we will give an overview of the physiological and molecular aspects related to stress. Finally, we will address the epigenetic effects of meditation on gene expression. The results of the studies reported in this review demonstrate that mindful practices modulate the epigenetic landscape, leading to increased resilience. Therefore, these practices can be considered valuable tools that complement pharmacological treatments when coping with pathologies related to stress.

Lasting impact of postnatal maternal separation on the developing BNST: Lifelong socioemotional consequences

Nearly one percent of children in the US experience childhood neglect or abuse, which can incite lifelong emotional and behavioral disorders. Many studies investigating the neural underpinnings of maleffects inflicted by early life stress have largely focused on dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. Newer veins of evidence suggest that exposure to early life stressors can interrupt neural development in extrahypothalamic areas as well, including the bed nucleus of the stria terminalis (BNST). One widely used approach in this area is rodent maternal separation (MS), which typically consists of separating pups from the dam for extended periods of time, over several days during the first weeks of postnatal life - a time when pups are highly dependent on maternal care for survival. MS has been shown to incite myriad lasting effects not limited to increased anxiety-like behavior, hyper-responsiveness to stressors, and social behavior deficits. The behavioral effects of MS are widespread and thus unlikely to be limited to hypothalamic mechanisms. Recent work has highlighted the BNST as a critical arbiter of some of the consequences of MS, especially socioemotional behavioral deficits. The BNST is a well-documented modulator of anxiety, reward, and social behavior by way of its connections with hypothalamic and extra-hypothalamic systems. Moreover, during the postnatal period when MS is typically administered, the BNST undergoes critical neural developmental events. This review highlights evidence that MS interferes with neural development to permanently alter BNST circuitry, which may account for a variety of behavioral deficits seen following early life stress. This article is part of the Special Issue on 'Fear, Anxiety and PTSD'.

Tet Enzyme-Mediated Response in Environmental Stress and Stress-Related Psychiatric Diseases

Mental disorders caused by stress have become a worldwide public health problem. These mental disorders are often the results of a combination of genes and environment, in which epigenetic modifications play a crucial role. At present, the genetic and epigenetic mechanisms of mental disorders such as posttraumatic stress disorder or depression caused by environmental stress are not entirely clear. Although many epigenetic modifications affect gene regulation, the most well-known modification in eukaryotic cells is the DNA methylation of CpG islands. Stress causes changes in DNA methylation in the brain to participate in the neuronal function or mood-modulating behaviors, and these epigenetic modifications can be passed on to offspring. Ten-eleven translocation (Tet) enzymes are the 5-methylcytosine (5mC) hydroxylases of DNA, which recognize 5mC on the DNA sequence and oxidize it to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC). Tet regulates gene expression at the transcriptional level through the demethylation of DNA. This review will elaborate on the molecular mechanism and the functions of Tet enzymes in environmental stress-related disorders and discuss future research directions.

Investigating the effects of maltreatment and acute stress on the concordance of blood and DNA methylation methods of estimating immune cell proportions

BACKGROUND

Immune cell proportions can be used to detect pathophysiological states and are also critical covariates in genomic analyses. The complete blood count (CBC) is the most common method of immune cell proportion estimation, but immune cell proportions can also be estimated using whole-genome DNA methylation (DNAm). Although the concordance of CBC and DNAm estimations has been validated in various adult and clinical populations, less is known about the concordance of existing estimators among stress-exposed individuals. As early life adversity and acute psychosocial stress have both been associated with unique DNAm alterations, the concordance of CBC and DNAm immune cell proportion needs to be validated in various states of stress.

RESULTS

We report the correlation and concordance between CBC and DNAm estimates of immune cell proportions using the Illumina EPIC DNAm array within two unique studies: Study 1, a high-risk pediatric cohort of children oversampled for exposure to maltreatment (N = 365, age 8 to 14 years), and Study 2, a sample of young adults who have participated in an acute laboratory stressor with four pre- and post-stress measurements (N = 28, number of observations = 100). Comparing CBC and DNAm proportions across both studies, estimates of neutrophils (r = 0.948, p < 0.001), lymphocytes (r = 0.916, p < 0.001), and eosinophils (r = 0.933, p < 0.001) were highly correlated, while monocyte estimates were moderately correlated (r = 0.766, p < 0.001) and basophil estimates were weakly correlated (r = 0.189, p < 0.001). In Study 1, we observed significant deviations in raw values between the two approaches for some immune cell subtypes; however, the observed differences were not significantly predicted by exposure to child maltreatment. In Study 2, while significant changes in immune cell proportions were observed in response to acute psychosocial stress for both CBC and DNAm estimates, the observed changes were similar for both approaches.

CONCLUSIONS

Although significant differences in immune cell proportion estimates between CBC and DNAm exist, as well as stress-induced changes in immune cell proportions, neither child maltreatment nor acute psychosocial stress alters the concordance of CBC and DNAm estimation methods. These results suggest that the agreement between CBC and DNAm estimators of immune cell proportions is robust to exposure to child maltreatment and acute psychosocial stress.

Is DNA methylation in the brain a mechanism of alcohol use disorder?

Alcohol use disorder (AUD) is a worldwide problem. Unfortunately, the molecular mechanisms of alcohol misuse are still poorly understood, therefore successful therapeutic approaches are limited. Accumulating data indicate that the tendency for compulsive alcohol use is inherited, suggesting a genetic background as an important factor. However, the probability to develop AUD is also affected by life experience and environmental factors. Therefore, the epigenetic modifications that are altered over lifetime likely contribute to increased risk of alcohol misuse. Here, we review the literature looking for the link between DNA methylation in the brain, a common epigenetic modification, and AUD-related behaviors in humans, mice and rats. We sum up the main findings, identify the existing gaps in our knowledge and indicate future directions of the research.

Methyl Donors, Epigenetic Alterations, and Brain Health: Understanding the Connection

Methyl donors such as choline, betaine, folic acid, methionine, and vitamins B6 and B12 are critical players in the one-carbon metabolism and have neuroprotective functions. The one-carbon metabolism comprises a series of interconnected chemical pathways that are important for normal cellular functions. Among these pathways are those of the methionine and folate cycles, which contribute to the formation of S-adenosylmethionine (SAM). SAM is the universal methyl donor of methylation reactions such as histone and DNA methylation, two epigenetic mechanisms that regulate gene expression and play roles in human health and disease. Epigenetic mechanisms have been considered a bridge between the effects of environmental factors, such as nutrition, and phenotype. Studies in human and animal models have indicated the importance of the optimal levels of methyl donors on brain health and behavior across the lifespan. Imbalances in the levels of these micronutrients during critical periods of brain development have been linked to epigenetic alterations in the expression of genes that regulate normal brain function. We present studies that support the link between imbalances in the levels of methyl donors, epigenetic alterations, and stress-related disorders. Appropriate levels of these micronutrients should then be monitored at all stages of development for a healthier brain.

DNA methylation signature of psychological resilience in young adults: Constructing a methylation risk score using a machine learning method

Resilience is a process associated with the ability to recover from stress and adversity. We aimed to explore the resilience-associated DNA methylation signatures and evaluate the abilities of methylation risk scores to discriminate low resilience (LR) individuals. The study recruited 78 young adults and used Connor-Davidson Resilience Scale (CD-RISC) to divide them into low and high resilience groups. We randomly allocated all participants of two groups to the discovery and validation sets. We used the blood DNA of the subjects to conduct a genome-wide methylation scan and identify the significant methylation differences of CpG Sites in the discovery set. Moreover, the classification accuracy of the DNA methylation probes was confirmed in the validation set by real-time quantitative methylation-specific polymerase chain reaction. In the genome-wide methylation profiling between LR and HR individuals, seventeen significantly differentially methylated probes were detected. In the validation set, nine DNA methylation signatures within gene coding regions were selected for verification. Finally, three methylation probes [cg18565204 (AARS), cg17682313 (FBXW7), and cg07167608 (LINC01107)] were included in the final model of the methylation risk score for LR versus HR. These methylation risk score models of low resilience demonstrated satisfactory discrimination by logistic regression and support vector machine, with an AUC of 0.81 and 0.93, accuracy of 72.3% and 87.1%, sensitivity of 75%, and 87.5%, and specificity of 70% and 80%. Our findings suggest that methylation signatures can be utilized to identify individuals with LR and establish risk score models that may contribute to the field of psychology.

Migraine in childhood: Gender differences

Migraine is a common neurological disorder in developmental age, involving up to 20% of children and adolescents. Although gender differences in migraine epidemiology and clinical characteristics have been largely investigated in adulthood, this issue is considerably less known in pediatric patients. We aim at providing an overview of gender differences in pediatric migraine. The most recent literature was reviewed taking into account the epidemiological, pathophysiological, and clinical differences between boys and girls with migraine. Although many aspects need to undergo further investigation, we conclude that different aspects of childhood migraine syndrome may vary depending on the gender and age, especially with regard to pubertal development.

Molecular pathways of major depressive disorder converge on the synapse

Major depressive disorder (MDD) is a psychiatric disease of still poorly understood molecular etiology. Extensive studies at different molecular levels point to a high complexity of numerous interrelated pathways as the underpinnings of depression. Major systems under consideration include monoamines, stress, neurotrophins and neurogenesis, excitatory and inhibitory neurotransmission, mitochondrial dysfunction, (epi)genetics, inflammation, the opioid system, myelination, and the gut-brain axis, among others. This review aims at illustrating how these multiple signaling pathways and systems may interact to provide a more comprehensive view of MDD's neurobiology. In particular, considering the pattern of synaptic activity as the closest physical representation of mood, emotion, and conscience we can conceptualize, each pathway or molecular system will be scrutinized for links to synaptic neurotransmission. Models of the neurobiology of MDD will be discussed as well as future actions to improve the understanding of the disease and treatment options.

Prenatal Stress and the Developing Brain: Postnatal Environments Promoting Resilience

Heightened maternal stress during pregnancy is associated with atypical brain development and an elevated risk for psychopathology in offspring. Supportive environments during early postnatal life may promote brain development and reverse atypical developmental trajectories induced by prenatal stress. We reviewed studies focused on the role of key early environmental factors in moderating associations between prenatal stress exposure and infant brain and neurocognitive outcomes. Specifically, we focused on the associations between parental caregiving quality, environmental enrichment, social support, and socioeconomic status with infant brain and neurocognitive outcomes. We examined the evidence that these factors may moderate the effects of prenatal stress on the developing brain. Complementing findings from translational models, human research suggests that high-quality early postnatal environments are associated with indices of infant neurodevelopment that have also been associated with prenatal stress, such as hippocampal volume and frontolimbic connectivity. Human studies also suggest that maternal sensitivity and higher socioeconomic status may attenuate the effects of prenatal stress on established neurocognitive and neuroendocrine mediators of risk for psychopathology, such as hypothalamic-pituitary-adrenal axis functioning. Biological pathways that may underlie the effects of positive early environments on the infant brain, including the epigenome, oxytocin, and inflammation, are also discussed. Future research in humans should examine resilience-promoting processes in relation to infant brain development using large sample sizes and longitudinal designs. The findings from this review could be incorporated into clinical models of risk and resilience during the perinatal period and used to design more effective early programs that reduce risk for psychopathology.

Sex matters: The impact of oxytocin on healthy conditions and psychiatric disorders

Oxytocin (OT) is involved in the regulation of physiological processes and emotional states, with increasing evidence for its beneficial actions being mediated by the autonomic and immune systems. Growing evidence suggests that OT plays a role in the pathophysiology of different psychiatric disorders. Given the limited information in humans the aim of this study was to retrospectively explore plasma OT levels in psychiatric patients, particularly focusing on sex-related differences, as compared with healthy controls. The patients studied here were divided into three groups diagnosed with obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD) or major depressive disorder (MDD). Plasma OT levels were significantly different between healthy men and women, with the latter showing higher values, while none of the three psychiatric groups showed sex-related differences in the parameters measured here. The intergroup analyses showed that the OT levels were significantly higher in OCD, lower in PTSD and even more reduced in MDD patients than in healthy subjects. These differences were also confirmed when gender was considered, with the exception of PTSD men, in whom OT levels were similar to those of healthy men. The present results indicated that OT levels were higher amongst healthy women than men, while a sex difference was less apparent or reversed in psychiatric patients. Reductions in sex differences in psychopathologies may be related to differential vulnerabilities in processes associated with basic adaptive and social functions.

The role of DNA methylation in progression of neurological disorders and neurodegenerative diseases as well as the prospect of using DNA methylation inhibitors as therapeutic agents for such disorders

Genome-wide studies related to neurological disorders and neurodegenerative diseases have pointed to the role of epigenetic changes such as DNA methylation, histone modification, and noncoding RNAs. DNA methylation machinery controls the dynamic regulation of methylation patterns in discrete brain regions.

Objective

This review aims to describe the role of DNA methylation in inhibiting and progressing neurological and neurodegenerative disorders and therapeutic approaches.

Methods

A Systematic search of PubMed, Web of Science, and Cochrane Library was conducted for all qualified studies from 2000 to 2022.

Results

For the current need of time, we have focused on the DNA methylation role in neurological and neurodegenerative diseases and the expression of genes involved in neurodegeneration such as Alzheimer's, Depression, and Rett Syndrome. Finally, it appears that the various epigenetic changes do not occur separately and that DNA methylation and histone modification changes occur side by side and affect each other. We focused on the role of modification of DNA methylation in several genes associated with depression (NR3C1, NR3C2, CRHR1, SLC6A4, BDNF, and FKBP5), Rett syndrome (MECP2), Alzheimer's, depression (APP, BACE1, BIN1 or ANK1) and Parkinson's disease (SNCA), as well as the co-occurring modifications to histones and expression of non-coding RNAs. Understanding these epigenetic changes and their interactions will lead to better treatment strategies.

Conclusion

This review captures the state of understanding of the epigenetics of neurological and neurodegenerative diseases. With new epigenetic mechanisms and targets undoubtedly on the horizon, pharmacological modulation and regulation of epigenetic processes in the brain holds great promise for therapy.