Progress in Epigenetics of Depression

Epigenetic Mechanisms of Obesity: Insights from Transgenic Animal Models

Obesity is a chronic disease with prevalence rates that have risen dramatically over the past four decades. This increase is not due to changes in the human genome but rather to environmental factors that promote maladaptive physiological responses. Emerging evidence suggests that external influences, such as high-fat diets, modify the epigenome-the interface between genes and the environment-leading to persistent alterations in energy homeostasis. This review explores the role of epigenetic mechanisms in obesity, emphasizing insights from transgenic animal models and clinical studies. Additionally, we discuss the evolution of obesity research from homeostatic to allostatic frameworks, highlighting key neuroendocrine regulators of energy balance.

Variations in BDNF and Their Role in the Neurotrophic Antidepressant Mechanisms of Ketamine and Esketamine: A Review

Brain-derived neurotrophic factor (BDNF) is critical for neuroplasticity, synaptic transmission, and neuronal survival. Studies have implicated it in the pathophysiology of depression, as its expression is significantly reduced in brain areas such as the prefrontal cortex and hippocampus in patients with depression. Our narrative review focuses on the relationship between BDNF, ketamine, and esketamine, specifically by summarizing human studies investigating BDNF variations in patients treated with these two drugs. BDNF plays a pivotal role in neuroplasticity and neurotrophic mechanisms that can be enhanced by traditional antidepressants, which have been shown to increase BDNF levels both peripherally and in targeted brain regions. Ketamine and its S-enantiomer, esketamine, exert both rapid and sustained antidepressant effects through activation of glutamate-related pathways, with neurotrophic effects involving BDNF, as demonstrated in experimental studies. However, clinical findings have shown mixed results, with most indicating an increase in plasma BDNF in patients treated with intravenous ketamine, although some studies contradict these findings. In addition to this, there are few studies of BDNF and esketamine. Currently, the limited number of studies suggests the need for further research, including larger sample sizes and investigations of BDNF and intranasal esketamine, which has been approved by several regulatory agencies for the treatment of treatment-resistant depression.

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.

Deciphering Depression: Epigenetic Mechanisms and Treatment Strategies

Depression, a significant mental health disorder, is under intense research scrutiny to uncover its molecular foundations. Epigenetics, which focuses on controlling gene expression without altering DNA sequences, offers promising avenues for innovative treatment. This review explores the pivotal role of epigenetics in depression, emphasizing two key aspects: (I) identifying epigenetic targets for new antidepressants and (II) using personalized medicine based on distinct epigenetic profiles, highlighting potential epigenetic focal points such as DNA methylation, histone structure alterations, and non-coding RNA molecules such as miRNAs. Variations in DNA methylation in individuals with depression provide opportunities to target genes that are associated with neuroplasticity and synaptic activity. Aberrant histone acetylation may indicate that antidepressant strategies involve enzyme modifications. Modulating miRNA levels can reshape depression-linked gene expression. The second section discusses personalized medicine based on epigenetic profiles. Analyzing these patterns could identify biomarkers associated with treatment response and susceptibility to depression, facilitating tailored treatments and proactive mental health care. Addressing ethical concerns regarding epigenetic information, such as privacy and stigmatization, is crucial in understanding the biological basis of depression. Therefore, researchers must consider these issues when examining the role of epigenetics in mental health disorders. The importance of epigenetics in depression is a critical aspect of modern medical research. These findings hold great potential for novel antidepressant medications and personalized treatments, which would significantly improve patient outcomes, and transform psychiatry. As research progresses, it is expected to uncover more complex aspects of epigenetic processes associated with depression, enhance our comprehension, and increase the effectiveness of therapies.

Models for depression recognition and efficacy assessment based on clinical and sequencing data

Major depression is a complex psychiatric disorder that includes genetic, neurological, and cognitive factors. Early detection and intervention can prevent progression, and help select the best treatment. Traditional clinical diagnosis tends to be subjective and misdiagnosed. Based on this, this study leverages clinical scale assessments and sequencing data to construct disease prediction models. Firstly, data undergoes preprocessing involving normalization and other requisite procedures. Feature engineering is then applied to curate subsets of features, culminating in the construction of a model through the implementation of machine learning and deep learning algorithms. In this study, 18 features with significant differences between patients and healthy controls were selected. The depression recognition model was constructed by deep learning with an accuracy of 87.26 % and an AUC of 91.56 %, which can effectively distinguish patients with depression from healthy controls. In addition, 33 features selected by recursive feature elimination method were used to construct a prognostic effect model of patients after 2 weeks of treatment, with an accuracy of 75.94 % and an AUC of 83.33 %. The results show that the deep learning algorithm based on clinical and sequencing data has good accuracy and provides an objective and accurate method for the diagnosis and pharmacodynamic prediction of depression. Furthermore, the selected differential features can serve as candidate biomarkers to provide valuable clues for diagnosis and efficacy prediction.

Astrocytic ALKBH5 in stress response contributes to depressive-like behaviors in mice

Epigenetic mechanisms bridge genetic and environmental factors that contribute to the pathogenesis of major depression disorder (MDD). However, the cellular specificity and sensitivity of environmental stress on brain epitranscriptomics and its impact on depression remain unclear. Here, we found that ALKBH5, an RNA demethylase of N6-methyladenosine (m6A), was increased in MDD patients' blood and depression models. ALKBH5 in astrocytes was more sensitive to stress than that in neurons and endothelial cells. Selective deletion of ALKBH5 in astrocytes, but not in neurons and endothelial cells, produced antidepressant-like behaviors. Astrocytic ALKBH5 in the mPFC regulated depression-related behaviors bidirectionally. Meanwhile, ALKBH5 modulated glutamate transporter-1 (GLT-1) m6A modification and increased the expression of GLT-1 in astrocytes. ALKBH5 astrocyte-specific knockout preserved stress-induced disruption of glutamatergic synaptic transmission, neuronal atrophy and defective Ca2+ activity. Moreover, enhanced m6A modification with S-adenosylmethionine (SAMe) produced antidepressant-like effects. Our findings indicate that astrocytic epitranscriptomics contribute to depressive-like behaviors and that astrocytic ALKBH5 may be a therapeutic target for depression.

Ketamine reverses stress-induced hypersensitivity to sunk costs

How mood interacts with information processing in the brain is thought to mediate the maladaptive behaviors observed in depressed individuals. However, the neural mechanisms underlying impairments in emotion-cognition interactions are poorly understood. This includes influencing the balance between how past-sensitive vs. future-looking one is during decision-making. Recent insights from the field of neuroeconomics offer novel approaches to study changes in such valuation processes in a manner that is biologically tractable and readily translatable across species. We recently discovered that rodents are sensitive to "sunk costs" - a feature of higher cognition previously thought to be unique to humans. The sunk costs bias describes the phenomenon in which an individual overvalues and escalates commitment to continuing an ongoing endeavor, even if suboptimal, as a function of irrecoverable past (sunk) losses - information that, according to classic economic theory, should be ignored. In the present study, mice were exposed to chronic social defeat stress paradigm, a well-established animal model used for the study of depression. Mice were then tested on our longitudinal neuroeconomic foraging task, Restaurant Row. We found mice exposed to this severe stressor displayed an increased sensitivity to sunk costs, without altering overall willingness to wait. Mice were then randomly assigned to receive a single intraperitoneal injection of either saline or ketamine (20 mg/kg). We discovered that stress-induced hypersensitivity to sunk costs was renormalized following a single dose of ketamine. Interestingly, in non-defeated mice, ketamine treatment completely abolished sunk cost sensitivity, causing mice to no longer value irrecoverable losses during re-evaluation decisions who instead based choices solely on the future investment required to obtain a goal. These findings suggest that the antidepressant effects of ketamine may be mediated in part through changes in the processing of past-sensitive information during on-going decision-making, reducing its weight as a potential source of cognitive dissonance that could modulate behavior and instead promoting more future-thinking behavior.

Epigenetics and suicide: investigating altered H3K14ac unveiled differential expression in ADORA2A, B4GALT2 and MMP14

Background: Environmental factors make an important contribution to suicide. Histone tails are prone to different modifications, leading to changes of chromatin (de)condensation and consequently gene expression. Materials & methods: Level of H3K14ac was studied with chromatin immunoprecipitation followed by high-throughput DNA sequencing. Genes were further validated with RT-qPCR; using hippocampal tissue. Results: We showed lowered H3K14ac levels in individuals who died by suicide. The genes ADORA2A, B4GALT2 and MMP14 showed differential expression in individuals who died by suicide. Identified genetic and protein interactions among genes show interactions with suicide-related genes. Conclusion: Further investigations of histone modifications in association with DNA methylation and miRNA are needed to expand our knowledge of the genes that could significantly contribute to suicide.

Neuroepigenetic Editing

Epigenetic regulation is intrinsic to basic neurobiological function as well as neurological disease. Regulation of chromatin-modifying enzymes in the brain is critical during both development and adulthood and in response to external stimuli. Biochemical studies are complemented by numerous next-generation sequencing (NGS) studies that quantify global changes in gene expression, chromatin accessibility, histone and DNA modifications in neurons and glial cells. Neuroepigenetic editing tools are essential to distinguish between the mere presence and functional relevance of histone and DNA modifications to gene transcription in the brain and animal behavior. This review discusses current advances in neuroepigenetic editing, highlighting methodological considerations pertinent to neuroscience, such as delivery methods and the spatiotemporal specificity of editing and it demonstrates the enormous potential of epigenetic editing for basic neurobiological research and therapeutic application.

Post-stroke depression: epigenetic and epitranscriptomic modifications and their interplay with gut microbiota

Epigenetic and epitranscriptomic modifications that regulate physiological processes of an organism at the DNA and RNA levels, respectively, are novel therapeutic candidates for various neurological diseases. Gut microbiota and its metabolites are known to modulate DNA methylation and histone modifications (epigenetics), as well as RNA methylation especially N6-methyladenosine (epitranscriptomics). As gut microbiota as well as these modifications are highly dynamic across the lifespan of an organism, they are implicated in the pathogenesis of stroke and depression. The lack of specific therapeutic interventions for managing post-stroke depression emphasizes the need to identify novel molecular targets. This review highlights the interaction between the gut microbiota and epigenetic/epitranscriptomic pathways and their interplay in modulating candidate genes that are involved in post-stroke depression. This review further focuses on the three candidates, including brain-derived neurotrophic factor, ten-eleven translocation family proteins, and fat mass and obesity-associated protein based on their prevalence and pathoetiologic role in post-stroke depression.

A sex-specific genome-wide association study of depression phenotypes in UK Biobank

There are marked sex differences in the prevalence, phenotypic presentation and treatment response for major depression. While genome-wide association studies (GWAS) adjust for sex differences, to date, no studies seek to identify sex-specific markers and pathways. In this study, we performed a sex-stratified genome-wide association analysis for broad depression with the UK Biobank total participants (N = 274,141), including only non-related participants, as well as with males (N = 127,867) and females (N = 146,274) separately. Bioinformatics analyses were performed to characterize common and sex-specific markers and associated processes/pathways. We identified 11 loci passing genome-level significance (P < 5 × 10-8) in females and one in males. In both males and females, genetic correlations were significant between the broad depression GWA and other psychopathologies; however, correlations with educational attainment and metabolic features including body fat, waist circumference, waist-to-hip ratio and triglycerides were significant only in females. Gene-based analysis showed 147 genes significantly associated with broad depression in the total sample, 64 in the females and 53 in the males. Gene-based analysis revealed "Regulation of Gene Expression" as a common biological process, but suggested sex-specific molecular mechanisms. Finally, sex-specific polygenic risk scores (PRSs) for broad depression outperformed total and the opposite sex PRSs in the prediction of broad major depressive disorder. These findings provide evidence for sex-dependent genetic pathways for clinical depression as well as for health conditions comorbid with depression.

Hypericin Ameliorates Depression-like Behaviors via Neurotrophin Signaling Pathway Mediating m6A Epitranscriptome Modification

Hypericin, one of the major antidepressant constituents of St. John's wort, was shown to exert antidepressant effects by affecting cerebral CYP enzymes, serotonin homeostasis, and neuroinflammatory signaling pathways. However, its exact mechanisms are unknown. Previous clinical studies reported that the mRNA modification N6-methyladenosine (m6A) interferes with the neurobiological mechanism in depressed patients, and it was also found that the antidepressant efficacy of tricyclic antidepressants (TCAs) is related to m6A modifications. Therefore, we hypothesize that the antidepressant effect of hypericin may relate to the m6A modification of epitranscriptomic regulation. We constructed a UCMS mouse depression model and found that hypericin ameliorated depressive-like behavior in UCMS mice. Molecular pharmacology experiments showed that hypericin treatment upregulated the expression of m6A-modifying enzymes METTL3 and WTAP in the hippocampi of UCMS mice. Next, we performed MeRIP-seq and RNA-seq to study m6A modifications and changes in mRNA expression on a genome-wide scale. The genome-wide m6A assay and MeRIP-qPCR results revealed that the m6A modifications of Akt3, Ntrk2, Braf, and Kidins220 mRNA were significantly altered in the hippocampi of UCMS mice after stress stimulation and were reversed by hypericin treatment. Transcriptome assays and qPCR results showed that the Camk4 and Arhgdig genes might be related to the antidepressant efficacy of hypericin. Further gene enrichment results showed that the differential genes were mainly involved in neurotrophic factor signaling pathways. In conclusion, our results show that hypericin upregulates m6A methyltransferase METTL3 and WTAP in the hippocampi of UCMS mice and stabilizes m6A modifications to exert antidepressant effects via the neurotrophin signaling pathway. This suggests that METTL3 and WTAP-mediated changes in m6A modifications may be a potential mechanism for the pathogenesis of depression and the efficacy of antidepressants, and that the neurotrophin signaling pathway plays a key role in this process.

Integrating genetics and transcriptomics to study major depressive disorder: a conceptual framework, bioinformatic approaches, and recent findings

Major depressive disorder (MDD) is a complex and heterogeneous psychiatric syndrome with genetic and environmental influences. In addition to neuroanatomical and circuit-level disturbances, dysregulation of the brain transcriptome is a key phenotypic signature of MDD. Postmortem brain gene expression data are uniquely valuable resources for identifying this signature and key genomic drivers in human depression; however, the scarcity of brain tissue limits our capacity to observe the dynamic transcriptional landscape of MDD. It is therefore crucial to explore and integrate depression and stress transcriptomic data from numerous, complementary perspectives to construct a richer understanding of the pathophysiology of depression. In this review, we discuss multiple approaches for exploring the brain transcriptome reflecting dynamic stages of MDD: predisposition, onset, and illness. We next highlight bioinformatic approaches for hypothesis-free, genome-wide analyses of genomic and transcriptomic data and their integration. Last, we summarize the findings of recent genetic and transcriptomic studies within this conceptual framework.

Epigenetic clock analysis reveals increased plasma cystatin C levels based on DNA methylation in major depressive disorder

Major depressive disorder (MDD) is a common mental illness and a major public health concern worldwide. Depression is associated with epigenetic changes that regulate gene expression, and analyzing these changes may help elucidate the pathophysiology of MDD. Genome-wide DNA methylation (DNAm) profiles can function as 'epigenetic clocks' that can help estimate biological aging. Here, we assessed biological aging in patients with MDD using various DNAm-based indicators of epigenetic aging. We used a publicly available dataset containing data obtained from the whole blood samples of MDD patients (n = 489) and controls (n = 210). We analyzed five epigenetic clocks (HorvathAge, HannumAge, SkinBloodAge, PhenoAge, and GrimAge) and DNAm-based telomere length (DNAmTL). We also investigated seven DNAm-based age-predictive plasma proteins (including cystatin C) and smoking status, which are components of GrimAge. Following adjustment for confounding factors such as age and sex, patients with MDD showed no significant difference in epigenetic clocks and DNAmTL. However, DNAm-based plasma cystatin C levels were significantly higher in patients with MDD than controls. Our findings revealed specific DNAm changes predicting plasma cystatin C levels in MDD. These findings may help elucidate the pathophysiology of MDD, leading to the development of new biomarkers and medications.

Epigenotoxicity: a danger to the future life

Environmental toxicants can regulate gene expression in the absence of DNA mutations via epigenetic mechanisms such as DNA methylation, histone modifications, and non-coding RNAs' (ncRNAs). Here, all three epigenetic modifications for seven important categories of diseases and the impact of eleven main environmental factors on epigenetic modifications were discussed. Epigenetic-related mechanisms are among the factors that could explain the root cause of a wide range of common diseases. Its overall impression on the development of diseases can help us diagnose and treat diseases, and besides, predict transgenerational and intergenerational effects. This comprehensive article attempted to address the relationship between environmental factors and epigenetic modifications that cause diseases in different categories. The studies main gap is that the precise role of environmentally-induced epigenetic alterations in the etiology of the disorders is unknown; thus, still more well-designed researches need to be accomplished to fill this gap. The present review aimed to first summarize the adverse effect of certain chemicals on the epigenome that may involve in the onset of particular disease based on in vitro and in vivo models. Subsequently, the possible adverse epigenetic changes that can lead to many human diseases were discussed.

Glucocorticoid Receptor Gene (NR3C1) Expression in the Pathogenesis of Depression in Cancer

Background

This study aimed to compare the NR3C1 expression among cancer patients with major depressive disorder (cancer depression), cancer patients without major depressive disorder (cancer non-depression), and major depressive disorder patients without cancer (general depression), as a preliminary investigation of epigenetic changes in the glucocorticoid receptor gene.

Methods

From May 2019 to November 2019, patients were recruited from the Department of Psychiatry, Cancer Center in Busan, Korea. For gene expression studies, primers were designed using the Primer3 web tool (http://frodo.wi.mit.edu/primer3), and amplification reactions were performed.

Results

Expression levels of NR3C1 were lower in cancer depression and general depression than in cancer non-depression group. Given that we observed downregulation of the NR3C1 gene expression in depressive patients regardless of cancer status, it appears that methylation changes in NR3C1 may contribute to the pathophysiology of depression.

Conclusion

The results of this study imply that the expression of NR3C1 may be decreased in major depressive disorder.

Ketamine Regulates the Autophagy Flux and Polarization of Microglia through the HMGB1-RAGE Axis and Exerts Antidepressant Effects in Mice

Depression is a leading cause of disability worldwide. Here, we explored the role of the HMGB1-RAGE pathway in lipopolysaccharide (LPS)-induced depression-like behavior and microglial autophagy flux, neuroinflammation, and polarization in a mouse model. Male C57BL/6 mice were infused with LPS in the abdominal cavity to induce a depression model. They then underwent testing to assess behavior and cognition. Real-time fluorescent quantitative polymerase chain reaction was used to detect the expression of the M1/M2 microglia polarization markers, HMGB1, and RAGE. Microglial activation and phenotypic transformation in the hippocampus were identified. mRFP-GFP-LC3 and Western blotting were used to detect autophagy flux in each treatment group. Finally, an LPS-induced BV2 cell model was developed to verify the involvement of the HMGB1-RAGE pathway, autophagy flux, and polarization. Ketamine improved LPS-induced depression-like behavior, inhibited the LPS-induced upregulation of HMGB1 and RAGE and the nuclear translocation of HMGB1. Moreover, ketamine reversed the blocked autophagy flux of microglia caused by LPS and regulated microglial autophagy flux through the HMGB1-RAGE pathway and microglial polarization. These results suggest that ketamine may reduce HMGB1 and RAGE accumulation in patients with depression, thereby providing a new therapeutic target for preventing and treating this disease.

M6A RNA Methylation-Based Epitranscriptomic Modifications in Plasticity-Related Genes via miR-124-C/EBPα-FTO-Transcriptional Axis in the Hippocampus of Learned Helplessness Rats

BACKGROUND

Impaired synaptic plasticity has been linked to dynamic gene regulatory network changes. Recently, gene regulation has been introduced with the emerging concept of unique N6-methyladenosine (m6A)-based reversible transcript methylation. In this study, we tested whether m6A RNA methylation may potentially serve as a link between the stressful insults and altered expression of plasticity-related genes.

METHODS

Expression of plasticity genes Nr3c1, Creb1, Ntrk2; m6A-modifying enzymes Fto, methyltransferase like (Mettl)-3 and 14; DNA methylation enzymes Dnmt1, Dnmt3a; transcription factor C/ebp-α; and miRNA-124-3p were determined by quantitative polymerase chain reaction (qPCR) in the hippocampus of rats that showed susceptibility to develop stress-induced depression (learned helplessness). M6A methylation of plasticity-related genes was determined following m6A mRNA immunoprecipitation. Chromatin immunoprecipitation was used to examine the endogenous binding of C/EBP-α to the Fto promoter. MiR-124-mediated post-transcriptional inhibition of Fto via C/EBPα was determined using an in vitro model.

RESULTS

Hippocampus of learned helplessness rats showed downregulation of Nr3c1, Creb1, and Ntrk2 along with enrichment in their m6A methylation. A downregulation in demethylating enzyme Fto and upregulation in methylating enzyme Mettl3 were also noted. The Fto promoter was hypomethylated due to the lower expression of Dnmt1 and Dnmt3a. At the same time, there was a lower occupancy of transcription factor C/EBPα on the Fto promoter. Conversely, C/ebp-α transcript was downregulated via induced miR-124-3p expression.

CONCLUSIONS

Our study mechanistically linked defective C/EBP-α-FTO-axis, epigenetically influenced by induced expression of miR-124-3p, in modifying m6A enrichment in plasticity-related genes. This could potentially be linked with abnormal neuronal plasticity in depression.

Depressive disorder and antidepressants from an epigenetic point of view

Depressive disorder is a complex, heterogeneous disease that affects approximately 280 million people worldwide. Environmental, genetic, and neurobiological factors contribute to the depressive state. Since the nervous system is susceptible to shifts in activity of epigenetic modifiers, these allow for significant plasticity and response to rapid changes in the environment. Among the most studied epigenetic modifications in depressive disorder is DNA methylation, with findings centered on the brain-derived neurotrophic factor gene, the glucocorticoid receptor gene, and the serotonin transporter gene. In order to identify biomarkers that would be useful in clinical settings, for diagnosis and for treatment response, further research on antidepressants and alterations they cause in the epigenetic landscape throughout the genome is needed. Studies on cornerstone antidepressants, such as selective serotonin reuptake inhibitors, selective serotonin and norepinephrine reuptake inhibitors, norepinephrine, and dopamine reuptake inhibitors and their effects on depressive disorder are available, but systematic conclusions on their effects are still hard to draw due to the highly heterogeneous nature of the studies. In addition, two novel drugs, ketamine and esketamine, are being investigated particularly in association with treatment of resistant depression, which is one of the hot topics of contemporary research and the field of precision psychiatry.

Nutrition, Epigenetics, and Major Depressive Disorder: Understanding the Connection

Major depressive disorder (MDD) is a complex, multifactorial disorder of rising prevalence and incidence worldwide. Nearly, 280 million of people suffer from this leading cause of disability in the world. Moreover, patients with this condition are frequently co-affected by essential nutrient deficiency. The typical scene with stress and hustle in developed countries tends to be accompanied by eating disorders implying overnutrition from high-carbohydrates and high-fat diets with low micronutrients intake. In fact, currently, coronavirus disease 2019 (COVID-19) pandemic has drawn more attention to this underdiagnosed condition, besides the importance of the nutritional status in shaping immunomodulation, in which minerals, vitamins, or omega 3 polyunsaturated fatty acids (ω-3 PUFA) play an important role. The awareness of nutritional assessment is greater and greater in the patients with depression since antidepressant treatments have such a significant probability of failing. As diet is considered a crucial environmental factor, underlying epigenetic mechanisms that experience an adaptation or consequence on their signaling and expression mechanisms are reviewed. In this study, we included metabolic changes derived from an impairment in cellular processes due to lacking some essential nutrients in diet and therefore in the organism. Finally, aspects related to nutritional interventions and recommendations are also addressed.

Beyond the neuron: Role of non-neuronal cells in stress disorders

Stress disorders are leading causes of disease burden in the U.S. and worldwide, yet available therapies are fully effective in less than half of all individuals with these disorders. Although to date, much of the focus has been on neuron-intrinsic mechanisms, emerging evidence suggests that chronic stress can affect a wide range of cell types in the brain and periphery, which are linked to maladaptive behavioral outcomes. Here, we synthesize emerging literature and discuss mechanisms of how non-neuronal cells in limbic regions of brain interface at synapses, the neurovascular unit, and other sites of intercellular communication to mediate the deleterious, or adaptive (i.e., pro-resilient), effects of chronic stress in rodent models and in human stress-related disorders. We believe that such an approach may one day allow us to adopt a holistic "whole body" approach to stress disorder research, which could lead to more precise diagnostic tests and personalized treatment strategies. Stress is a major risk factor for many psychiatric disorders. Cathomas et al. review new insight into how non-neuronal cells mediate the deleterious effects, as well as the adaptive, protective effects, of stress in rodent models and human stress-related disorders.

Mechanism of METTL3-mediated m6A modification in depression-induced cognitive deficits

Depressive disorder (DD) is associated with N6-methyladenosine (m6A) hypermethylation. This study sought to explore the molecular mechanism of Methyltransferase-like 3 (METTL3) in cognitive deficits of chronic unpredictable mild stress (CUMS)-treated rats and provide novel targets for DD treatment. A DD rat model was established via CUMS treatment. Cognitive deficits were assessed via body weighing and behavioral tests. METTL3, microRNA (miR)-221-3p, pri-miR-221, GRB2-associated binding protein 1 (Gab1) expressions in hippocampal tissues were detected via RT-qPCR and Western blotting. m6A, DiGeorge syndrome critical region gene 8 (DGCR8)-bound pri-miR-221 and pri-miR-221 m6A levels were measured. The binding relationship between miR-221-3p and Gab1 was testified by dual-luciferase and RNA pull-down assays. Rescue experiments were designed to confirm the role of miR-221-3p and Gab1. METTL3 was highly expressed in CUMS rats, and silencing METTL3 attenuated cognitive deficits of CUMS rats. METTL3-mediated m6A modification facilitated processing and maturation of pri-miR-221 via DGCR8 to upregulate miR-221-3p. miR-221-3p targeted Gab1. miR-221-3p overexpression or Gab1 downregulation reversed the role of silencing METTL3 in CUMS rats. Overall, METTL3-mediated m6A modification facilitated processing and maturation of pri-miR-221 to upregulate miR-221-3p and then inhibit Gab1, thereby aggravating cognitive deficits of CUMS rats.

Sex differences in the blood-brain barrier: Implications for mental health

Prevalence of mental disorders, including major depressive disorder (MDD), bipolar disorder (BD) and schizophrenia (SZ) are increasing at alarming rates in our societies. Growing evidence points toward major sex differences in these conditions, and high rates of treatment resistance support the need to consider novel biological mechanisms outside of neuronal function to gain mechanistic insights that could lead to innovative therapies. Blood-brain barrier alterations have been reported in MDD, BD and SZ. Here, we provide an overview of sex-specific immune, endocrine, vascular and transcriptional-mediated changes that could affect neurovascular integrity and possibly contribute to the pathogenesis of mental disorders. We also identify pitfalls in current literature and highlight promising vascular biomarkers. Better understanding of how these adaptations can contribute to mental health status is essential not only in the context of MDD, BD and SZ but also cardiovascular diseases and stroke which are associated with higher prevalence of these conditions.

Helicid Reverses the Effect of Overexpressing NCALD, Which Blocks the sGC/cGMP/PKG Signaling Pathway in the CUMS-Induced Rat Model

Background

Increasing evidence has shown that apoptosis in the hippocampus is closely related to depressive-like behavior. We previously reported that helicid had good antidepressant activities, which manifested as the alleviation of depression-like behaviors and the reversal of the high expression of neurocalcin delta (NCALD) in chronic unpredictable mild stress (CUMS) rats. The aim of this study was, therefore, to characterize the antidepressant-like effects and underlying mechanism of helicid on CUMS rats by silencing NCALD and using rescue experiments.

Methods

We developed the CUMS rat model using CUMS stimulation from week 0 to week 6. The rats were treated with helicid, or NCALD silenced, then we overexpressed NCALD using adeno-associated virus. We also measured the protein levels of sGCα1, sGCβ1, PKG1/2, and cleaved caspase-3 in hippocampal tissues using western blotting and measured cGMP using an ELISA.

Results

Treating CUMS rats by silencing NCALD or by the administration of helicid improved the depressive-like behavior. The levels of proteins, including sGC, PKG, cleaved caspase-3, and cGMP, in hippocampus all decreased. NCALD overexpression reversed these decreases and reversed the alleviation of depression-like behaviors in CUMS rats. Limitation. We only detected the antidepressant effects of helicid in the hippocampus; therefore, other parts of brain should also be studied.

Conclusions

Inhibition of NCALD, as well as helicid administration, alleviated antidepressant-like behavior by regulating the expressions of apoptotic cytokines and the sGC/cGMP/PKG signaling pathway. Overexpressing NCALD reversed the amelioration effects of silenced NCALD and helicid administration.

Fat mass and obesity-associated protein regulates RNA methylation associated with depression-like behavior in mice

Post-transcriptional modifications of RNA, such as RNA methylation, can epigenetically regulate behavior, for instance learning and memory. However, it is unclear whether RNA methylation plays a critical role in the pathophysiology of major depression disorder (MDD). Here, we report that expression of the fat mass and obesity associated gene (FTO), an RNA demethylase, is downregulated in the hippocampus of patients with MDD and mouse models of depression. Suppressing Fto expression in the mouse hippocampus results in depression-like behaviors in adult mice, whereas overexpression of FTO expression leads to rescue of the depression-like phenotype. Epitranscriptomic profiling of N6-methyladenosine (m6A) RNA methylation in the hippocampus of Fto knockdown (KD), Fto knockout (cKO), and FTO-overexpressing (OE) mice allows us to identify adrenoceptor beta 2 (Adrb2) mRNA as a target of FTO. ADRB2 stimulation rescues the depression-like behaviors in mice and spine loss induced by hippocampal Fto deficiency, possibly via the modulation of hippocampal SIRT1 expression by c-MYC. Our findings suggest that FTO is a regulator of a mechanism underlying depression-like behavior in mice.

In search of sex-related mediators of affective illness

Sex differences in the rates of affective disorders have been recognized for decades. Studies of physiologic sex-related differences in animals and humans, however, have generally yielded little in terms of explaining these differences. Furthermore, the significance of these findings is difficult to interpret given the dynamic, integrative, and highly context-dependent nature of human physiology. In this article, we provide an overview of the current literature on sex differences as they relate to mood disorders, organizing existing findings into five levels at which sex differences conceivably influence physiology relevant to affective states. These levels include the following: brain structure, network connectivity, signal transduction, transcription/translation, and epigenesis. We then evaluate the importance and limitations of this body of work, as well as offer perspectives on the future of research into sex differences. In creating this overview, we attempt to bring perspective to a body of research that is complex, poorly synthesized, and far from complete, as well as provide a theoretical framework for thinking about the role that sex differences ultimately play in affective regulation. Despite the overall gaps regarding both the underlying pathogenesis of affective illness and the role of sex-related factors in the development of affective disorders, it is evident that sex should be considered as an important contributor to alterations in neural function giving rise to susceptibility to and expression of depression.

DNA methylation in stress and depression: from biomarker to therapeutics

Epigenetic mechanisms such as DNA methylation (DNAm) have been associated with stress responses and increased vulnerability to depression. Abnormal DNAm is observed in stressed animals and depressed individuals. Antidepressant treatment modulates DNAm levels and regulates gene expression in diverse tissues, including the brain and the blood. Therefore, DNAm could be a potential therapeutic target in depression. Here, we reviewed the current knowledge about the involvement of DNAm in the behavioural and molecular changes associated with stress exposure and depression. We also evaluated the possible use of DNAm changes as biomarkers of depression. Finally, we discussed current knowledge limitations and future perspectives.

Perinatal stress and methylation of the NR3C1 gene in newborns: systematic review

Adverse experiences in the perinatal period have been associated with the methylation of the human glucocorticoid receptor gene (NR3C1) and long-term diseases. We conducted a systematic review on the association between adversities in the perinatal period and DNA methylation in the 1 _F region of the NR3C1 gene in newborns. We explored the MEDLINE, Web of Science, Scopus, Scielo, and Lilacs databases without time or language limitations. Two independent reviewers performed the selection of articles and data extraction. A third participated in the methodological quality assessment and consensus meetings at all stages. Finally, ten studies were selected. Methodological quality was considered moderate in six and low in four. Methylation changes were reported in 41 of the 47 CpG sites of exon 1 _F. Six studies addressed maternal conditions during pregnancy: two reported methylation changes at the same sites (CpG 10, 13, 20, 21 and 47), and four at one or more sites from CpG 35 to 39. Four studies addressed neonatal parameters and morbidities: methylation changes at the same sites 4, 8, 10, 16, 25, and 35 were reported in two. Hypermethylation associated with stressful conditions prevailed. Hypomethylation was more often associated with protective conditions (maternal-foetal attachment during pregnancy, breast milk intake, higher birth weight or Apgar). In conclusion, methylation changes in several sites of the 1 _F region of the NR3C1 gene in newborns and very young infants were associated with perinatal stress, but more robust and comparable results are needed to corroborate site-specific associations.

Genome-wide DNA methylation and gene expression analyses in monozygotic twins identify potential biomarkers of depression

Depression is currently the leading cause of disability around the world. We conducted an epigenome-wide association study (EWAS) in a sample of 58 depression score-discordant monozygotic twin pairs, aiming to detect specific epigenetic variants potentially related to depression and further integrate with gene expression profile data. Association between the methylation level of each CpG site and depression score was tested by applying a linear mixed effect model. Weighted gene co-expression network analysis (WGCNA) was performed for gene expression data. The association of DNA methylation levels of 66 CpG sites with depression score reached the level of P < 1 × 10^-4. These top CpG sites were located at 34 genes, especially PTPRN2, HES5, GATA2, PRDM7, and KCNIP1. Many ontology enrichments were highlighted, including Notch signaling pathway, Huntington disease, p53 pathway by glucose deprivation, hedgehog signaling pathway, DNA binding, and nucleic acid metabolic process. We detected 19 differentially methylated regions (DMRs), some of which were located at GRIK2, DGKA, and NIPA2. While integrating with gene expression data, HELZ2, PTPRN2, GATA2, and ZNF624 were differentially expressed. In WGCNA, one specific module was positively correlated with depression score (r = 0.62, P = 0.002). Some common genes (including BMP2, PRDM7, KCNIP1, and GRIK2) and enrichment terms (including complement and coagulation cascades pathway, DNA binding, neuron fate specification, glial cell differentiation, and thyroid gland development) were both identified in methylation analysis and WGCNA. Our study identifies specific epigenetic variations which are significantly involved in regions, functional genes, biological function, and pathways that mediate depression disorder.

The advent of fear conditioning as an animal model of post-traumatic stress disorder: Learning from the past to shape the future of PTSD research

Translational research on post-traumatic stress disorder (PTSD) has produced limited improvements in clinical practice. Fear conditioning (FC) is one of the dominant animal models of PTSD. In fact, FC is used in many different ways to model PTSD. The variety of FC-based models is ill defined, creating confusion and conceptual vagueness, which in turn impedes translation into the clinic. This article takes a historical and conceptual approach to provide a comprehensive picture of current research and help reorient the research focus. This work historically reviews the variety of models that have emerged from the initial association of PTSD with FC, highlighting conceptual pitfalls that have limited the translation of animal research into clinical advances. We then provide some guidance on how future translational research could benefit from conceptual and technological improvements to translate basic findings in patients. This objective will require transdisciplinary approaches and should involve physicians, engineers, philosophers, and neuroscientists.

Environmental enrichment improves lifelong persistent behavioral and epigenetic changes induced by early-life stress

This study aimed to evaluate the effects of environmental enrichment (EE) in Wistar rats subjected to maternal deprivation (MD). MD was performed in the first post-natal days (PND) ten for 3 h/day. The groups were: control; deprived without EE; and deprived with EE. The EE was applied for 3 h/day. Forced swimming test (FST) and open field test were performed, and histone deacetylase (HDAC) and DNA methyltransferase (DNMT) activities in the prefrontal cortex (PFC) and hippocampus were evaluated on 31, 41, and 61 PND. MD altered spontaneous locomotor activity and immobility time in FST, but the effects were sex- and developmental period dependent. In deprived females at PND 31, 41, and 61, HDAC and DNMT increased in the PFC and hippocampus. In females exposed to EE for 20 days, there was a decrease of HDAC in the hippocampus and DNMT in the PFC and hippocampus. Exposure of females to EE for 40 days can reverse HDAC and DNMT increase in all brain areas. In deprived males at PND 31, 41, and 61, HDAC and DNMT increased in the hippocampus, and in the group exposed to EE for 40 days, there was a decrease in hippocampal activity. In PFC of male deprived rats at PND 61 and EE for 40 days, there was a reduction of HDAC and DNMT. MD induced lifelong persistent behavioral and epigenetic changes, and such effects were more evident in female than male rats. EE can be considered an essential non-pharmacological strategy to treat long-term trauma-induced early life changes.

Brain proteome-wide association study implicates novel proteins in depression pathogenesis

Depression is a common condition, but current treatments are only effective in a subset of individuals. To identify new treatment targets, we integrated depression genome-wide association study (GWAS) results (N = 500,199) with human brain proteomes (N = 376) to perform a proteome-wide association study of depression followed by Mendelian randomization. We identified 19 genes that were consistent with being causal in depression, acting via their respective cis-regulated brain protein abundance. We replicated nine of these genes using an independent depression GWAS (N = 307,353) and another human brain proteomic dataset (N = 152). Eleven of the 19 genes also had cis-regulated mRNA levels that were associated with depression, based on integration of the depression GWAS with human brain transcriptomes (N = 888). Meta-analysis of the discovery and replication proteome-wide association study analyses identified 25 brain proteins consistent with being causal in depression, 20 of which were not previously implicated in depression by GWAS. Together, these findings provide promising brain protein targets for further mechanistic and therapeutic studies.

Intersectional analysis of chronic mild stress-induced lncRNA-mRNA interaction networks in rat hippocampus reveals potential anti-depression/anxiety drug targets

Despite studies providing insight into the neurobiology of chronic stress, depression and anxiety, long noncoding RNA (lncRNA)-mediated mechanisms underlying the common and distinct pathophysiology of these stress-induced disorders remain nonconclusive. In a previous study, we used the chronic mild stress paradigm to separate depression-susceptible, anxiety-susceptible and insusceptible rat subpopulations. In the current study, lncRNA and messenger RNA (mRNA) expression was comparatively profiled in the hippocampus of the three stress groups using microarray technology. Groupwise comparisons identified distinct sets of lncRNAs and mRNAs associated with the three different behavioral phenotypes of the stressed rats. To investigate the regulatory roles of the dysregulated lncRNAs upon mRNA expression, correlations between the differential lncRNAs and mRNAs were first analyzed by combined use of weighted gene coexpression network analysis and ceRNA theory-based methods. Subsequent functional analysis of strongly correlated mRNAs indicated that the dysregulated lncRNAs were involved in various biological pathways and processes to specifically induce rat susceptibility or resiliency to depression or anxiety. Further intersectional analysis of phenotype-associated and drug-associated lncRNA-mRNA networks and subnetworks assisted in identifying 16 hub lncRNAs as potential targets of anti-depression/anxiety drugs. Collectively, our study established the molecular basis for understanding the similarities and differences in pathophysiological mechanisms underlying stress-induced depression or anxiety and stress resiliency, revealing several important lncRNAs that represent potentially new therapeutic drug targets for depression and anxiety disorders.

Incorporating K-mers Highly Correlated to Epigenetic Modifications for Bayesian Inference of Gene Interactions

Objective::

A gene interaction network, along with its related biological features, has an important role in computational biology. Bayesian network, as an efficient model, based on probabilistic concepts is able to exploit known and novel biological casual relationships between genes. The success of Bayesian networks in predicting the relationships greatly depends on selecting priors.

Methods::

K-mers have been applied as the prominent features to uncover the similarity between genes in a specific pathway, suggesting that this feature can be applied to study genes dependencies. In this study, we propose k-mers (4,5 and 6-mers) highly correlated with epigenetic modifications, including 17 modifications, as a new prior for Bayesian inference in the gene interaction network.

Result::

Employing this model on a network of 23 human genes and on a network based on 27 genes related to yeast resulted in F-measure improvements in different biological networks.

Conclusion::

The improvements in the best case are 12%, 36%, and 10% in the pathway, coexpression, and physical interaction, respectively.

Oligonucleotides as therapeutic tools for brain disorders: Focus on major depressive disorder and Parkinson's disease

Remarkable advances in understanding the role of RNA in health and disease have expanded considerably in the last decade. RNA is becoming an increasingly important target for therapeutic intervention; therefore, it is critical to develop strategies for therapeutic modulation of RNA function. Oligonucleotides, including antisense oligonucleotide (ASO), small interfering RNA (siRNA), microRNA mimic (miRNA), and anti-microRNA (antagomir) are perhaps the most direct therapeutic strategies for addressing RNA. Among other mechanisms, most oligonucleotide designs involve the formation of a hybrid with RNA that promotes its degradation by activation of endogenous enzymes such as RNase-H (e.g., ASO) or the RISC complex (e.g. RNA interference - RNAi for siRNA and miRNA). However, the use of oligonucleotides for the treatment of brain disorders is seriously compromised by two main limitations: i) how to deliver oligonucleotides to the brain compartment, avoiding the action of peripheral RNAses? and once there, ii) how to target specific neuronal populations? We review the main molecular pathways in major depressive disorder (MDD) and Parkinson's disease (PD), and discuss the challenges associated with the development of novel oligonucleotide therapeutics. We pay special attention to the use of conjugated ligand-oligonucleotide approach in which the oligonucleotide sequence is covalently bound to monoamine transporter inhibitors (e.g. sertraline, reboxetine, indatraline). This strategy allows their selective accumulation in the monoamine neurons of mice and monkeys after their intranasal or intracerebroventricular administration, evoking preclinical changes predictive of a clinical therapeutic action after knocking-down disease-related genes. In addition, recent advances in oligonucleotide therapeutic clinical trials are also reviewed.

Impact of Supplementation and Nutritional Interventions on Pathogenic Processes of Mood Disorders: A Review of the Evidence

This narrative review was conducted using searches of the PubMed/Medline and Google Scholar databases from inception to November 2019. Clinical trials and relevant articles were identified by cross-referencing major depressive disorder (and/or variants) with the following terms: folate, homocysteine, S-adenosylmethionine (SAMe), L-acetylcarnitine, alpha-lipoic acid, N-acetylcysteine, L-tryptophan, zinc, magnesium, vitamin D, omega-3 fatty acids, coenzyme Q10, and inositol. Manual reviews of references were also performed using article reference lists. Abnormal levels of folate, homocysteine, and SAMe have been shown to be associated with a higher risk of depression. Numerous studies have demonstrated antidepressant activity with L-methylfolate and SAMe supplementation in individuals with depression. Additionally, the amino acids L-acetylcarnitine, alpha-lipoic acid, N-acetylcysteine, and L-tryptophan have been implicated in the development of depression and shown to exert antidepressant effects. Other agents with evidence for improving depressive symptoms include zinc, magnesium, omega-3 fatty acids, and coenzyme Q10. Potential biases and differences in study designs within and amongst the studies and reviews selected may confound results. Augmentation of antidepressant medications with various supplements targeting nutritional and physiological factors can potentiate antidepressant effects. Medical foods, particularly L-methylfolate, and other supplements may play a role in managing depression in patients with inadequate response to antidepressant therapies.

Sperm microRNAs confer depression susceptibility to offspring

Evidence that offspring traits can be shaped by parental life experiences in an epigenetically inherited manner paves a way for understanding the etiology of depression. Here, we show that F1 offspring born to F0 males of depression-like model are susceptible to depression-like symptoms at the molecular, neuronal, and behavioral levels. Sperm small RNAs, and microRNAs (miRNAs) in particular, exhibit distinct expression profiles in F0 males of depression-like model and recapitulate paternal depressive-like phenotypes in F1 offspring. Neutralization of the abnormal miRNAs in zygotes by antisense strands rescues the acquired depressive-like phenotypes in F1 offspring born to F0 males of depression-like model. Mechanistically, sperm miRNAs reshape early embryonic transcriptional profiles in the core neuronal circuits toward depression-like phenotypes. Overall, the findings reveal a causal role of sperm miRNAs in the inheritance of depression and provide insight into the mechanism underlying susceptibility to depression.

Epigenetic Neuropharmacology: Drugs Affecting the Epigenome in the Brain

This review explores how different classes of drugs, including those with therapeutic and abuse potential, alter brain functions and behavior via the epigenome. Epigenetics, in its simplest interpretation, is the study of the regulation of a genes' transcriptional potential. The epigenome is established during development but is malleable throughout life by a wide variety of drugs, with both clinical utility and abuse potential. An epigenetic effect can be central to the drug's therapeutic or abuse potential, or it can be independent from the main effect but nevertheless produce beneficial or adverse side effects. Here, I discuss the various epigenetic effects of main pharmacological drug classes, including antidepressants, antiepileptics, and drugs of abuse.

Enantiopure methoxetamine stereoisomers: chiral resolution, conformational analysis, UV-circular dichroism spectroscopy and electronic circular dichroism

Enantioseparation and assignment of absolute configuration of methoxetamine (MXE) enantiopure stereoisomers; a promising novel antidepressant for management of treatment-resistant depression.

Central and peripheral stress-induced epigenetic mechanisms of resilience

PURPOSE OF REVIEW

Resilience is an adaptation process presented by an individual despite facing adversities. Epigenetic changes, such as histone acetylation/methylation and DNA methylation, have been demonstrated to mediate stress response. In this review, we summarize recent findings on epigenetic mechanisms contributing to stress resilience.

RECENT FINDINGS

Epigenetic modifications of genes involved in synaptic plasticity, endocrine, immune, and vascular systems are linked to resilience. For instance, increased DNA methylation of the nonneuronal growth factor Gdnf in specific brain regions promotes stress resilience. Additionally, high DNA methylation at the glucocorticoid receptor gene was associated with resilience in both rodents and humans. At the immune level, chronic stress induces increased DNA methylation at IL6 gene, a mediator of stress vulnerability. Moreover, epigenetic adaptations of the blood--brain barrier have been recently associated with stress resilience, which could lead to innovative therapeutic approaches to treat depression.

SUMMARY

Identification of both central and peripheral epigenetic changes promoting stress resilience represent promising novel targets in the development of preventive and personalized medicine. Nevertheless, more research is needed to establish sex specific differences and to identify novel epigenetic mechanisms, such as serotonylation and dopaminylation, that hold great promises for the field of psychiatry.

The Way to a Human's Brain Goes Through Their Stomach: Dietary Factors in Major Depressive Disorder

Globally, more than 250 million people are affected by depression (major depressive disorder; MDD), a serious and debilitating mental disorder. Currently available treatment options can have substantial side effects and take weeks to be fully effective. Therefore, it is important to find safe alternatives, which act more rapidly and in a larger number of patients. While much research on MDD focuses on chronic stress as a main risk factor, we here make a point of exploring dietary factors as a somewhat overlooked, yet highly promising approach towards novel antidepressant pathways. Deficiencies in various groups of nutrients often occur in patients with mental disorders. These include vitamins, especially members of the B-complex (B6, B9, B12). Moreover, an imbalance of fatty acids, such as omega-3 and omega-6, or an insufficient supply with minerals, including magnesium and zinc, are related to MDD. While some of them are relevant for the synthesis of monoamines, others play a crucial role in inflammation, neuroprotection and the synthesis of growth factors. Evidence suggests that when deficiencies return to normal, changes in mood and behavior can be, at least in some cases, achieved. Furthermore, supplementation with dietary factors (so called "nutraceuticals") may improve MDD symptoms even in the absence of a deficiency. Non-vital dietary factors may affect MDD symptoms as well. For instance, the most commonly consumed psychostimulant caffeine may improve behavioral and molecular markers of MDD. The molecular structure of most dietary factors is well known. Hence, dietary factors may provide important molecular tools to study and potentially help treat MDD symptoms. Within this review, we will discuss the role of dietary factors in MDD risk and symptomology, and critically discuss how they might serve as auxiliary treatments or preventative options for MDD.

Androgen deficit changes the response to antidepressant drugs in tail suspension test in mice

Depressive symptoms are throughout our life, especially in the older population, the sex hormones reduction link to a high risk of depression. In this study, we investigated whether bilateral orchiectomy (ORX) modifies mice behaviors and antidepressant drugs effects through tail suspension test (TST). We evaluated behavioral changes at 1 week, 2 weeks, 1 month, and up to 2 months after ORX. The behavior responses to doxepin, fluoxetine, and venlafaxine at 1 week, 2 weeks, 1 month, and 2 months after ORX were evaluated. No apparent difference was detected among the durations of immobility of the control group, sham operation group, and ORX group in the TST at 1 week and 2 weeks after ORX. But the immobility time of ORX group was obvious longer than that of both control group and sham operation group at 1 month and 2 months after ORX. Only the antidepressant effect of venlafaxine was observed at 1 week and 2 weeks after ORX, while the antidepressant response to fluoxetine decreased 1 month and 2 months after ORX. The response to antidepressant drugs was strongly modified in ORX mice. Our results suggest that not all antidepressant drugs are suitable for depression with androgen deficiency.HighlightsMice with low androgen were more prone to depression-like behaviors.The response to antidepressants changed under the condition of low androgen in mice.Not all antidepressant drugs are appropriate for patients with low androgen.

Epigenetic landscape of stress surfeit disorders: Key role for DNA methylation dynamics

Chronic exposure to stress throughout lifespan alters brain structure and function, inducing a maladaptive response to environmental stimuli, that can contribute to the development of a pathological phenotype. Studies have shown that hypothalamic-pituitary-adrenal (HPA) axis dysfunction is associated with various neuropsychiatric disorders, including major depressive, alcohol use and post-traumatic stress disorders. Downstream actors of the HPA axis, glucocorticoids are critical mediators of the stress response and exert their function through specific receptors, i.e., the glucocorticoid receptor (GR), highly expressed in stress/reward-integrative pathways. GRs are ligand-activated transcription factors that recruit epigenetic actors to regulate gene expression via DNA methylation, altering chromatin structure and thus shaping the response to stress. The dynamic interplay between stress response and epigenetic modifiers suggest DNA methylation plays a key role in the development of stress surfeit disorders.

Resilience to Stress and Resilience to Pain: Lessons from Molecular Neurobiology and Genetics

What biological factors account for resilience to pain or to behavioral stress? Here, we discuss examples of cellular and molecular mechanisms within disparate parts of the nervous system as contributors to such resilience. In some especially well-studied humans, it is possible to identify particular neuronal cell types in the peripheral nervous system (PNS) and pinpoint specific genes that are major contributors to pain resilience. We also discuss more complex factors that operate within the central nervous system (CNS) to confer resilience to behavioral stress. We propose that genetic and neurobiological substrates for resilience are discoverable and suggest more generally that neurology and psychiatry hold lessons for each other as investigators search for actionable, biological underpinnings of disease.

Can I Get a Witness? Using Vicarious Defeat Stress to Study Mood-Related Illnesses in Traditionally Understudied Populations

The chronic social defeat stress model has been instrumental in shaping our understanding of neurobiology relevant to affect-related illnesses, including major depressive disorder. However, the classic chronic social defeat stress procedure is limited by its exclusive application to adult male rodents. We have recently developed a novel vicarious social defeat stress procedure wherein one mouse witnesses the physical defeat bout of a conspecific from the safety of an adjacent compartment. This witness mouse develops a similar behavioral phenotype to that of the mouse that physically experiences social defeat stress, modeling multiple aspects of major depressive disorder. Importantly, this new procedure allows researchers to perform vicarious social defeat stress in males or females and in juvenile mice, which typically are excluded from classic social defeat experiments. Here we discuss several recent advances made using this procedure and how its application provides a new preclinical approach to study the neurobiology of psychological stress-induced phenotypes.

RNA Editing and Modifications in Mood Disorders

Major depressive disorder (MDD) is a major health problem with significant limitations in functioning and well-being. The World Health Organization (WHO) evaluates MDD as one of the most disabling disorders in the world and with very high social cost. Great attention has been given to the study of the molecular mechanism underpinning MDD at the genetic, epigenetic and proteomic level. However, the importance of RNA modifications has attracted little attention until now in this field. RNA molecules are extensively and dynamically altered by a variety of mechanisms. Similar to "epigenomic" changes, which modify DNA structure or histones, RNA alterations are now termed "epitranscriptomic" changes and have been predicted to have profound consequences for gene expression and cellular functionality. Two of these modifications, adenosine to inosine (A-to-I) RNA editing and m6A methylations, have fascinated researchers over the last years, showing a new level of complexity in gene expression. In this review, we will summary the studies that focus on the role of RNA editing and m6A methylation in MDD, trying to underline their potential breakthroughs and pitfalls.

Aging increases vulnerability to stress-induced depression via upregulation of NADPH oxidase in mice

Brain aging proceeds with cellular and molecular changes in the limbic system. Aging-dependent changes might affect emotion and stress coping, yet the underlying mechanisms remain unclear. Here, we show aged (18-month-old) mice exhibit upregulation of NADPH oxidase and oxidative stress in the hippocampus, which mirrors the changes in young (2-month-old) mice subjected to chronic stress. Aged mice that lack p47phox, a key subunit of NADPH oxidase, do not show increased oxidative stress. Aged mice exhibit depression-like behavior following weak stress that does not produce depressive behavior in young mice. Aged mice have reduced expression of the epigenetic factor SUV39H1 and its upstream regulator p-AMPK, and increased expression of Ppp2ca in the hippocampus-changes that occur in young mice exposed to chronic stress. SUV39H1 mediates stress- and aging-induced sustained upregulation of p47phox and oxidative stress. These results suggest that aging increases susceptibility to stress by upregulating NADPH oxidase in the hippocampus.

BAHD1 haploinsufficiency results in anxiety-like phenotypes in male mice

BAHD1 is a heterochomatinization factor recently described as a component of a multiprotein complex associated with histone deacetylases HDAC1/2. The physiological and patho-physiological functions of BAHD1 are not yet well characterized. Here, we examined the consequences of BAHD1 deficiency in the brains of male mice. While Bahd1 knockout mice had no detectable defects in brain anatomy, RNA sequencing profiling revealed about 2500 deregulated genes in Bahd1-/- brains compared to Bahd1+/+ brains. A majority of these genes were involved in nervous system development and function, behavior, metabolism and immunity. Exploration of the Allen Brain Atlas and Dropviz databases, assessing gene expression in the brain, revealed that expression of the Bahd1 gene was limited to a few territories and cell subtypes, particularly in the hippocampal formation, the isocortex and the olfactory regions. The effect of partial BAHD1 deficiency on behavior was then evaluated on Bahd1 heterozygous male mice, which have no lethal or metabolic phenotypes. Bahd1+/- mice showed anxiety-like behavior and reduced prepulse inhibition (PPI) of the startle response. Altogether, these results suggest that BAHD1 plays a role in chromatin-dependent gene regulation in a subset of brain cells and support recent evidence linking genetic alteration of BAHD1 to psychiatric disorders in a human patient.

Current challenges and possible future developments in personalized psychiatry with an emphasis on psychotic disorders

A personalized medicine approach seems to be particularly applicable to psychiatry. Indeed, considering mental illness as deregulation, unique to each patient, of molecular pathways, governing the development and functioning of the brain, seems to be the most justified way to understand and treat disorders of this medical category. In order to extract correct information about the implicated molecular pathways, data can be drawn from sampling phenotypic and genetic biomarkers and then analyzed by a machine learning algorithm. This review describes current difficulties in the field of personalized psychiatry and gives several examples of possibly actionable biomarkers of psychotic and other psychiatric disorders, including several examples of genetic studies relevant to personalized psychiatry. Most of these biomarkers are not yet ready to be introduced in clinical practice. In a next step, a perspective on the path personalized psychiatry may take in the future is given, paying particular attention to machine learning algorithms that can be used with the goal of handling multidimensional datasets.